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PB 161593

92

RESEARCH PROGRAM OF THE

RADIATION PHYSICS DIVISION,

NATIONAL BUREAU OF STANDARDS

I U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS
THE NATIONAL BUREAU OF STANDARDS

Functions and Activities

The functions of the National Bureau of Standards are set forth in the Act of Congress, March

3, 1901, as amended by Congress in Pubhc Law 619, 1950. These include the development and,|

maintenance of the national standards of measurement and the provision of means and methods foi making measurements consistent with these standards; the determination of physical constants anc

properties of materials; the development of methods and instruments for testing materials, devices

and structures; advisory services to government agencies on scientific and technical problems; in-^ vention and development of devices to serve special needs of the Government; and the development

of standard practices, codes, and specifications. The work includes basic and appUed research,

development, engineering, instrumentation, testing, evaluation, calibration services, and various

considtation and information services. Research projects are also performed for other government

agencies when the work relates to and supplements the basic program of the Bureau or when the

Bureau's unique competence is required. The scope of activities is suggested by the Usting oi

divisions and sections on the inside of the back cover.

Publications

The results of the Bureau's work take the form of either actual equipment and devices or pubUshed papers. These papers appear either in the Bureau's own series of pubhcations or in the journals

of professional and scientific societies. The Bureau itself pubhshes three periodicals available from

the Government Printing OflBce: The Journal of Research, pubUshed in four separate sections,

presents complete scientific and technical papers; the Technical News Bulletin presents sununar>- and preliminary reports on work in progress; and Basic Radio Propagation Predictions provides

data for determining the best frequencies to use for radio conununications throughout the world.

There are also five series of nonperiodical pubhcations: Monographs, Apphed Mathematirs Series,

Handbooks, Miscellaneous Publications, and Technical Notes. Information on the Bureau's pubhcations can be found in NBS Circular 460, Pubhcations of the

National Bureau of Standards ($1.25) and its Supplement ($1.50), available from the Superintendent^

of Documents, Government Printing Office, Washington 25, D.C.
NATIONAL BUREAU OF STANDARDS

technical ^^ote

92

MAY 1961

RESEARCH PROGRAM OF THE

RADIATION PHYSICS DIVISION,

NATIONAL BUREAU OF STANDARDS

W. R. Ney AND L. S. Taylor

NBS Technical Notes are designed to supplement the Bureau's regular publications program. They provide a means for making available scientific data that are of transient or limited interest. Technical Notes may be

listed or referred to in the open literature. They are for sale by the Office of Technical Services, U. S. Department of Commerce, Washington 25, D. C.

DISTRIBUTED BY

UNITED STATES DEPARTMENT OF COMMERCE

OFFICE OF TECHNICAL SERVICES

WASHINGTON 25, D. C.

Price $1.50

FOREWORD

The Radiation Physics Division had its roots in the old Optics

Division, which was one of the original divisions of the National Bureau

of Standards established in I9OI. In 19^7, the Optics Division was

reorganized and a new division, the Atomic and Radiation Physics

Division, formed from those sections and activities concerning atomic

and radiation physics. Because of the natural grouping of some of the

activities in the new division, it was decided in 19^9 to subdivide the

division into two branches or laboratories, the Atomic Physics Laboratory

and the Radiation Physics Laboratory. This subdivision was carried further in i960 when the two laboratories were made the bases of two new

divisions, the Atomic Physics Division and the Radiation Physics Division,

The Radiation Physics Division is thus an outgrowth of the X-ray

Section, which was established in the Optics Division in I927. The Scope

of the activities of the X-ray Section began to broaden in about 19^0

under the pressure of war research. Following the advent of atomic

energy, the demands upon the laboratory developed rapidly, particularly

in the directions of high- energy-radiation research and radiation instrumentation. By 19^9^ the program had developed to the point where it

seemed desirable to divide the activities of the X-ray Section into five

sections. X-ray, Radiation Theory, High Energy Radiation, Radiological

Equipment, Nucleonic Instrumentation, and group them together with the

Radioactivity Section to form the Radiation Physics Laboratory, In

January 1957 the Neutron Physics Section was formed and these seven

sections formed the basis for the establishment of the Radiation Physics

Division in I96O,

This report sets forth the organizational plan of the Division

together with a brief presentation of the activities carried out in the

various sections. It covers only programs upon which there has been

activity within the past year. However, in some instances brief mention

is made of the direction of future work for which plans have already

been made

Lauriston S, Taylor, Chief

Radiation Physics Division

iii
TABLE OF CONTENTS

Page

I« Mission of the Radiation Physics Division, ••••••..• 1

II» Organization of the Radiation Physics Division ., 2

III. Staff of the Radiation Physics Division, . , . , , 3

IV. Facilities of the Radiation Physics Division 12

V. Introduction to the Program, •.•••••»..•••••• 23

VI, Detailed programs of the Sections* •••••••••••.. 24

1, X-ray Section, .,,,,,,,,,,,,,,,,,,,, 2Z.

2, Radioactivity Section 26

5, Radiation Theory Section ., ,, 29

k-. High Energy Radiation Section, , 31

5. Radiological Equipment Section 37

6. Nucleonic Instrumentation Section .,,,,,,,,,,, /^J.

7, Neutron Physics Section, ,.,,,,,,,,,,,,,, 42

8, Health Physics Group ••...•, 44

VII, Activities Associated with Outside Organizations ,,,,,, 45

iv
RESEARCH PROGRAM OF THE RADIATION PHYSICS DIVISION,

NATIONAL BUREAU OF STANDARDS

Abstract: This report describes the research program of the

Radiation Physics Division, It includes a statement of the

mission of the division, a list of senior staff members,

descriptions of the facilities available to the division

staff, and detailed descriptions of the research programs

of the various sections of the division,

I. MISSION OF THE RADIATION PHYSICS DIVISION*

The National Bureau of Standards must provide national leadership in accurate and uniform techniques of physical measurement of

radiations and their interactions with matter. The radiations con- sidered by the Radiation Physics Division are those available from

radionuclides and from particle accelerators with energies between

5 kev and 200 Mev,

Therefore, the mission of the Division is to obtain basic experimental and theoretical data concerning the interactions of radiation

with nuclei^ atoms, and molecules, as well as with bulk matter; the

investigation, development, and improvement of radiation sources and

standards; and the development of improved techniques and instruments

for the detection and measurement of these radiations.

The Division is concerned with the development and improvement

of: flux and dosimetry standards for neutrons, electrons. X-rays and

gamma-rays; X-ray and radioactivity standards; nuclear data; radiation

protection standards; and definitions of quantities and units. The

Division is also concerned with the international correlation of these

data. Complementing the provision of radiation standards for physical measurement must be a general measurement and research competence.

This competence must especially be developed in those new areas of

radiation physics where sufficiently accurate basic data are unavailable.

Examples of research areas included in this statement are: radiation dosimetry and protection; radiation penetration; electron, atomic,

and nuclear cross sections.

This statement represents the present thinking of the Division but

is still under development and hence should not be considered conclusive.
II. ORGANIZATION OF THE RADIATION PHYSICS DIVISION

The Radiation Physics Division of the National Bureau of

Standards is divided into seven sections. The division organization

is as follows:

RADIATION PHYSICS DIVISION, Lauriston S, Taylor, Chief

1. X-ray Section

2. Radioactivity Section

3. Radiation Theory Section

k. High Energy Radiation Section

^. Radiological Equipment Section

6, Nucleonic Instrumentation Section

7. Neutron Physics Section

H. 0. Wyckoff, Chief

Wo Bo Mann, Chief

L, V. Spencer, Acting Chief

Ho W. Koch, Chief

S. W. Smith, Chief

L. Costrell, Chief

R. S. Caswell, Chief
III. Staff of the Radiation Physics Division

The senior professional staff members of the Radiation Physics

Division are listed below. In addition, there are 8 junior professional

and 17 subprofessional personnel together with 14 administrative employees.

BAY, Zoltan L. (NBS 1955)

PhD. University of Budapest, 1926, mathematics and astronomy.

University of Budapest, 1923-26, assistant professor; Physikalisch Technische Reichsanstalt, Berlin, 1926-30, research; University of Szeged,

Hungary, 1930-36, professor; Research Laboratory of Tungsram, Budapest,

1936-48, Chief of Laboratory; Technical University of Budapest, 1938-48,

professor; George Washington University, Washington, D.C., 1948-55,

research professor.

Present: X-ray Section; measurement of W; fast coincidence experiments.

BERGER, Martin J. (NBS 1952)

PhD. University of Chicago, 1951, scattering in photographic emulsions;

University of Chicago, 1951-52, Post-doctoral Fellow in statistics.

Present: Radiation Theory Section; transport theory for gamma rays,

neutrons and charged particles; radiological physics; development of

Monte Carlo methods.

BEVERLY, William B. (NBS 1959)

PhD. University of Virginia, 1959, neutron polarization.

Present: Neutron Physics Section; neutron polarization, neutron spectroscopy.

BRUECKMANN, Robert E. (NBS 1948)

M. S.E. Princeton University, 1950, research in microwave radio.

Manhattan Project, 1944-46; Princeton University, 1946-48, laboratory

instructor; NBS Radiological Equipment Section, 1948-57, applicational

engineering of X-ray equipment.

Present: Nucleonic Instrumentation Section; development and design of

instrumentation for nuclear physics research.

CASWELL, Randall S. (NBS 1952)

PhD. Massachusetts Institute of Technology, 1951, average energy of

beta-ray spectra.

M. I.T, , 1947-50, teaching and research assistant; University of Kentucky,

1950-52, Associate Professor of Physics; The American University, 1955 to

present, Adjunct Professor of Physics.

Present: Chief, Neutron Physics Section; experimental neutron physics,

neutron cross section calculations.

CAVALLO, Lucy M. (NBS 1947)

B.A. Hunter College, 1947, work in biochemical analysis; course in Radioisotope Techniques at GRINS.

Present: Radioactivity Section; radioisotope standardization.
CHIN, Jack (NBS 1954)

B.S. St. Mary's University, 1951, physics.

Present: Neutron Physics Section; neutron sources and detectors.

COSTRELL, Louis (NBS 1946)

M.S. University of Maryland, 1949, electrical engineering; B.S. University of Maine, 1939, electrical engineering.

Westinghouse, 1939-41, generator design; Navy Dept. BuShips, 1941-46,

Electrical Section; NBS Radioactivity Section, 1946-49, radioactivity

measurements and instrumentation.

Present: Chief, Nucleonic Instrumentation Section; telemetering systems,

electronic instrumentation development.

COYNE, J. Joseph (NBS 1960)

B.S, Loyola College, Baltimore, 1950, physics.

Catholic University, 1955-60, graduate student, teaching assistant and then

research assistant, nuclear structure.

Present: Radiation Theory Section; nuclear cross sections and penetration.

DANOS, Michael (NBS1954)

PhD. University of Heidelberg, 1950, physics, theory of photonuclear re- actions, physics of metal surfaces; M.S. Techn. Univ. of Hannover, 1948,

electrical engineering.

Columbia University, 1952-54, Res. Assoc, microwave physics and theory of

radiation; Guggenheim Fellow, 1959, Univ. of Heidelberg, Germany.

Present: Theoretical studies of photonuclear reactions. Validity of sum

rule calculations. Effects of long and short range correlations on the

nuclear photoeffect.

DeLaVERGNE, LeRoy (NBS 1953)

B.S. Queens College, City of New York, 1943, physics.

Naval Research Laboratory, 1943-46, Sound Division; graduate studies - University of Rochester, 1946-52.

Present: Radiological Equipment Section, radiation instrument studies and

calibration.

DCMEN, Steve (NBS 1951)

B.A. State Teachers College, Indiana, Pa., 1949, mathematics and physics;

M.S. University of Maryland, 1958, physics.

Present: Development of methods for absolute determination of high energy

X-ray intensities.

EHRLICH, Margarete (NBS 1948)

PhD. Catholic University, 1955, X-ray scintillation spectrometry;

University of Vienna, 1934-38; Grady Memorial Hospital and Emory University,

1940-48, medical laboratory and X-ray technology.

Present: Radiological Equipment Section; photographic sensitometry and

dosimetry.
EISENHAUER, Charles M. (NBS 1938)

B.S. Queens College, 1931, mathematics; Columbia University, 1933-36.

