NBS TECHNICAL NOTE 813

NBS Reactor:

Summary of Activities

Julyl972loTuneT973

National

Bureau

of

Standards Vm
NATIONAL BUREAU OF STANDARDS

The Rational Bureau of Standards' was established by an act of Congress March 3, 1901. The Bureau's overall goal is to strengthen and advance the Nation's science and technology

and facilitate their effective application for public benefit. To this end, the Bureau conducts

research and provides: (1) a basis for the Nation's physical measurement system, (2) scientific and technological services for industry and government, (3) a technical basis for equity in trade, and (4) technical services to promote public safety. The Bureau consists of the Institute for Basic Standards, the Institute for Materials Research, the Institute for Applied Technology,

the Institute for Computer Sciences and Technology, and the Office for Information Programs.

THE INSTITUTE FOR BASIC STANDARDS provides the central basis within the United

States of a complete and consistent system of physical measurement; coordinates that system

with measurement systems of other nations; and furnishes essential services leading to accurate and uniform physical measurements throughout the Nation's scientific community, industry, and commerce. The Institute consists of a Center for Radiation Research, an Office of Measurement Services and the following divisions: Applied Mathematics — Electricity — Mechanics — Heat — Optical Physics — Nuclear

Sciences - — Applied Radiation - — Quantum Electronics 3 — Electromagnetics 3 — Time

and Frequency ' — Laboratory Astrophysics 3 — Cryogenics \

THE INSTITUTE FOR MATERIALS RESEARCH conducts materials research leading to improved methods of measurement, standards, and data on the properties of well-characterized materials needed by industry, commerce, educational institutions, and Government; provides

advisory and research services to other Government agencies; and develops, produces, and

distributes standard reference materials. The Institute consists of the Office of Standard Reference Materials and the following divisions: Analytical Chemistry — Polymers — Metallurgy — Inorganic Materials — Reactor

Radiation — Physical Chemistry.

THE INSTITUTE FOR APPLIED TECHNOLOGY provides technical services to promote

the use of available technology and to facilitate technological innovation in industry an<j Government; cooperates with public and private organizations leading to the development of

technological standards (including mandatory safety standards), codes and methods of test; and provides technical advice and services to Government agencies upon request. The Institute consists of a Center for Building Technology and the following divisions and offices: Engineering and Product Standards — Weights and Measures — Invention and Innovation — Product Evaluation Technology — Electronic Technology — Technical Analysis — Measurement Engineering — Structures, Materials, and Life Safety ' — Building

Environment * — Technical Evaluation and Application 4 — Fire Technology.

THE INSTITUTE FOR COMPUTER SCIENCES AND TECHNOLOGY conducts research and provides technical services designed to aid Government agencies in improving cost effec- tiveness in the conduct of their programs through the selection, acquisition, and effective

utilization of automatic data processing equipment; and serves as the principal focus within

the executive branch for the development of Federal standards for automatic data processing

equipment, techniques, and computer languages. The Institute consists of the following

divisions: Computer Services — Systems and Software — Computer Systems Engineering — Information Technology.

THE OFFICE FOR INFORMATION PROGRAMS promotes optimum dissemination and

accessibility of scientific information generated within NBS and other agencies of the Federal Government; promotes the development of the National Standard Reference Data System and

a system of information analysis centers dealing with the broader aspects of the National Measurement System; provides appropriate services to ensure that the NBS staff has optimum

accessibility to the scientific information of the world. The Office consists of the following

organizational units: Office of Standard Reference Data — Office of Information Activities — Office of Technical

Publications — Library — Office of International Relations.

1 Headquarters and Laboratories at Gaithersburg, Maryland, unless otherwise noted; mailing address Washington, D.C. 20234.

3 Part of the Center for Radiation Research.

3 Located at Boulder, Colorado 80302.

* Part of the Center for Building Technology.
NBS Reactor: Summary of Activities

July 1972 to June 1973

National Bureau of StafKferiife

R 2 9 1974

Robert S. Carter

Reactor Radiation Division

Institute for Materials Research

National Bureau of Standards

Washington. D.C. 20234

*^fAU Of

U.S. DEPARTMENT OF COMMERCE, Frederick B. Dent, Secretary

NATIONAL BUREAU OF STANDARDS, Richard W. Roberts, Director

Issued February 1974
National Bureau of Standards Technical Note 813

Nat. Bur. Stand. (U.S.), Tech. Note 813,135 pages (Feb. 1974) , CODEN: NBTNAE

U.S. GOVERNMENT PRINTING OFFICE

WASHINGTON: 1974

For sale by the Superintendent of Documents, U.S. Government Printing Office, Washington, D.C. 20402 (Order by SD Catalog No. 03.46:813). Price $1.55
FOREWORD

The National Bureau of Standards Reactor was built not only to serve

the needs of the NBS but also those of the greater Washington Scientific

Community and other government agencies. The Reactor Radiation Division

was established to operate the reactor and to foster its scientific and

technological use. Toward this end, the Division has a small nucleus of

scientists experienced in the use of reactors for a wide range of scientific and technical problems. In addition to pursuing their own research

and developing sophisticated experimental facilities, they actively seek

out and encourage collaboration with other scientists, engaged in challenging programs, whose work can benefit from use of the reactor, but

who as yet do not have the reactor experience necessary to take full

advantage of the facilities available. The Division also provides

irradiation services to a wide variety of users as well as engineering

and other technical services.

The reactor operates at 10 MW and is designed to provide a broad

spectrum of facilities ranging from intense neutron beams to extensive

irradiation facilities, making it one of the most versatile high flux

research reactors in the country. Thus it is able to serve a large

number of scientists and engineers in a broad range of activities both

within and outside the NBS.

This report attempts to summarize all the work done which is dependent on the reactor including a large number of programs outside the Division. The first section summarizes those programs based primarily on Reactor Radiation Division (RRD) initiatives whereas the second and

third sections summarized collaborative programs between RRD scientists

and other NBS or non-NBS scientists respectively. The fourth section

summarizes NBS work originating entirely outside of RRD which requires no collaboration with RRD scientists. The section entitled, "Service

Programs" covers those programs originating outside NBS but for which

RRD provides irradiation services. The remaining sections are selfexplanatory.

iii
ABSTRACT

This report summarizes all those programs which depend on the NBS

reactor. It covers the period from July 1972 through June 1973. The

programs range from the use of neutron beams to study the structure and

dynamics of materials through nuclear physics and neutron standards to

sample irradiations for activation analysis, isotope production and

radiation effects studies.

Keywords: Activation analysis; crystal structure; diffraction; isotopes:

molecular dynamics; neutron; nuclear reactor; radiation.

Cover photograph: Reactor Building

National Bureau of Standards

Gaithersburg, Maryland

iv
TABLE OF CONTENTS

Page

FOREWORD iii

ABSTRACT iv

A, REACTOR RADIATION DIVISION PROGRAMS 1

Neutron Scattering Studies of Hydrogen in Transition Metals ... 1

1. Tantalum Hydride 1

2. Palladium Hydride 2

Phase Transitions, Orientational Disorder, and Crystal Dynamics

of Ionic and Molecular Solids 6

1. Alkali Hydrosulfides 6 2. Ammonium Bromide and Ammonium Iodide 9 3. Infrared and Raman Band Shape Analysis of Chloroform and

Dicyanoacetylene 9 Analyses of the Dynamics of KCN, NaCN, and Related Crystals

Debye-Waller Factors 15

The Dynamics of Simple Liquids 16

1. Liquid Rubidium 16

2. Small Wave Vector Excitations 16

Elementary Excitations in Quantum Liquids 17

1. *He,9 5- 3He ? os 19

2. Liquid 3 He 19

Rigid Body Thermal Motion in Crystallographic Refinement 20

Studies on Twinning 21

Thermal Neutron Flux Measurements 25

Intercomparison of Neutron Dif fractometers 26

Direct Tests for Violation of CP Invariance 26

Cold-Neutron Time-Of-Flight Facility 27

Cold-Neutron Source 28

B, RRD-NBS COLLABORATIVE PROGRAMS 30

Inelastic Neutron Scattering of a Neon Near the Critical Temperature 30

An Observation of the Deviation from Ornstein-Zernike Theory in

the Critical Scattering of Neutrons from Neon 31

v
TABLE OF CONTENTS

Page

The Structure Factor of Neon Near T 33

Study of hindered Rotation in Hydroxylammonium Perchlorate by

Constrained Least-Squares Refinement 34

A Bifurcated Hydrogen Bond in Ca(H

2 PO,)H2 ..... 35

The Crystal Structure of H

3

P0, '1/2^0 37

The Crystal Structure of Lead Deuterium Orthophosphate 38

Neutron Diffraction Structure Determination of Dichlorotetrapyrazolecopper(II), Cu(C H

4

N

2

) 4

C1

2

. .' 41

Calibration of Detectors for Argon-41 44

C, INTERAGENCY AND UNIVERSITY COLLABORATIVE PROGRAMS 45

Dynamics of Ammonium Ions in NH.C10, and NH,N0« 45

Group Theoretical Analysis of Neutron Scattering in Crystals. . . 46

Temperature Dependence of the Phonons in HCP Be 47

Magnetization of Rare Earth Compounds by Neutron Diffraction. . . 49

Excitation Spectra of an Amorphous Ferromagnet 49

Absence of Magnetic Order in MnO-P^O,. Glass '. . . . 52

Structural Studies of Amorphous Solids 53

Precision Measurement of Thermal Neutron Scattering Amplitudes. . 53

The Structure of Na-ZnCl. '3H.0 54

2 4 2

Crystal Structure of NH.C10, at 300K, 78K and 10K by Neutron

Diffraction ...... * 55

Refinements of the Crystal Structure of KN~ and $-NaN by Neutron

Diffraction 7 57

Crystal Structure of Dinitro-Pentamethylene-Tetramine 58

Three-Axis Neutron Spectrometer 59

D, NON-RRD NBS PROGRAMS 60

Activation Analysis Section: Summary of Activities 60

1. Research Projects 60

2Standard Reference Material (SRM) Analyses 68

3. Cooperative and Service Analyses 70

4. Facilities 71

5. Conclusion 73

Integral Reaction Rate Measurements for the NBS Neutron Standards

Program 74

vi
TABLE OF CONTENTS

Page

Precision Measurement of the Compton Wavelength of the Electron . 76

60Co Gamma Ray Anisotropy Thermometry . . . 77

Emission of Long-Range Alpha-Particles in the Subthermal-,

Thermal- and Resonance-Neutron Fission of239 Pu 77

Extreme-Angle Emission of Long-Range Alpha Particles in the

Thermal Neutron Fission of 23 ^U « . 81

Development of Fast-Neutron Beams 85

Proton-Recoil Spectrometer Research 87

Parity Violation in Neutron Capture Gamma-Ray Emission 93

A Search for Doubly Radiative (N, P) Capture 97

E, SUMMARY OF REACTOR OPERATIONS . • • 101

F, SERVICE PROGRAMS 103

Activation Analysis Program of the Food and Drug Administration

at the NBSR 103

1. Multi-element Analysis of Foods 103

2. MTELMT: A Computer Language for the Reduction of Neutron

Activation Analysis Data 103

3. An Automated Data Acquisition System for Neutron Activation

Analysis 106

The Use of Neutron Activation Analysis on Biological Samples by

the Veterans Administration Hospital 109

Trace Elements in the Environment and Radioactive Decay Studies . 109

The Use of Activation Analysis in Scientific Crime Detection

by the Federal Bureau of Investigation Ill

U. S. Postal Service Activation Analysis Program 112

The Use of Neutron Activation Analysis in Scientific Crime Detection 113

Activation Analysis Program of the U. S. Geological Survey. . . . 113

Combined Effects of Radiation and Shock Waves in Materials. . . . 115

Neutron Irradiation of LPE Bubble Domain Garnets 116

Chemical Studies on Lunar Materials and Meteorites 116

G, STAFF ROSTER 118

H, PUBLICATIONS 122

vxx

A, Reactor Radiation Division Programs

NEUTRON SCATTERING STUDIES OF HYDROGEN IN TRANSITION METALS

We have continued our study in collaboration with H. E. Flotow of

Argonne National Laboratory, of the binding and diffusion of hydrogen

isotopes in bcc and fee transition metals, including their relationship

to intermetallic forces and hydride phase transitions. A study on the

concentration-dependence of hydrogen diffusion in TaHx was completed and

neutron scattering measurements were begun on a single crystal of TaH

n

__ to provide more precise measurements and analysis of the behavior of

hydrogen in this system. It should be noted that the bcc refractory

metals and their alloys are prime candidates as first wall materials in

nuclear fusion power reactors, so that measurements on the microscopic

and macroscopic effects of hydrogen isotopes in these materials are particularly appropriate. Work has also continued in our study of hydrogen

isotopes in palladium. Our effort to prepare and examine high concentration

(3-phase) crystals of PdD^rt n has been stimulated in part by the discovery

>U. / of superconducting phase transitions at ^10°K in the hydride.

1. Tantalum Hydride - J. J. Rush, J. M. Rowe and R. C. Livingston

Analysis of our neutron quasielastic and inelastic scattering data

for Ta_H in its a (bcc) and $ phases has enabled us to prepare a paper

which provides considerable information on the diffusion of hydrogen in

this hydride, including the concentration dependence of the diffusion.

These results also provide an interesting comparison with our previous

results on VH (see our 1972 progress report, NBS TN 758). The widths

of the quasielastic peaks for a-phase Ta„H and TaH_ -_ are shown in Fig. 1

along with theoretical widths predicted for models assuming jumps between

octahedral and tetrahedral sites. It can be seen that the tetrahedraljump model provides the best overall fit to the experimental results, as reported in NBS TN 758, but that in no case is in agreement completely

satisfactory. Residence times T between 2.4 ps (300°C) and 7 ps (153°C)
REACTOR RADIATION DIVISION PROGRAMS

were derived for Ta? H (compared to previous values between 1.6 (340°C)

and 4.0 ps (148°C) for TaH

n

- j.) . These results indicate a significant

concentration dependence of the diffusion rates in a-TaH (contrary to

suggestions from previous NMR results) with activation energies for diffusion

of 10.4 ± 1.2 KJ/mol in TaH and 15 ± 1.2 KJ/mol for Ta^H. In addition

On

"effective" mean square amplitudes of proton vibration of 0.02 to 0.04A

were obtained from the momenturn- transfer ((£) dependence of the quasielastic peak intensities. These are in reasonable agreement with values

predicted from our measured vibration frequencies, but they are from 3 to

9 times lower than values obtained previously for a-VH , which exhibits

vibrational frequency distributions very similar to those for a-TaH but has a much more rapid diffusion rate (t^0.5 to 1 ps) . This comparison

provides additional evidence for our previous suggestion that the apparent

Debye-Waller factors derived from neutron data for these and similar hydrides

are strongly dependent on the rate of hydrogen diffusion. Our results

have been compared in detail with other results on hydrogen-isotope

diffusion in refractory metals.

During the past year we have also loaded a large single crystal of

tantalum to a concentration of TaH_ __ , as a continuation of our program

to study the diffusion process and effects of interstitial hydrogen

isotopes on intermetallic bonding in the bcc refractory metals. The

study of single crystal samples should enable us to obtain more detailed

information on the hydrogen diffusion mechanism in these metals by

allowing measurements in different crystal orientations (rather than

measurements averaged over crystallite orientation) and by thus providing

a more detailed comparison with theoretical models.

We have very recently measured neutron quasielastic scattering

spectra for the TaH

n __ single crystal at seven crystal orientations.

The data is presently being analyzed and will be discussed in the next

annual report

2. Palladium Hydride - J. M. Rowe and J. J. Rush

In collaboration with H. G. Smith of Oak Ridge National Laboratory,

we have measured phonon dispersion curves for a single crystal of PdH_ ~~

2
REACTOR RADIATION DIVISION PROGRAMS

in order to examine the possible effect of interstitial hydrogen on the

electronic structure (Fermi Surface) of the metal. Our results show

that the addition of 3% H to Pd does not significantly alter the lattice

dynamics. In particular, the anomaly in the [110]T branch (thought to

be related to Kohn anomalies) does not change in shape or strength. The

measured dispersion curve for the [110] branch of PdH __ is shown in

Fig. 2.

As part of our effort to study the 3 phase of PdD (apparently

superconducting at PdD _ ) we have, in collaboration with H. E. Flotow

and R. Kleb of ANL, designed constructed and tested a high pressure cell

for loading deuterium to as high a concentration as possible in a large

single crystal of Pd. This rather delicate loading procedure will be

attempted in the near future.
REACTOR RADIATION DIVISION PROGRAMS

cp

ii ^

CM

II II

/ a

o

oo oo o

O 00 00

<sf- ^r sr . o

ro oj — CD

inbX

o

\-

CD

ECCM s~*

cO 3

J 4-1

: o

s 3

• 3 o o

EC -H

(0 4J H 3

M

O

iw

0)3

43O

CO

3

a)oJ

603

s

•H

CO

CO3

co O

co 4*

co

a)

4-1 COCO iH

0) CN CO ^ co

i-J iH 3

3 cr <

co

4-1 3

cu6

•H

}-i cuex

cu

COf

<+4 rH

CO 43 cu 43

4-1 4J

CO 60

co 3

4= -H

4-1 4J

rH C

>H O

3 O

(4-1 CU

CU

XI

CUU

a,

CO

4-1 T3

COo

•H

4-1 CUuo

cu

4-1

cu 43

XI

CU X

CO

CO X)

XJ

X>

cu 43H

O

CO

cu 43H

§

•HN

4J

£3

CUoJ

xj

cu

(3

cu XI

COo

u

43

cu 43H

cu>

•H

4JO

CUpCO

cuu

0) X

O

e

CO

V4 Xf

CU X.

CO

4-1 o

o

XIc

CO

CO

J-i X

CU 43

CO

4-> CU

cu X4->

£3

cu

cu 4J

CU 43

COa.

CO3

O

cu3

CO 4J9

4-1 CO3

•H

43

X) }-i 3 O

CO m

CU

!-< CO

COcuu

3

4-> CO

CUa

B

cu

4-J

CO3

o

•HM

CO>

4J

CO

cu X

o

6

CO

s^ X

cu 43

CO

CU X4-1

4-1 •H

M-I

4-1 CO

CU 43

cu X4-1 6

o

i+-i X

<u>

•HU

CU *3

COCU3

iH

cO>

O

43

CO

2/1 (,.oasd)

6/>y 60

•H
REACTOR RADIATION DIVISION PROGRAMS

—I— • i 1 1 1

TRANSVERSE •

^j> o • • ' • • ~

roO • •

•o • • • • i • •

>%

CU .d

4-> 4=a CO C CO

COu * J3 g

/TMN o

rH X. CD H CO

V-r'

d ai

4-1 o

CO

C

u

cu cu > M

0) CO c

cd £ u 3 u H

13 • en CO cu o H H • rH CO EC CO o

T3

a CO i0 Pu

CU CO 6 CU J2

•H

4-1 Cu 4-1

5-i

u c O o o

«w MH

4-1

C CO rH a** oH

4J rH 3

CO

4-> 3 0) CO CO u H a) CD M <m

S-iO

cu • *• C .d W o H T3 d H

CO Pu

i-i • cu CU C 4=

a. o 4-1 CO •H •H 4-1 6

T3 CJ o

cu s-<

}-i j-j 14-1 O •H

4-1 X) CU O rH

cu i—i ,a > O cO I H ^ cu rH CO CM > i——i H

ex) 3 d 3 cu 4= 3.

CO 4-1 •H > 4-) c CO

5=-. •H •H o "3 C 60 c

cu

G

H 3 H

cr* 4-1 0)

CU CO 43 M 00

<4H CO T3

ex rH

CU o 3

Xi

u

O

H

a & q

in o o

ro

O

cvi (ZH1) *

CN

M)

•H
REACTOR RADIATION DIVISION PROGRAMS

PHASE TRANSITIONS, ORIENTATIONAL DISORDER, AND CRYSTAL DYNAMICS

OF IONIC AND MOLECULAR SOLIDS

Work has continued on detailed investigations of orientational disorder and order-disorder phase transitions in prototype crystals by

neutron scattering techniques and by Raman and infrared spectroscopy.

The precise nature of the rotational disorder in the high temperature

cubic phases of broad classes of inorganic and organic solids is not

generally well understood, nor is the microscopic basis of the changes

in physical and thermodynamic properties associated with these orderdisorder transitions. During the past year higher resolution quasielastic neutron studies and the analysis of an extensive series of Raman

scattering measurements on M XY type crystals (alkali hydrosulfides)

have provided new detailed information on the order-disorder phase transformations in these materials. Experiments on ammonium halide single

crystals and several globular organic molecules have also been initiated.

1. Alkali Hydrosulfides - J. J. Rush, R. C. Livingston and J. M. Rowe

a. Raman Scattering

Our Raman scattering investigation of the alkali hydrosulfides^

NaSH, CsSH and RbSH between 30 and 400°K (in collaboration with G. J.

Rosasco of Division 313) has been completed, including most of the analysis

and interpretation of the spectroscopic data. Examples of the spectra

for NaSH and CsSH are shown in Fig. 1 and 2. These Raman spectra provide

clear evidence (in addition to our neutron diffraction measurements mentioned in last year's Report, NBS 758) for the existence of previously

unobserved low-temperature phases in each compound. In addition the

results show that the order-disorder transitions in these solids are associated with significant changes in the details of their crystal

dynamics.

The spectrum at 358°K in the NaCl phase of NaSH (Fig. 1) shows a single broad peak due to SH stretching vibrations at 2541 cm and a diffuse almost featureless maximum (not shown here) in the region of
REACTOR RADIATION DIVISION PROGRAMS

the SH librations. In passing through the transition to the trigonal,

D~, , phase at ~355°K the stretching peak narrows significantly. The

trigonal-phase spectra (Fig. 1) also exhibit broad bands due to SH librations (~450 cm ) and translational lattice modes (~80 and 160 cm ) in

reasonable agreement with our previous neutron scattering results (see NBS

TN 758) . All translational lattice modes are Raman "inactive" in the D^.,

space group, so that the observed peaks are most likely "density of

states" maxima attributable to the orientational disorder (probably two

fold) in this phase. Finally at ~115°K the character of the spectra in

Fig. 1 changes again. The stretching mode band is sharpened considerably

and shifted to higher frequency. Simultaneously the lattice mode region

shows a dramatic sharpening of the translatory vibration peaks, as well

as a splitting of the libration band. These changes in the NaSH spectra

clearly indicate a new crystal phase, most likely involving total ordering

of the SH ions

.

The measured spectra for CsSH (Fig. 2) and RbSH, which will not be

discussed in detail here, show changes which are analogous to the NaSH

results. These include dramatic spectral changes at low temperatures

which also give clear evidence of low-temperature "ordered" phases for

each of the crystals, with transition temperatures of ~113°K (CsSH) and

~123°K (RbSH) . An interesting feature of our results for all these

crystals is that the low temperature disorder-order transition appears

to occur gradually over a range of temperatures (VL0-20 ) in each case. Further details of our neutron diffraction and optical results will be

presented in a future report.

b. Neutron Scattering

The orientational disorder of the hydrosulfide ions in CsSH (CsCl

phase) and RbSH (NaCl phase) has been investigated by quasielastic neutron

scattering with high energy resolution (AE.. «„ = 0.25 meV) , using

neutron time-of-flight techniques. Examples of the experimental scattering

spectra, S (Q,oo) are shown in Fig. 3, plotted vs. frequency in ps

-1

(1 meV = 1 ps ) . These results have been corrected for multiple scat-
REACTOR RADIATION DIVISION PROGRAMS

scattering contributions. The results in Fig. 3 represent to our knowledge the clearest demonstration yet observed of the theoretically

predicted separation of quasielastic neutron scattering by reorienting

ions or molecules into a broadened (Lorentzian) component whose width is

dependent on the reorientation rate and an unbroadened component whose

intensity vs. momentum transfer, Q, is dependent on the distribution of

orientations in the crystal. Theoretical scattering laws for instantaneous jumps between six [100] directions in a cubic lattice are also shown,

in Fig. 3 for comparison with experimental results. The experimental

scattering laws were fitted by least squares to the sum of a Lorentzian

component and a delta function broadened by the instrumental resolution.

From this fitting procedure the ratio of elastic intensity to total

intensity was derived and the results are shown in Fig. 4 for both CsSH

and RbSH, again compared to the theoretical ratios predicted for the [100]

orientation model.

The results in Fig. 3 and 4 enable us to clearly rule out either a free rotation model for the orientational disorder (which predicts line

broadenings an order of magnitude larger than observed) or a small-step

rotational diffusion model which predicts a monotonic increase in the

width of the broadened component with Q. The model which provides the

only satisfactory fit to the experimental results is a model involving

instantaneous jumps between a finite number of equibrium orientations,

such as the [100], [110] and [111] crystal directions. Unfortunately all

three of these models represent the data reasonably well so that no clear

preference for a particular jump geometry can be established from the

results.

Residence times, T, between SH ion reorientation have been derived

from the theoretical fits to the data, which are about 1 ps for CsSH at

373 °K and about 0.4 ps for RbSH at 414 °K (the values vary somewhat with

jump model) . Mean-square proton vibrational amplitudes were also

2 derived from the variation of elastic intensity with Q . It should be

noted that the T values obtained for RbSH (and NaSH) at temperatures

10-20° above their trigonal-^cubic transition are only about a factor of
REACTOR RADIATION DIVISION PROGRAMS

5 higher than the time for a free-rotational jump between equivalent

orientations (MD.07 ps) . Finally our results clearly suggest that in

most cases measurements on single crystals will be necessary to establish

the details of orientational disorder in solids . As noted below we are extending our measurements to single crystal ammonium halide samples to

pursue further the refinement of neutron quasielastic scattering techniques and theoretical analysis procedures toward the detailed measurement of orientational disorder in solids.

