/*

eHT OF oo* £

z \

National Bureau of Standards

Library, E-01 Admin. Bldg.

OCT 6 1981

1 SI 1 23

too

NBS TECHNICAL NOTE 860

I0O

.US7S3

H75"

NrtMiffftSBBJI niBBEES SSBB BBBB BSEB Brill

-rr L

rrr t

rrr L

rrr Lrrr rrrr rrrr
NATIONAL BUREAU OF STANDARDS

The National 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 " — 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 and

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 * — 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.

1 Part of the Center for Radiation Research.

:l Located at Boulder. Colorado 80302.

* Part of the Center for Building Technology.
itionai I Standards MAY 5 1975

)£\oo NBS Reactor: Summary of Activities

**?* July 1973 to June 1974

D , i —l —

his

Robert S. Carter

Reactor Radiation Division

Institute for Materials Research

L| ,$, National Bureau of Standards

Washington, D.C. 20234

'T££htf*&aJ nofe r\6. 860

>? °7°*

\

*<"»Mu of

\

(A

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

NATIONAL BUREAU OF STANDARDS, Richard W. Roberts, Director

Issued April 1975
National Bureau of Standards Technical Note 860

Nat. Bur. Stand. (U.S.), Tech. Note 860, 143 pages (Apr. 1975) CODEN: NBTNAE

U.S. GOVERNMENT PRINTING OFFICE

WASHINGTON: 1975

For sale by the Superintendent of Documents, U.S. Government Printing Office, Washington, D.C. 20402 (Order by SD Catalog No. C13.46:860).

Price $2.05
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.

XII
ABSTRACT

This report summarizes all those programs which depend on the NBS

reactor. It covers the period from July 1973 through June 1974. The

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

dynamics of materials through nuclear physics, and neutron standards and

neutron radiography to sample irradiations for activation analysis,

isotope production and radiation effects studies.

Key words: Activation analysis; crystal structure; diffraction; isotopes;

molecular dynamics; neutron; nuclear reactor; radiation;

radiography.

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. Hydrogen Diffusion in a Single Crystal of Tantalum. . . 1

2. Lattice Dynamics of Palladium Deuteride 5

3. Lattice Dynamics of Niobium Deuteride 9

Crystal Dynamics, Phase Transitions and Orientational

Disorder in Ionic and Molecular Solids. 11

1. Alkali Hydrosulf ides 12

2. Ammonium Halides 16

3. Lattice Dynamics of Alkali Cyanides ..... 22

4. Lattice Dynamics (Other) 23

Symmetry Analyses of Neutron Scattering in Crystals

Application of Time-Reversal Symmetry 24

Rigid Rotator Model for KCN, NaCN 25

Neutron Diffraction Study of NaSH and RbSH 26

1. Trigonal Phase of RbSH 27

2. Studies on Phase III of RbSH 28

Dynamics in Simple Liquids 30

Intercomparison of Neutron Dif fractometers 33

Thermal Neutron Flux Measurements . 34

Neutron Radiography 35

Gauge Theories 43

B. RRD-NBS COLLABORATIVE PROGRAMS 44

4 Scattering of Neutrons From He Near the Critical Temperature 44

Neutron Diffraction Measurements of Neon Near Its Critical

Temperature 44

Crystallographic Methods for the Study of Phase Transformations 47

Determination of Lattice Distortions from Simultaneous

Diffraction Effects 50

v
TABLE OF CONTENTS

Page

Hydrogen Bonded Dimers in SnHPO, 52

Atomic Ordering in A-15 Compounds of V-Ni and V-Co Systems. . 53

The Crystal Structure of Lead Deuterium Orthophosphate. ... 55

The Low Temperature Phase of Tantalum Oxide .... 57

C, INTERAGENCY AND UNIVERSITY COLLABORATIVE PROGRAMS 59

Crystal Structure of Diaceto-pentamethylene-tetramine .... 59

Crystal Structure of 1,5 Diaceto-3,7, Dinitro-1,3,5 ,7,

Tetrazacyclo-octane 61

Refinement of the Crystal Structure of Monovalent Metal

Azides 62

The Structure of Deuterium Feroxide 64

The Lattice Dynamics of Deuterium Peroxide 65

Lattice Dynamics of KN_ at 298K .... +—."*. • 67

Polarized Raman Study of Ammonium Perchlorate at Low

Temperatures 69

Sublattice Magnetization of Rare Earth Laves Phase Compounds. 71

Annealed Amorphous TbFe„ 71

Structural Studies on Amorphous Magnetic Alloys ....... 73

Dynamic Spin Behavior in an Amorphous Magnet 75

Small Angle Neutron Scattering From Amorphous Magnets .... 77

Lattice Dynamical Studies of Beryllium at Elevated Temperatures 79

Neutron Scattering From Amorphous Selenium 79

Scattering Amplitudes - Small Angle Scattering. 80

Three Axis Neutron Spectrometer 81

D. NON-RRD NBS PROGRAMS 82

Activation Analysis Section: Summary of Activities 82

1. Research Projects 82

2. Standard Reference Materials (SRM) Analyses 91

3. Cooperative and Service Analyses 95

4. Facilities 97

5. Conclusions 98

Standard Neutron Fields and Integral Reactor Rates 99

Two-keV Filtered Beam 104

vi
TABLE OF CONTENTS

Page

25-keV Filtered Beam 108

Precision Measurement of the Wavelengths of Nuclear Gamma

Lines and the Compton Wavelength of the Electron. . . . 114

E, SUMMARY OF REACTOR OPERATIONS H6

F, SERVICE PROGRAMS 117

The Neutron Activation Analysis Program of the Food and Drug

Administration at the NBSR 117

1. Multielement Analysis of the Total Diet Samples .... 117

2. MULTELMT 119

U.S. Postal Service Activation Analysis Programs 120

Activation Analysis Program of the U.S. Geological Survey . . 121

The Use of Neutron Activation Analysis in Scientific Crime

Detection 122

Lunar Sample Analysis for 17 Trace Elements 123

Trace Elements in the Environment and Radioactive Decay

Studies 124

Trace Elements in Oceanic Floor Rocks 125

Sea and Atmosphere Pollution Studies 126

Phosphorus Content of a Vertebrate Visual Pigment Determined

by Neutron Activation Analysis 126

G, STAFF ROSTER 128

H, PUBLICATIONS 132

vii

A. Reactor Radiation Division Programs

NEUTRON SCATTERING STUDIES OF HYDROGEN IN TRANSITION METALS

New results have been obtained in our continuing studies of the

binding and diffusion of hydrogen isotopes in bcc (refractory) and fee

transition metals. This work is being done in collaboration with

scientists from the Argonne and Oak Ridge National Laboratories. The study

of the microscopic behavior of such metal-hydrogen systems is of con- siderable interest for a variety of reasons including the possible use

of the refractory metals and alloys in nuclear fusion reactors and

hydrogen storage systems and the discovery of superconductivity in palladium alloy hydrides. During the past year we have (1) completed our

first study of the details of the hydrogen diffusion process in a single

crystal of a bcc metal (tantalum) , (2) completed the preparation of a large single crystal of 3-phase PdD

n fi _ and measured the lattice

dynamics of this crystal by coherent neutron scattering—the first such

measurement yet accomplished and (3) we have completed the first measurements in our study of the lattice dynamics in a bcc metal-hydride (a=NbD )

.

The latter two experiments are being analyzed to derive information on

the effects of interestitional hydrogen on the electronic structure and

intermetallic forces in fee and bcc metals.

1. Hydrogen Diffusion in a Single Crystal of Tantalum - J. M. Rowe

J. J. Rush

Analysis has been completed of a detailed neutron quasielastic

scattering study of the diffusion of a defect concentration of hydrogen

in a tantalum single crystal (TaH Q2 ) . This work and the other hydride

studies described below have been carried out in collaboration with H. E.

Flotow of Argonne National Laboratory.

It was clear to us from our own and other previous neutron studies

of hydrogen diffusion in the TaH , VH and other hydride systems using

polycrystalline samples that extending our research to single crystal

samples was highly desirable in order to obtain more detailed information

on the diffusion mechanisms . Such measurements yield a much more extensive data set as a function of crystal orientation and eliminate the

1
REACTOR RADIATION DIVISION PROGRAMS

averaging over crystallite orientations which obscures theoretical analysis of quasielastic scattering results on polycrystals . In the present

experiments neutron spectra (incident E =5 mev", AE =0.26 meV) were

o o measured at 584 K at seven different orientations i> of the single

crystal with respect to the incident beam and over a range of momentum

°-l transfers (Q) from 0.5 to 2.5A

Examples of the symmetrized scattering functions S(Q,uj) in the small

energy transfer region obtained from our measured neutron spectra are shown

in figure 1. In order to test the applicability of the two most probable

simple jump models for hydrogen in Ta , i.e., instantaneous jumps between

near-neighbor octahedral or tetrahedral interstitial sites, we chose first

to fit the detailed shape of the measured quasielastic peaks directly to the

predictions of these models with the residence time t as a parameter.

Both of these models predict a quasielastic scattering peak composed of

a sum of lorentzians with Q-dependent widths and weighting factors depending on the type of occupied sites. It turns out that neither of these

models comes close to providing a satisfactory fit over the entire

set of measured quasielastic peaks. This result is in sharp contrast to our recent study of hydrogen diffusion in a single crystal of (fee)

palladium, in which all the data were fit very well by a model assuming

instantaneous jumps between octahedral sites. On the other hand, we were

able to fit all the observed quasielastic peaks very well to a single

resolution-broadened lorentzian with the width of the lorentzian as a fitting parameter. These fits are shown by the solid lines in figure 1.

Such a result is surprising, since no model involving simple jump

diffusion between octahedral and tetrahedral sites, including o<-»-t and second neighbor jumps predicts such a lineshape dependence.

The unusual nature of our results is further illustrated in Fig. 2,

where the full-widths at half maximum of the observed quasielastic peak

vs. Q (for different values of i>) are shown along with the linewidths

predicted from the octahedral and tetrahedral jump models. It can be

seen that both the linewidths and their variation with shows are quite

different, on the whole, from the predictions of the two models. Most

2
REACTOR RADIATION DIVISION PROGRAMS

«

00in rH 1 CC c

+j 4-1 o

« CD H • >. 4-1 4-» CM ^ 3 X

o O iH cu

• O 4-1 O T3 CC K C cu CU

cO cfl s-l J2 H 4-» •TM\ 01 M X C

O to- 4-> •H

4-t ^-• 4-1 TD 3 a CU

1-4 cu ,£>

• CU CO •H

CO «4-l cu >-i > CO u CJ c Cu CD /—

N

cO 0) <U 3 U >-4 TD

•s 4-J ~CT CD CD N_^ e cu ccj Jtn 3 e

4-> •H T3

CD C rH CU S cu 4-> cd s T3 4-1 iH o H •H e iH U-l oo O

C iw CD CD

•rl o C

s-i CU co

0) en r; •H

4-1 o» H N

4-1 3 4J

CO H ti U CO • CU

id > -£ o

•o rH C i-H (U CO O

N U •H T3 •H <u 4-J CU ^ > CO e

4-1 cu 4-1 cu 0) w C TJ e CU cfl a j-i •H o

p-. o U u

C/0 4-1 o Xi

( m'0)S r'ois
REACTOR RADIATION DIVISION PROGRAMS

30

^=-45° — Oct. — Tet.

•

•

/ /

/

20

^=-15°

/-'""*

Q (A')

Fig. 2. Experimental full widths at half-maximum, w- »«, vs. |Q|

measured for various crystal orientations. Theoretical linewidths for the octahedral and tetrahedral models are also shown,
REACTOR RADIATION DIVISION PROGRAMS

notably the experimental results are much more isotropic than those

predicted by any simple jump model involving these interstitional sites.

We note here that the linewidth values at small 0, which reflect diffusion

behavior over large distances, predict a macroscopic diffusion constant

-5 2 -1

(2.8x10 cm s ) which is in excellent agreement with macroscopic diffusion

measurements using the Gorsky effect. Moreover the mean-square vibration

—2

amplitude (u ) derived from the total quasielastic scattering intensities

°2

is 0.04A , in reasonable agreement with the values given previously in our report on quasielastic scattering by polycrystalline TaH . In

addition, the t values obtained from the "best fits" of the tetrahedral

and octahedral jump models to the data were 1.2 and 1.8 ps respectively,

in good agreement with our previous polycrystal results.

There is no obvious explanation for the lineshapes and isotropic

character of the quasielastic width curves observed in the present experiment. The results could be explained in part by assuming that the interstitial sites occupied by the hydrogen atoms are not well localized.

Clearly more work, both theoretical and experimental, will be necessary

in order to attain a detailed understanding of hydrogen diffusion in

Ta (and in other bcc metals) . Our own measurements on TaH

n n? are being

extended to larger momentum transfers.

2. Lattice Dynamics of Palladium Deuteride - J. M. Rowe and J. J. Rush

In collaboration with H. G. Smith at ORNL, we have measured the

phonon dispersion relations of B-phase PdD- ,_ by coherent inelastic

neutron scattering from a single crystal sample. Apart from our earlier

limited investigation of a-phase PdH_ _ , these results are the first

available for any metallic (non-ionic) hydride, and provide the first

detailed information on the interatomic forces in such systems . The

superconducting transition temperature of this sample is almost certainly

less than 1 K (in contrast to the T 's of ^10 K recently discovered for

c B-phase palladium hydride samples closer to PdH ) but the results may be

valuable in understanding the superconducting behavior at higher concentrations.
REACTOR RADIATION DIVISION PROGRAMS

The sample was prepared by adding high purity deuterium gas to a

12 mm Dx 50 mm long single crystal of palladium. The initial loading

was carried out at temperatures greater than 300 C (necessarily under

high pressure, ^0.6 kbar) to avoid the two-phase region of the phase

diagram. Phonon data were collected at 78, 150, 200 and 295 K. Some

typical phonon groups measured at lected temperatures are shown in

figure 3. Peaks r e to incoherent . mattering (by deuterium) are also indicated. The most important points to be noted are that the centroids of

the groups do not change appreciably as a function of T, while the groups

themselves broaden consider My as T increases, thus indicating strong

anharmonicity. In figure 4 are shown the dispersion relations for PdDn

. p3

obtained from these measurements. Data from different temperatures have

been combined in this figure. The solid lines represent the results of

a 12-parameter least squares fit of a fourth-nearest-neighbor Born-von

Karman model to the data, with third neighbor Pd-D force constants fixed

at zero values. A fit of similar quality can be obtained with a simple

screened shell model. The dotted lines are the dispersion curves measured for pure Pd at 300 K. It can be seen that the PdD_ , acoustic

modes are 20-30% lower than for pure Pd; a result quite consistent with

the observed lattice expansion (^5%)

.

The frequency of the optic modes near the zone centers (figure 4) is

low in comparison with most other hydrides, thus employing a weak nearest

neighbor PdD force constant. This is in general agreement with the

results of incoherent scattering spectra, but the detailed shape of the

vibration frequency distributions derived from the present work are quite

different from those obtained from the incoherent scattering studies. The

dispersion of the longitudinal optic modes is large. Moreover, the fact

that the frequency of the LO mode in the [100] direction reaches a maximum before the zone boundary implies strong second-like neighbor D-D

interactions, comparable to the first like-neighbor Pd-Pd interaction.

The existence of strong effective interactions between second-neighbor

deuterium atoms is an indication that electronic screening effects are important, even though "the present specimen is expected to have I <1 K,
REACTOR RADIATION DIVISION PROGRAMS

c3

o

D

1

1 II

(2,0,2) '

i

"""*• • \ /•

• 295 K

/ •\

• • • 9 ••• /

•

/

•2* \

• *. \

• \••• • >* 1 \ *^220K

• •

1• 1

/

\9\7B K

1 » •

/ \ • •

/ P S. •

Co)

, _L _L

A -x78 k/

\-.>

/

\

(A) v.

8 10 12 7 11 13 15 17

1 .-.! 1 /

• \\ 295 K

•

#x» • s\ -• • \

/ * /

N« 78 K

v..

(-.4,0,2)

(C)

| | |

1.6 2.0 2.4 2.8 7 9 11 FREQUENCY (THz)

13 15 17

am

Fig. 3. Selected phonon groups at several temperatures in PdD,, , ., . The

U . J arrow in part (d) indicates an incoherent peak due to the flat

TO modes.

7
REACTOR RADIATION DIVISION PROGRAMS

17

IS

15

14

13

12

II ~ 10 x— O > 9

o

UJ

UJ

triv 7

6

5 K

i—i—

r

[100]

l—i—

r

CM03

T/* J /

LUG

o a o = •

>

I 1 1 0.2 0.4 0.6 08 1.0 0.8 0.6 0.4 0.2 0.1 0.2 0.3 0.4 0.5

£ = aq/2 77-

Fig. 4. Phonon dispersion curves in PdD„ , . The solid curves are

U ,o 5

calculated based on a Born-von Karman model with twelve parameters

The solid (open) symbols are phonon groups obtained at 150°K

(295°K) . The dotted curves are the dispersion curves observed

for pure Pd at 300 K.

8
REACTOR RADIATION DIVISION PROGRAMS

We are currently testing deuterium loading procedures to try to

produce a

?, high" T (> 4 K) single crystal sample of Pd - q) which would

allow us to study the crystal dynamics, electronic structure and an- harmonic effects of the superconducting hydride closer to stiochiometry.

Experiments are also in progress to remeasure the incoherent inelastic

scattering spectra for the PdH and PdD at small momentum transfers, for

comparison with the frequency distributions derived from our dispersion

curve results.

3. Lattice Dynamics of Niobium Deuteride - J. M. Rowe, N. Vagelatos and

J. J. Rush

Following up on our work on PdD , discussed above, we have established a program to measure the lattice dynamics of a-phase bcc metal

deuterides (we use deuterium to minimize the incoherent scattering) . The

first step in this program is to measure for low concentrations and we

have now completed measurements of the phonon dispersion relation in

NbD . _ in the three major symmetry directions at 473 K. The sample must

be maintained at temperatures above 200 °C in order to avoid the two-phase

(a+3) region and thus prevent destruction of the single crystal sample.

For a direct comparison, we have also measured pure Nb at 473 K - our results at this temperature are in good agreement with the trends established in earlier work by the Chalk River group on the temperature depend- ence of phonon frequencies in pure Nb

.

In an attempt to establish the effects of adding deuterium to Nb, we have fitted both the Nb and NbD . _ to several different models ineluding interplanar force constants , the double shell model used by

Weber and Bilz to explain the lattice dynamics of transition metal

carbides and Nb-Mo alloys , and to a sixth neighbor Born-von Karman model

with general forces. For all of these models, we observe that the effective range of the forces decreases only slightly for the NbD ..,., suggesting that the dynamics are still dominated by long range metallic

forces. These general observations are in accord with the results of

Powell, Martel and Woods on Nb-Mo alloys. Therefore, we have compared

our results for the difference between NbD 1 ^ and Nb phonon frequencies

9
REACTOR RADIATION DIVISION PROGRAMS

in the three symmetry directions with the same quantity for the Nb

.85

Mo - - alloy measured by Powell ct at., as determined from the interplanar

force constants given in their paper (this model fits the data very well)

This comparison is shown in figure 5 . The two results should agree if one could interpret the addition of D to Nb in terms of a simple filling

of the electronic band states of pure Nb by the extra electrons of the

deuterium, ad the rigid band model works well for the Nb-Mo alloys.

From the results in the figure, this is an obvious over-simplification

for the NbD .^ alloy. There are several possible reasons for the differences shown in figure 5, including the effects of local strain, Nb-H

4

2

-2

4

2

-2

4

2

-2

. [ooi]t

# • • • #

#€Nb85 Mo

l5~ €Nb

- [|0 °] L °

€

NbD, "€Nb

.ID

" • _ 0.5 1.0

0.5 1.0 -o— O U"° o

u o

0.5 1.0

>

E

- [M0]T2

-.«*999829S?

- [" 0] L • • • •••o°o° o

< 0.5 0.5

- [mo]t

•••••••••

o _ o • • '• o ° o o o

- [IH]L

- ft 8 o o o

0.5 1.0

_ 0.5 1.0

Fig. 5. Differences in phonon energies between pure Nb and NbD _ and

Nb oc Mo 1C.. (NbDn

- C -Nb) vali

Mo ,,.-Nb) values are at 21°C.

(NbDn , C -Nb) values are at 200°C at the Nb A oc U .Ij U

.

oj

.15

10
REACTOR RADIATION DIVISION PROGRAMS

interactions, perturbation of the Nb bands by the interstitial deuterium,

lattice parameter changes, D-D interactions or temperature effects

(Nb „_ Mo _c has only been measured at 293 K) . Further analysis will be

needed to establish which, if any, of the above factors is dominant.

We are presently preparing higher concentration alloys of NbD in

order to explore the effects of t)-d interactions.

CRYSTAL DYNAMICS, PHASE TRANSITIONS AND ORIENTATIONAL

DISORDER IN IONIC AND MOLECULAR SOLIDS

Work has continued on our program to study the details of orderdisorder phase transitions, interatomic forces and rotational behavior

in prototype crystals by a combination of neutron scattering and optical

spectroscopic techniques.

The precise nature of the orientational disorder in the hightemperature phases of broad classes of inorganic and organic materials

is not generally well understood, nor is the microscopic basis of the

changes in physical and thermodynamic properties associated with these

order-disorder transitions. During the past year we have completed

the analysis of neutron quasielastic scattering studies of orientational

disorder in a single crystal of NH.Br, and in polycrystalline RbSH in

its trigonal phase. This work is also aimed at demonstrating and refining

the application of the nqs method to the study of dynamical disorder in

such systems. Some progress has also been made in a neutron diffraction

study of the alkali hydrosulf ides , which is discussed in another section

of this report. In addition we have completed the first coherent neutron

scattering measurements of the lattice dynamics of an ammonium halide

single crystal in the high temperature (fee) phase and have extended our optical and neutron scattering investigation of alkali cyanide crystals.

Much of this work has been carried out in collaboration with Argonne

National Laboratory.

11
REACTOR RADIATION DIVISION PROGRAMS

1. Alkali Hydrosulf ides - J. J. Rush, J. M. Rowe, R. C. Livingston

a. Quasielastic Scattering Study of Trigonal RbSH

We have completed a study of details of the dynamical disorder of

the SH ions in the intermediate trigonal phase of RbSH by quasielastic

neutron scattering. This is the first neutron scattering study of orientational disorder in a low-temperature phase of such a crystal.

*Ot

Fig. 1. Composite of the suggested crystal structures of RbSH. In the

trigonal phase (dashed lines) one of the body diagonals of the

original fee cubic structure is shortened. Rb, 9; S, O; 1/2 H,'

12
REACTOR RADIATION DIVISION PROGRAMS

The experiments were carried out on a sample of RbSH whose synthesis

has been described previously, using a 5 meV neutron beam with an instrumental resolution of 0.25 meV = 0.40 ps~ (FWHM) . Time-of-flight

neutron spectra were measured for the sample and a blank at 373 and

393 K (below the cubic «-* trigonal transition at «403°K) over a range

of scattering angles from 5 to 120°.

The structure of RbSH in both the high temperature fee phase and

the intermediate trigonal phase is shown in Fig. 1. The alignment of

(SH) ions (along the trigonal axis) shown in the figure is that deduced

in our previous neutron diffraction study of isomorphous NaSH. This

trigonal axis is closely related to a [111] axis in the fee phase. For

the simple case of instantaneous SH ion jump reorientation between

only two sites (in this case 180° flips, presumably along the trigonal

axis as shown in figure 1, it can be shown that the symmetrized quasielastic

scattering function is given by

S(Q,u>) = I V

[C o (0)6 (to) + C

1 (Q) L(w)],

where a is the mean-square hydrogen vibration amplitude, Q = momentum

transfer/*, u = energy transfer/*, C = [1+ . (QR)]/2 and C

± = ]l-j (QR)]/2 are the elastic and quasielastic (lorentzian) intensity factors • R = distance between H sites (twice the S-H bond distance = 2.70A). The

single lorentzian component of the predicted scattering law is given by:

T

U

2+(2/t) 2

where t is the residence time.

In order to test this two-site jump model we have fitted our experimental results to the above scattering law experssion (broadened by the

measured Gaussian resolution functions) as well as to several other

models involving random orientation among the [100], [110] or [111] directions in the pseudocubic trigonal structure. Several examples of the

experimental scattering laws obtained from our neutron spectra are shown

in figure 2, along with the results of the fit to the two-site jump model.

In figure 3 the ratio of pure elastic to total intensity in the quasielastic

13
REACTOR RADIATION DIVISION PROGRAMS

COH

>-<

GO<

o

CO

1.0

0.5

0.4

0.2

0.3

0.2

0.1

RbSH 393K r = 4.0ps

Q=0.80A"'

C =0.766

»ii «

r- Q = I.93AH

C =0.355

Q=2.34A_I C =0.393

FREQUENCY TRANSFER w(ps"')

Fig. 2. Examples of the experimental quasielastic peaks for RbSH.

The solid curves and elastic intensity factors C represents

the best fits to the observed peaks using the two-site jump

model. The dashed line curves are the lorentzian components

derived from the same fit.

14
REACTOR RADIATION DIVISION PROGRAMS

peaks derived from the experimental results are plotted vs. Q. Also

shown are the predicted intensities for the two-site model and for an eight

site model involving random reorientation among all possible directions

along the four body diagonal of the pseudo cubic cell (Fig. 1). From

OO —i r RbSH

• 373K,t =5.3 ps

o 393 K,t =4.0ps

Fig. 3. Pure elastic to total intensity ratios vs. of the observed

quasielastic peaks for RbSH. Also shown are the predicted

behavior for the two-site jump reorientation model (solid line)

and an eight-site model involving random reorientation among

the eight possible directions along the four body diagonals of

the pseudocubic cell (figure 1)

.

