Reference

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NBS

Publications

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NBS TECHNICAL NOTE 1160

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

NBS Reactor:

Summary of Activities

July 1980 Through June 1981

100

.U5753

lio . 1160

1982
NATIONAL BUREAU OF STANDARDS

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

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

research and provides: (1) a basis for the Nation's physical measurement system, (2) scientific and technological services for industry and government, (3) a technical basis for equity in trade, and (4) technical services to promote public safety. The Bureau's technical work is per- formed by the National Measurement Laboratory, the National Engineering Laboratory, and

the Institute for Computer Sciences and Technology.

THE NATIONAL MEASUREMENT LABORATORY provides the national system of

physical and chemical and materials measurement; coordinates the system with measurement

systems of other nations and furnishes essential services leading to accurate and uniform

physical and chemical measurement throughout the Nation's scientific community, industry,

and commerce; conducts materials research leading to improved methods of measurement,

standards, and data on the properties of materials needed by industry, commerce, educational

institutions, and Government; provides advisory and research services to other Government

agencies; develops, produces, and distributes Standard Reference Materials; and provides

calibration services. The Laboratory consists of the following centers:

Absolute Physical Quantities^ — Radiation Research — Chemical Physics —

Analytical Chemistry — Materials Science

THE NATIONAL ENGINEERING LABORATORY provides technology and technical ser- vices to the public and private sectors to address national needs and to solve national problems; conducts research in engineering and applied science in support of these efforts; builds and maintains competence in the necessary discipUnes required to carry out this research and technical service; develops engineering data and measurement capabilities;

provides engineering measurement traceability services; develops test methods and proposes

engineering standards and code changes; develops and proposes new engineering practices;

and develops and improves mechanisms to transfer results of its research to the ultimate user. The Laboratory consists of the following centers:

Applied Mathematics — Electronics and Electrical Engineering^ — Manufacturing

Engineering — Building Technology — Fire Research — Chemical Engineering^

THE INSTITUTE FOR COMPUTER SCIENCES AND TECHNOLOGY conducts

research and provides scientific and technical services to aid Federal agencies in the selection,

acquisition, application, and use of computer technology to improve effectiveness and

economy in Government operations in accordance with Public Law 89-306 (40 U.S.C. 759), relevant Executive Orders, and other directives; carries out this mission by managing the Federal Information Processing Standards Program, developing Federal ADP standards

guidelines, and managing Federal participation in ADP voluntary standardization activities; provides scientific and technological advisory services and assistance to Federal agencies; and

provides the technical foundation for computer-related policies of the Federal Government.

The Institute consists of the following centers:

Programming Science and Technology — Computer Systems Engineering.

'Headquarters and Laboratories at Gaithersburg, MD, unless otherwise noted; mailing address Washington, DC 20234. 'Some divisions within the center are located at Boulder, CO 80303.
Mjj

- j V « . NATIONAL hVJUa* LtBBART

JUL 1 9 1982

NBS Reactor:

..e^cc /e^

Summary of Activities a^T^-3

J uly 1980 Through June 1981 ^cn^o

Frederick J. Shorten, Editor

Reactor Radiation Division

National Measurement Laboratory

National Bureau of Standards

Washington, DC 20234

% V ,. . .

in Q*

U.S. DEPARTMENT OF COIVIMERCE, IVIalcolm Baldrige, Secretary

NATIONAL BUREAU OF STANDARDS. Ernest Ambler, Director

Issued June 1982
National Bureau of Standards Technical Note 1160

Nat. Bur. Stand. (U.S.), Tech. Note 1160, 204 pages (June 1982)

CODEN: NBTNAE

U.S. GOVERNMENT PRINTING OFFICE

WASHINGTON: 1982
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 coininunity . 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 these programs carried out by scientists in

the Reactor Radiation Division and their collaborators. The second 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.

Ill
FOREWORD

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. 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 1980 through June 1981. 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.

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 endorsement 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 AND COLLABORATIVE PROGRAMS .... 1

Surface Vibrational Spectroscopy with Neutron Inelastic

Scattering 1

Lithium Self Diffusion in the Ionic Conductor LiAl 4

Rotation-Translation Coupling in Ionic and Molecular

Crystals 5

Theory of Quasielastic Scattering from Vanadium Deuterides

at Large Momentum Transfers 10

Phonon Dispersion of Graphite Intercalation Compounds .... 11

Unification of the Fundamental Forces I3

Theory of Neutron Scattering from Hydrogen in Metals

Including the Effects of Tunneling 15

Computer Simulation of the Molecular Dissociation of a Diatomic Crystal 17

Spin Wave Excitations in Dilute Pd(Fe) 22

Magnetic Properties of the Superconductor (Ce_ Th )Ru^ ... 24

1-x X 2 Mean Field Behavior of Ferromagnetic HoRh.B, 25

4 4 Magnetic Properties of Cubic and Hexagonal HoMn 28

Magnetic ° and Structural Properties ^ of Th.Mn„_D and Y.Mn„„D . 30

6 23 x 6 23 X

Preferential Atomic Ordering and Magnetic Structures in

Y,(Fe^ Mn )„ 33

6 1-x X 23

Amorphous Structure of TbFe„ and YFe„ 36

Comparison of the Fits of Two Models to the Same Set of Powder

Diffraction Data 39

Precise Wavelength Determination for the Multidetector Powder

Dif f ractometer 40

vx
TABLE OF CONTENTS

Use of the Pearson Type VII Distribution in the Neutron

Profile Refinement of the Structures of LiReO„ and

Li^ReO^ 41

Powder Neutron Diffraction Study of the Nonstoichiometric

Solid Solution of Lithium Tantalate 9LiTaO : Ta ... 46

Structure Refinement of Lil'D by Neutron Diffraction ... 53

Neutron Powder Diffraction Study of the Fast-Ion Conductor

CuAgS Between 20° and 115°C 57

The Structure of the Rhombohedral Phase of Na Sc2(P0,)„ . . 64

Search for a Low Temperature Phase Transition in LiH .... 67

Crystal Structure of Ammonium Nitrate Phase III 67

Refinement of 2-Nitroguanidine by Neutron Powder

Diffraction 7q

Studies of Ribonuclease A by X-ray and Neutron

Diffraction -ji

Refinement of the Crystal Orientation Matrix for the FlatCone Dif f ractometer 74

Advanced Neutron Methods 78

Phase Decomposition in the Ni Rich Side of Ni|Ni Al

Miscibility Gap: A Small-Angle Neutron Scattering

Study 83

Compositional and Magnetic Inhomogenieties in

Fe /-tCo ^ qB -i/Si _^ Amorphous Ribbon 91

Computational Methods in the Non-Linear Theory of Spinodal

Decomposition 94

Relaxation Behavior of SiC Fibers in SiC/Al Composite

Material Under Stress 95

Nuclear Safeguards Standards for Detector Calibration

Tomography 97

Resonance Neutron Tomography 101

Vll
TABLE OF CONTENTS

Design Study of a Facility for Neutron-Activation Autoradiography of Paintings at the National Bureau of

Standards Reactor 106

Nuclear Waste Management 112

B. NON-RRD PROGRAMS H^

Activation Analysis Group FY 81 114

Precision Gamma-ray and X-ray Wavelengths 141

Neutron Dosimetry for Reactor Pressure Vessels 144

Observation of Field Parameters for the Intermediate-Energy

Standard Neutron Field (ISNF) 150

Fissionable Deposit Mass Assay for Absolute Fission Rates

in the FFTF 154

Neutron Personnel Dosimeter Calibration and Testing .... 156

Flux Measurement in the Small Angle Neutron Scattering

Facility 158

Preparation of a Certified Fission Product Counting

Standard 159

Recycled Oil Program 162

C. REACTOR OPERATIONS AND SERVICES 164

D. SERVICE PROGRAMS 168

Activation Analysis Program of the Food and Drug Administration

at the NBSR 168

Positron Annihilation in Cu Alloys 171

U.S.G.S. Activation Analysis Program 179

E. PERSONNEL ROSTER 181

F. PUBLICATIONS • 187

Vlll
A. Reactor Radiation Division and Collaborative Programs

SURFACE VIBRATIONAL SPECTROSCOPY

WITH NEUTRON INELASTIC SCATTERING

R. D. Kelley

(Surface Science Division)

R. R. Cavanagh

(Molecular Spectroscopy Division)

and

J. J. Rush

Neutron inelastic scattering (NTS) has been used to measure the

vibrational spectra of hydrogen and carbon monoxide chemisorbed on Raney

nickel (a high surface area nickel powder) . The neutron spectra were measured using the BT-4 triple-axis spectrometer at the NBS Reactor. A

cold (77 K) beryllium-filter analyzer was used which transmits only

scattered neutrons of energies 55.2 meV and thus provides a "fixed"

final energy of '^3 meV. The energy resolution was about 5.5 to 6 percent

over the whole energy range (e.g., AE '^^ 5.5 meV at 80 meV and 12 raeV at

200 meV) . The sample, approximately 90 g of a commercial Raney nickel, was contained in a stainless steel cell and mounted i^n a variable temperature cryostat which allows "in situ" gas dosing.

In agreement with previous work, the spectrum of a monolayer of

hydrogen adsorbed at 300 K has peaks at 72, 117, and 142 meV. These

peaks were assigned (based on theoretical predictions) to the vibrational

fundamentals of multiply-bonded atomic hydrogen on nickel. We have now

combined a) measurements of the vibrational spectra as a function of

hydrogen coverage and b) neutron scattering intensity calculations of

model hydrogen-nickel adsorption geometries to conclude that the predominant binding site for hydrogen adsorbed on the nickel powder is one

of three-fold symmetry.

Measurements of the scattering intensity at 10 percent, 50 percent,

and 100 percent of a monolayer of hydrogen chemisorbed on the Raney

nickel indicate that the two dominant high-frequency vibrational modes
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

(117 and 142 meV) track the H coverage very closely at a constant

intensity ratio of 2:1. The low-frequency mode ('^74 meV) has a maximum

intensity at '^'10 percent of an H monolayer.

Figure 1 is the NIS vibrational spectrum of H(10 percent of a monolayer) + D(20 percent of a monolayer) which had been chemisorbed at

300 K. The hydrogen-nickel vibrational modes are found at 138 meV,

123 meV, and 72 meV (the analogous deuterium modes are shifted by '\^/2,

and occur at 104 meV, 86 meV, and '^50 meV) . The frequency changes and

the narrowing of the peak widths at low coverage are thought to be the

result of adsorbate-adsorbate (in particular H H) interactions and are discussed in another paper. The peak at "^172 meV is believed to be

due to the first overtone of the 86 meV Ni-D vibration.

The fact that the 117 and 142 meV peak intensities vary directly

with hydrogen coverage at a constant ratio strongly suggests that they

originate from vibrations at a single type of site. Further, since

these two features dominate the incoherent scattering, such a site must

dominate the sites available for hydrogen chemisorption. As discussed

below, we believe this to be a three-fold site. The low-frequency mode

(72 meV) has been assigned — based on theoretical calculations, neutron

scattering and neutron diffraction studies of hydrogen in transition

metals, and an EELS-LEED study of H on Ni(lOO) — to the symmetric

stretching vibration of a hydrogen chemisorbed on a four-fold site.

1. Intensity calculations of model hydrogen-nickel geometries

The assignment of the two higher frequency modes is facilitated by

the non-electrodynamic nature of the NIS process (no dipole or polarizability selection rules) . Both the frequency and the NIS intensity of

the normal modes involving hydrogen motions can be calculated, the

required parameters being the effective force constants, the bond lengths,

and the S3nmiietry of the hydrogen bonding sites. Using model geometries

for the H-Ni system and a normal mode analysis, one can attempt to

reproduce the observed NIS spectrum. Such calculations have been /
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

Figure 1. NIS spectra (scattering intensity vs. energy transfer) for

H(10 percent of a monolayer) + D(20 percent of a monolayer)

chemisorbed on Raney nickel.

performed. Binding in a three-fold s3Tranetric site demands a two to one intensity ratio for the observed spectral features. That is, the site

sjmmietry requires a degenerate set of modes independent of the chosen

force constants or bond lengths. Only one set of force constants and

bond lengths are consistent with the observed NIS features. Specifically,

o o d . = 1.89 A; k = 0.58 mdyne/A. This bond length is in good agreement

with the bond length found in LEED experiments for H on Ni(lll). Thus^

the 117 meV feature can be assigned to a doubly degenerate mode parallel

to the surface plane and 142 meV feature to the vibrational mode perpendicular to the surface plane in the three-fold S37mmetric site.

When a monolayer of CO is co-adsorbed with a monolayer of H at

120 K, virtually no change is observed in the NIS spectrum of the chemisorbed hydrogen (the inelastic neutron scattering cross section of CO is

very low relative to hydrogen) . This observation demands that the

chemisorbed CO does not displace H and further that the chemisorption
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

binding site for CO is not the three-fold S5mimetry preferred by hydrogen.

At higher temperatures the hydrogen spectrum changes indicating interactional effects between H and CO. At room temperature, increased

intensity at low frequency (<70 meV) and at high frequency (>150 meV)

suggests the presence on the surface of hydrocarbon fragments.

Extensive measurements on the temperature dependence of the chemisorption of ethylene and acetylene have also been obtained and are being

analyzed.

These experiments are indicative of the potential of NIS for not

only identifying surface species but of using chemisorbed hydrogen to

characterize the structure of high surface area polycrystalline metals

(i.e., catalysts) and of molecules adsorbed on their surfaces.

LITHIUM SELF DIFFUSION IN THE IONIC CONDUCTOR LiAl

T. 0. Brun and S. Susman

(Argonne National Laboratory, Argonne, IL)

and

J. J. Rush and J. M. Rowe

The properties of nearly stoichiometric 6-phase LiAl are of

considerable interest both for scientific and technological reasons. This fast-ion conductor is used as an electrolyte in proposed lithiumbased batteries now being developed for use in automobiles. A key

property for this use is the self diffusion of lithium ions through the

lattice. There exist no reliable measurements of the macroscopic

diffusion constant in this material, and little is known about the

mechanisms for Li-ion diffusion. It is known that vacancies on the

Li-sublattice are connected to the diffusion process, but little is known

about the dynamics and microscopic mechanisms of this phenomenon.

Since Li-7 cross section is half incoherent (.76 out of 1.26), this

substance is a difficult but natural candidate for study by neutron quasielastic scattering. In fact, it is an excellent model system for such
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

studies, since in no other substance is the vacancy concentration so high.

We have completed a detailed study of the Li self diffusion mechanism

in a single crystal of Li , ^Al , using the BT-4 triple axis spectrometer

. 4y . -)i T at NBSR. With a crystal of less than 1 cm in volume, we have studied the

neutron quasielastic scattering at 800K along the principal symmetry axes,

with an energy resolution of 90 yeV. The results for the lineshapes have

been compared to a model based upon vacancy diffusion, which is in excellent

agreement with the experimental results, thus confirming the basic diffusion

— fi ? mechanism. A diffusion constant of 7 . 9 x 10 cm /sec has been derived

at 800K from the results, which is the first quantitative measurement

of this fundamental property.

ROTATION-TRANSLATION COUPLING IN IONIC AND MOLECULAR CRYSTALS

1. Critical Dynamics in Nd . Br

J. M. Rowe, J. J. Rush, R. Pynn , A. Heidemann , K. H. Michel

We have successfully measured the coherent critical quasielastic

neutron scattering in a single crystal of ND.Br at 225 K (T + 7 K) using

the IN-10 back reflection spectrometer at the Institut Laue Langevin in

Grenoble, France. The measurements were performed at the point (0.5, 0.5,

1.0) in the cubic brillouin zone. This point becomes a superlattice reflection

in the low temperature y phase in which the (ND, ) ions are fully orientationally ordered. The results are shown in figure 1, where the solid line

represents the results of a least squares fit of a Lorentzian fitted to

the data. From this fit, we obtain an intrinsic quasielastic width of

0.28 + .1 iJeV for this scattering, compared to a predicted width of 0.50 yeV

from simple theory. (The dashed line in the figure is the result of a measurement below T where the scattering is elastic, and thus represents

the resolution.) The present result shows clearly that the simple theory

which ignores all collective effects except those included by mean-field

theory is inadequate to explain the results. In this simple theory^ the

single particle reorientations are the source of the translation-rotation

5
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAl-IS

coupling which leads to the phase transition. The results obtained here

suggest that many-body effects on the transport coefficients cannot be

neglected. Further experiments are planned.

2. KCN KBr, Structure and Dynamics

X 1-X

^

-|. *^

J. M. Rowe, J. J. Rush, S. Susman , D. G. Hinks , K. H. Michel

and M. Klein

In the past year, many new results have been obtained in the mixed

crystal system. Single crystal diffraction measurements on pure KCN as

a function of temperature have been completed at 300, 250, 200, and 170 K. These results agree well with earlier measurements at 300 K and 175 K. The

salient result from this study is that the orientations of the (CN) ion

become more isotropic as the temperature is lowered, a result in direct

contradiction to expectations based upon a static crystal field potential.

These results can be understood qualitatively on the basis of an effective

potential for (CN) orientations which includes the effect of lattice strains

coupled to orientations. The effective potential due to such strains has

deep minima along cubic [100] directions, in contrast to the static crystal

field potential which has minima along [111] directions. The final potential,

which is the sum of these two potentials is nearly isotropic and depends

critically on the parameters used to describe the ion-ion potentials. In

addition, there is a direct interaction between (CN) ions due to quadrupolequadrupole coupling which favors [100] orientations. In lowest order, the

effective potential is temperature independent, but when self-consistent

methods are applied, the magnitude of the strain-mediated potential becomes

strongly temperature-dependent, leading to a temperature dependent total

potential. Thus, as the temperature is lowered, the (CN) orientations

change from predominantly [111] towards [100]. However, the first-order phase

transition at 168 K interrupts this process before [100] orientations

*Institut Laue Langevin, Grenoble, France.

**Universiteit Instelling Antwerp, Antwerp, Belgium.

^National Research Council of Canada, Ottawa, Canada.

+Argonne National Laboratory, Argonne, Illinois.
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAJIS

become favored. In the low-temperature structure (which is orthorhombic)

the ions orient along cubic [110] axes. In addition to the theoretical

work on the strain-mediated interactions, we have initiated a program to

do molecular dynamics simulations of the alkali-cyanides and mixed cyanidehalide systems. The results of these simulations were critical to the new

understanding of the behavior of KCN outlined above. A key result was the

finding that the inclusion of the quadrupole-quadrupole interaction was

essential. In fact, the comparison of experiment and simulation showed

that the quadrupole moment in KCN was reduced by at least a factor of two

from its value in the free ion. This astonishing result led to quantum

calculations of the properties of the (CN)~ ion which showed that induced quadrupole moments were also important and that the free molecule

was not linear, a result in accord with very recent experiments.

We have also completed a single crystal diffraction study of (KCN)q c (KBr)Q c at several temperatures between 10 and 300 K. For this mixed

crystal, we also find that the (CN)~ ion orientations are predominantly

[111] at 300 K, and tend continuously towards [100] as the temperature

8

-2-1 1 2

Energy (MeV)

Figure 1. Measured spectra for ND.Br. Points measured at 225 K (7 K

above T ) and dashed line at 213 K (errors for this are too

small to show) are both normalized to equal peak intensity.

The solid line is the result of the least squares fit to the

data described in the text.
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

1.0 "

Figure 2

>

a

ok.

*•> ow

'£<

100 200 300

Temperature (K)

The anisotropy of (CN) orientations in (KCN) q. 5(KBr) q 5, as measured by 1/n T.(F-^/F2 - 1)^> where F-^ and F2 are the

structure factors of pairs of reflections with different

h, k, 1 and equal h2 + k2 + l2.

Elastic Intensity Near [2,2,0]

2.2

2.1-

2.0-

1.9-

1.8-

Figure 3, Elastic intensity near the [270] Bragg point in KCNq 3KBro.5

measured at 51 and 150 K.

8
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

is reduced. However, since there is no phase transition to a long-range

ordered state in this crystal, the trend continues all the way down to

10 K. At 10 K, the orientations are certainly not at all [111] but we

cannot say that [100] is strongly preferred over [110]. In addition, the

anisotropy of orientation, as measured by reflections of distinct (hkl)

but equal h"^ + k^ + 1^ goes through a minimum near 100 K then rises again.

This behavior is shown in figure 2. The temperature of the minimum is almost

that at which the transverse velocity of sound along [100] directions goes

through a minimum and the elastic diffuse intensity starts to increase. The

2 elastic diffuse intensity in this mixed crystal has a characteristic shape

around the (220) Bragg point as shown in figure 3. We have calculated this

3 intensity based upon the model of Michel and Rowe for spin-glass behavior,

and are able to reproduce these contours exactly. We have also verified

that KCN Q^KBr exhibits similar behavior at low temperatures.

. y-> . 05

Another recent study has been undertaken of the elastic diffuse

scattering in pure KCN and NaCn, in order to look for the effects of the

rather different (CN) orientations in this crystal. These measurements

showed very strong structured diffuse scattering in NaCN at 300 K and almost none in KCN at 300 K or 170 K. We interpret this result as a direct

reflection of the predominantly [100] orientations in NaCN as compared to

predominantly [111] orientations in KCN. This hypothesis is being checked

by molecular dynamics simulation.

Finally, we have undertaken a powder diffraction study of (KCN) (KBr)

iC J- ^ for X >_ 0.8. The first results for x = 0.8 showed that the low temperature

structure in this mixture (which does undergo a first order phase transition)

is not that of KCN, but rather a monoclinic structure. Further, the complete

sample does not transform, and part of the sample remains cubic down to

4 K. In light of this unexpected result we are currently measuring samples

with X = 0.90 and 0.95.

1. J. M. Rowe, J. J. Rush, R. Pynn, A. Heidemann, and K. H. Michel,

J. Chem. Phys. 74, 5323 (1981).
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

2. J. M. Rowe, J. J. Rush, D. G. Hinks, and S. Susman, Phys. Rev. Lett.

43, 1158 (1979).

3. K. H. Michel and J. M. Rowe, Phys. Rev. B22_, 1417 (1980).

THEORY OF QUASI ELASTIC SCATTERING FROM VANADIUM

DEUTERIDES AT LARGE MOMENTUM TRANSFERS

N. F. Berk

Work is continuing on the theory of the direct detection of host

relaxation in metal hydrides by quasielastic neutron scattering. The

mechanism for such scattering is assumed to be phase incoherence produced

by small, random displacements of the host atom equilibrium positions

which are caused by the elastic interaction between the host and diffusing

impurity nucleii. A preliminary treatment based on the methods of Krivoglaz

2

and Repetskii predicts that the response near w = is dominated by the

long-ranged part of the interaction, which leads to an integrable singularity

of the scattering function. Application of the theory has been made to

3 unpublished measurements by Magerl and Wipf on quasielastic scattering

from vanadium deuterides at large momentum transfers (4 ;< Q <^ 10 A

" ) . Impurity and host scatter incoherently with comparable cross sections in

this system, and the difference in thermal Debye-Waller factors serves to

provide contrast between them at large scattering wavevectors. The results

of the study have been inconclusive, however, due mainly to relatively

large energy resolution {y 8 meV) at the high Q-values. New experiments

with tighter resolution are scheduled. Apparently the theory also needs

to be extended to develop more systematically than before the regime of

large energy transfers and the role of the short range part of the hostimpurity interaction, in order to accomodate the constraints of finite

Instrumental resolution into the description of this subtle effect.

1. N. F. Berk and A. Magerl, Bull. Am. Phys. Soc. 2_6, 337 (1981)

10
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

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

2325 (1967).

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

PHONON DISPERSION OF GRAPHITE INTERCALATION COMPOUNDS

A. Magerl

and

H. Zabel

(University of Illinois, Urbana, IL)

The [001] L phonon branch of pyrolytic graphite is well described by

a sinusoidal function |l|, indicating that these modes are determined only

by nearest neighbor forces. The symmetry, the area mass density, and the

forces between the planes change upon intercalation. The [001] L phonons

are insensitive to any stacking sequence of graphite and/or intercalated

planes. Therefore, there are n graphite planes and one intercalated layer

within the repeat distance for a stage n compound. Correspondingly, the

[001] dispersion consists of (n + 1) phonon branches.

We measured the [001]L dispersions for stage 1 K and Cs, stage 2 K,

Rb and Cs and stage 3 K. The results for the stage 1 compounds together

with earlier data on Rb [2] and the stage 2 compounds are shown in figures

1 and 2, respectively.

Calculations of the [001]L dispersion of intercalated graphite by

several Born-von Karman models revealed that this formalism is not

appropriate to describe the donor compounds. However, extending the model

to include an interaction with an electronic layer between alkali and graphite

planes results in a shell model, which can consistently describe the measurements for all compounds. The fits are shown as solid lines in figures 1

and 2.

1. R. Nicklov, N. Wakabayaski, and H. G. Smith, Phys. Rev. 55, 4951 (1972).

2. W. D. Ellenson, D. Semmingsen, D. Guerard, D. G. Onn, and J. Fisher,

Mater. Soi. Eng. M. 137 (1977).

11
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

Figure 1. [001]L phonon dispersion for stage 1 intercalated graphite.

The solid lines represent fits by a shell model. Data for stage

1 Rb are from reference 2.

,3 .5 Qc/27r3 .5 Qc/2ir

Figure 2. [001]L phonon dispersion for stage 2 intercalated graphite.

The solid lines represent fits by a shell model.

12
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

UNIFICATION OF THE FUNDAMENTAL FORCES

R. C. Casella

The successes of the Glashow-Weinberg-Salam-Ward model in describing

the scattering of electrons, muons, and their neutrinos from hadrons and

among themselves, has led to the consensus that a unification of the

electromagnetic and weak forces has been achieved, which is comparable

in scope to the earlier unification of electricity and magnetism by

Maxwell and Faraday. At the heart of this effort lies the notion that

both interactions are mediated by the exchange of vector bosons, which,

in the presence of an asyrometric vacuum, assume the form of the wellknown photon field A (x) and the fields of the (hopefully) soon-to-bediscovered intermediate vector bosons, W~ and Z . Formally, the content

of the theory is expressed in terms of the gauge invariance^ of a suitably

chosen Yang-Mills Lagrangian. The gauge particles are in fact the

materialization of the vector gauge fields (generalizations of A (x)

in elctromagnetism) introduced to implement this invariance under local

phase transformations on the fundamental fermion fields, i|^(x) :

^(x) ^ expj-iF^0^(x)f^(x). (1)

(F is the a th generator of the underlying gauge group.) Moreover, the

idea, supported by experiment, that the strong forces are also mediated

by the exchange of vector particles (gluons) has led to attempts by Pati,

Salam, Georgi, Glashow, and others to unify the strong with the electroweak forces. This, in turn, has led to the possibility of proton decay

and neutron-antineutron oscillations, the latter potentially observable

2

in reactor experiments. Thus far, attempts to achieve further unification

by including the gravitational forces have met with enormous difficulty.

I believe that a major reason for this frustration lies in the fact that

the classical gravitational field is a (second-rank) tensor field, as first demonstrated by Einstein from the observation that, in the Newtonion

limit, it is the energy density which is the source of the gravitational

13
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRA^IS

field. Energy density is the component T of the general stress-energy

tensor T which is the source term in the observationally verified

Einstein field equations

G = k T . (2)

yv yv

This tensor property of the classical Einstein field sets it apart from

the vector gauge fields (photons, intermediate bosons, and gluons) in

the unified strong-electroweak theory. Within the context of perturbation

theory, it has been shown by Weinberg and others that due to the unique

sign of the energy density, the assumption of microscopic vector fields

mediating the gravitational interaction leads to the result that the

classical interaction is repulsive, contrary to observation. Nevertheless,

the drive to unify leads to me to look for nonperturbative solutions, in

which the underlying microscopic field is of vector character, somehow

generating bilinearly the macroscopic tensor field of Einstein. It is

anticipated that some progress will eventually come in this direction.

At a less ambitious level, I find that the introduction of effective

potentials in internal spaces can lead, by analogy with the solid-state

work on tunneling, to experimentally accessible relations between the

fundamental fermion (i.e., quark and lepton) masses. In a preliminary

investigation, I find that the mass of the t guark is predicted to lie

in the range 25 GeV to 30 GeV.

1. Cf., R. C. Casella, II Nuovo Cimento 42A , 377 (1977).

2. See, e.g., R. C. Casella, NBS Tech. Note No. 1142, p. 60, (ed.,

F. Shorten, 1981).

14
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAI-IS

THEORY OF NEUTRON SCATTERING FROM HYDROGEN IN METALS

INCLUDING THE EFFECTS OF TUNNELING

R. C. Casella

The continuing program involving the theory of neutron scattering

from systems in which molecular tunneling takes place in solids has

been extended to include the case of hydrogen in metals such as niobium,

which has recently been investigated experimentally by Magerl, Rush, and

2

Rowe at the NBS Reactor.

At low temperatures, dilute (< 0(1%) concentration) hydrogen atoms

in metals such as niobium and tantalum, also doped with 0(1%) concen- tration oxygen atoms, become trapped at the latter sites in what are believed to be two-well centers. Tunneling of the hydrogen between the

two potential minima near the oxygen provides an interesting system in

which molecular (atomic) tunneling in solids can be studied. Because

of the very large low-energy n-p scattering length it is possible to

study the excitations directly via neutron scattering. This has been

done both for transitions among the tunnel-split components of the

3 vibronic ground state and also for transitions from them to the first

2 and second vibronically excited states. The picture is complicated by

local strains which can produce relative displacements in the energy of

the component well minima. This greatly reduces the ratio of inelastic

to elastic neutron scattering within the ground doublet according to a model developed in Ref. 3. The reduction is by a factor sin22 9 where 6 is a mixing angle between the left and right single-well states, describing

their admixture in tight-binding approximate tunneling eigenstates. (The

average is over some assumed distribution of the strain induced relative

displacements.) In principle, for zero strain (infinite dilution) the

elastic and inelastic differential cross sections for scattering within

the ground doublet ought to be comparable. It is important to understand

theoretically the neutron induced transitions to the tunnel-split excited

states in order to confirm the model directly. I have shown that if

separated considerably from the ground doublet, the excited doublet can

15
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

be characterized by a mixing angle (j) , generally different from 6.

Matrix elements for transitions from either component of the ground

doublet to either of the tunnel-split excitations depend upon both 6 and (}). Under suitable experimental conditions, however, the differential

cross section for excitations from both components of the ground doublet

to either component of the excited doublet can be shown to be independent

4 5

of 6 and of (}). ' Thus the ratio A of inelastic cross sections,

A J /j^N excited / , ,j^. ground ,-v A = da/dfi), , ^, / da/dQ)° . ^, , (1) inelastic / inelastic

is enhanced by a (concentration dependent) factor l/sin^20). The

numerator in the expression for A is diminished by the transition form

factor F(q') where q' is the momentum transfer in the higher energy inelastic neutron scattering experiment involving vibronic excitation.

For small q', F(q') '^ (q'.D) , where D is the dipole transition matrix

element. For small momentum transfer q in the lower energy experiment

involving transitions within the ground doublet, the denominator

'^ (q.r/2) where r denotes the spatial displacement of the well minima

within each two-well complex. Thus, in the limit q' -> 0, q -^ such

that ratio p of the larger to the smaller remains fixed, A remains finite,

4

I find, in this limit,

A = (p^/8) (kp/k^) (-hca/V^)/ (sin226). (2)

Here, (k /k ) is the ratio of the final to the initial momenta of the

r 1 neutron in the higher energy experiment, ^lo is the vibronic excitation

energy, and V is the barrier height between the potential minima.

General expressions have also been derived for A and various other cross

•> ^, 5 section ratios when the small q, q expansion is not justified. Because

of the disparate conditions under which the higher [0(100 meV) ] and lower

[0(0.2 meV)] energy neutron scattering experiments are run in Nb:0(l%) H,

0(1%) 0, many difficult normalization problems have to be dealt with in

order to determine

appear worthwhile.

2 order to determine A even semiquantitatively. Nevertheless, it would

16
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

1. R. C. Casella, Phys, Rev. B20, 5318 (1979).

2. A. Magerl, J. J. Rush, and J. M. Rowe, private communication

(unpublished)

3. H. Wipf, A. Magerl, S. M. Shapiro, S. K. Satija, and W. Tomlinson,

Phys. Rev. Lett. 46, 947 (1981).

4. R. C. Casella, paper to be presented at the International Conference

on Phonon Physics, Bloomington, Indiana (1981).

5. R. C. Casella, to appear in Physioal Review.

COMPUTER SIMULATION OF THE MOLECULAR DISSOCIATION

OF A DIATOMIC CRYSTAL

S. F. Trevino

Energetic Materials Division, ARRADCOM, Dover, NJ 07801

and

D. H. Tsai

Thermophysics Division

Computer molecular dynamics has been successfully employed in the

study of dense matter under conditions far removed from equilibrium.

We have been interested in applying this technique to a molecular system

capable of undergoing thermal dissociation and we report here for the

first time simulation of systems which exhibit both equilibrium and non- equilibrium chemical kinetics.

Our model consists of 256 particles interacting with each other in

a pairwise manner through a compound Morse potential:

e |exp[-2a^(r-r^)] - 2 exp[-a^(r-r^) [ > ^ ^ "^ ^^^

1(a)

£ iexp[-2a2(r-r2)] -2 exp[-a2(r-r2)

] | +Qe, r < r^^^ 1(b)

v(r) =

17
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAl^IS

with r, = 1, r„ = .15, a, = In 2/. 35, a„ = In 2/20 and has two values,

viz 4 or 8. r,. is the interparticle separation for which the two

dis

expressions for v(r) are equal. Two particles i and j are considered to

form a diatomic molecule if their separation r,. is less than r , . , eq.

ij axs Kb). If r . is greater than or equal to r , . , the molecule is dissociated,

xj ciis

eq. 1(a). The molecular bond, once formed, is considered to be saturated,

and a neighbor k is assumed to interact with i (or j) through eq. 1(a) even if r,, (or r., ) is less than r,. . The interaction is assumed to

ik jk dis

extend to the 12 nearest molecular neighbors or their dissociated products.

