NATL INST, Of ST4N0 i TECH R.I.C.

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NBS

PUBLICATIONS

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O NBS TECHNICAL NOTE 1 21

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

NBS Reactor:

Summary of Activities

July 1984 Through

June 1985
m he National Bureau of Standards' was established by an act of Congress on March 3, 1901. The

1^ 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 essentiaJ 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

capabilities; provides engineering measurement traceability services; develops

test methods and proposes engineering standards and code changes; develops

and proposes new engineering practices; and develops and improves

mechanisms to transfer results of its research to the ultimate user. The

Laboratory consists of the following centers:

Applied Mathematics

Electronics and Electrical Engineering'

Manufacturing Engineering

Building Technology

Fire Research

Chemical Engineering^

77?^ 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

77?^ 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 Gaithersburg, MI), unless otherwise noted; mailing address

Gaiihersburg. MD 20899, ^Somc divisions within the center are located al Boulder, CO 80303. 'Located ai Boulder, CO, with some elements at Ciaithcrsbure, MD.
NBS Reactor:

Summary of Activities

July 1984 Through

June 1985 k1^ -'^•^' 4^

NBS 8ESEAECH ItJFORMATIOH

CC'ITEH

^26/00

Frederick J. Shorten, Editor

Reactor Radiation Division

Institute for IMaterials Science

and Engineering

National Bureau of Standards

Gaithersburg, MD 20899

December 1985

.^^^' °' -o.

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

NATIONAL BUREAU OF STANDARDS, Ernest Ambler, Director
National Bureau of Standards Technical Note 1217

Natl. Bur. Stand. (U.S.), Tech. Note 1217,175 pages (Dec. 1986)

CODEN: NBTNAE

U.S. GOVERNMENT PRINTING OFFICE

WASHINGTON: 1985
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 was increased from 10 to 20 MW during the past year

and provided 25 experimental facilities ranging from intense neutron beams to

extensive irradiation facilities, making 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

irradiation services. The remaining sections are self-explanatory.

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

Division for his extensive contributions to the editing, organization, and

preparation of this report, and T. L. Lindstrom, K. E. Ferrel, M. H. Clark,

and S. Tassey for efforts in typing manuscripts.

iR. A. ^^S>czfcv

R. S. Carter

Chief, Reactor Radiation Division

National Bureau of Standards

ill
ABSTRACT

This report summarizes all those programs which depend on the NBS

reactor. It covers the period from July 1984 through June 1985. The

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

dynamics of materials through nuclear physics and neutron standards to sample

irradiations for activation analysis, isotope production, radiation effects

studies, neutron radiography, and nondestructive evaluation.

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

molecular dynamics; neutron; neutron radiography; nondestructive

evaluation; nuclear reactor; radiation.

DISCLAIMER

Certain trade names and company products are identified in order to

adequately specify the experiment 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 Control of Pore Size In Zeolite RhO 1 Structural Characterization of the Lithium Insertion Compound

LiFedDClMoO^ 1 The Structure of aBaBr^'BaClp 2

Structural Changes in Nasicon Solid Solutions, Na. Zr^Si P__ O.p* at

Elevated Temperatures 4

Structure of Barium Titanium Niobium Oxides 10

Neutron Powder Diffraction Study of the Structure of the Compound

Geometrical Ambiguities in the Indexing of Powder Patterns 11 Texture of Extruded Uranium Alloys by Neutron Diffraction 12

The Nondestructive Determination of Near-Surface Residual Stresses in

Depleted Uranium Alloys 15

Crystal Data 21 Local Modes in Dilute Metal-Hydrogen Alloys 22

Neutron Scattering Studies of Hydrogen in Yttrium 25

Stochastic States Theory of Neutron Scattering from Self-Trapped Defects in

Solids 29

Theory of Processes Contributing to Quasielastic Neutron Scattering from

Hydrogen in Metals 33

Translation-Rotation Coupling - Alkali Cyanide/Alkali Hal ides 35

Interaction of Vibrating H Atoms on the Surface of Platinum Particles by

Isotope Dilution Neutron Spectroscopy 36

Incoherent Inelastic Neutron Scattering Study of the Interaction of Adsorbed

Hydrogen with Oxygen on Platinum Black 39

Neutron Scattering Studies of Zeolite RhO 42

Study of Dynamical and Static Scaling of the X Transition in He 44 * Simulation of a Slightly More Complex Chemical Reaction 45

Neutron Scattering Studies of Diluted Magnetic Semiconductor Systems

Cd, Mn Te and Zn, Mn Se 46

1-x x 1-x X

Long-Range Incommensurate Spin State in Dilute YGd Alloys 49
TABLE OF CONTENTS

Field Dependence of the Two-Spin Correlation Function in a Reentrant Spin

Glass 52

Neutron Scattering Study of the Spin Dynamics of Amorphous Fe-QNi.QZr.Q. . .55

Magnetic Order in the Superconductor Tm-Fe^Sic- 58 d i

Magnetic and Superconducting Properties of Holmium- Rich (Er._ Ho )Rh|.B|, . .60

Advanced Neutron Methods 61

Cold Neutron Research Facility 63

NBSR Cold Neutron Source 64

The NBS Neutron Time-Of -Flight Spectrometer 66

The Phase Shift and Multiple Scattering in Small Angle Neutron Scattering:

Application to Beam Broadening from Ceramics 68

Study of Plasma Spray Coatings by Small Angle Neutron Scattering 72

Critical Fluctuation and Phase Behavior of a Binary Polymer System 73

Small Network Structure Studied with Small Angle Neutron Scattering 78

SANS Study of a Concentrated Protein Solution 79

Joint Neutron and X-ray Structural Refinement of Porcine Insulin 81

Neutron Activation Autoradiography Study of Paintings 83

B. NON-RRD PROGRAMS 86

Nuclear Methods Group: Overview 86

High Resolution Neutron Depth Profiling (NDP) and Secondary Ion Mass

Spectrometer (SIMS) of Boron Through Oxide-Silicon Interfaces 88

High-Sensitivity Determination of Idoine Isotopic Ratios by Thermal and Fast

Neutron Activation .93

Neutron-Capture Prompt-Y Activation Analysis and Related Studies ..... .95

IAEA Coordinated Research Program on Human Daily Dietary Intakes of

Nutritionally Important Trace Elements 99

Determination of Gold and Platinum in Human Urine, SRM 2670 . .100

Multielement Analysis of Biological Macromolecules 103

Development of Biomonitoring Specimen Bank in the United States 107

Facilities and Equipment for Activation Analysis Ill

Atmospheric and Environmental Studies by Instrumental Neutron Activation

Analysis .112

Characterization of the NBSR at 20MW 120

Summary of Reactor Related Activities Carried Out by the Neutron Field

Standards Group 130

Neutron Driven Gamma Ray Field , . .138

vi
TABLE OF CONTENTS

Experimental Microdosimetry 140

C. REACTOR OPERATIONS AND SERVICES U?

D. SERVICE PROGRAMS 150

The Food and Drug Administration's Neutron Activation Facility 150

Preparation of F-18 Labeled Radiotracers Using NBS Reactor-Produced F-18 . .151

Production of F-18 on Low Flux Reactors 151

E. PERSONNEL ROSTER 153

F. PUBLICATIONS 1 60

vii

A, Reactor Radiation Division and Collaborative Programs

CONTROL OF PORE SIZE IN ZEOLITE RHO

G. D. Stucky

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

and

E. Prince

Selectivity in organic reactions is generallly determined by a few

kilocalories/mole, which in zeolite catalysis translates into differences of a few

tenths of an angstrom in zeolite pore dimensions. Framework flexibility can be used

to control reaction selectivity by using the response of the three dimensional

surface to temperature, sorbate and cation coordination. For zeolite, Rho, a simple

distortion involving the "breathing" of a double 8-ring can be modeled as a function

of the cubic unit cell dimension. The degree to which the ring opening will distort

is given by a parameter D, which measures the degree of ellipticity of the double 8-

ring opening. Neutron diffraction studies of LiRho have shown a mechanism for

inducing this distortion by design. This has been confirmed by the temperature

dependent contraction of the unit cell of CaRho which results in the smallest unit

cell reported for a Rho zeolite. Dehydration of BeRho lowers the crystal system

symmetry from cubic to monoclinic, indicative of the stronger metal atom framework

interaction expected for the smaller divalent cation.

STRUCTURAL CHARACTERIZATION OF THE LITHIUM

INSERTION COMPOUND, LiFe(II)ClMoO^

C. C. Torardi

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

and

E. Prince

The structure and magnetism of the new layered tetragonal antif erromagnet

FedlDClMoO^ has been recently described (1,2). Reaction of this compound with Lil

in acetonitrile under inert atmosphere yields the lithium-inserted monoclinic

material LiFe(II)ClMoO|, . This topochemical redox reaction is completely reversible.

Neutron powder diffraction data were collected on the lithium phase, and the

structure has been determined using the NBS Rietveld profile refinement computer

programs.
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

The title compound is monoclinic,m space group P2 /m, with a = 6.9944(6), b = 6.8714(6), c = 5.0144(5) A, and 3 = 91.272(5)°. Although two crystallographic sites

exist between the FeClMoO^, layers for lithium occupation, only one site is occupied.

This results in a fully ordered structural arrangement. Lithium is octahedrally

coordinated to four oxygen and two chlorine atoms. FeO^^Clp octahedra in LiFe ClMoO|, are so much less distorted than in the parent compound which contains FeO,.Cl square

pyramids with an additional CI atom 3.02A from iron.

I » C. C. Torardi, J. C. Calabrese, K. Lazar, and W. M. Reiff J. Solid State Chem.

51, 376 (1984).

2. NBS Technical Note 1207, ed. F. J. Shorten (1984)

THE STRUCTURE OF 2BaBr2-BaCl2

H. A. Eick

(Michigan State University, East Lansing, MI)

and

E. Prince

1 Both BaClp and BaBr_ exhibit orthorhombic PbCl^-type symmetry. An x-ray

diffraction study of the BaBrp-BaClp system indicated a non linear variation of the a and c parameters (space group Pnma) with composition, but a linear variation of b

1 parameter and the volume. Data collected in an x-ray powder diffraction study of

the phase, BaBrCl, when fit by Rietveld line profile procedures, indicated the phase

to be anion-ordered with the chloride ions occupying only the tetrahedral holes and

the bromide ions occupying only the square pyramidal holes. In an effort to

determine if at other compositions, i.e., a CI/Br ratio of about 0.5, anion ordering

would force the symmetry of the system to change or cause a doubling of the unit cell

parameters, a neutron diffraction study of an intermediate composition, 2BaBrp»BaClp,

was undertaken.

The sample submitted for analysis was prepared by fusing in Al 0^ crucibles

confined in high vacuum an intimately ground mixture of BaClp and BaBr_ mixed in the

molar stoichiometric ratio of 2:1. The BaClp, purchased from CERAC, Inc., Milwaukee,

Wisconsin, was placed in an AlpO_ crucible and fused in high vacuum prior to use.

The BaBrp was prepared from BaO (Fisher Scientific) by a conventional NH|.C1/HC1

chlorination procedure, and was then fused as was the BaClp. X-ray powder

diffraction analysis of both reactants and the products indicated the presence of

only reflections assignable to the Pnma-PbCl^ type structure.
REACTOR RAD,IATION DIVISION AND COLLABORATIVE PROGRAMS

Neutron diffraction data collected over the range 17°<2e<122<» on the NBS

neutron diffractometer at ambient temperature (A = 1.5500A), were refined by Rietveld

line profile least-square analysis procedures at Michigan State University with the

programs REFINE provided by E. Prince.

The structure refined to an R value of 7.73 (statistically expected value:

4.97) with 36 variables. Cell, positional, and anisotropic thermal parameters are presented in table 1. The half width parameters u,v, and w are 4178(151), 230(47),

and 716(11), respectively.