2. Ammonium Bromide and Ammonium Iodide - R. C. Livingston, J. M. Rowe

and J. J. Rush

Single crystals of ammonium bromide and ammonium iodide (up to 1" x

1" x 1/4") suitable for quasielastic neutron scattering experiments have

been grown from an aqueous solution doped with urea by slow evaporation.

Preliminary measurements have been obtained in a neutron quasielastic

scattering study of ion reorientation in the bcc phase of NH.Br has been

initiated. Equipment has been built with which single crystals can be

grown by either slow evaporation or by lowering the temperature of a saturated solution under highly controlled conditions. A project is underway

to grow single crystals of deuterafced ammonium bromide and ammonium

iodide suitable for further neutron inelastic scattering studies.

3. Infrared and Raman Band Shape Analysis of Chloroform and Dicyanoacetylene - R. C. Livingston

As part of a continuing program in the study of molecular plastic

crystals and related compounds, we have measured in collaboration with

W. G. Rothschild of the Scientific Research Staff at Ford Motor Company,

infrared and Raman band shapes for several vibrational modes in the symmetric top molecule chloroform (CHC1

3

and CDC1

3

) , and in the linear molecule dicyano-acetylene (C,N

2

) . The correlation functions obtained by

Fourier transforming the band contours yields information about the reorientation rates around specific molecular axes, which are determined by the

symmetry of the vibration and the molecular symmetry. Raman data in paral-
REACTOR RADIATION DIVISION PROGRAMS

lei and perpendicular geometries allow us to separate the intrinsic

linewidth from the rotational broadening in both Raman and infrared bands,

Although isotopic corrections were applied to the chloroform data, we are

35

now preparing isotopically pure chloroform, (CH Cl_) as a check on our earlier data. The chloroform data will be used to check the M and J

rotational diffusion models for a symmetric top :as proposed by McClung.

10
REACTOR RADIATION DIVISION PROGRAMS

Fig. 1. Smoothed Raman spectra for three crystal phases of NaSH.

Spectra slit widths are indicated by vertical bars.

11
REACTOR RADIATION DIVISION PROGRAMS

2550 2500 2450 500

CM'

400

CM"

300

Fig. 2. Smoothed Raman spectra for three crystal phases of CsSH.

12
REACTOR RADIATION DIVISION PROGRAMS

6 -4- -2 2 4 6

-6-4-20246

2 " (c) CsSH

IT)Q. 1

373K .

1 Q=2.54A

3 1 / \ Q 1 \

CO

n "—^/.

\

RbSH

4I3K

Q = 0.6IA

-6 2

aj(ps')

Fig. 3. Examples of quasielastic scattering spectra for CsSH and RbSH

at several values of wave-vector transfer Q. Also shown (solid,

lines) are theoretical scattering laws calculated for the [100]

jump reorientation model with T = 1.3 ps for CsSH and 0.49 ps

for RbSH.

13
1.0

0.8

0.6-

>-

CO

z

UJ

<

I-o

o

jZ 0.4

CO

<

-J

0.2

REACTOR RADIATION DIVISION PROGRAMS

I

CsSH 373K

RbSH 4I3K

[100] MODEL

.0 2.0

Q (A" 1 )

Fig. 4. The ratio of the intensity of the unbroadened component to the

total intensity of the quasielastic peak as a function of wavevector transfer (Q) , The solid line is the predicted ratio for

an instantaneous jump model assuming the SH ion aligns randomly

in the 6 [100] directions of the cubic structure.

14
REACTOR RADIATION DIVISION PROGRAMS

ANALYSES OF THE DYNAMICS OF KCN, N*CN, AND RELATED CRYSTALS—

DEBYE-WALLER FACTORS

R. C. Casella

Data of J. Rush, M. Rowe, E. Prince and others on both elastic and

inelastic neutron scattering in KCN, NaCN, and related compounds indicates

anomalous behavior of the Debye-Waller factors in elastic scattering as well as the disappearance of the longitudinal acoustic phonons with

increasing energy transfer and complete absence of the optical and

librational branches as revealed by inelastic neutron scattering in the

high temperature phase. These data present a severe problem in theoretical

understanding. The problem is being attacked at two levels. First, based

upon the experimentalists insights provided by Rush, Rowe and Prince,

phenomenological models such as freely rotating CN ions are being constructed. Second, at a fundamental level, an extensive study of the

origin and limits of applicability of the Debye-Waller factor in neutron

scattering, the degree of reliance on the harmonic approximation, etc.

has begun. This work is based upon (and hopefully will clarify and

extend) earlier work of Glauber Van Hove, and others. It is hoped that

the model-building and fundamental approaches will merge at a later stage

and lead to a theoretical understanding of the data. Moreover, potential

application to the continuing group-theoretical program, discussed in a separate paragraph, of the fundamental analyses of the Debye-Waller factor

is foreseen.

15
REACTOR RADIATION DIVISION PROGRAMS

THE DYNAMICS OF SIMPLE LIQUIDS"

J. M. Rowe

In contrast to the lattice dynamics of solids, the dynamics of simple

liquids are at present poorly understood. The main reason for this is, of

course, the lack of long range order in liquids which precludes the use of

simplifying assumptions such as the harmonic approximation and one phonon

approximation. This in turn means that for liquids, it is essential to

measure the shape of the absolute neutron scattering cross-section as a function of wave-vector and energy transfer over the widest possible

range for both variables. This information must then be compared with

models of the liquid state in order to extract information about the

forces acting in the system. Recent results for liquid argon have shown

the power of this technique and our present program is to extend such

measurements to other simple liquids, particularly to liquid metals.

1. Liquid Rubidium

In collaboration with J. R. D. Copley of Argonne National Laboratory,

the coherent scattering function S(Q,a)), which is proportional to the

inelastic neutron scattering cross-section, has been measured at 315°K

?-l over a range of wave-vector transfers from 0.8 - 6.5A . The data have

been corrected for multiple scattering, resolution and others effects,

and the corrected results have been used to construct the first two

frequency moments. These moments are a sensitive test of absolute accuracy,

and are thus very useful in assessing the reliability of the derived

scattering function. The final results comprise the most complete and

accurate representation of a coherent scattering function yet obtained

for a simple liquid metal. Comparison with molecular dynamics calculations

and with models for dense liquids will give detailed information about the

effective ion-ion potential in the liquid metal.

2. Small Wave Vector Excitations

It is well known that at very small wave vectors (large wavelengths)

propagating excitations in the form of sound waves exist for all liquids.

16
REACTOR RADIATION DIVISION PROGRAMS

At large wave-vectors no such excitations have been seen for simple

classical liquids. The transition region between these two regimes is of

fundamental importance to the theory of liquids, but to date it has been

little explored experimentally because of intensity and multiple scattering limitations. Utilizing a new code for calculation of multiple

scattering, an experiment to study this regime in liquid Rb has been set

up in collaboration with J. R. D. Copley of Argonne National Laboratory.

Preliminary results show the existence of well-defined propagating modes

o-l

at wave-vectors extending to 0.8A . Further experiments to clarify an unexplained zero-frequency peak are presently underway. In conjunction

with these experiments, Aneesur Rohman of Argonne National Laboratory has

initiated a molecular dynamics computer study of this same system. The

combined results of these two programs will be used to establish the

physical basis underlying this result for Rb , which contrasts sharply

with liquid argon and liquid sodium.

ELEMENTARY EXCITATIONS IN QUANTUM LIQUIDS

J. M. Rowe

In recent years, the techniques of neutron inelastic scattering have

been used to establish directly the frequency-wave vector dispersion

4 relation of liquid He as a function of temperature and pressure in both

the superfluid and normal phases . These results have led to deeper theoretical understanding of this important quantum fluid. On the other

hand, liquid JHe, which is a Fermi liquid (as opposed to liquid He which

is a Bose liquid) has not been studied by neutron scattering because of

the very large neutron absorption cross-section of this isotope. Consequently, much less is known about the dynamics of this system in the short

3 wavelength regime. Recent measurements have suggested that He becomes a superf luid at very low temperatures (<8 mK) , a result which is certainly

3 4 intimately related to the dynamics of the fluid. Mixtures of He - He

have important applications in low temperature refrigerators , and measure17
REACTOR RADIATION DIVISION PROGRAMS

5 10 15

ENERGY TRANSFER (K)

4 4

Fig. 1. The experimental scattering law data for He(i) and the He

.95

He

n r(0) liquids at three selected angles of scattering for

a temperature of 1.6K. The solid and broken lines represent

fits to the data which will not be discussed here. The value

of wave vector transfer Q shown is determined at the energy

corresponding to the peak.

18
REACTOR RADIATION DIVISION PROGRAMS

ment of the dynamics of these systems has also been hindered by the very

3 high absorption cross-section of He. Recent measurements we describe

3 4 here on a He n

_ - He QC. solution have been used to elucidate the basic

3 4

He - He interaction and represent the first step in a program to mea3 sure the neutron inelastic scattering from He itself.

1.

4

He

t95 -

3

He

>05

In collaboration with D. L. Price and G. E. Ostrowski of Argonne

National Laboratory, measurements of the elementary excitations on a

-

3

He

.95 .05

4 3

He oc. - 'He nc. soluton at 1.6°K have been completed. The measurements

extended over a wave-vector range of 0.8 - 2.5°A , and were compared to

4 similar results on pure He. In this experiment, the ratio of neutron

scattering to absorption was 1:500, and the relatively new measurement

technique of pseudo-statistical chopping for energy analysis was used in

order to increase the statistical accuracy of the results. The data were

analysed to yield the shift in energy and decrease in lifetime of the

4 excitations compared to pure He. The results of this analysis are in

good agreement with recent laser Raman studies of the bound two roton

state in such mixtures. Compared to the Raman studies which yield information about only one portion of the elementary excitation spectrum, the

neutron results provide information over .a wide range of wave-vector

transfers, and so give information inaccessible to other techniques. The

present results, which give direct information on the excitation spectrum,

are in disagreement with earlier conclusions based upon indirect measurements of fourth sound velocities, super fluid fractions and ion mobilities,

This in turn shows that the theories used to extract information about the

excitations from these previous measurements are seriously in error. Examples of the data taken are shown Fig. 1. The present experiments

will be extended to other concentrations and to lower temperature.

2. Liquid 3

He

Planning for measurements on pure He has begun. The essential

requirements are for sample holders having good thermal conductivities at

19
REACTOR RADIATION DIVISION PROGRAMS

low temperatures (<100 mK) and for the cryogenic equipment to achieve

o 4

these temperatures. At present, the He - He dilution refrigerator

required is being designed, and delivery is expected late in 1973. The

sample holder is also being designed and will arrive before the refrigerator. Experiments are expected to begin early in 1974, in collaboration

with D. L. Price, K. Skold and G. E. Ostowski of Argonne National Laboratory.

RIGID BODY THERMAL MOTION IN CRYSTALLOGRAPHIC REFINEMENT

E. Prince

The formulas for constraining thermal parameters in crystallographic

refinement: have been extended to include the S tensor of Schomaker and

Trueblood . The formulas have been incorporated into a least-squares

refinement program and applied to refinement of the heteropoly anion

SiW, „0. (see NBS Technical Note 567) and the ammonium ion in NH.C10.

12 4 4 4

various temperatures (described elsewhere in the report)

.

1 E. Prince and L. W. Finger, Acta Cvyst. B29 , 179 (1973).

2 V. Schomaker and K. N. Trueblood, Acta Cvyst. B24, 63 (1968).

20
REACTOR RADIATION DIVISION PROGRAMS

STUDIES ON TWINNING

A. Santoro

1. Preface

The geometrical conditions required for the formation of twins and

rules governing the mutual orientation of the individual crystals in a twinned edifice have been analyzed as part of a continuing study of the

properties of crystal lattices. Convenient and general procedures for

characterizing twinning have been derived. The twinning condition and

the description of the twin obliquity obtained as a result of this

research, represent significant generalizations of Friedel's classical

theory. :

Some of the results of this work have been applied to the study of

the twinning associated with the metal-insulator transition in Cr-doped

V0_ . This application, described in one of the following sections,

shows that the procedures developed for determining the geometrical

properties of twins are useful for interpreting the complex x-ray and

neutron diffraction patterns produced by twinned samples. We will now

summarize the work done in this area during the past year.

2. Characterization of Twinning

Let us consider two crystals, not necessarily of the same species,

and let us suppose that their lattices are described by the triplets of

primitive, non-coplanar , translations a! and a'.'. The two crystals may

form a regular aggregate if their lattice dimensions and their mutual

orientation are such that they have, exactly or approximately, a superlattice in common. It can be shown that these two conditions are met if

the equation

WijVik " A

iJ

=

° (k '"' 1,3 * 1,2,3) C1)

is satisfied with rational coefficients B... The elements A!, and A'.'. in the above expression are the scalar products

A' = a! • a! , A" = aV • a". ih 1 j xj 1 j

^riedel, G. (1926). L&oons de ovistaliographie . Paris: Berger-Lerrault.

Reprinted (1964), Paris: Blanchard.

21
REACTOR RADIATION DIVISION PROGRAMS

Equation (1) expresses the geometrical conditions necessary for the formation of regular aggregates such as syntaxic and epitaxic growths and

twins. The rational elements B.. define the mutual orientation of the

individuals in the aggregate.

Twins are regular aggregates constituted by individual crystals of

the same species. The twinning condition, therefore, is expressed by

equation (1) in which it is A' = A". It is possible to show that equation

(1) is more general than Friedel's conditions of twinning. The use of

this equation permits one to predict not only the possible twin laws

associated with a crystalline material, but also the well known regular

associations of crystals mutually oriented according to non-crystallographic

rotations. Equation (1) also permits one to give a very general description of the "twin obliquity".

Work on this subject has been completed and a paper has been submitted for publication in Acta Crystallographica.

3. Twinning in Cr-Doped V0- - M. Marezio and P. D. Dernier (Bell Laboratories) and A. Santoro

Cr-doped V0_ undergoes a metal-insulator transition in which the

high-temperature phase, with a rutile-type structure, is slightly

distorted into a monoclinic structure. As the distortion results in a final phase having symmetry lower than that of the initial phase, the

transition is usually associated with twin formation.

Table I shows the crystal data relative to the samples of Cr-doped

V0

9 analyzed in the present study. In Table II are shown the twin laws

predicted by the theory. Each of the samples studied was twinned on more than one law and, with the exception of [010] qf. o , all the predicted

twin laws were observed at least once. The appearance of the diffraction patterns depends on the particular

twin laws operating in each sample. Thus, the laws (100) and (001) can be easily detected as they produce doubling of the diffraction spots.

The laws (201) and (20l) , however, are characterized by a small value

of the obliquity and individuals twinned with these laws give reflections

almost exactly superposed. In fact, a spot with film coordinates h,k,£

22
REACTOR RADIATION DIVISION PROGRAMS

is formed by the superposition of three reflections, one from each

Individual of the twin, having indices

(hU)

T

, (2£ k h/2)

XI , (2£ k h/2) ni .

It follows that spots with h and k both odd are produced only by individual I, while spots with k odd and inconsistent with the lattice parameters

are produced only by individuals II and III. This observation on the

geometrical characteristics of the diffraction patterns makes it possible

to determine the volume of the sample belonging to each individual and to

obtain the structure from the intensities measured from twinned samples.

The structure of Vn __-Cr_ no/ 0„ was in fact determined, and refined to 0.976 0.024 2 an R factor of 2.9%, once the twinning problem was solved.

It is possible to show that , if twinning takes place with the laws

(201) and (201) , the diffraction patterns simulate a lattice having a cell related to the true one by the axes transformation 102/010/002 and

a space group Cc or C2/c. This is another case in which twinning, if

not detected, can lead to erroneous parameters and space groups.

Work on this subject has been completed and a paper is in press in

Acta Crystallographica.

4. Possible Applications

Other possible applications of the results of our study on twinning

are the following:

(i) As the method proposed for deriving the possible twin laws

associated with a crystalline material can be easily adapted to automatic

computations, it is feasible to systematically check whether the known

twins abide by the rules of Friedel without exceptions and to clarify,

where the structure is known, the relationship between the geometrical

and the structural theories of twinning. Such extensive critical

evaluation of published crystal data would result in a more complete and

reliable characterization of crystalline materials.

2M. Marezio, B." B. fycWhan, J. P. Remeika and P. D. Dernier., Phys. Pev.

B5j; 2541-2551 (1972).

23
REACTOR RADIATION DIVISION PROGRAMS

Work in this area, in collaboration with A. D. Mighell (Inorganic

Materials Division, IMR) , is contemplated.

(ii) Epitaxial relationships amoung the crystalline species con- stituting urinary and biliary calculi have been suggested, but are far

from being exhaustively investigated. 3 ,lf Since the necessary geometrical

conditions for the formation of epitaxic and syntaxic growths can be

found with relative ease by using the results of the present work, it

becomes possible to carry out an extensive study of the geometrical"

and structural properties of the calculi's components.

Experimental and theoretical work in this area, in collaboration with

Dr. A. D. Mighell (Inorganic Materials Division, IMR) is planned.

TABLE I

Crystal data for Cr-doped V0„ at room temperature

V0

2

+0.5 at,,%Cr V0

2

+2.5 at.%Cr

a 9.081(1)

oA 9.0664(7)1

b 5.7*81(1) 5.7970(5)

c 4.516(1) 4.5255(4)

8 90.91°(1) 91.88°(1)

Space group 0,2 lm C2/m

24
REACTOR RADIATION DIVISION PROGRAMS

TABLE II

Possible twin laws for Cr-doped V0- . Twin axes and planes are referred to the monoclinic cells whose parameters are given in

Table I.

yO

2

+0.5 at.%Cr V0

2

+a.5 at.%Cr

[010] 90 o 2

(201) E[102] 180 o 2 0.3° 0.1°

(201)E[102] 18()O 2 0<3 Qil o (100)=[001] 180 o i o.9' 1.88

(001)=[100] 180 o 1 0.9° 1.88

o

3 K. Lonsdale, Nature 217 , 56-58 (1968).

K. Lonsdale, and D. J. Sutor, Soviet Physics-Crystallography (Transl.),

16, 1060-1068 (1972).

THERMAL NEUTRON FLUX MEASUREMENTS

V. W. Myers and M. Ganoczy

A manganese sulfate bath has been used at a beamport for determining

the absolute thermal neutron intensity of the beam. Boron loaded cobalt

glass beads were activated in the known thermal flux. The beads were

then used for calibrating a Nal well detector. The data from this experiment is being analyzed. An unknown thermal flux could be measured by

activating a cobalt glass bead in the flux and then counting it in the

calibrated well detector.

25
REACTOR RADIATION DIVISION PROGRAMS

INTERCOMPARISON OF NEUTRON DIFFRACTOMETERS

V. W. Myers

Collaboration is continuing in a program of the International Union

of Crystallography for the comparison of neutron flux at various neutron

spectrometers. Gold foils are activated in the diffracted beam. Foils

were counted at NBS for irradiation at the Oak Ridge HFIR. In addition,

foils will be irradiated at NBSR, Georgia Technical Research Reactor, and

possibly other facilities and counted at NBS. This study should be

completed by June 1974.

DIRECT TESTS FOR VIOLATION OF CP INVARIANCE

R. C. Casella

In 1968-69 it was first demonstrated independently of the CPT

theorem that time reversal symmetry (T) is violated in the CP-violating

pionic decays of the neutral kaon. 1 (Previously the result had been

deduced from the CPT theorem coupled with the data of Fitch, Cronin, and

collaborators.) This more general demonstration of T violation was subsequently verified by Kabir, Steinberger, and others. Because of the

importance of the violation in Nature of the fundamental CP and T

_3

(VLO ) effect, it is essential to base the conclusions on as few theoretical assumptions as possible. One assumption which, in one form or another, has entered into the deductions of symmetry breaking by Christenson

et a_l . , Lee, Oehme, and Yang, Wu and Yang, Casella, Kabir, and others is the

well-known Weisskopf-Wigner approximation for decaying states. Recently,

in collaboration with B. Robertson, we have devised tests, one of which,

when applied to preliminary data of Steinberger and collaborators at CERN,

indicates that the CP violation can be established independently of the

validity of the Weisskopf-Wigner approximation. Experiments of Banner

26
REACTOR RADIATION DIVISION PROGRAMS

et_ al_. independently corroborate this conclusion. A paper reporting on

our work will appear. The fundamental origin of the CP and T violations

remains an intriguing mystery.

*R. C. Casella, Phys. Rev. Lett. 21, 1128 (1968); 22, 554 (1969)

COLD-NEUTRON TIME-OF-FLIGHT FACILITY

R. S. Carter, A. A. Cinquepalma, D. H. Fravel,

and J. B. Sturrock

The cold neutron time-of-flight facility is designed for inelastic

neutron scattering studies of solids and liquids. A neutron beam from

the reactor is filtered through polycrystalline beryllium to eliminate

o neutrons with wavelengths shorter than 3.92A. The beam then passes

through a four rotor phased chopper system which chops the beam into

short bursts of neutrons of selected energy. The sample to be studied is

placed immediately after the choppers and the scattered neutrons are detected in a large bank of detectors arranged along the arc of a circle

with a 2.4 meter radius. The detectors are located in a shielding room. The detector information is fed into a multi-channel analyzer and the

neutron energy determined from the flight time of the neutrons from the

sample to the detectors.

The facility has been completed and a study of the background counting

rates was initiated. The results to date showed that many of the detectors

appeared to have an unusually large sensitivity to Y~rays resulting in

excessive back ground counting rates. This problem is undergoing further

study. The shielding from sources other than the facility beam itself

appears to be adequate (^2 c/m per detector) for those detectors which do

not have an abnormal gamma-ray sensitivity. The beam from the facility

itself, however, introduced a neutron background of as much as 15 counts

per minute per detector for those detectors nearest the beam. The

addition of 6" of Be in the beam was necessary to reduce the fast neutron

background from the beam to managable proportions (^2-3 counts per min27
REACTOR RADIATION DIVISION PROGRAMS

ute per detector from fast neutron scattering and ^2 counts per minute

room background) . Methods to minimize the scattering of thermal neutrons

are being investigated.

COLD-NEUTRON SOURCE

R. S. Carter, E. M. Guglielmo, and F. J. Shorten

The NBS reactor includes a special port, 22" in diameter, which

penetrates the reflector up to the edge of the fuel elements. This large

opening was designed to provide space for the insertion of a cold neutron

source close to the core. By inserting a large, low temperature moderator

it is possible to significantly increase the available intensity of very

o low energy neutrons (A>4A) which are very useful for many types of

molecular dynamic studies.

The moderator will be a cylinder of D„0 ice 14" in diameter by 12"

long. A small amount of ELO may be added to optimize the moderating

property of the source. The source will have a reentrant hole 4" deep by

8" in diameter for beam extraction. The hole will be filled with beryllium which has the property of reflecting the higher energy neutrons back

into the moderator while passing the lower energy neutrons . The moderator

will be maintained at 25 K by cold helium gas passing through tubing in

the moderator. The vacuum cryostat containing the moderator will be

constructed of thin-walled aluminum to minimize heating by capture gamma

rays. The cryostat will be mounted on a shielding plug and the whole

assembly will roll inside a second plug and shield assembly which itself

will roll into the special port of the NBSR. The shield mounted on the

second plug surrounds the cryostat and consists of about 4" of lead and

bismuth which greatly reduces the gamma ray heating of the moderator.

Two 6" and two 2" diameter beams can be extracted from the cold source through the reactor shield. One of the 6" beams will be used for the

cold neutron time-of-flight facility while the others await future

development

.

28
REACTOR RADIATION DIVISION PROGRAMS

The helium for cooling is provided by an all helium refrigerator

using a turbine expansion engine developed by the NBS cryogenic laboratory

in Boulder. It has a one kilowatt capacity at 25 K which is sufficient

to handle the heat generated in the moderator at twice the current reactor

power

.

The bismuth tip and cryostat are the only items which remain to be

installed. The cryostat has undergone extensive testing during the past

year and meets all necessary requirements. The bismuth tip which had to

be completely refabricated is still not completed. Many of the components

have been made but final assembly and the pouring of the bismuth and lead

have yet to be done.

29
B, RRD-NBS Collaborative Programs

INELASTIC NEUTRON SCATTERING OF a NEON NEAR THE CRITICAL TEMPERATURE

B. Mozer

(Inorganic Materials Division)

Inelastic neutron scattering experiments on neon within 10 milliKelvin of the critical temperature have been carried out using the high

resolution Fermi chopper time-of-flight system. Small angle scattering

o data was obtained for a number of angles from 3.5 to 12.5° using 2.8A

o neutrons and 1.4A neutrons from the second order transmitted by a filter.

The angular range covers a kappa region for elastic and quasi-elastic

o-l

scattering of 0.144 to 0.490 A for the first order beam and double that

for the A/2 beam. The scattering from each wavelength is distinct and

allows additional information to be collected during the experiment. The

kappa values used overlap the intense scattering associated with critical

phenomena as observed in the diffraction experiments. The wavelength and

energy resolution of the system for the first order neutrons are 1.95%

and 3.90% respectively. The latter corresponds to an energy resolution

of about 0.4 meV. Incoming beam energy resolution is about 0.25 meV.