Armed Forces Special Weapons Project, 1933-54; Brookhaven National Laboratory, 1932-57, experimental work in cold neutron scattering.

Present: Radiation Theory Section; calculation of gamma ray and neutron

penetration through matter.

FULLER, Everett G. (NBS 1930)

PhD. University o£ Illinois, 1950, photodisintegration of deuterium by

the continuous X-ray spectrum from a betatron; B.A. Amherst College, 1942,

physics; M.S. University of Illinois, 1947, physics.

University of Illinois, 1949-50, Res. Assoc, preliminary experiments on

the photodisintegration of He and the high energy effect in the deuteron.

Present: High Energy Radiation Section; precision measurements of photoneutron production cross sections. Studies of the scattering and absorption

of photons by deformed nuclei. Study of the nuclear photoeffect in oriented

nuclei.

GARFINKEL, Samuel B. (NBS 1949)

M.S. University of Michigan, 1948, physics.

NBS Electron Physics Section, 1949-51, tracer micrography and mapping magnetic fields; NBS Mechanical Instruments Section, 1951-57, development of

carbon dioxide hypsometer, research on thin film hygrometer elements, and

development of a logarithmic meter for use in weather balloon soundings.

Present: Radioactivity Section; in charge of development and preparation

of beta-ray and gamma- ray standards of radioactivity.

GERSTENBERG, Henry M. (NBS 1957)

B.E.E. University of Delaware, 1957, electrical engineering.

Present: High Energy Radiation Section; Development of experimental equipment for use with 50 Mev betatron. Measurement of neutron yield curves.

HAYWARD, Evans V. (NBS 1950)

PhD. University of California, 1947, cloud-chamber studies of cosmic rays;

M.A. University of California, 1945, physics; B.A. Smith College, 1942,

physics.

University of California Radiation Laboratory, 1947-50, cloud- chamber studies

of synchrotron and cyclotron radiation.

Present: High Energy Radiation Section; precision measurements of photoneutron production cross sections; studies of the scattering and absorption

of photons by deformed nuclei; and study of the nuclear photoeffect in

oriented nuclei.

HAYWARD, Raymond W. (NBS 1950)

PhD. University of California, 1950, studies of beta and gamma- ray spectroscopy; B.S. Iowa State College, 1943.

Naval Research Laboratory, 1943-45, electronic engineer; University of

California, 1946-48, teaching assistant; University of California, 1948-50,

AEC Pre-doctoral Fellow; Fellow, American Physical Society.

Present: Radioactivity Section; beta decay, spontaneous nuclear transitions.
HILL. Owen H. (NBS 1956)

B.S. U.S. Naval Academy, Annapolis, Md. , 1926, engineering.

Commissioned officer, U.S. Navy and U.S. Navy Reserve, 19 years.

Civilian experience, 1929-1940, engineering technology in the mechanical,

electrical and structural branches; and design and analysis of systems for

land and shipboard applications.

Present: Radiation Theory Section; general engineering services in support

of research in structure shielding against radioactive fallout; civil defense radiological measuring instruments, decontamination processes, disposal of radioactive wastes, etc.

HIRSHFELD, Alan T. (NBS 1960)

PhD. Columbia University, 1961, heat capacities of niobium in normal and

superconducting states.

Present: Radioactivity Section; cryogenic aspects of nuclear polarization

experiments.

HOBBS, Thomas G. -\ (NBS 1959)

B.S. Lincoln Memorial University, 1958, mathematics.

Vanderbilt University and Oak Ridge Natioilal Laboratory, 1958-59, A.E.C.

Fellow in Radiological Physics.

Present: Radiation Physics Division, Health Physics Group.

HOPPES, Dale D. (NBS 1950)

PhD. Catholic University, anticipated 1961, beta particle emission from

oriented nuclei; M.S. Catholic University, 1956; B.S. Purdue University

1950.

Present: Radioactivity Section; nuclear spectroscopy.

HUBBELL, John H. (NBS 1950)

M.S. University of Michigan, 1950, physics.

NBS Constitution and Microstructure Section, 1950-51, X-ray diffraction

analysis standards; NBS Thermodynamics Section, 1951, properties of steam.

Present: Radiation Theory Section; geometrical radiation problems, X-ray

attenuation coefficients, supporting work in gamma-ray diffusion and bremsstrahlung theoretical calculations, experimental work on measurement of

diffused gamma rays.

HUTCHINSON, J.M.R. (NBS 1958)

M.S. University of Washington, 1957, physics.

Present: Radioactivity Section; radioactivity standards.

KOCH, H. William (NBS 1949)

PhD. University of Illinois, 1944, photofission thresholds and betatron

X-ray ionization distributions; M.S. University of Illinois, 1942, physics;

B.S. Queens College, 1941, physics.

Clinton Labs., Oak Ridge, Tenn. , 1945-46, physicist; Univ. of Illinois,

1944-49, Asst. Professor, betatron design and nuclear physics research.

Present: Chief, High Energy Radiation Section; precision measurements of

X-ray absorption coefficients in the energy range 10-100 Mev. Direct determination of photonuclear absorption cross sections. Planning new facilities

for the Gaithersburg laboratory.
LAMPERTI, Paul J. (NBS 1959)

B.S, Manhattan College, 1958, physics.

General Atomic (Division of General Dynamics), 1958-59, Fusion Program.

Present: X-ray Section; X-ray standards.

LEISS, James E. (NBS 1954)

PhD. University of Illinois, 1954, photomeson production and brerasstrahlung cross section analysis; M.S. University of Illinois, 1951, physics;

B.S. Case Institute of Technology, 1946, physics.

University of Paris, Nov. 1959- July 1960, study of design and operation of

electron accelerators.

Present: High Energy Radiation Section; neutral photomeson production

from hydrogen and other elements; the study of (7,p) and (yjnp) reactions;

analyzing data on inelastic electron scattering data taken at the University of Paris; designing experimental equipment to be used with the new linear

accelerator.

LOFTUS, Thomas P. (NBS 1949)

B.S. University of Scranton, 1959, physics.

U.S. Navy, 1943-46; NBS Central Radio Propagation Laboratory, 1949-51,

prediction of radio frequencies; NBS Radiological Equipment Section,

1951-54, calibration and performance studies of radiological instruments.

Present: Radiological Equipment Section; in charge of Gamma Ray Laboratory.

MANN, Wilfrid B. (NBS 1951)

PhD. University of London, 1934, exchange of energy between a platinum

surface and gas molecules; D.Sc. University of London, 1951.

Imperial College, London, 1929-1936, thermal conductivities and electron

diffraction; University of California, Berkeley, 1936-38, cyclotron and

artificial radioactivity; Imperial College, London, 1938-46, electrostatic

generators; Canadian N.R.C., 1946-48, Radioactive Standards Laboratory;

British Embassy, Washington, D.C., 1948-51; Alternate delegate and scientific

advisor UNAEC, 1946-51.

Present: Chief, Radioactivity Section; radioactivity standardization,

nuclear decay schemes, raicrocalorimetry, low- level and gas counting.

MARLOW, William F. (NBS 1957)

B.S. George Washington University, 1941, chemistry.

E.I. duPont de Nemours, Inc., 1941-44 and 1946-50, chemist; Office of Synthetic Rubber, 1951-53, chemist; U.S. Army Research and Development Laboratories, 1953-57, chemist.

Present: Radioactivity Section; radiochemistry, carbon- 14 and tritium

standards; carbon- 14 half- life; measurement of and preparation of standards

of very low levels of radioactivity.

MAXIMON, Leonard C. (NBS 1958)

PhD. Cornell University, 1952, bremsstrahlung and pair production theory.

Graduate Division of Applied Mathematics, Brown University, 1952-56,

assistant professor; Norwegian Technical University, Trondheim, Norway,

1956-57; University of Manchester, Manchester, England, 1957-58, Turner

and Newall Fellow.

Present: Radiation Theory Section; scattering theory.
Mclaughlin, wiiiiam l. (nbs 1951)

B.S. (sumroa cum laude) Hampden- Sydney College, 1949, physics; Graduate

studies, Duke University, 1949-50; Rotary International Foundation Fellowship-University of Tlibingen, Germany, 1950-51; Graduate studies, George

Washington University, 1956- . Evans Signal Laboratory (U.S. Army), 1954-56.

Present: Radiological Equipment Section; photographic sensitivity and

dosimetry.

McLERNON, Franklin D. (NBS 1955)

B.S. George Washington University, 1952, physics; George Washington University, 1952-55.

Present: X-ray Section; delayed coincidence experiments.

MEDLOCK, Robert W. (NBS 1952)

B.S. West Virginia State College, 1949, mathematics.

Walter Reed Army Hospital, 1949-52, hospital attendant.

Present: Radioactivity Section; radiochemistry, carbon- 14 and tritium

standards.

MOSBURG, Earl, Jr. (NBS 1956)

PhD. Yale University, 1956, nuclear interactions and unstable particles

produced by protons from the cosmotron; B.S. Yale University, 1952,

physics; Sloane-Silliman Fellowship, 1952-53; DuPont Fellowship, 1955-56.

Present: Neutron Physics Section; neutron standards, neutron elastic and

inelastic scattering.

MCTZ, Joseph W. (NBS 1949)

PhD. Indiana University, 1949, low- energy beta- ray spectra; M.S. Cornell

University, 1942, hysteresis loss of high polymers.

Signal Corps Radar Laboratory, 1942-43, UHF triode generators; Armour

Research Foundation, 1943-46, elastic properties of high polymers and magnetic records.

Present: X-ray Section; X-ray spectrometry and polarization.

NEY, Wilbert R. (NBS 1956)

B.S. Yale University, 1957, physics; Rochester University, 1957-58.

NBS Engineering Metrology Section, 1956-60, development of metrology for

determination of stability of gaging materials.

Present: Scientific Assistant to Chief, Radiation Physics Division.

NOYCE, Ralph H. (NBS 1960)

B.A. Grinnell College, 1955, physics. Graduate Assistant, Georgetown

University, 1956-58.

Bendix Radio, 1955-56, digital logic design; NBS Electron Devices Section,

1958-60, optical properties of mica.

Present: Neutron Physics Section; measurement of neutron source emission

rate.

8
PENNER, Samuel (NBS 1957)

PhD. University of Illinois, 1956; M.S. University of Illinois, 1954,

physics; B.A. University of Buffalo, 1952, physics.

N.S.F. Postdoctoral Fellow, 1956-57; University of Maryland- NBS Graduate

School, 1959- , Instructor. Stanford University, summer 1960.

Present: High Energy Radiation Section; neutral photomeson production from

hydrogen and other elements, study of (y,p) and (y,pn) reactions; design of

magnetic analyzing and deflecting systems for the new linear accelerator.

PETREE, Ben (NBS 1951)

PhD. University of Wisconsin, 1951, scattering and absorption of fast

neutrons; B.S. University of Kansas, electrical engineering* 1943.

Present: High Energy Radiation Section; calorimetric methods for measurement of absorbed energy.

PLACIOUS, Robert C. (NBS 1952)

M.S. University of Iowa, 1953, specific ionization of cosmic ray mesons;

B.S. University of Rochester, 1950.

Present: X-ray Section; Bremsstrahlung cross sections.

PRUITT, John S. (NBS 1953)

PhD. Johns Hopkins University, 1952, energies and angular distributions of

neutrons using nuclear emulsions; B.S. Antioch College, 1947, physics.

Present: High Energy Radiation Section; development of methods for absolute

determination of high energy X-ray intensities.

RICHARDSON, Allan C.B. (NBS 1957)

M.S. University of Maryland, 1958, physics, isotherms of methane at

pressures to 60 atmosphers; B.S. College of William and Mary, 1954,

chemistry.

Institute of Molecular Physics, 1954-58, graduate Assistant.

Present: Neutron Physics Section; neutron elastic and Inelastic scattering

cross sections, neutron age measurements.

SCHARF, Karl (NBS 1957)

PhD. University of Vienna, Austria, 1927, photoelectric effect in submicroscopic particles.

Technische Hochschule, Dresden, Germany, 1928-33, teaching and research

assistant, magneto- optics, solid state physics; Industrial laboratories,

Paris and Vienna, 1933-35, electric gas discharges; Palestine and Israel

Government, Public Works Department, 1935-52, electrical engineering (head

of electrical section 1948-1952); Israel Institute of Technology, Haifa,

Israel, 1952-56, senior lecturer, physics, electroluminescence; Cornell

University, 1956-57, research associate, field emission microscopy.

