NBS TECHNICAL NOTE

U.S. DEPARTMENT OF COMMERCE/ National Bureau of Standards

NBS Reactor:

Summary of Activities

July 1979 to June 1980
NATIONAL BUREAU OF STANDARDS

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NBS Reactor: Summary of Activities

July 1979 to June 1980

NATIONAL BCBRAC

OF JTANBARB3

LIBRARY JUN 1 5 1981

Frederick J. Shorten, Editor

Reactor Radiation Division

National Measurement Laboratory

National Bureau of Standards

Washington, DC 20234

,***T °

F o0t

U.S. DEPARTMENT OF COMMERCE, Malcolm Baldrige, Secretary

NATIONALBUREAUOFSTANDARDS, ErnestAmbler, Director

Issued May 1981
-

National Bureau of Standards Technical Note 1 142

Nat. Bur. Stand. (U.S.), Tech. Note 1142, 211 pages(May 1981) CODEN: NBTNAE

U.S. GOVERNMENT PRINTING OFFICE

WASHINGTON: 1981

For sale by the Superintendent of Documents, U.S. Government Printing Office, Washington, D.C. 20402

Price (Add 25 percent for other than U.S. mailing)
FOREWORD

The National Bureau of Standards Reactor was built not only to serve the needs of the NBS but also those of other government agencies

and the greater Washington Scientific Community. 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 ac- tively 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 more than

25 experimental 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 summarize collaborative programs between RRD scientists

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

summarizes NBS work originating entirely outside the RRD which requires

no collaboration with RRD scientists. The section entitled, "Service

Programs" covers those programs originating outside NBS but for which

RRD provides irradiation services. The remaining sections are selfexplanatory.

iii
FOREWORD

Due to mechanical difficulties during FY 80, the reactor operated

only about six months during the period covered by this report. This

severely curtailed the experimental program and is reflected in the

reduced number of projects summarized here.

Appreciation is extended to F. J. Shorten of the Reactor Radiation

Division for his extensive contributions to the editing, organization,

and preparation of this report, and T. Hatley, T. Mangum, L. Sprecher,

and S. Long for efforts in typing manuscripts.

R. S. Carter

Chief, Reactor Radiation Division

National Bureau of Standards

IV
ABSTRACT

This report summarizes all those programs which depend on the NBS

reactor. It covers the period from July 1979 through June 1980. The

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

dynamics of materials through nuclear physics and neutron standards to

sample irradiations for activation analysis, isotope production,

radiation effects studies, neutron radiography, and nondestructive

evaluations.

Key words: Activation analysis; crystal structure; diffraction;

isotopes; molecular dynamics; neutron; neutron radiography;

nondestructive evaluation; nuclear reactor; radiation.

DISCLAIMER

Certain trade names and company products are identified in order

to adequately specify the experimental procedure. In no case does such

identification imply recommendation or endoresement by the National

Bureau of Standards, nor does it imply that the products are necessarily

the best available for the purpose.
TABLE OF CONTENTS

FOREWORD iii

ABSTRACT v

A, REACTOR RADIATION DIVISION PROGRAMS 1

Mixed Crystals of (KCN) x

( KB

r

> 1 _x1

Neutron Scattering from Coherent Admixtures of Phonons with

Libronic Excitations of Diatomic Impurities in Solids . . 1

Lattice Dynamics of 3 NbD 2

High Frequency Excitations in Metal-Hydrogen Systems 4

Theory of Quasielastic Neutron Scattering from Vanadium

Deuterides at Large Momentum Transfers 5

Joint Refinement of the X-Ray and Neutron Diffraction Data

for Ribonuclease-A 6

Use of the Pearson Type VII Distribution in Crystal Structure

Refinements by the Profile Fitting Method 8

Estimates of Standard Deviations in Rietveld Powder

Refinement 20

Peak Shapes and Widths on the High Resolution Powder

Diffractometer 23

Optimum Strategy for Extracting Intensities from Noisy Data

Collected with a Linear Detector 25

Measurements for Nuclear Safeguards - NRC 29

Nuclear Applications to Antiquities 32

Comparison of Non-Reactor-Based Neutron Radiographic

Facilities 34

Measurement of the L/D Ratio 40

Resolution of a Radiographic Facility 46

The Use of Neutron and X-Radiography to Evaluate

Lithium/ Iodine Pacemaker Batteries 50

Thermal Neutron Imaging Screen Development 57

Inclusion of Proton Spin in the Tunneling Wave Functions for

Triangular Molecules of the Type XH~ in Solids 59

vi
TABLE OF CONTENTS

Neutron-Ant ineutron Oscillations 60

Microscopic Reversibility, Time-Reversal Invariance, and

the Boltzmann H-Theorem 62

Color Graphics and Imaging System 65

The Small-Angle Scattering Facility 66

B. RRD COLLABORATIVE PROGRAMS 70

ErFe — Finite Temperature Spin Waves 70

Temperature Renormalization of Spin Wave Energies in HoCo9

. . . 74

Spin Glass-Ferromagnetic Phase Transition in Amorphous

(Fe Ni ) P B n ,Al n

_ 76 x 1-x .75 .16 .06 .03

Neutron Scattering Studies of the Magnetic Superconductor

(Ce 0.65Tb

0.35

)Ru

2 77

Ferromagnetic Phase Transition in the Reentrant Superconductor

(Er .llH°.89 )Rh

4

B

4

80

Magnetic Percolation in the Pseudobinary Superconductor

(Ce. Ho )Ru„ 82

1-x x 2 Neutron-Scattering Study of Spin Waves in the Antiferromagnet

RbMnCl 85

Structural Investigation of Th,Mn„„Dn, 88

6 23 16

Preferential Ordering° of MN and FE Atoms in Y, (Fe n Mn )._. . . 91

6 1-x x 23

Studies of Electron Density in Carbonate Minerals 93

Neutron Powder Diffraction Study of the Structure of Li^ReO . . 96

Powder Neutron Diffraction Study of Chemically Prepared

B-Pb0

2 100

Further Work on Geometrical Ambiguities in the Indexing of

Powder Patterns 110

Small-Angle Neutron Scattering Study of a Two-Phase Tungsten

Alloy 116

vii
TABLE OF CONTENTS

Small-Angle Neutron Scattering Study of the Microstructural

Development During Precipitation Strengthening of

Ni Based Superalloys 118

Thermal Motions in Ammonium Perchlorate 124

The Detection of an Order-Disorder Phase Transition in a Molecular Crystal by Computer Molecular Dynamics 128

C, NON-RRD PROGRAMS

Activation Analysis: Summary of 1980 Activities 130

Precision Gamma Ray and X-Ray Wavelengths 159

Mass Assay of Standard Deposits , 161

Reactor Filtered Beams 163

Use of the Thermal Column at the NBS Reactor to Determine the

Effective Mass of U-235 in a Miniature Fission Chamber. . . 163

Dynamic Scattering from Polymer Solutions 171

Small-Angle Neutron Scattering on Atactic Polystyrene with

High Labeled Chain Concentration 176

Evaluation of Neutron Spectrum in the Intermediate-Energy

Standard Neutron Field 180

D, REACTOR OPERATIONS AND SERVICES 183

E, SERVICE PROGRAMS 186

Activation Analysis Program of the Food and Drug Administration

at the NBSR 186

U.S.G.S. Activation Analysis Program 189

F, PERSONNEL ROSTER 192

G, PUBLICATIONS 197

V1XX
A, Reactor Radiation Division Programs

MIXED CRYSTALS OF (KCN) Y (KBr) 1

• X 1 " X

J. M. Rowe and J. J. Rush

and

K. H. Michel

(UIA, Antwerp, Belgium)

and

S. Susman and D. G. Hinks

(Argonne National Laboratory, Argonne, IL)

and

S. Shapiro

(Brookhaven National Laboratory, Upton, NY)

In the past years measurements of neutron scattering on these

mixed crystal systems have been extended in two ways. First, we have

measured the interaction of tunnelling between levels of the ground

state of a (CN)~ ion with the [100]TA modes with x = 0.0003 using the

triple-axis spectrometers at Brookhaven National Laboratory.' This is

the first direct spectroscopic observation of such an interaction, and

it fully confirms the predictions based upon earlier results of polarized Raman scattering by Liity and co-workers. At the same time we have

extended and further refined our models for neutron scattering in

systems with x = 0.25, 0.50 to include the concept of a dipole glass.

We have developed theoretical models which explain most of the features

observed, although several statistical mechanics problems persist.

NEUTRON SCATTERING FROM COHERENT ADMIXTURES OF PH0N0NS WITH

LIbRONIC EXCITATIONS OF DIATOMIC IMPURITIES IN SOLIDS

R. C. Casella

Further analysis on this problem, the bulk of which was carried

out during the prior period, included discussion of the experimental
REACTOR RADIATION DIVISION PROGRAMS

2 results of J. M. Rowe, J. J. Rush and collaborators on the neutron

scattering from the coherent state containing a tunnel-split component

of the libronic ground state in KBr:CN . They observed an interaction

3 in the T„ configuration, as predicted by my analysis, which explained

the earlier observed E interaction with the first libronic excitation.

g

My results allow a reconciliation between the broad features of, on the

one hand, the infrared and Raman data of F. Luty and co-workers at Utah,

and on the other, the neutron data of the NBS-BNL-ANL team on KBrrCN

- 3 4

and of R. M. Nicklow and collaborators at Oak Ridge on KC1: CN . '

These latter authors, who first proposed the coherent-admixture model,

report some difficulty in fitting the detailed line shapes on the basis

of a simple two-level version of the m< successes of the model are impressive.

4 5 of a simple two-level version of the model. ' Nevertheless, the overall

1. R. C. Casella, NBS Tech. Note No. 1117, p. 26, (ed., F. Shorten)

(1980).

2. J. M. Rowe, J. J. Rush, S. M. Shapiro, D. G. Hinks, and S. S. Susman.

Phys. Rev. B21, 4863 (1980).

3. R. C. Casella, Phys. Rev. B_20, 5318 (1979).

4. R. M. Nicklow, Invited paper at the APS Solid State Meeting (March,

1980) and discussion thereafter.

5. R. M. Nicklow, W. P. Crummett, M. Mosteller, and R. F. Wood,

preprint (1980).

i

LATTICE DYNAMICS OF 6 NbD1

A. Magerl

(University of Munich, Munich, Germany)

and

(National Bureau of Standards, Washington, DC)

and

J. M. Rowe

Recent measurements of the phonon dispersion of NbD oc both in the
REACTOR RADIATION DIVISION PROGRAMS

0.8 0.6 0.4 0.2 0.2 0.4 0.6 0.8 Wave Vector (Reduced Units)

Figure 1. Phonon branches of 3 phase NbD shown in the Brillouin zone

of the bcc lattice of the host metal Nb.

2 3 phase and the a' phase by Shapiro et al have shown unexpected peaks

throughout the Brillouin zone with little dispersion at about 18-19 meV.

We have calculated the phonon frequencies and the one phonon structure

factor of 3 phase NbD with a simple Born-von Karman model. The orthorhombicity

of the crystal structure due to the ordering of the D and the multidomain

nature of the crystals as used up-to-date was taken into account.

The salient feature from this model is the large number of observable

phonon branches, as shown in figure 1. We want to emphasize the phonon

modes at about 20 meV with a relatively large structure factor, which show

up almost independent of the phonon wave vector. Careful investigation of

the eigenvectors of these modes revealed that the structure factors for

these modes are almost entirely due to a large vibrational amplitude of the

Datons for particular modes in the 3 phase structure. Similar peaks observed

in the a' phase may be attributed to the same mechanism and/or to short

range order.
REACTOR RADIATION DIVISION PROGRAMS

1. A. Magerl, J. M. Rowe, and D. Richter, "On the Observation of LowEnergy Excitations in NbD - A Simple Lattice Dynamical Model,"

(to be published)

.

2. S. M. Shapiro, Y. Noda, T. 0. Brun, J. Miller, H. Birnbaum, and

Kajitani, "Observation of Low-Frequency Excitations of Deuterium

and Hydrogen in Niobium," Phys. Rev. Lett. 41, 1051, (1978).

HIGH FREQUENCY EXCITATIONS IN METAL- HYDROGEN SYSTEMS

A. Magerl

(University of Munich, Munich, Germany)

and

(National Bureau of Standards, Washington, DC)

and

J. J. Rush and J. M. Rowe

A new neutron spectrometer with an extremely high signal/background

ratio has been put into operation recently. It is now possible to measure

600

400

200

£ 600

c

3O 500

400

300

200

100

1 r NbO 0.013^0.013 300K

NbO0.013H0.013

78K

i 50 100 150

Energy (meV)

200

Figure 1. Shows as a first result the spectra of NbO H nm , at two

d* e- r- UU_Lj»L/VJ_Lj liferent temperatures.
REACTOR RADIATION DIVISION PROGRAMS

the vibrations of hydrogen atoms up to an energy of 200 meV in a so far

unreached low concentration regime. These measurements are valuable to

study the single defect behavior of the hydrogen atoms. We have successfully

performed measurements on NbHx with a concentration as low as x = .001

(atomic ratio).

Vibrational spectroscopy for systems like NbNxHy or NbVxHy

(.001 < x, y <: .01) can be used to provide a basic understanding of the

thermodynamics of these ternary systems. Especially, information about

the phase diagrams and thermodynamic potentials can be obtained from these

measurements

.

THEORY OF QUASIELASTIC NEUTRON SCATTERING FROM

VANADIUM DEUTERIDES AT LARGE MOMENTUM TRANSFERS

N. F. Berk

Recent time-of-flight measurements by A. Magerl and H. Wipf of

neutron scattering from vanadium deuterides strongly suggest that at

large momentum transfers (4 £ Q <^ 10 A ), the observed quasielastic

intensity is dominated by incoherent scattering from vanadium atoms.

The main source of this large-Q linewidth is believed to be phase

incoherence produced by small, random displacements of the host atom

equilibrium positions which are caused by the long-ranged interaction

between the host atoms and the diffusing impurity nucleii. At present

there is no specific theory of such large-Q, quasielastic neutron

scattering from the host crystal, but a similar mechanism has been

suggested for Mossbauer spectra that are anomolously broadened and

shifted apparently as a result of interaction between the resonant

2 3 nucleus and diffusing defects. ' Therefore, as a first approach to

this difficult problem we are developing a theory along the lines

originally taken by Krivoglaz and Repetskii but with its range of

applicability extended to the regimes of high impurity concentration and
REACTOR RADIATION DIVISION PROGRAMS

large energy and momentum transfer. If a fit of experiment is possible

with the theory, it will provide information both about the impurity

diffusion and the dynamical response of the host atoms to the

diffusing species. We will also explore the possibility that the same mechanism produces a quasielastic contribution to coherent neutron

scattering.

1. A. Magerl and H. Wipf, private communication.

2. M. A. Krivoglaz and S. P. Repetskii, Sov. Phys. Solid State B, 2325

(1967).

3. A. Bl'asius, R. S. Preston, and U. Gonser, Proceeding of the Fvtihjdhrstagung

der Deutschen Physikalischen Gesellshaft, 1978.

JOINT REFINEMENT OF THE X-RAY AND

NEUTRON DIFFRACTION DATA FOR RIBONUCLEASE-A

Lennart Sjolin and Alexander Wlodawer

(National Institutes of Health, Bethesda, MD)

and

(National Bureau of Standards, Washington, DC)

Neutron diffraction experiments on single crystals of proteins

allow direct locating of the positions of hydrogen atoms, leading to

elucidation of additional details of the enzymatic mechanism, enzymesubstrate interaction, and the structure of bound solvent. The difficulty in interpretation of neutron diffraction results lies in an inherently lower quality of neutron data compared to analogous x-ray

intensities, due to low fluxes of neutron sources and high background

caused by inelastic scattering by hydrogen present in the sample. In

addition, aliphatic site chains are difficult to locate at moderate

resolution, since scattering of carbon is almost exactly balanced by

that of attached hydrogens.
REACTOR RADIATION DIVISION PROGRAMS

- Joint Refinement,

Ribonuclease - A, 2.8A

3/80

35

30

25

20

• Neutron Data

o o

O O o X-Ray Data

o o o o o

10

Cycle Number

Figure 1. Progress of the joint x-ray neutron refinement of

ribonuclease A.

HIS-48 NO H

1 /' ~*\ /"^-V*"^^ 'v

\\>-

I /

• i

\ N

Figure 2, Difference Fourier map showing one of the histidine side

chains. Hydrogen atoms in negative density, deuterium in

positive density.
REACTOR RADIATION DIVISION PROGRAMS

For these reasons, a procedure for joint refinement of neutron and

x-ray data has been established. A conjugate gradient refinement

program of Konnert and Hendrickson was modified to allow simultaneous

refinement against both types of data. The procedure was tested by

o refining the data in a range of 2.8 - 10 A obtained from monoclinic

crystals of ribonuclease-A. The number of observed x-ray reflections

was 2899 and neutron reflections 2549. The starting model was obtained

by appending calculated hydrogen positions to the coordinates refined on

the basis of x-ray data alone at 2.5 A (R = 25.2%). All hydrogens

attached to oxygen or nitrogen were assumed to be exchanged for deuterium, while those attached to carbon were assumed not to exchange. The

initial neutron R factor was 39.9%. In 11 cycles of joint refinement,

the x-ray R factor dropped to 23.6% and neutron to 30.0%. Difference

Fourier maps allowed correction of positioning and assignment of a large

number of hydrogens, and the process is continuing. Diffraction data

o have also been collected for extending the resolution to 2.0 A.

USE OF THE PEARSON TYPE VII DISTRIBUTION

IN CRYSTAL STRUCTURE REFINEMENTS

BY THE PROFILE FITTING METHOD

A. Santoro and E. Prince

Crystal structure refinement by profile fitting of powder diffraction data was originally developed for the neutron diffraction technique

(Rietveld, 1969). The reason for this is due to the fact that the

instrumental function of neutron diffractometers in general conforms

closely to a Gaussian distribution. The case of x-ray powder data is

more complex. Instrumental x-ray peak shapes are non-Gaussian and have

been described, more or less successfully, by means of Lorentzian or Canchy functions (e.g., Klug and Alexander, 1974), or by a composite of

several Lorentzians (Huang and Parrish, 1975a, b) , or by means of

8
REACTOR RADIATION DIVISION PROGRAMS

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REACTOR RADIATION DIVISION PROGRAMS

120,-

100 -

r>4O

X

V) +>c

3

O

O

80 -

60-

40-

20-

Parameters

1 151.

- • 11. • • 4 8338.

257.

^m 5 10.0000

0.0040

6 0.4010

0.0080

—

CHI = 6.11

—

P**£l L^

10

Angle

11

Figure 2. Gaussian least-squares fit of a "modified" Lorentzian calculated from the equation

„ -2

y = yo

1 +

2a

2

"modified' Lorentzians (Sonneveld and Visser, 1975; Malmros and Thomas,

1977; Khattak and Cox, 1977). Recently Hall, Veeraraghavan , Rubin, and

Winchell (1977) have proposed the use of the Pearson type VII distribution (Elderton and Johnson, 1969), and this function has been applied to

profile refinement by Immirzi (1978, 1980) in a study of isotactic

polypropylene. The important feature of the Pearson distribution is

that it can be varied gradually from a Gaussian to a Lorentzian, through

the modified Lorentzian, by simply changing the value of one of the

parameters defining the function.

In the course of a powder neutron diffraction study of Li„Re0_,

LiRe0_, and Fe„0, , it became apparent that the neutron diffraction peaks

produced by samples of these compounds could not be described by a Gaussian function. Examples of Gaussian least-squares fits of these

10
REACTOR RADIATION DIVISION PROGRAMS

peaks are shown in figure 1. To a degree, all the peaks of figure 1

appear quite similar to Lorentzian or modified Lorentzian distributions

fitted with Gaussian functions (figure 2)

.

Under these circumstances it is not possible to carry out a refinement of the structures with the original program developed by

m = 2 rn = 2

Figure 3. Calculated Pearson VII distributions for m = 1, 2, and 100.

The curve with m = 100 is indistinguishable from a Gaussian.

The functions were calculated so that they have the same full

width at half maximum and the same value of the area I.

11
REACTOR RADIATION DIVISION PROGRAMS

Rietveld (1967) , because it is based on the assumption of peaks with

Gaussian intensity distribution. We are therefore in the process of

generalizing our refinement procedure by using Pearson type VII

functions.

The Pearson type VII distribution for the least-squares calculations is

y(x) = y 1 +

<* - V

2

ma

-m

(1)

Calling I the area under the curve, we have

2 A i +

(x - , )

ma

-m

dx = if yo

1 +

(x - x

o

)

ma

-m

dx (2)

Putting

we obtain

.. (x - x ) -1 -, , o

z = 1 H ^ ma

(3)

I

h m-3/2.. .-h , yJ a m z (1 - z) dz

o

h *, i w h r(m - h)T(H) = y a m B(m -%,%)= y a m -^

T(m)

" yo

a(m7r) T(S5

(4)

The full width w , at the level that is 1/p of the maximum can be easily

obtained because

[l + (w

p

/2)

2

/(ma

2

)] = 1/p , (5)

12
REACTOR RADIATION DIVISION PROGRAMS

or

w = 2a[n,(p

1/m -l)p . (6)

For the full width at half maximum H

H = 2a m(: 1/m

-»T (7)

By combining the previous expressions, the Pearson type VII distribution

can be written

, N _ o r/0 l/m , N , 1 h r (m) 1

y(x) = I 2|_(2 - D/ttJ T(m _ h) h

4(x - x ) .. . 1 4- jZ— (2

1/m

H

- 1)

For m = 1 we have

and

a = H/2 , yQ = (2I)/(Hir)

t \ T 2 1 y(x) = I-- l +

4(x - x ) o_

H

2

-1

This is the Lorentzian or Cauchy function. For m = 2, since

-m

(8)

(9)

r(m)— _ h .. -h

TT- - TT - 2TT r (m - h)

we obtain

y(x) = I 4(2 2 - l)

2 1

TT H

4(x - x ) 1 +

°—

{2 2 - 1)

H

-2

, (10)

which is the so-called "modified" Lorentzian introduced by Sonneveld and

Visser (1975) and used by Malmros and Thomas (1977) and by Khaltak and

Cox (1977).

13
REACTOR RADIATION DIVISION PROGRAMS

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14
REACTOR RADIATION DIVISION PROGRAMS

— 1 9 —TTI For m -* °° the expansion of [1 + m (x - x ) /a ] according to the

binomial series, becomes identical with the expansion of the exponential

2 2 exp[-(x - x ) /a ] . In addition, since

lim

m * °° r(m)

m (m - h)

= 1

we have

y = I/air

and the function can be written

y(x) = I 2(ln2/TT) 2 | exp -(41n2)

H

2 (11)

which is the Gaussian function used almost exclusively until recently in

profile fitting refinements.

Examples of Pearson type VII functions, calculated with m = 1, m = 2,

and m = 100, are shown in figure 3.

Figure 4 shows the peaks of figure 1 fitted with the Pearson

type VII distribution. The values of x f°r these fits are systematically lower than the corresponding ones obtained with the Gaussian

function (figure 1) . This is a clear indication that the Pearson

distribution is more appropriate than the Gaussian to treat the diffraction data from the samples analyzed in this study.

Non-Gaussian peak shapes produced by neutron diffraction are caused by the physical conditions of the samples, rather than by instrumental factors. For example, particular distributions of crystallite

sizes could be responsible for the observed effects. (Figure 5, in

fact, shows that some of the peaks of figures 1 and 4 can be fitted

equally well with two Gaussian functions with the same means but

15
REACTOR RADIATION DIVISION PROGRAMS

different widths.) Structural distortions, and the consequent strains

induced in the structure, may also cause a more or less pronounced

departure from a Gaussian distribution.

Under these circumstances there are no physical reasons why m, the

parameter appearing in equation (6) which defines the peak shape, should

be constant over the entire 20 angular range. In fact, in the case of

Fe„0, , the value of m varies with 26 as indicated in figure 6. It seems

that at low values of the diffraction angle the peak shape is close to a modified Lorentzian, while at high values of 29 a Lorentzian distribution is more appropriate to describe the observed peaks. It is indeed

difficult to find a physical justification for this kind of behavior,

and no studies of this type have been reported so far in the literature

for either neutron or x-ray diffraction data. If the variation of m

with 20 can be described by some suitable function, it can be incorporated into the refinement procedure.

In figure 7, H, the full width at half maximum, is plotted vs. 26

for a number of single peaks in the powder pattern of Fe„0,. Clearly,

the behavior of H(20) can be described quite adequately in this case by

the equation

H = Utan + Vtan0 + W (12)

which is used in the original program written by Rietveld (1969)

.

It has to be expected that in a significant number of cases, the

variations of m and H with 20 will be more irregular than those shown in

figures 6 and 7. For example, when peak shapes are dictated by crystallites with odd crystal habits (such as plate-like or needle-like) and

particular size distributions, m and H may change from reflection to

reflection in an apparently unrelated way, and reflections close to one another in 20 may well have widely different values of m and H. In

these cases the Rietveld technique is not applicable, and refinement

will be possible only if some other procedure can be used to decompose

overlapping peaks into the contributions from individual Bragg reflections.

16
120,-

100-

o

r"x

c

3Oo

80-

60-

40

20-

REACTOR RADIATION DIVISION PROGRAMS .

r- 5a Parameters 90 r- •

1 128.

2. ' 4 238.

99. 5 23.8460

_ Fixed

6 0.7514

0.0880

7 756.

96.

\ 8 23.8460

Fixed

— \ 9 0.4189

0.0239

# CHI = 0.89

- mf\£*

I

' I

I

I I 23 24

Angle

25

5b Parameters

Figure 5. The two peaks of Li

?ReO„ fitted by two Gaussians exactly

superposed and having different full widths at half maximum.

-

I

\ *

I 10 20 30 40 50 60

26

70 80, 90 100 110

Figure 6. Plot of m versus 29 for Fe 0,

.

17
REACTOR RADIATION DIVISION PROGRAMS

In light of the above results, it seems that the angular dependence of m and H must be ascertained by analyzing the powder pattern

prior to the profile refinement proper, and that the profile fitting

programs should be modified so that the variation of these two parameters can be taken properly into account. Work in this direction is

presently being done in our laboratory.

It is hardly necessary to emphasize the importance of finding a function which adequately describes the peak shape in the case of x-ray

diffraction. Such function would permit the extension of structural

profile refinement methods to the, x-ray case and, by least-squares

fitting individual peaks, would also allow to determine with high

precision the height, angular position, and width of the peaks. This,

in turn, would greatly facilitate the use of automatic indexing procedures and upgrade the quality of the information available in powder

data files. Work is, therefore, planned to find if the Pearson distribution is also adequate for the x-ray powder technique.

1.2

1.0-

0.8

0.6

0.4

• /II

I

IIII

III

I •

•/ /

—• #» •

J L J 1i i 10 20 30 40 50 60 70 80 90 100 110

26

Figure 7. Plot of H versus 26 for Fe„0.

.

3 4

18
REACTOR RADIATION DIVISION PROGRAMS

1. W. D. Elderton and N. L. Johnson, Systems of Frequency Curves,

Cambridge Press, New York, pp. 77-78 (1969).

2. M. M. Hall, V. G. Veeraraghavan, H. Rubin and P. G. Winchell, J.

Appl. Cryst. 10, 66-68 (1977).

3. T. C. Huang and W. Parrish, Acta Cryst. A31 , S198 (1975).

4. C. P. Khattak and D. E. Cox, J. Appl. Cryst. 10, 405-411 (1977).

5. H. P. Klug and L. E. Alexander, X-ray Diffraction Procedures, J. Wiley, New York, 2nd edition, p. 635 (1974).

6. A. Immirzi, llth International Congress of Crystallography , Collected Abstracts, Warsaw (1978).

7. A. Immirzi, private communication (1980).

8. G. Malmros and J. 0. Thomas, J. Appl. Cryst. 10, 7-11 (1977).

9. H. M. Rietveld, J. Appl. Cryst. 2, 65-71 (1969).

10. E. J. Sonneveld and J. W. Visser, J. Appl. Cryst. 8, 1-7 (1975).

19
REACTOR RADIATION DIVISION PROGRAMS

ESTIMATES OF STANDARD DEVIATIONS IN RIETVELD POWDER REFINEMENT

E. Prince

In a recent paper Sakata and Cooper assert that the standard

2 deviations of refined parameters are estimated incorrectly in the Rietveld

method of refinement, which fits a model to the total powder pattern.

They base their argument on an analysis in which expressions are derived

for estimating the standard deviation by the Rietveld method and by an alternative method using the integrated intensities of individual peaks.

They then compare the results of the two methods as applied to several

experimental data sets, and observe that the standard deviations estimated

by the Rietveld method are, in these cases, smaller than those estimated

by the integrated intensity method.

An important difference between the two methods lies in the way that

they estimate the intensities of individual resolved peaks. In the integrated

intensity method the intensity of the kth peak, I, , is given by

K. if

Ik

= I Y. - Nb, (1)

i=i

o where Y. is the intensity at point i, N is the number of points in the peak,

b is the background level, and the sum is taken over those points whose

intensity exceeds background. Assuming Poisson statistics, the variance of

2

Ik

, cr (Ik

), is given by

if c

2 (Ik

) =

I Y. + N

2a

2 (b), (2)

i=i

o

2 where a (b) is the variance of the background level, which is assumed to

have been determined separately. In -the Rietveld method it is assumed that

that shape of the kth peak can be described by a function, G(i,k), that is

normalized, so that

I G(i,k) = 1. (3)

i=i

o 20
REACTOR RADIATION DIVISION PROGRAMS

I, can then be estimated by finding the values of I, and b that minimize

AC K

the function

i

i S (4) = I w.{y

± - [I G(i,k) + b] I

2

, i=i '

'

where the weight, w., again assuming Poisson statistics, is equal to

1/Y.. In this case the variance of I, is given by

1 k

a

2 (Ik

) = 1/ I [G

2 (i,k)/Y.]. (5)

i=i

o Sakata and Cooper showed that expression (2) and (5) are identical if

the background, b, is exactly zero. In the presence of background, however,

2 even if the background is very well determined, so that a (b) is negligible,

expression (5) is smaller than expression (2). The difference is about a factor of 2 if background and peak intensity are comparable. Therefore,

if G(i,k) is a good representation of the peak shape, the Rietveld method

yields more precise estimates of peak intensities than does the integrated

intensity method.

If the weights applied to different Bragg peaks are different, the

refined parameters will also differ slightly. However, the fact that one

set of parameter estimates differs from another does not imply that either

is biassed. In fact it is an established principle of statistical estimation

that the estimates of model parameters are not biassed by the choice of

3 weight, although the weights do affect the estimates of standard

deviations.

The integrated intensity method minimizes the function

"B 2

M

I " J "k (Ikob.- Wc' > (6)

k=l

2

where N is the number of Bragg peaks in the pattern and w, = l/<* (I ), as given by equation (2). The Rietveld method minimizes the function

21
REACTOR RADIATION DIVISION PROGRAMS

M 9

~\

1=1 L k=k J

where w. = 1/Y., N is the total number of points in the pattern, and the sum over k includes all reflections that contribute to Y.. If the pattern

1

consists entirely of resolved peaks, the two methods can be compared.

Equation (7) can be rewritten in the form

"

B r 2

Nk

( n

*P " ^L^kobs- Wc> + J1'l( ,l - b - \obS

G(i ' k)

J}

8)

where N is the number of points contributing to the kth reflection and

k

w, = 1/a (L) as given in equation (5). This expression consists of two

sets of terms that may be viewed as a sum of squares involving the difference

between observed and calculated values of the integrated intensity and a sum of squares involving observed and calculated intensities within a single

peak. Except for the differences in weights, as discussed above, the first

set of terms is identical to equation (6) , while the second is a sum of

terms like those in equation (4). The statistic

N

B

'

SL

" .WW" Wc>2/

<"B " P) ' C9)

k=l

where P is the number of refined parameters, is known as the "lack of fit mean square." The statistic

,2 B k

S

R

=

I I w, [Y, Ii _G(i,k)]/(N^NR I I w [Y ) - b - I G(i,k)]/(N - N ) c=l i=l X X kobs B

is known as the "replication mean square." Each of these is an unbiassed

2 estimate of the overall variance, and they have X distributions with (N - P)

2 2 and (N - N ) degrees of freedom, respectively. The ratio S T /S should be

-D L K

approximately equal to one, because the two quantities are estimates of

the same thing and has the F distribution with (N - P) and (N - N ) degrees

D D of freedom. A statistical test based on the F distribution may be used to

determine whether the model is an adequate fit to the data.

22
REACTOR RADIATION DIVISION PROGRAMS

If the model fits the data, the standard deviations calculated by

the Rietveld method will be smaller than those calculated by the integrated

intensity method by an amount that reflects the difference between equation

(5) and equation (2). Contrary to the assertion of Sakata and Cooper,

differences that exceed this amount are due not to incorrectness in the

Rietveld procedure but to lack of fit between model and data.

1. M. Sakata and M. J. Cooper, J. Appl. Cryst. 12, 554 (1979).

2. H. M. Rietveld, J. Appl. Cryst. 2, 65 (1969).

3. A proof of the fact that the choice of weights does not bias the

parameter estimates appears in Applied Regression Analysis by

N. R. Draper and H. Smith (John Wiley and Sons, New York), page 80,

PEAK SHAPES AND WIDTHS ON THE HIGH RESOLUTION

POWDER DIFFRACTOMETER

E. Prince

A theoretical analysis by Caglioti, Paoletti, and Ricci suggested

that the individual peaks from a neutron powder diffractometer can be

represented by Gaussian curves with widths that can be described, as a function of scattering angle, by the formula

H

2 = Utan

2

9 + Vtan9 + W

2 Experimental studies have shown that this formula described the

pattern moderately well, but that the actual widths are larger than

would be calculated from the Caglioti et. al. formula given the actual

divergences of the various collimators. It has also been observed

experimentally that the parameters U, V, and W must be refined for each

powder pattern, that they can be markedly different for different

substances, and that they tend to be very highly correlated. Because

it seemed that the very sharp peaks of the BT-1 powder diffractometer

might represent conditions beyond the assumptions of the UVW model,

23
REACTOR RADIATION DIVISION PROGRAMS

and because the determination of magnetic moments, which often depend

critically on a few strong, low angle peaks, it appeared to be desirable

to make a careful study of actual shapes and widths.

To facilitate this study a computer program has been written which

can be run interactively. It takes designated angle ranges from a binary

file of data that have been PREPped for input to the Rietveld program,

to the peak region, and puts out the position, height, width, background,

finas a peak within the range, fits a Gaussian-plus background function

and goodness-of-fit parameter, so that the adequacy of the Gaussian

shape model may be assessed.