During the refinement process with both anion thermal parameters isotropic, the

bromine anion occupancy of both anion positions was allowed to vary, the overall

occupancy only being constrained to the mixed composition. Under these condltlns,

the occupancy of anion position 1 refined to 1.009(16). It was thus assumed that the

Table 1. Positional, Anisotropic Thermal, and Cell Parameters for 2BaBr2»BaCl2. The

dlgit(s) in parenthesis indicate the estimated standard deviation of the last

dlgit(s).

X Y Z

Ba 0.2603(4) 0.25 0.1203(3)

Brl 0.0293(3) 0.25 0.8292(3)

(Br,Cl)2 0.1446(2) 0.25 0.4329(2)

B(1,1) B(2,2) B(3,3) B(1,2) B(1,3) B(2,3)

Ba 0.67(15) 1.40(16) 2.23(15) 0.29(12)

Brl 1.62(14) 1.62(13) 1.55(13) 0.00(10)

(Br,Cl)2 1.38(10) 1.56(10) 1.19(9) 0.29(9)

Lattice Parameters

a = 8.2031(3)

b = 4.8606(2)

c = 9.6359(4)
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

square pyramidal hole was occupied exclusively by bromine atoms, and occupancy was

removed as a variable. Thus, even at this intermediate composition, anions do not

randomly substitute in the structure. However, no evidence for a doubling of one of

the lattice parameters to accommodate an ordering of the chloride and bromide anions

within the tetrahedral holes was found. An examination of the plot output indicated

a generally good fit of the data throughout the entire spectrum, but a couple of

spurious reflections were present in the region ^09<2Q<^^^° . A Hamilton's test of

the R values obtained with and without all thermal parameters aniostropic indicated

the anisotropic parameters to be significant.

The lattice parameters agree well with the values expected from Hodorowitz, et

al., and the positional parameters are in excellent agreement with those derived for

1 2

BaBrCl, and in fair agreement with those reported for BaBr..

1. S. A. Hodorowitz, E. K. Hodorowitz, H. A. Eick, J. Solid State Chemistry 48, 351-

6(1982).

2. E. B. Brackett, T. E. Brackett, R. L. Sass, J. Phys. Chem. 67, 2132-5(1963).

STRUCTURAL CHANGES IN NASICON SOLID SOLUTIONS,

Na_ Zr_Si P_ 0,^, AT ELEVATED TEMPERATURES

1+x 2 X 3-x 12

J. J. Didisheim and B. J. Wuensch

(Massachusetts Institute of Technology, Cambridge, MA)

and

E. Prince

The ionic electrical conductivity of solid solutions between sodium zirconium

phosphate and sodium zirconium silicate, Na, Zr^Si P_ 0,^, rises four orders of

1+x 2 X 3-x 12

magnitude from the modest conductivity of the endmember compositions to a maximum

near x = 2. This change in conductivity seems closely correlated to change in

crystal structure. The a axis of these hexagonal or monoclinic pseudo-hexagonal

phases (for 1.6 < x < 2.2) increases monotonically with x. The length of the c axis

(and the cell volume, as a result), however, rises to a maximum value and then

decreases upon further substitution of the larger Si ion for P. The composition with

maximum cell volume falls close to that of maximum conductivity. To understand the

structure changes which give rise to these anomalies and, presumably, the enhanced

conductivity, Rietveld analyses of the crystal structure of solid solutions as a 1-3 function of composition had been earlier performed at room temperature with

neutron powder diffraction data obtained from phases with x = 1.0, 2.5 and 3.0
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

(hexagonal, space group R3c) and x = 1.6 and 2.0 (monoclinic space group C2/c). The

results revealed that the principal change in the framework with composition is a rotation of the orientation of the tetrahedral (P, Si) groups up to x = 2, followed

by a progressive return to the original orientation for larger values of x. The

rotation acts to stretch the height of an octahedral cavity fully occupied by Na(1),

and this change in length accounts almost entirely for the variation in c. The

rotation also acts to open the saddle-point arrangement of oxygen ions that separates

neighboring Na ions. The radius of this "window" was found to attain a maximum

+ value, close to the ionic radius of Na , near the composition of maximum

conductivity. One would expect this to lower the barrier to a diffusive jump between

alkali ion sites. Evidence that this is indeed the case is provided by the fact that

the temperature factors for the Na ions increase sharply to a maximum near x = 2,

suggesting a softening of the potential well in which they reside. The Na ions that

occupy one of two types of interstices available in the framework assume temperature

factors that are too large to be physically reasonable. Moreover, the observed Na-O

bond distance is much too large, and the maximum in scattering density in this site,

as revealed by Fourier and difference syntheses, does not fall at the center of the

site. This suggests that a static atomic displacement occurs as a result of the

"stretching" of the cavity described above, and that the thermal motion is only

apparent.

The studies of the phases are currently being extended to elevated

temperatures. The objectives are to (a) examine possible order-disorder

transformations among the alkali-ion sites, one of which was found to be fully

occupied in all compositions at room temperature, (b) distinguish positional disorder

from time-averaged thermal vibration of the sodium ions through the temperature

dependence of the temperature factor coefficients, and (c) establish the extent to

which anisotropic thermal expansion shifts the composition at which optimum size occurs for the "window" between neighboring Na sites, thereby providing further

insight into the role of charge carrier concentration, as opposed to mobility, in

determination of the enhanced conductivity.

Measurements have begun with examination of the high conductivity compositions

near x = 2. Neutron powder diffraction data have been obtained at 275° and 320°C for

a sample with x = 2.0 and at 320°C for x = 1.6. Refinement of the structure with

these three data sets is still in progress, but is sufficiently close to convergence

that values for the atomic coordinates are likely close to their final values. These

parameters are presented in table 1 . Comparison of the results with the roomtemperature structures at these compositions is not straightforward, as phases with

1.6 < X < 2.2 are monoclinic under ambient conditions but transform to the
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

rhombohedral structure at the temperatures at which the present measurements were

performed. The monoclinlc structures are strongly pseudo-hexagonal, however. The

atomic positions found for the monoclinlc room-temperature were thus converted to

coordinates expressed relative to hexagonal axes for purposes of comparison in table

1.

The atomic positions in the high-temperature rhombohedral phases may be seen to

remain remarkably close to those in the corresponding monoclinlc phase. The shift in

the framework cations is very slight, amounting to 0.001 c (0.02A) or less for Zr and on the order of 0.001 a (0.009 A) for Si. The coordinates for the oxygen ions also

remain fairly invariant, but a shift of 0.1 24A in the z coordinate of 0(2) indicates

some rotation of the orientation of the tetrahedral groups. The other significant

shift in position is the location of Na(2), which moves 0.1 5A along a. As the alkali

ions are located in shallow potential wells, it is expected that relatively small

rearrangements of the framework ions might result in significant displacement of the

mobile alkali ions. The lattice constants indicate an anisotropic expansion
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

Table 1. . Comparison of Atomic Coordinates in NASICON Solid Solutions

' _ Op at Room Temper

Standard Deviations in Parentheses)

.

Na, . Zr_Si P- 0,^ at Room Temperature and at Elevated Temperature (Estimated

1 +x 2 X 3~x 12*^ K \

X = 1.6 X = 2.

23°c''' 320°C 23''C''" 275°C 320°C

Nad) occupancy 1.0 1.01(7) 1 .0 1* 1.01(7)

Na(2) occupancy **

0(1)

0.53(2)

[0.533 ideal]

** 2* 0.667(2)

[0.677 ideal]

X 0.6429 0.626(3) 0.6231 0.636(2) 0.633(5)

Zr z 0.1476 0.1483(3) 0.1464(5) 0.1464(5) 0.1474(4)

(Si,P) X 0.2898 0.2897(8) 0.2840 0.283(10 0.288(1)

X 0.1780 0.1735(6) 0.1805 0.1772(9) 0.177(1)

y -0.0432 -0.0349(7) -0.0459 -0.035(1) -0.0368(9)

z 0.1890 0.1944(2) 0.1869 0.1950(3) 0.1940(3)

X 0.1942 0.1949(6) 0.1974 0.192(1) 0.1928(8)

y 0.1780 0.1708(6) 0.1754 0.1713(8) 0.1714(8)

z 0.0926 0.0915(2) 0.0941 0.0922(2) 0.0924(3)

0(2)

a(A)

c(A)

8.9954

22.9716

9.0039(5)

23.080(2)

9.0351

22.9810

9.0581(8)

23.070(3)

9.0538(7)

23.070(3)

The monoclinic room-temperature structures have been referred to pseudo-hexagonal

axes to permit comparison.

* Not yet refined.

** Na(2) is split into two symmetry-independent sites in the monoclinic structures.

These are not equally occupied.
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

Table 2. Comparison of "Window" Sizes Along Diffusion Paths in NASICON Solid

Solutions Na "^^p^^ ^•^- ^12 ^^ ^oof" Temperature and at Elevated Temperature

(a) Path 1 [Nad) - Na(2)1

23°C* 275°C 320°C

X = 1 .6 0.970, 1.025, 1 .125 A (1.0^10 A, av.) 1 .035 A

X = 2.0 0.933, 1.057, 1.139 A (1.0M3 A, av.) 1.0M1 A 1 .030 A

(b) Path 2 [Na(2) - Na(2)]

23°C* 275°C 320°C

X = 1 .6 0.963, 1 .021 , 1 .004 A (0.996 A, av.) _

1 .013 A

X - 2.0 0.923, 1 .002, 1 .022 A (0.982 A, av.) 1.021 A 1.009 A

* Three symmetry-independent paths exist between a given pair of species in the

monoclinic room temperature structures.
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

-5 -6 -1

coefficients are 1.6 10 and 3.2 10 °C parallel to and normal to the c axis,

respectively. All of the above structural changes, however, include both the

discontinuous displacement that accompany the mpnoclinic to rhombohedral phase

transformation and changes caused by thermal expansion. Separation of these two

influences must await comparison of phases that are entirely within the field of

stability of the rhombohedral structure type.

The refinements provide no evidence for change in the occupancy of the Na sites

to the temperatures examined to date. The Na(1) site remains fully occupied. Table

2 compares the computed critical radius of the sphere that could just pass through

the oxygen ion configuration that separates neighboring Na(1 ) and Na(2) sites (path

1) and also two neighboring Na(2) positions (path 2). Detailed comparison with the

values in the room-temperature structures is again complicated by the fact that three

distinct symmetry independent paths exist in the monoclinic structures. Table 2

accordingly includes an average value for the room temperature windows. The window

size found at elevated temperatures is close to the average found for both types of

diffusive paths at room temperature as a result of the small magnitudes of the atomic

displacement. The radius at elevated temperature, however, varies less from

composition to composition than do the radi of the individual paths at room

temperature. This suggests that the saddle point configuration at elevated

temperatures may be less critically dependent upon composition than is the case at

room temperature. Confirmation of these trends must await extension of these

analyses to a wider range of compositions and temperature, but the observations seem

to have bearing on the reason why the composition of maximum conductivity for the

NASICON solid solution system appears to shift with increased temperature.

1. L. J. Schioler, B. J. Wuensch and E. Prince, NBS Tech. Note 1178, F. J. Shorten,

ed., 42 (1983).

2. B. J. Wuensch, L. J. Schioler and E. Prince, Proceedings of the Conference on High Temperature Solid Oxide Electrolytes Vol. 11 -- Cation Conductors.

Brookhaven National Laboratory BNL-51728, 55, October 1983.

3. L. J. Schioler, B. J. Wuensch and E. Prince, NBS Tech. Note 1190, F. J. Shorten,

ed., 9 (1984).
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

STRUCTURE OF BARIUM TITANIUM NIOBIUM OXIDES

J. L. Soubeyroux

(CNRS - Laboratoire de Chimie de Solide, Bordeaux, France)

and

(National Bureau of Standards, Gaithersburg, MD)

and

R. S. Roth

(Center for Material Science)

and

A. Santoro

High resolution diffraction measurements have been made on compounds of

the ternary system BaO-Ti O^-Nb^O^ . These compounds can be studied

c. do

particularly well by neutron diffraction techniques because of the high

contrast between the scattering lengths of the titanium atoms (-0.3^^

-12 -12

10 cm.) and of the niobium atoms (0.702 10 cm.).