Note that an isolated molecule formed through eq. 1(b) is metastable

with respect to its dissociated products. The method of Parrinello and

2 Rahman is used to perform the study under constant zero pressure. The

sample was prepared by starting with the molecules arranged in the

lowest temperature phase of nitrogen (Pa3), heating the crystal slowly

through an orientational order-disorder phase transition, quenching the

system to a temperature of .05e, and allowing equilibrium to become re- established in the crystal. The resulting sample exhibited disorder

among the molecular orientations as reflected in a broad angular correlation

function. In this and subsequent experiments, the equations of motion

3 2 1/2 were solved in time steps of At = .GIt where x = (mr.. /e) and m is

the mass of the particle.

In the first dissociation experiment with Q = A, the enthalpy of

the system was raised initally by .72e and thereafter by .25e four more

times. At each enthalpy level, the system was allowed to evolve for

3500 time steps. The kinetic energy, pressure, volume, and distribution

of molecules and free particles were monitored. Figure 1 shows the

kinetic energy and the number of free particles for this run. During

the latter part of each of the five constant enthalpy steps, indicated

by the boxed intervals in figure 1, the system attained a constant

temperature and a constant number of free particles on average. For the

chemical reaction

A2?==i2A

18
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

3000 6000 9000 12000 15000

TIME STEP

Figure 1. The lower figure is the kinetic energy per particle and the

upper the concentration of free particles as a function of

time for Q = 4. The boxed intervals indicate the regions

over which equilibrium averages are obtained. The insert is

a plot of In K (the equilibrium reaction rate) ,vs. 1/T and

the straight line the least squares fit.

r

in which the forward rate constant is k and the reverse rate constant

is k_ , the quantity

K = k^/k_-L

can be obtained at each temperature from the number of free particles

4

at that temperature. Its temperature dependence can be written as

K = f exp |-(H-L-H_-L)/kT\

The insert in figure 1 shows InK vs 1/T. The least squares fit of the

data with a straight line gives H^ - H_^ = 1.57 £. This implies that the

barrier H for the forward reaction is greater than the barrier H_^ for

the reverse reaction, despite the metastability of the isolated molecule,

eq. 1. This is a reflection of the many-body effect experienced by the

molecules in the field of their neighbors.

19
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

COO

I-<

LULUCC

-

200

3S 150

100

G

G

O ^

50

,^<^ 1 r 1 1 1 1 1 > 1 1 1

o

DC

LUZ

UJ

O G* n Q G G ra Q

1. G% cB^QB

% ° 3=^^^ "^

.8 G O'^ ^

G% , [^j^

.6 G a3Q

.4

.2 _G%—L- —

1

1 1 1 1 1 1 1 L_ 1 600 1200 1800 2400

TIME STEP

3000

Figure 2. The lower figures are the kinetic energy per particle and the

upper the concentration of free particles for Q = 8. The

squares correspond to the enthalpy increment of .4e and the

circles to .8e.

In the second dissociation experiment with Q = 8, ,the system was

allowed to evolve after the enthalpy of the original sample was raised

by each of three values, .15e, .4e and .8£. In the case of .15e, the

temperature reached .16e, one molecule decomposed and the system remained

in this condition for 6000 time steps. The results for the other two runs are shown in figure 2. For .4e, slow and partial decomposition

persisted for the first 2000 time steps after which more rapid decompositon

occurred until all the molecules were reacted. For .8e, rapid decompostion

occurred almost immediately until all the molecules were reacted.

These results show that with Q = 4, the system undergoes wellbehaved endothermic reactions when it is heated, and exhibits equilibrium

chemistry. With Q = 8, the system undergoes an explosive exothermic

reaction when it is heated, and the reaction rate as well as the induction

time depend on the temperature of the system.

20
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

We thank N. Berk, R. D. Mountain, and W. Braun for their discussions

and interest in this work. This work was supported in part by the Army

Research Office under contract MIPR No. ARO 2-79.

1. A. Paskin and G. J. Dienes, J. Appl. Phys. _43, 1605 (1972); W. T.

Ashurst and W. G. Hoover, Phys. Rev. All, 658 (1975); D. H. Tsai

and R. A. MacDonald, Phys. Rev. 514, 4714 (1976); D. H. Tsai and

R. A. MacDonald, High Tempuratures-High Pressures^ 8^, 403 (1976);

V. Y. Klimenko and A. N. Dremin, Detonatsiya, Chernogolovka, eds. 0.

N. Breusov et al. (Akad Nauk., USSR, 1978) p. 79; B. L. Holian, W.

G. Hoover, B. Moran and G. K. Straub, Phys. Rev. All, 2798 (1980).

2. M. Parrinello and A. Rahman, Phys. Rev. Lett. _45, 1196 (1980).

3. D. H. Tsai, in Accurate Characterization of the High Pressure

Environment, ed. E. C. Lloyd (Natl. Bur. Stds. Spec. Publ. 326,

Washington, DC 1971) pp. 105-123.

4. Walter J. Moore, Physioal Chemistry

second edition (Prentice-Hall

Inc, 1956) Chapter 17.

21
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

SPIN WAVE EXCITATIONS IN DILUTE Pd(Fe)

J. W. Lynn

(University of Maryland, College Park, MD)

and

(National Bureau of Standards, Washington, D.C.)

and

J . J . Rhyne

and

J. I. Budnick

(University of Connecticut, Storrs, CT)

The properties of magnetic impurities, such as Fe, Co, or Ni in Pd,

have attracted considerable interest because of the formation of "giant

moments" in this system. In the range of impurity concentrations where

these giant-moment clusters are isolated from each other, the system is

thought to form a spin-glass state at low temperatures, whereas at high

concentrations a transition to a conventional ferromagnetic state is

observed. In the intermediate concentration range, a crossover from

ferromagnetic to spin-glass behavior should be observed.

The critical concentration for ferromagnetism to occur is '^^O. 12 percent Fe, and a relatively uniform ferromagnetic state is achieved for Fe

concentrations exceeding '^3 percent. To study the dynamics of this

system in the dilute ferromagnetic region, we have carried out tripleaxis measurements on a 9.1 gm powder sample of Pd(1.5 percent Fe) . The

incident energy was fixed at 4.87 meV, and a cold Be filter was placed

in the incident beam to suppress the transmission of higher energy

neutrons and reduce the ambient background. Figure 1 shows the observed

magnetic scattering (after subtraction of nonmagnetic background scattering) at 40 K and 50 K (T = 67 K) . Relatively well-defined spin-wave

excitations are observed, which are seen to shift to lower energy as T

is approached. The dispersion of these excitations is consistent with a

22
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

Pd (1.5% Fe) Q == 0.12 a'

Ei = 4.87 meV

Figure 1. Observed spin-wave scattering at two temperatures below

T (67 K) , showing that the scattering shifts to smaller

energies with increasing temperature. At this momentum

transfer, the energy transfer is restricted by conservation

of momentum and energy to 0.6 meV.

quadratic dispersion relation with D 2; 40 meV-A at 40 K. Further work

as a function of temperature and concentration is in progress.

23
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

MAGNETIC PROPERTIES OF THE SUPERCONDUCTOR (Ce-,_^Tb^) RU2

J. A. 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 polycrystalline specimens of (Ce^ Tb )Ru_, for x=0.07, 0.18 and 0.44, in

1-x X 2

order to study the inelastic magnetic scattering as well as the development

of magnetic correlations at low temperatures.

High resolution neutron inelastic scattering on the lowest Tb

concentration sample shows the existence of an excitation at ^^0.75 meV

at He temperature. At T=15K this excitation decreases in intensity while

another excitation at "^0.35 meV appears. These two peaks are consistent

with the energy levels scheme predicted from the experimental values of

the Lea, Leask, and Wolf parameters x and W found for the (Ce^_ Ho )Ru„

system. According to this prediction the ground state is a T singlet

1

and the two first excited states are a T, and a F^ triplets respectively.

4 5

Further inelastic scattering shows the existence of an excitation

2

at ^^3.3 meV in all the samples. The relative intensity of this excitation

increases with increasing Tb concentration and this is attributed to Tb-Tb

exchange interaction. A very weak peak appearing at '^6.6 meV is also

consistent with the predicted energy levels scheme. As the Tb exchange

3

appears to be larger than the Ho exchange in the related Ho system, further

measurements at a lower concentration of Tb will be necessary to establish

the single ion crystal field level diagram unambigously

.

Small angle neutron scattering measurements have been carried out on the x=0.18 sample in order to study the spatial and temperature dependence

of the magnetic correlations in this system. Momentum transfer values between

0.04 and 0.15a were measured and the data were found to be well represented

by an Ornstein-Zernike correlation function. The correlation range increased

from ?=8S at 5K to ^=16^ at T=1.17K with no sign of saturation. This

behavior is similar to that found in the related Ho system.

24
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

1. J. W. Lynn, D. E. Moncton, L. Passell, and W. Thomlinson, Fhys. Rev.

B21, 1, 70 (1980).

2. J. A. Fernandez-Baca and J. W. Lynn, NBS Teohnioal IHote 1142, F. Shorten

Ed. 77 (1981).

3. J. A. Fernandez-Baca and J. W. Lynn, J. Appt. Physios _52, 3, 2183

(1981).

MEAN FIELD BEHAVIOR OF FERROMAGNETIC HoRh^B^

J . W . Lynn

(University of Maryland, College Park, MD)

and

(National Bureau of Standards, Washington, DC)

and

R. N. Shelton

(Iowa State University, Ames, lA)

The pseudoternary alloy (Er Ho )Rh,B, exhibits both magnetic

and superconducting properties. Pure ErRh.B, becomes superconducting

1

at T . = 8.6 K, then reenters the normal conducting state at T „ = 0.9 K

cl „ ° cz as it becomes ferromagnetic. With the substitution of Ho for Er, all

three phase ^ transitions (T , , T „ and T..) decrease in temperature. Around

cl c2 M

^ X '^^ 0.3 T „ and T^, reverse direction and increase with x, and the three phase

c2 M

boundaries meet at a multicritical point ^ at x = 0.89, T^, = 6.0 K. Our M

susceptibility and neutron scattering studies on an alloy in this concen4 tration region showed the magnetic phase transition was mean-field like

in that we obtained a critical exponent 3 = 1/2 for the order parameter,

and we found very little critical scattering at small wavevectors. To

further characterize the magnetic transition, we have carried out neutron

scattering experiments on pure HoRh.B, , which shows no superconducting

phase transition. Figure 1 shows the {101} Bragg peak intensity, which is

proportional to the square of the magnetization. The diffraction data

25
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

2500 1-

2000

It)« 1500

* 1000

500

HoRh4B4

Ei= 14.8 meV

40' - 25' - 25' - 40'

Background

5.0 5.5 6.0 T(K)6.5

Figure 1. Intensity of the {lOl} Bragg peak as a function of temperature.

established the Ho moment is directed along the unique tetrogonal axis, with

a low temperature saturated moment y„ = (8.34 + 0.3)]J_. The solid curve

Z — B

is the mean-field result for S = 1/2, which is seen to agree well with the

experimental results over the entire temperature range. Mean-field

3 behavior has already been observed in the specific heat data.

Our inelastic scattering data show that the crystal-field ground state

is a doublet, with the first excited state at 4.3 meV. Therefore, S = 1/2

is to be expected. If the spins are locked along the c-axis, then the system

would correspond to a three-dimensional Ising ferromagnet. Mean-field

26
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

behavior (with logarithmic corrections) would then be expected if the

coupling is dipolar in nature since the marginal dimensionality d* is

three in this case. However, the observed T of 6.5 K is too large to

c ° be due to dipolar coupling alone. The only other way to have (apparent)

mean-field behavior is if the range of the exchange interaction is very

long. We suspect this is the case since the magnetization is strongly

coupled to the conduction electron system at lower Ho concentrations,

producing the reentrant superconducting phase transition. The range of

the coupling in this case is of the order of the London penetration

depth X, which is typically of the order the hundreds of angstroms. For

pure HoRh.B, the superconductivity does not appear since T^ > Tj,2(^5 K) , but the propensity to be a superconductor is still present, leading to the

apparent mean-field behavior of the magnetization.

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. Moncton, D. B. McWhan, J. Eckert, G. Shirane, and

W. Thomlinson, Phys. Rev. Lett. 39, 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. J. W. Lynn and R. N. Shelton (to be published). J. W. Lynn, in Ternary

Superconductors, ed . by Shenoy, Dunlap , and Fradin, (North-Holland, 1981)

p. 57.

27
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

MAGNETIC PROPERTIES OF CUBIC AND HEXAGONAL HoMn2

J. Rhyne

and

K. Hardman

(Chemical Stability and Corrosion Division)

and

S. Malik and W. Wallace

(University of Pittsburgh, Pittsburgh, PA)

HoMn„ crystallizes in the cubic Laves phase C-15 (Fd3m) structure

which has two inequivalent sites, one for the Ho (a) and one for the Mn (d)

The structure can be transformed to the hexagonal Laves phase C-14 (P6„/mmc)

structure by a careful annealing procedure. In this structure, the Mn

occupies two sites (a and h) , and the Ho occupies an f site.

High resolution neutron magnetic profile refinement studies have

been performed on both the cubic and hexagonal phases at 295 K and 4 K.

Bulk magnetization measurements gave a Curie temperature of 26 K for both

phases and essentially equal saturation magnetizations, the latter values

being affected by the large crystal field anisotropy of the Ho, particularly

in the hexagonal structure.

The neutron refinement method calculated 4 K sublattice magnetization

values for both the Ho and the Mn sites as given in table 1. R-factors for

the profile fits are also given and indicate excellent agreement between the

experimental data and the nuclear and magnetic model. Ho and Mn spins are oriented antiparallel resulting in a f errimagnetic structure. The spins

are aligned in the basal plane of the hexagonal HoMn„ as expected from the

symmetry of the Ho 4f electron charge distribution.

28
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

Table 1. Cubic and hexagonal HoMn^ structural and magnetic parameters

obtained from neutron profile refinement (Neu) and magnetization

(Mag) data.

Latt. Param. (A) u^^CUj) U*^(u,) ^^„„^ T^ (Mag)

CUBIC 7.518 8.12 -0.84 6.45 (Neu) 26 K

6.4 (Mag)

HEX 5.282 (a) 9.40 -0.64 (a) 7.5 (Neu) 26 K

8.622 (c) -1.03 (h) 6.4 (Mag)

R factors of fit above and below Curie temperature (R^^p^ = weighted

profile R factor, R , = calculated statistical "perfect fit" R

exPd

factor, R = magnetxc model R factor only):

mag.

Cubic Hexagonal

R /R ^ (295 K) 8.66/4.76 5.01/3.32

w.p. expd.

R /R ^ (4 K) 7.73/3.05 6.31/3.08

w.p. expd.

R (4 K) 4.3 3.55

mag.

29
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

MAGNETIC AND STRUCTURAL PROPERTIES OF Th5Mn23Dx AND Y5Mn23Dx

K. Hardman

(Chemical Stability and Corrosion Division)

and

J. J. Rhyne and E. Prince

and

H. K. Smith, S. K. Malik, and W. E. Wallace

(University of Pittsburgh, Pittsburgh, PA)

The magnetic behavior of the isostructural compounds Y,Mn-„ and

b 2 J Th.Mn_„ is drastically altered on hydrogenation (or deuteration) . Y,Mn__

is a f errimagnetic compound with T = 486 K and a bulk magnetization value

of 13 y /f.u. (formula unit). The long-range magnetic order vanishes on

B hydrogen absorption. In contrast, Th,Mn-„ is a Pauli paramagnet, while

Th Mn H exhibits long-range magnetic ordering with T = 329 K and a bulk magnetization value of 18.5 y_/f.u.

B

Th^Mn22 and X^n^^^ are f.c.c. (space group Fm3m) with 116 atoms

per unit cell and four formula units per unit cell. There is one thorium or yttrium site and four manganese sites (b, d, f ^

, and f_). The

magnetic structure of Y^Mn^o is collinear with spins along the <111>

direction with the b and d sites coupled antiparallel to the two f sites.

All magnetically ordered spins within each of the sites are coupled in

the same direction. At liquid helium temperatures, the magnetization of

the manganese moments is 1.8 y /Mn atom at the f sites and greater than d

2 y /Mn atom at the b and d sites.

The compounds Th,Mn„„D., and Y,Mn-„D-_ were studied at 295 and 4 K

6 23 16 6 15 II

by neutron diffraction profile refinement methods. The pressure isotherms

of Th-Mn„„D and Y,Mn„„D were measured at 295 K. Th,Mn„„D exhibits a

6 23 X 6 23 X 6 23 x pressure plateau between 17 and 24 atoms of deuterium, while Y,Mn_„D has

6 23 X no plateau from 13 to 24 atoms of deuterium.

The site occupancies and atomic positions of the deuterium atoms were

determined for both compounds. At 295 K there are 5.67 and 8 deuterium

atoms in the tetrahedral f sites of Y Mn_„D__ and Th.Mn„-D., respectively

D Li 2.1 D 23 16

30
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAJIS

Table 1. Th,Mn„„D.,-4 K-P4-innin structural parameters.

6 23 16 2

X y z N

Th e 0.213 (0.214) 2

f 0.224 (0.214) 0.224 (0.214) 2

g 0.207 (0.214) 0.793 (0.786) 2

Mn b 0.5 1

Mn c 0.5 2

Ji 0.25 (0.25) 0.25 (0.25) 0.75 (0.75) 4

Mn k^ 0.005 (0) 0.359 (0.358) 0.182 (0.179) 8

Mn k2 0.017 (0) 0.259 (0.264) 0.363 (0.368) 8

D k^ 0.005 (0) 0.204 (0.204) 0.097 (0.102) 8

D i 0.249 (0.22) 0.500 (0.5) 4

h

0.353 (0.36) 0.350 (0.36) 0.146 (0.14) 4

31
REACTOR RADIATION DIVISION AND COLLABORATIVE PR0GRAI4S

(space group Fm3m) . However, the octahedral a site (one atom), which is

fully occupied in the yttrium compound, is virtually empty in the thorium

compound. The trigonal i site (8 atoms) in Th Mn D , is two-thirds full,

b z J lb

while the tetrahedral j site (9) was occupied in Y Mn_„D^_. The remaining

b A5 LL

deuterium atoms in Y,Mn„„D„„ occupied the tetrahedral k site (6.13 atoms).

6 23 22

Y,Mn„„D„„ becomes primitive tetragonal (P4-/mnm) and undergoes a magnetic phase change around 160 K corresponding to a transition in the

magnetic susceptibility. Neutron diffraction data suggest this change

to be from the paramagnetic phase to a short range magnetic cluster

phase, in that antiferromagnetic peaks as well as magnetic contribution

to nuclear peaks are present.

A structural and magnetic phase change occurs in Th,Mn__D., below

6 z3 16

80 K. At 4 K, Th,Mn_„D^, has a tetragonal structure (P4o/nmm). The atom

6 /3 16 2

positions and occupancy are given in table 1. The values in parenthesis

are the face-centered cubic equivalent atomic positions. The lattice has

been slightly stretched along the c axis and contracted along/ the a axis

o o I from that of FCC structure with a = 9.077 A and c = 12.961 A.

Th,Mn_-D^, becomes f errimagnetic below the ordering temperature. Its

b L5 lb

magnetic coupling structure is similar to that of Y,Mn„„ except that the

b Li

d site has broken down into two sites which are c and j. The magnetic

moment spins on the b and c sites are coupled antiparallel to the j and two

k sites. Although the bulk magnetization values (12.32 y^/f.u. in Th,Mn__D , a b 2.5 lb

and 13.23 y^/f.u. in Y,Mn„„) are similar, the magnetic moments are generally

D b Li

less than in Y,Mn__. The magnitude of the moments in Th,Mn„„D,, at 4 K

b Li b 23 16 are 0.56, 2.62, 1.67, 0.99, and 0.44 y--/f.u. for b, c, j, k. , and k. sites

respectively. The striking differences

B

in these compounds suggest

12

that

electronic and steric effects are dominant in determining the magnetic and

structure order.

32
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

PREFERENTIAL ATOMIC ORDERING AND MAGNETIC STRUCTURES IN

K. Hardman

(Chemical Stability and Corrosion Division)

and

J. J. Rhyne

and

W. James

(University of Missouri, Rolla, MO)

The ternary system Y,(Fe^_ Mn )„„ exhibits unusual magnetic behavior.

The end numbers, Y,Mn^„ and Y Fe-„, magnetically order around 485K and

D /J b zj

have magnetic moments with magnitudes of 2 to 3y /atom. However, the Curie

B

temperatures and bulk magnetization values of the intermediate composition

ternary compounds are drastically reduced. In the compositional region,

x=0.4 to 0.75, there exists no long range magnetic ordering.

The crystal structure of Y , (Fe, Mn )_„ is face-centered cubic (Fm3m)

,

6 1-x X 23

isotypical with Th Mn-„. There are four nonequivalent lattice sites occupied

o Zj

by Mn and/or Fe atoms and one lattice site (e) , occupied by the six Y atoms.

The four transition metal crystallographic sites are as follows: b (one

atom), d (six atoms), and f and f (eight atoms each).

Neutron diffraction studies of eleven compounds across the compositional

range of the Y , (Fe, Mn )„^ system reveal the presence of substantial

6 1-x X 23

preferential atomic ordering of Fe and Mn atoms on the four transition metal

crystallographic sites. As shown in figure 1, the most striking result of

the atomic ordering 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

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.

33
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRALIS

The neutron results show that both Y,Fe and Y Mn are magnetically

6 L5 o zj

ordered with different magnetic moments on the four transition metal

crystallographic sites. The Fe moments in Y,Fe-„ are ferromagnetically

coupled while the Mn moments on the b and d sites are coupled antiparallel

to those on the two f sites in Y Mn„_. The magnitude and coupling of the

D z J Mn moments is very similar to those found in the polarized neutron diffraction

study of a single crystal of Y,Mn_-.

o Li

The sublattice magnetizations of the Mn rich compounds (x=0.8, 0.9,

1.0) are given in figure 2a. In all three cases the Mn moments on the b

and d sites remain coupled antiparallel to the two f sites. The introduction

of Fe into Y Mn sharply weakens the Mn-Mn interactions and leads to the

o Z J sharply reduced curie temperatures and magnetizations of figure 2a. Figure

2b illustrates the sublattice magnetization on the iron-rich ternary

compounds which shows a corresponding drop on the introduction of Mn atoms

favoring antiferromagnetic exchange onto the iron sites. The Y , (Fe^ to^^a 0-7)00

(J. /J U.z/ z

J

Figure 1.

0)E

.0

!Eu

£o

c

o

3*••

(0a

a> Q

20 40 60 80 100

X-Mn Concentration (%)

Preferential site ordering on Mn atoms expressed as a percentage

departure from a stoichiometric distribution.

34
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRMIS

0) UL\£0

10 20 30

X-Mn Concentration (%)

Figure 2a. Mn magnetic moments on the four independent sublattices as a function of Mn composition. The Fe atoms are not ordered in

the composition range. The arrows indicate the relative

spin direction on each site.

Figure 2b,

70 80 90 100

X-Mn Concentration (%)

Fe sublattice magnetic moments as a function of Mn composition,

The Mn atoms are not ordered. All iron moments are coupled

parallel except for x=0.27 which has the antiparallel configuration shown.

35
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

compound, which is close to composition for the breakdown of long range

order, exhibits antif erromagnetic coupling between the Fe spins as opposed

to the ferro order of the other Fe rich compounds.

1. A. Delapalme, J. Deportes, R. Lemaire, K. Hardman, and W. J. James,

J. Appl. Fhys. 50, 1987 (1979).

AMORPHOUS STRUCTURE OF TbFe2 AND YFe2

P. D 'Antonio and J. Konnert

(Naval Research Laboratory, Washington, DC)

and

J . J . Rhyne

and

C. R. Hubbard

(Ceramics, Glass, and Solid State Science Division)

A high precision structural refinement was performed on neutron

and x-ray diffraction data taken on TbFe and neutron data on YFe using

1

the RADILS technique.

The procedure allowed the calculation of radial distribution

functions form from spacious scaling, background, and termination errors

and the determination of the atomic coordination numbers, average interatomic distances, and disorder parameters. The latter are due to a combination of thermal disorder (Debye-Waller) and positional disorder

peculiar to the amorphous structure.

Figure 1 shows the reduced atomic radial distribution function for

YFe„ and calculated Gaussian components arising from first through third

Fe-Fe coordination spheres, first and second Y-Fe spheres and, first Y-Y

coordination. The corresponding coordination numbers (N) , atomic

separation distances (r) and thermal plus positional disorder parameters

(a) are given in table 1 for amorphous YFe„ and TbFe^ (neutron—N and

x-ray—X) . The table also lists equivalent values for crystalline laves phase

36
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

o O CM a\ a\ o

< rH CM CM CM CM CO m •k • • • • • • 3

O D o o O o o o

a.u

o O o m ON tH 00 o

e < vO o iH m r«. CM 3 CS • • • • • • <U V4 ts ro cn »* -* ir, u (K o >• >M. o O o o o O

D • CN4 -* •* -* CM -J

«« z t-H CM (N CO CM

(0h

01 u

u m C^ iH i-H CM o\ g < iH iH CM CM CM iH

cd •K • • • • » «

CD D o o O o o O

>< U

1 tM •

<U (U o <SI fO 00 o\ en

•o fc < u-1 o •* iH p^ rH h J3 • • • • • • o H ^ CM CO m >a- -* ir» n

•H

•o

•a O o CM •* 00 O

c • • • • • «8 Cvj m r>. C7^ 00 00 Z rH H CM CM iH

to 00 O

OJ • < 1-1 i-H O CM • • c o D o o

(S pL, iJ >- z

(0 1 -H 01 CM

•O C (D CM vO

•H

•H iH

fa < m o

u CM r-l E <e O XJ

4J CO

CO >.

Wl h o CM

(U o

CM to C O z 1-1 r-l

•rt U

-•o Z 0)M r^ rH « CO < r-l CM

to o. • • h £ D o o

o> o

J3 <J 3 •« c c CM a\ m

CO (U < -3- o

c fa «t • O CM >< Vj CM f^

•H 4) •W fa

CO ^

C EH •H o CM

•O •> • • ti CM " z CM lO O Q) iH 1-1 O fa O f«

00 Olo Or^r^vOr^cn CM CMCM mncMncM>*

o oo oooooo

r^ avOCM<fvOfnaOrHiri OCM<-Ln<3-CNr^0000CMi-l

OOmcMfMcOroOmOOO

>*O0^^^vDfn.H00CM»3•0^ iHCM CMCMCMCMCMrH

r-l O CM CJ\ CM cn CI CM

CD O C3 C3

O O O

m CM 00

m in m o

C^ «* 00 -*

CM CM CM

IS H

u

c

to 0)

4-1 fa 0)

to 1 fa •H <u 1 Q fa oc:

01 0) fa

1

0) fa

fa

0) 0) fa Bi fa

37
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

phase YFe (YFe -C) for comparison. It is noted that Fe-Fe coordination

values are largely exchanged in the amorphous structure which the R-Fe

(rare earth-ion) and R-R values differ considerably between the amorphous

and crystalline structures.

y Fe N

1^ 4 —

10

r(A)

Figure 1. Reduced radial distribution function 47Tp(r) for amorphous

YFe showing individual Gaussian coordinator components a corresponding average interatomic distances.

1. P. D 'Antonio and J. H. Konnert, J. AppZ. Cryst. 12_, 634 (1979)

38
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAIIS

COMPARISON OF THE FITS OF TWO MODELS TO THE SAME

SET OF POWDER DIFFRACTION DATA

E. Prince

It frequently happens that it is necessary to compare two models

that both appear to give reasonably good fits to a powder diffraction

pattern when refined by the Rietveld method. Hamilton's R-factor ratio

2

test, can only be used if it is possible to define independent statistics

2

both of which have X distributions. This condition can be met if the

parameters of one model form a subset of the parameters of the other, but

it may not be possible otherwise. A statistical test that can be used in

3 more general cases was introduced by Williams and Kloot. This test

involves looking for correlations between the differences in the predictions

of the models and the differences between the observed data and the arithmetic

means of the model predictions. ^ Let Z, = Y . - (1/2) (Y. . + Y„ ,), and

X oi Ici 2ci

X. = (Y . . - Y^ .), where Y . is the observed intensity at point i and

1 icx 2ci oi \ Y, . and Y- . are the intensities predicted by model 1 and model 2, respecIci 2ci f J J r tively. We want to determine the slope, X, of the regression line Z = AX.

This is the value of X which minimized the function

N

f(A) =

I

(Z. - XX. )^,

i=l

N

which isX= I Z.X. / I X.

1-1 / 1=1

The estimated variance of X is given by

a^2 ^ ^(^ _ 1^2^ r N -9 N ;

y z^ - x^ y x^

1 1

i=l 1=1

(N - 1) I X

i=l

The (1 - a)%' confidence interval for X is X + o. T. , where T. ^ ,„ is the — A 1-a l-a/2

/

(|)(t,v)dt = 1 - a/2.

39
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

and (t)(t, V) is the density function for student's t distribution with

V = (N-1) degrees of freedom.

The comparison of two proposed models for a lithium defficient

4

lithium tantalate gave a slope for the regression line of -0.01877 +

0.01069 with 95% confidence, showing that model 2 was a significantly

better fit to the data than model 1.

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

2. W. C. Hamilton, Aata Cryst. 18, 502 (1965).

3. E. J. Williams and N. H. Kloot, Aust. J. Appl. Soi. A, 1 (1953).

4. A. Santoro, R. S. Roth, and M. Austin (this report, page 46 ).

PRECISE WAVELENGTH DETERMINATION FOR THE MULTIDETECTOR

POWDER DIFFRACTOMETER

E. Prince

The maximum utility of the high-resolution powder dif fractometer

depends partly on as precise as possible determination of the wavelength.

In order to calibrate the instrument, we calculated a diffraction pattern

from yttrium iron garnet (YIG) , Y Fe_0 . This compound was known

because it is cubic with a relatively large unit cell, giving many wellresolved diffraction peaks. The lattice constant of a sample of was determined by Ms. E. Evans, of the International Center for Powder

o Diffraction Standards, to be 12.3779(3) A; Using this value and a Rietveld refinement of the neutron powder pattern, the wavelength is YIG

1.5423(1) A.

40
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

USE OF THE PEARSON TYPE VII DISTRIBUTION

IN THE NEUTRON PROFILE REFINEMENT OF THE STRUCTURES

OF LiRe03 AND Li2Re03

A. Santoro and R. S. Roth

and

R. J. Cava and D. W. Murphy

(Bell Laboratories, Murray Hill, NJ)

In the course of a powder neutron diffraction study of LiReO„ and

Li-ReO_, it became apparent that the peaks produced by samples of the two

compounds had tails too broad to confoirm to a Gaussian distribution. In

fact, an attempt to fit some isolated reflections with Gaussians gave

unreasonably high values of the goodness of fit x (figure 1). The agreement

between observed and calculated values, however, improved dramatically

2 3 when the Pearson type VII function ' was used to fit the same experimental

data (figure 2). This function was taken into consideration because it can be varied gradually from a Lorentzian to a Gaussian by changing the

value of one of its parameters. On the basis of these preliminary results,

it was decided to use the Pearson distribution in an attempt to refine the

structures of LiReO- and Li_ReO^ with the profile analysis method.

1. Pearson Type VII Distribution

The Pearson function is represented by the equation

,T l

^^'"" - A

'^' r(m) I r, ^ 726, _ 29o\

-

'i - 2'

y

F^jr(m - 1/2) H

' ^ \

H

j

(2^/"^ - 1) -m

(1)

where I is the integrated intensity; H, the full width at half maximum;

26 , the Bragg angle of the reflection;

peak shape. For m = 1, Eq. (1) becomes:

26 , the Bragg angle of the reflection; and m, a parameter defining the

y^ = (4l)/(H7T)[l + 4(26^ - 2e^)^/H^] "*- (2)

which is a Lorentzian. For m = 2, we obtain:

, = [4I(2-'-^^ - l)"'-^^/(H7T)][l + {4(26. - 26_)^/H^}(2-^/^ - 1)]

^

41

y. = [41(2"'" - 1) '"/(H7T)][1 + {4(26. - 26 )"/h"}(2"'" - 1)] (3)

1 1 o
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

4 5 6

which is the so called "modified Lorentzian." ' ' Finally it can be

shown that, for m -^ °°, Eq. (1) becomes a Gaussian:

y. = 2I[(£n2)/-^]-^''^(l/H) exp [-(4£n2) (26^ - 20^)^/H^] (4)

For values of m as low as 20 or 25, the Pearson function is practically

undistinguishable from a Gaussian.

2. Experimental

Neutron diffraction data were collected with a five-detector

dif fractometer at the National Bureau of Standards Reactor using a waveo length A = 1.5416(3) A produced by the reflection 220 of a Cu monochromator

.

The horizontal divergences of the first, second, and third collimator were 10', 20', 10' arc, respectively. The neutron data were anlyzed with

the Rietveld method, modified by Prince to include the Pearson function.

In the calculations, the value of ra was assumed to be 20-independent . The

background was assumed to be a straight line with finite slope and was refined together with the profile and structural parameters. Both

structures were refined with different values of the Pearson parameter m. The final results for the refined structures are given in tables 1 and 2.

3. Discussion

It has been noted previously that the value of m was considered to

be 20-independent. This is almost certainly an approximation which was adopted for both rhenium compounds, because line overlapping prevented

the experimental determination of the variation of m with the diffraction

angle. In those cases in which well separated peaks are available over

the entire angular range, the value of m, in general, decreases as 2G

increases. For example, in the case of a sample of Fe 0, , the peaks have

the shape of a modified Lorentzian at low diffraction angles and become

close to a Lorentzian at high angles (figure 3). It is difficult to find

a unique explanation for the departure of the powder diffraction lines from

Gaussian shape. Instrumental factors can be excluded by the fact that the

dif fractometer, used with identical experimental conditions, gives

Gaussian peaks with standard materials such as Al (x between 1.1 and 1.2)

42
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

Table 1. Results of the profile refinement of the structure of LiReO„,

itom Position X y z B

Re 6a 0.18(6)

18 b 0.3801(7) -0.012(1) 0.2540(9) 0.27(6)

Li 6a 0.227(1) 1.6(3)

m = 1.5, R = 5.66, R = 5.55, R^ = 7.04, R = 5.00

Space group: R3c, Tf= 6; Number of observations: 2464

Number of independent Bragg reflections: 49

Table 2. Results of the profile refinement of the structure of Li ReO-.

