NBS

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NATL INST. OF STAND « TECH R.IX.

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i/i Q NBS TECHNICAL NOTE 1231

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

NBS Reactor:

Summary of Activities

July 1985 Through

June 1986
Tm he National Bureau of Standards' was established by an act of 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 performed by the National Measurement Laboratory, the National

Engineering Laboratory, the Institute for Computer Sciences and Technology, and the Institute for Materials

Science and Engineering

.

The National Measurement Laboratory

Provides the national system of physical and chemical measurement;

coordinates the system with measurement systems of other nations and

furnishes essentia] services leading to accurate and uniform physical and

chemical measurement throughout the Nation's scientific community, in- dustry, and commerce; provides advisory and research services to other Government agencies; conducts physical and chemical research; develops,

produces, and distributes Standard Reference Materials; and provides

calibration services. The Laboratory consists of the following centers:

• Basic Standards'^

• Radiation Research

• Chemical Physics

• Analytical Chemistry

The National Engineering Laboratory

Provides technology and technical services 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 disciplines required to carry out this research and technical service; develops engineering data and measurement

capabiUties; 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

The Institute for Materials Science and Engineering

Conducts research and provides measurements, data, standards, reference

materials, quantitative understanding and other technical information fundamental to the processing, structure, properties and performance of materials; addresses the scientific basis for new advanced materials technologies; plans

research around cross-country scientific themes such as nondestructive

evaluation and phase diagram development; oversees Bureau-wide technical programs in nuclear reactor radiation research and nondestructive evaluation; and broadly disseminates generic technical information resulting from

its programs. The Institute consists of the following Divisions:

Ceramics

Fracture and Deformation ^ Polymers

Metallurgy Reactor Radiation

'Headquariers and laboratories ai Gaiihcrsburg, MD, unless otherwise noted; mailing address Gaiihersburg, MD 20899. -Some divisions within the center are located at Boulder, CO 80303. 'Located at Boulder. CO. with some elements at Ciaithersburg, MD,
NBS Technical Note 1231

WBS

RESEARCH

INFORMATION CENTER

U

NBS Reactor:

Summary of Activities

July 1985 Through

June 1986

Frederick J. Shorten, Editor

Reactor Radiation Division

Institute for Materials Science and Engineering

National Bureau of Standards

Gaithersburg, Md 20899

December 1986

U.S. Department of Commerce

Malcolm Baldrige, Secretary

National Bureau of Standards

Eraest Ambler, Director
National Bureau of Standards Technical Note 1231

Natl. Bur. Stand. (U.S.). Tech. Note 1231, 161 pages (Dec. 1986)

CODEN: NBTNAE

U.S. GOVERNMENT PRINTING OFFICE

WASHINGTON: 1986

For sale by the Superintendent of Documents, U.S. Government Printing Office, Washington DC 20402
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 as a National Center for the

application of neutron methods to problems of national interest. The Reactor

Radiation Division was established to operate the reactor and to foster its

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

of scientists experienced in the use of reactors for a wide range of scientific and

technical problems. In addition to pursuing their own research and developing

sophisticated experimental facilities, they actively seek out and encourage

collaboration with other scientists engaged in challenging programs whose work can benefit from use of the reactor, but who as yet do not have the reactor experience

necessary to take full advantage of the facilities available. The Division also

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

other technical services.

The reactor power has recently been increased from 1 to 20 MW. The increased

power combined with its 25 experimental facilities ranging from intense neutron beams

to extensive irradiation facilities, makes it one of the most versatile high

performance 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 the programs carried out by scientists in the Reactor Radiation Division

and their collaborators. The second section summarizes NBS work originating outside

NBS for which the Division provides reactor facilities and irradiation services. The

remaining sections are self-explanatory.

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 K. E. Ferrel for efforts in typing manuscripts.

1^. ^. (AJfX^^

R. S. Carter

Chief, Reactor Radiation Division

National Bureau of Standards

m
ABSTRACT

This report summarizes all those programs which use the NBS reactor. It covers

the period for July 1985 through June 1986. 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, 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.

IV
TABLE OF CONTENTS

FOREWORD iii

ABSTRACT iv

A. REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS 1 Translation-Rotation Coupling - (KCN) (KBr), 1 X 1-x

Neutron Scattering Study of the Vibrational Density of State in Icosaheral

and Crystalline Al^ oMn_ „ 2

u . o u . ^ Isotope Effects in the PDH System-Lattice Dynamics of PDT M Hydrogen Pairing and Anisotropic Potential for Hydrogen Isotopes in Yttrium. 5

Neutron Spectroscopic Study of Hydrogen Adsorption on Ruthenium Sulfide

Catalysts . 7

An Incoherent Inelastic Neutron Scattering Study of the Absorption and

Absorption of Hydrogen by Palladium Black 10

Adsorbate Dynamics and the Deammoniation Process in Ammoniated Zeolite RhO . 13

Neutron Scattering Studies of Ultrastable Zeolite Y 15

Coherent Scattering of Low Energy Neutrinos from Crystals 16

X-Ray Diffraction Studies of the Amorphous (Fe Ni ) Si B Alloys. ... 17

The Magnetic Structure in Dy-Y Superlattices 18

Antiferromagnetic Structure of the Cubic Superconductor ErPd Sn 21

Spin Dynamics of Amorphous Fe^_ Ni Zr,^ 23 90-x X 10

Neutron Scattering Study of the Spin Freezing in Amorphous Tb„^Fe^^ and

Tb25Fe^^ 25

Magnetic Excitations in the XY-Heisenberg System Tb Sc 25

Static and Dynamic Spin Correlations in Dilute Magnetic Semiconductors with

High Mn Concentrations 28

Magnetic Phase Transition Under Pressure in the Reentrant Superconductor

Tm_Fe_Si^ 30

Spin Dynamics in the Heusler Alloy NiMnSb 32

Magnetic Field-Induced Transition in Y, Gd 33

1 -X X Inelastic Scattering Studies of Very Dilute Magnetic (Semimagnetic)

Semiconductors 35

Neutron Powder Diffraction Studies of Lithium and Silver Exchanged Zeolite

Rho 37

A Structural Study of (Sr, Nd)Cl_ ,^ 38

The Structures of the Transition Aluminas and Their Precursors 41 Neutron Powder Diffraction and Rietveld Refinement of Cerium Aluminate

Phosphors k2
TABLE OF CONTENTS

Neutron Powder Diffraction Study of the Zeolites BAlSi„0^ • XH^O, with B=C , id ^ s Rb, D, and Na ^3

Bismuth Valence Order-Disorder Study in BaBiO by Powder Neutron

Diffraction H6

Studies of Titanium Aluminum Alloys 46

Texture Measurements in Deformed Metals Using Neutron Diffraction 47

Microstructure Study of Age-Hardened U - 0.75 wt5^ Ti Alloy 49

Structure Factor of He-4 in the Vicinity of the Gas-Liquid Phase Transition. 54

The Structure Factor of Liquid He-4 at Small Angles for Several

Temperatures 56

Crystal Data Center 58

Neutron Activation Autoradiography Study of Paintings 59

Advanced Neutron Methods 67

SANS Study of Chemical Absorbates Bound to Pore Surfaces ... 69

Small Angle Neutron Scattering Study of Precipitation in High Strength Low

Alloy Steels 70

SANS Study of Strengthening Mechanisms in Single-Crystal Superalloys .... 71 Molecular Response to Large Strain Deformation in Epoxies - A SANS Study . . 73

Static and Kinetic Studies of Polystyrene/Poly (Vinylmethylethen) Blends . . 76

Compatibility of Hydrogenated and Deuterated Polystyrene 76

Theory of Spatial Correlation and Diffraction for the Leveled Wave Model of

Random Bicontinuous Structures and Interfaces 77

Renewal Theory Approach to Spatial Correlations in Random Two-Phase Media. . 80

High Resolution, Multidetector Powder Diffractometer 82

Cold Neutron Research Facility 83

NBSR Cold Neutron Source 85

B. NON-RRD PROGRAMS 87

Nuclear Methods Group: Overview 87

Determination of Ultratrace Lithium and Boron by Neutron Activation and Mass

Spectrometric Measurement of He-3 and He-4 89

Determination of Total Zinc and Selenium in Human Blood Serum 92

The Determination of Chromium-50 in Human Blood and Its Utilization for Blood

Volume Measurements 95

Evaluation of USDiet-I Total Human Diet Samples for Nutritional Constituents 97

Determination of Silicon by Fast Neutron Activation Analysis 99

Specimen Banking and Analysis in the National Status and Trends Program. . . 100

VI
TABLE OF CONTENTS

Activation Analysis Opportunities Using Cold Neutron Beams 104

Neutron Dosimetry Group: Overview 109

Atmospheric and Environmental Studies by Instrumental and Neutron-Capture

Prompt Y-Ray Activation Analysis 112

Precision in Routine I.N. A. A. Over A Two Year Period at the NBSR 122

Neutron Depth Profiling at NBS 127

Calibration of a Neutron Driver Gamma Ray Source 128

C. REACTOR OPERATIONS AND SERVICES 133

Engineering Services 133

D. SERVICE PROGRAMS 135

Neutron Activation Analysis at the Food and Drug Administration 135

Purification of Reactor-Produced Fluorine-l8 Fluoride Using High Pressure

Ion Chromatography 136

E. PERSONNEL ROSTER 138

F. PUBLICATIONS 145

vix

A. Reactor Radiation Division and Collaborative Programs

TRANSLATION-ROTATION COUPLING - (KCN)^(KBr)^_^

J. M. Rowe and J. J. Rush

and

J. Bouillot

(Institut Universitaire de Technologie, Annecy, France)

and

K. H. Michel

(University of Antwerp (UIA), Wilrijk, Belgium)

and

F. Luty

(University of Utah, Salt Lake City, UT)

We have extended our neutron powder diffraction studies of (KCN) (KBr)

samples to x = 0.7, a range which has been shown to transform to a rhombohedral

structure in which the quadrupoles are ordered, by a nearly continuous transition.

This work had two goals - first, to quantify the anomalous temperature dependence of

mean square displacements observed in the high temperature cubic phase as the

transition temperature is approached from above, and second, to refine the structure

of the low temperature rhombohedral phase by the Rietveld method. The results

obtained in the cubic phase show that the mean square displacements decrease with

decreasing temperature in the range 200-150 K, as expected, then increase as temperature is decreased from 150-115 K, exactly as would be predicted for a soft

mode driven second order transition in which the soft mode is the elastic constant

c^^. Although we were unable to approach T closely enough to fully test the

predictions of non-classical critical behavior, we have confirmed the anomalous

temperature dependence of the mean square displacements. Below the transition

temperature, we observe a mixed phase in which a portion of the sample has a monoclinic structure, and the rest has a rhombohedral structure. We were unable to

produce a single phase sample at low temperature, in contrast to the results of Ref.

1, a result which we attribute to the different states of strain in our powder

samples and the single crystal used for the x-ray measurements. As a result, we are forced to analyse the data using a mixed structure refinement program, and have not

yet been able to obtain satisfactory results at temperatures just below the

transition. However, we have achieved a satisfactory refinement at 8 K, from which

we conclude that the trigonal axis has contracted at the transition, and the (CN)

ions are oriented perpendicular to this axis, a somewhat surprising result. From our refinement, it appears that the ions are disordered in this plane, although one might

expect to find an ordered "pinwheel" structure based on the nature of the quadrupolar

1
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

forces that dominate the interactions between (CN) ions. Attempts to properly

refine the structures at higher temperatures are continuing.

We have also continued to refine the theoretical description of translationrotation coupling, and to relate this to the many observations on mixed cyanide

crystals. At the present time, we are concentrating on two aspects - first, the

random fields created by the substitution of either halide ions or different alkali

metals, and second, to explain the unusual diffraction lineshapes observed in single

crystal diffraction peaks. These calculations are quite complex, requiring extensive

analytical and numerical analysis, but the results to date are encouraging.

Current ongoing efforts in this program include structural measurements of

other mixed systems and neutron and Brillouin scattering measurements (in

collaboration with S. Satija, University of Delaware) on (RbCN) (RbBr) single

crystals.

NEUTRON SCATTERING STUDY OF THE VIBRATIONAL DENSITY OF STATES IN

ICOSAHEDRAL AND CRYSTALLINE Al. Q„Mn_ __ u.ou Kj.du

P. F. Miceli, S. E. Youngquist, D. A. Neumann and H. Zabel

(University of Illinois, Champaign, IL)

and

J. J. Rush and J. M. Rowe

The discovery at NBS of "quasicrystals" with long range bond orientational

order displaying five-fold symmetry has led to intense current research interest.

While most of the present activity has concentrated on this striking icosahedral

symmetry, the effects that this new type of order has on the physical properties are

also of fundamental significance. Recent calculations of the electron and phonon

density of states of "quasiperiodic" structures have predicted characteristic

difference from the density of states of crystalline systems.

NBS scientists, in collaboration with researchers from the University of

Illinois, have performed the first measurement of the vibrational density of states

in a quasicrystal , Al^Mn, using the BT-4 spectrometer at the NBSR. Neutron spectra

were measured under a variety of different conditions of wavevector and energy

transfer in order to assure that the resulting weighted density of vibrational states

represented as thorough an averaging as possible over reciprocal space. In order to

determine the role of structure, vibration spectra were also measured on a sample of

the same composition displaying long range translational order. A summary of the

weighted density-of-states results is shown in figure 1.
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

Icosahedrol AL pMn.

10 20 30 40 50 Energy Transfer (meV)

Figure 1. Weighted vibrational density of states g(E) measured for the (a)

icosahedral ( quasicrystal ) and (b) crystalline phases of Al^ QgMn,

under various conditions of momentum transfer and fixed final energy,

Contrary to some theoretical predictions, the measured density of states do not

show the existence of localized states and demonstrate that the quasicrystal and

crystalline materials as elastically similar. At high vibrational energies, however,

the quasicrystal shows a relative excess of phonon density. These neutron scattering

results thus provide a direct test for models of the interatomic forces and dynamics

of the icosahedral phase.
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

0.71

ISOTOPE EFFECTS IN THE PDH SYSTEM-LATTICE DYNAMICS OF PDT

J. M. Rowe and J. J. Rush

and

J. E. Schirber

(Sandia National Laboratory, Albuquerque, NM)

and

J. M. Mintz

(Sandia National Laboratory, Livermore, CA)

The origin of the reverse isotope effect in PdH and PdD (T =8, 10 K

respectively) has been attributed to the existence of strongly anharmonic optic

modes, which lead to a change in X, the electron-phonon coupling constant which

appears in an exponential, that overcomes the change in the mean phonon energy, which

appears as a factor, in the McMillan theory of superconductivity. This conclusion

was based on a comparison of the coherent neutron scattering data for PdD. ^- (which

.d3

determines the phonon dispersion relation), to incoherent neutron scattering data for

PdH„ r. This comparison led to the conclusion that the effective force constant

. b

determining optic mode energies in PdH was 1 .2 times that for PdD. Recently, T was

also measured for PdT, and found to be 12 K, once again displaying a reverse isotope

effect. We have prepared a single crystal of PdT^ with a volume of 0.4 cc, and

measured the phonon dispersion relation, thus allowing for a much more accurate

comparison of the phonon terms appearing in the McMillan theory. Analysis of these

0.0 0.5 1.0 0.5 0.0 0.5 r A X 2 r A L

Figure 1: Measured dispersion relation for PDT^ at 80 K. Solid lines a result of a fit to a Born-von Karman model.
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

results, shown in figure 1, demonstrate conclusively that anharmonicity alone cannot

explain the reverse isotope effect, although it does go in the correct direction. A

re-analysis of earlier incoherent neutron scattering results for PdH . and PdD . (summarized in 1985 annual report) shows that even for PdH and PdD, anharmonicity

cannot explain the measured T 's. The present results show that the theory of

c superconductivity must be re-examined as it applies to materials with the large meansquare displacements characteristic of PdH, PdD, and PdT.

HYDROGEN PAIRING AND ANISOTROPIC POTENTIAL FOR HYDROGEN ISOTOPES IN YTTRIUM

I. S. Anderson, J. J. Rush, T. Udovic and J. M. Rowe

The properties of the YH system in the a or solid solution phase have been the

subject of a great deal of study and controversy in recent years, especially since,

for X < 0.2, the a-phase persists down to very low temperatures. In the present work we have investigated the potential for H and D in a-phase [Y(H,D)^ ,o] by neutron

u . I o spectroscopy, using the BT-M crystal spectrometer with either Be or a new Be/graphite

composite filter for final energy analysis. The spectroscopic results for a YH ^

single crystal, with energy scans arranged so that the momentum transfer Q was almost

parallel or almost perpendicular to the c-axis of the hexagonal crystal, are shown in

figure 1. For Q |[ c-axis a single prominent peak is observed at 100 meV, while for

Q _[_ c a dominant single peak is observed at 13^ meV. These results not only show

clearly that virtually all the hydrogen resides in tetrahedral type sites (as opposed

to the suggestion of partial octahedral-site occupancy from previous results on polycrystalline samples). More importantly these spectra demonstrate that the

potential of the tetrahedrally bound H (and D) is highly anisotropic and (in the c- direction) anharmonic, in spite of the fact that the t-sites are only slightly

distorted from regular tetrahedral symmetry. Measurements of higher harmonics of

these vibration modes for both H and D samples also demostrate clearly that the c- axis vibrations show a much higher degree of anharmonicity than those in the ab

plane.

Further measurements, using a high resolution composite Be/graphite filteranalyzer, are shown in figure 2. These results show that there is a splitting of the

c-axis vibration modes at low temperature, which further demonstrates the analomous

hydrogen bonding potential in this crystal direction and, in fact, confirms the

presence of pairing of hydrogens on either side of the Y atoms at low temperature.
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

0.18

60.0 100.0 1400

E{meV)

180.0

Figure 1. Measured neutron spectra of YH p^ single crystal, for

Q _|_ c-axis (b)

.

J_ G-axis (a) and

previously suggested by neutron diffuse scattering patterns. The spectral changes as

a function of temperature in figure 2 also show the existence of an increasing

fraction of unpaired protons at higher temperature (peak at 7^.7 meV at 240 K), and

is consistent with the interpretation of diffuse scattering results. This is the

first example of such pairing in metal-hydrogen systems, which must reflect an associated perturbation of the local electronic structure.
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

YDo,

T=200K

70.0 74.0 78.0

E (meV)

82.0 70.0 74.0 78.0

E(meV)

82.0

Figure 2. Measured spectra for polycrystalline YD. , as a function of temperature

U . 1 o Solid lines are the results of fits assuming Gaussian peak shapes.

NEUTRON SPECTROSCOPIC STUDY OF HYDROGEN ADSORPTION ON

RUTHENIUM SULFIDE CATALYSTS

T. J. Udovic and J. J. Rush

and

W. H. Heise, K. Lu, Y.-J. Kuo, and B. J. Tatarchuk

(Auburn University, Auburn, AL)

Hydrodesulfurization (HDS) selectivity over ruthenium sulfide (RuSp) catalysts

can be altered by varying the surface pretreatment conditions. For example, reaction

experiments have indicated that thiophene HDS proceeds primarily via direct

hydrogenolysis over catalysts pretreated in 10% H S/H at 673 K, whereas the pathway

for thiophene hydrogenation to tetrahydrothiophene followed by hydrogenolysis becomes
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

25 50 75 100 125 150 Energy Loss (meV)

175 200

Figure 1. IINS spectrum at 80 K for hydrogen adsorbed on RuS^ after surface

pretreatraent with ^0% H S/H at 673 K.

comparable to the direct HDS pathway over catalysts pretreated in 1005S H S. To help

understand the role of hydrogen in this reaction system, incoherent inelastic neutron

scattering (IINS) is currently being utilized to probe the adsorbed nature of

hydrogen on unsupported RuS catalysts.

Hydrogen adsorption results in table 1 indicate that the irreversible H uptakes on RuSp increase with both adsorption temperature and degree of surface

sulf idizat ion . Ruthenium sulfide surfaces pretreated in 1005^ H S at 673 K possess

the maximum H adsorption capacity at 373 K, 63/^ of the adsorption capacity for Ru

metal surfaces. Yet, Ru metal surfaces pretreated in 105^ H S/H at 673 K are fully

poisoned toward H adsorption due to the formation of a "skin sulfide" barrier

containing one-half monolayer of surface sulfur atoms in a different chemical state

(as evidenced by x-ray photoelectron spectroscopy and reaction experiments) than in

the bulk sulfide RuS . Recent neutron scattering results have indicated that the H/RuS„ vibrational

spectra, and therefore the surface species, are qualitatively independent of

adsorption temperature and pretreatment conditions; only scattering intensities vary,

reflecting the differences in H uptake. The IINS spectrum for hydrogen adsorbed at

373 K on RuS pretreated in ^0% H S/H at 673 K is depicted in figure 1. The main

scattering features appear as a doublet at 78 and 88 meV with the corresponding

second harmonics near 156 and 176 meV. These are assigned to the bending modes of a sulfhydryl (SH) group in agreement with the vibrational spectra for (SH) on other
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

Table 1 - Sulf idization and temperature effects on H chemisorption

2 Irreversible H Uptake (pmoles/m ) Catalyst Surface Pretreatment (673 K) 300K 373K

Ru 100^ H^ - 10.2

Ru 105^ H S/H

RuS ^0% H S/H 1 .0 2.2

RuS 1005S H S 1.4 6.5

sulfide surfaces (1-3). The weak scattering feature at 44 meV is tentatively

assigned to H motion associated with a sulfur phonon mode in agreement with the

expected energy for such a mode. Substitution of deuterium for hydrogen resulted in

the harmonic isotopic energy shifts to 55 and 64 meV. Isotope dilution neutron

spectroscopy experiments utilizing 15? H/85$ D indicated no significant change in the

H vibrational peak structure for the Ru-S-H bending modes, suggesting that the

doublet at 78 and 88 meV represents two different vibrational modes rather than the

phonon dispersion of a single bending mode due to adsorbate-adsorbate dynamic

coupling interactions.

1. C. J. Wright, D. Fraser, R. B. Moyes, and P. B. Wells, Appl. Catal. j_, 49 (1981).

2. C. Sampson, J. M. Thomas, S. Vasudevan, and C. J. Wright, Bull. Soc. Chim. Belg.

90, 1215 (1981 ).

3. R. J. Koestner, M. Salmeron, E. B. Kollin, and J. L. Gland, Chem. Phys. Lett.

125, 134 (1986).
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

AN INCOHERENT INELASTIC NEUTRON SCATTERING

STUDY OF THE ADSORPTION AND ABSORPTION

OF HYDROGEN BY PALLADIUM BLACK

J. M. Nicol

(University of Maryland, College Park, MD)

and

R. D. Kelley and T. E. Madey

(Surface Science Division)

and

J. J. Rush

The interaction of hydrogen with palladium surfaces is of considerable interest

because of its catalytic properties in reactions such as the selective hydrogenation

of alkynes to alkenes and its ability to form metallic hydrides for hydrogen storage.

Studies of the interaction of hydrogen with both single crystal and polycrystalline

Pd samples have been carried out using such techniques as high-resolution electron

energy loss spectroscopy, low energy electron diffraction, thermal desorption, and

inelastic incoherent neutron scattering (IINS).

In the present work we have used IINS to study the interaction of hydrogen with

Pd black, and exceptionally high surface area metal powder with an initial surface

2

area of 40 m /gm. Unlike similar studies of surface hydrogen species on Raney Nickel

and platinum black, the Pd-hydrogen system is more complex due to the ability of Pd

to absorb hydrogen. The a- and g-Pd hydrides have been well characterized by IINS,

particulary at NBS. In addition to the surface and bulk species there is strong

evidence for a "sub-surf ace"hydrogen species, formed below the topmost layer of Pd

atoms, which may act as an intermediate between the surface and bulk hydrogen. It

was the aim of the present work to investigate the adsorption of hydrogen on Pd

black, the existence of subsurface hydrogen by IINS, and the interaction of

chemisorbed oxygen with these species. The initial results of these studies (along

with preliminary interpretations) are described here.

The IINS spectra were measured on the BT4 spectrometer at the NBS reactor,

operating with a liquid nitrogen cooled Be filter analyzer. The spectrum of Pd black

after hydrogen titration at 80 K, followed by evacuation and heating at 373 K is

shown in figure la. Scattering intensity observed at 58, 94, 100 and 119 meV shows

the presence of a significant amount of residual hydrogen (ca. 0.6 - .75 monolayers).

This suggests that all of the residual hydrogen is much more strongly bound than bulk

hydrogen, which would have been removed during evacuation at 373 K. We thus assume

that all of the features seen in figure la are associated in some way with surface

10
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

60

40

20

oo "

-20

-10

n r "T

1

1 r

da)

t

+ t

\' . .

f

I f t

'

^ ^Uh

(1b) ^,

f

J I I L

li u^ H^^

^ M I

I

f t f

f }^

I I t

Si

30 40 50 60 70 80 90 100 110 120 130 140 EmeV

Fieure 1. (a) IINS Spectrum at 80 K of cleaned Palladium black

(b) difference spectrum after the addition of 1 monolayer of oxygen to

1(a), 1 warming to 293 K and cooling to 80 K. (Negative scattering

intensity represents species removed by oxygen attack.)

1 J 1 1 1 1 1 1 1 1

PdH 0.34 750 -

»

*

""

0)

(0u

(A ••. s 500 _

• • —

c

35

•

•

• 250

•

• .11 Ill 30.0 60.0 90.0 120.0 150.0 180.0 EmeV

Figure 2. IINS Spectrum of the 3-hydride of Palladium black at 80 K

11
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

sites. This was confirmed by an interesting chemical titration experiment. When

oxygen was adsorbed (1 monolayer of atoms) on the surface at 80 K, very little

change in the spectrum was observed. On warming the sample to 293 K and cooling

again to 80 K all features in the spectrum associated with hydrogen disappeared

(figure lb). As no features due to surface OH groups were observed, the residual

scattering intensity is felt to be due to weakly bound water. The removal of the

hydrogen scattering intensity due to the reaction of surface oxygen is also a good

argument that the features in a Figure la are due to chemisorbed H species, and not

due to impurity modes such as H bound to surface carbon or oxygen.

The feature at ca. 58 raeV, which is removed by oxygen, is suggestively close in

frequency to that of the bulk g-hydride. For comparison the spectrum of the B"

hydride of Pd black is shown in figure 2. The mode due to interstitial hydrogen is

observed at 60 meV. However, a comparison of the width of the peak for g-hydride in

Figure 2 and the peak observed in the Pd black spectrum (figure la) suggest that they

are due to quite different species. In addition, since it is known that the a and B hydrides of Pd are easily removed by evacuation at ambient temperatures, the cleaning

of the Pd black surface should have removed all hydride species. We also observe

this feature to react with surface oxygen, its intensity to be independent of

temperature, and its concentration to increase only at hydrogen concentrations of

greater than 1 monolayer. These factors lead us to speculate that the feature we are observing is due to subsurface hydrogen, whose site symmetry is similar to that of

the B-hydride.

Force constant calculations and further experimental work are currently being

undertaken to try to establish site geometries. We also hope to improve the

procedure for removing residual hydrogen from the palladium surface without a significant reduction in the surface area.

12
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

ADSORBATE DYNAMICS AND THE DEAMMONIATION PROCESS IN AMMONIATED ZEOLITE RHO

T. J. Udovic, R. R. Cavanagh, and J. J. Rush

and

J. M. Nicol

(University of Maryland, College Park, MD)

and

(National Bureau of Standards, Gaithersburg, MD)

and

G. D. Stucky

(University of California, Santa Barbara, CA)

and

M. J. Wax

(W. R. Grace and Co., Columbia, MD)

and

G. A. Jones and D. R. Corbin

(E. I. duPont de Nemours and Co., Wilmington, DE)

Quasielastic and inelastic neutron scattering experiments involving ammoniated

zeolite rho have been performed in order to investigate the rotational dynamics of

+ bound NH|^ as well as characterize the deammoniation process over the temperature

range 473 - 723 K. Figures 1 and 2 illustrate the IINS spectra reflecting the

deammoniation process. Vibrational features of the bound NH^ near 1 80 meV (bending

modes) and below 50 meV (large amplitude rotational and translational modes) are

found to diminish as the deammoniation temperature is increased. The low-energy

spectra show initial intensity loss in the 28 - 35 meV region at the earliest stage

of deammoniation followed by intensity loss in the 38 - 45 meV region during the

+ latter stages of deammoniation. This is suggestive of NH^ ions bound at two

different kinds of sites in zeolite rho, the more weakly bound and the more strongly

bound species desorbing below and above ca. 623 K, respectively. The desorption

process for both species involves NH formation leaving behind a bound proton. This

process is evident in the IINS spectra during the latter stages of deammoniation by

the gradual appearance of the scattering features for H-rho: the large-amplitude

doublet feature at 44 and 50 meV , the feature at 93 meV associated with proton

coupling to a symmetric T-O stretching mode, and the features at 142 and 131 meV

1 associated with in- and out-of-plane T-O-H bending modes.

The reorientation of NH^ ions has been characterized by low-energy quasielastic

neutron scattering. The dependence of the elastic incoherent structure factor on momentum transfer suggests that the more strongly bound NH^ undergoes 120°

13
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

Z

O

O

V

'A V ''^:^V/>-^, 623K

^^^^ ^^-x******* 723K

f^ 473K

50 100 150 200

ENERGY LOSS (meV)

Figure 1. High energy IINS spectra at 80 K of ammoniated zeolite rho following

deammoniation at 473-723K, collected using the BT-M beryllium filter

detector.

(0

.•;.'.''•'.^

I >!. ***

ft, H H*** **

i

* !\ 473K

t 1 ' ftO'Sk' / * ^V * ^^^t^

723K

10 20 30 40 50 60 70

ENERGY LOSS (meV)

Figure 2. Low-energy IINS spectra at 80K of ammoniated zeolite rho following

deammoniation at '473-723K, collected in the BT-4 triple-axis conf igeration

at 13.8 mev constant final energy.

lA
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

reorientations around a random axis and is coordinated through a single hydrogen

to the zeolite framework. The temperature dependence of the quasielastic component

indicates a very low (ca. 20 meV) barrier to reorientation of the more tightly bound

ml ions, which have been located by x-ray diffraction to be approximately in the

center of the "windows" (eight-membered rings) which separate the cages in the

2

zeolite-rho structure.

Current studies are investigating the reversibility of the deammoniation

process by characterization of H-rho after the reintroduction of NH .

1. M. J. Wax, R. R. Cavanagh, J. J. Rush, G. D. Stucky, L. Abrams, and D. R. Corbin,

J. Phys. Chem. 90, 532 (1986).

2. L. B. McCusker, Zeolites 4, 51 (1984).

NEUTRON SCATTERING STUDIES OF ULTRASTABLE ZEOLITE Y

J. M. Nicol

(University of Maryland, College Park, MD)

and

(Surface Science Division)

and

T. J. Udovic and J. J. Rush

A study of the acid sites (protons) in ultrastable zeolite Y has been initiated

by inelastic incoherent neutron scattering. Spectra at temperatures between 80 and

373 K have been collected using the BT4 spectrometer, with a nitrogen cooled Be

filter analyzer. The initial results indicate a rearrangement of the protons with

increasing temperature. A similar behavior has been previously reported for zeolite

H-rho.

Further studies are planned over a wider energy range by quasielastic and

inelastic neutron scattering. A Force constant analysis will also be undertaken.

1. M. J. Wax, R. R. Cavanagh, J. J. Rush, G. D. Stucky, L. Abrams and D. R. Corbin,

J. Phys. Chem., 90, 532 (1986).

15
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

COHERENT SCATTERING OF LOW ENERGY NEUTRINOS FROM CRYSTALS

R. C. Casella

I have considered the problem of neutral current neutrino scattering from

1 macroscopic crystals. It has been known since the work of Freedman that neutralcurrent scattering of neutrinos from the nucleons in a nucleus can be coherent,

leading, for sufficiently long wavelengths, to cross sections which are proportional

to the square of the nuclear baryon number. When extended to macroscopic objects

containing N nuclei, it has recently been reported that coherent cross sections

2 2 2 proportional to N have been observed. Normally, one expects such N enhancements

to occur only when the wavelength of the incident particles is larger than the sample

size. The question of the existence of coherence is relevant to but not identical

2 with that of possible N effects. I find that coherent scattering can indeed occur

on the scale of an entire crystal for incident neutrino wavelengths comparable to the

3 internuclear separation or less, but that the cross section remains linear in N.

Hence coherence cannot explain the reported

exerted on a crystal by reactor antineutrinos.'

Hence coherence cannot explain the reported observation of a macroscopic force

2

2

For sufficiently small momentum transfers, q

neutrino processes follow from the standard-model Hamiltonian

2 << M o» neutral current

H = (G//2)[v T^(1 - Y^)v][q(C^Y^ + C^Y^^)q]. (1)

2 where C = I - 2Q sin and C = - I_, G is the Fermi coupling and q is an

elementary

y weak

J isodoublet:

Who

q = (v,!l), (u,d'), (p,n), or (A^,A_). The first entries

are the leptons and quarks of each family. For smaller momentum transfers the

nucleon isodoublet is treated as elementary, while for sufficiently low energies we may treat the entire nucleus as elementary with A the I = ± 1 /2 components of q.

When, in the latter case, vector coupling dominates, the scattering amplitude a(E,0)

in the neutrino-nucleus cm. frame satisfies

a(E,0) = (1//2)(GE/2tt)[Z(1 - H sin^G,,) - N^] cos(0/2). (2)

w n

Here E and are the incident energy and scattering angle in the cm. frame and is

w the weak angle. This leads to cross sections which are quadratic in baryon number A

= Z + N . I have calculated directly the net force exerted on a crystal by the

coherent scattering of every neutrino from the N nuclei, assuming phase coherence is

maintained even for neutrino wavelengths much smaller than the lattice constant, but

16
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

larger than nuclear dimensions. Letting b denote the constant multiplying the

quantity E cos(0/2) in Eq.(2) for a(E,0) and F , the net force exerted by a current-

^

3 density source distribution J (E) of (anti)neutrinos, I find

z

F = m-n/S) N e~^^ b^

z

° dE E^ J (E). (3)

Here E is a cut-off energy above which the scattering becomes incoherent and exp(-

2W) is the temperature dependent Debye-Waller factor due to thermal vibrations of the

nuclei. F is linear in N. While coherence can occur in the scattering of neutrinos

^

2

of wavelengths much smaller than the sample size, an N enhancement is possible only

for ultra-low-energy neutrinos with wavelengths of order the linear dimensions of the

2

crystal. Therefore, the reported observation of a macroscopic force exerted on a

2 crystal by ant ineutr inos from a fission reactor cannot be explained by an N

enhancement at the crystalline level of the nuclear cross-section due to coherence.

1. D. Z. Freedman, Phys. Rev. D, 9_, 1389 (1974).

2. J. Weber, Phys. Rev. C, 31, 1468 (1985).

3. R. C. Casella, "Coherent Scattering of Low Energy Neutrinos from Macroscopic

Objects", Proc. of the 2nd Conf. on the Intersections Between Particle and

Nuclear Physics, Lake Louise, Canada, 1986, Am. Inst, of Physics (in press).

X-RAY DIFFRACTION STUDIES OF THE AMORPHOUS (FE Ni ) Si B ALLOYS

S. C. Yu and J. W. Lynn

(University of Maryland, College Park, MD)

and

(National Bureau of Standards, Gaithersburg, MD)

The atomic structures of single roll-quenched amorphous (Fe._ Ni ) Si B (atomic %, S x S 1) alloys have been studies by x-ray diffraction. Interference

functions, atomic distribution functions and radial distribution functions were calculated from the data. We find that the nearest neighbor distance decreases from

2.54 ± 0.01 A for X = (Fe^^Si^^B ) to 2.49 ± 0.01 A for x = 1 (Ni Si^^B ), while

the average coordination number (ON) of 12.50 ± 0.18 is independent of x. The values

corresponding to the nearest neighbor distance were 2.493 A (for Fe Si B ),

2,448A (for Ni^^Si^ ^B^ ^) , 2.498 A (for Fe^gSi^^B^^^ ^"^1 2.453 A (for Ni^gSi ^ ^B^ ^ )

,

calculated from the radii of each element for CN = 12 using the homogeneous

17
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

crystalline model. We can see that the nearest neighbor distance of Fe Si B is

larger than Ni Si._B . From an earlier report we can see that this tendency still

holds in the amorphous state. For example, the nearest neighbor distance of

amorphous Fe gSi B alloy is 2.58 A and that of amorphous Ni ^.Si B alloy is 2.55

A. In addition, the nearest neighbor distance in TM Si B (TM = Fe, Ni) is

shorter than TM nSi.-^B alloy. These trends are in good agreement with our results

but there are some numerical differences which are likely due to differences between

the amorphous alloys, and to the crystalline model. These results are consistent

with the measured densities of the samples, which are found to increase with

increasing Ni content.

1. Y. Waseda, "The Structure of Non-crystalline Materials", (McGraw-Hill, New York,

1980) p. 128.

