UNITED STATES OF AMERICA

DEPARTMENT OF COMMERCE

A Century of Excellence in

Measurements, Standards,

and Technology

A Chronicle of Selected NBS/NIST Publications

1901-2000

NIST Special Publication 958

David R. Lide, Editor

January 2001

U.S. Department of Commerce

Donald L. Evans, Secretary

National Institute of Standards and Technology

Karen H. Brown, Acting Director
In this volume, according to NIST policy, measurements are expressed in SI units except in some cases where

reference is made to the conventional units used at the time of the original publications.

Certain commercial equipment, instruments, or materials are identified in this paper to foster understanding.

Such identification does not imply recommendation or endorsement by the National Institute of Standards and

Technology, nor does it imply that the materials or equipment identified are necessarily the best available for the

purpose.

Natl. Inst. Stand. Technol., Spec. Publ. 958, 395 pages (Jan. 2001) CODEN: NSPUE2

For sale by the Superintendent of Documents, U.S. Government Printing Office, Washington,

DC 20402–9325
Foreword

As NIST celebrates its 100th birthday and we look back at what has been accomplished,

the variety of NIST’s contributions to science and technology and to the economy of our

nation is truly remarkable. This book, which consists of vignettes describing some of the

classic publications from our first century, can only sample that variety. For every publication included, there were numerous others of comparable worth that had to be left out.

Few if any of the world’s technical institutions have had such an eclectic, yet essential,

evolving mission—from testing concrete and railroad track scales to quasicrystals and

Nobel Prize-winning work on laser cooling of atoms; from developing radio beacons for

aircraft navigation to building early computers for data processing and developing sophisticated models for the spread of fires. It is difficult to find any area of science and

technology in which NIST/NBS has not played some important role.

The talented staff who work for NIST take pride in their work. Communicating results

to the public is a critical task for us. While publication of paper documents will undoubtedly be around for some time to come, electronic publication via the World Wide Web is

already a key vehicle for NIST to distribute information quickly. No doubt Internet-based

dissemination of our information will continue to grow in importance.

Given the skill, enthusiasm, and dedication of our current staff, I feel confident that this

splendid institution will produce an even greater contribution to the United States during

the next hundred years. I am particularly proud to have had the opportunity to be at the

helm of NIST as we transition into the 21st Century. And our recent employee survey

shows that the vast majority of NIST people are equally proud to work here.

Enjoy browsing this book. It is a tribute to the men and women who have served NIST

with distinction since 1901.

Raymond G. Kammer

Director

December 2000

iii
Centennial Publication Selection Committee

The following individuals served on the Committee that developed the criteria for

selecting publications to be included in this volume. The Committee solicited nominations,

selected the publications to be included from the approximately 450 nominations that were

submitted, and coordinated the preparation of short accounts of the chosen publications:

• Brian Belanger, Director’s Office (Chair)

• Walter Leight, Technology Services (Vice Chair)

• Ronald Boisvert, Information Technology Laboratory

• Susan Makar, Office of Information Services

• John Mayo-Wells, Electronics and Electrical Engineering Laboratory

• Ronald Munro, Materials Science and Engineering Laboratory

• Dale Newbury, Chemical Science and Technology Laboratory

• Hans J. Oser, Standards Alumni Association

• Daniel Pierce, Physics Laboratory

• H. Steffen Peiser, Standards Alumni Association

• Dennis Swyt, Manufacturing Engineering Laboratory

• W. Reeves Tilley, Standards Alumni Association

• Richard Wright, Building and Fire Research Laboratory

iv
Acknowledgments

Subcommittees Representing the Operating Units of NIST

Building and Fire Research Laboratory

Richard Wright, Chair

Jack Snell

James Hill

Andrew Fowell

Joel Zingeser

Harold Marshall

Karen Perry

Sivaraj Shyam-Sunder

Geoffrey Frohnsdorff

George Kelly

David Evans

Richard Gann

William Grosshandler

Chemical Science and Technology Laboratory

Dale E. Newbury, Chair

Charles M. Beck II

William R. Kelly

William J. Gadzuk

Roger D. Van Zee

Electronics and Electrical Engineering Laboratory

John Mayo-Wells, Chair

Norman B. Belecki

Jack Ekin

Douglas L. Franzen

Clark Hamilton

David A. Hill

Dave Rudman

Richard L. Steiner

W. Robert Thurber

Harry A. Schafft

Thomas R. Scott

Information Technology Laboratory

Ronald Boisvert, Chair

Martha Gray

John Cugini

M. Carroll Croarkin

Gordon Lyon

Manufacturing Engineering Laboratory

Dennis Swyt, Chair

Theodore Doiron

Donald Eitzen

Ernest Kent

Charles McLean

Materials Science and Engineering Laboratory

Ronald Munro, Chair

Norman Berk

Sam Coriell

Freddy Khoury

Physics Laboratory

Daniel T. Pierce, Chair

Charles W. Clark

Bert M. Coursey

James E. Faller

Albert C. Parr

Donald B. Sullivan

Wolfgang L. Wiese

Technology Services

Walter Leight, Chair

Charles Ehrlich

Ernest Garner

John Rumble

Charles Sturrock

Nancy Trahey

Standards Alumni Association

H. Steffen Peiser, Chair

John A. Bennett

Edith L. R. Corliss

Walter J. Hamer

John D. Hoffman

Ralph P. Hudson

Robert Kamper

Hans J. Oser

Jacob Rabinow

John A. Simpson

W. Reeves Tilley

v
List of Vignette Contributors

James S. Albus

Charles M. Beck II

Brian Belanger

N. B. Belecki

Norman F. Berk

Barry Bernstein

Stanley Block

Ronald F. Boisvert

Lewis M. Branscomb

Maureen Breitenberg

Carroll Brickencamp

E. A. Brown

Richard Bukowski

William E. Burr

John Cahn

Robert J. Celotta

Geraldine Cheok

Charles W. Clark

Sam Coriell

Bert Coursey

M. Carroll Croarkin

John Cugini

Tom Davis

Richard D. Deslattes

Ted Doiron

R. Dziuba

Charles Ehrlich

J. W. Ekin

Bruce R. Ellingwood

R. E. Elmquist

David Evans

James Faller

Fred Fickett

B. Fonoroff

D. L. Franzen

Stephen Freiman

Geoffrey Frohnsdorff

Edwin Fuller

J. W. Gadzuk

Ernest Garner

Saul Gass

Frank Gayle

Thomas E. Gills

Alan Goldman

Martha M. Gray

Daniel Gross

Walter J. Hamer

Carol Handwerker

Jonathan E. Hardis

Allan H. Harvey

Jim L. Heldenbrand

D. A. Hill

James E. Hill

John Hoffman

Ralph P. Hudson

A-M. Jeffrey

Vicky Lynn Karen

Takashi Kashiwagi

Elliot Kearsley

Sharon J. Kemmerer

Freddy Khoury

J. R. Kinard, Jr.

Russell A. Kirsch

Ralph Klein

Joan Koenig

Richard H. Kropschot

Robert D. Larrabee

James Lawrence

Walter G. Leight

Tom Lettieri

Johanna M. H. Levelt Sengers

Don Libes

David R. Lide

Richard M. Lindstrom

Daniel W. Lozier

William Luecke

John W. Lyons

Ted Madey

J. F. Mayo-Wells

Calvin S. McCamy

Howard McMurdie

James R. McNesby

Norman E. Mease

Alan D. Mighell

Michael R. Moldover

Raymond D. Mountain

Ronald Munro

Victor Nedzelnitsky

Harold Nelson

Dale E. Newbury

Anita O’Brien

Dianne P. O’Leary

Helen Ondik

Hans J. Oser

Albert C. Parr

H. Steffen Peiser

Daniel T. Pierce

Gasper Piermarini

Michael T. Postek

James E. Potzick

Thomas M. Proctor

Stanley Rasberry

Curt Reimann

A. G. Repjar

Ralph A. Richter

Steven Rolston

John R. Rumble, Jr.

Harry A. Schafft

F. Scire

Thomas R. Scott

Robert Sienkiewicz

Tom Siewert

Deborah Smyth

Richard N. Spivack

Kenneth D. Steckler

Donald B. Sullivan

Y. Tang

E. C. Teague

John Tesk

W. R. Thurber

W. Reeves Tilley

Terrell Vanderah

J. S. Villarrubia

George Walton

Wolfgang L. Wiese

E. R. Williams

William K. Wilson

Christoph Witzgall

Richard Wright

John Yates

R. D. Young

Robert R. Zarr

Joel P. Zingeser

Other Acknowledgments

In addition to the individuals listed above, several others have played a key role in the preparation of this volume.

Particular thanks are due to Susan Makar for meticulous checking of the bibliographic references; to Ilse Putman for

an excellent typesetting job; to Carolyn Stull for carefully editing the final manuscripts; and to Kristy Thompson for

designing and maintaining the web site for the Centennial Publications project.

vi
Table of Contents

Introduction.............................................................................. 1

1901-1930

The Absolute Measurement of Inductance ...................................................... 5

Determination of the Constants of Total Radiation From a Black Body .............................. 7

The Testing of Thermal Insulators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

Precipitation Hardening of Metal Alloys. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

Construction and Operation of a Simple Homemade Radio Receiving Outfit . . . . . . . . . . . . . . . . . . . . . . . . . . 16

Methods for Standardizing and Testing Precision Gage Blocks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

Recommended Minimum Requirements for Small Dwelling Construction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

Visibility of Radiant Energy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

Test of the Severity of Building Fires. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28

Calculation of Compounds in Portland Cements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33

Development of the Visual-Type Airway Radio-Beacon System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38

1931-1950

A Hydrogen Isotope of Mass 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43

Air Flow and Turbulence in Boundary Layers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46

Thermodynamic Properties of Water and Steam for Power Generation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49

Absolute Pressure Calibrations of Microphones. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53

Absolute Determination of the Ampere. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56

Radio Proximity Fuzes. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59

Stability of Double-Walled Manganin Resistors. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63

Manufacture of Paper for War Maps and Other Applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66

Transmission of Sound Waves in Gases at Low Pressures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69

Atomic Energy Levels and Other Spectroscopic Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73

Iteration Method for the Solution of the Eigenvalue Problem of Linear Differential and Integral Operators. . 77

1951-1960

Methods of Conjugate Gradients for Solving Linear Systems. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81

Computer Development at the National Bureau of Standards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 86

Thermal Converters as AC-DC Transfer Standards for Current and Voltage Measurements

at Audio Frequencies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90

Selected Values of Chemical Thermodynamic Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93

Applied Inorganic Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97

The Diamond Anvil Pressure Cell. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100

Polymer Crystallization With Folded Chains . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 104

Cryogenic Engineering. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 107

Reversal of the Parity Conservation Law in Nuclear Physics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111

1961-1970

Effects of Configuration Interaction on Intensities and Phase Shifts. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 116

Electromagnetic Waves in Stratified Media . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 120

“Second Breakdown” in Transistors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 123

Stress Relaxation With Finite Strain . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 126

Realistic Evaluation of the Precision and Accuracy of Instrument Calibration Systems . . . . . . . . . . . . . . . . . . 129

Experimental Statistics. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 132

Handbook of Mathematical Functions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 135

vii
1961-1970 — Cont.

Paths, Trees, and Flowers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 140

Concepts, Terminology, and Notation for Optical Modulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 145

Theory of Light Scattering in Fluids. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 149

Scaling Analysis of Thermodynamic Properties in the Critical Region of Fluids . . . . . . . . . . . . . . . . . . . . . . . 152

Resonance Tunneling of Field Emitted Electrons Through Adsorbates on Metal Surfaces . . . . . . . . . . . . . . . . 155

Quantitative Electron Probe Microanalysis. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 160

Limits for Qualitative Detection and Quantitative Determination . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 164

Traceability: An Evolving Concept . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 167

Code for Information Interchange—ASCII. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 172

Consumer Information Series. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 174

Theory of Isoperibol Calorimetry for Laser Power and Energy Measurement . . . . . . . . . . . . . . . . . . . . . . . . . . 178

Influence of Water on Crack Growth in Glass . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 181

Phase Equilibria Diagrams. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 184

Determination of Reduced Cells in Crystallography . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 188

1971-1980

Speed of Light From Direct Frequency and Wavelength Measurements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 191

Connecting Visible Wavelength Standards With X Rays and  Rays . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 194

Laser Cooling of Atoms. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 200

Spin-Polarized Electrons . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 203

Needs for Radioactivity Standards and Measurements in Different Fields . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 209

The Topografiner: An Instrument for Measuring Surface Microtopography. . . . . . . . . . . . . . . . . . . . . . . . . . . . 214

Electron-Stimulated Desorption . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 219

Photochemistry of Small Molecules . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 224

Role of Standard Reference Materials in Measurement Systems. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 227

Metrology and Standardization to Assist Industrializing Economies. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 230

Publications Taking Us Toward a Metric America . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 234

A New Approach to Manipulator Control: The Cerebellar Model Articulation Controller . . . . . . . . . . . . . . . . 237

Three Dimensional Metrology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 241

Initial Graphics Exchange Specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 246

Data Encryption Standard . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 250

OMNIDATA and the Computerization of Scientific Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 254

FORTRAN Test Programs. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 258

Design and Evaluation Criteria for Energy Conservation in New Buildings . . . . . . . . . . . . . . . . . . . . . . . . . . . 260

Computer Program for Heating and Cooling Loads in Buildings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 266

Methods for Testing and Rating the Performance of Heating and Air Conditioning Systems. . . . . . . . . . . . . . 270

System for Fire Safety Evaluation of Health Care Facilities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 275

Estimation of Rate of Heat Release by Means of Oxygen Consumption Measurements. . . . . . . . . . . . . . . . . . 280

Probability-Based Load Criteria for Structural Design. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 283

Resistivity-Dopant Density Relationship for Phosphorus-Doped Silicon . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 289

1981-1990

Critical Data for Critical Needs. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 291

Materials at Low Temperatures. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 294

Optical Fiber Characterization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 297

Quasicrystals. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 300

Protein Crystallography by Joint X-Ray and Neutron Diffraction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 303

Strain Effects in Superconducting Compounds. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 306

Dental Research at the National Bureau of Standards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 309

Handbook for Standard Reference Materials Users . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 313

A Practical Josephson Voltage Standard at One Volt . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 315

Plane-Wave Scattering-Matrix Theory of Antennas and Antenna-Antenna Interactions . . . . . . . . . . . . . . . . . . 319

The Automated Manufacturing Research Facility. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 322

viii
1981-1990 — Cont.

Submicrometer Linewidth Metrology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 328

Observation of Atoms Laser-Cooled Below the Doppler Limit. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 331

Laser-Excited Hot-Electron Induced Desorption. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 334

Measurement of the Universal Gas Constant Using an Acoustic Resonator. . . . . . . . . . . . . . . . . . . . . . . . . . . . 339

Thermal and Oxidative Degradation of Polymers. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 344

HAZARD I: Software for Fire Hazard Assessment. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 347

Analysis of the Catastrophic Rupture of a Pressure Vessel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 350

Curing Those Uncontrollable Fits of Interaction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 353

Baldrige Criteria for Performance Excellence. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 357

1991-2000

The Advanced Technology Program . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 359

NIST Manufacturing Extension Partnership . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 363

Questions and Answers on Quality . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 366

Uniformity in Weights and Measures Laws and Regulations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 368

Certification of 10 m Diameter Polystyrene Spheres (“Space Beads”) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 371

Bose-Einstein Condensation in a Dilute Atomic Vapor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 375

Index. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 379

ix
Introduction

The National Bureau of Standards was established by Congress on March 3, 1901, with a charge to take

custody of the standards of physical measurement in the United States and to solve “problems which arise

in connection with standards.” Although minor (and transient) variations occurred in the name of the

institution, it was known for most of the century as NBS until Congress mandated a major name change,

accompanied by new responsibilities, in 1988. Thus the “Bureau” completed its first century as the National

Institute of Standards and Technology, or NIST. This volume commemorates the centennial by presenting

brief accounts of selected classic publications of NBS/NIST which illustrate at the same time the rich history

of its scientific and technical accomplishments and the broad scope of its contributions to the Nation.

If asked to select one word that best describes the work of the institution, most people familiar with

NBS/NIST would choose “measurement.” Indeed, the theme of precise, accurate measurements runs through

the first century’s history. Seventeen years before the founding of NBS, Lord Kelvin wrote [1],

“When you can measure what you are speaking about, and express it in numbers, you know

something about it; but when you cannot measure it, when you cannot express it in numbers, your

knowledge is of a meager and unsatisfactory kind: it may be the beginning of knowledge, but you

have scarcely, in your thoughts, advanced to the stage of science.”

His statement captures very elegantly the philosophy and culture of NBS/NIST. The measurement

methodology described in this volume runs the gamut from cutting-edge research in atomic physics to new

ways of measuring the heat released in building fires; from measuring the response of the human eye to

different colors to selecting the best sets of data for improving rocket engine performance; and from

automating manufacturing processes to advising consumers on how to buy tires for their cars. These

publications illustrate the support NBS/NIST has given to U.S. industry and to other Federal agencies in

solving specific measurement problems, as well as the impact of Bureau work on the scientific community

at large and on the general public.

With so many diverse audiences to serve, communication of the results of its work has been a major

concern since the founding of NBS. In a remarkably prescient article published in Science in 1905, Edward

B. Rosa, one of the 11 initial NBS staff members (the only one with the title of “Physicist”) outlined his

vision of the future of the Bureau [2]. In addition to its mission to maintain the standards of measure of the

United States and to advance the art of precise measurements, he added a third mandate, “To distribute

information regarding instruments and standards to manufacturers, state and city sealers of weights and

measures, scientific and technical laboratories, and to any and every one applying for such information”—a

daunting challenge which the Bureau has taken very seriously. Rosa went on to stress the interdependence

of the three functions and to explain that the distribution of information would be “accomplished through

correspondence and the circulars and bulletins issued by the bureau,” thereby setting the stage for the broad

publication program illustrated in this book.

There are, of course, other mechanisms by which the Bureau has disseminated its information. Staff

members have described their work through lectures at academic and industrial establishments and to foreign

audiences. Participation in national and international standards committees has been a very significant

transfer mechanism. Thousands of guest workers from industry, academia, and other national laboratories

have spent time working in Bureau laboratories, taking new technology and new ideas back to their home

institutions (as envisioned by Rosa in his 1905 article). Unique facilities—the research reactor, synchrotron

radiation source, and automated manufacturing research facility, to name only a few—have drawn scientists

and engineers to NBS/NIST where they could carry out measurements that would be difficult or impossible

elsewhere. Nevertheless, formal publications have arguably been the most influential single mechanism for

the institution to reach its diverse audience over the century. It is the intention of this book to give the flavor

of those publications.

1
The book consists of short accounts describing 102 representative publications that had a significant

impact during NBS/NIST’s first century. These 102 were chosen, out of tens of thousands that have appeared

in print, to illustrate the range of activities covered by the publication program. Many others are equally

deserving of mention and, in fact, some of these are listed in the bibliographies accompanying each account.

The final selection was made by a committee of representatives of the major units in the current NIST

organizational structure plus the Standards Alumni Association, which looked especially at candidate

publications from the early days of NBS. This committee considered over 400 nominations from NIST staff

and alumni in arriving at the final 102. An effort was made to cover the most significant NIST/NBS

programs, including those in which formal publications are not the dominant communication mechanism.

The selected publications are arranged in the book by time periods. Those from the first half of the century

are grouped into two periods, 1901-1930 and 1931-1950. The publications from the second half are listed

by decade. Within each decade certain papers on related topics have been grouped together. An index of

subjects and individuals appears at the end.

Certain important works were not considered for this book, even though they had significant input from

staff members, because they were not, strictly speaking, NBS/NIST publications. Among these is the

International Critical Tables [3], a seven-volume series prepared in the 1920s whose contributors included

hundreds of scientists from all parts of the world, in addition to many NBS staff members. The Editor-inChief was E. W. Washburn, Chief of the NBS Chemistry Division, and the Editorial Board included G. K.

Burgess, Director of NBS. The preface, written on behalf of the National Research Council (the official

publisher), gives special acknowledgment to NBS for its leadership. The International Critical Tables was

the definitive source for accurate data for the next 30 to 40 years, used at every level of science and

technology, from undergraduate teaching to engineering design. It remained in print until about 1980, and

it is still found (and still used as a reference) in every major library of the physical and engineering sciences.

Also in this category are countless standards documents in which NBS/NIST staff played a major role but

which were published by ASTM, ANSI, ASHRAE, and other national standards organizations as well as by

international groups such as ISO, CODATA, IUPAC, and the various committees of the International Bureau

of Weights and Measures (BIPM). Such documents tend to be anonymous in the sense of bibliographic

citations, but Bureau representatives are frequently among the prime movers in the committees that prepare

them. As a particular example, NBS/NIST has made strong input to the Consultative Committee on Units

(CCU), the group responsible for promulgation of the International System of Units (SI), the “modern metric

system” [4]. Special mention should also be given to the Fundamental Physical Constants, a continuing

project in which Barry N. Taylor and other NIST physicists have played the dominant role over the last

quarter of the century. Their set of CODATA Recommended Values of the Fundamental Physical Constants

[5] has been universally adopted for worldwide use.

For those interested in the full history of NIST, several publications are available. The 1905 paper by Rosa

[2], which summarizes the work during the first few years, has already been mentioned. Three official

histories have been written. Measures for Progress, by Rexmond Cochrane, covers the first 50 years [6]. Elio

Passaglia’s A Unique Institution follows with coverage of the 1950-1969 period [7]. James Schooley rounded

out the history of the first century with Responding to National Needs: The National Bureau of Standards

Becomes the National Institute of Standards and Technology (1969-1993) [8]. These books give extensive

administrative, financial, and personnel details, as well as summaries of the technical work during each

period.

The contributions of NBS during the two world wars, which could not be published at the time the work

was done, is very well documented in two reports which make fascinating reading. The book War Work of

the Bureau of Standards [9] describes about 200 projects undertaken during World War I; these range from

studies of shoe leather and metal for military identification tags to utilization of the Bureau’s expertise in

spectroscopy to improve methods of aerial photography. Bureau metallurgists were particularly active in

helping the military develop specifications and testing methods for items ranging from armor plate and steel

helmets to horseshoe nails. The story for the second world war is given in NBS War Research. The National

Bureau of Standards in World War II [10], edited by former Director Lyman J. Briggs. While the best known

NBS contribution was the proximity fuze (described in more detail in one of the accounts in this book),

almost every part of the organization became involved in war work of some kind. Director Briggs was

appointed by President Roosevelt in 1939 as chairman of the first committee to investigate the feasibility of

2
building an atomic bomb; ultimately, about 60 NBS staff members worked on the bomb project. NBS made

a major contribution in developing methods to purify uranium and graphite, which was used as a moderator

in the reactors that produced plutonium, and the first experiments on separating uranium isotopes by thermal

diffusion were done in a Bureau laboratory.

The publications described in this book appeared in a variety of media, which is characteristic of

NBS/NIST publications as a whole. Many appeared in scholarly journals of scientific and engineering

societies; a few came out as books through commercial publishers. The rest appeared in one or another of

the Bureau’s own publication series. It may be useful to describe these briefly. The Journal of Research of

the National Institute of Standards and Technology, which traces its origin to 1928, publishes research papers

by staff members in all fields covered by NIST. Larger works of long term-interest have appeared in the

Monograph and Handbook series, and the Special Publication series is available for works that do not

conveniently fit into other categories. Interim or transient reports appear as Technical Notes or NISTIRs

(where “I” can mean either Internal or Interagency). Some NIST programs have their own series, e.g., the

Building Science Series, the National Standard Reference Data Series (NSRDS-NBS), the Applied Mathematics Series (AMS), and the Federal Information Processing Standards (FIPS). The Bureau has also joined

outside organizations in certain publication series, for example, the Journal of Physical and Chemical

Reference Data, started in 1972 as a joint endeavor of NBS, the American Institute of Physics, and the

American Chemical Society. This journal has published almost 600 critically evaluated data compilations,

submitted both by NIST scientists and outside authors, as well as 21 supplementary hard-cover monographs.

The classic documents described in this book are traditional publications on paper. The last decade of

NBS/NIST’s first century saw the start of a major revolution in communications with the emergence of

electronic publishing. NIST scientists are already making heavy use of this medium, and the bibliographies

in this book show many references to Internet sites. A number of NIST Laboratories and Programs have

established World Wide Web sites which receive heavy use by the scientific community. This form of

publication is developing too fast to give a comprehensive list of sites, but the following examples convey

the flavor of NIST’s current efforts:

• Physical Reference Data <http://physics.nist.gov/PhysRefData/>—fundamental constants, atomic and

molecular spectra, x-ray attenuation, and radiation dosimetry data.

• Chemistry WebBook <http://webbook.nist.gov>—evaluated data on thermal properties and spectra of

thousands of chemical compounds, including the heavily used NIST/EPA/NIH Mass Spectral Library.

• Digital Library of Mathematical Functions <http://dlmf.nist.gov>—under development as a modern

version of the 1964 classic Handbook of Mathematical Functions.

• Fire Research Information Services < http://fris.nist.gov>—provides access to fire test data, publications,

and fire modeling programs.

• MSEL Data on the Web <http://www.msel.nist.gov/dataontheweb.html>—mechanical, thermal, and

chemical properties of ceramics, metals, and polymers.

• Protein Data Bank <http://nist.rcsb.org/pdb>—3-D crystal structure of proteins.

These and other NIST web sites are already accessed thousands of times each day, and use of the sites

is growing rapidly. As it enters its second century, we can expect the National Institute of Standards and

Technology to take full advantage of the new opportunities for disseminating the results of its work.

David R. Lide

Bibliography

[1] Sir William Thomson (Lord Kelvin), Lecture to the Institution of Civil Engineers (May 3, 1883), in Popular Lectures and

Addresses Vol. 1, p. 80, Macmillan and Co., London & New York, (1891).

[2] Edward B. Rosa, The National Bureau of Standards and its Relation to Scientific and Technical Laboratories, Science 21, 161-174

(1905).

[3] Edward W. Washburn (ed.), International Critical Tables of Numerical Data of Physics, Chemistry, and Technology; published

for National Research Council by McGraw-Hill Book Company, New York (1926/1932).

3
[4] Le Syste`me International d’Unite ́s (SI), 5 e E ́ dition, Bureau International des Poids et Mesures, Sevres, France (1985) [includes

English translation]; see also Barry N. Taylor, Guide for the Use of the International System of Units (SI), NIST Special

Publication 811, National Institute of Standards and Technology, Gaithersburg, MD (1995).

[5] Peter J. Mohr and Barry N. Taylor, CODATA Recommended Values of the Fundamental Physical Constants: 1998, J. Phys. Chem.

Ref. Data 28, 1713-1852 (1999).

[6] Rexmond C. Cochrane, Measures for Progress. A History of the National Bureau of Standards, NBS Special Publication 275, U.S.

Government Printing Office, Washington, DC (1966).

[7] Elio Passaglia, A Unique Institution. The National Bureau of Standards, 1950-1969, NIST Special Publication 925, U.S.

Government Printing Office, Washington, DC (1999).

[8] James Schooley, Responding to National Needs: The National Bureau of Standards Becomes the National Institute of Standards

and Technology (1969-1993), NIST Special Publication 955, U.S. Government Printing Office, Washington, DC (2000).

[9] War Work of the Bureau of Standards, Miscellaneous Publications of the Bureau of Standards, No. 46, U.S. Government Printing

Office, Washington, DC (1921).

[10] Lyman J. Briggs (ed.), NBS War Research. The National Bureau of Standards in World War II, U.S. Department of Commerce

(1949).

4
The Absolute Measurement of Inductance

This paper [1] represents the first Bureau of

Standards scientific contribution of Edward B. Rosa,

Chief Physicist and first Division Chief (Electricity

Division) of NBS. Rosa was an outstanding and prolific

physicist and writer, having provided the basis for the

century-long international pre-eminence of NBS/NIST

in electrical metrology. He authored or co-authored

some 75 NBS papers ranging in topic from fundamental

electrical measurements through practical papers on

electromagnetic calculations and applied measurement

techniques to descriptions of basic work in electrolysis

and photometrics. As an example of his breadth of interest, Rosa invented an ingenious respiration calorimeter

with Wilbur O. Atwater that was to prove highly useful

in subsequent pioneer investigations of food values and

problems of nutrition in this country. Towards the end of

his career he carried out an exhaustive study of government research and its relation to the federal budget,

which had an influence on the establishment of the

Bureau of the Budget, the predecessor of the present

Office of Management and Budget. His name is

pronounced “Ro-zay,” with emphasis on the second

syllable.

The first Director of the Bureau, Samuel Wesley

Stratton, found that the most urgent task of this new

appointment was to find an outstanding individual to

plan and direct the electrical research program that had

dominated the arguments for the creation of the Bureau.

His attention was drawn to Edward Bennett Rosa.

Rosa (1861-1921), of Dutch ancestry, had taught

physics and chemistry after getting his B.S. degree at

Wesleyan University in Connecticut and then entered

the Johns Hopkins University as a graduate student in

physics under Henry A. Rowland. Receiving his doctorate in 1891, he returned to Wesleyan as associate professor of physics, becoming full professor the next year.

Stratton hired him as a physicist at $3,500, and a decade

later, with his electrical group firmly established as the

premier division of the Bureau, he was made chief

physicist.

The paper [1] reflects an early commitment to outstanding work in the electrical metrology field by a

fledgling organization. This was in response to overwhelming needs in U.S. industry for a single, consistent

basis for measurements of power, current, impedance,

and voltage to support the electrical power industry, the

transition of manufacturing from mechanical to electrical power, and the burgeoning electrical instruments

industry, as well as the growing position of the U.S. in

world trade and science.

At the 1908 International Conference on Electrical

Units and Standards in London, it was recommended

that representatives of the National Measurement

Institutes (i.e., counterparts to NBS/NIST) should meet

and agree on new values of international units as

defined by the mercury ohm and silver voltameter. In

April and May 1910, the International Technical

Committee met in Washington at NBS. Scientists from

Germany, France, and Great Britain brought standard

resistors and standard cells that had been carefully

evaluated in terms of their national units. As Chief of

the Electricity Division, Rosa headed this committee.

Comparisons made at the meeting showed that the

Fig. 1. Edward B. Rosa, who set the pace for the high level of

research at the Bureau in its first two decades. Rosa probably sat for

this portrait about 1915, but according to Francis Silsbee, who knew

him, it could have been made at almost any time, for Rosa did not

change much in all his years at the Bureau.

5
resistance unit represented by the German standards was

only 1  10–5 larger than that of the British. Results of

work then in progress under Rosa were in reasonable

agreement, and the committee recommended that all

countries use, as the international ohm, the mean of the

values found by Germany and Great Britain [2,3].

The present NIST impedance calibration laboratory

(ICL) promotes the use of the SI units farad and henry

through capacitance and inductance calibrations for

customers, both inside and outside NIST. The ICL

provides calibrations of nominal-valued capacitors in

the range from 0.001 pF to 1 F in the frequency range

from 100 Hz to 10 kHz. Customers include aerospace

companies, instrumentation companies, the U.S. armed

forces, secondary calibration laboratories, and other

U.S. and foreign national laboratories. The ICL also

provides capacitance calibrations at 1 kHz that are used

by the high-frequency calibration laboratories at NIST

for their calibrations at frequencies above 1 MHz.

The SI impedance unit, the henry, is obtained from

the capacitance and resistance units, the farad and ohm.

The ICL provides calibrations of inductors in the range

50 mHz to 10 Hz in the frequency range from 65 Hz to

10 kHz. The inductance value is found using the

.

Maxwell-Wien bridge [4], which derives the value of

the inductor by comparison against two resistors and a

capacitor.

Prepared by A-M. Jeffrey, N. B. Belecki, and J. F.

Mayo-Wells, based on The Ampere and Electrical Units

[5], authored by members of the Electricity Division.

Bibliography

[1] Edward B. Rosa and Frederick W. Grover, The Absolute

Measurement of Inductance, Bull. Bur. Stand. 1, 125-152 (1905).

[2] F. B. Silsbee, Establishment and maintenance of the electrical

units, NBS Circular 475, National Bureau of Standards,

Washington, DC (1949).

[3] Report to the International Committee on Electrical Units and

Standards, NBS Miscellaneous Publications 16, National Bureau

of Standards, Washington, DC (1912).

[4] Thomas L. Zapf, Calibration of inductance standards in the

Maxwell-Wien bridge circuit, J. Res. Natl. Bur. Stand. 65C,

183-188 (1961).

[5] R. E. Elmquist, M. E. Cage, Y-H. Tang, A-M. Jeffery, J. R.

Kinard, R. F. Dziuba, N. M. Oldham, and E. R. Williams, The

Ampere and Electrical Units, J. Res. Natl. Inst. Stand. Technol.,

January-February (2001).

6
Determination of the Constants of Total

Radiation From a Black Body

This paper [1] presents a critical review of the state of

knowledge about the constant of nature that relates the

quantity of radiant heat and light to the temperature of

the radiant object. Studies of this issue at the beginning

of the 20th century ultimately led to the discovery of

quantum mechanics, the keystone of modern physics.

The continuity of this work at NIST for the remainder of

the century also led to fundamental changes in the way

that optical metrology is now carried out.

In 1905 Samuel W. Stratton, the Director of the National Bureau of Standards, persuaded a young research

associate at the Washington Carnegie Institute to come

to the NBS laboratories to undertake research programs

in infrared spectroscopy. Thus William Weber Coblentz

began a nearly 40-year career at NBS that resulted in

over 400 publications in diverse areas of optical research. Stratton’s original intent was to use Coblentz as

an assistant in his own laboratory, but these demands

were modest and Coblentz was able to pursue his own

interests in infrared spectroscopy and radiometry, begun

as a graduate student at Cornell. One of the suggestions

offered by Stratton led to the work cited here and to the

establishment of the science of radiometry at NBS.

The first decade of the 20th century was a very important time in the development of concepts in modern

physics. One of the of the great mysteries of the era was

the underlying principle behind blackbody radiation, the

heat and light emitted from hot objects. (Black objects

are studied in order to eliminate the effect of reflection.)

Max Planck in Germany had developed a theory that

appeared to explain the phenomenon in proper detail,

but it required the introduction of a revolutionary new

idea. In Planck’s theory, the energy of light and other

electromagnetic radiation was quantized in discrete increments. The proportionality between the energy increment and the frequency of the radiation became

known as Planck’s constant.

The spectral distribution of blackbody radiation, that

is, its radiance at different wavelengths, is determined by

its temperature. Early on, the quantitative details were

described by presuming two constants of nature, which

became known as the first and second radiation constants. Additionally, the total energy of the radiation

emitted was shown to be proportional to the fourth

power of the temperature. This proportionality constant

was named the Stefan-Boltzmann constant after the theoretical physicists who first calculated the relationship.

The Stefan-Boltzmann constant can be expressed in

terms of the other radiation constants or the fundamental

constants now known as Planck’s constant, the Boltzmann constant, and the speed of light. This process of

unifying basic phenomena and verifying the ideas with

accurate experiments was central to the development of

physics at the turn of the century.

On a visit to Europe, Stratton observed that a number

of the national laboratories in Europe were expending

considerable effort in measuring the radiation constants

for describing the spectral distribution and total radiation from blackbody sources. Stratton suggested to

Coblentz that it would be good if NBS could contribute

to this effort and recommended that Coblentz direct his

efforts in this regard.

The accuracy that Coblentz was able to

achieve with his early instruments is a

testimony to his diligence, rare experimental insight, and scientific capability.

During 1914–16, Coblentz developed an absolute

radiometer, measured the Stefan-Boltzmann constant,

and reported the results in the review article [1]. To

perform this measurement he constructed a thermopilebased electrically calibrated radiometer to measure the

total power from a blackbody radiator [2]. The temperature of the blackbody varied between 1000 K and

1400 K, and hence most of the radiation was in the

infrared region of the spectrum. Based upon designs by

Ångstro ̈m and others, Coblentz designed a radiometer

incorporating an electrical heater so that the optical

power could be measured by comparing it to an equivalent amount of electrical power, each causing the

radiometer to rise to the same temperature. A thermopile consists of an array of thermocouple junctions

that are connected in series and parallel to produce a

changing voltage as their temperature changes. Coblentz

experimented with various arrangements of joining the

thermocouple junctions in order to improve their sensitivity and response time. He was able to achieve a sensitivity of about 10 nW [3].

7
Using these thermopile detectors, Coblentz was able

to measure the radiation constants to within 0.5 % of

their presently accepted values. His result for the StefanBoltzmann constant was within 1 % of its present value,

and he was able to calculate a value for Planck’s constant

that differed from the modern value by only 0.8 %. His

results were among the best in the world at that time,

and additionally, he was able to show that the shape of

the blackbody spectrum, its intensity as a function of

wavelength, agreed with Planck’s theory.

In carrying out these difficult measurements he used

the expertise he gained in graduate school while making

infrared measurements of the absorption spectrum of

various gases and materials. He knew how to account

correctly for the effects of atmospheric water and

carbon dioxide, as well as impurities that could cause

anomalous absorption. He designed and built both

absolute and relative detectors, and he constructed

monochromators appropriate to the task of performing

the spectral measurements of blackbody radiators. The

manufacture of these devices required exquisite and

detailed work, with small receivers and intricate wiring

of the thermopiles.

Coblentz is considered the originator of molecular

infrared spectroscopy in the United States, and a society

named after him, the Coblentz Society, arranges scientific meetings and other activities for specialists interested in the infrared region of the spectrum for a variety

of analytical and other purposes [4]. His body of spectroscopic work during his career at NBS is too extensive

to review here—in these and other fields, he published

more than 400 papers in leading scientific journals.

Coblentz also had a life-long interest in astronomy.

He actively participated in astronomical observations

until his retirement in 1945, and he contributed significantly to the art of stellar observations by developing

sensitive radiometers that could be used for stellar

photometry [5]. These were used in many observatories

throughout the United States.

Coblentz applied his technology to the early NBS

efforts in human visual photometry and developed an

early experiment to determine the so-called mechanical

equivalent of light. To do this he measured the visual

wavelength response of a number of observers and then

calculated the radiant luminous efficiency of a blackbody source at known temperatures [6,7]. His early

work in photometry, including work on standard

sources and human visual response, helped set the stage

for the work of Tyndall and Gibson that resulted in the

modern system of photometry used throughout the

world. The photometric units of luminous flux and

luminous intensity were maintained by the world’s

national laboratories using candles, gas flames, and

incandescent lamps until the candela was defined in

1979 by the CIPM in terms of optical power. The work

Coblentz performed in the Stefan-Boltzmann and other

blackbody studies was the progenitor of the detector

development used in the visual photometry efforts.

In the late 1960s, scientists sought a more precise

value of the Stefan-Boltzmann constant by utilizing new

technology. Blevin and Brown at the CSIRO in Australia

developed a more precise experiment and measured the

total radiation at the gold melting point to obtain a value

within 0.1 % of that calculated from the fundamental

constants [8]. At NBS, Ginnings and Reilly built a

new version of the classic Coblentz experiment, but

with a modern innovation—their electrical-substitution

radiometer operated at liquid-helium temperature in

order to gain sensitivity and reduce noise [9]. For a

variety of reasons, including the difficulty in correcting

for diffraction and scattering effects, Ginning and Reilly

did not achieve the accuracy they desired. However, in

the attempt they developed a new type of radiometer,

the cryogenic radiometer, that has ignited a modern

revolution in radiometric accuracy.

Using ideas from the Ginnings and Reilly work,

Quinn and Martin at the National Physical Laboratory

(NPL) in the United Kingdom developed a new cryogenic instrument and succeeded in measuring the

Stefan-Boltzmann constant to within 0.02 % of the

value calculated from the fundamental constants [10].

This landmark work by Quinn and Martin, and further

work by the NPL team, provided a basis for establishing

the cryogenic radiometer as the fundamental highaccuracy instrument for all radiometric standards work

[11]. NIST’s work in cryogenic radiometry was continued by Yokley, who built a very highly sensitive

cryogenic radiometer for calibrating very low level, low

temperature thermal sources [12].

The cryogenic radiometer and its inherent accuracy of

0.05 % or better has revolutionized optical and photometric measurements. No longer do we think in terms of

primary, standard sources of light. Instead, the best

standards work is based upon measurements and comparisons of detectors of light [13, 14]. The 1979 redefinition of the candela in terms of optical power takes full

advantage of cryogenic radiometry to put modern

photometric standards on a detector basis [15].

Cryogenic radiometry, together with new technology in

silicon photodiodes, low-noise amplifiers, and precision

optical filters, has spawned new types of standards for

the candela, lumen, and lux. Further developments have

placed the spectral radiance and irradiance scales on an

absolute detector base through the accurate measurement of the temperatures of blackbody sources with

narrow-band filtered photodetectors. All of these will

continue to improve over time as further improvements

to filters and the detectors are anticipated.

8
The fundamental strategy originated at NBS by

Coblentz in making radiometric and photometric

measurements with electrically calibrated optical

detectors set the stage at NIST for the present-day and

future standards work. The continued importance of

better measuring the Stefan-Boltzmann constant spurred

the development of the modern cryogenic radiometer,

which is found today in most national standards laboratories throughout the world. The legacy of Coblentz’s

work in the early 20th century to develop even more

sensitive optical detectors is a continuing effort to keep

pace with such needs. The accuracy that Coblentz was

able to achieve with his early instruments is a testimony

to his diligence, rare experimental insight, and scientific

capability. His work is the cornerstone of radiometry,

photometry, and infrared spectroscopy at NIST.

Prepared by Albert C. Parr.

Bibliography

[1] W. W. Coblentz, Present status of the determination of the

constant of total radiation from a black body, Bull. Bur. Stand.

12, 553-582 (1916).

[2] W. W. Coblentz and W. B. Emerson, Studies of instruments

for measuring radiant energy in absolute value; an absolute

thermopile, Bull. Bur. Stand. 12, 503-551 (1916).

[3] W. W. Coblentz, Various modifications of bismuth-silver thermopiles having a continuous absorbing surface, Bull. Bur. Stand. 11,

131-187 (1914).

[4] Coblentz Society, 761 Main Street, Norwalk, CT 06859-0002;

(http://www.galactic.com/Coblentz/Index.htm)

[5] W. W. Coblentz, A comparison of stellar radiometers and radiometric measurements on 110 stars, Bull. Bur. Stand. 11, 613-656

(1915).

[6] W. W. Coblentz and W. B. Emerson, Relative sensibility of

the average eye to light of different colors and some practical

applications to radiation problems, Bull. Bur. Stand. 14, 167-236

(1918).

[7] W. W. Coblentz and W. B. Emerson, Luminous radiation from a

black body and the mechanical equivalent of light, Bull. Bur.

Stand. 14, 255-266 (1918).

[8] W. R. Blevin and W. J. Brown, A precise measurement of the

Stefan-Boltzmann constant, Metrologia 7, 15-29 (1971).

[9] D. C. Ginnings and M. L. Reilly, Calorimetric measurement of

thermodynamic temperatures above 0 C using total blackbody

radiation, in Temperature; Its Measurement and Control in Science and Industry, Vol. 4, Instrument Society of America, Pittsburgh (1972), pp. 339-348.

[10] T. J. Quinn and J. E. Martin, A radiometric determination of the

Stefan-Boltzmann constant and thermodynamic temperatures

between –40 C and +100 C, Philos. Trans. R. Soc. London

A316, 85-189 (1985).

[11] J. E. Martin, N. P. Fox, and P. J. Key, A cryogenic radiometer for

absolute radiometric measurements, Metrologia 21, 147-155

(1985).

[12] C. R. Yokley, A radiometric calibration facility for low temperature blackbodies, Final Report to the NASA Lyndon B. Johnson

Space Center, contract T-955C, November 23, 1976.

[13] A. C. Parr, A National Measurement System for Radiometry,

Photometry, and Pyrometry Based Upon Absolute Detectors,

NIST Technical Note 1421, National Institute of Standards and

Technology, Gaithersburg, MD (1996).

[14] T. R. Gentile, J. M. Houston, J. E. Hardis, C. L. Cromer, and

A. C. Parr, National Institute of Standards and Technology highaccuracy cryogenic radiometer, Appl. Opt. 35, 1056-1068

(1996).

[15] C. L. Cromer, G. Eppeldauer, J. E. Hardis, T. C. Larason,

Y. Ohno, and A. C. Parr, The NIST Detector-Based Luminous

Intensity Scale, J. Res. Natl. Inst. Stand. Technol. 101, 109-132

(1996).

9
The Testing of Thermal Insulators

At the turn of the 20th century the refrigeration industry

in the United States was becoming a commercial reality.

Mechanical refrigeration technology had achieved

economic viability as a means of producing ice for

cooling and was on the threshold of moving into households as an everyday appliance. Advances were underway to provide mechanical “air conditioning” for public

buildings, such as theaters, department stores, and skyscrapers. In general, the early 1900s saw the evolution of

a scientific approach to refrigeration through companysponsored research and development. It was the

technical progress in the area of cooling and heating for

industrial processes and thermal comfort that stimulated

the development of thermal insulation standards at

NIST.

As described in Measures for Progress: A History of

the National Bureau of Standards, Congress, at the

request of the refrigeration industry, appropriated funding in 1913 for investigation of physical

constants involved in the construction and operation of

large-scale refrigeration machinery. Under Hobart C.

Dickinson, D. R. Harper 3rd, and N. S. Osbourne,

studies were conducted that included the investigation of

insulating materials used in the construction of largescale refrigeration structures. Of particular interest to

the mechanical engineer was the development of usable

data pertaining to heat transmission in thermal insulation needed for design purposes. For this purpose,

Dickinson is credited with independently developing an

absolute method of measurement called the guarded hot

plate for homogenous slab-like materials.

In 1916, Dickinson and fellow NBS colleague Milton

S. Van Dusen published The Testing of Thermal Insulators [1], a classic description of an NBS study to identify

the causes of discordant experimental results for heat

transfer through homogeneous solid materials and

engineering systems. The publication contained accurate determinations of heat flow through air spaces and

through 30 insulating materials; it also promoted the

usage of standard terminology for thermal conductivity

measurements obtained for solid materials and compound walls. Shortly after their first publication, Van

Dusen published The Thermal Conductivity of Heat

Insulators [2], which provided detailed information on

the design and theory of operation of the apparatus, as

well as additional thermal conductivity measurements

of insulating materials. Important and insightful publications in their day, these papers are still considered

recommended reading for all students of heat transfer

through thermal insulation.

At NBS the guarded hot plate quickly became the

foundation for thermal conductivity measurements of

heat insulators, and this encouraged the development of

other apparatus for the measurement of thermal conductivity of solids, not only for building materials but also

for metals, refractories, and ceramics. In fact, one might

argue that either directly or indirectly the apparatus has

motivated nearly eight decades of thermal conductivity

work on solids at NBS/NIST. An early spin-off was the

development of the guarded hot box, which was based

on similar principles of operation and was utilized

for heat transmission measurements of simple and

Fig. 1. Hobart C. Dickinson (1875-1949). While traveling in Europe,

Dickinson learned that Richard Poensgen in Germany had independently developed and been using a guarded hot plate for thermal

conductivity measurements since 1910. Thus, Poensgen is generally

credited as the first to develop the guarded hot plate method.

10
compound walls. From 1915 to 1934,Van Dusen and

others developed a comparative apparatus for measuring

the thermal conductivity of metals up to 600 C. Late in

his career, in 1948, Dickinson developed a relatively

simple steady-state method for thermal conductivity

measurements of refractory solids. The apparatus

employed a steam calorimeter for measuring the

thermal conductivity of refractory solids from 400 C to

1500 C [3].

The long-term impact of the guarded hot plate

technology was evident in several areas outside NBS.

One of the first was the outgrowth of consensus

engineering design data. The guarded hot plate

originally developed by Dickinson and Van Dusen was

refined over several years, and about 1928 Van Dusen

[4] constructed a version of the apparatus that operated

consistently until 1983. The thermal conductivity data

obtained from this apparatus, along with the data from

the early NBS publications [1,2], were aggregated with

other data and tabulated in handbooks as design heat

transmission coefficients for the engineer. These design

data have served the engineering community effectively

for several decades. In recent years, most of the original

NBS data has been compiled in electronic format and

will be available in NIST Standard Reference Database

81, Heat Transmission Properties of Insulating and

Building Materials (Web Version 1.0).

However, the single most important impact of the

guarded hot plate technology was the standardization of

the test method in North America. This remarkable step

has been extremely effective in reducing the differences

among laboratories with respect to thermal testing.

After many years of effort, NBS researcher Henry E.

Robinson and others produced a tentative edition of the

test method in 1942. By joint action, the American

Society of Heating and Ventilating Engineers (ASHVE),

American Society for Testing and Materials (ASTM),

American Society for Refrigeration Engineers (ASRE),

and the National Research Council (NRC) produced a

Standard Method of Test for Thermal Conductivity of

Materials by Means of the Guarded Hot Plate. In 1945,

the method was formally adopted as a standard and

designated ASTM Test Method C 177. The code set up

the requirements for conducting tests and for construction of a guarded hot plate apparatus. It is interesting to

note that the standard’s adjunct still contains the design

drawings for the 1929 version of the NBS guarded hot

plate apparatus. ASTM Test Method C 177 became the

cornerstone for all thermal insulation testing in North

Robinson was instrumental in disseminating ASTM

Test Method C 177 through laboratory intercomparison

testing, development of insulation reference materials,

and refinement of the measurement method. In 1947,

Robinson and colleague Thomas W. Watson extended

the temperature range of Van Dusen’s guarded hot plate

apparatus. A few years later, NBS completed one of the

first published laboratory intercomparisons of thermal

conductivity tests of insulation [5].

America. Over the decades, the standard test method has

achieved international acceptance as the most accurate

absolute test method for the measurement of thermal

conductivity of heat insulators.

This series of tests clearly demonstrated the need for

suitable means to calibrate the apparatus at industrial

and other laboratories. Shortly thereafter, a program

was devised for supplying to industry measured samples

of suitable insulating materials for calibration purposes.

By 1977 more than 300 laboratories had been served,

resulting in considerable improvement in the quality of

thermal conductivity data on insulating and building

materials reported in technical journals and handbooks.

In 1977 the ASTM Committee C-16 on Thermal and

Cryogenic Insulating Materials recommended that this

program become an official part of the NBS Standard

Reference Materials Program. Presently, NIST provides

the thermal testing community with several thermal

insulation SRMs for thermal resistance.

Fig. 2. Henry E. Robinson (1911-1972), installing a pair of corkboard specimens for interlaboratory testing (circa 1948).

11
In 1964, Robinson presented an elegant modification

of the test method. The basic design of a line-heatsource guarded hot plate was presented to a thermal

conductivity conference sponsored by the National

Physical Laboratory in England. The design was

reported in Nature [6] as follows:

H. E. Robinson (U.S. National Bureau of

Standards) discussed forms of line heat

sources that could be used as heaters in

apparatus for measurements at lower

temperatures on insulating materials in

disk and slab form. These new configurations lend themselves more readily to mathematical analysis, they are more simple to

use and would appear to be able to yield

more accurate results.

The design was novel. In contrast to a (conventional)

guarded hot plate that used uniformly distributed

heaters, line-heat-source guarded hot plates utilized

circular line-heat sources at precisely specified locations. By proper location of the line-heat-source(s), the

temperature at the edge of the meter plate can be made

equal to the mean temperature of the meter plate,

thereby facilitating temperature measurements and

thermal guarding. The benefits offered by a line-heatsource guarded hot plate included simpler methods of

construction; improved accuracy; simplified mathematical analyses for calculating the mean surface temperature of the plate as well as determining the errors

resulting from heat gains or losses at the edges of the

specimens; and superior operation under vacuum

conditions.

After Robinson, another generation of NBS

researchers continued development of the line-heatsource technology. In 1971, M. H. Hahn [7] conducted

an in-depth analysis of the line-heat-source concept and

investigated several design options. The design, mathematical analysis, and uncertainty analysis for a prototype line-heat-source guarded hot plate were published

in 1974 by Hahn, Robinson (posthumously), and D. R.

Flynn [8]. Construction of the prototype apparatus was

completed in 1978 [9]. Because of the promising results

from the prototype, NIST began plans for a second,

larger line-heat-source guarded hot plate apparatus. In

1980, a ruling by the U.S. Federal Trade Commission

concerning the labeling and advertising of home

insulation dramatically accelerated the construction of

this apparatus.

With the energy crisis in the 1970s, there was growing demand for thick insulation and a resulting concern

from the Federal Trade Commission that the existing

standards for insulation measurement, based on 25 mm

thick specimens, were not protecting consumers’ interests. In response to concerns from industry and the

Federal Trade Commission, NBS expedited development of the one-meter line-heat-source guarded hot

plate. Near the end of 1980, the second line-heat-source

guarded hot plate apparatus was completed with the

efforts of Hahn, B. A. Peavy, F. J. Powell, and others

[10]. Industry subsequently testified to Congress [11]

that the improved accuracy provided savings of $90

million per year to consumers in insulation costs alone.

It is not surprising that NIST now plans to continue

developing the measurement technique into the 21st

century with a new design that will extend the current

temperature range.

After starting at NBS in 1903, Hobart C. Dickinson

was the co-author of several fundamental papers on

thermometry. In 1910, he returned to Clark University

for his Ph.D. His doctor’s thesis was on combustion

calorimetry, and his calorimeter design, with some

refinements, yielded the most accurate results attainable

for its time. From 1912 to 1917 he was in charge of

work at the Bureau of Standards on the constants of

refrigeration in a program sponsored by the American

Society of Refrigeration Engineers. His contributions to

this program were papers on the calorimetry of ice and

on the thermal conductivity of insulating materials. At

the onset of World War I, the Bureau Director, Samuel

Wesley Stratton, asked him to assist in the development

of aircraft engines, and he participated in the design of

the Liberty Engine, which was one of the engineering

triumphs of that time. After the war the activities of the

section were expanded to embrace automobiles and their

behavior on the road. From 1921 to 1923 he organized

and directed the research department of the Society of

Automotive Engineers at the headquarters in New York

City, and in 1933 he was president of that society.

Dickinson was an ardent hiker and preferred to spend

his vacations in the mountains. In his later years he

served the Potomac Appalachian Trail Club in its

program of shelter building. On his first trip to the

Canadian Rocky Mountains with the Alpine Club of

Canada he took only a small spare blanket and waterrepellent sheet when he should have taken all his own

bedding. Confronted with bleak prospects, he remembered his measurements on insulating materials, and

with his usual resourcefulness gathered balsam boughs

in considerable quantity to put between his blanket and

his sheet. The result astonished him, and he soon learned

that a relatively small thickness of balsam furnished

sufficient insulation to keep him pleasantly warm even

on freezing nights.

Prepared by Robert R. Zarr.

12
Bibliography

[1] H. C. Dickinson and M. S. Van Dusen, The Testing of Thermal

Insulators, ASRE J. 3 (2), 5-25 (1916).

[2] M. S. Van Dusen, The Thermal Conductivity of Heat Insulators,

Trans. Am. Soc. Heat. Ventilat. Eng. 26, 385-414 (1920).

[3] D. R. Flynn and D. A. Didion, A Steam Calorimeter Apparatus

for Refractories, in Conference on Thermal Conductivity

Methods, Battelle Memorial Institute, Columbus, Ohio (1961)

pp. 81-90.

[4] M. S. Van Dusen and J. L. Finck, Heat Transfer through Insulating Materials, American Institute of Refrigeration 17, 137-150

(1928).

[5] H. E. Robinson and T. W. Watson, Interlaboratory Comparison

of Thermal Conductivity Determinations with Guarded

Hot Plates, in Symposium on Thermal Insulating Materials:

Cincinnati Spring Meeting, American Society for Testing Materials, March 7, 1951, (ASTM STP 119), American Society for

Testing Materials, Philadelphia, PA (1951) pp. 36-44.

[6] R. P. Tye, Thermal Conductivity, Nature 204, 636-637 (1964).

[7] M. H. Hahn, The Line Heat Source Guarded Hot Plate for

Measuring the Thermal Conductivity of Building and Insulating

Materials, Ph.D. Dissertation, Catholic University of America,

Washington, DC (1971).

[8] M. H. Hahn, H. E. Robinson, and D. R. Flynn, Robinson

Line-Heat-Source Guarded Hot Plate Apparatus, in Heat Transmission Measurements in Thermal Insulations (ASTM STP 544),

American Society for Testing and Materials, Philadelphia, PA

(1974) pp. 167-192.

[9] M. C. I. Siu and C. Bulik, National Bureau of Standards LineHeat-Source Guarded Hot Plate Apparatus, Rev. Sci. Instrum.

52, 1709-1716 (1981).

[10] F. J. Powell and B. G. Rennex, The NBS Line-Heat-Source

Guarded Hot Plate for Thick Materials, in Thermal Performance

of the Exterior Envelopes of Buildings II: Proceedings of the

ASHRAE/DOE Conference (ASHRAE SP 38), American Society

of Heating, Refrigerating, and Air-Conditioning Engineers,

Atlanta, GA (1983) pp. 657-672.

[11] National Bureau of Standards Authorization, Hearing Before the

Subcommittee on Science, Technology, and Space of the Committee on Commerce, Science, and Transportation; United States

Senate; Ninety-Eighth Congress; First Session, on National

Bureau of Standards Authorization; Serial No. 98-3, 67

(February 22, 1983).

13
Precipitation Hardening of Metal Alloys

Precipitation hardening, or age hardening, provides

one of the most widely used mechanisms for the

strengthening of metal alloys. The fundamental understanding and basis for this technique was established in

early work at the U. S. Bureau of Standards on an alloy

known as Duralumin [1,2]. Duralumin is an aluminum

alloy containing copper and magnesium with small

amounts of iron and silicon. In an attempt to understand

the dramatic strengthening of this alloy, Paul D. Merica

and his coworkers studied both the effect of various heat

treatments on the hardness of the alloy and the influence

of chemical composition on the hardness. Among the

most significant of their findings was the observation

that the solubility of CuAl2 in aluminum increased with

increasing temperature. Although the specific phases

responsible for the hardening turned out to be too small

to be observed directly, optical examination of the

microstructures provided an identification of several of

the other phases that were present. The authors

proceeded to develop an insightful explanation for the

hardening behavior of Duralumin which rapidly became

the model on which innumerable modern high-strength

alloys have been developed.

In his Institute of Metals lecture [3], Merica summarized the Merica, Waltenberg, and Scott paper as follows: “The four principal features of the original

Duralumin theory were these: (1) age-hardening is

possible because of the solubility-temperature relation

of the hardening constituent in aluminum, (2) the hardening constituent is CuAl2, (3) hardening is caused by

precipitation of the constituent in some form other than

that of atomic dispersion, and probably in fine molecular, colloidal or crystalline form, and (4) the hardening

effect of CuAl2 in aluminum was deemed to be related

to its particle size.”

At a symposium devoted to precipitation from solid

solution, held nearly four decades after the original

papers, R. F. Mehl noted [4], “The early work of

Merica, Waltenberg, and Scott was the first contribution

to theory: it demonstrated the necessity of a solid

solubility decreasing with temperature; this paper had

not only science but even prescience, for it suggested

that some sort of precipitate-matrix interaction might

contribute to hardening, long before coherency was

even conceived. There are few better examples of the

immense practical importance of the theory in the

history of science; before Merica no new age-hardening

alloys were discovered—the worker did not know where

to look; following Merica, new age-hardening alloys

came in a flood.”

The importance of the theoretical suggestion for the

development of new alloys is clear from the historical

record [5]. At the end of the 19th century, cast iron was

the only important commercial alloy not already known

to western technology at the time of the Romans. When

age hardening of aluminum was discovered accidentally

by Wilm [6], during the years 1903-1911, it quickly

became an important commercial alloy under the trade

name Duralumin.

The two NBS studies published in 1919 explored both

the application of phase diagrams to the phenomenon

and the consequences of various heat treatments on the

subsequent time evolution of mechanical properties.

The latter study tentatively concluded that age hardening of aluminum was a room-temperature precipitation

phenomenon and suggested that it should be possible for

other alloys to be hardened by a thermal treatment

leading to precipitation. Merica et al. suggested that

examination of the relevant phase diagrams would reveal

which alloys were candidates for such precipitation

hardening and would provide both the solutionizing

temperature and the range of temperature needed for the

precipitation process.

This prescription proved to be astonishingly successful for developing new alloys. It led to a “golden age” of

phase diagram determination that lasted two decades. It

contributed to the development of a variety of fields in

materials science and launched a scholarly debate that

overthrew old concepts and definitions concerning alloy

phases.

In the 15-year interval between the discovery by

Wilm and the suggestion by the Bureau of Standards

group, only one other age-hardening system had been

discovered, but not published. Aging of Duralumin was

thought to be a unique and curious phenomenon.

However, by 1932, Merica could tabulate experience

with fourteen base metals that had been discovered to

harden by precipitation in a total of more than one

hundred different alloy combinations. Even that list was

already incomplete and underestimated the true worldwide effort that the theoretical suggestion had stimulated. Most of today’s high strength commercial

aluminum and nickel-based alloys are precipitation

hardened, as are many titanium and iron-based alloys.

Despite the practical success of the theory, there

was skepticism since the precipitates did not grow to

14
optically observable size until long after the hardening

had begun. Almost 20 years passed before the

precipitates responsible for the hardening were detected

experimentally by small-angle x-ray scattering. When

finally detected, they became known as Gunier-Preston

(GP) zones. Today, they are regarded as true precipitates

of a metastable coherent phase, obeying the laws of

thermodynamic equilibrium, and are depicted as a

metastable feature in phase diagrams.

The precipitation hardening hypothesis is now

credited with insights into other phenomena, most

particularly slip motions in crystals as presented in the

slip interference theory [7]. The latter theory is

acknowledged as the precursor to modern dislocation

theory [8].

.

Paul Dyer Merica had a rather remarkable career [9].

After attending DePauw University for three years, he

went to the University of Wisconsin, earning an A. B

degree in 1908. He then taught chemistry in China

before receiving his Ph. D. in Metallurgy and Physics

from the University of Berlin in 1914. He joined the

U.S. Bureau of Standards that same year, holding the

positions of research physicist, associate physicist,

physicist, and metallurgist. In 1919 he joined the International Nickel Company, rising to become president

and director from 1951 until his retirement in 1955.

Throughout the course of his career, Merica received

numerous awards, including the Franklin Institute

Medal, the James Douglas Gold Medal, the Robert

Franklin Mehl Award from the Minerals, Metals &

Materials Society, the Fritz Medal, and, in 1942,

he became a member of the National Academy of

Sciences.

Prepared by Sam Coriell with reference to the

historical account by John Cahn [5].

Bibliography

[1] P. D. Merica, R. G. Waltenberg, and H. Scott, Heat Treatment of

Duralumin, Bull. Am. Inst. Min. Metall. Eng. 150, 913-949

(1919); also P. D. Merica, R. G. Waltenberg, and H. Scott, HeatTreatment of Duralumin, Sci. Pap. Bur. Stand. 15, 271-316

(1919).

[2] P. D. Merica, R. G. Waltenberg, and J. R. Freeman, Jr., Constitution and Metallography of Aluminum and Its Light Alloys with

Copper and with Magnesium, Trans. Am. Inst. Min. Metall. Eng.,

Vol. LXIV, pp. 3-25 (1921); also P. D. Merica, R. G. Waltenberg,

and J. R. Freeman, Jr., Constitution and Metallography of

Aluminum and Its Light Alloys with Copper and with Magnesium, Sci. Pap. Bur. Stand. 15, 105-119 (1919).

[3] P. D. Merica, The Age-Hardening of Metals, Trans. Am. Inst. Min.

Metall. Eng. 99, 13-54 (1932).

[4] R. F. Mehl, Introduction and Summary, in Precipitation from Solid

Solution, R. F. Mehl, et al., American Society for Metals,

Cleveland, OH (1959) pp. 1-5.

[5] J. W. Cahn, A Historical Perspective on the Utilization of Phase

Diagrams for Precipitation Hardening, Bull. Alloy Phase

Diagrams 4, 349-351 (1983).

[6] A. Wilm, Physikalisch-metallurgische Untersuchungen u ̈ber

magnesiumhaltige Aluminiumlegierungen, Metallurgie 8, 225-

227 (1911).

[7] Z. Jeffries and R. S. Archer, The Slip Interference Theory of the

Hardening of Metals, Chem. Metall. Eng. 24, 1057-1067 (1921).

[8] C. S. Smith, Dictionary of Scientific Biography, Vol. VII, Charles

Scribner’s Sons, New York (1973) pp. 92-93.

[9] Zay Jeffries, Paul Dyer Merica, in Biographical Memoirs,

Vol. XXXIII, National Academy of Sciences, Columbia University Press, New York (1959) pp. 226-240.Fig. 1. Paul Merica, ca. 1932 (Reproduced with permission of the

AIME).

15
Construction and Operation of a Simple

Homemade Radio Receiving Outfit

The 1922 Bureau of Standards publication, Construction and Operation of a Simple Homemade Radio

Receiving Outfit [1], is perhaps the best-known of a

series of publications on radio intended for the general

public at a time when the embryonic radio industry in

the U.S. was undergoing exponential growth.

While there were a number of earlier experiments

with radio broadcasts to the general public, most historians consider the late fall of 1920 to be the beginning

of radio broadcasting for entertainment purposes.

Pittsburgh, PA, station KDKA, owned by Westinghouse,

received its license from the Department of Commerce

just in time to broadcast the Harding-Cox presidential

election returns. In today’s world where instant global

communications are commonplace, it is difficult to

appreciate the excitement that this event generated.

News of the new development spread rapidly, and

interest in radio soared. By the end of 1921, new broadcasting stations were springing up all over the country.

Radios were selling faster than companies could manufacture them. The demand for information on this new

technology was almost insatiable. The Radio Section of

the Bureau of Standards provided measurement knowhow to the burgeoning radio industry as well as general

information on the new technology to the public. Letters

to the Bureau seeking information on radio technology

began as a trickle, and then soon became a flood.

Answering them became a burden.

Circular 120, published in April 1922, began:

“Frequent inquiries are received at the Bureau of

Standards for information regarding the construction of

a simple receiving set which any person can construct in

the home from materials which can be easily secured.

This publication has been prepared to meet these

inquiries.” The circular also noted that the Bureau was

cooperating with the Bureau of Markets and Crop

Estimates of the Department of Agriculture. In the early

days of radio, broadcasts to farmers of crop price reports

were an important public service.

In 1921 factory-made radios were very expensive.

Many of them cost more than $2000 in today’s dollars,

and less affluent families could not afford to have one.

When the Bureau published this circular (which sold for

only five cents) on how to build a simple crystal radio at

home, it was an instant success. Thousands of orders

Fig 1. The crystal radio described in Circular 120.

Fig. 2. Diagram showing the antenna and ground connections to the

radio.

16
flowed in from every state. The circular showed how

almost any family having a family member handy with

simple tools could make a radio. The circular states

“Satisfactory results have been obtained from sets

constructed according to these instructions by persons

having no previous experience with radio.” The authors

stated that the cost of the materials for the radio and

associated headphones and antenna system should not

exceed $10.

Newspapers around the country urged readers interested in radio to order a copy, and in many cases they

reprinted the entire article. Even today, antique radio

collectors searching attics and basements often come

across dusty home-built crystal radio sets that were

obviously constructed using the Bureau’s plans. No

doubt the remarkably rapid growth of the radio industry

in the U.S. during the 1920s (analogous to the growth in

Internet-related businesses today) was aided considerably by information provided to the public by the

Bureau, such as this circular and the other items noted

in the bibliography [2-6].

Circular 120 proved such a success that the Bureau

published a number of other circulars on radio technology intended for the general public, as noted in the

bibliography. All were popular. In some cases,

commercial radio manufacturers copied the circuits

proposed by the Bureau. During the same era, other

radio publications of the Bureau captured public attention as well, though perhaps in smaller quantities than

Circular 120. Radio Instruments and Measurements [7],

Circular 74, published first in 1918 with a second

edition published in 1924, became a best seller in the

post-WW I era. Its principal authors were most likely

J. H. Dellinger, J. M. Miller, F. W. Grover, and G.C.

Southworth. The authors of Circular 120 are not stated,

but some of those same individuals likely contributed to

it. J. Howard Dellinger’s story is particularly interesting.

He came to the Bureau in 1907 as a laboratory assistant

at $900 per year, and retired as Chief of the Central

Radio Propagation Laboratory in 1948. He headed the

Radio Section for much of its existence. Appendix D of

Reference [9] is a biography of Dellinger.

The Principles Underlying Radio Communication [8],

Signal Corps Radio Communication Pamphlet No. 40,

published in 1919 and issued in a revised edition in

1922, is another interesting example of a popular radio

book. Written by the Bureau of Standards for training

Army Signal Corps officers, it was an expanded and

updated version of Circular 74, noted above, but was

also widely used by college students and others studying

radio. In spite of the “pamphlet” designation, it was

actually a 600-page book. Thomas Edison said

“. . . This is the greatest book on this subject that I have

ever read, and I want to congratulate you and your

Bureau on its production.”

While the general public was interested in radio

information for the lay person, the fledgling radio

industry needed in-depth technical assistance from the

Bureau, which it got. The Bureau helped radio manufacturers make better measurements for quantities such

as resistance, capacitance, voltage, and frequency.

Results of Bureau research on antennas and radio wave

propagation, direction finders, vacuum tube characteristics, and testing were eagerly utilized by major

Fig. 3. Details of the outdoor antenna recommended for use with the crystal radio.

17
companies such as General Electric, Westinghouse,

Western Electric, and RCA, as well as by a myriad of

small radio companies no longer in existence. At the

same time that the Bureau was providing information to

people constructing radios on their kitchen tables, Radio

Section staff members were presenting technical papers

on radio at conferences and in journals such as the

Proceedings of the Institute of Radio Engineers. A good

example of the latter is the classic work by John Miller,

who discovered and explained “the Miller effect”—a

feedback effect in triode vacuum tubes that limited their

ability to amplify at radio frequencies [9].

Circular 120 described in detail not only the crystal

radio itself but also how to construct an antenna and

ground system. To minimize the cost, the circular

suggested winding the tuning coil on a discarded

cylindrical oatmeal box. For years afterwards, home

experimenters used oatmeal boxes as coil forms for

homemade radios. The crystal radio did not require

batteries, but it did require the user to purchase a

commercially made set of headphones (or telephone

receivers as they were called in those days), since that

accessory was not suitable for home construction.

One can just imagine the thrill of a farm family that

had never heard a radio broadcast before trying the new

set for the first time, and one of the family members

crying out, “Come listen! I am hearing something!” The

electronics revolution was underway and the Bureau

played a significant part in accelerating the new

technology.

Prepared by Brian Belanger.

Bibliography

[1] Construction and Operation of a Simple Homemade Radio

Receiving Outfit, Circular of the Bureau of Standards, No. 120,

U.S. Government Printing Office, Washington, DC, April 24,

1922.

[2] Construction and Operation of a Two-Circuit Radio Receiving

Equipment with Crystal Detector, Circular of the Bureau

of Standards, No. 121, U.S. Government Printing Office,

Washington, DC, July 17, 1922.

[3] Sources of Elementary Radio Information, Circular of the

Bureau of Standards, No. 122, U.S. Government Printing

Office, Washington, DC, June 22, 1922. (Updated to second

edition, Sept. 12, 1923.)

[4] Description and Operation of an Electron-tube Detector Unit for

Simple Radio Receiving Outfits, Circular of the Bureau of

Standards, No. 133, U.S. Government Printing Office,

Washington, DC, November 10, 1922.

[5] Auxiliary Condensers and Loading Coil Used with Simple

Homemade Radio Receiving Outfits, Circular of the Bureau

of Standards, No. 137, U.S. Government Printing Office,

Washington, DC, Feb. 23, 1923.

[6] Description and Operation of an Audio-Frequency Amplifier

Unit for Simple Radio Receiving Outfits, Circular of the Bureau

of Standards, No. 141, U.S. Government Printing Office,

Washington, DC, March 24, 1923.

[7] Radio Instruments and Measurements, Circular of the Bureau of

Standards C74, U.S. Government Printing Office, Washington,

DC, 1918. (Second edition published in 1924.)

[8] The Principles Underlying Radio Communication, Signal Corps

Radio Communication Pamphlet No. 40, U.S. Government

Printing Office, Washington, DC (1919). (Written by Bureau

staff members.)

[9] W. F. Snyder and C. L. Bragaw, Achievement in Radio: Seventy

Years of Radio Science, Technology, Standards, and Measurement at the National Bureau of Standards, NBS Special

Publication 555, National Bureau of Standards, Boulder, CO

(1986).

18
Methods for Standardizing and Testing

Precision Gage Blocks

This paper by C. G. Peters and H. S. Boyd [1] summarizes the efforts at NBS in the early 1920s to improve

the calibration of precision gage blocks. Since their invention at the turn of the twentieth century, gage blocks

have been the major source of length standardization for

industry, and their calibration is one of the most important high precision calibrations made in dimensional

metrology. In most measurements of such enduring importance, it might be expected that the measurement

would become much more accurate and sophisticated

over 80 years of development. Because of the extreme

simplicity of gage blocks, this has only been partly true.

The most accurate measurements of gage blocks have

not changed dramatically in accuracy in the last 70

years, because one of the major sources of uncertainty

is the geometry of the gaging face of the block. The very

best gage blocks have always had the gaging surfaces

flat to 20 nm or better, but these blocks were very rare

at the turn of the last century. This level of geometry

simply was not necessary to obtain the measurement

accuracy needed by industry of the time. What has

changed is the much more widespread necessity of such

accuracy. Measurements that previously could be made

only with the equipment and expertise of a national

metrology laboratory are routinely expected in private

industrial laboratories.

By the end of the nineteenth century, the idea of

interchangeable parts begun by Eli Whitney had been

accepted by industrial nations as the model for industrial manufacturing. One of the drawbacks to this new

system was that, in order to control the size of parts,

numerous gages were needed to check the parts and set

the calibrations of measuring instruments. The number

of gages needed for complex products, and the effort

needed to make and maintain the gages, was a significant expense. The major step toward simplifying this

situation was made by C. E. Johannson, a Swedish machinist.

Johannson’s idea, first formulated in 1896 [2], was

that a small set of gages that could be combined to form

composite gages could reduce the number of gages

needed in the shop. For example, if four gages of sizes

1 mm, 2 mm, 4 mm, and 8 mm could be combined in

any combination, all of the millimeter sizes from 1 mm

to 15 mm could be made from only these four gages.

Johannson found that if two opposite faces of a piece of

steel were lapped very flat and parallel, two blocks

would stick together when they were slid together with

a very small amount of grease between them. The width

of this “wringing” layer is about 25 nm, which was so

small relative to the tolerances needed at the time that

the block lengths could be added together with no correction for interface thickness. Eventually, the wringing

layer was defined as part of the length of the block,

allowing the use of an unlimited number of wrings

without correction for the size of the wringing layer.

In the United States, Henry Ford enthusiastically

adopted the idea, and the use of gage blocks was eventually adopted as the primary transfer standard for

length in industry. By the beginning of World War I, the

gage block was already so important to industry that the

Federal Government had to take steps to ensure the

availability of blocks. At the outbreak of the war, the

only supply of gage blocks was from Europe, and this

supply was interrupted.

In 1917 inventor William Hoke came to NBS proposing a method to manufacture gage blocks equivalent to

those of Johannson [3]. Funds were obtained from the

Ordnance Department for the project, and 50 sets of 81

blocks each were made at NBS. There were problems,

Fig. 1. Gage Blocks. The blocks on the left were manufactured at the

Bureau of Standards during World War I. In the center are the descendants of the Bureau of Standards blocks, square “Hoke” style blocks.

The rectangular style is the international standard, used all over the

world.

19
of course. The major problem was the difficulty of

making a flat surface. Nearly any error in the system

tends to produce block faces shaped like a dome. The

solution was to make a hole in the center of the block,

preventing the dome in the center. While nearly all gage

blocks today are rectangular or square cross-section, the

holes in the center of square blocks are the direct

descendants of the NBS blocks, and are called “Hoke

blocks.”

Besides making gage blocks, NBS was also,

obviously, engaged in measuring gage blocks. While the

standard of length, the International Prototype

Meter, was a line scale, the precedent of comparing

length to the wavelength of light was well established.

Albert Michelson, the great American scientist well

known for his speed of light measurements, had been

asked by the International Committee of Weights and

Measures to measure the meter in terms of light waves

in the early 1890s. By 1893 Michelson had compared

the International Prototype Meter to the wavelength of

the red emission line of cadmium. The average value

of 1,553,164.5 wavelengths at 15 C and standard

atmospheric pressure is remarkably close to the current

value.

By 1920 work was underway at the International Bureau of Weights and Measures (BIPM) and in some of

the national measurement institutes to build interferometers to measure end standards. The work of

Peters and Boyd [1], published in the NBS Journal of

Research, is a very complete report on the NBS effort.

The paper begins with a basic discussion of interference and the accuracy of the optical method of

measurement of length, flatness, and parallelism. The

uncertainty estimates, for blocks of good geometry, are

about the same as currently realized. The interference

section leads to a discussion of measuring flatness using

a master optical flat and an interferometric viewer: the

Pulfrich Viewer. This same instrument is still used at

NIST to calibrate master optical flats. The discussion

of the interpretation of interference fringes is still an

accurate and practical teaching tool.

That section is followed by a section discussing one of

the more subtle problems with gage blocks, the

effects of wringing blocks together into a stack. Their

eventual advice is the same we give out today: make up

a stack of three or more blocks that equal the nominal

height of another block, e.g., compare a stack of 2 mm,

3 mm, and 5 mm to the 10 mm block. They show examples of the growth of two stacks, and even throw in a

warning not to rub the block on the user’s wrist to make

the wringing film more substantial. This horrid practice,

subjecting steel gage blocks to salt water, is still used

and occasionally showed up in textbooks into the 1960s.

The calibration of gage blocks is covered in the next

few sections. The details include the thermal expansion

of gage blocks and their temporal stability, with examples of each of these effects. Finally, there are three

sections on comparing gage blocks, the development of

standard gages, and the use of gage blocks to measure

other types of gages.

The section on comparing gages of the same nominal

length describes how two blocks can be compared by

wringing them next to each other on the same reference

plate. The fringe patterns are discussed, and the use of

a third block to break the ambiguity between concave

and convex curved blocks is discussed. The next section

explains how to generate a set of gages by subdivision.

By comparing two 50 mm blocks to a 100 mm block,

and then comparing the two 50 mm blocks to each

other, an accurate calibration of the 50 mm blocks is

made. Using wrings of two or more blocks, the entire set

of gage blocks can be generated. Included is a short

discussion of how two end blocks with small lines on

them can be wrung to the ends of a gage block, making

the stack into a line scale. The distance between the lines

is measured with the two auxiliary blocks wrung

together, and then again with the unknown gage wrung

between them. The difference is the length of the

unknown gage. This method is still occasionally used

because of the high accuracy of instruments designed to

measure line standards, such as meter bars.

Finally, there is a section showing how interferometric methods can be used to compare gage blocks to

gage balls and cylinders.

Overall, the paper is surprisingly modern in its

treatment of interferometry as a length measurement

tool. Moreover, the use of examples and line drawings to

explain the material makes the paper a useful introduction to the subject for beginning metrologists.

Chauncy G. Peters was born in Emerald, Wisconsin,

in 1897. After obtaining a physics degree at Ripon

College, he did graduate work at the University of

Wisconsin. From Wisconsin, in 1913, he was brought to

NBS by Samuel W. Stratton, the first Director. Stratton

had worked with Albert Michelson at the University of

Chicago and had a personal interest in optics. He also

had long expressed concern over the foreign monopoly

of high quality optical glass, and the Optics Division of

NBS became one of his major interests. Peters had a

long and active career as Staff Chief for Interferometry

from 1919 until his retirement in 1949 [3].

After his interferometry studies of the 1920s Peters

began studies of the optical and mechanical properties

of glasses, eventually working with Frederick Knoop on

diamond indenters for microhardness testing. One style

indenter invented by Peters was later commercialized as

20
the “Tukon Hardness Tester.” During World War II

his primary work was to investigate making holes in

diamonds by electric discharge methods and to devise

methods of using these diamonds as wire dies. His

career then came full circle, returning to interferometric

length testing in a paper Interference Methods for

Producing and Calibrating End Standards, with W. B.

Emerson in 1950 [4].

H. S. Boyd is, unfortunately, a more obscure figure.

He was the co-author with Peters on a number of interferometry publications, but was an NBS employee for

only a few years. Checking the phone books in the NBS

Historical Archives for the years 1910 to 1930 shows

entries for Boyd from 1919 to 1922; thus it appears that

he was a scientist or technician in the Interferometry

Section, but left NBS in 1922.

Prepared by Ted Doiron.

Bibliography

[1] C. G. Peters and H. S. Boyd, Interference Methods for Standardizing and Testing Precision Gage Blocks, Sci. Pap. Bur. Stand. 17,

677-713 (1922).

[2] F. H. Rolt, Gauges and Fine Measurements, 2 vols., Macmillan

and Co., London (1929).

[3] Rexmond C. Cochrane, Measures for Progress: A History of the

National Bureau of Standards, NBS Miscellaneous Publication

275, National Bureau of Standards, Washington, DC (1966).

[4] Chauncey G. Peters and Walter B. Emerson, Interference Methods

for Producing and Calibrating End Standards, J. Res. Natl. Bur.

Stand. 44, 419-442 (1950).

21
Recommended Minimum Requirements for

Small Dwelling Construction

From its beginning, NBS had studied properties of

building materials in order to meet the construction

industry’s recognized need for specific technical information. It was not until 1921, however, when Herbert

Hoover became Secretary of Commerce, that these

activities were brought together under a Division of

Building and Housing and grew into a significant and

effective program. The impact of this effort was noted

with the publication of the Building and Housing Series,

and perhaps the most important document in the series

was the very first publication, Recommended Minimum

Requirements for Small Dwelling Construction [1]. This

publication is often viewed as the first national model

building code, and the Building and Housing Series [2]

established NBS as an important source of information

to serve the public and stimulate economic growth.

The significance of this publication and the events

leading to its release are documented most clearly in the

book, Measures for Progress [3].

“ . . . Hoover entered office determined to

recover the Nation, singlehandedly if necessary, from its wartime splurge, its consequent

depletion of resources, and the general economic demoralization into which it had

plunged. Recovery, by raising as rapidly as

possible the level of productivity, was the first

essential; reconstruction would follow.

“Hoover’s plan for recovery, in order to open

employment offices again and start the wheels

of industry, was to stimulate building and

housing, lend direct assistance to both new

and established industries, and minister to the

new aviation and radio industries. Reconstruction, providing long-range benefits to the

economy, aimed at a progressive elevation of

the standard of living, principally by a

campaign to eliminate economic wastes.

“Although the building trades themselves

badly needed reconstruction, they offered the

most likely means of achieving immediate and

massive results in reviving depressed industry

and providing maximum employment across

the Nation. The housing shortage as a result

of the war was estimated at more than a million units. Stimulate homebuilding, and the

brick, lumber, glass, hardware, plumbing,

appliance, textile, and furniture industries

and all that served and supplied them would

revive.”

Hoover’s new division of building and housing set its

sights on revising an infrastructure consisting of poor

housing designs, costly materials and labor, outdated

building and zoning regulations that were barriers to

development, and a shortage of mortgage funds. The

circumstances at the time of issuance of Recommended

Minimum Requirements for Small Dwelling Construction are summed up in a preliminary report of the 1920

Senate Committee on Reconstruction and Production:

“The building codes of the country have not

been developed upon scientific data but rather

on compromise; they are not uniform in practice and in many instances involve an additional cost to construction without assuring

more useful or more durable buildings.” [4]

NBS’s program was announced with national publicity. Information was to be published on home building,

home ownership, technical revisions to construction

codes, plumbing codes, zoning ordinances, etc., suitable

for adoption within codes or as separate ordinances.

Beyond these recommended minimums, NBS was to

provide standards for better construction practices that

would improve workmanship, seek simplification and

standardization of building materials, reduce dimensional variations and deviations, and otherwise serve to

lower costs. To meet these objectives, Recommended

Minimum Requirements for Small Dwelling Construction included an extended appendix in which information was presented on good construction going beyond

the limits of minimum safe standards.

The spring of 1922 saw the start of a major spurt in

the construction of housing. Secretary Hoover chaired

the National Advisory Council of the Better Homes in

America movement. This program mobilized chambers

of commerce, women’s clubs, and better homes and

gardens organizations to promote more and better

housing across the country. The Department of

Commerce’s housing division, working with NBS and

in consultation with building officials, architects,

engineers, fire chiefs, materials experts, and their

related associations, gathered and organized technical

22
information, statistics, and other data. NBS published

Recommended Minimum Requirements for Small

Dwelling Construction as the first in the B&H Series

[5]. The consumer-oriented documents sold hundreds of

thousands of copies and were reprinted and serialized in

newspapers and magazines.

New homes construction in 1922 was reported at over

700,000 units, nearly doubling the total from the prior

year. By 1925 housing production had risen to 937,000

units. The 8-year period of 1922-1929 saw an average of

750,000 homes per year completed, far in excess of the

450,000 units per year estimated as being necessary to

overcome the postwar shortage.

Recognition of the importance of sound and economical construction, coupled with home ownership as a

significant contributor to the welfare of the nation, was

manifested in December 1931 when over 3000 civic

leaders from around the country came to Washington to

attend the President’s Conference on Home Building

and Home Ownership. The conference emphasized

improvements in the building code situation and the

importance of sound regulations.

In the spring of 1932 Recommended Minimum

Requirements for Small Dwelling Construction was

re-issued as Building and Housing Publication No.18

(BH18) [4] and superseded BH1. The 102 page publication consisted of three parts: Introduction, Minimum

Requirements for Safe and Economical Construction of

Small Dwellings, and Appendix. The introduction

provides background, purpose and intent information

for the reader. The minimum requirements are organized by types of construction with separate sections

describing different types of horizontal and vertical

space dividers and miscellaneous components (e.g.,

chimneys and fireplaces, heating appliances). The bulk

of the document is the appendix, which provides

detailed technical information on a wide variety of

materials and methods of construction assembled from

a number of industry sources.

BH18 was a continuation of the work of the Department of Commerce’s Building Code Committee. The

committee consisted of seven members (four of whom

were members of the original group) and was chaired

by William K. Hatt, professor of civil engineering and

director, Laboratory for Testing Materials, Purdue

University. The committee continued to operate under

the Division of Building and Housing of NBS with

James S. Taylor, Chief. George N. Thompson of NBS,

who served as Secretary of the Committee from its

inception, provided direct liaison with NBS and thereby

contributed the scientific and engineering knowledge

necessary to develop the technical information

and answer committee questions throughout the

deliberations.

Recommended Minimum Requirements for Small

Dwelling Construction was the forerunner for the

Federal Housing Administration’s Minimum Property

Standards, which provided quality requirements for the

post World War II housing construction boom, and for

the One and Two Family Dwelling Code (OTFDC) [6],

published first in 1971 by the three model code organizations. In 1972 the Council of American Building

Officials (CABO) was formed, and later in that decade

CABO took over the publication of the OTFDC. This

code provides the technical requirements for most of the

Nation’s conventionally constructed housing. In 1994

the CABO constituency formed the International Code

Council (ICC), and in 2000 the ICC published the

International Residential Code [7], which supersedes

the OTFDC.

Fig. 1. Approved details of balloon frame construction.

23
In 1933, as a result of an economy program in the

Federal Government, the American Standards Association (ASA) established a Building Code Correlating

Committee to take over the work of the Department of

Commerce’s Building Code Committee. Technical

questions that arose in ASA sectional committees

continued to form the basis for many scientific investigations at NBS. George N. Thompson became chairman

of ASA’s Building Code Correlating Committee, then

chairman of its successor, the Construction Standards

Board.

NBS provided leadership in many important

construction standards activities by directly sponsoring

the following American Standards: the National

Electric Safety Code (ASA C2); the Safety Code for

Elevators (ASA A17); Building Code Requirements for

Minimum Design Loads in Buildings and other Structures (ASA A58); and Building Code Requirements for

Masonry (ASA A41). In addition, NBS staff members

participated actively in the development of other

American Standards for building construction including: the National Electrical Code (ASA C1); the Safety

Code for Building Construction (ASA A10); Building

Code Requirements for Fire Protection and Fire

Resistance (ASA A51); and the Safety Code for

Mechanical Refrigeration (ASA B9). These standards

were recognized in virtually all state, local, and model

building codes in the U.S., and by all federal construction agencies. They unified technical requirements for

buildings based on consensus of the construction industry, and contributed substantially to the efficiency and

economy of construction while improving safety and

quality. NBS research results, many of which are documented in the 150 titles of the NBS Building Materials

and Structures Reports published between 1938 and

1957, provided the foundation for many of the provisions. Many of their technical requirements survive as

the basis for today’s construction standards and codes.

When the American Standards Association decided

to incorporate in 1947, the U.S. Department of

Commerce withdrew as a member body, and NBS

ceased to lead construction standards management

activities until its participation in the renamed

American National Standards Institute’s Construction

Standards Management Board was renewed in the

1970s. However, technical contributions to and participation in consensus standards committees has

continued unabated to the present time. A number of

particularly significant contributions are described

elsewhere in this centennial publication.

Prepared by Joel P. Zingeser.

Bibliography

[1] F. P. Cartwright and the Building Code Committee of the Department of Commerce, Recommended Minimum Requirements for

Small Dwelling Construction, Building and Housing Publication

BH1, National Bureau of Standards, U.S. Government Printing

Office, Washington, DC, July 1922.

[2] For a summary, see P. R. Achenbach, Building Research at the

National Bureau of Standards, Building Science Series 0,

National Bureau of Standards, U.S. Government Printing Office,

Washington, DC, October 1970.

[3] R. C. Cochrane (with J. R. Newman), Measures for Progress,

A History of the National Bureau of Standards, NBS Miscellaneous Publication 275, National Bureau of Standards, U.S.

Department of Commerce (1966).

[4] Department of Commerce, Building Code Committee, Recommended Minimum Requirements for Small Dwelling Construction,

Building and Housing Publication No. 18, National Bureau of

Standards, U.S. Government Printing Office, Washington, DC

(1932).

[5] Additional publications included: BH2-Recommended Minimum

Requirements for Plumbing in Dwellings and Similar Buildings;

BH3-A Zoning Primer; BH4-How to Own Your Home; BH5-

A Standard State Zoning Enabling Act; BH6-Recommended

Minimum Requirements for Masonry Wall Construction; BH7-

Minimum Live Loads Allowable for Use in Design of Buildings;

BH8-Recommended Practice for Arrangement of Building Codes.

[6] International Conference of Building Officials, Inc., Building

Officials and Code Administrators International, Inc., and Southern Building Code Congress International, Inc., One and Two

Family Dwelling Code, 1971.

[7] International Code Council, Inc., International Residential Code,

2000.

24
Visibility of Radiant Energy

This classic paper [1] from 1923 reports the results of

one of the most enduring projects ever undertaken at

NBS, research into the physical description of human

vision. The principal result of this work was the

“visibility curve,” a quantified model of how well a

typical person can see the different wavelengths (colors)

of light. Today this model function, essentially unchanged, underlies all physical measurements of photometric quantities and their interpretation in photometric

units of measure.

It has been understood since the time of Isaac Newton

that white light is a combination of a spectrum of different wavelengths, each seen as a pure color. Light is a

form of radiant energy, with a power that can be measured in watts, but the connection between this physical

description (or the “mechanical” description as it was

then known) and the visual result in the human eye was

not well established. This was the challenge undertaken

by K. S. Gibson and E. P. T. Tyndall: to carry out a

study of the visibility of radiant energy or, in quantitative terms, the ratio of the luminous (perceived) power to

the radiant (physical) power at the different wavelengths

in the spectrum.

Gibson and Tyndall were neither the first nor the last

to study the visibility of light, but their work is perhaps

the most notable for its thoroughness, timeliness, and

impact. The first experiments on this subject were

undertaken by Fraunhofer in 1817, and the first energy

measurements were made by Langley in 1883 [2].

By 1905, Goldhammer had crystallized the idea of a

definite relationship between visibility and power at

each wavelength, and at the young NBS, Nutting introduced the term “visibility curve” in 1908 [3]. The

Bureau’s forefront research continued through the subsequent decade, leading to the major study of the

sensitivity of the eye across the spectrum by Coblentz

and Emerson in 1918 [4].

However, these and other data accumulated around

the world were not consistent. Different experimental

methods were a chief cause. In the equality-of-brightness matching method, two lights were projected onto a

split-screen viewer, while with the flicker method, two

lights were alternately projected on a simple viewing

screen in rapid succession. In each case, the lights were

adjusted in a known way until an observer declared a

brightness match. The equality-of-brightness method

was the more precise of the two, but only so long as the

color quality of both lights was similar. When the colors

were very different, different observers would make

different matches. The flicker method did not give as

sharp results for similar lights, but the data quality was

not much affected by color differences.

Seeing the need to bring closure to the question,

Edward P. Hyde (who had left the NBS staff in 1908 to

go to the General Electric Nela Research Laboratories),

as president of the U. S. National Committee of the

International Commission on Illumination (the CIE),

requested the Bureau of Standards to make an additional

investigation using the so-called step-by-step method.

This form of equality-of-brightness matching, where

comparisons were made between a series of only

slightly different colors, held promise as a means of

obtaining more reliable data.

Gibson and Tyndall were neither the

first nor the last to study the visibility

of light, but their work is perhaps the

most notable for its thoroughness,

timeliness, and impact.

NBS undertook the challenge under the sponsorship

of General Electric. Director Burgess appointed a

special committee of experts to oversee the work, which

was conducted by Gibson and Tyndall. The University

of Nebraska loaned a Brace spectrometer to the Bureau,

to be incorporated into an elaborate apparatus that made

the best use of the Bureau’s primary standard lamps.

Special care was taken in all aspects of the experiment; issues that were believed to affect the consistency between previous experiments—such as the

size and brightness of the viewing fields—received

particular attention.

The results included the brightness-matching data

from 52 observers, some of them in common with

previous studies. As hoped, the new equality-of-brightness data were within the range of data obtained with

flicker methods (except in the outer regions of the

spectrum).

However, the strength of the paper was not so much

in the new experimental results as it was in its extensive

analysis and critical review of all existing data. Gibson

25
and Tyndall carefully compared their own results with

those of their predecessors and proposed a mean visibility curve based upon the accumulated data from more

than 200 different observers. They were guided in this

task by the prevailing theories of the day, which were

believed to dictate certain balance in the curve [5].

The result was a smash success, quickly winning

wide acclaim. In 1924, the 6th Session of the CIE

adopted the Gibson-Tyndall curve as a world standard.

In 1933, the Comite ́ International des Poids et Mesures

(the supervisory body of the world’s metric system)

followed suit.

The achievement of Gibson and Tyndall might have

remained an academic one were it not for the changing

needs in metrology and the advances of technology. As

surprising as it might seem today, until 1948 there was

no universal standard for the brightness of light. The

“standard candle,” once made from whale oil, is a part

of popular lore, but in reality, different laboratories each

had their own favorite “standard.” Some used gas

lamps, some used liquid-fueled lamps, and following

the trend towards electric lighting at the turn of the

century, some (including NBS) used electric lamps. It

was difficult to compare lighting devices to the

standards, and the standards to each other, because

different fuels and different lamp constructions would

produce lights of different color. The only available

instruments that could reliably report how bright a light

appeared, or how lights compared to standards, were

humans, and as we already know, equality-of-brightness matching was unreliable when the colors were

significantly different.

Research in the 1930s, interrupted by World War II,

led to international agreement in 1948 to use a platinum-point blackbody as the sole international standard

of the luminous intensity of light. When objects are hot,

they give off light. By “blackbody,” we mean that the

object does not reflect ambient light—all the light we

see from it is thermally generated, an intrinsic function

of the object’s temperature. The trick was to operate a

blackbody at a temperature that anyone could reproduce—in this case, the temperature of molten platinum

as it begins to freeze while cooling. Many felt that this

would provide the necessary world-wide stability and

uniformity. A unit of measure of luminous intensity was

then defined, now known as the candela, to relate the

new blackbody standard to a typical standard candle of

times past.

This development had an unintended consequence.

Unlike the previous lamp and flame standards, the

behavior of blackbodies are calculable from first

principles, using Planck’s radiation law. We had a light

source that we understood in detail. The other piece

of the puzzle was an understanding of how the eye

responded to this light, and this is where the work of

Gibson and Tyndall fit in. Suddenly, it became feasible

to design and build electrical devices to measure brightness just as a human would, or at least the ideal human

modeled by the Gibson-Tyndall curve 25 years earlier.

The definition of the candela in 1948 had the effect of

eliminating the need to have someone actually looking

through a visual comparator, a process today called

“visual photometry.” It began an era of “physical photometry” in which luminous intensity could be evaluated

through more objective measurements, yielding better

precision and accuracy.

As time went on, the platinum-point standard fell into

disfavor. The devices were difficult to maintain, their

temperature was much lower than that of common

electric lamps, and the melting-point temperature itself

was too uncertain. This limited how well their emission

spectra could be calculated. Finally, in 1974, Bill Blevin

from the National Measurement Laboratory in Australia

and Bruce Steiner at NBS published the seminal paper

that said ‘enough is enough.’ They formally proposed

that the SI base unit for photometry, the candela, be

redefined so as to provide an exact numerical relationship between it and the SI unit of power, the watt [6].

They stated the case so well that, in 1979, the world

metrology community effected a redefinition of the

candela.

The 1979 redefinition puts even more reliance upon

the work of Gibson and Tyndall. It says, “the candela is

the luminous intensity, in a given direction, of a source

that emits monochromatic radiation of frequency

540  1012 hertz and that has a radiant intensity in that

direction of (1/683) watt per steradian.” That specific

frequency corresponds to a wavelength of 555 nm,

which is where the peak of the Gibson-Tyndall curve

lies. In order to determine the luminous intensity of light

at other wavelengths, one uses the Gibson-Tyndall curve

(more precisely, its modern, smoothed form, denoted as

V()) to find the corresponding number of watts. The

era of visual photometry is truly over. Today, essentially

all photometry is physical photometry, relying upon this

definition and the V() curve to characterize any real

light source or the performance of any tangible light

detector.

This success of the Bureau in the early 1920s led to

another important success towards the end of the

decade. Having solved the problem of modeling brightness, Bureau staff next turned their attention to modeling color. This was a field that remained active well into

the 1960s, but in those early days, a young staff member

named Deanne Judd made his mark through another

compelling analysis of existing data, resulting again in

establishing the principles and methods that led to international consensus [7]. In 1931, the CIE adopted the

26
system for quantitative color nomenclature that has

continued to be used for 70 years. Judd, serving as the

U.S. Joint Representative to the CIE, was one of the

principal architects of that standard. His paper laid out

technical recommendations that were accepted a year

later, together with additional data developed by John

Guild of the National Physical Laboratory (NPL) in the

UK [8].

The system of colorimetry that Judd envisioned in

1930 has been a foundation for technologies not even

dreamed of then—color photography (Kodachrome

was invented in 1935), color television, modern color

printing, and digital imaging. The tools of today’s

electronic commerce—color scanners, color-calibrated

computer monitors, and all manner of color printers—

all still rely on the 1931 CIE color system for “device

independent” color specifications.

As beautiful as the Gibson and Tyndall work was, it

was not without warts. The most famous occurs in the

blue-violet portion of the spectrum, where they were

forced to choose between conflicting data. They wrote,

“The I. E. S. [Illuminating Engineering Society] data in

the violet have been accepted by the authors for lack of

any good reason for changing them, but the relative as

well as absolute values are very uncertain and must be

considered as tentative only.” Their guess was wrong,

but it so quickly earned acceptance that it did not remain

“tentative” for very long. Years later, Judd attempted to

institute an “improved” version of the visibility curve

[9], but the Gibson and Tyndall version had been so

thoroughly adopted that the revision never gained wide

usage.

The second problem is more subtle and beguiling.

The world of Gibson and Tyndall did not include the

narrow-band light sources so common today: the phosphors in fluorescent lamps and CRT displays, lasers and

LEDs, and the high-efficiency outdoor lighting that

turns nighttime into a murky orange. The modern

system of physical photometry based upon a simple

visibility curve is no longer enough, not because of

flaws in the curve, but because the human visual system

is much more complex than this simple model suggests.

Our vision responds nonlinearly to combinations of

narrow-band lights, and perceived brightnesses can

differ markedly from the predictions of their model. In

a sense, it is the same problem that was recognized in

the 1920s as the limitation of equality-of-brightness

matching. The data told a story which was not understood then, nor of much technological importance.

Today, vision researchers are revisiting the issue in an

attempt to improve upon the standard model.

Nonetheless, to the extent that we continue to use

electronic instruments to observe our surroundings, and

to the extent that physical photometry remains the gold

standard around the world for the metrology of lighting,

the Gibson and Tyndall curve continues to play an

essential role in estimating our perception of light more

than 75 years after its introduction.

Kasson S. Gibson received his education at Cornell

and joined NBS in 1916. In addition to the work

described here, he made important contributions to the

design of optical filters for transforming radiation from

incandescent lamps to simulate natural daylight. He

headed the work on photometry and colorimetry at NBS

from 1933 to his retirement in 1955, publishing over 100

papers in spite of his administrative responsibilities.

Gibson served as president of the Optical Society of

America from 1939 to 1941 and was a Fellow of the

American Physical Society, Illuminating Engineering

Society, and American Association for the Advancement of Science. He died in 1979 at the age of 89.

Edward P. T. Tyndall worked at NBS in 1917-1919

and later returned for shorter stays as a visiting

researcher. He spent most of his career as Professor of

Physics at the University of Iowa, where he did important research on the optical and electrical properties of

metals. He distinguished himself as a teacher and supervised 74 masters and doctorate students. He also died in

1979 at age 86.

Prepared by Jonathan E. Hardis.

Bibliography

[1] K. S. Gibson and E. P. T. Tyndall, The Visibility of Radiant

Energy, Sci. Pap. Bur. Stand. 19, 131-191 (1923).

[2] Y. Le Grand, Light, Colour and Vision, 2nd ed., translation by

R. W. G. Hunt, J. W. T. Walsh, and F. R. W. Hunt, Chapman and

Hall Ltd., London (1968).

[3] P. G. Nutting, The Luminous Equivalent of Radiation, Bull. Bur.

Stand. 5, 261-308 (1908).

[4] W. W. Coblentz and W. B. Emerson, Relative Sensibility of the

Average Eye to Light of Different Colors and Some Practical

Applications to Radiation Problems, Bull. Bur. Stand 14, 167-236

(1918).

[5] P. K. Kaiser, Photopic and Mesopic Photometry: Yesterday, Today

and Tomorrow, in Golden Jubilee of Colour in the CIE, The

Society of Dyers and Colourists, Bradford, UK (1981).

[6] W. R. Blevin and B. Steiner, Redefinition of the Candela and the

Lumen, Metrologia 11, 97-104 (1975).

[7] D. B. Judd, Reduction of Data on Mixture of Color Stimuli, Bur.

Stand. J. Res. 4, 515-548 (1930).

[8] W. D. Wright, The Historical and Experimental Background to the

1931 CIE System of Colorimetry, in Golden Jubilee of Colour in

the CIE, The Society of Dyers and Colourists, Bradford,

UK (1981).

[9] D. B. Judd, Report of U. S. Secretariat Committee on Colorimetry and Artificial Daylight, CIE Proceedings Vo1. 1, Part 7, p. 11

(Stockholm, 1951), Central Bureau of the CIE, Paris. See also G.

Wyszecki and W. S. Stiles, Color Science: Concepts and Methods,

Quantitative Data and Formulae, 2nd ed., John Wiley & Sons,

New York (1982) p. 330.

27
Test of the Severity of Building Fires

From its earliest years, NBS has had international

leadership in the measurements, standards, and technologies associated with prevention of human suffering

and losses of lives, property, and societal capabilities to

unwanted fires. A major milestone in fire safety

engineering, internationally, was publication of Tests of

the Severity of Building Fires [1] in 1928. Its author was

Simon H. Ingberg, Chief, Fire Resistance Section, U.S.

Bureau of Standards.

Fire statistics published by the National Fire Protection Association [2] show that about two million fires

are reported in the United States each year, causing

4000 deaths and 8 billion dollars in property damage.

This is bad, but it used to be worse. Early in the 20th

century, with a much smaller U.S. population, twice as

many people died each year. At that time the fire death

rate per 100,000 population was 9.1, in contrast to 1.6

today [2]. The buildings that burned in the early 1900s

often collapsed as fire spread throughout the structure.

Fire measurement at NBS quantified the intensity and

duration of building fires. Simon Ingberg related the

measured fire temperatures and duration to equivalent

exposure to the standard furnace fire time-temperature

curve [3]. Today’s fire resistant construction is evaluated

using the ASTM E119 standard fire exposure based on

the same approach. Ingberg’s work provided vital information about the relationship between fire severity as

measured in full-scale room and building fire tests and

endurance ratings in the standard test method. This

provided the guidance for building codes requirements

and design approaches for fire resistive construction to

contain fire spread in buildings. Today, as a result of

confinement, detection, and suppression fire protection

strategies, most fires in buildings never grow beyond the

room in which the fire started.

In Ingberg’s own words:

“One of the main objects of public regulation of

building construction is to prevent undue hazard to

life and neighboring property from fire. Fire

exposure to buildings and building members arises

from interior and exterior origins. The evaluation of

the exterior exposure can be done with difficulty in

quantitative terms, and the gradual accumulation of

data from actual fires will probably continue as the

main guidance in providing the proper protection.

The present paper will deal mainly with methods

of gauging the severity of fires resulting from

the burning out of contents of buildings whose wall,

floor, and column constructions are fire resistive to

such an extent as to be capable of withstanding a

complete burning out of building contents without

collapse of major details. It is only when the problem is so confined that there is much possibility of

obtaining experimentally quantitative information

pertinent to the answer sought. The severity of fires

completely consuming the combustibles of frame

buildings and masonry-walled buildings with combustible interior construction is of interest mainly as

it concerns the exposure to adjacent or neighboring

buildings and the fire exposure on party and fire

walls and on record containers. As it concerns the

severity of fires in buildings with interior combustible construction protected with incombustible

floor, ceiling and wall finishes, the present discussion will apply up to the limit set by the fire

resistance of such protection.

Indications of the intensity of building fires have

been obtained from fused metals and from general

fire effects on materials on which information is

extant as to their reaction to temperature or fire

exposure such as in test fires. The fire ruins or

reports of fires give, however, little information of

the duration of the temperatures in any given portion

of the building. The absence of data to enable

constructions or devices giving a certain performance in the standard fire test to be applied as

protection against fire conditions in buildings with

as much precision as results of strength tests are

applied for load carrying purposes, led me to

consider the possibility of conducting burningout tests in suitably designed structures to obtain the

needed information. If such tests could be made to

yield quantitative information on the equivalent fire

duration to be expected with given building types

and occupancies, it would help measurably to place

the whole structure of fire resistance requirements

on a rational basis. Fire is a contingent condition that

may or may not involve a building or given portion

thereof in its lifetime. In theory, at least, the owner

should be required to make provision for safety to

life within and near the building, and for protection

to adjacent and neighboring property only as it

concerns the building type and size proposed and

the occupancy it is intended to house. With require28
ments more or less uniform for all occupancies the

tendency would be to require more than the needed

protection for buildings with the lighter occupancies

from the fire hazard standpoint, and not enough

for those with greater amounts of combustible

contents.”

Ingberg addressed these objectives by constructing

two single-story fire test buildings on the NBS site of

sizes 4.9 by 9.1 meters and 9.1 by 18.3 meters. Various

arrangements of furnishing, shelving, and paper (discarded records) were used to assemble realistic representations of offices and records storage rooms (see

Fig. 1 and Fig. 2, respectively). Tests included variations,

Fig. 1. The interior of the small test building arranged to represent a typical office with metal

furniture on a cement floor. (Used with permission of NFPA.)

Fig. 2. Steel shelving in the small fire test building arranged to represent a records room.

(Used with permission of NFPA.)

29
such as the use of non-combustible metal furnishings

instead of wooden furnishings, to examine the change in

fire intensity. Building ventilation was provided to maximize fire conditions by adjusting openings in windows

(Fig. 3). Temperatures were measured at 35 to 40 points

in the smaller building and 100 in the larger.

Results of ten large-scale tests were analyzed and

tabulated to relate the combustible content (in terms of

either mass or calorific energy per unit area) to the

equivalent fire duration (in hours and minutes) of a

standard fire furnace test exposure temperature curve.

Except for the fact that average room temperatures in

the fire tests generally increased after ignition, then

decreased from a peak as fuel was depleted, the two

curves were not identical in shape. So the challenge for

Ingberg was to adopt a method for gauging the overall

severity of a fire test relative to the standard fire exposure. He proposed that the area under the time-temperature curve, but above selected base-line temperatures,

represented an approximate gauge of exposure severity.

He recognized that this is an approximation, but that no

better measure of comparison could be conveniently

applied. This remains true today.

Ingberg’s tests related severity of fires resulting from

a total combustible content (including finished floors

and trim) in offices and record rooms ranging from

49 kg/m2 to 290 kg/m2 to be the equivalent to standard

furnace fire exposures of 1 h to 7.5 h, respectively.

As a result of Ingberg’s work, it became possible to

develop fire codes and design approaches that related

the combustible load in a room, based on its contents and

use, to the performance of fire-resistant construction

details in the standard fire test.

NBS under Ingberg’s leadership continued to explore

fire severity, including notable full scale tests in buildings near the corner of 10th and B streets, NW, in

downtown Washington, DC, scheduled for demolition to

obtain space to construct today’s Justice Department

Building on the Federal Triangle (Fig. 4). In 1928, this

full-scale fire test of buildings ignited, then allowed to

burn without application of water, was unique in the

history of fire protection engineering. In the test conducted on Sunday morning, June 17, 1928, fire conditions in adjacent five-story and two-story brick openjoist construction buildings were measured for the

purpose of comparison to the standard furnace exposure

conditions and duration. In addition, the test gathered

data about fire exposures to support test standards for

fire resistant safes and other record containers.

It remained necessary to provide uniform fire-resistance classifications for building constructions as a

sound basis for permitting the use of new systems of

construction that could be demonstrated to be comparable in performance to systems prescribed by building

codes. A Subcommittee on Fire-Resistance Classifications was organized under the auspices of the U.S.

Fig. 3. Smoke billows from small test building on the NBS site through open windows

adjusted to control ventilation in one of Ingberg’s office occupancy fire test. (Used with

permission of NFPA.)

30
Government’s Central Housing Committee on Research,

Design, and Construction. Subcommittee members were

officials of federal agencies including Public Buildings

Administration, Federal Housing Administration,

United States Housing Authority, and Home Owners’

Loan Corporation. Ingberg served as technical advisor

to the subcommittee, led the program of research,

and wrote its seminal report, Fire Resistance Classifications of Building Constructions [4] in 1942. The

report contained:

1. A classification of four types of construction

(Fireproof, Incombustible, Exterior-Protected,

and Wood) covering the whole range of basic

building construction properties that influence

fire hazard.

Fig. 4. Burning test buildings near the corner of 10th and B Streets, NW, in Washington 10

to 20 minutes after ignition on Sunday morning, June 17, 1928. These burning buildings are

on the present day site of the Justice Department Building. The Old Post Office building is

in the background. (Used with permission of NFPA.)

31
2. Estimations of fire severity based on surveys of

combustible contents of buildings housing typical

occupancies.

3. Fire-resistance ratings of building constructions

and fire-resistance classifications of roofing

materials derived from analyses of test results at

NBS and other laboratories.

Ingberg’s work on fire severity and fire resistance

was adopted by national standards and model building

codes, which in turn became the bases for the legal

building codes of local and state governments throughout the U.S. His principles and recommendations remain

the basis for today’s standards and building codes for

determining the effects of combustible building contents

and furnishings on the severity of fires for which buildings are required to be designed. His classifications of

building types remain the basis for requirements for fire

resistance of building components such as walls, floors,

roofs, doors, and windows.

Simon Ingberg was born in Ringsager, Norway on

June 24, 1877, emigrated to the United States with his

parents in 1881, and grew up on a farm near Hendrum,

Minnesota [5]. After finishing his junior year in high

school, he taught in the public schools of Norman and

Polk counties, Minnesota, for ten years prior to going to

college. He received a B.S. in civil engineering from

the University of Minnesota in 1909, and an M.S. in

theoretical and applied mechanics from the University

of Illinois in 1910. After 1 year on the faculty of Lehigh

University, and work with a Chicago structural engineering firm, he joined NBS in 1914 as an associate

physicist. His first assignment was to oversee fire tests

sponsored by NBS at Underwriters’ Laboratories in

Chicago.

In 1915 Ingberg was placed in charge of a new fire

resistance section in the Heat Division of NBS, and he

traveled extensively for six years to oversee fire testing

in Chicago and in NBS laboratories in Pittsburgh and

Washington. These included studies of concrete and

steel columns and development of a furnace for studying

the fire resistance of wall panels. During the 1920s and

1930s, his studies included fire protection of steel

columns; strength of brick masonry; influence of the

mineral content of concrete on fire performance;

strength of steel, iron, and wood at high temperatures;

self-heating and ignition of agricultural products; test of

carbon dioxide for fire control in buildings; fire hazards

of vaults for nitrocellulose film; cigarette ignition of

mattresses; the cigarette as a fire hazard; flame spread

test methods; performance of fire detection devices; surveys of fire loads in buildings; severity of building

fires; chimney fires; and theater proscenium curtains.

Federal funds were limited, and only with industry

support was it possible to conduct much of the fire

resistance work.

Ingberg was told he had to retire in 1947 shortly

before his 70th birthday. He did not stop work, but made

his garage into a fire test facility, and continued to

prepare papers with NBS colleagues as a guest

researcher. From 1954 to 1969, he was employed as a

consultant to Rohm and Haas Company, which was

promoting the use of plastics in buildings. A part of his

advice was the recommendation: “You should so conduct yourselves that when your products are involved in

a disastrous fire, and they certainly will be, that there

is nothing in the occurrence for which you must

apologize.” In 1963 ASTM gave Ingberg its Award of

Merit, and in 1970 ASTM Committee E-5 on Fire

Standards established the Simon Ingberg Award to

recognize those who have continued outstanding accomplishments, like his, in advancing fire safety.

Prepared by David Evans, Daniel Gross, and Richard

Wright

Bibliography

[1] S. H. Ingberg, Tests of the Severity of Building Fires, Q. Natl. Fire

Prot. Assoc. 22, 43-61 (1928).

[2] John R. Hall, Jr. and Arthur E. Cote, America’s Fire Problem and

Fire Protection, in Fire Protection Handbook, Eighteenth Edition,

Arthur E. Cote, (ed.), National Fire Protection Association,

Quincy, Massachusetts (1997).

[3] Standard Test Methods for Fire Tests of Building Construction and

Materials, ASTM E-119, 1997 Annual Book of ASTM Standards,

Section 4 Construction, Volume 04.07 Building Seals and

Sealants; Fire Standards; Dimension Stone, American Society for

Testing and Materials, West Conshohocken, PA (1997) pp. 441-

461.

[4] John W. Dunham, William J. O’Connor, S.H. Ingberg, Bert M.

Thorud, and Charles N. Diener, Fire-Resistance Classifications of

Building Constructions, Building Materials and Structures Report

BMS92, National Bureau of Standards, Washington, DC (1942).

[5] Alexander F. Robertson, Simon H. Ingberg—Pioneer in Fire Research, ASTM Stand. News 13 (2), 50-53 (1985).

32
Calculation of Compounds in

Portland Cements

The National Bureau of Standards–National Institutes of Standards and Technology has had an illustrious history of research on the most widely-used,

man-made materials of construction, cement and concrete—materials which are often taken for granted,

because of their commodity nature and generally

successful use in the structures that comprise about

80 % of the Nation’s fixed wealth. The level of NBSNIST’s cement and concrete materials research effort,

in contrast to its structural research effort, has varied

substantially over the century, with two highly productive periods separated by an almost dormant

period from about 1960 to 1980. While some important

contributions were certainly made prior to 1924, an

outstanding period stretched from 1924 to 1954 when a

strong NIST cement research program was complemented by an equally strong and synergistic industrysupported program, the Portland Cement Association

Fellowship at the National Bureau of Standards. The

Director of the PCA Fellowship for the whole of its

30-year life was Dr. Robert Bogue, a major figure in the

history of cement research.

Robert Herman Bogue, a physical chemist, was born

in Southborough, Massachusetts, on September 27,

1889. Before taking the position as Director of the PCA

Fellowship in 1924, he had obtained degrees from Tufts

University (B.S., 1912), Massachusetts College (M.S.,

1915), and the University of Pittsburgh (Ph.D., 1920),

and had gained professional experience as an Assistant

Professor at Montana State College, 1915-17, a Fellow

of the Mellon Institute, 1917-22, and an Associate

Professor at Lafayette College, 1922-24. His research

interests at that time appear to have been the chemistry

of gelatine and the colloidal behavior of proteins—

subjects remote from the inorganic materials that would

be central to the rest of his professional career.

As Director of the PCA Fellowship, Bogue exercised

a remarkably far-sighted leadership that made the

Fellowship a major contributor to what would now be

described as the materials science of concrete. Among

Bogue’s personal contributions was a landmark paper,

Calculation of Compounds in Portland Cement [1],

published in 1929. To understand the significance of the

paper, it is necessary to know a little about portland

cement and its manufacture.

Portland cement was invented in 1824. Its essential

ingredient is cement clinker, a granular product from the

high temperature (~1500 C) processing of an appropriately proportioned, finely-ground mixture of minerals

that are sources of the common oxides CaO, SiO2,

Al2O3, and Fe2O3; (for convenience in this paper, and in

accord with cement industry usage, these oxides will

frequently be referred to by the single letters C, S, A and

F, respectively). Typical raw materials that are sources

of these oxides in clinker production are, in the same

order, limestone, quartz sand, clay, and iron ore. The

cement manufacture ends with the intergrinding of

clinker with a mass fraction of about 5 % gypsum

(CaSO4 2H2O) to produce the fine cement powder,

usually gray in color, of which almost 100 million

tonnes (1 tonne = 1000 kg) are produced in the U.S.

each year. (The gypsum is added to control the rate of

setting of the cement.)

Until the publication of Bogue’s paper, there was

much controversy about the compositions of the

compounds present in the clinker, even though the

elemental compositions of clinker and cement (always

expressed in terms of simple oxides) were determined

routinely in cement plants and other laboratories.

Publication of the paper obviously met an objective

Bogue had set for the Fellowship since, in the text of an

address given to the American Concrete Institute [2]

two years earlier in 1927, he wrote: “ . . . this is an age

of advancement. The cry for new knowledge is in the air.

.... Questions are being asked now in all seriousness

which a few years ago would have been regarded as

absurd because unanswerable. . . . . All of this brings us

to the belief that an unraveling of the laws governing the

constitution of cement clinker and the behavior of the

constituents of cement when made into concrete may

hold developments which today can only be sensed but

not definitely apprehended.” In the same address, he

made the nature of the problem to be solved clear by

saying, “Of fundamental importance, above all others,

and for the reasons given above, are the studies which

will give us information of the nature of the constituents

in clinker. Some of these have been known for some

time. Others have been guessed at, but the guesses of the

various authorities do not always agree. One group

believes that a complex compound containing lime,

33
alumina, and silica is present in clinker; another group,

that lime and one of the silicates form a loosely bound

compound known as a solid solution; and still another

group, that the lime and silica form two separate

silicates. . . . . But other components than lime and

silica are present, and we must learn the manner of their

combination. Into what compounds do the alumina, iron

oxide, and magnesia go? What change is observed in the

composition of the product resulting from the use of

different percentages of these and still other constituents

of the raw material?”

From petrographic studies, Bogue knew that portland

cement clinker usually contained four main compounds

(referred to as alite, belite, celite and felite) of unknown

composition (Fig. 1), but there was, as yet, no practical

way of determining their quantities. From the growing,

but still incomplete, knowledge of the phase relationships in the CaO-SiO2-Al2O3-Fe2O3 (or C-S-A-F)

system, Bogue concluded that the main compounds

in clinker were tricalcium silicate (Ca3SiO5 or C3S),

dicalcium silicate (Ca2SiO4 or C2S), tricalcium aluminate (Ca6Al2O6 or C3A), and tetracalcium aluminoferrite (Ca4Al2Fe2O10 or C4AF), and that the quantities

of each could be calculated from the oxide composition

of the clinker, provided the high temperature reactions

had gone to completion in producing the equilibrium

products and no significant amount of unreacted material remained. On this basis, at least to a useful approximation, Bogue was successful in unraveling “the laws

governing the constitution of cement clinker” and he

presented a set of simultaneous equations, together with

nomographs, for calculating the amounts of the major

compounds—the “potential compound composition”—

of a clinker or a portland cement from the results of

analyses for the major oxides (CaO, SiO2, Al2O3, and

Fe2O3) together with determinations of MgO, loss on

ignition, and acid-insoluble residue. He realized that the

compounds were unlikely to be pure because of the

presence of unwanted minor oxides in the raw materials, but he did not have data that would enable him to

take the minor oxides into account in his calculations.

In spite of this limitation, Bogue believed that the

calculated amounts of the compounds were close

enough to reality to be useful. That this is true is amply

demonstrated by the fact that Bogue’s equations

became, and 70 years later still remain, the basis for

the classification scheme used in the ASTM C-150

specification for portland cement.

Ability to calculate compositions of cements in terms

of the amounts of the main compounds present provided

a valuable new tool for explaining, or predicting, differences in engineering performance among portland

cements. This was true even though, when he wrote his

paper, Bogue did not know that the composition of the

aluminoferrite phase could vary much more than the

compositions of the other major compounds; the

“C4AF” phase is, in fact, a member of a solid solution

series of which the end members are Ca6Al4Fe2O15

and Ca2Fe2O5 (or C6A2F and C2F); however, for most

portland cements, the composition of the aluminoferrite

phase is reasonably close to the composition assumed by

Bogue.

The ability to calculate the amounts of the major

compounds in a clinker or cement had important

implications. There was now the possibility of studying

relationships between the amounts of the compounds in

a cement and the cement’s engineering performance in

concrete, especially in relation to “durability.” Beginning in 1940, this led to the inclusion of the Bogue

equations in the ASTM specification for portland

cements, because it was then certain that the amounts

of the major compounds was one of the factors that

determined engineering performance. The ASTM Type

of a portland cement (I, II, III, IV or V) [3] is still

determined, at least in part, by its “potential compound

composition,” colloquially referred to as its “Bogue

composition.” Thus, an ASTM Type IV Portland

Cement is a “low heat cement,” required to be low in

C3S and low in C3A; it was developed for use in massive

concrete structures, specifically for construction of the

Hoover Dam. An ASTM Type V Portland Cement is a

“sulfate-resistant cement,” which is required to contain

a maximum of 5 % by mass of C3A; it was developed

for use in concrete that will be in contact with

sulfate-rich soils or waters; and an ASTM Type II

Portland Cement (containing a maximum of 8 % by

mass of C3A) is both a “moderate heat” and a

“moderately sulfate resistant” cement. There is no

need to explain to a cement chemist, whether in the

Fig. 1. Polished and etched section of portland cement clinker showing evidence of four major compounds (phases) such as would have

been seen by Bogue (courtesy of Paul Stutzman).

34
United States or in many other countries, what is meant

when the “Bogue composition” is referred to.

Bogue’s legacy from his years as Director of the PCA

Fellowship is reflected not only in his technique for

calculating phase compositions of cements but also in

many experimental studies, often carried out with his

participation, of phase relationships in systems relevant

to cement and concrete. Representing H2O, K2O, and

Na2O by H, K and N, respectively, some of the systems

studied were of the anhydrous systems: C-A-S, C-N-A,

C-M-C2S-C5A3, C2S-KCS, N-C-A-S, and C-CA-C2F;

and the hydrous systems studied included: C-S-H,

the garnet-hydrogarnet system, C-A-H, C-N-S-H, and

hydrogarnet in C-A-S-H. Bogue was clearly one of the

more eminent cement chemists of his day, and his

scholarly text, The Chemistry of Portland Cements [4],

remained the single most comprehensive and authoritative source of knowledge of cement chemistry from the

time of its first publication at least until the mid-70s.

It was probably a coincidence that, in 1929, the

year Bogue’s paper was published, the NBS Director

responded to a Congressional request to set up a program to ensure that cements used in federal construction

projects be of the required quality. This began as an

NBS-managed and operated program which, over

several years, evolved into a partnership with ASTM as

the Cement Reference Laboratory (CRL). The CRL

evolved further and enlarged its scope to include

concrete, becoming what is now the ASTM-sponsored

Cement and Concrete Reference Laboratory (CCRL).

In its present form, the CCRL is a research associateship

which, through laboratory inspection and proficiency

sample programs, provides quality assurance to testing

laboratories that use ASTM standards, including ASTM

C-150 with its Bogue calculations, in the testing of

cement and concrete. An important development made

to improve the efficiency of the CCRL proficiency

sample program was described in the 1959 paper,

“Statistical Aspects of the Cement Testing Program” [5]

by the renowned NBS statistician, W. J. Youden. Youden

showed how the amount of information obtainable from

an interlaboratory test program could be increased

substantially by issuing proficiency samples in pairs—a

procedure which is widely used both nationally and

internationally.

While Bogue’s paper gave new insight into the

amounts of the major compounds in portland cements, it

did not provide any clue as to how the compounds might

be distributed within and among individual cement

particles. Indeed, in spite of the fact that particle size

distribution and fineness are important characteristics

which affect the performance of cements, there were no

useful ASTM standard methods for their determination

until the sedimentation method for determination of

particle size distribution was adopted in 1933 and the air

permeability method for determination of fineness was

adopted in 1943. Both methods are still commonly

known by the names of the NBS researchers who

developed them, Wagner and Blaine, respectively.

Attainment of the capability to determine the distribution of the cement compounds within cement

particles was long delayed. It was not until 1997 that

another researcher at NIST, Dale Bentz, showed its

importance (Fig. 2) in accounting for differences among

cements [6]. In Bogue’s day, this might have been

viewed as an attempt to answer one of those questions

that “would have been considered absurd because

unanswerable.”

As mentioned earlier, NBS research into the materials

science of cement and concrete fell to a low level

between 1960 and 1980. Then in 1981, in response to

the national need for research on cement and concrete

made apparent by the Nation’s failing civil engineering

infrastructure, NBS established a cement hydration

competence project. The complexity of cement

chemistry and of the physical and mechanical changes

accompanying the cement hydration reactions suggested

that computer simulation should be an important part of

the program. In 1986, a paper by Hamlin Jennings and

Steven Johnson of NBS, Simulation of Microstructure

Fig. 2. Modern technology: Backscattered electron image of a

polished section of portland cement particles from CCRL Proficiency

Sample No.115 embedded in an epoxy resin. The major portland

cement clinker phases in the cement particles can be identified, with

reasonable confidence, by their grey levels in the image and the habits

of the crystals. More definitive information about the distribution of

the cement phases within and among the particles can be obtained

using x-ray imaging to apply false color based on the elemental

compositions of the individual crystals. (Micrograph courtesy of

Paul Stutzman).

35
Development During the Hydration of a Cement

Compound [7], received the Best Paper Award from the

Cements Division of the American Ceramic Society and

was featured on the cover of the magazine Science

News. This was the beginning of a program which has

made NIST the world leader in the computational

materials science of concrete and other cement-based

materials. The series of publications has progressed

from simulations of the 3-dimensional random porous

structures formed in hardening cement pastes to calculations of the diffusivities and elastic moduli of the

structures; to the rates of reaction and heat evolution

during the hardening of cement pastes taking into

account the experimentally-determined phase composition (which is not dependent on Bogue’s calculation

method) and phase distribution; to the effects on

diffusivity of concrete attributable to the aggregates

imbedded in the hardened cement paste and the interfacial zones around them; to calculations of the service

life of chloride-exposed, steel-reinforced concrete, to

the rheological properties of concentrated dispersions

of irregularly-shaped particles with predictions of

the effects of interparticle forces; to the effects of

embedded electrically-conducting fibers on the electrical properties of mortars; to the effect of randomlydistributed thermoplastic fibers on the fire resistance

of high-strength concrete; and to the moisture distribution in concrete under a variety of curing conditions

and its effect on shrinkage. Together, these developments illustrate the concept of virtual cement and concrete in which the properties of concrete mixtures made

from as-yet-unavailable hypothetical materials might

be predicted, thereby providing a powerful new tool for

product development. As papers on the simulation

models are approved for publication, they are added to

the web-based Electronic monograph on the computational materials science of concrete [8] initiated by

Edward Garboczi and Dale Bentz in 1996, more recently

joined in the venture by Kenneth Snyder, Nicos Martys,

and Chiara Ferraris. The continually-evolving

monograph (Fig. 3) is a repository for NIST’s contributions to the computational materials science of concrete

Fig. 3. Announcing the web-based “Electronic monograph on the computational materials science of concrete”—equivalent to about 1500

printed pages of NIST models for predicting the structure and properties of cement and concrete, and growing by several hundred pages each year.

36
through which they are made available to the world. The

monograph has now reached the equivalent of 1500

printed pages in length and continues to grow. In a

typical month, the monograph’s web-site is accessed by

more than 1000 persons from about 40 countries.

The advances in computational materials science of

concrete have been complemented by advances in

techniques for cement characterization, particularly in

electron micrographic petrography, and application of

quantitative x-ray diffraction analysis. NIST research in

both areas has led to new ASTM standards, and both

techniques have been applied to characterization of a

suite of three portland cement clinkers which have been

designated NIST Reference Materials.

From his writings, one feels that Bogue would have

appreciated the recent work at NIST because it seems to

be in complete philosophical accord with his views and

because it has benefitted so much from the program he

led from 1924 to 1954. For example, early in the life of

the PCA Fellowship, Bogue commented, “Just in

what department our investigations will prove to be of

greatest value, we do not know, but we are convinced

that scientific information on the nature of the

compounds of clinker and of the reactions of these

compounds, holds promise of application in many

directions. Perhaps the eventual direct application may

be in manufacture, in raw material, in control, or it may

be in the utilization of cement in concrete. . . . This is

one of our ambitions; one of the reasons for our existence. The other is to extend the field of usefulness of

concrete by the development of a material which will

possess to a higher degree the virtuous qualities for

which concrete is now well known. Or, perhaps, even

go beyond these to the opening up of new possibilities

in construction, or art, or industry which are not yet

conceived. In the case of many commodities, supply

follows the demand, but in the case of the new discoveries of science, a market is born where none existed

and the creation of the product opens to reality trails of

progress, of achievement, which formerly were lighted

only by the Aladdin’s Lamp of Imagination.” The range

of impacts of Bogue’s work illustrates the correctness of

his vision.

Prepared by Geoffrey Frohnsdorff.

Bibliography

[1] Robert H. Bogue, Calculation of the Compounds in Portland

Cement, Ind. Eng. Chem., Anal. Ed. 1, 192-197 (1929).

[2] Robert H. Bogue, Portland Cement in Concrete Engineering,

Concrete, 30 (3), 33-36 (1927).

[3] Standard Specification for Portland Cement, ASTM C-150,

Annual Book of ASTM Standards, Vol. 04.01, Cement, Lime and

Gypsum, American Society for Testing and Materials, West

Conshohocken, PA (1999).

[4] Robert H. Bogue, The Chemistry of Portland Cement, Reinhold

Publishing Co., New York (1947).

[5] W. J. Youden, Statistical Aspects of the Cement Testing Program,

Proc. Am. Soc. Test. Mater. 59, 1120-1128 (1959).

[6] Dale P. Bentz, Three-Dimensional Computer Simulation of

Portland Cement Hydration and Microstructure Development,

J. Am. Ceram. Soc. 80, 3-21 (1997).

[7] Hamlin M. Jennings and Steven K. Johnson, Simulation of

Microstructure Development During the Hydration of a Cement

Compound, J. Am. Ceram. Soc. 69, 790-795 (1986).

[8] Edward J. Garboczi, Dale P. Bentz, Kenneth A. Snyder, Nicos S.

Martys, Paul E. Stutzman, and Chiara F. Ferraris, An electronic

monograph: Modelling and Measuring the Structure and Properties of Cement-based Materials, (http://ciks.cbt.nist.gov/garboczi/), National Institute of Standards and Technology.

37
Development of the Visual-Type Airway

Radio-Beacon System

The object of the research reported in this paper was

to provide a system of navigational aids by which aircraft could be flown on a course in fog or in any condition of visibility or no visibility. After World War I civil

aviation had become a serious enterprise with mail,

express, and passenger flights. Weather and conditions

of visibility hampered regular schedules that had now

become highly desirable for the new industry to be

commercially successful. The requirements of airmail

service necessitated night flying to meet the “next day”

delivery schedules the Post Office wanted to establish

across the nation. This research paper [1] summarizes

the work done at the Bureau of Standards between 1926

and 1929 for the purpose of making possible blind

flying and landing of aircraft.

Navigational instruments available at that time were

the altimeter, the bank-and-turn indicator, the rate-ofclimb indicator, and the compass. With these instruments it was possible to continue to fly in fog, but it was

only by radio means that the pilot could be certain of

staying on course and finding the landing field when the

ground was invisible. Accurate as a compass may be, it

cannot tell the pilot that the aircraft has drifted off

course. The altimeter (simply a barometer) gives only an

approximation of the height above ground and cannot

warn of obstacles in the flight path.

The Bureau of Standards began work on radio navigation for the military during World War I. Since military

aircraft did not fly on fixed airways, they required direction-determination service on independent courses. The

radio direction finder, using loop antennae and sensitive

receiving sets aboard airplanes, was chosen as a homing

device well adapted to military needs. However, the

method was not useful for nonmilitary aviation because

great difficulties were experienced with this type of

receiving apparatus. There were two reasons for nonacceptance by civilian aircraft: the expense and weight

of the receiving equipment, and the inherent slowness

and complexity of operating the radio direction finder.

Although the direction finder could not tell when wind

drift had shifted the aircraft off-course, the method

eventually brought the aircraft home to its destination,

often by a circuitous route.

A new method was developed with the direction

finder based on the ground. Every plane in commercial

transport service carried a radiotelephone transmitter

and receiver, used with a trailing-wire antenna. Permanent direction-finding stations were located at certain

principal airports. For an aircraft to find its position,

it transmitted a radio request to the airport, whereupon

two or more direction-finding stations each observed

the radio waves transmitted by the airplane; triangulation yielded the airplane’s position, which was then

transmitted to the pilot. But this system required an

airplane to carry both receiving and transmitting equipment, and it was not effective when a large number of

airplanes simultaneously requested position coordinates

since the ground station could serve only one plane at a

time.

The Bureau’s first crude radio guidance system for

aircraft was tested in 1921 when a pilot flew along a

course designated by signals from two transmitters on

the ground. A prototype radiobeacon produced two

years later by the Bureau for the Army Air Service was

put aside in favor of further work on the radio compass.

Without passengers, flying the mail was considered

“high adventure,” and the pilots liked it that way. Thus

the prevailing attitude of pilots discouraged further

refinements of navigational systems, and work on the

beacon did not resume until 1926.

The radiobeacon system described in this paper was

an outgrowth of the project undertaken by the Bureau of

Standards for the Army Air Service in 1920. The Air

Service had requested the Bureau to devise a method

whereby a directional transmission would serve as a

guide to airplanes along a chosen course. Army Air

Corps engineers added further refinements to the

Bureau prototype. In July of 1926 the Department of

Commerce decided to establish an Aeronautics Branch,

which requested its research division at the Bureau of

Standards to carry out necessary experimentation and

development to provide civilian aircraft with navigational aids. The work over the next three years led

to very major improvements, the results of which are

reported in this paper.

In order to engage in blind flying and blind landing—

that is, flying under conditions of no visibility—the pilot

must know the position in three dimensions at all times.

This can be achieved with indicators on the aircraft

instrument panel that record the signals from a small

direction beacon, giving the pilot the longitudinal or

approach position, plus an inclined ultrahigh frequency

radio beam that continuously reports the height above

ground. For such a scheme to work, an important

38
difficulty still remained because the Commerce Department transmitted weather information to planes on a

different frequency. This meant that the pilot had to

keep switching frequencies and also contend with interference from marine radios. Adding a device allowing

voice communication about weather conditions without

interruption to the range service (radiobeacon) solved

the difficulty. It was fortuitous that the inventive talents

of Harry Diamond and his team made possible the

assembly of the first visual-type radiobeacon system

that enabled a pilot to keep on course and to know his

approximate position at all times while in flight.

In the paper on the assembly of the visual-type

radiobeacon system, the authors describe the property

that “direction service could be given to any number of

planes flying the course, and that each airplane only had

to carry a receiving set, with no other special equipment

whatsoever. The pilot would obtain the necessary

information pertaining to magnitude of course deviations hands-free and without having to rely on

earphones. The means to accomplish this was the

development of vibrating-reed indicators that alerted

the pilot to any off-course condition. The system had to

be also entirely free from errors due to wind drift.

Finally, all heavy radio equipment would have to be on

the ground, the receiving set on the plane to be light of

weight and simple.”

In 1919, Francis Dunmore and F.H. Engel [2] had

already developed a radiobeacon system that mapped

out “highways” that a pilot could follow by listening to

the signal pattern on a radio receiver. But the landing of

an aircraft after arrival at an airport is three-dimensional, as shown in Fig. 2. The pilot must have lateral

guidance to stay within the confines of the runway

during the approach to the field, and the pilot must also

have longitudinal guidance in the approach to the

landing field in order to know the distance from the

landing point. Finally, the pilot must have vertical

guidance to decrease the altitude gradually as the plane

glides towards the field.

A major step forward came with the replacement of

the voice communication system (radiotelephone) by a

visual indicator in the cockpit. The means to accomplish

this was a set of tuned reeds that would tell the pilot

by how much he was off course and whether to steer

left or right to get back on the right course. A test of

Fig.1. The early blind landing experiments conducted at College Park, MD, used a plane with a canvas hood over

the pilot’s seat. The copilot took over if plans went awry (from Ref. 3).

39
the direction finder system came in 1929 when a pilot

took off from Philadelphia on a day of low visibility and

was told to fly to College Park, Maryland—120 miles

away. The pilot, unfamiliar with the route or the landmarks and with no maps, had to follow solely the guidance given by the beacon indicator on the instrument

board. He not only flew in a straight line to Washington,

but when over the College Park field, the location of

which he did not know, the sudden drop in the reed

deflections signaled that he was at the journey’s end,

and he completed the flight with a visual landing.

However, a pilot needed more precise longitudinal

guidance in order to prepare for a blind landing. For that

purpose, Diamond and Dunmore devised a “distance

indicator” instrument for the airplane based on measuring the field strength of the incoming radio signal.

The instrument would calibrate itself by two marker

beacons, one located about 2000 feet from the runway

and the other at the edge of the runway. The authors

describe in great detail various systems and techniques

that would meet these requirements: the receiving

equipment they developed for use on board the aircraft,

Fig. 2. Definition of the glide path consists of a localizer course for lateral guidance, an outer and middle marker

to tell the pilot the distance to the runway, and a glide path (UHF) transmitter for the vertical guidance (from

Ref. [3]).

40
the marker beacons that inform the pilot when passing

over one of the locations, and considerations for fog

landings.

The next phase of the problem—providing vertical

guidance for the pilot in the descent for landing—was

solved by another transmitter antenna located near the

runway localizer transmitter. Using ultra-high frequencies this time, the second antenna would send out a

radio wave pattern, parabolic in shape and sharply

enough defined to form an invisible ramp that the pilot

would follow as the plane glided down to earth. (This

was probably the very first practical use of ultra-high

radio frequencies).

In 1930 Diamond added a 15-pound unit to the radio

range beacon and radiotelephone in the cockpit that

made possible the first blind landing of an airplane

entirely by radio guidance [4]. The test came on

September 5, 1931, when an airplane, on loan from the

Bureau of Air Commerce with pilot Marshall S. Boggs

at the controls, made the first blind landing in the

history of aviation using only radio signals for lateral,

longitudinal, and horizontal guidance. (A previous

blind landing had been accomplished in July 1929 when

Lt. James Doolittle brought down a hooded plane using

a sensitive barometric altimeter and a gyro-stabilized

horizon indicator, together with a radio lateral course

indicator and marker beacon, also supplied by the

Bureau.) This blind-landing system was turned over to

the Department of Commerce in 1933.

Diamond and Dunmore admitted that, for a time in

1933, they thought that they had sold the system to the

Commerce Department for adoption. They believed it

was inherently simple and practicable and could be

mastered by a pilot in five hours of practice. Their

hopes for adoption were not fulfilled until the beginning

of World War II.

After 1933, the U.S. Civil Aeronautics Administration (CAA) continued to experiment with other systems.

The difficulty remained with the definition of the glide

path. The Lorenz A.G. of Germany in 1934 announced

a blind landing system similar to that of Diamond and

Dunmore, but that system failed to provide a smooth

glide path and hence fell short of adoption there. France

became the first nation to adopt the Diamond-Dunmore

system in 1935.

In 1937, a U.S. committee proposed the standardization of the best features of all systems that had been

tested up to that time. Indianapolis was to be the test site,

but satisfactory results did not come until Diamond’s

ultra-high-frequency antenna system was employed to

obtain a straight “equi-signal” glide path. Diamond and

Dunmore also improved the stability and sharpness

of the runway localizer course and suggested further

improvements in equipment and instrumentation. In

1939 a committee of the National Academy of Sciences,

meeting at the request of the President, recommended

the adoption of the system, called “Indianapolis” and

later the “CAA Instrument Landing System (ILS).”

Installation of ten such systems at key airports began.

However, World War II stopped the commercial

development of blind landing systems and the armed

forces took over the ILS, labeling it “SCS-51.” It was

used by the Allies throughout the war and was put to a

crucial test during the Berlin airlift from June 1948 to

September 1949. But even before that, in 1946, the CAA

began installing the ILS on a wide scale for commercial

use throughout the United States.

Now, 60 years later, the principles of this blind

landing system are still the basis for air traffic control

systems worldwide. The introduction of the global

positioning system (GPS) was a major technological

innovation able to guide airplanes across the vast oceans

Fig. 3. By watching the pointers on the combined instrument, the pilot follows the glide path and runway

localizer course to a safe landing. LEFT: He is on the runway course but above the glide path. CENTER: He is

below the glide path and to the right of the runway. RIGHT: He is “on the beam.” (From Ref. 3)

41
which were previously inaccessible to standard radionavigation methods, thereby closing some big “black

holes” in global air traffic control. Furthermore, radar

provides the means to control the movement in the

vicinity of most major airports today. Summary reports

about this phase of NBS Research appear in [5] and [6].

Francis W. Dunmore and Harry Diamond were both

born and raised in the vicinity of Boston. Dunmore got

his degree in physics from Penn State in 1915, while the

younger Diamond graduated from M. I. T. with a degree

in electrical engineering in 1922. He worked for

General Electric and B.F. Sturtevant Companies in

Boston, taught electrical engineering and picked up

another degree from Lehigh University. Diamond came

to the Bureau of Standards’ radio laboratory in 1927,

not long after it was handed the responsibility for the

research and development work of the Commerce

Department’s newly organized Bureau of Air Commerce. Diamond would soon become the chief of the

Aeronautics Branch there. Prior to World War II,

Diamond, Dunmore, and Wilbur Hinman developed

methods for remote weather measurements with the first

practical “meteorological radiosonde.” In 1939 they had

developed the “remote weather station,” a ground-based

radiosonde for automatic telemetering in remote and

inhospitable locations. During World War II Diamond

was transferred into the newly established Ordnance

Division where he materially contributed to the development of the radio proximity fuse. In 1940, he received

the Washington Academy of Sciences Engineering

Award for his work, and the IRE honored him with

its Fellow Award in 1943 for his efforts in radiometeorology. The successor organization, IEEE, has

renamed that award in honor of Harry Diamond. The

NBS organization chart listed him as Chief of the

Ordnance Development Division in 1945. Diamond was

personally presented with Navy and War Department

Certificates for Outstanding Service in 1945 [7]. His

untimely death in 1948 was a profound loss for the

National Bureau of Standards, which had relied heavily

on Diamond’s visions and plans for the post-war development of civilian technology. To honor him, NBS

named the newly constructed electronics laboratory the

Harry Diamond Laboratories. That organization was

turned over to the U.S. Army in 1952 and continues to

operate under that name to this day.

Prepared by Hans J. Oser.

Bibliography

[1] J. H. Dellinger, H. Diamond, and F. W. Dunmore, Development of

the Visual Type Airway Radio-Beacon System, Bur. Stand. J. Res.

4, 425-459 (1930).

[2] F. H. Engel and F.W. Dunmore, A Directive Type of Radio Beacon and Its Application to Navigation, Sci. Pap. Bur. Stand. 19,

281-295 (1923).

[3] Robert Robinson, Diamond-Dunmore, Federal Science Progress

1 (3), 16-20 (1947).

[4] Rexmond C. Cochrane, Measures for Progress: A History of the

National Bureau of Standards, NBS Miscellaneous Publication

275, National Bureau of Standards, U.S. Government Printing

Office, Washington, DC (1966) pp. 294 ff.

[5] NBS Research in Navigation, Tech. News Bull. Natl. Bur. Stand. 34

(6), 80-85 (1950). (Summary of a talk by Edward U. Condon

before the Eastern Regional Meeting of the Institute of Navigation, February 10, 1950.)

[6] Frank G. Kear, Instrument Landing at the National Bureau of

Standards, IRE Trans. Aeronaut. Navig. Electron. ANE-6, 61-67

(1959).

[7] Nelson R. Kellog, I’m Only Mr. Diamond, A Biographical Essay,

Public Affairs Office (History), U.S. Army Laboratory Command, November 1990.

42
A Hydrogen Isotope of Mass 2

Before the publication of this definitive paper on the

discovery of deuterium [1,2], the existence of a heavy

isotope of hydrogen had been suspected even though

Aston [3] in 1927, from mass spectrometric evidence,

had discounted the presence of the heavier isotope at a

hydrogen abundance ratio 1

H/2H < 5000. (The modern

best estimate of that ratio is 5433.78 in unaltered

terrestrial hydrogen.) Harold Urey, however, continued

to suspect the existence of the heavier isotope, based

upon evidence from the sequence of properties of

known nuclides and from faint satellite peaks in the

Balmer series of the atomic hydrogen spectrum in the

visible region. Birge and Menzel [4] had gone further by

estimating the abundance ratio 1

H/2H at about 4500

from the difference in the atomic weight of hydrogen

measured by chemical versus mass spectrometric

means.

Still, the world of science was unwilling to acknowledge the existence of a hydrogen isotope without direct

experimental proof. Thus Urey solicited the collaboration of a physicist he had known well at Johns Hopkins

University, Ferdinand Brickwedde, who had moved to

the National Bureau of Standards after completing his

graduate work and had begun to assemble an unexcelled

center for thermodynamic measurements, especially at

low temperature.

This was a time when isotopes, because of their identical configuration of extra-nuclear electrons, were

believed to be chemically inseparable. Prout’s old

hypothesis of atomic weights being whole-number

multiples of that of hydrogen now applied more satisfactorily to isotopes than to elements, but—apart from the

effects from some radioactive processes applicable

exclusively to elements of high atomic number—all

atomic weights were still regarded as constants of

nature.

Urey, Brickwedde, and their colleagues evidently did

not share that contemporary viewpoint. These scientists

had knowledge of the differences in nuclear spins, as

well as magnetic and quadrupole moments, between

isotopes of the same element. They had mastered

quantum physics and thermodynamics, so surely they

expected differences in physical and chemical properties and hence would have anticipated some differences

in reaction dynamics and equilibria. They probably

estimated the chemical differences among isotopes to be

small, perhaps too small to be measured by contemporary experiments. Any successful separation, therefore,

was likely to be achievable largely by virtue of the

difference in masses of isotopes of the same element. A

suspected isotope of hydrogen had a mass two or three

times that of the predominant 1

H. The search for a

hypothetical hydrogen isotope caused great excitement

and led to a high-stakes competition among laboratories.

None exceeded Urey and his coworkers in understanding

and determination to find proof for the existence of an

isotope of hydrogen by a clear-cut measurement.

Actually, Urey and George Murphy had found, but not

yet published, spectrographic evidence for the lines of

2

H obtained from samples of commercial tank hydrogen. These lines, however, were seen only after long

photographic exposures. The suspicion persisted that

these extra lines could have arisen from irregularities in

the ruling of their grating or from molecular hydrogen.

Urey and Brickwedde recognized that the proportional mass difference of a possible hydrogen isotope 2

H

or 3

H was most likely to show in molecular hydrogen

(H2). A fractional distillation near the hydrogen triple

point (about 14 K) gave the best chance of achieving a

high concentration of the hypothesized 2

H. Despite the

considerable experimental difficulties, Brickwedde at

NBS undertook the attempt to separate partially the

hypothetical isotope by fractional distillation of liquid

hydrogen [1,2].

Murphy much later [5] recalled the fear of being

beaten in the race for priority in a proof for the existence

of 2

H at a time when Brickwedde reported a manufacturing delay in the large NBS hydrogen liquifier. The

delay, however, appears to have been well used. The

authors attempted a quantitative calculation of the

enrichment to be expected. By making use of the equality of free energy of gas and solid in equilibrium and the

Debye theory of the solid state, they calculated, with

minor additional assumptions, the ratio of the vapor

pressures p(

1

H2)/p(

1

H2H) at the triple point as 2.688.

For the actual experiment Brickwedde started with

400 ft3 of hydrogen gas which was liquefied after

precooling with liquid air boiling at reduced pressure.

Liquid hydrogen was then fed into a 1.6 L evaporation

flask. Evaporation took place until about 1/3 of the

hydrogen remained, which was then fed into sample

tubes and transported to Columbia University for

atomic spectroscopic comparison with normal hydrogen by Murphy [1,2]. Assuming the above-quoted

abundance ratio to be 4500 [3], the mole fraction left in

the still should by their calculation have increased by a

43
factor of 4000. (It would have been higher, if 3

H were

involved.) Although the concentration factor of 4000

was never achieved, the 2H concentration was so greatly

enhanced that its existence could be demonstrated from

the spectroscopic measurements without any remaining

doubt. A Letter to the Editor [1] narrowly achieved the

desired priority and alerted the scientific community to

the upcoming full paper [2], which was recognized as

much for the low-temperature advances—the first of a

series of similarly significant low-temperature measurements related to superconductivity at NBS [6]—as for

the scientific significance of a separable stable hydrogen isotope. This full paper [2] earned Urey the 1934

Nobel Prize for Chemistry.

Although he refrained from stealing the limelight and

the priority from the Urey, Brickwedde, and Murphy

classic experiment, Edward Washburn of NBS, in

association with Urey [7], published in 1931 a demonstration of the existence of 2

H based upon a simpler and

subsequently much more important method of enrichment. Washburn and Urey argued that chemically

unbonded 2

H+ might have a lower mobility and/or

higher cathodic potential in electrolysis. In fact,

such concentration was demonstrated in a number of

samples, including those from residual solutions from

commercial electrolytic cells that had operated continuously for two to three years. These samples were examined spectroscopically by Murphy at Columbia, and the

quantification of the enrichment was also carried out at

NBS using water density measurements. The high

accuracy of these measurements stands as a great tribute

to NBS. This work is recorded in many papers authored

or co-authored by E. R. Smith. In a very elegant experiment, for example [8], the authors compared the densities of four kinds of samples: natural water, water

prepared by combining hypothetically enriched hydrogen with normal oxygen, water prepared by combining

natural hydrogen with enriched oxygen, and water

prepared by combining hypothetically enriched hydrogen with enriched oxygen. Thus they were able to show

not only that the 2

H enrichment is real, but that the

enrichment of the higher isotopes of oxygen is also

measurable. Washburn showed great ingenuity in

searching out waters that were enriched or denuded in

2

H. In one experiment he and his son compared water

from sap taken from the top of a tree with water from

the roots. The results showed conclusively that 2

H

existed and that isotopic compositions, and also atomic

weights, could no longer be regarded as invariable.

The 2

H isotope, as early as in 1934 [9], was named by

Urey as deuterium (symbol D) with a nucleus called

deuteron (symbol d). As is common to many significant

discoveries in science, this event was widely anticipated but, in contrast with most other discoveries, its

applications followed swiftly. Within a year, an NBS

group had used isotopic composition in an electrolytic

process control. A Cambridge group under Rutherford

[10] had prepared deuterated compounds such as

D3PO4, bombarded them with deuterons, and correctly

identified the reaction: D+D = T+H (T is the symbol for

the new radioactive isotope of hydrogen of mass 3,

called tritium). The nuclear reaction type (d,n) was also

identified, in which the neutron that is produced carries

off the excess energy in the deuteron (the excess energy

over that of a neutron separated from the nucleus of 1

H).

Within a decade of the discovery of D, the thermodynamic properties of the hydrogen isotopic species had

been measured (see, for example, Fig. 1) and definitive

values published by NBS [11]. Furthermore, the

application to a fledgling nuclear industry was realized,

and the cosmological significance began to be

appreciated.

The literature resulting from the discovery of

deuterium grew very fast. As early as 1935, Urey with

Gordon Teal [12], who much later became Director of

the NBS Institute for Materials Research, wrote a

comprehensive review of the methods of separation of

deuterium, its properties in gas, liquid, and solid phases,

the chemical kinetics of deuterated compounds, analytical applications for deuterium, the nuclear spin and

Fig. 1. Melting point pressure as a function of temperature for H2,

HD, and D2 (from [11]).

44
moments, and the atomic and molecular spectra. The

discovery of deuterium had started a whirlwind of

change in science.

The above description may give the false impression

of a straightforward, orderly path to the discovery of

deuterium. To correct that illusion, the reader might

enjoy reading Brickwedde’s memoirs [13] written

after all the dust had settled and after Urey, Murphy, and

Washburn had died. In that article Brickwedde first pays

great tribute to Urey “who proposed, planned, and

directed the investigation. Appropriately, the Nobel

Prize for finding the heavy isotope of hydrogen went to

Urey.” Brickwedde then points out that the work

stumbled on by a succession of errors, some detrimental, some accidentally fortunate to furthering

progress. One such error was made on authoritative, but

false, advice that electrolysis could not alter significantly the hypothetical isotopic composition of hydrogen, so that the first sample of hydrogen used by

Brickwedde for fractional distillation by the above

described tour de force was already denuded in deuterium! At that juncture, Washburn at NBS was again

the hero who suggested the preparation of the hydrogen

sample was faulty.