Atom Position X y z (*) B^ '

Re 6a 0.21

18b 0.3580(9) 0.008(2) 0.2449(8) 0.21

Li(l) 6a 0.188(1) 1.4

Li(2) 6a 0.831(1) 1.4

(*) Thermal parameters were not refined for this compound.

m = 3, R = 8.05, R = 7.58, R = 9.77, R^ = 7.71

Space group: R3c,^Z = 6; Number of observations: 2505

Number of independent Bragg reflections: 65

43
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

200

Angle

Figure 1. Least-squares fit of a Gaussian to the intensity data of a single peak of LiReO„. (x = 2.21).

200

Angle

Figure 2. Least-squares fit of a Pearson distribution to the same data

of figure 1 (in = 1.2, x

= 1.16).

44
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

lU

3r

2-

->s

'il

H

I •"--«..„>

± ± J. ± ± J

10 20 30 40 50 60

29

70 80 90 100 110

Figure 3. Plot of m versus 26 for a sample of 'Fe. 0^.

Broadening caused by particular distributions of crystallite sizes may be

a possible reason for the observed shapes. However, other factors, such

as structural distortions or thermal diffuse scattering, could play an important role in determining the observed intensity distributions.

The results obtained for the two rhenium compounds show conclusively

that the Pearson function can be applied successfully to neutron profile

refinements. However, a detailed understanding of the factors which may

cause departures from the Gaussian shape is still needed, especially to

predict the variation of m with 26.

1. H. M. Rietveld, J. Appl. Cvyst. _2, 65-71 (1969).

2. W. D. Elderton and N. L. Johnson, Systems of Fvequenoy Curves

(Cambridge Press, NY, 1969), pp. 11 -IS.

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

J. Appl. CrySt. 10, 66-68 (1977).

45
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

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

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

6. C. P. Khattak and D. E. Cox, J. Appl. Cryst. 1Q_, 405-411 (1977).

7. E. Prince, Batl. Bur. Stand. U.S. Tech. Bote 1117 (edited by F. J. Shorten, 1980), pp. 8-9.

POWDER NEUTRON DIFFRACTION STUDY OF THE NONSTOICHIOMETRIC

SOLID SOLUTION OF LITHIUM TANTALATE 9LiTa03:Ta205

A. Santoro

and

R. S. Roth and M. Austin

(Ceramic, Glass, and Solid State Science Division)

Lithium tantalate, LiTaO_, exists over a fairly large nonstoichometric solid solution range. Some of the most important properties of

the compound depend on the Li/Ta ratio, and for this reason possible

mechanisms of nonstoichiometry have received considerable attention in

the past. The most important models proposed so far for the defective

structure of LiTaO„ are those of: (i) Lerner, Legras, and Dumas [J. of

Crystal Growth, 3^, 231, (1968)], schematically represented in figure 1;

(ii) Nassau and Lines [J. Appl. Phys, 4]^, 533, (1970)], represented in

figure 2; and (iii) Raeuber [Current Topics in Materials Science, Vol. I,

edited by E. Kaldis, North Holland Publishing Co. (1977)], represented in

figure 3. Figure 4 shows the structure of stoichiometric LiTaO- and explains

the sjnubols used in the previous illustrations. Due to lack of experimental

data it has not been decided which of these models is present in the structure

of nonstoichiometric LiTaO^. We have, therefore, attempted to solve the

defective structure of the compound by dualizing with the Rietveld method

the neutron intensities collected at the NBSR with the high resolution

powder dif f ractometer

.

46
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAIIS

LiMe

Me

Me

Me

Me

c-axis

i

Lila)

Lilb)

Figure 1. (a) Stacking sequence of cations in the nondefective structure

of LiMeOo. The horizontal lines indicate the oxygen layers,

(b) The defective structure proposed by Lerner et al. (1968).

The Me ion which substitutes the lithium ion is shifted along

the c_-axis so that it occupies an octahedral site rather than

the triangular environment of oxygen ions of the original Li+.

The nonstoichiometric lithium tantalate was prepared by mixing commercially available LiTaO^ and Ta^O^ (99.9% purity) in the molar ratio 9:1

and by heating the mixture in a platinum crucible for 19 hours at 1000°C.

The product of this treatment was ground and reheated at 1550° C for 18 hours.

Intensity data were collected with the same conditions used for other

compounds (see, e. g., NBS Technical Note 1142, May 1981, edited by F. Shorten,

p. 104). The models refined with the profile fitting method [Rietveld, H. M.,

J. Appl. Cryst., 1_, 65, (1969)] are illustrated in figure 5 and the

results of all the refinements are given in table 1.

In order to choose between the models, we have to test the hypothesis

that they give equally good descriptions of the structure. The hypothesis

is analyzed in a different part of this report (E. Prince, "Comparison of

the Fits of Two Models to the Same Data Set) where it is shown that the model

of Nassau and Lines gives a fit to the data better than those given by the

other two models.

47
REACTOR RADIATION DIVISION AND COLIABORATIVE PROGRAMS

D i-l u c < P*

(U •H m u

u m «

D e ^J »

nJ aj c ^^

lA U j: r~

T-l to u 4-1 vO

ai tx 1-1 OS

(U •H iH

j: oo a) s v»^ ^-N w c X tfl r^ C -H tJ X n) O O O -^

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a o m 0) 4) • 0. o. b; s 3 o CO ca D" c <u O. x (U H M 2 t« M

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tjs O rsj s.' <Tv O CM

to -^ >3- ~a r^ 00 m m r-» 00

lA O O CO O vT O so cT\ m •* o

o o O O O O .H O O O O rH

o o u o

O O O CO m S^ V-^ ^^ y-V o o ^-^ o o CO r^ O CM ro CM O

CO to CTS O Csl v^ OS O (N

-a- CO r^ -* iH r^ ^a* >—<T -a- 1^ "^ lA m r» m

i/s CO fsj in o r^ m o O CO o -a- O so o^ irt *^ O

v^ r-l o CO CO CO CO CO CO CM

U-l CO in CO CM ^ O

O O O O iH

CM -a- CM

s.^ ^-^ ^ ^^

-* r-l O CM Oi O CM s—

-a- -a i~~ < o CO o -a- o

O O O O r-l

o o u o

tjs vO o t3s O CM m m r- ^ so C3S in *a o

O O O O rH O O O O rH

!< >s N M C >< >% N oa c X ;»s N « c X >> N pa c X >, ^4 pq e X >. N pg s

^

48
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

O O 00 Cs| CM (M

CM

fa fa c c

o o

•o TJ

0) 41

(A 0]

cfl cS J3 J3 00 -*

00 O

O O O 1-1 00 ^^ n

CM o> en

r^ o

o c IT> ts

CM eg CO

in

O O 00 ^^ O O 00 O CM O 00 ^-^ 00 00 00

CM CO CM r-» cn CM C CO o O CO o

o

00

>ri O o in ^^ vo vo CM m

CM O CM O <M O

o o m O O i-H

r^ O CM O CM O

CO

(T>

\0 O O CO ^-v O O CO

00 CM 00

CM CO CM r~» CO CM

COO

O CM O O CM O

o

m

COmm

X >\ n to a X >. N PQ c X >. N « c

CM

•rt •H

49
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAllS

Me Me

Me Me

Me

Me

Me Me Me

(a) (b) (c) Figure 2. The stacking-fault model proposed by Nassau and Lines (1970)

showing the three-cation fault. (b) Me -rich compositions.

(c) Li -rich compositions. The reference nondefective

structure is shown in (a)

.

Me Me

Me

Me

Me

Me Me

-Li- -Li-

(a) (b)

Figure 3. (a) Nondefective reference structure of LiMe03. (b) Symmetric

nonpolar stacking disorder proposed by Raeuber (1977).

50
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAI-IS

Me

Figure 4. The structure of LiTaO^ in space group R3c. On the right of

the figure is the schematic representation of the structure

used in all the other illustrations.

The changes introduced in the structure of LiTaO by the presence, of

defects indicate that 9LiTaO„ : Ta„0(. approximates a centrosymmetric con- figuration more closely than stoichiometric LiTaO„ does. Since at the

Curie point the symmetry of LiTaO„ is R3c, this result implies that the

Curie temperature of the nonstoichiometric compound should be lower than

that of the stoichiometric material. This conclusion is in full agreement

with experimental observations.

51
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS'

Atom

Ta4

Li2

Li3 Ta2

Ta3

Lil

Tal

Me

Me

Me

-LiMe

-Li—

Occup.

29

0.33

002

27

0.33

(a)

077

0.50

28

0.27

0.00

SD I—^A Me ^

SD

SD

D

S

SD

SD

Me

Me

I

Me

-LiMe

V

Occup.

0.0128

0.0133

0128

0.33

(b)

77

0.75

0.62 0.50

0.2726

0.00 SD

SD

SD I;% Me

I—

S ^—Li—

Me

Me

Me

-LiMe

r

Occup.

0.28

01

0.33

0128

33

78

67

50

33

0.28

00

SD

SD

SD

SD

Figure 5. The "average" defective structures analyzed in the present

study: (a) Model proposed by Lerner et al. (1968); (b) Model

proposed by Nassau and Lines (1970); (c) Model proposed by Raueber

(1977). The letters S and D indicate whether the corresponding

atom is present in the stoichiometric or in the defective

structure. The approximate values of the occupancies and of

the z-coordinates of each metal atom are also indicated. As in

the previous figures, the heavy horizontal lines indicate the

layers formed by the oxygen atoms. The labeling of the atoms

is the same as that given in table 1.

52
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAl^lS

STRUCTURE REFINEMENT OF Li I -020 BY NEUTRON DIFFRACTION

P. M. Skarstad

(Medtronic Energy Technology, Brooklyn Center, MN)

and

E. Prince and J. J. Rush

Lithium iodide is widely used as a solid electrolyte in long-lived

low-drain batteries with high energy density. A dispersed-phase solid

electrolyte containing lithium iodide monohydrate as one phase also has

2 3 been used effectively in low-rate solid state cells. ' The monohydrate

of lithium iodide has been shown to be one to two orders of magnitude more

4 5 6 conductive than lithium iodide itself by several investigators. ' ' A

higher conductivity for the monohydrate might well be expected on the

basis of a formal similarity to the a-AgI family of solid electrolytes.

The basic antiperovskite-like arrangement of the iodide and oxygen

atoms in the small cubic unit cell (a = 4.30 A) of LiI*H was determined

7 from x-ray powder diffraction data by Weiss. Likely positions for the

lithium and hydrogen atoms can be inferred from the iodide-oxygen arrangement. However, these cannot be determined from the x-ray data.

We have investigated the structure of LiI*D_0 by neutron diffraction.

Both single-crystal and powder techniques were employed for structure

refinements over the temperature range 14 K to 300 K. At room temperature

the diffraction data are adequately modeled by independent harmonically

vibrating atoms. The single lithium atom in the unit cell is disordered

over the face-center sites of space group Pm3m, and the two deuterons are disordered over an eightfold siteset along the cell diagonals.

No unit cell in this structure can be cubic if the time of observation is fast with respect to the reorientation rate of water molecules. No

splitting or significant broadening of peaks is observed that would indicate

a differentiation of the unit cell axes down to 14 K, the lowest temperature

of the investigation. Table 1 shows the cubic cell constants at the various

temperatures

.

The simple structural model used at room temperature is not adequate

53
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAllS

below 128 K. Although refinement based on observed reflections gave a weighted *' R index, R , below 0.05 at both 128 K and 80 K, several of the w

unobserved reflections had calculated structure amplitudes very

substantially above the threshold for observable intensity. Accordingly,

in spite of the very small degree of overdeterminat.- on, fourth cumulant

coefficients for the oxygen atoms were incorporated in the model. This

results in significant " reductions in R , from 0.046 to 0.040 at 128 K and w

from 0.039 to 0.030 at 80 K. More importantly the calculated intensities

of the unobserved reflections, even though these reflections had no influence

on the refinement, were no longer above the threshold for observability.

The refined structure parameters are listed in table 2.

The actual distribution of scattering density may be expressed in

terms of the fourth cumulant coefficients by means of an Edgeworth expansion.

For a cubic site, the Edgeworth series is

0(x,y,z) = exp[-(l/2)r^](l + [1/24] \\^-^^l\(x) + H^(y) + H^(z)]

+ 6^K^^22 [H2(x)H2(y) + H2(x)H2(z) + H2(y)H2(z)] ()

.

T .u- • /^ 2^1/2 . 2^1/2 , ,^ 2^1/2 In this expression x = u /<u > , y = u /<u > , and z = u /<u > , X y z

where u , u , u are displacements from the equilibrium position in the

X y' z '^ 2

X, y, and z direction, respectively, and <u > denotes the second moment

of the density distribution about its mean. If the distribution were due

to thermal displacements only, this would correspond to a mean-square

displacement of a nucleus from ics equilibrium position. In this formula

2 2 2 2 r = X + y + z , and H„ and H, denote Hermite polynomials. They are

H2(x) = x^ - 1,

H^(x) = x^ - 6x^ + 3.

Using these, the density function becomes

54
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

(J)(x,y,z) = exp [-(l/2)r^ ] ) 1 + (1/24) [ \m(x^ + y^ + z^ - 6r^ + 9)

^„ r^2. 22. 22 „2

1122 + 6"K,_„(x y + X z + y z - 2r + 3)] [

All constant and quadratic terms in the expressions multiplied by the

fourth cumulants are isotropic. The quart ic terms divide into a function

4 with lobes pointing in <100> directions multiplied by K and a function

4 1111

with lobes pointing in <111> directions multiplied by K . However, if

4 4 4 2 2

K_

^ ^ = 3 K the quartic terms reduce to K (r ) , so they are also isotropic. Because this condition is satisfied within one standard

deviation in LiI'H„0, the density distribution for the oxygen is essentially

spherical, but with a radial variation that has positive kurtosis, i.e.,

it has more area in the tails than a Gaussian curve with the same variance.

An attempt was made to determine if the observed density distribution

for the oxygen could be approximated by the sum of six spherical harmonic

distributions each displaced from the body center of the unit cell along a

4 different <100> axis. A calculation of the K coefficient for such a distribution gave the somewhat surprising result that it is identically

zero, independent of the magnitude of the displacement. In other words,

the sum of three Gaussian curves with the same width, evenly spaced but with

the middle one four times as high as the others, has the same fourth moment

as a single Gaussian curve with the same second moment. It follows from the

result that a six spheres model cannot account for the observed data. The

distribution must be approximated rather by a set of prolate ellipsoids

pointing along the <100> directions.

Table 1. The cubic cell edge of LiI*H at various temperatures as determined by neutron powder diffraction.

T

a

o

14 K 4.2434(1) 1

80 K 4.2487(1) S

130 K 4.2565(2) 1

298 K 4.2955(2) S

55
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRALIS

^

l-l o

0) .

t-l fi

H) ro

iJ e

q; IX, ^ U)

i-i o

rt •H D. JS

4) 05 Vi Vj 3 O

o 01 3 U M ca

r- O in in o o

o o

o o

rH o o o

<U 1-1 o o

o <o • •

D.

•-\ ^^

<* iri rH v^ ^> ^ 00 XO

1-1 CvJ n r-( •H rH O O

i4 CQ O O • O C • -3- I I

CM \D ^-N tN OS rH tn

^-^ rH C7N rH rH rH rJ

a^ -^ -w' -— ^_^ ^^ v_/

II ro <Ni omen ovr^

cQ n o rH <r v3- o> O O rH O O O

o CQ > ro s^' ^«^ — CM s^ ^^ 2 CM v^* o en fn v-^ <n r- U LO -3- vO r-i ro CT\ -* o

o vO o r^ o ON o p

CJ m rH o o o u

<tf u

•o

>^ ^ ^ o

o a

c (fl ro CO c CU m CO E 3 n to CO m u c^ o o (N CO o o Cvl 4) o • • • • • • • • •o

' o rH , rH rH rH

•HT)O

CM

UOO

ro

OCO

o>

CO

CM

01 rH G

XI o

CO u H <

56
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

1. C. C. Liang and C. F. Holmes in Proceedings of the Symposia on Biomedical Implantable Applications and Ambient Temperature Lithium

Batteries, N. Margalit and B. B. Owens, eds.. Proceedings Vol. 80-4

(The Electrochemical Society, Princeton, NJ, 1980) pp. 27-33.

2. B. B. Owens and H. J. Hanson, U. S. Patent 4,007,122.

3. B. B. Owens, K. Fester and T. Kuder, Extended Abstracts 11-1, #25,

The Electrochemical Society, (1977).

4. S. Pack, B. B. Owens, and J. B. Wagner, J. Electvoahem. Soc. 121 , 2177-2179, (1980).

5. P. Hartwig and W. Weppner, Abstract C210, Third International

Meeting on Solid Electrolytes, Tokyo, (1980).

6. P. M. Skarstad, D. R. Merritt, and B. B. Owens, Abstract C217, Third

International Meeting on Solid Electrolytes, Tokyo, (1980).

7. E. Weiss, Z. anovg. allgem. Chem. 340, 203-206 (1965).

NEUTRON POWDER DIFFRACTION STUDY OF THE FAST- I ON

CONDUCTOR CuAgS BE1>/EEN 20° AND 1150C

C. Skarda and B. J. Wuensch

(Massachusetts Institute of Technology,

Cambridge, MA)

and

E. Prince

The compound CuAgS, which exists in nature as the mineral stromeyerite, occurs on the binary join midway between two fast-ion conductors, Cu„S

and Ag„S. The structures of the high temperature phases of both end

members have been determined in single-crystal neutron diffraction

studies [Cava, R. J. (June, 1978). Ph.D. thesis. Department of Materials

Science and Engineering, Massachusetts Institute of Technology] . But their

low temperature forms are complex and invariably twinned, unlike the simpler,

untwinned CuAgS. A single crystal of CuAgS, however, does not appear to

57
REACTOR RADIATION DIVISION AND COLLABORATIVE PR0GRA14S

survive the transition to its fast-ion phase, which offers the interesting

possibility of two cation species becoiraning mobile. For these reasons,

powder profile analysis by the Rietveld method was undertaken in an attempt

to describe the structure of CuAgS in both its low and high temperature

and high temperature modifications.

An x-ray diffraction study [Skinner, B. J. (1966). Econ. Geol.,

61, 1-26] indicated that stromeyerite encompasses the narrow composition

range Cu^ ^Ag,_ S, where <^ x £ 0.07, with Cu substituting in part for

Ag. Orthorhombic at room temperature, the stoichiometric compound undergoes

a transition at 93.3°C to a hexagonal phase, in which the S atoms retain

their hep configuration but the cations disorder. A third phase, appearing

at 127. 5 °C and characterized by fee packing of sulfur, is not considered

in the present investigation.

Although the structure of orthorhombic stromeyerite had been solved

[Frueh, A. J. (1955). Z. Krist. , 106, 299-307], It was poorly determined

with R = 30%, and required refining. The unit cell contains 4 CuAgS.

Displaying the S3mmietry of space group Cmcm, the structure consists of

Table 1. Experimental conditions for powder diffraction study of CuAgS.

Monochromatic beam: reflection 220 of a Cu crystal

Neutron wavelength: 1.5423 A

Mosaic spread of monochromator: 15 min. of arc Horizontal divergences:

a) in-pile collimator: 10 min. of arc

b) monochromatic beam collimator: 20 min. of arc

c) diffracted beam collimator: 10 min. of arc Region from 26 = 20° to 122° scanned in 0.05° steps

Detectors: 20-42°, 40-62°, 60-82°, 80-102°, 100-122°

Sample container: V can of 1 cm diameter

-12

Scattering lengths: Cu = 0.76 x 10 cm

Ag = 0.597 X lO"-'-^ cm

S = 0.285 X lO""*"^ cm

58
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRA>IS

zigzagging chains of silver and sulfur atoms paralleling the c axis.

Trigonal Cu-S layers (as in Cu S) alternate with layers of loosely packed

face-centered silver atoms parallel to the (001) face.

Above the phase transition, CuAgS enters a region of solid solution

with hexagonal Cu^S [Skinner, Loc. cit.], suggesting that the two compounds

are structurally related. Single-crystal neutron diffraction [Cava, Loc.

cit.] showed that Cu_S exhibits symmetry of space group P6^/mmc, with

close-packed S atoms in site 2(d). The cations are statistically divided

between two sites: I) 0.7068 Cu in the 3-coordinated site 2(b) within

close-packed S layers; and II) 0.2156 Cu in the 12 (k) site x 2x z , with

X = 0.2573 and z = 0.4339 at 120°C. This distribution of atoms was considered a possible model for hexagonal CuAgS, for which no structural

work had previously been done.

The large sample of CuAgS required for the neutron powder diffraction

study was prepared by heating a 1:1 Cu S:Ag„S 35-g mixture in an evacuated,

sealed Vycor tube at 250°C for five days, followed by a five-day annealing

at 90° C. X-ray analysis of the specimen revealed that a trace of free

silver existed as a second phase, probably the result of some sulfur loss

at high temperature. The powder was packed into a thin-walled vanadium can

1 cm in diameter and mounted in a top-heated furnace which could be placed

directly in the neutron beam. To facilitate thermal conduction along

the V can and through the sample, the furnace chamber was evacuated. The

temperature of the sample was not directly measured, but that of the furnace

was precalibrated as a function of current flow through the heating unit.

Diffracition data were collected with the experimental conditions given

in table 1.

Initially four sets of intensities were measured, with the furnace

at room temperature, at 100°C, at 115°C, and at 250°C. The diffraction

patterns indicated, however, that the compound remained in its orthorhombic

phase through the 115°C setting. It was concluded that poor heat transfer

through the dense ceramic CuAgS prevented the sample from reaching the

temperature of the furnace. To enhance thermal conductivity, a strip of

59
REACTOR RADIATION DIVISION AND COLLABORATIVE PR0GRAII3

esi

CMON

CM H E H

• o O Eo

>

n

II OJ I-l CD o a C8 u D X a O

O. td

U-l 00

lU o<

u 01 (U ^-N 3 i-i u r^

4J a CO a u o. -3- u m CO CM o r^ & a\ e

0) r^

4Ja

1 o o o

V4

vfi fn m

iH r^ ON

•• • • • u-l w a\ r-) o 0^ M o fSI a^ O ^

r-i O -J- m CN T-\ .H o o <

a II 11 II ^-^

I-l vO o 3 > 3 N

<M

en

4J en c vO

0)s vO

(Uc g •H

<W .a « f«» h vr

0) 0^ r^ <!• >4 r~ m \o 3 n • r-i O U r-- • CM U M vC 3 ao II II M « II <

u M &? PL< a> n s w 1 -3- oi bT ce: z «w CO O en

4J

09 o

tH ^ 3

CO 1

<u ta a

• CM

9)

f-l X>«H

M o

CMCM

C7\

-3-

cq

CNO

H

o

o

d

m ^ vO -*

N-^ N-^ St cn

00 iH

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C3N 00 c^

.-( CM -3-

r~. m <y\ CT\ r~ \o d CN d

o

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U1 ON 'c»

CN m iH

o

d

U1

CNd

o

d

o

d

o

o

a

CN

3 -3- 00-* a

-*

60
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAl^lS

CO

CM GO

r^ m »»

rH C-4 «* m ro s-^ ^-^ N—

< ro m r^ o ^-N m iH f^ fv* m • • •

s--' n CM d

VO

CM CS /"v ^N /-N 00 «3- o r^ O 6 II .H in o

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'I • en

• CM iH

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fo sr vO 00 CT> o sr o> ml in «3- Oi

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O o o to J P=r

1

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CD

(U

cn

01 H

e

•-X CM 1 CO o

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< x-^

61
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

silver foil with lateral branches was inserted in the V can; silver shot was placed at both ends of the CiiAgS powder to a depth of 0.5 cm, insuring

thermal contact between the foil and vanadium. With this arrangement,

another set of intensity data was collected at a furnace setting of 115°C,

at which point the sample had transformed completely to the hexagonal phase.

For future high-temperature neutron powder diffraction studies of ceramic

materials, a container should be constructed which would permit better

thermal conductivity, perhaps by running one or more thin vanadium rods

through the interior of the cylinder.

Results of the refinement of the room temperature phase are given

in table 2. Although the formation of free silver during the original

calcining suggested that the sample was somewhat Cu-rich, the fit obtained

assuming perfect stoichiometry was so good that adjustment of the Cu:Ag

ratio would provide no basis for comparing models. Thus all refinement

was carried out as though for stoichiometric CuAgS.

Analysis of the data collected at the nominal temperature of 100°C

yielded an isotropic thermal parameter for sulfur of 1.99. Assuming that

this value varies linearly with temperature for the S atoms, the actual

temperature of the sample was estimated to be 50°C. Table 3 gives the

parameters refined for this data.

The highly disordered hexagonal phase gave a weak diffraction pattern

at 115°C. Profile analysis was performed over the narrow range 33.80°

33.80° ;£ 26 ;< 62.00°, which included the six or seven Bragg reflections

present. To reduce the number of parameters, the half-w^^dth values U, V,

\ and W were held fixed at estimates obtained from the room-temperature

phase refinement, and the zero-point was not refined. Initial calculations were carried out for a structure consisting only of sulfur. Atoms were

placed in the 2(d) sites of space group P6«/mmc occupied by the sulfur

atoms in hexagonal Cu^S. This partial model yielded an R„ of 36.22%. A

difference Fourier showed residual densities in sites corresponding to

the Cu sites in Cu^S. Close lattice match (within about 4%) between

Cu«S and CuAgS gave further indication that the two compounds are isostructural. Therefore, various models were tested using the occupation

62
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAllS

Table 4. Results of structure refinement for CuAgS: 115°C phase.

R„ = 22.85

Bragg

N-P = 556

a = 4.1389(10)

(unrefined)

u = 5238.0

V = 2001.0 w = 1491.0

z = 0.0

c = 7.0817(27)

scale factor = 0.083(1)

V = 105.06(5)

n occupancy

S

2(d)

6m2

Cul

2(b)

6m2

Cu2

12 (k)

m

Ag

12 (k)

m

0.3333 0.6667 0,7500 3.26(1.28) 0.0833 1.0

0.2573 0.5146 0.4339 8.61(1.39) 0.0244 0.04887

0.0 0.0 0.25 12.03(1.61) 0.0589 0.7068

0.2573 0.5146 0.4339 8.61(1.39) 0.0833 0.1667

numbers and atomic positions proposed by Cava for Cu„S. A best fit of

R^ = 22.85% was obtained for the model described in table 4. Ag and Cu are not completely disordered, but the partial site 2(b) is populated

solely by Cu, so that most of the Cu atoms remain coplanar with S as in

the low temperature phase. The remainder of the cations partially fill

the 12 (k) positions. Lack of data prevented refinement of atomic

coordinates and occupancies. However, the value of R , when taken in

conjunction with the evidence for correlation between CuAgS and Cu„S, seems

to indicate that the model is a viable one, until successful growth of a single crystal of hexagonal CuAgS makes further analysis possible.

63
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

THE STRUCTURE OF THE RHOMBOHEDRAL PHASE OF Na3Sc2(P04)3

E. Prince

and

T. Brun and S. Sussman

(Argonne National Laboratory)

The compound Na Si„(PO,)^ is a fast ion conductor at elevated

temperatures. Studies of resistivity as a function of temperature indicate

that there is a phase transition at about 60°C which is associated with an abrupt increase in conductivity. Above the transition the conductivity

increases steadily, with an activation energy of 0.49 eV, up to a temperature

of about 180°C. Above 180°C the activation energy drops to 0.20 eV. The

crystal structure at room temperature has been reported to be monoclinic,

o o o space group Cc, with cell constants a = 16.10 A, b = 8.928 A, c = 9.109 A,

3 = 127.15°. This unit cell doesn't differ very much from a rhombohedral

cell, and it is unclear how strong the evidence is for the lack of a center

of symmetry. The crystal structure above the phase transition was previously

unknown, although it was believed to be rhombohedral.

In an effort to elucidate the nature of the phase transition and

the mechanism of conductivity, neutron powder patters were collected, on

the multidetector powder dif fractometer , at 25°C, 100°C, and 225°C. The room temperature structure with space group Cc has too many parameters to

refine with powder data. An attempt was made to refine the structure in

space group C2/c, but the fit was only fair (R = 9.86%, R = 4.89%, so

the fit is not consistent with the statistical precision of the data).

This refinement did, however, yield a satisfactory set of refined lattice

parameters: a = 16.0679(15) A, b = 8.9234(6) A, c = 9.0894(8) A, 3 = 126.994(4)'

Analysis of these constants and of the shapes of a few critical peaks

establishes that the true symmetry of this phase is monoclinic or lower.

At the higher temperatures the powder pattern sharpens up in a manner that is consistent with a transition to a rhombohedral structure.

At both 100 °C and 225 °C models based on space group R3c gave reasonably

64
lEACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAIIS

o iH a\ v£> 00 CO en m

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65
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

satisfactory•^ fits to the data. (R = 6.28%, R = 3.83% at 100 °C;

wp e

' R = 5.81%, R = 3.87% at 225 °C.) At 100 °C the cell constants are wp e o a = 8.9273(2) A, c = 22.3668(6) A. At 225 °C they are a = 8.9274(1) A,

o c = 22.5493(6) A. It is interesting to note that all of the thermal

expansion is along the c axis. The refined parameters are listed in

table 1.

The most notable feature of the structure is that three sodium atoms

occupy four sites in two crystallographically non-equivalent sets, set 6b

with point symmetry 3 and set 18e^ with point symmetry 2. At both temperatures

the occupancies of these sites were refined, with a constraint applied to

force the total number to remain at three. At 100°C this refinement resulted

in an entirely insignificant change from a model in which the b^ site was entirely full and the e^ site was only two thirds full. At 225°C there is a significant shift toward a model with vacancies on both sites. At both

temperatures the thermal motions of both sites are extremely anisotropic,

with the b^ site having a very large amplitude perpendicular to the c axis

and the e^ site having a large amplitude parallel to the c axis. This is

entirely consistent with a model for the electrical conductivity in which

the sodium ions are free to move through channels perpendicular to the c axis

in the vicinity of the b^ sites and through channels parallel to the c axis

in the vicinity of the e^ sites. The two types of channels are connected to

each other, but neither is connected to others of its own type. Thus, the

difference in activation energy may be associated with the appearance of

vacancies on both types of site.

1. V. A. Ehemov and V. B. Kalinia, Sov. Phys. Cvystallogr. 393 (1978)

66
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAIIG

SEARCH FOR A LOW TEMPERATURE PHASE TRANSITION IN LiH

Q. Johnson

(Lawrence Llvermore Laboratory, Livermore, CA)

and

E. Prince

Some years ago Yates, Westenholm, and Blngharn reported a specific

heat anomaly in LiH at about 20 K. They speculated that this might re- present a phase transition from an NaCl type structure to a CsCl type structure.

A transition of this type is a possible mechanism for a volume change at

high pressure observed by the high pressure crystallography group at

Livermore. Although it seemed that a more likely explanation of the low

temperature specific heat was the condensation of bubbles of hydrogen trapped

in the crystal, it was desirable to make a direct check for a CsCl type

phase. Accordingly, a high-resolution powder pattern was obtained at 4.2 K

on the multidetector powder dif fractometer at NBS from a sample of Li D.

There was no evidence in this powder pattern of any phase other than the

NaCl type phase.

1. B. Yates, G. H. Westenholm, and K. Bingham, J. Phys. C: Solid

State Phys. 1_, Yli^^ (1974).

CRYSTAL STRUCTURE OF AMMONIUM NITRATE PHASE III

C. S. Choi and H. J. Prask

(Energetic Materials Division, LCWSL, ARRADCOM, Dover, NJ)

and

(National Bureau of Standards, Washington, DC)

1 2

Two recent powder neutron diffraction studies ' of the structure

of AN phase III have reported two different orientations for the ammonium

group. The present study was undertaken to resolve the controversy. Using

a single crystal of AN containing 5 wt. % KNO„ in solid solution form, three67
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAI^IS

Table 1.

ion

ND,

NH,

Comparison of thermal motions of the ammonium ions in the

structure of phase 2 and 3.

phase Temperature (K)

357-398

305-357

disorder principal axes

(angle) T..(A°2) L,,(°)

90° .058 14.4

.058 14.4

.065 10.3

^42° .055 22.4

.034 19.1

.015 16.0

m

©

A

fi) /O

^-~~- H4'

Q

^\ H2[ H2/

\ \ H3'

^J

HI

.'-'V/^

Mirror Plane

^-'H3

HI'

m

Figure 1. The ammonium group of AN phase III viewed along the z-axis. The

ammonium groups are orientationally disordered by an angle of

42° about an axis parallel to the z-axis. The two alternate

molecular sites are related by mirror symmetry.

68
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRA^IS

dimensional neutron diffraction data were collected. The structure of

the ammonium group was determined by a Difference Fourier synthesis and was refined with a tetrahedral rigid body constraint for the ammonium

group. The final residual indices were R = 0.043 and R = 0.042. The w

ammonium groups are disordered orientationally with two alternate sites

which are related by mirror sjrmmetry and have one of their 4-axes directed

approximately parallel to the c-axis direction. Figure 1 is the c-axis

view of the ammonium ion and its alternate sites marked with the envelopes

of the thermal ellipsoids. Several interesting features were found in

the strucuture:

1. The ammonium group which possesses a mm symmetry in free form

does not have the mirror symmetry in the crystal despite the m symmetry of

the molecular site. Instead, the two disordered molecular sites are related

to each other with the m symmetry.

2. One-dimensional rotational reorientations of 42 about the c- axis direction appear likely for the NH, groups.

3. The observed reorientation angle, 42 , is not fixed by the molecular

or crystal symmetry, and hence, may be temperature dependent.