The compound BaTi-, onNb^ nocO- „n has the cubic perovskite structure

u . oy u . uoD ^ . y

y

with a = 4.015 A. The titanium and niobium atoms are randomly distributed in

the octahedral sites with a mean metal-oxygen distance of 2.07 A. The compound Ba^TiNb|^O.o , also written Ba(Ti, .^Nb^ ,^)0_, is a six-layer

arrangement of the perovskite structure. The refinement of the structure has

been performed in the R 3m space group with the hexagonal parameters a = 5.7756(1)A and c = 42.409(1 )A. The resulting structure leads to a statistical

distribution of the titanium and niobium atoms in the octahedral sites. The

octahedra share corners to form a five -sequence. The metal-oxygen distances

4+ 5 + range between 1.83 and 2.19 A, in good agreement with Ti and Nb ionic

radii. A sample of the compound was amaeled in order to introduce ordering in

the structure. The refinement of this new sample shows no ordering of the

metal atoms.

The compound BanTi^Nb^Op^, also written Ba(Ti_ .gNb^i/g )0-, , is the eight

layer repeat sequence. The hexagonal parameters determined are a = 5.7908(3)A

and c = 18.853(1 )A. The refinement of the structure is in progress.

10
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

NEUTRON POWDER DIFFRACTION STUDY OF THE STRUCTURE

OF THE COMPOUND LIq o^^^q ^e^^^i\

E. Lukacevic, A. Santoro

and

R. S. Roth

(National Bureau of Standards, Gaithersburg, MD)

The structure of the title compound has been analyzed by neutron powder diffraction techniques and by the Rietveld method. The material crystallizes with the

symmetry of space group 14. /a. The lattice parameters ae a = 5.335, c = 11.479 A.

3+

The framework structure is of sheelite type. The La ions are statistically distributed on the sites 4b. The Mo ions fully occupy sites 4a and the ions sites

16f with X = .1413, y = .0116, z = .2074 The R-factors at this stage of refinement

are R„ = 6.52, R = 6.27, R, = 8.01 and the expected value is R„ = 4.46. There are

N p W n- several possible locations for the Li ions. A likely position would be site 8e with

z 2 3/8- I" this configuration the Li ions would be placed halfway, along the caxis, between the Mo and the La cations. So far, however, attempts to locate the

Li ions have been unsuccesful and refinements of the structure seem to be peculiarly

insensitive to the Li positions.

GEOMETRICAL AMBIGUITIES IN THE INDEXING OF POWDER PATTERNS

A. Santoro

It is well known that powder patterns can often be indexed on more than one

lattice. In most cases the ambiguities in the indexing are accidental in origin

(errors in the measurements of angular positions, extinctions related or unrelated to

the symmetry operations of the structure, however, in reflections produced by

impurities, etc.). There are cases, however, in which the ambiguities are not

accidental but geometrical in nature. These cases arise when two or more different

lattices give calculated patterns having the identical number of distinct lines in

identical 26 angular positions. The number of planes contributing to each reflection

and the indices hkS, of the planes are in general different. The lattices which are

consistent with the same powder pattern Ae related to one another in a rather simple

manner, i.e . by a transformation matrix having simple rational elements. Lattices so related are called "derivative lattices". The problem of geometrical ambiguities has

already been studied (1). The previous analysis, however, was based mainly on concepts of number theory and the critical role played by symmetry was not

emphasized. Consequently, no general method was given for finding the conditions that

11
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

lattices must obey in order to generate geometrical ambiguities. A new procedure has

now been devised, simpler than the previous one, which allows one to determine also

ambiguities that Ae possible only when some types of space group extinctions are present in one of the two structures. This procedure is based on general properties

of transformations and on the theory of derivative lattices (2).

(1) A. D. Mighell and A. Santoro (1975). J. Apl. Cryst. 8_, 372-37^1.

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

TEXTURE OF EXTRUDED URANIUM ALLOYS BY NEUTRON DIFFRACTION

C. S. Choi and H. J. Prask

(U.S. Army Armament R&D Center, Dover, NJ)

and

(National Bureau of Standards, Gaithersburg, MD)

It has been reported that extruded uranium/tungsten composites show improved

mechanical strength at high extrusion ratios. Since the room-temperature stable

phases of uranium alloys (a or a' phase) possess a highly anisotropic crystal

structure, the extruded uranium samples are expected to be highly textured, and

hence to exhibit anisotropic mechanical properties depending on the orientation

texture. We have studied two hydrostatically extruded samples, a U-0.75wt/K Ti alloy

and a (U-Ti)/W composite alloy. Both samples were extruded in two steps, 6 to 1 area reduction at 600° C followed by 4 to 1 area reduction at 500° C, and have

approximate dimensions of 7.6mm in diameter and 40mm in length. Since the pole

figure diffractometer had poor instrumental resolution, only three reflections,

(111), (112)and (131), were resolved adequately with sufficient intensity for study.

All three reflections were used for the texture study of the extruded U-Ti alloy,

but only (112) and (131) were used for the composite sample because of the

overlapping of the a-U (111) reflection with the W(111) reflection. All of the pole

figures showed almost perfect concentric circular contour-lines about the direction

of the cylinder axis, which is an indication of fibre texture. The two dimensional

pole density distributions were reduced to one-dimensional distributions by

averaging the intensity over the (j)-angle at each tilt angle, yielding accurate peak

positions as shown in figure 1 . The observed peak positions should correspond with

the angles between the (hkl) plane normals and the fibre axis in an ideal fibre

texture. The plane normals for the fibre axes were determined by comparing the

observed peaks with the calculated interplanar angles. It was found that the uranium

phase of the samples possesses a duplex figure texture with either [010] or [340] as

12
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

fibre axis. Assuming the orientational distribution of the fibre axes is a Gaussian

form, the pole density P(p) of an (hkl) reflection with tilt angle p. is given by

F(p)= I [ §

A(p - p,)'

exp - R{ ? exp -

i = 1 H3i40Si'^Pi '340 j=1 H^^QSinp.

A(p-p, )'

DIG

}]

where I is a constant related to the total crystal reflectivity, k=Hin2, H is the

full width at half maxmum, N. ia the number of equivalent (hkl) planes which have

1000

(A)

U(I3I) (B)

U(I3I)

U(II2) U(II2)

1000

500

I ' I I I

I II I -10 10 30 50 70 90 110 TILT ANGLE (DEGREE)

400-

-10 10 30 50 70 90 110 30 60 90 120 150 180 TILT ANGLE (DEGREE) CHI -ANGLE IN DEGREE

Figure 1. Pole density distributions of the three reflections, U(131) , U(112) and

U(111), for the two extruded alloys. The small circles refer to the

observed values and the solid curves to the calculated distributions

based on the [010]/[340] duplex fibre texture. The figures in (A)

correspond to (U-Ti) alloy and those in (B) to the composite alloy. The

U(020) distribution in (B) is the [010] fibre axis distribution measured

directly by the chi-angle rocking of the composite alloy. The dotted

lines in the (131) distributions indicate background level added for the

refinement.

13
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

100

010 031

Figure 2. The inverse pole of the uranium phase of the composite alloy, with

contour-heights in arbitrary units. The figure at left is the view from

the fibre axis direction and that at right is the perpendicular view.

the identical tilt angle p., and R is a relative frequency of [QIC] for the fibre

axis. The ideal duplex fibre texture model was fitted to the experimental intensity

distribution patterns by a non-linear least-squares refinement, with I, H..^, H^^i^f

and R as adjustable parameters. The calculated profiles agreed very well with the

observed as shown in figure 1 . This analysis revealed a quantative picture of the

orientation distribution; (a) the width of the fibre axis distributions for the two

extruded samples were approximately 18° for the [3^0] fibre axis and approximately

35" for the [010] axis, and (b) the frequency of the [010] axis was about 2.8 times

that of the [3^0] fibre axis.

The pole density distribution as function of tilt angle can be rewritten in

generalized form if we use the Miller indices for the expression of the interplanar

angles p. and eliminate the summation operation over the total number of peaks, as

follows:

F(p,hl<fi,) = K[(H2ijQ)"^exp-A{(p-B2i^Q)/H2^Q}^ + R(HQ^Q)"''exp-A{ (p-Bq^q)/Hq^q}*]

Where, B^^ = acos(3ha +4kb )/{(9a +I6b ) q}, B^^q = acos(kb /q),

and q = { (ha*)2+(kb*)2+(j,c*)2}^^^.

14
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

The term sinp. in the pole density distribution function is eliminated in this

generalized form because F(p,hkJl) refers to all [hk£] poles within the diffraction

cone with tilt angle p.. When the tilt angles of the sample are fixed to p=0° or

90°, the function gives the number of the [hkS,] poles oriented with their axes

parallel or perpendicular to the fibre axis, respectively. The inverse pole figure

viewed from the equatorial direction may be obtained by replacing the arccosine in

the B„j^- and B-,_ by an arcsine. Figure 2 shows their inverse pole figures of the

a-U phase using the parameters R = 2.8, and the FWHM's in radians (converted from

Hoiin ^ '\'\°, H^.- =21°, the values corrected for the instrumental resolution). The

340 010 ^ ^ ^ pole densities were projected on the plane defined by the equation: ha +kb +Jlc = s, where s is an arbitrary constant . The contour lines are the probability densities

on an arbitrary scale, starting from 1 with a step interval of 20.

THE NONDESTRUCTIVE DETERMINATION OF NEAR-SURFACE

RESIDUAL STRESSES IN DEPLETED URANIUM ALLOYS

H. J. Prask and C. S. Choi

(U.S. Army Armament R&D Center, Dover, NJ)

and

(National Bureau of Standards, Gaithersburg, MD)

Depleted uranium -0.75 wtyS Ti alloy ("DU") has become a principal material for

armor-piercing projectiles because of its high density, hardness, ductility, and high

ultimate tensile and yield strengths. These properties are achieved by a fabrication

process which involves a fast quench to ambient temperature from the Y-phase

CSOOOC), followed by aging at ~400°C. This yields the desired mechanical properties

with the Ti "dissolved" in the single-phase a'-U host lattice. However, optimization

of performance has probably not been achieved because of an inability to characterize

certain properties in the course of the fabrication process. One of the most

important of these is residual stress.

Last year we described a new technique, energy-dispersive neutron diffraction

(EDND), by which the first nondestructive characterization of sub-surface residual

stress in DU was achieved. (1) Because of the expected susceptibility to stresscorrosion cracking, and because of the difficulties encountered with stress

measurements in this material by means of x-ray diffraction, we have sought to extend

the EDND stress measurements to the surface region of DU. In the following, results

are described for a stress-free, powder test sample and two production-type DU

specimens.

15
REACTOR RADIATION DIVISION 'AND COLLABORATIVE PROGRAMS

The details of the application of EDND to sub-surface residual stress

measurements have been given in ref. 1. (For convenience, we define "sub-surface" as the sample region in which the differential volume, AV, of figure 1 is entirely

within the sample.)

What is measured is strain, e, which is reflected in the change in d-spacing

which residual stresses produce:

E = (d - d° )/d° ^ ^ hkl hkl^ hkl (1)

where d ° represents the stress-free d-spacing of the (hkl) reflection. With

n K X reference to the spherical-coordinate geometry of figure 2, measured strain, e' , is

related to residual stress by

Source Detector

Sample

Figure 1. Upper: Perspective schematic showing how absorbing masks (e.g. Cd) can be

used with Bragg 's Law to define the examined volume, AV; lower: plan view

of movement of AV through the (translated) sample.

16
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

2 2 2 2

e!, = 1/2 S-(hkl)[o, .COS <{)sin ip + o„^sin(|) sin ijj

<l>\\) 2 1 1 22

2 2

+ o^_cos t|^ + o.2Si"2(()Sin ij; + o. o°oS(j)Sin2ii; (2)

02^sin<J)Sin2ijj] + S^ChkDCo^^ + O22 "^ °-5^^*

The S, (hkl) are "diffraction elastic constants" which, in general, depend on

the reflection studied.