Energy resolution would be almost doubled for A/2 detected neutrons.

Preliminary data analysis shows some quasielastic broadening for the

smaller angles. This small broadening does not seem capable of being

resolved into two components associated with Brillouin scattering from a liquid at the critical point. At a larger angle, the line shape changes

into a spectrum of two barely resolvable peaks. This splitting of the

spectrum could be interpreted as a splitting associated with a propagating

phonon mode in the liquid. At larger angles the spectra is considerably

broadened and the signal almost lost. Analysis of the scattering from the

A/2 neutrons has just begun and can be used for checking the consistency

of the interpretation of the scattering from the first order neutron within the decreased energy resolution. Scattering of the higher energy

neutrons by neon is observed to produce a well defined signal showing

broadening at the larger momentum transfers.

30
RKD-NBS COLLABORATIVE PROGRAMS

AN OBSERVATION OF THE DEVIATION FROM ORNSTEIN-ZERNIKE THEORY

IN THE CRITICAL SCATTERING OF NEUTRONS FROM NEON

V. P. Warktflwiz and M. S. Green

(Temple University, Philadelphia, Pa.)

and

B. Mozer

(Inorganic Materials Division)

One-component fluids near their critical point have long been known

to display a striking phenomenon called critical opalescence in which

incident radiation is strongly scattered. L. S. Ornstein and F. Zernike 1

in 1914 proposed a theory to describe the scattering of radiation by a fluid near its critical point. They obtained the following result which

is good for small values of the momentum transfer Q:

KQ) « [Q

2

+ a/O 2 ]'1

; where

Q = (4ir/X)sin 6/2; A is the wavelength of the incident radiation; is

the scattering angle;

I(Q) is the intensity of the scattered radiation;

£ is the range of density fluctuation correlations in the fluid.

Ornstein-Zernike theory has long been accepted as providing a reasonably good explanation of critical opalescence. It has also been

extended to describe critical scattering in two-component and magnetic

systems with a fair degree of success. However, certain theoretical and

experimental results suggested that Ornstein-Zernike theory might not be

exact and led M. E. Fisher 2 to propose the following modification of the

Ornstein-Zernike formula

KQ) - [Q

2 -Kl/9 2

r

1+rl/2

. The critical exponent T\ is a measure of the deviation from OrnsteinZernike theory. Other forms for I(Q) have also been proposed, 3 but for

(Q?) large and r\ small they all reduce to I(Q) a (Q ) . We have performed an experiment which was designed specifically to

look for a departure from Ornstein-Zernike theory in the critical

2 scattering of neutrons from neon in the region (Q large. This was

31
RRD-NBS COLLABORATIVE PROGRAMS

done on a diffractometer set up at the thermal column where a thermal

neutron beam with a high cadmium ratio and sufficient intensity was

provided. In order to obtain sufficiently small values of Q without

going to very small scattering angles, it was necessary to produce an incident beam with wavelengths in the range 4 to 9 angstroms. This was

accomplished by using a monochromator composed of a liquid nitrogen

cooled beryllium filter followed by a mechanical velocity selector. The

monochromator produced a spectrum with wavelengths between 4 and 7 angstroms peaked at 5 angstroms. Such a broad spectrum could be used

because neither the width of the spectrum nor its shape was required in

the analysis of the data. The diffractometer was controlled by the NBS

reactor time-shared diffractometer control system. Data was taken over

the angular range -3° to 10° with a statistical precision of about 0.5%.

The critical point was determined from our own measurements of the

coexistence curve of neon using a sample cell with a built-in capacitor.

A preliminary analysis of the data indicated the critical exponent

r| to be greater than 0.10 and less than 0.18.

*L. S. Ornstein and F. Zernike, Proa. Roy. Aaad. Sal. Amsterdam 17, 793

(1914)

2M. E. Fisher, J. Math. Phys. 5_, 944 (1964).

3 H. L. Swinney and B. E. A. Saleh, Phys. Rev. A7, 747 (1973).

32
RRD-NBS COLLABORATIVE PROGRAMS

THE STRUCTURE FACTOR OF NEON NEAR T

Q

B. Mozer

(Inorganic Materials Division)

and

V. W. Warkulwiz

(Temple University, Philadelphia, Pa.)

The structure factor of neon near the critical temperature, T , has

been determined from neutron diffraction experiments. One experiment

was performed on neon at a thermodynamic state within 8 to 10 multiKelvin of Tc. The measurements were divided into three parts. The

first measurement consisted of a scattering experiment for small momentum

transfers, k = 4tt sin0/X, which were performed at the thermal column as described by Warkulwiz, Green and Mozer. The next two parts of the measurements were performed at the BT-2 spectrometer where a 2.4A beam of

neutrons was used to provide data for a momentum transfer region of 0.2

to 3.5A which overlapped with the small angle, small k data. The last

part of the experiment was performed with a 1A beam of neutrons to

o-l

obtain the structure factor from 2.5 to 9A and to provide overlap with

o the 2.4A data. The second experiment was performed on Neon about 2.0

Kelvin above Tc.

The scattering data for the two thermodynamic points are essentially

identical except in the forward direction where the critical scattering

is pronounced. Structure is observed for momentum transfers as large as

o-l

9A associated with the hard core of the interatomic potential. The

overall structure except in the forward direction, is similar to that of

liquid neon reported by de Graaf and Mozer 1 in the liquid state. Further

data analysis is in progress.

l L. A. de Graaf and B. Mozer, J. Chem. Phys. 55_, 4967 (1971).

33
RRD-NBS COLLABORATIVE PROGRAMS

STUDY OF HINDERED ROTATION IN HYDROXYLAMMONIUM

PERCHLORATE BY CONSTRAINED LEAST-SQUARES REFINEMENT

E. Prince and J. Rush

and

B . Dickens

(Polymers Division)

Hydroxylammonium perchlorate, NH^OHCIO, , (referred to hereafter as HAP) crystallizes in the orthorhombic space group P2.cn, with- cell dimensions a=7.52A, b=7.14A, c - 15.99A. There are two crystallographically

independent formula units in the unit cell, which contains a total of

eight formula units.

Several years ago a preliminary set of neutron diffraction data was

collected from a crystal of HAP because neutron cross-section measurements

gave an indication of large amplitude thermal motions of hydrogen atoms in

this compound. Consideration of the crystal structure of this compound

made it seem likely that this large amplitude motion was a torsional

oscillation, or hindered rotation, of the NH_ end of the NH-OH ion about

the NO bond. At the time of the preliminary experiment no attempt was made to refine the structure because the available programs for leastsquares refinement could treat curvilinear thermal motion only by introducing a much larger number of parameters than could possibly have physical significance. Because the techniques developed to treat the motions

of the methyl groups in durene ' 2 seemed to be applicable to this problem

a new, more extensive data set was collected. For least-squares refinement a model was constructed in which conventional, anisotropic temperature

factors were assigned to the atoms in the perchlorate groups and to the OH

hydrogen atoms, but the ONH- portions of the hydroxylammonium ions were

treated as rigid bodies. Isotropic translation and libration parameters

were assigned to the groups and in addition the hydrogen atoms bound to

the nitrogen were considered to be in torsional oscillation about the

NO bond. Preliminary refinement with anisotropic temperature factors for

the atoms of the perchlorate groups and the hydroxyl hydrogen atoms but

34
RKD-NBS COLLABORATIVE PROGRAMS

with isotropic temperature factors for the ONH groups give a weighted R

index of .081. The special model, which actually has fewer adjustable

parameters, refined to a weighted R .051, a highly significant improvement

Figure 1 is a stereoscopic pair showing one half of the unit cell. The

apparent r.m.s. amplitude of torsional oscillation of the NH_ groups is

about 26°, which would correspond to a peak displacement for a harmonic

oscillator of 37° from the equilibrium position. Because the potential

maximum would correspond to a displacement of 60°, this is consistent

with frequent reorientation or hindered rotation.

Fig. 1. The crystal structure of NH OHC10, . Half the unit cell is shown

viewed along a_. The thin lines indicate hydrogen bonds.

X E. Prince and L. W. Finger, Acta Cryst. B29 , 179 (1973).

2 E. Prince, L. W. Schroeder, and J. J. Rush, Acta Cryst. B29 , 184 (1973).

A BIFURCATED HYDROGEN BOND IN Ca(H2 P04 )H2 L. W. Schroeder

(Polymers Division)

and

E. Prince

On the basis of a redetermination of the structure of Ca(H_P0,)H

9 from x-ray data, Dickens and Bowen (1971) proposed a bifurcated hydrogen

bond involving the water molecule. A study of the infrared spectrum of

35
RRD-NBS COLLABORATIVE PROGRAMS

this material by Berry (1968) led to the suggestion that the protons may

be distributed over several sites.

A set of neutron diffraction data, 1228 reflections observed within

the limiting sphere of 100 deg. ii. 26 angle, was collected on a fairly

large crystal of dimensions 3 mm x 5 mm x .37 mm. All the hydrogen atoms

were located from a Fourier synthesis calculated with signs based on

the previous structural model. Refinements including isotropic extinction

led to an R index of .06 and a weighted R of .09. A comparison of Fo and

-12

Fc showed that many reflections with Fc < 1.0 (x 10 cm) had Fo values

as much as 5 times greater than Fc. These reflections (about 60) were

suspected of suffering effects of simultaneous diffraction and were

eliminated from subsequent refinements which led to R and weighted R

indexes of .055 and .068. Positional parameters did not change significantly, but some thermal parameters changed by 3-4 times their standard

deviations.

The differences between our model and the previous one based on x-ray data are insignificant in terms of bond distances and angles between all atoms except hyc^ogen. No evidence of disordered protons in the

structure was found and the previously proposed bifurcated hydrogen bond

was located. Our results imply that the extra features of the infrared

spectrum observed by Berry result from coupling of various proton motions

rather than crystal disorder.

B. Dickens and J. S. Bowen, Acta Cryst. B27 , 2247 (1971).

E. E. Berry, Spectrochimica Acta 24A, 1727 (1968).

36
RRD-NBS COLLABORATIVE PROGRAMS

THE CRYSTAL STRUCTURE OF H3P04 -i/2H2

B. Dickens, L. W. Schroeder

(Polymers Division)

and

E. Prince

Although the coarse details of the crystal structure of H_P0, '1/2FL0 were known from an earlier x-ray investigation using photographic data,

there was ambiguity in the suggested hydrogen bonding scheme. The

structure was therefore refined using neutron diffraction data.

H_P0, *1/2H,.0 is very hygroscopic and melts at 29.3°C. After several

failures to glue a crystal onto a rod in a nitrogen atmosphere, a suitable crystal was grown by successive remelting of several smaller crystals

in a quartz tube sealed by epoxy cement. Because of the method of crystal

growth, the crystal adhered poorly to the tube well and had to be re- oriented frequently under computer control. However, secondary extinction

exerted much less effect on the data then is normal for solution grown

crystals, and extinction corrections, normally a problem in neutron

diffraction, presented no difficulty. The hydrogen atoms were found and

the structure refined with anisotropic temperature factors to

R = [Zo)(|F |-|f I ) 2

I Za3 1 F I 2

] = 0.022 using 1208 observed reflections,

w LV| o''c ll 'o l The structure is shown in figure 1. Both crystallographically

discrete H_P0, molecules have similar environments, being extensively

hydrogen bonded to each other and the water molecule. The water molecule

forms hydrogen bonds of normal strength to the H-PO molecules. These

hydrogen bonds are appreciably non-linear because of repulsion between

the water hydrogens and the hydrogens accepted by the water oxygen in

hydrogen bonds for the H_P0 molecules. Four close H...H distances, in

the range 2.161(3) to 2. 290 (3) A, imply H...H van der Waals interactions,

similar to the case in Ca(OH)..

37
RRD-NBS COLLABORATIVE PROGRAMS

Fig. 1. Stereographic illustration of the crystal structure of H^Po,«

1/2H

? 0. The water molecule oxygen and the P of one of the two

crystallographically discrete H_PO, molecules are both shaded.

THE CRYSTAL STRUCTURE OF LEAD DEUTERIUM ORTHOPHOSPHATE

C. S. Brickenkamp

(Inorganic Materials Division)

and

E. Prince

Except for the hydrogen atom position, the x-ray crystal structure

of PbHPO, essentially has the space-group symmetry P2/c. Consideration

of the most probably hydrogen position, however, favored the noncentrosymmetric space group Pc, subgroup of P2/c, and this was confirmed by

subsequent piezoelectric and pyroelectric measurements.

The neutron diffraction study of the deuterium-substituted lead

phosphate, PbDPO, was undertaken: (1) to obtain more accurate values for

all atomic positions (the crystal used for x-ray data was later found to

be a split crystal) ; (2) to determine the position of the deuterium atom

in order to explain the direction of the polar axis found in the pyroelectric tests and to contribute to our ultimate goal of discovering the

mechanism involved in the thermal decomposition of PbHPO, to Pb„P

? 0_; and

(3) to attempt to resolve, if necessary, any full-matrix-least-squares

refinement difficulties due to the close proximity of the deuterium

38
RRD-NBS COLLABORATIVE PROGRAMS

position or positions to the pseudo-center of symmetry. Table I gives

crystal data and atomic positions for PbHPO, as determined with x-rays

and for PbDPO, as far as refinement has proceeded with the neutron

diffraction study.

Table 1. Crystal data and atomic parameters for PbHPO, and PbDPO,

.

PbHP0

4

a= 4.688(4)A

b = 6.649(5)1

c = 5.781(5)1

3 = 97.11(2)°

space group: Pc

z = 2

D =5.661 g/cm3

m

3

D" - 5.631 g/cm

X = .7107 (MoK ) 525 unique reflections

R = 0.11

PbDPO

a = 4.6855(5)A

b = 6.6911(7)1

c = 5.7867(8)1

3 = 97.10(1)°

space group : Pc

z = 2

X = 1.232

361 unique reflections

R = .10 (2nd cycle)

39
RRD-NBS COLLABORATIVE PROGRAMS

m m

• CO m o 1—1 CM o o

•~N cn o o o o O? • • • • M o o o o

CO 1 CM

CO. CM+ wncom

<=>? CO co in oo o

4-1 rH O O rH o

CO cn o o o o

rH • « • • CQ o o o o

Csl + vO VO

4*5 v»^ V—

4= CM O 00

CM •-* o o

rH cn c

cn • • • •

Csl o o o1 o1 +

1 1

CM •—

\

/—s S~\ o? O IT) /->\ O •-* CO s^ >—' <r i-h m

CO CM CO 00 ^^ N—' *—

ca Ph CO CM rH CM pH +

a. cn H N vj O

O O O CM

CM 3 • • • • 4»S o o o o o •—

\

CM n O

CM 00 •~\ Pm ca <f *TMN '"S, <^N

CU v-" CM si" vO PJ + • CJ CM ID v_y \s v—' •H

CO CO CM i—) <T> CJx Q\

CM ti p- cn HOHN t3

4=" o CO o o o o CU iH •H • • • • C

rH U ti o o o o •H ca cO •H 14-1 v_/ •H CU

1 > T3 ^~\ ^-^ U

<—

i

cu CU 00 y~^ O /-s v-x ^

id ti ^<fHC0

•H CO x—'

v—' v—

<f

Q) T3 M-l f-H CO CM CO O O

H CU •—I rH rH CO CO Pm

CO >-i cn c « • • t3 v • • • • 43

CO a o o o o Ph

•H CO u O

T3 CO Ph s~\ ^\

CU ffl vo sr

CO •a 43 v-x s.t 3 CU

4-» Ph O rH m m is is C CO N CM CM O CO O 6 • • • • •H •H o o o o

CO P 1 I CO CO

CU CU

!-i ^~\ a> CU •-s<r x u N H(-n/-n

CU CO >«• s—' < <f n CO >> CT o •H ffi O CO is

p CO rH CM CO O

u cu • • • • CO 43 o o o o

<4-l 4J 1

CU CU u }-l •~N X-\ 3 c0 vo m

4-> CU >»• v_x

cO vo O

u c K IS VO

CU •H o m co cm a • • • • e CO o o o o

cu }-i 4J CU 43 •—\ s~\ cu 6 rH CM e

3 r> n—' v^

53 Ph Pm O O

CM CM CM CM sf CM CO

CO IS CM St VO CM o O O O O iH O CM o o o o o o o

I I v CM CM CM rs CO CO

CO V—' V»' >—f S»«/ v_/ N.X o iH co a> m cs co O O O O CM O r-{

• o o o o o o

o

I I i

CM CO CM co m CO <j- >-• N—/ W S.^ V-/ N^ >W

CO <7\ CT> CM CO CM O O O O O iH O iH o o o o o o o

r ' r r r i*

CM CM iH CM is CO sf

S_/ V„^ \_/ V_^ V_/ N^ W

cm iH o m rs m rs

CM iH O O in rH CO o o o o o o o

iH CM CM CO <}- CM Sf

V»^ >—' V—' V—' S—' SX V/

00 00 «4J is is so <J- O O O rH iH O CM O O O O O O O

cm «* cn < /-\ vo <*

n_^ v^ v v.^ r-1 v_^ s_x co o cm m ^^ vo in CM N H H «* CM on o o o o o o o

CM CM CM s" CM CO

00 s-' ^"^ N-' s-' v >-• C\ vO <f vO O 00 CM <f CO is ts vo is 00

CM CM O CO O CO St r i*

VO ^N ^S ^N ^N >^S /-S ^ iH iH CM CO CM CO On is \0 CM CM O CM

tT> O CO is <f 00 CM

rH CM CO O CO O m

o- cn co <f co <r

<J\ s^ v-x sx s-/ n-' v-x CM is in O is rH <f O <T\ 00 VO vO in CTi O s- CO CM CO CM s"

I* I*

rH CM CO <f rH

r> v_x s_^ \«^ v v-^ Pm Ph O O O O O

40
KRD-NBS COLLABORATIVE PROGRAMS

NEUTRON DIFFRACTION STRUCTURE DETERMINATION OF

DICHLOROTETRAPYRAZOLECOPPER(II), Cu(c3M4N2 )4CI 2

A. Mighell and C. Reimann

(Inorganic Materials Division)

and

A. Santoro and E. Prince

As part of a study of compounds with complex cations, tne structure

of dichlorotetrapyrazole(II) , Cu(C„H,N„) ,C1» has been determined using

neutron diffraction. The purpose of this neutron investigation was to

obtain accurate hydrogen parameters, to verify that internal hydrogen

bonding occurs, to distinguish the ring carbon and nitrogen atoms,

and to compare the geometry of the Cu(CLH,lO , CI- with that of

Ni(C

3

H

4

N

2

) 4

Cl

2

1 and NiCC^N^Br^ 2

Dichlorotetrapyrazolecopper(II) crystallizes in the monoclinic space

group C2/c with Z=4 and lattice parameters a=13.657, b=9.20, c=14.90A and

6=118.045°. Single crystal neutron intensities were collected and the

structure was refined by full matrix least squares to an R value of 4.5%.

Considerable difficulty was encountered in the refinement because of

extinction in many of the intense reflections. For this reason, further

refinement to correct for extinction is planned.

The complex is centrosymmetric with the copper atom located at a center of symmetry. All other atoms are in general positions. There are

two pyrazole ligands and one chlorine atom in the structure that are crystallographically independent. The figure shows the Cu(Pz),Cl_ complex.

A comparison of the bond distances of this structure with those of the

related Ni(Pz),Cl

? complex are given in the Table. The bond distances

in Cu(Pz),Cl„, compared to the related nickel complex are similar in the

pyrazole ligands but differ significantly in the coordination distances.

The Cu-Cl distance is 2.84A compared to the Ni-Cl distance of 2.51A.

Likewise the average Cu-N coordination distance is 2.02A compared to

2.09A in the nickel complex

This neutron study makes it possible to distinguish unambiguously

41
RRD-NBS COLLABORATIVE PROGRAMS

Table 1. Comparison of bond distances in Cu(Pz),Cl- and Ni(Pz),Cl 9

,

Bond Cu(Pz),Cl * Ni(Pz).Cl **

4 2 Me-Cl 2.840(2) 2.507(1)

Me-N(l) 2.0]5(1) 2.097(2)

Me-N(3) 2.010(2) 2.087(2)

Ring 1

N(l)-N(2) 1.346(3) 1.345(4)

N(2)-C(l) 1.347(3) 1.357(4)

C(l)-C(2) 1.391(5) 1.371(7)

C(2)-C(3) 1.399(3) 1.393(5)

C(3)-N(l) 1.332(3) 1.329(4)

C(l)-H(l) 1.069(7)

C(2)-H(2) 1.065(7)

C(3)-H(3) 1.072(8)

N(2)-H(7) 1.006(8)

Ring 2

N(3)-N(4) 1.337(4) 1.342(6)

N(4)-C(4) 1.337(4) 1.333(6)

C(4)-C(5) 1.373(5) 1.356(6)

C(5)-C(6) 1.396(5) 1.389(6)

C(6)-N(3) 1.320(3) 1.321(4)

C(4)-H(4) 1.088(7)

C(5)-H(5) 1.092(7)

C(6)-H(6) 1.084(11)

N(4)-H(8) 1.024(7)

*Neutron diffraction data

**X-ray diffraction data

42
RRD-NBS COLLABORATIVE PROGRAMS

the ring carbon and nitrogen atoms and thus establish that the ring is

coordinated to the transition metal via the nitrogen atom. Also it is

possible to accurately determine the hydrogen atom positions. In the

two independent pyrazole rings there are 6(C-H) distances and 2 (N-H)

distances. The average N-H distance of 1.03A is significantly shorter

than the average C-H distance of 1.08A. In the complex, CoCC-H.tO,. (N0o )_

,

J 4 Z o 5 2. also studied by neutron diffraction a similar difference in N-H and C-H

bond lengths is observed.

The accurate location of the hydrogen atoms established that there

is internal hydrogen bonding in the complex. These bonds are presumed

to be responsible for the fact that the planes of the pyrazole rings are vertical to the plane defined by the coordinating pyrazole nitrogen atoms

N(l) N(l f ) N(3) N(3'). The N-H... CI hydrogen bonds are stronger than

the C-H... CI bonds because the hydrogen atoms attached to the nitrogen

atoms N(2) and N(4) are closer to the chlorine atoms than the hydrogen

atoms attached to C(3) and C(6). The distances for these four possible

internal hydrogen bonds are: in ring one, N(2)-H(7) . . ,C1 is 2.40Aand

C(3)-H(3)...C1 is 2.66A. In ring two, N(4)-H(8) . . .CI is 2.28A and

C(6)-H(6) . . .CI is 2.73A. As the N-H... CI bonds are stronger than the

C-H... CI bonds, the rings are tipped slightly toward the chlorine atoms as shown by the following angles

:

.N(2) Cu

For ring 1, N(ir = 125° and N(l) = 128°;

x Cu X C(3)

.N(4) Cu

for ring 2, N(3) = 122° and N(3) = 132°.

X Cu X C(6)

Both the ring tipping and the shorter hydrogen bond distance involving

H(8) , show that ring 2 is more strongly hydrogen bonded than ring 1.

43
RRD-NBS COLLABORATIVE PROGRAMS

Fig. 1. Stereo view of the Cu(Pyrazole) ,C1_ complex. The copper atom

is located at a center of symmetry of the space group. Bond

distances and angles are indicated in the accompanying table.

1 Reimann, Mighell and Mauer, Acta Cryst. 23, 135 (1967).

2 Mighell, Reimann and Santoro, Acta Cryst. B25, 595 (1969).

3 Prince, Mighell, Reimann and Santoro Cryst. Struct. Comm. 1_, 247 (1972).

CALIBRATION OF DETECTORS FOR ARGON-41

H. E. DeSpain

(Center for Radiation Research)

A technique for calibrating detectors for argon-41 is being developed. The NBSR is used to produce a sample of argon-41, which is consequently assayed and injected into a detector. Efforts thus far have

been concentrated in perfecting a method for reproducible counting and

gas transfer.

44
C, Interagency and University Programs

DYNAMICS OF AMMONIUM IONS IN NH4CI 4 AND KH4N03

H. Prask and S. Trevino

(Picatinny Arsenal, Dover, N.J.)

and

J . J . Rush

Quasielastic neutron scattering studies have been made for polycrystalline samples of NH.NCL and NH.CIO, as a function of temperature.

These studies were performed using the PA-NBS three-axis spectrometer

with an energy resolution of 0.56 meV.

In the case of NH.N0-, numerous measurements have shown that the

4 3

occurrence of structural phase transitions is dependent upon the presence

of water in the samples. In view of this the present work was aimed at

ellucidating the interrelation of water content and NH, dynamics. The

NH.NCL samples were studied "wet" (< 1% H~0 by weight) at temperatures

of 23°C (Phase IV), 45°C (III), 95°C(II), 120°C (II) and 132°C (I).

After drying at 132°C, the samples were studied at 95°C (II), 60°C (II)

45°C (IV) and 23°C (IV).

The present results confirm that dried samples of NH.NO do not

exhibit the Phase III structure, but transform IV^II directly. The

quasielastic neutron data, obtained for a range of momentum transfers

(0.6 - 4.2 A ) at each temperature, are consistent with a jump-rotational

reorientation for all phases. Furthermore, the broadening of the quasielastic peaks for Phase II (95°C) with and without water are significantly

different, suggesting that "surface" water affects NH, binding throughout

the bulk of the crystal.