15
REACTOR RADIATION DIVISION PROGRAMS

these figures it can be seen that the measured results are in reasonable

agreement with the predictions of the two-site model, while the eight

position model is obviously in serious disagreement. In fact on other

reorientation model (free rotation, rotational diffusion, isotropic

planar reorientation or jumps between more than two sites) could predict

the observed behavior for the elastic component. The lack of a perfect

fit could be due to several factors , including uncertainty in the S-H

direction and the possibility of occasional orientation of the ions along

other directions in the trigonal cell. The x values derived from the

two-site model fits at 373 and 393 K are 5.3±0.A and 4.0±0.4 ps,

respectively. These values are an order of magnitude larger than those

reported previously in our neutron study of the fee phase of RbSH. Thus

a comparison of these and previous results shows that the high temperature

transition in this crystal involves a change from a two fold dynamic

disorder of the SH ions in the trigonal phase to a much faster (t^0.5 ps)

reorientation among at least six equilibrium orientations in the cubic

phase

.

From the present results we have also derived values for the hydrogen

°2

mean-square amplitudes (a) of 0.17 and .19A at 373 and 393 K, and (assuming a classically activated process) an activation energy for reorientation

of 17±4 KJ/mol on the trigonal phase.

2. Ammonium Halides - J. M. Rowe, N. Vagelatos , J. J. Rush, R. C

Livingston

a. Quasielastic Scattering in a Single Crystal of NH.Br

The analysis of the results of a quasielastic neutron scattering

study of the mechanism of ammonium ion reorientations in a single crystal

of NH.Br in the disordered CsCl phase has been completed. The aim of

this investigation was both to establish the reorientation mechanism

and to elucidate the advantage of single crystal measurements in detailed

neutron studies of orientational disorder in solids. The potential advantages of single crystal samples in the study of molecular reorientations

16
REACTOR RADIATION DIVISION PROGRAMS

are similar to those mentioned previously for metal hydride studies, i.e.,

such measurements avoid the average over crystallite orientation which

obscures polycrystalline results and provides a richer, more comprehensive

data set as a function of crystal orientation.

It has been established by previous neutron diffraction and NMR

studied that in the disordered CsCl phase of NH.Br (and NH.C1 and NH.I)

that the NH, ions in each unit cell are reorienting between two equilibrium positions so that the N-H bonds are directed at random along

the [111] directions of the crystal. This dynamic disorder must involve

either 90° jumps around the two-fold (C_) axis of the (HN . ) ions or a combination of reorientations around the two and threefold (C.,) axes. The derivation of neutron cross-section (scattering law) expressions

which describe the quasielastic spectra for reorientation around two and

(or) three-fold axes of the H , ions, assuming instantaneous jumps, is

straightforward, but will not be presented here. These expressions again

predict a quasielastic peak (with both a purely elastic component and a broadened component comprised of a sum of lorentzians) whose shape as a function of Q is dependent on the distance between equilibrium proton

sites and t

? (t^), the average time that a proton stays at a site before

+

jumping to a new site by an NH, reorientation around a twofold (threefold) axis. Examples of the scattering laws S (Q,w) obtained from experin mental cross sections measured for a single crystal of NH.Br (incident

E = 5 meV, FWHM =0.26 meV) as a function of momentum (Q) and energy

(hw) transfer and crystal orientation (ty) are shown in figure 4. The first

approach used in fitting the extensive data set provided by our singlecrystal experiment was to fit the measured scattering laws to a model

allowing random reorientations around both C and C. axes, with associated residence times t„ and t . t„ and t„ were varied using a nonlinear

least squares program. The "best fit" in each fitting attempt resulted

in x values with i3>>T2» thus providing strong evidence for a model

involving only C_(90°) reorientations. Further variations in the fitting

procedures were tried, including separate fits assuming pure C„ and C„

reorientations. The best fit values of x« obtained in this case were

17
REACTOR RADIATION DIVISION PROGRAMS

+'0* ., \ 0=2.5A' f

0.0

\\

008

006

0.01

002 y V

+*24\

Q'2.5A'

010

0.0B

006 A 004

002 A

^•/v

v_

Aps-) j(ps"' w (pS"' u(ps-)

Fig. 4. Examples of the experimental scattering laws plotted vs. w for

NH/ Br at several crystal orientations (i|;) and momentum transfers. The solid lines are the "theoretical" S(Q,w)'s (resolution-broadened) obtained by fitting to a model assuming re- orientations around the C_ axis, while the dashed lines show

the lorentzian components derived from the fit.

18
REACTOR RADIATION DIVISION PROGRAMS

equal for all different crystal orientations to within the fitting errors,

whereas t_ values varied by a factor of two for various orientations

again giving strong evidence for C» reorientations. Finally we applied

2 a x test for statistical significance which showed that the difference

in the fits obtained for the C- and C„ models was significant at the

*0.5% level.

The extensive fitting and analysis outlined above shows conclusively

that the dominent reorientation mechanism in the CsCl phase of NH Br is

by instantaneous 90° jumps about the C„ axes, although a small ad-mixture

of C~ jumps cannot be ruled out. The t value derived from the. fitting

procedure is 3.2±0.4 ps at 373 K, which is consistent with the corr- lation time of ^2.5 ps predicted by extrapolation of NMR results. It

should be particularly noted that the statistical reliability of this

result is directly due to the large amount of data available for testing

the hypotheses, and that this in turn shows that single crystal samples

are essential (except for very simple cases) for the precise determination

of reorientation mechanisms using neutron quasielastic scattering.

Our measurements and analyses will next be extended to a single

crystal study of NH . I in its high temperature fee phase. Little detailed

information is available on the more complex orientational disorder in

the phase of the ammonium halides and in analogous phases of a wide range

of molecular crystals.

b. Lattice Dynamics of Ammonium Iodide

As a result of our continuing interest in the lattice dynamics of

orientationally disordered crystals and in view of the difficulties

encountered in the alkali cyanide measurements, a study of the phonon

dispersion relations in deuteroammonium iodide has been undertaken.

Additional interest was generated by the fact that ammonium iodide has a different crystal structure at room temperature than the ammonium halides

12 3 studied thus far by coherent inelastic neutron scattering . At room

temperature both NH.C1 and NH.Br (ND.C1 and ND.Br) crystallize with the

4 4 4 4

CsCl structure, where it is relatively easy to visualize the possible

19
REACTOR RADIATION DIVISION PROGRAMS

orientations of the tetrahedral NH (ND.) ions in the CsCl lattice

4 sites . Under the same conditions NH.I (ND.I) has the NaCl structure + +

4 4

where NH, (ND.) ions occupy sites of octahedral symmetry and their

5 orientations are not at all obvious . 3 Single crystals of ND^I (up to 2x2xlcm ) suitable for inelastic

neutron scattering measurements have been grown by slow evaporation under

controlled conditions from D~0 solutions of deuterated ammonium iodide

doped with urea. Deuteration of the NH.I + urea was accomplished by

several H-D exchanges consisting of dissolving the hydrogenous or partly deuterated granular mixture in D

? 0, allowing the H-D exchange to

reach equilibrium, and evaporating the solvent. 6-7 such exchanges re- sulted in approximately 99% deuteration of the ammonium iodide-urea

mixture

.

Dispersion curves for phonons propagating in the high symmetry

directions in ND.I at room temperature have been measured by coherent

inelastic neutron scattering using the triple axis spectrometer. The

results of these measurements are shown in figure 5. Acoustic phonons were well defined, the uncertainties in individual frequencies generally

being 1-3%. Optic phonons were considerably more difficult to measure

because of the necessarily worse resolution conditions under which these

measurements were performed and the relatively low signal to background

ratio due to the deuterium incoherent and multiphonon "background."

This difficulty is reflected in the larger errors assigned to these phonons.

Intensity and resolution limitations precluded the observation of the

highest frequency LO phonons, (i.e. near the Brillouin zone center) and

the entire L0[111] branch. No attempt was made to investigate the

rotational or librational modes by the triple axis method. It is interesting, however, that optical translatory modes as well as acoustic modes

near the zone boundary were observed for ND.I which were difficult or impossible to observe in the equivalent phase of the alkali cyanide crystals,

At the present time, the rotational modes are being studied by the

time-of-flight technique. The triple axis and time-of-flight data will

be analyzed in terms of theoretical models, e.g. the shell model, which

20
REACTOR RADIATION DIVISION PROGRAMS

have been previously used to analyze the phonon dispersion relations of

other ammonium halides. We also intend to study the phonon dispersion

curves of ND,I temperatures close to the NaCl-»-CsCl phase transition.

In addition, the neutron quasielastic scattering from this crystal will

be measured in order to obtain information about the orientational

disorder of ND. ions in the fee lattice and the rate of reorientation

4

between energetically equivalent orientations.

25

20

-I—I—I—I—I—I—i—

r

$

-i 1 1 1 r

NDJ4

|

15-.•4 *

w

10

0.

•T

o o

A *.!•

i i r

o •

1 '

fi

•T2 OL

AT,

° ° rs ° A A

° A A o O

• Ao

••4

a.

•T

OL

25

20

15

10

o° I

O m

I l l 05

[ooc]

10 0.5

[UO]

05

[CU]

REDUCED WAVE VECTOR COORDINATE^

Fig. 5. Phonon dispersion curves measured for ND.I at 293°K.

Smith, H. G., J. G. Traylor, W. Reichardt, Phys. Rev. 181 1218 (1969)

Teh, H. C, B. N. Brockhouse, Phys. Rev. 8B, 3928 (1973).

Yamada, Y. , Y. Noda, J. D. Axe, G. Shirane, Phys. Rev. 9B_ 4429 (1974)

Levy, H. A., S. W. Peterson, J. Chem. Phys. 21_, 366 (1953).

Levy, H. A., S. W. Peterson, J. Chem. Phys. 75_, 1536 (1953).

21
REACTOR RADIATION DIVISION PROGRAMS

3. Lattice Dynamics of Alkali Cyanides - J. M. Rove , J. J. Rush,

N. Vagelatos

New results have been obtained in investigation of phonons in the

orientationally disordered room temperature phase (NaCl structure) of

KCN and NaCN in collaboration with D. L. Price of Argonne National

Laboratory. In this study use has been made of both the coherent inelastic neutron scattering and infrared reflection techniques.

The neutron measurements, mainly of phonons propagating in the [001]

symmetry direction, were performed on large single crystal samples prepared at ANL. Well defined neutron groups were observed corresponding

to low frequency acoustic phonons, i.e. near the center (T point) of the

Brillouin zone. They became progressively less well defined away from

the zone center and especially near the zone boundary. In general, it

appears that phonons are better defined in NaCN. No optic phonons were definitively assigned in either crystal by the neutron technique.

Infrared reflection spectra for NaCN and KCN were also measured

from polycrystalline pellets, using the IMR Central Raman-IR facility.

As is generally the case, the observed maximum reflectance was sensitive

to the pellet surface. The KCN spectrum consisted of a single well

defined band which, when analyzed in terms of a single classical damped

oscillator model, yielded: TO(D=13'/±5cm~ and LO(r)=225±20cm~ . No

clear evidence of a TO mode in the above frequency region was observable

by the neutron technique. The NaCN reflection spectra were not as intense

or as well defined as those of KCN and similar analysis was not performed.

The apparent reasons for the difficulties encountered in the inelastic neutron scattering measurements are the very low signal to back-

-2W

ground ratio, the low Debye-Waller factor (e ), and the coupling between

the rotations and the translational modes (see also the summary of theoretical work on these systems by R. Casella in this report) . The background was high because of the incoherent scattering (NaCN) , multiphonon

and quasielastic contributions. The Debye-Waller factor is low because

of the large thermal displacements of both the metal and CN ions, which

limits the Q-space accessible for the measurements. The rotation22
REACTOR RADIATION DIVISION PROGRAMS

translation coupling shortens the phonon lifetimes and thus broadens

the scattered neutron groups. Such effects can also be expected to

influence the dynamics of a wide variety of other complex crystals

exhibiting orientational disorder. Any one of the above factors could

make the observation of phonons difficult. All three appear to con- tribute in the NaCN, KCN measurememts . Further analysis and measurements

at lower temperatures KCN are planned.

4. Lattice Dynamics (Other)

a. CdTe - J. M. Rowe

In collaboration with D. L. Price, Argonne National Laboratory, Ken

Zanio, Hughes Research Corporation and R. M. Nicklow, Oak Ridge National

Laboratory, we have measured the lattice dynamics of a single crystal of

CdTe. Because of the large neutron absorption of the naturally occurring

isotopic mixture of Cd, the crystal was specially grown from a sample

114 enriched in Cd , a relatively non-absorbing isotope. Even after this

enrichment, the absorption cross-section of the sample was more than 100

barns for thermal neutrons, so that the measurements were quite difficult

and could only have been done at a very high flux reactor (the HFIR, ORNL)

.

The results for CdTe complete the isolectronic series a-Sn, InSb and

CdTe (Agl cannot be obtained in the zincblende structure) , allowing a detailed study of the effects of increasing ionicity and band gap with

all other parameters nearly constant. (Note that a-Sn has p zero direct

band gap.) It is hoped that the availability of such complete and detailed

results will stimulate renewed theoretical efforts to understand the

lattice dynamics of zincblende semiconductors on a sound microscopic basis.

23
REACTOR RADIATION DIVISION PROGRAMS

SYMMETRY ANALYSES OF NEUTRON SCATTERING IN CRYSTALSAPPLICATION OF TIME-REVERSAL SYMMETRY

R. C. Casella

It is well known that the number of independent parameters in the

phonon dynamical matrix C(k) can be reduced by accounting for crystal

symmetry. Moreover, although time reversal symmetry T is known to be

broken in certain weak mesonic decays , no evidence exists which would

invalidate this principle in the electromagnetic interactions responsible

for chemical binding. Hence, we may assume its validity when treating

the phonon spectrum of solids as determined by neutron scattering.

Based upon the classic Wigner-Herring work in this field, I have

derived an algorithm for computing the number of independent real

parameters in C(k) for an arbitrary space group when all space-time

symmetries are taken into account

.

The application of T invariance to phonons has been discussed by

2 Maradudin and Vosko and recently by Warren . My interest was motivated

by discussions with M. Rowe who has indicated that programs for reducing

the dynamical matrix, which have as their basis the Warren analysis,

appear to contain inherent inconsistencies . I have taken an independent

approach from that of Maradudin-Vosko and of Warren, opting against

increasing the little group G(k) to G(k,-k) and then doubling G(k,-k) to

find the so-called co-representations for the antiunitary operators

including time reversal. Instead, the method developed applies directly

to the little group representations D^-(S) where B is a (unitary) element

of the little group. Moreover, "mutiplier representations" are introduced only in connection with applying the Wigner-Herring test, thereby

simplifying the analysis considerably.

The new algorithm can also be applied to crystals in the rigid-molecule approximation which has been treated group theoretically by myself

and S. Trevino and recently applied to NaNO by S. Trevino, H. Prask,

and myself.

24
REACTOR RADIATION DIVISION PROGRAMS

In collaboration with M. Rowe and S. Trevino, it is planned to

apply the algorithm to specific examples

.

1

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

2 J. L. Warren, Rhys. Rev. B9, 3603 (1974).

RIGID ROTATOR MODEL FOR KCN, NaCN

R. C. Casella

An analysis of a system of heteronuclear diatomic "free rotators"

with centers of mass lying on a vibrating crystal lattice has been made.

The analysis includes a fundamental field-theoretic deviation of the

Debye-Waller factor within the context of the model. Expressions for

the differential cross sections for elastic and inelastic neutron

scattering have been obtained within the approximations of rotational

transitions involving AJ=±1 only and AJ=±1, ±2 only. Line-shape factors

are found which are similar to those for homonuclear diatomic liquids

given by Sears

.

It is planned to extend the analysis to include an additional point

atom and compare the results with the neutron data of J. Rush and M.

Rowe for the NaCN and KCN systems. Moreover, it may be interesting to

apply our general group theoretical analysis of neutron scattering from

librating rigid molecules in a crystal to those systems and to examine

how the structure function F (k) varies with k along the (100) direction.

This may be particularly interesting for the KCN system where neutron

scattering does not pick up the optical branch (although infra red

measurements of N. Vagelatos do) and the acoustics branches lose strength

as |k| increases along that direction.

R. C. Casella and S. F. Trevino, pftvs . ReVt B6_, 4533 (1972).

25
REACTOR RADIATION DIVISION PROGRAMS

NEUTRON DIFFRACTION STUDY OF NaSH AND RbSH

A. Santoro and J. J. Rush

Sodium and rubidium hydrosulf ides , NaSH and RbSH, exist in several

crystal modifications. Below the melting point these compounds are both

cubic (phase I). When the temperature is lowered, they undergo a first

order transition (at ^358 K and ^403 K for NaSH and RbSH, respectively)

into a trigonal phase (phase II) and a second transition (^113 K and

^123 K, respectively) into a modification (phase III) whose symmetry has

not yet been determined . Space group and heavy atoms positions for phases I and II have been

2 determined by X-ray diffraction for both compounds . Neutron diffrac3 4

tion" and inelastic scattering studies on NaSH have shown that the

SH ions in the cubic phase are reorienting between at least six quasiequilibrium positions, and that in the trigonal phase they are aligned

along the three-fold axis with equal probability of finding them pointing

in either direction.

The x-ray results show that the heavy atoms positions in the trigonal phases of RbSH and NaSH are analogous. So far, however, the location

of the hydrogen atom has not been crystallographically determined in the

case of RbSH. The present neutron diffraction study was undertaken to

complete the structural analysis of the trigonal modification of RbSH

and to determine the structure of phase III for both compounds. In

what follows we give preliminary results of our investigation.

Rush, J. J., R. C. Livingston, G. J. Rosasco, Solid State Com., 13_,

159-162 (1973).

2 West, C. D., Zeit. Krist., 88, 97-115 (1934).

3 Schroeder, L. W. , L. A. deGraaf, and J. J. Rush, Chem. Phys. 55 , 5363-5369.

4

Rowe, J. M. , R. C. Livingston and J. J. Rush., J. Chem. Phys. 59_,

6652 (1973); J. J. Rush, L. A. deGraaf, and R. C. Livingston, J. Chem.

Phys., 58, 1438 (1973).

26
REACTOR RADIATION DIVISION PROGRAMS

1. Trigonal Phase of RbSH

The neutron diffraction powder pattern of trigonal RbSH can be

o readily indexed on the cell found by x-ray (a=4.525A, a=69.3°). Of the

eight lines observed in the pattern, only three are completely free from

interferences if one assumes the space group R3m. With such limited

number of data it is only possible to test if reasonable models for the

structure are consistent with the observed intensities. As refining of

the thermal and positional parameters is clearly impossible, reasonable

values for these parameters must be assumed. (In our case, for example,

the SH band length was approximately the same as in NaSH, and the

thermal parameters used were derived from the previous neutron scattering

work.)

As for the case of NaSH, three models were considered and the

comparison between observed and calculated intensities is shown in Table

I for each model. In agreement with the results found for NaSH, the

structure favored is the one with the SH ions lying along the trigonal

axis and pointing with equal probability in either direction (model A)

.

Structures in which the hydrogen atoms are completely ordered are possible. One possibility is to orient all the SH ions in the same direction along the trigonal axis. This model, however, can be excluded

because electrostatic interactions favor the ordering of these ions in

opposite directions along the jacent trigonal axes. Other ordered

structures satisfying this correlation of orientation can also be ruled

out, as they would be based on unit cells larger than the one derived by

x-rays and therefore, would give more diffraction lines than are actually

observed.

The proposed structure of the trigonal phase of RbSH can be confirmed and better thermal and positional parameters can be obtained, by

carrying out a total profile analysis of our neutron diffraction pattern*,

Work in this direction is planned in the near future.

* This method does not make use of the individual intensities of the

Bragg reflections, but used the entire shape of the powder pattern to

decide between various models and to refine structural parameters. The

27
REACTOR RADIATION DIVISION PROGRAMS

2. Studies on Phase III of RbSH

All the diffraction lines of phase II are present in the powder pattern of phase III, practically in the same angular positions and approximately with the same intensities. However, the pattern of phase III

contains a number of extra lines. This observation strongly suggests

that the structure of phase III is based on a superlattice of the trigonal

lattice of phase II. This interpretation of the powder pattern is con- sistent with the hypothesis that the transition from phase III is asso- ciated with an ordering of the hydrogen atoms which are "disordered"

between the positions uuu and uuu in the trigonal structure.

The smallest superlattice which indexes the powder pattern is monoo o o clinic (a=4.52A, b=5.14A, c=6.85A, 3=101.2°) and it is obtained from

the trigonal cell by means of the transformation 100/011/111. There

are two formula units of RbSH per unit cell.

The most reasonable model for the structure of this phase appeared

to be the one with the two SH ions contained in the monoclinic cell

still lying along the old trigonal axis, but pointing in opposite

directions*. This model, however, gave results inconsistent with the

experimental results. Specifically, the proposed structure predicts

observable intensity for reflections which are experimentally unobserved.

Attempts to orient the SH ions away from the trigonal axis proved

equally unsuccessful. This and other inconsistencies between observed

and calculated intensities may be due to shifts in the relative positions of the rubidium and sulfur atoms, or to incorrect assignment of

the hydrogen positions, or to both factors.

*The positional parameters for this structure, referred to the monoclinic cell, are:

Rb

SH

1/4,1/4,1/4; 3/4,3/4,3/4

1/4,1/4,3/4; 3/4,3/4,1/4

l/4-2u, 1/4, 3/4-u; 3/4+2u, 3/4, 1/4+u

number of parameters which can be refined with this technique is com- parable to that normally encountered in a single-crystal studies of

moderately complex structures.

28
REACTOR RADIATION DIVISION PROGRAMS

Further work planned for this structure comprise - (i) A low-temperature x-ray study which should give the positional parameters of the

heavy atoms without ambiguity; (ii) The use of the total profile analysis

of the neutron diffraction pattern for deciding between structures with

more complex conf iguations of the SH ions. This part of our study

involves the derivation of crystallographic methods for generating systematically all structural models consistent with superlattices of multiplicity higher than 2 (i.e. with unit cells containing more than 2 formula units of RbSH)

.

Table 1. Observed and Calculated Intensities for the Trigonal

Modification (Phase II) of RbSH

HKL

100

111 + 110

110

211 + 111

210 + 200

221

222 + 220 + 210

2ll

311

211

321 + 310

220

332

310

For all models - S : 000

Model A - 1/2H : i Model B - 1/6H ; OOz, do, z00; z=0.267

Model C - 1/6H : xxO , xOx, Oxx; z=0,235

2 °2 2 °2 ? °9

<U >R= 0.10A ; <IT>

S

=0.05A ; <U>

Rb =0.035AZ

29

obs

Model A Model B Model C

40.7 39.9 37.5 31.5

57.4 52.6 50.9 60.6

16.1 13.9 26.2 40.2

41.6 42.9 30.6 21.4

18.7 18.4 21.2 28.4

unobs

.

.7 1.0 4.8

22.0 26.6 21.5 18.3

17.3 16.1 21.1 23.2

VW .6 1.7 1.3 vw 4.1 8.3 7.3

25.2 29.2 23.6 30.]

unobs

.

2.8 4.9 5.5

VW 2.5 3.9 3.6

VW 6.3 6.0 7.0

R= 7.9% R=16.5% R=33.8%

; Rb : 1/2 1/2 1/2

iuu, uuu ; u=0.118
REACTOR RADIATION DIVISION PROGRAMS

DYNAMICS IN SIMPLE LIQUIDS

J . M . Rowe

As discussed in last year's report (NBS Technical Note 813),

the dynamical behavior of simple liquids is at present poorly understood.

Our program addresses this problem by obtaining accurate, detailed measurements of the scattering function of various simple liquids in absolute,

normalized form which can then be compared to both molecular dynamics and

model calculations. We are also exploring the transition from the wellunderstood hydrodynamic regime (very long wavelength fluctuations) to

the short wavelength high-frequency regime. Some recent results for

liquid rubidium, one of the simplest liquid metals are discussed below.

Future work will extend the measurements to polyvalent metals and alloys.

In collaboration with J. R. D. Copley and A. Rohman, Argonne National

Laboratory, the scattering function of liquid rubidium at 313K (just

above the melting point) have been measured for wave-vectors between

°-l

0.3 and 5.5 A and compared to molecular dynamics (MD) results. The

MD calculations were done for 500 atoms interacting with an effective

two body potential determined from the phonon dispersion relations of the

solid. As pointed out in last year's report, we were able to clearly

observe evidence of propagating collective excitations for wavelengths

as short as 6A, which is a typical interatomic spacing in liquid Rb. For

shorter wavelengths, no evidence of such propagating collective modes was

observed. This is in complete contrast to the results for liquid argon,

o when no structure was observed for wavelengths as long as 10A. The

molecular dynamics calculations are in very good agreement with the

details of the measurements although minor discrepancies remain. In

particular, the observed propagating mode is reproduced by the MD calculation. This is shown in figure 1, where the frequency of the observed

mode is plotted as points for the neutron scattering results and a line

for the MD results (Note that the wave-vector transfer k= 2 it /wave length) . The agreement at shorter wavelengths is shown in Fig. 2 by a direct

30
REACTOR RADIATION DIVISION PROGRAMS

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0

K (A"')

Fig. 1. A comparison of the frequency of propagating collective

excitations in liquid rubidium at 313K as measured by neutron

scattering (•) and as calculated by molecular dynamics (—)

.

31
REACTOR RADIATION DIVISION PROGRAMS

i i i i

0.4 0.8 2.0 2.4 2.8 3.2 3.6 4.0

t (pS8C)

Fig. 2. A comparison of the time dependent pair correlation function

of liquid rubidium at 313K as measured by neutron scattering

(•) and as calculated by molecular dynamics (—)

.