4. As shown in figure 1, H(3) and H(4) are not structurally equivalent;

the H(3) involves with a weak H-bond, whereas H(4) involves two stronger

H-bonds. Rotational reorientations of 42° entail H(4)->H(3) ' and H(3)^H(4) '

so that each hydrogen alternates sites of relatively weak and strong bonding.

The large librational components of the rigid ammonium ion—compared with

Phase II in table 1—may possibly arise from the disturbance due to the

sudden change of interaction at the two dissimilar sites.

1. B. W. Lucas, M. Ahtee, and A. W. Hewat, Acta Cryst. B36, 2005-2008

(1980).

2. C. S. Choi, H. J. Prask, and E. Prince, J. Appl. Cryst. 13, 403-409

(1980).

69
REACTOR RADIATION DIVISION AlTD COLLABORATIVE PROGRAMS

REFINEMENT OF 2-NITROGUANIDINE BY NEUTRON POVJDER DIFFRACTIOTnI

C. S. Choi

(Energetic Materials Division, LCWSI, AERADCOM, Dover, NJ)

and

(National Bureau of Standards, Washington, DC)

The crystal structure of 2-nitroguanidine was studied earlier by

Bryden, Burkardt, Huges, and Donahue (1956), but did not report the H

positions. This study was undertaken to determine the H positions by using

neutron powder diffraction method, A powder diffraction intensity profile

was measured up to 118 in scattering angle by using the five detector

neutron dif fractometer with collimation of 10', 20', and 10'. The refinement was carried out by means of the modified Rietveld method with isotropic

temperature factors for all atoms and obtained the final R indices,

R. = 0.057 and R =0.020. The molecules are linked together by a three1 w

dimensional network of hydrogen bonds. The bond lengths are given in

figure 1.

Figure 1. ORTEP drawing of nitroguanidine molecule.

70
REACTOR RADIATION DIVISION AET) COLLABORATIVE PROGRAMS

STUDIES OF RIBONUCLEASE A

BY X-RAY AND NEUTRON DIFFRACTION

A. Wlodawer

and

L. Sjblin

(Laboratory of Molecular Biology, National Institutes of Health,

NIADDK, Bethesda, MD)

and

(National Bureau of Standards, Washington, DC)

The structure of ribonuclease A has been refined with the X-ray

o and neutron data at 2.0 A resolution. The refinement proceeded in

several steps. Initially only the x-ray data were used and the structure

o was refined by a restrained-parameter least-squares procedure at 2.0 A

resolution and rebuilt using computer graphics. The final agreement

factor R = Z(||f I - If ||)/e|f I was 0.159. The positions of the 951

I' o ' ' c 'I ' o

' main-chain atoms have been determined with an estimated accuracy of

o 0.17 A. In addition, the model included a phosphate group in the active

site and 176 waters, many of them with partial occupancy. The bond

lengths in the refined structure of RNase A differ from the ideal values

o by an overall root-mean-square deviation of 0.022 A; the corresponding

o value for angle distances is 0.06 A. The r.m.s. deviation of planar

o atoms from ideality is 0.017 A, and the r.m.s. deviation of the peptide

torsion angles from 180° is 3.4°. The model is in good agreement with

the final difference Fourier maps.

Two active site histidines. His 12 and His 119, form hydrogen bonds

to the phosphate molecule. His 119 is also hydrogen bonded to the car- boxyl of Asp 121 (figure 1) and His 12 to the carbonyl of Thr 45. The

observed sequence of hydrogen bonds is in good agreement with the postulated mechanism of change transfer involving His 119, Asp 121, His 12,

and the phosphate. The structure of the RNase A is very similar to that

of RNase S, particularly in the active site region. The r.m.s. discrepancy

71
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

•«Jtv,

Figure 1. The electron density superimposed on the model of residues 119-

121. oThe distance between NE2 of His 119 and ODl of Asp 121 is

2.59 A. The quality of the map for His 119 is comparable to

that for the two neighboring side chains, as well as for most

of the remaining parts of the molecule.

-1

CA «o

Figure 2. Superimposed C^ coordinates for the final model of RNase A and

for the refined structure of RNase S. dashed

.

RNase A solid, RNase S

72
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

Figure 3. Sections through difference Fourier maps for five side chains

of RNase A. The maps were calculated at 2.8-A resolution, with

coefficients (Fq - ¥^)a^. The atoms belonging to these side

chains, as well as a phosphate molecule, were removed from the

structure factor calculation. All maps were contoured at the same arbitrary level. Solid lines, positive density; dashed

lines, negative density; zero contour is omitted. The low

density around the CB atoms is caused by the negative scattering of the attached hydrogens not resolved at this resolution,

(a) Histidine-12; (b) histidine-48; (c) histidine-105; (d) histidine-119; (e) tyrosine-25 (note that deuterium DH lies below

the contoured plane)

.

73
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

o of all atoms for residues 1-16 and 24-123 is 1.06 A, and the r.m.s.

o discrepancy for the active site region is 0.6 A. The comparison of the

C positions in the two models is shown in figure 2.

01, o In the next step of analysis, x-ray data to 2.0 A and neutron data

o to 2.8 A respectively were used in a joint refinement. This procedure

converged with the crystallographic R factors of 0.162 (x-ray) and 0.258

(neutron) . Refined neutron data enabled unambiguous assignment of the

orientation of all four histidines, including the active site His 12 and

His 119 (figure 3).

Recently joint refinement has been extended to include neutron data

o to 2.0 A resolution. The R factors are currently at 0.159 (x-ray) and

0.190 (neutron), and the refinement and rebuilding is being continued.

New data include a more detailed description of the network of hydrogen

bonds, especially those involving solvent and an analysis of the pattern

of amid hydrogen exchange.

REFINEMENT OF THE CRYSTAL ORIENTATION MATRIX

FOR THE FU\T-CONE D I FFRACTOMETER

A. Wlodawer and L. Sjolin

(National Institutes of Health, Bethesda, MD)

and

(National Bureau of Standards, Washington, DC)

and

A. Santoro

A procedure for refining a crystal orientation matrix for the flatcone dif fractometer has been developed. The positions of the centers

of gravity of reflections obtained during routine data collection are transformed in such a way that they can be used as input to the leastsquares procedures of Busing and Levy (1967) or Shoemaker and Bassi

(1970) . The orientation matrix can be refined on the basis of the

positions of all observed reflections, and not only of a selected sample,

74
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

thus increasing its reliability. The procedure is particularly suited

for protein crystallographic studies, as it makes it possible to compensate

for crystal movements and electronic drifts encountered during data

collection.

Let us assume that the position of each reflection has been

accurately determined by finding its center of gravity in the (d, ij;) space,

where d represents the position of a point along the counter and ^ the

rotation angle. This can be used to obtain better estimates of the

orientation matrix and the lattice parameters of the crystal with a method

similar to that proposed by Busing and Levy (1967) or with the procedure

given by Shoemaker and Bassi (1970) and Shoemaker (1970). If we adopt

the first method, we may assume that the Bragg condition is satisfied

for the center of gravity of a reflection, and we may take as an

(*) observation the value ^, corresponding to this point.

The only requirement here is that the scattering vector u make an angle of 90° + 6 with the primary beam direction, i.e.,

u^2 = - sin e (1)

where

^£ = ^d ^c ^

^^^

From Equations (1) and (2), we obtain

(u,„ cos y^) sin ip + (u,„ cos ii = (u,^ sin y, - sin 6) (3)

(p3 d c 9/ c (pi d

and the calculated value ip corresponding to the observation ^p can be

obtained since

(*) Here and in what follows we will adhere to the procedure of Busing and

Levy (1967) of indicating with the subscript d_ the instrumental dial

readings and their matrices, with the subscript c_ the calculated

angles and their matrices, and without subscripts the quantities evaluated

from the trial parameters. All other symbols, as well as the reference

systems used here, are defined in Busing and Levy (1967) and/or Prince

et al. (1978).

75
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

From the above considerations it is clear that the observations most

easily obtainable with a linear detector operated in flat-cone geometry- are analogous to the type 5 observations analyzed by Busing and Levy (1967)

.

On the other hand, the input required by the procedure of Shoemaker

and Bassi (1970) and Shoemaker (1970) requires precise values of the setting

angles of reflections analyzed with the geometry of a four-circle diffractometer. From these the coordinates h of the corresponding reciprocal

lattice points can be evaluated, and the observational equations are

V""*- h, = V""'" V h = h' (5)

where all the symbols have the same meaning as those defined by Shoemaker

and Bassi (1970). This procedure can be extended to flat-cone geometry

in the following way. From the settings (|), X> ^j V^i ^^"^ "^ > which center a reflection on the linear detector, we may calculate the vector h, in the

Cartesian system attached to the $-circle with the equations

where

and

1

= ^^^^ (7)

h, = cos T sin y

hg2 - cos T cos y -1 (8)

The coordinates h (Equation 6) are sufficient as input to Shoemaker's

procedure, but their use requires some modification. If one desires to use the unmodified procedure, the required input consists of the setting

angles of reflections in four-circle geometry which are given by

76
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAI'lS

20 = cos (cos T cos y)

o

to = o The procedure was tested on a crystal which was deliberately misset

and was shown to perform successfully. Even when the maximum misalignment

for individual reflections was as large as .5 in ^, the recalculated

matrix properly centered all reflections. The limits of convergence were

reached when the reflections were becoming only partially recorded in

their boxes, since under these conditions the apparent centers of gravity

would no longer correspond to the true position of each reflection.

Since incompletely recorded reflections can be recognized as such and

properly marked, it is possible to extrapolate the positions of their

centers of gravity and to use them in the recalculation of the orientation

matrix. Under these conditions the intensity data are not useful anyway,

and the level has to be recollected. We have found that, as long as the

centers of gravity of the reflections did not fall outside of their

predicted boxes, the procedure was powerful enough to ensure that during a subsequent scan they would be completely enclosed within their boxes, even though they would not necessarily be very well centered.

1. W. R. Busing and H. A. Levy, Acta Cryst. 22, 457-A64 (1967).

2. E. Prince, A. Wlodawer, and A. Santoro, J. Appl. Cryst. 11, 173-

178 (1978).

3. D. P. Shoemaker, J. Appl. Cryst. 3^, 179-180 (1970).

4. D. P. Shoemaker and G. Bassi, Acta Cryst. A26, 97-101 (1970).

77
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAilS

ADVANCED NEUTRON METHODS

J. M. Rowe, C. J. Glinka, N. Berk, J. LaRock,

R. H. Williams, and D. Fravel

1. Small Angle Neutron Scattering (SANS)

a. The Small-Angle Scattering Spectrometer

During the past year, construction and installation of all of the

major components of the new small-angle scattering (SANS) spectrometer

1 2 described in previous reports ' have been completed. A photograph of

the instrument is shown in figure 1. By May 1981, construction had

progressed to the point that the 25 x 25 cm position-sensitive detector,

3 the smaller of two such detectors purchased for the facility, could be

installed at the end of the instrument's 8 m evacuated flight path. Since

then calibration measurements and operational testing of the entire

2

instrument and its data acquisition system have been underway. Some of

the highlights of the assembly and testing phases are summarized below.

Flux: Following the installation of the beam port shutter and the

liquid-nitrogen-cooled beam filter, consisting of 25 cm of beryllium and

15 cm of single crystal bismuth, the neutron flux was measured at the

entrance to the 4.5m pre-sample flight tube. The instrument's mechanical

velocity selector had not been installed at this time and, therefore, all

o neutrons with wavelengths greater than 4 A were included in the measurement,

The measurements were made by G. Lamaze and D. Gilliam of the Nuclear

Radiation Division using a precisely calibrated double fission chamber.

7 2

The measured flux was 1.1 x 10 n/cm -sec. From this value we have calculated the flux at the sample position taking into account the transmission

of the velocity selector and the colllmation along the flight tube. For a

o wavelength of 6 A (AX/A = 0.25) and a reactor power of 10 MW, the flux at

4 2

the sample for the tightest collimation available is 2 x 10 n/cm -sec, and

5 2

for the coarsest collimation, 3 x 10 n/cm -sec. The latter number has now

been verified by direct measurements with the velocity selector installed.

The cadmium ratio for the beam is > 1,000 indicating an extremely low

fast neutron component.

78
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

High Resolution Collimation System: Along the 4.5 m evacuated

flight tube preceeding the sample position, a series of twelve cadmiumplated masks, with nine apertures each, have been precisely aligned in

order to define nine independent beams which converge to a point at the

center of the detector. The positions and profiles of the beams on the

detector were measured individually and found to coincide thus verifying

the focussing effect of the collimation system.

Post-Sample Flight Path: The evacuated post-sample flight path

consists of three shielded cylindrical sections which mount on a frame

that can be rotated about the sample position. In addition, the section

which houses the detector rolls along rails in the frame so that the sampleto-detector distance can be changed from 3.5 m to 2.0 m by removing the

middle flight path section. This arrangement provides considerable

flexibility in positioning the detector as needed for a particular experiment,

Beam Stop: Incorporated in the detector shield is an external

positioning device for manipulating a thin aluminum tube which holds a beam stop in front of the detector. With this device, the beam stop

can be quickly and accurately adjusted to any possible beam position on

the detector while the flight path is under vacuum. Initially we used

cadmium for the beam stop, however, the detector has a non-negligible

sensitivity to the capture gamma rays from cadmium. We are now trying

alternative materials, which produce fewer capture gammas, in seeking

a more suitable beam stop.

Sample Chamber: An evacuated sample chamber has been installed

which is coupled to the two flight paths by steel bellows to avoid having

windows along the beam line. The chamber can be isolated from the rest

of the flight path by closing gate valves on either side of the chamber. A

sample can then be changed and the chamber reevacuated in about ten minutes.

An automatic sample changer will be added to the chamber in the near

future so that up to four samples can be changed without intervention.

2

Detector: Earlier calibration measurements of the 25 x 25 cm detector showed that this detector has a resolution of 4 mm in both

79
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

directions and a linear position versus pixel relationships. Recent

measurements have been aimed at determining the efficiency of the detector

over its entire active area. Incoherent scattering measurements have

shown that the efficiency is constant over a 24 x 24 cm area except

along the two narrow vertical strips (^ 4 mm wide each) where the

efficiency drops by about 10%. Data in these regions (which comprise

only '^3% of the active area) must either be disregarded or normalized

pixel by pixel for the dip in the detector's response.

The 65 X 65 cm detector for the SANS facility was received from

3 the manufacturer in June 1981 and was installed in July. When testing

and calibration of this detector is completed, the SANS facility will then

be fully operational. Based on our experience thus far, and the expected

performance of the larger detector, the operating characteristics of the

facility are given in table 1. As of September 15, 1981, data are being

collected using the 65 x 65 cm detector.

Figure 1. Photograph of the new SANS spectrometer.

80
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

Table 1. Operating parameters of the NBS SANS facility.

o Wavelength: variable from 4 to 10 A (AX /A '^^ 0.25)

Collimation: single pair of irises or 9 channel converging

collimation

Minimum Q: 0.003 A""*- at 6 A, 0.002 a""*" at 9 A

Q range: 0.002 A~ to 0.5 A~

Sample size: 0.4 to 2.5 cm diameter

Flux at sample: 10 4to 3 x 10 5/2 n/cm -sec depending on slit sizes

(at 10 MW) and wavelength (These fluxes will be doubled at

2

Detector: 65 x 65 cm position-sensitive counter with 5 x 5 mm resolution

b. Data Display and Analysis

SANS data are examined at the instrument with the aid of interactive

computer graphics. Running totals of neutron counts recorded along

individual rows and columns of the area detector are graphically monitored

on line with automatic scaling and update. The entire detector field is

inspected at the end of a data collection run using displays of constant

intensity contour maps and three-dimensional perspective plots, each of

which offers a variety of viewing options. Immediate hard copy is provided.

Data from completed sets of runs are transferred to a minicomputer for

further study using a color imaging graphics unit and for general processing.

The color display unit effectively maps the area detector data field onto

a user selected color field for detailed interactive examination. A

computer terminal command environment provides access to a system of image

analysis procedures that have been especially developed here for application

to SANS. Computer software utilities have also been installed for use with

standard data processing schemes. Among these are means for producing

background corrected and calibrated data, and for averaging data over annular

rings and ring segmented with respect to an arbitrary center. The data

81
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

reduction facilities provide for the logical masking of arbitrary detector

elements using computer mask files created with the color graphics system

as part of the image processing analysis.

2. Neutron Time-of-Flight Facility (TOF)

The new neutron time-of-f light facility is designed to allow studies

of neutron inelastic scattering by means of time-of-f light techniques over

a wide range of incident energies and energy transfer resolution. A monochromatic beam is obtained by Bragg reflection from two parallel single

crystals of pyrolytee graphite. This beam is then chopped by a compact

Fermi chopper into short bursts ("^ 5-20 ysec) every 3000-5000 ysec, thus

yielding a duty cycle of from .1 to 1%. These bursts of neutrons are scattered by the sample, and their time of arrival at the detectors, some

2.4 m away, is used to measure the energy transferred in the scattering

process. The inherent low-duty cycle is compensated by two factors—first,

"all" scattered energies are measured simultaneously (and hence all energy

transfers) and second, by the use of multiple (up to 64 in the present case)

detectors at various angles, allowing coverage of a wide range of momentum

transfers simultaneously. While the latter technique is also applicable

in principle to 3-axis instruments, it is of limited utility in such cases. The instrument is best adapted to isotropic samples, although diffuse scattering

from single crystals is also of interest.

The facility at NBS is presently being completed at the CTW beam

port. The crystal monochromators have been installed and many of the detectors

have been installed and tested. Two of the choppers have been built and

tested. The data acquisition system has been assembled and installation

and testing are in progress. The facility will be operational before

January 1, 1982. When completed, it will offer excellent intensity and

better resolution than any current NBS facility, with a maximum resolution

of 25 yeV. It will be at the forefront of such instruments in the USA.

82
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

1. C. J. Glinka, et al., NBS Tech. Note 1117, F. Shorten, Ed., 66 (1980).

2. C. J. Glinka, et al. , NBS Teoh. Note 1142, F. Shorten, Ed., 66 (1981).

3. Product of the Technology for Energy Corp., Knoxville, TN.

PHASE DECOMPOSITION IN THE Ni RICH SIDE OF

NilNi'sAl MISCIBILITY GAP:

A SMALL-ANGLE NEUTKON SCATTERING STUDY

Satish P. Singhal

(State University of New York, Stony Brook, N.Y.)

and

Harvey A. Alperin

(Naval Surface Weapon Center, White Oak, MD)

and

F. Biancanello

(Metallurgy Division)

and

H. Herman

(State University of New York, Stony Brook, N.Y.)

The solid state thermomechanical processing of recent high performance

superalloy components essentially involves the precipitation of a variety

of metastable phases either by nucleation and growth (NG) or spinodal

2 decomposition (SD). The existing theories describing these phenomena

however, have been used only as a coarse guide-line by alloy designers.

The advancement of predictive capabilities of the more promising recent

3 theories for alloy design applications needs a careful comparison between

the theory and the experimental data. The present small angle neutron

scattering (SANS) study on the Ni-Al alloy system has been carried out

with these objectives in mind.

Approximately 1 mm thick samples of Ni - 14.4 at. % Al alloy were homogenized and quenched from 1200°C. The phase diagram (fig- 1) shows

83
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAJIS

• Taylor and Floyd (Metallographic)

O Taylor and Floyd (x-ray) o Williams (Resistivity) A Coherent Miscibility Gap

a Coherent Spinodal

1200 /

/ 1

/

>

1000 J* ,

a L a+y' y' yV)8

o

2, 800 /

> I 1

H Of \

1

600

/ 1 1

400 1 1 1 -1 1 L

Ni

8 10 12

Wt % Al

14 16 18

Figure 1. Ni(a) and Ni^Al(Y') side of Ni-Al phase diagram.

A E A, coherent miscibility gap limit for Ni-14.4 at % Al alloy.

O E B, coherent spinodal point for the above composition.

the Y(Ni) 1 Y* (Ni~Al) solvus line. The theoretically calculated locations

of the coherent miscibility gap and spinodal are also shown by points

A(900°C) and B(572°C) for our alloy. Isothermal aging on the as-quenched

samples was carried out at the temperatures of 540, 600 and 629 °C. Other

experimental details have been described elsewhere.

In general, following Cahn and Hilliard in a binary miscibility gap

(MG) , two regions of phase separation are defined; one comprising NG and

84
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

the other SD. At the spinodal this and other classical theories predict

a singularity in various measurable quantities. A gradual transition from

NG to SD is, therefore, not descrlbable by these theories. This problem

has been avoided by a recent phenomenologlcal theory of nucleation, based

on "cluster dynamics" by Binder and Stauf f er (BS) . A further

advantage of this theory is that it does not make any assumptions about

the criticallty of nucleus size or require any steady state approximations.

Although the existence of the spinodal is ignored by the BS theory,

presently it is valid up to the maximum concentration bounded by the

percolation threshold for a particular lattice type*. Numerical

9 3a computations and phenomenologlcal approximations ' based on the BS

theory suggest that the peak intensity (I ) and peak position (Q ) in

m m

the SAS spectra of an Isothermally decomposing alloy exhibit a power

law dependence** on the aging time (t) according to the equations

1=1 + at*^ (1)

Q^ = b . t

^ (2)

For the Ni - 14.4 at. % Al alloy figure 2 and 3 show the time dependence

of I and Q_ derived from the SANS spectra at three aging temperatures.

We see that, except in the early stages, where measurement errors are

large, the behavior described by equations (1) and (2) is adequately

obeyed.

* For fee crystals this is about 20 at. % solute; so Ni - 14.4 at. % Al

alloy is in this limit. [See ref. (8) for other lattices.]

** It must be pointed out here that a similar prediction has also been

made by Langer, Bar-On, and Miller (LBM) theory. The LBM theory,

though most successful in the spinodal region, has been shown to give

results in disagreement with experimental data in that region of the

phase diagram, which is of interest in this experiment.

85
REACTOR RADIATION DIVISION AND COLLABORATIVE PR0GRA1'4S

Phenomenologically, however, the time, temperature relationship

for the transformation kinetics in an alloy follows a 'C' curve

behavior. This is because the kinetics are limited by the driving force near the MG boundry, but at the lower temperatures, it is limited by the

diffusion coefficient . Therefore, if the kinetics of phase decomposition

are to be studied closely, based on equations (1) and (2), a very

important issue arises as to the temperature and composition dependence

of the exponents cj) and (J)'. The theoretical predictions about such

3a dependences are only qualitative but for a quantitative understanding

a small body of SANS and computer simulation results are now available.

These, and the results of the present study, have been summarized in

table 1. Some of the conclusions based on this table will now be

discussed. At first sight, we observe that in contrast to ((>, the value

of 4)' is less sensitive to (i) alloy system, (ii) method of experimentation

and computation, and (iii) alloy concentration. The value of (}) ' seems

to be in the range 0.1 to 0.3. However, one must remember that the

3 12 number of particles per unit volume (Nv) is 'v [(Q /2II) ]; therefore

even minor systematic variations in the value of c() ' have a great

bearing*** on Nv.

In the present study we have found an apparent linear dependence

of (|)' on the reduced temperature (T/T ). The fact that this dependence

^. -, . ^ 1- . ? . , 13a & 13b . ^ was not displayed by the computer simulation results points

either to the inherent limitation of these methods or to the alloy model

chosen for these studies.

For Ni-Al and Au-Pt systems (f) increases linearily with T/T ; but

in the temperature range of study, the increase is faster for Ni-Al.

*** It must be pointed out here that in the limit t -^ o, Nv give the

nucleation rate predicted by classical theories.

86
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

H

W

Pi

ISw

M

Piw

X

w

w !5 « M

<d H

H W

Pio

pa

o

c

<u

"4-1

Pi

o

00d

CO en m

4J CO

4J vf o .H in c o a\ <r in o 1—

1

ro 00 \c ^ m CM iH m •H r^ ^ r^ ^ r^ <r 00 O iH CN 04 m in r-- 00 O

• • • • • • « • • • a. o o o o o o O ro o o o o o o o o

rHa

•H

VD nH in in o >X5 o

iH CN CNJ CN CM iH <-{ CO

• • • • • • • • O o o o o o o o

I I I

in Csl v£> pH OJ C^l o o o

VO 00 a^ odd

CO in ON iH 00 CTi CM CO in in in ^oo^ in r^ vo r^ r^ o o o o o o o o o o

uo

x:

FQ U

pq u

o

COo

u

o

M-l

0) P

(U

4-1

4-1 •HrH

•r) •HO

CO •H

d

5-1 <u x:ou

oo

H

w

!3O

f^

X!W

Piw

13O

P-i

eq u

PQ U

73

CO

CO iH 4-1 (U d

13 CU CU o 6 3 S -H cr

V-i -H

>^ a; d

o a x

iH X O

<: = H

CMd

CO ao o

d -H

•H )-l CO cu M B

d

C/D rH

(U

I o

CO S

COd

o

•H

4-1 CO

4-) d

a-S

oa

c

o

•H

COde

•H

c/:i

00d

•H

CD M r-i

CU 5-1

• O

13

I CO

4Jd

a.e

o

d

00d

•H

CO

de

•H

C/D

(U 5-1 O T3 CU

• O 4-1 C/5 S

13

I CO

d

S

o

rHd

13d

4J CO d

Nl CO

<tj CO

13d

4J CO

4J CM CO < CO

C3> in

13d

<

I •H

IS

CO

0)

4-1

d

o

•H

4-1 CO

5-1 4-1 d

0)o

d

oo

0)

4-1 d

i-HO

CO

CU

5-1 d

4-1 . CO >.

5-1 00

CU U

a 0) E d

cu d)

4-1 d

CX'H

CO CO bO 5-1 4-1 >^ CO

4-i •H 00d

•H>

rHO>

d

•H

pq u

CJ
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

5-

4-

3-

1 a629°C

• 600°C

540°C

• <

A

•

•

•

- •

•

1

•

1 1

+

L 3 4 5 6 7 8

In ta (min.)

Figure 2. Variation of normalized peak intensity (I ) as a function of

aging time (ta)

2.5-

3.0

O

c 3.5-

4.0

• 540°C

n

•

600°C

A629°C

• •

•

1

A

1 ,, 1 6 7

In ta (min.)

Figure 3

Variation of peak position (Q ) as a function of aging time (ta)

88
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

The Al-Zn data compared to the Ni-Al data extrapolated to T/T 'v 0.92

is low for both cf) and (}> ' . On the other hand, it is much higher for (J) at Tyrr '^^ 0.97. We must point out here, that in the Al-Zn study at

T/t£°" '^ 0.97; complications were seen due to incoherent precipitation

MG

at the grain boundary.

In conclusion, we can say that the SANS data on the isothermal

phase decomposition kinetics in Ni-Al system is in qualitative agreement

with a recent nucleation theory based on cluster dynamics. Additionally

it exhibits an apparent linear temperature dependence of the power law

exponents for the peak intensity and peak position, in clear disagreement with the computer simulation results. For a rigorous comparison of

the Ni-Al data with the BS theory, it is necessary to obtain the complete

scattering function (I vs. Q) from the theory. Such numerical computa16

tions based on non-lxnear equatxons are m progress

1. R. Mehrabian, B. H. Kear, and M. Cohen, Rapid Solidification Processing,

Principles and Technologies^ II: Second International Conference on Rapid Solidification Processing^ Reston, VA (1980).

2. J. W. Christian, The Theory of Transformations in Metals and Alloys

I3 Pergammon Press (1975). For example see Chapter 10.

3. a. K. Binder and D. Stauffer, "Theory for the Slowing Down of the

Relaxation and Spinodal Decomposition of Binary Mixtures," Phy

Rev. Lett. 33^, 1006-1009, (1974).

b. K. Binder and D. Stauffer, "Statistical Theory of Nucleation,

Condensation, and Coagulation," Advances in Physics, 25(4) , 343-396

(1976).

c. K. Binder, "Theory for the Dynamics of 'Clusters' II. Critical

Diffusion in Binary Systems and Kinetics of Phase Separation,"

Phys. Rev. B, 15, kklb-khhl , {1911).

4. For the procedure for such calculations see C. M. F. Jantzen and H. Herman

in Phase Diagrams in Materials Science and Technology, Vol. 5 (1978),

Ed. by A. M. Alper, New York: Academic Press.

5. S. P. Singhal, H. A. Alperin, H. Herman, and F. Biancanello, WS Technical

Note, 1142 , 118-123, (1979-80).

89
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

6. J. W. Cahn and J. E. Hilllard, "Free-Energy of a Non-Uniform System

III: Nucleatlon in a Two Component Incompoversible Fluid," J. Chem. Phys.

1959 , 30, 688-699.

7. a. R. Becker, "Die Keimbildung bei der Ausscheidung in Metallischen

Mischkristallen," Ann. Physik^ 32^, 128 (1938).

b. G. Borelius, "Zur Theorie der Unwandlungen von Metallischen Mischphasen

IV. Die Ausscheidung Ungeordneter Misgohphasen, " Ann. Physik^ 28,

507 (1937).

c. J. N. Hobstetter, "Stable Transformation Nuclei in Solids," Trans

AIME, 19A9 180 121-130.

8. D. Stauffer, "Scaling Theory of Percolation Clusters," Physios Reports,

54(1) , 1-74 (1979).

9. K. Binder, C. Billotet, and P. Mirold, "On the Theory of Spinodal

Decomposition in Solid and Liquid Binary Mixtures," Z. Physik, S30,

183-195 (1978).

10. J. S. Langer, M. Bar-On, and H. Miller, "New Computational Methods in

the Theory of Spinodal Decomposition," Phys. Rev. All, 1417-1429 (1975).

11. See Chapter 15 in Reference 2.

12. G. Laslaz, P. Guyot, and G. Kostorz, "Decomposition Kinetics in Al-6.8 at

% Zn," J. de Physique, Colloque C7, 406-410 (1977).

13. a. J. Marro, A. B. Bortz, M. H. Kalos, and J. L. Lebowltz, "Time

Evolution of a Quenched Binary Alloy II Computer Simulation of a Three-Dimensional Model System," Phys. Rev. B12, 2000-2011 (1975).

b. A. Sur, J. L. Lebowitz, J. Marro, and M. H. Kalos, "Time Evolution

of a Quenced Binary Alloy IV. Computer Simulation of a ThreeDimensional Model System," Phys. Rev. B15, 3014-3026 (1977).

14. T. Hirata and D. H. Kirkwood, "The Prediction and Measurement of Precipitate

Number Densities in a Nickel-6.05 wt . % Aluminum Alloy," Acta. Met. 25 , 1425-1433 (1977).

15. S. P. Singhal, H. Herman, and G. Kostorz, paper presented in the

International Conference on Solid-Solid Phase Transformations,

Aug. 10-14, 1981, Carnegie Mellon University , Pittsburgh, PA.

16. N. Berk, S. P. Singhal, and H. A. Alperin, work in progress.

90
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

COMPOSITIONAL AND MAGNETIC INHOMOGENIETIES IN

Fe g7 Co ^g B -,4 Si q^ AMORPHOUS RIBBON

H. A. Alperln

(Naval Surface Weapons Center, White Oak, MD)

and

(National Bureau of Standards, Washington, DC)

and

S. P. Singhal

(State University of New York, Stony Brook, NY)

and

(National Bureau of Standards, Washington, DC)

Iron-boron ribbons with ^18% cobalt, prepared by rapid quenching

exhibit an amorphous structure. Upon low-temperature annealing in a magnetic field, the magnetostrictive properties are greatly enhanced.

In this preliminary study, neutron scattering was employed to investigate

the compositional and magnetic microstructures induced by the field

annealings. Both wide angle and small angle neutron scattering (SANS) were used. A saturating magnetic field (H) applied parallel to the scattering

vector was used to eliminate the magnetic scattering and hence give the

non-magnetic scattering component. Since the same measurement repeated

with H=0 gives the sum of the magnetic and nuclear scattering, the difference

of the two measurements gives the magnetic scattering (for H=0)

Thirty sheets of (2ym thick x 1.27 cm wide x 3 cm long) ribbon

annealed at 370 c for 10 minutes in a magnetic field (in the ribbon plane

and perpendicular to its length) were used for conventional wide angle

scattering at a neutron wavelength of 0.973A and were compared to a similar as- quenched sample. The resulting amorphous diffraction patterns (taken with

an external magnetic field of lOOOG along the scattering vector which is

sufficient to eliminate all magnetic intensity) were practically identical.

This indicates that i) the field annealing treatment did not cause any

crystallization of the ribbon and ii) there is at most, only very small

changes in atomic rearrangement in the bulk of the sample upon field

annealing

91
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

SANS measurements were made with the NBS linear detector instrument

on samples, each having 8 sheets, at a neutron wavelength of 6.5 A with

(and without) an external field of lOKG applied along the scattering

vector (i.e. in the plane of the ribbon) and for two 90° orientations

of the sample (rotated about the normal to the ribbon face) to look for

anisotropies in the scattering. In contrast to the as-quenched sample

which shows no (compositional) inhomogenieties (i.e. no small angle

scattering was observed) , upon field annealing there is a great increase

in the SANS showing that the compositional microstructure has changed

significantly and in addition, exhibits a small but measurable anisotropy.

A very large anisotropy is seen in the magnetic microstructure (at H=0)

the details of which can be explained by assuming that these inhomogenieties

are located in domain walls.

Figure 1 shows the angular dependence of the scattered intensity

(according to the Guinier Law) for the field annealed sample measured

in the two orientations "vertical" and "horizontal" which designate the

orientation of a direction transverse to the ribbon length (i.e. the

direction of the magnetic field during annealing) . The Guinier Law

q - 47Tsin9/X and 2 9 is the scattering angle) then a straight line will

2 result with slope equal to -R where R is the radius of gyration of the

g 8

scattering entities. The "vertical" and "horizontal" measurements for the

nuclear (compositional) scattering are immediately fit with R 's of '^'ISSA. Note the small spatial asymmetry of this scattering as indicated by the

different intensities. It is clear, however, that a single R will not fit

the magnetic scattering; so we have analyzed the data in terms of two R 's.

O

The high-q points are fit by R = 135A (which is the same as for the nuclear

scattering) and after subtracting this contribution from the measured values

we are left with another straight line (labeled "corrected" in the figure)

which yields an R of "^lllk which is the same for both "vertical" and

g

"horizontal" orientations even though the intensities are very different

for these two cases.