Figure 1 is a summary of some preliminary results from this study.

The solid curve is calculated from the UVW formula using the parameters

from a profile refinement of a-alumina, using the pattern from which the

0.8 r

0.7

£ 0.6

o

J. 0.5

CO X

0.4

0.3

0.2

O Th 6 Mn 23D-|6

LaFe2

o a-AI2 3

A LilH 2

<*>

20 40 60

29

80 100 120

Figure 1. Peak widths on the high-resolution powder dif f ractometer

for various components.

24
REACTOR RADIATION DIVISION PROGRAMS

width points marked with circles were taken. The fit of the formula is

quite good over the range of this well-resolved pattern, and it may be

taken, at least tentatively, as an indication of true instrumental

resolution when the sample is a well-crystallized, and strain-free powder

.

The points marked by squares come from an alloy that is, presumably,

imperfectly annealed, and the diamonds come from an alloy that has been

hydrided in the solid state, again, presumably, well below the annealing

temperature. These samples show different degrees of what is probably

strain broadening. The indication is that these patterns differ from

the a-alumina pattern primarily in an addition to the width that is

nearly constant with angle, and that the shape of the curve is relatively

unaffected. Studies of magnetic moments will require much more information in the low angle region, below 20 29.

1. Caglioti, Paoletta, & Ricci, Nuel. Instr. , 3, 223-228 (1958).

2. Santero, Maiezio, Roth, & Minor. NBS Teoh. Note 1117, 94-110 (1980).

OPTIMUM STRATEGY FOR EXTRACTING INTENSITIES

FROM NOISY DATA COLLECTED WITH A LINEAR DETECTOR

Lennart Sjolin and Alexander Wlodawer

(National Institutes of Health, Bethesda, MD)

and

(National Bureau of Standards, Washington, DC)

The problem of optimizing the signal-to-noise in the crystallographic data is of utmost importance to macromolecular crystallographers

who have to measure thousands (or even hundreds of thousands) of reflections from each crystal. Since the total scattering is divided into so many reflections, the intensity of an average reflection is rather low

and often not much different from the background. The signal-to-noise

25
REACTOR RADIATION DIVISION PROGRAMS

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REACTOR RADIATION DIVISION PROGRAMS

problem is particularly acute in the collection of neutron scattering

data from protein crystals, in which strong incoherent scattering from

hydrogen atoms creates very high background which could be lowered only

by complete exchange of deuterium for hydrogen. This work was initially

directed to improving the quality of data collected from the crystals of

ribonuclease-A on a flat-cone dif fractometer equipped with a positionsensitive linear detector and subsequently extended to other methods of

data collection.

The procedure we created (the "dynamic mask procedure") is

designed to calculate the position and extent of a reflection peak in a box containing, in addition, some background points in the presence of

considerable noise. It is equally applicable to one-, two-, and threedimensional data, but in what follows we will concentrate on the twodimensional case, since extension of the method is straightforward.

Let us assume that a particular reflection is completely enclosed

within a box and that no other reflections are intruding into the background. Since the noise level is high (see figure 1), any point within

the box may be found to be above the average background level, but only

the points belonging to the actual reflection are expected to be con- tiguous. Random noise can be suppressed by smoothing the data, by

Figure 2. The dynamic mask procedure applied to a two-dimensional data

array, showing: (a) the raw data from the linear detector;

(b) the "sigma array"; and (c) the final mask calculated from

the "sigma array".

27
REACTOR RADIATION DIVISION PROGRAMS

including at each point some contribution from its neighbors. We have

chosen a generalized version of the formula used by Spencer and

Kossiakoff (1980):

I. , = A

+ B

+ C

(I i-l, j-1

+ I i-1, j+1+ I

i+1, j-1

+ Ii+1, j+l}

(I. . . + I. .,- + I. . . + I..- .) l, j-1 x, j+1 l-l, j i+l, 2

i,J

The best values found for very noisy data were A=l, B=2, and C=3,

providing strong smoothing effects. For less noisy data, decreased

contribution of the neighbors gave better results. The effect of

different smoothing constants can be seen in figure 1. It is also

evident that this procedure somewhat widens the peak boundary.

Once the data have been smoothed, it is possible to apply a "statistical filter" to distinguish between the data belonging to the

peak and to the background. These procedures were modified in the

neutron case to include the initial estimate of the background from the

"universal background" data. Once the background level and its variance

have been established, either directly on the basis of the points

unlikely to contain peak information or on the basis of the universal

background, the background is subtracted from each point and a flag is

set, depending on whether the net intensity exceeds the background by

less than a(0), between a and 2a (1), 2a and 3a (2), over 3a (3). This

so called "sigma-array" can be seen in figure 2. It is quite evident

that the peak is contiguous, while the noise in the background points is

random. We can now create a mask for this reflection from the con- tiguous part of "sigma-array," including all points flagged 1, 2, or 3.

We call this mask "dynamic," since it is calculated independently for

each medium or strong reflection and its shape, size, and position of

the center are not constrained.

28
REACTOR RADIATION DIVISION PROGRAMS

Integrated intensities are now calculated from the original data

array by summing all elements indicated as peak by the mask and subtracting their background. The procedure has been used to collect

^20,000 reflections from a ribonuclease-A crystal. The refinement of

the neutron data is in progress and will be reported later.

1. S. Spencer and A. Kossiakoff, J. Appl. Cryst. , to be published.

MEASUREMENTS FOR fJUCLEAR SAFEGUARDS - NRC

Y. T. Cheng, M. Ganoczy, and D. A. Garrett

The continuing effort for Nuclear Safeguards project was devoted

to 1) further development of software and 2) the final detail designs of

the facility.

By utilizing the self indication effect for each different isotope, one can then attempt to analyze an unknown sample made of U-233, U-235,U-238

and/or Pu-239 nondestructively . The equation of self indication effect

for individual isotope sample indicates that the detector response, S, , is proportional to the energy sum of the product of <}>(E), the transmitted

neutron flux, and a (E) , and the fission cross section of the detector

p r

-a (E)X

S k

« /<KE)a

F

(E)dE = y<J>o (E)e a

F

(E)dE (1)

k k

where <j> (E) is the initial neutron flux and a (E) is the total macroscopic

cross section of sample isotope, and X is the thickness of the sample.

A collection of highly-enriched ( _> 95%) samples U-233, U-235,

U-238 and Pu-239 in the forms of metallic disks and with thickness

ranging from 5 to 270 mils will be obtained for our use. Equation 1

enables the calculating of d> (E)'s apart from a yet to be determined

o normalization constant with the measured detector response S, and known

29
REACTOR RADIATION DIVISION PROGRAMS

values of a (E)'s and a (E)'s. The relative <j> (E)vs. E curve can be

k

° derived with different sample and detector material combinations and

thus lends itself for easy cross checking. However, as it has been

discussed earlier, the best sensitivity will be obtained when one uses

the same material for both sample and detector. Furthermore, the

relative <l> (E) vs. E curve can be checked with that obtained using other

methods. This provides an independent means of beam characterization

and a chance to evaluate the self indication technique as a whole.

Once the calibration for the detecting system using known sample

types and thicknesses has been established, one can then attempt to

differentiate and quantify among U-233, U-235, U-238 and Pu-239 in an unknown sample. Equation 1 for a mixed composition sample becomes

/d

(E)

-E aT

(E)X.

e i=l i a (E)dE

Fk

(2)

where i can be of U-233, U-235, U-238 and Pu-239 and k will be U-233,

U-235, Pu-239 or Pu-241 because the fission cross sections of U-238 is

very small.

If a (E)X. < 1 and we drop 3rd and higher order terms then

-E a (E)X 4 e i-1 l ± x

- n [1 - a (E)X. v fca Z (E)X/]

i=l i i

- 1 - Z a (E)X t \ I i a (E)a (E)X X

i=l l ±

X i=l j=l iLj

J

and Equation 2 becomes

yVE>

-E a (E)X

e i=l i a (E)dE

F

k

- S

4 - E K..X. + E L..X.

. ., lk l . n lk l i=l i=l

30

E M. ..X.X. (3)
REACTOR RADIATION DIVISION PROGRAMS

Floor Plate

D2

Level

Poison

I— Sleeve

Upper Grid Plate

.J -

Fuel Section

V~

Figure 1. Schematic drawing of the Nuclear Safeguards Facility

31
REACTOR RADIATION DIVISION PROGRAMS

where S° = AQ

( E) aF

( E) dE

• K.

K

ik ~ f*o iE) aT

(E) °F (E)dE

ik \ y\<E)

k

°T?(E) a (E)dE

1 Fk

and M... = A> (E) aT

(E) a (E) a (E)dE ijk Jo T T F

S° is proportional to the detector response with no sample and the values

of K , and L., can be extracted from the series expansion of Equation 1

xk ik

for each unmixed sample. M... can be calculated from the d> (E)vs. E

ij k

T o curve and known values of a (E) , a (E) and a (E)

.

1 . i

.

13 r«k

The effect of dropping 3rd and higher order terms in the series

expansion is small. Since the average values for a (E) is less than

200 barns and if we assume a typical sample thickness of 25 mils, the

effect will only be M3.7%. We then apply equation 3 to each and different

fission detector looking over the same unknown sample. A computer program

has been written to solve these multiple equations for various X's.

The final detail design of the facility has successfully gained the

approval of NBSR Hazards Evaluation Committee.

imUlllak applications to amtquities

Y. T. Cheng, M. Ganoczy, and D. A. Garrett

During the past year we concluded the first phase and started the

second phase of the feasibility study to employ nuclear technology for

authenticating and studying reportedly valuable oil paintings. The

project is funded by the Smithsonian Institution and the National Gallery

of Art.

32
REACTOR RADIATION DIVISION PROGRAMS

The first phase of this project was conducted using a TRIGA reactor

at the Armed Forces Radiobiology Research Institute (AFRRI), Bethesda,

Maryland. Three test paintings were studied by both thermal-neutron

induced-autoradiography and high-resolution gamma ray spectroscopy. The

autoradiographs of test paintings show the usefulness of this

technique.

The main emphasis of the initial phase, aside from establishing

the necessary expertise in technical and skill areas, is to assess the

suitability of the AFRRI reactor for this particular purpose. The

requirements are that the reactor at its present condition or after

reasonable modification can provide a 4' X 6" (or larger) thermal

9 -2 -1

neutron field having a flux of 3 X 10 n-cm -s (or higher) , and the

unwanted high energy neutron and gamma ray components should be low.

The following table compares the doses received by the painting

from both gamma and fast neutron radiation of the Brookhaven National

Laboratory Medical Reactor Facility, The Armed Forces Radiobiological

Research Institute and the proposed NBS reactor thermal column. As

references, one should note that the painting receives a dose of ^ 20

Rads during a typical x-ray study. Based on the measurements made for

the background radiation inside the exhibition room of the National

Gallery of Art, a painting would receive approximately 150-200 Rads over

a projected lifetime of 1,000 years. The radiation doses listed in the

table are physical doses (in units of the rad) received by a typical

T painting during the neutron-autoradiography study. All numbers are

12 -2 normalized to a thermal neutron fluence of 8 x 10 n-cm except for

12 -2

the BNL graphite reactor where a fluence of 3.6 x 10 " n-cm was used.

BNL BNL AFRRI

Graphite Reactor Medical Reactor Reactor NBSR

Gamma Ray Dose 5500 1800 1500 * 10

Fast Neutron Dose 38 80 70 ^ 01

The present stage of radiation damage study indicated that for

inorganic materials (pigments) 10 Rads or more are required before any

33
REACTOR RADIATION DIVISION PROGRAMS

macroscopic changes of its properties can. be detected. The threshold

for organic materials (medium, varnish, supports, etc.), especially

hydrogenous materials are lower (10 Rads) . The doses which the painting

received at the AFRRI reactor were 50 to 100 times less than the threshold,

However, there is always an uneasiness toward the situation that one is

proposing to have our national treasures exposed to radiations. A

thorough microscopic study of the radiation damage is very involved and

tedious due to the many varying factors (types of radiations, rate and

amount of radiation, materials mixing, etc.), and its ability for

simulating and predicting long term radiation effects is at best, uncertain.

This prompted the start of the second phase of the project, i.e.,

to conduct a feasibility study of modifying the NBSR thermal column for

neutron- induced autoradiography use. The initial dosage measurements

12 -2 indicate the integrated fluence of 8 x 10 n-cm is comparable to the

20 Rads dose in an x-ray study of painting, while the fast neutrons

contributed an insignificant amount, i.e., less than 0.1 rad

.

COMPARISON OF NON-REACTOR-BASED

NEUTRON RADIOGRAPHIC FACILITIES

W. L. Parker and D. A. Garrett

The work reported here is sponsored by the U. S. Naval Ordnance

Station at Indian Head, Maryland, and has involved visiting three operating neutron radiographic facilities of different types which do not use a reactor. Radiographs were taken of explosive devices supplied by

the Navy and of various test objects and quality indicators.

Measurements were made of the L/D at different distances from the

aperture, and the size and position of the effective aperture determined.

A measure of the neutron to gamma ratio has been obtained, and the uniformity of the beam measured.

34
REACTOR RADIATION DIVISION PROGRAMS

The most important property of the facility, of course, is the

length of time required to get a satisfactory radiograph. This is determined by the uses to which the facility will be put.

Non-technical features of the facility of interest are: maintenance

and operating costs, downtime experience, and the amount of technical

help needed for operation.

The three facilities visited were a Cf-252 source plus multiplier

at the Mound Laboratory in Miamisburg, Ohio, a 2.5 MeV Van de Graaf

neutron generator plus moderator at the Pantex Plant near Amarillo, Texas,

and a D-T fast neutron generator plus moderator being developed at the

Advanced Technology Center of the Vought Corporation in Grand Prairie,

Texas, for the Army Materials and Mechanics Research Center.

1. Mound Laboratory

The Mound Facility uses a Cf-252 source to provide the original

neutrons (by spontaneous fission) which are then multiplied and moderated

by the multiplier. This is a subcritical reactor with a kof 0.990 which

produces a thermal neutron multiplication of 28 times. The strength of

the Cf-252 source at the time of the visit was about 25 milligrams.

It is the largest, heaviest, and most expensive of the facilities

and would probably require the most construction if an existing building

can not be used. It has a vertically-down beam, and the construction

expense and amount of shielding required could be considerably reduced

if a vertically-up beam is acceptable so that most of the shielding is

supplied by the earth.

Measurements of L/D by the NBS method were made using radiographs

of both the Aerotest and the NBS test objects. The results indicate that

the effective aperture is about 2.5 inches in diameter and about 12 inches

downstream (toward the object) from the aperture end of the collimator.

This reduces the maximum available L/D from the nominal value of 107

(=240/2.25) to approximately 90.

Measurements of the film densities of a radiograph for which only

part of the film was covered by a converter give D /D =0.25. At L =

35
REACTOR RADIATION DIVISION PROGRAMS

240 inches the density falls off by 8 percent at 8 inches from the center

of the film.

At the maximum available L/D a 12 hour exposure on SR film with a vapor-deposited Gd converter gives a density of 1.60.

The facility is often used at an L/D of about 36. At this setting

the resolution at a distance of one inch from the cassette should be

about 1.5 line pairs per mm. The resolution attainable at one inch should

be close to 3.9 line pairs per mm at the maximum L/D.

One of the attractive features of the facility is the fact that it can be left unattended. This permits overnight exposures without additional

labor costs.

For the same L/D and the same density the radiographs compare favorably with those from the NBS facility.

2 . Pantex Plant

The facility at the Pantex Plant uses a Van de Graaf accelerator to

produce a beam of 2.5 MeV deuterons which strike a beryllium target to

9 10 produce neutrons by the Be(d,s) B reaction. These neutrons are then

moderated.

The Van de Graaf accelerator is mounted vertically with the beam

coming down to strike the target at center of the moderator. There are

two horizontal collimators, although only one beam seems to be in use at

the moment. The Van de Graaf and the moderator could probably be made

portable, but it might be difficult. Shielding requirements are probably

less stringent than for the Californium multiplier.

Measurements of L/D by the NBS method were made using the Aerotest

object only on four radiographs and the NBS object only on one radiograph.

It is apparent from the values of L/D and the shape of the shadow patterns

that the aperture is square. The effective aperture is about 2.6 inches

square and located about 5 inches downstream from the aperture end of the

collimator. Because of the size of the room and backscatter from the wall

the maximum distance from the aperture is 10 feet which gives a maximum

L/D of about 44.

36
REACTOR RADIATION DIVISION PROGRAMS

Measurements of the film densities with and without a converter

give D /D =0.22. At L - 10 ft. the density falls off by only 3 percent

at 8 inches from the center of the film.

At the maximum available L/D a 4 hour exposure on SR film using a vapor-deposited Gd converter gives a density of about 2.1.

The facility is often used at an L of 6 feet which gives an L/D of

about 26. At this setting the resolution at one inch from the cassette

is 0.85 line pairs per mm. The maximum resolution attainable at one inch

would be about 1.5. (it is shown in the previous report that resolution

using a square aperture is roughly 18 percent less than that for a circular aperture of the same size.)

One drawback is that the Van de Graaf requires constant supervision

with an operator present continually while the facility is in use. The

major maintenance problems arise from the rupturing of the Be target.

It has the definite advantage over the other two systems of not having a source which is continuously degrading. It can have the same problems

as any other active vacuum system.

The radiographs compare favorably with those from the NBS facility.

3. Vought - Advanced Technology Center

The Vought facility uses as a neutron source a sealed tube generator

3 4 which produces 14 MeV neutrons by the H(d,n) He reaction. These neutrons

are then moderated.

It is the smallest of the facilities and is semi-portable. It will

be taken from Texas to the Yuma Proving Ground for testing. It is so designed that the source-moderator-collimator combination can be rotated

through 180 to provide a beam in any direction from vertically-up to

vertically-down. Shielding requirements should be about the same as for

the Van de Graaf system, or less because of the lower neutron production.

Measurements of I./D by the NBS method were made from radiographs of

the Aerotest object only. Although the aperture of the facility is reported

to be square, both the values of L/D and the shape of the shadow patterns

indicate that the effective aperture is approximately a 2.5 inch circle

37
REACTOR RADIATION DIVISION PROGRAMS

about 30" below the top of the cover plate over the end of the collimator.

These are the design values. It was said that there could be a reason

for a square aperture to appear to be circular, but it is not known what

that explanation is.

An optimum position of the cassette seems to be about 13 inches

above the cover plate, giving an L/D of about 17. The optimum radiograph

at this distance was made using M film and an experimental, proprietary

screen being developed for Vought by Nuclear Enterprises, Inc. A 2 hour

exposure produced a density of 1.23. The quality of the radiographs is

not quite as good as if SR film and a Gd converter had been used but this

would require prohibitively long exposure times. The quality is certainly

acceptable.

For this position and L/D the resolution at one inch would be about

3/4 line pair per mm (3 line pairs per mm at 1 cm)

.

Measurements of the densities with and without a converter give

D /D =0.20. The density falls off by about 10 percent at 6 inches

from the center of the film.

This facility has a definite advantage over the other two because

of its small size and portability. Vought is developing a real-time

imaging system to be used with it, but it was not demonstrated.

Aside from the low flux, with resulting long exposure times, even

for low resolutions, the other major difficulty would be operating expense.

The warranty on a tube is 200 hours of operation before the intensity

drops below 50 percent of its original value. At $15,000, or more, per

tube the system could become quite expensive to operate if any large

volume of work is to be handled.

The facility does not seem to require constant supervision as does

the Van de Graaf generator, but it is not presently left unattended for

any lengthy periods of time.

38
REACTOR RADIATION DIVISION PROGRAMS

4 . Summary

The Vought facility is the smallest and lightest of the three and

could most easily be made portable. If it is used on a regular basis

the operating costs would be high - $3,000 for a 40 hour week if the tube

must be replaced after its warranty period. Its biggest drawback, however,

is the neutron production rate which is about five percent of that of

the other two facilities. This means prohibitively long exposure times

or small values of L/D which will limit the resolution attainable.

The Mound facility and the Pantex facility have roughly equal rates

of neutron production. At a medium L/D (of the order of 50) very satisfactory radiographs can be made in a 4 hour exposure, which can, of course,

be reduced by using faster film-converter combinations than SR with vapordeposited Gd.

The Cf multiplier would probably require a larger capital investment

and may involve licensing procedures which could limit its use. If the

Californium must be paid for, the materials cost would be more than for

the Van de Graaf generator but less than for the Vought system if the

latter is in continual use. The constant supervision required for the

Van de Graaf would cut down considerably on the operating cost advantage

of the Cf multiplier.

It seems safe to say that any new neutron radiographic facility

must be custom designed to fit the uses to which it will be put.

39
REACTOR RADIATION DIVISION PROGRAMS

MEASUREMENT OF THE l/d RATIO

W. L. Parker and D. A. Garrett

The last report of this work describes a method for determining

the L/D ratio for a neutron radiographic facility from microdensitometric

measurements made of the shadow images of a series of small, identical,

and parallel linear obstacles placed at uniformly increasing distances

from the image plane. Also described were the test objects used—one borrowed from Aerotest Operations and one built at the National Bureau

of Standards.

The report also defines the important parameters: L and h—the

distances of the source and obstacle from the image plane, respectively,

and D = 2R and d —the widths of the source and the obstacle, respectively,

The method consists of approximating the microdensitometer tracings

by trapezoids and measuring the widths of the base (w.) and the top (w ) of the trapezoid. When w, and w are plotted vs. h, the resulting plots

should be approximately straight lines from whose slopes the value of

L/D can be determined.

Work this year has been largely concerned with a theoretical treatment of the images to be expected when the source is circular instead of

linear, as was assumed in the earlier treatment.

1 . Theory

The detailed analysis will be published elsewhere and only the

results are given here.

One of the most important derived parameters is the value of h for

which the umbra goes to zero. As was shown previously it is given by

b = Ld /D. (1)

o For a parallel linear source and linear obstacle the shadow patterns

will be symmetrical trapezoids whose height will be constant as long as

h < b with w, increasing and w decreasing as h increases until the

pattern becomes a triangle when h = b. For h > b, the pattern is again

a trapezoid whose height decreases, while w, and w both increase as h

a c increases. The area of the trapezoid should remain constant.

40
REACTOR RADIATION DIVISION PROGRAMS

For the case of a circular source and linear obstacle when h < b

the pattern will have a constant central region and will approximate a trapezoid with rounded corners. When h > b, there is no constant region,

and the patterns deviate more and more from a trapezoid as h increases.

Figures la and lb are calculated shadow patterns for the same parameters (L/D = 68.8, h = 0.25, 0.75, 1.25,..., 4.25 inches) for the linear source—parallel linear obstacle and the circular source—linear obstacle,

respectively. Figure lc is a reproduction of microdensitometer tracings

from a radiograph taken with the same parameters. The agreement of figures

lb and lc is excellent although, if the two figures are superimposed,

there are some slight discrepancies.

The slopes of the plots for w and w are found by fitting the data

by linear regression to equations of the form

w = a

Q + a-jhU-h/L)

-1

. (2)

The slope values: a. , , an and a n are defined in the last report.

Id lc lc+

The average slope is defined as follows:

alav

= (2a

ld + a lc- + alc+)M (3)

The theoretical value of a., is MD/L, where M is the linear magnification

lav

of the microdensitometer.

It follows then, that

(L/D) = M/a Linear-Linear (*)

exp lav

where (L/D) exp represents the value of L/D obtained by this method.

The case of a circular source and linear obstacle is different.

As is evident from figure lb, the patterns are approximately trapezoidal

only for quite small values of h. Furthermore, when h > b there is no region of constant illumination. It is assumed that the measurement line

when h < b is drawn through the "half-power point" with the slope of the

shadow pattern at that point, and that the intersections of this line

with the top and bottom of the trapezoid determine w. and w . When this

41
REACTOR RADIATION DIVISION PROGRAMS

100

Calculated Patterns

Linear-Linear

-0.05 0.05

Z (inches)

Figure 1(a). Shadow patterns for Linear Source - Parallel Linear Obstacle,

100

80-

c

<1) 60

+Jc

o

>

+•> 40

CO

CD cc 20

Calculated Patterns

Circular-Linear

0.05 0.05

Figure 1(b). Shadow patterns for Circular Source - Linear Obstacle,

42
REACTOR RADIATION DIVISION PROGRAMS

100iDensitometer Tracings

0.05

Figure 1(c). Densitometer tracings for radiograph with same parameters

as figures 1(a) and 1(b).

I75 r

Figure 2. Measured values of (L/D) for NBS reactor,

exp

43
REACTOR RADIATION DIVISION PROGRAMS

is done, it is found that a.. = M(tt/4)D/L and

(L/D) = TrM/4a.. Circular-Linear (5)

exp lav

.

When b < h < 2b, the plot of w vs h(l-h/L) is still very close

to a straight line. It can be shown that a. , for this range will differ

from that for h < b by only a few percent. Since measurement errors are normally of this order of magnitude, the present technique uses a value

of a, .. obtained for measurements for < h < 2b. Values of w for h > b

Id c are not used and a, = (a-, + a.. )/2. lav Id lcIt is apparent that the effect of going to a circular source, at

least when h < b, has been to replace D by ttD/4. In other words, the

normalized patterns for a circular source will approximate those for a linear source whose width is (tt/4)D. This agrees very well with the

experimental results.

The method described here which leads to equation (4) or (5) will

be called the NBS method of determing L/D.

The NU method developed by the Aerotest Operations group uses only w . Linear regression is used to find an expression such as equation (2)

c for w which is then extrapolated to find the value of h for which w = 0. c

r c The resultingb value of h shall be called b . It is found that the

exp

resulting values of L/D are

(L/D)^, = b /d , Liuear-Linear (6)

NU exp o

(L/D) = -rrb /4d . Circular-Linear (7)

2. Experimental Results

The NBS method of determining L/D has now been used at the NBS 10

MW Research Reactor and at three non-reactor-based facilities. The range

of L/D measured is from 12 to 170.

Figure 2 shows the results of measurements from twelve radiographs

taken at the NBS facility of the NBS test object described in the last

report. The size of the circles indicates the standard error. The

straight lines were obtained by linear regression to fit the equation

44
REACTOR RADIATION DIVISION PROGRAMS

(L/D)

exp

= L

o /D + L

' /D ' (8)

L' is measured from the face (biological shield) of the reactor and L , o the distance of the source behind the reactor face is measured to be 32

inches.

The values of L and D resulting are within the standard error of

o

° what would be expected. Although a. , and a.. may differ by as much as twenty percent of their average, the NBS method appears to correct for

whatever artifacts are producing the discrepancy.

Similar results have been obtained from the radiographs taken at

the non-reactor-based facilities, thereby increasing confidence in the

validity of the method.

The values of (L/D) derived from a set of radiographs taken with

the same parameters as those for another set, but with a 0.070 inch lead

sheet between the test object and the cassette, agreed with those derived

from the normal set to within the standard error with the fluctuations

being random. Accordingly it is felt that the results are not affected

by capture gamma rays from the obstacles or background gamma rays from

the reactor.

The values of (L/D) obtained from equation (6) or (7) agree

generally to within 10 percent with the values of (L/D) obtained from

equation (4) or (5); but the internal consistency of the results from the

NU method does not seem to be as good as that from the NBS method.

The NBS method is preferred to the NU method for two reasons: first,

it uses more of the available data. In fact, for small values of L/D,

the number of measurements of w, used will be at least twice the number

a of measurements of w used. Second, the NU method uses the value of d , c ° which may not be known to the desired accuracy, while the NBS method

depends only on the fact that all the obstacles have the same width.

1. W. L. Parker and D. A. Garrett, NnS Teen, liote No. 1117 (ed. F. J,

Shorten, 1980).

45
REACTOR RADIATION DIVISION PROGRAMS

RESOLUTION OF A RADIOGRAPHIC FACILITY

W. L. Parker and D. A. Garrett

The common measure of resolution in radiography is line pairs per

unit length—usually per millimeter. For an array of parallel linear

obstacles of the same width, d , separated by a distance between their

sides equal to their width and situated at a given distance from the

image plane, what is the minimum d for which adjoining objects will be

recognized as separate? The resolution, n, will be a unit length divided

by twice the minimum value of d . J o What should be taken as the criterion for resolution? For the

diffraction pattern of two parallel identical slits the Rayleigh criterion

is that the first minimum of one pattern shall fall on the central maximum of the other. This results in the intensity midway between the two

2 maxima being 0.8106 = 8/n times the maximum intensity.

For the following discussion it is convenient to introduce two

dimensionless parameters defined as follows:

a = b/h = Ld /2Rh, (1)

a = d /R = 2ah/L (2)

o

If the Rayleigh position criterion is applied to the shadow patterns it

is found that the intensity at the midpoint of the composite pattern is

about 1.33 times the maximum for either pattern alone in the linearlinear case, and about 1.14 times in the circular-linear case. The patterns will not be resolved.

An obvious solution, which will be called the "Rayleigh intensity

criterion", is to make the midpoint intensity of the composite pattern

be 0.8106 times the maximum intensity for a single pattern.

In the linear-linear case, when b < h < 2b, the two trapezoids

overlap to give two trapezoidal "peaks" with an inverted trapezoidal

"valley" in between. The Rayleigh intensity criterion gives the following

result for the a required for resolution:

46
REACTOR RADIATION DIVISION PROGRAMS

a = (l+a)/(l+8/7r ) Linear-Linear (3) res The circular-linear case is more complicated and involves finding

the value of a which will satisfy the equation

I(d

o )/I(0) = 4/u2

. (4)

I(z) is the normalized intensity of the shadow pattern at a point whose

abscissa is z and involves both algebraic and inverse trigonometric

functions. The ratio can be expressed as a function of a and o only. For

a given value of a the resulting transcendental equation can be solved by

Newton's method. The resulting° values of a are found to be almost a res linear function of a, at least for small values of a, given by

a = 0.4494 + 0.566a Circular-Linear (5) res The expression is correct to better than a percent for the range < a < 0.10.

Figure 1 is a plot of the composite shadow patterns (calculated

for a = 0.0184) which just meet the criteria for resolution. All intensities are normalized to the value of the maximum (h < b) for the linearlinear case (a square source whose side is equal to the diameter of the

circular source)

.

Figure 2 shows the patterns for both sources calculated for the

value of a which just gives resolution for the square source. Each

pattern is normalized to its own maximum. It is obvious that if the

pattern for the square source is just resolved, the pattern for the circular source is very well resolved.

Figure 3 shows the patterns for that value of a which just gives

resolution for the circular source. The pattern for the square source

is perhaps recognizable as being produced by two separate obstacles, but

it is certainly not resolved in the usual meaning of the word.

It is convenient to introduce a parameter k = 2a . Combining

the definitions of n and a gives

k = (L/D)/nh (6)

47
REACTOR RADIATION DIVISION PROGRAMS

Composite Shadow

Patterns

Linear-Linear

I max = 100

« = 0.563

Circular-Linear

I max = 78.54

« = 0.460

2d 3d

Figure 1. Patterns at the Rayleigh intensity criterion.

100-

Composite Shadow

Patterns « = 0.563 —Linear-Linear

Circular-Linear

-3do -2do -do do

Z

Figure 2. Patterns for Linear-Linear Resolution.

2do 3do

48
REACTOR RADIATION DIVISION PROGRAMS

3d,

- 100

-*h = 0-^ Composite Shadow

Patterns

80 -

« =0.460

Linear-Linear

> Circular-Linec

+> 1 60

0)c / \/~^N

> / X_/\ s .> V

'"§ 40 /

0> // \

DC // \

// \\

// \\

// \\ 20

_l_

//

//

//

//

//

i

1 1

\\

\\

\\

\\

>\

i \ i

-2d, 2d, 3d,

Figure 3. Patterns for Circular-Linear Resolution.

Equation (6) can be solved for any of the three quantities of interest:

(L/D) . , h , or n. min max

In dealing with something as subjective as resolution accuracy to a few percent should be sufficient. It is found that a value of 0.02 for

a is representative of most of the cases which will be encountered. The

standard values of k are taken to be those for a = 0.02:

k = 0.92, Circular Source

k = 1.13. Square Source

As an example, the NBS facility was recently used to radiograph a small jet engine. The (L/D) was 170, and the source is circular. One of

the regions of interest was 200 mm from the cassette. Equation (6) gives

n = 170/184 = 0.92 line pairs per mm or about 23 line pairs per inch.

Detail of the order of a millimeter would just be observed. Had a square

source of the same size been used, the resolution would have been reduced

to 19 line pairs per inch.

49
REACTOR RADIATION DIVISION PROGRAMS

THE USE OF NEUTRON AND X~RADIOGRAPHY TO EVALUATE

LITHIUh/lODINE PACEMAKER BATTERIES

D. A. Garrett

and

R. C. Steinbring

(Wilson Greatbatch, Ltd., Clarence, NY)

and

M. Ganoczy

A program, initiated by the Food and Drug Administration (FDA) , has

used neutron radiography for studying internal changes in lithium/ iodine

batteries during accelerated discharge. Neutron radiographs were compared

with x-ray radiographs and the results indicate that the two techniques

are complementary to each other.

The lithium/ iodine battery system is the most widely used power

source for cardiac pacemakers and has amassed an outstanding reliability

record.

Lithium

Cathode

Material

Hermetic Feed Through

Anode Screen

Stainless Steel Case

Figure 1. Sketch of a typical lithium/ iodine battery showing various

components and structures.

50
REACTOR RADIATION DIVISION PROGRAMS

Wilson Greatbatch Ltd., a major manufacturer of lithium/ iodine cells,

has supplied the batteries for this program. These cells consist, primarily,

of:

A. a central lithium anode

B. the charge transfer complex of 20 parts iodine to 1 part

polyvinylpyridine (C

7 H7 N) . These components are hermetically sealed in a stainless steel case

as shown in figure 1.

In general, cells of this type have been designed to power cardiac

pacemakers for periods greater than 5 years. The lithium-iodine reactions

and the role of the polyvinylpyridine (PVP) have been studied and extensively evaluated by destructive techniques. However, this presentation

describes the application and results of two nondestructive techniques

utilizing neutron and x-radiography . The neutron radiographic portion

of this program was funded by the Food and Drug Administration (FDA) and

used the expertise and facilities of the National Bureau of Standards (NBS)

.

The x-ray exposures, accelerated discharge of the cells, and destructive test correlations were performed by the Reliability Group at

Wilson Greatbatch Ltd. (WGL)

.