Present: Radiological Equipment Section, solid state and chemical dosimetry.
SCHRACK, Roald A. (NBS 1951)

PhD, University of Maryland, 1961, neutral meson photoproduction from com- plex nuclei; M.S. University of California, 1950, physics; B.S. City

College of New York, 1945, mathematics.

NBS Central Radio Propagation Laboratory, 1949-51; NBS Atomic Physics Section, 1951-53, application of cyclotron resonance to light mass determination; NBS Electron Physics Section, 1953-56, X-ray microscope, field emission.

Present: High Energy Radiation Section; neutral meson production from complex

nuclei; Monte Carlo analysis of photomeson data.

SCHWEBEL, Abraham (NBS 1946)

PhD, University of Maryland, 1958, chemistry; M.S. New York University,

1938, organic chemistry; B,S. Brooklyn College, 1935, chemistry.

Water Service Laboratory, 1941-43, Chemist; University of Chicago Metallurgical Laboratory, 1943-44, Analytical Chemist; Carbide and Carbon

Chemical Corporation, 1944-46, Research Technician.

Present: Health Physicist; evaluation of radiation hazards in laboratories

using radionuclides or instruments producing ionizing radiations; radiochemistry; consultation on safe use of radionuclides and setting up of facilities for use of radionuclides. Teaching radiochemistry and health physics.

SMITH, Scott W.

' (NBS 1947)

PhD. University of Pittsburgh, 1931, index of refraction of liquids for

X-rays.

University of Rochester, 1931-37, Assistant Professor of Physics;

Kelley-Koett Manufacturing Co., 1937-47, Physicist.

Present: Chief, Radiological Equipment Section; radiation instrumentation

and X-ray equipment.

SPENCER, Lewis V. . (NBS 1948)

PhD, Northwestern University, 1948, photographic action of X-rays.

NBS Nuclear Physics Section, 1948-57, Physicist (Nuclear Physics);

Ottawa University, Ottawa, Kansas, 1957-60, associate professor of mathematics and physics.

Present: Acting Chief, Radiation Theory Section; theory of penetration and

diffusion of radiation in matter. Theoretical evaluation of cross sections

for inter-action of radiation with matter.

SPIEGEL, Valentine, Jr. (NBS 1955)

PhD. University of Notre Dame, 1956, elastic electron nuclear scattering

at 1,00, 1.75 and 2.50 Mev; B.A. Catholic University of America, 1950.

Naval Ordnance Laboratory, summers of 1950 and 1951, student aid and physicist.

Present: Neutron Physics Section; measurement of neutron ages in water and

heavy water, measurement of neutron dose in water, neutron polarization.

10
SPOKAS, Otto E. (NBS 1946)

George Washington University, 1938-47, electronics; Pennsylvania State

College, 1945-46, electronics.

NBS Ordnance Division, 1941-45, 1948-53, high-frequency antenna design and

measurements for proximity fuzes, dielectric measurements, component studies;

NBS Computer Laboratory, 1946-48, basic circuitry; Diamond Ordnance Fuze

Laboratory, 1953-54, electronic component studies.

Present: High Energy Radiation Section; electron spin resonance detector;

180 mev synchrotron circuitry.

STOCKMANN, Leroy L. (NBS 1926)

B.C.E. Catholic University, 1935, civil engineering.

NBS Radioactivity Section, 1926 to present; from 1948-60 in charge of radon

testing, radon analysis of ores and sludges.

Present: Radioactivity Section; instrumentation and counting; low- level

radioactivity measurements.

TAYLOR, Lauriston S. (NBS 1927)

D.Sc. (Hon.) University of Pennsylvania, 1960; A.B. Cornell University,

1926, physics; Cornell University, 1927-30; Stevens Institute, 1920-21.

Columbia University, 1929, X-ray diffraction, absorption sattelite fine

structure, oscillation hysteresis; NBS Optics Division, 1927-40, X- and

gamma-ray dosimetry, protection, standards, ionization chambers, scattering;

NBS Ordnance Development Division, 1940-42, Chie^ Proving Ground Group;

NBS Ordnance Development Division, 1943, Assistant Division Chief; Ninth Air

Force, 1943-46, Chief, Operational Research Division; NBS X-ray Section,

1946-48; AEC, 1948, Chief, Biophysics Branch; NBS, 1940-49, Chief, X-ray

Section; NBS, 1949-51, Chief, Radiation Physics Laboratory; NBS, 1951-60,

Chief, Atomic and Radiation Physics Division.

Present: Chief, Radiation Physics Division.

WEAVER, James T. (NBS 1956)

B.S. Lynchburg College, Va, , 1956, physics.

Present: Radiological Equipment Section; radiation instrument studies and

calibration.

WYCKOFF, Harold 0. (NBS 1941)

PhD. University of Washington, 1940, Cerenkov radiation.

NBS X-ray Section, 1941-43; Ninth Air Force, 1944-45, Asst. Chief, Operational Research Section; NBS X-ray Section, 1945-50; NBS, 1951, Chief, X-ray

Section.

Present: Chief, X-ray Section; X- and ganmia-ray attenuation, dosage measure- ment, radiation shielding and protection.

WYCKOFF, James M. (NBS 1951)

M.S. University of Rochester, 1951, continuously operating cloud chamber.

NBS Radioactivity Section, 1952-53, alpha-ray measurements.

Present: High Energy Radiation Section; X-ray measurements to determine

attenuation coefficients in the to 100 Mev region.

11
IV* FACILITIES OF THE RADIATION PHYSICS DIVISION

The present facilities of the Radiation Physics Division are housed

in four buildings at the National Bureau of Standards' Washington site

the High Voltage Laboratory, the Betatron Laboratory, the Gamma-ray

Laboratory, and the Materials Testing Laboratory. The equipment available to the division staff includes a full complement of stock laboratory

apparatus, certain specialized instnmientation adapted to the division

program, and a number of rather large scale, complex pieces of equipment

of unique importance to the research work of the division.

Also available to division staff members, by means of cooperative

programs, are the services and facilities of a number of the other

technical divisions of the Bureau. These, of course, are in addition to

the more general administrative and service assistance provided by the

Bureau administration.

The National Bureau of Standards is at the present time engaged in

designing new laboratories to be located at Galthersburg, Maryland. Plans

for the new NBS "campus" provide for 20 buildings to house the Bureau's

programs. Funds have now been appropriated to begin construction and

site development and it is expected that ground will be broken in the summer of I96I,

One of the new buildings at this site will be the Radiation Physics

Laboratory, The design of this laboratory has afforded an opportunity

to design a facility especially adapted to the unique requirements of the

research program of the Radiation Physics Division,

The planned laboratory consists essentially of four major areas:

the linear accelerator area, the cyclotron wing, the connecting wing,

and the north wing. The linear accelerator area will house the new

high- Intensity electron accelerator and consists essentially of a threelevel machine and control area and a three-room experimental complex.

The experimental rooms because of the radiation shielding required will

be k-0 feet below ground level and separated by concrete walls 12 feet

thick. The accelerator is described in more detail below. Provision has

been made in the two level cyclotron wing for the addition of a new

variable energy cyclotron (see description below). In additton, this wing

will house four neutron research labs, four radioactivity labs, and space

for associated facilities. The connecting wing, a two level area, will

contain X-ray and neutron experimental areas. The 5 Mev and the I.5 Mv

generators described below and other X-ray machines will be housed in

this wing. This area will also include a gamma-ray calibration range and

a 2-Mev Van de Graaffpositive ion accelerator for neutron research. The

north wing, a three story and basement structure, will include low-level

radioactivity laboratories, health physics laboratories, nucleonic instrumentation laboratories, and office space. An indication of the magnitude

of buildina is the fact that it Will contdin about 70,000 square feet of

usable floor area divided into some 72 laboratory areas and over 50 offices.

12
Described below are a nximber of the large-scale, specialized

pieces of equipment presently employed in the Division program and

also some of the equipment planned for installation in the

Gaithersbxirg laboratory. Also included are brief descriptions of

certain of the facilities available through cooperation with other

divisions of the Bureau.

1, X-ray Section

At the present time the section has available a d.c,

generator capable of supplying potentials of from^ near to l.k Mv,

This generator has a current capability of 15 jiilliamperes for con- tinuous operation. It may be connected to either^f two electron

accelerating tubes. At the present time one of these tubes is provided with a thick tungsten target for the generation of X-rays,

The other one has a thin window so that electron experiments can be

performed in air, other gases or solid materials.

This generator and the two accelerator tubes are to be replaced

at the time of the move to Gaithersburg, The new laboratory will

house a 3 Mv Van de Graaff with provisions for directing the electron

beam into either of two experiment rooms. Either of these rooms may

be used for X-rays or electron experiments. The current capability

of this unit will 'be of the order of 1 milliampere. It is also

planned to have a 1,5 Mv accelerator in the new laboratory. This

will also have current capabilities of the order of 1 milliampere.

The section has a free air ionization chamber with a plate separation of kh cm. This ionization chamber is contained within a large

pressure tank so that it may be operated at pressures up to 12

atmospheres. It is currently being used to examine the requirements

for measurement of X- and gamma-rays in roentgens. It is anticipated

that in the future it will be used to examine the details of

ionization production from electrons and X-rays, In order to collect

the ionization produced in such a high-pressure vessel, two very well

stabilized d,c, power supplies are available which will provide both

positive and negative potentials from O-5O kv, in steps of 1 kv.

For some of the work in time-of- flight measurements high-speed

coincidence circuitry has been developed. At the present time, the

circuitry is capable of measurements down to about lO" sec.

15
2. Radioactivity Section

Essential facilities utiliaed by the Radioactivity Sectionin its program are described below,

^jty Ionization Chamber

The NBS hTxy ionization chamber is used chiefly for the relative

standardization of gamma-emit ting radionuclides. It is a stable

instrument, as is evidenced by the reproducibility (within 1^) of its

response to radium reference standards over the past several years.

Its ultimate precision is ±0.02^. It is also characterized by its

linear current response to gamma radiation over an energy range of

,h Mev to 2 Mev, This is the case for samples of a given geometry

placed within the re-entrant source tube of the chamber. Given a radioactive sample of "standard" geometry, and given the relative

amounts of gamma rays and their energies within the range of ,k- to

2 Mev, an assay of the total amount of gamma- ray activity can be

determined to within ±2^ within an hour or less depending on the

strength of the source,

Low-Level Radioactivity Laboratory

An existing room in the Radioactivity Section has been extensively

renovated and modified to furnish a low-level radlochemistry laboratory

and a source preparation room, with an airlock at the entrance.

Special air- filtration and air-conditioning arrangements provide a clean, dust-free atmosphere. Special clothing and shoes or plastic

bootees are worn in these rooms.

The counting room is adjacent to the source preparation room and

is connected by a small wall air-lock through which ssimples may be

passed. This room is equipped with low-level alpha, beta and gamma

detectors shielded by mercury, iron, lead and anticolncldent counting

circuits or a combination of two or more of these. Activities as low

as lO"-'-^ curie can be measured.

One of the gamma detectors feeds into a 100-channel pulse- height

analyzer permitting the determination of radioactive nuclides present

in a given sample from the gamma- ray energy levels. This is particularly useful in the determination of radiochemical impurities in

chemical reagents.

Although radon testing for the public and for Federal and State

Government agencies has been discontinued, several units of the equipment have been retained. These are available for occaclonal check

measurements for Army, Navy, and Air Force health agencies for which

we formerly made routine analyses and for radon measurement of

emergency breath or air samples.

Ik
Radiochemical Laboratory, Four laboratories are present in

the Section for the purpose of providing facilities for radiochemistry. Two of these laboratories are equipped with special

hoods and foot-control sinks for the handling of radioactive

materials, while the other two provide counting facilities, one in

particular being for the gas counting of hydrogen-5 and carbon- l^J-,

Cryogenic Equipment Employed in Nuclear Spectroscopy, Through

the generosity of the Cryogenic Physics Section of the Heat Division,

the Nuclear Spectroscopy Project being carried out by the Radiation

Physics Division, has available the necessary cryogenic equipment

for performing radioactivity measurements involving oriented nuclei.