92
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAIIS

10.5

10.0 -

9.5

9.0-

8.5-

8.0-

75

Vert. Horiz. mag. D A

nuct. • O

q^ (10-5)

Figure 1. In intensity vs. q (q = 4TTsin9/A) for field-annealed amorphous

ribbon analyzed according to a Guinier Law.

A - magnetic scattering for "horizontal" sample orientation.

- magnetic scattering for "veritcal" sample orientation.

• - nuclear scattering for "vertical" sample orientation,

- nuclear scattering for "horizontal" sample orientation,

The meaning of the orientations are explained in the text. The

points with attached arrows are replotted from the data after

subtracting the straight lines fitted at large q2 and result

in the new straight lines labeled "corrected".

The results suggest that the compositional microstructure sets the

basic scale (135A) for the magnetic microstructure (probably domain walls)

but it is also possible for a magnetic inhomogeniety to be twice as large

by jumping over to the next compositional inhomogeniety.

93
F-EACTCR RADIATION DIVISION AND COLLABORATIVE PROGRAJ-IS

COMPUTATIONAL METHODS IN THE NON-LINEAR

THEORY OF SP I NODAL DECOMPOSITION

N. F. Berk

and

S. P. Singhal

(State University of New York, Stony Brook; NY)

and

(National Bureau of Standards, Washington, DC)

In 1975 Langer, Bar-On, and Miller (LBM) gave the first general

non-linear treatment of the kinetics of spinodal decomposition of binary

systems with conserved order parameter and thus moved beyond the classical

2 3 theories of Cahn-Hilliard and Cook , which are known to fail even in the

early stages of decomposition. In its full generality the LBM theory is

not amenable to practical application, requiring as it does a knowledge

of a hierarchy of correlation functions defined over a mesh of coarse

grain cells. Therefore, LBM suggested a decoupling scheme which

simplifies the theory while maintaining its essential non-linearity.

In this approximation the small angle scattering (SAS) intensity S(k,t)

is determined from the equation of motion

d^S = - 2Mk^(Kk^ + A(t))S + 2Mk^Tk^ (1)

where k is the scattering wavevector, M is the atomic mobility, and K

2

is the gradient energy coefficient introduced by Cahn and Hilliard.

In this equation

A(t) = <u9 f(c + u)>/<u^>, (2) u o where u = c - c is the compositional deviation of a coarse grain cell

and f is the Helmholtz free energy density of the cell whose composition

is assumed to remain spatially uniform during the phase separation. The

average in (2) is taken over the single cell compositional distribution

p (u) which itself satisfies a complicated non-linear diffusion-like

equation within the approximation. This set of three equations formally

provides a means of computing S(k,t) for a given form of f, which

94
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

incorporates the specific system attributes. Even the simplified theory

is difficult to treat numerically. To date, published treatments typically

assume that p,(u) has the form of a double gaussian whose evolution is

approximately determined by truncation of the set of equations for its

moments. Moreover, the main interest has focused on the theory near the

critical point, 1 - T/T '^ 10 , where f may be well approximated by the

^

2 h convenient Landau form (f = Au + Bu ) or its extensions to finite higher

order. However, these functional forms predict unphysical miscibility gaps

at lower temperatures and so are unsuited to application to real SAS data

from systems quenched deep into the spinodal region. As a result, the LBM

theory has yet to be systematically tested against a wide range of laboratory

experiments.

We have undertaken a research program to extend the LBM approximate

theory to realistic free energy functions and to further simplify the

still considerable numerical effort required to extract results for

comparison with experiment or metallic solid solutions. As a first step,

4 we are considering the subregular and regular solution models , which

are known to predict realistic miscibility gaps. We have also developed

a new set of equations for S(k,t) and A(t) based on the adoption of a double 6-function ansutz for p (u) . Seemingly a severe approximation

this form actually interpolates between the physically expected limits

of a single sharp peak at the quench and a pair of sharp peaks at the

miscibility gap in the steady state. Moreover, as the temperature is

lowered the average in (2) becomes increasing insensitive to the value of

the width parameter of the double gaussian model, suggesting that this

parameter is not the physically crucial one.

1. J. S. Langer, M. Bar-on, and H. Miller, Phys. Rev. A 11, 1417 (1957).

2. J. W. Cahn and J. E. Hilliard, J. Chem. Phys. 28, 258 (1958);

J. W. Cahn, Aata Met. 9_, 795 (1961).

3. H. E. Cook, Acta Met. 18, 297 (1970).

4. H. K. Hardy, Acta Met. ly 202 (1953); B. E. Sundquist, Trans. AIME,

236 (1966).

95
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

RELAXATION BEHAVIOR OF SiC FIBERS IN SiC/Al COMPOSITE

MATERIAL UNDER STRESS

H. A. Alperin

(Naval Surface Weapons Center, White Oak, MD)

and

(National Bureau of Standards, Washington, DC)

and

S. P. Singhal

(State University of New York, Stony Brook, NY)

and

(National Bureau of Standards, Washington, DC)

We have utilized the penetrating power of neutrons to measure the

elastic response of SiC fibers within an aluminum matrix composite material.

A cylindrical sample (1 cm diameter) formed by extrusion was placed on

the neutron dif f ractometer in a special fixture and subjected to compressive

loads of up to a maximum of 317 MPa while changes in the Bragg peak

positions were observed separately for the 3SiC (111) and the Al (111)

reflections. Several runs of d-spacing as a function of applied stress were taken and the following results obtained:

1. For the Al (111) reflection, within experimental error all

points fell on a straight line whose reciprocal slope is equal to E/v,

the ratio of Young's modulus of elasticity to the Poisson ratio. Taking

V = .31 we find E = 17.8 x 10 psi (1.2 x 10 MPa) which is to be compared

to '^j 15 X 10 psi obtained from mechanical measurements on these samples.

This value is considerably greater than the value 10.5 x 10 psi for an alluminum alloy, indicating that the composite material has been considerably

stiffened by the SiC fibers.

2. In contrast to the Al (111) reflection for which no relaxation

was observed, the 3SiC (111) reflection exhibited a relaxation in the

d-spacing under constant stress for periods of 6 hours and also when the

external stress was returned to zero. A tentative explanation for the above observations is that under

96
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

compression the yield stress for the aluminum matrix is exceeded at the

tips of the SiC fibers (which have been aligned along the cylindrical

axis by the extrusion process) so that plastic flow in the matrix

relieves the stress on the fibers but leaves the stress on the bulk of the

aluminum matrix unchanged. Further experiments are planned to verify

the explanation.

NUCLEAR SAFEGUARDS STANDARDS FOR DETECTOR CALIBRATION TOMOGRAPHY

W. M. Parker and Y. T. Cheng

The purpose of this project was to measure the transmission by U-235

and U-238 of the complete neutron spectrum coming from the NBS Research

Reactor. From these measurements it should then be possible to calibrate

I the NBS double fission chamber detectors used in the Nuclear Safeguard

project.

The uranium was available as uranium oxide in a finely powdered

form which had to be encapsulated to form samples of a known thickness

which could then be used for the transmission measurements. The containers

consisted of an outer shell which had a well to contain the sample and a plug to compress the powder. The plug was 0.002 to 0.003 inch oversize

and after loading was pressed into the container using an arbor press

which exerted a force of several tons. The mass of the specimen was measured with an accuracy of 0.1 of a milligram.

In order to get other information on the thickness of the specimen,

transmission measurements were made using gamma rays from a cobalt-60

source. A well collimated beam, 1/4 inch in diameter, was used, and

measurements were made for the lower peak (1.10 to 1.25 meV) , the upper

peak (1.25 to 1.40 meV) , and the two combined. The average of the three

measurements was used as the value for the gamma ray transmission.

Radiographs were taken of the samples using a 250 kvp x-ray system.

It is apparent from the radiographs that, for some of the samples,

97
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

leakage of the powder from the well had occurred and that in others the

distribution of the powder was not uniform. Finally, it is apparent

that the density of the powder varies from sample to sample. For nine

of the samples the radiographs indicate that the data should be reliable.

For these samples the gamma ray transmission values were fitted by

linear regression to the equation

1=1^ exp (-am^) (1)

where m is the mass of a cylinder of U„0o 6.4 mm in diameter. Figure 1

S JO

shows the data used and the fitted line. The equation was then used to

calculate m for the other samples. Three methods were used to calculate

the total mass of the samples used for the neutron transmission measurements.

They were as follows:

Method I is the one just described—a combination of the values of

m obtained from measurements made on the radiographs and the known masses of the reliable samples with the values of m for the other

samples calculated from the gamma ray transmission using equation (1)

Method II smooths the data by using equation (1) to calculate all

of the values of m from the gamma ray transmission.

Method III was suggested by the fact that when the neutron transmission

is plotted against the design values of the thickness, the resulting

curve appears to be as good as the one obtained from Methods I or II

which are based on the gamma ray transmission. Method III, in effect, assumes that all of the sample is effective in absorbing the neutrons.

As shown in previous reports, a plot of the neutron transmission

versus the thickness of the absorber is expected to follow the equation

1=1 (a + a,x + a^x^) (2)

o o 1 /

with the expected value of a being 1.

The neutron transmission was measured using a two compartment

fission chamber with one foil being U-235 and the other Pu-239. The

98
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

• U-235 Detector

o Pu-239 Detector

100 200 300 400

SRM U-970 UgOg Sample Thickness in Mils (97.66% Enriched)

Figure 1. Gamma ray transmission for 6.4 mm diam, U^Og sample,

I.Orx

(0

u

09 Q

co

•a

0)N

15Eo

0.5

• U-235 Detector

o Pu-239 Detector

100 200 300 400

SRM U-002 U3 Og Sample Thickness in Mills 99.98% Enriched

Figure 2. Data points for U-235 sample and a U-235 detector and curves using a and a^. The average values found using method II and

III.

99
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

absorbers were 97% enriched U-235 (NBS SRM U 970) and fully depleted U238 (NBS SRM U0002)

When the data are fitted to equation (2) by a least squares calculation,

a is found to be 0.9 for U-235, U-235 sample detector combination,

about 0.95 for U-235, Pu-239 pair and about 0.97 for U-238 with either

detector. No reasonable explanation for this is known.

It was decided to do two things. One is set a = 1 in equation (2)

and to weight the data so that larger values of x are given more weight.

The 26 data points were divided into groups of 9, 9, and 8 which were

given weights of 1, 2, and 3, respectively. The results for Methods II

Table 1. Calculated values of a and a„.

Absorber

U^

35

00m

CM

U

u

o

rO CO

<C CM

a = 4.941 cm

a = 9.534 cm

-1

-2

a = 3.776 cm

a = 6.233 cm

-1

-2

,238

a = 1.518 cm

a = 1.467 cm

-1

-2

a = 1.440 cm

-1

a = 1.321 cm

-2

and III agree quite well and are considered to be the best available

from the present data. Figure 2 shows the data points for a U-235

sample and a U-235 detector, where m^ is used as a measure of the thickness,

together with the curve obtained by taking a^ and a^ as the average of

the values found using Methods II and III. Table I gives the values of

a^ and a^ obtained by this method for all four combinations of sample

— 1 — 9 and detector, expressed in cm and cm . These are the numbers that

would apply if the sample is a solid metal foil.

It would be very difficult to estimate what the probable error is.

If the program is continued, it would be most desirable to repeat the

experiment using solid metal foils.

100
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

RESONANCE NEUTRON TOMOGRAPHY

Y. T. Cheng and D. A. Garrett

The effort on the resonance neutron tomography project during last

year was devoted to (1) the continuing development of software programming

and the library data set; (2) the construction of the reactor-based resonance neutron safeguards experimental system and the making of provisions for

Its use, (3) an experiment to verify the resonance neutron self-indication

effect with the NBSR, and (4) the Initial tomographic construction of a nuclear waste container.

In the first area, a mathematical analysis has been conducted and

a computer code written for solving multiple non-linear equations relating

fission detector response to fissile sample thickness. The cross section

data library has been further upgraded; this has helped to improve the

sensitivity for the self-indication effect.

The detail design of the reactor-based resonance neutron safeguard

experimental system was completed in April 1980 and has been approved by

the NBS Reactor Hazards Evaluation Committee. The NBS Shops Division was responsible for the construction of the system and the letting of bids to

private contractors.

In addition, glovebox provisions were made to the SRM Shop to permit

the handling of SRM UoOj. powders of various enrichments for the fabrication

of transmission cells.

In order to verify the resonance neutron self-indication effect with

the NBS reactor facility, an experiment was conducted to quantitatively

determine the U-235 and U-238 contents in three nuclear fuel pellets

supplied by General Electric Wilmington Manufacturing Department. The

known Information is in table 1.

A horizontal neutron beam of 1/4 in. (0.635 cm)-dlameter was extracted

from the NBSR core on port BT-7. The thermal neutron portion of the beam

was removed by using a 0.04 in. (0.102 cm)-thick Cd sheet as filter. The

filtered beam was then transmitted through the fuel pellet and detected

by NBS double fission ionization chamber detectors.

101
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

The experimental setup and fuel pellet holder are shown in figure 1.

The holder was made with a Incite block approximately 15 cm long, 5 cm wide,

and 1 cm thick. Four holes were drilled to accommodate the three fuel

pellets and a blank reference hole. The three fuel pellets, along with the

blank hole, were scanned by the neutron beam and detected with U-235, Pu-239

double fission chamber detectors and then with U-235, U-233 detectors.

The reason for using Pu-239 and U-233 detectors was that the fission cross section for U-238 was very small. A count rate of > 1000 cps was obtained

using very thin fission foil in all detectors, thus no corrections were made

for detector dead-time, self-absorptions, and background noise. A total

count of > 50,000 was accumulated for each data point.

Table 2 lists the measured U-235 and U-238 contents in grams in the

third pellet as compared to the known quantities.

The measured U-235 content in the third pellet is about 11 percent

of the known U-235 quantity when the U-233 and U-235 detectors set are used,

and about 15 percent with the U-235, Pu-239 set. The accuracies for the

measured U-238 content in the third pellet are 4 percent and 6 percent,

respectively, for the two sets of detectors. The fact that all neutrons

with energies below 0.5 eV were filtered out in the beam caused the Pu-239

detector to perform less satisfactorily relative to U-233 and U-235 detectors,

since 60 percent of the resonance strength for Pu-239 lies in the 0.3 eV

region. Nevertheless, the results indicate that a reasonably accurate

estimation of U-235 and U-238 contents can be obtained in a very short

time (< 1 min.) with the self-indication method with counting statistics

of 0.1 percent.

The tomographic reconstruction of a point object using the filtered

back projection technique has been carried out before. In an effort to

further study the reconstruction technique as applied to those actual fuel

pellets within a gallon-sized container. A second experiment was conducted

on the BT-7 beam port of the NBSR.

The experiment consisted of three parts: 1) the production of

reference calibrations, 2) the scanning of the waste container by the resonance neutron beam, and 3) the mathematical reconstruction of the

102
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

CNJ 1/4 inch Beam^

Q:;oO;.^V?; mi BT-7

pi

Micrometer o o o o 12 3 4

Figure 1. Neutron telescope and fuel pellet holder.

lliliil'i,!!,

ifiiiii

fill Mil

m.

m

JiUlfl

!i|R ii

I?

Figure 2. Tomographic construction of U-235 contents in the fuel pellets.

103
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

Table 1. Known characteristics of three nuclear fuel pellets supplied

by General Electric Wilmington Manufacturing Department.

Isotopic U-235 % U Density Length Diameter

enrichment %

3.9572 88.15 95.9243 0.432" 0.410"

2.5174 88.168 96.56 0.4395" 0.410"

1.194 88.14 95.52 0.434" 0.410"

Table 2. Measured U-235 and U-238 Contents, in grams, in the third pellet

as compared to the known quantities.

Known Measured with Measured with

quantities* U-235, Pu-239 detectors** U-233, U-235 detectors**

U-235 0.2174 0.185 + 0.03 0.193 + 0.03

U-238 5.2764 5.581+0.05 5.476+0.49

Corrected for 1/4" neutron beam size.

**Errors were estimated second order effects.

104
REACTOR RADIATIOiT DIVISION AND COLLABORATIVE PROGRAMS

container based on the results of 1 and 2. The reference calibrations

were necessary to interpret the responses of the fission detectors. The

responses were functions of particular neutron beam characteristics, detector

system efficiencies and the effect of neutron beam softening in the object

to be studied.

U-235 and U-238 reference discs were made from SRM U-097 and U-002

materials, respectively. The U-235/U-238 reference discs were then placed

in the resonance neutron beam and the transmitted beam recorded by both

U-235 and Pu-239 foils in the NBS double fission detectors. The selfindication effort is clearly demonstrated in the case of U-235 detector,

while the responses of Pu-239 detector to both U-235 and U-238 materials

are very similar due to the fact that Pu-239 resonant cross sections do

not match the total cross sections of either materials.

The waste container was first moved horizontally with respect to

the neutron beam at 1.6 mm intervals, the total width covered was 6.4 cm.

o At the end of each horizontal scan, the container was rotated 3 . Sixty

such rotations were acquired for each slice of the container to be

reconstructed. A total count of > 10,000 was recorded for each point

scanned on both U-235 and Pu-239 detectors. Dwell times on each point

varied from 15 sec. to 25 sec. The preliminary tomographic reconstruction of the slice of the

container that passes through the centers of all three pellets is shown

in figure 2. The heights of the three columns indicate the relative

U-235 contents. The errors are mainly introduced by the calibration

process. To minimize the errors, one has to use metallic reference discs

instead of the ones made from powder SRM's so the effective thickness of

each disc can be measured more accurately.

105
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

DESIGN STUDY OF A FACILITY FOR NEUTRON-ACTIVATION

AUTORADIOGRAPHY OF PAINTINGS AT THE

NATIONAL BUREAU OF STANDARDS REACTOR

Y. T. Cheng and D. A. Garrett

Art conservation laboratories regularly employ techniques such as x-ray radiography and microscopic examination of pigment layer cross sections in the study of paintings. X-ray radiographs, however, show

only the distribution of dense pigments such as lead white and thus

provide only part of the analysis. Relatively recently neutron-activation

autoradiography has been used. It extends the range of information that can be obtained by being able to measure the distribution of several

pigments other than lead and at the same time identify the elementary

composition of the painting.

A current drawback of the neutron technique is that the radiation

dose to the painting is two orders of magnitude greater at the existing

facilities than a typical x-ray examination. Although this is believed

to be well below the level that would damage the painting, it cannot be

shown that such radiation doses might not result in some deterioration

that would not appear until many years in the future. Therefore, it is

very important to reduce the radiation dose to as low a level as possible.

A proposal was submitted to the Smithsonian Institution and

subsequently a contract was awarded for a design study of a painting autoradiography facility that would reduce the radiation dose received by a painting by an order of magnitude compared to that available at other

reactors. The possibility of building such a facility is made feasible

by the unique thermal column built into the NBS reactor. The proposed

study will result in a detailed design of the facility, a cost estimate

for its fabrication, and more detailed estimates of the radiation fields.

For the feasibility study, firstly an experiment was carried out to

gather information concerning thermal neutron flux distribution, neutron

to gamma ratio, field nonuniformlty , size of usable thermal neutron field,

radiation shielding requirements, etc..

106
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

Figure 1. The relative thermal neutron flux distribution of the NBSR

thermal column.

The result of thermal neutron flux distribution at the NBSR thermal

column surface is shown in figure 1. The field is approximately 54 in.

X 54 in. in size and the flux, without any modification, varies by a factor of 4 from column center to the edges. If the nonuniformity of the

field is limited to 50 percent, then the usable field size is reduced to

9 -2 -1

a 3 ft. X 3 ft. area with a neutron flux of 6 x 10 n-cm -sec . However,

this usable field will expand to 5 ft. x 5 ft. area at the proposed first

painting irradiation position which is indicated in figure 2, the plan view

of the conceptual facility. The usable field will further expand to a

6 ft. X 6 ft. area at the second irradiation position and to 7 ft. x 6 ft.

and 8 ft. 4 in. x 7 ft. area at the third and fourth positions respectively.

The goal on one hand is to produce an irradiation field with a

9 -2 -1

thermal neutron flux in the range of 1 x 10 n-cm -sec or higher. So

13 -2

the painting can be exposed to a total neutron fluence of 1 x 10 n-cm

in a reasonable amount of time; this total fluence is considered necessary

to apply the neutron-activation autoradiography technique successfully.

107
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

Lithium Carbonate Neutron Absorber,.

Thermal Column Door

Steel Shot and Parafin Shielding

Figure 2. Plane view of the proposed NBSR neutron-activation autoradiography

facility.

On the other hand, the emphasis should also be placed upon reducing the

unwanted fast neutron and gamma ray doses received by the painting during

the activation process. The measurement of the thermal neutron and fast

neutron flux at the NBSR thermal column indicates a ratio of < 1,500 which

compares very favorably to the ratio of 34 at the BNL medical reactor.

This means the fast neutron dose the painting would receive at the NBSR

facility will be less than 20 Rads per study. Also shown in figure 2, a

2 in. thick lead sheet is placed between the thermal column and the painting

Irradiation stations. This serves to decrease the external gamma dosage from

an unfiltered value of 200 Rads to an estimated value of 20 Rads for the

painting activation process. With more filtering materials, the radiation

dosage given to paintings will be further reduced, but the activation time

will be proportionally lengthened. Our concept allows the flexibility of

changing the thickness and type of filtering materials to tailor the beam

for differing needs.

Figure 3 shows the side view of the conceptual facility. The roof

sections are of modular design. The section which incorporates the painting

108
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

Lithium Carbonate

Neutron Absorber

J=

Thermal Column Door

''%

Lead FilterPainting Activation

Positions

/' \

Graphite Liner

Graphite Thermal Column

—Graphite Reflector

Steel Shot and Parafin Shielding

Figure 3. Side view of the proposed NBSR neutron-activation autoradiography

facility.

suspension system can be relocated depending on the particular irradiation

station selected. A second lead filter, in addition to the one mentioned

above and a neutron stopping boral curtain, will be placed between the

radiation source and the irradiation station to allow safe installation

and removal of the painting. The interior of the facility will be lined

with neutron reflecting materials to further enhance the neutron-to-gamma

ratio.

Figure 4 shows the concept of the cart which will be used to transport

the painting from the irradiation facility to the counting room inside the

NBSR building after the painting has been irradiated. It will serve during

transportation both as a protection box for the painting as well as a biological shield to attenuate the induced radiation.

109
REACTOR RADIATION DIVISION AND COLLABORATIVE PR0GRA14S

Q. a

Figure 4. Painting transport cart.

The layout of the counting room is illustrated in figure 5. The

irradiated painting will be mounted on a horizontal vacuum table in

order to provide intimate contact between films and the painting for the

autoradiography process. The table can then be turned to a vertical

position for ease of the gamma-ray spectroscopy study. A steel mesh door

will separate the painting storage area and the rest of the counting room. In addition, the storage area will also have motion detectors and a fire

prevention facility to provide protection for the painting.

In conclusion, the NBSR thermal column, after the suggested

modifications, can provide a thermal neutron field suitable for neutronactivation autoradiography studies of paintings while at the same time

minimizing the radiation dose received by the paintings. The radiation

dose received by a typical painting at the proposed NBSR facility would

be about 70 Rads or less which includes an external dose of less than 40 Rads

from gamma rays and fast neutrons in the field and a dose of '^ 30 Rads

from beta particles and gamma rays emitted by activated elements in the

110
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

TILTING TABLE

I LEAD SHIELDING I

ALARM- n —AUX. DOOR

P^,o.-b- ^mmm^^'^^

mfyz 0..0. 5>-/'.->^

.o:; n:

r^. ^:^--^^^

Miiii^a'^^

ALARM

ELECTRONICS

X>

TV CAMERA

DETECTOR

TRACK

LIGHT BOXAUTOMATIC

DEVELOPER

=* figs'"

mm

rSii

V o .•?;•-j/fi?.- S^Q°-^6-;o;"?.',<:

v.p;.<:;3-o;Qq.<!

b^ar^^' ^°^- /<>/^c ^on:]:^;^n'-?-: LOCKING DOOR_A

Figure 5. Painting counting rocm.

painting. This dosage of ^ 70 Rads is slightly higher than the 20 Rads

figure for a comparable x-ray study but well below the doses of ^ 2,700

Rads from the existing neutron irradiation facilities.

Ill
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRA^IS

NUCLEAR WASTE MANAGEMENT

Y.T. Cheng & D.A. Garrett

A new program was initiated to study the radiation effects of

nuclear waste forms. It is designed to simulate long term radiation

damage to the integrities of waste forms and to characterize the structural changes in the waste forms both macroscopically and microscopically,

Our purpose is two fold to conduct the feasibility study of 1) using

NBSR as a viable irradiation source for radiation damage study;

2) establishing neutron measurement techniques to complement the more

common x-ray methods.

Li-6 and B-10 neutron activation methods were chosen to simulate

alpha particle and transmutation effects. Activation methods are preferred over the Cm-244 doping process which requires long waiting time

and special handling. The use of NBSR research reactor as neutron

source gives further flexibility in studying neutron and y effects.

The total radiation dosage and dose rate given to the waste form

can be moderated by varying the amount of Li and B dopants and by putting

the sample in different positions in the reactor. This also allows one

to change the n/y or a/y ratios to qualitatively study synergistic

effects.

The waste form currently under study is magnetophimbite

2+ 3+

(X M^ Oi n) • This is one of the four ceramic phases developed to

±z ly

contain high-level waste from the Savannah River Plant operations. Two

natural Li doped magnet op lumb it e samples (li^

^'-'^n '^'^"'"n "^i 7 s^ were

supplied to us by the Energy Systems Group of Rockwell International.

X-ray and neutron diffraction patterns of the sample were taken

as microscopic bench marks for the pre-irradiation characteristics of

the sample. Thermal neutron radiography and small angle neutron scattering facilities will be used to characterize the macroscopic properties

112
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

of the sample. The sample will be enclosed in sealed aluminum containers

20 2

and be exposed to thermal neutron fluence of 1.2x10 n/cm to simulate

the saturation y dosage. After irradiation, the sample will be allowed

to cool down for 30 days before being examined again by neutron and x-ray

techniques to characterize it's post-irradiation conditions.

113
B. NON-RRD PROGRAMS

ACTIVATION ANALYSIS GROUP FY 81

R. Zeisler

The Activation Analysis Group is part of the Inorganic Analytical

Research Division, Center for Analytical Chemistry. The group is

located in the reactor building and utilizes the facilities provided

here: stable climate counting rooms, clean and radiochemistry laboratories, a class 100 clean room, and the neutron irradiation facilities.

The group has an active research program and applies activation analysis

to many novel problems. The major research areas are summarized below

and more detailed descriptions of important accomplishments are included

in this report.

This year's 6th International Conference on Modern Trends in

Activation Analysis clearly showed the technique as a versatile and

sensitive tool in all branches of science and technology. Though the

fundamental principles on which activation analysis is based have remained

unchanged, incremental and crucial improvements are achieved by research

efforts focused on the evaluation and elimination of errors due to irradiation and counting procedures and errors due to sample handling,

and procedures leading to better sensitivity and higher selectivity.

The Activation Analysis Group participates successfully in these research

efforts and demonstrates the power of this mature technique through its

contribution to NBS and other programs. Our goal is to demonstrate that

activation analysis can fulfill part of the needs of analytical chemistry

for the determination of many components in complex matrices simultaneously

and over a broad dynamic range.

Based on the highly characteristic and well-defined nuclear properties of the elements, this technique is close to an ideal nondestructive

analytical method. It fulfills the two basic requirements of nondestructive techniques: specificity - the ability to correlate directly and

unambiguously the signal with the element sought, and selectivity -

114
NON-RRD PROGRAMS

the possibility of measuring the element in question in the presence of

other elements which emit signals of the same nature. The Activation

Analysis Group is emphasizing research efforts which bring the technique closer to the ideal. We use the different nuclear characteristics

of the elements when we apply our various activation analysis techniques:

instrumental and radiochemical neutron activation analysis (INAA and RNAA)

photon activation analysis (PAA) , prompt gamma activation analysis (PGAA)

and nuclear track technique (NTT) , and we investigate means and ways to

determine the specific signals more accurately and more selectively.

Concurrently, we are expanding our activities to include questions of

general analytical significance, e.g., sampling and sample preparation

for analysis.

Recent research accomplishments in the area of activation analysis

methodology are highlighted by the development of RNAA procedures for the

determination of platinum and tin in biological matrices. In both cases radiochemistry lowers the limit of detection and provides essentially

"background-free" counting of the specific signals free of interferences

from chemical blanks. Unprecedented low levels of platinum have been

determined using this new RNAA technique. Other research efforts are directed towards the determination of light elements as major constituents

of complex matrices, the accuracy and precision of PAA and PGAA are currently evaluated. A newly developed RNAA technique for the ultratrace determination of 1-129 will make the issuance of a certified

material feasible.

In connection with the pilot National Environmental Specimen

Bank (NESB) program research efforts resulted in a better understanding

of sampling characteristics of particulate biological matter. We have

investigated how to better homogenize these materials and what characteristics determine the subsequent subsampling of analytical test

portions in order to obtain meaningful analytical results. Problems

involving the appropriate number and size of samples (needed to

115
NON-RRD PROGRAMS

characterize bulk samples such as a human organ or part of an ecological

system) are studied in collaboration with statisticians.

INAA multielement determinations have provided a huge database for

the major environmental programs in which we participated during the

past year: Chesapeake Bay, NESB, and Hazardous Waste. The dynamic

range of activation analysis and its multielement capability is especially

useful to analyze varying concentrations and to discover unexpected oc- curance of elements. INAA is also used for the determination of halogens

in organic liquids obtained to analysis from the Recycled Oil Program

and from other sources. INAA multielement results have been used for

the certification of up to 20 elements in various new SRMs: Bovine

Liver, Orchard Leaves, Cast Iron Alloys, Basalt, Obsidian, Reduced Iron

Ore, and Fuel Oil. INAA has provided crucial information to another

NBS group on fused silica glass insulators.

We continue to emphasize the importance of state of the are equipment to be able to contribute in the same way in the future to the

mission of analycical chemistry at NBS with our strongest competence,

that is INAA. Major additions to our counting equipment and the

acquisition of a computer will help to follow this route. We also

will continue to take advantage of the specifics of nuclear techniques in

ultratrace determinations and chemical speciation studies by developing

RNAA techniques and applying activation analysis to new problems as in

the rapidly expanding field of bio-technology. With the new depthprofiling facility we will enter a new and important field in analytical

chemistry.

116
NON-RRD PROGRAMS

1. Research in Basic Problems of Analytical Chemistry

a. Application of Sampling Theory to Particulate Biological Samples

S. H. Harrison, B. Kratochvil, K. A. Fitzpatrick, and R, Zeisler

The quality of the analytical sample, as opposed to the quality of

the chemical analysis, is a too often disregarded factor in analytical

chemistry. The sample on which the results of a chemical analysis are finally based depends very much on the properties of the bulk sample and

the analytical test portion taken from the bulk sample [1] . Programs

like the pilot National Environmental Specimen Bank (NESB) are critically

dependent on the credibility of the analytical results, e.g., on the bulk

sample representation found in the analytical test portion. The NESB

tasks of evaluating storage conditions and analytical quality are carried

out by means of multiple analysis of many samples. This represents an

ideal test case for studying the application of sampling theory to the

investigation of the properties of particulate biological materials.

i Biological specimens, (e.g., human liver, mytilus edulis, etc.) are homogenized at cryogenic temperatures under contamination-free conditions,

in Teflon ball and disk mills to provide analytical test portions for

comparative analysis. The samples are always handled in a cryogenic

state and maintain particulate appearance after homogenization. Assuming

a particulate homogenate, the performance of the two types of mills,

ball mill and disk mill, was investigated. A radiotracer experiment was carried out and Ingamells' sampling constant. Kg, was determined after

collecting the data for a sampling program. Using the ball mill, a K = 32 e was determined. Based on the K value, one can conclude that

s

'^ the material is not well enough ground or well enough mixed. A result

of thii

0.95g.

this experiment was the design of a disk mill which yields a K of

To verify the particulate model, efforts were undertaken to actually

measure the particle size distribution of the homogenate obtained from

the two different milling procedures.

117
NON-RRD PROGRAMS

In general, sieving experiments are an easy way to determine

particle sizes; however, cryogenic sieving of frozen samples is much more

difficult. After some procedure development, the sieving experiments were carried out in a large LN freezer which provided the necessary cold

and dry atmosphere to avoid melting and particle agglomeration due to

moisture condensation. The results of sieving split liver samples,

previously ground in the two different mills, show that the disk mill

produces somewhat finer particles with virtual elimination of the course

(>40 mesh) fraction. Twenty five percent of the material ground in the

ball mill remained in the coarse (>40 mesh) fraction. The obvious effect

on subsampling is that smaller particles produce better homogeneity.

Using the information about particle size distribution and some assumptions as to the chemical nature of the liver, the weight of

sample required to hold the sampling standard deviation to a preselected

level can be theoretically calculated starting with the computation of

N, the number of particles. The value of N may be calculated from the

relation

N= ^i^ ' ^°° <^1- ^P> ' p(l-p)

d RP

where di and d2 are the densities of the two kinds of particles, d is

the density of the sample. Pi and ^P^ are the percentage compositions of

the component of interest in the two kinds of particles, P is the overall

average composition in percent of the component of interest in the

sample, R is the percent relative standard deviation (sampling error)

of the sampling operation, and p and 1-p are the fractions of the two

kinds of particles in the bulk material [1] . For a two component particle

mix made up of cells and fluids, and for 40 mesh particles, the element

Na requires a one gram sample to reduce the sampling error to one percent.

This is very consistent with our sampling constant of 0.95g.