For this initial study, several assumptions are made to extract stresses from

the measured strains. We assume that the principal axes of stress in the sample

coincide with the cylindrical geometry so that 0.^ = 0.-. = Op-, = 0. We also assume

elastic isotropy in the sample such that

1/2 S2(hkl) = (1 + y)/E and S^(hkl) = - y/E (3)

4 ''a

Figure 2. Specimen (P.) and laboratory (L. ) corrdinates at a point in the specimen.

The L'o or probe, direction coincides with themomentum transfer direction

1c or ^; Po Corresponds to the cylinder axis.

17
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

where y and E are Poisson's ration and Young's modulus, respectively.

At the surface, overall equilibrium requires that the stress normal to the

surface be zero. With this and the assumptions described we have at the surface

^i^, = (^^ " yVEJCoggSin (|)sin ^ + 02zCOs ij;) - (y/EJCogg + o^^). (4)

To test for anomalous shifts in peak positions arising from geometric effects,

we examined a copper powder in the same cylindrical geometry as the DU samples: 10

cm long by 2.38 cm in diameter. The AV for both copper and DU was nominally 1.5 cm

0.17 cm X 0.17 cm with the long dimension aligned parallel to the cylinder axis.

Although microstresses might be present in the individual grains of copper powder,

measured d-spacings should be identical at any point in the powder unless

instrumental effects distort the measurements.

For copper, we examined the (111) reflection at a scattering angle of 90° at

several positions in the sample. In figure 3 we show in a partial plan view the

examined differential-volume cross-sections and the beam-in/beam-out bisector or k

e=(-i t 6) X 10

^=(-1.4 + 5) X 10

Figure 3. Cross-sections of AV, drawn to scale relative to the sample cross-section,

for copper powder (open squares) and production-type DU (cross-hatched

parallelograms) near-surface measurements. The arrows indicate the kdirection for each measurement. Measured strains, e, are shown for the

copper powder.

18
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

direction. Measured strains which are also shown In the figure were determined In

the following way. Several measurements of the d-spaclng were made at the sample

center. The weighted mean of these yielded "d°" = 2.08714 _+ 0.00010 A. Strains at

the near-surface positions shown In figure 3 were then calculated according to eq (1)

from the d-spaclngs measured at these points. Measured strain values are obtained

without any assumptions or approximations.

In this test case, if Instrumental effects do not distort the measurements the

measured strains should all be zero. It is most interesting that for the five points

examined, only at one does the strain differ from zero by more than a standard

deviation. It is also most Important that even for differential volumes more than

half of which are outside the sample the strains —with the one exception— are zero within one standard deviation. Although these measurements do not represent a complete test of the EDND technique for near-surface studies, the results were sufficiently encouraging to begin preliminary studies of production type DU samples.

One area of considerable current Interest relating to DU-0.75 vt% Tl penetrator

fabrication is the effect of different processing techniques on surface residual

stresses and stress-corrosion susceptibility. Two process variations which are currently being studied are rolled bars solutlonlzed in an AVS furnace (DU-AVS) and

rolled bars solutlonlzed in an Induction furnace (DU-I). Subsequent processing steps

Include quick-quenching, aging, and rotary straightening for both samples.

At the surface, four sets (90° apart) of two measurements were made with i< in

the r-e plane. Because of an Instrumental shift not recognized until data collection

was completed, the two measurements made at each 90° position did not coincide

exactly. They differed In their position relative to the surface as shown in figure

3. However, since exactly the same problem occurred with both samples, the

measurements were analyzed as if no shift had occurred. In this case the (111)

reflection of DU was examined at a scattering angle of 82°. For this reason the AV

cross-section is a parallelogram rather than a square as for copper at 90°.

To obtain the near-surface residual stresses eq (^)is used, d° is known for

each sample from powder diffraction measurements so that both o.-than o^^ could be

o ZZ

obtained from measurements with k in the r-e plane; however, since the angle is near

90° the measurements are much more sensitive to o-. and o__. For the present we

evaluate only o . The results for the two samples are shown in figure 4.

As expected for a quenched cylinder, measured hoop stress on the surface Is

compressive. However, the AVS and induction furnace samples exhibit quite different

stress distributions around the circumference. It is interesting that for both

19
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

10

DU-I

-10-

DU-AVS

*

b*

~ -20 ^ -30

-40

-50

-60

J_ JL 90 180 270 90 180

Relative Position (Degrees)

270

Figure M. Preliminary results for near-surface hoop stresses for induction and AVS

furnace solutionized Du . Measurements were obtained at 90° intervals

around the circumference of the cylindrical samples with arbitrary zero position.

samples the average hoop stress is approximately 32 KSI; however, the variation

about the average is considerably greater for the AVS-furnace sample. To minimize

susceptibility to stress-corrosion cracking, it is imperative that the surface

stresses be (highly) compressive. In this regard it is of concern that one of the

AVS-furnace measurements approaches the tensile stress region. Follow-up

measurements are planned to characterize these samples more definitively.

1. H. J. Prask and C. S. Choi, NBS Tech Note 1190, 31-3^ (1984); NBSIR 84-2815, 53-

56 (1984); J. Nucl. Matls., 126, 124-131 (1984).

20
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

CRYSTAL DATA

V. Himes, J. Stalick and A. Mighell

and

J. Rodgers

(National Research Council of Canada, Ottawa, Canada)

The NBS Crystal Data Center maintains a data base that contains evaluated

crystallographic and chemical data on approximately 80,000 materials. The data fall

into the following categories: organics, organometallics, metals, intermetallics,

inorganics and minerals. During the year the data base has been significantly

upgraded and expanded. Approximately 16,000 existing inorganic entries have been

upgraded, processed by NBS*AIDS83, evaluated and added to the data base. In

addition, -5,000 organic entries corresponding to recently published data have been

added.

There are two fundamental ways that large crystallographic data bases can be

used. As a source of critically evaluated data, the data base can be used as a basis

for scientific research or as an aid to research. To permit scientists to utilize

the data base, we have developed software tools that can be distributed with the data

base or used to search the data base on-line at a central site.

NBS search software, which became an integral part of the Crystal Data

Distribution Package in June, 1985, is designed to be used on a variety of computers.

With the lattice-matching algorithm, unknown compounds can be identified by

comparison with entries in the data base. The method can be used once a cell has

been determined from a single-crystal or from a powder sample using diffraction

techniques. In addition, various types of lattice relationships between materials

can be readily established. The lattice-matching method offers a comprehensive

technique to characterize solid-state materials and is now in routine use at the

National Bureau of Standards, in industrial analytical laboratories, and by

crystallographic data centers.

The on-line search system is based on scientific software written both at NRC

and NBS, coupled with IBM systems software (the IBM host computer is located at the

National Research Council of Canada). Using Telenet or the equivalent, the NBS

Crystal Data File can be accessed on-line by scientists anywhere in North America or Europe. This system permits search and retrieval of any given data item or combination of items using Boolean operations. The type of data that can be searched

include chemical name and formula, cell parameters, cell volume, crystal system,

space group symbol and number, density, bibliographic data, chemical class, plus

21
REACTOR RADIATION DIVISION AND COLLABORfiTIVE PROGRAMS

additional data. During the year, this system has been used by the NBS Crystal Data

Center and by individual scientists to solve a variety of scientific problems in

diverse areas of chemistry and solid-state physics.

LOCAL MODES IN DILUTE METAL-HYDROGEN ALLOYS

J. J. Rush and J. M. Rowe

and

A. Magerl

(Institute Laue-Langerin, Grenoble, FRANCE)

Data analysis has been completed on the measurements of local vibrational modes

of hydrogen bound in vanadium, niobium and tantalum in the dilute a-phases. These

experiments were performed on the BT-4 spectrometer, using the high-intensity, lowbackground beryllium detector analyzer and a Cu-220 monochromator. They provide the

first direct information about the microscopic mechanism leading to large linewidths

for the local modes in these dilute metal-hydrogen alloys.

Figures 1 and 2 show neutron spectra measured at room temperature for VH- ^.^,

NbH and TaH with x = 0.180 and x = 0.037 (fast neutron background has been

subtracted). These spectra reveal several highly unusual features: (1) The widths

of the vibration peaks are in every case considerably wider {>. 10 meV) than the

instrumental recalcitron, in cohtrast to the very narrow linewidths anticipated for

the vibrations of dilute interstitial defects. The spectral peaks (two modes are

expected for H in a bcc tetrahedral site, one at low-energy and a doubly degenerate

mode at higher energy) are most broadened for VH

f^1p^ with somewhat smaller but

still substantial widths observed for H in Nb and Ta. The "peak" energies in meV

observed at 295 K for the three a-phase samples are: 106 and ~170 (VH q.^^' ^ ^"^ ^^^

163 (NbH ) and 114 and 154 meV (TaH ^^r?^ - ^ second unusual feature of these

results is that the high energy mode peak for TaH "(fig. 1) increases in energy

from: 154 to 163 meV as x is changed from 0.03 to 0.18, while the lower energy mode

remains unchanged. A third striking aspect shown in figure 2, is the anomalous shift

of the lower excitation peak in NbH. .._ to higher energy as the temperature is

u . 00b

lowered toward the a- 6 phase boundary.

After careful anlysis of the results in figures 1 and 2 and comparison with

earlier experimental work on high hydrogen concentration a' phase samples and H

2-4 5 trapped by impurities in Nb and with theoretical predictions , we conclude that

the broad vibratonal linewidths are associated with a delocalization of the excited

vibrational states of the interstitial defects. In fact an estimate of the ground

22
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

80 100 120 140 160 180 200

Energy (meV)

Figure 1. Spectra of local H modes measured at room temperature,

23
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

300

100

I NbH 0.0055

295K

300

100

•^ •

230K

1

X »»

^

500

300 A A

-A/\

100 _ /^ 78K

1 1 100 150 200

Energy (meV)

Figure 2. Temperature dependence of local H modes in NbH ^. The (a|a + 6) phase boundary is at = 200 K. The solid arrow shows thl^actual "peak" position

vs. T and the open arrow indicates the position at 295 K.

24
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

State tunnel spittling for self trapped protons in refractory metals suggests excited

state "splittings" ~10 meV, which is in qualitative agreement with our observations.

The anomalous shift of the low-energy density-of-states band for NbH toward the

position of the ordered (6) phase peak strongly suggests the existence of fluctuating

hydrogen short range order resembling the ordering in the low temperature phase.

Such "ordering" has never been directly observed over such a wide temperature range

("40° K) above the ordering phase transition. All these results are being combined

in a paper to be submitted to Phys. Rev. B.

1. D. Richter and S. M. Shapiro, Phys. Rev. B, 22, 599 (1980), and R. Hempleman, D.

Richter and A. Kollmar, Z. Phys. B, HH, 159 (1981).

2. A. Magerl, J. J. Rush, J. M. Rowe, D. Richter and H. Wipf, Phys. Rev. B, 27, 927

(1983).