The principal items in use are an adiabatic demagnetization

cryostat with an associated 125 kilowatt electromagnet and a large

capacity heliiim bath pximping system. All liquid helium is produced

on the premises. With this equipment, it is possible to achieve

temperatures as low as 0,001 K, sufficient for producing nuclear

polarization. Certain specialized electronic detection and counting

equipment used for these measurements consists of scintillation detectors operating at 0,01 K, gamma- ray polarimeters for the measurement

of both plane and circular polarization, and multichannel coincidence

and pulse- height measuring equipment.

Other Equipment . The Radioactivity Section has designed and constructed

compensated internal gas counters for the calibration of radionuclides,

such as hydrogen-3, carbon- l4 and sulfur-55^ that can be prepared as samples in gaseous form. The accuracy of measurement in these counters

is of the order of ±1'^,

A Peltier-effect microcalorimeter, capable of a precision of the

order of 0.1^ has also been developed.

15
5. Radiation Theory Section

While the Radiation Theory Section, being a theoretical group,

does not have need for a considerable amount of major experimental

equipment, other than desk calculators, it does make extensive use

of the facilities made available by the Applied Mathematics Division,

Some of these facilities are described below along with some of the

plans for their future expansion.

The services provided by the Computer Laboratory include the

assistance of the trained staff as well as the use of the electronic

computing equipment. The technical staff aids in the formulation of

problems and their solution, as well as in the programming and coding

of problems for solution on the IBM-70^ electronic computer

The electronic computer, which is available, has a 52,000 wordcore-memory, a drum and 10 tapes on line. The present off-line equipment consists of a card-to-tape converter and off-line printer. In

addition, there exists standard IBM electro-mechanical equipment.

An order has been placed with Royal McBee for a RPC-4000 computer,

which should arrive in the near future, and a small desk-size computer

to be used in exploratory scientific and technical work.

At the moment, the plans for the future indicate that the present

70^ system will be replaced by the most advanced system available. It

is anticipated that a computer of the IBM stretch type may be installed

at the Bureau even prior to the move to Gaithersburg, and certainly

by the time that the Bureau moves a computing facility of this magnitude

is expected. There will be a considerable increase in the staff to

fully utilize this large-capacity machine.

16
k. High Energy Radiation Section

The major facilities of the High Energy Radiation Section at present

consist of two sources of high energy radiation, a 50 Mev betatron and a 180 Mev synchrotron, A high intensity linear electron accelerator

(linac) is now being acquired. This new facility is scheduled for com- pletion early in 1965«. The principal features of this new accelerator

will be a very greatly increased intensity and the ready accessibility

of external electron beams. Table I gives a comparison of the present

accelerators as well as the new linear accelerator.

The linac will be housed in a special laboratory building at the

new Gaithersburg site of NBS, The electron beam from the linac Is first

sent into a magnet room where it is energy analyzed and deflected into

one of three experimental rooms. The energy of the electron beams in . these rooms will be variable from about 5 Mev to the maximum energy of

the accelerator. The energy resolution available will be controllable

from a few hundredths of a percent to about 10 percent. Energy stability

of the analyzed electron beams will be a few hundredths of a percent.

The magnetic deflection system designed to carry the electron beam

from the linac to the experimental rooms is such as to take an initially

parallel beam from the linac into a parallel beam in the 'experimental

rooms. The beams in the experimental rooms will be focused on the targets of experimental equipmient by additional quadrupole focusing elements

in the experimental rooms.

It is planned in the initial installation to have prepared three

major experimental setups. In one room will be located a high resolution

magnetic spectrometer, together with associated gear, for performing

electron scattering experiments. In the second installation will be a low resolution magnet, together with associated gear, for counting heavy

particles ( protons, deuterons, alphas). The third initial installation

will be equipment designed for generating monoenergetlc photon beams,

Monoenergetic photons will be generated by the annihilation in thin, low

Z foils of energetic positrons generated in electron-photon cascades by

the direct beam from the linac.

In addition to the three experimental rooms already mentioned, provision is also made for two small irradiation bays for radiation damage

and dosimetry studies, A slot is also to be left between two of the

experimental rooms to allow for neutron flight paths up to I50 feet for

photoneutron studies.

Although the linac will be an extremely powerful source of neutrons

for a neutron physics program, specific provision of a neutron facility

is not planned in the initial installation. Consideration is being

given to the needs of such an installation if this is considered desirable

in the future,

17
Comparisons of Present Accelerators and New Linear Accelerator

50 Mev Betatron I80 Mev Synchrotron Linear Accelerator

Radiations

Available

Type

Size

Orbit Radius

Weight

Accelerating

mechanism

Average beam

current

Beam power

available

Maximum beam

energies

Duty cycle

X-rays (Electrons

with difficulty

at low currents)

Circular

i|- 1/2x2 1/2x5 1/2 ft,

11 inches

10 tons

Rate of change of

magnetic flux

2x10 ampere

20 milliwatts

50 Mev

about 0.002

X-rays

Circular

18x8x10 ft. magnet

35 inches

150 tons

rf cavity in alternating magnetic

field

_o

2x10 ampere

100 milliwatts

180 Mev

about 0.0^

Electrons, X-rays

Linear

1-1/2 ft. diameter

x 100 ft. long

tube

5 tons

traveling electric

wave

5x10 ampere

^4-0 kilowatts

150 Mev at low

current

60 Mev at high

current

0.002

18
5. Radiological Equipment Section

Summary of Special Facilities Available for Carrying out the Programs ,

1, X-ray standards,

A, Free-air parallel-plate ionization chambers:

1, For X-rays produced at 20 to 100 kvcp,

2, For X-rays produced at 60 to 250 kvcp.

B, Constant potential X-ray machines for use with free-air standard

chambers:

1, Range to 50 kvcp,

2, Range 20 to 100 kvcp,

5o Range 50 to 250 kvcp.

2. Collimated-beam gamma-ray standard Instrument calibration ranges:

A. Cesixim 157: 2000 curies, 120 curies,

B, Cobalt 60: 1000 curies, 200 curies, 50 curies and 5 curies,

5, High- intensity gamma-ray water- shielded cobalt-60 sources:

A, 2000 curies,

B, 50,000 curies,

k. Radium calibration range,

5, X-ray machines for dosimetry research:

A, Two 50 to 250 kvcp.

B, One 50 to I50 kvcp.

19
6. Nucleonic Instrumentation Section

The equipment employed by the Nucleonic Instrumentation Sectx) n

includes the very considerable electronic apparatus necessary for

the operation of a full-scale electronic laboratory. In addition to

this and of particular significance to the division program, however,

are the several multi-channel pulse-height analyzers and the high speed

pulse test equipment maintained by the section.

7. Neutron Physics Section

Neutrons are provided for experimentation by a 2 Mev Van de Graaff

positive ion accelerator (see table attached) and by radioactive neutron

sources. Neutron sources available include Ra-Be(7 ,n) , Ra-Be(a ,n)

,

and Pu-Be(a ,n) . When required, short life neutron sources are obtained

such as Sb^^^ -Be(7 ,n) and Po^lO -Be(a: ,n)

Neutrons are produced by the Van de Graaff accelerator at energies

of 1 Mev and less bv the T(p,n) and the Li(p,n) reactions, from 2 Mev

to 5.3 Mev by the H (d,n) reaction and from 12 to 18 Mev by the T(d,n)

reaction. These neutrons are monoenergetic, which is valuable for

calibration of neutron spectrometers and dosimeters at specific neutron

energies, for measurements of neutron cross sections, and for precise

neutron penetration experiments. The neutrons from the H (p,n) and Li(p,n)

reactions are polarized, making possible studies of fast neutron polarization. The Van de Graaff accelerator is also used to provide monoenergetic

high energy gamma rays of 17.6 and 20 Mev by (p,7) reactions. The proton

and deuteron beams are available for direct use in charged particle experiments. Beam pulsing equipment has been ordered to make possible neutron

time-of-flight experiments with low background and improved time de solution.

The new equipment also makes possible use of the H^(d,n) reaction in time-offlight experiments.

The proposed variable energy cyclotron planned for installation

in the Gaithersburg laboratory will permit neutron cross section measurements over a wide range of fast neutron energies without the energy gaps

that exist with the Van de Graaff. The natural pulsing of the cyclotron

will permit time-of-flight experiments with orders-of-magnitude higher

instantaneous pulse currents. Since the incident neutrons are monoenergetic, time-of-flight may be used to measure the energy distribution

of the scattered neutrons and also for background reduction. The la rge

external beam of the cyclotron coupled with a flexible low resolution

or high resolution magnetic analyzing system may be used for many kinds

of charged particle and neutron nuclear physics experiments. For example,

the large external beam can be used for neutron and charged particle

polarization experiments where maximum intensity is required. For

charged particle scattering and reaction experiments, the small beam

with hig:i energy resolution will be used. The variable energy cyclotron

is the most flexible positive ion accelerator available in terms <f the

many kinds of particles which can be possible.

20
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21
8. Health Physics Group

The Health Physics Laboratory has a variety of portable

instruiftents such as geiger counters, scintillometers , gamma and

neutron detectors, ionization chamber instruments and air samplers.

The lalD ratory is equipped with proportional windowless flow counters

both for ordinary work and low- level work. A Tracerlab low level

(0.7 cpm - qk^^^ background) counter has been purchased to use in

low-level Sr counting. For the low-level detection of

gamma emitters, there is a single channel analyzer utilizing a 3-inch

Nal (Tl) counter.

22
V. INTRODUCTION TO THE PROGRAM

Most of the work of the Division can be grouped loosely into the

categories of "aimed" or applied research. By "aimed" is meant

research that is basic in character, but oriented so as to offer a reasonable possibility of being applicable to some specific problem or class of problems, the exact nature of which may not be known at the

timeo Aimed research also has the purpose of filling the broad re- quirements for scientific information that arise from practical problems; it implies that the research, however basic, is undertaken as a part of a concerted effort that has a place in the national requirements. This is in contrast to applied research, which has as its primary objective the solution of some defined problem--possibly even

resulting in the production of specific equipment or in a routine testing program.

To develop a program and staff of high capability, it is

necessary to take advantage of opportunities as they arise. Thus,

for example, when we develop the staff and facilities for some aimed

research, we frequently find ourselves in a unique position to carry

out some research of a pure or basic nature. By taking advantage of

such opportunities, the general background and experience of the staff

are strengthened and the members of the staff are placed in an improved

position for undertaking tasks of new kinds and complexity. Furthermore, through the encouragement of such possibilities, it has been

demonstrated that we can attract better scientific personnel than would

otherwise be possibleo This general policy has been followed by the

Division for the past several yearSy and its effectiveness has been

proved.

25
VI. DETAILED PROGRAMS OF THE SECTIONS

1. X-ray Section (^.01)

H. 0. Wyckoff, Chief

The program of the X-ray Section at the present time is devoted

primarily to experimental investigations in the dosimetry of X- and

gamma-rays and in the production of X-rays, For the most part its

interests are confined to the energy range below 3 Mev,

Dosimetry. At the present time, the section is interested in

research with both free-air .ionization chambers and cavity ionization

chambers. The section is responsible for the determination of correc- tion factors for the free-air ionization chambers and for the design

and testing of the national standards for measurement in roentgens. At

the present time such standards are available for the 20 kilovolt to

the million volt range. With these instruments, it is estimated that

the error does not exceed about 1»2^ below 500 kilovolts but is perhaps as much as 2^ in the million volt region provided measurements

are made at a distance of a half a meter or greater from the radiation

source. Presently investigations are underway to permit measurements

at less than a half a meter and at lower potentials than 20 kilovolts.

In addition, the section is responsible for the comparison of oux national standards with those of other national laboratories. For this

purpose, the section has established close liaison with the International

Commission on Radiological Units and Measurements, with the Bureau

International des Poids et Mesures, and with the responsible persons in

other national laboratories. To expedite such intercomparisons, the

section has developed transfer instrimients. It is expected that from

such intercomparisons it will be possible to further reduce the uncertainty of measurements.