118
NON-RRD PROGRAMS

Table 1. Na and Cl in Mussell Sieve Fractions (concentration in

mg/g dry weight)

Sieve Fraction >40 40-60 60-80 80-100 100-140 140-200 ' <200 Unsieved

Mesh Range

Na 54.0 53.8 57.2 61.9 65.5 70.7 71.8 61.0

Cl 79.8 96.7 102 110 116 121 128 111

In addition, trace element analysis experiments were carried out

to provide support data for the theoretical evaluations. In one experiment, ten subsamples of homogenized liver were analyzed for about 30

elements using nuclear methods. The element specific homogeneity was determined to be two to three percent for most elements and one percent

or less for Na, Fe, and Zn. In the other experiment, mussel (mytilus

edulis) samples were homogenized in a disk mill before being sieved.

The sieved fractions were then analyzed by INAA for trace elements.

Some interesting results from this experiment are shown in Table 1.

The results indicate a salt fraction which is more highly concentrated

in the fine particles.

The work shows that theoretical calculations of sampling parameters

compare favorably with experimental results. This information can provide important knowledge on the relation of the analytical test portion

to bulk material and, therefore, the quality and usefulness of the

analysis.

1. Kratochvil, B., and Taylor, J. K. , Sampling for Chemical Analysis,

Anal. Chem., 53 (1981) 924A.

119
NON-RRD PROGRAMS

b. Non-Normal Distribution of Blanks in Environmental Samples

R. R. Greenberg, H. M. Kingston, and E. S. Beary.

Many environmental studies involving the chemical analysis of

samples collected in the field require the subtraction of blank values

arising from filters, acids and other reagent solutions, containers

used to store the samples, etc. Typically, a number of blanks are analyzed,

the mean used as the most probable value, and the standard deviation used

to predict the probability of deviation from the mean. This approach is

accurate, however, only when the blanks are normally distributed. Frequently, this is not the case as illustrated by a recent analysis of five

47 mm Millipore filters. Iron concentrations of 0.2, 0.3, 0.3, 0.5,

and 1.9 yg/filter were found.

NBS has completed an extensive study of the Chesapeake Bay. As

part of this study, 24 blanks were collected and processed with the 102

water samples. These blanks, along with the samples, were then analyzed

by the neutron activation analysis. Several of the elements studied,

including Fe, Co and Zn, were clearly not normally distributed among

the blanks. The use of (normal) means and standard deviations greatly

underestimated the probability of elevated blank levels occurring in one

or more samples, and could have resulted in erroneous interpretations

of some of the data. Much better results were obtained using lognormal distributions to describe the blank behavior of these elements.

Fitting log-normal distributions to elements having normal blank distributions, did not significantly affect the results.

120
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2. Improvement and Development of Nuclear Analytical Techniques

a. Ultratrace Determination of Platinum in Biological Materials

R. Zeisler and R. R. Greenberg

Increasing interest in the determination of platinum has been spurred

recently by the wide spread use of the element in industrial and medical

applications. Two possible major sources contributing to the human

body burden are the noble metal catalysts used to reduce automobile emissions, and the administration of platinum containing drugs used in cancer chemotherapy. The intense interaction of platinum and its complexes

with biological systems makes it desirable to establish baseline data

and to monitor possible increases in human body burden. Previous attempts

to measure baseline concentrations of platinum have failed because the

reported sensitivities were several ng/g for the various techniques, while

the actual concentrations were at least one order of magnitude lower.

Many analytical techniques including neutron activation, however, have

been successfully applied to monitor elevated platinum levels, e.g.,

after administration of anticancer drugs consisting of platinum complexes

of the cis-(PtCl2L2) type (1).

To measure the naturally occur ing concentrations in human tissues

and other biological materials, a new neutron activation analysis scheme

based upon a radiochemical separation of the activation products has

been developed. This method fully utilizes the inherent sensitivity of

the activation reaction ^^®Pt (n,Y) '^^^Pt and counting of the daughter

nuclide Au-199 after radiochemical separation. The separation applied

here is highly specific for gold, in order to avoid common interferences,

as well as to provide "background free" counting of the respective gamma

activities. A decontamination factor of >10 for Na-24 has been achieved.

The only remaining interference to be considered is the reaction Au

(n,Y) ^^®Au (n,Y) ^^^Au from the naturally occurring gold in the samples.

This reaction can be quantitatively assessed with high precision and

taken into account by the determination of the gold using the same

121
NON-RRD PROGRAMS

Table 1. Platinum and Gold in Biological Standard Reference Materials

-12

CONCENTRATION 10 g/g

SRM

1571, Orchard Leaves

1572, Citrus Leaves

1577, Bovine Liver

This wo rk

Pt Au Pt ^ 200 1430 ± 80 89

60 ± 30 107 ± 9 NR

70 ± 30 56 ± 13 NR

Literature (2)

Au

89.2x10^ to 1.2x10^ 970 to 3500

NR

200 to 30000

NR = No data reported previously.

Table 2. Platinum and Gold in Human Liver Specimens

,-12

(.Concentration IL NESB ID

B0005

B0014

B0041 - A

B0041 - B

B0042

S0049

( Concentrat ion 10

^'

- g/g)

Pt Au

ND 2652 ± 1

54 ± 13 64 ±1

114 ± 23 71.9 ± 0.2

127 ± 60 143.1 ± 0.3

240 ± 70 298 ± 1

ND 496 ± 2

ND = Not detectable.

122
NON-RRD PROGRAMS

separation step. This analytical procedure, therefore, also provides

-12

excellent results for gold at the 10 g/g level.

Platinum and gold have been determined in three biological

Standard Reference Materials (Table 1) . The results for platinum are

found to be far below previously reported data (2) for orchard leaves,

and below the current limit of detection in this material. The gold

values, however, are in good agreement with the previous data, thus

confirming the completeness of the analytical scheme. For bovine liver,

both elements seem to be inhomogenously distributed, which would explain

the wide scatter of the previously reported data for gold. The

platinum concentrations found here are the first data reported for a presumably natural baseline in these materials which were collected

more than ten years ago. It would be of interest to analyze similar

materials collected recently. Possibly an increase of platinum in the

environment could be detected.

The application of the technique on human liver specimens

collected in the National Environmental Specimen Bank Program will

help to establish baseline information on human body burden. Platinum

concentrations in human livers have been found at the 0.1 ng/g level

(Table 2) . The determination of trace elements at these low levels

shows again the advantage of the nuclear activation techniques being

essentially blank free.

1. R. Zeisler, F. Lux, H. Seidenberger , H. Schoenenberger , W. Beck,

Nuclear Activation Techniques in the Life Sciences 1978 ^ p. 467,

IAEA Vienna, 1979.

2. E. S. Gladney, Compilation of Elemental Data for NBS Biological and

Environmental Standard Reference Materials, Los Alamos Scientific

Laboratory Informal Report, LA-84S8-MSj 1980, and Anal. Chem.

Acta. 118 (1980) 365.

123
NON-RKD PROGRAMS

b. Precise Determination of Aluminum by Instrumental Neutron

Activation

Richard M. Lindstrom and Ronald F. Fleming

Aluminum is the second most abundant cation in the earth's crust,

and activates so well with thermal neutrons that Al-28 often greatly

predominates in the gamma-ray spectrum of irradiated materials of

geological or botanical origin for the first few minutes after Irradiation.

For both these reasons Al is often useful as the normalizing element,

or marker for the crustal component of the sample. Because of the

short half-life (2.2405 min) , however, the determination of Al is subject to many inaccuracies: variation of irradiation conditions between

irradiations, uncertainties in timing, and the effect of high and varying

count rate, in addition to other sources of error that must be controlled

in work with long-lived nuclides.

We demonstrate here that these errors can all be made smaller

than the fundamental limit set by counting statistics, even when that

limit is below 0.5 percent. Achieving accuracy of this order requires

that the sample basis weight be determined to 0.1 percent, that the sample

and standard be irradiated simultaneously with small neutron self-shielding,

that counting geometry be controlled to 0.2 mm at 40 cm, that timing be

known to 0.2 sec, and that peak integration procedures be stable. In our measurements, samples in disk shape are irradiated between two

standard disks of Al foil. The 1779-keV Al-28 gamma activity is assayed

with a Ge(Li) dector and multichannel analyzer system adjusted for reliable

performance at integral count rates up to 40,000 counts per second, which

gives in excess of 10 net peak counts in the first of several 80-sec

counting intervals.

The transfer function from the observed number of net counts C to

the counting rate at the end of irradiation I (0) is modeled as the

following process:

I front end I ADC I' o

124
NON-RRD PROGRAMS

The relations between these rates are:

I (t) = I (O)exp(-Xt) (decay)

o I(t) = I (t)exp(-al (t)) (extending dead time)

o o I'(t) = I(t)/ (l+0i(t)) (nonextending dead time)

The solvation to this set of equations is:

A(t,) E ^Cexp(At ) exp(A-DT)-l .„. , , , .,

1 l-exp(-A-LT) X-m ' I„(0)exp(-aI^exp(-Xt^))

where DT = CT-LT is the ADC dead time and the pulse pileup parameter a

is determined from a linear fit of In A(t ) vs. exp (-At ) . The derivation has been presented elsewhere (1)

The procedure has been applied to the analysis of NBS SRM 1633a

Fly Ash. Samples were mixed with spectroscopic-grade graphite and pressed into pellets of constant geometry. The mean concentration and its

standard error were 14.085 ± 0.023 percent Al for four determinations

(Table 1) . Chi-squared tests of intermediate and final results showed

no significant variance beyond counting statistics, and hence the

procedure is capable of the desired precision.

The accuracy of the method is shown by the analysis of high-purity

single-crystal A1„0 , in which the amplifier shaping time, masses of

sample and standards, sense of the irradiated sandwich (sample-standardsample vs. standard-sample-standard), and counting geometry were varied

without visible effect. The mean concentration observed and its standard

error for six determinations was 52.77 ± 0.21 percent Al; the concentration calculated from the stoichiometry is 52.925 percent. The limit to

inaccuracy of the method is presently 0.3 percent relative, comparable

to the counting statistics obtained in the Fly Ash measurements. It

may be concluded that in favorable cases activation analysis can produce

aluminum data which are both precise and accurate at better than 0.5

percent relative.

125
NON-RRD PROGRAMS

Aluminum in SRM 1633a Fly Ash

(concentrations in percent)

Present Results;

Sample Fl F2 F3 F4

Concentration 14.120 14.059 14.113 14.050

Standard Deviation 0.045 0.045 0.046 0.044

Mean 14.085

Standard Deviation

of Mean 0.023

xVv 0.065, n = 4

Previous Results

INAA (NBS), Report of Anal. //5210, 5/79 14.07 0.33

PGAA (U. of MD), Anal. Chem. , 51, 2209 14.0 0.2

(1979)

Certificate (information only) (14)

1. R. M. Lindstrom and R. F. Fleming, in J. R. Vogt, ed .

,

Fvooeedings of the 4th Intevnationdl Conferenoe on Bucteav

Methods in Envivonmentdl and Enevgy Research (Columbia, MO,

1980; in press)

.

126
NON-RRD PROGRAMS

c. 1-129 Analysis

G. J. Lutz

Work is currently proceeding towards the certification of a botanical

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 the 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 collected on activated charcoal. The pre-irradiation

filtering is necessary to remove cesium, uranium, and tellurium which

. 1= .u ^' 133_ , .130^ 235,w .. 129^. .130^ interfere via the reactions Cs(n,a) I; U(n,f) I(n,Y) I; and

128^ , ,129^ 129^, ,130^ Te(n,Y) Te I(n,Y) I. The charcoal trap containing the iodine is sealed in quartz and

irradiated in the reactor. Subsequently a few milligrams of inactive iodine

carrier and an 1-125 spike are added. The major radioactivites are due to

chlorine, bromine, and impurities in the charcoal and quartz. 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

solution, but has been applied to gas phase separations.

Over a fairly wide temperature range, a bed of HMD will remove 99.9%+

chlorine and bromine from the oxygen stream while passing "^ 95% of the iodine.

127
NON-RRD PROGRAMS

d . Development of a Radiochemical Separation Procedure for Tin

R. R. Greenberg

Although tin has been shown to be essential for mammalian nutrition [1], it can be highly toxic in some forms [2]. Unfortunately, tin

cannot be readily determined in biological materials because of the

naturally occurring low levels. For example, very few biological reference materials with known tin concentrations are available. None of the

eight NBS biological SRMs issued have either certified or "information

only" values for tin. Relatively little reliable data concerning the

tin concentrations in human and animal tissues and body fluids exists.

Neutron activation analysis can be used to determine tin in most

biological materials at the naturally occurring levels if a radiochemical

procedure is used to separate tin from interfering elements and the background level of radiation (noise) is reduced. Both the Sn-113 and Sn-117m

isotopes can be used to quantify tin if the interfering Tb-160 (for Sn-113)

and Sc-Ay (for SN-117m) isotopes are removed. This has been accomplished

with a separation procedure based on the extraction qf Snli^ into toluene.

The sample is initially dissolved with nitric, sulfuric, and hydrofluoric

acids along with hydrogen peroxide, followed by a filtration step to remove precipitated oxides and sulfates from the final sulfuric acid

solution before extraction into toluene. Carriers are used to assure

a quantitative recovery (>99.8%) and maximize the decontamination.

Five samples of SRM 1571 (Orchard Leaves) have been analyzed by the

above procedure. The resulting concentration of 290 ± 17 (Is) ng/g

agrees favorably with two of the literature values (294 ± 16, 290 ± 20,

and 4100 ng/g) compiled by Gladney [3] . The resulting reduction in background radiation was better than a factor of 1000, and no Sc or Tb could

be detected using other, more intense, y-rays , indicating decontamination

factors of >20,000 for Sc and >1000 for Tb.

Research is continuing to further improve this method. A small

fraction of the selenium, '^17o accompanies the tin through the separation

128
NON-RRD PROGRAl'IS

and can elevate the background around the tin peaks in some matrices.

Therefore, efforts will be directed at selenium reduction. Other SRMs

with lower tin concentrations, such as Bovine Liver (SRM 1577) , will be

analyzed to evaluate the suitability of this procedure to provide

certification quality data for new SRMs.

1. Schwarz, K. , Milne, D. B., and Vinyard, E., Bioakem. Biophys.

Res. Commun., 40, 22 (1970).

2. Schroeder, H. A., Environment Id, 18 (1971).

3. Gladney, E. S., "Compilation of Elemental Concentration Data for

NBS Biological and Environmental Standard Reference Materials,"

Los Alamos Informal Report LA-8438-MS (1980).

3. Contributions for Analytical Programs

a. Multielement Analysis of Human Liver Samples

R. Zeisler, S. Harrison, K. Fitzpatrick

The Pilot Environmental Specimen Bank has completed its second

year of operation. One of the highlights of this year's accomplishments

has been the elemental analysis of 36 of the 300 human liver samples

collected. A comprehensive analytical protocol was developed which

includes the determination of most of the first-priority elements

proposed by the 1978 International Workshop on Monitoring Environmental

Materials and Specimen Banking (1) . Other elements regarded as possible

pollutants have been added to the protocol, as well as biological major

elements and trace elements, which can provide information about the

"normal" state of the specimen. The analytical protocol includes about

40 elements, which are determined by the following methods: atomic

absorption spectrometry (AAS) , isotope dilution- mass spectrometry (IDMS)

,

neutron activation analysis (NAA) , and voltammetry (VOLT) . The specific

elements determined and the analytical techniques employed for each

measurement are summarized in figure 1.

129
NON-RRD PROGRAMS

Be AAS

Al Mn Ni Cu As Se

Cd

VOLT

Ni Cu ZnCd

Pb

Mg

INAA

Al CI Ca Sc V Cr Mn Fe Co Cu Zn As Se Br Mo Ag Cd

La Au Hg

Ce Sm

IDMS

NI Cu

Tl Pb

Figure 1. The comprehensive analytical protocol for human livers uses four analytical techniques.

130
NON-RRD PROGRAMS

- Q.

in O

c

COD

o

<

o

- CO

0-)

u

60

•H

60

60 cN

3

o o

•H z

o u o 4J

0) OJ u. o

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131
NON-RRD PROGRAI^S

As applied, the analytical protocol is a part of the specimen

bank goal of producing a validated and documented chemical measurement

system, other parts of which are the sample collection protocol and

storage system previously reported. Aspects of the analytical protocol

which satisfy these criteria include the relation of the analytical test

portion to bulk sample, parallel determinations of Standard Reference

Materials, determination of several elements by more than one technique,

and the use of high precision, high accuracy techniques, e.g., IDMS

The data for the 36 liver samples is graphically represented in

figure 2. Remarkable is the very narrov; spread of some essential trace

elements, especially selemium. These results will contribute significantly

to the existing trace element data base for human livers for the purpose

of biomonitoring and specimen banking.

Nuclear methods other than INAA have been used this year on a select number of liver samples for procedure development and evaluation.

A radiochemical procedure (described in section 2a) determines Au and

Pt , elements occurring at very low concentrations and of significant

medical and environmental interest. In conjunction with v7orkers from

the University of Maryland, prompt gamma activation analysis (PGAA) was used to determine H, B, C, N, Na, P, S, Cl , K and Cd in several

samples including a homogeneity study. In the homogeneity study,

the results of the ten subsamples analyzed by PGAA agreed very well with

those of the eight subsamples analyzed by INAA.

Preliminary analyses by INAA of mussel (Mytilus edulis) samples were made this year as part of the development of an analytical protocol

for the aquatic accumulator specimen type. The dry weight trace element

with the exception of substantially higher concentrations for the

lithophilic elements, as would be expected from the sea water and sand

fractions in mussels.

132
NON-RRD PROGRAllS

b. Determination of Halogens in Organic Liquids by Neutron

Activation Analysis

R. Fleming

Significant progress has been made during the past year on the

measurement of halogen concentrations in organic liquids.

° We have demonstrated the reliable and accurate, simultaneous

determination of chlorine and bromine in a variety of lubricating

oils as part of the ASTM/NBS basestock consistency study under

the Recycled Oil Program.

° Analysis of total chlorine homogeneity in oils doped with polychlorinated biphenyls has been carried out in the development

of the PCB SRM-1581.

° Analysis of the bromine content of deuterated styrene monomer

samples to be used in small-angle neutron scattering measurements

has been carried out.

° In collaboration with the Tribochemistry Group (561) measurements

have been made of the chlorine and bromine contents of the saturated,

polar and aromatic fractions resulting from the ASTM D2007 clay-gel

separation of various lubricating oils.

Organic liquids provide nearly ideal matrices for neutron activation

analysis since carbon, nitrogen, hydrogen, and oxygen produce no countable

radioactivity. Each of the halogens, on the other hand, produces an activation product with its own unique half life and gamma ray energy

signal, as shown below.

Neutron Activation Products for the Halogens

Element (Hit) Product Halflife Gamma-ray Energies, keV

Fluorine

Chlorine

Bromine

lod Ine

20^

38

82

128.

CI

Br

11.0 sec 1633.8

37.2 mln 1642.2, 2167.6

35.3 hr 554.3, 776.5, 1044.1

25.0 mln 442.9

133
NON-RRD PROGRA^IS

The short halflife of F-20 dictates accurate timing ability and

for that reason we have not exploited fluorine analysis routinely. On

the other hand, since the fluorine activity will decay away rapidly,

its presence at any level does not degrade the measurement of the other

halogens. Conversely, because it has the longest halflife, large

amounts of bromine will reduce the sensitivity for the other halogens,

while bromine can be measured in the presence of any amount of them.

In effect, the different half lives accomplish an automatic and complete

chemical separation of fluorine, bromine, and the other two halogens.

Of course, since modern gamma-ray spectrometry systems have energy

resolution of better than 2keV (FWHM) , the lines used for quantification

are totally resolved.

The dynamic range of the measurements can be from ppb levels to

100%. The measurement reliability demonstrated in the basestock consistency work is +3% (2o) relative uncertainty over a twelve month period.

Since the technique is non-destructive, the sample can be available

after analysis for further measurement by this or other methods. Since

the technique is matrix-independent, not depending on chemical species

or on physical properties such as viscosity, density, opacity, etc., it

is well-suited for the fractionation work. In summary, the increasing

need for accurate, sensitive, unambiguous analysis of each of the

halogens in organic liquids has prompted the development of activation

analysis techniques optimized for this problem.

134
NON-RRD PROGRAMS

c. Multielement Determination in Two New Silicious Rock Standards

M. J. Blackman

The analysis of two new silicious rock standards: obsidian (SRM 278)

and basalt (SRM 688) by instrumental neutron activation analysis was completed and submitted to OSRM for certification. The elemental

concentrations determined are presented in table 1.

Table 1: Elemental Concentrations in Silicious Rock SRMs

(concentrations in mglg, except where noted)

Obsidian Basalt

Element SRM 278 SRM 688

Sc 5.11 ± 0.04 38.1 ± 0.3

Fe% 1.41 ± 0.02 7.24 ± 0.03

Co 1.48 ± 0.03 49.7 ± 0.2

Rb 134 ± 4 n.d.*

Cs 5.50 ± 0.19 n.d.*

Ce 62.2 ± 0.5 13.3 ± 0.7

Eu 0.838 ± 0.024 1.07 ± 0.07

Yb 4.45 ± 0.11 2.09 ± 0.13

Lu 0.725 ± 0.021 0.340 ± 0.014

Hf 8.38 ± 0.13 1.60 ± 0.12

Ta 1.21 ± 0.06 n.d.*

Th 12.49 ± 0.15 n.d.*

Sb 1.45 ± 0.08 n.d.*

Cr 6.1 ± 1.0 332 ± 5

Zn 55 ± 8 58 ± 7 Tb 0.99 ± .10 0.45 ± 0.04

*n.d. = not detected

135
NON-RRD PROGRAMS

4. Survey Analysis of Impurities in Silica Glass

R. Lindstrom

Eight samples of fused silica were analyzed by instrumental neutron

activation in a search for impurities that would impair the use of the

material as a high-temperature electrical insulator. Short-lived activation

products were measured after a 5-minute Irradiation in the RT4 pneumatic

tube and long-lived products after 6 hours in RT3. Several NBS Standard

Reference Materials were irradiated and counted under the same conditions

as elemental standards, and Hereaus AN grade quartz was used as a blank

28 28

for aluminum interference by the Si(n,p) Al reaction.

The results in table 1 show the concentrations of 28 trace elements

in the quartz samples analyzed. The data may be used as an indication of

the sensitivity of instrumental neutron activation for the measurement of

these elements (in such trouble-free matrices as quartz) with irradiation

and counting procedures in common use today at the NBSR.

136
NON-RRD PROGRAMS

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137
NON-RRD PROGRAMS

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138
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o

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.— Li + ! 1 r1 M

o ^

r-H O

d +1

(-1 —

^ o

d +'

00 og

rH O

o o 1 o o

O rH o +1 o +1

rH O

d +1

ON

CSl

c

3

o

o

6

ou

IMo

0) 4J3

a.e

oa

co

CO CTj -H -a > >-i

C a c3

(0 M

a; o

j=

4-1 co

0) •H

iJ 4_J to CO

>- cn u

<D c

•H Q) U a

c c —

o

CO u u

>-i 0)

0) J= o iJ

w ^ H

, 7i OC <D —i

00 u

3. C

•H c CO H u

)-i C5 a) OJ CJ > a H 3

00 e

01 c

1^ Vj

CO U-l

cn o

C c

O CO H

•P W

CO O

n •H

4J •U C CO

0) •H o J-l d CO o 4-1

139
NON-RRD PROGRAIIS

5. Facilities

a. Neutron Depth Profiling at the NBS Reactor

R. Fleming

Construction work has begun on a neutron depth profiling facility

at the BT-3 beam tube. When completed, this analytical tool will make

possible the near-surface measurement of concentration distributions

of He-3, Li-6, and B-10 as well as the investigation of its application

to other elements. A parallel development of an off-line profiling

facility for bismuth using in-core irradiation is also underway.

A key component for obtaining an intense, high-quality thermal

neutron beam is a good lowpass neutron filter. Therefore, the integrated

neutron transmission of room temperature, single crystals of silicon,

bismuth, lead and sapphire were measured. As suggested by Nieman,

et . al. (1) the sapphire crystals provide the best attenuation of fast

neutrons and gamma rays for a given thermal neutron transmission.

The neutron beam is scheduled to be opened early in FY 82 . At

that time, calibration and characterization of the facility will begin.

1. H. F. Nieman, D.C. Tennant and G. Dolling, "Single Crystal Filters

for Neutron Spectrometry", Rev. Soi. Instruments 51^ 1299 (1980).

b. Facility Enhancements

R. Lindstrom

The primary data acquisition and processing system for the

group is a Nuclear Data ND 6620. Data acquisition has become more

distributed with the connection of a recent ND66 MCA (belonging to

the Smithsonian Institution and the Health Physics Group) and a second NDlOO MCA to the system. The ND66 will eventually support four

detectors, and the NDlOO one in room C003 adjacent to the rabbit receivers,

A second 9-track magnetic tape drive has been added. A mofrm hsd

been installed to allow remote (off-site) control of all data

acquisition and processing via a portable terminal with an acoustic

coupler to the commercial telephone network.

140
NON-RRD PROGRAJIS

PRECISION GAMMA-RAY AfO X-RAY WAVELENGTHS

E. G. Kessler, Jr., R. D. Deslattes, D. Glrard , and W. C. Sauder

(Center for Absolute Physical Quantities)

Gamma- and x-ray wavelengths are measured using crystal diffraction

spectrometers. All wavelengths reported to date have been measured with

double flat crystal transmission spectrometers equipped with crystals

whose lattice spacing has been measured by x-ray/optical interf erometry.

Diffraction angles are measured interf erometrically with a precision of

-3

0.5 X 10 sec. A complete description of the instrumentation, measurement procedures, and results published over the past three years is

available in reference 1.

A measurement of the wavelength of the electron-positron annihilation

2 radiation (511 keV) which has been promised for a number of years has

still not been completed. This is due to the low priority we have

assigned this measurement and to problems with the positron source. The

proposed positron emitter is Cu-64 and thin sheets of Au plated Cu-64

have been irradiated in aluminum cans filled with D„0 in order to determine

the extent of Cu contamination of the D„0. In a previous irradiation,

extensive Cu contamination of the irradiation thimble water occurred.

A Mo-99 sample was obtained in order to measure the wavelength of

the 40.6 keV line. This line was used as a calibration line in a recent

3

accurate pion mass determination. The Mo-99 source has a half life of

67 hours and only 2% of the decays produce the 40 keV transition. In

addition the low energy of the gamma-ray leads to strong self-absorption

in a thick Mo-99 source. Count rates less than 1 per second were achieved.

The uncertainty in the measured energy (E = 40583.47 eV + 4.2 ppm) resulted

almost entirely from the counting statistics. The pion mass determination

consisted of energy measurements of pionic x-rays from tt-P and 7T-Ti using a bent crystal spectrometer calibrated with the Mo-99 40.6 keV line. The

measured value for the pion mass (m - = 139567.5 + 0.9 keV) is the most

accurate value ever reported.

The gamma-ray sources we have used so far have been long lived sources which were extracted from the NBS reactor for measurement. In order to make

141
NON-RRD PROGRAMS

high energy measurements (> 2 MeV) , it is necessary to use capture garamaray sources because of the low efficiency of our spectrometer. We have

submitted an instrument proposal to Institute Laue-Langevin (ILL) which

requests permission to place a flat crystal spectrometer in front of their

24m bent crystal spectrometer. Our spectrometer will be movable so that

both instruments may be used, but not simultaneously. This instrument

proposal has been accepted by ILL. The interest in more accurate high

energy gamma-ray wavelengths is for detector calibration, as standards for

relative measurements, and as possible input to the fundamental constants

through a wavelength-mass product.

An extensive number of high Z K x-rays produced at the 4 MeV electron

Van de Graaff have been measured during the past year. Measurements have

been made on Ka , Ka , K3, , and K^ for Ag, Xe, Ba, Nd , Sm, Er, Au, Pb , Th,

and U. Comparison of the measured wavelengths with accurate self-consistent

4 5 field calculations ' provides a test of the theoretical calculations. In an earlier publication using the then best available data, a discrepancy

between theory and experiment which was linear in Z was noted. Preliminary

analysis of our more extensive data shows a plateau in the discrepancy around

Z=60 and a significant decrease in the discrepancy around Z=90. Measurements on Xe are important because it is the only gaseous target which was

used. The Xe measurements appear to be consistent with those on the solid

targets.

A measurement of the erbium K edge has recently been published. This

measurement provided the energy calibration for kaonic potassium x-rays which

were measured using the critical absorption technique by Lum and Wiegand

of Lawrence Berkeley Laboratory. By comparing the measured and theoretical

values for the kaonic x-ray transitions, a value for the kaon mass was

2

deduced. Although the measured mass value (m.^ = 493.640 + 0.054 MeV/c ) is less accurate than a previous determination, it provides a valuable

check because an entirely different experimental technique was employed.

The efficiency of the flat crystal spectrometers is a few x 10

Thus only intense gamma- and x-ray transitions can be measured. In order

to have the facility measure weaker lines we are upgrading a bent crystal

142
NON-RRD PROGRAliS

o spectrometer we have been given by the University of Colorado. The

spectrometer will employ Dumond geometry, have a 4m radius crystal, and

an angle interferometer. This instrument will first be used to measure

weak x-ray lines such as hypersatellite lines.

1. R. D. Deslattes, E. G. Kessler, Jr., W. C. Sauder, and A. Henins,

Annals of Phys. 129 , 378 (1980).

2. W. C. Sauder and R. D. Deslattes, Jour. Res, mS Ilk, 2>i\l (1967).

3. D. C. Lu, L. Delker, G. Dugan, C. S. Wu, A. J. Caffrey, Y. T. Cheng,

and Y. K. Lee, Phys. Rev. Lett. 45, 1066 (1980).

4. K. N. Huang, M. Aoyagi, M. H. Chen, B. Crasemann, and H. Mark,

At. Data Nucl. Data Tables 18, 243 (1976).

5. J. P. Desclaux (private communication).

6. R. D. Deslattes, E. G. Kessler, Jr., L. Jacobs, and W. Schwitz,

Phys. Lett. Ilk , 411 (1979).

7. G. K. Lum, C. E. Wiegand, E. G. Kessler, Jr., R. D. Deslattes,

L. Jacobs, W. Schwitz, and R. Seki, Phys. Rev. D 23, 2522 (1981).

8. J. H. Jett, N. S. P. King, D. A. Lind, and P. Henneng, il/ueZ. Instr.

and Meth. 114, 301 (1974).

143
NON-RRD PROGRAMS

NEUTRON DOSIMETRY FOR REACTOR PRESSURE VESSELS

E. D. McGarry

(Nuclear Radiation Division)

Steel embrittlement due to neutron irraditation in reactor pressure

vessels has become an issue of growing concern as many commercial reactors move into their second and third decades of service. An interlaboratory

program involving the Hanf ord Engineering Development Laboratory (HEDL)

,

the Study Center for Nuclear Energy (CEN/SCK at Mol, Belgium), and the

NBS has addressed the problem of establishing accurate methods for the

neutron dosimetry measurements in the pressure vessel surveillance programs.

A reactor pressure vessel (RPV) simulator at the Oak Ridge Pool Critical

Assembly (PCA) served as the common irradiation test field for a blind

round-robin test of dosimetric measurement methods. The radiometric

analysis techniques at HEDL and CEN/SCK have been validated by calibrations

against NBS standard gamma sources, neutron fluence standards, and certified

fission standards. The latter are certified with respect to fissions in

fissionable deposits of known mass with an NBS fission chamber operated at

either the CFRMF reactor in Idaho or in the thermal column of the NBS reactor.

CEN/SCK performs the radioactivity measurements with a calibrated, transportable 3-in. X 3-in. Nal(Tl) gamma spectrometer system. For the In(n,n')

reaction, the measurements are "absolute"; for other reactions, they are referenced to benchmark field irradiations in the Mol Cavity, U-235 Fission

Spectrum Neutron Field. The CEN/SCK system has been used to make the majority

of radiometric measurements for the characterization program.

Table 1 provides an example of the results of a certif ied-f lux irradiation of the 4.5-hour In(n,n') reaction at the Cf-252 Fission Neutron

Spectrum Facility at NBS. The results were used to validate radiometric

measurements of the 4/12 SSC PCA-RPV configuration in November 1980. These

measurements were made only by CEN/SCK personnel using the portable Nal(Tl)

system. The expression for the flux, as derived from the source strength

and a distance measurement, is given near the center of the table. The

144
NON-RRD PROGRAMS

Table 1. Compensated beam geometry, certif ied-f luence irradiation to

activate 4.5-hour •^-'-^In(n,n' ) for calibration check of the

CEN/SCK Nal(Tl) gamma spectrometer for radlometrlc-sensor measure- ments in the LWR-PCA-PV mockup in November 1980.

Results of Certified Flux Radiation :

Sensors : 10-mil thick indium foils (99.999%) ID #1 & #10

Start of Irradiation : Friday, 21 Nov. 1980 at 18:05:00 EST

End of Irradiation: Sunday, 23 Nov. 1980 at 12:20:00 EST

Length of Irradiation : T = 152100 s AAT

Fraction of Saturation : (1-e- ) = 0.9985

Neutron Source : NBS Cf-252 Source #NS-100

Source Strength : (22 Nov. 1980) S = 3.837 x 10^ n/s + 1.4%

Foil-to-Foil Distance: d = 6.198 + 0.041 cm Cf-252 Flux Averaged over Foils

S

TTd ^ • In II +

P

& ^ = d/2

p = 0.635 cm

(j) = (3.179 X 10'^)(0.9796) = 3.11 x 10^ n/cm^-s + 1.9%

Corrections for Scattering : The indium reaction rate will require an adjustment to account for scattering of neutrons in the source encapsulation

and holding structures. It is estimated, by calculation, that because of

this scattering the 4.5-hour indium activity will be 0.6% + 0.8% too large.

Results of Radioactive Foil Analyses :

Foil Weights : ID #1 = 0.2272 g

ID #10 = 0.2270 g

U-235 Equivalent Flux : 7.30 x 10^/0.2271 = 3.21 x 10^ n/cm^-s + 2%

Conversion Factor to Cf-252 Flux : 1.05

Observed Cf-252 Flux: 3.21 x 10^/1.05 = 3.06 x 10'^ n/cm^-s

145
NON-RRD PR0GRA14S

Table 2. Summary of Cf-252 standard neutron field irradiations in the

period 1979 to 1980 to benchmark reference neutron characterization

measurements of the PCA-RPV mockup facility.