32
REACTOR RADIATION DIVISION PROGRAMS

comparison of the observed and calculated scattering function for selected values of the wave-vector transfer. The comparison is given in terms

of a time-dependent correlation function simply for computational reasons. This result, which is the most detailed comparison of experimental

results to MD calculations yet attempted, has strong implications for the

theory of the dynamics of simple liquids and for the reliability of

MD simulations. First, it establishes clearly that one can obtain useful

information about the potentials of interaction from the liquid dynamics

(a point not well established earlier). Second, it shows that at least for

Rb , the same potential can be used to explain both the liquid and solid

dynamics to a reasonable approximation. Third, it shows that collective

excitations can persist to very short wavelengths for some potentials.

Fourth, it shows that the MD simulations can reproduce the dynamics of

liquids even for wavelengths comparable to the size of the box for which

periodic boundary conditions are applied—a point which has been the

subject of much debate. Finally, more detailed investigations of other

potentials will allow us to establish those features of the potential

which are most sensitive to the dynamics and thus help in the testing of

various proposed forms for this potential.

INTERCOMPARISON OF NEUTRON DIFFRACTOMETERS

V. W. Myers

The Neutron Diffraction Commission of the International Union of

Crystallography has been involved in a program for the comparison of the

available monochromatic neutron flux at various diffraction instruments

around the world. NBS has collaborated in this program since its

inception in 1970. During the -past year, gold foils were activated in

the diffracted beam of the NBSR BT-1 dif fractometer and then counted.

H. Alperin and L. Rauber measured the scattering from an Al-0 powder

specimen on this instrument also. The results for the gold foils'

activities and the powder pattern where then communicated to A. F.

Anderson (Institutt for Atomenergi, Kjeller, Norway). Anderson and

33
REACTOR RADIATION DIVISION PROGRAMS

Sabine (Australian AEC) have issued a report describing the results of

this study. They show, for example, the flux at sample position versus

core flux and the flux ratio versus resolution. The NBSR BT-1 diffractometer results compare favorably with those of spectrometers at other

high flux research reactors. This intercomparison study is essentially

completed.

THERMAL NEUTRON FLUX MEASUREMENTS

V. W. Myers and M. Ganoczy

The data are being analyzed for the manganese sulfate bath which was

used for measuring the absolute thermal neutron intensity of a beam.

Boron loaded cobalt glass beads were activated in the known thermal flux

and then for calibrating a Nal well detector and its associated counting

system. This technique provides for the measurement of an unknown thermal

flux by activating a bead in the flux and then counting it in the calibrated system.

34
REACTOR RADIATION DIVISION PROGRAMS

NEITTRON RADIOGRAPHY

Harold Berger, Vernon W. Myers and Martin Ganozy

1 2 A program in neutron radiography ' was initiated in FY 1974.

The program is expected to provide leadership in the development of

standards for this expanding method of nondestructive evaluation (NDE)

.

In addition, the neutron radiographic facilities will be used to perform

application studies for NBS and other agencies and to develop techniques

to make neutron radiography more useful to industry.

A neutron beam facility has been set up at the NBS Reactor thermal

column. Beam characteristics can be changed in terms of beam intensity

7 2

.

and divergence. A maximum thermal neutron intensity of 1.5x10 n/cm 'sec

is available at a beam divergence ratio of 30 for L/D (L is the distance

from the aperture to the radiographic location, D is the aperture diameter

from which the neutron beam diverges) . The intensity can be decreased

and the beam divergence improved from those values. Typical beam

characteristics are as follows

:

Thermal Neutron intensity 2x10 n/cm "s Coverage 17.5 cm diam

Divergence L/D = 90

Cadmium ration (gold) 600

Gamma intensity 1 R/hr.

ft 9 Neutron to Gamma ratio 6x10 n/cm per mR

A diagram of the beam facility is shown in figure 1. Exposures may

be controlled by raising and lowering either the Boral Curtain or the

external shutter.

The beam facility has been used to investigate several image

detection systems. Two of these are particularly useful for initial

alignment radiographs and have been used to aid diffraction experiments

35
REACTOR RADIATION DIVISION PROGRAMS

by showing crystal placement inside furnaces and cryostats. One method

(a) utilizes Polaroid TLX film . An exposure of 7 seconds provides a result showing high contrast resolution better than 125 un. The Polaroid

film can be ready for viewing after 45 seconds development time. A

(a) radiographic paper, Kodak type 600, has also been used with even better

results (resolution of 25 ym) . An exposure time of 50 seconds provides

a good result and can be viewed after only 10 seconds development time.

Both detectors, used with scintillator converter screens, provide a result that can be viewed within about a minute. An example of a radiograph taken on paper is shown in figure 2

.

A real-time detection system, providing images at the normal

television frame rate of 30 frames /s has also been investigated ' 3 The image intensifier system, normally used for x-ray detection , also

responds to thermal neutrons because of the use of a new x-ray fluorescent screen containing the high neutron cross section material

gadolinium . The gadolinium oxysulfide screen used for these tests was about 0.5 mm thick and attenuated the thermal neutron beam 75 percent.

Tests of spatial resolution, contrast, and speed were conducted over a

o 6 9 thermal neutron intensity from 2.5x10 to 6x10 n/cm • s. Motion response varied over the range of intensities. High contrast

objects such as cadmium could be followed without image blur at linear

velocities of 2m/min at the high intensity. At an intensity of 6x10 n/cm • s any motion blurred the image.

High contrast resolution varied from 0.5 mm at the high intensity to

bare discernment of gross objects (5 cm diam or larger) at the lower

intensity. In terms of contrast, a 0.4 mm thick plastic step could be

observed through 1.27 cm of steel at the high intensity. The plastic

thickness required for observation increased as intensity was lowered.

5 2 For example, at 2.6x10 n/cm • s a plastic thickness of 0.5 mm was

(a) The use of proprietary names is for identification purposes only and

does not constitute an endorsement of any particular product or apparatus

(b) Tests performed in collaboration with the Old Delft Corporation of

America, Fairfax, VA, using their image intensifier Decalix SI-12 1/2.

36
REACTOR RADIATION DIVISION PROGRAMS

PiCOPQ

S3

(U XIu

•u

CO>.

4-1 •H.H

•HO

CO

>»

x:

ex

cOU

bOO

•H13

COU

do

l-i 4-1

CD

fi

<U x:

4-1

cl60

CO

COe

j-i 0)

4J

37
REACTOR RADIATION DIVISION PROGRAMS

Fig. 2. A neutron radiograph of a test piece, obtained on radiographic

paper. The high contrast rectangular images are of cadmium,

hole sizes vary from 2 mm to 0.25 mm dia. Closest hole spacing

is 25 ym. The stepped wedges on the right are of lead, cadmium

indium and plastic (as marked from top to bottom) . Stepped

objects on the left are steel (upper) and plastic (lower)

each varying in thickness from 2 mm to 0.25 mm.

38
REACTOR RADIATION DIVISION PROGRAMS

Fig. 3. A neutron radiograph of an aluminum sample. The sample was pre-cracked and cathodically polarized in HC1. The area of

attenuation around the double cantilever beam specimen crack is

thought to be due to hydrogen. Sample from the Naval Air

Development Center, Worminster, Pa.

39
REACTOR RADIATION DIVISION PROGRAMS

<L> •H

CO

U

O

4-1 o

cu

4-1 CU T3

bO3

•HV

co

3

CU

,3

P.

COU

toO O

•HT3

COH

3o

u

4-J 3

CU3

bO

•H

CO •H

>-l CU3

O

CU H

4-> 3

M

CO

CU60

toO 3

•H

PiCO

COO

•HU

T33

•H

CJ

too 3

•H

3

CO

cu

*-l

cu

>-l 3

4-1 CO •HO

6

cu

co

cu>

cu

cu x

co •H•3a

cu .3o

CO

cu

4-1 CO

toO a

•HXCO ^3

COCO

COUX

CU X4-1

M-lO

cubo

co6

•H

CU X4-1

CO&oxCO rC

a.

COu

toO o

•H

T)

cOU

3o

u

4-J 3

cu3

CU X

H

CU

o

cu

co

toO 3

•H

4J

CO3

cu

4-J

toO 3

•He

CO3

cO

4-1

14-4 o

CO

CO

cuu

CO *33

CO

toO 3

•H.3

CO X

4-1 M

COCU

u

cuCu

Cu

CUCu3

CO

rH

CO

CO

CD

CO

CU X

H

3

CU

toO O

U

>> ,3

CUCU

Cu

cOu

4->

CU .3

CO 4-1 CUu T3

CO 3

CO <U

CU 3

CO o

\^ •H

CO

CO O

3 u o u

•H o

4J u

COo e

•H o

T3 s-l 3 U-l

4-1 rH3

CO

cuo

4J

4-1 XtoO 3

O

X!

4-1

CUu

CO

cO3

3

O

CJ

COE

cu

4-1 CO en

S-i •H

<:

CO>

CO

CU X4-1

o

M-l

CO

CU tH&CO CO

CU

40
REACTOR RADIATION DIVISION PROGRAMS

Fig. 5. Two neutron radiographic views of a liquid-filled crack in an aluminum fatigue sample . In each case the arrow points to the

bottom area of the crack. In view A (left), the neutron beam

passes through almost 2 cm of penetrant; a high contrast image

results. In view B, the neutron beam passes through only the

small thickness of the crack and contrast is less . In the case of radiograph B, however, contrast of the crack front has

been enhanced by filling the crack with a slurry of GdO in

alcohol. The radiograph shows high contrast of the GdO and

indicates that it has not uniformly distributed.

41
REACTOR RADIATION DIVISION PROGRAMS

4 2 required; at 6x10 n/cm . s the plastic thickness had to be increased

to 1 mm to provide detection. Both these latter thermal neutron intensities represent values that can be achieved easily with non-reactor

neutron sources. The tests, therefore, may have impact on possible

users in industry. All the contrast and resolution results at the lower

neutron intensities were improved if the neutron image was integrated

for several frames. A complete report on these tests is in preparation.

Materials for normal photographic detection of thermal neutron

images, particularly gadolinium, indium, and dysprosium metal foils, are also available and have been used for application investigations for

NBS and other agency programs. Application studies have involved a variety of samples from many agencies. Most have been concerned with

the detection of hydrogenous material in a metal matrix. Materials have

included potting foam, adhesives and hydrides. Anomalies to be detected

included voids , cracks , inclusions and variations caused by hydriding

and corrosion. An example of a neutron radiograph showing excessive

hydrogen concentration charged in an aluminum sample under stress

corrosion is shown in figure 3. Figure 4 shows a neutron radiograph of

an aluminum landing strut in which corrosion under a brass bushing has

been detected.

At NBS, the major use of neutron radiography has been the characterization of fatigue cracks in aluminum. These cracks, fabricated in the

Mechanics Division, have been filled with penetrant and other hydrogenous

liquids, which act as contrast agents for thermal neutron radiography.

Experiments with several liquids containing boron, cadmium, and gadolinium

have been conducted in an attempt to enhance contrast so that reliable

visualization of the crack front can be achieved. Examples of some early

neutron radiographs of filled cracks are shown in figure 5

.

The neutron radiography program is just beginning to address the

problem of standards . NBS is represented on the new ASTM subcommittee

E07.05, Neutron Radiography. Plans are also under way to put in operation

at the reactor, a second more intense, lower cadmium ratio beam for

neutron radiography. The beam will be brought out of a vertical thimble.

42
REACTOR RADIATION DIVISION PROGRAMS

1. H. Berger, "Neutron Radiography," Annual Rev. Nucl. Science* E.

Segre, editor, 21, 335-364 (1971).

2. H. Berger, "The Present State of Neutron Radiography and its

Potential," Materials Evaluation, 30_, 55-65 (1972).

3. A. Klem, "Decalix With Isocon," Odelca Mirror, 9_, 2-4 (June, 1971)

4. K. A. Wickersheim, R. V. Alvers, and R. A. Buchanan, "Rare Earth

Oxysulfide X-Ray Phosphors," IEEE Trans. Nuclear Science, NS-17,

57-60 (1970).

GAUGE THEORIES

R. C. Casella

The experimental discovery of neutral weak currents in neutrinohadron scattering and neutrino-electron scattering has given added

impetus to Weinberg-type theories which have as their basis invariance

under a nonabelion local gauge group. We have begun a study of YangMills fields with a view towards understanding the Higgs mechanism for

acquiring mass under spontaneous symmetry breaking and mechanisms for

inducing time-reversal violation in K° meson decays. Quite apart from

the question of degenerate vacua, we also wish to understand the relative importance of local gauge invariance per se and the associated

imposed supplementary condition in maintaining masslessness of the

associated gauge boson (e.g., vanishing of the commutator of 3 A (y.)

at different space-time points in QED) . We believe this question is

relevant to an earlier remark of Lee and Yang that the (abelion) baryon

gauge group cannot be local since it would give rise to a long range

force proportional to baryon (nucleon) number which would be observable

in Etvos-type gravitational experiments.

43
B, RRD-NBS Collaborative Programs

4

SCATTERING OF NEUTRONS FROM HE NEAR THE CRITICAL TEMPERATURE

B. Mozer

(Inorganic Materials Division)

4

We have measured the diffraction of neutrons from He at the

critical temperature. In this experiment we were able to use the same sample cell that was used in a similar experiment on neon. Temperature

control was harder to maintain for this experiment but manual operation

of the system would allow 1-2 milli-Kelvin control near the critical

temperature. Diffraction data was obtained for two reduced temperatures

-4 -3 -4

8x10 and 2-3x10 above T , - 4x10 below T , and at 14K. The raw

c c data was corrected for background, short range correlations, and collimation effects as explained for neon. Theromdynamic data was obtained

to determine the critical density and critical temperature relative to our sensors , dielectric measurements using the capacitor in the- cell and

resistance measurements of the germanium sensor on a temperature controlled

copper block to which the sample cell was attached. The thermodynamic

data can yield a value of 6 for helium but this has not been determined

with great accuracy. The corrected diffraction data yields a value of

n = 0.100±0.015 somewhat smaller than neon but with less accuracy.

Analysis of the helium data for coefficients of series expansions or assumed forms of the scattering function have not been attempted.

NEUTRON DIFFRACTION MEASUREMENTS OF NEON NEAR ITS CRITICAL TEMPERATURE

B. Mozer

(Inorganic Materials Division)

In a brief note we reported preliminary neutron diffraction measurements of neon very close to T , the critical temperature. In that note

we described our observation of the deviation from Ornstein-Zernike theory

in the critical scattering of neutrons from neon. We were able to

extract the critical exponent n = 0.11±o\02 which is a measure of the

deviation from Ornstein-Zernike theory.

44
RRD-NBS COLLABORATIVE PROGRAMS

We have extended the measurements on neon verifying the earlier

results and obtaining data over a large range of temperatures in the

critical region. The temperature difference from T varies from 7x10

-2 ° to 3.17x10 in units of the reduced temperature. Angular measurements

were taken from 1 to 20 degrees in the scattering angle corresponding to

o_-i o roughly 0.022 to 0.436A momentum transfer for a 5A beam of neutrons.

o The wave length of the primary beam was varied from 4.5 to 7.5A to

obtain information on wave length dependence of the scattering. Collimation of the incoming beam was restricted by Soller slit collimators and

cadmium masks . Divergence of the incoming beam was less than 4 minutes

of arc in the vertical direction and 8 minutes of arc in the horizontal

direction. The scattered beam was collimated to 10 minutes of arc in

the horizontal direction with Soller slits. For most of the measurements

the vertical collimation was left open and was determined by the divergence at the detector which corresponds to 4/3 degrees of arc. We calculated the resolution correction factors using an Orstein-Zernike form for

the scattering law and then smearing this scattering behavior by taking

into account the various horizontal and vertical divergences with triangular

distribution functions. We then placed a Soller slit collimator in the

scattered beam with 20 minutes of arc vertical divergence. The correction

factors for the diffraction data in the latter case are essentially unity

over the angular range greater than 2.5 degrees. Taking the ratio of the

corrected data for 4/3 degree vertical divergence to the data for 20

minutes vertical divergence provided an experimentally determined cor- rection factor to check our calculations.

The resultant data was corrected for background, collimation and

short range correlations as determined from the structure factors

°-l

measured over a < range of 0.2 to 9. 0A . A constant multiple scattering

correction and small incoherent scattering correction were also applied

to the data.

From the corrected diffraction data and thermodynamic measurements

we found the following values for the critical exponents of neon

exhibited in table 1. We also found that our diffraction data could be

45
RRD-NBS COLLABORATIVE PROGRAMS

presented on a universal curve over the temperature range by plotting

Y 2

Ie versus (k£) where I is the corrected intensity e = (T-T )/Tc, k is

c the momentum transfer, and £ the correlation length. Preliminary analysis

indicates a universal curve for y = 1.18±.01 and v = 0.630±.004. Thus

static scaling concepts seem to apply to our diffraction data at this

stage in the analysis and seem to agree with the values determined in a straightforward way as quoted in table I.

Additional analysis of our data was undertaken to obtain estimates

for various coefficients in the series approximations to the scattering

function for large and small k£. Our estimates for these coefficients

are much larger than estimates calculated from the lattice-gas model

2 using the renormalization group approach .

Table I. Several critical exponents for neon

0.360±0.005 1.18±0.01 0.630±0.004 0.125±0.005 0.14±0.04

V. W. Warkulwiz, B. Mozer, and M. S. Green, Phys . Rev. Lett. 32_,

1410 (1974).

2M. E. Fisher and A. Aharony, Phys. Rev. Lett. 31, 1238 (1973).

46
RRD-NBS COLLABORATIVE PROGRAMS

CRYSTALLOGRAPHIC METHODS FOR THE STUDY OF PHASE TRANSFORATIONS

A. Santoro

and

A. D. Mighell

(Inorganic Materials Division)

In the automatic determination of a unit cell from powder diffraction

data, often a powder pattern can be indexed on more than one lattice

(de Wolff, 1961; 1968; Visser, 1969; Ishide and Watanabe, 1967, 1971).

In most cases the ambiguities in the indexing are due to accidental

causes such as errors in the measurements of the angular positions of

the diffraction lines, extinctions that are either related or unrelated

to the space group symmetry of the crystalline species under investigation,

and the presence of reflections produced by impurities. When ambiguities

of this type occur, it is not possible to assess the correctness or incorrectness of a unit cell with certainty, but procedures can be used

for estimating the reliability of a particular indexing (de Wolff, 1961;

1968).

Recently in the course of a neutron diffraction study of phase

transitions in rubidium and sodium hydrosulf ides, it was observed that

two different lattices, one of rhombohedral symmetry and the other of

monoclinic symmetry, give calculated powder patterns with the identical

number of distinct lines in identical 26 angular positions. The number

of planes (hkl) contributing to each reflection is not the same in the

two cases, however. These two lattices are related to each other by a transformation matrix whose elements are simple rational numbers.

An ambiguity of this type is geometrical in nature rather than

accidental and has not been recognized previously. It has to be expected

that cases similar to that encountered in the study of the hydrosulfides

play an important role in the automatic determination of unit cells from

powder data. Therefore, it is useful to analyze the conditions under

which these ambiguities occur. This analysis has been carried out and

47
RRD-NBS COLLABORATIVE PROGRAMS

some of the results are shown in table 1.

Geometrical ambiguities in the indexing of powder patterns do occur

in high-symmetry lattices. One of the main conclusions of our study

is that these ambiguities, where they exist, are systematic. For example,

any powder pattern consistent with a body-centered cubic cell (see case

1 in Table I) can also be indexed in terms of a tetragonal cell with a volume 1/4 that of the cubic cell, or in terms of orthorhombic P and

F cells having volumes 1/8 and 2/3 that of the original cubic cell,

respectively.

There are cases of geometrical ambiguities in which it is not

possible to decide on the reliability of the indexing on the basis of

the angular positions of the diffraction lines. For example, the low

temperature phases of sodium and rubidium hydrosulfides (Rush, Livingston

and Rosasco, 1973) give neutron powder patterns which can be indexed in

terms of a monoclinic and a rhombhedral cell (case 5 in table 1)

.

Both lattices are equally valid and the choice of one or of the other

depends exclusively on how the hydrogen atoms are ordered in the structure.

Similar situations may well exist in analogous order-disorder transformations . The indexing of the pattern of a-Li,B_0 (de Wolff, 1968) represents

an example of the occurrence of geometrical ambiguities in the automatic

determination of unit cells from powder data. The pattern of this compound can be indexed as orthorhombic and as hexagonal. The two lattices

are not the same (transformation matrix from orthorhombic to hexagonal:

110/110/001, case 4 in table 1). The true orthorhombic symmetry of the

structure was established in this case by single-crystal work rather

than from powder data.

The lattices of all the examples given in table 1 are related by

transformation matrices with simple rational elements, i.e. lattice II

is in all cases a derivative lattice of lattice I (Santoro and Mighell,

1972; 1973). This relationship between lattice I and II seems to be a necessary, but certainly not a sufficient, condition that the lattices

have to satisfy to be consistent with the same set of calculated lines.

48
RRD-NBS COLLABORATIVE PROGRAMS

Table 1. Examples of lattices giving geometrical ambiguities in the

indexing of powder patterns

Lattice I Lattice II Transformation I-*II

1) Cubic P

2) Cubic I

3) Cubic F

4) Hexagonal

5) Rhombohedral

Tetragonal P

Tetragonal P

Orthorhombic F

Orthorhombic P

Orthorhombic C

Orthorhombic I

Orthorhombic P

Monoclinic P

OiI/OlI/100

22 22

oil /Oil /loo

22 22 2

iiO/OOl/110

33

Uo/ooi/iio

i+i+ 2 22

loi/oio/lol

2 2 k i+

lol/loi/oio

6 6 2 2

IIo/IIo/ooi

22 22

lol/iol/oio

2 2 2 2

T. Ishida, and Y. Watanabe, J. Phys. Soc. Japan 23, 556-565 (1967).

T. Ishida and Y. Watanabe, J. Appl. Cryst. 4, 311-316 (1971).

J. J. Rush, R. C. Livingston, and G. J. Rosasco, Solid State Cornm. 13 , 159-162 (1973).

A. Santoro and A. D. Mighell, Acta Cryst. A28 , 284-287 (1972).

A. Santoro and A. D. Mighell, Acta Cryst. A29 , 169-175 (1973).

J. W. Visser, J. Appl. Cryst. 2_, 89 ~95 (1969).

P. M. Wolff, Acta Cryst. 14, 579-582 DE(1961)

.

P. M. Wolff, Acta Cryst. 1, 108-113 DE(1968)

.

49
RRD-NBS COLLABORATIVE PROGRAMS

DETERMINATION OF LATTICE DISTORTIONS FROM SIMULTANEOUS

DIFFRACTION EFFECTS

A. Santoro

A. D. Mighell

(Inorganic Material Division)

and

M. Zocchi

(Politecnico di Milano, Italy)

Phase transformations are not infrequently associated with symmetry

changes resulting in slight distortions of the crystal lattice. It is

therefore of interest to devise procedures not only for detecting changes

in symmetry, but also for determining uniquely which of the possible

distortions of a lattice has occurred in any particular case. Simultaneous diffraction offers an ideal method for analyzing phase transitions

of this type when single crystals are available.

Multiple, or simultaneous, diffraction of X-rays and neutrons occurs when two or more reflections satisfy the Bragg condition simultaneously.

Its effect is a more or less pronounced perturbation in the intensities

diffracted by each of the reflections involved. A pattern of these perturbations (Renninger pattern) can be obtained for any desired reflection

HKL (primary reflection) by measuring the intensity diffracted by the

reflection while the crystal is being rotated about the scattering

vector.

The sensitivity of the lattice parameters to the angular positions

of the Renninger peaks is greater than that of the conventional singlecrystal and powder methods. In the case of cubic crystals, for example, we have A

« da /a = cos 6tgtf»<ty (1)

where a is the reciprocal parameter, 6 is the Bragg angle of the

primary reflection HKL and ^=(^.-i|)„) /_ , where lj/. and iJj. are the angles

at which a second reflection hk£ diffracts simultaneously with HKL during

a 360° rotation about the scattering vector corresponding to HKL. Equation (1) compared quite favorably with the corresponding expression valid

50
RRD-NBS COLLABORATIVE PROGRAMS

for the powder method, i.e.

* da = catan 0d6 (2) a A further advantage offered by simultaneous diffraction over the conventional methods is that the Renninger peaks are far less affected by

systematic errors and far sharper than single-crystal and powder diffraction effects.

The peculiar geometry of simultaneous diffraction confers to the

Renninger patterns particular properties which can be used for the

detection of lattice distortions. Our method makes use of the fact that

in the absence of distortions certain peaks are superposed in the

Renninger pattern of particular primary reflections, and they are split

if the distortions are present. Without entering into the details of

the derivation, we have summarized in tables 1 and 2 the conditions

under which the distortions can be detected. The main conclusion of our study is that each of the possible distortions can be uniquely determined

from the splittings characteristic of that distortion.

Experimental work intended to verify the theoretical results is

planned in the near future.

Table I. Primary and Secondary Reflections Showing Distortions of the

Interaxial Angles

Primary Split Reflections Distortions

Reflection

H h. 1., H-h. 1. 6* 4 90°

l i' l l T

h. k. 0, H-h. k. v* 4 90°

l l i l

'

K k. 1., K-k. 1. a* 4 90° 11 1 1

h.ill k. 0, h. K-k. v + 90°

i ' .