3. D. Richter, J. J. Rush and J. M. Rowe, Phys. Rev. B, 27, 6227 (1983).

4. H. Wipf, et.al, Phys. Rev. Lett., 46, 947 (1981).

5. R.C. Casella, Phys. Rev. B, 27, 5943 (1983).

NEUTRON SCATTERING STUDIES OF HYDROGEN IN YTTRIUM

I. S. Anderson

(University of Maryland)

and

(National Bureau of Standards, Gaithersburg, MD)

and

T. J. Udovic, J. M. Rowe, and J. J. Rush

The dynamics of the yttrium-hydrogen system in the hep solid solution phase has

been studied in order to determine the hydrogen site occupation. There are two pairs

of sites with tetrahedral symmetry and one pair of sites with octahedral symmetry in

the yttrium unit cell aligned along the £ direction, and although neutron diffraction

1 studies have shown that the tetrahedral sites are predominantly occupied, recent

neutron energy loss measurements have shown evidence of multiple site occupancy

(though the oxygen impurity levels in the yttrium samples were not known). In an attempt to clarify the possible occupancies, we have made neutron energy loss

measurements to study the local vibrations of hydrogen in well-characterized yttrium

samples with varying amounts of oxygen and hydrogen. A typical spectrum taken on the

BT4 spectrometer at the NBS reactor operating with a cooled Be filter analyzer is

shown in figure 1 . For all the samples studied, two peaks were observed centered at

25
REACTOR RADIATION DIVISON AND COLLABORATIVE PROGRAMS

101 and 135 meV with no clear evidence of a second harmonic of the 100 meV peak. The

peak at 135 meV can be associated with hydrogen in a regular tetrahedral site and the

energy width of his peak was in all cases limited by the resolution of the

instrument. The origin of the peak at 100 meV is however unclear, the energy being

somewhat higher than would be expected for hydrogen in an octahedral site. The

relative intensities of the two peaks do not depend directly on oxygen concentration

indicating that oxygen trapping of the hydrogen does not give rise to the vibration

at 100 meV. Moreover from the known concentrations, one would have to explain the

trapping of 50 or more protons by each oxygen. However, on removing some hydrogen

from the sample under vacuum at 150°C the intensity of the peak at 135 meV was

reduced whereas the intensity of the peak at 100 meV remained unchanged. This

suggests that the origin of the latter peak is due to hydrogen which is more tightly

bound in the system. There is evidence that the relative intensity of the peak at

100 meV increases with time when the sample is left at room temperature.

oO

3000 -I 1 1 r— 1 1 1 1

YHo.ia 70 K

t

2000 -

f

1000 _ ;.

•

fr

••

1 1 1 •^s*

1 1 •1 1 80 100 120 140 160 180 200 220

E (meV)

Figure 1 . Typical neutron energy loss spectrum showing two local mode frequencies in

^"0.18-

26
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

120 n

.50 .75

Figure 2. Quasielastic spectra from a single crystal of YH a) Q //<1210>, b) Q

//<0001>. "-2

27
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

Figure 3-

300 K

Elastic incoherent structure factor for YH at 300 K. The solid line is

a model calculation for jumps between two' equivalent sites allowing only

455^ of the hydrogen to occupy these sites.

Earlier measurements of the diffusion of hydrogen in yttrium indicated the

existence of a local hopping motion of hydrogen probably between pairs of tetrahedral

sites. The BTH spectrometer was used in its triple-axis mode to study the

quasielastic scattering due to this local hydrogen motion in single crystals of

yttrium at room temperature. Figures 2a and 2b show typical spectra taken with the

momentum transfer vector Q_ perpendicular and parallel to the c_ axis respectively.

Although there is no quasielastic intensity when Q_ is perpendicular to the c_ axis,

there is clear quaiselastic intensity measured parallel to this axis showing that

the motion involves jumps along the £ direction. Moreover, the Elastic Incoherent

Structure Factor (EISF) shown in figure 3 is well described by a model for jumps

between pairs of tetrahedral sites if only a fraction 0.45 of the hydrogen atoms are

involved. A neutron energy loss measurement on the same crystals showed that the

relative intensity of the peak at 135 meV was also of the order of 0.45 indicating

that the hydrogen giving rise to the peak at 100 meV was not involved in the local

motion.

1. D. Khatamian, C. Stassis and B. J. Beaudy, Phys. Rev. B23, 624 (1981)

2. I. S. Anderson, A. Heidemann, J. E. Bonnet, D. K. Ross, S. K. P. Wilson, and M. W. McKergow, J. Less. Comm. Metals, 101, 405 (1984).

28
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

STOCHASTIC STATES THEORY OF NEUTRON SCATTERING

FROM SELF-TRAPPED DEFECTS IN SOLIDS.

N. F. Berk

We are investigating a stochastic states theory for the energy and wavevector

resolved spectrum of neutron scattering from self-trapped defects, such as hydrogen,

in solids. The basic idea of the model is illustrated by the two reflection

equivalent, aysmmetric double-well potentials in figure 1, which represent the

vibrational potentials of a defect self-trapped in the deeper of the two wells or pockets: either in the right hand well, as shown in 1 , or in the left hand well, as

in 2. Self-trapping on either side of the double well is described by the asymmetry

of the potential, where the asymmetry parameter e is taken to be the measure of the

local self-induced strain--or self-trapping--energy . Were the defect to remain

indefinitely in one of these neighboring configurations, say 1, its vibrational

spectrum would be determined by the rigid asymmetric potential, and neutron

scattering would reveal a sharp inelastic peak at energy E of the tunnel-split

ground-to-first-excited-state transition. Since the two potentials have identical

spectra, a static distribution of self-trapping configurations, 1 and 2, would

provide the same neutron spectrum as either one acting alone. The axiom of the

present model, however, is that unless either configuration is stabilized by external

forces, the system (solid + defect) undergoes dif f usive--_i_.£. , nonadiabatic

,

incoherent —transitions between the two stochastic states 1 and 2 at a rate given by

the model parameter X, which measures the effective hopping rate of the defect. The

vibrational Hamiltonian of the system is now time-dependent: H(t) = H / -, , where

C(t) is a Markov process on {1,2}, and H^ and H are the Hamiltonian operators for

the respective stochastic states. Because of the spatial displacement of the

asymmetry distinguishing 1 from 2, H. and H are noncommuting, [H. ,H„] * 0, and so are not simultaneously diagonalizable . The defect, therefore, cannot stay in an eigenstate of one or the other potential, 1 or 2, and the spectrum of neutron

scattering will be modified by the random potential well flipping that we take as a model for the hopping between the neighboring self-trapped configurations.

The consequences of the model for neutron scattering are worked out most

1 naturally in the stochastic states superoperator formalism developed by Blume , and

2 3 by Dattagupta and Blume , and further elucidated recently by Berk, et al . In

compact superoperator notation, the neutron scattering intensity is proportional to

29
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

I(Q,a)) = Re(e'^''|u[iaj]|e^^'') (1)

where uEico] is the Laplace transform of the average of the time-development

superoperator

U(t) = exp[i/Q h''(t)cIt] (2)

X X

where H is the Hamiltonian superoperator (Lioville operator), H A = [H,A], and where

(A|B) = trA for arbitrary operators A and B. As a first trial of these notions we have limited ourselves to the simplest case where both stochastic states are

described by a two-level tunneling system. Thus, in the pocket-state (left-right)

representation

«i'2 --^^xi^s^ <3)

where S., i = x,y,z, are the Pauli spin-1/2 operators and where 6 is the tunnel

" / 2 2 splitting for the limit of a symmetric potential; E = /(6 + e ). The position

operator in this representation is r = 2aS , where 2a is the distance between the two

wells or pockets. In this model (1) can be worked out explicitly, and we find the

formula (for the case 1 and 2 have equal a priori probabilities)

KQ.o)) = 2Ae^6^sin^Qa/[a)^(6^ + e^ - co^)^ + A^(a)^ - 6^)^]. (4)

The w-dependence of (4) is shown in figure 2 for fixed 6 = e = 1 and a range of

hopping rates X. For A

-»• 0, the spectrum consists of lifetime broadened inelastic

line at (D = E = /2~and a quasielastic peak at w = . As X increases both lines

broaden and the inelastic peak moves toward lower energies. Then as X continues to

increase, \ >> e, the quasielastic scattering becomes too broad to observe, while the

inelastic line motionally narrows and moves asymptotically toward the tunneling

30
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

Figure 1. Stochastic states, /I/ and /2/, representing neighboring self-trapped

configurations of a double-well defect vibrational potential. The model

assumes random potential well flips at a rate X.

Figure 2. Neutron scattering intensity obtained from (M).

31
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

transition energy for the averaged Hamiltonian H = (H. + H„)/2, E = 6 = 1. The

behavior of (M) is indicated succinctly in terms of the intensities at the special

frequencies w = 0, 6, and E. Thus, suppressing common factors,

1(0) = (e/6)^/A,

1(6)/ = A/e^, and

1(E) = (6/e)^/X. (5)

In particular, (5) shows the strong sensitivity of the relative intensities to e; as e increases, intensity shifts rapidly -- as e -- into the quasielastic line.

Since the model treats the hopping phenomenologically, there are no built-in

constitutive relations among the parameters to delimit their ranges of variation, and

not all of the behavior indicated in figure 2 may be physically meaningful in the

given application. This important aspect of the problem remains for futher

investigation, along with extensions to various degrees of complexity such as multilevel, multi-stochastic state generalizations.

1. M. Blume, Phys. Rev. 174 , 351 (1968).

2. S. Dattagupta and M. Blume, Phys. Rev. B jm, 4540 (1974).

3. N. F. Berk, J. Rosenthal, and L. Yarmus, Phys. Rev. B 28, 4963 (1983).

32
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

THEORY OF PROCESSES CONTRIBUTING TO QUASIELASTIC

NEUTRON SCATTERING FROM HYDROGEN IN METALS

R. C. Case 11a

I have investigated the role of thermally assisted virtual transitions of

dilute hydrogen in metals from localized-oscillator ground states to excitedoscillator band states at temperatures such that direct excitations thereto are negligible (k^T << A, where A is the hydrogen-oscillator excitation energy). These

processes can contribute to the line widths of quasielastic neutron scattering from

such materials. The analysis applies to the absorption and concomitant emission of

any type of bosonic mode which interacts with the hydrogen in the presence of a heat

bath at temperature T. Letting (1/t) be the nearest-neighbor jump parameter which

appears in the Chudley-Elliott expression for the neutron quasielastic linewidth, I obtain

Q Q' Q Q' 4 sinh [gw ' Q

where

ed) = I I e^^'^ e(k). (2)

k

Here e(k) describes the excited-oscillator energy-band dispersion in tight -binding

approximation, ' I is a nearest-neighbor interstitial displacement, Q denotes the

interacting boson mode, 3 = (1/kgT), and G is a coupling constant with the dimension

of energy (ft = 1). The second-order process which contributes to (1/t) involves (i)

absorption of a boson of energy Wq, leading to (ii) virtual excitation of the

hydrogen from the local oscillator ground state at x = 5 to an excited band state

with energy A + e(k), followed by (iii) deexcitation to a local state at x = t

,

accompanied by (iv) emission of a boson of energy w . When the boson spectrum

consists mainly of a narrow band of half-width Y centered at w, Eq.(1) reduces to the

approximate form

2Y (A - 0)) 4 sinh (gw)

For Bo) > (~1), the second factor in Eq. (3) takes on the approximate form

^-eo) ^ 2 e"^^*". (4)

33
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

Figure 1. Temperature dependence of the jump parameter (1/t). in (x /t) vs. w/k T.

The curve depicts the theoretical result given by the second factor in

Eq. (3) of the text. The first factor in eq (3) equals 1/t and is

chosen to give agreement with experiments (reference 3^ on dilute nydrogen

in niobium at T = 21 2K [•]. A few other data points are also indicated

[©].

which exhibits a break in the plot of in (1/t) vs. (1/T). The theoretical

temperature dependence in eq (3) is shown in figure 1, where comparison is made with

3 data for dilute hydrogen in niobium. The agreement is only qualitative and worsens

at the higher temperatures, where multiexcitations enter and real transitions to the

excited hydrogen band states can begin to occur. The boson peak energy, w = 68 meV,

is chosen to fit the low temperature data where the first term in eq (4)i is

adequate. This energy is considerably greater than the hard part of the niobium

phonon spectrum (= 20 meV). The physical nature of the bosons is not clear, nor is

their relative transparency to the neutron probe. Within the model, values of the

dimensionless coupling constant g appearing in eq (3) are consistent with the data

2

for T with g i 1 . Work is continuing in this area.