After receiving the degree of AB (chemistry) and

PhD (physics and mathematics) from Johns Hopkins

University, Ferdinand Graft Brickwedde started at NBS

in 1925 as postdoctoral Mansell Research Associate.

In 1926 he became Chief of the Low Temperature

Laboratory. In 1946 the Heat and Power Division was

restructured and Brickwedde was appointed its Chief in

recognition of his leadership potential. At the same time

Brickwedde organized and led the Thermodynamics

Section, one of the component parts of the new Division.

Besides his key contributions to the discovery of

deuterium, his research covered a diversity of topics

including measurement of thermodynamic properties,

the liquefaction of gases, the superfluidity of liquid

helium II, the absolute temperature scale, applications

of refrigeration, solar energy, rheology, octane rating,

and the properties of deuterium compounds. Simultaneously with his appointment at NBS, Brickwedde

served as a part-time physics professor at the University

of Maryland, where he gave graduate courses in statistical mechanics, relativity, electrodynamics, and quantum

mechanics. He organized the University of Maryland

Extension Program in physics at NBS. This program

was important in that it gave opportunities for NBS staff

to keep abreast of current developments in specialized

fields, to acquire knowledge in new fields, and to satisfy

interests to teach while at a non-academic establishment.

It also enabled many young staff members at NBS and

other Federal agencies to satisfy their course requirements towards advanced degrees by attending classes at

NBS after working hours. He also was consultant to

Los Alamos Scientific Laboratory, the University of

California Lawrence Livermore Laboratory, and a commission member of the International Institute of Refrigeration and the International Union of Pure and Applied

Physics. Brickwedde won the Hillebrand Prize of the

Chemical Society of Washington and was Associate

Editor of The Physical Review. As NBS expanded in the

early 1950s, he helped recruit young PhDs for the

new programs. He and his wife, Langhorne Howard

Brickwedde, an NBS electrochemist, were gracious

hosts to many of the new arrivals. In 1956 Brickwedde,

when only 53 years old, left NBS to accept the post of

Dean of Physics and Chemistry at Pennsylvania State

University and, in 1978, the Evan Pugh Research

Professorship there. He died in 1989 at the age of 86.

Prepared by Walter J. Hamer and H. Steffen Peiser.

Bibliography

[1] H. C. Urey, F. G. Brickwedde, and G. M. Murphy, A Hydrogen

Isotope of Mass 2, Phys. Rev. 39, 164-165 (1932).

[2] H. C. Urey, F. G. Brickwedde, and G. M. Murphy, Phys. Rev.

40, 1-15 (1932).

[3] F.W. Aston, Bakerian Lecture A new mass-spectrograph and

the whole number rule, Proc. R. Soc. London A115, 487-514

(1927).

[4] R. T. Birge and D. H. Menzel, The relative abundance of the

oxygen isotopes and the basis of the atomic weight system,

Phys. Rev. 37, 1669-1671 (1931).

[5] G. M. Murphy, The Discovery of Deuterium, in Isotopic and

Cosmic Chemistry, H. Craig, S. L. Miller, and G. W. Wasserburg (eds.), North-Holland Publishing Company, Amsterdam

(1964).

[6] F. G. Brickwedde, R. P. Hudson, and E. Ambler, Cryogenics,

Annu. Rev. Phys. Chem. 6, 25-44 (1955).

[7] E. W. Washburn and H. C. Urey, Concentration of the H2 Isotope of Hydrogen by the Fractional Electrolysis of Water; Proc.

Natl. Acad. Sci. U.S.A. 18, 496-498 (1932).

[8] E. W. Washburn, E. R. Smith, and F. A. Smith, Fractionation of

the isotopes of hydrogen and of oxygen in a commercial electrolyzer, J. Res. Natl. Bur. Stand. 13, 599-608 (1934).

[9] Harold Clayton Urey, in Nobel Lectures, Chemistry 1922-1941,

Elsevier Publishing Company, Amsterdam (1966) pp. 331-356.

[10] M. L. E. Oliphant, B. B. Kinsey, and Lord Rutherford, The

transmutation of lithium by protons and by ions of the heavy

isotope of hydrogen, Proc. R. Soc. London A141, 722-733

(1933).

[11] H. W. Woolley, R. B. Scott, and F. G. Brickwedde, Compilation

of thermal properties of hydrogen in its various isotopic and

ortho-para modifications, J. Res. Natl. Bur. Stand. 41, 379-475

(1948).

[12] H. C. Urey and G. K. Teal, The hydrogen isotope of atomic

weight two, Rev. Mod. Phys. 7, 34-94 (1935).

[13] F. G. Brickwedde, Harold Urey and the Discovery of Deuterium, Phys. Today 35 (9), 34-39 (1982).

45
Air Flow and Turbulence in Boundary Layers

Shortly after arriving at NBS in 1929 as an employee

in the Electrical Division, Galen B. Schubauer enrolled

in a graduate study program at Johns Hopkins University in Baltimore, as did about two dozen of his newly

hired colleagues. These studies required a commute to

Baltimore several times per week. The difficult trip was

made more efficient by cramming six to eight students

into a 1930s sedan, which made the trip much more

arduous. During his graduate studies, Schubauer’s

interest began to focus on aerodynamics, and on

boundary layer phenomena in particular. Consequently,

he transferred to the Aerodynamics Section of NBS,

then headed by Hugh L. Dryden, where he began an

illustrious career of research on this topic.

His 1935 paper, Air Flow in a Separating Boundary

Layer [1], provided great insight into separation (or

stall) of a laminar boundary layer developing over an

airfoil with the cross-section of an elliptic cylinder.

The purpose of the work was to test an approximate

solution to the applicable flow equations advanced by

K. Pohlhausen. Schubauer’s experimental results

showed that Pohlhausen’s solution produced good

agreement in the forward portion of the surface, but it

began to fail near the separation point on the surface and

could therefore not be used to predict the location of

the separation point. The next paper, The Effect of

Turbulence on the Drag of Flat Plates [2], concerned the

effects of free-stream turbulence on four objects: a flat

plate, a thin circular disk, a vane anemometer, and a

Pitot static tube. The results indicated that there is no

appreciable effect of turbulence on the vane anemometer and the Pitot static tube, but there is a small effect

on the drag of a flat plate and on the pressure difference

between the front and rear of a disk. Furthermore, the

effect of turbulence was found to be independent of the

air speed or Reynolds Number.

The hot-wire anemometer had emerged as the fundamental instrument for measuring boundary layer

turbulence as well as boundary layer velocity distributions. This instrument was known to be sensitive to other

parameters which could cause errors in the turbulence

and velocity measurements if proper corrections were

not made. Water vapor (humidity) in the air stream was

recognized to be such a possible extraneous parameter.

In his next paper [3], Schubauer quantified this effect by

verifying recent results published by W. Paeschke which

showed that the effect was to increase the hot-wire heat

loss at higher humidities, giving a fractional change of

about 2 % for an increase in relative humidity from

25 % to 70 %. It was concluded that the phenomenon

could be explained by the effect of humidity on the

thermal conductivity of air.

During the next decade, Schubauer continued to

focus his attention on the stability of the laminar

boundary layer. He was particularly interested in an

instability theory which had been under development

over a 40-year period and which was published in the

mid-1930s by two German investigators, W. Tollmien

and H. Schlichting, who were working independently.

This theory postulated that a small disturbance

introduced into a laminar boundary layer would lead to

transition of the laminar layer to a turbulent boundary

layer, depending primarily upon the frequency of the

disturbance and the longitudinal (in the flow direction)

Reynolds Number. For certain values of the governing

parameters the disturbance would be amplified and

transition would occur, but for other parameter values

the disturbance would be attenuated (or damped)

and would not cause transition. The regions where

disturbances are amplified or damped are separated by

a curve of “neutral stability” as shown in Fig. 1.

This curve is sometimes referred to as a “TollmienSchlichting noodle curve” because of its peculiar shape.

Working during the mid-1930s on his own time and

with available equipment, Schubauer began to investigate the T-S theory experimentally. His jury-rigged

experimental setup was substantially less than ideal, but

he was able to acquire enough data to convince himself

that the T-S theory was basically valid. However,

Dryden argued that the relatively crude experimental

setup employed by Schubauer could not possibly allow

measurement of the T-S phenomenon. There were too

many extraneous sources of disturbances in the flow,

and the signal-to-noise ratio of the available hot-wire

instrumentation was insufficient. Substantial improvement of the experimental equipment would be required

to provide necessary control of all the parameters and

make high quality measurements. Because of higher

priorities, Dryden would neither allow any of the

Aerodynamic Section’s current financial resources to be

used for this work nor assist in soliciting additional

funds for the research.

46
As time passed, Schubauer persisted and continued to

work nights and weekends with available equipment to

refine his experimental setup. Finally, in the late 1930s,

he was able to accumulate enough data to convince

Dryden that he was, in fact, able to measure and verify

the results of disturbances of known frequencies

injected into a laminar boundary layer and that the

results consistently fell very close to the T-S theory’s

predictions.

In the late 1930s, Dryden actively helped Schubauer

in securing funding to pursue this work. As World War

II approached, its value to the war effort was recognized

and it was given a Confidential classification. Now the

problem was no longer funding, but securing the

materials and equipment necessary to conduct a wellcontrolled experiment in a war-time economy. However, as the war progressed, advances in the field of

electronics were of great help in producing components

with which hot-wire instrumentation of higher signalto-noise ratio could be built, and ways were found to

reduce the wind tunnel free-stream turbulence levels

below the required level of about 0.1 % of flow rate.

As a result of the Confidential classification placed

on the work, Schubauer and his colleagues were prevented from publishing anything about it until after

World War II, except as an advance National Advisory

Committee for Aeronautics (NACA) Confidential

Report in 1943. By 1947, after Dryden had become the

head of NACA and Schubauer had become chief of the

NBS Aerodynamics Section, the work was published in

the open literature in the Journal of Research of the

National Bureau of Standards [4]. The paper was

co-authored by H. K. Skramstad, who was now chief of

the NBS Guided Missiles Section and who contributed

improvements to the hot-wire instrumentation and other

electronic components of the test apparatus. The results

were also published in other media, and additional

publications by Schubauer and his colleagues about this

same time described associated research work.

The T-S theory and its experimental verification by

Schubauer and Skramstad contributed greatly to the

fundamental understanding of the transition of fluid

boundary layers from laminar to turbulent flow. This has

led to extensive work in boundary layer control resulting

in a myriad of designs for controlling transition to make

lifting surfaces, internal flows, and submerged vehicles

more efficient. The value of the work has been recognized to the extent that it was nominated for the Nobel

Prize in Physics.

Galen Brandt Schubauer was born in Mechanicsburg,

PA. He graduated from Pennsylvania State University

and received a master’s degree in physics from the

California Institute of Technology and a doctorate in

physics from Johns Hopkins University. His honors

included the Fluid Dynamics Prize of the American

Physical Society, which he received in 1988 for seminal

research findings that concerned the design of wind

tunnels and other aspects of research. In 1944 he was

the recipient of the Washington Academy of Sciences

award for achievement in engineering sciences, and in

1947 he shared the Sylvanus Albert Reed Award of the

Institute of Aeronautical Sciences. He was a fellow of

the American Physical Society, the Washington

Academy of Sciences, and the American Institute of

Fig. 1. Zone of Amplification Enclosed by Neutral Curve, According to Schlichting.

(Adapted from Figure 13 of [4])

47
Aeronautics and Astronautics. He was a member of

the National Academy of Engineering and of the

Philosophical Society of Washington.

Upon his retirement from NBS in 1968, Allen V.

Astin, then Director of NBS, wrote “Few men have

served longer at the National Bureau of Standards than

Galen B. Schubauer, and probably none with more

dedication. His reputation as an international authority

in fluid mechanics, particularly in aerodynamics,

reflected credit on the man and, secondarily, on NBS

itself. Certainly the papers of Dr. Schubauer are of

interest to his friends, to this institution, and to the scientific community. They cover a period of time in which

science, technology, and the world itself were completely transformed; yet his last papers are as relevant as

his earliest....”

A bound volume [5] containing all of Schubauer’s

scientific publications that could be found (totaling 25)

was prepared by colleagues and given to the NBS

library. In the preface to this volume, P. S. Klebanoff

wrote “On April 30, 1968, Dr. Galen Brandt Schubauer

retired from the National Bureau of Standards. His

association with the Bureau was a most fruitful and

illustrious one, spanning a period of almost 38 years....

His research on boundary layers, flow instability and

turbulence not only provided new insight into these

important problems, but also provided for new avenues

of approach both theoretical and experimental. His

work contributed to the prestige of the National Bureau

of Standards and in large measure was responsible for

the stature of the Aerodynamics Section in the scientific

community. Many of his publications are widely cited

and are regarded as classical references in the field...”

Klebanoff continued, “It is perhaps a comment on

man’s nature that the occasion of one’s retirement is one

of the few times that it is considered appropriate to

express respect and affection....”

Prepared by Norman E. Mease and James E. Potzick.

Bibliography

[1] Galen B. Schubauer, Air Flow in a Separating Laminar Boundary

Layer, NACA Report No. 527, National Advisory Committee for

Aeronautics (1935).

[2] Galen B. Schubauer and Hugh L. Dryden, The Effect of Turbulence on the Drag of Flat Plates, NACA Report No. 546, National Advisory Committee for Aeronautics (1935).

[3] Galen B. Schubauer, Effect of Humidity on Hot-Wire Anemometry, J. Res. Natl. Bur. Stand. 15, 575-578 (1935).

[4] Galen B. Schubauer and Harold K. Skramstad, Laminar

Boundary-Layer Oscillations and Transition on a Flat Plate,

J. Res. Natl. Bur. Stand. 38, 251-292 (1947).

[5] G. B. Schubauer, Collected Papers, 1933–1968. Available

through the library of the National Institute of Standards and

Technology.

Fig. 2. Galen B. Schubauer.

48
Thermodynamic Properties of Water and

Steam for Power Generation

In the early 1900s, the electric power generation

industry was experiencing rapid growth and change.

The steam engines used for power in the previous

century had been displaced by turbines which generated electricity as they were rotated by pressurized

steam generated in boilers. Turbines and boilers were

operating at higher temperatures and pressures (and also

in increasingly complex cycles, which required more

sophisticated thermal design and analysis) in order to

attain greater thermodynamic efficiency. They were

also becoming larger as the demand for electricity

skyrocketed.

A major source of growing pains for the industry was

the lack of accurate and standardized values for the

properties of water and steam. For the design of power

plants and the boilers and turbines within them, it is

necessary to have accurate values of thermodynamic

quantities such as the vapor pressure (pressure at which

water boils at a given temperature) and the enthalpy of

vaporization or latent heat (amount of heat required to

generate steam from liquid water). More important, the

evaluation of the performance of purchased equipment

depends on the calculation of these properties. The

efficiency of a turbine is measured as the fraction of the

energy available in the steam that is converted to electricity, but that available energy is calculated to be a

different number depending on the values used for the

thermodynamic properties. A turbine might appear to

be 28 % efficient with one set of properties and only

27 % efficient with another set; because of the large

flows involved, these small differences could mean large

sums of money. It therefore became imperative to settle

on internationally standardized values for the properties

of water and steam, so that all parties in the industry

could have a “level playing field” on which to compare

bids and equipment performance. The paper Calorimetric Determination of the Thermodynamic Properties

of Saturated Water in both the Liquid and Gaseous

States from 100 to 374 C [1] describes the accurate

measurements carried out at NBS that were essential in

reaching agreement on the needed standards.

In the United States, this problem was first addressed

in 1921 by a group of scientists and engineers brought

together by the American Society of Mechanical

Engineers (ASME). The 1921 meeting led to the formation of the ASME Research Committee on Thermal

Properties of Steam. This committee, recognizing the

need for reliable data, collected subscriptions from

industry and disbursed the money to support experimental measurement of key properties of water and steam at

Harvard, MIT, and the Bureau of Standards. Because the

ASME committee was not as successful in their

fundraising as they had hoped, all three institutions

ended up subsidizing some of the research themselves in

recognition of its importance.

The need for standard, reliable data was also recognized in other countries (notably England, Germany, and

Czechoslovakia), and research efforts were coordinated

internationally. In the late 1920s and early 1930s, three

international conferences were held with the purpose of

agreeing on standardized values for the properties of

water and steam. This culminated in 1934 with the

adoption of a standard set of tables, covering the range

of temperatures and pressures of interest to the power

industry at that time. These tables gave the vapor pressure as a function of temperature, values of the volume

and enthalpy for the equilibrium vapor and liquid

phases along the vapor-pressure curve, and volumes and

enthalpies at points on a coarse grid of temperatures and

pressures. Each value had an uncertainty estimate

assigned to it. The data those tables were based on also

became the basis for a book of “Steam Tables” produced

by J. H. Keenan and F. G. Keyes [2]; the Keenan and

Keyes tables were the de facto standard for the design

and evaluation of steam power generation equipment

worldwide for the next 30 years.

The most important data behind these new steam

tables came from the laboratory of Nathan S. Osborne

at the National Bureau of Standards. Through most of

the 1920s and 1930s, Osborne and his coworkers

painstakingly built equipment and conducted measurements. The ASME had originally hoped for data within

three years of the project’s 1921 start, but fortunately

they were patient (and grateful to the NBS for subsidizing the work) and continued to support the project

through years of pioneering, but often frustrating,

apparatus development. Finally, beginning in the late

1920s, their patience was rewarded as data of unparalleled quality began coming from Osborne’s laboratory.

The primary experimental technique was calorimetry,

in which a measured amount of heat is added to a fluid

under controlled conditions. Osborne and coworkers had

previously performed calorimetric measurements on

ammonia. For measurements on water, several new

49
calorimeters were developed. One of these, constructed

from copper and used for the region below 100 C, has

been preserved in the NIST museum; it is shown in

Fig. 1.

The region of most industrial importance, however,

was at much higher temperatures (and correspondingly

higher pressures), well beyond what had been encountered in the ammonia work. Experiments at these conditions were also more difficult because water is very

corrosive at high temperatures. We briefly describe the

calorimeter that was built to overcome these difficulties

and that was used to take the data reported in the Osborne, Stimson, and Ginnings paper [1].

The heart of the calorimeter was a heavy-walled

325 cm3 vessel of chromium-nickel steel. The contents

were not stirred to achieve thermal equilibrium; instead,

heat was diffused by 30 internal silver fins. The vessel

contained a heater and carried a miniature platinum

resistance thermometer. The calorimeter was shielded

from the environment by two concentric silver shields

that were maintained at the calorimeter temperature at

all times. The calorimeter had two valves. The valve at

the top allowed a measurable amount of vapor to be

extracted, and the bottom valve allowed extraction of a

known amount of liquid water. The water simultaneously served as a pressure transfer medium to allow

measurement of the saturation pressure. During extraction of either vapor or liquid, the remaining liquid would

partially evaporate, and heat was supplied to the

calorimeter in order to keep the temperature constant.

The calorimeter was operated in three different

modes. The two isothermal modes in which either liquid

or vapor was extracted provided information on the

latent heat (enthalpy) of vaporization. The calorimeter

could also be sealed and heated, giving information on

the enthalpy and heat capacity of the liquid. By

combining these measurements with the vapor pressure

data and applying thermodynamic relationships, the

specific volumes and enthalpies of the coexisting phases

were calculated. The caloric properties, particularly the

heat of vaporization, are the key data for the design

and evaluation of steam power generation equipment

because they determine the heat that must be added in

the power cycle and the energy available in the steam to

be converted to electricity in the turbines.

These investigations covered the range from water’s

freezing point (0 C) to the end of the vapor pressure

curve at the critical point (approximately 374 C with

a pressure near 22 MPa, over 200 times normal atmospheric pressure). They were reported in a series of

papers [1, 3, 4, 5]. Reference [1] reports the heat of

vaporization and enthalpy data at higher temperatures,

which have proved to be the most industrially important

of these data over the years.

The impact of this work was both immediate and

enduring. As already mentioned, Osborne’s data were

incorporated (sometimes before they had even been

published) into the steam tables desperately needed by

industry at the time. Over 60 years later, much of the

data, notably the heats of vaporization, are still the most

accurate available. Many new steam tables have been

produced through the years, including several generations of official replacements for the 1934 international

standards. While these tables have taken advantage of

some newer data, particularly at higher temperatures

and pressures, the Osborne data have continued to be the

backbone of all international water property standards.

It is not an exaggeration to say that these data are

fundamental to the design and operation of all steam

power-generation facilities in the world today.

With the completion of Osborne’s work in 1939, the

most pressing industrial need for steam data had been

Fig. 1. Calorimeter used by Osborne et al. to study water properties

at temperatures below 100 C.

50
met. However, water property standards continued to be

improved as new data were taken and as better means for

representing data were developed. These standards are

important not only for the steam power industry, but also

for other industries such as chemical processing.

Accurate water property standards are also needed for

scientific research, both because of the direct scientific

importance of water and because water is commonly

used as a calibration standard. The NBS (and later

NIST) remained involved with these standards as an

active participant in the international conferences that

eventually evolved into the International Association for

the Properties of Water and Steam (IAPWS). Howard J.

White of NBS maintained the Secretariat of the Association for many years. When new international standards

were adopted in the 1960s, Joseph Hilsenrath of NBS,

an early leader in the application of computers to the

analysis of scientific and engineering data, was involved

in their development and dissemination. An improved

representation of water and steam properties was

adopted in 1984 under the leadership of NBS’s Lester

Haar, and tables from that formulation were published as

the widely distributed NBS/NRC Steam Tables [6].

The 1990s saw a new generation of improved property formulations, taking advantage of both new data

and improved computer optimization techniques.

IAPWS coordinated the international development and

testing efforts for these formulations. The latest stateof-the-art representation of water’s thermodynamic

properties was adopted by IAPWS in 1995 [7], and

properties calculated from current IAPWS standards for

general and scientific use are distributed in a computer

program by the NIST Standard Reference Data program

[8]. IAPWS also maintains a separate “industrial”

standard specifically for the steam power industry [9];

this standard sacrifices some accuracy in order to meet

the special requirements (computational speed and less

frequent revision) of that industry. NIST, through the

involvement of its personnel in the ASME subcommittee

which is the U.S National Committee for IAPWS, has

done much of the work in disseminating the new industrial standard in the United States [10]. All of these

standards, from the 1930s to the present, have been

anchored by the data of Nathan Osborne and his

coworkers.

Nathan S. Osborne graduated from the Michigan

College of Mines (now Michigan Technological

University) in 1899. He was one of the earliest

employees of the National Bureau of Standards, beginning his career there in 1903. Except for a period of two

years, when he returned to Michigan to teach at his alma

mater, he remained at the NBS until his retirement in

1939. During this time, he rose from the humble status

of Laboratory Assistant to the prestigious rank of

Principal Physicist. Prior to his work on water and

steam, Osborne was part of an effort, funded by special

Congressional appropriation at the behest of the refrigeration industry, to measure properties of interest in

refrigeration. The most significant result of this work

was a set of “ammonia tables” [11] that served as a

standard for many years. The latter half of his career

was mostly occupied by the work on water and steam;

recognition for this work included honorary doctorates

from his alma mater and from the Stevens Institute of

Technology. Osborne died in 1943 at the age of 68.

Harold F. Stimson received a Ph.D. in physics from

Clark University in 1915. His advisor, A. G. Webster,

was one of the founders of the American Physical

Society, and in the 1890s had been one of the first

scientists to advocate the creation of a national standards

laboratory. Stimson (known affectionately as “Stimmy”

to his colleagues) was hired by NBS in 1916 and worked

on the ammonia and water projects with Osborne.

Most of his subsequent work was concerned with

temperature measurement; he represented the United

States in the deliberations that resulted in a new International Temperature Scale in 1948 and participated in

its 1960 revision. He reluctantly retired in 1960 (later

describing reaching the then-mandatory retirement age

as being “fired”), but continued his interest in gas

thermometry research at the NBS for many more years.

He was known for giving haircuts to his colleagues; this,

too, continued after retirement. He maintained a large

vegetable garden, which he plowed using his station

wagon, until he was well into his 80s. An active mountaineer, he also played the cello and is on record as a

member of the Bureau of Standards orchestra in 1918.

Stimson died in 1985 at the age of 94.

Defoe C. Ginnings began his career at NBS after

receiving his Ph.D. in chemistry from the University

of Illinois in 1929. He worked at NBS for the next

40 years, using calorimetry and other techniques to

measure properties of fluids and solids, often at extreme

conditions. The calorimeters he designed were at the

leading edge of measurement technology. In addition to

the work on water and steam, he took important calorimetric data on a number of hydrocarbons, which proved

very valuable to the petroleum processing industries,

and made high-temperature measurements of materials

important in the defense and space programs. Ginnings

was known for his personal modesty and for his dedication to pioneering and high-quality experimental work.

He served as Chief of the Heat Measurements Section

through most of the 1960s. He died in 1971 at the age

of 65.

Prepared by Allan H. Harvey, with assistance from

Johanna M. H. Levelt Sengers.

51
Bibliography

[1] N. S. Osborne, H. F. Stimson, and D. C. Ginnings, Calorimetric

Determination of the Thermodynamic Properties of Saturated

Water in both the Liquid and Gaseous States from 100 to 374 C,

J. Res. Natl. Bur. Stand. 18, 389-447 (1937).

[2] Joseph Henry Keenan and Frederick G. Keyes, Thermodynamic

Properties of Steam Including Data for the Liquid and Solid

Phases, John Wiley and Sons, New York (1936).

[3] N. S. Osborne, H. F. Stimson, and E. F. Fiock, A Calorimetric

Determination of Thermal Properties of Saturated Water and

Steam from 0 to 270 C, Bur. Stand. J. Res. 5, 411-480 (1930).

[4] N. S. Osborne, H. F. Stimson, E. F. Fiock, and D. C. Ginnings,

The Pressure of Saturated Water Vapor in the Range 100 to

374 C, Bur. Stand. J. Res. 10, 155-188 (1933).

[5] Nathan S. Osborne, Harold F. Stimson, and Defoe C. Ginnings,

Measurements of Heat Capacity and Heat of Vaporization of

Water in the Range 0 to 100 C, J. Res. Natl. Bur. Stand. 23,

197-260 (1939).

[6] Lester Haar, John S. Gallagher, and George S. Kell, NBS/NRC

Steam Tables: Thermodynamic and Transport Properties and

Computer Programs for Vapor and Liquid States of Water in SI

Units, Hemisphere Publishing Corporation, Washington, DC

(1984).

[7] W. Wagner and A. Pruss, New International Formulation for the

Thermodynamic Properties of Ordinary Water Substance for

General and Scientific Use, J. Phys. Chem. Ref. Data, to be

published.

[8] A. H. Harvey, A. P. Peskin, and S. A. Klein, NIST/ASME Steam

Properties, NIST Standard Reference Database 10, Version 2.2,

Standard Reference Data Program, National Institute of Standards and Technology, Gaithersburg, MD (2000).

[9] W. Wagner, J. R. Cooper, A. Dittmann, J. Kijima, H.-J. Kretzschmar, A. Kruse, R. Maresˇ, K. Oguchi, H. Sato, I. Sto ̈cker, O.

Sˇifner, Y. Takaishi, I. Tanishita, J. Tru ̈benbach, and Th. Willkommen, The IAPWS Industrial Formulation 1997 for the Thermodynamic Properties of Water and Steam, J. Eng. Gas Turbines

Power, Trans. ASME 122, 150-182 (2000).

[10] William T. Parry, James C. Bellows, John S. Gallagher, and

Allan H. Harvey, ASME International Steam Tables for Industrial

Use, ASME Press, New York (2000).

[11] Tables of Thermodynamic Properties of Ammonia, Circular of

the Bureau of Standards, No. 142, U.S. Government Printing

Office, Washington, DC (1923).

Fig. 2. Harold Stimson (left) and Nathan Osborne in 1923, roughly the time when they

were beginning their experimental work on water.

52
Absolute Pressure Calibrations of Microphones

Historically, various techniques have been used in

acoustics to attempt to establish and to measure sound

pressures. At present the most accurate, precise, and

convenient methods over a broad range of frequencies

involve the primary calibration of laboratory standard

microphones by “reciprocity techniques.” The adoption

of these reciprocity techniques followed many years of

exacting work involving other measurement techniques

and other investigators. In the paper, Absolute Pressure

Calibrations of Microphones [1], Richard K. Cook

provided both theoretical and practical understanding of

these new techniques. By rigorous, systematic experimental work and analysis, he demonstrated the weaknesses of certain older, previously dominant methods.

Then, by comparing results from these older methods

with those of the new reciprocity techniques, he

established the superiority of the latter. Reciprocity

techniques were soon employed in critical inter-laboratory comparisons, which quickly led to the elevation

of these techniques to their dominant status as the

preferred method in primary acoustical calibrations and

measurements of sound pressure.

These measurements are important because sound

pressure, which is usually expressed as decibels relative

to a reference pressure of 20 Pa [2], is a critical

measure of acoustical signals. These signals may be

speech, music, or noise. Excessive sound pressure

causes hearing loss, interference with speech reception,

disrupted sleep, and other annoyances. A very large and

increasing number of national and international legal,

regulatory, and quality control standards for health,

safety, and commerce depend on measurements of

sound pressure. Primary methods at national metrology

institutes (NMIs) support these needs via various explicit or implicit chains of traceability. Such chains

relate measurements that necessarily entail high accuracy (for example, those of major calibration laboratories and instrument manufacturers) to measurements

that require lesser accuracy, such as practical laboratory

and field verifications and checks supporting survey

measurements for occupational hearing conservation

purposes.

Cook’s paper can be appreciated by considering it in

the historical context of some of the many techniques

that have been used to determine sound pressures in

given kinds of sound fields. All techniques have relative

advantages and disadvantages with regard to uncertainty, applicable ranges of frequency and amplitude,

and convenience. At various times, particular techniques

and apparatus became favored or dominant, and were in

turn superseded by newer methods.

In the late nineteenth century Rayleigh [3] determined the threshold of human hearing by using a microscope with an eyepiece-micrometer to measure the

displacement amplitude of the vibrating prongs of a

tuning fork, which excited an acoustical resonator as a

sound source. Later researchers in the twentieth century

[4,5,6,7] sought better and more convenient sound

sources of known strength, or better instruments for

measuring sound fields. The thermophone used an

alternating current (sometimes superposed on a larger

direct current) to produce a periodic variation of temperature in a conductive wire or foil. The temperature

variation in the wire or foil caused a layer of gas to

expand and contract, thereby producing a calculable

sound pressure. However, the method had numerous

components of uncertainty that were difficult to correct

for. Thermophones now are seldom, if ever, used for

primary calibrations.

Cook’s introduction of the reciprocity

method . . . and many other accomplishments were recognized in 1988

when the Acoustical Society of America

awarded him its Gold Medal “ . . . for

outstanding seminal contributions to

diverse areas of acoustics and to

standardization.”

Another calculable source of sound pressure is the

pistonphone, in which one or more mechanically driven

pistons produce a known time-varying volume displacement in a small (relative to a wavelength of sound) cavity

of known volume. Practical mechanical problems have

limited pistonphones to use at low frequencies, on the

order of 250 Hz.

The electrostatic actuator attempts to apply a known

source of equivalent sound pressure to the electrically

conductive diaphragm of a microphone. This device

uses an electrically conductive plate (usually slotted or

53
perforated) to which an alternating voltage is applied

relative to the microphone diaphragm. From the resulting alternating force of electrostatic origin, the equivalent sound pressure on the diaphragm is calculated.

As Madella [8] recognized, the actuator-determined

response of a microphone only approximates calibration

in the sound pressure field (this is often called a pressure

calibration). However, actuators are accurate enough to

be used for secondary calibrations.

The invention of the wide-frequency-range capacitor

(condenser) microphone by Wente [9] provided the next

advance in instrumentation for sound pressure measurements. The sensitivity of this device could be calibrated

by primary sources, and the microphone could then be

used to measure sound pressure. Wente used both a

pistonphone and a thermophone to calibrate the microphone [10]. He called this microphone a transmitter,

a word usage still found in present-day telephone

terminology, although much of the other literature uses

“transmitter” to mean a microphone driven as a sound

source. In the acoustics literature “response” is often

used equivalently with “sensitivity.” The unit of sensitivity is now expressed as the ratio of SI derived units

V/Pa, but the older literature, including reference [1],

uses the ratio (cm2 volts)/dyne. The sensitivity level

(response level) of a microphone is now usually expressed in decibels (dB) with respect to the reference

quantity 1 V/Pa.

Research continued as systematic differences between different sources of sound pressure became

evident. By 1932 Ballantine [11] described not only the

theory of the pistonphone, but also the underlying

mathematical physics and some experimental results for

the electrostatic actuator, the thermophone, and a small

moving-coil sound source for which the output planeprogressive-wave sound pressure was measured by the

Rayleigh disk method (also described in [4,5] with

further references).

In 1940, Cook’s analysis of these systematic differences led to his introduction of what became known as

the reciprocity method for the pressure calibration, or

determination of pressure sensitivity, of microphones

[1]. From extensive experiments, Cook observed good

agreement between calibrations by reciprocity and those

carried out using the electrostatic actuator, the pistonphone, and the optically measured displacement amplitude of smoke particles. However, he also observed

discrepancies between calibrations using thermophone

methods in air, hydrogen, and helium, as well as

discrepancies between these thermophone methods and

the other methods that among themselves produced

consistent agreement. His theoretical and experimental

work, along with the independent theoretical work of

MacLean [12], clearly established the validity of the

reciprocity method for calibrating microphones.

In the United States, both cooperative and independent research subsequently included Cook at the

National Bureau of Standards, Wiener and DiMattia

at the Cruft Laboratory at Harvard University, and

Olmstead and Hawley at the AT&T Bell Laboratories at

Murray Hill, New Jersey [6,13]. The development of

the Western Electric (WE) 640AA microphone [6,7]

provided a stable modern microphone. Although no

longer manufactured, the WE 640AA microphone still

satisfies the specifications [14] for an IEC type LS1Po

laboratory standard microphone, and numerous samples

have met the specification in reference [14] for the

long-term stability of a Type LS1P standard microphone (long-term drift in sensitivity level less than

0.02 dB/year). The newer WE 640AA microphones

were used in inter-laboratory comparisons of calibration

results among the laboratories of NBS, Harvard, and

AT&T Bell. For each of the three microphones for

which results were reported in 1945 [13], calibrations

among the laboratories agreed within 0.2 dB at

frequencies from 50 Hz to 9 kHz, typically somewhat

better at frequencies below about 5 kHz, and within

0.3 dB over the frequency range 9 kHz to 11 kHz. These

results demonstrated that measurements of sound

pressure over a wide frequency range using stable

standard microphones calibrated by the reciprocity

method were superior to the use of the best available

standard sources such as the thermophone.

This demonstrated superiority eventually led to the

dominance of reciprocity methods as the primary

calibration methods in acoustical laboratories of NMIs

around the world. Modern pressure calibrations of

microphones by reciprocity techniques are more

accurate, more elaborate, and may use much more

complex apparatus than Cook had available, but they are

fundamentally similar.

In 1982, Cook’s classic paper [1] was reprinted in its

entirety in the Benchmark Papers in Acoustics series [4].

Assessing the contributions of various researchers,

H. B. Miller [4, pp. 232-233] noted the significance of

accomplishments represented in Ballantine’s 1929 paper

[15] and stated that an extract from this paper “is so

similar to Schottky’s work and so foreshadowing that of

MacLean, that the wonder now is that Ballantine missed

being the inventor of the absolute reciprocity calibration

method. . . . Moreover, in his 1932 paper (Paper 25),

Ballantine omitted all reference to the method, thereby

presumably implying that he felt it had no future. . . .

All the greater credit, surely, belongs to Cook and to

54
MacLean for having the courage to challenge the

great prestige of Ballantine.” (Miller’s “Paper 25” is our

reference [11] ).

Cook’s introduction of the reciprocity method and his

many other accomplishments were recognized in 1988

when the Acoustical Society of America awarded

him its Gold Medal “ . . . for outstanding seminal

contributions to diverse areas of acoustics and to

standardization.” [16].

Richard K. (RK) Cook was born in Chicago and

obtained his B.S. in 1931, M.S. in 1932, and Ph.D. in

1935, all in the field of physics, from the University of

Illinois. In 1935 he joined the National Bureau of

Standards, and he spent most of his professional career

there. He served as the Chief of the Sound Section from

1942 until 1966, where he contributed extensively to the

technical literature on the subjects of microphones,

microphone calibration, architectural and room acoustics, reverberation room characterization, piezoelectric

properties of crystalline quartz and, eventually, the

field of infrasonics. During these years, he also served

as Associate Editor of Sound (1962-3), Senior Editor of

the Journal of the Washington Academy of Sciences

(1955), and Editor of the Acoustics section of the

American Institute of Physics Handbook. In 1966 he left

NBS temporarily to become Chief of the Geoacoustics

Group in the National Oceanic and Atmospheric

Administration, where he concentrated his technical

talents on infrasonics. He returned to NBS in 1971 as a

Special Assistant on Sound Programs, reporting to the

NBS Director, and served in this capacity until his

official retirement in 1976. After retirement, Cook acted

as a consultant to NBS on acoustical matters.

Cook also held a number of teaching posts,

instructing in mathematics for the U.S. Department of

Agriculture Graduate School between 1941 and 1950

and in various courses in mathematics, physics, and

engineering for the NBS Graduate School and Catholic

University. He acted as Adjunct Professor in the

Electrical Engineering Department of Brooklyn

Polytechnic Institute in 1956 while on sabbatical from

NBS and carrying out research at Bell Telephone

Laboratories.

He is a Fellow of the Acoustical Society of America,

the Washington Academy of Sciences, the American

Physical Society, and the American Association for the

Advancement of Science, and he served as President of

the Acoustical Society of America in 1954-1955.

Cook’s accomplishments span an extraordinary gamut

of the subdivisions of acoustics, with respect to both

physics and engineering, and they include exceptional

service to technical societies, standards committees, and

the body politic in general. Many people remember

RK’s involvement in their own particular fields, but he

is truly a “Renaissance Man of Acoustics.”

Prepared by Victor Nedzelnitsky .

Bibliography

[1] Richard K. Cook, Absolute Pressure Calibrations of Microphones, J. Res. Natl. Bur. of Stand. 25, 489-505 (1940). Also in

abbreviated form in Richard K. Cook, Absolute pressure calibration of microphones, J. Acoust. Soc. Am. 12, 415-420 (1941).

[2] International Electrotechnical Vocabulary—Chapter 801:

Acoustics and Electroacoustics, IEC 60050-801 Ed. 2.0 t: 1994,

International Electrotechnical Commission Central Office,

Geneva (1994).

[3] John William Strutt (Baron Rayleigh), The Theory of Sound, 2nd

ed., Macmillan, London (1896) [reprinted Dover, New York,

(1945)], Vol. II, Sec. 384.

[4] Harry B. Miller (ed.), Acoustical Measurements: Methods and

Instrumentation, Hutchinson Ross Publishing Company,

Stroudsburg, PA (1982), Vol. 16 in Benchmark Papers in Acoustics (R. B. Lindsay, series ed.).

[5] Leo Leroy Beranek, Acoustical Measurements, American

Institute of Physics for the Acoustical Society of America , New

York, (1988 Revised edition); (1949 edition published by John

Wiley & Sons, New York).

[6] R. K. Cook, A Short History of the Condenser Microphone, in

AIP Handbook of Condenser Microphones: Theory, Calibration,

and Measurements, G. S. K. Wong and T. F. W. Embleton (eds.),

American Institute of Physics Press, New York (1995) pp. 3-7.

[7] M. S. Hawley, F. F. Romanow, and J. E. Warren, The Western

Electric 640AA Capacitance Microphone: Its History and Theory of Operation, in AIP Handbook of Condenser Microphones:

Theory, Calibration, and Measurements, G. S. K. Wong and T. F.

W. Embleton (eds.), American Institute of Physics Press, New

York (1995) pp. 8-34.

[8] G. B. Madella, Substitution Method for Calibrating a Microphone, J. Acoust. Soc. Am. 20, 550-551 (1948).

[9] E. C. Wente, A Condenser Transmitter as a Uniformly Sensitive

Instrument for the Absolute Measurement of Sound Intensity,

Phys. Rev., Series II 10, 39-63 (1917).

[10] E. C. Wente, The Sensitivity and Precision of the Electrostatic

Transmitter for Measuring Sound Intensities, Phys. Rev., Series

II 19, 498-503 (1922).

[11] Stuart Ballantine, Technique of Microphone Calibration,

J. Acoust. Soc. Am. 3, 319-360 (1932).

[12] W. R. MacLean, Absolute Measurement of Sound Without a

Primary Standard, J. Acoust. Soc. Am. 12, 140-146 (1940).

[13] A. L. DiMattia and F. M. Wiener, On the Technique of Absolute

Pressure Calibration of Condenser Microphones by the

Reciprocity Method, Harvard University Psycho-Acoustics

Laboratory Report PNR-4 (1945).

[14] Measurement Microphones—Part 1: Specifications for Laboratory Standard Microphones, IEC 61094-1 Ed. 1.0 b: 1992,

International Electrotechnical Commission, Geneva (1992).

[15] Stuart Ballantine, Reciprocity in Electromagnetic, Mechanical,

Acoustical, and Interconnected Systems, Proc. Inst. Radio Eng.

17, 929-951 (1929).

[16] T. Proctor, Gold Medal Citation to Richard K. Cook, J. Acoust.

Soc. Am. 83, (Suppl. 1), S61 (1988).

55
Absolute Determination of the Ampere

Just before the outbreak of World War II, the

International Committee on Weights and Measures

(CIPM) began to consider moving from the existing

international system of units to a so-called absolute

system, the predecessor to the SI. In their first post-war

meeting in October of 1946, the CIPM resolved to make

that change on January 1, 1948. The decision was driven

in large part by the results of a study by the National

Bureau of Standards of absolute electrical experiments

around the world (including our own), and recommendations for the ratios of the international electrical units

to their absolute counterparts. These recommendations

were based on averages of the results of determinations

made in the United States and other countries. In this

study, NBS contributed two results relevant to the

determination of the ohm ratio and one determination of

the ampere ratio. Since no absolute volt determination

had been made, the volt ratio was computed from those

of the ohm and ampere.

The paper An Absolute Determination of the Ampere,

using Helical and Spiral Coils [1] gives one of the two

NBS values that went into the 1948 redefinition of the

ampere. It describes in detail the radically modified

fixed and moving coils of the current balance; the

measurements made on the coil dimensions; computations of their fields and interactions; and the force

measurements relating current through a coil to the

values of the national reference resistors and voltage

standards of the time.

The final recommended value of the absolute ampere

was constructed as the average of the results of

three experiments, one from the National Physical

aboratory and two from NBS [1,2]. This evaluation

also stood with that of the absolute ohm to provide

the internationally accepted volt representation until

1969, when improved measurements and the use of

the Josephson effect to determine the volt unit made a

further change practical.

H. L. Curtis and R. W. Curtis published an earlier

paper, An Absolute Determination of the Ampere [3], in

1934. This measurement used a Rayleigh current

balance, in which the electromagnetic force between

concentric coils is balanced by the gravitational force on

a mass. By 1944, three absolute-ampere and three

absolute-ohm experiments had been completed at the

Bureau [4], and similarly accurate absolute determinations of the ampere and ohm were available from

Britain.

Improved absolute measurements of current were in

some ways more difficult than those of the ohm, and

they proceeded by smaller steps. Before World War II,

at about the same time that the moving-coil current

balance was being used to determine the ohm, H. L.

Curtis and R. W. Curtis had started to prepare a balance

of a special design for the absolute ampere determination. In 1958 R. L. Driscoll reported results from this

Pellat balance [5]. The mechanical measurement was of

the torque on a small coil, with axis at right angle to the

magnetic field of a large horizontal solenoid. When the

current passing through the small coil was reversed, it

produced a force that could be balanced by a mass of

about 1.48 g placed on the balance arm. The large

stationary coil was wound on a fused-silica form, and

the balance beam was equipped with knife-edges and

supports machined from natural agate. The effect of the

measured dimensions of the small coil on the computed

mutual inductance was the largest contribution to

the uncertainty, which totaled about 8 A/A. Also

contributing to the uncertainty were the determination

of the balancing mass and the of the acceleration due to

gravity.

As soon as possible after completing the Pellat

balance measurement, Driscoll and Cutkosky [6]

repeated the 1934 Rayleigh current-balance determination of the ampere using the original apparatus.

The results of these two experiments, 1 NBS

ampere = (1.000 0130.000 008) absolute amperes by

the Pellat method, and 1 NBS ampere =

(1.000 0080.000 006) absolute amperes by the current balance, were in good agreement. This gave an

overall relative uncertainty in the ampere at NBS of

about 5 A/A at that time (1958) and verified that the

ratio of emf to resistance of the maintained standards

had been constant to within about one part in 105 since

1942.

Absolute experimental determinations of units are

now known as SI realizations, and the uncertainty of the

SI values of the electrical units are limited by the

uncertainty of their realizations in terms of the

kilogram, meter, and second. Results from the calculable capacitor experiment and other determinations of

the fine-structure constant recently have been combined

analytically [7] to yield a value of the von Klitzing

constant RK with a relative standard uncertainty of

410–9

. The Josephson constant KJ is based both on its

direct measurement by voltage balances and by

56
combining RK with a value of the Planck constant, the

latter obtained by realizing the watt in a special way.

This realization of the SI watt is achieved by the

moving-coil watt balance, which is a modern version of

the absolute ampere experiment.

The NIST watt balance has been designed to measure

the ratio of mechanical to electrical power, linking the

artifact kilogram, the meter, and the second to the

practical realizations of the ohm and the volt derived

from the quantum Hall effect (QHE) and the Josephson

effect, respectively. The first results from the NIST watt

experiment, sometimes called an ampere experiment,

were published in 1989 [8], giving a relative standard

uncertainty for KJ of 6.710–7

. That experiment was a

prototype for the next version in which the magnetic

field was increased a factor of 50 using a superconducting magnet, resulting in similar increases in the force

and voltage. During the next decade many improvements were made [9,10]. In 1998 the latest results were

published [11] by E. R. Williams, R. L. Steiner, D. B.

Newell, and P. T. Olsen. That work, which used a NIST

calculable capacitor measurement of RK, reports that

KJ = 483 597.892 GHz/V with a relative standard

uncertainty of 4.410–8

. This is the most accurate

measurement of the Josephson constant to date.

The experiment is automated and runs nightly and

over holidays to reduce vibrations. Recent measurements

recorded 989 values of the SI watt over a 4-month

period. The total uncertainty is dominated by Type B

uncertainty components, that is, components that have

to be evaluated by means other than statistical analysis

of repeated measurements. Of the possible Type B error

sources that contribute to the uncertainty, the three

largest components arise from the following: (1) the

index of refraction of air; (2) the present alignment

procedures; and (3) residual knife-edge hysteresis

effects during force measurements. Using the data

discussed above, Williams et al. [11] obtained a relative

standard uncertainty of 0.087 W/W.

By connecting the macroscopic unit of mass (the

kilogram) to quantum standards based on the Josephson

and quantum Hall effects, this result provides a significant improvement in the Josephson constant as well as

many other constants. For example, recent measurements of the Plank constant h can be derived directly

from this work with a relative standard uncertainty of

8.710–8

.

The NIST watt experiment is being completely rebuilt

to reduce the uncertainty by a factor of ten, with a goal

of less than 10 nW/W relative standard uncertainty. At

that level of measurement uncertainty, the watt-balance

experiment becomes a very good means of monitoring

the mass artifact that is used in the weighings. The

present definition of the unit of mass in the SI is based

on the International Prototype of the Kilogram, which is

a cylinder of platinum-iridium housed at the BIPM in

France. The Prototype and a set of duplicate standards

of mass accumulate contaminants on their surfaces, and

must be cleaned to achieve fractional changes over the

long term of less than 10 –8 per year. Since the kilogram is the last SI base unit defined in terms of a

material artifact, a quantum standard of mass founded

on electrical measurements would complete the modern

trend of removing all artifacts from the definitions of

SI units.

The largest uncertainties in the NIST watt experiment

of the 1990s arose from operating in air, which required

that the changing air buoyancy and refractive index be

calculated from many readings of pressure, temperature, and humidity sensors. Almost every part of the

balance assembly is being rebuilt to operate inside a

specially constructed vacuum system consisting of two

chambers, schematically represented in Fig. 1. The

upper chamber houses the balance section, and a toroidshaped chamber houses the inductive coils, located 3 m

below and centered about the liquid helium cryostat

containing the superconducting magnet.

Prepared by E. R. Williams, R. E. Elmquist, N. B.

Belecki, and J. F. Mayo-Wells based on excerpts from

the paper The Ampere and Electrical Units [12],

authored by members of the Electricity Division.

Fig. 1. Schematic representation of the electronic kilogram apparatus. The vacuum chamber and support tripod are shown in cut-away

view.

57
Bibliography

[1] Roger W. Curtis, Raymond L. Driscoll, and Charles L.

Critchfield, An absolute determination of the ampere, using helical and spiral coils, J. Res. Natl. Bur. Stand. 28, 133-157

(1942).

[2] Harvey L. Curtis, Roger W. Curtis, and Charles L. Critchfield,

An absolute determination of the ampere, using improved coils,

J. Res. Natl. Bur. Stand. 22, 485-517 (1939).

[3] Harvey L. Curtis and R. W. Curtis, An absolute determination of

the ampere, Bur. Stand. J. Res. 12, 665-734 (1934).

[4] Harvey L. Curtis, Review of recent absolute determinations of

the ohm and the ampere, J. Res. Natl. Bur. Stand. 33, 235-254

(1944).

[5] R. L. Driscoll, Measurement of current with a Pellat-type electrodynamometer, J. Res. Natl. Bur. Stand. 60, 287-296 (1958).

[6] R. L. Driscoll and R. D. Cutkosky, Measurement of current with

the National Bureau of Standards current balance, J. Res. Natl.

Bur. Stand. 60, 297-305 (1958).

[7] Peter J. Mohr and Barry N. Taylor, CODATA recommended

values of the fundamental physical constants: 1998, J. Phys.

Chem. Ref. Data 28, 1713-1852 (1999); Rev. Mod. Phys. 72,

351-495 (2000).

[8] P. Thomas Olsen, Randolph E. Elmquist, William D. Phillips,

Edwin R. Williams, George R. Jones, Jr., and Vincent E. Bower,

A measurement of the NBS electrical watt in SI units, IEEE

Trans. Instrum. Meas. 38, 238-244 (1989).

[9] Aaron D. Gillespie, Ken-ichi Fujii, David B. Newell, Paul

T. Olsen, A. Picard, Richard L. Steiner, Gerard N. Stenbakken,

and Edwin R. Williams, Alignment uncertainties of the NIST

watt experiment, IEEE Trans. Instrum. Meas. 46, 605-608

(1997).

[10] Richard L. Steiner, David B. Newell, and Edwin R. Williams, A

result from the NIST watt balance and an analysis of uncertainties, IEEE Trans. Instrum. Meas. 48, 205-208 (1999).

[11] Edwin R. Williams, Richard L. Steiner, David B. Newell, and

Paul. T. Olsen, Accurate measurement of the Planck constant,

Phys. Rev. Lett. 81, 2404-2407 (1998).

[12] R. E. Elmquist, M. E. Cage, Y-H. Tang, A-M. Jeffery, J. R.

Kinard, R. F. Dziuba, N. M. Oldham, and E. R. Williams, The

Ampere and Electrical Units, J. Res. Natl. Inst. Stand. Technol.,

January-February (2001).

58
Radio Proximity Fuzes

Residents of the United States born much after 1930

can have little appreciation for what it was like to mobilize for total war. In World War II, everyone and every

facet of daily life was affected. All citizens had to learn

to live with food and fuel rationing, and no new cars or

other consumer products made from steel could be

purchased. There were blackouts, air raid drills, scrap

drives, school children buying War Bonds (a 10 cent

stamp at a time), and, of course, able-bodied men and

women taken either into military service or placed in

critical jobs in industry and elsewhere. Institutions such

as the National Bureau of Standards were likewise

totally involved in the war effort. The Bureau found

itself with a number of very important technical assignments and, for a change, the resources to carry them out

In October 1939, after Albert Einstein and Leo Szilard

urged the President to launch a major research program

on the possibility of producing nuclear fission and

utilizing it in the likely war effort ahead, NBS Director

Lyman Briggs was placed in charge of a new Advisory

Committee on Uranium to look into this proposal.

By 1941 some 90 % of the NBS staff was doing war

work.

The Bureau worked on a great diversity of war

projects ranging from high technology to evaluating materials for blackout curtains and blackout masks. A major effort carried out with the Navy and the Radiation

Laboratory at MIT was the development and fielding of

the Bat, the first combat success with a fully automatic

guided missile (really a bomb with wings and a tail

looking rather like a modern Unmanned Aerial Vehicle

or UAV). The story of the Bat has significant technology

in common with the proximity fuze program; namely,

the use of electromagnetic radiation sources on flying

ordnance and the interpretation and use of the reflected

waves to carry out the mission.

Fig. 1. Sectionalized drawing of T-50 type bomb fuze. The same general arrangements of parts was used for all ring-type bomb fuzes (from [1]).

59
This is the atmosphere in which the Bureau undertook the work on proximity fuzes, work that had a

profound impact on NBS for many years thereafter as

well as providing the military with breakthrough applications of technology. Bureau staff at the end of World

War II prepared the book titled Radio Proximity Fuzes

for Fin-Stabilized Missiles [1]. It summarized all the

work done from about 1940 through 1945. It is a monograph; that is, a stand-alone comprehensive presentation

of the entire program. Allen Astin, then assistant chief of

the Ordnance Development Division of the Bureau,

edited the work. (Harry Diamond was chief; W. S.

Hinman, Jr. was chief engineer.) The work was published under the auspices of the National Defense

Research Committee (NDRC) and the Office of

Scientific Research and Development (OSRD) and

classified at the Secret level. It was declassified in 1960.

The volume under discussion is one of three covering the

work done by Division 4 of NDRC titled Ordnance

Accessories. It should be pointed out that parts of the

program were ably carried out by contracts with companies and universities, a mode of operation learned well

in the war and likely very comfortable for the Bureau

staff, given their history of collaborations with the

private sector. It has been asserted that the radio proximity fuze effort consumed “about 25 % of the electronics

manufacturing capacity and 75 % of the plastics molding capability” of the Nation during the war [2]. Authorship of the various chapters is by Bureau staffers who

spent the war in the Ordnance Development Division

and its subsequent subdivisions. Authors included such

well-known names as Robert D. Huntoon, Chester Page,

and Jacob Rabinow; Rabinow’s wife, Gladys, is listed as

a contributor to one chapter.

The problem assigned to the Bureau was to conceive

and realize a fuze system for non-rotating, fin-stabilized

munitions (ordnance) such that detonation could be

obtained at a specified distance from the target. Such

performance is desirable for two reasons: first it is often

difficult to produce a direct hit, and it is acceptable to

achieve detonation close to the target. A good example

is trying to hit an airplane or a rocket. A direct hit was

well beyond the technology available in the 1940s

and remains a challenge today for the anti-ballistic

missile program. Secondly, more damage can often be

obtained by detonation at some distance removed from

the target. Air bursts over ground targets are effective

over wider areas than explosions on the surface, where

much of the energy goes to producing a crater. Air

bursts are particularly effective against dug-in ground

troops and against stored materiel. The ordnance

addressed at NBS were rockets, bombs, and mortar

shells. Both the Army and the Navy provided performance specifications for such fuzes and the program

came to the Bureau for execution. The specifications varied for the several applications, and the program

was directed to make as much as possible common

to all.

The first job was to select the basic concept.

Although some thought was given to acoustic,

photoelectric, and passive radio systems, an active

radio scheme was adopted early on. As a result of the

Bureau’s great successes with radio earlier and with

radiosondes more recently, the choice of the radio

scheme led directly to a major technical strength of

NBS. Management could and did assemble a powerful

team, largely from within but augmented by cooperation

with the Navy and, at times, with our Allies in England.

Radio waves could be employed by using time-of-flight

measurements on the path from and reflected back to

the ordnance in flight or by using the Doppler shift of

the reflected radiation. The reflected waves are shifted

to a somewhat higher frequency as the missile flies

toward the target. Using the transmitting antenna as the

receiving antenna, this reflected wave sets up a beat

frequency in the oscillator circuit. Transmitting at

75 MHz to 110 MHz produced a beat frequency of a

few hundred hertz, the exact value depending on the

relative velocity of missile and target and the transmitting frequency. These details were considerably different for rockets, bombs, and mortar shells. Nonetheless

the concept worked in all cases.

It turns out that this situation is equivalent to a timevarying impedance at the antenna terminals. The

amplitude of this signal increases with the strength of

the reflection; i.e., with decreasing distance to the

target. By using the impedance, it is shown that the

sensitivity to reflection is independent of power level

over a wide range, thereby enabling application to many

different systems. A variety of interferences are treated

in detail in Chapter 2 of the book, including different

antenna designs, ground effects, target geometry,

and the like.

The differential signal from the antenna circuit was

fed to an amplifier and, depending on the design,

through a rectifying diode and thence to the grid of a

thyratron. When this signal reached a set magnitude, the

thyratron discharged into a detonator circuit and the

fuze mission was complete. Details of the control circuit

are in Chapter 3. The concept was first demonstrated in

February 1941. What lay ahead was a long, painstaking

series of engineering projects to put together a series of

fuzes that not only detonated the munitions successfully,

but also met the armed services requirements for safety,

reliability, ease of manufacture, and shelf life. In

addition, for most of the fuzes there was an additional

requirement that they had to fit into existing fuze wells

on existing ordnance. These practical considerations

60
were non-trivial and required considerable ingenuity.

Few of the available electronic components were

suitable. Industry was pressed into service to design and

prove out new triodes, diodes, pentodes, thyratrons, and

a variety of power supplies—an assignment carried out

in a timely fashion. The mechanical systems such as

safety designs and arming schemes, as well as alternate

detonation systems for situations where the proximity

fuze did not work for whatever reason, were described

in Chapter 4.

Chapter 3 also addresses the question of providing

electrical power to the circuits, both by batteries and

by mechanical generators. The batteries were either

ordinary dry cells or “reserve” types that were activated

by the forces of launch wherein an ampoule containing

the electrolyte was broken and the electrodes and

electrolyte brought together. The “reserve” concept was

demonstrated but not fielded; the idea would come to be

used often years later when the technique had been

perfected. Dry batteries were used in the early fuzes but

suffered shelf life problems. Much effort was directed

to the notion of a wind-driven turbine connected to a

generator. This had safety advantages—no possibility

of electric currents prior to flight—was fairly simple in

design and manufacture, and proved to be the method of

choice.

The remainder of the volume contains a catalog of

fuze types, details of laboratory testing, details of field

testing, a resume of actual performance at the latter

stages of the war, and a formal analysis thereof. It is

interesting to note the thoroughness of field testing as

exemplified by the number of units tested: for bombs—

15,000 dropped at Aberdeen Proving Ground in Maryland; for rockets fired from the ground—nearly 24,000

fired at Ft. Fisher in North Carolina and Blossom Point,

Maryland (plus a few at Aberdeen); and some 3000

mortar shells fired at Blossom Point and the field station

of the University of Iowa at Clinton, Iowa. Chapter 9

contains an analysis of performance. At the end of this

chapter is a summary of conclusions by the armed

services concerning results in combat.

Curiously, the driving force behind the work, Harry

Diamond, seems not to have written any of the report.

Nonetheless, he was the dominant figure throughout the

war and established an atmosphere that made the great

success possible. Diamond was a dynamo himself but

evidently a very remarkable man to work for. He

believed in delegation and a minimum of formality.

Here is a quote from an appreciation written after his

death [2]:

“It was a madhouse. I didn’t have a vacation during

the entire war. Nobody knew who was in charge

and nobody cared . . . they describe those days

with tangible affection, even as ‘great fun’. . . . If

someone needed help, they got help. If someone

needed equipment, they got it. No questions

asked. . . . ”

The armed services’ comments are of special interest

since they ensured the future post-war work at the NBS

laboratories. Fuzes for rockets and bombs went into

mass production and were used extensively toward the

end of the war. Mortar shell fuzes did not go into full

production. The conclusions from the services began

with the following statement:

“The general attitude of the using arms to the bomb

and rocket VT [proximity] fuzes at the end of

World War II was most favorable. Originally there

was much doubt as to their possible value as a

lethal weapon. The general attitude was that the

fuzes had very limited use, that they were unsafe,

and that a high percentage of them malfunctioned.

Combat experience in the various theaters changed

this view, and with the close of World War II the

using arms were very enthusiastic over the fuzes.”

Vannevar Bush is said to have considered the radio

proximity fuze the preeminent scientific and technical

advance of the war. Considering the Manhattan Project

and radar, this is a startling statement. Another historian

ranked the fuze as follows “Considering the magnitude

and complexity of the effort [it ranks] among the three

or four most extraordinary scientific achievements of the

war.” General George Patton said, after the fuze had

performed notably at the Battle of the Bulge, “The new

shell with the funny fuze is devastating...I think that

when all armies get this shell we will have to devise

some new method of warfare.” [2].

Allen Astin, in his closing comment, stated that, as of

1946, the Army Ordnance Department had already

formulated a further program and that the Ordnance

Development Division at NBS was working for the

Army on new fuze challenges.

It turned out that the NBS effort on fuzes continued

in a very strong manner in the post war years and that

military work came to dominate the work of the Bureau.

The basic concept of using the Doppler shift in

frequency of the reflected radiation and beating it

against the transmitter’s oscillator frequency continued

61
to be used in these fuzes after the war. Ultimately the

fuze systems became “first class radars” [3]. Technical

work focused, inter alia, on security from jamming and

thus involved various ways of disguising the signal.

The reserve battery power supply was perfected and

thermally-activated batteries became the method of

choice. A quick perusal of the table of contents of an

Army ordnance manual from 1963 shows major emphasis on continuous wave and pulsed Doppler fuzes. Eventually, of course, miniaturization through solid state and

integrated circuits became possible. Technical director

Horton marveled that the early fuzes using electron

tubes were able to survive the stresses of launch.

The Kelly Committee, an ad hoc group, was formed

by the NBS Visiting Committee and the National

Academy of Sciences at the request of Commerce

Secretary Sinclair Weeks after the uproar created by the

AD-X2 battery additive controversy. The Committee

report of 1953 recommended that the Bureau get back

to its congressional charter and separate the bulk of its

military work. Cochrane [4] says that 2000 staff were

transferred to other agencies, some 1600 of these in

three divisions that worked on fuzes. Those three

divisions had earlier been placed in the Harry Diamond

Ordnance Laboratory within NBS, the unit named in

honor of the memory of Harry Diamond, who died at

the early age of 48 years in 1948. The Army added the

word “Fuze” (and dropped the “Harry”) to the title on

receipt of the unit—thus, the Diamond Ordnance

Fuze Laboratory, or DOFL. The remainder of the

affected staff worked on guided missiles at a location in

California and were shifted to the Navy. The DOFL

remained at the Connecticut and Van Ness site until a

new laboratory site could be completed in White Oak/

Adelphi, Maryland. The move was carried out in 1973.

This is just one of many examples of significant

technical entities created out of the NBS over the years.

The DOFL had a distinguished history in the Army.

It continued to work on fuzes although eventually

turning over most of the work to various product

development and engineering centers, such as Picatinny

Arsenal and the Redstone Arsenal. The laboratory at

Adelphi developed major research programs in highpower microwaves, electronics, nuclear simulation,

radar, sensors, and signal processing—a broad, multiprogram laboratory. In 1992 it became one of the major

components of the new Army Research Laboratory and

the Adelphi site served as the new entity’s headquarters.

The central building in the complex carries prominently

on its fac ̧ade the name “Harry Diamond Building.”

Inside are portraits of Diamond and Hinman and

displays of the early fuze artifacts and documents. In a

curious coincidence John Lyons, ninth director of NBS/

NIST, became, in 1993, the first director of the new

Army Research Laboratory and made his offices in the

Harry Diamond Building. In a sense he felt he had

simply moved to one of the Bureau’s more significant

descendants. He served ARL as its director through

1998, when he retired.

Allen Astin went on to become the fifth director of

NBS and served the second longest tour of any director from 1952 to1969. Diamond died shortly after the

war; his close associate, W.S. Hinman, Jr., succeeded

Diamond as head of the program and became the first

technical director of the DOFL after it moved to the

Army. After staying with the DOFL for a few years,

Hinman moved on to become the Deputy Assistant

Secretary of the Army (Research & Development).

Robert Huntoon served as a senior manager at NBS

heading atomic and radiation physics. He later became

Associate Director of NBS for Physics and, still later,

Deputy Director as well. J. Rabinow had a distinguished career as an inventor and innovator, left NBS to

form a company which he later sold to Control Data.

He returned to NBS and served in various senior capacities and was at work at least part-time until his death in

1999 at the age of 89. Chester Page went on to head the

Electricity Division for many years and made many

contributions, not least of which were his efforts in

developing the concepts that became the international

system of units of measurement (SI).

Prepared by John W. Lyons with assistance from E. A.

Brown and B. Fonoroff (ret.) of the Army Research

Laboratory.

Bibliography

[1] Allen V. Astin (ed.), Radio Proximity Fuzes for Fin-Stabilized

Missiles, Vol. 1 of Summary Technical Report of Division 4,

NDRC, Vol. 1, National Defense Research Committee,

Washington, DC (1946).

[2] N. R. Kellog, I’m Only Mr. Diamond, biographical essay, U.S.

Army Laboratory Command, Army Materiel Command, Adelphi,

Maryland (1990).

[3] Private conversation in February 2000 with Billy Horton, retired

technical director at the Army’s Adelphi, Maryland laboratories.

[4] Rexmond C. Cochrane, Measures for Progress. A History of the

National Bureau of Standards, NBS Miscellaneous Publication

275, U.S. Government Printing Office, Washington, DC (1966) p.

497.

62
Stability of Double-Walled Manganin Resistors

The resistance standard described by James L.

Thomas [1] was the result of his extensive effort to

develop a new standard by systematically investigating

every factor affecting the stability of resistance—

time, surface effects, temperature, power, pressure—

detectable at the time. The result was a unique standard

which was used as part of the National Reference Group

of resistors beginning in 1931. Ten of them served solely

as the U.S. standard of resistance from 1939 until they

were supplanted by the quantized Hall effect (QHE) in

1990. They still serve as working standards at the one

ohm level and as a vital check on the QHE standard and

the scaling used in the NIST resistance calibration

service. The International Bureau of Weights and

Measures used this standard to maintain the international unit of resistance, and numerous other national

standardizing laboratories around the world used it

as their primary standard. This is still largely true for

laboratories without QHE standards.

In the period from 1935 to 1980, Thomas’s standard

provided a basis for evaluating the accuracy of ohm

determinations, particularly to compare realizations

based on calculable inductors with those based on

Thompson-Lampard calculable capacitors. Thomas’s

standard was commercialized by the Leeds and

Northrup Company and Honeywell, and these commercial versions are still used as primary resistance

standards by many industrial and commercial standards

laboratories, as well as the DOD primary and secondary

metrology laboratories. NIST still routinely calibrates

about 125 of them annually for domestic users.

Thomas’s standard remains the most stable resistor of

any available, although two more modern designs are

nearly a match in predictability.

Much of the research leading to this standard resistor

design is described in an earlier paper by Thomas

[2]. However, the paper Stability of Double-walled

Manganin Resistors [1] is the more popularly known and

describes the standard in its final form, after some major

modifications in size and connections.

In the 1920s, Thomas had taken up the task of improving the long-term stability of wire-wound resistors,

which were used to measure the current in absolute

determinations. When a resistor is made by winding

wire on a spool, parts of the crystalline structure of the

wire are stressed past their elastic limit. Thomas developed wire-wound standard resistors that were annealed

at high temperature, which released some of the internal

strains and reduced the rate of change of resistance with

time. Heat-treated manganin wire resistors developed by

Thomas incorporated hermetically-sealed, doublewalled enclosures, with the resistance element in

thermal contact with the inner wall of the container to

improve heat dissipation. These 1  Thomas-type

standards (see Fig. 1) proved to be quite stable with time

[1,2], and quickly came into favor as the primary reference for maintaining the resistance unit at NBS and at

many other national metrology institutes.

Work continued on improving the absolute measurements of electrical units and, in 1949, J. L. Thomas, C.

L. Peterson, I. L. Cooter, and F. R. Kotter published a

new measurement of the absolute ohm [3] using an

inductor housed in a non-magnetic environment. Using

the Wenner method of measuring a resistance in terms

of a mutual inductance and a rate of rotation, their work

gave a value of 0.999 994 absolute ohm for the new

as-maintained unit of resistance at NBS. The mean value

assigned to 10 Thomas-type standard resistors from this

experiment was found to have been the same between

1938 and 1948 to within 1 /. As Thomas et al.

wrote in the 1949 paper, this was “the first satisfactory

method that has been devised for checking the stability

of the unit as maintained by a group of wire-wound

resistors.”

From 1901 to 1990, the U.S. Legal Ohm was

maintained at 1  by selected groups of manganin

resistance standards. Four different types of resistance

standards have been represented in these groups, whose

numbers have varied from 5 to 17 resistors. From 1901

to 1909, the group comprised Reichsanstalt-type

resistance standards made by the Otto Wolff firm in

Berlin. These standards were not hermetically sealed

and consequently underwent changes in resistance as a

function of atmospheric humidity. In 1907 Rosa at NBS

solved the problem by developing a standard whose

resistance element is sealed in a can filled with mineral

oil [4]. The U.S. representation of the ohm was maintained by 10 Rosa-type 1  resistance standards from

1909 to 1930. Over the years, measurements of differences between the individual Rosa-type resistors

indicated that the group mean was probably not constant. In 1930, Thomas reported on the development of

his new design for a resistance standard having improved

stability [2]. The Thomas resistance standards were

more stable immediately following construction than

the Rosa-type resistors and two were added to the

63
primary group in 1930. Eventually, in 1932, the Rosatype resistors in the primary group were replaced by the

Thomas resistors. To reduce loading errors, Thomas in

1933 improved the design of his resistor by using

manganin wire of larger diameter mounted on a larger

diameter cylinder to increase the dissipation surface

area, as described in his paper [1]. A select group of the

new-design Thomas resistors was used to maintain the

U.S. Legal Ohm from 1939 until its re-definition in

1990 based on the quantum Hall effect.

The value of the U.S. representation of the ohm, or

“Legal Ohm” maintained at NIST has been adjusted

only twice. This occurred first in 1948 when the ohm

was reassigned using a conversion factor relating the

international reproducible system of units [3] to the

precursor of the International System of Units (SI)

derived from the fundamental units of length, mass, and

time. The second occasion was in 1990 when the ohm

became based on the quantum Hall effect. After 1960,

ohm determinations were made using calculable capacitors based on the Thompson-Lampard theorem and a

sequence of ac and dc bridges. Then came the discovery

of the QHE in 1980, which has provided an invariable

standard of resistance based on fundamental constants.

Consequently, on January 1, 1990 the U.S. Legal Ohm

was re-defined in terms of the QHE, with the internationally-accepted value of the quantum Hall resistance

(or von Klitzing constant, after the effect’s discoverer)

based on calculable capacitor experiments and other

fundamental constant determinations. At that time, the

value of the U.S. Legal Ohm was increased by the

fractional amount 1.6910–6 to be consistent with the

conventional value of the von Klitzing constant [5].

Shortly after the discovery of the QHE, NBS

developed a system based on the QHE to monitor

the U.S. Legal Ohm, then maintained by five Thomastype resistance standards, with a relative uncertainty

of a few times 10–8 [6]. This system consisted of a

constant current source, a potentiometer, and an

electronic detector. The current source energized

the QHE device and a series-connected reference

resistor of nominal value equal to the Quantum

Hall Resistance (QHR). With the potentiometer

balancing out the nominal voltage across either

resistance, the detector measured the small voltage

difference between the QHE device and reference

resistor. Scaling down to the 1  level was accomplished using specially-constructed Hamon transfer

standards.

Since January 1, 1990, the maintenance of the

U.S. Legal Ohm has been based officially on the QHE.

However, the complexity of the experiment and “oddvalue” resistance of the QHR does not make it practical

for the routine support of resistance measurements

where comparisons are normally made on standard

resistors of nominal decade values. Therefore, banks of

1 , 100 , and 10 k standard resistors maintain the

ohm between QHR measurements.

Today NIST provides a calibration service for standard resistors of nominal decade values from 10–4  to

1014 . To achieve low uncertainties, eight measurement

systems have been developed that are optimized for the

various resistance levels [7]. Over the years from 1982 to

1997, six of the systems, covering the full 19 decades of

resistance, have been automated. The main methods of

comparing standard resistors for NIST calibrations

Fig. 1. A double-walled 1  standard resistor of the Thomas type.

64
utilize direct current comparator (DCC) bridges and

resistance-ratio bridges.

An unknown standard resistor is indirectly compared

to a reference bank of the same nominal value using the

substitution technique, where the unknown and reference resistors are sequentially substituted in the same

position of a bridge circuit. A robotic switching device

is shown in Fig. 2. This technique tends to cancel errors

caused by ratio non-linearity, leakage currents, and lead

and contact resistances. To verify that the values of the

reference banks are consistent with the QHR, scaling

Bibliography

[1] James L. Thomas, Stability of Double-walled Manganin Resistors, J. Res. Natl. Bur. Stand. 36, 107-110 (1946).

[2] James L. Thomas, A new design of precision resistance standard,

Bur. Stand. J. Res. 5, 295-304 (1930).

[3] James L. Thomas, Chester Peterson, Irvin L. Cooter, and F. Ralph

Kotter, An absolute measurement of resistance by the Wenner

method, J. Res. Natl. Bur. Stand. 43, 291-353 (1949).

[4] Edward B. Rosa, A new form of standard resistance, Bull. Bur.

Stand. 5, 413-434 (1909).

[5] Norman B. Belecki, Ronald F. Dziuba, Bruce F. Field, and Barry

N. Taylor, Guidelines for Implementing the New Representations

of the Volt and Ohm Effective January 1, 1990, NIST Technical

measurements are completed periodically proceeding

from the 1 , 100  or 10 k banks, whose values are

based on recent QHR determinations, to the other reference banks. The up or down scaling is done in steps of

10 or 100 using either a CCC bridge, Hamon transfer

standards, or DCC bridge.

Prepared by R. Dziuba, N. B. Belecki, and J. F. MayoWells based on excerpts from the paper The Ampere and

Electrical Units [8], authored by members of the Electricity Division.

Note 1263, National Institute of Standards and Technology,

Gaithersburg, MD (1989).

[6] Marvin E. Cage, Ronald F. Dziuba, and Bruce F. Field, A test of

the quantum Hall effect as a resistance standard, IEEE Trans.

Instrum. Meas. IM-34, 301-303 (1985).

[7] Ronald F. Dziuba, Paul A. Boynton, Randolph E. Elmquist, Dean

G. Jarrett, Theodore M. Moore, and Jack D. Neal, NIST Measurement Service for DC Standard Resistors, NIST Technical Note

1298, National Institute of Standards and Technology, Gaithersburg, MD (1992).

[8] R. E. Elmquist, M. E. Cage, Y-H. Tang, A-M. Jeffery, J. R.

Kinard, R. F. Dziuba, N. M. Oldham, and E. R. Williams, The

Ampere and Electrical Units, J. Res. Natl. Inst. Stand. Technol.,

January-February (2001).

Fig. 2. Photograph of a programmable guarded switching system used in calibrating

customers’ resistors. The robotic translation stage moves in three axes to accomplish its

switching function and has whimsically been named “jake.”

65
Manufacture of Paper for War Maps and

Other Applications

The manufacture of robust paper for maps assumed

great importance early in World War II. Up to that time,

maps used by troops in combat tended to disintegrate

rapidly after being subjected to the water, mud, and

grime of the battlefield. On the basis of information

developed by the NBS Paper Section, the Army Map

Service of the Corps of Engineers formulated specifications for paper for the printing of maps. The most

critical requirements were very high resistance to tear,

high wet tensile strength, high dry tensile strength, high

opacity, and superior smoothness. Additionally, the

paper needed to be made from commercially available

raw materials to meet unprecedented tonnage requirements. The article Experimental Manufacture of Paper

for War Maps [1] documents the contributions of NBS

to this endeavor.

In the NBS Paper Section, this project was spearheaded by Charles G. Weber and Merle B. Shaw. They

attacked the problem by preparing many batches of

paper under a variety of experimental conditions on a

“Fourdrinier” semi-commercial paper-making machine.

This machine, invented by Nicholas Robert in France

and named after the Fourdrinier brothers in England

who commercialized it in 1804, is basically an endless

wire screen belt which runs continuously; a paper pulp

suspension flows onto the screen at one end and is

removed at the opposite end after most of the water has

been removed. The partially dried suspension is transferred onto a felt and transported over drying cylinders.

A simple Fourdrinier travels at a speed of less than one

mile per hour, but a modern, highly automated machine

can travel 30 times as fast.

One of the variables tested by NBS was the relative

amount of cutting and fraying, which affect fiber

strength. These variables are a function of “beating,” a

process in which an aqueous suspension of paper pulp is

passed continuously between a revolving roll and a

bedplate. Knives are installed on the roll and initially

separated from the bedplate by about 2.5 mm. Operating the beater with a wide bedplate-to-roll separation

frays the fibers, with little cutting, and generates a large

surface area. Operation with the roll close to the

bedplate produces more cutting and less fraying.

In the early 1940s, it was common practice to permit

extensive fraying of fibers as this produced a large

surface area for fiber-to-fiber bonding and thus a very

strong paper. When a papermaker held the paper up to

the light, his product looked very uniform, and this had

become a simple test for paper quality. However,

because of extensive fiber-to-fiber bonding, this paper

had a high coefficient of hygroscopic expansion, an

undesirable property for military maps. Shaw and

Weber found that the recently developed melamine resin

could be used as a bonding agent to increase wet

strength, and that the resin could take the place of

beating to increase dry strength. The reduced need for

beating diminished the interfiber bonding and consequently the hygroscopic expansivity of the sheet. At

first, paper makers objected to the disordered or “wild”

appearance when the paper was viewed by transmitted

light, as described above. Once it was recognized that

the disordered appearance was not a criterion for the

quality of map paper, this test was discarded.

With the assistance of NBS . . . production (of paper for war maps) exceeding

5000 tons per month was achieved

within 6 months. This was a substantial

contribution to the war effort.

Ultimately, numerous runs on the Fourdrinier showed

that the best paper was obtained by using 100 % strong

bleached sulfate pulps with the addition of melamineformaldehyde resin to increase wet strength, and

titanium dioxide to produce the desired opacity [1]. The

large scale of the Fourdrinier in the Paper Section

facilitated the transfer of this technology to factory

production. With the assistance of NBS, many paper

mills were able to meet or exceed the specification

prepared by the Army Map Service. Production exceeding 5000 tons per month was achieved within 6 months.

This was a substantial contribution to the war effort.

Further studies on paper for defense needs continued

after World War II. About 1952 the Naval Research

Laboratory and the NBS Paper Section cooperated in

the development of the first machine-made paper made

from glass fiber, without binder or additives [2]. The

paper, which resembles soft blotting paper, was found to

have numerous important applications, both in defense

66
and civilian life. It was many times more effective as an

air filter than commercial filters then on the market. It

was found to be a very effective smoke filter in gas

masks. All-glass paper is resistant to heat, moisture,

chemicals, and microorganisms, and it has excellent

electrical properties. It was used in diverse applications,

such as mine respirators, gas masks, and filter discs for

laboratory crucibles.

The first all-glass paper had a low tensile strength,

and thus required extra care in production, storage, and

handling. A 1955 study showed that the best bonding

was obtained if the beater was maintained at 85 F and

a pH within the range 3.0 to 4.0. Under these conditions

the fibers were well dispersed, resulting in a uniform

sheet of paper. The secret of the interfiber bonding and

the strength of fiberglass paper lies in the reaction of the

glass fiber with acid [3]. Most acids react so slowly with

glass under normal conditions that there is negligible

effect. However, very fine glass fibers expose a very

large surface area to the acid, which starts to dissolve

the soda and the lime in the glass, leaving on its surface

a thin gelatinous layer, rich in silica. When the fibers are

pressed together in the papermaking process, this gelatinous layer acts as an adhesive to bond the fibers.

Although the pH must be below 4.0 to obtain this effect,

the pH of the paper becomes neutral after the acid

solution drains from the paper.

Research on paper for currency has been another

important NBS contribution. The first work at NBS on

currency paper, supported by the Bureau of Engraving

and Printing, was initiated in 1924 and conducted by

Merle B. Shaw and George W. Bicking [4]. Paper

currency had to be redeemed after a few months of

circulation, and at that time the cost was substantial.

Shaw and Bicking developed a paper that was about

twice as strong as the paper then used for printing

currency. The wear-resistant quality of paper currency

was very much increased.

Until 1957, currency had been printed on flat-bed

presses on moist paper, but this process was too slow

for the expanding currency needs. New high-speed

rotary presses were obtained, and the Paper Section

developed a new paper for use in these presses. This

new paper was 75 % cotton and 25 % linen with

melamine resin, glue, and glycerol as additives, and it

was printed dry. On Oct. 5, 1957, the first dollar notes

printed on the new paper by the new high-speed rotary

intaglio presses using the dry-print method were placed

in circulation. A statistical evaluation, made by John

Mandel of the NBS Statistical Engineering Laboratory

[5], showed the old bills had a median life of approximately 122 days, while that of the new bills was

approximately 172 days. This was indeed a substantial

improvement of an undeniably short lifetime. The

manufacture of currency paper, within the guidelines

developed by the NBS Paper Section, has saved the U.S.

Government millions of dollars.

Over the years, the Paper Section’s standards-related

work consisted of (1) the development of methods

for evaluating the chemical and physical properties of

paper, (2) the development and evaluation of testing

machines, especially for active projects, and (3)

the statistical evaluation of test procedures. Where

possible, the work was directed toward the preparation

of test methods for the Technical Association of the

Pulp and Paper Industry (TAPPI) or for the American

Society for Testing and Materials (ASTM). This effort

continued throughout the lifetime of the section,

culminating in the establishment of a Collaborative

Testing Program in 1969, mostly through the initiative of

Theodore Lashof. Paper samples were distributed to

participating laboratories, test results were obtained,

and data returned to the NBS for analysis. A report was

prepared by NBS and distributed to the participating

laboratories. Through this program, cooperating laboratories could compare their results with those of other

laboratories and, thereby, evaluate their own testing

equipment, personnel, or laboratory conditions [6].

Eventually, the great growth of this program necessitated that it be shifted to the private sector. Collaborative

Testing Services, Inc., assumed responsibility for

the program, which now includes many other materials

in addition to paper. Laboratories all over the world

participate in this activity.

The NBS Paper Section also has a long history of

contributions to the development of standards for

permanent record paper and other contributions to the

science of preservation of records. In 1929, at the

request of the American Library Association and with

the support of the Carnegie Foundation, the Paper

Section implemented a study of the whole problem

of preservation of records. The National Archives,

created in 1934, later supplied the principal support,

along with the Department of Agriculture, the

Social Security Board, and manufacturers of record

materials.

We know today that a calcium carbonate filler in

paper almost guarantees long-term stability. Although

the use of calcium carbonate filler started in 1901,

almost 40 years passed before its advantages were

recognized. In the 1930s, M. B. Shaw and M. J. O’Leary

of the Paper Mill at NBS made 72 papers on the experimental Fourdrinier in a study of sizing and filler

materials on the stability of paper. Several papers with

an alkaline filler were included in the study at the

suggestion of Edwin Sutermeister, who was on the

advisory committee for the project. This study showed

that the stability of paper was an inverse function of

67
acidity and thus depended on alum content. An alkaline

filler gave paper maximum stability [7]. Unfortunately,

conventional rosin-alum sizing was not efficient in an

alkaline medium, so the process was not favorably

received until an alkaline sizing material was developed

in the early fifties. When fiber gradually increased in

price to the point where calcium carbonate filler was

cheaper than fiber, alkaline paper gained wide acceptance. The percentage of alkaline paper on the market

has increased in the last 20 years from a few percent to

more than 80 %.

In the early 1940s the Library of Congress asked

NBS for recommendations for the display of the

Charters of Freedom—the Declaration of Independence,

the Constitution, and the Bill of Rights. Herbert F.

Launer, who had done careful studies of the effect of

light on paper [8], suggested an atmosphere of helium in

a sealed enclosure at 25 % to 35 % relative humidity,

with a light filter that cut off at a wavelength of about

450 nm. These suggestions were followed when the

documents were enclosed for display [9]. Work on the

preservation of records after 1954 was supported by the

National Archives and Records Administration. As

NARA was interested in standards, the Paper Section

worked with the ASTM to develop six standards for

papers suited to permanent record storage [10].

Thus the contributions of the NBS Paper section

spanned a wide range of military and civilian applications. In conducting this work, the group identified

significant national needs, worked with other government agencies and industry to meet those needs in a

cost-effective way, and participated in the development

of essential test methods and specifications.

Prepared by William K. Wilson.

Bibliography

[1] Charles G. Weber and Merle B. Shaw, Experimental Manufacture of Paper for War Maps, J. Res. Natl. Bur. Stand. 37, 325-330

(1946).

[2] M. J. O’Leary, B. W. Scribner, J. K. Missimer and J. J. Erving,

Manufacture of Paper from Glass Fibers, Tappi 35, 289-293

(1952).

[3] M. J. O’Leary, R. B. Hobbs, J. K. Missimer and J. J. Erving,

Effects of Mechanical Preparation and pH on the Strength of

Glass-fiber Paper, Tappi 37, 446-450 (1954).

[4] Merle B. Shaw and George W. Bicking, Research on the Production of Currency Paper in the Bureau of Standards Experimental

Paper Mill, Technol. Pap. Bur. Stand. 21, 89-108 (1926).

[5] E. B. Randall, Jr. and John Mandel, A Statistical Comparison of

the Wearing Characteristics of Two Types of Dollar Notes,

Mater. Res. Stand. 2, 17-20 (1962).

[6] T. W. Lashof, The NBS-TAPPI Collaborative Reference

Program—beginning its second decade, Tappi 63 (4), 61-63

(1980).

[7] M. B. Shaw and M. J. O’Leary, Effect of Filling and Sizing

Materials on Stability of Book Papers, J. Res. Natl. Bur. Stand.

21, 671-695 (1938).

[8] H. F. Launer and W. K. Wilson, Photochemical Stability of

Papers, J. Res. Natl. Bur. Stand. 30, 55-74 (1943).

[9] Preservation of the Declaration of Independence and the Constitution of the United States, NBS Circular 505, National Bureau

of Standards, Washington, DC (1951).

[10] Six standards for paper for permanent records, Annual Book of

ASTM Standards, No. 15.09, American Society for Testing and

Materials, West Conshohocken, PA (1999).

68
Transmission of Sound Waves in Gases at

Low Pressures

Midway through World War II it became apparent

that a better understanding of the motion and interaction

of gaseous media with solid objects was needed. As

aircraft flew at higher altitudes, approaching the speed

of sound, strange shock wave effects interrupted normal

flight. Propulsion mechanisms became challenged by

the rapid increases in frictional drag. At the same time,

the fledgling nuclear industry was trying to accelerate

ion plasmas to higher speeds and energies, where confinement and wall heating were serious issues. The

normal kinetic theory of gases was inadequate to

describe these additional complex actions originating

from the frictional and viscous forces of real compressive fluids. Two different parts of this problem

existed. They are identified as nonlinearity, which

occurs at high speeds, and nonuniformity, which is the

behavior of the mechanics of rarefied gases.

Greenspan [1] described this behavior in the following way. “Nonuniform effects in gases are best studied at

small acoustic amplitudes where relaxation effects can

be observed. From kinetic-theoretical considerations

in a gas of smooth rigid spheres, the speed of sound

depends only on the mean speed of the molecules,

provided that the gas is sufficiently dilute so that

practically all of the molecular momentum is transferred

and that the mean collision rate is very high. Laplace’s

formula states that the sound speed depends on the

molecular mass and the temperature, and these determine the molecular speed. Any dispersion must depend

on the ratio of collision rate to sound frequency. A

suitable parameter for comparison is one proportional to

this ratio (pressure/frequency). For example, a sound

wave at an audio frequency of some kHz in a gas near

atmospheric temperature and pressures will have a mean

collision rate of order of 1010 s–1

. The medium is very

fine grain and the dispersion is negligible. As the sound

frequency is steadily increased, the frequency becomes

comparable at first to the collision rate of the slower

molecules. The collision rates becomes positive correlated with the molecular speed. The slower molecules

can not transfer the acoustic momentum coherently, and

this burden shifts to the faster molecules. Accordingly,

the speed of sound steadily increases with frequency.

The effect is negligible unless the frequency is very

high.”

In 1845 Stokes had first considered the effect of

viscosity of gases on the propagation of sound. Since

then, several approximations to the Boltzmann theory

were developed to describe the action of frictional and

viscous forces that affect gas dynamics. No singular

closed solution exists that covers all cases of a rarefied

or high speed gas. Some of the best known approximations are attributed to Stokes-Navier (1st order) and

Burnett (2nd order). In the mid 1940s, experimental

confirmation for these approximations was pursued

using shock wave experiments. However, this technique

cannot separate the combined effects of two distinct

behaviors of gases, nonlinearity and nonuniformity. One

way to make this separation is to use the small displacement condition of ultrasonic wave propagation to determine the nonuniformity behavior of the gas in the

absence of any nonlinear effects.

The first endeavor that Martin Greenspan undertook

after he began research in ultrasonics in 1946 was the

investigation of the effects of gas viscosity on the

acoustic propagation constant. At the suggestion of

R. K. Cook, then Chief of the NBS Sound Section,

“Moe” began the construction of an ultrasonic interferometer and necessary related gas control equipment. The

first element of research was to measure the attenuation

of sound as a function of pressure in rarefied helium at

1 MHz. This resulted in a paper describing the attenuation [2] over a pressure range of 0.5 kPa to 4 kPa and a

comparison of the results to the Kirchhoff (StokesNavier) approximation.

This was the first of a succession of research projects;

starting with attenuation measurements for sound waves

in several rarefied monatomic gases and eventually

continuing to diatomic gases. This research program

covered a 14-year period and resulted in eight archival

publications, two of which were review treatises of great

significance [1-8].

Shortly after this first paper, Greenspan recognized

the inadequacy of the theoretical explanation for the

deviation of the gas behavior from the classic theory.

He extended this work for the propagation of sound in

diatomic gases. At the time, no theory for the behavior

of more complex gas molecules existed. Greenspan

extended the existing theory to cover both translational

and thermal relaxational dispersions of sound energy

69
[5, 7]. He adapted a Stokes-Kirchhoff (S-K) function to

represent a diatomic gas by converting the conventional

S-K function into a dimensionless equation. This equation is described by two main variables: normalized

viscosity and normalized thermal conductivity. The

equation can be solved by eliminating the normalized

thermal conductivity, but the solution is very

formidable. However, an approximate solution can be

obtained by factoring the standard S-K function into

two parts; one associated with a sound wave and the

other related to a heat wave. Under special values of ,

the ratio of specific heats, this relationship compares

very favorably to the more exact solution. For the

thermal relaxational part, Moe chose a relationship

developed by Hertzfeld and Rice. He combined the

translational and the thermal relaxation descriptions in

a manner that produced two equations, a propagational

one and an attenuative one.

After his first experimental effort, the ultrasonic

interferometer was improved in several ways. The

device was redesigned as a double crystal interferometer with constant gas volume that allowed the

interferometer to operate in a nonresonant condition.

This suppressed the transverse modes. New transducers

were selected to run at the higher frequency of 11 MHz,

improving the resolution greatly. Also, the measuring

equipment was automated to measure continuously

both the propagation constant (sound speed) and

frictional component (attenuation) [4].

With the new equipment, Greenspan revisited the

case of helium [3]. He compared the measured attenuation and speed of sound to the predictions of both the

Stokes-Navier and the Burnett theories. He demonstrated how the measured data deviated from these

theories at pressures below 0.5 kPa. Fig. 1 compares the

real part and the imaginary part  of the propagation

constant for helium with computed functions of three

approximate theories: Stokes-Navier, Burnett, and

Super Burnett (Super Burnett theory is a separate

approximation of higher order). The parameters shown

on Figure 1 are:  = /c , = amplitude attenuation,

 = 2f, c is speed of sound at the frequency f, and p is

the dynamic pressure. These variables are normalized to

0 = /c0, the low frequency value. For comparison,

Moe selected an independent variable that was proportional to the ratio pressure/frequency. This variable, r, is

the traditional Reynold’s number divided by  and

is used in place of gas pressure alone because it is a

normalizing factor.

The next project was to measure sound speed and

attenuation in four rarefied monatomic gases (neon,

argon, krypton, xenon) [5]. When compared through the

independent variable r all of the data for the individual

monatomic gases collapse onto the same functional relationship. Again, Moe demonstrated the regions of agreement between the measurements and the various theories and identified the region where the measurements

deviated significantly. The results show that

simple monatomic gases can display sound dispersion

associated with normal gas viscosity. Some representative results of these measurements on the five

monatomic gases are shown in Fig. 2, which compares

Fig. 1. Helium propagation constant as a function of r. Solid line: Stokes-Navier. Short

dashed line: Burnett. Longer dashed line: Super Burnett. Circles: measurements at

11 MHz. Squares: previous measurements at 1 MHz.

70
 and from measurements of neon and argon with

three approximate theories: Stokes-Navier, Burnett, and

Super Burnett. All five gases behave in substantially the

same way. In the nondispersive range (r > about 10) the

measured values agree with the “classic” theory [3,6].

This work was extended to the measurement of

viscosity effects for the diatomic gases nitrogen and

oxygen and to dry air. Moe compared his theoretical

predictions [5] to the attenuation and propagation

constant of the diatomic gases as measured. The behavior at higher pressures follows the classic theory. As the

mean free path approaches the ultrasonic wave length,

Greenspan’s constructed theory fitted at the intermediate pressures. For lower pressures significant deviations

were found [7]

His work on propagation of sound in rarefied gases is

a classic example of how to examine a complex system

for relaxations resulting in a measured dispersion. He

was able to show that the Stokes-Navier equation gave a

surprisingly good quantitative account of attenuation

and dispersion of sound in monatomic gases down to

wavelengths approaching the mean free path. Moreover,

he succeeded in making measurements to much lower

pressures where the mean free path was significantly

greater than the wavelength, and found substantial

deviations from the theories. New theoretical manybody results are now judged by their agreement with

these data. For diatomic and polyatomic gases, where

molecular relaxation processes associated with vibrational and rotational modes occur in addition to the

translation relaxation, he was able to demonstrate

experimentally and theoretically how they combine to

affect acoustic dispersion and attenuation.

In summary, Greenspan’s work made a major contribution to the fields of acoustics and thermodynamics by

allowing the effects of nonuniformity in a rarefied gas

to be separated from those of nonlinear behavior.

He provided the first experimental data on elastic and

viscous behavior of a number of rarefied monatomic and

diatomic gases. His papers on this subject received more

than 250 citations, and his chapter in the prestigious

Physical Acoustics series is still widely read.

Martin (Moe) Greenspan was born in New York City

on May 8, 1912. He attended Cooper Union Institute of

Technology and received a B. S. degree in 1934. He

came to the National Bureau of Standards in 1935 and

was employed until his retirement in 1975. As a guest

scientist, he continued to contribute to NIST actively

until his death in 1987. He was a very productive,

prolific, and innovative researcher, not only in the area

described here, but in several other fields. From 1935

until 1945 he worked in engineering mechanics,

performing theoretical calculations on complex structures such as rigid knee bends, box girders, and

perforated plates. Such calculations were coordinated

with experimental tests producing a higher assurance of

confidence in the safety of these structures. Moe’s work

on stress distribution in perforated plates, for which he

received a Department of Commerce Silver Medal, was

an important contribution to modern elastic fracture

mechanics. During this period he authored at least

15 archival articles on theoretical engineering.

Fig. 2. Neon and argon at 11 MHz. Propagation constant as a function of r. Solid line:

Stokes-Navier. Short dashed line: Burnett. Longer dashed line: Super Burnett. Circles:

measurements in Ne. Squares: measurements in Ar.

71
In August 1946, at the invitation of its Chief, Richard

K. Cook, Moe joined the NBS Sound Section and began

his work on physical acoustics, as described above. In

the early 1950s he was approached by the Navy and

asked to help develop a means of measuring speed of

sound in the sea. Moe and Carl Tschiegg collaborated in

the development of an accurate, reliable and rugged

instrument now called an acoustic velocimeter. This

device measured the sound speed in a continuous

fashion in the deepest part of the sea. Since 1960, all

Navy submarines have been equipped with a variation of

this original device, which has also found extensive use

in the chemical industry. This work also won the

Department of Commerce Silver Medal. In the 1960s,

Greenspan and Tschiegg investigated ultrasonic cavitation in water. They directed their attention to the effects

of dissolved gases and neutron irradiation on the

threshold of cavitation, finding that both dissolved gas

and recoil atomic nuclei from neutron irradiation

weaken the water and lower the cavitation threshold.

In 1966 Moe became chief of the Sound Section and

in the 1970s turned his attention to problems in acoustic

emission. Acoustic emission (AE) is transient in character. The usual calibration procedure is inadequate for

AE transducer calibration. Moe was instrumental in

proposing the use of special transfer blocks which could

be excited by a step force function and which would

follow a simple Lamb’s solution. This was the basis of

the acoustic emission calibration facility that was developed by Frank Breckenridge and Carl Tschiegg in

collaboration with Moe. After his retirement, he examined the theoretical problem of an acoustic piston

radiator. In a 1979 paper he succeeded in extending and

improving the theory. Over his professional career

(1935-1986) Moe authored more than 60 technical

papers that were published in scholarly journals.

Despite the fact that Moe’s formal education ended

with his B. S. degree, he built a professional reputation

of knowledge of acoustics matched by few others.

His lecturing earned him an enviable international

reputation. In addition to his professional duties for

NBS, he lectured and taught courses in mathematics,

engineering and physics at the University of Maryland,

Catholic University, George Washington University,

NBS Graduate School, and the Department of Agriculture Graduate School. During the 1958-1959 academic

year he was a visiting lecturer at the UCLA Physics

Department. At the end of this duty he was offered a full

professorship by UCLA, but he declined, preferring to

return to his research duties at NBS.

Greenspan was a Fellow of the Acoustical Society of

America and was elected President for 1966-1967. He

chaired the Technical Council of the Society for 1967-

1968 and was the Society’s representative to the Council

of the AAAS. He was an Associate editor (1961-1966)

of the Journal of the Acoustical Society of America and

the Editor (1962-1973) of the Journal of Research of the

National Bureau of Standards, Section C. In addition to

the two Silver Medals awarded by NBS, he received the

Acoustical Society Silver Metal in Physical Acoustics

(1977), their Gold Metal (1983), and the Harry

Diamond Award of the IEEE (1980).

Prepared by Thomas M. Proctor.

Bibliography

[1] M. Greenspan, Transmission of Sound Waves in Gases at Very

Low Pressures, in Physical Acoustics, Vol. 2A, Academic Press,

New York (1965) pp. 1-45.

[2] M. Greenspan, Attenuation of sound in rarefied helium, Phys.

Rev. 75, 197-198 (1949).

[3] M. Greenspan, Propagation of sound in rarefied helium,

J. Acoust. Soc. Am. 22, 568-571 (1950).

[4] M. Greenspan and M. C. Thompson, Jr., An eleven megacycle

interferometer for low pressure gases, J. Acoust. Soc. Am. 25,

92-96 (1953).

[5] M. Greenspan, Combined translational and relaxational dispersion of sound in gases, J. Acoust. Soc. Am. 26, 70-73 (1954).

[6] M. Greenspan, Propagation of sound in five monatomic gases,

J. Acoust. Soc. Am. 28, 644-648 (1956).

[7] M. Greenspan, Rotational relaxation in nitrogen, oxygen, and

air, J. Acoust. Soc. Am. 31, 155-160 (1959).

[8] M. Greenspan, Translational Dispersion in Gases, in Dispersion

and Absorption of Sound by Molecular Processes, Estratto da

Rendiconti della Scuola Internazionale di Fisica Enrico Fermi,

XXVII Corso, Academic Press, New York (1963) pp. 73-100.

[9] Isadore Rudnick, Citation to Martin Greenspan, J. Acoust. Soc.

Am. 73, S33 (1983).

72
Atomic Energy Levels and Other

Spectroscopic Data

The key advances in our understanding of atomic

structure were made early in the 20th Century. Niels

Bohr developed his revolutionary theory of the hydrogen

atom in 1913, still largely on classical terms. Then, in

the 1920s, the generalization to other atoms and ions

came with the development of quantum mechanics, or

wave mechanics, by Schroedinger, Heisenberg and

others, after de Broglie postulated that all elementary

particles also have wave properties. Important later

generalizations and refinements were the relativistic

extensions by Dirac, as well as quantum electrodynamics by Feynman, Schwinger, and others. Even before

these developments took place, many highly precise

spectroscopic data had been obtained experimentally,

and these data could now be fully understood in terms of

atomic structure and quantum numbers. Thus, laboratory and astrophysical spectra could for the first time be

interpreted as specific classified transitions between

energy levels of atoms or positive ions.

The three volumes of tables in the Atomic Energy

Levels series cited here [1-3] represented a synthesis of

the data derived from studies of atomic spectra in the

first half of the century—studies which played a major

role in the revolution in physics just described. The

effort can be traced to an initiative of the National

Research Council, which in 1924 created a Committee

on Line Spectra of the Elements, with one of its main

goals being to encourage work on the analysis of atomic

spectra and to collect atomic structure data in a systematic manner. A first, still rather incomplete, tabulation

was undertaken by Bacher and Goudsmit in 1932 with

a book entitled Atomic Energy States as Derived from

the Analysis of Optical Spectra [4]. In the following

years, spectroscopic data were accumulated on a vast

scale, especially for somewhat heavier atoms and ions,

and in the middle 1940s, with the strong support of the

Line Spectra Committee, NBS Director E. U. Condon

agreed to undertake a new data compilation project at

NBS, after Bacher and Goudsmit declined to update

their book. Charlotte E. Moore, already an expert in

the compilation of atomic spectra and author of the

Princeton Observatory Multiplet Tables of Astrophysical

Interest of 1933 and 1945 [5], accepted a position at

NBS in 1945 to prepare a handbook of atomic energy

levels. This project achieved a first milestone in 1949

with the publication of Volume I of Atomic Energy

Levels, containing the spectra of hydrogen, (atomic

number Z=1) through vanadium (Z=23), 309 pages

strong [1]. In 1952, Volume II with the elements

chromium (Z=24) through niobium (Z=42) followed [2],

and in 1958 a third volume containing the spectra of

molybdenum (Z=42) through actinium (Z=89) completed this series [3], also known as NBS Circular 467.

In all these tables, the principal data presented are the

atomic energy levels (or “energy eigenstates”) compiled

from experimentally determined (published or unpublished) material. This was done for those stages of ionization for which reliable data existed. All data were

critically compiled, which means that in cases where

several experimental results were available, only the best

value was selected after critical evaluation. In addition to

the level values, the spectroscopic configuration and

term assignment, the total angular momentum quantum

number, and the ionization energy of the atom or ion

were presented, and all this material was arranged in a

highly organized, easily readable format.

The NBS/NIST critical tables on atomic

energy levels, wavelengths, and transition probabilities are the preeminent

resource for atomic spectroscopy data.

As laboratory and astrophysical studies of atomic

spectra and their application for plasma diagnostics and

modeling became increasingly sophisticated, another

principal spectroscopic quantity characterizing the

strength of spectral lines assumed critical importance.

This atomic constant is known as the atomic transition

probability, or oscillator strength, or line strength. But

atomic transition probabilities are much more difficult

to determine precisely, both experimentally and theoretically. In the 1930s to 1950s, they were determined only

on a small scale, and the uncertainties were—except for

hydrogen—often quite large. But the situation gradually

improved, and upon the urging of several scientific

communities, NBS started to compile critically atomic

transition probability data. Two volumes of Atomic

Transition Probabilities covering the first twenty

elements, i.e., hydrogen (Z=1) through neon (Z=10) and

sodium (Z=11) through calcium (Z=20) were published

in 1966 and 1969 by W. L. Wiese and coworkers [6,7].

These books were structured in a manner similar to the

energy level volumes and contained both the transition

73
probabilities and the equivalent expressions of oscillator

strength and line strength, since different user communities work with different quantities. Both experimental

and theoretical sources of data were utilized. In contrast

to the highly precise energy level and wavelength data,

the uncertainties of many transition probabilities were

still appreciable, larger by orders of magnitude than

those for wavelength and energy level data. Also, the

body of available data was much smaller. Uncertainties

can be directly determined for the experimental data,

but this is nearly impossible for calculated results. For

many prominent transitions, the available data were

redundant, but often disagreed with each other. Therefore, a system for judging the quality of transition

probability data became essential, and discussions of the

data selections were presented for each spectrum. To this

day, a coding system for the uncertainties is applied,

with letters A to D, where A-class data are estimated

accurate within 3 % and the lowest admissible class of

reference data is D, with uncertainties estimated

not to exceed 50 %. Detailed numerical uncertainty

estimates are still not realistic in many cases.

In toto, C. E. Moore’s atomic energy level books

covered 75 chemical elements and 485 spectra in different ionization states. They became an essential tool for

atomic, plasma, and astro-physicists as well as spectrochemists. About 7000 copies of each book were sold,

and the books were reprinted in 1971 as NSRDS-NBS

35. The books were featured by “Current Contents” as

a citation classic in 1990 [8] after they were cited in

more than 7900 publications. This number has since

then steadily increased to about 13 000 citations.

Similarly, the tables of atomic transition probabilities

became widely used and cited. A total of about 7000

copies were sold. They were featured as citation classics

[9] in 1989 and have been cited about 4000 times.

Almost from the beginning, the spectroscopic data

compilation program drew support from the user

communities because of the need for comprehensive

data sources that were critically evaluated. NASA

and the Department of Energy have been long-term

supporters of the data program and are continuing to

support it to this date. User communities also voiced

their strong support and published resolutions and

expressions of need for the NBS/NIST data compilations. Examples include several resolutions by the

General Assemblies of the International Astronomical

Union (IAU), the latest in 1976, that “the IAU highly

values the activities of NBS in the critical compilation

of atomic and molecular data, and considers these

activities essential for the advancement of astronomy”

[10]. The spectrochemical community devoted a special

issue of their journal Spectrochimica Acta to their

atomic data needs [11].

Numerous personal letters of support and gratitude of

leading physicists and astrophysicists have been

received over the years, among them letters from the

Nobelists Niels Bohr, Linus Pauling, Isidor Rabi,

Gerhard Herzberg, Alfred Kastler, and Arthur

Schawlow. Schawlow noted in one of his letters that

the NBS spectroscopic data tables were essential

tools in the search for new laser materials and laser

wavelengths.

The NBS/NIST data program has been, and continues

to be, involved in worldwide collaborations and services.

For example, NBS scientists have served as presidents of

the IAU Commission on Atomic and Molecular Data

and as chairs of IAU working groups; NBS/NIST is the

principal supplier of spectroscopy data to a worldwide

network of data centers under the auspices of the

International Atomic Energy Agency, Vienna; NBS

writes a regular column “News on fundamental reference data” for the journal Spectrochimica Acta B; and

the group collaborates with British, French, German,

Japanese, Russian, and Swedish groups as well as

several institutions in the United States on especially

pressing data needs. Outside groups have often turned to

NIST to find out where problems and discrepancies in

the data occur and where they can assist. Parallel to the

data compilation program, NIST has always maintained

a cutting-edge research program in spectroscopy, since

only hands-on participation with state-of the-art experimental and theoretical techniques gives NIST the

authority for making thorough, realistic judgments in

the critical evaluations.

Charlotte E. Moore did her Ph.D. at the University of

California, Berkeley, on the spectra of sunspots, then

worked at Princeton University Observatory and

produced there her first comprehensive spectroscopic

compilation, A Multiplet Table of Astrophysical Interest

[5], a first edition in 1933 and a revised and greatly

enlarged one in 1945. Shortly afterwards she came to

NBS, where she was a member of the Atomic

Spectroscopy Section until her retirement in 1968. She

was married to Bancroft Sitterly, an astronomer and

mathematician at American University, and was known

throughout NBS as “Mrs. Sitterly.” After retirement, she

continued her critical compilation work at NBS into her

mid-eighties and also worked for several years at the

Naval Research Laboratory on the ultraviolet spectrum

of the sun. During all her work, she interacted closely

with spectroscopists all over the world, not only obtaining valuable additional unpublished material but also

persuading the specialists to carry out more measurements and analyses that she badly needed for the tabulations. She thus exerted considerable influence on the

field of spectroscopy for many years. She died in 1990

at the age of 91.

74
Charlotte Moore received numerous awards and

honors, among them honorary Ph.D.s from Swarthmore

College, the University of Michigan, and the University

of Kiel, Germany; the Department of Commerce Gold

and Silver medals; and the William F. Meggers Award of

the Optical Society of America. In 1961, she was one of

six women who received the first Federal Woman’s

Award.

W. L. Wiese received his Ph.D. in 1957 at the University of Kiel, Germany, and after working for two years

at the University of Maryland, joined NBS in 1960. He

started a group on plasma spectroscopy as well as the

data center on atomic transition probabilities in 1962

and has led the Atomic Physics Division (formerly the

Atomic and Plasma Radiation Division) since 1977. He

was a Guggenheim fellow, received the A.V. Humboldt

Award, the Department of Commerce Gold and Silver

Medals, an honorary Ph.D. from the University of Kiel,

the Distinguished Career in Science Award of the

Washington Academy of Sciences, and other honors.

In recent years, William C. Martin—the leader of the

Atomic Spectroscopy Group from 1962 to 1998—and

his colleagues Charles Corliss, Arlene Musgrove,

Joseph Reader, Jack Sugar, and Romuald Zalubas

maintained the high quality of the NBS work on the

atomic energy level and wavelength tables and expanded

and updated much of Charlotte Moore’s work. Some of

their major works are cited in the selected bibliography

[12-16]. W. L. Wiese and his colleagues Teresa Deters,

Jeffrey Fuhr, and Georgia Martin continued the transition probability tabulations for heavier elements and also

updated the tables for some light elements [17-19].

In the past few years, the NIST atomic spectroscopists

combined their efforts and utilized the Internet as the

new dissemination medium to establish a unified comprehensive Atomic Spectra Database on the World Wide

Fig. 1. Charlotte Moore-Sitterly, seated on the far right, receives the Federal Woman’s Award in the White House from Lyndon B. Johnson, seated

on the far left.

75
Web [20] which contains spectral reference data for

91 000 wavelengths, 45 000 transition probabilities and

70 000 energy levels, covering all natural elements (and

some man-made ones up to Z=100) and—with many

stages of ionization included—a total of 450 spectra.

This database, with the latest version published in March

1999, has quickly become very popular, with about

45 000 hits per month and rising.

Prepared by Wolfgang L. Wiese .

Bibliography

[1] Charlotte E. Moore, Atomic Energy Levels, Vol. I (Hydrogen

through Vanadium), Circular of the National Bureau of Standards

467, U.S. Government Printing Office, Washington, DC (1949).

[2] Charlotte E. Moore, Atomic Energy Levels, Vol. II (Chromium

through Niobium), Circular of the National Bureau of Standards

467, U.S. Government Printing Office, Washington, DC (1952).

[3] Charlotte E. Moore, Atomic Energy Levels, Vol. III (Molybdenum

through Lanthanum and Hafnium through Actinium), Circular of

the National Bureau of Standards 467, U.S. Government Printing

Office, Washington, DC (1958).

[4] Robert. F. Bacher and Samuel Goudsmit, Atomic Energy States,

McGraw-Hill, New York (1932).

[5] Charlotte E. Moore, A Multiplet Table of Astrophysical Interest,

Princeton University Observatory, Princeton, NJ (1933); revised

in 1945.

[6] W. L. Wiese, M. W. Smith, and B. M. Glennon, Atomic Transition Probabilities, Vol. I Hydrogen through Neon, Natl. Stand.

Ref. Data Ser., Natl. Bur. Stand. (U.S.) 4, U.S. Government

Printing Office, Washington, DC (1966).

[7] W. L. Wiese, M. W. Smith, and B. M. Miles, Atomic Transition

Probabilities, Vol. II Sodium through Calcium, Natl. Stand. Ref.

Data Ser., Natl. Bur. Stand. (U.S.) 22, U.S. Government Printing

Office, Washington, DC (1969).

[8] W. L. Wiese and W. C. Martin, Reference Data of Atomic Spectroscopy—a Citation Classic Commentary on Atomic-Energy

Levels as Derived from the Analyses of Optical-Spectra, Vol. 1-3

by Moore, C. E., Curr. Contents Phys. Chem. Earth Sci. 47, 12

(1990); also in Curr. Contents Eng. Tech. Appl. Sci. 47, 12

(1990).

[9] W. L. Wiese, A Critical Table of Atomic Transition-Probabilities—A Citation Classic Commentary on Atomic TransitionProbabilities, Vol. 1, Hydrogen Through Neon by Wiese, W. L.,

Smith, M. W., and Glennon, B. M., Curr. Contents Phys. Chem.

Earth Sci. 40, 16 (1989); also in Curr. Contents Eng. Tech. Appl.

Sci. 40, 16 (1989).

[10] Trans. Int. Astron. Union XVI B, 33, D. Reidel Publish. Co.,

Dordrecht, Netherlands (1977).

[11] Special issue of Spectrochimica Acta, Vol. 43B, No. 1 (1988).

[12] W. C. Martin, Romuald Zalubas, and Lucy Hagan, Atomic Energy Levels—The Rare-Earth Elements, Natl. Stand. Ref. Data

Ser., Natl. Bur. Stand. (U.S.) 60, U.S. Government Printing

Office, Washington, DC (1978).

[13] Joseph Reader, Charles H. Corliss, W. L. Wiese, and G. A.

Martin, Wavelengths and Transition Probabilities for Atoms and

Atomic Ions, Part I. Wavelengths, Part II. Transition Probabilities, Natl. Stand. Ref. Data Ser., Natl. Bur. Stand. (U.S.) 68, U.S.

Government Printing Office, Washington, DC (1980).

[14] Jack Sugar and Charles Corliss, Atomic Energy Levels of the

Iron-Period Elements: Potassium through Nickel, J. Phys. Chem.

Ref. Data Vol. 14, Supplement No. 2 (1985).

[15] Charlotte E. Moore, Tables of Spectra of Hydrogen, Carbon,

Nitrogen, and Oxygen Atoms and Ions, Jean W. Gallagher (ed.),

CRC Press, Boca Raton, FL (1993).

[16] T. Shirai, J. Sugar, A. Musgrove, and W. L. Wiese, Spectral Data

for Highly Ionized Atoms: Ti, V, Cr, Mn, Fe, CO, Ni, Cu, Kr, and

Mo, J. Phys. Chem. Ref. Data, Monograph 8 (2000).

[17] G. A. Martin, J. R. Fuhr, and W. L. Wiese, Atomic Transition

Probabilities—Scandium through Manganese, J. Phys. Chem.

Ref. Data Vol. 17, Suppl. 3 (1988).

[18] J. R. Fuhr, G. A. Martin, and W. L. Wiese, Atomic Transition

Probabilities—Iron through Nickel, J. Phys. Chem. Ref. Data

Vol. 17, Suppl. 4 (1988).

[19] W. L. Wiese, J. R. Fuhr, and T. M. Deters, Atomic Transition

Probabilities of Carbon, Nitrogen and Oxygen—A Critical Data

Compilation, J. Phys. Chem. Ref. Data, Monograph 7 (1996).

[20] Atomic Spectra Database, (http://physics.nist.gov/PhysRefData/

ASD1/) National Institute of Standards and Technology. .

76
Iteration Method for the Solution of the

Eigenvalue Problem of Linear Differential and

Integral Operators

In 1946, the Office of Naval Research asked NBS to

help found a national center for mathematical computation. This center was to have four parts, the first of which

was the Institute for Numerical Analysis (INA). The

NBS director, E. U. Condon, sent his assistant, John

Curtiss, to the west coast, and it was decided to locate

the institute on the campus of UCLA. The INA was

successful in attracting several renowned scientists,

including Cornelius Lanczos, who was then working at

the Boeing Aircraft Company in Seattle. Lanczos, a

physicist and applied mathematician, had already been

very successful at devising algorithms for analyzing

a variety of mathematical models, and he was well

acquainted with the challenges of computation on desk

calculators. Since part of the INA mission was to promote the effective use of the new “high-speed” automatic digital computers, his expertise was quite relevant,

and he was immediately successful in solving problems

of interest to the researchers there.

Lanczos first turned his attention to the solution of

linear systems of equations and matrix eigenvalue

problems. The eigenvalue problem was of particular

interest to him, as he notes at the beginning of his paper

[1], since the “vibrations of elastic structures, the flutter

problems of aerodynamics, the stability problem of

electric networks, [and] the atomic and molecular vibrations of particle physics” [1, p. 255] can all be analyzed

in this way.

Computational researchers of that era faced a variety

of challenges. With only minimal understanding of the

effects of round-off errors on computations, they also

needed to deal with remarkably small computer

memories and limited computational capabilities. The

SWAC, for instance, the NBS Western Automatic

Computer, came on line in July 1950, capable of 16,000

operations per second on its 256 words of memory

[2, Appendix C]!

It was in this computational environment that

Lanczos investigated his method of “minimized iterations,” a continuation of some work begun at Boeing.

Lanczos’ presentation in this paper is almost matrixfree, not at all like the exposition of his algorithm in

contemporary textbooks [3, Chap. 9]. Yet the description is spare and elegant. He begins by noting that linear

differential and integral operator equations can be solved

by considering either of two series: the “LiouvilleNeumann expansion,” which only requires application

of the operator but can suffer convergence difficulties;

or the “Schmidt series,” which is unconditionally

convergent but requires knowledge of the eigensystem

(Section II). Lanczos makes the remarkable observation

that the first idea (which now is more commonly called

a Krylov subspace expansion) can be improved by

choosing a different set of basis functions, and he proposes a basis that is computationally convenient and

numerically better behaved. Even better, his basis gives

a finite expansion, rather than a series expansion, and

thus yields a terminating algorithm, better suited for

automatic computers. He devotes considerable attention

to a numerical example that illustrates the algorithm and

Fig. 1. Cornelius Lanczos in 1946 (Courtesy of Mrs. Eleanor

Boyk; used with permission from North Carolina State University

[12]).

77
presents a model for the bookkeeping involved in its use

(Section VI). But part of the genius of the paper is that

he doesn’t stop there, but turns his attention to the

very real numerical difficulties that can develop if the

algorithm is used on large matrices, which to him

mean those of dimension 12 or higher (Section VII).

These difficulties motivated a major improvement of the

algorithm: the development of a way to compute a basis

using a three-term recurrence. With this improvement,

he demonstrates the algorithm’s effectiveness on practical problems, such as computing the lateral vibrations of

a bar (Section IX) and vibrations of a membrane and a

string (Section X), through computational experiments

carried out by Fannie M. Gordon. In the last sections of

the paper, he discusses how to overcome complications

that arise when finding the eigensystem of an operator

rather than a matrix.

This work fit in very nicely with other developments

at INA. Researchers such as George Forsythe, J. Barkley

Rosser, and Magnus Hestenes were also thinking about

eigenvalue problems and the solution of linear systems,

and during the next two or three years they proposed and

tested a variety of approaches for “large” problems.

Lanczos, too, discussed the solution of linear systems

using the recurrence of his minimized iterations [4], and

recognized that it was mathematically equivalent to the

method of conjugate gradients [5], another noteworthy

NBS discovery discussed elsewhere in this volume.

Despite the original promise of the method of minimized iterations, very little attention was given to it

during the following 10 years. Other algorithms were

more successful on problems of moderate size, and

when “large” came to mean of dimension 1000 or

larger, even the three-term recurrence had significant

numerical difficulties. But two research projects

renewed interest in the algorithm. In 1966, Shmuel

Kaniel [6] studied the accuracy of the eigenvalue and

eigenvector estimates when Lanczos’ iteration is terminated early, as it must be when the size of the matrix is

prohibitively large. This opened the possibility of using

the algorithm to approximate the eigensystem, rather

than aim for full accuracy. In 1971, Chris Paige [7,8,9]

showed that even though round-off error ruins the

orthogonality of Lanczos’ basis, the necessary level of

accuracy can be maintained by judicious choice of

parameters and selective use of reorthogonalization.

Paige’s form of Lanczos’ algorithm was now a practical

alternative for truly large matrices.

Since then, continuous attention has been given to the

method. Almost 300 articles were published about

Lanczos’ algorithm and related Krylov methods in the

25 years following publication of Lanczos’ paper [10],

and copious citations to it continue to this day even

though it is a standard topic in textbooks and many

citations do not go back to this primary source. There

are several widely used numerical software packages,

including one due to Horst Simon and coworkers such

as Beresford Parlett at the University of California,

Berkeley, and another due to Jane Cullum and Ralph

Willoughby, developed at IBM. A package by David

Scott is available through NIST’s Guide to Available

Software (GAMS) project.

This Krylov subspace method of Lanczos, and its

later application to the solution of linear systems, was

recently designated one of the Top Ten Algorithms

of the Century [11] by Computing in Science and

Engineering, a joint publication of the IEEE Computer

Society and the American Institute of Physics.

A fascinating account of Lanczos’ life is given in

an essay by Barbara Gellai at the beginning of the

six volumes of his collected works [12,Vol 1, (1-3)-

(1-31)]. Cornelius Lanczos (born Korne ́l Lo ̈wy) began

and ended his life peacefully in Hungary, but his life

pivoted on three exiles. He was born in 1893, the eldest

son of a Jewish lawyer. He attended Jewish elementary

school, Catholic secondary school, and the University of

Budapest. His Ph.D. work concerning special relativity

received some attention by Einstein, but political

turmoil in Hungary and a ceiling for the number of Jews

at universities led Lanczos to move to Germany. He

continued his work in physics, and published an integral

formulation of the Schro ̈dinger equation [13] just before

Schro ̈dinger published his differential equation formulation, but Lanczos’ paper was misinterpreted for many

years. During this period, he spent a year as Einstein’s

assistant, continued his work, and married a German,

Maria Rupp.

In 1931, Lanczos began a second exile, as economic

and political troubles made life in Germany difficult.

Lanczos took a visiting position at Purdue University,

but unfortunately had to travel without his wife, who

had contracted tuberculosis and could not get a visa. He

continued his work on Einstein’s field equations, Dirac’s

equation, and other topics in physics, but increasingly

his attention focused on mathematical techniques,

and he developed the Tau method for approximating

functions by telescoping series [14]. His wife died in

1939, and he brought his son to the United States. During this period he also became known as an excellent

teacher, eventually writing many popular and groundbreaking textbooks, celebrated for their clarity and their

use of vivid examples. His approach to computation was

unique for the time: he worked with calculator, not slide

rule, and this led him to novel algorithmic approaches.

In the early 1940s he derived a method for evaluating

Fourier coefficients quickly [15], although the idea did

not become widely known until the popularization of

the (equivalent) Cooley-Tukey FFT algorithm.

78
During 1943-44, Lanczos had his first association

with NBS, working on the Mathematical Tables Project,

during a leave from Purdue. After some time at Boeing

Aircraft Company in Seattle, he joined the Institute

for Numerical Analysis of the NBS. This provided a

fertile working environment, and Lanczos investigated

algorithms for solving linear systems of equations and

eigenvalue problems. But eventually, politicized investigations led to the resignation of Edward Condon as

Director of NBS. Lanczos, too, came under investigation

for allegedly being a communist sympathizer, and this

may have contributed to his decision to begin a third

exile, in 1952, and then permanently in 1954, to the

Dublin Institute for Advanced Studies.

For the rest of his life, Lanczos maintained his ties to

Dublin, although he traveled and lectured extensively.

His expository skills were much renowned, and he won

the Chauvenet Prize for mathematical exposition in

1960 for one of his papers [16]. He married another

German, Ilse Hildebrand, and resumed his concentration

on physics research, including the geometry of spacetime, although his publications in mathematics continued. He died of a heart attack on his second visit back

to Hungary, in 1974.

Interest in Lanczos’ work continues, however. A

centenary celebration was held at North Carolina State

University, and his eigenvalue paper [1] in particular

continues to be a cornerstone of contemporary

eigenvalue computation and research, with over 850

citations in Science Citation Index between 1983 and

1999.

Prepared by Dianne P. O’Leary.

Bibliography

[1] Cornelius Lanczos, An Iteration Method for the Solution of the

Eigenvalue Problem of Linear Differential and Integral Operators, J. Res. Natl. Bur. Stand. 45, 255-282 (1950).

[2] Magnus R. Hestenes and John Todd, NBS-INA—The Institute for

Numerical Analysis—UCLA 1947-1954, NIST Special Publication 730, National Institute of Standards and Technology,

Gaithersburg, MD (1991).

[3] Gene H. Golub and Charles F. Van Loan, Matrix Computations,

Third Edition, Johns Hopkins University Press, Baltimore, MD

(1996).

[4] Magnus R. Hestenes and Eduard Stiefel, Methods of Conjugate

Gradients for Solving Linear Systems, J. Res. Natl. Bur. Stand.

49, 409-436 (1952).

Fig. 2. Olga Taussky Todd and Cornelius Lanczos. Taussky Todd (1906-1995) was one of the original members

of the NBS Institute for Numerical Analysis (1947-48) and was subsequently a consultant to the NBS Applied

Mathematics Division in Washington (1949-54). She was an insightful and prolific mathematician who made

many important contributions to early numerical analysis, especially in the areas of linear algebra and matrix

theory.

79
[5] Cornelius Lanczos, Solution of Systems of Linear Equations

by Minimized Iterations, J. Res. Natl. Bur. Stand. 49, 33-53

(1952).

[6] Shmuel Kaniel, Estimates for Some Computational Techniques

in Linear Algebra, Math. Comp. 20, 369-378 (1966).

[7] C. C. Paige, The Computation of Eigenvalues and Eigenvectors

of Very Large Sparse Matrices, Ph.D. Dissertation, University of

London (1971).

[8] C. C. Paige, Practical Use of the Symmetric Lanczos Process

with Re-Orthogonalization, BIT 10, 183-195 (1970).

[9] C. C. Paige, Computational Variants of the Lanczos

Method for the Eigenproblem, J. Inst. Math. Appl. 10, 373-381

(1972).

[10] Gene H. Golub and Dianne P. O’Leary, Some History of the

Conjugate Gradient and Lanczos Algorithms: 1948-1976, SIAM

Rev. 31, 50-102 (1989).

[11] Top 10 Algorithms of the Century, Comput. Sci. Eng. 2 (1),

(2000).

[12] William R. Davis, ed., Cornelius Lanczos, Collected Published

Papers with Commentaries, College of Physical and Mathematical Sciences, North Carolina State University, Raleigh, NC

(1998).

[13] Kornel Lanczos, U ̈ ber eine feldma ̈ige Darstellung der neuen

Quantenmechanik, Z. Phys. 35, 812-830 (1926).

[14] C. Lanczos, Trigonometric Interpolation of Empirical and

Analytical Functions, J. Math. Phys. 17, 123-199 (1938).

[15] G. C. Danielson and C. Lanczos, Some Improvements in

Practical Fourier Analysis and Their Application to X-Ray

Scattering from Liquids, J. Franklin Inst. 233, 365-380, 435-452

(1942).

[16] C. Lanczos, Linear Systems in Self-Adjoint Form, Amer. Math.

Monthly 65, 665-679 (1958).

80
Methods of Conjugate Gradients for

Solving Linear Systems

The advent of electronic computers in the middle of

the 20th century stimulated a flurry of activity in developing numerical algorithms that could be applied to

computational problems much more difficult than those

solved in the past. The work described in this paper [1]

was done at the Institute for Numerical Analysis, a

part of NBS on the campus of UCLA [2]. This institute

was an incredibly fertile environment for the development of algorithms that might exploit the potential

of these new automatic computing engines, especially

algorithms for the solution of linear systems and matrix

eigenvalue problems. Some of these algorithms are

classified today under the term Krylov Subspace

Iteration, and this paper describes the first of these

methods to solve linear systems.

Magnus Hestenes was a faculty member at UCLA

who became associated with this Institute, and Eduard

Stiefel was a visitor from the Eidgeno ̈ssischen Technischen Hochschule (ETH) in Zu ̈rich, Switzerland. At this

time, there were two commonly used types of algorithms for solving linear systems. The first, like Gauss

elimination, modified a tableau of matrix entries in a

systematic way in order to compute the solution. These

methods were finite, but required a rather large amount

of computational effort with work growing as the cube

of the number of unknowns. The second type of algorithm used “relaxation techniques” to develop a sequence of iterates converging to the solution. Although

convergence was often slow, these algorithms could be

terminated, often with a reasonably accurate solution

estimate, whenever the human “computers” ran out of

time.

The ideal algorithm would be one that had finite

termination but, if stopped early, would give a useful

approximate solution. Hestenes and Stiefel succeeded in

developing an algorithm with exactly these characteristics, the method of conjugate gradients.

The algorithm itself is beautiful, with deep connections to optimization theory, the Pad table, and quadratic

forms. It is also a computational gem, the standard algorithm used today to solve large sparse systems of

equations, involving symmetric (or Hermitian) positive

definite matrices, for which matrix modification methods are impractical.

Fig. 1. Wolfgang Wasow (left) and Magnus Hestenes (right).

81
The INA group was quite collegial, and many of the

ideas in this paper have roots in joint discussions among

many participants. Hestenes and Stiefel summarize the

development this way [1, pp. 409-410]:

“The method of conjugate gradients was

developed independently by E. Stiefel of

the Institute of Applied Mathematics at

Zurich and by M. R. Hestenes with the

cooperation of J. B. Rosser, G. Forsythe,

and L. Paige of the Institute for Numerical

Analysis, National Bureau of Standards.

The present account was prepared jointly

by M. R. Hestenes and E. Stiefel during the

latter’s stay at the National Bureau of

Standards. The first papers on this method

were given by E. Stiefel [1952] and by

M. R. Hestenes [1951]. Reports on this

method were given by E. Stiefel and J. B.

Rosser at a Symposium on August 23-25,

1951. Recently, C. Lanczos [1952] developed a closely related routine based on

his earlier paper on eigenvalue problem

[1950]. Examples and numerical tests

of the method have been by R. Hayes,

U. Hoschstrasser, and M. Stein.”

The papers referred to in this summary are those of

Stiefel [3], Hestenes [4], and Lanczos [5,6], the last of

which is discussed elsewhere in this volume.

It is interesting to hear two distinct voices in this

paper of Hestenes and Stiefel. Hestenes came to the

algorithm from the point of view of variational theory

and optimal control. In 1936 he had developed an

algorithm for constructing a set of mutually conjugate

basis vectors, but was advised by a Harvard professor

that it was too obvious for publication [7]. Yet this background, plus discouraging numerical experience by

George Forsythe in using the steepest descent algorithm

for solving linear systems, was grist for the mill in the

development of the conjugate gradient algorithm.

Stiefel, on the other hand, had a strong orientation

toward relaxation algorithms, continued fractions, and

the qd-algorithm, and he developed conjugate gradients

from this viewpoint.

The technical contributions of the paper begin in

Section 3, with a rather terse algebraic presentation

of the formulas of the conjugate gradient algorithm.

Motivation comes later, with the observation that the

recurrences lead to a sequence of approximations that

converge monotonically in the sense of reducing an

error function. At the same time, a sequence of polynomials can be constructed in order to find the eigensystem of the matrix. In the next section, the authors

explain that the algorithm is a special case of a conjugate direction algorithm, and it is this property that

yields finite termination. Algebraic properties are

further developed in Section 5, which presents some

alternate computational formulas. Sections 6 and 7 are

more geometric, discussing optimization properties of

the solution estimates. Section 8 turns to practical considerations: will round-off errors on electronic computers render this theoretically beautiful algorithm useless?

The rather conservative analysis led to the conclusion

that although round-off certainly hurts the algorithm,

reasonable precautions and end corrections could overcome this in most cases. Section 9 explored different

normalization options. In Section 10, “extensions” were

proposed; in particular, the authors discussed how

to solve nonsymmetric problems by considering the

normal equations, and how to choose a preconditioning

matrix in order to make the method applicable to

broader classes of matrices. Section 11 discusses the

construction of conjugate bases, and in Sections 12 and

13, the authors note that there is a close relation between

conjugate gradients and Gauss elimination. Other

relations are explored in later sections: continued

fractions and the theory of orthogonal polynomials

(Sections 14, 15, 17, and 18), and eigenvalue computations (Section 16).

The paper concludes with some numerical examples

demonstrating the usefulness of the algorithm on a

matrix of dimension 4 using exact arithmetic, a wellconditioned matrix of dimension 6 with some rounding

error, and an ill-conditioned matrix of dimension 3, in

which the conjugate gradient solution was about as

Fig. 2. Eduard Stiefel [From Zeitschrift fu ̈r angewandte Mathematik

und Physik 30, 139 (1979); used with permission].

82
accurate as that from Gauss elimination. The authors

remind us how difficult numerical computations were in

the middle of the 20th century: the algorithm had been

used to solve 106 difference equations on the Zuse

computer at ETH (with a sufficiently accurate answer

obtained in 90 iterations); to solve systems as large as

dimension 12 on an IBM “card programmed calculator”; and to solve small systems on the SWAC

(Standards Western Automatic Computer), which had

only 256 words of memory [2, Appendix C].

Hestenes and Stiefel’s paper remains the classic

reference on this algorithm, explaining the use of the

algorithm as both a finitely terminating method and as

a way of obtaining an approximate solution if halted

before termination. It is such a rich paper that it contains

the roots of virtually all of the advances in this area up

to the present time: for example, preconditioning to

accelerate convergence of the algorithm, variations that

can be used to solve systems of equations involving

nonsymmetric matrices, and evaluation of computational variants in order to choose the most numerically

stable one.

The algorithm garnered considerable early attention

but went into eclipse in the 1960s as naive implementations were unsuccessful on some of the ever-larger

problems that were being attempted. Work by John Reid

[8] in the early 1970s drew renewed attention to the

algorithm, and since then it has been an intense topic of

research. Today it is the standard algorithm for solving

linear systems involving large, sparse, symmetric (or

Hermitian) matrices. Strategies for constructing preconditioning matrices, which reduce the number of

iterations, remain a major research theme, as well as

understanding the convergence properties of some nonsymmetric variants. Some of the early history of the

algorithm is discussed in [9].

Despite the fact that the algorithm has become a

standard topic in numerical textbooks, the original

paper is still widely read and cited; Science Citation

Index lists over 800 citations between 1983 and 1999,

and it is clear that this algorithm, and the non-symmetric

variants developed to complement it, will remain the

standard algorithms for solving sparse linear systems for

the foreseeable future.

Fig. 3. Researchers associated with the NBS Institute for Numerical Analysis (1950). From left to

right: Mark Kac, Edward J. McShane, J. Barkley Rosser, Aryeh Dvoretzky, George E. Forsythe, Olga

Tausssky-Todd, Wolfgang R. Wasow, and Magnus R. Hestenes.

83
The conjugate gradient algorithm was but one claim

to greatness for these remarkable and multifaceted

researchers.

Magnus R. Hestenes [10] was born in Bricelyn,

Minnesota, in 1906. His undergraduate work was at

St. Olaf College, and his graduate work at the University

of Wisconsin and the University of Chicago. His first

faculty appointment was at Chicago, but he left in 1947

to accept a professorship at UCLA, where he taught

until his retirement. He had 34 Ph.D. students and was

a well-loved advisor and teacher, known for his nurturing kindness toward his very junior colleagues. Administrative duties over the years included chairing the

Mathematics Department, directing the university’s

computing center, and serving as vice president of the

American Mathematical Society. He also held appointments with the Rand Corporation, the Institute for

Defense Analyses, and the IBM Watson Research

Center. His association with NBS’s INA lasted from

1949 to 1954, when the INA was transferred from NBS

to UCLA. His best known works include many publications on the problem of Bolza, a famous paper on

quadratic forms in Hilbert space [11], and the conjugate

gradient paper with Stiefel. Hestenes remained scientifically active until his death in 1991, concentrating in his

later years on the method of multipliers and continuing

to write and publish.

Eduard Stiefel [12] was born in 1909 in Zu ̈rich,

Switzerland. He spent virtually his entire career at

the Eidgeno ̈ssischen Technischen Hochschule (ETH) in

Zu ̈rich, first as a student of mathematics and physics,

and then, following his habilitation degree in 1943, as a

professor. His early work was in topology, eventually

studying the geometry and topology of Lie groups. 1948

was a turning point for him, however. He founded

the Institut fu ̈r Angewandte Mathematik (Institute for

Applied Mathematics) at ETH, in collaboration with

Heinz Rutishauser and Ambros P. Speiser. Stiefel was a

visionary who realized the enormous significance of the

new computing technology and the impact it would have

on mathematics and science. When he discovered in

1949 that a major computing engine, the Z4 of the

German designer Konrad Zuse, was sitting in the small

alpine village of Neukitchen, Germany, he traveled there

and arranged for the machine to be rented and moved to

ETH. Zuse, isolated by wartime secrecy, had independently developed computing technology that in many

ways was superior to that available in the U.S. at the time

[13]. Stiefel’s initiative made ETH the first European

university with an electronic computer, putting it in

the forefront of numerical computation and computer

science. This led to several breakthrough developments

by him and his colleagues, including the qd algorithm,

the programming language ALGOL, and the conjugate

gradient algorithm. His own interests evolved toward

numerical algorithms, and he made substantial contributions in computational linear algebra, quadrature, and

approximation theory before turning his attention to

mechanics and celestial mechanics late in his life [14].

His technical works include over 60 journal publications

and a wonderful 1960s textbook on numerical mathematics. He died in 1978, a few months short of his 70th

birthday.

Computing in Science and Engineering, a publication

of the IEEE Computer Society and the American

Institute of Physics, named Krylov Subspace Iteration as

one of the Top 10 Algorithms of the Century [15], citing

in particular the pioneering work of Hestenes, Stiefel,

and Lanczos. The citation reads:

Krylov Subspace Iteration

Hestenes, Stiefel, Lanczos

Conjugate gradient methods are iterative

matrix algorithms for solving very large

linear systems of equations, especially efficient for sparse square matrices. Such

systems arise in various application areas,

such as modeling of fluid flows, reservoir

engineering, mechanical engineering, semiconductor device analysis, nuclear reaction

models, and electric circuit simulation.

These matrices can be huge, up to millions

of degrees of freedom. Modern improvements include GMRES and BI-CGSTAB.

Prepared by Dianne P. O’Leary.

Bibliography

[1] Magnus R. Hestenes and Eduard Stiefel, Methods of Conjugate

Gradients for Solving Linear Systems, J. Res. Natl. Bur. Stand.

49, 409-436 (1952).

[2] Magnus R. Hestenes and John Todd, NBS-INA—The Institute for

Numerical Analysis—UCLA 1947-1954, NIST Special Publication 730, National Institute of Standards and Technology,

Gaithersburg, MD (1991).

[3] Eduard Stiefel, U ̈ ber einige Methoden der Relaxationsrechnung,

Z. Angew. Math. Phys. 3, 1-33 (1952).

[4] M. R. Hestenes, Iterative Methods for Solving Linear Equations,

NAML Report 52-9, July 2, 1951, NBS, Los Angeles, CA.

Reprinted in J. Optim. Theory Appl. 11, 323-334 (1973).

[5] Cornelius Lanczos, Solution of Systems of Linear Equations by

Minimized Iterations, J. Res. Natl. Bur. Stand. 49, 33-53 (1952).

[6] Cornelius Lanczos, An Iteration Method for the Solution of the

Eigenvalue Problem of Linear Differential and Integral Operators, J. Res. Natl. Bur. Stand. 45, 255-282 (1950).

84
[7] Magnus Hestenes, Conjugacy and Gradients, Princeton History

Conference, Summer 1987.

[8] J. K. Reid, On the Method of Conjugate Gradients for the

Solution of Large Sparse Systems of Linear Equations,

in Large Sparse Sets of Linear Equations, J. K. Reid (ed.),

Academic Press, New York (1971) pp. 231-254.

[9] Gene H. Golub and Dianne P. O’Leary, Some History of the

Conjugate Gradient and Lanczos Algorithms: 1948-1976, SIAM

Rev. 31, 50-102 (1989).

[10] A. Miele, An Appreciation of Professor M. R. Hestenes,

J. Optim. Theory Appl. 14, 445-451 (1974).

[11] M. R. Hestenes, Applications of the Theory of Quadratic Forms

in Hilbert Space to the Calculus of Variations, Pacific J. Math.

1, 525-581 (1951).

[12] J. Waldvogel, U. Kirchgraber, H. R. Schwarz, and P. Henrici,

Eduard Stiefel (1909-1978), Z. Angew. Math. Phys. 30, 133-136

(1979).

[13] Konrad Zuse, Die Rolle der ETH bei der Computerentwicklung,

Z. Angew. Math. Phys. 30, 399-403 (1979).

[14] Eduard Stiefel, Comments on the Bibliography, Z. Angew. Math.

Phys. 30, 141-142 (1979).

[15] Top 10 Algorithms of the Century, Comput. Sci. Eng. 2 (1),

(2000).

85
Computer Development at the National

Bureau of Standards

The first fully operational stored-program electronic

computer in the United States was built at the National

Bureau of Standards. The Standards Electronic

Automatic Computer (SEAC) [1] (Fig. 1.) began useful

computation in May 1950. The stored program was held

in the machine’s internal memory where the machine

itself could modify it for successive stages of a computation. This made a dramatic increase in the power of

programming.

Although originally intended as an “interim” computer, SEAC had a productive life of 14 years, with a

profound effect on all U.S. Government computing, the

extension of the use of computers into previously

unknown applications, and the further development of

computing machines in industry and academia.

In earlier developments, the possibility of doing

electronic computation had been demonstrated by

Atanasoff at Iowa State University in 1937. The ENIAC

was completed in 1946 at the Moore School of the

University of Pennsylvania, but programming in that

machine consisted of setting appropriate switches and

plug connections. The ENIAC had demonstrated that

individual computations could be performed at electronic speed, but the instructions (the program) that

drove these computations could not be modified and

sequenced at the same electronic speed as the computations. Other early computers in academia, government,

and industry, such as Edvac, Ordvac, Illiac I, the Von

Neumann IAS computer, and the IBM 701, would not

begin productive operation until 1952.

In 1947, the U.S. Bureau of the Census, in cooperation with the Departments of the Army and Air Force,

decided to contract with Eckert and Mauchly, who had

developed the ENIAC, to create a computer that

would have an internally stored program which

could be run at electronic speeds. Because of a demonstrated competence in designing electronic components,

the National Bureau of Standards was asked to be

technical monitor of the contract that was issued,

to the company that became the Remington Rand

Corporation, for the development of the first commercial computer, the Univac. Actually, there were three

machines, two for the military and one for the Census

Bureau.

Fig. 1. SEAC, showing the magnetic tapes and wire cartridges, the operators console, and the racks of logic circuitry.

86
It became clear during 1948 that unexpected technical difficulties would delay completion of the Univacs.

The machine for the Office of the Air Comptroller was

primarily for use by George Dantzig, noted for his work

on Linear Programming applied to economic problems.

He urged the Air Force to contract with NBS for the

development of an interim machine which would serve

multiple purposes. Furthermore, the Bureau was in need

of a computer for its own scientific research. Consequently, NBS began development, in its own laboratory, of an interim machine for use by NBS, the Army

and Air Force, and the Census Bureau, which wished to

test automatic methods on the 1950 Census. The interim

machine at NBS was completed and put into continuous

operation in May 1950, a year before the first commercial machine was delivered. It was originally called the

Standards Eastern Automatic Computer to distinguish it

from the Standards Western Automatic Computer still

under development at the NBS Institute for Numerical

Analysis in Los Angeles.

In the early years of its use, SEAC was operated

24 hours per day, 7 days per week. During this time four

different kinds of demand were made on the machine.

It was used by mathematicians from NBS and many

other institutions to do the calculations that spurred the

advance of numerical analysis. It was also used by the

engineering staff of the Electronic Computers Laboratory to develop new components and to expand the

capabilities of SEAC. A maintenance staff kept

constant watch on the 12,000 diodes and over 1000

vacuum tubes by doing diagnostic testing. Finally, with

the support of other agencies, NBS developed entirely

new uses for computers and tested these uses on SEAC.

Despite these competing demands, SEAC achieved

reliable operation 77 % of the time during its critical

first three years of operation. This was both a surprise

and a source of encouragement to the young field of

computer development.

The mathematical applications of SEAC were well

represented by the publication of the NBS Handbook

of Mathematical Functions [2] (which is separately

described in this volume). One major calculation

carried out dealt with nuclear energy. The early engineering and maintenance developments are described in

an NBS Circular published in 1955: Computer Development (SEAC and DYSEAC) at the National Bureau of

Standards [1]. It consists of an introduction by S. N.

Alexander, the Chief of the Electronic Computer

Laboratory which developed SEAC, and reprints of

eight papers by NBS staff which were previously

published in various journals and computer conference

proceedings. Their titles give an idea of the scope of

NBS contributions to computer design.

Foreword, A. V. Astin

Introduction, S. N. Alexander

SEAC, S. Greenwald, S. N. Alexander, and Ruth C.

Haueter

Dynamic circuitry techniques used in SEAC and

DYSEAC, R. D. Elbourn and R. P. Witt

DYSEAC, A. L. Leiner, S. N. Alexander, and R. P. Witt

System design of the SEAC and DYSEAC, A. L. Leiner,

W. A. Notz, J. L. Smith, and A. Weinberger

High-speed memory development at the National

Bureau of Standards, R. J. Slutz, A. W. Holt, R. P.

Witt, and D. C. Friedman

Input-output devices for NBS computers, J. L. Pike and

E. L. Ainsworth

Operational experience with SEAC, J. H. Wright, P. D.

Shupe, Jr., and J. W. Cooper

SEAC-Review of three years operation, P. D. Shupe, Jr.

and R. A. Kirsch

The Greenwald, Alexander, and Haueter paper

describes the organization of SEAC from the block

diagram level down to the circuitry level. It exhibits

pictures of the tens of thousands of hand-constructed

components which today are manufactured by automatic methods. To us today, it seems even more amazing

than it did in 1950 that the thing could work at all!

This circuitry using diodes, vacuum tubes, and pulse

transformers is described in the Elbourn and Witt paper.

The memory of SEAC initially consisted of what we

would today describe as 3072 bytes, (not kilobytes or

megabytes!). This memory, in the form of acoustic

pulses in mercury columns, is described in the paper by

Slutz, Holt, Witt, and Friedman, as are subsequent

developments of a higher speed electrostatic memory

and a memory design using individual components for

each bit.

Because of the very limited memory capacity of

SEAC, it was important to be able to store information

on external media. These media were also used for

feeding data and programs to SEAC. The paper by Pike

and Ainsworth describes the various magnetic and

paper tape media which served this purpose. One

magnetic device was an adapted office dictating

machine, modified to store digital information.

Each programmer had one of these wire cartridges on

which the whole history of his or her programming

experience would be stored. These wire cartridges still

exist today, but there are no devices to read them,

thereby losing to history much of the detailed early

experience on the first computer!

87
The two papers by Wright, Shupe, and Cooper and

by Shupe and Kirsch describe how SEAC was maintained in productive operation despite the fact that

failure in any one of the tens of thousands of components or solder connections would render the computer

inoperative, or so it was believed. Actually, after

about ten years of ostensibly fault-free operation, it was

discovered by Kirsch that there had been a wiring error

in SEAC from the beginning of its useful life. A

program written in a certain way would have failed, but

the conditions for this failure had never occurred in the

many years of normal operation. Computers of today

are not as reliable as SEAC aspired to be, so we use

“workarounds” to live with errors.

Two important lessons learned from the design of

SEAC were incorporated in the design of DYSEAC in

1953. The reliability of SEAC’s components led to the

use of similar components in DYSEAC, and new kinds

of logical organization were also incorporated. These

are described in the two papers by Leiner, Alexander,

and Witt and by Leiner, Notz, Smith, and Weinberger.

DYSEAC was built in movable trailers for the U.S.

Army and is believed to be the first computer to use

printed circuits. In the short time after its construction

at NBS, before it was removed by the sponsoring

organization, it was possible to demonstrate some of

its important properties. It had extensive abilities for

real-time interaction with outside devices. One of these

was SEAC itself, which was able to interrupt computations on DYSEAC and send data into files on DYSEAC

without disruption of the DYSEAC computation. This

was an early example of hardware-based time-sharing.

Other examples that ultimately led to industrial process

control were first demonstrated on the DYSEAC.

The last of the four kinds of uses of SEAC was the

development of entirely new applications for computers.

The first uses of SEAC (and indeed most computers)

were for mathematical calculations. Soon thereafter it

was recognized that computers, as symbol manipulators,

could also process alphabetical information. This led to

so-called business data processing. But the ready

availability of SEAC for innovation without the need for

commercial motivation encouraged its use beyond these

two conventional areas. Two examples of the many

such innovative areas started on SEAC were Image

Processing and Chemical Structure Searching.

In 1957 the first picture was fed into a computer

when a rotating drum scanner was connected to SEAC

[3]. This project demonstrated that it was possible to

perform image processing operations on scanned

pictures, using the (for that time) great processing speed

of the computer. Progress in scanning technology can be

seen in the difference between one of the first scans and

a modern one (Fig. 2). Among the many disciplines

impacted at NBS by this new field of image processing

were metallurgy [4], character recognition [5], and

criminology [6]. Today, this technology, first started on

SEAC, allows us to do CAT scans in medicine, receive

satellite images from space, scan bar codes in grocery

stores, and do desktop publishing [7].

Experience with non-numerical processing techniques led to the realization that different kinds of data

structures could be manipulated with SEAC. One of

these was the structural diagram used in organic chemistry. In the process of examining new patent applications, the U. S. Patent Office needed to search files of

chemical compounds. Previously, chemical names had

been the only means of representing compounds, but

this type of search was not very satisfactory owing to

inconsistent nomenclature. It was shown [8,9] with the

use of SEAC that structural diagrams could be represented in digital form and searched on the computer,

thereby finding records that could not have been found

Fig. 2. Father and daughter—two scans separated by 40 years and

storage requirements in the ratio of 1400:1.

88
using nomenclature alone. Chemical structure searching

is now a multimillion dollar industry which plays a

major role, for example, in design of new drugs.

The rapidity with which SEAC and its descendants

influenced a wide variety of scientific, commercial,

and even intellectual disciplines encouraged the early

pioneers to believe that “Nothing will be restrained

from them which they have imagined to do” [10]. Many

people still believe that today.

Prepared by Russell A. Kirsch.

Bibliography

[1] A. V. Astin (ed.), Computer Development (SEAC and DYSEAC)

at the National Bureau of Standards, Washington, DC, National

Bureau of Standards Circular 551, U.S. Government Printing

Office, Washington, DC (1955).

[2] Milton Abramowitz and Irene A. Stegun (eds.), Handbook of

Mathematical Functions with Formulas, Graphs, and Mathematical Tables, National Bureau of Standards Applied

Mathematics Series 55, U. S. Government Printing Office,

Washington, DC, June 1964.

[3] R. A. Kirsch, L. Cahn, L. C. Ray, and G. H. Urban, Experiments

in processing pictorial information with a digital computer,

Proceedings of the Eastern Joint Computer Conference, Dec.

9-13, 1957, Institute of Radio Engineers, New York (1958).

[4] G. A. Moore and L. L. Wyman, Quantitative Metallography with

a Digital Computer, Application to a Nb-Sn Superconducting

Wire, J. Res. Natl. Bur. Stand. 67A, 127-147 (1963).

[5] Mary Elizabeth Stevens, Automatic Character Recognition, A

State-of-the-Art Report, NBS Technical Note 112, National

Bureau of Standards, Washington, DC, May 1961.

[6] J. H. Wegstein, A Semi-Automated Single Fingerprint Identification System, NBS Technical Note 481, National Bureau of

Standards, Washington, DC (1969).

[7] Russell A. Kirsch, SEAC and the Start of Image Processing at

the National Bureau of Standards, IEEE Ann. Hist. Comput. 20

(2), 7-13 (1998).

[8] Louis C. Ray and Russell A. Kirsch, Finding Chemical Records

by Digital Computers, Science 126, 814-819 (1957).

[9] Herbert R. Koller, Ethel C. Marden, and Harold Pfeffer, The

Haystaq System: Past, Present, and Future, in Proceedings of the

International Conference on Scientific Information, Washington,

DC, Nov.16-21, 1958, National Academy of Sciences,

Washington, DC (1959) pp. 1143-1179.

[10] Genesis, 11:6.

89
Thermal Converters as AC-DC Transfer

Standards for Current and Voltage

Measurements at Audio Frequencies

Francis L. Hermach’s paper [1] launched the field of

ac-dc thermal transfer metrology, which forms the basis

for ac voltage and current measurement and calibration

throughout the world. It laid the foundation for the

techniques of ac-dc transfer and provided the first

theoretical basis for the thermal transfer structures

used in all national measurement institutes (NMIs, i.e.,

counterpart organizations to NIST) today. Hermach was

the first to realize the very large improvement in capability that is possible when electrothermic elements are

used as ac-dc transfer devices instead of relying on

absolute instruments as had been the practice previously.

The impact of the paper was, therefore, nothing less

than the creation of an area of electrical metrology that

continues to provide the national and working standards

on which the world’s NMIs base their ac voltage and

current calibrations.

Although the paper contains construction details

and experimentally determined characteristics for new

instrumentation developed at NBS, it also has over

five pages of very detailed electrical, thermal, and

thermoelectric modeling for the critical elements in the

newly proposed thermal transfer standards. It contains

the very first solution to the steady state temperature

distribution in an ac-dc thermal transfer instrument and

includes effects of Peltier and Thomson heating and low

frequency error due to failure to average the applied

signal.

This ground-breaking publication is the most

cited work in the ac-dc thermal transfer field.

It has been and continues to be cited by scientists

and engineers in NMIs all over the world and

is regularly mentioned for providing the basis

of new calibration standards. Virtually every major NMI

has a copy in its technical library. The paper is still

disseminated routinely to metrologists who require a

solid foundation in the field of thermal transfer

measurements.

Hermach’s paper made a major contribution by

proposing and describing the use of electrothermic

instruments as transfer devices, as well as clearly

delineating the major physics elements limiting

their performance, thus creating a whole new area of

calibration standards.