L k.1111 1., k. L-l. a* ^ 90°

h. 1., h. L-l. g* 4 90°

51
RRD-NBS COLLABORATIVE PROGRAMS

Table II. Primary and Secondary Reflections Showing Distortions of the

Interaxial Angles

Primary Split Reflections Distortion

Reflection

h.+h., - h.+h., h.hO ; h.h. . a * b

h.+h., h.-h., h.h.O.; h .h .0 i 3 i J i i 3 3 3

h.+h., 0, -h.+h. h.Oh. ; h.Oh. . . a f c h.+h ., 0, h.-h. h^ ; h.Oh^

0,k

±

-Hc jf "k

i

+k

j

Ok^k.. ; Okj k

j ^ b 4 c*

0,k^+k., iJijk.-k. Ok.k. liJJ ; Ok.k.

HYDROGEN BONDED DIMERS IN SnHP04

L. W. Schroeder

(Polymers Division)

and

E. Prince

A previous x-ray determination, although of limited accuracy, of the

crystal structure of SnHPO, indicated the presence of hydrogen-bonded

-2

HPO. dimers. The length of the hydrogen bond as obtained in the

^ o previous study is 2.50A indicative of a strong hydrogen bond. This

-2

suggests that dimeric HPO, " may be a component of phosphate solutions

at higher pH values.

Recently, we have obtained extensive single crystal Raman and infrared data on SnHPO. in an effort to characterize the dimers in terms of

4

their vibrational spectrum. It is necessary to know the details of the

hydrogen bonding in order to place the interpretation of the spectrum

on a firm basis. We have collected 1724 neutron data from a crystal

of SnHPO, . Structure refinements will begin after the data have been

corrected for the effect of incoherent scattering by hydrogen.

52
RRD-NBS COLLABORATIVE PROGRAMS

ATOMIC ORDERING IN A-15 COMPOUNDS OF THE

V-NI AND V-CO SYSTEMS

R. M. Waterstrat and B. Dickens

(Polymers Division)

and

J . J . Rhyne

(Naval Ordnance Laboratory, White Oak, MD)

Neutron scattering has been used to determine the relative site

occupancy of V atoms on the "A" and "B" sites in compounds of V^-Co and

V__ rNi„- _. In the latter off-stoichiometric compound the atomic order

was maximized while in the Co compound the order parameter was found to

be 0.9±0.1. These compounds are isomorphic with the high temperature

super-conductor Nb-Sn.

The neutron technique is particularly valuable for determining

site order in these compounds due to the nearly identical values of the

x-ray scattering amplitudes of V and Ni (or Co) . In the neutron case these amplitudes are widely different and are not related to the atomic

number which allows the superlattice ordering Bragg lines (e.g. the [110])

to be strongly visible as shown in the accompanying comparison of x-ray

and neutron diffraction intensities on the nickel compound.

53
RRD-NBS COLLABORATIVE PROGRAMS

o

O

>-

-<OS

><

VANADIUm-NICKEL A15 PHASE

Neutron Diffraction Pattern

l"0) (200) (210) (211) (220) (310) (222) (320) (321)

(110) JU

X-ray Diffraction Pattern

v_

(200) (210) (211) (222) (320) (321)

DIFFRACTION ANGLE (20)

Fig. 1. X-ray and neutron scattering intensity from a V__ cNi_~ ,. A15

compound. The superlattice order peaks ([111] etc.) are clearly

visible in the neutron scattering which allowed the determination

of the order parameter.

54
RRD-NBS COLLABORATIVE PROGRAMS

THE CRYSTAL STRUCTURE OF LEAD DEUTERIUM ORTHOPHOSPHATE

C. S. Brickenkamp

(Inorganic Materials Division and Office of Weights and Measures)

and

E. Prince

Preliminary refinement of the structure of lead deuterium orthophosphate was reported in the summary of activities for 1972-73. After

refining the structure to an R of 0.10 with isotropic temperature factors,

a refinement with anisotropic temperature factors was attempted, but

the initial cycles did not converge. While R was reduced slightly,

parameter shifts remained large, and the temperature factor matrices

for several atoms went non positive-definite. In order to reduce the

number of parameters while keeping a more appropriate model than the

isotropic temperature factor model, the thermal parameters of the phosphate

group were constrained to be those appropriate to a rigid body, and the

components of J_ and L_ (but not S_) for the rigid body motion were refined.

With these constraints, and with an extinction parameter included, the

refinement proceeded to an R of 0.049 (R =0.063). A conventional refine- w

ment with anisotropic temperature factors then gave a final R of 0.036

(R =0.051). w

The crystal structure consists of phosphate groups bound into

chains by strong asymmetric hydrogen bonds. The 0-0 distance is 2.514

o o (5)A, the two 0-D distances are 1.032(6)A and 1.484(6), and the O-D-0

angle is 175.9(5)°. The phosphate group is a slightly distorted tetrahedron, with O-P-0 bond angles ranging from 106.5(4)° to 112.5(3)°.

o o The P-0 bond angles ranging from 1.515 (5) A to 1.573 (6) A, with the long

bond being to the hydrogen bond donor, as expected.

Table 1 summarizes the crystal data and table 2 gives a list of

the final atom parameters

.

55
RRD-NBS COLLABORATIVE PROGRAMS

/"> /"N /-"» m 00

sr O

P4u

O

CO Q

COu

CJ>

rO

cO H

m iH r*» iH m iH vO \~s 00 <T> 00 O vO VO is. iH

• • • • st vO m

II II ii II

CO X> o QQ

CJ

P-O

60

COO

COPcn

CN

CSJ

• • CO

CO CU •H CO

CO X> CU 0) Xi

CO 4-1 3

CO C H

o CO •H 0.

CO

CO c

0) •H H

P- CO X H

0) CU M e o 3

4J 55 o

CO

U-t

,

, <u •-x

rl o* 3 Ai

4-1 on

CO CM H CO.

cu CN ^ +

B o;

0) Xi

4-1 CO

cu CQ • £

CM+

COs

^! o

4= •H

• CM 4J st iH CO o cu •H

PL, CM > Q + <U ,0 CM XI

PL, ojCO T3

rl on H o CQ CO IH + TJ

CM C

CO ^S CO M CM 4-> cu CM CO 4J CQ

cu + X! s CM cu CO 42 4-1 H iH cd

CO rH {- Pm CO. •H

v—t 4-1 O 1 CO •H 1—1 CU 6

o P- CU

4-1 X u < w CO

• CN

cu rHJ3

CO H

on] CM CQ I

rH

iH CQ

X

Bo

4-> <

st 00 CT\ 00 o> r-s CTi V—

•^s \s v-x >»• v—

/

>_• 00 sr o\ r-- o on m

o I-l CM o sr r-l o

o o O o o o o

o o O o o o o

on m ct\ o> CT* onj a\ 00 00 en sr CM r^

lH! o r-l st rH vO CM iH ca ! o O o O c O O

o O o O c O O

I /-\ rH o O i-H CM CM VO tH iH rH rH tH iH

CN| CM on r«- CM 00 r*. vO HI rH rH CM CM iH rH O ca i O O o O O o O

O O o O O c O III III

I ^ ^^ /_^ /i> y^v ^_^

•-* O r-H iH iH tH iH

vO tH iH i-H tH iH rH

Cn' N^ V_x W W W W %_• on' cm cm cm vo o en a\ caj oc m vo oo en m sr O O H O tH O rH

I o o o o o o o

o> ON

CM w \^ \~s N_X v_/ >-x v_x CM on CJ\ cn VO CM <" CTv CQ vo m m r^ 00 00 a> o o o o O o o

o o o o O o o

^>. on 00 vO CM o\ <t

Oi tH rH r-^ CM iH rH vO C3> <t VO m CN O

on tH m VO •<t m tH

tH tH H O CM t-H CM o o O O O O O

00 00 CO 00

CT> m CM O O 00 on 00 on CM 00 r«- CM o rH sf m m

CM si- rH O on st

on sr r^ vo r^ vo s-\ Vy ^-^ ^^ ^-^ y~s V—f LO

cm vo vo sr si- sr ^^

cr> sr o vo r>. oi o

cy, o sr r*» on r- oo

t-H cm on o on o cmm

l l l l I

CM O O O O tH

rH rH rH x-\ rH r-i o sr o o o o\ m

o on on vo o oo o oo vo cm m oo

in on cm vo r

-* sr

Xi

PL, PL,

cm on sr

V_X '>w' V»/ o o o

56
RRD-NBS COLLABORATIVE PROGRAMS

THE LOW TEMPERATURE PHASE OF TANTALUM OXIDE

R. S. Roth

(Inorganic Materials Division)

and

E. Prince

Tantalum oxide, To~0 , is an end member of a series of tantalumtungsten oxides studied previously by x-ray diffraction by Stephenson

and Roth . The structure of these oxides are based on a framework of

various numbers of octahedral and pentagonal bipyramidal subunits. The

low temperature phase of Ta^O is difficult to prepare in single crystal

of any size, but the addition of small amounts of lithium oxide stabilizes the crystal structure so that large, good-quality crystals can be

o grown. The unit cell is orthorhombic, a_=6.198, b_=A0.29, c_=3.888 A, and

the structure conforms approximately to space group Pbmm. However, an

ideal structure in this space group must have the composition Ta 99 0,.«,

whereas the stoichiometry provides only 55 oxygen atoms , and the addition of lithium, at least if the lithium replaces tantalum, reduces the

oxygen content even further below the ideal value. X-ray diffraction

studies are dominated by the tantalum, because of its high atomic number.

A neutron diffraction study was undertaken in an attempt to determine

the roles of the light atoms in the crystal.

Because of the very long b_ axis reflections are very close together,

and if the usual scanning techniques were used there would be a tendency

for peaks to overlap. To get around this problem the data collection

program was altered to scan through reciprocal space along a line

approximately perpendicular to the short reciprocal lattice spacing

resulting in the use of a 6-26 scan for hOO reflections, an co scan for

OkO reflections, and a hybrid of the two for other reflections in the

hkO zone. All of the atomic positions lie in either the z=0 plane or

the z=l/2 plane, so there is little information in upper level reflections. Furthermore a very large fraction of the 1=0 reflections is

below the threshold of observability.

57
RRD-NBS COLLABORATIVE PROGRAMS

i . \ j / C—/ . " •

^

>-•-/• ..' i Js 1 <L \ / _^ L

Fig. 1. Fourier projection of the structure of L-To^O,., as viewed

looking down the C_ axis. 1/4 of the unit cell is shown.

Large peaks are and Ta superposed. Smaller peaks are

alone. Dot-dash lines represent the contour.

A Fourier projection along the c_ axis (figure 1) shows all of the

features of the ideal structure, but no significant additional features,

either as negative peaks that would indicate that the lithium was occu- pying "interstitial" sites or as positive peaks indicating alternative

positions for some oxygen atoms in accordance with the scheme proposed

by Stephenson and Roth. It appears that the structure contains so many

M-O-M linkages that a few can be missing here and there without any

effect on the stability of the crystal.

N. C. Stephenson and R. S. Roth, Acta Cryst. , B27 , 1037 (1971).

58
C, Interagency and University Colu\borative Programs

CRYSTAL STRUCTURE OF DIACETO-PENTAMETHYLENE~TETRAMINE

C. S. Choi

(Picatinny Arsenal, Dover, NJ)

and

A. Santoro

Diaceto-pentamethylene-tetramine, C

qH.fi N,0 , (hereafter referred to

DAPT) is one of the several intermediates in the manufacture of HMX

(cyclo-tetramethylene-tetranitramine) , Preliminary investigation by

precession photographs revealed the space group to be monoclinic P2 , . The unit cell dimensions are a=6.183(2), b=10. 101(2), c=17.037(4),

3=101.78(2)°, and contains 4 molecules per unit cell. A total of 1708

independent reflection intensities were measured within the limiting

sphere of 60° in 29 angle by using an automated x-ray diffractometer with

MaKa radiation. The structure was solved by the direct method using the

XRAY72 system and the hydrogen positions were located from the difference

map. The full matrix least squares refinements with anisotropic temperature factors for the heavy atoms and isotropic temperature factors

for the hydrogen atoms reduced the R- index to wR=0.041 and R=0.051.

The DAPT molecule is isostructural with the DPT (dinitro-pentamethylene-tetramine molecule which has been described previously in NBS

Technical Note 813, 1973). Fig. 1 is the ORTEP drawing of the DAPT

molecule. The molecule possesses a pseudo 2-fold rotation symmetry,

which is comparable to the pseudo mirror symmetry of the DPT molecule.

The two acetamide groups are both essentially planar. The bond lengths

and angles of the DAPT generally agree well with those of HMX and its

derivatives. Both oxygen atoms in the molecule are involved in

C-H. . .0 type hydrogen bonding. The molecules in the crystal are linked

together mainly by two weak hydrogen bonds, C(2)-H(3) . . .0(2) and C(5)-

o o H(9)...0(2), where the C...0 distances are 3.28A and 3.39A respectively.

59
INTERAGENTY AND UNIVERSITY COLLABORATIVE PROGRAMS

H(I2)

H(I5)

H(I3)

H(I4)

H(IO) H(9)

Fig. 1. A molecule of DAPT with thermal ellipsoids to enclose 50%

probability. The isotropic hydrogen atoms are scaled down

to an arbitrary small size.

Fig. 2. DADN molecule.

60
INTERAGENTY AND UNIVERSITY COLLABORATIVE PROGRAMS

CRYSTAL STRUCTURE OF 1,5 DIACETO-3,7 DINITRO-1,3,5,7,

TETRAZACYCLO-OCTANE

C. S. Choi

(Picatinny Arsenal, Dover, NJ)

and

A. Santoro

The compound, 1,5 diaceto-3,7, dlnitro-1,3,5,7, tetracyclo-octane,

C„H ,N,O

fi

, (hereafter referred to DADN) , is also a derivative of HMX.

Preliminary investigation by precession photograph with MaKa radiation

indicated that the space group is monoclinic P2- . with two molecules per

unit cell. The cell dimensions are a=7. 422(1) b=13, 253(2) c=6. 156(1) and

B=103.38(l)° . Using an automated 3-circle x-ray diffractometer with MaKa,

a total of 1342 independent reflections were measured within the limiting

sphere of 90° in 26 angle, of which 1149 reflections were recorded as observable. The structure was solved by the direct method using the

program X-RAY72 system, and the hydrogen atoms were located by difference

synthesis. The structure was further refined by the full matrix least

squares method to the final R-index, WR=0.05 and R=0.04. The DADN

molecule shown in figure 2 possesses a center of symmetry and is isostructural with the $-HMX molecule, which is an interesting contrast to the

TAT (1,3,5,7, tetraceto-1,3,5,7, tetrazacydo-octane, NBS Technical Note

758, 1972) molecule which has a conformation similar to the a-HMX with

2-fold rotation symmetry. The acetamide groups and the N-N09 groups are both planar. The bond lengths and angles agree well with those of the

HMX and its derivatives.

61
INTERAGENTY AND UNIVERSITY COLLABORATIVE PROGRAMS

REFINEMENT OF THE CRYSTAL STRUCTURE OF MONOVALENT METAL AZIDES

C. S. Choi

(Picatinny Arsenal, Dover, N.J.)

and

E. Prince

Monovalent metal azides are ionic crystals, consisting of spherical

metal cations and linear N_ anions. Both cations and anions always

occupy centrosymmetric sites in the crystal. Hence the thermal motions of

an azide anion may be treated as a rigid body motion if we neglect the

comparatively small amplitude of the N-N stretching vibrations.

KN

3;

The crystal structure of KN„, known to be I4/mcm, was refined to

wR=0.022 R=0.020 by the constrained rigid body method using 166 reflections.

o o The observed N-N distance, 1.174A, becomes 1.184(1) A when corrected for

libration. The rigid body parameters for Nr

anion obtained from the neutron

data refinement were fitted to a set of 145 x-ray reflections (obtained

by Miiller) . In this fit the scale factor, a secondary extinction parameter,

and the thermal parameters of the potassium cations were adjusted. The

fit was extremely good, with wR=0.026 R=0.022. The fit is far better than

Miiller' s results, which were wR=0.042 and R=0.038.

6-NaN

3

:

o A total of 94 independent reflections were collected, using 0.983A

wavelength neutrons. The structure was refined by the rigid N_ group

model to the final R-index wR=0.024 and R=0.026. The observed N-N distance,

o o 1.162A, becomes 1.180(1) A when it is corrected for libration. It is

interesting to notice that the libration amplitude of the N anion in

8-NaN_ (approximately 14°) is much larger than that in KN

3

(approximately

8°), although the temperature of the B-NaN sample (room temperature) is

only a few degrees above the phase transition temperature.

T£N :

62
INTERAGENTY AND UNIVERSITY COLLABORATIVE PROGRAMS

The reflections in an entire hemisphere of reciprocal space were

o investigated at room temperature out to a maximum 26 of 100° (>=0.983A).

Of 169 independent reflections within range, only 77 had observable

intensity. The structure was also investigated at lower temperature,

260 K, which is approximately 12°C above the transition point. Using

1.23A wavelength neutrons, 84 observed reflections were collected. At

both temperatures least squares refinements were not successful because

of the so-called false minimum catastrophe. This difficulty in the

refinement was resolved when a lower symmetry space group, I4cm, was

used as the initial space group. The correct space group, 14 /mem, was

used only at the final stage of the refinement. The final R- indices were,

wR=0.018 R=0.016 for the 260 K data and wR=0.027 R=0.039 for the room

temperature data. The N-N distances of the azide anions, after correction

o o for libration, were 1.184(1)A for the 260 K structure and 1.181(4)A for

the room temperature structure.

The librational motions and the N-N bond lengths of 8-NaN , KN_,

TUN (260 K) and T£N (300 K) , are summarized in table 1. It is clear

that the N-N bond lengths of the N anions of the monovalent metal

-J o azides are essentially the same, probably 1.182±0.002A.

Table 1, Libration tensor elements (radian )) and N-N bond

lengths of the azide anions

Libration

Tensor B-NaN

3

KN

3 T£N (260K) T£N (300K)

hi .0150 .0110 .0270 .0274

L

22

.0150 .0063 .0069 .0097

L

33

.0000 .0000 .0000 .0000

N-N bond length (A)

Corrected : 1.180(8) 1.184(6) 1.184(1) 1.181(4)

Uncorrected: 1.162 1.174 1.164 1.159

63
INTERAGENTY AND UNIVERSITY COLLABORATIVE PROGRAMS

THE STRUCTURE OF DEUTERIUM PEROXIDE

E. Prince

S. F. Trevino and C. S. Choi

(Picatinny Arsenal, Dover, NJ)

The crystal and molecular structure of H

9 0_ were determined in the

1 early 1960s by Busing and Levy . Extensive Raman and IR studies by

2 Armen, et at. on both H_0_ and DO have shown some interesting differences resulting from the isotope substitution. The 0-D stretch frequency

shows that the corresponding force constant is larger for the deuterated

compound. Also the 0-0 stretch frequency is the same for D~0 and for

H

9 ?

, although the increased mass might be expected to result in a lower

frequency. Because these effects suggest differences in molecular

structure, we undertook a neutron diffraction study of the deuterated

compound

.

A single crystal of D~09 was grown in a quartz tube approximately

2 mm inside diameter with one end drawn down to a fine capillary. A

seed nucleus was formed by dipping the end of the capillary in liquid

nitrogen, after which the entire sample was cooled to -14°C. When viewed

between crossed polarizers the resulting solid showed sharp extinction.

The crystal was mounted in a temperature-controlled cryostat, and was maintained at -15°C throughout the experiment.

The structure is tetragonal, space group P4, 2, 2 (or P4~2, 2).

The constants were determined on the dif fractometer . The cell constants,

determined on the dif fractometer , were aj=4. 035(5), b=7.97(l). There are

four D„0 molecules in the unit cell. Of 113 independent reflections

2. 2. o within the sphere defined by X=1.230A and 2 max-106° 107 had observable

intensity. The structure quickly refined to R-.027, Rw=.038, using

anisotropic temperature factors and an isotopic extinction parameter.'

o The 0-0 distance, uncorrected for thermal motion, is 1.453A, in

exact agreement with the Busing and Levy result for H-0- . The 0-D

o 2. Z distance, however, is 0.995A (with a riding model correction) as compared

o with 1.008A in HO. This is consistent with the observation of a stronger

64
INTERAGENTY AND UNIVERSITY COLLABORATIVE PROGRAMS

force constant. The dihedral angle is 91.1° which is significantly

different from 90.2° in HO. The 0-0-H bond angle is 101.9°, compared

with 102.7°. These results do not suggest an explanation for the fact

that the 0-0 stretching frequency is not reduced, although the more

compact molecule may have stronger 0-D and D-B repulsions

.

The data are further analyzed using a restricted rigid body

constrained refinement.

1

W. R. Busing and H. A. Levy, J. Chem. Phys., 42_, 3054 (1965).

2 Jose L. Arrau, Paul A. Giguere, Motoko Abe and Robert C. Taylor,

Spectrochimica Acta, 30A, 777 (1974).

THE LATTICE DYNAMICS OF DEUTERIUM PEROXIDE

S. F. Trevino and M. K. Farr

(Picatinny Arsenal, Dover, NJ)

and

J. L. Arrau and P. A. Giguere

(Laval University, Quebec, Canada)

The energy and momentum of phonons propogating along the crystallographic c direction in D„0 have been measured. A single crystal

(volume 5cc) of 99.5% D„0

9 was grown by the Stockbarger method. The

crystal was maintained at -30°C during the measurements which were performed on a triple axis spectrometer.

Deuterium peroxide crystallizes in an ordered tetragonal cell of

symmetry P4.2.2 with four molecules in the primitive cell. There are

-1

24 phonon branches of rigid body motion, all with energies below 300 cm with the exception of the four librational modes corresponding to rotations about the low moment of inertia 0-0 axis. The classification of

observed phonon resonances to symmetry species was accomplished by the

use of group theoretical selection rules. Figure 1 shows the results of

65
INTERAGENTY AND UNIVERSITY COLLABORATIVE PROGRAMS

Fig. 1. Phonon dispersion curves in D^ along the [00; ] direction.

Open circles indicate present neutron measurements at 244K,

solid triangles represent Raman data of Amau et at.

1

at 190K,

and solid circles are from the infrared measurements of

2 Giguere et at. at 90K.

66
INTERAGENTY AND UNIVERSITY COLLABORATIVE PROGRAMS

the measurements of the 20 low energy branches and T point data from

1 2 infrared and Raman studies '

. The branches are plotted in pairs corresponding to those symmetry species which stick together at the Z-point

(zone boundary). The solid lines are drawn as guides to the data. A

model is under development for fitting the data and should result in

valuable information concerning the hydrogen bonds and other forces which

constitute the crystal potential.

1. J. L. Arnau, P. A. Giguere, M. Abe, and R. C. Taylor, Speatroahim.

Acta 30A , 777 (1974)

.

2. P. A. Giguere and C. Chapados, Speatroahim. Acta Tl_> 1131 (1966).

LATTICE DYNAMICS OF KN3 AT 298K

S. Trevino, M. Farr and H. Prask

(Picatinny Arsenal, Dover, NJ)

The metal azides are a class of compounds, the chemical properties

of which range from quite stable to highly unstable. In comparison with

other "energetic" materials, they also have relatively simple crystal

structures and appear to offer the best prospects for a quantitative

description of the lattice dynamics of a homologous series of explosive

1 o substances. KN-, with two formula units per primitive cell and D,, space

group, is among the simpler of the metal-azide salts and has been the

subject of considerable spectroscopic study, including very limited

dispersion curve measurements . The dispersion curves of KN^ have now been measured much more com- pletely with the primary emphasis placed on the highest symmetry direction [00u]. Characterization of observed modes was greatly facilitated

2

by the use of group-theoretical selection rules for neutron scattering . Preliminary results are shown for the [OOy] direction in figure 1. A

rigid ion force model calculation to fit all observed spectroscopic

frequencies is in progress.

67
INTERAGENTY AND UNIVERSITY COLLABORATIVE PROGRAMS

200

150

100

50

7^

tf

/

/

/ X

[oo/]

KAzuJxfp

T (Eu)[i-^

R(A2g)

RjBig) - R(Eg)[

X

T(Eu)[

T(Eg)X R

X4 a T(Biu)^ —A A

^=S^

1.0

Fig. 1. Measured dispersion curves (various symbols), infrared (X,IR)

and Raman (X,R) spectroscopic results and irreducible representations of [OOu] lattice modes in KN at 298K (33cm~ =1 THz)

1. K. R. Rao, S. F. Trevino, H. Prask and R. D. Miscal, Phys. Rev.

B4, 4551 (1971).

2. R. C. Casella and S. F. Trevino, Phys. Rev. B6_, 4533 (1972).

68
INTERAGENTY AND UNIVERSITY COLLABORATIVE PROGRAMS

POLARIZED RAMAN STUDY OF AMMONIUM PERCHLORATE AT LOW TEMPERATURES

H. J. Prask

(Picatinny Arsenal, Dover, NJ)

and

G. J. Rosasco

(Inorganic Materials Division)

The dynamical behavior of NH, groups in NH.C10 (referred to hereafter as AP) has been the subject of considerable measurement and

speculation because of the very low barrier to NH, rotation in this

salt. However, it is only very recently that the structure has been

determined at low temperature . Following the structure determination,

we have made a direct examination of Raman-active vibrational modes at

low temperature (12 to 297K) in oriented single crystal AP and d-AP

The Raman spectrum of AP can be ascribed to three characteristic

types of modes: the "external" lattice phonons, the "internal" modes

of CIOt group, and the "internal" modes of NH, group. The ClOyiinternal

modes are relatively temperature insensitive and correlate with the C

16

S

site splittings of a tetrahedral ion in the D_, space group at all tem- +

peratures. The NH, internal mode spectra show large temperature effects

in going from 297K to 12K. At room temperature these spectra exhibit

extremely broad unresolved bands in the characteristics NH, stretching

and bending regions whereas at the lowest temperatures these bands are

sharp and the site group splittings well resolved. The low temperature

1 6

splittings and symmetries are compatible with the C site in V~,. The

external lattice mode region also shows dramatic temperature effects; in

particular, the lowest frequency modes of B. and B^ show anomalous

damping with increasing temperature as shown in figure 1.