Eighteen cells from three typical WGL pacemaker battery models were

utilized on this program. Only the results on one model, the 761/15, is

discussed in this presentation since it was the only model which could

be conveniently neutron radiographed in the vertical direction. Although

neutron radiography is a very sensitive technique it requires lengthy

time exposures. In this program, it was necessary to make 2 hour at a flux of 104 n - cm - sec - 1 neutron exposures to clearly define the

inner structure of cells which are 8.6 mm thick and 15 mm high.

The neutron radiographic facility of NBS consists of a 10 megawatt

nuclear reactor which utilizes enriched uranium (U-235) and is cooled and

moderated by heavy water (D_0) . For the neutron radiographic purposes

1 5 of this program, a thermal neutron flux of approximately 1.4x10 neutrons/

2 cm /sec was directed through a 5 inch beam tube. In order to minimize

non-collimated neutrons the tube was lined with a lithium carbonate

51
REACTOR RADIATION DIVISION PROGRAMS

Figure 2. Comparative radiographs of a fresh Model 761/15 battery. Note

the light anode in the neutron radiograph indicating strong

neutron absorption and dark image in the x-ray illustrating

low x-ray absorption.

Figure 3. Comparative radiographs of the same battery as shown in

figure 2 but discharged .450 Ah. Note light areas on neutron

radiograph which correspond to dark streaks on x-ray. These

are probably areas of high PVP content.

Figure 4. Same battery as previous figures but discharged a total of

.685 Ah. Note the void formations in upper right area. Also

note the lithium iodide layer clearly outlined on the x-ray.

52
REACTOR RADIATION DIVISION PROGRAMS

Figure 5. Sketch of the Polyvinylpyridine monomer showing the 7 hydrogen

atoms, 7 carbon atoms and 1 nitrogen atom.

absorber. Also, it was necessary to use thick lead and bismuth filters

to absorb high energy gamma rays which are also produced within the reactor,

The result is an excellent collimated beam of neutrons with a small

apparent aperture, thereby producing a radiograph of excellent clarity

and resolution. The batteries were positioned in this beam in front of

a gadolinium (Gd) conversion screen which was held in firm contact with

a single-emulsion type SR film by means of a vacuum cassette. This type

3 of technique has been described more fully by H. Berger of NBS.

The x-radiographs of the cells were made at the WGL facility with

a 160 Kilovolt x-ray generator and using type AA industrial x-ray film.

The batteries were radiographed using the two NDT techniques as fresh batteries and, periodically, as they were discharged under controlled

accelerated conditions in the WGL electrical test facility. The units

were discharged by placing a 10K ohm load resistor across the terminals

53
REACTOR RADIATION DIVISION PROGRAMS

and electrical readings were made periodically until the batteries had

discharged approximately .2 ampere-hour (Ah) of their capacity. At this

load, the model 761/15 wil discharge .2 Ah in about 35 days.

The batteries were then shipped to NBS for the neutron radiographs

and were subsequently returned to WGL for x-radiography and the next

discharge cycle.

During this phase of the program the batteries were discharged

.685 Ah in three stages, which is approximately 50% of the rated capacity

of this model.

Upon completion of the latest test cycle one unit was cross-sectioned

and the microscopic detail was compared to the radiographs of the techniques.

The results show that the techniques are complementary and give considerable

insight into cell dynamics.

It is well known that x-rays are generally absorbed in proportion

to the atomic number and density of the material they pass through. As

a result low density, low atomic number materials such as lithium (N=3) are relatively transparent to x-rays and as a result appear as dark images

on the x-ray film. However, iodine (N=53) absorbs x-rays strongly and

appears as a light or opaque film image.

Neutrons behave much differently in that they are absorbed by the

process of neutron capture, or scatter, a nuclear process, which is

dependent on the cross-sections of the atoms of the material being radiographed. As a result materials with low atomic numbers may exhibit high

4 neutron absorbing cross-sections. Indeed, lithium is a good abosrber

and hydrogen (N=l) is one of the most efficient scatterers. Neutron and

x-ray mass absorption coefficients relating to the battery materials are

given in table 1.

It can be seen in figures 2A and 2B that the components of the cell are imaged quite differently and are nearly direct opposites in their

dark and light images. The lithium anode can be clearly seen in both

radiographs but is light in appearance on the neutron radiograph and

dark in the x-radiograph.

54
REACTOR RADIATION DIVISION PROGRAMS

As the cell was discharged to .450 Ah (figures 3A and 3B) the dark

iodine rich areas are well defined on the neutron radiograph and fingers

of cathode material containing hydrogen rich PVP, which have been partially

depleted of iodine, can be readily seen as nearly white areas. In the

x-ray image at this stage, the PVP rich areas show up as dark streaks.

In the next figures, 4A and 4B, where the cells have been discharged

.685 Ah, several interesting features can be seen. These include the

formation of voids at the inner case surface and the well defined lithium

iodide layer in the x-ray image. It is interesting to note that the voids

appear to be almost identical on both film images i.e., voids are seen

as dark areas. The voids can be attributed to shrinkage of the internal

ingredients due to the more dense lithium iodide formation. This shrinkage has been calculated and observed by other workers.

At this stage of discharge approximately 2.8 grams of iodine have

been used up in forming the lithium iodide layer. Since the charge transfer

complex is becoming depleted of iodine the hydrogen component of the PVP

monomer takes on a much more prominent role in the neutron absorption

process. As shown in figure 5, the PVP monomer contains seven hydrogen

atoms in addition to 7 carbon atoms and 1 nitrogen atom giving a total

monomer weight of 105. Since hydrogen has an absorption cross-section

of 48.5, it's presence can be used as a tracer for locating and tracking

the PVP.

In the original fresh battery, the iodine to PVP weight ratio in

the charge complex was 20:1. At this stage of discharge (.685 Ah) the

ratio has now changed to approximately 14:1 or an increase in concentration

of PVP of about 1.4 times. While the hydrogen constituent is only 7/105

of this, it becomes very significant because of it's very high absorption

coefficient.

In figure 4A, the PVP the PVP shows up as light areas positioned

between the corrugations of the anode. In the corresponding x-ray image

the PVP shows up as dark streaks. These areas can also be seen on the

cross-section of this battery (figure 6)

.

55
REACTOR RADIATION DIVISION PROGRAMS

Figure 6. Cross-section of WGL 761/15 cell after .685 Ah discharge showing Lithium, Lithium Iodide layer, Iodide-PVP charge transfer

comples and voids.

Table 1. Mass Absorption Coefficient of Lithium/ Iodine Battery

Components

.

NEUTRON X--RAY

Lithium 3.7 units .125

Iodine .036 1 .33

Hydrogen (in PVP) 48.5 .28

Carbon (in PVP) .26 .142

Nitrogen (in PVP) .48 .143

PVP Composite 3.5 .152

It can be seen from this series of comparative radiographs that the

two techniques give considerable insight into the battery dynamics. By

using the techniques to complement each other and by utilizing the mass absorption coefficients it is possible to track the battery constituents

as a function of cell discharge. Neutron radiography offers significant

information on systems of this type as a function of cell discharge. It's

nondestructive nature makes it an extremely valuable tool.

56
REACTOR RADIATION DIVISION PROGRAMS

1. Greatbatch, W. Proa, of Symposium on Power Sources for Biomedical

Implantable Applications3 1980, pp. 3-15.

2. Liang, C. C. and Holmes, C. Y. 3 "Performance and Reliability of the

Lithium/ Iodine Battery" Journal of Power Sources 5 (1980), pp. 3-13.

3. Berger, H. "Detection Systems for Neutron Radiography" Standardization

News3 ASTM Vol. 4, No. 3 1976.

A. Garrett, D. A., Berger, H. "The Technological Development of Neutron

Radiography" Atomic Energy Review 15 2 (1977).

5. Skarstad, P. M. , Owens, B. B., Untereker, D. F. "Volume Changes on Discharge in Lithium/ Iodine (PVP) Cells" Abstract 23 Proceedings of

Electrochemical Soc. Vo. 77-2, Oct. 1977.

THERI«iAL NEUTRON II AGING SCREEN DEVELOPMENT

D. A. Garrett and J. J. Barrow

The most efficient method of imaging thermal neutron beams is

utilizing a physical mixture of 6LiF and ZnS(Ni) suspended in a low Z

binder which is transparent to the light emission of the ZnS(Ni). The

6 3 4

ZnS is caused to fluoresce by the decay products from the Li(n, H) He

reaction. A light-sensitive film is employed to register the imaged

neutron beam.

One problem encountered with this type of screen is that it is

partially transparent to the light generated in the screen matrix, one

contributing factor to the grainy image produced. We proposed to produce

a segmented screen which is divided into a pixel matrix, preventing crosstalk and subsequent graininess in the finished radiography. In other

words, the radiograph would appear as newsprint on a microscopic scale.

Although this in itself represents grain, if properly fabricated, each

pixel would be of uniform density.

57
REACTOR RADIATION DIVISION PROGRAMS

The first problem to be solved was to locate a binder which was neither exothermic, i.e., a two component mix, nor one which depended

upon volitization for setting. Either of these phenomena would cause difficulties in fabrication since it has been decided to extrude the

LiF/ZnS into a fine mesh, e.g. 500 lines/in, between two fused quartz

plates coated with mold release. Mixture shrinkage or nonvolitilazation

would have resulted.

We decided to attempt to employ a UV curing optical cement as the

binder. To accomplish this, a mold release had to be coated on each of

the quartz plates. Several silicone mold releases were tried, however

cured under the influence of the UV radiation. It was found that

a common household grease release used in the kitchen, would work, but was messy. It was then discovered through the adhesive manufacturer,

that certain mylars would pass the UV curing the adhesive, however not

adhering to the adhesive. These were tried with success. Several parameters in the LiF/ZnS must still be determined, e.g.,

light output as a function of particle size, Lif/ZnS ratio for optimum

light emission and the amount of binder required for a stable screen. Using 30y dia particles of each component, the optimum LiF/ZnS ratio

appeared to be a bell-shaped curve centered at the 50 w/o LiF-50 w/o ZnS

ratio. The error bars were quite large, however, and methods of achieving

a high degree of reproducibility must still be developed, the 50 w/o/50

w/o mixture determination did differ from previous work in the field.

58
REACTOR OPERATIONS AND SERVICES

INCLUSION OF PROTON SPIN IN THE TUNNELING WAVE FUNCTIONS FOR

TRIANGULAR MOLECULES OF THE TYPE XH3 IN SOLIDS

R. C. Casella

I have done a group-theoretical analysis of the combined spacespin tunnel states for such systems, of which the CH« group in

nitromethane (CH~N09

) is an example. The latter has been studied

extensively by S . F. Trevino via neutron scattering (among other)

techniques. My analysis employs an approximation due to A. Hdller.

For sufficiently strong covalent bonding, the probability of singleproton exchange is small compared with that for double exchange of the

protons. The latter results from a rigid rotation of a molecule through

tunnel barriers in a solid and does not require breaking a covalent

bond. In an approximation where one ignores bond breaking entirely, the

only requirement of the Fermi statistics is that the wave function be

totally symmetric under double exchange. Since, for a triangle, the

improper rotations (reflections) correspond to single proton exchange,

I consider only proper rotations. In the absence of spin, the two non- trivial irreducible representations, T-. and T , stick together as a consequence of time-reversal symmetry, T. The three spin-1/2 protons

allow construction of spin states with total spin 3/2 and 1/2. Using

double-exchange projection operators, I have constructed spin states

2 which are eigenstates of the S Casimir operator and which belong to the

irreducible representations A, T.. , or T . Time reversal invariance, in

the guise of Kramer's degeneracy, again plays a role. I have combined

the spin and space wavefunction to construct tunnel states which include

both spin and T- invariance effects. I have also considered the case when

one can no longer neglect the breaking of covalent bonds, constructing

states which are totally antisymmetric under single proton exchange.

Generally, the effect of bond breaking is expected to result in small

fine-structure splitting when the rigid molecule approximation is a good

one. Further work in this area is planned.

59
REACTOR OPERATIONS AND SERVICES

NEUTRON-ANTI NEUTRON OSCILLATIONS

R. C. Casella

Recent gauge theories unifying the strong with the electroweak

interactions have led to the possibility that baryon number, B may not

be conserved. The previously unquestioned rule, AB = 0, provides, for

example, for the stability of the proton against the decays proton -> positron + photon, proton -> positron + pions, etc.. It does so by

assigning B = 1 to the proton and B = to the decay products on the

right hand side of these reactions. The deep mine experiment of Reines

yields an upper bound on the rate of the (| AB| = 1) decay of the proton;

the reciprocal is an experimental lower bound on the proton lifetime,

30 namely 10 years. Once the AB = rule is challenged, the possibility

of I AB j =2 process such as oscillations between neutrons (B = 1) and

2 antineutrons (B = -1) enters. Because of a recent proposal to employ

the NBS reactor for the purpose of setting a bound on the period of

(or discovering) those conjectured oscillations I have begun a study of

the associated phenomenology. Provided the ambient magnetic field is

suitably suppressed, I find that, for sufficiently short flight times t

P-(t) = (cut) 2. (1)

Here, P-(t) is the probability that a neutron released from a nucleus at

t = will, upon interaction with a target at time t, be found to have

converted to an antineutron by an ideal detector of, say, the annihilation

products. For a flight path ^ 10 meters, a thermal neutron of speed

3 -2 ^ 10 meters/sec. will impinge on a target at t ^ 10 sec. Th^re exist

two crude theoretical estimates for to: oj ^ 10 sec. " and u) ^ 10 sec. From Eq.(l), these estimates imply that 10 neutrons per second

impinging on a target-detector of 100% efficiency will yield a count

rate of ^ 30 counts per year and ^ 10 counts per day, respectively. For

-2

t - 10 sec, it is necessary that the ambient magnetic field be reduced

1. S. F. Trevino and W. H. Rymes, preprint (1979).

60
REACTOR RADIATION DIVISION PROGRAMS

-3

to < 10 gauss along the flight path for Eq.(l) to hold. A more

detailed report of these preliminary findings, which are in essential

4

agreement with other studies, is being prepared.

1. J. C. Pati and A. Salam, Phys. Rev. Lett. 31, 661 (1973), H. Georgi

and S. L. Glashow, Phys. Rev. Lett. _32, 438 (1974). R. N. Mohapatra

and R. E. Marshak, Phys. Rev. Lett. 44_, 1316 (1980).

2. W. C. Sauder, private communication.

3. The smaller estimate is due to S. Glashow (Lectures at Cargese Summer

School, 1979) and the larger is due to Mohapatra and Marshak, Ref . 1.

4. These may be found in various unpublished preprints by M. Baldo-Ceolin,

by R. Mohapatra and R. Marshak and by R. Wilson.

61
REACTOR RADIATION DIVISION PROGRAMS

MICROSCOPIC REVERSIBILITY, TIME-REVERSAL INVARIANCE,

AND THE BOLTZMANN H-THEOREM

R. C. Casella

This very old subject has resurfaced in three contexts. (i)

Microscopic time-reversal invar iance T is known to be broken, as a consequence of the observed CP violation in the neutral K meson system,

either by invoking the CPT theorem, or by direct analysis of the juxtaposition of data from several experiments . (ii) Deviations from equilibrium

play an important role in recent theories explaining the preponderance of

2 matter vs. antimatter in the Universe. (iii) Molecular dynamics calculations often begin with distributions which deviate from equilibrium and

actually follow the approach thereto. My analysis, thus far, is limited

to quantum statistics. Two ways of obtaining the H- theorem are considered.

The first employs microscopic reversibility, A^ = A , where A, is the

probability per unit time for a system to undergo a transition from the

state |a> to the state |b>. The second does not assume microreversibility,

invoking only unitarity of the Heisenberg S-matrix. Both start with the

assumption that the temporal evolution of the distribution among states of

3 an ensemble of isolated physical systems is governed by a master equation,

d?

a /dt =

?

' (Aab

P

b

" \aP

a

) " (1)

P (t) is the probability that an arbitrarily selected system is in the

3, state I a> at time t. In terms of the S matrix, I find

A = 2tt |t, | 2 6(E, - E ) ba ' ba 1 b a

(2)

where S = 1 + iT and t, is an element of the reduced T matrix

ba

T, = 2tt t, 5(E, - E ). ba ba b a

(3)

62
REACTOR RADIATION DIVISION PROGRAMS

In terms of the entropy,

S = -

I Palog P (4) a

the H- theorem reads,

dS/dt > 0. (5)

Assuming micro reversibility, the master equation becomes

<Vdt -l[ Aab * (Pb- Pa>- <«

b

From Eq. (4) and Eq. (6),

dS/dt = I A

ab x (Pa

- P

b

) log P (7)

a,b

Again using A = A , Eq. (7) can be written in the fo rm

dS/dt - % I A

ab * (P - P ) log (P /P ). (8)

a,b

Since the right-hand side of Eq. (8) is manifestly positive, the H- theorem

follows immediately.

Unitarity of the S matrix implies

b b

Thus, Eq. (6) follows from Eq.(l), even when microscopic reversibility does

not hold. That is, even if A, ^ A , , Eq. (6) and Eq. (7) are still valid,

ba ab

but Eq.(7) no longer implies Eq.(8). Nevertheless, from the property that

S = 2, f (P ), where f(P) is a concave-downwards function of P, the H-theorem

a

a can be shown to follow from Eq. (6) and Eq.(9).

By relating the coefficients A directly to the S-matrix elements,

63
REACTOR RADIATION DIVISION PROGRAMS

St , it is possible to examine the effect of various symmetry operators

of S on the master equation. These operators include T = time reversal,

p = parity, and C = charge conjugation, alone or in various combinations,

such as CPT I find that T invariance does not necessarily imply the

microscopic reversibility condition, A, = A . However, under special

circumstances, such as a system of spinless particles, the combined PT

operation does; whence, if P is a good symmetry, T -invariance and microscopic reversibility are then equivalent. Also, in first Born approximation,

hermiticity of the interaction hamiltonian leads to microscopic reversibility,

independently of whether the hamiltonian is invariant under C, P, or T,

alone or in combination. However, this result does not generalize to higher

orders in the perturbation expansion since the T-matrix is generally not

hermitian. (If it were, the optical theorem would imply zero cross sections

for all reactions.)

Breakdown of microreversibility generally leads to the well-known

Poincare cycles. But this does not contravene the result that, for an

isolated system in equilibrium, all states, |a>, |b>, |c>, ... which are somehow interconnected by the master equation (and, hence lie on the energy

shell) are equally probable. This fact, together with the CPT theorem,

has implications with respect to the net generation of matter in the early

2 Universe. I plan to investigate this and related questions somewhat

further.

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

and references therein.

2. S. Weinberg, Phys. Rev. Lett. 43, 1566 (1979). F. Wilczek and A.

Zee, Phys. Rev. Lett. 43, 1571 (1979).

3. C. N. Yang and C. P. Yang, preprint (1979) and references therein.

64
REACTOR RADIATION DIVISION PROGRAMS

COLOR GRAPHICS AND IMAGING SYSTEM

N. F. Berk and J. M. Rowe

An important component of the SANS data acquisition and processing

facility being developed here is a new color graphics and imaging system

which will be used to display and analyze data from the area detector.

The system comprises a high-resolution raster scan color TV monitor for

image display, associated video boards and a microprocessor for picture

and color control, and an interface with our minicomputer for software

image processing.

The imaging function of the device can be viewed in mathematical

terms as producing a mapping of a two-dimensional data field onto a color

field. Specifically, each element of the area detector can be mapped onto

a picture element of the video monitor and assigned a color value according

to the value of the measured scattering intensity. In this way the neutron

data can be immediately visualized as a new data field in which regions of

equal scattering intensity are at once identifiable by their colors. Moreover, the color mapping function can be manipulated interactively without

erasing the image from the screen. This makes it possible to visually

average the data in different ways and to probe regions of the data field

in great detail while the image is being displayed. We anticipate that

these capabilities will have >a significant impact on the processing and

analysis of small angle neutron spectra, particularly when they are complex and strongly anisotropic.

Since installing the imaging system in early 1980, we have been

learning its many characteristics and have devoted a considerable effort

to improving and extending the software package supplied by the vendor.

We have also developed our own image processing programs and have undertaken preliminary applications of the system to simulated small angle data.

In addition, we are hopeful of developing other scientific applications

of the new imaging device. For example, we have explored its use in the

display of real-time random walks of various kinds, including self -avoiding

walks in which path color serves to identify previously visited points without

65
REACTOR RADIATION DIVISION PROGRAMS

having to store a large vector in the host computer.

1. C. J. Glinka, J. M. Rowe, and J. G. LaRock, this report,

THE SMALL-ANGLE SCATTERING FACILITY

C. J. Glinka, J. M. Rowe and J. G. LaRock

The new facility for small-angle neutron scattering (SANS) described

in the 1979 progress report is presently under construction at the NBSR.

An overhead and side view of the design of the new instrument is shown

in figure 1.

The key element of the SANS instrument is a large area position

sensitive proportional counter which will enable data over the entire

small-angle region to be recorded simultaneously. Two area detectors

2 3 of the Borkowski-Kopp type have been purchased for the instrument, a primary detector with a 65cm X 65cm sensitive area and a smaller back-up

detector with an active area of 25cm X 25cm. To date, the smaller detector

has been received and has met all performance tests. For example, figure

2 shows a typical measurement of the spatial resoluation and linearity

of the 25cm X 25cm detector. For this measurement a cadmium mask with

a row of 1.5mm diameter holes spaced 2.5cm apart was placed over the

face of the detector which was then scanned through a collimated 1cm

diameter neutron beam. The detector response is linear to a high degree

as can be seen by the open circles in figure 2 which are the channel

numbers of the measured peak positions on the right-hand scale. The

spatial resolution of the detector is given by the peak width which are

4mm (FWHM)

.

The data acquisition system associated with the area detector,

shown schematically in figure 3, has been assembled and is now undergoing

testing. The positional information for each neutron detected is contained

66
REACTOR RADIATION DIVISION PROGRAMS

NBS SANS SPECTROMETER

Bismuth- Velocity First Collimating

Rotating Shutter Beryllium Selector Aperture

4.5 m- -3.5 mFigure 1. Overhead and side views of the layout of the new SANS facility.

3-

o

-* 2

c

3OO

co

—I I

1 Channel = 1 .0 mm

J

_L 50 100 150

X, Channel Number

200 250

Figure 2. A typical measurement of the resolution and linearity of the

25cm X 25cm area detector for the SANS facility made by stepping

a 1.5mm diameter beam across the detector in 2.5cm steps.

67
REACTOR RADIATION DIVISION PROGRAMS

in the difference in rise times between the pulses produced at the two

2 ends of each cathode . The two time intervals, for the x and y directions. are directly digitized by counting pulses from a crystal controlled 125Mhz

DCOLOR IMAGING/ GRAPHICS TERMINAL

CONSOLE

TERMINAL

ACTIVE 1-D DISPLAY

1

/

1 PRE- AMP

/

/ /

1

1

-JTSCAfr-l

Figure 3. A schematic layout of the data acquisition system for the new

SANS facility.

68
REACTOR RADIATION DIVISION PROGRAMS

4

clock. Such a direct time digitizer eliminates the conversion time and

reliance on analog signals inherent in the more conventional time interval

measurement by means of a time-to-amplitude converter followed by an analog-to-digital converter. The clock frequency chosen provides 8-bits,

or 256 channels, for both x and y directions. A custom hardwired interface then forms a 16-bit memory address from the digitized positional

information. A standard DMA interface is used to transfer the address

to a dedicated minicomputer which increments the corresponding location

and checks for overflow. The throughput of this data acquisition system

has been measured to exceed 50Khz and thus the maximum data rate of the

system is limited by the detector response only (^ 20,000 cps) . An active

display of one row of detector pixels will be provided to visually monitor

the data collection. A completed data set can then be transferred to a VAX11/780 computer for data reduction and display on a color imaging

terminal.

Delivery of the larger area detector is scheduled for the early

Fall of 1980. The detector flight path and other mechanical components

of the instrument are to be completed at about the same time. Full

operation of the new SANS facility is anticipated in early 1981.

1. C. J. Glinka, et al. , NBS Teeh. Note 1117, F. Shorten, Ed., 33(1980).

2. C. J. Borkowski and M. K. Kopp, Rev. Soi. Ins trum. , 46_, 951(1975).

3. Technology for Energy Corp., Knoxville, TN.

4. Designed and built by the Electronics Division, Argonne National

Laboratory.

69
B. RRD Collaborative Programs

ErFe

2 — FINITE TEMPERATURE SPIN WAVES

J. J. Rhyne

and

N. C. Koon

(Naval Research Laboratory, Washington, DC)

Magnetic spin excitations in the Laves-phase structure compound

1 2

ErFe„ have been studied previously in this laboratory ' at 4 K and at room temperature primarily. The observable 4 K ground state excitations

shown in figure 1 consist of an in-phase spin precession acoustic mode

with an anonalously large q = gap of 8.3 meV plus a dispersionless

mode representing an out-of-phase precession of the rare earth spins.

The lack of dispersion reflects the vanishingly small exchange coupling

between the rare earth spins. A higher energy in-phase mode of the iron

spins is not shown in the figure.

At room temperature the acoustic mode shows essentially the same dispersion but is gapless. The flat optic mode remains degenerate

at the zone boundary. Previous studies of the intermediate tempera2

ture behavior of this flat mode revealed that both the low (c.f. 295 K)

and high (c.f'. 4 K) energy modes could be observed simultaneously with

no apparent shift in energy as the temperature was varied. The intensity did, however, smoothly shift from the high energy excitations into

the low energy mode as the temperature increased in a manner suggesting

2 a magnetic exciton effect. A molecular field calculation did, in fact,

confirm this excited state spin wave behavior.

Mean field models can not account for the temperature or wavevector dependence of the dispersive acoustic modes. Recently, careful

measurements have been made of the acoustic mode at intermediate temperatures and have been compared to the results of a Greens function random

3 phase approximation calculation. Figure la shows the calculated

dispersion curves at room temperature and illustrates the large number

of in-phase (dispersive) and out-of-phase (nondispersive) modes which

70
RRD COLLABORATIVE PROGRAMS

<*>24-

ErFe 2 J2

- 295K h

<JZ>Er= 3 - 6 1 "

> 9

£ l LJ O o 1 <SZ >F9 =0.66 16 .

9Fe _ Fe

= 30meV $

0Fe-Er=- 0.32 meV\"

9 Er-Er=0 I. O Expt. U — Model y

8-

(q.q.O) (q.q.q)

"Sp 4-

1 1 1 L -G>

0.8 0.4 0.2 0.4

Reduced Wave Vector (x comp.)

15

l ErFe o Optic Mode

o Acoustic Mode

T = 295K

0.5

Wave Vector

o °u n o—

9

1.0

Figure la. Room temperature spin wave modes found for ErFe

? (b) distinct

high and low temperature pairs of in-phase (acoustic) and

out-of-phase (optic) modes observed for ErFe„ at 4 K and at

295 K.

are degenerate at the zone boundary. These modes originate from transitions between adjacent magnetic levels, and all but one pair represent

excited state spin waves. The model calculation predicted two salient

features which were checked by experiment: (1) the "acoustic" mode at room temperature shown in figure 1 actually consists of two separate

modes (see figure 2) whose intensity varies inversely with q in such a manner as to appear to be one mode in a moderate resolution experiment.

High resolution scans at 80 K for q = 0.1 did in fact confirm the

existence of the two distinct in-phase modes as seen in figure 3 at

almost precisely the predicted energies and relative intensities

(Gaussian fitted solid lines in figure) . (2) the model also predicted

that the q = intercept of the groundstate acoustic mode (higher energy

dispersive mode in figure lb) should increase with temperature. A

careful study of the modes at q = 0.1 revealed this temperature depen71
RED COLLABORATIVE PROGRAMS

20 1 Theory

J

Fe . Fe

= 30 meV

J Fe-Er

= -0.3meV

A4

= 3.2 meV

A6

= -0.125 meV

Energy

(meV o 7

(5 0.5 1.0

Wave Vector (q,q,o)

Figure lc. Room temperature modes predicted by RPA theory for ErFe„

using experimentally determined exchange and crystal field

parameters. At the zone boundary in-phase (dispersive) and

out-of-phase (flat) components of each mode are degenerate.

150

cE

IDr-\V)c

3

O

o

120-

ErFe

2

T = 80K

(2.1,2.1,0)

Figure 2.

3

E (meV)

Simultaneous observation of two low lying dispersive modes

which make up the single "acoustic" mode of figure la. The

solid lines give the relative intensity as predicted by the

RPA model.

72
RRD COLLABORATIVE PROGRAMS

T(K)

Figure 3. Temperature dependence of the energy of ground state acous- tic mode of q = 0.1 compared to the prediction of the RPA

model.

dence in very close agreement with theory as shown in figure 3.

These experimental results and the agreement with the RPA model

calculation provides a relatively complete insight into the finite

temperature excitations in ErFe_.

1. J. J. Rhyne and N. C. Koon, J. Appl. Phys. 49, 2133 (1978).

2. N. C. Koon and J. J. Rhyne, Solid State Commun. 26, 537 (1978).

3. N. C. Koon and J. J. Rhyne, Intl. J. Magnetism (proc. ICM, Munich,

1979), to be published in 1980.

73
RRD COLLABORATIVE PROGRAMS

TEMPERATURE RENORMALIZATION OF SPIN WAVE ENERGIES IN HoCo

2

J . J . Rhyne

and

N. C. Koon

(Naval Research Laboratory, Washington, DC)

The Laves-phase compound HoCo 9 has the [110] direction as the easy

magnetic axis at low temperature. In the range 12-16 K, the spin direction gradually changes from the [110] direction into the [100] direction.

This shift in easy axis accompanies a rather large change in crystal

field energies which is directly observable by neutron scattering.

Figure 1 shows the observed ground state modes in HoCo„ at 4 K.

The two flat modes are crystal field-like transitions from the ground

state to first and third excited states as seen from the energy level

20

18

16

14

_12

>*10

(q.q.q)

RPA Theory

HoCo 2 Spin Waves 4K

(q.q.o)

Ho-Ho

=

A°4 =4.3meV

A°6 =-0.20meV

1B.Z.

i i i T i i 5 0.4 0.3 0.2 0.1 0.2 0.4 0.6 0.8 1.0

<^ x Reduced Wave Vector

36

32

28

24

20

16

12

8

4

Localized States W

0.006

0.0038

0.104

2.779

3.27

20.1

Figure 1. Dispersion relation for HoCo at 4 K for the [110] easy axis

direction. The solid lines and the energy level diagram are

the result of an RPA calculation using the exchange and

crystal field parameters shown.

74
RRD COLLABORATIVE PROGRAMS

0.2 0.4 0.6 0.8

(q,q,o),q x

1.0

Figure 2. (a) Lowest optic mode energy in the spin reorientation

temperature range. The spins slowly rotate from the [110]

direction to the [100] direction in this temperature range,

(b) Dispersion curve for two lowest modes above the spin

reorientation temperature along the [q,q,<f>] propagation

direction.

diagram on the right. The dispersive modes arise from an in-phase

precession of the spins with the upper one reflecting only the cobalt

sublattice. This mode has not been observed in the present work nor was

it seen in ErCo„. The solid lines are the result of a Green's function

random phase approximation (RPA) calculation of the mode energies using

the exchange and crystal field parameters shown.

Figure 2a shows the effect of the spin reorientation on the energy

t of the lowest out-of-phase mode in the range below 25 K. The mode

energy drops slowly from about 6 meV at 4 K to 3.6 meV when the reorientation is fully complete near 16 K. The dispersion curves for the

acoustic and lowest optic modes above the reorientation temperature are shown in figure 2b.

1. N. C. Koon and J. J. Rhyne, Crystalline Field and Structure Effects

in f-Electron Systems, edited by J. E. Crow, R. P. Guertin, T. W.

Mihalisin, Plenum Publishers, p. 125 (1980).

75
RRD COLLABORATIVE PROGRAMS

SPIN GLASS-FERROMAGNETIC PHASE TRANSITION

IN AMORPHOUS (Fe^l^) #7g P

B 16B

>0fi

Al -03

J. W. Lynn

(University of Maryland, College Park, MD)

and

(National Bureau of Standards, Washington, DC)

and

J . J . Rhyne

and

H. S. Chen

(Bell Telephone Laboratory, Murray Hill, NJ)

The amorphous magnetic metal-metalloid systems such as

1 2

(Fe Ni. ) -, C P -,B ~,-Al „„ have been found ' to be excellent examples

x 1-x . 75 .16 .06 .03

of three-dimensional isotropic ferromagnets at high Fe concentrations.

With the addition of nickel, which in this material behaves as a nonmagnetic diluent, the transition temperature and average exchange

interaction decrease. At sufficiently low concentrations the system is,

in fact, no longer capable of supporting long-range magnetic order but

3 4 rather undergoes a spin freezing phenomenon. ' We have been employing

neutron scattering techniques to study the microscopic energetics of

these random percolative systems.

The characteristic feature of a uniform ferromagnetic is a collective excitation whose energy E varies as the square of the momentum Q,

2

E = DQ . Here D is a temperature dependent constant of proportionality

which is maximum at T = and monotonically falls to zero at T = T , the

Curie temperature. Our measurements on a sample with x = 0.4 agree

with this general behavior in that well defined spin waves which obey a quadratic dispersion relation are observed, and they renormalize toward

zero energy as the Curie temperature (T = 380 K) is approached. Below

^80 K, however, D begins to decrease with decreasing temperature as the

spin glass state is approached. Associated with this decrease in D is

76
RRD COLLABORATIVE PROGRAMS

an increase in the spin wave linewidths. Qualitatively similar behavior

is found for the lower (nominal) concentration of x = 0.2, which has a Curie temperature of 118 K.

1. J. W. Lynn, G. Shirane, R. J. Birgeneau, and H. S. Chen, ATP Confer- ence Proceedings _34, 313 (1976)

.

2. R. J. Birgeneau, J. A. Tarvin, G. Shirane, E. M. Gyorgy, R. C.

Sherwood, H. S. Chen, and C. L. Chien, Physical Review B18 , 2192

(1978).

3. S. M. Bhagat, M. L. Spano, H. S. Chen, and K. V. Rao, Solid State

Comm. 33, 303 (1980).

4. S. M. Bhagat, J. A. Geohegen, and H. S. Chen, Solid State Comm. (to

be published)

.

NEUTRON SCATTERING STUDIES

OF THE MAGNETIC SUPERCONDUCTOR (Ce

Q 65 TbQ 3S >Ru2

J. Fernandez-Baca and J. W. Lynn

(University of Maryland, College Park, MD)

and

(National Bureau of Standards, Washington, DC)

Neutron scattering measurements have been carried out on a polycrystalline specimen of (Ce„ ,_ Tb

n _)Ru9 in order to study the crystal

field splittings as well as the development of magnetic correlations at

low temperatures.