THE MAGNETIC STRUCTURE IN DY-Y SUPERLATTICES

R. W. Erwin and J. J. Rhyne

and

J. Borchers, M. B. Salamon, R. Du and C. P. Flynn

(University of Illinois, Urbana, IL)

It has been shown by neutron diffraction techniques that a superlattice of 15

atomic planes of Dy alternated with 14 atomic planes of Y orders magnetically in a helix which remains phase coherent across the magnetically 'dead' Y layers and is

incommensurate with the bilayer periodicity. This is shown in figure 1, where

diffraction scans along the [OOOfi,] direction of the hep structure are plotted for

several temperatures below the Neel point T = 170 K. A primary nuclear Bragg peak

-1

of the superlattice is evident at Q = 2.22 A representing approximately the average

spacing of the superlattice growth planes. Only the first order nuclear satellite at

higher Q is visible which arises from the lattice mismatch between the Dy and Y

2 layers. The remaining peaks grow in intensity as the temperature is decreased and

are thus magnetic. The spacing of these peaks is 2it/L as for the nuclear peaks (L = bilayer thickness), but they are otherwise incommensurate with the nuclear peaks.

Note that the intensities of the magnetic satellites do not follow an obvious

pattern, but that the relative intensities are strongly temperature dependent. We

have been able to describe this effect by a simple model for the superlattice

structure factor, which shows that the turn angle of the helical order is different

18
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

200

160

120

2.60 Q, (A')

Figure 1. The temperature dependence of the diffraction scans along the [0008,]

direction shows that the Dy-Y superlattice orders in a helix which is

incommensurate with the bilayer thickness. Since several magnetic

satellites are clearly distinguishable, this coherence extends across

several layers of magnetically 'dead' yttrium.

in the Dy and Y layers. The superlattice thus retains in the separate layers

approximately the Fermi surface features which determine the magnetic periodicity in

bulk Dy and Y. However, the ferromagnetic transition found in bulk Dy at 85 K is

absent in the superlattice down to 5 K. This is the result of the strain clamping of

the Y inter-layers, which inhibits the Y-magnetostriction associated with the

ferromagnetic transition.

Several features in the magnetization process in an applied field have been

found to be unique to the superlattice. In Figure 2 are shown the diffraction scans

as in figure 1, but after a 25 kOe field has been applied in the basal plane. At 110

K the magnetic field weakens the coherence of the helical order as evident in the

broadening of the magnetic satellites (this occurs even in fields of only 1 kOe).

The breakdown of the long-range order possibly results because the external field

couples as a random field to the net Dy layer moment (the helix does not have an

2 integer number of wavelengths in the Dy layer). At 10 K, on the other hand, the

phase coherence is not destroyed by low fields. Instead an irreversible transition

19
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

is obtained to a remanent ferromagnetic state. Thus there is an extra magnetic

intensity on the main Bragg peak even after the magnetic field is switched off, and

the magnetic satellites of the helical order are not restored. We have also shown

that the original helical order can be restored by raising the temperature to about

ilO-60 K. The ramanent state is beleived to be the result of the energy barriers to

spin rotation caused by the strong increase of basal plane single-ion anisotropy at

low temperatures.

The coherence range of the helimagnetic order has been estimate from the

observed peak widths and known instrumental resolution to be about 350 A or four

bilayers. This coherence implies that the handedness of the helix is preserved

across the Y layers, so that the coupling can not be described as a simple scalar

RKKY interaction (unless some intrinsic effect chooses the same handedness in each Dy

layer). We beleive that this is strong evidence for an incipient conduction band

spin density wave in Y stabilized by the Dy local moments

1

200.

160.

120.

80.

40.

180 2.60

Figure 2. The diffraction scans are shown for the remanent state at several

temperatures. At high temperatures (110 K) the coherence of the

helimagnetic state is reduced by the applied magnetic field, while at low

temperatures (10 K) a metastable ferromagnetic remanent state is frozen in

by the strong basal plane anisotropy.

20
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

is obtained to a remanent ferromagnetic state. Thus there is an extra magnetic

intensity on the main Bragg peak even after the magnetic field is switched off, and

the magnetic satellites of the helical order are not restored. We have also shown

that the original helical order can be restored by raising the temperature to about

40-60 K. The ramanent state is beleived to be the result of the energy barriers to

spin rotation caused by the strong increase of basal plane single-ion anisotropy at

1 low temperatures.

The coherence range of the helimagnetic order has been estimate from the

observed peak widths and known instrumental resolution to be about 350 A or four

bilayers. This coherence implies that the handedness of the helix is preserved

across the Y layers, so that the coupling can not be described as a simple scalar

RKKY interaction (unless some intrinsic effect chooses the same handedness in each Dy

layer). We beleive that this is strong evidence for an incipient conduction band

1 spin density wave in Y stabilized by the Dy local moments.

1

.

J.J. Rhyne, R. W. Erwin, M. B. Salamon, Shantanu Sinha, J. Borchers, J . E . Cunningham and C. P. Flynn, to be published in Journal of the Less-Common Metals

1986; M. B. Salamon, Shantanu Sinha, J. J. Rhyne, J. E. Cunningham and C. P.

Flynn, Phys. Rev. Lett. 56_, 259 (1986).

2. R. W. Erwin, J. J. Rhyne, J. Borchers, M. B. Salamon, R. Du and C. P. Flynn, to

be published.

3. B. R. Cooper, Phys. Rev. 169 , 281 (1968); B. R. Cooper, Phys. Rev. Lett. J_9, 900

(1967).

ANTIFERROMAGNETIC STRUCTURE OF THE CUBIC SUPERCONDUCTOR ErPd Sn

J. W. Lynn and H. B. Stanley

(University of Maryland, College Park, MD)

and

(National Bureau of Standards, Gaithersburg, MD)

and

R. N. Shelton and P. Klavins

(Iowa State University, Ames, lA)

ErPd Sn is a Heusler alloy which crystallizes into the cubic Cu MnAl-type

structure (a=6.68 A). In common with some other Er containing ternary compounds,

2 3 ErMOgScg and ErMo^Sg , this alloy exhibits the coexistence of long-range

antiferromagnetic order and superconductivity. It differs from these however, by

21
REACTOR RADIATION DIVIISON AND COLLABORATIVE PROGRAMS

having a significantly higher percentage of magnetic Rare Earth ions, and in having a higher site symmetry (cubic). We have investigated the magnetic properties of this

interesting alloy by means of neutron scattering.

The powder sample was loaded into an aluminum flat-plate sample holder with a thickness of approximately 1 mm to minimize the effects of absorption. The fixed

incident neutron wavelength of 2.35 A together with horizontal Seller collimators of

--] 10'-10'-10' (no analyzer) gave a wave vector resolution of between about 0.012 A at

-1 1 a scattering angle of 17° and 0.023 A at 60°. ErPd Sn has been shown to have a superconducting transition at T = 1.17 K, and has a heat capacity anomaly at 1 K.

Measurements were therefore taken between 0.35 K and H K; the 4 K data representing

the non-magnetic (flat) background.

Four magnetic Bragg peaks were observed between 10 and 60 degrees which we have

identified as the (111), (113), (313) and (333) reflections of a fee type-II

antif erromagnet (space group Fd3m). This structure is characterized by the doubling

of the fee Er unit cell along all three crystallographic directions. Satellites of

these allowed reflections were also observed, however, which indicates that this

basic structure must be modulated.

All linewidths were found to be broader than instrumental resolution and

clearly non-Gaussian in shape (see Figure 1). This may arise from an inelastic spin

1100

900

(a)

700 - A

1 500 oo

-

300 - /

i

100 %,UV^-/

f

TTTlf^Ty . ^^A^+V**^

-100 1 1

1

1 1 1

1100

(b)

1

900 - 1

700 -

i 500 oO

-

300 -

u' \k

100 ^%tW!^^

Jrtr' \i *

TTTlfffTlf T ^^fV^'iV*'

-100 1

1

1 1 1 1 13.5 15.0 16.5 18.0 19.5

Scattering Angle

21.0 22.5 13.5 15.0 16.5 18.0 19.5

Scattering Angle

21.0 22.5

Figure 1. (Ill) magnetic Bragg reflection at 0.35 K. Background scattering,

represented by data taken at ^ K, has been subtracted.

(a) solid line is a Gaussian fit to the data

(b) Lorentzian fit to the data

22
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

wave contribution to the scattering which maximizes at reciprocal lattice points,

although increasing the temperature decreased the overall intensity without altering

the lineshape. Inelastic measurements revealed that there are indeed magnetic

excitations in the ordered state with energies below ~ 1 meV. In addition, we observed two crystal field excitations with energies of 7.'4 and 11.1 meV.

1. R. N. Shelton, L. S. Hausermann-Berg, M. J. Johnson, P. Klavins and H. D. Yang

(to be published)

2. R. N. Shelton, R. W. McCallum, H. Adrian, Phys. Lett. A56 213 (1976)

3. 0. Fischer, A. Treyvaud, R. Chevrel and M. Sergent, Sol. St. Commun. VJ_ 721

(1975)

SPIN DYNAMICS OF AMORPHOUS Fe-^ Ni Zr,^

90-x X 1

J. A. Fernandez-Baca and J. W. Lynn

(University of Maryland, College Park, MD)

and

(National Bureau of Standards, Gaithersburg, MD)

and

J.J. Rhyne

and

G.E. Fish

(Allied Corporation, Morristown, NJ)

The iron rich Fe-. Ni Zr,- amorphous system exhibits Invar characteristics , 90-x X 10

where the thermal expansion and a large positive spontaneous volume

magnetostriction nearly cancel below the Curie temperature. This system also has the

peculiarity that for x = there is no long range ferromagnetic order. Small angle

2 scattering experiments by Rhyne and Fish have shown that the spin correlation length

at low temperatures remains small (= 20 A) and nearly temperature independent,

reflecting the effect of competing ferromagnetic and antiferromagnetic exchange. The

addition of Ni in the system induces long range ferromagnetic order as it has been

shown in Fe__Ni. Zr , where spin waves have been observed in the whole range of

temperatures studied (0.55-0.89 T ).^

In order to obtain a better understanding of how this transition to long range

ferromagnetic order occurs we have performed inelastic neutron scattering experiments

to study the spin dynamics of Fe„- Ni Zr,^ for x = 5, 10. The experiments were 90-x x 10

"\

23
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

performed at the BT-9 triple axis spectrometer at the NBSR. The amorphous nature of

the system required that measurements be taken near the forward (000) beam position.

A fixed incident energy of 13-5 meV was used and a PG filter was placed after the

monochromator to suppress higher order wavelength contaminations. Seller slit

horizontal collimators of 1 5 '-1 2 '-1 1 '-25 ' were used to produce a FWHM of 0.35 meV at

the elastic position. Well defined spin waves were observed in all the range of

temperatures studied (0.33-0.90 T for Feo^Ni^Zr,^, and 0.28-0.83 T for

c o5 5 1 c FenoNii^Zr,^ ) . In analyzing the data, spin-wave energies and linewidth information

cso 10 I u were obtained by convoluting a double Lorentzian-type cross section with the

instrumental resolution and least-squares fitting to the observed spectra, after

subtraction of the background scattering.

The spin-wave energies at all temperatures under study were found to obey the

quadratic dispersion relation expected for an isotropic ferromagnet:

E= A + D(T)q^ + ...

' (1

)

where A = 0.05 meV is an effective anisotropy gap which originates mainly from the

dipole interaction, and shows no significant temperature dependence. The spin-wave

stiffness parameter 'D' exhibited a temperature dependence of the form : D(T) = D(0)[1-a(T/T )^''^] (2)

c

2 with D(0) = 42.05 ± 0.37 and 78.03 ± 0.49 meV-A for the samples with x = 5 and 10,

and a = O.83. The value of the coefficient 'a' is of the same order of magnitude of

4 the ones found in the Fe-B amorphous Invar system, and is significantly larger than

expected for a Heisenberg ferromagnet with short range interactions.

The intrinsic spin-wave linewidths r in the two systems under study did not

show significant temperature dependence in the temperature range 0.55-0.90 T . These

4 ° linewidth data could be fitted to a q dependence (predicted by hydrodynamic spin5 wave theory) or to a q dependence (predicted from the topological disorder in

amorphous systems). Also the ratio r /E ,that measures the relative damping of the

spin-wave excitations, was found to be significantly larger than in the Fe-B system.

These findings suggest that there might be spin-wave broadening mechanisms,

presumably due to the magnetic disorder, in addition to the magnon-magnon interaction

in the system.

1. K.Shirakawa, S.Ohnuma, M.Nose and T. Masumoto. IEEE Trans. Mag. ^A'^^O (1980).

2. J.J. Rhyne and G.E. Fish. J. Appl. Phys. 5X.3407 (1985).

3. J. A. Fernandez-Baca, J.J. Rhyne and G.E. Fish. J. Magn. Magn. Mat. 54-57 , 289

(1986); and NBS Technical Note 1217, ed . F. J. Shorten (1985) page 55.

4. J. A. Fernandez-Baca, J.W. Lynn, J.J. Rhyne, and G.E. Fish, J. Appl. Phys. 57, (1985)

24
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

NEUTRON SCATTERING STUDY OF THE SPIN FREEZING

IN AMORPHOUS Tb„^Fe^^ AND Tb^^Fe^^

15 55 25 75

M. L. Spano*

(Naval Surface Weapons Center, Silver Spring, MD 20903)

and

(National Bureau of Standards, Gaithersburg, MD 20899)

and

J. J. Rhyne

We have made small angle neutron scattering measurements (SANS) on Tb^cFecr and

Tb^cFe^i- as a function of temperature. These alloys, like others of the Tb-Fe

system, do not become ferromagnets at low temperature, but rather undergo a transition to a spin frozen state. This is characterized by the formation of

clusters of spin ordering which can be observed in SANS. There is a strong

temperature evolution of the scattering intensity reflecting the change in the order

parameter with temperature. The spin correlation length does not diverge at T

reflecting the destruction of the conventional second order phase transition by the

random anisotropy field. In the present study, both samples exhibit conventional

Lorentzian lineshapes in Q for T > T , but depart from this form below T . We have

fitted the latter lineshapes with the Lorentzian plus Lorentzian squared form

appropriate for random field systems. In the Tb,|-Fe^i- alloy the correlation length,

5, rises, with decreasing temperature, to a rounded maximum of about 90 A occurring

about 20 K below T = 298 K, as determined from magnetization results, before

decreasing to about 60 A at 4 K. This is in marked contrast to the Tb^rFe-,!- alloy,

in which ^ reaches an experimental infinity near its transition temperature of about

400 K. For both alloys the coefficient of the Lorentzian term rises sharply as T -*•

0, whereas the Lorentzian squared coefficient follows approximately the square of the

order parameter times E,~\

MAGNETIC EXCITATIONS IN THE XY-HEISENBERG SYSTEM Tb Sc,

X 1-x

R. W. Erwin and J. J. Rhyne

and

B. Beaudry

(Iowa State University, Ames, Iowa)

Although well defined spin waves have been observed in rare-earth alloys with

1 the non-magnetic diluent yttrium , there is very little known about the magnetic

excitations in the analogous alloys diluted with scandium. Such a study is of

25
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

400

320

240.

4. 8. Energy Transfer (meV)

12.

Figure 1. Scans of the energy transfer for wave vectors along the c direction show

that the magnetic excitations in Tb_ f:Sc„ ^. are extremely broad. The

observed peak positions do move to smaller energy transfer as the reduced

wave vector decreases and the peak widths concomitantly become sharper as

in conventional spin-wave behavior. The curves through the data points

serve as a guide to the eye.

interest since there is considerable experimental data which indicates that Sc alloys

2 have quite different magnetic properties from their Y counterparts . It is then

important to understand how these differences are related to the dynamic magnetic

excitations in these materials.

We have begun an investigation of the Tb Sc dilution system by probing the

magnetic excitations in a single crystal of Tb_ ^Sc ^ with inelastic neutron

scattering techniques.

These alloys have hep crystalline structures and order in a magnetic structure

consisting of a helix with the directions of the basal plane (XY) ferromagnetic

sheets modulated along the c-axis (perpendicular to the basal plane). The spins are restricted to align in the basal plane by strong crystal field anisotropy. For large

3 concentrations of Tb (x ^ 0.85) the low temperature ordered state is ferromagnetic

as in pure Tb for which T„ = 225 K and T = 217 K. As the Tb concentration

N c is decreased below about O.M the helix coherence length becomes finite and the

26
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

2 M magnetic behavior becomes increasingly spin-glass like ' . We have observed that the

presently studied alloy (x = 0.6) has a resolution limited correlation length with T

= 115 K.

N

In figure 1 are shown the low temperature (T = 10 K) energy scans for a range of

wave-vector transfers along the c direction. The magnetic excitations should be

* most straightforward to observe in the c direction for these basal plane helimagnets

5 as has been shown experimentally in a number of systems . However, our data in

figure 1 show that the magnetic excitations are extremely broad even for the

excitations at the smallest reduced wave vectors measured £; = . 4 mo% of the way

from the Brillioun zone center to the zone boundary) and at low temperatures (10 K = 0.12 T ). The peak positions do move towards smaller energy transfer as E, decreases

and in addition the peak width does become sharper, as expected for conventional

spin-wave behavior. Note that the effect of raising the temperature is to increase

the intensity at small energy transfers until at 80 K (= 0.7 T ) a peak is no longer

discernable at finite energy transfer as shown in figure 2 for E, = 0.6. Also shown

in figure 2 is the scan for E, = -0.6, demonstrating that the observed inelastic

scattering is predominantly due to magnetic excitations instead of phonons (the

2 phonon intensity would increase as Q where Q = 2 + C)-

240.

160.- c3

OU

cs

«z

80.

[0,0,2. -§]

*a<°TD® 5= -.06 80K

J. ^pfMSJfe^jwtm^Bi^i, ^=-0.06 5K

^0.6 5K

0.

—I T- 4. 8. 12. Energy Transfer (meV)

Figure 2. The energy scans along c at high temperatures show that the distribution

of scattering has become broadened to the point that a peak in the

intensity can no longer be observed at finite energy transfer. The scans

at ^ = ±0.6 show that the observed scattering is predominantly magnetic in

origin.

27
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

One possible method of explanlng the observed broadening of the excitations is

to invoke a distribution of exchange interactions between the Tb spins. This

distribution might then be much sharper in the yttrium dilution systems than in the

corresponding Sc systems, due to the verydif ferent conduction band susceptibilities

of Y and Sc . The fact that the excitations become visible at low temperatures may

be the result of the opening of a gap at zero energy transfer due to the strong

7 increase of basal plane anisotropy, as has recently been predicted .

1. N. Wakabayashi and R. M. Nicklow, Phys. Rev. BIO , 2049 (1974).

2. R. Abbundi, J. J. Rhyne, D. M. Sweger and R. Segnan, Phys. Rev. B1

8

, 3313 (1978); J. H. Ferrick, J. J. Rhyne and R. Segnan, J. Appl . Phys.

53 , 2232 (1982); K. Baberschke, P. Pureur, A. Fert, R. Wendler and S. Senoussi,

to be published.

3. H. R. Child and W. C. Koehler, J. Appl. Phys. 37, 1353 (1966).

4. B. V. B. Sarkissian and B. R. Coles, Comm. Phys. j_, 17 (1976); R. W. Erwin and

J. J. Rhyne, to be published.

5. A. R. Mackintosh and H. Bjerrum Moller, in Magnetic Properties of Rare

Earth Metals , edited by R. J. Elliot, Plenum Press, New York, 1972.

6. S. H. Liu, R. P. Gupta and S. K. Sinha, Phys. Rev. B4, 1100 (1971).

7. A. A. Kumar, C. L. Henley and W. M. Saslow, to be published.

STATIC AND DYNAMIC SPIN CORRELATIONS IN DILUTE MAGNETIC SEMICONDUCTORS

WITH HIGH Mn CONCENTRATIONS

T. M. Giebultowicz and J. K. Furdyna

(Purdue University, W. Lafayette, Indiana)

and

J. J. Rhyne

and

W. Y. Ching

(University of Missouri, Kansas City, MO)

and

D. L. Huber

(University of Wisconsin, Madison, WI)

Inelastic scattering spectra have been measured in Cd^ nr^'^r, £r-Te for several

_ U . Jb U . Db

points in Q-space along [120] and [110] directions in the (001) plane. These

directions have been chosen to avoid distortions of inelastic spectra due to twinning

28
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

Figure 1. Contour map of elastic scattering intensity in Zn^ j^cMn ctrSe at 4.2 K for

a 60° section of the basal plane. Crossed circles indicate the positions

of nuclear Bragg reflections. Black dots show the ideal positions of

magnetic superstructure reflections.

effects, which almost invariably occur in Cd Mn Te crystals with high x. Comparison

I X X of the measured data (corrected for instrumental effects, such as resolution, or A/2

-> contamination in the incident beam) with the dynamic structure factors S(Q,E),

1 calculated using the method by Ching and Huber , shows that this model gives an excellent description of the spin dynamics in Cd Mn Te, except for Q-points close

to the zone center (the origin of a "gap" in E that occurs in this point is yet not

clear). Fitting the theoretical lineshapes to measured spectra yields 2J = (13.8

0.2)K. This results provides the most accurate existing measurement of J for

Cd. Mn Te in the region of high Mn concentrations.

1 -X x Studies of the wurtzite-structured DMS system Zn. Mn Se have been continued.

1 -X X Results of systematic measurements of elastic diffuse scattering intensity within the

basal plan (shown as a contour map in figure 1 ) confirm that the short-range magnetic

order in this compound is closely related to the type of antiferromagnetic structure

which occurs in hexagonal g-MnS. The data reveal additionally two intriguing effcts:

a strong anisotropy of the diffuse peak lineshapes, and a small shift of the centers

of these peaks from ideal suprestructure positions. The first of these effects likely

arises due to a "conf igurational" anisotropy of the Mn-Mn exchange interactions,

which also occurs in cubic DMS systems. It is less clear, however, whether the shift

29
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

is an intrinsic feature in this type of short-range ordering, or caused, e.g., by

defects such as stacking faults.

1. W. Y. Ching, D. L. Huber, Phys. Rev. B25, 5761, and B26, 616^1 (1982).

MAGNETIC PHASE TRANSITION UNDER PRESSURE IN THE REENTRANT SUPERCONDUCTOR Tm_Fe-Si^

2 3 5

J. A. Gotaas

and

J.W. Lynn

(University of Maryland, College Park, MD)

and

(National Bureau of Standards, Gaithersburg, MD)

and

R.N. Shelton

(Iowa State University, Ames, lA)

The system Tm.Fe_Si^ is an ordinary ant i f erromagnet with a transition

^ J b

temperature of 1.1 K at ambient pressure [1]; under applied pressures of 2 to 21 kbar

there is a superconducting phase transition at a temperature T ^ >T , followed by a return to the normal state at a temperature T ^ in the vicinity of T,, as measured by

c2 •' N

^ ac susceptibility. The existence of thermal hysteresis under pressure suggests some

first-order character to the reentrant transition [2]. Previous neutron diffraction

measurements have shown no change in the nature of the magnetic state between ambient

pressure and 2.3 kbar (just above the critical pressure for the appearance of

superconductivity) [3].

We have now examined the nature of the magnetic ordering at higher pressures of

4.5 and 5.8 kbar, where the superconducting state is fully established before the

magnetic transition occurs. The magnetic structure remains unchanged under the

application of pressure. In particular, we find no evidence for the existence of any

ferromagnetic component to the structure which could be responsible for quenching the

superconducting state. Figure 1 displays the peak intensity of the first magnetic

peak (100) as a function of temperature for both 2.3 and 5.8 kbar. It can be seen

that intensity develops in the ordered state in the same way and that the sharp rise

which normally defines the transition occurs at approximately the same temperature.

The only apparent difference between the measurements at different pressures is the

presence of additional intensity above the transition temperature at 5.8 kbar. There

is a measurable increase in the peak width of the scattering above the transition,

30
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

which indicates that this extra intensity results from short range correlations.

There is no measurable thermal hysteresis in the magnetic peak intensity under

pressure, in contrast to the observed hysteresis in the reentrant phase transition at

higher pressures.

The destruction of the superconducting phase by an antiferromagnetic transition

is unique experimentally, although a number of theories predict suppression of the

"1—

r

Tm2Fe3Si5

o P =5.8 kbar A P = 2. 3 kbar

ao

J I \ L J I L

0.2 0.4 0.6 0.8 1.0 1.2 1.4 T(K)

Figure 1: Peak intensity of the (100) magnetic reflection as a function of

temperature, for pressures of 2.3 and 5.8 kbar.

superconductivity under some conditions [4, 5]. The absence of any increase in the

observed T , in contrast to the observed rise in the reentrant temperature T -[2],

may suggest that the superconducting state is not destroyed by the long range order

of the magnetic moments, but by the dynamical fluctuations of the moments in the

vicinity of the transition, as some theories have suggested [4]. In this case, there

may be a second superconducting transition at still lower temperatures as the spin

wave fluctuations become frozen out in the ordered state. The theory of Machida et

al. [5] also predicts the destruction of superconductivity at the magnetic phase

transition on different grounds, which is again followed by a second transition to

the superconducting state at lower temperatures. Our neutron diffraction

measurements would be insensitive to such a transition; such a possibility needs to

be explored by polarized beam techniques, or by susceptibility or resistivity

measurements.

31
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

1. A.R. Moodenbough, D.E. Cox and C.B. Vining, Phys. Rev. B32, 3103 (1985).

2. C.B. Vining and R.N. Shelton, Solid State Commun. 54_, 53 (1985).

3. J.W. Lynn, J. A. Gotaas and R.N. Shelton, NBS Technical Note 1217 , 58 (1985).

4. T.V. Ramakrishnan and CM. Varma, Phys. Rev. B2_4, 137(1981); K. Levin, M.J. Nass

and Charles Ro, in Superconductivity in Magnetic and Exotic Materials , ed. T. Matsubara and A. Kotani (Springer-Verlag) 198M, p. 104.

5. K. Machida, K. Nokura and T. Matsubara, Phys. Rev. B22, 2307 (1980).

SPIN DYMAMICS IN THE HEUSLER ALLOY NlMnSb

J. A. Gotaas and J.J. Rhyne

and

R.A. Robinson

(Los Alamos National Laboratory, Los Alamos, NM 87545)

We have begun neutron scattering measurements on the ferromagnetic Heusler alloy

NiMnSb (T = 750 K [1]), which band structure calculations have shown to possess the

unusual electronic property [2] that the majority spin electrons are metallic while

the minority spin electrons exhibit a band gap, leading to a semiconducting nature.

ou 1 1 NiMnSb

1 r

50 T = 295K

/ -

40 - V

30 - /

/o

20 - /

-

10 _y^ 1 1 0.1 0.2 0.3 0.4 0.5

q (reduced units)

Figure 1. Magnon dispersion curve for NiMnSb at room temperature (q is in reduced

units

.

32
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

In the related conventional Heusler alloy Ni MnSb, which has a normal band structure,

the moments are localized on the Mn atoms and the spin dynamics can be well described

by the standard Heisenberg model. It is known that the moment remains localized on

the Mn atoms in NiMnSb, so that one might also expect a Heisenberg description to be

valid here, although the Curie temperature is considerably greater than that of

Ni MnSb (where T = 334 K [1]). It is possible, however, that the peculiar band

structure may lead to significant differences in the spin dynamics, and it is the

goal of this work to explore that possibility.

To date, we have utilized BT6 and BT4 in the constant E mode to make

measurements at room temperature on a single crystal sample weighing 9.5 gm. We have

performed scans around the (111) and (220) reciprocal lattice points along the major

symmetry directions (00^), (^^0) and {E,E,0- We have found the magnon dispersion to

be isotropic along the major symmetry directions, and can be fit well by a simple

2

quadratic law up to energies of 42 meV, with a dispersion constant of 21 8 meV-A . Figure 1 displays the data for all measurements (with q in reduced units), along with

2

the fit E = D q , where D in reduced units is 311 meV.

Future experiments will extend these measurements to higher energies, as well as probing the behavior at elevated temperatures.

1. Y. Ishikawa and Y. Noda, AIP Conf. Proc. 24_, 145 (1975).

2. R.A. de Groot, F.M. Mueller, P.G. van Engen and K.H.J. Buschow, Phys. Rev.

Lettr. 50, 2024 (1983).

MAGNETIC FIELD-INDUCED TRANSITION IN Y, Gd

1-x X

J. A. Gotaas and J.J. Rhyne

and

L.E. Wenger

(Wayne State University, Detroit, MI)

and

J. A. Mydosh

(Kamerlingh Onnes Laboratorium, Rijksuniversiteit Leiden, The Netherlands)

Neutron scattering measurements have continued on the dilute alloys Y Gd (x = 0.01,0.022,0.03 and 0.044). As reported earlier , for x=0.022, this system orders in

a helical spin state at T=6.64K, with the spins lying in the basal plane and a modulation wave vector of 0.28c*. We have demonstrated that all compositions studied

order in the same way with transition temperatures which depend on concentration (T =

33
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

2.^, 12.0 and 18. 5K for x= 0.01,0.03 and 0.044, respectively) . In order to clarify

the origin of the long range order in this system, we have carried out additional

neutron diffraction measurements in an applied magnetic field for the concentrations

x=0.022 and 0.044.

We have studied the c axis satellites of the origin and (002) reflections in

magnetic fields of up to 7 Tesla applied in the basal plane of the sample and find no change in the modulation wave vector of 0.28c* and no evidence for the development of

higher harmonics which would indicate intermediate field-induced metastable periodic

spin states. Below a critical field which depends on concentration and temperature

(H = 0.25 T at 5.5K for x = 0.022 and 1.15 T at 4K for x = 0.044) the only observed

change in the scattering is a gradual decrease in the magnetic intensity at 0.28c*,

corresponding to the development of a net moment which should contribute a ferromagnetic component at the nuclear Bragg peak positions, although this additional

contribution is too small to be observed in these dilute alloys. At H , there is an abrupt reduction by a factor of two in the intensity at 0.28c* (see figure 1),

followed by a further gradual decrease as the applied field is increased. This

result is consistent with a change in magnetic structure from the helical state to a linear modulated state in which the moments remain collinear in the basal plane but

undergo a sinusoidal modulation in magnitude along the c axis. Such a magnetic

3 transition is predicted by a spin density wave model for the system, in which the Y conduction electrons are able to support a spin density wave through the interaction

700

Figure 1 Magnetic peak intensity at 0.28c* as a function of the applied magnetic

field for x = 0.044 at T = 4.25, 10.0 and 15. OK, displaying the sharp transition to the field induced state.

34
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

with the localized Gd moments in the matrix. Such a model is able to furnish

2 semiquantitative agreement with measurements of susceptibility and specific heat . Further experiments in applied fields will be carried out to verify the precise

nature of the field-induced state.

1. J. A. Gotaas, J.J. Rhyne, L.E. Wenger and J. A. Mydosh, NBS Technical Note 1217 , 49,(1985).

2. L.E. Wenger, Gary W. Hunter, J. A. Mydosh, J. A. Gotaas and J.J. Rhyne, Phys. Rev.

Lett. 56, 1090(1986).

3. A.W. Overhauser, Phys. Rev. Lett. 3, 414(1959).

INELASTIC SCATTERING STUDIES OF VERY DILUTE MAGNETIC (SEMIMAGNETIC) SEMICONDUCTORS

T. M. Giebultowicz and J. K. Furdyna

(Purdue University, W. Lafayette, Indiana)

and

J. J. Rhyne

and

W. Y. Ching

(University of Missouri, Kansas City, MO)

and

D. L. Huber

(University of Wisconsin, Madison, WI)

1-3 Recently, it has been demonstrated that inelasic neutron scattering can be

used as a method for studying the excitation levels of isolated pairs of magnetic

ions, and for direct determination of the nearest-neighbor exchange constant J.,^- We

have applied this technique for investigating the Mn-Mn exchange interactions in a series of DMS compounds Zn, Mn S, Zn, Mn Se, and Zn, Mn Te. Several single crystal

1-x X 1~x X 1 -X X and polycrystalline samples with concentrations x=0.01-0.05 have been studied using a triple-axis spectrometer in constant-Q mode. Energy transfer between the excited

states does not depend on temperature and momentum transfer, in contrast to the

scattered intensity . Taking advantage of this property, we have carried out

measurements at various temperatures and various points in Q-space in order to

distinguish pair scattering from other possible inelastic effects (e.g., phonon

scattering). Peak corresponding to the first and second excitation levels have been

identified for most of the studied specimens (see figure 1), and in some measurements

35
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

three levels have been observed. The values of 2J.,., have been determined to be 2.8,

NN

2.1, and 1.6meV, respectively, for the three studied materials. Our result for

Zn Mn Te is slightly higher (=5^) than the earlier reported value which was based

on observation of only one excited level

before for the other two materials.

Practically,^ no reliable J.,., data existed

NN

300

250

200

(0I 150 oo

100

50

"T

1 1 r

''^

.00 1.00 2.00 3.00 4.00

Energy Transfer (meV)

5.00 6.00

Figure 1. Pair scattering spectrum for Zn Mn Se (with x = 0.0625& per weight)

showing peaks corresponding to the first and second excited level. The

dashed line is the background level.

1. A. Furrer and H. U. Gudel, J. Mag. Mag. Mat. U, 256 (1979).

2. W. L. J. Buyers et al ., Phys. Rev. B30 . 6521 (1984).

3. L. M. Corliss et al .

, Phys. Rev. B33, 608 (1986).

36
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

NEUTRON POWDER DIFFRACTION STUDIES OF LITHIUM AND

SILVER EXCHANGED ZEOLITE RHO

G. D. Stucky and M. M. Eddy

(University of California, Santa Barbara, CA)

and

D. R. Corbin, L. Abrams and G. Jones

(E. I. du Pont de Nemours & Co., Wilmington, DE)

and

E. Prince

In molecular sieve chemistry fine tuning and design of connectivity, ordering

and surface chemistry are required at the nanometer level in order to control

electronic, chemical and transport properties. The ability to manipulate channel

openings and thereby control access to the active centers has long been recognized as

a major step in achieving more selective and efficient catalysts. To establish the

mechanism by which site preference alters pore dimensions and void characteristics,

the positions of the metal atoms in the structures of dehydrated lithium and silver

exchanged zeolite rho were determined and refined using neutron powder diffraction

methods. The framework of zeolite rho, which is composed of large a cages linked by

double eight-rings, is particularly flexible , with distortions from an ideal

structure (space group Im3m) varying greatly with different cations used for charge

Figure 1 . The tetrahedral site at the center of the double-8-ring which is occupied

by cesium.

37
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

balance. Most compositions have structures with space group iHSm.

We have studied by neutron powder diffraction two samples of zeolite rho, one with the composition Si_„ ^^1^^ .-f^s, ^Li,, qCs,, ^0|,o (lithium rho), and the other with

J(.D lU.D lo ^'O 4.J5 40

composition Si__ ^Al,„ ^Na^ ^_Ag,^ oCs^ ^cO|,o (silver rho). The refined parameters

JD . r T^.j U.Uj lU.O U.UD ho

for both structures are shown in table 1. The cesium in lithium rho occupies a nearly ideal tetrahedral site in the middle of the distorted double eight ring

(figure 1). In this site it blocks the channels and also prevents any further

distortion, leaving a cell parameter at room temperature (300 K) of 1^.4925(5) A.

The cesium is very difficult to remove, but there was reason to believe that lithium

rho did not represent the limit of distortion of the framework. Silver rho was therefore prepared with very little cesium. Its lattice parameter, 14.2251(6) A, is

the smallest yet observed in any sample of zeolite rho, and the framework is

therefore the most distorted ever observed.

1. J. B. Parise, L. Abrams, J. D. Jorgensen & E. Prince, J. Phys. Chem. 88_, 2303

(1984).

A STRUCTURAL STUDY OF (Sr,Ncl)Cl_ „

Harry A. Eick

(Michigan State University, East Lansing, MI)

and

E. Prince

Anion-excess fluorite structures have been an area of research activity for

many years. In 1964 Willis, in an attempt to explain the structure of f luori te-type

UO^ postulated "Willis Clusters" . These clusters presumably developed because the

2+x excess anions relaxed from the (1/2, 1/2, 1/2) and related sites sites along <110>

and <111>. To avoid extremely short anion-anion distances, it was necessary to

postulate clusters. The cations remained fixed at (000). Subsequently, Cheetham e_t 2 al. examined by neutron diffraction (Ca/Y)F„ ,. and determined that the cluster

model was consistent with their observations. Two types of clusters designated 2:2:2

2 and 3:4:2 were postulated.

Mason and Eick^ examined by single crystal x-ray diffraction the structure of

f luori te-type (Sr/Y)Cl ^ . They observed the presence of weak non-face-centered

reflections which were not accounted for by the cluster models. The superstructure

reflections were so weak, however, that structural data could not be deduced from

them.