AC voltages and currents in the frequency range from

low audio to hundreds of megahertz are measured most

accurately by comparison to dc standards using ac-dc

thermal transfer instruments. AC-DC thermal transfer

structures were first applied in the audio frequency

range and later at radio frequencies [2] for difference

measurements of voltage, current, and power. Hermach

and the staff of the NBS Electricity Division produced

important developments including the first description

of coaxial transfer standards and the first transmissionline analysis of such structures [3].

In general, the rate of transformation of energy from

electrical to thermal form in thermal converters is proportional to the root-mean-square (rms) values of current and voltage. The heater temperature is a function of

the square of the heater current even if the constants in

the defining equation that describes the underlying

physics vary with temperature or time. Since the

response of thermal converters is calibrated on direct

current at the time of use, ac-dc transfers are possible

with little decrease in accuracy from drift or external

temperature influences.

Traditional thermal converters contain wire heaters or

thin metal heater structures. The temperature of the

heater is typically monitored with one or more thermocouples, also made of wire or thin metal film. The

best-performing primary standards usually contain

many thermocouples in an arrangement that minimizes

ac-dc difference by reducing both heater temperature

and thermal gradients. Current research at NIST includes two areas directed at new thermal converters

suitable for both primary and working standards.

Multi-junction thermal converters (MJTCs) are used

in very high-accuracy ac-dc difference metrology

because they have very small ac-dc differences, follow

the rms law of excitation, and produce high output emfs.

MJTCs traditionally have been fabricated from wire

heater resistors and thermocouples. The project to

develop thin-film MJTCs (FMJTCs) involves the use of

micro-machining of silicon and photo-lithography on

thin films to produce high-performance thermal transfer

standards. Multilayer FMJTCs have been designed,

fabricated, and tested at NIST by J. R. Kinard, D. B.

Novotny, and D. X. Huang, and new improved converters are under development [4].

90
The basic elements of the devices are a thin-film

heater on a thin dielectric membrane, a silicon frame

surrounding and supporting the structure, and thin-film

thermocouples positioned with hot junctions near the

heater and cold junctions over the silicon. Carefully

selected materials in new thermal designs are required,

along with very accurate dimensioning of the heater and

thermocouples. The heater and thermocouples are sputter deposited and patterned with photolithography. Contributions to ac-dc difference from the Thomson effect

and other effects are further reduced by the appropriate

choice of heater alloy.

Integrated micropotentiometers are thermal transfer

devices that contain FMJTCs and thin-film output resistors fabricated as an integrated structure on the same

silicon chip. The figure shows an integrated micropotentiometer including the FMJTC structure. New versions of the FMJTCs and integrated micropotentiometers are under development that include new membrane

materials and vacuum packaging, with the help of novel

etching techniques such as front and back surface etching.

At audio frequency, thermal and thermoelectric

effects ultimately limit the measurement uncertainty in

conventional room-temperature thermal converters.

Heater powers as high as a few tens of milliwatts and

temperature differences as high as 100 K are common in

some thermal converters. To reduce these effects and

to achieve very high temperature sensitivity, a novel

sensor employing a superconducting resistive-transition

edge thermometer is being developed at NIST by C. D.

Reintsema, E. N. Grossman, J. A. Koch, J. R. Kinard,

and T. E. Lipe [5,6]. Since the new converter operates at

temperatures below 10 K and is mounted on a platform

with precise temperature control and very small temperature gradients, the thermal and thermoelectric errors

are potentially quite small. Because of the very high

temperature sensitivity of the superconducting transition, this converter also offers the possibility of direct

thermal transfer measurements at very low signal levels.

This transfer standard consists of a signal heater, trim

heater, and temperature sensor all mounted on a temperature-stabilized platform. The sensor resistance is

measured by an ac resistance bridge, and the temperature of the assembly is held constant by the closed loop

application of power to the trim heater. A NbTa thinfilm meander line is used as the thermal sensor, and it

is thermally biased to operate within its superconducting-resistive transition region. The signal heater in the

prototype device is a 7  thin-film meander line and the

trim heater is a 450  PdAu thin-film meander line,

both adjacent to the detector on the silicon substrate. To

ensure temperature stability, the entire converter assembly is mounted on a second platform controlled at a

slightly lower temperature. This intermediate stage is

thermally isolated, and controlled by a second ac resistance bridge using another transition edge sensor and

heater.

Using this new cryogenic converter, measurements

have been made at signal power levels of a microwatt,

which is around 1000 times lower than is possible with

room-temperature converters. Characterization using a

fast-reversed-dc source has shown that the thermoelectric errors are presently in the 1 V/V to 2 V/V

range. These early results are encouraging, but

considerable improvement both in the resistance

bridge performance and in the input transmission

line will be necessary for this new device to be a

candidate for consideration as a primary standard.

Prepared by J. R. Kinard, Jr., N. B. Belecki, and J. F.

Mayo-Wells, based on excerpts from the paper The

Ampere and Electrical Units [7], authored by members

of the Electricity Division.

Fig. 1. Integrated micropotentiometer including the thin-film multijunction thermal converter (FMJTC) structure.

91
Bibliography

[1] Francis L. Hermach, Thermal Converters as AC-DC Transfer

Standards for Current and Voltage Measurements at Audio

Frequencies, J. Res. Natl. Bur. Stand. 48, 121-138 (1952).

[2] F. L. Hermach and E. S. Williams, Thermal voltage converters for

accurate voltage measurements to 30 megacycles per second,

Trans. Am. Inst. Electr. Eng., Part 1 79, 200-206 (1960).

[3] Joseph R. Kinard, Thomas E. Lipe, Clifton B. Childers, and

Svetlana Avramov-Zamurovic, Comparison of high voltage

thermal converter scaling to a binary inductive voltage divider, in

1998 Conference on Precision Electromagnetic Measurements:

Digest, Institute of Electrical and Electronics Engineers, New

York (1998) pp. 381-382.

[4] J. R. Kinard, D. X. Huang, and D. B. Novotny, Performance of

multilayer thin-film multijunction thermal converters, IEEE

Trans. Instrum. Meas. 44, 383-386 (1995).

[5] Carl D. Reintsema, Erich N. Grossman, Jonathan A. Koch, Joseph

R. Kinard, and Thomas E. Lipe, AC-DC transfer at cryogenic

temperatures using a superconducting resistive transition-edge

temperature sensor, in IMTC Proceedings: IMTC ’97, IEEE

Instrumentation and Measurement Conference: Sensing, Processing, Networking, Vol. 1, Institute of Electrical and Electronics

Engineers, New York (1997) pp. 726-730.

[6] Carl D. Reintsema, Joseph R. Kinard, Thomas E. Lipe, Jonathan

A. Koch, and Erich N. Grossman, Thermal transfer measurements

at microwatt power levels, in 1998 Conference on Precision

Electromagnetic Measurements: Digest, Institute for Electrical

and Electronics Engineers, New York (1998) pp. 171-172.

[7] R. E. Elmquist, M. E. Cage, Y-H. Tang, A-M. Jeffery, J. R.

Kinard, R. F. Dziuba, N. M. Oldham, and E. R. Williams, The

Ampere and Electrical Units, J. Res. Natl. Inst. Stand. Technol.,

January-February (2001).

92
Selected Values of Chemical Thermodynamic

Properties

The theoretical framework of thermodynamics was

well established by the time NBS was founded, and

certain important applications, such as improving the

efficiency of steam engines, had been demonstrated.

However, the broad application of thermodynamics to

the design and control of industrial processes had to

await the accumulation and organization of a large

amount of experimental data, as well as theoretical

contributions from quantum mechanics and statistical

mechanics. The appearance of Selected Values of

Chemical Thermodynamic Properties [1] in 1952

marked a significant milestone in this process. This

book represented the culmination of 20 years of work

by Frederick D. Rossini and coworkers in evaluating

and systematizing the data that had appeared in the

world literature on thermochemistry. It tabulated

accurate values of the thermodynamic properties of all

inorganic and simple organic compounds that had been

investigated in a format that allowed prediction of the

outcome of many thousands of chemical reactions.

Such calculations, which indicate whether a reaction

will take place and, if so, the extent of reaction and

amount of heat released or absorbed, are immensely

important in research and engineering.

Selected Values, which was often referred to simply

as “Circular 500” after its NBS publication designation,

presented recommended values of the enthalpy (heat) of

formation, Gibbs energy of formation, entropy, and heat

capacity of individual chemical compounds in different

physical states (solid, liquid, gas, or aqueous solution).

All values were reduced to standard state conditions,

defined by parameters such as temperature (25 C) and

pressure (one standard atmosphere). Since the laws of

thermodynamics require that the change in properties

such as energy and entropy cannot depend on the path

followed in going from an initial to a final state—otherwise one could build a perpetual motion machine—the

net change in thermodynamic properties in a chemical

reaction can be calculated by addition and subtraction

of the standard state values for the substances taking

part in the reaction. This allows a simple prediction of

whether the reaction will occur at all and, if it does,

whether it will go to completion. In intermediate

situations, one can obtain a quantitative measure of the

extent of reaction from the equilibrium constant, which

is easily calculated from the tabulated standard state

values. Finally, most chemical changes involve either

an absorption or release of heat, and the amount of

this heat may be calculated from the same data. Thus

Selected Values provided an extremely powerful tool for

predicting the course of chemical reactions, a goal of

chemists since the earliest days of the science.

The book itself was 822 pages in length and covered

about 5000 chemical species. It was divided into two

parts, the first dealing with the thermodynamic properties in a particular physical state and the second with the

change in properties in transitions between states (such

as melting and vaporization). All data were internally

consistent, in the sense that all physical and thermodynamic relations existing between different properties

for the same substance, or the same property for different substances, were satisfied by the tabulated values.

The table layout in Circular 500 became the norm for

thermodynamic tabulations throughout the world.

Fig. 1. Frederick D. Rossini.

93
The preparation of Selected Values of Chemical

Thermodynamic Properties required analyzing data

from thousands of literature references appearing over

the previous century, selecting the most reliable values

in the judgment of the evaluators, and then optimizing

this massive database to derive a “best set” of standard

state values. Much of the data had to be corrected for

changes in temperature scales, unit definitions, atomic

weights, and other auxiliary data that can affect the

thermodynamic properties. Shrewd detective work was

sometimes required; for example, when a nineteenthcentury chemist had failed to report the ambient temperature during a measurement, newspaper archives were

consulted in order to estimate the laboratory temperature at the time. Since there was considerable redundancy in the data, related data sets were subjected to

statistical analysis using weighting factors based on the

evaluator’s appraisal of the accuracy of each measurement. In this way an internally consistent set of standard

state values was derived that gave the best fit to the much

larger database of experimental measurements. It was a

remarkable achievement that Rossini and his group did

this before the advent of computers and before the term

“database” was even coined. They anticipated by many

years the process of obtaining the best fit for a large set

of data of varying accuracy—a procedure which is now

commonplace in all scientific fields.

Subsets of these data had been released in loose-leaf

form to universities, industrial users, and others in the

1947-1950 period. The complete tables received wide

distribution as soon as they appeared in 1952 and went

out of print six years later. Demand continued, and NBS

reprinted the book in 1961. Selected Values became a

standard fixture in physical chemistry laboratories.

A generation of chemistry students used the book to

analyze their laboratory data, and researchers in many

fields used it to plan their experiments. Chemical

engineers used it in various stages of process design.

The late Henry Eyring, one of the major figures of

twentieth century chemistry, once asserted that Circular

500 saved U.S. industry enough money to pay the entire

cost of NBS since its founding. Unfortunately, it was

difficult to document that claim in a way that would help

NBS budget requests!

One of the early applications of Selected Values was

in the U. S. rocket program, which went into full gear

shortly after its publication. Chemical thermodynamics

was the key factor in boosting the performance of rocket

engines, and there was a major effort to find new fuels

and oxidizers as space competition with the Soviet

Union intensified. Many chemical reactions involving

exotic compounds were explored in the process of

searching for ways to increase rocket thrust. The data

in Selected Values were used to screen prospective

reactions and identify those that were promising enough

to warrant experimental investigation. A large DOD (and

later NASA) program was started in the mid-1950s to

extend the thermodynamic tables to the very high

temperatures involved in rocket engines (as noted, the

data in Selected Values are at room temperature). This

spawned the JANAF (Joint Army-Navy-Air Force)

Thermochemical Tables [2], a publication project in

which many NBS staff members took part. The JANAF

Tables, which are now in their fourth edition [3], have

had a major impact in combustion research and many

other areas of science and engineering; they have consistently been among the best sellers of the NIST Standard

Reference Data program.

Rossini left NBS shortly before the publication of

Circular 500 to become Chairman of the Chemistry

Department at Carnegie Institute of Technology, but the

work was carried on by two of the other authors, Donald

Wagman and William Evans. A full update had been

planned for the early 1960s, but the task proved to be far

greater than expected. An explosion of the literature

reporting new thermodynamic data took place as a

result of greater government funding, an increase in the

number of doctoral students, and, in particular, the

introduction of automated instrumentation for calorimetric measurements. When the Standard Reference

Data program was established at NBS in the mid-1960s,

the thermodynamic tables project was designated the

Chemical Thermodynamics Data Center and became a

cornerstone of the new program. Partial updates to

Circular 500 were issued between 1965 and 1981 in the

NBS Technical Note 270 series [4] as work was

completed on specific parts of the periodic table. Digital

computers became available during this period, which

greatly expedited the process of fitting the reaction data

to obtain the best set of standard state properties, but

considerable human effort was still required to assess

the accuracy of the reported measurements. A complete

revision of Circular 500, entitled The NBS Tables of

Chemical Thermodynamic Properties [5], was finally

published in 1982 as a supplement to the Journal of

Physical and Chemical Reference Data. This book has

become a fixture in chemistry libraries and laboratories,

and even today receives 150 or more citations each year.

The data from The NBS Tables have now been converted

to electronic form and included in the NIST Chemistry

WebBook, which receives heavy use on the NIST

Internet site [6].

Tabulation of thermodynamic data has continued as

an active field at NBS/NIST and has been broadened

from the primarily inorganic thrust of Circular 500

to more complex organic and biochemical substances.

Extensive tables of heat capacity and entropy data

on organic compounds have been published by

94
Eugene Domalski and colleagues. Robert Goldberg has

led a program to evaluate data on the thermodynamics

of enzyme-catalyzed reactions. Several data compilations on aqueous solutions have also appeared.

The data from Circular 500 and its updates and

offspring have circulated widely beyond the original

publications. It is fair to say that most tabulations

of chemical thermodynamic properties in textbooks,

popular handbooks, and online databases have been

extracted from the NBS/NIST publications described

here. More recently, these data have been incorporated

in software packages for engineering design applications and environmental modeling.

Frederick D. Rossini came to NBS in 1928 after

completing his Ph.D. at Berkeley, which was at that time

the leading center for chemical thermodynamics

research in the United States. He established an experimental program at NBS for measuring heats of combustion and other calorimetric properties with high

accuracy. By drawing upon expertise in the Electricity

and Heat Divisions of NBS, he advanced the state of the

art in this type of measurement. His careful attention to

the purification of his samples was another factor in

achieving a new level of accuracy. Many of his measurements of the heat of formation of basic chemical

compounds are still the best available. This high

accuracy in calorimetric measurements provided new

insights into the structure of organic compounds, for

example by giving precise values for the very small

energy differences between different geometric configurations of a complex molecule. Ernest Eliel, a distinguished organic chemist who used Rossini’s data in

studying the conformations of cyclohexane, likened this

feat to measuring the mass of a boat captain by first

weighing the boat with the captain aboard, then weighing it without the captain, and taking the difference [7].

In addition to his contributions to basic chemistry,

Rossini had a keen interest in applying thermodynamics

to industrial processes. In 1934 he became director of a

project on thermodynamic properties of hydrocarbons,

conducted at NBS under sponsorship of the American

Petroleum Institute (API). The measurements on energy

changes in isomerization of hydrocarbons carried out

under this project laid the foundation for improving

petroleum refining methods to give gasoline of higher

quality. He initiated a program to prepare very pure

samples of the pertinent hydrocarbons, which were

widely distributed and used in other laboratories for a

variety of physical measurements. These were, in effect,

Standard Reference Materials, although there was no

formal SRM program at that time. During World War II

this work on hydrocarbons played a critical role in the

development of high octane aviation fuels.

In parallel with his experimental research programs,

he developed an early interest in organizing and systematizing thermodynamic data. In 1936 he published

The Thermochemistry of the Chemical Substances [8],

co-authored by F. R. Bichowsky, a book which was a

precursor to Circular 500. The research program on

hydrocarbons lead to the establishment in 1942 of API

Project 44, under which data sheets were prepared on

the physical and thermodynamic (and later spectral)

properties of hundreds on hydrocarbons and related

compounds. These data were published in 1947 as NBS

Circular 461, Selected Values of Properties of

Hydrocarbons and Related Compounds [9], which

became a basic source of design data for the oil

industry.

After leaving NBS in 1950, Rossini served as

Chairman of the Chemistry Department at Carnegie

Institute of Technology until 1960. While there he

continued to oversee the API tables project, which he

had brought from NBS. This project evolved into the

Thermodynamics Research Center (TRC), under the

direction of Bruno Zwolinski, and later moved to Texas

A&M University. TRC continued to provide data to the

chemical and oil industries and became one of the

affiliated data centers of the NBS Standard Reference

Data program. In an interesting twist, TRC relocated

from Texas A&M to the NIST Boulder Laboratories in

2000, thus coming full circle from its origin at NBS

almost 60 years before as API Project 44.

Rossini himself moved from Carnegie to Notre Dame

in 1960 as Dean of Science and later Vice President for

Research. After his retirement from Notre Dame in

1971, he was given a part-time appointment at Rice

University, where he returned to experimental

measurements of thermodynamic properties. He later

retired to Florida and died in 1990 at the age of 91.

Rossini’s honors included the National Medal of

Science (awarded in 1977), membership in the National

Academy of Science, the Priestly Medal (highest award

of the American Chemical Society), Department of

Commerce Gold Medal, and countless others. He

chaired the Commission on Thermodynamics of the

International Union of Pure and Applied Chemistry

(IUPAC) for 15 years; this service was recognized by

the establishment of the Rossini Lectureship, now

awarded every 2 years to an outstanding thermodynamicist. In the 1960s he was the prime mover in

founding CODATA, the Committee on Data for

Science and Technology of the International Council of

Scientific Unions, and served as its first President from

1966 to 1970. CODATA has proved to be a valuable

forum for the NBS/NIST Standard Reference Data

program; many cooperative projects have been

95
organized under its umbrella, and two SRD Directors,

David Lide and John Rumble, have followed Rossini as

CODATA presidents.

Don Wagman and Bill Evans maintained the high

quality of the NBS work on thermodynamic tables for

another 30 years after Rossini left, culminating in the

publication of the previously mentioned NBS Tables of

Chemical Thermodynamic Properties [5]. Under the

auspices of CODATA they established a fruitful

collaboration with thermodynamicists in the Soviet

Union. This project on Key Values for Thermodynamics

[10], which included contributions from several

other countries as well, led to agreement on an internationally accepted set of values for the properties of

certain key compounds that play a ubiquitous role

in thermodynamic calculations. In addition to the

importance of the standardization effort, the project

promoted significant human contacts between

scientists during some of the most difficult years of the

cold war.

The appearance of Selected Values of Chemical

Thermodynamic Properties established NBS as the

world authority on thermodynamic properties of

chemical substances. This publication and its successors

have had a broad impact on research, education,

and industry. It ushered in a period of 50 years of

NBS leadership in providing reliable thermodynamic data to the scientific and engineering

communities.

Prepared by David R. Lide.

Bibliography

[1] Frederick D. Rossini, Donald D. Wagman, William H. Evans,

Samuel Levine, and Irving Jaffe, Selected Values of Chemical

Thermodynamic Properties, Circular of the National Bureau of

Standards 500, U.S. Government Printing Office, Washington,

DC (1952).

[2] D. R. Stull and H. Prophet, JANAF Thermochemical Tables,

Second Edition, Nat. Stand. Ref. Data Ser., Nat. Bur. Stand.

(U.S.), 37 (1971).

[3] Malcolm W. Chase, Jr., NIST-JANAF Themochemical Tables,

Fourth Edition, J. Phys. Chem. Ref. Data, Monograph 9 (1998).

[4] Donald D. Wagman, William H. Evans, Vivian B. Parker, Iva

Halow, Sylvia M. Bailey, and Richard H. Schumm, Selected

Values of Chemical Thermo-Dynamic Properties, Nat. Bur.

Stand. (U.S.) Tech. Note 270-3 (1968). This included Tech. Note

270-1 (1965) and 270-2 (1966); numbers 4 through 8 in the Tech.

Note 270 series appeared 1969 through 1981.

[5] Donald D. Wagman, William H. Evans, Vivian B. Parker,

Richard H. Schumm, Iva Halow, Sylvia M. Bailey, Kenneth L.

Churney, and Ralph L. Nuttall, The NBS Tables of Chemical

Thermodynamic Properties, J. Phys. Chem. Ref. Data, Vol. 11,

Suppl. 2 (1982).

[6] W. G. Mallard and P. J. Linstrom, eds., NIST Chemistry Web

Book, NIST Standard Reference Database Number 69, National

Institute of Standards and Technology, Gaithersburg MD (1998)

(http://webbook.nist.gov).

[7] E. L. Eliel, Biographical Memoirs, Volume 77, Frederick

Dominic Rossini, 1899-1990, National Academy Press,

Washington, DC (1999).

[8] Francis R. Bichowsky and Frederick D. Rossini, The Thermochemistry of the Chemical Substances, Reinhold Publishing Co.,

New York (1936).

[9] Frederick D. Rossini, Kenneth S. Pitzer, William J. Taylor, Joan

P. Ebert, John E. Kilpatrick, Charles W. Beckett, Mary G.

Williams, and Helene G. Werner, Selected Values of Properties of

Hydrocarbons, Circular of the National Bureau of Standards

461, U.S. Government Printing Office, Washington, DC (1947).

[10] J. D. Cox, D. D. Wagman, and V. A. Medvedev, CODATA Key

Values for Thermodynamics, Hemisphere Publishing Corp., New

York (1989).

96
Applied Inorganic Analysis

The 1929 first edition of Applied Inorganic Analysis

[1] was a classic of its time, commonly referred to as the

“analyst’s bible.” Co-authored by two Chief Chemists of

the National Bureau of Standards, Gustav Ernst Fredrik

Lundell and William Francis Hillebrand, the book represented the authors’ comprehensive knowledge and

broad practical experience. The 1953 second edition [2]

was a thorough revision by Harry Aaron Bright and

James Irvin Hoffman, who were Chief of the Analytical

Chemistry Section and Assistant Chief of the Chemistry

Division, respectively. Both editions of Applied Inorganic Analysis presented critical expositions of the

chemical methods of analysis as applied to a broad

range of complex matrices including metals, alloys,

rocks, minerals, ores, ore concentrates, and glass. Each

of the two editions stood alone as the authoritative

single-volume reference for inorganic analysis for many

years, and even today remains a valuable resource

for pre-instrumental, classical methods of chemical

analysis.

The story of the development of this remarkable book

began in 1878 after the young American chemist

William Francis Hillebrand completed a course in

metallurgy and assaying at the mining academy in

Freiberg, Germany. Fully intent on returning to

America and impressed with the opportunities for

young chemists as assayers, he took this course in order

to supplement the training in mineral analysis that he

had received from Bunsen, under whom he had earned

his Ph.D., magna cum laude, at the University of

Heidelberg, in 1875. Upon returning, he failed to find

suitable work in the East, so he made his way in 1879 to

Leadville, Colorado, where he became the third partner

in a small assaying firm. Samuel F. Emmons, an

occasional customer who was in charge of the Rocky

Mountain Division of the newly formed United States

Geological Survey (USGS), offered Hillebrand a job as

a chemist. Considering this offer to be the opportunity

of a lifetime, he quickly accepted, remaining in the

Denver laboratory of USGS until 1885, when he was

transferred to the Washington USGS laboratory. During

his 28 years at USGS, Hillebrand made more than 400

complete (for that day) analyses of various rock samples

[3].

In 1897 Hillebrand wrote a 50-page introduction to

USGS Bulletin No. 148 [4] on the methods of analysis

of silicate rocks, and this was translated into German

and published in Germany in 1899. In 1900 this

material was rewritten and enlarged to 114 pages and

issued as an independent document, USGS Bulletin

No. 176 [5]. This brought a flock of commendatory

letters, all confirming what L. V. Pirsson said: “We must

now look upon you as the final authority in silicate

analysis.” Another edition, which included the analysis

of carbonate rocks, appeared in 1907 as Bulletin

No. 305 [6]. This also was translated into German. An

expanded edition was published in 1910 as Bulletin

No. 422 [7], and the series culminated in 1919 as

Bulletin No. 700 [8], a book of 285 pages. Even in the

late nineteenth century and early twentieth century, the

problem was not so much the lack of a suitable method

for the final determination of an element as it was

the lack of preceding separation methods that made an

accurate determination possible, an occasional occurrence today. The significance of the analytical methods

in this series of bulletins lay in Hillebrand’s success in

developing a workable separation scheme for materials

as complex as silicate and carbonate rocks.

This book is expected to remain the key

reference work for highly accurate

classical analytical methods, and

although these methods are less commonly practiced today, analytical

chemists will continue to appreciate

the theory, chemical knowledge, and

artistry inherent to their application.

In 1908, Hillebrand became the second Chief

Chemist of the NBS. In 1917 he succeeded in bringing

G. E. F. Lundell from Cornell, where Lundell was an

assistant professor of chemistry. In 1923 Hillebrand and

Lundell together began writing Applied Inorganic

Analysis, a project that Hillebrand had been advised to

do 10 years earlier. A 900-page book was planned in

five parts: I. General Considerations; II. The Determination of the Elements; III. Silicate Rock Analysis; IV.

Carbonate Rock Analysis; and V. Miscellaneous

Methods of Analysis. Parts III and IV were essentially a

reprint of USGS Bulletin 700. The aim of the book

97
throughout was to present analytical methods that would

work in the real world of complex matrices. In the

introduction to the first edition, Lundell stated, “A fair

criticism of much of the work that has been published

on methods for the determination of the elements is that

a great deal is claimed on the basis of experiments that

have been carried out in pure solutions, and very little, if

anything, is said as to how the methods are to be applied

or what results can be expected in analyses of the more

or less complex materials in which the elements are

found. . . . The aim throughout the book therefore has

been to stress the preparation of the solution for the

determination that is to be made, rather than to describe

processes that can be used with certainty only in the

specific applications for which they were devised.” [2]

Herein lies the true greatness of this book. In addition to

the broad range of matrices covered, the separation

methods are discussed and developed in such a way that

the knowledgeable analyst can adapt them to other

complex matrices. Unfortunately, Hillebrand died in

1925 at a time when only about one-third of the book

had been completed. Lundell went on to complete the

book in 1929 using Hillebrand’s detailed notes and his

own already considerable expertise

The second edition of Applied Inorganic Analysis

was begun by Lundell in the late 1930s, at which time

he was the accepted dean of the world’s inorganic

analytical chemists. However, he had not completed the

book at the time of his death in 1950. The job of finishing the second edition was handed over to Harry Aaron

Bright (then Chief of the Analytical Chemistry

Section), and James Irvin Hoffman (then Assistant

Chief of the Chemistry Division). It is indeed fortunate

that the task fell to these two very capable men.

Hoffman came to NBS in 1919 and distinguished

himself with atomic weight determinations and the development of several significant chemical processes

that were essential to the American effort in World War

II. In 1938, he co-authored with Lundell Outlines of

Methods of Chemical Analysis [9], which was intended

as a companion volume to Applied Inorganic Analysis,

and this book became a classic in its own right. Harry

Aaron Bright joined the staff at NBS in 1913 as a

laboratory assistant and worked closely with Lundell

until Lundell retired in 1948. After Lundell’s death,

Bright became the recognized authority for the chemical analysis of metals and alloys in the U.S. Together,

Bright and Hoffman made a thorough revision of the

first edition of Applied Inorganic Analysis, adding

significant new material, much of which had been

developed at NBS by themselves together with R. K.

Bell, R. Gilchrist, J. L. Hague, H. B. Knowles, B. F.

Scribner, J. K. Taylor, and E. Wichers. There was

scarcely a page of the old edition that was not improved

either by the omission of out-of-date material, by the

inclusion of new references and footnotes, or by extensive additions to the text itself. For example, in the

intervening years between the editions, R. Gilchrist had

developed a completely new separation scheme for all

the precious metals in the absence of gold, and this

replaced the separation method of E. Wichers which had

appeared in the first edition. In order to prevent the book

from increasing to an unwieldy size, Part V of the first

edition on the analysis of glass, bauxite, and other refractories was unfortunately omitted.

That the first edition had become a classic was made

plain in the book reviews of the second edition. In his

book review which appeared in the August 1953 issue of

Analytical Chemistry, M. Gilbert Burford commented,

“A new edition of this classic work should be

welcomed by all chemists, and it is evident that the book

will continue to be invaluable.” He went on to say, “The

authors’ hope that ’here and there something helpful in

solving a pressing problem may have been presented’

should prove to be one of the classic understatements of

the year.” [10]. In his book review in the February 1954

issue of The Analyst, L. S. Theobald wrote: “In the

reviewer’s opinion, the work is the best of its kind. It is

one to be used both in the library and at the bench, and

it is indispensable to every chemist engaged in ‘Applied

Inorganic Analysis’.” [11].

The book contains a wealth of durable information

that continues to be relevant today. The basic material in

Parts I and II on sampling and sample preparation has

fundamental importance. Sections 4 and 5 of Part I

contain common and special methods of separation,

employing both inorganic and organic reagents, which

will remain useful in the preparation of samples for

instrumental analysis. The extended discussions in Part

II for each of the elements no doubt will prove to be the

most enduring material in this book. For each element

(or small group of elements), there is a detailed discussion of occurrence, importance, general considerations

of the chemical behavior that are important in its analysis, dissolution procedures for mineral forms of

the element, methods of separation, and methods of

determination.

This book is expected to remain the key reference

work for highly accurate classical analytical methods,

and although these methods are less commonly practiced today, analytical chemists will continue to appreciate the theory, chemical knowledge, and artistry

inherent to their application. Applied Inorganic Analysis

will continue to be a clear window on the past, providing

98
detailed discussions and procedures for those needing to

perform classical analytical determinations. Those

fortunate enough to own a copy have a masterpiece and

a treasure.

Prepared by Charles M. Beck II.

Bibliography

[1] W. F. Hillebrand and G. E. F. Lundell, Applied Inorganic Analysis, John Wiley & Sons, New York (1929).

[2] W. F. Hillebrand, G. E. F. Lundell, H. A. Bright, and J. I.

Hoffman, Applied Inorganic Analysis, Second Edition, John

Wiley & Sons, New York (1953).

[3] W. F. Hillebrand, A Plea for Greater Completeness in Chemical

Rock Analysis, J. Am. Chem. Soc. 16, 90-93 (1894).

[4] W. F. Hillebrand, Some Principles and Methods of Analysis

Applied to Silicate Rocks, in Analyses of Rocks with a Chapter

on Analytical Methods, Laboratory of the United States

Geological Survey, 1880-1896, Frank Wigglesworth Clarke and

W. F. Hillebrand, U.S. Geological Survey Bulletin, No. 148

(1897) pp. 15-64.

[5] W. F. Hillebrand, Some Principles and Methods of Rock Analysis,

U. S. Geological Survey Bulletin, No. 176 (1900).

[6] W. F. Hillebrand, The Analysis of Silicate and Carbonate Rocks,

U. S. Geological Survey Bulletin, No. 305 (1907).

[7] W. F. Hillebrand, The Analysis of Silicate and Carbonate Rocks:

A Revision of Bulletin 305, U.S. Geological Survey Bulletin 422,

(1910); slightly revised when reprinted in 1916.

[8] W. F. Hillebrand, The Analysis of Silicate and Carbonate Rocks:

A Revised and Enlarged Edition of Bulletin 422, U.S. Geological

Survey Bulletin 700 (1919).

[9] G. E. F. Lundell and James Irvin Hoffman, Outlines of Methods

of Chemical Analysis, John Wiley & Sons, New York (1938).

[10] M. Gilbert Burford, review of Applied Inorganic Analysis,

Second Edition, by W. F. Hillebrand, G. E. F. Lundell, H. A.

Bright, J. I. Hoffman, Anal. Chem. 25, 1279-1280 (1953).

[11] L. S. Theobald, review of Applied Inorganic Analysis, Second

Edition, by W. F. Hillebrand, G. E. F. Lundell, H. A. Bright, J.

I. Hoffman, Analyst (Cambridge, UK) 79, 113-115 (1954).

99
The Diamond Anvil Pressure Cell

Two intimately related scientific and technological

achievements occurred in the field of high pressure

research at the NBS laboratory during the second-half

of the 20th century: the invention of the diamond anvil

high pressure cell [1] in 1958 and the development of the

optical ruby fluorescence method of pressure measurement [2] in 1972. These two developments

together stimulated the profound advances in high

pressure research that evolved in the latter part of the

20th century.

The invention of the diamond anvil high pressure cell

(DAC) took place in the Constitution and Microstructure

Section (then headed by H. F. McMurdie) of the Mineral

Products Division (Irl C. Schoonover, Chief) in the late

1950s at the NBS laboratories in Washington. It was the

product of the joint effort of four individuals, Charles E.

Weir, Alvin Van Valkenburg, Ellis R. Lippincott, and

E. N. Bunting. Each of these scientists contributed a

separate and distinct expertise which, when combined

with the others, provided the impetus necessary for the

development of the new pressure cell. Weir had developed an intense interest and appreciation for the effect of

high pressure on the properties and structure of materials through his construction of a device to study porosity

of leather and the compressibility of teflon and other

materials. For this work, he received the Department of

Commerce Silver Medal in 1954. Van Valkenburg had

designed a high-temperature furnace for the synthesis

and growth of mica, but he also utilized a tetrahedral

anvil press for the synthesis of diamonds. Bunting

studied phase equilibria and electrical properties of

ceramic oxide systems. Lippincott, a guest scientist from

the University of Maryland, collaborated with these

individuals on measurement of infrared spectra of

inorganic materials. He had a special interest in shortrange interatomic forces and the perturbing effects of

neighboring atoms on each other—effects that would be

amplified by the change in lattice spacing produced

by high pressures. The presence of all four of these

individuals in the same laboratory space enabled a

fruitful exchange of ideas that eventually led to the

concept of a miniature high pressure device with an

optical access permitting the measurement of infrared

absorption spectra.

The DAC conceived in this setting [1] was a lever-arm

type device with a 180 optical transmission path which

permitted, for the first time, the infrared spectroscopic

measurements on powders squeezed between two

opposed diamond anvils. Among the first materials

studied were NaNO3, KNO3, AgNO3, ferrocene, ice, and

CaCO3. These initial studies demonstrated that

pressure-dependent shifts in frequency and changes in

intensity of infrared absorption bands could be

measured, and also led to the observation of large

changes in spectra as a result of pressure-induced phase

transitions. This NBS instrument was the prototype for

all subsequent opposed-anvil diamond cells with 180

optical transmission.

The first cell was handmade by Charles E. Weir, who

fabricated it utilizing only a lathe, drill press, hack saw,

soldering gun, threading tools, files, and a high speed

grinding wheel to polish down the culets of the

diamonds to form anvil faces. The gem diamonds were

obtained by Alvin Van Valkenburg from the General

Services Administration, which, at that time, served as

the custodian for contraband diamonds confiscated from

smugglers by government agents. In those days, such

diamonds were free for use by other government agencies, provided that their purpose could be justified. It is

of interest to note that without the availability of these

gratis gem diamonds, it is probable that the DAC would

not have been developed as rapidly as it was, because

during the early stages of its development many

diamond anvils were destroyed in the testing process.

Fig. 1. The original DAC, on display in the NIST Museum.

100
To replace them would have been prohibitively expensive. The original instrument, small enough to fit in the

palm of one’s hand, can be seen today on display in the

NIST Museum.

By 1971, the DAC had undergone several stages of

refinement and had been adapted to other measurement

techniques by NBS and various other laboratories in the

United States. Still, it was not fully appreciated as a

scientific instrument because there remained a very significant problem. There was no convenient, precise

method for determining the pressure being exerted on

the sample in the diamond anvil cell. Pressures had

either to be calculated (force per unit area) or measured

from compression data (utilizing an equation of state,

e.g., of sodium chloride) obtained by an x-ray powder

diffraction method. However, the former procedure was

very inaccurate, and the latter, although more accurate,

was tedious and time consuming, often requiring as

much as fifteen hours to make one pressure determination. Consequently, in 1970, acceptance of the DAC as a

tool in high pressure research was somewhat limited. It

was used primarily in laboratories engaged in research

of geological interest where very high pressures simulating the earth’s interior were desired, while the accuracy

in the value of the pressure was not yet of primary

importance.

In 1971, this situation changed dramatically. The high

pressure group at NBS was under the ever-present prodding of management to develop a better method for

measuring pressures in the DAC. The problem was discussed one day in the NBS cafeteria among John (Jack)

B. Wachtman, Jr., Chief of the Inorganic Materials

Division, Stanley Block, Chief of the Crystallography

Section, and Dean Barnett, a guest scientist at NBS on

sabbatical leave from Brigham Young University. While

they were having lunch together, the table conversation

turned to possible techniques for measuring pressure.

Wachtman suggested various methods, all of which had

been considered already and found to be unsuitable.

Finally, Wachtman asked the pivotal question, “Have

you considered fluorescence spectroscopy?” As it

happened, they had not, but replied that they would look

into it. Encouraged by this meeting, Stanley Block,

Dean Barnett, Gasper Piermarini, and Richard Forman

began to study the pressure-dependence of several

fluorescing materials. Some of these materials happened to be on the shelves in Forman’s spectroscopy

laboratory, while others were obtained from H. S. Parker

and W. S. Brower of the Solid State Chemistry Section.

Those materials included ruby (Al2O3), YAlO3, YAG,

MgO, and a few others. While several materials had a

readily observable pressure dependence, ruby exhibited

Fig. 2. Charles Weir, ca. 1960. Fig. 3. A. Van Valkenburg, 1962.

101
by far the most promising results. Ruby’s main fluorescence lines (the R-line doublet lines) were intense and

sharp, and the lines shifted toward the red end of the

spectrum with increasing pressure. Significantly, pressure could be detected in situ using only a very small

amount of ruby crystal (comprising only 1 % of the

available volume) as the internal pressure sensor.

Further, because ruby is chemically inert, it could be

present in the sample chamber to detect pressure without interfering with any other experimental specimen in

the chamber.

Recognizing the significance of these observations, it

was of paramount importance to calibrate the R-line

shift against reliable pressure values. This calibration

was accomplished at NBS [3] using an x-ray powder

diffraction method to measure the compression of NaCl

and relating this to the measured shift in the wavelength

of the ruby R1-line. The corresponding pressure was

calculated from the compression data utilizing an established equation of state for NaCl. The R1-line shift was

found to be linear with pressure (2.7400.016 kbar

Å–1 up to about 19.5 GPa. In subsequent work [4], the

linearity was confirmed to about 29 GPa. The success

of this calibration quickly established the ruby scale as

a secondary pressure standard, and it became the de

facto standard for measuring pressures in a DAC.

Fig. 4. A schematic diagram of the opposed diamond anvil assembly

to illustrate the 180 optical transmission characteristics and the

concept of Bridgman opposed anvils. A thin metal gasket containing

a 250 m diameter hole for encapsulating a sample (liquid or solid or

both) is squeezed between the two anvils.

Fig. 5. Gasper Piermarini and Stanley Block by the ruby fluorescence apparatus used with

the DAC, ca. 1984.

102
In the years following the introduction of the DAC and

the ruby pressure standard, numerous breakthroughs in

high pressure research and technology were achieved at

the NIST/NBS laboratory. Milestones or “firsts” were

achieved in several areas, including the generation of

ultrahigh pressures through improvements in the design

of the original NBS DAC [4]; the development of a

camera for obtaining x-ray powder diffraction data at

high pressure [5]; the measurement of hydrostatic limits

in pressure-transmitting media utilizing the ruby

method [6]; the introduction of a metal gasket to encapsulate liquids and other materials under pressure

between the diamond anvils [7]; the development of the

methodology for determining crystal structures at high

pressure in the DAC from single crystal x-ray diffraction

intensity data (first application: growth and structure of

a single crystal of ice VI) [8]; the application of the DAC

to Raman spectroscopy [9]; and the measurement of the

viscosity of liquids at ultrahigh pressures in the DAC by

the classical Stokes method [10].

In 1974, Block and Piermarini were awarded the

Department of Commerce Gold Medal for their work on

the design, construction, and application of the high

pressure system, including the diagonal pressure cell,

the ruby fluorescent method of pressure measurement, and associated characterization techniques. These

achievements ignited and fueled an explosion of activity

in high pressure research by laboratories throughout

the world, a profuse activity that continues unabated

today.

Prepared by Gasper Piermarini and Stanley Block.

Bibliography

[1] C. E. Weir, E. R. Lippincott, A. Van Valkenburg, and E. N.

Bunting, Infrared Studies in the 1- to 15-Micron Region to

30,000 Atmospheres, J. Res. Natl. Bur. Stand. 63A, 55-62

(1959).

[2] R. A. Forman, G. J. Piermarini, J. D. Barnett, and S. Block,

Pressure Measurement Made by the Utilization of Ruby SharpLine Luminescence, Science 176, 284-285 (1972).

[3] G. J. Piermarini, S. Block, J. D. Barnett, and R. A. Forman,

Calibration of the Pressure Dependence of the R1 Ruby Fluorescence Line to 195 kbar, J. Appl. Phys. 46, 2774-2780 (1975).

[4] G. J. Piermarini and S. Block, Ultrahigh Pressure DiamondAnvil Cell and Several Semiconductor Phase Transition Pressures in Relation to the Fixed Point Pressure Scale, Rev. Sci.

Instrum. 46, 973-979 (1975).

[5] G. J. Piermarini and C. E. Weir, A Diamond Cell for X-ray

Diffraction Studies at High Pressures, J. Res. Natl. Bur. Stand.

66A, 325-331 (1962).

[6] G. J. Piermarini, S. Block and J. D. Barnett, Hydrostatic Limits

in Liquids and Solids to 100 kbar, J. Appl. Phys. 44, 5377-5382

(1973).

[7] Alvin Van Valkenburg, Visual Observations of High Pressure

Transitions, Rev. Sci. Instrum. 33, 1462 (1962).

[8] S. Block, C. E. Weir, and G. J. Piermarini, High-Pressure

Single-Crystal Studies of Ice VI, Science 148, 947-948 (1965).

[9] B. A. Weinstein and G. J. Piermarini, Raman Scattering and

Phonon Dispersion in Si and GaP at Very High Pressure, Phys.

Rev. B 12, 1172-1186 (1975).

[10] G. J. Piermarini, R. A. Forman and S. Block, Viscosity Measurements in the Diamond Anvil Pressure Cell, Rev. Sci. Instrum. 49,

1061-1066 (1978).

Fig. 6. The R-line luminescence spectrum of ruby in the DAC: curve

A, ruby at ambient atmospheric pressure; curve B, ruby in a mixture

of ices VI and VII at about 2.2 GPa; curve C, ruby in a nonhydrostatic

mixture of CCl4 III and IV at about 4 GPa.

103
Polymer Crystallization With Folded Chains

The Hoffman-Lauritzen theory of the formation of

polymer crystals with folded chains, set forth four

decades ago [1,2,3], owes its origin to the discovery in

1957 [4,5,6] that characteristically thin single crystals of

polyethylene can be grown from dilute solutions. These

crystals are thin platelets or lamellae, typically about

10 nm thick. As first proposed by Keller of the University of Bristol (UK) in his seminal paper [5], the long

polymer chains are more or less regularly folded between the upper and lower lamella surfaces with the

chain stems between successive folds oriented preferentially normal to the plane of the lamellae. Following

very shortly after this discovery was the realization that

lamellar crystals of polymers other than polyethylene

also exhibited chain folding. More than that, chain folding was an essential feature of the crystallization of

polymers from the molten state. In the latter case, polymers were found to undergo spherulitic crystallization,

but the spherulites were composed of radiating structural units that were found to be lamellar and bore a

kinship to solution grown crystals. In short, following

the events of 1957, it was evident that a theory was

needed to explain the then startling occurrence of

chain folding and its general effects on polymer crystallization.

In 1961 and 1962 [1,2] Hoffman and Lauritzen

presented their theory for the formation of chain-folded

crystals based on surface nucleation concepts. Hoffman

had visited Keller in Bristol earlier (in 1959) and had

discussed the subject with him. Returning from the UK

by air (traveling via the Azores because of a storm in

the North Atlantic), Hoffman began to develop certain

aspects of the theory. (The authors later joked that this

was likely the only theory germinated between the

Azores and New York that year). In their two papers,

Hoffman and Lauritzen established the foundation of the

kinetic theory of polymer crystallization from solution

[1] and from the melt [2], paying particular attention to

the energetics of the formation of chain-folded nuclei.

Definite predictions were given under certain assumptions concerning the experimentally observed variation

in lamellar thickness with crystallization temperature,

the metastability and the melting point of lamellae, and

the temperature dependence of the kinetics of crystallization rate. As the theory was extended, it began to

receive attention and experimental support at NBS

and elsewhere. In 1971, Hoffman and Lauritzen

were awarded the High Polymer Physics Prize of the

American Physical Society. The citation read in part

“for their Kinetic Theory of Polymer Crystallization.”

The theory was presented in a book chapter [3] in

which Hoffman and Lauritzen benefitted substantially

from the participation of G. T. Davis. The chapter was

written at the behest of N. B. Hannay, who was then vice

president of research at Bell Telephone Laboratories,

where a number of scientists were working in the field

of polymer physics and polymer crystallization in particular. In this chapter, the treatment of chain-folded crystallization was further extended and organized, and the

extended work was applied to various polymers covering

such topics as spherulite growth rate, the crystallization

temperature dependence of the lamellar thickness, as

well as the thermodynamic properties of chain-folded

crystals. The chapter is especially notable in that it has

been used extensively for teaching purposes.

From time to time since the original papers, other

NBS personnel have been involved in the ‘chain-folding’

venture. Noteworthy contributions, mostly but not

entirely experimental, were made by J. J. Weeks, G. S.

Ross, L. Frolen, F. Gornick, and F. Khoury, and significant theoretical developments were made by E. A.

Di Marzio, C. M. Guttman, E. Passaglia, and I. C.

Sanchez. Further, from the broad perspective of the

NBS/NIST history, it may be noted that research on

polymer crystallization at NBS preceded by many years

the discovery of chain folding. The long tradition of

research on crystallizable polymers is exemplified by

the pioneering works of L. A. Wood and N. Bekkedahl

in the later 1930s and 1940s [7] and L. Mandelkern in

the 1950s [8].

John Hoffman received his B.S. degree in chemistry

in 1942 from Franklin Marshall College and his Ph.D. in

physical chemistry in 1949 from Princeton University.

He participated in the Manhattan Project (1944-1946,

while in U. S. Army) and subsequently (1949-1954) was

in the R&D branch of General Electric. In 1954,

Hoffman joined NBS as a Research Chemist, becoming

Chief of the Dielectrics Section in 1957 and Chief of the

Polymers Division in 1964. From there, he advanced to

Director of the Institute for Materials Research (1967-

1978) and then Director of the National Measurement

Laboratory (1978-82 ). Hoffman retired from NBS in

1982, but continued his career as Professor at the

University of Maryland (1982-1985), Director and CEO

of the Michigan Molecular Institute (1985-1990), and as

Research Professor in the Department of Materials

104
Science and Engineering at Johns Hopkins University

(1990-present). Throughout his career, he has received

numerous awards, including the Soldiers Medal

(military decoration, 1946), the U. S. Department of

Commerce Gold Medal (1965), the Samuel Wesley

Stratton Award of NBS (1967), and election to the

National Academy of Engineering (1980).

John Lauritzen, Jr. received an A.B. in mathematics

in 1949 (University of Miami, Ohio) and a Ph.D. in

physics in 1955 (California Institute of Technology).

He came to NBS as a physicist in the Electricity Division in 1956, before joining the Polymers Division in

1964. In 1968, he was appointed Senior Scientist, NBS

Institute for Materials Research, a post he held until his

death (October 11, 1976). His research included the

theory of polymer crystallization, dielectric relaxation

in molecular compounds, statistical mechanics, and

multi-component rate theory. His distinguished career

was acknowledged in receiving the Samuel Wesley

Stratton Award with E. Di Marzio and E. Passaglia in

1971.

G. T. (Tom) Davis received his B. Chem. Eng. in 1956

from Cornell University and his Ph.D. in physical

chemistry in 1963 from Princeton University. In his

early work, he was a research chemist in the Chemical

Research Division, Esso Research and Engineering Co.

(1956-1960) and an Assistant Professor of Chemistry at

the University of Virginia (1963-1964). In 1964-1966,

he was awarded an NRC-NSF Post Doctoral Fellowship

at NBS and, two years later, he was appointed a

research chemist in the Polymers Division of NBS.

He advanced to the position of Group Leader in the

Polymers Division in 1984 and served in that position

until 1998, before retiring in 1999. For his meritorious

work in polymer science and engineering, he was

awarded the U. S. Department of Commerce Bronze

Medal in 1980.

Prepared by Freddy Khoury in consultation with John

Hoffman and Tom Davis.

Fig. 1. John Hoffman, 1961.

Fig. 2. John Lauritzen, 1961.

105
Bibliography

[1] John I. Lauritzen, Jr. and John D. Hoffman, Theory of Formation

of Polymer Crystals with Folded Chains in Dilute Solution, J. Res.

Natl. Bur. Stand. 64A, 73-102 (1960).

[2] John D. Hoffman and John I. Lauritzen, Jr., Crystallization

of Bulk Polymers With Chain Folding: Theory of Growth of

Lamellar Spherulites, J. Res. Natl. Bur. Stand. 65A, 297-336

(1961).

[3] John D. Hoffman, G. Thomas Davis, and John I. Lauritzen, Jr.,

The Rate of Crystallization of Linear Polymers With Chain

Folding, Chapter 7 in Treatise on Solid State Chemistry: Vol. 3:

Crystalline and Noncrystalline Solids, N. B. Hannay (ed.), Plenum

Press, New York (1976) pp. 497-614.

[4] P. H. Till, Jr., The Growth of Single Crystals of Linear

Polyethylene, J. Polym. Sci. 24, 301-306 (1957).

[5] A. Keller, A Note on Single Crystals in Polymers: Evidence for a

Folded Chain Configuration, Philos. Mag., Ser. 8, 2, 1171-1175

(1957).

[6] E. W. Fischer, Stufen- und spiralfo ̈rmiges Kristallwachstum bei

Hochpolymeren, Z. Naturforsch. 12a, 753-754 (1957).

[7] Lawrence A. Wood and Norman Bekkedahl, Crystallization of

Unvulcanized Rubber at Different Temperatures, J. Res. Natl. Bur.

Stand. 36, 489-510 (1946).

[8] L. Mandelkern, Crystallization Kinetics in Polymeric Systems, in

Growth and Perfection of Crystals (Proceedings of an International Conference on Crystal Growth held in Cooperstown,

New York, August 1958), R. H. Doremus, B. W. Roberts, and D.

Turnbull (eds.), John Wiley and Sons, New York (1958) pp. 467-

595.

106
Cryogenic Engineering

Cryogenic Engineering by Russell B. Scott [1] was

written between 1955 and 1959 as a text book, reference

book, and data book. It covered liquefaction and separation of gases; thermometry; instrumentation; thermal

insulation; storage, transport, and transfer of liquids;

and properties of fluids and solids. It contains the best

detailed description of the liquefier project that

was conducted in the early 1950s at the NBS Boulder

Laboratories. The book has been reprinted several

times, most recently in 1995, and more than 6000 copies

have been sold.

The NBS cryogenics program started in 1904 when

Congress appropriated funds to purchase the two-literper-hour hydrogen liquefier exhibited at the St. Louis

World’s Fair by the British Oxygen Company. It was

rarely used until 1925, when F. G. Brickwedde, and later

Russell Scott, started producing liquid hydrogen for

research and as a coolant to liquefy helium. In the early

1930s, Harold C. Urey of Columbia University set out to

prove experimentally the existence of an isotope of

hydrogen which we now call deuterium. As described

elsewhere in this volume, he asked Brickwedde to

liquefy hydrogen and, by distillation, to concentrate

isotopes for spectroscopic analysis. Urey found deuterium present in the sample [2] and was awarded the

Nobel Prize. In 1934, Scott, Brickwedde, Urey, and

Wahl [3] published the hydrogen ortho/para uncatalysized conversion rates, and in 1948, Woolly, Scott, and

Brickwedde [4] published a compilation and critical

evaluation of the thermal properties of the isotopes of

hydrogen.

In the 1940s, the emphasis in the field of cryogenics

changed dramatically from research to engineering,

which stimulated great improvements in system performance. Some of the engineering applications that

evolved over the next decades included storage and

shipment of gases such as oxygen, nitrogen, hydrogen,

helium, and natural gas in liquid form; production of

oxygen for making steel; rocket and aircraft fuels;

energy transport and storage; electronics; and facilities

for high-energy physics. NBS was one of the few U.S.

laboratories with equipment, personnel, and experience

to meet the national need for information and data.

During World War II, Brickwedde and Scott participated in the Manhattan Project [5], measuring the

thermodynamic properties of materials used in the

atomic bomb, including uranium. After the war,

Brickwedde became a consultant on cryogenics at the

Los Alamos Scientific Laboratory (LASL), working

with Edward Hammel and members of the LASL

cryogenic group. NBS Director Edward U. Condon,

who had played a part in the work at Los Alamos during

the war, wanted to expand NBS research in atomic and

nuclear physics and encouraged Brickwedde to facilitate

collaboration with LASL.

When President Truman authorized the design and

testing of a hydrogen bomb in 1950 to counter a threat

from the Soviet Union, the U.S. Atomic Energy

Commission, through LASL Director Norris Bradbury,

asked NBS to participate. He requested that NBS build

a large hydrogen-liquefaction plant; set up and run a

hydrogen/deuterium electrolysis plant; test prototype

dewars for Los Alamos; assist MIT and Arthur D. Little

Company (ADL) in the design and construction of

dewars and refrigerators; test hydrogen transport

dewars; and train personnel in large-scale hydrogen

production and hydrogen handling.

Russell Scott, assisted by William Gifford, Victor

Johnson, and Dudley Chelton, designed and built

the critical components (heat exchangers and gas

purifiers) for four 320 L/h hydrogen/deuterium

liquefiers in the NBS shops in Washington. The NBS

staff quickly expanded to include Bascom Birmingham,

Richard Kropschot, Douglas Mann, Robert Powell,

Robert Jacobs, Leon Wagner, and Peter Vander Arend.

In 1950, the City of Boulder gave NBS a 28-acre

site for relocation of the Central Radio Propagation

Laboratory and, later, other NBS units from

Washington. Under NBS direction, Stearns Roger

Engineering erected two of the liquefiers in Boulder.

The third liquefier was erected by Holmes and Narver

on the Eniwetok Atoll, site of an upcoming nuclear test,

under the direction of Herrick Johnston of Ohio

State University, with assistance from George Freeman

and Leon Wagner of NBS. The fourth liquefier was used

for spare parts.

In order to obtain deuterium, two water electrolyzers

were installed in Boulder, heavy water was imported

from Canada, and work was begun to produce

deuterium gas needed for the upcoming nuclear test.

The deuterium was compressed into high-pressure tanks

and shipped to the atomic proving station on Eniwetok

in the Marshall Islands where it was condensed using

the NBS liquefier.

107
The thermonuclear device was designed at Los

Alamos [6]. Liquid hydrogen used to test the components was safely transported from where it was produced in Boulder to Los Alamos in dewars designed

and built by the Cambridge Corporation. Because of

program priorities, the Cambridge Corporation and

LASL took on the primary responsibility for the design

and testing of the dewars. In March and April 1952,

Herrick Johnston and his staff visited Boulder to participate in liquefier operation as part of the preparation for

assembling and operating the liquefier on Eniwetok. On

November 1, 1952, the Eniwetok Atoll was evacuated of

all personnel, and the “ivy MIKE” shot was detonated.

It was the first hydrogen thermonuclear device and was

regarded as extremely successful, yielding 10.4 megatons of TNT equivalent and providing scientific data for

future tests and development of weapons. The liquefier

described in Scott’s book played a critical role in the

success of this test.

In 1953, the NBS staff (Brickwedde, Scott, Baird,

Birmingham, Chelton, Freeman, Gifford, Goddard,

Johnson, Kropschot, Powell, and Vander Arend) were

awarded the Department of Commerce Gold Medal for

“The design, construction and operation of large and

unique hydrogen and nitrogen liquefiers.”

As the need for cryogenics in nuclear testing diminished, the NBS cryogenics facilities, led by Russell

Scott, turned attention to a growing national need for

scientists and engineers to be trained in cryogenics, as

well as to the measurement and collection of very low

temperature data. Scott organized the Boulder staff into

discipline-oriented groups to provide the data necessary

for cryogenic design. These groups included Thermodynamic Properties of Cryogenic Fluids; Mechanical

and Thermal Properties of Solids; Instrumentation

(thermometry, liquid level, pressure); Systems (liquefaction and refrigeration, fluid flow, dewar design, distillation); Data Center (compilation, critical evaluation and

dissemination of data); and Production of Cryogenic

Fluids (hydrogen, helium, nitrogen).

Scott was committed to on-going training, and in

1954 he initiated the first Cryogenic Engineering

Conference (CEC) in Boulder, which attracted more

than 400 participants. The technical papers were

Fig. 1. The Cryogenics Building at the NBS Boulder Laboratories was the first ever designed specifically for cryogenic-engineering research.

Photograph from NBS Archives, taken in 1968.

108
published in the first volume of Advances in Cryogenic

Engineering (ACE). Since then there have been a total

of 40 CEC conferences with commensurate ACE publications involving an estimated 25,000 participants.

An entire generation of engineers and scientists has

used Scott’s Cryogenic Engineering, which not only

outlines fundamentals, but also includes detailed design

principles and techniques. It was the first of its kind and

is still considered an important reference today. The

book begins with a description of how fluids are liquefied and gas mixtures are separated. The examples

illustrate the basics of design and operation for all types

of cryogenic equipment. Thermometry is fundamental

to all of cryogenics. The book includes a discussion of

temperature scales and temperature measurements, as

well as guidance on how to avoid common errors when

making these measurements. It continues with a discussion of representative technology including heat

exchangers, valves, transfer lines, expansion engines,

and insulation technology—since once gases are liquefied, they are ready for transfer, storage, and transport.

Both tables and graphs are used to illustrate typical

thermal insulations. The small heats of vaporization

coupled with relatively large temperature differences

warrant sophisticated insulations. These insulations

almost always require double-walled high vacuum

designs. The vacuum space is often filled with

low-density powder or multilayers of radiation-reflecting material. The thermodynamic properties of cryogenic fluids—helium, hydrogen, neon, nitrogen, and

oxygen—are presented graphically. The book also includes data on the thermal and mechanical properties of

some of the more widely used structural materials. Each

chapter cites references to handbooks and review

articles that are fundamental to cryogenic research. In

the preface, Scott acknowledged the assistance of NBS

staff members who contributed to the preparation of the

book and who helped establish NBS as a world-class

research facility and a national resource.

In 1960, Scott was invited by the director of the

UCLA Engineering Extension Division to teach a twoweek short course using Cryogenic Engineering as the

text. Assisted by R. H. Kropschot, Scott presented his

first course in December 1960. The UCLA course was

taught annually for more than 35 years by a variety of

instructors from the NBS Boulder Laboratories. Other

courses followed in Boulder, at various NASA facilities,

universities, National Laboratories, and other institutions. Over the years, an estimated 5,000 students have

taken these NBS-initiated short courses. In 1967, Scott

received the Department of Commerce Gold Medal for

Exceptional Service for “Exceptional Leadership

and Meritorious Authorship in the Development of

Cryogenic Engineering.”

Fig. 2. Russell B. Scott (second from right) receives gift at his retirement in 1965. The presentation is being made

by (from left to right) F. G. Brickwedde (Pennsylvania State University), former Director Edward U. Condon

(NBS), Division Director B. W. Birmingham (NBS), Associate Director Edward Hammel (LASL), and Director

Allen Astin (NBS). Photograph from NBS Archives.

109
Scott’s legacy is more than a book and the organization that he helped to build at NBS. Members of his staff

participated in all the major U.S. cryogenic engineering

programs for more than 25 years. Some examples of his

legacy may be mentioned. In his Nobel acceptance

speech, Luis Alvarez (University of California, Berkeley) acknowledged the work of Chelton, Mann, and

Birmingham for design contributions to the Lawrence

Berkeley Laboratory hydrogen bubble chamber. NBS

programs funded by NASA supported Centaur, the first

hydrogen/oxygen space vehicle; storage of hydrogen

and oxygen for fuel cells and breathing oxygen; hydrogen/oxygen safety; fluid and solid properties; instrumentation; and fluid flow. Measurements, compilation,

and critical evaluation of the thermodynamic properties

of fluids by NBS scientists (Corruccini, Goodwin,

McCarty, Strobridge, Roder, Diller, Weber, and

Younglove) have fulfilled governmental and industrial

requirements for engineering design. They assisted in

the design and construction of the NASA hydrogen

liquefiers (the Bear Plants—Baby, Mama, and Papa);

design of high energy physics accelerators and detectors; and the formulation of LNG safety procedures. A

data book describing safety regulations and thermodynamic properties [7] was developed for the liquefiednatural-gas (LNG) industry. And finally, one of Scott’s

legacies most often cited is that of technology transfer,

which has had a wide impact as former NBS employees

move into new positions in industry and academia.

Russell B. Scott was born in Ludlow, Kentucky, on

April 17, 1902. He received his B.S. (1926) and M.S.

(1928) in physics from the University of Kentucky and

joined NBS immediately afterward. He was Director of

the Boulder Cryogenics Laboratory from 1952 to 1962

and Director of NBS Boulder Laboratories from 1962 to

1965. He died September 24, 1967 in Boulder.

Prepared by Richard H. Kropschot.

Bibliography

[1] Russell B. Scott, Cryogenic Engineering, D. Van Nostrand Co.,

Princeton, New Jersey (1959); reprinted Oct. 1959, Aug. 1960,

May 1962, and in 1995.

[2] H. C. Urey, F. G. Brickwedde, and G. M. Murphy, A Hydrogen

Isotope of Mass 2, Phys. Rev. 39, 164-165 (1932).

[3] R. B. Scott, F. G. Brickwedde, Harold C. Urey, and M. H. Wahl,

The Vapor Pressures and Derived Thermal Properties of Hydrogen and Deuterium, J. Chem. Phys. 2, 454-464 (1934).

[4] Harold W. Woolley, Russell B. Scott, and F. G. Brickwedde, Compilation of Thermal Properties of Hydrogen in Its Various Isotopic

and Ortho-Para Modifications, J. Res. Natl. Bur. Stand. 41, 379-

475 (1948).

[5] Richard Rhodes, The Making of the Atomic Bomb, Simon and

Schuster, New York (1986).

[6] Richard Rhodes, Dark Sun: The Making of the Hydrogen Bomb,

Simon and Schuster, New York (1995).

[7] Douglas B. Mann, LNG Materials and Fluids: A User’s Manual of

Property Data in Graphic Format, NBS Cryogenics Division,

National Bureau of Standards, Boulder, Colorado (1977).

110
Reversal of the Parity Conservation Law

in Nuclear Physics

In late 1956, experiments at the National Bureau of

Standards demonstrated that the quantum mechanical

law of conservation of parity does not hold in the beta

decay of 60Co nuclei. This result, reported in the paper

An experimental test of parity conservation in beta

decay [1], together with ensuing experiments on parity

conservation in -meson decay at Columbia University,

shattered a fundamental concept of nuclear physics that

had been universally accepted for the previous 30 years.

It thus cleared the way for a reconsideration of physical

theories, especially those relating to symmetry, and led

to new, far-reaching discoveries regarding the nature

of matter and the universe. In particular, removal of

the restrictions imposed by parity conservation first

resolved a serious conflict in the theory of subatomic

particles, known at the time as the tau-theta puzzle, and

later led to a fuller understanding of the strong, electromagnetic, and weak interactions. The better understanding of their characteristics has led to a more unified

theory of the fundamental forces.

The beta-decay experiments were carried out by

C. S. Wu of Columbia University in collaboration with

NBS staff members Ernest Ambler, Raymond W.

Hayward, Dale D. Hoppes, and Ralph P. Hudson. The

Bureau’s low temperature laboratory was chosen for the

experiments because of its millikelvin-region research

capability [2] and the staff"s experience in the spatial

orientation of atomic nuclei [3], an essential feature of

the beta-decay study.

Basically, parity conservation in quantum mechanics

means that two physical systems, one of which is a

mirror image of the other, must behave in identical

fashion. In other words, parity conservation implies that

Nature is symmetrical and makes no distinction between

right- and left-handed rotations, or between opposite

sides of a subatomic particle. Thus, for example, in

beta decay there should be no preferential direction of

emission with respect to the direction of the spin of the

emitting nucleus, i.e., no (nuclear) spin—(electron)

momentum correlation.

Since 1925, physicists had accepted the principle that

parity is conserved in all types of interactions. During

the 1950s, however, phenomena were found in highenergy physics that could not be explained by existing

theories. The available accelerators produced a variety

of subatomic particles. One such particle is the shortlived K meson emitted in the collision of a high-energy

proton with an atomic nucleus. The K meson seemed to

arise in two distinct versions, one decaying into two 

mesons, the other decaying into three pions, with the

two versions being identical in all other characteristics.

A mathematical analysis showed that the two-pion and

the three-pion systems have opposite parity; hence,

according to the prevalent theory, these two versions of

the K meson had to be different particles.

Early in 1956, T. D. Lee of Columbia University

and C. N. Yang of the Institute for Advanced Study,

Princeton University, made a survey [4] of experimental

information on the question of parity. They concluded

that the evidence then existing neither supported nor

refuted parity conservation in the “weak interactions”

responsible for the emission of beta particles, K-meson

decay, and such. They thus proposed that the K-meson

itself may have definite parity, and the observed opposite parity of the two systems of decay products may be

the manifestation of parity non-conservation in its

decay. They suggested that parity may not be conserved

in weak interactions, saw that there was no experimental

evidence that proved that this was or was not true, and

proposed a number of experiments that would provide

the necessary evidence. One of the proposed experiments, which involved measuring the directional intensity of beta radiation from oriented 60Co nuclei, seemed

to them to be the best prospect for success in testing

their hypothesis. Yang and Lee had turned to betaspectroscopist and Columbia University friend and

colleague Chien-Shiung Wu for advice on how to pursue

their preferred suggestion. Wu, in turn, approached

Henry Boorse of Columbia and his close associate Mark

W. Zemansky of the City College of New York, who

together ran a modest research program in cryophysics

at Columbia. Although these scientists lacked the

"parity-required" facilities, they were active members in

the international low-temperature-physics community,

well acquainted with the NBS program and the recent

move thereto of Ernest Ambler, a graduate from the

Oxford (UK) “cryonuclear physics” research program

[5]. It was they who suggested that Wu make initial

contact with Ambler and, in fairly short order, arrangements were made to carry out this experiment in the

Bureau’s low-temperature laboratory.

The envisaged experiment was far from routine and

involved many unknowns at the outset. The source of the

-rays would have to be in intimate contact with the

111
cooling medium (paramagnetic crystal) and also on the

surface, so that the beta particles could get out of the

crystal. Could the contact and refrigeration be made

adequate? Would back-scattering be, in consequence, a

major drawback? How to count the -rays? In situ?

Remotely? And either way—exactly how? What of the

external magnetic field necessary for polarizing the

cobalt nuclei without heating up the refrigerating salt?

What was the optimum activity of the -source—large

being best for detection sensitivity, small for minimizing

local heating?

Polarization of the nuclei was achieved by cooling a

paramagnetic crystal containing 60Co to within 0.003 K

and subjecting it to a magnetic field. At this temperature

the effects of thermal agitation are so small that atomic

nuclei can line up in a given direction within the crystal

lattice when a magnetic field is applied. The magnetic

polarity of the nucleus is determined by its direction of

spin and, under the influence of a magnetic field, most

of the 60Co nuclei align themselves so that their spin

axes are parallel to the field. If parity is conserved in

beta decay, then the intensity of the beta emission should

be the same in either direction along the axis of spin.

This, of course, was the critical question in the 60Co

experiments. It was resolved by measuring the intensity

of beta emission in both directions, i.e., along and

against the field direction.

The 60Co was located in a thin (50 m) surface layer

of a single crystal of cerous magnesium nitrate (CMN).

The crystal was placed in an evacuated flask which, in

turn, was immersed in liquid helium within a Dewar

flask surrounded by liquid nitrogen. An inductance coil

on the surface of the inner flask was used to measure the

temperature of the crystal in terms of its magnetic

susceptibility. CMN is extremely anisotropic: the

trivalent sites in its plate-like natural form are almost

non-magnetic along the (out-of-plane) c -axis, but are

uniformly magnetic in the plane. Co ions, however,

would go into divalent sites which are contrary magnetically, i.e., most easily magnetized along the crystallographic c -axis. Thus in magnetic anisotropy, CMN

should be ideal for the experiment: major (magnetic

cooling) field in the plane, small polarizing (solenoid)

field perpendicular to the plane, with negligible temperature-raising effect. But might not that polarizing field

exert a torque on the crystal of sufficient strength to

break a typically fragile thermally-isolating mounting?

A major experimental problem was the location of a

radiation counter within the evacuated flask for detection of beta particles. This problem was solved by

placing a thin anthracene crystal inside the chamber

to serve as a scintillation counter. The anthracene

crystal was located about 2 cm above the 60Co source.

Scintillations caused by beta particles striking the

crystal were transmitted through a glass window and a

120 cm lucite rod acting as a light pipe to a photomultiplier at the top of the flask. The resulting pulses were

counted on a 10-channel pulse-height analyzer. It proved

possible to design the light pipe so as to hold the resultant contribution to the liquid-helium loss rate to a tolerable level.

In addition to the beta counter within the vacuum

chamber, two sodium iodide gamma scintillation counters were used externally to measure the directional

intensity of the more penetrating gamma radiation. In

this way the investigators were able to determine the

degree of polarization of the 60Co nuclei. The two

gamma counters were biased to accept only the pulses

from the photopeaks in order to discriminate against

pulses from Compton scattering.

Close to midway through the six-month work-up

period, the team reached the conclusion that problems

arising from outgassing within the crucial chambers of

the apparatus would never be surmounted, and the entire

assembly was re-designed from stainless steel to glass

and a new version quickly constructed and assembled.

Cooling to the low temperature necessary for nuclear

alignment was accomplished by the process of adiabatic

demagnetization using a magnetic field of about 2.3 T

(23 kilogauss). This process involved isothermal magnetization and subsequent isentropic demagnetization of

the paramagnetic salt, CMN, which supported the 60Co

specimen. The heat produced by magnetization was

removed by transfer through helium “exchange gas” and

the boiling off of liquid helium in the surrounding

dewar. The specimen was then thermally isolated by

pumping out the exchange gas and upon demagnetization the temperature fell to about 0.003 K.

Next, a vertical solenoid was raised around the lower

end of the outer dewar to provide a magnetic field for

polarization of the 60Co nuclei. After the beta emission

had been measured for this condition, the direction of

the magnetic field was reversed and the beta emission

again measured for the nuclei now polarized in the

opposite direction. It was found that the emission of beta

particles is greater in the direction opposite to that of the

nuclear spin. Thus, a spinning 60Co nucleus has a beta

emission distribution that is not the same as that of its

mirror image. This result unequivocally demonstrated

that parity is not conserved in the emission of beta

particles by 60Co.

Beyond the primary question resolved by this experiment, another matter of great interest was “how large

was the effect” since, in principle, the asymmetry—if

observed at all—could have turned out to be anywhere

from zero to maximum (asymmetry parameter from

0 to 1); it was, in fact, maximum. Thus the general

opinion (largely derisory!) about the likelihood of the

112
proposal of Lee and Yang bearing fruit changed

overnight, and the nuclear physics community

scrambled to try out other tests that would now be quite

feasible. In fact, colleagues of C. S. Wu were able to

design an experiment at the Columbia University

cyclotron and demonstrate within a day or two the

“parity effect” in a --e decay experiment [6], long

before the NBS-Wu team could carry out all the “check

experiments” they anticipated would now be demanded

by the skeptics!

After those checks had been completed, a second

experiment was performed [7] using 58Co, which is a

positron emitter. In this case the positrons were emitted

preferentially in the opposite direction to that of the

electrons, that is, + particles are preferentially emitted

along the direction of the nuclear spins. This provided

additional confirmation of the conjecture of Lee and

Yang and supported the new theory that was being

developed at the time to explain parity non-conservation.

While the general U.S. physics community reacted

rapidly with great interest and excitement to these

momentous events, culminating in extraordinary jampacked sessions at the New York meeting of the American Physical Society in January 1957, other sentiments

intruded upon the otherwise euphoric scene: Skepticism

leveled at the original Lee-Yang proposal was replaced,

in some minds, by disbelief in the results of these

validating experiments, for parity conservation was an

article of faith not to be discarded lightly. The

NBS team’s colleague from Washington’s Carnegie

Institution Department of Terrestrial Magnetism,

Fig. 1. The page of Ernest Ambler’s notebook recording the first definitive evidence that

parity is not conserved. The comment to that effect at the top left of the page was added

by Ralph Hudson.

113
Georges M. Temmer, was on a laboratory odyssey in

Western Europe at the time of the first news outbreak.

At one point, Temmer found himself in the presence of

eminence grise Wolfgang Pauli, who asked for the latest

news from the United States. Temmer told him that

parity was no longer to be assumed “conserved.”

“That’s total nonsense” averred the great man. Temmer:

“I assure you the experiment says it is not.” Pauli

(curtly): “Then it must be repeated!” [8].

Not long after this, the world settled down to

the realization that Lee and Yang had been right. Interestingly, though, a reluctance to believe that NBS staff

had played a significant role (indeed, any role for some

minds) in the crucial experiment began to spread in the

less-informed parts of the U.S. scientific community,

and elsewhere. Even as early as that European tour of

Temmer’s, he encountered this. At a colloquium, also in

Switzerland, and present when the proceedings were

interrupted for an announcement of the “triumph at

Columbia U.,” Temmer spoke from the floor to make

the correction that the work had been carried out at the

National Bureau of Standards; he was—more or less

politely—“hooted down.” And despite his international

standing—even especially in that particular community—he was pitied as being extraordinarily “mistaken.”

Later on, and forever afterward, hardly a speaker or

writer referred to the event in any other term than “the

Wu experiment” and only C. N. Yang himself and Chief

Cryogenic Notable Nicholas Kurti went out of their way

to try to set the record straight.

The further developments of the theory, together with

a large number of follow-up experiments, have led to the

unification of the weak and electromagnetic interactions. A description of both the history and the physics

is available in the Nobel lectures by Weinberg, Salam,

and Glashow [9].

In 1957, NBS moved rapidly to include those of

its staff in the "parity experiment team" in its

Honors & Awards for that year, presenting them with

the Commerce Department"s Award for Exceptional

Service (the Gold Medal). In 1964 it added its own

highest recognition, the Samuel Wesley Stratton Award.

In 1962, the Franklin Institute of Philadelphia awarded

its John Price Wetherill Medal to the full team.

C. S. Wu resumed her full-time preoccupation with

-decay research at Columbia University and the

concomitant training of graduate students there. Over

the years she received many honors, including the

National Medal of Science (1975), the Wolf Prize in

Physics (1978), and election to the Presidency of the

American Physical Society (1975), the first woman

to achieve that distinction. Wu died in New York in

February 1997 at the age of 84 [10].

Ralph Hudson was appointed Chief of the Heat

Division at NBS in 1961, and Ernest Ambler moved up

to take his place as Chief of the Cryogenic Physics

Section. For several years Ambler continued to carry out

research, in collaborative efforts on oriented nuclei and

superconductivity. He then went on to occupy a series of

positions of increasing responsibility at NBS, culminating in Director of the agency—after several years as

Acting Director—a post he held from 1978 to 1988

[11]. During this period, he received the President’s

Award for Distinguished Federal Civilian Service. Prior

to his retirement from NIST in 1989, at the age of 65, he

was Acting Undersecretary for Technology in the

Department of Commerce.

Hudson continued to do research, as administrative

preoccupations would permit, on cryothermometry and

low-temperature magnetism. A review article coauthored by him received NBS’s Condon Award in 1976

for distinguished authorship [12]. In the NBS reorganization of 1978, the Heat Division was abolished and

Hudson became Deputy Director, under Karl G.

Kessler, of the Center for Absolute Physical Quantities,

with additional responsibility for managing the

standards activity in Mass and Length. He resigned in

1980 and went to work at the International Bureau of

Weights & Measures in Se`vres, France, as Director of

Publications and editor of the international journal

Metrologia. Upon retirement therefrom in 1989, at the

age of 65, he returned to the Washington area and took

a three-year temporary post at the National Science

Foundation as Program Director for Low-Temperature

Physics.

Raymond Hayward, after involvement with his

colleagues in several follow-up experiments in the

Low-Temperature Laboratory, returned to duty in the

Radioactivity Section (Wilfrid B. Mann, Chief). When

a separate Nuclear Spectrometry Section was created he

was appointed Chief. He wrote a monumental treatise

on the dynamics of particles of higher spin (>1/2) [13],

after which he devoted himself to the study of gravitation. He retired in 1980 at the age of 59.

Dale Hoppes continued experimental studies of betaparticle distributions from oriented nuclei [14] in the

Nuclear Spectrometry Section, earning a Ph.D. from

The Catholic University of America in 1961. He later

returned to the Radioactivity Section, where he was

involved in activity and gamma-ray-probability

measurements. When Mann retired in 1981, Hoppes

took over as Radioactivity Group Leader until his retirement from NIST in 1992 at the age of 64.

Prepared by Ralph P. Hudson.

114
Bibliography

[1] C. S. Wu, E. Ambler, R.W. Hayward, D. D. Hoppes, and R. P.

Hudson, Experimental test of parity conservation in beta decay,

Phys. Rev. 105, 1413-1415 (1957).

[2] See, for example, D. de Klerk and R. P. Hudson, Installation for

Adiabatic Demagnetization Experiments at the National Bureau

of Standards, J. Res. Natl. Bur. Stand. 53, 173-184 (1954);

E. Maxwell, Isotope effect in the superconductivity of mercury,

Phys. Rev.78, 477 (1950) ; D. de Klerk, R. P. Hudson, and J. R.

Pellam, Second sound propagation below 1 K, Phys. Rev. 93,

28-37 (1954).

[3] Low-Temperature Alinement of Radioactive Nuclei, NBS Tech.

News Bull. 40, 49-51 (1956); see also E. Ambler, R. P.

Hudson, and G. M. Temmer, Alignment of Cerium-141 and

Neodymium-147 Nuclei, Phys. Rev. 97, 1212-1221 (1955);

E. Ambler, R. P. Hudson, and G. M. Temmer, Alignment of

Three Odd-A Rare-Earth Nuclei, Phys. Rev. 101, 196-200

(1956).

[4] T. D. Lee and C. N. Yang, Question of parity conservation in

weak interactions, Phys. Rev. 104, 254-258 (1956).

[5] J. M. Daniels, M. A. Grace, and F. N. H. Robinson, An Experiment on Nuclear Alignment: the Anisotropy of -Radiation from

Oriented Cobalt-60 Nuclei, Nature 168, 780-781 (1951); E. Ambler, M. A. Grace, H. Halban, N. Kurti, H. Durand, C. E. Johnson, and H. R. Lemmer, Nuclear Polarization of Cobalt 60,

Philos. Mag. 44, 216-218 (1953).

[6] R. L. Garwin, L. M. Lederman, and M. Weinrich, Observations

of the failure of conservation of parity and charge conjugation in

meson decays: the magnetic moment of the free muon, Phys.

Rev. 105, 1415-1417 (1957).

[7] E. Ambler, R. W. Hayward, D. D. Hoppes, R. P. Hudson, and

C. S. Wu, Further Experiments on  Decay of Polarized Nuclei,

Phys. Rev. 106, 1361-1363 (1957).

[8] G. M. Temmer—private communication. Temmer, a gifted

scientist of infectious enthusiasm, had played an important

part in establishing the solid reputation of the NBS Cryogenic

Physics Section’s nuclear orientation program, first while

employed in the NBS Radioactivity Section, later after moving to

the Department of Terrestrial Magnetism.

[9] Steven Weinberg, Conceptual foundations of the unified theory

of weak and electromagnetic interactions, Rev. Mod. Phys. 52,

515-523 (1980); Abdus Salam, Gauge unification of fundamental forces, ibid., pp. 525-538; Sheldon Lee Glashow, Towards a

unified theory: Threads in a tapestry, ibid., pp. 539-543..

[10] R. L. Garwin and T. D. Lee, Obituaries: Chien-Shiung Wu, Phys.

Today 50 (10), 120,122 (1997).

[11] E. Ambler, Historical Perspective: 1973-1989, in NBS/NIST: A

Historical Perspective, A Symposium in Celebration of NIST"s

Ninetieth Anniversary, March 4, 1991, NIST Special Publication

825, National Institute of Standards and Technology, Gaithersburg, MD (1992) pp. 31-40.

[12] R. P. Hudson, H. Marshak, R. J. Soulen, Jr., and D. B. Utton,

Recent Advances in Thermometry below 300 mK, J. Low Temp.

Phys. 20, 1-102 (1975).

[13] Raymond W. Hayward, The Dynamics of Fields of Higher

Spin, NBS Monograph 154, National Bureau of Standards,

Washington, DC (1976).

[14] A. T. Hirshfeld and D. D. Hoppes, Transition Mixing Ratios

Determined from a Study of the Electron and Gamma-Ray

Distributions from Oriented Iridium-192, Phys. Rev. C 2, 2341-

2349 (1970).

115
Effects of Configuration Interaction on

Intensities and Phase Shifts

One of the enduring goals of scientific work at the

National Institute of Standards and Technology (NIST)

has been the expression of measurements in terms

related directly to natural phenomena of an invariant and

absolute character.

For example, the unit of time, the second, is now

defined as exactly 9,192, 631, 770 periods of oscillation

of the radiation associated with a specified quantum

transition between states of the 133Cs atom. This makes

it possible, in principle, for any laboratory to realize the

value of the second by preparing a sample of 133Cs in

conditions that make it resemble a group of identical

atoms unperturbed by their immediate environment.

Of course, such an ideal realization is not attainable in

practice. This permanent fact of life has provided steady

stream of work over the years for theoretical physicists

at NIST: there is always a need for models that can

provide better quantitative links between realistic and

ideal situations.

Ugo Fano (1912– ) is believed to be the first theoretical physicist hired by NIST, and he has certainly been

one of the most influential to date. His 1961 paper

Effects of Configuration Interaction on Intensities and

Phase Shifts [1] is one of the most frequently referenced

journal articles by a NIST author, having been cited over

3200 times in the scientific literature. This paper treats

a subject of fundamental interest to metrology and

physics: the excitation spectra of quantum-mechanical

systems. Its key result, the simple formula given in

Eq. (3) below, is now well known to physicists as the

“Fano profile” or “Fano line shape.” It addresses the

challenge of expressing observed phenomena in a

concise manner that can be derived from first principles.

The celebrity enjoyed by this formula derives from the

basic importance of the systems it describes, its wideranging practical utility, and the historical context in

which it emerged. These aspects are discussed in turn

below, though they cannot be entirely disentangled.

Among the phenomena key to the early development

of quantum mechanics were atomic spectra, i.e., the

colors of light absorbed or emitted by free atoms. Such

light was found to consist largely of discrete frequencies

whose distribution is a characteristic property of the

atomic species involved (see Fig. 1). The existence of

these discrete frequencies led Niels Bohr [2] to postulate

a model of atomic structure in which the atom can

subsist only in certain states of well-defined energy,

although transitions between such states can be induced.

Transitions between two states may be associated with

accompanying optical radiation, of angular frequency

0 = 2E/h, where E is the difference in energies of

the two states, and h is Planck’s constant. At this level of

detail, the modern concept of atomic structure is the

same as Bohr’s. Thus, accurate data on intrinsic atomic

frequencies has great fundamental and practical value.

For example, as noted above, such frequencies now

provide the legal definition of the second. NIST has for

many years maintained a program to generate, evaluate,

and maintain a database of relevant atomic spectral

properties; that effort is summarized elsewhere in this

volume.

Bohr’s basic idea, that transitions between atomic

states are associated with radiation of a definite

frequency, needs to be broadened somewhat to describe

phenomena actually encountered in the laboratory. For

example, if one prepares a sample of atoms in a highenergy state, they may make transitions to a lowerenergy state by emission of optical radiation. This

process will take place over some period of time. Under

simplifying but widely applicable assumptions, Viktor

Weisskopf and Eugene Wigner [3] showed that quantum

mechanics describes the time dependence of the intensity of emitted radiation, I(t), as following the law of

exponential decay,

I(t)  exp(–t), (1)

where t is the time, measured from the moment of state

preparation, and  is a rate constant that can be regarded

as the inverse of the lifetime of the higher state. This law

Fig. 1. Visible emission spectrum of the hydrogen atom (spectral

lines of the Balmer series). The atomic radiation has been dispersed

by a spectral grating and projected onto a photographic plate, to show

the discrete frequency components of the radiation. The frequency

increases to the right, with white indicating higher intensity (i.e., this

is a photographic positive). If viewed by the eye, these lines would

appear blue-violet. Figure courtesy of Prof. C. R. Vidal.

116
expresses a simple idea: the instantaneous probability of

decay of a given atom is independent of the time t at

which it occurs. Exponential decay is encountered in a

number of physical systems, such as the natural transmutation of radioactive elements.

An alternative mode of observation of exponential

decay is the resolution of its frequency spectrum. This is

a straightforward and convenient practice in optical

spectroscopy, where the various frequency components

of radiation may be spatially dispersed by reflecting it

from a diffraction grating, or by passing it through a

prism, and projecting it onto a screen, photographic

plate, or detector array. By this means, the spectrum of

a white light source is spread out into the familiar rainbow pattern. On the other hand, the spectrum of an

atomic radiation governed by the decay law of Eq. (1),

exhibits the “Lorentzian” profile, or line shape,

I()  1/[(–0)

2

+ (/2)2], (2)

where I() is the intensity at the angular frequency ,

and 0, as stated above, is proportional to the difference

in energy between atomic states. In this representation,

 plays the role of the “width” of the spectral feature.

This expresses Heisenberg’s uncertainty principle: the

energy of a state is indeterminate by an amount

inversely proportional to its lifetime. For most optical

spectra generated by atoms, the ratio /0 is of the

order 10–6. Thus the human eye would perceive the

spectrum of Eq. (2) as being a remarkably pure

(monochromatic) and bright color, localized at the

appropriate position on the viewing screen. However, if

examined in detail, atomic spectra can exhibit significant deviations from the form of Eq. (2). The differences are due to the actions of physical processes

neglected in the simplifying assumptions mentioned

above.

Fano’s 1961 treatment deals with one of the more

important classes of such processes: those in which

there are alternative pathways for a transition between

atomic states. In quantum mechanics, the existence of

alternative pathways invariably gives rise to the

phenomenon of interference : the probability amplitudes associated with travel along the different paths

combine with a phase relationship, just as the crests and

troughs of classical wave motion can combine to yield

a null displacement. In the model considered by Fano,

which has been found to have broad applicability, the

interference phenomenon inevitably gives rise to a

“dark spot,” i.e., the spectral intensity vanishes at a

particular frequency. The line shape formula derived by

Fano, in his chosen notation, takes the form

I()  (q+)

2

/(1+2), (3)

where  = 2(–0)/ is the angular frequency, measured from the line center 0 in units of , and q is a

parameter that describes the interference between pathways. When q is much greater than 1, one of the

pathways has the predominant transition amplitude, and

Eq. (3) becomes equivalent to Eq. (2) in the region

where the signal is strongest.

Fano was first motivated to understand this phenomenon 25 years previously, as a student of Enrico

Fermi in Rome. Fermi suggested to Fano that, as a

research project, he should try to understand photoabsorption spectra of the noble gases that had recently

been observed by Hans Beutler of the University of

Berlin [4].

Beutler’s spectra exhibited broad, highly asymmetric

absorption series, quite uncharacteristic of atomic

spectra known at the time. In contrast to the wellseparated, sharp features visible in Fig. 1, Beutler’s

spectra showed structures whose width was comparable

to their separation.

The origin of this phenomenon was correctly

proposed by Beutler to be associated with the

phenomenon of autoionization, which had previously

been identified in atomic spectra by Ettore Majorana [5]

and Allen Shenstone [6].

Autoionization occurs upon excitation of an electronic configuration that has an energy higher than that

needed to ionize (i.e., remove one electron from) the

atom. For example, two atomic electrons may be

excited, with a total energy that is sufficient to access an

alternative configuration, in which one of the electrons

relaxes to a state of lower energy, while the other

escapes from the atom. This phenomenon is analogous

to a possible, though we hope unlikely, rearrangement of

the Solar System, in which the energy released by

a contraction of the orbit of Jupiter could be used to

liberate the Earth from its orbit about the Sun. In the

simplest case of autoionization of a state of two excited

electrons, the two interfering quantum-mechanical

pathways may be envisaged as follows. One involves the

direct ejection of one electron from the atom, leaving

behind a positively-charged ion; the other generates a

state of two excited electrons, which then relaxes by

energy exchange to yield the same final state, a free

electron and a positive ion.

In a paper published in 1935 [7], Fano showed that

spectral profiles of the type observed by Beutler could

indeed be generated by quantum mechanical interference in autoionization, and he presented a formula

equivalent to that of Eq. (3). However, his presentation

did not involve a quantitative analysis of Beutler’s data,

which was quite complicated, and still, in its time,

somewhat of an anomaly in atomic spectroscopy. When

Fano returned to this class of problems in 1961, key

developments in experimental technique had elevated it

to a frontier research area of atomic physics.

117
The new experimental situation of the 1960s evolved

along two fronts, on both of which NIST made pioneering contributions that would be adopted world-wide:

high-resolution electron spectroscopy, and the application of synchrotron radiation.

John Simpson and Chris Kuyatt led the electron

spectroscopy effort in the Electron Physics Section at

NIST. They designed electron current sources and

detectors that enabled electron scattering by atoms to be

investigated in unprecedented detail [8]. Among the

signal achievements of this technique was the identification of numerous “negative ion resonances” analogous

to the doubly-excited electronic states encountered in

photoabsorption. An electron colliding with an atom

can lose energy by exciting an atomic electron, and be

captured by the field of the residual ion. This can give

rise to a transient state in which the incident and excited

electrons orbit the positively charged ion core, which

subsequently decays by the capture of one electron

and the release of the other. This situation provides

for interference of two quantum-mechanical amplitudes: one for direct scattering of the incident electron,

the other involving the temporary capture/excitation

process, which results eventually in a scattered electron.

The experimental data treated explicitly by Fano in his

1961 paper were in fact provided by such an experiment. The formation of these resonances was mediated

by correlation of electronic motions, a phenomenon not

encompassed by the traditional “mean field” concepts

of atomic structure. The study of such resonances

therefore provided insight into unexplored avenues of

atomic and molecular physics, which developed as a

major research theme in the 1960s with interest

extending to the present day.

In the early 1960s the emergence of synchrotron

radiation sources greatly expanded the range of optical

spectroscopy. At NBS, which played a leading role in

the field, the development of a synchrotron radiation

source was an offshoot of a program of investment in

betatron electron accelerators which started in the late

1940s. The betatrons were originally obtained to

provide high-energy electron beams for the production

of x rays. These accelerators also yielded, at first as an

unappreciated byproduct, a broad band of synchrotron

radiation spanning the electromagnetic spectrum from

the radio to the x-ray domains. This broad-band capability was not matched by any other laboratory-based

radiation source; in particular, synchrotron radiation

provided exceptional coverage of the far ultra-violet

spectral region, i.e., radiation with wavelengths between

about 5 nm and 150 nm, vs the 500 nm wavelength characteristic of visible light. Far ultraviolet radiation has

sufficient energy to cause multiple electron

excitation in all elements, so that electronic states of

the type observed by Beutler would become ubiquitous

rather than exceptional.

Robert Madden was hired by NBS to head the Far

Ultraviolet Physics Section and was charged with converting one of the betatron machines into a dedicated

source of synchrotron radiation for far ultraviolet spectroscopy and radiometry, the Synchrotron Ultraviolet

Radiation Facility (SURF). In collaboration with

Keith Codling, David Ederer, and others, Madden made

numerous pioneering explorations of this spectral

region. The first major results of this work are shown in

Fig. 2: the absorption spectra of helium, neon, and

argon gas [9]. The helium spectra were particularly

striking, because they confounded initial theoretical

expectations that two series of lines would be observed,

rather than the single one displayed here. A companion

publication by John Cooper, Fano, and Francisco Prats

[10] showed that effects of electron correlation would

tend to favor strongly transitions to one of the two series.

This result hinted at the existence of characteristic

features of two-electron dynamics that might be found

in other spectra; this became a prominent theme in

atomic physics during the next two decades and is still

of interest today.

Fig. 2. Absorption spectra of helium, neon, and argon atoms in the

extreme ultraviolet spectral region, from [9]. These are images of

photographic plates exposed to radiation from the NBS electron synchrotron (now the Synchrotron Ultraviolet Radiation Facility—

SURF). The synchrotron radiation was passed through a gas cell and

then dispersed by a diffraction grating to show the dependence of

absorption upon wavelength (which is indicated in Ångstrom

units: 1 Å = 10–10 m). Increased blackness indicates increased absorption by the gas. Note that in contrast to Fig. 1, these spectral lines

clearly exhibit asymmetric profiles.

118
An example [11] of the application of the Fano profile

formula to the synchrotron radiation data is shown in

Fig. 3. The quantitative determination of the parameters

q, 0, and  that are obtained from this type of analysis

is essential for comparison of experiment and theory, or

for comparison of experiments of two different types.

For example, Fig. 3 describes an atomic state excited by

photoabsorption; the same state can be excited by other

means—in fact, it was this very same state, produced by

electron-impact excitation, that was analyzed in Fano’s

1961 paper—but the values of 0 and  should be independent of the mode of excitation since they are intrinsic

characteristics of the excited state.

Ugo Fano, who did his graduate work in Italy under

Fermi in the early 1930s, was hired by NBS in 1946

with a charge to build up the fundamental science base

of the x-ray program. In his 19 years at NBS he provided

guidance and inspiration to many of the Bureau’s physicists and chemists. After moving to the University of

Chicago in 1965, he led his graduate students in the

detailed analysis of noble-gas photoabsorption spectra.

The analysis of these spectra was a noteworthy achievement of multichannel quantum defect theory, developed

by Fano and coworkers along lines laid out by Michael

Seaton. This theory had a pronounced influence on

high-resolution laser spectroscopy in the 1970s and

1980s; its development is summarized in two articles in

the February 1983 issue of Reports on Progress in

Physics [12].

At NIST, the Fano profile formula evokes memories

of a remarkably productive era of atomic and electron

physics, one in which there was strong interplay between theory and experiment, as well as between electronic and optical spectroscopy. Many legacies of this

era are visible in NIST programs today. For example, the

Electron Physics Section spawned the topografiner

project, work on resonance tunneling in field emission,

and the development of spin-polarized electron sources

and detectors—all of which are described elsewhere in

this volume. The success of the SURF synchrotron

source inspired to the worldwide development of

synchrotron radiation as a research tool. SURF has since

gone through two major upgrades and today serves as

the nation’s primary standard for source-based radiometry over a wide region of the optical spectrum. Fano’s

theory of spectral line shapes continues to be applied to

a wide range of physical problems: his 1961 paper was

cited over 150 times in the scientific literature in 1999.

Prepared by Charles W. Clark .

Bibliography

[1] U. Fano, Effects of Configuration Interaction on Intensities and

Phase Shifts, Phys. Rev. 124, 1866-1878 (1961).

[2] N. Bohr, On the constitution of atoms and molecules, Philo.

Mag. 26, 1-25 (1913).

[3] V. Weisskopf and E. Wigner, Berechnung der natu ̈rlichen Linienbreite auf Grund der Diracschen Lichttheorie, Z. Phys. 63, 54-73

(1930).

[4] H. Beutler, U ̈ ber Absorptionsserien von Argon, Krypton und

Xenon zu Termen zwischen den beiden Ionisierungsgrenzen

2

P0

3/2 und 2

P0

1/2, Z. Phys. 93, 177-196 (1935).

[5] Ettore Majorana,Teoria dei tripletti ' incompleti, Nuovo

Cimento, N. S., 8, 107-113 (1931).

[6] A. G. Shenstone, Ultra-ionization potentials in mercury vapor,

Phy. Rev. 38, 873-875 (1931).

[7] Ugo Fano, Sullo spettro di assorbimento dei gas nobili presso il

limite dello spettro d’arco, Nuovo Cimento, N. S., 12, 154-161

(1935).

[8] C. E. Kuyatt, J. Arol Simpson, and S. R. Mielczarek, Elastic

resonances in electron scattering from He, Ne, Ar, Kr, Xe, and

Hg, Phy. Rev. 138, A385-A399 (1965).

[9] R. P. Madden and K. Codling, New autoionizing atomic energy

levels in He, Ne, and Ar, Phys. Rev. Lett. 10, 516-518 (1963).

[10] J. W. Cooper, U. Fano, and F. Prats, Classification of twoelectron excitation levels of helium, Phys. Rev. Lett. 10, 518-521

(1963).

[11] R. P. Madden and K. Codling, Two-electron excitation states in

helium, Astrophys. J. 141, 364-375 (1965).

[12] U. Fano, Correlations of two excited electrons, Rep. Prog. Phy.

46, 97-165 (1983); M. J. Seaton, Quantum defect theory, Rep.

Prog. Phy. 46, 167-257 (1983).

Fig. 3. The absorption coefficient vs. wavelength for the strongest

absorption feature of helium (around 206 Å) shown in Fig. 2, from

[11]. Note that wavelength increases to the right here, opposite to the

display of Fig. 1. The points are experimental data; the solid line is a

fit to the Fano profile formula (Eq. 2), with the values q and  as

indicated. This feature is associated with excitation of the 2s2p 1P0

state of the helium atom.

119
Electromagnetic Waves in Stratified Media

This book [1] was written at an important point in the

development of applications of electromagnetic (radio)

waves to communications, navigation, and remote sensing. Such applications require accurate propagation predictions for a variety of path conditions, and this book

provides the theoretical basis for such predictions. The

book is based on fundamental research in electromagnetic wave propagation that James R. Wait performed in the Central Radio Propagation Laboratory

(CRPL) of NBS from 1956 to 1962. The mathematical

theory in the book is very general, and the “stratified

media” models are applicable to the earth crust, the

troposphere, and the ionosphere. The frequencies of the

communication, navigation, and remote sensing applications treated in this book range all the way from

extremely low frequencies (ELF) to microwaves.

The mathematical theory of electromagnetic wave

propagation is based on Maxwell’s equations [2], formulated by James Clerk Maxwell in the 1860s. Experimental propagation studies in free space [3] and over the

earth [4] also go back over 100 years. Research in radio

science, standards, and measurements began in NBS in

the early 1900s, and the long history of radio in NBS has

been thoroughly covered by Snyder and Bragaw [5].

CRPL was moved to Boulder in 1954, and Wait joined

the organization in 1955.

The mathematics of electromagnetic wave propagation in stratified (layered) media is very complicated,

and progress in propagation theory in the early 1900s

was fairly slow. Wait’s book [1] included the most useful theory (much of which he developed) and practical

applications that were available in 1962. A hallmark

Fig. 1. What it’s all about: In conventional transmission, short waves (in the range of 25 MHz to 60 MHz) are propagated beyond the visible

horizon by reflection from the upper layers, or F region, of the ionosphere. In propagation by ionospheric forward scatter the energy of radio waves

is scattered by small irregularities in the ionization of the lower ionosphere, i.e., the lower portion of the E layer and below this layer, providing

for reception of signals much beyond the line of sight. The diagram is taken from the January 1956 issue of the NBS Technical News Bulletin.

120
of the book is that the theory was sufficiently general

that it has served to guide further theoretical and experimental propagation research to this day. Continuing

demand for the book led IEEE Press to reissue it in

1996.

Chapter I provides a general introduction to the book.

Chapter II is fundamental to the entire subject because

it covers reflection of electromagnetic waves from horizontally stratified media. The incident field can be either

a plane wave (as from a distant source) or a spherical

wave (as from a nearby antenna). The theory utilizes a

novel iterative approach that matches the electric and

magnetic field boundary conditions at each layer interface. Then the entire layered medium can be replaced by

a single interface with an equivalent surface impedance

(ratio of tangential electric and magnetic fields). This

approach has been found very useful by many other

researchers in simplifying the analysis of complex

layered geometries [6], such as printed circuit boards.

Chapter III treats the case where the electromagnetic

properties of the reflecting medium vary smoothly,

rather than discontinuously as in a multi-layered

medium. For some special profiles, such as linear or

exponential, the solutions can be given exactly in terms

of known mathematical functions. This type of treatment has been particularly useful in obtaining solutions

for reflection of pulses from the ionosphere [7].

Whereas the methods in Chapters II and III are exact,

approximate methods are developed in Chapter IV.

These methods are less accurate, but they have the

advantages of simplicity and physical interpretation. In

general, these methods track the fields in a manner

similar to ray tracing. The approximate methods have

been found to be particularly useful for calculating

reflections from complex ionospheric profiles [8].

Chapter V brings curved boundaries into the theory

by treating wave propagation along a spherical surface.

This theory is particularly important for analyzing

ground-wave propagation along the surface of the earth

[9]. The most important effect that can be predicted

using this theory is the rapid attenuation of field strength

beyond the shadow boundary. For example, the extent of

daytime AM radio coverage can be determined if the

ground properties are known. The most general theory

can make use of the impedance boundary condition

developed in Chapter II to predict field strength as a

function of distance even when the curved earth model

includes layering [10].

When the ionosphere is added to the curved earth

model, mode theory is required to calculate field

strength in the earth-ionosphere waveguide. Chapter VI

presents a self-contained treatment of mode theory

that starts with very complex mathematics and ends

with fairly simple and convenient approximations. The

formulations are very general, and the transmitting

antennas can be electric or magnetic dipoles of arbitrary

orientation. At low frequencies, the earth-ionosphere

waveguide acts like a cavity that can resonate [11]

and enhance the background noise (typically due to

lightning).

The very low frequency (VLF) band is particularly

useful for long distance communication and navigation

[12] because of the low attenuation rates of the earthionosphere waveguide modes. Chapter VII presents

VLF approximations that are particularly useful in

simplifying the general mode theory of Chapter VI.

Numerous attenuation and phase velocity calculations

are presented for use in communication and navigation

system calculations, and the effects of earth or sea water

conductivity are also included. Antenna height is also

shown to be important.

The ionosphere is an ionized medium, or plasma. The

earth’s magnetic field alters the electromagnetic

properties of the ionosphere, in particular making it

anisotropic. Chapter VIII covers electromagnetic propagation effects encountered in such a magneto-plasma.

Again both layering and curvature are taken into

account, and practical VLF propagation effects are

analyzed in detail. These results have direct application

to navigation systems [13].

Chapter IX contains extensive comparisons of theory

and measurement at VLF. Interesting effects such as

direction of propagation (important because of the

earth’s magnetic field) and time of day are shown by

both theory and experiment [14]. The sources can be

either antennas or lightning strikes, and attenuation

rates of theory and experiment are generally in good

agreement [15].

Chapter X continues in the spirit of Chapter IX

except that it covers extremely low frequencies (ELF).

Different mathematical approximations are required to

fit this lower frequency range (1 Hz to 3000 Hz) even

though propagation is still primarily due to a waveguide

mode. At this frequency range, the fields can penetrate

sea water allowing communication with submarines

[16]. Good agreement between theory and experiment

[17] is again obtained.

The relationship between waveguide modes and rays

is clearly developed in Chapter XI. This provides very

useful insight because the ionosphere “sky wave” is

often interpreted as an ionospheric reflection for a

particular ray path. The mathematical results are

sufficiently general that they can be applied to a variety

of layered media problems [18].

121
Chapter XII is particularly important for current applications because it covers propagation of microwaves

in the troposphere. General mathematical formulations

are obtained, and tropospheric ducting is covered in

detail. Microwave propagation in personal communication systems [19] is one of many possible current

applications of the theory.

Wait’s book synthesized the results of a large number

of observations and experiments, some of which had

been carried out at the Bureau over the years [5]. Louis

W. Austin’s investigations on radio wave propagation for

the Naval Wireless Telegraphic Laboratory (in close

association with, and located at NBS) dated back to

1909. In a Bureau publication of 1911, Austin accounted

for anomalies in his observations as being due to absorption of radio signals in the ionized layer above the Earth.

In a 1913 paper he explained the increased strength of

nighttime signals by reflection from an ionized layer that

is less uniform during the day.

The fading of radio signals was of much concern to

the Radio Laboratory at NBS and was a puzzlement to

operators and scientifically minded observers from the

very beginning of radio. In 1920 a cooperative program

was initiated by the Radio Laboratory with the American Radio Relay League (ARRL) in a broadside

approach by enlisting a large number of radio amateurs

to observe fading effects. The vagaries of transmission

observed by the growing multitude of listeners in the

broadcast frequencies gave added incentive to study

fading phenomena. The cooperative program on fading

studies with the ARRL and later with several universities

and radio stations continued until 1927.

The Bureau’s first measurements of the height of

ionosphere layers were made in February 1929 by

T. R. Gilliland, using a pulse technique. Transmissions

came from the Naval Research Laboratory in southeast

Washington, with reception at a Kensington, Maryland,

field site 5 miles north of the Bureau grounds. By 1930

an organized study of the ionosphere was underway.

Thereafter came the many-faceted and extensive

program of probing the secrets of the ionosphere and the

vagaries of radio propagation under the able direction of

John H. Dellinger, who later became Chief of the NBS

Central Radio Propagation Laboratory.

James R. Wait (1924–1998) was born in Canada and

received his Ph.D. from the University of Toronto in

1951. He joined the Central Radio Propagation Laboratory in Boulder in 1955 and remained in the Boulder

Laboratories until 1980. He was a professor at the

University of Arizona from 1980 to 1998. He published

8 books and more than 800 papers on electromagnetics

in his long career. Of his many awards, he received IEEE

Heinrich Hertz Medal, primarily for the research

reported in this book [1].

Prepared by D. A. Hill.

Bibliography

[1] James R. Wait, Electromagnetic Waves in Stratified Media, Pergamon Press, New York (1962).

[2] Robert Stratman Elliot, Electromagnetics: History, Theory, and

Applications, IEEE Press, Piscataway, NJ (1993).

[3] John H. Bryant, Heinrich Hertz: The Beginning of Microwaves,

Institute of Electrical and Electronics Engineers, New York

(1988).

[4] G. Marconi, Wireless telegraphy, J. Inst. Electr. Eng. 28, 273-

316 (1899).

[5] Wilbert F. Snyder and Charles L. Bragaw, Achievement in Radio:

Seventy Years of Radio Science, Technology, Standards, and

Measurement at the National Bureau of Standards, NBS Special

Publication 555, National Bureau of Standards, Boulder, CO

(1986).

[6] Thomas B. A. Senior and J. L. Volakis, Approximate Boundary

Conditions in Electromagnetics, The Institution of Electrical

Engineers, London (1995).

[7] D. A. Hill and J. R. Wait, Reflection of pulses from a linearly

varying ionosphere model with a vertical magnetic field, Radio

Sci. 6, 933-937 (1971).

[8] K. G. Budden, Radio Waves in the Ionosphere, Cambridge

University Press, Cambridge, England (1961).

[9] James R. Wait, The ancient and modern history of EM groundwave propagation. IEEE Antennas Propag. Mag. 40 (5), 7-24

(1998).

[10] David A. Hill and James R. Wait, Ground wave attenuation

function for a spherical earth with arbitrary surface impedance,

Radio Sci. 15, 637-643 (1980).

[11] P. V. Bliokh, A. P. Nikolaenko, and Y. F. Fillippov, Schumann

Resonances in the Earth-Ionosphere Cavity, IEE/Peter

Peregrinus Ltd., Stevenage, England (1980).

[12] Arthur D. Watt, VLF Radio Engineering, Pergamon Press,

Oxford (1967).

[13] J. Ralph Johler, On the analysis of LF ionospheric radio propagation phenomena. J. Res. Natl. Bur. Stand. 65D, 507-529 (1961).

[14] W. L. Taylor, VLF attenuation for east-west and west-east daytime propagation using atmospherics, J. Geophys. Res. 65, 1933-

1938 (1960).

[15] A. Glenn Jean, William L. Taylor, and James R. Wait, VLF phase

characteristics deduced from atmospheric wave forms,

J. Geophys. Res. 65, 907-912 (1960).

[16] Michael L. Burrows, ELF Communications Antennas, IEE/Peter

Peregrinus Ltd., Stevenage, England (1978).

[17] F. Hepburn, Atmospheric waveforms with very low-frequency

components below 1 kc/s known as slow tails, J. Atmos. Terr.

Phys. 10, 266-287 (1957).

[18] L. M. Brekhovskikh, Waves in Layered Media, Academic Press,

New York (1960).

[19] K. Siwiak, Radiowave Propagation and Antennas for Personal

Communications, Artech House, Boston, MA (1995).

122
“Second Breakdown” in Transistors

This paper [1] provided the first detailed characterization of a serious and, at the time, poorly understood

failure mechanism of power transistors, called second

breakdown, which could occur well within the power

dissipation limits of these devices. It addressed the

problem that early transistors (those prior to the bipolar

field-effect transistors that are common today) failed

while operating well within switching voltage and

current conditions that should have posed no threat of

failure. The paper was followed by others [2-8] and, in

1967, by a comprehensive review article [9] and bibliography [10]. While second breakdown is still a reliability problem in power transistors and metal oxide semiconductor field-effect transistors (MOSFETs), it is controlled through device design and the specification of

safe operating areas that are based on the work reported

in this paper. An important aspect of the paper it that it

represents the genesis of NIST’s support for the semiconductor industry. Work for that industry is now conducted throughout NIST; in particular, there is an Office

of Microelectronics Programs and a Semiconductor

Electronics Division.

This work was initiated in response to a request to the

National Bureau of Standards from the standards arm of

the Joint Electron Devices Engineering Councils

(JEDEC), operating under the Electronics Industries

Association. The reasons cited for their request were

several. To achieve an adequate understanding of the

mechanism would have required a long-term effort not

likely to be undertaken by any individual member

company. Nevertheless, it was needed by a large

segment of the industry. The literature on second breakdown was slight and inconclusive. Finally, different,

controversial opinions, in part due to company prejudices, were widespread. To assist NBS to conduct its

research on second breakdown, member companies

provided power transistors for testing, copies of reports

of their experience, and access to their engineers and

scientists concerned with this reliability problem.

In the paper “Second Breakdown” in Transistors [1],

each of the mechanisms that had been proposed in the

literature was examined and shown to be inadequate.

A more complete description of the characteristics of

second breakdown was given and it was shown that it is

a fundamental property of the transistor. On the basis of

an observed delay time before the initiation of the breakdown, it was proposed that the phenomenon is related to

a thermal mechanism. It was shown that the onset of

second breakdown cannot be predicted simply in terms

of voltage and current, as had been the practice, but that

it is important to characterize second breakdown in

terms of the energy dissipated in the transistor, and

further, that the energy threshold (or delay time) is

dependent on other factors such as ambient temperature

and the biasing base current of the transistor.

The conclusions in this paper provided the basis for

all current methods to specify reliable operating limits

of power transistors. These specifications are given in

terms of safe areas of operation for collector current and

voltage that are dependent on the biasing base current

and the switching dynamics.

The literature was slight and inconclusive . . . Controversial opinions were

widespread.

July 1995 marked 40 years of NBS/NIST programs to

support the semiconductor industry. Quoting a press

release issued at the time, “The Commerce Department

and the U.S. semiconductor industry next month [July

1995] will celebrate the 40th anniversary of a partnership in a field that has enabled such technological

advances as the development of sophisticated diagnostic

medical devices, laptop computers, and home breadmaking machines. These advances have profited from

the support the industry has received in the past 40 years

through the semiconductor research program at the

Commerce Department’s National Institute of Standards

and Technology.”

These efforts began in July 1955, when electronics

scientist Judson C. French was entrusted by NBS

management with a budget of $10,000 and a mission to

see what kind of support NBS could give to the growing

transistor industry. French approached the American

Society for Testing and Materials and the Electronic

Industries Association to help define a need that NBS

could fulfill. Each organization identified measurements

critical to dealing with the great discrepancies in both

manufacturing and product specifications that were still

unresolved by member companies. So, armed with a

project from each organization, NBS embarked on a

new program of measurement research that would,

123
decades later, inspire the Semiconductor Industry

Association to note that “NIST is the only place in the

U.S. where the broad range of measurements needed for

semiconductor processing are routinely and systematically developed.”

In the early 1970s, NBS was requested by the

Defense Advanced Research Projects Agency to help

the Defense Department develop integrated circuits

with increased performance and reliability levels. Both

military and private-sector organizations profited from

the measurement improvements. In one case, the investigation of wire bonding of integrated circuits established

new procedures, now implemented in commercially

available equipment, that increased circuit yields by as

much as 35-fold and made possible large military hybrid

circuits that utilize more than 500 wire bonds each.

In 1981, Charles River Associates conducted studies

to investigate the economic benefits provided by NBS

work in semiconductor technology. These studies found

that industry respondents received several benefits from

the use of NBS results, including improved product

reliability, increased production yields, increased ability

to meet customer specifications, improved product

features, cost reductions, and new directions of

company research.

The report concludes that “the overall industry productivity level was approximately one percent higher for

the years 1973 to 1977 [which were covered by the

studies] than it would have been had the technical information acquired from NBS not been available” and that

the median rate of return to the economy and society on

investment in the NBS work was 140 percent per year.

Later comparisons with industry data showed that NBS

had provided four percent of the total industry productivity increase during the period.

Work spawned by reference [1] is profusely evident in

industry. NIST’s work on photomask linewidths led to

a tenfold reduction of intercompany measurement

discrepancies, stimulated the production of new instrumentation, extended the range of use of optical microscopes, and provided techniques and calibration

standards that have been adopted industry-wide. All

U.S. semiconductor device manufacturers use NIST

measurement methods and standards. A study of the

benefits of this work estimated a $30 million annual

savings to the photomask producers alone.

NIST designed and built the world’s most accurate

ellipsometer to develop and issue standard reference

materials for measurement of silicon dioxide layer

thicknesses between 10 nm and 200 nm, measurements critical to industry for precise manufacturing

control.

NIST stimulated the first marketplace use of

integrated circuit test structures, which are devices

formed on the wafer during manufacture that can be

probed electrically to measure properties of materials,

quality of processing steps, device operation, and

mechanical properties. Test structures based on electrical measurements have been developed at NIST

for measuring dimensions (so-called “critical dimensions”); overlay, a measure of registration between layers

of a device; and electrical linewidth with uncertainties

in the 10 nm range.

Results of NIST’s methods of evaluating susceptibility to electromigration—which causes the interconnect

metal on modern integrated circuits to fail—have been

used by at least 14 companies. An independent study

reported that benefits to this industry, including reduced

production and transaction costs as well as improved

research efficiencies, led to an estimated aggregate

social rate of return of 117 %.

Harry A. Schafft began his NBS career in 1958 as an

Electronics Engineer in the Semiconductor Electronics

Division. In addition to his research on second breakdown in transistors, he started a program in 1982 to

improve the characterization of interconnect metallizations for their resistance to electromigration. This work

resulted in the development of three American Society

for Testing and Materials (ASTM) standards and numerous journal publications. His recent work has focused on

developing and coordinating techniques for building in

the reliability of semiconductor devices by identifying

and controlling critical process fabrication parameters.

Other areas in which he has made contributions include

photovoltaic electric power systems, measurement

problems related to wire bonds, and measurement

technology required by the cardiac pacemaker industry.

He is a Fellow of the the Institute of Electrical

and Electronics Engineers (IEEE) and received a

Department of Commerce Bronze Medal in 1983 and a

Silver Medal in 1992.

Judson C. French joined the National Bureau of

Standards in 1948. He conducted and later directed

research and development in microwave gas tubes and

semiconductor materials and devices prior to his

broader assignments in research management. He

served as Chief, Electron Devices Section (1968-1973);

Chief, Electronic Technology Division (1973-1978);

Director, Center for Electronic and Electrical Engineering (1978-1991); and Director (1991-1999) and

Director Emeritus (1999), Electronics and Electrical

Engineering Laboratory. French has served as a member

of the Optoelectronic Computing Systems Center Policy

Board at the University of Colorado since 1992 and as

124
an observing member of the Board of Directors of the

National Electronics Manufacturing Initiative, Inc.,

since 1998. He has co-chaired the Joint Management

Committee of the U.S.—Japan Joint Optoelectronics

Project since 1992. He is a member of the National

Academy of Engineering and a Fellow of the IEEE, and

he has received Department of Commerce Silver and

Gold Metals and the Edward Bennett Rosa Award of

NBS. In 1980 he received the Presidential Rank of SES

Meritorious Executive and, in 1984 and 1993, the rank

of Distinguished Executive.

Prepared by Harry A. Schafft.

Bibliography

[1] H. A. Schafft and J. C. French, “Second Breakdown” in Transistors, IRE Trans. Electron Devices ED-9, 129-136 (1962).

[2] Harry A. Schafft, Average Power Dissipated in a Diode Swept

Along Its Reverse Characteristic, NBS Technical Note 240,

National Bureau of Standards, Washington, DC (1964).

[3] H. A. Schafft and J. C. French, Breakdown Characteristics of

Semiconductor Materials, Electro-Technology 75 (6), 77-83

(1965). [4]H. A. Schafft, Avoiding Second Breakdown, in

Proc. 13th Int. Scientific Congress on Electronics, Rome, June

1966 (1966) pp. 117-130.

[5] H. A. Schafft and J. C. French, A Survey of Second Breakdown,

IEEE Trans. Electron Devices ED-13, 613-618 (1966).

[6] H. A. Schafft and J. C. French, Second Breakdown and Current

Distributions in Transistors, Solid-State Electron. 9, 681-688

(1966).

[7] H. A. Schafft, G. H. Schwuttke, and R. L. Ruggles, Second

Breakdown and Crystallographic Defects in Transistors, IEEE

Trans. Electron Devices ED-13, 738-742 (1966).

[8] H. A. Schafft, Second Breakdown in Transistors, in Proc. Second

Symp. on Reliability in Electronics, Budapest, October 1968,

(1968) p. 225.

[9] Harry A. Schafft, Second Breakdown—A Comprehensive

Review, Proc. IEEE 55, 1272-1288 (1967).

[10] Harry A. Schafft, Second Breakdown in Semiconductor

Devices—A Bibliography, NBS Technical Note 431, National

Bureau of Standards, Washington, DC (1967).

125
Stress Relaxation With Finite Strain

Soon after World War II, the development and use

of synthetic polymers, such as rubber and plastics,

burgeoned. The rapidly expanding uses of these materials demanded a better understanding of their fundamental properties, especially their mechanical properties. At that time engineers were more accustomed

to dealing with materials such as metals, which

behaved very differently under stress than did polymers.

When a reasonable load is placed on a metal, it

will bend or deform by an amount uniquely determined

by its elastic properties. Sustaining the load for a longer

period of time does not produce any further elastic

deformation. For synthetic rubbers or polymers,

such uniquely determined deformation cannot be

assumed to occur. Inevitably, and often dramatically,

the deformation corresponding to a given load will

change as time progresses. Such behavior is called

time-dependent.

It was necessary, then, to learn how to deal with

time-dependent properties in these new materials, to

discover which properties were controlling and controllable, to learn how to measure such properties, and to

understand how to handle them in engineering design.

What was needed was a rather ambitious undertaking,

namely the construction of a fully three-dimensional

theory that obeyed the laws of thermodynamics and

that went beyond the assumption commonly known as

linearity. The paper Stress Relaxation with Finite Strain

[1], published in 1962 by Bernstein, Kearsley, and

Zapas, was a major milestone in meeting this

challenge.

By linearity we mean the following: If you double the

load, you double the displacements involved in the corresponding deformation. More generally, a model is said

to be linear if, when one multiplies a load by any factor,

all displacements are multiplied by the same factor. In

theoretical models, it is more convenient to deal with

relative displacements called strains. Essentially, a strain

is a change in a length divided by a reference length. For

linearly elastic models, the strain is simply proportional

to the stress that produces it. For nonlinear models, such

simple and unique proportionality does not occur. That

was the fundamental problem for models of synthetic

rubber and polymers.

In early work, Herbert Leaderman in the Rubber

Section at NBS attempted to adapt his very successful

linear models to the new materials. He did this by trying

various nonlinear strain measures, with which he reformulated his models. But such stratagems proved to be

simply perturbations, or slight variations, on the theme

of linear models, and offered only very limited insights

into the effects of nonlinearity.

Fig. 1. Louis Zapas, Elliot Kearsley, and Barry Bernstein, ca. 1991.

126
Beginning in 1962, a fresh attack was made on this

problem in the Rheology Section of the Mechanics

Division of NBS by a team composed of physicist Elliot

A. Kearsley and chemical engineer Louis J. Zapas of the

Rheology Section, together with mathematician Barry

Bernstein of the Mathematical Physics Section in the

Mathematics Division. By allowing for very wide variations in characteristic times and characteristic temperatures, this group observed what appeared to be striking

qualitative similarities in the nonlinear viscoelastic

behavior of widely different materials. With respect to

certain characteristic quantities, the qualitative behaviors of polymeric materials ordinarily treated as solids

and of materials ordinarily treated as liquids seemed

indistinguishable. Motivated by this observation, the

NBS team constructed a phenomenological model of

nonlinear viscoelasticity within the following limitations:

(1) It is inherently nonlinear, not a perturbation of

linear viscoelasticity.

(2) It is consistent with all the geometric and thermodynamic constraints appropriate to the mechanics of a material deforming in three-dimensional

space.

(3) It models the known qualitative characteristics of

viscoelastic materials.

(4) It is based on a generalized micromechanics

of viscoelastic materials, but is not tied to the

details of any particular material.

This effort resulted in a model representing a material

whose responses in shear arise from a time-dependent

potential bearing the dimensions of entropy. Furthermore, this potential depends not simply on the current

value of deformation, but rather on the whole past-time

history of the deformation. In other words, to compute

its value at a given time, one needs to know the history

of the deformation as a function of time. In producing

elastic effects, this potential plays the role of an elastic

strain-energy function. It induces an elastic stress in a

current configuration derived from a weighted sum of

partial stresses arising from the deformations of past

configurations to the current configuration. As the

current configuration evolves, each particular past

configuration recedes in time, and the weight of its

contribution to the current stress recedes accordingly,

resulting in viscous energy loss.

In addition, the notion of the “material clock” was

incorporated. Consider a temperature-sensitive clock

that runs faster at higher temperatures than at lower

temperatures. Suppose that what determines how long

ago in the past a particular event occurred is, to the

material, effectively the time interval on that temperature-sensitive clock rather than the time interval on the

temperature-insensitive laboratory clock. Such a conceptual clock, with its rate adjusted appropriately for the

material with respect to the laboratory clock, is what

one means by a material clock.

The first public presentation of this work occurred at

the annual meeting of the Society of Rheology in 1962.

At that time, a version of the model suitable for use

under isothermal conditions was presented in a series

of three talks. This presentation was followed by a

summary of the model published as a paper in the 1963

transactions of the Society [1]. Subsequently, a more

complete version including thermodynamic considerations was published in the NBS Journal of Research in

1964 [2].

For the next few years, attention to this model was

pursued only at NBS and a few other laboratories where

experimental studies were conducted to establish the

successes and limitations of the model for treating the

mechanics of polymeric materials. However, by 1970,

inherent difficulties in alternative competing models led

researchers to turn in greater numbers to the NBS

Fig. 2. Schematic of a stress-relaxation apparatus. The rigid support

cylinder determines the ratio of final to initial length (extension ratio)

of the sample while the displacement of the spring measures the force

on the sample.

127
model. The authors had called the model “a perfect

elastic fluid” by analogy to the concept of a perfect gas.

However, as the number of citations to the 1963 article

began to climb, the model became widely known as “the

BKZ fluid” or, on occasion, as “the K-BKZ fluid.”

During the next decade, the use of the BKZ fluid became ubiquitous among rheologists. By 1988 the BKZ

model was so well established in rheological circles that

the Society of Rheology, at its annual meeting, held a

session entitled “25 Years of the BKZ Theory” to mark

the 25th anniversary of its initial publication and to

review the subsequent developments. The BKZ model is

now expounded in most texts on mechanical properties

of materials and is commonly taught in courses for

students of polymer science and of chemical and mechanical engineering.

According to the BKZ model, the response of a material to any deformation history can be calculated from

measured behavior in stress-relaxation. This is a very

convenient property for calculation. Furthermore, the

limitations of the BKZ model have been well established. Despite some failings, it has been shown to afford an excellent representation of the mechanical behavior of most polymeric materials in most situations.

Consequently, versions of the BKZ model are widely

used in finite-element calculations; in designing injection molding and blow molding processes; in film

stretching and extrusion processes; and in designing

systems for processing and handling materials with

complex rheology. Such processes occur, for example, in

the fabrication of plastic objects, in packaging, in food

processing, and in the mixing of paints and other

coatings. Modifications and ornamentation of the model

are still being proposed and tested to overcome the

known failings, and the end is not in sight. On the

occasion of the 25th anniversary of the publication of

the BKZ paper, R. I. Tanner opined in a presentation [3],

“I believe that we will continue to use the (BKZ) theory,

. . . I do not think that the theory will fade away rapidly

since it is the optimal type of single-integral equation

.... ”

Prepared by Elliot Kearsley and Barry Bernstein.

Bibliography

[1] B. Bernstein, E. A. Kearsley, and L. J. Zapas, A Study of Stress

Relaxation with Finite Strain, Trans. Soc. Rheol. VII, 391-410

(1963).

[2] B. Bernstein, E. A. Kearsley, and L. J. Zapas, Thermodynamics

of Perfect Elastic Fluids, J. Res. Natl. Bur. Stand. 68B, 103-113

(1964).

[3] R. I. Tanner, From A to BKZ in Constitutive Relations, J. Rheol.

32, 673-702 (1988).

128
Realistic Evaluation of the Precision and

Accuracy of Instrument Calibration Systems

Prior to the publication of Realistic Evaluation of the

Precision and Accuracy of Instrument Calibration

Systems by Churchill Eisenhart [1], the terms

“precision” and “accuracy” were used in a qualitative

manner to characterize measurements. These terms

appeared in many American Society for Testing Materials (ASTM) standards long before any common agreement or understanding had been reached as to their

meanings and consequences. Circa 1950, individuals

and organizations began concerted efforts to right this

situation. Churchill Eisenhart was drawn to this issue

as it related to calibrations, which he called refined

measurement methods. As Chief of the Statistical

Engineering Laboratory (SEL), Applied Mathematics

Division, he set out to put the concepts of accuracy and

precision on a solid statistical basis for NBS scientists

and metrologists.

His paper on the subject, published in 1961 [1], was

to become the preeminent publication on the subject.

With impeccable scholarship and commitment to detail,

Eisenhart synthesized his own work [2] and the writings

of statistical theorists and practitioners, Walter

Shewhart [3], Edwards Deming, Raymond Birge [4],

and R. B. Murphy [5], into concepts of quality control

that could be applied to measurement processes.

Three basic concepts in the paper were immediately

accepted by metrologists at NBS, namely: (1) a

measurement process requires statistical control;

(2) statistical control implies control of both reproducibility and repeatability; and (3) a measurement result

requires an associated statement of uncertainty that

includes any possible source of bias.

In this paper, for the first time, measurements themselves were described as a process whose output can

be controlled using statistical techniques. Eisenhart

reinforced the conclusion, probably first drawn by

Murphy [5], that “Incapability of control implies that

the results of measurement are not to be trusted as an

indication of the physical property at hand—in short,

we are not in any verifiable sense measuring anything”—when he says, “a measurement operation must

have attained what is known in industrial quality control

language as a state of statistical control . . . before it

can be regarded in any logical sense as measuring

anything at all.”

Eisenhart’s paper, coupled with work by other SEL

statisticians, had a lasting and profound effect on

measurement processes at NBS/NIST and throughout

the metrology community. W. J. Youden revolutionized

interlaboratory testing with methods for ruggedness

testing [6] and for quantifying bias in test methods [7]

and scientific measurements [8]. In his work with

industrial chemists and ASTM committees, Youden left

a huge body of literature on the subject of bias. His

papers, which are too numerous to cite, have a common

theme in the use of experimental design to shed light on

sources of error in a measurement process. He was

especially interested in interlaboratory testing as a

means of uncovering biases in measurement processes

[9], and the so-called Youden plot [10] has become an

accepted design and analysis technique throughout the

world for interlaboratory comparisons.

Statistical activity at NBS in the 1950s was characterized by the development of experimental designs; in the

Fig. 1. Churchill Eisenhart.

129
late 1950s, with the advent of electronic computing,

Joseph Cameron created calibration designs with

provisions for check standards for the NBS calibration

laboratories. Cameron, Youden, and Eisenhart then

merged the check standard concept with quality control

procedures in Eisenhart’s paper to form a cohesive

practice, known as measurement assurance [11-13], as a

means of tying measurement results to a reference base

and quantifying the uncertainty relative to the reference

base. The first documentation of a measurement

assurance program in a NBS calibration laboratory

appears to be a tutorial by Paul Pontius and Joseph

Cameron [14] on mass calibrations. Measurement

assurance programs now abound in metrology and are

regularly applied to measurements as diverse as dimensional measurements of gage blocks standards and

semiconductor devices [15-16].

Eisenhart’s exposition of sources of error in a measurement process led to the accepted practice of the day

for reporting uncertainty as described by Harry Ku

[17], and a paper co-authored with Ron Colle ́ and Ku

[18] was a forerunner of the 1993 ISO Guide to the

Expression of Uncertainty in Measurement [19] and the

companion NIST guideline by Barry Taylor and Chris

Kuyatt [20].

Churchill Eisenhart was brought to NBS from the

University of Wisconsin in 1946 by Edward Condon,

Director of NBS, to establish a statistical consulting

group to “substitute sound mathematical analysis for

costly experimentation.” He was allowed to recruit his

own staff and, over the years, he brought many notable

and accomplished statisticians to SEL. He served as

its Chief from 1947 until his appointment as Senior

Research Fellow in 1963. He retired in 1983, and his

final contribution to NIST was the formation of the

Standards Alumni Association, which he headed until

his death in 1994.

In its early days, SEL was drawn into outside studies

as NBS became more involved in industrial activities.

The study that brought the most controversy to NBS and

the most recognition to Eisenshart’s group was the

AD-X2 battery additive case. The NBS Director,

A.V. Astin, had been pressured by various senators and

the battery additive producer to run a test of the additive.

Under extreme time constraints, the statisticians came

up with appropriate experimental designs for the tests

[21] and assigned the treatment of additive or noadditive to 32 batteries blindly and at random. The

experiments, run by the Electricity Division, confirmed

that the additive had no significant positive effect on

batteries, but in what was quickly to become an interesting sidelight of history, the Assistant Secretary of

Commerce for Domestic Affairs announced that Astin

had not considered the “play of the marketplace” in his

judgment and relieved him as Director of NBS. Eventually, the National Academy of Sciences was called in to

review NBS’s work, which was labeled first rate, and

Astin was reinstated [22].

Fig. 2. Joseph Cameron and Jack Youden of the Statistical Engineering Laboratory explaining a measurement

design.

130
Over his long and illustrious career, Eisenhart was

awarded the U. S. Department of Commerce Exceptional Service Award in 1957; the Rockefeller Public

Service Award in 1958; and the Wildhack Award of the

National Conference of Standards Laboratories in 1982.

He was elected President of the American Statistical

Association (ASA) in 1971 and received the Association’s Wilks Memorial Medal in 1977. Eisenhart was

honored with an Outstanding Achievements Award of

the Princeton University Class of 1934 and with Fellowships in the ASA, the American Association for the

Advancement of Science, and the Institute of Mathematical Sciences. He was a long-time member of the

Cosmos Club.

In this later years, Eisenhart indulged his interest in

the history of statistics, and particularly in the evolution

of least-squares. He corresponded regularly with those

who had like interests. In a memorial lecture given in his

honor at the National Institute of Standards and Technology on May 5, 1995, Stephen Stigler [23] says that “I

wrote to him that he had set the standard for scholarly

research in our field, and that is how I thought of him—

the standard.”

Prepared by M. Carroll Croarkin.

Bibliography

[1] Churchill Eisenhart, Realistic Evaluation of the Precision and

Accuracy of Instrument Calibration Systems, J. Res. Natl. Bur.

Stand. 67C, 161-187 (1963).

[2] C. Eisenhart, The Reliability of Measured Values—Part I,

Fundamental Concepts, Photogramm. Eng. XVIII, 542-554

(1952).

[3] Walter A. Shewhart, Statistical Method from the Viewpoint of

Quality Control, The Graduate School, U.S. Department of

Agriculture, Washington, DC (1939).

[4] W. Edwards Deming and Raymond T. Birge, On the Statistical

Theory of Errors, Rev. Mod. Phys. 6, 119-161 (1934); with

additional notes dated 1937 (The Graduate School, Department

of Agriculture, Washington, DC).

[5] R. B. Murphy, On the Meaning of Precision and Accuracy,

Mater. Res. Stand. 1, 264-267 (1961).

[6] W. J. Youden, The Collaborative Test, presented at the referees’

Seventy-sixth Annual Meeting of the Association of Official

Agricultural Chemists, Washington, DC, Oct. 16, 1962.

[7] W. J. Youden, How to Evaluate Accuracy, Mater. Res. Stand. 1,

268-271 (1961).

[8] W. J. Youden, Systematic Errors in Physical Constants, Phys.

Today 14 (9), 32-43 (1961).

[9] W. J. Youden, Experimental Design and ASTM Committees,

Mater. Res. Stand. 1, 862-867 (1961).

[10] W. J. Youden, The Sample, the Procedure and the Laboratory,

Anal. Chem. 32 (13), 23A37A (1960).

[11] J. M. Cameron, Measurement Assurance, NBS Internal Report

77-1240, National Bureau of Standards, Washington, DC (1977).

[12] Brian Belanger, Measurement Assurance Programs Part I: General Introduction, NBS Special Publication 676-I, National Bureau of Standards, Washington, DC (1984).

[13] Carroll Croarkin, Measurement Assurance Programs Part II: Development and Implementation, NBS Special Publication 676-II,

National Bureau of Standards, Washington, DC (1984).

[14] P. E. Pontius and J. M. Cameron, Realistic Uncertainties and the

Mass Measurement Process: An Illustrated Review, NBS Monograph 103, National Bureau of Standards, Washington, DC

(1967).

[15] Carroll Croarkin, John Beers, and Clyde Tucker, Measurement

Assurance for Gage Blocks, NBS Monograph 163, National Bureau of Standards, Washington, DC (1979).

[16] Carroll Croarkin and Ruth N. Varner, Measurement Assurance

for Dimensional Measurements on Integrated-Circuit Photomasks, NBS Technical Note 1164, National Bureau of Standards,

Washington, DC (1982).

[17] Harry H. Ku, Expressions of Imprecision, Systematic Error, and

Uncertainty Associated with a Reported Value, Measurements &

Data, 2 (4), 72-77 (1968).

[18] Churchill Eisenhart, Harry H. Ku, and R. Colle ́, Expression of

the Uncertainties of Final Measurement Results: Reprints, NBS

Special Publication 644, National Bureau of Standards, Washington, DC (1983).

[19] Guide to the Expression of Uncertainty in Measurement, International Organization for Standardization, Geneva, Switzerland

(1993).

[20] Barry N. Taylor and Chris E. Kuyatt, Guidelines for Evaluating

and Expressing the Uncertainty of NIST Measurement Results,

NIST Technical Note 1297, National Institute of Standards and

Technology, Gaithersburg, MD (1994).

[21] Battery AD-X2, Hearings before the Select Committee on Small

Business, United States Senate, Eighty-Third Congress, First

Session, On Investigation of Battery Additive AD-X2, Washington, 1953.

[22] NBS Report 2447 on Battery Additive AD-X2, U.S. Government

Printing Office, Washington, DC (1953).

[23] S. M. Stigler, Statistics and the Question of Standards, J. Res.

Natl. Inst. Stand. Technol. 101, 779-789 (1996).

131
Experimental Statistics

NBS Handbook 91: Experimental Statistics [1] was

first published in 1963. The material for the book was

originally commissioned and printed in a limited edition

by the U.S. Army as a series of five Army Ordnance

Pamphlets OSRDDP 20-110-114. The publication was

prepared in the Statistical Engineering Laboratory

(SEL) of NBS under a contract with the former Office

of Ordnance Research. Although originally intended for

the needs of the Army, it proved to be equally useful

to research and development groups, both within and

outside the government.

The Handbook is organized in five sections; namely,

1. Basic Statistical Concepts and Analysis and Interpretation of Measurement Data

2. Standard Techniques for Analysis and Interpretation

of Enumerative and Classificatory Data

3. The Planning and Analysis of Comparative Experiments

4. Special Topics

5. Tables

It is a monumental work which brings together under

one cover the combined experience and expertise of the

Statistical Engineering Laboratory. Mary Gibbons

Natrella was principal author with overall responsibility

for the entire publication, but there are contributions on

polynomial and multivariable relationships, sensitivity

testing, use of transformations, and expression of

uncertainties by other members of the SEL. Chapters 1,

20, and 23 were written by Churchill Eisenhart, founding father of the SEL; Chapter 6 was written by Joseph

Cameron, who later became Chief of SEL, and Chapter

10 is based on material prepared by Mary Epling.

Some original tables were prepared by Paul Somerville;

Norman Severo assisted with Section 2, and Shirley

Young Lehman helped with the collection and analysis

of examples.

Mary Natrella had a special gift for elucidating

difficult statistical concepts, and these expositions are

the strength of the book. The workbook style of the

volume probably accounts for its popularity and acceptance by statisticians and non-statisticians alike. It is

replete with examples; the page for each example

is divided, with the statement of the problem and recommended solution on the left-hand side and detailed

step-by-step calculations on the right-hand side. Mary

Natrella also believed in attention to detail. The Foreword states that “some procedures in the Handbook

have been explained and illustrated in detail twice: one

for the case where the important question is whether

the performance of a new material, product, or process

exceeds an established standard; and again for the case

where the important question is whether its performance

is not up to the specified standard.”

The Handbook was an immediate success at NBS, in

the Army, and throughout the Department of Defense.

It eventually received wide acclaim in other government

agencies, industry, and universities. Churchill Eisenhart

was fond of quoting a statistician who said that “the best

thing about the Handbook is that it is correct.”

The Handbook is recognized for its deep and longlasting impact on the application of statistics to the

planning and analysis of scientific experiments. It was

reprinted in 1983 for commercial sale by Wiley Interscience as part of its Selected Government Publications

series. In 1985, the American Society for Metals published a condensation of four chapters on planning and

Fig. 1. Mary Gibbons Natrella.

132
analysis of comparative experiments as part of the

Statistics Section of Volume 8 of the 9th edition of the

ASM Handbook. It has been NIST’s second-best selling

publication, after the Handbook of Mathematical Functions, which is covered elsewhere in this volume. The

material is still current after more than thirty years, and

this year alone it received close to forty journal citations

as measured by the Science Citation Index.

NIST still receives requests for this book, and its contents are the basis for training courses taught by the

Statistical Engineering Division (SED) and companies

such as SEMATECH that are involved in technology

development. It has proved such an inspiration that a few

years ago Patrick Spagon of the Statistical Methods

Group of SEMATECH approached SED with a proposal for updating and recreating the book with examples directed towards the semiconductor industry. That

proposal has evolved into a publication for the World

Wide Web [2] that is currently under development by a

team that includes: James Filliben, William Guthrie,

Alan Heckert, and Carroll Croarkin of SED; Paul Tobias, head of the Statistical Methods Group, and Chelli

Zey of SEMATECH; Barry Hembree of AMD; and Ledi

Trutna, a private consultant.

Mary Natrella joined the Statistical Engineering Laboratory of NBS as a mathematical statistician in April

1950 after Churchill Eisenhart noticed her work as a

sampling inspection expert in the U.S. Navy’s Bureau of

Ships. At the Navy, she worked on a team that developed

the now famous MIL-STD-105A, Sampling Procedures

and Tables for Inspection by Attributes (1950), which

was to become a government wide standard. Her

“Report of Proceedings of the Subcommittee for Preparation of MIL-STD-105A,” issued as a companion document to the standard, was distributed to government

groups developing sampling inspection plans, as well as

to professional and technical organizations, and was still

in demand in the 1970s.

Fig. 2. Partial page from NIST/SEMATECH Engineering Statistics Handbook showing graphical techniques for deciding if the relationship

between two variables is linear.

133
The SEL was a pioneering group dedicated to application in the physical sciences of the statistical methods

developed by R. A. Fisher, J. Neyman, and E. S. Pearson

in England and Walter Shewhart in the United States.

Mary Natrella served as a consultant on statistical planning and analysis of experiments to NIST scientists, and

her training course on “Statistics of Measurement” was

heavily attended for many years. Her most notable

publication is Handbook 91, which was 7 years in

preparation and required all her talents as teacher and

consultant. During this time, Mary also contributed

several sections to NBS Special Publication 300 [3] and

worked with Carroll Brickenkamp and Steve Hasko of

the NIST Office of Weights and Measures on NBS

Handbook 133: Checking the Net Contents of Packaged

Goods [4], which has been adopted by the National

Conference on Weights and Measures. She performed

her last service for the Statistical Engineering Division

by serving as Acting Division Chief for the 2 years prior

to her retirement in 1986.

The 1980’s brought the culmination of Mary’s career,

with recognition on many fronts. She was elected a

Fellow of the American Statistical Association (ASA)

in 1981. In 1982, she received the Department of

Commerce’s Superior Federal Service Award. She was

a long-time member of American Society for Testing

Materials (ASTM) Committee E-11 on Quality and

Statistics. In 1984, for her work as chairman of Subcommittee E11.03 on Statistical Analysis and Control

Techniques, she was awarded the Society’s Award of

Merit, which carries the designation of Fellow.

In the year 2000 Mary Natrella has been further

honored by the establishment of an endowed scholarship

fund which will provide $1000 scholarships each year

for two students to attend the Quality and Productivity

Research Conference (QPRC). The scholarships were

established by the Quality and Productivity section of

the American Statistical Association, under the chairmanship of Veronica Czitrom of Lucent Technologies,

with funds donated by Mary’s husband, Joseph V.

Natrella, and the QPRC Steering Committee. The

purpose is to honor Mary’s 36 years as author, teacher,

and consulting statistician and her many contributions to

the statistical community.

Prepared by M. Carroll Croarkin.

Bibliography

[1] Mary Gibbons Natrella, Experimental Statistics, NBS Handbook

91, National Bureau of Standards, Washington, DC (1963);

reprinted 1966.

[2] Paul Tobias and Carroll Croarkin (eds.), NIST/SEMATECH

Engineering Statistics Handbook, (http://www.itl.nist.gov/

div898/handbook/index.html), National Institute of Standards

and Technology (1999).

[3] Harry H. Ku (ed.), Precision Measurement and Calibration: Statistical Concepts and Procedures, NBS Special Publication 300, Vol. 1, National Bureau of Standards, Washington, DC

(1969).

[4] C. S. Brickenkamp, S. Hasko, and M. G. Natrella, Checking the

Net Contents of Packaged Goods, NBS Handbook 133, Third

Edition, National Bureau of Standards, Gaithersburg, MD (1988).

134
Handbook of Mathematical Functions

The Handbook of Mathematical Functions with

Formulas, Graphs, and Mathematical Tables [1] was the

culmination of a quarter century of NBS work on core

mathematical tools. Evaluating commonly occurring

mathematical functions has been a fundamental need as

long as mathematics has been applied to the solution of

practical problems. In 1938, NBS initiated its Mathematical Tables Project to satisfy the increasing demand

for extensive and accurate tables of functions [2].

Located in New York and administered by the Works

Projects Administration, the project employed not only

mathematicians, but also a large number of additional

staff who carried out hand computations necessary to

produce tables. From 1938 until 1946, 37 volumes of the

NBS Math Tables Series were issued, containing tables

of trigonometric functions, the exponential function,

natural logarithms, probability functions, and related

interpolation formulae. In 1947, the Math Tables Project

was moved to Washington to form the Computation

Laboratory of the new National Applied Mathematics

Laboratories of NBS. Many more tables subsequently

were published in the NBS Applied Mathematics Series;

the first of these, containing tables of Bessel functions

[3], appeared in 1948.

On May 15, 1952, the NBS Applied Mathematics

Division convened a Conference on Tables. Milton

Abramowitz of NBS, who had been a member of the

technical planning staff for the Math Tables Project,

described preliminary plans for a compendium of

mathematical tables and related material. Abramowitz

indicated that the Bureau was in need of both technical

advice and financial support to carry out the project.

With the support of the National Science Foundation

(NSF), a two-day Conference on Tables was held at the

Massachusetts Institute of Technology on September

15-16, 1954, to discuss the prospects for such an undertaking. Twenty-eight persons attended, including both

table producers and users from the science and engineering community. The report of the conference concluded

that

“an outstanding need is for a Handbook of

Tables for the Occasional Computer, with

tables of usually encountered functions and a

set of formulas and tables for interpolation

and other techniques useful to the occasional

computer.”

(Note that here the term computer refers to a person

performing a calculation by hand.) The report recommended that NBS manage the production of the Hand

book and that NSF provide financial assistance. The

conference elected the following committee to carry

out its recommendations: P.M. Morse (Chair),

M. Abramowitz, J.H. Curtiss, R.W. Hamming, D. H.

Lehmer, C.B. Tompkins, and J.W. Tukey. The committee was successful in persuading both NBS and NSF to

support the project, and it began officially in December

of 1956.

The Mathematics Division of the National Research

Council also had an interest in mathematical tables.

Since 1943, they had been publishing a quarterly

journal entitled Mathematical Tables and Other Aids to

Computation (today known as Mathematics of Computation). To provide technical assistance to NBS, as well

as independent oversight for NSF, the NRC established

a Committee on Revision of Mathematical Tables. Its

members were P. M. Morse (Chair), A. Erde ́lyi, M. C.

Fig. 1. Portrait of Milton Abramowitz.

135
Gray, N. C. Metropolis, J. B. Rosser, H. C. Thacher, Jr.,

John Todd, C. B. Tompkins, and J. W. Tukey. This group

of luminaries in the fields of applied mathematics

and physics provided guidance to NBS throughout the

project to produce the Handbook.

Milton Abramowitz, who was then Chief of the

Computation Laboratory of the NBS Applied Mathematics Division, led the project. Abramowitz was born

in Brooklyn, NY, in 1915. He received a B. A. from

Brooklyn College in 1937 and an M. A. in 1940.

He joined the NBS Math Tables Project in 1938 and in

1948 received a Ph.D. in Mathematics from New York

University. Abramowitz’ dedication, enthusiasm, and

boundless energy led to substantial progress in the

project during its first year. The proposed outline for the

Handbook called for a series of some 20 chapters, each

with a separate author. Authors were drawn from

NBS staff and guest researchers, as well as external

researchers working under contract. Most chapters

would focus on a particular class of functions, providing

formulas, graphs, and tables. Listed formulas would

include differential equations, definite and indefinite

integrals, inequalities, recurrence relations, power

series, asymptotic expansions, and polynomial and

rational approximations. Material would be carefully

selected in order to provide information most important

in applications, especially in physics. Consequently,

the higher mathematical functions, such as Bessel

functions, hypergeometric functions, and elliptic

functions, would form the core of the work. Additional

chapters would provide background on interpolation in

tables and related numerical methods for differentiation

and quadrature.

Philip J. Davis of NBS first prepared Chapter 6, on

the gamma and related functions, to serve as a model for

other authors. This chapter portrayed the telegraphic

style that is a hallmark of the Handbook, i.e., the

material is displayed with a minimum of textual description. In the course of developing his chapter, Davis

became interested in the history of the topic. This led to

a historical profile published in 1959 [4], which won

the prestigious Chauvenet Prize for distinguished

mathematical exposition from the Mathematical

Association of America.

The Handbook project occurred during the period

when general-purpose electronic computing machinery

was first coming into use in government research

laboratories. (Early computer development of SEAC at

NBS is described elsewhere in this volume.) Nevertheless, most of the tables in the Handbook were generated by hand on desk calculators. However, even at that

time it was clear to the developers of the Handbook

that the need for tables themselves would eventually be

superseded by computer programs which could evaluate

functions for specified arguments on demand.

By the summer of 1958, substantial work had been

completed on the project. Twelve chapters had been

completed, and the remaining ones were well underway.

The project experienced a shocking setback one weekend in July 1958 when Abramowitz suffered a heart

attack and died. Irene Stegun, who was Assistant Chief

of the Computation Laboratory, took over management

of the project. Stegun, who was born in Yonkers, NY in

1919, had received an M. A. from Columbia University

in 1941, and joined NBS in 1943. The exacting work of

assembling the many chapters, checking tables and

formulas, and preparing the work for printing took

much longer than anticipated. Nevertheless, the

Handbook of Mathematical Functions, with Formulas,

Graphs, and Mathematical Tables was finally issued as

Applied Mathematics Series Number 55 in June 1964

[1]. The volume, which is still in print at the U.S.

Government Printing Office and stocked by many

bookstores and online booksellers, is 1046 pages in

length. The chapters and authors are as follows.

Fig. 2. Portrait of Irene Stegun.

136
1. Mathematical Constants, D. S. Liepman.

2. Physical Constants and Conversion Factors, A. G.

McNish.

3. Elementary Analytical Methods, M. Abramowitz.

4. Elementary Transcendental Functions, R. Zucker.

5. Exponential Integral and Related Functions, W.

Gautschi (American University) and William F.

Cahill.

6. Gamma Function and Related Functions, P. J.

Davis.

7. Error Function and Fresnel Integrals, W. Gautschi

(American University).

8. Legendre Functions, I. A. Stegun.

9. Bessel Functions of Integer Order, F. W. J. Olver.

10. Bessel Functions of Fractional Order, H. A.

Antosiewicz.

11. Integrals of Bessel Functions, Y. L. Luke.

12. Struve Functions and Related Functions, M.

Abramowitz.

13. Confluent Hypergeometric Functions, L. J. Slater

(Cambridge University).

14. Coulomb Wave Functions, M. Abramowitz.

15. Hypergeometric Functions, F. Oberhettinger.

16. Jacobian Elliptic Functions and Theta Functions, L.

M. Milne-Thomson (University of Arizona).

17. Elliptic Integrals, L. M. Milne-Thomson (University of Arizona).

18. Weierstrass Elliptic and Related Functions, T. H.

Southard.

19. Parabolic Cylinder Functions, J. C. P. Miller (Cambridge University).

20. Mathieu Functions, G. Blanch (Wright-Patterson

Air Force Base).

21. Spheroidal Wave Functions, A. N. Lowan (Yeshiva

University).

22. Orthogonal Polynomials, U. W. Hochstrasser

(American University).

23. Bernoulli and Euler Polynomials—Riemann Zeta

Function, E. V. Haynsworth and K. Goldberg.

24. Combinatorial Analysis, K. Goldberg, M. Newman,

and E. Haynsworth.

25. Numerical Interpolation, Differentiation, and Integration, P. J. Davis and I. Polonsky.

26. Probability Functions, M. Zelen and N. C. Severo

27. Miscellaneous Functions, I. A. Stegun.

28. Scales of Notation, S. Peavy and A. Schopf

(American University).

29. Laplace Transforms.

The public reaction to the publication of the Handbook was overwhelmingly positive. In a preface to the

ninth printing in November 1970, NBS Director Lewis

Branscomb wrote

“The enthusiastic reception accorded the

‘Handbook of Mathematical Functions’ is

little short of unprecedented in the long

history of mathematical tables that began

when John Napier published his tables of

logarithms in 1614. Only four and one-half

years after the first copy came from the press

in 1964, Myron Tribus, the Assistant Secretary for Commerce for Science and Technology, presented the 100,000th copy of the

Handbook to Lee A. DuBridge, then Science

Advisor to the President.”

The Handbook has had enormous impact on science

and engineering. Likely the most widely distributed

NBS/NIST technical publication of all time, the government edition has never gone out of print, and it has

appeared as a Dover reprint since 1965. It has been

reprinted (in all or part) by other publishers, such as

Moscow Nauka, Verlag Harri Deutsch, and Wiley Interscience. Government sales exceed 150,000 copies, with

commercial sales estimated at three to six times this

number. The Handbook’s citation record is also remarkable. More than 23,000 citations have been logged by

Science Citation Index (SCI) since 1973. Remarkably,

the number of citations to the Handbook continues

to grow, not only in absolute numbers, but also as a

Fig. 3. Photograph of Handbook.

137
fraction of the total number of citations made in the

sciences and engineering. During the mid-1990s, for

example, about once every 1.5 hours of each working

day some author, somewhere, made sufficient use of the

Handbook to list it as a reference. The success of the

Handbook was due to several factors. It collected in one

place, and in a well-organized way, the most important

information needed to make use of mathematical functions in practical applications. It served to standardize

notations and normalizations for the special functions of

applied mathematics, thus easing the communication of

scientific results. In 1965, Irene Stegun was awarded a

Gold Medal from the Department of Commerce for her

efforts in completing the project.

A number of difficult mathematical problems that

emerged in the course of developing the Handbook

engaged researchers in the NBS Applied Mathematics

Division for a number of years after its publication.

Two of these are especially noteworthy, the first having

to do with stability of computations and the second with

precision.

Mathematical functions often satisfy recurrence

relations (difference equations) that have great potential

for use in computations. However, if used improperly,

recurrence relations can quickly lead to ruinous errors.

This phenomenon, known as instability, has tripped up

many a computation that appeared, superficially, to be

straightforward. The errors are the result of subtle

interactions in the set of all possible solutions of the

difference equation. Frank Olver, who wrote the

Handbook’s chapter on Bessel functions of integer

order, studied this problem in great detail. In a paper

published in 1967 [5], Olver provided the first (and only)

stable algorithm for computing all types of solutions of

a difference equation with three different kinds of

behavior: strongly growing, strongly decaying, and

showing moderate growth or decay. Part of the impact of

this work is reflected today in the existence of robust

software for higher mathematical functions. Olver

worked on such topics in the Mathematical Analysis

Division of NBS, and this work provided the foundation

for his very influential later book on asymptotic analysis

Fig. 4. Screen shot of the NIST Digital Library of Mathematical Functions.