1. R. C. Casella, Phys. Rev. B 27, 5943 (1983).

2. R. C. Casella, Phys. Rev. B 28, 2927 (1983)

3. J. VOlkl and G. Alefeld, in Hydrogen in Metals I (ed., G. Alefeld and J. Volkl,

Springer-Verlag, New York, 1978), p. 330.

34
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

. TRANSLATION-ROTATION COUPLING - ALKALI CYANIDE/ALKALI HALIDES

J. Bouillot

(University of Maryland)

and

F. Luty

(University of Utah)

and

K. H. Michel

Universiteit Instelling Antwerp

and

J. M. Rowe

The structure work on mixtures of alkali cyanide/alkali halide has been extended

to (KCN) (KCl) with x=0.8 and 0.9 as a function of temperature. In addition, the

data for (KCN) (KBr) has been re-analysed, allowing for the presence of a triclinic phase as suggested by x-ray data. As a result of this additional work, the

phase diagram of the mixed crystals has now become reasonably clear, although some problems remain in the interpretation of the data. It is now well established that

the mixed crystals go from the cubic high temperature phase to a monoclinic phase,

and that at high concentrations (x > 0.9 for KCN/KBr; x > 0.8 for KCN/KCl), a mixed

phase develops, with a triclinic phase and an orthorhombic phase co-existing. It has

further been established that electric dipole order is only established in the

orthorhombic phase - neither the pure cyanides (RbCN, CsCN) nor the mixed crystals in

any ordered phase except the orthorhombic (KCN/KBr, KCN/KCl) ever show electric

dipole order at any temperature. The peak shapes observed for the mixed crystals

suggest the presence of strain, and this in turn implies that sample history may well

influence the observed phase transitions.

We are also beginning a study of the (RbCN) (RbBr) system, in which the pure

RbCN transforms to a monoclinic structure at low temperatures, in the hope that this

system will be less complex, and therefore more susceptible to detailed analysis. In

addition, we are preparing (KCN) (NaCN) samples in order to study the effects of

alkali ion disorder.

With respect to the theory of the pure alkali cyanides, progress has been made

on several fronts. A detailed study of the local properties of alkali cyanides,

including Debye-Waller factors, orientational probabilities and reorientations has

been completed, and gives good agreement with experiment in KCN. The effects of

molecular symmetry on the interactions between translational and rotational motions

35
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

been completed, and gives good agreement with experiment in KCN . The effects of

molecular symmetry on the interactions between translational and rotational motions

has also been explored, and used to show the importance of this property for the

types of behavior observed in the various alkali cyanides. At the present time, we are beginning a study of the predicted neutron scattering cross-sections of high

concentration mixed crystals, when the usual expansions in terms of (small)

displacements no longer works, and are also extending the current models to the optic

mode damping.

INTERACTION OF VIBRATING H ATOMS ON THE SURFACE OF PLATINUM PARTICLES BY

ISOTOPE DILUTION NEUTRON SPECTROSCOPY

J. J. Rush and J. M. Rowe

and

R. R. Cavanaugh and R. D. Kelly

(Center for Chemical Physics)

Recent developments in electron energy loss-spectroscopy and rare gas atom

scattering have yielded important Information on the dispersion of surface modes on metals or alkali halides and thus on the details of surface forces and interactions.

There are considerable difficulties, however, in extending such studies to the

dynamics of chemisorbed hydrogen or molecular species. We describe here the first

results of a study of the vibrational spectrum of hydrogen chemisorbed on the surface

of platinum particles by isotope dilution neutron spectroscopy. These results

demonstrate that such neutron measurements are a sensitive probe of the vibrational

density of states which reflect the degree of phonon dispersion, and thus directly

relate to the dynamic interactions between hydrogen or hydrogeneous species on a catalyst surface.

Neutron spectra were measured at 80° K on the BT-M beryllium-filter

spectrometer, with an energy resolutin of betweeen 5 and 7 meV over the energy range

scanned. The spectra of chemisorbed H at various H/D ratios were obtained by

appropriate subtraction of "blank" (highly deuterated) sample spectra from the

results for various H concentrations.

The neutron spectrum between 3^ and 100 meV for H at saturation coverage is

shown in figure 1 . Spectra were taken over a much wider energy range (30 - 250 meV)

for a variety of surface conditions, which will be reported later. The full coverage

H spectrum shows a broad (~30 meV FWHM) band peaked at 66 meV with a shoulder at ~77

meV. Our own work, as well as other neutron studies indicate that this band is

associated with a second vibration peak at ~160 meV, and that both modes are due to H

36
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

bound on 2 or 3 fold coordinated sites. While such "density of states" spectra can

provide critical information on surface bonding, their interpretation is often not

straightforward, particularly in view of the complex surface of a catalyst. One

could for, e.g., explain such a broad band as due to (1) impurities, (2) closely

related species on the surface, (3) anharmonicity of the metal-hydrogen forces or (4)

significant dispersion of the hydrogen vibration modes reflecting strong H-H dynamic

coupling.

Our recent neutron scattering measurement of the dynamics of hydrogen mass

defects in palladium deuteride suggested to us that similar measurements could be

valuable in probing the dynamics of hydrogenous species on surfaces. The idea is

simple: namely that the substitution of chemically identical light (or heavy) mass

defects, such as H for D, on a surface overlayer leaves the surface electronically

and chemically unchanged, but can greatly change the dynamical coupling between

oscillators or rotators on the surface. The predictions of the theory of the

dynamics of isolated mass defects are given by:

/

g(u))d(o = _1 ,. V 2 2 2

^ ^

where gCu) is the density of states of the host crystal or surface overlayer,

/g(a))dw =1, e = M - M-/M . M . .is the mass of the defect (host) atom, and w As

the defect local mode frequency. This expression shows that for a large mass ratio

the position of the defect mode is related to the width of the host density of states

and thus to the coupling between oscillators.

In figure 1 we show the neutron spectrum measured for 10^ H distributed in a deuterated monolayer on platinum black. A comparison with the spectrum for the

saturated H monolayer shows a significant shift (from 66 to 73 meV) and narrowing of

the peak, and an apparent disappearance of the higher energy shoulder present in the

1005S H results. This result suggests that the dominant effect creating the complex

density of states of the H monolayer is dispersion of the surface optical vibrations,

produced by strong H-H interactions, similar to those found in f.c.c. metal hydrides.

Other phenomena which could broaden the vibrational spectrum, such as strong

anharmonicity or the influence of defects or mixed site occupancy, should not produce

any large change in spectral bands as the H/D ratio is varied.

37
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

To further test these conclusions we have compared our results to the

predictions of eq (1), which has been shown t work well for H vibrations in bulk

^^^^0.60^.02* ^"® ^° ^^® "^^^ neutron scattering cross section of D, we have not been

able to measure the D vibrational spectrum of D absorbed on the surface. However, if we assume harmonic forces, we can derive this density of states by scaling the energy

spectrum in figure 1 for the 100? H overlaywer by 1//2. Using this scaled spectrum,

eq (1) predicts a local oscillator energy for an H defect of

66meV

73 meV

40 60 80 100

Neutron Energy Loss (meV)

Figure 1. Neutron energy loss spectra between 3^ and 100 meV at 80° K for a saturation coverage of H isotopes on cleaned Pt block. Results for IOO5J H are shown by the dashed lines. The energy resolution (FWHM) is indicated

by the horizontal bar.

72.8 meV, in excellent agreement with the peak observed at 73 meV j^ 1 for ^0% H in

figure 1 . The observed peak is broadened beyond instrumental resolution due to the

fact that defects at this concentration are far from isolated. This comparison

demonstates clearly that the complex spectrum for the H overlayer is primarily due to

dispersion of a vibration mode associated with a single type site on the Pt surface,

which in turn reflects strong interaction of H atoms. In fact the observed spectral

width suggests a H-H interaction of about 20/S of the Pt-H force constant.

38
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

The present results show that neutron isotope-dilution spectroscopy can be a powerful probe of the origin of complex vibration bands for chemisorbed hydrogenous

species and can provide direct information of the dynamical non-bonded (as opposed to

chemical) interactions of such species. The method could be extended to low

frequency oscillations or rotations of molecular groups (e.g. NH , NH , CH ) on catalytic surfaces to provide insights on the intermolecular potentials experienced

on catalysts, which are currently difficult or impossible to probe by other

spectroscopies

.

INCOHERENT INELASTIC NEUTRON SCATTERING STUDY OF THE INTERACTION OF ADSORBED HYDROGEN

WITH OXYGEN ON PLATINUM BLACK

T. J. Udovic and J.J. Rush

and

R. R. Cavanagh and R. D. Kelley

(Center for Chemical Physics)

Interest in the surface chemistry of hydrogen on platinum stems from the

involvement of hydrogen in the many important catalytic reactions that occur over

this metal as well as its use as a titrant of platinum-catalyst surface area. In

particular, various investigators have studied the adsorption of hydrogen on platinum

and its interaction with oxygen; such information is beneficial for elucidating, for

example, the mechanism of hydrogen oxidation. These studies have been concerned with

determining hydrogen adsorption site geometry and hydrogen-oxygen surface reactivity.

Vibrational spectroscopies such as high-resolution electron energy loss spectroscopy

12 3 ^ (EELS) '

, incoherent inelastic neutron scattering (IINS) ', and infrared

5 spectroscopy have proved to be useful techniques for investigating this adsorption

system.

In the present work, IINS has been utilized to probe the nature of adsorbed

hydrogen and its interaction with oxygen on platinum black (i.e., high-surface-area

2 -1

platinum particles / 20 m g ). Figures 1 and 2 summarize the experimental results.

The IINS spectrum for platinum black at 80 K, after hydrogen reduction at 383 K

followed by vacuum evacuation at 473 K, is illustrated in figure la. Scattering

intensity at 52, 104, 152, and 208 meV indicates the presence of "residual" hydrogen

species (ca. 0.4 monolayers) believed to be associated with surface defect sites.

The effect of adding a monolayer of oxygen to this surface at 80 K is illustrated by

the difference spectrum in figure lb. The vibrational modes associated with the

"residual" hydrogen species have been replaced by a scattering feature at 128 meV

2 indicative of the bending mode of adsorbed hydroxyl (-0H) species . Figure 2a

39
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

%*{

1b

t t'J i i . 1

( f

f

50 100 150 200

Energy Loss E (meV)

250

Figure 1. a) IINS spectrum for platinum black at 80K after hydrogen reduction at

383K followed by vacuum evacuation at 473K, b) difference spectrum after

addition of a monolayer of oxygen at 80K (positive scattering intensity

represents species removed by oxygen addition).

50 100 150 200 250

Energy Loss E (meV)

Figure 2. a) INNS spectrum for a monolayer of "adsorbed" hydrogen on platinum black

at 80K, b) difference spectrum after addition of ca . 1/3 monolayers of

oxygen, c) incremental difference spectrum after further addition of ca. 2/3 monolayers of oxygen (positive scattering intensities in difference

spectra represent species removed by oxygen addition).

40
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

illustrates the IINS spectrum for a monolayer of "adsorbed" hydrogen on platinum

black at 80 K with scattering intensity evident at 68, 115, and 166 meV. Figure 2b

is the difference spectrum following addition of ca. 1/3 monolayers of oxygen (i.e.,

O/H = 1/3) at 80 K. The vibrational features at 68 and 166 meV diminish in the same

ratio, unlike the feature at 1 1 5 meV. This is suggestive of the existence of at

least two types of hydrogen adsorption sites, one associated with features at 68 and

166 meV (more susceptible to oxygen attack) and one associated with the feature at

115 meV (less susceptible to oxygen attack). Figure 2c is the incremental difference

spectrum following the further addition of ca. 2/3 monolayers of oxygen (i.e., total

O/H « 1) at 80 K. Now, the feature at 115 meV diminishes along with further loss in

intensity at 68 and 166 meV. Concomitant with this loss is the appearance of the

scattering feature at 128 meV, again indicative of the appearance of adsorbed

hydroxyl species.