Two of the most important factors needed for the evaluation of

cavity ionization chamber measurements are the stopping power and the

energy required to produce an ion pair in the gas (w). Research is

currently underway in the section to determine more accurate values for

both of these factors. ' One method for obtaining the stopping power

ratio is to compare .the ionization results obtained with a free-air

chamber and with a cavity chamber. Such measurements have recently been

completed with cobalt-60 and cesium- 157 gamma-ray soiirces. The uncertainty of the ratio of these two measurements is estimated to be about

5^, However, measurements are now underway with a gold-198 gamma-ray

source. It is expected that the maximum uncertainty in the ratio of

the two measurements will not exceed about 2^, One can also determine

the product of the stopping power and W by comparison of measurements

21* I
made with a calorimeter and a cavity chamber. With the acquisition

of the Bureau's new 50 kilocurie cobalt source such measurements will

be easily possible. Some thought has been given to such measurements.

Many values of W for electrons and alpha particles have been

reported in the literature. Here W is the average energy required to

produce an ion pair as the ionizing particle is reduced from its maximum

energy to zero. Generally, the numerical values so obtained are in fairly

good agreement. However, a different value is obtained for fast and for

slow collection of the ionization produced by alpha particles. At the

present time the section is investigating the value of W obtained by

both of these methods with a single source in order to cl&At up

this discrepancy.

These data indicate that W for some gases increases as the particle

energy decreases. These results indicate that a more interesting factor

for investigation would be the differential quantity; that is, the charge

produced by a small energy loss In the region of energy E, For convenience this will be called w = AE,f An. An initial investigation with

alpha particles in air near 5 Mev indicates that the value of w for these

particles is very nearly the same as that obtained for electrons. This

experiment was possible because the stopping power is well known in this

energy region. However, it would be of interest to determine w at lower

energies. For this purpose It is necessary to determine small increments

of E. A time-of- flight method using high-speed coincidence techniques

is now being developed for such measurements.

With the development of these techniques it is expected that fruitful

areas of future research will be opened. For example, it will be possible

to investigate the response of solid state radiation detectors at different

energies.

X-ray Production. Present calculations of X-ray production are based on the Born- approximation and for the medium electron energy range

(say 50 kev to few Mev) are known to be in error. For this reason the

section has pioneered in the experimental determination of the absolute

cross section of continuous X-ray spectra and its polarization. These

X-rays are produced in thin targets so that the producing electron

direction is known. As a logical extension of this effort the section

now has under investigation the spectral distribution as the target thickness is increased. Here the electrons soon lose their initial monodirectional

property by scattering. Such investigations not only provide data for the

evaluation of the continuous X-ray losses but also give ideas about the

electron scattering.

A second logical extension of this initial effort, which is now

under consideration, is the distribution of electron directions resulting

from the continuous X-ray production process. If the electrons ejected

from the various shells do not provide too high a background, the above

distribution can be investigated by coincidence methods.

25
2. Radioactivity Section (^,02)

W. B. Mann, Chief

The Radioactivity Section has several main objectives ranging

from basic nuclear research to routine testing. Its activities

include: (l) the development of techniques and facilities for

measuring radioactivity, (2) the preparation and distribution

of standard samples of both the naturally occurring and artifically

produced radioactive elements, (5) the analysis of room-air, breath,

and ore samples for radon and radium content, (k) the development

of techniques of low-level counting and the preparation of low level

standards of radioactivity, and (5) investigations in the field of

nuclear spectroscopy. To carry out these programs, the section is

comprised of an Alpha-Ray Standards Laboratory, a Beta- and GammaRay Standards Laboratory, a Nuclear Spectroscopy Laboratory, a LowLevel Counting Laboratory, and a Radiochemical Laboratory.

Radioactivity Standards . The Section presently prepares and

distributes polonium-210, americium-2^4-1 and uranium-oxide (UtjOq)

alpha-ray standards and beta- or gamma-ray standards of the

following naturally occurring or artifically produced radioactive

nuclides: hydrogen-5, carbon- 1^4-, sodium- 22, scandium-46, zinc-65,

krypton-85, strontium-85, niobium-95^ mercury-203 Slid radium-226,

and also rock and ore standards containing thorium, radium, and

uranivmi.

There are also available point- source gamma-ray standards

in the energy range 0.279 to 1.28 Mev, namely of sodium- 22,

manganese-5^, zinc-65^ strontium-85, niobium-95 ^ii^ mercury-203.

The Radioactivity Section also maintains the national radioactivity

standards, for testing and calibration purposes but not for distribution, of the following nuclides: sodium-2^, phosphorus-32,

sulfur-35, potassium-il-2, iron-59, cobalt-60, strontium-yttrium-90,

iodine-131, cesium-barium-137, tantalum-182, gold-198 and thallium26k, Radioactivity standards of the nuclides in this last group

are no longer distributed by the National Bureau of Standards as such standards are now commercially available.

This radioactivity- standards program is the responsibility

of the Alpha- Ray Measurements Laboratory and the Beta- and GaimnaRay Standards Laboratory,

Alpha- Ray Standards , A program to provide alpha-particle

standards has been established on a long-range basis. Presently,

alpha-particle-emitting standards are furnished in a number of

different intensities, the source material being uranium oxide

(U^On), polonium-210, or americium-2^4-1,

26
The recipients of the alpha- emit ting standards are engaged in

many diverse activities, such as medical research or application,

physical and industrial research, oil prospecting, radiation protection, and thermonuclear-weapons development. The demand for these

standards Is a continually increasing one as new applications are

found*

Beta- and Gamma-Ray Standards , This standardization program, is

concerned with the preparation of the beta- and gamma-ray standards

and is discussed in the section entitled "Radioactivity Standards,"

The techniques used for the production of national radioactivity

standards are the usual ones of k- itp counting, coincidence counting and

internal gas counting. The emphasis in recent years, and currently, in

k «P counting and i»Jt X-ray counting, has been on methods of source preparation with a view to minimizing and determining source self-absorption.

The Radioactivity Section, together with other national laboratories,

is Cftdperating in trying to establish international uniformity in the

measurement of national radioactivity standards. With this end in view

it has already participated in the measurement of phosphorus-32 which

was distributed internationally on behalf of the International Bureau

of Weights and Measures,

Low-Level Radioactivity Measurements, Work is in progress on

methods of measuring the amounts of radionuclides present at very low

concentrations (lO"-'^^ to 10" '•^ curies/ml) and on preparing standards

of radioactivity at these concentrations. Radionuclides under present

investigation are natural uranium, radium-226, thorium-250, strontiumyttrlum-90; other nuclides to be investigated at the earliest opportunity

include sulfur-55^ cobalt-60, ruthenium- 106, and cesium-barium- 1 37

The general program includes the determination of low levels of radiocontamination by any nuclide of materials and reagent chemicals, and,

possibly, the preparation of materials and reagent chemicals free from

any detectable radioactivity.

Two methods of radon analysis are being investigated both of which

will eliminate the necessity of removing all oxygen from breath and air

samples before measurement. Radon analysis, to a limited degree, will

also become a part of the low-level measurements program.

27
Radiochemlstry Studies . Counting in formamide solution for

secondary calibrations of certain radionuclides has been re-evaluated.

Nuclides that can be satisfactorily counted by this procedure include

carbon- 1^, sodium-22, sodium- 2^4-, sulfur- 35^ phosphorous-32, strontivimyttrium-90, iodine-131, thallium-20^0 The sodium carbonate-C-'-^ standard

has been recalibrated, and a benzoic acid-C-'-^ in toluene has been

prepared and calibrated. Preparations are well underway for the

calibration of hydrogen-J and sulfur-55 standards by absolute gas

counting, and these measurements should be made shortly.

Plans have been started for a study of adsorption of radionuclides

on glass. Of particular interest are the adsorption of low concentrations of radionuclides from solution, and the adsorption of carbon

dioxide on glass. In the latter case, it is planned to use carbon-1^

as a tracer, and also to try to determine the effect of relative

concentration of carbon-l4 on the adsorption.

Nuclear Disintegration Studies . Using the techniques of

beta- and gamma-ray spectroscopy combined with cryogenic techniques

for achieving nuclear polarization, experimental investigations

are under way to determine detailed mechanisms of radioactive

disintegration processes. The results of these studies have had a profound effect on the understanding of the weak interaction process

and elementary particle physics in general and are currently contributing

to the understanding of certain aspects of nuclear structure.

The rapid developments in the field of nuclear spectroscopy in the

past few years have greatly extended the scope of this project. While

nuclear spectroscopy used to imply the measurement of the energies and

intensities of radiations emitted by certain nuclides so that a complete disintegration scheme could be made, the connotation of the

term now implies that measurements are also made of the correlations

among the direction of emission and the polarizations of the radiations

and the polarizations of the parent and daughter nuclei.

The emphasis of the program has been to study those nuclides that

are of considerable theoretical or experimental interest. Examples of

these are cobalt-60, cobalt-58, and cobalt-56 used in the study of

parity nonconservation effects for both electron and positron emitters

and manganese-52 for the study of time reversal invariance and the role

of isotopic spin admixtures in the relative contribution of spin-flipping

and non- spin- flipping beta transitions. Currently measurements are being made with beta emitters where a change of parity is involved. The

matrix elements in these transitions depend rather sensitively on the

radial details of the nuclear wave functions. This relativistic type

of matrix element occurs only in the beta-decay process.

This type of measurement of the beta decay from polarized nuclei

was first performed in this laboratory, and this laboratory is the only

one in the United States and one of few in the world that has a program

of this type of nuclear spectroscopy.

28
5. Radiation Theory Section {k-,03)

L. Vo Spencer, Acting Chief

This Section operates under several broad objectives: (l) to

constitute the focal point for the theoretical work of the division,

(2) to investigate the problems of radiation penetration and diffusion

in matter, and (3) to produce, collect, and evaluate fundamental data

on radiation constants and properties.

General Theoretical Work. A considerable amount of consultation

on the theoretical aspects of work of other Sections is in progress at

all times. Where a sustained theoretical effort has been necessary in

other Sections, theoretical personnel have been added to their staffs.

Nevertheless, some work on targets of opportunity has been in progress

in the Nuclear Physics Section at all times. For example, considerable

effort has been devoted to problems of nuclear theory.

Radiation Penetration and Diffusion, A few years ago, there existed

an important gap in our knowledge of the action of high-energy radiations

on matter. On the one hand, the elementary processes are to a great ex- tent well understood and are under attack by the most advanced centers of

research in physics. On the other hand, for most conditions encountered

in practice, the action of radiation on matter involves a large number of

atomic processes. The resulting complication of radiation phenomena

caused the work on radiation protection to rely on large-scale tests of an engineering character whose results could not be extrapolated to different conditions. This situation affected not only the development of

ordinary radiological protection but even more the novel and extensive

design of nuclear reactors and of devices for radiological defense.

The importance of a solid knowledge in this field for naval and aircraft

propulsion and for atomic warfare and defense needs hardly be stressed

and is demonstrated by the large stuns spent by various agencies for

shielding and for related purposes.

This problem has been under continuous study since 19^8 with the

support of the Office of Naval Research and the Atomic Energy Commission,

and later also of the Defense Atomic Support Agency and the Office of

Civil and Defense Mobilization, Almost complete solutions of the

theoretical problems of gamma- ray and electron penetration and degradation

in infinite media have been obtained (under conditions where the shower

mechanism is unimportant). Some model experiments have provided satisfactory experimental verification of the theory.

The theoretical progress has been achieved by preliminary analytical

solutions of schematized problems, utilized in later steps as mathematical

models to be fitted to the actual situation by numerical calculations.

Additional results are also provided by Monte Carlo calculations, which

provide in effect the solution of schematized experimental problems.

29
Related experimentation, especially on electron penetration

and diffusion, is carried out by other Sections, Studies of backscattering and transmission of electrons and positrons performed in

the last few years in the Radioactivity Section (^.02) fall in this

line.

Data on Radiation Interactions , Data on elementary processes

of interaction of radiations with matter constitute the starting

point for the solution of specific complex problems. Such data

are adequately available from theory only for processes that involve one or two atomic particles. Processes involving many-electron

atoms are inadequately known in detail even though their theoretical

principles are well established. Experimental data cover only a small fraction of the required range of information. Here again,

as in the theory of radiation diffusion, the problem is to develop

effective computational methods to deal with a complicated situation,

and an attempt is being made to apply to this problem the techniques

that have been developed for radiation diffusion.