At small wavevectors the intensity increases with the decreasing

temperature indicating the development of ferromagnetic correlations.

The intensity saturates at T *v> 4 K with no peak in its' temperature

dependence. There is also no temperature dependence of the intensity of

the {111} Bragg peak, so that there is no long range ferromagnetic order

at this concentration. These observations agree with the results of

Roth and collaborators on the Tb system.

77
RED COLLABORATIVE PROGRAMS

500

< Ce82Tb18> RU 2 K = 1 .60 A

1

*«*•••,*

X

-2.0 10

E (meV)

Figure 1. Inelastic scattering data from (Ce ,,. Tb„ ~,-)Ru~ at

T = 4.2 K and T = 20 K. At 4.2 K there is 'magnetic scattering which peaks at ^3.3 meV. At 20 K another transition

appears at ^6.6 meV.

The system Ce., Tb Ru„ is a substitutional alloy in which the

Q I X X X Z fy Tb ions replace Ce randomly. The site symmetry is cubic (43m) and

3+ has 12 Ru nearest neighbors and four Ce (or Tb ) next nearest neigh3+

bors. When situated in the crystal, the 13-fold degeneracy of the Tb

free ion is lifted, at least partially, by the effect of the electrical

interaction of the neighboring ions. This splitting is very important

for understanding the magnetic properties of the system since it determines the ground state of the ion. The simplest theoretical approach is

3 given by the "crystal field model" in which the interaction is represented by an equivalent electrostatic field of the same symmetry. The

3+

most significant interaction on the Tb sites is due to the 12 Ru

nearest neighbors, so we may use, as a first approximation, cubic symmetry. This procedure has been found to give good results in the related

system (Ce Ho )Ru

' I-x x 2

78
RRD COLLABORATIVE PROGRAMS

Inelastic scattering measurements (see figure 1) reveal the existence of an excitation at ^3.3 meV with additional scattering between

0.0 and 3.3 meV, at 4 K. At T = 20 K additional scattering appears at

^6.6 meV while the 3.3 meV peak appears to shift to lower energy. This

scattering has been identified as magnetic since the intensity as a function of K follows qualitatively the magnetic form factor f (K)

dependence. In comparison with the (Ce-Ho)Ru„ system, we note that the

exchange interaction is significantly larger for Tb as evidenced by the

higher spin freezing temperature (4 K for 35% Tb as compared to 2.0 K

for 38% Ho) and by the observed width to the scattering which is presumably due to exchange broadening. Further measurements are in

progress.

1. S. Roth, Appl. Phys. 15, 1 (1978), and references therein.

2. W. B. Pearson, Handbook of Lattice Spacings and Structures of

Metals and Alloys, Vol. 2, p. 67, Pergamon Press (1967).

3. See, for example, M. T. Hutchings, Sol. St. Phys. 16, 227 (1964).

4. J. W. Lynn, D. E. Moncton, L. Passell, and W. Thomlinson, Phys. Rev,

B21, 70 (1980); J. W. Lynn and C. J. Glinka, J. Mag. and Magnetic

Materials 14, 179 (1979).

79
RRD COLLABORATIVE PROGRAMS

FERROMAGNETIC PHASE TRANSITION

IN THE REENTRANT SUPERCONDUCTOR (Er Ho

8 g)Rh

4

B

4

J. W. Lynn

(University of Maryland, College Park, MD)

and

(National Bureau of Standards, Washington, DC)

and

R. N. Shelton

(Iowa State University, Ames, IA)

Pure ErRh.B, becomes superconducting at T - = 8.6 K, then reenters

the normal conducting phase at T = 0.9 K as it becomes ferromag2 netic. The substitution of Ho for Er increases the magnetic transition

temperature, along with the reentrant superconductive transition T „ while gently suppressing the upper superconducting transition. These

3 three phase boundaries meet in a multicritical point at a concentration

of 0.89 Ho and a temperature of ^6 K. We have prepared a sample slightly rich in Er such that the sample is superconducting over a small

temperature interval; the multicritical point may then be reached by the

4 application of hydrostatic pressure. Figure 1 shows the development of

ferromagnetism at T = 5.55 K, as measured in the {101} Bragg peak at

ambient pressure. Susceptibility measurements on the same sample yield

T * 5.7 K, T = 5.4 K, so that there appears to be a small temperature interval in which the ferromagnetism and superconductivity coexist.

At low temperatures we obtain a magnetic moment y =7.78+0.3 y-,

with the moment directed along tetragonal c axis. The reduced moment

compared to the free ion value suggests that crystal field effects are important, and indeed crystal field transitions have been directly

observed in inelastic neutron scattering spectra.

The nature of the magnetic transition is of some interest; the

transition appears continuous and reversible. We also have noted that

the intensity appears to be linear in T - T , which since

80
RRD COLLABORATIVE PROGRAMS

2(3

I M

(1)

would imply that 3 = 1/2, the mean field value. Mean field behavior has

3 already been noted in specific heat data. In addition small angle

scattering measurements reveal the absence of any critical scattering,

although the paramagnetic scattering is easily observed. We thus

conclude that the transition is indeed mean-field like. This behavior

is most probably due to the proximity to the multicritical point, where

the magnetization by itself is not the primary order parameter. The

pressure dependent work is underway.

3000

cE

w 2000 +>c

3oO

1000

•-•

{Er 11 Ho 89 )Rh 4 B 4 (101) Peak Intensity

P =

••

#

t

•l

3 4

T(K)

Figure 1. Intensity of the (101) Bragg peak as a function of temperature.

81
RRD COLLABORATIVE PROGRAMS

1. W. A. Fertig, D. C. Johnston, L. E. deLong, R. W. McCallum, M. B.

Maple and B. T. Matthias, Phys. Rev. Lett. 38, 987 (1977).

2. D. E. Monoton, D. B. McWhan, J. Eckert, G. Shirane and

W. Thomlinson, Phys. Rev. Lett. 3_9, 1164 (1977).

3. H. B. Mackay, L. D. Woolf, M. B. Maple and D. C. Johnston, Phys.

Rev. Lett. 42, 918 (1979). Errata; 43, 89 (1979).

4. R. W. Shelton, C. U. Segre and D. C. Johnston, Sol. St. Comm. 33,

843 (1980). —

MAGNETIC PERCOLATION IN THE

PSEUDOBINARY SUPERCONDUCTOR (Ce 1-X Ho

x )Ru

2

J. W. Lynn

(University of Maryland, College Park, MD)

and

(National Bureau of Standards, Washington, DC)

and

C. J. Glinka

In the superconducting system (Ce- Ho )Ru„ small concentrations

of Ho have been found to enhance the superconducting state while concen- trations in excess of 30% are needed to suppress superconductivity.

Central to the question of the interplay between ferromagnetism and

superconductivity is the role that magnetism plays in this observed

suppression. Investigations by Wilhelm and Hillenbrand indicated that

the ferromagnetic phase boundary (as determined by susceptibility)

intersected the superconducting boundary at a concentration of 0.27 and

2 a temperature of 1.6 K. Earlier neutron work for x = 0.27 showed

that ferromagnetic correlations do indeed develop at low temperatures,

o but the range of the correlations ceased to increase above 80 A at a temperature of 0.5 K, and that no transition to long range order

occurred.

82
RRD COLLABORATIVE PROGRAMS

n800

15

8 10

0)

03

0)c

Z, 5

< Ce62

H°38> RU

2

600 c

E

in +>

i Io

u H4oo r

Background

B a

• Peak + Background

o Gaussian Peak Intensity

d Integrated Intensity

200 (0 Q.

8

T(K)

Figure 1. {111} Bragg peak scattering as a function of temperature.

The additional intensity below 2 K is the magnetic contribution to the scattering, which is limited in width by the

instrumental resolution and signifies long range ferromagnetic order.

One possibility for the truncation of this transition is that the

system is simply too dilute to support the ferromagnetic state. In this

C-15 Laves phase the rare-earth ions occupy a diamond lattice, with a rather low coordination number of z = 4. If the coupling is dominated

3 by nearest-neighbors then the percolation threshold P is 0.425, a concentration well above the magnetic-superconducting "coexistence"

region. We might then interpret the suppression of the superconductivity at high concentrations as due to the increase of the average size of

magnetic islands as the concentration increases, with the value of the

ferromagnetic correlation range being bounded by this cluster size.

83
RRD COLLABORATIVE PROGRAMS

The actual exchange interaction may extend beyond nearest neighbors,

which will reduce the percolation threshold, but the range may not be

sufficient to produce long range order in the observed coexistence

region.

To investigate this possibility we have carried out measurements

on a sample with 38% Ho, which lies outside the superconducting region

for all temperatures. The small angle scattering measurements still

showed no characteristic peaks in the intensity as a function of temperature as might be expected fot a ferromagnetic phase transition. Rather

°-l the scattering for Q > 0.05 A flattened off at T *\j 2 K in a fashion

similar to the 27% alloy at 0.5 K. The scattering at smaller wavevectors, however, continued to increase slowly with decreasing temperature. Thus in these data there is no indication of a ferromagnetic

phase transition. Nevertheless figure 1 shows that below 2 K the

intensity of the {111} Bragg peak increases, demonstrating that there is

a spontaneous magnetization developing at low temperatures.

To interpret these data we note that for p > p the system

consists of finite clusters, which freeze at low temperatures, as well

as an infinite cluster which will order at some temperature T . (If

p < p there are only finite clusters and hence there can be no long

range order.) The observed scattering will be the sum of these two

4 contributions, which may not exhibit a peak in the small-angle scattering as a function of temperature particularly if a substantial portion

of the magnetic atoms belong to finite clusters. The strength of the

magnetic Bragg scattering indeed shows that less than half the atoms

belong to the infinite cluster. Calculations of the pair connectivity

function are underway in order to make a detailed comparison between

theory and experiment.

84
RRD COLLABORATIVE PROGRAMS

1. M. Wilhelm and B. Hillenbrand, Z. Naturforsch. Teil A2b_, 141 (1971)

J. Phys. Chem. Solids 31, 559 (1970).

2. J. W. Lynn, D. E. Moncton, L. Passell and W. Thomlinson, Phys. Rev.

521, 70 (1980).

3. J. W. Essam, "Phase Transitions and Critical Phenomena," Vol. II,

p. 197, ed. by C. Domb and M. S. Green (1972).

4. Below T (^2 K) there is also a contribution from domain wall

scattering at the smallest wavevectors. The strength of this

scattering is proportional to the order parameter and has been

observed in other low temperature ferromagnets such as HoMo,S» and

(Er n Ho )Rh.B.. 1-x x 4 4

NEUTRON-SCATTERING STUDY OF SPIN WAVES IN THE

ANTIFERROMAGNET RbMnCl

3

H. A. Alperin

(Naval Surface Weapons Center, White Oak, MD)

and

(National Bureau of Standards, Washington, DC)

and

M. Melamud*

(NSWC and American University, Washington, DC)

RbMnF

q is a transparent ant if erromagnet with T = 94K. The

structure is of the hexagonal BaTiO.-type belonging to the space group

P6„/mmc with 6 formula units per unit cell; the six magnetic Mh ions

occupy the 2a and 4f sites. Below T„ the magnetic structure consists of

N

ferromagnetic planes stacked in the sequence A(+) , B.. (-) , B- (+) , A(-) , B (+) , B_(-) along the c-axis. The spin direction is perpendicular to

2+ the c-axis. There are two kinds of sites in the Mn ions; the A-sites

(containing "lone spins") and the B-sites (containing much closer spin

*Permanent address: Nuclear Research Center-Negev, Beer Sheva, Israel,

85
RRD COLLABORATIVE PROGRAMS

pairs) . The prinicipal magnetic exchange interactions can therefore be

described by J and JTM. Ad do

This study (at low temperature) of the spin wave spectrum of RbMnCl_

was undertaken with the objective of answering the following question:

RbMnCI

4K

Calculated

S A =2.4

S B =2.5

J bb /Jab = "* - 65

JAB = 0.441

1.92

2.0

1.65

L 0.55

0.2 0.4

[qOO]

0.2 0.4

[00 q]

Figure 1. Spin wave dispersion spectrum of RbMnCI- . The solid curves

are calculated according to the Heisenberg theory.

Are the magnetic interactions to be represented by the conventional

Heisenberg model where J

AB

and J

BB are of the same order of magnitude

(probably acting via the intervening CI ions -180° and 90° superexchange,

respectively) or might RbMnCI be representative of a new class of

86
RRD COLLABORATIVE PROGRAMS

magnetic materials; one in which the system is dominated by very strongly

coupled spin pains, which are in-turn, weakly coupled together, i.e. with

J

BB

>>J

AB

? 3

A large cylindrical single crystal (^2.5 cm in volume) was used

to collect data at liquid helium temperature on a triple axis spectrometer

employing the constant-Q method, at a fixed scattering (final) energy of

14.7 meV. Measurements were performed with the scattering vector along

three principal directions; [001], [110], and [100].

Samuelsen and Melamud have derived expressions for the dispersion

relations for both the conventional (Heisenberg) and the strong coupling

models. For J /J. >> 1, although the (doubly degenerate) acoustic

BB AB

modes for the two models are similar, the (doubly degenerate) optic

mode along the c-axis is split in the conventional case while it is

not for the strong coupling model.

The experimental results immediately rule out the strong coupling

model since two distinct optic branches were observed in the [OOq]

direction (and in other directons as well) . Figure 1 shows the experimental

results for the [qOO] and [OOq] directions and the curves calculated

according to the Heisenberg theory. The fit is seen to be quite good.

In performing the calculations, the spin moments on the A and B manganese

atoms were allowed to vary. The two sets of parameters shown on the

figure gave equally good fits to the data although the values for S ~ 5/2 are to be preferred. However, the ratio J /J. = 1.64 (+ .1) is

BB AB —

independent of the value of the moments and shows very clearly that in

spite of the rather large difference between r Ar> (^ 5A) and rBT1 ( % 3A)

AB ijD

the ratio J^/J.- is not very large, indicating that superexchange

BB AB

rather than direct exchange is operative. The values of J.^ and J„„

found here are comparable to those found in other similar manganese

halides.

1. E. J. Samuelsen and M. Melamud, J. Phys. C: Solid State Physios

7, 4314 (1974).

87
RRD COLLABORATIVE PROGRAMS

STRUCTURAL INVESTIGATION OF ThgMn^g

K. Hardman and J. J. Rhyne

and

K. Smith and W. E. Wallace

(University of Pittsburgh, Pittsburgh, PA)

The magnetic behavior of the isostructural compounds, Y,Mn„- and

d 25

Th-MnooJ are drastically altered upon hydrogenation. Y,Mn__ is a ferrib 25 o 25 - magnetic compound with T = 486 K and a bulk magnetization value of 13y /f .u. Upon hydrogen absorption the long range magnetic order vanishes. In

contrast, Th,Mn„_ is a Pauli paramagnet, while Th,Mn„„H„

n exhibits long

range magnetic ordering with T = 329 K and a bulk magnetization value

of 18.5u_/f .u. Th,Mn„„ is a face centered cubic, space group Fm3m, with

a D 25

116 atoms per unit cell and four formula units per unit cell. There

exists one Th site and four Mn sites (b, d, f -, and f

9 ).

The deuterium absorption isotherm shows a large plateau from 17 to

24 deuterium atoms. The sample was prepared at pressures just short of

the plateau to obtain a single phase compound. The maximum number of

deuterium atoms that can be experimentally absorbed into the Th,Mn„„ is

around 30. Neutron diffraction spectra at 4 and 295 K were collected

using the high resolution 5-detector powder unit. The data were analyzed

using the NBS profile fitting program based on the Rietveld method.

Profile fitting programs are especially useful in studying the R/-T

9

„ compounds in that they actually account for peak overlap which occurs predominately at high scattering angles.

The neutron diffraction fitted profile results determined that

there were approximately 16 atoms of deuterium present in the compound

and these atoms filled the f tetrahedral site and 2/3 of the trigonal i

sites. The atomic positions are shown on a two-dimensional projection

along the z axis of 1/4 the unit cell in figure 1- Figure 2 shows the

neutron diffraction pattern and profile fit from the first two of the

five detectors (Bragg angle range 10-55 ) . The x value (weighted Rprofile/R-expected) for the full spectrum from 10 to 115 for Th,Mn

2

„

88
RRD COLLABORATIVE PROGRAMS

at room temperature is 1.58. Ideal structural models have generally

been found to refine to x' s £. 2. This profile fit of the calculated

model (smooth line) with the data (points) can be seen in figure 2.

This study has shown that the deuterium atoms in Th,Mn9 _D.., occupy

only the tetrahedral f site and trigonal i site. In contrast, Commandre

2 et. al. have found in Y,Mnn „D that deuterium atoms preferentially

6 23 x occupy both the octahedral a site and tetrahedral f and j sites.

0.5-i

0.4-

0.3-

g

0.2-

>

0.1-

0-

T 1 1

1 01 0.2 0.3 0.4 0.5

x (lattice units)

A Th <7) Mn

Q Mn (§) Mn

® Mn

€ Dj

Figure 1. Two dimensional projection of atom positions along the

z[001] axis in 1/4 of the unit cell of Thg Mn.23 T)^. The

z[001] coordinate is given for each site. The positions of

all atoms are those obtained from the profile refinement fit

89
RRD COLLABORATIVE PROGRAMS

6000r

4500-

I 3000

1500-

295K

_JLJ ill Hi^LIMM I Amw/wJL

20 25 30 35 40 45 50 55

Angle (2 S

)

Figure 2. Experimental neutron scattering profile obtained from the

first two detectors of the five detector NBS powder diffractometer. The solid line is the calculated model using the

parameters in Table I.

1. S. K. Malik, T. Takeshita, and W. E. Wallace, Solid State Comm. 23,

599 (1977).

2. M. Commandre, D. Fruchart, A. Rouault, D. Sauvage, C. B. Shoemaker, and

D. P. Shoemaker, J. de Physique 40, L-639 (1979).

90
RRD COLLABORATIVE PROGRAMS

PREFERENTIAL ORDERING OF MN AND FE ATOMS IN Y

6

(Fe-|_ xMn

x

) 23

K . Hardman

and

W. J. James

(Department of Chemistry and Graduate Center for Materials

Research, University of Missouri-Rolla, MO)

The crystal structure of Y,(Fe1 _ Mn )„„ compounds is face-centered

cubic (Fm3m) , isotypical with Th,Mn_ . There are four nonequivalent

lattice sites occupied by Mn and/or Fe atoms, and one lattice site

occupied by Y atoms. The intermediate compositions are particularly

interesting in that the magnetizations and Curie temperatures are drastically reduced from those of the end members, Y,Mn„„ and Y,Fe„~.

o A5 6 Z3

In particular, there is no long-range magnetic ordering in the compositional

region, x = 0.5 to 0.75. Although Fe-Mn interactions are expected to

be antiferromagnetic and may compete with the ferromagnetic Fe-Fe, this

does not account for the assumed paramagnetism of Y,(Fe. Mn ) 9

„ system

in the above compositional range. In many compounds, the long-range

magnetic ordering of the Fe and Mn moments is dependent on the local

chemical environment of these atoms. Previous studies (e.g. see reference

2) have assumed Mn and Fe atoms to be distributed stoichiometrically on

each crystallographic site. However, atomic ordering in this system can strongly affect the local environment of the Mn and Fe and lead to

significant changes in magnetic orders.

Neutron diffraction studies offer the most straight-forward approach

in determining possible atomic ordering. The nuclear scattering data

indicate very readily the degree of preferred ordering on nonequivalent

crystallographic sites in that the nuclear scattering lengths of Mn and

-12

Fe differ in both sign and magnitude, h, = -0.37 and b_ = 0.95 x 10 b b Mn Fe

cm. The data were analyzed with the NBS version of the Rietveld profile

method. In the refinement of the data, a constraint was imposed such

that the sum of the' Fe and Mn atoms would produce full occupancy at each

transition metal site. This allowed a refined stoichiometry of the

ternary to be determined.

91
RRD COLLABORATIVE PROGRAMS

Neutron diffraction data for several ternaries were collected to

determine if prefertial atomic ordering effects existed for the entire

Y,(Fe1 Mn ) 9

» system. The figure shows the degree of ordering as the %

departure of Mn concentration from stoichiometry versus the overall Mn

concentration. The most striking result is the preference of Fe atoms

for the f, site and the preference of Mn atoms for the f~ site. The Mn

atoms exhibit a preference for the b site, especially if the f„ site is

occupied with a majority of Mn atoms. The d site appears to be stoichiometrically occupied in the Mn-rich ternary compounds but shows a preference

for Fe atoms in the Fe-rich compounds. Since the b site contributes

only 1 atom/f.u. and little ordering occurs on the d site, the atomic

ordering of the ternary system is largely dependent on the two f sites.

The greatest degree of atomic ordering occurs in the compositional range

where the compounds are paramagnetic.

£• 30

**o

Eo 20 £

O

o 10

Eo1_c§

o -10

0)

k_3*•> -20

COa

0) Q

- Y

6 (Fe 1x Mn x '23

* r^ j )

-

1 I 1 "

Figure 1.

-30 —

20 40 60 80 100

X-Mn Concentration (%)

The % departure of Mn for stoichiometry vs. the overall Mn

concentration. The positive % departure values represent Mn

rich sites and the negative % departure values represent Fe

rich sites.

1. H. R. Kirchmayr and W. Steiner, J. Phys. Suppl. 32., Cl-665 (1971).

2. G. Hilscher and H. Rais, J. Phys. F: Metal Phys. 8, 511 (1978).

92
RRD COLLABORATIVE PROGRAMS

STUDIES OF ELECTRON DENSITY IN CARBONATE MINERALS

E. Prince

and

R. Peterson and G. V. Gibbs

(Virginia Polytechnic Institute and State University, Blacksburg, VA)

As part of studies of electron density distribution in carbonate

minerals, neutron diffraction data sets have been collected from single

crystals of two forms of CaC0„, calcite and aragonite, and from a crystal

of magnesite, which is isomorphous with calcite, but with magnesium

substituted for calcium. Crystal data for these crystals are given in

table 1. Data were collected from two different crystals of calcite.

With the exception of 00& reflections all reflections were observed in

at least two symmetry equivalent positions, and most reflections were

observed three times. The internal R factors between equivalent reflections were 3.1% and 2.5% for the larger and smaller crystal, respectively.

Least squares refinement of structure and thermal parameters showed the

effects of extreme secondary extinction, with more than 20% of reflections

having correction factors (F /F ) less than 0.3. The extinction parac c meter is strongly correlated with thermal parameters, and the anisotropic

temperature factor tensors were non-positive definite, an unsatisfactory

situation. Similar results were obtained from the crystal of magnesite.

It may be possible to refine these structures by omitting the most

severely extinguished reflections, or to determine reliable structure

parameters from powder data. Otherwise electron density studies in these

crystals will be extremely difficult.

For aragonite, an orthorhombic crystal, data were collected from

three octants of the reciprocal lattic , and, again excepting OOjt

reflections, all reflections were observed at least twice, and most were

observed three times. The agreement factor for equivalent reflections

was 1.6%. The structure refined to a weighted agreement index of

R = 3.9%, and there was no evidence of important correlations between

extinction and thermal parameters. Table 2 is a summary

93
RRD COLLABORATIVE PROGRAMS

Table 1. Crystallographic data for carbonate minerals.

Calcite Aragonite Magnesite

CaCO. CaC0

3 MgC03

R3C Pmcn R3C

4.989 A 4.9598 A 4.637 A

Composition

Space group

Cell constants a

b

c 17.07 A

4.9598 A

7.9641 A

5.7379 A

Reflections (X= 1.273A, 26max = 120°)

observed 102 314

unobserved 9 15

15.023 A

87

Figure 1. View of the carbonate group in aragonite, showing bond

lengths and thermal ellipsoids.

of the structure parameters. As may be seen in figure 1, the shortest

principal axes of the thermal ellipsoids of the two independent oxygen

atoms are nearly parallel to the C-0 bonds, as they should be.

94
RRD COLLABORATIVE PROGRAMS

4-> /—

s

•~\ /—

\

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CU s_^ v^ •*^s w •H CO O O <t CO O CN O O O O •H ca O O O O <4-l 4-1 • • • • CU 1 O /~\ O rH

QJ co O O O sr

£1 rH O O O +J ca O O O

CO • • • • CO 1

(3 *~\

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60 co rH O O O rH

CM ca O O O O

CD GO. O O O O

U CN • • • •

ctf 1 +

CO

t-l rH /""

\

/—

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/-\ ss

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4-1 CO v—

/

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H ,C

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s—

^^

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O O

CN • • • • • H

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O %_• N—' >—

/

v-^ 60 + rH r^. CN -3- CM

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r4CM ca O O O cO ^ O O

CM • • • • U CN O oa m /-N /—

N

s—\ /""N + CM rH CN rH

CO ^/ v_^ \s v_^

J-ICM -d- CT> m r*.

Q) ^3 N cr> <• sr CM

+J rH m rH rH

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• •

• CU CN 4-1 CU

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rH CO CO rH CM

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95
RRD COLLABORATIVE PROGRAMS

NEUTRON POWDER DIFFRACTION STUDY OF THE STRUCTURE OF Li

2

Re0

3

R. J. Cava

(Bell Laboratories, Murray Hill, NJ)

and

A. Santoro

and

R. S. Roth

Ceramics, Glass, and Solid State Science Division

In a confirming study of, ionic conductors containing Li , the structure

of Li„ReO„ has been studied with the neutron powder technique.

Neutron diffraction measurements were made at room temperature with

the five-counter high resolution neutron dif fractometer at the NBSR, using

the experimental conditions given in table 1.

The structure was refined with the Rietveld method (1969) modified

by Prince (1979) to process simultaneously the five sets of data obtained

from the five channels of the multiple detector dif fractometer . The initial

model of the structure was refined in space group R3c with six molecular

units Li ? ReO„ per unit cell and with the Re atoms located in positions 6(b),

the Li atoms in positions 12(c), and the atoms in positions 18(e) . In

this refinement (as well as in those that follow) , the structural parameters

were refined together with the lattice and profile parameters, and with ten

additional parameters, two for each channel, defining linear backgrounds.

Isotropic temperature factors for each atoms were kept fixed in these calculations, but an overall temperature factor was allowed to vary. The R

factors obtained in this refinement are given in table 2. The value of R.. is unreasonably high (18.97%). This fact, together with a resulting overall

temperature factor Q = -1.17 A may indicate that the symmetry assigned to

the structure is not correct. A refinement in space group R3c was therefore

carried out with the Re, Lil, and Li2 atoms in positions 6(a) and the atoms

in positions 18(b). The R factors obtained from these calculations (also

reported in table 2) indicate that the structure is probably acentric, but

* Hexagonal axes have been used throughout these refinements,

96
RRD COLLABORATIVE PROGRAMS

Table 1. Experimental conditions used to collect the powder intensity

data for Li ReO .

Monochromatic beam: reflection 220 of a Cu monochromator

Wavelength: 1.5416(3) A*

Horizontal divergences: (a) in-pile collimator: 10' arc;

(b) monochromatic beam collimator: 20' arc;

(c) diffracted beam collimator: 10' arc

Monochromator mosaic spread: 'v. 15' arc

Sample container: vanadium can ^ 10 mm in diameter

Angular ranges scanned by each detector: 15-40, 35-60, 55-80,

75-100, 95-120

Angular step: 0.05°

Number of independent Bragg reflections: 65

still the value of R is too high (16.7%) and the value of Q too low

(-1.14 A"). At this point a close examination of some single peaks in

the powder pattern showed that the peak shape can be described better

with a modified Lorentzian than with a Gaussian (see Santoro and Prince,

this report) . The refinement program was therefore modified so that the

Pearson type VII distribution could be used and calculations were carried

out with m = 2 (modified Lorentzian)*. No improvement, however, was obtained with this method. This is an indication that other factors, such

as the presence of impurities in the sample, affect the observed intensities.

A final refinement was then carried out by excluding from the calculations

a number of regions of the powder pattern, especially in correspondence

of the tails on both sides of each identifiable peak. The R factors obtained

-

For a description of the Pearson distribution see Santoro and Prince,

this report.

97
RRD COLLABORATIVE PROGRAMS

Table 2. R-factors obtained in the refinements of the structure of Li ReO

Space Group R,. R_ R^ R X

R3c No regions excluded 18.97 10.61 13.53 7.71 1.75

R3c No regions excluded 16.70 10.05 12.77 7.71 1.66

R3c Pearson function with m=2 16.71 10.01 12.71 7.71 1.65

R3c Regions excluded 15.06 9.52 11.93 7.55 1.58

. 7U(ob.) - i(c«i) | I 2,I(obs)

R^ = 100 x y|Y(obs) - Y(cal)|

lY(obs)

Ry = 100 x ( )>[Y(obs) - Y(cal)J

_

)

( JWY

2 (obs) ) + C) ) R

E

= 100x \SS^1

(j;wY

2 (ob

2U/2

1/2

N, P, and C are the number of observations, the number of refined parameters,

and the number of constraints, respectively.

in this last refinement are better than these calculated previously (Table 2)

,

but the values of Rj. and Q (15.06% and -1.12, respectively) are still

unreasonable. The structural parameters obtained in this calculation are given in table 3.

A preliminary analysis of the structure shows that all parameters,

with the exception of the overall temperature factor, have no unusual or suspicious features. We must conclude, therefore, that the structure

determined in this study is basically correct. It may Well be, however,

that the symmetry is even lower than R3c and that structural distortions

and/or impurities in the sample affect significantly the experimental

intensities. The non-Gaussian peak shape of the diffraction lines is certainly

an indication that the physical conditions of the sample do require an

98
RRD COLLABORATIVE PROGRAMS

analysis more detailed than the one made up to this point. As a knowledge

of the accurate structure of the compound is important in the understanding

of its electric properties, work in this direction is still being done at

the present time.

Table 3. Results of the profile refinement of the structure of Li

? ReO„

Atom Position

in R3c

Re 6(a)

18(b)

Lil 6(a)

Li2 6(a)

n

0.3572(12) 0.0134(12)

Numbers in parentheses are standard deviations on the last decimal figures,

0.0127(9) 0.4 1/3

0.2484(9) 0.6 1.0

0.2009(18) 1.0 0.29(3)

0.8485(24) 1.0 0.29(2)

1. H. M. Rietveld, J. Appl. Cvyst., 2, 65-71 (1969)

2. E. Prince, NBS Technical Note 117, 8-9 (1979).

99
RRD COLLABORATIVE PROGRAMS

POWDER NEUTRON DIFFRACTION STUDY

OF CHEMICALLY PREPARED 3~Pb0

2

Peter D' Antonio

(Naval Research Laboratory, Washington, DC)

and

A. Santoro

B-PbO~ is the major constituent of the lead-acid battery. A

detailed knowledge of its structure is essential in correlating electrochemical activity with the atomic arrangement of the electrode constitutents of the battery. Such knowledge is also important in understanding

the nature of the chemical bonds in compounds with rutile-type structures (Baur, 1956; 1958; 1961; Baur and Khan, 1971). Structural studies

of 3-PbO- have been carried out by x-ray (Tolkacev, 1958) and neutron

powder diffraction techniques (Leciejewicz and Padlo, 1962, indicated by

LP in what follows) . The oxygen positions in the structure could not be

determined with any precision in the x-ray work. On the other hand, in

the neutron diffraction experiment only data up to sin9/X =0.3 were

used, and the structure was only partially refined because no temperature factors were introduced in the calculations. More importantly, in

this study the value of the> positional parameter of the oxygen atoms was obtained with such a large standard deviation that it is impossible to

establish if the PbO, octahedra are compressed or elongated along their

b

axial direction (Baur and Kahn, 1971). As the distortions of octahedra

in rutile-type AB„ oxydes are of theoretical interest, we thought it

worthwhile to refine the structure of 3-PbO» with the Rietveld method

(Rietveld, 1969).

The sample used to collect the neutron diffraction data was chemically prepared, Baker reagent grade, 3-PbO , lot #4604. The

measurements were made at room temperature with a five detector diffractometer at the National Bureau of Standards Reactor (Prince and Santoro,

1980) , using the experimental conditions summarized in table 1.

100
RRD COLLABORATIVE PROGRAMS

The powder pattern of 3-PbO consists of isolated peaks as well as resolved and unresolved clusters. The distribution of the reflections

is such that the angular interval scanned by each detector contains a sufficient number of points free from diffraction lines to permit a reliable evaluation of the background contribution to the observed

intensities at all the 26 diffraction angles. Some of the diffracted

lines were slightly asymmetric near the gaussian tails. This may be

caused by impurities in the sample or by crystallite size effects. In

any event, the regions affected were excluded from all subsequent

calculations.

The structure was refined with the Rietveld method (Rietveld,

1969) modified to simultaneously process the data from the five channels

of the multiple detector dif fractometer. The neutron scattering amplitudes were b(Pb) =0.94 and b(0) = 0.58 x 10 cm. The initial values

of the lattice parameters and of the positional parameter x of the

oxygen atoms were those obtained by LP (1962) and the initial profile

parameters U, V, and W were calculated theoretically (Caglioti, Paoletti,

and Ricci, 1958). The anisotropic temperature factors of the Pb and

atoms were refined together with the other parameters. Their introduction in the calculations is justified because the data were measured

to a sufficiently high sin0 /A and because the background intensity was reliably determined. The initial values of these parameters were set

equal to those of comparable oxides (e.g. Baur and Khan, 1971). All

parameters were allowed to vary simultaneously until the shifts were

less than 0.3 times the standard deviation. The results of the refinement are given in table 2 and the observed and calculated profiles are shown in figure 1.

The lattice parameters obtained in the refinement agree closely

with those measured by LP with a back reflection camera and with those

determined by Naidu (as quoted by Baur and Khan, 1971). The small

systematic deviations are probably due to the uncertainty with which the

101
RRD COLLABORATIVE PROGRAMS

i:

^JV\J\JJU^_Jvj\

1200-

I0SO

160

Figure 1. Observed (dots) and calculated (continuous line) profiles for

3-Pb09. Each section of the figure is recorded with a different detector of the five-detector diffractometer with

an overlapping of the patterns of 5° in 20.

102
RRD COLLABORATIVE PROGRAMS

Figure 2. Three-dimensional view of the structure of B-PbO-. The atoms are represented by their thermal ellipsoids. The labeling of

the atoms is the same as that used in Table 3.

Figure 3. Projection of the structure of B-PbO on the plane (001).

Atoms are joined to show the packing of the PbO, octahedra.