38
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

H Bendall and co-workers effected a single crystal neutron diffraction study of

(Sr/Pr)Cl„ .„. In contrast to Mason and Eick, they do not report the presence of

superstructure reflections. Furthermore, their report does not indicate that they even looked for such reflections! From difference Fourier sections, three features

were identified: (1) nuclear density was observed at (1/2, v, v); (2) intensity at

(w,w,w) with w = O.H was less than that at (1/2, v, v), indicative that the 2:2:2

cluster model was inappropriate and (3) nuclear density was observed at (x,x,x), x = 0.28.

As might be expected, these workers encountered refinement difficulties with

high correlations between some parameters. Furthermore, they found that the cation

appeared to be slightly displaced from (000), but their attempts to refine a displaced cation were unsuccessful.

Bendall e_t a_I^. also examined by neutron powder diffraction SrCl , Sr„ „La„ ,C1^ ,„, and Sr_ n^La^ . qC1„ .q. These specimens were prepared by quenching

O.y U.l 2. ID U.Oc: U.IO <d . \ o in water molten samples of the appropriate molar ratios sealed in dried silica

ampoules. For the analysis of the Sr. n-^Lia. , nClo -, o data five structural models

U.o2 u.lo <d . \ o were considered:

a. No anion interstitials; anion occupancy refined.

b. (1/2, V, v) interstitials, T-factors independent.

c. (w,w,w) interstitials, T-factors independent.

d. (1/2, V, v) and (w, w, w) interstitials, T-factors independent

e. (1/2, V, v) and (x, x, x) x = 0.286 interstitials, T-factors independent.

Models b and e gave R values of 8.2 and 8.3 percent, respectively. Because

Fourier sections indicated the same features as those observed for the single

(Sr/Pr)Cl2 iQ crystal, model e was considered the best model, even though it had more

parameters. Again, Fourier maps suggested that some cations were displaced from the

ideal site, but attempts to account for the displacement failed because of high

correlations between the magnitude of the displacement and the temperature factor.

In addition, these authors found a modulated background which they attributed to

interactions betweeen defects.

5 Laval and Frit reviewed the Ca., .Y F„ data and proposed a new structural

(1-x) x 2+x ^

^ model based upon an archimedian antiprism, a 4:M:3 cluster. This cluster which

contains square antipr ismatic , rather than cubic cation coordination, fits all the

previously reported data for this fluorite system and elimates some of the very short

anion distances that result from the 2:2:2 or 3:^:2 cluster. These authors suggest

that nearly identical 4:4:^1 or 4:4:5 clusters could equally well be present.

39
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

Bevan and Lawton from geometrical considerations propose for heavily doped

anion excess fluorite structures (i.e., MF , X > 2.26), regular polyhedral models

based also upon cation centered square antiprisms. They indicate that these

polyhedral models are good approximations for anion-excess fluorite structures, and

can be the starting point of successful x-ray structural refinements.

In view of these recent developments in structural models for the anion-excess

fluoride fluorite structure, it seemed appropriate that they be considered for the

strontium chloride doped systems. Furthermore, since the structural studies reported

for Sr_ ooLa^ . oCl„ ,0 indicated possible cation displacements, and since the samples

(J. o<iU. 102.10

on which the analyses was performed were quenched, it was thought that carefully

annealed homogeneous samples should be examined.

The sample was prepared by a homogeneous preparatory route. The appropriate

molar quantities of Nd (99.97», Michigan Chemical Company, principal impurity, 500

ppm Ca) and Sr(OH) 'SH (Baker Chemical Company) together with a 6x molar excess of

NH^Cl/mole of cation, were dissolved in an HCl/H solution, evaporated to dryness,

7 and thermally decomposed in accordance with the procedure described by Meyer and Ax.

The reaction product was placed in two outgassed alundum boats which were subsequently sealed under vacuum into outgassed quartz tubes. The specimens were

heated to 870° C, above the melting point of the mixture, in a MINI BRUTE furnace

whose temperature was controlled to ± 0.1° C. They were held molten for 1 hour, then

cooled to 680° C. The temperature was then decreased slowly over the course of 13

days to 400° C, then to room temperature over a 12 hour period. A sample of the

product mixed with NBS certified Si [a = 5.43062 (4) A] was examined by the Guinier

x-ray diffraction procedure. The product was cubic, with a = 6.976 (2) A. Data analysis is still in progress.

1. B. T. M. Willis, Proc. Br. Ceram. Soc . 1, 9 (1964).

2. A. K. Cheetham, B. E. F. Fender and M. J. Cooper, J. Phys. C . ^1, 3107 (1971).

3. E. Mason and H. A. Eick, J. Solid State Chem . 47, 314 (1983).

4. P. J. Bendall, C. R. A. Catlow and B. E. F. Fender, J. Phys. C . 17, 797 (1984).

5. J. P. Laval and B, Frit, J. Solid State Chem . 49, 237 (1983).

6. D. J. M. Bevan and S. E. Lawton, Acta Cryst . B42, 55 (1986).

7. G. Meyer and P. Ax, Mat. Res. Bull. 17, 1447 (1982).

40
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

THE STRUCTURES OF THE TRANSITION ALUMINAS AND THEIR PRECURSORS

R.S. Zhou and L. Snyder

(Alfred University, Alfred, NY)

and

E. Prince

The transition aluminas are a series of hydroxyl and microstructure stabilized

materials which result from heating gibbsite, bayerite or boehmite. They are not

true polymorphs of Al 0_ but rather contain varying amounts of residual hydroxyl

Ions. The hydroxyl concentration, equivalent to a loss on ignition, ranges from more than ^0% for "amorphous alumina" to less than M for the best crystallized high

temperature phases like theta and kappa. The final high temperature product is the

Irreversible transformation to alpha alumina.

The low temperature products are often called activated aluminas, in that they

have high surface activity and very large specific surface areas. These materials

are of high technological importance being widely used as catylitic substrates.

On heating the trihydroxides of aluminum, proton migration occurs, allowing the

formation of water which vaporizes. The resulting structure and the role of the

remaining hydrogens in stabilizing it are unknown. It is reasonable to speculate

that the layers Al(OH)^ octahedra lose their interconnecting hydrogen bonds first,

which induces the observed fine cracking in the material. In the first stage of

heating, the structurally ordered regions are on the order of 100 Angstroms,

rendering the material x-ray amorphous. Diffusion and ion rearrangement follows,

increasing the size of the structurally ordered regions. The reordering takes place

within the framework of the original hydroxide crystal and thus the starting material

helps determine the structure at any subsequent temperature.

Structural information is desired on these materials because of their

technological importance. However, the minimal effect of hydrogen scattering on x- ray diffraction patterns has resulted in no information on the role of hydrogen in

stabilizing these structures. This investigation is looking at a number of aluminum

hydroxides and the various deuterated transition products using neutron diffraction.

The pattern fitting Rietveld method is being used to structurally characterize these

phases. A considerable effort has been expended on xttempts to prepare the phases of

interest in a pure state. We have had success wit' eta and theta to date and have

taken neutron data on these phases. We are cur.-ently preparing the delta and kappa

phases and hope to get neutron data on these in the near future.

41
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

A neutron powder diffraction pattern of deuterated transition theta-alumina was

run on the five detector high resolution NBS Neutron dif f ractometer . This pattern

contains 1 80 independent reflections but is poorly resolved due to specimen

broadening resulting from poor crystallinity . The pattern has been refined using the

NBS version of the Rietveld refinement program in conjunction with Fourier analyses

and normal probability analyses.

Analysis of the Fourier and difference Fourier, after refinement of the x-ray

parameters, clearly shows a deficient Al site and the presence of the deuterium. The

x-ray structure has space group C2/m. The current reliability factor Rw in space

group C2/m without protons is 6.425^. Removing the mirror results in space group 02

and adding 0.135 protons per asymmetry unit produces a current residual error of

6.37?. The true space group will be established in later refinements. The hydrogen

is 1.129 Angstroms away from one of the three oxygens and about 0.6 Angstroms away

from the density deficient aluminum position. The defect configuration is consistent

with an sp2 hybridized bond to the oxygen. Other disordered positions for the

deuterium are being investigated.

The neutron diffraction pattern of a deuterated eta alumina has been recorded.

A newly proposed model is being refined using the Rietveld method with initial

success.

NEUTRON POWDER DIFFRACTION AND RIETVELD REFINEMENT OF

CERIUM ALUMINATE PHOSPHORS

G. P. Hamill

(GTE Laboratories, Inc., Waltham, MA)

and

E. Prince

The Rietveld refinement of the cerium aluminate phosphor, CeAl,_ ^0^, „^, room

temperature and 20ZK. neutron diffraction patterns indicates some structural

properties which have been anticipated but never observed or confirmed in this

material. As in the similar structures of cationic conductors (eg. lithium

impregnated Beta"-alumina battery electrodes) there is a highly asymmetric thermal

motion of the principal cation, Ce, in the plane sandwiched between the spinel

blocks. One can picture the preferred vibrations of the cerium atoms as disk-shaped

in the x-y plane with very small motion along the crystallographic "c" axis. This is an indication of a strong bonding between the cerium atoms and the nearest neighbor

oxygens in the spinel blocks. Any vacancies in nearby oxygen sites therefore occur

42
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

in the conducting plane with a corresponding anisotropic motion of the cerium

position with only ten or eleven nearest neighbor oxygens instead of the normal

twelve.

The analysis of the nearby aluminum atom in the conducting plane also shows a highly anisotropic thermal motion. In this case, however, it is needle-shaped along

the "c" axis. The site in the conduction plane has three nearest neighbor oxygens in an equilateral triangle geometry. Directly above and below this site are more stable

tetrahedral sites into which the aluminum atoms can "fall" in response to some oxygen

vacancy in a nearby site. The 20°K. data are encouraging in this respect. Since one would expect a "freezing" of thermal motion at low temperatures, the atoms are expected to reduce their motion if they are in stable sites. The aluminum atom

exhibits higher relative motion at low temperatures (assuming fixed location). The

potential for several aluminum sites - tetragonal and triangular coordination - is

high.

Further refinement will aim at checking for additional sites for the cerium and

aluminum atoms in response to local vacancy/occupancy of oxygen atom sites. A correlation between specific site vacancies and the symmetrical or asymmetrical

configuration surrounding the cerium atoms will be tested. Note that although the

data obtained at room temperature and the subsequent structure refinements may be

less clear than those at cryogenic temperatures, the samples of greater interest are those at a room temperature which provide the proper emission spectra.

In an associated research project, a more complete set of EXAFS data at both

room and cryogenic temperatures will be obtained through a Principal Research Team at

Beam Line 1 8B at Brookhaven's National Synchrotron Light Source. In this way, data

on the average crystal structure and localized site geometry will be combined to

obtain a full understanding of these structures and the effects on the emission

spectra of the two materials.

NEUTRON POWER DIFFRACTION STUDY OF THE ZEOLITES BA1SI 0,

WITH B=Cs, Rb, K, and Na

Francis W. Beech

(University College of London, London, England)

and

A. Santoro and R. S. Roth

This study was undertaken to compliment the recent investigations of Block and

Piermanini (1986) into the pressure induced phase transitions displayed by these

43
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

Table I Results of the refinement of CsAlSi 0^ in space group iMl/a cd-Ions Si and

Al disordered.

Atom

Cs

Aid)

Sid)

Al(2)

Si(2)

od)

0(2)

0(3)

R^=n.i9

a=13.67MaS

c=13.7087X

Position X y

16 0,.3824(6) Oj6324 1/8

16 0,.1576(7) 0.

ti

4076 1/8

II

32g

•1

0.118H(8) 0.6610(7)

II II

32g 0.10^7(8) 0.1382(6)

II 0.7239(7) 0.1149(7)

II 0.1297(7) 0.7132(6)

R =7

P

.91 R, =10.08 R^=4.66

B

3.76

1.31

1/2

1/6

0.5813(7) 1 .30

II »i

0.7199(6) 2.52

0.1340(8) 2.52

0.0980(8) 2.52

X=2.163

1/3

1/3

2/3

1 .0

1 .0

1.0

Table II Results of the refinement of CSAlSi 0, in space group

Al disordered.

14. /a . Si and Al

Atom Position B

Cs 16 f

Aid) II Sid) II

Al(2) II

Si(2) II

Al(3) 11

Si(3) It

0(1) 11

0(2) II

0(3) II

0(4) It

0(5) It

0(6) It

R^8.13 R 6.47

P x-rays a=13.6632

c=13.7227

Neutrons a=13.675

c=13.709

0.126(1)

0.121(1)

It

0.591(1)

It

0.659(1)

II

0.120(1 ) 0.7264(9)

0.135(1)

0.8716(9)

0.849(1 ) 0.4618(7)

R,=8.28

N

0.127(1 ) 0.662(1)

II

0,124(1 ) 0.583(1)

0.134(1) 0,667(1)

0.592(1) 0.123(2)

3.5(2)

1.3(4)

It

0.8(3)

II

1.3(3)

0.1462(9) 0.724(1) 2.3(3)

0.116(1) 0.134(1) 3.0(3)

0.725(1) 0,099(1) 2.3(3)

0.3379(8) 0.5316(9) 2.6(3)

0.9641(9) 0.120(1) 1.7(3)

0,386(1) 0,139(1) 1.3(2)

R^=4.65

c/a = 1 .004

c/a = 1 .002

X=1 .781

1 .0

1/3

2/3

1/3

2/3

1/3

2/3

1 .0

1 .0

1 ,0

1 .0

1 .0

1 .0

44
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

materials. Their results have reopened the controversy concerning the basic

structural arrangements in these materials. This problem is exemplified in the

Cesium case by the inability to reconcile the observed optical birefrigence with the

cubic space group suggested for the material by Newman. Due to the multile twinning

displayed in single crystals of these materials powder neutron diffraction data was

were collected on the instrument BT1 which was subsequently analysed using the

Richield technique.

The Powder samples were synthesised by means of a soft-gel technique. The

reactants A1 (i(C3H„0)_, Si (C_H^0)4 and the alkali metal acetates were obtained from

commercial sources and used without further purification. Due to the hydroscopic

nature of some of the materials considered in this study all operations were

conducted either in an argon atmosphere drybox or under argon purge. It was

discovered that the tetraethyl onthesillicate has a significantly lower hydrolyis

rate than the other reaction components and this factor resulted initially in

diphasic materials. The key to obtaining single phase materials in this case lie in

prehydrolysing the tetraethyl on the silicate. The single phase amphorous gels

produced by this route were crystallised by subsequent heat treatments and the

crystalline powders were characterised by x-ray techniques.

The neutron data for the cesium material were analysed in the cubic space group

laSd suggested by Newman and the deniative tetragonal space groups 1^1 /acd and I4l/a.

Significantly not all peaks in the data set could be accounted for in the cubic

setting which rules the possibility out. The final values for the refinements in the

tetragonal settings are reported in Tables 1 and 2.

In the case of the rubidium and potassium analogues refinements to differentiate

between the tweo tetragonal possibilities clearly showed that the space group for

these materials is lH^/a. All the above results are being prepared for publication.

The above refinements were postponed using the assumption that the framework

Al/Si were statistically distributed over the possible crystallographic positions.

Attempts to induce ordering of these ions into the refinement have so far met with

little success due to the apparent insensitivity of the space group to ion ordering

in the framework. Work is continuing on this intriguing problem. Work is also in

progress to relate these synthetic materials with their hydrated geological

equivalents in an attempt to understand the role of absorbed water molecules in

etermining the observed molecular structure.

45
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

BISMUTH VALENCE ORDER-DISORDER STUDY IN BaBiO BY POWDER

NEUTRON DIFFRACTION ^

C. Chaillout and M. Marezio

(Laboratoire de Cristallographic, Grenoble, France)

and

A. Santoro

and

J. Remeika

(AT & T Bell Laboratories, Murray Hill, NJ)

Two structural arrangements have been shown to exist for the perovskite-like

compound BaBiO by powder neutron diffraction data. The first is characterized by a 3+5+ partial (75%) order of the Bi and Bi cations on the two crystallographically

independent sites, while in the second arrangement the two cations are almost 1005S

disordered. The structure of eleven differently-prepared BaBiO samples showed that

the deciding factor for obtaining one or the other arrangement is the temperature at

which the sample is prepared or subsequently heat-treated. On the contrary, the

cooling rate and the atmosphere (air or oxygen) do not seem to be important

parameters. DTA measurements indicated that BaBiO undergoes an additional phase

transition at 860°C on heating and 8lO°C on cooling. This transition probably

3+ 5 + corresponds to the disproportionation of the Bi into Bi and Bi cations. This

conjecture explains why the heat-treatment at 800°C yields compounds containing

partial cation ordering. Since the symmetry is cubic above and below the 8lO°^G

transition, the 75^ ordered BaBiO stable between 8lO°C and ^80°C would contain a trigonal dynamical distortion which would be the precursor of the static trigonal

distortion which takes place at ^80°C. In every compound the partial ordering is

always 75/S . This has been interpreted as an indication that an additional ordering

of Au Cu type could exist on the two Bi sublattices.

STUDIES OF TITANIUM ALUMINUM ALLOYS

R. M. Waterstrat

(American Dental Association Health Foundation Research Unit)

and

E. Prince

The phase diagram of the titanium-aluminum system is complex near the Ti rich

end, and it has proved difficult to determine it unambiguously because precipitates

of low temperature phases form rapidly even when the sample is quenched from high

46
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

temperature. Because of the negative scattering amplitude of Ti for neutrons,

neutron powder diffraction is well suited to the study of these alloys. A vacuum furnace has been constructed to enable powder diffraction measurements in situ at

temperatures up to 1200°C, and samples of Ti-Al with compositions ranging from U to

45 atomic percent Al have been studied at 900°C and 1000°C. 145S and ]6% samples have

the disordered a-Ti structure at both temperatures. At 205^ Al the superlattice lines

of ordered Ti Al are present. The sample with composition 825J Ti - ] 8% Al was

particularly interesting. At 900°C, well crystallized Ti Al is present. At 1000°C

the diffraction pattern is very weak, although the composition is a long way away

from the "null matrix" composition. This may be due to short range order, which can produce a large "effective temperature factor".

1. R. D. Shull, A. J. McAlister and R. C. Reno, Proceedings of the Fifth

International Conference on Titanium (1984).

TEXTURE MEASUREMENTS IN DEFORMED METALS

USING NEUTRON DIFFRACTION

R. C. Reno

(University of Maryland - Baltimore County, Baltimore, MD)

and

(National Bureau of Standards, Gaithersburg, MD)

and

R. J. Fields

(Fracture and Deformation Division)

Since crystallographic texture in deformed metals has a profound influence on mechanical properties, methods which quantify texture are extremely useful. Using a four-circle neutron dif f ractometer at the NBS Reactor, we have begun a study of

texture in several materials, including copper rods, high-strength low alloy (HSLA)

steel, and rolled 5052 aluminum sheet. The dif fractometer is used to generate pole

figure data (see figure 1 & 2) which can be analyzed to determine preferred

crystallographic orientation in each specimen. The advantages of using neutron

diffraction to create pole figures stem from the deep penetration of neutrons into

metallurgical samples. This is especially important when one must examine samples

which cannot be made thin enough for x-ray pole figure studies or which contain large

grains or large-scale inhomogeneities. The use of neutrons for texture studies does,

however, have its drawbacks. Neutron measurements are slow and expensive and must be

47
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

CU (111) Sample 4-C CU (200) Sample 4-C CU (220) Sample 4-C

Remo-Texture Measurements.

Figure 1. Neutron pole figures for creep-cavitated copper. These show that [100]

and [111] directions are aligned preferentially along the rod axis. Also,

[111] texture is stronger than the [100] texture.

[100] [111]

Remo-Texture Measurements.

Figure 2. Neutron pole figures for 5052 rolled aluminum sheet. [100] directions are predominantly parallel to the rolling and transverse directions.

48
REACTOR RADIATION DIVISION AND COLIABORATIVE PROGRAMS

carried out at a reactor. When rapid determinations of texture must be made, perhaps

on materials still on a production line, an alternative is desirable. In these cases we rely on ultrasound velocity measurements to provide texture information. Since,

however, ultrasonic propagation is sensitive to sample inhomogeneit ies as well as texture, it is essential that results from both techniques be compared before the

structure of a sample is fully understood. Figure 1 shows pole figure data for

copper rods that have been subjected to low tensile stress at high temperatures. An

analysis of this data indicates that the fiber texture of these rods consists of a mixture of [111] and [100] orientations along the axis, approximately a 72?

contribution from the [111] orientation. This data is useful in understanding the

ultrasound velocity measurements which, in this material, are sensitive to voids.

Figure 2 shows pole figures for rolled 5052 aluminum sheet. It can be deduced

from the figures that most crystals are oriented so that [100] directions are

parallel to the rolling and transverse directions of the sheet. A fit of the pole

figures to an expansion in spherical functions up to order J, = 4 gives w2 coefficients as follows:

w = 0.122 ± 0.006

400

w, = -0.022 ± 0.006

W440 = °-°'3 ±0.007

1

.

H. M. Ledbetter and R. J. Fields, submitted to Acta Metallurgica

2. Ryong-Joon Roe, J. Appl. Phys. 37, 2069 (1966)

MICROSTRUCTURE STUDY OF AGE-HARDENED U - 0.75MT% Ti ALLOY

C. S. Choi and H. J. Prask

(U. S. Army Armament R&D Center, Dover, NJ)

and

(National Bureau of Standards, Gaithersburg, MD)

It is well known that heat treatment (i.e. quenching and subsequent aging) of

depleted uranium alloys increases the mechanical strength of the alloys through

precipitation hardening. This study is aimed at understanding the mechanism of the

precipitation hardening (or aging) by characterizing the crystallographi c and

microstructural properties of the alloys as function of aging amount. The cast ingot

of depleted uranium alloy containing 0.755^ titanium was hot rolled to a plate form

with a thickness of approximately 0.2 inches, about ]0% reduction at each step, in a

49
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

Table 1. Sample preparation data.

Samples were prepared in the following sequence.

Cast ingot, hot rolled to 0.2" in 10% steps, T-phase treatment at 800C for

3 hours, water-quenched, cold rolled (1 -2%) and then aged.

Samples aging dosages hardness(HRC)

No. 1 no aging 31.9(M)

No. 2 500C / 10^ sec 38.0(10)

No. 3 500C / 10^ sec 52.3(8)

No. n 550C / 10^ sec 52.3(6)

NO. 5 550C / 10^ sec 43.6(18)

No. 6 600C / 10^ sec 38. M6)

No. 7 pure uranium

vacuum oven. The plates were homogenized at 800C for 3 hours and quenched in water,

and then cold-rolled and cut to platelets of approximately 2 x 10 x 30 mm size. The

platelets were divided into six groups, and aged differently as shown in table 1. The

hardness of the aged alloys was measured for one of each group using a Rockwell

Hardness Tester. The results are included in table 1.

1. Neutron Powder Diffraction (wide angle) Measurement

The diffraction patterns of the aged samples, measured by the multi-detector

high resolution dif f ractometer , showed a two phase structure consisting of a-U and

U Ti. Therefore the refinements were performed in two steps: the first step was the

normal Rietveld refinement for the uranium phase, excluding the regions of the deltaphase peaks; the second step was a delta-phase refinement for the whole pattern using

a multi-phase Rietveld refinement program. The structural parameters of a-U as obtained in the earlier study was used for all samples throughout the refinements.

The width function parameters, unit cell dimensions, and preferred orientation

parameters of the uranium phase and other profile parameters including backgrounds

were refined in the first step. In the second step of the refinement (i.e., two-phase

refinement), the scale factors of the two phases were determined, with all other

parameters as obtained in the first step kept unchanged, using the entire profile.

The scale factors obtained by this multi-pattern refinement were used for the

determination of the delta-phase concentration. To examine the trend of lattice

distortion as a function of the heat treatment, the b-axis lengths and the unit cell

volumes were normalized to the corresponding value of a-phase as-cast DU (DUAC)

alloy, i.e. b = 5.8537(2), V = 83-17(1), and plotted as a function of aging. The two

curves showed essentially an identical aging-dependence: both parameters are reduced

50

i
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

after the Y-quench; further shrinkage occurs in the initial stage of aging; maximum

3 shrinkage occurs at the aging dosage of sample No. 3 (10 sec. at 500C); expansion

occurs with subsequent aging.

2. Neutron Small Angle Scattering Study

The SANS facility at the NBS reactor was used for the study of the particle

size distribution of the precipitates (or aggregate) and the internal structure of

the aggregate. Since the wavelength spread and the angular spread of collimators are

the two main factors of the instrumental resolution, the uncertainty of distance

determination (or size uncertainty) becomes;

Ar = 2tt{(AX/X)^ + (ilTrA0/XQ)^}^ ^^/Q (1).

Since the size uncertainty is inversely proportional to Q, the SANS intensity

function I(Q) of an aggregate should show the characteristics of a homogenious

density particle at the lower Q region. The characteristic scattering of the internal

structure occurs only at higher Q region where Ar is smaller than the individual

element of the aggregate. To study the overall size of the aggregate and the internal

structure of the aggregate, the measurements were made in two ways; the lower Qranges (.007 < Q < .08) using 9A wavelength neutrons for the former and the higher Qranges (.01 < Q < .15) using 5A neutrons for the later.

a. Particle Size Distributions

We assume that the scatterers are globular particles in the Q-ranges below the

crossover point, and hence the scattering intensity distribution of 9A neutron

measurement obey Gulnier's law. A multi-group guinier particle model;

(do/dfi) = KZ(n.p^v.^exp(-R^Q^/3)) (2)

was used for the analysis of the particle size distribution. The least-squares

2 2

parameters determined were the amplitude A. (= Kn.p v.) and the radius of gyration

R.. Four different size-groups were required to describe the entire scattering

profile for each sample. The distribution of the particle sizes obtained were quite

similar between the five aged samples, ranging between 20A - 31 A, 58A - 76A, 1 1 6A -

140A, and 239A - 286A, respectively, for the four size-groups. Therefore, the size

distributions were reanalized using an identical set of size-groups (20A, 60A, 130A,

and 260A ) for all samples. Then the amplitudes of the four particle sizes were

refined simultaneously by the non-linear least squares method. The particle-size

51
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

100 150 200 250 Radius in Angstrom Units

300

Figure 1 . The particle size distributions (volume fraction vs Guinier radius) of the

delta-phase precipitates in the aged samples, as obtained by SANS study

with 9A neutrons.

distributions thus obtained are shown in figure 1, The amount of the smallest

particles of the precipitates increases with aging until it reaches a maximum at

sample #4 (550C/1 GOOsec) , then it decreases with increased aging. On the other hand,

the concentrations of the larger size-groups increase monotonically with increased

aging. The number of precipitate particles increases rapidly up to sample No. ^ and

then gradually decreases with increasing aging. This analysis also supports the twostage aging model derived from the crystallographic parameters,

b. Fractal behavior

The intensity distributions of 5A neutron measurement were plotted as log(I) vs log(Q) to search for straight lines at the higher Q-ranges up to experimental Q limit

-1

(0.15A ). The exponent of the power-law was determined from the slope of the

straight line obtained by the least-squares fit to the log-log data within selected

Q-ranges (by visual estimation). The results are shown in table 2. The Porod regions

-1

(D = 4) have not been observed up to 0.15 A (the experimental Q limit) for any of

the five samples. If the distributions represent the power-law property of a fractal,

the observed fractal dimensions of the five aged samples are about 1.5 for sample #2

and then becoming gradually larger with increasing aging to about 2.4 for sample #6, as shown in table 2.

3. The effect of the temperature gradient by rapid quench.

In the quenching of a large cylindrical uranium alloy sample, the outer surface

cools first while the interior remains hot because of the finite thermal

conductivity. This temperature gradient creates a radially varying residual stress

52
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

Table 2. The fractal dimensions D, the Q ranges and the chi-squares of the

refinement for the aged DU samples, as determined by the power-law

properties of fractals.

1 Sample D Q . (A ') min

Chi

2 1 .51 (1) .08 - .15 4.23

3 1 .8M(1) .085 - .15 3.54

M 2.03(1) .07 - .15 3.65

5 2.24(1 ) .06 - .15 2.85

6 2.39(1) .06 - .15 2.81

distribution with highly compressive tangential and axial stresses in the outer

surface and tensile stress in the interior, and causes a void formation in the

interior of cylindrical alloys. An additional concern for specimens of radius greater

than =1 cm is the uniformity of the Y to a' conversion throughout the sample, because

of the quench-rate difference by positions.

A thin, disk-shaped sample, 24mm diameter and 2mm thichness, was obtained from

a 33 mm diameter gamma-quenched U - 0.75wt^ Ti alloy rod. To search for any evidence

of delta-phase formation in the sample, an x-ray powder diffraction pattern was measured from 5 to 70 in scattering angle, using Mo-K radiation. The diffraction

a pattern revealed clearly the UO peaks but no trace of TiU„ compound.

Subsequently, SANS measurements were conducted on this sample at four different

radial positions of the disk, at R = 0, 3, 6, and 9mm. The sample was mounted

perpendicularly to the incident beam (5.5A wavelength) with a beam cross-section of

6mm diameter. The scattering intensities at the four positions were measured under

identical conditions including the monitor counts. The result indicated that the

scatterer size distribution could be represented by three particle-sizes,

approximately 6, 22, and 44A, for the two outer positions, and by four sizes which

included 100A particles in addition to the above three sizes. Probably the three

smaller particles are combination of UO particles and the lattice dislocations, and

the 100A particles are voids.

53
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

STRUCTURE FACTOR OF HE-4 IN THE VICINITY OF THE GAS-LIQUID PHASE TRANSITION

B . Mozer

and

B. LeNeindre

(Laboratoire des Interactions Moleculaires et des Hautes Pressions,

CNRS, Universitaire Paris Nord, France)

and

B. Farnoux

(Laboratoire Leon Brillouin, Centre des Etudes Nucleaires - Saclay, France)

The structure factor of He-4 in the region of the gas-liquid antical point has

been measured by neutron scattering for small wave vector differences, q = 4TTSin0/2,

and at large wave vector differences. These measurements provide the data which can permit an evaluation of the cross-over behavior between large and small wave length

fluctuations as described in the modern theories of critical phenomena.

The sample all was designed and built at NBS to fit onto an I.L.L. type

cryostat in use at Saclay. The cell was in an adiabatic configuration and from our measurements of the thermodynamic behavior of the system, we could ascertain a temperature regulation of 1 - 2 yK around the critical point T = 5.2 K. This

regulation was measured by a calibrated NBS germanium thermometer kindly furnished to us by E. Pfieffer of the Temperature Division. Other resistance thermometers were

used to measure the temperatures at various parts in the cell. The density of the

behavior was measured via the capacitance of the liquid and evaluated from published

thermodynamic data. Our preliminary diffraction data was obtained mostly for reduced

temperatures below the critical point and one point above the critical point.

Neutron diffraction data was taken at 5, 8, and 15 A at the small angle spectrometer,

PAXY, and at 5 A on the banana detector spectrometer in the guide hall. These

-3 -1 -1

measurements cover a q range from 0.001 x 10 A to 0.25 A for the small angle

-1

measurements and from 0.2 to 2.5 A for the banana detector. Figure 1 shows the log

of the intensity versus log q for all our measurements except at the smallest angles.

The regions of overlap are evident from the figure. The structure factor is

normalized so as to be unity for very large q and corresponds to a reduced

-4

temperature of t = (T - T )/T = -0.5 x 10 . Figure 2 shows the data including that

at the smallest q values and part of the data obtained with the banana detector.

We have found from our data a value for the compressibility exponent, Y = 1.158

if we take the accepted value of the exponent for the correlation lengths, v = 0.63.

We also find that the ratio of the prefactors for the correlation length at

temperatures above the transition to that below the transition to be

54
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

-4.1 -3.6 -3.1 -2.5 -2.1 -1.6 -1.1 -0.6 -0.1 0.4 1.0

ln(q = 47rSing ) A

Figure 1. Ln intensity vers_us in q for the structure factor of helium at T = (T - T )/T = -2.5 X 10 . All the data taken is represented here except that

for tne smallest q values.

0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0

q = 47TSin0/A

Figure 2. Singular contributions to scattering, I (q), as regulated by dispersion in

af c = 0.04, c = 0.45, 0.37, 0.29,

0.21. b) c^ = 0, c, = 1 - c and c = 0.5, 0.6, 0.7, 0.8.

2 1 S S

wavevector pool, with Ak = k/20

R = 5 /C

o o 2.401 .14

= 2.11 .

We are in the process of analyzing this data to determine the cross-over region and

other critical exponents.

55
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

THE STRUCTURE FACTOR OF LIQUID HE-4 AT SMALL ANGLES FOR SEVERAL TEMPERATURES

B. Mozer

and

B. LeNeindre

(Laboratoire des Interactions Moleculaires et des Hautes Pressions,

CNRS, Universitaire de Paris Nord, France)

and

B. Farnoux

(Laboratoire Leon Brillouin Centre d 'Etudes Atomiques - Saclay, France)

Preliminary small angle neutron scattering experiments were performed at

Saclay on a sample of liquid He-4 at the liquid-gas phase transition, the Atransition, and temperatures between these transitions. The sample cell in adiabatic

configuration was designed and made at NBS. The sample cell was attached to an insert for an I.L.L. type cryostat in use at Saclay. Temperature regulation was in

the range of 1 - 3 yK using an NBS calibrated germanium resistor and carbon resistors

for secondary thermometers. The thermodynamic states of theHe-4was determined by

measuring the capacitance of the helium and converting this to the density via the

Clausius-Mosotti equation, knowing the temperature, and using published thermodynamic

data of other workers.

The neutron diffraction data at small angles was obtained on the PAXY

spectrometer at Saclay using 3, 5, 8 and 15 Angstrom neutrons in order to cover a

-1

range of wave vector differences from q = 0.0008 A to 0,25 A

The most striking results away from the phase transitions and nearer to the X transition is shown in Figure 1 where we observe the structure factor to decrease

from its value at q = 0, which can be determined from thermodynamics, to almost zero

-1

at q = 0.06 A and then rise again.

This behavior of the structure factor explains our difficulty in attempting to

measure the quasi-elastic scattering around the A-transition using the spin-echo

spectrometer at I.L.L. in collaboration with F. Mezei. The spin-echo experiments

were performed at the smallest of q values for that machine and unfortunately they

lie in the region of the hole in the structure factor.

There has been no other measurements of the structure factor in this region of

q-space and all other measurements have suggested a smooth liner extrapolation of

other data from the smallest q's measured, 0.16 A to the value at q = given by

thermodynamics. Our preliminary measurements indicate the occurence of possible

oscillatory behavior of the structure factors at small q values. We are proposing

additional measurement to see just how the small angle scattering joins the

56
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

have been documented so that the database can readily be implemented on several

international on-line systems.

To permit scientists to use the database, we are developing software tools that can be distributed with the database or used to search the database on-line at a central site. NBS software (NBS*LATTICE) , which is an integral part of the CRYSTAL

DATA Distribution Package, is designed to carry out a variety of functions. With the

lattice-matching program function, an unknown compound can be identified by

comparison of its lattice with those in the database. The required lattice

parameters are determined using x-ray or neutron diffraction techniques. The

lattice-matching method offers and excellent way to characterize solid-state

materials and is now being used at NBS, in industrial analytical laboratories, and

crystallographic data centers. Currently a concerted effort is being made to extend

the method to analyze data obtained from electron diffraction experiments.

Using the on-line NRCC-NBS CRYSTAL DATA Search System, the database can be

accessed by scientists worldwide. This system integrates scientific with database

management software. The scientific software has been expanded to facilitate its

application to materials analysis and design. All key data elements can be searched

and answers to queries can be obtained using highly efficient Boolean type search

strategies. Statistical analyses for all of the data items, and combinations of

items, can readily be carried out. During the year, this system has been used by

scientists to solve a variety of problems in chemistry and solid-state physics.

On-line demonstrations of the System at scientific meetings have been well attended.

Future efforts of the Crystal Data Center will focus on several areas of

activity. First, in 1987 the next version of the NBS CRYSTAL DATA Distribution

Package will be released. Both the database and the software components of this

package will be upgraded. The database will be expanded and will include ~1 15,000

entries with 1.7 million data records. Each entry will include all data types that

are input or created by the NBS*A1DS83 program. All of the data will be used to

upgrade the on-line NRCC-NBS CRYSTAL DATA Search System. Second, minerals data will

be processed and evaluated in order to produce a comprehensive minerals subfile with

at least one entry for each known mineral. Third, research will be carried out,

scientific software will be developed, and scientific papers on CRYSTAL DATA products

will be written.

57
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

previously measured part of the structure factor for q ^ 0.16 — as well as to try to

pin down the behavior of the smallest q values.

-2.0

-I 1 1 1 1 1

1 1 r

6.4

5.2

*

* *

*

4.0

* • «

2.8

«

1.6

I \

0.4 -

0.8 _

J I I l_* I L. J L

0. 0.16 0.32 0.48 0.64 0.80 0.96 1.12 1.28 1.44

Q X 10-^

Figure 1 . The long of the intensity of the small angle scttering from liquid He-4 at

3K for 5 A - * and 8 A - • incoming neutron beams versus the wave vector

difference q = 4it sin0/A. The decrease in the scattering to almost zero

in the region 0.06 A has been shown by us in a number of measurements at

different temperatures not near the liquid-gas phase transition.