235

U Fission Equivalent Fluxes

Date Foil ID

4

HEDL(a) Mol(b)

115^ , ,Nll5m^ ^ In(n,n ) In Reaction

9/21/79 2.031 X 10^ 2.028 X 10^

9/21/79 5 2.027 X

10'' 2.027 X lO'^ 9/21/79 6 2.062 X 10^ 2.060 X 10^

9/21/79 7 2.044 X 10^ 2.061 X 10^

11/23/80 1 N/A 3.21 X 10^

11/23/80 10 N/A 3.21 X 107

58,,,, ,58^ Ni(n,p) Co Reaction

9/21/79 BR 2.033 X 10^ 2.033 X 10^

9/21/79 BP 1.994 X 10^ 2.011 X 107

NBS(c)

2.02 X 10' + 2.2%

2.02 X 107 + 2.2%

2.05 X 10^ + 2.2%

2.05 X 107 + 2.2%

3.27 X 107 + 2.4%

3.27 X 107 + 2.4%

2.01 X 10' + 2.5%

2.01 X 107 + 2.5%

(a) Derived from HEDL-measured absolute reaction rates per nucleus and evaluated average uranium-235 fission spectrum cross sections of 189 mb for

indium, 108.5 mb for nickel and 0.705 mb for aluminum.

(^) Derived from benchmark-field calibration at Mol U-235 Fission Spectrum;

absolute reaction rates also obtained for indium and nickel.

'^)nBS values are based upon compensated-geometry irradiations and, therefore, are derived from a source strength S-252, the average counting rate of

a pair of foils and the distance d between them:

In

I

-252 ^252

where: r = d/2

p = foil radius

For the '^'"^In(n,n' )'^"^^^In reaction, ol^yd^^ = 1.05 % 0.03

In, In

CO CO —OCT J _9'3C

For the Ni(n,p) Co reaction, a, / a, = 118 mb/108.5 mb

Ni / Ni

146
NON-RRD PROGRAIIS

Table 3. Summary of other U-235 standard neutron field irradiations in

the period 1978 to 1980 to benchmark reference PCA dosimetry.

235

U Fission Equivalent Fluxes

Date

11/9/78

11/17/78

Foil Id

N7(A)

N8(B)

(d)

HEDL

(a) Mol (b) NBS (c)

115^ , ,xll5m^ „ In(n,n ) In Reaction

N/A

N/A

N/A

1.94 X lOlO

1.86 X lOlO

1.87 X 1.89 X lOlO 10-"-*^ + 2.4%'-^'^

1.89 X lOlO 1.86 X lOlO + 2.4%

1.87 X lOlO 1.86 X lOlO + 2.4%

1.88 X lOlO 1.92 X lOlO + 2.7%

1.88 X lOlO 1.93 X lOlO + 2.7%

11/17/78 Ml

27 24

Al(n,a) Na Reaction

1.91 xlO^^^^) 1., X 10

10

1.90 X

10"""° + 3.5%^^-^

Spring 1979 CD

CO ^o

Ni(n,p) Co Reaction

1.97 X

10-^°^^^ 1.95 X

10-^°*-^^ 2.00 x

10"^° + 3.5%

(a)(b)g^^ footnotes (a) and (b) Table 2.

^^^All fluxes reported here have been reduced by 2.0+1.5% to account for excess -'--'-^^In (4.5-hour) activity caused by scattering within the NBS

U-235 Cavity Fission Source.

vd)This set is slightly suspect because of questions about the actual indium

foils sent, as indicated by the foil ID in brackets.

(^)No adjustment for scattering in the cavity fission source were made to

the NBS-reported flux. It is believed that in-scattering effects are balanced by inelastic scattering removal in the 40-mil thick aluminum foil.

^^^Values of foil disintegration rates reported by HEDL and Mol, respectively, were 8257 dps + 1.8% and 8164 dps + 1.7%, on January 29, 1979,

10 a.m. (Mol time). A second group from Mol reported 8373 dps + 1.8%.

-235

Fluxes were derived on the basis of a,. = 108.5 mb.

Nx

147
78 K

^ 76K7AK

72K -

70 K

NON-RRD PROGRAMS

ACTIVITY NOT MEASURED

AT NBS ... DEDUCED FROM OTHER FOILS IN SET AND DASHED CURVE

SHAPE OF DASHED CURVE TAKEN FROM FtllinWING FIGURE FROM THE

9/23/78 NICKEL FOIL IRRADIATION

ITEM A

FOILS IRRADIATED ON: O 11/7/78 « 12/16/78 X 11/10/78

BOTTOM

LOCATION OF ALUMINUM | f-FOIL FOR IRFAD1AT10NS-*1 ON 11/17/78 & 12/17/78 '

40 80 120 160 200

DISTANCE IN MILS FROM THE BOTTOM OF THE ALUMINUM FOIL HOLDER FOR THE CAVITY FISSION SOURCE

(SEE ITEM A). THE OBSERVED ACTIVITY IS PLOTTED AT THE CENTER THICKNESS OF THE FOIL.

<O

CD<DC

<

UJ

\

^\I

T //

/

/

Figure 1. Comparison of results of indium foil irradiated in three different

cavity fission source certified fluence runs.

960r

950

>-^ 940

930

920

910

l\

I'i

A

v^ y

I

/

±1 %

Figure 2,

T —I -T——,——I- 1 ~n

40 80 120 160 200

DISTANCE IN MILS FROM INSIDE BOTTOM OF '/2-in. FOIL POSITIONING PIECE

U-235 cavity fission irradiation of nickel foils CJ, CK, CL, and

CM. (Irradiation time: 112380 s, 9/23/81, 21:37:00 EST).

148
NON-RRD PROGRAMS

expression enclosed In square brackets Is an adjustment for the fact that

the foil, of radius p , Is a disk and not all points on Its surface lie on a sphere of radius r. Table 2 and 3 are summaries of similar types of Irradiations, some

In the Cf-252 and others In the U-235 standard neutron fields at NBS.

Certain significant aspects of these tables should be recognized. First,

-, c , -, , 115-r / ,.115m^

at least one type of dosimeter, namely the In(n,n ; In reaction,

was measured In every period of significance, as defined by the run-to-run

monitoring activities reported earlier. Second, for all reactions checked:

In(n,n ) In, Ni(n,p) Co, and Al(n,a) Na agreement is good to

excellent, to within 2.5%, over the three-year period. In some cases,

however, this agreement Is not overly significant because the Mol and HEDL

fluxes are derived from reported reaction rates; and agreement with the NBSreported flux depends upon the exact spectrum-averaged cross section used.

The details are given In the footnotes of Table 2 and 3.

As opposed to the derivation of fluxes from spontaneously fissionable

point sources such as Cf-252, those obtained from thermal-neutron driven

U-235 sources require considerable more effort to certify. Some explanation

of techniques and reproducibility of results is afforded by Figures 1 and

2. One problem area, identified by the larger uncertainty of + 3.5% on the

27 24

(n,a) Na irradiation, resulted from the larger thickness of the aluminum

foil (40 mil compared to routinely used 5 to 10 mil thicknesses). Consequently,

estimating the true flux within the foil volume is more of a problem.

149
NON-RRD PROGRAMS

OBSERVATION OF FIELD PARATCTERS FOR THE INTERMEDIATE-ENERGY

STANDARD NEUTRON FIELD (iSNF)

R. Dallatore, C. Eisenhauer, D. Gilliam, J. Grundl,

G. Lamaze, and E. D. McGarry

(Nuclear Radiation Division)

Currently the ISNF is receiving increased interest as a dosimetry

standard field in several areas of application from cross-section

adjustment studies for fast reactor applications, to damage evaluations

in light-water reactor pressure vessels, which is the subject of an ongoing program at ORNL being sponsored by the Electric Power Research

Institute.

In the past year two ISNF field parameters were subject to

secondary experimental checks of limited accuracy in order to improve

general confidence regarding design principles and primary neutron flux

measurement methods.

1. Central neutron fluence based on neutron source strength of

fission disk drivers

This flux determination is a direct and absolute check of the

neutron transport calculations for ISNF but it is complicated and not

amenable to high accuracy.

The measurement steps are as follows:

1. Relative neutron source strength of the eight driver disks

(see Figure 1) — relative gross gamma counting of irradiated fission

disks

•

2. Absolute number of fissions produced in a single disk during a monitored ISNF irradiation.

a. Prepare U-235 fission activation counting standard in thermal

column cavity irradiation. Establish number of fission produced in

disk on basis of absolute fission chamber monitor in the cavity.

b. Determine total fissions produced in a single disk during ISNF

irradiation with a Pu-2 39 fission chamber operated in the central ISNF

field.

Counting of Ba-140 fission-product activity in disk relative

150
NON-RRD PROGRAMS

It is to be noted that the primary method for establishing the

ISNF central flux is that of neutron flux transfer from the NBS Cf-232

fission neutron irradiation facility. The accuracy of that technique

is close to + 3%.

2. Experimental check of superposition principle applied to ISNF

geometry

Spherical symetry in the ISNF system is an important property

for a standard neutron field whose neutron spectrum is specified on

the basis of neutron transport calculation and the physical and nuclear

parameters of its constituents. The eight fission disks are placed at

a fixed radius in the cavity — see figure 1 — but physically are only

small sections of the complete shell source which is entered into the

transport calculation. Because there is only radial dependence of

material densities in the ISNF, angular position of sources must be

indistinguishible for source neutrons which arrive at the center of the

system. All paths from source to center remain the same if the source

is rotated about the center. Thus each fission disk contributes to

the central neutron flux according to its source strength alone, not

to its position.

There are some minor departures from spherical symetry in the

ISNF (instrument penetration for example) . The extent to which these

departures are negligible is not difficult to check in principle since

the ISNF can be operated with a single fission source disk. A

sensitive spectral index observed for a one-disk ISNF irradiation

should be the same as for an eight-disk irradiation. The spectral

index chosen for this test was S , „ and has the following

characteristics in the INSF spectrum:

151
NON-RRD PROGRAMS

to the fission activation counting standard.

3. Integrated neutron source strength for monitored ISNF irradiation

integrated number _ total fissions| fission in all 8 disks

of neutrons in disk #3 fission in disk //3

step 2 - - step 1 -

X

[V, total

per fi

neutrons

ssion

The neutron transport calculations yield a central ISNF flux per source neutron. Applying this value to the observed integrated source strength gives the expected neutron fluence for a particular monitored

irradiation. source neutrons

-central ISNf] central flux , R.^.qIs] ^

r^ neutron flux L J [_ 001385

1 neutron/secj

- step 3 -

1 1 *. ^ • calculation

12 2 = 1.5-xlO neutrons/cm

The monitor for this irradiation was a fission chamber operated with a 105 yg deposit of Pu-239and 248 yg deposit of U-238. The ISNF spectrumaveraged cross section for Pu-239 from the transport calculation

provides the necessary parameter to obtain an ISNF fluence from the

observed fission/gm from the chamber

central ISNfI [• . o i n^ . • / 1 v fi qo u 1 v 0-602

= 6.63x10 fis/gm X 1.82 barns X „„^ neutron fluxj L ° J L J 239

12 2 = 1.45x10 neutrons/cm

The difference between the neutron fluence based on fission disk source strength to that obtained with a Pu-239 fission chamber is close to 5%.

It is estimated that the accuracy of this involved experiment is no better than + 5%.

152
NON-RRD PROGRAl'IS

Figure 1. A schematic drawing of the ISNF spherical cavity.

90% response range

low

ISNF spectrum: 8.3 keV

U235(n,f) response: 0.9

U238(n,f) response: 1400

med ian

0.59 MeV

0.26

2.3

high

3.5 MeV

3.1

5.9

The spectral index measurement was carried out with a double fission

chamber and included chamber rotations and separate measurements of

backgrounds with 1 disk and with eight disks. The final result

obtained was:

TTooc/TTooo *- 1 • J ISNF w/8 driver disks ^ m ^j t i /o<y U235/U238 spectral index: ir^rrr^; r,—^—

Tt—;— = 1.016+1 1/2% ISNF w/1 driver disk —

The accuracy for this result is dominated by the reactor background

for the 1-disk run which was 12% and 21% for the U235 and U238

detectors, respectively. This is to be compared with normal reactor

backgrounds for eight disk runs of 1.4% and 2.8% for those detectors.

153
NON-RRD PROGRAMS

FISSIONABLE DEPOSIT MASS ASSAY FOR ABSOLUTE FISSION RATES IN THE FFTF

D. M. Gilliam

(Nuclear Radiation Division)

One part of the Fast Flux Test Facility (FFTF) Reactor Characterization Program was a measurement of absolute fission rates of eight

major fuel isotopes at two different positions within the reactor. The

instruments employed in these tests were fission ionization chambers

for which the absolute efficiency and fissionable deposit mass assay

have been rigorously established.

Most of the fifteen fissionable deposits used in these tests were vacuum-evaporated fluoride deposits made by the CBNM laboratory

at Geel. The U-238 deposits were oxide deposits prepared at Los Alamos

National Laboratory; one Pu-239 deposit and the Pu-241 deposit were

made at the Oak Ridge National Laboratory. Mass assay of these deposits

was carried out by comparison to NBS reference deposits. Both alpha

counting and fission counting comparisons (in both thermal neutron beams

and fast neutron fields) were employed. The reference deposit mass assay was based on two or more independent methods wherever possible.

Absolute alpha assay was employed in every case, and the isotope

dilution mass spectrometry was used for U-235, U-238, Pu-239, and

Pu-240. The deposit masses and estimated errors along with lists of

isotopic impurities are given in table 1.

I

154
NON-RKD PROGRAMS

TABLE 1

FFTF-RCP ABSOLUTE FISSION CHAMBER REFERENCE FISSION FOILS

PRINCIPLE ISOTOPE

ISOTOPE DEPOSIT ID

02N-9

MASS

Th-232 621 yg ±2 %

Np-237 37K-05-1 68.3 ± 1.1 %

U-233 23K-02-8 30.71 ± 1.5 %

batch impurity composition

(atom percent)

U-235

U-238

U-238

Pu-239

Pu-240

Pu-241

23K-02-8 30.71 + 1.5 % U-232

U-233

U-234

U-235

U-236

U-238

<0.6. ppm

99.76

0.018

0.009

<1.0 ppm

0.21

25A-03-1 30.96 + 0.77% U-234 0.1822

25A-03-2 30.91 + 0.77% U-235 99.0829

U-236 0.0353

U-238 0.6996

28G-5-1 735.7 + 1.2 % U-234

U-235

U-236

U-238

0.00016

0.01755

<0. 00001

99.9823

28NC-5-1 651.7 + 0.9 % U-234

U-235

U-238

0.0054

0.7194

99.2752

49K-005-1 0.0983 + 0.8 % Pu-238 <0.001

49K-001-3F 1.788 + 0.6 % Pu-239 99.978

49K-0-3F 4.893 + 0.6 % Pu-240 0.021

49K-02-3F 25.33 + 0.5 % Pu-241 0.0005

49K-03-2F 35.10 + 0.5 % Pu-242 0.0005

49K-4-1 468.1 + 0.6 % Pu-244 <0.0002

40L-2-3F 221.4 + 0.8 % Pu-238

Pu-239

Pu-240

Pu-241

Pu-242

Pu-244

Am-241

0.0109

0.6727

98.5191

0.4289

0.3679

0.0006

0.17

41K-03-l(L) 8.71 + 2.5 % Pu-238 0.001

(10/13/80) Pu-239 0.972

Pu-240 0.255

Pu-241 98.653

Pu-242 0.118

Pu-244 0.002

Am-241 15.0

155
NON-RRD PROGRAMS

NEUTRON PERSONNEL DOSIMETER CALIBRATION AND TESTING

R. B. Schxvartz

(Nuclear Radiation Division)

The reactor filtered beams, with energies of 2 keV, 24 keV, and

144 keV, together with the thermal column beam, were used for several

important neutron dosimeter tests, as well as for the calibration of a Bonner sphere set.

In October 1980, a new neutron dosimeter, developed by the Israel

Atomic Energy Commission, was tested at the three filtered beams. This

dosimeter was designed to act as a simple neutron spectrometer so that,

unlike all other dosimeters, it would not be necessary to know anything

about the neutron spectrum in order to evaluate the reading. The NBS

filtered beams comprised the only facility in the world where this important

concept could be experimentally evaluated. The tests done at the reactor

and at the NBS californium facility showed that the concept did, indeed,

work. The results of these tests allowed the designers to "fine-tune" the

design, so that in later field tests it gave quite accurate results. This

dosimeter is now available commercially from an American company and is

being considered for use at at least one reactor power station. Further

tests will be done on the commercial version.

The filtered beams are also being used to help evaluate the possibilities

of using dye dosimeters for personnel protection. Since these dosimeters

are generally sensitive to gammas, the 144 keV beam was especially valuable

since it has the highest ratio of neutron-to-gamma dose equivalent of any

of the NBS neutron calibration facilities ("^ 100:1). This work is being

done by both the NBS Radiation Physics Division and by a commercial company.

The work is still in the preliminary stages, and the results so far have been

rather inconclusive. Since the dyes offer the promise of high sensitivity

and nearly tissue equivalent response, much more work will be done with

these dosimeters.

156
NON-RRD PROGRMIS

Tests were also done at the filtered beams and with the thermal

column beam,, of the use of silicon diodes as dosimeters. In principle, the

resistivity should change with dose, but the sensitivity turned out to be

too low to be of practical use. No further tests of these particular

devices are planned.

Routine calibrations of more conventional dosimeters were performed

for several DOE laboratories, commercial companies, and one hospital,

using the four reactor beams. In addition the Aberdeen Proving Ground

Bonner sphere set was calibrated at thermal and with the 24 keV beam.

157
NON-RRD PROGRAMS

FLUX MEASUREMENT IN THE SMALL ANGLE NEUTRON SCATTERING FACILITY

G. Lamaze and D. Gilliam

(Nuclear Radiation Division)

On April 1, 1981, a flux measurement was made using an NBS double

fission chamber containing a deposit of U-235 in one chamber and a deposit

of Pu~239 in the other. The principal parameters and calculations are given below:

Mass of Pu-239 deposit (491-1-4) = 104.4 yg: N = 2.63 x

10"*"^

atoms (+0.4%)

Counting rate with extrapolation to zero and dead-time correction:

R = 5956 c/sec (+0.3%)

Correction for self absorption of fission fragments: CI = 1.0054

(+0.35%)

Correction for neutron scattering : C2 = (1.054) (+2.0%)

flux = R X CI X C2/(N X Sigma)

flux = 2.16 X

10""'"'^ (+2.1%) /Sigma

2

where Sigma is the spectrum averaged cross section in cm .

Mass of U-235 in deposit (25k - 1 - 2) = 132.2 yg: N = 3.39 x lO"""^ (+0.5%)

R = 6164 c/sec (+0.3%)

CI = 1.0072 (+0.35%)

C2 = (1.054)~-'- (+2.0%)

Correction for Pt transmission loss: T = 1.066 (+0^7%)

flux = R X CI X C2 X T/(N X Sigma)

flux = 1.85 X

10"-'"'^ (+2. 2%) /Sigma

Sigma has been estimated by assuming a Maxwellian distribution with

a temperature of 30 meV ('^^ 75 C) and a sharp cutoff at 5.3 meV

o (lambda = 3.93 A). This yields the following values:

Sigma (Pu) = 2138 b

Sigma (U) = 1817 b

158
NON-RRD PROGRAMS

If there are transmission losses In the beam tube that are 1/v In

nature, the spectrum shape will be changed resulting In a different value

of Sigma. Assuming different values for the transmission at 3 meV, the

following values were obtained:

2

Trans Sigma (Pu) Sigma (U) flux (n/cm /sec)

100% 2138 b 1817 b 1.01 x 10^ (+4%)

75% 2072 b 1760 b 1.05 x 10^ (+4%)

50% 2009 b 1707 b 1.08 x 10^ (+4%)

A flux measurement of the fine beam was also made and it was found to

equal 16.0% of the principal beam. This value was in good agreement with

a measurement of this beam made on March 4, 1981.

PREPARATION OF A CERTIFIED FISSION PRODUCT

COUNTING STANDARD

D. M. Gilliam

(Center for Radiation Research)

Standards of this kind are comprised of foils of fissionable

material which are activated by neutrons while an active fission chamber

running simultaneously is employed to determine the number of fissions/per

gram of fissionable material. These standards are provided to reactor

dosimetry laboratories for calibration of radiometric fission product

analysis systems.

In the present case, a natural uranium activation foil was irradiated in the well-thermalized neutron field of the NBSR thermal column

cavity. Fission products were generated only by the U-235 component of

the natural uranium foil, while the U-238 served only as a passive

diluent

Table 1 gives details of the calibration method and table 2 lists

the irradiation parameters and the certified integrated fission count.

159
NON-RRD PROGRAMS

Table 1. Fission counting standard calibration.

Back-to-back Active Monitor Deposit: 2-5U-4-4-9

On 5.5 mil Pt backing, supplied by

N. Dudey (formerly) of ANL.

Effective mass (including any contamination

in the fission chamber)

96.6 X 10~^

g of U-235.

+ 0.8%

Established by comparisons to both an enriched

U-235 deposit and a normal uranium deposit.

These independent comparisons were consistent

within 0.3%.

Q

Accumulated Monitor Counts: 8.594 x 10 fissions

With corrections for (2.3 + 0.8)% dead-time,

1.1% printing time (118 printing intervals), and

(0.23 + 0.2)% extrapolation to zero pulse height.

Monitor fissions/g = 8.896 x 10

+ 1.14%

Foil-Backing Self-Shielding Correction:

(Fiss/g) ^ . .,/(Fiss/g) ., , = 0.9966 + .2% "act. foil '^monitor dep —

Ref: ILRR 9th Prog. Kept. p. NBS-24.

U-235 Mass of Activation Foil: 471.5 + 3 mg total U x .007104 wt%U-5

-^ 3.349 g U-5 in the activation foil.

+ 0.81%

Integrated Fission Count for the Activation Foil:

(8.896 X lO-'-^fiss/g + 1.14%) x (3.349 mg + 0.81%) x (0.9966 + 0.2%)

= 2.970 X lO""""^ fissions

+ 1.4%

160
NON-RRD PROGRA>IS

Table 2. Results.

Irradiation Start (1/2 power): 18:58:59 EDT

Irradiation Finish (1/2 power): 15:03:51 EDT

Irradiation Length: 72,392 + 15 sec Start-up Time: '^ 40 sec. Shut-down Time: '^j 35 sec. Power Variation: +0.8%

Integrated Fission Count 2.970 X 10

+ 1.4%

TT

fissions

Foil Composition: Nat. Uranium Metal Foil

Foil Mass: 471.5 + 3 mg

Foil Thickness: 0.196 mm (7.7 mils)

Neutron Field: NBSR Thermal Column Cavity

Fissioning Isotope: U-235 > 99.5%

Energy Spectrum of Neutrons Inducing Fission:

12-22-80

12-23-80

Thermal

161
NON-RRD PROGRAMS

RECYCLED OIL PROGRAM

D. A. Becker

(Office of Recycled Materials)

The reactor facility has been utilized for the past several years

for activation analysis on recycled oil samples, by the Activation

Analysis Group/Center for Analytical Chemistry. In particular, R. Fleming

has provided analytical results on the accurate determination of chlorine

and bromine in many such samples where there was no other acceptable method

available.

Because of the writers' long experience and continuing interest in

the neutron activation analysis technique, he has maintained a capacity for

research in this field. This brief report will describe the equipment

used, followed by a short description of his on-going areas of research.

1. Equipment

The equipment currently used includes a Nuclear Data ND-60 pulse

height analyzer, with a Texas Instruments Model 745 electronic data terminal

readout. At present, a Ge(Li) detector approximately 60 c.c. in active

volume is being shared with the FDA. The detector has a 1.86 keV resolution

for the 1.333 MeV gamma-ray of Co-60, and an absolute peak efficiency

as shown in table 1.

Table 1. Absolute peak efficiency for 60 cc (Ge(Li) detector**

Nuclide y^ ^ ^ y/s* Total Net Counts Absolute Efficiency (%)

8004 0.355

4105 0.200

3707 0.180

* NBS point source SRM, corrected for decay

** At 5.0 cm geometry (3 holder)

2. Research

Current research efforts are focussed on two problems. The first is

the development of separation methods to evaluate halogen speciation in

re-refined oils. Since it is known that the halogens occur in used oils in

162

"^Cs 0.662 4105

^^Co 1.172 3732

^\o 1.333 3736
NON-RRD PROGRAMS

both the inorganic and organic forms, it appears necessary to be able to assess the relative effects on lubrication performance of each of these

forms. This effort is also being addressed in different ways by the

Tribochemistry Group/CMS and the Activation Analysis Group/CAC.

In addition to the above, an accurate and reliable method for the

determination of aqueous solutions of tin organometallics is being evaluated,

in cooperation with the Chemical Stability and Corrosion Division/CMS.

Such a method is necessary in order to establish the viability of a speciation technique developed in their laboratory.

1. D. A. Becker, "Research Methodology in Used Oil Recycling," in

Proceedings, Conference on Atomic and Nuclear Methods in Fossil Energy

Research, (In Press).

163
C. Reactor Operations ainId Services

Routine round-the-clock operation was resumed follov/ing the lengthy

shutdown of the previous 3^ear. Except for a 2-month shutdoxvTi to install

and connect the new cooling tower and secondary cooling system, reactor

operations was almost continuous for the balance of the year. Most of

the technical effort this year was directed towards extensive modernization of the reactor and the preparation of safety analyses and environmental appraisal in connection with upgrading the reactor to 20 M^J. In December 1980, application was made to the Nuclear Regulatory

Commission to double reactor power to 20 >W and to renev; the operating

license for another period of 20 years. Extensive documentation in support

of the application were prepared and submitted. After publishing its

intent to consider the application, the NRC determined that an Environmental

Impact Statement would be required because the higher pox^fer level put the

NBS reactor in a different class. Additional documentation had to be supplied

and a public hearing was held on the scope of the Environmental Impact

Statement. The NRC is continuing its safety evaluation of the application

for upgrade and a decision is expected early in 1982. Once the new license

is issued, it will make the NBS reactor the highest powered licensed research

reactor in the country. This will permit major expansion of current programs

and initiation of new programs not previously possible at the lower power

level.

Application and use of the reactor continued to be very extensive

and wide ranging. More than 50 major organizations from within and outside

NBS are involved. There are now 25 simultaneously operable experimental

and irradiation facilities contributing more than 125,000 instrument hours

per year.

2. Reactor Operations

The reactor operating schedule returned to normal this year following

the lengthy shutdo\%rn of the previous year. The first batch of new high

performance elements were loaded into the reactor this year. The new

fuel element design has considerably increased operating cycle time

resulting in significant cost savings. It is projected that the average

fuel element lifetime will increase from the previous 300 operating days

164
REACTOR OPERATIONS AND SERVICES

to more than 400 operating days. This is more than 33 percent gain in

fuel utilization efficiency. A summary of overall operating statistics

for the period July 1, 1980 to June 30, 1981 is presented in the following

table. While the on-line time was 65 percent for the whole year, the actual

operating efficiency was an outstanding 80 percent if the planned extra

shutdown time is excluded. The more than two thousand irradiations made

involved tens of thousands of samples and specimens. Overall, the

operating record for last year was one of the best in the history of the

facility.

NBSR OPERATING SUMMARY FY 80

No. of days at 10 MW 238

On-line time at 10 MW 65%

Average U-235 burnup 52%

No. of Irradiations 2600

Hours of Irradiations 3300

Hours per Irradiation 1.3

2. Irradiation Services

Heavy utilization of the reactor for activation analysis and

irradiation services resumed after the lengthy shutdown of the previous

year. Again multitudes of samples involving foods, drugs, environmental

monitoring, geological and mineral studies, forensic investigation, and

standard reference materials were irradiated at the NBS reactor.

High precision measurements to detect extremely low level changes

in the environment were initiated. A three-fold program is being

carried out independently by NBS, other government agencies, and universities. This involves world-wide sampling for man-made or natural

phenomenon of specific concern. Included among these is the study of the

effect of the eruption of Mount St. Helen on the environment. A

comprehensive study of trace and toxic elements has been carried out over the entire length and depth of Chesapeake Bay. Extensive data are currently being evaluated in collaboration with the Environmental Protection

Agency.

165
REACTOR OPERATIONS AND SERVICES

A new procedure has been developed to determine the platinum

concentration In biological materials at the currently natural occurring

levels of 10 to 10 g/g- This is the first time ever that a certifiable number for platinum has been generated which will be incorporated in several important standard reference materials. This development is a significant breakthrough as it will provide base-line data

for monitoring of platinum concentration in the environment and to

detect changes as a result of the introduction of catalytic converters

in automobiles, for example.

Finally, one of the more important analyses recently completed

using the NBS reactor was the examination by the FBI of evidence involved

in the shooting of the President.

3. Engineering Services

Besides regular engineering and design services provided to reactor

operations, experimenters, and users, the engineering staff was heavily

involved in a comprehensive program of reactor modernization. A new

high efficiency cooling tower was installed, tested, and is operational,

utilizing two speed motor controls, providing energy conservation. The

entire secondary cooling system, including pumps, piping, and controls, was redesigned and modified to provide for more efficient and smoother

operation. Old booster pumps were utilized as main pumps to save costs

of new pumps. A 24 inch return line was Installed from the heat exchangers

to the cooling tower to reduce the pressure on the pumps to provide more

flow. Two separate suction lines with sumps were installed to increase

the suction pressure at the pump intakes to eliminate possible cavitation.

This also makes it possible to use one set of pumps to reverse flow

through the heat exchangers to clean heat exchanger tubing. The new

cooling tower was raised four feet higher than the old tower to further

Increase the suction pressure on the pumps. Major portions of the

reactor console are being redesigned to introduce modern, up-to-date

equipment and components. Detector elements such as force balance type

transmitters for flow, level, and pressure measurements are being replaced

166
REACTOR OPERATIONS AND SERVICES

with the latest state-of-the-art strain gauge electronic transmitters.

Old recording instruments are being replaced with modern recorders. When

the entire modernization program is completed, it will provide for greatly

improved, more efficient, and reliable operation and will clear the way

for the 20 MW conversion as soon as the license amendment is received.

167
D. Service Programs

ACTIVATION ANALYSIS PROGRAM OF THE FOOD AND DRUG ADMINISTRATION

AT THE NBSR

W. C. Cunningham and W. B. Stroube, Jr.

(Food and Drug Administration, Washington, DC)

The Food and Drug Administration maintains a neutron activation

analysis (NAA) unit in the Reactor Building of the National Bureau of

Standards. The neutron activation program at FDA includes both research

and analytical support for special projects. This report will focus upon

one research project. In addition, examples are given where NAA has been

used as an analytical support tool.

1. Research

Multielement Analysis by Neutron Activation of Tissues from Swine

Administered Copper Supplemented Diets

Many swine diets are supplemented with Cu at high dietary concentrations

to improve weight gain and feed efficiency. A number of researchers have

demonstrated that dietary Cu concentrations of 250 ppm cause a large

elevation of Cu in liver and to a lesser extent in kidney.

The main objective of the present study was to obtain additional data

on levels of Cu and other elements in liver primarily for pigs with dietary

copper levels near 60 ppm. Neutron activation analysis (NAA) was chosen

for this study because the elements of interest could be determined non- destructively at the levels expected in the tissues.

In this study, eighty-four weanling crossbred pigs were divided into

three replicate groups and randomly allotted to seven treatments to provide

21 pens of four pigs per pen. Copper sulfate was added to the basal diet

to provide dietary treatments ranging from 15 to 154 ppm and feed and water

were constantly available. The animals were slaughtered at 95 kg average

body weight

168
SERVICE PROGRAMS

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169
SERVICE PROGRAMS

Table 1 gives the range for the elemental abundances of the elements

determined in the liver tissues. All values are given in either ppm (yg/g) or ppb (ng/g) and are expressed on a dry matter basis. The observed difference

within groups fed the same level of dietary copper is attributed to animalto-animal variability.

The data in table 1 illustrate that some animals in the three highest

dietary copper groups had elevated copper abundances in the liver. While

these three groups had an approximately even distribution of values between

the low and high copper values in the tissues, the means for these groups

were significantly higher. It can also be seen that even at 95 and 154 ppm

dietary copper, some animals had no increase in copper levels in the tissues.

While this study was limited to seven dietary levels with twelve animals

per level, the data show that at dietary copper values of about 80 ppm,

liver copper abundance increases for certain animals.

2. Service

An example of the NAA Lab's service to other divisions within FDA is

its cooperation during the past year with the Division of Nutrition. The

NAA Lab assisted the Division of Nutrition by analyzing Infant formulas

for several metals. This was part of a compliance study of infant formulas

to verify their contents. The study was prompted by the occurrence of

several cases of metabolic alkalosis which resulted from chloride-deficient

formula.

A related study involved the NAA analyses of pig blood, urine and

tissue samples for chlorine. This was part of a pilot study to observe

the effects of chlorine deficient diets upon the animals.

The following are additional examples of service projects performed

during the past year.

o Determination of Sb at the one ppb level in coffee,

o Multielement analysis of volcanic ash.

o Determination of F and Na in feed contaminants.

170
SERVICE PROGRAJIS

1. W. B. Stroube, Jr., W. C. Cunningham, J. T. Tanner, B. D. Bradley,

and C. Graber, "Multielement Analysis by Neutron Activation of Tissues

from Swine Administered Copper Supplemented Diets," Journal of

Radioanalytioal Chemistry, accepted June 1981.

POSITRON ANNIHILATION IN Cu ALLOYS

L. M. Pecora and A. C. Ehrlich

(Naval Research Laboratory, Washington, DC)

For the past several years we have been performing positron

annihilation experiments in Cu-based alloys by measuring the angular

correlation of Y~i^ays emitted from a single crystal sample. We continued

this work in the past year by examining several Cu-Ge and Cu-Zn alloys in

the fee a-phase. Our method consists of using the samples themselves

as positron sources (Cu-64 is the source) . This is accomplished by

irradiating each sample in the NBS reactor for the approp:^iate time.