Ammonium perchlorate was studied by means of quasielastic neutron

scattering at temperatures of 55, 66, 78, 105, 130 and 150°K. Over this

range of temperatures , the maximum widths of the neutron spectra range

from the instrumental resolution width to -lmeV. This represents a significant change in NH, dynamics, although it is now well-established

that no structural phase change occurs over this temperature interval.

45
INTERAGENCY AND UNIVERSITY PROGRAMS

Quantitative analysis of both NH.NO. and NH.C10, quasielastic neu- tron scattering data is in progress.

GROUP THEORETICAL ANALYSIS OF NEUTRON SCATTERING IN CRYSTALS

S. Trevino and H. Prask

(Picatinny Arsenal, Dover, N.J.)

and

R. Casella

Work on the continuing program of application of symmetries to

classify the phonon spectra of materials via inelastic neutron scattering

has advanced. The general methodology of treating harmonically vibrating

and librating rigid molecules, developed during the period of the previous

progress report, has undergone continued application and comparison with

experiment. In addition to our fundamental paper on the subject now

published, two further papers, one on the aforementioned applications and

one, a general theoretical paper oriented towards chemists, are presently

in preparation or contemplated. The selection rules have been calculated

for the crystal NaNO_. Table 1 gives the results for a few significant

reciprocal lattice points at the zone center. Examination of the table

reveals the power of the selection rules. For example, the identification

of the E translational phonon obtained using the (0,4,-1) point and the

rotational phonon observed at the (0,2,13) point is accomplished unambigously. In addition, it was found that the two A_ phonons were not pure

modes but mixed translation-rotation phonons by combining the observations

at the (0,0,15) and (0,2,1) reciprocal lattice points. Most of the modes

at the T point have been observed and classified by this procedure.

Finally, a more complete discussion of the Debye-Waller factor in the

context of the group theoretical analysis is contemplated.

46
INTERAGENCY AND UNIVERSITY PROGRAMS

TEMPERATURE DEPENDENCE OF THE PHONONS IN HCP Be

H. Alperin, S. Pickart, and J. Rhyne

(Naval Ordnance Laboratory, White Oak, Md.)

An inelastic neutron scattering experiment is in progress to

determine if there is a correlation between an anomalous increase

in ductility in polycrystalline Be at 'WOOK and the fundamental force

constants. Last year's progress report described our room temperature

results for the phonon dispersion curves in the [0001] and [1120]

propagation directions, and selected phonons in these groups have

now been redetermined at 695 °K.

Phonon energy vs. wavevector relations for the c-axis direction are shown in Figure 1 for room temperature and 695 °K. It can be seen that

there is an overall softening of the modes at the high temperature as a function of increasing wavevector. Similar results were observed for the

[1120] propogation direction, amounting to a percentage shift of ^2.9%.

To determine whether this behavior is anomalous , one has to remember

that phonon-phonon interactions, arising from anharmonic effects, normally

broaden the energy width and decrease the phonon energy as the temperature increases. The theoretical behavior of anharmonicity is insufficiently known to make definite predictions as to the magnitude of this

effect, but we may relate our observations to some previous measuremsnts.

These previous results, when scaled to the same temperature interval

relative to the melting temperature as in our case, showed a percentage

shift of 3.7%, so we conclude that the effects we observe are most

probably due to normal temperature effects and are not anomalous.

These results do not disprove the presence of an anomaly, which

may occur at a higher temperature or a section of the Brillouin zone not

yet explored. The measurements are being extended to higher temperatures

and other propogation vectors to examine these possibilities.

1 K. E. Larson, S. Holmryd and N. Dahlborg, Inelastic Scattering of Neutrons in Solids and Liquids, p. 587 (IAEA, 1961).

A 7-
INTERAGENCY AND UNIVERSITY PROGRAMS

100

90 hep Be

[0001]

o 295 K

® 675 K

0.2 0.3 0.4 0.5

Fig. 1. Dispersion curves (energy transfer vs. wavevector) in hep

Be at room temperature and 69 5K for transverse and longitudinal

branches (acoustic and optic)

.

48
INTERAGENCY AND UNIVERSITY PROGRAMS

MAGNETIZATION OF RARE EARTH COMPOUNDS BY NEUTRON DIFFRACTION

J. Rhyne and S. Pickart

(Naval Ordnance Laboratory, White Oak, Md.)

The determination of the siiblattice magnetization is of critical

importance in studying the magnetism of compounds. In the case of

the Laves phase rare earth compounds (e.g., TbFe„) which have a ferrimagnetic arrangement of rare earth and transition metal spins , individual

sublattice magnetizations can not be determined by conventional magnetometer experiments. The only direct method of obtaining the magnetization

is by neutron diffraction In which the rare earth and transition metal

magnetizations may be determined individually by analyzing the magnetic scattering contribution to the total neutron Bragg intensity.

We have applied the method to a series of the Laves phase compounds

including TbFe- , ErFe_ , TmFe_ and DyFe~ and have obtained the magnetizations as a function of temperature from 4 K to the Curie Temperature

(typically 700 K) . The rare earth spins which are largely polarized by

the strong Fe-Fe exchange field show an essentially conventional temperature dependence of the magnetization, while the iron magnetization

remains essentially constant from low temperature up to near the critical

temperature where it rather abruptly decreases to zero. Models for this

magnetic behavior and its effect on the magnetostrictive properties are being developed.

EXCITATION SPECTRA OF AN AMORPHOUS FERROMAGNET

H. Alperin, J. Rhyne and S. Pickart

(Naval Ordnance Laboratory, White Oak, Md.)

A new class of magnetic materials has emerged from the discovery

that sputtered rare earth-iron alloys are magnetically and crystallographically amorphous . * These materials are different from previously

reported amorphous magnets in that they contain no glass former atoms

(P, C, Si or B), can be prepared in bulk form and contain 100% of

49
INTERAGENCY AND UNIVERSITY PROGRAMS

magnetic atoms, thus possessing relatively strong magnetization. Selected compositions of these materials, which can readily be formed w,ith

varying rare earth-iron ratios, are presently being developed for

application as permanent magnet, thin film memory elements, and magnetostrictive transucers.

In order to fully exploit such applications, basic knowledge concerning the nature of the magnetic state in a spatially disordered

system of atoms must be obtained. The magnetic excitations, or spin

waves, which can be measured by neutron scattering, reflect the dynamics

of such a system and are thus essential to adequately test theoretical

models of the fundamental spin interactions.

Inelastic magnetic time-of-flight spectra have been obtained at

various temperatures from amorphous TbFe„ , and show significant differences from the crystalline state. These spectra are shown in Fig. 1

for the two phases at room temperature and indicate that , compared to

the crystalline phase, the amorphous material has a broadened spectrum

that is shifted to lower energies. This effect has been predicted by

various theoretical treatments 2

, and results both from a depletion of

high-frequency modes caused by the break-up of short wavelength correlations, which shifts- the peak in the density of states to lower energy,

and from the increased lifetime of the spin waves which smears out

discrete modes.

At temperatures above T of the amorphous phase (433K) the frequency

spectrum is similar to that of a typical paramagnet, i.e. peaked at

energy transfer of zero, but preliminary measurements through the Curie

transition has failed to show any vestige of critical scattering, which

is expected on general thermodynamic grounds at any second-order phase

transition. It is planned to repeat these measurements with improved

resolution to explore the possibility that the critical fluctuations are confined to a wavevector smaller than used in the experiment (0.04A ) or in a smaller temperature interval £(T-T /T <.01],

c c

50
INTERAGENCY AND UNIVERSITY PROGRAMS

IOOO

z 800

3

TbFe 2 (CRYSTALLINE)

26 = l0.5°,E = l4.3meV

T=295K

-28 -24 -20 -16 -12 -8

AE(mev)

*

TbFe 2 (AMORPHOUS)

500 29 =10.5°, E =l4.3meV

77) T=295K

=; 400 - 3

>

cr< 300 - QL

\- • • . CD

• (T 5?i^* vs. S 200

• >^^ " • V . •• "? '•/f *^v. • ° 100 .' */ •V** ,•*" *... CO *—^1 * _~*-~^^* •^' "-'-VAV

-28 -24 -20 -16 -12 -8 AE imev)

-4

Fig. 1. Corrected time-of-flight spectra for polycrystalline (a) and

amorphous (b) TbFe- at room temperature.

J. Rhyne, S. Pickart and H. Alperin, Phys. Rev. Lett. 29, 1562 (1972).

2 See references cited in Amorphous Magnetism (Hooper and de Graaf , Eds.)

Plenum Press, N.Y. (1973).

51
INTERAGENCY AND UNIVERSITY PROGRAMS

ABSENCE OF MAGNETIC ORDER IN MnO~P2 5 GLASS

J. Rhyne and H. Alperin

(Naval Ordnance Laboratory, White Oak, Md.)

The question of antiferromagnetic ordering in glasses loaded with

transition metal atoms has been widely discussed in the literature, and

its answer would be of considerable importance to amorphous magnetism.

Magnetic susceptibility data on a 50 mole per cent MnO-P„0 glass by

J. Friebele indicated a paramagnetic-antiferromagnetic transition temperature of 90 K, below which the Mn spin groups supposedly order antiferromagnetically. The technique of neutron scattering provides a sensitive test of magnetic order, particularly antiferromagnetic order

in which a doubled magnetic periodicity generates additional scattered

intensity at angular positions not observed in the pagamagnetic phase.

We examined a sample of the 50 mole per cent MnO-P„0 glass by

neutron scattering over the temperature range from 300 K to 2 K and

found it to be a structurally homogeneous amorphous material, but without any evidence of long range antiferromagnetic order, in contrast to

the inference from the susceptibility results, but in agreement with

previous results 1 on cobalt-loaded glasses. These results indicate that

if antiferromagnetic interactions exist between the Mn and Co spins, they

are of such a short range nature that no measurable spin-spin correlation

(as seen in the case of TbFe„) exists. The neutron study gave no evidence of ordered clustering of the Mn atoms within the glassy matrix

such as has plagued some other amorphous magnetic glass work.

Further work is planned on these and other analogous "magnetic"

glass systems to further investigate the general question of magnetic

interactions in amorphous materials.

J Review papers by Egani, Sacli, Simpson, Terry and Wedgewood, Proa. Intl.

Symposium on Amorphous Magnetism3 Plenum Press (1973)

.

J. Friebele, Thesis, Vanderbilt University.

52
INTERAGENCY AND UNIVERSITY PROGRAMS

STRUCTURAL STUDIES OF AMORPHOUS SOLIDS

J. H. Konnert, J. Karle and G. A. Ferguson

(Naval Research Laboratory, Washington, D.C.)

The atomic arrangement in vitreous solids is the subject of an increasing number of current investigations. This renewed interest is

stimulated, in part, by recent technological advances made possible by

use of materials existing in the glassy state. Such advances include

semiconductors, fiber communication and laser devices.

Basic structural studies of simple glasses using the diffraction

technique have been reported. 1 New data reduction procedures were

developed, and employed in the analysis of these simple systems, to

reveal structural detail which had not been previously observed. The

present experimental program is designed to obtain high precision

diffraction data on selected samples of semiconducting materials. These

materials include As„Se_, AsTe and As„S . Data reduction, employing the

methods mentioned above, will be applied to study temperature dependent

structural details of these systems.

1 J. H. Konnert, J. Karle and G. A. Ferguson, Soienoe 179, 177-179 (1973)

PRECISION MEASUREMENT OF THERMAL NEUTRON SCATTERING AMPLITUDES

C. Schneider

(U.S. Naval Academy, Annapolis, Md.)

Prism refraction measurements have yielded a value of 4.147(2) fm

for the scattering amplitude of the silicon nuclear potential. Refraction

profiles are analyzed by computer with automatic corrections for higher

order contamination wavelengths. The extension of the prism technique

to materials of several barns per atom attenuation cross-section has

been accomplished by calculating the small correction due to preferential

attenuation across the prism for a standard slit arrangement. Reversal

of the prism will be used to confirm this correction. Preliminary mea53
INTERAGENCY AND UNIVERSITY PROGRAMS

surements on a Ge prism yielded b = 8,28(8) fm for the nuclear scattering

amplitude in good agreement with other determinations.

A small variation of the torsion goniometer calibration with torque

applied to the mounting plate has been studied and found useful in

simplifying the calibration, A very slow (<10 msec/hour) angular drifting

of the double crystal spectrometer due to small temperature gradients

between the crystals has been observed to cycle on a daily basis with a maximum amplitude of 0.1 sees. arc. The double crystal spectrometer has

been studied as a tool in the measurement of thin film in homogenieties

by mirror .reflection.

Use of the double crystal geometry to observe the small angle

scattering of neutrons from critical fluctuations, polymers, defects and

magnetic inhomogeneities is under consideration. For most experiments,

the angular range of interest is from several seconds to several degrees

arc so that the instrument would benefit from interchangeable crystal

pairs of various matched mosaics.

THE STRUCTURE OF N32ZnCL4

• 3H 2

R. J. Khanna

(University of Maryland)

and

E. Prince

Sodium zinc chloride trihydrate, Na

2 ZnCl,«3H 0, crystallizes in the

trigonal space group P31m, with a=6.876A, c=5.955A, and 1 formula unit

per unit cell. A data set was collected on this compound in order to

determine the configuration of the water molecule and the arrangement of

hydrogen bonds. The data are being analyzed at the University of

Maryland

.

54
INTERAGENCY AND UNIVERSITY PROGRAMS

CRYSTAL STRUCTURE OF NH4

Cl0

4 AT 300K, 78K AND

10K BY NEUTRON DIFFRACTION

C. S. Choi and H. J. Prask

(Picatinny Arsenal)

and

E. Prince

Earlier studies of NH.C10, structure by several investigators

suggested that the ammonium group in the crystal is undergoing essentially

free rotation at room temperature. No. low temperature structural studies

had been performed. To investigate the orientation and the thermal

motion of the ammonium group in the crystal, a single crystal neutron

diffraction study was undertaken for three different crystal temperatures,

300K, 78K and 10°K.

The NH . ClO, crystal has an orthorhombic unit cell, Pmna, with the

cell dimensions a = 9.20, b = 5.82, c = 7.45 for 300±K, a = 9.02, b =

5.85, c = 7.39 for 78°K and a = 8.94, b = 5.89, c = 7.30 for 10°K.

Initial positions for H atoms were obtained from the room temperature

data by the difference Fourier synthesis for which the F was obtained

from the heavy atoms only. Hydrogen peaks (negative) were observed

in the map with sufficient clarity to indicate that the NH, are not

undergoing completely free rotation even at room temperature.

Since the amplitudes of thermal motions of the H atoms in the

ammonium group are so large, they cannot be represented satisfactorily

by the conventional thermal ellipsoid. Hence the structure was refined

by the rigid body refinement method developed by Prince and Finger.

The refinement converged rapidly for the structure at 10°K and at 78°K

but it failed to converge for the room temperature data. The thermal

motions of the ammonium groups at room temperature are still too large

to be handled by the rigid body refinement method, which is based on

the normal distribution function simplified to third cumulant.

The librations of the ammonium group at low temperatures (10°K and

78°K) are very large only about one principle axis. The root mean

square angular displacement about the "unique" axis was 26° for the

55
INTERAGENCY AND UNIVERSITY PROGRAMS

structure at 10°K and 36° for that at 78°K but the orientations of the

principle axes remained essentially the same. The oscillation amplitudes

about the other two principle^ axes were approximately the same at each

temperature, about 9° at 10°K and 16° at 78°K. Each ammonium group is

surrounded by ten oxygen atoms with short N...0 distances ranging from

o o 2.9A to 3.2A. This almost isotropic environment leads to a very low

barrier for reorientation, as has been proposed from other work. Among

these ten oxygens, four appear to be hydrogen bonded to the four H atoms

of the ammonium group.

AP(78°K)

Fig. 1. The ammonium group and its oxygen neighbours (78°K) viewed

along the axis of the largest libration motion. The thermal

ellipsoids are sealed to include 20% probability.

56
INTERAGENCY AND UNIVERSITY PROGRAMS

REFINEMENTS OF THE CRYSTAL STRUCTURE OF KN 3 AND

3-N*N3 BY NEUTRON DIFFRACTION

C. S. Choi

(Picatinny Arsenal, Dover, N.J.)

The crystal structures of KN„ and $-NaN„ are well known since the

pioneering work by Hendricks and Pauling in 1925. The potassium azide

and sodium azide form typical ionic type crystal structures with linear

and symmetric N_ anions. The N-N distances of the N„ anions reported by

o earlier x-ray investigators are not precise and range from 1.145A to

o 1.17A with large standard deviations. This study is aimed to obtain

accurate N-N distance of the azide anions by using neutron diffraction

techniques. These alkali metal azides are meta-stable and suffer severe

radiation damages by x-rays but not by the thermal neutrons.

KN„ crystallizes in tetragonal 14/mcm with the unit cell dimensions

a = 6.304(1) and c = 7. 540 (2) A. The reflection intensities of 161 out of

o 195 independent reflections were measured with 0.983A wavelength neutrons,

The structure was refined by full matrix least squares methods to yield

R-index of Rw = 0.022 and R = 0.024. The N-N distance was 1.174(1)1

o without correction and 1.184A after correction with the riding model.

The crystal structure of 8-NaN_ is being refined.

Fig. 1. Crystal structure of KN

3 projected along c-axis,

57
INTERAGENCY AND UNIVERSITY PROGRAMS

CRYSTAL STRUCTURE OF DINITRO-PENTAMETHYLENE-TETRAMINE

C. S. Choi and S. Bulusu

(Picatinny Arsenal, Dover, N.J.)

and

F. Mauer

(Inorganic Materials Division)

The title compound, C,.HinN,0, , code named as DPT is one of the

several derivatives of HMX (cyclo-tetramethylene-tetranitramine) . The

crystal structure of DPT was studied by x-ray diffraction with MoKa

radiation. Preliminary investigations by precession photographs revealed

DPT

Fig. 1.

the space group to be monoclinic P2./C. The unit cell dimensions are

a = 9.345(5), b = 8.284(5), c = 11.566(5) and 6 = 105.6(1)°, and contains

four molecules per unit. cell. A total of 1420 independent reflection

intensities were observed by an automated three circle dif fractometer

58
INTERAGENCY AND UNIVERSITY PROGRAMS

equipped with a solid state detector. The crystal structure was solved

by the symbolic addition procedure and was refined by the full matrix

least squares method to the final R-index R = 0.035 and Rw = 0.037.

The DPT molecule consists of an eight -membered C-N ring with an additional methylene group bridging between the two valley points of the

ring, and two planar nitro groups attached to the C-N ring, as shown in

the Fig. 1. The DPT molecule possesses a pseudo mirror symmetry about

the plane passing through the N-N axes of both nitro groups and C atom

of the methylene bridge. The bond lengths and angles of the molecule

generally agree with those of HMX and RDX. The DPT molecule has rather

tight intramolecular packing and exhibits several short intramolecular

interatomic distances.

THREE-AXIS NEUTRON SPECTROMETER

H. Prask and S. Trevino

(Picatinny Arsenal, Dover, N.J.)

and

R. Carter, J. Rowe, J. Rush and A. Cinquepalma

A high-efficiency, high-versatility three-axis neutron spectrometer

has been designed for use at the NBSR. The new instrument will incorporate an automatic shutter system in the monochromator shield so that

variable E. scans are possible, combined with the variable E. . scans

in fin

used with present instruments . The angular range for monochromator

(29 ) and sample (<p) will be increased significantly over present instruments: -10° < 29 < 100°, -120° < <J> < 120°. Two complete analyzer

systems will be employed, increasing the rate of data collection by as much as a factor of two.

Fabrication of the new instrument is nearing completion.

59
D, Non-RRD NBS Programs

ACTIVATION ANALYSIS SECTION: SUMMARY OF ACTIVITIES

P. D. LaFleur and D. A. Becker

(Analytical Chemistry Division)

The Activation Analysis Section of the Analytical Chemistry Division

is physically located in the NBS Reactor Building. It has at present

fifteen members , and has programs in a variety of areas related to trace

element analysis. These programs include both research projects, and

analytical programs on a wide variety of real sample matrices. Summaries

of the work in these areas are included below.

1. Research Projects

a. Sampling and Analysis of Chesapeake Bay Organisms and Sediments

for Trace Metal Profile Determinations.

Determination of water quality involves a comprehensive study of an aquatic system, rather than analysis of water only. Food chain organisms,

sediments, and water all must be included in such a study. A project has

been initiated in the Activation Analysis Section for the determination of

trace metals in Chesapeake Bay organisms and sediments, as well as water.

Sampling and analytical methodology is under development for this study.

Also included is a fresh water tributary to the Bay, the Patuxent River,

as described in the following project.

Members of the Activation Analysis Section went into the Bay on the

Chesapeake Bay Institute Research Vessel, H. Ridgley Warfield to

experience and participate in the aquatic sampling techniques. Samples

taken include oysters, plankton, sediment, annelids living in the

sediment, and water samples. Improved sampling techniques for organisms

and sediments are in the process of being developed, which which will

reduce the possibility of trace element contamination during sampling

and storage. Analysis of the various types of samples to determine

their trace element profile has begun. It is expected that variations

in these profiles will be observed, depending on sediment depth, sampling

area, time of year, and other factors.

60
NON-RRD NBS PROGRAMS

The results of this project will also allow correlation with mercury

biotransformation studies taking place in the NBS Inorganic Materials and

Metallurgy Divisions.

b. Trace Elements in Water.

A cooperative research program between the NBS Activation Analysis

Section and the University of Maryland is concerned with trace element

analysis in natural waters. One of the primary objectives of this program at the present time is the development of adequate sampling and

sample handling techniques for water analysis. At present, natural

water samples are being taken using a teflon sampling device developed

in this program. The samples are then filtered directly into a specially prepared 1 mil polyethylene film container, and frozen immediately (while still in the sampling area) in liquid nitrogen.

In order to irradiate samples for long periods of time, and as a pre-irradiation concentration step, a freeze-drying technique was used

to remove the water without melting, allowing the impurities to remain

behind on the polyethylene film. Radioactive tracers were used to study

the retention yields of this freeze-drying procedure. It was found that

the elements quantitatively retained on the film when freeze-drying a 100 ml river water sample (pH adjusted to 1.5) include: Na, Sc, V, Cr,

Fe, Co, Zn, As, Se, Br, Rb , Sr, Cd, Sb , Cs , Ba, Ce and Tb . Work has

begun on the determination of trace element profiles from the 100 ml

samples of Patuxent River water using these techniques.

c. Forensic Activation Analysis.

In cooperation with the NBS Law Enforcement Standards Laboratory

(LESL) , the Activation Analysis Section has this past year had a program

in the examination and evaluation of the neutron activation analysis

technique for the determination of gunshot residues. This program in

general covered the areas of sampling methodology, radiochemical separation procedures, stability of residues on the hand as a function of time

firing, and the evaluation of background levels of barium and antimony to

61
NON-RRD NBS PROGRAMS

be found in the general population. This is an on-going program, and will

continue during the next year.

d. The Application of a Mass Separator to Activation Analysis.

The mass separator research program of the Activation Analysis

Section is concerned with the development of practical analytical procedures for the application of electromagnetic isotope separation

techniques to activation analysis.

As the need to determine trace elements of interest in biological

and environmental samples at lower and lower concentrations increases,

interference from other elements in the sample also increases, and

ultimately is the limiting factor in the application of nuclear activation

analysis techniques. An isotope separator has been used, along with

radiochemical separations, to provide a single radionuclide in a form

suitable for counting. By evaluation of the parameters of isotope

separator operation, and determining the fraction of a given nuclide

which is actually deposited on a catcher foil, it is possible in some

cases to determine a given trace element without interference from any

other trace element. The ultimate sensitivity for a given trace element

would then be dependent only upon the nuclear parameters for production

of suitable radionuclides and the mass separator yields.

Over the past year, the operating characteristics of the mass separator have been studied and procedures were developed for the determination of lead and cadmium in environmental samples. This work will

continue with particular emphasis on the determination of iodine in

biological and environmental samples and upon the determination of

cerium in samples of the Trace Elements in Glass SRM's.

e. Activation Analysis Using an Isotopic Calif ornium-252 Source.

At the 1968 International Conference on Modern Trends in Activation

252 Analysis, a significant paper recommended Cf as a neutron source for

activation analysis. They pointed out the advantages in cost, half-life,

252

volume, and gamma and heat emission of Cf relative to other isotope

62'
NON-RRD NBS PROGRAMS

252 sources and the advantages of Cf over accelerator sources such as largely eliminating maintenance, the dependable, continuous and stable

neutron emission, and a lessening in shielding requirements. Since that

time about seventy journal articles and conference proceedings have ap252 peared in the literature describing Cf activation analysis. These

have dealt with determinations varying from the in vivo determination of

sodium to field exploration for minerals. An evaluation of the utility

252

of Cf activation analysis must include estimates of sensitivities.

These are at least 200 sensitivity tables for thermal neutron

activation analysis in the literature. From any of these and the determination of the yields of one or two thermal neutron reactions with a 252 specific Cf source, a sensitivity table can be estimated for that

specific source. This is not the case, however, for fast neutron act252 ivation analysis with the isotope source. As has been noted, the Cf

fission neutron spectrum is sufficiently different from that of ^^^U,

that serious error may be introduced if any of the average cross section

235 data readily found in the literature for the U fission neutron spectrum,

252 are used in calculations related to Cf experiments. These yields of

reactions of analytical interest have been made and reported elsewhere.