CRYSTAL DATA CENTER

A. D. Mighell, J. K. Stalick, and V. H. Himes

The Crystal Data Center is concerned with the collection, evaluation, and

dissemination of data on solid-state materials. The Center maintains a database

which includes chemical and crystallographic information on all types of substances

with known unit cells. The materials fall into the following categories: inorganics,

organics, organometallics, metals, intermetallics, and minerals. For each substance,

there are a variety of input and derived data parameters including: the conventional

and reduced cell parameters, the space group, the compound name and formula,

calculated and observed densities, literature reference, and critical comments.

During the year, the database has been significantly upgraded and expanded with

respect to the number of entries and the number of records per entry. The database

now contains more than 100,000 entries with an average of fourteen 80 character

records per entry. Detailed specifications and definitions for all of the data items

58
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

NEUTRON ACTIVATION AUTORADIOGRAPHY STUDY OF PAINTINGS

Y. T. Cheng and J. S. Clin

(Smithsonian Institution, Washington, DC)

and

M. Ganoczy

The Smithsonian Institution initiated a project to study by neutron induced

autoradiography and gamma spectroscopy the works of painter Thomas Wilmer Dewing

(1851 - 1938) in the National Museum of American Art as well as selected key

paintings from other locations. Of special importance to the Smithsonian

Institution, due to his representation by 24 works at the National Museum of American

Art and U2 works at the Freer Gallery of Art, Dewing was a significant turn of the

century painter, and a noted member of "The Ten" American Impressionists.

Neutron induced autoradiography stands alone as the only available technique

that allows the observation of multiple pigment applications beneath the surface of an oil painting. It offers the art historian, therefore, an unparalleled opportunity

to observe the working method of an artist, quite literally, from the ground up.

Previously dependent upon the x-ray radiograph and documentation external to the

canvas, such as related sketches, surviving letters, and diaries, the art historian

now is able to witness firsthand the artist's creative process as it moves from the

preliminary drawing to the subsequent paint layers comprising the final image. The

pigments used by the artist are also of special interest, and can, in part, be

determined from the gamma ray energy spectra measurements conducted simultaneously

with the autoradiography process.

This study will provide unique information on each individual painting

examined, and establish a standard against which other works by the artist can be

compared in the future. The range of works autoradiographed , as well as their

distribution throughout Dewing's career, will provide the necessary scope or base for an accurate overview of his working methods. The results can lead to further studies

of the artist's technique to include investigations of the pigments and painting

media used. While extensive pigment studies have been done on European paintings,

less investigation has been conducted on American works of art. The research will

contribute to our knowledge of pigments used in this country. The results can be

applied to future autoradiographic studies of works by Dewing's contemporaries and

perhaps, ultimately, a body of information will be established illustrating the

working methods and pigments used by American painters.

59
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

Thomas Wilmer Dewing was member of "The Ten American Painters", a group of

artists who banded together In 1898 and subsequently have been associated with the

impressionist movement In America. Dewlng's colleagues in "The Ten" Included William

Merrltt Chase, Wlllard Metcalf , John H. Twachtman, J. Alden Weir, Chllde Hassam,

Robert Reid, Frank Benson, Edmund Tarbell and others who are now considered major

figures In late nineteenth century American Art. Today the works of these artists,

Dewing Included, are widely exhibited, bring large prices and are subjects of

catalogues raisonne. Dewlng's oeuvre , which include oils, pastels and sllverpoints

,

is relatively small. Such comparative rarity has driven sales of his work to very

high princes while his exquisite paintings and sensitive drawings are sought by

collectors and museums alike. In addition to the significant holdings at the

Smithsonian Institution, Dewing is also represented at the Metropolitan Museum of

Art, New York City; The Museum of Fine Arts, Boston; The Philadelphia Museum; The

Detroit Institute of Fine Arts; The Terra Museum and the Art Institute, both in

Chicago; and smaller institutions across the country.

Interest in applying the neutron induced antoradiography method to the works of

Thomas Wilmer Dewing (1851 - 1938) first arose when the artist's canvas Toblt and the

Angel (1887, Metropolitan Museum of Art) was lent to Brookhaven National Laboratories

for autoradiography in 1975. While x-rays revealed little more than the structure of

the ground, autoradlographs recorded the dramatic changes that occurred while the

painting was being executed. The Metropolitan Museum's subsequent autoradiography of

works by Rembrandt, Van Dyck and Vermeer demonstrated that a full understanding of an artist's methods could only be achieved by studying a series of works systematically.

Collaboration between the art historian and the scientist in interpreting the

data generated was proved to be a crucial aspect of the Metropolitan Museum of Art's

project. Likewise, this study will require similar effort.

Thus far eight works by Thomas Dewing have been autoradlographed using the NBSR

facility, four during the past year, as part of an on-going research project, most of

which show that the artist employed significant changes In his compositions.

Moreover, several reveal extensive overpainting. As the latter have darkened under

the brown and black pigments, it is only through autoradiography that the original

design can be seen. The study and visual presentation of Dewlng's distinctive and

complex type of paint application can be facilitated by means of autoradiography.

Autoradlographs of Tobit and the Angel (1887, Metropolitan Museum of Art), Lady

with a Rose (catalogued 1924, National Museum of American Art), The Duet (1922,

Kennedy Galleries and Edward Sheln), A Nude (catalogued 1922, Akron Art Museum),

60
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

Portrait of Mrs. Houston (1880, National Museum of American Art), have revealed these

various aspects of Dewing's work. They indicate that Dewing altered his compositions

in most of the paintings studied thus far. Details of the alterations are not

apparent in the x-ray radiographs. Often the information is obscured by the canvas

weave and the supporting structure. Figure 1 is a picture of the painting, A Nude as we see it today and figure 2 shows the corresponding x-ray radiograph. For

comparison, figure 3 is the fifth autoradiograph of A Nude representing distribution

of pigments containing manganese; figure 4 is the sixth autoradiograph showing the

area of sodium containing pigments and figure 5, the ninth autoradiograph, shows the

distribution of cobalt containing pigments. These figures demonstrate that neutron

induced autoradiography is more than a complementary technique to conventional x-ray

radiography for painting examination and study.

Thomas Dewing's working methods are complex. Each of the five paintings that

have been autoradiographed appear to have been constructed in a different manner.

For example, A Nude , as in figure 5, was begun with line drawing; Lady with a Rose , (figures 6 and 7) was begun by blocking the background around the figure and the

Portrait of Mrs. Houston (figures 9 and 10), was painted premier coup with no preparatory drawing at all. The original pose of Lady with a Rose , revealed by the

autoradiography process, shows a placid figure with folded hands, a youthful face

with upturned nose, high cheekbones and a demure cap of hair (figure 7).

Subsequently overpainting the work. Dewing made the sitter more animated by raising

her arm. He further added an element of sophistication by giving her an aquiline

profile. The autoradiographs also delve below the deceptively smooth surface of the

painting to reveal its structure. He laid in the initial background hue with rough

palette knife marks that were blocked in around the figure (figure 3). Subsequent

strokes of another pigment were placed in another direction in order to soften and

smooth the underpainting . The final effect of the first version was a precisely

rendered figure surrounded by a shimmering, mottled atmosphere. The remarkable

similarity of the underpainting to The Garland (figure 8), a well documented painting

by Dewing at the Freer Gallery of Art, assisted the art historian in suggesting a date of 1916 for the original painting underneath Lady with a Rose.

61
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

Figure 1. A NUDE, oil on panel, 10.5" x 13.5"

Figure 2. X-ray radiograph of A NUDE,

62
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

Figure 3. Fifth autoradiograph of A NUDE, taken 3 hours after painting

activation.

Figure 4. Sixth autoradiograph of A NUDE, taken 1 day after painting

activation.

63
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

Figure 5. Ninth autoradiograph of A NUDE, taken 20 days after painting

activation.

Figure 6. LADY WITH A ROSE, oil on canvas, 24" x 20"

64
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

Figure 7. Seventh autoradiograph of LADY WITH A ROSE, taken 10 days after

painting activation.

Figure 8. THE GARLAND, oil on canvas, 25" x 19".

65
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

Figure 9. PORTRAIT OF MRS. HOUSTON, oil on canvas, 19.5" x 14.5".

Figure 10. Fifth autoradiograph of PORTRAIT OF MRS. HOUSTON, taken 3 hours

after painting activation.

66
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

ADVANCED NEUTRON METHODS

1 . Small Angle Neutron Scattering (SANS)

The SANS instrument operated virtually without interruption during the past

year. A record number of scientists (60) from government, university and industrial

laboratories and eight NBS Divisions used the facility for experiments in polymers

(41$), metallurgy (17$), chemistry and physics (^2%), magnetism (11$), ceramics (9%)

and biology (7%), where the percentages give the distribution of beam time in each

area. Included in these totals are the first proprietary measurements carried out on

the facility, by Eastman Kodak Company and IBM Almaden Research Laboratories, in

which the full costs of operating the facility are borne by the users' laboratory in

accord with recently established NBS guidelines. In the following paragraphs, some

of the past year's SANS highlights are briefly noted. In many cases more complete

summaries of the work alluded to can be found in articles elsewhere in this report.

The first application of SANS to characterize the adsorbate structure in

chemically modified microporous particles used in chemical separation and processing

has been carried out by the Reactor Radiation (C. Glinka), Ceramics (W. Haller) and

Organic Analytical Research (L. Sander) Divisions. Using contrast variation

techniques, dramatic scattering signals from the adsorbate phases have been observed

which are directly related to their conformation on the pore surfaces of the

particles. In a closely related effort, researchers from Exxon (S. Sinha and J.

Huang), the University of Delaware (S. Satija), and the University of Maryland (H.

Stanley) have conducted measurements on binary fluids entrained in porous media to

investigate the onset of preferential wetting and the effects of the pore structure

on the miscibility of the fluids.

The tendency of low concentrations (~0.5$) of hydrogen in a-Pd to cluster under

the influence of large internal stresses was convincingly demonstrated in a collaborative effort (J. Rush and C. Glinka) with the Max Planck Institute (R.

Kircheim) . Characteristic cluster sizes of about 100 A were observed in mechanically

deformed Pd foils while no evidence for clustering was seen in strain-relieved foils;

a result with significant implications for studies of hydrogen embrittlement

.

Scientists from General Electric's Advanced Materials Laboratory (C. Austin and

R. Darolia) used SANS to monitor the effects of extended exposure to high

temperatures on the microstructure of single-crystal, superalloys being developed as turbine blade materials for advanced aircraft. These measurements were successful in

correlating a drop in stress-rupture strength of certain alloys, containing a few

percent rhenium, with the formation of an unwanted phase of small, incoherent

67
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

precipitates. The relationship between precipitate size and distribution and the

mechanical strength of real engineering alloys was also the subject of SANS

measurements by C. S. Choi and H. Prask, of the Army's Materials Corammand, who

examined uranium-titanium alloys, and of R. Fields (Fracture and Deformation

Division) who analyzed copper-rich precipitates in high strength, low alloy steels.

In a fundamental study of the kinetics of precipitate formation, M. Chisholm

(Carnegie-Mellon University) followed the earliest stages in the growth of cobalt

precipitates in CuCo binary alloys for comparison with computer molecular dynamics

simulations of the precipitation process.

Through the use of deuterium labeling to highlight the network structure in

epoxies, W. Wu and B. Bauer of the Polymer Division have recently obtained

significant results regarding the molecular modes of deformation in strained epoxies.

They have observed in epoxies with short crosslink spacings typical of commercial

materials that there is essentially no change in the average crosslink distance in

samples strained up to 30^. This remarkable result suggests that the macroscopic

deformation is controlled by some type of defect motion, analogous to the way

dislocations determine strain in metals.

The interest in developing low-temperature processing routes to achieve high

density ceramics has prompted K. Rhyne and T. Coyle of the Ceramics Division to use

SANS to study the first stages of the polymerization of silica in solution. By

chemically controlling the rate of aggregation, they have been able to observe and

characterize the cluster growth in real time.

The magnetic correlations which characterize the spin glass state continue to

be central to recent SANS measurements in magnetism. P. Mangin (Institut LaueLangevin) and J. Rhyne have recently measured the concentration, temperature and

magnetic field dependence of the magnetic scattering in the reentrant spin-glass,

amorphous FeCr. They find that below the spin-glass transition temperature the

scattering can be separated into two components, the Lorentzian-shaped component and

a Lorentzian-squared component. Furthermore, the Lorentzian-squared component, but

not the Lorentzian component, depends on whether or not the sample has been cooled in an applied field, an observation that gives new insight into the physical origin of

the correlations in the spin glass state.

The chain conformation in new varieties of polymer blends and microphase

separated block copolymers has been systematically measured by C. Han (Polymers

Division) and several collaborators. Han and coworkers have also studied the

fluctuations in semidilute solutions of polystyrene that are precursors to gel

formation in an effort to better understand how the gelation may be controlled.

68
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

SANS STUDY OF CHEMICAL ADSORBATES BOUND TO PORE SURFACES

C. J. Glinka and N. F. Berk

and

L. C. Sander

(Center for Analytical Chemistry)

and

W. Haller

(Ceramics Division)

Previous work on the characterization of microporous silica particles by small

angle neutron scattering (SANS) has been extended to the study of linear hydrocarbon

chains chemically grafted to the internal pore surfaces of such particles. The aim

of this work has been to relate the structure of the bonded adsorbate layers to the

performance of chemically modified microporous particles used in chemical separation

(e.g. in high performance, reverse-phase liquid chromatography) and processing.

The measurements were made on microparticles of silica controlled pore glass

with pore diameters ranging from 7 to 30 nm. This material is prepared by controlled

phase separation of the SiO -B O^-Na system and subsequent leaching of the boronrich phase which results in an interconnected pore space and a narrow pore size

distribution. Alkyl chain monomers of various length (ranging from 4 to 18 carbon

atoms per monomer) were bonded to the pore surfaces and the pores then filled with a solution whose scattering density was chosen to match that of the skeletal material

(silica). In this way the pore scattering is minimized while the signal from the

thin (4 - 20 A) bonded layers is accentuated.

A typical set of measurements is shown in figure 1 for a glass with 120 A

diameter pores. The crosses denote the scattering from the pores in the dry,

unbonded glass. The position, Q , of the prominent peak in this pattern is closely

related to the pore size, d, through d = 2iT(t)/Q where ^ is the porosity. The three

lower intensity curves in the figure are for bonded phase particles immersed in the

pore masking solution. In these curves there is also a peak at Q , but also a weaker

secondary feature at Q ' ~ 2Q . This higher order peak shifts and becomes more

prominent as the monomer chain length increases and thus is directly related to the

effective thickness of the adsorbate layer.

The scattering from the unbonded particles can be accurately fitted using a

2 model for phase separated glasses first proposed by Cahn. Analytic and numerical

calculations are now in progress to apply this model to the scattering from the

adsorbate layers in order to extract quantitative information regarding the

uniformity and thickness of the layers.

69
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

.00 .02 .06 .08 .10 .12 16 .18

Figure 1. Small angle scattering from controlled pore glass (CPG) particles having

120 A diameter pores.

(+) - pore scattering from unbonded particles

(A, o, p) - scattering from alkyl chains (C^^, C^ and C „ monomers,

respectively) bonded to the pore surfaces of the particles.

1. C. J. Glinka, L. C. Sander, S. A. Wise, M. L. Hunnicutt and C. H. Lochmuller,

Analytical Chem., 57, 2079 (1985).

2. J. W. Cahn, J. Chem. Phys., 42, 93 (1965).

SMALL ANGLE NEUTRON SCATTERING STUDY

OF

PRECIPITATION IN HIGH STRENGTH LOW ALLOY STEELS

R. C. Reno

(University of Maryland - Baltimore County, Baltimore, MD)

and

(National Bureau of Standards, Gaithersburg, MD)

and

R. J. Fields

(National Bureau of Standards, Gaithersburg, MD)

In our continuing investigation of A710 steel, we have utilized small angle

neutron scattering (SANS), transmission electron microscopy (TEM), and MSssbauer

effect (ME) to study precipitation processes. SANS measurements on unaged steel,

-i] -1 water quenched from 900°C, show Porod behavior (laq ) over the range q > 0.005 A

70
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

Average particle size deduced from the SANS data is ~^0 nm. MQssbauer measurements

on this material show the presence of ~^% retained austenite. We are presently

trying to determine if this austenite phase is responsible for the observed SANS

results.

After aging the steel for one hour at 480°C, no austenite phase can be found by

Mossbauer effect and the SANS results show a Porod region followed by a region where

-2 -1

the intensity obeys a q behavior (for q > 0.05 A ). Since the predominant

impurity in this steel is copper, we have in the past attributed our SANS results to

scattering from copper-rich precipitates. However, we are now investigating the

possibility that significant scattering may result from manganese - or chromium -

rich regions of this steel.

SANS STUDY OF STRENGTHENING MECHANISMS IN SINGLE-CRYSTAL SUPERALLOYS

C. Austin and R. Darolia

(General Electric Company, Cincinnati, OH)

and

C. J. Glinka

Single-crystal, nickel-based "superalloys" are complex, precipitationstrengthened alloys now widely used for turbine blades in high performance aircraft.

The unusual high temperature strength and creep resistance of these alloys derives

from a homogeneous dispersion of coherent Y' (Ni Al) precipitates and the absence of

grain boundaries, respectively. The addition of various elements to the alloys'

composition can further enhance their high temperature strength although the

mechanisms for this enhancement are in many cases not well understood.

In this study, small angle neutron scattering (SANS) has been used to monitor

changes, due to high temperature exposure, in the microstructure of superalloys

containing a few weight percent rhenium. This work was prompted by mechanical tests

which showed that the addition of rhenium produces an initial increase in strength

which, however, is not maintained over long exposure times.

Figure 1 shows a typical SANS intensity contour plot for a superalloy specimen

in its initial, "as prepared" state. The sample was oriented with a [100] cubic

direction parallel to the incident beam. The Y' precipitates in the material, which

are roughly one micron in size and account for over 70? of the volume, are cuboidal

in shape with edges along [100] directions. The strong scattering seen in figure 1 along [100] directions is due to the narrow (~20 nm), planar Y-phase regions between

71
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

[100]

\

[100]

/

\S^^^^^

i/>^'^^\

( (

I

1 0.02A'''

Figure 1. Isointensity contours observed on the two-dimensional SANS detector for a superalloy specimen oriented with its [100] direction parallel to the

incident beam.

210.

180.

150

r 120.-

Figure 2. The net, circularly averaged, small angle scattering for a superalloy

sample containing 35^ rhenium after subtracting the scattering from a sample containing no rhenium. The peak in the scattering is due to a fine

dispersion of small precipitates which develop in the rhenium containing

alloy after 500 hours aging at 1050 C.

72
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

the precipitates and provides an indirect means of monitoring changes in the T' morphology. Regions of the scattering pattern away from [100] directions are, on the

other hand, relatively free from Y' scattering and thus are sensitive to

microstructural changes unrelated to the Y' morphology.

SANS measurements were made on samples with and without rhenium which had been

aged at 1050 C for up to 500 hours. After 500 hours the rhenium containing samples

gave additional, isotropic scattering which is seen most clearly (see figure 2) by

subtracting the scattering from an identically treated sample containing no rhenium.

The residual scattering, shown in figure 2, is indicative of a fine dispersion of

small precipitates with a mean spacing of 15 - 20 nm . The lack of any directional

dependence in this scattering indicates that these precipitates are not coherent

which may explain the decrease in mechanical strength of the rhenium containing

samples at long aging times.

MOLECULAR RESPONSE TO LARGE STRAIN

DEFORMATION IN EPOXIES - A SANS STUDY

Wen-li Wu & Barry J. Bauer

(Polymers Division)

The molecular mechanisms of deformation in crossl inked polymers has been a subject of extensive research. However, most of the effort has been concentrated on those materials with rather low crosslink density such as rubbers. Neutron

scattering has been the main research technique for determining the molecular

response to the deformation process. The junctions within the crosslinked materials

were found to deform following a scheme closely predicted by a phantom network model.

For materials of high crosslinking density such as epoxies, no experimental results

about the changes in the molecular dimension using any direct measuring methods have

been reported.

Based on our previous experience in the determination of the network structure

of epoxies using neutron scattering techniques, it is apparent that the epoxies

composed of partially deuterated DGEBA and Jeffamines are the ideal candidates for

the deformation study. The average distance between crosslinks can easily be

calculated from the positions of the scattering peaks. All of specimens were

deformed in the pure shear mode. A pair of specially designed aluminum plates were

used to keep the specimens in their deformed state during the scattering

measurements.

73
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

Figure 1 . Neutron scattering curves of deformed epoxy containing a mixture of D-2000

to D-^GGO amines. Stretch ratio was 25$.

- along the stretch direction

- along the undeformed direction

0. 0.08 0.15 0.23 0.30 0.38 0.45 0.53 Q(AM

Figure 2. Neutron scattering curves of deformed epoxy containing D-4GG amine

Stretch ratio was 2^%. °- along the stretch direction

- along the undeformed direction

74
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

For those epoxies containing a mixture of D-2000 and D-MOO amines, the average

distance between the crosslinks along the amine chains was found to be 60A and the

distance along the epoxy links was 17A. The corresponding scattering maxima (Figure

1, open square) were located at 0.1 and 0.37 A . The maximum amount of deformation

before the samples rupture is about 50^. Within this strain limit, the amine chains were found to elongate with the macroscopic strain as reflected by the shift of the

main scattering peak to a lower q (Figure 1, solid square). No elongation occured

along the epoxy chains as evidenced by the fact that the position of the second peak

remained unchanged upon deformation.

As the molecular weight of the amine decreased to 400 or D-'^OO amine was used

by itself, the average distance between the cross links along the amine was about 17A

while the distance along the epoxy chain stayed unchanged. The maximum strain before

sample failure was 30/5. No change in the distance between crosslinks along either

the amines or the epoxy chains was noticed within this strain limit. The scattering

curves of a D-400 epoxy along the stretch direction (solid square) and the undeformed

direction (open square) are given in figure 2. The stretch ratio of this specimen

was 2m,

The above observation is rather striking and may also have some important

practical implications since most thermosetting resins used as composite matrices

have molecular weights below 400. In light of the above observation, the question to

be addressed is what is deformed in a specimen with a macroscopic strain up to 30?,

given that the majority of the molecules do not deform. There are at least two

possible explanations for the above observation. The first is a defect-control

model; the deformation is concentrated in localized defect regions while the major

portion of the molecules lie outside these defects. The analog of this defect model

in metals or other crystalline materials is the dislocation. The generation and

movement of dislocations accommodates the macroscopic strain while the lattice

dimensions of the crystals remain unchanged. But the unanswered question for epoxies

is what is the defect. The second possible explanation is the unfolding of the

molecular networks; however, a prerequisite for such a mechanism is that the average

network within a bulk sample is topologically two dimensional. Experiments are now

underway to elucidate the deformation mechanisms in greater detail. Amines and

epoxies with different functionality and composition are now included in this work to

establish the generality of this finding.

75
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

STATIC AND KINETIC STUDIES OF POLYSTYRENE/ POLY(VINYLMETHYLETHER) BLENDS

C. C. Han, F. L. McCrackin and B. J. Bauer

and

M. Okada

(Tokyo Institute of Technology, Tokyo, Japan)

and

Y. Muroga

(Nagoya University, Nagoya, Japan)

and

Q. Tran-Cong

(Kyoto Institute of Technology, Kyoto, Japan)

The study of static and kinetic phase behavior provides not only a fundamental

understanding of polymeric systems but also practical materials applications. This

has long been recognized in the field of inorganic glasses and metallic alloys. In

the polymer field, effort has been concentrated on the equilibrium studies of phase

behavior. Although some kinetic studies have been carried out, so far relationships

and subtleties between thermodynamics and kinetics have not been explored

consistently. We have made a systematic study of the equilibrium phase behavior of

deuterated polystyrene/poly ( vinylmethylether ) blends by the small angle neutron

scattering (SANS) technique, and the phase separation kinetics by the temperature

jump light scattering (TJLS) technique. Static properties, such as the spinodal

temperatures and binary interaction parameters, x» have been obtained from the static

study and then used in the prediction of and comparison with kinetic results. The

consistency and also the discrepancy between theories and experiments have been

compared quantitatively in detail.

COMPATIBILITY OF HYDROGENATED AND DEUTERATED POLYSTYRENE

C. C. Han and B. J. Bauer

and

H. Yang and R. Stein

(University of Massachusetts, Amherst, MA)

and

E. Kramer

(Cornell University, Ithaca, NY)

A 50/50 blend of deuterated polystyrene (PSD.M = 255 x 10 ) and polystyrene

3 ^ (PSH.M^ 233 X 10 ) was studied by small-angle neutron scattering (SANS) for its

76
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

interaction parameter, x/^n' correlation length, E,, and susceptibility, S(q = 0) at

various temperatures. The interaction parameter x/v^ has a value of less than 10 , which is within the error limit of being zero in the measurement temperature range.

The error bound cannot exclude the possibility of an upper critical solution

temperature (UCST). However, this UCST, if it exists, will be well below the glass

transition temperature for any PSD/PSH blends with reasonable molecular weight.

Phase separation of PSD/PSH blends does not occur under common experimental

conditions and phase separation of isotopically labeled polymers is not a general

phenomenon but a specific property of individual polymers.

THEORY OF SPATIAL CORRELATION AND DIFFRACTION

FOR THE LEVELED WAVE MODEL OF

RANDOM BICONTINUOUS STRUCTURES AND INTERFACES

N. F. Berk

We are involved in a theoretical program for small angle scattering from

extended open structures that is relevant to contemporary interests in problems of

interfacial morphology, such as the study of hydrocarbon wetting of porous glass and

phase separation in microemulsions. There is a need in such areas to generate welldefined mathematical models of substrate and interspace morphologies of extended

bicontinuous structures in order to have firm bases for interpreting scattering data.

Our model generalizes an idea originally discussed by Cahn. The material

density field, p(r), of a two-phase system is defined by the following algorithm.

One starts by constructing a field, S (r), obtained by adding together N sinusoidal

waves having common wavelength, X = 1</2it, but randomly chosen directions, k , phase

constants, (j> , and amplitudes A :

N

S (?) = I A^cosCkk^.?^ - <D^).

n=1

The set of all points r that satisfy the equality S (r) = a is called the a-set of

the function S (r) and determines a surface in three dimensions that everywhere

separates regions where S (r) < a from regions where S (r) > a. For given valves of

level parameters a and b we define p(r) = 1 wherever a S S (r) S b and p(r) = 0,

otherwise. Thus p(r) is uniform over the interspace bounded by the non-intersecting

a-set and b-set surfaces. We call this the leveled wave model. The prototype of

such behavior is obtained with b = and a = -°°, which corresponds to an extended,

77
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

(a) (b)

Figure 1. Computer simulations of leveled density fields (p = is black) for N

50. a) 0-set interface b) -1-set and +1-set interfaces. See text.

bicontinuous interface separating one phase with volume fraction c = 1 /2 and p(r) = 1 from the other with volume fraction 1 - c and p(r) = 0. More generally, for finite a and b, the phase in which p(r) = 1 has volume fraction c and the regions it

separates, both with p(r) = 0, have volume fractions c and c , with c. + c_ = 1 - c. Figure 1 gives examples of computer simulations in planar sections for N = 50. The

regions in which p(r) = 1 are shown in white, p(r) = 0, in black. Figure la shows

The

morphology of Figure la suggests a highly porous, spongy structure while the white

the prototype case while in Figure lb, -a = b << 1 for the same S (r).

interspace of Figure lb (c<<1, c = c = 1/2) may model the wetting of pore surfaces

or a microemulsion surfactant interlayer. Simulations show that such morphologies

stabilize rapidly with increasing N, so that the limiting averaged behavior as N ^ "

is meaningfully identified with structures generated by large but finite N.

We have developed an exact method of study for the self-correlation function of

the leveled wave model, <Ap(r)Ap(0)> = c(A - c)Y(r) in the N = » limit and have

obtained analytic results in special cases. For example, for the prototype 0-set

2 morphology, Y(r) = — arcsin(j (kr)), where j (x) = sinx/x. This exhibits both linear

TT O O

behavior a small r, a consequence of the sharp interface, and sinusoidal oscillations

of wavelength A at large r, reflecting the sinusoid population from which the field

is constructed. In general we find the model has a Porod correlation length given by

_2 2

dT

dr

1

=

= c(A - c)/3A/[e + e ], where a and 3 replace a and b in the

infinite N limits and are scaled to the rms amplitude at the wave sum.

78
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

The exact scattering intensity, I(q), of the model consists of two singular

parts and a non-singular, featureless, remnant we will not exhibit here. The

singular contributions are represented by

2 c IgCq) = ^

[c^6(q - k) + 2I

0(2k - q)] (1)

2 2 2 2 — D -a 2 "6 -a 2

where c = (e - e ) and c = (ge - ae ) . Also in (1), 6 = material

contrast, V = sample volume, and ©(•) is the Heaviside function. The first term is a sharp line at q = k, which is caused by long ranged order, and is anticipated from

various numerical and analogue simulations of the prototype model. The second term

is a hyperbolic singularity at q = 0, also caused by long ranged order, which has no precedence in previous studies. Moreover these two singularities tend to exclude one another. In the case corresponding to Figure la, we have c = 1 and c = 0, so that

only the sharp line persists; while in the complementary situation of Figure lb, we have c = and c ^ 0, so that only the hyperbolic divergence is manifest. We have

also generalized the model to incorporate a polydispersive wavelength population into

the unleveled wave sum. Figure 2 shows two families of analytic results

corresponding to the singular contribution to the scattering I (q), as regulated by a wavevector spread Ak = 0.05k. In Figure 2a c = O.OM is constant but c , Cp vary.

Figure 2. Singular contributions to scattering, I (q), as regulated by dipersion in

wavevector pool, with Ak = k/20.

0.21. b)

f c = 0.04, c, = 0.45, 0.37, 0.29,

^2 = °' <=! = 1 - c and c = 0.5, 0.6, 0.7, 0, s s

79
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

The case c. = Cp gives the curve without a peak at q = k but with the largest

amplitude at q = 0. As c ,Cp move away from the isometric configuration, the

scattering at q = diminishes while the peak at q = k emerges and grows. Figure 2b

corresponds to a single interface as in Figure la but with variable composition, c =

1 - c, c = 0. Here the line at q = k diminishes and the intensity at q = grows as

c departs from 1/2.

In summary, the scattering from leveled wave structures reveals two distinctive

but related singularities that reflect in different ways the underlying order in the

model. The sensitivity of these features to compositional details may serve as important signatures for interpreting small angle scattering data from real systems

that may be approximated by these mathematical methods.

RENEWAL THEORY APPROACH TO SPATIAL

CORRELATIONS IN RANDOM TWO-PHASE MEDIA

N. F. Berk

The spatial self-correlation function P(r) of an isotropic two-phase medium can

be expressed equivalently as the probability of finding both ends of a random r-join

lying within the same phase or as the relative volume of the intersection of a phase

with its r-translate. In the latter view, the system can be subdivided into thin

straw-like tubes parallel to r, and for a sufficiently random system the selfcorrelation of the bulk should be characteristic of that along an arbitrary

(infinitely long) straw, as in a one-dimensional problem. This is true effectively

by definition for models in which the only information is the spatial frequency

distribution of intersections (nodes) of the interface with an arbitrary, infinite

straight line. Then the calculation of the self-correlation can be posed as the

question: for the given probability density f(x) of finding adjacent nodes separated

by X, what is the probability that a randomly chosen r-join is cut by an even number

of nodes, including none? The answer is equivalent to the required probability,

P(r), that both ends of an r-join lie in the same phase (i.e., only in even numbered

or in odd numbered intervals along the line). This can be couched as a problem in

renewal statistics - the "renewals" being ordered occurrences of nodes - which we have solved using standard methods. (Analogous renewal problems have been discussed

in different contexts.)

80
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

We have found P(r) to be given by

P(r) = P^(x,r)dx,

where P (x.r) = Jlim P (x.r.x ) and P (x,r,x ) satisfies the integral equation

e x +-<» e o e o

o

•r P (x,r,x ) = p(x - X ,|x |) + p(x' - X ,|x |)P (x - x',|r - x' I )dx'

'o

Here p(x,r) = g(x,r)0(x-r) is the conditional probability density that, given a node

at x = 0, the first node to exceed r falls at x. 0(«) is the Heaviside unit step

function and g(x,r) satisfies Samuelson's integral equation

g(x,r) = f(x) + fmin(x,r

)

f(x - y)g(y,r)dy,

o

where f(x) is the nodal frequency distribution for the interface. The relation of

P (x,r) to p(x,r) is essentially an extension of Samuelson's equation relating p(x,r)

to f(x). This is our central result.

Two examples are useful.

1. f(x) = ae~"^,

~1

where a is the mean nodal spacing. After some work, we find P(r) = 1/2 + 1/2 y(r),

~2ar where Y(r) = e , which is the Debye-Brumberger-Anderson formula. Thus, Debye's

model of a random interface is equivalent to the Poisson nodal distribution, an observation that is well-known from several points of view.

2. f(x) = 2axe"'^^,

-1

where a is again the mean nodal spacing. This first-order Poisson distribution has

-1

Its mode at x = a , which can be interpreted as introducing some degree of short

ranged order. Here one eventually obtains the deceptively simple result, Y(r) = e

'^^

cosar. The scattering intensities for these models are proportional to

Kq) = 2

r T(r)j (qr)dr,

o

and we have for the two cases

Kq) = 2a/(q^ + a^)^, (1)

81
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

the well-known Debye scattering function, and

Kq) = 2aq^/(2a^ + q^)^, (2)

1/4 which fall sharply to zero at q = and is peaked at (12/5)'' 'a. Both scattering

functions exhibit the Porod law, I(q) ~ q as q -^ », which is a consequence of the

sharp interface of the two-phase model

.

HIGH RESOLUTION, MULTIDETECTOR POWDER DIFFRACTOMETER

E. Prince and A. Santoro

A new, high-resolution neutron powder diffractometer is under construction that

will enhance the capabilities for structure studies at the NBS reactor by extending

the range in which high resolution data can be collected to shorter d-spacings and by

increasing data rates for all patterns. A schematic layout of the instrument is

shown in figure 1. The provision for several monochromator positions will enable a resolution curve to be chosen that is suitable for a particular sample, depending on

the d-spacing range in which the important information is found. The thirty-two

detectors will have Seller collimators with a horizontal divergence of 7' of arc and

a vertical divergence of up to 9°, with provision for different vertical divergences

for different detectors, according to the angle range they cover, so as to maximize

sensitivity without sacrificing peak shape.

32 Detectors (up to 9° vertical divergence)

Figure 1 . Schematic layout of the new NBS high resolution, powcJer diffractometer,

82
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

COLD NEUTRON RESEARCH FACILITY

J. M. Howe, C. J. Glinka, T. Udovic, I. S. Anderson,

I. G. Schroder, J. LaRock, W. Knill, and R. Williams

No funds were appropriated for the construction of the new cold neutron

research facility for Fiscal Year 1986, and therefore, no detailed design or construction could take place. Funds to begin construction were again included in

the President's budget for FY1987, and the matter is now before the Congress. In the

meantime, conceptual design efforts and construction and upgrading of the two

instruments to be installed within the existing Reactor building continued. The cold source itself will be discussed in the following section.

1

.

Conceptual Design

A set of alternative possible arrangements of the neutron guide tubes to be

installed in the cold source assembly has been explored, and the heating rates, guide

illumination and total beam area have been varied to determine the optimum

configuration. More detailed design of the actual guide tube insert is now underway,

and the construction requirements are now being specified. Preliminary contact with

the supplier of the neutron guides has been initiated in order to better estimate the

cost of the assemblies. In addition, a set of options which will allow either a reduced or staged development of the facility are being prepared in order to

determine costs, capacity and the possibility future expansion. A neutron filter to

be used for intermediate wavelengths, based on the special properties of molecular

hydrogen in the liquid state, has been designed, and will be tested in the coming

year.

A concerted effort to refine the conceptual design of the new experimental hall

is underway, with an emphasis on staged development and on more flexible use of

available space. In particular, a different floor design which will provide better

vibration isolation and a significantly reduced construction cost is being explored.

Cost estimates are being refined, and a set of alternative proposals for project

staging have been developed. As a result of this effort, detailed design of the new

facility can begin immediately with the availability of construction funds.

2. Neutron Time-of Flight Spectrometer

Construction of the major components of this facility is now complete. Final

testing of the monochromator assembly and the new data acquisition system, based on a 32-bit minicomputer using a Camac interface, is underway preparatory to installation

of the monochromator during the scheduled August reactor shutdown for refuelling.

This test period has been quite extensive in view of the fact that the assembly

83
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

cannot be accessed during reactor operation, so that extreme reliability is required.