Typical activities range from 10 to 20 Curies. The active samples are transported to the Naval Research Laboratory where they are placed in a Hot Cell between two Tantalum Tube collimators which allow only y-rays

at certain angles to pass through and be detected. The detected y^^ys

are coincidence counted by standard nuclear instrumentation. Figure 1

shows the geometry of the apparatus.

The coincidence counts are proportional to an integral over the

electronic momentum density of the sample along a line in momentum space

(see Fig. 1). We have shown how to "invert" the data thus reconstruct

the momentum density p(p) in a plane in momentum space which can be

interpreted as representing the quantum mechanical probability of finding

an electron with momentum p, i.e. p(p) = X*(p)X(p) where X(p) is the

electronic wave function in momentum space.

171
SERVICE PROGRAMS

1. Experiments

During the past year we have measured angular correlations of

y-rays on the following samples in the respective planes shown: Cu (111),

CUg^GSg (111)' Cug2 52^7 5 (11°)' ^''85^''l5

^11°^' ^^"^ ^"^15^^25 '^^^^^ • ^^^ samples were cylindrical in shape and single crystals. The cylinder axis

of the sample determined the plane sampled in momentum space. The momentum

density was reconstructed in each respective plan. The CuGe experiments

completed a "full set" of experiments which were begun the previous year

(1979-1980) on the alloys Cu Ge (110), Cu^^Ge^ (110), and Cu^^^^eg (110)

and allowed us to examine the change in p(p) of Cu upon alloying with Ge.

2. Results

Reconstruction of p(p) in a particular plane for each alloy allows

us to examine p(p) as a function either in single directions, i.e. sections

of p(p), or as a function of two momentum variables i.e. as a surface.

We have presented some examples of typical p(p) results for pure Cu and

CUg^Geg in both the (110) and the (111) planes.

Figure 2 shows sections of p(p) in three high symmetry directions

in (110) for pure Cu. Obvious structures are the Fermi break between 5

and 6 mrad, the positron annihilation enhancement peaks just below the

Fermi breaks, the anisotropy between (001) and (110) in the core contribution

between 6 and 8 mrad, and the higher momentum components on [002] in the

[001] direction. Figure 3 shows the same function in the entire plane.

Note that three of the four Cu necks are evident here.

Figure 4 shows p(p) in (110) for Cu_„Ge . Although there are subtle

92 o changes in the Fermiology which are reflected in p(p), the greatest change

is the vanishing the trough along [001] at about 7 mrad (see Fig. 3) and

its replacement by a bulge in p(p). This constitutes a reversal of the

[110] - [001] core anisotropy seen in Cu. Causes of this will be discussed

in the next section.

Figure 5 shows sections of p(p) for Cu in (111) and Figure 6 shows

the associated 2-D surface which represents p(p) in the entire (111) plane.

172
SERVICE PROGRAMS

Changes in p(p) in this plane were mostly in Fermiology and not as radical

as the (110) changes noted.

Figure 6 shows changes in Fermi radii upon alloying Cu with Ge.

At present the CuZn data is being analyzed and is not in a form for

presentation.

2. Comparison with Theory

In order to determine what changes in the wave functions are necessary to cause the [110] - [001] anisotropy changes in p(p) which occur

in CuGe alloys and which were mentioned in the previous section we obtained

2

self consistent APW results and used these to generate momentum-space wave

functions in a tight binding-like scheme. A typical wave function looked

like

X(p) = C^0^ -H C H- C^0^ = Z C^0^

)L-o

where 0,0, and 0. are s, p, and d atomic orbitals and C , C , C, are s'p d s'p'd

the appropriate coefficients for their admixture to make up x(p)« Since

P(p) ~ Ix (p) I ws riow have the possibility of determining how the

coefficients Cp change on alloying Cu with Ge, i.e. we can estimate changes

in wave function hybridization. The APW wave functions showed that

although the bands which contribute to p(p) in the core region in the

2 area of the anisotropy are primarily of d character (C, ~ 1), the s and p

a orbital values are quite large and hence small changes in s and p admixture

will readily show up. The reason for the original [110] - [001] anisotropy

in pure Cu is that the wave function along [110] has more p mixed in than

does the wave function along [001] which has no p at the brillouin zone boundary by syimnetry. This causes p.^^^, > Prr,,^-.-] in the core region

(6-8 mrad) . However, this anisotropy reversed in Cu_-Geo and we have

^rnmi "^ Pnini' ^^^ only possibility is that the s component along

[001] must increase. This means that we now have evidence for a change

in s-d hybridization in CuGe alloys. This work was recently published

3

in Physical Review Letters, June 1, 1981 issue.

173
SERVICE PROGRAMS

N,

Na(Pz)= /dPx Pip)

Figure 1. Schematic of the Geometry and appropriate coordinate systems

used in the experiment. A, slice of the Cu (110) plane in

momentum space is shown as an example of sampling of p(p)

by a measurement at a particular collimator angle.

174
SERVICE PROGRAMS

Pure Cu

P(P) (110)

Figure 2. Sections of p(p) along three high syiranetry directions in (110)

for pure Cu.

175
SERVICE PROGRAMS

[110]

Pip) Cu

[110]

Figure 3. p(p) reconstructed in the entire (110) plane for Cu,

Cug2Ge8

p(P) (iio)

[1111 -> Py. \[001]

Figure 4. Same as 3 except for Cu GCg (110).

92

176
SERVICE PROGRAMS

P(P) (111)

Pure Cu

5 10 15 20

Figure 5. Sections of p(p) in 3 directions in the (111) plane for pure Cu.

^Tf^ \ [110]

Figure 6. Surface plot of p(p) in (111). Note the 6 higher momentum

components and the 6 core maximum between them at 8 mrad

around the main conduction band peak.

177
SERVICE PROGRAMS

5.0

O McLarnon and

Williams

A T. Suzuki. ET AL • NRL DATA (110)

D NRL DATA (111)

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Figure 7. Graphs of Fermi radii from the CuGe data plotting p , Fermi radii, as a function of electrons per atom (e/a). ^

178
SERVICE PROGRAMS

1. L. Pecora and A. C. Ehrlich, Phys. Rev. B^ 1^, 719 (1979).

2. D. A. Papaconstantopoulos, et al. , Phys. Rev. B, 15, 4221 (1977)

3. L. M. Pecora and A. C. Ehrlich, Phys. Rev. Lett. 46, 1476 (1981)

U.S.G.S. ACTIVATION ANALYSIS PROGRAM

P. A. Baedecker, L.J. Schwarz

C.A. Palmer, and G.A. Wandless

(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) alternation 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. In addition to neutron irradiation at the NBS reactor,

epithermal irradiations using the JEEP-II reactor in Kjeller, Norway are

used for the analysis of rocks with high Uranium and/or Phosphorous

contents, or to improve the sensitivity for certain elements.

b. INAA is being applied to the determination of 35 major and trace

elements in various minerals found in coal and fly ash. Size and

density separates of fly ash and low temperature ashed coal are being

analyzed. This data in conjunction with x-ray diffraction and scanning

electron microscopy can be used to identify the association between

trace elements and their host minerals. Size and density separations of

179
SERVICE PROGRAMS

whole coal are also being analyzed to help determine the citing of

trace elements for coal utilization.

2. Radiochemical Neutron Activation

We continue to supplement our INAA determinations by group separations for the rare earth elements in those materials where REE abundances are very low, particularly in mafic and ultramafic rocks and some separated minerals. New procedures using x-ray f luourescence analysis

have been developed for chemical yield determinations for our group

separation procedures.

180
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181
PERSONNEL ROSTER

Division 354

J. Arras

P. Cassidy

D. Hoaney

I. Jensen

F. Moore

J. Shublak

Division 532

R. A. Dallatore

C. Eisenhauer

D. Gilliam

J. A. Grundl

S. T. Hwang

G. Lamaze

L. Li

E. McGarry

I. G. Schroder

R. Schwartz

W. Slater

V. Spiegel

Division 501

H. Berger

Division 506

D. Becker

Division 520

E. Kessler

W. Sauder

Division 522

R. Dove

Division 532

A. Wasson

NON-RRD NBS STAFF LOCATED AT REACTOR

Division 500

B. Carpenter

Division 551

D. Allen

R. Fleming

K. Fitzpatrick

S. Harrison

JLangland

R. Lindstrom

G. Lutz

J. Mitchell

T. Mitlehner

L. Pilione

M. Vinocur

R. Zeisler

GUEST WORKERS A^D C01JJ\B0RAT0RS

Division 533

R. Placious

Division 541

J. Kelly

T. Madey

Division 544

D. Tsai

Division 545

R, Kavanagh

Division 553

H. Rook

182
PERSONNEL ROSTER

Division 561

E. N. Pugh

Division 562

F. Blancanello

E. Case

J. Early

R. Fields

Division 563

R. Bowen

C. Han

M. Mathew

S. Takagi

R. Waterstrat

Division 564

R. Reno

R. Shull

Division 565

C. Hubbard

A. Mighell

R. Roth

Aberdeen Proving Ground

C. Helmbach

Argonne National Laboratory

T. Brun

H. Flotow

0. Hinks

S. Susman

J. Viccaro

Battelle, N. W.

L. Brackenbush

G. Endres

Brookhaven National Laboratory

P . Levy

Federal Bureau of Investigation

R. Asbery

R. Bilko

D. B. Davies

J. Haverkost

J. W. Kilty

E. Mitchell

C. Peters

J. P. Riley

Food and Drug Administration

M. Allegrlni

W. Cunningham

W. Stroube, Jr.

J. Tanner

National Gallery of Art

B. Miller

C. Parkhurst ^

National Institutes of Health

D. Davies

R. Frank

J. Weinstein

Naval Research Laboratory

P. D' Antonio

A. Ehrlich

M. Fatemi

W. Hendricksen

J. Karle

N. Koon

L. Pecoia

Naval Surface Weapons Center

H. Alperin

M. Lia

G. Rlel

R. Williams

183
PERSONNEL ROSTER

Oak Ridge National Lab

F, Kam

H. Smith

Technical University of Munich

H. Metzger

H. Wlpf

Carnegie Institute of Washington University of Antwerp

B. K. Kotharl

Institute Laue Langevln, France

M. Marezlo

J. Hodeau

Smithsonian Institution

M. Blackman

T. Chase

J. Mlshara

J. Olln

L. Zacherman

U. S. Geological Survey

P. Baedecker

J. Morgan

G. Wandless

KFA Jiillch, Germany

D. Rlchter

American University

J . Malamas

Iowa State University

R. Shelton

S. Moss

Massachusetts Instltue of Technology

University of Illinois

B. Averbach

C. Skarda H. Zabel

B. Wuenscher

University of Maine

Reed College

H. Patterson

W. Parker

184

K. Michel

University of Arizona

R. Salemme

P. Weber

University of Alabama

J. Segrest

University of California

(Lawrence Llvermore Laboratories)

D . Hanklns

University of Chicago

E. Anders

R. Wolf

University of Connecticut

J. Budnlck

University of Grenoble, France

J . Hodeau

M. Marezlo

University of Houston
PERSONNEL ROSTER

University of Maryland

D. Anderson

N. Aras

J. Baca

D. Ballantine

C. Barley

D. DeLozler

D. Demers

I

.

Gokman

G. Gordon

J

.

Lynn

J. Parrington

J. Phelan

W. Sonnefeld

M. Thompson

G. Tuncel

W. Walters

J. Weber

W. Zoller

University of Missouri (Columbia)

D. Alger

University of Missouri (Rolla)

W. James

State University of New York

H . Herman

University of Pittsburgh

R. Buttera

S. Malik

W. Wallace

University of Rhode Island

S. Pickart

University of Wisconsin

J . Hinkley

H. Yu

Allied Chemical Corporation

G. Leibowitz

G. Fish

A. Maeland

Bicron Corporation

R. Gulp

B-K Dynamics

N. Chesser

EG & G Idaho Falls

V. Gupta

General Electric Company

J. L. Provo

Israel AEG Soreq Nuc. Res. Center

Y. Elsen

Metronic, Inc.

P. Skarstad

Monsanto Research Corporation

W. Brotherton

ManTech Corporation

D. Bracher

Oklahoma Memorial Hospital

D. W. Anderson

Sandla Corporation

J. Harris

Siemens Gammasonlcs, Inc.

R. Oswald

185
PERSONNEL ROSTER

Nuclear Energy Center, Mol, Belgium

A. Fabry

Westinghouse-Hanford Corp.

W. McElroy

J. Rawlins

186
F. Publications

COLLABORATIVE PROGRAMS

ALPERIN, H. A., MELAMUD, M. , and HOROWITZ, A. , "Neutron Scattering Study of

Spinwaves in the Antif erromagnet RbMnCl3," J. Appl. Phys. 52, 2225

(1981).

BARKIGIA, K. M. , RAJKOVIC-BLAZER, L. M. , PEPE, M. T. , PRINCE, E. , and

QUICKSALL, C. 0,, "Molybdoarsinate Heteropoly Complexes. The

Structure of the Hydrogen-tetramolybdodimethylarsinate (2-) Anion by

X-ray and Neutron Diffraction," Inorg. Chem. 19, 2531-2537 (1980).

BIZZARO, W., YARMUS, L. , ROSENTHAL, J., and BERK, N. F. , "EPR Linewidth of

Triplet Excitons in Molecular Crystals, II, Tetracene," Phys. Rev B23 , 5673 (1981).

BERK, N. F., BIZZARO, W. , ROSENTHAL, J., and YARMUS, L. , "EPR Linewidth of

Triplet Excitons in Molecular Crystals. I. Theroy and Experiment:

Pyrene," Phys. Rev. 523, 5661 (1981).

CASELLA, R. C. , "Detection of Impurity Tunneling in Solids via Coherent

Phonon Coupling and Direct Neutron Scattering," Pvoc. of International

Confevenoe on Phonon Physios (submitted).

CASELLA, R. C. , "Theory of Neutron Scattering from Hydrogen in Metals

Involving Transitions to Excited Tunnel-Split States, Phys. Rev. B

(submitted)

CHOI, C. S. and PRASK, H. J., "Texture, Nondestructive Characterization,"

Enoy. Matls. Sei. and Eng. (in press)

CHOI, C. S., "Refinement of 2-Nitroguanidine by Neutron Powder Diffraction,"

Acta Cryst. (in press).

CHOI, C. S., PRASK, H. J., and PRINCE, E., "Phase Transitions in Ammonium

Nitrate," J. Appl. Cryst. 13, 403-409 (1980).

CHOI, C. S. and MARINKAS, P. L. , "Refinement of Dipara-anthracene, " Acta

Cryst. B36, 2491-2493 (1980).

FERNANDEZ-BACA, J. A. and LYNN, J. W. , "Neutron Scattering Studies of the

Magnetic Superconductor (Ce3_^j^Tbx^Ru2, " J. Appl. Phys. 52., 2183-2185

(1981).

GARRETT, D. A. and BRACHER, D. A., "Real-Time Radiologic Imaging: Medical

and Industrial Applications STP-716," American Society for Testing

and Materials (1980).

187
PUBLICATIONS

GLINKA, C. J., "The National Bureau of Standards Small Angle Neutron

Scattering Spectrometer," Proa, of Symposiim on Neutron Scattering

(submitted)

GLINKA, C. J., PRASK, H. J., and CHOI, C. S., "Neutron Diffraction and

Small-Angle Scattering as Nondestructive Probes of the Microstructure

of Materials," Mechanics of Nondestructive Testing^ pp. 143-164 (1980).

HARDMAN, V. K. , RHYNE, J. J., PRINCE, E. , SMITH, H. K. MALIK, S. K. , and

WALLACE, W. E., "Magnetic and Structural Properties of Th5Mn23Dx and

YgMn23D^," The Rare Earths in Modem Science and Technology^ Vol. Ill

(in press)

HARDMAN, V. K. , RHYNE, J. J., and JANES, W. J., "Magnetic Structures of

^6(^^l-x^x)23 Compounds," J. Appl. Phys. 52, 2049 (1981).

HARDMAN, V. K. , RHYNE, J. J., SMITH, K. , and WALLACE, W. E., "Structural

Investigation of Th^Mn23P]^5 by Neutron Diffraction," J. of Less Common

Metals lk_, 97-102 (1980).

KELLEY, R. D. , CAVANAGH, R. R. , RUSH, J. J., and MADEY, T. E., "Neutron

Inelastic Scattering Study of C2H^ Absorbed on Raney Nickel," Surface

Science 97.^ L335 (1980).

KOON, N. C. and RHYNE, J. J., Ground State Spin Dynamics of ErCo ," Phys.

Rev. B23, 207-214 (1981).

LONG, G. J., HARDMAN, V. K. , and JAMES, W. J., "A Mossbauer Effect Study

of the Manganese-Rich Y5(Fei_xMnx)23 Compounds," Solid State Commun.

34, 253 (1980).

LYNN, J. W. , ERWIN, R. W. , RHYNE, J. J., and CHEN, H. S., "Spin GlassFerromagnetic Phase Transition in Amorphous (FexNi2_x)o. 75-^0. 16-^0. 06^-'-0. 03

>"

J. Appl. Phys. 52., 1738-1740 (1981).

LYNN, J. W. , "Neutron Scattering Studies of Ternary Magnetic Superconductors,"

Ternary Superconductors^ p. 51 (1981).

MAGERL, A., ROWE, J. M. , and RICHTER, D. , "Oservation of Low-Energy

Excitations in NbD: A Single Lattice-Dynamical Model," Phys. Rev.

Lett. 523, 1605-1608 (1981).

MAGERL, A. , and ZABEL, H. , "Phonons in Graphite-Potassium Intercalation

Compound: C35K," Phys. Rev. Lett. 2^, 444 (1981).

MICHEL, K. H. and ROWE, J. M. , "On the Existence of an Orientational Glass

State in (KCN)^(KBr) .^ Mixed Crystals," Phys. Rev. 522, 1417-1428 (1980).

188
PUBLICATIONS

NICHOLSON, W. L. and PRINCE, E. , "A Robust/Resistant Technique for Crystal

Structure Refinement," Acta Cvyst. (submitted).

PLACIOUS, R. C, GARRETT, D. A., KASEN, M. B., and BERGER, H. , "Dimensioning

Flaws in Pipeline Girth Welds by Radiographic Methods," J. Am. Soo. for

Nondestructive Testing 39, 755 (1981)

.

PRASK, H. J., CHOI, C. S., and TREVINO, S. F. , "Nondestructive Testing of

Armament-System Components by Means of Neutron Diffraction," Proo.

of the Army Science Conf. (1980)

.

PRINCE, E., "Comparison of Profile and Integrated Intensity Methods in

Powder Refinement," J. Appl. Cryst. (in press).

PRINCE, E., "Comparison of the Fits of Two Models to the Same Data Set,"

Acta Cryst. (in press).

RHYNE, J. J., HARDMAN, V. K. , MALIK, S. K. , and WALLACE, W. E., "Magnetic

Properties of Cubic and Hexagonal HoMn2," The Rare Earths in Modem

Science and Technology^ Vol. Ill (in press).

RHYNE, J. J., "Magnetic Materials," Encyclopedia of Physics^ pp. 547-550

(1981).

RHYNE, J. J., "Magnetic Inelastic Neutron Scattering Studies of Rare Earth

Metals and Laves-Phase Compounds," Science and Technology of Rare

Earth Metals^ pp. 261-290 (1980).

ROWE, J. M., RUSH, J. J., PYNN, R. , HEIDEMANN, H. , and MICHEL, K. H.

,

"Observation of Critical Dynamics in ND4Br by High-Resolution Neutron

Spectroscopy," J. Chem. Phys. lh_, 5323-5324 (1981).

RUSH, J. J., MAGERL, A., ROWE, J. M. , HARRIS, J. M. , and PROVO, J. L.

,

"Tritium Vibrations in Niobium by Neutron Spectroscopy," Phys. Rev.

(submitted)

.

RUSH, J. J., ROWE, J. M., and MAELAND, A. J., "Neutron Scattering Study

of Hydrogen Vibrations- in Polycrystal and Glassy TiCuH," J. Phys. FIO,

L283-L285 (1980).

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-VDg^y," Phys. Rev. B21, 5613-5616 (1980).

SANTORO, A., ROTH, R. S., and AUSTIN, M. C, "Powder Neutron Diffraction

Study of the Nonstoichiometric Solid Solution of Lithium Tantalate

9LiTa03:Ta205," Acta. Cryst. (submitted).

189
PUBLICATIONS

SANTORO, A., CAVA, R. J., MURPHY, D. W. , and ROTH, R. S., "Use of the

Pearson Type VII Distribution in the Neutron Profile Refinement of

the Structures of LiRe03 and Ll2Re03," Pvoo. of Symposium on Neutron

Scattering (submitted)

SANTORO, A., CAVA, R. J., MURPHY, D. W. , and ROTH, R. S., "Structural

Aspects of Lithium Insertion in Oxides: LlxRe03 and Ll2FeV308,"

Proa, of International Conference on Fast Ionic Transport in Solids

(in press)

SANTORO, A., MIGHELL, A. D., and RODGERS , J. R. , "Determination of the

Relationship Between Derivative Lattices," Acta Cryst. A36 , 796-800

(1980).

SANTORO, A., and D'Antonio, P., "Powder Neutron Diffraction Study of

Chemically Prepared 6-Pb02," Acta Cryst. B36, 2394-2397 (1980).

i SANTORO, A., MAREZIO, M. , ROTH, R. S., and MINOR, D. B. , "Neutron Powder

Diffraction Study of the Structure of CeTa04, CeNb04, and NdTa04,"

J. Solid State Chem. 35., 167-175 (1980).

SINGHAL, S. P., ALPERIN, H. A., BIANCANELLO, F. , and HERMAN, H. , "Phase

Decomposition in the NlRlch Side of NI/NI3AI Misclblcity Gap: A

Small-Angle Neutron Scattering Study," Scripta Metall. (submitted).

SINGHAL, S. P., HERMAN, H. , and KOSTORZ, G., "Small-Angle Neutron

Scattering Study of Nonllnearity of Spinodal Reaction in a S3Traiietrlc

Au-60 at % Pt Alloy," Proc. of International Conference on Solid-Solid

Phase Transformation (submitted).

SINGHAL, S. P., "The Au-Pt (Gold Platinum) System," Alloy Phase Diagram

Bulletin #4 (1981).

SJOLIN, L., and WLODAWER, A., "Improved Technique for Peak Integration

for Crystallographic Data Collected Using Position-Sensitive

Detectors: A Dynamic Mask Procedure," Acta Cryst. (in press).

STROUBE, JR., W. B., CUNNINGHAM, W. C, TANNER, J. T. , BRADLEY, B. D.,

and GRABER, C, "Multielement Anaysis by Neutron Activation of

Tissues from Swine Administered Copper Supplemented Diets,"

(to be published)

STROUBE, W. C, BOYER, K. W. , JONES, J. W. , LINSCOTT, D. , WRIGHT, S. K. , "Trace Element Levels in Tissues from Cattle Fed Sewage Sluge-Amended

Diet," Journal of Toxicology and Environmental Health, 8:281-295 (1981)

190
PUBLICATIONS

STROUBE, W. B., JR. and TANNER, J. T. , "Application of Neutron Activation

Analysis in a Regulatory Agency," Vvoceeding of the Fourth Intemat'ional

Conference on Nuclear Methods in Environmental and Energy Research^

ed. J. R. Vogt, (1980).

TAYLOR, H. C, RICHARDSON, D. C, RICHARDSON, J. S., WLODAWER, A., KOMORIYA, A.,

and CHAIKEN, I. M. , "Active" Conformation of an Inactive Semisynthetic

Ribonuclease-S," J. Mot. Biol. 149, 313-317 (1981).

TREVINO, S. F. and RYMES , W. H. , "A Study of Methyl Reorientation in Solid

Nitromethane by Neutron Scattering," J. Chem. Phys. 73^, 3001-3006 (1980).

TREVINO, S. F., PRINCE, E., and HUBBARD, C. R. , "Refinement of the Structure

of Solid Nitromethane," J. Chem. Phys. 73^, 2996-3000 (1980).

TSAI, D. H. and TREVINO, S. F. , "Thermal Relaxation in a Liquid Under

Short Compression," High Pressure Science and Technology, p. 1051 (1980).

ROSENTHAL, J., YARMUS, L. , and BERK, N. F. , "Triplet Exciton Annihilation

and Triplet Spin Relaxation in Molecular Crystals," Phys. Rev. B23 , (1981).

WIPF, H., MAGERL, A., SHAPIRO, S. M. , SATIJA, S. K. , and THOMLINSON, W.

,

"Neutron Spectroscopic Evidence for Hydrogen Tunneling States in Niobium,"

Phys. Rev. Lett. 26, 947 (1981).

WIPF, H., MAGERL, A., SHAPIRO, S. M. , SATIJA, S. K. , and THOMLINSON, W.

,

"Neutron Scattering Measurements of Low-Temperature Hydrogen Tunneling

in Niobium," Proc. of Coral Gables Conf. on Hydrogen in Metals (1981).

WLODAWER, A., BOTT, R. , and SJOLIN, L. , "The Refined Crystal Structure of

Ribonuclease A at 2.0 A Resolution," J. Biol. Chem. (submitted).

WLODAWER, A. and HENDRICKSON, W. A., "A Procedure for Joint Refinement of

the X-ray and Neutron Single-Crystal Diffraction Data for Macromolecules,"

Acta Cryst. (submitted).

WLODAWER, A. and SJOLIN, L. , "Improvement of the Quality of the Data Collected

Using a Position-Sensitive Detector," J. Nuol. Instrum. and Methods (in

press)

.

WLODAWER, A. , SJOLIN, L. , and SANTORO, A. , "Refinement of the Crystal

Orientation Matrix for the Flat-Cone Dif fractometer, " J. Appl. Cryst.

(in press)

.

WLODAWER, A. and SJGLIN, L. , "Improvement of the Quality of the Data

Collected Using a Position-Sensitive Detector," Nucl. Instrum. Meth.

,

(in press)

.

191
PUBLICATIONS

WLODAWER, A. and SJOLIN, L. , "Orientation of Histidine Residues in

Ribonuclease-A: A Neutron Diffraction Study," Proo. of National

Aoademy of Science, USA T8, 2853-2855 (1981)

WLODAWER, A., "Studies of Ribonuclease-A by X-ray and Neutron Diffraction,"

Acta Cryst. S36, 1826-1831 (1980).

192
PUBLICATIONS

INDEPENDENT PROGRAMS

ANDERSON, D. L. , FAILEY, M. P., ZOLLER, W. H., WALTERS, W. B.,

GORDON, G. E., and LINDSTROM, R. M. , "Facility for Non-Destructive

Analysis for Major and Trace Elements Using Neutron-Capture GammaRay Spectroscopy," J. Radioanal. Chem. ^ M^, 97 (1981).

EISENHAUER, C. , and SCHWARTZ, R. , "Difficulties in Calculating SpectrumAverage Values of Dose Equivalent," HeaZth Physios (1981).

GILLIAM, D. M. , FULLER, J. L. , GRUNDL, J. A., and DAUGHTRY, J. W.

,

"Absolute Fission Rates in the FFTF, Trans. Am. Nuol. Soo., 3]_,

(November 1981)

.

EISENHAUER, C. M. , and SHWARTZ, R. B., "The Effect of Room-Scattered

Neutrons on the Calibration of Radiation Protection Instruments,"

Proaeedings of the Fourth Symposium on Neutron Dosimetry (1981)

.

GILLIAM, D. M., FULLER, J. L., GRUNDL, J. A. , and RAWLINS, J. A., "FFTF

Reactor Characterization Program: Absolute Fission Rate Measurements,"

TC-1963, Hanford Eng. Dev. Lab. (1981).

GILLIAM, D. M., and BAUN, M. , "Calibrating the FFTS , " Dimensions (1981).

EISENHAUER, C. M. , and GRUNDL, J., "Benchmark Referencing of Neutron

Dosimetry Measurements, LWR-PV Irradiation Surveillance Dosimetry,"

Prog. Report^ NUREG/CR-1240, Vol. II (1981).

GREENBERG, R. R. , and KINGSTON, H. M. , "Simultaneous Determination of

Twelve Trace Elements in Estuarine and Sea Water Using Pre-Irradiation

Chromatography," J. Radioanal. Chem. ^ (in press).

GREENBERG, R. R. , ZOLLER, W. H. , and GORDON, G. E. , "Atmospheric Emissions

of Elements on Particles from the Parkway Sewage-Sludge Incinerator,"

Environ. Soi. Teohnol, 1_5, 64 (1981)

.

GRUNDL, J., EISENHAUER, C. , MCGARRY, E. D. , and SPIEGEL, V., with

MCELROY, W. , et al., "LWR Pressure Vessel Surveillance Dosimetry

Program, Eighth Reactor Safety Research Information Meeting,"

mc Annual Report, NUREG/CR-1747 (April 1981).

HARRISON, S. H., ZEISLER, R. , ANDERSON, D. L. , "Evaluation and Analysis

of Environmental Specimen Bank Samples by Nuclear Methods,"

J. Radioanal . Chem. (to be published)

.

193
PUBLICATIONS

HARRISON, S. H., ZEISLER, R. , WISE, S. A., eds., "Pilot Program for the

National Environmental Specimen Bank - Phase 1," (1981).

HARRISON, S. H., GILLS, T. E. , MAIENTHAL, E. J., ROOK, H. L., WISE, S. A.,

ZEISLER, R. , and GOLDSTEIN, G. M. , "The National Environmental

Specimen Bank Pilot Program," Pvoo. of the Z4th Annual Conferenoe

on Trace Substances in Environmental Health, Columbia, MO., p. 329.

(1980).

LINDSTROM, R. M. , and FLEMING, R. F. , "Accuracy in Activation Analysis:

Count Rate Effects," Proo. of the 4th Int. Conf. Nucl. Method in

Env. and Energy Res., (1980).

MCGARRY, E. D. , FABRY, A., GOLD, R. , KELLOGG, L. , and KAM F. , "Current

PCA Specifications for Transport Theory Validation, LWR-PV Surv.

Dos. Improvement Program, NUREG/CR-1861, Section 8 (1981).

MCGARRY, E. D. , FABRY, A., and GRUNDL, J., "Experimental Program:

Integral Measurements in LWR Pressure Vessel Surveillance Dosimetry

Improvement Program, PCA Experiments and Blind Test," NUREG/CR-1861,

Section 2.0, 2.1, 2.3 and 4.0 (1981).

MCGARRY, E. D. , "Determination of the Effective Mass of U-235 in the

Fission Chamber Used for Absolute Core Power Measurements in PCA,

LWR-PV Irr. Surv. Program," Progress Report, NUREG/CR-1241, Vol. 11

(1981).

MCGARRY, E. D. , "Test of Radiation Exposure Calculations for Reactor

Pressure Vessels," Dimensions (1980).

POWELL, L. J., MURPHY, T. J., and GRAMLICH, J. W. , "The Absolute Isotopic

Abundance and Atomic Weight of a Reference Sample of Silver," (to

be published ) in J. of Res. Nat. Bur, Stand.

SCHWARTZ, R. B., and EISENHAUER, C. M. , "Use of a 02^ Moderated ^^^cf

Source for Dosimetry Testing and Calibrations," Proceedings of

Eighth WE Workshop on Neutron Dosimetry (1981) .

SPIEGEL, v., EISENHAUER, C. M. , WINKLER, G. , and SMITH, D. L.

,

"Measurement of the Average Activation Cross Section for the Reaction

°3cu(ri,a) °^Co in the Spontaneous Fission Neutron Field of

Californium-252, Nucl. Sci. & Eng. 78, No. 4, p. 415 (1981).

ZEISLER, R. , "Trace Element Analysis," in Pilot Program for the National

Environmental Speciman Bank - Phase I, p. 29, NTIS , Springfield, VA

(in press)

.

194
PUBLICATIONS

ZEISLER, R. , and GREENBERG, R. R. , "Ultratrace Determination of Platinum

in Biological Materials Via Neutron Activation and Radiochemical

Separation," J. Radioanal. Chem. (to be published).

195
NBS-n4A IREV. 2-8C1 U.S. DEPT. OF COMM.

BIBLIOGRAPHIC DATA

SHEET (See instructions)

1. PUBLICATION OR

REPORT NO,

NBS TN 1160

2. Performing Organ. Report No. 3. Publication Date

June 1982

4. TITLE AND SUBTITLE

NBS Reactor: Summary of Activities

July 1980 Through June 1981

5- Edited by:

Frederick J. Shorten

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. None

8. Type of Report & Per4od Covered

July 1980 through

June 1981

9. SPONSORING ORGANIZATION NAME AND COMPLETE ADDRESS (Street. City. State. ZIP)

Same as #6

10, SUPPLEMENTARY NOTES

I I Document describes a computer program; SF-185, FlPS Software Summary, is attached.

11, ABSTRACT (A 200-word or less factual summary of most significant information. If document includes a si gnificant

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 1980 through June 1981. 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; alphabetical order; capitalize only proper names; and separate key words by semicolons)

Activation analysis; crystal structure; diffraction; isotopes; molecular djmamics;

neutron; neutron radiography; nondestructive evaluation; nuclear reactor; radiation.

13, AVAILABILITY

m Unlimited

I I For Official Distribution. Do Not Release to NTIS

I I Order From Superintendent of Documents, U.S. Government Printing Office, Washington, D.C. 20402.

r~Y^ Order From National Technical Information Service (NTIS), Springfield, VA. 22161

14. NO. OF

PRINTED PAGES

204

15, Price

USCOMM-DC 6043-P80

l^U.S. GOVERNMENT PRINTING OFFICE: 19 8 2-360-997/2118




NBS TECHNICAL PUBLICATIONS

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bodies. Special Publications—Include proceedings of conferences sponsored by NBS, NBS annual reports, and other special publications

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studies of special interest to physicists, engineers, chemists,

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the authority of the National Standard Data Act (Public Law

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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 (AlP). Subscriptions,

reprints, and supplements available from ACS, 1 155 Sixteenth St., NW, Washington, DC 20056.

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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 tech- nological 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^rom

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 II, 1973) and Part 6 of Title 15 CFR (Code of Federal Regulations).

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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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