138
and special functions [6]. This book has been cited more

than 800 times, according to SCI.

Another important problem in mathematical computation is the catastrophic loss of significance caused by

the fixed length requirement for numbers stored in

computer memory. Morris Newman, who co-authored

the Handbook’s chapter on combinatorial analysis,

sought to remedy this situation. He proposed storing

numbers in a computer as integers and performing operations on them exactly. This contrasts with the standard

approach in which rounding errors accumulate with

each arithmetic operation. Newman’s approach had its

roots in classical number theory: First perform the

computations modulo a selected set of small prime

numbers, where the number of primes required is determined by the problem. These computations furnish

a number of local solutions, done using computer

numbers represented in the normal way. At the end, only

one multilength computation is required to construct the

global solution (the exact answer) by means of the

Chinese Remainder Theorem. This technique was first

described in a paper by Newman in 1967 [7]; it was

employed with great success in computing and checking

the tables in Chapter 24 of the Handbook. Today, this

technique remains a standard method by which exact

computations are performed. Newman’s research on this

and other topics, performed at NBS, formed the basis

for his 1972 book [8], which quickly became a standard

reference in the applications of number theory to

computation.

Research into the functions of applied mathematics

has continued actively in the 36 years since the Handbook appeared. New functions have emerged in importance, and new properties of well-known functions have

been discovered. In spite of the fact that sophisticated

numerical methods have been embodied in welldesigned commercial software for many functions, there

continues to be a need for a compendium of information

on the properties of mathematical functions. To address

this need, NIST is currently developing a successor to

the Handbook to be known as the Digital Library of

Mathematical Functions (DLMF) [9]. Based upon a

completely new survey of the literature, the DLMF will

provide reference data in the style of the Handbook

in a freely available online format, with sophisticated

mathematical search facilities and interactive threedimensional graphics.

Prepared by Ronald F. Boisvert and Daniel W. Lozier.

Bibliography

[1] Milton Abramowitz and Irene A. Stegun, eds., Handbook of Mathematical Functions With Formulas, Graphs, and Mathematical

Tables, NBS Applied Mathematics Series 55, National Bureau of

Standards, Washington, DC (1964).

[2] Arnold N. Lowan, The Computation Laboratory of the National

Bureau of Standards, Scripta Math. 15, 33-63 (1949).

[3] Tables of the Bessel Functions Y0(x), Y1(x), K0(x), K1(x) 0<=x<=1,

NBS Applied Mathematics Series 1, National Bureau of Standards, Washington, DC (1948).

[4] Philip J. Davis, Leonhard Euler’s Integral: A Historical Profile of

the Gamma Function, Am. Math. Monthly 66, 849-869 (1959).

[5] F. W. J. Olver, Numerical Solution of Second-Order Linear Difference Equations, J. Res. Natl. Bur. Stand. 71B, 111-129 (1967).

[6] F. W. J. Olver, Asymptotics and Special Functions, Academic

Press, New York (1974). Reprinted by A. K. Peters, Wellesley, MA

(1997).

[7] Morris Newman, Solving Equations Exactly, J. Res. Natl. Bur.

Stand. 71B, 171-179 (1967).

[8] Morris Newman, Integral Matrices, Academic Press, New York

(1972).

[9] D. Lozier, F. W. J. Olver, C. Clark, and R. Boisvert (eds.),

Digital Library of Mathematical Functions, (http://dlmf.nist.gov)

National Institute of Standards and Technology, .

139
Paths, Trees, and Flowers

“Jack Edmonds has been one of the creators of the

field of combinatorial optimization and polyhedral

combinatorics. His 1965 paper ‘Paths, Trees, and

Flowers’ [1] was one of the first papers to suggest the

possibility of establishing a mathematical theory of

efficient combinatorial algorithms . . . ” [from the

award citation of the 1985 John von Neumann Theory

Prize, awarded annually since 1975 by the Institute

for Operations Research and the Management

Sciences].

In 1962, the Chinese mathematician Mei-Ko Kwan

proposed a method that could be used to minimize the

lengths of routes walked by mail carriers. Much earlier,

in 1736, the eminent Swiss mathematician Leonhard

Euler, who had elevated calculus to unprecedented

heights, had investigated whether there existed a walk

across all seven bridges that connected two islands in

the river Pregel with the rest of the city of Ko ̈nigsberg

on the adjacent shores, a walk that would cross each

bridge exactly once.

Different as they may sound, these two inquiries have

much in common. They both admit schematic representations based on the concept of graphs. Thus they are

problems in graph theory, a twentieth century discipline

which combines aspects of combinatorics and topology.

Given a set of items called nodes and a second set of

items called arcs, a graph is defined as a relationship

between such sets: For each arc, two of the nodes are

specified to be joined by this arc. The actual, say

physical, meaning of such nodes and arcs is not what

distinguishes graphs. Only formal relationships count.

In particular, the bridges of Ko ̈nigsberg may be considered as arcs, each joining a pair of the four nodes which

correspond to the two islands and the two shores.

The commonality between the two graph-theoretical

problem formulations reaches deeper. Given any graph,

for one of its nodes, say i0, find an arc a1 that joins node

i0 and another node, say i1. One may try to repeat this

process and find a second arc a2 which joins node i1 to

a node i2 and so on. This process would yield a

sequence of nodes—some may be revisited—successive

pairs of which are joined by arcs (Fig. 3). The first and

the last node in that sequence are then connected by this

“path.”

Fig. 2. The graph of the bridges of Ko ̈nigsberg.

Fig. 1. The bridges of Ko ̈ningsberg.

Fig. 3. Open and closed paths in the graph.

140
(Think of a route along street segments joining intersections.) If each pair of nodes in a graph can be connected by a path, then the whole graph is considered

connected. A path in a graph is called closed if it returns

to its starting point (Fig. 3).

Mei-Ko Kwan’s “Chinese Postman Problem,” as it is

now generally called (since first suggested by Alan

Goldman, then of NBS), is to determine, in a given

connected graph, a shortest closed path which traverses

every arc at least once—delivers mail on every assigned

street block. Euler also considers closed paths meeting

all arcs, but aims at characterizing all graphs which

accommodate an Euler tour, a closed path that crosses

each arc exactly once. As Euler found, they are precisely

those connected graphs in which each node attaches to

an even number of arcs, or in other words, every node is

of even degree. By this result, there can be no Euler tour

over the bridges of Ko ̈nigsberg. Euler’s examination

typifies the classical combinatorial query: Do certain

constructs exist and if so, how many?

The following question also illustrates the flavor of

classical combinatorics: how many isomers are there of

the hydrocarbon CnH2n+2? Each such isomer (Fig. 4) is

characterized by the joining patterns of the carbon

atoms as nodes and bonds as arcs. The corresponding

arrangements, therefore, represent graphs. These graphs

have a very special property: For any two of their nodes

there exists a unique connecting path without repeat

arcs. Such a graph is called a

“tree.”

Every isomer defines a tree of carbon atoms whose

nodes are of degree four or less. Conversely, every such

tree uniquely characterizes an isomer. In graph-theoretical terms, the question is: How many trees with n nodes

are there with node degrees not exceeding four? (For

n = 40, the number is 62,481,801,147,341, as determined by ingenious use of “generating functions.”)

Here is one more topic in the same vein. A matchmaker has a list of k single men and l single women. Her

experience of many years enables her to discern which

pairs are compatible. She considers a number of compatible matches that might be arranged simultaneously.

How can she be sure that she arrived at the largest

possible number of such matches?

A theorem by one of the founders of graph theory,

the Hungarian mathematician De ́nes Ko ̈nig in 1931,

suggests an answer to that question. He considered the

Fig. 4. The carbon graphs of the isomers of C6 H14.

Fig. 5. A matching in a graph; two of the augmenting paths are

highlighted by........

141
graph whose nodes are the matchmaker’s clients and

whose arcs join the compatible pairs, leading to the

graph-theoretical concept of matching. A matching in a

graph is any subset of its arcs such that no two arcs in

the matching meet at a common node (Fig. 5).

Similar concepts are that of a packing or independent

set, namely, a subset of the nodes no two of which are

connected by an arc, and of a cover, namely, a subset of

the nodes that meets every arc.

The matchmaker’s graph has the special property that

each of its nodes is of one of two kinds, male or female,

and every arc connects nodes of different gender. For

such a bipartite graph, Ko ̈nig’s theorem states that the

number of arcs in a maximum matching equals the

number of nodes in a minimum cover. However, this

deep result ignores the problem of actually finding a

minimum cover in order to prove the optimality of a

matching.

Given a particular matching in any graph, an exposed

node is one that is not met by any arc of the matching.

An alternating path, that is, a path whose every other

arc is part of the matching, is called augmenting if it

connects two exposed nodes. Indeed, switching arcs

in and out of the matching along an augmenting path

results in a new matching with one more arc in it. It is

a 1957 theorem by the French mathematician Claude

Berge that a larger matching exists not merely if, but

also only if, the current matching admits an augmenting

path. The classical graph theorist would look at this

elegant characterization of maximum matchings and

ask: what more needs to be said?

That outlook had been changing during and after

World War II. The extensive planning needs, military

and civilian, encountered during the war and post-war

years now required finding actual solutions to many

graph-theoretical and combinatorial problems, but with

a new slant: Instead of asking questions about existence

or numbers of solutions, there was now a call for

“optimal” solutions, crucial in such areas as logistics,

traffic and transportation planning, scheduling of jobs,

machines, or airline crews, facility location, microchip

design, just to name a few. George B. Dantzig’s

celebrated “Simplex Algorithm” for linear programming was a key achievement of this era.

The Chinese Postman is a case in point. He does not

care about how many tours of his street blocks there are

to choose from nor whether there are indeed Euler tours.

He cares about delivering his mail while walking the

shortest possible distance. (Admittedly, mail carriers,

Chinese and otherwise, don’t really think in terms of the

Chinese Postman Problem. But how about garbage

collection in a big city?)

And then there were computers, and the expectation

that those electronic wizards would handle applied

combinatorial optimizations even if faced with the large

numbers of variables which typically rendered manual

computations impractical.

Enter Jack Edmonds. Edmonds did his undergraduate work at the George Washington University. He

recounts—as one of the pioneers featured in the volume

History of Mathematical Programming: A Collection

of Personal Reminiscences [20] his varied interests

and activities of that period. Thus he designed toys

and games with expectations of monetary rewards,

which unfortunately did not materialize. A stint as

a copy boy at the Washington Post found him at the

night desk during President Eisenhower’s heart attack

in 1955. Mathematics, however, survived as his overriding interest. Fascinated by the study of polytopes

by the Canadian Mathematician H. S. M. Coxeter,

Edmonds’ master thesis at the University of Maryland

(1959) addressed the problem of embedding graphs

into surfaces [6].

Fig. 6. Jack Edmonds.

142
In 1959 he joined NBS, became a founding member

of Alan Goldman’s newly created Operations Research

Section in 1961, and was steered towards precisely

the endeavor of developing optimization algorithms

for problems in graph theory and combinatorics. In

particular, he was drawn to two fundamental problems:

the “Maximum Packing Problem” and the “Minimum

Cover Problem” of determining largest packings and

smallest covers, respectively, in a given graph [2].

Edmonds quickly recognized the major challenge

of that task, a challenge that he called “the curse of

exponentiality.” While plainly “finite,” many of the

known graph-theoretical algorithms required exponential effort, or their authors had not detailed their procedures in a way that avoided such exponentiality.

Consider the “Maximum Matching Problem” of

finding the largest matching in a given graph. Recall that

a matching can be enlarged whenever there is an

augmenting path, that is, an alternating path connecting

two exposed nodes. As a consequence, there exists an

“algorithm” which in a finite number of steps—everything is finite here—determines whether a matching is

maximum or shows how to improve it. “All” that’s

needed is to examine, at each step, the alternating paths

originating at exposed nodes. It’s just that there are so

darn many of them!

In a general framework, computational problems have

a natural size, for instance, the number of nodes or arcs

in a graph. For algorithms, computational effort can

then be defined as the number of basic computational

steps, such as individual additions or multiplications,

and depends on problem size. If computational effort

increases as fast or faster than exponentially with

problem size, then it is said to require exponential effort.

Polynomial time, by contrast,—Edmonds used the term

good—prevails if computational effort is bounded by a

power d of problem size n. The notation O(n d

) is used

to indicate that level of complexity.

Regardless of technological progress, computers are

helpless when faced with exponential effort. To wit,

the “Traveling Salesman Problem.” Here a connected

graph is given along with a particular length for each

arc. What is wanted is a closed path of least total length

that visits every node. The sequence of visits essentially

defines such a round trip. Consider, for instance, the

48 state capitals of the contiguous United States and

Washington, DC, as nodes of a graph with an arc

between any two of them. From a base in Washington,

all those capitals are to be visited while minimizing

the total distance traveled. Thus there are 48! (factorial)

round trips in the running. A future supercomputer,

spending 1 nanosecond per trip, would require more

than 31044 years to examine all possible trips.

Stressing the integral role of complexity, Edmonds

became the leading proponent of a new direction: to

develop good algorithms for problems in graph theory

and combinatorics (or to identify problems for which

such algorithms can be proven not to exist). This has

spawned a new area of research that has grown and

flourished for four decades and is still going strong. It is

not by accident that a graph-theoretical optimization

problem, namely, the Traveling Salesman Problem, is

now frequently used as a complexity standard, calling a

problem NP-complete if it requires computational effort

equivalent to that of the Traveling Salesman Problem.

In 1961, while attending a summer workshop at the

RAND corporation in Santa Monica, California,

Jack Edmonds discovered a good algorithm for the

Maximum Matching Problem, whose complexity he

conservatively pegged at O(n 4

).

That algorithm is described in the paper Paths, Trees,

and Flowers [1]. In its title, the words “paths” and

“trees” refer to the standard graph-theoretical concepts.

The algorithms augmenting paths are found by a “tree

search” combined with a sophisticated process of

shrinking certain subgraphs called blossoms into single

nodes of a reduced graph. Hence the term

“flowers”

in the title.

Why was it a breakthrough? The answer is that all

good graph-theoretical algorithms known at the time

addressed “unimodular” problems such as the “Shortest

Path” and “Network Flow” problems, the rigorous proof

for the latter having been given by Edmonds with collaboration by Richard M. Karp [13]. These are problems

that could be formulated as integrality-preserving linear

programs, which by themselves did not create good

algorithms but indicated the potential for such.

Edmonds’ matching algorithm was the very first

instance of a good algorithm for a problem outside that

mold.

In addition, Paths, Trees, and Flowers contributed a

major theoretical result: a generalization of Ko ̈nig’s

theorem that holds for matchings in all kinds of graphs,

not just bipartite ones.

Edmonds also conjectured in this paper that both the

Maximum Packing Problem and the Minimum Cover

Problem were intrinsically harder than the Maximum

Matching Problem. Indeed, both of the former problems

were subsequently shown to be NP-complete.

In one of his seminal papers [3-10] published in

the Journal of Research of the National Bureau of

Standards, Edmonds [7] extended his algorithm to find

matchings that optimize the sum of given arc weights,

and, perhaps more importantly, he laid the foundation

143
for a polyhedral interpretation of matching theory which

was pursued, for instance, in the doctoral thesis by

William R. Pulleyblank [15] advised by Edmonds.

Subsequently, Edmonds found other good algorithms,

for instance, in his path-breaking research on combinatorial abstractions of matrices, called matroids [4, 12,

14-17, 19]. And, last but not least, he and Ellis L.

Johnson used the matching paradigm to arrive at a first

good algorithm for the Chinese Postman Problem [18].

In 1969, Edmonds accepted a professorship of

mathematics at the University of Waterloo, where a list

of distinguished doctoral students is testament to his

special gift of guiding and motivating young mathematicians. He remains to this day an active and highly

influential researcher in the field of graph theory and

combinatorics.

Why is it important to identify even a few graphtheoretical and combinatorial problems with good

solution algorithms, when there is such a great variety of

real-life optimization tasks, most of them defined in a

less clear-cut fashion? The utility of good algorithms

for idealized problems and their theory is that they suggest generalizations, variations, promising avenues of

attack, treatable approximations, iterative applications,

and also flag problem formulations best to avoid. In all

these roles, Edmonds’ matching algorithm has been an

indispensable and inspirational part of the toolkit for

combinatorial optimization and its multiple applications

to modern technology.

Prepared by Christoph Witzgall with help by Ronald

Boisvert, Geraldine Cheok, Saul Gass, Alan Goldman,

and James Lawrence.

Bibliography

[1] Jack Edmonds, Paths, Trees, and Flowers, Canad. J. Math. 17,

449-467 (1965).

[2] Jack Edmonds, Covers and Packings in a Family of Sets,

Bull. Amer. Math. Soc. 68, 494-499 (1962).

[3] Jack Edmonds, Existence of k-Edge Connected Ordinary Graphs

with Prescribed Degrees, J. Res. Natl. Bur. Stand. 68B, 73-74

(1964).

[4] Jack Edmonds, Minimum Partition of a Matroid into Independent Subsets, J. Res. Natl. Bur. Stand. 69B, 67-72 (1965).

[5] Jack Edmonds, Lehman’s Switching Game and a Theorem of

Tutte and Nash-Williams, J. Res. Natl. Bur. Stand. 69B, 73-77

(1965).

[6] Jack Edmonds, On the Surface Duality of Linear Graphs, J. Res.

Natl. Bur. Stand. 69B, 121-123 (1965).

[7] Jack Edmonds, Maximum Matching and a Polyhedron with

0,1-Vertices, J. Res. Natl. Bur. Stand. 69B, 125-130 (1965).

[8] Jack Edmonds and D. R. Fulkerson, Transversals and Matroid

Partition, J. Res. Natl. Bur. Stand. 69B, 147-153 (1965).

[9] Jack Edmonds, Optimum Branchings, J. Res. Natl. Bur. Stand.

71B, 233-240 (1967).

[10] Jack Edmonds, Systems of Distinct Representatives and Linear

Algebra, J. Res. Natl. Bur. Stand. 71B, 241-245 (1967).

[11] Jack Edmonds, Matroid Partition, in Mathematics of the Decision Sciences, Part I, (Proceedings of the Fifth Summer Seminar

on the Mathematics of the Decision Sciences, Stanford University, Stanford, CA, 1967), American Mathematical Society,

Providence, RI (1968) pp. 335-345.

[12] Jack Edmonds, Submodular Functions, Matroids, and Certain

Polyhedra, in Combinatorial Structures and their Applications

(Proceedings of the Calgary International Conference on Combinatorial Structures and their Applications, University of Calgary,

Calgary, Alberta, Canada, 1969), Gordon and Breach, New York

(1970) pp. 69-81.

[13] Jack Edmonds and Richard M. Karp, Theoretical Improvements

in Algorithmic Efficiency for Network Flow Problems, in

Combinatorial Structures and their Applications (Proceedings of

the Calgary International Conference on Combinatorial

Structures and their Applications, University of Calgary,

Calgary, Alberta, Canada, 1969), Gordon and Breach, New York

(1970) pp. 93-96.

[14] Jack Edmonds, Matroids and the Greedy Algorithm, Math.

Programming 1, 127-136 (1971).

[15] W. Pulleyblank and Jack Edmonds, Facets of 1-Matching

Polyhedra, in Hypergraph Seminar (Proceedings of the First

Working Seminar on Hypergraphs, Ohio State Univ., Columbus,

Ohio, 1972) Lecture Notes in Mathematics Vol. 411, SpringerVerlag, Berlin (1974) pp. 214-242.

[16] Jack Edmonds, Edge-Disjoint Branchings, in Combinatorial

Algorithms (Courant Computer Science Symposium 9, Naval

Postgraduate School, Monterey, CA, 1972), Algorithmics Press,

New York (1973) pp. 91-96.

[17] Peyton Young and Jack Edmonds, Matroid Designs, J. Res. Natl.

Bur. Stand. 77B, 15-44 (1973).

[18] Jack Edmonds and Ellis L. Johnson, Matching, Euler Tours, and

the Chinese Postman, Math. Programming 5, 88-124 (1973).

[19] Jack Edmonds, Matroid Intersection, in Discrete Optimization I

(Proceedings of the Advanced Research Institute on Discrete

Optimization and Systems Applications, Alberta, Canada, 1977);

Ann. Discrete Math. 4, 39-49 (1979).

[20] Jan Karel Lenstra, Alexander H. G. Rinnooy Kan, Alexander

Schrijver, History of Mathematical Programming, A Collection

of Personal Reminiscences, North-Holland, Amsterdam (1991).

144
Concepts, Terminology, and Notation for

Optical Modulation

In the early 1960s, the National Bureau of Standards

aided the photographic and printing industries by

conducting research on precise measurement of optical

transmission and reflection density, providing physical

standards to calibrate instruments, and writing national

and international documentary standards on optical

density measurement. Optical density is a logarithmic

measure of the darkness of a photograph or printed

image. Although the science was hardly new, it suffered

from loose concepts and imprecise terminology.

The same problems were encountered in photometry,

radiometry, colorimetry, and spectrometry. This publication [1] represented a major step forward in removing

the confusion and promoting the use of precise concepts

in optical measurements.

Physics textbooks defined “reflectance” as the ratio

of the amount of light reflected from a surface to the

amount of incident light. Workers who said they were

measuring reflectance actually measured the ratio of the

amount of reflected light to the amount of light reflected

from a standard diffuse white surface. They generally

regarded the measurement of the light reflected from the

white surface as merely a convenient way of measuring

the incident light. There was no generally accepted

terminology to distinguish these two kinds of measurements. The concepts thus were blurred.

The degree of confusion may be illustrated by an

example. Light incident on white paper is diffusely

reflected in all directions, only a minute fraction being

reflected to the pupil of the eye. The ratio of the amount

reflected in that direction to the amount incident is a

very small number, perhaps under 0.001. On the other

hand, the ratio of the amount reflected in that direction

to the amount reflected in the same direction from a

standard diffuse white surface may be as much as 0.9.

These are two different concepts—two different

physical quantities, with vastly different numerical

values. Such considerations led to a thorough analysis of

the basic concepts and terminology in this field. The

term “reflectance” was retained for the concept defined

in textbooks. The measurement relative to a white

standard was called “reflectance factor.” That term is

now used internationally in photography, printing, and

color science.

Considerations of transmission measurements had

even more important consequences. The textbook

definition of “transmittance” is the ratio of the amount

of transmitted light to the amount of incident light. The

most important applications of transmission are motionpicture projection, slide projection, projection printing

(enlarging), and the viewing of x rays and other transparencies on viewing boxes. A projector forms an image

on a screen because the film absorbs or scatters some

light, so the illumination at each point is some fraction

of what it would be without the film. It might appear

that one would need no more than the concept

“transmittance” to quantify this process. However, some

projectors were made to view microfilm images that

scattered light. The light source was moved to one side,

so the light beam passed through the film gate but was

not directed toward the projection lens. With no film in

the gate, the screen was dark. When film was inserted,

some light was scattered in the direction of the projection lens and the screen became brighter. In Concepts, Terminology, and Notation McCamy defined

“transmittance factor” as the ratio of the screen luminance with the film in place to the screen luminance

without film. The concept called “transmittance factor”

had not been previously differentiated from “transmittance.” In the projector just described, the transmittance factor would be much greater than one. By

definition, transmittance cannot be greater than one.

“Transmittance” and “transmittance factor” are different concepts—two different physical quantities, with

different numerical values.

There was no generally accepted collective term for

ratios such as those describing reflection, transmission,

or some combination of them, so the general term

“modulation” was introduced, based on the idea that

objects modulate the flow of light. The combination of

light source and optics directing light to a specimen was

called an “illuminator” or “irradiator” and the optical

system collecting and evaluating the light reflected or

transmitted in a specified direction was called a

“receiver.” Light flowing from an illuminator to a

specimen was called “influx” and that evaluated by the

receiver was called “efflux.” A guiding principle was

that the physical quantity measured was a function of the

145
ratios measured and of the geometrical and spectral

specifications of the illuminator and receiver. A wellknown mathematical notation signifying a functional

relationship was extended and formalized to provide

a compact notation describing the geometrical and

spectral conditions for such measurements.

Perhaps the most important contribution of this paper

was the adoption of the fundamental “principle of

simulation”: To measure optical modulation, the geometrical and spectral conditions of measurement must

simulate the geometrical and spectral conditions for the

use of the modulation. Before this analysis, the standard

method of measuring the optical density of a film was

to measure the amount of light entering the entrance

port of an integrating sphere and then measure the

amount entering the sphere with the film covering the

entrance port. This method assured purists that all the

transmitted light would be measured. NBS provided

precise calibrations by this method, relating the optical

modulation to the inverse-square law of illumination. In

practical densitometers the bulky integrating sphere was

replaced with a piece of diffusing opal glass. At low

values of density, it was impossible to correlate the

standard sphere density with opal-glass density because

there were interreflections between the film and the

white opal glass. The principle of simulation demanded

an answer to the question: “What is the use of the

calibrated standards?” In this case they were used to

calibrate densitometers. The physical quantity being

calibrated so precisely was not the physical quantity

being measured in practical applications. Either the

calibration procedure had to be changed or the practical

instruments had to be upgraded. Again applying the

principle of simulation, it was realized that when a film

was used for photographic contact printing there were

interreflections between the film and the white printing

paper. When films, such as x rays, were viewed on a

viewing box, there were interreflections between the

film and the diffuse illuminator screen. The practical

opal-glass densitometers were measuring exactly the

right physical quantity, so the “ideal” standard sphere

method was abandoned and the opal-glass method was

standardized. The same approach led to the development

of the standard method of measuring projection density,

using geometry simulating practical projectors. Great

accuracy and precision are useless if the basic concept

of the quantity to be measured is wrong [1].

During this analysis, McCamy was Chairman of

the Densitometry Subcommittee of the American

Standards Association, which later became the American National Standards Institute. The subcommittee was

a sounding board during the work, so the whole

system was readily adopted as a national standard [2].

That national standard was equally endorsed by the

International Organization for Standardization (ISO), in

an international standard [3]. The color measurement

community recognized the need for a term and readily

adopted “reflectance factor,” but the rest of the

terminology was only gradually assimilated and the

system of notation was eventually standardized by the

Committee on Color and Appearance of the American

Society for Testing and Materials (ASTM) [4,5]. Further

parts of the system are being adopted in the current

revision of the International Lighting Vocabulary of the

International Commission on Illumination (CIE) [6]. A

method of greatly simplifying the geometric notation by

reference to conical geometry, introduced in this paper,

was called “McCamy’s conical method” and recommended by later authors at NBS/NIST [7]. The paper

was reprinted in NBS Special Publication 300, Precise

Measurement and Calibration, Volume 7, Radiometry

and Photometry [8] and Volume 10, Image Optics [9].

Calvin S. McCamy was born in 1924, received a

B.Ch.E. in Chemical Engineering and an M.S. in

Physics at the University of Minnesota. He taught there

Fig. 1. Calvin S. McCamy at about the time Concepts, Terminology,

and Notation for Optical Modulation was published.

146
and at Clemson University and then joined the Fire

Research Section of NBS (1958-1964) and subsequently

served as Chief of the Photographic Research Section

(1958-1964) and Chief of the Image Optics and Photography Section (1964-1970).

In the Photographic Research Section and later the

Image Optics and Photography Section, he designed a

nomograph to compute the color filter required to take

well-balanced colored pictures with a given film and

illumination [11]. It was made available on a single sheet

from the U.S. Government Printing Office or NBS and

was very popular with amateur and professional photographers. It was the subject of many feature articles in

popular and professional photographic magazines and

became a common feature of color filter catalogs.

When demonstrations by Edwin Land led to widespread speculation that cheaper and better color television could be possible by using two primary colors

rather than three, McCamy demonstrated to the Federal

Communications Commission that a two-color system

was not acceptable. That lecture-demonstration, by

means of three projectors, allowed people to witness

many visual phenomena. It generated such widespread

interest that he was invited to present it fifty times at

NBS, major universities, major industrial research

laboratories, and scientific society meetings in 1959-

1961 [12]. Among other phenomena, he demonstrated

that under certain conditions, people perceive colors in

black-and-white images. He was invited to repeat that

lecture-demonstration forty years later, in February

2000 [13].

Photographic wedges are widely used in photographic science. The wedge may be straight, the density

varying linearly with length, or it may be circular, the

density varying linearly with rotational angle. Since

density is the logarithm of the reciprocal of transmittance, the transmittance varies logarithmically.

When the density is gradually changing and is measured

over a finite area, it is difficult to know where on the

wedge the actual density value is measured. Some finite

area is required for measurement. NBS could measure

uniform areas precisely, but wedges could not be

calibrated because the required theoretical relationships were unknown. McCamy derived the mathematical relationship between the measured density and

the location to which it may be assigned, for a rectangular aperture on a straight wedge, a circular aperture on

a straight wedge, a sector aperture on a circular wedge,

and a circular aperture on a circular wedge [14]. The

last case was commonly encountered and, for that case,

the mathematical derivation was remarkably complex.

McCamy also designed the resolution target used

internationally to test microfilm cameras, and his

laboratory made as many as 25,000 per year as standard

reference materials for the industry. He designed and

provided other test targets to calibrate instruments used

to measure the image structure characteristics of optical

and photographic systems. He developed a laboratory

camera to measure how much information a photographic film or plate could record on a given area.

Scientists involved in manufacturing electronic components came to the Bureau to study the camera, and the

general features of it came into widespread use in the

production of tiny electronic components. McCamy

derived a formula to compute the information storage

capacity of a photographic system, in bits per square

millimeter, from the measured resolving power [15].

All these activities supported the development and

utilization of the U.S. satellite reconnaissance system,

which was highly classified during the cold war.

When it was discovered that the vast stores of federal

and state government records on microfilm were developing blemishes that might destroy vital archival information, McCamy mustered the support of many government agencies and many private interests to conduct a

wide-ranging investigation. His laboratory discovered

the cause of the blemishes. The microfilms were stored

in cardboard boxes and the aging cardboard emitted

minute amounts of hydrogen peroxide, which attacked

the film. The task was difficult because the concentration of peroxide was less than 10–9 mol/L and the

molecules were so labile that they were dissipated on

passing through two centimeters of air [16-19].

As Vice President for Research of the Macbeth

Division of the Kollmorgen Corporation in 1970–1990,

after leaving NBS, McCamy continued research on

optical design, precise transmission measurements,

color measurement, optical filter design, simulation of

daylight for color inspection, geometric attributes of

appearance, densitometry in photography and color

printing, color order systems, color standards, and

related mathematics. He substantially improved the

classical absolute method of photometry based on the

inverse-square law of illumination, and he designed the

Macbeth ColorChecker Color Rendition Chart, which

is used internationally to evaluate color-imaging

systems. At the request of Congress in 1978, he analyzed all known photographs and x rays related to the

assassination of President Kennedy and testified before

the House Select Committee on Assassinations. His

method of analyzing images of long firearms is used

routinely by the U.S. Federal Bureau of Investigation.

He continued to be active in national and international

standardization of photography, color printing, and color

science, chairing committees of the American National

Standards Institute, the American Society for Testing

and Materials, the International Commission on

Illumination (CIE), and the International Organization

147
for Standardization (ISO). He wrote the spectral specifications for optical character recognition for the banking

industry and the Universal Product Code for the grocery

and other retail industries.

He is on the Advisory Board of the Munsell Color

Science Laboratory at the Rochester Institute of Technology and was Adjunct Professor at Rensselaer Polytechnic Institute, President of the Kollmorgen Foundation, and Trustee of the Munsell Foundation. He was

elected fellow of the Optical Society of America, Society of Photographic Scientists and Engineers, Royal

Photographic Society of Great Britain, Society of Motion Picture and Television Engineers, and the Washington Academy of Sciences and has been honored for his

lectures. He received the 1997 Bruning Award of the

Federation of Societies for Coatings Technology and the

1999 Godlove Award of the Inter-Society Color Council.

Prepared by Calvin S. McCamy.

Bibliography

[1] C. S. McCamy, Concepts, Terminology, and Notation for

Optical Modulation, Photogr. Sci. Eng. 10, 314-325 (1966).

[2] Photography—Terms, Symbols, and Notations—Density

Measurement, ANSI PH2.16—1984 (R1990), American

National Standards Institute, New York.

[3] Photography—Terms, Symbols, and Notations—Density

measurements, ANSI/ISO 5/1—1984, International Organization for Standardization (ISO), Geneva, Switzerland.

[4] Standard Terminology of Appearance, ASTM E 284-98a,

American Society for Testing and Materials (ASTM), West

Conshohocken, PA.

[5] Standard Practice for Specifying the Geometry of Observations

and Measurements to Characterize the Appearance of Materials, ASTM E 176795, American Society for Testing and

Materials (ASTM), West Conshohocken, PA.

[6] International Lighting Vocabulary (E) (F) (G) (R), CIE

Document No. 17.4 (1987), International Commission on

Illumination (CIE), Vienna, Austria.

[7] F. E. Nicodemus, J. C. Richmond, J. J. Hsia, I. W. Ginsberg, and

T. Limperis, Geometrical Considerations and Nomenclature for

Reflectance, NBS Monograph 160, National Bureau of

Standards, Washington, DC (1977).

[8] H. K. Hammond III and H. L. Mason (eds.), Precise Measurement and Calibration, Volume 7, Radiometry and Photometry,

NBS Special Publication 300, National Bureau of Standards,

Washington, DC (1971).

[9] Calvin S. McCamy (ed.), Precise Measurement and Calibration,

Volume 10, Image Optics, NBS Special Publication 300,

National Bureau of Standards, Washington, DC (1973).

[10] C. S. McCamy, A five-band recording spectroradiometer, J. Res.

Natl. Bur. Stand. 56, 293-299 (1956).

[11] C. S. McCamy, A nomograph for selecting light balancing filters

for camera exposure of color films, Photogr. Sci. Eng. 3, 302-304

(1959).

[12] C. S. McCamy, A demonstration of color perception with

abridged color-projection systems, Photogr. Sci. Eng. 4, 155-159

(1960); C. S. McCamy, Colors perceived with abridged color

projection systems (Abstract), J. Opt. Soc. Am. 50, 510(A)

(1960).

[13] C. S. McCamy, Abridged Color Revisited—or Sleeping Beauty

II, invited presentation at the Inter-Society Color Council, 2nd

Panchromatic Conference on “Color in Its Surround,” Savannah,

GA, February 20, 2000.

[14] C. S. McCamy, Theory of optical wedges as flux modulators,

J. Opt. Soc. Am. 66, 1350-1355 (1976).

[15] C. S. McCamy, On the information in a microphotograph, Appl.

Opt. 4, 405-411 (1965).

[16] C. S. McCamy, Inspection of processed photographic record

films for aging blemishes, NBS Handbook 96, National Bureau

of Standards, Washington, DC (1964).

[17] C. S. McCamy, S. R. Wiley, and J. A. Speckman, A survey of

blemishes on processed microfilm, J. Res. Natl. Bur. Stand. 73A,

79-99 (1969).

[18] C. S. McCamy and C.I. Pope, Current research on preservation

of archival records on silver-gelatin type microfilm in roll form,

J. Res. Natl. Bur. Stand. 69A, 385-395 (1965).

[19] C. S. McCamy and C. I. Pope, Redox blemishes—their cause and

prevention, J. Microgr. 3, 165-170 (1970).

148
Theory of Light Scattering in Fluids

This review of light scattering theory [1] brought

together a range of concepts which had been developed

over more than half a century. Light scattering has been

used to measure thermal properties of liquids and solids

ever since Einstein showed that the intensity of light

scattered by density fluctuations is proportional to the

isothermal compressibility of the fluid. Density fluctuations, in turn, can be considered to be a sum of pressure

fluctuations and entropy fluctuations. Independently,

Brillouin and Mandel’shtam realized that the pressure

fluctuations are associated with acoustic modes and

would shift the frequency of the scattered light by an

amount proportional to the speed of sound. In 1935,

Landau and Placzek published a short note in which the

contribution of the entropy fluctuation component of

density fluctuations to the scattering of light was identified and shown to be unshifted in frequency. The intensity ratio of the two components of the scattered light

(entropy fluctuation component divided by the pressure

fluctuation component) is equal to the ratio of (Cp–Cv )/

Cv, the specific heat difference divided by the constant

volume specific heat. (This has come to be known as the

Landau-Placzek ratio.) They also noted that the spectral

width of the light scattered by the non-propagating

density fluctuations would be proportional to the

thermal diffusivity of the fluid.

Prior to the advent of the He-Ne gas laser, it was not

possible to exploit these ideas fully because the spectral

width of available light sources was larger than the

frequency broadening due to the non-propagating

fluctuations. It was only possible to estimate sound

speed and heat capacity ratios if a great deal of care was

taken. This changed when He-Ne lasers became available as light sources that were nearly monochromatic

and coherent. Heterodyne and homodyne detection

schemes now made it possible examine the structure of

scattered light in detail. In short order, light scattering

became an active research topic and tool with particular

attention paid to scattering near critical points, where

the scattering intensity is large. It would not be an

understatement to say that the prospect of using a new

technique to study dynamics near critical points was

exciting.

The theoretical ideas mentioned above were not organized in a form that would be readily accessible to the

students entering the field. The necessary theory can be

extracted from three of the volumes of the Landau and

Lifshitz series, Statistical Physics, Fluid Mechanics, and

Electrodynamics of Continuous Media, but only if one

knows where to look. Thus, a review article putting the

pieces together was timely. At the urging of M. S.

Green, Chief of the Statistical Physics Section, Raymond

Mountain prepared the review article Spectral Distribution of Scattered Light in a Simple Fluid [1] that brought

these theoretical ideas together. The emphasis of the

article was on how the spectra are related to fluid properties. The review also showed how light scattering

theory was related to the theory of sound propagation in

a liquid. It was an opportunity to put statistical mechanics in contact with experiments. In structuring the

article, use was made of the work of I. L. Fabelinskii,

S. M. Rytov, and R. Pecora.

The underlying idea in the theory of scattering by

fluctuations is that scattering provides an average

over the fluctuations in both space and in time.

Statistical mechanics provides the theoretical

framework needed to relate the observed scattered

light to fluid properties, and that is the approach

followed in the paper. The result is an explicit

formula connecting the intensity and frequency

distribution of the scattered light to the thermodynamic

and transport properties of the fluid.

This theory of light scattering is phenomenological. It

provides the connection between the spectrum of the

scattered light and various thermodynamic and transport

properties of the fluid. The use of the inherently macroscopic equations of hydrodynamics to describe events

on the scale probed by light scattering may seem to be

an unjustified extrapolation. It is not for two reasons.

First, the fluctuations that lead to light scattering have a

size on the order of the wavelength of light, that is

micrometers. The distance between near neighbor

molecules in a liquid is on the order of tenths of a

nanometer, over a thousand times smaller. Second, the

time scale of these fluctuations is much longer than the

time intervals associated with molecular scattering

processes. With these considerations in mind, the use of

hydrodynamic fluctuation theory is quite reasonable.

This approach would break down for the case of scattering from a gas, where the mean-free-path of a molecule

is on the order of the wavelength of light. (Although not

part of the review, this has been demonstrated experimentally. Agreement between theory and experiment is

recovered when kinetic theory of gases is used in place

of hydrodynamics to describe the time evolution of the

fluctuations [2].)

149
The spectrum of the scattered light consists of a

central, unshifted component with a width proportional

to the thermal diffusivity and two BrillouinMandel’shtam components that are shifted in frequency

by an amount proportional to the adiabatic sound speed.

The width of the shifted components is proportional to

the acoustic attenuation coefficient. If a He-Ne source is

used and the scattered light is observed at an angle of

90 from the direction of propagation of the incident

light, the widths of these spectral features are on the

order of megahertz and the shifts are on the order of

gigahertz.

When the fluid is close to the liquid-vapor critical

point, the density fluctuations are large enough to make

the scattering visible to the naked eye. The fluid takes

on a milky color, called critical opalescence. Since

critical opalescence was a “hot topic,” the review

utilized the theory to predict how the scattered light

would appear for states close to the critical point of

carbon dioxide, a substance for which the relevant

thermodynamic and transport property data were

available. There followed some speculations on how

these predictions would be modified very close to the

critical point. (These speculations were later shown to

be only crude approximations to the observations since

renormalization ideas were not included [3].) Finally, a

cautionary note was sounded about carefully characterizing the state of the system being studied. “It is important to keep in mind that light-scattering experiments

are only as good as the PVT data used to specify the

thermodynamic state of the scattering system. ”

Since hydrodynamic fluctuation theory is also

pertinent to acoustic wave propagation and attenuation,

a section discussing the connections between light

scattering and sound propagation was included. In both

situations, the same dispersion relation is used. The

difference is that in light scattering the wavelength is

fixed and the frequency varies, while in acoustic wave

propagation the frequency is held fixed and the wavelength is allowed to vary. The lesson is that the interpretations of the two types of measurements are different, a point that had not been widely appreciated.

The article provides an introduction to the theory that

can be readily understood by most physical scientists.

The review was well received and was widely referenced. It has been reprinted in collections. In 1980 it

was highlighted in Science Citation Index as a “Citation

Classic,” meaning that it had been cited more than 250

times since the article was published. Many of the

features of the review had been incorporated into books

by then [2,4].

Some of the theory expounded in the review did not

conform to the experimental results on the scattering of

light in molecular liquids. In many cases, the ratio of

the intensity of the central component to the Brillouin

components (the Landau-Placzek ratio) exceeded the

specific heat ratio for the liquid. This experimental

finding indicated that the spectrum of the scattered light

contained additional features. This led Mountain to

develop a hydrodynamic fluctuation theory for the

spectrum of the scattered light that included internal

molecular degrees of freedom, such as vibrational

states. This theory predicts that some of the intensity

associated with the sound modes is transferred to an

unshifted, but quite broad, spectral feature which is

separate from the entropy fluctuation component, which

has a spectral width proportional to the thermal diffusion coefficient. The existence of this component was

demonstrated experimentally at the same time the short

note describing the feature appeared [5-7]. This feature

is sometimes called the “Mountain peak” although it is

a fairly weak, broad feature in the spectrum of many

liquids. The story is different for polymers and for

strongly supercooled liquids, where there are many

internal degrees of freedom that have a major influence

on the density fluctuations, so that the additional feature

is large.

The same sort of theory developed for one-component liquids has been developed for mixtures. In that

case, the dominant fluctuations that lead to scattering

are composition fluctuations. The spectrum of these

fluctuations are more complex due to the additional

variable (composition) in the problem [8-10].

Raymond D. Mountain came to NBS as a Postdoctoral Research Fellow in 1963 and became a regular

staff member of the Heat Division in 1965. The review

article was prepared while he was a postdoc. He became

chief of the Statistical Physics Section in 1968 when

M. S. Green left NBS for Temple University, and served

Fig. 1. The spectrum of light scattered by density fluctuations is

sketched here. The central component, centered at 0 the frequency of

the incident light, has a width on the order of MHz. The other components are shifted from the incident frequency by an amount on the

order of GHz. Hence, the break indicated on the horizontal axis. The

Landau-Placzek ratio is the ratio of the area under the central component to the area under the other two components.

150
in this position until 1982. In 1986 he was named a

NIST Fellow. He received the Department of Commerce

Gold Medal in 1983 for his research on the liquid state.

In 1974 he was named a Guggenheim Fellow and spent

a year at the Institute for Theoretical Physics in Utrecht,

The Netherlands.

Prepared by Raymond D. Mountain.

Bibliography

[1] R. D. Mountain, Spectral Distribution of Scattered Light in a

Simple Fluid, Rev. Mod. Phys. 38, 205-214 (1966).

[2] J.-P. Boon and S. Yip, Molecular Hydrodynamics, McGraw

Hill, New York (1980).

[3] P. C. Hohenberg and B. I. Halperin, Theory of dynamic critical

phenomena, Rev. Mod. Phys. 49, 435-479 (1977).

[4] B. J. Berne and R. Pecora, Dynamic Light Scattering: With

Applications to Chemistry, Biology, and Physics, John Wiley and

Sons, New York (1976).

[5] R. D. Mountain, Interpretation of Brillouin Spectra, J. Chem.

Phys. 44, 832-833 (1966).

[6] R. D. Mountain, Thermal relaxation and Brillouin scattering in

liquids, J. Res. Natl. Bur. Stand. 70A, 207-220 (1966).

[7] R. D. Mountain, Density fluctuations in fluids having an internal

degree of freedom, J. Res. Natl. Bur. Stand. 72A, 95-100 (1968).

[8] R. D. Mountain, Spectral structure of critical opalescence:

Binary mixture, J. Res. Natl. Bur. Stand. 69A, 523-525 (1965).

[9] R. D. Mountain and J. M. Deutch, Light scattering from binary

solutions, J. Chem. Phys. 50, 1103-1108 (1969).

[10] L. Fishman and R. D. Mountain, Activity coefficients of

solutions from the intensity ratio of Rayleigh to Brillouin

scattering, J. Phys. Chem. 74, 2178-2182 (1970).

151
Scaling Analysis of Thermodynamic Properties

in the Critical Region of Fluids

This paper [1] was an outgrowth of the renewed interest, beginning in the early 1960s, in the problem of how

to describe the critical point, the limit point of phase

transitions. This interest came about in part from new

abilities to make light scattering and neutron scattering

measurements and in part from theoretical work that

pointed toward universal property behavior at and near

critical points. The universal behavior was thought to be

independent of the substance and of the type of phase

transition. A 1965 conference held at NBS [2] brought

this work into focus and set the stage for the developments that followed. The conference stimulated much

new research, including important contributions from

Anneke Sengers and Mel Green of NBS.

The prospect of a unifying principle, universality

of critical point behavior, excited the interest of many

scientists. The “classical theory” of the critical point

makes the strong assumption that the free energy of the

fluid is an analytic function of the density and temperature at the critical point. (Fluid terminology will be used

here, keeping in mind that the concepts are equally

applicable to other critical points, such as the Curie

point of a ferromagnet or the Ne ́el point of an antiferromagnet, with the appropriate change of variable names.

For a fluid, the critical point is characterized by a

particular value of the density, c, and of the temperature, Tc. At the critical point, the density of the liquid

phase becomes equal to the density of the coexisting

vapor phase.) This means that the thermodynamics of

the fluid in the critical region can be expressed in terms

of a Taylor’s series expansion of the free energy about

the critical point in terms of the difference of the

temperature and density from the critical temperature

and critical density. The classical theory makes predictions that were known (if not always remembered) to be

in conflict with experimental results. Soon after the

conference it was shown that near the critical point,

thermodynamic properties, such as the equation of state,

could be described usefully in a scaled form [3,4]. The

scaling theory includes the classical theory as a special

case, but does not require the free energy to be analytic

at the critical point. The units to use are appropriate

combinations of the critical temperature, critical

density, and critical pressure for a fluid and the

analogous variables for magnetic systems. The scaling

form has the additional feature that symmetries can

be expressed simply in terms of the scaled, reduced

variables.

A very important task involved the critical evaluation

of existing data on many different fluids and magnetic

systems. This was needed to determine how the universal behavior is reflected in the thermodynamics of the

critical point. It is one thing to postulate a form for the

equation of state and the chemical potential in terms of

scaled variables, and quite another thing to demonstrate that the form is useful over a significant range

of the variables. That demonstration is the contribution

of this paper [1] and of subsequent companion papers

[5,6].

The paper contains an extensive discussion of how

thermodynamic properties of a fluid close to the critical

point are to be formulated in a proper manner and, at

the same time, in a way that permits comparison with

experiments. It would be inappropriate to go through

the arguments in detail, so only a bare outline will be

presented here.

First, the reader is introduced to some power law

descriptions of thermodynamic anomalies in the

critical region. An example is the coexistence curve,

 = B(–t)



, where  = (–c)/c and t = (T–Tc)/Tc.

Other power laws describe the critical isotherm, the

isothermal compressibility, and the specific heat at

constant volume. (The classical theory predicts  = 1/2,

while the experimental value is on the order of 0.32.)

Next, a scaled form for the equation of state, as described by Widom and by Griffiths [3,4], is discussed.

Thermodynamics is properly formulated in terms of the

Helmholtz free energy as a function of the temperature

and the volume. The equation of state is then a partial

derivative of the free energy, often in terms of the

pressure as the volume derivative of the free energy. The

chemical potential is seen from the data to reflect the

symmetry properties of the critical point better than

does the pressure, so the equation of state is described

in terms of the chemical potential as the density

derivative of the free energy per unit volume.

The form for the coexistence curve suggests the

introduction of a scaling variable, x = t /1/

, that

reflects the properties of the critical region. The next

stage of the paper involves casting these ideas into a

scaling function, h(x ), that allows them to be tested

using experimental data.

152
With these tools in hand, the existing thermodynamic

property data for Ar, Xe, CO2, 4He, and water are

examined carefully. The scaling formulation is shown to

work quite well for the existing data, but the scaling

hypothesis is far from being fully verified. An example

of the type of fit to experiment is shown in Fig. 1 where

data for carbon dioxide are matched to the form for

h(x ).

A problem identified in the paper was that the range

of density and temperature around the critical point over

which scaling is applicable could not be decided on the

basis of existing data, which stimulated a number of

new experiments.

Although not part of this paper, some very interesting

comments on how this work evolved are found in a later

paper on the problem [7]. Some of the human side of

research is revealed in that reference.

A large amount of research has been performed to

extend the analysis started in this paper. The task of

identifying the domain where scaling is applicable has

gone through several phases. The renormalization

group approach to critical phenomena has been central

to these developments [8]. One result is the formulation

of “practical” free energy surfaces for industrially

important fluids that are consistent with the new understanding of the critical region of the fluid [9]. Another

result is the development of a “cross-over” theory that

connects the scaling formulation with the rest of the

thermodynamic space in a continuous way. Finally,

a very large amount of experimental work has been

carried out with the result that many of the questions left

unanswered by this paper now have clear answers.

There are numerous industrial processes where

supercritical fluids play a significant role. Only two will

be mentioned here.

Supercritical fluids are utilized as solvents in supercritical extraction processes. The density of a supercritical fluid can be varied over a wide range of values by

small changes in the pressure. This means that solutes

extracted at high fluid densities can be extracted from

the solvent simply by lowering the pressure.

Supercritical water is a medium where oxidation

reactions can proceed at relatively low temperatures.

This is an attractive alternative for hazardous waste

destruction, since incineration produces undesirable

by-products as a result of the high flame temperatures.

Fig. 1. This plot illustrates the accuracy of the scaling representation for carbon dioxide in the critical region.

The scaling variable, x, has the value –x0 on the liquid vapor coexistence curve. The solid line is fit to a particular

form for h(x) while the points are determined directly from the experimental data.

153
J. M. H. (Anneke) Levelt Sengers joined NBS in 1963

as a member of the Equation of State Section. A partial

list of honors includes NIST Senior Fellow, Member of

the National Academy of Engineering, and Member of

the National Academy of Sciences. Her work on critical

phenomena has taken many forms. In addition to the

careful analytical work described here, she has performed many crucial experiments. She has worked

extensively on the formulation of practical equations of

state for water and steam [10]. In addition, she has

examined the history of the development of the ideas

underlying the scaling approach and has written some

interesting and informative historical pieces [11,12].

M. S. Green joined NBS in 1954 and became the first

Chief of the Statistical Physics Section in 1960. He was

intensely interested in critical phenomena and organized

the very successful conference that was held at NBS

in 1965 [2]. In 1968 he left NBS to join the Physics

Department of Temple University in Philadelphia.

He maintained contact with NBS until his death in 1979.

An excellent tribute to Mel by H. J. Raveche ́ is found

in the M. S. Green memorial volume [13].

M. Vicentini-Missoni was a guest worker at NBS

while on leave from the University of Rome.

Prepared by Raymond D. Mountain.

Bibliography

[1] M. Vicentini-Missoni, J. M. H. Levelt Sengers, and M. S. Green,

Scaling Analysis of Thermodynamic Properties in the Critical

Region of Fluids, J. Res. Natl. Bur. Stand. 73A, 563-583 (1969).

[2] M. S. Green and J. V. Sengers (eds.), Critical Phenomena;

Proceedings of a Conference Held in Washington, DC, April

1965, NBS Miscellaneous Publication 273, National Bureau of

Standards, Washington, DC (1966).

[3] B. Widom, Equation of State in the Neighborhood of the Critical

Point, J. Chem. Phys. 43, 3898-3905 (1965).

[4] R. B. Griffiths, Thermodynamic Functions for Fluids and Ferromagnets near the Critical Point, Phys. Rev. 158, 176-187 (1967).

[5] M. Vicentini-Missoni, J. M. H. Levelt Sengers, and M. S. Green,

Thermodynamic anomalies of CO2, Xe, and He4 in the critical

region, Phys. Rev. Lett. 22, 389-393 (1969).

[6] M. Vicentini-Missoni, R. I. Joseph, M. S. Green, and J. M. H.

Levelt Sengers, Scaled equation of state and critical exponents in

magnets and fluids, Phys. Rev. B 1, 2312-2331 (1970).

[7] J. M. H. Levelt Sengers and J. V. Sengers, How Close is “Close

to the Critical Point,” in Perspectives in Statistical Physics, M. S.

Green Memorial Volume, H. J. Raveche ́ (ed.), North-Holland,

Amsterdam (1981) pp. 239-271.

[8] Z. Y. Chen, A. Abbaci, S. Tang, and J. V. Sengers, Global

thermodynamic behavior of fluids in the critical region, Phys.

Rev. A 42, 4470-4484 (1990).

[9] J. M. H. Levelt Sengers, Significant Contributions of IAPWS to

the Power Industry, Science, and Technology, in Physical

Chemistry of Aqueous Systems: Meeting the Needs of Industry.

Proceedings of the 12th International Conference on the Properties of Water and Steam, H. J. White, J. V. Sengers, D. B.

Neumann, and J. C. Bellows (eds.), Begell House, New York

(1995).

[10] J. M. H. Levelt Sengers, J. Straub, K. Watanabe, and P. G. Hill,

Assessment of Critical Parameter Values for H2O and D2O,

J. Phys. Chem. Ref. Data 14, 193-207 (1985).

[11] J. M. H. Levelt Sengers, Critical exponents at the turn of the

century, Physica 82A, 319-351 (1976).

[12] J. M. H. Levelt Sengers, Liquidons and gasons; Controversies

about the continuity of states, Physica 98A, 363-402 (1979).

[13] H. J. Raveche ́, Dedication to M. S. Green, in Perspectives in

Statistical Physics, M. S. Green Memorial Volume, H. J. Raveche ́

(ed.), North-Holland, Amsterdam (1981) pp. vii-xiv.

154
called a probe hole, can be made in the screen so that

electron emission from a surface region composed of

only 15–30 atoms passes through the hole and then

into the energy analyzer. This allows electron spectroscopy studies to be performed on the emission from

just these few atoms. Deflection grids are used to focus

the emitted current from a chosen portion of the surface

over the probe hole. This experimental arrangement is

shown in Fig. 1.

When a single atom, molecule, or cluster is adsorbed

onto that portion of the surface emitting through the

probe hole, if the adsorbate has an electron quasibound

state near the Fermi level of the tip, then a substantial

increase in the probe-hole current can occur as a result

of resonance-tunneling enhancement through the adsorbate. New adsorbate-induced structure in the observed

TED reflects the local density of electronic states of

the adsorbate, which in turn leads to an unambiguous

electron spectroscopy of single adsorbed atoms.

The physical origin of the effect can be understood

from the potential energy diagram and wave functions

shown in Figure 2. The “triangle barrier” field-emission

configuration suggested earlier is here augmented by a

potential well whose width 2w is roughly the diameter

of the adsorbed atom, which is located a distance s from

the surface. The electronic state of this atom is characterized by a discrete level which has been broadened

into a band, referred to as the local density of states and

labeled a() in Fig. 2. Enhanced tunneling occurs for

those tip states m whose energy is resonant with a(),

in which case the coherent process of tip-to-atom

tunneling constructively interfering with atom-to-free

space tunneling occurs with much greater probability

(by factors sometimes as large as 102–104) than for

direct tip-to-free space tunneling. It is this magnification

or amplification that is responsible for the collimated

emission from the single adsorbate rising far above

the background emission from other parts of the field

emitter surface and, as detailed years later [3], is the

underlying principle that enables atomic resolution in

the scanning tunneling microscope.

In considering the spectroscopic characteristics of

emission from the composite surface, it is most informative to measure and display R, the ratio of the change in

TED to the original TED, as a function of energy.

For typical adsorbate conditions, the theory outlined in

the initial communication [1] shows that this ratio, for

emission from the adsorbate-covered surface area, is

R() 

a

[a ()/m ()]exp[2 ()(s+wa )]

where the summation includes all the adsorbate states

contributing to the tunneling, a () is the adsorbate

density of states derived from state a, usually represented by a Lorentzian lineshape [4]

a () ≡ 1



a

(–a )

2

+a

2

Fig. 1. Schematic drawing of a field emission microscope adapted for energy distribution

measurements. The (110) plane of the emitter is positioned over the probe hole. Note that

although an electrostatic deflection analyzer is shown here, the data reported in [1] were

acquired with a retarding potential analyzer.

156
with a and a, the resonance position and width, depending upon the particular state, m () the substrate

density of states, wa the “radius” of the atomic state,

()  [(2m/)(e–)]1/2 , and e the workfunction

of the tip. Observed structure in the TED that provides

the desired spectroscopic information arises from

a (). The enhancement is mainly a consequence of

the fact that now the rate-limiting step is tunneling

from the adsorbate to vacuum, through a barrier that

is reduced compared to the full direct metal-vacuum

tunneling barrier. This enhancement is accounted for by

the exponential factor. As was noted in the original

paper [1], this realization of resonance tunneling involving an adsorbed atom (discrete state mixed with a

continuum) can be (and was!) put in one-to-one

correspondence with the Fano lineshape theory [4]

which is the topic of another NBS/NIST classic publication outlined in this volume.

The initial spectroscopic experiments were carried

out for single zirconium atoms deposited on a tungsten

field emission tip; the published TED ratio is shown in

Figure 3 together with two “relatively good fits” to

the theoretical curve. This spectrum, crude even by

standards a year later, nonetheless was a landmark. It

expressed the first confirmation of the rather speculative

beliefs of the time that the electronic energy level

spectra of adsorbed atoms were related to the free atom

spectra shifted and broadened ~1 eV by interaction with

the surface. Refined and extended presentations of this

study soon followed which reached a much wider

audience [5,6].

An unusually creative and imaginative period of

research by the three coauthors over the next few years

produced a wealth of new insights into the microscopic

aspects of surfaces. The surface topografiner [7]

invented and constructed by Young during this time

period (and discussed elsewhere in this volume) was an

initial version of the scanning tunneling microscope for

which the 1986 Nobel Prize in Physics was awarded to

Binnig, Rohrer, and Ruska. The field emission spectroscopy work of this period (mostly from NBS)

has been summarized and reviewed by Gadzuk and

Plummer in their Reviews of Modern Physics article

[8], which is still one of the most definitive and comprehensive sources of widely used information and wisdom

on this topic. The theory of resonance tunneling developed during this period is applicable in many areas of

current interest and activity, for instance resonance

tunneling in nanostructures such as quantum wells,

quantum dots, and in the STM , as discussed in the 1993

Physical Review paper by Gadzuk [3].

The members of the trio have followed varied life

trajectories over the ensuing decades. In 1973 Plummer

joined the faculty at University of Pennsylvania, where

he served as director of the Materials Research Laboratory from 1990 to 1992. Since 1992 he has held a joint

Fig. 2. Schematic model showing the idealized potentials relevant in field-emission resonance tunneling. The electron wave functions are: m , the unperturbed metal function; a,

the localized adsorbate resonance function; and f , the emitted electron function. The

adatom centered at z=s, with diameter equal to 2w, shows a Lorentzian-like local density

of states labeled a.

157
appointment as a Distinguished Professor of Physics at

the University of Tennessee and as a Distinguished

Scientist in the Solid State Division of Oak Ridge

National Laboratory. He has authored or co-authored

more than 260 papers reporting on a wide variety of

physical and chemical properties of surfaces and interfaces, as probed with a multitude of experimental techniques, always maintaining close coupling with theory.

He received the 1983 Davisson-Germer Prize from the

American Physical Society. Gadzuk remains at NBS/

NIST, and for several years he was a “permanent” visiting professor jointly at NORDITA (Copenhagen) and

Chalmers University (Goteborg). His research activities,

resulting in over 150 papers, have been mainly in

surface-related areas of theoretical atomic, molecular,

solid state, and chemical physics, with special attention

focused on the fundamental similarities existing in

seemingly different fields of physics. He is currently

interested in the dynamics of molecular processes at

surfaces, particularly those aspects pertinent to the

development of Femtochemistry at Surfaces involving

hot electrons produced both by ultrafast lasers and

by tunneling devices. He was a recipient of the Arthur

S. Fleming Award, given annually to the ten outstanding

young men and women in the U.S. Federal service.

Following the resonance tunneling work, Young brought

to fruition his scanning device for measuring surface

topography which, as acknowledged by the 1986

Physics Nobel Committee, was a prototype of the

scanning tunneling microscope. After abrupt termination of this project in 1971, Young remained at NBS

in both a technical and administrative role, first as a

Section Chief and then a Division Chief, directing NBS

activities in mechanical metrology and robotics until

his formal retirement in 1981. Since then he has actively

pursued his interests as an inventor; as a private consultant to industry and government (including NIST)

on topics in metrology, STM, vibration isolation, and

instrument development; and as a grandfather and

a sailor. In recognition of his invention of the Topografiner, in 1986 he received a Presidential Citation, and

in 1992 he was presented the Gaede-Langmuir Award of

the American Vacuum Society.

Prepared by J. W. Gadzuk.

Fig. 3. Energy dependence of the ratio of the adsorbate-induced change in the TED to that of

the clean surface, R ≡ j'()/j0'()vs. for a single zirconium atom on a tungsten field emission

tip. Comparison of experiment with theory. The top energy axis is taken with respect to a zero

at the bottom of the tungsten conduction band, while the zero for the bottom axis is at the

vacuum potential outside the tip.

158
Resonance Tunneling of Field Emitted

Electrons Through Adsorbates on

Metal Surfaces

Initiation of the modern era of surface science, generally acknowledged as starting in the late 1960s, was

made possible by two distinct qualitative leaps forward.

One was the Sputnik-inspired development of ultra-high

vacuum and electron-optical technologies. The other

was the recognition and development of theoretical and

measurement techniques for studying surface properties

and processes on the (single!) atomic level. The field

emission spectroscopy result reported in this 1969 NBS

paper [1] was the first work in which the electronic

energy level spectra of adsorbed atoms was observed

and theoretically interpreted. All subsequent electron

energy level spectroscopy of adsorbed atoms and

molecules, whether based on tunneling processes such

as in this work or on photon-induced processes, can

legitimately be considered as logical consequences of

this pioneering study. The spectroscopic information

so obtained is the essential ingredient required in all

quantum mechanical modeling of chemical bonding,

catalysis, dynamics, and reactivity at solid surfaces, and

it is for this reason that the advances reported in this

paper have had lasting and historical significance.

The situation at NBS at the time was particularly well

suited for the laboratory to become one of the three or

four pre-eminent international centers of excellence

leading the transformation of then-existing surface

studies from a qualitative mystical art into a quantitative

and intellectually stimulating hard science in which

the basic systems and processes under study could

be understood at the most fundamental atomic level.

Major efforts in atomic and electron physics were

focused on the development of monochromatic electron

sources and energy analyzers (of special importance

here, the work of John Simpson and Chris Kuyatt)

and in their utilization for basic atomic physics studies,

particularly those theoretically inspired by Ugo Fano

(discussed elsewhere in this volume). A major direction

in electron beam production relied upon field emitted/

tunneled electrons as a promising source, and it was

within this context that Russ Young came to NBS in

1961 and soon was attracting world-wide attention for

his measurements and interpretation of field emission

energy distributions as a new probe of the electronic

state of surfaces [2]. Ward Plummer arrived at NBS in

1967 as an NRC postdoctoral fellow to work with

Young. In parallel with this surface work in atomic

physics, complementary experimental research within

the domain of physical chemistry (also discussed

elsewhere in this volume) and in metallurgy (by Al

Melmed) gave a cross-disciplinary flavor, across NBS

organizational boundaries, to surface science. This

situation was successfully used to persuade NBS

management to create a new inter-institute position for

a surface theorist, which enabled Bill Gadzuk to join

NBS in 1968. Almost immediately, it became clear

that the intellectual and personal chemistry among

Plummer, Gadzuk, and Young was right, and a highly

productive collaboration proceeded for the next several

years in the area of electron spectroscopy of surfaces, in

which all sorts of new things were discovered, studied,

and understood. The topic of this paper [1] has perhaps

had the most long lasting and global significance,

both because it was the first definitive experimental/

theoretical study of the quantum states of adsorbates

and also because the basic phenomenon of resonance

tunneling has been so important in microelectronics and

in nanostructures.

The field-emission microscope (FEM) and its derivative spectroscopies are based on the fact that a modest

positive potential (1 keV–3 keV) applied between a

sharpened conducting tip (radius 100 nm) and a flat

or concentric spherical electrode, positioned a macroscopic distance (1 cm–10 cm) away, will result in an

electric field at the emitter surface whose strength is

1 V/nm–10 V/nm, as depicted in Figs. 1 and 2. This

field is strong enough to allow electrons to quantum

mechanically tunnel from the tip (on the left) into the

free space (on the right). Energy analysis of the emitted

electrons reveals a total energy distribution (TED) of

emitted electrons that is exponentially decreasing in

number below the sharp, high energy Fermi edge

and which has an 1.0 eV width under typical field

emission conditions [2]. If a fluorescent screen is

introduced behind the accelerating electrode, then a

spatial distribution of the electron emission from the tip

can be imaged. This distribution will have a spatial

resolution of a few nanometers. Contrast in the image is

due to variations in electron emission across the tip

surface, historically attributed to variations in the

surface work function. Furthermore, a “small” hole,

155
called a probe hole, can be made in the screen so that

electron emission from a surface region composed of

only 15–30 atoms passes through the hole and then

into the energy analyzer. This allows electron spectroscopy studies to be performed on the emission from

just these few atoms. Deflection grids are used to focus

the emitted current from a chosen portion of the surface

over the probe hole. This experimental arrangement is

shown in Fig. 1.

When a single atom, molecule, or cluster is adsorbed

onto that portion of the surface emitting through the

probe hole, if the adsorbate has an electron quasibound

state near the Fermi level of the tip, then a substantial

increase in the probe-hole current can occur as a result

of resonance-tunneling enhancement through the adsorbate. New adsorbate-induced structure in the observed

TED reflects the local density of electronic states of

the adsorbate, which in turn leads to an unambiguous

electron spectroscopy of single adsorbed atoms.

The physical origin of the effect can be understood

from the potential energy diagram and wave functions

shown in Figure 2. The “triangle barrier” field-emission

configuration suggested earlier is here augmented by a

potential well whose width 2w is roughly the diameter

of the adsorbed atom, which is located a distance s from

the surface. The electronic state of this atom is characterized by a discrete level which has been broadened

into a band, referred to as the local density of states and

labeled a() in Fig. 2. Enhanced tunneling occurs for

those tip states m whose energy is resonant with a(),

in which case the coherent process of tip-to-atom

tunneling constructively interfering with atom-to-free

space tunneling occurs with much greater probability

(by factors sometimes as large as 102–104) than for

direct tip-to-free space tunneling. It is this magnification

or amplification that is responsible for the collimated

emission from the single adsorbate rising far above

the background emission from other parts of the field

emitter surface and, as detailed years later [3], is the

underlying principle that enables atomic resolution in

the scanning tunneling microscope.

In considering the spectroscopic characteristics of

emission from the composite surface, it is most informative to measure and display R, the ratio of the change in

TED to the original TED, as a function of energy.

For typical adsorbate conditions, the theory outlined in

the initial communication [1] shows that this ratio, for

emission from the adsorbate-covered surface area, is

R() 

a

[a ()/m ()]exp[2 ()(s+wa )]

where the summation includes all the adsorbate states

contributing to the tunneling, a () is the adsorbate

density of states derived from state a, usually represented by a Lorentzian lineshape [4]

a () ≡ 1



a

(–a )

2

+a

2

Fig. 1. Schematic drawing of a field emission microscope adapted for energy distribution

measurements. The (110) plane of the emitter is positioned over the probe hole. Note that

although an electrostatic deflection analyzer is shown here, the data reported in [1] were

acquired with a retarding potential analyzer.

156
with a and a, the resonance position and width, depending upon the particular state, m () the substrate

density of states, wa the “radius” of the atomic state,

()  [(2m/)(e–)]1/2 , and e the workfunction

of the tip. Observed structure in the TED that provides

the desired spectroscopic information arises from

a (). The enhancement is mainly a consequence of

the fact that now the rate-limiting step is tunneling

from the adsorbate to vacuum, through a barrier that

is reduced compared to the full direct metal-vacuum

tunneling barrier. This enhancement is accounted for by

the exponential factor. As was noted in the original

paper [1], this realization of resonance tunneling involving an adsorbed atom (discrete state mixed with a

continuum) can be (and was!) put in one-to-one

correspondence with the Fano lineshape theory [4]

which is the topic of another NBS/NIST classic publication outlined in this volume.

The initial spectroscopic experiments were carried

out for single zirconium atoms deposited on a tungsten

field emission tip; the published TED ratio is shown in

Figure 3 together with two “relatively good fits” to

the theoretical curve. This spectrum, crude even by

standards a year later, nonetheless was a landmark. It

expressed the first confirmation of the rather speculative

beliefs of the time that the electronic energy level

spectra of adsorbed atoms were related to the free atom

spectra shifted and broadened ~1 eV by interaction with

the surface. Refined and extended presentations of this

study soon followed which reached a much wider

audience [5,6].

An unusually creative and imaginative period of

research by the three coauthors over the next few years

produced a wealth of new insights into the microscopic

aspects of surfaces. The surface topografiner [7]

invented and constructed by Young during this time

period (and discussed elsewhere in this volume) was an

initial version of the scanning tunneling microscope for

which the 1986 Nobel Prize in Physics was awarded to

Binnig, Rohrer, and Ruska. The field emission spectroscopy work of this period (mostly from NBS)

has been summarized and reviewed by Gadzuk and

Plummer in their Reviews of Modern Physics article

[8], which is still one of the most definitive and comprehensive sources of widely used information and wisdom

on this topic. The theory of resonance tunneling developed during this period is applicable in many areas of

current interest and activity, for instance resonance

tunneling in nanostructures such as quantum wells,

quantum dots, and in the STM , as discussed in the 1993

Physical Review paper by Gadzuk [3].

The members of the trio have followed varied life

trajectories over the ensuing decades. In 1973 Plummer

joined the faculty at University of Pennsylvania, where

he served as director of the Materials Research Laboratory from 1990 to 1992. Since 1992 he has held a joint

Fig. 2. Schematic model showing the idealized potentials relevant in field-emission resonance tunneling. The electron wave functions are: m , the unperturbed metal function; a,

the localized adsorbate resonance function; and f , the emitted electron function. The

adatom centered at z=s, with diameter equal to 2w, shows a Lorentzian-like local density

of states labeled a.

157
appointment as a Distinguished Professor of Physics at

the University of Tennessee and as a Distinguished

Scientist in the Solid State Division of Oak Ridge

National Laboratory. He has authored or co-authored

more than 260 papers reporting on a wide variety of

physical and chemical properties of surfaces and interfaces, as probed with a multitude of experimental techniques, always maintaining close coupling with theory.

He received the 1983 Davisson-Germer Prize from the

American Physical Society. Gadzuk remains at NBS/

NIST, and for several years he was a “permanent” visiting professor jointly at NORDITA (Copenhagen) and

Chalmers University (Goteborg). His research activities,

resulting in over 150 papers, have been mainly in

surface-related areas of theoretical atomic, molecular,

solid state, and chemical physics, with special attention

focused on the fundamental similarities existing in

seemingly different fields of physics. He is currently

interested in the dynamics of molecular processes at

surfaces, particularly those aspects pertinent to the

development of Femtochemistry at Surfaces involving

hot electrons produced both by ultrafast lasers and

by tunneling devices. He was a recipient of the Arthur

S. Fleming Award, given annually to the ten outstanding

young men and women in the U.S. Federal service.

Following the resonance tunneling work, Young brought

to fruition his scanning device for measuring surface

topography which, as acknowledged by the 1986

Physics Nobel Committee, was a prototype of the

scanning tunneling microscope. After abrupt termination of this project in 1971, Young remained at NBS

in both a technical and administrative role, first as a

Section Chief and then a Division Chief, directing NBS

activities in mechanical metrology and robotics until

his formal retirement in 1981. Since then he has actively

pursued his interests as an inventor; as a private consultant to industry and government (including NIST)

on topics in metrology, STM, vibration isolation, and

instrument development; and as a grandfather and

a sailor. In recognition of his invention of the Topografiner, in 1986 he received a Presidential Citation, and

in 1992 he was presented the Gaede-Langmuir Award of

the American Vacuum Society.

Prepared by J. W. Gadzuk.

Fig. 3. Energy dependence of the ratio of the adsorbate-induced change in the TED to that of

the clean surface, R ≡ j'()/j0'()vs. for a single zirconium atom on a tungsten field emission

tip. Comparison of experiment with theory. The top energy axis is taken with respect to a zero

at the bottom of the tungsten conduction band, while the zero for the bottom axis is at the

vacuum potential outside the tip.

158
Bibliography

[1] E. W. Plummer, J. W. Gadzuk, and R. D. Young, Resonance Tunneling of Field Emitted Electrons Through

Adsorbates on Metal Surfaces, Solid State Commun. 7, 487-491

(1969).

[2] R. D. Young, Theoretical Total-Energy Distribution of FieldEmitted Electrons, Phys. Rev. 113, 110-114 (1959).

[3] J. W. Gadzuk, Single-atom point source for electrons: Fieldemission resonance tunneling in scanning tunneling microscopy,

Phys. Rev. B 47, 12832-12839 (1993).

[4] U. Fano, Effects of Configuration Interaction on Intensities and

Phase Shifts, Phys. Rev. 124, 1866-1878 (1961).

[5] E. W. Plummer and R. D. Young, Field-Emission Studies of

Electronic Energy Levels of Adsorbed Atoms, Phys. Rev. B 1,

2088-2109 (1970).

[6] J. W. Gadzuk, Resonance-Tunneling Spectroscopy of Atoms

Adsorbed on Metal Surfaces: Theory, Phys. Rev. B 1, 2110-2129

(1970).

[7] R. Young, J. Ward, and F. Scire, The Topografiner: An Instrument

for Measuring Surface Microtopography, Rev. Sci. Instrum. 43,

999-1011 (1972).

[8] J. W. Gadzuk and E. W. Plummer, Field Emission Energy Distribution[s] (FEED), Rev. Mod. Phys. 45, 487-548 (1973).

159
Quantitative Electron Probe Microanalysis

The recognition and understanding of the role of the

microstructure in controlling the macroscopic behavior

of a material has been a major theme of science and

technology throughout the history of NBS/NIST. In

materials science, the late 19th century saw the development of the sample preparation procedures we know

today as “metallography” and “materialography,” and

the emergence of optical microscopes with resolution

performance at the physically defined optical limit.

Applied to practical technological issues such as understanding the thermomechanical processing of steel to

control its strength and ductility, the new microstructural science revealed a vast array of microstructural

features, many of which were obviously compositional

in nature. By 1912, the noted Harvard scientist

Prof. Albert Sauveur could remark “To realize the

practical importance of metallography, it should be

borne in mind that the physical properties of metals

and alloys—that is, those properties to which those

substances owe their exceptional industrial importance—are much more closely related to their proximate

than to their ultimate composition, and that microscopical examination reveals, in part at least, the proximate

composition of metals and alloys, whereas chemical

analysis seldom does more than reveal their ultimate

composition” (Here the “ultimate composition” is what

we today would refer to as the bulk composition,

while the “proximate composition” refers to the local

microstructural composition.) Sauveur continued in his

enthusiastic and colorful prose: “Unfortunately the

chemist too often is able to give us positive information

in regard to the proportion of the ultimate constituents

only, his reference to proximate analysis being of the

nature of speculation. Ultimate analysis has reached a

high degree of perfection in regard to accuracy as well

as to speed of methods and analytical chemists have

built up a marvelous structure calling for the greatest

admiration, their searching methods never failing to lay

bare the ultimate composition of substances. But how

much darkness still surrounds the proximate composition of bodies and how great the reward awaiting the

lifting of the veil!”

The beginning of the solution to Sauveur’s dream

came in 1949 with the first results from the electron

probe x-ray microanalyzer (EPMA) by Raymond

Castaing, a student of A. Guinier at the University of

Paris. Castaing presented an extraordinary thesis that

described both the complete development of a unique

measurement tool for microstructural characterization

and a detailed treatment of the underlying physics of

electron/x-ray interaction with matter that would

provide the framework for developing the new technique

into a rigorous quantitative analysis tool. The first stage

of this task took nearly 20 years and the contributions

of many scientists from Europe, Japan, and the United

States, including those of Kurt F. J. Heinrich

and his colleagues at NBS. To evaluate the state of the

development of quantitative analysis and to stimulate

further progress in the measurement science of electron

probe microanalysis, Heinrich organized a special

workshop in June of 1967 that brought together the

leaders of the field. The document of this gathering,

NBS Special Publication 298, Quantitative Electron

Probe Microanalysis [1], edited by Heinrich, became

the “bible” of the rapidly developing field. It was

understood from Castaing’s thesis work that a quantification scheme should proceed from the measurement of

the x-ray intensities emitted by the unknown and, under

the same beam conditions, from a simple standard suite

consisting of pure elements and/or binary compounds.

What was needed were correction factors based upon

physical calculations of electron penetration and scattering, x-ray absorption, and consequent secondary x-ray

fluorescence to convert relative measured x-ray intensities into relative concentrations. Extensive work to

develop practical expressions for these factors and

obtain the physical data (e.g., x-ray mass absorption

coefficients, electron backscatter coefficients, etc.) was

being done by researchers organized essentially along

national lines. NBS Special Publication 298 brought

together the various camps to present their work and the

critical details on just how they proposed to implement

these complex calculations. Most importantly, SP 298

contained the first robust tests based upon critical data

sets that provided a rigorous comparison of the performance of different implementations of correction

factors. Thus, the strengths and weaknesses of the

algorithms under development could be accurately

assessed, and future directions for continuing research

could be sensibly planned, propelling the field forward.

SP 298 also surveyed newly emerging areas of application, such as biological materials, where a solution was

provided to the problem that radiation damage to the

specimen limited the utility of the results. Changes in

the electron bombarded region could be compensated

through measurements of the high energy x-ray

continuum.

160
Kurt Heinrich came to NIST in 1963 from the

Dupont Research Station to initiate a competence for

NBS in the area of electron beam microanalysis, which

had grown slowly through the 1950s until the great

acceleration of scientific and technological efforts in

the post-Sputnik era led to the development of several

commercial EPMA instruments. Heinrich assembled

an electron beam group initially including Robert

Myklebust, Charles Fiori, Donald Vieth, and Stanley

Rasberry, with the close collaboration of Harvey

Yakowitz from the Metallurgy Division. Visitors

included Jean Henoc of Centre National d’Etudes de

Telecommunication (France) and Carol Swyt of the

National Institutes of Health. Fig. 1 shows an example of

an early EPMA instrument at NBS. Later, Ryna

Marinenko, John Small, Eric Steel, and Dale Newbury

joined the effort toward development of the measurement science of elemental microanalysis and its application to a wide variety of problems in materials science,

semiconductor technology, environmental chemistry,

failure analysis, and forensic analysis.

EPMA involves the use of finely-focused electron

beams with incident energies usually selected in the

range from 10 keV–25 keV to excite characteristic

x rays from a microscopic target. Initially, the lateral

spatial resolution of EPMA was limited by the electronoptical performance to the minimum beam size that

could be focused with sufficient current for practical

x-ray spectrometry by wavelength dispersive spectrometry (crystal diffractometry). The micrometer

spatial resolution that Castaing reported in his thesis

stood for nearly 20 years because microampere currents

were needed to excite a sufficient x-ray flux to overcome

the low efficiency of diffraction spectrometers. Large

current demanded large beam size. This problem was

substantially solved with the development of the

semiconductor energy dispersive spectrometer (Si-EDS)

with geometric and quantum efficiencies that permitted

practical x-ray spectrometry with beam currents in the

nanoampere range. Heinrich collaborated on the watershed paper introducing the semiconductor EDS to the

electron probe field [2]. With semiconductor EDS,

microanalysts could take advantage of the rapid, parallel

developments in imaging that took place in the

late-1960s with the advent of high resolution scanning

electron microscopes (SEM). The EPMA quickly

evolved into an SEM electron-optical platform capable

of imaging with beam diameters of 50 nm and smaller,

Fig. 1. Kurt Heinrich with his EMPA apparatus.

161
equipped with both crystal diffractometers (for high

spectral resolution) and semiconductor EDS (for continuous viewing of the complete x-ray spectrum). Moreover, with submicrometer beam diameters, the EPMA

could achieve spatial resolutions limited only by the

physics of electron scattering. For intermediate and high

atomic number specimens (Z > 20), lateral and depth

spatial resolutions below 1 m became possible. The

modern EPMA/EDS/WDS can thus image and then

selectively analyze discrete sample masses of the order

of 1 pg (10–12 g), e.g., an isolated particle, with

fractional detection limits of 1 fg (10–15 g) or less within

this picogram sample. This extremely small sample

mass was six or more orders of magnitude below the

minimum mass that could be studied with contemporary

“conventional” chemical analysis [3].

Despite the small mass of the sample selected by the

beam interaction, the EPMA measurement can be

performed quantitatively with a relative accuracy of

0.5 % or better and precision of 0.5 %. The framework for quantification that was laid down by Castaing

was refined and enhanced by numerous workers, and the

Heinrich group made many important contributions to

the success of the method. The x-ray spectrum is

affected by a wide range of physical phenomena. The

incident electron beam undergoes elastic and inelastic

scattering (energy loss) leading to a complex distribution in depth of electron density and ionization power as

well as the loss of electrons from the target due to

backscattering through the cumulative effects of elastic

scattering. The characteristic x rays produced through

inner shell ionization must propagate through the

specimen, often over a distance of micrometers, to

escape through the surface in the direction of the x-ray

detector. Along this path, the x rays are subject to

photoelectric absorption which attenuates the intensity.

Photoelectric absorption leads to secondary fluorescence through ionization of inner shells of the absorbing

specimen atoms, which subsequently emit their characteristic x rays. This secondary emission is an additional

source of intensity beyond that due to direct electron

excitation of those same atoms. The great complication

is that each of these radiation interactions, (1) electron

scattering, retardation, and ionization power, (2) x-ray

absorption, and (3) secondary x-ray fluorescence, is a

function of composition, which is unknown. Finally,

absorption in the components of the spectrometer and

the spectrometer response (efficiency) modify the emitted spectrum to yield the final observed spectrum.

Determination of these interelement or “matrix effects”

and instrumental effects form the basis for quantitative

analysis. NBS/NIST scientists employed a threepronged approach for this research: (1) studies of the

parameters of electron beam/x-ray interactions that form

the physical basis of matrix corrections; (2) development of computer software incorporating the physical

corrections for efficient calculations; and (3) development of microanalysis standard reference materials.

The study of the interaction of electrons and x rays

with matter was an area of intense interest to physics in

the first half of the 20th century. By the time EPMA had

arisen in the 1950s, physics had moved on to much

higher and much lower energies, and interest in measuring data for the EPMA energy range had waned. Those

who were interested in developing accurate corrections

for electron/x-ray matrix effects in EPMA needed

accurate values of key parameters such as electron

backscattering coefficients, loss of x-ray production due

to backscattering, x-ray mass absorption coefficients,

etc. Whenever possible, literature values were utilized,

but many critical values were simply unavailable, so

extensive measurements and simulations were undertaken by the EPMA community, including the NBS/

NIST group [4-8].

Consistent with the mission of NBS/NIST, matrix

correction methods for quantitative analysis have been

made accessible to U.S. industry and academia through

the development of state of the art software that incorporated the laboratory measurement advances in a

form that could be readily implemented elsewhere. The

development of quantitative EPMA closely follows the

remarkable evolution of computing power that is the

major theme of the second half of the 20th century. As

each advance took place in central computing power in

the early years, and then in personal computing power

in later years, NBS/NIST quantitative microanalysis

software was developed to take full advantage of the

improving speed and capacity of computers. Thus there

are two parallel series of publications, one set of scientific papers that detail the NBS/NIST contributions to

the basic understanding of electron beam/x-ray interactions and matrix corrections for quantitative EPMA

analysis, and a second set of papers documenting

the software implementation of the mathematical

algorithms for these corrections. The open description

of this software code enabled U.S. manufacturers of

x-ray spectrometry to incorporate NBS/NIST developments into their products [9-13].

The third component of the NBS/NIST program in

microanalysis research has been the development

of NBS/NIST Standard Reference Materials (SRM)

appropriate to the electron probe microanalysis case,

which places an unusually great demand on sample

homogeneity. The EPMA beam selects a region with

micrometer dimensions, so for measurement reproducibility, we must require that our sample be homogeneous

down to a much finer scale, ideally approaching the

atomic scale. While NIST offers a great many SRMs,

162
Nature seems generally to abhor homogeneity on the

microstructural scale, so that most SRMs created for

“bulk” applications do not satisfy the stringent requirements for microstructural homogeneity necessary for

EPMA. Most arbitrarily selected groupings of elements

when properly synthesized together do not form a

uniform material on the micrometer scale. Careful

selection and rigorous homogeneity testing of metallic

alloys and glasses has resulted in a series of microanalysis SRMs which serve the community in the important

role of test materials [14-16].

Finally, these techniques for quantitative EPMA were

developed in an environment in which problem solving

was encouraged and promoted. Collaborations

throughout NBS/NIST and with other federal agencies brought many challenging applications for

EPMA, including materials science, failure analysis,

electronic technology, biological science, and forensic

analysis.

Prepared by Dale E. Newbury.

Bibliography

[1] K. F. J. Heinrich (ed.), Quantitative Electron Probe Microanalysis, NBS Special Publication 298, National Bureau of Standards,

Washington, DC (1968).

[2] R. Fitzgerald, K. Keil, and K. F. J. Heinrich, Solid-State EnergyDispersion Spectrometer for Electron-Microprobe X-ray Analysis, Science 159, 528-530 (1968).

[3] K. F. J. Heinrich, D. E. Newbury, R. L. Myklebust, and C. E.

Fiori (eds.), Energy Dispersive X-ray Spectrometry, NBS Special

Publication 604, National Bureau of Standards, Washington, DC

(1981).

[4] K. F. J. Heinrich, Electron Probe Microanalysis by Specimen

Current Measurement, in Fourth International Symposium on

X-ray Optics and X-ray Microanalysis, Orsay, France, 1965,

Hermann, Paris (1966) pp. 159-167.

[5] K. F. J. Heinrich, X-ray absorption uncertainty, in The Electron

Microprobe, T. D. McKinley, H. F. J. Heinrich, and D. B. Wittry

(eds.), John Wiley and Sons, New York (1966) pp. 296-377.

[6] Kurt F. J. Heinrich, Errors in theoretical correction systems in

quantitative electron probe microanalysis—a synopsis, Anal.

Chem. 44, 350-354 (1972).

[7] Kurt F. J. Heinrich, Dale E. Newbury, and Harvey Yakowitz

(eds.), Use of Monte Carlo Calculations in Electron Probe

Microanalysis and Scanning Electron Microscopy, NBS Special

Publication 460, National Bureau of Standards, Washington, DC

(1976).

[8] J. A. Small, D. E. Newbury, and R. L. Myklebust, X-Ray

Bremsstrahlung Intensities from Elemental Targets, NBS Technical Note 1245, National Bureau of Standards, Gaithersburg, MD

(1988).

[9] Kurt F. J. Heinrich, Robert L. Myklebust, Harvey Yakowitz,

Stanley D. Rasberry, A Simple Correction Procedure for Quantitative Electron Probe Microanalysis, NBS Technical Note 719,

National Bureau of Standards, Washington, DC (1972).

[10] H. Yakowitz, R. L. Myklebust, and K. F. J. Heinrich, FRAME:

An On-Line Correction Procedure for Quantitative Electron

Probe Microanalysis, NBS Technical Note 796, National Bureau

of Standards, Washington, DC (1973).

[11] Jean Henoc, Kurt F. J. Heinrich, and Robert L. Myklebust, A

Rigorous Correction Procedure for Quantitative Electron Probe

Microanalysis (COR 2), NBS Technical Note 769, National

Bureau of Standards, Washington, DC (1973).

[12] R. L. Myklebust, C. E. Fiori, and K. F. J. Heinrich, FRAME C:

A Compact Procedure for Quantitative Energy-Dispersive

Electron Probe X-ray Analysis, NBS Technical Note 1106,

National Bureau of Standards, Washington, DC (1979).

[13] Charles E. Fiori and Carol R. Swyt, Desk Top Spectrum Analyzer,

United States Patent 5,299,138, March 29, 1994.

[14] Kurt F. J. Heinrich, Robert L. Myklebust, Stanley D. Rasberry,

and Robert E. Michaelis, Preparation and Evaluation of SRMs

481 and 482: Gold-Silver and Gold-Copper Alloys for Microanalysis, NBS Special Publication 260-28, National Bureau of

Standards, Washington, DC (1971).

[15] R. B. Marinenko, F. Biancaniello, L. DeRobertis, P. A. Boyer,

and A. W. Ruff, Preparation and Characterization of an IronChromium-Nickel Alloy for Microanalysis: SRM 479a, NBS

Special Publication 260-70, National Bureau of Standards,

Washington, DC (1981).

[16] R. B. Marinenko, Preparation and Characterization of K-411

and K-412 Mineral Glasses for Microanalysis: SRM 470, NBS

Special Publication 260-74, National Bureau of Standards,

Washington, DC (1982).

163
Limits for Qualitative Detection and

Quantitative Determination

A visiting professor at NIST once pointed out that our

measurement professionals are given a difficult task by

some of our customers. In a (macroscopically) continuum universe, we are asked to perform measurements

with tools and techniques of finite precision and in the

end to produce digital answers, preferably binary: yes

or no, safe or unsafe, above or below the regulatory

limit. A common triple question arises in the measurement of environmental radioactivity, atmospheric

ozone, gold in rock, or the efficacy of a flu treatment: Is the signal there? What is the chance that we

will detect it? How big is it?

Until Lloyd Currie’s paper Limits for Qualitative

Detection and Quantitative Determination: Application

to Radiochemistry [1] was published, there was enough

inconsistency in the definition of “detection limit” to

conceal a great deal of disagreement. In just over seven

pages, this tightly written communication established a

high level of uniformity in answering these questions.

The paper contains fundamental information that has

made it influential far beyond its size, and it is rich

enough to be discussed actively in e-mail newsgroups

over 30 years later. This is surely one of the most

often cited publications in analytical chemistry. The

Science Citation Index lists 1280 published references to

this paper—so far.

Currie asks and answers a disarmingly simple

question: What do we mean by the detection limit of a

measurement process? He found that the literature

“revealed a plethora of mathematical expressions and

widely-ranging terminology.” The same terms have

been used to denote both the amount that can be

detected and the amount that can be measured, which

are very different quantities. Statistical justification for

some common recipes has been absent or incorrect.

To show graphically how serious the problem was

(and is), he used literature definitions to compare detection limits, defined by eight common recipes, or rules of

thumb, for a simple measurement: counting a radioactive source for 10 minutes with a detector that is 10 %

efficient and has a background of 20 counts per minute.

Currie then arranged the values of the detection limit in

serial order, and found that the range of these definitions

spans a factor of nearly 1000. His Figure 1, reproduced

here, clearly showed the need for a consistent, statistically and physically defensible, definition of this

common term.

Currie then defined measures of detectability, firmly

based on the statistical theory of hypothesis testing.

He began by defining the concepts of qualitative and

quantitative analysis limits. Three limiting levels were

defined:

• The critical level LC, the signal level above which

an observed instrument response may be reliably

recognized as “detected.”

• The detection limit LD, the true net signal level that

may be expected a priori to lead to detection.

• The determination limit LQ, the signal level above

which a quantitative measurement can be performed

with a stated relative uncertainty.

Numerical values of these levels depend on four criteria, most importantly the standard deviation 0 of the

blank, or background. By choosing a probability 

(error of the first kind) for falsely deciding that the

Fig.1. “Ordered” detection limits—literature definitions. The detection limit for a specific radioactivity measurement process is plotted

in increasing order, according to commonly-used alternative definitions. LC, LD, and LQ are the critical level, detection level, and determination limit as derived in the text.

164
signal is present when in fact it is not, the critical level

LC is calculable. Choosing a probability  (error of the

second kind) for deciding that the signal is absent when

it is in fact present permits the detection limit LD to be

calculated. Finally, specifying the maximum tolerable

statistical error in a quantitative measurement allows

the determination limit LQ to be computed. “The levels

LC, LD, and LQ are determined entirely by the errorstructure of the measurement process, the risks,  and

, and the maximum acceptable relative standard

deviation for quantitative analysis. LC is used to test an

experimental result, whereas LD and LQ refer to the

capabilities of [the] measurement process itself.”

Currie then gives recipes for calculating these

quantities, for the conventional assumptions of a normal

distribution; 5 % errors of the first and second kind; the

uncertainty of the blank independent of the signal level;

and quantitation at 10 % or better. His Table I has been

reprinted in many textbooks and operating manuals:

For radioactivity or a similar counting measurement,

where the data are digital and the distribution PoissonNormal, the equations are particularly simple; for

example, if the background is exactly zero with no

uncertainty, then LC = 0 counts, LD 2.71, and

LQ = 100. In agreement with experience, this means that

any observed count will be evidence of a non-zero

signal, and 100 counts gives a standard uncertainty of

100/(100) = 10 %. A more rigorous formulation for

LD, for extreme low-level counting, using the exact

Poisson distribution, was given by Currie in 1972. Here,

LD = 3.00 replaces the Poisson-Normal approximation

of 2.71 counts [2].

To make his 1968 paper still more concrete, three

specific illustrations of analytical procedures were

given, with worked-out equations for the three quantities: spectrophotometry, radioactivity, and a complex

case of activation analysis.

This seminal paper has been elaborated in many

contexts (e.g., [3]) and has led to an American Chemical

Society symposium on the topic [4]. Currie’s formulation was so convincing that it has been universally

incorporated in many rules of practice governing

measurement procedures, international standards [5],

regulations [6], and software. The culmination of

Currie’s early work was seen in the adoption of a

harmonized international position (ISO-IUPAC) on the

nomenclature, concepts, and formulation of detection,

decision, and determination limits [7]. The IUPAC position has been further embedded in the new edition of its

definitive guide for analytical chemistry [8]. Few scientific papers have been so definitive and decisive, or so

clearly set the standards of subsequent discourse. This

work is central to the NBS/NIST role in measurement

science.

Lloyd A. Currie attended the Massachusetts Institute

of Technology and then received his Ph.D. in 1955 at the

University of Chicago under Willard Libby. After

serving on the faculty at Pennsylvania State University,

he came to the National Bureau of Standards in 1962.

In addition to chemometrics, his specialty has been

atmospheric radioactivity, especially 37Ar and 14C.

His research group pioneered the application of microradiocarbon measurements for the discrimination of

anthropogenic and natural carbonaceous pollutants.

He has held visiting faculty appointments at the Universities of Bern and Gent, and was a Commerce Science

Fellow in the U.S. House of Representatives Science

Committee and the office of Congressman Mike

McCormack. He has served as a consultant or advisory

panel member for NASA, NSF, IAEA, IUPAC, and other

organizations. Currie is a Fellow of the American

Institute of Chemists, holds Department of Commerce

Gold and Silver Medals, and was named a NIST Fellow

in 1994.

Prepared by Richard M. Lindstrom.

Bibliography

[1] Lloyd A. Currie, Limits for Qualitative Detection and Quantitative Determination: Application to Radiochemistry, Anal. Chem.

40, 586-593 (1968).

[2] L. A. Currie, The Measurement of Environmental Levels of Rare

Gas Nuclides and the Treatment of Very Low-Level Counting

Data, IEEE Trans. Nucl. Sci. NS19 (1), 119-126 (1972).

[3] Lloyd A. Currie, The Many Dimensions of Detection in Chemical

Analysis—with Special Emphasis on the One-Dimensional

Calibration Curve, in Trace Residue Analysis: Chemometric

Estimations of Sampling, Amount, and Error, David A. Kurtz

(ed.), American Chemical Society, Washington, DC (1985),

pp. 49-81.

[4] Lloyd A. Currie, Detection: Overview of Historical, Societal,

and Technical Issues, in Detection in Analytical Chemistry (ACS

Symp. Ser. 361), L. A. Currie (ed.), American Chemical Society,

Washington, DC (1988) pp. 1-62.

Table I: “Working” Expressions for LC, LD, and LQ*

LC LD LQ

Paired observations 2.33 B 4.65 B 14.1 B

“Well-known” blank 1.64 B 3.29 B 10 B

*Assumptions:  =  = 0.05; kQ = 10;  = 0 = constant

165
[5] Lloyd A. Currie, Nomenclature in Evaluation of Analytical

Methods Including Detection and Quantification Capabilities,

Pure Appl. Chem. 67, 1699-1723 (1995).

[6] Lloyd A. Currie, Lower Limit of Detection: Definition and

Elaboration of a Proposed Position for Radiological Effluent

and Environmental Measurements (Report NUREG/CR-4007),

U.S. Nuclear Regulatory Commission, Washington, DC

(1984).

[7] L. A. Currie, International Recommendations Offered on Analytical Detection and Quantification Concepts and Nomenclature,

Anal. Chim. Acta 391, 103-134 (1999).

[8] L. A. Currie, ch. 2 (Presentation of the Results of Chemical

Analysis) and ch. 18 (Quality Assurance of Analytical Processes),

in IUPAC Compendium of Analytical Nomenclature, Ja ́nos

Incze ́dy, Tama ́s Lengyel, and A. M. Ure, eds., Blackwell Science,

Oxford (1998).

166
Traceability: An Evolving Concept

The concept of traceability to national measurement

standards has evolved considerably over the past 25 to 30

years. The 1980 paper, Traceability: An Evolving

Concept, by Brian Belanger [1], is often cited by other

authors writing on this subject. This paper and others by

NBS/NIST authors have shown why the concept of

traceability is not meaningful unless it incorporates

quantified measurement uncertainty. Traditionally,

measurement traceability has been described as an

unbroken chain of comparisons to a primary or reference standard as maintained by a national measurement

institute (NMI)—NIST or its counterpart institutions in

other countries. The requirement that measurements be

traceable to NIST or some other NMI was a response to

needs for ensuring consistency among measurements

made in different countries or domestic locations (e.g.,

a liter of gasoline in California should be the same as a

liter of gasoline in New York), enabling interchangeability of parts, and facilitating industrial quality

control.

The concept of establishing measurement standards

and relating measurement results to those of a “higher

authority” has been recognized for centuries. When the

pyramids were built in Egypt, the length of the

pharaoh’s forearm was defined as the cubit, and

measurements made for its construction were based on

that national standard of length. Today, we have fundamental principles of physics, rather than the pharaoh, to

rely on for length standards, but the principle is the

same—having national standards for key measurements

upon which everyone agrees (ideally tracing to internationally agreed upon standards).

In 1962, the U.S. Department of Defense (DOD)

impacted significantly on the evolution of traceability

by requiring traceability for DOD laboratories, contractors, and subcontractors in MIL STD 45662A. All

measuring and test equipment had to be calibrated

utilizing reference standards whose calibration was

certified as traceable to the National Bureau of

Standards, had been derived from acceptable values of

fundamental constants, or had been derived by the ratio

type of self-calibration techniques. Reference standards

used in the calibration of DOD equipment and systems

had to be supported by certificates, reports, or data

sheets attesting to the date, accuracy, and conditions

under which the results were obtained. Although other

U.S. government agencies established requirements

for traceability to NBS, the requirements of MIL-STD45662A were the most significant, since DOD was one

of the largest purchasers of goods and services in the

world.

During the 1970s, many organizations asked NBS

for advice on how to comply with traceability requirements, since these requirements usually included

language to have measurements “traceable to NBS.”

Unfortunately, these agencies as well as industrial

organizations included traceability requirements

without considering the technical or scientific implications of traceability, or even having a consensus

definition as to what it meant. As a result, there was

confusion, misinformation, misinterpretation, and lack

of agreement among the diverse and large community of

Fig. 1. Charles Ehrlich, Brian Belanger, Stanley Rasberry, and Ernest

Garner (left to right).

167
testing and/or calibration facilities, vendors, suppliers,

and end-users of the products or services covered by the

requirements of a contract or regulation.

Since contract auditors were not metrologists, they

did not go beyond checking to see whether the contractor had calibration certificates from NBS on file. A

paper trail tracing back to NBS primary or reference

standards or SRMs can be of dubious value in ensuring

that actual measurements are valid.

A story that may well be apocryphal was widely

repeated to illustrate the shortcomings of the conventional view of traceability: There was a defense

contractor that had a set of gage blocks calibrated by

NIST at regular intervals and used the calibration

certificates to prove to auditors that the company was

“traceable to NBS” for its dimensional measurements.

Allegedly, the company never opened or used the box of

gage blocks. Each time the box returned to NBS

for recalibration the seals were found unbroken.

Auditors focused only on documentation for instruments

or artifacts—not the entire measurement process.

A measurement device might be properly calibrated and

in good working order, but if the operator did not know

how to use it properly, the resulting measurements could

still be inaccurate.

Also during the 1960s and 1970s, internationallyrenowned NBS statisticians Churchill Eisenhart, Harry

Ku, and Joe Cameron taught that to have valid measurements, one must be able to quantify the random error

(Type A), as well as put bounds on the maximum possible systematic errors (Type B) of the measurements, and

to show that the total uncertainty is sufficiently small

to accomplish the purpose at hand. The concept of

the “Measurement Assurance Program,” or MAP, was

developed during this era, and NBS worked with its

customers to help them understand it. By the late 1970s,

the clamor in both industry and government was increasing to define better what traceability meant.

Within NBS, it was clear that unless measurement

uncertainty is quantified and monitored, traceability is

meaningless. The American Society for Testing and

Materials, ASTM, was forming a new Committee E-46

on Quality Systems, and the topic of traceability was

one of the items the committee was struggling with.

Committee E-46 was looking to NBS to help define

how traceability related to quality systems.

Brian Belanger, an electrical engineer, came to NIST

in 1977 to work in the Institute for Basic Standards

(IBS), then directed by Arthur McCoubrey. Shortly

after Belanger arrived at NBS, Joe Cameron retired as

Chief of the Office of Measurement Services, and

Belanger was named to replace him. Cameron had

introduced him to Eisenhart and Ku, and he quickly

became an advocate for measurement assurance

programs. Discussions with John Simpson, another

NBS manager who was particularly articulate on the

inadequacies of the conventional approach to traceability, also served to convince Belanger that things

needed to change. Having read some earlier papers on

traceability by Joe Cameron and Harmon Plumb [2-3],

and with the encouragement of Art McCoubrey,

Belanger set about to write an article on traceability

for ASTM Standardization News.

The paper stressed that to be meaningful, traceability

needed to evolve beyond an emphasis on auditing a

paper trail and, instead, focus on whether the measurement process was in control with regard to random

errors and drift, and whether the measurements had an

acceptably small possible offset from national standards.

In other words, the thrust of the paper was to insert the

idea of measurement assurance into the traceability

debate. The key concepts are that measurement uncertainty must be quantified relative to national standards

and that data must be produced on a continuing basis to

demonstrate that the measurement process is in a state

of statistical control. Belanger recommended that

traceability be defined as follows:

Fig. 2. Joseph Cameron.

168
“Traceability to designated standards (national, international, or well-characterized reference standards based upon fundamental

constants of nature) is an at tribute of some

measurements. Measurements have traceability to the designated standards if and only

if scientifically rigorous evidence is produced

on a continuing basis to show that the

measurement process is producing measurement results (data) for which the total

measurement uncertainty relative to national

or other designated standards is quantified.”

Full acceptance of the definition proposed by

Belanger became an accomplished fact at NBS and,

ultimately, at the NMI’s of other major industrial countries. Indeed, it is a necessary and essential condition

that a world class NMI produce “scientifically rigorous

evidence” on a continuing basis to show that its

measurement processes are quantifiable and in a state of

statistical control. At the other end of the measurement

hierarchy—the manufacturer’s shop floor, small testing

facilities, and calibration vendors—“scientifically rigorous evidence” and quantifiable uncertainty were more

nearly perceived as a barrier to traceability and an

unnecessary luxury. Even so, there was strong support

for the concept within NBS and staff reinforced the

message in their own writings and talks during the

1980s. By 1986, an American Society for Quality

Control (ASQC) writing group had developed ANSI/

ASQC Standard M1 on Calibration Systems, which

included a definition of traceability based on the

concept of quantified uncertainty.

As support for the new approach to traceability began

to grow in the United States, metrologists in other countries gradually began to endorse the approach as well.

In the 1993 edition of the International Vocabulary of

Basic and General Terms in Metrology (VIM) traceability is defined as follows:

“Property of the result of a measurement or

the value of a standard whereby it can be

related to stated references, usually national

or international standards, through an unbroken chain of comparisons all having stated

uncertainties.”

While this definition does not explicitly embrace the

concept of measurement assurance as a means of

demonstrating that the measurement process is in a state

of statistical control, it does embrace all of the other

basic elements of the approach to traceability

outlined in Belanger’s paper. The VIM definition has

perhaps gained the widest acceptance on both the

national and international scene of any definition of

traceability published to date.

Thinking on the subject continued to progress at

NIST as well as elsewhere. In 1992 the Testing and

Evaluation Committee of ASTM invited the Calibration

Program to reflect on the decade of the 1980s and to

give an assessment of new developments and trends in

traceability. Ernest Garner and Stanley Rasberry of the

Office of Measurement Services responded to the invitation with a paper [4], which was published in the

ASTM Journal of Testing and Evaluation. Identifiable

trends included: increased attention to defining and

minimizing the number of measurement comparisons in

the unbroken chain to NIST; local representation (i.e.,

intrinsic standards such as the Josephson Junction for

voltage and the Quantum Hall Effect for resistance);

greater use and acceptance of laboratory accreditation;

significant movement to quality programs based upon

internationally recognized documentary standards; and

the emergence of multinational, regional trade organizations requiring improved mutual recognition, equivalency of measurements and confidence among accreditation and metrology bodies. The authors also called

attention to the critical implications of transferring SI

units from the point of realization (usually an NMI)

to an end user, who then had to determine what uncertainty was required to satisfy the intended purpose.

Fig. 3. Harmon Plumb.

169
Maintaining a measurement quality assurance system to

ensure that total uncertainty was within specified limits

at all times was recommended.

While the use of the concept of traceability was

becoming more popular, its implementation was still

less than ideal. During his years as Leader of the

NIST Pressure Group in the late 1980s and early 1990s,

Charles Ehrlich developed both an appreciation and

frustration for the way that traceability was being

treated in that field. He became increasingly concerned

that while uncertainty in measurement was being recognized as an important component of traceability, the use

of appropriate measurement assurance methods both

before and after calibrations was not. Further, the

community was taking different approaches to what

constituted traceability, creating considerable confusion. In the mid-1990s Ehrlich teamed with Rasberry,

who shared many of the same concerns, to move

the traceability discussion ahead. Their collaboration

produced the next and most recent contribution to this

NBS/NIST traceability series, the paper Metrological

Timelines in Traceability [5]. Besides appearing in the

NIST Journal of Research, this paper was also published

in the journal Metrologia and, by invitation, in the

Bulletin of the International Organization of Legal

Metrology (OIML). Evidence of the continued interest

in the metrology community of furthering the traceability concept came when this paper received the “best

paper” award in the management category at the

1997 National Conference of Standards Laboratories

Symposium.

The Metrological Timelines paper, which calls attention to the time element in controlling measurements

(implied in the term “continuously” in Belanger’s

paper), explains the modern view of traceability very

thoroughly, and introduces the concept of the metrological timeline. Ehrlich and Rasberry emphasize that

what is a valid “traceable” measurement today may not

be valid at a later time unless the organization(s) in the

unbroken chain have in place adequate measurement

assurance procedures. They further emphasize that the

responsibility for traceability resides not just with the

NMI, but also with the lower level laboratory, which

must put in place a process for guaranteeing that an

instrument sent to an NMI for calibration is behaving the

same way when it returns from the NMI as it did before

it was sent. Ehrlich and Rasberry also elaborate on other

aspects of traceability, such as multiple routes to traceability, equivalence of measurements, recalibration

intervals and the use of intrinsic standards in traceability. They propose that the key questions to be answered

concerning traceability are: “ What corrections should

be applied to a measurement result obtained at a given

time with my instrument to match the result that would

be obtained using the instrument (standard) to which

traceability is desired? What is the uncertainty of this

corrected measurement result?” They also note that

“An uncertainty cannot be stated rigorously without

demonstrated traceability.”

Since traceability is an important ingredient of

laboratory accreditation and international mutual

recognition agreements, the importance of adopting a

rigorous approach to traceability goes well beyond

issues such as contractual compliance for defense

contractors. Organizations such as NORAMET (The

North American Metrology Cooperation), ISO, and

OIML are using approaches that stress that quantified

measurement uncertainty is a key aspect of traceability. While great progress has been made, traceability

continues to evolve.

Brian C. Belanger holds a B.S. from Caltech and a

Ph.D. from the University of Southern California, both

in Electrical Engineering. After four years at the

General Electric Research and Development Center,

working in superconductivity, cryogenics, and high

voltage dielectrics, he joined the Federal government in

1972, becoming a program manager at the Atomic

Energy Commission (AEC), with responsibility for

developing high capacity superconducting underground

power cables. He joined NBS in 1977, soon becoming

Chief of the Office of Measurement Services in the

Institute for Basic Standards. Belanger served as NBS’

liaison to the Department of Defense (early 1980s), as

Associate Director for Program Development in the

Center for Electronics and Electrical Engineering

(1987-90), as a Senior Technology Advisor to the

Assistant Secretary for Technology Policy at the

Commerce Department (1990), as the Deputy Director

of the Advanced Technology Program (1991-98), and

finally, as Executive Director of the NIST Visiting

Committee on Advanced Technology.

Joseph M. Cameron received his B.S. in Mathematics

in 1942 from the University of Akron and an M.S. in

Statistics in 1947 from North Carolina State. He joined

the NBS staff in 1947, and served as Chief of the

Statistical Engineering Section in the NBS Applied

Mathematics Division. In 1969 Cameron was appointed

Chief of the newly formed Office of Measurement

Services in the Institute for Basic Standards. He retired

in 1977 and died in January 2000.

After completing his B.S. in Physics at the University

of Miami and his Ph.D. in Surface Physics at the University of Pennsylvania, and working for five years in the

semiconductor industry, Charles D. Ehrlich joined the

Pressure and Vacuum Group at NBS/NIST in 1984,

working to help establish the first leak calibration

program. He served as Group Leader of the Pressure

Group from 1987-1994, followed by two years in the

170
NIST Program Office. Ehrlich is currently Chief of the

Technical Standards Activities Program.

Ernest L. Garner has a measurement background at

NIST/NBS in high accuracy mass spectrometry of the

elements to include atomic weight determinations,

elemental abundance by isotope dilution, natural

isotopic variations of the elements, and characterizing

the sources of uncertainty in thermal ionization mass

spectrometry.

Harmon H. Plumb received his B.A. in Physics from

Middlebury College in 1947, and his M.S. and Ph.D.

degrees from Northwestern University in 1948 and

1954, respectively. He joined the NBS Cryogenic

Physics Laboratory in 1955, working to establish

low temperature scales. Prior to joining NBS, Plumb

performed basic research on ice single crystals for the

Corps of Army Engineers, and from 1949 to 1950 he

was a physics instructor at Miami University, Oxford,

Ohio. He died in 1985.

Stanley D. Rasberry began his career at NIST in 1959,

while studying for a degree in physics at the Johns

Hopkins University. He developed and applied spectrometric techniques to the chemical analysis of a wide

variety of materials, especially those intended as

standard reference materials (SRMs). During the late

1960s, he was privileged to work with Joe Cameron to

improve and computerize procedures for quantifying the

homogeneity of candidate SRMs. The collaboration

provided an appreciation that SRMs could serve as links

for the traceability of chemical measurements to

national standards. Later, Rasberry became Chief of the

Standard Reference Materials Program and subsequently Director of the Office of Measurement

Services, where he also directed NIST efforts in

standard reference data, weights and measures, calibration services, and the National Voluntary Laboratory

Accreditation Program. The Measurement Services

assignment gave him the opportunity to explore and

develop traceability concepts together with Garner and

Ehrlich. Following retirement, in 1997, Rasberry has

continued to consult with NIST and has explored new

modes of demonstrating traceability, including the use

of proficiency testing with results being compared to

those of an NMI.

Prepared by Brian Belanger, Stanley Rasberry, Ernest

Garner, Carroll Brickencamp, and Charles Ehrlich.

Bibliography

[1] Brian C. Belanger, Traceability: An Evolving Concept, ASTM

Stand. News 8 (1), 22-28 (1980).

[2] J. M. Cameron and H. Plumb, Traceability—with Special Reference to Temperature Measurement, Society of Automotive

Engineers, Report 690428, National Air Transportation Meeting

(1969).

[3] Joseph M. Cameron, Traceability? J. Qual. Technol. 7, 193-195

(1975).

[4] Ernest L. Garner and Stanley D. Rasberry, What’s New in Traceability, J. Test. Eval. 21, 505-509 (1993).

[5] Charles D. Ehrlich and Stanley D. Rasberry, Metrological Timelines in Traceability, J. Res Natl. Inst. Stand. Technol. 103, 93-

105 (1998).

171
Code for Information Interchange–ASCII

At the onset of the computing era, computers were

designed and built with particular applications in mind.

For example, SEAC, the Standards Electronic Automatic Computer, described elsewhere in this volume,

was built at NBS in the late 1940s principally to handle

certain classes of mathematical problems. SEAC had a

manual keyboard for direct input, a teletype printer for

direct output and punched paper tape for indirect operation. The idea of sharing the information from this

computer with another computer was not one of the

original concepts in the design. Very few computers

were operational at the time, so such opportunities were

greatly limited. Communication among humans was

accomplished using the telephone, teletype, and typewriter, and these devices did not automatically lend

themselves to machine-machine communication.

As computers became more common and areas of

application increased, connecting computers to share

the processing load or to share data became more

important. SEAC and DYSEAC, for example, were

connected at NBS in the 1950s. The electronic language

of nearly all machines was, and continues to be, binary

code, ones and zeros. Programmers encoded commands

for the machines and data in binary code. Eventually

higher level languages were developed so that commands were easier to write and debug. Alphabetic

characters, numerals, and punctuation marks were

needed to develop and use such higher-level languages.

Each character had to be represented as some combination of binary digits. The problem was that different

computers used different combinations of ones and

zeros to represent the basic characters. This meant that

an ‘a’ on one machine might have the same representation as an ‘m’ on another machine or, more commonly,

a ‘<’ on one machine would be ‘!’ on another. A related

problem occurred when one used computers to sort

lists of alphanumeric data. In some code sets, letters

preceded numerals, while in others the reverse was true.

Since sorting algorithms treated the binary representations like numbers, a list sorted on one computer could

differ in order from the same list sorted on another. The

only way that commands or data could move from one

computer to another and be interpreted correctly would

be for all parties to agree on what each combination of

ones and zeros stood for. Work on such a code for

information interchange started in 1961. By 1967 the

“7-bit coded character set” had evolved to include the

letters of the alphabet, numbers and certain control

characters required by the computers for a total of 128

characters. Obtaining a consensus on this standard was

not simple because several sets of codes developed by

large computer vendors were already in widespread use.

Control Data, for example, used the 6-bit FIELDATA

code, while IBM used the 8-bit EBCDIC. John L. Little,

an NBS staff member from 1953 to 1987, held the

positions of vice-chair and chair of X3.2.4, the national

voluntary standards committee that developed the

standard. X3.2.4 was chartered by the American

Standards Association (ASA), which became the United

States of America Standards Institute (USASI) in 1966,

then the American National Standards Institute (ANSI)

in 1969. Little worked for years to develop this standard.

His strong, quiet, and deliberate way of working with

members to obtain consensus was critical to the

project’s success. In 1968, USASI published the 7-bit

American Standard Code for Information Interchange

(ASCII).

Most modern developments in the

computer field, such as the Internet,

would not have been possible without

this underlying [ASCII] code.

NBS was interested in these standards efforts in the

late 1960s because of new legislative directions.

On October 30, 1965, the Brooks Bill (P.L. 89-306)

authorized the Department of Commerce:

“(1) to provide scientific and technological

advisory services to other agencies with regard to ADP

equipment and related systems;

(2) to make appropriate recommendations to the

President concerning the establishment of uniform

Federal automatic data processing standards; and

(3) to undertake research in computer science

and technology as needed to fulfill the above

responsibilities.”

The Secretary of Commerce delegated the responsibility for implementing these provisions to the National

Bureau of Standards. This legislative authority was

augmented by Bureau of the Budget guidelines issued

172
in December 1966 that divided NBS work into five

programmatic areas: advisory and consulting services,

development of voluntary commercial standards, recommendations for uniform Federal standards, research

on computer sciences and techniques, and computer

service activities. Thus, research began in 1965 in the

Center for Computer Sciences and Technology that

would support voluntary national and international

standards, and where appropriate be recommended for

other agency use.

In November 1968, NBS sealed the fate of ASCII by

adopting it as its first Federal Information Processing

Standard (FIPS). This standard, published as FIPS

Pub 1, Code for Information Interchange [1], and issued

under the signature of President Lyndon Johnson, specified a code and character set for use in Federal information processing systems, communications systems, and

associated equipment. The endorsement of the Federal

government, then the largest purchaser of computer

equipment, was probably the single most important

reason for the subsequent wide adoption of ASCII.

(Fig. 1)

In practice, the 7-bit ASCII code is often embedded

in a comparable 8-bit code, where the leftmost bit is set

to zero. This is convenient because most computers

transfer information in units of 8 bits (a “byte”). In

some cases, the leftmost bit is used as a parity bit. In

“even” parity, for example, the leftmost bit is set so that

the number of 1 bits is always even. This allows for

automatic 1-bit error detection, a useful feature when

transmission lines are noisy.

ASCII might well be called the first computer interoperability standard. Most modern developments in

the computer field, such as the Internet, would not be

possible without this underlying code. To this day, all

data interchanges start and end as sets of ASCII characters. When all else fails, systems still will accept “plain

text files” which are coded in ASCII. ASCII has turned

out to be an excellent code that has lasted for over

30 years, and has been fundamental to the development

of the U.S. computer industry.

Prepared by Martha M. Gray.

Bibliography

[1] Code for Information Interchange, Federal Information Processing Standards Publication (FIPS Pub) 1, National Bureau of

Standards, Washington, DC, November 1, 1968.

[2] Charles E. Mackenzie, Coded Character Sets: History and Development, Addison-Wesley Publishing Co., Reading, MA (1980).

[3] Brooks Bill Issue Study of the National Bureau of Standards, NBS

Report 10 608, Center for Computer Sciences and Technology,

National Bureau of Standards, Washington, DC, September 1971.

Fig.1. The first letters of the alphabet with their ASCII equivalents, as given in FIPS PUB 1.

173
Consumer Information Series

The many thousands of papers produced by NIST/

NBS in the past century have mainly been technical in

nature, directed to an audience of research scientists and

engineers. Some, of course, were issued in a form more

readily understandable to a wider audience, but were

focused on groups of individuals with a particular

interest in the subject matter. It is roughly estimated,

however, that only a tiny percentage of our publications

were written specifically with the consuming public

in mind in order to make technical results generally

available for their practical value to all citizens. The

utility of these publications aimed at the general public

is attested by the fact that hundreds of thousands of them

were ordered by keenly interested consumers.

One of the earliest example of a publication designed

for the public at large was the 1922 Circular [1] on

constructing a radio, described elsewhere in this

volume. In the following years, especially during the

1930s and 1940s, the Bureau had occasion to conduct

tests of various types of material and then made selected

reports available from the Government Printing Office

at low cost. Many of these [2-9] had limited audiences,

but a few [10, 11, 12] had broad appeal to homeowners

and potential homebuyers. Thus How to Own Your Own

Home [11] sold 300,000 copies in 1923, and Care and

Repair of the Home [12], which drew fire from private

sector business interests, sold more than 500,000 copies

between 1931 and 1940.

The early 1970s saw an explosion of consumer

activism in the United States, leading to the establishment of such Federal agencies as the Consumer

Product Safety Commission (CPSC). In response to a

Presidential order, the Bureau formed a Center for

Consumer Product Technology (CCPT) with divisions

for product engineering, product systems analysis,

product safety, and law enforcement standards—and

with a dedicated mission to provide useful information

to the general public. Guides in the Consumer Information Series (CIS) [13-22] were prepared by Bureau

experts and CCPT staff. These booklets were distributed

in very large numbers and at very low cost through the

Government Printing Office and by the Consumer

Information Center in Pueblo, Colorado. (Fig. 1)

A special foreword in each publication, by the NBS

Director, called attention to technological changes that

affect products and the marketplace; the confusion that

stems from the proliferation of products and materials

about which the shopper has little useful information;

and the availability of results from the technical work

that should be shared with the citizens who, after all,

support the Bureau’s work with their taxes.

The first Guide in the Series, NBS CIS1 Fibers and

Fabrics [13], provided a detailed account of both natural

(i.e., cotton, linen, silk, and wool) and 16 man-made

fibers, describing for each material its properties, uses,

and appropriate care. It also discussed blends and

combinations, as well as the features of wash-and-wear

fabrics. The information was presented in a form to

facilitate user selection of fabrics that would satisfy

personal needs and desires. In addition, the laundering

or dry-cleaning recommendations and the susceptibility

of some fabrics to flammability or application of

excessive heat were probably of equally great value.

A glossary defined the terms used to describe the

manufacturing processes and attributes of the cited

materials, and a table of trademarks of commercial

synthetic materials, obtained from listings of the Federal

Trade Commission, aided shoppers when encountering

generic fabrics otherwise identified only by trade

names.

How to Own Your Own Home sold

300,000 copies in 1923, and Care and

Repair of the Home, which drew fire

from private sector business interests,

sold more than 500,000 copies.

Tires—Their Selection and Care [14] gave the

automobile owner or driver a well-illustrated tutorial on

the kinds (not brands) of tires available and how they

should be chosen and maintained for optimum safety,

efficiency, and cost savings. In addition to describing

tire care and tire construction and features, the Guide

addressed the factors that should influence tire selection, plus driving habits and effects that depend on the

chosen tires and their care. Moreover, the publication

pointed out that there was then no reliable system for

grading tires in terms of quality, a situation that still

prevails.

174
Information needed for selecting and applying adhesives for use in the home and hobby shop was made

available in Adhesives for Everyday Use [15]. This practical guide described the different types of adhesives

and their characteristics, along with typical applications

for the various materials that are to be bonded and the

end use of the application. It also illustrated and outlined

the steps that should be taken when preparing the

materials, applying the adhesives, and ensuring a strong

bond.

Facts About Hearing and Hearing Aids [16] was

prepared by NBS specialists in sound and testing, with

assistance from a number of other agencies concerned

with audiology (the science of measuring hearing

capability) and the medical aspects of hearing and its

loss. It gave a comprehensive description of the hearing

process, the causes and treatment of hearing loss, and

steps that might be taken to compensate for such loss,

including the availability of well-described types of

hearing aids then on the market. The guide offered

suggestions on how to select a hearing aid, how to use

it, and proper maintenance and care.

Based on Bureau research on paper and photographic

film, Care of Books, Documents, Prints and Films [17]

explained the composition and kinds of paper, and

preservation techniques. It covered the nature of books

and documents, the factors that degrade them over the

course of time, and recommended methods of caring for

them, as well as techniques for making minor repairs,

letting professional restorers carry out major repairs and

restoration of damaged books and documents. This

guide also offered a short section on the appropriate

care for photographic films, negatives, and prints.

A beautifully illustrated (in color, of course!) guide,

Color in our Daily Lives [18], was one of the most

popular publications in this series; it was distributed to

classrooms across the country and to the general public.

In easily readable textbook fashion, color was related to

light, and families of color hues were shown for each of

red, green, blue, and yellow. Similarly, there were

illustrations of families of dark, light, vivid, and grayish

colors; relationships among different colors with respect

to hues, lightness, and vividness; and the influence on

perception of colors when juxtaposed with other colors.

Fig. 1. Covers of booklets in the Consumer Information Series and other typical pamphlets intended

for use by homeowners.

175
Color harmony, the use of colors by individuals (for

cosmetics or apparel) or in various environments,

and suggestions for experimentation were other topics

included in the guide.

Starting in 1973, when What About Metric? [19]

was published, the Bureau began a long, continuing

campaign to acquaint the public with the decimal-based

metric system, which was then being adopted by

the rest of the world; more recent examples from

the metric program are described elsewhere in this

volume. The CIS Guide explained why metric was

being adopted in almost all countries; the differences

between customary (such as inches and pounds)

measurements and those in the metric system (e.g.,

meters and grams); and how to convert from one system

to the other.

The energy crisis of the early 1970s had a major

impact on consumers as a result of fuel shortages and

increasing fuel costs. Homeowners and renters were

influenced to turn down thermostats and to wear extra

clothing in the house, while at the same time considering longer term techniques for maintaining comfortable

living conditions yet simultaneously saving money.

Making the Most of Your Energy Dollars [20] presented

information on the value of increasing different types of

home insulation and the economic and climatic factors

that should be considered in determining whether

and how much to invest for these purposes. The guide

offered sample worksheets for background calculations

and referred readers to several available “How To”

publications.

Corrosion of metal, which exacts a heavy economic

toll on consumers and the nation, has long been a subject

of study at NBS/NIST. Useful advice was therefore put

together for the guide entitled Corrosion—Facts for the

Consumer [21]. This publication described the different

types of corrosion, how to prevent or minimize it, where

it occurs most frequently around the home and the

automobile, how to remove corrosion when it occurs,

and what protection techniques to look for when buying

metal objects.

By the end of NBS/NIST’s first century, almost

everyone had become aware of and was gaining the

benefits from bar code scanning, automated teller

machines, and other now-commonplace reliance on

computerization in daily life. However, in 1978 these

“magical” systems were mysterious to most folks,

but were explained to the public in the guide entitled

Automation in the Marketplace [22]. Simple language

described the Universal Product Code and the use of

laser bar code scanners and electronic cash registers

connected to computers. It set forth the advantages to

consumers of automated systems installed in groceries,

retail stores, and banks, and alluded to NBS research in

encryption to protect privacy and ensure security.

The foregoing summaries reflect not only a small

subset of the institution’s broad research programs,

but also the impact that the results can have on the

knowledge base for the citizenry. In particular, these

publications—as well as small brochures such as those

for smoke detectors, home security, and home security

alarms [23-25]—contained information that could be

used immediately by all readers for practical purposes.

Although the Consumer Information Series no longer

exists per se, similar information is still provided to the

general public through various releases to mass media

and resultant publicity.

The NBS authors whose CIS guides are listed in the

bibliographic citations that follow evidence the wide

range of technical talent characteristic of the NBS/NIST

staff during its first century. Josephine M. Blandford

was a senior NBS textile technologist responsible for

research on evaluation and quality control of textile

materials and apparel components, with two books

published by the Apparel Research Foundation, Inc. F.

Cecil Brenner, was a fiber scientist who served as Chief

of the NBS Textile and Apparel Technology Center,

then as the Tire Systems Division Chief at the National

Highway Transportation Safety Administration’s

Safety Research Laboratory, and later a consultant to

the Environmental Protection Agency. He developed the

government standard for tire safety and performance.

Karl F. Plitt was Chief of the Product Engineering

Section, responsible for testing and research into safety

and performance characteristics of products used by

fire and law enforcement officials and the consuming

public, including adhesives, plastics used for safety

goggles and helmets, and children’s toys. Edith L. R.

Corliss, trained in physics, performed research in

electricity, optics, and astronomy before becoming an

expert in acoustics, measurement of hearing, and speech

communications systems. William K. Wilson, a chemist,

was Chief of the Paper Evaluation Section for 15 years,

then a guest worker at the National Archives. [J. L. Gear

was on the staff of the National Archives.]

Deane B. Judd, trained as a mathematician and

physicist, was Assistant Chief of the Optics and

Metrology Division and in charge of the Bureau’s colorimetric work. His many awards included gold medals

from the Department of Commerce and the Illuminating

Engineering Society and recognition by the Society of

Motion Picture Engineers, the Inter-Society Color

Council, and the Optical Society of America. Louis E.

Barbrow, a physicist who served as Chief of the Photometry and Colorimetry Section and Chief of the Optics

Metrology Branch, later coordinated metric activities

176
at NBS and served as a consultant to the National

Conference on Weights and Measures.

Madeleine Jacobs, a chemist who later became

Editor-in-Chief of the American Chemical Society’s

Chemical & Engineering News, served in the NBS

Office of Information Activities and was later Director

of Public Affairs at the Smithsonian Institution. Stephen

Peterson was an economist who conducted extensive

research in the area of building economics.

Jerome Kruger, Chief of the Corrosion Section of the

Metallurgy Division, was a chemist whose research

work led to receipt of Silver and Gold Medals from the

Department of Commerce, the NBS Samuel Wesley

Stratton Award, as well as awards from the National

Association of Corrosion Engineers, the British Institute

of Corrosion, and the Electrochemical Society. Shirley

Radack, a Supervisory Computer Specialist, managed

program coordination and support activities for the

Institute of Computer Science and Technology (ICST) at

NBS and was responsible for review and approval of

Federal Information Processing Standards and for

outreach activities with the public and private sectors.

Grace Burns was a special assistant to the Director of

ICST.

Prepared by Walter G. Leight and W. Reeves Tilley.

Bibliography

[1] Construction and Operation of a Simple Homemade Radio

Receiving Outfit, Circular of the Bureau of Standards, No. 120,

U.S. Government Printing Office, Washington, DC (1922).

[2] Hubert R. Snoke and Braxton E. Gallup, Accelerated Weathering Tests of Mineral-Surfaced Asphalt Shingles, J. Res. Natl.

Bur. Stand. 18, 669-681 (1937).

[3] Irvine C. Gardner, Charts for Testing Lens Resolution, NBS

Miscellaneous Publication M166, National Bureau of Standards,

U.S. Government Printing Office, Washington, DC (1940).

[4] Sun Lamps, Health Lamps; Carbon and Mercury Arc Lamps,

Letter Circular LC 631, National Bureau of Standards, Washington, DC, February 12, 1941.

[5] Painting of Steam and Hot Water Radiators, Letter Circular LC

445, National Bureau of Standards, Washington, DC, July 19,

1935.

[6] Corrosion of Metals Used in House Construction, Technical

Information on Building Materials 1 (TIBM 1), National Bureau

of Standards, Washington, DC, March 3, 1936.

[7] Donald B. Brooks and Ronald E. Streets, Automotive

Antifreezes, National Bureau of Standards Circular 474, U.S.

Government Printing Office, Washington, DC (1948).

[8] Automobile Engine Lubricating Oils, Letter Circular LC 613,

National Bureau of Standards, Washington, DC (Revised to

Sepember 15, 1940).

[9] F. W. Smither, Washing, Cleaning, and Polishing Materials,

Circular of the National Bureau of Standards C 424, U.S.

Government Printing Office, Washington, DC (1939).

[10] Safety for the Household, Circular of the National Bureau of

Standards, No. 397, U.S. Government Printing Office, Washington, DC (1932).

[11] John M. Gries and James S. Taylor, How to Own Your Home: A

Handbook for Prospective Home Owners, Building and Housing

Publication BH 17, National Bureau of Standards, U.S. Government Printing Office, Washington, DC (1931).

[12] Vincent B. Phelan, Care and Repair of the Home Including

Minor Improvements, Building and Housing Publication BH 15,

National Bureau of Standards, U.S. Government Printing Office,

Washington, DC (1931).

[13] Josephine M. Blandford and Lois M. Gurel, Fibers and Fabrics,

NBS Consumer Information Series 1 (CIS 1), National Bureau

of Standards, Washington, DC, November 1970.

[14] F. C. Brenner, Tires, Their Selection and Care, NBS Consumer

Information Series 2 (CIS 2), National Bureau of Standards,

Washington, DC, November 1970.

[15] Karl F. Plitt, Adhesives for Everyday Use, NBS Consumer

Information Series 3 (CIS 3), National Bureau of Standards,

Washington, DC, November 1970.

[16] Edith Corliss, Facts About Hearing and Hearing Aids, NBS

Consumer Information Series 4 (CIS 4), National Bureau of

Standards, Washington, DC, November 1971.

[17] William K. Wilson and James L. Gear, Care of Books,

Documents, Prints and Films, NBS Consumer Information

Series 5 (CIS 5), National Bureau of Standards, Washington,

DC, December 1971.

[18] Deane B. Judd, Color in Our Daily Lives, NBS Consumer

Information Series 6 (CIS 6), National Bureau of Standards,

Washington, DC, March 1975.

[19] Louis E. Barbrow, What About Metric, NBS Consumer Information Series 7 (CIS 7), National Bureau of Standards, Washington,

DC, October 1973.

[20] Madeleine Jacobs and Stephen R. Peterson, Making the Most of

Your Energy Dollars in Home Heating and Cooling, NBS

Consumer Information Series 8 (CIS 8), National Bureau of

Standards, Washington, DC, June 1975.

[21] Jerome Kruger, Corrosion—Facts for the Consumer, NBS

Consumer Information Series 9 (CIS 9), National Bureau of

Standards, Washington, DC, March 1978.

[22] Shirley M. Radack and Grace G. Burns, Automation in the

Marketplace, NBS Consumer Information Series 10 (CIS 10),

National Bureau of Standards, Washington, DC, March 1978.

[23] Smoke Detectors, What They Are and How They Work, LC 1074,

National Bureau of Standards, Washington, DC, December

1976.

[24] Home Security Starts at Your Door, LC 1088, National Bureau of

Standards, Washington, DC, January 1976.

[25] Home Security Alarms—What They Are and How They Work, LC

1079, National Bureau of Standards, Washington, DC, March

1977.

177
Theory of Isoperibol Calorimetry for Laser

Power and Energy Measurement

This paper [1] describes the first and most thorough

analysis concerning the behavior of isoperibol calorimeters developed at NIST and used by NIST (and other

laboratories) as standards for laser power and energy

measurements. For over 30 years, instruments based on

the principles described in the paper have been used as

primary standards to relate absorbed laser energy to

dissipated electrical energy and thus to provide traceability to SI units. A family of such instruments provides the basis for calibrations that span a wide range of

laser types and power ranges—wavelengths from 193

nm in the ultraviolet to 10.6 m in the infrared, and

power levels from nanowatts to over 100 kW. New

instruments based on the same principles continue to be

developed as NIST capabilities are extended to meet

emerging needs. In some cases (e.g., certain wavelengths or power levels), NIST is the only national

metrology laboratory with the capability to provide

needed laser calibrations, and, consequently, it provides

traceability to organizations throughout the world.

Lasers, as opposed to other sources of electromagnetic radiation, typically emit light in a well-defined

beam that may have very high irradiance and a nonuniform irradiance profile. Laser light also has very

high spatial and temporal coherence. Although these

properties contribute to the usefulness of lasers for

many applications, they also can complicate the performance of accurate measurements of laser power and

energy.

In the early 1960s, during the period of initial

development of the laser, NBS began developing

standards and appropriate measurement techniques to

characterize laser radiation. The very first NBS laser

energy standard was a “liquid cell calorimeter” developed by Don Jennings [2]. It used an aqueous solution

of CuSO4, contained in a cell with a quartz window to

absorb the radiation from pulsed lasers such as ruby and

Nd:glass. A small amount of dark ink was added to the

solution to increase the wavelength absorption range.

Thermocouples were used to measure the corresponding

temperature increase from laser light absorption. An

electrical heater, immersed in the liquid, provided a

means to calibrate the responsivity of the device

electrically. Although designed for measuring the

energy from pulsed lasers, the liquid-cell calorimeters

also worked well for measuring the energy or average

power from continuous (cw, as opposed to pulsed) laser

sources. For a number of years, these liquid-cell

calorimeters were used as primary standards at NIST

and at military primary standards laboratories for

calibrating laser power and energy meters.

In July of 1969, Dale West, Chief of the Heat

Measurements Section of the Heat Division, who had

been working for a number of years in the field of

high-temperature calorimetry, moved from NBS in

Gaithersburg to NBS in Boulder to join Don Jennings’

Quantum Electronics Section of the Quantum Electronics Division. As leader of the Laser Power and Energy

Project, West applied his knowledge of “bomb calorimetry” (a technique for measuring the energy released

by a combustion reaction that produces a large increase

in temperature and pressure) to the task of measuring

the amount of power and energy contained in laser

radiation. He quickly recognized that isoperibol

calorimeters would make excellent primary standards

for this application and would allow increased accuracy

over the liquid-cell calorimeters in use at that time. The

term “isoperibol” refers to a calorimeter in a constant

temperature environment. In 1970, West and Kenneth

Churney wrote and published Theory of Isoperibol

Calorimetry for Laser Power and Energy Measurements

[1] in which they developed the underlying concepts for

isoperibol laser calorimetry. Thereafter, until his retirement in 1974, West designed and built various models

of laser calorimeters that implemented the principles

established in this paper. He also published numerous

other papers in which he discussed various aspects of

laser power and energy measurements.

In this seminal paper [1], West and Churney start

with the first law of thermodynamics and, in a logical

sequence, develop the equations that govern the resulting thermal response of an isoperibol calorimeter when

exposed to laser radiation. They clearly explain the

assumptions and conclusions that lead to their final

formula for the “corrected temperature rise” of the

calorimeter. West and Churney showed that the

corrected rise is proportional to the stored thermal

energy in the calorimeter minus the heat energy lost

during the measurement. In further papers, West gives

more detailed guidance (and even a software program

[3]) that enables the reader to apply the corrected-rise

calculations to actual data acquisition and analysis.

These analytic techniques are still used today for many

situations in laser-measurement laboratories. The clear

178
and thorough treatment of the calorimeter behavior

enabled timely and widespread public acceptance

of these devices as primary standards for laser energy

measurements.

West was known for his rigorous, meticulous

approach to metrology and uncertainty analysis. Before

building any final devices, he built numerous test

fixtures and samples to evaluate thoroughly the heatflow patterns, with special emphasis on the equivalence

of electrical and laser energy deposition. The isoperibol

calorimeters that West designed for laser measurements

basically consist of cylindrically shaped absorbing

cavities surrounded or enclosed by temperaturecontrolled metal jackets. The jackets provide the

isoperibol (i.e., constant temperature environment)

conditions necessary as prescribed in the paper. During

use, laser radiation enters the absorbing cavity (typically coated with a black paint or other highly absorbing

material) where the absorbed optical energy is converted to thermal energy. The resulting temperature

increase is then monitored with thermal sensors

(e.g., thermocouples or resistors). Heater wires are

thermally attached to the cavities to calibrate the

instruments by injection of known amounts of electrical energy. Using West and Churney’s equations

developed in the paper, the characteristic output of

the temperature sensors can then be quantitatively

correlated with the measured amount of injected

electrical energy.

The first significant calorimeter that West produced

based on these principles was the C-series calorimeter

[4,5], which was designed to measure the output of low

to medium power (1 mW–1 W) lasers. Assisted by

William Case and Alvin Rasmussen for certain aspects

of the construction, such as the temperature control

circuitry and the electrical wiring, West did much of the

construction at his desk (e.g., attaching the thermocouples and positioning the cavity inside the temperature-controlled jacket). The calorimeter worked amazingly well and its output reproduced the characteristic

behavior pattern predicted in the paper. The C-series

calorimeters are still used on a daily basis over 30 years

later. A cross-section of this calorimeter design is shown

Fig. 1.

To accommodate higher powers (up to 1000 W), West

then designed and built several larger calorimeters, designated as the K-series [6]. The absorbing

cavities for these calorimeters used cone-shaped

mirrors to spread the laser radiation over a large area of

the absorbing surface to reduce the irradiance and thus

Fig. 1. Cross-section of C-series isoperibol laser calorimeter.

179
prevent damage of the absorbing paint. At about this

same time (i.e., early 1970s), Douglas L. Franzen and

Leonard Schmidt, with West’s technical oversight and

advice, designed and built a type of isoperibol calorimeter called the Q-series [7] to measure pulsed laser

radiation. As with Jennings’ liquid cell calorimeter, the

Q-series devices use a volume absorbing technique to

distribute the absorbed energy throughout the absorbing

material. In particular, Franzen used neutral-density

absorbing glass having specific absorption coefficients

to absorb safely the pulsed laser radiation of Q-switched

Nd:YAG lasers. Then, in the mid-1970s, two large

(400 kg) calorimeters, called the BB-series [8,9], were

built by Richard Smith, George Chamberlain, and

Phillip Simpson to measure military lasers having

powers up to 100 kW (cw). Although these large,

massive calorimeters were inherently different from

the earlier, smaller calorimeters in many respects, their

outputs are, nevertheless, governed by the isoperibolcalorimeter equations developed in West and Churney’s

paper.

More recently, Rod Leonhardt, Chris Cromer, Marla

Dowell, T. R. Scott, and David Livigni have developed

specific models of isoperibol calorimeters for measuring the pulsed, ultraviolet radiation emitted by excimer

lasers [10,11]. The inherently high photon energies and

large peak powers of these lasers complicate accurate

measurement, which is one reason why no other

national laboratories have such capability at this

time. The NIST calorimeter cavities contain specially

selected glass which can absorb the radiation without

suffering damage or degradation while keeping fluorescence to a minimum. Again, analysis of the calorimeter

output uses the algorithms developed in West and

Churney’s papers. For special high-accuracy laserpower measurements at low power or energy levels,

many national metrology laboratories, including the

NIST Optoelectronics Division [12], now use cryogenic

radiometers to compare laser power to electrical power

with very low associated uncertainties (<0.01 %). At

cryogenic temperatures, the thermal properties (such as

specific heat capacity and thermal conductivity) of the

metal cavity change rapidly with temperature; consequently, the temperature response is not sufficiently

linear to apply West’s isoperibol calorimeter principles.

However, the essential structure of these devices in

many ways mirrors the basic construction of West’s

original C-series calorimeter (i.e., a cylindrical cavity

surrounded by a constant temperature environment and

having an electrical heater attached).

Today, 30 years later, West and Churney’s correctedrise equation and associated isoperibol-calorimeter

analysis described in this paper still permeate the field

of laser power and energy measurements. The array

of calorimeters described above, whose behaviors are

governed by the principles discussed in the paper,

are still in operation, many on a daily basis. In addition,

almost all standard calorimeters for mea-suring laser

power and most radiometers (even those that are not

isoperibol) are designed using the same basic structure

of West’s C-series, his first isoperibol calorimeter.

Prepared by Thomas R. Scott.

Bibliography

[1] E. D. West and K. L. Churney, Theory of Isoperibol Calorimetry

for Laser Power and Energy Measurements, J. Appl. Phys. 41,

2705-2712 (1970).

[2] D. A. Jennings, Calorimetric Measurement of Pulsed Laser

Output Energy, IEEE Trans. Instrum. Meas. IM-15, 161-164

(1966).

[3] E. D. West, Data Analysis for Isoperibol Laser Calorimetry,

NBS Technical Note 396, National Bureau of Standards,

Boulder, CO, February 1971.

[4] E. D. West, W. E. Case, A. L. Rasmussen, and L. B. Schmidt, A

Reference Calorimeter for Laser Energy Measurements, J. Res.

Natl. Bur. Stand. 76A, 13-26 (1972).

[5] E. D. West and W. E. Case, Current Status of NBS Low-Power

Laser Energy Measurement, in Conference on Precision Electromagnetic Measurements, Jul 1-5, 1974, London, England, IEEE

Trans. Instrum. Meas. IM-23, 422-425 (1974).

[6] E. D. West and L. B. Schmidt, A System for Calibrating Laser

Power Meters for the Range 5-1000 W, NBS Technical Note 685,

National Bureau of Standards, Boulder, CO, May 1977.

[7] D. L. Franzen and L. B. Schmidt, Absolute Reference Calorimeter for Measuring High Power Laser Pulses, Appl. Opt. 15,

3115-3122 (1976).

[8] Richard L. Smith, Thomas W. Russell, William E. Case, and

Alvin L. Rasmussen, A calorimeter for high-power CW lasers,

IEEE Trans. Instrum. Meas. IM-21, 434-438 (1972).

[9] George E. Chamberlain, Philip A. Simpson, and Richard L.

Smith, Improvements in a Calorimeter for High-Power CW

Lasers, IEEE Trans. Instrum. Meas. IM-27, 81-86 (1978).

[10] Rodney W. Leonhardt, Calibration Service for Laser Power and

Energy at 248 nm, NIST Technical Note 1394, National Institute

of Standards and Technology, Boulder, CO, January 1998.

[11] M. L. Dowell, C. L. Cromer, R. W. Leonhardt, and T. R. Scott,

Deep Ultraviolet (DUV) Laser Metrology for Semiconductor

Photolithography, in Characterization and Metrology for ULSI

Technology: 1998 International Conference, March, 1998,

American Institute of Physics, Woodbury, New York (1998)

pp. 539-541.

[12] D. J. Livigni, C. L. Cromer, T. R. Scott, B. C. Johnson, and

Z. M. Zhang, Thermal characterization of a cryogenic radiometer and comparison with a laser calorimeter, Metrologia 35,

819-827 (1998).

180
Influence of Water on Crack Growth in Glass

As early as the 1920s, the strength of glass and other

brittle materials was understood to be limited by the

presence of small cracks. Under stress, the small cracks

would grow into larger cracks until reaching a critical

size, at which point the material would fracture

catastrophically. It also was well known that humid

environments reduced the strength more severely than

did dry environments. Furthermore, a glass loaded at a

stress below its ultimate strength did not show infinite

life, but rather failed without warning after some finite

time. Understanding the nature of this “delayed failure”

had become a vital issue for industries that wanted, and

perhaps needed, to use glass as an engineering material.

This was the setting in which Sheldon Wiederhorn,

newly arrived at the Bureau after a short stint at DuPont,

began his research into the growth of cracks in glass.

In two papers, the first in 1967 [1] and the second in

1970 [2], Wiederhorn became the first to quantify crack

growth rates using fracture mechanics techniques that

were only just then emerging as a means of analyzing

crack phenomena. In doing so, he laid the foundation for

understanding the environmentally enhanced fracture of

all brittle materials.

Wiederhorn’s work was the culmination of a

sequence of advances that occurred over a period of

approximately 120 years. In the mid-1890s, Brodmann

[3] conducted experiments on the strength of glass and

found that specimens whose surfaces were etched in

HF solution were significantly stronger than specimens

tested without etching. That result provided the first

reported evidence that glass fails from surface defects.

The next major advance occurred in 1920 when Griffith

[4] established unequivocally that glass fails from

surface flaws and that the strength of glass is determined

by the density and severity of such flaws. More than two

decades passed before Orowan [5] clearly asserted that

the relevant surface energy of fracture should be a function of the environment in which it is measured. Gurney

[6] then showed that moisture enhanced fracture could

be explained in terms of thermodynamic concepts.

Stuart and Anderson [7] subsequently extended those

ideas to model delayed failure using chemical rate

theory. In that same time frame (although unknown to

Wiederhorn until after his 1967 paper), Irwin [8]

and Irwin and Kies [9] were advancing the analytical

concepts of fracture mechanics and their application

to brittle materials. These experimental and theoretical

advances formed a convergent timeline in Wiederhorn’s

papers of 1967 and 1970.

The critical feature in Wiederhorn’s work was

the direct observation of a growing crack. Prior to

Wiederhorn’s study, all research into delayed failure had

been conducted by measuring the times to failure and

only inferring the extension of microscopic cracks.

Although others had observed the subcritical growth of

macroscopic cracks, Wiederhorn was the first to

quantify their growth rates. He used a diamond stylus

to scratch the surface of a glass specimen and then

observed the growth of the crack through a microscope

while the specimen was being stressed. Using a double

cantilever beam specimen, he applied a constant load to

the ends of the slide and made crack velocity measurements using a traveling microscope and a filar eyepiece.

Wiederhorn’s study established several characteristics

of the effect of water vapor on crack motion in glass at

room temperature (see Fig. 1). Wiederhorn observed

that his results could be separated into three qualitatively

different regions indicating three distinct mechanisms

controlling crack growth: (I) a slow growth region in

which the crack velocity depended exponentially on the

load; (II) a plateau region in which crack growth was

limited by the diffusion rate of water to the crack tip;

and (III) a region in which crack growth was rapid and

Fig. 1. The effect of water vapor on crack motion in glass at room

temperature for relative humidity ranging from 0.017 % to 100 %.

181
independent of the amount of water in the environment.

The data of region I were in complete accord with the

static fatigue theory put forward previously by Charles

and Hillig [10] which indicated that water vapor

produced a corrosive attack on the glass at the crack tip.

Wiederhorn reasoned that this corrosive attack continued into region II, but the plateau occurred because the

crack extension could not proceed any faster than was

allowed by the diffusion rate of water to the crack tip.

In region III, the crack velocity was independent of

water vapor. Later, Wiederhorn et al. [11-13] showed

that the dielectric properties of the environment

controlled crack growth in region III.

The fracture mechanics formalism he adopted in

these two papers captured the dependence of the growth

rate on the size of the crack and the stress. Wiederhorn

also showed the crack growth rate depended on humidity in accord with an existing theory of delayed failure

in glass. These two contributions demonstrated that the

delayed failure did indeed result from the subcritical

growth of cracks, and put the prediction of glass lifetime

under load on a solid theoretical foundation.

This work influenced the scientific and engineering

community in two ways. First, it illustrated the power

of fracture mechanics as a tool for investigating the

fracture behavior of ceramics. Shortly after the publication of Ref. [1], a host of other groups launched fracture

mechanics studies of brittle failure of ceramics.

Second, engineers used the method of quantifying crack

growth to develop new techniques for assuring the

reliability of structural ceramics. Both of these themes

became important fields of research in ceramics. The

recognition of the importance of the environment at the

crack-tip to crack growth led to a series of studies

[11,12,13] of crack growth rate in electrolytes as a

function of zeta potential, ionicity, and pH. Of these,

only pH was critical in establishing the relationship

between crack velocity and stress intensity factor.

These studies showed that ion exchange between the

electrolyte and the glass at the crack tip determined the

crack tip pH and consequently the relationship between

crack velocity and stress intensity factor.

In those works and others, Sheldon M. Wiederhorn

has researched the mechanisms of fracture in glasses

and brittle ceramics for more than 35 years. He joined

the Physical Properties Section of the Inorganic Solids

Division at NBS in 1963. Recently, his work has led him

to investigate the creep and creep rupture of structural

ceramics. The Department of Commerce recognized his

accomplishments in awarding him both the Silver Medal

(1970) and the Gold Medal (1982), in addition to the

NBS Samuel Wesley Stratton Award (1977) for his work

in brittle fracture. The American Ceramic Society

(ACerS) independently recognized his work, awarding

him the Ross Coffin Purdy Award (1971), the Morey

Award (1977), and the John Jeppson Award (1994).

ACerS further elected him a Fellow (1970) and named

him a Distinguished Life Member (1999). In 1985,

he was chosen by ACerS to present the distinguished

Sosman Lecture, on the subject of subcritical crack

growth in glass, at the Annual Meeting of the American

Ceramic Society. In 1991 he was elected a member

of the National Academy of Engineering. He has held

various positions of administrative responsibility at

NIST (Section Chief, Division Chief, and Group

Leader), and is now a Senior NIST Fellow in the

Materials Science and Engineering Laboratory.

Prepared by Edwin Fuller, William Luecke, and Stephen

Freiman.

Fig. 2. Sheldon Wiederhorn, 1964.

182
Bibliography

[1] S. M. Wiederhorn, Influence of Water Vapor on Crack Propagation in Soda-Lime Glass, J. Am. Ceram. Soc. 50, 407-414

(1967).

[2] S. M. Wiederhorn and L. H. Bolz, Stress Corrosion and Static

Fatigue of Glass, J. Am. Ceram. Soc. 53, 543-548 (1970).

[3] C. Brodmann, Einige Beobachtungen u ̈ber die Festigkeit von

Glassta ̈ben, Vorgelegt von W. Voigt in der Sitzung 3, 1894.

[4] A. A. Griffith, The Phenomena of Rupture and Flow in Solids,

Philos. Trans. R. Soc. London, Ser. A 221, 163-198 (1920).

[5] E. Orowan, The Fatigue of Glass Under Stress, Nature 154,

341-343 (1944).

[6] C. Gurney, Delayed Fracture in Glass, Proc. Phys. Soc., London

59, 169-185 (1947).

[7] Derald A. Stuart and Orson L. Anderson, Dependence of

Ultimate Strength of Glass Under Constant Load on Temperature, Ambient Atmosphere, and Time, J. Am. Ceram. Soc. 36,

416-424 (1953).

[8] George Irwin, Fracture Dynamics, in Fracturing of

Metals, American Society for Metals, Cleveland, Ohio (1948)

pp. 147-166.

[9] G. R. Irwin and J. A. Kies, Critical Energy Rate Analysis of

Fracture Strength, Weld. J. 33, Welding Research Supplement,

193-s–198-s (1954).

[10] R. J. Charles and W. B. Hillig, in Symposium on Mechanical

Strength of Glass and Ways of Improving It, Florence, Italy,

September 25-29, 1961, Union Scientifique Continentale du

Verre, Charleroi, Belgium (1962) pp. 511-527.

[11] S. M. Wiederhorn and H. Johnson, Effect of Electrolyte pH on

Crack Propagation in Glass, J. Am. Ceram. Soc. 56, 192-197

(1973).

[12] S. M. Wiederhorn and H. Johnson, Influence of SodiumHydrogen Ion Exchange on Crack Propagation in Soda-Lime

Silicate Glass, J. Am. Ceram. Soc. 56, 108-109 (1973).

[13] S. M. Wiederhorn, S. W. Freiman, E. R. Fuller, Jr., and C. J.

Simmons, Effects of Water and Other Dielectrics on Crack

Growth, J. Mater. Sci. 17, 3460-3478 (1982).