This has allowed a thorough shakedown of the data acquisition software and refinement

of the system design. As presently defined, it will be possible to control the

instrument from any terminal on the NBS Reactor network, and to inspect the data and

operating conditions at any time. In order to prevent inadavertent changes to the

spectrometer operation, each experimenter will be allowed to choose a password that

will be required before any operation parameter can be changed. The entire system is

designed for maximum user friendliness, with single key strokes sufficient to access

most information. The evacuated flight path, neutron detectors, and associated

electronics have been assembled, and the final detector shielding has been fabricated

and tested. On the basis of current tests, the irreducible background will meet or exceed the design requirement of less than one count per minute per detector. The

full facility will be operational by October of this year, although some sample area

refinements will not be completed until early 1987. Initial research applications

planned include extensive work on catalysts, ionic conductors, and high technology

alloys and magnetic materials.

3. Small Angle Neutron Scattering Instrument Upgrade

In order to make efficient use of the cold source flux, several aspects of the

current SANS instrument are being improved. A spare 64 cm. detector has been

ordered, with the new fill gas that has improved the Y-ray background. This detector

will be delivered in 1987. In addition, a new data acquisition system based on the

same hardware as that used for the neutron time of flight spectrometer is being

assembled. This new system will include high speed histogramming memory that will

allow rapid acquisition of data in separate memory areas that can be moved into the

computer while a new area is being filled, thus allowing real time experiments. A

new interface between the existing direct time to digital encoder and the

histogramming memory has been fabricated, and is being tested. The new memory will

also allow for larger data arrays, so that the data can be taken on a finer grid.

The system is easily expandable for future needs. The data acquisition programs will

be based on a concept similar to that described above for the time-of-f light

spectrometer. The ability to control and interrogate the spectrometers from any

terminal on the network will allow for routine operation from remote locations, using

existing dial up lines on the network.

84
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

NBSR COLD NEUTRON SOURCE

R.S. Carter, P. A. Kopetka, M. Ganoczy, M. J. Kahn

The cold source cryostat (see figure 1) was received and underwent extensive

testing. All components were helium leak tested and determined to be leak-tight.

Procedures were developed for freezing ice in the ice chamber and several successful

freezes were accomplished.

The cryostat was set up at the thermal column radiography port and neutron

radiography used to determine the ice chamber volume and monitor the ice level as the

freezing progessed. The ice was frozen in layers to prevent damage to the ice

chamber. A neutron radiograph of the half full ice chamber is shown in Figure 2.

After the freezing tests were completed, the cryostat was moved to the

refrigerator location and temporarily connected to allow low temperature cooling

tests external to the reactor. Ice was again frozen in the cryostat and then cooled

to low temperature. The tests were conducted successfully, but they indicated that

some cryostat modifications were needed. These modifications are now underway.

Containment Gas Fil Cover Gas Fill

LN2

He Refrigerant

Ballast

Tank

Figure 1. The Cold Source Cryostat

85
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

Figure 2. The half filled ice chamber,

86
B. NoN-RRD Programs

NUCLEAR METHODS GROUP: OVERVIEW

R. Fleming

(Center for Inorganic Chemistry)

The development and application of nuclear analytical techniques for greater

accuracy, higher sensitivity and better selectivity are the goals of the Nuclear

Methods Group. A high level of competence has been developed in reactor-based

activation analysis, which includes instrumental and radio-chemical neutron

activation analysis (INAA and RNAA), and in LINAC-based activation analysis using

photons (PAA). In addition, the group has a unique capability in neutron beam

analysis with both prompt gamma activation analysis (PGAA) and neutron depth

profiling (NDP). The NDP technique utilizes prompt charged particle emission to

determine elemental distributions within the first few micrometers of a surface while

the PGAA technique utilizes prompt gamma-ray emission to measure the total amount of an element in a sample, regardless of its distribution. These techniques provide an arsenal of tools to address a wide variety of analytical problems in science and

technology.

The activities of the past year have been highlighted by our involvement in the

7th International Conference on Modern Trends in Activation Analysis, new

measurements carried out at other research facilities, and by a major renovation of

our laboratory space in the Reactor Building. The MTAA-7 meeting, which was held in

Cophenhagen in June, commemorated the fiftieth anniversary of the discovery of

activation analysis by Hevesy and Levi. NBS scientists were authors of ten of the

papers presented at this conference. The opportunity was also provided for visits to

the laboratories of several of our European colleagues.

In addition to our ongoing use of the nearby reactors at the University of

Maryland and the University of Virginia, primarily for fast and epithermal activation

analysis, Group members carried out measurements on the neutron beam facilities at

the new cold neutron source at Julich and the intense guided thermal neutron beams at

Grenoble. The Julich work, which was reported at the MTAA-7, provided the first

demonstration of the use of cold neutron beams for prompt gamma activation analysis.

At the ILL reactor, which currently has the world's most intense thermal neutron

beams, the neutron depth profiling facility was used to demonstrate the profiling of

oxygen with the 170 (n,a) 1 4C implementation of NDP for oxygen must await the very

intense beams of the proposed NBS Cold Neutron Facility to be practical.

The Group's contribution to the certification of Standard Reference Materials

is illustrated by multielement measurements done on the following SRM's: Fly Ash,

87
NON-RRD PROGRAMS

Flint Clay, Plastic Clay, Dolomitic Limestone, Rice Flour, and Wheat Flour. At major

levels, the determination of silicon by fast neutron activation analysis has been

demonstrated. Preliminary measurements of trace levels of lithium and boron in

biological materials will be published using a thermal neutron irradiation followed

by helium gas mass spectrometric determination for quantification.

Research into biomedical problems has again been strong this year centered

around the activities of the joint NBS/NOAA/EPA Environmental Specimen Bank. A new

stable isotope technique for the measurement of total blood volume in humans has been

reported based on the NAA determination of the Cr--51/Fe-59 ration in samples spiked

with Cr-50. The characterization of biological macromolecules by a combination of

gel electrophoresis and neutron activation analysis is under development. A special

large volume irradiation facility has been contructed for this purpose. A

systematic effort has begun on the accurate and efficient measurement of trace

elements in human serum, focused initially on zinc and selenium. The crucial step of

valid sampling of biological materials was reviewed in a special issue of the

1 Bureau's Journal of Research.

The strong interaction with industrial scientists using neutron depth

profiling, prompt gamma activation analysis, and neutron activation analysis has

continued with a growing number of guest workers, research associates, and joint

publications. The long-term NDP study of the mobility of helium in nickel has been

completed. The measurement of distributions of lithium and boron in metals, glasses,

and polymers continues to produce important results.

The joint NBS/FDA/USDA study of trace elements in human diet, sponsored by the

International Atomic Energy Agency, has completed its second year. A total of 30

biologically important minor and trace elements have been measured on the total diet

material, USDIET-I. A second composite diet material is being prepared for study and

as a candidate for an NBS Reference Material.

During the coming year the Group will continue to improve the accuracy and

sensitivity with which nuclear methods are applied to elemental measurement. This

will address the problems of sample preparation, irradiation, and counting with the

goal of reducing and quantifying the various sources of systematic error in analysis

by nuclear methods.

Journal of Research of the National Bureau of Standards 91, No. 2, March

1986 Special Issue: Biomedical Sampling.
NON-RRD PROGRAMS

DETERMINATION OF ULTRATRACE LITHIUM AND BORON

BY NEUTRON ACTIVATION AND MASS SPECTROMETRIC

MEASUREMENT OF He-3 AND He-4

W. B. Clarke, M. Loekebakker , and R. D. Barr

(McMaster University, Hamilton, Ontario, Canada)

and

R. G. Downing and R. F. Fleming

(Center for Analytical Chemistry)

A technique for the analysis of lithium and boron at less than 10 nanograms per

gram concentration levels was developed during the last year. The irradiation

facilities and a noble gas mass spectrometer at McMaster University and the pneumatic

irradiation facility at the thermal column of National Bureau of Standards Research

Reactor were used in developing the technique.

The method takes advantage of the fact that Li-6 has a large cross section for

the thermal neutron reaction Li-6 (n,H-3) He-^. The minute quantity of tritium

produced during thermal neutron irradiation of nanogram quantities of lithium is

contained in the irradiation vial. Samples are irradiated to a total thermal neutron

fluence of approximately 3 x 10 n/cm ^ and then allowed to decay for a period of a few days. The sensitivity of a statically operated mass spectrometer previously

developed for oceanographic studies of helium isotopes and tritium is capable of

quantifying the He-3 from the decay of H-3 ^^q/^-) = 12.35 years). Furthermore, in

the development stage of the technique it became apparent that boron could be

reliably determined in the same sample by mass spectrometr ic assay of the He-4

produced by way of the thermal neutron reaction B-10 (n,He-M) Li-?.

In brief, the sample preparation consists of freeze drying a sample in a liner

made of ultra-pure polyethylene. The liner and sample are then placed in a lead tube

which has been pinched sealed at one end. The other end of the lead tube is attached

to a high vacuum line, evacuated to completely remove atmospheric helium dissolved in

the sample and liner, and then pinched off from the vacuum manifold to form a leaktight container for subsequent irradiation. The vacuum is about 10 ~ torr inside of

the sealed lead capsule. The dimensions of the sealed tube are about 1 cm in

diameter and about 6 - 7 cm long. This allows M tubes, 2 samples, and 2 standards,

to fit side-by-side in an NBS polyethylene pneumatic irradiation rabbit. The lead

container is quite rugged and has excellent integrity in the sense of inward leakage

of atmospheric helium or outward loss of the reaction products.

One attractive aspect of this procedure is that the only chemical treatment of

the sample consists of removal of water and other volatiles during freeze drying.

89
NON-KRD PROGRAMS

Repeated analysis of blanks carried through the entire process show that sporadic

contamination is less than 0.02 ng for lithium and less than 0.5 ng for boron from

all sources.

The liner acts as a catcher foil for the tritons and alpha particles emitted

from the outer edge of the enclosed sample. The resulting gas atoms will rapidly

diffuse out of the polyethylene during analysis. If the sample were instead residing

against the lead tubing an unknown quantity of the He-4 and H-3 would become

permanently embedded at the inside wall of the lead container. For very small

samples this "lost" material would make for a significant loss of product during the mass spectrometric analysis.

The first samples analyzed were blood and separated components of blood because

of the observation that lithium may contribute to the regulation of blood cell

formation. In the past, a major difficulty in determining pathways of lithium and

boron in biological systems has been that analytical methods described in the

literature are difficult and often unreliable at such natural ultratrace levels.

Initially, irradiations were performed at the McMaster reactor in Hamilton,

Ontario. This proved unsatisfactory for two major reasons. First, irradiation times

longer than 10 hours sometimes caused the rupture of the lead containers due to excess pressure built up, mostly hydrogen, produced by gamma ray decomposition of the

sample and of the polytheylene liner. Second, a large fraction of the neutrons at

the irradiation position were of sufficient energy to induce the interfering

reactions N-1 4(n,H-3) ,C-1 4, C-1 2(n,He-i< )Be-9, 0-l6(n,He-4)C-1 3, and N-1 4(n,He-i|)B-n . Each of these is a potentially serious interference in a biological material. As a result, the NBS research reactor was selected as the site for irradiation because of

highly thermalized flux of neutrons avalilable in the thermal column of the 20 MW

research reactor. Helium and triton forming interferences, from thermal neutron

capture on H-2, S-32, S-33, 0-17, K-39, Cl-35, and Ca~HO, have been evaluated for

each of the samples under investigation.

Table 1 gives some of the results obtained by the neutron activation - mass spectrometric technique on whole blood. Additional analyses on human blood, blood

components, along with the possible medical implications are being submitted to the

International Journal of Radiation and Isotopes. This more in-depth publication will

also include results from analyses on other biological materials.

In the coming year, the technique will be further improved upon by better

control on the irradiation conditions, and closer evaluation of the potential

90
NON-RRD PROGRAMS

Table 1. Lithium and boron in whole blood.

No. of Lithium Boron

Donor samples (ng g wet wt.) (ng g wet wt.) wet wt./dry wt

A 0.58 + 0.09 16.3 ± 2.6

B 0.54 ± 0.09 16.2 ± 1.7

D 0.91 + 0.12 28.4 ± 3.8

E 0.30 + 0.06 15.3 ± 2.8

F 0.49 ± 0.08 20.3 ± 1.5

G 0.37 ± 0.10 17.9 ± 3.4

H 0.56 + 0.10 23.7 ± 3.6

I k 0.49 ± 0.06 19.5 ± 1.5

J 2 0.93 ± 0.05 79.5 ± 1 .5

K 2 0.66 + 0.08 30.6 ± 1 .0

1 0.41 + 0.03 21 .7 ± 1.9

L 1 0.39 + 0.03 48.4 ± 2.0

M 1 0.96 ± 0.04 63.0 ± 1 .9

AVERAGE 0.58 ± 0.06 30.8 ± 5.6

5.01

5.01

4.86

5.13

5.09

4.75

4.67

4.62

4.80

4.70

4.76

4.89

4.71

Notes: The first seven samples listed were irradiated in the McMaster reactor, and

the others were irradiated in the NBS thermal column. Errors for individual

values are estimates of analytical precision, and errors for average values

are standard errors, i.e. one standard deviation of the means.

systematic errors present in the analysis. Inorganic materials are being prepared

for determination of lithium and boron content as well.

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DETERMINATION OF TOTAL ZINC AND SELENIUM IN HUMAN BLOOD SERUM

R. R. Greenberg and G. V. Iyengar

Establishment of precise and accurate analytical measurements for trace

elements in various biomedical specimens is crucial in order to provide reliable

reference values for various applications in environmental and health related

investigations. In dealing with biological samples, it is not uncommon to experience

contamination or other methodological problems for even such common elements as Cu,

Fe and Zn which occur at relatively high concentration levels in many samples, such

as blood serum, milk and urine. Other, more analytically difficult elements, e.g..

Or, Mo, Mn and Se in blood serum, present considerable challenges in obtaining

meaningful analytical output. A comprehensive quality assurance (QA) program is an essential requirement for such studies, beginning with the biological and analytical

validity of the sampled material, followed by chemical analysis using critically

controlled analytical procedures. The requirement for QA is even more important if

the analyzed specimen is intended to serve as a reference material. For such uses,

it is not only desirable to generate a homogeneous materials, but the measurement

process applied should be capable of keeping the analytical errors as low as

possible, e.g., ^ - 2 %. Such a measurement capability has been demonstrated in our laboratory using instrumental neutron activation analysis (INAA) to determine Zn and

Se in a pooled human serum sample.

It is of practical significance to note that real world clinical specimens are

very precious, and often they are obtainable only in limited quantities, e.g. blood

serum. Therefore, implicit confidence in the chosen analytical technique is

necessary. There are currently many ongoing studies investigating the effects of Zn

and Se as protective agents against various types of cancers and nutritional

disorders. In view of the ubiquitous nature of Zn, it is often easy to contaminate

samples with this element during the sample preparation steps prior to the actual

determination step. Selenium is a particularly difficult element to determine in

many biological materials in view of the volatility of a number of Se compounds, and

the difficulty of decomposing some organo-selenium compounds. In this context, INAA

offers a number of advantages compared to other analytical techniques including:

high sensitivity; lack of matrix effects; minimal sample pretreatment, and non- destructive capability, which eliminates analytical problems due to sample

dissolution and to volatility losses of Se. In addition the measurements can be

repeated on the same samples, if necessary, utilizing the non-destructive nature of

the technique.

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Zinc and Se have been determined, using INAA, in seven replicates from a pooled

human serum sample provided by the Organic Analytical Research Division. Care was

taken in each step of the analysis to keep the total systematic error to one percent

or less. Serum samples (approximately 500 mg each) were weighed into acid-washed,

ultrapure quartz vials, lyophilized at -40° C, and sealed. A quartz vial containing

500 yL of high purity (subboiling-distilled) water was processed simultaneously with

the samples as a blank, and two samples of Bovine Liver, SRM 1577 were prepared for

use as control samples. A new standard solution was prepared gravimetr ically

containing both Zn and Se, and was deposited gravimetrically onto filter papers

placed inside of quartz vials. A Se standard used in the certification analysis of

Milk Powder, SRM 1549, was also prepared in the same manner as an additional check.

The height of the filter papers in the quartz ampoules was exactly matched to that of

the lyophilized serum samples to eliminate both irradiation and counting geometry

effects. The samples, standards, controls and blank were irradiated together in two

polyethylene irradiation containers (rabbits) for three hours in the RT-3 pneumatic

tube facility of the NBS reactor. One month after irradiation, the samples were

removed from the rabbits, washed in nitric acid to remove any surface contamination

from the quartz vials, and counted at a distance of 5 cm from the gamma-ray detector,

for approximately one day each. Zinc was quantitated using the 1115 keV gamma ray

from Zn-65, and Se was quantitated using the 136, 265, and 400 keV gamma-rays from

Se-75.

The results of this analysis are listed in Table 1 and are very encouraging.

The observed precision (relative standard deviations) for the concentrations of both

elements in the seven replicate samples was one percent, which was consistent with

the counting statistics. The Se results obtained using each of the three different

gamma-rays were in close agreement, and the observed concentrations in the Bovine

Liver control samples were in close agreement with the certified values. The two Se

standards agreed to within a few tenths of a percent, and this difference could be

explained by the uncertainty due to counting statistics. The concentrations of both

elements were in the reference range for "normal" individuals, indicating that this

serum pool may be useful as a reference material. It may also be used as a research

material for validating methodologies for analytical techniques whose systematic

errors are less completely understood than are those of INAA.

In view of the closely bio-regulated concentration levels of many essential

elements in tissues and body fluids, it may be necessary to achieve the level of

precision and accuracy demonstrated in this investigation, to successfully identify

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Table 1 . Concentrations of Zn and Se Observed in Human Blood Serum - Pool 8642-TS

(BM 28)

Sample

HS-1

HS-2

HS-3

HS-4

HS-5

HS-7

HS-8

Zn (yg/g)

1 .2373 ± 0.0066

1 .2il6l ± 0.0102

1.2438 ± 0.0095

1 .2299 ± 0.0108

1 .2243 ± 0.0095

1 .2511 ± 0.0093

1.2313 ± 0.0063

Se (ng/g)

117.42 ± 0.81

118.40 ± 1 .26

114.72 ± 1 .13

117.71 ± 1 .24

116.74 ± 1 .12

116.18 ± 1 .06

116.87 ± 0.70

Mean ± 1

s

1 .2377 ± 0.0098 116.86 ± 1 .19

Blank 0.0143 ± 0.0006 <0.2

Systematic

2 error 0.012 1.17

Recommended

3 value 1 .223 ± 0.021 116.9 ± 2.3

Uncertainties for individual measurements are 1 sigma counting statistics.

"Estimated total systematic error at 95% confidence level.

Uncertainties are the estimated overall analytical uncertainty at the 95/6 confidence

level.

subtle differences, if any, in specimens from normal individuals compared to those

from pathological cases.

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THE DETERMINATION OF CHROMIUM-50 IN HUMAN BLOOD

AND ITS UTILIZATION FOR BLOOD VOLUME MEASUREMENTS

R. Zeisler

(Center for Analytical Chemistry)

and

I. Young

(National Institute of Health, Bethesda, MD)

Systematic studies involving the measurement of maternal blood volume increases

are needed since subnormal increases have been associated with maternal complications

and intrauterine growth retardation in a few instances. To establish a possible

link, a new measurement procedure for the maternal blood volume is required that

would be accurate enough to determine the 20 to ^0% small difference between normal

and subnormal increases during pregnancy.

Currently, only the radioisotope dilution technique employing chromium-51

(Cr-51 ) as a label for red blood cells can provide results with a standard error

smaller than 5%. However, this technique cannot be used with pregnant women and also

would impose severe restrictions on a large scale field study because of the

radioisotope involved. Therefore, the Cr-51 radioisotope technique should be

replaced by a dilution technique that utilizes enriched chromium-50 (Cr-50) as a label. The Cr-50 can then be determined by instrumenatal neutron activation analysis

or mass spectrometry.

The current investigations focus on the development of an INAA procedure for

the determination of red cell blood volumes (RCBV) via Cr-50 isotope dilution.

Although INAA procedures were introduced in the 1970's to measure the stable isotope

tracer Cr-50 in several clinical applications, the procedure was not routinely

implemented for RCBV determinations. A possible reason for this may be the fact that

low level determinations of Cr-50 (a U.35% abundant isotope of natural chromium) are

needed for reliable results. These were unavailable at the time. Only recently the

knowledge about sources of contamination and the experience in contamination control

has enabled us to determine chromium at naturally occuring low levels in such

difficult samples as blood, serum, etc.

Besides the establishment of validated sampling procedures for the clinical

blood samples, additional precautions were needed for the stable isotope technique

with INAA because of interfering activation reactions and small activities produced.

These were resolved with irradiations in highly thermalized neutron fields and

background reduction during counting by Compton suppression. The application of the

procedures to the measurement of natural chromium in total blood yielded the first

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Table 1 . RCBV Measurements on Blood Bank Units and Monkeys

Sample Cr--50/Fe-59 Ratios

A.

1 A A^m b

Blood Bank Units

#B66371 A 1.93 1.38E-2^ 6.6E-ii

B 1 .92 1.17E-2 9.3E-i|

#PL 1il6 A 4.28 1.98E-2 11.1E-4

Volumes [g]

V V V

i Cr-50 grav/Cr-51

467 526

532

556 547

2.99

2.43

B 4.30 2.03E-2 8.2E-4 536

Monkeys

#497 A 2.76 3.52E-2 5.4E-4 3-79 302 294

B 2.76 3.08E-2 4,0E-4 344 283

#499 A 2.85 3.17E-2 3.3E-4 3.84 349 354

B 2.88 3.26E-2 2.2E-4 350 343

#512 A 2.53 2.69E-2 3.59 338 356

B 2.55 2.74E-2 334 355

Volumes are given in mass units because V. was determined by weight.

The measurement of the red cell blood volume (RCBV) with chromium labeled

erythrocytes is based on the simple principles of mass balance in a dilution

experiment. A known amount of labeled blood is injectd into the cardiovascular

system. From its dilution the volume is calculated. Considering background, the

following equation applies:

RCBV ~ V ^ ^ where

X A - A^ m b

A, = background of natural chromium in blood

b

A. = specific activity or concentration in labeled blood

V. = volume of the injected labeled blood sample

A = measured specific activity or concentration after dilution

ra V = unknown blood volume.

X

results reported by INAA at a consistent low level of <2.5 ng/mL (0.3 to 2.5 ng/ml)

in samples from human volunteers and rhesus monkeys.

Based on the INAA procedure, a new approach to the blood volume, measurement via

Cr-50 isotope dilution has been developed. It utilizes the ratios of the induced

activities of Cr-51 to the iron-59 (Fe-59) instead of the calculation of specific

activities or concentrations since the iron concentration in the blood cells remains

unchanged during the dilution experiment. This makes the method independent of

sample size and irradiation and counting parameters that may add to the uncertainty

of the measurements. Only the volume or mass of the labeled blood which is injected

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into the subject's blood stream for dilution must be known exactly. The dilution

factor is then determined on a second blood sample and the volume can be calculated.

Prior to a study with human volunteers, two RCBV measurement experiments were

carried out to test the validity of the newly developed approach. One experiment

involved two blood bank units, where the amount of blood could be easily determined

to check the results. The second experiment involved three monkeys ( rhesus macaca mulatta ) , where the RCBV was determined via the traditional Cr-51 radioisotope

technique in addition to the Cr-50 stable isotope experiment. The results are summarized in Table 1

The estimated uncertainty for the new procedure is not exceeding several

percent and results may be more reliable than with the classical Cr-51 procedure.

The first comparison of the two techniques confirmed this estimate. However, three

measured values did not agree with the actual amounts or the results of the other

technique. This may be due to the experimental circumstances where either

contamination could have occurred or it could not be assured that the labeled blood

had been completely injected into the cardiovascular system. If such shortcomings

can be avoided, this novel approach is well suited as a clinical tool to study

problems associated to the maternal blood volume due to its simplicity and inherent

accuracy and precision.

EVALUATION OF USDIET-I TOTAL HUMAN DIET SAMPLES

FOR NUTRITIONAL CONSTITUENTS

V. Iyengar

(Center for Analytical Chemistry)

A multination study, sponsored by the International Atomic Energy Agency, is

aimed at obtaining comparative data on dietary intakes of 25 biologically important

minor and trace elements in a variety of developed and developing countries. Three

Federal Agencies, namely the National Bureau of Standards (NBS), the Food and Drug

Administration (FDA) and the U.S. Department of Agriculture (USDA) are participating

in this study. The scope of the study provides an unique opportunity to develop a coordinated approach by the collaborators of these 3 agencies for the U.S. part of

the study.

The combined expertise of the participants is aimed towards the needed

developments and improvements of analytical methodology for the accurate assessment

of the dietary intakes of trace elements. Aspects of quality assurance in sampling,

sample preparation, analysis and data evaluation have been addressed by

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intercomparison studies of minor and trace elements in dietary reference materials

(NBS rice flour SRM 1568a, NBS wheat flour SRM 1567a and two mixed diet samples,

namely IAEA-H9 and TDD-1D) using different analytical techniques. Precision and

accuracy aspects related to Flame Atomic Absorption Spectrophotometry, Atomic

Emission Spectrophotometry with an inductively coupled plasma source and Neutron

Activation Analysis were evaluated by analyzing the same test materials by all the

three methods.

As a contribution to this project a benchmark mixed U.S. diet research

materials using 201 different foods from the FDA Total Diet Study (TDS) has been

prepared. According to the FDA-TDS study, a 25-30 year old male consumes daily a total of 3075 g from these 201 foods. This represents the group with highest caloric

intake per day and has been used as a basis for all the calculations in the present

study. The first batch comprises of about 10 kgs of mixed diet.

Proximate analysis has been carried out on USDIET-I (fresh material) and the

following results were obtained; total volatiles = 83.8 %, ash content 0.66 %, fat = 2.92 %, protein = 3-42 %, carbohydrates = 9.2 5^ and total caloric energy (kcal/IOOg)

= 76.76.

Over 30 minor and trace elements have been characterized in USDIET-I using a combination of analytical techniques. A comparison of the daily intakes of Ca, Cu,

Fe, Mg, Mn, Na, P and Zn from this total diet material with those of FDA-TDS figures

calculated from single food analysis results showed that the mixed diet concept is a viable approach. The daily intakes from USDIET-I were also compared with the

Recommended Daily Dietary Allowances suggested by the National Academy of Sciences.

The agreements were generally very good. However, analysis for a number of elements

such as Cd, Cr, Hg and Mo that occur at low concentration levels in individual foods,

demonstrated the feasibility of a reliable assessment of their daily intake by use of

a total diet material, e.g., USDIET-I.

A number of organic nutrients have also been determined in USDIET-I, and their

stability during storage is being evaluated. The Initial findings suggest that

USDIET-I may also be useful to develop reference materials for organic nutrients.

There is a great need for these types of reference materials. Thus it may pave the

way for considering production of a single SRM certified for both organic and

inorganic nutrients.

Simultaneously, the long-term implications of biomonitoring of foods is being

studied by storing about 3 kgs of USDIET-I as originally composited. Dietary

collections from different regions of the U.S. are currently underway.

Representative portions of these total diets from future collections will also be

preserved in the Biomonitoring Specimen Bank.

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DETERMINATION OF SILICON BY FAST

NEUTRON ACTIVATION ANALYSIS

D. A. Becker

An Instrumental neutron activation analysis method has been developed for the

determination of silicon in a variety of matrices, utilizing fast neutrons. This

method has been applied to the certification of silicon in SRM 1632 b, Trace Elements

in (Bituminous) Coal, and in the determination of silicon in a number of marine

sediments.

The nuclear reaction used for the analysis is the silicon-29 (n , p ) aluminum-29

reaction, with counting of the 1273 Kev gamma ray (half-life is 6.5 minutes). A

boron nitride capsule is used to hold the sample, which absorbs the thermal neutrons

while passing the fast neutrons. This substantially lowers the overall radioactivity

of the sample, while not affecting the analysis for silicon. In particular, the BN

reduces the interference due to production of aluminum-28 by thermal neutrons.

The University of Maryland nuclear reactor was used for the irradiations, since

its design (light water cooled and moderated) provides a greater intensity of fast

neutrons than the NBS reactor, even though the thermal neutron intensity is less than

3% of the NBSR (which was designed specifically to provide a maximum intensity of

thermal neutrons). Irradiation times ranged from one to six minutes, depending on

the silicon concentration in the samples.

For the coal analysis, four bottles were analyzed in duplicate, with sample

sizes ranging from 0,58 to 0.75 gram. The silicon concentration found was 1.35 ±

0.03/S (S.D.; Is). Good agreement was obtained between all four bottles.

For the sediment analysis (made as part of a series of specimen bank samples

for NOAA and described elsewhere in this report) silicon concentration ranged from 23

to 31/S. Excellent agreement was obtained for check samples of NBS SRM 16M6

(Estuarine sediment), the IAEA sediment samples, and NRC-Canada reference sediments,

although none of these are known to a high degree of accuracy.

From the above data it is estimated that analysis for silicon using aluminum-29

can be made for 2 mg of silicon with approximately 3 percent counting statistics, or 0.2 percent silicon in a one gram sample. Further, if no aluminum or phosphorus is

present in the sample, this level could most likely be lowered to 0.02 percent,

through use of the aluminum-28 isotope. Work is continuing on additional types of

samples and to establish experimental detection limits for silicon.

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SPECIMEN BANKING AND ANALYSIS IN THE NATIONAL STATUS AND TRENDS PROGRAM

R. Zeisler, S. F. Stone, B. J. Koster, D. A. Becker, and M. P. M. Tillekeratne

Recently, environmental monitoring has been complemented by programs for

systematic and controlled long term storage of environmental samples, i.e.

environmental specimen banking (ESB). The necessity, usefulness and importance of

ESB has been demonstrated for current monitoring as well as for preserving the

representation of the past for examination in future years. In 1984, the National

Oceanic and Atmospheric Administration (NOAA) has initiated a specimen bank for

estuarine and coastal samples, as part of its National Status and Trends (NS&T)

Program. This specimen bank has been incorporated in the research activities of the

Pilot Environmental specimen Bank which is housed at NBS. The research includes all

steps of the ESB operation with special emphasis on quality assurance in the

selection, collection, preparation, storage, and analysis of marine samples according

to validated procedures.

The NS&T program is sponsoring two monitoring projects for the U.S. coastal

waters: the Mussel Watch with 154 collection sites and the Benthic Surveillance with

50 collection sites. The mussel watch collects bivalves and sediments from tidal

sites whereas the Benthic Surveillance collects bottom feeding fish and sediments

from estuarine and continental shelf sites. Over 40 sites nationwide are now

included in the ESB. The sampling techniques applied in these programs have been

refined and modified in cooperation with the field scientists to fulfill the

requirements of the ESB and to ensure comparability between the samples used in

realtime monitoring and the baked samples. Protocols have been developed for the

sampling and preparation of the specimens that greatly reduce the risk of

contamination. Special tools and implements, chiefly made from titanium and Teflon,

are used to prepare the samples for transport and storage at liquid nitrogen

temperature. The samples are prepared for analysis in a clean-room by contamination

free blending (sediments) or cryogenic homogenization (tissues) in Teflon disk mills.

A unique sequence of instrumental analytical methods involving X-ray

fluorescence and neutron activation analysis procedures has been employed for the

determination of 44 elements in marine bivalves. The individual procedures are a X-ray fluorescence method based on backscatter with fundamental parameter

corrections, prompt gamma activation analysis, and neutron activation analysis with

instrumental and radiochemical procedures. This analytical approach has been

expanded to include the analysis of sediments and fish tissues. It is possible to

use a single subsample of about 250 mg and follow it through three instrumental

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Table 1 . Results for the Determination of Selected Elements in Sediment Samples from

the Benthic Surveillance Program (yg/g except as noted)

Element SOOIA^ S010A S013A S019A S022A S028A Error

DP EB NR MRD cc CB

Al % 6.60 7.70 7.45 4.18 6.86 6.47 0.03 - 0.04

6.64 7.74 7.50 4.16 6.80

Si % 30.81 20.55 26.33 36.56 23.56 24.45

30.49 20.55 26.53 34.79 22.23 25.66

V 61.5 110.1 89.8 42.5 93.0 115.2 2.9 - 5.0

55.1 106.0 94.2 46.6 97.4 110.1

Cr 35.2 105.5 28.1 39.4 52.4 111 .2 2.5 - 3.5

38.1 81.5 34.6 39.4 55.5 113.1

Mn 366 631 662 277 550 1020 4.0 - 10.0

419 608 667 277 553 1083

Fe % 1.85 4.11 2.99 1 .440 3.21 4.94 0.01 - 0.03

1 .88 4.46 3.32 1 .542 3.61 5.29

Zn 51.9 145.9 67.5 48.1 134.2 350.2 1 .2 - 4.0

51.5 160.3 67.8 51 .2 146.7 353.9

As 5.21 18.1 <3.2 6.51 10.7 23.9 0.3 - 1 .2

3.27 16.1 2.6 7.18 10.1 22.3

Sb 0.50 3.42 <0.2 0.38 0.70 1.30 0.04 - 0.13

0.49 2.95 <0.2 0.47 0.71 1 .46

Hg <0.3 <0.5 <0.4 <0.3 <0.4 <0.6

<0.3 0.54 <0.4 <0.3 <0.4 <0.6 0.01

DP - Dana Point, CA

EB - Elliott Bay, WA

NR - Nisqually Reach, WA

CC - Corpus Christi, TX

CB - Chesapeake Bay, MD

MRD - Mississippi River Delta, LA

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Table 2. Determination

(lig/g except as of Selected Elements

noted)

in Two Reference Materials Us)ing INAA

Element SRM 1646 IAEA SD-N-1/2

Certified Certj.fied

This Work Mean ± 2s This Work Mean (C.I.)

Al % 5.91 ± O.OM

5.97 ± 0.03

6.25 ± 0.20 3.66 ± 0.02 (3.58 - 3.85)

Si % 31 .61 (31) 28.16 (26.1 -• 29.2)

V 92.2 ± 4.4

93.0 ± 2.9

88.0 ± 10.0 77.7 ± 3.2 77.7(65.0 - 80.7)

Cr 80.1 ± 0.8 76.0 ± 3.0 144.3 ± 1 .1 149(125.0 - 161 .0)

Mn 360.5 ± 5.7

369.7 ± 5.7

375.0 ± 20.0 809.9 ± 9.2 777(728.0 - 801 .0)

Fe % 3.456 ± 0.027 3.35 ± 0.1 3.456 ± 0.027 (3.53 -- 3.78)

Cu <390 (3.7) <300 72.2(68.1 - 75.2)

Zn 137.4 ± 2.0 136.0 ± 6.0 423.2 ± 3.9 439(423.0 - 452.0)

As 11 .95 ± 0.27

10.85 ± 0.44

11.6 ± 1 .3 65.03 ± 0.92

64.40 ± 0.88

50(42.4 - 60.0)

Cd <6.3

<11

0.36 ± 0.07 11 .8 ± 1.3

9.1 ± 1 .5

11 .0(10.0 - 12.0)

Ag 2.14 ± 0.23 2.3(2.0 - 3.2)

Sb 0.43 ± 0.08 (0.4) 3.48 ± 0.10 3.62(3.20 -3.95)

Hg <0.4 0.063 ± 0.012 2.65 ± 0.15 (0.06 - 1.72)

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analyses, nondestructively, and a final radiochemical procedure, which consumes the

sample. The advantage of this approach is obviously the reduced sample preparation

which minimizes contamination or loss and assures the true correlation of elements

since all results are based on the same subsample, i.e., eliminating uncertainties

due to sample to sample variations.

Analytical quality assurance has been accomplished by two means: First, the

sequential analytical procedure allows for the independent determination of up to

twenty elements by the two or three techniques involved. Since the same subsample is

used by all techniques, any deviation of the results would indicate a possible bias

of one technique. Secondly, a sufficient number of certified reference materials has

been analyzed in parallel with the monitoring samples. Good agreement of the

analytical results with the certified values will allow conclusions on the accuracy

of the results obtained for the monitoring samples.

Analytical data have been obtained for tissue samples from earlier bivalves

3 specimens and from sediment samples collected during the 1985 NS&T project year.

Results for selected elements in six NS&T sediment samples using instrumental neutron

activation analysis are shown in table 1. Due to the limited number of individual

samples that were available, no assessment of environmental status can be made at

this time. However, the primary emphasis of this work is on high quality

multielement determinations. The results obtained on referencce materials (table 2)

confirm that the applied analytical approach is in control.

1. S. A. Wise and R. Zeisler, Eds., International Review of Environmental Specimen

Banking, NBS Spec. Publ . 706, U.S. Government Printing Office, Washington (1985).

2. S. A. Wise, R. Zeisler, Environ. Sci. Technol ., 18, 302A (198^1).

3. S. F. Stone, R. Zeisler, Proc . 5th Conf. on Nuclear Methods in Environment and

Energy Technology, J. R. Vogt, ed . NTIS U.S. Dept . of Commerce, Springfield, VA,

CONF-840i108 (1984).