103
RRD COLLABORATIVE PROGRAMS

OCM • H

CM 1 O ir> 43 CjS PMI •> CQ O

«no t-4.l e

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104
RRD COLLABORATIVE PROGRAMS

Table 2. Results of the refinement of the structure of |3-PbO .

This work

(*)

(++)

Naidu

LP (1962)

Tolkacev (1958) 4.946

c/a x (***)

m

4.9578(2) 3.3878(2) 0.68333(5) 0.3067(2) 0.30835

4.9568(5) 3.3866(2) 0.68322(8)

4.955 (3) 3.383 (2) 0.6827 (7) 0.309 (4) 0.3083

3.379 0.6832 0.308 0.3083

Atom

Pb

Position ^n=e

22

2a

4f

B. 3. 33 "12

55(4) 50(1) 3(6)

97(5) 80(2) -50(7)

; 13=e23

x 10 4(+)

Profile parameters: U = 0.50(2), V = -0.36(3), W = 0.210(8) (deg )

R = 4.71%, R = 12.28%, R = 14.44%, R . = 6.05%, X = 2.4 ( ** ) p w expected

(+ (ks quoted by Baur and Khan (1971)

The thermal parameters are of the form

(**),

exp[-(h2 3

i;L k

2 3 22 + £2

3 33

+ 2hk3

12 + 2h£3

13 + 2k£3

23 )]

The R-factors are defined in several publications (e.g., Rietveld, 1969)

(***) c

2 .1

m

8a

j + t", with c and a measured by Naidu.

(++) The cell dimension errors obtained in the neutron refinement do not

include the error in the neutron wavelength.

105
RRD COLLABORATIVE PROGRAMS

Table 3. Principal distances and angles in the octahedral

coordination sphere of 3-PbO,..

This work LP (1962)

Pb-0(3,4,5,6) ( *

) = (Pb-0)

1 2.1689(7)

^

2.157(12) A

Pb-0(1,2) = (Pb-0)

2 2.1500(11) 2.165(20)

0(3)-0(4)

0(5)-0(6)

0(l)-0(3,4,5,6)

0(2)-0(3,4,5,6)

0(3)-0(6)

0(4)-0(5)

0(3)-Pb-0(4)

0(5)-Pb-0(6)

2.7107(22) 2.677(40)

3.0542(5) 3.056(8)

3.38668(2) 3.383(2)

77.35(5)° 76.7(8)

(*) \^.The labeling of the atoms is given in Figure 2.

These distances were calculated by using x=0.3067(2) ~.nd the

lattice parameters measured by Naidu (Baur and Khan, 1971). o The distance (Pb-0) corresponding to x of Table II is 2.1615 A.

m m

106
RRD COLLABORATIVE PROGRAMS

neutron wavelength is known (table 2) and therefore Naldu's parameters

are used in all subsequent calculations. The values of the profile

parameters U, V, and W are in agreement with those observed for other

compounds analyzed with the same experimental conditions (e.g., Santoro,

Roth, and Minor, 1979). The anisotropic thermal factors are of the same order of those reported for similar compounds (Baur and Khan, 1971).

From figure 2 it can be seen that the major vibrational motion of the

oxygen atoms is perpendicular to the planes {110}, in agreement with the

results of Baur and Khan (1971) for rutile-type SiO„ and for GeO~.

The structure of 3-PbO~ is shown in figure 2 with the atoms represented by their thermal ellipsoids. The six oxygen atoms surrounding

the lead atoms form slightly distorted octahedra. In figure 3 the

oxygen atoms are connected to show the packing sequence of the octahedra. The structure consists of vertical columns of edge sharing PbO,

octahedra. These columns are oriented along the [001] direction and

form sequences of corner sharing octahedra along the <110> directions,

with the octahedra alternately rotated by 90° about [001],

The principal interatomic distances and angles in the PbO, octahedron are compared with the results of LP in table 3 (the values

reported in column 3 of the table have been recalculated to facilitate

comparison and to correct some errors in the results of LP) . The four

equatorial bonds (Pb-0)

1 lie in the planes {110} and the two axial bonds

(Pb-0)„ are normal to these planes.

According to our results, and contrary to those of LP, (Pb-0).. > (Pb-0)„, i.e., the octahedron of the oxygen atoms surrounding the lead

atom is slightly compressed along the axial direction. This result,

however, is significant only if the value of the standard deviation a associated with the positional parameter x can be considered reliable.

In a recent analysis of the profile fitting procedure, Sakata and Cooper

(1978) have concluded that the Rietveld method weights the observations

incorrectly and that the estimated standard deviations are smaller by a

107
RRD COLLABORATIVE PROGRAMS

factor of at least 2 than those given by a refinement based on integrated intensities. On the other hand, Prince (1980) has pointed out

that the high precision of the Rietveld method is a consequence of the

fact that each peak is assumed to be Gaussian, so that each data point

within the peak becomes an independent measurement of the intensity.

This results in a more precise estimate of the diffracted intensity. In

agreement with Prince's conclusions, it has been shown in a number of cases (e.g. Andresen, Hewat, and Sabine, 1978; Cheetham and Taylor,

1977) that the Rietveld method gives quite realistic standard deviations

associated with the atomic coordinates. The high precision of the

Rietveld method translates into high accuracy only if the model is

adequate, i.e., free of hidden factors such as unrecognized structural

distortions, non-gaussian peak shape, etc. No problems of this kind are apparent in our experiment. All the parameters calculated in the

refinement are quite reasonable, including the thermal and profile

parameters which are very sensitive to errors in the adopted structural

model and to the physical conditions of the sample used to collect the

data. Finally, the correlation coefficients involving x and the other

refined quantities are low, the largest of them being only 10%.

To remove any doubts, a second evaluation of the positional

parameter was obtained by carrying out a refinement based on integrated

intensities. These were obtained by fitting least-squares gaussians to

27 single or separable reflections. This refinement gave x = 0.3066(6)

with an R-factor, based on structure factors, of 2.0% (the R factor

2 based on F was 3.6%). As expected, the standard deviation cr is larger

than that obtained with the Rietveld method (the same is true for the

standard deviations associated with the thermal parameters) . Even in

this case, however, the difference between the value of x obtained in

the refinement and that reported by LP can be considered significant.

Thus, the point representing 3-PbO~ in the plot of x versus c/a shown in

figure 2 of Baur and Khan's paper (1971) is located below the line

108
RRD COLLABORATIVE PROGRAMS

corresponding to the conditions for undistorted octahedra in the structure. It follows that $-PbO„ is in the same category with the fluorides

of Mg, Mn Fe, Co, and Zn and the oxides of Cr, Ru, and Os. A conclusion

of this study is that 3-PbO~ is closer to the Born model, and its

bonding has more ionic character, than previous structural investigations implied.

1. A. F. Andresen, A. W. Hewat, and T. M. Sabine, Conference on Diffraction Profile Analysis, Abstracts, Cracow, Poland (1978).

2. W. H. Baur, Acta Cryst. 9, 515-520 (1956).

3. W. H. Baur, Acta Cryst. 11, 488-490 (1958).

4. W. H. Baur, Acta Cryst. 14, 209-213 (1961).

5. W. H. Baur and A. A. Khan, Acta Cryst. B27 , 2133-2139 (1971).

6. W. R. Busing, K. 0. Martin, and H. A. Levy, ORFLS , Report ORNL-TM305, Oak Ridge National Laboratory, Oak Ridge, Tennessee (1963).

7. G. Caglioti, A. Paoletti, and F. P. Ricci, Nuol. Instrwn. 3, 223-

228 (1958).

8. A. K. Cheetham and J. C. Taylor, J. Sol. State Chem. 21, 253-275

(1977).

9. J. Leciejewicz and I. Padlo, Naturwissensehaften 16_, 373-374

(1962).

10. E. Prince, J. Appl. Cryst., submitted for publication (1980).

11. E. Prince and A. Santoro, NBS Technical Note 1117, Editor F. J.

Shorten, 11-12 (1980).

12. H. M. Rietveld, J. Appl. Cryst. 2 65-71 (1969).

13. M. Sakata and M. J. Cooper, Report HL78/2359 AERE Harwell, U.K.

(1978).

14. A. Santoro, R. S. Roth, and D. Minor Acta Cryst. B3_5, 1202-1205

(1979).

15. J. C. Taylor and P. W. Wilson Acta Cryst. B30 , 554-555 (1974).

16. A. Tolkacev, Vestnik Leningradskogo Univ. No. 4, 152 (1958).

109
RRD COLLABORATIVE PROGRAMS

FURTHER WORK ON GEOMETRICAL AMBIGUITIES

IN THE INDEXING OF POWDER PATTERNS

A. Santoro

and

A. D. Mighell

(Ceramics, Glass, and Solid State Science Division)

By definition, two or more different lattices give a "geometrical

ambiguity" when they generate powder patterns having the identical

number of distinct diffraction lines with identical values of (sin0)/X,

but not necessarily with identical multiplicity. For example, it is

easy to prove that a body centered cubic lattice of conventional unit

cell vectors a. (1=1, 2, 3) and the tetragonal P lattice obtained with

the transformation

£. = E. B. . a. (J = 1, 2, 3) (1)

in which

-1/2 1/2'

$

=

[ kl/2

(2)

satisfy the above definition of geometrical ambiguity. It follows that

the powder pattern consistent with one lattice can be indexed equally

well in terms of the other (in this particular case, the lattices con- sistent with the same powder pattern are four, the other two being

orthorhombic F and orthorhombic P).

Geometrical ambiguities have been studied by Mighell and Santoro

(1975) with the following procedure.

Let us consider a reciprocal lattice A described by the translatxons a.. The reciprocal lattice vectors of A are given by

ru = E . h . a

.

h l x x

(3)

110
RRD COLLABORATIVE PROGRAMS

with

h

± = . . . -1, 0, 1, . . . (4)

If we perform the transformation

* % -1

« = Q) ] (5)

we generate a new lattice T described by the translations (primitive)

b.. The reciprocal lattice vectors of T are given by

->•* * -V* b. = £ . B. . a.

i J 1J 3

r.kill = S. k. b. (6)

with

k. = . . . -1, 0, 1, . . . (7)

The vectors r can be expressed in terms of the base a. by making use of

equation (5)

r. - Z. A. a. (8) k J J J

where

£. = S. k. B. . (9)

J i i ij

The lattices A and F will give a geometrical ambiguity if, for each

vector r, in A there is a vector r. in V such that

h k

1 h1

' k

1

and vice-versa.

The method used by Mighell and Santoro (1975) to verify equation 10

consists in proving if two quadratic forms represent the same set of

numbers. For the example represented by equations (1) and (2) we have

*2 / 2 2 2 *2 , rh

Z = (h£ + h* + hp a (11)

111
RRD COLLABORATIVE PROGRAMS

2 2 2 where h.. + h~ + h = 2n (body centered lattice) , and

*2 2 2 2 *2

r^ = 2(2k^ + k^ + kp a (12)

It can be proven, with standard methods of number theory, that

2 2 2 2 2 2

h

1 + h~ + h„ = 2n and 2 (2k + k„ + k„) represent the same set of numbers

when the triplets h. and k. are cycled over all the permissible integers. Therefore, the two lattices A and T do indeed give a geometrical ambiguity.

A significant disadvantage of this approach is that it cannot be

generalized to the point where conditions for the occurrence of ambiguities can be established. In particular, the method does not allow one

to understand in a direct way the critical role played by the symmetry

in searching for such conditions, and consequently, it does not make it

possible to devise a systematic procedure for finding all the geometrical ambiguities which may occur in frequently encountered lattices.

Therefore, we have analyzed the problem with a new procedure, simpler

and more general than the one used previously (Mighell and Santoro,

1975).

Let us consider the transformation

b. = E. B. . a. (13)

i J ij J

and let x and x' be triplets of real numbers and h and h' triplets of

integers. We have

%' - 8 fe

< 14 >

and

-3-* ->* a. = E. B.. b. (15)

k -k A reciprocal vector is expressed in A and r by the equations

•>* •** -** •- ^

r = E.illh. a. = Z.ijjiji S. h. B.. b. (16)

112
RRD COLLABORATIVE PROGRAMS

Since the h. are integers, r is a reciprocal lattice vector in A . It 1

* will be a reciprocal lattice vector also in V if, and only if, #h!.-.Z. h. B.. (17) i J 3 iJ

i.e., if the numbers Z. h. B.. are also integers. If these numbers are

not integers, then r is a reciprocal lattice vector in A but not in

*

r . If we write the transformations

and _-

*u <G A>

(18)

we may say that a peak h in the powder pattern of A will be coincident

(i.e. having the identical value of sin9/X) with a peak in the powder

pattern of T if the numbers x' are integers. And, conversely, a peak

h' of T will be coincident with a peak of A if the numbers x are

integers.

This type of solutions will certainly exist if the elements B.. of

matrix B are rational numbers, i.e., if A and T are derivative

lattices. Three cases are possible: (1) some peaks of the pattern of

lattice A are coincident with some peaks in the pattern of V and viceversa; (2) all the peaks of A are coincident with peaks of T, but the converse is not true; (3) all the peaks of A are coincident with peaks

of r and vice-versa. The necessary and sufficient conditions for

This is a sufficient, not a necessary condition. The necessary

condition for the occurrence of coincidences is that at least a column

of matrix H B must be rational. Matrix £ is unimodular with H.

.

integers. Its use here is necessary to deal with cases such as

[(R + 2) ( 2) I/RRI/RRI] which can be readily transformed into

[R( 2)I/RRI/RRI] . In the above matrices R and I indicate a rational and

an irrational number, respectively.

113
RRD COLLABORATIVE PROGRAMS

case (1) to occur have been found previously. Cases (2) and (3) can be

understood by discussing a specific example. Consider the transformation matrix A to T

(19)

Tranformations (18) are:

x'. - h x = h*

y' = k y = k' (20)

z' = (-k + JD/3 z = k

1 + 3£'

The triplets x are always integers, that is, all the diffraction

lines in the pattern of Y are also present in the pattern of A. The

converse, however, is not true. For example if h = (101), then x' =

(10 1/3). If, however, A is cubic primitive, each line of general

indices in the pattern of A is the superposition of 48 reflections, the

indices of each of them being obtained by permutation of place and sign

of the three integers h, k, and I. Under these conditions, it can be

proven that, if a reflection h does not give integral solutions for x',

there is at least one reflection h , metrically equivalent to h, which

does and, as a result, each line in the pattern of A will have a coinciding line in the pattern of T. Clearly, the multiplicity is different

in the two cases. Returning to our example, the reflection h = (101)

does not give integral solutions for x' , but h = (Oil), which is

metrically equivalent to h in the cubic system, does, and therefore, the

reflection 010 of r will occur exactly at the same sin0/X of the reflections 101 and 011 of the cubic lattice A.

The case represented by matrix (19) was not recognized in the

previous study of geometrical ambiguities (Mighell and Santoro, 1975).

On the basis of this example we may state that:

114
RRD COLLABORATIVE PROGRAMS

"The necessary and sufficient condition that lattices A and T must

satisfy to give a geometrical ambiguity is that every reciprocal lattice

vector of one of the two lattices must be either a reciprocal lattice

vector or be metrically equivalent to a reciprocal lattice vector of the

other lattice."

What this means in practice is that the metric symmetry of the two

lattices must be such that a group of equivalent reciprocal lattice

vectors in a lattice has at least one representative which also belongs

to the other lattice.

The previous discussion shows that symmetry plays a vital role in

the occurrence of geometrical ambiguities. In fact, it can be shown

that ambiguities exist only if one of the two lattices is cubic, hexa2

gonal, rhombohedral , or tetragonal.

A straightforward method to discover all the cases of geometrical

ambiguities consists in generating all the unique B matrices with

"simple" rational elements B. . and in transforming with them the high

symmetry lattices. Each transformation can then be analyzed very much

in the same way used to analyze the example discussed previously.

Programs for doing these calculations are now being developed, and the

results will be given in the next report.

2This statement requires a clarification. Geometrical ambiguities

also occur for lattices of low symmetry. This can be seen in Table 1 of

the paper by Mighell and Santoro (1975) (for example, the orthorhombic

lattices F and P of case (2)). In these instances, however, the ratios

->-> -*- -> of the scalar products a. • a. (and those of b. • b.) are rational

i J i J numbers, i.e., these lattices have derivative lattices of higher symmetry. It can be proven that the treatment of cubic, hexagonal,

rhombohedral, and tetragonal lattices also includes these cases.

1. A. D. Mighell and A. Santoro, J. Appl. Cryst. 8, 372-374 (1975)

115
RRD COLLABORATIVE PROGRAMS

SMALL-ANGLE NEUTRON SCATTERING STUDY OF A

TWO-PHASE TUNGSTEN ALLOY

H. J. Prask and C. S. Choi

(Energetic Materials Division, LCWSL, ARRADCOM, Dover, NJ)

and

(National Bureau of Standards, Washington, DC)

and

S. Singhal

(National Bureau of Standards, Washington, DC)

and

(State University of New York at Stoney Brook, NY)

One of the principal types of anti-tank munitions employed by the

Army incorporates a tungsten-alloy "kinetic-energy" penetrator. The

penetrators which are prepared by means of isostatic pressing, sintering,

heat treatment and cold working—are comprised of a "tungsten" phase

and a "matrix" phase. Improvement in the performance of these munitions

is sought by varying the composition, heat treatment, or degree of

cold work. A previous neutron diffraction study showed the variations

in texture of the matrix phase as a function of degree of cold work in

.97W-.018Ni-.012Fe by weight alloy. In this composition alloy, the

matrix phase is virtually invisible to x-ray diffraction.

Another aspect of interest for these samples is the hardening

which is observed when a second heat treatment is given the alloy after

swaging. For a nominal .90W-.07Ni-.03Fe alloy ("tungsten" phase: ^ .998W-0.0005Ni-0.0015Fe; matrix phase: ^ .22W-.55Ni-.23Fe by weight)

yield strength and hardness are each found to increase by approximately

20% after heat treatment. Preliminary SANS measurements have been made

on three .90/. 07/. 03 samples. All three samples were sintered and heat

treated (20 hrs . at 1000°C) ; two of the samples were swaged (24% R.A.)

and one of these was further heat treated (5 hrs at 500 C)

.

In the SANS configuration employed the useable momentum-transfer

range was Q>0. 01A . For all three samples the data were found to

116
RRD COLLABORATIVE PROGRAMS

4

correspond very well to Porod distributions (i.e. I(Q) = k/Q ).

A Porod distribution is expected for scatterers with well-defined

boundaries and radii of gyration fulfilling the condition RgQ > 1.

This indicates that Rg > 110A for the scatterers in all three samples.

In addition it was found that the scattered intensity, which is proportional to the product of (number of scatterers X surface area per

scatterer) is in the ratio 1/1.79+0.02/1.95+0.02 for the unswaged,

swaged, and swaged with second heat treatment samples, respectively.

Further SANS and wide-angle neutron diffraction measurements are planned to better understand the differences observed in the results

for the three samples. Specifically, quantitative results characterizing

the nature of the scatterers (i.e. precipitate or void) and size and

concentration are needed to understand the hardening process.

1. C. S. Choi and H. J. Prask, NBS Tech. Note 1117, 139-42 (1980).

117
RRD COLLABORATIVE PROGRAMS

SMALL-ANGLE NEUTRON SCATTERING STUDY OF THE MICROSTRUCTURAL

DEVELOPMENT DURING PRECIPITATION STRENGTHENING OF NI BASED SUPERALLOYS

S. P. Singhal

(State University of New York, Stony Brook, NY)

and

(National Bureau of Standards, Washington, DC)

and

H. A. Alperin

(Naval Surface Weapons Center, White Oak, MD)

and

(National Bureau of Standards, Washington, DC)

and

H . Herman

(State University of New York, Stony Brook, NY)

and

F. Biancanello

In present day aerospace technology, the Ni based superalloys form

the basis of aircraft engine turbine blade materials, which are used

under most aggressive conditions of the temperature, stress, and chemical

environment. In order to achieve microstructures which can retain a respectable stability of properties, the superalloys not only contain

several alloying additions, but also undergo a complex series of thermal

treatments. A considerable degree of "commercial" success has been

achieved in production and usage of these alloys; although the "precise"

mechanism of formation, growth, and degradation of microstructural

properties remains relatively understood.

At the NBS reactor we have begun a program to study the kinetics

of precipitation strengthening and subsequent microstructural changes

during the creep and high temperature fatigue deformation of these

alloys.* In Ni based superalloys, the major strengthening constituent

*Some recent studies have indicated that creep deformation in these alloys

is synchronons with the coarsening of y

r

. Therefore, creep behavior of these

alloys is highly dependent on the stability of y' under ambient temperature

and stress conditions.

118
RRD COLLABORATIVE PROGRAMS

is gamma prime (y'). The "precise" composition of y

1 varies during the

different stages of heat treatment but in general it can be given as Ni,, s [Al + Ml where M could be the elements like Ti, Ta, and Nb etc.

(4-x) J x A high volume fraction and fine dispersion of y' are needed to enhance

the properties for high temperature applications.

In the present study a binary alloy of Ni-14.7 at % Al was quenched

from 1200 C from a single phase region. Quenched samples of the thickness

^ 0.1 cm were aged isothermally at the temperatures of 540 and 600 C.

Figures 1(a) and 1(b) show the Small-Angle Neutron Scattering (SANS) curves for the alloy aged at 600 C. The measurements were performed

using neutrons of wavelength ^ 6A (FWHM + 20%) to avoid the complicating

effects of double Bragg scattering. The Q range (= ? ) of these

-1

experiments was between 0.009 and 0.09 A . Depending upon the number

density of the structural inhomogenities , the structural features in the

range of 600 to 60 A dimensions could be easily measured by the present

choice of parameters.

The as-quenched samples showed a flat scattering profile (figure

1(a)) indicating that quenching was severe enough to supress the formation

of y'. After one hour of aging at 600 C a well defined peak is developed

in the small-angle scattering curve (figure 1(b)). With further aging,

this peak moves towards the lower scattering vectors. Depending upon

the type of model used to analyze the aging kinetics, such a peak shifting

is interpreted as either coarsening of y' particles formed during aging

or coarsening of wavelength of modulated y

1 structure formed by spinodal

decomposition mechanism.

The mechanism of the formation of y' in Ni-Al alloys has been a subject of some controversy in the recent past. Ardell and Nicholson and'

2 3 Kirkwood ' have concluded on the basis of their electron-microscopic

studies that y' is formed by a nucleation and growth mechanism. However,

4 Gentry and Fine carried out the measurement of saturation magnetization

as a function of aging time and indicated that the decomposition takes

place by a spinodal mechanism. It must be realized at this point that the

aging temperatures used by various authors ranged from 400 to 800 C.

119
RRD COLLABORATIVE PROGRAMS

Figure 1(a)

.

c

70-i

60-

50-

40-

- 30-

20-

10-

1 1 1 1 1 1 1 0.004 0.013 0.022 0.031 0.040 0.049 0.057 0.066

Scattering Vector (A ) Intensity (I) vs. scattering vector (Q) . Spectra for

solid-quenched and aged Ni-14.7 atomic % Al alloy.

[1-as-quenched, 2-1 hr., 3-3 hr . , 4-5 hr., 5-10 hr .

,

6-15.5 hr., and 7-24 hr. at 600°C]

120i100

V)c

3

oU

80

60-

40-

20-

I ±

Figure 1(b)

280 300 320 340 360 380 400

Channel Number

Intensity vs. scattering vector for Ni-14.7 atomic %

alloy aged 1 hr. at 600°C.

120
RRD COLLABORATIVE PROGRAMS

Figure 2

Ed

-2.8

-3.0 - \

-3.2

\l

-3.4

•\

-3.6

1 L

V^2

4 5 6 7 8

In ta (minutes)

Variation of peak position (Q ) as a function of aging

time (t ).

m

a

9f8

£

c

1 I 6 7

In ta (minutes)

8

Figure 3. Variation of normalized peak intensity (I ) as a function

of aging time (t )

.

3 m

121
RRD COLLABORATIVE PROGRAMS

Ardell and Nicholson and Kirkwood performed their isothermal aging

experiments at temperatures of 750°C and above. On the other hand,

the aging temperatures used by Gentry and Fine were in the range of 425

to 450 C. It is, therefore, possible that Gentry and Fine's experiments

were carried out in the spinodal region of the phase diagram. The aging

temperatures used in our study are intermediate to these two studies.

Figure 2 shows a log- log plot of Qm i.e. scattering vector at

maximum intensities as a function of aging time. It would appear from

this curve that two regimes of the decomposition process are clear. In

regime I, the time dependence of Qm is given by the equation

-1/4

Qm = 0.15 t

' a where t is the aging time. This is suggestive of the fact that during

a -1/3

stage I the system has not yet entered the conventional t coarsening

regime (See reference 4). In regime II the rate of coarsening appears

to have slowed down, although one needs to carry out the experiments for

longer aging times to confirm this. Similar behavior was seen by

Wilkes and Saundersen during the coarsening studies in a Cu-Ni-Cr alloy

where they observed a transient arrest in coarsening kinetics before

-1/3 entering into t type of growth.

Figure 3 shows a log-log plot of normalized peak intensity (Im) as

a function of aging time. One of the striking features of this curve is an intermediate slowing down of the growth of peak intensities between

aging times of 10 and 15.5 hours. According to recent theoretical analysis

of Ditcheck and Schwartz , in later stages of spinodal decomposition the

peak intensity approaches a constant value having no time dependence

(e.g. see figure 3 of reference 6). An alloy in this state is said to

be in the "stationary state" of the spinodal process. From figure 3 it

appears that after an aging time of 10 hours at 600 C the alloy has reached

this stationary state. The main characteristic of the stationary state is

that the amplitude of the compositional modulation wave approaches the

value dictated by the phase boundaries of the metestable miscibility gap.

122
RRD COLLABORATIVE PROGRAMS

Similar behavior was seen by Singhal in the later stages of the spinodal

decomposition In a Au-60 at % Pt alloy. The rise in peak intensities

on further aging (after 15.5 hrs) can be attributed to Ostwald Ripening

o type of process where larger particles grow at the expense of smaller

ones due to the higher surface to volume free energy ratio of the latter.

Detailed analysis of these and other features of phase decomposition in

Ni-Al alloys is in progress presently.

1. A. J. Ardell and R. B. Nicholson, "On the Modulated Structures of

Ni-AR Alloys," Acta. Met. 14, 1295 (1966).

2. D. H. Kirkwood, "Precipitate Number Density in a Ni-AR Alloy at

Early Stages of Aging," Acta. Met. 18, 563 (1970).

3. A. W. West and D. H. Kirkwood, "Nucleation and Precipitate Densities

in a Nickel-Alluminum Alloy," Scripta Met. 10, 681 (1976).

4. W. 0. Gentry and M. E. Fine, "Precipitation in Ni-11.1 Atomic % Al

Alloy and Ni-13.8 Atomic % Al Alloys," Acta. Met. 20, 181 (1972).

5. P. Wilkes and R. I. Saunderson, "Coarsening in the Cu-Ni-Cr System,"

Acta. Met. 26, 1357 (1978).

6. B. Ditcheck and L. M. Schwartz, "Diffraction Study of Spinodal

Decomposition in Cu-10 W% Ni-6 W% Sn," Acta. Met. _28, 807 (1980).

7. S. P. Singhal, "Small-Angle Neutron Scattering and TEM Studies of

the Phase Decomposition in the Au-Pt System," Ph.D. Thesis State

University of New York at Stony Brook, (1980).

8. J. M. Lifshitz and V. V. Slyozov, "The Kinetics of Precipitation

from Supersaturated Solid-Solutions," J. Phys. Chem. Solids 19,

35 (1961).

123
RRD COLLABORATIVE PROGRAMS

THERMAL MOTIONS IN AMMONIUM PERCHLORATE

C. S. Choi and H. J. Prask

(Energetic Materials Division, LCWSL, ARRADCOM, Dover NJ)

and

(National Bureau of Standards, Washington, DC)

Huller has recently developed a theoretical model for rotational,

quantum-mechanical tunneling of tetrahederal XH, groups in solids and

applied the model to the interpretation of neutron inelastic scattering

measurements of tunneling states in NH.CIO, . Relative librational force

constants extracted from the analysis were found to be in excellent

agreement with librational amplitudes determined from our low-temperature

2 single-crystal neutron diffraction measurement. However, a force-model

3 calculation did not yield hydrogen equilibrium positions in agreement with

the measured structure. In view of this, we have redetermined the crystal

structure using ND.C10,, both single-crystal and powder, to confirm our previous results and to more completely characterize ammonium-ion

dynamics in the 10 to 80K temperature range.

1. Single Crystal Study

Reflection data were collected at two different temperatures, 20K

and 75K, within the scattering sphere up to 0.6 A in sinO/X.

In the crystal structure refinements (space group Pnma) , the

deuterium atoms of the ammonium group were constrained to rigidbody thermal motions. The refinement for the 20K structure converged

rapidly to the final R indicies R = 0.038 and Rw = 0.037. The

refinement of the 75 K structure was repeated with several different

fixed values of secondary extinction coefficients, and final R value

R = 0.094 and Rw = 0.096 were obtained. Shifts in atomic positions

are compared with those of the hydrogeneous compound at different

temperatures in figure 1. The positional shifts (nonhydrogeneous

atoms) are more pronounced at temperatures below 78K, which may

124
RRD COLLABORATIVE PROGRAMS

be attributed to the sharp increases in the librational motion of

ammonium group observed in that temperature region. The structure

and thermal motions of the ND, groups are essentially the same as those of NH, except for small temperature-dependent positional

shifts and changes in libration amplitudes.

2. Powder Diffraction Study

The librational amplitude of the ND, group at 30K, 45K, and 60K were studied by a neutron powder diffraction refinement with

instrumental parameters: A = 1.542A _, 29 (mono) = 74.2 , 20max = 120°, A(20) = 0.1? and collimation of 20 f -20'-10'.

Positional parameters of the perchlorate group were obtained from

the single crystal structures of 20K and 75K by linear interpolation

(proportional to temperature changes) and were excluded from the

refinement. The ND, group was treated as rigid with translational

and librational motion only. The R indices of the refinements were R= 5.6 Rp = 4.0 Rw = 5.2 Re =1.9 for the 30K structure and

6.1, 3.8, 4.9 and 1.9 respectively for the 60K structure. The

45K structure study has not been completed.

3. Librational Motion of the Ammonium Group.

The root-mean-square amplitudes of librations for the ammonium

group at different temperatures are summarized in Table 1. The

deuterated and hydrogenous ammonium groups both undergo very

large amplitude libration about an axis with essentially identical

orientation in the observed temperature region, 10K to 78K. The

temperature dependent rms amplitudes show a saturated value,

approximately 30 , at temperatures 60K and above.

The amplitudes of librational motion obtained from the single-crystal

data has been used to extract librational frequencies in a harmonic

approximation (Table 1) . It is interesting to note that at the lowest

temperatures the isotope shift of the librational frequency corresponding

125
RRD COLLABORATIVE PROGRAMS

Table 1. Summary of rigid body librat ion amplitudes of ammonium group,

Principal

Temperature Axis 'n W (Cm )

Li

* o rms

L

( ) 1 m

0.

n

10K 1 44 20.8 0.6845 0.7290

2 147 11.4 0. 1. 0.

3 187 10.1 -.7290 0. 0.6845

78K 1 52 29.6 0.6901 0. 0.7237

2 98 16.4 0. 1. 0.

3 110 15.0 -.7237 0. 0.6901

b) ND

4

ion

20K 1 41 16.1 0.6487 0. 0.7610

2 101 9.7 0. 1. 0.

3 145 8.1 -.7610 0. 0.6487

(30K)** 1 22.0 0.6215 0. 0.7834

2 10.4 0. 1. 0.

3 4.9 -.7834 0. 0.6215

(60K)** 1 29.7 0.6184 0. 0.7859

2 10.9 0. 1. 0.

3 5.4 -.7859 0. 0.6184

75K 1 35.5 28.5 0.6608 0. 0.7505

2 59 17.8 0. 1. 0.

3 79 13.8 -.7505 0. 0.6608

* librational frequencies from Cruickshank . ** Neutron powder diffraction refinement.

126
RRD COLLABORATIVE PROGRAMS

to the largest amplitude libration is on the order of only 10% whereas

the isotope-shifted frequencies of librations about the other two axes

is close to the expected V2~ shift (i.e. VT /I ). This result is very

n D

important for the interpretation of Raman data in which a very temperaturedependent mode was observed in NH.C10, at 50cm in the polarization in

4 which the large amplitude libration should be observed. However, the

isotope shift in ND.C10, was found to be only 0.89 suggesting that this was not the expected libration. The present diffraction result, on the

other hand, indicates that this mode is very probably the expected

libration.

ci

<**-

°,

-o Ax

-» Az

--o Ax

>Az

<**=-

-o Ax

-• Az

-oAx -•Az

i 1—

i

1 i 1

1 r

1 00K 200K

Temperature 300K

Figure 1. Comparison of atomic positions at various temperatures Ax

and Az, in A unit, are the positional changes of each atom

from its 10 K structure.

1. A. HUller, Phys. Rev. B, 16, 1844, (1977).

2. C. S. Choi, H. J. Prask & E. Prince, J. Chem. Phys. } 61, 3523, (1974)

3. A. Hllller, Private communication, (1979).

4. G. J. Rosasco & H. J. Prask, Solid State Commun. } 16, 135, (1975).

127
RRD COLLABORATIVE PROGRAMS

5. D. W. J. Cruickshank, Acta Cryst. 3 9, 1005 (1956).

THE DETECTION OF AN ORDER-DISORDER PHASE

TRANSITION IN A MOLECULAR CRYSTAL BY COMPUTER

MOLECULAR DYNAMICS

S. F. Trevino

(ARRADCOM, LCE, Dover, NJ)

and

(National Bureau of Standards, Washington, DC)

and

D. H. Trai

(Thermophysics Division)

We have recently begun a program designed for the investigation

of the mechanisms by which energy released by a chemical reaction

redistributes itself in condensed matter. The general outline of the

work is as follows . We wish to model a diatomic molecule which is

capable of dissociation into a state of lower energy (thus leading to a release of kinetic energy) . This dissociation is effected through the

interactions with neighboring molecules. In addition, we wish to allow

recombination so as to better mimic nature. For this purpose, a pairwise

potential is constructed of two parts, each a (6-12) type. The intermolecular potential whose minimum corresponds to the larger distance is

chosen as the Lennard-Jones 12-6 potential. The intramolecular potential

is scaled in a somewhat arbitrary fashion and is given by:

/4e

ltra { n

12 6^

a a { + e nr nr ) 2 where e and a are the same parameters as in the Lennard-Jones potential,

and n is a scale factor. We have used n=3 and n=4. Having thus defined

the pairwise interaction of all the atoms, computer molecular dynamics

is used to obtain the response of a collection of such particles to

various stimuli. The initial step in our investigation is the construction

of a perfect crystal modeled in the standard method by using periodic

128
RRD COLLABORATIVE PROGRAMS

boundary conditions of an array of diatomic molecules. The initial

configuration consists in placing the center of mass of the molecule on

an FCC lattice and allowing them to relax until a stable orientational

configuration is obtained. This process led to a crystal structure very

similar to that of N in its lowest temperature phase with the single

exception that the cell was slightly tetragonal (c/a = 0.97) rather

than cubic. The crystal was heated while holding the volume constant

and various properties were monitored. These included the total energy,

the kinetic energy, the intramolecular distance, the single molecule

angular correlation function (G(y) = E 6(y - y ) dy where the sum is over the particles in the model and y is the angle which the molecular

axis makes with the z-axis, for example), etc. The initial intention of

this experiment was to observe chemical decompositions. For this purpose,

the intramolecular separation was carefully monitored. It was observed

that, although the amplitude of the molecular stretch increased with

temperature, the maximum separation of the two atoms of the molecule was

never much larger than the distance to the minimum of the first potential.