183
Phase Equilibria Diagrams

When the American Ceramic Society celebrated its

own centennial review in 1998 [1], the NIST/ACerS

publication of phase diagrams was cited as one of the

two most important accomplishments of the Society

affecting the worldwide development and application of

ceramics. Working together, NIST and ACerS have

published more than 20 000 phase diagrams. (Fig. 1)

Phase diagrams are graphical representations of the

regions of distinct chemical and structural behavior of

materials in thermodynamic equilibrium. The regions

are defined by the composition of the material and

by the measurement conditions. Most importantly for

ceramics industries, the diagrams are constructed as a

function of composition and temperature. The properties of a material, and thus its functionality, often

depend critically on what region is used in the preparation of the material. Often, the processing conditions

must be maintained in very narrow regions of temperature and composition in order to achieve a material with

a desired property. Phase diagram data were essential,

for example, in the development of a durable material

now used worldwide in more than 500 million catalytic

converters to control emissions from cars and trucks.

Thus phase diagrams are not only vital to understanding

the behavior of ceramics and metal alloys; they are also

essential for manufacturing the materials reproducibly,

effectively, and economically.

The NIST/ACerS collaboration on phase diagrams

can be traced back to the year 1933 when F. P. Hall

(Pass and Seymour, Inc., Syracuse, New York) and

Herbert Insley (NBS) published a compilation of 178

diagrams in the Journal of the American Ceramic

Society [2]. These authors published a supplement to

this collection in 1938 [3] and then revised and extended

the entire compilation in 1947 [4], at which time

the collection contained 507 diagrams. A further supplement was compiled and published by Howard

McMurdie (NBS) and Hall in 1949 [5]. By 1964, the

need and growing demand for reliable phase equilibria

diagrams was abundantly clear, and the collaboration

between NIST and ACerS began in earnest with the

founding of Phase Diagrams for Ceramists as a separate

publication series [6]. The first volume, published without a volume number, was prepared by Ernest M. Levin,

Carl R. Robbins, and Howard McMurdie as a revision

and expansion of the previous compilations. The 1964

edition contained 2066 diagrams. Since that time, the

series has expanded to twelve regular volumes, three

volume supplements, and three special monographs.

In the process of this expansion, the series acquired a

much broader scope than was originally anticipated. To

reflect that broader scope more accurately, the name of

the series was changed to Phase Equilibria Diagrams.

Also, in keeping with advancing technology, a computerized version of the collection was developed for use on

personal computers. Today, the compilations encompass

systems containing oxides; salts; semiconductor

elements; borides, carbides, and nitrides for structural

ceramics; high-temperature superconductors; and

systems containing a mix of these compounds. More

than 45000 copies of individual volumes have been

sold to ceramic industries, research laboratories, and

academic libraries.

The sustained success of the series beyond the initial

volumes has been due in part to the contributions of

numerous distinguished individuals who have served in

various editorial capacities. An acknowledgment of the

General Editors for the published volumes is given in

Fig. 1. Diagram 9529 from Volume XI. The phase diagram for the

BaO-TiO2-Nb2O5 system determined at NBS by R. S. Roth and his

colleagues has provided key data for understanding and processing

barium titanate dielectric ceramics important for wireless communications technology.

184
the table. In addition to the General Editors, the production of a single volume also involves associate editors,

managing editors, text editors, and editorial assistants.

Among the outstanding efforts of the individuals who

have served in these capacities are the exceptional

contributions of McMurdie (since the inception of

the series) and Robert S. Roth (for both editorial and

experimental work since Vol. IV). Helen M. Ondik

(since Vol. VI) has been especially noted for her

meticulous attention to details. She was awarded the

Department of Commerce Silver Medal in 1971 and was

appointed to a Department of Commerce Science

and Technology Fellowship for 1976–1977. Mary A.

Clevinger (since Vol. IV) has been a mainstay in numerous aspects of the project, including editing, coordination, and layout. The project is now under the general

management of Terrell A. Vanderah, under whose

leadership the project staff is undertaking a complete

modernization to a computerized desktop publishing

system and an internet-ready electronic database.

No list of individuals who have made outstanding

contributions to this work is complete without naming

Peter K. Schenck and Carla G. Messina. These two

individuals were responsible for creating the computercontrolled operations that produced Volume VI and all

the succeeding volumes. Peter Schenk’s programs

for digitizing and plotting phase diagrams (both onscreen and for hard copy) have been compared to other

Table

Vol. General Editors

VIII

I E. M. Levin, C. R. Robins, and H. F. McMurdie

II E. M. Levin, C. R. Robins, and H. F. McMurdie

III E. M. Levin and H. F. McMurdie

IV R. S. Roth, T. Negas, and L. P. Cook

V R. S. Roth, T. Negas, and L. P. Cook

VI R. S. Roth, J. R. Dennis, and H. F. McMurdie

VII L. P. Cook and H. F. McMurdie

VIII B. O. Mysen (Geophysical Laboratory)

IX G. B. Stringfellow (U. Utah)

X A. E. McHale (Consultant)

XI R. S. Roth

XII A. E. McHale and R. S. Roth

A91* A. E. McHale

A92* A. E. McHale

A93* A. E. McHale

M1 J. D. Whitler and R. S. Roth

M2 T. A. Vanderah, R. S. Roth, and H. F. McMurdie

M3 H. M. Ondik and H. F. McMurdie

* A: Annual Supplements

 M: Monographs of Special Topics

1: Phase Diagrams for High Tc Superconductors

2: Superconductors II

3: Phase Diagrams for Zirconium and Zirconia Systems

graphics programs by outside graphics experts and have

been found to be unequaled. For his outstanding work,

he received the Department of Commerce Bronze

Medal in 1981.

Howard McMurdie has been involved with the series

since its inception. McMurdie began his long association with NIST/NBS when he accepted a position in the

Lime and Gypsum Section of the Clay and Mineral

Products Division of NBS in April 1928. During the

early years in this position, he took a course, taught by

Herbert Insley, on the use of the petrographic microscope. That contact proved important later when Insley

established the Petrographic Laboratory in the Glass

Section of NBS in 1935 and selected McMurdie as his

assistant. Insley left NBS about 1944 to take a position

at the Pennsylvania State University, but their paths were

to cross again about 1947 when Insley returned to NBS

as director of the Ceramic Division. Insley selected

McMurdie as Chief of the Constitution and Microstructure Section, which later became the Crystallographic

Section. McMurdie pursued the study of phase diagrams

Fig. 2. Howard McMurdie, 1961.

185
in that position up to his official retirement in 1966, at

which time he became a research associate at NBS; he

has been associated with the phase diagram program

continuously since that time, a career spanning more

than 70 years!

Robert Roth received his Ph.D. in geology from the

University of Illinois in 1951, whereupon he joined the

staff at NBS. From the beginning, his work has been

dedicated to the discovery of new materials, revealing

the existence of phase relations and investigating the

structural nature of ceramic compounds. His second

publication, of approximately 200 over his career, was

entitled “Piezoelectric Properties of Lead ZirconateLead Titanate Solid Solution Ceramics.” That material,

now commonly known as PZT, is one of the most

important advanced electronic ceramic materials known

to this day, with applications as diverse as providing the

spark in charcoal grills and gas stoves to positioning

mirrors in giant telescopes. His particular interest in the

phase equilibria relations of the oxides of titanium,

niobium, and tantalum has resulted in his outstanding

contributions to the field of dielectric ceramics. His

work in the 1970s on the exploration of the barium

titanate systems, and his phase diagrams of those

systems, played a critical role in their subsequent

commercialization in cellular base stations. He also

played a large role in the development of barium

neodymium titanate and zirconium tin titanate. All of

these ceramics are still the materials of choice as lowloss dielectric resonators at microwave frequencies. In

recent years, his effort to elaborate the complex phase

diagrams of ceramic copper oxide superconductors is

credited with providing the standards upon which many

research groups base their processing of the important

superconducting material Ba2YCu3O7. For his exceptional research activities and his tireless efforts as senior

editor of numerous volumes of Phase Diagrams for

Ceramists and Phase Equilibria Diagrams, he has

received numerous awards, including the Department of

Commerce Silver Medal, NBS Special Service Award

for Meritorious Publication, the Department of

Commerce Gold Medal, the Sosman Memorial Lecturer

Award (American Ceramic Society), and the John

Jeppson Award (American Ceramic Society). He has

been elected Fellow of the Mineralogical Society of

America, the Geological Society of America, and

the American Ceramic Society. He retired from NIST

in 1991.

Outside support for the phase equilibria program has

been strong, with respect to both technical contributions

to the work and the financial commitment necessary to

maintain the program. Indeed, the American Ceramic

Society made an appeal to its industrial members to

contribute to a fund, which ACerS administers yet today,

specifically to support the program. Industry and

individuals responded with contributions that have

amounted to nearly 2.5 million dollars [1]. Those funds

are used to support ACerS staff who work at the NIST

Gaithersburg facility directly in collaboration with

NIST staff.

An independent assessment of the NIST/ACerS phase

equilibria program was conducted by TASC, Inc. in

1997 [7]. Their assessment concluded that without the

dedicated NIST/ACerS program, the ceramics industry

would incur substantial costs for internal research and

experimentation and would experience significant delays

in introducing innovative ceramic materials to their

markets. In their conservative estimate, TASC, Inc.

found that the NIST/ACerS program has a remarkable

benefit-to-cost ratio of approximately 10 to 1.

Fig. 3. Robert Roth, 1961.

186
Today, the phase diagrams published by the NIST/

ACerS program are proving to be vital to the development of emerging technologies. For example, carefully

determined phase stability regions are essential for

improving the manufacture of bulk superconductingwires and tapes. Advanced ceramics with high dielectric

constant, low dielectric loss, and reliable temperature

stability are needed to improve the performance and to

lower the cost of the components of cellular communications circuits. To meet these needs and others, current

work includes studies of materials used in a variety of

areas such as high temperature superconductors, wireless communications, electronic packaging, fuel cells,

and sensors.

Prepared by Ronald Munro, Howard McMurdie, Helen

Ondik, and Terrell Vanderah.

Bibliography

[1] Robert Butler, Samantha Adams, and Meghan Humphreys, The

American Ceramic Society: 100 Years, The American Ceramic

Society, Columbus, Ohio (1998), pp. 3, 119-120.

[2] F. P. Hall and Herbert Insley, A Compilation of Phase-Rule Diagrams of Interest to the Ceramist and Silicate Technologist, J. Am.

Ceram. Soc. 16, 455-567 (1933).

[3] F. P. Hall and Herbert Insley, Supplement to “A Compilation of

Phase-Rule Diagrams of Interest to the Ceramist and Silicate

Technologist,” J. Am. Ceram. Soc. 21, 113-164 (1938).

[4] F. P. Hall and Herbert Insley, Phase Diagrams for Ceramists, J.

Am. Ceram. Soc. 30, Part II, 1-152 (1947).

[5] Howard F. McMurdie and F. P. Hall, Phase Diagrams for

Ceramists: Supplement No. 1, J. Am. Ceram. Soc. 32, Part II,

154-164 (1949).

[6] Ernest M. Levin, Carl R. Robbins, and Howard F. McMurdie,

Phase Diagrams for Ceramists, The American Ceramic Society,

Columbus, Ohio (1964).

[7] Michael L. Marx, Albert N. Link, and John T. Scott, Economic

Assessment of the NIST Ceramic Phase Diagram Program, Planning Report 98-3, TASC, Inc., Arlington, Virginia (1998).

187
Determination of Reduced Cells in

Crystallography

In theory, physical crystals can be represented by

idealized mathematical lattices. Under appropriate

conditions, these representations can be used for a

variety of purposes, such as identifying, classifying, and

understanding the physical properties of materials.

Critical to these applications is the ability to construct a

unique representation of the lattice. The vital link

that enabled this theory to be realized in practice was

provided by the 1970 paper of A. Santoro and A. D.

Mighell, Determination of Reduced Cells [1]. This

seminal paper led to a mathematical approach to lattice

analysis initially based on a systematic reduction procedure and the use of standard cells. Subsequently, the

process evolved to a matrix approach based on group

theory and linear algebra, which offered a more abstract

and powerful way to look at lattices and their properties.

In the early 1960s, the Crystal Data Center at NBS

started to build a database with chemical and crystallographic information on all classes of materials, including inorganics, organics, minerals, and metals. An

immediate challenge was to organize the information in

a systematic manner so that database users could readily

determine material relationships. For example, one

might wish to identify an unknown material by comparing its structure with structures already in the database.

But this is not as simple as it might seem. The following

anecdote illustrates the nature of the problem.

On an archaeological expedition, two colleagues were

analyzing patterned designs on the walls of ancient

buildings. They noted that by simply translating a small

piece, or unit, of the design, one could create the entire

pattern. Each researcher independently searched the

archaeological site, selected a favorite design, and drew

a repeat unit (a unit cell) on a notepad to take home.

Later in their hotel, the colleagues carefully compared

their repeat units. Finding them to be quite different

in appearance, they concluded that their repeat units

defined different wall patterns. Upon returning home,

they used the repeat units to recreate the wall patterns

on their computers. To their surprise, the two wall

designs were identical.

What happened? Why were they tricked into thinking

that they had two patterns when in reality their unit cells

described only one? The answer is illustrated by the

simple example of a 2-dimensional lattice in Fig. 1.

Since there are no terminal edges in the idealized

lattice, the entire array of dots can be generated by

translating the small rhombus of dots labeled A, B, C,

D. Here, translating means moving the unit cell right,

left, up, and down, where “right and left” are defined as

movements parallel to the direction AD, while “up and

down” are defined by the direction AB. However, notice

that the skewed parallelogram labeled E,F,G,H can be

translated to generate exactly the same array of dots. In

this case, “right and left” are defined as movements

parallel to the direction EH, while “up and down” are

defined by direction EF. At first glance, these two unit

cells neither look the same nor translate in the same way,

yet the readily apparent differences between a rhombus

and a skewed parallelogram cannot be observed in the

infinite lattices that they generate.

Exactly the same problem exists in describing the

idealized lattice of a physical crystal. In this case,

instead of a 2-dimensional planar wall pattern designed

by man, we have a 3-dimensional crystal (e.g., a mineral

such as an emerald, a ruby, or a diamond) designed by

nature. Like the wall pattern which can be created by

translating a 2-dimensional unit cell (a parallelogram), a

crystal lattice can be created using a 3-dimensional

building block (a parallelepiped), as illustrated in Fig 2.

Fig. 1. An infinite variety of unit cells, vastly different in appearance

and specification, can generate the same mathematical lattice.

188
This figure shows the case of a crystal with rhombohedral unit cell (parameters a = 10.0 Å, = 55.0), and

the equally correct alternative hexagonal cell (with

a = 9.235 Å and c = 25.38 Å. Either cell when translated will generate the same crystal lattice.

More generally, the parallelepiped of the unit cell may

be defined abstractly by three noncoplanar vectors

a, b, c . However, to achieve the full utility of theory and

practice, everyone must end up with the same a, b, c

even though alternative parallelepipeds might be constructed with equal validity. The problem is that the

equivalence of alternative parallelepipeds is not so

readily established that computerized search routines

could easily recognize two alternatives as being equivalent. Because there are infinite varieties of alternative

cells, Santoro and Mighell chose to pursue the development of a procedure that would arrive at a unique

representation.

The first step toward a unique representation was to

recognize that any lattice could be defined on the basis

of a cell with the smallest possible volume (known as a

primitive cell). But for a given lattice, which of the

many possible primitive cells should be selected?

Some four decades earlier, Niggli [2] had considered

this aspect of cell definition and had defined what was

termed a reduced cell which turned out to be a unique

cell. What remained to be established was the mathematical theory and associated algorithms for calculating

the reduced cell starting from any cell of the lattice. It

was this practical realization of reduced cells that was

achieved in the 1970 paper of Santoro and Mighell.

For a cell to be reduced, two sets of conditions,

termed the main and special conditions for reduction,

must be satisfied. The main conditions ensure that one

has selected a cell based on the three shortest vectors of

the lattice. The special conditions ensure that one has

determined a unique cell for those cases in which the

lattice has more than one cell with the same shortest

three vectors. Based on the theory in the 1970 paper,

algorithms were designed and software written that

could be applied universally to any cell ever published or

determined in the laboratory.

Application of the reduced cell to both the database

work and the laboratory research at NIST was immediately successful. For example, reduction played a central

role in the determination of the crystal structure of

benzene II, a high-pressure polymorph of benzene that

requires a pressure of about 1.2 GPa to stabilize. Using

the NIST high-pressure diamond anvil cell (DAC),

which is described elsewhere in this volume, benzene II

became the first crystal structure determined in situ by

high-pressure single crystal x-ray diffraction techniques

[3]. Because of its narrow aperture, the diffraction data

from the DAC were highly restricted. There was,

however, a sufficient amount of data to determine

the reduced cell for the specimen and to establish

unambiguously that the crystal system was monoclinic.

Other techniques, which required more extensive data,

would have failed in this task.

In routine structure determination work, reduction

became a practical tool for analyzing difficult cases in

which traditional visual methods often failed. This was

especially true for a rhombohedral crystal, where it is

hard to find the right orientation to see the 3-fold

symmetry. As a result, the structure determination

for such a crystal was difficult and often incorrect. So

extreme was the frustration level that it was said, in jest,

that the best thing that could happen would be for the

crystal to fall off the instrument and disappear in a crack

in the floor. Reduction procedures, however, instantly

resolved the difficulty, and the resulting highly characteristic reduced cell and form [4] immediately led the

experimentalists to the correct answer.

Additional successes derived directly from the

uniqueness property of the reduced cell, because it leads

directly to a general method for materials characterization. By classifying all materials using the reduced cell,

one obtains the basis for a powerful method for

compound identification [5,7]. In this scheme, a unit

cell of an unknown is transformed to the reduced cell,

which is then matched against the file of known

materials represented by their respective reduced cells.

Fig. 2. The rhombohedral unit cell (with axes OA,OB,OC) and the

larger hexagonal cell (with axes OE,OF,OG) define the same threedimensional mathematical lattice.

189
Combining the reduced cell match with an element type

match further enhances the selectivity. In practice, cell

matching has proved an extremely practical and reliable

technique to identify materials. Today this identification

strategy is widely used, as it has been integrated into

commercial x-ray diffractometers [8].

Due somewhat to serendipity, the most significant

and lasting value of this work is probably not reduction

itself. Rather, reduction has played a key transition role

in helping to move the rather conservative discipline of

crystallography in new directions with new insights.

The research on reduction proved that there are excellent reasons for looking at the crystal lattice from an

entirely different point of view. Consequently, with

time, many other lattice-related papers followed,

including papers on sublattices and superlattices,

composite lattices, and coincidence site lattices. At

NIST, the mathematical analysis of lattices was pursued

further and evolved to a matrix approach that offered a

more abstract and powerful way to look at lattices and

their properties.

The matrix approach, in particular, has many applications, including for example, symmetry determination

[6,7]. In sharp contrast to other methods that focus on

the consequences of symmetry (such as dot products,

d -spacings, etc.), the matrix approach deals with

symmetry in its most abstract form, represented as

matrices. The basis of the matrix approach is to generate

the matrices that transform the lattice into itself. The

resulting set of matrices comprise a mathematical group

obeying the formal relations of group theory. These

matrices may be used both theoretically and practically

to analyze symmetry from any cell of the lattice. In this

formulation, the mathematics and algorithms used to

analyze symmetry become extremely simple since they

are based on manipulating integers and simple rational

numbers using elementary linear algebra. The matrix

approach, therefore, provides both the conceptual and

practical framework required in performing the experimental procedures in a logical and general manner.

The ability to determine a unique reduced cell and the

subsequent achievements in lattice analysis, especially

the matrix approach, have been critical milestones in

crystallography. They established an important mathematical rigor in crystallography and in the materials

sciences and have stimulated many practical applications.

Antonio Santoro is a current member of the NIST

Center for Neutron Research. His primary interests are

the determination of crystal structures from neutron

powder diffraction data and the application of the bond

valence method to structural distortions.

Alan Mighell retired from NIST in 1998, after

leading the Crystal Data Center for many years.

Currently, he is a guest research scientist in the Materials

Science and Engineering Laboratory at NIST. His principal research interests include the design and development of procedures for materials identification and for

establishing lattice relationships.

Prepared by Alan D. Mighell, Vicky Lynn Karen, and

Ronald Munro.

Bibliography

[1] A. Santoro and A. D. Mighell, Determination of Reduced Cells,

Acta Crystallogr. A26, 124-127 (1970).

[2] P. Niggli, Krystallographische und Strukturtheoretische Grundbegriffe, Handbuch der Experimentalphysik, Vol.7, part 1,

Akademische Verlagsgesellschaft, Leipzig (1928).

[3] G. J. Piermarini, A. D. Mighell, C. E. Weir, and S. Block, Crystal

Structure of Benzene II at 25 Kilobars, Science 165, 1250-1255

(1969).

[4] A. D. Mighell, A. Santoro, and J. D. H. Donnay, Reduced-cells

section, International Tables for X-ray Crystallography, Vol. 1,

530-535 (1952).

[5] A. D. Mighell, The Reduced Cell: Its Use in the Identification of

Crystalline Materials, J. Appl. Crystallogr. 9, 491-498 (1976).

[6] Vicky L. Himes and Alan D. Mighell, A Matrix Approach to

Symmetry, Acta Crystallogr. A43, 375-384 (1987).

[7] Vicky L. Karen and Alan D. Mighell, Apparatus and Methods for

Identifying and Comparing Lattice Structures and Determining

Lattice Structure Symmetries, U.S. Patents 5,168,457 and

5,235,523 (1992, 1993).

[8] Susan K. Byram, Charles F. Campana, James Fait, and Robert A.

Sparks, Using NIST Crystal Data Within Siemens Software for

Four-Circle and SMART CCD Diffractometers, J. Res. Natl. Inst.

Stand. Technol. 101, 295-300 (1996).

190
Speed of Light From Direct Frequency and

Wavelength Measurements

The National Bureau of Standards has had a long

history of interest in the speed of light, and no doubt this

interest contributed to the measurement described here

[1]. As early as 1907, Rosa and Dorsey [2] determined

the speed of light from the ratio of the capacitance of a

condenser as measured in electrostatic and electromagnetic units. Over the ensuing years NBS developed

still other methods to improve upon the accuracy of this

important physical constant.

By the late 1960s, lasers stabilized in frequency

to atomic and molecular resonances were becoming

reliable research tools. These could be viewed as providing stable reference for either optical frequency or wavelength. This duality of frequency and length produced

the obvious suggestion that a simultaneous measurement of frequency and length for the same laser transition would yield a very good measurement of the

speed of light. In fact, a 1958 measurement of the

speed of light by Froome [3] was done by determining

the frequency and wavelength of a microwave source

at 72 GHz. The frequency measurement was fairly

straightforward, since frequency in the microwave and

lower ranges can be readily measured with great

accuracy. The speed-of-light measurement was limited

primarily by the difficulty in measuring the very

long wavelength (about 0.4 cm) of the 72 GHz radiation.

Clearly, a better measurement would result if higher

frequencies could be employed, where wavelengths

could be more accurately measured. The measurement

technology of that era was not up to the task. The wavelength of visible radiation could be measured fairly well,

but no accurate methods for measuring visible frequencies were available. Whereas frequency could be

measured quite well in the microwave to millimeter-wave region, wavelength measurements were

problematic.

The measurement of the speed of light by the Boulder

group involved the development of a new method. The

approach taken was to synthesize signals at progressively higher and higher frequency using harmonicgeneration-and-mixing (heterodyne) methods and to

lock the frequency of a nearby oscillator or laser to the

frequency of this synthesized signal [4]. Photodiodes,

as well as metal-insulator-metal diodes, fabricated by

adjusting a finely tipped tungsten wire against a

naturally oxidized nickel plate, were used for harmonic

generation and mixing. With this approach, a frequencysynthesis chain was constructed linking the microwave

output of the cesium frequency standard to the optical

region, so that the group could directly measure the

frequency of a helium-neon laser stabilized against the

3.39 m transition of methane. When the measurements

were completed, the uncertainty limitation was found to

be the asymmetry of the krypton line on which the

definition of the meter was then based. The experiment

thus showed that the realization of the meter could be

substantially improved through redefinition.

This careful measurement resulted in a reduction of

the uncertainty of the speed of light by a factor of nearly

100. The methods developed at NIST were replicated in

a number of other laboratories, and the experiments

were repeated and improved to the point where it was

generally agreed that this technology could form the

basis for a new definition of the meter. An important

remaining task was the accurate measurement of stillhigher (visible) frequencies which could then serve as

more practical realizations of the proposed new definition. The Boulder group again took the lead and

provided the first direct measurement of the frequency

of the 633 nm line of the iodine-stabilized helium-neon

laser [4], as well as a measurement of the frequency of

the 576 nm line in iodine [5]. These measurements, and

similar measurements made at other laboratories around

the world, were the last ingredients needed to take up the

redefinition of the meter.

The new definition of the meter, accepted by the 17th

Confe ́rence Ge ́ne ́rale des Poids et Mesures in 1983, was

quite simple and elegant: “The metre is the length of the

path traveled by light in vacuum during a time interval

of 1/299 792 458 of a second.” A consequence of this

definition is that the speed of light is now a defined

constant, not to be measured again. NBS had played

a key role in pioneering measurement methods that

resulted in this redefinition and in the optical frequency

measurements that contributed to practical realizations

of the definition. In subsequent years, measurement of

other stabilized-laser systems added to the ways in

which the meter could be realized. This way of defining

the meter has proven to be particularly robust, since

unlike a definition based on a standard such as the

krypton lamp, length measurement can be continuously

improved without resorting to a new definition.

191
The measurement methods developed at NBS during

this period also led to the development of high-resolution spectroscopic methods utilizing tunable frequency

sources in the optical region [7,8]. These techniques

produce results with at least 100 times smaller uncertainty than traditional spectroscopy involving wavelength measurement. The lower uncertainty has had

impact in areas, such as radio astronomy and investigations of the upper atmosphere, where better determinations of spectral lines have facilitated studies of important molecules in space and in the stratosphere. Another

notable result was the use of the methods to generate

extensive tables of accurately measured spectral lines

across the infrared spectrum [9]. These tables have contributed significantly to the reliability of laboratory

spectroscopic measurements throughout this spectral

region.

It is worth noting that management terminated the

NBS work on frequency-synthesis chains shortly after

completion of the work that led to the meter redefinition. Staff involved in this effort then redirected their

efforts toward other programs. Ken Evenson, Russ

Petersen, and Joe Wells initiated new work on highresolution frequency-based spectroscopy using the

mixing methods developed for the frequency-synthesis

chain, while Bruce Danielson and Gordon Day eventually became involved in optical-fiber metrology and in

other optical communication measurements. John Hall

went on to develop high-performance laser systems

within the Quantum Physics Division, a joint NISTJILA enterprise, and Dick Barger left NBS to work at

the University of Colorado. Russ Petersen died suddenly

in 1983, just two months after the redefinition of the

meter was made official, and Dick Barger died in 1998.

Ken Evenson, Bruce Danielson, and Joe Wells have

since retired from NIST.

Prepared by Donald B. Sullivan.

Fig. 1. Winners of the Gold Medal from the Department of Commerce for their measurement of the speed-of-light. Shown left to right in front

are Ken Evenson (project leader), Bruce Danielson and Gordon Day and in back left to right are Dick Barger, John Hall, Russ Petersen, and

Joe Wells.

192
Bibliography

[1] K. M. Evenson, J. S. Wells, F. R. Petersen, B. L. Danielson, G. W.

Day, R. L. Barger, and J. L. Hall, Speed of Light from Direct

Frequency and Wavelength Measurements of the Methane-Stabilized Laser, Phys. Rev. Lett. 29, 1346-1349 (1972).

[2] E. B. Rosa and N. E. Dorsey, A new determination of the ratio of

the electromagnetic to the electrostatic unit of electricity, Bull.

Bur. Stand. 3, 433-604 (1907); A comparison of the various

methods of determining the ratio of the electromagnetic to the

electrostatic unit of electricity, Bull. Bur. Stand. 3, 605-622

(1907).

[3] K. D. Froome, A new determination of the free-space velocity of

electromagnetic waves, Proc. R. Soc. London, Ser. A 247, 109-122

(1958).

[4] D. A. Jennings, C. R. Pollock, F. R. Petersen, R. E. Drullinger, K.

M. Evenson, and J. S. Wells, Direct frequency measurement of

the I2-stabilized He-Ne 473-THz (633-nm) laser, Opt. Lett. 8,

136-138 (1983).

[5] C. R. Pollock, D. A. Jennings, F. R. Petersen, J. S. Wells,

R. E. Drullinger, E. C. Beaty, and K. M. Evenson, Direct

frequency measurements of transitions at 520 THz (576 nm) in

iodine and 260 THz (1.15 m) in neon, Opt. Lett. 8, 133-135

(1983).

[6] Documents concerning the new definition of the metre, Metrologia 19, 163-178 (1984).

[7] K. M. Evenson, D. A. Jennings, and F. R. Petersen, Tunable

far-infrared spectroscopy, Appl. Phys. Lett. 44, 576-578 (1984).

[8] M. Inguscio, L. R. Zink, K. M. Evenson, and D. A. Jennings,

Sub-Doppler tunable far-infrared spectroscopy, Opt. Lett. 12,

867-869 (1987).

[9] Arthur G. Maki and Joseph S. Wells, Wavenumber Calibration

Tables From Heterodyne Frequency Measurements, NIST Special

Publication 821, National Institute of Standards and Technology,

Gaithersburg, MD (1991).

193
Connecting Visible Wavelength Standards

With X Rays and Rays

The 1996 centenary of W. K. Ro ̈ntgen’s discovery of

x rays celebrated the penetrating visions offered by

these “strange rays.” Aside from their ubiquitous application to imaging the interior structure of visually

opaque systems, x rays continue to have important applications in elucidating the geometrical and electronic

structure of matter. In addition to the synchrotron radiation facilities, conventional x-ray sources available in

modest laboratory environments have wavelengths well

suited to reveal the arrangements of atoms in crystalline

solids and biological molecules. In addition, spectroscopy of absorbed and emitted x rays reveals the

electronic structure of atoms, molecules and materials.

In a similar way, nuclear -rays reflect the energy level

structure of nuclei in a wavelength range that extends

as far beneath the scale of x-ray wavelengths as x-ray

wavelengths lie below visible wavelengths.

X-ray diffraction, first reported in 1912, connects

x-ray wavelengths with the dimensions of crystal

lattices, but fails to connect either of these scales with

the dimensions of macroscopic objects. From the early

1930’s to the early 1970s, x-ray spectroscopy was an

important contributor to the determination of fundamental constants such as NA, h/e, and hc/e. These

measurements were, however, limited by uncertainty in

the connection between the x-ray scale and visible reference wavelengths. Up to the mid-seventies, the only well

established direct connection was by means of ruled

grating diffraction of long wavelength x-ray lines, a

procedure that even in its late development was not

sufficiently accurate. The paper X-ray to Visible Wavelength Ratios [1] represents the first results of a more

direct and robust connection between these disparate

spectral domains.

Because relative measurements of x-ray wavelengths

were more accurate than those linking x-ray wavelengths to macroscopic standards, early workers in the

x-ray region introduced local reference standards that

approximated sub-multiples of optical units, but were

more sharply defined. The local unit in the x-ray region

was called the xu, a unit that was intended to approximate 0.001 Å (0.1 pm). Although originally defined by

assigning a conventional value to the lattice spacing of

rock salt, and later that of calcite, the x-unit was more

often specified by assigning particular values (in xu) to

the wavelength of one of the widely used reference lines

in the x-ray region.

It was not until around 1930 that the 1926 demonstration of x-ray diffraction by a ruled optical grating

achieved a refinement capable of providing a useful

conversion factor between x-ray and optical units.

Results from this work were at variance with the local

x-ray unit calculated by making use of the electron’s

charge determined by Millikan’s oil drop experiment.

The disagreement (>0.2 %) remained controversial for

over a decade. In the end, it was shown that the oil drop

measurement of e contained an error arising from the

viscosity of air.

Realization of the first x-ray interferometer by Bonse

and Hart in 1965[2] opened another route to x-ray

wavelengths, and subsequently to the -ray region. The

path to a significant measurement began with Hart’s

“Ångstro ̈m ruler” [3], an articulated silicon monolith

able to scan over an extended, though limited, range.

Subsequently, Bonse and TeKaat demonstrated the

quasi-static re-assembly of separated components while

retaining favorable intensity contrast [4]. The first

combined x-ray and optical interferometer was realized

at the NBS [5].

The subject paper [1] reported combined X-Ray and

Optical Interferometry (XROI) of the lattice period of a

silicon crystal, followed by accurate spectrometry to

determine the two most commonly used x-ray reference

wavelengths, Cu K1 and Mo K1. This measurement

plan connected manifestly invariant quantities. The

crystal spacing was determined with respect to the

optical reference in the XROI measurement and then

used, through absolute angle measurement, to link the

optical “standard” to x-ray transition wavelengths.

Although it has been proposed that the lattice period of

silicon (at specific temperature, pressure and purity)

should be treated as a “constant of nature” [6], we

restrict such usage to transitions between atomic energy

levels (x rays), or between nuclear energy levels (rays).

The subject paper describes both parts of the

measurement (for x rays) with an emphasis on the XROI

component owing to its perceived difficulty and novelty.

The original cartoon illustration shown in Fig. 1 has

been widely reproduced in textbooks and elsewhere,

possibly on account of its deceptive simplicity. The

stationary and moving platforms were supported by a

flexure stage. In actual data taking, the mechanical stage

was “locked” to an optical interference maximum by

means of a piezoelectric actuator situated in the drive.

194
The possibility of a significant (1.810–6

) problem

in this early measurement was suggested by a series of

excellent measurements carried out at the PhysikalischTechnische Bundesanstalt (PTB) under the guidance of

the late Peter Seyfried [7]. The discrepancy remained a

puzzle until the NBS apparatus was retrofitted with

additional interferometers designed to track the “pitch”

and “yaw” errors. It became clear that the constancy in

x-ray interference contrast over scans of hundreds of

optical periods, from which rectilinear motion had been

inferred, arose instead from mechanical noise that

limited the maximum interference contrast [8].

The principal short term impact of this paper was its

provision of enabling technology for three other efforts.

The most familiar of these is the first “modern” determination of the Avogadro constant, NA, connecting the 12C-based scale of atomic masses with the artifact-based

scale for macroscopic mass [9, 10]. This was followed

by the first applications of the same measurement

paradigm to the determination of the energy scale for

nuclear -rays [11], and extension of the methods of the

initial paper to the principal K-series x-ray lines of

tungsten[12], several rare earth elements, plus thorium

and uranium [13]. These short-term efforts led to a

longer term multinational effort addressing the

Avogadro constant, and a joint program of NBS/NIST

and Institut Laue-Langevin that has extended optically

based wavelength measurement in the -ray region up to

7 MeV.

NBS work on the Avogadro constant via the X-Ray

Crystal Density (XRCD) approach began around 1970.

The basic idea dates from 1913-14 when W. H. Bragg

and W. L. Bragg used the inverse of NA to infer the

lattice constant of rock salt (NaCl). Subsequently, the

XRCD procedure has appeared in several forms, not

only addressing the problem of NA determination, but

also establishing the most modern (and likely the last)

local wavelength unit for x rays, the A* unit [14]. All

work in this area, prior to that at NBS in the early 70s,

had two principal limitations.

Fig. 1. Schematic of early x-ray and optical interferometry apparatus.

195
The first limitation was use of liquid water as a

density standard. Although much effort had gone into

establishing the density of Standard Mean Ocean Water

(SMOW), application of this value to a particular local

water sample is problematical. In addition, water in its

fully cleaned and degassed form is unstable with respect

to re-dissolution of atmospheric gases, and it is relatively corrosive. To get around this problem, the NBS

Mass Group introduced a density scale based on solid

objects and used a fluorocarbon immersion fluid that

was non-corrosive and had a significant capacity to

dissolve gases [15]. Solid objects used in this initial

work were readily available highly regular steel

spheres.

A second limitation arose from the use of “tabulated”

atomic weights. Such tabulated values approximate the

world average of the geochemically variable isotopic

abundances. Such variability in the case of silicon is

large enough to prevent a significant determination of

NA. The NBS work was the first to employ the

(now standard) practice of direct isotopic abundance

measurement of the actual material used in the density

measurement [16]. The importance of this is illustrated

in Fig. 2 where we have shown a plot of crystal density

as a function of the mean molar mass (atomic weight).

Lattice changes over the normal range of abundance

variability are small enough that the ratio of mean molar

mass to density should be constant, determined by the

slope of the line shown in Fig. 2.

Just as the x-ray region had a local unit, so too did the

-ray domain. In this case, the de facto standard

was based on a rather complex determination of the

transition energy of the 198Hg daughter of 198Au*. The

numerical value for this approximately 411 keV transition was used as a reference value for most other -ray

transitions. In this role, it was (properly) used without

Fig. 2. Density response of silicon to molar mass changes.

196
uncertainty. However, in the case of fundamental

constants or tests of physical theory, the uncertainty

naturally entered directly.

Responding to a generally accepted need to improve

this reference transition, NBS mounted an effort to extend the optically based measurement chain into the

-ray region. Results for both the 411 keV and the

675 keV transitions in a strong 198Au source activated in

the NBS reactor were reported in 1978 along with new

measurements of nine transitions in 192Ir covering the

range from 205 keV to 612 keV. In the case of the

411 keV line from 198Au the result was 2510–6 higher

than the previous value and claimed a forty-fold

improvement in accuracy [11].

The combined effects of this initial work and subsequent efforts toward improved linkages among the

several wavelength regions have effectively unified the

entire electromagnetic scale. The efforts arising from

the subject paper may be thought of as beginning the

process of extending the reach of frequency synthesis

from the visible wavelength region into the domain of

x rays and rays. The improved visible-to-x-ray and

visible-to--ray connections yielded new values for

certain elementary particle masses, more critical tests of

quantum electrodynamics (QED) (in the spectroscopy

of one-electron heavy ions), a new, SI-based, all-Z

tabulation of x-ray transitions, and improved estimates

of nuclear binding energies with sufficient accuracy to

impact nuclear mass values. Aside from these developments, which were anticipated, the NIST -ray instrumentation has had significant unanticipated usefulness

in the determination of lifetimes of nuclear excited

states in the sub-picosecond range and determination of

interatomic potentials in the 10 eV to 100 eV range.

Several of the national metrology institutes (NMIs)

have formed an international Avogadro group focusing

on a possible atomic replacement for the artifact

kilogram. Major programs are currently underway in

Germany, Japan, Italy, and Australia. The needed

isotopic abundance ratios are being determined at the

Institute for Reference Materials and Measurements

(IRMM) in Belgium, sponsored by the European Union.

Most of the procedures in this worldwide effort are

direct descendants of the initial NBS effort of the

1970’s. NIST no longer has significant activity in this

area with the exception of relative lattice parameter

measurements and ad hoc contributions to the understanding of the troublesome molar volume anomaly in

the period from 1994 to 2000. Overall, the initial

Avogadro work at NBS led to improved methods of

measurement in the areas of density, displacement, and

molar mass as well as to the viable possibility of an

atomically based replacement for the artifact kilogram.

The first generation of -ray measurements at NBS

used radioactive sources activated in the NBS reactor.

Extension of this work to higher energies required

access to short-lived excited nuclei only accessible

through targets internal to a high flux reactor. Only the

research reactor at the Institut Laue-Langevin (ILL) in

Grenoble is configured to allow access to such sources.

A new -ray instrument specifically matched to this

application was installed at the ILL in the mid-eighties

and is now included in the ILL facilities inventory as

GAMS4.

GAMS4 extends the optically based -ray wavelength

scale to energies far higher than were accessible with

activated sources from the NBS reactor. It has allowed

determination of specific -ray transition energies

leading to new values for the neutron mass [17] and to

the possibility of a -ray/atomic mass determination of

the molar Planck constant [18]. The neutron mass was

addressed at an early stage and recently revisited with

further improved results [19]. Because of the evolution

in other parts of the fundamental physical constants, the

molar Planck constant is now accurately established

indirectly. The associated -ray measurements now are

verifiers of high accuracy trap-based mass spectrometry

results.

In addition to its use in high accuracy measurements,

GAMS4 delivers higher spectroscopic resolving power

than had been available previously. This exceptional

resolution revealed (initially unexpected) broadening

and fine-scale structural detail within individual -ray

profiles. The basic understanding of these line shapes

as recoil-induced Doppler profiles, modulated by

collisional deceleration, emerged from a brief but very

fruitful period in 1987 [20]. Our principal ILL collaborators, Hans Bo ̈rner and his associates, have further

developed the understanding of this complex process

[21]. GAMS4 is now seen as an effective means for

determination of nuclear excited state lifetimes in the

sub-picosecond domain [22] and a fertile test bed for

models of interatomic potentials in the 10 eV to 100 eV

range [23]. This work has been widely recognized

in Europe. It was identified as one of the two most

significant nuclear physics results for 1992 [24]. Bo ̈rner

received the 1990 Roentgen prize of the German

Physical Society, and a student who used GAMS4 for his

thesis research received the F. Schlafli Prize of the

Swiss Academy of Natural Sciences [25].

Two international workshops on applications of high

precision -ray spectroscopy have now taken place. The

first was in Grenoble in 1992, and the second, in South

Bend, Indiana, in 1998, is summarized in a special issue

of the NIST Journal of Research, January-February

2000. Most contributions to these meetings were based

197
on experimental work carried out using GAMS4 or on

theoretical developments in molecular dynamic simulations attuned to past or future experimental results from

GAMS4. As an ILL user facility, GAMS4 applications

are part of the normal proposal stream. Up to 2000,

when this commentary is being prepared, requests for

access to GAMS4 have exceeded available time by a

factor of two. In response to this proposal pressure, and

to increase the very low efficiency of GAMS4, the ILL

has undertaken new instrument development. This

new facility, GAMS5, is operational but still under

development.

Publication of the first comprehensive (all-Z)

theoretical study of x-ray transition energies [26] came

just after the first few of the new NBS experimental

measurements. The extraordinary clarity of the initial

comparisons and the unexpected linear Z-dependence of

the discrepancy invited extension and refinement on the

part of both theory and experiment. This first

comprehensive calculation was in the Dirac-HartreeSlater framework, and the puzzling Z-dependence

shown in Fig. 3 was found to be due to use of incorrect

values for nuclear radii. Subsequent refinements

included some relativistic corrections and inclusion of a

properly diffuse nuclear boundary [27].

Following this early period, a collaboration with Paul

Indelicato (Paris) was initiated, aimed at progressively

more refined, more rigorous and more detailed calculations. These initial efforts involved theoretical work

at the level of multi-configuration Dirac-Fock with

approximate allowance for QED effects. As this work

progressed through stages of increasing refinement and

understanding, it became clear that hole-state dynamics

would have to be considered. NIST was fortunate in this

respect to engage the collaboration of Eva Lindroth,

who brought the techniques of many-body perturbation

theory to bear on estimation of level shifts due to

coupling of inner vacancy states to their associated

decay continua [28].

All of these theoretical developments have now been

linked with an expanded and improved experimental

framework to produce a new and unprecedented view of

principal x-ray transitions for all elements from neon to

fermium. Previous attempts at such a synoptic overview

have been for the most part entirely empirical, while

there have been a few attempts to produce a comprehensive theoretical database. The NIST effort has combined

these two approaches with certain important changes.

First, the experimental database is skeletal rather than

comprehensive. Items included in the experimental

database were either measured directly in accordance

with the best of modern practice, or were referenced

to other transitions that had been directly measured

according to best practice. Second, the theoretical

component was constructed with a high level of rigor

that included not only a multi-configuration basis

set with relativistic and QED corrections, but also the

modification of these levels due to their coupling to

associated decay continua.

Richard Deslattes began work in the Crystal

Chemistry Section of the Analytical Chemistry Division

in 1962. He subsequently headed a newly named

Quantum Metrology Section in the Physics Division

of the Center for Absolute Physical Quantities. This

Section became for a brief time the Quantum Metrology

Division in the Physics Laboratory. Its remnants remain

as the Quantum Metrology Group of the Atomic Physics

Division of the NIST Physics Laboratory. In 1981-2 he

served as Director of the Physics Division of the

Fig. 3. Atomic transition response to errors in nuclear radii.

198
National Science Foundation. In 1983 he was designated

as a Senior NBS Fellow. In 1984-5 he was a U.S. Senior

Awardee of the Alexander von Humboldt Stiftung,

visiting the University of Heidelberg and working at

the Max Planck Institute for Nuclear Physics, the

Gesellschaft fu ̈r Schwerionenforschung and the Institut

Laue-Langevin. His awards include the Gold and Silver

Medals of the Commerce Department.

Albert Henins came to NBS in 1970 as a Physicist.

He continued to serve in that capacity until his retirement in 1998.

Prepared by Richard D. Deslattes.

Bibliography

[1] Richard D. Deslattes and A. Henins, X-Ray to Visible Wavelength Ratios, Phys. Rev. Lett. 31, 972-975 (1973).

[2] U. Bonse and M. Hart, An X-ray interferometer, Appl. Phys.

Lett. 6, 155-156 (1965).

[3] M. Hart, An Ångstro ̈m Ruler, Br. J. Appl. Phys., Ser. 2 1,

1405-1408 (1968).

[4] U. Bonse and E. te Kaat, A Two-Crystal X-Ray Interferometer,

Z. Phys. 214, 16-21 (1968).

[5] Richard D. Deslattes, Optical and X-Ray Interferometry of a

Silicon Lattice Spacing, Appl. Phys. Lett. 15, 386-388 (1969).

[6] J. Martin, U. Kuetgens, J. Stu ̈mpel, and P. Becker, The silicon

lattice parameter—an invariant quantity of nature?, Metrologia

35, 811-817 (1998).

[7] Peter Becker, Klaus Dorenwendt, Gerhard Ebeling, Rolf Lauer,

Wolfgang Lucas, Reinhard Probst, Hans-Joachim Rademacher,

Gerhard Reim, Peter Seyfried, and Helmut Siegert, Absolute

Measurement of the (220) Lattice Plane Spacing in a Silicon

Crystal, Phys. Rev. Lett. 46, 1540-1543 (1981).

[8] Richard D. Deslattes, Mitsuru Tanaka, Geoffrey L. Greene,

Albert Henins, and Ernest G. Kessler, Jr., Remeasurement of a

Silicon Lattice Period, IEEE Trans. Instrum. Meas. IM-36, 166-

169 (1987).

[9] R. D. Deslattes, A. Henins, H. A. Bowman, R. M. Schoonover,

C. L. Carroll, I. L. Barnes, L. A. Machlan, L. J. Moore, and W.

R. Shields, Determination of the Avogadro Constant, Phys. Rev.

Lett. 33, 463-466 (1974).

[10] R. D. Deslattes, A. Henins, R. M. Schoonover, C. L. Carroll, and

H. A. Bowman, Avogadro Constant-Corrections to an Earlier

Report, Phys. Rev. Lett. 36, 898-900 (1976).

[11] E. G. Kessler, Jr., R. D. Deslattes, A. Henins, and W. C. Sauder,

Redetermination of 198Au and 192Ir -Ray Standards between 0.1

and 1.0 MeV, Phys. Rev. Lett. 40, 171-174 (1978).

[12] E. G. Kessler, Jr., R. D. Deslattes, and A. Henins, Wavelength

of the W K1 x-ray line, Phys. Rev. A 19, 215-218 (1979).

[13] E. G. Kessler, Jr., R. D. Deslattes, D. Girard, W. Schwitz,

L. Jacobs, and O. Renner, Mid-to-high-Z precision x-ray

measurements, Phys. Rev. A 26, 2696-2706 (1982).

[14] Ivars Henins and J. A. Bearden, Silicon-Crystal Determination

of the Absolute Scale of X-Ray Wavelengths, Phys. Rev. 135A,

A890-A898 (1964).

[15] H. A. Bowman, R. M. Schoonover, and C. L. Carroll, The Utilization of Solid Objects as Reference Standards in Density Measurements, Metrologia 10, 117-121 (1974).

[16] I. L. Barnes, L. J. Moore, L. A. Machlan, T. J. Murphy, and W.

R. Shields, Absolute Isotopic Abundance Ratios and the Atomic

Weight of a Reference Sample of Silicon, J. Res. Natl. Bur.

Stand. 79A, 727-735 (1975).

[17] G. L. Greene, E. G. Kessler, Jr., R. D. Deslattes, and H. Bo ̈rner,

New Determination of the Deuteron Binding Energy and the

Neutron Mass, Phys. Rev. Lett. 56, 819-822 (1986).

[18] E. G. Kessler, G. L. Greene, M. S. Dewey, R. D. Deslattes, H.

Bo ̈rner, and F. Hoyler, High accuracy, absolute wavelength

determination of capture gamma-ray energies for E5 MeV and

the direct determination of binding energies in light nuclei,

J. Phys. G: Nucl. Phys. 14 Suppl., S167-S174 (1988).

[19] E. G. Kessler, Jr., M. S. Dewey, R. D. Deslattes, A. Henins,

H. G. Bo ̈rner, M. Jentschel, C. Doll, and H. Lehmann, The

deuteron binding energy and the neutron mass, Phys. Lett. A 255,

221-229 (1999).

[20] H. G. Bo ̈rner, J. Jolie, F. Hoyler, S. Robinson, M. S. Dewey,

G. Greene, E. Kessler, and R. D. Deslattes, Determination of

Short Lifetimes with Ultra High Resolution (n,) Spectroscopy,

Phys. Lett. B 215, 45-49 (1988).

[21] H. G. Bo ̈rner, J. Jolie, S. J. Robinson, R. L. Gill, and R. F.

Casten, New Reactor Based Methods to Measure Short Lifetimes of Nuclear Excited States, Neutron News 2 (4), 20-24

(1991).

[22] H. G. Bo ̈rner and J. Jolie, Sub-picosecond Lifetime Measurements by Gamma Ray Induced Doppler Broadening, J. Phys. G:

Nucl. Phys. 19, 217-248 (1993).

[23] M. Jentschel, K. H. Heinig, H. G. Bo ̈rner, J. Jolie, and E. G.

Kessler, Atomic collision cascades studied with the CrystalGRID method, Nucl. Instrum. Methods Phys. Res., Sect. B 115,

446-451 (1996).

[24] Encyclopedia Britannica, in Yearbook of Science and the Future

(1992) pp. 395-396.

[25] N. Stritt, J. Jolie, M. Jentschel, H. G. Bo ̈rner, and C. Doll,

Investigation of the interatomic potential using the crystal

gamma-ray-induced Doppler-broadening method on oriented Ni

single crystals, Phys. Rev. B: Condens. Matter 59, 6762-6773

(1999).

[26] Keh-Ning Huang, Michio Aoyagi, Mau Hsiung Chen, Bernd

Crasemann, and Hans Mark, Neutral-atom electron binding

energies from relaxed-orbital relativistic Hartree-Fock-Slater

calculations, 2 Z 106, At. Data Nucl. Data Tables 18, 243-

291 (1976).

[27] Mau Hsiung Chen, Bernd Crasemann, Michio Aoyagi,

Keh-Ning Huang, and Hans Mark, Theoretical Atomic InnerShell Energy Levels, 70 Z 106, At. Data Nucl. Data Tables

26, 561-574 (1981).

[28] P. Indelicato and E. Lindroth, Current status of the relativistic

theory of inner hole states in heavy atoms, Comments At. Mol.

Phys. 32, 197-208 (1996).

199
Laser Cooling of Atoms

The concept of radiation-pressure cooling of atoms

was independently suggested in 1975 for the case of a

gas of neutral atoms by Ha ̈nsch and Schawlow, and for

atomic ions bound in an electromagnetic trap by

Wineland and Dehmelt. While the notion that momentum exchange from a photon moving in the opposite

direction could slow an individual atom was well understood, until this time no one had come up with a means

for producing an aggregate cooling of a larger ensemble

of atoms (a gas). If all atoms in a hot gas absorb

photons, then some will be heated and some cooled, and

the ensuing equilibrium temperature is not lowered. The

general feature of the cooling concepts is that a gas of

atoms or ions can be cooled by ensuring that photon

absorption takes place preferentially when the atoms or

ions are moving against the flow of photons from a

laser.

In 1978, following these ideas, Wineland, Drullinger,

and Walls performed their seminal experiment [1]

in which they demonstrated the very first radiationpressure cooling below ambient temperature of any

atomic species. The key to the experiment was the

variation in photon absorption associated with the

Doppler frequency shift. They used a collection of

positive magnesium ions contained in an electromagnetic trap subjected to laser radiation near the

280 nm resonance of the magnesium ion. When this

laser radiation was tuned slightly below resonance,

cooling to below 40 K was observed. For this particular

tuning, those ions with motions opposing the laser

radiation are Doppler shifted toward resonance and

are more likely to absorb photons, thus slowing their

motions. Ions moving away from the source are Doppler

shifted further from resonance and are thus less likely to

absorb photons. Since the re-radiation from this excited

state is symmetric, the net effect averaged over the

ensemble of atoms is a cooling of the gas of ions. The

very next year, Wineland and Itano [2] published a paper

providing the first detailed theoretical analysis of laser

cooling, which served as the foundation for the rapid

development of this field. In ensuing years, they

improved their methods and soon cooled ions to

millikelvin temperatures.

This experimental demonstration stimulated the

development of a large number of ion-cooling groups

around the world and encouraged others to attempt to

cool neutral atoms. In fact, it was only a few years later

(in 1982) that a beam of neutral atoms was cooled by

Bill Phillips and his collaborators at NIST (as described

elsewhere in this volume). These ideas have contributed

significantly to atomic-clock technology. Clocks using

both trapped ions [3] and cooled neutral atoms [4] have

now demonstrated frequency uncertainties of a few

parts in 1015, an improvement of an order of magnitude

over conventional atomic-clock technology. Further

improvements will certainly be demonstrated over

the next few years. The potential of the cooled-ion

standards can be appreciated by recognizing that, for a

small group of ions, the systematic frequency shifts are

now understood at an uncertainty level of 1 part in 1018.

Based on this early work, NBS established an Ion

Storage Group in Boulder; the Group now includes five

full-time staff members and a number of postdoctoral

associates, guests, and students. After the initial cooling

experiments, the methods were improved, but particularly striking results were obtained by cooling at the

sideband frequency created by the periodic motion of

the trapped ions. Using this method, the Group

achieved, for the first time, cooling to the zero-point

energy of motion [5,6], the fundamental limit for any

cooling technique.

Fig. 1. A schematic diagram of a linear ion trap using alternating and

static electric fields to confine linear arrays or “strings” of ions. The

expanded ultraviolet image at the bottom shows the fluorescence

image of an array of positive mercury ions.

200
A unique aspect of the ion-cooling work has been the

ability to do experiments with individual atoms. The

NBS Group developed remarkable techniques that

allowed them to observe and control both the motional

and internal quantum states of individual ions, and

thereby to confirm experimentally some of the fundamental concepts upon which quantum mechanics is

based. For example, they observed individual quantum

transitions of a single ion with 100 % probability [7],

performed Young’s classical light interference

experiment with radiation scattered by two ions [8],

performed absorption spectroscopy on a single ion [9],

observed fundamental quantum-projection noise [10],

and demonstrated a “Schro ̈dinger-cat” entangled superposition state of an atom [11]. The ability to control

completely the states of ions has led them to show that

properly coupled ions can perform simple quantumlogic operations [12]. While the realization of a useful

quantum computer faces severe obstacles, the projected

performance of such a computer is so great that many

groups worldwide have now begun to pursue this objective. The NIST Ion-Storage Group continues to work at

the forefront of this field.

Another important line of work that grew out of this

program has been the study of the behavior of larger

groups of ions that form what are called nonneutral

plasmas [13]. The NIST Group has cooled these

plasmas to the point where they exhibit liquid and

even crystalline behavior [14]. The surprising thing

is that these cooled plasmas exhibit behavior analogous

to that of very dense, hot neutron stars. In addition,

they can be controlled well enough to allow precision

studies of fundamental equilibria and dynamical

behavior.

Fig. 2. The three physicists involved in this first laser-cooling experiment. Pictured from left to right are Dave Wineland, Bob Drullinger, and

Fred Walls.

201
The three NIST-Boulder authors of this seminal paper

continue to work in the Time and Frequency Division in

Boulder, and each has become a world leader in a key

program within the Division. Dave Wineland heads the

Ion Storage Group, which continues to open up new

areas of research based on trapped, laser-cooled ions.

Of most recent note is his world leadership in the area

of quantum logic and entangled quantum states. In

recognition of his many accomplishments, Wineland has

been elected a Member of the National Academy of

Sciences, a Fellow of the American Physical Society

and a Fellow of the Optical Society of America. He

has been awarded a long list of honors, including the

Davisson-Germer Prize of the American Physical

Society, the William F. Meggars Award of the Optical

Society of America, the I. I. Rabi Award of the IEEE,

the Einstein Medal for Laser Science of the Society of

Optical and Quantum Electronics, the DOC Gold and

Silver Medals, NIST’s Samuel Wesley Stratton Award

and NIST’s Edward Uhler Condon Award. Following the

ion-cooling experiment, Bob Drullinger contributed

to the optical frequency measurements that led to the

redefinition of the meter, then went on to lead the

development of NIST-7, an optically pumped cesiumbeam frequency standard that became NIST’s primary

frequency standard in 1993. This is clearly the most

accurate atomic-beam standard ever built. For this work

he was awarded the DOC Gold Medal and the I. I. Rabi

Award of the IEEE. Fred Walls went on to lead the

development of a passive hydrogen maser of exceptional

merit. He then shifted to the development of low phasenoise and amplitude-noise electronics of importance

to time-and-frequency metrology and to the accurate

measurement of spectral purity. He has become the

world leader in this field, and in recognition of this

leadership was elected a Fellow of the American

Physical Society. He has also been recognized with the

very first Time and Frequency Award given by the

European Frequency and Time Forum, the I. I. Rabi

Award of the IEEE, three DOC Silver Medals, IEEE’s

Millennium Medal, and NIST’s Edward Bennett Rosa

Award.

Prepared by D. B. Sullivan.

Bibliography

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40, 1639-1642 (1978).

[2] D. J. Wineland and W. M. Itano, Laser cooling of atoms, Phys.

Rev. A 20, 1521-1540 (1979).

[3] D. J. Berkeland, J. D. Miller, J. C. Bergquist, W. M. Itano, and

D. J. Wineland, Laser-cooled mercury ion frequency standard,

Phys. Rev. Lett. 80, 2089-2092 (1998).

[4] S. R. Jefferts, D. M. Meekhof, J. Shirley, T. E. Parker, C. Nelson,

F. Levi, G. Costanzo, A. DeMarchi, R. Drullinger, L. Hollberg,

W. D. Lee and F. L. Walls, The accuracy evaluation of NIST-F1,

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[5] F. Diedrich, J. C. Bergquist, W. M. Itano, and D. J. Wineland,

Laser cooling to the zero-point energy of motion, Phys. Rev. Lett.

62, 403-406 (1989).

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cooling of a bound atom to the 3D zero-point energy, Phys. Rev.

Lett. 75, 4011-4014 (1995).

[7] J. C. Bergquist, R. G. Hulet, W. M. Itano, and D. J. Wineland,

Observation of quantum jumps in a single atom, Phys. Rev. Lett.

57, 1699-1702 (1986).

[8] U. Eichmann, J. C. Bergquist, J. J. Bollinger, J. M. Gilligan, W.

M. Itano, D. J. Wineland, and M. G. Raizen, Young’s interference experiment with light scattered from two atoms, Phys. Rev.

Lett. 70, 2359-2362 (1993).

[9] D. J. Wineland and W. M. Itano, Spectroscopy of a single Mg+

ion, Phys. Lett. 82A, 75-78 (1981).

[10] W. M. Itano, J. C. Bergquist, J. J. Bollinger, J. M. Gilligan, D. J.

Heinzen, F. L. Moore, M. G. Raizen, and D. J. Wineland,

Quantum projection noise: Population fluctuations in two-level

systems, Phys. Rev. A 47, 3554-3570 (1993).

[11] C. Monroe, D. M. Meekhof, B. E. King, and D. J. Wineland, A

‘Schro ̈dinger Cat’ superposition state of an atom, Science 272,

1131-1136 (1996).

[12] C. Monroe, D. M. Meekhof, B. E. King, W. M. Itano, and D. J.

Wineland, Demonstration of a fundamental quantum logic gate,

Phys. Rev. Lett. 75, 4714-4717 (1995).

[13] J. J. Bollinger and D. J. Wineland, Strongly coupled nonneutral

ion plasma, Phys. Rev. Lett. 53, 348-351 (1984).

[14] T. B. Mitchell, J. J. Bollinger, D. H. E. Dubin, X.-P. Huang, W.

M. Itano, and R. H. Baughman, Direct observations of structural

phase transitions in planar crystallized ion plasmas, Science 282,

1290-1293 (1998).

202
Spin-Polarized Electrons

In numerous experiments involving electrons, the

ability to manipulate the spin of the electron gives

unique additional information. For many years,

however, such experiments were extraordinarily rare

because of the absence of a good source of spin-polarized

electrons. Up to the time this paper appeared, sources of

spin-polarized electrons produced electron beams of

very low intensity or polarization, or both, putting most

polarized electron experiments out of reach and making

those remaining heroic efforts. When GaAs SpinPolarized Electron Source [1] appeared in print, a large

number of proposed measurements were standing by,

awaiting an improved source of spin-polarized electrons. The GaAs source proved to be the gateway to

many fundamentally new types of experiments in

atomic, condensed matter, nuclear, and particle physics.

The principle of the GaAs polarized electron source

relies on 1) the photoexcitation of spin-polarized

electrons in a solid and 2) their escape into vacuum. The

origin of the spin polarization can be understood by

referring to Fig. 1. GaAs is a direct-gap semiconductor

with the band gap, Eg, at the center of the Brillouin zone

as in the E(k) plot of the energy bands vs. crystal

momentum k shown on the left side of Fig. 1. The

relative intensities for transitions between mj sublevels

by photoexcitation with circularly polarized + and –

(positive and negative helicity) light are shown on the

right side of Fig. 1. The polarization is defined as

P = (N↑–N↓)/(N↑+N↓)where N↑(N↓) are the number of

electrons with spins parallel (antiparallel) to a quantization direction. Thus, for + light, quantum mechanical

selection rules give the theoretical polarization,

Pth = (1–3)/(1+3) = –0.5 for band gap photoexcitation.

An important characteristic of the GaAs source is that

the sign of the spin polarization of the excited electrons

can be easily changed by reversing the helicity of the

incident light without affecting other parameters of the

electron beam.

Fig. 1. On the left are depicted the energy bands of GaAs at the center of the Brillouin zone showing the band

gap energy Eg and the spin-orbit splitting of the valence band . On the right are shown the allowed transitions

between mj sublevels for circularly polarized light, + (solid lines) and – (dashed lines), with relative transition

probabilities given by the circled numbers.

203
Ordinarily, electrons excited to the conduction band

minimum would be approximately 4 eV below the

vacuum level and could not escape from the GaAs.

However, by treating the surface of p-type GaAs with

Cs and O2 it is possible to lower the vacuum level at the

surface below the energy of the conduction band

minimum in the bulk to achieve the condition known as

negative electron affinity (NEA) shown in Fig 2. NEA

GaAs surfaces are extremely efficient photoemitters,

which explains their widespread use in photomultiplier

tubes, image intensifiers, and night vision devices. It is

a lucky happenstance of nature that the world’s best

photoemitter is also an efficient source of spin-polarized

electrons.

The purpose of the paper GaAs Spin-Polarized

Electron Source was to describe how this effect, which

had been discovered [2] a few years previously in

spin-polarized photoemission experiments by Pierce

and coworkers at the ETH-Zurich, could be used to

provide a compact spin-polarized electron gun. GaAs

Spin-Polarized Electron Source gives a comprehensive

account not only of the theory of operation of this

device, but also of its design, special materials preparation, construction, characterization, and performance. A

crucial step is the cleaning of the GaAs photocathode

surface, first by a series of chemical processes, and then

by heating to just the right temperature in ultrahigh

vacuum. The detailed descriptions of this and the subsequent activation of the GaAs photocathode were

important to enable others to build their own polarized

electron guns. The analysis of the electron optics

included the characteristics of the emitted beam, the

cathode region, a 90 spherical deflector to change the

longitudinal polarization of the emitted electrons to a

polarization transverse to the electron momentum, and

the transport and focusing system. The modular design

provided a 1 keV electron beam suitable for transport

through an isolation valve and on to the electron optics

of a particular experiment. In this first application, the

subsequent electron optics was designed to provide a

collimated electron beam with variable energy from a

few eV to a few hundred eV, as one would use in

a variety of condensed matter physics experiments

like spin-polarized low-energy electron diffraction

(SPLEED).

The availability of an intense source of electrons with

easily modulated degree of spin polarization had immediate impact. The two interactions, the spin-orbit interaction and the exchange interaction, that give rise to

spin-dependent electron scattering from surfaces were

investigated at NBS and given as examples of applications in the paper GaAs Spin-Polarized Electron Source.

The spin-orbit interaction is due to the interaction of

the spin of the electron with its own orbital angular

momentum in scattering from a strong potential and is

larger for materials of high atomic number. Large

spin-dependent effects were observed in polarized

electron scattering from a W(100) surface [3]. The spin

dependent scattering asymmetry is readily determined

by measuring the ratio of the part of the scattered intensity that varies with the modulation of the incident

electron spin polarization to the part that is spin

independent. Thus, the spin-dependent information

is obtained from simple intensity measurements. The

second example was scattering from a single-crystal

Ni(110) surface where the spin dependence is due to the

exchange interaction [4]. The exchange interaction is a

consequence of the Pauli principle requiring the total

wave function including spins to be asymmetric with

respect to permutation of the particles. These polarized

electron scattering measurements from a ferromagnetic

surface pioneered a new, sensitive means to measure the

degree of surface magnetic order. In another experiment

[5] using the GaAs source, spin-polarized electron

scattering from a ferromagnetic glass confirmed theoretical predictions that the temperature dependence of

the surface magnetization at low temperatures should

have the same power law as that of the bulk. However,

the discovery of a larger prefactor than predicted led

to recognition that the exchange coupling between the

surface and the bulk is reduced.

Fig. 2. GaAs surface activated with Cs and O2 to achieve negative

electron affinity EA(vacuum level E	 lower than the conduction-band

minimum). Electrons excited across the band gap Eg by photons of

energy 
 thermalize to the conduction-band minimum, diffuse to the

surface, and escape into the vacuum.

204
In the 1980s, at NBS and in laboratories around the

world, because of spin-polarized electron guns of the

type described in GaAs Spin-Polarized Electron Source,

researchers began making spin-polarized versions of

their favorite electron spectroscopies. A case in point is

spin-polarized inverse photoelectron spectroscopy

(SPIPES). Inverse photoemission (IPES) is complementary to ordinary photoemission spectroscopy (PES).

In particular, it permits investigation of unfilled states

between the Fermi level and the vacuum level that are

inaccessible in ordinary PES. Such states are crucial

since it is the d-holes in transition-metal ferromagnets

that are the “active ingredients” of the magnetism.

SPIPES probes the spin-dependent nature of these

states, in effect providing a magnetic spectroscopy of

electron states. The first SPIPES measurements [6]

were made on Ni(110) at NBS in a collaboration with

Bell Laboratories colleagues who were involved in some

of the first IPES measurements. Other spin polarized

spectroscopies using the GaAs source were spinpolarized electron energy loss spectroscopy (SPEELS)

[7] and spin-polarized low energy electron microscopy

(SPLEEM) [8].

Among the longer term impacts of the paper

GaAs Spin-Polarized Electron Source and the device

described there is the use of such spin-polarizedelectron guns in the development of detectors of spinpolarized electrons. In early measurements at NBS, it

was found that not only was the scattering of electrons

from a magnetic surface spin dependent, but so also was

the electron current absorbed in the target [9]. An

electron spin analyzer was developed based on this

effect [10]. While this spin analyzer turned out to be

difficult to use, it was applied in a very important

measurement of the spin polarization of the secondaryelectron energy distribution generated when an unpolarized electron beam is incident on a ferromagnet [11].

Energy- and spin-resolved measurements carried out at

NBS showed that a ferromagnetic metal yields an

abundance of highly polarized secondary electrons. This

suggested the possibility of achieving high resolution

imaging of magnetization of a surface by measuring

the polarization of secondary electrons generated in a

scanning electron microscope. This technique has come

to be known as scanning electron microscopy with

polarization analysis or SEMPA. The SEMPA magnetization image is formed by measuring the spin polarization of the secondary electrons as the SEM beam is

“rastered” across the sample surface as shown schematically at the top of Fig. 3. The traditional Mott spinpolarization analyzer is large and heavy, in short

cumbersome, and not suited for easy attachment to a

scanning electron microscope. A new type of spin

analyzer was developed at NBS, using the GaAs spinpolarized-electron gun to survey the phase space of

materials, electron energies, and scattering conditions.

This new low-energy diffuse-scattering spin analyzer

[12] was fist-sized and at least as efficient as its big

brother, the high-energy Mott analyzer. SEMPA has

since been applied to numerous industrial problems by

imaging domains in recording media, recording heads

and other magnetic sensors, and magnetic randomaccess memory elements. The power of seeing the

domains in high-resolution SEMPA images has proven

very helpful in the development of magnetic randomaccess memory devices [13].

An especially important application of spin-polarized

electrons is illustrated by a SEMPA investigation that

took place in the early nineties [14]. At that time, there

was a great deal of excitement within the condensed

matter physics and magnetism communities as a consequence of a new discovery. A new kind of coupling

was found to exist between magnetic layers separated by

non-magnetic materials in very thin multilayer structures. The direction and extent of the coupling appeared

to depend on the thickness of the non-magnetic layer in

a way that did not correspond to any known theory and

appeared not to depend strongly on the spacer material.

Several innovations made the SEMPA investigation of

this magnetic coupling unique. First, an Fe whisker was

used as an atomically-perfect substrate. Second, the Cr

spacer layer was grown in the shape of a wedge so that

the variation of spacer thickness would be continuous as

shown at the top of Fig. 3. Third, reflection high energy

electron diffraction of the Cr wedge before the top Fe

layer was deposited determined the average thickness at

each point along the wedge to 0.1 atomic layer. Finally,

SEMPA produced a single magnetization image of the

top Fe layer, lower part of Fig. 3, where the magnetization changes back and forth from being parallel to

the magnetization of the Fe whisker substrate (white

regions) to antiparallel (black) as the Cr spacer thickness

increases. Two superposed but distinct periods of

oscillation of the exchange coupling with Cr thickness

were observed. By varying the Cr growth temperature, it

was possible to vary the roughness and show that

rougher interfaces result from lower temperature

growth. For such rough layers, the long-period coupling

dominates as illustrated at the bottom right of

Fig. 3. This explains why the short-period coupling

had not been observed in the less perfect samples

previously studied. Clearly, the universal period idea

was shown to be invalid. The existence of the second

period helped show the relationship of the coupling

periodicity to the electronic structure of the spacer-layer

material.

205
Our discussion of the impact of GaAs Spin-Polarized

Electron Source has so far been restricted to examples

from condensed matter physics. At the time of publication of this paper, there were also experiments in the

area of electron-atom collision physics just waiting for

such a spin-polarized electron gun. When polarization

techniques are used to fully state select the target and the

incident electron polarization, then a complete or

“perfect” scattering experiment is possible. In this case

the quantum amplitude and phases can be measured

instead of the cross-sections. Since cross-sections are

sums of squares of complex amplitudes, direct determination of the individual amplitudes provides a more

helpful comparison to, and a much more stringent test

of, theoretical models. Using a GaAs polarized electron

gun to scatter from a beam of Xe atoms, and measuring

the change in polarization after scattering, the spin-orbit

interaction was investigated in a complete experiment

[15]. At NIST, the exchange interaction was carefully

investigated in extensive experiments of elastic and inelastic polarized-electron scattering from state-selected

Na beams [16].

GaAs Spin-Polarized Electron Source has been cited

approximately 250 times, though nowadays the GaAs

spin-polarized-electron gun is taken as accepted technology and its origins are often no longer cited. As

discussed in a 1995 review [17], for most atomic and

condensed matter experiments, the polarized electron

gun described in GaAs Spin-Polarized Electron Source

is more than adequate and remains the source of choice.

Fig. 3. In scanning electron microscopy with polarization analysis (SEMPA) the spin polarization of secondary

electrons generated by a moving SEM beam is measured to obtain an image of the magnetization. Two such

images of the magnetization of the top layer of a Fe/Cr (wedge)/Fe(001) sandwich are shown at the bottom of

the figure for growth of the Cr wedge on the Fe whisker substrate at 200 C and 300 C. White (black) shows

that the top Fe layer is coupled ferromagnetically (antiferromagnetically) to the Fe substrate.

206
GaAs polarized-electron sources for experiments in

the areas of nuclear and particle physics, while working

on the same principle, have been developed specifically

to meet particular accelerator requirements such as a

very high cathode voltage or a particular time structure

of the beam. Advances over the years in GaAs type

polarized electron sources, especially the progress toward higher polarization while maintaining sufficient

beam intensity, can be attributed in large part to the

demanding requirements on polarized electron sources

for accelerator applications. Spin-polarized electrons

play a crucial role in many particle physics experiments

today.

The authors of GaAs Spin-Polarized Electron Source

formed a strong team. The electron-optical design was

led by Chris Kuyatt, assisted by Anija Galejs. Kuyatt

was Section Chief of the Surface and Electron Physics

Section at the time of the beginning of construction of

the spin-polarized electron source. By the time the paper

was published, he had become Chief of NIST’s Center

for Radiation Physics. In the 1960s, he and John Simpson

developed high resolution electron monochromators and

energy analyzers [18] and with them investigated sharp

resonances in the electron transmission in gases [19].

The explanation of the resonance lineshapes is found in

the landmark paper by Ugo Fano [20] (discussed

elsewhere in this volume). Kuyatt worked at NIST until

his death in 1998.

Robert Celotta, who became group leader after

Kuyatt, and later a NIST Fellow, continues to do both

research and serve as Group Leader of the Electron

Physics Group. Dan Pierce also became a NIST Fellow

and continues his research in the NIST Electron

Physics Group. Together, Celotta and Pierce received the

Edward Uhler Condon Award for distinguished achievement in written exposition as a result of their contribution to the paper GaAs Spin-Polarized Electron Source.

They also shared the Department of Commerce

Gold Medal and the American Vacuum Society GaedeLangmuir Prize for their development of advanced,

spin-polarized electron beam technology. Celotta and

Pierce were given the first NIST William P. Slichter

Award, which recognizes the growing need to promote

cooperative partnerships between government and

industrial researchers.

Stan Mielczarek and Anija Galejs worked as physicists in the Electron Physics Group until their retirements in 1990 and 1988 respectively. Bill Unertl was a

National Research Council Postdoctoral Associate who

left to take a faculty position at the University of Maine,

where he is now Professor of Physics. Gwo-Ching Wang

was a postdoctoral fellow and now is Professor of

Physics at Rensselaer Polytechnic Institute.

The National Bureau of Standards received IR-100

Awards in 1980 and 1985 (selected by Industrial

Research and Development Magazine as one of the 100

most significant technical innovations of the year) for a

Surface Magnetometer and for an Electron Gun, both of

which were outgrowths of the development described in

GaAs Spin-Polarized Electron Source.

Prepared by Daniel T. Pierce and Robert J. Celotta.

Bibliography

[1] D. T. Pierce, R. J. Celotta, G.-C. Wang, W. N. Unertl, A. Galejs,

C. E. Kuyatt, and S. R. Mielczarek, GaAs Spin Polarized

Electron Source, Rev. Sci. Instrum. 51, 478-499 (1980).

[2] D. T. Pierce, F. Meier, and P. Zu ̈rcher, Negative Electron Affinity

GaAs: A New Source of Spin-Polarized Electrons, Appl. Phys.

Lett. 26, 670-672 (1975); D. T. Pierce and F. Meier, Photoemission of Spin-Polarized Electrons from GaAs, Phys. Rev. B

13, 5484-5500 (1976); D. T. Pierce, F. A. Meier, and H. C.

Siegmann, Source of Spin Polarized Electrons, U.S. Patent

3,968,376, issued July 6, 1976.

[3] G.-C. Wang, B. I. Dunlap, R. J. Celotta, and D. T. Pierce,

Symmetry in Low-Energy Polarized-Electron Diffraction, Phys.

Rev. Lett. 42, 1349-1352 (1979).

[4] R. J. Celotta, D. T. Pierce, G.-C. Wang, S. D. Bader, and G. P.

Felcher, Surface Magnetization of Ferromagnetic Ni(110): A

Polarized Low-Energy Electron Diffraction Experiment, Phys.

Rev. Lett. 43, 728-731 (1979).

[5] D. T. Pierce, R. J. Celotta, J. Unguris, and H. C. Siegmann,

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(1982).

[6] J. Unguris, A. Seiler, R. J. Celotta, D. T. Pierce, P. D. Johnson,

and N. V. Smith, Spin-Polarized Inverse Photoelectron Spectroscopy of Solid Surfaces: Ni(110), Phys. Rev. Lett. 49, 1047-

1050 (1982).

[7] J. Kirschner, D. Rebenstorff, and H. Ibach, High-Resolution

Spin-Polarized Electron-Energy-Loss Spectroscopy and the

Stoner Excitation Spectrum in Nickel, Phys. Rev. Lett. 53, 698-

701 (1984); D. L. Abraham and H. Hopster, Spin-Polarized

Electron-Energy-Loss Spectroscopy on Ni, Phys. Rev. Lett. 62,

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[8] E. Bauer, Low Energy Electron Microscopy, Rep. Prog. Phys. 57,

895-938 (1994).

[9] H. C. Siegmann, D. T. Pierce, and R. J. Celotta, Spin-dependent

Absorption of Electrons in a Ferromagnetic Metal, Phys. Rev.

Lett. 46, 452-455 (1981).

[10] R. J. Celotta, D. T. Pierce, H. C. Siegmann, and J. Unguris, An

Electron Spin Polarization Detector: Spin-Dependent Absorption

of a Polarized Electron Beam, Appl. Phys. Lett. 38, 577-579

(1981).

[11] J. Unguris, D. T. Pierce, A. Galejs, and R. J. Celotta, Spin and

Energy Analyzed Secondary Electron Emission from a Ferromagnet, Phys. Rev. Lett. 49, 72-76 (1982).

[12] J. Unguris, D. T. Pierce, and R. J. Celotta, Low-Energy Diffuse

Scattering Electron-Spin Polarization Analyzer, Rev. Sci. Instrum. 57, 1314-1323 (1986).

[13] J. Daughton, Non-volatile Electronics, private communication.

[14] J. Unguris, R. J. Celotta, and D. T. Pierce, Observation of Two

Different Oscillation Periods in the Exchange Coupling of Fe/Cr/

Fe(100), Phys. Rev. Lett. 67, 140-143 (1991).

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[15] W. Wu ̈bker, R. Mo ̈llenkamp, and J. Kessler, “Perfect” Elastic

e–

-Xe Scattering Experiment, Phys. Rev. Lett. 49, 272-275

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[16] J. J. McClelland, M. H. Kelley, and R. J. Celotta, Spin-Dependent

Superelastic Scattering from Pure Angular Momentum States of

Na(3P), Phys. Rev. Lett. 56, 1362-1365 (1986); J. J. McClelland,

M. H. Kelley, and R. J. Celotta, Superelastic Scattering of SpinPolarized Electrons from Sodium, Phys. Rev. A 40, 2321-2329

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208
Needs for Radioactivity Standards and

Measurements in Different Fields

This 1973 paper was written at a critical point in the

development of applications of radioactivity and nuclear

power, and it defined the needs of standards laboratories

of the world for the remainder of the century. Although

the paper [1] was co-authored by members of the

Radioactivity Section, it was largely written by Wilfrid

Mann and represents the fruition of his years of reflection on radionuclide metrology.

Standards are needed for radioactive materials to

permit their accurate measurement for purposes of

health, worker protection, and public safety. The

National Bureau of Standards developed a program for

standards and calibrations of radium-226 (1600 year

half life) in the early part of the century [2,3], but this

program was limited mainly to naturally-occurring

radionuclides in the uranium and thorium series until

the late 1940s. Following World War II, man-made

radionuclides from reactors, linear accelerators, and

cyclotrons became available for more routine uses in

medicine, agriculture, and industry. The Bureau then

began development of primary standardization techniques that could be applied to classes of radionuclides,

such as pure beta-particle emitters [4], gamma-ray

emitters, and alpha-particle emitters. In 1951, Lauriston

S. Taylor envisioned a world-leadership role for NBS in

radionuclide metrology and recruited Wilfrid Mann

from the Chalk River laboratories in Canada. Throughout the 1950s and 1960s Mann built and expanded the

Bureau’s capabilities in radionuclide metrology [5],

including techniques such as microcalorimetry, betagamma coincidence counting, gas counting, defined

solid-angle alpha counting, and photon spectrometry.

Metrology also required developing expertise in

sample preparation, radiochemistry, isotope separation,

sampling for environmental analyses, and measurement

quality assurance. Thus, by the end of the 1960s NBS

was ready to assume national leadership in measurements for radioactivity, and a timely report from the

National Academy of Sciences [6] stressed the needs for

radioactivity standards for public health, medicine, and

nuclear science.

Needs for Radioactivity Standards was written just as

the applications of radiopharmaceuticals in nuclear

medicine were beginning a very rapid expansion.

During the same period, the U.S. nuclear industry (and

the industrialized world) were very positive about the

prospects for cheap, abundant “atomic energy,” and the

utilities were building new nuclear power stations all

over the country. Most of the 104 power reactors operating today were ordered during the 1970s. In each of the

national standards laboratories, metrologists were considering how to meet the needs of these emerging technologies. This paper was the keynote presentation of the

formative meeting of the International Committee

for Radionuclide Metrology (ICRM). The paper both

summarizes the status of radionuclide standards and

explores the needs for standards, measurements, and

traceability for the emerging fields of nuclear medicine

and nuclear power. It provided a blueprint for national

and international traceability.

In the first nine pages Mann laid the foundation for

radionuclide metrology by introducing the concepts,

terminology and historical developments of measurement standards and radioactivity standards. This entertaining and informative introduction was absolutely

necessary to his later development of the concept of

traceability. He points out that “criterion” and

“standard” are synonyms in the English language.

Criterion comes from the Greek, while standard is

derived from the old French “estandart.” It was a flag

raised on a pole to indicate the rallying point of an army.

Our battlefields of today have shifted from armed

combat to economic warfare, and this sense of the word

standard still resonates with U.S. industry. Derived

standards of radioactivity differ from the base quantities

of time, length, and mass in two important respects.

First, radioactivity is an ephemeral quantity. The substance is decaying with some half life (a good example

is the 6 hour half life 99mTc used in nuclear medicine)

such that often the material no longer exists after

the measurements are completed. In most cases, the

standard must reside in a system (protocol, people,

detector, and associated electronics) that can be used to

measure a disintegration rate (activity) from first principles. Second, there are a few thousand radionuclides,

and they are found in many matrices (gas, liquid, solid,

soil, air filters), so that choices must be made on

the select few nuclides and matrices for “national

standards.” Needs for Radioactivity Standards addressed

the basic issues of identifying emerging technologies,

ordering priorities, developing measurement quality

assurance programs, and establishing traceability for

key measurements at the national and international

levels. Following the historical background, Mann gave

special emphasis to needs for radiopharmaceuticals and

for monitoring radioactivity in the environment.

209
In the area of radiopharmaceuticals, NBS was forging

ties directly to the manufacturers and to professional

medical groups, such as the College of American

Pathologists (CAP), as well as to the Food and Drug

Administration (FDA). This paper reported some of the

first round-robins with clinical users for solution

standards of the radionuclides 51Cr, 59Fe, and 131I. These

first sets of measurements were evaluated by the manufacturers, FDA, and the professional groups. It was

readily agreed that such exercises were important to

establish mutual trust between manufacturers and with

the FDA drug reviewers. For the small group of manufacturers, equity-in-trade was an important consideration. Bulk radionuclides were routinely produced and

sold as raw materials, and a few percent discrepancy

in the assay between manufacturers could lead to

thousands of dollars in disputed sales. Thus, a small

expenditure on a common program at NBS would

ensure that all parties were measuring the same quantity

of activity. The FDA had a need to verify the calibrations of the suppliers as well. If they were in the same

calibration program with the manufacturers, it would

simplify their work on audits for quality control.

However, the CAP did not have a mechanism for a

long-term formal program in this area. Wilfrid Mann

and Lucy Cavallo negotiated with the industry to set up

a consortium of radiopharmaceutical manufacturers in

North America to produce such standards on a continuing basis under the auspices of the Atomic Industrial

Forum [7].

During the 1970s and 1980s this program addressed

the critical needs of the industry for short-lived radionuclide standards for diagnostic imaging in nuclear

medicine. One of the most difficult of these standardizations was the 6 hour half life 99mTc. It has long been the

most important nuclide in terms of diagnostic imaging

and accounts for over 90 % of the 13 million applications per year in the United States. Technetium-99m, a

metastable form of technetium-99, is produced by a

chemical extraction from a 99Mo-99mTc generator, and

the product must be purified to eliminate traces of the

67 hour parent nuclide. The logistical hurdles were also

severe, as air cargo shipping of radioactive materials

with a six hour half life before the days of rapid commercial air freight was problematic. Lucy Cavallo

worked out the rapid procedures for chemical separations and source preparations for these two nuclides, and

Robert Ayres and Alan Hirshfeld later reported on the

standardization by 4
-coincidence counting [8].

These protocols for rapid standardization of high activity levels of radionuclides, developed by Lucy Cavallo

and Ronald Colle ́, were adopted by industry and are still

in use today. The program continued to expand and

added approximately one new nuclide each year; at

present, there are 28 radiopharmaceutical SRMs [9].

Ten of these 28 SRMs are distributed each year.

After 1987 the focus shifted towards radionuclides for

use in therapy. Radionuclides have been used in therapy

for many years, but in the recent past improvements in

sealed source preparation and radiopharmaceutical

targeting strategies have led to much greater use and,

accordingly, demands for standards. An example of the

continuing leadership of NIST in this area was the recent

international workshop organized by Bert Coursey and

Brian Zimmerman to identify the needs for standards for

therapeutic nuclides [10]. The long-term impact of the

NBS/NIST radiopharmaceutical standards program was

evaluated recently in an economic impact study by

Albert Link [11], who found that this program had a 97

to 1 benefit to cost ratio based solely on the economic

benefits. The benefits in terms of improved quality of

health care (better diagnostics, more effective therapies)

to the U.S. public are even more significant than the

economic benefits.

Prior to this 1972 conference, Mann had established

competence at the Bureau on low-level radioactivity

measurements, which are important for environmental

monitoring. J.M.R. (Robin) Hutchinson had developed

a number of low-level counting instruments [12]

for gamma-ray and alpha-particle emitters, and Lloyd

Currie had considered the statistics of low-level counting

[13], with an experimental emphasis on 3

H and 14C. In

1963, Currie transferred to the Analytical Chemistry

Division and has achieved international prominence in

atmospheric carbon measurements.

Needs for Radioactivity Standards reported on a new

and very promising program for gamma-ray emissionrate SRMs for use in the emerging nuclear power industry. In early 1972, there were serious disagreements

between the Atomic Energy Commission (AEC) and the

new Environmental Protection Agency (EPA) on how to

analyze liquid effluents from the six operating nuclear

power stations. A meeting was organized at Oyster

Creek nuclear power station in Tom’s River, New Jersey,

in February 1972 that included the AEC, the EPA, the

New Jersey radiation health authorities, the utility, and

Robin Hutchinson and Bert Coursey from NBS. It was

decided that NBS would prepare mixed gamma-ray

standard sources which would be used by all participants to calibrate their Ge(Li) spectrometers. Participants then received a set of blind samples from NBS

which they measured as unknowns, and then reported

their results to NBS. This very successful exercise led

quickly to production of a set of Standard Reference

Materials. The gamma-ray spectrum from one of these

early SRMs is shown in Fig. 1. The nine principal lines

210
in the spectrum correspond to emissions from seven

nuclides which were mixed in the proportions that the

peak areas were approximately the same for a given

counting time. This allowed the user to calibrate the

system for all gamma-ray emitting fission and activation

products at one time.

Hutchinson built on this example and organized a

wider group of laboratories to consider the more

difficult problems of environmental radioactivity in

natural matrices. This led to a meeting of the International Committee on Radionuclide Metrology

(ICRM) at Woods Hole, Massachusetts, in October of

1977. Participants considered the global problem of

radioactivity in the environment and the standards that

would be needed, as well as the required research in

radiochemistry and the physics of low-level counting.

Recommendations were made to produce standards of

biological materials, soil, sediments, and waters, each to

be certified for as many radionuclides as possible [14].

Hutchinson recruited Kenneth Inn, a young chemist

from Arkansas, to take the lead on design of sampling

and preparation of these natural matrix SRMs. One of

the most popular of these was the Rocky Flats Soil

SRM 4353 [15]. They quickly found that the man-made

plutonium isotopes were not homogeneously distributed

in the material (as the natural uranium and thorium

were). This was due to the presence of hot particles

in the soil from operations at the Rocky Flats plant in

Colorado. In the past when Mann had encountered

statistical problems in data analysis, he had turned

to Bureau statisticians W.J. Youden and H.H. Ku. To

help with the statistical analyses of these new data,

Hutchinson and Inn turned to Walter Liggett and James

Filliben. Their joint papers [15] provide a model for the

interpretation of data from small samples near nuclear

facilities (for example, swipe samples taken from

nuclear facilities during International Atomic Energy

Agency inspections).

Many of the NIST technical groups have to deal with

the concepts of traceability to NIST. Mann recognized

that this would be a critical problem for the nuclear

industry, and that there would be slightly different

requirements from the pharmaceutical industry, the

nuclear utilities, the AEC (later DOE) laboratories, and

those interested in environmental measurements. The

direct and indirect traceability that he articulated in

Needs for Radioactivity Standards had the common

thread that one had to participate in a hierarchical

measurements system which involved periodic blind

testing of the laboratory’s capabilities in order to assure

traceability. The key federal regulators—the FDA for

pharmaceuticals, the EPA for the environment, and the

Fig. 1. Gamma-ray spectrum of a mixed radionuclide standard obtained with a 50 mL source positioned 2.54 cm from a 11 cm3 Ge(Li) detector.

Figure 9 in reference [1]. The lowest energy calibration point is the 88.0 keV gamma ray from 109Cd , and the highest energy point is the 1836 keV

gamma ray of 88Y.

211
Nuclear Regulatory Commission (NRC) for the power

stations—accepted these definitions from NBS and

worked with NBS and the user communities to set up

measurement assurance programs and, later, accredited

calibration laboratory programs to meet the common

needs of the users and the regulators, with NBS serving

as an impartial third party to prepare the SRMs and

solve critical measurement problems. This paper has

been widely cited in the U.S. and the international

community for the past quarter century as the White

Paper on achieving traceability in radioactivity

measurements. A few of those present at that first

meeting at Oyster Creek in 1972 were on the ANSI

Subcommittee N42.2 that prepared an American

National Standard—Traceability of Radioactive Sources

to the NIST and Associated Instrument Quality Control

[16].

Wilfrid Mann was born in Ealing in the United

Kingdom on August 4, 1908. He received his Doctorate

in Physics from Imperial College of Science and Technology in London in 1937 and did postdoctoral work

during the 1930s in Copenhagen and Berkeley. While

at Berkeley he worked with E. O. Lawrence on the

cyclotron in the Radiation Laboratory and was the

discoverer of the radioisotope 67Ga, which is still in use

in nuclear medicine [17]. His supervisor at Imperial

College was G. P. Thompson, the British physicist in

charge of the Tube Alloys project during the war years

(the British nuclear program which was incorporated

into the Manhattan Project). He had Mann assigned to

the British Embassy in Washington. His interactions

with his supervisor at the Embassy, Kim Philby, and

another coworker there, Guy Burgess, gained Wilfrid

considerable notoriety when the two were implicated

in one of the biggest spy scandals of the century. In

memoirs written much later [18], Wilfrid was able to

show that he was not involved in nuclear matters while

stationed in Washington and could not have taken

part in their nefarious activities. Following his tour in

Washington, Thompson assigned Mann to work with

Sir John Cockcroft at the Canadian nuclear facilities at

Chalk River. At this point he began careful measurements to intercompare the national radium standards of

the UK, Canada, and the United States. This work was

continued when he came to NBS in 1951 as the head of

the Radioactivity Section. For the next 40 years Wilfrid

Mann was one of the most influential researchers in his

field. At intervals of a few years over this period of

four decades Mann prepared books, handbooks, and

extended monographs to describe completely the

current state of the art in radionuclide metrology. The

first of these were NBS Circular 594 [4] in 1958 and

NBS Handbook 80 in 1961 [19]. These were followed

by a book Radioactivity and Its Measurement with

Samuel Garfinkel in 1966 and an expanded second

edition with Robert Ayres in 1980 [20]. Following his

retirement from NBS in 1980, he collaborated with

Albrecht Rytz and Alfred Spernol on Radioactivity

Measurements: Principles and Practice [21]. Perhaps

his most lasting contribution to metrology was the

monumental task of editing A Handbook of Radioactivity Measurements Procedures [22], NCRP Handbook 58. The first edition was published in 1978; the

second in 1985 sold more copies than any other

handbook of the NCRP and set out the principles of

radionuclide metrology for a generation.

Prepared by Bert Coursey.

Bibliography

[1] L. M. Cavallo, B. M. Coursey, S. B. Garfinkel, J. M. R.

Hutchinson, and W. B. Mann, Needs for Radioactivity

Standards and Measurements in Different Fields, Nucl. Instrum.

Methods 112, 5-18 (1973).

[2] N. Ernest Dorsey, Physics of Radioactivity, Williams and

Wilkins, Baltimore, MD (1921).

[3] Bert Coursey and Johnathan Coursey, Marie Curie and the NBS

Radium Standards, (http://www.physics.nist.gov/GenInt/Curie/

main.html), National Institute of Standards and Technology.

[4] H. H. Seliger and A. Schwebel, Standardization of BetaEmitting Nuclides, Nucleonics 12 (7), 54-63 (1954).

[5] W. B. Mann and H. H. Seliger, Preparation, Maintenance, and

Application of Standards of Radioactivity, National Bureau of

Standards Circular 594, U.S. Government Printing Office,

Washington, DC (1958).

[6] Ad Hoc Panel (L. R. Zumwalt, Chair) of the Committee on

Nuclear Science, National Research Council, (U.S.), National

Uses and Needs for Standard Radioactive Materials: A Report,

National Academy of Sciences, Washington, DC (1970).

[7] R. Colle ́, AIF-NBS Radioactivity Measurements Assurance

Program for the Radiopharmaceutical Industry, in Measurements for the Safe Use of Radiation, Sherman P. Fivozinsky

(ed.), NBS Special Publication 456, National Bureau of

Standards, Washington, DC (1976) pp. 71-76.

[8] Robert L. Ayres and Alan T. Hirshfeld, Radioactivity Standardization of 99mTc and 99Mo, Int. J. Appl. Radiat. Isot. 33, 835-841

(1982).

[9] Daniel B. Golas, NIST Radiopharmaceutical Standard Reference Materials and the NEI/NIST Radiopharmaceutical Measurement Assurance Program, Appl. Radiat. Isot. 49, 329-334

(1998).

[10] B. M. Coursey, Radionuclides for Bone Palliation, Special Issue

of Appl. Radiat. Isot., Vol. 49, No. 4, April 1998.

[11] A. N. Link, Economic Evaluation of Radiopharmaceutical

Research at NIST, Planning Report 97-2, National Institute of

Standards and Technology, Gaithersburg, MD (1997); and B. M.

Coursey and A. N. Link, Evaluating Technology Based Public

Institutions: The Case of Radiopharmaceutical Standards

Research at the National Institute of Standards and Technology,

Res. Eval. 7, 147-157 (1998).

[12] J. M. R. Hutchinson, W. B. Mann and P. A., Mullen, Sum-Peak

Counting with Two Crystals, Nucl. Instrum. Methods 112, 187-

196 (1973).

[13] Lloyd A. Currie, Limits for Qualitative Detection and Quantitative Determination. Application to Radiochemistry, Anal. Chem.

40, 586-593 (1968).

212
[14] J. M. R. Hutchinson, International Committee for Radionuclide

Metrology Newsletter: Report of the Woods Hole Conference

on Development of Naturally Contaminated Radioactivity

Standards, Environ. Int. 2, 49-50 (1979).

[15] K. G. W. Inn, W. S. Liggett, and J. M. R. Hutchinson, The

National Bureau of Standards Rocky Flats Soil Standard

Reference Material, Nucl. Instrum. Methods 223, 443-450

(1984).

[16] American National Standard—Traceability of Radioactive

Sources to the National Institute of Standards and Technology

(NIST) and Associated Instrument Quality Control, ANSI

N42.22-1995, Institute of Electrical and Electronics Engineers,

New York (1995).

[17] Wilfrid B. Mann, Nuclear Transformations Produced in Zinc by

Alpha-Particle Bombardment, Phys. Rev. 54, 649-652 (1938).

[18] Wilfrid Basil Mann, Was There a Fifth Man?: Quintessential

Recollections, Pergamon Press, Oxford (1982).

[19] W. B. Mann (ed.), A Manual of Radioactivity Procedures,

National Bureau of Standards Handbook 80 (NCRP Report No.

28), U.S. Government Printing Office, Washington, DC (1961).

[20] W. B. Mann, R. L. Ayres and S. B. Garfinkel, Radioactivity and

Its Measurement, Second Edition (SI Units), Pergamon Press,

Oxford (1980).

[21] W. B. Mann, A. Rytz, A. Spernol, and William L. McLaughlin,

Radioactivity Measurements: Principles and Practice, Pergamon Press, Oxford (1988).

[22] W. B. Mann (ed.), A Handbook of Radioactivity Measurements

Procedures, 2nd Edition, (NCRP Report No. 58) National

Council on Radiation Protection and Measurements, Bethesda,

MD (1985).

213
The Topografiner: An Instrument for

Measuring Surface Microtopography

Russell Young, John Ward, and Fredric Scire published their paper on the topografiner in 1972 [1].

Nearly 30 years later, it is tempting to say that scanning

probe microscopy (SPM) needs no introduction. The

number of papers concerning this technique is now

approaching 5000 per year (Fig. 1), so that hardly any

technical professional with an interest in microscopy

can have escaped acquaintance with one or more of its

variants. The explosion of SPM activity began after

publication of atomic resolution images of silicon [2] in

1983 and the award of the Nobel Prize in Physics to

Binnig and Rohrer in 1986 made scanning tunneling

microscopy (STM) famous. Today, SPM has found

applications in physics (e.g., crystal and surface

electronic structure of metals and semiconductors,

superconductivity, liquid crystals), chemistry (e.g.,

catalysis, electrochemistry, Langmuir-Blodgett films,

polymer morphology), biology (structure of nucleic

acids, cells, proteins, lipids, etc.) and other fields.

A recent chemistry-oriented review [3] referenced 33

other SPM-related reviews and books published in the

preceding 2-year period alone!

There are four essential elements of a scanning probe

microscope that distinguish it from other microscopes:

1) a very sharp mechanical probe, the tip of which is

maintained in close proximity to the sample surface;

2) detection of a surface property (e.g., a tunneling

current) that changes rapidly in the vicinity of the

surface and therefore provides a very sensitive indicator

of the tip-sample distance; 3) use of an electronic

feedback system to control the tip-sample distance or to

maintain a controlled low-force contact—essential to

prevent damage to the sharp tip; and 4) the ability to

position the tip with respect to the sample in three

dimensions with sub-nanometer resolution, as for

example through the use of piezoelectric devices. In

the earliest implementations, a voltage was applied

between the tip and a conducting sample. The feedback

system maintained the resulting field emission or tunneling current at a constant value by adjusting the tip height

as needed. The tip was then raster-scanned laterally

across the surface (Fig. 2). The feedback loop responded

by moving the tip normal to the surface, thereby tracing

the surface topography at constant current and therefore

approximately constant tip-sample separation. The

resulting adjustments to the tip position were monitored,

and they formed a record, to first approximation, of the

surface topography. Other scanning probe microscopies

use other near-surface properties, for example tipsample force (AFM) or capacitance (SCM). Sometimes

one property is monitored for feedback purposes while

the image is formed from another, as in NSOM

(near-field scanning optical microscopy).

The first successful scanning probe microscope was

Russell Young’s topografiner [1]. In this instrument, a

field emission current between the tip and sample was

employed for feedback control. The Royal Swedish

Fig. 1. Growth of publications in scanning probe microscopy, as

determined by searching the ISI Science Citation Index.

Fig. 2. Scanning the tip across a surface. This figure is from Ref.

4, where the concept of what eventually became the topografiner

was first described.

214
Academy of Sciences’ press release announcing Binnig

and Rohrer’s Nobel prize for the scanning tunneling

microscope gave substantial attention to Young’s work:

“The first to succeed in doing this [building an instrument that operated on the principle of maintaining a

small constant distance between the sample surface and

a sharp mechanical stylus] was the American physicist

Russell Young at the National Bureau of Standards in

the USA. He used the phenomenon known as field

emission . . . However, Young realized, that it should

be possible to achieve better resolution by using the

so-called tunnel effect.” [5]

A schematic of the topografiner is shown in Fig. 3.

The specimen was mounted between spring- loaded

copper clamps. This permitted thin specimens, for

example replicas, to be held taut. An electrical current

through the specimen could heat it for cleaning. A tungsten tip was attached to molybdenum bridges between

two molybdenum rods. The emitter could be heated for

cleaning by passing current through the bridges to

which it was attached. The emitter assembly was

mounted on a vertical “piezo.” Piezoelectric ceramic

materials expand and contract with applied voltage,

producing continuously controllable motion with subnanometer resolution and a typical range of a few

micrometers. The sample was brought into range of this

device using a differential screw, which itself had a

range of a bit more than 250 m. The sample and tip

were originally placed within this distance of each other

manually, using an optical microscope to view the

tip-sample separation and making coarse adjustments

using the threaded connection in the tube that joined the

tip assembly to the specimen assembly. The X and Y scan

piezos deflected the rod supporting the emitter, thereby

producing motion of the tip in the plane of the

specimen.

The tip-sample separation was maintained by a feedback controller that adjusted the voltage on the vertical

piezo to maintain a constant current through the tipspecimen junction. To form the images, the voltage

applied to this piezo was recorded with either an x-y

recorder or a storage oscilloscope during scanning.

Unlike later STMs, the topografiner was rigidly attached

to its vacuum chamber. Vibration isolation was all external. The chamber was mounted on a vibration isolation

table and enclosed by an acoustical shield. Inside,

a pressure of about 510–8 Pa (410–10 Torr) was

maintained.

Young et al. discussed several tip-sample interactions.

Two of these, field emission and metal-vacuum-metal

tunneling, were explored in some detail. When the

electric field in the vicinity of the tip is high enough,

electrons may tunnel from the metal tip through the

work-function barrier into nearby vacuum states. The

amount of current is governed by the Fowler-Nordheim

equation. This form of tunneling can work even at large

tip-sample distances, provided the potential difference is

kept high enough to create a large enough field. In

metal-vacuum-metal (MVM) tunneling, the tip and

sample are sufficiently close that electrons can tunnel

directly from one to the other. It was with this form of

tunneling that STMs later resolved individual atoms on

surfaces. Young et al. calculated that for the field and

work function expected for their operating conditions

and tip, MVM tunnel current became an important contribution for tip-sample separations less than 2 nm and

completely dominated the measured current by 1 nm.

With the servo loop inactive, Young et al. measured

current-voltage (I-V) curves at a variety of tip- sample

separations, which they estimated ranged from 1.2 nm

to 2.7 nm. At the lowest separation, they were measuring currents of up to 5 nA at voltages below 0.5 V. These

conditions would be widely regarded in light of presentday experience with STMs as being well within the

MVM tunneling regime, supporting their claim [1,6]

that these were the first recorded MVM I-V curves.

They mention several applications of MVM studies,

including the measurement of tunneling spectra, thus

anticipating scanning tunneling spectroscopy, which

was implemented by others in the early 1980s.

Fig. 3. Schematic of the topografiner (from Ref. [1]).

215
Despite the recognized advantages, the instrument

was not operated closed loop in the MVM tunneling

mode because of vibrational noise and instability in the

feedback electronics in that mode. Instead, images were

acquired in field emission mode. A section of the paper

was devoted to demonstrating that the measurements

were consistent with Fowler-Nordheim tunneling. The

imaging capability was demonstrated on a 180 line/mm

diffraction grating replica (Fig. 4). Young et al. estimated the resolution to be 3 nm perpendicular to the

surface and 400 nm in the plane. They estimated the

instrument was capable of an ultimate resolution of

0.3 nm (one atomic layer) perpendicular to the surface,

limited by noise, and 20 nm in the lateral direction,

limited by tip radius.

In yet another imaging mode, secondary electrons

generated by the field emitted electrons upon impact

with the sample were collected by a nearby electron

multiplier (see Fig. 3). The secondary yield as a function

of tip position produced an image of the surface

analogous to that created in a scanning electron microscope. This is interesting because it implements an

imaging mode in which a property of the surface other

than the one being employed by the feedback system is

used to create images. The detector does not need to

have focusing optics in order to determine the source of

the particles because the tip localizes the excitation.

This mode anticipated similar strategies employed later,

for example the collection of photons generated at the

tunnel junction of an STM.

The development of the topografiner began in the

context of a burst of surface studies following World War

II, when many new surface analysis techniques were

becoming available. In the late 1960s surface scientists

sought to study single-crystal surfaces, where theory

and experiment could be compared in the study of

corrosion, catalysis, surface electronic properties, and

other surface properties of importance to the nascent

microcircuit industry.

At NBS, Young collaborated closely with other

surface scientists (see the account in this volume on

Resonance Tunneling of Field Emitted Electrons

through Adsorbates on Metal Surfaces). The seeds of

the ideas leading to the topografiner are discernible in

Young’s prior experiences. Before receiving his B.S.

degree in physics, he served in the military for three

years during World War II. Concerning this time, he

said, “I used radar to automatically track enemy planes

and simultaneously direct antiaircraft guns to intercept

them. Tight servo loops were used to lock in the plane’s

position. I had previously studied television theory

which uses a raster scan to form the picture.” During

and immediately after his Ph.D. studies, he was active in

the study of field emission, attracting wide attention,

for example, for an important paper on the energy

distribution of emitted electrons as a probe of the

electronic state of surfaces [7]. It was natural, given his

search for a new surface characterization microscope,

for Young to combine these technologies.

In 1966, Young investigated and published the performance of an instrument he called the field emission

ultramicrometer [4]. This was a device for sensing

surfaces with a field emission tip and measuring

distances or displacements. It resembled the topografiner in its use of field emission as a probe of

tip-sample separation, but did not use feedback to

control the separation and did not have the capacity to

scan the tip in the plane of the sample. In the final figure

of that paper, part of which is reproduced here as

Fig. 2, Young suggested the addition of these elements to

create a microscope with extremely high vertical

resolution that could record the detailed contour of a

complex surface.

Fig. 4. Topographic map of ruled diffraction grating with the

Topografiner. Labeled distances are in ångstro ̈ms. 1 Å = 0.1 nm.

(From Ref. [1]).

216
In 1969 a project to carry out this plan was approved

by NBS management. Young was able to employ a

technician, Fredric Scire. Starting with the availability

of laboratory space in 1970, Scire and Young worked

closely together designing, constructing, testing, and

publishing the topografiner investigation. John Ward

joined the project after the instrument had been substantially constructed. He developed tip preparation

methods and performed early experiments on operation

of a field emission probe in air. The electronic characteristics and sensitivity of the topografiner, and the

observation of metal-vacuum-metal tunneling with it,

were described in 1971 [6]. The instrument’s first

published images were included in Young’s review of

surface microtopography techniques for Physics Today

[8]. In July of 1971, shortly before publication of those

articles, NBS management terminated the topografiner

project to concentrate effort into a program to provide

calibration artifacts to the microcircuit industry. The

final design of the instrument, together with the theory

of its operation and its actual performance, were

afterwards published in the title paper [1].

Today, we have the advantage of many years of

instrument development, tens of thousands of publications by researchers all over the world, and the commercial production of SPMs, which have become a ubiquitous and relatively inexpensive tool. But Young and his

coworkers were breaking new ground with the topografiner, not following any existing recipe. If first attempts teach anything, then second attempts must be

better, so it is no surprise that the topografiner had

deficiencies compared to current instruments. But the

remarkable thing, from the perspective of a modern

SPM researcher, is the soundness of judgement with

which Young, Ward, and Scire analyzed the deficiencies

of their own instrument and planned improvements to it.

For example, the topografiner differed from current

implementations of the STM by the absence, in the

topografiner, of a logarithmic or otherwise variable

amplifier in the feedback control circuit. With the

benefit of experience, we can say that this is most likely

the reason the topografiner’s feedback control became

unstable in MVM tunneling mode. The exponential

increase of tunnel current with decreasing tip-sample

separation means the servo loop gain increases exponentially as the tip enters tunneling range. The high gain

coupled with inevitable mechanical resonances results

in an unstable amplifier condition. Remarkably, Young

had correctly diagnosed the problem. The paper

included a graph of servo loop gain for various tipsample separations and described the resulting instability. At the time the project was cancelled Young’s

proposed program included a task to “Develop improved

servo loop with ability to handle variable gain feature

inherent in field emission devices... ” [9]. This

improvement alone might have made possible the

acquisition of images in MVM tunneling mode.

The instrument also had in common with Binnig and

Rohrer’s first STM a rather soft mechanical loop. The

resulting low resonance frequencies exacerbate

feedback loop stability problems, forcing the instrument

to be operated at lower scan rates. Later instruments

raised the mechanical resonance frequency by reducing

the amount of mass that had to be moved by the z piezo

and making the mechanical loop between the sample

and the tip as small as possible. Young et al. commented

in their section on the servo loop that “these mechanical

resonances, which must be eliminated in the next

generation of the instrument, cause phase shifts and thus

servo loop instabilities.”

As mentioned earlier, the topografiner was rigidly

attached to its vacuum chamber. Beginning with Binnig

and Rohrer, vibration isolation systems for SPMs

include an isolation level between the instrument and its

vacuum chamber (if there is one). This greatly reduces

the transmission of acoustical noise, picked up by the

large vacuum chamber, to the instrument. Instead, the

topografiner was surrounded by an acoustical isolation

shell. Even without internal vibration isolation, the

topografiner demonstrated noise levels as low as 0.3 nm.

This level of noise would not have prevented scanning in

MVM tunneling mode, and its reduction would have

been an evolutionary improvement.

The achievements of the project are better appreciated by reflecting upon some of the difficulties with

which the principals had to contend. The topografiner

did not have computerized data acquisition, taken for

granted in today’s instruments. The first integrated

circuit computers were only beginning to be available at

the time of the project (The PDP 8 was introduced in

1970), so data acquisition was with x-y recorder

and storage oscilloscope. Feedback circuitry was a

challenge. Severe funding limitations prevented the

purchase of modern electronic equipment.

Perhaps chief among their difficulties was the

difficulty inherent in being the first in any exploration.

One to a certain extent stumbles around in the dark,

aware of some goals without knowing precisely how to

reach them and perhaps completely unaware of other

treasures that may lie within reach. One such was

atomic resolution. The possibility of laterally resolving

individual atoms by such a technique was not suspected

by anyone at that time. Young et al., and later Binnig and

Rohrer, at first viewed tips as “a kind of continuous

matter with some radius of curvature” [10]. The lateral

resolution was therefore expected to be limited to

something on the order of the tip radius, at that time

approximately 100 nm for state of the art field emission

217
tips. Images of atoms were an unexpected gift, a consequence of the existence of minitips or other roughness

on the tip surface, together with the strong distance

dependence of tunneling, which causes the nearest

minitip to dominate.

We should not let speculation about could-have-beens

detract from the accomplishment that was. In the space

of the two years from first funding to project termination, Young et al built a new kind of microscope which

was non-contacting, non-damaging, capable of three

dimensional imaging, and which compared favorably in

its topographic resolution to the best instruments of the

time. They demonstrated a new principle of operation,

analogs of which are now making significant contributions to every area of microscopy. And they obtained

the first I-V characteristic curves for metal-vacuummetal tunneling.

In addition to the notice, already mentioned, in

the 1986 Nobel citation, Russell Young received a

Presidential Citation in 1986. In 1992 he received the

Gaede-Langmuir Award from the American Vacuum

Society “for his invention of the Topografiner, an

instrument which led to the development of the

scanning tunneling microscope.” Today, the topografiner resides at the Smithsonian Institution.

Prepared by J. S. Villarrubia, with assistance from R. D.

Young, F. Scire, E. C. Teague, and J. W. Gadzuk.

Bibliography

[1] R. Young, J. Ward, and F. Scire, The Topografiner: An Instrument for Measuring Surface Microtopography, Rev. Sci.

Instrum. 43, 999-1011 (1972).

[2] G. Binnig, H. Rohrer, Ch. Gerber, and E. Weibel, 77 Reconstruction on Si(111) Resolved in Real Space, Phys. Rev. Lett. 50,

120-123 (1983).

[3] L. A. Bottomley, Scanning Probe Microscopy, Anal. Chem. 70,

425R-475R (1998).

[4] R. D. Young, Field Emission Ultramicrometer, Rev. Sci. Instrum.

37, 275-278 (1966).

[5] Press release, Royal Swedish Academy of Sciences, October 15,

1986 (Text in brackets not in original).

[6] R. Young, J. Ward, and F. Scire, Observation of Metal-VacuumMetal Tunneling, Field Emission, and the Transition Region,

Phys. Rev. Lett. 27, 922-924 (1971).

[7] R. D. Young, Theoretical Total-Energy Distribution of FieldEmitted Electrons, Phys. Rev. 113, 110-114 (1959).

[8] R. D. Young, Surface microtopography, Phys. Today 24 (11),

42-49 (1971).

[9] R. D. Young, memorandum to Dr. John Simpson, July 19, 1971.

[10] G. Binnig and H. Rohrer, Scanning Tunneling Microscopy—

from Birth to Adolescence, Rev. Mod. Phys. 59, 615-625 (1987).

218
Electron-Stimulated Desorption

It has now been almost 30 years since the 1971

review article entitled Electron-Stimulated Desorption

as a Tool for Studies of Chemisorption: A Review [1]

appeared. At that time, the authors, Theodore Madey

and John Yates, were young scientists working together

in the Surface Chemistry Section of the Physical

Chemistry Division of NBS. Few could have predicted

that the subject of this review would multiply and remultiply, until today the electron-stimulated desorption

phenomenon and a number of related subjects form a

cornerstone of chemistry and physics on surfaces—and

that the personal collaboration forged at the time would

last for 19 years at NBS, resulting in over 100 joint

publications, as well as a deep and lasting friendship.

Surface chemistry is traditionally driven by the

thermal excitation of adsorbed species. In areas such

as heterogeneous catalysis, thin film deposition by

chemical vapor deposition, and corrosion passivation,

one often thinks only of thermally-driven surface

processes. In the late 1960s, quantitative studies of the

thermal desorption of molecules chemisorbed on single

crystal surfaces were just beginning. Questions about

molecular dissociation and atom recombination processes were being studied on well-defined single crystal

surfaces for the first time, both by Yates and Madey at

NBS and by other investigators. In this fundamental

work simple molecules, such as H2, CO, N2, CH4, and

NO, were employed so as not to make the chemistry

complex.

The study of desorption processes initiated by

electronic excitation instead of thermal excitation represented a departure from conventional research activities

at the time and provided a special personal fascination

for the authors which has to the present remained

strong. The desorption of adsorbed species by nonthermal processes (i.e., electronic activation) became a

new focus of the work starting about 1965. As a consequence of their work, Madey and Yates were invited by

P.A. Redhead (a pioneer in electron stimulated surface

processes, and the editor of the Journal of Vacuum

Science and Technology) to write a critical review of

what was being done worldwide in the area of electron

stimulated desorption, a surface phenomenon which had

already received the acronym ESD.

It is interesting to note that the title of the review

contains the word “Tool.” In 1971, many new surface

measurement techniques were being devised in the

surface physics community and were being transferred

to some degree to the surface chemistry, engineering,

and materials science communities in the form of exciting and useful new tools for research. The workers at

NBS were inclined to think of ESD as a new measurement method for the study of adsorption. The review

uncovered more than 100 papers dealing with phenomena related to ESD, extending back to 1918. At the time

of the writing of the review, the vast majority of the

important papers had been written within the previous

10 years. The most influential work had been done

independently by Menzel and Gomer [2, 3] and by

Redhead [4] in 1964. The basic electronic excitation

mechanism for ESD is now termed the MGR mechanism worldwide in honor of their central contribution.

The 1971 review summarized the experimental

methods that had been employed to date for the study of

ESD, the theoretical foundation for thinking about the

electronic excitation on the surface, and the subsequent

desorption process. The authors also included almost all

of the particular chemical systems that had been

studied by ESD at the time. Since positive ionic

fragments are often liberated in ESD, the review

contains a number of examples of the use of mass

spectrometers and other devices as ion detectors.

It also contains criticisms of certain mechanistic

ideas which were in the literature, as well as a selection

of experimental data that were regarded as being

the most reliable (including much of the authors’ own

data).

In addition to electron-impact induced adsorbatesurface bond breaking (desorption), molecules on

surfaces may be chemically converted to other species

by electron impact, and the review article illustrated this

by including one of the authors’ own studies in which

adsorbed N2 molecules were converted to adsorbed N

atoms on a tungsten surface, one of the first examples of

this phenomenon.

The review was 30 pages long and contained 152

references. It was not possible in a review of that length

to do justice to all of this information. In order to

summarize the work in these papers, a table was devised

to list the principal findings; this table was arranged

chronologically and by the adsorbate/adsorbent system

and the experimental method. Not surprisingly, work on

tungsten and molybdenum surfaces dominated, since

during much of the 10 years prior to the review, it was

known that atomically clean surfaces of these elements

could be prepared through high temperature heating in

ultrahigh vacuum. Much of this work was done without

the luxury of Auger spectrometers for surface analysis.

219
Since 1971, well over 1000 papers on ESD have been

published. Both Yates and Madey have published

additional review articles in the field [5-8], and in 1991

65 reviews of ESD existed in the literature [6]. The

acronym ESD, while still employed, has been replaced

somewhat by the more encompassing acronym DIET

(Desorption Induced by Electronic Transitions). An

international meeting on this topic is held every two and

a half years; the eighth meeting, organized in 1999

at Rutgers University by Ted Madey, attracted 80

attendees. The acronym DIET includes electronic

excitation by photons as well as electrons, and in recent

years photodesorption has become a dominant area

in which both authors are working at their separate

universities.

The writing of the review article was carried out on

two continents. John Yates was working in Britain at the

time, and many mailings of manuscript and figures were

done in both directions to meet deadlines. One of the

critical mailings from Britain was lost (and never found)

as a result of the use of the Armed Forces mailing

system because of a mail strike in Britain. The authors

were caught off guard after publishing the 1971 review,

since they were soon notified that it had become a

Science Citation Classic by Citation Indices. They later

remarked to Paul Redhead, “If we had thought we were

writing a Classic, we would have written it in Latin.”

One of the most exciting developments emanating

from this collaboration had to do with the discovery

of the ESDIAD (electron stimulated desorption ion

angular distribution) phenomenon in 1974. Here the

positive ion desorption products were found to be

ejected in sharp beams whose direction was closely

related to the direction of the chemical bond being

ruptured in the electronic excitation process [9]. Fig. 1

shows the early ESDIAD apparatus and the three

authors of the first paper, as well as photographic

images of the ion angular distributions obtained.

Both Yates and Madey have left NBS for the academic

world, and many honors have come to them, leading to

professional recognition not only for the collaborative

work done at NBS, but also for more recent work done

independently at the University of Pittsburgh and at

Rutgers University. The early work at NBS was centrally important to their professional development and to

many of the rich opportunities they experienced since

leaving government service. Indeed, the period from

1963 to the 1980s was generally one of extraordinary

freedom in research at NBS in the field of surface

science. Other NBS staff members who were their

colleagues or friends and who numbered among the

founders of the field include E. W. Plummer, J. W.

Gadzuk, R. D. Young, C. J. Powell, A. Melmed, R.

Klein, and M. D. Scheer. The research benefited from

the support of the Administration at NBS during this

time, both at the Director’s level (A. Astin, L.

Branscomb, R. Roberts, E. Ambler) and at intermediate

levels (M. B. Wallenstein, J. D. Hoffman, J. McNesby,

M. D. Scheer, and R. Klein). Without excellent

scientific colleagues and visionary administrators, NBS

would not be historically recognized for its important

role in establishing, and continuously nurturing to this

day, the exciting and technologically important field of

surface science.

It is appropriate to complete this account by citing

recent articles from each of the authors’ laboratories

which are connected conceptually to the ESD

phenomenon. In the first example, a photochemical

dissociation process, involving an oriented O2 molecule

chemisorbed with its O-O axis parallel to the step-edge

sites of a Pt single crystal, is found to preferentially eject

an O atom toward a neighboring CO molecule to produce CO2 which then desorbs [10]. This selectivity measured for target CO molecules on the step sites compared to CO molecules located on the terrace sites is

termed surface aligned photochemistry (SAP), and is

schematically illustrated in Fig. 2. This is the first

observation of SAP involving molecular alignment on a

stepped single crystal template.

The second example addresses an issue that has long

puzzled planetary astronomers: what is the origin of the

copious atomic sodium vapor in the rarefied atmosphere

of the planet Mercury, and of our Moon? An image of

this effect is shown in Fig. 3. A detailed DIET study of

a model system (sodium atoms and ions adsorbed on

SiO2 surfaces, simulating moonrocks) identified the

likely scenario: when ultraviolet light from the sun

strikes the lunar surface, it excites the surface electronically and causes desorption of sodium atoms [11].

Electrons in the solar wind can also cause ESD of

sodium from the lunar surface, but the more plentiful

solar photons are the main culprits.

In conclusion, ESD and other DIET processes today

impact a host of scientific issues, including structure and

dynamics of adsorbed molecules, quantum stateresolved desorption, dynamics of charge transfer, and

surface photochemistry. DIET processes also provide

insights into the science and technology of radiation

damage, which affects quantitative surface analysis

using electron and photon beams, partial pressure

measurements, stability of x-ray optics, electron- and

photon-beam lithography, and molecular synthesis

in interstellar space. ESD and DIET continue to be scientifically exciting, growing fields!

Prepared by Ted Madey and John Yates.

220
Fig. 1. (a) 1974 photograph of the first NBS ESDIAD system, a hybrid of glass and metal. From left to right,

T. E. Madey, J. T. Yates, Jr., and J. J. Czyzewski. Madey’s left hand is pointing to the ESDIAD tube; the ESDIAD

patterns were photographed from below (from [9]).

(b) ESD Ion Angular Distribution (ESDIAD) patterns for desorption of oxygen ions (O+

) from W(100). This

sequence shows the effect of heat treatment on ESD patterns for oxygen on W(100).

Temperatures corresponding to each pattern are (a) <400, (b) 630, (c) 705, (d) 795, (e) 865 and (f) 930 K

(from [9]).

221
Fig. 2. Surface Aligned Photochemistry—The most probable reaction process is

illustrated for the photoexcitation of adsorbed O2 on a step site on a Pt single crystal

and leading to reaction with step-bound CO molecules to produce CO2 [10].

Fig. 3. Image of lunar sodium atmosphere due to DIET from the

lunar surface [11,12].

222
Bibliography

[1] Theodore E. Madey and John T. Yates, Jr., Electron-Stimulated

Desorption as a Tool for Studies of Chemisorption: A Review,

J. Vac. Sci. Technol. 8, 525-555 (1971).

[2] D. Menzel and R. Gomer, Desorption from Metal Surfaces by

Low-Energy Electrons, J. Chem. Phys. 41, 3311-3328 (1964).

[3] D. Menzel and R. Gomer, Electron-Impact Desorption of

Carbon Monoxide from Tungsten, J. Chem. Phys. 41, 3329-3351

(1964).

[4] P. A. Redhead, Interaction of Slow Electrons with Chemisorbed

Oxygen, Can. J. Phys. 42, 886-905 (1964).

[5] T. E. Madey, Electron- and Photon-Stimulated Desorption:

Probes of Structure and Bonding at Surfaces, Science 234, 316-

322 (1986).

[6] R. D. Ramsier and J. T. Yates, Jr., Electron-Stimulated Desorption: Principles and Applications, Surf. Sci. Rep. 12, 243-378

(1991).

[7] J. T. Yates, Jr., J. Ahner and D. Mocuta, Tracking the Motion of

Chemisorbed Molecules on Their Adsorption Sites, Proc. Natl.

Acad. Sci. U.S.A. 95, 443-449 (1998).

[8] T. E. Madey, History of Desorption Induced by Electronic

Transitions, Surf. Sci. 299/300, 824-836 (1994).

[9] J. J. Czyzewski, T. E. Madey, and J. T. Yates, Jr., Angular

Distributions of Electron-Stimulated-Desorption Ions: Oxygen

on W(100), Phys. Rev. Lett. 32, 777-780 (1974).

[10] C. Emil Tripa and J. T. Yates, Jr., Surface-Aligned Reaction of

Photogenerated Oxygen Atoms with Carbon Monoxide Targets,

Nature 398, 591-593 (1999).

[11] B. V. Yakshinskiy and T. E. Madey, Photon-stimulated Desorption as a Substantial Source of Sodium in the Lunar Atmosphere,

Nature 400, 642-644 (1999).

[12] A. E. Potter and T. H. Morgan, Coronagraphic observations of

the lunar sodium exosphere near the lunar surface, J. Geophys.

Res.—Planets 103, 8581-8586 (1998).

223
Photochemistry of Small Molecules

The classic text book in photochemistry is that of

Noyes and Leighton, The Photochemistry of Gases

published in 1941. In 1966, a comprehensive volume by

Calvert and Pitts brought the field up to date, but it soon

became obvious that the field of photochemistry was

expanding too rapidly to be covered in a single comprehensive volume. In fact, in the latter part of the 20th

century organic photochemistry and physical photochemistry existed as separate disciplines with largely

separate constituencies. Organic photochemistry included such molecules as methane (CH4), whereas NO

and other oxides of nitrogen are inorganic. The book by

Hideo Okabe, Photochemistry of Small Molecules [1],

published in 1978, is so titled to convey the author’s

intent to include both organic and inorganic molecules,

but to direct his attention to simple molecules of both

genres. The author’s definition of “small” as five or

fewer atoms is arbitrary and, unfortunately, excludes

much of his own seminal work on the photochemistry of

ethane and propane, which contain eight and eleven

atoms respectively.

In his Photochemistry of Small Molecules Okabe

provides an elegant discussion of the spectroscopy of

atoms and molecules as well as of the rotational, vibrational, and electronic energy states. In photochemical

research, small molecules often have discrete electronic

spectra, and any discussion of mechanisms of photochemical reactions must be consistent with these

spectra. Accordingly, Okabe gives special attention to

the details of what was known about the spectra. He

systematically presents chapters on photochemistry and

spectroscopy of diatomic, triatomic, and polyatomic

molecules (i.e., four and five atom) in Chapters V, VI

and VII of the book. His discussion of the basis of

photochemical correlation rules and selection rules is

very thoroughly presented. His knowledge of the relevant spectroscopy is at a very high level, and his incorporation of spectroscopic aspects into his discussion of

the photochemistry, if not unique, is certainly extraordinary.

Okabe’s subject, the photochemistry of small

molecules, came into prominence in the 1960-1980

period just at the time when planetary modelers were

struggling to provide a quantitative understanding of the

chemistry of the atmospheres of the giant planets and

their moons. The key molecules were methane and

ammonia, and the electromagnetic radiation driving the

chemistry was the Lyman alpha solar emission line in

the vacuum ultraviolet at 121.6 nm. It was Okabe and his

NBS colleagues who provided much of the hard science

in support of this objective. The table had been set for

the writing of this scholarly book by the appearance in

1964 of a review of the field of vacuum ultraviolet

(VUV) photochemistry by McNesby and Okabe [2].

The long term impact of Okabe’s work is illustrated by

Nobel Laureate Roald Hoffmann’s devoting a chapter in

his 1995 book [3] to Okabe’s 1961 paper on the photolysis of ethane [4] (“a text book case for the application

of the scientific method”). Another Nobel prize winner,

Yuan T. Lee, published a paper in 1999 [5] with his

colleagues in which testimony is given that Okabe was

the discoverer of molecular elimination of hydrogen in

VUV photolysis of hydrocarbons. The Lee paper was

the first in which molecular elimination from propane

was studied using very sophisticated techniques not even

imagined at the time of Okabe’s 1961 discovery. Lee

and coworkers used 157 nm laser excitation of propane

and employed photofragment translational spectroscopy

to measure directly the site-specific molecular elimination of hydrogen. They determined that the elimination

of molecular hydrogen from the central carbon atom

was the dominant process. This is what Okabe concluded 37 years earlier on the basis of experiments with

deuterated propanes [6,2].

As a result of the book and his series of research

papers, Okabe became widely known as a leader in the

field of vacuum ultraviolet photochemistry. There have

been more than 600 (non-self) citations to Photochemistry of Small Molecules, and it continues to be

regarded as the definitive text on this subject.

Prior to Okabe’s work at NBS (which extended from

1959 to 1983), little attention was given to photochemical requirements for measurements in the vacuum

ultraviolet, such as spectral purity of light sources,

appropriate window materials, and the effect of temperature on the transmittance of these materials. When he

first joined the photochemistry group at NBS, he was

given the choice of a project to pursue, but was urged to

consider photochemistry in the vacuum ultraviolet and

soon made this commitment. He quickly recognized the

necessity of establishing the purity and monochromaticity of his light sources. Early attempts to study VUV

photochemistry with electroded resonance lamps were

plagued by outgassed impurities which made it impossible to know the active wavelengths in the photolysis.

Okabe’s meticulous methods produced the first high

224
intensity rare gas resonance lamps with outputs of

essentially pure wavelength. He achieved this by use of

a scanning vacuum monochromator to establish the

purity of the resonance lines of xenon, krypton, and

argon, the first time this powerful technique was used by

a photochemist. The simplicity of the design of the

resonance lamps is illustrated in Fig. 1. By powering the

light sources with a microwave generator and gettering

the impurities, light sources of spectacular chromatic

purity were produced (Fig. 2), which facilitated studies

of the photolysis of small molecules in the vacuum

ultraviolet.

There was particular interest in the NBS group in

studying the kinetics of the reactions of methyl (CH3)

radicals. Virtually all such studies had been done by

producing CH3 by near ultraviolet photolysis of such

large molecules as acetone. The difficulty always was

the concurrent formation of large organic fragments accompanying the methyl radicals and the complications

attending the resulting chemistry. The simple solution to

these problems seemed rather obvious—to photolyse

ethane (CH3-CH3) since the conventional wisdom

was that the weaker C-C bond would break, producing

nothing but methyl radicals. What Okabe learned very

quickly came as a tremendous surprise to him and to his

colleagues. The conventional wisdom was wrong: the

reaction product was almost entirely hydrogen rather

than the expected methane. Further experiments with

deuterium strategically placed at various locations in the

molecule gave still more surprising results—that the

molecular hydrogen produced came nearly exclusively

by molecular elimination from one end of the molecule,

not one hydrogen atom from each carbon atom.

This result was to change everyone’s thinking about

VUV photochemistry of ethane and other simple

hydrocarbons of planetary interest, because the major

planetary light source, Lyman alpha at 121.6 nm, had

nearly the same frequency as the krypton resonance line

at 123.6 nm. The extension of this research to methane

photolysis, where H2 was also found to be ejected,

caused modelers of atmospheric dynamics of the giant

planets, which are rich in methane, to alter their models.

This result attracted the attention of NASA, which then

partially supported the NBS work for a number of years,

with the objective not only to understand planetary

atmospheric dynamics but also to satisfy their well

known interest in the origin of life in the solar system.

In all cases the key molecules are water, methane,

ammonia, and carbon dioxide (all “small molecules”)

and ethane.

Hideo Okabe was born 13 December 1923 in

Nagano-ken, Japan. During World War II he was an

undergraduate at the University of Tokyo; he was deferred from military service because he was a science

student. Needless to say, these were trying times for him

as bombs fell all around on a regular basis. As a student

he was twice bombed out of his rooming house. After a

protracted course of study during these ordeals, Okabe

completed the requirements for an undergraduate degree

in engineering in 1947. The idea of coming to the

United States seemed attractive in a milieu that was

driven by the devastation of Japan, resulting in its

inability to support graduate education adequately. He

had developed an interest in photochemistry during

these years and ultimately applied for admission to

the University of Rochester to work with the dean of

academic photochemists, W. Albert Noyes, Jr. Hideo

was awarded the Ph.D. from the University of Rochester

in 1957, after which he received a post-doctoral appointment at the National Research Council of Canada

with E. W. R. Steacie. Both Noyes and Steacie endorsed

Okabe as one of their better students, and he was offered

and accepted an NBS staff position in 1959. Shortly

Fig. 1. Resonance lamp design.

Fig. 2. Krypton resonance lamp with and without (----) getter.

225
after joining NBS he was granted a leave of absence to

return to Japan for a short stay for the purpose of marrying his bride, Tomoko Shoji. The newlyweds returned to

the United States and eventually he and Tomoko had

three children. Okabe was a Visiting Scholar at Bonn

University in 1963 and a Visiting Professor at Tokyo

Institute of Technology in 1978, the year recognition

came in the form of a Gold Medal from the U.S. Department of Commerce and the publication of Photochemistry of Small Molecules [1]. In 1983 Okabe’s

position at NBS was eliminated in a reorganization and

he opted for early retirement, although he remained

active at NBS as a consultant for a number of years.

A colleague, then at Howard University in Washington

but a former member of the NBS group, William M.

Jackson, took him on as a senior researcher in his

laboratory. Okabe still works at Howard as Research

Professor of Chemistry in the Institute of Atmospheric

Research and has two remaining graduate students.

Prepared by James R. McNesby with assistance from

Ralph Klein.

Bibliography

[1] Hideo Okabe, Photochemistry of Small Molecules, John Wiley &

Sons, New York (1978).

[2] J. R. McNesby and H. Okabe, Vacuum Ultraviolet Photochemistry, Adv. Photochem. 3, 157-240 (1964).

[3] R. Hoffmann, The Same And Not The Same, Columbia University

Press, New York (1995).

[4] H. Okabe and J. R. McNesby, Vacuum Ultraviolet Photolysis of

Ethane: Molecular Detachment of Hydrogen, J. Chem. Phys. 34,

668-669 (1961).

[5] S. M. Wu, J. J. Lin, Y. T. Lee and X. Yang, Site Specificity in

Molecular Hydrogen Elimination From Photodissociation of

Propane at 157 nm, J. Chem. Phys. 111, 1793-1796 (1999).

[6] H. Okabe and J. R. McNesby, Vacuum Ultraviolet Photochemistry. IV. Photolysis of Propane, J. Chem. Phys. 37, 1340-

1346 (1962).

226
Role of Standard Reference Materials in

Measurement Systems

In 1906 the National Bureau of Standards started to

issue samples of materials for standardizing analytical

techniques and methods. Today, the NIST

inventory of standard samples, which are issued under a

NIST-registered trademark, SRM, consists of over

230,000 units of more than 1300 different products.

Each year nearly 34,000 units are sold to over 7000

customers, 30 % of whom are foreign. Each of the 1300

current SRMs is the result of collaboration between

NIST and representatives of science and industry; thus

SRMs serve as crucial reference points in establishing a

comprehensive measurement system for the United

States.

NBS Monograph 148, The Role of Standard Reference Materials in Measurement Systems [1], provides

SRM users with a systems approach to meaningful

measurements through which SRMs can be used to

produce measurement results that are precise and whose

systematic errors are either eliminated or well understood. Monograph 148 presents five major components

of this approach; their relationships are depicted in

Fig. 1.

The authors of Monograph 148 recognized the need

to articulate the role of SRMs in the U.S. measurement

system, to explain how SRMs are certified, and to

clarify what a NIST certification means in both a legal

and technical sense. For many years this document has

assisted the growing number of SRM users in the proper

use of SRMs, especially in countries that were in the

process of developing a national measurement system of

their own based on reference materials and reference

methodology. Although reference materials represent

only one aspect of the total measurement system, NIST

SRMs have always been a key mechanism for transferring NIST science and technology through channels of

industry and commerce.

Monograph 148 describes the important role that

NIST SRMs play in the U.S. measurement system, in

terms of both general and specific uses across a broad

spectrum of analytical disciplines and areas of impact.

In today’s technologically advanced world, standardization is essential as measurements are applied to an evergrowing list of properties and materials. The eight

authors of this monograph brought years of experience

and knowledge from eight different measurement

disciplines, including statistics, to the composition of

the document. Such diversity has made the monograph

a classic reference among practitioners in the field of

measurement systems.

The Role of Standard Reference Materials in

Measurement Systems is divided into four sections plus

appendices. The first section introduces the reader to the

fundamentals of measurement and outlines a systematic

approach to the process of obtaining measurements that

are meaningful. Understanding such concepts allows

one to understand the role that SRMs can play in a

measurement system. While the introductory chapter

provides the rationale for using SRMs, the second

section discusses general concepts of usage, including

the pitfalls that the user faces and their impact on

measurement results. The third section provides users,

especially new users, with a clear description of the

SRM as a tool by which measurement methods, instruments, and systems can be validated or calibrated. The

user is told how the pertinent information is condensed

Fig. 1. Systems approach to the use of Standard Reference Materials

in ensuring reliable measurements.

227
into a certificate which provides qualitative statements

and quantitative values, using data generated from tests

and state-of-the-art measurements performed at NBS or

a cooperating institution. The authors succinctly guide

the users through the critical aspects of the SRM

measurement and certification process. Realizing that

the requirements for SRMs will become more exacting

and complex in the future, the authors describe in

section four the impact on standardization activities in

five selected industries. Even today, those industries

(metal, polymer, inorganic, clinical, nuclear) constitute

areas where measurement needs are still in high demand

or where requests for new types of reference materials

have grown to unprecedented proportions.

The authors of NBS Monograph 148 provided the

first documented account of a measurement system that

would ensure meaningful measurements using standard

Reference Materials as an integral part of the national

measurement infrastructure. Monograph 148 continues

to be used by practitioners and reference materials

users, both nationally and internationally.

The authors represented a wide range of technical

expertise. The principal author, J. Paul Cali, was Chief

of the Office of Standard Reference Materials at NBS

from 1966 to 1978, with responsibility to manage the

production and certification of SRMs. Cali was an

analytical chemist and an international authority on

certification of reference materials, especially those

used in environmental protection and clinical chemistry.

The kinds of materials certified under Cali’s direction

included steel, non-ferrous alloys, Portland cement,

glass, plastics, environmental, and clinical types. In a

time when accuracy in measurement was becoming

critical to quality assurance efforts, these SRMs had a

decided impact in tens of thousands of laboratories on

every continent.

In 1976, Cali received the DOC Exceptional Service

Award (Gold Medal) for “highly effective leadership of

the NBS Standard Reference Materials Program and

improving clinical measurement standardization

throughout the world.” In the same year he was the

recipient of the Edward Bennett Rosa Award, NBS/

NIST’s highest award for contributions to measurement

advances.

Thomas W. Mears, an organic chemist, joined the

Office of Standard Reference Materials in 1968 and

coordinated the development of reference materials for

high-octane gasoline, jet fuels, dielectric materials,

and other hydrocarbon fuels. He was awarded the

Department of Commerce Silver Medal for Meritorious

Service for his research in synthesis, purification,

and analyses during his career at NBS and for the

development of a number of superior Standard Reference Materials and analytical methods.

Robert E. Michaelis joined NBS as a physicist in

charge of spectrographic standard samples in 1952, after

previous service as an engineering officer with the U.S.

Air Force from 1942 to 1946 and as a technologist in

charge of spectrochemical analysis in the U.S. Steel

Research & Development Laboratory from 1947 to

1952. Beginning in 1963, he was assigned the major

responsibility for the planning, preparation, testing and

characterization for all metal Standard Reference

Materials, certified either as to their chemical composition or their physical properties. Michaelis received

many awards and honors, including the Meritorious

Service Award (Silver Medal) from the Department of

Commerce in 1963.

William P. Reed was supervisor of the Analytical

Quality Control Laboratory at Hercules Powder

Company before joining NBS in 1963 as a research

chemist working in the field of Neutron Activation

Analysis. In 1967, he was reassigned to the Office of

Standard Reference Materials, where he coordinated

reference materials activities in the nuclear and environmental fields. He also served two years as Chief of the

Office of Standard Reference Materials. He was instrumental in establishing and maintaining cooperative

programs between NBS and a number of foreign

laboratories and organizations, including the International Atomic Energy Agency and the Geel Laboratory

of the European Economic Community.

Richard W. Seward received a B.S. degree in

engineering from the U.S. Military Academy in 1957

and joined NBS in 1963 as a technical editor/writer; he

served as Managing Editor of the NBS Technical News

Bulletin from 1965 to 1970. He was Technical Representative for Standard Reference Materials from 1970 to

1984 and Project Manager from 1984 to 1989. In 1982

he was awarded the DOC Bronze Metal “for outstanding

management of Standard Reference Materials marketing and customer service activities.”

Connie L. Stanley joined the National Bureau of

Standards in 1954, conducting research in electroplating

in the Electrodeposition Section of the Chemistry

Division. He later worked as an organic chemist in the

Engine Fuels Section of the Heat Division, where he

was involved with the preparation of pure hydrocarbons

and the determination of their physical properties.

He joined the Office of Standard Reference Materials

in 1972 as an SRM Coordinator for environmental

standards.

H. Thomas Yolken was engaged in corrosion research

in the Metallurgy Division from 1960 until 1966 and

later was Special Scientific Assistant to the Director,

Institute for Materials Research, involved in technical

program planning. He was Deputy Chief, Office of

Standard Reference Materials from 1971 to 1975 and

228
also Manager of the NBS Measurements for Nuclear

Safeguards program. He was the author of more than

20 journal articles dealing with corrosion of metals,

optics, Standard Reference Materials, and nuclear

safeguards.

Harry Ku was a leading NBS statistician, who joined

the Statistical Engineering Laboratory in 1958. He was

very active in statistical consulting with Bureau

scientists, combining his engineering background with

his graduate education in the field of statistics.

Ku’s varied experience in support of experiments

included problems of sampling the design for collection

and reduction of data and the proper statement of

uncertainties. Technical areas in which his assistance

was important include nuclear and environmental

standards, radioactive isotopes, and reference materials

for biological use. He paid particular attention to the

problem of minimization of technical effort necessary to

achieve the accuracy required.

Prepared by Thomas E. Gills.

Bibliography

[1] J. P. Cali, T. W. Mears, R. E. Michaelis, W. P. Reed, R. W. Seward,

C. L. Stanley, H. T. Yolken, and H. H. Ku, The Role of Standard

Reference Materials in Measurement Systems, NBS Monograph

148, National Bureau of Standards, Washington, DC (1975).

229
Metrology and Standardization to Assist

Industrializing Economies

In 1971, representatives from 16 countries, from

16 international and national organizations, and from

5 industrial companies came to a conference center in

Northern Virginia to meet with representatives from the

Agency for International Development (AID) of the

U.S. Department of State and the National Bureau of

Standards. They came to discuss how NBS promotes

productivity growth and innovation in the United States

and how the economies of developing countries might

benefit from collaboration with NBS [1]. As raw materials prices sagged worldwide, these countries looked to

industrialization as a source of growth. But where

would they turn for help in developing their basic

infrastructure?

Such countries were generally well accustomed to

international discussions such as are provided by the

United Nations, and to government-to-government

negotiations. They appreciated economic assistance

from the U.S. AID. However, AID claimed no primary

responsibility and only limited expertise in commercial

technology. NBS, with its extensive links to private

industry, was the agency best positioned to help these

countries understand how the U.S. industrial development system works. To fulfill the dreams of industrializing economies (IEs), Glenn Schweitzer, head of AID’s

Office of Science and Technology, in cooperation with

Edward L. Brady at NBS, developed the idea of cosponsorship of this Seminar. The goal was to determine

to what extent these IEs (this label became preferred

over “Less Developed Country,” or “LDC”) could be

given access to the knowledge and experience NBS had

with measurement and documentary standards, as well

as to constructive contacts with industry that were

mutually beneficial. Industry is the primary source of

expertise in technology in which IEs wanted to share

and advance in a self-reliant way.

After experience in both research and diplomacy,

Edward Brady had been brought to NBS in 1963 to

establish the Standard Reference Data Program. Brady

knew well that NBS had no clear Congressional

mandate to assist IEs. Thus NBS, at this Seminar,

wanted to listen to IEs needs and then to judge whether

it was possible to devise projects that could tackle goals

that were in the common interest of NBS and some IEs.

The recommendations from the Seminar were strongly

positive and very hopeful. The response by Lewis

M. Branscomb, who had just been confirmed as NBS

Director, and two former NBS Directors, Allen V. Astin

and Edward U. Condon (representing UNIDO the

United Nations Industrial Development Organization),

were realistically encouraging. To a few voices at NBS

who doubted whether these activities related strongly to

the NBS mission, Branscomb suggested that the NBS

staff, by guiding IEs, could better understand its own

relationships with industry, standards associations, and

the public [1, p. 7].

The activities that were taken in response to the

Seminar received a general evaluation after seven years

[2]; it strongly favored continuation of the projects that

had been started. During the remaining years of the 20th

century, assistance to IEs grew rapidly and became a

significant and flourishing operational feature of NBS

and NIST, which now publishes biennially a volume

summarizing the International Activities [3].

Generally, since 1971, NBS/NIST has

been the only technical institution in

the U.S. Government that IEs could look

to for guidance on technology-based

development strategies. . . . It is an

unheralded but highly significant role

with the result that NBS/NIST is much

better known in foreign capitals than in

our own.

Among the topics in which assistance was given,

pride of place belongs to measurement standards and

their use in measurement science (metrology). In the

United States, NBS/NIST has a primary responsibility

in this field, including ensuring international conformance under the Convention of the Meter, a treaty

adopted by the United States and 42 other signatories.

The International Bureau of Weights and Measures

[4] operates under that Convention as the technical

laboratory that enables national metrology laboratories

to intercompare their national measurement standards.

At the time of the Seminar [1], BIPM was engaged

in the dynamic process of refining and introducing

230
the International System of Units (SI). NBS helped

many IEs to follow and understand the mathematically

beautiful, but really quite complex, recommendations of

BIPM. NBS/NIST style calibrations link measurements

in a chain of comparisons with BIPM standards.

Through familiarity with the technical rigor of NBS

metrology, the concept of self-evaluation with selfassurance of measurement quality spread to many IE

laboratories.

However, the highest levels of metrological technology, required for international comparisons of measurement standards representing the base units, does little to

ensure equity in the retail markets of IEs or to bring

credibility to their international trade. Nevertheless, the

possession of a platinum-iridium kilogram standard, or

an interferometer that compares wavelengths of laser

emissions directly with a national meter bar, received

undue attention in many of the least developed countries.

These problems were addressed during an NBS

arranged seminar in Korea [5] with the title: “Metrology

in Industry and Government: How to Find Out Who

Needs What Services.”

Another topic in which NBS/IE collaboration has

been very strong is that of documentary standards for

health, safety, the environment, products, buildings, etc.

Most such standards are not published by NBS, but by

the hundred or so important national and international

standards-writing organizations. They often look to NBS

to provide expertise, technical experimentation, and a

reference collection. In the early 1970s, NBS technical

staff members served as unbiased technical experts on

some 1500 voluntary technical standards committees.

A part of this work was devoted to dissemination of

standards information, and a portion of that played in the

international arena through many joint seminars such as

those cosponsored with the International Organization

for Standardization (ISO). The first of these had the title

of “Technological Knowledge Base for Industrializing

Countries” [6]. It had the dual purpose of helping to

prepare the U.S. for the UN Conference on Science and

Technology for Development (UNCSTD) in Vienna,

with the benefit of constructive input from IE representatives who had experience of NBS assistance. Former

NBS Director Lewis M. Branscomb was a member of

the U.S. delegation to the UNDP conference in Vienna.

A special feature of the NBS/NIST influence, with

which many IEs were initially uncomfortable, is the

American preference, wherever possible, for voluntary

instead of mandatory standards. Experience has shown

that consensus is more easily achieved when voluntary

standards are developed. Furthermore, they are then

better understood and adhered to by industry and the

public. Tort law acts to compel compliance with well

established voluntary, as well as mandatory, standards.

The Standard Reference Materials program has been

another topic for strong collaboration [1, p. 95-105].

Standard Reference Materials (SRMs) bring great

benefits to industries. Measurements on materials are

needed for raw material selection, process control, and

quality assurance. By virtue of SRMs, good measurements are no longer simply the prerogative of the highly

industrialized nations with primary metrological laboratories. High-quality measurements can now be made

locally in IEs just as they are made in manufacturing

centers of highly industrialized countries. One or more

of the material properties of SRMs are determined by

NBS/NIST with high, generally certified, accuracy.

SRMs can then be used for calibration of measuring

equipment or direct comparison with closely similar

local materials. NBS is the world leader in the supply of

reference materials. The optimization of selected SRM

candidates, their manufacture, and their introduction are

demanding. Assistance from physicists and chemists

from IEs who help to certify and use these materials

continues to be significant.

Essential to industry is also the availability of evaluated data, especially on material properties. Through the

National Standard Reference Data System, NSRDS,

Congress gave NBS a leadership role. To evaluate such

data from the primary literature and make them available in a user friendly mode is a task for which NBS has

received help not only from scientists throughout the

United States and other industrialized countries, but

from IE specialists as well. China, for instance, has

taken a significant part, first on a bilateral basis with

NIST and, more recently, through membership in

CODATA, under the International Council of Scientific

Unions, in which Lewis Branscomb, David Lide, and

John Rumble of NBS/NIST have successively taken

leadership positions.

To understand how yet another aspect of IEs’ collaboration has benefited both NBS and the IEs, we should

turn back in the history to former NBS Director G. K.

Burgess [7], who instituted the innovative Guest Worker

Program almost 75 years ago. After the Seminar [1], L.

M. Branscomb permitted the Guest Worker Program to

be extended to include staff members of counterpart IE

institutions, provided their stay at NBS/NIST was at

least six months and provided they worked on NBS’

own projects and, initially, provided the cost was not

borne by NBS. After their return home, these visitors

often introduced projects in their own institutions that

were similar to their assigned NBS studies. Both NBS

and the IE institutions benefited from this more efficient

231
use of scarce scientific talent. In the ten years following

the Seminar, guest scientists came to NBS from 43

countries. Since then that program has expanded. Today,

about one fifth of the NIST technical staff are guest

workers, many of them from IE countries, sharing

the commitment to accuracy, reliability, and quiet

confidence in service to the United States and to their

home institutions.

Even before the Seminar [1], in 1967, President

Lyndon Johnson, on a visit to Korea and Taiwan, called

for NBS to send an advisory team on measurement and

standardization. A small team under Forest K. Harris

responded by brief visits to both countries. On consideration of the reports by the team, AID wondered whether

similar studies, that is surveys of standardization and

measurement services, were potentially helpful to a

wide range of IEs, while also in the interests of NBS and

the United States. That possibility came up again during

the Seminar [1] and found a strong affirmative response.

Eventually, 10 countries were so “surveyed” (one per

year until 1980) with respect to their individual

standardization and measurement service needs. In

sequential order, these countries were: Korea, Ecuador,

Turkey, Bolivia, The Philippines, Thailand, Guyana,

Indonesia, Pakistan, and The Sudan. The survey events

followed a general pattern set at NBS’ request: The

government of the target country requested the survey

and committed itself to all in-country expenses for the

NBS team and its own counterpart team. The targetcountry team leader also became committed to be available, on request by NBS, for one or more similar future

surveys of other countries in a different part of the

world. An NBS team member then visited the country to

meet with the counterpart team leader. Jointly they

identified the most important needs and outlined a team

itinerary. The NBS team leader identified the most

suitable team members from NBS or other agencies and

representatives from other target countries. The entire

multi-country team assembled at NBS for a week’s

workshop to examine critically and debate NBS

measurement and standardization services, with emphasis on voluntary standards, calibration programs,

certified reference materials, standard reference data

management, and NBS relations in support of industry.

The team was then ready to spend two weeks in the

country with a full program of visits and discussions.

With target country approval, a detailed final report was

issued on the results achieved. In subsequent years,

evaluation and follow-up programs were commonly

requested and executed. Literature references exist for

the 10 survey reports, the respective preliminary workshops, and any follow-up seminars.

It was a special feature of the original Seminar [1]

that, at the invitation of the Scientific Apparatus Makers

Association, the delegates from abroad were given the

opportunity to remain at NBS for an additional week

when the IE visitors could observe NBS operations and

visit a number of scientific instrument manufacturers.

These workshops have been so well appreciated by AID

and the IEs themselves that they have become with little

change, but with suitably updated content, a regular,

continuing feature at NIST.

Whereas most of the above projects are essentially

bilateral, a significant portion of continuing AID/NBS

assistance to IEs is aimed at multilateral collaboration.

An early example is the Seminar in Bolivia on “A

System of Standardization and Metrology for Latin

America” with advisors from Turkey, Thailand, and

Korea. [8]. From this modest beginning the Interamerican Metrology System (SIM) evolved with 34 member

countries. It celebrated its 20th anniversary in 1999. A

regional seminar that focused on a more specific problem was that in Singapore on “Testing and Certification

for Export Products in Industrializing Countries” [9].

South-East Asia is another region which has since

instituted strong contact with NIST. Being unable

to maintain active bilateral relations with the many

countries of Africa, NIST has started regional mechanisms in South Africa, Kenya, Ghana, and Egypt.

NBS collaboration in the Middle East has a long

history that precedes the original Seminar [1] to the time

when the Congressional PL 480 Program was established. It freed certain non-convertible local currency

assets for use in science research of interest to U.S.

federal agencies. During the 1970s, NBS received such

funds in Israel, Yugoslavia, India, Pakistan, Egypt, and

Tunisia [10]. This NBS program had 67 research

projects and was particularly successful in Israel, where

it led to a continuing binational agreement for industrial

research cooperation. After about 1979, most of the

remaining PL 480 projects naturally melted into the

regional IE cooperations. With India, for example,

projects are continued under the U.S.-India Forum in

Science and Technology and received strong support

from an initially independent effort by Peter

Heydemann of NBS/NIST.