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ACTIVATION ANALYSIS OPPORTUNITIES USING COLD NEUTRON BEAMS

R. M. Lindstrom and R. Zeisler

and

M. Rossbach

(Nuclear Research Center (KFA) Julich, F. R. Germany)

The application of neutron-capture prompt gamma-ray activation analysis (PGAA)

has been pursued to date at only a few laboratories on a full-time basis, only partly

because of the need for continuing access to a reactor neutron beam. Irradiation

times of several hours are required for most samples in which many elements are to be

measured, hence the throughput is low because only one sample can be irradiated and

measured at a time.

The low sensitivity is not due to a low neutron capture rate, but to a low

detection efficiency for the resulting gamma rays, because of the necessary bulk of

active and passive shielding around the detector. Simply moving the detector closer

to the sample increases the efficiency, but at the cost of higher backgrounds and

other consequences of operating instruments in high radiation areas. Isenhour and

Morrison have concluded that, for equal neutron fluence rates, PGAA is superior to

conventional (delayed) NAA in the intensity of gamma-ray emission for 61 out of 63

elements considered. The comparison fails, of course, when the fluence rate in an

internal irradiation position is compared with that in an external beam. In general,

-5

beams provide only about 10 of the thermal neutron fluence rate of an in-core

irradiation position. Further limitations are imposed on the technique by the

inferior signal to background ratios in a PGAA facility as compared to a shielded

gamma spectrometer used for delayed counting. In existing PGAA facilities, the

baseline under the desired spectral peaks has several components:

1The Compton continuum from high-energy gamma rays in the sample spectrum.

2. A continuum of scattered gamma rays from the neutron source. Despite the low

scattering probability for photons at high angles, in an unfiltered beam the

utility of low-energy capture lines is impaired.

3. Lines and continuum from neutron capture in the sample support, beam tube, beam

stop, shielding, and detectors. This may come from a penumbra of thermal

neutrons or from fast neutrons which travel several centimeters in low-Z

materials before being absorbed. Radiations from H, B, C, Al, and Fe are

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commonly present in background spectra, as is N from liquid nitrogen vessels and

from air in unevacuated beam tubes. This component increases with the neutron

scattering power of the sample.

4. Environmental background, both continuum and discrete, from the reactor and from

nearby experiments in the often crowded space of a reactor experimental hall.

This includes decay radiation from neutron activation products of structural

parts and shielding, as well as leakage of neutrons and gamma radiation from beam

ports and spectrometers.

All except the first of these background components are much less important in a cold

neutron facility.

From the point of view of chemical analysis, the ideal neutron field has the

2 largest possible number of activating particles per cm 'S on the sample, and the

smallest possible number of interfering particles at the detector. A narrow beam is

desirable so that the gamma-ray detector can be moved near the sample and the size of

the shielding may be minimized. For PGAA, unlike neutron scattering measurements,

the beam need not be collimated parallel, but should be uniform across the target.

2

A guided beam of cold neutrons meets these requirements exactly. The slowest

neutrons from the reactor are reflected with high efficiency from the walls of the

2 guide tube, while the fast neutrons and gamma rays decrease as 1 /r with distance

from the source. Therefore the signal to noise ratio is high. Since the apparatus

is not near the reactor and other experiments, the background from these sources is

low and there is room between experimental facilities to construct efficient

shielding. The capture rate is also higher with cold than with thermal beams. Since

capture cross sections for most target nuclei are inversely proportional to the

2

neutron velocity, the same number of neutrons per cm 'S at 30 K gives three times the

reaction rate as at 300 K.

The recently commissioned ELLA Neutron Guide Laboratory at the FRJ-2 (DIDO)

3 reactor of the Nuclear Research Center JUlich provides cold neutron beams with the

aforementioned qualities. A new neutron guide has been constructed which extracts

O p neutron beams of intensity 8.4 x 10 n/cm 'S from a hydrogen cold source through a 48-cm cooled Bi filter. The guide used for the PGAA experiments is straight and of 5

x 10 cm cross section. The irradiation position is 50 m from the cold source. The

target - detector assembly and the signal processing circuitry are illustrated in

figure 1

105
NON^RRD PROGRAMS

Neutrons emerged from the guide through a thin aluminum window to irradiate the

sample, suspended in air by 13 um Teflon threads. The neutron beam was collimated to

a diameter of 2 cm by two Li-5 aperture plates. Excess neutrons downstream from the

sample were stopped in an open-ended box slightly larger than the beam, fabricated of

metallic Li-6 pressed into slabs and encapsulated in aluminum foil. No gamma-ray

shielding of the neutron beam itself was required; when the neutrons were

experimentally removed by a Li-6 stop, the residual gamma radiation at the sample

position was only 50 ySv/h (5 mR/h).

The detector used was an Ortec GAMMA-X Plus intrinsic germanium diode (22.65S

efficiency, 1.72 keV resolution (fwhm) at 1.33 MeV) equipped with a small cryostat

with 24 h holding time. The front face of the detector can was placed 23 cm from the

sample. The detector was surrounded by Pb shielding to reduce the background from

neutron capture in the aluminum window. A collimating aperture 2 cm in diameter by

20 cm long admitted gamma rays from the sample, illuminating 605^ of the face of the

detector crystal. A transistor reset charge-sensitive pramplifier was used in

connection with an Ortec 673 main amplifier and gated integrator to allow good

throughput at high count rate. The signals were collected with a Nuclear Data 581

ADC (10 ys conversion time into 16384 channels) and a Nuclear Data Micro-Multichannel

Analyzer connected to a VAX 11/750 computer. An Ortec ADCAM multichannel analyzer,

connected to a personal computer, collected 8192-channel data in parallel and

provided live spectral display. The application of loss-free counting circuits is

being tested for the measurement of rapidly decaying nuclides after stopping the beam

in front of the target.

Samples examined include Standard Reference Materials, industrial, biological,

and environmental specimens, and air filters. Synthetic standards were irradiated to

study the systematic errors in hydrogen containing matrices and other limitations on accuracy with existing facilities.

The main advantages of cold neutron beams were verified in the experiments.

Q p The neutron intensity at the sample position was 2 x 10 n/cm 'S, and the cadmium

4 ratio (with 25 ym Au foil covered by 510 ym Cd) was 1.0 x 10 . Autoradiography of

indium foils exposed to the beam showed good uniformity, with barely visible

striations parallel to the long walls of the guide. The PGAA sensitivity, expressed

in counts/s*g, was a factor 4.5 higher than the present sensitivity at the UMd-NBS

facility, and a factor 9 higher than the published sensitivities at the previous

reactor power of 10 MW. Except for the high gamma-ray field from the window (which

had been designed to minimize scattering, not capture), the beam was clean and the

106
NON-RRD PROGRAMS

backgrund low. The hydrogen background in the spectrum of a Teflon sample envelope

5 was 100 yg, four times lower than the better of two major PGAA facilities.

In the analysis of plant and animal tissue, the limiting factor for both the

sensitivity and the accuracy of PGAA determinations is the amount of hydrogen in the

sample. The strong hydrogen capture gamma ray at 2223.2 keV is accompanied by a high

Compton continuum, making the capture lines of other elements below 1995 keV much

less sensitive than they would otherwise be. Active Compton suppression can reduce

this baseline substantially, but not eliminate it. Since the scattering cross

section of bound H is much larger for cold than for thermal neutrons, large

quantities of hydrogen in the analytical matrix lead to a smaller signal from the

elements of interest, and therefore the maximum sample size is limited. A rigorous

experimental and theoretical study of this problem remains to be done.

With the high gamma-ray detection efficiency possible with cold neutron beams,

the practical limitation on the analytical usefulness of PGAA will be the ability to

collect data at high counting rates without distortion. Recent advances in active

ft 7 ft collimation ' and in loss-free acquisition techniques make it likely that the

collection time for electrons in germanium may become the rate-limiting step. With

large Ge detectors coupled with compact high-Z gating detectors, Ge-Ge coincidence

counting can be done with profit. Multiparameter counting offers a clean resolution

of the problem of interfering lines in a crowded spectrum.

'p¥n i m<^^^^^9^n nrr \"" 'P-i" v«wn^^ff*"wiMP«M«v<

^^LUiM^^^i^^^^M**** NEUTRON GUIDE

COMPUTER MCA

CRM

AMP

SAMPLE

V3STOP

DETECTOR

A. PRE PULSER

Figure 1 . Experimental Arrangement

107
NON-RRD PROGRMS

Further enhancement in sensitivity is possible since neutron optics may be used

9 Q ? to focus cold neutrons onto a small area. If a 10 cm x 10 cm beam of 10 n/cm 'S

could be focused on a 1 x 1 mm area by a shaped supermirror or a zone plate, the

1 ^ 2 fluence rate would become a highly attractive 10 n/cm -s. The techniques already

developed for the micro-scale electron- and ion-probe analogs of this situation are directly applicable for the formation of two-dimensional images, with millimeter

resolution, of the elements which produce prompt radiations under neutron

bombardment.

1. T. L. Isenhour and G. H. Morrison, Anal. Chera. 38 (1966), 162.

2. H. Maier-Leibnitz and T. Springer, J. Nucl . Energy 17 (1963), 217.

3. K. Werner, T. Springer, and J. Duppich, in 0. Harling, L. Clark, Jr., and P. von

der Hardt (eds) "Use and Development of Low and Medium Flux Research Reactors"

Munich: Karl Thiemig (1984), p. 783.

4. R. M. Lindstrom and D. L. Anderson, in S. Raman (ed) "Capture Gamma-Ray

Spectroscopy and Related Topics - 1984" New York: Am. Inst. Physics, (1985), p.

810.

5. D. L. Anderson, W. H. Zoller, G. E. Gordon, W. B. Walters, and R. M. Lindstrom,

in T. von Egidy, F. Gonnenwein, and B. Maier (eds) "Neutron-Capture Gamma-Ray

Spectroscopy and Related Topics", London: Institute of Physics (1982), p. 655.

6. R. M. Lieder, H. Jager, A. Neskakis, T. Venkova, and C. Michel, Nucl. Inst.

Methods Phys. Res. 220 (1984), 363.

7. N. R. Johnson, C. Baktash, and I. Y. Lee, IEEE Trans. Nucl. Sci. NS31 (1984),

243.

8. G. P. Westphal, J. Radioanal. Chem. 70 (1982), 387.

9. A. G. Klein and S. A. Werner, Rep. Prog. Phys. 46 (1983), 259.

Acknowledgments: We thank K. Werner and J. Duppich for generously making available

the facilities of the ELLA guide hall, R. Thomas for computer assistance, and P.

Giesen (EG&G GmbH) for the loan of equipment and software.

Certain commercial equipment, instruments, or materials are identified in this paper

in order to specify adquately the experimental procedures. Such identification does

not imply recommendation or endorsement by the National Bureau of Standards, nor does

it imply that the materials or equipment identified are necessarily the best

available for the purpose.

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NEUTRON DOSIMETRY GROUP: OVERVIEW

J. Grundl

The Neutron Dosimetry Group of the Center for Radiation Research (CRR) is engaged in

the development and application of standard and reference neutron fields as permanent facilities for neutron dosimetry standardization, for neutron detector

calibrations, and for reaction rate cross section measurements. Strong interactions

with outside organizations, both in the federal and private sector, are important

programmatic characteristics. A substantial component of the Groups activities

involve the use of the NBS Research Reactor thermal column and tangential beams

where facilities designed and built by the Neutron Dosimetry Group are in operation.

1 . Dosimetry for Materials Performance Assessment

(a) First time ever production of neutron fluence standards with 30-year Cs-1 37

activity occurred this year. Neutron fluence standards are neutron sensors

(activation foils generally) in which a radioactive species relevant for dosimetry

is induced by irradiation in a standard neutron field. The NBS Cavity Fission

Source was used to expose U-238 to a certified neutron fluence of about 2 x 10

2 n/cm which is sufficient to produce a measurable 30-year Cs-1 37 fission-product

activity. These fluence standards are used to verify commercial neutron fluence

measurements made with similar uranium foil dosimeters, such as are used in reactor

pressure vessel surveillance.

(b) Quality assurance measurements of tantalum impurity in niobium were performed for several commercial and government laboratories using the thermal

92 92m

neutron irradiation facility at the reactor. The Nb(n,n') Nb reaction for

fast-neutron dosimetry results in an X-ray emitting state with a 16-year half-life.

If significant quantities (>20 ppm) of tantalum are generated in a neutron field

with an appreciable slow neutron component, the tantalum becomes radioactive and

decays with emission of the same energy X-ray as the Nb-92m.

2. Integral Neutron Cross Section Measurements

(a) The Department of Energy (DOE) is sponsoring a multi-laboratory effort to measure fission-spectrum-averaged cross sections of a relatively new reaction of

interest for high fluence (>10 n/cm ) neutron dosimetry. The reaction is

92 92m Nb(n,n') Nb with a 1 6-year half-life. Many laboratories are involved because

high fluence, standard-neutron-field irradiations are required and because the

Nb-92m is an X-ray emitter which complicates the activity determination. NBS has

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17 2 completed a 30-day, 10 n/cm irradiation in the Cavity Fission Source for this

project. The NBS Radioactivity Section will participate in the X-ray activity

determinations together with the INEL Laboratory in Idaho, the University of

Arkansas, and Harwell Laboratory in England. The 30-day irradiation in the NBS

Facity Fission Source, an essential component of the measurement, was six times

longer than any previously performed with this source. A notable goal of the

irradiation was successfully achieved: The U-235 fission disks were handled with

minimal personnel radiation exposure.

(b) Our productive and pleasant collaboration with the University of Virginia

Department of Nuclear Engineering and Engineering Physics is continuing. Professor

T. Williamson is presently analyzing data taken at NBS during his sabbatical year.

A paper on the measurement of photofission cross sections in the NBS neutron driven

gamma ray field will be presented at the 6th ASTM-Euratom Symposium on Reactor

Dosimetry. Photofission cross sections of Np-237 , U-235, U-238 , and Th-232 were measured in both iron and cadmium capture gamma ray fields. These cross sections

are important for correcting the neutron response of fission dosimeters used in all areas of materials performance assessment under stress of radiation. Professor

Williamson and his students have also continued their analysis of data on the

Nb-93(n,n') spectrum-averaged cross section for U-235 fission neutrons. Niobium

foil materials were irradiated in the Cavity Fission Source of the NBS Reactor in

exposures of six and four days duration. The activity of each foil is measured by

comparing the number of counts with the counts from NBS SRM 4267-8, a Nb-93m

activity standard. Preliminary results indicate an overall 3 percent uncertainty.

Final results will be presented at the 6th ASTM-Euratom Symposium on Reactor

Dosimetry.

(c) Integral tests of 10-100 keV-range neutron activation cross sections for

Au, In, and Cu have been begun at the Intermediate Energy Standard Neutron Field

(ISNF) facility at the reactor thermal column. In these tests, the neutron fluence

rate is determined by a Pu-239 fission chamber monitor. Subsidiary measurements are being made to check for suspected problems of epi-thermal neutron leakage through

the penetration for the monitor chamber stem. The neutron field near the

penetration has been mapped by exposing of activation foils in the region of the

penetration and comparing the results with foils activated in the ISNF with the

penetration closed. The ISNF is ideally suited to cross section tests in this

10-100 keV region, and these tests may contribute to understanding the

inconsistencies in the B-10 cross section in this energy range.

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NON-RRD PROGRAMS

(d) The spectrum integrated helium generation cross section for B-10 in the NBS

Intermediate-Energy Standard Neutron Field (ISNF) was measured by the HAFM technique

some time ago and found to be discrepant with prediction by a surprising 10 percent.

A paper was presented last year which investigated this discrepancy and others

related to it. Since then some preparations have been made to make an independent

measurement of this cross section in ISNF with the NBS double fission chamber. Such

an active measurement in the high-intensity gamma fields within the NBS reactor

thermal column poses severe experimental problems. The reaction products (Li -7

recoil and alpha particle) which can be nicely resolved in a thermal beam outside of

the thermal column cannot yet be adequately discerned in the ISNF arrangement inside

of the thermal column. It may be necessary to use a Cf fission neutron source to

drive the ISNF geometry in order to perform this measurement. There is good reason

to carry out this measurement, if at all possible, because of the basic importance

of the B-10 reaction as a standard against which many other cross sections are measured and the confidence which exists concerning the 1 /v shape of the reaction

cross section.

3. Smaller Projects

(a) Several man months of effort were spent this year in documenting the

calibration services offered in association with the NBS Fission Neutron

Irradiation Facilities. Two documents, now in the NBS review process, will be

published as NBS Internal Reports. They describe two services: Activation Foil

Irradiations-Californium Fission Sources (44080C) and Activation Foil

Irradiation-Cavity Fission Sources (M4090C). The documents describe the

characteristics, theory and operation of these benchmark neutron fields, including

the traceability of their calibration to NBS-I. Available neutron fluences are given along with the uncertainty of relevant exposure parameters. The documents

also detail operating procedure for performing irradiations in the hope of

establishing some institutional memory.

(b.) Preliminary work in support of a proposed neutron life-time experiment

has begun. The responsibility of the Neutron Dosimetry Group in the proposed

experiment would be the determination of the average linear density of neutrons in

the neutron beam, downstream from an electromagnetic proton trap. A detachable

neutron detector would be absolutely calibrated in a series of subsidiary

measurements employing both cold neutron beams and thermal neutron beams. The

active neutron detector will consist of a thin B-10 deposit, viewed by four surface

barrier detectors. A study of possible materials for the backing of the B-10

111
NON-RRD PROGRAMS

deposit has been made, and thin (0.38 mm) crystalline silicon wafers have been

chosen as the backing material. These single-crystal backings will scatter thermal

neutrons less than half as much as would the thinnest possible Al backing (0.13

mm). Furthermore, these crystal wafers are extremely smooth, flat, and rigid, so that good solid angle reproducibility and stability can be maintained.

(c) Prototype fission-scintillation counters developed by Lawrence Livermore

National Laboratory (LLNL) were calibrated in tests at the reactor thermal column.

The neutron sensitivity data provided by these tests was used by LLNL scientists to

make crucial settings of the recording oscilloscopes prior to weapons tests at the

Nevada site in March, 1985. These data are also being used in interpretation of

the test results.

ATMOSPHERIC AND ENVIRONMENTAL STUDIES BY INSTRUMENTAL AND

NEUTRON-CAPTURE PROMPT Y-RAY ACTIVATION ANALYSIS

G. E. Gordon, D. L. Anderson and J. M. Ondov

(University of Maryland, College Park, MD)

We continue to make extensive use of instrumental neutron activation analysis

(INAA) and neutron-capture prompt Y-ray activation analysis (PGAA) for continued

development and testing of the methods themselves and to determine concentrations of

about ^0 elements in particles, gases, rain and fog from the atmosphere, in related

source materials such as crustal dust and coal fly ash, and in standards appropriate

for use in this field. By measuring concentrations of such a large number of

species, we are able to identify contributions from certain types of air-pollution

sources to the atmospheric burden at ambient sampling sites, a technique now known as "receptor modeling". Examples of these studies are briefly discussed in the

following sections.

1 . Rare Earth Elements in Zeolite Catalysts and Rare Earth Source Materials

1 Since last year's report, Olmez and Gordon published a paper in which they

showed that refineries using zeolite catalysts and, to a lesser extent, oil-fired

power plants are often strong sources of airborne rare earths. Furthermore, the rare earths released by these sources are borne by fine particles and have a pattern

different from the crustal abundance pattern, being richer in light rare earths

(e.g., La/Sm >20 vs. La/Sm of 5-6 for crust). To investigate the reasons for the

unusual rare earth pattern, M. Kitto has been using both INAA and PGAA to analyze

about a dozen types of catalysts and several ores and products from the principal

U.S. supplier, MolyCorp. The analyses are not yet in final form, but major results

112
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Table 1. Summary of results from Analyses of 13 Zeolite Catalysts

Avg Sigma Max Min No. pts. Crustal Values

2 3 Wedepohl Taylor

La/Sm 61 76 305 8.43 13 6.7 4.9

La/Ce 2.21 1.79 5.16 0.36 13 0.58 0.49

La/Nd 1.80 0.54 2.61 1.11 10 1 .47 1 .06

La/Gd 530 681 2468 2.38 11 5.6 5.5

Al/Si 0.86 0.42 2.02 0.46 13 0.26 0.29

to date are shown in table 1 . Indeed, we see that the light rare earths (La, Cd, Nd)

in the catalysts have about the same ratios among themselves as the crustal values,

but that, in many of the catalysts, the light rare earths (e.g., La) are vastly

enriched relative to heavy rare earths (Gd, Sm). We intend to publish a full paper

on this study in the near future.

2. Compositions of Airborne Particles at Mauna Loa Observatory, Hawaii

Since 1979, our group has collected weekly samples almost continuously at Mauna

Loa Observatory (MLO) in Hawaii to monitor long-term trends and identify the sources

of particles in that area of the Pacific. A fairly complete set of data has existed

for some time up to Jan., 1983, when eruptions of Kilauea and, later, Mauna Loa,

volcanoes interrupted sample collection and analysis. During the past year, Diane

Hermann has been analyzing the vast number of samples collected since that time. The

500

MJJASONDJFMAWIJJ ASONDJFMA

Time of Year (May 83-Apr 85) MJJASON DJFMAMJJ ASONDJFMA

Time of Year (May 83-Apr b5)

Figure 1. Atmospheric Particulate Concentrations of Al and Na at Mauna Loa

Observatory, May 1983 - April 1985.

113
NON-RRD PROGRAMS

data from "shorts" INAA are now rather complete and the "longs" INAA measurements are now being made. Examples of the trends for Al and Na observed in shorts INAA are shown in figure 1. Aluminum is a good indicator of crustal dust, which shows huge

increases each spring because of the transport of Asian dust from deserts in China.

Sodium is a good indicator of marine aerosol. Its fluctuations are probably due to

storms in the ocean. There are a number of missing values because the frequent

volcanic eruptions since Jan., 1983 caused interruptions of sampling due to power

outages, etc.

3. Compositions of Emissions from Volcanoes

In projects initiated by Prof. W. H. Zoller, who has moved to the University of

Washington, the group has studied emissions from volcanoes for a number of years.

During the past year, Olmez et al . published results of their study of Kilauea

volcano, for which the following is the abstract:

"During May 1983, gas and particulate samples were collected at the cooling

vents of Kilauea volcano in Hawaii. Three vents on the southeast rift zone were

sampled using base-treated filter packs to absorb acidic gases and Teflon filters for

particles. The samples were analyzed for ^0 elements by nondestructive neutron

activation analysis. As with other volcanoes, the chalcophilic and volatile elements

were enriched by up to seven orders of magnitude relative to erupted basalt. Unlike

5 the case of other volcanoes, iridium was observed to be highly enriched (10 fold) at

the two higher temperature vents, and the degree of enrichment appears to be related

to both high temperatures and high fluorine content of the gases. Estimates of the

emission rates of Ir during eruptions of Kilauea based on the measurements reported

here and those of the Hawaiian Volcano Observatory yield an emission rate of about 3

g Ir per 10 m of magma. This rate amounts to only about 0.3 % of the Ir present in

the magma that is being released by the volcano. This previously unidentified Ir

source to the atmosphere and ocean may have a significant influence on the

geochemical cycle of Ir on the earth. The uniqueness of Kilauea in its emissions of

Ir is probably related to the deep source of magma, which contains significant levels

of Ir (0.32 ppb) and high levels of the halogens F and CI."

4

.

South Pole Aerosol

The following is the abstract of a paper about to be submitted to Science by G.

5 Tuncel and W. H. Zoller:

"The average particle-borne Ir concentration in the South Pole atmosphere is

-17 3 (7.3 ± 3.1) X 10 g/m . From this value, it is shown that the concentration of

extraterrestrial material in the South Pole atmosphere is not large enough to explain

114
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the enrichments of anomalously enriched elements; however, meteoritic material

contributes significantly to the observed concentrations of Co, Fe and Mn. The

accretion rate for sporadic background extraterrestrial material is calculated as

11 ,000 tons/yr."

5. Regional Scale Receptor Modeling

The following is summarized from S. Tuncel's thesis:

Samples of atmospheric particles were collected by the Environmental Protection

Agency (EPA) from May, 1980 to Dec. 1981 at 3 rural sites in the Ohio River Valley

(ORV): West site in KY, Center site in IN and East site in OH. All samples were

7 analyzed by x-ray fluorescence (XRF) at EPA. The XRF data and associated wind

trajectories were used to select 200 of the ORV samples in the fine fraction for

further analysis by INAA to provide data for about MO species in each sample. A

summary of the combined XRF/INAA data for selected elements in samples were collected

from air masses arriving from the southwest is given in table 2.

Chemical mass balances (CMBs) were used to resolve elemental concentrations for

each sample into 11 components: coal, oil and refuse combustion, soil and marine

aerosol, emissions from refineries, motor vehicles, iron-and-steel plants, copper and

cement plants, and regional sulfate. Oil emissions and soil were the least

significant sources among the 11 in fine particle fractions from the ORV. On the^

average, 80/6 of the mass was explained, nearly all of it as regional sulfate. Coal

emissions and regional sulfate contributed comparably to the As and Se

concentrations. Of the fitted elements, Mn was the most severly underpredicted,

especially at the West station. The problem is apparently caused by point sources of

Mn ( f erromanganese plants) at the west end of the Valley. Aside from Mn and,

possibly, Mo and W, very few elements showed more than factor-of-two variations for

different wind trajectory groups, ranging from those coming up the Valley to those

coming from industrial cities around the Great Lakes.

During the summer of 1983, EPA, DOW and EPRI and their contractors collected

ambient samples at a site near Deep Creek Lake, MD and in stacks and plumes of

several coal-fired power plants upwind of the site. These samples have been

subjected to XRF in other laboratories and are being analyzed by INAA by our group.

6. Analysis of Materials from the East Pacific Rise

Using INAA and PGAA we have analyzed over fifty smoker and worm tube samples

from the 13° N and 21° N East Pacific Rise sites. With Dr. J. N. Valette-Silver

(formerly with the Carnegie Institution of Washington and now with our group) and Dr.

Jody Deming of the Chesapeake Bay Institute, the Johns Hopkins University, we have

115
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Table 2. Concentrations of Selected Elements in Fine Fraction at Three ORV Sites in

Air Masses with Southwest Back Trajectories

Element

West Site

(n = 16)

Concentration (ng/m )*

Centei' Site

(n = 14)

East Site

(n = 23)

Na

Al

Si

S

01

110 ± 60

180 ± 170

570 ± 520

2500 ± 1400

30 ± 90

70 ± HO

150 ± 120

360 ± 240

4100 ± 1600

35 ± 21

90 ± 60

110 ± 1 80

230 ± 340

3400 ± 2600

50 ± 55

K

Ca

Sc

V

Mn

120 ± 50

105 ± 70

0.04 ± 0.04

1.4 ± 0.8

18 ± 17

115 ± 50

80 ± 30

0.03 ± 0.02

0.8 ± 0.5

4.7 ± 1 .3

90 ± 65

55 ± 35

0.09 ± 0.14

0.8 ± 0.6

7 ± 8

Fe

Zn

As

Se

Br

140 ± 1 15

11 ± 6

0.9 ± 0.5

1 .9 ± 0.8

4.1 ± 2.0

90 ± 50

14 ± 6

0.9 ± 0.4

1 .9 ± 0.7

4.9 ± 1 .5

120 ± 240

26 ± 19

1 .4 ± 1.3

2.0 ± 1 .3

6 + 4

In

Sb

La

Sm

Pb

0.01 ± 0.009

0.6 ± 0.5

0.27 ± 0.25

0.03 ± 0.02

34 ± 15

0.01 ± 0.01

0.5 ± 0.2

0.2 ± 0.14

0.02 ± 0.01

53 ± 11

0.06 ± 0.2

0.6 ± 0.4

0.12 ± 0.11

0.014 ± 0.017

56 ± 22

^Uncertainties are standard deviations of a single observation

116
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° 4

Uranium Standard

"23.57 ug

239 Np

239 99M0

Np

u

239 Np

Alvinella Tube

Sample 3d--166±3 ug/g uranium

59Fe «2Br

80 120 160 200 240 280

Energy-keV

Figure 2. Gamma-Ray Spectra of (top) uranium standard and (bottom) 13°N East Pacific

Rise worm tube sample following neutron irradiation.

reported unusually high (up to 600 ppm) concentrations of uranium in the biogenic

tube structure of Alvinella Pompejana Gaudata, a small worm living in the vicinity of

the hydrothermal chimneys. This enrichment may be due to either passive physical

absorption or to active biochemical or microbial processes. In figure 2 are shown Yray spectra of one sample and a uranium standard following neutron activation. We

are completing the full elemental analysis of these samples.

7. Gomparison Study of Filters for Gas-Phase Sampling of the Atmosphere

We have recently completed the analysis of a series of atmospheric filter

samples taken to evaluate the relative attributes of base-treated filters and

activated charcoal-impregnated filters when used for gas-phase sampling. We found

that the elements B, S, and As were strictly in the form of acidic species (most

likely H Bo , SO , and As , respectively), while Gl, Br, I, Se, Sb and Hg species

were both acidic and non-acidic (organic or elemental) in nature. The charcoal

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filters had severe blank problems for most elements, and their large Mn content

limited the INAA for short-lived irradiation products. The results of this

experiment will be reported in a manuscript to be submitted to Atmospheric

Environment . It is anticipated that these species may be important as "tracers of

opportunity" for a number of natural or anthropogenic processes.

8. Boron and Selenium as Gaseous and Particle Tracer Elements for Coal-Fired

Power Plant Emissions

9

As reported previously , gas-phase boron (as H B0_) and particulate Se may be a useful tracer for SO^ and SO^ derived from coal-burning utilities. Figure 3 shows

the correlation of these species over a period of two months at College Park, MD in

1984. Using simple input parameters (identical, evenly-spaced power plants burning

9 10 11

"typical" coal ' ) and the modified (by GEO) Hybrid Receptor Model , we find

remarkably good agreement between our data and the predicted B/SO , S/Se, and

S(p)/S(g) ratios (table 3). We are working to refine the input parameters to better

represent the coal-related emissions for the Ohio River Valley. We are also

collecting particles, acidic gas-phase species, and rainfall at College Park, MD in

order to complete a continuous year-long data set. We hope to use the data to

unravel some of the details of the wet deposition of the sulfur species.

9. Ultrafine Particle Generation

In part of the work being done under funding from the Electric Power Research

Institute, we (with Dr. Willliam R. Kelley of NBS) are experimenting with various

techniques for generating ultrafine tracer particles to be used in source tagging

experiments. In these experiments, ultrafine particles of K, Mn, and Nd are made

4.5

CO

D S(P)/2

13 15 17 19

Sample Number

+ SeXIOOO * S(g)/4

21 23

'^ B(g)x100

Figure 3. Concentrations of particulate S and Se and gas-phase S and B at College

Park, MD.

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Table 3. Comparison of Hybrid Receptor Model with Observed Concentrations at College

Park, MD (CP) and Wallops Is., VA (WI).

Concentration Predicted Observed CP Observed WI

at Distance (km ) (May and June) (July)

species 100 700 1000 1800 15 samples 12 samples

gases

SO^ (yg/m^) 16 27 28 0.2 16 ± 5 8.1 ± 4.9

B (yg/m^) 12 22 23 0.53 16 ± 7 70 ± 50

particles

S0^~^ (yg/m^) 1.0 14 19 11 11 ± 5 13.2 ± 7.5

Se ing/nr) 0.7 2.5 3.0 1 .0 2.3 ± 1 .1 1 .76 ± 0.91

ratios

S(p)/S(g)

B(g)/S02 : S(p)/Se(p)

0.04

X 1000 0.75

570

0.35 0.46 26.0 0.46 ± 0.21 1 .20 ± 0.38

0.81 0.82 1 .80 1 .00 ± 0.42 7.9 ± 2.7

1900 2100 3100 1560 ± 680 3040 ± 770

either by combustion or by dispersing dilute solutions of the tracer materials with

air atomizing nozzles. Size distributions of the residue aerosols are measured with

a mobility analyzer. To provide a check on the mobility analyzer, we are using a five-sage micro-orifice impactor (MOI) with cut points at 1.03, 0.53, 0.142, 0.083,

and 0.037 ym. Total tracer-particle mass is also being measured with a 47 mm filter

sampler. Tracer particle mass on the filter and MOI samples is determined by

measuring K, Mn, or Nd by INAA.

In table 4, we compare cumulative mass data obtained with the MOI with those

inferred from the mobility measurements for a run in which a 3 ppm Mn solution in

absolute methanol was aspirated into an air-atomizing nozzle at an air pressure of

1,585 kPag. About 665^ of the mass was collected on the backup filter of the impactor

and is, therefore, less than 37 nm. The mobility data, including the CNC measurement

of particles less than 10 nm, suggest that at most ^0% of the mass is accounted for

by particle less than 37 nm. The data would agree if the average efficiency of the

mobility analyzer for particles would account for 25^ of the mass. This is quite

likely since it is known that the mobility analyzer is only 3% efficient for 3 nm

119
NON-RRD PROGRAMS

Table 4. Comparison of cumulative mass distributions obtained with an MOI and DMPS

system for the Sonicore and SSC-1 nozzles, percent less than stated size.

Sonicore nozzle SSC-1 nozzle

DMPS MOI DMPS MOI

d i am

.

mass <size, diam. mass <size, diam. mass <size, diam. mass <size, nm % nm % nm % nm %

10.il9 6.2 37 66.2 10.49 5.0 37 65.5

1 1 .^9 7.0 83 67.6 11 .49 5.6 83 67.2

12.96 7.8 142 90.4 12.96 6.4 142 97.7

15.43 9.1 530 98.2 15.43 7.7 530 99.5

17.97 11 .2 1030 99.6 17.97 9.7 1030 -

20.45 14.1 20.45 12.4

23.45 18.1 23.45 15.8

26.93 23.3 26.93 20.2

31 .40 29.8 31 .40 26.2

36.41 38.2 36.41 34.7

41 .89 47.2 41 .89 45.1

48.37 56.9 48.37 58.6

55.86 66.4 55.86 73.6

64.81 74.1 64.81 85.7

75.30 80.6 75.30 94.7

86.79 85.7 86.79 99.5

99.75 89.7 99.75 100.0

115.19 92.6 115.19 100.0

133.16 94.9 133.16 100.0

153.61 96.9 153.61 100.0

177.99 98.5 177.99 100.0

205.99 100.0 205.99 100.0

237.39 100.0 237.39 100.0

120
NON-RRD PROGRAMS

particles. However, we are cautious in accepting the impactor data because of the

possibility that the mass on the backup filter may include some larger particles as

the result of particle bounce. Transmission electron microscopy measurements in

progress may tell us whether or not particle bounce is important. However, we are making additional measurements with the impactor with He as a diluent to reduce the

impaction cut points, and plan other measurements with a parallel diffusion battery.

INAA is ideal for these studies because of its excellent sensitivity for the tracer

elements.

1. I. Olmez and G. E. Gordon, Rare Earths: Atmospheric Signatures for Oil-Fired

Power Plants and Refineries, Science 229 , 966-968 (1985).

2. K. H. Wedepohl, in Origin and Distribution of the Elements , L. H. Ahrens, ed.

(Pergamon Press, London, 1968) pp. 999-1016.

3. S. R. Taylor, Abundance of Chemical Elements in the Continental Crust: A New

Table, Geochim. Cosmochim. Acta 28, 1273 (1972).

H. I. Olmez, D. L. Finnegan and W. H. Zoller, Iridium Emissions from Kilauea

Volcano", J. Geophys. Res. 9]_, 653-663 (1986).

5. G. Tuncel and W. H. Zoller, Iridium Concentrations in the South Pole Aerosol:

Estimation of Meteorltic Component, Science (to be submitted).

6. S. G. Tuncel, Regional Scale Receptor Modeling in the Northeast U.S., Ph.D.

thesis. Department of Chemistry and Biochemistry, University of Maryland,

College Park, MD 207^2.

7. R. W. Shaw, Jr. and R. J. Paur, Atmos. Environ. V[_, 2031 (1983).

8. J. N. Valette-Silver , A. Bates, D. Anderson, J. Deming, and W. H. Zoller,

Uranium Enrichments in Smoker Material Collected for the East Pacific Rise , 1985

Annual Meeting, American Geophysical Union, Seattle, WA.

9. M. E. Kitto and D. L. Anderson, Simultaneous Collection of Particles and Gases

from Coal-Fired Power Plants , National Meeting of the American Chemical Society,

New York, NY (1986).

10. G. E. Gordon and I. Olmez, in APCA Specialty Conference on Receptor Methods for

Source Apportionment: Real World Issues and Applications, Williamsburg, VA

1985.

11. C. W. Lewis and R. K. Stevens, Atmos. Environ. 19, 917 (1985).

121
NON-RRD PROGRAMS

PRECISION IN ROUTINE I.N. A. A. OVER A TWO YEAR PERIOD AT THE NBSR

M. J. Blackman

(Smithsonian Institution, Washington, D.C.)