Our interpretation of this result is that in a perfect crystal lattice,

decomposition is greatly hindered by the presence of neighboring molecules;

and in addition, that increasing the pressure on the system also inhibits

decomposition. It is clear to us from this that the role of defects

(vacancies) is of crucial importance to the mechanisms of decomposition

in the solid. It is our intent to study these details with our model.

As the heating was continued, a lambda type order-disorder phase transition

was detected. The transition is characterized by a pronounced continuous

increase in internal energy as a function of temperature and in the

width of G(y) as a function of y until at just above the transition

temperature G(y) is essentially a constant with y.

129
C. Non-RRD Programs

ACTIVATION ANALYSIS: SUMMARY OF 1980 ACTIVITIES

Rolf Zeisler

The Activation Analysis Group has eight full-time and one part-time

employees. Of these employees, seven are research scientists, one of

whom is on detail for the Office of Measurements for Nuclear Technology

and two are technical support personnel. The group hosts a guest worker

from the Smithsonian Institution. The group is physically located in the

reactor building where it utilizes office modules, measurement and counting

laboratories (including one class 100 clean room), and radiochemistry

laboratories.

The Activation Analysis Group, in support of the Inorganic Analytical

Research Division, conducts research and analysis in four basic program

areas :

1. Basic Research in Nuclear Analytical Chemistry

This activity is primarily aimed at improving the analytical measurement

system using nuclear techniques. This includes analytical method development, improvement of instrumental and radiochemical analysis schemes, and

all areas of analytical quantitation. Recent efforts are highlighted

by high precision and high accuracy instrumental analysis of aluminum and

the comparative determinatidn of iodine in biological matrices after irradiation

with thermal and fast neutrons and photons.

2. Analytical Research Applied to Specific Programs

This activity utilizes the group's analytical capability to provide

reliable analytical data in the study of systems dependent on trace

element composition. Specific efforts have been made in sampling and sample

preparation methodology in order to provide meaningful analytical samples.

The extended instrumental capabilities help the Activation Analysis Group

to provide the vast number of analytical data, which combined with the

results of other analytical techniques provide essential information on environmental and biological systems. The information is needed for

example in the Chesapeake Bay Program and in the Pilot National Environmental Specimen Bank Program.

130
NON-RRD PROGRAMS

3. Analytical Support for the SRM Program

Analysis performed on new Standard Reference Materials (SRM's) are an extremely important area of the group's activity. Extreme

emphasis is placed on the accuracy of analytical results. These efforts

are backed by the essentially blank free activation analysis procedures

and vast applications of instrumental analysis.

4. Service Analysis

Service Analyses are a small but important part of the group's

analytical program, chiefly undertaken to expedite another NBS program

or when the analytical capability cannot be obtained otherwise. There

are many cases where a unique measurement is needed, thus triggering

development of new nuclear analysis capabilities.

The summaries of the work completed this year in the four basic

program areas are included below. More detailed descriptions of

projects can be obtained from literature references or individual program

reports.

131
NON-RRD PROGRAMS

1. Basic Research in Nuclear Analytical Chemistry

a. Pulse Pileup Correction Methods

R. M. Lindstrom

A significant source of error in activation analysis is the loss

of counts at high counting rates due to pulse pileup. Wyttenbach1 showed

that a simple model based on the non-extending dead time formalism can

correct for this loss with acceptable errors at dead time above 20%. His

formulation, however, involved an unnecessary mathematical approximation;

a better formula for the correction factor is

I Cbrue) /I (observed) = exp (P • DT/LT) , where

DT = CT - LT

CT = elapsed clock time

LT = elapsed live time

P = a constant, proportional to the amplifier time constant t.

A FORTRAN program, PILSET, has been written to determine P and its

statistical uncertainty from a set of observations of a reference source

in the presence of variable amounts of interfering activity. The dependence

of P on the amplifier time constant x is shown in figure 1. The detector

resolution is plotted on the same graph; a balance between good resolution

and small pileup correction requires setting t at 1-2 ys for most work.

This model has been tested in an interlaboratory comparison of source strength measurements, organized by the International Atomic Energy Agency

(IAEA). Two separate sets of measurements were reported, one with pileup

corrections made as described above, and another using a commercial pileup

rejector - livetime corrector. As can be seen by figure 2, both methods

give acceptable agreement with the source strengths given by IAEA.

132
NON-RED PROGRAMS

2 4 6 AMPLIFIER TIME CONSTANT r, fxs Figure 1. Pileup parameter P versus amplifier time constant T,

52 9.7 17.9 % DT 2.4 6.0 11.7

1.02 -

i i 10 <LUS .98

I 1.0 UJ

g 1.02 § 1.0

98

1.02

1.0

0.98

Lu-^i i.

-jj_5 i.

-H- 15 *5~ j i

28 4 37.1 • HARDWARE

18.7 24.3 o SOFTWARE

H J M i-5 $2— Zn 65 1115 keV

_L

Mn-54 834 keV

Ba 133 356 keV

• HARDWARE/IAEA

o SOFTWARE/IAEA

(displaced 'A cm right)

*5

Co 57 122 keV

500 1000 1500 kBg Source strength

Figure 2. Hardware versus software pileup correction.

133
NON-RKD PROGRAMS

b. High-Accuracy Aluminum Determination by Neutron Activation

R. F. Fleming and R. M. Lindstrom

Aluminum, the second most abundant cation in the earth's crust, is

certified in only two of the thirteen environmental and biological SRM's

in the current catalog, largely because there are few reliable methods

of measuring this element at NBS. Non-destructive neutron activation

has progressed recently so that we understand and can eliminate all sources of systematic error. Precision is limited by counting statistics,

but this may be very small .

v

The initial phases of this work have been successfully completed.

The kinetic equations have been solved rigorously, with all parameters

included: radioactive decay, dead time, and pulse pileup. The aluminum

concentration of a material (single-crystal sapphire) of precisely known

composition, with an accuracy limited only by counting statistics at the

0.5% level. All systematic biases have either been compensated for or

the necessary corrections have been measured and verified. The measured

aluminum concentration was found to be 52.78 + 0.30%, which can be compared

2 to the true value of 52.952%. (The reduced x is 2.1.) The major corrections

required to the data were for count rate dependent effects, as expected.

In extreme cases these corrections were as great as 15%. The next phase

of this work is to apply the capability established to the more complex

matrices of the SRM bauxites. Soon after irradiation essentially all

activity is Al-28. Therefore, during irradiation and counting are necessary for results as good as those for sapphire.

Results to data on the bauxites are extremely encouraging. Sources

of bias, due to the coarseness of commercially available time bases and

of irradiation and counting geometry, have been detected and eliminated

with improved experimental design. The dominant remaining uncertainty

in the best of our measurements may be neutron absorption by the hydrogen

in the sample and its container. The magnitude of this effect is difficult

to calculate; it could be a few tenths of a percent. Normalizing, the

concentrations to SRM 676, our best results for the four bauxites is as follows:

134
NON-RRD PROGRAMS

SRM 69b

Aluminum certified 0.895+0.004

(relative)

Aluminum measured

(relative)

0.900+0.004

0.898+0.003

696

1.000+0.006

1.000+0.004

1.000+0.003

697

0.840+0.004

0.828+0.004

0.835+0.003

698

0.884+0.007

0.873+0.005

0.879+0.003

We are close to showing that activation analysis is a fully reliable

method of aluminum measurement, able to stand alone for certification if

carefully done. We expect to demonstrate even higher accuracy in the future

for other elements.

c. Determination of Total Iodine in Biological Materials

G. J. Lutz

During a visit to the University of Michigan reactor several

months ago, we conducted some irradiations inside a boron nitride cup

and lid. This effectively screens out the thermal component of the

neutron flux and relatively enhances capture reactions which have significant resonance in the epithermal region as well as fast neutron reactions.

Although iodine exhibits an excellent intrinsic sensitivity for

determination by thermal neutron activation analysis, the limit of nondestructive determination in biological materials is 10-20 ppm. This

is because the activation product 1-128 has a short half-life and a not

particularly favorable decay scheme. The photopeak associated with the

decay of 1-128 is obscured by Compton continua of higher energy photopeaks of the activation products of various elements, including manganese,

sodium, bromine, chlorine, and aluminum. When the irradiation is conducted

with epithermal neutrons, the production of 1-128 is reduced by about an

order of magnitude, but the production of interfering nuclides is reduced

by roughly two orders of magnitude. Lower levels of non-destructive

determination of iodine are then of the order of tenths of parts per

million.

It is expected that NBS will certify one or more of its biological

SRMs for total iodine content. Currently at NBS, the two most reliable

135
NON-RRD PROGRAMS

methods for iodine seem to be the epithermal neutron activation analysis

described above and instrumental photon activation analysis. A rather

limited comparison of some samples by both methods has been accomplished

and results from this exploratory work agree at levels of approximately

2 ppm of iodine to within 15-20%.

We have obtained some kelp tablets and have crushed (to powder)

,

homogenized and dried a portion of them. Their iodine content is

approximately 200 ppm. This level makes errors due to counting by either

activation method highly unlikely. Whether we continue to get discrepancies of 15-20% or the two independent methods agree within random

error at this level will provide clues as to the source of the problem.

d. Lithium and Lithium-6 Analysis with the Nuclear Track Technique

B. S. Carpenter (NBS) and L. J. Pilione (Pennsylvania State

University)

Introduction

The concentration and distribution of lithium can be determined

with the nuclear track technique if elements, such as boron, are not

present in relativley large amounts. The alpha particles produced

by (n, a) reactions of different elements are for the most part indistinguishable with the nuclear track technique. In this investigation

an absorbing material is placed between the sample and the detector such

that the alpha particles are screened out while the tritons produced in

the Li(n, a) H reaction penetrate and produce etchable tracks. The

triton track density produced in this fashion, is proportional to the

lithium concentration and the lithium-6 isotopic abundance of the sample.

Methods and Analysis

To observe the effects of absorber thickness on the triton track

density — cellulose nitrate detectors (Kodak Pathe CA 80-15) were cut

2 into strips (- 0.5 cm ) and heat sealed inside various thicknesses of

linear polyethylene (12.5-55 u meters). One-half dram vials (y 1 ml

capacity) were filled with a standard lithium solution (1358 ppm Li,

7.45% Li) and the detector-absorber package positioned in the center of

136
NON-RRD PROGRAMS

the vial. The samples were exposed to thermal neutrons in the D~0

facility at the Breazeale Reactor, Pennsylvania State University. The

detectors were retrieved and chemically etched in 2.5 N NaOH @ 50 + 0.5°C

for 25 minutes. Random fields of view were selected on both sides of

the detector surface and the triton tracks counted with a Leitz optical

microscope.

The data presented in table 1 indicates that the triton track density

remains constant for absorber thicknesses between 12.5 and 25 y-meters

(the uncertainties represent one standard deviation = 1/ (total number

of triton tracks)^.

As a check on the screening effect of the absorber (12.5-25 y meters)

against a-particles — detector absorber packages were placed in vials

containing boron solutions (1000 ppm) . The samples were processed as before and no tracks above background were observed in the detector.

14 14

The background tracks resulted from the reaction N(n, p) C in the

cellulose nitrate detector. The proton and triton tracks were found to

be indistinguishable. In all cases blanks were exposed along with the

samples and the proton track density subtracted out from the total to

yield the net triton track density. This background set the lower limit

of detection at 100 ppm Li, 7.4% Li-6.

Lithium solutions of known concentration and isotopic abundance

were selected to verify the relationship between the triton track density

and the lithium concentration and isotopic abundance. The known samples

and blanks were processed as described previously (25 y meter absorber)

.

It can be seen from table 2 that a linear relationship exists between

the triton track density and the lithium concentration. The effect of

isotopic abundance was found by calculating the ratio of the triton

track density to the lithium concentration for each sample. The results

shown in table 3 indicate a linear relationship exists.

The isotopic abundance of the Atomic Absorption Standard was not

specified by the manufacturer. Using the measured ratio and table 3,

the isotopic abundance was found to be 7.48 + 0.44%.

137
NON-RED PROGRAMS

Conclusion

It has been found that the concentration or isotopic abundance of

lithium in solution can be determined using the nuclear track technique

without interference problems from other elements present in the solution.

The limit of detection is 100 ppm Li, 7.43% Li with an accuracy of

+ 6%. The process time/ sample is ^ 15 minutes.

Table 1. Triton track density vs absorber thickness

Absorber Thickness (y meter)

12.5

15.5

18.5

21.5

25.0

28.0

33.0

35.0

40.0

45.0

50.0

5 2 Triton Track Density (*10 t/cm )

7.28 ± 0.29

7.21

7.00

7.00

7.40

7.00

5.80

5.14

3.98

3.01

0.28

0.28

0.28

0.30

0.28

0.23

0.21

0.16

0.12

1.74 ± 0.07

138
NON-RRD PROGRAMS

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139
NON-RRD PROGRAMS

Table 3. Triton track density/lithium concentration vs lithium-6 isotopic abundance

Triton Track Density/Lithium

Concentration (*10 3 t/cm2

) ppm

1.08 ± 0.08

1.97 ± 0.11

4.75 ± 0.32

10.1 ± 0.56

2.16 ± 1.31

Lithium-6 Abundance (%)

4.60

7.43

20.0

45.0

95.9

1. R. L. Fleischer, P. B. Price, and R. M. Walker, Nuclear Tracks in

Solids: Principles and Applications> University of California Press3 Berkley (1975).

2. B. S. Carpenter and L. J. Pilione, NBS Technical Note 9693 89-90, 1978,

140
NON-RKD PROGRAMS

2. Analytical Research Applied to Specific Programs

a. The National Environmental Specimen Bank (NESB)

S. H. Harrison and R. Zeisler

In the past year, the NESB program has progressed from the research

and development phase into the first year of implementation of the pilot

bank. This year was highlighted by the completion of the Specimen Bank

laboratory and storage facility, implementation of the sample collection

protocol, initiation of trace element analyses on banked samples, and

further improvement and evaluation of the sample homogenization procedure.

The construction of the clean room facility was completed in

November 1979. This facility, located in the NBS Reactor building, houses

the specimen bank laboratory and storage rooms. Since construction was

completed, it has been equipped with the items necessary for processing

and storing samples. These items include upright compressor freezers

operating at -80 C and -25 C, liquid nitrogen freezers holding samples

in nitrogen vapor at temperatures less than -120 C, a dust-free cabinet

for storing freeze-dried samples, a cabinet for storage of histological

slides, oxygen monitor, biohazard hood, refrigerated shelf freeze dryer,

and equipment for sample homogenization.

The collection of human liver specimens, the first sample type to

be studied in the pilot bank of the NESB, was initiated this year through

contracts with three medical schools. A very careful sample collection

protocol is being used by pathologists and their assistants. Liver

specimens are shipped to NBS at cryogenic temperatures by an express air

freight service. A total of 300 samples are targeted to be collected in

the first year. About 10% of these will be processed for analysis by

homogenization and subsampling into Teflon PFA jars.

The samples collected this year are analyzed for their trace element

content only. The trace organic analysis is under methodology development

this year and will be used for real sample analysis next year. Three

inorganic analytical techniques will be used routinely for sample analysis,

These are neutron activation analysis, voltammetry, and atomic absorption

141
NON-RRD PROGRAMS

Table 1. Instrumental neutron activation analysis of normal human liver,

Element Concentration

(yg/g fresh wet)

Na 760

Mg 120

Al 0.74

CI 360

K 2790

Cr 0.05

Mn 0.83

Fe 154

Co 0.039

Cu 7.1

Zn 63

Se 0.35

Rb 3.7

Mo 0.90

Ag 0.05

Cd 0.93

Sb 0.007

142
NON-RRD PROGRAMS

spectrophotometry. Instrumental neutron activation analysis of the human

liver samples is used to provide data on Na, Mg, Al, CI, K. Cr, Mn, Fe,

Co, Cu, Zn, Se, Br, Rb, Mo, Ag, Cd, Sb, La, and Hg. Representative data

is presented in table 1. Radiochemical activation analysis has been used

to analyze the livers for Cu, Cd, As, Se, Sb, and Mo. For major element

analysis, prompt gamma activation analysis looks to be a promising technique

after preliminary investigation of a liver sample. In addition to activation

analysis methods, voltammetry is used to analyze for Cu, Cd, Pb, Ni, and

Zn, and atomic absorption spectrophotometry is used for Be, Al, Cr, Ni,

Sr, Se, Ba, and Pb.

The brittle fracture technique for cryogenic homogenization of samples

2 was pioneered by G. Iyengar. We have modified his design, which was only

capable of handling 5 to 10 g of sample per batch, so that 250 g of frozen

liver can be homogenized at a time and the preliminary results indicate

that 1 g subsample of the homogenate is a satisfactory representative of

the whole.

1. "Sampling and Sample Handling Protocols for Human Livers,"

S. H. Harrison in Pilot Program for the National Environmental

Specimen Bank-Phase I, Sally H. Harrison, Rolf Zeisler, and

Stephen A. Wise, Editors, NBS Special Publication in preparation.

2. Iyengar, G. and Kasperek, K. , J. Radioanalytical Chem. , p. 301-315

(1977).

143
NON-RRD PROGRAMS

b. Analysis of Chesapeake Bay Water and Associated Suspended Solids

R. R. Greenberg, H. M. Kingston, and E. S. Beary

As part of a multidisiplinary and multiagency study of the

Chesapeake Bay, 102 water samples and the filtered suspended solids from

these samples are being analyzed by neutron activation analysis. The

samples were collected 1 m below the surface, and 1 m above the bottom

at 52 different locations throughout the bay. Approximately 30 full-process

blanks were also collected and are being analyzed. Pre-irradiation, ionexchange chromotography is used to concentrate the elements of interest

from the water samples, and separate them from interfering matrix elements

such as Na, Cl# and Br. After filtration, 100 mL of water is passed

through pre-cleaned chelex 100 chelating resin in a class 100 clean room. The resin is washed with 1.0 M ammonium acetate, washed with ultrapure

water, dried, and irradiated for four hours in rt-3. Samples of SRM 1643a

(trace elements in water) are being processed and analyzed with the bay

water samples to check the accuracy of the procedure used.

The results of the analyses completed indicate great variation among

samples, as illustrated in table 1. The concentration of many elements

in the filtered particulate fractions vary over two orders of magnitude.

To a large extent, this is due to differences in total mass loadings on

the filters. Various factors can influence the amount of particulate

material suspended in the bay water such as: current; tide; temperature;

wind conditions; etc., making interpretation of the data difficult. One

approach which appears to be useful in this study is to compare the

elemental ratios among the different sample locations instead of the

absolute concentrations. By normalizing to a crustal element, such as

Sc, the problems caused by differing mass loadings are essentially eliminated.

The particulate Fe concentration, for example, in sample 11005 (table 1)

is 150 times greater than in sample 11032, however, their Fe/Sc ratios

are essentially the same (3200 compared to 3700).

When completed, this study may prove useful in identifying anthropogenic

and/or natural sources to the Chesapeake Bay. In addition, since these

144
NON-RRD PROGRAMS

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145
NON-RRD PROGRAMS

samples were collected concurrently with sediment, pore water, and benthic

studies, both the water to sediment equilibrium and the aquatic population

will be correlated .

c. 1-129 Analysis

G. J. Lutz

A project has recently been initiated to set up the equipment for

1-129 analysis with a view of certifying a botanical Standard Reference

Material for its 1-129 content.

The analysis consists of a pre-irradiation separation, an irradiation

in the reactor, and a post-irradiation separation. The pre-irradiation

separation involves spiking the sample with 1-125 traces for subsequent

yield determination and combustion of the sample in a stream of oxygen.

The off gases are filtered through glass wool to trap out any particulate

material and the iodine is trapped on activated charcoal. The preirradiation filtering is necessary to remove cesium, and tellurium which

133 130 235 could interfere via the reactions respectively Cs(n,a) I, U(n,f)

129 T

, .130T

, 128^ , .129„, - 129

I(n,y) T , ,130T I, and Te(n,y) Te I(n,y) I.

The charcoal trap containing the iodine is then sealed in quartz

and irradiated in the reactor for a suitable length of time. After a short cooling period, a few milligrams of inactive iodine carrier is

added. The major activities are those due to chlorine, bromine, and

impurities in the activated charcoal. The charcoal and carrier are burned

in a stream of oxygen. The off gases are again passed through a plug of

glass wool to filter out particulate material. The collecting trap

consists of a bed of hydrated manganese dioxide (HMD) followed by a charcoal

trap for collecting the iodine. HMD is one of a series of selective ion

retention media developed during the past several years. It is usually

used for separations from aqueous solutions, but has been applied to gas

phase separation.

Over a fairly wide temperature range, a bed of HMD will remove

146
NON-RRD PROGRAMS

99.9%+ of chlorine and bromine from a gas stream while passing > 95% of

the iodine.

Tracer studies have been completed on the pre- and post-irradiation

separations and the final apparatus to be used is being constructed.

d. Consistency Study of Re-Refined Lubricating Oils

R. F. Fleming

The Bureau was mandated in the Energy Policy and Conservation

Act of 1976 to develop and evaluate a set of test procedures necessary

to establish the "substantial equivalency" of a re-refined lubricating

oil when compared to virgin oils. As part of this effort, the Recycled

Oil Program (Office of Recycled Materials) has set up a study of approximately 40 tests to be performed on eleven lubricating oils (six rerefined, four virgin, and a check sample) each month for a year. As

part of these tests, the concentration of chlorine and of bromine are

being determined by neutron activation analysis. It is the consistency

of these measurements over the twelve month period which is of particular

interest, although absolute concentrations may also be found important.

Since neutron activation analysis of the oils is capable of a sensitivity of 30 ppb for both elements, it is the only analytical

method which can provide the required precision and accuracy for this

study. Preliminary results indicate that the measurements easily distinguish between virgin and re-refined oils, and are able to monitor

significant changes in halide concentrations with time.

147
NON-RRD PROGRAMS

3. Certification Analysis of SRM's.

a. New Biological SRM's: Bovine Liver and Citrus Leaves

R. R. Greenberg, R. Zeisler, R. M. Lindstrom, G. J. Lutz,

S. Harrison, and J. V. Bailey

Two new bovine liver Standard Reference Materials (1577A and

1577B) , and a new citrus leaves SRM (1572) have recently been prepared

and are currently being analyzed. Both instrumental neutron activation

analysis (INAA) and radiochemical neutron activation analysis techniques

have been used. The elemental concentration determined so far are

listed in table 1.

148
NON-RRD PROGRAMS

Table 1.

Element

Ag

Ag

Al

As

As

Ba

Br

Ca (%;

Cd

CI

Co

Cr

Cr

Cs

Cu

Cu

Fe

K (%)

Mg

Mn

Mo

Na

Rb

Sb

Sc

Se

Se

Zn

Elemental Concentrations in New Biological SRMs Concentration

yg/g unless % indicated.

Method

INAA

RNAA

INAA

INAA

RNAA

INAA

INAA

INAA

RNAA

INAA

INAA

INAA

RNAA

INAA

INAA

RNAA

INAA

INAA

INAA

INAA

RNAA

INAA

INAA

RNAA

INAA

INAA

RNAA

INAA

Bovine Liver

SRM-1577A

0.050 + 0.011

0.045 + 0.001

3.1 + 0.8

0.046 + 0.004

9.0 + 0.1

0.430

2760

0.242

0.43

0.29

153

158

194

0.96

520

9.6

3.2

2200

12.7

0.0029

0.004

120

0.005

0.28

+ 0.13

± 8

+ 1

± 4

+ 0.05 + 180

+ 0.8

+ 0.1

+ 30

+ 0.3 + 0.0003

0.73 + 0.02

0.72 + 0.04

124 + 1

Bovine Liver

SRM-1577B

0.040 + 0.010

2.9 + 1.0

9.7 + 0.1

2700 + 160

0.255 + 0.006

0.31 + 0.21

163 + 10

195 + 4

0.97 +0.09

520 + 120

9.3 + 0.3

2190 + 30

12.9 + 0.3

0.73 + 0.04

125 + 2

Citrus Leaves

SRM-1572

93 +5

3.12 + 0.14

21.4 +0.6

3.18 + 0.09

0.74 +0.09

0.098 + 0.005

92 +7

1.90 + 0.07

6100 + 200

22.6 + 0.9

160 + 13

5.0 + 0.2

O.OlOy + 0.0007

30.5 + 0.9

149
NON-RRD PROGRAMS

b. Analysis of Obsidian SRM 278 and Basalt SRM

M. J. Blackman

Two new silicious rock standard reference materials: obsidian,

a natural glass with the approximate composition of granite; and basalt,

a basic igneous rock were analyzed by instrumental neutron activation.

Sodium, manganese, potassium, and dysprosium were sought. Table 1 presents

the results of this analysis.

Table 1. Na, Mn, and Dy in Obsidian SRM and Basalt SRM.

Obsidian Basalt

Na % 3.62 + 0.06* 1.61 + 0.02*

Mn ug/g 395 + 14 1285 + 13

Dy ug/g 5.73+0.59

* indicate 2 standard deviations

150
NON-RRD PROGRAMS

4. Service Analysis

a. Measurement of the Co-60 to Co-59 Ratio in Microparticles

R. F. Fleming and R. M. Lindstrom

If a cobalt-bearing steel is subjected to neutron irradiation and

at a subsequent time the ratio of cobalt-60 to cobalt-59 atoms and the

ratio of iron-55 to iron-54 atoms are measured, it is possible to

determine both the decay time since the end of irradiation and the

neutron fluence to which the particle was exposed. For this purpose,

we developed two methods for the determination of the cobalt ratio and

applied them to particles ranging in mass from 80 ng to 300 yg. The

measurements were carried out at the ORR reactor in Oak Ridge during the

period of the NBSR shutdown.

The first method is the approach of conventional neutron activation

analysis. The sample was irradiated along with a known mass of elemental

cobalt as a standard. The 58.6 keV gamma emitted by the 10.47 minute

Co activity produced was counted using a thin Ge photon detector.

This gave the Co-59 mass. The number of Co-60 atoms was determined by

counting the particle against a Co-60 standard source (SRM-4210) . This

gave the specific activity of the particle as Ci of Co/gram Co.

The direct measurement of the Co/ Co ratio was also done by NAA.

For this, a known mass of cobalt was irradiated along with a Co-60 source

of known activity. In addition to the Co(n,y) Co gamma, we also

measured the activity of the 67.4 eV gamma from the 99 minute Co-61

produced by Co(n,y)

counting system since

produced by Co(n,y) Co. This provided a calibration of the irradiation/

N

61

60

N

59

60m

g59r 60m £ 60m

Q60r 61

e 61

151
NON-RRD PROGRAMS

Xt- where

with

AQ

= ACe

(l-e-h)(l-e"AA)

X6 e -1

X6

X = decay constant

C = net counts in

t = irradiation time

A = live time of count

6 = dead time of count

t^ = time from irradiation end/to start of count

a = activation cross section

T = gammas per decay

e = detector efficiency

The measurement gave the calibration factor (in square brackets) as 0.229

(+ 10%) so that the specific activity is given as

Ci60Co/ ,_ = 264

g

59

Co

61

60m

This second method has the important advantage that all geometry effects

during irradiation and counting are eliminated. This proved to be

crucial in the case of particle D10A which was not visible and hence

difficult to position precisely. The results are given below by both

methods showing excellent agreement, except for D10A for which the direct

method gives the more reliable result.

Particle Weight (yg)

60

co Activity

(yCi)

Ci

6

°Co/gm 59Co

Direct Conventio

G2 300.3 12.8 - 0.91

Dl 66.2 9.30 1.36 1.34

RF 28.0 8.97 10.4 10.2

Gl 15.7 5.58 11.6 11.6

HEX 7-1 134.3* 257 - 19.6

D10A 0.083 2.59 335 282

Estimated from dimensions.

152
NON-RRD PROGRAMS

b. Study of the Selenium Dependancy of Cardiac Mitochondrial

Glutathione Peroxidase

R. Zeisler

Introduction:

Cardiac mitochondria generate significant quantities of hydrogen

peroxide as a byproduct of normal metabolism. This toxic product must,

of course, be disposed of before it causes severe damage to mitochondria

and surrounding organelles. For this reason, the existing defenses of

mitochondria to hydrogen peroxide attack are naturally of interest.

There are two major enzyme classes able to destroy hydrogen peroxide.

Catalase is one of these. This enzyme catalyzes the conversion of two

moles of hydrogen peroxide to one mole each of oxygen and water. The

second class is the glutathione dependant peroxidases. These enzymes

use glutathione to reduce hydrogen peroxide to water. The known gluatathione peroxidases are all soluable enzymes which contain selenium in

their active site. Indeed, tissue activity of this enzyme appears to be

strictly dependant on dietary selenium. This enzyme and its selenium

dependancy is of considerable economic importance as well. Selenium

deficiency leads to diseases of economic importance in pigs, lamb, and

chicken. In most of these cases, the diseases have been associated with

a resultant lack of glutathione peroxidase activity. This enzyme may

also be involved in protection against chemical carcinogens and radiation

damage. In spite of all of this, it is obvious that there are considerable

species variation in sensitivity to selenium deficiency and this has

suggested that other mechanisms of peroxide removal must exist and that

in certain species these mechanisms supplaint the selenium dependant

glutathione peroxidase. For this reason, we have reexamined the whole

problem.

Results:

We have isolated mouse cardiac mitochondria and found them to be

a rich source of glutathione peroxidase. Furthermore, this mitochondrial

activity was unaffected by prolonged selenium deficiency sufficient to

153
NON-RKD PROGRAMS

eliminate the previously described selenium dependant enzyme in the

cytosol. Next we studied distribution within the mitochondria and found

it to sediment with the mitochondrial membrane, not with the mitochondrial

matrix. All of this information suggested that we were dealing with a new enzyme which was membrane bound and not dependent on dietary selenium.

We next took, whole mitochondria, mitochondrial membrane^ and

mitochondiral matrix from normal and selenium deficient animals and

measured glutathione peroxidase activity and selenium content via neutron

activation analysis. The results showed that the deficient animals had

half the selenium concentration of the control animals in each fraction

examined. These results serve to further demonstrate the difference

between this newly described enzyme and the well known selenium dependent

glutathione dependant glutathione peroxidase.

Future Plan:

To finally prove the selenium independance of this enzyme we need

to purify it to homogeniety and show absence of selenium in that

preparation.

c. High Resolution Depth Profiling Using Thermal Neutron Beams

R. F. Fleming and I. G. Schroder (Nuclear Radiation Division)

The joint effort with Sandia Laboratories Albuquerque, NM (Dr. J.

M. Harris) to investigate the use of thermal neutron beams to determine

the amount and depth profile of isotopes such as He-3, Li-6, and B-10 in

metal and semiconductor substrates, has continued.

The depth profiling technique using thermal neutron beams involves

illuminating a target with a beam of thermal neutrons and measuring,

with an energy-dispersive detector (silicon surface barrier), the energy

distribution of the charged particles produced. Since the incident

neutron energy is completely negligible compared to the reaction Q-value

(E ) the charged particles produced are both monoenergetic and isotropic.

Those particles which escape from the sample lose energy along their

exit path at a known rate dE/dx. The energy distribution of these

particles at a fixed escape geometry is measured by a silicon surface

154
NON-RRD PROGRAMS

barrier detector. When subtracted from the initial energy (E ), the

energy loss distribution is obtained, which can be directly related to

the depth distribution of the parent isotope via the known stopping

power. Though the sensitivity, resolution, and maximum depth analysis

vary greatly among isotopes, being dependent upon the reaction cross section and the Q-value, the neutron technique has significant advantages

over conventional charged particle profiling methods such as Rutherford

backscattering, proton- induced x-ray (PIXE) , sputter-auger or ion beam

analysis, especially for low-Z targets. These advantages include: the

non-destructive nature of the neutron beam probe; the spatially uniform

probe efficiency in samples which do not strongly attenuate the neutron

beam; the lack of kinematic broadening so that the target depth distribution

is monotonically related to the exiting particle energy via the particle's

stopping power; and finally, the relative ease and speed of the measurements

as the energy spectrum from an energy-dispersive detector gives a measure

of the entire depth distribution in a single run. The work to date has involved implants of He-3, Li-6, and B-10 as well as actual tritide targets of both ScT~ and ErT

?

. Figure 1 shows an energy spectrum with a "surface" layer of He-3 on a Sc substrate.

Figure 2 shows the broad proton distribution from the He-3 accumulated

in a 1.5 ym thick ErT target. These metal tritides (MT~) are stoichiometrically

loaded with tritium which, as it undergoes its natural 12-year beta

decay, produces the helium-3. These tritides are fabricated as targets

for high yield 14-MeV neutron generators which are used for defense,

medical therapy, and analytical purposes. The buildup of the helium-3

and its migration in the tritide may have a significant effect on the

long term integrity of the neutron targets.

The measurements performed with implantation loaded He-3 targets

15 3 have shown that sensitivities of less than 10 He-3 atoms/cm are possible and that by unfolding the observed proton spectrum and using

the appropriate stopping power, depth resolution of less than 100 A can

be obtained.