Heydemann had been a member of the NBS/AID

team survey of Pakistan’s standardization and measurement services (see above). Subsequently he arranged

seminars and training courses in Pakistan and India. His

many contacts in India prompted the Department of

State to appoint him as Science Counselor at the

U.S. Embassy in India (1988-1993), resulting in

expanded collaborations between U.S. and Indian

232
technical organizations. At the same time, Heydemann

had the opportunity to collaborate with U.S. companies

trading with India, with a focus on standards and

measurement problems. After Heydemann’s return to

NIST as Director of Technology Services, he established

a Standards in Trade Program to assist U.S. companies

to overcome technical barriers in foreign countries.

From this program’s initial activities in Saudi Arabia, it

expanded to countries in the Middle East, Europe, and

Latin America. Five NIST standards experts placed in

foreign markets, together with the staff of the Global

Standards Program in the Office of Standards Services,

have been credited with adding almost one billion

dollars per year in U.S. exports. Very recently, the

Secretary of Commerce confirmed the policy of NIST’s

support for international trade by making a special

award to the NBS Director for International and

Academic Affairs, B. Stephen Carpenter, “ . . . an

ambassador of goodwill for U.S. measurement capabilities all around the globe.”

Among other projects that NBS carried out with

AID support was a successful 3-year interlaboratory

collaboration across national boundaries with Instituto

de Pesquisas Tecno ́logicas of Sa ̃o Paulo, Brazil.

Although relevant notes exist, this NBS/IPT program is

not well documented, partly because Brady hoped after

retirement to write a small book on that experience. The

time was no longer given to him.

Generally, since 1971, NBS/NIST has been the only

technical institution in the U.S. government that IEs

could look to for guidance on technology-based development strategies. Not only the directors, but virtually all

senior staff members of NBS/NIST have actively participated in these IE projects. It is an unheralded but highly

significant role with the result that NBS/NIST is much

better known in foreign capitals than in our own.

Edward L. Brady (1919-1987) received a BA and an

MA from the University of California at Los Angeles

and a Ph.D. at the Massachusetts Institute of Technology, under the guidance of Martin Deutsch. His thesis

on angular correlations between successive nuclear

gamma rays is still regarded as an important contribution. In 1942 he joined the Manhattan Project at the

University of Chicago. Later he was assigned to the

Clinton Laboratories in Oak Ridge and the GE Knolls

Atomic Power Laboratory in Schenectady. Brady

enjoyed work in international relations, where, in

addition to his scientific knowledge and experience, his

human qualities and tact made him outstanding. He

served as U.S. Atomic Energy Commission Representative to the United Kingdom and as Advisor to the U.S.

Mission to the International Atomic Energy Agency in

Vienna. He came to NBS in 1963 as the first Director of

the Standard Reference Data program and later became

NBS Associate Director for Information Programs.

Brady was a man of compassion, dignity, culture, and

grace. His life’s early end occurred after a struggle with

cancer which his wife, Evelyn, associated with exposures to radiation during his work on atomic-energy

projects.

Prepared by Lewis M. Branscomb.

References

[1] H. L. Mason and H. S. Peiser (eds., with Foreword by L. M.

Branscomb), Metrology and Standardization in Less-Developed

Countries: The Role of a National Capability for Industrializing

Economies, Proceedings of a Seminar Held at Airlie House,

Warrenton, VA, February 1-4, 1971; NBS Special Publication

359, National Bureau of Standards, Washington, DC (1971).

[2] H. Steffen Peiser and John A. Birch (eds.), Standardization in

Support of Development, NBS Special Publication 507, National

Bureau of Standards, Washington, DC (1978).

[3] Marian F. McCurley (ed.), NIST International and Academic

Activities for FY 1997/1998, NIST Special Publication 940,

National Institute of Standards and Technology, Gaithersburg,

MD (1999).

[4] Chester H. Page and Paul Vigoureux (eds.), The International

Bureau of Weights and Measures, 1875-1975: Translation of

the BIPM Centennial Volume, NBS Special Publication 420,

National Bureau of Standards, Washington, DC (1975).

[5] H. Steffen Peiser, Raymond C. Sangster, and Wun Jung, Metrology in Industry and Government: How to Find out Who Needs

What Services, Proceedings of a Regional Seminar held at the

Korea Standards Research Institute, Dae Jeon, Korea, 1978,

NBS Special Publication 539, National Bureau of Standards,

Washington, DC (1979).

[6] Raymond C. Sangster (ed.), The Technological Knowledge Base

for Industrializing Countries, NBS Special Publication 543,

National Bureau of Standards, Washington, DC (1979).

[7] G. K. Burgess, Research Associates at the Bureau of Standards,

NBS Circular 296, National Bureau of Standards, Washington,

DC (1925).

[8] H. Steffen Peiser and Robert S. Marvin (eds.), Regional Seminar

on a System of Standardization and Metrology for Latin America,

NBS Interagency Report 76-988, National Bureau of Standards,

Washington, DC (1976).

[9] H. Steffen Peiser and Robert S. Marvin, Testing and Certification for Export Products in Industrializing Countries,

NBS Special Publication 438, National Bureau of Standards,

Washington, DC (1976).

[10] H. S. Peiser, Recalling the PL-480 Program at NBS, NBS/NIST

SAA Newsletter, 13-14 December, 1998.

233
Publications Taking Us Toward a

Metric America

For almost its entire existence, NBS/NIST has been

interested and directly involved in America’s bumpy and

prolonged transition to the metric system of measurement. This involvement has had and continues to have

many facets. On the technical front, NIST works with

scientists from around the world to achieve continually

improving precision in metric system measurements and

unit definitions, and NIST policy specifies metric units

in all staff reports. On a public policy front, the Bureau

has for many years striven to increase the American

public’s understanding and acceptance of metric

measurement units.

One prime example of an informative and easily read

metric publication which effectively reaches out to a

non-traditional NBS/NIST audience is the Metric Style

Guide for the News Media [1]. Originally published in

1976 with revisions and updates in 1992 and 1997, the

publication serves as a compact and accurate “metric

literacy” reference document, giving the reader an

overview of the units and the grammar of the metric

system. Size approximations are provided to help

readers visualize common metric units, and easy-to-use

tables of common metric prefixes and conversions are

also included. The Style Guide makes the point that

Americans will compete more successfully in the global

marketplace when they understand and speak the

international language of measurement.

The news media have an important role in assisting

the American public as we make the transition to the

international language of measurement. Correct and

positive use of metric terms and symbols by the media

helps to smooth this transition. For almost 25 years, the

Style Guide has continued to be extremely popular, not

only with the news media, but also with school teachers

and the general public. Teachers, especially, have praised

the pamphlet for its ability to aid in the teaching of

metric literacy. Approximately 200,000 copies of the

Style Guide have been printed and distributed.

Two other NBS/NIST publications, The Chart of

the Modern Metric System [2] and A Brief History of

Measurement Systems with a Chart of the Modern

Metric System [3], also serve as important tools in the

effort to promote metric literacy. These publications are

especially notable for their long-lived popularity and

widespread dissemination. The first of these [2] is a

full-color wall chart (ISO A1-sized poster) which highlights, graphically illustrates, and explains the seven

base units of the SI metric system. The chart’s usefulness in helping students learn and understand the metric

system is enhanced by the inclusion of three welldesigned and easy-to-use tables: metric system prefixes,

common conversions, and SI names and symbols for

units that are derived from the base units.

A sister publication to the large wall chart is the

equally-popular 1/4-sized (ISO A3 size) small wall

chart [3]. On the reverse side of the small wall chart, a

well-written article explains the importance of weights

and measures to all societies and traces the history and

development of both the English and the metric systems

of measurement.

After more than three decades of life, the two charts

and the measurement history article remain among the

Metric Program’s most requested items. Several hundred thousand of these colorful and informative wall

charts have been produced, and they can be found hanging everywhere from elementary school classrooms to

the offices of physicists. Originally designed and printed

in 1968, both of the charts have been revised and

reprinted several times, with major changes made in

1986 and 1997.

The Bureau’s involvement in the national debate over

metrication reached a critical pitch in the late 1960s. In

a project that would later be described by Lewis

Branscomb as the biggest NBS project of his directorship, the Bureau embarked on the U.S. Metric Study. In

the Metric Study Act of 1968 (P.L. 90-472), Congress

directed the Secretary of Commerce to conduct an

extensive study to determine the advantages and disadvantages of increased metric use in the United States

and to submit a full report to Congress within three

years. The Secretary of Commerce delegated responsibility for the study to NBS.

The Metric Study Group was directed by Daniel

De Simone with a team of over 40 NBS program

managers and supporting staff. Also heavily involved in

the study were 50 private-sector members of a Metric

System Study Advisory Panel. The panel members were

appointed by the Secretary of Commerce from organizations representing a wide spectrum of interests. The

chairman of the panel was Louis Polk, a director of the

Bendix Corporation.

Following a detailed blueprint, the study sought facts

and opinions from over 700 major groups representing

every sector of society—including labor unions, trade

234
associations, professional societies, education associations, consumer-related organizations, and many others.

Input was obtained through a series of multi-day public

hearings, surveys, correspondence, and other supplementary investigations.

The report to Congress was published as a 190-page

NBS Special Publication entitled A Metric America: A

Decision Whose Time Has Come [4]. Intended for wide

distribution, this landmark publication details the

findings and conclusions of the U.S. Metric Study. The

report includes several specific recommendations

for the Nation to achieve a smooth and coordinated

transition to the metric system of measurement. Many

of these recommendations were summarized in the

report’s transmittal letter to Congress which was signed

by Secretary of Commerce Maurice H. Stans. This letter

is reproduced as Fig. 1.

Fig. 1. Letter from the Secretary of Commerce to Congress transmitting the NBS Report on the U.S. Metric

Study.

235
In addition to the main summary report, 12 supporting volumes were produced as part of the project—for

a grand total of over 2300 pages of published text. These

supporting volumes were entitled:

International Standards (NBS SP 345-1)

Federal Government: Civilian Agencies (345-2)

Commercial Weights and Measures (345-3)

The Manufacturing Industry (345-4)

Nonmanufacturing Business (345-5)

Education (345-6)

The Consumer (345-7)

International Trade (345-8)

Department of Defense (345-9)

A History of the Metric System Controversy in the

United States (345-10)

Engineering Standards (345-11)

Testimony of Nationally Representative Groups

(345-12).

Because of its importance as the summary document

of the most significant study on national metrication

issues ever conducted by the United States government,

the Metric America publication has been (and continues

to be) cited as a reference in hundreds of books,

magazines, and newspaper articles—the current edition

of Encyclopedia Britannica being one example.

The report was cited heavily when the 92nd and the

93rd Congresses debated legislative proposals and

national conversion issues. Finally, four years after the

report was first published, the Metric Conversion Act

was passed by the 94th Congress in 1975 and signed

into law by President Ford. The Act was an important

milestone, yet disappointing to many of the U.S. Metric

Study contributors because several of the report’s

recommendations—such as the importance of a care

fully planned transition, target dates, and a coordinated

national program—were not implemented in the final

language of the legislation.

In 1988, amendments to the Metric Conversion Act,

Congress gave a significant boost to the metric effort by

declaring the metric system to be the preferred system of

measurement for U.S. trade and commerce. Unfortunately, even today, many of the issues and debates

surrounding national metrication still linger.

As America enters the new millennium and NBS/

NIST enters its second century, there is an increased

desire by Americans to work, communicate, and live as

part of the larger, global community—and the metric

system is the global community’s language of measurement. Increased public understanding and acceptance of

metric measures is an on-going effort which NIST

continues to support through several excellent publications and many other outreach activities.

Prepared by Ralph A. Richter.

Bibliography

[1] Metric Style Guide for the News Media, NBS Letter Circular 1137,

National Bureau of Standards, Washington, DC, December 1976.

[2] Chart of the Modernized Metric System, NBS Special Publication

304, National Bureau of Standards, Washington, DC (1968).

[3] Brief History and Use of the English and Metric Systems of

Measurement with a Chart of the Modernized Metric System, NBS

Special Publication 304A, National Bureau of Standards,

Washington, DC (1968).

[4] A Metric America: A Decision Whose Time Has Come, NBS

Special Publication 345, National Bureau of Standards,

Washington, DC, July 1971.

236
A New Approach to Manipulator Control:

The Cerebellar Model Articulation Controller

The Cerebellar Model Articulation Controller

(CMAC) [1, 2] is a neural network that models the

structure and function of the part of the brain known as

the cerebellum. The cerebellum provides precise coordination of motor control for such body parts as the

eyes, arms, fingers, legs, and wings. It stores and

retrieves information required to control thousands of

muscles in producing coordinated behavior as a function

of time. CMAC was designed to provide this kind of

motor control for robotic manipulators. CMAC is a kind

of memory, or table look-up mechanism, that is capable

of learning motor behavior. It exhibits properties such as

generalization, learning interference, discrimination,

and forgetting that are characteristic of motor learning

in biological creatures.

In a biological motor system, the drive signal for each

muscle is a function of many variables. These include

feedback from sensors that measure position, velocity,

and acceleration of the limb; stretch in muscles; tension

in tendons; and tactile sensations from various points on

the skin. Feedback also includes information from the

eyes via the superior colliculus and visual cortex about

the positions of the hands and feet relative to their

intended targets. Drive signals to the muscles also

depend on higher level ideas, plans, intentions, motives,

and urges. These may be specified by variables that

identify the name of the task to be performed and

specify the goals that are desired, the procedures and

knowledge required to achieve those goals, and the priorities that have been assigned to achieving those goals.

A block diagram of a typical CMAC is shown in

Fig. 1. CMAC modules are designed to accept both

input command variables from higher levels and feedback variables from sensors. Each CMAC merges these

two inputs into a set of memory addresses wherein are

stored the correct motor response. The combined input

selects a set of memory locations from a large pool of

memory locations. The output is the sum of the contents

Fig. 1. A block diagram of a CMAC for a single joint actuator. The vector S consists of an input command from

higher motor centers combined with feedback from sensors in the joints, muscles, and skin of a limb. Each CMAC

separately computes a S ⇒ A* mapping. A* is the set of locations in memory selected by the mapping. The selected

locations in A* contain weights corresponding to synaptic strength between parallel fibers and dendrites on a

cerebellar Purkinje cell. The computed output is the sum of the weights stored in the A* address set. In this example,

the output is a drive signal pj to the j-th joint actuator controller. The output signal may define a desired position,

velocity, or force of the j-th joint actuator depending on the command.

237
of the selected memory locations. Feedback input from

sensors causes the behavior to evolve along a goaldirected stimulus-response chain. As feedback changes,

the output changes. This, in turn, causes the sensory

feedback to change further. The result is a closed servo

loop that makes the behavior reactive. The input command from above effectively selects a region of memory

wherein the proper set of stimulus-response pairs to

generate the desired behavior can be stored.

For each command, a string of stimuli produces a

string of responses. For a different command, the same

stimuli may produce a different string of responses.

The result is that a CMAC module decomposes

each different input command into a different string of

subcommands. Each different string of subcommands

corresponds to a different behavior. Thus, whenever the

command changes, a different behavior is generated.

For example, a command such as <pick up object X>

will select a region of memory where motor behavior

appropriate for picking up an object is stored. A different command such as <scratch itch at skin location Y>

will select a different region of memory where scratching behavior is stored.

CMAC learns correct output responses for various

input conditions by modifying the contents of the

selected memory locations. For each input, the learning

process computes the difference between the CMAC

output and the desired output (provided by a teacher) as

shown in Fig. 1. This difference determines a correction

factor that is added to the contents of each of the

selected memory locations. The rate of learning

depends on a gain factor that determines the magnitude

of the correction factor.

The S ⇒ A* mapping employed by CMAC has the

property that any two input vectors that are similar (i.e.,

close together in input space) will select a highly overlapping subset of locations in the A* set. Thus, the

output response of a CMAC to similar input vectors will

tend to be similar because of many memory locations in

common. Hence, CMAC tends to generalize (i.e., to

produce similar outputs for similar inputs.) The amount

of generalization depends on the number of overlapping

memory locations in the A* set.

On the other hand, any two input vectors that are

dissimilar (i.e., far apart in input space) will select a

highly disjoint subset of locations in the A* set. Most

often, there will be no common memory locations in

A*. Thus, the output response of a CMAC to dissimilar

input vectors can be independent, making it easy for

CMAC to distinguish between dissimilar input vectors.

This means that CMAC can classify or recognize input

patterns. The sparse nature of the A vector makes it

possible for CMAC to learn to classify a large number

of patterns.

The ability to generalize between similar inputs

enables CMAC to quickly learn smooth mathematical

functions such as are typical of control system operators

in a memory of reasonable size. The S ⇒ A* mapping

and the resulting property of generalization also gives

CMAC many of the properties of a fuzzy controller.

To deal with the complexity of motor behavior

required to perform tasks in the natural world without

either side-stepping the computational difficulties

(as with teleoperated systems) or ignoring most of the

relevant variables (as with conventional automation)

it is necessary to partition the control problem into

manageable subproblems. This may be accomplished

through a hierarchical organization such as is typical in

military, government, and business organizations. In a

hierarchical control structure, each agent at each level

of the hierarchy takes direction from a supervisor in the

level above and issues directives to subordinates in the

level below. Each level has its own set of knowledge,

skills, and abilities. Each agent performs task decomposition by decomposing input commands from above

into output commands to one or more agents at the next

lower level. Agents within the same organizational unit

often work together to accomplish tasks that require

cooperative behavior.

CMAC modules are specifically designed to be integrated into a hierarchy wherein tasks are decomposed

into subtasks at each level. At each level, the input S is

a combination of a command vector from a higher level

plus a feedback vector from sensors or from a world

model or peer agents. The output P is a command to a

lower level module, a next state, and possibly a message

to a peer.

At each level, task commands are combined with

feedback to select an appropriate subtask command to

be issued to the next lower level. When command input

changes, the transfer function of the CMAC can change.

This enables higher level commands to select among a

library of transfer functions, each of which can generate

strings of task commands to the next lower level.

By this process, a hierarchy of CMAC modules can

decompose a complex high-level task into a string of

drive signals for individual actuators as shown in Fig. 2.

A hierarchy of similar building blocks in the brain can

be used to implement a hierarchy of behaviors such

as observed by Tinbergen [3] and others in simple

creatures such as fish, birds, and insects.

CMAC was based on a neurophysiological model of

the cerebellum published by Albus in 1971 and 1972

[6, 7]. This model was, in turn, inspired by a series of

experiments performed by Eccles [8] and others during

the 1960s that showed a striking resemblance between

the structure and function of the cerebellum and the

Perceptron neural net developed by Rosenblatt [9] in

238
the 1950s. The Albus model, combined with a similar

model published in 1969 by David Marr [10], have

become known as the Marr-Albus model of the cerebellum. The Marr-Albus model has had a profound influence on brain research in the cerebellum and remains

one of the most widely accepted and frequently cited

models of the cerebellum today.

The short-term impact of CMAC research was

modest. CMAC was awarded an IR-100 award and a

Department of Commerce Silver Medal, but had little

immediate effect on the field of neural nets. At the time

of its publication, the field of neural networks had fallen

into a state of disrepute. Minsky and Papert had recently

published their influential book entitled Perceptrons in

which they demonstrated some of the theoretical limitations of neural networks [11]. Over-reaction to the

negative conclusions of the Minsky-Papert critique had

a profound impact on neural net researchers. Virtually

all interest in (and funding support for) neural network

research evaporated for almost a decade. Serious interest

in neural network research did not recover until the late

1980s with the invention of back propagation, adaptive

resonance theory, Hopfield nets, and a number of other

new discoveries.

Since 1990, CMAC has began to attract increasing

levels of interest. CMAC has been used for computing

plant models for feedforward control on-line in

real-time. Miller has shown that CMAC can be used to

implement a real-time adaptive controller for various

robotic applications [12]. Miller and others have shown

that CMAC learning typically converges at least an

order of magnitude faster than back propagation. As the

properties of CMAC have become apparent, more and

more researchers have begun to apply CMAC to their

areas of interest. CMAC has become well known by

students and researchers in adaptive learning mechanisms and is the subject of neural network studies in a

number of laboratories in several countries. The CMAC

papers have been cited in the literature over 240 times.

At least as important as its contribution to the field of

neural nets, is the influence CMAC has had in providing

the conceptual foundation for the Real-time Control

System architecture known as RCS. The fact that

CMAC could learn a set of transfer functions and transition matrices meant that a CMAC could be designed to

implement any state-table or expert system rule base.

The CMAC input vector (command, feedback, and

state) corresponds to the IF predicate. The output vector

corresponds to the THEN consequent and next state. At

each compute cycle, the CMAC input vector is compared with the lines on the left side of a state table. For

the matching line, the right side of the state table

provides the output subcommand and next state. Thus,

any CMAC can be emulated by a finite state machine.

RCS is a control system built from a hierarchy of finite

state machine modules.

RCS was initially developed by Barbara et al. [4] to

implement controllers for sensory-interactive robots.

RCS enabled NBS robots to use visual feedback to

acquire randomly oriented objects and pursue moving

targets. During the early 1980s, RCS evolved into the

hierarchical shop control system architecture for the

Automated Manufacturing Research Facility (AMRF)

[5]. In the AMRF, RCS was implemented on the

Horizontal Machining Workstation, the Cleaning and

Deburring Workstation, the Material Handling Workstation, and the Advanced Deburring and Chamfering

System. During the late 1980s, RCS was developed into

a control system for the DARPA Multiple Undersea

Autonomous Vehicle program and was adopted by

NASA for the Space Station Telerobotic Servicer. RCS

was adopted by the U.S. Bureau of Mines as a control

Fig. 2. A hierarchy of CMAC controllers. In response to each input

command from a higher level, each CMAC generates a string of

output commands to a lower level. These output commands are stimulus-response behaviors that are selected by input commands and

driven by feedback variables. This hierarchy of CMACs can be used

to partition a manipulator control problem into a manageable set of

sub-problems.

239
system for automated mining operations. At MartinMarietta, Barbera and Fitzgerald developed RCS for

the Army TMAP unmanned vehicle. Later at Advanced

Technology Research Corporation, Barbera and

Fitzgerald used RCS to build an Automated Stamp

Distribution Center and to design a General Mail

Handling Facility for the U.S. Postal Service. Commercial versions of RCS are currently being used for controlling machine tools and laser cutting machines. RCS

was adapted by General Dynamics Electric Boat as a

control system for the next generation nuclear submarine. At NIST, RCS has been used for the Enhanced

Machine Controller, the Next Generation Inspection

System, the Automated Welding Manufacturing System,

the RoboCrane, a computer controlled Man-Lift, and the

NIST Unmanned Ground Vehicle [13]. Most recently,

RCS has been adopted by the Army for the Demo III

Experimental Unmanned Vehicle program [14]. RCS is

currently under consideration for the Army’s Future

Combat Systems program.

By the end of the century, RCS evolved into a canonical reference model architecture with sufficient structure to enable the development of metrics and interface

standards for intelligent systems. Elements of RCS have

been incorporated into standards activities in both

civilian and military sectors. RCS is currently influencing the development of interface standards for machine

tools under the Open Modular Architecture Controller

(OMAC) group, and for military vehicles under the Joint

Architecture for Unmanned Ground Systems Standards

(JAUGS) project [15, 16].

For his work on CMAC and RCS applied to the

AMRF, Albus was awarded the Department of

Commerce Gold Medal, the NIST Applied Research

Award, the Japanese Industrial Robot Association

Research and Development Award, and the Robot

Industries Association Joseph F. Engelberger Award.

For the past ten years, Albus has been working on a

theoretical foundation for the engineering of intelligent

systems [17]. He is currently a Senior NIST Fellow in

the Intelligent Systems Division of the Manufacturing

Engineering Laboratory.

Prepared by James S. Albus.

Bibliography

[1] J. S. Albus, A New Approach to Manipulator Control: The

Cerebellar Model Articulation Controller (CMAC), J. Dyn. Syst.

Meas. Control, Trans. ASME 97, 220-227 (1975).

[2] J. S. Albus, Data Storage in the Cerebellar Model Articulation

Controller (CMAC), J. Dyn. Syst. Meas. Control, Trans. ASME

97, 228-233 (1975).

[3] Niko Tinbergen, The Study of Instinct, Clarendon Press, Oxford

(1951).

[4] Anthony J. Barbera, M. L. Fitzgerald, James S. Albus, and

Leonard S. Haynes, RCS: The NBS Real-Time Control System,

in Robots 8: Conference Proceedings, Vol. 2, Detroit, Michigan,

June 1984, Society of Manufacturing Engineers, Dearborn, MI

(1984) pp. 19-1–19-33.

[5] J. A. Simpson, R. J. Hocken, and J. S. Albus, The Automated

Manufacturing Research Facility of the National Bureau of

Standards, J. Manuf. Syst. 1, 17-31 (1982).

[6] J. S. Albus, A Theory of Cerebellar Function, Math. Biosci. 10,

25-61 (1971).

[7] James Sacra Albus, Theoretical and Experimental Aspects of a

Cerebellar Model, Ph.D. Thesis, University of Maryland, College Park, MD (1972).

[8] John C. Eccles, Masao Ito, and Ja ́nos Szenta ́gothai, The Cerebellum as a Neuronal Machine, Springer-Verlag, New York (1967).

[9] F. Rosenblatt, The Perceptron: A probabilistic model for information storage and organization in the brain, Psychol. Rev. 65,

386-408 (1958).

[10] D. Marr, A Theory of Cerebellar Cortex, J. Physiol. (London)

202, 437-470 (1969).

[11] Marvin Minsky and Seymour Papert, Perceptrons: An Introduction to Computational Geometry, MIT Press, Cambridge, MA

(1969).

[12] W. Thomas Miller, III, Sensor-based control of robotic manipulators using a general learning algorithm, IEEE J. Robot. Autom.

RA-3, 157-165 (1987).

[13] J. S. Albus, The NIST Real-time Control System (RCS): An

Application Survey, in Proceedings of the AAAI 1995 Spring

Symposium Series, Stanford University, Stanford, CA, March

27-29, 1995.

[14] J. S. Albus, 4-D/RCS Reference Model Architecture for

Unmanned Ground Vehicles, in Proceedings IEEE International

Conference on Robotics and Automation, San Francisco, April

22-28, 2000, Institute of Electrical and Electronics Engineers,

New York (2000) pp. 3260-3265.

[15] Homepage of the OMAC Users Group (http://www.

arcweb.com/omac), OMAC Users Group (2000).

[16] Joint Architecture for Unmanned Ground Systems (JAUGS)

(http://www.jointrobotics.com/Jaugs), U.S. Department of

Defense.

[17] James S. Albus, Outline for a Theory of Intelligence, IEEE

Trans. Syst. Man Cybern. 21, 473-509 (1991).

240
Three Dimensional Metrology

Building a precision machine has always been a

very expensive and time-consuming job. The project

described in this paper [1] was part of a revolution in the

design and building of precision measuring machines

and machine tools. Two very important principles were

described in the paper: the error correction of a measuring machine and multiple redundancy and statistical

analysis of measurement algorithms. Both concepts

were fairly new at the time, and by presenting a theoretical study, implementation, and an example calibration,

the paper was truly a tour de force of advanced metrological thinking. A little vocabulary is needed before

describing the paper.

For the machines under discussion, there are usually

three axes of motion. Of course, none of these motions

are perfect. There are, in fact, six main errors associated

with straight line motion. A simple case of onedimensional motion is a waybed, or linear slide. The

part is supposed to move in a simple line along the

Y axis. The six errors are shown in Fig. 1: scale (the

slide doesn’t move the desired distance), straightness

(the slide can move up/down or left/right), pitch

(angular motion front/back), roll (angular motion, left/

right) and yaw (rotation about the Z axis).

Historically, to make a precision machine the geometry of the ways needed to be as perfect as possible, an

expensive and difficult job. The idea of correcting the

motion of an assembled machine had been around, but

was difficult to implement. There were a number of

scale correction schemes, and even some attempts to

measure errors and use correction tables [2], but the

process was awkward for measuring machines and not

really useful for machine tools.

By the 1960s, the idea of measuring the error motions

and making corrections was discussed in precision

engineering circles under the name “deterministic

metrology” [3]. The idea was simply that machines

make errors of two kinds. Some errors are random, and

thus can’t be predicted or corrected; others are repeatable and thus available for mathematical modeling and

correction. The impetus for this was the computer. With

a computer the motion of each axis could be measured,

the error put in a table, and then used rather easily

because the computer did the calculations.

At NBS, John Simpson, the Director of the Center for

Manufacturing Engineering, was a rather philosophical

scientist [4], an early and enthusiastic believer in the

idea of deterministic metrology. Under his guidance,

NBS decided to implement these ideas on a threedimensional coordinate measuring machine (CMM).

One of the earliest critical decisions was which CMM to

use as a test bed. A low accuracy machine would have

the largest potential change in accuracy, but most low

accuracy machines had large amounts of random error

which could not be corrected. A high accuracy machine

would have more modest potential, but would probably

have small random errors. Eventually, the choice was for

a high accuracy machine, an M5Z CMM from Moore

Special Tool, Inc. The actual machine is shown in

Fig. 2.

The M5Z was not only an extremely accurate

machine to begin with, its repeatability was truly

remarkable. A very good source of dimensional metrology information, and an excellent description of how to

make a CMM like the M5Z, is Foundations of Mechanical Accuracy by Wayne Moore [5]. The X and Y motion

repeatability was around 25 nm (1 microinch), and

somewhat worse in Z. Thus, nearly all of the admittedly

small errors could be measured and potentially

corrected for in a computer program.

There were some problems. First, the best way to

make the corrections with the computer would be to

have the computer run the CMM. At the time the project

started, there were no commercial CMMs run by

computers, so NBS built a system to run the M5Z from

scratch. Such an effort in the early 1970s was, in itself,

groundbreaking. The second problem was that the

Fig. 1. Six error motions of a one dimensional waybed.

241
machine was much more repeatable than the precision

of the major scale of the machine, the lead screw. For

this, laser interferometers were added to the machine as

the scales, and what was one of the most accurate lead

screws in the world was used to move the machine.

Next, because of the inherent accuracy of the

machine, the measurement of the motion errors was a

state-of-the-art job. Fig. 3 shows a family portrait of the

M5Z and some of the equipment used to map the error

motions. It included external laser interferometers,

straightedges, LVDTs, electronic levels, and a large

amount of fixturing.

An interesting note is that there is a vertical cylinder

at the center of the very bottom of Fig. 3. This is the

stepper motor that provides fine motion, about 13 nm

(0.5 microinch) per step. There is one for each axis.

Unfortunately, step motors produce heat because they

draw current all of the time. The small vertical bar in

front of the motor is a copper tube through which

thermostated water was circulated to keep the motor at

20 C.

There are other possible error motions than the six

discussed earlier; they are the error motions of a rigid

body. Suppose one pushes a box across the floor, but

does not push at the center of the box. As it moves it will

rotate. If the box is rigid the angle of rotation of all parts

of the box is the same. If the box is not rigid, but can

bend, the rotation measured at different parts of the box

can be different. Since it was not known how the M5Z

would move, or how important the bending would be,

the errors were measured on a 5 cm  5 cm  5 cm

(2 inch  2 inch  2 inch) lattice grid over the whole

range of motion of the machine. For example, the pitch

of the table was measured over the entire machine volume. Further studies showed that most machine movements can be represented in terms of rigid-body motion,

Fig. 2. Moore Special Tool M5Z Coordinate Measuring Machine

242
and consequently can be characterized fairly well with

simpler measurements. For example, measurement of

the table pitch along only one line, rather than a number

of measurements along parallel lines, can be used. An

early project to implement this simpler “rigid body”

error map was completed at NBS in the early 1980s

[6].

The implementation of error mapping CMMs and

machine tools changed the design criteria of the

machines in a very important way. Previously, a very

accurate machine needed to be very repeatable and to

have very small error motions. As for any system, two

restraints are more expensive than one. With error

mapping, the accuracy requirements could be relaxed

because the error motions could be measured and

programmed into the control computer or, in the case of

CMMs, either the controller or the analysis computer.

This made accuracy less expensive and, in fact, much of

the rapid gain in CMM performance of the 1980s was

based on these new design ideas. Virtually all CMMs

are now error mapped; the time between the prototype

error mapping experiments to industrial implementation

was only a few years.

After a brief introduction to the goals of the project,

the authors of the paper [1] discuss the basic kinematics

of the measuring machine. Of great importance are the

definitions of the various coordinate systems and

the transformations between them. The mathematical

system varied greatly from paper to paper in the early

years, and it took some time for a consensus to form. A

reasonable discussion of these issues is given in the

book edited by John Bosch [7].

The next section of the paper discusses the view of

measurements as a “production process with a product,

numbers, whose quality may be controlled by the

methods of statistical sampling.” This is a very important idea and is a basic part of much of the NBS

measurement philosophy; it was first elucidated by

Churchill Eisenhart in his 1963 paper, Realistic

Evaluation of the Precision and Accuracy of Instrument

Fig. 3. M5Z and some of the equipment needed to measure the error motions of the three

axes.

243
Calibration Systems [8], described elsewhere in this

volume. The idea of multiple measurements with fixturing changes (rotating grid plates between measurements, for example) to sample the uncorrected errors, as

well as the simple repeatability of the instrument,

has been used very successfully and is an important

technique in the analysis of measurement uncertainty

[9,10].

The actual machine calibration is briefly described in

the next section. It is of some interest still because the

quasi-rigid body assumptions are not generally used

today. Thus the method described is a bit more work,

but generates a better map.

Finally, the algorithm and measurement process to

calibrate a ball plate are discussed. This same procedure, with repeated points to measure drift and multiple

measurements in different orientations is the same basic

method we use today. For more detailed information on

this subject, there are a number of sources [11].

Robert Hocken earned a bachelor degree in physics at

Oregon State University in 1969 and went on to a Ph.D.

in physics at the State University of New York at Stony

Brook in 1973. He came to NBS in 1973 as an NRC

Postdoctoral Fellow and worked on the properties of

fluids near their liquid-vapor critical points. From

thermophysics he moved to the Dimensional Technology

Group and later became Chief of the Automated

Production Technology Division. These organizations

were the home of the M5Z project described in the

paper. From NIST, Hocken went to the University of

North Carolina at Charlotte to start a program in precision engineering. As the Norvin Kennedy Dickerson,

Jr., Distinguished Professor, he built what is now the

Center for Precision Metrology at UNC Charlotte. This

program, almost unique in the United States, has earned

an international reputation for quality research in

engineering and metrology. A very good introduction to

Hocken and his program can be found in an article in

Quality Magazine [12].

John A. Simpson received his B.S., M.S., and Ph.D.

in physics from Lehigh University. From 1948 to 1956

he was in the NBS Electron Physics Section, rising to

Section Chief. In 1971 he became Deputy Chief of the

Optical Physics Section and was named Acting Chief

of the Mechanics Division in 1975. In 1978 he became

the first Director of the Center for Manufacturing

Engineering, now named the Manufacturing Engineering Laboratory. Among his many accomplishments was

the Automated Manufacturing Research Facility [13]

(described elsewhere in this volume), a multi-discipline

test bed for advanced concepts in manufacturing,

including the deterministic metrology discussed in this

paper.

Bruce Borchardt is the only author remaining at

NIST. He began working summers and holidays in the

Atomic Spectroscopy Division while a student at Yale.

After receiving his B.S. in physics in 1971, he became

a dimensional metrologist. He has worked on coordinate

measurement most of his career and is one of the world’s

most experienced metrologists in coordinate metrology.

John Lazar was a mechanical engineer in the

Dimensional Technology Section and later Automated

Precision Technology Division. Besides the M5Z

project, in the 1970s he designed and built a number of

laser interferometer based measuring instruments for

gage blocks, and a long range micrometer for wires,

balls, and other common dimensional gages. Each of

the instruments was about 10 years ahead of similar

commercial instruments.

Charles Reeve was, at the time, a member of the

division, but he specialized in the statistical analysis of

calibrations. Nearly all of the documentation of the

Engineering Metrology Group calibrations was written

in the 1970s by Reeve. He eventually joined the

Statistical Engineering Division and is currently a

statistician for the Westinghouse Savannah River Co. in

Aiken, South Carolina.

Phil Stein received a bachelor degree in physics from

Columbia College and was one of the few graduates of

the NBS-sponsored graduate program in Measurement

Science at George Washington University. He worked at

NBS from 1963 to 1978 and had the primary interest in

the automation of the M5Z. He left NBS to pursue

his interest in computers and automation and is now

a private consultant. His interest in metrology and

measurement also continued, and he is now a Fellow of

the American Society for Quality and past Chair of

the ASQ Measurement Quality Division. He also is a

columnist for the Measurement Quality Division

newsletter, “The Standard.”

Prepared by Ted Doiron.

Bibliography

[1] R. Hocken, J. A. Simpson, B. Borchardt, J. Lazar, C. Reeve, and

P. Stein, Three Dimensional Metrology, CIRP Ann. 26, 403-408

(1977).

[2] Chris Evans, Precision Engineering: an Evolutionary View,

Cranfield Press, Bedford, UK (1989).

[3] James B. Bryan, The Deterministic Approach in Metrology and

Manufacturing, in Proceedings of the International Forum on

Dimensional Tolerancing and Metrology, CRTD-Vol. 27, The

American Society of Mechanical Engineers, New York (1993)

pp. 85-95.

[4] John A. Simpson, Foundations of Metrology, J. Res. Natl. Bur.

Stand. 86, 281-292 (1981).

244
[5] Wayne R. Moore, Foundations of Mechanical Accuracy, Moore

Special Tool Company, Bridgeport, CT (1970).

[6] G. Zhang, R.Veale, T. Charlton, B. Borchardt, and R. Hocken,

Error Compensation of Coordinate Measuring Machines, CIRP

Ann. 34, 445-448 (1985).

[7] John A. Bosch (ed.), Coordinate Measuring Machines and

Systems, Marcel Dekker, Inc., New York (1995).

[8] Churchill Eisenhart, Realistic Evaluation of the Precision and

Accuracy of Instrument Calibration Systems, J. Res. Natl. Bur.

Stand. 67C, 161-187 (1963).

[9] R. J. Hocken and B. R. Borchardt, On Characterizing Measuring

Machine Geometry, NBSIR 79-1752, National Bureau of

Standards, Washington, DC (1979).

[10] M. R. Raugh, Absolute two-dimensional sub-micron metrology

for electron beam lithography, Precis. Eng. 7, 3-13 (1985). [11]

Theodore D. Doiron, Grid plate calibration at the National

Bureau of Standards, J. Res. Natl. Bur. Stand. 93, 41- 51 (1988).

[12] Samantha Hoover, A Working Education in Metrology, Qual.

Mag., pp. 36-39, October 1999.

[13] J. A. Simpson, R. J. Hocken, and J. S. Albus, The Automated

Manufacturing Research Facility of the National Bureau of

Standards, J. Manuf. Syst. 1, 17-32 (1982).

245
Initial Graphics Exchange Specifications

Drawings created with Computer-Aided Design

(CAD) tools, which were introduced in the 1960s,

represented tremendous productivity gains over paper

drawings, such as ease to revise and archive. CAD

tools also opened new opportunities, such as enabling

manufacturing instructions to be derived automatically

and executed directly from the drawing. Nevertheless, as

computer design and manufacturing tools proliferated to

meet increasingly complex and diverse engineering

needs, so did the formats that each tool used to capture

and store product data. While paper drawings can be

marked up by anyone with a pencil, a product model

that cannot be interpreted by the necessary CAD tool

is useless. For organizations to share designs across

various CAD and Computer-Aided Manufacturing

(CAM) tools, their data files must be formatted in a

manner that the tool can recognize. This requirement has

become increasingly important in an age where large

manufacturers often form joint ventures to address a

business opportunity, and where partners in a supply

chain are being called upon to deliver an increasingly

complex array of services.

Most companies find it difficult to enforce the use of

a common set of CAD/CAM tools within their organization, much less across (multiple) supply chains and

among joint venture partners. Because of the lack of any

common set of tools, a common format for neutral file

exchange is needed. Using a neutral standard for

transferring information across systems drastically

reduces the requirements for translators. The cost

benefits are suggested by the reduction in necessary

translators shown in Fig. 1. It illustrates that by using a

neutral file exchange, the number of translators

(for N systems) can be reduced from scaling as n (n–1)

to 2n.

In 1979, a series of events catalyzed the CAD vendor

and user community to create the first national standard

for CAD data exchange, which is documented in the

report Initial Graphics Exchange Specification, Version

1.0 [1]. CAD systems were less than ten years old, and

only a handful of products had any significant market

penetration. Even at this early stage, users were overwhelmed by the inability to share data among these

tools and with their own internally developed databases.

Fig. 1. Illustration of the benefits of using a neutral file exchange.

246
In September 1979, frustration came to a head at the

two-day Air Force Integrated Computer-Aided Manufacturing (ICAM) Industry Days meeting [2]. On the

first day, a representative from General Electric

(GE) challenged a panel of CAD vendors, which

included ComputerVision, Applicon, and Gerber, to

work together to enable an exchange mechanism. While

this need was intuitive from a user’s perspective,

this was a very threatening proposition to the CAD

vendors—who feared that sharing the structure of their

databases publicly would be tantamount to giving away

their competitive advantage. It would have been easy to

gloss over the challenge; after all, the major vendors all

had at least token representation on the ANSI (American

National Standards Institute) committee responsible for

CAD standards. Instead, the ComputerVision representative responded with a challenge of his own: if Boeing

and General Electric (and perhaps others) would contribute the CAD translators they had already developed,

the vendors would share their database structures.

What led to this offer was just the right mix of

business motivation and intrigue. Large Navy contracts

were looming on the horizon, and no vendor wanted to

look unresponsive to customer requirements.

In the evening after the panel, several interested

parties gathered and asked themselves if a common

translator was really possible. The room had the right

mix of people and ideas at the right time. This included

an Air Force, Navy, and NASA representative, each

willing to fund $25,000 for such an effort. A National

Bureau of Standards representative, after a call to his

boss at home for approval, was willing to champion it as

chair and coordinator. The IGES Organization was

formed by NBS in the spring of 1980. With the fundamentals to a common translator decided, conversation

turned to a name for this new translation project. A

minimalist approach was suggested:

I – Interim, to suggest that it would not replace

ANSI’s work

G – Graphics, not geometry, to acknowledge that

academics may come up with superior mathematical descriptions

E – Exchange, to suggest that it would not dictate how

vendors must implement their internal databases

S – Specification, not to be as imposing as a standard.

The panel reported on the second day, and the wheels

were set in motion to create an “IGES.” Once the panel

admitted that a common translation mechanism was

possible, it was impossible to stop the momentum of the

customers’ enthusiasm and expectations. Applicon and

ComputerVision agreed to open up their internal databases, GE offered its internal database structure, and

Boeing supplied the structure of its Computer Integrated

Information Network (CIIN) database. Both GE and

Boeing contributed their existing translators. A core

team formed, including representatives from NBS

(Roger Nagel), Boeing (Walt Braithwaite), and GE (Phil

Kennicott). Team members had worked closely with

each of the vendors on internal integration projects. This

prior experience built the expertise and trust needed to

craft a solution in a very short time, and neither vendor

felt it gave an unfair advantage to the other.

Soon after the ICAM Industry Days, NBS called an

open meeting at the National Academy of Sciences

(October 10, 1979). Around 200 people attended to

herald the birth of IGES. There was an atmosphere of

extraordinary excitement, although not everyone was

readily supportive. In addition, although it was hotly

debated, the name was accepted eventually with the

minor change from “Interim” to “Initial.”

After two critical reviews, the IGES team released its

first draft in 1980, containing geometry, graphical data,

and annotations. The IGES specification was brought to

the ANSI Y14.26 committee for standardization. The

first version of IGES was adopted as an ANSI standard,

Y14.26M-1981 [3].

IGES successfully met a critical need. The IGES

publication [1] establishes information structures to be

used for the digital representation and communication of

product definition data. The specification is concerned

with the data required to describe and communicate the

essential engineering characteristics of physical objects

such as manufactured products. Such products are

described in terms of their physical shape, dimensions,

and information that further describe or explain the

product. The processes that generate or utilize the

product definition data typically include design, engineering analysis, production planning, fabrication,

material handling, assembly, inspection, marketing, and

field service. [4]

The Initial Graphics Exchange Specification is the

U.S. national standard for the exchange of data between

dissimilar CAD systems. The IGES standard, now in its

sixth revision, has been expanded to include most concepts used in major CAD systems. All major and

most minor non-PC-based CAD systems support some

version of the IGES standard. Some of the over 1000

PC-based CAD systems (including all of the major

ones) include some IGES support.

This first edition of IGES [1] served as a landmark to

introduce a change in the way manufacturers thought

about capturing and sharing their information about

product data. As enhancements to the original version

continued and IGES became an American National

Standard, the IGES Specification was routinely in the

top best sellers from the National Technical Information

247
Service (NTIS). Records show that through 1988 NTIS

sold 2055 copies of IGES 3.0, and through 1991 sold

1295 copies of IGES 4.0. This U.S. national standard

was also renowned internationally; it was adopted

nationally by Australia, Japan, and the United Kingdom,

to name a few. IGES was the precursor and provided the

technical groundwork to the international standardization effort known as STEP—Standard for the Exchange

of Product model data. The national and international

impact on the development and deployment of product

data standards in manufacturing has provided economic

benefits to many implementing companies using

product data standards for exchanging their data.

Examples of improvement brought about by the use

of IGES include [5]:

• Electric Boat Corporation, along with the rest of

the SEAWOLF (the US Navy’s newest attack

submarine) Team, pioneered the use of IGES to pass

construction data in digital format directly from

design to manufacturing.

• Honeywell Commercial Flight Systems (Minneapolis Operations), with its use of IGES, reduced

engineering change orders from 40-120 (1989) to

0-3 (1991).

• Piccione Machine Tool & Gear made a significant

CAD/CAM investment, using IGES for a neutral

exchange format. Consequently, the process of

manipulating their data was reduced from a manual

operation of 200 hours to a mostly automatic process

which was completed in less than two working days.

• Unique Tool & Gauge Inc.’s CAD/CAM department

has the responsibility of importing customer CAD

files into CAM for manufacturing. Utilizing several

software packages, the company found with effective IGES translation they were able to use their

IGES prowess as a competitive advantage offering

services above and beyond what they were

previously able to offer.

Today, IGES is still used as a universal tool, providing

a neutral format for many companies to transfer

engineering data between CAD/CAM systems. As of

late 1999, over 25 vendors offered commercial IGESsupporting tools [6].

In 1987, the three authors of The Initial Graphics

Exchange Specification were recognized collectively for

their contributions to the development of IGES Version

1.0 by receiving the AIMTECH Joseph Marie Jacquard

Memorial Award. The first author, Roger Nagel, was a

NBS staff member at the time and is now the Harvey

Wagner Professor of Manufacturing Systems Engineering in the Electrical Engineering & Computer Science

Department at Lehigh University. He created Lehigh’s

Robotics Research Institute, established and directed the

Manufacturing Systems Engineering Program, and

served as Executive Director of Lehigh’s Iacocca

Institute for Competitiveness Research. While an

employee of NIST, Nagel was a key member of the

scientific team developing the Factory Hierarchical

Control System in the Robotics Group. This work on

hierarchical control systems, performed with James

Albus, Tony Barbera, and Gordon Vanderbrug, has been

the basis of hundreds of computer-based control systems

for automation over the last 20 years. Nagel continues to

serve as a technical advisor and consultant to NIST’s

Manufacturing Engineering Laboratory.

The other two authors were from industry. Walt

Braithwaite is currently Corporate Vice President

for Company Offices Administration at the Boeing

Company. He has held numerous positions within

Boeing, including Director of Program Management

for the 737 and 757 airplane programs and Chief of

Engineering Operations for the 747 and 767 programs.

As the lead engineer responsible for technical direction

in developing an information network to integrate

computer-aided design and computer-aided manufacturing, he led development of Boeing’s common data

format and translators, which were used as a basis for

developing the IGES protocol.

Philip Kennicott joined the General Electric Research

Laboratory in 1961 where he made contributions in the

fields of x-ray crystallography and spark-source mass

spectrography. As a consultant to General Electric’s

Computer Aided Design Center, he was instrumental in

making General Electric the largest user of CAD/CAM

equipment in the world in the 1970s. This work led to

the concept of a neutral database, the basis for the

General Electric contribution to IGES. Within the IGES

community, Kennicott served as a leader of many

technical activities, including Editor of the continually

evolving IGES standard. He also led a technical team to

develop the Department of Energy Data Exchange

Format, the first IGES application protocol. He continued this work at Sandia National Laboratories in 1989

and retired from Sandia in 1997.

Prepared by Sharon J. Kemmerer.

248
Bibliography

[1] Roger N. Nagel, Walt W. Braithwaite, and Philip R. Kennicott,

Initial Graphics Exchange Specification IGES, Version 1.0,

NBSIR 80-1978, National Bureau of Standards, Washington, DC

(1980).

[2] Brad Smith, Roger Nagel, and Joan Wellington, IGES—Initial

Graphics Exchange Specification, in Autofact III: Conference

Proceedings, November 9-12, 1981, Detroit, Michigan, Society of

Manufacturing Engineers, Dearborn, MI (1981).

[3] Sharon J. Kemmerer (ed.), STEP, the Grand Experience, NIST

Special Publication 939, National Institute of Standards and

Technology, Gaithersburg, MD (1999).

[4] Initial Graphics Exchange (IGES), (http://www.nist.gov/sc4/

national/usa/iges/iges.htm), National Institute of Standards and

Technology. [5]Product Data Exchange Technologies Success

Story Booklet, 1997 IPO Winter Meeting.

[6] IGES Workshop/Tools, (http://www.nist.gov/iges/igesTools.html),

National Institute of Standards and Technology.

249
Data Encryption Standard

In 1972, the NBS Institute for Computer Sciences and

Technology (ICST) initiated a project in computer

security, a subject then in its infancy. One of the first

goals of the project was to develop a cryptographic

algorithm standard that could be used to protect sensitive and valuable data during transmission and in

storage. Prior to this NBS initiative, encryption had been

largely the concern of military and intelligence organizations. The encryption algorithms, i.e., the formulas or

rules used to encipher information, that were being used

by national military organizations were closely held

secrets. There was little commercial or academic

expertise in encryption. One of the criteria for an

acceptable encryption algorithm standard was that the

security provided by the algorithm must depend only on

the secrecy of the key, since all the technical specifications of the algorithm itself would be made public. NBS

was the first to embark on developing a standard encryption algorithm that could satisfy a broad range of

commercial and unclassified government requirements

in information security.

Ruth M. Davis, then Director of ICST, asked the

National Security Agency (NSA) to help evaluate the

security of any cryptographic algorithm that would be

proposed as a Federal standard. She then initiated the

standard’s development project by publishing an invitation in the Federal Register (May 15, 1973) to submit

candidate encryption algorithms to protect sensitive,

unclassified data. NBS received many responses

demonstrating interest in the project, but did not receive

any algorithms that met the established criteria.

NBS issued a second solicitation in the Federal Register

(August 17, 1974) and received an algorithm from the

IBM Corp., which had developed a family of cryptographic algorithms, primarily for financial applications.

After significant review within the government, NBS

published the technical specifications of the proposed

algorithm in the Federal Register (March 17, 1975),

requesting comments on the technical aspects of the

proposed standard. NBS received many comments on

the security and utility of the proposed standard and

held two public workshops during 1976 on its mathematical foundation and its utility in various computer

and network architectures. After intense analysis of the

recommendations resulting from the workshops, NBS

issued the Data Encryption Standard (DES) as Federal

Information Processing Standard (FIPS) 46 on November 23, 1977 [1].

Many NBS, NSA, and IBM technical staff members

participated in this initiative, which combined expertise

from government and industry. In 1973 the Bureau hired

Dennis Branstad to lead the new computer security

project and to coordinate the DES development process.

Miles Smid joined NBS in 1977 to aid in the adoption

of the DES in numerous American National Standards.

Both worked with their former NSA colleagues to

ensure that the standard met its technical criteria and

was useful in many commercial and government

applications. The major IBM contributors to the design

of the DES algorithm and its subsequent adoption as a

Federal standard included: Horst Feistel, inventor of a

family of encryption algorithms of which DES is a

member; Alan Konheim and Don Coppersmith, mathematicians in the IBM research organization; Walter

Tuchman, director of the IBM cryptographic competency center and the primary designer of the final DES

algorithm; and Carl Meyer and Mike Matyas, who

worked with Tuchman in specifying the DES and

analyzing its security.

DES did more to galvanize the field of

cryptanalysis than anything else. Now

there was an algorithm to study....

Today, DES is still the primary

algorithm used to protect data in the

financial services industry.

After NBS published the DES, the algorithm was

adopted as an ANSI standard [2] in 1981 and incorporated in a family of related standards for security in the

financial services industry. The DES became the

world’s most widely used encryption algorithm, particularly to protect financial information. Today, the American financial services industry depends almost entirely

on the DES to encrypt financial transactions.

250
The DES algorithm is a block cipher that uses the

same binary key both to encrypt and decrypt data

blocks, and thus is called a symmetric key cipher. DES

operates on 64-bit “plaintext” data blocks, processing

them under the control of a 56-bit key to produce 64 bits

of encrypted ciphertext. Similarly, the DES decryption

process operates on a 64-bit ciphertext block using the

same 56-bit key to produce the original 64-bit plaintext

block.

DES uses a sequence of operations, including several

substitution and permutation primitives, to encrypt a

data block. These primitives are subsequently used to

reverse the encryption operation. Horst Feistel defined a

variety of substitution and permutation primitives which

are iteratively applied to data blocks for a specified

number of times [3,4]. Each set of primitive operations

is called a “round,” and the DES algorithm uses 16

rounds to ensure that the data are adequately scrambled

to meet the security goals. The secret key is used to

control the operation of the DES algorithm. Each key

contains 56 bits of information, selected by each user to

make the results of the encryption operations secret to

that user. Any of approximately 1016 keys could be used

by the DES, and an attacker trying to “crack” a DES

encrypted message by “key exhaustion” (trying every

key) must, on average, try half of the total possible keys

before succeeding.

The development of the DES was not without controversy. There were two main objections:

1. NSA worked with NBS throughout the DES development, evaluated the proposed DES algorithm, and

recommended several changes to IBM. Specifically,

IBM made changes to the S-boxes, the nonlinear

substitution transformations that are the heart of the

algorithm, to improve the security of the DES.

During one of the public workshops, Tuchman

stated that he had changed the S-boxes to satisfy a

security requirement that he had not previously

known, and that his group had optimized S-box

operations to satisfy a technical constraint of the

electronics that they were currently using. Some

critics suspected that NSA had deliberately weakened, rather than strengthened, the S-boxes, or

perhaps even introduced a “trap door” that would

enable the intelligence part of the agency to decrypt

messages encrypted by the DES.

2. A commonly accepted definition of a good symmetric key algorithm, such as the DES, is that there

exists no attack better than key exhaustion to read an

encrypted message. Critics argued that the 56-bit

DES key was too short for long-term security, and

that expected increases in computer power would

soon make a 56-bit key vulnerable to attack by

exhaustion [5]. NBS responded that the standard was

adequate against any practical attack for the anticipated life of the standard and would be reviewed for

adequacy every five years. Moreover, although NBS

did not stress this in their public response, NBS and

Tuchman knew that the “DES core” could be used

three times on the same block of data to extend the

effective key length to 112 or 168 bits. The critics

were not satisfied, contending that encrypted datawould remain sensitive for more than 5 years and

that DES would be very hard to change once it

became widely used.

In retrospect, the DES has proved to be much better

than initially thought by its critics. After a quarter

century, the DES has proved remarkably resistant to

cryptanalytic attack, including attacks unknown in the

open literature in the 1970s. It seems certain that, as

Touchman stated, the S-box changes did strengthen the

DES in order to withstand several attacks that were not

public in 1977.

However, the critics were correct about the continuing

improvement in electronic technology. While the lifetime of the DES standard was originally estimated to be

15 years, it is still a Federal Information Processing

standard 23 years later. Due to the improvements in

technology, any 56-bit secret-key algorithm such as the

DES is now vulnerable to key exhaustion using massive,

parallel computations. In 1997, a message encrypted

with the DES was “cracked” in about 5 months by key

exhaustion using a large network of computers. In 1998,

the Electronic Freedom Foundation (EFF) constructed a

special purpose electronic device to decrypt messages

encrypted by the DES using custom-built semiconductor chips at a cost of about $130,000 [6]. The EFF “DES

Cracker” can find the key used by the DES to encrypt a

message in an average of about 4.5 days, and using more

chips could reduce this time.

The current Data Encryption Standard (FIPS 46-3)

[7] recommends an iterative use of the original DES

algorithm (as the DES development team envisioned in

the 1970s) known as “Triple DES” or “DES-3.”

DES-3 encrypts each block three times with the DES

algorithm, using either two or three different 56-bit

keys. This approach yields effective key lengths of

112 or 168 bits. DES-3 is considered a very strong

algorithm, and one recent paper [8] suggests that a

112-bit symmetric key algorithm such as DES-3 should

be secure until about the year 2050. The original 56-bit

DES algorithm is widely used to protect financial

transactions today and can easily be modified to be

interoperable with DES-3 and a 112-bit key. Some

cryptographers regard DES-3 as the most conservative

251
choice for very long-term data protection, since the

core DES algorithm has been so thoroughly analyzed.

NIST not only made a significant contribution in

technology through its development of the DES, but

also gained valuable experience in developing such

important, but potentially controversial, standards. In

1997, Miles Smid, then manager of the Security

Technology Group, initiated the Advanced Encryption

Standard (AES) development project. The anticipated

AES, is intended to be the DES successor and, like

the DES, will be a symmetric key block encryption

algorithm. The AES will offer larger key sizes (up to

256 bits) than the DES. However, since DES-3 appears

to be secure for some time in the future, the primary

near term advantage of the AES is that it will be

designed for software implementation and be much

faster than DES-3 on most platforms. Barring some

unforeseen breakthrough in cryptanalysis or computing

power, the AES should be secure for many decades. In

response to a public solicitation by NIST, interested

parties submitted 21 candidate algorithms to be considered for adoption as the AES. Of those submitted,

fifteen met NIST’s initial criteria for consideration and

five very good algorithms were selected in August 1999

for additional analysis and review. NIST expects to announce the final selection in 2001. NIST, having gained

increased stature within the security technology

community through its experience gained by its DES

initiative, is able to conduct the selection process in an

open manner that virtually precludes suspicion of secret

trap doors.

Dennis Branstad, who shepherded the development

of the original DES, received his Ph.D. in Computer

Science from Iowa State University, and worked at the

National Security Agency before coming to NBS in

1973. Denny is widely respected in the cryptographic

community for his technical abilities, his sage judgment

and his considerable interpersonal skills. He has been a

mentor and friend to many in the Computer Security

Division. At the time of his retirement in 1994, Denny

was a NIST Fellow.

Miles Smid received his BS in mathematics from the

Univ. of Chicago and his MA in mathematics from the

Univ. of Maryland. Miles came to NBS from the

National Security Agency in 1977 and worked on the

development of numerous Federal Information Processing Standards and ANSI standards in cryptography.

Miles was the manager of the NIST Security Technology Group through most of the 1990s, a difficult period

of contentious, highly charged policy as well as technical issues in cryptography. Nevertheless, he managed to

be respected by nearly everyone, whatever their policy

views, as both a cryptographer and a “straight shooter.”

Miles orchestrated the still ongoing AES effort in a

manner that seems to have satisfied a very broad range

of often-contentious interests and which promises to

result in a very broadly accepted and used standard.

Miles was Acting Chief of the Computer Security

Division at the time of his retirement in 1999.

The DES can be said to have “jump started” the

nonmilitary study and development of encryption

algorithms. In the 1970s there were very few cryptographers, except for those in military or intelligence organizations, and little academic study of cryptography.

There are now many active academic cryptologists,

mathematics departments with strong programs in

cryptography, and commercial information security

companies and consultants. A generation of cryptanalysts has cut its teeth analyzing (that is trying to

“crack”) the DES algorithm. In the words of cryptographer Bruce Schneier [9], “DES did more to galvanize

the field of cryptanalysis than anything else. Now there

was an algorithm to study.” An astonishing share of the

open literature in cryptography in the 1970s and 1980s

dealt with the DES, and the DES is the standard against

which every symmetric key algorithm since has been

compared.

One of the consequences of this development of nonmilitary cryptography has been validation of the basic

model of public specification and review of encryption

algorithms that NBS pioneered with the DES. The

DES is well trusted because it has been so intensely

studied, but the past 20 years are replete with examples

of algorithms designed in secret, whose users attempted

to keep the algorithm secret. In many of these cases,

not only was the algorithm exposed by reverse engineering or by leaks, but the algorithm, or the overall cryptographic system that used it, was also shown to be

insecure after it was already in wide use in products

such as digital cellphones or digital video disk players.

In addition, many software products offer ad hoc, homebrew encryption which has been cracked by experts

after only a few days of study, and there are commercially available products that decrypt files protected

by such programs. Time has shown that the public

approach NBS chose for developing the DES standard

was the best approach from a security point of view.

Security by obscurity does not work.

In summary, the DES was a pioneering and farsighted

standard which helped set a new paradigm for openly

published and reviewed encryption standards. The DES

has been an enormously useful and influential standard

and remains, when used in its Triple DES mode, secure

today, a quarter century after it was first proposed. It is

252
also, today, still the primary algorithm used to protect

data in the financial services industry. The new AES

standard builds on the legacy of DES and should meet

our needs well into the new century.

Prepared by William E. Burr.

Bibliography

[1] Data Encryption Standard, Federal Information Processing

Standards Publication (FIPS PUB) 46, National Bureau of

Standards, Washington, DC (1977).

[2] Data Encryption Algorithm (DEA), ANSI X3.92-1981, American

National Standards Institute, New York.

[3] Horst Feistel, Cryptography and Computer Privacy, Sci. Am. 228

(5), 15-23 (1973).

[4] Horst Feistel, Block Cypher Cryptographic System, US Patent

3,798,359, March 19, 1974.

[5] Whitfield Diffie and Martin E. Hellman, Exhaustive Cryptanalysis of the NBS Data Encryption Standard, Computer 10 (6),

74-84 (1977).

[6] Electronic Frontier Foundation, Cracking DES: Secrets of Encryption Research, Wiretap Politics and Chip Design,

O’Reilly & Associates, Inc., Sebastopol, CA (1998).

[7] Data Encryption Standard (DES), Federal Information Processing

Standards Publication (FIPS PUB) 46-3, National Institute of

Standards and Technology, Gaithersburg, MD (1999).

[8] Arjen K. Lenstra and Eric R. Verheul, Selecting Cryptographic

Key Sizes (http://www.cryptosavvy.com/) October 1999.

[9] Bruce Schneier, Applied Cryptography, Protocols, Algorithms,

and Source Code in C, Second edition, John Wiley and Sons,

New York (1996) p. 267.

253
OMNIDATA and the Computerization of

Scientific Data

For much of its history, the National Bureau of

Standards has been a leader in providing the most

reliable available technical data to scientific and engineering users. The Bureau has operated large-scale data

evaluation programs in a wide variety of disciplines and

has distributed the results through various publication

channels. With the advent of modern computers, it was

natural for NBS data experts to explore how computers

could be used both for internal data management

activities and for the public dissemination of NBS data

collections. During the 1970s, the Office of Standard

Reference Data (OSRD) and the various data centers

that it coordinated embarked on a number of projects

aimed at utilizing the growing power of digital computers to improve the efficiency and effectiveness of the

SRD program. NBS quickly became recognized as a

pioneer in this area.

At that time, there was a tendency for each data group

to develop computer programs to handle the particular

type of scientific data of concern to it. Since the SRD

program covered such diverse classes of data, there was

an incentive for OSRD to investigate the possibility

of developing general purpose programs capable of

managing a broad range of data. This effort led to

the creation of the database management program

OMNIDATA, described in the book OMNIDATA, An

Interactive System for Data Retrieval, Statistical and

Graphical Analysis and Data-Base Management: A

User’s Manual [1], authored by Joseph Hilsenrath

and Bettijoyce Breen. This represents the first major

publication of the National Bureau of Standards in the

area of computerized scientific data management.

In the early 1970s when the OMNIDATA project

was begun, data retrieval, data analysis, and data file

maintenance were largely done in the batch mode, with

programmers submitting punched cards for processing

on a mainframe computer and, after an indeterminate

period of time, receiving a printout of results. Also,

computer programs designed to run routinely were

almost always inflexible, and the writing of ad hoc

programs to answer specific questions often entailed

expense and delay out of proportion to the urgency of

the problem that motivated the question in the first place.

When early commercial general-purpose data management programs began to appear, primarily intended for

business applications, they had adequate and roughly

comparable search and retrieval capability, file definition features, and report generators. None, however, had

enough data analysis and data manipulation facilities

to handle the numerical and alphanumeric data files

required for scientific use, nor did they address unique

characteristics of scientific information, such as Greek

and mathematical symbols, uncertainties, and varying

number of significant figures, all of which added to the

complexity to scientific data.

OMNIDATA was designed to overcome many of

these shortcomings. Programs were written to analyze

and store data. Rudimentary graphics packages created

visualizations of data. The 45 unique modules and the

supervisory program of the OMNIDATA system could

be used not only by the computer professional, but also

by the novice with little or no knowledge of computers.

It could be run in demand mode, interactively from a

computer terminal on a time-shared computer system.

In addition to handling such administrative files as

personnel, training, inventory, and travel, the system was

robust enough to handle diverse scientific data files,

including crystal structure data, thermochemical data,

chemical kinetics data, and data on physical properties.

Finally, OMNIDATA was designed and written to

be modular, a hallmark of truly efficient computer

programming and systems design, and a visionary

precursor to what is today called component-based

software.

Most of the individual modules provided tools for

data retrieval, analysis, and reporting. Specifically,

the system had facilities for searching and reporting;

plotting and graphical analysis; arithmetic operations

in general, and statistical analysis in particular; file

partitioning and subsequent sequential analysis on

subfiles; keyword indexing of bibliographic files;

flagging, coding, and decoding of data items; analysis

of questionnaires and surveys; and a large variety of data

management and validation routines of use to both the

end user of the data and the database administrator.

An important feature of OMNIDATA was its ability

to convert data files from other formats for use in the

OMNIDATA system and to generate data arrays

that could be accessible to other programs written

in languages including FORTRAN, COBOL, and

XBASIC. Also, the OMNIDATA system interfaced with

the OMNITAB II program [2], used extensively at NBS

and elsewhere, to provide a repertory of well-tested and

highly accurate statistical routines.

254
The OMNIDATA system allowed for flexibility in file

size. With it, one could profitably automate files

from those with few records of a small number of data

elements to elaborate databases of many records with

numerous data fields. In contrast to other management

information systems of the era, which limited the

number of data items that could be searched or manipulated, each module in OMNIDATA was capable of operating on every data item, and the user could search on

any field, even down to the character level. Its modularity, flexibility, and data analysis capabilities made

OMNIDATA unique. It was a forerunner of the database

management systems marketed today and the systems so

essential to the functioning of the World Wide Web.

The use of OMNIDATA quickly spread to other parts

of NBS, beyond the Standard Reference Data Program,

so much so that there were continuing problems in

providing support and extensions for a diverse group of

users. The legacy of OMNIDATA was not the software

itself, but the realization that scientific data projects

could successfully convert to computerized operation—

and that they would have to do so in order to continue as

viable projects.

The lessons of OMNIDATA were critical to the push

to computerize both the internal data operations and the

dissemination of databases, which began in earnest in

the 1980s. The effort was led by Bettijoyce Breen and

John Rumble, Jr., who joined the Office of Standard

Reference Data in 1980. During this decade every NBS/

NIST data activity created databases of references

containing the data of importance to its area of responsibility. Many developed specialized data entry

programs that captured not only this bibliographic information, but also the numeric tabular and graphical data

contained therein. In addition, the data centers developed suites of software that supported data evaluation

through the use of discipline specific analysis, statistical

procedures, and correlation techniques. At the beginning of this effort, most of the software incorporated the

ideas found in OMNIDATA, with significant extensions

to take care of specialized requirements.

Many of the data handling software packages developed at NBS were used by outside organizations. The

NIST Crystal Data Center developed AIDS 80, a powerful package that evaluated and managed crystallographic data [3]. The NIST Alloy Phase Diagram Data

Center created a suite of graphical digitization and

database management tools that supported the international Alloy Phase Diagram Program run jointly by

the American Society of Metals and NBS [4]. A similar

set of graphics software was developed for handling

ceramics phase diagrams under the NBS-American

Ceramic Society Phase Diagram for Ceramists Program

[5].

The computerized dissemination of NBS collections

of evaluated data proceeded likewise. In the late 1970s,

NBS worked with the Environmental Protection Agency

and the National Institutes of Health to create and operate the Chemical Information System (CIS), which was

the first online system to provide scientific numerical

data. The CIS featured a powerful substructure and

nomenclature search system that allowed users not only

to search for data on a specific substance, but also to

identify classes of chemical compounds with particular

structural features. The CIS integrated databases built

by many groups, including NBS thermochemistry and

crystallographic data centers.

At the same time, the Standard Reference Data

program began offering magnetic tapes of formatted

data files suitable for outside users to load onto their

own mainframe computers. It was the responsibility of

the users to build their own search software and to

manage the data. The PC revolution of the 1980s

changed all that, and OSRD quickly began offering files

similar to those on magnetic tapes on floppy disks. It

soon realized, however, that users wanted self-contained

packages that were easy to install and that included

built-in user interfaces. By 1985 two systems were under

advanced development. Steve Stein, then of the Center

for Chemical Physics, was building an MS-DOS mass

spectral data system, and Chuck Wagner of Surfex and

John Rumble, Jr., of NBS were building an x-ray

photoelectron spectroscopy (XPS) database on an

Apple platform. The mass spectral database was

released in 1987 and became an immediate success.

Today it is incorporated into virtually every mass

spectrometer sold. The next two years saw many other

NBS databases released including the XPS database.

In 1982, NBS scientific database management efforts

addressed another area, that of materials data. In

November of that year, NBS cosponsored with FIZ

Karlsruhe (a German government technical information

center) and CODATA (the ICSU Committee on Data for

Science and Technology) a workshop on computerized

materials data. This Fairfield Glade meeting, named

after its location in Tennessee, spawned an international

activity to build an online materials data system. The

proceedings from that workshop, Computerized Materials Data Systems [6], edited by Jack Westbrook and

John Rumble, Jr., were widely circulated worldwide and

became the “bible” for planning such an online system.

The seminal meeting addressed the full range of topics

related to online materials data systems, including their

scope, user interfaces, system development, legal and

economic issues, and barriers to be overcome. The

Fairfield Glade Workshop concluded that it was not only

possible to build such a system, but that one should be

built as soon as possible.

255
Over the next five years, over 15 additional workshops were held covering the full range of engineering

materials disciplines, potential user industries, and

many other aspects. A prototype system was built with

funding from NBS, the Department of Energy, and

the Department of the Army. The Metals Properties

Council, a trade association of the metals industry,

worked with NBS and other groups to establish the

non-profit Materials Property Data Network (MPDN).

The MPDN, which soon became part of the STN dialup network of the Chemical Abstracts Service, was a

successful online data system in the pre-Internet era.

One offshoot of this effort was the establishment of

ASTM Committee E49 on Computerization of Materials Properties Data. This committee, which was chaired

by John Rumble from 1988 to 1993, rapidly became the

international focal point for standards relating to all aspects of the computerization of materials data, and these

standards are in wide use today.

The blossoming of NBS/NIST computerized data dissemination continued unabated until about 1994, when

two concurrent changes hit the computer world. These

were the release of the Microsoft Windows operating

system and the Internet explosion. In one short period,

the NIST PC databases and older online systems such as

the MPD Network became obsolete as users demanded

Windows versions of existing MS DOS data products. In

addition, the Internet, and especially the World Wide

Web, revolutionized online data delivery. Where previous online systems required years of development, the

Web required only months of work. At the present time,

NIST operates 15 Web-based data systems that receive

thousands of users every day.

Today’s scientific database environment is a long way

from the mainframe world of 1976 when Hilsenrath and

Breen issued their first manual for OMNIDATA, and

even of 1986, when the first MPDN prototype came

online. These changes have made the creation of databases considerably easier and have brought easy access

for users worldwide to the full range of NIST evaluated

data. The ideas in OMNIDATA and Computerized

Materials Data were germinal in articulating the core

principles of scientific database management and online

dissemination. The distance traveled since then is a

tribute to Hilsenrath, Breen, and Rumble and their foresight in leading NBS to the forefront of computerizing

scientific data.

Joseph Hilsenrath began his career at NBS in 1948,

first as a scientist/mathematician specializing in employee training, then as an experimental researcher in

high pressure physics, after which he became Chief of

the Equation of State Section of the Heat Division. As

the first computers became available at NBS, he became

interested in the preparation of tables of thermodynamic

data and in putting computer know-how in the hands of

Everyman. His OMNITAB statistical packages received

wide use in NBS and other Government agencies. He

moved to the Office of Standard Reference Data in

1967, where he led the development of computerized

typesetting methods that saw use throughout the

Government. He retired in 1974, but for many years

remained active in NBS reference data activities.

Bettijoyce Breen joined NBS in 1969 as a computer

programmer for the Office of Standard Reference Data

after receiving her B.S. in chemistry from William

and Mary College. After completion of the work on

OMNIDATA, she supervised the introduction of the next

generation of computerized typesetting technology into

NBS and later became head of the OSRD Data Systems

Development Group. This group helped the various data

centers in NBS and elsewhere to automate their operations and oversaw the preparation of database packages

for public dissemination. She received an M.S. in

Chemical Information from American University in

1975 and became active in the Chemical Information

Division of the American Chemical Society, serving as

both Treasurer and Chair of the Division. In 1990, as

Bettijoyce Breen Lide, she joined the NIST Advanced

Technology Program (ATP), where she set up the first

ATP management information system. As an ATP program manager, she established the program on Information Infrastructure for Healthcare and later headed the

Information Technology and Applications Office. In

1999 she received the George Uriano Award of NIST for

fostering industrial-government interactions.

John Rumble, Jr. joined NBS in 1980 as the OSRD

program manager for materials data. In addition, he

played a strong role in computerizing NBS/NIST data

activities in all disciplines. Rumble became Chief of the

Office of Standard Reference Data in 1994. He has been

active in many activities related to standards for scientific and technical information and was elected President

of CODATA in 1998. He is also a Fellow of the ASM

International and the American Society for Testing and

Materials.

Prepared by John R. Rumble, Jr.

256
Bibliography

[1] Joseph Hilsenrath and Bettijoyce Breen, OMNIDATA, An Interactive System for Data Retrieval, Statistical and Graphical Analysis and Data-Base Management: A User’s Manual, NBS Handbook 125, National Bureau of Standards, Washington, DC

(1978).

[2] Joseph Hilsenrath, Guy G. Ziegler, Carla G. Messina, Philip J.

Walsh, and Robert J. Herbold, OMNITAB: A Computer Program

for Statistical and Numerical Analysis, NBS Handbook 101,

National Bureau of Standards, Washington, DC (1966); David

Hogben, Sally T. Peavy, and Ruth N. Varner, OMNITAB II:

User’s Reference Manual, NBS Technical Note 552, National Bureau of Standards, Washington, DC (1971).

[3] A. D. Mighell, C. R. Hubbard, and J. K. Stalick, NBS*AIDS80: A

FORTRAN Program for Crystallographic Data Evaluation, NBS

Technical Note 1141, National Bureau of Standards,

Washington, DC (1981).

[4] Thaddeus B. Massalski (ed. in chief), Binary Alloy Phase

Diagrams, Vols. 1-3, Second Edition, ASM International,

Materials Park, OH (1990).

[5] Richard M. Spriggs and Stephen W. Freiman ACerS/NIST Phase

Equilibria Update, Am. Ceram. Soc. Bull. 75 (1), 83-85 (1996).

[6] J. H. Westbrook and J. R. Rumble, Jr., Computerized Materials

Data, National Bureau of Standards, Gaithersburg MD (1983).

257
FORTRAN Test Programs

The career of Frances E. (Betty) Snyder Holberton,

the lead author of SP 399, NBS FORTRAN Test

Programs [1], closely tracks the evolution of information

technology (IT) for the four decades following World

War II. Her work at NBS (1966-1983) and her leadership in preparing this landmark publication are best

understood in the context of her earlier career.

Her first work remains perhaps the most notable:

she was a member of the first team of programmers

(composed of six women) to work on the ENIAC [2,7],

the first operational, general purpose, electronic digital

computer. “Programming” in those early days did

not consist of writing code; rather, it meant setting

thousands of switches and connecting dozens of cables

so as to route data correctly through the machine.

ENIAC was built at the Moore School of Electrical

Engineering at the University of Pennsylvania.

Completed in late 1945, it is widely regarded as a milestone in the history of computer technology. After five

years at the Moore school, Holberton left in 1947 to

work at the Eckert-Mauchly Electronic Control

Company to participate in the development of the

UNIVAC.

Her work on the UNIVAC included the development

of the C-10 language, one of the first to use mnemonic

(symbolic) instructions (e.g., “a” for add, “b” for bring).

She also wrote the first sort-merge software, notable as

perhaps the first case of a program whose function was

to generate another program—a key idea in the notion of

a programming language compiler. Compilers make it

possible to express computer programs in high-level

languages, such as FORTRAN, C, or Java, instead of the

low-level instructions which are directly processed by

the computer hardware. A line of FORTRAN, such as

ANGLE = ATAN (SGMENT / SQRT(X*X + Y*Y))

will typically generate several instructions in machine

language (so-called object code); producing this

machine code directly would be quite tedious and

error-prone.

From the appearance of the line of FORTRAN above,

one might reasonably guess that its purpose is to square

two quantities, labeled X and Y, add them, take the

square root of that sum, divide that quantity into

SGMENT, take the arctangent of the quotient and save

the result as ANGLE. All well and good, but will this

line of code work equally well (or work at all) when

processed on different vendors’ machines? Note that

vendors A and B may well have completely different

underlying hardware (i.e., their low-level machine codes

are not the same). Furthermore, each has very likely

written its own compiler—so the translation process

itself from FORTRAN (the so-called source code) to

machine code may well be different. Even assuming that

the A and B compiler-writers make no unintentional

errors, we still need to make sure that they are working

toward the same goal. The very notion of a formal

language implies strict rules about the spelling and

meaning of its expressions [4,6]. For instance, the

square root function must be spelled “SQRT,” not

“SQROOT.” Furthermore, even assuming that both

compilers accept the standard spelling (i.e., they accept

the source code and generate machine code), the

problem of semantics remains. For instance, in our

example, does the arctangent function return its result

in degrees or radians? COBOL and FORTRAN

standards committees were established [8] to ensure that

just such issues were resolved in a uniform way, and

Betty Holberton was an active participant on these

committees. As a result, software written according to

the standard could be expected to run consistently on a

wide variety of machines. Given the cost of developing

large software products, this is no small benefit.

By the early 1960’s, industry standards for high-level

languages such as FORTRAN and COBOL were

becoming widely accepted. One problem remained:

how to be sure that the standard was being implemented

correctly by the various vendors? Put another way:

how to measure the validity of the compiler software

itself?

Although metrology had always been a core function

of NBS, devising measurement methods for information

technology nonetheless represented a novel challenge.

Previous work had typically addressed the measurement

of physical quantities, such as temperature, electrical

charge, mechanical strength, composition, etc. But

many of the artifacts of information technology are

essentially logical structures. True, software is realized

on some physical medium, but most often it is the

logical behavior of the software that is of greatest

interest, not the details of its physical implementation.

(Of course, NBS has had a hand in developing tests for

the physical media of computers as well.)

One way to determine the validity of a piece of software is simply for a skilled programmer to read it;

258
indeed, code review is an important part of the software

engineering process. Nonetheless, such a subjective

procedure could hardly serve as the basis for an

“official” determination that a compiler did or did not

conform to the language standard. Moreover, there are

operational issues: how well trained are the reviewers?

How long would it take them to verify a single compiler?

There was a need for a largely automated and objective

method for checking compiler conformance to the

standard.

This was the problem addressed by Holberton and her

colleague Elizabeth Parker in NBS FORTRAN Test

Programs. Their solution was a set of test programs that

methodically exercised all the features of the language

to be checked. If the routines were accepted by the

compiler and generated the expected output, then the

compiler was basically reliable (although no finite set of

tests could ever prove that a compiler is completely

correct). If not, then the errors would be noted and

reported back to the vendor for correction. At first, the

only official use of the test sets was to certify conforming implementations, which were then eligible for

purchase by Federal agencies. Of course, this provided

a strong incentive for vendors to produce standardconforming software. In time, the idea of test sets to

support software standards became widely accepted.

This basic strategy is used to this day to validate

software development tools, such as language compilers

for C and Java and so-called Application Programmer

Interfaces (APIs) such as SQL (for database operations)

and OpenGL (for 3-D graphics). Since the same

programs are used for all vendors, the testing process is

transparently fair and objective. Of course, a human

operator has to run the tests and examine the output, but

this is not much different than a chemist obtaining the

results of an experiment from a balance or other

measuring instrument.

Furthermore, the test programs were ordered, checking the most basic language features first and then

progressing to the more sophisticated aspects. This gave

the operator good evidence about which features were

the cause of any failures detected. NBS/NIST has since

participated in the design, development, and operation

of several comprehensive software test sets [3]. It should

be stressed that, while the operation of the tests is mostly

automated, the development of the tests requires a high

degree of skill and understanding of the standard being

applied. Test sets often comprise tens, or even hundreds

of thousands, of lines of code. Conformance testing

remains an important part of the NIST mission [10].

Betty Holberton worked for Remington-Rand in the

early fifties, and then began her long career in government, first at the Applied Mathematics Laboratory of

the David Taylor Model Basin (1953-1966), then at the

National Bureau of Standards until her retirement in

1983. Her government work was spent largely in the

development and testing of standards for computer

languages. In 1997, her many achievements were

recognized by the Association for Women in Computing, which presented her with its highest honor, the

Augusta Ada Lovelace Award [9]. Also in 1997, Women

in Technology International (WITI) inducted all six of

the original ENIAC programmers into their Hall of

Fame [5].

Prepared by John Cugini.

Bibliography

[1] Frances E. Holberton and Elizabeth G. Parker, NBS FORTRAN

Test Programs, NBS Special Publication 399 (3 volumes),

National Bureau of Standards, Washington, DC, October 1974.

[2] Rachel K. Adelson, Programmed to Succeed: Betty Holberton

(http://www.awc-hq.org/livewire/199705.html), Association for

Women in Computing.

[3] J. Cugini, Interactive Conformance Testing for PHIGS,

Eurographics ’91, September 1991 (ftp://ftp.nist.gov/pub/vvrg/

pvt/pvt-design.ps). This paper discusses some recent issues in

the application of conformance testing to graphics.

[4] I. D. Hill and B. L. Meek, Programming Language Standardisation, Ellis Horwood Ltd., Chichester, England (1980).

[5] Kathryn A. Kleiman, Speech for WITI 1997 Hall of Fame

Ceremony (http://www.witi.com/center/witimuseum/halloffame/

1997/eniac.shtml), Women in Technology International.

[6] Terrence W. Pratt, Programming Languages: Design and

Implementation, 2nd ed., Prentice-Hall, Englewood Cliffs, NJ

(1984).

[7] Thomas Petzinger, Jr., The First Computers Were The

Women Who Invented Programming (http://members.aol.com/

douglaseby/Page83.html). Wall Street Journal article on ENIAC

programmers, November, 1996.

[8] American National Standard FORTRAN, ANSI X3.9-1966. This

is the original FORTRAN standard, long since superseded by

more recent versions.

[9] Announcement of the 1997 Augusta Ada Lovelace Award (http://

www.awc-hq.org/lovelace/1997.htm), Association for Women in

Computing.

[10] Homepage of the NIST Software Diagnostics and Conformance

Testing Division (SDCT) (http://www.itl.nist.gov/div897/),

National Institute of Standards and Technology.

259
Design and Evaluation Criteria for Energy

Conservation in New Buildings

In the early 1970s, one-third of the energy consumed

in the United States was used to heat and cool buildings

and to provide illumination, water heating, and other

building services. Shortages of fuel oil, gas and electricity were quite prevalent on a localized basis in the winter

of 1972-73. Temporary closing of schools, shutdowns of

industry and government facilities during spells of

severe weather, and electrical brownouts created strong

demands in several states for regulations that would

provide for equitable distribution of available supplies

during periods of shortage. Responding to these

demands in the spring of 1973, the National Conference

of States on Building Codes and Standards (NCSBCS)

requested the National Bureau of Standards (NBS) to

develop a set of design and evaluation guidelines for

energy conservation in buildings that states could use

pending development of a national consensus standard.

These requirements were to be nationally applicable and

effective for buildings of all types. NBS drew on its

long-term research expertise in the prediction and

measurement of building thermal performance and

lighting to formulate a technically and economically

effective approach to the design of new energyconserving buildings. In February 1974, shortly after

the OPEC oil embargo, NBSIR 74-452, Design and

Evaluation Criteria for Energy Conservation in New

Buildings [1], became available for use.

Most states have delegated their constitutional

authority for establishing and enforcing building codes

to local units of government. In the late 1960s, Charles

T. (Chuck) Mahaffey of NBS conceived a plan to

address the problem of non-uniformity in U.S. building

codes and standards, based on the way the states and

NBS cooperated in the National Conference of Weights

and Measures, Cement and Concrete Reference

Laboratories (CCRL), and American Association of

State Highway and Transportation Officials (AASHTO).

As an outgrowth of an exploratory meeting in which

state officials in Wisconsin played a major role,

NCSBCS was formed on November 20, 1967, at an

organizational meeting attended by delegates from

16 states. It was agreed that NCSBCS would provide

a forum for discussing administrative problems in

building regulation at the state level, and develop

and seek adoption of uniform and comprehensive state

building codes and standards. NBS officially furnished

secretariat services from April 1970 until

October 1976, housed NCSBCS until September 1976,

and continued to provide technical support [2,3,4].

NCSBCS soon took up the question of regulations to

conserve energy use in buildings. Its Standards and

Evaluation (S&E) Committee noted that “the sense of

urgency connected with the energy crises may cause

some states to enact hastily prepared legislative

requirements ill-suited to solving the national problems

involved.” At the Committee’s request, Paul R. (Reece)

Achenbach summarized NBS research in the field of

energy use in buildings. As a result, the Committee

members voted as follows:

1. [We] endorse the concept that energy conservation is

of national concern and that related building design

and construction is properly a building code subject.

2. Consistent with state NCSBCS objectives, uniform

national performance-oriented reference standards

should be generated.

3. [We] request continued NBS activity in this area, and

specifically the following: Report to the S&E Committee with recommendations on the possible content

and strategy for generation of a building related

energy conservation reference standard, including

the consideration of cost implications. Since the

scope of building codes had historically been limited

to life safety issues, Item 1 led to a major shift in

building regulatory policy in the United States (and

Canada).

In August 1973, NCSBCS formally asked for NBS

assistance in developing a four-part energy conservation

program, including development of a draft performance

standard for state regulatory reference and call for a

sponsor to act as the secretariat for eventually processing the standard through the American National

Standards Institute (ANSI). NBS agreed: 1) to develop

the design and evaluation criteria for energy conservation in new buildings (NCSBCS would offer these to a

suitable sponsor as a basis for developing an energy

conservation performance standard); and 2) to advise

NCSBCS on options for advancing its criteria through

the consensus process.

260
The 1974 energy document was developed by a 15-

man NBS Task Group and 5 advisors with Reece

Achenbach as Program Manager and Jim Heldenbrand

as Project Manager. The Task Group investigated a

number of different approaches, rating as most likely

to attain the objectives a “framework of performance

standards supported by performance requirements of

subelements.” It was chosen largely because available

technical knowledge and economic tools limited a

broader performance approach, and because time was

short.

The resulting document [1] was regarded as primarily

a component performance approach, but it also

contained some specification (prescriptive) requirements and had some features of a building performance

standard. As illustrated in Fig. 1, it provided three

design paths for obtaining a building with acceptable

design energy requirements. The basic approach was to

describe the performance criteria for the components of

a building envelope, and the heating, air conditioning,

ventilating, domestic water heating, and lighting systems

to provide for efficient use of energy. Having first

determined the annual energy requirement of a given

design in accordance with this basic approach, the

designer could use any other combination of building

and equipment characteristics that would require equal

or less energy on an annual basis for the same building

function. Under the third alternative, the designer would

receive a bonus of up to half of any energy supplied

by solar or wind-powered equipment in determining the

annual energy requirements for the proposed building.

The 1974 document saw a need for more energy and

economic information to improve the energy performance criteria. The information fell into four areas:

1. procedures and data for determining economic

efficiency;

2. energy analysis data

• part-load efficiency data; control characteristics

• air distribution

• standard weather data for energy analysis

• engineering data for nonconventional systems

• simplified and reliable energy calculation procedures;

3. testing procedures;

4. infiltration.

NBS was positioned to advance the state of researchbased data and procedures in several of these areas. The

building energy conservation program at NBS accelerated in the early 1970s, having begun with heat transfer

work by the Heat Division in the first 10 years of NBS’

existence and continued with the establishment of the

Building Technology Division in 1947 with Douglas

Parsons as its Chief. In the 1960s this work was conducted in the newly established Building Research

Division with James R. Wright as Chief. Much of the

building research work is documented in two series of

publications, Building Materials and Science (over 150

publications) and the current Building Science Series.

Building research through 1968 was well documented

by Achenbach [5].

Fig. 1. Three paths to approval of energy-based design.

261
The energy crisis demanded more sophisticated engineering calculation methods and design, based on quantitative predictions. NBS was ready for the challenge

with its background in heat transfer, use of a temperature controlled building shell enclosing a full scale

bungalow at the Connecticut Avenue site for measuring

efficiency of heating and cooling systems, and the

experience of testing and rating heat pumps, including

projects in situ. At the Gaithersburg site, NBS had

state-of-the-art laboratory facilities, including environmental chambers for controlled temperatures from

–45 C to 65 C (–50 F to 150 F) with humidity

control, as well as outdoor testing facilities, including

the Bowman house. Engineering (slide rule) calculations normally consisted of estimating the “steady-state”

maximum heating and cooling loads using peak weather

data, heat and air transfer calculations, and estimates of

imponderables like occupant living patterns, rate of

window and door openings, and hot water and appliance

usage. When energy was cheap and readily available,

this system worked well because equipment could be

oversized with factors of safety. What was needed for

the high-cost energy crisis was accurate predictions

based on measured data, hourly weather data covering

all seasons of the year in any location and the dynamic

profile of hourly energy required by a proposed building

design for a full year. A rapid computer capability was

available for computations at NBS; the National Oceanic

and Atmospheric Administration could supply hourly

weather data for a whole year or for many years for

many cities in the United States and globally; and the

American Society of Heating, Refrigerating, and

Air-Conditioning Engineers (ASHRAE) was rapidly

coming up on the learning curve of dynamic computer

calculations.

Tamami (Tom) Kusuda at NBS developed a dynamic

computer calculation program called the National

Bureau of Standards Load Determination Program

(NBSLD), described elsewhere in this volume, to

address these problems in depth. With availability of a

70,000 cubic foot environmental chamber at NBS, a

series of experiments was devised to validate NBSLD

using three-dimensional structures whose exteriors

could be subjected to dynamic temperature and humidity boundary conditions. The results of experimental

validation testing of NBSLD were published in Building

Science Series (BSS) 45 in 1973 [6] and in BSS 57 in

1975 [7]. The response factor space load prediction

methodology of NBSLD was found to be accurate, and

the agreement between calculated and observed heating

energy rate was considered excellent. This work had

landmark impact because the tools for energy design

and savings procedures were convincingly demonstrated to be reliable.

NBS recommended that its 1974 energy conservation

document be used as a basis for development of a

national voluntary consensus standard. NCSBCS

requested that ASHRAE process the NBS report as a

national consensus standard [1]: ASHRAE established

an extraordinary effort to analyze and refine the

NBS report and, in August 1975, published ASHRAE

Standard 90-75 (revised 1977) Energy Conservation in

New Building Design, with the technical support of IES

(now IESNA).

In January 1977, representatives of NCSBCS and the

three model building code organizations put ASHRAE

90-75 into code language under sponsorship of the

Energy Research and Development Administration

(ERDA) and submitted it to public review and hearings.

In December, 1977 the final version was published by

the Council of American Building Officials (CABO).

Subsequent revisions are known as the Model Energy

Code (MEC) [8]. Over the ensuing decade, all 50 states

enacted regulations based on the ASHRAE 90 Series

Standards, the Model Energy Code, or one of several

regional and State codes that also used these ASHRAE

Standards as a technical base. ANSI approved a jointly

sponsored revision, ANSI/ASHRAE/IES 90A-1980, as

an American National Standard [9]. Standard 90A-1980

was a revision of Sections 1-9 of ASHRAE 90-75.

An addendum was issued in 1987 to supplement the

residential requirements in 90A.

In view of the need for more procedures and data for

determining economic efficiency, the NBS/CBT Office

of Applied Economics (OAE) addressed the U.S.

Department of Energy’s (DOE) Building Energy

Performance Standards (BEPS) program—and the

need to revise ASHRAE Standard 90 to save more nonrenewable energy—with three publications published

in 1978-81: The Role of Economic Analysis in the

Development of Energy Standards for New Buildings

[10], A “Reference Building” Approach to Building

Energy Performance Standards for Single-Family

Residences [11], and Economics and Energy Conservation in the Design of New Single-Family Housing [12].

These economic applications to standards for building

energy design were based on principles published in

1974 by Stephen R. Petersen in BSS 64 [13] and on

OAE Chief Harold E. Marshall’s support of development by ASTM Committees of consensus standards for

economic definitions, terms and practices as tools for

evaluating energy conserving investments in buildings

and building systems [14]. OAE wrote a separate

NBSIR report as the basis for each of these ASTM

262
Standards. These standards have come into use world

wide for making both energy and other types of building

investment decisions. The economic methods and software initiated with Petersen’s work in 1974 and continued to the present have provided the underpinnings of

ASTM standard methods universally used for evaluating

the economics of energy conservation in buildings.

In 1983-84 the ASHRAE 90 project was reorganized

into two project committees, 90.1 covering commercial

and high-rise residential buildings and 90.2 covering

low-rise residential buildings. A major revision of the

commercial building requirements, ASHRAE/IESNA

90.1-1989, was approved by the ASHRAE Board of

Directors (BOD) on June 24, 1989 for publication, later

updated by seven addenda. ANSI approved ANSI/

ASHRAE/IESNA 90.1-1989 with addenda as an

American National Standard on July 9, 1996 [15].

In this revision, the complexity and size of the Standard

90 Series was considerably increased by incorporating

building design criteria based on dynamic (e.g., diurnal)

heat flow analysis and hourly weather conditions rather

than assuming steady-state conditions.

ASHRAE/IES Standard 90.1-1989 for commercial

and high-rise residential buildings and the CABO Model

Energy Code 1992 for low-rise residential buildings

were referenced as minimum requirements in Congressional legislation entitled the Energy Policy Act of 1992

[16]. An energy conservation standard for federal buildings was also developed by DOE under this Public Law

and published in DOE regulations, in recognition of

different tax laws and economic objectives.

During the 1990s, Standing Standard Project

Committee (SSPC) 90.1 maintained the standard by

issuing numerous addenda and three public reviews of a

major rewrite. The ASHRAE Board of Directors (BOD)

voted on June 24, 1999 to approve publication of the

revised Standard 90.1-1999 as an ASHRAE/IESNA

Standard [17] (Fig. 2), pending ANSI approval of the

Fig. 2. ASHRAE/IESNA Standard 90.1-1999, Energy Standard for Buildings Except

Low-Rise Residential Buildings.

263
revision as an American National Standard. This

revision incorporates nine addenda to 90.1-1989, a

reorganized document, scope expanded to cover new

systems and equipment in existing buildings, code

compatible language, and publication in separate IP

(inch-pound) and SI versions. More than two-dozen

newly proposed addenda were also recommended by the

SSPC for public review approval. Over the years, the

Standard 90 Series has been the best seller among

ASHRAE Standards.

A case study in NISTIR 5840, Benefits and Costs of

Research: Two Case Studies in Building Technology

[18], provided estimates of the economic impacts from

past BFRL research leading to the introduction of

ASHRAE Standard 90-75—specifically, that portion

of the standard dealing with single-family residential

energy conservation. The goal of this study was to

demonstrate how standardized evaluation methods can

be used to evaluate the benefits and costs of research.

The energy costs of houses designed according to 90-75

was compared to those of pre-1973 oil embargo

standards. More than $900 million (in 1975 dollars) of

the energy savings from 90-75 modifications in

single-family houses were directly attributable to BFRL

activities that promoted the development of ASHRAE

90-75.

The late Paul R. Achenbach, a mechanical engineer

and chief of the Building Environmental Division of

the Center for Building Technology, was born in

Alberta, Canada. During his 43 year career at NBS,

which started in 1937, he pioneered many new developments in the testing, evaluation, and modeling of the

performance of building heating and air-conditioning

equipment. Many dealt with improving the energy

efficiency of this equipment and buildings decades

before a concern for energy conservation became

widespread. He initiated the programs on energy

conservation in buildings and communities at NBS

in 1970, for which he received the Department of

Commerce Gold Medal in 1975. He had previously

received the DOC Silver Medal in 1956 and the NBS

Edward B. Rosa Award in 1970 for outstanding

achievement in the development of engineering

standards.

Throughout his career, Achenbach placed great

emphasis on getting his work and that of his staff

transferred into practice through the publications, conferences, and standards of ASHRAE. He served on the

ASHRAE Board of Directors, and as its Vice President,

receiving its Distinguished Service Award; he was

named a Fellow and received its highest award for technical achievements, the F. Paul Anderson Award.

He served as the Department of Commerce representative on the U.S. National Committee of the International

Institute of Refrigeration (IIR) and was an honorary

president of Commission VII of IIR.

Prepared by Jim L. Heldenbrand.

Bibliography

[1] Jim L. Heldenbrand (ed.), Design and Evaluation Criteria for

Energy Conservation In New Buildings, NBSIR 74-452, National

Bureau of Standards, Washington, DC (1974). Revised in 1976.

Includes a February 27, 1974 letter, bound into the document,

from F. Karl Willenbrock, Director of the Institute for Applied

Technology, NBS, to Bernard E. Cabelus, 1973-74 NCSBCS

President.

[2] Jim L. Heldenbrand, Development and Application of Design

Performance Standards for Energy Conservation in Buildings,

Industrialization Forum, 8 (3), 9-20 (1977) (Ref. p. 9).

[3] P. R. Achenbach and J. L. Heldenbrand, Development of Performance-Based Energy Conservation Standards for Buildings, in

Proceedings, First Canadian Building Congress: Energy and

Buildings, Toronto, 25 to 27 October 1976, NRCC 15870,

Canadian Committee On Building Research of the National Research Council of Canada, Ottawa, Canada (1976) pp. 213-224

(p. 214).

[4] Delmont C. Thurber, NCSBCS Lifetime Historian, History of

the National Conference of States on Building Codes and

Standards, Inc. 1967—. . . ., NCSBCS, Herndon, VA (updated

annually). The foreword includes a useful, edited version of early

NCSBCS history written by Gene A. Rowland, first NCSBCS

President, 1967-68, with comments by Bernard E. Cabelus,

NCSBCS President in 1973-74. The main document includes a

chronology and narratives of events of the first 20 years, and

yearly updates of later NCSBCS conferences.

[5] Paul R. Achenbach, Building Research at the National Bureau of

Standards, Building Science Series 0, National Bureau of

Standards, Washington, DC, October 1970.

[6] Bradley A. Peavy, Frank J. Powell, and Douglas M. Burch,

Dynamic Thermal Performance of an Experimental Masonry

Building, Building Science Series 45, National Bureau of

Standards, Washington, DC, July 1973.

[7] B. A. Peavy, D. M. Burch, F. J. Powell, and C. M. Hunt, Comparison of Measured and Computer-Predicted Thermal Performance of a Four-Bedroom Wood-Frame Townhouse, Building

Science Series 57, National Bureau of Standards, Washington,

DC, April 1975.

[8] Robert Brown and Carolyn Fitch, Introduction to Energy Codes,

originally published in Technical Bulletin, National Conference

of Building Codes and Standards, May 1994, and republished in

Southern Building, September/October 1994, pp. 29-31 (Ref.

p. 30).

[9] Energy Conservation In New Building Design, ANSI/ASHRAE/

IES 90A-1980, American Society of Heating, Refrigerating

and Air-Conditioning Engineers, Inc., New York, May 16,

1980.

[10] Stephen R. Petersen, The Role of Economic Analysis in the

Development of Energy Standards for New Buildings, NBSIR

78-1471, National Bureau of Standards, Washington, DC, May

1978.

[11] Stephen R. Petersen and Jim L. Heldenbrand, A “Reference

Building” Approach to Building Energy Performance Standards

for Single-Family Residences, NBSIR 80-2161, National Bureau

of Standards, Washington, DC, October 1980.

264
[12] Stephen R. Petersen, Economics and Energy Conservation in the

Design of New Single-Family Housing, NBSIR 81-2380, National

Bureau of Standards, Washington, DC, August 1981.

[13] Stephen R. Petersen, Retrofitting Existing Housing For Energy

Conservation: An Economic Analysis, Building Science Series

64, National Bureau of Standards, Washington, DC, December

1974. Also, Stephen R. Petersen, BLCC—The NIST Building

Life-Cycle Cost Program, first software release, 1985, is based on

BSS 64.

[14] Standard Practice for Measuring Life-Cycle Costs of Buildings

and Building Systems, ASTM E917, American Society for

Testing and Materials, West Conshohocken, PA.

Standard Practice for Measuring Benefit-to-Cost and Savingsto-Investment Ratios for Buildings and Building Systems, ASTM

E964, American Society for Testing and Materials, West

Conshohocken, PA.

Standard Practice for Measuring Internal Rate of Return and

Adjusted Internal Rate of Return for Investments In Buildings

and Building Systems, ASTM E1057, American Society for

Testing and Materials, West Conshohocken, PA.

Standard Practice for Measuring Net Benefits for Investments in Buildings and Building Systems, ASTM E1074,

American Society for Testing and Materials, West

Conshohocken, PA.

Standard Practice for Measuring Payback for Investments in

Buildings and Building Systems, ASTM E1121, American

Society for Testing and Materials, West Conshohocken, PA.

Standard Guide for Selecting Economic Methods for Evaluating

Investments in Buildings and Building Systems, ASTM

E1185, American Society for Testing and Materials, West

Conshohocken, PA.

[15] Energy Efficient Design of New Buildings Except Low-Rise

Residential Buildings, ANSI/ASHRAE/IESNA 90.1-1989,

American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc., Atlanta, GA, June 29, 1989; with supplemental addenda approved as an American National Standard

on July 9, 1996.

[16] Energy Policy Act of 1992, Public Law 102-486, Title I-Energy

Efficiency, Subtitle A-Buildings, Sec. 101. Building energy

efficiency standards, October 24, 1992.

[17] Energy Standard for Buildings Except Low-Rise Residential

Buildings, ASHRAE/IESNA 90.1-1999, American Society of

Heating, Refrigerating and Air-Conditioning Engineers, Inc.,

Atlanta, GA, June 24, 1999.

[18] Robert E. Chapman and Sieglinde K. Fuller, Benefits and Costs

of Research: Two Case Studies in Building Technology, NISTIR

5840, Office of Applied Economics, Building and Fire Research

Laboratory, National Institute of Standards and Technology,

Gaithersburg, MD, July 1996 (Ref. pp. 47 and 69).

265
Computer Program for Heating and

Cooling Loads in Buildings

In the late 1960s, under the sponsorship of the

Department of Housing and Urban Development,

Tamami Kusuda began to develop a computer program

to help architects and engineers predict the thermal

performance of a building. Important enough at the

time, this work was to balloon in significance in the

context of the energy shortages and rapidly escalating

energy prices of the 1970s. The computer program

was named the National Bureau of Standards Load

Determination (NBSLD) program [1,2]. It combined

algorithms for transient conduction in the building

structure, solar heat gains and radiant transfer, and

convection between building surfaces and the room

air to allow the prediction of temperatures and heating

and cooling loads under dynamic conditions. Moreover,

the algorithms employed in NBSLD were adopted

by the American Society of Heating, Refrigerating

and Air-Conditioning Engineers (ASHRAE) as

a recommended procedure for computerized energy

calculations. They were presented to the Society

in a special publication [3] which was sold for many

years.

Fig. 1. Analogous electric circuit for heat exchange process in a room.

266
NBSLD simulated a very simple building model

because of the computer limitations of its time. The

model included the walls, windows, ceiling, and floor of

a single space which might represent a room or an entire

building. The user described the geometry of this space,

the thermal properties of the building surfaces, optical

properties of windows, air infiltration, heat sources such

as equipment and occupants, and weather data, including temperature, humidity, and solar radiation values for

periods from one day to an entire year. The program

converted the building data into the coefficients of a

set of simultaneous equations which were solved for

temperatures of all the building components as they

responded to the internal and external heat sources over

time. By fixing the space air temperature to a desired

value, the solution of the simultaneous equations gave

the amount of energy that had to be added or removed,

i.e., heating or cooling loads, necessary to maintain that

temperature.

NBSLD was the result of many years of leadership in

this field by Kusuda. His earlier work included development of numerical methods to quickly compute

transient conduction through building walls [4] and to

determine the thermal properties of moist air [5].

He organized the first three symposia on the Use of

Computers for Environmental Engineering Related to

Buildings. The first was held at NBS in 1970 [6], the

second in Paris in 1974, and the third in Banff, Canada,

in 1978. NBSLD was developed with the cooperation of

ASHRAE’s Task Group on Energy Requirements, in

particular the Subcommittee on Heating and Cooling

Load Calculations which Kusuda chaired. The members

Fig. 2. Physical model of a typical room represented by the circuit in Fig. 1.

267
of the subcommittee shared their specialized work and

computer algorithms. Kusuda developed and implemented the NBSLD framework for putting the

algorithms together, and, together with NBS staff, filled

in the missing components of the complete model. The

Bureau’s experimental facilities were used for validation

of the program [7,8].

Kusuda’s work with the Task Group on Energy

Requirements and subsequent technical committees led

to his recognition as a fellow of ASHRAE, the society’s

highest honor. In 1969 the Automated Procedures

Engineering Consultants (APEC) awarded Kusuda its

first Honorary Membership to recognize his pioneering

work on the use of computers for heating, cooling and

ventilating engineers.

NBSLD and related research were applied to the

energy crisis of the 1970s in the analysis of energy

conservation options for specific buildings [9] and in the

development of general guidelines [10,11]. Kusuda’s

work continued in related areas, such as using sunlight

in place of electric lighting [12] and studying heat

exchange to the ground from buildings and pipes [13].

Recognition for this work includes a Lifetime

Achievement Award from the International Building

Performance Simulation Association and Silver and

Gold Medals from the Department of Commerce.

In addition to the research and energy conservation

design done with the NBSLD program, the documentation of its algorithms provided the basis for the development of other building energy simulation programs,

both public and private. The algorithms were used

almost immediately in the U.S. Army Construction

Engineering Research Laboratory’s (CERL) first building energy analysis program [14]. In the following years

CERL developed new program code to simulate multiple rooms and allow a greater degree of integration of

the building loads with the air handling system and plant

equipment such as boilers and air conditioners. CERL’s

BLAST program [15] was released in 1977. The gradual

development of multizone airflow calculations has led to

a tool [16] for studying indoor air quality and even

designing smoke control systems.

At present, the Department of Energy is developing

the EnergyPlus program [17], which merges the best

features of BLAST and the DOE-2 program. In particular, it is using the heat balance [18] concepts from

BLAST which were derived from NBSLD. Because of

the need to gather the latest such procedures in a single

document, as was originally done by Kusuda, ASHRAE

is currently working to provide improved algorithms

based on a quarter century of research since the

publication of the NBSLD algorithms.

Tamami Kusuda was born in Seattle, Washington.

His family returned to Japan before World War II and

lived there during the war (and the bombing). He

received his B.S. degree from Tokyo University in 1947

and his M.S. and Ph.D. degrees from the University of

Minnesota in 1952 and 1955.

Prepared by George Walton.

Bibliography

[1] Tamami Kusuda, NBSLD, the Computer Program for Heating

and Cooling Loads in Buildings, Building Science Series 69,

National Bureau of Standards, Washington, DC (1976).

[2] T. Kusuda, NBSLD, Computer Program for Heating and

Cooling Loads in Buildings, NBSIR 74-574, National Bureau of

Standards, Washington, DC (1974).

[3] ASHRAE Task Group on Energy Requirements, Procedure for

Determining Heating and Cooling Loads for Computerizing

Energy Calculations: Algorithms for Building Heat Transfer

Subroutines, American Society of Heating, Refrigerating and

Air-Conditioning Engineers, New York (1975).

[4] T. Kusuda, Thermal Response Factors for Multi-Layer

Structures of Various Heat Conduction Systems, ASHRAE

Trans. 75 (Part 1), 246-271 (1969).

[5] T. Kusuda, Algorithms for Psychrometric Calculations,

(Skeleton Tables for the Thermodynamic Properties of Moist

Air), Building Science Series 21, National Bureau of Standards,

Washington, DC (1970).

[6] T. Kusuda (ed.), Use of Computers for Environmental Engineering Related to Buildings, Building Science Series 39, National

Bureau of Standards, Washington, DC (1971).

[7] Bradley A. Peavy, Frank J. Powell, and Douglas M. Burch,

Dynamic Thermal Performance of an Experimental Masonry

Building, Building Science Series 45, National Bureau of Standards, Washington, DC (1973).

[8] B. A. Peavy, D. M. Burch, F. J. Powell, and C. M. Hunt,

Comparison of Measured and Computer-Predicted Thermal

Performance of a Four Bedroom Wood-Frame Townhouse,

Building Science Series 57, National Bureau of Standards,

Washington, DC (1975).

[9] Tamami Kusuda, James E. Hill, Stanley T. Liu, James P.

Barnett, and John W. Bean, Pre-Design Analysis of Energy

Conservation Options for a Multi-Story Demonstration Office

Building, Building Science Series 78, National Bureau of

Standards, Washington, DC (1975).

[10] G. Kelly, T. Kusuda, and J. Hill, Potential for Energy Conservation in Heating, Ventilating, and Air-conditioning Equipment

for Buildings, in Energy Conservation Through Effective

Energy Utilization, Jesse C. Denton, Stephen Webber, and John

Moriarty, (eds.), NBS Special Publication 403, National Bureau

of Standards, Washington, DC (1976) pp. 163-191.

[11] T. Kusuda, Use of Simulation Models of Buildings in Assessing

Energy Conservation Strategies, in Energy Conservation Strategies in Buildings: Comfort, Acceptability, and Health, Jan A. J.

Stolwijk (ed.), John B. Pierce Foundation, New Haven, CT

(1978).

268
[12] T. Kusuda and J. W. Bean, Comparison Between a Simplified

Daylighting Calculation Procedure and a Comprehensive Interreflection Model Calculation Procedure, in Proceedings of the

Third International Symposium on the Use of Computers for

Environmental Engineering Related to Buildings, Alberta,

Canada, CNRC Publ. 17376, National Research Council of

Canada, Ottawa, Canada (1978).

[13] T. Kusuda, M. Mizuno, and J. W. Bean, Seasonal Heat Loss

Calculation for Slab-on-Grade Floors, NBSIR 81-2420,

National Bureau of Standards, Washington, DC (1982).

[14] D. Hittle and B. Sliwinski, CERL Thermal Loads Analysis

and Systems Simulation Program Volume 2: Program

Reference Manual, CERL Interim Report E-81, US Army

Construction Engineering Research Laboratory, Champaign,

Illinois (1975).

[15] D. C. Hittle, The Building Loads Analysis and System Thermodynamics (BLAST) Program, CERL Technical Report E-119,

US Army Construction Engineering Research Laboratory,

Champaign, Illinois (1977).

[16] George N. Walton, CONTAM96 User Manual, NISTIR 6056,

National Institute of Standards and Technology, Gaithersburg,

MD (1997).

[17] D. B. Crawley, L. K. Lawrie, C. O. Pedersen, R. J. Liesen, D. E.

Fisher, R. K. Strand, R. D. Taylor, F. C. Winkelmann, W. F. Buhl,

A. E. Erdem, and Y. J. Huang, EnergyPlus: A New-Generation

Building Energy Simulation Program, in Building Simulation

’99, Volume I, Kyoto, Japan, International Building Performance

Simulation Association (1999) pp. 81-88.

[18] R. Strand, F. Winkelmann, F. Buhl, J. Huang, R. Liesen, C.

Pedersen, D. Fisher, R. Taylor, D. Crawley, and L. Lawrie,

EnergyPlus: Enhancing and Extending the Capabilities of the

Building Heat Balance Simulation Technique for Use in EnergyPlus, in Building Simulation ’99, Volume I, September 1999,

Kyoto, Japan, International Building Performance Simulation

Association (1999) pp. 653-660.

269
Methods for Testing and Rating the

Performance of Heating and Air

Conditioning Systems

The U.S. Congress enacted the Energy Policy

and Conservation Act (EPCA, Public Law 94-163) in

December 1975. It was subsequently amended four

times, most recently in 1992. As amended, EPCA

requires:

• the U.S. Department of Energy (DOE) to establish

energy conservation standards (minimum efficiency

or maximum energy use) for all major energy

consuming products in a residence,

• the National Bureau of Standards (NBS) to develop

test procedures for the same products, and

• the U.S. Federal Trade Commission (FTC) to

develop a program of labeling the products to

encourage purchase of energy efficient equipment.

EPCA required NBS to develop test procedures for

each product for the determination of estimated annual

operating cost and at least one other useful measure of

energy consumption likely to assist consumers in

making purchasing decisions. An additional requirement of the law was that “any test procedures prescribed

be reasonably designed to produce test results which

reflect energy efficiency, energy use, or estimated

annual operating cost during a representative average

use cycle and not be unduly burdensome to conduct.”

Beginning in 1975, NBS staff reviewed the test procedures already in use within the appliance and heating

and cooling industry. By the early 1980s, test procedures

were in place for all covered products. Throughout the

development, NBS staff worked closely with industry

representatives experienced in testing the equipment to

obtain their review and recommendations, particularly

on energy conservation innovations that were being considered for future products.

This review found many test procedures that could be

used with minor modifications and recommended them

for adoption. The industry procedures that required little

change were primarily for “white” appliances, those

used for cooking, cleaning, refrigerating food, etc.

For them, the performance and annual cost of operation

were primarily dependent on the use schedule. Therefore, NBS adopted steady-state tests plus a calculation

procedure assuming a specific daily operating schedule.

In the case of residential heating and cooling systems,

however, entirely new procedures had to be developed,

as described in these publications [1,2]. At the time,

steady-state tests were used in the industry for central

heating and cooling equipment. However, the equipment

cycled on and off frequently throughout most days.

During the start-up and shut-down periods, most of the

equipment experienced non-trivial energy losses or inefficiencies associated with warm-up, cool-down, and/or

migration of refrigerant. In addition, the performance of

this equipment was almost independent of the user

(except for thermostat setting) and primarily dependent

on the weather conditions. As a result, NBS staff

developed new procedures for this type of equipment

that included steady-state and cycling tests coupled with

a calculation procedure that accounted for the changing

weather conditions throughout the heating and cooling

seasons.

Kelly and Chi published the initial procedure for

central furnaces and boilers in 1978 [1]. The testing

required was simple, but the estimation of yearly performance was done through an elaborate calculation procedure. They found that the performance of furnaces and

boilers under part-load, on-off operation could be

described by a simple “time-constant” model, and that

data required to determine the time-constant could be

obtained during “warm-up” and “cool-down” periods

before and after a steady-state test without extensive

cycling tests.

Based on the test data, five major loss terms were

calculated and subtracted from 100 to obtain the value

of the seasonal efficiency.

1. Latent Heat Loss, due to the presence of uncondensed water vapor in the flue gas.

2. On-Period Sensible Heat Loss, due to the heating

of combustion products and excess air from room

temperature up to the flue gas temperature.

3. On-Period Infiltration Loss, due to heating on-cycle

combustion and relief air from the outdoor temperature up to room temperature.

4. Off-Period Sensible Heat Loss, due to the heating of

the off-cycle draft air up to a temperature in excess

of the indoor air temperature.

270
5. Off-Period Infiltration Loss, due to the heating of

the off-cycle draft and relief air from the outdoor up

to the indoor air temperature.

In developing the calculation procedure, Kelly and

Chi found that they could evaluate the loss terms at

the heating season average outdoor air temperature

and obtain virtually identical results with a more

complicated “bin” analysis with a separate calculation

of efficiency for each “bin.” In addition, the manufacturer had to calculate an annual fuel utilization

efficiency (AFUE) which differed from the seasonal

efficiency if there was consumption of energy by a pilot

light operating during the non-heating season.

After the publication of the original test procedure,

Kelly and his colleagues modified it to handle advances

in furnace and boiler technology such as:

1. pulse combustion and condensing furnaces [6]

2. modulating and two-step controls on furnaces and

boilers [7]

3. furnaces with inlet dampers [8]

4. furnaces with post purge design [9].

Didion and Kelly [2] used the same approach in

developing the test and calculation procedure for central

air conditioners and heat pumps as for furnaces and

boilers. However, because of the different ways refrigerant migrated from one component to another during

the off-cycle, they could not describe the performance

during the off-cycle by a simple time constant model.

As a result, the testing procedure was considerably more

complicated and required cycling tests.

The tests for central air conditioners and heat pumps

operating in the cooling mode consisted of three steadystate tests and one cycling test. In all tests, the capacity,

electrical energy input, and coefficient of performance

(COP) were determined. Didion and Kelly expected to

develop a procedure with only two tests: one at full

capacity and one at some part-load condition requiring

the unit to cycle. In both tests, the indoor coil would be

wet with dehumidification occurring. However, in preliminary studies, they found that a wet-coil cycling test

at part-load conditions presented significant experimental problems. The capacity was determined by measuring the enthalpy increase across the indoor coil. This

measurement was unreliable under periodically varying

conditions. Fortunately, they found that the ratio of the

COP in the cycling mode to that under steady-state

conditions was the same for dry-coil and wet-coil conditions for the same part-load conditions. Consequently,

two tests were conducted to determine a degradation

coefficient describing the losses due to cycling under

dry-coil conditions. These results were used to modify

a wet-coil steady-state test where the unit would normally cycle. Manufacturers could use an assumed value

of the degradation coefficient in lieu of conducting the

two dry coil tests. Finally, a full-load steady-state test

was conducted at a hot outdoor temperature.

Fig. 1. Maciej Chwalowski prepares central air conditioning units for test.

271
As with furnaces and boilers, Didion and Kelly

intended to use a bin method for calculating a

seasonal energy efficiency ratio (SEER), where the

performance was weighted by the number of hours the

unit operates in each temperature bin. Again, they found

the variation in SEER with climate for typical units to

be only slight. Consequently, the SEER was calculated

for a climate with a specific average operating outdoor

temperature.

Four tests were also required for heat pumps operating in the heating mode: a full load steady-state test at

a high outdoor temperature and one at a low temperature

to determine how the capacity and power varied with

temperature differences; a third test to determine cycling degradation; and a fourth to determine the effect

of frosting on the outdoor coil. The calculation procedure to obtain a heating season performance factor

(HSPF) was a bin method. They were not able to find a

short-cut procedure as with furnaces and boilers and air

conditioners operating in the cooling mode.

After the publication of the original test procedure,

Didion and his colleagues modified it to handle

variable-speed equipment [10]. This increased the

number of mandatory tests to ten and optional tests to

five. In addition, they developed procedures to rate

mixed systems: those where the indoor coil of one tested

system is installed with the outdoor compressor-condenser unit of another tested system [11,12].

The development of the new test procedures for

central heating and cooling caused a revolution in the

way industry tested such equipment. They resisted and

fought the changes for several years because of the

increased cost and complexity of testing. Ultimately the

tests were accepted, used throughout the industry, and

adopted by the American Society of Heating, Refrigerating, and Air-Conditioning Engineers (ASHRAE) as

ASHRAE Standards 103 (Central Furnaces and Boilers)

and 116 (Unitary Air Conditioners and Heat Pumps).

Residential equipment accounted for 20 % of U.S.

national energy consumption during the last quarter of

the 20th century. The development of these test procedures, a labeling program for some of the equipment,

and the threat of mandatory standards resulted in

substantial increases in U.S. equipment efficiency. The

American Council for an Energy Efficient Economy

(ACEEE) [13] reported average efficiency increases

from 1972 to 1987 of 96 % for refrigerator-freezers,

35 % for central air conditioners and heat pumps, 30 %

for room air conditioners, and 18 % for gas furnaces.

George E. Kelly came to NBS in 1970 as a National

Research Council/NBS Postdoctoral Research Associate. For two years, he conducted research on condensation and the theory of droplet growth in homogeneous

nucleation. He joined the predecessor organization of

the Building and Fire Research Laboratory (BFRL) in

1972 and began immediately working on the program of

testing heating and cooling equipment for seasonal performance described above. Because of its significant

impact, George received the Department of Commerce

Silver Medal in 1978. He went on to establish a significant new research program on building controls beginning in 1980. Over a period of 20 years, he and his

staff gained a world-wide reputation for their work.

They developed an advanced dynamic building/HVAC

Fig. 2. David Aaron adjusts flow conditions in refrigeration loop where flow restrictors

are evaluated.

272
control simulation program HVACSIM+, pioneered an

innovative method for testing and evaluating computerized control systems using a building emulator, and

developed a standard communication protocol for

building controls, BACnet, which was adopted nationally as ASHRAE Standard 135, adopted internationally

by ISO, and named by Engineering News Record in

1999 as one of the 100 top innovations of the 20th

century in the construction industry. For his work,

George was named the Department of Commerce

Engineer of the Year in 1992. He was promoted to

Chief of the Building Environment Division of BFRL in

1999.

David A. Didion came to NBS in 1971 and immediately began working on the performance of heating and

cooling equipment. He too received the Department of

Commerce Silver Medal in 1981 for his work. In 1980,

Dave and his staff began an intense research program on

refrigeration machinery and the use of refrigerant

mixtures to improve their performance. When ozone

depletion in the stratosphere was recognized as an international environmental crisis and the first international

protocol/regulation was established in 1987, chlorofluorocarbons (CFC) were phased out of use in refrigeration equipment. Dave’s research team was ideally

poised to lead the national effort in identifying

Fig. 3. Brian Dougherty prepares super-efficient heat pump for tests.

273
refrigerant mixtures that ultimately replaced the CFCs.

For this work he was recognized with numerous awards;

among them the Department of Commerce Gold Medal

(1987), the NIST Applied Research Award (1987), the

Edward Uhler Condon Award (1988), the William P.

Slichter Award (1995), and the first Gustov Lorenzen

Prize from the International Institute of Refrigeration

(1999). He was elevated to NIST Fellow in 1995.

Prepared by James E. Hill.

Bibliography

[1] Joseph Chi and George E. Kelly, A Method for Estimating the

Seasonal Performance of Residential Gas and Oil-Fired Heating

Systems, ASHRAE Trans. 84, Part 1, 405-421 (1978).

[2] David A. Didion and George E. Kelly, New Testing and Rating

Procedures for Seasonal Performance of Heat Pumps, ASHRAE

J. 21 (9), 40-44 (1979).

[3] George E. Kelly, Joseph Chi and Mark E. Kuklewicz, Recommended Testing and Calculation Procedures for Determining

the Seasonal Performance of Residential Central Furnaces

and Boilers, NBSIR 78-1543, National Bureau of Standards,

Washington, DC, September 1978.

[4] G. E. Kelly and W. H. Parken, Jr., Method of Testing, Rating,

and Estimating the Seasonal Performance of Central AirConditioners and Heat Pumps Operating in the Cooling Mode,

NBSIR 77-1271, National Bureau of Standards, Washington,

DC, April 1978.

[5] Walter H. Parken, George E. Kelly, and David A. Didion, Method

of Testing, Rating, and Estimating the Heating Seasonal

Performance of Heat Pumps, NBSIR 80-2002, National Bureau

of Standards, Washington, DC, April 1980.

[6] George E. Kelly and Mark E. Kuklewicz, Recommended Testing

and Calculation Procedures for Estimating the Seasonal Performance of Residential Condensing Furnaces and Boilers, NBSIR

80-2110, National Bureau of Standards, Washington, DC, April

1981.

[7] Esher Kweller and Robert L. Palla, Jr., A Test Method and

Calculation Procedure for Determining Annual Efficiency for

Vented Household Heaters and Furnaces Equipped with

Modulating-Type Controls, NBSIR 82-2497, National Bureau of

Standards, Washington, DC, May 1982.

[8] Stanley T. Liu, George E. Kelly, and Charles P. Terlizzi, Testing

and Rating of an Atmospheric, Gas-Fired Furnace Equipped

with a Burner Air Inlet Damper, NISTIR 4717, National Institute

of Standards and Technology, Gaithersburg, MD, November

1991.

[9] Stanley T. Liu, George E. Kelly, and Charles P. Terlizzi, Evaluating the Off-Cycle Losses of a Gas-Fired, Power Vented Furnace

Employing Post Purge, NISTIR 4908, National Institute of

Standards and Technology, Gaithersburg, MD, August 1992.

[10] Piotr A. Domanski, Recommended Procedure for Rating and

Testing of Variable Speed Air Source Unitary Air Conditioners

and Heat Pumps, NISTIR 88-3781, National Institute of

Standards and Technology, Gaithersburg, MD, May 1988.

[11] Piotr A. Domanski, Rating Procedure for Mixed Air-Source

Unitary Air Conditioners and Heat Pumps Operating in the

Cooling Mode—Revision 1, NISTIR 89-4071, National Institute

of Standards and Technology, Gaithersburg, MD, May 1989.

[12] Piotr A. Domanski, Rating Procedure for Mixed Air-Source

Unitary Heat Pumps Operating in the Heating Mode, NISTIR

90-4298, National Institute of Standards and Technology,

Gaithersburg, MD, May 1990.

[13] Howard S. Geller, Residential Equipment Efficiency: 1988

Update, American Council for an Energy-Efficient Economy,

Washington, DC, August 1988.

274
System for Fire Safety Evaluation of

Health Care Facilities

The Fire Safety Evaluation System (FSES) for

Health Care Facilities [1] was the first of a series of

FSES documents covering a variety of types of occupancies including apartment buildings [2], prisons and

jails [3], office and laboratory buildings [4], overnight

accommodations in National Parks [5], and board and

care facilities [6]. These have provided means for

meeting or exceeding the level of safety prescribed by

the applicable code while providing the designer with a

wide range of cost saving and functional options.

The FSES’s have been adopted into building codes

and similar regulations and have been institutionalized

by the establishment of a special technical committee of

the National Fire Protection Association (NFPA)

charged with the responsibility for Alternative Methods

for Life Safety in Buildings. This committee maintains

NFPA Standard 101A [8] in support of the FSES’s,

thereby ensuring that each FSES remains current and

an appropriate reflection of the changing safety levels

prescribed by building codes and regulations. This

description, however, focuses on the FSES for Health

Care Facilities, as a representative sample of the

complete series.

The FSES for Health Care Facilities was part of a

broad fire safety effort sponsored by the Department of

Health and Human Service in response to an important

need to develop a means for meeting the fire safety

objectives of prescribed codes without necessarily being

in explicit compliance with the code. In the 1960s, with

the birth of the Medicare and Medicaid programs,

Congress prescribed conformance with the requirements of the Life Safety Code, National Fire Protection

Association Standard 101, in all nursing homes and

hospitals receiving funds under those programs. A

nation-wide inspection and enforcement program was

established to ensure compliance. Most, if not all,

inspected facilities were found to be in some degree of

non-compliance with the specific requirements of the

Life Safety Code. A significant number were closed

as a result. Others undertook correction programs.

Many, including some of the Nation’s largest and most

prestigious hospitals, were declared to fail this safety

standard.

The FSES for Health Care Facilities was developed

to discover alternate solutions, delivering at least an

equivalent level of safety as compared to that produced

by exact compliance with the detailed prescriptions of

the Life Safety Code. In the case of one large hospital

complex, the use of the FSES reduced the cost of

compliance from an estimated $30 million to $60

million to less than $2 million. Equally important,

the development of alternative approaches allowed

the improvements to be made without interruption of

hospital services.

The FSES is a grading system designed to determine

the overall level of fire safety of an existing or proposed

facility in comparison with a hypothetical facility that

exactly matched each requirement of the Life Safety

Code. The enclosed figure shows Table 4 and 5 of the

FSES for Health Care Facilities. These two tables are

the most critical to the evaluation. These tables describe

most of the universe of common building factors that

determine fire safety, such as type of construction,

partitioning and finishes, hazardous activities, fire detection and suppression, and fire alarm systems. For

practical considerations, however, factors relating to

building utilities, furniture, and emergency procedures

are handled elsewhere in the FSES.

The levels of parameter values in Table 4 represent

the levels of performance that exist in the real world of

health care facilities. Some are those required by the

code, while others have either more or less impact on

safety than the code requirements.

The values assigned to each level are dimensionless,

developed through consensus and designed to be comparative in relative value in both the evaluation of the

levels within a parameter and between parameters. The

specific values for each element in a parameter were

developed by iteration through three separate Delphi

panels. The base scale of measurement was established

by these panels with the directive that the most powerful

safeguard was assigned a score of 10, and an element

that neither added to or detracted from safety was score

0. Using this scale, all other elements were scored with

negative numbers representing an element detrimental

to life safety and positive numbers representing elements additive to life safety.

Computer analysis was used to evaluate all possible

permutations. The overall safety of the resulting solutions was then evaluated by the Delphi groups. The

iterative process of adjusting parameter element values

and appraising the resultant level of safety continued

until all of the panels concurred that all solutions indicating a level of fire safety that equaled or exceeded the

level provided by rigid conformance with the letter of

the code did deliver that indicated level of safety.

275
The parameter values established in Table 4 are

transferred to Table 5. Table 5 evaluates the importance

of each parameter to the fire safety sub-objectives

of fire containment, extinguishment, and people movement. This approach avoids the overdependence on any

single parameter and ensures a degree of redundancy as

expected as part of the overall fire safety of a facility.

The scoring derived from Table 5 is compared with

the score developed by the previously mentioned

hypothetical facility. If the score of the facility under

evaluation equals or exceeds that of the hypothetical

facility in all sub-objectives, the facility is deemed to be

in conformance with the objectives of the Life Safety

Code.

The validity of the FSES rests primarily on:

a. the completeness of the universe of parameters

and parameter factors in Table 4;

b. the appropriateness of the relative parameter

values assigned in Table 4; and

c. the relationships established in Table 5.

The details of how this validity was achieved are

contained in reference [1]. An informative discussion of

the relevance of the approach to validity is available in

Nelson’s paper An Approach to Enhancing the Value of

Professional Judgement in the Determination of Performance Criteria [7].

Fig. 1a. Illustration of the FSES rating system (Part 1).

276
The FSES for Health Care Facilities was adopted by

the National Fire Protection Association as part of the

1981 edition of the Life Safety Code. It provided a

recognized means of developing alternative approaches

to determine compliance with the code in that and later

editions of the Life Safety Code.

Subsequently, the Life Safety Code adopted FSES’s

developed by NBS/NIST covering Detention and Correctional Occupancies (i.e., prisons and jails), Board and

Care Occupancies, and Office Occupancies. In 1995 the

National Fire Protection Association created

a new document NFPA 101A, Guide on Alternative

Fig. 1b. Illustration of the FSES rating system (Part 2).

277
Approaches to Life Safety [8] to gather and contain the

FSES’s in a single publication and place them in the care

of a single technical committee. Harold Nelson was the

initial chair of this committee, and upon his retirement

the chair was given to David Stroup, also of NIST.

The FSES’s have stood the test of time and are now

a regular part of life safety design in many buildings.

They have both improved safety and reduced costs. In

the NIST study Benefits and Costs of Research: A Case

Study of the Fire Safety Evaluation System by Chapman

and Weber [9], an estimated savings of almost $1 billion up to 1995 was credited to the FSES for Health

Care Facilities. Unmeasured but significant savings

have also been achieved by the other FSES’s.

In the early 1980’s Chapman and his colleagues [10]

extended the work of Nelson’s team by the development of a cost optimizer computer program enabling the

user to determine the best cost acceptable alternatives to

achieving equivalent safety with the Life Safety Code

requirements for Health Care Facilities. In 1994 this

work was used to develop the computer program

ALARM 1.0, Decision Support Software for CostEffective Compliance with Fire Safety Codes [11].

Nelson retired from NIST in 1992 but continues

actively as a consultant in fire safety matters. Nelson’s

honors include the Department of Commerce Silver and

Gold Medals; Federal Research Laboratory Consortium

Special Award for Technology Transfer; Society of Fire

Protection Engineers, Harold E. Nelson Professional

Service Award (inaugural awardee); Standards Medal of

the National Fire Protection Association; and the

Kawaoe Metal of the International Association for Fire

Safety Science for lifetime contributions to fire safety

science.

Fig. 2. Harold Nelson.

278
In the long term, the principal importance of the fire

safety evaluation systems lies not only in the specific

objective of delivering safety with lower cost and greater

design flexibility, but also in the demonstration that a

total performance approach to fire safety is feasible.

Prepared by Harold Nelson.

Bibliography

[1] H. E. Nelson and A. J. Shibe, A System for Fire Safety Evaluation of Health Care Facilities, NBSIR 78-1555-1, National

Bureau of Standards, Washington, DC (1978).

[2] H. E. Nelson and A. J. Shibe, A System for Fire Safety Evaluation for Multifamily Housing, NBSIR 82-2562, National Bureau

of Standards, Washington, DC (1982).

[3] H. E. Nelson and A. J. Shibe, The Development of a Fire Evaluation System for Detention and Correctional Occupancies,

NBSIR 84-2976, National Bureau of Standards, Washington,

DC (1984).

[4] H. E. Nelson, Fire Safety Evaluation System for NASA Office/

Laboratory Buildings, NBSIR 86-3404, National Bureau of

Standards, Gaithersburg, MD (1986).

[5] H. E. Nelson, A. J. Shibe, B. M. Levin, S. D. Thorne, and L. Y.

Cooper, Fire Safety Evaluation System for National Park

Service Overnight Accommodations, NBSIR 84-2896, National

Bureau of Standards, Washington, DC (1984).

[6] H. E. Nelson, B. M. Levin, A. J. Shibe, N. E. Groner, R. L.

Paulsen, D. M. Alvord, and S. D. Thorne, A Fire Safety Evaluation System for Board and Care Homes, Final Report, NBSIR

83-2659, National Bureau of Standards, Washington, DC (1983).

[7] H. E. Nelson, An Approach to Enhancing the Value of Professional Judgement in the Derivation of Performance Criteria, in

Proceedings of the 3rd ASTM/CIB/RELIM Symposium on the

Performance Concept in Buildings, Lisbon, March 29–April 2,

1982.

[8] Guide on Alternative Approaches to Life Safety, ANSI/NFPA

101A-1998, National Fire Protection Association, Quincy, MA

(1998).

[9] Robert E. Chapman and Stephen F. Weber, Benefits and Costs of

Research: A Case Study of the Fire Safety Evaluation System,

NISTIR 5863, National Institute of Standards and Technology,

Gaithersburg, MD (1996).

[10] Robert E. Chapman, A Cost-Conscious Guide to Fire Safety in

Health Care Facilities, NBSIR 82-2600, National Bureau of

Standards, Washington, DC (1982).

[11] S. F. Weber and B. C. Lippiatt, ALARM 1.0—Decision Support

Software for Cost-Effective Compliance with Fire Safety Codes,

NISTIR 5554, National Institute of Standards and Technology,

Gaithersburg, MD (1994).

279
Estimation of Rate of Heat Release by

Means of Oxygen Consumption Measurements

Intuitively, the rate of heat release from an unwanted

fire is a major indication of the threat of the fire to life

and property. This is indeed true, and a reliable measurement of a fire’s heat release rate was a goal of fire

researchers at NBS and other fire laboratories at least as

early as the 1960s. Historically, heat release measurements of burning materials were based on the temperature rise of ambient air as it passed over the burning

object. Because the fraction of heat released by radiant

emission varies with the type of material being burned,

and because not all the radiant energy contributes to

temperature rise of the air, there were large errors in the

measurements. Attempts to account for the heat that was

not captured by the air required siting numerous thermal

sensors about the fire to intercept and detect the additional heat. This approach proved to be tedious, expensive, and susceptible to large errors, particularly when

the burning “object” was large, such as a full-sized

room filled with flammable furnishings and surface

finishes.

A novel alternative technique for determining heat

release rate was developed at NBS during the 1970s. It

had distinct advantages over the customary approach,

but its widespread acceptance was hampered by uneasiness in the fire science community concerning potential

errors if the technique were used in less-than-ideal

circumstances. In 1980 Clayton Huggett, a fire scientist

at NBS, published the seminal paper [1] that convinced

the fire science community that the new technique was

scientifically sound and sufficiently accurate for fire

research and testing. The technique is now used worldwide and forms the basis for several national and

international standards.

The underlying principle of the new heat release rate

technique was “discovered” in the early 1970s. Faced

with the challenge of measuring the heat release of

combustible wall linings during full-scale room fire

tests, William Parker, Huggett’s colleague at NBS,

investigated an alternative approach based on a simple

fact of physics: in addition to the release of heat, the

combustion process consumes oxygen. As part of his

work on the ASTM E 84 tunnel test, Parker [2] explored

the possibility of using a measurement of the reduction

of oxygen in fire exhaust gases as an indicator of the

amount of heat released by the burning test specimens.

Indeed, for well-defined materials with known chemical

composition, heat release and oxygen consumption can

both be calculated from thermodynamic data. The problem with applying this approach to fires is that in most

cases the chemical compositions of modern materials/

composites/mixes that are likely to be involved in real

fires are not known. In the process of examining data for

complete combustion (combustion under stoichiometric

or excess air conditions) of the polymeric materials with

which he was working, Parker found that, although the

heat released per unit mass of material consumed (i.e.,

the specific heat of combustion), varied greatly, the

amount of heat released per unit volume of oxygen

consumed was fairly constant, i.e., within 15 % of the

value for methane, 16.4 MJ/m3 of oxygen consumed.

This fortunate circumstance—that the heat release

rate per unit volume of oxygen consumed is approximately the same for a range of materials used to

construct buildings and furnishings—meant that the

heat release rate of materials commonly found in fires

could be estimated by capturing all of the products of

combustion in an exhaust hood and measuring the flow

rate of oxygen in that exhaust flow. The technique was

dubbed oxygen consumption calorimetry, notwithstanding the absence of any actual calorimetric (heat)

measurements.

Later in the decade, Huggett [1] performed a detailed

analysis of the critical assumption of constant proportionality of oxygen consumption to heat release.

Parker’s assumption was based on enthalpy calculations

for the complete combustion of chemical compounds

to carbon dioxide, water, and other fully oxidized

compounds. Indeed, a literature review by Huggett

revealed that Parker’s findings were actually a rediscovery and extension of the work of W. M. Thornton [3],

published in 1917, which found that the heat released

per unit amount of oxygen consumed during the

complete combustion of a large number of organic gases

and liquids was fairly constant. Nevertheless, since in

real fires and fire experiments the oxygen supply is

sometimes limited, incomplete combustion and partially

oxidized products can be produced. Huggett’s paper

examined in detail the assumption of constant heat

release per amount of oxygen consumed under real fire

conditions and assessed its effect on the accuracy of

heat release rate determinations for fires.

Instead of expressing results on a unit volume basis,

as Parker did, Huggett expressed results in the more

convenient and less ambiguous unit mass of oxygen

280
consumed. Huggett began by presenting values for the

heat of combustion and heat of combustion per gram of

oxygen consumed for typical organic liquid and gas

fuels, assuming the products are CO2, H2O (g), HF,

HCl, Br2, SO2, and N2. Notwithstanding large variations

in the molar heat of combustion (up to a factor of 4) for

this group of fuels, the heats of combustion per unit

mass of oxygen consumed fell within 3 % of their

average value of 12.72 kJ/g. Huggett explained that this

near constancy was not surprising because the energetic

processes are the result of breaking either carboncarbon or carbon-hydrogen bonds, and these have

similar bond strengths.

An examination of the same data for typical synthetic

polymers, some of which Parker did not consider,

produced similar results; for this class of materials the

heats of combustion per unit mass of oxygen consumed

fell within 4 % of their average value of 13.03 kJ/g.

Fuels of natural origin (e.g., cellulose, cotton, newsprint, corrugated box, wood, etc.), which are likely to be

found in large quantities in building fires, have heats of

combustion per unit of oxygen consumed that range

within 5.3 % of their average of 13.21 kJ/g.

The results presented so far assumed complete

combustion. Huggett explored the effects of incomplete

combustion on the assumption of constant heat release

per unit mass of oxygen consumed. He did this by

making several conservative, but realistic, assumptions

concerning incompleteness of combustion for a range of

materials likely to be found in a structural fire. For

example, carbon monoxide often is present in a fire’s

combustion products, but usually at a very low level, and

rarely exceeds 10 % of the carbon dioxide concentration

produced by the fire. Huggett then calculated the heat of

combustion per unit mass of oxygen consumed for the

burning of cellulose in limited air, such that the carbon

monoxide concentration was about 10 % of the carbon

dioxide concentration. The result was 13.37 kJ/g of O2,

compared with 13.59 kJ/g for the excess air case. The

difference was very small and, if necessary, could be

corrected for if the carbon monoxide concentration was

measured.

Another consideration was that cellulosic fuels tend

to form a carbonaceous char that can affect the heat

release rate. By examining a hypothetical reaction that

forces production of pure carbon, Huggett demonstrated

that the effect was small: 13.91 kJ/g of O2 when pure

carbon was produced vs. 13.59 kJ/g when the

reaction took place in excess air.

Other partial oxidation reactions can occur and affect

the heat release rate. Huggett argued that although their

details are unknown, the effects could be assessed via

representative examples; the actual material in the

example was not important since only the chemical

bonds that were rearranged by the reaction significantly

affected the results. He considered partial oxidation of

propylene, polyacrylonitrile (which produces hydrogen

cyanide under some combustion conditions), and polytetrafluoroethylene and argued that under worst-case

conditions the heats of combustion per unit mass of

oxygen consumed range from 10.76 kJ/g to 13.91 kJ/g;

thus such substances, if present in small quantities,

would not introduce a significant error in heat release

based on oxygen consumption. All these scenarios were

considered limiting cases; the effect in real fires usually

would be less than that presupposed in the analyses.

In situations where large quantities of incomplete

combustion products were produced, corrections could

be made if these products were measured.

Huggett concluded that the assumption of constant

heat release rate per unit mass of oxygen consumed

would be sufficiently accurate for most fire and fire-test

applications. For fires burning conventional organic

fuels, Huggett recommended the constant 13.1 kJ/g,

which should produce heat release rate results accurate

to 5 % or better. Ever since its publication, this value

has been the accepted value for oxygen-consumption

calorimetry when burning conventional materials.

Huggett examined other factors that influence the

overall accuracy of oxygen consumption calorimetry.

For example, dilution by products of combustion in the

exhaust flow, where the oxygen concentration measurement is made, is a source of error because the number of

moles of products is not the same as the number of

moles of oxygen consumed. This dilution factor is a

function of the fuel’s stoichiometry and can be taken

into account if the stoichiometry is known. In general,

however, this is not the case and the dilution factor must

be estimated. Through analysis of limiting cases,

Huggett reasoned that if an appropriate dilution factor

were not available, then assuming a value of 1.6 would

lead to an error of less than 6 % in the amount of oxygen

consumed.

This watershed paper by Huggett was published just

as the rate of heat release was beginning to be recognized as the central property affecting fire growth [4].

The novel new technique was rapidly incorporated by

Babrauskas and Twilley [5] in their invention of the

Cone Calorimeter, a bench-scale device now used

worldwide for heat release rate measurements. It also

became the technique used in fire calorimeters of larger

(room) size at NIST and at most fire laboratories

throughout the world. The oxygen-consumption

technique forms the basis for several national (ASTM

[6], NFPA [7]) and international (ISO [7]) standards.

Clayton Huggett graduated from the University of

Wisconsin and received his Ph.D. in chemistry from the

University of Minnesota. During World War II he and

his colleagues at Minnesota developed the fuel for the

U.S. Navy’s first air-to-air missile. Subsequently he

281
worked on rocket propellants with Amcel Propulsion

and on the fire safety program for the Apollo rockets

while at the Arthur B. Sloan Foundation, with ties to the

Atlantic Research Corporation. A patent issued to him

for habitable but combustion discouraging atmospheres

still is used today. Clayton joined the Center for Building

Technology at NBS in 1970 and began his research in

flammability of apparel. In addition to heat release rate

measurements and applications, he studied flame spread

on floor coverings in corridors and the flammability of

electrical insulating materials. He retired from NBS in

1985 while in the position of Deputy Director of the

Center for Fire Research.

Prepared by Kenneth D. Steckler.

Bibliography

[1] C. Huggett, Estimation of Rate of Heat Release by Means of

Oxygen Consumption Measurements, Fire Mater. 4, 61-65

(1980).

[2] W. J. Parker, An Investigation of the Fire Environment in the

ASTM E 84 Tunnel Test, NBS Technical Note 945, National

Bureau of Standards, Washington, DC, August 1977.

[3] W. M., Thornton, The Relation of Oxygen to the Heat of Combustion of Organic Compounds, Philos. Mag., Ser. 6 33, 196-203

(1917). [4]V. Babrauskas and R. D. Peacock, Heat Release Rate:

The Single Most Important Variable in Fire Hazard, Fire Saf. J.

18, 255-272 (1992).

[5] V. Babrauskas, Development of the Cone Calorimeter—a Benchscale Heat Release Rate Apparatus Based on Oxygen Consumption, Fire Mater. 8, 81-95 (1984).

[6] Standard Test Method for Heat and Visible Smoke Release Rates

for Materials and Products using an Oxygen Consumption

Calorimeter ASTM E 1354-99, Annual Book of ASTM Standards,

4.07, American Society for Testing and Materials, West

Coshohocken, PA (1999).

[7] Heat Release Rates for Materials and Products Using an Oxygen

Consumption Calorimeter, (revision and redesignation of ANSI/

NFPA 264-1995), ANSI/NFPA 271-1998, National Fire Protection Association, Quincy, MA (1998).

[8] Fire Tests—Reaction to fire—Part 1: Rate of heat release from

building products—(Cone calorimeter method), ISO 5660-1:1993,

Technical Corrigendum 1, International Organization for

Standardization, Geneva (1993).

282
Probability-Based Load Criteria for

Structural Design

Structural codes and standards provide the foundation of good engineering practice and a framework for

addressing safety and serviceability issues in structural

design. They identify natural and man-made forces that

must be considered, define magnitudes of these forces

for design, and prescribe methods for determining

structural resistance to these forces. The framers of

these documents on which the structural engineer places

so much reliance must address the question: “How safe

is safe enough?” on behalf of society as a whole. Code

development is a grave responsibility and, for the most

part, has clearly been done well since failures of

constructed facilities are rare. On the other hand, such

failures, when they do occur, are highly visible and their

consequences are severe in human and economic terms

for all involved. This publication, Development of

a Probability-based Load Criterion for American

National Standard A58 [1], marked a major advance in

the approach to formulating such codes.

At the root of the structural safety problem is the

uncertain nature of the man-made and environmental

forces that act on structures, of material strengths, and

of structural analysis procedures that, even in this computer age, are no more than models of reality. The

natural consequence of uncertainty is risk. Structural

engineering, as applied to civil construction and in

contrast to other engineering fields, relies heavily on

analysis and computation rather than on testing because

of the scale and uniqueness of typical civil projects in

both public and private sectors. Structural codes are

linked to computational methods of safety assessment,

and their primary purpose is to manage risk and

maintain safety of buildings, bridges and other facilities

at socially acceptable levels.

Until the 1960s, the safety criteria in structural

codes were based on allowable stress principles. The

structural system being designed was analyzed under the

assumption that it behaved elastically (the fact that

structures seldom behave elastically to failure was disregarded). Uncertainties were addressed by requiring

that the computed stresses did not exceed a limiting

stress (at yielding, rupture, instability) divided by a

factor of safety. These factors of safety were selected

subjectively; one might, for example, identify the load

acting on a structure and then design the structure so

that the elastic stresses due to that load remain below

60 % of the stress at yield (implying a factor of safety

of 5/3). Of course, no one knew what the risk of failure

was for such a structure. The factor of safety of 5/3

simply represented a value judgment on the part of the

standard-writers, based on past experience. During the

past century, with the advent of formal structural

calculations, the trend in the factor of safety generally

has been downward.

This judgmental approach to safety works well as

long as the technology being dealt with is stable or

evolves slowly and there is opportunity to learn from

experience in the standard development process.

Occasionally, of course, engineers become overconfident, ignorance catches up, or construction practice

overreaches the state of the art; then failures occur.

More than in most other engineering disciplines, the

profession of structural engineering seems to have

progressed by learning from its mistakes. To the discomfort of many structural engineers, this learning

process usually takes place in the public arena.

During the late 1960s and 1970s, a number of natural

disasters occurred worldwide that caused extensive loss

of life and property damage and focused the attention of

the structural engineering community and the public on

the need to advance building practices for disaster

mitigation. Professional staff from the Structures Division in the Center for Building Technology (CBT) of the

National Bureau of Standards were involved in a number

of the damage surveys and failure investigations that

followed these disasters. Among the more notable of

these were the structural failure investigations that

followed the San Fernando, California, Earthquake of

1971, the Managua, Nicaragua, Earthquake of 1972,

and the Miyagi-ken-oki Earthquake of 1978; the investigation of snow and rain load conditions prior to the

collapse of the Hartford Civic Arena roof in 1978; and

the evaluations of wind loads, wind load effects, and

building performance following Hurricane Camille on

the Gulf Coast (1969) and Cyclone Tracy in Darwin,

Australia (1974). These and other investigations of

building performance revealed a number of deficiencies

in the provisions for structural safety appearing in the

codes of practice of the time, and emphasized the need

for improvements in design for natural hazards.

283
Fig. 1. Collapse of the Psychiatric Unit of the Olive View Medical Hospital (San Fernando Earthquake of February 9, 1971).

Fig. 2. Collapse of the Hartford Civic Arena roof following a winter storm with snow and

freezing rain (January 18, 1978).

284
The late 1960s also witnessed the beginnings of the

move toward a new philosophy of structural design in

the United States, Canada, and Western Europe. The

shortcomings of allowable stress design were recognized in many quarters, and a search was underway for

more rational approaches to distinguish between various

conditions (termed limit states) that affect building performance, to ensure safety under rare but high-hazard

conditions, and to maintain function under day-to-day

conditions. Concurrently, the new field of structural

reliability was developing around the notion that many

of the uncertainties in loads and strengths could be

modeled probabilistically. Advances were being made in

first-order reliability analysis, stochastic load modeling

and supporting statistical databases. Several probabilistic code formats were suggested [2], including an early

version of Load and Resistance Factor Design (LRFD)

for steel buildings [5]. However, these early proposals

were relatively narrow in scope and dealt with single

construction technologies in isolation from one another.

With this lack of coordination, there was a risk that as

different standard-writing groups moved toward probability-based limit states design, each would develop load

requirements independently, and that these load requirements would be mutually incompatible in structural

engineering practice, where construction technologies

usually are mixed. Leaders of the profession agreed

that structural load requirements must be independent

of construction technology to facilitate design with

different construction materials.

At that time, the Secretariat for American National

Standard Committee A58 on Minimum Design Loads

for Buildings and Other Structures was administered in

the Structures Division of the Center for Building Technology. The antecedents at NBS for this standard dated

back to 1924, when the Building and Materials Division

published a report under the auspices of the Department

of Commerce Building Code Committee on Minimum

Live Loads. Research on probabilistic methods in structural codes was a central thrust in the CBT throughout

the 1970s, with the work of Bruce Ellingwood in probabilistic analysis of live and snow loads [3,7] and load

combinations for reinforced concrete design [4], and of

Simiu and Marshall in wind loads [6]. This work stood

at the intersection of research and practice, and its

products were internationally recognized in both

research and professional communities. Various

standard-writing groups in the United States agreed that

the A58 Standard was the logical place for materialindependent load criteria to appear.

In 1978, Ellingwood accepted the challenge of

leading the development of a set of common probability-based load requirements for limit states design that

would be compatible with all common construction

technologies. He arranged for three other leaders in

reliability-based structural codes, T. V. Galambos,

J. G. MacGregor, and C. A. Cornell, to join him at

NBS during the summer of 1979 to develop a set

of load requirements using advanced structural reliability analysis methods and statistical databases. The

Fig. 3. Damage to buildings due to hurricane winds (Hurricane Camille, August 17,

1969).

285
objectives of this joint effort were to: (1) recommend a

set of load factors and load combinations for inclusion in

the A58 Standard that would be appropriate for all types

of building construction (e.g., structural steel, reinforced

and prestressed concrete, engineered wood, masonry,

cold-formed steel and aluminum); and (2) provide a

methodology for various material specification groups

to select resistance criteria consistent with the A58

load requirements and their own specific performance

objectives.

The product of this collaboration is NBS Special

Publication 577, Development of a Probability-based

Load Criterion for American National Standard A58

[1], which was published in June 1980. Subsequent

developmental work on probability-based codes in the

United States in such diverse applications as buildings,

bridges, offshore structures, navigation facilities, and

nuclear power plants in the intervening two decades can

all be traced back to this one seminal document.

The basic notions underlying the probability-based

load requirements and resistance criteria contained in

NBS Special Publication 577 are relatively simple.

Structural failure occurs if the resistance, R, is less than

the structural action, Q, due to the applied loads. If R

and Q are modeled as random variables, the limit state

(or failure) probability can be computed as the probability that R is less than Q [1]. Much of the early history

of structural reliability revolved around difficulties in

performing this computation. If a desired or target

limit state probability for design can be established

(by assessing historically acceptable designs, professional consensus, or legislative or regulatory fiat), then

structural design should strive to achieve solutions

yielding limit state probabilities close to that target

value. Design solutions with higher limit state probabilities are unacceptable from a safety point of view;

designs with lower probabilities are needlessly

expensive.