Beginning in June 1984 and continuing to date, alliquots of SRM 579 - Brick

Clay have been included as a check standard in 61 separate irradiations of

archaeological ceramics. The goals of the analysis of the ceramics were to routinely

analyze a large number of samples (1100) for as many elements as possible (32 sought)

with as much precision as possible. Working within these constraints, irradiations

and counting times could not be tailored to specific elements.

The irradiations were carried out with reactor power at 10 MW in the RT-3

pneumatic facility and with reactor power at 20 MW in the RT-1 and RT-4 pneumatic

facilities. The length of the irradiations were varied in accordance with the

neutron flux in each facility so that the fluence was approximately the same.

Samples and standards, in .5 ml polyethylene microcentrifuge tubes, were packed in a single band in the "rabbit" to minimize linear flux gradients. No special attention

was given to the placement of standards or check standards within the band, and

therefore any radial flux variation was not controlled. The gamma counting was

carried out on two different detectors with similar resolution, but quite different

counting efficiencies (8.35^ vs. 34.85S). Two different automated sample changers were used, one with a fixed geometry of 10 cm and the other with variable geometry. Each

sample was counted twice, the first count after a 5 day decay and the second after at

least a 30 day decay. The counting times were varied according to the detector

efficiency and the sample to detector geometry so that the counting statistics were

approximately equal for each element determined in each aliquots.

Initially about 10 grams of SRM 679 was dried for 24 hours at 110° C and cooled

and stored in a dessicator. Fifty four nominal 100 mg. aliquots were weighed as needed over the two year period, in addition, seven nominal 40 mg. alloquits were

also analyzed in separate irradiations. The Initial stock of SRM 679 was

periodically redried. During this period at least three different balances were used

for weighing.

SRM 1633 (coal flyash) was the comparitor standard used to quantify 23 elements

in SRM 679. Table 1. lists the elements sought, their radionuclides, associated

gamma energies, and the concentration values used for the standard. Commercially

available computer software was used to process the gamma ray data with several

upgrades and a shift in computer systems occurring during the duration of the

experiment. In summary, while the requisite care in accordance with good analytical

122
NON-RRD PROGRAMS

Table 1. Experimental Parameters

Gamma Ray Concentrations in

Elements Nuclide Energy (keV) SRM1633 Standard Count

Na Na-24 1369 0.32% * 1

K K -42 1525 1.61% * 1

Ca Ca-46 1296 4.70% * 1

Sc Sc-46 889 27.0 ppm * 2

Cr Cr-51 320 131 ppm # 2

Fe Fe-58 1099

1292

& 6.20% * 2

Co Co-60 1173

1333

& 41.5 ppm • 2

Zn Zn-65 1115 213 ppm 2

As As-76 559 61.0 ppm # 1

Rb Rb-86 1077 12 5 ppm * 2

Sb Sb-122 564 6 . 9 ppm * 1

Cs Cs-134 796 8 . 6 ppm * 2

Ba Ba-131 496 2700 ppm * 1

La La-140 1596 8 2.0 ppm * 1

Ce Ce-141 145 146 ppm * 2

Sm Sm-153 103 12.9 ppm 1

Eu Eu-152 1408 2 . 5 ppm * 2

Tb Tb-160 879 1 . 9 ppm * 2

Yb Yb-175 396 6 . 4 ppm 1

Lu Lu-177 208 1 . ppm * 1

Hf Hf-181 482 7 . 9 ppm * 2

Ta Ta-182 1221 1 . 8 ppm * 2

Th Pa-233 312 2 4.8 ppm * 2

U Np-239 106 11.6 ppm # 1

* Ondov, J.N., Zoller, W.H., Olmez, I., Aras, N.K., and Gordon, G.E.

Analytical Chemistry, vol 47, pp. 1102-1109, 1975.

# Certificate of Analysis, SRNs 1632 and 1633, OSRH, National Bureau

of Standards, Department of Commerce, Washington, D.C. 20234.

123
NON-RRD PROGRAMS

Table 2. SRM679 BRICK CLAY: NOMINAL 100 MILLIGRAM SAMPLES

Na

PCT

K

PCT

Se

PPM

Cr

PPM

Fe

PCT

Co

PPM

Zn

PPM

As

PPM

Number Averaged 54 52 54 54 54 54 53 54

Mean Cone. .135 2.28 22.8 108 8.91 26.5 129 9.80

Group Sigma ( %

)

2.4 8.3 1.4 3.0 2.9 1.6 3.3 6.0

Counting Error ( (single sample)

%) 0.8 3.5 0.1 1.8 0.2 0.5 2.7 4.3

Upper 95% Limit

Lower 95% Limit

.142

.129

2.66

1.90

23.5

22.2

114

101

9.42

8.40

27.3

25.6

138

121

11.0

8.6

Rb

PPM

Sb

PPM

Cs

PPM

Ba

PPM

La

PPM

Ce

PPM

Sm

PPM

Eu

PPM

Number Averaged 54 54 54 54 54 54 54 54

Mean Cone. 225 0.97 9.63 454 56.4 102 9.06 1.68

Group Sigma (%) 9.3 9.9 2.7 12.9 1.4 1.9 1.6 2.1

Counting Error (%) 5.0 8.2 1.9 10.5 0.3

( single sample

)

Upper 95% Limit

Lower 95% Limit

267

184

1.16

0.78

10.2

9.1

572

337

57.9

54.8

106

99

9.35

9.77

Tb

PPM

Yb

PPM

Lu

PPM

Hf

PPM

Ta

PPM

Th

PPM

U

PPM

Number Averaged 53 54 54 54 53 54 53

Mean Cone. 1.21 4.07 0.62 4.59 1.21 14.3 2.25

Group Sigma (%) 13.0 4.8 6.6 3.5 6.8 2.2 15.9

Counting Error (%)10.0 3.2 4.8 2.7 6.4 1.6 13.3

( single sample

)

Upper 95% Limit 1.52 4.46 0.70 4.91 1.37 14.9 2.97

Lower 95% Limit 0.89 3.69 0.53 4.27 1.04 13.7 1.53

124
NON-RRD PROGRAMS

Table 3. SRM679 BRICK CLAY: NOMINAL 40 MILLIGRAM SAMPLES

Na

PCT

K

PCT

Sc

PPM

Cr

PPM

Fe

PCT

Co

PPM

Zn

PPM

As

PPM

Number Averaged 7 7 7 7 7 7 7 7

Mean Cone. 0.138 2.38 23.2 108 9.17 26.9 130 9.69

Group Sigma (%) 1.9 12.4 2.4 2.4 3.0 3.4 4.2 6.6

Counting Error ( (single sample)

%) 2.9 15.6 0.1 1.4 0.2 0.4 2.2 12.8

Upper 95% Limit

Lower 95% Limit

0.144

0.131

3.10

1.66

24.6

21.9

114

102

9.84

8.49

29.1

24.6

143

116

11.3

8.11

Rb

PPM

Sb

PPM

Cs

PPM

Ba

PPM

La

PPM

Ce

PPM

Sm

PPM

Eu

PPM

Number Averaged 7 7 7 7 7 7 7 7

Mean Cone. 214 0.93 9.70 468 56.2 105 9.09 1.71

Group Sigma ( %

)

10.5 10.6 4.0 11.4 1.2 2.2 1.1 1.7

Counting Error (

( single sample

)

%) 5.1 2.8 1.4 6.3 0.4 0.7 0.6 1.4

Upper 95% Limit

Lower 95% Limit

269

159

1.18

0.69

10.6

8.7

599

337

57.8

54.6

110

99

9.33

8.85

1.78

1.64

Tb

PPM

Yb

PPM

Lu

PPM

Hf

PPM

Ta

PPM

Th

PPM

U

PPM

Number Averaged 7 7 7 7 7 7 6

Mean Cone. 1.22 4.29 0.61 4.63 1.30 14.7 2.13

Group Sigma (%) 11.3 8.3 9.0 3.9 7.7 2.9 21.5

Counting Error (%) 8.2

( single sample

)

Upper 95% Limit 1.56 5.17 0.75 5.07 1.55 15.8 3.30

Lower 95% Limit 0.89 3.42 0.48 4.19 1.06 13.7 0.95

125
NON-RRD PROGRAMS

procedures was taken for each analysis, there was a great deal of variability in

irradiation facilities, counting equipment, and processing software. The data set

for SRM 679 ought then to provide a baseline for analytical precision in instrumental

neutron activation analysis over time at a single facility.

Table 2. shows the results of 54 analyses of nominal 100 mg. samples. Of the

23 elements quantified in SRM 679, over half (14) have a precision of better than 5%

(1 standard deviation), with five elements better than 2% precision. Only three

elements had precisions worse than 10^ Ba - 12.9/5, Tb - 13.0^, and U - 15.9/S.

Typical counting statistics for each of these elements in SRM 679 are: Ba - 10.555;

Tb - 10.0^; and U - 13-355. For these three elements all but about 2 to 3 55 of the

sample variance can be attributed counting error. When the elements with very low

counting errors (Sc, Co, La, and Sm) are examined, the sample variance not attributed

to counting error is 1 to 1.555. All random and systematic errors, exclusive of

counting error, appear therfore, to contribute only about 1.555 to the sample

variance, this includes potential sample inhomogeneity.

Table 3. shows the results of the 7 analyses of nominal 40 mg. samples. When

these results are compared to those for the nominal 100 mg samples, the

concentrations for all 23 elements fall within 1 standard deviation in the two sets.

The implication is that to within about 1.555 to 2.0%, 40 mg. aliquots of SRM 679 and

the standard SRM 1633 are both homogeneous and directly comparable to 100 mg

.

aliquots.

Examination of these two data sets shows that for a large number of elements

instrumental neutron activation analysis can routinely achieve better than 5%

precision regardless of changes in irradiation facilities, instrumentation, and

computer processing software. With some special effort at tailoring irradiation and

counting times to the nuclides displaying less precision, precision of better than 555 could be achieved routinely for all 23 elemental concentrations reported here.

126
NON-RRD PROGRAMS

NEUTRON DEPTH PROFILING AT NBS

R. G. Downing J. T. Maki, and R. F. Fleming

(Center for Analytical Chemistry)

The neutron depth profiling facility has been involved in a number of

industrial and basic science activities over the last year. Over twenty academic and

industrial scientists are collaborating with NBS through the use of NDP on modern

material problems of mutual interest. Several of the companies have established

direct computer links with our computers to facilitate the analysis of data.

Oxygen was nondestructively and quantitively profiled by NDP in a thin metal

oxide film for the first time this year. Scientists from Eastman Kodak prepared the

film from enriched oxygen-17 gas. Oxygen-17 has a relatively small neutron cross

section for the emission of an energetic alpha particle, making it particularly

difficult to profile. Elements such as oxygen, chlorine, and nitrogen would be

profiled more routinely with the installation of the proposed cold neutron guide

hall.

The metal oxide film and several thin boron implanted glass films were taken to

the Institute Max von Laue-Paul Langevin (ILL) for study during the summer. Working

with R. Henkelmann of Garching, Germany, the ILL depth profiling facility and the NBS

facility have been cross calibrated. The ILL NDP facility is stationed on a thermal

guide tube and consequently has significantly lower background than the NBS thermal

beam. As a result, experiments were carried out at ILL to look at deeper elemental

profiles as well as at elements which have lower-energy, charged particle emission.

Other work includes the completion of a study of helium release from single

crystal nickel. This project culminates the thesis research work of J. T. Maki from

the Nuclear Engineering Department at the University of Michigan, Ann Arbor. Two

research papers are being submitted from work on boron implantation and diffusion in

infrared detector materials. This research is through a joint project with Aerospace

Corp., Los Angeles, CA. Also, the first profiles of lithium diffusion on a few

minute time scale were made during the last year. Diffusion constants were derived

for several compositions of polymer films without the typical destructive analysis.

The polymer work has been carried out at the initiation of scientists from the

Polymers Division at NBS.

Finally, the facility itself is evolving to meet the increasing work load. A turbomolecular vacuum pump was installed to increase system reliability and to reduce

down time between samples. Two rotational sample stages were acquired which will be

installed in the NDP target chamber. The stages will allow precise alignment of

127
NON-RRD PROGRAMS

sample-to-detector geometry. This in turn will result in increased depth resolution

in the profiles of certain types of samples. Further improvements in the facility

are being developed to handle the increasing variety of measurements and experiments

performed by NDP.

CALIBRATION OF A NEUTRON DRIVEN GAMMA RAY SOURCE

T. G. Williamson

(University of Virginia, Charlottesville, Virginia)

and

G. P. Lamaze, D. M. Gilliam and C. Eisenhauer

(Center for Radiation Research)

Cadmium and iron cylinders in the thermal column cavity of the National Bureau

of Standards Reactor (NBSR) provide intense sources of capture gamma rays. The

neutron and gamma ray fields in these cylinders have been measured and the fields

used for photofission measurements. The thermal column cavity is a 0.3 m diameter

spherical cavity in the graphite thermal column of the NBSR. The capture gamma ray

sources are horizontal cylinders located so that the cylinder center is near the

center of the cavity.

The cadmium capture gamma ray source is an extruded cadmium cylinder 1 ram thick

and 55 mm diameter with a 1 mm thick cadmium cap on the end closest to the reactor.

The cadmium cylinders can be enclosed in a 6.4 mm sheath of lithium glass to

eliminate the cadmium capture gamma rays and to measure the background of gamma rays

from the core and from neutron capture in the surrounding graphite. A lithium glass

labyrinth in the cylinder away from the core minimizes streaming from scattered

radiation.

The iron cylinder was machined from carbon steel containing 0.2? carbon. Other

constituents measured by NAA include manganese, 0.1%, chromium 0.08?, arsenic,

0.005?, copper, 0.012?, and antimony, 0.0017?. The cylinder was tapered to fit in

the spherical cavity with the following dimensions:

Inner radius 37.5 mm Outer radius 47.0 mm Length

maximum 234 mm miminum 215 mm

1.28
NON-RRD PROGRAMS

Eight 3 mm diameter aluminum rods were fastened to the iron to support it in the

graphite cavity. During irradiations a 3 mm aluminum sleeve and 6.4 mm of lithium

glass fit inside the cylinder to minimize the thermal neutron fluence in the cylinder

(figure 1). The lithium glass cylinder has a lithium glass end cap on the reactor

150 mm

Figure 1. Iron cylinder in thermal column cavity

end and a labyrinth in the cylinder away from the core to minimize streaming of

scattered neutrons.

The neutron fluence at the surface of the cylinders was measured by exposing

dilute gold foils on the exterior of the cylinders and also by direct counting of the

activated cylinders in collimated geometry. Foils were taped to the outer radius of

each cylinder equally spaced around the circumference at the center and at each of

the ends. The foil activities were measured with a calibrated germanium detector.

For both cylinders the top to bottom variation at each of the three axial positions

was less than 10% and the right-to-left variation less than 3%- The ratio of the

foil activity at the end away from the reactor to that at the end nearest to the

reactor was 0.67 for both cylinders. The thermal neutron fluence rate at the outer

1 1 2 radius and axial center of the iron cylinder is 1.42 x 10 n/cm -s and on the

1 2 cadmium cylinder 4.83 x 10 n/cm -s. The gamma ray distribution along the axis is calculated for a cylindrical shell

source. For a source distribution which varies linearly along the cylindrical axis,

z, the source term is

S(z) = S(1 + az)

2 S is the gamma ray source - photons/cm -s

a is the slope of the distribution.

129
NON-RRD PROGRMS

With the origin of the z axis at the center of the cylinder and S the source

strength at z = 0, the distribution is the following

^/S = 1/2 {ARCTAN(Z1/R) + ARCTAN(Z2/R) } for the constant term

and

$/S = (Ra/H) LN {(Z1^ + R^)/(Z2^ + R^)} for the linear term,

where Z1 + Z2 = L, the cylinder length, and R is the cylinder radius.

With attenuation of photons in the cylinder the uniform term becomes

f/S = (1/2) EXP(-b) {K(0l,b) + K(e2,b)}

b is attenuation length - yt

K line source attenuation function

01 and 02 angles from a point on axis to the cylinder ends.

The cadmium cylinder has a cadmium cap on the end nearest to the reactor which

provides an additional gamma ray source. The axial distribution of gamma rays from

this source is

$/S1 = (1/i|) LN {1 + (R^/Z3^)}

2

SI is source at the end cap - photons/cm -s

Z3 is the distance from the end.

1000

oco

u

0) w

«

Q.C3

Oo

100

10

1

\

1

1 r U-238 in Cadmium Cylinder

o Net Counts + Lithium Glass Cover

° Curtain Down

1 1 r

o o

D D

-15 -12 -9 -6 -3 3 6 9 2 15

Axial Position - cm Figure 2. U-238 in cadmium cylinder

130
NON-RRD PROGRAMS

For cadmium the axial gamma ray distribution was calculated by approximating

the gamma ray source as a cylinder at the outer cadmium surface with no attenuation

of the photons through the cadmium or the aluminum support cylinder.

For iron a one dimensional radiation transport calculation in cylindrical

geometry (ANISN) was done to obtain the radial distribution of thermal neutrons and

of capture photons. The location of the radial averaged thermal neutron fluence was

chosen as the location of a shell source of photons and the photons were attenuated

by material between this shell and the center of the cylinder. The iron capture

gamma ray spectrum contains photons at all energies up 9 Mev, however, about 35% of

the gamma rays are in the energy interval from 7 to 8 Mev. The threshold for

photofission in the isotopes in this investigation is about 6 Mev. Thus the

attenuation coefficient for this calculation was that at 7.0 Mev for iron, aluminum

and pyrex glass. The attenuation length from a shell at M3 mm, the location of the

average thermal neutron fluence, to the cylinder center is yt = 0.2. Of this

attenuation length, 67% is in iron, 225^ in glass and 1 1 /& in aluminum. These values

were used to calculate the distribution of the capture gamma ray intensity along the

cylindrical axis relative to the photon source strength.

Photofission measurements were made with NBS miniature fission chambers.

Paired fission chambers were placed in the cylinders so that fission count rates

could be taken at various positions along the cylindrical axis. The chamber

designations and material masses are tabulated below:

Chamber Designation Mass

U-238 HD-5~2 691.1 ± 1.3% yg

U-235 S-002-1 1.921 ± 0.65& pg

Th-232 L-5-2 603.5 ± 2.0? yg

Np-237 S-2-2 260.6 ± 1.2% yg

Measurements were taken with the boral curtain up and down, and for the cadmium

cylinder, with and without the lithium glass cover. Data for U-238 in cadmium are

shown in Figure 2. The response with the boral curtain down is about 2% of the

response with the bare cadmium cylinder and the response with the lithium glass cover about 10%. The lithium glass data was used as background to obtain the net response

to the cadmium capture photons.

The calculated and measured distributions for Th-232 is shown in Figure 3- The

value of the parameter a, the slope of the linear term, was adjusted to give the best

fit of the calculated distribution to the measured distribution for a span of 60 mm

on either side of the center of the cylinder (the 5 measured points nearest the

131
NON-RRD PROGRAMS

150

120 -

T5C

o

u

a>

(/3 90

60

30 -

-

1 1 1 1 1 1 1 TH-232 in Iron Cylinder

o Measured

1 1

- — Calculated \

- V

X -

-

o /

-

-

1 1 1 1 1 1 1

1

1

-15 -12 -9-6-3 3 6

Axial Position - cm

12 15

Figure 3- Th-232 in iron cylinder

center). The measured quantity is fissions per second (cps) per atom and the

calculated quantity is the capture gamma ray fluence rate. The ratio of these values

is photofission cross section. Cross sections calculated from the detector foil masses and the ratio of the measured to the calculated distributions averaged over

the center five points are tabulated below:

Photofission Cross Section - mb

Cadmium Iron

U-238 0.28 2.90

Th-232 0.14 1.M3

Np-237 0.66 7.47

These are spectrum averaged cross sections for the cadmium capture gamma ray spectrum

and for the iron capture gamma ray spectrum respectively.

In the cadmium cylinder the photon fluence rate at the center is 2.4 x 10

2

,11

photons/cm^-s and the dose rate 0.83 Mrads/h (8300 Gy/h) and in iron the photon

10 2 fluence rate is 4.8 x 10 photons/cm -s and dose rate 0.36 Mrads/h (3600 Gy/h). The

5 fast neutron fluence rate at the center measured with Ni (n,p)Co is 2.3 x 10

2 neutrons/cm -s.

132
C. Reactor Operations and Services

REACTOR OPERATIONS AND SERVICES

T. Raby

The past year was the first full year of operation at the higher power level of

20 MW, double the previous power level. The new power level proved very successful

and in general operations were routine and smooth.

1 . Reactor Operations

Reactor operation was continuous over the last year except for periods of

refueling and maintenance. A summary of the operating statistics for the period July

1, 1985 to June 30, 1986 is presented in the following table:

No. of days at 20 MW 285

On-line time at 20 MW 1S%

Average U-235 burnup 6H%

No. of Irradiations 2080

Hours of Irradiations 3577

Hours per Irradiation 1 .7

2. Irradiation Services

Extensive irradiation services were provided to many users from within and

outside NBS. In all, more than 2000 irradiations involving thousands of samples were

performed.

ENGINEERING SERVICES

J. Nicklas

In addition to normal engineering and design services provided to reactor

operations, experimenters and users, the engineering staff is involved in a continuing effort to upgrade the reactor instrumentation in addition to normal

surveillance calibrations.

The shim arm test assembly used for testing shim arm mechanisms and clutch

release assemblies is about finished and is available for spare parts for reactor

shim arms. Fifty fuel assemblies have been inspected and accepted from the DOE contractor

by the NBSR staff. An additional 25 fuel assemblies have been fabricated and are

awaiting acceptance. Fuel compacts now being made contain 350 gms per element, a

133
REACTOR OPERATIONS AND SERVICES

Change from 300 gm elements. The first 200 plates of the 350 gm elements will be

radiographed to determine that the process is under control.

The full element handling tool heads have been modified slightly by adding

another spring pin to the mounting block which bears on the lifting shaft to increase

its resistance to rotation. This resistance' will assure locking of the element to

the upper grid and provide operators with a more positive feel when transferring

fuel. A new tool for the transfer of fuel from the reactor core to the storage pool

was made and tested.

A method has been developed to plug heat exchanger tubes with rubber plugs.

The previous method of pounding metal plugs into the tubes required entry into the

bonnet with subsequent high radiation exposure to personnel and was limited to

personnel that could enter a 12 inch manhole.

A tool for pulling the fuel transfer arm bearings has been designed and

fabricated. The original carbon steel bearings are causing an occasional sticking of

the transfer arms which causes some loss of feel when transferring fuel.

The second tritium monitor has been installed, tested and completed. Two more modern design differential transmitters have been installed in the process

demineralized water system.

The instrument group has also provided assistance to the experimental

researchers with electronics repair, modification and interface designing. An

uninterruptible power supply system was planned, purchased and installation is

underway at this time. The UPS system will provide continuous clean power to the

experimental computer and associated instrumentation during brief power interruption.

An instrumentation panel for monitoring the Cryogenics Bismuth Tip experiment

facility is in the assembly and testing stage.

134
D. Service Programs

NEUTRON ACTIVATION ANALYSIS AT THE FOOD AND DRUG ADMINISTRATION

W. C. Cunningham and W. B. Stroube, Jr.

(U.S. Food and Drug Administration, Washington, DC)

The Food and Drug Administration (FDA) maintains a neutron activation analysis

(NAA) facility in the reactor building of the National Bureau of Standards (NBS).

The NAA program at FDA includes analytical support for regulatory activities and

special projects as well as applications research. NAA complements the other

analytical techniques used at FDA and serves as a reference technique for quality

assurance practices.

During the past year the NAA laboratory of FDA was involved in many areas including regulatory analysis, methods development and applications research. In

regulatory work, both radiochemical and instrumental NAA were used as reference

techniques, providing broad-based multielement information. Methods development and

applications research were performed as part of an ongoing FDA effort to improve its

ability to protect the public. In one area the FDA NAA facility applied its various

procedures to the analysis of food supplements, mineral supplements and herbal

products. This work will enable the FDA NAA facility to react more quickly when

these products must be analyzed. Radiochemical research included tracer experiments

designed to discover the mechanisms responsible for chromium losses that occur during

various digestion procedures.

Epithermal neutron activation analysis (ENAA) applied to food matrices has been

a joint ongoing project between the FDA Elemental Research Section and the NBS

Nuclear Methods Group. Early work on applying ENAA to the determination of iodine in

infant formula demonstrated the usefulness of the technique for food analysis. As

the scope of the project increased, two other research reactors, located at the

University of Virginia and at the University of Maryland, were used to show the

utility of the technique. This year ENAA studies were expanded to include a wide

variety of food matrices. This work was presented at the 7th International Meeting

2 on Modern Trends in Activation Analysis (MTAA) . As evidenced by the high interest

industry has shown in this procedure, the work has met a clear analytical need.

Several small reactors are now offering ENAA services that are based on the

methodology developed under this project.

135
SERVICE PROGRAMS

1. W. B. Stroube, Jr. and G. J. Lutz, in Production, Regulation and Analysis of

Infant Formula, Association of Official Analytical Chemist, Arlington, VA, 1985,

P.M24.

2. William B. Stroube, Jr. and George J. Lutz, Proceedings of the 7th MTAA, 1986, J. Radioanal. Chem., in press.

PURIFICATION OF REACTOR-PRODUCED FLUORIME-18 FLUORIDE USING

HIGH PRESSURE ION CHROMATOGRAPHY

J. M. Bennett, M. A. Channing, and R. D. Finn

(National Institutes of Health, Bethesda, MD)

Reactor-produced F-18 labeled fluoride is an important alternative for

facilities which do not have access to a particle accelerator. Fluorine-l8 can be

prepared via a two-step nuclear reaction:

^Li(n,a)^H and ^^0(^H,n)^^F

In our experiments two quartz tubes (3 mm i.d. x 90 mm) containing 0.4 g of 95.565K

5 14 enriched Li CO have been irradiated for 2 hours at a thermal flux of 1.3 x 10 n

-2 -1 -^ cm sec at the National Bureau of Standards Nuclear Reactor. Typically, 170 mCi

of fluorine-l8 is produced concurrently with 60 mCi of tritium (EOB). A method has

been developed utilizing high performance ion chromatography (HPIC) to not only

separate, but isolate and purify the fluorine-l8 species as its tetramethylammonium

salt. Potential sources of cationic and anionic contaminants have been identified

and examined by analytical HPIC, while radionuclidic impurities have been determined

using gamma spectroscopy and scintillation counting.

The reactivity of the final reagent fluoride was determined by monitoring its

incorporation as fluorine-l8 labeled 2-f luoro-2-deoxy-D-glucose upon reaction with

methyl 4,6-0-benzylidene-2, 3-cyclic sulfate- B-D-mannopyranoside.

Radionuclide purity from gamma-emitting contaminants was ascertained by gamma

spectrum analysis with a hyper-pure germanium detector in conjunction with a Nuclear

Data 683 series programmable MCA/computer system. The product had no detectable

gamma activity after purification other than the 511-KeV gamma peak of F-18.

Radionuclide purity from tritium and other beta-emitting contaminants was checked with a Beckman LS 5800 liquid scintillation counter after the decay of F-l8

was virtually complete. The tritium activity in the final product represents an

136
SERVICE PROGRAMS

average of 14 ± 1.6 pCi in a final volume of 20 mL containing 6.1 ±1.8 mCi of F-18

3 activity (Table 2). This value of H is well within the maximum permissable body

burden.

Conclusions

- Utilization of strong anion exchange (SAX) chromatography for trapping

F-1 8-f luoride eliminated interfering cationic and anionic species and also lowered

the tritium by-product to a permissable level.

DDI/HjO Vacuum; Pressure

DDI/H,0: Eluent

Rotovap

Waste

Figure 1. Reactor-produced F-18 fluoride purification apparatus.

- Although neutron bombardment of trace impurities present in lithium-6 enriched

lithium carbonate ( Li C0_) may produce a variety of radionuclides, examination of

the final reagent mixture by beta and gamma spectroscopy showed only the expected

fluorine-l8 and tritium to be present.

1ft fi - Starting with approximatley 90 mCi of F/ Li^CG- and after a 70 min, purification

1 8

typically, 40 mCi (uncorrected) of the TMAOH/TMAF F-fluoride reagent was produced.

This reagent effected incorporations of ^ 955S upon reaction with methyl 4, 6-0-

benzylidene-2, 3-cyclic sulfato-B-D-mannopyranoside.

13 7
E. Personnel iIoster

REACTOR RADIATION DIVIS ION

iJ60

R. S. Carter, Chief

T. M. Raby, Dep uty Chlief »E. C. Maxwell, Admin. Officer

»S. E. Tassey, Secretary

S. C. Shatzer, Clerk-Typist

Neutron Radiography Division Sta,ff Cold Neutron Program

M. Ganoczy R. Casella J. M. Rowe (3/'^)

#T. Cheng B. Mozer

F. Shorten

//I. C. +M,

P.

I.T.

R. »G.

W. #H.

Anderson

Glinka (3/4)

Kahn

Kopetka

Schroder

Udovic

Williams

Greene

Knill (1/2)

Stanley

REACTOR OPERATIONS ENGINEERING SERVICES

T. M. Raby, Chief J. H. Nicklas, Chief

J. F. Torrence, Deputy Chief C. Harrison, Secretary

C. Harrison, Secretary

NEUTRON CONDENSED MATTER SCIENCE

J. J. Rush, Chief

M. Clark, Secretary

+L. Clutter, Secretary

Reactor Operators

R. Beasley

M. Bell

N. Bickford

J. Clark

F. Clark

H. Dilks

L. Lindstrom

M. McDonald

W. Mueller

T. Myers

J. Ring

R. Sprow

R. Stiber

A. Toth

D. Wilkison

Mechanical Design

E. Guglielmo

J. Sturrock

Electronics

R. Conway

R. Hayes

L. Shuman

Crystallography

Magnetic and

Amorphous Materials

•Part-time

+WAE, Coop, Intermittent

//Guest Scientist, research assoc. (Full Time)

°Post-doc

E, Prince J. Rhyne

A. Santoro #J. Fernandez-Baca

#C. Choi °R. Erwin

//v. Himes #T. Giebultowicz

J. LaRock (1/2) »J. Lynn

A. Mighell #P. Mangin

W. Rymes (1/2) #M. Spano

/M. Soubeyroux W. Knill (1/2)

»J. Stalick //Y ; Yu

//F. Beech

Advanced

Neutron Methods

Metal Hydrides and

Mol ecular Materials N. Berk

D. Fravel (1/2)

D. Fravel (1/2) C. Glinka (1/4)

//H. Prask J. Gotaas

J. Rowe (1/4) #S. Krueger

W. Rymes (1/2) J. LaRock (1/2)

//H. Savage

//S. Trevino

//J. Nicol

138
PERSONNEL ROSTER

NON-RRD NBS STAFF LOOTED AT REACTOR

Division 35^

D. Brown

C. Campbell

I . Jensen

F. Moore

J. Shubiak

J. Wang

Division 532

E. Boswell

C. Eisenhauer

D. Gilliam

J. Grundl

G. Lamaze

E. McGarry

R. Schwartz

V. Spiegel

A. Wasson

Division 551

D. Becker

8. Carpenter

G. Downing

K. Fitzpatrick

R. Fleming

R. Greenberg

J. Langland

R. Lindstrom

G. Lutz

J. Maki

B. Norman

S. Stone

R. Zeisler

GUEST WORKERS AND COLLABORATORS

Division ^100

J. Cahn

Division 420

F. Brinckman

J. Blendell

T. Coyle

S. Frieman

K. Erase

E. Fuller

E. Lewes

K. Hardman-Rhyne

G. Olson

R. Roth

B. Steiner

W. Haller

Division 430

R. Fields

Division 440

B. Bauer

T. Davis

C. Han

C. Chiang

R. Waterstrat

W. Wu

Division 450

F. Biancanello

R. Reno

R. Shaefer

R. Shull

Division 520

G. Greene

E. Kessler

Division 533

R. Placious

139
PERSONNEL ROSTER

Division 5^1

R. Cavanagh

R. Kelly

T. Madey

Division 5^3

R. Harrison

I. Weber

A. Wlodawer

Division 552

B. Koster

L. Sander

S. Wise

Division 553

C. Poston

H. Rook

J. Snell

Division 725

J. Ehrstein

Division 77^

H. Hanbley

J. Straty

Aberdeen Proving Ground

C. Heimback

Armed Forces Institute of Pathology

D. Nagarajan

Army Armament Research and

Development Command

C. Choi

H. Prask

S. Trevino

Federal Bureau of Investigation

R. Bilko

J. Haverkost

J. Kilty

P. Kostella

M. Moscop

C. Peters

J. Riley

P. Tangren

P. Thompson

Food and Drug Administration

W. Cunningham

W. Stroube, Jr.

J. Tanner

National Institutes of Health

J. Bennett

M. Channing

W. Eckelman

R. Finn

R. Frank

A. Katki

M. Neuder

H. Savage

Naval Research Laboratory

K. Grabowski

A. Imam

N. Koon

Naval Surface Weapnos Center

J. Cullen

G. Riel

M. Spano

Smithsonian Institution

R. Bishop

M. Blackman

T. Chase

Y. Cheng

J. Mishara

E. Myers

J. Olin

R. Wright

140
PERSONNEL ROSTER

Argonne National Laboratory

S. Susman

Battelle Pacific Northwest

Laboratories

L. Brackenbush

F. Brauer

G. Endres

M. Failey

R. Sanders

Chalmers Institute of Technology

L. Sjolin

C.N.R.S. Grenoble, France

C. Chaillout

D. Gignoux

M. Marezio

J. Soubeyroux

D. Tranqai

G. Zaccai

CSURO - Australia

R. Hill

Institut Laue-Langevin

Grenoble, France

A. Magerl

R. Pynn

Institute of Nuclear Sciences

R. Drascovic

KFA JiJlich, Germany

R. Hempleman

D. Richter

M. Steepler

Los Alamos National Laboratory

R. Robinson

J. Wilkerson

Max-Planck Institute

R. Huber

R. Kirchheim

E. Lukacevic

J. Walter

Oak Ridge National Laboratory

J. Hayter

F. Kam

Sandia National Laboratory

J. Schirber

D. Varsick

Alfred University

R. Snyder

R. Zhow

Cambridge University (U.K.)

J. Horton

G. Squire

Carnegie-Mellon University

E. Boltich

W. Wallace

Georgetown University

H. Mallek

Iowa State University

R. Shelton

Kyoto University (Japan)

H. Hasegawa

T. Hashimoto

Q. Trancong

McMaster University

W. Clarke

141
PERSONNEL ROSTER

Michigan State University

E. Case

Y. Fan

S. Solin

M.I.T.

S. Chen

J. Didiskein

M. Green

B. Wuensch

Northwestern University

H. Calderon

J. Ketterson

S. Kirn J. Weertman

Oregon State Graduate School

P. Davis

Purdue University

J. Furdyna

T. Giebultowicz

A. Overhauser

San Jose State University

A. Ling

State University of New York

H. Greenblatt

H. Herman

University of Annecy, (France)

J. Bouillot

University of Antwerp (Belgium]

K. Michel

University of California

(Santa Barbara)

M. Eddy

C. Levii

R. Odette

G. Stucky

University of California (San Diego)

J. Arnold

K. Nishiizumi

University of Cincinneti

H. Jackson

University of Illinois

J. Borchers

S. Hardcastle

D. Heumann

P. Miceli

M. Salamon

S. Sinha

S. Youngquist

H. Zabel

University of Maryland

D. Anderson

I. Anderson

A. Bates

J. Dodd

S. Faller

J. Fernandez-Baca

A. Fiesel

G. Gordon

F. Guenther

M. Han

D. Herman

J. Hoff

M. Kitto

S. Krueger

Q. Li

J. Lynn

C. LeCompte

L. McCarthy

J. Nicol

J. Ondov

J. Robertson

A. Sheffield

P. Sheridan

H. Stanley

S. Stone

C. Thompson

G. Tuncel

S. Tuncel

J. Valette-Silver

W. Waters

Y. Yu

W. Zoller

142
PERSONNEL ROSTER

University of Michigan

D. Vincent

Univrsity of Millan (Italy)

M. Zocchi

University of Missouri

W. Ching

W. James

T. Little

S. Werner

University of Muenster

F. Kemper

University of Nancy (France)

P. Mangin

University of New Hampshire

R. Blakemore

University of Notre Dame

R. Ricker

University of Rhode Island

D. Andrauskas

S. Hasanain

S. Pickart

University of Virginia

T. Williamson

University of Washington

K. Mottet

W. Zoller

University of Wisconsin

D. Huber

Aerospace Corporation

R. Bowman

J. Knudsen

Alcoa Technical Center

C. Jensen

R. Rioja

Allied Corporation

G. Fish

A. Maeland

Atomic Energy of Canada, LTD

W. Lennard

Baker Chemical Company

R. Ganapathy

Bell Laboratories

R. Cava

H. Chem

J. Mitchell

D. Murphy

J. Remeika

J. Riley

Bell-Northern Research Ltd.

F. Shepherd

W. Vandevorst

Directed Technologies, Inc.