155
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In the accompanying table are listed the feasible thermal neutron

induced charged reactions which represent strong candidates for thermal

neutron depth profiling. Along with each reaction and their relevant

characteristics are listed the calculated sensitivity of each based on a count rate of 0.1 cps, a detector solid angle of 1%, and a neutron flux

o of 10 . By far the most attractive candidates are He-3, Li- 6, and B-10

since they are stable and have large cross sections. We have obtained

results for all three reactions. Besides the importance of He-3 in

metal tritides, both He-3 and Li-6 depth distributions are of great

interest to the thermonuclear fusion community for first-wall reactor

design and for diffusion into metals. The distribution of lithium and

especially boron in semiconductors is of course of great concern to the

electronics community. In fact the recent explosive growth of ion beam

depth profiling has been driven primarily by this need. Both Be-7 and

Na-22 are of interest because of their huge cross sections even though

the targets would be radioactive. (The radioactivity has the advantage,

however, of allowing absolute measurement of the number of target atoms

by gamma counting.) The study of sodium diffusion into metals and

glasses is a long standing problem. The Ni-59 reaction would allow

study of nickel diffusion into host metals—the physics of this reaction

has already been thoroughly investigated at the NBSR.

At present, construction of a high purity 10° n/cm2 /sec thermal

neutron beam dedicated to depth profiling at the BT-3 port of the NBSR

has begun. With this beam, the previous work will be continued and many

of the problems associated with table I will be investigated. The

feasibility of the present technique must be demonstrated for radioactive

samples (Be, Na, K) and for those isotopes with low reaction cross sections (N, 0, S, CI) which would be suitable for depth profiling only

for matrices in which they form a major constituent.

157
NON-RRD PROGRAMS

5. Facilities

a. Facilities for Activation Analysis: Counting and Computation

R. M. Lindstrom

A number of gamma- and x-ray detectors are in use for assaying

radioactive samples. These include four first-line detectors (two large

Ge(Li) and two Gamma-X) , five Ge(Li) detectors in the range of 12+2

percent relative efficiency, two special-purpose detectors (Ge(Li) well

and low-energy photon spectrometer), and two older, smaller Ge(Li) detectors

in reserve. Three detectors have automatic sample changers for unattended

counting of series of samples. Data are acquired through six analogdigital converters (ADCs) on an ND6620 computer-based data acquisition

system and through three ND100 and one TN1710 hardwired multichannel

analyzers (MCAs) . Two of the MCAs can be controlled by and transfer

data to and from the ND6620; all have magnetic tape and printer output.

Most data processing is done with the ND6620 system. In addition

to the ADCs the system consists of two display and acquisition (DAS)

terminals, a central processor, 224 kbytes of memory, 10 Mbytes of disk,

7-track and 9-track magnetic tape, two additional terminals, and a fast

printer. The software purchased with the system is used for most work,

and additional programs have been written for ADC assignment, pileup

calibration, linear regression, and weighted mean calculations.

b. Activation Analysis Studies of Archaeological Artifacts

M. J. Blackman

The analysis of archaeological artifacts by instrumental neutron

activation has continued. The goal of these investigations has been to use trace and minor element profiling in provenience studies and to

examine the production and distribution of the various objects. The

materials so far analyzed include ceramics from the southeast and southwest U. S. and from Western Asia; clay samples from the U. S. and Western

Asia; and chert and nephrite from Labrador, Canada.

158
NON-RRD PROGRAMS

PRECISION GAMMA-RAY Ah© X-RAY WAVELENGTHS

E. G. Kessler, Jr., W. C. Sauder, and R. D. Deslattes

(Center for Absolute Physical Quantities)

Gamma- and x-ray wavelengths are measured using two crystal transmission

spectrometers. These spectrometers are unique in the world because (1)

crystals whose lattice spacing has been measured by x-ray/optical

interferometry are used, and (2) angle measuring interferometry of high

_3

accuracy (y 0.5 x 10 sec) and absolute calibration is used. More

experimental details are available in references 1, 2, and 3.

Over the past two and one-half years a significant number of waveV.5

3 4 lengths ' from Au-198, Ir-192, Yb-169, and Tm-170 have been published

along with the W Kol x ray

A measurement of the wavelength of the electron-positron annihilation

radiation (511 keV) has been attempted but failed because of source irradiation and manipulation problems. The positrons which are produced

in the radioactive decay of a Cu-64 source form positronium whose short

lived singlet state leads to a three photon decay. The narrowing of the

annihilation line is accomplished by mixing the singlet and triplet states

in a magnetic field and by thermalizing the positronium in a cryogenic He

6

gas.

Significant changes in the Cu-64 source design and manipulation are being made to insure a successful measurement of this line. Thin sheets

of Cu foil plated with Au appear to be inert in the irradiation thimble

water and should prevent Cu contamination of the thimble water as was previously experienced. A simplified source-manipulator connection should

permit easy insertion of the radioactive source into the He dewar. A

measurement should occur in early 1981.

Some high Z K x rays produced at the 4 MeV electron Van de Graaff

have been measured during the past year. Measurements over a wide Z-range

7 8 permit tests of self-consistent field calculations. ' Because of the

low efficiency of the two crystal spectrometers, only Ka , Koto* Kg , and

Kg transitions can be accurately (< 10 ppm) measured in a reasonable

159
NON-RRD PROGRAMS

time. Measurements of Ag (Z = 47), Er (Z = 68), Au (Z = 79), Pb (Z = 82),

and U (Z = 92) have been made and measurements of additional elements such

as Xe (Z = 54), Ba (Z = 56), Sm (Z = 62), and W (Z = 74) are anticipated.

Also during the past year, final analyses of the shape and energy

of the erbium K absorption edge has been completed. This measurement

was made to provide an energy calibration for kaonic potassium x rays which

9

were studied by Lum and Wiegand of Lawrence Berkeley Laboratory. Because

the 6-5 transition in kaonic potassium is coincident with the erbium K edge,

a measurement of the absorption of the kaonic x rays by calibrated foils

permits the assignment of energies to the kaonic x rays. The mass of the

kaon can be deduced by comparing measured and theoretical values for the

kaonic transition. A kaon mass value accurate to + 110 ppm has been

determined. A joint publication including the kaonic x-ray measurements

and the foil calibration is in preparation.

Accurate higher energy (> 1 MeV) gamma-ray standards are needed for

detector calibration, as standards for relative measurements, and as a possible input to the fundamental constants. The highest energy that we

have directly measured is 675 keV although an energy of 1.1 MeV has been

obtained by summation. Over the next year we plan to extend our measurements

above 1 MeV in order to ensure that accurate high energy measurements are possible using the present crystals and angle measuring techniques.

1. R. D. Deslattes, Proc. Int. School of Physics 'Enrico Fermi', Course

68 (1978).

2. R. D. Deslattes, E. G. Kessler, Jr., W. C. Sauder, and A. Henins,

Annals of Physios (to be published)

.

3. E. G. Kessler, Jr., R. D. Deslattes, A. Henins, and W. C. Sauder,

Phys. Rev. Lett. 40, 171 (1978).

4. E. G. Kessler, Jr., L. Jacobs, W. Schwitz, and R. D. Deslattes,

Nuol. Instr. and Meth. 160 , 435 (1979).

5. E. G. Kessler, Jr., R. D. Deslattes, and A. Henins, Phys. Rev. A

19, 215 (1979).

160
NON-RRD PROGRAMS

6. W. C. Sauder and R. D. Deslattes, Jour. Res. NBS 71A, 347 (1967),

7. R. D. Deslattes, E. G. Kessler, Jr., L. Jacobs, and W. Schwitz,

Phys. Lett. Ilk , 411 (1979).

8. K-N. Huang, M. Aoyagl, M. H. Chen, B. Crasemann, and H. Mark, At.

Data Nucl. Data Tables 18, 243 (1976).

9. G. K. Lum and C. E. Wiegand, Bull. Am. Phys. Soo. 23, 64 (1978).

MASS ASSAY OF STANDARD DEPOSITS

D. M. Gilliam and W. E. Slater

(Nuclear Radiation Division)

The NBS collection of fissionable deposits includes four fissile

isotopes: U-235, Pu-239, U-233, and Pu-241. An archive deposit with

mass in the 10- to 300- microgram range is maintained for each isotope.

For both U-235 and Pu-239, the standard deposit mass has been determined

to an accuracy of + 0.5%, or better, by two independent techniques:

isotope dilution mass spectrometry (IDMS) and absolute alpha counting.

However, for the Pu-241 and U-233 deposits, no IDMS analysis is yet

available to confirm the alpha assay. A second assay path for Pu-241

and U-233 was needed, and the path of comparison to the more accurately

known U-235 and Pu-239 deposits in a monoenergetic thermal neutron beam

was selected.

A 35-meV beam from a crystal spectrometer—filtered by oriented

graphite to exclude the A/2 impurity—was chosen for the comparison.

ENDF/B-V cross sections were used for conversion of fission rate ratios

to mass ratios. The results are tabulated in the table.

161
NON-RRD PROGRAMS

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162
NON-RRD PROGRAMS

REACTOR FILTERED BEAMS

Robert B. Schwartz

(Nuclear Radiation Division)

Neutron response as a function of energy was determined for the

neutron personnel dosimeters used at the Battelle Pacific Northwest

Laboratory and at Argonne National Laboratory. The measurements were

made using the thermal, 2 keV, 24 keV, and 144 keV beams at the NBS

reactor, and with the Cf-252 spontaneous fission source. These measure- ments will allow the dosimeter readings to be interpreted properly once

the neutron spectrum in the working environment is known.

USE OF THE THERMAL COLUMN AT THE NBS REACTOR TO DETERMINE

THE EFFECTIVE MASS OF U-235 IN A MINIATURE FISSION CHAMBER

E. D. Mc Garry

(Nuclear Radiation Division)

In support of the Light Water Reactor (LWR) Pressure Vessel

Surveillance Dosimetry Improvement Program,* absolute core-power measurements were made in a research reactor** at the Oak Ridge National Laboratory

(ORNL) . The reactor power was deduced from extensive measurements of

the fission rate of U-235 in a miniature fission chamber that was inserted

down between the fuel plates in the core. The reactor power measurements

were a cooperative effort of ORNL, NBS and the CEN/SCK Laboratory in

Mql, Belgium, The NBS function was to provide a measurement of the

amount of U-235 in the fission chamber.

(*) The U.S. Nuclear Regulatory Commission's LWR-PV Surveillance Dosimetry

Improvement Program administered for the NRC Metallurgy and Materials

Research Branch by the Westinghouse-Hanford Engineering Development

Laboratory, Richland, Washington.

(**) The subject reactor is the Pool Critical Assembly (PCA) located in

the canal of the Bulk Shielding Reactor (BSR) at ORNL.

163
NON-RKD PROGRAMS

The method used to deduce the mass of U-235 in the miniature chamber was to compare its fission rate in a neutron field with that of another

chamber containing a known mass of U-235. The neutron field chosen for

this investigation was that in a 30-cm cavity within the graphite

thermal column of the NBS reactor. (See figure 1.) The following

paragraphs discuss why the mass sought is an effective mass rather than

the true absolute mass of U-235 in the miniature chamber.

First, the two chambers have different geometries. The miniature

chamber, used for the power measurements, is a high-pressure, ionization

chamber containing a few micrograms of U-235 in a cylindrical geometry

1.5 mm in diameter, 10 mm in sensitive length and 1.2 m in overall

length. The NBS chamber is a dual, parallel-plate type ionization

chamber which can accomodate two light, 1.25 cm-diameter deposits of

fissionable material on thin (5-mil thick), back-to-back discs of platinum

or other suitable materials. The NBS chamber is shown in figure 2 and

described in detail in reference 1. Because of the big difference in

size, the possible perturbation of the flux by the NBS chamber was

examined in detail. The effect of field gradients on repositioning, or the relative positions, of the chambers was also examined.

The effects of relative spatial locations, as well as chamber

perturbations, were investigated with a mockup of the NBS chamber

through and around which the miniature CEN/SCK could be positioned.

Table 2 shows where measurements were taken and fiugre 4 shows the

results. The perturbation at the CEN/SCK chamber, because of the presence

of the NBS chamber, is approximately 2% and of the same magnitude whether

the smaller chamber is inside of or along side of the NBS chamber.

Therefore, a measurement configuration was then chosen with the CEN/SCK

chamber beside the NBS chamber so that the perturbation at the smaller

chamber was the same as at the center of the mockup . This means the

perturbation is the same as that at the NBS deposits in the real chamber.

The chamber perturbation therefore cancels from the fissionrate ratio

measurements to within +0.3% uncertainty.

164
NON-RRD PROGRAMS

However, the flux perturbation issue is more complex because there

is also a flux perturbation by the 5-mil platinum backing on each deposit, none of which were included in the mockup chamber. Only one deposit on platinum was used for the fission-rate comparison measurements. The

perturbation because of this backing was estimated anaytically to be 2.5

+1.5% and the ratios must be adjusted for this perturbation.

Also, there is an unmeasurable perturbation by the nominal 10-mil

steel walls of the CEN/SCK chamber. However, this perturbation is common

to both the measurements in the NBS thermal column and to the reactor

power measurements at ORNL, at least insofar as the neutron spectra are

similar. Because the perturbation is small, on the order of + 2%, it

has been assumed that to + 0.5% it cancels from both NBS and ORNL measurements. This perturbation is, therefore, implicitly included in the

effective mass of U-235 in the miniature chamber.

The last reason for measuring an effective mass is related to the

shape of the voltage pulse-height distribution from the fission chamber.

Figure 3 shows this distribution in the NBS chamber for two different

deposit thicknesses. When the "valley" between the noise and the bulk

of the distribution is well defined, and the peak-to-valley ratio is

large, essentially all fission events can be counted because their pulse

heights exceed a discriminator set anywhere in the valley. When the

valley is not well defined, the fraction of true fissions counted is a function of the discriminator setting. This is the situation with the

miniature chamber so its relative effective mass is a function of the

discriminator setting. (See figure 5.) This effect produces less than

+0.2% uncertainty in the effective mass determination.

Final results of the measurements are summarized in table I and the

paragraph following the table.

165
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r'JED.

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Line of Motion

L

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Positioning Tube

I I I I I I A B C D E F

Positions at which CEN/SCK

Chamber measurements were made.

I Table 2. Mockup of the NBS fission chamber with a through hole for the

CEN/SCK miniature cylindrical fission chamber.

Positions at which CEN/SCK chamber measurements were made

A. Full in Position . . . The tip of the CEN/SCK chamber

at this point is 1 1/4" beyond the

front edge of the NBS dummy

chamber.

. . Tip is 1/2 way between A & C.

. . Tip is flush with front edge of NBS

dummy chamber.

Tip is really 1/2 way between the frontand back-edge positions, which should mean

tip is in middle of chamber.

. Tip of CEN/SCK chamber is flush with end

of positioning tube.

2nd Half Way Point . . . Tip is 1/2 way between positions

E & G.

Full Out Position . . . Tip is inside positioning tube

1 1/4" behind back edge of dummy

chamber.

B.C.

1st Half Way Point

Front Edge . .

D. Middle

E.

F.

G.

Back Edge

*Note: It is estimated from handling experience that CEN/SCK chamber can be repositioned at a point in the cavity to + 2.5 mm.

167
NON-RRD PROGRAMS

Channel for Boral Curtain

Concrete 14" Lead

Bismuth

Figure 1. Plan view of a 30-cm cavity in the graphite of the thermal

column of the NBS reactor. The cavity, when empty as shown,

provides a region of isotropic thermal flux for miscellaneous

irradiations and flux to drive two U-235 fission sources,

positioned at the opposite ends of a cadmium pill box, for

irradiations in a U-235 fission spectrum. The cavity may

also be loaded with a B-10 shell inside of which exists the

Intermediate-energy Standard Neutron Field (ISNF), a standard fast reactor type of spectrum.

Figure 2. NBS fission chamber which normally contains two back-to-back

fissionable deposits on 5-mil thick steel backings. For the

subject measurements only one deposit was in the chamber.

This reduced the amount of thermal flux depression in the

vicinity of the deposit.

168
NON-RRD PROGRAMS

~i

1 r

• HEAVY DEPOSIT

196 >,g/cm 2 •LIGHT DEPOSIT 4^g/cm 2

| II I I I I I | I

I

I I

20 v 40 v 60 80 VPF . K 120 V I40 200 300 400 PULSE HEIGHT (CHANNELS)

OBSERVED PULSE HEIGHT DISTRIBUTIONS FROM DOUBLE FISSION CHAMBER

Figure 3. Observed pulse height distributions from double fission

chamber.

DATA "SHADOWED" BY CHAMBER

1ST DATA SET. NO MOCKUP NBS CHAMBER

BUT TUBING AFTER 1.28 INCHES. 2ND DATA SET. NBS MOCKUP CHAMBER

NEXT TO CEN/SCK CHAMBER BUT NO

TUBE AFTER 1.28 INCHES.

DISTANCE IN INCHES FROM CAVITY CENTERLINE (<g "0" Inches) (Negative Values Indicate Positions Further From Reactor) Figure 4. U-235 fissions in NBS 30-cm spherical, thermal column

cavity with curtain down.

169
NON-RRD PROGRAMS

1.04 i1.03

<

o

LU

1.02

1.01

1.00

T

1%

1

_L _L

0.1 0.2 0.3 0.4 0.5 0.6 DISCRIMINATOR SETTING (Fraction of Peak Location)

0.7

Figure 5. Effective U-235 mass versus discriminator setting for CEN/SCK

fission chamber #1879.

The average value in table I, 6.444 + 0.17%, must be corrected for fission

fragment absorption in the 31.2 ug NBS deposit and in the nominal

4.7 yg CEN/SCK deposit. The correction factor is 1.001172/1.00043 = 1.00129 + 0.00032. As mentioned, the ratio also has to increase by

2.5% + 1.5% because of perturbation in platinum in the NBS chamber. The

resulting ratio is 6.614. To the statistical uncertainties of 0.17%, and

1.5% systematic uncertainties +0.5% must be added to account for possible

non-cancellation of the previously described perturbation effects. There

is also the additional 0.2% uncertainty associated with the discriminator

settings. Because of the nature of these various uncertainties, they

tend to add in quadrature and the final ratio is 6.614 + 1.6%.

170
NON-RRD PROGRAMS

Based upon a measured consensus mass of the NBS fission deposit

(No. 25A-03-1) of 31.22 micrograms + 1.4%, the effective mass of the

CEN/SCK miniature fission chamber used for absolute PCA core-powder

measurements is:

31.22 + 1.4%

= 4.72 + 2.1% micrograms U-235

6.614 + 1.6%

The associated discriminator setting for this result is 0.54 of the

maximum of the pulse height distribution.

1. J. A. Grundl and D. M. Gilliam (NBS), N. D. Dudey and R. J. Popek

(ANL) "Measurement of Absolute Fission Rates", Nuclear Technology

25, 237 (February 1975)

.

DYNAMIC SCATTERING FROM POLYMER SOLUTIONS

A. Z. Akcasu and M. Bermounz

(University of Michigan, Ann Arbor, MI)

and

C. C. Han

Polymer Science and Standards Division

Quasi-elastic neutron and light scattering experiments on polymer

solutions have been used increasingly in recent years to study polymer

solution dynamics . In these experiments one measures the intermediate

scattering function S(qjt) as a function of time t for different values

of the momentum transfer, q. The measurement of S(q3 t) directly by

neutron scattering has been possible only very recently with the appli2 cation of the spin-echo technique . Interpretation of such scattering experiments requires, ideally,

a theory that can predict S(q3 t) as a function of t and q under actual

experimental conditions, which are characterized by the temperature and

171
NON-RRD PROGRAMS

concentration of the solution, and by a chain model consistent with the

chemical structure of the polymer. Unfortunately, exact expression of

S(q3 t) is available, at present, only for a single unperturbed (0-

condition) Gaussian chain without hydrodynamic interaction (Rouse model)

,

and in the infinite chain limit, with hydrodynamic interaction and preaveraged Oseen tensor (Rouse Zimm model) . In this sense, a complete

interpretation of dynamic scattering experiments on polymer solutions is an unsolved problem.

Some progress has been possible via knowledge of the asymptotic

behaviour of S(q 3 t) for large and small times, and in certain ranges of

^-values. It is known that S(q3 t) decays exponentially after large

2

times with a decay constant, Dq where D is the diffusion coefficient

of the polymer as a whole. Hence, D is determined readily by fitting

an exponential function to S(q3 t)-data for sufficiently large t. This

procedure v is workable only when q'R « 1, where R is the radius of

9 9

gyration of the polymer. When this condition is not satisfied S(q3 t)

decays below the noise level before the asymptotic exponential behaviour

is reached. This is due to the contribution of the internal modes to

the relaxation of S(q3 t) during the experiment. One may extend the qrange of the above procedure to larger q-values by representing S(q3 t) as superposition of two exponentials to take into account the effect of

the most slowly decaying internal mode, as suggested by Pecora '

. However, one finds that the range of (^-values and the time interval in which

only the first internal mode is important are very narrow, as we have

demonstrated. The effect of the internal modes during the experiment

becomes important all at once when R >2-3 and thus makes the measurement

of the decay constant of the first internal mode very inaccurate, if not

impossible.

In the intermediate q'-region defined by qR >>1 and qa«l, where a

is the statistical segment length, the relaxation of S(q3 t) is determined

by all the internal modes collectively. Using an unperturbed single

172
NON-RKD PROGRAMS

gaussian chain model, de Gennes , and Dubois-Voilette and de Gennes

showed that S(q3 t) can be expressed as a function of a single variable

t^9.(q)t in the double limit of qa->0 and qR -+x. They referred to the

scaling factor, ti(q) , as "characteristic frequency", and found that

Q.(q)~q in the Zimm limit. This property of S(q3 t) has been used to

2 7 interpret scattering experiments ' in the intermediate (^-region by

fitting the shape function, calculated for the unperturbed Gaussian

chain, to S(q3 tj-data, obtaining Q,(q) as function of q, and representing

ti(q) by a power law q to see whether the exponent a deviates from the

theoretical value 3. One difficulty with this procedure is that the

conditions qa«l and qR >>1 are usually not strictly satisfied in an experiment. In the small- and large-q ends of this interval, the

molecular and segmental diffusion effects, respectively, become increasingly important. In addition, S(q3 t) displays, as a function of time,

a cross over from Rouse-like behaviour to Zimm-like behavior at a finite time. This cross over time is inversely proportional to

4

t(C /n a)/qa] where (?Q

/Ti a) is the draining parameter, £ is the friction

coefficient per monomer, and nQ

is the viscosity of the solvent. Although

the Zimm behavior is always reached asymptotically after sufficiently

long times, it may not always be attained before S(q3 t) decays below

the noise level during an experiment. One final difficulty with the

above approach is that the characteristic frequency, obtained in an experiment in which the conditions qa«l and qR >>1 are not quite sat-

& 3 isfied, does not have to obey strictly a simple q -power law as predicted

by the asymptotic theory.

In this paper we propose an alternative method for the interpretation of scattering experiments in terms of the initial slope tt(q) of

the normalized intermediate scattering function^) (q3 t)*S(q3 t)/S(q3 Q) , and a q-dependent shape function f(t3 q). The initial slope is defined

by:

tt(q)=-llm dA(q,t)/dt (1)

173
NON-RRD PROGRAMS

The short times involved in this definition are larger than the memory

times of the solvent. We anticipate that the dynamics of the chain will

be governed by a diffusion equation in which the solvent effects are averaged out.

The shape function is introduced through:

i($(q,t)zexp[f(Qt3 q)]

Clearly, f(O3 q)=0 and

df(t3 q)

dt

= -1.

t=0

In the small- and large-q limits, f(t3 q) behaves as f(t3 q)^t3 since (A (q3 t) decays exponentially in these ^-ranges. In the mathematical limit of qa-H) and qR -* °°, it becomes a function of t only, and Q

coincides with the characteristic frequency introduced by Dubois-Violette

and de Gennes

.

One of the merits of the present approach is that the initial

slope Sl(q) is calculable for all values of q as a function of temperature

8 9 and concentration, in terms of the "blob" model of chain statistics '

. Thus, in an experiment, one is no longer restricted only to narrow

asymptotic q-regions and dilute solutions at (9-condition . The main

difficulty with this method, however, is that the initial slope is hard

to measure in the intermediate q-range. We avoid this difficulty by

providing the shape function f(t3 q) as a function of t for several values

of q in this as well as other ^-regions, and for a few values of the

draining parameter (£ / r\ a). By comparing these theoretical shape functions

with the experimental lnrf\(q3 t) one can determine simultaneously both

the initial slope Q,(q) and the statistical segment length a, or the

radius of gyration, R , depending on the range of q-values involved.

The experimental U(q) can thus be compared with its theoretical expression that includes concentration and temperature effects. The tacit

assumption in this procedure, as well as those used earlier, is that the

shape function is less sensitive to temperature and concentration effects

174
NON-RRD PROGRAMS

than the initial slope, so that it can be approximated by its expression

for a single Gaussian chain in O-condition.

In Reference 10, we have obtained theoretically various formulations

of the scattering function Q/(q3 t) . We have calculated the exact expressions of Qf (q3 t) for simple chain models. We also calculated directly

the initial slope Q,(q) for various chain models and experimental conditions

,

Finally we explained a procedure the the interpretation of both neutron

and light scattering experiments using the above mentioned results, with

application to real light scattering data on polystyrene in toluene.

.

1. For example: (a) Chu, B. "Laser Scattering", Academic Press,

(1974); (b) "Photon Correlation and Light Beating Spectroscopy",

(Ed. H. Z. Cummins and E. R. Pike), Plenum Press, (1974; (c) Berne,

B. J. and Pecora, R. "Dynamic Light Scattering", Wiley, (1976).

2. Richter, D. et al, Phys. Rev. Lett. 1978, 41, 1484.

3. Pecora, R. J. Chem. Phys. 1965, 43, 1562.

4. Pecora, R. J. Chem. Phys. 1968, 49, 1032.

5. de Gennes, P. G. Physics, 1967, 3, 37.

6. Dubois-Voilette, F and de Gennes, P. G. Physics, 1967, 3, 181.

7. Adam, M. and Delsamo, M. Macromolecules , 1977, 10, 1229.

Daoud, M. Thesis, Universite de Paris 1977.

Larnous, B. et al, Physics, 1978, 39, 77

Akcasu, A. Z., Benmouna, M. and Han, C. C, Polymer (in press).

175
NON-RRD PROGRAMS

SMALL-ANGLE NEUTRON SCATTERING ON ATACTIC POLYSTYRENE

WITH HIGH LABELED CHAIN CONCENTRATION

S. J. Bai

(Reactor Radiation Division/ University of Michigan)

and

Charles C. Han and David J. Lohse

(Polymer Science and Standards Division)

The application of small-angle neutron scattering (SANS) to polymer

systems has been following the approach of light and x-ray scattering.

In the determination of single molecular chain behavior, low labeling

chain concentration is usually required to minimize the contribution due

1 2

to multi-chain interference. Recently, it has been pointed out ' that

because of the uniqueness of isotope labeling technique multi-chain interference can be accounted for and subtracted from the neutron measurement.

Thus, high concentration of labeled chain can be used for SANS investigation

provided the labeled chain and the un-labeled chain can be treated as identical except their scattering lengths.

For bulk atactic polystyrene (PS), the coherent elastic differen3 tial cross section reduces to

S(Q) = C(l-C)(bH-b

D

) 2

S

g (Q) + [Cb

D + (l-C)bH

] 2

S

T

(Q) (1)

where C is the labeled chain concentration, b and b are the scattering

lengths of hydrogenated PS (PSH) and deuterated PS (PSD) monomers,

respectively. S (Q) is the single chain form factor.

s

S (Q) is the total form' factor of the whole system.

&• (&)+£,. -4-4'A (3)

where R. is the CM. position of the i-th chain, and J_. , is the position

of the i'-th monomer of the i-th chain relative to R. . The bracket

176
NON-RRD PROGRAMS

denotes an ensemble average over all accessible states of the system.

It is shown in Eq. (1) that two bulk PS samples with different labeled

chain concentration would generally be sufficient to obtain S (Q) from

their coherent scattering intensities.

For all molecula

in the low-Q region by

For all molecular chain configurations, S (Q) can be approximated

s

s i(Q)

-i„(1 + <L_|L_) W

where Rg is the radius of gyration of the molecular chain. The slope

-1 2 of S (Q) versus Q reveals Rg which used to understand the distribution

of the chain configuration. For polymer chains in a e-solution, the

molecular chains assume a random distribution with a simple relation

between the molecular shape and the molecular weight. This relation is

Rg * Mw

0,5

(5)

where Mw is the molecular weight of the polymer.

In our experiment, PSH and PSD of approximately matched molecular

weights of 9500 and 32,000 were used. The PS species were co-dissolved

in p-xylene with PSD/PS ratio from zero to 0.30. The solvent was removed

by freeze-drying. PS mixtures were then molded to become bulk samples

close to 0.065 cm thick. Neutron measurements were performed on BT5(NBS)

SANS spectrometer. The Q-region was extended from about 0.012 A to

0.097A

)_1

. Figure 1 -12 is an example of measured single chain form factor S (Q)

S presented as S (Q) versus Q . In this case, PSD/PS concentration C

is 20 percent, and PS molecular weight Mw is 32,000. From the slopeintercept treatment of the low-Q region of figure 1 we obtain an Rg of

48X.

Our values of Rg are shown as open triangle (A) in figure 2, which

is a collection of SANS on PS results. Symbols correspond to 0-solution

of PSD in cyclohexane at 36°C (+) , bulk PS with low C (o) , and bulk

PS with high C (o) .

177
0.8 i0.6

NON-RRD PROGRAMS

<_ 0.4

O

en

(/) \

0.2

• •

0.012

Figure 1,

500 1-

200

K ioo

50 DC

!0

101LL J L I I 10

2 5 a 2 5

10 10 : 5 „« 6

10

M w

Figure 2

.

178
NON-RRD PROGRAMS

It is evident from our results that small molecules, with countour

length as small as 250A, of bulk PS still preserve a configuration with

random distribution. Also the validity of the high labeled chain con- centration approach is demonstrated when the labeled chain and the unlabeled chain can be identically treated and have similar molecular

weight. This greatly facilitates SANS experiment which has been limited

by the comparably small flux from all available neutron sources. We are presently extending this study to PS-cydohexaire solutions

in both dilate and semidilate regions. Our emphasis is centered on the

question of chain expansion with finite concentration of "6-temperature",

1. C. Williams et al. , J. Polym. Soi.: Polym. Lett. Ed. 3 17, 379

(1979).

2. A. Akcasu ejt al_. , J. Polym. Soi.: Polym. Phys. Ed. 3 18

(1980) .

3. G. C. Summerfield, J. S. King, and R. Ullman, J. Appl. Cryst.j 11,

548, (1978).

4. P. Debye, J. Phys. Cehm. 3 51, 18 (1947).

5. P. Florg and J. Rehner, J. Chem. Phys. 3 11, 512 (1943).

6. J. P. Cotton et al. , Macromolecules3 7, 863 (1974).

7. J. S. King et_ al. , (to be published).

179
NON-RRD PROGRAMS

EVALUATION OF NEUTRON SPECTRUM IN THE INTERMEDIATE-ENERGY

STANDARD NEUTRON FIELD

J. Grundl and C. Eisenhauer

(Nuclear Radiation Division)

Specification of the neutron spectrum for the Intermediate-Energy

Standard Neutron Field (ISNF) was completed this year. Included are error bounds for the spectrum over its full energy range and also

propagated uncertainties for most of the neutron reaction rates which

have been or will be measured in the system. The spectrum evaluation

was based on an exhaustive study of the spectrum sensitivity to physical

and nuclear parameters of the system and was backed up by density and

chemical impurity determinations and neutron beam transmission measurements.

Table 1 shows the effect on the ISNF spectrum of variations in the

important physical parameters of the system. Ratios of the perturbed

spectrum to the standard ISNF spectrum are given in 14 energy groups

for the indicated variation in each parameter. Correlations of the

spectrum changes associated with the parameter uncertainties showed an unexpected pattern of errors for the neutron reaction rates. Table 2

shows the effect of variations in the physical parameters on the

calculated reaction rates in ISNF. Variations in the scattering properties

of carbon, which would be expected to have effects at low energies,

produce significant variations in threshold reaction rates such as U-238

(n,f). Typical reaction rate errors attributable to ISNF spectrum

uncertainties are in the range + 0.5% to + 1.4% exclusive of fission

spectrum uncertainties; with fission spectrum uncertainties included

the errors are + 0.6% to + 2.5%.

180
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182
d. Reactor Operations and Services

Shortly after the beginning of this reporting year, a mechanical

problem which developed with one of the shim arms forced an extended

reactor shutdown of nearly seven months. The problem was finally traced

to a swelling of the cadmium blade which necessitated replacement of all

four blades. The replacement process, which had never been done before,

proved to be both difficult and complex because everything had to be

done remotely due to the highly radioactive components and environment

involved. In addition, a great deal of preparation had to be made including preparation of methods and procedures, design and construction

of heavy shield cask, design and fabrication of tools and equipment,

and fabrication of critical replacement parts.

The old shim arms were the original installed in the reactor

during construction more than 12 years before. They had already lasted

significantly longer than expected due to a very effective fuel management program. The blades had approximately two more years lifetime and were scheduled for replacement in 1981 during the conversion to 20 MW.

The shim arm replacement operations were performed entirely in-house.

They were carried out smoothly and efficiently and with absolute safety.

There was little or no exposure to personnel.

During this period several other major tasks were undertaken. They

included inspection of the reactor internal piping and overhaul of the

fuel transfer system. A new fuel element design was installed in the

reactor that will provide even greater fuel utilization efficiency,

already one of the best in the country. Significant progress was made

towards reactor modernization including procurement of a new cooling

tower and design of all new or modified systems.

1. Reactor Operations

Reactor operating schedule was curtailed last year due to the

replacement of the shim arms. Most of the effort of operations and

183
REACTOR OPERATIONS AND SERVICES

engineering personnel was directed towards returning the reactor to

normal as quickly as possible. A summary of overall statistics is presented in the following table for the period July 1, 1979 - June 30, 1980.

NBSR OPERATING SUMMARY FY 80

No. of days at 10 MW 122

On-line time at 10 MW 33%

Average U-235 burnup 50%

No. of Irradiations 1160

Hours of Irradiations 1600

Hours per Irradiation 1.4

2. Irradiation Services

During the short period the reactor operated last year there was perhaps the heaviest use of irradiation facilities in the history of the

reactor. Activation Analysis continued on a large scale. Among these

are analyses of foods, drugs, environmental samples, forensic investigation, development of energy resources and raw materials, and the production of important standard reference materials.

Among new programs that have been initiated are the establishment

of a National Environmental Sample Bank and ultraprecise analysis of

atmospheric samples from all over the world. Discussions are also

underway with NIH, the National Naval Medical Center, and Johns Hopkins

for the production of fluorine-18 in a pioneering program for direct

study of functions of vital organs and human cells.