Because the data on gamma-ray absorption are spotty and contain

serious gaps in certain energy regions, a compilation, evaluation,

and analysis of known data has been prepared and has met with great

success in its circulation, A series of publications is planned

that will provide critical data and a discussion of present knowledge

on various effects of radiations on matter. In addition to the work

on gamma-ray absorption, completed tasks include detailed and complete

calculations of the Compton scattering law, studies of the distribution

of oscillator strengths and of atomic form factor, and electron ranges

and stopping powers.

The work carried out thus far in this line of critical analysis

has clearly shown a requirement for a basic theoretical attack upon

the problem, going much beyond the original formulation of the project.

Increasing attention is being devoted to this phase of the work, the

more so because university laboratories that used to lead in this

field have recently been pushing in other directions.

30 !
k. High Energy Radiation Section (koOh-)

H. W. Koch, Chief

The program of the High Energy Radiation Section deals with the

study of X-ray and electron interactions with matter in the energy

range from 2 to l80 Mev. An understanding of this program and its

relation to the Bureau's mission of providing basic data, standards,

and technique developments requires an appreciation of our present

inadequate knowledge of the details of the interaction of X-rays and

electrons. This section was established in order to satisfy the need

for some of the basic data and physical measurement techniques required

in various areas of science and technology. An increasing application

of high-energy radiations is being made to radiology, radiography,

nuclear physics research, and the recent radiation processing of

materials by the use of intense, high-energy electron beams. The

research of the section has resulted in data on fundamental electromagnetic interactions (i.e., bremsstrahlung and pair production) and on fundamental photonuclear interactions (i.e., elastic nuclear scattering,

total nuclear absorption, photoneutron, photoproton, and photomeson cross

sections); also, this research has resulted in the development of instruments and standards for the measurement of X-ray intensity and absorbed

dose and has formed the basis for contributions by staff members to

various national advisory committees.

The research' of this section is conducted by a total of 20 people

working with two electron -accelerators, a 50-Mev betatron and a l80-Mev

synchrotron. In addition, a third accelerator - a 100-Mev linear electron

accelerator (linac) with k-0 kilowatts in the electron beam - has been

funded by Congress. This new accelerator will produce the same energies

and radiations as the existing betatron and synchrotron. However, the

electron beam powers from the linac will be 100,000 times the powers

' presently available. This accelerator will, therefore, make possible

many new types of investigation not possible with the present accelerators.

A, Present Program

Detailed knowledge of the interaction of high-energy X-rays with

matter requires an examination of the characteristics of the X-ray source,

the X-rays, and their macroscopic and microscopic interactions with atoms

and nuclei. This complete examination is required especially for a nuclear physics program and can be useful in a thorough understanding

of all other applications of high-energy radiations. The High Energy

Radiation Section has emphasized a program of basic research and has,

therefore, carried out an active program with the betatron and synchrotron

in the following fields: l) Photonuclear Physics; 2) Radiation Physics;

and 5) Measurement Techniques and Standards. These programs have led

to significant data for inclusion in the recommendations made by the

National Committee on Radiation Protect ion, and Measurements.

51
1, Photonuclear Physics. The high-energy X-rays from the betatron

and synchrotron are being used to study the X-ray interaction with the

atomic nucleus. The predominant processes that result from this interaction are neutron and proton emissions around 20 Mev and meson emissions

around I50 Mev.

a. Photoneutron Cross Sections. A detailed examination of the shape

of the photoneutron cross section has been made for a wide range of target

materials. This cross section has a simple resonance shape for a spherical

nucleus such as gold or lead. However, for a deformed nucleus, such as tantalum, the cross section is composed of two resonances peaked at

12,5 and 15 Mev, Both the theory and experiment of this process were developed at NBS and have resulted, as a by-product, in a relatively

accurate method of measuring nuclear quadrupole moments or nuclear

de format ions

,

b, Photoproton Cross Sections, The photoproton cross section of

carbon in which the residual boron nucleus is left in the ground state has

been measured. This cross section is shown to decrease from its value at

the giant resonance peak-energy of 22 Mev to about one hundredth of this

value at 60 Mev, Angular distributions measured at five energies exhibit

an asjmmietry around 90° which increases rapidly with increasing energy.

In addition to these and other cross-section data that are of interest

to nuclear theorists, the measurements provide a sensitive means of

calibrating the energy scales of electron accelerators at energies in

the 25 to 50 Mev region,

c, Photomeson Cross Sections , Angular distributions of neutral

mesons photoproduced by IJO-Mev bremsstrahlung from the synchrotron have

been measured for carbon, aluminum, copper, cadmium, and lead. The

experimental distributions have been compared to Monte Carlo predictions

and thereby have provided a 3^ measurement of the r,m. s, radii of nucleon

center distributions. These results are 0,3 ferml lower than the electron

scattering results obtained at Stanford University, which measure the

r,m, s, radii of charge distributions. The difference is understandable

on the basis of the proton size. The photomeson data also provide an accurate method for calibrating the synchrotron energy scale at 137 Mev,

d. Nuclear Elastic Scattering Cross Sections , Differential cross

sections for the elastic scattering of X-rays by the nucleus have been

measured at X-ray energies ranging from k to k-0 Mev for a wide range of

atomic nvmibers. The cross sections versus energy tend to exhibit two

maxima, one below the particle threshold that corresponds to scattering

by individual nuclear levels, and one that is related to the giant resonance for X-ray absorption. The dispersion relations have been

used to relate X-ray absorption with the scattering in the giant resonance

region and have provided a valuable check on the absolute absorption cross

sections Inferred from photoneutron cross section measurements. For the

deformed nuclei, such as tantalxim, holmium, and erbium, the scattering . cross sections when compared with the predictions made by the dispersion

relation from the measured absorption cross section strongly support the

hypothesis that the polarizabllity of these nuclei has a tensor character,

52
12 The scattering from the single 15.1-Mev level in C has permitted an evaluation of level parameters for that level. The knowledge of the

width of this level has been very Important to recent developments in

the theory of weak interactions. It has also provided the most

accurate method available for calibrating the absolute energy scale

of a high-energy accelerator at 15. 1 Mev.

e. Total Nuclear Cross Sections . Total nuclear cross sections

between X-ray energies of 15 and 80 Mev have been measured using long

absorbers of carbon, water, and aluminum, A scintillation spectrometer

developed at NBS has been able to resolve the total nuclear cross sections

in the X-ray spectra transmitted by the absorbers and to locate the

energies and magnitudes of the gross structure in these cross sections,

2, Radiation Physics .

a. Pair Production Cross Sections . The long absorber technique

employing the good resolution spectrometer has also been used to evaluate

the total attenuation cross sections for 60-Mev X-rays on carbon, water,

and alximinum. The analysis of the data suggests that the experimental

results are larger than the theoretical predictions by about 2^ and

attributes the difference to the pair process. Recent calculations show

that the radiative corrections to the pair production process approximately

confirm the experimental conclusions.

b. Bremsstrahlung Cross Sections . Experimental determinations of

the cross sections for the production of X-rays by the bremsstrahlung

process have been made. The resonance fluorescence of the narrow 15»1 Mev

level in carbon was used to measure the shape of the high-energy tip of

the X-ray spectrum with very good energy resolution, A scintillation

spectrometer was used to measure the absolute differential cross sections

at other parts of the spectrum for beryllium, aluminim, and gold. Based

on experiments such as these, a critical review of experiments and theories

of the bremsstrahlung process has been published in collaboration with

the X-ray Section (^.Ol).

5. Measurement Techniques and Standards ,

a. Calorimeter for Measuring X-ray Beam Energy. The total integrated

X-ray energy incident on a patient or experimental arrangement is a physical quantity which, can be measured accurately. This section has

used both a calorimeter and a scintillation spectrometer to measure this

quantity. These measurements can be used to calibrate a continuous duty

monitor so that its response serves as an indication of the total X-ray

energy. The section can now assist in the routine calibration of transmission monitors of this tjrpe, A standard instrument has been developed

and experimentally calibrated so that when it is placed in a bremsstrahlung

beam with a peak X-ray energy between 6 and I70 Mev, and a diameter of less

than 20 centimeters, the ionization charge collected during the X-ray

exposure can be used to evaluate the total energy to within ±2^. Several

of these standard Instruments have been calibrated and are available on

loan to transfer the NBS absolute calibration to other laboratories.

35 .
b. Absorbed Dose Calorimeter . The development of an absorbed

dose calorimeter has also been undertaken along with an investigation

of the feasibility of using this calorimeter to calibrate a small

volume ionization chamber. Absorbed dose rates of 50 ergs/gram- sec can

be measured with the calorimeter to within 2$ accuracy. This effort

is part of the division's basic dosimetry studies. There is no plan

to use the results to incorporate a calibration service for absorbed

dose instrument s„

c. Absolute Calibrations of Accelerator Energy Scales . Nuclear

constants, such as photoneutron, photoproton, and photomeson thresholds,

are important for providing calibrations to the energy scales of

electron accelerators. However, these thresholds cannot supply a detailed examination of the stability and pulse-to-pulse variations in

energy of the betatron and synchrotron. Therefore, an instrument was developed which can do this and is capable of measuring time-varying

and space-varying magnetic fields such as are encountered in circular

particle accelerators (i.e., betatrons, synchrotrons, and cosmotrons).

The instrument uses electron paramagnetic resonance of the free radical

in the DPPH molecule. Magnetic fields over a range from 2900 to ^4-200 gauss and rates of rise of about 5500 kilogauss sec' can be measured

to a 0,1^ accuracy.

d« X-ray Scintillation Spectrometer . Continuing efforts to

improve the energy resolution of high-energy scintillation X-ray spectrometers have been made. The latest results have produced a sodiumiodide spectrometer with a resolution of 2,5^ at I7.6 Mev, which is

comparable to that of a pair spectrometer, but with a detection

efficiency several orders of magnitude better than the pair spectrometer. The improved resolution was obtained by placing a second crystal spectrometer so as to detect a single annihilation photon escaping

from the front surface of the main spectrometer crystal which was a 9 inch diameter by G,h inch long sodium iodide crystal. The second

crystal was set in coincidence with the main crystal.

Jh
B, Future Programs

1, Photonuclear and Radiation Physics . Many of the experiments

completed at NBS with the betatron and synchrotron Involve processes

that occur very Infrequently, The Increase in Intensity by a factor of

100,000 that appears possible with the new accelerator would make possible

and productive a whole new area of research. Precision experiments on

elastic and inelastic scattering of electrons and positrons will be

possible and should supply unique information on fundamental electromagnetic and nuclear processes. Other experiments that previously re- quired months of effort and exposure time, if achievable at all, might

now be accomplished in hourso For example, it will probably be possible

to measure the polarization effects in the nuclear photoeffect that will

provide extremely valuable information regarding nuclear wave functions.

Polarization investigations are almost non-existent with conventional

electron accelerators. In addition, the proposed accelerator will produce

strong beams of positrons and neutrons, and relatively strong beams of

monoenergetlc X-rays that can be used for research. None of these

radiations are produced in sufficient quantities with the betatron and

synchrotron to be used for direct experimental studies.

2, Absorbed Dose Standards and Measurement Techniques .

a. Dosimetry, Existing dosimetric standards are based on absorbed

doses of hundreds of rads and dose-rates of tens of thousands of rads per

hour. Nuclear physics research, personnel protection studies, investigations of solid state phenomena, and industrial developments have created

pressing needs for additional standards. In addition, the military

services are rapidly developing needs for standards in the range from

100,000 to 10 million rads and future demands for standards at 10 billion

rads can be predicted with certainty. The proposed accelerator will

provide 100 billion rads per hour. This dose rate, added to those available

from the existing cobalt, radium, X-ray and electron beam sources at NBS,

will make it possible to conduct investigations of dosimetry problems in

most of the Important ranges of energies and dose rates presently in use

or expected in the foreseeable future. Considerable effort must be

expended over a long period of time, however, in order to achieve the

accuracy necessary to establish national standards,

b. Physical Measurement Techniques , A prerequisite to the work on

dosimetry or any research with the accelerator will be the development of

controls for the Intense electron beams. Instruments must be developed to

monitor the electron-beam current, the energy, and the spatial distribution

of the beam. Magnetic systems of different types must be devised to analyze

and focus the beam. The development of better methods for controlling and

measuring electron beams will continue to be important during the lifetime

of the accelerator. While these techniques will be needed for the proper

use of the machine by NBS, they are also applicable to the use of such

machines by other research institutions and by industrial organizations.