In probability-based limit states design, the structural

reliability formulation is presented in such a way as to

make it practical for design by engineers who may not

be familiar with reliability concepts or have access to

the necessary statistical data. Structural safety requires

that

Required strength < Design strength (1)

where the required strength is determined from

structural analysis utilizing the specified design loads,

and the design strength is calculated from principles of

structural mechanics with specified material strengths

and structural element dimensions. With the performance requirement that the member reliability should

exceed a target reliability, Eq. (1) can be restated for

practical design purposes as

i Qi <  Rn (2)

In this equation, Rn is the nominal strength corresponding to the limit state of interest and Qi is the

nominal load. These strengths and loads traditionally

have been provided in codes and standards, and most

engineers are familiar with them. The factors  and i

are resistance and load factors that reflect (1) uncertainty in strength and load, and (2) consequence of

failure, reflected in the target reliability measure. The

right hand side of Eq. (2) is the purview of each material

specification (steel, concrete, engineered wood, etc.).

The left-hand side is defined for all construction materials by American National Standard A58, Building Code

Requirements for Minimum Design Loads for Buildings

and Other Structures [8], the national load standard

referenced by the Model Codes and other regulatory

documents in the United States.

The probability-based load criteria in NBS Special

Publication 577 [1] were first implemented through the

voluntary consensus process in the 1982 edition of

American National Standard A58. They have appeared

in all editions of that Standard (the standard has been

published as American Society of Civil Engineers

(ASCE) Standard 7 since 1985) since then, most

recently ASCE Standard 7-98, and have remained

essentially unchanged since 1982. They have been

adopted by reference in all standards and specifications

for limit states design in the United States, including the

American Institute of Steel Construction’s LRFD

Specification for Steel Structures (1986, 1994 and 2000

editions), ASCE Standard 16-95 on LRFD for Engineered Wood Construction, and American Concrete

Institute Standard 318-96 (Appendix B). They also have

been adopted in the International Building Code 2000,

the new single model code in the United States. In

retrospect, the move toward probability-based limit

states design may seem like a small step, but in fact it

was not. It required a thorough re-examination of the

philosophical and technical underpinnings of the current

bases for structural design, as well as the development of

supporting statistical databases. Much of this supporting research is still utilized in code development and

improvement activities worldwide. It has become the

basis for structural design as it is now practiced by

professional engineers in the United States.

It is unlikely that these probability-based load

criteria efforts would have been completed and

implemented in professional practice successfully

had they been managed by any other than CBT/NBS.

286
CBT was viewed as representing the structural engineering community at large rather than any one special

interest group. The load criteria were completed successfully because they were developed by engineering

researchers who were familiar, first of all, with the

structural engineering issues involved, as well as with

the reliability tools necessary for analyzing uncertainty

and safety.

In a more general sense, the load criteria that were

developed in this study and reported in NBS Special

Publication 577 have had a profound influence on structural codes used worldwide in design of buildings and

other structures. The approach taken—developing supporting statistical databases, calibrating to existing

practice, and calculating load and resistance factors to

achieve desired reliability levels—was followed in a

subsequent National Cooperative Highway Research

Program study to develop limit states design procedures

for highway bridges, now published as an American

Association of State Highway and Transportation

Officials standard. The National Building Code of

Canada will adopt a similar approach to combining

loads in its 2000 edition. Standard development

organizations in other countries, including Australia,

New Zealand, South Africa, Japan, and Western Europe

(through the Eurocodes) have adopted similar load

combination requirements for structural design. The

NBS Special Publication 577 load combinations have

been recognized internationally as the first developed

using modern probability-based load combination

analysis techniques. They have stood the test of time,

and only minor changes have been required as a result

of additional research and advances in other areas of

structural load modeling during the past two decades.

The probabilistic approach to structural safety

embodied in this groundbreaking activity continues to

resonate in the structural engineering community. The

aftermath of natural and man-made disasters during the

past two decades, rapid evolution of design and

construction methods, introduction of new technologies, and heightened expectations on the part of the

public, all have made judgmental approaches to

ensuring safety of the built environment increasingly

difficult to defend. The traditional practice of setting

safety factors and revising codes based solely on

experience does not work in this environment, where

such trial and error approaches to managing uncertainty

and safety may have unacceptable consequences. In an

era in which standards for public safety are set in an

increasingly public forum, more systematic and quantitative approaches to engineering for public safety are

essential. The probabilistic approach addresses this

need, and in the past two decades has been widely accepted worldwide as a new paradigm, for design of

new structures and evaluation of existing facilities. NBS

Special Publication 577 was the path-breaking study in

this area.

Bruce Ellingwood held the position of Research

Structural Engineer in the Structures Division of the

Center for Building Technology, NBS, at the time this

work was conducted. Ellingwood was responsible for

administering the Secretariat of the A58 Committee,

and provided the technical leadership for the load

combination development. He left NBS in 1986 to

accept an academic appointment at Johns Hopkins

University, where he chaired the Department of Civil

Engineering from 1990 to 1997. He currently holds the

Willard and Lillian Hackerman Chair in Civil Engineering, and continues to be actively involved in a number of

standard-writing activities. Theodore V. Galambos was

Professor at Washington University, and widely recognized as the father of LRFD for steel structures. He

accepted a position at the University of Minnesota in

1981, from which he retired in 1997. He maintains an

active schedule, particularly with the American Institute

of Steel Construction. Professor James G. MacGregor

recently retired from the University of Alberta, Canada.

He has been a leading figure in both the American

Concrete Institute and the Canadian Standards Association for three decades and continues his involvement

with concrete standards activities in Canada and the

United States. C. Allin Cornell was Professor at MIT,

and had proposed one of the early probability-based

structural codes in the late 1960s. In recent years as

Professor at Stanford University, his research and

consulting activities have involved risk analysis of

offshore structures and other critical facilities and

earthquake-resistant design of building structures.

A number of archival publications were prepared

from the NBS study. Most notably, references [9] and

[10] were awarded the American Society of Civil

Engineers’ Norman Medal in 1983. The Norman Medal

is the oldest and most prestigious of ASCE’s prizes, and

is awarded annually to the paper(s) that the ASCE

Awards Committee and the Board of Directors judge

most significant and meritorious for the advancement of

the civil engineering profession. Reference [11] was an

invited contribution to the inaugural issue of the Journal

of Structural Safety, which in the intervening period has

become the leading international journal in the field of

structural reliability and integrated risk assessment.

Prepared by Bruce R. Ellingwood.

287
Bibliography

[1] Bruce Ellingwood, Theodore V. Galambos, James G. MacGregor,

and C. Allin Cornell, Development of a Probability-Based Load

Criterion for American National Standard A58, NBS Special

Publication 577, National Bureau of Standards, Washington, DC

(1980).

[2] C. Allin Cornell, A Probability-Based Structural Code, J. Am.

Concr. Inst. 66, 974-985 (1969).

[3] Bruce Ellingwood and Charles Culver, Analysis of Live Loads in

Office Buildings, J.Struct. Div., ASCE 103, 1551-1560 (1977).

[4] Bruce Ellingwood, Reliability-Based Criteria for Reinforced

Concrete Design, J. Struct. Div., ASCE 105, 713-727 (1979).

[5] Mayasandra K. Ravindra and Theodore V. Galambos, Load and

Resistance Factor Design for Steel, J. Struct. Div., ASCE 104,

1337-1353 (1978).

[6] Emil Simiu, Michael J. Changery, and James J. Filliben,

Extreme Wind Speeds at 129 Airport Stations, J. Struct. Div.,

ASCE 106, 809-817 (1980).

[7] Bruce Ellingwood, Wind and Snow Load Statistics for Probabilistic Design, J. Struct. Div., ASCE 107, 1345-1350 (1981).

[8]Minimum Design Loads for Buildings and Other Structures,

ANSI Standard A58/ASCE Standard 7.

[9] Theodore V. Galambos, Bruce Ellingwood, James G.

MacGregor, and C. Allin Cornell, Probability-Based Load

Criteria: Assessment of Current Design Practice, J. Struct. Eng.,

ASCE 108, 959-977 (1982).

[10] Bruce Ellingwood, James G. MacGregor, Theodore V. Galambos, and C. Allin Cornell, Probability-Based Load

Criteria: Load Factors and Load Combinations, J. Struct. Eng.,

ASCE 108, 978-997 (1982).

[11] Bruce Ellingwood and Theodore V. Galambos, Probabilitybased Criteria for Structural Design, Struct. Saf. 1, 15-26 (1982).

288
Resistivity-Dopant Density Relationship for

Phosphorus-Doped Silicon

This paper [1], together with its companion [2],

Resistivity-Dopant Density Relationship for BoronDoped Silicon, documents the work done from about

1975 to 1980 to obtain a more accurate relationship

between the resistivity and dopant density of silicon.

The conversion between these two material properties is

widely used in the semiconductor industry since silicon

is the primary material which has powered the information age. A conversion is needed because many applications involve relating resistivity, which is known or can

be readily measured, to dopant density, the desired

quantity which is very difficult to measure directly.

To model the processing of an integrated circuit, the

conversion is used to calculate the surface carrier

concentration of a diffused layer from the sheet

resistance—junction depth product and to determine the

dopant density profile from incremental sheet resistance

measurements. Significant error in the results of these

measurements occurs when incorrect expressions are

used to relate resistivity and dopant density.

The work was initiated because of disagreements

between measured values and those calculated using the

existing relationships. Numerous measurement methods

were used for the redetermination of the relationship

for silicon doped with boron (p-type) or phosphorus

(n-type). Results were obtained from more than 77

wafers, mostly donated by industry, that spanned the

dopant density range from 1013 cm–3 to 1020 cm–3

. For

dopant densities less than 1018 cm–3

, resistivity and

junction capacitance-voltage measurements were made

on processed wafers. For more heavily doped material,

data were obtained from Hall effect and resistivity

measurements on samples cut from bulk silicon wafers.

These primary methods were supplemented for

phosphorus-doped material by neutron activation analysis and a photometric technique [3], and for borondoped material by the nuclear track technique [4].

Analytical curves were fitted to the resistivity-dopant

density product as a function of resistivity and dopant

density for temperatures of both 23 C and 27 C.

Similar curves were obtained for the calculated carrier

mobility as a function of resistivity and carrier density.

A comprehensive report on the work, including tables

of the data and curve fitting details, was published as an

NBS Special Publication [5]. For phosphorus-doped

silicon, the results of this work differed by 5 % to 15 %

from the then commonly used curve. For boron-doped

silicon the results differed significantly from the p-type

curve in use at the time. A maximum deviation of 45 %

occurred at a boron density of 51017 cm–3

. Because of

the large differences, ASTM Committee F-1 decided

that the semiconductor industry needed a recommended

conversion. The results of this work formed the basis of

a new ASTM Standard Practice [6] for the conversion

between resistivity and dopant density. It remains

the accepted conversion to use, and either the original

publications or the ASTM document are referenced in

many papers and textbooks, as well as in five other

ASTM measurement standards. The graph of dopant

density vs. resistivity in Fig. 1, reproduced from the

ASTM standard, is the reference chart normally used

by workers in the field. This chart and the associated

analytical fits are commonly referred to as the Thurber

curves.

W. Robert Thurber was born in Butte, Nebraska, on

July 10, 1938. He received an A. B. degree in physics

from Nebraska Wesleyan University in 1960 and an

M. S. degree in physics from the University of Maryland

in 1963. He has been with NIST since 1962 and is

presently an experimental physicist in the Semiconductor Electronics Division.

He has had broad experience in the measurement of

the electrical and optical properties of semiconductors.

Past projects include the electrical properties of golddoped silicon, infrared absorption due to oxygen in

silicon and germanium, and microelectronic test structures for the measurement of parameters important for

integrated circuit processing. The characterization of

impurities in semiconductors using deep level transient

spectroscopy (DLTS) is another area of expertise.

A novel method to detect nonexponential capacitance

transients was developed. Thurber was heavily involved

in writing an ASTM method on transient capacitance

measurements and was in charge of a round robin to

verify the method.

Thurber has also worked on the high-priority project

to investigate the problems of infrared detectors used on

the NOAA GOES satellites. An ac impedance method

was developed for measuring the very high resistivity of

silicon ingots used for detector applications. He also

did research on the photo response in p-type silicon

containing oxygen. Recently, he assembled a Hall effect

and resistivity measurement system which he is using to

characterize GaAs samples for an upcoming inter289
national Hall effect round robin which NIST will coordinate. He helped put together a tutorial Hall effect web

page which invites viewer comments and will also be

used to report results of the round robin.

Prepared by W. R. Thurber.

Bibliography

[1] W. R. Thurber, R. L. Mattis, Y. M. Liu, and J. J. Filliben, Resistivity-Dopant Density Relationship for Phosphorus-Doped Silicon,

J. Electrochem. Soc. 127, 1807-1812 (1980).

[2] W. R. Thurber, R. L. Mattis, Y. M. Liu, and J. J. Filliben,

Resistivity-Dopant Density Relationship for Boron-Doped

Silicon, J. Electrochem. Soc. 127, 2291-2294 (1980).

[3] W. Robert Thurber, A Comparison of Measurement Techniques

for Determining Phosphorus Densities in Semiconductor Silicon,

J. Electron. Mater. 9, 551-560 (1980).

[4] W. Robert Thurber and B. Stephen Carpenter, Boron Determination in Silicon by the Nuclear Track Technique, J. Electrochem.

Soc. 125, 654-657 (1978).

[5] W. R. Thurber, R. L. Mattis, Y. M. Liu, and J. J. Filliben, The

Relationship Between Resistivity and Dopant Density for Phosphorus- and Boron-Doped Silicon, NBS Special Publication 400-

64, National Bureau of Standards, Washington, DC (1981).

[6] Standard Practice for Conversion Between Resistivity and Dopant

Density for Boron-Doped, Phosphorus-Doped, and ArsenicDoped Silicon, ASTM Designation: F 723-99 (originally published as F 723-81), Annual Book of ASTM Standards, Vol. 10.05,

American Society for Testing and Materials, West Conshohocken,

PA, April 2000.

Fig. 1. One of the two “Thurber Curves”; there is a companion curve for phosphorous-doped silicon. Plotted is

resistivity-dopant density product as a function of resistivity at 300 K for boron-doped silicon. The junction

capacitance voltage and Hall effect measurements are compared with the published work of Thurber and

Carpenter [4] and other values in the literature. The solid curve is an analytical fit to portions of these data. Values

of the product of charge, resistivity, and boron density are on the right ordinate.

290
Critical Data for Critical Needs

As a national laboratory dedicated to the advancement of measurement science and engineering, NBS/

NIST recognized early in its history that the assessment

of the quality of measurement results is a fundamental

component of its mission. The 1981 paper by David

Lide, Critical Data for Critical Needs [1], offers both a

status report and a prognosis of major changes expected

from the revolution in information technology that was

beginning at that time.

The compilation and critical evaluation of material

property data as an important NBS function can be

dated to the Bureau’s involvement in preparation of the

International Critical Tables [2] in the 1920s. NBS

played a leadership role in the project to produce this

seven-volume series, whose contributors included

hundreds of scientists from all parts of the world. The

Editor-in-Chief was E. W. Washburn, Chief of the

NBS Chemistry Division, and the Editorial Board

included NBS Director G. K. Burgess. Many Bureau

staff members contributed to the work, which is still

used and cited 80 years later. Over the ensuing decades,

NBS started new specialized data activities in areas

such as phase equilibrium for ceramics (1930s),

chemical thermodynamics (also 1930s), and atomic

spectroscopy (late 1940s). However, the rapid build-up

of government-supported science and engineering after

World War II brought increased demands for a systematic program, fully integrated into the NBS research

agenda.

NBS leaders such as Allen Astin, Edward Brady, and

Lewis Branscomb worked with Congress and President

Johnson’s administration to establish the world’s first

formal government-endorsed data evaluation program.

This effort culminated in the enactment of the Standard

Reference Data Act of 1968 (PL 90-298, now designated as 15 U.S.C. 290). This Act of Congress established the National Standard Reference Data System

(NSRDS), a coordinated and comprehensive program

with an objective to “ensure that reliable reference data

are easily accessible by scientists, engineers, and the

general public.” NBS was given the responsibility for

coordination of the NSRDS, but other government

agencies and private organizations were expected to

participate.

In response, NBS set up a series of formal data

evaluation centers that covered a wide range of physical,

chemical, and materials disciplines. Joint projects were

started with other agencies, professional societies, trade

associations, and foreign laboratories. Several publication channels were established, in particular the Journal

of Physical and Chemical Reference Data, which was

published in partnership with the American Institute

of Physics and the American Chemical Society. This

journal served not only as an outlet for compilations

done at NBS, but also attracted many data reviews and

compilations from outside authors. Other scientific societies were engaged to publish compilations on specialized topics. As an example, four volumes of the Crystal

Data Determinative Tables, prepared at NBS, were published through the Joint Committee for Powder Diffraction Standards [3].

The start of the 1980s saw NBS data activities on the

brink of a new era. With data evaluation procedures for

different types of data now well established, taking

advantage of the computer revolution became the next

obvious step. At the same time, major private sector

organizations realized the advantage of working with

NBS to improve the quality and accessibility of data of

importance in their world of interest. As this new era

began, the paper Critical Data for Critical Needs was

published in Science. The genesis of this paper dates to

the 1980 International CODATA Conference in Kyoto,

Japan, where the keynote speaker was Phillip Abelson,

then Editor of Science. Abelson was intrigued by

the talks he heard on new technology for automated

retrieval and dissemination of scientific data, as well as

the evidence of growing international collaboration,

and he offered Science as a vehicle for publicizing these

developments. At once the paper documents the progress towards better quality data as well as the opportunity presented by computerization and by cooperative

ventures. The paper sub-headings indicate its coverage:

classes of data; the growing need for good data; quality

control of data bases; the electronic revolution in data

dissemination; and the need for cooperation.

The discussion could not be clearer, nor the vision

better defined. What had been accomplished to date was

impressive, but the future was equally promising.

The paper begins by creating a context for NBS data

work, namely that of the “information explosion” of the

last 25 years. In reaction to this exponential increase in

scientific and technical information, numerous organizations had begun creating electronic collections of

literature citations, abstracts, and even documents

themselves in an effort to facilitate identification and

retrieval of relevant information. However, the bulk of

291
that work was concerned with helping users locate the

scientific literature that reported research results. If

users were to take advantage of the power of computers,

the entire range of scientific content including the data

resulting from research, which are usually in numerical

or graphical format, would have to be available in

electronic form. The remainder of the paper covered all

major aspects of scientific data storage, retrieval, and

dissemination.

After defining what is meant by the term “data”—

repeatable measurements, observations and statistical

results—Lide discussed the importance of quality in

data activities. As science and engineering were

confronting increasingly complex problems, from

depletion of the ozone layer to shortage of critical

materials, important decisions required data of the best

quality to be available. With the advent of computer

modeling as a major technology, data quality was even

more important because of the potential for modeling

results whose dependency on input data would be

difficult to trace. The National Standard Reference Data

System, as established by NBS, was a concerted attempt

to involve expert scientists in the effort to assess

the quality of reported measurements. As already

mentioned, NSRDS maintained a series of continuing

data centers with expertise in a well-defined discipline.

Lide described several of these data centers and their

current approach to evaluation of laboratory data on

well-defined substances and materials. He also described parallel activities of the World Data Centers,

which had been established by the International Council

of Scientific Unions to perform a similar data quality

assessment task for observational data in fields such as

geophysics, oceanography, and atmospheric physics.

The paper then turns to the challenges of the electronic revolution and, somewhat surprisingly, defines

the two paradigms for computer delivery of data that are

still used today: installation on one’s own computer and

access via networking to remote data collections. At the

time the paper was written, the first recognizable personal computers were just beginning to appear. Yet the

essential features of scientific databases stored on PCs

are all addressed, namely local control, heavy use, inclusion of search software, and the facility to transfer

data to computational software and other applications.

The description of online data services is equally prescient, even though it was based on a model of subscription services in which the user connects directly to a

remote computer rather than through the World Wide

Web of the year 2000. What is particularly interesting

is the recognition that users routinely require a multitude of data resources to solve real-life problems, so

that online data resources need to be integrated together

to provide maximum impact and benefit.

The last major section of the paper describes a time

of rapidly evolving cooperation to handle the flood of

data and to take advantage of the electronic revolution.

The cost of data evaluation is high, the volume of data

too great, and the change in technology too rapid for any

group to go it alone without ample resources. Further, in

many cases, the need for consistency among collections

of recommended data can be a prime motivator to work

together rather than in competition. Lide mentions

CODATA, the Committee on Data for Science and

Technology of the International Council of Scientific

Unions, as a major factor in bringing together data

experts on an international basis.

The paper concludes with a prediction of three trends:

the need for reliable data becoming more pressing;

computer-based data dissemination methods, especially

online systems, growing in use; and coordination

in the development of computer-based systems being

essential.

Unlike the majority of papers in this Centennial

volume, this paper does not present original research

results. Instead, it describes one of NBS’s largest and

best-known programs, the Standard Reference Data

Program. More importantly, the paper describes quite

accurately what challenges the NBS data programs were

facing in the last three decades of the NBS/NIST first

century. At the time of publication, NBS was beginning

a series of intensive and large-scale cooperative

programs that changed the availability and quality of

data in many areas of interest to industry. The names of

the programs suffice for description:

Fig. 1. A sample of current Standard Reference Data products.

292
• American Society for Metals–NBS Alloy Phase Diagram Program

• American Ceramics Society–NBS Phase Diagrams

for Ceramists Program

• National Association of Corrosion Engineers–NBS

Corrosion Data Program

• Design Institute for Physical Property Data

(DIPPR), in cooperation with the American Institute

of Chemical Engineers

• NIST fluids property data programs, in cooperation

with the Gas Producers Association, the Compressed Gas Association, and the Supercritical Fluids Extraction Consortium.

The trend continues today with NIST recently

forming the Research Collaboratory for Structural

Biology with Rutgers University and the University of

California at San Diego to operate the Protein Data

Bank.

In the years following the publication of Lide’s paper,

NBS/NIST expanded its data activities even further to

include engineering data and even data used to

“calibrate” statistical and other kinds of software. At the

same time, the proliferation of personal computers,

as envisioned by Lide, transformed forever the dissemination of NIST/NBS data. By 1995, over 70 PC databases were available for sale from NIST. Parallel efforts

on traditional online services and the Internet/World

Wide Web brought even increased availability. As of

May 2000, NIST was already providing online access to

its evaluated data via 15 web-based systems.

The basic components of the NIST data activities in

2000 remain essentially the same as defined in Lide’s

paper. Quality is the defining feature. The hallmark of

NIST data work remains the evaluation by recognized

experts. Easy availability is equally important so that the

return on the taxpayer investment in data is maximized

by the widest possible dissemination of data. Finally,

cooperation ensures that limited resources are not

wasted on duplicative efforts and that users are not

confronted by competing claims for best quality.

Data evaluation remains an important component of

the overall NIST measurement portfolio, providing a

snapshot at a given time of the quality of measurement

technology in different fields. NIST is the world’s leader

in the evaluation of physical science and other data, a

tribute to the foresight and vision of leaders such as

David Lide, Edward Brady, and many others. The paper

Critical Data for Critical Needs remains a classic

in defining the scope and importance of data in the

advancement of science and technology and of the

impact computers have had on scientific data work.

David R. Lide was hired by NBS in 1954 to set up a

microwave spectroscopy laboratory in the Thermodynamics Section of the Heat and Power Division. In the

early 1960s he led the integration of NBS research

programs in infrared, microwave, and ultraviolet

spectroscopy into a single Molecular Spectroscopy

Section, which he headed until he became Director of

the Office of Standard Reference Data in 1969. He was

active in various national and international organizations, including stints as Secretary General and later

President of CODATA and President of the Physical

Chemistry Division of the International Union of Pure

and Applied Chemistry. He received Department of

Commerce Silver and Gold Medals and the Samuel

Wesley Stratton Award of NBS for his research in

spectroscopy, as well as the Herman Skolnik Award and

the Patterson-Crane Award of the American Chemical

Society for contributions to chemical information. After

leaving NIST in 1988, he became Editor-in-Chief of

the CRC Handbook of Chemistry and Physics and has

published several other books and electronic databases.

Prepared by John R. Rumble, Jr.

Bibliography

[1] David R. Lide, Jr., Critical Data for Critical Needs, Science 212,

1343-1349 (1981).

[2] Edward W. Washburn (editor-in-chief), International Critical

Tables of Numerical Data, Physics, Chemistry, and Technology,

Vols. 1-7, published for the National Research Council by the

McGraw-Hill Book Company, New York (1926-1933).

[3] J. D. H. Donnay and Helen M. Ondik (eds.), Crystal Data Determinative Tables, Vol. 1-4, Third Edition, National Bureau of

Standards and Joint Committee on Powder Diffraction Standards,

Swarthmore, PA (1972-1978).

293
Materials at Low Temperatures

An offhand comment by a long forgotten colleague

provided the impetus to develop one of the most

comprehensive books available on the study of materials

at low temperature. As the 30-year era of the NBS

Cryogenics Division was coming to a close, it was

remarked, perhaps more than once, that the accumulated expertise of the division should be gathered and

preserved. Thus, the idea was born to pull together a

tutorial text and apply the resident expertise to a critical

evaluation of the existing data on cryogenic materials. It

is rare enough that such an opportunity presents itself,

but rarer still that 13 authors should work together to

create such a text. That the result had widespread impact

and influence on the low-temperature community,

however, was no surprise.

The book, Materials at Low Temperatures [1],

consists of 14 chapters, each a combination of tutorial

text and critical data analysis for 14 different properties

of materials at cryogenic temperatures. It was written

during the years 1980-1982 by the staff members of the

former Cryogenics Division while the Division was being disbanded during a major reorganization, with the

staff being distributed throughout three different Centers that have since evolved into three laboratories: Electronics and Electrical Engineering Laboratory (EEEL), Materials Science and Engineering

Laboratory (MSEL), and Chemical Science and Technology Laboratory (CSTL). The 590-page book represents the consolidation of an estimated 600 staff-years of

experience accumulated by the Division staff while it

led the world in research and development of cryogenic

technology. The history of that experience can be traced

from its beginning with nuclear weapons, through the

rapid growth of the space age, and into the world of

low-temperature physics and superconductivity.

The book contains nearly 3000 references to extensive collections of theoretical and experimental work,

much of it data for the critical analyses. The book is

organized into the following 14 chapters:

Chapter 1 – Elastic Properties, H. M. Ledbetter

Chapter 2 – Specific Heat, L. L. Sparks

Chapter 3 – Thermal Expansion, A. F. Clark

Chapter 4 – Thermal Conductivity and Thermal

Diffusivity, J. G. Hust

Chapter 5 – Electrical Properties, F. R. Fickett

Chapter 6 – Magnetic Properties, F. R. Fickett and

R. B. Goldfarb

Chapter 7 – Mechanical Properties, D. T. Read

Chapter 8 – Fracture Mechanics, R. L. Tobler and

H. I. McHenry

Chapter 9 – Martensitic Phase Transformations, R. P.

Reed

Chapter 10 – Compatibility of Materials with

Cryogens, J. C. Moulder and J. G. Hust

Chapter 11 – Structural Alloys, H. I. McHenry

Chapter 12 – Composites, M. B. Kasen

Chapter 13 – Superconductors, J. W. Ekin

Chapter 14 – Temperature, Strain, and Magnetic Field

Measurements, L. L. Sparks

Each chapter is complete on its own, yet there is an

interweaving that was done by the editors, drawing from

the interactions of the authors, who were all colleagues

and who compared notes and ideas as they were writing.

The book is readable by the most inexperienced

Fig. 1. Practical superconducting wires often are composite structures consisting of many fine superconducting filaments embedded in

a matrix of normal metal to give the composite stability. When an ac

current is passed through the superconductor, substantial energy

losses can occur due to eddy currents. These losses must be minimized so that they do not heat the superconductor above its critical

temperature. Subdividing the copper sheathing with sheets or fins of

low conductivity Cu-Ni helps to reduce those losses. The figure

shows a multifilamentary superconductor with cupronickel barriers

(white areas) to prevent coupling currents from flowing around

filament clusters and the outer copper stabilizing sheath. Copper areas

are dark and the Nb-Ti filaments are gray. [Figure courtesy of

Imperial Metal Industries.]

294
layman while remaining a valuable reference to even the

old hands of cryogenics. This coherent presentation is

exemplified by the chapter on thermal expansion by

A. F. Clark. He begins with a simple observation:

“Warming a solid body from absolute zero requires

energy. In a free body, this energy manifests itself in two

ways: an increase in temperature and a change in

volume. Both of these are directly related to the additional vibrational energy of the individual atoms; the

former simply because more atomic energy states are

excited, the latter because the mean interatomic distance

changes with energy. The ratio of the change in energy

to the change in temperature is the specific heat. The

ratio of the change in volume to the change in temperature is the thermal expansion.” Thus, in this remarkably

lucid introduction, Clark establishes the significant

conceptual relation between two extremely important

properties, specific heat and thermal expansion. He

goes on to explain, “ . . . the volume expansion is due to

the anharmonic behavior of atomic vibrations and the

specific heat is due primarily to the vibrations themselves . . . ” From there, one quickly proceeds to learn

about the wide-ranging importance of understanding the

thermal properties, from the dimensional stability

needed to maintain the critical alignment of a large

telescope operating in the very cold environment of

space while being warmed by the sun, to the earthbound

commercial consequences of the thermal expansion or

contraction of a low-temperature storage tank. In a

commercial storage tank for liquefied natural gas

(LNG), the tank itself cools as the LNG is added. The

volume of the fully cooled storage tank may be as much

as thirty thousand liters smaller than it was at the

ambient temperature! Having explained the concepts

and the consequences, Clark then proceeds to review

the essential theoretical elements and the principal

measurement methods, and concludes with an evaluation of the pertinent data.

Fig. 2. An interior view of a liquefied natural gas tank lined with a low thermal expansion alloy. [Figure courtesy

of McDonnell Douglas, Astronautics Laboratory and Gaz-Transport.]

295
The approach exemplified by Clark’s chapter is

followed throughout the book by a collection of authors

who, at the time of writing, were considered by many

to be the world’s best experts on virtually all aspects

of cryogenic technology. To have some of the best

researchers in the field outline and explain the lowtemperature behavior of materials creates an unusually

complete reference. To have those same experts evaluate

the available data, explain them, and indicate future

research directions, creates a sound, thorough, and

scientifically excellent work.

The book has been used as a text in courses on

cryogenic technology and as a reference by cryogenic

engineers and low-temperature physicists throughout the

world. Book reviews of that time used such words as

“extraordinarily useful,” “extensive,” “understandably

written,” and “indispensable reference.” Personal

feedback to the authors was, and some cases still is,

always very positive. Two categories of users were often

more lavish in their praise, those new to the field and

those in the depths of low-temperature experiments,

responding respectively to the tutorial text and the data

evaluations, the two primary objectives of the book.

The volume, published by the American Society for

Metals, sold out rapidly. Of the approximately 1000

books printed, none are still available for purchase.

Copies are widely distributed in university, government,

and industrial laboratories throughout the world. These

books have been seen on shelves from New England to

New Zealand, from China to Scotland, and from

Argentina to Finland. Visits to the many laboratories

that have copies show them all to be both dog-eared and

treasured. But probably the strongest indication of use

has come from personal feedback to the authors, all of

it anecdotal and all of it very positive. Typical are “It’s

always within reach,” “I never let it out of the office,”

and “It’s always researched whenever we start something new.”

The extent of the compilation and evaluation of data

is truly comprehensive. Even today, newly measured

data fit within the ranges and predictions of the authors.

The explanatory text is, of course, still valid and just as

relevant as when the book was published. For anyone

attempting to design, build, or interpret an experiment at

low temperatures, even 17 years later or 17 years hence,

the book is, and will be, an extraordinarily useful

reference.

Richard Reed received his Ph.D. in physical metallurgy in 1966. At NBS, he served as Chief of the

Fracture and Deformation Division through 1986.

Officially retired now, he still consults on the lowtemperature properties of materials. Reed and Clark are

credited with founding the International Cryogenic

Materials Conference, and each has served as editor of

many conference proceedings and journals.

Alan Clark received his Ph.D. in physics in 1964.

With a specialty in low-temperature physics and superconductivity, he has served as Group Leader of both

the Superconductor and Magnetic Measurements group

(NBS-Boulder) and the Fundamental Electrical

Measurements group (NIST-Gaithersburg). He also has

served as a Liaison Scientist for the Office of Naval

Research, London. He is now Deputy Chief of the

Optoelectronics Division (NIST-Boulder).

Of the thirteen authors, six are still employed at NIST,

three in EEEL (Al Clark, Jack Ekin, and Ron Goldfarb)

and three in MSEL (Fred Fickett, Hassel Ledbetter, and

Dave Read). Five are retired from NIST (Jerry Hust, Bud

Kasen, Harry McHenry, Dick Reed, and Larry Sparks);

several of these now have small consulting businesses.

One (John Moulder) is deceased.

Prepared by Fred Fickett.

Bibliography

[1] Richard P. Reed and Alan F. Clark (eds.), Materials at Low

Temperatures, American Society for Metals, Metals Park, OH

(1983).

296
Optical Fiber Characterization

NBS Special Publication 637, Optical Fiber Characterization [1], is a two-volume compilation of previously

published NBS Technical Notes concerning the characterization of optical fibers used for telecommunications.

The Technical Notes appeared in the late 1970s and

early 1980s, which was the period of commercial

infancy of optical telecommunications fiber. During

that period, the commercially viable fibers were of the

multimode type rather than single mode; that is, they

supported the transmission along the fiber of a number

of electromagnetic modes having different combinations of electric field and magnetic field configurations.

Consequently, SP 637 (as this publication is commonly

called) is mainly concerned with the characterization of

multimode fiber. While single mode fibers could be

fabricated, the technology to exploit them was not

readily available at the time. In the earliest fiber, large

concentrations of the highly polar hydroxyl radical (OH)

in the glass caused high loss at the long wavelengths

effective for single-mode operation. Also, the small core

size of single-mode fiber requires connectors, splices,

and special sources to be aligned with high dimensional

accuracy, and it took years to develop such components

that could be manufactured at an acceptable cost.

Multimode fibers with core diameters in the 50 m to

100 m range could be easily joined with low loss, and

light from laser diodes with large emitting areas could

be readily launched into the large cores in a simple

manner. The large core size also allowed the use of LED

(light emitting diodes) sources in designing practical

systems.

There were no standard measurement procedures

available in the early period of development of optical

fiber. An effort was started by the military to draft

“mil standards” for fiber. It was a useful start, and a

standards document was produced. However, the

technical challenges were difficult, and rapid changes

were occurring in the industry. A larger United States

standards effort, principally among manufacturers,

started in the Electronic Industries Association

(EIA). NBS staff attended the first EIA organizational

meetings where attendees determined the important

technical areas and established a network of committees. It was soon evident that there was a role for NBS.

Manufacturers had developed their own measurement

methods, and in many instances different technical

Fig. 1. A schematic diagram of early apparatus used to measure material dispersion by simultaneous propagation of pulses from pairs of laser

diodes. Such measurements are important in avoiding interference between pulses of different wavelengths that are transmitted down a single

optical fiber.

297
approaches were being employed. NBS acted as a

neutral party to evaluate many procedures through

round robin comparisons.

Fiber optic technology is measurement intensive.

Measurements can take place at fabrication, cabling,

incoming inspection, and installation. Compared to

single mode fibers, multimode fibers present significant

characterization problems; thus quality control measurements were a substantial production cost for multimode fiber. The large core sizes result in hundreds of

propagating waveguide modes having independent loss

and group delay. Consequently, the transmission properties depend on how light is launched into the fiber; i.e.,

which waveguide modes are excited by the source. An

early measurement round robin in 1979, conducted by

NBS, revealed significant interlaboratory differences in

the measurement of the attenuation coefficient. Such

differences resulted from difficulties in achieving a

common distribution of launched light and in following

a specified methodology. In subsequent years, NBS

worked closely with the Electronic Industries Association (EIA, which gave birth to the Telecommunications

Industry Association), at its request, to standardize light

launch conditions for measuring the transmission properties of graded-index optical fibers. Many of the issues

involved in selecting and creating the launching conditions are contained in the chapters of SP 637.

Another factor adding to measurement uncertainty

was the use of multiple test methods based on different

technical approaches. Standards groups often allowed a

multiplicity of test methods for any given parameter. A

large part of the technical effort at NBS during this

period was to determine the systematic differences

between test methods.

It is of interest to put the work contained in SP 637 in

historical perspective. Multimode fiber dominated the

first telecommunication systems. The first wavelengths

utilized were near 850 nm, followed later by applications at 1300 nm. In the early 1980s, the OH content of

the glass, and consequently the attenuation, was greatly

reduced. The highly desirable properties of single mode

fiber became technically accessible, and operation was

possible at a wavelength of 1550 nm, where the attenuation is a minimum. Compared to multimode fiber, single

mode offers both reduced attenuation and substantially

higher bandwidth. Thus today’s long distance and

metropolitan networks consist solely of single mode

fiber.

Nevertheless, multimode fiber has found an important niche in high speed local area data networks

with concepts such as “fiber to the desk” and “gigabit

ethernet.” The large core fiber offers inexpensive

connections, high launching efficiency with large area

sources, and the use of inexpensive plastic optics.

Data rates for the more advanced systems are in the

range of 1 Gbit/s to 10 Gbit/s. The Vertical Cavity Surface Emitting Laser (VCSEL) is a common source for

high-speed multimode networks. This laser typically

operates near 850 nm, which was the first wavelength

window in the early multimode systems. Therefore, the

contribution of SP 637 remains technically relevant to

current high-speed local area networks.

Fig. 2. An example of group-delay material dispersion with pulses at 824 nm wavelength (left pulse in each oscilloscope photograph) and 803 nm

wavelength before (left photograph) and after propagating through a 1 km length of fiber.

298
Among the measurements on multimode optical fiber

discussed in SP 637, attenuation is perhaps the most

important fiber parameter because it establishes the

maximum length of fiber along which signals may be

sent without requiring a repeater (a device that amplifies

the signal for transmission along the next section of

fiber). At the time SP 637 appeared, a premium was

charged for lower loss fibers, so there was a financial

incentive for reliable values of the attenuation parameters. Next in importance is probably bandwith, a

measure of the potential information carrying capacity

of the fiber. Bandwidth is specified in the frequency

domain, but can be measured in either the time or

frequency domains. SP 637 describes methods for

obtaining 200 ps duration pulses from laser diodes for

time-domain measurements, along with methods for

launching the light into the fiber. SP 637 also describes

a system for measuring the fiber frequency response

directly in the frequency domain.

The author also discusses the radiation pattern of

light at the exit end of the optical fiber and describes

systems for measuring radiation patterns, giving

comparisons with other methods for measuring core

diameter and “numerical apertures.” The radiation

pattern measurements are straightforward and without

much controversy in their implementation, but they are

important because they are commonly practiced in the

trade and commerce of fibers.

SP 637 also describes a technique called “refractiveray scanning (RNF)” to determine the refractive index

profile across a fiber diameter. The index profile is not

a parameter specified in the trade and commerce of

fibers, but it is very important to fiber manufacturing.

Only by having the appropriate near-parabolic shaped

index profile can the full bandwidth potential of gradedindex fibers be achieved. SP 637 describes the construction of an RNF system and a novel method for calibrating the absolute value of refractive index using a series

of index-matching fluids of known refractive index.

The efforts described in SP 637 provided the impetus

for future NBS/NIST programs in optical fiber metrology. In following years, the work was greatly expanded

and concentrated on single-mode fibers. Within NIST,

staff was added, and the program grew from project to

group status. Fiber metrology is now a major component

of the Optoelectronics Division. In 1980, NBS staff

initiated the “Symposium on Optical Fiber Measurements.” This conference, held biennially for 20 years, is

one of the premier international conferences on optical

fiber measurements. NIST staff now chair committee

positions within the Telecommunications Industry

Association and serve on the program committees

of major conferences devoted to lightwave communications.

Douglas L. Franzen joined NBS as a National

Research Council Postdoctoral Fellow in 1970 and spent

his first six years developing improved methods of

measuring the output power of lasers. In 1976, he and

two colleagues initiated the Optical Fiber Measurement

Program at NBS. Thirteen standards, which provide the

measurement basis needed by manufacturers to control

and enhance quality and to demonstrate compliance

with purchase specifications, are based on Franzen’s

research. In 1980, he helped found the biennial

Symposium on Optical Fiber Measurements, and he has

continued to serve as its general chairman. His work

has been recognized by a number of awards, including

election as a Fellow of the Optical Society of America;

Department of Commerce Bronze, Silver, and Gold

Medals; the Applied Research Award of NIST; and the

NTT (formerly Nippon Telegraph and Telephone

Corporation) Director’s Award, for collaborative work

on an innovative optical sampling instrument.

Gordon W. Day has been a leader in optoelectronics

work at NBS/NIST since 1976. He has advanced the

NIST efforts to meet special measurement needs of

the emerging lightwave communications industry,

especially for optical fibers, lasers, and optical fiber

sensors. In 1993 he was given the responsibility of

forming a new division at NIST dealing with optoelectronics. Day’s research has been in the metrology

related to optoelectronics and has resulted in more than

130 publications and a variety of awards, such as

the Gold and Silver Medals of the Department of

Commerce, two IR-100 Awards from R&D Magazine,

and a Technology Transfer Award from the Federal

Laboratories Consortium. He is a fellow of both the

Institute of Electrical and Electronics Engineers (IEEE)

and the Optical Society of America. In 1999-2000 he

was President of the IEEE Lasers and Electro-Optics

Society.

Prepared by D. L. Franzen.

Bibliography

[1] G. E. Chamberlain, B. L. Danielson, G. W. Day, D. L. Franzen,

R. L. Galawa, E. M. Kim, and M. Young, Optical Fiber Characterization, Volumes 1 and 2, NBS Special Publication 637,

National Bureau of Standards, Gaithersburg, MD (1982).

299
Quasicrystals

The well ordered world of solid materials was forced

to reassess its rules of order by the spectacular results of

D. Shechtman, I. Blech, D. Gratias, and J. W. Cahn [1].

By the year 1801, the fundamental laws of crystal

morphology had been well established, and in the last

two decades of that century, theories of the internal

symmetries of crystals were being discussed [2]. Early

in the following century, 1912-1916, the development

of x-ray diffraction techniques allowed the periodic

arrangement of atoms in a crystal to be established

experimentally [3]. By 1984 it was universally accepted

that an x-ray diffraction pattern with sharp peaks could

only be the result of a periodic arrangement of atoms or

molecules occurring in a crystalline solid, and every

possible crystal symmetry was known [4].

In general, crystals are classified according to their

allowed translational and rotational symmetry operations. Each possible crystal lattice is characterized by

having a smallest structural unit, called a unit cell, and

when those cells are stacked together face-to-face, an

infinite region of space can be filled without leaving a

single hole. Quite notable in the mathematics of crystal

symmetry is the impossibility of a three dimensional

crystal possessing a five-fold axis of rotation.

“We report herein the existence of a metallic

solid which diffracts electrons like a single

crystal but has point group symmetry m3 5 ––

(icosahedral) which is inconsistent with

lattice translations.” [1]

That pronouncement appearing in Physical Review

Letters in 1984 heralded the discovery of a new class of

materials, now called quasicrystals, which possessed the

heretofore forbidden icosahedral point symmetry!

It is not surprising that there followed immediately

several years of raging controversy regarding the origin

of the diffraction symmetry, but importantly, sufficient

results from electron diffraction experiments were

reported in this initial paper to confirm that the icosahedral symmetry was indeed real. The primary point of

contention was the well-known experience that disallowed diffraction patterns could be produced artificially as a result of a superposition of multiple allowed,

but rotated, patterns. As a crystal is grown, it is not

uncommon for the growth direction to change suddenly

resulting in a process called twinning. Indeed, John

Cahn said [5], “My reaction was, ‘Go away, Dany. These

are twins and that’s not terribly interesting.’”

However, to produce the five-fold symmetry,

twinning would have to occur five times in succession.

That hypothesis can be tested experimentally by focusing the diffraction beam on smaller and smaller regions

of the specimen. When the size of the diffraction

volume becomes too small to enclose all five twins, the

five-fold symmetry must disappear. Such was not the

case in the work of Shechtman, Blech, Gratias, and

Cahn! The five-fold symmetry persisted to the smallest

dimension that was examined, about 10 nm, and there

was no evidence of twinning.

Rather quickly, a number of models were developed

to explain the icosahedral symmetry of the diffraction

patterns. The leading contenders were a relatively disordered “icosahedral glass” phase and a highly ordered

tiling model.

The icosahedral glass model, initially proposed by

Shechtman and Blech [6] and developed by Stephens

and Goldman [7], is composed of many interconnected

aligned polyhedra of icosahedral symmetry. These

glasses possess long range orientational order, but no

long range translational symmetry. Although these

structures do not form a regular lattice, models indicate

Fig. 1. Stereographic projection of the symmetry elements of the

icosahedral group m35 ––.

300
that they are able to produce diffraction peaks as sharp

as those that were measured in the earliest icosahedral

phases. However, the glass models have too great a

degree of disorder to be consistent with the extremely

sharp diffraction spots of icosahedral phases such as

Al-Cu-Fe and Al-Cu-Ru phases that were observed

subsequently.

The tiling models are based on a concept devised by

Roger Penrose in 1974 for tiling the plane quasiperiodically using two tile shapes rather than a single unit cell

[8]. In 1981 Alan Mackay generalized the Penrose tiling

to three dimensions using two types of rhombohedra

[9]. In the following year, Mackay designated the twoand three-dimensional patterns as “quasi-lattices” and

speculated on possible structures where atoms sit on the

quasi-lattice points of the 2-D structure. He showed that

these structures give rise to optical diffraction patterns

with ten-fold symmetry! In 1984 Peter Kramer and

Reinhardt Neri of Tubingen [10] and Dov Levine and

Paul Steinhardt [11] of the University of Pennsylvania

independently developed a three-dimensional generalization of Penrose tilings by projecting a three dimensional cut through a higher-dimensional periodic lattice.

These three-dimensional tilings filled space using two

or more rhombohedra and the calculated diffraction

patterns were quite similar to the 3-fold and 5-fold

patterns published by Shechtman, et al. Other models

using the 6-D projection approach were developed and

shown to be capable of matching the diffraction patterns

quite well.

By rotating tiles or clusters of tiles in a Penrose

pattern, structures intermediate to the perfectly ordered

Penrose tiling models and the icosahedral glass models

can be obtained. This additional disorder generates a

strain which is consistent with the experimentally

observed systematic broadening of diffraction spots.

The disordered tiling model thus can account for the

varying degrees of strain observed for various alloy

systems. It has been suggested that the presence of

disorder even contributes to the stability of the structures through an increase in entropy.

The physical realization of quasicrystals and the intellectual understanding of their formation thus has been

achieved. At the foundation of this discovery is the work

of Shechtman, Blech, Gratias, and Cahn, which has

spawned an entirely new branch of materials science.

Already, papers numbering in the thousands have been

published on this subject in the disciplines of physics,

crystallography, and mathematics. It may be noted that

Shechtman and Cahn have continued to lead, stimulate,

and encourage much of this work.

Dan Shechtman is the Philip Tobias Professor of

Materials Science at the Israel Institute of Technology

(Technion, Haifa, Israel). His work on both the theoretical and experimental aspects of quasi-periodic structures has earned him numerous awards. He received

the Physics Award from the Friedenberg Fund for the

Advancement of Science and Education in 1986;

the International Award for New Materials from the

American Physical Society in 1987; the New England

Academic Award of the Technion for Academic

Excellence in 1988; the Rothchild Prize in Engineering

in 1990; and the Weizmann Prize in Science in 1993.

While quasicrystals remain a major focus of his work,

he is also pursuing research on chemical vapor

deposited (CVD) diamond wafers, metallic multilayers,

and rapidly solidified metallic alloys.

John Cahn has had a remarkably prolific career as

scientist and teacher. He has published approximately

250 papers and delivered approximately 400 invited

lectures to technical audiences worldwide. The excellence of his work has been recognized in more than

thirty national and international awards, including the

Fig. 2. John Werner Cahn, NIST Senior Fellow, received the 1998

National Medal of Science, conferred by the President of the United

States on the recommendation of the National Science Foundation.

301
Nation’s highest scientific award, the National Medal of

Science (1998). He was conferred with membership in

both the National Academy of Sciences (1973) and the

National Academy of Engineering (1998). He has

received gold medals from organizations as diverse as

the U.S. Department of Commerce, the Japan Institute

of Metals, and Acta Metallurgica. He has been accorded

the status of Fellow at NIST, the American Academy of

Arts and Sciences, the Japan Society for the Promotion

of Science, the American Institute of Metallurgical

Engineers, and the ASM International. He has been

honored no less than eleven times as a Distinguished

Lecturer and has received honorary doctorates from

Universit d’Evry (France, 1996) and Northwestern

University (1990), and an honorary professorship from

Jiao Tong University (Shanghai, China, 1980). His

awards for distinguished work include the Harvey Prize

(Israel Institute of Technology, 1995), the Rockwell

Medal (International Technology Institute, 1994), the

Hume-Rothery Award (AIME, 1993), the Michelson

and Morley Prize (Case Western University, 1991), the

Sauveur Award (ASM International, 1989), the Stratton

Award (NBS, 1986), the von Hippel Award, (Materials

Research Society, 1985), the Dickson Prize (CarnegieMellon University, 1981), and the S. B. Meyer Award

(American Ceramic Society, 1966). He is currently

Senior Fellow in the NIST Materials Science

and Engineering Laboratory where he is continuing

his pioneering work on the thermodynamics and

kinetics of phase transitions, diffusion, and interface

phenomena.

Prepared by Ronald Munro in consultation with Frank

Gayle and Carol Handwerker.

References

[1] D. Shechtman, I. Blech, D. Gratias, and J. W. Cahn, Metallic

Phase with Long-Range Orientational Order and No Translational Symmetry, Phys. Rev. Lett. 53, 1951-1953 (1984).

[2] P. P. Ewald (ed.), Fifty Years of X-Ray Diffraction, International

Union of Crystallography (1962).

[3] J. M. Bijvoet, W. G. Burgers, and G. Ha ̈gg (eds.), Early Papers

on Diffraction of X-rays by Crystals, International Union of

Crystallography (1969).

[4] F. W. Gayle, Introduction to: Metallic Phase with Long-Range

Orientational Order and No Translational Symmetry, in The

Selected Works of John W. Cahn, W. Craig Carter and William C.

Johnson (eds.), The Minerals, Metals & Materials Society,

Warrendale, Pennsylvania (1998).

[5] Mort La Brecque, Opening the Door to Forbidden Symmetries,

Mosaic (Washington, D.C.) 18 (4) 2-13+ (1987/8).

[6] D. Shechtman and I. A. Blech, The Microstructure of Rapidly

Solidified Al6Mn, Metall. Trans. A 16A, 1005-1012 (1985).

[7] Peter W. Stephens and Alan I. Goldman, Sharp Diffraction

Maxima from an Icosahedral Glass, Phys. Rev. Lett. 56, 1168-

1171 (1986).

[8] R. Penrose, The Role of Aesthetics in Pure and Applied Mathematical Research, Bull.-Inst. Math. Appl. 10, 266-271 (1974).

[9] Alan L. Mackay, De Nive Quinquangula: On the Pentagonal

Snowflake, Sov. Phys. Crystallogr. 26, 517-522 (1981).

[10] P. Kramer and R. Neri, On Periodic and Non-periodic Space

Fillings of m Obtained by Projection, Acta Crystallogr. A40,

580-587 (1984).

[11] Dov Levine and Paul Joseph Steinhardt, Quasicrystals—A New

Class of Ordered Structures, Phys. Rev. Lett. 53, 2477-2480

(1984).

302
Protein Crystallography by Joint X-Ray and

Neutron Diffraction

By 1984, the quest to understand the internal dynamics of protein molecules had created a pressing need for

well-refined, high resolution data on protein structures.

In a landmark contribution to the field of protein crystallography [1], Wlodawer, Walter, Huber, and Sjo ̈lin

undertook an innovative joint application of x-ray and

neutron diffraction methods to determine the structure

of a new crystal form of bovine pancreatic trypsin

inhibitor (BPTI). This work was the first to determine

the atomic positions in a protein of this size to within the

diameter of a hydrogen atom. By comparing structures

from two crystalline forms of BPTI, the paper offered

the first detailed analysis of how protein structure is

affected by molecular packing. In addition, the paper

provided the first detailed experimental picture, atomby-atom, of hydrogen-deuterium exchange in a folded

protein, revealing the existence of eleven “protected”

amine hydrogens which exchanged at anomalously slow

rates. This work also established that joint x-ray-neutron

refinement could produce structural detail consistent

with the then emerging technique of two-dimensional

NMR protein crystallography and provided the baseline

data for the further development of multi-dimensional

NMR.

X-ray and neutron beams falling on a crystal are

diffracted by its atomic constituents, and the periodic

structure of the crystal causes the diffracted rays to be

sharply defined. The directions and intensities of the

diffracted rays are sensitively determined by the threedimensional arrangement of the atoms and by specific

aspects of their interactions with the incident radiation.

Proteins do not occur as crystalline material in nature.

However, it is possible to grow their structures artificially into crystals, which then can be studied by

diffraction methods. BPTI previously had been prepared

in a crystalline form (form I) that was not suitable for

high resolution studies but, importantly, Walter and

Huber had just succeeded in synthesizing BPTI into a

new crystalline form (form II) that appeared to be more

promising [2] for structural studies.

Protein crystallography raises many challenges. It is

hard to make protein crystals of the size and quality

needed for diffraction studies. Even with good data, the

large number of atoms in proteins and their steric

complexity make it difficult to determine such structures accurately at resolutions near 0.1 nm (1 Å), the

diameter of a hydrogen atom. A major theoretical

constraint also intrudes. Diffraction patterns depend

only on pairwise relationships among atomic positions,

and these are not unique attributes of structures. Protein

crystallography does not yield a direct route from the

experimental data to the atomic structure. The determination of atomic positions requires analytical procedures in which putative structures are refined against the

data in stages of increasing detail, a computationally

intensive process in which chemical and biological

knowledge and intuition play significant parts.

Bovine pancreatic trypsin inhibitor is one of the most

thoroughly studied of all proteins, even though it is of

minor biological moment. BPTI was interesting at the

time of this work because it is a small protein (only 58

amino acids) with well-understood functionality. Its

three-dimensional structure had already been determined to 2.5 Å resolution using x-ray diffraction and

related techniques as early as 1970 by Robert Huber and

coworkers [3] in a crystal form that became known as

Fig. 1. Alexander Wlodawer, ca. 1999.

303
form I. Subsequent studies had increased the x-ray

resolution of the structure to 1.5 Å, and a large amount

of work on BPTI structure and dynamics using various

techniques had appeared in the 1970s and early 1980s.

In fact, BPTI was the first protein for which detailed

experimental information about the folding of the

polypeptide chain became available. The quality of

protein crystals was the major limitation to increasing

the resolution of diffraction studies. In the early 1980s

resolution was extended to an ångstrom or slightly less,

but in proteins smaller than BPTI.

The work described in the 1984 paper was started

when coauthor Lennart Sjo ̈lin, Wlodawer’s postdoctoral

worker at NBS (but then already on the faculty of the

Chalmers Polytechnic in Goteburg, Sweden), learned

that coauthors Robert Huber (who would win the 1988

Nobel Prize in Chemistry) and Jochen Walter at the

Max-Planck-Institute for Biochemistry in Martinsried,

Germany, had managed to grow a new crystal of BPTI,

which they called form II. In Alex Wlodawer’s words:

“Since that molecule was at that time the ‘hydrogen

atom’ of protein chemistry, and most physico-chemical

techniques being developed were initially tested with it,

we wanted very much to take neutron data on that

protein. The previously available crystals, however, were

tricky to grow and simply not good enough—they did

not grow very large and did not diffract very well. So the

new crystal form, growing easily, large, and with superb

diffraction, was of clear interest. Lennart got Huber

and me together on this project, and we were off and

running.” The authors also were alert to the scientific

implications of having a new crystal form of BPTI to

compare with the well-characterized form I, so that

changes in protein structure could be correlated with the

different molecular packings in the two forms.

However, Alex continues: “In the meantime, we found

out that Wayne Hendrickson, one of the most prominent

American crystallographers, also had these crystals, and

we were afraid that he would go after the neutron data

at Brookhaven.” Wlodawer and Hendrickson, together,

had already pioneered the simultaneous refinement of

x-ray and neutron data in 1982 [4], showing that it can

provide more information about protein structure than

either type of data alone. Hydrogen locations, in particular, can be determined more precisely with neutrons

since hydrogen is a strong neutron scatterer while being

nearly invisible to x rays. “So there was also an element

of competition as well,” Alex allows. Wlodawer and

Sjo ̈lin were in a good position to move quickly, since

they had already published several papers on the joint

refinement technique and were well armed with

methodology. Moreover, neutron beam time and excellent instrumentation were available to them at the NBS

Research Reactor, and Division 856 (the Reactor Radiation Division, now the NIST Center for Neutron

Research) possessed a Vax 11/780, one of the most

powerful minicomputers of the day, and an Evans &

Sutherland display system, the most powerful tool available for three-dimensional visualizations of molecular

structures.

Although Alex mentions the form II BPTI crystals as

“growing easily,” the 1984 paper describes an involved

preparation protocol, including a two-month period of

undisturbed growth from a seed crystal, followed by

another three months for heavy water exchange for the

neutron measurements. Heavy water greatly reduces

background neutron scattering from the protein crystal.

In addition, the exchange of deuterium atoms from

the heavy water for hydrogen atoms in the structure

provides additional information about the hydrogen

locations in the protein. Curiously, the paper informs us

that the heavy water used “was manufactured in 1983 by

the facility in Rjukan, Norway.” Alex explains: “The

heavy water that we used came from the famous facility

in Rjukan, Norway, and was produced in 1938. As many

know, the Allies took great pains to destroy the place

during WWII to prevent the Germans from having

access to heavy water. So, in the page proofs, I had the

bright idea that since half the authors were German, I

should just insert the Rjukan bit (otherwise having no

bearing on the contents of the paper). I did just that in

the Materials and Methods section (p. 303), and then

forgot about it. Last year, however, I told the story to

somebody who looked up the paper and told me that the

year of production of the sample was given as 1983,

killing the joke. Clearly, an eager editor caught my

‘obvious’ error in transposing the numbers (how could

anybody use a 1938 sample in 1984?) and ‘corrected’

me. So it goes.”

The paper did not have an immediate impact, but

after a year’s gestation its influence grew very rapidly.

Wlodawer attributes its long-range influence to several

factors. The work resulted in one of the best-refined

protein structures at that time, and so the paper has been

extensively quoted as a baseline for the quality of

protein structures. The work on hydrogen-deuterium

exchange was influential, since interest in the kinetics of

exchange persisted for some time. Also, its results bear

on many fields of current interest, including protein

folding and protein chemistry. Its achievement of a high

resolution protein structure, especially the accurate

hydrogen positions, was, and continues to be, influential

in the field of NMR, which is also sensitive to hydrogen

locations. Since BPTI had been chosen as a platform for

the development of two-dimensional NMR in the early

1980s, the appearance of this paper was very well timed

from a historical perspective. “I suspect the paper will

be cited for quite a few years longer,” Alex says.

304
The paper concludes with the words: “This paper is

dedicated to Professor Paulina Wlodawer on the occasion of her seventieth birthday.” Alex adds: “On a personal note, I am happy that this is the paper that

will have its lifetime extended by inclusion in the NIST

history. This was the only paper ever that I dedicated to

my mother, who is a biochemist and provided major

impetus for me becoming a scientist. Thus if one of my

papers should be remembered, I am glad that this is the

one.”

Alexander Wlodawer, a native of Poland, received his

Ph.D. from the University of California, Los Angeles, in

1974. Having completed his postdoctoral training at

Stanford University, he joined the National Bureau of

Standards in 1976, where he engaged in many studies of

protein crystallography until 1987, when he moved to

the ABL-Basic Research Program at the National

Cancer Institute-Frederick Cancer Research and

Development Center. From October 1998 to March

1999, he was on sabbatical as an elected Visiting Fellow

of Sidney Sussex College, University of Cambridge. In

1999 Wlodawer was appointed the Associate Director of

the Program in Structural Biology in the Division of

Basic Sciences of the National Cancer Institute, where

he is Chief of the Macromolecular Crystallography

Laboratory and of the Protein Structure Section. He is a

member of the American Crystallographic Association

and the Protein Society and has been an elected officer

in both organizations.

Robert Huber shared the 1988 Nobel Prize in

Chemistry with Johann Deisenhofer and Hartmut

Michel for “the determination of the three-dimensional

structure of a photosynthetic reaction centre.” He is

in the Department for Protein Crystallography at the

Max-Planck-Institut fu ̈r Biochemie, Martinsried,

Germany. Lennart Sjo ̈lin is an Associate Professor

in the Department of Inorganic Chemistry, Protein

Crystallography Group, at the Chalmers University of

Technology in Goteborg Sweden.

Prepared by Norman F. Berk.

Bibliography

[1] A. Wlodawer, J. Walter, R. Huber, and L. Sjo ̈lin, Structure of

Bovine Pancreatic Trypsin Inhibitor, Results of Joint Neutron and

X-ray Refinement of Crystal Form II, J. Mol. Biol. 180, 301-329

(1984).

[2] J. Walter and R. Huber, Pancreatic Trypsin Inhibitor—a New

Crystal Form and Its Analysis, J. Mol. Biol. 167, 911-917 (1983).

[3] R. Huber, D. Kukla, A. Ru ̈hlmann, O. Epp, and H. Formanek, The

Basic Trypsin Inhibitor of Bovine Pancreas. I. Structure Analysis

and Conformation of the Polypeptide Chain, Naturwissenschaften

57, 389-392 (1970).

[4] A. Wlodawer and W. A. Hendrickson, A Procedure for Joint

Refinement of Macromolecular Structures with X-ray and

Neutron Diffraction Data from Single Crystals, Acta Crystallogr.

A 38, 239-247 (1982).

305
Strain Effects in Superconducting Compounds

This paper [1] was presented by invitation at the 1983

International Cryogenic Materials Conference at a

crucial point in the scale-up of superconductor magnet

applications. It synthesizes a wide range of electromechanical strain data into what has become known as

the Strain Scaling Law, which has had a strong impact

on the design of large-scale, high-field superconductor

magnet coils since that time. The Strain Scaling Law

was the result of a unique high-field electromechanical

measurement capability, developed by Jack Ekin at

NBS, which led to the discovery and systematization of

the intrinsic strain effect in practical superconductors.

In the years leading up to this work, it was known that

superconductors have a “critical surface” that is a

function of temperature, current density, and applied

magnetic field. It had not been known that the

critical surface also depends on an additional fundamental parameter, mechanical strain. Fig. 1 shows the

scaling of the superconductor critical surface with this

variable.

This discovery was especially important to the development of large-scale superconductor applications

because early work had focused only on small coils of

superconducting wire in which the magnetic forces were

small. However, the need to handle large forces emerged

with the development of large-scale magnets for particle

accelerator machines, magnetic plasma confinement in

fusion energy, superconducting magnetic energy storage

(SMES), and medical magnetic resonance imaging

(MRI) systems.

Ekin had focused primarily on the electrical properties of metals and superconductors in his thesis work at

Cornell University and postdoctoral work at Rutgers

University before joining NBS in 1975. The focus of his

group at NBS was predominantly on mechanical properties, which led him to probe the unexplored niche

between the electrical and mechanical research worlds.

This coincidence of two fields of expertise ultimately

resulted in the discovery of the superconductor strain

effect and the Strain Scaling Law.

Fig. 1. J-B-critical surface for multifilamentary Nb3Sn superconductors.

306
Prior work in this unique electromechanical field was

scarce and had focused on small experimental samples

of new superconducting materials, including thin films

[2], monofilamentary wires [3], and single crystals [4].

However, the intrinsic non-hydrostatic strain effect was

not measured in practical filamentary NbTi conductors

until 1975, when the first measurements on the effect of

strain on critical current (Ic) were reported by Ekin,

Fickett, and Clark [5]. The interaction could not be

explained simply by superconductor filament breakage,

heating, or cross-sectional area reduction, but appeared

to be intrinsic to the superconducting material itself.

About a year later, a much larger effect of strain on

Ic was found in multifilamentary Nb3Sn conductors by

Ekin [6], Easton and Schwall [7], and McDougall [8].

This area of research then expanded when an accompanying strain effect was found for critical temperature Tc

[9,10], as well as the upper critical field (Bc2) [11,12].

Ekin’s systematic high-field measurements synthesized

these effects into a strain scaling law that was first

presented by him in a widely cited earlier paper in

1980 [13]. Then, in Strain Effects in Superconducting

Compounds, he demonstrated that the Strain Scaling

Law had wide applicability in virtually all practical

high-field superconductors at the time. Fig. 2 is the first

set of nearly universal curves showing the effect of

strain on the upper critical field Bc2 of the set of superconductors having the A-15 crystal structure. Each of

these curves corresponds to the thick-line curve shown

in the base plane of the critical surface in Fig. 1; they

are the prime determinant of the entire superconductor

critical surface.

The paper also presented the first strain-effect data on

a relatively new superconductor, Nb3Al. As seen in

Fig. 2, Nb3Al has a remarkably small strain effect in

comparison with Nb3Sn, the most widely studied superconductor of the day. This discovery of the relative strain

insensitivity of Nb3Al resulted in an international effort

to produce this superconductor material commercially

in practical lengths. That goal has been realized, and

Nb3Al is currently being explored for use in a new class

of high-field magnets made using a much more efficient

“react-and-wind” technique. These magnets are being

developed for use in energy storage, high energy physics

accelerators, and medical imaging systems.

Today, NIST continues to be the world leader in

electromechanical measurement techniques, particularly since the advent of high-temperature superconductors, as well as the mechanical challenges inherent to

these brittle ceramic oxide materials. Most superconductor applications are also being scaled up in size with

an attendant increase in magnet stress, underscoring the

Fig. 2. Effect of uniaxial strain on the upper critical field of practical A-15 superconductors.

307
need for precise measurements of electromechanical

performance. NIST measurement expertise is also

sought for its third party independence in evaluating

superconductor performance, particularly with the

expansion of superconductor applications in the

electric power industry, which is currently undergoing

deregulation.

Jack Ekin was born in Pittsburgh, Pennsylvania, on

August 31, 1944. He received a B.S. degree in physics

from the University of Michigan, Ann Arbor, in 1966;

a Fulbright Scholarship for beginning graduate study in

physics at the University of Heidelberg; and a Ph.D. in

solid state physics from Cornell University in 1971.

From 1971 to 1973 he was a Postdoctoral Research

Associate at Rutgers University. In 1973, he joined

NBS through a National Research Council Research

Associateship. He joined the permanent staff at NBS

as a research physicist in 1975, where his work has

specialized in the study of electromechanical properties

of superconductors, transport properties and critical

current measurements, thin film interfaces in high

temperature superconductors, and development of low

resistivity contacts to high temperature superconductors. He has published over 150 articles and several

book chapters on low-temperature transport properties

of superconductors and normal metals, and received six

patents for superconductor fabrication methods and

devices. Currently, his research at NIST is focused on

electromechanical measurements for the development

of the “second generation” high temperature superconductors, the extension of the Strain Scaling Law

from one to three dimensions, and the writing a textbook

on cryogenic measurement techniques.

Prepared by J. W. Ekin.

Bibliography

[1] J. W. Ekin, Strain Effects in Superconducting Compounds,

Adv. Cryo. Eng. 30, 823-836 (1984).

[2] W. A. Pupp, W. W. Sattler, and E. J. Saur, Superconductivity of

Thin Nb3Sn Films Under Tensile Stress, J. Low Temp. Phys. 14,

1-13 (1974).

[3] J. P. McEvoy, Effect of uniaxial stress on the superconducting

transition temperature of monocrystalline Nb3Sn, Physica 55,

540-544 (1971).

[4] M. Pulver, Kritisches Verhalten von V3Si und Nb3Sn unter uniaxialem Zug im transversalen Magnetfeld, Z. Phy. 257, 261-271

(1972).

[5] J. W. Ekin, F. R. Fickett, and A. F. Clark, Effect of stress on the

critical current of niobium-titanium (NbTi)

multifilamentary composite wire, Adv. Cryo. Eng. 22, 449-452

(1977)

[6] J. W. Ekin, Effect of stress on the critical current of Nb3Sn

multifilamentary composite wire, Appl. Phys. Lett. 29, 216-219

(1976).

[7] D. S. Easton and R. E. Schwall, Performance of multifilamentary Nb3Sn under mechanical load, Appl. Phys. Lett. 29, 319-321

(1976).

[8] I. L. McDougall, Stress induced degradation of critical currents

in filamentary Nb3Sn, in Proceedings of the Sixth International

Cryogenic Engineering Conference, Grenoble, 11-14 May 1976,

K. Mendelssohn (ed.), IPC Science and Technology Press,

Guildford, England (1976) pp. 396-399.

[9] Thomas Luhman and M. Suenaga, The influence of thermally

induced matrix stresses on the superconducting properties of

Nb3Sn wire conductors, IEEE Trans. Magn. MAG-13, 800-802

(1977).

[10] H. Hillmann, H. Kuckuck, H. Pfister, G. Rupp, E. Springer,

M. Wilhelm, K. Wohlleben, and G. Ziegler, Properties of multifilamentary Nb3Sn conductors, IEEE Trans. Magn. MAG-13,

792-795 (1977); G. Rupp, Improvement of the critical current of

multifilamentary Nb3Sn conductors under tensile stress, IEEE

Trans. Magn. MAG-13, 1565-1567 (1977).

[11] G. Rupp, Stress induced normal-superconducting transition in

multifilamentary Nb3Sn conductors, IEEE Trans. Magn.

MAG-15, 189-192 (1979).

[12] J. W. Ekin, Strain dependence of the critical current and critical

field in multifilamentary Nb3Sn composites, IEEE Trans. Magn.

MAG-15, 197-200 (1979).

[13] J. W. Ekin, Strain scaling law for flux pinning in practical superconductors. Part 1: Basic relationship and application to Nb3Sn

conductors, Cryogenics 20, 611-624 (1980).

308
Dental Research at the National

Bureau of Standards

George Colby Paffenbarger was a man of considerable insight. Nearing the end of his life as a result of

prostate cancer, he perceived a need to educate the

dental profession and the public about the enormous

benefits to dentistry and public health that were

being wrought through the cooperative research of the

American Dental Association (ADA) and the National

Bureau of Standards. Tax dollars, allocations from ADA

dues, and funding from the National Institute of Dental

Research were being used to support this work, and it

was important for everyone to know that this investment

was yielding benefits which far exceeded costs. Elsewhere, an oversupply of graduating practitioners and

a reduced demand for dental care was leading to the

closing of some dental schools and an attendant pressure

to reduce all sources of funding for dental research.

What George Paffenbarger saw, and others did not,

was the continued evolution of (then unappreciated)

dramatic benefits from dental research, even as the

primary emphasis for research began to shift away from

treatments for caries (the incidence of which had

already declined) to treatments for other oral diseases

and conditions. Paffenbarger’s solution to this problem

was to publish a paper [1] that would place the ADA/

NBS dental research program into a clear and succinct

context.

Paffenbarger undertook this project in collaboration

with John A. Tesk and W. E. Brown at NBS. Together,

they documented the development of modern dental

materials research, beginning with the inception of a

dental research program at NBS in 1919.

The beginning can be traced to a request by the U.S.

Army to develop a bid specification for the purchase

of dental amalgam. That effort, headed and championed

by Dr. Wilmer Souder, focused on the properties of

amalgams, including their compositions, dimensional

changes on setting, compressive strengths, and flow

characteristics [2]. That work led to the collaboration

between NBS and the Weinstein Research Laboratory to

measure the physical properties of the whole range of

materials being used by dentists, for which the literature

of the day was rather scant and often controversial [3].

The impact of that eight-year study is credited with the

development of the cooperative program of the ADA and

NBS, which continues to this day.

The review by Paffenbarger, Tesk, and Brown paints

a picture of a remarkable and far-reaching program that

touches on every aspect of dentistry and, hence, public

health. The thrust of the program was not simply the

measurement of properties or even the development of

standards and certification programs. Dental professionals and the public needed to be informed about the

significance of the results, particularly with respect to

self-serving promotions of products that had been

propagated unchecked early in the century. “Aside from

probable deceptive claims (for the exploitation of dental

materials) exposed in the individual surveys, reports

were published by the Association at NBS showing the

fraudulent nature of some of the deceptions.” [1]

Dental practices were also an important part of the

program. As the ADA/NBS program began to understand more about the physical and chemical properties

of amalgams, the influence of impurities and contaminants on the degradation of restorations also began to be

understood. In one case, the practice of dentists mulling

the amalgam mix in the palms of their hands was found

to add moisture and sodium chloride to the mix, which

subsequently led to severe corroding of zinc-bearing

amalgams [4].

Fig. 1. George C. Paffenbarger.

309
The growth of the ADA/NBS program was breathtaking in itself. Since the 1950s, the program has

included research on crystal structures, crystal chemistry of minerals, solubility studies, calcium phosphate

cements, topical fluoridation procedures, enamel

etching, the formation mechanisms of caries, the in situ

microanalysis of carious and sound enamel, the characterization of cardiovascular calcifications, and the

development of new materials and instruments. Among

the most noteworthy developments that sprang from this

program are the modern high-speed-turbine, contraangle handpiece; the panoramic x-ray unit; modern

dental composite restoratives and sealants; and the

national and international standards programs for

dentistry.

With respect to the waning support for dental

research in the mid-1980s, this accounting by

Paffenbarger et al. was successful in helping to sway the

members of the ADA to preserve its support of dental

research and to seek alternative methods to help curtail

the rise in ADA dues. It was clear that the ADA/NBS

program had saved the public and the dental profession

billions of dollars over the years, at a cost that seemed

insignificant in comparison to the benefit.

George Paffenbarger received the degree of DDS

from Ohio State University in 1924 and after a brief time

in private practice and teaching, joined the research

staff of the ADA at NBS in 1929. During part of his

tenure, Paffenbarger served as Director of the ADA

research unit at NBS. Among his most recognized

research contributions were his investigations into the

stability of both dental impression materials and

polymer based denture materials, and studies of the

retentive mechanisms of dental cements. He also

became a staunch champion of the modern tooth-colored composite restoratives that emanated from the

research of R. Bowen (another accomplished ADA

researcher at NBS). He was also instrumental in the

development of dental standards activities throughout

the world. Paffenbarger was recognized by numerous

academic institutions, including Ohio State (his alma

mater), Fairleigh Dickenson, Georgetown, and Nihon

(Japan) Universities, through the receipt of honorary

degrees. St. Andrews University, Scotland, invited him

to be Praelector In Dentistry for the Faculty of

Medicine. He was an honorary member of numerous

national and international dental societies and organizations, including the ADA, the Japanese Dental Association, the Federation Dentaire Internationale, and French,

German, British, Argentine societies. He was also a

Fellow of the Washington Academy of Science. He was

the recipient of an almost countless number of awards,

including the Wilmer Souder award, the highest award

for dental materials research bestowed by the International Association for Dental Research (IADR, a

society that he also helped to found). During World War

II, Paffenbarger served in the United States Navy, with

responsibility for procurement and testing of dental

supplies. By 1959, when he retired from the United

States Naval Reserve, he had risen to the rank of

Rear Admiral . When he lectured before domestic dental

societies he was known to emphasize the importance of

dental research by saying “now this is something that

you paid for, but look at what you’ve gotten in return.”

He was an unyielding opponent of the drawing of

conclusions from poor research and unsubstantiated

results, but he was a warm, friendly mentor for those

who recognized the need for improvements in their work

and who sought his counsel to strive toward the ideals of

excellence that embodied his life.

Fig. 2. The contra-angle handpiece, developed in the ADA/NBS program, is used in virtually every modern dental office in the world.

Fig. 3. Walter E. Brown.

310
Walter Brown received his Ph.D. degree from

Harvard University in 1949. From 1948 to 1962 he

conducted research on the crystallography and

chemistry of calcium phosphates for the Tennessee

Valley Authority. In 1962 he joined the ADA research

unit at NBS, where he directed research on the solubility and crystal chemistry of mineralized tissues, including tooth calculus. He became director of the ADA unit

in 1967 and served in that capacity until his retirement

in 1983, after which he continued as a research associate until his death, from Parkinson’s disease, in 1993.

Brown, like Paffenbarger, received numerous honors

and awards. He was recognized universally for his

contributions to the crystallography, chemistry, and

biochemistry of calcium phosphate compounds. His

theories are among the main underpinnings of modern

calcium phosphate chemistry. His pioneering studies of

the physicochemical properties of mineralized tissues,

such as teeth and bone, provided the foundation for

much of the modern research on diseases such as dental

caries, osteoporosis and arteriosclerosis, and in the

development of topical fluoride treatments for teeth.

His work also lay at the heart of modern calcium biomaterials. During his life it was said that he was known

“from biomineralization to fertilizer” and he delighted

in both the truth and the humor of that statement.

Among his awards were the Mineralized Tissue

Research award of the IADR, the highest award of its

kind; an NBS citation for “Outstanding Leadership of

the ADA Research Group at NIST,” and the Rudjer

Institute (Zagreb, Yugoslavia) Founder’s Plaque for

“contributions to scientific exchange”; he was also

an honorary member of the ADA. He followed

Paffenbarger as Director of the ADA research unit at

NIST.

John Tesk received his Ph.D. degree from Northwestern University in 1963. Prior to his NBS experience, which began in 1978, his career encompassed

employment as: Engineer-in-Training with a company

in the natural gas industry; Assistant Professor of Materials Engineering at the University of Illinois, Chicago;

consultant to Argonne National Laboratory on low

temperature neutron damage in metals and, later,

Assistant Metallurgist with Argonne on the development

of the breeder reactor; Director of Research with a

dental company; and Director of Education Services,

with the Institute of Gas Technology, for training of

engineers and technicians in Algeria. As an employee of

NBS, he served as Leader of the Dental and Medical

Materials Research group, which included the ADA

researchers, from 1983 to 1994. In 1994 he was given

the assignment of searching for other health-related

needs toward which NIST expertise might be applied. In

1995, along with Stephen Hsu (a renowned tribologist in

the Ceramics Division) and six of the world’s largest

orthopedic companies, he formed the first orthopedic

Cooperative Research and Development consortium in

the Materials Science and Engineering Laboratory. The

consortium’s goal was to develop a reliable, accelerated

screening test for orthopedic implant joint bearing

materials (wear being a primary cause necessitating the

removal of these joint implants). Because of the variety

of both his experiences and the topics of his publications, John often joked that he was “known well for not

being well known.” His honors include the Bronze

Medal from NBS and awards from the ADA and the

American Society for Testing and Materials for work

in national and international standards. In 1998, for

contributions made in collaboration with many Japanese

dental researchers (including a best paper award, coauthor, Professor Kenzo Asaoka) he became the third

foreigner elected to honorary membership in the

Japanese Society for Dental Materials.

Prepared by John Tesk and Ronald Munro.

Fig. 4. John A. Tesk.

311
Bibliography

[1] G. C. Paffenbarger, J. A. Tesk, and W. E. Brown, Dental Research

at the National Bureau of Standards: How It Changed the

Practice of Dental Health Service, J. Am. Dent. Assoc. 111, 83-89

(1985).

[2] W. Souder and C. G. Peters, Investigation of Physical Properties of

Dental Materials, Dent. Cosmos 62, 305-335 (1920).

[3] R. L. Coleman, Physical Properties of Dental Materials (Gold

Alloys and Accessory Materials), Bur. Stand. J. Res. 1, 867-938

(1928).

[4] I. C. Schoonover, W. Souder, and J. R. Beall, Excessive Expansion

of Dental Amalgam, J. Am. Dent. Assoc. 29, 1825-1932 (1942).

312
Handbook for Standard Reference

Materials Users

Standard Reference Materials (SRMs) are wellcharacterized materials produced in quantity and

certified for one or more physical or chemical properties. They are issued under the NIST trademark and are

characterized using state-of-the-art measurement

methods. SRMs are designed to ensure the accuracy,

traceability, and compatibility of measurement results

in many diverse fields of science, industry, and technology both in the United States and throughout the world.

SRM users recognize that reliable measurements

can help avoid costly manufacturing mistakes and

unnecessary over-design of products and systems. Good

measurements can provide the basis for sound and

economical environmental and safety regulations and

can improve health care by enhancing the validity of

clinical tests and procedures. Thus the use of SRMs for

measurement reliability contributes to the strength of

this nation’s economy and the well being of its citizens.

Many users of SRMs are interested in the details of

the procedures used at NIST to certify the SRMs. In

1985, the late John Keenan Taylor prepared SP 260-100,

Handbook for SRM Users [1] to provide guidance for

the use of SRMs and to explain the philosophy behind

the SRM Program. The book is dedicated to the dissemination of information on the phases of preparation,

measurement, certification, and use of SRMs. While

written from the viewpoint of a chemist, the basic

concepts described are applicable to most areas of

metrology. Taylor arranged the Handbook by sections in

a logical progression, starting with the concepts of

precision and accuracy, followed by discussions of

calibration procedures and quality assurance of the

measurement process, the use of SRMs to evaluate

various kinds of measurements, and the reporting of

data with evaluated limits of uncertainty. The statistical

considerations most frequently applicable for the evaluation and interpretation of measurement data are

reviewed in the Appendices. Each section is written with

some degree of independence so that it can be comprehended without frequent reference to the content of

others.

The original Handbook was published in 1985 and

required a second printing in 1987. In 1992, work was

begun on a revision of Special Publication 260-100 [2]

to upgrade dated information and to reflect significant

changes that had occurred within NIST and the Standard

Reference Materials Program since the document was

first issued in 1985. N. M. Trahey of the Standard

Reference Materials Program performed an extensive

editorial and technical review of the Handbook and its

appendices. The text was determined to be consistent

with current NIST guidance on measurements, but

various sections and appendices (including Sections 8

and 9, Appendices A, B, and C, and the Guide for

Requesting Development of Standard Reference

Materials) required revision. There were extensive

revisions in Appendix C. Statistical Tools, rewritten in

accordance with current NIST policy by S. B. Schiller of

the NIST Statistical Engineering Division. Two other

sections and the remaining appendices were rewritten

by N. M. Trahey, who also prepared new introductory

material. The editing process had not yet begun when

John Taylor passed away, and every effort was made to

preserve those parts of the text that Taylor had prepared,

essentially as he wrote them. Fifteen years after the

original Handbook for SRM Users was published, the

Standard Reference Materials Program continues to get

approximately 800 requests for copies per year.

The National Bureau of Standards began to provide

reference materials, originally known as standard

samples, in 1906 in response to the needs of the metals

industry. The SRM inventory has since become far more

diverse and now contains over 1300 different SRMs and

related samples. A large number of materials useful in

physical metrology and engineering are included. Some

technical areas are covered more completely than others

for historical reasons, priorities for national issues, and

to some extent the degree of industrial awareness of the

quality assurance concept. Modern SRMs take into

consideration the fact that a given substance for which

an analysis is carried out may occur in different matrix

environments. Thus the users must be made aware of the

need to take the specific environment into account.

The Handbook is still making an impact on SRM

users. It contains some of the course material used

by John Taylor to teach classes at NBS/NIST and at

national and international meetings of the American

Chemical Society and the Pittsburgh Conference on

Analytical Chemistry and Applied Spectroscopy. At

those meetings Taylor spent many hours in dialogues

with reference materials users, analysts, and accreditors

regarding reference materials and their importance in

the metrology of chemical and physical measurements.

Eight years after his death, the Handbook continues to

313
spark conversations with those who knew him and used

his book. Former students are eager to tell how his

teachings influenced their careers, and they cite the

Handbook as one book they consider a collector’s item

that they will always keep in their library.

For 3 years at the Pittsburgh Conference, the Standard Reference Materials Program honored the

author by sponsoring the J. K. Taylor Symposium on the

Development and Use of Reference Materials. Taylor

himself conceived the workshop, based on his feeling

that U.S. industry needed to be both educated and

informed of NIST’s Standard Reference Materials role

regarding measurement quality and data comparability.

John Keenan Taylor joined the National Bureau of

Standards in 1929 at the age of 16; while working at the

Bureau, he received his B.S. in Chemistry from George

Washington University and later his PhD in Physical

Chemistry from the University of Maryland. Over the

course of a professional career spanning 57 years, Taylor

performed research and directed activities in the

Microanalysis, Gas and Particulate Science, and

Standard Samples (a forerunner of the Standard

Reference Materials Program) Sections of the NBS

Analytical Chemistry Division. Even after his retirement

from NBS in 1986, he devoted much of his time and

attention to measurement quality control and assurance

in the field of analytical chemistry. Taylor served as

coordinator for Quality Assurance of the NIST

Chemical Science and Technology Laboratory and

continued to write articles, design seminars, and teach

classes on the subject of quality assurance as applied to

chemical measurements until shortly before his death on

March 26, 1992.

Taylor was honored by the Department of Commerce

with its Silver and Gold Medals. He was a member of

the American Chemical Society, the Alpha Chi Sigma

Chemical Fraternity, the American Institute of

Chemists (AIC), and several ASTM technical committees, including Committee D22 on Sampling and

Analysis of Atmospheres which he chaired from 1984 to

1990. He received an Award of Merit from ASTM,

the Fitch Memorial Chemistry Award from George

Washington University, the DC Educational Society

Award, the AIC Honor Award, and the Chemical

Society of Washington Achievement Award. He

authored three books and some 200 scientific journal

publications, served as editor of four books, and held

two patents.

Prepared by Thomas E. Gills.

Bibliography

[1] John K. Taylor, Handbook for SRM Users, NBS Special Publication 260-100, National Bureau of Standards, Gaithersburg, MD

(1985).

[2] John K. Taylor (edited by Nancy M. Trahey), Handbook for SRM

Users, 1993 Edition, NIST Special Publication 260-100, National

Institute of Standards and Technology, Gaithersburg, MD (1993).

314
A Practical Josephson Voltage Standard at

One Volt

This paper [1] is considered the seminal, definitive

paper describing the revolutionary one-volt Josephsonjunction array standard. NIST changed forever highaccuracy voltage measurements with this development,

which built on earlier work at NIST and a microwave

feed design from the then West German standards

laboratory, Physikalisch-Technische Bundesanstalt

(PTB). The basic element of the array is the Josephson

junction, in the form of a superconductor-insulatorsuperconductor sandwich. When irradiated with microwave energy, such a junction exhibits a dc potential

uniquely determined by the frequency of the radiation,

the electronic charge, and Planck’s constant, with a

single junction providing a few millivolts. In other

words, a Josephson junction can act as a superb

frequency-to-dc voltage converter. A properly designed

and fabricated array of junctions can be excited to

produce a series of very accurate quantized voltages, or

steps.

As developed and demonstrated by the NIST team

[1-8], a Josephson-junction-based voltage standard

system consists of microwave source and feed, cryostat,

probe, chip, and readout and control system. Microwave

energy is fed into the chip mounted in the probe’s chip

carrier and cooled by liquid helium. The array standard

microchip is fabricated by techniques analogous to

those used to fabricate silicon integrated circuits,

although with very different material systems.

For almost 80 years, starting in 1901, the U.S. Legal

Volt was maintained by several groups of standard cells.

There was a large effort in the late nineteenth century

and the early twentieth century to establish a standard for

electromotive force (emf) based on electrochemical reactions within chemical cells. The first legal unit of

voltage for the United States was based on the Clark

cell, developed by Latimer Clark in 1872, with its output

assigned a value of 1.434 international volts by the 1893

International Electric Congress. Public Law 105, passed

by the U.S. Congress in 1894, made this the legal

standard of voltage in the U.S. During the years between

1893 and 1905, the standard cell devised by Edward

Weston was found to have many advantages over the

Clark cell [9]. The Weston cell consists of a cadmium

amalgam anode and a mercury-mercurous sulfate

cathode with a saturated cadmium sulfate solution as the

electrolyte. In 1908, at the London International

Conference on Electrical Units and Standards, the

Weston cell was officially adopted for maintaining

the volt. After 1908, only Weston cells were used

for maintaining the national standard in the United

States.

The Weston standard cell can be disturbed by transport or if it is subjected to a change in temperature or a

small electrical current. When at times it was necessary

to eliminate cells—due to changes in emf of a cell

relative to the mean of the group—new cells could

be added. In 1965 the National Reference Group of

standard cells [10] included 11 cells made in 1906,

seven cells made in 1932, and 26 cells made in 1948.

Long-term stability of the volt reference was also

maintained by comparisons of neutral and acid cells,

preparing and characterizing new cells, and through

international comparisons and absolute ampere and ohm

experiments. According to Driscoll and Olsen [11], the

results of the absolute current-balance measurements

could be regarded “as assigning a value to the emf of the

standard cell used to control the strength of the current”

and as a check on the emf of the NIST standard cell

bank. The use of the Weston cell as the national standard

of voltage was supported by a considerable amount of

research in electrochemistry and related fields at NBS.

Before the Josephson effect was discovered, it was

difficult to provide incontrovertible evidence regarding

the long-term stability of the U.S. Legal Volt. However,

considerable evidence indicated that the unit of emf

preserved with standard cells was unlikely to have

changed by any significant amount, relative to the best

measurements of the time, from the early 1900s to the

1960s.

In the late 1950s, research in solid-state physics

stimulated the growth of the semiconductor industry. A

new type of voltage standard based on a solid-state

device, the Zener diode, appeared in the early 1960s.

W. G. Eicke at NBS first reported the possibility of

using Zener diodes as transport standards [12]. In the

following years, after several manufacturers started

making commercial Zener voltage standards, these

references began to replace standard cells in commercial use. Although Zener voltage standards exhibit

higher noise characteristics than standard cells and are

affected by environmental conditions of temperature,

atmospheric pressure, and relative humidity, they are

now widely used in many metrology laboratories

because of their robust transportability.

315
In 1962, Brian Josephson, a graduate student at

Trinity College, Cambridge, England, predicted that

electrons can tunnel in pairs (Cooper pairs) between two

superconductors separated by a thin insulating barrier

(a weak link or Josephson junction). An applied dc

voltage V across the barrier would generate an ac current

at the frequency f = 2eV/h, where e is the elementary

charge and h is Planck’s constant. Conversely, an applied

ac current of frequency f would generate a dc voltage Vn

at the quantized values

Vn = nhf /2e ,

where n is an integer and the value of 2e/h is approximately 483.6 MHz/V.

One of the issues was whether this relationship was

materials independent. In 1968 Parker, Langenberg,

Denenstein, and Taylor [13] compared, via a potentiometer, the Josephson voltages of junctions consisting

of five different superconducting materials and various

combinations of thin-film tunnel junctions or point

contacts with 1.018 V Weston saturated standard cells

[10] calibrated by NBS. They obtained a value of 2e/h

with a one-standard-deviation fractional uncertainty of

3.610–6

.

It was argued on fundamental grounds that the above

must be exact. The use of superconducting-quantuminterference device (SQUID) null detectors in the early

1970s allowed this to be tested to a few parts in 109

,

and thus the Josephson effect had obvious potential for

use as a voltage standard [14]. By the early 1970s,

NIST staff had set up a potentiometric measurement

system in Gaithersburg that compared 2 mV to 10 mV

dc Josephson junction voltages with 1.018 V standard

cells to a few parts in 108 [15,16]. International

comparisons in 1971-72 among national metrology

institutes (NMIs), including NBS, the National Physical

Laboratory (NPL) in the U.K., the National Research

Council (NRC) in Canada, the National Standards

Laboratory (NSL) in Australia, and the PhysikalischTechnische Bundesanstalt (PTB) in Germany, as well as

the International Bureau of Weights and Measures

(BIPM), found that the measured values of 2e/h agreed

with each other to within 210–7 [17].

These results from the NMIs suggested the course of

adopting a value of 2e/h for use in maintaining units of

voltage. The United States was the first nation to do this,

and the value of 2e/h to be used at NBS was chosen to

prevent a discontinuity when NIST converted from

standard cells to the Josephson effect [18]. NBS

began maintaining and disseminating the U.S. volt

based on the Josephson effect in July 1972, using a

10 mV measurement system with relative uncertainty of

210–8

. Soon after, the Consultative Committee on

Electricity (CCE) of the CIPM recommended the value

KJ–72 = 483 594 GHz/V, which was adopted by all

countries except the United States, France, and the

Soviet Union.

In many applications, Josephson junctions were

undoubtedly better references than standard cells, which

are sensitive to environmental conditions, can shift

values on transport, and can drift by a few parts in 108

per year. The typical 5 mV to 10 mV reference output

from early Josephson devices made from a few junctions required both very low-level voltage balances and

scaling by a factor of 100, both of which seriously

limited the accuracy of measuring 1.018 V standard

cells.

Then in 1977, M.T. Levinson and colleagues showed

that unbiased Josephson junctions would spontaneously

develop quantized dc voltages when irradiated with

microwaves, opening the path to successful Josephson

junction arrays. C. A. Hamilton, R. L. Kautz, F. L.

Lloyd, and others of the NBS Electromagnetic

Technology Division at Boulder began developing and

improving Josephson standards based on series arrays

of junctions operated near zero dc voltage bias [3,19].

Stable 1 V zero-crossing arrays were operating at

NBS [1] and PTB [20] by 1985, using about 1500 junctions and rf fields of 70 GHz to 90 GHz. Arrays with

output voltages at the level of 1 V soon were used in

NMIs throughout the world [21]. By 1989, NIST had

made a 19 000 junction, 12 V array [2]. The widespread

use of Josephson junction arrays in national standards

laboratories, and better SI determinations of 2e/h, led

the CCE to recommend a new exact conventional value

for the Josephson constant:

KJ–90 = 483 597.9 GHz/V ,

which is fractionally larger by 810–6 than the 1972

conventional value. The new value was adopted worldwide on January 1, 1990, and thereby became the new

basis for the U.S. Legal Volt. This definition of KJ–90 is

the present volt representation, based on an ideal

Josephson voltage standard. The conventional value

was assumed by the CCE to have a relative standard

uncertainty of 0.4 V/V. By convention, this uncertainty is not included in the uncertainties of the representation of the volt, since any offset from the SI volt

will be consistent among different laboratories using the

Josephson effect standard.

The term “intrinsic standard” is sometimes used to

describe a type of standard, such as a Josephson Voltage

Standard (JVS), quantum Hall resistance standard, triple

point cell, deadweight pressure gauge, etc., based on

physical laws rather than on the stability of physical

316
artifacts that depend on bulk materials properties. There

are approximately twenty industrial and military calibration laboratories throughout the United States that

operate a JVS as a basis for traceable calibration measurements. The JVS consists of many cryogenic and

microwave components, and each of these, as well as the

environment and the user technique, can contribute

uncertainty to the voltage measurement. Accordingly, it

is necessary to make intercomparisons among independent JVS laboratories, to ensure the correctness of

the measurements in these laboratories, just as it is at the

international level. In 1991 NIST conducted the first

JVS laboratory comparison experiment using transportable 10 V Zener standards, in which five other U.S.

industrial and military laboratories participated [22].

Such comparisons are now carried out regularly under

the auspices of the National Conference of Standards

Laboratories, an industry trade association, with

support from NIST as necessary.

Prepared by Y. Tang, N. B. Belecki, and J. F. Mayo-Wells

based on excerpts from the paper The Ampere and

Electrical Units [23], authored by members of the

Electricity Division.

Bibliography

[1] C. A. Hamilton, R. L. Kautz, R. L. Steiner, and Frances L. Lloyd,

A Practical Josephson Voltage Standard at 1 V, IEEE Electron

Device Lett. EDL-6, 623-625 (1985).

[2] Clark A. Hamilton, Frances L. Lloyd, Kao Chieh, and Wayne C.

Goeke, A 10-V Josephson Voltage Standard, IEEE Trans.

Instrum. Meas. 38, 314-316 (1989).

[3] R. L. Kautz and Frances L. Lloyd, Precision of Series-Array

Josephson Voltage Standards, Appl. Phys. Lett. 51, 2043-2045

(1987).

[4] Frances L. Lloyd, Clark A. Hamilton, J. A. Beall, Diane Go,

R. H. Ono, and Richard E. Harris, A Josephson Array Voltage

Standard at 10 V, IEEE Electron Device Lett. EDL-8, 449-450

(1987).

[5] Clark A. Hamilton, Richard L. Kautz, Frances L. Lloyd, Richard

L. Steiner, and Bruce F. Field, The NBS Josephson Array

Voltage Standard, IEEE Trans. Instrum. Meas. IM-36, 258-261

(1987).

[6] R. L. Kautz, C. A. Hamilton, and Frances L. Lloyd, Series-Array

Josephson Voltage Standards, IEEE Trans. Magn. MAG-23, 883-

890 (1987).

[7] C. A. Hamilton, R. L. Kautz, and Frances L. Lloyd, The NBS

Josephson Array Voltage Standard, in CPEM 86 Digest: 1986

Conference on Precision Electromagnetic Measurements, June

23-27, 1986, National Bureau of Standards, Gaithersburg, MD,

Ronald F. Dziuba, (ed.), Institute of Electrical and Electronics

Engineers, New York (1986) pp. 108-109.

Fig. 1. One-volt NIST Josephson Junction array standard having 3020 junctions. The chip was designed and built by staff of the Electromagnetic

Technology Division in Boulder in the cryoelectronic fabrication laboratory. It operates at liquid-helium temperatures; microwave energy is fed

to four chains of junctions through the finguide structure at the left. The thin tapered structures at the end of each chain are terminations to prevent

reflection of energy back up the chain.

317
[8] C. A. Hamilton, F. L. Lloyd, and R. L. Kautz, A Josephson

Series Array Voltage Standard at One Volt, in Proceedings of the

NCSL Workshop and Symposium, July 15-18, Boulder, CO,

(1985) pp. 71-77.

[9] F. B. Silsbee, Establishment and Maintenance of the Electrical Units, NBS Circular 475, National Bureau of Standards,

Washington, DC (1949).

[10] Walter J. Hamer, Standard Cells—Their Construction, Maintenance, and Characteristics, NBS Monograph 84, National

Bureau of Standards, Washington, DC (1965).

[11] R. L. Driscoll and P. T. Olsen, Application of nuclear resonance

to the monitoring of electrical standards, in Precision Measurement and Fundamental Constants, D. N. Langenberg and B. N.

Taylor (eds.), NBS Special Publication 343, National Bureau of

Standards, Washington, DC (1971) pp. 117-121.

[12] W. G. Eicke, Commentaires sur l’utilisation des diodes de zener

comme etalons de tension, Comite ́ Consultatif d’E ́lectricite ́, 11e

Session, BIPM, Paris, France (1963) pp. 1874-1877.

[13] W. H. Parker, D. N. Langenberg, A. Denenstein, and B. N.

Taylor, Determination of e/h, using macroscopic quantum phase

coherence in superconductors: I. Experiment, Phys. Rev. 177,

639-664 (1969).

[14] B. N. Taylor, W. H. Parker, D. N. Langenberg, and A.

Denenstein, On the use of the ac Josephson effect to maintain

standards of electromotive force, Metrologia 3, 89-98 (1967).

[15] F. K. Harris, H. A. Fowler, and P. T. Olsen, Accurate

Hamon-pair potentiometer for Josephson frequency-to-voltage

measurements, Metrologia 6, 134-142 (1970).

[16] B. F. Field, T. F. Finnegan, and J. Toots, Volt maintenance at NBS

via 2e/h: a new definition of the NBS volt, Metrologia 9, 155-

166 (1973).

[17] Woodward G. Eicke and Barry N. Taylor, Summary of international comparisons of as-maintained units of voltage and

values of 2e/h, IEEE Trans. Instrum. Meas. IM-21, 316-319

(1972).

[18] Barry N. Taylor, History of the present value of 2e/h commonly

used for defining national units of voltage and possible changes

in national units of voltage and resistance, IEEE Trans. Instrum.

Meas. IM-36, 659-664 (1987).

[19] R. L. Kautz, Noise, chaos, and the Josephson voltage standard,

Rep. Prog. Phy s. 59, 935-992 (1996).

[20] J. Niemeyer, L. Grimm, W. Meier, J. H. Hinken, and E. Vollmer,

Stable Josephson reference voltages between 0.1 and 1.3 V for

high-precision voltage standards, Appl. Phys. Lett. 47, 1222-1223

(1985).

[21] Richard L. Steiner and Bruce F. Field, Josephson array voltage

calibration system: operational use and verification, IEEE Trans.

Instrum. Meas. 38, 296-301 (1989).

[22] R. L. Steiner and S. Starley, MAP voltage transfer between 10 V

Josephson array systems, in Proceedings of the NCSL Workshop

and Symposium NCSL’91, Natl. Conf. Stand. Lab., Boulder, CO

(1991) pp. 205-209.

[23] R. E. Elmquist, M. E. Cage, Y. Tang, A-M. Jeffery, J. R. Kinard,

R. F. Dziuba, N. M. Oldham, and E. R. Williams, The Ampere

and Electrical Units, J. Res. Natl. Inst. Stand. Technol., JanuaryFebruary (2001).

318
Plane-Wave Scattering-Matrix Theory of

Antennas and Antenna-Antenna Interactions

This monograph [1] represents David Kerns’s final

compilation on the subject of near-field antenna measurements. It was published shortly before he retired,

and it remains the best and most exhaustive treatment of

planar near-field scanning theory. The author developed

much of the material in the course of teaching graduate

electrical engineering courses in the University of

Colorado.

As outlined in the author’s preface, the monograph is

distinguished by the use of plane-wave spectra for the

representation of fields in space and by the consideration of antenna-antenna (and antenna-scatterer) interactions at arbitrary separation distances. The plane-wave

representation is eminently suitable for this purpose as

well as for the expression of conventional asymptotic

quantities of antenna theory, such as power gain, effective area, and polarization.

The primary objective of the monograph is to facilitate the critical acceptance and proper application of

antenna and field measurement techniques deriving

more or less directly from the plane-wave scatteringmatrix (PWSM) theory of antennas and antenna-antenna interactions. A secondary objective is to present

some recent and some new theoretical results based on

this theory. To some extent the second objective

supports the first one.

The expository plan is based upon experience at NBS

in developing, discussing, teaching, and reporting on the

PWSM theory and techniques, as well as upon observing at close hand the development of major NBS facilities for practical antenna measurement applications. All

field and antenna measurements involve measurements

of antenna outputs and inputs. This part of the total

process is the approximate dividing line between the

domain of antenna theory and the domain of microwave

measurement techniques including instrumentation. Or

perhaps instead of a dividing line there is a gap or

crevice.

Elaborate measurements made on expensive antennas

with expensive measuring equipment can be (and have

been) vitiated by improper microwave network calculations or by improper adjustments due to improper

interpretation of impedance-matching requirements.

This is in part a reflection of omitted, inadequate, or

even incorrect discussions of relatively simple network

calculations in the literature.

Fig. 1. The figure provides a hint of the complexity of the analyses addressed in the monograph. It represents

a pair of antenna systems operating in a homogeneous, isotropic, dissipationless medium; one antenna is

transmitting, and the other receiving. The complete treatment of a transmission system must include effects of

scattering by both antennas and thus automatically includes treatment of reflection systems, in which one antenna

functions in both transmitting and receiving modes and the other antenna represents an arbitrary passive (linear)

scattering object.

319
One quantity, characteristic of the type of antenna

measurements of interest here, is the transfer normalization required to obtain the ratio of receiving antenna

output to transmitting antenna input correctly in magnitude and relative phase. This normalization, even if done

correctly with good instruments and good technique,

may represent the single largest contribution to the inaccuracy or uncertainty of the eventually determined antenna or field data. In short, to be able to make good

microwave antenna measurements, one must be able to

make good microwave measurements. This is true regardless of the brand of antenna theory that one uses.

The theoretical basis and the techniques of microwave

network calculations receive little or no emphasis in

most books on electromagnetic theory and, apparently,

surprisingly little in the training and background of

microwave and microwave-antenna engineers. Chapter I

of this monograph is intended to supply some of the

missing emphasis. It consists of a revision and adaptation of part 1 of the book by Kerns and Beatty [2] with

an added section giving basic microwave network equations selected and discussed with antenna measurement

applications in mind. The general theoretical foundation

provided in this chapter has an additional role in the

present monograph.

The use of the plane-wave representation of the spatial fields (as contrasted to the use of spherical or cylindrical waves) simplifies and strengthens the theoretical

analogy between an antenna and an ordinary waveguide

junction (or N-port) described in terms of a finite

number of discrete waveguide input or output modes,

and it greatly simplifies the analogy between coupled

antennas and coupled waveguide junctions.

Chapter I is intended to be concise as well as elementary, but it is elementary only with respect to its principal subject. The reader is assumed to have a good working acquaintance with Maxwell’s equations, vector

analysis, and elementary matrix algebra. Transmissionline theory may be underrepresented in the discussion,

but the use of the traveling-wave resolution of fields

more or less automatically takes care of the need for

transmission-line equations.

Chapter II gives a formulation of the PWSM theory of

antennas and antenna-antenna interactions together with

basic analytical techniques for measurement applications. The formulation is relatively thorough and

complete, whereas the measurement techniques are

treated briefly. The reason for this imbalance is that the

measurement techniques are acquiring their own

literature, to which references are given. Chapter II

contains all of the material in the previous most complete discussion of the PWSM theory [3] with revisions

to improve the exposition. The bias is toward the subject

of measurements as an end and not merely as a means,

with emphasis on accurate measurements, or at least

measurements with controlled approximations. Both

generality and detail are required to avoid over-idealization, to permit the framing of precise definitions, and

to permit cognizance and the possibility of control of

approximations. Less general theorems and simplified

formulas might improve appearances of the pages of the

monograph, but would tend to be much less convenient

and useful to a measurement-oriented person interested

in accurate measurements. It is much easier to reduce,

than to increase, the generality of a given set of

equations.

The generality of the PWSM formulation is such that

it is not necessary to single out any particular types or

classes of antennas for purposes of discussion of

measurement equations. The measurement related

theorems and equations are valid for arbitrary types of

antennas, such as the so-called linear antennas, aperture

antennas, and arrays of antenna elements.

The third and last chapter is in essence a rather

lengthy research paper. It relies upon the first three of

the four sections of Chapter II for definitions, theorems,

and motivation; in turn, the analytical results obtained in

Chapter III support and illustrate Chapter II.

The use of examples is a feature of the exposition (38

numbered examples are included, most of them in

Chapter III). The examples serve several purposes:

the rederivation or restatement of certain well-known

results in the PWSM format is expected to lend perspective, establish confidence, and show some of the connections to existing theory. Examples are used to

provide extensions of the text material not readily available elsewhere and to form part of the development of

the subject. Most of the examples are suitable as

material for exercises (but so also are many equations

and assertions for which detailed argument is not given).

Kern’s ground breaking 1960 paper [4] on the Theory

of diffraction in microwave interferometry was the

seminal work that marks the beginning of modem nearfield antenna metrology. Under the leadership of Kerns

and other pioneers at NBS, near-field techniques have

become the preferred methods for characterizing the

radiating properties of microwave antennas. In addition

to the well-known NIST antenna group, several universities maintain active near-field measurement research

programs. Half a dozen companies market near-field

scanning equipment and well over 200 laboratories

worldwide routinely perform near-field measurements.

The IEEE Antennas and Propagation Society has

published a special issue (IEEE Transactions on Antennas and Propagation, June 1988) and regularly features

sessions on near-field techniques at its conferences.

Prepared by A. G. Repjar and J. F. Mayo-Wells.

320
Bibliography

[1] David M. Kerns, Plane-Wave Scattering-Matrix Theory of

Antennas and Antenna-Antenna Interactions, NBS Monograph 162, National Bureau of Standards, Washington, DC

(1981).

[2] David M. Kerns and Robert W. Beatty, Basic Theory of

Wave-guide Junctions and Introductory Microwave Network

Analysis, Pergamon Press, Oxford (1967) p. 29 ff.

[3] David M. Kerns, Plane-wave scattering-matrix theory of antennas

and antenna-antenna interactions: formulation and applications,

J. Res. Natl. Bur. Stand. 80B, 5-51 (1976).

[4] D. M. Kerns and E. S. Dayhoff, Theory of diffraction in

microwave interferometry, J. Res. Natl. Bur. Stand. 64B, 1-13

(1960).

321
The Automated Manufacturing

Research Facility

Over the years, NBS/NIST has built various experimental facilities to support its assigned functions of

custody, maintenance, and development of national

measurement standards, and provision of the means and

methods for making measurements consistent with

those standards. Such facilities include a nuclear

reactor, a cold neutron source, a linear accelerator, a fire

research facility, and dead weight force generators. It

was in this tradition that the Automated Manufacturing

Research Facility (AMRF) was established. The AMRF

was designed to anticipate the measurement and

standards needs of the discrete parts manufacturing

industry in the 1990s and beyond. This 1982 paper [1]

describes the history of NBS efforts to meet the

measurement needs of U.S. manufacturing industries,

beginning with artifact standards and calibrations

during the first half of the century, and evolving to

measurement protocols based on laser interferometer

calibrations of coordinate measuring machines by the

1960’s. The paper also describes early work in control

system architectures that provided the basis for the

AMRF research in interface standards for information

exchange within computer-based manufacturing

systems.

During the 1970s, two significant trends had become

clear:

1) Computers were playing an increasingly important role in manufacturing.

2) Measurements were increasingly integrated

into the closed-loop control of machines and

processes.

The first trend meant that interface standards would

be needed to facilitate exchange of information between

computer systems. The second meant that in-process

measurement technology would be needed for real-time

feedback control. To address interface standards, the

AMRF focused on developing information exchange

requirements and a reference model architecture to

understand the interactions between components of

computer-based manufacturing systems. To address the

in-process measurement issues, the AMRF focused on

methods for instrumenting machines and integrating

measurements into the machining process. Inspection

would be performed on-line while parts were being

manufactured, in addition to, or instead of, off-line after

the fact.

Prior to the 1970s, most measurements of manufactured products were based on artifact standards such

as gage blocks, thread gages, and line scales. NBS

supported industry by providing calibrations that tied

these artifacts to national and international standards of

length. Industry compared their manufactured products

with these artifact standards by statistical quality control

methods. Products were typically inspected off-line

after the manufacturing process had been completed.

During the 1960s and 1970s, the concept of Measurement Assurance Programs began to emphasize the

system aspects of measurement. Coordinate measuring

machines (CMMs) were introduced into the inspection

process and closed loop feedback methods became part

of metrology management. CMMs increased the

reliability with which comparison with artifacts could

be accomplished and improved productivity by reducing

the time required to make measurements. Of course,

coordinate measuring machines were themselves

subject to errors that were consequently introduced into

the measurement process. However, these errors were in

large part systematic. Simpson and Hocken observed

that a typical coordinate measuring machine was an

order of magnitude more repeatable than it was accurate

[2]. This suggested that if the systematic errors were

modeled and stored in a computer, then the computer

could compensate for those errors. During the 1970s,

NBS work in calibration and computer correction of

coordinate measuring machine errors made a significant

contribution to measurement technology for manufacturing [3]. The concept of in-process measurement and

computer based error compensation also provided the

conceptual foundation for the AMRF approach to

measurement technology.

Also during the 1970s, NBS work in robotics and

neural networks began to address issues of intelligent

control. The goal of this research was to bridge the gap

between high level concepts of artificial intelligence

(such as perception, knowledge representation, and

planning) and low level concepts of feedback control.

The approach was to develop a system architecture that

could support the decomposition of high level manufacturing tasks into lower level subtasks in a succession

of hierarchical steps until, at the bottom, subtask

commands could be input directly to servo control loops.

At each level of the hierarchy, signals from sensors

were processed to extract the information needed for

322
real-time control decisions at that level. This sensoryinteractive goal-directed control architecture became

known as the Real-time Control System (RCS.) RCS

was intended to be a reference model architecture with

a canonical form that could be used to define standard

interfaces between modular components [4].

Concurrent with the development of RCS, work was

begun on interface standards to facilitate exchange of

information between various commercial ComputerAided Design (CAD) systems. Under the technical

leadership of Roger Nagel and Bradford Smith, the

Initial Graphics Exchange Specification (IGES), which

is described elsewhere in this volume, became a national

standard. IGES was an immediate success. Within a few

years, virtually all manufacturers of CAD systems

provided IGES interfaces for their systems [5]. Together,

the RCS control architecture and the IGES data

exchange standard provided the conceptual foundation

for the AMRF work on interface standards [6]. Fig. 1 is

a diagram of the AMRF control system architecture.

AMRF consisted of six workstations integrated into a

group technology cell. Orders were input through cell

control [7]. (The shop control shown in Figure 1 was

never implemented.) There were three machining

workstations, a cleaning and deburring workstation, an

inspection workstation, and a material handling workstation. Part designs and process plans were developed

interactively by human programmers off-line. A

management information system provided information

about the status of the factory [8, 9, 10].

Fig. 1. Architecture for the NBS Automated Manufacturing Research Facility (AMRF). On the right is a hierarchical database containing process

plans and control programs that define how to manufacture parts. On the left is a hierarchical database containing information about the state of

the parts and machines in the AMRF. In the middle are the controllers that compute plans, sequence commands, measure results, and compute

actions to compensate for errors between plans and results. The arrows represent a communications system that moves information throughout the

architecture [1].

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The six workstations included the:

1) Horizontal Machining Workstation

The major subsystems of the HWS included a

horizontal spindle milling machine, a robot, and a set of

buffers. The machine tool was equipped with a tool

changer, a pallet shuttle, and an automatic vise for

holding parts. The buffers were used to store tools,

parts, and fixtures. They were serviced by an automatic

wire-guided vehicle. All of the HWS subsystems were

coordinated by the RCS workstation controller. The

robot, machine tool, buffer, and automatic fixture were

also equipped with RCS control systems that enabled

them to accept commands from the workstation

controller. The robot had vision and tactile sensors that

enabled it to sense the position and orientation of parts

and tools, and to load and unload them to and from the

machine tool. The robot vision system used structured

light to detect the three-dimensional position and orientation of parts in a buffer tray and to measure their

size and shape. Tactile sensing enabled the robot to

“feel” a part being grasped and to sense when it had

been properly inserted into a fixture for machining. The

HWS robot had the dexterity to remove a part from the

fixture, turn it over, and re-insert it for machining the

opposite side. It could also load tools into the machine’s

tool carousel. The robot was equipped with a quickchange wrist so that different grippers for different

shaped parts and tools could be handled. The RCS

controllers, each typically consisting of several computers on a bus, were integrated through an experimental

AMRF network and database [11, 12, 13].

2) Vertical Machining Workstation (VWS)

The VWS consisted of a vertical spindle milling

machine, a robot, and a menu-driven programming

system whereby parts could be designed and machined

automatically from a feature-based design. A simple

two-and-a-half dimensional part could be designed and

machined within an hour, allowing half an hour for

design input. Workstation activity was divided into

design, process planning, data execution, and physical

execution stages. To make VWS operation safe and

accurate, extensive error prevention and verification

procedures were incorporated in the data preparation

stages. Automatic verification included design editor

dialogues, design enhancement, design verification,

process plan verification, work-piece verification, and

part model checking. Interactive verification included

design drawing, work-piece model drawing, and tool

path drawing [14, 15, 16].

3) Turning Workstation (TWS)

The major components of the TWS included a turning lathe, a robot to load and unload parts and tools, and

buffers to store parts, tools, and fixtures. The TWS was

equipped with position sensors, accelerometers, thermal

sensors, and laser interferometers. A special purpose

gripper was developed with a micro-manipulator that

enabled the robot to perform high precision insertions

required for loading parts in the lathe collet. The

Turning Workstation addressed problems associated

with untended turning operations. These included

automatic tool changing, work piece loading and unloading, and tool setting. The TWS enhanced the accuracy of the turning lathe by real-time software error

compensation. Thermally induced errors were predicted

based on calibration and measurement of machine

position, direction of motion, and temperature profile.

During machining, predicted errors were compensated

by machine servo algorithms. Software error correction

improved overall machine accuracy by about an order of

magnitude [17].

4) Inspection Workstation (IWS)

The IWS contained a four-axis coordinate measuring

machine, a robot, and a variety of inspection probes for

measuring part dimensions and surface finish. Parts

were delivered to the IWS by automatic wire-guided

vehicles. They were loaded onto the coordinate measuring machine by the robot and inspected. Measurements

were compared against dimensions and tolerances in the

part design data. Statistics were kept on dimensions

within tolerance so that machining operations could be

adjusted to maintain quality. Dimensions outside of

tolerance were flagged. Surface finish data was also

collected [18].

5) Cleaning and Deburring Workstation (CDWS)

The CDWS consisted of two robots, a set of buffing

wheels, a set of deburring tools, a part holding fixture,

a washer/dryer, and a storage buffer. Both robots had

integrated force/torque sensors that enabled them to

sense forces and modify their motions so as to correct

for small errors and tool wear. One robot performed

buffing operations. The second had a tool changer that

enabled it to use a variety of abrasive brushes and deburring tools. The CDWS controller had a computeraided programming system that enabled an operator to

select tool orientation, force, and speed parameters for

each deburring operation. The system then automatically generated a control program for the tool path and

324
manipulation operations necessary to load each part into

a fixture and perform the specified set of deburring

operations [19, 20].

6) Material Handling Workstation (MHWS)

The MHWS workstation consisted of a part and tool

storage carousel, a storage and retrieval system, an

automatic wire-guided delivery cart, and a workstation

controller. The storage carousel had sufficient capacity

for one week of operation. The MHWS controller

responded to requests by the other workstations for

delivery and pickup of parts and tools. The MHWS

planned a route and dispatched its delivery cart to the

appropriate workstation at the proper time [21].

The AMRF also included three infrastructure support

projects. These were the Integrated Manufacturing Data

Administration System (IMDAS) [22], the AMRF

Network Communications system [23, 24], and the

Hierarchical Control System Emulator [25]. IMDAS

provided the database management services necessary

to store and retrieve the control programs that specify

how to manufacture each part, and the part data files

that specify geometry and tolerances for each part

feature. The Network Communications system provided

the data transmission services required to support the

AMRF control system architecture. The control system

emulator enabled programmers to develop software in a

virtual environment. Control programs could be tested

and debugged on emulated machines that were indistinguishable from real machines to the control system

software.

During its lifetime, several thousands of people

visited the AMRF and explored with its scientists and

engineers issues of concern to their companies. Examples of the comments received from industrial visitors

are:

“The AMRF provides a good architecture for

factory automation which we are using in our

internal factory automation program. We are

picking up a lot of concepts such as feedback

loops, world modeling, and planning. We are

developing a generic cell based on the AMRF

architecture.” [26].

Mr. Bob Solberg, Chairman,

Factory Automation Council

Boeing Computer Services,

Boeing Company

In 1984 I joined the Aircraft Engine Group of

General Electric as the Manager of Automation for a flexible turning center to be built

in Lynn, MA. The NBS/AMRF hierarchical

control structure was one of the models we

used in designing the computerized control

system for that plant. More than this, the

AMRF provided us with a reference, something we could check ourselves against. Some

of the things being done at the AMRF are

profound in my view. For example, AMRF

researchers introduced error maps to facilitate the use of computer-based temperature

correction to upgrade the precision of a

milling machine.” [26].

Mr. Robert D. French, Manager

T700/CT7 Engine Programs

General Electric Company,

Aircraft Engine Business Group

Over the years, technology from the AMRF was

transferred into industrial production. As a follow-on to

the AMRF Turning Workstation, NBS researchers

designed and built a flexible manufacturing workstation

for the Mare Island Naval Shipyard. The Mare Island

workstation was developed to manufacture a family of

40 different pipe connectors designed to inhibit the

transmission of sound in nuclear submarines. The workstation was equipped with an NC lathe, live tooling, a

robot, an automated storage and retrieval system, and

an AMRF style control system. It was designed to

work unattended. Previous manual techniques required

17 hours to produce a typical part. The new workstation could manufacture the same part in as little as

20 minutes.

Lessons learned from the Mare Island workstation

were put into practice in another version of the AMRF

Turning Workstation built for the Portsmouth Naval

Shipyard. The Portsmouth workstation was designed to

manufacture and inspect class-1 fasteners (i.e., critical

bolts, studs, and cap screws) for nuclear submarines.

These fasteners were made of k-monel, a very strong,

corrosive-resistant metal that is difficult to machine.

Personnel from the Portsmouth shipyard worked closely

with NIST scientists to make the technology transfer

successful [27].

The RCS control system architecture developed for

the AMRF was adapted for use in several areas outside

of manufacturing. Under DARPA funding, RCS was

325
adapted for control of multiple autonomous undersea

vehicles. DARPA also supported the adaptation of RCS

for command and control systems aboard next generation nuclear submarines. The U.S. Bureau of Mines

adopted RCS as an architecture standard for automated

mining operations. RCS was adopted by the U.S. Postal

System for control of a stamp distribution center and a

general mail facility. NASA adopted a version of RCS

called NASREM (NASA/NBS Reference Model) as a

controller for the Space Station telerobotic servicer.

NASREM was also adopted by the European Space

Agency as a model for their robotics program. For the

past ten years, RCS has been used by the Army for their

research program in Unmanned Ground Vehicles [28].

The Air Force Next Generation Controller program and

the industry led Open Modular Architecture Control

(OMAC) consortium have been influenced by the

AMRF control architecture.

Among the long term results of the AMRF was the

influence it had on the transformation of NBS to NIST.

According to a report by the National Academy of

Sciences [29]:

“The AMRF served as a platform to develop needed

technology for flexible, integrated, and automated

manufacturing of discrete parts. Originally conceived

as a testbed for integration of advanced automation,

it successfully proved a number of concepts and eliminated less promising ones. It has played a significant

role in the identification and development of emerging

technologies in manufacturing. It has had considerable

influence on various private efforts throughout the

nation. It was also the catalyst for the legislative process that resulted in the Technology Competitiveness

Act” (the section of the Omnibus Trade Act of 1988

which reauthorized NBS and NIST.)”

Besides changing the name from NBS to NIST, the

Trade Act added two new programs to the NIST responsibilities: The Advanced Technology Program (ATP),

and the Manufacturing Technology Centers (MTC)

which became the Manufacturing Extension Partnership (MEP.) The MTC program was originally conceived as a mechanism for transferring manufacturing

technology from the AMRF to industry.

The AMRF was jointly funded by NBS and the Navy

Manufacturing Technology Program. The program

managers for the Navy were Jack McInnis and. Steve

Linder. The number of people involved in the AMRF is

much too large to give proper credit to everyone by

name or to cite every related publication. The bibliography gives a sampling of the more significant

publications.

Prepared by James S. Albus.

Bibliography

[1] J. A. Simpson, R. J. Hocken, and J. S. Albus, The Automated

Manufacturing Research Facility of the National Bureau of

Standards, J. Manuf. Syst. 1, 17-32 (1982).

[2] John A. Simpson, Mechanical Measurement and Manufacturing,

in Control and Dynamic Systems: Advances in Theory and

Applications, (Manufacturing and Automation Systems: Techniques and Technologies, Vol. 45), Richard H. F. Jackson and C.

T. Leondes, (eds.), Academic Press, San Diego (1992) pp. 17-30.

[3] M. A. Donmez, D. S. Blomquist, R. J. Hocken, C. R. Liu and

M. M. Barash, A General Methodology for Machine Tool

Accuracy Enhancement by Error Compensation, Precis. Eng. 8,

187-196 (1986).

[4] Anthony J. Barbera, M. L. Fitzgerald, James S. Albus, and

Leonard S. Haynes, RCS: The NBS Real-Time Control System,

in Robots 8: Conference Proceedings, Vol. 2, Detroit, Michigan,

June 1984, Society of Manufacturing Engineers, Dearborn, MI

(1984) pp. 19-1 19-33.

[5] Bradford Smith, Gaylen R. Rinaudot, Kent A. Reed, and Thomas

Wright, Initial Graphics Exchange Specification (IGES) Version

4.0, NBSIR 88-3813, National Bureau of Standards, Gaithersburg, MD (1988).

[6] James S. Albus, Anthony J. Barbera, M. L. Fitzgerald, Ernest

Kent, Harry Scott, and Roger Kilmer, A Control System for

an Automated Manufacturing Research Facility, in Robots 8:

Conference Proceedings, Vol. 2, Detroit, MI, June 1984, Society

of Manufacturing Engineers, Dearborn, MI (1984) pp. 13-28–

13-44.

[7] C. R. McLean, A Cell Control Architecture for Flexible

Manufacturing, SME Technical Paper MS88-473, SME

Cell Controllers Clinic, Schaumburg, Illinois, April 26-27,

1988.

[8] J. S. Albus, C. R. McLean, A. J. Barbera, and M. L. Fitzgerald,

An Architecture for Real-Time Sensory-Interactive Control of

Robots in a Manufacturing Facility, in Proceedings of the Fourth

IFAC/IFIP Symposium on Information Control Problems in

Manufacturing Technology, Gaithersburg, Maryland, October

1982, pp. 81-90.

[9] Mary Mitchell, Yuhwei Yang, Steve Ryan, and Bryan Martin,

Data Model Development and Validation for Product Data

Exchange, NISTIR 90-4241, National Institute of Standards and

Technology, Gaithersburg, MD, January 1990.

[10] Albert T. Jones and Charles R. McLean, A Proposed Hierarchical Control Model for Automated Manufacturing Systems,

J. Manuf. Syst. 5, 15-25 (1986).

[11] Albert J. Wavering and John C. Fiala, The Real-Time Control

System of the Horizontal Workstation Robot, NBSIR 88-3692,

National Bureau of Standards, Gaithersburg, MD, December

1987.

[12] W. G. Rippey and H. A. Scott, Real-time Control in a Machining

Workstation, in Proceedings of the 20th Annual Meeting and

Technical Conference, Numerical Control Society, Cincinnati,

Ohio, April 10-13, 1983, Numerical Control Society, Glenview,

IL (1983).

[13] Harry Scott and Kathleen Strouse, Workstation Control in a

Computer Integrated Manufacturing System, in Autofact 6:

Conference Proceedings, Anaheim, CA, October 1984, Society

of Manufacturing Engineers, Dearborn, Michigan (1984) p. 22.

[14] T. R. Kramer and J. Jun, Software for an Automated Machining

Workstation, in Proceedings 3rd Biennial International Machine

Tool Tech Conference, September 1986.

326
[15] T. R. Kramer, Process Planning for a Milling Machine from a

Feature-Based Design, in Proceedings of Manufacturing International ’88, Atlanta, Georgia, April 1988, ASME Vol. III,

American Society of Mechanical Engineers, New York (1988)

pp. 179-189.

[16] T. R. Kramer and W. T. Strayer, Error Prevention and Detection

in Data Preparation for a Numerically Controlled Milling

Machine, in Proceedings of 1987 ASME Annual Meeting, (ASME

PED Vol. 25), American Society of Mechanical Engineers, New

York (1987) pp. 195-213.

[17] Alkan M. Donmez, Robert J. Gavin, Lew Greenspan, Kang B.

Lee, Vincent J. Lee, James P. Peris, Eric J. Reisenauer, Charles

O. Shoemaker, and Charles W. Yang, The Turning Workstation in

the AMRF, NBSIR 88-3749, National Bureau of Standards,

Gaithersburg, MD (1988).

[18] Howard T. Moncarz, Architecture and Principles of the

Inspection Workstation, NBSIR 88-3802, National Bureau of

Standards, Gaithersburg, MD (1988).

[19] H. G. McCain, R. D. Kilmer, and K. N. Murphy, Development

of a Cleaning and Deburring Workstation for the AMRF,

in Deburring and Surface Conditioning ’85: Conference

Proceedings, September 23-26, 1985, Chicago, Illinois, Society

of Manufacturing Engineers, Dearborn, Michigan (1985).

[20] F. M. Proctor, K. N. Murphy, and R. J. Norcross, Automating

Robot Programming in the Cleaning and Deburring Workstation

of the AMRF, in Deburring and Surface Conditioning ’89, San

Diego, CA, February 1989, Society of Manufacturing

Engineers, Dearborn, Michigan (1989).

[21] S. Szabo, M. Juberts, and R. D. Kilmer, Automated Guided

Vehicles at the National Bureau of Standards Automated

Manufacturing Research Facility, Journal of Unmanned Vehicle

Systems, pp. 38-47, Summer 1984.

[22] D. Libes and E. Barkmeyer, The Integrated Manufacturing Data

Administration System (IMDAS)—An Overview, Int. J. Comput.

Integr. Manuf. 1, 44-49 (1988).

[23] Siegfried Rybczynski, Edward J. Barkmeyer, Evan K. Wallace,

Michael L. Strawbridge, Don E. Libes and Carol V. Young,

AMRF Network Communications, NBSIR 88-3816, National

Bureau of Standards, Gaithersburg, MD (1988).

[24] Charles McLean, Mary Mitchell, and Edward Barkmeyer, A

Computer Architecture for Small-Batch Manufacturing, IEEE

Spectrum 20 (5), 59-64 (1983).

[25] Howard M. Bloom, Cita M. Furlani, and Anthony J. Barbera,

Emulation as a Design Tool in the Development of Real-Time

Control Systems, in 1984 Winter Simulation Conference

Proceedings, Dallas, Texas, November 28-30, 1984, Institute of

Electrical and Electronics Engineers, New York (1984) pp. 627-

636.

[26] W. P. Meade, The National Bureau of Standards’ Automated

Manufacturing Research Facility (AMRF)—A Manufacturing

Technologies Resource Center, Management Collaborative

Group, Chapel Hill, NC (1988).

[27] K. B. Lee, Computer-Controlled Fastener Manufacturing Workstation,Technical Paper Series 941719, Society of Automotive

Engineers, Warrendale, PA (1994).

[28] J. S. Albus, The NIST Real-time Control System (RCS): An

Application Survey, in Proceedings of the AAAI 1995 Spring

Symposium Series, Stanford University, Stanford, CA, March

27-29, 1995.

[29] An Assessment of the National Institute of Standards and

Technology Programs, Fiscal Year 1990, National Academy

Press, Washington, DC (1991).

327
Submicrometer Linewidth Metrology

In 1987, the semiconductor industry was undergoing

a technological transition into the submicrometer range

of device dimensions. Small dimensions that are very

important to device performance or yield are called

critical dimensions (CD). Optical metrology technology

was adequate to measure the critical dimensions above

1 m, but as these dimensions shrunk into the submicrometer regime, the industry felt that the development of a new technology would be necessary. Scanning

electron microscopy began to be employed as the new

“tool” to measure submicrometer structures. In an effort

to assist the industry in this transition, two papers were

published in the same issue of the NBS Journal of

Research summarizing the knowledge on optical

metrology at that time. These papers discussed the

capabilities for extension into the submicrometer regime

and reported on the promising scanning electron

microscopy and its potential to take over from optical

metrology. The two pioneering review papers,

Submicrometer Linewidth Metrology in the Optical

Microscope [1] by Diana Nyyssonen and Robert

Larrabee, and Submicrometer Microelectronics Dimensional Metrology: Scanning Electron Microscopy [2] by

Michael T. Postek and David C. Joy, helped to reorient

the metrology direction of the semiconductor industry,

with impacts being felt even today.

By the year 1987 optical microscopes had been used

for looking at small things for several centuries and had

been optimized for this purpose. However, they were not

optimized for accurate dimensional metrology in the

submicrometer regime. Scanning electron microscopes

had also been used for looking at small things, but only

for decades instead of centuries. They also were not

optimized for submicrometer dimensional metrology.

Accurate measurements of submicrometer dimensions

in both kinds of microscopes were more difficult to

make and interpret than was generally recognized at that

time.

These two back-to-back papers [1,2] served to clarify

a number of misconceptions by those in industry who

were actually manufacturing the microscopes or using

them to make critical submicrometer dimensional

measurements. Both papers were aimed directly at

submicrometer measurements for quality control

purposes in the semiconductor and magnetic-storage

tape-head industries. An unusually large number of

requests for reprints were received from readers in the

United States, and the oral feedback revealed that the

papers were extensively faxed between colleagues

in foreign countries. It is impossible to document the

savings to industry due to the resulting improvements in

quality control attributable to these papers because

quality control information is often considered proprietary. Anecdotal feedback at subsequent technical

meetings and during the authors’ visits to industry

clearly indicated that material in the papers was

important and that the savings were substantial.

As the dimensions of interest continued to shrink in

the years following publication, these papers helped

set the stage: 1) for the improvements in the basic

instrumentation used for optical and SEM metrology, 2)

for the motivation to develop theoretical models for

interpretation of such measurements, and 3) for the

more intelligent use of the resulting measurement data.

The information in these papers is still relevant to submicrometer metrology even though much progress has

occurred since their publication. They should still

provide useful background information on micrometer

and submicrometer measurements for new metrologists

and for new, or more demanding, applications in the

new millennium (e.g., for linewidth and overlay

measurements in the semiconductor industry and for

critical dimensions in tape-head, microfabrication,

micromachining industries).

The submicrometer optical metrology paper [1]

assessed the capabilities and limitations of optical

submicrometer dimensional metrology and how well it

would be able to meet the measurement needs of future

semiconductor processing technologies (e.g., linewidth

measurements). The fact that the wavelength of the

commonly used visible light in the optical measuring

tools was comparable to the feature sizes of interest led

to serious limitations. The paper discussed the need to

model mathematically the effects of diffraction in the

image and thereby develop a meaningful criterion for

deciding which point on the image corresponds to the

edge of the feature whose dimensions were being

measured. Nyyssonen and Kirk developed such a model

[4] and Nyyssonen used that model for the calibration of

NIST’s first photomask linewidth standards [5]. The

modeling (and the measurement) is much more difficult

for opaque specimens (e.g., silicon wafers) and

becomes increasingly difficult as the feature heights

become larger than about a quarter wavelength and as

the aspect ratio (feature-height/width) approaches unity.

These factors, plus the non-vertical edge shapes of the

328
features, severely compromised the accuracy of dimensional measurements in the submicrometer regime.

The general problem of optical linewidth metrology was discussed with emphasis on: 1) definition of

linewidth for non-ideal features, 2) precision and accuracy (now referred to as Type 1 and Type 2 errors),

3) effects of measurement errors on process control,

4) instrument design, 5) resolution of the measuring

microscope, 6) optical-based linewidth standards, and

7) alternative linewidth measurement techniques. The

factors affecting measurements of small feature dimensions were discussed and illustrated by calculated image

waveforms for a typical patterned polysilicon line on a

silicon dioxide layer upon a silicon substrate. In these

calculations the waveform changed as the silicon

dioxide layer thickness was varied and the edge geometry of the line deviated from vertical. In addition, the

different kinds of microscopes used in optical metrology

were discussed and illustrative image profiles under

various illumination conditions were presented.

Perhaps the main message of this paper was that

submicrometer optical metrology was more difficult

than commonly envisioned at the time and that many

factors came into play that were often overlooked,

ignored, or inadequately treated in practical applications. With the ongoing impetus of the semiconductor

industry toward ever-smaller submicrometer dimensions

at that time, this attitude had to change if the anticipated

future needs for decreased measurement uncertainty

and increased accuracy were to be met. This paper

helped set the stage for the change that did, in fact,

occur.

The scanning electron microscope used in low accelerating voltage mode was initially felt to be the panacea

for the problems encountered by optical submicrometer

metrology. The paper by Postek and Joy [2] demonstrated that, although the SEM was capable of precise

measurements, accuracy was another issue altogether. It

also pointed out a number of pitfalls associated with the

instrument, making use of a simple micrograph of a

dime (Fig. 2). This micrograph drove home the point

that just because an image came from an SEM did not

mean that it was an accurate representation. As important as it was to understanding the instrumental problems, this paper also pointed out that the main limitation

of the SEM for accurate submicrometer metrology is the

electron beam/sample interaction, which affects the

generation and collection of the measured signals. This

was the first paper to stress the need for understanding

the electron beam/sample interaction as a requirement

for accurate metrology with the SEM.

Following the publication of this paper, a heightened

awareness of the issues associated with SEM metrology

prompted significant improvements in the instrumentaFig. 1. Comparison of calculated image profiles of the edge of an

opaque vertical-wall small-height (e.g., photomask) line. The ordinate

is relative transmitted light intensity and the abscissa is the distance

from the edge of the line in micrometers. The step-function rise to full

transmission shown by the straight lines in the figure represents what

one would ideally expect. The bright-field image (solid curve) and the

confocal image (dashed curve) show that the edge is not located at the

point of 50 % of full transmission.

Fig. 2. Scanning electron micrograph of a dime. This image and the

discussion in the original paper clearly demonstrated to the reader that

one cannot assume that just because the micrograph was taken with

an SEM and that the magnification and linescale are displayed that

they are accurate. The proper magnification should be 4.6x. This

simple demonstration showed that the read-out of the commercial

SEM should not necessarily be trusted at face value and thus led many

users to scrutinize their SEM measurements more carefully, setting

the stage for many new improvements in SEM metrology.

329
tion as described in later publications [7,10]. Today,

fully automated CD-SEM instruments are routinely be

ing utilized in semiconductor production applications

throughout the world.

Diana N. Nyyssonen joined NBS as a physicist in

1969 and quickly developed the first photomask

linewidth standards. Her work at NBS showed how

optical image simulation modeling could be used as a

tool for applying optical microscopes in submicrometer

metrology and, by so doing, exceed the classical resolution limits of imaging microscopes. She won the

Department of Commerce Silver Metal for her work in

this area. In 1985, she left NBS to form her own R&D

company specializing in optical dimensional metrology. She later joined IBM Corporation and specialized

in scanning probe microscopes.

Robert D. Larrabee joined NBS in 1976 as a physicist

specializing in the electrical characterization of bulk

silicon. In 1985 he became the Group Leader of

the Microelectronics Dimensional Metrology Group,

replacing Diana Nyyssonen. Under his leadership, the

group continued the existing photomask linewidth

projects and initiated new SEM metrology programs

with Michael Postek and other members of his group

[3]. He held the position of Group Leader until his

retirement in 1994. In 1999 he participated in the award

of the Department of Commerce Bronze metal Team

Award for his post-retirement work in developing a new

optical overlay metrology tool and a novel standard for

use in its alignment.

David C. Joy is currently a Distinguished Scientist,

Director of the EM Facility, and Professor at the

University of Tennessee. He also holds a joint appointment with Oak Ridge National Laboratory, where he is

a member of the Staff in the Materials and Ceramics

Division. Since publication of the subject paper, he has

contributed to the improvements in SEM and SEM

modeling. He has recently published two books, Monte

Carlo Modeling for Microscopy and Microanalysis and

Semiconductor Characterization by Scanning Electron

Microscopy. He has contributed to the evolution of the

scanning electron microscope as a viable production

tool through his research in low accelerating voltage

electron microscopy, modeling, electron holography,

and nano-tip development.

Michael T. Postek is currently the Leader of the

Nano-scale Metrology Group at NIST. Since this paper

appeared, he has worked closely with International

SEMATECH and its member companies in the development of scanning electron microscopy as a tool for

semiconductor production. He has been awarded a 1998

R&D 100 award for the development of SEM Monitor (a

tool used to test the performance level of automated

production SEMs) and two Department of Commerce

Silver Medals for his work in metrology with the

scanning electron microscope. He is currently completing development of an accurate low accelerating voltage

SEM magnification standard (SRM 2090), a sharpness

standard RM 8091, and a production-critical SEM width

standard.

Prepared by Michael T. Postek and Robert D. Larrabee.

Bibliography

[1] Diana Nyyssonen and Robert D. Larrabee, Submicrometer

Linewidth Metrology in the Optical Microscope, J. Res. Natl.

Bur. Stand. 92, 187-204 (1987).

[2] Michael T. Postek and David C. Joy, Submicrometer Microelectronics Dimensional Metrology: Scanning Electron Microscopy,

J. Res. Natl. Bur. Stand. 92, 205-228 (1987).

[3] Robert D. Larrabee and Michael T. Postek, Parameters Characterizing the Measurement of a Critical Dimension, in Handbook

of Critical Dimension Metrology and Process Control, (SPIE

Critical Review, Vol. CR52), Kevin M. Monahan (ed.), SPIE

Optical Engineering Press, Bellingham, WA (1994) pp. 2-24.

[4] Michael T. Postek, Scanning Electron Microscope-based

Metrological Electron Microscope System and New Prototype

Scanning Electron Microscope Magnification Standard,

Scanning Micros. 3, 1087-1099 (1989).

[5] R. D. Larrabee, L. Linholm, and M. T. Postek, Microlithography

Metrology: Scanning Electron Microscope Metrology, in Handbook of VLSI Microlithography: Principles, Technology and

Applications, William B. Glendinning and John N. Helbert

(eds.), Noyes Publications, Park Ridge, NJ (1991) pp. 148-238.

[6] Michael T. Postek, Jeremiah R. Lowney, Andras E. Vladar,

William J. Keery, Egon Marx, and Robert D. Larrabee, X-ray

Lithography Mask Metrology: Use of Transmitted Electrons in

an SEM for Linewidth Measurement, J. Res. Natl. Inst. Stand.

Technol. 98, 415-445 (1993).

[7] Michael T. Postek, Critical Issues in Scanning Electron Microscope Metrology, J. Res. Natl. Inst. Stand. Technol. 99, 641-671

(1994).

[8] Michael T. Postek, Andras E. Vladar, Samuel N. Jones and

William J. Keery, Interlaboratory study on the lithographically

produced scanning electron microscope magnification standard

prototype, J. Res. Natl. Inst. Stand. Technol. 98, 447-467 (1993).

[9] J. R. Lowney, M. T. Postek, and A. E. Vladar, A Monte Carlo

Model for SEM Linewidth Metrology, in Integrated Circuit

Metrology, Inspection, and Process Control VII, (Proceedings

SPIE 2196), SPIE, Bellingham, WA (1994) pp. 85-96.

[10] M. T. Postek, Scanning Electron Microscope Metrology, in

Handbook of Critical Dimension Metrology and Process

Control, (SPIE Critical Review, Vol. CR52), Kevin M. Monahan

(ed.), SPIE Optical Engineering Press, Bellingham, WA (1994)

pp. 46-91.

330
Observation of Atoms Laser-Cooled Below the

Doppler Limit

This 1989 paper [1] reported a breakthrough which

led to a Nobel Prize for William D. Phillips—the first

Nobel to be awarded to a NBS/NIST staff scientist. The

experiment described in the paper demonstrated that

light from a laser could be used to cool atoms to a much

lower temperature than was previously thought possible.

The fact that light carries momentum and can exert a

force on objects was realized by James Clerk Maxwell

in his theory of electromagnetism, developed in the 19th

century. At the turn of the century, experiments by

Lebedev [2] and Nichols and Hull [3] for the first time

measured these forces in the laboratory. This concept of

radiation pressure helped explain why comet tails point

away from the sun and was important in understanding

the stability of certain types of stars, but it had little

laboratory relevance until the advent of the laser. In

1975, two groups proposed the counter-intuitive idea

that radiation pressure from a laser could be used to cool

atoms [4,5]. By carefully choosing the frequency of the

laser, it appeared possible to cause the atoms to emit

light at a slightly higher frequency (energy) than they

absorbed, carrying away the thermal energy of the atom.

This frequency difference derived from the Doppler

shift due to the motion of the atoms. Doppler cooling

was first demonstrated [6] with trapped ions in 1978

(at NBS by the Wineland group).

William Phillips joined the Electricity Division at

NBS in 1978 to work on the gyromagnetic ratio of the

proton and the SI ampere experiments, with the understanding that he could devote some of his time to developing laser cooling ideas for neutral atoms and atomic

beams. He was joined in his efforts by a long-term

visitor to NBS, Harold Metcalf from the State University of New York at Stony Brook. Several of the key

achievements in neutral-atom laser cooling were

produced by what would become the Laser Cooling

Group. These included the demonstration of efficient

ways of decelerating atomic beams with laser light:

Zeeman cooling [7], in which the changing Doppler

shift of a decelerating atomic beam is compensated by

a spatially-varying magnetic field, and “chirped” cooling [8], where the Doppler shift is compensated by a

changing laser frequency. These two methods are still

the only methods used today to decelerate atomic

beams. Another significant accomplishment of the

Laser Cooling Group was the first trapping of neutral

atoms with magnetic fields [9] in 1985. Magnetic

trapping is now widely used in dozens of experiments

studying Bose-Einstein condensation of dilute gases.

By the late 1980s a few groups around the world were

investigating the properties of “optical molasses,” the

name given to a “sticky” configuration of laser beams

that could cool and hold on to atoms for as long as a few

seconds. The action of the light upon the atoms created

a viscous environment for the atoms, hence the

“molasses” appellation. A group at Bell Laboratories,

headed by Steven Chu, had measured a temperature of

240 K [10] for a sample of sodium optical molasses,

in accord with the Doppler cooling theory that had been

developed a few years earlier. The NBS group had

made a number of measurements of the properties of a

sodium molasses, such as the lifetime of the atoms

in the molasses. Each measurement they made had

disturbing discrepancies between the results and the

Doppler theory. At the urging of one of the members of

the team, Paul Lett, then a recently arrived postdoctoral

fellow, they set out to measure the temperature of the

atoms. This was something that they had shied away

from earlier because its measurement was rather

difficult and it had already been done at Bell Labs. They

crafted a new, sensitive technique to measure the velocity distribution of the cold atoms, and thus extract the

temperature. The time-of-flight technique they developed looked for fluorescence from atoms that traversed

a probe laser beam after being released from the

molasses. The duration of the pulse of fluorescence

would be inversely proportional to the atomic velocity,

which would allow the extraction of the temperature.

For reasons of convenience, they placed the probe

above the molasses (at 240 K the atoms would have

plenty of thermal velocity to overcome gravity to reach

the probe). After a number of puzzling days with no

signals, they moved the probe under the molasses and

immediately saw a strong pulse of fluorescence (Fig. 1).

To their great surprise, the temperature that they found

was 40 K (the atoms were so cold that gravity turned

them around before they could reach the probe placed

above the molasses). This result was six times lower

than what the theory had predicted was the ultimate

limit, the so-called Doppler limit, as well as contradicting the Bell Labs results [11]. To assure that

some unknown feature of their new measurement

technique was not deceiving them, they measured the

temperature with three other methods, all of which were

331
in agreement—the temperature of optical molasses was

much lower than anyone had thought possible. This was

announced in Physical Review Letters and was rapidly

confirmed in other laboratories around the world (including that of Chu, who had moved to Stanford).

Almost as rapidly, a new theory of laser cooling was

developed that explained these results [12]. Not only did

it extend the simple theory by taking into account the

detailed atomic structure of the atoms, but it also

showed that there existed qualitatively different lasercooling mechanisms that had not been anticipated.

(Claude Cohen-Tannoudji shared the 1997 Nobel Prize

in Physics with Phillips and Chu, in part for his development of the sub-Doppler laser-cooling theory.)

Spurred in part by the spectacularly low temperatures

possible with these new cooling mechanisms, lasercooling experiments blossomed around the world with

more than 100 laboratories involved in such research by

the late 1990s. These ultracold temperatures have had an

impact in many areas of atomic physics, spawning

whole new areas of research, such as ultracold collision

physics and optical lattices. They were critical as the

first step in the creation of the much sought after BoseEinstein condensation of an atomic gas, achieved in

1995 at NIST/JILA [13]. The table-top aspect of lasercooling experiments has spurred their introduction into

many undergraduate laboratory courses, providing for

many students the first exposure to modern laser

technology and atomic physics.

The most significant societal impact of this discovery

is in time-keeping, one of the traditional core responsibilities of NBS/NIST. The second is defined with

respect to a microwave transition in the cesium atom,

which fortuitously is an ideal atom to laser-cool. The

sub-Doppler laser-cooling temperature for cesium

(1 K to 2 K) can be 100 times lower than the Doppler

limit. Because such cold atoms move so slowly, they can

be observed for a much longer time than was previously

possible, dramatically increasing the precision and

accuracy of a cesium frequency standard. Using an idea

from 1954, well ahead of its time but now made possible

with sub-Doppler laser cooling, the cesium atoms form

an atomic fountain, undergoing a one meter high

parabolic trajectory in the earth’s gravitational field

with a resulting hundred-fold increase in the observation

time. This has led to an immediate improvement of the

performance of frequency standards and, as of this

writing, the definition of the second is in large part

determined by laser-cooled cesium atomic clocks,

including NIST’s F-1 fountain standard which came on

line in December 1999.

William Phillips joined the Electricity Division at

NBS in 1978, and began his research in laser cooling

soon thereafter, while continuing involvement in the

Ampere experiment. Paul Lett, Richard Watts,

Christoph Westbrook, and Phillip Gould were all postdoctoral fellows in the group in 1988 at the time of the

publication of the sub-Doppler cooling paper. Lett has

remained at NIST as a staff physicist in the Laser Cooling and Trapping Group; Watts was a staff physicist in

the Photon Physics Group at NIST, but died in 1996;

Westbrook left NIST in 1993 to become a staff physicist

Fig. 1. Time-of-flight measurement of the temperature of optical molasses. The points

show the experimental measurements of the time-of-flight distribution of atoms falling

from an optical molasses through a probe laser beam situated 12 mm below. The solid lines

show the predicted distribution curves for 40 K and 240 K (the predicted lower limit

of Doppler cooling). The band around the 40 K curve reflects the uncertainty in the

measurement of the geometry of the molasses and probe.

332
at l’ Institut d’Optique, Orsay, France; Gould left NBS in

1988 to become a professor of Physics at the University

of Connecticut. Harold Metcalf was a visiting scientist at

NBS/NIST and is a professor of physics at the State

University of New York at Stony Brook. The Laser

Cooling and Trapping Group moved to the Atomic

Physics Division in the Physics Laboratory at NIST in

1991. The group has continued to be an active, prolific

group, with over 25 publications in premier journals

such as Physical Review Letters, Nature, and Science.

They are recognized world leaders in the areas of laser

cooling, ultracold collision physics, optical lattices, and

Bose-Einstein condensation. Phillips was recognized as

a co-recipient of the 1997 Nobel Prize in Physics “for

development of methods to cool and trap atoms with

laser light” [14].

Prepared by Steven Rolston.

Bibliography

[1] P. D. Lett, R. N. Watts, C. I. Westbrook, W. D. Phillips, P. L.

Gould and H. J. Metcalf, Observation of atoms laser cooled

below the Doppler limit, Phys. Rev. Lett. 61, 169-172 (1988).

[2] P. Lebedev, Untersuchungen u ̈ber die Druckkra ̈fte des Lichtes,

Ann. Phys. 6, 433 (1901).

[3] E. F. Nichols and G. F. Hull, A Preliminary communication on

the pressure of heat and light radiation, Phys. Rev. 13, 307-320

(1901).

[4] D. Wineland and H. Dehmelt, Proposed 1014  <  laser fluorescence spectroscopy on T1+ mono-ion oscillator III, Bull. Am.

Phys. Soc., Ser. II, 20, 637 (1975).

[5] T. W. Ha ̈nsch and A. L. Schawlow, Cooling of gases by laser

radiation, Opt. Commun. 13, 68-69 (1975).

[6] D. J. Wineland, R. E. Drullinger and F. L. Walls, Radiationpressure cooling of bound resonant absorbers, Phys. Rev. Lett.

40, 1639-1642 (1978).

[7] W. D. Phillips and H. Metcalf, Laser deceleration of an atomic

beam, Phys. Rev. Lett. 48, 596-599 (1982).

[8] J. V. Prodan and W. D. Phillips, Chirping the Light—Fantastic?

Recent NBS Atom Cooling Experiments, in Laser-cooled and

Trapped Atoms, W. D. Phillips (ed.), NBS Special Publication

653, National Bureau of Standards, Washington, DC (1983)

pp. 137-141.

[9] A. L. Migdall, J. V. Prodan, W. D. Phillips, T. H. Bergeman, and

H. J. Metcalf, First observation of magnetically trapped neutral

atoms, Phys. Rev. Lett. 54, 2596-2599 (1985).

[10] S. Chu, L. Hollberg, J. E. Bjorkholm, A. Cable and A. Ashkin,

Three-dimensional viscous confinement and cooling of atoms by

resonance radiation pressure, Phys. Rev. Lett. 55, 48-51 (1985).

[11] The high temperatures measured at Bell Labs have been

attributed to the stray magnetic fields from an ion pump.

[12] J. Dalibard and C. Cohen-Tannoudji, Laser cooling below the

Doppler limit by polarization gradients: simple theoretical

models, J. Opt. Soc. Am. B 6, 2023-2045 (1989).

[13] M. H. Anderson, J. R. Ensher, M. R. Matthews, C. E. Wieman,

and E. A. Cornell, Observation of Bose-Einstein Condensation in

a Dilute Atomic Vapor, Science 269, 198-201 (1995).

[14] Steven Chu, The manipulation of neutral particles, Rev. Mod.

Phys. 70, 685-741 (1998); Claude N. Cohen-Tannoudji, Manipulating atoms with photons, ibid., pp. 707-719; William D.

Phillips, Laser cooling and trapping of neutral atoms, ibid., pp.

721-741. These papers are the Nobel lectures in physics, 1997.

Fig. 2. Current permanent staff members of the NIST Laser Cooling and Trapping Group,

as photographed in Stockholm for the awarding of the 1997 Nobel Prize in Physics. From

the left: Paul Lett, Steven Rolston (joined NBS in 1988 ), William Phillips, and Kristian

Helmerson (joined NIST in 1991).

333
Laser-Excited Hot-Electron Induced

Desorption

The quest for femtochemistry provided a guiding

motivation for many researchers [1,2] far in advance of

the award of the 1999 Nobel Prize in Chemistry to

Ahmed Zewail “for his pioneering investigation of

fundamental chemical reactions, using ultra short laser

flashes, on the time scale on which the reactions

actually occur” [3]. The rich array of possibilities that

femtochemistry potentially offered within the domain

of surface-science-related phenomena was the driving

force for a very significant research effort, starting in

the mid 1980s, involving core members of the Surface

Dynamical Processes Group within the Surface Science

Division (SSD). This group was first part of the Center

for Chemical Physics, then the Center for Atomic,

Molecular, and Optical Physics, and most recently the

Chemical Science and Technology Laboratory. The

initial desorption results with pulsed laser-induced

surface processing reported in 1988 [4] strongly suggested that an entirely new physical mechanism, different from that operating in gas phase femtochemistry,

was required to account for the laser-induced molecular

processes on solid surfaces. Stimulated by this discovery, a transient quantum wave packet model was

conceived, developed, and first reported in the 1990

paper Laser- excited hot-electron induced desorption: a

theoretical model applied to NO/Pt(111) [1]. In this

model, laser-excited hot electrons produced within the

solid are inelastically scattered from the surface

chemical system via resonance formation of a temporary negative ion. This picture has become a standard

paradigm for modeling, and hence understanding,

almost all hot-electron-induced molecular processes at

surfaces involving not only laser excitation, but also

STM (Scanning Tunneling Microscope)-, tunnel junction-, and electrochemically-produced hot electrons.