To characterize these modes as to rotational or translational nature,

high resolution spectra were measured for AP at 18, 49 and 82K, and d-AP

at 18K. The shift upon deuteration shows that the modes are predominantly

translational in character. It is believed that the damping arises from

anharmonic coupling of the large amplitude NH, rotatory motions with the

Bn and B„ translations. Correlation of these results with changes lg 3g

observed in the internal mode spectra is in progress

.

69
INTERAGENTY AND UNIVERSITY COLLABORATIVE PROGRAMS

297K

-I I I I I I I I I l_

II3K

-J I I I I I L70K

i i

' i

^V^v.J k=Z

200 180 120 80 40

297 K

Fig. 1. Smoothed Raman Spectra as a function of temperature for the B

lg

and B_ modes in NH.C10. . Relative intensities are arbitrary.

3g 4 4

1. C. S. Choi, H. J. Prask and E. Prince, J. Phys. Bev. y in press.

70
INTERAGENTY AND UNIVERSITY COLLABORATIVE PROGRAMS

SUBLATTICE MAGNETIZATION OF RARE EARTH

LAVES PHASE COMPOUNDS

J . J . Rhyne

(Naval Ordnance Laboratory, White Oak, MD)

Neutron diffraction provides a unique method for determining the

magnetic sublattice magnetization in materials which have more than one magnetic site, for example the series RT~ where R is a rare earth atom

and T is either Fe, Ni or Co. We have continued work on the RFe„ series

compounds to obtain the temperature dependence of rare earth and Fe

sublattice magnetization in the ordered range from 4K to the Curie

temperature, typically 650-700 K. In the Laves phase materials, the rare earth-iron exchange is significantly weaker than the iron-iron

exchange and results in a different temperature dependence for the

magnetization of the two atom sites. At 0K» the rare earth element exhibits

the free ion value for the magnetic moment, while the iron moment is

significantly reduced to 1.6 - 1.8 y (Bohr Magnetons) by band structure

B

effects from the 2.2 y observed in elemental iron. A theoretical

B

model to explain the observed sublattice magnetization and its temperature

dependence is being developed.

ANNEALED AMORPHOUS TbFe

2

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

(Naval Ordnance Laboratory, White Oak, MD)

One facet of the investigations of amorphous rare-earth transition

metal compounds has been the nature of the recrystallization process and

its effect on the magnetic properties. We have recently studied the

effect of annealing on the coercive force and structure of initially

amorphous TbFe„. As the material became crystalline the coercive field

abruptly increased from 100 Oe in the amorphous state to 3.75 kOe in

the recrystallized state after a 525°C anneal. An analysis of the

broadening of the magnetic and nuclear components of the Bragg lines

71
INTERAGENTY AND UNIVERSITY COLLABORATIVE PROGRAMS

13 14

28 (DE6)

Fig. 1. Fine particle broadening of (111) reflection in recrystallized

inititally amorphous TbFe„

.

(see figure 1) in the annealed specimen indicates that the amorphous structure is completely replaced by Laves phase microcrystallites of average

size 100±10A after a 415°C anneal. Further annealing to 525°C increased

the particle size to 150±10A, much smaller than the critical size for

single magnetic domains.

Feasibility of this method for fabricating fine particle, high

coercive force permanent magnets has thus been demonstrated; indeed,

the resultant materials have a respectable energy product of 8.7 MGO

(1 MGO = 10 ergs/cm ) , compared to 20 MGO obtained for the best

commercially processed SmCo,. magnets.

72
INTERAGENTY AND UNIVERSITY COLLABORATIVE PROGRAMS

This large value of the energy product, achieved without optimization, means that the annealed cubic rare earth-Fe- compounds show

considerable promise for permanent magnet material that do not require

grinding, orientation and sintering.

STRUCTURAL STUDIES ON AMORPHOUS MAGNETIC ALLOYS

J. Rhyne, S. Pickart and H. Alperin

(Naval Ordnance Laboratory, White Oak, MD)

Our previously reported diffraction data on amorphous TbFe„ and new

data on YFe. have been analyzed by Fourier transformation to give the

atom correlation functions. This requires the separation of the magnetic

component of the scattering and was accomplished by elastic diffraction

methods above T in TbFe- , whereas in YFe„ it is negligible because there

is no rare-earth moment

.

Figure 1 shows this correlation function obtained for TbFe„ . A

series of peaks is observed that correspond closely to combinations of

rare-earth and iron metallic radii, as indicated. The height of the

peaks agrees well with a model that predicts probabilities solely on the

number of ways of achieving the various combinations —the so called dense

random packing (DRP) model. The result for YFe„ can almost be superimposed on Figure 1, as expected since the radii and neutron scattering

amplitudes are approximately equal. These results lend considerable

confidence to the model, and the next step will be to construct spin

models, based on DRP positions, for comparison with our observed spin

correlation functions from magnetic scattering.

We have also completed neutron diffraction studies on a series of

Tb Fe n with x = .12, .45 and .75 (in addition to x = .33 described

x 1-x

above). All the compositions were found to be amorphous, demonstrating

one of the potential advantages of these amorphous alloys , namely that

73
INTERAGENTY AND UNIVERSITY COLLABORATIVE PROGRAMS

TbFe 2 [AMORPHOUS)

ATOMIC = RDF

• = Fe ATOM

O = Tb ATOM

2.5 5.0

r|A)

7.5 10.0

Fig. 1. Multiple Atomic Pair Correlation Function for TbFe„. The arrows indicate combinations of Fe and Tb atoms in contact

at their Goldschmidt radii (see text)

.

they can be fabricated over a wide composition range with no restriction

to definite compounds, as are crystalline alloys.

J. J. Rhyne, S. J. Pickart and H. A. Alperin, Phys. Rev. Letters t 29_

1562 (1972).

74
INTERAGENTY AND UNIVERSITY COLLABORATIVE PROGRAMS

DYNAMIC SPIN BEHAVIOR IN AN AMORPHOUS MAGNET

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

(Naval Ordnance Laboratory, White Oak, MD)

and

D. L Price

(Argonne National Laboratory, Argonne, IL)

We have previously shown that the magnetic spin distributions in

atomically amorphous materials are themselves also amorphous in nature.

A second fundamental question to be answered regarding this new class

of materials is , how do the magnetic moments fluctuate in time in

response to some disordering influence? In particular, what are the

nature of the excitations, what is the relation between their energies

and momenta and how do these quantities for an amorphous magnet compare

to the crystalline form? These questions have now been answered by

means of neutron inelastic time-of-flight scattering measurements on an amorphous TbFe„ sample prepared by sputtering and a polycrystalline sample

of the same composition. Representative data (almost entirely of magnetic origin) are summerized in Figure 1. The most striking result is

that at 295K (which is below the Curie point) , in contrast to the

crystalline ferrimagnet which exhibits the usual discrete, well-defined

spin wave excitations, the spectrum of the amorphous magnet is smeared

out and shifted to lower energies. This can be understood as due to

the inability of the shorter wavelength (higher energy) excitations to

propagate in a disordered structure. The occurrence of localized modes,

the lack of atomic order and finite lifetime effects contribute to the

smearing out of well-defined excitations.

Above the Curie temperature (4A3K) the peak at AE = is considerably broadened, indicative of paramagnetism.

75
INTERAGENTY AND UNIVERSITY COLLABORATIVE PROGRAMS

0.2

0.2

0.1

TbFe2 TOF INELASTIC SCATTERING

Q=l.25 A"

1

443 K AMORPHOUS

POLYCRYSTAL

295 K

,^Wjq

I I I I

1.2

1.0

0.8

0.6

0.4

0.2

12 15 18 21 AE (meV)

Fig. 1. Time-of-flight , neutron inelastic scattering spectrum of

amorphous and crystalline TbFe„ for a momentum transfer of

o-l

q = 1.25A . The Curie temperature of amorphous material is

^385 K.

76
INTERAGENTY AND UNIVERSITY COLLABORATIVE PROGRAMS

SMALL ANGLE NEUTRON SCATTERING FROM AMORPHOUS MAGNETS

S. Pickart, H. Alperin and J. Rhyne

(Naval Ordnance Laboratory, White Oak, MD)

In addition to spin and atom correlations and excitation spectra,

neutron scattering can provide information about long-wavelength static

fluctuations in the magnetization density from amorphous magnets by the

method of small-angle, quasielastic scattering. We have obtained

striking new results by this method on the compounds TbFe_ and YFe_ that

provide insight into the nature of the magnetic transition and the spontaneously ordered state in these materials

.

Data for TbFe9 are shown in figure 1. Two features are apparent in

this figure: a weak "critical" anomaly near T and a giant, temperature

dependent component below T . The scattering above T behaves like the

critical scattering normally observed in a ferromagnet, but the spin

correlation length remains finite at T instead of diverging. The hitherto unobserved component below T can be analyzed on a model analogous to

particle-size broadening and yields a cluster size comparable to the

correlation length at T . We have therefore proposed a new model for the

amorphous magnetic transition in which the critical spatial fluctuations

are "frozen-in" at T and survive as a sort of magnetic "graininess"

2° C

below T of ^10 A dimensions (not related to any structural inhomogeneities) . The origin of this effect is as yet unknown but depends on the

presence of a magnetic rare-earth since YFe„ showed only scattering

similar to that above T . However, the correlation length is much smaller

c o in YFe9

, never reaching more than 10A even at low temperatures, consistent

with the fact that it does not order magnetically.

77
INTERAGENTY AND UNIVERSITY COLLABORATIVE PROGRAMS

1»•o

en 6

o

cr

UJ

>- 4

CO

O

CRITICAL SCATTERING IN

AMORPHOUS TbFe 2

k5 = 2.577 A~'

q=0.04A"

q=O.I4A-'

~=-J- 300 340 380

T(K)

420

Fig. 1. Small angle neutron scattering from amorphous TbFe- in the

critical region, corrected for absorption and instrumental

background. (Data taken for q = ,02A would be off scale and are not plotted for convenience, while data at higher q con- tinue to decrease slightly and are essentially flat with T.)

78
INTERAGENTY AND UNIVERSITY COLLABORATIVE PROGRAMS

LATTICE DYNAMICAL STUDIES OF BERYLLIUM AT ELEVATED TEMPERATURES

H. Alperin, J. Rhyne, S. Pickart

(Naval Ordnance Laboratory, White Oak, MD)

Measurements of the phonon dispersion of beryllium have been extended

to higher temperatures (778°C) in order to look for changes with temperature that could be correlated with the ductility anomaly. Measurements

have also been taken in the [1010] propagation direction, thus completing

all three principal directions. A general fall-off of phonon energies

with increasing temperature is noticed but there is no obvious indication of any anomaly. However, at room temperature, at the zone boundary

of the [1120] direction it is noticed that the LA(//) mode is degenerate

with the TA(//) mode and not with the L0(//) mode. This is opposite to

the situation in zinc and magnesium but similar to that in brittle

holmium. It is now planned to carefully follow these mode orderings

to see if there is a reversal at a higher temperature.

NEUTRON SCATTERING FROM AMORPHOUS SELENIUM

L. Rauber and V. Minkiewicz

(University of Maryland, College Park, MD)

The scattering function S^oo) for amorphous selenium has been

studied for a wide range of temperature, energy transfer, and momentum

transfer. The measurements have established that the dominant features

of S^jw) consist of a sheet of scattering at zero energy transfer along

with low energy phonon side bands. The sheet of scattering at zero energy transfer is the counter part of the Bragg scattering in the

ordered phase. This zero energy component has a strong temperature

dependence, and increases with decreasing temperature. This temperature

dependence reflects the dependence of the Debye-Waller factor on temperature. A Debye model was used to fit this temperature dependence, and was found to be very satisfactory, yielding a Debye temperature of

94K. This value should be contrasted with that found for the ordered

79
INTERAGENTY AND UNIVERSITY COLLABORATIVE PROGRAMS

phase of 123K. This decrease in the Debye temperature in going from the

system with long-range order to the amorphous state could be a general

feature of all disordered lattices, and indicates an increase in the low

energy part of the phonon density of states in the disordered state.

The phonon contribution to SCO^uO was then compared with the theory

of multiple phonon scattering developed by Sjolanden. Using the same Debye temperature that was obtained from the elastic component (i.e.

8 =94 K) , the theory satisfactorily reproduces the observed spectra.

SCATTERING AMPLITUDES - SMALL ANGLE SCATTERING

C. S. Schneider

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

Prism refraction experiments using Ge , Cu and SiO single crystal

90° prisms have been carried out. This work completes for the present our program of precise measurements of neutron scattering amplitudes. The

refracted angles A can be fit to a trigonometrically exact equation for

the refractive index deviation from unity: 6=r-[sin <f>-sin (<t>-A) ]=—r

where <J> is the glancing angle of the beam from the first prism surface and

A has been corrected for the small attenuation-dispersion and second order

collimation effects. Thus the nuclear scattering amplitude for silicon

becomes b„.= 4.1478(16) fm while the new results are b^ =8.1898(16) fm

Si Ge

and b = 7.646(6) fm. The quartz results are being analyzed.

Design and fabrication of the raised double—crystal small angle

scattering (SAS) neutron diffractometer have proceded, with final

assembly due late this year. The first pair of crystals used to raise

the beam is mosaic copper and they serve to lower background nicely.

The SAS diffractometer will initially use Bonse-Hart multiple reflection

crystals in order that the low angles of diffraction (seconds of arc)

from low density defects in the micron size range may be observed.

This is the limit of application of SAS instruments so that all other

80
INTERAGENTY AND UNIVERSITY COLLABORATIVE PROGRAMS

size distributions will be more easily extracted from the diffraction

intensities. This instrument can have a number of applications in the

study of particle and defect size and density distributions, etc. in

solutions and in solid state and polymer physics and metallurgy.

THREE AXIS NEUTRON SPECTROMETER

A. Cinquepalma, W. Rymes, J. M. Rowe, J. J. Rush, and R. S. Carter

and

H . Prask and S . Trevino

(Picatinny Arsenal, Dover, NJ)

The fabrication of this high-efficiency, high-versatility three axis

neutron spectrometer has been completed. The two complete analyzer

systems, which will be employed in order to increase the rate of data

taking, have been constructed and tested. All shielding necessary to

interface the spectrometer to the NBSR beam port has been designed and

fabricated. This includes a pneumatically operated shutter located in

the saddle between the spectrometer and the beam port which serves to

close off the main neutron beam. The shutters insert can be replaced

with an insert housing an LN_ cooled beryllium filter, should this be

desirable. Installation of the facility should be completed this coming

fall.

81
D. Non-RRD [IBS Programs

ACTIVATION ANALYSIS SECTION: SUMMARY OF ACTIVITIES

D. A. Becker and P. D. LaFleur

(Analytical Chemistry Division)

The Activation Analysis Section of the Analytical Chemistry

Division is physically located in the NBS Reactor Building. It has

at present eleven full time members, and has programs in the areas of

reactor neutron activation analysis, isotopic source neutron activation

analysis, photon activation analysis, and polarography . 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. Water Sampling and Sample Handling for Trace Element Analysis

S. H. Harrison, and P. D. LaFleur

The study of natural water systems to determine their trace and

ultratrace element profiles is now of great interest to environmental

chemists. The validity of the data being produced is directly related

to the validity of the sampling procedures used. In the Analytical Chemistry

Division there is a continuing project to study and develop water sampling

and pre-analysis handling procedures for trace element profile determinations,

In order to investigate sampling protocols, an analysis technique

capable of multielement determinations on a single sample was needed.

Nondestructive neutron activation analysis of freeze-dried water was chosen for this purpose. This technique was used to evaluate a Teflon

water sampler developed in our Division. This evaluation consists of

replicate sampling studies and a comparison of results with those from

a popular commercial water sampler. To demonstrate that the sampling,

treatment and analysis procedure developed is applicable to environmental

problems, a study of two waterways, suspected of abnormal trace element

content, was initiated.

82
NON-RRD NBS PROGRAMS

During this evaluation, the sampling, storage and handling techniques

used are reevaluated, and changed if necessary in order to provide a convenient, workable and scientifically valid water sampling system.

Radioactive tracer studies for determining the trace element retention

of 21 elements during the freeze-drying process have been completed.

The results show that all but the most volatile elements (e.g. Hg,) are quantitatively retained in a residue resulting from the freeze-drying

of 100 g of filtered river water. Talks presenting this data have been

given at the 8th (1973) MARM of the ACS (American Chemical Society) and

the Fall 1973 Meeting of the ANS (American Nuclear Society) . A manuscript

for publication in Analytical Chemistry is in preparation.

b. Forensic Activation Analysis - T. E. Gills, L. T. McClendon and

D. A. Becker

In cooperation with the NBS Law Enforcement Standards Laboratory

(LESL) , the Activation Analysis Section of the Analytical Chemistry Division

has a program for the examination and evaluation of the neutron activation

analysis technique for the determination of gunshot residues (GSR)

.

This technique analyzes for minute quantities of the elements barium

and antimony, which are components of the primer material and are deposited

on certain areas of the hand during discharge of a firearm.

Various methods for residue collection as well as the neutron activation technique for barium and antimony analysis, have already been examined

and evaluated, and recommended procedures for both these areas are presently being written. The activation analysis procedure involves irradiating

the residues in a nuclear reactor to make them radioactive, chemically

separating the elements of interest (i.e., barium and antimony), and

then quantitating them on a radioactivity detection system.

In addition to the procedures, information on the stability of

residues on the hand as a function of time after firing, and on the

evaluation of background levels of barium and antimony to be found in

the general population is being obtained and evaluated. This program

83
NON-RRD NBS PROGRAMS

is contributing significantly to the scientific basis for the GSR technique,

and will greatly assist law enforcement officers in their criminal investigations.

In another cooperative program with LESL, the Activation Analysis

Section is evaluating the use of trace element profiles (TEP) for the

unique identification of automobile headlight glass. The TEP technique

entails the measurement of many trace elements in a specific piece of

headlamp glass, and compares the concentrations of these trace elements

to another piece of glass thought to come from the same source. This

TEP technique has been used before in forensic analysis, and has been

shown to be extremely useful in a number of areas.

c. The Application of a Mass Separator to Activation Analysis -

H. L. Rook, J. E. Suddueth and D. A. Becker

Iodine-129 is an isotopic species of considerable interest. It is

produced in trace quantities by natural processes and has a half life

7 129

of 1.59x10 years. Thus, a steady state concentration of ' I had been

established in the biosphere prior to the advent of the nuclear age.

Since that time, its concentration is believed to be steadily increasing.

Thus, for health and safety reasons, a reliable method for determining

129

I concentrations in biological and ecological matrices is of great

interest

.

129

Due to the long half life of I, low level counting techniques

are not normally sensitive enough to enable its direct determination

at natural levels.

A unique procedure has been developed for the determination of

129

I which couples neutron activation with mass separation. The procedure

results in a significant improvement in sensitivity, thus allowing analyses

to be performed on a variety of matrices which heretofore had not been

investigated

.

Mass separation is an extremely important tool as it offers the

130 T £ 126 x ,„.-...:. only means of separating I from I in the irradiation products.

84
NON-RED NBS PROGRAMS

This fact, plus the virtual elimination of other radioactive contaminants

accounts for the improved sensitivity.

Method development and analytical procedures have been completed

-13 -14 129 and analytical results at the 10 to 10 gram I level have been

demonstrated on real samples.

d. Radiochemical Separation of Selenium, Arsenic, Zinc, Cadmium,

and Mercury in Environmental Matrices by Neutron Activation Analysis -

E. Orvini, T. E. Gills, and P. D. LaFleur

Recently, heavy metal contamination of the environment has been

recognized as serious pollution problem. Among these metals, particular

attention is being given to Se, As, Zn, Cd, and Hg.

Neutron activation analysis is capable of high sensitivity for

the determination of these elements. However, the most sensitive and

useful (n,y) reactions involve short half lived isotopes of As, Zn , Cd,

and Hg, thus requiring chemical separation of these elements from the

activated matrix.

A procedure has been developed for the simultaneous determination

of selenium, arsenic, zinc, cadmium, and mercury in different environmental

matrices. The radiochemical separation method involves the combustion

of the samples, followed by reduction with carbon monoxide and volatilization of the metals at high temperature. The method was initially tested

with radiotracer experiments; then by analyzing some NBS Standard Reference

Materials. The procedure has been used to determine the Se, As, Zn

,

Cd and Hg concentration of some new Standard Reference Materials being

prepared by the National Bureau of Standards.

e. Selective Radiochemical Separation of Chromium in Biological and

Environmental Matrices - L. T. McClendon

Chromium has now been identified as an essential trace element

in human nutrition. At high concentrations, or in different chemical

states, it can also cause deleterious or toxic effects. There is thus

a definite need for reliable methods of analysis for chromium at the

85
NON-RRD NBS PROGRAMS

trace level. A recent laboratory intercomparison on fossil fuels (coal,

fly ash, fuel oil), which was conducted jointly by the Environmental

Protection Agency (EPA) and the National Bureau of Standards (NBS),

pointed up the sad state of chromium determinations as performed by

most of the analytical community. Three standard analytical techniques

were used—atomic absorption, emission spectrometry, and activation

analysis. Of the twenty-two laboratories which reported results for

chromium in fly ash—an environmental matrix in the process of being

certified for a number of elements, including chromium, at NBS —only

two were within the NBS recommended value of 131 ± 2 yg/g. The others

ranged from 21 yg/g to 289 yg/g, with no discernible pattern. As a result of these round robin analyses, and other considerations, it became

evident that more biological and environmental materials needed to be

analyzed and certified for their chromium content.

When the chromium concentration is less than one microgram/gram,

a radiochemical separation is almost obligatory to optimize the sensitivity

and to eliminate interferences and the long time delay for analysis.

An efficient chemical separation for chromium is certainly advantage*- ous for biological and environmental materials. A destructive NAA technique,

using a tribenzylamine-chloroform solution to extract chromium, has

been developed at NBS to determine the chromium content in five materialsfly ash, coal, orchard leaves, urine, and bovine liver. The results

using this radiochemical separation technique have been good, and have

agreed closely with those which were able to be analyzed nondestructively

by NAA.

f. Activation Analysis Using an Isotopic Californium-252 Source -

P. D. LaFleur and J. E. Suddueth

Previous research efforts in the area of Cf-252 activation analysis

have included the determination of specific elements in metal organic

Standard Reference Materials, the evaluation of lead analysis for paint

samples, and the production of an experimental set of sensitivity tables

86
NON-RRD NBS PROGRAMS

for Cf-252 activation. During the past year, a new set of eight (8)

larger size Cf-252 sources were obtained, and subsequently evaluated

as to neutron flux variation and absolute neutron flux obtainable. The

7 -2 -2

absolute flux value obtained was A. 6x10 n*cm sec at the maximum

thermal neutron flux position. These measurements were made on a copper

foil, using the Cu (n,y)Cu nuclear reaction.

An effort is currently underway to evaluate the best possible precision and accuracy obtainable with these sources. To date the results

indicate that a precision of ±0.3% is obtainable, with an accuracy

slightly greater than this. These procedures are presently being evaluated

in the analysis of sodium and chlorine in a clinical blood serum reference

material.

g. Photon Activation Analysis Using the NBS LINAC - R. Lindstrom and

D. Becker

With George Lutz on a leave of absence in West Berlin, the Activation

Analysis Section had need for someone to take over the LINAC activation

facility. We were fortunate in having Richard Lindstrom agree to take

over this responsibility, and he is in the process of evaluating a number

of photon activation analysis systems for the determinations of elements

not readily analyzed by neutron activation techniques. The elements

of primary interest include nickel, lead, calcium, and magnesium. Several

light elements are determinable in a variety of matrices through the use

of short-lived radionuclides. These include carbon, nitrogen, oxygen,

and silicon. In addition, some effort is being made to develop analytical

capabilities for several elements which are determinable by neutron

activation techniques but not easily determined by other trace element

analytical techniques, such as arsenic and antimony.

87
NON-RRD NBS PROGRAMS

h. High Sensitivity Activation Analysis - D. A. Becker and J. E.

Suddueth

Activation Analysis has progressed from its comparatively recent

beginnings into one of the most versatile and useful trace element analytical

methods currently available. It has the capability of analyzing almost

any matrix, for many different elements, either destructively or nondestructively . At the National Bureau of Standards, activation analysis

must compete with the other trace element techniques which are available,

and must consistently provide analytical results which are both accurate

and precise in order to remain competitive.

These requirements for high accuracy and precision have evolved

into an active program of critical evaluation of those variables and

factors which affect all aspects of the technique. This had led to

a systems analysis approach to evaluation, in which the technique has

been divided into four specific areas of involvement. The first is

Sampling and Sample Handling, and includes obtaining the sample as well

as all manipulations up until irradiation. Area 2 is called Irradiation

Parameters, and includes all aspects of irradiation. This irradiation

may be by nuclear reactor, LINAC, or by any other irradiation source.

This aspect was discussed in last year's Progress Report, concerning

the neutron flux characterization of the NBS Nuclear Reactor. Area 3

is Radiochemical Separations and is the only area which is not absolutely

necessary for each analysis. Of interest in this area would be dissolution

and separation procedures. Area 4 is Detection Systems, and is the

subject that was investigated this past year, namely, the evaluation

of accuracy and precision in conventional gamma-ray counting systems.