252 The NBS Cf facility consists of 8 sources of 50 yg each at the

time of these experiments. They are arranged in an octagonal array around

the irradiation position. Samples are packaged in a polyethylene snapcap vial of 1 cm diameter and 2.5 cm length. This is wrapped with 1 mm

thick cadmium foil and placed in a larger polyethylene vial with spacers

to assure that the sample is in the position of maximum neutron flux. A

compressed air pneumatic transfer system sends the vials to the irradiation

position and return.

The (n,n ? ) reactions were of particular interest in this study. In

addition some (n,p), (n,a) and (n,2n) yields were measured. The conditions

for analysis were one gram of the element irradiated with a source

252 strength of one milligram of Cf , with the flux being 3.5% of the total

neutron output. The determination of lead in paint using this system has

also been made.

63
NON-RRD NBS PROGRAMS

Since large amounts of lead in the paint on walls in dwellings are potentially -hazardous to children, especially in certain susceptible age

groups who may ingest it, a rapid and quantitative analytical technique

for lead would be most useful. Most analytical methods for screening

suspect homes require lengthy dissolution times or other chemical pro252 cedures. Activation analysis with unmoderated neutrons from a Cf source inducing the nuclear reaction Pb'(n,n') Fb and/or Pb(n,n')

O f\ "7 * -Tb followed by gamma spectrometery with Ge(Li) or Nal(Tl) detectors

respectively is shown to be a reliable and potentially rapid nondestructive

method for this determination. The lower limit of determination in a 1.5

252

gram sample of paint with a 600 ug source of Cf is of the order of one

percent. Larger sources would increase the sensitivity or permit more

rapid analyses. The potential exists for partially automating the

determination

.

f. High Sensitivity Activation Analysis.

Nuclear activation analysis is widely recognized as a sensitive method

of trace analysis with the possibility of producing results with excellent

accuracy and precision, when carefully done. The technique is widely

applied in the analysis of environmental, biomedical, oceanographic, and

industrial samples for their trace element content. With the judicious

application of neutron and high energy photon irradiations , most of the

elements in the periodic table may be determined. Although there is

much discussion in the literature of the very high sensitivity and the

capacity for excellent accuracy suing these techniques , neither property

is fully realized in practical analysis because of such factors as lack

of knowledge of neutron or photon flux distributions and/or energy spectra

and possible contamination during pre-irradiation processing, or occasionally, from the irradiation container itself. Since improvement of measurement science is an integral part of the NBS mission, it was felt important

for NBS to play a leadership role in defining problem areas and pursuing

solutions to these problems.

To this end, considerable effort has been expanded over the last

64
NON-RRD NBS PROGRAMS

several years in the characterization of the NBS reactor and LINAC irradiation facilities, in terms of flux distribution and density. Work in

the past year has been focused on the characterization of neutron spectra

in the NBS reactor to assess possible effects of resonance absorption and

interfering nuclear reactions. These studies will also be continued. In

addition, analytical procedures have been developed for the determination

of chromium, zinc, hafnium, and other elements using activation analysis

with radiochemical separations. These methods have been applied to

biological samples, such as the NBS Standard Reference Materials (SRM)

orchard leaves and bovine liver, in the Trace Elements in Glass SRM's,

and in pure materials analysis.

g. The NBS Measurement System for Natural 37Ar.

A project to determine the cosmic-ray production rate and the

37 natural levels of 35-day Ar in the atmosphere has been underway at the

National Bureau of Standards for the past year. The prime objective of

37 this project is to determine the (absolute) spatial dependence of Ar

production in the atmosphere, on the one hand, and the spatial distri37 bution of the naturally-produced Ar (observed concentrations) on the

other. This information will then be used, through cooperation with

L. Machta (N.O.A.A.), to derive information about atmospheric mixing.

37 -3

As the lowest Ar concentrations of interest are but 10 dpm/l-Ar,

very high sensitivity measurement techniques are required. Among the

techniques which we have adopted are: quantitative separation of the

3 noble gases from about 1 m of air, using a CaC_ reactor; gas chromatographic separation of the argon fraction; isotopic enrichment (by a factor of ^70) of purified argon; use of specially selected low-level gas

proportional counters together with massive shielding and anticoincidence

mesion cancellation; and the application of pulse discrimination based upon

both amplitude (energy) and rise time. On-line computer techniques are being applied for data acquisition and system control.

Using this system, we have completed the first measurements of cosmic

•in ray produced J Ar from the southern hemisphere. By means of thermal

65
NON-RRD NBS PROGRAMS

37 diffusion the very low natural specific activity of Ar was enriched by

about a factor of 70 to 100 in a period (6-10 days) significantly less

37 than the half-life (35.1 day£) of Ar. Results of southern hemispheric

samples confirmed that the time scale for interhemispheric (north-south)

37 atmospheric mixing is significantly longer than the half-life of , Ar.

h. Quantitative Applications of ^'O Tracer Using. the Nuclear Track

Technique

Many nuclides emit charged particles (p, d, t, a and fission fragments) after capturing a thermal neutron. However, some of these isotopes

are unacceptable for quantitative applications of the Nuclear Track

Technique because they either have low thermal neutron cross-sections or

low isotopic abundances or both. Such is the case with 0, which has

a very low isotopic abundance (0.04%) and a moderately low thermal neutron

cross-section (0.235b); however, since oxygen compounds highly enriched

in are available, the analytical application of the 0(n,a) C

reaction may be feasible.

In collaboration with the Weizmann Institute of Science, Rehovot,

Israel, a study was undertaken at the National Bureau of Standards to

determine the feasibility of using this isotope as a tracer in biological

systems. The group at the Weizmann Institute supplied two oxygen-17

enriched compounds, Al^O- with 20% and citric acid with 7% 0.

These compounds were pressed into pellets in a KBr pellet die using a hydraulic press . The pellets were then sandwiched between two pieces of

cellulose acetate (CA) and vacuum sealed in a polyethylene bag. The

combination was then irradiated in a highly thermal neutron environment

in the NBS RT-4 pneumatic tube facility.

13 After a 2 sec irradiation in a thermal neutron flux of 1.33x10 n*

-2 -1 cm sec , the combination was separated and the detectors were etched

in a solution of 7 parts 6.5N NaOH and 5 parts 12% NaC10_ for 30 minutes

at 40°C. The etched detectors were then rinsed, dried and the track

density counted with the aid of an image analyzing microscope.

Consideration must be given to the interfering elements such as

66
NON-RRD NBS PROGRAMS

boron and lithium as both of these will produce alpha tracks when they

capture a neutron. A concentration of VLO ppm of boron will interfere

with oxygen determination, while the lithium concentration must be at

least 100 ppm before it interferes seriously. In this study there was

no interference problem. Application of this technique for oxygen

determination and particularly oxygen distribution in biological tissue

appears practical and a study of this possibility is in progress.

i. A Method for the Determination of "are Earths Using Neutron

.Activate.on .Analysis and Reversed-Phase Chromatoeraohy.

Recently, the interest in the quantitative determination of rare earth elements has grown considerably, especially in space programs.

There has also been a need for quantitative methods for rare earth element

determinations in different matrices at the National Bureau of Standards.

We have therefore applied some of our earlier qualitative investigations

with di(2-ethylhexyl) orthophosphoric acid (HDEHP) to separations of

these elements for their subsequent quantitative determination.

The chemical separation was made using a column (11 cm x 40 cm) of

"Corvic" powder (poly (vinyl chloride-vinyl acetate)) loaded with HDEHP

and operated at a constant temperature. Since our earlier solvent

extraction studies with HDEHP had shown perchloric acid to be the most

favorable of three acids (HC1, HN0«, HCLo.) for rare earth separation » the optimum operating conditions (time, flow, acid concentration, etc.) were established using this acid.

The rare earth elements in NBS Standard Reference Material 480,

Trace Elements in Glass, a sodium glass to which 61 trace elements,

(including the thirteen naturally occurring rare earths), were added,

have determined by neutron activation analysis. The samples were

irradiated in RT-4 , chemically separated using the above procedure,

and then counted on a Ge(Li) detector. A total of 11 different rare

earths were determined at the 500 ppm and 50 ppm levels in the glass,

with good precision and accuracy.

67
NON-RRD NBS PROGRAMS

2. Standard Reference Material (SRM) Analyses

Much of the section's efforts during the past year have been

directed towards the development of high precision and accuracy in

neutron activation analysis, with a primary aim being the analysis and

certification of NBS Standard Reference Materials.

In total, the section during the past year has analyzed 163 SRM

samples while determining 251 elemental concentrations. These analyses

encompassed a variety of materials, including coal, fly ash, fuel oil,

molybdenum concentrate, glasses, urine, tuna fish, orchard leaves,

bovine liver, and several metals.

For a number of the above mentioned SRM's the Activation Analysis

Section was responsible for a large fraction of the total effort applied

towards their production and certification. These materials are discussed further below.

a. Biological SRM's

The biological SRM's already issued include the Orchard Leaves (SRM

1571) and the Bovine Liver (SRM 1577) . At present SRM 1571 has 19 elements

certified and information values for 10 additional elements. Of these 29

elements, over half were determined by neutron activation or the nuclear

track technique. SRM 1577 presently has 11 elements certified, with

information values on 11 additional elements. Again, over half of these

elements were determined by nuclear techniques. Several additional

biological materials are under development at present, including a Tuna

Fish Standard (SRM 1578) , which should be issued soon with a number of

toxic elements certified for trace content.

b. Fossil Fuel SRM's

Trace element characterization of fossil fuels has gained a considerable amount of importance because of the need to identify and quantify

the emission of certain toxic elements and/or compounds into the atmosphere.

The literature on the analysis of fossil fuels and their by-products con- tains much analytical data; however, emphasis in many cases is placed on

68
NON-RRD NBS PROGRAMS

the extreme sensitivity of the method used rather than the accuracy

obtained. There was felt to be a need for fossil fuel standards so that

pollution monitoring devices can be calibrated, and the data obtained can

be more meaningful in terms of accuracy and precision. In a joint program

with the Environmental Protection Agency, the National Bureau of Standards

is in the process of certifying coal, fly ash, fuel oil, and gasoline as Standard Reference Materials

To determine the homogeneity of the fossil fuels both macro and

trace elements were analyzed using non-destructive neutron activation

analysis. Elements such as vanadium, manganese and aluminum were readily

detected and measured with a precision of 1-2%. Replicate analysis gave a good indication that the fossil fuels were homogeneous within these

limits. For the determination of As, Cd, Hg, Se, and Zn the most sensitive

and useful (n,y) reactions involve short-lived nuclides. To obtain good

sensitivities for these elements, they must be chemically separated from

the activated matrix. The method used was a modified combustion technique,

which simultaneously determined As, Cd , Hg, Se, and Zn. The radiochemical

separation involves the combustion of the sample followed by reduction

with carbon monoxide and subsequent volatilization of the metals. The

results obtained by this method were in good agreement with other

analytical techniques. In most cases, the accuracy and precision of

analysis was from 2-5%.

In addition to the homogeneity testing, activation analysis was used

to analyze for 9 elements in these materials. At present, the fossil

fuel SRM's are undergoing additional analyses by a number of different

analytical techniques, including activation analysis, and at least three

of them (coal, fly ash, and fuel oil) should be issued in the next year.

c Calibrated Glasses as SRM Neutron Monitors for Fission Track

Studies.

Four glasses of different uranium concentrations, SRM 961 (461 ppm) > SRM 962 (37.4 ppm), SRM 963 (0.823 ppm) and SRM 964 (0.0721 ppm), were

prepared for use as neutron monitors to aid fission track studies. These

69
NON-RRD NBS PROGRAMS

glass wafers were irradiated in the NBS reactor and the neutron flux was monitored using copper and gold foils.

The glasses were polished, polycarbonate and mica detectors were

affixed to either side of each glass, and this configuration was sealed

in polyethylene. Each package was placed in an individual irradiation

container; included in every tenth container were a gold and copper neutron monitor.

In order to allow the user selection of thermal to fast neutron

ratios, two glasses which were irradiated in separate reactor locations

are provided. Glasses were irradiated in reactor facility RT-3 which has

a Cd ratio for Au and Cu of 10.2 and 65, respectively, and RT-4 which has

a Cd ratio for Au and Cu of 87 and 536, respectively.

These Fission Track Glass SRM's will aid fission track laboratories

in the interlaboratory comparison of data and in monitoring neutron flux

levels in their irradiation facilities.

3. Cooperative and Service Analyses

In addition to the analyses on SRM's, a large number of additional

analyses were made on non-SRM materials. These include cooperative

analyses, where the analysis is made on samples of mutual interest to

NBS and some other organization, and also service analyses, where the

technical expertise of the section is needed by an NBS or other governmental agency.

During the past year, the Activation Analysis Section has completed

cooperative and service analyses to the extent of 131 samples, for 347

elemental determinations. These samples were obtained from five other

NBS laboratories, and such other agencies as the Frederick Cancer Institute,

the U. S. Army (Fort Belvoir) , and the National Institutes of Health.

The determinations included over 30 different elements, in matrices ranging

from high purity silicon, glasses and coal, to drugs and organic polymers.

In particular, two extended programs of analyses were undertaken in cooperation with other NBS laboratories, which are described below.

70
NON-RRD NBS PROGRAMS

a. Clay and Clay-Based Papers Study

A cooperative analytical program was initiated with the Fibrous

Systems Section of the Product Evaluation Technology Division here at

NBS. This laboratory is concerned with the trace element profiles of a variety of clays and clay-based papers.

The analyses were performed for both short-lived and long-lived

radionuclides. The short-lived elements (Al, V, Ti, Mn, CI and Mg) were

determined after irradiation in RT-5 , the thermal column pneumatic tube

facility. The longer-lived radionuclides were determined after irradiation in RT-3, and included over twenty (20) elements in the initial

survey analyses. Work on this project is continuing during the coming

year.

b. Determination of Gold in High Purity Silicon

Another cooperative program which took place in the past year was with the Semiconductor Characterization Section of the Electronic Technology Division of NBS. This laboratory required the accurate, nondestructive analysis for low concentrations of gold in a highly purified

elemental silicon matrix. This gold had been added during manufacture

as a dopant, in order to modify the silicon's electronic characteristics.

The analyses were required to be accurate because the data were needed

for "cause and effect" relationships between the analyzed gold content

and the electronic characteristics as found by measurements on the same

samples. This program has been of considerable assistance to their project, and will be continued in the future.

4. Facilities

During the past year, there were two particular facilities projects

in the Activation Analysis Section which may be of interest and which are included here. The first concerns our irradiation capabilities, namely,

the approval and manufacture of RT-6. The second concerns our detection

capabilities, namely the calibration of all four Ge(li) detectors for their

total absolute photopeak efficiency at a variety of geometries and gamma71
NON-RRD NBS PROGRAMS

ray energies

a. Pneumatic Tube Facility RT-6

Significant progress has been made in the past year in cooperation

with the Reactor Radiation Division on the preparation of pneumatic tube

facility RT-6. This facility is to be located in the vertical tube

location VT-3 in the reactor reflector area. It will use a small size

polyethylene rabbit as the irradiation container, and should have characteristics somewhere between RT-3 and RT-4. The prime advantage for

this facility will be the location of the send-receive terminals , which

are located in two of the B-wing hot laboratories. These locations will

allow the use of RT-6 for very short-lived radionuclides, with counting

on the Ge(L9) detector systems also located in the B-wing. This system

should be available early next year.

b. Calibration of Ge(Li) Detector Systems

In the past, two of our Ge(Li) and one 7.5 cm x 7.5 cm Nal(Tl)

detector systems had been partially calibrated for their total absolute

photopeak efficiencies. These measurements were made at a few different

geometries using several NBS SRM y~ray Point Source Standards. Now,

however, a recently issued NBS SRM Mixed Radionuclide Point Source

Standard (SRM 4215) has made additional calibrations much easier. This source contains 9 radionuclides, with a total of 11 calibrated y-ray

peaks, all at approximately the same relative intensity. These peaks,

ranging from 0.0877 MeV ( Cd) to 1.836 MeV ( Y) , are calibrated in

y/s with total uncertainties of 3% or less. Using this source, all of our Ge(Li) detector systems were calibrated for this y-ray energy range

at distances of 0-30 cm. These efficiencies have been found to be

extremely useful in the estimation of sensitivities for activation

analysis, in calculating estimates of elemental concentrations when no standards are available, and in the evaluation of various detector

systems.

72
NON-RRD NBS PROGRAMS

5. Conclusion

The Activation Analysis Section of the Analytical Chemistry Division

has been active in a number of significant research areas. They have also

analyzed a wide variety of sample types for many different elements. Work

is continuing in most of these areas, as well as in several additional

projects recently initiated.

73
NON-RRD NBS PROGRAMS

INTEGRAL REACTION RATE MEASUREMENTS

FOR THE NBS NEUTRON STANDARDS PROGRAM

J. A. Grundl and I. G. Schroder

(Nuclear Sciences Division)

Neutron standards activities at the reactor this year have centered

around the reactor thermal column facility where the extracted thermal

beam has been employed in support of integral cross section measurements

and an extensive program of absolute fission rate calibrations for'AEC's

Interlaboratory LMFBR Reaction Rate Program (ILRR) . Two elements of this

support work prominent during the period covered by this report are outlined below:

1. Performance Maximization and Operational Checks of the NBS Double

Fission Chambers. The NBS Double Fission Chamber is a high-resolution

double ionization chamber of minimized volume and mass designed to

measure absolute fission rates in a wide variety of neutron environments.

The performance characteristics and the absolute efficiency of the

chamber have been investigated in the reactor thermal column beam (nv

^6 x 10 , gold cadmium ratio >10^) . Some results of these investigations

are as follows

— establishment of a triple-sealer method for obtaining and verifying

the fission pulse rates from the double chamber. This method, simple

and convenient , provides a redundant readout of the primary pulse

rate, a continuous monitor of the extrapolation-to-zero of the

fission pulse height distribution, and a sensitive check of gain

stability. — determination of the linearity of dead time corrections for random

4

pulse rates of up to 10 per second. — measurement of the absolute efficiency of the chamber for detecting

fission fragment. The observed efficiency, between 0.998 and 0.985,

appears to vary linearly with the thickness of the fissionable

deposits.

The NBS fission chambers may be assembled with any of a number

239

of fissionable deposits (e.g. Pu, enriched or normal uranium,

74
NON-RRD NBS PROGRAMS

237

and Np) , and has been operated successfully in a half-dozen different

neutron fields important for fast neutron standardization: — core center of the CFRMF Reactor at Idaho Falls , Idaho (purpose

fission activation detector calibrations for the ILRR Program mentioned above)

— ZZ standard neutron facility at the CEN-SCK Laboratories in Mol,

Belgium (purpose: international comparison of absolute fission

detectors, and spectrum characterization). — thermal neutron beam (purpose: calibration of a triple-axis neutron

spectrometer at the NBS Research Reactor)

252

Cf spontaneous fission neutron source at the NBS Van de Graaff

low-scatter room (purpose: absolute fission cross section measurements) . — NBS thermal column beam (purpose: intercalibration of the NBS fission

chamber and ANL fission track recorders)

— Van de Graaff neutron facility at the Univ. of Toronto (purpose:

investigation of proposed BIPM intercomparison of Van de Graaff

facilities)

Each of these neutron environments presented unique operational requirements for the fission chamber, and each of these requirements was met by

means of beam measurements at the NBS reactor thermal column.

2. Preliminary Mass Assay of Fissionable Deposits * Fission rate ratios

obtained with pairs of fissionable deposits placed back-to-back in

the double fission chamber and then exposed to the thermal column beam

is part of the effort to establish the masses of principle isotopes

for the NBS set of fissionable deposits. Comparing fissile deposits

of similar isotopic composition is a simple type of measurement now

underway which will provide an inventory of deposits of various thicknesses

and known relative masses. The significance of these rather routine

ratio measurements may be realized when it is noted that the fission

rate measurements undertaken in the neutron fields listed under item

1 above covered a neutron flux range of nearly four orders of magnitude,

and required the operation of three individual double fission chambers

containing six fissionable deposits.

75
NON-RRD NBS PROGRAMS

Comparing fissionable deposits of different isotopic composition is

only beginning. An example of this work is the mass ratio between a

O O c U and a normal uranium deposit which has been obtained based upon

fission counting and the isotopic composition of normal uranium. The latter

is established to ±.1% by the NBS Mass Spectrometry Section. An independent mass ratio for the same pair of deposits based on absolute alpha

counting by the NBS Radioactivity Section agrees with the fission counting

method to better than 0.5%.

PRECISION MEASUREMENT OF THE C0MPT0N WAVELENGTH OF THE ELECTRON

W. C. Sauder, E. G. Kessler and R. D. Deslattes

Optical Physics Division

We intend to measure the Compton wavelength of the electron by

means of precision crystal diffraction spectroscopy of the radiation

emitted in two-photon annihilation of positronium. This will yield a non- quantum electrodynamic determination of the fine structure constant

at the one ppm level. The measurement will be carried out with a twoaxis, Laue case transmission crystal diffraction spectrometer that was

designed and constructed at NBS. This instrument is capable of determining Bragg angles of 2.5 degrees or less with an angular sensitivity of

-4

better than 10 arc second.

In addition to performing the annihilation measurements employing a

64 high activity (20 kilocurie) Cu source, we will determine the wavelengths (and therefore energies) of several nuclear gamma lines in the

region 80-1000 keV.

During the current year we have completed the installation and

testing of the experimental apparatus, including the source cryostat

that will provide a 7° K helium moderator in a 0.2 T magnetic field for

the annihilating positronium. At the present time we are beginning the

angular calibration of the spectrometer.

76
NON-RRD NBS PROGRAMS

6

°CO GAMMA RAY ANISOTROPY THERMOMETRY

H. Marshak, R. J. Soulen and D. B. Utton

(Heat Division)

A new stabilized counting system will enable us to improve the

precision of the comparison measurements between a Co y-ray anisotropy

thermometer and a Josephson junction noise thermometer. In addition, a new "bottom" for our dilution refrigerator will enable us to extend our measurements from 20 mK to 12 mK or lower. This will also help to

improve the precision of our measurements since the anisotropy increases

bv a factor of tvo.

A NMR/ON experiment was performed on a 15 microns thick sample and

no effect was seen. X-ray analysis of the sample indicated it was no

longer a single crystal. A new sample is being prepared and x-ray

analysis is being carried out along each step in its production; e.g.

both before and after irradiation.

Some work was also done on studying the thermal contact problem

of our Co thermometer in the temperature region of 20 to 40 mK.

EMISSION OF LONG-RANGE ALPHA-PARTICLES IN THE

SUBTHERMAL-, THERMAL" AND RESONANCE-NEUTRON FISSION OF

239

P(J

I. G. Schroder

(Nuclear Sciences Division)

An analysis of the slow neutron fission resonances in 235

U and

239

Pu

has led not only to a classification of the fission widths into two groups

for each spin value but also to a separation of these resonances into two

groups according to the degree of mass asymmetry of the fragments. All

these measurements though firmly establishing the existence of two resonance groups disagree on the detailed assignment of individual resonances

to each group. Prompted by these ideas many investigators, in recent

years, have looked for a correlation between the emission of long-range

alpha particles (LRA) in fission and some of the observed characteristics

77
NON-RRD NBS PROGRAMS

of the fission process in the slow-neutron resonance region. The many

results obtained do not agree even qualitatively. No detailed measure239

ments exist in the case of Pu, in spite of the fact that this isotope

shows the greatest variation in the degree of mass asymmetry of any

known isotope in the low-neutron energy region, i.e. the mass distribution

peak-to-valley ratio for the 0.297 ev resonance is twice as large as the

ratio for thermal fission. The purpose of the present experiment was therefore to study the possible dependence on neutron energy of the

binary-to-ternary ratio and of the energy distribution of LRA emitted in

239

the low-energy neutron fission of Pu.

To study the characteristics of LRA emission in the subthermal- and

thermal-neutron regions respectively, a beryllium and a quartz filter

(both at liquid nitrogen temperature) were used in conjunction with a mechanical monochromator ; this monochromator was employed to select only

a given portion of the filtered neutron distribution. Lastly a samarium

239 filter was used to isolate the 0.297 eV resonance in Pu. Solid state

detectors were used to detect both alpha-particles and fission fragments.

The relative values of the binary-to-ternary fission ratio were

obtained by taking, in each neutron group, the ratio of half the total

number of fission counts above 45 MeV to the number of counts above 7.5

MeV in the corresponding LRA spectrum. This restriction on the ternary

spectrum was imposed so that no correction would be necessary for the

background present below 7 MeV. The only corrections made were therefore

for the small fluctuations in the reactor-beam intensity. The results

obtained are shown in Table 1. To look for a possible variation in the

energy distribution of the LRA with neutron energy the ratio of the number

of alpha particles above 7.5 MeV to those above 12.5 MeV (in order to

separate the lower energies) was calculated for each of the distributions

obtained in the three intervals measured. The results obtained from this

analysis are shown in Table 2. The errors indicated in both these tables

arise from the small uncertainties in the energy calibration of the LRA

and the statistical error due to counting. As can be seen from these

results no variation is observed in the binary-to-ternary fission ratio

78
NON-RED NBS PROGRAMS

or In the. energy of the LRA for the energy intervals considered to within

the precision of these measurements.