3. Engineering Services

Aside from the engineering support provided to reactor operations

and experimenters, engineering services was heavily involved in three

major areas. These are the successful resolution of the shim arm problem

and subsequent replacement, reactor modernization, and procurement and

inspection of new fuel elements for future reactor use. The shim arm problem was probably one of the most demanding ever encountered in the operating history of the NBSR. Extensive engineering,

184
REACTOR OPERATIONS AND SERVICES

design, fabrication, machining, and procurement were required. Engineering services personnel were also involved in several aspects of the

actual replacement and installation of components, all performed remotely

under-water. The careful planning and conduct of all operations resulted

in the smooth and efficient reassembly and reinsertion of the new assemblies into the reactor. These were perhaps the most crucial and potentially

damaging operations of the entire project.

Production of the new fuel element design was started this year and

the first batch of elements were inspected, accepted, and delivered in

time for use in the reactor.

Significant progress was made towards the reactor modernization.

The new cooling tower design was completed and a contract was awarded

for construction in the summer of 1980. Similarly the cooling tower

basin design was finalized and construction has already started. Design

of the extensive secondary piping, relocation of pumps, and a new chemical treatment center was also completed. A portion of the new secondary

system is already in place with the balance to be completed once the new

cooling tower is installed. All electrical connections design and specifications were also finalized. A comprehensive design plan of new

nuclear, process, and monitoring instrumentation has been prepared. Most

of the components and equipment have been specified and obtained. These

will be assembled, tested, and installed periodically whenever reactor

shutdown permits.

185
E. Service Programs

ACTIVATION ANALYSIS PROGRAM OF THE

FOOD AND DRUG ADMINISTRATION AT THE NBSR

W. B. Stroube, Jr. , W. C. Cunningham, and M. Allegrini

(Food and Drug Administration, Washington, DC)

Neutron Activation Analysis (NAA) work performed by the Food and

Drug Administration (FDA) is conducted in the reactor building located at

the NBS. NAA has been used by the FDA for trace metal analyses of materials

such as foods, drugs, and plant and animal tissues. The NAA group conducts

research projects, provides services (such as analyses of special samples,

when required information cannot be obtained from FDA field labs) and

participates in interlaboratory studies. Since data obtained by NAA is

complementary to other analytical techniques, sustained interactions with

other FDA groups occur. Examples of two projects performed within the

past year by the NAA group are discussed below.

1. Analysis of Sewage Sludge

Municipal sewage sludges have increasingly been used as crop

fertilizers. Since sewage sludge contains high levels of many elements

which have either toxicological or nutritional significance, questions

have been raised concerning the practice of allowing food animals to

graze on cropland to which sewage sludge had previously been applied.

The Department of Animal Sciences at Colorado State University

conducted a study on cattle which were fed a diet containing a substantial

amount of sewage sludge. The purpose of this study was to determine

whether the addition of the sludge to the diet caused the levels of certain

metals to be altered in various tissues. The data obtained indicated

that the levels of some elements were elevated in some tissues from

cattle which had been fed the sludge.

Recently, the FDA Metals Group has combined the efforts of

Inductively Coupled Plasma (ICP) and NAA to obtain information for many

FDA visiting scientist from Institute of Food Science, University of

Pavia, vai Taramellis-Pavia, Italy.

186
SERVICE PROGRAMS

additional elements in the cattle tissues. Liver, kidney, spleen, brain

and muscle tissue samples (from both control and experimental cattle)

were analyzed, as well as the control and amended diets, feces from the

control and experimental cattle, and the undiluted sewage sludge.

Agreements between ICP and NAA data were very good. The data indicated

that the levels of Pb and Cd in kidney and of Pb, Cd,and Cu in liver

in the human consumption of these tissues to be of concern on a regular

basis. Most elements, however, were not raised to high enough levels

to cause alarm.

2. Determination of Iodine

The deficiency of dietary iodine has been shown to cause goiter.

In recent years, however, there has been some indication that excessive

iodine intake can contribute to thyroid disorders in susceptible individuals,

While excessive iodine intake does not appear to be a problem elsewhere,

recent reports show an increasing iodine consumption by the people of

North America. Therefore, it is important to be able to monitor iodine

levels with good accuracy and precision.

Radiochemical NAA is currently being used to determine the average

daily iodine intake of Americans. This is being accomplished by analyzing

food samples collected at many locations throughout the United States.

Provisions are made for three age groups - infant (6 mo.), toddler (18 mo.)

and adult. The iodine intake is being determined for each age group.

The analysis technique being used is a modification of the combustion

2 and gas phase separation procedure reported by Rook. Parameters in this

procedure were modified to improve iodine recoveries and analytical

precision from the sample matrices of this study. Parameters which were

modified include the size of the hydrated manganese dioxide (HMD) trap,

I

the quantity of iodine carrier, the oxygen flow and the heating temperature

of the HMD trap.

The modified method was tested with ten different food composites

in order to evaluate the matrix influence. Recoveries were found to be

95% with a 3% coefficient of variation, indicating that the separation

187
SERVICE PROGRAMS

does not depend on the food matrix. The performance of the method has

been tested using NBS standard reference materials without certified

iodine values. The average concentrations and standard deviations

(dry weight) found with five determinations each were: Spinach (SMR 1570)

1.325 + 0.055 ug/g; Oysters (SMR 1566) 3.209 + 0.134; Bovine Liver

(SMR 1577) 0.249 + 0.012 ug/g. All NBS reference materials were dried

in an oven at 100°C 24 hr prior to analysis.

To date, approximately 200 composite food samples have been assayed.

Since additional samples are being analyzed and the data obtained to date

have not been fully studied, results are preliminary. The daily adult

intake, based on the levels found in the composites and assuming a 3900 Kcal

caloric intake, ranges between 268 and 1212 ug/day.

1. Kenneth W. Boyer, John W. Jones, Douglas Linscott, Steven K. Wright,

William Stroube, and William Cunningham, manuscript submitted to

Journal of Toxicology and Environmental Health, July 1980.

2. H. L. Rook, J. Radioanal. Chem. 39, 351 (1977).

188
SERVICE PROGRAMS

U.S.G.S. ACTIVATION ANALYSIS PROGRAM

P. A. Baedecker and J. W. Morgan

(U.S. Geological Survey, Reston, VA)

1. Instrumental Neutron Activation Analysis

a. The Geological Survey has an ongoing program of Automated INAA

which provides data for 24 to 30 elements in 3000 to 4000 rock mineral

and coal samples per year. The technique is applied to studies related

to: 1) the characterization of tectonic setting; 2) magma chamber

eruptive sequences; 3) trace element partitioning to study petrologic

history; 4) mechanisms of ore deposition; 5) alteration studies; 6) the

formation of Mn nodules and metal rich sediments; 7) the origin of coals

and peats; 8) compilation of a baseline of coal compositions; and 9)

trace element studies to assist other geologic and geochemical investigations

During the past year the Georgia Tech Research Reactor was used during

the six month period that the NBS reactor was shut down. Epi-thermal

irradiation using the JEEP-II reactor in Kjeller, Norway are used for

the analysis of rocks with high Uranium and/or Phosphorous contents.

b. The INAA procedure is being applied to the analysis of microscopic

metal grain from chondrite meteorites , and to characterize iron meteorites

collected in Antarctica in association with the Smithsonian Museum of

Natural History.

c. A review of computer methodology in the analysis of gamma-ray

2 spectra has recently been completed.

2. Radiochemical Neutron Activation

a. Group separations of rare earth elements (REE) U.S.G.S. standard

rocks. The group separation method is being applied to U.S.G.S. standard

rock in which REE abundances are near or below the limits of detection

of our INAA procedure.

b. Mafic and ultramafic rocks and separated minerals.

We continue to supplement our INAA determinations by group separations

in those materials where REE abundances are very low.

189
SERVICE PROGRAMS

c. Ultra trace determinations of siderophile and volatile elements

in meteorites, and in lunar and terrestrial rocks

Separations. Our current suite of siderophile elements (Au, Ge,

Ir, Ni, Os, Pd, Re) is being extended by including separation steps for

Ru (distillation) and Pt (anion exchange)

.

Lunar green glasses. Mafic and ultramafic glass spheres found on the Moon tend to have surface-correlated enrichments of volatile and

siderophile elements. Last year, we showed that the siderophile element

pattern in Apollo 17 black and orange glasses resembled that of a II B

3 iron meteorite. Currently we are studying the bulk content of these

elements in surface etched Apollo 15 green glasses (in conjunction with

Roman Schmitt of Oregon State University) and also plan to extend the

study to unetched specimens.

Lunar and terrestrial ultramafic rocks. Our study of a suite of

4 5 terrestrial ultramafic rocks is now complete ' and we intend to accumulate

a similar data set for the few lunar ultramafic rocks available.

Strangways Crater, Australia. A suite of samples of impact melts

and country rocks from the Strangways crater have been analyzed for

siderophile and some volatile elements. The signficant enrichments of

Ni in impact melts are accompanied by only small enhancements of Ir and

Os, suggesting that the impacting object was not chondritic in composition.

As shown for the Lonar crater , there is evidence of loss of Re and Se

by volatilization during the impact process. In order to establish

precise compositional mixing models to relate melt rocks with parental

country rocks, this suite of samples is also being studied by INAA.

Antarctic iron meteorites. After INAA, the suite of 10 Antarctic

irons will be analyzed for Pt metals, Au, Re, Ge, for further chemical

characterization.

190
SERVICE PROGRAMS

1. P. A. Baedecker, "Siderophile Element Fractionation in the Metal

Phase of the Bruderheim Chondrite," Lunar and Planetary Science XI3 Part I3 49-51 (1980).

2. P. A. Baedecker, "Comparisons of Peak-Search and Photopeak-Integration

Methods in the Computer Analysis of Gamma-Ray Spectra," Proceedings

of the Fourth International Conference on Nuclear Methods in Environmental and Energy Research (Univ. of Missouri, April 14-17, 1980)

(in press)

.

3. J. W. Morgan and G. A. Wandless, (1979) "74001 Drive Tube:

Siderophile Elements Match IIB Iron Meteorite Pattern," Proc. Lunar

Planet. Sci Conf. 10th p. 327-340.

4. J. W. Morgan, G. A. Wandless, R. K. Petrie, and A. J. Irving, (1980)

"Composition of the Earth's Upper Mantle - I. Siderophile Trace

Elements in Ultramafic Nodules." Proc. Lunar Planet. Sci. Conf. 11th,

in press.

5. J. W. Morgan, G. A. Wandless, R. K. Petrie, and A. J. Irving, (1980)

"Composition of the Earth's Upper Mantle - II. Volatile Trace Elements

in Ultramafic Xenoliths." Proc. Lunar Planet. Sci. Conf. llth3 in

press.

6. J. W. Morgan, (1978) "Lonar Crater Glasses and High-Magnesium Australites

Trace Element Volatilization and Meteoritic Contamination." Proc.

Lunar Planet. Sci. Conf. 9th p. 2713-2730.

J. W. Morgan, G. A. Wandless, R. K. Petrie, and A. J. Irving, (1980)

"Composition of the Earth's Upper Mantle - I. Siderophile Trace Elements

in Ultramafic Nodules." Tectonophysics3 in press.

191
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Division 354

P. Cassidy

K. Eggert

D . Hoaney

T. Hobbs

F. Moore

J. Shubiak

Division 532

M. Baier

R. A. Dallatore

C. Eisenhauer

D. Gilliam

J. A. Grundl

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McGarry

I. G. Schroder

R. Schwartz

W. Slater

V. Spiegel

Division 501

H. Berger

STAFF ROSTER

NON-RRD NBS STAFF LOCATED AT REACTOR

Division 506

D. Becker

Division 551

J. Bailey

M. J. Blackman

B. Carpenter

R. Fleming

T. Gills

S. Harrison

J. Koskoris

R. Lindstrom

G. Lutz

J. Mitchell

T. Mitlehner

L. Pilione

M. Vinocur

R. Zeisler

GUEST WORKERS AND COLLABORATORS

Division 520

A. Henins

L. Jacobs

E. Kessler

W. Sauder

W. Schwitz

Division 522

R. Dove

H. Marshak

Division 532

R. Caswell

A. Wasson

Division 533

R. Plaeious

Division 541

R. Kavanagh

J. Kelly

T. Madey

Division 544

S . Greer

D. Tsai

Division 553

H. Rook

193
STAFF ROSTER

Division 562

F. Biancanello

J. Early

Division 563

R. Bowen

C. Han

Division 564

R. Reno

R. Shull

Division 741

P. Brown

Argonne National Laboratory

R. Armani

T. Brun

R. Dun lap

H. Flotow

0. Hinks

S

.

Susman

J. Viccaro

Battelle, N. W.

W. Nicholson

Brookhaven National Laboratory

P . Levy

D. Richter

Federal Bureau of Investigation

R. Asbery

D. B. Davies

J. Haverkost

J. W. Kilty

E. Mitchell

C. Peters

J. P. Riley

Food and Drug Administration

M. Allegrini

W. Cunningham

D. Daly

W. Stroube, Jr.

J. Tanner

Harry Diamond Laboratory

C. Heimbach

National Gallery of Art

B. Miller

J. Olin

C. Parkhurst

K. Siverfelt

National Institutes of Health

D. Davies

R. Frank

J. Weinstein

Naval Air Defense Command

W. Williams

Naval Research Laboratory

C. Bond

P. D'Antonio

A. Ehrlich

M. Fatemi

J. Karle

N. Koon

F. Kuchas

K. Murray

V. Rath

L. Pecoia

Picatinny Arsenal

C. S. Choi

H. J. Prask

S . Trevino

194
STAFF ROSTER

Carnegie Institute of Washington

B. K. Kothari

Smithsonian Institution

M. Blackman

T. Chase

J. Mishara

S. O'Dell

L. Zacherman

U. S. Geological Survey

P. Baedecker

J. Morgan

American University

J. Ferrick

R. A. Segnan

Colorado State University

C. E. Patton

Howard University

G. A Ferguson

Iowa State University

R. Shelton

Israel Institute of Technology

Y. Segal

Massachusetts Institute of Technology

B. Averbach

Reed College

W. Parker

Technical University of Munich

H. Metzger

H. Wipf

University of Antwerp

K. Michel

University of Arizona

R. Salemme

P. Weber

University of Alabama

J. Segrest

University of California

(Lawrence Livermore Laboratories)

J. Browne

D. Hankins

University of Chicago

E. Anders

R. Wolf

University of Houston

S. Moss

University of Illinois

H. Zabel

University of Maine

H. Patterson

University of Maryland

D. Anderson

N. ARas

D. Ballantine

G. Barley

D. Finnegan

195
STAFF ROSTER

I . Gokman

G. Gordon

W. Johnson

J . Lynn

J. Parrington

J. Phelan

S . Re ingrover

W. Sonnefeld

M. Thompson

W. Walters

J. Weber

J. Winer

M. Yiu

W. Zoller

University of Missouri (Rolla)

W. James

State University of New York

H . Herman

University of Paris

B. Le Neindre

University of Pittsburgh

R. Buttera

S . Sankar

W. Wallace

University of Rhode Island

S. Pickart

Virginia Poly Technic Institute

R. Peterson

G. Gibbs

University of Wisconsin

J. Hinkley

J. Perepesco

H. Yu

Allied Chemical Corporation

G. Leibowitz

A. Maeland

B-K Dynamics

N. Chess er

Fedders Air Conditioning Company

W. Simpkins

General Electric Company

F. Luborsky

J. Walter

Lockheed Missle & Space, Inc.

D. Webster

Metronic, Inc.

P. Skarstad

Monsanto Research Corporation

W. Brother ton

Man Tech Corporation

D. Bracher

Sandia Corporation

J. Harris

Wilson Greatbach, Ltd.

R. Steinbring

Nuclear Energy Center, Mol, Belgium

A. Fabry

196
PUBLICATIONS

G. Publications

COLLABORATIVE PROGRAMS

BARKIGIA, K. M. , RAJKOVIC -BLAZER, L. M. , POPE, M. T., PRINCE, E. , and

QUICKSALL, C. 0., "Molybdoarsinate Heteropoly Complexes. The

Structure of the Hydrogentetramolybdodimethylarsinate (2-) Anion by

X-ray and Neutron Diffraction," Inorganic Chemistry, (in press).

BRACHER, D. A., GARRETT, D. A., and HELLER, C, "Theory and Design of

Instrumentation for Bridge Investigations," Proceedings of the

Mechanical Failures Prevention Group (1980)

.

CASELLA, R. C, "Neutron Scattering from Coherent Admixtures of Phonons

with Libronic Excitations of Diatomic Impurities," Phys. Rev. B20}

5318 (1979)

.

CHOI, C. S., PRASK, H. J., and TREVINO, S. F. , "Non-destructive Investigation of Texture by Neutron Diffraction," J. Appl. Cryst. 123 327-331 (1979).

CHOI, C. S., PRASK, H. J., and PRINCE, E., "Phase Transitions in

Ammonium Nitrate," J. Appl. Cryst. (in press).

CHOI, C. S., and MARINKAS, P. L., "Refinement of Dipara-anthracene,"

Acta. Cryst. (in press).

CULLEN, J. ALPERIN, H. , MELAMUD, M. HATHAWAY, K. , and RHYNE, J. J.,

"Magnetoelasticity and Moment Rotation in Amorphous Rare EarthIron Alloys," Int'l J. of Magnetism and Magnetic Materials 15_3 593 (1980).

D'ANTONIO, P. and SANT0R0, A., "Powder Neutron Diffraction Study of

Chemically Prepared B-Pb0 9 ," Acta. Cryst. (in press).

DOMBECK, T. W., LYNN, J. W. , WERNER, S. A., BURN, T., CARPENTER, J.,

KROHN, V. and RINGO, R. , "Production of Ultra-Cold Neutrons Using

Doppler-Shif ted Bragg Scattering and Intense Pulsed Neutron

Spallation Source," Nuc. Instr. and Meth. 165, 139 (1979).

197
PUBLICATIONS

FISH, G. E., RHYNE, J. J., BURN, T., VICARRO, P. J., NIARCHOS , D.,

DUNLAP, B. D., SHENOY, G. K. , SANRAR, S. G. , and WALLACE, W. E.,

"Neutron Scattering Studies of Hydrides of the Laves-Phase Rare

Earth Compounds RFe2," Rare Earths in Modern Science and Technology

II, Plenum Publishers, p. 569 (1980).

FORESTER, D. W. , KOON, N. C, SCHELLENG, J. H. , RHYNE, J. J., "Amorphous

YFe- - A Concentrated Spin Glass," J. Appl. Phys. (to be published).

FORESTER, D. W. , KOON, N. C, SCHELLENG, J. H. , and RHYNE, J. J.,

"Spin Glass

Concentrated

;s and Magnetic Blocking Transitions in Amorphous YFe~ -

:ed Spin Glass," J. Appl. Phys. 50_3 7336-41 (1979).

GLINKA, C. J., ROWE, J. M. , LIBOWITZ, G. G. , and MAELAND, A., "Neutron

Crystal-Field Spectroscopy of CeD„ -io>" Journal of Physics: C 12 , 4229 (1970).

GLINKA, C. J., PRASK, H. J., and CHOI, C. S., "Neutron Diffraction and

Small-Angle Scattering as Nondestructive Probes of the Microstructure of Materials," Proceedings of the Conference on Mechanics

of Nondestructive Testing , (ed. by W. W. Stinchcomb, Plenum Press

pp. 143-164 (1980).

HARDMAN, K. , JAMES, W. J., and YELON, ¥. B., "Preferential Ordering of

Mn and Fe Atoms in Yg(fe Mn ) 9 o>" Journal of Physics and Chemical

Solids (in press)

.

HARDMAN, K. , RHYNE, J. J., SMITH, K. , and WALLACE, W. E., "Structural

Investigation of ThgMn^D, , by Neutron Diffraction," Journal of

the Less Common Metals (in press)

.

KELLEY, R. D., CAVANAGH, R. R. , RUSH, J. J., and MADEY, T. E., "Neutron

Inelastic Scattering Study of C2H4 Adsorbed on Raney Nickel,"

Surface Science (in press).

KELLEY, R. D., RUSH, J. J., and MADEY, T. E., "Vibrational Spectroscopy

of Adsorbed Species on Nickel by Neutron Inelastic Scattering,"

Chemical Physics Letters 66^, 159-164 (1979)

.

KOON, N. C, and RHYNE, J. J., "Exchange and Crystal Field Excitations

in Rare Earth Iron and Rare Earth Cobalt Laves-Phase Compounds,"

Crystalline Electric Fields and Structural Effects in f-Electron

Systems3 edited by J. E. Crow, R. P. Guertin, and T. W. Mihalisin,

Plenum Publishing, p. 125 (1980).

LYNN, J. W., "Crystal Field Effects in Magnetic Superconductors,"

Crystalline Electric Fields and Structural Effects in f-Electron

Systems3 edited by J. E. Crow, R. P. Guertin, and T. W. Mihalisin,

Plenum Publishing, p. 547 (1980).

198
PUBLICATIONS

LYNN, J. W., MONCTON, D. E. , PASSELL, L. and THOMLINSON, W. , "Magnetic

Correlations and Crystal Field Levels in the Superconductor

(Ce e73Ho e 27)Ru2, M Phys. Rev. B21, 70 (1980).

LYNN, J. W. and GLINKA, C. J., "Magnetic Properties of the Superconducting

Alloy System (Ce^ Ho )Ru2 - A Neutron Scattering Study," J. Magnetism

and Magnetic Materials 14, 179 (1979)

.

LYNN, J. W. and SHELTON, R. N. , "Neutron Scattering Studies of Magnetic

Superconductors," J. Magnetism and Magnetic Materials _18, 1577 (1980).

MAGERL, A., ROWE, J. M. and RICHTER, D., "On the Observation of Low

Energy Excitations in NbD - A Simple Lattice Dynamical Model,"

Phys. Rev. B 22, 1417 (1980).

MICHEL, K. H. , and ROWE, J. M. , "On the Existence of an Orientational

Glass State in (KCN) (KBr)i_ Mixed Crystals," Phys. Rev. B (in press).

NICHOLSON, W. W., and PRINCE, E., "Arobust /Resistant Technique for

Crystal Structure Refinement," Acta Cryst. A (submitted).

PRASK, H. J. CHOI, C. S., and TREVINO, S. F. , "Nondestructive Testing

of Armament-System Components by Means of Neutron Diffraction,"

Proc. of the Army Science Conference (in press)

.

PRASK, H. J., and CHOI, C. S., "Texture, Nondestructive Characterization,"

Ency. Matls. Sci. and Eng. (submitted)

.

PRINCE, E., "Comparison of Profile and Integrated Intensity Methods in

Powder Refinement," J. Appl. Cryst. (submitted).

RHYNE, J. J. "Amorphous Magnetic Materials - Chapter 16," Handbook on

the Physics and Chemistry of Rare Earths } ed. by K. A. Gschneider

and L. Eyring, North Holland Publishing, (1979).

RHYNE, J. J. and KOON N. C, "RPA Theory of Magnetic Excitations in

Rare Earth-Transition Metal Compounds: Application of ErCo2 and

ErFe2," Int's. J. of Magnetism and Magnetic Materials 15_, 349 (1980).

RHYNE, J. J., KOON, N. C, and DAS, B. N. , "Ground State Excitations in

HoCo 2 ," Intl. J. of Magnetism and Magnetic Materials 14, 273 (1979).

RHYNE, J. J., KOON, N. C. and ALPERIN, H. A., "Magnetic Excitations in

ITbFe

," Rare Earths in Modern Science and Technology II3 Plenum

Publishers, p. 313 (1980).

199
PUBLICATIONS

RHYNE, J. J., "Magnetic Inelastic Neutron Scattering Studies of Rare

Earth Metals and Laves-Phase Compounds," Proa, of the Science and

Technology of Rare Earth Materials (in press)

.

RHYNE, J. J., "Magnetic Materials," Article for the Encyclopedia of

Physics3 ed. by R. G. Lerner and G. L. Trigg, Addison-Wesley

Publishing, (in press).

ROWE, J. M. and MAGERL, A., "Neutron Diffuse Scattering Intensities in

Niobium," Phys3 . Rev. B 21, 1706-7 (1980).

ROWE, J. M., RUSH, J. J., SHAPIRO, S. M._HINKS, D. G. , and SUSMAN, S.,

"Neutron Scattering Studies of (CN) Defects in KBr," Phys. Rev.

B 21, 4863-4868 (1980).

ROWE, J. M., RUSH, J. J., HINKS, D. G. and SUSMAN, S., "Neutron Scattering

Study of the Dynamics of KCN 5KBr ," Phys. Rev. Lett. 43, 1158-61

(1979).

'*

RUSH, J. J., ROWE, J. M. , GLINKA, C. J., VAGELATOS , N. , and FLOTOW, H. E.,

"Coherent Neutron Scattering Study of the Vibrations of Interstitial

Deuterium in a-VD

Q

," Phys. Rev. B 21, 5613-5616 (1980).

RUSH, J. J., ROWE, J. M., and MAELAND, A. J., "Neutron Scattering Study

of Hydrogen Vibrations in Polycrystal and Glassy TiCuH," Journal

of Physics F (in press)

.

SANTORO, A. and WLODAWER, A., "Absorption Correction for Weissenberg

Diffractometers," Acta Cryst. A3_6, 442-450 (1980).

SANTORO, A., MIGHELL, A. D., and RODGERS, J. R. , "Determination of the

Relationship Between Derivative Lattices," Acta Cryst. (in press).

SANTORO, A., MIGHELL, A., and RODGERS, J., "Lattice Relationships:

The Determination of Matrices that Will Relate Any Given Pair of

Lattices," Acta Cryst. (in press).

SANTORO, A., ROTH, R. S., and MINOR, D. , "Neutron Powder Diffraction

Study of the Structure of CeTaO^, CeNbO^, and NdTaO^," Journal of

Solid State Chemistry (in press)

.

SANTORO, A., MAREGIE, M. , ROTH, R. S., and MINOR, D., "Neutron Powder

Diffraction Study of the Structure of CeTaO^, CeNbO^, and NdTaO^,"

Journal of Solid State Chemistry (in press)

.

SANTORO, A., "Use of Derivative Lattices in the Indexing of Powder

Patterns," Acta Cryst. (submitted).

200
PUBLICATIONS

INDEPENDENT PROGRAMS

CARPENTER, B. S., and PILIONE, L. J., "Lithium and Lithium-6 Analysis

in Solutions by the Nuclear Track Technique," Anal. Chem. 3 (in

press)

.

CARPENTER, B. S., and JONES, F. E., eds., "Measurements and Standards

for Nuclear Materials Safeguards," NBSIR 80-2033, May 1980.

CANADA, T. R., and CARPENTER, B. S., eds., "Measurement Technology for

Safeguards and Materials Control," NBS Spec. Publ. 582 (1980).

CARPENTER, B. S., PILIONE, L. J., SCHRODER, I. G. , ROE, J. W. , and

SANATINI, S., "Evaluation of Reactor Track-Etch Power Monitor,"

ANS Transactions, Vol. 33, 21 (1979).

GREENBERG, R. R. , "Simultaneous Determination of Mercury and Cadmium in

Biological Materials by Radiochemical Neutron Activation Analysis,"

Anal. Chem. , 5_2, 676 (1980).

HARRISON, S. H., MAIENTHAL, E. J., GILLS, T. E. , and ZEISLER, R.

,

"Protocal for the Collection, Storage, and Analysis of Human Organs

the Pilot Bank Project of the National Environmental Specimen Bank,"

in Trace Substances in Environmental Health, XIII, D. P. Hemphill,

ed., U. of Missouri, Columbia, June 1980 (in press).

LINDSTROM, R. M. , and FLEMING, R. F. , "Accuracy in Activation Analysis:

Count Rate Effects," to be published in Proc. of 4th International

Conference on Nuclear Methods in Environmental and Energy Research

(Univ. of Missouri, Columbia) 1980.

LINDSTROM, R. M. , "Measuring Trace Elements in Semiconductors: Methods

and Pitfalls," Solar Cells, 1 (2) , 117 (1980).

LUX, F., ZEISLER, R. , and REHER, J., "Aktivierungsanalytische Utersuchungen

uber die Probenmengenabhangigkeit der Streuung der Spurenelementgehaltswerte von Bleiweiss sowie uber den cisalpinen Typ von Bleiweiss aus einem Rugens-Gemalde, " Radioohem. Radioanal. Letters s U2, 341 (1980).

MITCHELL, J. W., RILEY, JR., J. E., and CARPENTER, B. S., "Major

Elemental Boron Determination by the Nuclear Track Technique,"

ANS Transactions, Vol. 34, 143 (1980).

SCHWARTZ, R. B., EISENHAUER, C. M. , GILLIAM, D. M. , SPIEGEL, V. and

WASSON, 0. A., Trans. Am. Nuo. Soc. 34, p. 621 (1980).

201
PUBLICATIONS

TREVINO, S. F. 5 "An Observation of One-Dimensional Reorientation

and Tunnel Splitting of the Ground and First Excited State

in a Low Barrier System: Solid Nitromethane , " J. Chem. Phys.

(Letter to the Editor) 71, 1973-4 (1979)

.

TREVINO, S. F., PRINCE, E., and HUBBARD, C. R. , "Refinement of

the Structure of Solid Nitromethane," J. Chem. Phys. (in press)

TREVINO, S. F. and RYMES, W. H., "A Study of Methyl Reorientation

in Solid Nitromethane by Neutron Scattering," J. Chem. Phys.

(in press)

.

WLODAWER, A., SEGREST, J. P., CHANG, B. H. , CHIOUETTE, R. , and

WEINSTEIN, J. N., "High Denisty Lipoprotein Recombinants:

Evidence for a Bicycle Tire Micelle Structure Obtained by

Neutron Scattering and Electron Microscopy," FEBS LETTERS 104 , 231-235 (1979).

ABRAHAMSSON, S., LINDQVIST, 0., SJOLIN, L., and WLODAWER, A.,

"Preliminary Investigation of a New X-ray Film," J. Appl.

Cryst. (submitted)

.

WLODAWER, A. , "Studies of Ribonuclease-A by X-ray and Neutron

Diffraction," Acta Cryst. B (in press).

202
NBS-114A (rev. 2-sci U.S. DEPT. OF COMM. BIBLIOGRAPHIC DATA

SHEET (See instructions)

1. PUBLICATION OR

REPORT NO. NBS TN 1142

2. Performing Organ. Report NoJ 3. Publication Date

May 1981

4. TITLE AND SUBTITLE

NBS Reactor: Summary of Activities

July 1979 to June 1980

5. AUTHOR(S)

Frederick J. Shorten, Editor

6. PERFORMING ORGANIZATION (If joint or other than NBS. see instructions)

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

7. Contract/Grant No.

8. Type of Report & Period Covered

July 1979 to June 1980

9. SPONSORING ORGANIZATION NAME AND COMPLETE ADDRESS (Street. City. State, ZIP)

Same as item 6.

10. SUPPLEMENTARY NOTES

J Document describes a computer program; SF-185, FIPS Software Summary, is attached.

11. 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 1979 through June 1980. The programs range from

the use of neutron beams to study the structure and dynamics of materials through

nuclear physics and neutron standards to sample irradiations for activation

analysis, isotope production, radiation effects studies, neutron radiography,

and nondestructive evaluation.

12. KEY WORDS (Six to twelve entries; o/phobetico/ order; capitalize only proper names; and separate key words by semicolons)

Activation analysis; crystal structure; diffraction; isotopes; molecular dynamics;

neutron; neutron radiography; nondestructive evaluation; nuclear reactor; radiation.

13. AVAILABILITY

J5Q5| Unlimited

| | For Official Distribution. Do Not Release to NTIS ^ Order From Superintendent of Documents, U.S. Government Printing Office, Washington, D.C.

20402.

I I Order From National Technical Information Service (NTIS), Springfield, VA. 22161

14. NO. OF

PRINTED PAGES

211

15. Price

*U S GOVERNMENT PRINTING OFFICE: 1981 345-925/8294 USCOMM-DC 8043-P80

NBS TECHNICAL PUBLICATIONS

PERIODICALS

JOURNAL OF RESEARCH—The Journal of Research of the National Bureau of Standards reports NBS research and develop- ment in those disciplines of the physical and engineering sciences in which the Bureau is active. These .iclude physics, chemistry,

engineering, mathematics, and computer sciences. Papers cover a broad range of subjects, with major emphasis on measurement

methodology and the basic technology underlying standardization. Also included from time to time are survey articles on topics

closely related to the Bureau's technical and scientific programs. As a special service to subscribers each issue contains complete

citations to all recent Bureau publications in both NBS and non- NBS media. Issued six times a year. Annual subscription: domestic

$13; foreign $16.25. Single copy. $3 domestic: $3.75 foreign. NOTE: The Journal was formerly published in two sections: Section A "Physics and Chemistry" and Section B "Mathematical

Sciences." DIMENSIONS/NBS—This monthly magazine is published to in- form scientists, engineers, business and industry leaders, teachers,

students, and consumers of the latest advances in science and

technology, with primary emphasis on work at NBS. The magazine

highlights and reviews such issues as energy research, fire protection, building technology, 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 $11;

foreign $13.75. NONPERIODICALS

Monographs—Major contributions to the technical literature 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 in- terested industries, professional organizations, and regulatory

bodies. Special Publications—Include proceedings of conferences 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 worldwide program coordinated by NBS under

the authority of the National Standard Data Act (Public Law

90-396).

NOTE: The principal publication outlet for the foregoing 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, 1 155 Sixteenth St., NW, Washington, DC 20056.

Building Science Series—Disseminates technical information 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 procedures

published by the Department of Commerce in Part 10, Title 15, of

the Code of Federal Regulations. The standards establish nationally recognized requirements for products, and provide all concerned interests with a basis for common understanding of the

characteristics of the products. NBS administers this program as a supplement to the activities of the private sector standardizing

organizations. Consumer Information Series—Practical information, based on NBS research and experience, covering areas of interest to the con- sumer. Easily understandable language and illustrations provide

useful background knowledge for shopping in today's technological marketplace. Order the above NBS publications from: Superintendent of Documents, Government Printing Office, Washington, DC 20402. Order the following NBS publications—FIPS and NBSIR 's—from

the National Technical Information Services, Springfield, VA 22161

.

Federal Information Processing Standards Publications (FIPS

PUB)—Publications in this series collectively constitute the Federal Information Processing Standards Register. The Register

serves as the official source of information in the Federal Govern- ment regarding standards 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, 1973) and Part 6 of Title 15 CFR (Code of Federal Regulations).

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 dis- tribution is handled by the sponsor; public distribution is by the National Technical Information Services, Springfield, VA 22161,

in paper copy or microfiche form.
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