It should be mentioned at this point that some of the factors to

be discussed may seem relatively minor to some analysts, with magnitudes

of one or a few percent each. Their significance to an organization

like NBS is obvious. In addition, however, if such variables are left

uncontrolled and two or more should sum, they may very well adversely

affect even routine analytical results. It is important, therefore,

that any good analyst be at least aware of such potential problems.
NON-RRD NBS PROGRAMS

Basically, most activation analysis detection systems consist of

a single gamma-ray detector [Ge(Li), Ge, or Nal(Tl)] and associated

electronics, with a sample positioning device of some sort. With such

a system, a variety of sample radioactivity levels and sizes can be

counted rather easily. What is often not realized is that even relatively

small differences between sample and standard, or from sample to sample,

in any one of many variables can often result in a significant bias

in the resulting count rates.

In an attempt to experimentally evaluate the systematic biases

associated with gamma-ray counting, they were separated into eight (8)

sub-groups as follows: Configuration, Positioning, Density, Homogeneity,

Intensity, Radioisotopic Purity, Peak Integration, and Nuclear Constants.

These sub-groups were then individually examined and investigated, and

the results will be published in the open literature,

i. The Determination of Oxygen in Human Tissue Using the Nuclear Track

Technique - B. S. Carpenter

While the reactor is being used to analyze materials that touch

our everyday lives, chemists in the Activation Analysis Section are also using it to expand the frontiers of medicine. Several lines of

evidence suggest that the amount and distribution of oxygen in human

tissues may be critical for certain diseases. A low level of oxygen

in the brain, for instance, has been linked with mental disorders. And

certain types of tumors are characterized by either too much or too

little oxygen.

But until the "Nuclear Track Technique," it was difficult for

"in situ" measurement and location of oxygen in tissues. It happens

that ordinary oxygen (oxygenl6) is not easily measurable at the trace

level, but oxygen-17 is. Therefore, the first step is to replace a fraction of the oxygen in the body by oxygen-17 (which is not as difficult

as it sounds) and the samples, say from the brain, are put into the

reactor mounted on a film of plastic. When the oxygen-17 is irradiated,

it ejects alpha particles that produce tracks in the film, tracks that

89
NON-RRD NBS PROGRAMS

appear similar, though of course smaller, to the tail of a comet. By

measuring and analyzing these tracks, and counting them, one can accurately

tell the amount and location of the oxygen-1 in the tissue being studied.

This is a method used in a collaborative program with the Weizmann Institute

of Science in Israel. This work is continuing in an attempt to evaluate

and use the information thus gained for medical diagnostic and research

purposes

.

j. Effect of Progressive Etching on Fission Track Ages - G. M Reimer

Fission track ages of some minerals are often interpreted as cooling

ages not related to any discrete thermal event . This is particularly

true of apatite, for which fission track ages are usually younger than

those determined by other radiometric methods using the same rock sample.

These younger ages are the result of annealing the spontaneous fission

tracks which > in effect, reduces the track etching rate. This lower

etching rate, with respect to the bulk etching rate of the material,

samples in fewer fission tracks being revealed than if the sample were

unannealed

.

Special consideration must be given to the etching of samples so that ages obtained can be related on a common basis . As a phenomenon

of subjective optical counting criteria and etching, the observed number

of tracks increases as the etching proceeds. Ultimately, an "etching

plateau" is reached where the track density remains constant . An annealed

sample would have a lower plateau than an unannealed equivalent . In

practice, it is usually convenient to etch to a degree short of the

plateau because of increasing interference from enlarged crystal defects

and overetched tracks. It is also difficult to know exactly when the

plateau has been reached.

An experiment with apatite shows that the etching plateau is reached

at different times for an annealed sample and an unannealed sample.

Apatite was annealed so that no spontaneous tracks were revealed even

by prolonged etching. This annealing was done because the spontaneous

tracks may have already been partially annealed and the maximum plateau

90
NON-RRD NBS PROGRAMS

might not be reached. The apatite was irradiated to induce fission.

One portion of this sample was annealed again, but this time only partially.

The average true track length equaled 77% of the average true track

length of the other portion (measured after a 30-sec etch) . Etching

was with 5% HNO , 20 °C, in five-sec intervals. The results indicate

that the spontaneous-to-induced ratio changes as a function of etching

time

.

If fission track ages of the same mineral are to be compared or related in any way on an absolute basis, particularly for a study of

a localized geologic area, it is critical that the samples be etched

identically. This is especially important when the spontaneous tracks

of some samples appear to be underetched, since they may be, in fact,

partially annealed. Only then can meaningful interpretations of the

thermal effects be made.

k. Polarographic Analysis - E. J. Maienthal

During the past year the emphasis in the polarographic laboratory

has been largely on the analysis and development of methods for the

analysis of a large number of both essential and hazardous trace elements

in a variety of biological and environmental materials. The methods

usually involve wet or dry ashing of the sample, sometimes a simple

chemical separation (such as solvent extraction or ion exchange) and

polarographic determination. Trace quantities of aluminum, antimony,

arsenic, cadmium, copper, iron, lead, nickel, titanium, zinc and zirconium

have been determined in matrices such as orchard leaves, spinach, freezedried urine, blood, river bottom sediments, fossil fuels, and borosilicate

glass.

2. Standard Reference Materials (SRM) Analyses

Much of the Section's efforts during the past year have directed

towards the development of high precision and accuracy in neutron activation

analysis, with the primary aim being the analysis and certification

91
NON-RRD NBS PROGRAMS

of NBS Standard Reference Materials

.

In total, the Activation Analysis Section during the past year

has analyzed 185 SRM samples, while determining 463 elemental concentrations. These analyses encompassed a variety of materials, including

coal, fly ash, fuel oil, glasses, urine, orchard leaves, sediments,

cholesterol, and steels. 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 - P. D. LaFleur and D. A. Becker

Biological SRM's already issued include Orchard Leaves (SRM 1571)

and Bovine Liver (SRM 1577). At present, SRM 1571 has 20 elements certified and information values for 9 additional elements. Of thesa 29

elements , over half were determined by activation analysis or the nuclear

track technique. SRM 1577 presently has 11 elements certified, with

information values on 12 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 research material, a Spinach SRM, and several additional botanical

Standard Reference Materials

.

b. Fossil Fuel SRM's - P. D. LaFleur and D. A. Becker

Emissions from the burning of fossil fuels is a possible major

source of contamination for some trace elements. A joint program between

the Environmental Protection Agency and NBS has resulted in a characterization of samples of coal and coal fly ash as well as fuel oil for use as Standard Reference Materials . These materials were analyzed

using a number of different analytical techniques, with a major role

being provided by the nuclear techniques

.

The approach that has been used was to obtain samples of the required

materials for processing and issuance as Standard Reference Materials.

92
NON-RRD NBS PROGRAMS

This processing included insuring the material had a limited particle

size range, proving homogeneity on the final bottles of samples, and

finally analyzing and certifying these materials for trace element content

content.

At present, the Trace Elements in Fly Ash (SRM 1633) is ready to

be issued. The certificate has been completed and is ready for printing.

The Fly Ash will be certified for 12 trace elements , with information

numbers on 7 additional trace elements. This material will be available

for sale in the very near future.

The Trace Elements in Coal (SRM 1632) is also ready to be issued.

The analyses have been completed and the certificate is ready for printing.

This material will be certified for 14 trace elements' with information

numbers on 5 additional trace elements. This Standard Reference Material

will also be available for sale in the very near future.

The Trace Elements in Residual Fuel Oil (SRM 1634) is undergoing

final analyses. At present 13 trace elements have been determined in

this material. Four of these elements are currently able to be certified,

while many of the others are undergoing analysis by the second analytical

techniques. This material should be finished late in 1974.

c. Trace Elements in Water SRM - H. L. Rook and J. Moody

The National Bureau of Standards is currently developing two mercury

in water standards. One standard is in the ppm concentration range,

to be used as a spike with natural water samples . The second is in

the ppb concentration range and will be used as a benchmark standard.

The most important criteria in developing these standards, as with all

SRM's issued by NBS, are homogeneity and stability of the certified

species. For mercury in water, homogeneity is no problem. Stability,

however, has been a constant problem for anyone storing solutions containing

trace mercury. Mineral acids have been employed as stabilizing agents

and are usually successful in the ppm range and above. However, in

the ppb concentration range, significant mercury is often lost to the

container walls, even when large amounts of acids are added. In an attempt to solve this problem, a study of various mechanisms to stabilize

93
NON-RRD NBS PROGRAMS

trace mercury solutions was undertaken.

After several attempts, a successful method has been developed

for stabilizing part-per-billion ionic mercury in water. Tracer studies

using carrier-free mercury-203 were conducted in order to evaluate the

various methods. Finally, a method using ionic gold to inactivate the

active sites on pre-cleaned quartz containers was found to be successful.

Analytical methods for the determination of mercury at the ppb level

have been developed using neutron activation analysis, isotope dilution

spark source mass spectroscopy, and atomic absorption spectroscopy.

The neutron activation method used a modification of the combustion

separation developed for the determination of mercury in biological

materials. Blank levels were kept low by the use of ultra-pure reagents

and by isolating all work to a class 100 clean room. Precision of the

method was estimated to be ±6% based on replicate analyses.

A second program for Trace Element in Water SRM's has been initiated.

This program is to develop a standard containing 8 trace elements, at

these levels, which are stable in solution together. Preliminary research

on this problem has just begun.

d. Environmental SRM's - H. L. Rook and J. K. Taylor

In addition to the above mentioned biological, fossil fuel, and

water SRM's, all of which could be considered environmental standards,

the Analytical Chemistry Division, in cooperation with the Office of

Standard Reference Materials, is presently in the process of obtaining

and preparing two additional SRM's specifically for environmental standards.

These are a fresh water sediment material, and an urban air particulate

material. The sediment Standard Reference Material is in the process

of being gathered near Chicago, and it will then be freeze-dried, pulverized,

and particle sized before bottling as a Standard Reference Material.

When this has been completed, analysis for homogeneity and certification

will begin.

Procedures for the gathering of a large quantity of air particulate

from the St. Louis area have been initiated. However, a number of difficulties have been encountered which have delayed the project significantly.

94
NON-RRD NBS PROGRAMS

As soon as a sufficient quantity of urban air particulate has been gathered,

the material will also be thoroughly mixed and bottled, measured for

trace element homogeneity, and then if suitable, analyzed for trace

element content and certification.

3. Cooperative and Service Analyses

In addition to the many Standard Reference Materials , a large number

of additional analyses were made on non-SRM materials. These include

both the 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 Activation Analysis Section

is required by NBS or another Government agency.

During the past year the Activation Analysis Section has had a total of nine different cooperative and service analytical projects,

resulting in the analysis of 58 different samples and 251 elemental

determinations. These samples were obtained from four other NBS laboratories, and a number of other Government agencies, including the National

Institutes of Health, the National Institute of Occupational Safety

and Health, Environmental Protection Agency, Philadelphia Veteran's

Administration Hospital, the Federal Highway Administration, Naval Research

Laboratory, and the Department of Transportation. Determinations included

29 different elements, in matrices ranging from biological materials

such as urine and thyroid granules, to brake fluid, concrete, clays,

and a tungsten-aluminum alloy. In particular, two extended programs

of analyses were undertaken in cooperation with another NBS laboratory

and the National Institute of Occupational Safety and Health. There are described further below.

a. Clay and Clay-based Papers Study - S. H. Harrison

The cooperative analytical program initiated last year with the

Fiberous Systems Section at NBS has continued. This laboratory is con- cerned with the trace element profiles of a variety of clays and claybased papers.
NON-RRD NBS PROGRAMS

The analyses were performed for both short-lived and long-lived

radionuclides. Eight short-lived elements were determined after irradiation in the thermal column pneumatic tube facility (RT-5) , while 19

longer-lived radionuclides were determined after irradiation in RT-3.

The results to date include the analysis of 14 samples for as many as

27 trace elements. This program should be completed in the near future.

b. Determination of Toxic Trace Elements in Body Fluid Reference

Sample - T. E. Gills, L„ T. McClendon, E. J. Maienthal, D. A. Becker

The measurement of elemental concentrations in body fluids has

been widely used to give indication of exposure to certain toxic materials

and/or a measure of body burden. To understand fully the toxicological

affect of these trace elements on our physiological system, meaningful

analytical data is required along with accurate standards or reference

samples . The National Bureau of Standards has prepared for the National

Institute for Occupational Safety and Health (NIOSH) a number of reference

samples containing selected toxic trace elements in body fluids. The

reference samples produced include mercury in urine at three concentration

levels, five elements (Se, Cu, As, Ni , and Cr) in freeze-dried urine

at two levels, fluorine in freeze-dired urine at two levels, and lead

in blood at two concentration levels . These reference samples have been

found to be extremely useful for the evaluation of field and laboratory

analytical methods for the analysis of toxic trace elements. In particular

the use of at least two calibration points (i.e., "normal" and "elevated"

levels) for a given matrix provides a more positive calibration for

most analytical techniques over the range of interest for occupational

toxicological levels of exposure.

Neutron activation analysis was used to determine the mercury in

urine , and the five trace elements in freeze-dried urine . For the mercury

in urine reference material, mercury-203 tracer was used to establish

suitable storage conditions for stability. The analysis was made using

mercury-197, with a chemical separation of the mercury before counting.

For the selected trace metals in freeze-dried urine, they were all analyzed

96
NON-RED NBS PROGRAMS

using a radiochemical separation after neutron irradiation. The arsenic,

copper, and selenium were separated together as the sulfides, while

nickel was determined as the dimethylglyoxine and chromium by the solvent

extraction procedure described earlier in this report. Copper and nickel

were also determined polarographically in the samples, with good agreement

to the neutron activation results.

4. Facilities

During this past year, there were two particular facilities projects

in the Activation Analysis Section which may be of interest and are included here. The first concerns our irradiation capability, namely,

the installation and evaluation of RT-6 pneumatic tube facility. The

second concerns the re-evaluation and improvement of our radioactivity

detection capabilities. These two projects are described below.

a. Pneumatic Tube Facility RT-6 - J. E. Suddueth and D. A. Becker

The ET-6 pneumatic tube facility has been completed and was inserted

during the past year. This facility is located in the vertical tube

location VT-3 in the reactor reflector area. It uses the small size

polyethylene rabbit (7/8" dia.) as the irradiation container, and should

have irradiation characteristics somewhere between ET-3 and ET-4.

The prime advantage of these facility is 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 ET-6 for very short-lived radionuclides,

with counting on the germanium-lithium detector systems, also located

in the B-wing.

Initial testing of this facility revealed that there was a small

tritium leak somewhere in the outer containment shell of the terminal.

Thus, the tube was shut down until the leak could be located and repaired.

This repair is scheduled to take place during the heat-exchanger replacement shut-down, in the fall of 1974.

97
NON-RRD NBS PROGRAMS

b. Evaluation and Modernization of Radioactivity Detection Systems -

R. W. Shideler and D. A. Becker

Evaluation of the existing radiation detection systems in this

Section reveal two serious shortcomings. First of all, there was a severe lack of large-memory pulse height analyzer systems available

for use . Second , an automatic sample changer was urgently required

to automate the counting of large numbers of samples for certain of our projects. Both of these problems are well on their way toward solution

at the present time. Two 4096-channel pulse height analyzers of modern

design, each with their own computer compatible magnetic tape deck,

have been obtained and should be received shortly. In addition, an automatic sample changer has been designed in conjunction with the Special

Analytical Instrumentation Section of the Analytical Chemistry Division,

and is currently being constructed. This device should provide jam-free

operation with multiple sample capabilities for the counting of up to

20 samples without stopping. The acquisition of these instruments should

materially assist the Section in the completion of its projects.

5. Conclusions

The Activation Analysis Section of the Analytical Chemistry Division

has been active in a large number of significant research areas. During

the past year, they have analyzed for a total of 39 different elements,

in 243 samples, for a total of 713 elemental determinations. They have

also made significant progress in a number of very difficult research

areas. Work is continuing on many of these projects, as well as in

several additional projects recently initiated.

98
NON-RKD NBS PROGRAMS

STANDARD NEUTRON FIELDS AND INTEGRAL REACTION RATES

J. A. Grundl, D. M. Gilliam, V. Spiegel, Jr., and I. G. Schroeder

(Neutron Standards Section)

Efforts this year continue to be centered around the reactor thermal

column facility. Preparing NBS double fission chambers for operation at

laboratories around the world, performing fissionable deposit mass assays

and carrying out preliminary thermal fission yield determinations were

prominent activities during the period covered by this report. Once

again interaction with reactor technology via the Interlaboratory LMFBR

Reactor Rate Program (ILRR) was the strongest motivation behind much of

the work undertaken. Preparations for the new Intermediate-Energy

Standard Neutron Field (ISNF) was carried forward: final construction,

hazards evaluation, and operational proof-testing are complete. A brief

outline of these activities follows.

1. Fission Chambers for Off-Site Operation.

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 assembled fission

chamber, internal pieces, and two fissionable deposits are shown in

figure 1. Performance characteristics, summarized in last year's Reactor

Radiation Division Report, were investigated more systematically this

year: The linearity of chamber dead time was established to random pulse

4

rates of up to 2x10 sec, and was observed to be proportional to pulse

width over that range. The absolute efficiency of the chamber was found

2 to be nearly linear for fissionable deposit thickness from V500 yg/cm

2 down to ^5 yg/cm . The results of this latter investigation are shown

in figure 2. During the year fission chambers were constructed and checked

out for operation in the following programs : (1) continuation of international comparisons of absolute fission rate measurement scales; (2)

interlaboratory flux measurements sponsored by the Bureau Intenational

des Poids et Mesures, Paris (Intercomparison of 14 MeV neutron fluxes at

Van de Graaff accelerators) ; (3) absolute fission rate determinations in

99
NON-RRD NBS PROGRAMS

the CFRMF Reactor, at Aerojet Nuclear Corp., and the Big Ten critical

assembly at the Los Alamos Scientific Laboratory. Each of these neutron

environments presented unique operational requirements for the fission

chamber, and each requirement was met by means of beam measurements at

the NBS Reactor thermal column.

2. Mass Assay of the NBS Fissionable Deposits

At the present time the National Bureau of Standards set of fission-

,, . . '. , , -. . . 239B 235TT 238TT 237XT able deposits includes five major isotopes, Pu, U, U, Np,

233 and U, from more than a dozen batches of fissionable materials.

Masses of the fissionable deposits are based on interrelated measurements

of specific alpha activities, isotopic concentrations, and fission

fragment emission rates . When completed each fissionable deposit will

have associated with it an absolute alpha disintegration rate, and a fission rate ratio which will establish the mass relative to one or more reference fissionable deposits of the same type. The reference

deposits are kept aside from the normal course of programmatic fission

rate measurements.

Fission rate ratios obtained at the reactor thermal column from

back-to-back fission counting of fissile deposit pairs are used to

238

derive certain principal isotope mass ratios: (1) a mass ratio of U

235

in natural uranium deposits to U in an enriched uranium deposit based

235

on the well-established isotopic concentration of U in natural uranium;*

235 239

(2) an isotopic mass ratio between U and Pu deposits based on the

thermal cross section ratio f( U)/ f( Pu) ; and (3) mass transfer

ratios among deposits of the same principal isotope, in particular

2 235 ratios for very light 5 yg/gcm U deposits required for monitoring

high-flux fast-neutron irradiations. These thermal fission comparison

235 -3

*The U atom fraction in natural uranium, 7.201±0.0010 x 10 for

NBS Standard Reference Material ("Belgium Congo" pitchblende) , is not

observed to vary by more than ±0.1% for uranium processed from other

geological formations.

100
NON-RRD NBS PROGRAMS

measurements are carried out in a 5 cm diameter thermal-neutron beam

emerging from the thermal column. Proper averages are taken for fission

chamber rotation and electronic interchange. In order to circumvent

errors associated with non-l/v and epithermal response differences of

235 239

U and Pu, auxiliary ratio measurements were performed in a monoenergetic 0.025 eV beam. The agreement between the monoenergetic and the

Maxwelliam-averaged results obtained at the thermal column was better

than 1%.

3. Thermal Fission Yields for Long-Lived Fission Products.

Fission products with half-lives in the range of a few weeks to a 148

few decades and including stable end products like Nd are important

for monitoring fission rates in large-scale reactor fuel tests and in

the design of reactor core reloadings . Two unique capabilities at NBS

make it possible to undertake with relative ease, new and entirely

independent measurements of these fission yields: (1) intense thermal

fluxes at the NBS reactor thermal column; and (2) the capability to measure

absolute fission rates over a large dynamic range. Preliminary experi235

ments involving U are complete and fission yields for five longlived fission products have been reported. These measurements were

carried out in collaboration with Hanford Engineering Development

Laboratory, Aerojet Nuclear Corp., and Argonne National Laboratory.

4. The Intermediate-Energy Standard Neutron Field.

Intermediate-energy Standard Neutron Field (ISNF) represents

an advanced effort to create a primary standard neutron field with a smoothly varying energy spectrum between 1 keV and 5 MeV. This energy

range is just that of core neutrons in presently conceived U.S. fast

breeder reactors. The ISNF design is fundamentally simple: a fission

spectrum source driving a one-dimensional geometry of graphite and boron-10,

The spherically-symmetric ISNF cavity arrangement, is assembled at the

center of the reactor thermal column where it will be driven by fission

source disks operating at a total fission rate of up to 10 watts. Construction of the ISNF is essentially finished with the exception of the

101
NON-RRD NBS PROGRAMS

or

LU

CD<Xoo

CO

CO

u_

LU

_lOQ

CO

OQ

LU oIEa

JC(J > • )£

"co _

Q_J

at

-•—Q.

-1E

'co

o.

J-l

•§

COao

•HM

CO

•rl Pn§oo

C/J pa53

cu H

00 •H

Pn

102
NON-RRD NBS PROGRAMS

URANIUM

DEPOSITS

PLUTONIUM

DEPOSITS

100 200 300 400 500

DEPOSIT THICKNESS (/xg/cm 2

)

Fig. 2. The extrapolation-to-zero pulse height for the NBS Double

Fission Chamber versus thickness of fissionable deposit.

Error bars on data points are given as ±2cr for better display.

thin shell of boron-10. Facilities for insertion and removal of the

system from the thermal column with the reactor at full power are also complete and have received final approval of the Reactor Division

Hazards Evaluation Committee. Brief operational proof-tests of the ISNF

were carried out just before the extended reactor shutdown in August, 197A

103
NON-RRD NBS PROGRAMS

TWO-keV FILTERED BEAM

R. B. Schwartz and I. G. Schroder

(Nuclear Sciences Division)

and

E. D. McGarry

(Harry Diamond Laboratory)

The existence of "neutron windows" in the total cross section has

permitted the development of a series of neutron filters which transmit

neutrons in a narrow energy band from a reactor spectrum. Thus, high

intensity beams have been obtained at 2 keV, 24.5 keV and 144 keV using

scandium, iron, and silicon filters respectively. The existence of other

energy windows in these filters reduce the purity of such beams. This

has proved up to now to be a major problem in the development of a monoenergetic filtered beams. The production of such high intensity

filtered beams was pioneered at the Materials Testing Reactor , but

unfortunately the MTR was phased out before the development of these

beams could be completed. The filters themselves were subsequently

transferred to NBS for use in the neutron standards program.

The 2-keV window in scandium results from overlap of the interference

minima from the s-wave resonances at 3.24 and 4.27 keV, producing a cross

2 section with a minimum value of only 50 mb . Unfortunately, there are

also many other windows in scandium at higher energies. These windows

are responsible for a neutron background in the energy region between

7 keV and 800 keV. In the work of Simpson, et al., this background flux

was equal to ^2/3 of the 2 keV flux. The problem is inevitable in any

facility in which a scandium filter looks at a reactor core. The higher

energy neutron background severely limits the utility of this filter and

constitutes a major source of uncertainty.

The problem is solved in the NBS reactor by the use of a through

tube in conjunction with a resonant scatterer. The through tube passes

10 cm outside of the edge of the reactor core, and the collimating system

containing the filter only sees a scatterer at the center of the tube.

104
NON-RRD NBS PROGRAMS

(See figure 1) . This design eliminates unwanted core neutrons and core

gammas. To scatter the neutrons, we make use of the 2.375 keV resonance

in manganese. Although the resonant energy does not exactly match the

energy of the 2 keV window, the Mn resonance is sufficiently broad

(r = 400 eV) that at 2 keV the scattering cross section is still >100

3 barns. Physically, the scatterer is a 3 mm thick Mn-Al alloy, containing

57 atomic percent manganese.

The advantage of this design may be seen in the spectra shown in

figure 2. (These data were taken with a 1 atm hydrogen photon-recoil

counter.) The solid line shows the spectrum obtained with the 110 cm

Sc filter; the dashed curve shows the effect of adding, one cm of Ti to

the Sc. It can be seen that even without the Ti, the main secondary peak

at 29 keV has an area of only 3% of the 2 keV peak. The addition of the

Ti reduces this peak (as well as the ones at 7 , 15 , and 40 keV) by a factor of about 2-1/2, at the cost of only 17% of the 2 keV peak. There

were no peaks observed at energies higher than 144 keV. The measurements

with the Ti have not yet been extended above 50 keV. Since the Ti cross

3 section is ^10 b at 60 keV and decreases with energy we do not, however,

expect the Ti to have a significant effect at higher energies.

In terms of total flux (i.e., the area under the peaks), the higher

energy contaminants amount to approximately 6% of the 2 keV flux without

the titanium; the addition of the titanium reduces their contribution to

^3% of the 2 keV flux.

0. D. Simpson, J. R. Smith and J. W. Rogers, Pr>oo Symp. Neutron

Standards and Flux Normalization; CONF-701002, U.S. Atomic Energy

Commission, 362 (1971); also, Proa. Third Conf. Neutron Cross Sections

and Technology , CONF-71031, 598 (1971).

2' W.L. Wilson, "Neutron Cross Section Measurements and Gamma Ray Studies

of lt5 Sc," M.S. Thesis, University of Idaho Graduate School, Dec. 1966

(unpublished)

.