NBS should serve a leading role in the development of such new measurements

and control techniques.

35
c. Shielding . Detailed theoretical and experimental research on the

absorption of high- intensity, high-energy X-ray and neutron beams by concrete, lead, and other materials should be carried out to provide data for use in the design of shielding for future industrial and government installations. The requirements described in the section on facilities for the

NBS installation call for 12- foot thick concrete barriers and a 100- foot

exhaust stack to remove safely the ozone and radioactivities produced in

the air of the laboratory rooms. These dimensions point up the Immediate

need for accurate design data to promote the efficient and economical

design of other installations. Past studies of lover intensity sources at

NBS have been of great service to hospitals and laboratories in reducing

costs while at the same time assuring safe radiation levels for personnel

in radiological installations.

56
5» Radiological Equipment Section {h,0^)

S. W. Smith, Chief

The program of the Radiological Equipment Section is, for the

most part, centered about experimental problems involving standards

for low- and medium-energy X-rays and gamma rays, of both dosimetric

and performance character. It may be conveniently divided into the

following. categories: (l) primary and secondary standards, (2) certification of radium and calibration of encapsulated gamma-ray sources,

(3) radiological instruments calibrations and investigations, (k-)

investigations in radiation dosimetry with photographic emulsions,

chemical systems, solid state devices, etc, and (5) high- intensity

gamma rays for irradiation purposes.

Primary and Secondary X-ray Standards . The laboratory has, since

1928, maintained primary gviarded- field free-air standard ionization

chamisers against which all moderate energy X-ray exposure dose measurements in this country are compared. The standard which covers the

range of 60 to 25O kv, has been compared with a number of European

standards indicating close agreement, A free-air chamber for lower

energy X-rays in the range 20 to 100 kv has been constructed and its

characteristics studied. The design factors for a standard for Grenz rays

generated at 5 to 5O kv are being investigated. Standards for measurements at low energies for the very high dose rates (up to 10° r/min)

from beryllium-window X-ray tubes are of particular importance.

Secondary standards, usually in the form of cavity or enclosed

chambers, have been under continuous study by the laboratory for many

years, A wide variety of these have been investigated and developed,

and further studies are underway. Chambers of this type have been

developed (il-.Ol) for use as transfer standards for intercomparing the

free-air standard chambers of various countries. Measurements so far

carried out have indicated their usefulness for this purpose. Cavity

chambers have been used for the calibration of the laboratory's

standard gamma-ray collimated-beam instrument ranges. They have been

used also for the calibration of radiac instrument calibration ranges

employing Co"*^ or Csl5T^ developed for the Navy and Signal Corps,

Considerably more than a hundred of these calibration ranges have been

calibrated by the laboratory for these agencies.

57
Certification of Radium and Calibration of Gamma-Ray Sources, The Gamma Ray Laboratory was specifically designed to carry out the

measurement of encapsulated radium, Co" , Csl5T^ and other gamma-ray

sources. Improvement in the measurement techniques and calibration . procedures has resulted in substantial increases in efficiency without sacrificing accuracy requirements, and at the same time has

achieved a reduction in radiation exposure to personnel. The radium

measurements are in terms of radivim content certified to 0.7 percent,

and most of these sources are used for medical treatment purposes.

Small cobalt-60 preparations are measlired in terms of roentgens per

hour at a given distance and are generally used as laboratory standards.

Radiological Instrument Calibrations and Investigations , Radiation Instruments, usually of the condenser ionization- chamber

r-meter type, are submitted by instrument manufacturers, medical

institutions, research laboratories, the public and other Government

agencies, for calibration as laboratory secondary standards, on X-rays

of various energies and gamma rays. The number of requests for such

calibrations has made it necessary to place some limitations on the

frequency of recallbration and the number of calibration points for a given laboratory, in order to make this service both effective and

available to the maximum number of laboratories requiring it.

All types of radiation detection and measuring instruments and

devices are calibrated for energy dependence, dose-rate dependence,

and other factors affecting the instruments' response to radiation.

These instruments Include ionization chambers, Geiger-Mueller counters,

scintillation counters, chemical-solution dosimeters, radiation- sensitive glasses, etc. A major portion of this program is conducted for

the Department of Defense, Atomic Energy Commission, and Civil Defense,

who are engaged in large-scale development and procurement programs.

For a number of years, agencies lacking testing facilities have submitted prototype instruments for evaluation of sensitivity, energy

dependence, and other characteristics. On the whole, the Bureau's

Radiation Physics Laboratory probably has the most completely staffed

and equipped laboratory for this type of work in the country. The

results of the studies carried out for the above agencies are put into

report form and distributed to the interested agencies.

Radiation Sensltometry of Photographic Emulsions and Dosimetry

With Chemical, Solid State and Other Devices , The laboratory has been

conducting a broad program for investigating the radiation sensitivity

of photographic emulsions for more than ten years. Investigations of

the sensltometric factors for most commercial films, with regard to

energy dependence, useful range, and rate dependence, have been carried

out, and are being continued and extended. This has covered a wide

range of energy, exposure dose, and exposure dose rates for X- and gamma

rays, and for neutrons and electrons. Particular emphasis has been

placed on attempts to extend the useful range of film dosimeters in both

directions, such that gamma-ray doses in the range from lo~2 to 10 ^ r may now be measured with good precision, using commercially supplied films

38
Measurements made with film-sclntillator combinations showed that

exposure doses as low as 10"^ r can be measured, but that rate dependence at the lower rates limits the accuracy. Interpretations of total

exposures in the range from 10^ to lo" r were made possible by measuring changes in the transmission of near-infrared by the films, as a result of increased print-out darkening by exposures in the megaroentgen

range.

Processing and calibration procedures have been studied to arrive at

optimum procedures, particularly for use with energy- independent film

dosimeters. The validity of the reciprocity law for instantaneous bursts

of X-rays at intensities up to 1100 r/sec has been substantiated for the

ascending branches of the characteristic curves, when vigorous processing

is used. Reciprocity law failure and associated variations in curve

shape, as well as changes in the maximum density levels, were demonstrated

for the reversal branches of the curves, when nonvigorous processing is

used. The possibilities of serious misinterpretation of doses as a result

of these variations have been noted. Tests of the reciprocity law

at intensities up to 10" r/sec are in process.

Extensive studies of the photographic response to successive ex- posures of different types have been carried out, including double

exposures to X- and :y:-radiation of different photon energy and intensity,

to gamma radiation and visible light, and to visible light and infrared

radiation. It was shown that it is possible to predict the gross photographic behavior as a result of exposures to two types of radiation in

succession. Further studies including other radiation types and evaluation methods are planned.

Studies of effects of variations of temperature and relative

hvunidity, both during exposure and during storage of the film before

processing, have been performed. These results are important for

evaluating personnel dosimetry procedures in which films are allowed

to remain in their holders over periods of up to three months, before

being processed and read. Special intercomparisons and evaluations of

various personnel monitoring facilities have been made, resulting in

suggestions for standardizing and improving the methods employed by

various Government and private laboratories.

Calculations were carried out to determine the relative response

of photographic emulsions to X- and gamma-ray photons, to electrons,

and to neutrons on the basis of energy and number of quanta truly

absorbed in the emulsion, and these data were compared with experimental

results.

Increasing interest is being shown in the use of solid-state devices

for measuring ionizing radiations. Solid-state devices are of rugged

construction, can be produced in small sizes, are simple to operate and

have a long shelf life. They also show very good reproducibility in the

measured radiation effects and have a quick response.

39
Measurements were carried out to investigate the possibility of

using silicon solar cells for dosimetry of ionizing radiations,

Silicon solar cells, which are photovoltaic cells of the p-n junction

type, showed a favorable response of such cells to X-rays with regard

to proportionality to exposure dose, response time and dependence on photon energy. Measurements are being carried out to establish the

influence of radiation damage on the photoresponse of such cells at

high exposure dose rates of high-energy radiations. Investigations

will be further extended to other solid state devices, in order to

develop a solid state dosimeter suitable for X- and gamma rays.

Radiation- induced chemical reactions are used in increasing

measure for quantitative measurement of ionizing radiations. Different

systems have been developed which show a high stability and allow a high degree of accuracy in measuring the product of the radiation

chemical reaction. Chemical dosimeters allow the direct measurement of

absorbed energy. They consist usually of aqueous solutions which have

an absorption characteristic similar to that of body tissue and body

fluids. Chemical dosimeters can be used for different types of radiaover a wide range of doses and dose rates.

The most widely used system of chemical dosimetry is the ferrous

sulfate dosimeter (Fricke dosimeter). Investigations were carried out

of the energy dependence of G-values (ferric ion yield per 100 ev absorbed energy) for medium energy X-rays, The values obtained showed

a good agreement with values obtained with high-energy X- and gamma

rays. Further measurements are being carried out under different

experimental conditions to confirm the obtained values. An investigation has been completed of the spectrophotometric method of determining the radiation-produced ferric ion yield. It has been shown

that the sensitivity of this method can be increased by measuring the

absorbance of the irradiated ferrous sulfate solution at a wavelength

of 22^ m |j^, instead of 30^ ni |j., as is the usual standard method.

Smaller temperature dependence and less acidity dependence of the

absorbance at 22^1- m|i is a further advantage of this method. Investigations will be extended to other chemical dosimetry systems.

High Intensity Gamma Rays for Irradiation, Investigation of

the radiation effects on materials and Cf th6 Stabilization of foods and

pharmaceuticals with radiation has greatly increased the dose rates

required, and thus, the need for extended or new dosimetry procedures.

A 2000-curie Co source, consisting of 12 capsules arranged in a circular array and shielded by water in a 12- ft pool, has been used

for the past five years for important investigations carried out, such

as the study of the effects of irradiation of polymers. As the duration

of exposure required with the 2000-curie Co°^ source is, in many instances,

excessively long, a 50,000-curie source is being procured. This will

greatly extend the range of radiation effects which can be investigated

and, at the same time, permit extension of dosimetric procedures to

systems for measuring much higher dose rates.

ho
6, Nucleonic Instrumentation Section Q\-„06)

L. Costrell, Chief

The Nucleonic Instrumentation Section is concerned with several

projects in the instrumentation field and also serves as a complementary

unit to other sections in the Division^ The Section has a responsibility

for the electronic instrumentation needs of the Division, This is a growing responsibility in view of the increase in both quantity and

complexity of electronic instrumentation in experimental nuclear physics.

The Section develops, designs, and constructs special instrumentation

as required for the nuclear physics program of the Division. For this

purpose the Section develops and maintains a competence in nuclear

detection techniques, in general electronic design, in high speed

circuit techniques, etc. The emphasis is subject to continual change

as the field advances. For example, though most instrumentation of

concern to the section is for microsecond resolution, millimicrosecond

and sub-millimicrosecond techniques are receiving increasing attention.

These techniques have broad application in several sections in the

division. Development and design and the maintaining of a competence

in the nuclear instrimientation field is a continuing program that

necessitates keeping abreast of the latest developments.

In addition to somewhat conventional instrumentation design, the

section undertakes complex developments that fill a need in the nuclear

instrumentation field. The charge- storage pulse-height analyzer

development of this section fits into this category. The section also

utilizes detection instrumentation, to a limited extent in performing

specific experiments for which a need exists and which the section, by

virtue of its capabilities and its equipment is in a position to handle.

Over the past several years the section has been heavily engaged in

special projects for the armed forces and the U, S, Atomic Energy

Commission, This has included several weapons test projects involving

the expenditure by the section of over four million dollars. Remotecontrol radiation monitoring systems developed by the section have been

used in several tests by the AEC,

A routine function of the section is the repair and maintenance of

electronic and radiation detection instrumentation for the division.

kl
7. Neutron Physics Section (k-^O'j)

R, S. Caswell, Chief

Neutron Standards , Ra-Be(Y,n) sources and a moderating assembly

producing a measured thermal neutron flux serve as standards for neutron

emission rate and thermal neutron flux respectively. The national neutron

'Standard source has been calibrated by two methods: (l) by the activation

of calibrated foils in a water bath; and (2) by activation of a manganese

sulfate solution in water, A new calibration is underway using a Sb^^^-Be

photoneutron source in heavy water. This method eliminates uncertainties

due to the ratio of the manganese activation cross section and the hydrogen

thermal neutron disappearance cross section. The national standard source

is then compared to the" absolutely calibrated Sb^^^-Be source by a precise,

but relative, method.