Force constant calculations and further experimental work are currently

underway to establish the hydrogen adsorption site geometries on platinum black. It

seems clear, however, that these sites are quite different than those established

previously for hydrogen adsorbed on small particles of nickel (which also has an FCC structure). This is suggestive of a strong correlation between adsorption site

geometry and morphological behavior of the metal catalyst particles.

1. A.M. Baro, H. Ibach, and H.D. Bruchmann, Surface Sci. 88, 384 (1979).

2. G.B. Fisher and B.A. Sexton, Phys. Rev. Lett. 44, 683 (1980).

3. J. Howard, T.C. Waddington, and C.J. Wright, in Neutron Inelastic Scattering,

Vol II, IAEA, Vienna, 499 (1978).

4. A Renouprez, P. Fouilloux, and B. Moraweck, in Growth and Properties of Metal

Clusters (J. Bourdon, ed.) Elsevier, Amsterdam/New York, 421 (1980).

5. L.T. Dixon, R. Barth, and J.W. Gryder, J. Catal. 37_, 368 (1975).

6. R.R. Cavanagh, R.D. Kelley, and J.J. Rush, J. Chem. Phys. 77, 1540 (1982).

41
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

NEUTRON SCATTERING STUDIES OF ZEOLITE RHO

M. J. Wax and R. R. Cavanagh

(Center for Chemical Physics)

and

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

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

and

J. J. Rush

Catalytic activity for hydrocarbon cracking catalysts has frequently been

associated with the various proton binding sites in zeolites. Direct spectroscopic

measurements of these sites can permit one to follow the local properties of such

adsorbed species as the zeolites are brought into the temperature range where their

activity and selectivity is greatest.

Recent diffraction work on zeolite-rho has demonstrated that significant

changes occur in the unit cell of this material (a non-centrosymmetr i c to

centrosymmetric transition) upon either dehydration or deammoniation. In the present

experiments, quasielastic and inelastic neutron scattering have been used to probe

the diffusive motion which occurs near the transition temperature and to monitor the

vibrational density of states of the adsorbed protons.

The incoherent inelastic scattering spectrum for the zeolite is shown in figure

1. Data taken above and below the structural transition temperature is shown. In

addition, peaks in the IINS spectrum predicted by a simple force field model of the

low temperature species are indicated by the intensity band. Comparison of the data

obtained at the two different temperatures is facilitated if one focuses on the low

energy range of the spectrum. As the temperature is lowered, a distinct increase in

intensity is observed below 50 meV, accompanied by the loss of structure at 27 meV.

This increased scattering intensity at low energy transfer is best accounted for by

the presence of a new large amplitude vibrational mode which is reversibly generated

upon heating. These results suggest a rearrangement of the protons bound in the

zeolite cages at high temperature, which could be correlated with changes in chemical

reactivity.

These initial studies of the modes of chemically active sites in zeolite-rho

are currently being extended to examine the nature of the ammonia exchanged form of

this material. Initial experiments have already detected the thermally activated

reorientation of the ammonia and have yielded some insight into the vibrational

density of states of the bound ammonia. Work is underway to extend and refine the

42
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

E (omM

200 400 600 800 1000 1200 1400 1600

If [

700

600

g 800

400

300

I I I

k

ViiWIli'

640 K '

%\/V#

40 60 80 100 120 140 160 180

E (m«V)

600

600

400

300

200

Figure 1. Neutron spectra measured for zeolite H-Rho at two temperature. The Break

in the plotted intensities at 48 meV represents a change in

monochromators.

study of these prototype catalytic materials. Cold neutron studies of the rotational

dynamics of chemisorbed species in zeolites are also planned using the new time-offlight spectrometer being developed at the NBS cold-source.

43
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

STUDY OF DYNAMICAL AND STATIC SCALING OF THE \ TRANSITION IN HE

B. Mozer

and

B. Farnoux

(Laboratoire Leou Brillouin, CEN-Saclay, FRANCE)

and

B. LeNeindre

(Laboratoire des Interactions Moleculaires

et des Hautes Prersions, CNRS, Velletaueuse, FRANCE)

and

D. Brochier, F. Mezei, and S. Pujol

(Institut Laue-Langevin Grenoble, FRANCE)

In order to verify recent modifications to the theory underlying the critical

behavior of He-4 at the A transition, we attempted to measure the critical dynamics of

second sound on INI 12 just below the X transition with as fine a temperature

— fi 1 regulation (10 K) as used in light scattering experiments . The sample cell was initially constructed at NBS and modified, finished, and carefully calibrated a I.L.L.. For the measurement, the sample cell was filled with He-4 so as to be at a pressure of 25 atmospheres at the A transition. The temperature of the bath was held

to 1.4 K and regulated to 10 Kelvin using the I.L.L. regulating system. The sample

cell itself in a calibrated thermal leak configuration was regulated to 1-3 x 10 K

using an AC resistance bridge and heater powered from the amplified error signal.

Several germanium resistance thermometers calibrated at NBS were used in the

regulation circuit as well as in various parts of the sample cell to obtain a temperature profile. The temperature remained stable over periods sufficiently long

to collect neutron data of high-statistical accuracy

Inelastic neutron scattering data was first attempted for various values of wave vector difference, q, from the lowest value possible at IN1 1 of q = 0.25 A and

larger. Our best efforts with good statistics showed no difference in scattering

—ft —1 above the background over reduced temperatures, t = (T - T)T , 10 < t < 10 for

A A constant q or variable q for constant t. We then attempted to measure the static

structure factor using IN1 1 as a diffractometer over the same temperature range and a wide range of q. Again we found no change in the intensity for small values of q at

various t's. As a final test of our system, we measured the great increase in

intensity at small q's as we allowed the He-4 system to traverse the critical gasliquid phase transitions. The later measurement confirmed the temperature

regulation, alignment, sensitivity, etc. of the system.

44
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

It is difficult to reconcile these null results with other known measurements

around the A transition. The bulk compressibility at our pressure and smallest t is

2

known to increase 4 or 5 fold over the compressibility away from the transitions . Therefore, we expect at q = a ^ to 5 fold increase in intensity of the structure

factor over the same temperature range. Assuming Ornstein-Zernicke or modified

Ornstein-Zernicke behavior because of cross-over problems at q * 0, we should have

been able to see intensity changes in the structure factor both as a function of t at

fixed q or as a function of q at fixed t. Furthermore, at our smallest reduced

1 temperature, the intensity ratio of second sound to first sound in unity which also

should have allowed us to see the second sound signal. We suggest that a future

measurement of the static structure factor at the transition at the smallest

available q's must at least be made as to confirm the cross-over modifications to

scaling theory.

1. G. Winterling, F. S. Holmes and T. J. Greytak, Phys. Rev. Lett., 30^, 427 (1973).

2. H. Kierstad, Phys. Rev., 153 , 258 (1967)

3. R. A. Ferrell, private communication.

SIMULATION OF A SLIGHTLY MORE COMPLEX CHEMICAL REACTION

D. H. Tsai

(Thermophysics Division)

and

S. F. Trevino

(U.S. Array Armament R and D Center, Dover, NJ)

and

(National Bureau of Standards, Gaithersburg, MD)

In a continuing work on the simulation of chemistry in the condensed phase of

matter, we have extended the model to the reaction

AB ->• A + B - energy (1 ) A + A -> Ap + energy (2)

B + B -»• B^ + energy (3)

in an attempt to simulate a slightly more complex chemical system. The initial

reaction is endothermic and the subsequent reactions (2) and (3) are exothermic. The

properties of the system have been investigated and the response to heat pulse and

shock loading is in progress .

45
, REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

NEUTRON SCATTERING STUDIES OF DILUTED MAGNETIC SEMICONDUCTOR SYSTEMS

Cd^^^Mn^Te and Zn^_^Mn^Se

T. M. Giebultowioz

(Purdue University, W. Lafayette, Indiana)

and

(National Bureau of Standards, Gaithersburg, MD)

and

J. J. Rhyne

and

W. Y. Ching

(University of Missouri, Kansas City, MO)

and

D. L. Huber

(University of Wisconsin, Madison, WI)

and _ .J. K. Furdyna

1 (Purdue University, W. Lafayette, IN)

1. Experiments *^ and model studies on Cd, Mn Te.

1-x X

Studies of low-temperature spin dynamics in Cd^ ^c-Mn^ ^c Te have been enhanced

U. io U. 03

significantly because of the recent increase of the reactor power to 20 MW. New

studies of the inelastic magnetic scattering at T=4.2 K have been carried out for

points in Q-space lying far away from the center of the diffuse magnetic peak

(1,1/2,0), in which region the previously existing data were of poor quality and

could not be used for analyzing the spectrum features in detail. The results

obtained presently appear to be in excellent agreement with the lineshapes predicted

2 theoretically on the basis of a computer simulation model of the zero-temperature

spin dynamics in cubic dilute magnetic semiconductor (DMS) systems (fig. 1). A

comparison of the measured and calculated dynamic structure factors S(Q,(d) yields the

value of exchange constant for the nearest neighbors J^.^^ = 13±1 K.

Similar computer methods as in spin dynamics calculations have been applied for

modeling the static spin correlations in Cd, Mn Te. Results of such simulations

1-x X

predict that the short-range Type III antiferromagnetlc order In this system is of

anisotropic character, and should be described in terms of two different inverse

correlation ranges which correspond to antiferromagnetlc coupling of spins within

(100) -type planes (<), and to couplings between the planes (<||)i respectively. As

we have reported previously , diffraction experiments on Cd„ -,cMn- c^Te provided a qualitative support for these findings. Further model studies have revealed that the

ratio k,/K|| is strongly dependent on the ratio J ,.,„/J„„ between the exchange

_L I I NNN NN

46
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

800 -

*/

£600 - .y/ \ T = 4.2K

\ Q = (2. 1/2, 0) r*\(0§400

1/

O y

'•

> • ^^~V--_ • • 200

n _j_ 1 1. J- 1 1 1 6 8 10 12 14

Energy Transfer (meV)

16 18 20

Figure 1. The spectrum of inelastic neutron scattering in Dc. -,^Mn_ ^^Te at 4.2 for

^ OOD O.DD

Q = (2iT/a)(2, 1/2,0). The solid curve is the best fit of the theoretical

spectrum (corrected for instrumental resolution), corresponding to J = 12.8k. The dashed line is the background.

U) (Deg)

Figure 2. Extended w-scan in Zn^^^^Mn^^^^Se showing several diffuse magnetic peaks

at symmetry equivalent positions.

47
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

constants for the next-nearest and the nearest neighbors. In order to obtain

accurate experimental values of ki/kii to be compared with the theory, we carried out

measurements of the (1,1/2 0) peak profiles for various scanning directions in Qspace, with particular attention to the role of instrumental effects. By comparing

the measured and calculated data we find that the ratio J>,,,„/J,„, in Cd, Mn Te is NNN NN 1 -X X

0.12.

The mechanism of the Mn-Mn exchange interactions in DMS, and methods of

measuring these interactions have recently attracted a great deal of interest

Our studies demonstrate that neutron scattering methods offer an opportunity of

determining the exchange constants for systems with high Mn concentrations, which is

5 6 a region not accessible by most of the other experimental techniques *

. Of

particular interest is the determination of the ratio J»,»,„/J„»,« The value we have

NNN NN

found for Cd_ -.^Mn. ^^Te is the first direct measurement of this quantity in a DMS.

0.35 0.65

2. Spin ordering phenomena in Zn. i.^Mn. ^^Se

(J .Md u. dd

This compound is the first wurtzite-structured DMS system investigated by

neutron scattering. Diffraction measurements carried out at low temperatures (4.2

K^T^45 K) revealed diffuse magnetic peaks (Fig. 2), the positions of which indicate

an antif errimagnetic order of the same type that occurs in the wurtzite structured

7 modification of B~MnS . The width of the peaks shows, however, that the range of such

spin correlations in Zn^ i,r-Mn_ ^^Se is only =10A, which is a considerably

u. HO u. 00

lower value than in case of cubic DMS systems with the same Mn concentration. A

closer investigation of the peak lineshapes reveals that the elastic structure factor

S(Q) in the basal plane can be described with a good approximation by an anisotropic

Lorentzian function of the form 1/(1 + q^ /< + q^/K^ ), with k /< = 2.1 (however,

^x X ^y y X y

the physical mechanism of this anisotropy is not yet as clear to us as in case of

cubic DMS systems.). Studies of temperature dependences of < , < , and the

scattering intensity show no noticeable features in the measured curves at T = 24 K,

at which temperature the spin glass transition occurs in Zn^ nr-Mn. ^-.-Te, as indicated

0.45 0.55

by a pronounced cusp in the magnetic susceptibility vs. T (Ref. 8).