3

M. D. Goldberg, S. F. Mughabghab, B. A. Magurno, and V. M. May;

"Neutron Cross Sections, Vol. IIA, Z=21 to 40;" BNL 325, Second

Edition, Supplement No. 2 (Physics-TID-4500) Feb. 1966.

105
NON-RRD NBS PROGRAMS

REACTOR

SHIELD

WALL

COLLIMATOR

ezz^zzzzzz

SCANDIUM

FILTER

NBS REACTOR

FUEL

ELEMENT

MAGANESE

SCATTERER

2

Fig. 1. Schematic representation of the NBS Reactor showing the filter,

collimator and scatterer in the through tube. (Not to scale.)

The neutron intensity is V5xl0 neutrons/s , in a 2 cm diameter

beam. The gamma ray background is ^1 Mr/hr.

Further studies are now being conducted to optimize the thickness

of the scandium and the titanium.

106
NON-RRD NBS PROGRAMS

10*

>4>W

TE

''o u

X

UJ>

-JUJ

10

rTTT] 1 1—I IUM|

SCANDIUM FILTERED

NEUTRON BEAM

110 cm SCANDIUM -

PLUS Icm TITANIUM

A

100 200

NEUTRON ENERGY (keV)

Fig. 2. Neutron spectrum through scandium filter. The solid curve represents the spectrum with a 110 cm scandium filter alone,

and the dashed curve the spectrum observed with the addition

of 1 cm of titanium.

107
NON-RRD NBS PROGRAMS

25-keV FILTERED BEAM

E. D. McGarry and C. R. Heimbach

(Harry Diamond Laboratories, Washington, DC)

and

I. G. Schroder

(Nuclear Sciences Division)

An iron-filtered, neutron-beam facility that provides a wellcollimated source of 25-keV neutrons has been installed in a vertical,

2.5-inch diameter thimble of the National Bureau of Standards (NBS)

Reactor. For selected physics experiments and monoenergetic calibration

of neutron dosimeters, the beam flux may be tailored to provide

5 2

5 x 10 n/cm »s with 99 percent 25-keV neutrons. For other experiments,

such as calibration of fast-neutron spectrometers, fluxes of 10 n/cm ,s may be obtained with as many as 13 identifiable peaks in the range

25 keV to 1.5 MeV.

The 25-keV, f iltered-beam facility is shown in Fig. 1. It consists

of four principal parts: (1) the collimating system; (2) the iron

filter; (3) a secondary filter of aluminum; (4) a titanium neutron

scatterer. The facility is a completely assembled and gas-sealed tubular

configuration 5.4 meters long. The bottom section of the assembly is a 3.4 meter aluminum tube filled with one atmosphere of helium to minimize

air scattering and to provide a low-scattering path through the DO

reactor coolant. This aluminum tubing also positions a 4.5 centimeter

by 0.64 centimeter titanium neutron-scattering element in the immediate

vicinity of the reactor fuel. The titanium preferentially scatters

25-keV neutrons into the iron filter. The use of a resonance scatter

between the fuel elements, as opposed to aiming the collimating system

directly at the fuel, eliminates substantial quantities of core neutrons

5 2 and core gammas. For a neutron intensity of 5 x 10 n/cm-s, in the

one-centimeter diameter beam, the gamma ray background is less than 2 mR/hr.

108
NON-RRD NBS PROGRAMS

There are two collimator sections in the assembly. The lower

collimator is composed of a carbon-steel pipe, one centimeter inside

diameter, through 1.2 meters of lead shielding. The upper collimator

is a titanium tube, also one centimeter in diameter, through 1 meter of

lead.

Between the collimators is the principal neutron filter ; 30

centimeters of Armco electromagnet iron. This iron is relatively

impurity free (99.99% iron) and has a measured resonance-interference

minimum of 0.41 barns in the total cross section at 24.5 ± 0.3 keV.

There are other less pronounced minima in the iron cross section between

50 keV and 1 MeV. The principal contributions are at 82 keV, 137 keV,

and 270 keV. However, these peaks are quite effectively removed by the

secondary aluminum filter. Figure 2 shows a spectrum filtered through

30 centimeters of iron and 35 centimeters of aluminum. By an analysis

of the areas under the peaks, shown in figure 2, 99 percent of the neutrons

are in the 25-keV peak and the remaining one percent is primarily in the

137-keV peak and 270-keV peak. We have compared this distribution with

that filtered through 30 centimeters of iron and no aluminum. The

2

spectrum, suitable for energy calibration of a neutron spectrometer in

the range 25 keV to 650 keV, is shown in figure 3. Here, only 83 percent

of the total flux is in the 25-keV peak. The second most intense peak

is that at 137 keV; however, without the aluminum, many other peaks are

evident. A study is being made of the spectral content of the beam

with a range of filtering materials.

The spectra were measured with a hydrogen- gas , proton-recoil

spectrometer. The hydrogen, at five atmospheres, is contained in a 2.5 centimeter diameter stainless-steel tube. Because of the extremely

low gamma background, the spectra can be obtained without the use of

gamma-discrimination techniques. For example, figure 4 shows the raw proton-recoil pulse-height distribution from which the spectrum of

figure 3 was obtained. The quality of the data are to a large extent

attributable to the excellent low-noise qualities of the charge-sensitive

109
NON-RRD NBS PROGRAMS

EVACUATION/ FILL VALVE

-=^A

He SEAL

540 CM.

Ti NEUTRON

SCATTERER

C02 SEAL _ FLOOR LEVEL

35 CM. ALUM.

-UPPER COLLIMATOR

30 CM. IRON

JO THERMAL NEUTRON

FILTER

-LOWER COLLIMATOR

^t,^^i*lu "in* D2 LEVEL

ALUM. TUBE

UPPER GRID PLATE

UPPER FUEL

SECTION

LOWER GRID PLATE

Fig. 1. The facility.

110
NON-RKD NBS PROGRAMS

I>

J*

10*

I CO

est'E

o

10'

UJ

>I0

IrJ or

10

NEUTRON-ENERGY SPECTRUM OF IRON

FILTERED REACTOR BEAM

* 30 cm IRON

% 35 cm ALUMINUM

RELATIVE AREAS

PEAK ENERGY PERCENT

. OF FLUX

25 keV

82

137

270

99.1%

0.1

0.5

0.3 • •

i

A

# •1

100 200 300

NEUTRON ENERGY (keV)

Fig. 2. Neutron-energy spectrum of iron filtered reactor beam.

Ill
NON-RRD NBS PROGRAMS

io5 -

10" _

102

1

- >

«

r»» _ *N

:: 5

•FOR COMPARISON- _ ' S

ft > •- ENERGIES AS MEASURED BY

TIMEOF-FLIGHT METHOD BY I

°! it OTHER INVESTIGATORS 5 ,1

1

'I 1 ?

j

1!

i r

6A

>«

00 >

j

1 • CM JC

i « r- o

—J i • - 2

* — s

[

l t • * • • :- I.

I 1

- i l i

1 7 • •

v \ 8

-

i * > -* / 1 7 _• •

- j

I

i • • I Mr

* 1 ' •

"J • .I : v•

i

i .'*' -

1 • * % f - • ? "- <?

_

- i 1

-

1 keV/CHANNEL = 2.65 H ' ti i 1 1 1 100 150 CHANNEL OF 266

250

Fig. 3. Flux as a function of energy from a beam scattered from the

NBS reactor core by titanium and filtered through 30 cm of

iron.

112
NON-RRD NBS PROGRAMS

io6

10'

> 10"

10J

\

"\

V-., DATA WERE OBTAINED DURING A

40.000 SECOND EXPOSURE OF THE DETECTOR TO A PREDOMINENTLY

25-keV NEUTRON BEAM

DETECTOR VOLTAGE = +3730 VOLTS; DIAMETER = ONE INCH; L/D RATIO = 2.0

keV/CHANNEL = 2.65

I 50 150

CHANNEL OF 256

200 250

Fig. 4. Proton pulse-height distribution as collected on a multichannel

analyzer from a 5-atmosphere hydrogen protein-recoil detector.

113
NON-RED NBS PROGRAMS

preamplifier used. The major contribution to the resolution, which

varies inversely with energy from 5.3 percent at 600 keV to 9 percent

at 25 keV, is the relative absence of wall and end effects on protonrecoil track lengths. This is because the one-centimeter beam can be

directed at the center of the hydrogen-filled tube oriented with the

anode perpendicular to the beam. Very few protons interact with the

distorted electric field near the ends of the tube. Furthermore, the

ionizat ion-track lengths in the 1.25 centimeter radius around the anode

are 0.03 centimeters for 25-keV protons and 1.0 centimeter for 700-keV

protons. Accordingly, greater than 85 percent of the observed pulses

will correspond to protons that are completely stopped in the gas.

A new design is being considered to minimize the number of neutrons

scattered by the D^O below the titanium scatterer.

R. C. Block, et al., Trans. Am. Nuol. Soo. 15, 531 (1972).

2 J. E. Powell and J. W. Rogers, Nuol. Instr. and Meth. 87, 1, 29 (1970).

PRECISION MEASUREMENT OF THE WAVELENGTHS OF NUCLEAR

GAFMA LINES AND THE C0MPT0N WAVELENGTH OF THE ELECTRON

W. C. Sauder, E. G. Kessler and R. D. Deslattes

(Optical Physics Division)

The goals of this experiment are precise measurements of the wavelengths of nuclear gamma lines and the Compton wavelength of the electron.

The measurements are performed on a two-axis, Laue case transmission

crystal diffraction spectrometer. The instrument has an angular range

-4

of 2.5 degrees and an angular sensitivity of better than 10 arc seconds.

Some of the gamma lines that will be measured are the 412 keV line

198 1 82 170

of Au, the 100 keV line of Ta, the 84 keV line of Tm, and several

169 lines of Yb. The source of the Compton wavelength radiation is two114
NON-RRD NBS PROGRAMS

photon annihilation of positronium. The positron emitter, a multi64 kilocurie Cu source, will be housed in a cryostat which provides a 7 K

environment in a 0.2 T magnetic field for the annihilating positronium.

The spectrometer, the source and detector positioning apparatus, the

container for the y sources, and the annihilation cryostat have been

completed and tested. During the past year motor drive and fringe counting

circuitry has been designed and constructed. Equipment for calibrating

the crystal axes via a 72 sided optical polygon has been constructed and

the calibration procedure has begun. Germinatium crystals have been cut

and mounted. A data acquisition system has been assembled and tested.

Measurement of tl end of the year.

198

Measurement of the 412 keV line of Au should be completed before the

115
E , Summary of Reactor Operations

Operating productivity continued at a very high level. Outstanding

among these are 75% on-line time and a 54% burnup rate. A summary of

operating statistics for this and previous years is presented in the

following table.

NBSR Operating Summary

1971 1972 1973 1974

Reactor Operations to date, MWh 124,000

Reactor Operations for year, MWh 51,000

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

No additional problems were experienced with the main heat exchanger

this year. However, operation at reduced power was continued during hot

weather periods. The main heat exchanger, which is made of aluminum, will

be replaced by stainless steel units during the next few months.

4,000 175 ,000 229 ,000 290 ,000

1,000 51 ,000 67 ,000 61 ,000

5,400 5 ,200 7 ,000 6 ,600

213 214 279 254

58% 58% 77% 70%

24 26 28 24

48% 45% 52% 54%

6 6 7 6

10 11 14 6

3,000 4 ,000 4 ,300 3 ,000

4,000 3 ,400 3 ,000 5 ,000

116
F, Service Programs

There was a major shift in the manner in which service irradiations

were performed this year. While the total number of irradiations decreased, irradiations times increased substantially to the point where

some of the facilities were overloaded a good fraction of the time. Discontinued use of neutron activation in the analysis of most gunshot residue

samples also contributed to the reduction in the total number of irradiations. Highlights of some of the major service programs are presented

in the following sections.

THE NEUTRON ACTIVATION ANALYSIS PROGRAM OF THE

FOOD AND DRUG ADMINISTRATION AT THE NBSR

J. T. Tanner and M. H. Friedman

(Food and Drug Administration, Washington, DC)

The activation analysis unit of the Food and Drug Administration

(FDA) is located at the National Bureau of Standards in the Reactor

Building. Neutron activation analysis (NAA) has been used by the FDA

for trace metal analysis of foods, drugs, hair, laundry aids, and cosmetics. The service of this group is available to anyone within the FDA

both in the headquarters laboratory and in the field. The program described below accounts for the main effort of NAA at the FDA.

1. Multielement Analysis of Total Diet Samples

The "Total Diet" program of the Food and Drug Administration (FDA)

is a continuing market basket study in which 117 food items are collected,

prepared in a "table-ready" fashion, and composited into 12 commodity

groups for analysis for selected metals, pesticides, and certain industrial

chemicals to determine the average daily intake of these contaminants in

the diet. The sampling is intended to represent the 2-week diet of a 15- to 20- year old male in each of four regions of the country in which

the samples are collected: Northeastern, Southeastern, Central, and

117
SERVICE PROGRAMS

Western. The details of the selection, collection, preparation, and

compositing of the samples are described elsewhere . The homogenized,

slurried composites of each commodity group are divided into 100 gram

portions. The different commodities are: Dairy products; meat, fish and

poultry; grain and cereal products; potatoes; leafy vegetables; legume

vegetables; root vegetables; garden fruits; fruits; oils and fats;

beverages; and sugars.

The FDA Kansas City District Laboratory has the main responsibility

for analysis of the Total Diet samples. In addition to pesticides, these com- posites are routinely analyzed for Hg, As, Se, Pb, Cd, Zn, Ca, Fe, P, and I. At various times the Neutron Activation Analysis (NAA) group of the FDA

has aided the Kansas City Laboratory when improved limit of detection

was required. Mercury was determined in Total Diet composites for one

2 year by NAA. These results have been reported elsewhere . During the past year the FDA has been testing and evaluating NAA

methodology for the surveillance of a number of trace elements in foods.

Elements which are of interest to FDA include Fe, Co, Sb, Rb , Cs , Zn, Se,

Cr, Sc, Hg, Ag, K, Mg, Na, Dy, Mn, Ni , V, Al, In, CI, Br, I, Pb, Cd, As,

and Ca. Some of these elements produce long lived radionuclides on neutron

irradiation and therefore offer the possibility of determination by instrumental NAA (INAA). These include Fe, Co, Sb , Rb, Cs, Zn, Se, Cr, Sc, Hg,

and Ag. Others are short lived and may also be determined by INAA. These

are K, Mg, Na, Dy, Mn, Ni, V, Al, In, CI, Br, I, Ca, and As. While it

may not be possible or practicable to determine all of these elemnents by

INAA at least some of them possibly can be determined (Fe, Co, Zn, Sb

,

Rb, Se, K, Mg, Na, Mn, Al, and Br) and upper limits established for other

elements. The purpose will be to provide additional information for elements not determined by the Kansas City Laboratory, provide an interlaboratory comparison within FDA, and provide greater sensitivity for some elements where only upper limits are now obtained.

118
SERVICE PROGRAMS

Our initial survey will consist of a one year Total Diet sampling.

These are the same samples which have been analyzed for mercury

earlier. Based on the results obtained, the time required per analysis,

and the total work load, the use of INAA for routine surveillance will be

evaluated

.

In addition to INAA, group separation methodology for multielement

analysis is being developed for FDA by researchers at the Washington State

University. This will provide improved sensitivities for some elements.

2. MULTELMT: A Computer Language For the Reduction of Neutron Activation

Analysis Data. . To carry out the program of the Food and Drug Administration outlined

above, many y~ray spectra have to be recorded by a multi-channel analyzer

and then reduced. Since each spectrum typically consists of 2048 channels

with many y

- ray photopeaks , it is expedient to reduce the data with a large computer. It was desirable, however, to maintain the flexibility

inherent in a manual calculation. This was done by constructing a specialized language called MULTELMT. In this language the user "talks" to

the computer in a language resembling English and tells it how to reduce

the data.

MULTELMT consists of 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. The analysis calculation is done by comparing a sample with a standard. 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 measurement, 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-logarithmic plots and 3) provide an accurate energy calibration.

119
SERVICE PROGRAMS

The data reduction system has worked well to date, even when the

elements of interest are present at very low levels.

Duggan, R.E., and F. J. McFairland, "Residues in Food and Feed."

Pesticides Monitoring Journal, Vol. 1, pp 1-5 (1967).

2

Tanner, J. T. , and W. S. Forbes, "Determination of Mercury in Total

Diet Samples by Neutron Activation," Anal. Chim. Acta, (in press).

U.S. POSTAL SERVICE ACTIVATION ANALYSIS PROGRAMS

J. B. Upton

(Crime Laboratory, Washington, DC)

During the past fiscal year, the U.S. Postal Service Crime Laboratory

used neutron activation analysis routinely to compare questionable and

known samples of evidentiary value such as paint, safe insulation, paper,

plastics and metals. While there was a considerable reduction in the

number of burglaries directed toward postal property due to improved

security measures, the use of neutron activation for the analysis of particles of evidence in this type case which related suspects to the crime

scene further contributed to curtailment of this activity through successful prosecutions.

NAA was also used in the analysis of components of bombs sent through

the mails. In one important bomb case resulting in court conviction, NAA

was used to compare insulation from the wire used in the construction of

the explosive device to that recovered from the suspect's home. Results

obtained regarding the trace elemental composition of the two insulation

samples, along with additional physical property data, demonstrated the

wires were associated by both manufacture and batch production.

NAA has proved to be a very useful and necessary tool in the field

of forensic chemistry and efforts to obtain analytical research data

regarding different types of materials are continuing.

120
SERVICE PROGRAMS

ACTIVATION ANALYSIS PROGRAM OF THE U.S, GEOLOGICAL SURVEY

J . J . Rowe

(U.S. Geological Survey, Reston, VA)

The U.S. Geological Survey is applying Neutron Activation Analysis

to the determination of trace concentrations of elements in geological

materials. The improved sensitivity of Activation Analysis, for some

elements, supplements other analytical techniques in the analysis of

rocks, minerals and waters for geochemical studies related to ore formation, magmatic differentiation, alternation, hydrothermal transport,

energy reserves (coal, petroleum, geothermal and nuclear) and environmental

problems

.

The Radioactivation and Radiochemical Analysis project is developing

a comprehensive instrument method, using sample changers and computer

data reduction to provide data on trace concentrations of Ba, Ce, Co, Cr,

Eu, Fe, Gd, Hf, Nd, Rb, Sb, Se, Ta, Th, Yb , Zn and Zr in igneous and metamorphic rocks. Sulfide minerals have been analyzed for Mn, As, Sb, Se,

Ag, Hg and Au using instrumental and radiochemical methods. Lunar samples

have been analyzed for Al, V, Mn, Hf , and Ta. Thermal waters have been

analyzed for gold for the Heavy Metals Program and a comprehensive analytical program is planned for the study of Geothermal Energy. A group

separation procedure coupled with high resolution Ge(Li) detectors is

being developed to extend the method to the determination of very low

concentrations of Cs, Rb, As, Sb, Se, Hg, Ta and the rare earths. Radiochemical separations are being developed and used to satisfy specific

analytical problems. The fire assay radiochemical method for the determination of gold has been extended to silver. Sensitivity of gold and

silver are 0.1 ppb and 40 ppb respectively.

121
SERVICE PROGRAMS

THE USE OF NEUTRON ACTIVATION ANALYSIS IN

SCIENTIFIC CRIME DETECTION

C. H. Hoffman

(U.S. Treasury Department, Washington, DC)

The Treasury Department's ATF Forensic Laboratory has routinely used

NAA for examining a wide variety of trace physical evidence such as paint,

soil and glass. While other methods have supplanted NAA in the crime

laboratory to some extent, it is felt that no other method offers the

sensitivity required for examining those tiny traces of materials so vital as evidence in criminal cases. During FY74, the ATF Forensic Laboratory made 172 irradiations,

using 136 hours of reactor time to analyze 4369 samples. The materials

examined are summarized below:

Sample Type Number of Samples

Gunshot Residue 4200

Bullet Lead 72

Human Hair 40

Paint 30

Soil 11

Glass 8

Ink 8

A large scale study of paints and human hair will be started in

August, 1974. The trace elemental profiles of these materials will be

studied with a view toward establishing the frequency distribution, and

the statistical worth of the various elements measured.

122
SERVICE PROGRAMS

LUNAR SAMPLE ANALYSIS FOR 17 TRACE ELEMENTS

E . Anders

(University of Chicago, Chicago, IL)

During the last year we have analyzed 60 samples for 17 trace elements (Ag, Au, Bi, Br, Cd, Ge, Ir, Ni, Rb, Re, Sb, Se, Te, Tl, U, and Zn)

by radiochemical neutron activation using the NBS Reactor.

Variations in the abundance of siderophile elements (Au, Ge, Ir, Ni,

Re, Sb) in lunar breccias, impact melts and soil separates has enabled

the identification of at least 5 types of meteoritic material thought to

be derived from major basin-forming events (Ganapathy et al., 1974;

Morgan et al., 1974). Measurement of the abundance of volatile trace

elements in lunar igneous rocks has made it possible to construct a detailed chemical model for the Earth and Moon based on the seven distinct components seen in meteorites (Ganapathy and Anders, 1974).

The model is consistent with petrological and geophysical constraints.

In addition, a suite of 11 anorthosites from W. Greenland were

analyzed for the same elements. These rocks are of interest since they

appear to be the closest terrestrial analogues to lunar anorthosites,

and again provide evidence of the fundamental composition differences

between Earth and Moon (Morgan et al., in preparation).

R. Ganapathy and E. Anders (1974), Bulk compositions of the Moon and

Earth, estimated from meteorites, Proo. Fifth Lunar Sai. Conf.j Geoohim.

Cosmoahim. Aata, Suppl. 5, in press.

R. Ganapathy, J. W. Morgan, H. Higuchi, and E. Anders (1974), Meteoritic

and volatile elements in Apollo 16 rocks and in separated phases from

14306, Proa. Fifth Lunar Sai. Conf. t Geoohim. Cosmoahim. Acta, Suppl. 5

in press

J. W. Morgan, R. Ganapathy, H. Higuchi, and E. Anders (1974), Lunar

basins: Tentative characterization of projectiles, from meteoritic elements in Apollo 17 boulders, Proa. Fifth Lunar Sai. Conf. 3 Geoahim.

Cosmoahim. Acta, Suppl. 5, in press.

J. W. Morgan, R. Ganapathy, and H. Higuchi (1975), Volatile and siderophile

trace elements in anorthositic rocks from Fiskenaesset , W. Greenland:

Comparison with lunar and meteoritic analogues. Manuscript in preparation.

123
SERVICE PROGRAMS

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)

Our group has made extensive use of the NBSR for the irradiation of

numerous samples for trace element analysis using instrumental neutron

activation analysis (INAA) . Routinely the samples are analyzed using

a two-irradiation sequence. The first irradiation is for the shortlived isotopes, with the samples being counted on our Northern Scientific

computer-based, Ge(Li) y~ray counting system. This system consists of

2-4096 channel analyzers controlled by a mini computer and is portable so

that it can be moved to a location near the pneumatic tubes of the NBSR.

After the second irradiation for the intermediate (several days) and

long-lived isotopes, the samples are returned to the University for

y-ray counting. All data is put onto computer compatible magnetic tape

for analysis on the Univac 1108 computer on campus

.

During the past year samples from each of the following sources have

been analyzed during an extensive air pollution episode: coal- and oilfired power plants, municipal and sewage sludge incinerators and motor

vehicles. Additional related samples of fuels (oil and coal), dust and

rock of the surrounding areas have been analyzed by INAA.

Work has continued on samples from the South Pole as part of a study

of global atmospheric aerosols. New samples were collected during the

last year and will be completed during the next few months from a new

sampling facility at Pole Station. Samples were also collected at the

Icelandic volcano Heimaey and analyzed. These samples showed fairly

high enrichments of the more volatile trace metals in the fumerol deposits

and aerosols near the vents.

As part of our program studying the radioactive decay of neutronrich isotopes, we conducted a set of fission experiments in conjunction

124
SERVICE PROGRAMS

with personnel from Lawrence Livermore Laboratory. Dr. Richard A. Meyer

and Mr. Jerry Landrum of the LLL radiochemistry group came to do experiments

on

133in

Te, 133g

Te and Te separated from the fission of U. The decay

was studied using our two-parameter Ge(Li)-Ge(Li) coincidence system.

* i. c 131m-, 161„, 105D Work has proceeded on other studies of the decay of Te, Gd, Ku,

117

Cd.

TRACE ELEMENTS IN OCEANIC FLOOR ROCKS

F. A. Frey

(Massachusetts Institute of Technology, Cambridge, MA)

The NBS Reactor pneumatic facilities are used to do neutron activation analysis of oceanic floor rocks. The primary objective is to

determine by gamma ray spectroscopy the abundance in these rocks of

elements present in the parts per million range, i.e. trace elements.

Such elements are Sc, Cr, Co, Ba, rare-earth elements, Th and U. Neutron

activation analysis is the most sensitive analytical technique available

for many of these elements.

The following problems are being studied.

1. Basaltic rocks from the ocean floor are believed to have been

erupted as magmas from areas of diverging plates such as oceanic ridges

,

and thus they are an important aspect of sea-floor spreading. A knowledge

of trace element abundances in these rocks is useful in understanding

melting processes within the earths upper mantle and in determining the

chemical composition of the oceanic upper mantle.

2. After eruption as magmas, oceanic basalts are subjected to a variety of chemical alteration processes involving interaction with

seawater. Some of these reactions may be important in controlling the

composition of seawater; others may be important in concentrating metals

which later evolve into continental ore deposits. In some manner oceanic

floor rocks must be involved with the formation of volcanoes in island

125
SERVICE PROGRAMS

arcs (e.g. Japan) and continental margins (e.g. Western U.S). A knowledge

of trace element behavior during alteration of basalt with seawater is an important aspect of understanding these major geological problems.