Lastly, as this experiment shows no variation in the relative values

239

of the binary-to-ternary fission ratio in Pu with neutron energy one

can use a reactor beam to determine the value of this quantity. The

problem in making such a measurement is in evaluating the hidden part of

the LRA distribution (Fig. 1). In order to "circumvent this problem the

239 235

LRA distribution of both Pu and U were measured in the same geometry and the known value of the binary-to-ternary fission ratio of the

second was used to normalize the first. The value thus formed was then

compared with those obtained by analyzing the shape of the LRA distribution,

The results of the measurement and subsequent analysis yields a value of

412 ± 11 for the binary-to-ternary fission ratio for the thermal neutron

239 fission of "*Pu.

239

Table 1. Relative values of the binary-to-ternary fission ratio in Pu

in the subthermal-, thermal- and resonance-neutron regions

Neutron energy region

subthermal

thermal

resonance

Binary-to-ternary ratio

(relative)

509 ± 14

514 ± 10

503 ± 12

Table 2. Ratio of long-range a-particles above 7.5 MeV to those above

12.5 MeV in the subthermal-, thermal- and resonance-neutron

fission of Pu.

Neutron energy region

subthermal

thermal

resonance

Ratio

1.29 ± 0.05

1.32 ± 0.04

1.31 ± 0.06

79
NON-RRD NBS PROGRAMS

350

10 20 30 40 50 60 70 80 90 100

CHANNEL NUMBER

Fig. 1. Typical LRA spectrum,

background.

Shaded area represents estimated

80
NON-RRD NBS PROGRAMS

EXTREME-ANGLE EMISSION OF LONG-RANGE ALPHA PARTICLES IN THE

THERMAL NEUTRON FISSION OF 235

U

I. G. Schroder

(Nuclear Sciences Division)

An experiment has been performed in order to seek a correlation

between the kinetic energy of long-range alpha particles emitted at extreme

angles (0°<0<150°) with respect to the line of emission of the light

fission fragments and the kinetic energy of the fission fragments. An

annular surface barrier detector (alpha detector) subtended an angle of

235 ±30° at the target ( U) with respect to a fission fragment detector

placed behind the annular detector. An annular aluminum foil was introduced between the alpha detector and the source. This let through alpha

particles ~ 6 MeV but stopped all fission fragments. A coincidence

circuit (15ns resolving time) demanded coincidence between the two

detectors (Fig. 1). The coincident output from these two detectors were

recorded on a 2-dimensional pulse-height -analyzer. The results obtained

show that extreme-angle alpha particles have higher than average kinetic

energies (Fig. 2A) and rate of emission. This energy distribution is in

good agreement with the extrapolated angle vs. energy data of Carles et

al at Bordeaux (Fig. 3). Furthermore these alpha particles are associated

with fission fragments in the region of minimum kinetic energy (Fig. 2B)

between the light and heavy fission fragments.

81
NON-RRD NBS PROGRAMS

235

u A- DETECTOR

1 1

F- DETECTOR

MM

JX

-\\- | PREAMP

" s\\

PREAMP

w F

Mir

5C/

V7

AMPLIFIER

/

TIMING

SCA

f "Tl

< JG

AMPLIFIER

' f GATE 'i

FAST

COINCIDENCE

'

A (Y) , n

(X) F

DEL/

AMP

X

A NAL.YZ ER ( DELAY

AMP

Fig. 1. Experimental arrangement and associated electronics.

82 •
NON-RRD NBS PROGRAMS

u

CUcw

pq

CO .Ho

•H

4-)

COI8c

coi

ai

S-i 4-1 xv

siNnoo

T3

>>00u

a)P

CU

CU

p,

•H

T3

•HO

C/j

coa) >H

CJ •H

•Uum

ooc

cSI CUIu

4JOoBo

•H

CO

'J) •HE

•a)

4-1

C T3 o a) H 4-1

4-1 CO 2 -H a a h o

j-< en

4-1 CO

CO - cO

CDc

CUeM

03u

4-1CC

•H

CD01

4-1oco

•H

4-)

CO •H

T3

M-lOdo

•H

CO

CO •H

CO£o£

4-) •H

3= T3

a)

4-1 •Hao

CO

COCOGo

•H

4-1 Hn

4-J CO •H

00

CI •Hdoa

encuuuouc

CUM

CUu

Ou

O)

S-i

CO

CUs

Pi

0) ^!. o

PQ

a) l-H

CJ •H

4-J

!-J ai3

00 •H

83
NON-RRD NBS PROGRAMS

•Ud

•Ho

a. T3

•HHO

in# CO

CD

T-ia

•H

4Ju

cda.11a

CD00d

CO1bOdo

iH

M-lO

>>

60U

CDd

CDd

cfl CD6dodo • •H 4-1 CO d

CO CD •H s € •H

CD }-l CO

14-1 ex o X

CD

CD fH 4J bO d d CD

cd CO

CD

d

U o (X

CD CO O 4-) d d

CD CD TJ CO d CD CD J-i ex (X

CD CD o ^ (A*W) D 3 CO

bO

84
NON-RRD NBS PROGRAMS

DEVELOPMENT OF FAST~NEl^RON BEAMS

E. D. McGarry

(Harry Diamond Laboratories, Washington, D.C.)

and

I. G. Schroder

(Nuclear Sciences Division)

A cooperative research program between the Neutron Standards Section, NBS and Harry Diamond Laboratories (HDL) has been initiated to

develop fast-neutron beams for the purposes of

(1) Developing better techniques to measure neutron-energy spectra

in the vicinity of an operating reactor;

(2) Providing beams with known spectra for in situ studies of

damage to electronic components, with the possibility of incorporating

controlled-temperature studies of damage annealing.

A principal feature of the program is to utilize the energy-resolution capability of certain neutron spectrometers to study fast spectra

while circumventing the inherent inability of the spectrometers to operate

in the high gamma backgrounds near reactors. The technique is to scatter

high-flux spectra by selective filtering to obtain a variety of different

energy distributions, collimate the beams, and measure their neutronenergy spectra with high-resolution spectrometers.

HDL is interested in the beams from the standpoint of radiationdamage to electronic materials. Such facilities provide the means to

evaluate the significance of spectral changes to parameters frequently

studied in radiation-damage experiments. Furthermore, it is possible

to examine the capability of neutron dosimeters to monitor the fluence of

interest to the damage studies. In particular, HDL plans to measure

spectral indicies (ratios of foil activities) and determine which of the

indicies are sensitive to differences among measured beam spectra. The

foils can then be used by experimenters to evaluate spectra in or near

pulsed reactors. The ultimate goal is to develop a more definitive

method for quality control of fast-fluence measurements for those

radiation-damage experiments that are plagued by perturbed and unknown

85
NON-RRD NBS PROGRAMS

spectra.

Three features of the fast-neutron beams appear to be of greatest

interest to users. These are: intensity; reproducibility; and credibility

of the measured spectra. Only the second of these is easily obtainable.

The credibility aspect necessarily dictates the early phases of the spectrum-development program, because one must be able to examine the effects

of filtering and scattering to obtain known spectra of any intensity.

The tools for the study are fast-neutron spectrometers which use

either proton-recoil proportional counters or helium-3 gas between

semiconductors detectors. Present efforts involve instrumenting and

calibrating the spectrometers for beam-geometry measurements and fabricating a collimator to extract beams from the immediate vicinity of the fuel

of the NBS reactor during full-power operation. Of particular interest is

the inclusion of an iron filter and titanium scatterer to provide a highpurity beam of 26-keV neutrons. Initially, this monoenergetic beam will

provide a direct check on the energy calibration of the proton-recoil

spectrometer.

86
NON-RRD NBS PROGRAMS

PROTON-RECOIL SPECTROMETER RESEARCH

E. D. McGarry

(Harry Diamond Laboratories, Washington, D.C.)

and

I. G. Schroder

(Nuclear Sciences Division)

In preparation for measurements of fast-neutron spectra of beams

from the NBS reactor, we are studying the voltage pulse-height response

functions from cylindrical proton-recoil counters in well-collimated

beams with known spectra. A natural starting point for this work is to

examine pulse-height distributions from the N(n,p)C reaction in a thermal-neutron beam. In particular, we wish to know the extent to

which pulse-height distributions are distorted because of the truncation

of proton-recoil tracks in the tube walls and because of space-charge

saturation at high gas gains (high voltages)

.

Fig. 1 shows an experimental setup at the thermal column of the NBS

reactor. A beam, 1/4-inch in diameter, is incident upon a proton-recoil

counter positioned perpendicular to the beam. Use of beams smaller than

three-quarters of the inside diameter of the tube minimizes pulse disotortion because of wall effects and essentially eliminates distortions from

the non-uniform electric field in the vicinity of the field tubes at either

end of the anode. The photograph, Fig. 1A, shows a 5/8-inch proton-recoil

tube connected to an aluminum housing for the high-voltage connection and

the signal-coupling capacitor. All these components are mounted on an indexing way (from a lathe) to provide a means of repositioning the tube

to within several mils.

To determine the extent of pulse distortion cause by the non-uniform

electric field along the anode, the tube is moved perpendicular to the

beam, in 1/8-inch increments, from one end of the tube to the other. This

provides an exact determination of the center of the electrically-sensitive

volume. Fig. IB shows the central, next displaced, and final location of

the beam for the experimental results presented in Fig. 2.

The data for Fig. 2 were collected with an applied voltage of

87
NON-RRD NBS PROGRAMS

+2650 volts. The pressure and gas composition are 595 cm (Hg) of hydrogen, 26 cm (Hg) of methane, and 26 cm (Hg) of nitrogen for a total

pressure of 647 cm (Hg) or nearly 8 atmospheres. The best resolution is

4,5 percent and is obtained with the beam positioned to within ±l/16-inch

of the center of the 1.25-inch anode. Fig. 2A and 2B compare the centeredbeam configuration with and without a 0.030-inch thick cadmium filter.

On the average, there are six counts /channel in the higher-energy channels

of Fig. 2B (not visible on the two thousand counts-full-scale eraDhs nf

Fig. 2). Comparing Fig. 2B with the remaining five figures, we see that

the pulse-height distribution in the channels between the main gamma

background (to the left in each figure) and the principal proton peak is

due to protons rather than gamma interactions. The decreased pulseheights are because of truncation in the walls. Even in the case of

Fig. 2A, the area under the distorted distribution is 15% to 20% of the

area under the peak. Notice that there is a shift of the main peak

toward lower energies as the beam nears the region of the field tubes.

However, all the distortion in Fig. 2E and Fig. 2F is not due to the

non-uniformity of the electric field. As the beam is moved toward the

field tubes, there is an increased probability of protons reaching the

insensitive region of gas beyond the ends of the field tubes. This

leakage has the same effect on the pulse-height distribution as truncation

of proton-recoil trancks in the walls of the counter.

Fig. 3 shows variation in the shape of the proton-recoil pulseheight distribution as a function of the applied voltage. In general,

there is a range of 600 volts (from 2300 volts to 2900 volts) over which

14 14 resolution of the ' N(n,p)C proton peak is better than 6%. This range

provides about a factor of 10 difference in the amount of gain available

at the anode. By operating the tube at selected voltages, five or six

overlapping energies energy ranges can be used to span the neutron-energy

range from 10 keV to 100 keV without significant differences in resolution.

88
NON-RRD NBS PROGRAMS

Fig. 1A. A 5/8-inch diameter proton-recoil tube positioned in front of a 1/4-inch diameter collimator in a port of the NBS thermal column,

89
NON-RRD NBS PROGRAMS

(TO1-o

UJ I 2O X o

UJ lil > cs

1- 2

to ..J o o a >

COUJ

CCUJX

0.COO

UJ

or

CO

CO

UJ

ena o 13

4-1 S

00 13

Pi cu #t •H CJ 4-1 S cd c o rH cu J! (X 6

CO CO cu •H a

cu 13 cO 43 iH 3 c <3-

4-1 cu CO 43 •H iH £ T3

•HO 13

X CJ a CJ

a) CO

d

n

13

•H1 c CU 00 o M ^^ u cu iH o 4->

»-l c 4-) a cu CO

CJ

U

13 •H

a)

a <4-l

C cu • o XI A Cj •H !S r-H ^

4-1 CO

O c •v U 43

cu

a 4J CO 6 CO (3

CU cu cu

cu 43 o M > CO o CU cu 43 42 43 CO

CO 4-1 4-1 (3o

CU u-t >. •H X, o i-H 4-1 u

CO <g •HCO

<4-l c O o o Cu •H • o 4-1 4-1 iH

•H CO 43 CO 4J o 00 (3

cd o •H •H .H H '-!-i

CU CU CU o X 43 43 w 4-t 4-1 4-1 M

rH

00

•H

90
NON-RRD NBS PROGRAMS

FIG 2A SPECTRUM WITH 6EAM CENTERED CN THE ! 25 -INCH LONG ANODE OF THE PROTON- RECOIL TURE

FIG 2C SPECTRA WITH BEAM AT CENTER AND WITH BEAM DISPLACED 1/8- INCH TO LEFT

FK3. 28 BACKGROUND SPECTRUM DUE TO GAMMA SPECTRUM OBTAINED

WITH A CADMIUM PLATE BETWEEN BEAM AND PROTON- RECOIL COUNTER

^«' iiai »»

*s -ySvYntJ.

F1G 2D SPECTRA WITH BEAM AT CENTER AND WITH BEAM DISPLACED

1/4 -INCH TO LEFT.

FIG 2E SPECTRA WITH BEAM AT CENTER AND WITH BEAM DISPLACED 3/8-INCH TO LEFT HERE, EDGE OF DISPLACED BEAM SEES THE END OF THE FIELD TUBE

FIG 2F SPECTRA WITH BEAM AT CENTER AND WITH BEAM DISPLACED

1/2 -INCH TO LEFT HERE, DISPLACED BEAM IS CENTERED

ON THE END OF THE FIELD TUBE.

Fig. 2. Pulse-height distribution of the N(p,n)C reaction as a function of the location of the neutron beam along the 1.25-

inch-long anode of a proton-recoil tube . Graphs 2c through

2f have graph 2a, the center anode distirbution, as an overlay.

The peak region of the central distribution is intensified in

all cases for clarity. Graph 2b indicates the insignificance of

the background in the vicinity of the peak.

91
NON-RRD NBS PROGRAMS

\>|' I »t^ »^ll «—S*» +N...W... . .. ^ , «•'

FIG 3A N(n,p)C PULSE-HEIGHT DISTRIBUTION FOR 2000 VOLTS BIAS. -FK3 36 N(n,p)C PULSE—HEIGHT DISTRIBUTION TOR _2350 VOLTS BIAS

FIG ~5C N(n.p)C PULSE-HEIGHT DISTRIBUTION TOR -2650 VOLT BIAS -FIG. 3D N(n,p ) C PULSE-HEIGHT DISTRIBUTION FOR 2800 VOLT BIAS

~(G "3E N(-n,p)C TULSE—HEIGHT _DISTRBUTION "FOR 3100 VOLTS BIAS TIG. "3F TMN( n,p )C PULSE—HEIGHT DISTRIBUTION TOR3300 VOLTS BIAS

Fig. 3. Variation of the recoil proton pulse-height distribution as a function of the applied high voltage. The ionization pulses are

due to protons from the N(n,p)C reaction, induced by a 1/4-

inch beam of thermal neutrons incident on the central region of

the anode.

92
NON-RRD NBS PROGRAMS

PARITY VIOLATION IN NEUTRON CAPTURE GAMMA-RAY EMISSION

J. L. Alberi and R. Wilson

(Harvard University, Cambridge, Mass.)

and

I. G. Schroder

(Nuclear Sciences Division)

Several theories of weak interactions suggest that parity nonconserving effects may be seen in the internucleon force. One such

effect is parity mixing in nuclear states which is due to weak forces

between hadrons which conserve strangeness but violate parity. The fact

-4

that parity violation in nuclei has been found to be of the order of 10

—fi to 10 lends credence to the assumption that this effect arises from the

self interaction of the strangeness conserving and strangness changing

parts of the hadronic current (current x current scheme) . A manifestation of parity mixing in nuclear states is the circular polarization of

neutron capture gamma-rays. As one knows a fully circularly polarized

photon is a superposition of equal amounts of states of opposite. parity.

This follows from the fact that the states with opposite helicity transform into each other under the parity transformation. If one then has

a nucleus decaying through an EL (or ML) transition the presence of

circular polarization requires a small parity non-conserving admixture of

ML (or EL) radiation of the same multipolarity. A search for such parity

113 violating effects has been undertaken by studying the reaction Cd(n,Y)

114

cd.

113 Thermal neutron capture in Cd populates a high-energy capture

state that is 9.04 MeV above the ground state and has angular momentum

and parity (1 ). The transition (9.04 MeV) direct to the ground state

(0 ) and the transition (8.51 MeV) to the first excited state (2 ) are

the gamma rays expected to exhibit parity-violating effects. In both

of these electromagnetic transitions, the predominant parity-allowed

transition is magnetic dipole (Ml) , while any parity-vilating admixture

to the capture-state wave function yields an electric dipole (El) transsit ion, which interferes with the magnetic dipole to produce circularly

93
NON-RRD NBS PROGRAMS

polarized gamma rays. Allowed magnetic transition probabilities are less

2

than allowed electric transition probabilities by (v/c) , where v is the

velocity of the nucleons. The relative amplitudes of the weak and strong

interactions (V ,/V ) is expected to be 10 . The parity-violating

mixture to the capture-state wave function has been calculated to be

2 -50(V , /V J ), and with the enhancement (c/v) noted above, the circular wk str l

polarization is expected to be of the order of 10

An elemental Cd target, placed at the center of one of the tangen113 tial tubes of the NBS reactor provided the source of Cd capture gamma

rays which were collimated by a Bl-Pb collimator designed to view only

the target at the detector. The gamma rays were analyzed by a Compton

transmission polarimeter that converted the circular polarization of the

gamma beam into a count rate change by reversing the polarization of the

electrons in the Si-Fe polarimeter. Gammas were detected with a 4" x 5"

Nal crystal adequately shielded magnetically to prevent any systematic

errors arising from the leakage flux from the polarimeter. The photomultiplier-associated electronics were standard except for the provisions

taken to deal with the high overall count rate (several megahertz) . After

clipping the signal (80 nsec) at the anode of the photomultiplier the

pulses were processed through a dual (fast-slow) discriminator system which

achieved a 5-kHz count note above an 8 neV discriminator threshold.

A digital switching analyzer was designed and built to process the

discriminator output. This analyzer scaled the output of the integral

discriminator and at the same time, correlated the direction of analyzing

magnet polarization. The input was counted by one 70-MHz scaler for the

duration of each counting period, 1 sec, and then added to one of two

registers, depending on the direction of the analyzing magnet polarization.

This method was used to prevent systematic errors arising from the

variation of the deadtime in the two separate scalers. During reversal of

magnet spin polarization, the scaler was gated off to prevent any spurious

inductive effects from the magnetic field. Figure 1 illustrates another

feature of the switching analyzer. ..ather than reversing the electron

polarization in the analyzing magnet in a repetitive square-wave pattern

as shown for L=0, the more complicated pattern shown for L=4 was used.

94
NON-RRD NBS PROGRAMS

All the switching patterns shown in this figure have the ability to cancel

systematic effects due to nonrandom drifts in count rate to the time dependence shown at the right of the figure. Such nonrandom drifts are caused

by temperature fluctuations. However by using the L=4 pattern the effect

of such drifts was less than 5 x 10

Various sources of systematic error were investigated and an upper

limit measured or calculated for them. The possible sources of error arise

from a) the internal bremsstrahlung from the core of the reactor which can

be scattered by the target and which is circularly polarized b) from second

order Compton scattering (J • (k. x kf

) which can influence the count-rate

asymmetry by changing the transmission if the apparatus is not totally

spatially symmetric; c) stray magnetic fields which can induce gain changes

in the photomultiplier and produce a spurious count -rate; d) magnetostriction and self -polarization. Table I gives the upper limits on these

systematic errors. Control runs were taken by replacing the Cd target with one of Ti

which is expected to show no circular polarization. All experimental

procedures were followed as with Cd. The energy threshold was set at

6.3 MeV, i.e., at the peak of the dominant gamma line. This procedure

mimics the rising slope of the Cd energy spectrum. The Ti runs were also

used to measure the amount of internal bremsstrahlung present as this

target was 10 times more sensitive to this effect than Cd. Table II

113

shows the results of the circular polarization experiment on Cd for

two values of discrimator threshold energy as well as the Ti control experiment; the errors quoted are purely statistical. These results are within

the range of the estimates quoted above. As can be seen by comparing

Tables I and II, the statistical errors are much larger than the systematic

errors and hence the latter can be neglected.

The results of the present experiment on the circular polarization

113 of gamma rays from capture of neutrons by Cd agrees both in sign and

magnitude with the asymmetry of gamma rays from the capture of polarized

neutrons measured by Abov for the 9.1 MeV gamma ray. The relative sign

of the asymmetry and circular polarization for the 8.6 MeV and 9.1 MeV

95
NON-RRD NBS PROGRAMS

transitions are opposite. We seem to find that 8.6 MeV gamma rays have

the same sign of circular polarization as the 9.1 MeV gamma rays. The

asymmetries will be opposite; mixing these two gamma rays can result in

no asymmetry when asymmetry experiments are done with a lower bias; this

has been observed by Abov and others.

Table II. Results of main and control experiments.

Bias 6 x 10

-5

113 Cd(n, Y) 114

Cd

113 Cd(n,y) 114

Cd

48Ti(n,Y)49Ti

8.00 MeV

8.50 MeV

6.28 MeV

3.6 ± 0.90

6.3 ± 2.6

0.4 ± 0.6

P

y

x 10

-2T

6.0 ± 1.5

10 ± 4.2

Table I. Upper limits on systematic errors,

1. Internal bremsstrahlung

2. Oex*(k. x k_) Compton term

f

r 3. Stray magnetic field

4. Magnetostriction and self-polarization

6 = (4±6) xlO

<10"7

-7

<7.5 x 10

<10"8

-7

PATTERN ORDER

L =

L = l

L = 2

L= 3

L = 4

lS1

p

U LJ~l

TERMS CANCELLED

t°

t°, t"

t°, t

1 , t 2 jtj u^t',t2 ,t'

injuiJiJiJiJijnj^

7 ig. 1. Switching patterns from zeroeth to fourth order.

96
NON-RRD NBS PROGRAMS

A SEARCH FOR DOUBLY RADIATIVE (N,P) CAPTURE

R. G. Arnold and B. T. Chertok

(American University, Washington, D.C.)

and

I. G. Schroder

(Nuclear Sciences Division)

and

J. L. Alberi

(Harvard University, Cambridge, Mass.)

Following a suggestion by R. J. Adler that the long standing discrepancy (9%) between the measured and the calculated thermal n-p capture

cross sections might be ascribed to capture leading to emission of two

photons, an experiment was performed to search for this mode of decay.

The method used was to look for two gamma-rays emitted in coincidence

from an H„0 target in a beam of thermal neutrons. The spectrum of gammarays from two-photon events is continuous with E + E

9 = 2 MeV and is

expected to be peaked at E. = E-. The phase space of the two-photon

events is schematically represented in Fig. 1A. The experimental conditions were determined primarily by the requirement of detecting gammarays with a broad energy distribution that are in true coincidence admist

a large background of accidental events.

The cross section for doubly radiative (n,p) capture was determined

relative to the cross section for single photon capture by comparing the

singles coincidence counting rate (Fig. IB) with the singles rate for 2.2

MeV capture gamma-rays (Fig. 1A) from the same target. Accidentals were

obtained from the delayed coincidence spectrum (Fig. 1C) , and the

coincident oxygen background was determined by replacing the H„o with

an equivalent D^O target. To reduce the accidental counting rate the

targets used were surrounded by a large isotopically enriched (96%)

Li„CO and a "fast-slow" coincidence configuration (Fig. 2) was employed

using two constant-fraction discriminators and a TAC in the "fast" leg

(1.8 nsec fwhm) and cross-over discriminators in the "slow" leg (2t = 30

nsec) . The energy resolution of the system [Nal] was 5% at 1.3 MeV.

97
NON-RRD NBS PROGRAMS

Analysis of the data obtained in the experiment indicates that

two-photon (n,p) capture events have not been observed. An upper limit

at the three standard deviation confidence level of 0. < 1.0 mb can be

placed on the doubly radiative cross section. Therefore the two photon

cross section does not explain the discrepancy between the experimental

(n,p) capture cross section and the effective range theory prediction.

Since this measurement was completed several new calculations and

predictions have appeared. Two of these new calculations include the

catastrophic pion current which had been omitted in earlier works, and a rescattering current which is in qualitative agreement with the previously

calculated 3-3 resonance contribution. Agreement with experiment is

reported although the question of double counting of resonance and pion

currents carried over from high energy duality leaves the good quantitative

agreement in some doubt. A more complete treatment of the negative energy

parts of the catastrophic pion current is a further question. This is

being examined with two-nucleon negative-energy wave functions.

98
NON-RRD NBS PROGRAMS

*T . :

• '

* .;

/

,i

i ,

— T

\

•».'