The standard thermal neutron flux has been recalibrated by a method

based on the thermal neutron activation cross section of gold, using

^jt p-y coincidence counting. The new calibration, together with a previous calibration based on the thermal neutron reaction cross section

of boron, provides a flux known to about 1,5']^ (standard error).

Intercomparison of this flux with the absolutely calibrated fluxes of

other laboratories in the United States and in the world has been

underway for several years and is continuing.

Neutron sources calibrated by NBS are used as standards for fast

neutron flux measurement, cross section measurements, fast neutron

dosimetry, and to produce known thermal neutron fluxes in moderators.

Gold foils activated in the standard thermal neutron flux are used

chiefly by groups working with nuclear reactors to check or to establish

their own thejrmal neutron flux measurements.

Neutron dosimetry measurements are made with proportional counter

detectors which distinguish between neutrons and gamma rays. The

neutron dosimeter (y- Insensitive) is calibrated in known fluxes of

monoenergetic neutrons from the Van de Graaff accelerator. The gamma

ray dosimeter (neutron- insensitive) is calibrated in X-ray and gamma-ray

fields of known exposure dose. The pair of instrimients is then used in

mixed gamma ray and neutron radiation fields to determine the doses,

A precision long counter is being developed in cooperation with

Hanford Laboratories as a standard instrument for the measurement of

fast neutron flux.

Neutron Penetration, Measurements have been made of the thermal

neutron distribution, the Indium resonance age and the fast neutron

distribution about monoenergetic neutron sources in water and heavy

water. The current experiment on fast neutron dose from k-,0 Mev

neutrons in water is to be followed by spectral measurements of neutrons

from monoenergetic sources following penetration through various shielding

materials.

42
Neutron Cross Sections . Experimental measurements of neutron

elastic and Inelastic cross sections and angular distributions by

tlme-of-fllght are being carried out on the 2-Mev Van de Graaff

accelerator. Measurements for calclxmi and carbon at 1^,0 Mev are partially complete. The beginning of the neutron flight Is Indicated

by detection. of the alpha particle from the H5(d,n)He^ reaction which

produces the neutron. The scattered neutron Is detected In a large

plastic scintillator after a flight from the scattering sample of

1,2 meters. Internal pulsing for the accelerator and an astigmatic

Mobley magnet system, both on order, will reduce backgrounds and

sharpen time resolution (below the 2,5 nanosecond currently obtained)

and permit measurements at energies of 5 Mev and below.

Polarization experiments for spin-zero nuclei will be carried

out using the pulsed beam from the Van de Graaff accelerator for

spin zero nuclei. It is hoped in the future to use aligned nuclei

in cooperation with members of the Cryogenic Physics section.

Theoretical calculations using the nuclear optical model are being made of neutron cross sections and polarization. These

calculations give results directly comparable to the elastic scattering

measurements and to the polarization experiments. In addition results

of these calculations are useful for neutron penetration. Calculations

such as the moments method code being developed in the Radiation

Theory Section are of considerable Importance,

iv3
8. Health Physics Group

The Health Physics Laboratory has as its main objective the

maintenance throughout the National Bureau of Standards of good

practices in the handling of ionizing radiations and radioisotopes.

It is charged with monitoring of personnel, machines giving rise

to ionizing radiations such as X-ray machines, X-ray spectrometers,

cyclotrons, betatrons, and Van de Graaff generators, as well as laboratories in which radioisotopes are used. In connection with

the use of isotopes, it is sometimes necessary to make bio-assays

for such nuclides as tritium and uranitun, nSome development work

is in progress for the determination of Sr ,

The laboratory offers its services to anyone in the Bureau

desiring to install equipment or laboratories and in need of advice

on shielding, type of equipment required, handling of wastes and

other related problems.

kk
VIII ACTIVITIES ASSOCIATED WITH OUTSIDE ORGANIZATIONS

In addition to its experimental and theoretical programs, the

Radiation Physics Division has definite and immediate responsibilities

in certain specific areas, the two most Important of which are radiation protection and radiological units. Activities in these fields are carried out mainly through participation in the committee activity of

national or international organizations. One form of this participat;ion is the provision of information and data developed in the research

program for use in the published reports of the various organizations.

National Committee on Radiation Protection and Measurements

One of the Division's major programs has been in the field of

radiation protection, through the medium of the National Committee on

Radiation Protection and Measurements. This activity cuts across all

of the Sections of the Division. The National Committee on Radiation

Protection and Measurements was organized and sponsored by the National

Bureau of Standards in 1929^ and is now recognized as the focal point

for radiation protection activities in the United States, The principal

participating organizations are the national radiological and medical

organizations, United States Public Health Service. Atomic Energy

Commission, and the three military services. At present, it has

published 28 handbooks and several others are in preparation. These

cover such fields as permissible internal and external radiation dose,

medical X-ray protection, radium protection, betatron protection,

neutron protection, radiological instrumentation, safe handling of

radioactive isotopes, radioactive-waste disposal, and radioactive

decontamination.

International Commission on Radiological Units and Measurements

The International Commission on Radiological Units and Measurements (iCRU), since its inception in 1925, has had the responsibility

for developing (l) the basic principles of units, standards, and measurements needed in radiation dosimetry; and (2). the specification of

radiation treatment. In connection with its radiation standards program,

the Radiation Physics Division has been an active participant in all

related ICRU committee activities for the past 25 years. Several members of the Division staff are active in the programs of the ICRU and

the chairmanship and secretaryship of the Commission have been held by

Division staff members for several years.

International Bureau of Weights and Measures

The International Bureau of Weights and Measures was established

in 1875 • This organization provides a central point for the intercomparison of national standards. Initially, it dealt with standards

of length and mass but as new fields opened up its scope was broadened.

Recently it was decided to include the measurement of ionizing radiations,

^5
Members of the Radiation Phyfilcs Division were active in the discussions leading to the decision and in the preparation of recommendations for the organization's activities in this field. Division personnel are also members of the group which reviews future activities of

the International Bureau in the radiation measurement field.

International Commission on Radiological Protection

The International Commission on Radiological Protection is con- cerned with the international formulation and implementation of the

basic principles of radiation protection. The membership of the ICRP

and its. several committees has for many years included members of the

staff of the Radiation Physics Division, Participation in the activities

of the Commission has been continuous since its formation in 1928, and

one of the staff members was its secretary for Ik- years. Through its

activities -involving the National Committee on Radiation Protection

and Measurements, this Division provides an ideal tie between the two

organizati ons

Federal Radiation Council

The Federal Radiation Council was formed in 1959 to provide a Federal policy on hximan radiation exposure. A major function of the

Council is to advise the President with respect to radiation matters,

directly or indirectly affecting health, including guidance for all

Federal agencies in the formulation of radiation standards and in the

establishment and execution of programs of cooperation with States,

The Council has established a Working Group and a Division staff member

acts as the Commerce Department representative on this group. Staff

members have also been members of the temporary staffs utilized by the

Council in the preparation of its reports,

American College of Radiology Commission on Radiologic Units, Standards

and Protection

This body was formed in 19^6 to coordinate the activities of the

several national radiological organizations in the United States; it

is an outgrowth of the consolidation of the corresponding committees

of these societies. Division staff members have been quite active in

the Commission programs and the chairmanships of these committees had

for many years before 19^6 been held by Radiation Physics Division staff

members, as is the secretaryship of the new group.

h6
American Standards Association - Nuclear Standards Board

The National Bureau of Standards has actively supported the

programs of the American Standards Association in furthering the

development of standards of practice such as codes, specif icatloa^,

and safety standards. Radiation Physics Division staff members have

been quite active in these efforts. The Safety Code for the Indistrial

use of X-rays (ASA, 54,1) was prepared in 1946 by the ASA Safety

Standards Board under the sponsorship of NBS. A new code on this

subject is now in preparation and Division staff members are participating in this work.

Because of the rapid development of application of nuclear

energy, the ASA in 1957 established the Nuclear Standards Board to

develop standards in this field. Division staff members are active

on the Nuclear Standards Board itself and on a number of the Sectional

Committees established by the Board to deal with specific problems.

In addition to the above activities. Radiation Physics Division

staff members work actively with numerous other committees whose

main interests are in line with the general Division program.

h'J USCOMM—DC

U. S. DEPARTMENT OF COMMERCE

Lutbier H. Hodges, Secretary

NATIONAL BURfcAU OF STANDARDS

A. V. Astin, Director THE NATIONAL BUREAU OF STANDARDS

The scope of activilics of llic National Bureau of Standards at its major laboratories in Wasliinglon, D.C., and Boulder,

Colorado, is suggested in the following listing of the divisions and sections engaged in /technical work. Tn general, each section carries out specialized research, development, and engineering in the field indicated by its title. A brief description of the activities, and of the resultant publications, appears on the inside of the front cover. WASHINGTON, D.C.

Electricity. Resistance and Reactance. Electrochemistry. Electrical Instruments. Magnetic Measurements.

Dielectrics. Metrology. Photometry and Colorimetry. Reftactometry. Photographic Research. Length. Engineering

Metrology. Mass and Scale. Volumetry and Densimetry. Heat. Temperature Phvsics. Heat Measurements. Cryogenic Physics. Equation of State. Statistical Physics.

Radiation Physics. X-ray. Radioactivity. Radiation Theory. High Energy Radiation. Radiological Equipment.

Nucleonic Instrumentation. Neutron Physics.

Analytical and Inorganic Chemistry. Pure Substances. Spectrochemistry. Solution Chemistry. Analytical

Chemistry. Inorganic Chemistry.

Mechanics. Sound. Pressure and Vacuum. Fluid Mechanics. Engineering Mechanics. Rheology. Combustion

Controls. Organic and Fihrous Materials. Rubber. Textiles. Paper. Leather. Testing and Specifications. Polymer

Structure. Plastics. Dental Research. Metallurgy. Thermal Metallurgy. Chemical Metallurgy. Mechanical Metallurgy. Corrosion. Metal Physics'

Mineral Products. Engineering Ceramics. Glass. Refractories. Enameled Metals. Crystal Growth.

Physical Properties . Constitution and Microstructure. Building Research. Structural Engineering. Fire Research. Mechanical Systems. Organic Building Materials,

Codes and Safety Standards. Heat Transfer. Inorganic Building Materials. Applied Mathematics. Numerical Analysis. Compulation. Statistical Engineering. Mathematical Physics.

Data Processing Systems. Components and Techniques. Digital Circuitry. Digital Systems. Analog Systems«

Applications Engineering.

Atomic Physics. Spectroscopy. Radiomelry. Solid Slate Physics. Electron Physics. Atomic Physics.

Instrumentation. Engineering Electronics. Electron Devices. Electronic Instrumentation. Mechanical Instru- ments. Basic Instrumentation. Physical Chemistry. Thermochemistry. Surface Chemistry. Organic Chemistry. Molecular Spectroscopy. Molecular Kinetics. Mass Spectrometry. Molecular Structure and Radiation Chemistry.

• Oflice of Weights and Measures. BOULDER, COLO.

Cryogenic Engineering. Cryogenic Equipment. Cryogenic Processes. Properties of Materials. Gas Liquefaction.

Ionosphere Research and Propagation. Low Frequency and Very Low Frequency Research. Ionosphere

Research. Prediction Services. Sun-Earth Relationships. Field Engineering. Radio Warning Services. Radio Propagation Engineering. Data Reduction Inslrumentalion. Radio Noise. Tiopospheric Measurements.

Tropospheric Analysis. Propagation -Terrain Effects. Radio-Meteorology. Lower Almospheie Physics.

Radio Standards. High Frequency Electrical Standards. Radio Broadcast Service. Radio and Microwave

Materials. Atomic Frequency and Time Interval Standards. Electronic Calibration Center. Millimeter- Wave

Research. Miciowave Circuit Standards. Radio Systems. High Frequency and Very High Frequency Research. Modulation Reseaich. Antenna Research. Navigation Systems. Space Telecommunications.

Upper Atmosphere and Space Physics. Upper Atmosphere and Plasma Physics. Ionosphere and Exosphere

Scalier. Airglow and Aurora. Ionospheric Radio Astronomy.
NBS