N. Chesser

Eastman Kodak

T. Houssain

M. Landry

C. Swanson

E. I. DuPont de Nemours Co.

G. Jones

D. Corbin

c. Torardi

1A3
PERSONNEL ROSTER

Exxon

R. Busch

J. Dozier

J. Gethner

J. Huang

D. Lohse

S. Sinha

General Electric Co,

C. Austin

R. Bonnan

R. Darlia

L. Provo

A. Taub

W. R. Grace

M. Wax

R. Wormsbecker

GTE Laboratories

M. Downey

D. Oblas

G. Hamill

IBM (Yorktown Heights)

M. Schaefer

R. Gambino

Intel Corporation

N. Cox

Mobil Central Research Laboratory

D. Olsen

Motorola, Inc.

S. Wilson

Rockwell International

M. Brown

Southerwest Research Institute

R. Page

Westinghouse-Hanford Corp.

W. McElroy

144
F. Publications

COLLABORATIVE PROGRAMS

Anderson, I. S., Rush, J. J., Udovic, T. J., and Rowe, J. M., " Hydrogen Pairing and

Anistropic Potential for Hydrogen Isotopes in Yttrium", Phys. Rev. Lett, (in

press).

Berk, N. F., and Hardman-Rhyne, K. A., " Characterization of Alumina Powder Using

Small Angle Scattering, I: Theory", J Appl. Cryst. j_8 467 (1985).

Berk, N. F., and Hardman-Rhyne, K. A., "The Phase Shift and Multiple Scattering in

Small Angle Neutron Scattering: Application to Beam Broadening from Ceramics",

Proc. of the 1985 Santa Fe Intern. Conf. on Neutron Scattering: Physica 136, 218

(1986).

Berk, N. F., " Exact Properties of Model for Biocont inuous Structures", Phys. Rev.

Lett. , 1986 (in press)

.

Bonnet, J. E. ; Rose, D. K., Faux, D. A., and Anderson, I. S., "Long Range and Short

Range Ordering of H and D Atoms in Solid Solution in Yttrium", J. Less Common

Metals (in press)

.

Bordet, P., Mchale, A., Santoro, A., and Roth, R. S, "Powder Neutron Diffraction

Study of ZrTiO,,, Zr^Ti^O^,, and FeNb_0.", J. of Solid State Chem. 64; 30-46

(1986).

4 5 7 24 2 6 —

Bouillot, J., Rowe, J. M., and Rush, J. J., "Structure of (KCN) (KBr) Mixed

Crystal by Neutron Powder Diffraction", Phys. Rev. (in press).

Cava, R. J., Santoro, A., Murphy, D. W., Zahurale, S. M., Fleming, R. M., Marsh, P.,

and Roth, R. S, "The Structure of the Lithium Inserted Metal Oxide 6-LiV ", J. Solid State Chem. (in press).

Cavanagh, R. R., Rush, J. J., and Kelley, R. D., "Incoherent Inelastic Neutron

Scattering: Vibrational Spectroscopy of Adsorbed Molecules on Surfaces. Methods

of Surface Characterization, T. E. Madey and J. Yates, eds.. Plenum, NY (1986).

Casella, R. C, "On the Theory of Coherent Neutrino Scattering from Crystals. IL

Nuovo Cimento (in press).

Casella, R. C, "Coherent Scattering of Low Energy Neutrinos from Macroscopic

Objects", American Institute of Physics Conference Proceedings (in press).

Chaillout, C, Remeika, J. P., Santoro A., and Marezio M., "Bismuth Valence OrderDisorder Study in BaBiO by Powder Neutron Diffraction", Solid State

Communications 56, 833 (1985^.

Choi, C. S., George, C, Gilardi, R., Alippen-Anderson, J. L., Marchand, A. P., and

Reddy,r).^S^. , "Structure of 6,6,10,10-Tetranitropentacyclo

[5.30.0 ^^.0 'Idecane, C.^HqOq. Acta Cryst. C4l 788-791 (1985).

Choi, C. S., and Prask, H. J, "Texture of Extruded Uranium Alloy by Neutron

Diffraction", J. Appl. Cryst. ]_8, 413-418 (1985).

Didisheim, J. J., Prince, E., and Wuensch, B. J., "Neutron Rietveld Analysis of

Structural Changes in Nasicon Solid Solutions Na Zr Si P P at Elevated

145
PUBLICATIONS

Temperatures: x = 1.6 and 2.0 at 320°C", Solid State Ionics 18-1

9

, 94iJ-958

(1986).

Eick, H., and Prince, E., "A Neutron Diffraction and Electron Microscopy Examination

of 2BaBr2BaCl ", Acta. Cryst. C_|42, 915-917 (1986).

Erwin, R. W., Lynn, J. W., Rhyne, J. J., and Chen, H. S., "Spin Stiffness Anomaly in

bI'tS TlT857"'

SP^""^^^"^ ^^^0.25^^0.75^0.75^0.16^0.06^^0.03"' ^^ ''^^^' ^''^^- ^

Erwin, R. W., Lynn, J. W., and Magerl, A., "The Reentrant Spin-Glass Order Parameter

in (Fe^ ^Ni^ ^.n (Fe Ni )^^P^ ) P ^B^Al^", ^B^Al ", Proc. of the International International Conference Conference on Magnetism Magnetisr

985, North-floliand, Amsterdam, 101 (1985).

Fan, Y. B., Solin, S. A., Neumann, D., Zabel, H., and Rush, J. J., "Elastic Neutron

Scattering Studies of the Structure of Graphite Interacalated with Potassium and

Ammonia", Phys. Rev. B (in press).

Fernandez-Baca, J. A., Lynn, J. W., Rhyne, J. J., Fish, G. E., "Spin Dynamics of

Amorphous Fe^ o^B^ ,„", Physica 136B, 53 (1986).

U . cSD U . 1 4 Fernandex-Baca , J. A., Rhyne, J. J., and Fish, G. E., "Neutron Scattering Study of

the Spin Dynamics of Amorphous Fe Ni Zr ", J. Magnetism and Magnetic Materials

5^-57 , 289 (1986). r 2

i

Fischer, R. X., Baur, W. H., Shannon, R. D., Staley, R. H., Vega, A. J., Abrams, L.,

and Prince, E., "Neutron Patterns from Tilings with Five-Fold Symmetry", J. Phys. Chem. (in press).

Fisher, R. X., Baur, W. H., Shannon, R. D., Staley, R. H., Vega, A. J., Abrams, L.,

and Prince. E., "Neutron Powder Diffraction Study and Physical Characterization

of Zeolite D-rho", J. Phys. Chem. (in press).

Giebultowicz, T. M., "Monte Carlo Simulation of Dilute Magnetic Semiconductors for

High Concentrations of the Magnetic Component", J. Magnetism and Magnetic

Materials 5^-57 , 1287-1288 (1986).

Giebultowicz, T. M., Overhauser, A. W., and Werner, S. A., "Direct Observation of the

Charge-Density Wave in Potassium by Neutron Diffraction", Phys. Rev. Letters 56 , No. 14, 1485-1^88 (1986).

Giebultowicz, T. M., Rhyne, J. J., Ching, W. Y., Ruber, D. L., Galazka, R. R.,

"Static and Dynamic Spin Correlations and Exchange Interactions in Cd Mn Te",

J. Magnetism and Magnetic Matls. 5^-57 , 1U9 (1986). ^

^

Gignoux, D., and Rhyne, J. J., "Spin Excitations in TbNi by Inelastic Neutron

Scattering", J. Magnetism and Magnetic Matls. 5^-57 , 1179 (1986).

Glinka, C. J., Rowe , J. M., and LaRock, J. G., "The Small Angle Neutron Scattering

Spectrometer at the National Bureau of Standards (in press).

Gotaas , J. A., Rhyne, J. J., Wenger, L. E., and Mydosh, J. A., "Long-Range

Incommensurate Spin State in Dilute YGd Alloys", J. Magnetism and Magnetic

Materials 5^-57, 93 (1986).

146
PUBLICATIONS

Hardcastle, S. E., Neumann, D. A., Zabel, H., and Rush, J. J., "Critical Behavior of

the Interlayer Shear Constant in Stage 2 K and Rb Graphite Intercalation

Compounds", Synthetic Metals (in press).

Hardman-Rhyne, K. A., and Berk, N. F., "Characterization of Alumina Powder Using

Small Angle Scattering, II: Experiment", J. Appl. Cryst. ]8_, 473 (1985).

Hardman-Rhyne, K. A., Erase, K. G., and Berk, N. F., "Applications of Multiple Small

Angle Scattering to Studies of Ceramic Processing", Proc . of the 1985 Santa Fe

Intern. Conf. on Neutron Scattering, Physica B 136 B, 223 (1986).

Hardman-Rhyne, K. A., and Berk, N. F., "Ceramics Material Characterization Using

Small Angle Neutron Scattering Techniques", Materials Characterization for

Systems Performance and Reliability, eds. James W. McCauley and Volker Weiss,

Plenum Press, New York, 257-269 (1986).

Hardman-Rhyne, K. A., Berk, N. F., "Small Angle Neutron Scattering Form Porosity in

Sintered Alumina, Communication of the American Ceramic Society, 1986 (in

Press)

.

Hemplemann, R., and Rush, J. J., "Neutron Vibrational Spectroscopy of Disordered

Metal-Hydrogen Systems, Proceedings of NATO Workshop, Rhodes, Greece, Physica B

( in press)

.

Hlmes, V. L., and Mighell, A. D., "NBS lattice - A Program to Analyze Lattice

Relationships," NBS Tech. Note 121^1, U. S. Dept. of Commerce NBS (1985).

Jin, L., James, W. J., Lemaire, R., and Rhyne, J., "Magnetic Structure of DyCo-", J.

Less-Common Metals, (in press).

Jin, L., James, W. J., Lemaire, R., and Rhyne, J. J., "Magnetic Structure of DyFe.",

J. Less-Common Metals 1 18 , 269 (1986).

Kircheim, R., Huang, H. Y., Carstanjen, H. D., Rush, J. J., and Udovic, T. J.

"Inelastic Neutron Scattering and Resistivity of Hydrogen in Cold-Worked

Palladium", J. Less Common Metals (in press).

Lukacevic, E., Rush, J. J., and Santoro, A., "Neutron Powder Diffraction and

Inelastic Scattering Study of the Structures of Zr Pd, Zr PdD and

Zr PdD ,", Acta Cryst. (in press)

Lukacevic, E., Santoro, A., and Roth, R. S., "Neutron Powder Diffraction Study of the

Structure of the Compound Li^ _,„^La„ ^..^MoO,,", Solid State Ionics 18-19, 922-

928 (1986). °-3^25 °-5^25 ^

Lynn, J. W. "Helium Condensation Observed in Small Angle Neutron Scattering", Physica

136 B, 117-119 (1986).

Lynn, J. W., and Rhyne, J. J., "Spin Dynamics of Amorphous Magnets", Chapter in Spin

Waves and Magnetic Excitations, edited by S. K. Sinha and A. S. Borovik-Romanov,

North Holland Physics Publishers (in press).

Magerl, A., Rush, J. J., and Rowe, J. M., "Local Modes in Dilute Metal-Hydrogen

Alloys", Phys. Rev. B33, 4, 2093-2097 (1986).

147
PUBLICATIONS

Miceli, P. F., Youngquist, S. E., Neumann, D. A., Zable, H. , Rush, J. J. and Rowe, J. M., "Neutron Scattering Study of the Vibrational Density of States in Icoshedral

and Crystalline Al OQ^n p^". Phys. Rev. Lett, (in press).

Michel, K. H., and Rowe, J. M., "Molecular Symmetry and Translation-Rotation Coupling

in Orientationally Disordered Crystals", Phys. Rev. B32_, 9, 5818-5832 (1985).

Michel, K. H., and Rowe, J. M., "KCN, A Model System of Translation Rotation Coupling

in Orientationally Disordered Crystals", J. Chimie Phys.. 82_, 2-3, 199-20^1

(1985).

Mighell, A. D., and Himes, V. L., "Compound Identification and Characterization Using

Lattice-Formula Matching Technqiues", Acta Crysta. _A, 101-105 (1986).

Mozer, B, Gratias, D., and Shechtman, D., "Neutron Diffraction Studies of the

Icosahedral Phase of Al-Mn Alloys", J. de Physique Collogue, No. 3, (in press).

Murphy, D. W., Cava, R. J., Rhyne, K., Roth, R. S., Santoro, A., Zahurak, S. M., and

Dye, J. L., "Structural Aspects of Insertion Reactions of the Pyrochlore

KNbWO.", Solid State Ionics 18-19 , 799-801 (1986).

Nossal, R., Glinka, C. J., and Chen, S. H., "SANS Studies of Concentrated Protein

Solutions. I. Bovine Serum Albumin. Biopolymers", 25, 1157-1175 (1986).

Prask. H. J., and Choi, C. S., "Neutron Diffraction Characterization of TungstenNickel-Iron Alloys", Technical Report AREAE-TR 85015, AD-Eil01 , 461, ARC, Dover,

NJ (1986).

Prask, H. J, and Choi, C. S., "Encyclopedia of Materials Science and Engineering, 7_, 4095-97, edited by M. B. Bever, Pergamon Press, NY (1986).

Prask, H. J. and Choi, C. S. , "Texture, NDE Characterization Encyclopedia of Materials

Science and Engineering", 7_, 4095, edited by M. B. Beuer, Pergamon Press, New

York (1986).

Prask, H. J., and Choi, C. S. , "Sub-Surface Residual Stress Measurements by Means of

Neutron Diffraction: Aluminum, Steel, and Depleted Uranium, Materials

Characterization for Systems Performance and Reliability", edited by J. W.

McCauley and W. Weiss, Plenum Press, NY and London (1986).

Prince, E., and Nicholson, W., "The Influence of Individual Reflections on the

Precision of Parameter Estimates in Least Squares Refinement. Structure and

Statistics in Crystallography, Ed. A. J. C. Wilson, Adenine Press, Guilderland,

NY, 183-195 (1985).

Prince, E., "Precision and Accuracy in Structure Refinement by the Rietveld Method",

Structure and Statistics in Crystallography, Ed. by A. J. C. Wilson, Adenine

Press, Guilderland, NY, 93-103 (1985).

Rhyne, J. J., "Magnetic Properties of Amorphous Metals", Invited Paper, Research

Opportunities in Amorphous Solids with Pulsed Neutron Sources Workshop, Argonne

Natl. Lab., J. of Non-Crystalline Solids 76, 129 (1985).

Rhyne, J. J., "Effects of Random Field Interactions in Amorphous Rare Earth Alloys.

Invited paper", INTERMAG Conf., St. Paul, MN, IEEE Trans. Mag. 2]_, 1990 (1985).

148
PUBLICATIONS

Rhyne, J. J., "Quenching of Long-Range Magnetic Order by Random Interactions in

Amorphous Alloys", Invited paper, International Conference on Neutron

Scattering, Santa Fe, NM, Physica 136 B, 30 (1986).

Rhyne, J. J., Cooper, B. R., Huber, D. A., Koon, N. C, and O'Handley, R. C. editors,

Proceedings of the International Conference on Magnetism ICM-85, J. Magnetism

and Magnetic Materials North Holland 54-57 (1986).

Rhyne, J. J., Erwin, R. W., Salamon, M. B., Sinha, S., Cunningham, J. E., Borchers,

J., and Flynn, C. P., "Long-Range Incommensurate Magnetic Order in Dy-Y

Multilayers", Invited Paper, Seventeenth Rare Earth Research Conference,

Hamilton, Canada, J. Less-Common Metis, (in press).

Richter, D., Hempelmann, R., Rush, J. J., Rowe, J. M., Eckert, J., Goldstone, J. A.,

and Tonks, D., "Localized Vibrations of Hydrogen in Metals", Physica B (in

press)

Rowe, J. M., Bouillot, J., Rush, J. J., and Luty, F. , "Structural Phase Diagram of

Mixed (ICN) (KA) Crystals by Means of Neutron Powder Diffraction", Physica B 136, ^498-502^(1986)"-X

Rowe, J. M., Rush, J. J., Schirber, J. E., and Mintz, J. M., "Isotope Effects in the

PdH System - Lattice Dynamics of PdT ", Phys . Rev. Lett, (in press).

Rowe, J. M., Rush, J. J., Michel, K. H., Comment on Dielectric Susceptibility

Measurements in (KCN) (KBr) ", Phys. Rev. Lett, (in press).

Rush, J. J., and Rowe, J. M., "Chemical Physics with Emphasis on Low Energy

Excitations", Physica B137 , 169-182 (1986).

Rush, J. J., Cavanagh, R. R., Kelly, R. D., and Rowe, J. M., Interaction of

Vibrating H Atoms on the Surface of Platinum Particles by Isotope Dilution

Neutron Spectroscopy", J. Chem. Phys. 83_, 5339-53^1 (1985).

Salamon, M. B., Sinha, S., Rhyne, J. J., Cunningham, J. E., Erwin, R. W., Borchers,

J., and Flynn, C. P., "Long-Range Incommensurate Magnetic Order in a Dy-Y

Multilayer", Phys. Rev. Lett. 56, 259 (1986).

Schioler, L. J., Wuensch, B. J., and Prince, E., "The Relation Between Structural

Change and Fast Ion Conduction in the NASICON Solid Solution System. Solid State

Ionics (in press).

Schroder, I. G., Linperi, Li, Gilliam, D. M., McGarry, E. D^, Eisenhauer, C. M.,

"Measurement of Aboslute Fission Cross Sections for Cf Spoutaneous Fission

Neutrons", Trans. Amer . Nuc . Soc 50, 15^ (1985).

Schroder, I, G., GiJ 1 1. am , D, M., Carlson, A. D., and Bright, Hutchinson, J. M. R.,

"International U Fission Foil Mass Intercomparison" , Trans. Am. Nuc. Soc. (in

press).

Smith, H. K., Rhyne, J,. J., Hardman-Rhyne, K. A., and Wallace, W. E. , "Thermodynamics

of Hydrides and Deuterides of R^Fe„^and R^Mn^^", J. Less Common Metals (in

, 6 23 6 23 press)

149
PUBLICATIONS

Spano, M. L., and Rhyne, J. J., "Effects of Applied Fields on the Magnetic Order of

Amorphous Tb Fe Alloys", Magnetism and Magnetic Matls. 5^-57 . 300 (1986).

Stalick, J, K., and Mighell, A. D., "Crystal Data Version 1.0 Database

Specifications, NBS Tech. Note (in press).

Torardi, C. C., Reiff, W. M., Lazar, K., and Prince, E. , "Structures and Low

Temperature Magnetism of the New Lithium and Sodium Insertion Compounds:

LiFedDClMoO. and NaFe(II)ClMoO^", J. Chem. Phys . Solids (in press).

Torardi, C. C., and Prince, E., "Structure of the Lithium Insertion Compound

Li Fe (Mo0^)3 from Neutron Powder Diffraction Data", Materials Research

Bulletin^, 719-726 (1986).

Trevino, S. S., and Tsai, D. H., "The Simulation of Condensed Matter Chemistry and

Destontion", Proceedings of the 1986 Army Science Conference, 1986 (in press).

Udovic, T. J., and Kelley, R. D., "Neutron Scattering Studies of Hydrogen in

Catalysts. Hydrogen in Catalysis: Theoretical and Practical Aspects, Z Paal and

P. G. Menon, eds., Marcel Dekker, Inc., NY (1986).

Wax, M. J., Cavanagh, R. R., Rush, J. J., Stucky, G. D., Abrams , L., and Corbin, D.

A., Neutron Scattering Study of Zeolite Rho", Phys. Chem. 90, 532 (1986).

Weiss, G. H. , Shmueli, U., and Prince, E., Discussion of Fourier Representations of

Pdfs Arising in Crystallography", J. Res. NBS 90_, 513-515 (1985).

Wenger, L. E. , Hunter, G. W., Mydosh, J. A., Gotaas, J. A., and Rhyne, J. J., "Spin

Density Wave Transition in Dilute YGd Single Crystal", Phys. Rev. Lett. 56_,

1090 (1986).

Werner, S. A., Rhyne, J. J., and Gotaas, J. A., "Spin Density Wave Magnetism in

Copper-Manganese Alloys", Solid State Commun. 56_, ^157 (1985).

Yu, H., Kitano, T. , Kim, C. Y., Amis, E. J., Chang, T., Landry, M. R., Wesson, J. A.,

Han, C. C, Lodge, T. P., and Glinka, C. J., "Uniaxial Deformation of Rubber

Network Chains by Small Angle Neutron Scattering", Macromolecules (In press).

INDEPENDENT PROGRAMS

Alberts, W. G., and Schwartz, R. B., "Comparison of the Filtered-Neutron Beams at the

NBS and PTB Reactors by Calibrating a Spherical Remmeter, Proc. Fifth Symposium

on Neutron Dosimetry, 17-21 Sept. 198, Munich, Germany, EUR 9762 EN Volume 1 (1985).

Anderson, D. L., Sun, Y, Failey, M. P., and Zoller, W. H., "Neutron-Capture Prompt

Gamma-Ray Multielement Analysis of Twenty-Two Geochemical Reference Standards,

Geostandards Newsletter 9_, 219-228 (1985).

Becker, D. A., "The Role of Reactor Characterization in NAA Quality Assurance", J.

Radioanal. Nucl. Chem, (in press).

150
PUBLICATIONS

Blackman, M. J., "The Provenience of Obsidian Artifacts from Late Chalcolithic Levels

at Aphrod i s ias , Turkey", in Prehistoric Aphrodisias, ed . M. Joukowsky,

(Archaeologia Transatlantica Vol. IV) Louvain-la-Neuve, Institut Superieur

D'Archelogie et Histoire de L'Art Brown University (in press).

Blair, W., Olson, G., Brinckman, F., Paule, R., and Becker, D., An International

Butyltin Measurement Methods Intercomparison: Sample Preparation and Results of

Analysis, NBSIR 86-3321 (1986).

Carpenter, B. S., Gramlich, J. W., Greenberg, R. R., Machlan, L. A., DeVievre, P.,

Eschbach, H. L., Meyer, H., Van Audenhove, J. Connolly, V.E. Trahey, N. M., and

Zook , A. C, "Standard Reference Materials: UranIUM-235 Isotope Abundance

Standard Reference Materials for Gamma Spectrometry Measurements", NBS Spec.

Publ. 260-96 (in press).

Carpenter, B. S., and Pilione, L. J., "The Use of Delayed Nuclear Track Counting for

Determinging Bismuth", Journal of Radioanalytical and Nuclear Chemistry (in

press)

.

Carpenter, B. S., Horvath, C., and Vogt, C. R., "The Production of Porous

Microspheres by the Nuclear Track Techniques", Nuclear Tracks and Radiation

Measurements (in press).

Bowman, R. C, Jr., Robertson, R. E., Knudsen, J. R., and Downing, R. G., "Studies of

Boron Implantation Through Photochemically Deposited SiO Films on Hg _ Cd Te"

,

Proceedings of the International Conference on Optical and Optoelectronic

Applied Sciences and Engineering, 1986 (in press).

Downing, R. G., Maki, J. T., and Fleming, R. F., "Application of Neutron Depth

Profiling to Microelectronic Materials", ACS Symposium Series No. 295, L. A. Casper, ed .

, I63-I8O (1984).

Downing, R. G., Maki, J.T., and Fleming, R. F. , "Analytical Applications of Neutron

Depth Profiling", Proceeding of the 1986 Modern Trends in Activation Analysis

(in press).

Fleming, R. F., and Lindstrom, R. M., "Precise Determination of Aluminum by

Instrumental Neutron Activation" (in press).

Garry, V. F., Pohlman, B. L., Wick, M. R., Garvey, J. S., Zeisler, R. , "Chronic

Cadmium Introxication: Tissure Response in an Occupationally Exposed Patient",

Am., J. Indust. Med. (in press).

Gilliam, D. M., and Lamaze, G. P., "Absolute Neutron Flux Determination - A Problem

for the Determination of t , Proceedings of Workshop on The Investigation of

Fundamental Interactions with Cold Neutrons, NBS-SP711 36 (1986).

Greenberg, R. S., "The Role of Neutron Activation Analysis in the Certification of

NBS Standard Reference Materials", Proc.of the Seventh International Conference

on Modern Trends in Activation Analysis (in press).

Greenberg, R. R. , Fleming, R. F., and Linstrom, R. M., "Elemental Characterization of

Four Coal Standard Reference Materials via Instrumental Neutron Activation

Analysis and Neutron-Capture Prompt Gamma Activation Analysis" (in press).

151
PUBLICATIONS

Greenberg, R. R., "Elemental Characterization of the National Bureau of Standards

Milk Powder Standard Reference Materials by Instrumental and Radiochemical

Neutron Activation Analysis", Analy. Chera. (in press).

Grundl , J. A., Eisenhauer, C. M., "Compendium of Benchmark Neutron Fields for

Reactor Dosimetry-Standard Neutron Fields Entries", NBSIR 85-3151 (1986).

Grundl, J. A., "Pursuing Public and Professional Perception of Nuclear Energy With

the Smithsonian Lady Godiva Replica and Demonstration/Display", Proc . of Fast

Burst Reactor Workshop, Albuquerque, NM (1986).

Han, C, Okada, Y., Murgoga, Y., McRackin, F. L., Bauer, B. J., and Tran-Cong, Q.,

"Static and Kinetic Studies of Polystene/Poly (vinylmethylether ) Blends",

Polymer Engineering and Science 26_, No. 1 (1986).

Iyengar, G., v., and Tanner, J.T., "Biological and Dietary Reference Materials for

Organic and Inorganic Nutrients", Food Laboratory Newsletter, No. 4, 20-25

(19850.

Iyengar, G. V., "Sample Validity in Biological Trace Element Research Studies", J.

Radioanal. Nucl. Chem. (in press).

Iyengar, G.V., Tanner, J. T. , Wolf, W. R., and Zeisler, R., "Preparation and

Characterization of Mixed Diet Composite USDIET-I: Determination of Energy,

Phytic Acid and Elemental Concentration", IAEA Coordinated Research Programme on Human Daily Dietary Intakes of Nutritionally Important Trace Elements (in

press)

Kitto, B. M. E. and Aanderson, D. L. "Simultaneous Collection of Particles and Gases

from Coal-Fired Power Plants", Proc. of the National Meeting of the American

Chemical Society, New York, NY (1986).

Kotra, J. P., and Zoller, W. H., "A High Volume, Aircraft-Based Filter Sampling

System for the Collection of Atmospheric Particles and Reactive Gases (in

press)

Lindstrom, R. M., Zeisler, R. , and Rossbach, M., "Activation Analysis Opportunities

Using Cold Neutron Beams", submitted to Proc. 7th MAA, Copenhagen (1986).

Lindstrom, R. M., "Activation Analysis of Semiconductor Materials, in L. A., Casper,

ed., "Microelectronics Processing: Inorganic Materials Characterization", (ACS

Symp. Ser. No. 295), Am Chem. Soc .

, Washington, 29^-307 (1986).

Linidstom, R, M., and Anderson, D. L. , "Analytical Neutron-Capture Gamma-Ray

Spectroscopy: Status and Prospects", S. Raman, ed.. Capture Gamma-Ray

Spectroscopy and Related Topic - 1984 (AIP Conf . Proc. No. 125), Am. Inst.

Physics. New York 810-819 (1985).

Lauenstein, G. G., Schantz., M. M. Wise, S. A., Zeisler, R., "Specimen Banking in the

National Status and Trends Program: Development of Portocols and First Year

Results", Proc. Oceans '86 (in press).

Maki, J. T,, Fleming, R. F. , and Vincent, D. H., "Deconvolution of Neutron Depth

Profiling Spectra", Nuclear Instruments and Methods in Physics Research B1

, 1^7

(1986).

152
PUBLICATIONS

Michel, R., Iyengar, G. V., and Zeisler, R., "Current Aspects of Multielements

Analysis in the life Sciences, Instrumental Multielement Analysis, Sansoni , B.,

ed., VCH Publishers, Deerfield Beach, FL, 607-6I8 (1985).

Myers, E. , "Chemical Composition of the Sackler Maiolica Ceramics, "Appendix in

Forthcoming Catalogue on the Sackler Maiolica, Lois Katz. The Arthur M. Sackler

Foundation, New York, NY (in press)

Olin, J. S. , and Blackman, M. J., "The Proceedings of the 1984 Archaeometry

Symposium Institutio Press, Washington, DC (in press).

Olmez, I. Gulovali, M.C. and Gordon, G. E. , "Trace Element Concentrations in Lichens

near a Coal-Fired Power Plant", Atmos. Environ. j_9, 1663-1669 (1985).

Olmez, I. and Gordon, G. E., "Rare Earths: Atmospheric Signatures for Oil-Fired

Power Plants and Refineries", Science 229 , 966-968 (1985).

Olmez, I., Finnegan, D. L. and Zoller, W. H. , Iridium Emissions from Kilauea Volcano,

J. Geophys. Res. 91, 653-663 (1986).

Ondov, J. M. "Cascade Impactors in the Chemical and Physical Characterization of

Coal-Combustion Aerosol Particles", in Fossil Fuels Utilization: Environmental

Concerns, R. Markuszewski and B. Blaustein, ed .

, Am. Chem. Soc. (1986).

Riley, J. E., Jr., and Linstrom, R. M., "Determination of Boron in Borosilicate

Glasses by Neutron Capture Prompt Gamma-Ray Activation Analysis (in press).

Schwartz, R., "Experiences in Calibration of Neutron Survey Instruments", Proc.

Workshop on Radiation Survey Instruments and Calibrations (1985).

Stone, S. F., Hancock, D., and Zeisler, R. , "Characterization of Bioligical

Macromolecules by Electrophoresis and Neutron Activation," Journal of

Radioanalytical and Nuclear Chemistry (in press).

Stroube, W. B., Jr., and Lutz, G. J., "Analysis of Foods for Iodine by Gp Thermal

Neutron Activation Analysis", J. Radioanal. and Nucl. Chem. (in press).

Tanner, J. T., Smith, J. S., Angyal, G., Defibaugh, P. W,, Villalobos, M. C, Bueno,

M. P., Iyengar, G. V., Wolf, W. R., and Zeisler, R., "In Search of SRMs for

Organic Nutrients", 2nd International Workshop on Biological Reference

Materials, work, W. R. ed . (in press).

Tuncel, S. G., Olmez., I., Parrington, J. R. , Gordon, G. E. and Stevens, R. K.,

"Trace Elements no Airborne article in Rural Areas: Development of Regional

Sulfate Signatures, in Receptor Models for Source Apportionment: Real World

Issues and- Applictions, T. G. Pace, ed . (Air Pollution Control Assn.,

Pittsburgh, PA 116-126 (1985).

Tuncel, G. and Zoller, W. H,, "Iridium Concentrations in the South Pole Atmosphere:

Estimation of Meteroritic Component, Science (in press).

153
PUBLICATIONS

Yang, H., Stein, R. S., Han, C., Bauer, B., Kramer, E., "Compatibility of

Hydrogenated and Deuterated Polystyene", Polymer Communications 27, 12 (198).

Wise, S. A. and Zeisler, R., "The U. S. Pilot Environmental Specimen Bank Program",

NBS (US) Spec. Publ. 706, 3^-45 (1985).

Wise, S. A. and Zeisler, R., eds . , "International Review of Environmental Specimen

Banking", NBS (US) Spec. Pub. 706, 62 (1985).

Zeisler, R. , Stone, S. F., Fitzpatrick, K. A., Wise, S. A., "The Eighth U. S. - German Seminar of State and Planning on Environmental Specimen Banking and The

International Review of Environmental Specimen Banking", NBS (US) Spec. Publ

706, 1-3 (1985).

Zeisler, R., "The Sampling and Analysis of Human Livers", NBS J. Res., 9J_, 75-85

(1986).

Zeisler, R., "Foreword: Symposium on Standardization f Collection and Preparation of

Biomedical Samples for Trace Element Analysis," NBS J. Res., 9J_, 45-^6 (1986).

Zeisler, R., and Young, I., "The Determination of Chromium-50 in Human Blood and Its

Utilization for Blood Volume Measrement", J. Radioanal. Nucl. Chem. (in press).

154
WBS-n4A iREv. 2^c

i. Publication Date December 1986

U.S. DEPT. OF COMM.

BIBLIOGRAPHIC DATA

SHEET (See insitvctions)

1. PUBLICATION OR

REPORT NO. NBS/TN-1231

2. Perfortnlni Orfan. Report No

4. TITLE AND SUBTITLE

NBS Reactor: Summary of Activities July 1985 Through June 1986

5. AUTHOR(S)

F. J. Shorten, Ed.

6. PERFORMING ORGANIZATION (If joint or other than NBS. see instructions)

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

Gaith e rs burg, MP 20899 _^

7. Cor^tract/Grant No.

I. Type of Report & Period Covered

July 1985 to June 1986

9. SPONSORING ORGANIZATION NAME AND COMPLETE ADDRESS (Street. City. State. ZIP)

Same as item 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 significant

bibliography or literature survey, mention it here)

This report summarizes all those programs which depend on the NBS reactor. It

covers the period from July 1985 to June 1986. 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 dynamics;

neutron; neutron radiography; nondestructive evaluation; nuclear reactor; radiation.

13. AVAILABILITY

I xl Unlimited

[ I For Official Distribution. Do Not Release to NTIS

|X I Order From Superintendent of Documents, U.S. Government Priming Office, Washington, D.C.

20402.

I I Order From National Technical Information Service (NTIS), Springfield, VA. 22161

14. NO. OF

PRINTED PAGES

161

15. Price

U.S. Government Printing Office: 1986 0-181-076 (40202) USCOMM-DC e049-P(0

NBSTechnical Publications

Periodical

Journal of Research—The Journal of Research of the National Bureau of Standards reports NBS research and development in those disciplines of thephysical and engineering sciences in which the Bureau is active. These include physics, chemistry, engineering, mathematics, and computer sciences. Papers cover a broad

range of subjects, with major emphasis on measurement methodology and the basic technology underlying

standardization. Also included from time to time are survey articles on topics closely related to the Bureau's

technical and scientific programs. Issued six times a year.

Nonperiodicals

Monographs—Major contributions to the technical literature on various subjects related to the Bureau's scientific and technical activities. Handbooks—Recommended codes of engineering and industrial practice (including safety codes) developed in cooperation with interested industries, professional organizations, and regulatory bodies.

Special Publications—Include proceedings of conferences sponsored by NBS, NBS annual reports, and other

special publications appropriate to this grouping such as wall charts, pocket cards, and bibliographies.

Applied Mathematics Series—Mathematical tables, manuals, and studies of special interest to physicists,

engineers, chemists, biologists, mathematicians, computer programmers, and others engaged in scientific and

technical work.

National Standard Reference Data Series—Provides quantitative data on the physical and chemical properties

of materials, compiled from the world's literature and critically evaluated. Developed under a worldwide pro- gram coordinated by NBS under the authority of the National Standard Data Act (Public Law 90-3%).

NOTE: The Journal of Physical and Chemical Reference Data (JPCRD) is published quarterly for NBS by

the American Chemical Society (ACS) and the American Institute of Physics (AIP). Subscriptions, reprints,

and supplements are available from ACS, 1155 Sixteenth St., NW, Washington, DC 20056.

Building Science Series—Disseminates technical information developed at the Bureau on building materials,

components, systems, and whole structures. The series presents research results, test methods, and {perfor- mance criteria related to the structural and environmental functions and the durability and safety

characteristics of building elements and systems.

Technical Notes—Studies or reports which are complete in themselves but restrictive in their treatment of a

subject. Analogous to monographs but not so comprehensive in scope or definitive in treatment of the subject

area. Often serve as a vehicle for final reports of work performed at NBS under the sponsorship of other government agencies.

Voluntary Product Standards—Developed under procedures published by the Department of Commerce in Part 10, Title 15, of the Code of Federal Regulations. The standards establish nationally recognized re- quirements 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 consumer. E^ily understandable language and illustrations provide useful background

knowledge for shopping in today's technological marketplace.

Order the above NBS publications from: Superintendent of Documents, Government Printing Office,

Washington, DC 20402. Order the following NBS publications—FIPS and NBSIR 's—from the National Technical Information Service, Springfield, VA 22161.

Federal Information Processing Standards Publications (FIPS PLB)—Publications in this series collectiveK constitute the Federal Information Processing Standards Register. The Register serves as the officiiil source of

information in the Federal Government regarding standards issued by NBS pursuant to the Federal Properlv'

and Administrative Services Act of 1949 as amended. Public Law 89-306 (79 Stat. 1 127), and as implemented

by Executive Order 1 1717 (38 FR 12315, dated May II, 1973) and Part 6 of Title 15 CFR (Code o'i Federal

Regulations).

NBS Interagency Reports (NBSIR)—A special series of interim or final reports on work perforniai b\' NBS

for outside sponsors (both government and non-government). In general, initial distribution is handled by the sponsor; public distribution is by the National Technical Information Service, Springfield, VA 22161. in paper copy or microfiche form.
U.S. Department of Commerce

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Penalty for Private Use $300