*T

;.'•-•/

% *

13NNVH3 U3d SJ.NDO0

43 CU • 4J . 4J TJ 43 > ,4-1 CU 4-1 60

1-1 CU CU • >. 4-1 0) CU 60 CU C

5 4-1 60 CU rH S T3 60 U 60 •H

4-1 J-i S-i rH 60 CU rl CO S-i N

E o ctj 3 CO Ci v© CO CO 4-1 CO H

3 rH rH 4-1 CJ TJ •H • d 4J 4-1 43 E

S-i CU Cu •H cu U rH o 4-1 •H u CU CO 4-1 13 d CO O CN o •H d

cj CO 4= CJ CO CO T3 O CO CN C3 CN IS •H

01 •H 4J e ^ 4-1 & K n E

Cu Cu cu CO CO • CU •H

CO S-I o d 43 60 rH M £3 CU 43 cu PQ ^

O 4J CJ cu CU rH o 43 4-1 X. CN 42

co 4-1 c CO 43 r-i r-i •H 4-1 4-J CJ>

cu cj u o H C 4J 43 TJ rH cu o •4-1 CO 43 E O CJ 43 4J 43 1 CU

t>0 4-1 4-1 o •H 4-1 o •H CO 4-1 •H 4-1 £3 d 0) cj 4= • O u 60 U •H & •H •H •H

•H Tj cu cu CO > 42 U-i CU 4-> & & O E

CO 4-1 4-1 cu Pi 42 Q T~\ S-i CU CU cu d X (3 i-^ d Pn PQ u cu

CO C T3 iH (U •H CO e 4-1 o 60 > rH Tj • e d P 1 cu T3 h-i e cu • 4-1 CU c T3 d S-i d T3 C e CO •H rH 3 ^ , o (3 u 4-1 S-i •H

cd o jz: CO d O rl •H d 4-1 CJ 4-1 P=4 CN u o 4-1 Crt 60 o o cu CJ CJ) 0) 4-1 cu a 4-1 CO -d g CU 5-i cu cu CU II o 4= o O ^ cu u 60 cu CO Cu 'd

cO e 4J S-i 43 TJ CO d ^ CO CO •H d

cu d 14-1 Cu cu CO O rH CJ cu Pu cO

CO u M-l 4*; •H •H CO cO cu CJ CU • 4-1 O CO O CO 42 60 (3 42 CJ £3 CJ E rH H

0) a >. £ cu CU 60 C cu C3 d CJ H

CO cu CU CO 4-1 Cu CO U •H a> cu 'O cu S-i CO Cu CO (-1 CO CO 43 T3 •H T3 4-1 CO d

43 CO d CU cu 5 CU 4-1 •H CJ •H CJ 4-1 o

cu o CO 43 > 43 rH CJ d a CU d •H

CU Cu g 4-1 J-l > H d c C3 •H c Cu cO 60 d 4= CO £ d CU 4-1 •H •H o •H CO 4-J CU o H CU - CO <4-l CJ s cu O a o CO S-i 4-1 S-I 6C O • CO C3 O CJ rH d o cu vjO CO d O T3 CO o d

43 • cu > CU 43 • c •H 4-1 CU 4-1 d a •H

CU 4-1 4= cu a 4-> o CI cu 4J Cu 1^ Cu 'O

a; 4J E co S-i x, CO e CO s •H d CO o 60 CU ^ & 4-1 N o r-\ o CO o rH 5 u cu CN CO 42 o CU •H S-i CU S-i CU •H CO u cO 4-1 rH a CO rH Cu T3 Cu S-i 4-> d

4-1 CO CN1 cu T3 CU d 4-1 rt co TJ

cu a CO CU 42 cu (3 E CU CU cu CU N •H

43 c •H 14-1 CO 4-1 T3 CU U 43 43 43 43 •H CO H CN T3 o ^ CO C •H CO O H H H H rH CU P3 •H X

Pu CJ O

•H O

(3

CU

1-1 CI ?9E

S-i /^ 0) d cu t) 60 •H cu S-i y-—

V

^^v /-"S •-^ S-i cu cd 43 o i—

i

43 C3 CU O cu o 42 U TJ CU o 43

v-^ 4J 4-1 14-1 H •H u CJ u 4-1 ^«-^ v—

^ v—y d 4-1

60

•H

Pu 99
NON-RRD NBS PROGRAMS

Fig. 2. Block diagram of electronics,

100
E, Summary of Reactor Operations

July 1, 1972 to June- 30, 1973 was the best year in the history of the

facility. Performance statistics were also the best in the history of the

facility. Significant among these are an on-line time at power of more

than 80% equivalent to 77% at full power and a fuel burnup rate of more

than 50%. These were accomplished in spite of eight main heat exchanger

leaks, a 4-1/2 day per week summer schedule and a 10-20% reduction in

power during the spring and summer months in order to preserve the heat

exchanger. A summary of operating statistics for this and previous years

are present in the following table.

NBSR Operating Summary

Reactor Operations to date, MWh

Reactor Operations for year, MWh 59,000

Hours Reactor Critical

Number of Days at 10 MW

On-line time at 10 MW

Number of fuel elements used

Average U-235 Burnup

Number of Refueling Operations

Number of Unscheduled Shutdowns

Number of Irradiations

Number of Visitors

Nov. 1969 Oct. 1970 Oct. 1971 July 1972

to to to to

Nov. 1970 Oct. 1971 Oct. 1972 July 1973

i 78,000 124,000 175,000 229,000

fh 59,000 51,000 51,000 67,000

6,000 5,400 5,200 7,000

247 213 214 279

67% 58% 58% 77%

44 24 26 28

34% 48% 45% 52%

11 6 6 7

! 3 10 11 14

1,500 3,000 4,000 4,300

4,000 4,000 3,400 3,000

Aside from the eight heat exchanger leaks, there were no other significant operational difficulties. Seven of the leaks occured in the first

five months of the year. Subsequent reduction in secondary flow of about

20% and plugging of additional tubes that were suspect, reduced the

number of leaks to only one in the remaining seven months. The new stain101
SUMMARY OF REACTOR OPERATIONS

less steel heat exchangers are scheduled to be delivered and installed in

the spring of 1974.

Towards the end of the period there were indications of a possible

small leak in one of the fuel elements in the core. This could result in a future reactor shutdown in order to locate and remove the faulty element

102
F, SERVICE PROGRAMS

Service and irradiation programs again continued at a very high

level. In all, approximately 4,300 irradiations involving 47,000 samples were performed this year. There was also a considerable increase in

sample irradiation times. The irradiations again covered a wide range of

programs. Highlights are presented in following sections.

ACTIVATION ANALYSIS PROGRAM OF THE

FOOD AND DRUG ADMINISTRATION AT THE NBSR

J. T. Tanner and M. H. Friedman

(Food and Drug Administration, Washington, D.C.)

1. Multi-element Analysis of Foods

During the past few years work on mercury has progressed to the point

where its occurrence and distribution in foods have been established.

Interest has been directed lately to other elements which are either

potential or known hazards. These include Se and As. The FDA NAA group

has been working on methods to determine several elements routinely in

food samples.

The first method involves a radiochemical separation by volatilization

of Se, Hg, and As. Once these elements are separated from the food

matrix their radioactivities may be determined to establish their levels

in foods. By developing a rapid radiochemical separation and analysis

method a large number of food samples may be surveyed routinely.

In addition to doing radiochemical analyses, an instrumental method

is being developed to determine elements such as Na, Br, Zn, Co, Sc, Sb

,

and Fe. By using automated counting techniques and computer reduction

of data a large number of samples may be surveyed.

2. MTELMT; A Computer Language For the Reduction of Neutron Activation

Analysis Data

Neutron activation analysis (NAA) data reduction often employs a "custom built" computer program which takes into account the special

requirements of the particular problem and equipment. Consequently there

are many NAA programs written in high level languages such as FORTRAN and

103
SERVICE PROGRAMS ,

ALGOL. However, the flexibility and power of these languages require the

programmer to specify a large number of details, many of which are only of

peripheral interest in solving the problem. If the specification of

peripheral details could be avoided then a program could be written or changed with less effort. The MTELMT language (mnemonic for multi-element)

was written to reduce NAA data while avoiding the need to specify

unnecessary details. In this language the user "talks" to the computer

in a language resembling English and tells it how to reduce the data.

MTELMT consists a number of interacting subroutines written in

FORTRAN V and has been run on the UNIVAC 1108 computer at the National

Bureau of Standards. It is used to reduce gamma or x-ray spectra for

either a single element, or combination of elements. It computes the

micrograms or ppm of the element (s) present, the uncertainty of the

measurement , and for those cases where the amount of the element is below

the sensitivity of the measurements, calculates an upper limit. In

addition, the language can be used to: (1) automatically search a spectrum, find the peaks and output the energies and areas of the peaks,

(2) make linear or semi-logarithic CALCOMP plots and (3) provide an accurate energy calibration.

The language consists of the set of commands given in Table 1.

These commands can be given in any reasonable order. For example, the

order in which FRZDRY and TIMEIN commands are giv°.n is not important.

However, these commands must be given before the ANALYZM command. The

language is set up so that information which is not necessary for data

reduction need not be input. For example, if the sample was not freeze

dried, then;. the FRZDRY command need not be given and the associated correction

would not be made. The language is designed to be as automatic as possible.

Accordingly, the simple command GRAPH1 causes a CALCOMP plot to be made

regardless of how many channels the spectrum contains. Although the grammar

of the language is simple, if a grammatical error is made, a diagnostic

message is printed. For example, if the PRNTEC command is given but

energy calibration information was not input then a diagnostic message

would be printed out.

104
SERVICE PROGRAMS

In summary, with this language NAA data can be reduced easily,

accurately, quickly and reliably while avoiding the need to specify

unnecessary details for data reduction in special cases.

TABLE I. Commands used by MTELMT and their function.

Command Mnemonic Function

CDFRMT

SRCHTP

card format

control

card data

tape data

search tape

FLSKIP file skip

REWIND rewind

GRAPH1 graph

GTITLE graph title

ENCALI energy calibration in

ENCALO energy calibration out

PRNTEC print energy

calibration

RABBIT rabbit no.

STNDRD standard

Specifies format of spectra punched on IBM

cards.

Controls options of other commands.

Reads a spectrum with the format specified

by CDFRMT from IBM cards.

Reads the next spectrum on the magnetic tape

into the computer.

Searches the magnetic tape for the identification

number wanted and then reads spectrum into the

computer.

Moves the tape to the start of the next file.

Rewinds the magnetic tape.

Causes a CAL COMP plot to be made of spectrum

in computer with identification number label.

Words following GTITLE will appear on the CAL

COMP plot made by GRAPHl.

Enables energy calibration information for up

to 20 peaks to be fed into computer.

Prints out the energy for a specified channel

number

.

Prints a complete table of energy vs. channel

number.

Specifies rabbit number of samples being analyzed,

Specified information characterizing the standard,

105
SERVICE PROGRAMS

SAMPLE sample

FRZDRY freeze-dry

TIMEIN time in

INTPRM integration

parameters

ANALYZM analyze in

manual mode

CMPTAC

APKFND

FWHMIN

compute area

and centroids

auto peak

find

full-widthhalf-max in

Specified information characterizing the sample.

Specifies the ratio of dry to wet weight for

materials which have been freeze dried.

Specified counting time and time of day for

samples and standards

Specifies location of peaks and how background is to be subtracted.

Causes a calculation of the centroid and

ppm (or micrograms) to be executed based on parameters fed in by INTPRM, STNDRD, SAMPLE

and TIMEIN.

Computes areas of peaks and centroids based

on the values of parameters fed in by ENCALI

and INTPRM.

Causes computer to search spectrum currently

in memory for peaks and prints out their

centroid, net area, background and estimate

of error in net area.

Specifies estimate of fwhm characterizing

spectra which helps APKFND find peaks more

reliably.

3. An Automated Data Acquisition System For Neutron Activation Analysis

For the past few years the need to analyze large numbers of samples

by neutron activation analysis for a variety of trace elements has increased

to the point where it is no longer feasible to operate an analyzer and

detector for 8 hour periods during the day. A much better approach would

be to have a reliable, automated system which operates 24 hours a day,

7 days a week. This paper describes how such a system was constructed

using commercially available equipment with only slight modification.

The heart of the system is a Nuclear Data 4410 programmable analyzer

(minicomputer) with a 16 K memory. Instructions are given to the analyzer

through a teletypewriter. Data may be received by either the teletype,

magnetic tape, or an X-Y plotter. The magnetic tape system is a PEC 7

track tape which is computer-compatible. A small cassette unit may also

be used but only for loading programs or for the temporary storage of data.

106
SERVICE PROGRAMS

u

ou

uo

T3

o

x:u

>H

[5

<U60c

x:o

E

cc) GO

c*

CD

a) H

X?a

0)

COC

•H

OJ 4JW

toO C

&

C

x:

COu

(DO c

COu

a.e

td

to

o

C

o

U

Pn

•U X=

too •H

Pn

107
SERVICE PROGRAMS

The sample changing is done using a Nuclear Chicago (Model 1185)

automatic gamma sample changer which has been modified to accept a Ge(Li)

detector. This was done by cutting the cabinet in two horizontally, just

below the sample top, and inserting aluminum plate until the desired height was achieved. The internal supports were modified so that the lead

shielding was retained around the top part of the changer but removed at

the bottom to allow room for the detector's Dewar. The detector sits on

a platform which can be rolled in and out of the changer and which can also be raised and lowered to any desired height to allow the detector

geometry to be varied with respect to the sample. While the detector is

in the changer it is retained by spring straps. The changer has a capacity of 200 samples, and solids or.. liquids may be counted individually

or in a mixed sequence. A front and rear view of the sample changer with

the Ge(Li) detector in position is shown in Figure 1.

A control program was developed which, when the proper instructions

are given, will count the sample for a preset time, look at the spectrum,

integrate four preselected peaks of interest and type these areas out

on the teletype, identify the sample by a preselected code number, dump

the entire spectrum onto magnetic tape, erase the memory, change the

sample, and begin the sequence again. In addition, a print-out on the

teletype of the elapsed time from the start of the routine in 0.1 minute

units is given at the beginning and end of each operation to allow

half -life corrections if necessary. The first peak area of interest to

be integrated is checked at regular intervals to ensure that the memory does

not overflow during the counting time. If the count rate is too high,

the sample is rejected, the time counted is printed out, and the sequence

is started on the next sample. If necessary, the data may be further

reduced using a large computer since the complete spectrum is stored

on the magnetic tape.

Using this system it has been possible to operate 24 hours a day for

extended periods of time. The 200 sample capacity also makes weekend

operation practical. The ease of sample handling and ability to recount

samples easily have increased the capability and effectiveness of the

operation without necessitating additional manpower.

108
SERVICE PROGRAMS

THE USE OF NEUTRON ACTIVATION ANALYSIS ON BIOLOGICAL SAMPLES

BY THE VETERANS ADMINISTRATION HOSPITAL

J. C. Smith

(Veterans Administration Hospital, Washington, D. C.)

Human blood serum was analyzed for zinc in an effort to develop an internal reference standard for our laboratory; specifically, pooled

serum was irradiated for one hour (RT-4) . Analysis by the neutron

activation technique was compared with four reported methods using atomic

absorption spectrophotometry. The results are now being compiled for

publication. A project entitled "Trace Element Profiles in Normal and

Neoplastic Prostates", was submitted to the National Prostatic Cancer

Project.

The main purpose of that study was to compare the trace element

profile in cancerous, normal, and hyperplastic prostate tissue using

neutron activation analysis. Unfortunately, this study has not been

initiated due to lack of funding.

TRACE ELEMENTS IN THE ENVIRONMENT

AND* RADIOACTIVE DECAY STUDIES

W. H. Zoller, G. E. Gordon and W. B. Walters

(University of Maryland, College Park, Md.)

During the past year we have been using instrumental neutron

activation analysis (INAA) to determine concentrations of about 20 to 30

trace elements in atmospheric particulate material and, pollution source

materials. This represents a portion of a large project designed to

determine the composition and characteristics of materials released to

the atmosphere by several types of major pollution sources: coal- and

oil-fired power plants, incinerators, motor vehicles, and airport activities.

In connection with these studies we have irradiated and analyzed many of

each of the following types of samples:

109
SERVICE PROGRAMS

a. Atmospheric particulate samples collected in the Baltimore Harbor

Tunnel, at Friendship and National airports, in College Park, and in

rural areas near Washington, D.C.

b. Many types of crude oil and various distillate and residual fractions

from them.

c. Automobile tires, lubricating oils and brake shoes.

d. Municipal incinerator fly ash.

We are now analyzing and interpreting the results of these measurements

to determine the amounts of various trace elements injected into the

atmosphere by the major sources under study. Soon we will begin INAA of

coal and fly ash from a coal-fired power plant and atmospheric samples

collected nearby in the field. We will be also analyzing similar sets of

samples from an oil-fired power plant and a municipal incinerator.

In order to check our INAA procedures for trace-element analyses, we

participated in the NBS-EPA round-robin analyses of the new environmental

standards that were conducted during the latter half of 1972. We turned

in concentration values for about 20 elements in the coal, fly ash and

residual oil standards.

We have continued the analysis and interpretation of atmospheric

particulate samples collected at the South Pole in an effort to determine

world-wide background levels and global transport of trace elements in

the atmosphere. Despite the fact that the particulate loading inVthe

polar atmosphere is orders of magnitude below that of typical urban

areas, meaningful values for the concentrations of about 15 elements can be

measured by INAA. This is accomplished by using filter materials that

have reproducible blank values, collecting particles from enormous volumes

of air (several thousand m ) , taking extreme care in the handling of samples

to prevent contamination, and observing y rays from irradiated samples

with Ge(Li) detectors of high resolution and efficiency. The lowest

measurable atmospheric concentrations were those obtained for Eu, which

3 -15

went as low as 15 f g/m (f g = f emtogram =10 g) , corresponding to about

3

60 atoms/cm ! Mr. John Ondov collected additional samples at Pole Station

during January 1973 and we expect to send about two people from the group

110
SERVICE PROGRAMS

there during the coming summer season at the Pole. In order to seek

possible natural sources of elements observed at the Pole, we are analyzing

filter samples and lava collected near the Icelandic volcano in June, 1973.

Work is currently in progress on the study of the radioactive decay

of

107

Cd,

117

Cd isomers, 105

Ru,

131m

Te, and

161

Gd. In these studies, the

energies, intensities, and coincidence relationships are measured with

high accuracy for the y rays emitted by each radionuclide. The resulting

data are combined to deduce the level structure for the daughter nuclides.

THE USE OF ACTIVATION ANALYSIS IN SCIENTIFIC CRIME DETECTION

BY THE FEDERAL BUREAU OF INVESTIGATION

J. P. Gallagher

(Federal Bureau of Investigation, Washington, D. C.)

The FBI Laboratory has continued to use neutron activation analysis

(NAA) as a method of elemental analysis for major, minor and trace

constituents in materials such as metals, biologicals and plastics. The

qualitative and quantitative measurement of antimony and barium on lifting

mechanisms such as paraffin or cotton removed from the hands of a suspected

shooter is accomplished by NAA.

Research into the effects of various activities on the retention of

antimony and barium is under way. When a firearm is discharged, antimony

and barium, which are components of most primer mixtures, can be deposited

on the hand. Test firings are made and then the subject involves himself in

controlled activities such as being handcuffed, washing and wiping his

hands and placing his hands in his pockets. Another phase of the research

project concerns itself with measuring the concentrations of antimony and

barium on the hand holding the weapon after the passage of time regardless

of the activities the subject Is engaged in. Antimony and barium

determinations by NAA are well-known by law enforcement agencies and they

comprise a significant portion of the cases in which NAA is employed.

Ill
SERVICE PROGRAMS

Plans are being made to purchase a new multichannel analyzer with

data reduction capabilities. This will permit single element analysis to

be conducted more efficiently.

U, S, POSTAL SERVICE ACTIVATION ANALYSIS PROGRAM

J. B. Upton

(U. S. Postal Service, Washington, D. C.)

The U. S. Postal Service is continuing to use neutron activation

analysis as one of its most important and convenient methods of the

elemental analysis. Because it is non-destructive and possesses extremely

sensitive quantitative and qualitative analytical capabilities, NAA is

presently unsurpassed in obtaining trace elemental compositions of evidentuar;

samples. Items of evidence routinely examined by the U. S. Postal Service

Crime Laboratory, utilizing NAA, include paint, metals, safe insulation

and glass.

Presently, the Laboratory is expanding its NAA capabilities and has

acquired a Lithium Drifted - Germanium Detector. Analytical data obtained

from using the new detector has been most helpful in identifying isotopes

that are either short lived or have gamma ray energies that are very close

together.

In one important case involving a mail shipment and loss of a ring of

great value, it became necessary to establish whether or not the sender

had actually shipped the ring in the package mailed. Unused ring boxes

identical to the one the ring was allegedly shipped in were sampled and

analyzed by NAA for their elemental composition. Through Laboratory

testing and comparison of data obtained from the standard boxes with the

analytical results obtained from the questioned ring box, it was clearly

demonstrated that a ring had previously been placed in the box in question.

112
SERVICE PROGRAMS

THE USE OF NEUTRON ACTIVATION ANALYSIS IN

SCIENTIFIC CRIME DETECTION

K . B . Snow

(U. S. Treasury Department, Washington, D. C.)

During FY 73 the Bureau of Alcohol, Tobacco and Firearms used the

NBS reactor facility to perform 406 separate irradiations. These

irradiations involved some 1200 separate criminal cases and over 9100

individual samples.

While the majority of the samples were cotton swabs connected with

gunshot residue detection, other types of materials irradiated included

paint, metal, soil, hair, and narcotics. This wide range of materials

is indicative of the Bureau's continuing interest in the development and

application of neutron activation analysis in the field of criminalists.

ACTIVATION ANALYSIS PROGRAM OF THE U.S. GEOLOGICAL SURVEY

J . J . Rowe

(U. S. Geological Survey, Washington, D.C.)

Using the National Bureau of Standards Reactor, the U.S. Geological

Survey has applied neutron activation analysis and isotope dilution to the

analysis of rocks and minerals for trace constituents in relation to

various geochemical studies.

During the last fiscal year, more than 1,000 samples of soils were

analyzed for arsenic by an isotope dilution method (Brown, Simon and

Greenland, in preparation) to determine background levels of arsenic.

Gold at trace levels is routinely determined using a fire assay

radiochemical method (Rowe and Simon, 1968) . These analyses are part of an ongoing study of the geochemistry of gold related to gold mineralization,

Analyses are made of continental, Hawaiian, Pacific Island arc, Atlantic

Ridge and Icelandic samples. These studies are serving to identify

magnetic sources involved in the formation of geologic features. Extensive

analyses (more than 1,000) have indicated that gold mineralization is

113
SERVICE PROGRAMS

largely determined by geologic, geochemical and geophysical factors

other than the concentration of gold at various places in the mineralizing

system, (Tilling, Gottfried and Rowe, 1973).

Instrumental neutron activation, using a synthetic multielement

standard has been applied to the determination of antimony, tantalum

and hafnium in the U.S. Geological Survey standard rocks (SRG-1, SDC-1,

MAG-1, BHVO-1, QLO-1, RGM-1 , STM-1, SCO-1, G-2 , GSP-1 , AGV-1 and BCR-1)

The standard samples are homogeneous for the three elements determined at

F

95 except for MAG-1 which is homogeneous with respect to antimony and

hafnium at F q__, (Schwarz and Rowe, in press).

Using fire assay radiochemistry, gold was determined in the U.S.G.S.

standard rocks which ranged from 0.4 to, 10 ppb. The standards were

homogeneous for gold, except for SDC-1.

Numerous analyses were performed on samples submitted by geologists.

Some of these were the instrumental neutron activation analysis of samples

of shalerites, galenas, pyrite and chalcopyrite for Mn, Sb, As, Se, Ag,

Au and Hg. Instrumental methods were also applied to the determination

of Th, Ta, Hf , Sc, Cs, Eu and Sb in samples from Hawaii, Montana, Iceland,

and Wyoming. A procedure using post irradiation radiochemistry was applied to the determination of tungsten in various rocks and minerals.

F. W. Brown, F. 0. Simon and L. P. Greenland, "The Isotope-dilution

determination of arsenic in soils (in preparation)

J. J. Rowe and F. 0. Simon, "The Determination of Gold in Geologic

Materials by Neutron Activation Analysis Using Fire Assay for the Radiochemical Separations", U.S. Geological Survey Circular 599.

3 li. J. Schwarz and J. L. Baker, "Gold Content of U.S.G.S. Standard Rocks,

U.S. Geological Survey Prof. Paper 840 3 edited by F. J. Flanagan (in

press)

L. J. Schwarz and J. J. Rowe, "Determination of Antimony, Hafnium, and

Tantalum in the U.S.G.S. Standard Rocks, U.S. Geological Survey Prof.

Paper 840> edited by F. J. Flanagan (in press).

5 R. I. Tilling, D. Gottfried and J. J. Rowe, "Gold Abundance in Igneous

Rocks: Bearing on Gold Mineralization, Econ. Geol. 68_, 168-186 (1973).

114
SERVICE PROGRAMS

COMBINED EFFECTS OF RADIATION AND SHOCK WAVES IN MATERIALS

C. M. Cialella

(Ballistic Research Laboratories, Aberdeen Proving Ground, Md.)

The objective of this study is to determine the influence of lattice

vacancies, formed by neutron irradiation of a solid specimen, on the

subsequent fracture of the solid by shock loading. The purpose of this

study is to harden ABM materials by developing "vacancy getters" which

would quench the vacancies created by the neutron irradiation.