SEA AND ATMOSPHERE POLLUTION STUDIES

P. E. Wilkniss

(Naval Research Laboratory, Washington, DC)

During the year, laboratory experiments and chemical analyses were

continued in connection with studies on sea water and atmospheric aerosol

chemistry, transport and fractionation of chemicals from the sea surface

to the atmosphere, and the transport and distribution of pollutants in

the ocean and the atmosphere. These studies require the analysis of Hg,

Pb, Ag, Fe, Mn, Sc, Na, K, S, Ca, Sr, Br, CI and I.

The NBS reactor has been used to analyze samples of sea water, rain,

fog condensate, atmospheric aerosols and atmospheric dust for microgram

amounts of the above named elements. Radioactive tracers for some elements were made at the NBS facility and used in laboratory experiments

at NRL. These experiments are to determine transport mechanisms, distribution and partitioning of man-made pollutants and naturally occurring

elements in the natural systems under study.

PHOSPHORUS CONTENT OF A VERTEBRATE VISUAL PIGMENT DETERMINED BY

NEUTRON ACTIVATION ANALYSIS

W. Robinson, R. Frank and W. Hagins

(National Institutes of Health, Bethesda, MD)

Isolated vertebrate retinal rod outer segments incorporate phosphorous from ATP covalently into rhopodsin when bleached by light.

As much as four moles of phosphorous per mole of rhodopsin can be incorporated. It has recently been reported that there is a light-stimulated

incorporation of phosphorous into rhodopsin in the living retina but

126
SERVICE PROGRAMS

no stoichiometry can be determined with the tracer method used.

We are attempting to determine the stoichiometry of this phosphorylation reaction in vivo to shed some light on its possible role in photoreception. Retinal rod outer segments from retinas of dark-adapted or light-adapted frogs are solubilized in detergent and fractionated by

polyacrylamide gel electrophoresis . The rhodopsin containing band is

excised, dried and subjected to slow neutron bombardment (RT4) for 12

hours in the NBS reactor. The irradiated gel slices are then depolymerized with hot H.CL, evaporated to dryness and dissolved in a small volume

32 of water. After addition of scintillation fluid, P can be counted

utilizing a narrow window of the scintillation counter.

Trial experiments with casein, a well-characterized phosphoprotein,

have demonstrated a linear relationship between the amount of protein

32 applied to the gel and the P counted.

have yet been obtained with rhodopsin.

32 applied to the gel and the P counted. Only very preliminary results

127
G. Staff Roster

uoa

a

CO

tO 5^ 3

U rH N <0

CU rH CJ CO 4-1 00 CD O r-l r-l M CO S CD O

cu co co ^x PQ U O g CO Kfr!S>h

COo >> •H <4-l «

co a; o

^.•H a) xl X CO cO fa <j n rH

•a

CO CO •< u CO o

1 43 <u a. o 4-J CO CO X! 0) iH CU u >> to 3 4-1 3 CD CJ CO o CO rH 3 Pi & cr

1 > 3 a) a) 4-) 00 CU O o 3 cd •H S &

3 •V 00

J-i • u •H r-l n o CO 3 tO 4J 1-3 u U fa fa ed pi CO H >

3

53 »-3 PQ <! p w •-3 & <J <: 2:

#

S3 ^ o <U M IW O

I- CO CD •H f£ M •H 4-1 4-1 i

> X! <4-l CO M OJ CJ O -H CJ P o l*-J 3

•H Q) t*. • O

^^ S3 M-l •H 4-1 3 «H o O O M-l 43 3 •H 4-1 1—4 M o O cj a e a

H- H • 0) T3 CU a

< <f 3 n P <! o M rH o n cu >— o n •H CD 0t * Pi ^ 3 CO 4J ^ rH a

p2 •H>

i-t CO X)

CO H -0) CO O

erf o

•Hp

CJ Pi | | H • • CO -rH CJ CO g g CO <

H • • • • Pi Pi H w w

CO H-l a) a)

CJ >H

•H x *

> CJ >, u -

a) « o

CO CO CU CO CO o

bOiH >» rH 6 ^

3 ^ •» CU rH rH c CJ •H O 4-1 iH >^ 01 CU o o

>-i -H 4-1 Xt CO N •H w CO u

cu S3 •H CJ & 5-1 N tH 0) J* i-l cu > CO c r-i •H to >s o 3

3 • CO cu o CO r-l 3 CO CO 4-) •H ffi P PQ u Q fa O X "3 CO N> W "-3 P fa Pi •n O w pi W *-}

n

>>

4J3

a

co or 3 <4-J Q

O CU •H •H >.

4-1 43 CU »

CO CJ o O

r-i 3 CU 3

CU «K CU CO tl O

&, ^ M >. U 3 QJ CO o 43 ^ A 0) O CO 3 TJ r-J 3

CO O 4-1 rH 4-* CU 6 CO O •H CU •H 00

J-1 Pi H iH CO rH ,* ^ O,^! CO 00 CU 42 4ti 3

o to CO rH O CO CO tO rH rH 3 43 •H H 3

4-J • • 43 01 0) •H U CU 43 •H CU •H U 4-) •H O

o

CO g fa <! PQ PQ PQ PQ CJ CJ Q S3 Pi CO CO & >>

Pi H •"3 O Pi g S3 W Q < 33 p -J Pi Pi P PQ

CU

4-1

4Jw

toex

r-4 o

r-l COu

oa

H

•K

128
Division 240.01

P. R. Cassidy

H. E. DeSpain

E. J. Embree

J. J. Shubiak

F. Moore

Division 241.05

R. A. Dallatore

D. Gilliam

H. T. Heaton

J. A. Grundl

I. G. Schroder

R. Schwartz

V. Spiegel

Division 313.00

B. Mozer

STAFF ROSTER

N0N-RRD NBS STAFF LOCATED AT REACTOR

Division 310.08

D. A. Becker

B. S. Carpenter

T. E. Gills

S. H. Harrison

S. R. Lantz

R. M. Lindstrom

G. J. Lutz

E. J. Maienthal

L. T. McClendon

D. Peattie

G. M. Reimer

K. L. Roberts

H. L. Rook

J. Stemple

J. E. Suddueth

Division 213.04

D. G. Eitzen

Division 221.03

R. J. Soulen, Jr,

D. B. Utton

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

GUEST WORKERS AND COLLABORATORS

Division 311.05

B. Dickens

L. W. Schroeder

R. M. Waterstrat

Division 313.01

C

.

W . Reimann

Division 313.03

R. S. Roth

Division 313.04

G. J. Rosasco

Division 313.05

A. G. Evans

Division 313.06

A. B. Mighell

C . S . Brickencamp

129
STAFF ROSTER

Aberdeen Proving Grounds

C. M. Cialella

Air Force Materials Laboratory

J. Holloway

R . Rowand

Argonne National Laboratory

H. Flotow

D. L. Price

K. Reimann

K. Skold

Federal Bureau of Investigation

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*

General Dynamics - Ft. Worth

W. Dungan

Harry Diamond Laboratory

C

.

Heimbach

D. McGarry

M. Rosenhaft

C. Soares

T. Wright

National Institutes of Health

G. Flinn, Jr.

R. Frank

W. Hagins

W. Robinson

National Park Service

J. B. Smith

Naval Air Development Center

J. Erthal

F. Williams

Naval Air Systems Command

S. Goldberg

Naval Ordnance Laboratory

H. Alperin*

D. I. Gordon

P. Hesse

D. A. Kubose

S. J. Pickart*

D. Polansky

J. J. Rhyne*

R. S. Sery

R. H. Williams

Naval Ordnance Systems Command

L . Leonard

Naval Research Laboratory

D. J. Bresson

A. C. Ehrlich

G. A. Furgeson

J . Karle

J. H. Konnert

P. E. Wilkniss

Oak Ridge National Laboratory

M. Mostoller

H. G. Smith

Picatinny Arsenal

C. S. Choi*

H. J. Prask*

M. K. Farr*

U.S. Geological Survey

F. W. Brown

R. Finkelman

L

.

P . Greenland

J J . Rowe

G. Sellers

F. 0. Simon

130
STAFF ROSTER

U.S. Postal Service

M. Beckman

G. R. Stangohr

J. Upton

U.S. Treasury Department

R. L. Brunelle

P. C. Buscemi

C. M. Hoffman

F. A. Lundgren

V.A. Hospital

J. Smith

American University

R. G. Arnold

B. T. Chertok

R. A. Segnan

R. Simon

D. M. Sweger

Carnegie Institute of Washington

L. W. Finger

Massachusetts Institute of Technology

F. A. Frey

McGill University

G

.

Donnay

J. D. H. Donnay

R. F. Martin

Politeenico di Milan

M. Zocchi

Temple University

V . Warkulwiz

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

The Ford Motor Company

W. G. Rothschild

Gamma Industries

D. Garrett

Intelcom Rad Tech

D. Rundquist

Old Delft Corp .

D. Bracher

Xonics Corp

P. Scott

*Located full time at Reactor.

131
H, Publications

COLLABORATIVE PROGRAMS

ALPERIN, H. A., RHYNE, J. J., PICKART, S. J., "Neutron Scattering from

an Amorphous Ferrimagnet , " Proceedings , International Conference

on Magnetism, (Nauka, Moscow, USSR, 1974) Vol. IV, p 358.

ALPERIN, H. A., "The Rotation of Polarized Neutrons Scattered From

Cr,

(Nl

Cr~0 ," Proceedings , International Conference on Magnetism,

[NauRa, Moscow, USSR, 1974) Vol. Ill, p. 12.

CHOI, C. S., PRASK, H. J. and PRINCE, E., "Crystal Structure of NH.C10,

at 298, 78 and 10K by Neutron Diffraction," J. Chem. Phys. 3 in press.

CHOI, C. S., and BULUSU, S., "Crystal Structure of Dinitropentamethylene

Nitramine," Acta Cryst. 3 in press.

COPLEY, J. R. D., ROWE, J. M. , "Density Fluctuations in Liquid Rubidium.

I. Neutron-Scattering Measurements," Phys. Rev. A9_, 1656 (1973).

COPLEY, J. R. D., ROWE, J. M. , "Short-Wavelength Collective Excitations

in Liquid Rubidium Observed by Neutron Scattering," Phys. Rev. Lett.,

32_, 49 (1974).

DICKENS, B., PRINCE, E., SCHROEDER, L. W. , and BROWN, W. E., "Ca(H PO,).,

A Crystal Structure Containing Unusual Hydrogen Bonding," Acta

Cryst. B29 , 2057 (1973).

GRUNDL, J. A., DUNDAY, N. D., POPEK, R. J., "Measurement of Absolute

Fission Rates," ANS Transactions 17, 516 (1973).

LIVINGSTON, R. C, ROTHSCHILD, W. G., RUSH, J. J., "Molecular Reorientation in Plastic Crystals: Infrared and Raman Band Shape Analysis

of Noepentane," J. Chem. Phys., 59_, 2498-2508 (1973).

LIVINGSTON, R. C, ROWE, J. M. , and RUSH, J. J., "Neutron Quasielastic

Scattering Study of the Ammonium Ion Reorientations in a Single

Crystal of NH Br at 373°K," J. Chem. Phys. 60, 4541 (1974).

MAREZIO, M., DERNIER, P. D., and SANTORO, A., "Twinning in Cr-Doped

VO ," Acta Cryst. A29 , 618 (1973).

PICKART, S. J., RHYNE, J. J., and ALPERIN, H. A., "Anomalous Small Angle

Scattering from Amorphous TbFe and YFe '' Phys. Rev. Lett. } to

be published

PICKART, S. J., RHYNE, J. J., ALPERIN, H. A. and SAVAGE, H. T.,

"Neutron Diffraction of Sputtered and Annealed Tb-Fe Alloys,"

Phys. Rev. Lett. A 47A, 73-74 (1974).

132
PUBLICATIONS

PRASK, H., TREVINO, S., KEMMEY, P., TSAI , D., McDONALD, R. and YIP, S.,

"Computer Simulation Studies of the Microscopic Behavior of Shocked

Solids," Proceedings , Conf. Mechanisms of Explosives and Blast

Waves, Yorktown, VA, 1973, in press.

PRASK, H., CHOI, C, IQBAL, Z. and TREVINO, S., "Correlation of the

Vibration of Molecular and Stability in Energetic Materials,"

Proceedings j 1974 Army Science Conf., West Point, NY, in press.

PRINCE, E., DICKENS, B. and RUSH, J. J., "A Study of One-Dimensional

Hindred Rotation in NH 0HC10 ,," Acta Cryst. B30 , 1167 (1973).

RHYNE, J. J., PICKART, S. J. and ALPERIN, H. A., "Magnetism in Amorphous

Terbium lorn," AIP Conf. Proc. Series JL8, 563 (1974).

RHYNE, J. J., SCHELLING, J. H. AND KOON, N. C, "Anomalous Magnetization

of Amorphous GdFe

?

, TbFe„ , and YFe

? ," Phys. Rev.,to be published.

RHYNE, J. J., "Local Anisotropy and Exchange Effects in Amorphous TbFe_,"

Proceedings, International Conference on Crystalline Electric Fields,

(Montreal, Quebec, 1974) to be published.

ROWE, J. M., NICKLOW, R. M. , PRICE, D. L. and ZANIO, K. , "Lattice

Dynamics of Cadmium Telluride," Phys. Rev., to be published.

ROWE, J. M., RUSH, J. J., FLOTOW, H. E., "Neutron-Quasielastic-Scattering

Study of Hydrogen Diffusion in a Single Crystal of Tantalum," Phys.

Rev., B9, 5039 (1974).

ROWE, J. M., RUSH, J. J., and SMITH, H. G., ""In-Band" Modes of

Vibration of PdH

Q

," Phys. Rev., B8, 6013 (1973).

ROWE, J. M., LIVINGSTON, R. C, and RUSH, J. J., "Neutron Quasielastic

Scattering Study of SH~ Reorientation in Rubidium Hydrosulfide in

the Intermediate Temperature Trigonal Phase," J. Chem. Phys. 59_,

6652 (1973).

ROWE, J. M., PRICE, D. L., and OSTROWSKI, G. E., "Inelastic Neutron

Scattering From a Liquid 3 He-lf He Mixture," Phys. Rev. Lett., 31_

510 (1973).

RUSH, J. J., LIVINGSTON, R. C, deGRAAF, L. A., FLOTOW, H. E. and ROWE,

J. M., "Study of Hydrogen Diffusion in Tantalum Hydrides by Inelastic

Neutron Scattering," J. Chem. Phys. 59, 657 (1973).

RUSH, J. J., "Study of Large-Amplitude Vibrations in Molecules by

Inelastic Neutron Scattering," in Critical Evaluation of Chemical

and Physical Structural Information, edited by David R. Linde, Jr.,

and Martin A. Paul (National Acad, of Sci., Washington, D.C. 1974).

133
PUBLICATIONS

SAVAGE, H. T., CLARK, A. E., PICKART, S. J., ALPERIN, H. A., RHYNE, J. J.,

"Effects of Annealing on the Coercivity of Amorphous TbFe9 ,"

Proceedings, INTERMAG Conf., (Toronto, Canada, May 14-17, 1974) to

be published.

SANTORO, A., "Characterization of Twinning," Acta Cryst. 3 A30 , 224-241

(1974).

SCHROEDER, L. W. , PRINCE, W. , and DICKENS, B., "Hydrogen Bonding in

Ca(H

2

PO.) 2* H2° As Determined by Neutron Diffraction," Acta Cryst. , in press.

TREVINO, S. F., PRASK, H. J. and CASELLA, R., "Group Theoretical Selection

Rules and Experimental Determination of Lattice Modes in NaNO^ via

Inelastic Neutron Scattering," Phys. Rev. 10B , 739 (1974).

TREVINO, S. F., PRASK, H. J., SHEN, T. Y., and MITRA, S. S., "OrderDisorder Phenomenon in Sodium Nitrate Studied by Low Frequency

Raman Scattering," Sol. St. Corwn. 3 in press.

SCHNEIDER, C. S., "A Precise Refractometer for Thermal Neutrons," Rev.

Sci. Instr. 44, 11, 1594 (1973).

WARKULWIZ, V. P., MOZER, B. and GREEN, M. S., "Observation of the

Deviation From Ornstein-Zernike Theory on Critical Scattering of

Neutrons From Neon," Phys. Rev. Lett., 32_, 1410 (1974).

WATERSTRAT, R. M. , and DICKENS, B., "Atomic Ordering in A15-Type Phases

in the Vanadium-Nickel and Vanadium-Cobalt Systems," J. Appl. Phys.*

to be published.

INDEPENDENT PROGRAMS

BECKER, D. A., LAFLEUR, P. D., "Characterization of a Nuclear Reactor

for Neutron Activation Analysis," J. Radioanal. Chem. 19_, 149 (1974).

CARPENTER, B. S., SAMUEL, D., and WASSERMAN, I., "Quantitative Applications of 17 Tracer," Rad. Effects 19, 59 (1973).

CARPENTER, B. S., "Lithium Determination by Nuclear Track Technique,"

J. Radioanal. Chem. 19, 233 (1974).

CARPENTER, B. S., and LAFLEUR, P. D., "Nitrogen Determination in Biological Materials by the Nuclear Track Technique," Anal. Chem. 46_, 8

(1974).

CARPENTER, B. S., GILLIAM, D. M. and REIMER, G. M., "Induced Tracks in

Glass From Monoenergetic and Thermal Neutrons," ANS Transactions

18, 90 (1974).

134
PUBLICATIONS

CURRIE, L. A., "On the use of Small Calculators Having Stacked Registers,"

Anal. Lett., 6_, 9, 847 (1973).

FRIEDMAN, M. H., and TANNER, J. T., "An Automated Activation Analysis

Data Acquisition System," Waeat Journal, to be published.

FRIEDMAN, M. H., FORBES, T. M. and TANNER, J. T., "Instrumental Neutron

Activation Analysis for Bromine in Pig Tissue," Anal. Chim. Acta

67_, 277 (1973).

FRIEDMAN, M. H., MILLER, E., and TANNER, J. T., "Instrumental Neutron

Activation Analysis for Mercury in Dogs Administered Methylmercury

Chloride: Use of a Low Energy Photon Detector," Anal. Chem. 67 , 236 (1974).

LUTZ, G. J., "Determination of Lead in Paint With Fast Neutrons From a 252 Cf Source," Anal. Chem. 46, 4, 618 (1974).

LUTZ, G. J., "The Analysis of Biological and Environmental Samples For

Lead by Photon Activation," J. Radioanal. Chem. 19_, 239 (1974).

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. 16 , 123

(1973).

REIMER, G. M. and CARPENTER, B. A., "Thorium Determination in Glass

Using the Fission Track Technique," Nature 247 , 101 (1974).

ROOK, H. L., LUTZ, G. J., and LaFLEUR, P. D., "The Use of a High Efficiency Mass Separator in Activation Analysis," J. Radioanal. Chem.

15, 557 (1973).

ROOK, H. L., LaFLEUR, P. D. and SUDDUETH, J. E., "Trace Element Determination Using a High Yield Electromagnetic Isotope Separator and

Neutron Activation—The Determination of Cadmium," Nual. Instr. and

Methods, 116 , 579 (1974).

TANNER, J. T., FRIEDMAN, M. H. and HOLLOWAY, G. E., "Arsenic and Antimony

in Laundry Aids by Instrumental Neutron Activation Analysis," Anal.

Chim. Acta, in press.

TANNER, J. T. and FORBES, W. S., "Determination of Mercury in Total Diet

Samples by Neutron Activation," Anal. Chim. Acta, in press.

YATES, J T., MADEY, T. E. and ROOK, H. L., "Wear of English Monumental

Brasses Caused by Brass Rubbing," Nature 243, 422 (1973).

135
NBS-114A (REV. 7-73)

U.S. DEPT. OF COMM. BIBLIOGRAPHIC DATA

SHEET

1. PUBLICATION OR REPORT NO. NBS Tech. Note 8602. Gov't Accession

No.

3. Recipient's Accession No.

4. TITLE AND SUBTITLE

NBS Reactor: Summary of Activities July 1973 to June 1974

5. Publication Date April 1975

6. Performing Organization Code

7. AUTHOR(S)

Robert S. Carter

8. Performing Organ. Report No.

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 No.

12. Sponsoring Organization Name and Complete Address (Street, City, State, ZIP) 13. Type of Report & Period Covered 7-1-73 to 6-30-74

14. Sponsoring Agency Code

15. SUPPLEMENTARY NOTES

16. ABSTRACT (A 200-word or less factual 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 1973 through June 1974. The

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

dynamics of materials through nuclear physics, and neutron standards and

neutron radiography 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; radiography.

18. AVAILABILITY [^Unlimited

] For Official Distribution. Do Not Release to NTIS

fe I Order From Sup. of Doc, U.S. Government Printing Office Washington, D.C. 20402, SD Cat. No. C13 46:860

I 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

143

22. Price $2.05

USCOMM-DC 29042-P74

« U.S. GOVERNMENT PRINTING 0FFICE:1975- 583-018/15
NBS TECHNICAL PUBLICATIONS

PERIODICALS JOURNAL OF RESEARCH reports National Bureau

of Standards research and development in physics,

mathematics, and chemistry. It is 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 (formerly Technical News Bulletin) —This monthly magazine is published to inform

scientists, engineers, businessmen, industry, teachers,

students, and consumers of the latest advances in science and technology, with primary emphasis on the work at NBS. The magazine highlights and reviews such

issues as energy research, fire protection, building tech- nology, metric conversion, pollution abatement, health and safety, and consumer product performance. In addition, it reports the results of Bureau programs in measurement standards and techniques, properties of matter and materials, engineering standards and services, instrumentation, and automatic data processing. Annual subscription: Domestic, $9.45; Foreign, $11.85.

NONPERIODICALS Monographs—Major contributions to the technical liter- ature on various subjects related to the Bureau's scientific and technical activities. Handbooks—Recommended codes of engineering and

industrial practice (including safety codes) developed

in cooperation with interested industries, professional

organizations, and regulatory bodies.

Special Publications—Include proceedings of confer- ences sponsored by NBS, NBS annual reports, and other

special publications appropriate to this grouping such

as wall charts, pocket cards, and bibliographies.

Applied Mathematics Series—Mathematical tables, manuals, and studies of special interest to physicists, engineers, chemists, biologists, mathematicians, computer programmers, and others engaged in scientific and technical work.

National Standard Reference Data Series—Provides

quantitative data on the physical and chemical properties of materials, compiled from the world's literature and critically evaluated. Developed under a world-wide

program coordinated by NBS. Program under authority

of National Standard Data Act (Public Law 90-396). NOTE: At present the principal publication outlet for these data is the Journal of Physical and Chemical

Reference Data (JPCRD) published quarterly for NBS

by the American Chemical Society (ACS) and the American Institute of Physics (AIP). Subscriptions, reprints, and supplements available from ACS, 1155 Sixteenth

St. N. W., Wash. D. C. 20056.

Building Science Series—Disseminates technical infor- mation developed at the Bureau on building materials, components, systems, and whole structures. The series presents research results, test methods, and performance criteria related to the structural and environmental functions and the durability and safety characteristics of building elements and systems.

Technical Notes—Studies or reports which are complete

in themselves but restrictive in their treatment of a

subject. Analogous to monographs but not so comprehensive in scope or definitive in treatment of the subject area. Often serve as a vehicle for final reports of work performed at NBS under the sponsorship of other government agencies.

Voluntary Product Standards—Developed under pro- cedures published by the Department of Commerce in Part 10, Title 15, of the Code of Federal Regulations. The purpose of the standards is to establish nationally

recognized requirements for products, and to provide

all concerned interests with a basis for common under- standing of the characteristics of the products. NBS

administers this program as a supplement to the activities of the private sector standardizing organizations. Federal Information Processing Standards Publications (FIPS PUBS)—Publications in this series collectively constitute the Federal Information Processing Standards Register. Register serves as the official source of information in the Federal Government regarding stand- ards issued by NBS pursuant to the Federal Property and Administrative Services Act of 1949 as amended,

Public Law 89-306 (79 Stat. 1127), and as implemented

by Executive Order 11717 (38 FR 12315, dated May 11,

1*973) and Part 6 of Title 15 CFR (Code of Federal

Regulations). 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 technological

marketplace.

NBS Interagency Reports (NBSIR)—A special series of interim or final reports on work performed by NBS for

outside sponsors (both government and non-government). In general, initial distribution is handled by the sponsor; public distribution is by the National Technical Information Service (Springfield, Va. 22161) in paper

copy or microfiche form.

Order NBS publications (except NBSIR's and Biblio- graphic Subscription Services) from: Superintendent of Documents, Government Printing Office, Washington,

D.C. 20402. BIBLIOGRAPHIC SUBSCRIPTION SERVICES

The following current-awareness and literature-survey

bibliographies are issued periodically by the Bureau:

Cryogenic Data Center Current Awareness Service A literature survey issued biweekly. 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 pre- ceding bibliographic services to National Technical Information Service, Springfield, Va. 22161.

Electromagnetic Metrology Current Awareness Service Issued monthly. Annual subscription: $100.00 (Special rates for multi-subscriptions). Send subscription order and remittance to Electromagnetics Division, National Bureau of Standards, Boulder, Colo. 80302.
U.S. DEPARTMENT OF COMMERCE

National Bureau of Standards

Washington, D.C. 20234

OFFICIAL BUSINESS

Penalty for Private Use. $300

POSTAGE AND FEES PAID

U.S. DEPARTMENT OF COMMERCE COM-215

FOURTH CLASS MAIL

U.S. MAIL

^oUJT'O/y

^6-l9lfe