For this reason among others, the consequences of this

coupled theoretical and experimental research are

expected to have an active and lasting impact on our

understanding and control of many of the most important electron-induced surface processes of chemical

significance [5].

The decade of the 1970s was filled with the excitement accompanying the initial development, utilization,

and theoretical interpretation of surface-sensitive spectroscopic probes which enabled a quantum mechanical

description of clean and composite surfaces. Our ability

to determine not only the electronic state of the surface

[6], but also the properties characterizing the quantized

nuclear motion of the bound constituent atoms, as revealed in vibrational spectroscopies [7], were opening

up entirely new vistas in conceptualizing and understanding surface properties and processes. Once the

machinery for static surface characterization was in

place, it was natural to address next the intellectual and

technical challenges presented in surface dynamics.

This was understood to mean the observation and control of time-dependent fundamental processes that are

the atomic-level (both spatial and temporal) building

blocks determining the rates for excitation, decay,

growth, aging, chemical reactions, catalysis, etc. Bondselective nonequilibrium placement of energy within a

molecular system, subsequent energy flow and redistribution, intentional use of the out-of-equilibrium state,

and production of far-from-statistical product distributions and branching ratios became the new goals.

In the late 1970s, Rich Cavanagh came to NBS as an

NRC Postdoctoral Fellow working with John Yates,

initially on infrared and neutron surface vibrational

spectroscopy and thermal desorption. About the same

time, David King joined the laser chemistry group

headed by John Stephenson to study time-dependent,

laser-assisted molecular processes in the gas phase. A

propitious collaboration was initiated between Cavanagh

and King which produced the first-ever quantum-statespecific (translational, vibrational, and rotational)

energy distribution measurements of molecules thermally desorbed from metal surfaces (NO/Ru(001)) in

which laser excited fluorescence (LEF) techniques were

used to deduce the internal state population distributions

[8]. In early 1988, new NRC Postdoctoral Fellows Steve

Buntin and Lee Richter joined Cavanagh and King to

study “fast” pulsed laser-induced desorption, again

using LEF to interrogate the desorbed molecules. This

combination of laser applications, both as an active

participant in the process under study (desorption) and

also as a diagnostic tool (energy distributions), was

crucial in the development of femtosecond surface

chemistry [9,10]. In their “paradigm-establishing” 1988

note in Physical Review Letters [4], convincing

evidence was presented which suggested that, contrary

to expectations, desorption was caused not by local laser

heating of either the substrate lattice or by the direct

pumping of the adsorbate-surface bond, but instead by

some as yet unknown mechanism involving electrons

334
that were “super-heated” far in excess of the surface

temperature. As more fully understood later, the degree

of excess electron heating is very dependent on the

temporal width of the incident laser pulse; tens of

femtosecond pulses produce much hotter electrons (but

for a shorter length of time!) and, as a result, cause

different surface reactions than do pico-to-nanosecond

pulses with equal energy content [9,11]. This distinction

has turned out to be very important in the pursuit of

surface femtochemistry [9,10]

From the theoretical point of view, Bill Gadzuk had

for a long time been keenly interested in the electronic

properties of adsorbed systems [6]. By the 1980s, his

considerations had also shifted towards problems in

surface dynamics, particularly ones involving atomic

motion triggered by electron charge transfer [12] and

resonance scattering [13] involving atoms on surfaces.

At the time of the first laser desorption experiments, he

was working with John Yates (formerly from the SSD,

then and now at the University of Pittsburgh [14]) on

what appeared to be resonant electron stimulated

desorption [15]. Together with Charles Clark, he developed a model that explained observations from Yate’s

group showing a highly sensitive dependence of the

desorption yield of NO/Pd(111) on the energy of the

incident exciting electron beam, exactly in the fashion of

a hot-electron resonant desorption process [16]. Since

the model did not care how the energetic or hot electrons got “hot,” it was as applicable to the laser-induced

hot-electron desorption phenomena under study experimentally by Buntin et. al [4] as to the external electronbeam experiments of Yate’s group [15]. With this

realization, it was relatively easy to work the ESD

theory [15,16] into a theory for laser desorption, an

exercise which produced the 1990 paper [1] and later

refinements [2].

The proposed optically driven non-thermal desorption version of the general hot-electron model unfolds in

the following way. The incident photon pulse excites a

non-equilibrium continuous distribution of hot electrons

with energies in the range Fermi < in < Fermi+h where

Fermi is the Fermi level of the substrate and h the

photon energy, as illustrated in Fig.1. This results in a

transient flux of hot electrons incident upon the surface

from within. For those photoexcited electrons resonant

with the lowest unoccupied “level” of the adsorbate

(labeled as the 2* orbital for NO/Pt), the incident

electron with energy in may hop onto the adsorbed NO,

reside in this resonance for a time R, and then scatter

back into an unoccupied conduction band state with

energy fin  in, leaving behind some part of the

adsorption system excited with energy  = in– fin. With

regards to the NO-surface interaction, labeled Va(z) in

Fig.2, when the incident electron becomes trapped in

Fig. 1. Energy level diagram for inelastic hot electron scattering through the lowest

unoccupied molecular orbital (LUMO) resonance associated with the adsorbed molecule,

also showing the highest occupied molecular orbital (HOMO) resonance level.

335
the 2* resonance, an additional ionic attraction is

turned on, resulting in an augmented negative ion/

surface potential labeled V–(z). The desired attribute is

that the intermediate state is one in which attractive

forces are applied to the NO–

, thus requiring different

equilibrium geometries for the two charge states.

With these thoughts in mind, it was hypothesized that

the actual resonance desorption event occurs in the

following way. Upon capture of the incident electron in

the 2* orbital, 	0, the ground state wavepacket characterizing the nuclear motion of the adsorbed NO, suddenly finds itself as 	(t), a time-evolving non-stationary

state on V–(z), as in a Franck-Condon transition, and

thus accelerates inwards towards the surface. After a

time interval R = the negative ion resonance lifetime,

the trapped electron on NO– departs, and the moving

displaced and distorted wavepacket is returned to Va(z),

possibly on the steeply repulsive inner wall, again as a

Franck-Condon transition, but this time involving the

projection of a moving initial state wavepacket on both

the discrete bound and continuum desorptive states of

Va(z). The theory established that the translational

energy distribution of excited states resulting from this

sequence of electronic transitions is given by:

P(;R ) = 1

2 




–


dt' e it' 	(t' = 0;R )	(t';R )

which is the Fourier transform of the time-dependent

overlap of 	(t' = 0;R ), the state initially prepared on

Va at = R after experiencing the forces on the negative

ion, with 	(t';R ) the subsequent neutral state which

time evolves on Va. Theoretical methods for evaluating

such expressions using intuitively straightforward semiclassical Gaussian wavepacket dynamics were available

at that time and were incorporated into the theory [13].

The desorption or bond-breaking probability per resonance event ≡ PD(R) is given by the integral over

those states with energy greater than D, the desorption

energy as represented by the area under the filled-in

region of the final state distribution labeled P() in

Fig. 2. As is apparent, the dynamics on V–(z), the intermediate state potential energy curve, can easily lead to

a substantial electron-assisted desorption probability.

The desorption rate, which is in principle a measurable quantity of importance, is proportional to the

product of PD(R) multiplied by the rate of electron

capture into the resonance which, by microscopic

reversibility equals 1/R, the decay rate or inverse

resonance lifetime. The theory provided relationships

between the independent parameters defining the

desorption system, namely: the time scale for atomic or

wave packet motion on the potential curves in Fig. 2 and

R, the resonance lifetime, both given in terms of 0, the

oscillator frequency of the well; D, the desorption

energy; and z, the displacement of the minimum of

V– with respect to Va which is a measure of the force

on the adsorbate when it is a temporary negative ion.

An example of the theoretical results [2] are shown as

dNdes/dt vs. 0R plots in Fig. 3 for a range of z, with

D  1 eV (as for NO/Pt). An initial increase in desorpFig. 2. Schematic potential energy curves for center of mass translational motion of

adsorbed neutral and negative ion species with respect to the surface, showing wavepacket

propagation throughout the time sequence involving the negative ion resonance. The

distribution of final adsorbate states between vibrationally excited bound and desorptive

continuum states is shown as P() versus .

336
tion rate is experienced as R increases from zero due to

the increasing displaced nuclear dynamics. Larger z,

hence larger forces, results in larger desorption rates.

Ultimately the diminishing electron capture rate implied by longer R wins out, the desorption rate achieves

a maximum and then decreases with further increases in

R. Emphasis has been placed on the crucial role of R

because it is also the time interval between switching on

and off the intermediate state potential. Human control

of this attribute allows for the selective control of reaction outcomes [17], the hallmark of femtochemistry

[2]. The unification of system characteristics of this sort

has provided an intuitively clear picture of resonant hot

electron induced bond excitation processes that has

subsequently been used as the basic model in many new

and developing areas of molecular processing in surface

science, surface femtochemistry, current-driven STM

atom transfer, manipulation, and fabrication, and in

novel meso-scopic and nanotechnology applications.

Throughout the decade since this work was carried

out, all five participants have remained active in various

roles at NIST. The experimentalists continued their

forefront studies in controlled, time-resolved molecular

processes at surfaces, particularly those involving timedelay, pump-probe techniques to observe time-resolved

phenomena at the femtosecond level. Some of this work

has been summarized in a Feature Article in the Journal

of Physical Chemistry [9]. The authors have presented

numerous invited talks at international scientific meetings, workshops, and Gordon Conferences, introducing

the surface science, chemical physics, and chemical

technology worlds to the allures and potentialities of

surface femtochemistry. Lee Richter is currently developing new chemically sensitive probes for biologically

interesting surfaces and interfacial systems based on

near field scanning optical microscopy and on sumfrequency generation [18]. Steve Buntin is engaged in

the study of radical reactions with well characterized

surfaces that are of industrial relevance [19].

It appears that doing laser-excited surface experiments is good training for management careers at NIST.

Over the intervening years, Rich Cavanagh has risen to

become Chief of the Surface and Microanalysis Science

Division. Buntin has succeeded him as leader of the

Surface Dynamical Processes Group. Dave King spent

five years as a program manager in the Advanced

Technology Program and now serves as Science Advisor

to the Undersecretary of Commerce for Technology.

Bill Gadzuk has remained engaged in theoretical studies

involving hot electrons, femtochemistry, tunneling

phenomena [6], and related topics. In a recent commissioned Topical Review that appeared in the Journal

of Physics B [20], he emphasized the intellectual

stimulation provided by numerous NIST colleagues

from other organizational units. As in many other NBS/

NIST achievements, these cross-disciplinary interactions have played a key role in the success of his

research. In at least one vision of an ideal world, this is

how things should work!

Prepared by J. W. Gadzuk.

Fig. 3. Desorption rate versus resonance lifetime (in units of 0 = 2/T where T, the

vibrational period associated with the adsorption potential well, 70 fs for NO/Pt) with

selected values of displacement for V–, the negative ion potential, with respect to Va, as

labeled. While the absolute scale of the dNdes/dt axis is arbitrary, the curves are properly

scaled with respect to each other.

337
Bibliography

[1] J. W. Gadzuk, L. J. Richter, S. A. Buntin, D. S. King, and R. R.

Cavanagh, Laser-excited hot-electron induced desorption: a

theoretical model applied to NO/Pt(111), Surf. Sci. 235, 317-333

(1990).

[2] J. W. Gadzuk, Resonance-assisted, hot-electron-induced desorption, Surf. Sci. 342, 345-358 (1995).

[3] Ahmed H. Zewail, Femtochemistry: Atomic-Scale Dynamics of

the Chemical Bond, J. Phys. Chem. A 104, 5660-5694 (2000).

[4] Steven A. Buntin, Lee J. Richter, Richard R. Cavanagh, and

David S. King, Optically Driven Surface Reactions: Evidence

for the Role of Hot Electrons, Phys. Rev. Lett. 61, 1321-1324

(1988).

[5] W. Ho, Reactions at Metal Surfaces Induced by Femtosecond

Lasers, Tunneling Electrons, and Heating, J. Phys. Chem. 100,

13050-13060 (1996).

[6] E. W. Plummer, J. W. Gadzuk, and R. D. Young, Resonance

Tunneling of Field Emitted Electrons Through Adsorbates on

Metal Surfaces, Solid State Commun. 7, 487-491 (1969).

[7] John T. Yates, Jr. and Theodore E. Madey (eds.), Vibrational

Spectroscopy of Molecules on Surfaces, Plenum Press, New

York (1987).

[8] Richard R. Cavanagh and David S. King, Rotational- and Spinstate Distributions: NO Thermally Desorbed from Ru(001),

Phys. Rev. Lett. 47, 1829-1832 (1981).

[9] R. R. Cavanagh, D. S. King, J. C. Stephenson, and T. F. Heinz,

Dynamics of Nonthermal Reactions: Femtosecond Surface

Chemistry, J. Phys. Chem. 97, 786-798 (1993).

[10] J. W. Gadzuk, Hot-Electron Femtochemistry at Surfaces, in

Femtosecond Chemistry, Vol .2, J. Manz and L. Wo ̈ste (eds.),

VCH Verlagsgesellschaft, Weinheim (1995) pp. 603-624.

[11] Hua Guo, Peter Saalfrank, and Tamar Seideman, Theory of

photoinduced surface reactions of admolecules, Prog. Surf. Sci.

62, 239-303 (1999).

[12] J. W. Gadzuk, Surface Harpooning, Comments At. Mol. Phys. 16,

219-240 (1985).

[13] J. W. Gadzuk, The Semiclassical Way to Molecular Dynamics at

Surfaces, Annu. Rev. Phys. Chem. 39, 395-424 (1988).

[14] Ted Madey and John Yates, Electron-Simulated Desorption, in A

Century of Excellence in Measurements, Standards, and Technology: A Chronicle of Selected NBS/NIST Publications, 1901-

2000, David R. Lide (ed.), NIST Special Publication 958, U.S.

Government Printing Office, Washington, DC (2001) pp. 219-

223.

[15] Alon Hoffman, Xingcai Guo, John T. Yates, Jr., J. W. Gadzuk,

and C. W. Clark, Electron-stimulated desorption and surface

species conversion: The observation of a desorption resonance

for atomic oxygen on the Pd(111) surface, J. Chem. Phys. 90,

5793-5800 (1989).

[16] J. W. Gadzuk and C. W. Clark, Resonance enhanced electron

stimulated desorption, J. Chem. Phys. 91, 3174-3181 (1989).

[17] Stuart A. Rice and Meishan Zhao, Optical Control of Molecular

Dynamics, John Wiley, New York (2000).

[18] Lee J. Richter, Teresa P. Petralli-Mallow, and John C. Stephenson, Vibrationally resolved sum-frequency generation with

broad-bandwidth infrared pulses, Opt. Lett. 23, 1594-1596

(1998).

[19] Steven A. Buntin, Dynamics of the H atom abstraction of D

adsorbed on Si(100), J. Chem. Phys. 108, 1601-1609 (1998).

[20] J. W. Gadzuk, Breathing mode excitation in near-harmonic

systems: resonant mass capture, desorption and atoms in optical

lattices, J. Phys. B: At. Mol. Opt. Phys. 31, 4061-4084 (1998).

338
Measurement of the Universal Gas Constant

Using an Acoustic Resonator

Competition is a great motivator. The 1988 measurement of the universal gas constant R at NIST [1] was

stimulated by an error made at a rival national metrology

institute, Great Britain’s National Physical Laboratory

(NPL). In 1976, a group at NPL reported a “new” value

for the universal gas constant R that had a standard

uncertainty of 8.4 ppm (1 ppm = 1 part in 106). The

“new” value was 159 ppm larger than the “older”

1972 value of R that had an uncertainty of 31 ppm

(See Fig. 1.).

The mutually inconsistent “old” and “new” values of

R troubled many scientists, including Ralph Hudson,

Chief of the Heat Division of NBS. Ralph solicited

proposals to redetermine R in novel ways. In response,

Mike Moldover proposed to determine R by measuring

the speed of sound in argon using a spherical acoustic

resonator [2]. This proposal was never formally funded;

it was never a milestone in a performance plan.

However, Moldover was encouraged to proceed on a

part-time basis. Soon, Jim Mehl at the University of

Delaware became a collaborator. Guest scientists Martin

Trusler and Terry Edwards joined in the mid 80s,

followed by Rich Davis, NBS’ expert in mass metrology.

Twelve years after research began, the measurements

were successfully completed. As shown in Fig. 1,

NIST’s 1988 value of R (and NPL’s corrected 1978

value) are consistent with the “old” value of R albeit

with the much smaller standard uncertainty of 1.7 ppm.

The NIST result R = 8.314 472(15) J mol–1 K–1 was

recommended by CODATA in 1999, and the research

effort was honored with NIST’s Stratton Award.

After completing the measurement of R in 1988,

Moldover and his collaborators [3] used the same acoustic resonator in the temperature range 217 K to 303 K to

measure the thermodynamic inconsistency of the

ITS-90, the International Temperature Scale of 1990.

(The ITS-90 is a set of carefully crafted recipes for

accurately determining the temperature from procedures such as measuring the resistance of very pure

platinum wire.)

In characteristic NBS/NIST fashion, the insights

gained from measuring R and studying the ITS-90 are

being applied to industrial problems. NIST’s Fluid

Science Group uses acoustic resonators to measure

the thermodynamic and transport properties of gases,

including environmentally acceptable refrigerants and

semiconductor process gases. In 1997, the spherical

resonator was given to NIST’s Temperature Group

where Dean Ripple and his collaborators rebuilt it to

study the ITS-90 up 800 K.

In order to place the 1988 measurement of R in

context, we shall describe the role that R plays in

temperature metrology, the connection between R and

the speed of sound, and the remarkable symmetry that

made the accurate acoustic measurement of R possible.

Then, to convey the flavor of the metrology, we

describe the measurement of the resonator’s volume.

We conclude with a few remarks concerning acoustic

thermometry.

With commercially available thermostats, platinum

resistance thermometers, and triple point cells, it is

much easier to reproduce any particular temperature

than it is to measure any of the fundamental statistical

mechanical quantities that characterize that temperature

(e.g., the average kinetic energy E in a mechanical

degree of freedom). Simply put, it is much easier to

measure a “T” than E. This very practical consideration

led the designers of the International System of Units

(SI) to define temperature as an independent physical

quantity. The definition specifies that the kelvin (K) is

the unit of the temperature and that the temperature of

the triple point of water Tw is exactly 273.16 K. In this

context, the Boltzmann constant is kB = 2E/Tw and the

Fig. 1. History of measurements of R. The standard uncertainty of

NIST’s 1988 measurement is 14 J mol–1 K–1, a value that is

approximately the size of the plotted symbol.

339
universal gas constant is R = NA kB = 2ENA/Tw , where

NA is the well-known Avogadro constant, which relates

the atomic mass unit to the kilogram. Thus, the 1988

measurement of R was equivalent to measuring E at the

temperature Tw.

The 1988 measurement of R immediately led to a

5-fold reduction in the uncertainty of both the Boltzmann constant kB and the Stefan-Boltzmann constant .

[ ≡ 25 kB

4

/(15h 3c 2) is used in radiation measurements. Here, h is Planck’s constant and c is the speed of

light.] The more accurate values of R, kB, and  will be

used by national metrology institutes for calibrating a

few vital primary thermometers that have designs that

do not permit their use at Tw. (Primary thermometers,

such as gas, noise, acoustic, and radiation thermometers

measure E or its equivalent, and are used to calibrate

other thermometers, such as platinum resistors.)

The most common use of R is in calculating gas

densities 
 from the virial equation of state:

pV = 
RT [1+b (T)
+...

Today, the uncertainty of R is much smaller than the

uncertainties of the other quantities in this equation.

The 1988 measurement of R was based on measuring

the speed of sound in argon. The speed of sound u was

deduced from the resonance frequencies fn of radially

symmetric acoustic oscillations of argon enclosed by a

thick spherical shell that had a carefully measured

internal volume (V  3 L. See Fig. 2.) An exactly

known eigenvalue zn connects these quantities through

u = V1/3 fn /zn . A detailed theory correcting this equation

had to be derived and tested by rigorous measurements

[4].

In a dilute gas, the speed of sound u is connected to

E by kinetic theory and hydrodynamics:

E =1

2 m2

rms = 3

2 kBT , u 2 = 2

rms

(Here, vrms is the root mean square speed of a gas

molecule, m is the mass of one molecule, and  is the

heat capacity ratio that has the zero-pressure limit 5/3

for the monatomic gases.) These equations can be

rewritten in terms of the molar quantities M = NAm and

R = NAkB to get a simple equation for R:

R = M

T

lim

p →0

u 2

 = M

273.16 K

3

5

lim

p →0 

V1/3 fn

zn



2

Thus, to measure R one must measure M, V, and fn,

all at Tw, and extrapolate to the limit of low pressure.

The thermodynamic temperature of a dilute,

monatomic gas can be deduced from the ratio of two

speed of sound measurements, one at T and a second at

Tw:

T = 273.16 K[u (T)/u (Tw)]2

In some respects, primary acoustic thermometry is

easier than measuring R. Neither V nor M must be

measured accurately. For thermometry, the thermal

expansion of V must be measured accurately, and this is

done using microwave resonances.

Fig. 2. Cross-section of the resonator and pressure vessel. “T” indicates the acoustic transducers; “PRT” indicates the platinum

resistance thermometers. The pressure vessel was immersed in a

thermostatted bath (not shown). The isothermal shield was installed

after the measurement of R to reduce the temperature gradients when

the resonator was used for thermometry at temperatures down to

217 K.

340
The frequencies fn are sensitive to small, smooth

departures from perfect spherical geometry in the

second order, provided that the volume is unchanged.

Thus, a spherical shell built to machine-shop tolerances,

e.g., one part per thousand, could be used to measure R

with an uncertainty on the order of the square of (one

part per thousand) = 1 ppm. In fact finer tolerances were

achieved in this work. This was confirmed by the

0.34 ppm internal consistency of the speed-of-sound

results obtained using five different radially symmetric

acoustic modes spanning the frequency range 2.5 kHz

to 9.5 kHz.

The weak dependence of the frequencies on shape

imperfections appears in S. A. Moszkowski’s 1955

calculation of energy levels in deformed nuclei. In the

course of the gas constant work, Mehl and Moldover

generalized this symmetry to vector (electromagnetic)

fields confined by a conducting sphere [5]. Their generalization made it practical to determine the thermal

expansion of spherical shells from the resonance

frequencies of a few, selected microwave modes within

the shell.

The 1988 paper concerning R took a year to write and

filled 60 pages of the Journal of Research of the NBS

[1]. It took 43 pages to describe the experimental

procedures and the analysis of the data. Instead of

summarizing this exhaustive work, we shall convey its

flavor by outlining only the measurement of the

resonator’s volume V.

The principle of the volume measurement was

simple. The mercury required to fill the resonator was

weighed and the known density of mercury was

used to convert the weight to a volume. To implement

this principle with the required accuracy, the resonator

was reconfigured to resemble a dilatometer. The

valve in the top of the resonator was replaced with a

glass capillary tube and the acoustic transducers were

replaced with carefully designed plugs. The reconfigured resonator was immersed in a bath thermostatted

at Tw.

For the weighings, the mercury was held in an

especially designed weighing vessel. For each volume

determination, the vessel was weighed when it was full

of mercury and again after the mercury required to fill

the resonator had been pumped out of it. As a check,

the vessel was weighed again after the mercury was

returned to it.

If a bubble were in the mercury inside the resonator,

the weighings would have underestimated the volume of

the resonator. Concern about this led to a delicate test

for bubbles. After the mercury was pumped into the

resonator, it overflowed, partially filling the glass

capillary tube atop the resonator. A measured overpressure of argon was applied to the mercury meniscus in

the glass capillary causing the meniscus to move downward. The change of the meniscus’ height was

compared with that expected from the known compressibility of mercury and the calculated compliance of the

19 mm-thick, stainless steel shell. Because bubbles are

much more compliant than mercury and steel, this

test would have detected a bubble with a volume of

310–7 V.

The calculation of the shell’s compliance used its

dimensions, the tabulated properties of stainless steel,

and a simple model. However, this calculation is not

completely trustworthy because the shell was a complex, assembled object. Thus, the calculation was

checked by a measurement. This was done while gas

was sealed within the shell. The pressure outside the

shell was reduced, causing the shell to expand slightly

and the acoustic resonance frequencies to decrease by

(–12.80.4)10–6 MPa–1

. The compliance determined

in this way was 6 % larger than the calculated compliance; however, this difference was within the combined

uncertainties.

The effect of the mercury’s pressure on the volume

and the sagging of the resonator when it was filled with

40 kg of mercury were taken into account.

When the acoustic transducers were replaced with

mercury-compatible plugs for the weighings, the

volume of the resonator changed. This volume change

was measured in an auxiliary experiment where the

plugs and transducers were interchanged in a small

acoustic coupler. These coupler experiments also

accounted for the effective volume that resulted from the

transducers’ compliance.

Because mercury is a mixture of isotopes, the density

of mercury varies slightly, depending on its source and

how it is handled (e.g., purified by multiple distillation).

The mercury used in the volume determination was

taken from a vault at NBS where it had been stored since

A. H. Cook had standardized it in 1961. Thus, its

density near 20 C was well known 24 years before it

was used. A sample of this mercury was compared to a

sample from a similar stock maintained at the Australian

national metrology laboratory, CSIRO. Within the

uncertainty of the comparison, any changes that might

have occurred during 24 years of storage were identical

at NBS and CSIRO.

Cook’s recommended data for the thermal expansion

of mercury between Tw and 20 C was used; however,

the uncertainty of the thermal expansion data was the

largest contributor to the uncertainty of the volume.

(See Table 1.) Several years later, Moldover and several

colleagues showed that the thermal expansion of the

spherical cavity, as deduced from microwave resonances

within it, was consistent with that deduced from

mercury dilatometery.

341
Two complete volume determinations were made in

September 1985 and a third was made in April 1986.

The standard deviation of their mean was 0.29 ppm. The

weighings were extraordinarily reproducible.

The measurements of the temperature T, molar mass

M, and the resonance frequencies fn , received as much

attention as the measurement of the resonator’s volume

V. Thus, it was not an accident that the uncertainties of

T, M, fn , and V were approximately equal (0.8 ppm; see

Table 1.).

After the 1988 measurement of R was completed,

Moldover and his collaborators used the resonator to

measure (T – T90), the difference between the thermodynamic temperature and ITS-90. In Fig. 3, their results

in the range 217 K to 303 K are highlighted by a solid

curve and are labeled “NIST Acoustic (1999).”

The “NIST Acoustic (1999)” data had a standard

uncertainty of 0.6 mK, which is approximately 2 ppm of

T. This uncertainty is much smaller than that of any

other method of measuring (T – T90). In Fig. 2, the

“UCL Acoustic (1994)” results were obtained by Ewing

and Trusler using a smaller, less elaborately characterized, spherical acoustic resonator. It is very reassuring

that the NIST and UCL results agree, within combined

uncertainties.

Fig. 3 implies that ITS-90 can be improved with the

help of primary acoustic thermometry. It is possible that

this will be done after primary acoustic thermometry is

extended to 800 K, perhaps in the next few years.

Mike Moldover joined the Heat Division at NBS in

1972 and began working with acoustic resonators in the

late 1970s. He has made accurate measurements of

many thermophysical properties, including density, heat

capacity, viscosity, dielectric constant, speed of sound,

surface tension, and refractive index. Many of these

measurements were made very near liquid-vapor critical

points. Moldover is now developing an atomic standard

of pressure that will require measurements of the dielectric constant of helium with part per billion uncertainties. He is a NIST Fellow and Leader of the Fluid

Science Group of the Process Measurements Division.

Martin Trusler and Terry Edwards were postdoctoral

guest researchers at NIST during the redetermination of

R. Trusler is now on the Chemical Engineering Faculty

of Imperial College in London and Edwards is now on

the Faculty of the Centre for Oil and Gas Engineering of

the University of Western Australia. Jim Mehl has maintained a strong collaboration with NBS/NIST since

1979. During this interval he has been a Professor of

Physics, Department Chair, and Associate Dean at the

University of Delaware. Now retired from Deleware,

Jim continues to collaborate with the NIST group. Rich

Davis was a physicist in the Length and Mass Division

of NIST. He is now Head of the Mass Section at the

BIPM in Sevres, France.

Prepared by Michael R. Moldover.

Table 1. Relative standard uncertainties in parts per million from

various sources in the redetermination of R

(Volume)2/3

Density of mercury at 20 C 0.28

Storage and handling of mercury 0.20

Thermal expansion of mercury (0 C to 20 C) 0.67

Random error of volume determination 0.20

from weighings

Temperature

Random error of calibrations 0.8

Temperature gradient 0.4

Molar Mass

40Ar standard 0.7

Comparison of commercial argon to 40Ar 0.26

Zero-pressure limit of (fn /zn )

2

Standard deviation of u0

2 from 70 observations

(at 14 pressures) 0.68

Thermal boundary-layer correction 0.30

Possible error in positions of transducers 0.55

Square root of the sum of the squares 1.7

Fig. 3. Comparison of the Kelvin thermodynamic temperature T and

the International Temperature Scale of 1990 T90. The “NIST Acoustic

(1999)” data were obtained using the gas-constant resonator.

342
Bibliography

[1] M. R. Moldover, J. P. M. Trusler, T. J. Edwards, J. B. Mehl, and

R. S. Davis, Measurement of the universal gas constant R using

a spherical acoustic resonator, J. Res. Natl. Bur. Stand. 93, 85-144

(1988).

[2] Michael R. Moldover, Meyer Waxman, and Martin Greenspan,

Spherical acoustic resonators for temperature and thermophysical

property measurements, High Temp. High Pressures 11, 75-86

(1979).

[3] M. R. Moldover, S. J. Boyes, C. W. Meyer, and A. R. H. Goodwin,

Thermodynamic temperatures of the triple points of mercury

and gallium and in the interval 217 K to 303 K, J. Res. Natl. Inst.

Stand. Technol. 104, 11-46 (1999).

[4] Michael R. Moldover, James B. Mehl, and Martin Greenspan,

Gas-filled spherical resonators: Theory and experiment,

J. Acoust. Soc. Am. 79, 253-272 (1986).

[5] James B. Mehl and Michael R. Moldover, Measurement of the

ratio of the speed of sound to the speed of light, Phys. Rev. A 34,

3341-3344 (1986).

343
Thermal and Oxidative Degradation

of Polymers

In recent decades synthetic polymeric materials, because of their unique physical properties, have rapidly

replaced more traditional materials such as steel and

nonferrous metals, as well as natural polymeric materials such as wood, cotton, and natural rubber. However,

one weak aspect of synthetic polymeric materials compared with steel and other metals is that these materials

are combustible under certain conditions. Thus the majority of polymer-containing end products (for example,

cables, TV sets, electric appliances, carpets, furniture)

must pass some type of regulatory test to help ensure

public safety from fire. However, traditional pass/fail

tests have not provided any information regarding the

relationship between flammability properties and the

physical and chemical characteristics of polymeric materials. Such information is needed to develop more

fire-safe materials, a need that has accelerated because

of European environmental concerns about the use of

halogenated flame retardants (because of potential formation of dioxins in the incineration of spent end products). The paper Effects of Weak Linkages on the Thermal and Oxidative Degradation of Poly(methyl

methacrylate) [1] is one of a series published on this

topic by the members of the Materials Fire Research

Group at NBS/NIST from 1985 to 1994 [2-11]. These

papers report a new approach that studies the effects of

molecular-level structure of polymers on their thermal

stability and flammability properties instead of a traditional global thermal-balance approach. This series of

studies is built upon the pioneering work on thermal

degradation of polymers conducted at NBS from the late

1940s to early 1970s [12].

Providing the technical basis for industrial clients to

design less flammable materials requires unfolding the

structural features that determine thermal stability. This

paper [1] reports a study of the thermal and oxidative

degradation mechanisms of an acrylic polymer in atmospheres of nitrogen and air by measuring the change in

the sample mass while various specially polymerized

samples were heated from 80 C to 480 C. Thermal

degradation of the acrylic polymer, polymerized using a

free-radical method, proceeds in three steps of mass

loss: the first and easiest (scheme 1 in Fig. 1) is initiated by scissions of head-to-head linkages at about

160 C (representing one type of defect at the polymer

backbone); the second (scheme 2) by scissions

at the chain-end initiation from vinylidene ends

at around 270 C; and the last (scheme 3) by random

scission within the polymer chain (at the weakest

bonds).

Fig. 1. Three chain scission steps leading to thermal degradation in acrylic polymers.

344
The first two mass loss steps were not observed with

ionically polymerized samples, which indicates that the

first two steps are caused by the defects in the polymer.

Although the existence of head-to-head linkages could

not be demonstrated, the vinylidene ends in the polymer

were detected by the 1H NMR spectrum. No significant

differences were seen in the thermal or oxidative

degradation of the acrylic polymer when it was polymerized with the free-radical method using two common initiators. It was found that gas-phase oxygen traps

polymer radicals resulting from chain scissions at

head-to-head linkages, and no mass loss was observed

from this step in air. Similarly, oxygen traps radicals

generated by end initiation, but mass loss is only

delayed to slightly higher temperatures, presumably

because of a slight gain in the thermal stability of the

oxygen-trapped polymers compared with end initiation.

This series of studies involved not only experimental

observations, but also theoretical calculations in which

kinetics equations were solved for each polymer chain.

Detailed thermal degradation models were developed

based on random initiation, depropagation of free

radicals, and termination of free radicals; calculations

were made with the assumption of steady-state free

radical concentration [4], and without that assumption

[5]. The kinetic rate constants for each reaction were

derived by comparing experimentally measured

molecular weights of polymer samples collected at

various temperatures and exposure times with the

theoretically calculated results [6]. The final paper of

the series on thermal degradation investigated the

behavior of primary radicals generated from random

scissions by measuring evolved degradation products

with a mass spectrometer [9].

The influence on thermal stability by the abovediscussed defects in the polymer have been studied and

published [7,8,10]. The results show that a higher

thermal stability increases piloted-ignition delay time

and gasification rate of the polymer, but initial

molecular weight does not affect ignition delay time.

On the other hand, initial molecular weight of the

polymer has significant effect on flame spread rate

because low molecular weight materials will flow more

readily when heated. The physical and chemical roles

of the condensed phase in the burning process of polymeric materials were published as a summary of this

series of studies [11].

The molecular-level study of the thermal degradation

and flammability properties of polymers described

above was pursued further by Marc Nyden and coworkers at NIST. They used molecular dynamic simulations

of thermal degradation of polyethylene to identify

factors that might be effective in reducing polymer

flammability by promoting the formation of residual

char [13]. The results predicted that the formation of

cross-linking, for example by exposure of polyethylene

to ionizing radiation, enhanced further cross-linking

when the polymer is burned. An increase in ignition

delay time was observed for irradiated polyethylene

samples compared to unexposed samples. A similar

approach has been pursued by Charles Wilkie at

Marquette University, Richard Lyon at the FAA

Technical Center, and James McGrath at Virginia

Polytechnic Institute and State University.

Because of the increasing demand for non-halogenated flame retardant additives for polymeric end

products, this molecular-level study has been extended

to include flame retardant mechanisms of polymers

containing small quantities of inorganic flame retardant

additives. As a result of advances in nanoscale science

and technology, molecular-level studies of the effects of

trace additives in clay-polymer nano-composites are

demonstrating enhanced physical properties with simultaneous improvements in the flammability properties of

polymers. This contrasts with the traditional approach,

which improves the flammability but often degrades

mechanical properties.

The study described in this paper involved the synthesis of specific polymers, analytical characterization of

the synthesized polymers, and careful thermogravimetric analysis. Two different groups, the Materials

Fire Research Group at NIST and Department of

Chemistry at Osaka University, contributed their own

expertise to this highly collaborative undertaking. The

group at Osaka University synthesized and characterized all polymer samples used in the study, while the

group at NIST performed the thermogravimetric

analyses.

Takashi Kashiwagi joined NBS in 1971 after he

received his Ph.D. from Princeton University. He was a

group leader from 1988 to 1998 in the Fire Science

Division. He is currently a materials research engineer

working on improved fire-safe materials, as well as

studying ignition and flame spread in a microgravity

environment. He was a principal investigator of the

ignition and flame spread experiment conducted on

Space Shuttle flight STS-75.

Atsushi Inaba received his Ph.D. in chemical

engineering from Tokyo University in 1981 and was a

guest scientist at NBS from May 1984 to March 1986.

He is currently Director of the Research Planning Office

of the National Institute for Resources and Environment

in Japan.

James E. Brown joined the Polymer Division of NBS

in 1956 as a research chemist, moved to the Fire Science

Division in 1975, and retired in 1996. Koichi Hatada, a

professor in the Department of Chemistry at Osaka

University, was known internationally for his work on

345
stereoregular and living polymerization and copolymerization. He retired from Osaka University in 1998 after

serving as vice president of the University. Tatsuki

Kitayama is a professor in the Chemistry Department of

Osaka University. Eiji Masuda was a student under

Prof. Hatada and is currently a senior research scientist

at Polyplastics Co. in Japan.

Prepared by Takashi Kashiwagi.

Bibliography

[1] Takashi Kashiwagi, Atsushi Inaba, James E. Brown, Koichi

Hatada, Tatsuki Kitayama, and Eiji Masuda, Effects of Weak

Linkages on the Thermal and Oxidative Degradation of

Poly(methyl methacrylates), Macromolecules 19, 2160-2168

(1986).

[2] Takashi Kashiwagi, T. Hirata, and J. E. Brown, Thermal and

Oxidative Degradation of Poly(methyl methacrylate): Molecular

Weight, Macromolecules 18, 131-138 (1985).

[3] Toshimi Hirata, Takashi Kashiwagi, and James E. Brown,

Thermal and Oxidative Degradation of Poly(methyl methacrylate): Weight Loss, Macromolecules 18, 1410-1418 (1985).

[4] Atsushi Inaba and Takashi Kashiwagi, A Calculation of

Thermal Degradation Initiated by Random Scission. 1. SteadyState Radical Concentration, Macromolecules 19, 2412-2419

(1986).

[5] Atsushi Inaba and Takashi Kashiwagi, A Calculation of

Thermal Degradation Initiated by Random Scission, Unsteady

Radical Concentration, Eur. Polym. J. 23, 871-881 (1987).

[6] Atsushi Inaba, Takashi Kashiwagi, and James E. Brown, Effects

of Initial Molecular Weight on Thermal Degradation of

Poly(methyl methacrylate): Part 1—Model 1, Polym. Degrad.

Stab. 21, 1-20 (1988).

[7] T. Kashiwagi and A. Omori, Effects of Thermal Stability and

Melt Viscosity of Thermoplastics on Piloted Ignition, in TwentySecond Symposium (International) on Combustion: At the

University of Washington, Seattle, Washington, August 14-19,

1988, The Combustion Institute, Pittsburgh, PA (1988) pp. 1329-

1338.

[8] T. Kashiwagi, A. Omori, and J. E. Brown, Effects of Material

Characteristics on Flame Spreading, in Fire Safety

Science—Proceedings of the Second International Symposium, Hemisphere Publishing Corp., New York (1989)

pp. 107-117.

[9] Takashi Kashiwagi, Atsushi Inabi, and Anthony Hamins, Behavior of Primary Radicals during Thermal Degradation of

Poly(Methyl Methacrylate), Polym. Degrad. Stab. 26, 161-184

(1989).

[10] Takashi Kashiwagi, Atsumi Omori, and Hidesaburo Nanbu,

Effects of Melt Viscosity and Thermal Stability on Polymer

Gasification, Combust. Flame 81, 188201 (1990).

[11] T. Kashiwagi, Polymer Combustion and Flammability—Role of

the Condensed Phase, in Twenty-Fifth Symposium (International) on Combustion: At the University of California, Irvine,

California, July 31-August 5, 1994, The Combustion Institute,

Pittsburgh, PA (1994) pp. 1423-1437.

[12] S. L. Madorsky, Thermal Degradation of Organic Polymers,

Interscience Publishers, New York (1964).

[13] Marc R. Nyden, Glenn P. Forney, and James E. Brown, Molecular Modeling of Polymer Flammability: Application to the

Design of Flame-Resistant Polyethylene, Macromolecules 25,

1658-1666 (1992).

346
HAZARD I: Software for Fire Hazard

Assessment

NIST Handbook 146, HAZARD I—Fire Hazard

Assessment Method [1], represents the culmination of a

long-term program aimed at placing the prediction of

fire outcomes on an objective and scientific basis. In the

1970s, NIST supported Harvard University to develop

numerical models that could predict the temperature

in a room containing a fire. These early models were

difficult to use and interpret; required large, mainframe

computers that were available only in academic institutions; and were plagued with long execution times, often

interrupted by software crashes. Major pieces of fire

physics and most fire chemistry were not well enough

understood to be included in the models, so that predictive accuracy was disappointing. As a result, these early

models were little more than academic playthings which

were seldom put to practical use.

In 1983, NIST’s fire program established a goal to

develop a tool that could evaluate the role of the fire

performance of an individual material or product in the

outcome of a specific fire in a specific compartment or

group of compartments. The first year of the project

was devoted to determining the capabilities needed to

accomplish this, and the effort was somewhat daunting.

Not only would it be necessary to predict the fire environment in the space resulting from the material or

product burning, but it would also require understanding

the movement and behavior of occupants and the

physiological and psychological effects of exposure to

this fire.

Since the project started before the personal computer revolution, the initial plan was to develop the

software to run on NIST’s mainframe and to equip a

“fire simulation laboratory” at NIST with terminals and

graphics equipment so that scientists and engineers

could learn how to use the software to address practical

problems. Once the usefulness of these models were

appreciated, the larger engineering firms were expected

to invest in the hardware needed to exploit the technology. It was expected that these firms would have the

computers to run the software in their own offices by

the end of the century.

By 1986 the NIST multi-compartment model, FAST

(Fire and Smoke Transport) [2] had been enhanced so

that its predictions were credible when applied within

specific bounds. NIST’s pioneering development of

oxygen consumption calorimetry provided a means

to measure the rate at which mass and energy were

released from a burning item. By expressing a material’s

fire performance in terms of conserved quantities, it was

possible to describe burning behavior for a predictive

model. A NIST psychologist was developing a unique

evacuation model with embedded behavioral rules

derived from interviews with fire victims. Finally, the

NIST combustion toxicology program was producing

data that showed toxicological effects were primarily

from a small number of toxic species.

Also at this time, the personal computer revolution

was well underway. It became clear that a computer on

every desktop would soon be a reality, so the NIST

software was now targeted at that group of users. Efforts

were expended on an improved user interface that would

both simplify data entry at the front end and provide

graphical output support to make the results more

understandable and useful at the back end.

The first version of the HAZARD I software and

documentation [1] was released in 1989. The software

was clearly focused on material and product manufacturers as a tool to assess the fire hazards of their products and a means to justify higher costs associated with

better performing products. However, the manufacturers

were underwhelmed because the methods required skill

to apply and were unproven.

Several factors soon began to change perceptions of

the potential of HAZARD I. There was political pressure

to regulate combustion toxicity, with one state actually

promulgating a regulation. NIST produced a fire hazard

analysis that showed burning rate was much more

important as an indicator of fire hazard than toxicity.

In addition, a well respected fire protection engineer

became interested in learning these new techniques and

successfully applied HAZARD I to absolve clients of

liability in civil litigation involving a fire. This led to

additional uses in both civil and criminal litigation and

represented the first significant application of modern

fire models.

The publication of NIST Handbook 146 was a watershed for NIST in several ways. While NIST had developed and distributed other software products (such as

DATAPLOT, a scientific graphing package), HAZARD I

was an engineering analysis tool that could be used to

make (literally) life and death decisions. It contained a

broad range of engineering and scientific methodology

that needed to be appropriately documented. Documentation consisted of a Technical Reference Guide which

underpins the equations and assumptions and explains

how they are coded, a set of worked examples, and a

347
Users’ Guide to the software. The product was packaged as a commercial product with printed binders for

the manuals, shrink wrapped disks with the software

and installation program, and even a printed function key

template. This Handbook received special scrutiny on

technical, policy, and legal fronts and was the model for

most NIST software to follow.

The HAZARD I product was distributed under a

formal agreement with the National Fire Protection

Association (NFPA), a not-for-profit standards organization. They offered for purchase an initial package,

upgrades when issued by NIST, and discounts for their

members. Over a decade they sold several thousand

copies.

One interesting aspect of this development relates to

the exclusion of government-developed software from

copyright. Since the software is in the public domain,

users are legally unencumbered by the cautions in the

documentation. A solution was found by including a

users’ registration card to be signed, dated, and returned

in order to qualify for technical support. The signature

on the card was below a statement that the signer read

and agreed to the limitations in the documentation—

thus creating a contractual agreement. Later, a Government Accounting Office study of the copyright policy

that applies to government software cited two specific

examples of critical government software that should

have copyright protection—Grateful Med from the

National Library of Medicine and HAZARD I. Several

legislative proposals on this issue were considered, but

never adopted.

By 1990, successes in litigation led the fire protection

engineering community to begin to use HAZARD I

in building design. While building codes prescribed the

minimum required fire safety features of buildings,

they also contained a provision recognizing alternative approaches that can be shown to provide

equivalent protection. Demonstrating this equivalence

to regulatory authorities was always the difficult

part. Now HAZARD I could be used to show equivalence in safety to occupants rather than having to

prove that an alternative approach performed the same

function.

The acceptance of HAZARD I in demonstrating code

equivalence led to a global revolution in building codes.

It became possible for codes to specify only the desired

outcomes in terms of life safety and property protection

and to allow any solutions that provided that level of

performance. Such performance-based codes had long

been discussed, but were impractical until means were

available to measure fire safety performance quantitatively. The U.S. building regulatory community began

work on a performance code in 1996 that is expected to

be published in 2000. As similar codes are developed

and adopted in other countries, they are eliminating

non-tariff barriers to trade that result from unique testmethods that are being replaced by nearly uniform performance objectives. HAZARD I and its components are

Fig. 1. The HAZARD I software and documentation package.

348
specifically cited in most of these codes and supporting

guidelines documents as an acceptable means of demonstrating compliance with the codes.

HAZARD I included several technological advances

that were crucial to its acceptance in practice. First, the

fire model, FAST, was more robust and easier to use

because of a significant investment in the user interface

software. There were embedded databases of material

properties, and additional references to data were cited.

One of the criteria used by the development team was to

require as inputs only data that are available and to cite

sources for everything. Many other models of the time

used engineering estimates that required coefficients to

be entered by the user based solely on judgment rather

than properties for which measurement methods and

handbook values existed.

The equation solver used was carefully selected to

work efficiently and seldom failed to converge. The

software could be run interactively (with real-time

graphics) for exploratory purposes or in batch mode to

generate case files or for sensitivity analysis in engineering applications.

The FAST model predictions were compared to a

range of full-scale experimental data and these comparisons were published to form a body of verification literature. Further, a suite of test cases stressed the model in

different ways to see if it would fail. This test suite was

run each time the model was modified. Computer Aided

Software Engineering (CASE) tools were used to document changes to the model and to allow changes to be

reversed if necessary. Each revision of the software was

backward compatible so that users would not have to

work excessively to re-run older cases, and the effect

of changes was documented. Each of these aspects

followed good (commercial) software development

practice.

The EXITT (for Exit Time) [3] evacuation model

differed from most of its contemporaries in the inclusion

of a behavioral module. Other evacuation models of the

day had everyone making the correct decisions and,

while some allowed for user-selected decision delays,

people marched quickly toward the exits. In HAZARD I,

people investigated the fire until seeing smoke or flame,

assisted other family members, or even (children) hid or

waited for instructions from an adult. The result was an

amazingly realistic sequence of actions and an evacuation process that convinced users and authorities of its

applicability.

The toxicology module TENAB (for Tenability) [1]

was, and still is, the only attempt to model physiological

effects of the inhalation of a mixture of toxic gases.

Based on correlations to data from animal exposures, but

with an implementation that mimics important physiological interactions, the model produced results that

aligned well with actual fire experience. In one case,

HAZARD I successfully predicted the development of

the fire, including a prediction of which occupants

successfully escaped and which died, including the

location of the bodies and the autopsy results on each.

This particular case involved NIST using HAZARD I to

support a Justice Department attorney to defend the

federal government in a wrongful death suit from a fire

on a military base. The final analysis indicated no fault

by the government, and the day following the deposition

of the NIST staff, the plaintiff’s counsel offered to settle

this $26.5 million suit for $180 thousand.

NIST’s pioneering work to develop engineering tools

to predict fire performance in buildings, and especially

the HAZARD I methodology, represented the enabling

technology for the move to performance-based building

and fire codes which are being adopted globally. The

methods and models included in HAZARD I are

routinely cited in these performance-based codes and in

their associated codes of practice, worldwide. These

performance methods are reducing the costs of fire

safety and are eliminating non-tariff barriers to trade for

U.S. companies.

Prepared by Richard Bukowski.

Bibliography

[1] Richard W. Bukowski, Richard D. Peacock, Walter W. Jones, and

C. Lynn Forney, HAZARD I—Fire Hazard Assessment Method,

NIST Handbook 146, National Institute of Standards and Technology, Gaithersburg, MD (1989).

[2] Walter W. Jones, A Model for the Transport of Fire, Smoke, and

Toxic Gases (FAST), NBS Internal Report 84-2934, National

Bureau of Standards, Gaithersburg, MD (1984).

[3] Bernard M. Levin, EXITT—A Simulation Model of Occupant

Decisions and Actions in Residential Fires: Users Guide and

Program Description, NBS Internal Report 87-3591, National

Bureau of Standards, Gaithersburg, MD (1987).

349
Analysis of the Catastrophic Rupture of a

Pressure Vessel

On July 23, 1984, an explosion followed by a fire

occurred at a petroleum refinery in Chicago, killing 17

people and causing extensive property damage [1].

NBS was requested by the Occupational Safety and

Health Administration (OSHA) to conduct an investigation into the failure of the pressure vessel that eyewitnesses identified as the initial source of the explosion and fire. This vessel was an amine absorber tower

used to strip hydrogen sulfide from a process stream of

propane and butane. The vessel was 18.8 m tall, 2.6 m

in diameter, and constructed from 25 mm thick plates of

type ASTM A516 Grade 70 steel.

The investigation was complicated by the damage

caused by the explosion and fire. The explosive force

had been sufficient to propel the upper 14 m of the

vessel a distance of 1 km from its original location,

while the base remained at the center of the subsequent

fire.

Sections of the vessel were shipped to NBS in August

1985, where a multi-disciplinary team sought the cause

of the failure. The team was led by Harry McHenry,

who was the Deputy Chief of the Fracture and

Deformation Division and a leading expert in fracture

mechanics. The study eventually involved 23 staff

members from three different Divisions from both the

Boulder and Gaithersburg laboratories of NBS.

The investigation that followed was a diagnostic

masterpiece pursued with textbook elegance and

deliberation. After documenting the history of the

vessel prior to its rupture, testing of the vessel segments

began with nondestructive evaluation techniques.

Magnetic particle inspection was applied to reveal

hundreds of cracks confined mainly to the inner

surfaces along the welds between Courses 1 and 2 of

the vessel and between Courses 2 and 3. Ultrasonic

measurements subsequently detected clear indications

of delamination damage confined to Course 1. However, thickness measurements, made with a micrometer,

showed that Courses 1 and 2 had wall thicknesses well

within the prevailing allowances for pressure vessels.

More aggressive measurements were then undertaken to examine the mechanical and chemical characteristics of the initial and replacement components. Test

after test showed that all initial and replacement components satisfied the industry standard specifications. The

cause of failure did not become clear until metallography results were combined with stress corrosion

cracking and hydrogen embrittlement tests, followed by

a fracture mechanics analysis. It appeared that a preexisting crack had extended through more than 90 % of

the wall thickness and was about 800 mm in length.

Further, it was determined that hydrogen embrittlement

had reduced the fracture resistance of the steel by

more than half. After approximately 6 months of

investigation, the findings were published as NBSIR

86-3049 [1].

Fig. 1. Schematic of the original pressure vessel consisting of a series

of sections know as Courses.

350
The vessel had been put into service in 1970 and had

undergone several repairs and modifications before the

July 1984 incident. The failure investigation determined

that the vessel fractured along a path that was weakened

by extensive cracking adjacent to a repair weld joining

a replacement section to the original vessel. These preexisting cracks initiated in areas of hard microstructure

known to be susceptible to hydrogen stress cracking.

This hard microstructure formed during the repair

welding of the replacement section. The cracks grew

through the vessel wall as a result of hydrogen pressure

cracking. When the depth of the largest of these preexisting cracks exceeded 90 % to 95 % of the wall

thickness, the remaining thin ligament of steel in the

cracked section ruptured and leakage occurred. This

crack triggered a complete fracture of the vessel circumference at the operating stress level of only 35 MPa

(roughly 10 % of the rated strength of the steel) because

the toughness of the vessel steel had been reduced by

hydrogen embrittlement.

Fig. 2. The pressure vessel ruptured adjacent to the repair weld joining Courses 1 and 2.

351
The NBS publication pointed out previously unrecognized interactions between pressure vessel steel, the

thermal cycles that occur during repair welds, and

hydrogen-containing environments. Rapid dissemination of this information was important because many

other vessels in the petrochemical and chemical processing industries might have had histories with a

similar combination of these factors, and so might also

be at risk of a similar catastrophic failure. In late 1986,

the findings of the report were summarized in articles

published in Corrosion Science [2] and Materials

Performance [3], journals which were widely read by

industrial process engineers and safety officials in these

industries.

OSHA recognized the technical complexities involved

in assessing the mechanical integrity of the various

items of equipment used in process industries such as

petroleum refineries and petrochemical manufacturing.

To provide the OSHA inspectors and regulators with

necessary technical information regarding the design

and construction and related factors affecting the

integrity of process equipment, OSHA engaged NIST to

perform two additional tasks:

(1) Prepare an information document titled: “Guidelines for Pressure Vessel Safety Assessment” for

distribution within OSHA, and

(2) Organize and conduct a training course (Course

340, Hazard Analysis in the Chemical Processing

Industries) for OSHA inspectors, with informative

lectures concerning pressurized equipment. The

first course was taught at NBS (Boulder) in 1988.

The publication of the findings in Corrosion Science

[2] and Materials Performance [3] allowed industrial

process engineers and inspection personnel to update

the inspection plans for plants under their control. Now

that they were aware of the conditions found in this

study, the inspection personnel could search for similar

problems (such as hydrogen blisters and cracks) during

the next annual or biennial shutdowns of processing

plants under their control, and inspection intervals could

be adjusted accordingly.

Several years following the failure incident and the

NBS/NIST report, OSHA issued a final rule titled

“Process Safety Management of Highly Hazardous

Chemicals, Explosives and Blasting Agents.” This rule

was published as 29CFR Part 1910 in the Federal

Register on February 24, 1991, and became effective on

May 26, 1992. The rules have had a major impact on the

process industry, particularly those parts that indicated,

for example, that inspection and testing procedures to

assess the mechanical integrity of process equipment

shall follow recognized and generally good engineering

practices. These rules have prompted cooperatively

funded activities in the process and allied industry

sectors which focus on the preparation of technical

documents that describe and define methodology,

procedures, and techniques that constitutes “recognized

and good engineering practices.” The first document

developed in this activity was expected to be completed

and available in early 2000.

Meanwhile, the OSHA training center has continued

to offer the NBS-developed training course on hazard

analysis to its inspectors. So far, the course has been

held 11 times, and about 230 inspectors have attended it.

Harry McHenry retired in 1999 as the Chief of the

Materials Reliability Division (the successor to the

Fracture and Deformation Division). Bob Shives retired

from the Metallurgy Division in 1992, but continues as

a Guest Researcher, working on hardness standards.

David Read continues as a Physicist in the Materials

Reliability Division and is now studying the mechanical

behavior of thin films. David McColskey continues as a

Physical Scientist in the Materials Reliability Division

and is now studying acoustic emission and the behavior

of thin films. Charles Brady retired from the Metallurgy

Division in 1988, and Patrick Purtscher left NIST in

1999 to become an Engineer with the Portsmouth Naval

Yard in Portsmouth, New Hampshire.

Prepared by Tom Siewert.

Bibliography

[1] Harry I. McHenry, T. Robert Shives, David T. Read, J. David

McColskey, Charles H. Brady, and Patrick T. Purtscher, Examination of a Pressure Vessel that Ruptured at the Chicago Refinery

of the Union Oil Company on July 23, 1984, NBSIR 86-3049,

National Bureau of Standards, Boulder, Colorado (1986).

[2] H. I. McHenry, P. T. Purtscher, and T. R. Shives, Observations of

Hydrogen Damage in a Failed Pressure Vessel, Corros. Sci. 27,

1041-1057 (1987).

[3] H. I. McHenry, D. T. Read, and T. R. Shives, Failure Analysis of

an Amine-Absorber Pressure Vessel, Mater. Perform. 26 (8),

18-24 (1987).

352
Curing Those Uncontrollable Fits

of Interaction

Expect: Curing Those Uncontrollable Fits of Interaction [1] was the seminal paper on Expect, a software

tool for automation of other software. The Expect software itself was a solution to a long-standing problem:

how to automate software designed to be operated by a

human. There are very good reasons for automating

software. An obvious one is testing— if a piece of software only works when a human is interacting with it,

testing it is very expensive. Another problem is that

humans are rather “ unreliable.” Repeating an interaction

for the 10th time, people won’t be paying nearly as

much attention as they might have on the first and

second times.

Many software applications have control languages,

preferences, settings, and other mechanisms for providing automated control. Macros are just one modern example of such programmability. However, before Expect

each application used a different such language, if any.

This meant that users had to learn lots of languages, one

for each application. And in many cases, languages

were quite limited or totally nonexistent.

Passwords were just one example. Many programs

had all sorts of similarly useless requirements for

manual operation. Part of the problem arose from

software reuse, often in unexpected ways. One of the

hallmarks of any long-lived software is its application in

Expect combined several ideas. The first was a

general purpose control language. No more would

people have to learn a new language for every application. The second idea was providing an effective

simulation of a human pressing keys at a keyboard.

Surprisingly, many programs are quite sensitive to

whether a human is there or not— and understandably.

For instance, a program intended to accept passwords

doesn’t want people scripting them since there is a loss

in security because embedded passwords are readable

by others. Such programs go out of their way to prevent

automation. Not surprisingly, many programs could

be entirely automated— except for their passwords.

But even if the programs were used in secure settings,

the programs offered no way of bypassing this manual

step.

Perhaps entering a single password doesn’t sound

time consuming. But imagine creating passwords each

semester for fifty thousand students. Or logging in

(including entering passwords) to configure several

hundred network routers. Or test them. And so on.

all sorts of ways unenvisioned by its authors. A good

example of this was Expect’s earliest application— in the

construction at NBS of a semi-automated factory [2].

This factory was constructed of dozens of one-of-a-kind

pieces of hardware and lots of software. Much of the

353
associated software had been written in the context of

separate projects, which made perfect sense at the time.

It was hard enough to design and develop a robot at all,

much less to design and develop a robot that worked in

a complex factory. Expect was used as a kind of glue

that integrated many of the pieces together. It wasn’t a

network or a communications protocol, but merely

plugged the many assorted holes that the Automated

Manufacturing Research Facility software designers

had written in for themselves.

At the prestigious 1990 Summer Usenix conference

in Anaheim, California, this paper announced the development of the Expect software to a world that was ripe

for such automation software. The paper not only

described how Expect solved the general problem but it

included a dozen classes of software problems that were

solved by Expect in order to make sure that readers

could walk away with ideas for immediate application to

their own environment.

Publication of the paper spurred use of Expect

dramatically; NBS saw downloads of Expect hit 4000 in

its first year. The bulk of these downloads were .com

and .edu sites, but also included 90 U. S. military sites

and 170 U. S. federal sites. Two years later, downloads

were in the hundreds of thousands of sites, aided

by other users making Expect available on network

gateways in Australia, Netherlands, Germany, Japan and

other countries. Now Expect is bundled with many CD

and DVD software distributions and vendor-supplied

operating system releases.

Ultimately, the Curing paper [1] became a base upon

which further exploration and development occurred.

Hundreds of other papers, as well as textbooks, graduate

theses, technical courses, and other writings followed,

each describing Expect as an essential element of

various research projects as well as crucial in day-to-day

operations. A sampling of Expect’s published uses

include quality assurance, network measurements,

automated file transfers and updates, tape backups,

automated queries to multiple heterogenous online

databases, computer security sweeps, network router/

bridge/repeater/server configurations, test instrument

simulation, account administration, stock price retrieval,

500-user simulation, control of unreliable processes,

and library management.

Subsequent to the original development of Expect,

additional work at NIST continued, including innovative

ideas such as automatically generating control systems

by watching real interactions (Autoexpect) and wrapping legacy line-oriented systems with modern GUIs

without any change to the underlying application

(Expectk).

354
As the figure suggests, the Autoexpect paper had a

strange but accurate title. The full title was How to

Avoid Learning Expector—Automating Automating

Interactive Programs [3]. As with the Curing title,

Because of its odd typography, the Writing a Tcl

Extension paper was almost impossible to cite correctly,

but nonetheless was given the Best Paper Award at the

conference where it was presented.

The final development of the Curing paper was the

publication of the book Exploring Expect [4]. Not surprisingly, the book contains significant novel material

many of the Expect papers and topics used humor as a

very effective writing technique. Perhaps the most

amusing title was applied to a retrospective paper on

Expect titled:

in its 602 pages. Yet despite being a comprehensive

tome, its origins can clearly be traced back to the

Curing paper. The book appeared in numerous

Best Books of the Year lists and has now become

the normative reference, superseding the Curing

paper as the standard citation for the Expect technology.

355
The paper and book were written by Don Libes, a

computer scientist at NBS/NIST. He has written

approximately 100 computer science papers and articles

plus several textbooks. Besides Exploring Expect, he

also wrote two classics in the UNIX literature: Life With

UNIX [5] and Obfuscated C and Other Mysteries [6].

Recognition of Expect and the related papers is also

demonstrated by various non-government awards that

Don earned, including the Award for Excellence in

Technology Transfer, Federal Laboratory Consortium

(1998), two Best Presentation Awards, USENIX Association (1996, 1997), Best Paper Award, USENIX Association (1997), Federal 100 Award, FOSE & FCW (1993),

Innovation Award, International Communications

Association (1992), and Tcl Achievement Award, Tcl

Consortium (2000).

Prepared by Don Libes.

Bibliography

[1] D. Libes, expect: Curing Those Uncontrollable Fits of Interaction,

in Proceedings of the Summer 1990 USENIX Conference,

Anaheim, CA, June 11-15, 1990, (http://expect.nist.gov/doc

/seminal.pdf).

[2] C. Furlani, E. Kent, H. Bloom, and C. Mclean, Automated

Manufacturing Research Facility of the National Bureau of

Standards, in Proceedings of the 1983 Summer Computer

Simulation Conference, Vancouver, BC, Canada, July 11-13,

1983.

[3] Don Libes, How to Avoid Learning Expect— or— Automating

Automating Interactive Programs, in Proceedings of the Tenth

USENIX System Administration Conference (LISA X), Chicago,

IL, September 30— October 4, 1996, (http://expect.nist.gov/doc/

autoexpect.pdf).

[4] Don Libes, Exploring Expect: A Tcl-Based Toolkit for Automating Interactive Programs, O’Reilly & Associates, Inc., Sebastopol,

CA (1995), (http://www.oreilly.com/catalog/expect).

[5] Don Libes and Sandy Ressler, Life With UNIX: A Guide for

Everyone, Prentice Hall, Englewood Cliffs, NJ (1989).

[6] Don Libes, Obfuscated C and Other Mysteries, John Wiley and

Sons, New York (1993).

356
Baldrige Criteria for Performance Excellence

In the 1980s, there was a growing realization by many

business analysts and consumers that the quality of U.S.

products and services was falling behind that of other

leading nations, especially Japan. Some industry and

government leaders saw the need for an emphasis on

quality as a necessity for doing business in an ever

expanding, and more demanding, global market. Many

American businesses either did not understand the

quality problem or did not know where to begin. Some

U.S. business leaders, noting the success of the Deming

Prize in improving the quality of Japan’s products,

suggested that a U.S. quality award might create an

incentive for quality improvement and a basis for

sharing information on successful quality strategies.

A difficult choice for a U.S. award was whether it

should be managed by a private or government entity.

Some argued that only those directly experienced in

business could provide the needed understanding.

Others believed that only a Presidential Award could

bring the needed national visibility and recognition. The

final decision was to utilize the strengths of both

sectors. The pending legislation called for a publicprivate partnership in which each sector plays a crucial

role. In August 1987 Congress enacted legislation

establishing the Malcolm Baldrige National Quality

Award and assigned overall management of the Award to

the National Bureau of Standards (soon to become

the National Institute of Standards and Technology).

Congress selected NBS/NIST to design and manage the

Award program because of its role in helping U.S.

companies compete, its world renowned expertise in

measurement quality and quality assurance practices,

and its reputation as an impartial third party. NIST

worked with key private sector leaders to create a private

organization, the Foundation for the Malcolm Baldrige

National Quality Award. In 1988, the Foundation raised

$10M to support the purposes of the Award.

Congress named the award in honor of Malcolm

Baldrige, Secretary of Commerce during the period

when the legislation was developed. Just prior to the

enactment of the legislation, Mr. Baldrige died after a

rodeo accident. This naming was in recognition of the

efforts of Secretary Baldrige to strengthen U.S. competitiveness. The Award is the country’s highest level of

recognition for performance excellence and has been

presented annually by the President since 1988.

The intent of the Award is to recognize U.S. companies for their achievements in quality and business

performance and to raise awareness about the importance of quality and performance excellence as a

competitive edge. It was envisioned that the Award

would serve as a standard of excellence to aid U.S.

companies in achieving world-class quality. Rather than

recognize specific products or services, the Award

Program would recognize role-model business practices

and emphasize the sharing of best practices. Three

Award categories were initially permitted: manufacturing, service, and small business.

A key step in implementing the new Law was developing the criteria for the Award. In late 1987, NBS/

NIST created the basic criteria concept and category

structure as well as the basis for a multi-stage evaluation.

In parallel with this Award design, a network of private

sector experts was created to implement and expand the

design and to serve as evaluators. A design feature of the

Award Program was the commitment to annual revision

of the criteria to reflect key learnings and changing

business needs. The first Award Criteria were published

in the Application Guidelines for the Malcolm Baldrige

National Quality Award in1988. [1]

Although the criteria were needed to serve as a basis

for making Awards, their use was intended mainly for

organizational self-assessment and improvement. The

1988 Application Guidelines included Award Criteria

based upon seven evaluation Categories. Each Category

consisted of two or more Examination Items, which

serve as the basis for Awards and for self-assessment.

The Award Criteria represented a major new vehicle for

the United States to define best quality practices and to

disseminate practices more quickly using an approach

that permits self-diagnosis. Thus the Criteria serve as

the focal point in education and cooperation, going

beyond the requirements of the Award contest, via a kind

of excellence standard.

The Criteria take a systems approach to organizational excellence. They incorporate a set of core values

and concepts that reflect beliefs and behaviors found in

high performing organizations. The Criteria are expressed as operational requirements, including key

processes and measures that connect processes to comprehensive business results. The business results include

not only financial and market results, but also product

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and service quality, public responsibility, employee

development, and other key requirements. Accordingly,

the Criteria provide a common language for businesses— large and small, manufacturing and service. A

key characteristic of the Criteria is that the requirements

are nonprescriptive— they do not require the use of

specific tools and techniques. Users of the Criteria are

asked to demonstrate success via well-defined processes and outstanding results. In this way, successful

tools, techniques, and processes are identified and used

as a basis for sharing.

Starting in 1998, the Baldrige Award was opened to

health care and education organizations. In order to

accommodate to these communities, while supporting

cross-sector cooperation, the business Criteria were

adapted and published for health care and education

organizations [2,3]. The adaptation of the Criteria to

health care and education is largely a translation of the

requirements language and basic concepts of business

excellence to parallel requirements in health care and

education excellence. The common framework for all

sectors of the economy has resulted in cross-sector

cooperation and sharing of best practice information.

Although the Baldrige Award and the Award recipients are the very visible centerpiece of U.S. quality

improvement, a broader national quality program has

evolved around the Award and the Criteria. A 1995

report, Building on Baldrige: American Quality for the

21st Century, by the private Council on Competitiveness, said, “ More than any other program, the Baldrige

National Quality Award is responsible for making

quality a national priority and disseminating best

practices.” [4].

“ The Baldrige public/private partnership has accomplished more than any other program in revitalizing the

American economy,” said Barry Rogstad, president of

the American Business Conference and past chairman

of the Baldrige Program’s Board of Overseers.

Following are some highlights of the program’s first

decade:

• Called the “single most influential document in the

modern history of American business,” almost 2

million copies of the Baldrige Criteria for Performance Excellence [1] have been distributed. This

number does not include many hundreds of thousands of copies available in books, from state and

local award programs, or downloaded from the

Award’s World Wide Web site.

• For the past six years, a hypothetical stock index

made up of publicly-traded U.S. whole companies

that have received the Baldrige Award has significantly outperformed the Standard & Poor’s (S&P)

500 Index.

• State and local quality programs— most modeled

after the Baldrige program— have grown to over 50

in 1999. The national network of awards and sharing

of practices involves several thousand volunteers

each year.

• Internationally, 45 quality programs are in operation.

Most are modeled after the Baldrige Award Criteria

and evaluation approach, including a new award

established in Japan in 1996.

• Baldrige criteria and case studies are used extensively in U.S. business schools.

Prepared by Curt Reimann and Debbie Smyth.

Bibliography

[1] Application Guidelines, Malcolm Baldrige National Quality

Award, 1988, Baldrige National Quality Program, National

Institute of Standards and Technology, Gaithersburg, MD.

[2] Health Care Criteria for Performance Excellence, 1998, Baldrige

National Quality Program, National Institute of Standards and

Technology, Gaithersburg, MD; most recent edition 2000.

[3] Education Criteria for Performance Excellence, 1998, Baldrige

National Quality Program, National Institute of Standards and

Technology, Gaithersburg, MD; most recent edition 2000.

[4] Building on Baldrige: American Quality for the 21st Century,

Council on Competitiveness, Washington, DC (1995).

358
The Advanced Technology Program

The Advanced Technology Program (ATP) is a competitive cost-sharing program in which the Federal

Government works in partnership with industry to foster

the development and broad dissemination of challenging, high-risk technologies that offer the potential for

significant, broad-based economic benefits for the

nation. This unique government-industry research partnership fosters the acceleration not only of dramatic

gains in existing industries, but also of the development

of emerging technologies leading to revolutionary new

products, industrial processes and services for the

world’s markets while working to spawn industries of

the 21st century. ATP’s focus on civilian technologies

offers the potential for substantial increases in productivity and competitiveness of firms; provides consumers

with new, better, and lower-cost products and services;

and increases high-wage employment in the United

States.

From 1990 through 1999, the ATP made multi-year

awards for a total of 468 projects, including over 157

joint ventures, involving more than 1,000 participants

(not including the many subcontractors and informal

partners and collaborators that participate in many of

the projects). These projects entail approximately $3.0

billion of research, of which industry committed slightly

more than half ($1.53 billion).

Since its inception, the Program’s direct and indirect

impacts have been substantial. In its brief existence, the

ATP has helped shape the face of long-term enabling

technology development undertaken by industry. It has

also developed, by necessity, a wide variety of new tools

for evaluating the impact of technology investment on

the economy. Furthermore, it has often provided

expertise at an important juncture—staff members,

who are often leaders in their field, provide the critical

insights to their peers necessary to assess how a certain

technology has evolved and describe its potential future

trajectories.

The ATP Proposal Preparation Kit [1] was the means

by which the program has been introduced to the public.

Its publication in 1990, as well as subsequent editions,

spelled out the ATP’s selection criteria and provided a

manual for submitting a proposal. It was developed by

the ATP specifically to help the public understand the

program and addresses ATP’s selection criteria. In the

first year, nearly 1,000 copies of these guidelines were

distributed to potential proposers; by the time the

competition began for the year 2000, requests topped

50,000 copies. With such wide distribution, the kit

serves many purposes: it informs the public of the

nature of the program, answers questions about the

program, and supplies all of the necessary information

to complete an application, offering “one-stop shopping” for the potential proposal writer. From the outset,

the Proposal Preparation Kit has undergone annual

revisions to reflect both the needs of the public and the

changes to the program.

The Proposal Preparation Kit has had widespread

impact; to date, the rules contained within it have influenced the formation of almost 4,500 project teams. As

such, it has changed the face of long-term technology

development considered by industry. While the ATP has

funded approximately 10 % of these proposals, anecdotal evidence suggests that the kit was influential in

fostering collaboration even when proposals were not

funded.

A critical part of the ATP program management has

been the development of methodologies and tools for

assessment of impact and broad-based economic

benefits. The ATP relies on the presence of expected

private returns to induce companies to plan, propose,

and cost-share research with the government. If the

research is successful in overcoming its technical

hurdles, the ATP relies on awardees to pursue commercial development of the new technology with private

capital. The ATP applies its criteria to the proposals it

receives to identify those projects expected to accomplish ATP’s public-interest mission and objectives.

Selected projects must demonstrate that they have the

potential to generate social rates of return (the return to

the nation) far in excess of the private rates of return on

investment. In addition, selected projects must demonstrate that, without ATP funding, the private sector

would be unwilling to do the research in either a timely

fashion or a scale needed to realize the social benefit

potential.

A study conducted by economist William F. Long [2],

an ATP contractor, provides the most detailed examination to date of the outcomes of the earliest ATP projects.

The study covers all 38 ATP projects completed by the

end of March 1997. It documents research accomplishments and highlights subsequent work by the participants to commercialize the results. It also provides nearterm outlooks for the technologies. In the high-risk environment in which the ATP-funded projects operate, failure is to be expected. Thus the report also highlights the

359
reasons for failure of 12 terminated projects that had

been selected between 1991 and March 1997.

The 38 projects surveyed by Long cover a broad range

of ATP investments. The technologies were distributed

over seven broad areas—chemicals and chemical processing; materials; discrete manufacturing; energy and

environment; biotechnology; information, computers

and communication; and electronics—with the majority

in electronics. Industry participants provided $65.7

million, a little more than half the funding, while the

ATP contributed $64.6 million to the 38 projects.

Notable new technologies highlighted by Long

include a merger of tissue-engineering and textileweaving to help regenerate lost or damaged tissue in the

body, an application of high-temperature superconductors to improve cellular phone service, and a suite of

process-monitoring and control technologies that are

cutting costs and improving quality throughout much of

the U.S. auto industry. Other new technologies developed under the projects ran the gamut from a desktop

bioreactor capable of growing large amounts of human

stem cells isolated from bone marrow for cell replacement therapy, a device now in clinical trials; to a computer programming tool to simplify the task of writing

software for parallel-processing computers, which

already is in commercial use; to a new navigation system

for mobile robots which is being used to guide delivery

robots in hospitals.

This analysis shows that technical success has not

always led to commercial success. In a few cases, financial reverses or corporate takeovers left technically

successful projects in abeyance. In other cases, commercialization activities are expected to take longer. For

example, projects with medical applications generally

had yet to be widely applied because they must go

through a long process of clinical trials.

Fig. 1. ATP Proposal Preparation Kit.

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Other projects, however, have shown strong early

returns. The process-monitoring and control technologies for the auto body industry, developed by a consortium of large and small companies, have been adopted in

more than half of the Chrysler and General Motors

plants in the United States and Canada. When the technologies are fully implemented, annual savings in production costs are expected to range from $65 million

to $160 million for one of the most important U.S.

industrial sectors.

A project pursued by one small start-up company

developed a novel technology for processing very large

semiconductor wafers, allowing the United States to be

the first in the market with processing equipment for the

next generation of 300 mm semiconductor wafers. A

small New Jersey firm developed a new laser light

source, which is the most powerful tunable source of

laser light over much of the ultraviolet spectrum, and

already has incorporated it in three new products for

laser surgery and other applications.

The Long study is influential because it is among the

first to demonstrate through a systematic assessment of

the ATP portfolio the breath of the impact of the public

investment undertaken by the ATP. In his introductory

comments for the report, former Commerce Secretary

William Daley characterized the report’s influence by

stating, “this new study fills in the details behind the

statistical analyses of the ATP and demonstrates the

overall success of the program. These pages say that the

ATP is working. Industries as diverse as biotechnology,

electronics, manufacturing and software have new technologies in place, today, that they wouldn’t have had

here and now without the ATP. The projected benefits to

the nation’s economy from just three of these early

ATP projects would pay for every ATP project funded

to date.” Daley concluded by stating, “this report is a

portrait of a program that works.”

Since the ATP funds the research underlying the

development of enabling technologies that are expected

to have benefits extending substantially beyond the

direct ATP award recipient, impact evaluation remains a

challenge. Even under the best of circumstances, technology diffusion takes time, and tracking and measuring

externalities, or spillover effects, is often complicated

and difficult. As such, program and project assessment

requires that the ATP go well beyond such traditional

measures as return-on-investment, firm profitability, or

increased tax revenues. Available evaluation tools often

are insufficient to meet the task.

A special issue of the Journal of Technology Transfer

[3] highlights a collection of ATP evaluation studies and

illustrates the variety of evaluation issues ATP faces.

The works in the publication are among the first to

demonstrate the conceptual challenges ATP is faced

with and the wide variety of tools developed by the ATP.

That publication features articles on methodology, the

evaluation program, results from the path-breaking ATP

“Business Reporting System” database, survey-based

research, and a macroeconomic impact study. Other

papers in the volume examine the effects of collaboration, special concepts that need to be considered in

examining social benefits, and counterpart programs in

the industrialized world.

In the Journal of Technology Transfer issue [3],

Adam Jaffe, of Brandeis University, reflects on the importance to the ATP of generating and measuring

“economic spillovers.” It illustrates with simple models

how the benefits of ATP projects may extend beyond

the direct ATP award recipients through market and

knowledge spillover effects. The paper also discusses

network spillovers. Jaffe recommends that the ATP fund

projects for which expected social benefits are

large and substantially exceed expected benefits to

the awardees. He recommends that evaluation efforts

include measures of spillover effects. This paper is

influential in that it affected the way in which the

Advanced Technology Program, as well as others,

undertakes economic analysis. Jaffe’s paper codified the

economic concepts used by the ATP and has served

as a springboard for many other research projects

underway.

Rosalie Ruegg the Director of the Economic

Assessment Office of the ATP, provides an overview of

the ATP, explains how the program operates, how it

seeks to accomplish its mission, and what it has funded

to date. She identifies the major components of ATP’s

evaluation program and identifies research areas of

particular interest. The program is internationally

recognized and has made a substantial impact in the

evaluation community. In the United States, Congress

has directed other agencies to model their evaluation

programs on the ATP. Furthermore, state governments

seek assistance from ATP in establishing their evaluation

programs.

Jeanne Powell from the ATP presents and analyzes

data from ATP’s “Business Reporting System” database

to evaluate short and medium term project effects.

She describes ATP’s principal data collection tool

and identifies a number of pathways through which

ATP-funded technologies are generating impact. The

enabling nature of the funded technologies is suggested

by the many potential applications that have thus far

been identified. The survey-based database employed in

this study is unique because it is among the first in the

world that allows a researcher to explore the inner-workings of firms and technology projects at such a magnitude. As such, the tools used in this paper serve as the

basis for future evaluation efforts.

361
ATP’s effects on the speed with which research is

conducted and technology is commercialized are examined by Frances Laidlaw. Laidlaw questions not only

whether, and by how much, the ATP accelerates

research, but also the value of acceleration; whether

saving time during the research stage translates into

saving time downstream; and whether project participants realize any time-related benefits outside the walls

of the project. This paper demonstrates that acceleration

of technology development and commercialization is

one of several ways that the ATP can affect economic

outcomes of the projects it funds.

The researchers at CONSAD Research Corporation

report on a detailed case analysis performed for an ATPfunded research joint venture whose focus was on new

dimensional control technology for discrete manufacturing. They analyze the multiple impacts of the new

technology applied in the automobile manufacturing

sector and apply a macroeconomic model to project

national economic impacts resulting from quality

improvements in vehicles made by U.S. producers. This

paper demonstrates the feasibility of a macroeconomic

input-output model dealing with the impact of technological innovations.

Other relevant issues are discussed in this series.

Albert Link, a Professor of Economics at the University

of North Carolina at Greensboro investigates the effects

on research efficiency of collaboration in an ATPsponsored joint venture. Also, Andrew Wang examines

the special considerations that need to be undertaken in

modeling the social benefits of medical technologies.

Finally, Connie Chang of the ATP office, signals ATP’s

interest in counterpart programs that operate in most

industrialized countries.

Prepared by Robert Sienkiewicz and Richard N. Spivack.

Bibliography

[1] Advanced Technology Program Proposal Preparation Kit, National

Institute of Standards and Technology, Gaithersburg, MD, November 1999.

[2] William F. Long, Advanced Technology Program Performance of

Completed Projects: Status Report Number 1, NIST Special

Publication 950-1, National Institute of Standards and Technology,

Gaithersburg, MD (1999).

[3] Symposium on Evaluating A Public-Private Partnership: The

Advanced Technology Program, Special issue of J. Technol.

Transfer, Vol. 23, no. 2, Summer 1998.

362
NIST Manufacturing Extension Partnership

The NIST Manufacturing Extension Partnership

(MEP) is a nationwide network of locally managed centers offering technology assistance and the latest business practices to help smaller manufacturers

improve their competitiveness. The MEP was created in

1988 as a new extramural responsibility assigned to

NIST by the Omnibus Trade and Competiveness Act—

the same Act that changed NBS into NIST. At the heart

of MEP is a network of more than 400 manufacturing

extension centers and field offices located throughout

the country. The program became operational in 1989,

and today’s network delivers services to manufacturers

in all 50 states and Puerto Rico. The 1999 report

to Congress, The NIST Manufacturing Extension

Partnership, A Network for Success [1], summarizes the

progress in the first decade of MEP.

More than 385,000 small and mid-sized manufacturers make vital contributions to the economy. About

98 % of the nation’s manufacturers are small to

medium-sized, defined as having fewer than 500

employees. They supply more than 50 % of the added

value in U.S. manufacturing and employ nearly 12

million people. That accounts for 65 % of all U.S.

manufacturing workers with high-skilled, high-wage

jobs, paying an average 58 % more than the average

retail earnings.

As large manufacturers depend more on suppliers for

parts and services, the performance and capabilities of

smaller manufacturers become even more critical. Yet,

according to a National Research Council report,

“Many of these small firms . . . are operating far below

their potential. Their use of modern manufacturing

equipment, methodologies and management practices is

inadequate to ensure that American manufacturers will

be globally competitive.” Limited budgets, lack of

in-house expertise, and lack of access to the newest

technologies are but a few of the significant barriers

faced by smaller manufacturers— barriers that MEP

helps firms overcome.

MEP centers are local resources serving their local

markets. Linked together through the National Institute

of Standards and Technology’s Manufacturing Extension Partnership, they are part of a national network of

manufacturing and business experts. They exist as the

result of a partnership among the federal government,

state and local governments, and industry to help local

manufacturers. They are created through a competitive,

merit-based process where funding is contingent upon

successful annual reviews of each center. MEP centers

are supported by contributions from public and private

organizations that match federal funding.

While part of a national network, MEP centers

are independent, non-profit organizations. They offer

products and services that meet the specific needs of the

region’s local manufacturers. Each center works directly

with area firms to provide expertise and services

tailored to their most critical needs, ranging from

process improvements and worker training to business

practices and applications of information technology.

Solutions are offered through a combination of direct

assistance from center staff and work with outside

consultants. MEP centers are staffed by knowledgeable

manufacturing engineers and business specialists who

typically have years of practical experience gained from

working on the manufacturing floor and/or managing

plant operations. MEP center staff also know the local

business community and the available local resources,

and they can access national resources through the

MEP network. As a result, centers help small firms to

overcome barriers in locating and obtaining privatesector resources.

MEP centers work with companies that are willing

to invest time, money, and/or human resources to

improve their business. Typical MEP clients include

manufacturers who:

• Have been unable to locate the proper resources or

technologies they need.

• Want expert, impartial advice in helping them

evaluate alternative solutions.

• Need help solving a specific problem, such as determining the cause of product defects, modifying

plant layout to improve workflow, or establishing

employee training.

• Want assistance in reversing negative business situations—such as sales decreases, loss of market share,

or cost increases.

• Want to implement new technologies or processes

that will help establish them as market leaders.

• Seek to improve their ongoing business operations

for peak performance.

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Through these centers, MEP provides small and midsized manufacturers with access to a wealth of tools,

techniques, and other resources from over 2,500 public

and private affiliations. Initiatives with the U.S. Departments of Labor and Agriculture, EPA, Small Business

Administration, National Association of State Development Agencies, the Kauffman Center for Entrepreneurial Leadership, and hundreds of universities and community colleges are but a few examples of how MEP

leverages public and private resources to make a comprehensive range of technical services and assistance

available to small manufacturers.

The report to Congress [1] includes a section on

evaluation, which is a key element of all MEP programs

and activities. Results are used to assess the effectiveness of services and their impact on the performance of

client firms and to help guide planning at both the center

and national levels. By measuring short- and long-term

impacts, MEP can also assess economic returns on the

federal investment in manufacturing extension services.

Results of ongoing surveys confirm that MEP

services—delivered to more than 84,000 small and

mid-sized manufacturers since 1989—are yielding

sizable benefits. For example, a sample of 4,554 client

companies reported that, as a direct result of MEP

assistance during 1998, they:

• Created or retained a total of 7,186 jobs

• Increased revenues by $294 million

• Invested a total of $291 million in modernization

• Realized a cost savings of $29 million in materials

and labor

• Reduced inventories by $20 million.

Other independent studies have also yielded solid

evidence of performance and economic benefits. An

analysis by the U.S. General Accounting Office found

that a substantial majority of firms using extension

services, including those provided by the MEP, credited

this assistance with helping them to improve productivity, product quality, customer satisfaction, profits, and

other critical facets of their operations.

Since the program’s inception in 1989, MEP has

recognized the value and impact small manufactures

have on our everyday lives. Whether through national

initiatives such as the Y2K Conversion 2000 Jumpstart

kit—distributed to more than 320,000 manufacturers

throughout the country—or through local contact, MEP

is providing hands-on help to America’s small manufacturers. One significant way that MEP does this is

through education on lean manufacturing. As a result of

a partnership between MEP’s centers and Productivity,

Inc., the smaller manufacturers have access to “lean

manufacturing” training previously available only to

large companies. Originating in Japan in the 1970’s,

lean manufacturing is a concept that eliminates manufacturing activities or actions that add no real value to

the product or service. Field manufacturing specialists

at NIST MEP centers around the country receive training in lean manufacturing through the partnership.

Several success stories that show the impact that the

MEP centers have had on American manufacturers

across the country through various products and/or

services are included in the report [1]. A typical

example is the case of Contine Corp., located in Erie,

Pennsylvania, which employs 28 people in its 15,000-

square-foot facility and offers a full range of job shop

services to manufacturers of electromechanical devices.

The company added plastic injection molding capabilities after purchasing Bayside Precision Inc. in 1990,

which further enhanced its ability to serve the market.

Contine was concerned about its Y2K preparedness for

internal and external systems. The company recognized

that it might need to replace or upgrade software and/or

hardware, but it neither had a plan nor did it know where

to start. For assistance, Contine contacted the Northwest

Pennsylvania Industrial Resource Center (NWIRC), a

NIST MEP network affiliate.

NWIRC’s information technology field engineer met

with Contine systems staff and proposed that the company undergo a Y2K awareness briefing. After the

briefing, Contine asked NWIRC to initiate a full Y2K

readiness project and to assume the role of project director for the company’s Y2K team. NWIRC installed

MEP’s Y2K project tool and trained the team how to use

it. Throughout the next 3 months, the Center met regularly with the team to evaluate progress and establish

new landmarks. The results of the identification and

testing of Contine’s systems indicated that the company

needed to spend approximately $50,000 to replace its

existing network server and “jobshop” software applications. After NWIRC talked with various outside consultants and evaluated the inner-workings of their information systems, it determined that the company also should

upgrade five of its workstations to improve productivity.

Within 2 months, Contine purchased, installed, and

tested the new equipment and software while the team

continued to conduct on-going Y2K readiness testing.

The new technology allowed Contine to enhance its

capabilities and increase its efficiency for Y2K and for

years to come. In addition, as a result of the company’s

364
efforts to assure its Y2K readiness, it was able to prevent

disruption of the flow of products to customers,

which in turn protected the employees from short- and

long-term layoffs.

Prepared by Anita O’Brien.

Bibliography

[1] A Report to Congress- The NIST Manufacturing Extension

Partnership, A Network for Success, Manufacturing Extension

Partnership, National Institute of Standards and Technology,

Gaithersburg, MD, July 1999.

365
Questions and Answers on Quality

Product quality depends on many process variables,

such as the caliber of the components or materials used;

type of equipment used in design, production, handling,

installation, testing and shipping; the equipment calibration and maintenance procedures; the training and

experience of production and supervisory personnel; the

level of “workmanship”; and sometimes the environmental conditions (temperature, humidity, level of dust

particles) in the area where the product is produced.

The process, organizational structure, procedures, and

resources that manufacturers and suppliers use to

control these variables to produce a product or service of

consistent quality to meet defined specifications is

called a quality system.

In 1979, the International Organization for Standardization (ISO), a worldwide federation of over 90 countries founded in 1946 to promote the development of

international standards to facilitate the exchange of

goods and services worldwide, formed Technical

Committee (TC) 176 on Quality Management and

Quality Assurance. The Committee’s purpose was to

address the worldwide trend towards increasingly

stringent customer demands with regard to quality. This

committee was tasked with addressing the growing

confusion in the conduct of international trade resulting

from differing quality system requirements at national

and lower jurisdictional levels. As a result of TC 176’s

work, ISO released a series of five standards in 1987, the

ISO 9000 Standard Series. These standards provided

guidance on selection of and requirements for a basic

quality management system.

Soon compliance with the standards became recognized and required by many foreign and domestic buyers

and by some governmental regulators. In addition, quality system registration was seen and used by manufacturers as a competitive marketing tool.

Quality system registration or approval entails the

assessment and periodic audit of the adequacy of a supplier’s quality system by a third party, known as a

quality system registrar. When a supplier’s system

conforms to the registrar’s interpretation of an ISO 9000

standard, the registrar issues the supplier a “certificate

of registration.” It should be noted that it is the supplier’s

quality system that is registered, not an individual

product.

This increasing demand for compliance with or

registration to the ISO 9000 standards, combined with

the lack of adequate and accurate information on the

topic, created significant problems for both U.S. industry and government agencies. To fill this void, NIST

published two basic primers on the ISO 9000 Series

and the usage of the ISO standards. The two reports,

Questions and Answers on Quality, the ISO 9000

Standard Series, Quality System Registration, and

Related Issues [1] and More Questions and Answers on

the ISO 9000 Standard Series and Related Issues [2],

addressed such issues as: the types of requirements

included in the standards; how the U.S. registration

system operates; how the ISO 9000 standards were

being used in the European Union’s new regulatory

scheme; mutual recognition efforts at the international

level; how federal agencies were using the standards

within their regulatory and procurement programs; and

information on other ISO 9000 based standards, such as

the QS 9000 Standard—a standard published by the auto

industry to define a set of quality system requirements for suppliers to the “Big Three” and other auto

companies.

The ISO 9000 Standards increased the visibility of

and U.S. concerns over the impact of international

standards on U.S. competitiveness to a degree

never encountered before. The NIST reports provided

timely and accurate information that was sorely

needed by both the private and government sectors

to formulate adequate responses to these issues—

information not being provided by the private sector

at that time. The reports were written in an easy-to-read

question-and-answer format, providing information

in a way managers could use to make informed

decisions regarding the application of the ISO 9000

Standard Series within company and governmental

operations.

The use of the ISO 9000 standards is now a key

domestic and international business strategy for many

U.S. companies—one that is becoming increasingly

necessary for survival. U.S. industry has become acutely

aware that information on these and other national and

international standards and related conformity assessment activities is vital to ensure continued competitiveness in the U.S. and global marketplaces.

The Questions and Answers on Quality reports have

been and continue to be widely distributed by NIST and

by private sector companies and educational institutions.

The popularity of and demand for these reports far

exceeded anything that the Office of Standards Services

had anticipated or had ever experienced.

366
These reports are part of NIST’s growing effort to

respond to the need for accurate and timely information

on subjects related to national and international

standards and conformity assessment. Other related

reports are listed on the Office of Standards Services

web site [3]. NIST has also formed federal working

groups to address such issues, has responded to many

thousands of requests for information on these topics,

and has provided staff members to give lectures at

numerous workshops and at various public and private

sector fora.

Maureen Breitenberg is internationally recognized as

a leading authority on conformity assessment issues,

standards, guidelines and practices. Her many publications have been used nationally and internationally to

address trade-related issues. They have been widely

distributed by NIST to private sector organizations,

other U.S. federal agencies, state agencies involved in

trade development and assistance, U.S. embassies,

foreign governments, colleges, universities, and libraries

for education and training purposes and for responding

to trade related inquiries. Several have been translated

and/or reprinted by foreign and domestic government

and private sector organizations. Her latest publication,

the 1999 edition of SP 739, Directory of Federal

Government Certification and Related Programs [4],

has been highlighted as a very useful resource in terms

of depth of content, authority, and how well the information is presented.

Breitenberg received the NIST Bronze Medal in

1992. She was also elected to the Government and

Industry Quality Liaison Panel’s Leadership Team,

which resulted in harmonizing federal agency quality

system requirements for suppliers to the government.

The Panel received the Vice President’s National

Performance Review (Golden Hammer) Award in 1995

for its efforts.

Prepared by Maureen Breitenberg.

Bibliography

[1] Maureen Breitenberg, Questions and Answers on Quality, the

ISO 9000 Standard Series, Quality System Registration, and

Related Issues, NISTIR 4721, National Institute of Standards and

Technology, Gaithersburg, MD (1991).

[2] Maureen Breitenberg, More Questions and Answers on the

ISO 9000 Standard Series and Related Issues, NISTIR 5122,

National Institute of Standards and Technology, Gaithersburg, MD

(1993).

[3] NIST publications on standards and conformity assessment

activities are listed on the web site (http://ts.nist.gov).

[4] Maureen Breitenberg (ed.), Directory of Federal Government

Certification and Related Programs, NIST Special Publication

739, 1999 Edition, National Institute of Standards and Technology,

Gaithersburg, MD (1999).

367
Uniformity in Weights and Measures

Laws and Regulations

Today we take it for granted that when we buy a

pound of hamburger, whether we are in New York,

St. Louis, or California, we will be getting the same

amount of product for our money. A hundred years ago

consumers could not be so sure that a “pound” in one

state was the same as a “pound” in another. Concerns

about the uniformity of weights and measures standards

and laws from state to state led the National Bureau of

Standards to convene the first “Conference on the

Weights and Measures of the United States” in January

1905. This first meeting laid the foundation for the

creation of the National Conference on Weights and

Measures (NCWM), which continues to this day. The

NCWM is the primary mechanism used by NIST to

fulfill its responsibility, as stated in its Organic Act, to

work with the states “in securing uniformity in weights

and measures laws and methods of inspection.” Only 11

delegates attended the first Conference; however, there

are now over 3,000 NCWM members representing state

and local weights and measures jurisdictions, the

Federal Government, industry, consumers, and other

countries.

NBS published the report of the 1905 Conference and

has since published the reports of the 83 other Conferences held since that first meeting [1]. The reports

document the history of the NCWM’s development of

standards in the form of model weights and measures

laws, regulations, and practices. When state and local

weights and measures jurisdictions adopt these

standards, they become mandatory. The reports of the

Conference serve as a legislative history of the requirements in the model laws; therefore, state officials, the

NIST Office of Weights and Measures, Federal and

international standards agencies, members of the public,

and others often consult the reports to identify the intent

of the requirements. The reports contain a wealth of

technical and historical information, including special

addresses by NCWM Chairmen and by NBS/NIST

Directors, who have served as Honorary Presidents of

the NCWM. It would not be practical to describe all the

reports in this centennial book; however, particular

attention is called to the report of the first Conference

because of its historical significance. In addition, it

contains a history of U.S. weights and measures

from the beginnings of the country up to 1905. This

historical information was used as the basis for later

NBS publications, such as SP 447, Weights and

Measures Standards of the United States, A Brief

History [2].

Over the years, the uniform laws, regulations, and

practices developed by NIST in cooperation with the

NCWM have been gathered together and published in a

series of NIST Handbooks. Two Handbooks of particular note are Handbook 44, Specifications, Tolerances,

and Other Technical Requirements for Weighing and

Measuring Devices [3], and Handbook 130, Uniform

Laws and Regulations, in the areas of legal metrology

and engine fuel quality [4].

Handbook 44 was first published in 1949, having

been preceded by similar handbooks of various designations and in several forms, beginning in 1918. This

Handbook has become the standard for specifications

and tolerances for commercial weighing and measuring

devices in the United States. These devices include

scales, liquid-measuring devices, volumetric measures,

linear-measuring devices, mass flow meters, grain

moisture meters, timing devices, near infrared grain

analyzers, and multiple dimension measuring devices.

All 50 states have adopted the Handbook as the legal

basis for regulating commercial weighing and measuring devices. It is updated by NIST each year following

the Annual Meeting of the NCWM to include changes

adopted at the meeting. A NIST staff member serves as

Technical Advisor to the NCWM Specifications and

Tolerances Committee, which recommends changes and

additions to the Handbook. Nearly 3,000 copies of the

Handbook are distributed annually to NCWM members.

Another thousand copies are sold through the Government Printing Office and hundreds of copies are

distributed to Depository Libraries throughout the

country. In addition, many associations reprint portions

of the Handbook to distribute to their members. In a

number of states, commercial weighing and measuring

device servicepersons and agencies are required to

demonstrate their knowledge and understanding of the

Handbook in order to be registered by the states. The

significance of the Handbook is further indicated by the

fact that it serves as the basis for the National Type

Evaluation Program (NTEP), a cooperative effort of

NIST and the NCWM. NTEP evaluates models of

weighing and measuring devices to determine if they

meet the requirements of Handbook 44. Forty-four

368
states require that only weighing and measuring devices

with an NTEP Certificate of Conformance can be

installed in commercial applications in the state. (Fig. 1)

NIST Handbook 130 compiles the latest uniform laws

and regulations and related interpretations and guidelines adopted by the NCWM. In 1979, NBS issued the

first compilation of the various laws and regulations that

had been adopted by the NCWM under the title “Model

State Laws and Regulations.” The name of the publication was later changed to make it clear that the standards

in the publication were recommended for adoption by

local as well as state jurisdictions. Handbook 130 is the

standard for uniform weights and measures laws and

regulations in the United States. It has been estimated

that weights and measures laws and regulations impact

transactions involving $4.5 trillion (52.8 %) of the

$8.51 trillion U.S. Gross Domestic Product (1998

figures). NIST technical advisors, working with

members of the NCWM Laws and Regulations Committee, have helped develop and maintain the standards in

Handbook 130. These standards have been widely

adopted by the weights and measures community. For

Fig. 1. A New Mexico Weights and Measures Inspector tests a Liquefied Petroleum Gas Meter to determine its compliance with NIST Handbook

44 requirements.

369
example, 44 states have adopted a Weights and Measures

Law based on the uniform law in Handbook 130. As of

1999, 45 states have adopted Packaging and Labeling

requirements and 42 states have adopted Method of Sale

requirements based on the uniform regulations in

Handbook 130.

Prepared by Joan Koenig.

Bibliography

[1] Reports of the National Conference on Weights and Measures

1905—1999. Various editors over the years. Latest report: Henry

V. Oppermann and Joan Koenig (eds.), Report of the 85th

National Conference on Weights and Measures, NIST Special

Publication 957, National Institute of Standards and Technology,

Gaithersburg, MD (2000).

[2] Lewis V. Judson, Weights and Measures Standards of the United

States, A Brief History, NBS Special Publication 447, National

Bureau of Standards, Washington, DC (1976).

[3] Specifications, Tolerances, and Other Technical Requirements for

Weighing and Measuring Devices, NIST Handbook 44 (various

editors over the years; editors of the 2001 edition: Tina G.

Butcher, Terry L. Grimes, and Juana Williams).

[4] Uniform Laws and Regulations, in the areas of legal metrology

and engine fuel quality, NIST Handbook 130, (various editors over

the years; editors of the 2001 edition: Thomas Coleman and Terry

L. Grimes).

370
Certification of 10 m Diameter Polystryrene

Spheres (“Space Beads”)

There are numerous examples in trade and commerce

in which small particles play an important role, either as

the commodity of trade itself, as unwanted contaminants in a product or an environment, or as a basis for

comparison between a “normal” particle and an

“abnormal” one. Many of the products we buy come in

the form of small particles, powders, or particle suspensions, including medicines, cosmetics, food products,

paints, talcum powder, cements, photocopier toners, and

milk (which is essentially a suspension of microdroplets

of fat in water). In other cases, small particles are

unwanted, for example in cleanrooms for microelectronics or pharmaceutical manufacturing, in lubricating oils

in motor vehicles, and in the air we breathe and the

water we drink. There are also situations where one

would like to compare a known, standard particle to

an unknown, test particle as in the case of blood-cell

testing. In all of these instances, particle standards play

a key role, enabling quality control, product uniformity,

conformance to standards, traceability to NIST,

interchangeability of instrumentation, uniformity of

measurement, or some combination of these goals.

With these benefits in mind, the National Bureau of

Standards set out, in the early 1980’s, to develop a range

of particle-sizing Standard Reference Materials (SRMs)

for use in calibrating and certifying instruments that

measure particle size, whether as products, by-products,

or contaminants. In cooperation with ASTM Committee

E-29 on Particle Size Measurement, researchers in the

Precision Engineering Division (PED) at NBS developed a series of five SRM’s consisting of monosized

polystyrene microspheres with diameters of 0.3, 1, 3,

10, and 30 m [1-4]. The three smallest particles,

donated by commercial vendors, were certified first,

since such small microspheres were comparatively

easy to grow using conventional polymer emulsion

techniques. However, for the two larger diameters,

10 m and 30 m, the techniques that existed at the

time did not yield rigid particles of the required sphericity because of the detrimental effects of gravity on the

microsphere growth process. (At the time, there were

techniques to make large microspheres, but these were

relatively soft and unsuitable for use as SRMs, which

must be rigid and stable.)

At about the same time that NBS was certifying its

series of particle-sizing SRMs, a group of researchers

led by John Vanderhoff of Lehigh University and

Dale Kornfeld of NASA Marshall Space Flight Center

was conducting experiments aboard the space shuttle

to determine the effect of microgravity on chemical

reaction rates of emulsion polymerization, as well as on

the morphology (shape) of polymer microspheres grown

in microgravity [5]. The first experiments of the

Monodisperse Latex Reactor (MLR) were conducted in

1982 aboard space shuttle flight STS-3 and resulted in

microspheres as large as 5 m in mean diameter. A

subsequent experiment on a later shuttle flight, STS-6,

produced particles of 10 m mean diameter. In 1984,

the NBS group obtained samples of the 5 m and the

10 m materials and did a detailed intercomparison

between the space-made particles and earth-made particles of similar composition [1,2]. In both cases, the

space-made materials were found to be superior in

terms of individual particle sphericity, narrowness of

size distribution, and, importantly, in particle rigidity.

An agreement was then made between NASA and NBS

for NASA to provide a sufficient quantity of the 10 m

material to make up 600 5 mL vials containing liquid

suspensions of the polystyrene microspheres for use as

an SRM. The agreement also called for NBS to receive

the 30 m polystyrene spheres to be grown on a subsequent shuttle flight.

To certify SRM 1960, the so-called “space beads”

(Figs. 1 and 2), researchers at NBS, led by Tom Lettieri

of the PED, developed three new particle-sizing

techniques, which are described in the publication

Certification of SRM 1960: Nominal 10 m Diameter

Polystyrene Spheres (“Space Beads”) [1]. These techniques were center distance finding (CDF), resonance

light scattering (RLS) from a liquid suspension of

microspheres, and metrology electron microscopy

(MEM). The primary certification technique for

SRM 1960, center distance finding, was developed by

Ike Hartman of the PED. CDF uses a conventional

optical microscope and relies on the fact that the microspheres act like tiny lenses when placed on a glass slide

in the microscope. The microspheres were spread onto

a slide such that they formed long chains of contacting

spheres, rather than the regular hexagonal arrays formed

in conventional array sizing. This ensured that the particles were in close contact, compared to conventional

array sizing where the non-zero diameter distribution of

the microspheres leads to voids, cracks, gaps, and other

flaws in the arrays. These flaws lead to uncertainties in

371
the mean sphere diameter measured with conventional

array sizing, uncertainties that are avoided when particle

chains are used. If the microspheres are illuminated

from below and the microscope is focused just above

them, then the tiny focal spots can be photographed

and the distance between the spots determined very

accurately. Using CDF, the mean sphere diameter for

SRM 1960 was determined to be 9.890.04 mm: this

was the certified mean diameter for the SRM.

Supporting measurements were made using RLS

and MEM. In the RLS technique, developed by Tom

Lettieri, a tunable dye laser was used to generate

resonance light-scattering intensity patterns from the

microspheres as they were suspended in water. As the

laser was tuned through its wavelength range, relatively

sharp peaks in the light-scattering intensity appeared at

certain wavelengths. Although this technique had been

used before by others to investigate sharp resonances

from single microspheres, this was the first time that

such resonances were detected in a suspension of many

microspheres: this could be done because the spheres

had a very narrow size distribution (<1 % standard

deviation). By comparing the experimental resonance

wavelengths with those calculated by Egon Marx of the

PED using Mie scattering theory, the NBS researchers

were able to use RLS to arrive at a mean diameter of

9.900.03 m for the SRM 1960 microspheres. This

result was in excellent agreement with those from both

CDF and MEM.

The other supporting metrology technique was

MEM. Gary Hembree of the PED used MEM to

measure the microspheres in a scanning electron microscope (SEM). With MEM, the spheres are mounted onto

the microscope stage as in a conventional SEM. However, in a conventional SEM the electron beam is rasterscanned past the stationary spheres, whereas in the

MEM technique developed at NBS, the electron beam is

held stationary while an individual particle is moved

through the beam via a piezoelectric scanning stage.

The scattered electron intensity is measured versus stage

position and, from this, a particle profile is generated.

These profiles could then be used to determine the

diameter of the individual particles. Using MEM, a

mean diameter of 9.890.06 m was obtained for the

SRM 1960 spheres, in excellent agreement with the

other two metrology techniques. Indeed, the remarkable

agreement among the three metrology techniques, and

the relatively small uncertainty in the diameter, likely

made SRM 1960 the best characterized particle-size

standard in the world at the time. An important point

in these measurements was that the three metrology

techniques were independent of each other, in that none

of the measurements relied in any way on measurements

from the other techniques. This is always good practice

when certifying an SRM.

In 1985, SRM 1960 was first offered for sale to the

public through the NBS Office of Standard Reference

Materials (OSRM), making the SRM the first commercial product to be manufactured in space (SRM-1961,

the nominal 30 m spheres, was the second space-made

product). The sale of the space beads was reported in

hundreds of newspapers, magazines, and television/radio

news stories around the world, from the New York Times

to the CBS Nightly News to ABC’s Good Morning

America. The work was also featured on a National

Public Radio program and on an Australian science

show, Beyond 2000. Later on, SRM 1960 won an

IR-100 award from Research & Development magazine

for being among the top 100 products of 1985.

Over the years, SRM 1960 has proven to be a valuable

tool for the calibration of particle-sizing instruments in

the United States and around the world. Samples have

been purchased by dozens of U.S. and foreign companies for use as primary particle-sizing standards. These

companies include not only the makers of particlesizing standards and instrumentation, but also “every

day” users who need to maintain accuracy and traceability of their measurements. Among the primary users are

Fig. 1. Scanning electron photomicrograph of Standard Reference

Material 1960 microspheres.

372
major pharmaceutical companies, Fortune 500 petrochemical and chemical companies, small-to-midsized biomedical instrumentation companies, particle

standard supply houses, and numerous firms, of all

sizes, involved in the measurement of particle size.

Several U.S. Government and non-profit labs, including

NASA Ames, Battelle Northwest, EPA, FDA, Los

Alamos, Sandia, and the USGS have also purchased

SRM 1960. In the international arena, the material has

been used by research laboratories in Australia, Austria,

Brazil, Canada, England, France, Germany, India, Italy,

Japan, Korea, Mexico, Norway, Spain, Switzerland, and

Thailand. Sales of SRM 1960 average about 25 vials per

year through the NIST OSRM. The OSRM also offers

for sale another version of the space beads, SRM 1965,

which are standard microscope slides with small

patches of particles in both regular arrays and microsphere chains. These have been used throughout the

world for educational and training purposes, as well as

to satisfy the needs of those who wish to own something

“made in space.” In addition to OSRM, the microspheres are also sold through the European

Community’s Bureau Communautaire de Reference

(BCR).

The demand for SRM 1960 is spurred, in part, by its

incorporation into several document standards in the

United States. For example, the U.S. Pharmacopeia, in

its test entitled “Particulate Matter in Injections,” specifies the use of SRM 1960 for calibrating the liquidborne particle counters used in the test. As a waterquality standard, SRM 1960 is listed by the National

Oceanic and Atmospheric Administration (NOAA) in

its compilation of Standard and Reference Materials for

Marine Science as a physical standard for the assessment

of water and sediment quality. The particles have also

found application in the monitoring and assessment of

air quality, especially with regard to the Environmental

Protection Agency (EPA) PM10 standard that specifies a

cutoff of 10 m for the aerodynamic diameter of particulate emissions from motor vehicles, smokestacks, and

Fig. 2. Photograph of SRM 1960 showing a vial of the SRM, the certificate, and the package.

373
other industrial emission sources. In the medical field,

SRM 1960 has been valuable as a calibration standard

for blood-cell counting and sorting, as the mean diameter of the SRM is very near that of human red blood

cells. Thousands of hospitals and medical testing

laboratories throughout the U.S. use blood-cell counters

to check for sickle cell anemia, Tay-Sachs disease,

and other blood abnormalities, and SRM 1960 helps to

ensure the quality and accuracy of such tests.

SRM 1960 will, undoubtedly, find more applications in

the medical field as biotechnology and medical diagnostics become more pervasive in our daily lives.

In addition to the above applications of SRM 1960,

other areas of scientific research where the material

has found use include: electron microscopy; chemical

chromatography; powder metallurgy; ceramics; food

processing; photographic films; and basic particle

research, among many others. The rigid demands of

ISO9000 will likely increase the importance of particlesizing standards such as SRM 1960, as companies

become more concerned with quality control, conformance assessment, and reliability issues.

Of the four authors of the space beads paper, two,

Tom Lettieri and Egon Marx, are still at NIST. Tom

started at NBS in 1978 after graduate school at the

University of Rochester, joining the Pressure Group to

do high-pressure optical studies of liquids. Less than

two years later, he joined the PED to conduct optical

metrology studies of small particles, rough surfaces, and

noncontact methods for dimensional measurement. Tom

is now a Program Manager with the NIST Advanced

Technology Program, where he helps select and

manage industrial technology projects in the area of

optics/photonics. Egon Marx did his graduate studies

in nuclear physics under the direction of Murray

Gell-Mann at the California Institute of Technology.

After a few years of teaching at Drexel University,

Egon went to work at Harry Diamond Laboratories,

conducting theoretical investigations in electromagnetic

(EM) interference. His interests at NIST have included

EM scattering, surface roughness, linewidth metrology,

and quantum electrodynamics. Two authors, Gary

Hembree and Ike Hartman, left NIST not long after

the space beads project was finished. Gary came to

NBS after completing graduate studies in electron

microscopy at Arizona State University (ASU). After

several years at NBS, he returned to ASU to work with

the world-renowned electron microscopy group there.

Ike Hartman came to NBS after spending a number of

years at General Electric doing optics and imaging

research. At NBS, he worked in various areas of optical

metrology, including microscopy, particle sizing,

electro-zone particle counting, and linewidth metrology.

He retired from NIST after a long and satisfying career

in optics, both in his native Netherlands and in the

United States.

Prepared by Tom Lettieri.

Bibliography

[1] T. R. Lettieri, A. W. Hartman, G. G. Hembree, and E. Marx,

Certification of SRM 1960: Nominal 10 m Diameter

Polystyrene Spheres (“Space Beads”), J. Res. Natl. Inst. Stand.

Technol. 96, 669-691 (1991).

[2] G. Mulholland, G. Hembree, and A. Hartman, Sizing of

Polystyrene Spheres Produced in Microgravity, NBSIR 84-2914,

National Bureau Standands, Gaithersburg, MD (1985).

[3] T. R. Lettieri, Optical Calibration of Accurate Particle Sizing

Standards at the U.S. National Bureau of Standards, in Optical

Particle Sizing: Theory and Practice, Ge ́rard Gouesbet and

Ge ́rard Grehan (eds.), Plenum Press, New York (1988).

[4] Nancy M. Trahey (ed.), NIST Standard Reference Materials

Catalog 1998-1999, NIST Special Publication 260, National

Institute of Standards and Technology, Gaithersburg, MD (1998).

[5] D. Kornfeld, Monodisperse Latex Reactor (MLR), NASA TM86847, NASA, Washington, DC (1985).

374
Bose-Einstein Condensation in a Dilute

Atomic Vapor

An unavoidable consequence of quantum mechanics

is that, for sufficiently short length scales, all objects

appear to be “wavy.” We do not notice this effect in our

everyday lives because, for objects larger than an electron, the length scale over which the waviness occurs is

fantastically short, far too small to be observed by the

unaided eye. Nature makes an exception to this rule,

however, in the case of extreme cold. As objects are

cooled very close to absolute zero, their characteristic

quantum-mechanical wavelengths become increasingly

long. This tendency towards ever-expanding wavelength

culminates in a dramatic phenomenon known as “BoseEinstein Condensation” (BEC).

BEC was originally conceived in 1925 by Albert

Einstein, who calculated that if a gas of atoms could be

cooled below a transition temperature, it should suddenly condense into a remarkable state in which all the

atoms have exactly the same location and energy—in

modern language, the wave-function of each atom in a

Bose-Einstein condensate should extend across the

entire sample of gas. For a dilute gas, the requisite

transition temperature is so low as to be unachievable by

the technology of Einstein’s day. By the 1980s and early

1990s, however, cooling techniques had advanced to the

point where a number of experimental groups around the

world felt emboldened to attempt to realize Einstein’s

original vision. Many of the necessary advances came

from NBS/NIST atomic physics laboratories. The first

successful creation of dilute-gas BEC, announced in

the NIST publication Observation of Bose-Einstein

Condensation in a Dilute Atomic Vapor [1], was both a

natural continuation of a 75-year tradition of NBS

pre-eminence in spectroscopy (which is detailed in

several other entries in this book [2-5]) and a striking

confirmation that present-day NIST research is at the

cutting edge of modern technology.

The scientific motivation to create and study BEC in

a gas stemmed from the long-held belief that the

mechanism underlying BEC is the same mechanism

responsible for the mysterious effects of superconductivity and superfluidity. Indeed, in the broadest sense the

electrical currents that flow (without resistance) in a

superconducting metal and the liquid currents that

persist (without viscosity) in superfluid helium are

basically Bose condensates. But liquids and solids are

much more complicated than the relatively simple

gas-phase system that Einstein first envisioned, and it is

not easy to connect the elegant mechanism that Einstein

proposed with the complex behavior of solids and

liquids. If one could create a Bose condensate in a gas,

it was reasoned, one would have a well-characterized

model system, a system that might illuminate the

counter-intuitive behavior of its liquid and solid predecessors.

The technical motivation for creating a BEC was

equally compelling. Much of the standards and metrology work that NIST is charged with performing relies

on precise spectroscopy of various internal resonances

in atoms. When it comes to spectroscopy, the general

rule of thumb is “colder equals more accurate.” Colder

atoms move more slowly, which means they can be

probed longer, with correspondingly narrower resonance lines. In addition, systematic errors are often more

easily controlled at lower temperatures. For a gas of

atoms, the natural and obvious limit of improved cooling

is exactly the Bose-condensed state. Thus from both

technological and scientific viewpoints, there were

compelling reasons to push the techniques of refrigeration to the ultimate limits with the goal of creating BEC.

The first condensates were formed at NIST at temperatures well under a microkelvin. To reach these unprecedented temperatures required a two-stage cooling

technique. The first stage of refrigeration is provided by

laser cooling. Of the three or four most prominent players in the development of laser cooling, two (David

Wineland and Bill Phillips) are long-standing Bureau

scientists; two of their most influential papers are

described in this volume [6,7]. As powerful as laser

cooling is, it is not sufficient on its own to reach BEC

temperatures. The second stage of cooling is known as

evaporative cooling. The laser-cooled atoms are collected in a magnetic trap (another NIST development

[8]) which provides near-perfect thermal isolation from

the surrounding environment. Via a technique known as

rf evaporation [9], the trapped atoms with the most

energy are ejected from the magnetic trap. The remaining atoms have, on average, less energy per atom, and

are therefore colder. After evaporation has cooled the

atoms to a temperature perhaps another factor of a hundred colder than the laser-cooled sample, the condensate

begins to form.

The presence of condensates was originally detected

by velocity-distribution information observed in timeof-flight images. The magnetic fields used to confine

375
the atoms were very suddenly turned off. The residual

thermal and quantum energy of the atoms caused them

to fly apart. After a brief delay, the atoms were illuminated with a strobed flash of laser light, and their image

was captured on an electronic screen. The atoms with

large thermal velocities in the trapped cloud ended up

far from the center of the image; atoms with relatively

low velocities did not travel as far during the delay time

and contributed to the central portion of the recorded

density. Fig. 1 shows a series of three such images; from

left to right they correspond to images taken of three

clouds at progressively lower temperatures [10]. In the

left-most image, the atoms are not yet condensed; the

distribution of velocities is well approximated by a

conventional Maxwell-Boltzmann thermal distribution.

In the center image, the condensate has begun to form;

the central spire corresponds to the near-stationary

atoms of the condensate. The final, right-most cloud is

a near-pure condensate. The central feature amounts to

a photographic image of a single, macroscopicallyoccupied quantum wavefunction.

The original observation of BEC in a gas of atoms

occurred in June of 1995. A few months earlier, several

groups (most notably the NIST/CU collaboration in

Boulder, and groups at Rice University and at MIT)

were very close to achieving Bose-Einstein condensation. All three groups presented their progress in invited

talks at the May 1995 meeting of the American Physical

Society. The audience was left with the impression that

the long-standing goal of BEC might be realized quite

soon. There was a pronounced sense of keen, but goodspirited, competition that added to the general anticipation felt in the physics community.

Ultimately, the NIST group prevailed and its paper [1]

appeared, as the cover article, in Science magazine on

July 14th, 1995. In the same issue, Science also ran a

“perspective” piece by Keith Burnett, of Oxford University, in which he referred to the achievement of BoseEinstein condensation as a sort of “Holy Grail” of

physics. The announcement of Bose-Einstein condensation attracted an unusual amount of attention from

the lay public. There were front-page articles in the

Washington Post, the New York Times and the Los

Angeles Times, and even professional entertainers made

remarks about scientists creating new states of matter.

The scientific press was also duly impressed: the work

was written up in all the major science magazines;

the paper won the AAAS Newcomb-Cleveland award;

and in December 1995 Science deemed BEC the

“Breakthrough of the Year.”

In the years immediately following NIST’s breakthrough result, there was an enormous surge of interest

in the field of BEC. Within a few months, the group at

MIT had successfully created a sample of BEC over a

hundred times larger than the initial NIST result [11].

Theoretical calculations performed at NIST predicted

that the condensate clouds should support standingwave acoustic modes [12], with resonance frequencies

determined by solutions to a macroscopic quantum

wave equation. Within a year, these predictions were

Fig. 1. A series of images of progressively colder clouds of rubidium gas. In the center

image, a Bose-Einstein condensation can be seen emerging from the background thermal

gas. A color version of this image was featured on the 1996 calendar distributed by the

American Physical Society.

376
experimentally verified by the original NIST group in

Boulder [13] and also by the group at MIT [14].

The field of BEC research continues to expand.

Around the world, many experimental groups are now

capable of producing the substance. For a recent review,

see reference [15]. Hundreds of theoretical papers on

BEC are published every year. The major atomic physics

and low-temperature conferences all have multiple

sessions devoted to BEC, and every year a number of

specialty workshops are held on the topic around the

world. The original experimental paper [1] has now

been cited in the scientific literature more than 1000

times, and citations continue to accrue at a rate of more

than 200 per year.

The first major application of BEC has been to make

possible the development of “atom lasers,” intense

beams of coherent atoms which are very analogous to

the more conventional “photon lasers” of light. BEC is

the starting point for this rapidly evolving technology—

after atoms are cooled into a BEC, they are ejected out

of the trap in a highly collimated, monoenergetic beam

[16, 17].

The longer-term technological and economic significance of BEC and the “atom laser” will never rival that

of the optical laser. The ability to create coherent-like

beams of atoms will likely find specialized applications,

however, in certain high-technology fields: BEC will

enhance the capability of very-high-precision, atom-interferometric metrology. On a more speculative note,

one could imagine coherent-source atomic lithography

being used in certain nanofabrication situations.

Eric Cornell’s graduate work was on precision mass

spectroscopy; he received his Ph.D. from MIT in 1990.

He began trying to reach Bose-Einstein condensation in

the same year. Since 1992 he has been a staff physicist

in NIST’s Quantum Physics Division. He is a Fellow

of JILA and Professor Adjoint in the University of

Colorado Physics Dept. His work in Bose-Einstein

Condensation has been recognized by many prizes and

awards, including NIST’s Samuel Wesley Stratton

Award, the Department of Commerce Gold Medal, the

Fritz London Prize in Low Temperature Physics, the

King Faisal International Prize in Physics, the Lorentz

Medal (Royal Netherlands Academy) and the Benjamin

Franklin Medal in Physics. Cornell has also made contributions in the field of atom optics, including developing techniques for guiding beams of atoms through

microscopic channels in hollow glass fibers.

Carl Wieman, a professor in the University of

Colorado Physics Department and a Fellow of JILA

since 1984, is internationally known for his work on

parity violation in atomic cesium and for his experiments in laser cooling. He is a recipient of numerous

international prizes and awards. Wieman and Cornell

have collaborated on the Bose-Einstein Condensation

project since 1990.

Mike Anderson did his graduate work at the University of Colorado and joined Cornell’s group as a

postdoctoral fellow in 1993. He left in 1996 to join

Meadowlark Optics in Frederick, Colorado; he is

currently Vice President of Engineering there. Mike

Matthews and Jason Ensher were graduate students in

the University of Colorado Physics Department.

Matthews is now a staff scientist at 3M in Austin, Texas,

and Ensher is currently doing postdoctoral research

in ultra-cold molecular physics at the University of

Connecticut in Storrs.

Prepared by James Faller.

Bibliography

[1] M. H. Anderson, J. R. Ensher, M. R. Matthews, C. E. Wieman,

and E. A. Cornell, Observation of Bose-Einstein Condensation

in a Dilute Atomic Vapor, Science 269, 198-201 (1995).

[2] W. W. Coblentz, Present status of the determination of the

constant of total radiation from a black body, Bur. Stand. Bull.

12, 553-582 (1916).

[3] C. E. Moore, Atomic Energy Levels as Derived from the Analyses of Optical Spectra, NBS Circular 467, Vol. I, National

Bureau of Standards, Washington, DC (1949), and subsequent

extensions.

[4] U. Fano, Effects of Configuration Interaction on Intensities and

Phase Shifts, Phys. Rev. 124, 1866-1878 (1961).

[5] K. M. Evenson, J. S. Wells, F. R. Petersen, B. L. Danielson,

G. W. Day, R. L. Barger, and J. L. Hall, Speed of Light from

Direct Frequency and Wavelength Measurements of the

Methane-Stabilized Laser, Phys. Rev. Lett. 29, 1346-1349

(1972).

[6] D. J. Wineland, R. E. Drullinger, and F. L. Walls, RadiationPressure Cooling of Bound Resonant Absorbers, Phys. Rev. Lett.

40, 1639-1642 (1978).

[7] P. D. Lett, R. N. Watts, C. I. Westbrook, W. D. Phillips, P. L.

Gould, and H. J. Metcalf, Observation of atoms laser cooled

below the Doppler limit, Phys. Rev. Lett. 61, 169-172 (1988).

[8] A. L. Migdall, J. V. Prodan, W. D. Phillips, T. H. Bergeman, and

H. J. Metcalf, First Observation of Magnetically Trapped Neutral Atoms, Phys. Rev. Lett. 54, 2596-2599 (1985).

[9] N. Masuhara, J. M. Doyle, J. C. Sandberg, D. Kleppner, T. J.

Greytak, H. F. Hess, and G. P. Kochanski, Evaporative Cooling

of Spin-Polarized Atomic Hydrogen, Phys. Rev. Lett. 61, 935-

938 (1988); D. E. Pritchard, K. Helmerson, and A. G. Martin,

Atom Traps, in Atomic Physics 11, World Scientific, Singapore

(1989) pp. 179-197.

[10] Fig. 1 in this vignette amounts to a three-dimensional rendering

of the data presented in Fig. 2 of Ref. 1.

[11] K. B. Davis, M.-O. Mewes, M. R. Andrews, N. J. van Druten,

D. S. Durfee, D. M. Kurn, and W. Ketterle, Bose-Einstein

Condensation in a Gas of Sodium Atoms, Phys. Rev. Lett. 75,

3969-3973 (1995).

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[12] M. Edwards, P. A. Ruprecht, K. Burnett, R. J. Dodd, and Charles

W. Clark, Collective Excitations of Atomic Bose-Einstein

Condensates, Phys. Rev. Lett. 77, 1671-1674 (1996).

[13] D. S. Jin, J. R. Ensher, M. R. Matthews, C. E. Wieman, and

E. A. Cornell, Collective Excitations of a Bose-Einstein

Condensate in a Dilute Gas, Phys. Rev. Lett. 77, 420-423

(1996).

[14] M.-O. Mewes, M. R. Andrews, N. J. van Druten, D. M. Kurn,

D. S. Durfee, C. G. Townsend, and W. Ketterle, Collective

Excitations of a Bose-Einstein Condensate in a Magnetic Trap,

Phys. Rev. Lett. 77, 988-991 (1996).

[15] W. Ketterle, D. S. Durfee, and D. M. Stamper-Kurn, Making,

probing and understanding Bose-Einstein condensates, in BoseEinstein Condensation in Atomic Gases, Proceedings of the

International School of Physics—Enrico Fermi, IOS Press,

Amsterdam (1999) pp. 67-176; E. A. Cornell, J. R. Ensher, and

C. E. Wieman, Experiments in dilute atomic Bose-Einstein

condensation, ibid., pp. 15-66.

[16] M.-O. Mewes, M. R. Andrews, D. M. Kurn, D. S. Durfee, C. G.

Townsend, and W. Ketterle, Output Coupler for Bose-Einstein

Condensed Atoms, Phys. Rev. Lett. 78, 582-585 (1997).

[17] E. W. Hagley, L. Deng, M. Kozuma, J. Wen, K. Helmerson,

S. L. Rolston, and W. D. Phillips, A Well-Collimated QuasiContinuous Atom Laser, Science 283, 1706-1709 (1999).

378
Index

The index includes subjects and names of NBS/NIST staff members mentioned in the accounts of the publications,

as well as names of those who prepared the accounts. The page number listed is the starting page of the account.

A

Abramowitz, Milton, 135

AC-DC transfer standards, 90

Achenbach, Paul R. (Reece), 260

acoustic thermometry, 339

acoustics, 53, 69

AD-X2, 129

adhesives, 174

Advanced Technology Program, 359

aerodynamics, 46

Agency for International Development, 230

Ainsworth, E. L., 86

air conditioning, 10, 270

Albus, James S., 237, 322

Alexander, S. N., 86

algorithms, 77, 81, 250

alloys, 14

Ambler, Ernest, 111

American Ceramic Society, 184

ampere, 56

AMRF, 322

analytical chemistry, 97, 164, 188

Anderson, Michael, 375

antennas, 319

Antosiewicz, H. A., 135

Arend, Peter Vander, 107

ASCII, 172

ASHRAE, 260

Astin, Allen V., 59, 230, 291

atomic energy levels, 73

atomic spectra, 73, 116, 200

atomic weights, 194

ATP, 359

Atwater, Wilbur O., 5

Austin, Louis W., 120

autoionization, 116

Automated Manufacturing Research Facility, 322

aviation, 38

Avogadro constant, 194

Ayres, Robert, 209

B

Babrauskas, V., 280

Baldrige Criteria, 357

Barbrow, Louis, E., 174

Barger, Dick, 191

Barnett, Dean, 100

Beck, Charles M., II, 97

Bekkedahl, N., 104

Belanger, Brian, 16, 167

Belecki, Norman B., 5, 56, 63, 90, 315

Bell, R. K., 56, 63, 90, 315

Bentz, Dale, 33

Berk, Norman F., 303

Bernstein, Barry, 126

Bichowsky, F. R., 93

Bicking, George W., 66

Birmingham, Bascom, 107

blackbody radiation, 7, 25

Blandford, Josephine M., 174

Block, Stanley, 100

Bogue, Robert, 33

Boisvert, Ronald F., 135, 140

Boltzmann constant, 339

Borchardt, Bruce, 241

Bose-Einstein condensation, 331, 375

boundary layers, 46

Bowen, R., 309

Boyd, H. S., 19

Brady, Charles, 350

Brady, Edward L., 230, 291

Bragaw, C. L., 120

Branscomb, Lewis M., 135, 230, 234, 291

Branstad, Dennis, 250

Braun, E., 347

Breckenridge, Frank, 69

Breen, Bettijoyce, 254

Breitenberg, Maureen, 366

Brenner, F. Cecil, 174

Brickencamp, Carroll, 167

Brickwedde, Ferdinand G, 43, 107

bridges of Ko ̈nigsburg, 140

Briggs, Lyman J., 1

Bright, Harry Aaron, 97

broadcasting (radio), 16

Brown, E. A., 59

Brown, James E., 344

Brown, Walter E., 309

Building and Housing Series, 22

building codes, 22, 275, 283, 347

building materials, 10, 22

Building Science Series, 260

buildings, 260, 266

Bukowski, Richard, 347

Buntin, Steve, 334

Bunting, E. N., 100

Burgess, G. K., 230, 291

Burns, Grace, 174

Burr, William E., 250

379
C

CAD/CAM, 246, 322

Cage, Marvin E., 56, 63, 315

Cahill, William F., 135

Cahn, John, 300

Cali, J. Paul, 227

calibration, 129, 227, 230

calorimetry, 93, 178

Cameron, Joseph, 129, 132, 167

candela, 7, 25

Carpenter, B. Stephen, 230

Cavallo, Lucy M., 209

Cavanagh, Rich, 334

Celotta, Robert J., 203

Cement and Concrete Reference Laboratory, 33

cement, 33

ceramics, 181, 184

cerebellar model articulation controller, 237

chain folding, 104

Chamberlain, G. E., 297

Chang, Connie, 359

Charters of Freedom, 66

Chelton, Dudley, 107

chemical analysis, 97, 164, 188

Chemical Information System, 254

chemical kinetics, 224

chemical structure searching, 86

Chemical Thermodynamics Data Center, 93

Chemistry WebBook, 93

Cheok, Geraldine, 140

Chi, J., 270

Chinese postman problem, 140

Churney, Kenneth, 178

Civil Aeronautics Administration, 38

Clark, Al F., 294, 306

Clark, Charles W., 116, 334

Clevinger, Mary A., 184

Coblentz Society, 7

Coblentz, William W., 7, 25

CODATA, 1, 93, 291

Codling, Keith, 116

Collaborative Testing Services, Inc., 66

Colle ́, Ron, 129, 209

color standards, 25, 145, 174

colorimetry, 25

combinatorial algorithms, 140

compilers, 258

computer-aided manufacturing, 246, 322

computers, 86, 172, 250, 254

concrete, 33

condensed matter physics, 203

Condon, Edward U., 73, 77, 107, 230

configuration interaction, 116

conformance testing, 258

conjugate gradients method, 81

consumer information, 174

control systems, 237

Cook, Richard K., 53, 69

Cooper, J. W., 86

coordinate measuring machine, 241

Cooter, I. L., 63

Coriell, Sam, 14

Corliss, Charles, 73

Corliss, Edith L. R., 174

Cornell, Eric, 375

corrosion, 174

Coursey, Bert, 209

Critchfield, C., 56

critical point, 149, 152

Croarkin, M. Carroll, 129, 132

Cromer, Chris, 178

Cryogenic Engineering Conference, 107

cryogenics, 43, 107, 111, 294

crystallography, 100, 188, 300, 303

Cugini, John, 258

currency, 66

current measurement, 90

Currie, Lloyd, 164, 209

Curtis, H. L., 56

Curtis, R. W., 56

Curtiss, John, 77

Cutkosky, R. D., 56

D

Danielson, Bruce L., 191, 297

data analysis, 132

data encryption, 250

database management, 254, 291

Davis, G. T., 104

Davis, Philip J., 135

Davis, Rich, 339

Davis, Ruth M., 250

Davis, Tom, 104

Day, Gordon W., 191, 297

Dellinger, John H., 16, 120

densitometers, 145

dental research, 309

DeSimone, Daniel, 234

Deslattes, Richard D., 194

desorption, 219

detection limit, 164

deterministic metrology, 241

Deters, Teresa, 73

deuterium, 43

developing countries, 230

diamond anvil pressure cell, 100

Diamond Ordnance Fuze Laboratory, 59

Diamond, Harry, 38, 59

Dickinson, Hobart, 10

Didion, David A., 270

DIET, 219

Digital Library of Mathematical Functions, 135

DiMarzio, E. A., 104

dimensional metrology, 19

direction finder, 38

disaster alleviation, 283, 350

Doiron, Ted, 19, 241

Domalski, Eugene, 93

dopant density, 289

Dowell, Marla, 178

Driscoll, R. L., 56

Drullinger, R. E., 200

Dryden, Hugh L., 46

Dunmore, Francis, 38

Duralumin, 14

380
dwelling construction, 22

Dziuba, Ronald F., 56, 63, 315

E

economics, 260

Ederer, David, 116

Edmonds, Jack, 140

Edwards, Terry J., 339

Ehrlich, Charles, 167

Eicke, W. G., 315

Eisenhart, Churchill, 129, 132, 167, 241

Ekin, Jack W., 294, 306

Elbourn, R. D., 86

electrical units, 5, 56, 63, 90

electromagnetic wave propagation, 120

electron probe microanalysis, 160

electron sources, 203

electron spectroscopy, 116

electron-stimulated desorption, 219

Electronic Computers Laboratory, 86

Ellingwood, Bruce R., 283

Elmquist, R. E., 56, 63, 315

Emerson, W. B., 25

encryption, 250

energy conservation, 260, 266, 270

energy, 174

Engel, F. H., 38

Epling, Mary, 132

equation of state, 152

Evans, David, 28

Evans, William, 93

Evenson, Ken, 191

exchange formats, 246

Expect, 353

F

Faller, James, 375

Fano, Ugo, 116, 203

Federal Information Processing Standard, 172, 250

femtochemistry, 334

Ferraris, Chiara, 33

fiber optics, 297

fibers and fabrics, 174

Fickett, Fred R., 294, 306

field emission spectroscopy, 155

field emission, 214

Filliben, James J., 132, 209, 289

Fiori, Charles, 160

FIPS, 172, 250

fire and fire research, 28, 275, 280, 344, 347

fluid properties, 149

Flynn, D. R., 10

Fonoroff, B., 59

Food and Drug Administration, 209

Forman, Richard, 100

Forney, C. L., 347

Forsythe, George, 77, 81

FORTRAN, 258

fracture mechanics, 181, 350

Franzen, Douglas L., 178, 297

Freeman, George, 107

Freiman, Stephen, 181

French, Judson C., 123

frequency measurements, 191

frequency standards, 200, 331

Friedman, D. C., 86

Frohnsdorff, Geoffrey, 33

Frolen, L, 104

Fuhr, Jeffrey, 73

Fuller, Edwin, 181

fundamental physical constants, 1

G

Gadzuk, J. William, 155, 214, 219, 334

gage blocks, 19

Galawa, R. L., 297

Galejs, Anija, 203

gamma rays, 194

Garboczi, Edward, 33

Garfinkel, Samuel B., 209

Garner, Ernest, 167

gas constant, 339

Gass, Saul, 140

Gayle, Frank, 300

Gibson, Kasson S., 25

Gibson-Tyndall curve, 25

Gifford, William, 107

Gilchrist, R., 97

Gilliland, T. R., 120

Gills, Thomas E., 227, 313

Ginnings, Defoe C., 7, 49

glass, 181

Goldberg, Karl, 135

Goldberg, Robert, 93

Goldfarb, Ron B., 294

Goldman, Alan, 140

Gordon, Fannie M., 77

Gornick, F., 104

Gould, Phillip, 331

graph theory, 140

Gray, Martha M., 172

Green, M. S., 149, 152

Greenspan, Martin, 69

Gross, Daniel, 28

Grossman, E. N., 90

Grover, Frederick W., 5, 16

guarded hot plate, 10

Guide to Available Software, 77

Guthrie, William, 132

Guttman, C. M., 104

H

Haar, Lester, 49

Hague, J. L., 97

Hahn, M. H., 10

Hall, John, 191

Hamer, Walter J., 43

Hamilton, Clark A., 315

Handwerker, Carol, 300

Hardis, Jonathan E., 25

381
Harper, D. R., III, 10

Harris, Forest K., 230

Hartman, Ike, 371

Harvey, Allan H., 49

Hasko, Steve, 132

Haueter, Ruth C., 86

Haynsworth, Emilie V., 135

Hayward, Raymond W., 111

HAZARD1 software, 347

health care facilities, 275

hearing, 53

hearing aids, 174

heat release in fires, 280

heat transfer, 10

heating and cooling systems, 266, 270

Heckert, Alan, 132

Heinrich, Kurt F. J., 160

Heldenbrand, Jim L., 260

Hembree, Gary, 371

Henins, Albert, 194

Hermach, Francis L., 90

Hestenes, Magnus, 77, 81

Heydemann, Peter, 230

high pressure research, 100

Hill, D. A., 120

Hill, James E., 270

Hillebrand, William Francis, 97

Hilsenrath, Joseph, 49, 254

Hinman, W. S., Jr., 59

Hirshfeld, Alan, 209

Hocken, Robert, 241, 322

Hoffman, James Irvin, 97

Hoffman, John, 104

Holberton, Frances E. (Betty) Snyder, 258

Holt, A. W., 86

Hoppes, Dale D., 111

Huang, D. X, 90

Hudson, Ralph P., 111, 339

Huggett, Clayton, 280

Huntoon, Robert D., 59

Hust, Jerry G., 294

Hutchinson, J. M. R. (Robin), 209

HVAC, 266, 270

hydrocarbons properties, 93

hydrogen isotopes, 43

I

icosahedral crystal symmetry, 300

IGES, 246

image processing, 86

impedance, 5

Inaba, Atsushi, 344

inductance, 5

Industrializing Economies, 230

information security, 250

infrared spectroscopy, 7, 100

Ingberg, Simon, 28

initial graphics exchange specification, 246

Inn, Kenneth, 209

inorganic analysis, 97

Insley, Herbert, 184

Institute for Numerical Analysis, 77, 81

insulation, thermal, 10

Interamerican Metrology System, 230

interferometry, 19, 194

International Association for the Properties of Water and Steam, 49

International Bureau of Weights and Measures, 1

international cooperation, 230

International Critical Tables, 1, 291

International Temperature Scale of 1990, 339

Internet sites, 1

ion storage, 200

ionosphere, 120

ISO 9000, 366

isotopes, 43

Itano, W. M., 200

J

Jacobs, Madeleine, 174

Jacobs, Robert, 107

JANAF Tables, 93

Jeffrey, Anne-Marie, 5, 56, 63, 315

Jennings, Don, 178

Jennings, Hamlin, 33

Johnson, Stephen, 33

Johnson, Victor, 107

Jones, W. W., 347

Josephson voltage standard, 315

Journal of Physical and Chemical Reference Data, 291

Journal of Research of NBS/NIST, 1

Joy, David C., 328

Judd, Deane B., 25, 174

K

Karen, Vicky Lynn, 188

Kasen, M. B., 294

Kashiwagi, Takashi, 344

Kautz, Richard L., 315

Kearsley, Elliot A., 126

Kelly Committee, 59

Kelly, George, E., 270

Kemmerer, Sharon J., 246

Kern, David, 319

Khoury, Freddy, 104

Kim, E. M., 297

Kinard, Joseph R., 56, 63, 90, 315

kinetics, 224

King, David, 334

Kirsch, Russell A., 86

Klein, Ralph, 219, 224

Knowles, H. B., 97

Koch, J. A., 90

Koenig, Joan, 368

Kotter, F. R., 63

Kropschot, Richard H., 107

Kruger, Jerome, 174

Ku, Harry, 129, 167, 209, 227

Kusuda, Tamami (Tom), 260, 266

Kuyatt, Chris E., 116, 129, 155, 203

382
L

laboratory accreditation, 167

Laidlaw, Frances, 359

Lanczos, Cornelius, 77, 81

Land, J. L., 368

Larrabee, Robert, 328

laser cooling, 200, 331, 375

laser excited desorption, 334

laser frequency measurements, 191

laser power and energy measurement, 178

Lashof, Theodore, 66

Launer, Herbert F., 66

Lauritzen, John, Jr., 104

Lawrence, James, 140

Lazar, John, 241

Leaderman, Herbert, 126

Ledbetter, Hassel, 294

Lehman, Shirley Young, 132

Leight, Walter G., 174

Leiner, A. L., 86

length standards, 19

Leonhardt, Rod, 178

Lett, Paul, 331

Lettieri, Tom, 371

Levelt Sengers, Johanna M. H., 49, 152

Levin, Ernest M., 184

Libes, Don, 353

Lide, Bettijoyce, 254

Lide, David R., 1, 93, 230, 231

Liepman, David S, 135

Liggett, Walter, 209

light properties, 25

light scattering, 149

Lindstrom, Richard M., 164

line shape, 116

linear systems of equations, 81

linewidth metrology, 328

Lipe, T. E., 90

Lippincott, Ellis, 100

Little, John L., 172

Liu, Y. M., 289

Livigni, David, 178

Lloyd, Francis L., 315

low-temperature materials, 294

Lozier, Daniel W., 135

Luecke, William, 174

Luke, Yudell, 135

luminous intensity, 25

Lundell, Gustav Ernst Fredrik, 97

Lyons, John W., 59

M

Madden, Robert, 116

Madey, Theodore, 219

Mahaffey, Charles T., 260

Malcomb Baldrige Quality Award, 357

Mandel, John, 66

Mandelkern, L., 104

Mann, Douglas, 107

Mann, Wilfrid Basil, 209

manufacturing, 322, 363

Manufacturing Extension Partnership, 363

maps, 66

Marienko, Ryna, 160

Marshall, Harold E., 260

Martin, Georgia, 73

Martin, William C., 73

Martys, Nicos, 33

Marx, Egon, 371

Mason, H. L., 230

mathematical functions, 135

mathematical tables, 77, 135

matrix eigenvalue problems, 77

Mattis, R. L., 289

Mayo-Wells, John F., 5, 56, 63, 90, 315, 319

McCamy, Calvin S., 145

McColskey, David, 350

McCoubrey, Arthur, 167

McHenry, Harry I., 294, 350

McMurdie, Howard, 100, 184

McNesby, James R., 224

McNish, A. G., 135

Mears, Thomas W., 227

Mease, Norman E., 46

measurement assurance, 129, 167, 209

measurement systems, 227

measuring machines, 241

Mehl, J. B., 339

Melmed, Al, 155, 219

MEP, 363

Merica, Paul D., 14

Messina, Carla G., 184

metallurgy, 350

meter, 191

metric system, 174, 234

metrology, 241

Michaelis, Robert E., 227

microanalysis, 160

microfilm preservation, 145

microphones, 53

microtopography, 214

microwave antennas, 319

microwave propagation, 120

Mielczarek, Stan, 203

Mighell, Alan D., 188

Miller, J. M., 16

minerals and rocks, 97

missiles, 59

Mohr, Peter J., 1

Moldover, Michael R., 339

Moore, Charlotte E., 73

Moulder, John C., 294

Mountain, Raymond D., 149, 152

Munro, Ronald, 184, 188, 300, 309

Musgrove, Arlene, 73

Myklebust, Robert, 160

N

Nagel, Roger, 246, 322

National Advisory Committee for Aeronautics, 46

National Applied Mathematical Laboratories, 135

383
National Conference on Weights and Measures, 368

National Defense Research Committee, 59

National Standard Reference Data System, 1, 230, 291

National Type Evaluation Program, 368

Natrella, Mary Gibbons, 132

navigational aids, 38

NCSBCS, 260

near-field antenna measurements, 319

Nedzelnitsky, Victor, 53

Nelson, Harold, 275

neutron diffraction, 303

Newbury, Dale E., 160

Newell, D. B., 56

Newman, M., 135

Nobel Prize, related to NBS/NIST work, 43, 111, 155, 214, 331

Novotny, D. B., 90

nuclear medicine, 209

Nyyssonen, Diana, 328

O

O’Brien, Anita, 363

O’Leary, Dianne P., 77, 81

O’Leary, M. J., 66

Oberhettinger, Fritz, 135

Office of Scientific Research and Development, 59

ohm, 63

Okabe, Hideo, 224

Oldham, Nile M., 56, 63, 315

Olsen, P. T., 56

Olver, F. W. J., 135

Omnidata, 254

Ondik, Helen M., 184

operations research, 140

optical density, 145

optical fibers, 297

optical interferometry, 194

optical modulation, 145

Ordnance Development Division, 59

Osbourne, Nathan S., 10, 49

Oser, Hans J., 38

oxygen consumption calorimetry, 280

P

Paffenbarger, George Colby, 309

Page, Chester, 59

Paige, L., 81

paper, 66

parity conservation, 111

Parker, Elizabeth, 258

Parker, William, 280

Parr, Albert, 7

Parsons, Douglas, 209

particle-sizing standards, 371

Passaglia, E., 1, 104

Peacock, R. D., 347

Peavy, B. A., 10

Peavy, S, 135

Peiser, H. Steffen, 43, 230

Peters, Chauncy, 19

Petersen, Russ, 191

Peterson, C. L., 63

Peterson, Stephen, 174, 260

phase equilibria diagrams, 184

Phillips, William, 200, 331, 375

photochemistry, 219, 224

photography, 145

photomask standards, 328

photometry, 7, 25

Pierce, Daniel T., 203

Piermarini, Gasper, 100

Pike, J. L., 86

Planck’s constant, 7

plastics, 344

Plitt, Karl F., 174

Plumb, Harmon, 167

Plummer, E. Ward, 155

Polonsky, Ivan, 135

polymer crystallization, 104

polymers, 126, 344

polystyrene spheres, 371

Pontius, Paul, 129

Portland Cement Association Fellowship, 33

Postek, Michael T., 328

Potzick, James E., 46

Powell, Cedric J., 219

Powell, F. J., 10

Powell, Jeanne, 359

Powell, Robert, 107

precipitation hardening, 14

precision and accuracy, 129

pressure calibration, 100

Proctor, Thomas M., 69

protein crystallography, 303

Protein Data Bank, 1

proximity fuzes, 59

Purtscher, Patrick, 350

Q

quality award, 357

quality control, 313

quality standards, 366

quantum mechanics, 111

quasicrystals, 300

R

Rabinow, Jacob, 59

Radack, Shirley, 174

radiant energy, 25

radio, 16, 120

radio-beacons, 38

radioactivity standards, 209

radiochemistry, 164

radiometry, 7

radionuclides, 209

radiopharmaceuticals, 209

Rasberry, Stanley, 160, 167

Read, Dave T., 294, 350

Reader, Joseph, 73

reduced cells, 188

384
Reed, Richard P., 294

Reed, William P., 227

Reeve, Charles, 241

reflectance, 145

refrigeration, 10

Reilly, M. L., 7

Reinstsema, C. D., 90

Repjar, A. G., 319

resistance standards, 63

resistivity in silicon, 289

rheology, 126

Richter, Lee, 334

Richter, Ralph A., 234

Ripple, Dean, 339

Robbins, Carl R., 184

Robinson, Henry, 10

robotics, 237

Rolston, Steven, 331

Rosa, Edward B, 1, 5

Ross, G. S., 104

Rosser, J. Barkley, 77, 81

Rossini, Frederick D., 93

Roth, Robert S., 184

Ruegg, Rosalie, 359

Rumble, John R., Jr., 93, 230, 254, 291

S

Sanchez, I. C., 104

Santoro, Antonio, 188

scaling theory, 152

scanning probe microscopy, 214

scanning tunneling microscope, 155

Schafft, Harry A., 123

Scheer, M. D., 219

Schenck, Peter K., 184

Schiller, Susannah, B., 313

Schmidt, Leonard, 178

Schooley, James, 1

Schoonover, Irl, 100

Schubauer, Galen, 46

Scire, Fredric, 214

Scott, H, 14

Scott, Russell B., 107

Scott, Thomas R., 178

Scribner, B.F., 97

SEAC, 86, 172

second breakdown, 123

security alarms, 174

semiconductor device metrology, 328

semiconductors, 289

SEMPA, 203

Sengers, Johanna, 49, 152

Severo, Norman C., 132, 135

Seward, Richard W., 227

Shaw, Merle B., 66

Shives, T. Robert, 350

Shupe, P. D., 86

SI (International System of Units), 1, 5, 25, 56, 63, 90, 191, 194, 234,

315

Sienkiewicz, Robert, 359

Siewert, Tom, 350

silicon, 289

Simiu, E., 283

Simpson, John A, 116, 155, 167, 203, 241, 322

Sjo ̈lin, Lennart, 303

Skramstad, Harold K., 46

Slutz, R. J., 86

Small, John, 160

Smid, Miles, 250

Smith, Bradford, 322

Smith, J. L., 86

smoke detectors, 174

Smyth, Deborah, 357

Snyder, Kenneth, 33

Snyder, W. F., 120

software testing, 258, 353

Somerville, Paul, 132

sound pressure, 53

sound waves, 69

Southard, Thomas H., 135

Southworth, G. C., 16

space beads, 371

Sparks, Larry L., 294

spectroscopy, 7, 73, 116, 155, 194, 200, 331, 375

speed of light, 191

spin-polarized electrons, 203

Spivack, Richard N., 359

standard reference data, 49, 73, 93, 184, 230, 254, 291

standard reference materials, 209, 227, 230, 313, 371

Stanley, Connie, 227

Statistical Engineering Laboratory, 129, 132

statistics, 129, 132, 164, 167

steam tables, 49

Steckler, Kenneth D., 280

Steel, Eric, 160

Stefan-Boltzmann constant, 7, 339

Stein, Phil, 167

Stein, Steve, 254

Steiner, Bruce, 25

Steiner, Richard L., 56, 315

Stephenson, John, 334

Stigler, Stephen, 129

Stimson, Harold F., 49

Stratton, Samuel Wesley, 5, 7

stress relaxation, 126

Stroup, David, 275

structural design, 283

Sugar, Jack, 73

Sullivan, Donald B., 191, 200

superconductors, 306

supercritical fluids, 152

surface science, 155, 214, 219, 334

synchrotron radiation, 116

T

Tang, Yi-hua, 56, 63, 315

Taylor, Barry, 1, 129

Taylor, James, 22

Taylor, John Keenan, 97, 313

Teague, E. C., 214

Technical Association of the Pulp and Paper Industry, 66

technology development, 359

Tesk, John A., 309

thermal conductivity, 10

thermal converters, 90

385
thermal insulation, 10

thermodynamics, 49, 93, 152

Thomas, James L., 63

Thompson, George N., 22

three-dimensional metrology, 241

Thurber, W. Robert, 289

Tilley, W. Reeves, 174

time-dependent materials, 126

tires, 174

Tobler, R. L., 294

topografiner, 214

traceability, 167, 209

Trahey, Nancy M., 313

transistors, 123

Trusler, J. P. Martin, 339

Tschiegg, Carl, 69

turbulence, 46

Tyndall, Edward P. T., 25

U

Ugiansky, Gil M., 368

uncertainty, 129

Unertl, Bill, 203

Univac, 86

universal gas constant, 339

Universal Product Code, 174

V

Van Dusen, Milton, 10

Van Valkenburg, Alvin, 100

Vanderah, Terrell A., 184

velocity of light, 191

Vicentini-Missoni, M., 152

Vieth, Donald, 160

Villarrubia, J. S., 214

viscoelasticity, 126

visibility of radiant energy, 25

volt and voltage measurement, 90, 315

W

Wachtman, John B., 100

Wagman, Donald, 93

Wagner, Leon, 107

Wait, James R., 120

Walls, F. L., 200

Waltenberg, R. G., 14

Walton, George, 260, 266

Wang, Andrew, 359

Wang, Gwo-Ching, 203

war work at NBS, 1, 46, 59, 66

Ward, John, 214

Washburn, E. W., 1, 291

Watts, Richard, 331

wavelength standards, 194

Web Book (Chemistry), 93

Weber, Charles G., 66

Weeks, J. J., 104

weights and measures, 368

Weinberger, A., 86

Weir, Charles E., 100

Wells, Joe, 191

West, Dale, 178

Westbrook, Christoph, 331

Westbrook, Jack, 254

White, Howard J., 49

Wichers, E., 97

Wiederhorn, Sheldon, 181

Wieman, Carl, 375

Wiese, Wolfgang L., 73

Williams, Edwin R., 56, 63, 315

Wilson, William K., 66, 174

Wineland, David J., 200, 375

Witt, R. P., 86

Witzgall, Christoph, 140

Wlodawer, Alexander, 303

Wood, L. A., 104

Wooley, H. W., 107

World Wide Web sites, 1

Wright, J. H., 86

Wright, James R., 260

Wright, Richard, 28

X

x-ray diffraction, 188, 303

x-ray wavelength measurements, 194

Y

Yates, John, 219, 334

Yokley, C. R., 7

Yolken, H. Thomas, 227

Youden, W. J., 33, 129, 209

Young, M., 297

Young, Russell D., 155, 214, 219

Z

Zalubas, Romuald, 73

Zapas, Louis J., 126

Zarr, Robert, 10

Zelen, Marvin, 135

Zimmerman, Brian, 209

Zingeser, Joel P., 22

Zucker, Ruth, 135

386