The samples consisted of three single crystals of copper and four

aluminum cylinders with the following dimensions and weights:

a. Cu, 1.137 cm dia. , 2.535 cm long, 22.99 g

b. Cu, 1.103 cm dia., 2.5A1 cm long, 21.74 g

c. Cu, 0.635 cm dia., 2.545 cm long, 7.22 g

d. 1100A1, 1.27 cm dia., 2.54 cm long, 8.7 g

e. 1100A1, 2.53 cm dia., 2.54 cm long, ~ 34.6 g

f. 2024A1, 1.27 cm dia., 2.54 cm long, ~ 9.0 g

g. 2024A1, 2.54 cm dia., 2.54 cm long, 35.8 g

To insure a sufficient number of vacancies to observe their effects

20 2 a total of 10 n/cm was requested.

The samples will be characterized before irradiation, after

irradiation and then following shock loading. A combination of techniques

including optical and electron microscopy, x-ray topography, and stored

energy measurements will be employed to characterize the defect state at

each stage.

The samples have been irradiated and are being prepared for shock

loading and analysis. The results will be reported in next year's

publication.

115
SERVICE PROGRAMS

NEUTRON IRRADIATION OF LPE BUBBLE DOMAIN GARNETS

R. S. Sery and H. R. Irons

(Naval Ordnance Laboratory, Silver Spring, Md.)

Five LPE iron garnets (IG) were irradiated in the NBS reactor to

15 2 15 2

0.4 x 10 n/cm initially, and finally to a total of 2 x 10 n/cm

(y ^ 10 R) , where E > 10 keV. Samples included GdEr-, GdY-, GdYTm-,

GdYYb- and GdYLa- IG's (e.g., Gd

.44

La

0.04

Y

2 .52

Fe

4.01

Ga0.99°12) * ^^

pre- and post irradiation measurements were made for both doses. Properties

measured, percentage errors, and ranges of properties were: characteristic

length, 1 (±10%, 0.5 to 0.9 urn) ; saturation moment, 4ttM (±7%, 120 to

s 170 G); collapse field, H (±5%, 43 to 130 G) ; mobility, UTT (±25%, 120 to

o w 540 cm/Oe sec); anisotropy field, IL. (±10%, 220 to 1470 G)

A pre-irradiation pressure vessel test of the samples - carried out

at 11 psi and 75°C - showed that the properties were not affected by

this simulation of reactor ambient conditions. The subsequent

irradiations indicated that neutron plus gamma irradiation, to the dose

levels reached, had negligible effects on these properties. The fractional

number of vacancies, interstitials and combinations of either is estimated

to be ^ 5 x 10 . This fraction of defects is considered to be too small

to cause significant changes in characteristic properties. Moreover,

the sizes of the radiation induced defects are smaller by orders of

magnitude than- the voids, inclusions and other defects - normally occurring

during fabrication - which interfere with bubble generation and propagation.

CHEMICAL STUDIES ON LUNAR MATERIALS AND METEORITES

E. Anders, R. Ganapathy and J. Morgan

(University of Chicago, Chicago, 111.)

Neutron activation methods were used to determine the abundances

of 20 rare elements that occur on the moon and meteorites in the

range of 10" 9 and 10~12 gram per gram sample. On the basis of this

study the amount of meteor itic materials on the moon was calculated.

116
SERVICE PROGRAMS

In addition it was possible to characterize the chemical composition of

the projectiles that produced major impacts on the moon. The study of meteorites is being expanded- in order to understand

the chemical fractionations which occurred on chondrites. Recent results

indicated that the observed fractionations took place in the solar

nebula rather than on meteoritic parent bodies.

117
G, Staff Roster

u

oa

ft CO

cO >> c H N <u rH O CO 4-1

(1) o u u

CO d CL> O

cd co >>*: u O S co

Pi S > Fn

COo

•H

CO

ftCO

I eno

•u

cu 52

CH >>

CD •; •H O ^ cu cO CJ co c

o

a (0 +j X >-i ft CO o

CO cu cu in too CU 14 !>>

=3 •u 3 CO C a CO o co Pi 4-i cr > •H G cu CU 4-1 toO 3 CO > •H 3 I

a T3

• rH •H >-< •H >-i o CO 3

•-3 CJ> CJ> pn i-J Ph Pi Pi co H

-" J <: o Pi w 1-2 rs < <C

o

O

M

M

PiO

O

o

m

cu •HX

u

m

CLi >. H •u J3 3

u a

cu

*i o

)-i CU »

-!-> >i

!-! ,o

03 c« CJ Pi

. . co s

. . pi H

*

S-i cuu

•H

4-( -u

•-M CO o •He

• o

(3 •H •H 4J e ft TJ 0)

<ti a

0)

•> <*

CU CO

CO «H w w

co m

cu cu O -H

•H ^

> CJ u

cu « CN CO CO O a)

• toOrH

«sf c ^s H •H O

en >-i -H

CU 5s

CDC • •H K

too C • W "-3

K

>^a

cu CO o

t^ fH s M

#t CU H rH c o u rH J*, CU cu o o

4-1 ,C rt N •H CO CO M

•H CJ 3 n IS) -1 £ ,*! M > CO a 1-1 •H too >• o 3

CO CU o cfl M 3 J2 03 ,u Q PQ u o Fn o 5fi •-> CO

# . m # # . • . . Q P-i Pi •"3 O W Pi w >-)

CO

}-i CUa, o

y>o

4-) O

CO<u Pi

4-1 H

3

ft

CU

U-i O

cu •H A X. CU CJ CJC « CU ^ }-l ,n >-l « o

Pi H

. . s fe

« . EH •-)

<^!

cu <;

CO

•> CO 4J S-i iH CU

CO ^

<: m

o ^

cu

CO

CO

cu 0)

c

COE co ft ^!

CO iH ^ -H fQfi WBUUfi

cu •H CU

toO CU ,£3 a x -h

•H O 4-1 Pi CO CO

o

CO

too C

o piS2;wQ<t;KQ ,-)PiPiOpci

cu

4J

4J

COftH

o

u

COo

fts

cu H

118
STAFF ROSTER

NON-RRD NBS STAFF LOCATED AT REACTOR

Division 240.01

P. R. Cassidy

H. E. DeSpain

E. J. Embree

J. J. Shubiak

F

.

Moore

Division 241.05

R. A. Dallatore

J. A. Grundl

I. G. Schroder

A. Fabry (Cen-Sek, Belgium)

Division 313.00

B. Mozer

Division 310.08

D. A. Becker

B. S. Carpenter

L. A. Currie

T. E. Gills

E. S. GjLadney

S. H. Harrison

P. D. LaFleur

S. R. Lantz

R. M. Lindstrom

G. J. Lutz

L. T. McClendon

G. M. Reimer

H. L./ Rook

R. W. Shideler

J. E. Suddueth

GUEST WORKERS AND COLLABORATORS

Division 221.03

H. Marshak

R. J. Soulen, Jr,

D. B. Utton

Division 221.05

R. D. Mountain

H. J. Raveche

Division 232.06

R. D. Deslattes

W. C. Sauder

E. G. Kessler

Division 242.02

L. D. Miller

F. J. Schima

Division 311.03

J. D. Barnes

Division 311.05

B. Dickens

L. W. Schroeder

Division 313.01

C. W. Reimann

Division 313.06

A. D. Mighell

C . S . Brickencamp

Aberdeen Proving Grounds

C. M. Cialella

Argonne National Laboratory

H. Flotow

D. L. Price

Brookhaven National Laboratory

J. L. Alberi

119
STAFF ROSTER

Federal Bureau of Investigation U. S. Geological Survey

D. B. Davies

J. W. Kilty

J. M. Little

G. P. Mahoney

J. P. Riley

Food and Drug Administration

M. Friedman*

R. E. Simpson

J. T. Tanner*

Harry Diamond Laboratory

D. McGarry

Naval Ordnance Laboratory

H. Alperin*

D. I. Gordon

D. A. Kubose

S. J. Pickart*

J. J. Rhyne*

R. S. Sery

R. H. Williams

Naval Research Laboratory

D. J. Bresson

A. C. Ehrlich

G. A. Ferguson

J. Karle

J. H. Konnert

L. F. Paolella*

P. E. Wilkniss

Picatinny Arsenal

C. S. Choi*

H. J. Prask*

R. S. Singh*

S. F. Trevino*

U. S. Atomic Energy Commission

J. C. Glynn

F. W. Brown

R. Finkelman

L . P . Greenland

J . J . Rowe

G. Sellers

F. 0. Simon

U. S. Postal Service

M. Beckman

G. R. Stangohr

J. Upton

U. S. Treasury Department

R. L. Brunelle

P. C. Buscemi

CM. Hoffman

F. A. Lundgren

M. J. Pro

V. A. Hospital

J. Smith

The Ford Motor Company

W. G. Rothschild

American University

R. G. Arnold

B. T. Chertok

R. A. Segnan

R. Simon

D M. Sweger

Carnegie Institute of Washington

L. W. Finger

McGill University

GDonnay

J. D. H. Donnay

R. F. Martin

Temple University

M. Green

V. P. Warkulwiz*

120
STAFF ROSTER

University of Chicago

E. Anders

R. Ganapathy

University of Maryland

J

.

Barker

P. Buhl

R. A. Cahill

T. J. Conry

E. Gladney

C. Glinka

G. E. Gordon

J. Graber

S

.

Harrison

A. Jones

R. Khanna

V. J. Minkiewicz

F. J. Munno

J

.

Ondov

L. Raber

J. Reednick

W. B. Walters

W. H. Zoller

U. S. Naval Academy

C. S. Schneider

*Located full time at Reactor

121
H, Publications

COLLABORATIVE PROGRAMS

BARNES, J. D., "Inelastic Neutron Scattering Study of the "Rotator" Phase

Transition in n-Nonadecane", J. Chem. Phys. 58^, 5193 (1973).

CASELLA, R. C. and TREVINO, S. F. , "Group-Theoretical Selection Rules in

Inelastic Neutron Scattering within the Rigid Molecule Model", Phys.

Rev. B6, 4533 (1972).

CASELLA, R. C. and ROBERTSON, B. , "Direct Tests for Violation of CP

Invariance" (Phys. Rev. Lett., in press).

CHOI, C.S. and ABEL, J.E., "The Crystal Structure of 1,3 ,5 ,7-tetraceto1,3,5,7,-tetrazacyclo-octaine", Acta Cryst. B29 , 651 (1973).

DEGRAAF, L. A., RUSH, J. J. and LIVINGSTON, R. C, "Inelastic Neutron

Scattering", Proa. Symp. 5th3 Grenoble (I.A.E.A. Vienna, 1972), p.

247.

KONNERT, J., KARLE, J. and FERGUSON, G. A., "Crystalline Ordering in

Silicon and Germanum Glasses", Science 179 , 177 (1973).

LEUNG, P. A., RUSH, J. J. and TAYLOR, T. I., "Study of Hindered Rotation

in Crystals by Neutron Transmission Measurements : Comparison of

Calculated and Measured Scattering Cross Sections", J. Chem. Phys.

57_, 175 (1972).

LIVINGSTON, R. C, ROTHSCHILD, W. G. and RUSH, J. J., "Molecular Reorientation in Plastic Crystals: Infrared and Raman Band Shape Analysis

of Neopentane" (J. Chem. Phys., in press).

MAREZIO, M., DERNIER, P. D. and SANTORO, A., "Twinning in Cr-Doped Vo ",

Acta Cryst. (to be published)

MOZER, B. and LENEINDRE, B. L., "Neutron Diffraction Studies of the X

Transition of Liquid ^He at Constant Density", Phys. Rev. A. (to be

published)

MOZER, B., DEGRAAF, L. A., and LENEINDRE, B., "Neutron Diffraction Studies

of Liquid ^He", Phys. Rev. A. (to be published).

MYERS, V. W., "Klein-Gordon Equation for a Charged Particle Interacting

with an Electromagnetic Wave", J. Franklin Inst. 295 , 497 (1973).

PICKART, S. J., ALPERIN, H. A. , HOLTZBERG, F. and MCGUIRE, T. R. , "Magnetic Structures of Eu, Gd S", ATP Conf. Proc, No. 10, 1569 (AIP,

1973).

l x x

122
PUBLICATIONS

PRINCE, E. and FINGER, L. W. , "Use of Constraints on Thermal Motion in

Structure Refinement of Molecules with Librating Side Groups", Aota

Cvyst. B29 , 179 (1973).

PRINCE, E., SCHROEDER, L. W. and RUSH, J. J., "A Constrained Refinement

of the Structure of Durene", Aota Cvyst. B29_, 184 (1973).

PRINCE, E., DONNAY, G. an< ,aRTIN, R. F., "Neutron Diffraction Refinement

of an Ordered Orthoclase Structure", Am. Mineralogist 58_, 500 (1973),

PRINCE, E., MIGHELL, A. D. , REIMANN, C. W. and SANTORO, A., "Hexakis

(Imidazole) Cobalt (II) Nitrate [Co(C_H,N ),2(NO ) ", Cvyst. Stvuot.

Comm. 1, 247 (1972).

6 *

l b J l

RHYNE, J. J., PICKART, S. J. and ALPERIN, H. A., "Direct Observation of an Amorphous Spin Polarization Distribution", Phys. Rev. Lett. 29 , 1562 (1972).

RHYNE, J. J., PICKART, S. J. and ALPERIN, H. A., "Amorphous Spin Polarization in a Tb-Fe Compound", Amovphous Magnetism (Plenum Press,

New York, 1973), p. 373.

ROWE, J. M., RUSH, J. J., DEGRAAF, L. A. and FERGUSON, G. A., "Neutron

Quasielastic Scattering Study of Hydrogen Diffusion in a Single

Crystal of Palladium", Phys. Rev. Lett. 29, 1250 (1972).

ROWE, J. M., HINKS, D. G. , PRICE, D. L. , SUSSMAN, S. and RUSH, J. J.,

"Single Crystal Neutron Diffraction Study of Sodium Cyanide", J.

Chem. Phys. 58, 2039 (1973).

ROWE, J. M., LIVINGSTON, R. C. and RUSH, J. J., "Neutron Quasielastic

Scattering Study of SH~ Reorientation in the Cubic Phases of Cesium

and Rubidium Hydrosulfide", J. Chem. Phys. 58_, 5469 (1973).

ROWE, J. M., RUSH, J. J. and SMITH, H. E., "The 'In-Band' Modes of Vibration of PH _ " (Phys. Rev., in press).

RUSH, J. J., DEGRAAF, L. A. and LIVINGSTON, R. C, "Neutron Scattering

Investigation of the Rotational Dynamics and Phase Transitions in

Sodium and Cesium Hydrosulfides", J. Chem. Phys. 58_, 3439 (1973).

RUSH, J. J., "Study of Large-Amplitude Vibrations in Molecules by

Inelastic Neutron Scattering", Advances in Chem. (to be published).

RUSH, J. J., LIVINGSTON, R. C. and ROSASCO, G. J., "Raman Scattering

Study of Crystal Dynamics and Order-Disorder Transitions in Alkali

Hydrosulf ides" (Solid-State Comm., in press).

SANTORO, A. and MIGHELL, A. D., "Coincidence-site Lattices", Aota Cvyst.

123
PUBLICATIONS

A29 , 171 (1973).

SANTORO, A., "Characterization of Twinning", Acta Cryst. (to be published).

SCHNEIDER, C. S., "Forward Scattering Amplitude of Silicon for Thermal

Neutrons", Rev. Sci. Inst, (to be published).

SINGH, R. S., TREVINO, S. F., and PRASK, H. J., "Long-Wavelength (KM3)

IR Active Phonons of NaHF and KHF", J. Chem. Phys. 58, 4703 (1973).

TREVINO, S. F. and PRASK, H. J., "Neutron Spectroscopy", Progress in

Nuclear Energy3 Chapter 2, Series IX, I_I, (Pergamon Press, Oxford,

1972).

INDEPENDENT PROGRAMS

ARAS, N. K., ZOLLER, W. M. , GORDON, G. E. , LUTZ , G. J., "Instrumental

Photon Activation Analysis of Atmospheric Particulate Mineral,

Anal. Chem. 3 45, 8, 1481 (1973).

ARNOLD, R. G., CHERTOK, B. T. , SCHRODER, I. G. , and ALBERI , J. L. , "Search

for Doubly Radiative np Capture", Phys. Rev. C. (to be published).

BECKER, D. A. and LAFLEUR, P. D., "Characterization of a Neutron Reactor

for Neutron Activation Analysis" (J. Radioanal. Chem., in press).

CARPENTER, B. S., "Lithium Determination by the Nuclear Track Technique"

(J. Radioanal. Chem., in press).

FRIEDMAN, M. H., MILLER, E. and TANNER, J. T., "Instrumental Neutron

Activation Analysis for Mercury in Dogs Administered Methyl Mercury

Chloride: Use of a Low Energy Photon Detector" (Anal. Chem., in

press) .

FRIEDMAN, M. H. , FARBER, M. , and TANNER, J. T., "Instrumental Neutron

Activation Analysis of Bromine in Pig Tissue" (Analytica Chimica

Acta, in press)

GILLS, T. E., and LAFLEUR, P. D., "The Determination of Hafnium in Standard Reference Materials Using Bis (2-ethylhexyl) phosphate (HDEHP)

with Neutron Activation Analysis" (J. Radioanal. Chem., in press).

LAFLEUR, P. D., and THOMPSON, B. A., The Encyclopedia of Chemistry3 3rd

edition, C. Pampel and G. C. Hawley, Editors, Van Nostrand Reinhold,

N. Y., Chapter on Spectroscopy, p. 1030 (1973).

LEFLEUR, P. D., "Biological Matrix Standard Reference Materials for Trace

Element Determinations" (J. Radionanal. Chem., in press).

124
PUBLICATIONS

LAFLEUR, P. D., "Biological Maztrix Standard Reference Materials for

trace Element Determinations" (J. Radioanal. Chem., in press).

LUTZ, G. J., "The Analysis of Biological and Environmental Samples for

Lead by Photon Activation" (J. Radioanal. Chem., in press).

MARGOSIS, M., and TANNER, J., "Determination of Mercury in Pharmaceutical

Products by Neutron Activation Analysis", J. Pharmaceutical Science

61, 936 (1972).

MCCLENDON, L. T., and LAFLEUR, P. D., "Determination of Rare Earths in

Standard Reference Material Glass Using Neutron Activation Analysis

and Reversed-Phase Chromatography" (J. Radioanal. Chem., in press).

REIMER, G. M., WAGNER, G. A. and CARPENTER, B. S., "The Thermal Stability

of Fission Tracks in the Standard Reference Materials Glass Standard

(National Bureau of Standards)" Bad. Effects 15_, p. 272 (1972).

ROOK, H. L., LUTZ, G. J., and LAFLEUR, P. D. , "The Use of a High Efficiency

Mass Separator in Activation Analysis" (J. Radioanal. Chem., in press),

TANNER, J. T., and FRIEDMAN, M. H., "Arsenic and Antimony in Laundry Aids

by Instrumental Neutron Activation Analysis" (Analytica Chimica Acta,

in press)

.

125

NBS-114A (REV. 7-73)

U.S. DEPT. OF COMM. BIBLIOGRAPHIC DATA

SHEET

1. PUBLICATION OR REPORT NO. NBS TN-8132. Gov't Accession

No.

3. Recipient's Accession No.

4. TITLE AND SUBTITLE

NBS Reactor: Summary of Activities July 1972 to

June 1973

5. Publication Date February 1974

6. Performing Organization Code

7. AUTHOR(S)

Robert S. Carter

8. Performing Organ. Report Nc

9. PERFORMING ORGANIZATION NAME AND ADDRESS

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

10. Project/Task/Work Unit No.

11. Contract/Grant Nc

12. Sponsoring Organization Name and Complete Address (Street, City, State, ZIP)

Same as No. 9

13. Type of Report & Period Covered Interim

7/1/72 to 6/30/73

14. Sponsoring Agency Code

15. SUPPLEMENTARY NOTES

16. ABSTRACT (A 2 00- word or less {actual summary of most significant information. If document includes a significant

bibliography or literature survey, mention it here.)

This report summarizes all those programs which depend on the NBS reactor.

It covers the period from July 1972 through June 1973. The programs range

from the use of neutron beams to study the structure and dynamics of

materials through nuclear physics and neutron standards to sample

irradiations for activation analysis, isotope production and radiation

effects studies.

17. KEY WORDS (six to twelve entries; alphabetical order; capitalize only the first letter of the first key word unless a proper name; separated by semicolons)

Activation analysis; crystal structure; diffraction; isotopes; molecular

dynamics; neutron; nuclear reactor; radiation.

18. AVAILABILITY [^Unlimited

1 For Official Distribution. Do Not Release to NTIS

1 Order From Sup. of Doc, U.S. Government Printing Office Washington, D.C. 20402, SD Cat. No. C13

| ] Order From National Technical Information Service (NTIS)

Springfield, Virginia 22151

19. SECURITY CLASS

(THIS REPORT)

UNCLASSIFIED

20. SECURITY CLASS

(THIS PAGE)

UNCLASSIFIED

21. NO. OF PAGES

135

22. Price $1.55

USCOMM-DC 29042-P74

NBS TECHNICAL PUBLICATIONS

PERIODICALS JOURNAL OF RESEARCH reports National Bureau of Standards research and development in physics, mathematics, and chemistry. Comprehensive

scientific papers give complete details of the work,

including laboratory data, experimental procedures,

and theoretical and mathematical analyses. Illustrated with photographs, drawings, and charts. Includes

listings of other NBS papers as issued.

Published in two sections, available separately:

• Physics and Chemistry (Section A)

Papers of interest primarily to scientists working in these fields. This section covers a broad range of physical and chemical research, with major emphasis on standards of physical measurement, fundamental

constants, and properties of matter. Issued six times a year. Annual subscription: Domestic, $17.00; Foreign, $21.25.

• Mathematical Sciences (Section B)

Studies and compilations designed mainly for the mathematician and theoretical physicist. Topics in mathematical statistics, theory of experiment design,

numerical analysis, theoretical physics and chemistry,

logical design and programming of computers and

computer systems. Short numerical tables. Issued quarterly. Annual subscription: Domestic, $9.00; Foreign,

$11.25.

DIMENSIONS, NBS

The best single source of information concerning the Bureau's measurement, research, developmental, co- operative, and publication activities, this monthly

publication is designed for the layman and also for the industry-oriented individual whose daily work

involves intimate contact with science and technology —for engineers, chemists, physicists, research managers, product-development managers, and company

executives. Annual subscription: Domestic, $6.50; Foreign, $8.25.

NONPERIODICALS Applied Mathematics Series. Mathematical tables, manuals, and studies. Building Science Series. Research results, test methods, and performance criteria of building materials, components, systems, and structures. Handbooks. Recommended codes of engineering

and industrial practice (including safety codes) de- veloped in cooperation with interested industries, professional organizations, and regulatory bodies. Special Publications. Proceedings of NBS conferences, bibliographies, annual reports, wall charts, pamphlets, etc. Monographs. Major contributions to the technical

literature on various subjects related to the Bureau's

scientific and technical activities. National Standard Reference Data Series.

NSRDS provides quantitative data on the physical

and chemical properties of materials, compiled from

the world's literature and critically evaluated. Product Standards. Provide requirements for sizes, types, quality, and methods for testing various industrial products. , These standards are developed co- operatively with interested Government and indust^

groups and provide the basis for common understanding of product characteristics for both buyers and

sellers. Their use is voluntary.

Technical Notes. This series consists of communications and reports (covering both other-agency and

NBS-sponsored work) of limited or transitory interest. Federal Information Processing Standards

Publications. This series is the official publication within the Federal Government for information on

standards adopted and promulgated under the Public Law 89-306, and Bureau of the Budget Circular A-86

entitled. Standardization of Data Elements and Codes

in Data Systems.

Consumer Information Series. Practical information, based on NBS research and experience, covering areas of interest to the consumer. Easily understandable language and illustrations provide useful background knowledge for shopping in today's tech- nological marketplace.

BIBLIOGRAPHIC SUBSCRIPTION SERVICES

The following current-awareness and literature-survey bibliographies are issued periodically by the Bureau

:

Cryogenic Data Center Current Awareness Service (Publications and Reports of Interest in Cryogenics).

A literature survey issued weekly. Annual subscription: Domestic, $20.00; foreign, $25.00.

Liquefied Natural Gas. A literature survey issued quarterly. Annual subscription: $20.00. Superconducting Devices and Materials. A literature survey issued quarterly. Annual subscription: $20.00. Send subscription orders and remittances for the preceding bibliographic services to the U.S. Department

of Commerce, National Technical Information Service, Springfield, Va. 22151. Electromagnetic Metrology Current Awareness Service (Abstracts of Selected Articles on Measurement

Techniques and Standards of Electromagnetic Quantities from D-C to Millimeter-Wave Frequencies). Issued monthly. Annual subscription: $100.00 (Special rates for multi-subscriptions). Send subscription order and

remittance to the Electromagnetic Metrology Information Center, Electromagnetics Division, National Bureau

of Standards, Boulder, Colo. 80302. Order NBS publications (except Bibliographic Subscription Services)

from: Superintendent of Documents, Government Printing Office, Washington, D.C. 20402.
U.S. DEPARTMENT OF COMMERCE

National Bureau of Standards

Washington, O.C. 20234

OFFICIAL BUSINESS

Penalty for Private Use. $300

POSTAGE AND FEES PAIO

U.S. DEPARTMENT OF COMMERCE COM-215