1. T. M. Giebultowicz and J. J. Rhyne, NBS Technical Note 1207 , 66 (1985); also, T. M. Giebultowicz, J. J. Rhyne, w. Y. Ching, and D. L. Huber , J. Appl. Phys. 57_.

3415 (1985).

2. W. Y. Ching, D. L. Huber, and K. M. Leung, Phys. Rev. B22, 381 6 (1985); W. Y.

Ching and D. L. Huber, Phys. Rev. B25, 5761 (1982), and B2_6, 6164 (1982).

3. B. E. Larson, K. C. Haas, H. Ehrenreich, and A. E. carlsson, to be published in

the Proceedings of the International Conference on Magnetism, San Francisco 1985 .

48
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

4. A. Lewicki, J. Spalek, J. K. Furdyna, and R. R. Galazka, ibidem*

5. Y. Shapira, S. Foner, D. H. Ridgley, K. Dwight, and A. Wold, Phys. Rev. B36, 4021

(1984).

6. R. W. Aggarwal, S. N. Jasperson, and R. R. Galazka, to be published*

7. L. M. Corliss, N. Elliot, and J. Hastings, Phys. Rev. 104 , 924 (1956),

8. P. H. Keesom, private communication*

LONG-RANGE INCOMMENSURATE SPIN STATE IN DILUTE YGd ALLOYS

J. A. Gotaas

(University of Maryland, College Park MD)

and

(National Bureau of Standards, Gaithersburg, MD)

and

J.J. Rhyne

and

L.E. Wenger

(Wayne State University, Detroit, MI)

and

J. A. Mydosh

(University of Leiden, The Netherlands)

and

(University of California, Santa Barbara, CA)

Recent susceptibility and specific heat measurements on the Y-Gd alloy system

have indicated that the boundary concentration between helical spin ordering and a spin glass state is lower than previously believed [1], with the spin glass occurring

only for Gd concentrations below 2% [2], In the light of this indirect evidence, we have carried out neutron diffraction measurements on Y(2.25^Gd) to directly determine

the magnetic state.

Measurements were made on BT-6 with a variety of collimations in both the

double-axis diffraction configuration and in the triple-axis mode with energy

analysis to select out only the elastic scattering, using incident neutrons of 1 .709A

wavelength. A single crystal of nominal concentration Y(2.25JGd), with the natural

istopic abundant Gd, was shaped into a thin (1 mm) disk to reduce absorption.

Diffraction patterns display magnetic satellite peaks about the allowed (COS,)

reciprocal lattice positions, including the origin, separated by 0.28c* from the

nuclear peaks. Thus the magnetic moments order in a modulated state with a wavelength of ~20A and a propagation vector along the c axis [3], with moments in the

basal plane. The diffraction peaks in the ordered state are resolution limited,

indicating that the scattering originates from a long-range ordered state. No change

^ 49
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS '

4 6

Temperature (K)

8 10

Figure 1. Magnetic intensity at the ordering wave vector of the oscillatory

structure as a function of temperature.

1.0

0.8

c•So.6

(0 _NV

c

o> ^0.4

"OuI

0.2

Y (2.2% Gd)

-f Gd (after [4]

)

— S = 7/2 Brjilouin Function

0.2 0.4 0.6 0.8

Reduced Temperature

1.0

Figure 2. Reduced magnetization versus reduced temperature for Y(2.2^Gd) [ metal [ + ] and the Brillouin function for 8=7/2 [line].

], Gd

50
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

in the position or width of the satellite peaks is seen from the transition

temperature (6.64 K) down to 1.5 K.

The temperature dependence of the magnetic peak intensity at q-0.28c*, which is

2

proportional to m , is shown in figure 1, where the arrow indicates the estimated Tj..

Intensity is present above the transition temperature, which would normally be

interpreted as critical scattering. However this magnetic scattering persists at

least to 25K (~4T„), with a monotonia decrease with temperature. The

incommensurate peak is broadened above T^,, Indicating shortened correlation lengths,

which however remain approximately 330±35A at 8 K and 315±35A at 12 K.

Figure 2 presents the square root of the magnetic intensity (proportional to

the magnetization) versus temperature. For comparison, we include the magnetization

of Gd metal [M] and the Brillouin function for S= 7/2 (which should be appropriate

for a Gd moment), with the data plotted in reduced variables by normalizing the

magnetization to the saturation value and the temperature to the transition

temperature. Since our data only extend down to 1.5K (0.226T ), we have normalized

the moment scale to that of Gd at the equivalent reduced temperature. The similarity

between the curves is apparent and Indicates no unusual properties of the Gd moment

in the ordered state.

The magnetic scattering can be placed on an absolute basis by comparing to the

known nuclear scattering cross sections. The expression for the magnetic form factor

depends in detail on the magnetic structure assumed for the system. The

Incommensurate satellites indicate that the magnetic moments order in a modulated

state, but the intensities will be determined by the exact nature of the phase. Rare

earths and their alloys commonly order in the basal plane spiral, with the moments in

a given basal plane aligned ferromagnetically, but each plane rotated with respect to

neighboring planes. The interlayer turn angle derived from the displacement of the

incommensurate peaks is 50.4°. Assuming this structure, we derive a value for the Gd

moment at 1 .5K of 6.26±0.90]i-. after correcting the data for extinction effects (-3556) on the intensity. Any deviation from the nominal concentration would lead to a shift

in the calculated value of the magnetic moment.

1. B.V.B. Sarkissian and B.R. Coles, Commun. Phys. _]_, 17 (1976).

J.B. Sousa, J.M. Moreira. M.E. Braga, S.B. Palmer, S. Bates and B.J. Beaudry, J.

Phys. FJ_5 1171 (1985).

2. L.E. Wenger and J. A. Mydosh, J. Appl . Phys. 55 1850 (1984). P. Pureur , A. Fert,

R. Wendler and K. Baberschke, J. Appl. Phys. 57 3230 (1985).

3. W.C. Koehler, Ch. 3 in Magnetic Properties of Rare Earth Metals , ed. R.J. Elliott

(Plenum Press, London, 1972). W.C. Koehler, J. Appl. Phys. 32_ 20S (1961).

51
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

FIELD DEPENDENCE OF THE TWO-SPIN CORRELATION FUNCTION

IN A REENTRANT SPIN GLASS

R. W. Erwin and J. W. Lynn

(University of Maryland, College Park, MD)

and

(National Bureau of Standards, Gaithersburg, MD)

Previous investigations of the reentrant spin-glass state have been continued

by studying the magnetic field dependence of the two-spin spatial correlations in the

metallic-glass (Fe., ocNi^v rrir )^irP-i cB/-Al_ using small angle neutron scattering (SANS)

\) . do u . Id id loo i

techniques. In this magnetically isotropic system the application of a uniform

magnetic field allows a determination of the correlation functions for spin

components both parallel and transverse to the applied field direction. The

scattering function can then be separated as,

S(q,e) = (1 - cos^e)S^^(q) + (1 + cos^e)S^'^(q) , (1)

where q is the magnitude of the wave vector transfer and is the angle between q and

ZZ XX

the field direction. S and S are defined as conf igurational (domain) averages.

The present alloy exhibits a conventional second-order ferromagnetic phase

transition when cooled below T = 198 K. At lower temperatures spin-glass behavior

°

2

is observed, which includes a strong decrease of the low-field d.c. magnetization.

The signature of the low temperature spin-glass state in the zero-field neutron

scattering is the appearance of a component with a Lorentzian-squared wave vector

3 dependence. Thus the scattering function can be written in the form,

S(q) = -y^^^ + -|5

2

2'' ^"^^^^ • ^^^

K + q (k + q )

The first term is the product of the thermal population factor and the usual

Lorentzian wave-vector-dependent susceptibility arising from the spin-wave

fluctuations. Associating the last two terms with the static magnetic configuration

2

of the spin system leads by a sum rule to the conclusion that B a q - m and

2 2 2 Cam, where q is the Edwards-Anderson order parameter <<S.> > and m is the

square of the site-averaged magnetization. Note that the last term (C) is

52
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

unobservable for the present neutron scattering measurements and that B is an order

parameter for the spin glass.

The angular dependence of the SANS data in an applied field was fit to the

z z functional form in eq (1), to extract the separate correlation functions S and

S^^. These functions could then be analyzed via eq (2) to obtain the parameters XXX z z z (A ,B ,K ) and (A ,B ,k ). These fits have been performed over a wave vector range

-

1

-

1

(0.012 A S q ^ 0.40 A ) which ensures that inelasticity corrections are

negligible, although resolution corrections are important. Care has also been taken

to align the sample ribbons with the magnetic field direction in order to minimize

demagnetizing fields. The results are shown in figure 1 for three temperatures: just

below T , 0.75 T and 0.05 T . Although these data are preliminary, there are several significant trends to be noted. First, for some temperature range below T

X z the data are described simply by a Lorentzian q-dependence (B = B =0), while at

lower temperatures curvature of the Ornstein-Zernike plots produces fits with non-

'e2

zero values of the parameters B^. The temperature and field dependences of B^ are then in qualitative accord with the same dependences measured by bulk magnetization

with the assumption that B^ « q - m . Also observe that the Lorentzian amplitude

A is independent of applied fields up to 0.2 Tesla over the entire temperature range

measured. This fact lends support to the conjecture that the transverse Lorentzian

term in the scattering function arises from dynamic spin-wave fluctuations. Further

z X evidence for this argument is the fact that just below the Curie temperature A = A

(as H -» 0) as predicted for isotropic f erromagnets . Additionally, in the

X z ferromagnetic temperature regime k and k have qualitatively the field dependences

4 X 2 X X z X predicted by mean-field theory , where A a q_./D, (k )

<x A /x (q=0,H) and < ^ < . i-ji\ X

X Here D is the spin-wave stiffness and x (q=0,H) is the bulk transverse

susceptibility. These mean-field results also explain the temperature independence

X X of A near T where q^./D is slowly varying, as well as the increase of A in the

spin-glass temperature regime where the spin-wave stiffness is decreasing as q is

Cj A

2 monotonically increasing. In contrast, at low temperature k rises less rapidly with

X z applied field than < . This would be expected for static fluctuations where < should decrease for sufficiently large applied fields as the spins are increasingly

z X aligned. Of course, the observed increase of k and k may be due to the

preferential alignment of the larger clusters of spins over the smaller clusters.

In conclusion, the anisotropy induced by an applied field for the magnetic

scattering from an amorphous reentrant spin-glass alloy has been shown to yield self53
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

10K 150K 190K

0.3

§ 0.2

J

a

I 0.1

A (Lor) CD B(Lor2)B •'

CD oLlJ

_0.04

b^ 0.02

I

' "

I I m s o s

zz

XX

•-CD- -O—-7t

iS.Ju.,1 .1 ..I'ffl ..

'1 1 r

erg:

1 r

C)''^'^ Cf)

K

T r

z

H (Tesia) x 10

Tc = 198K

J-^ _i.

I I I

Figure 1 . Parameters determined from the fits to the SANS data using the form of the

scattering function in eqs (1) and (2) in the text.

consistent information about the static and dynamic parts of the two-spin correlation

functions. A quantitative comparison with theory will require further measurements.

1. R. W. Erwin, J. W. Lynn, J. J. Rhyne and H. S. Chen, J. Appl. Phys. 57, 3^73

(1985).

2. P. Mazumdar, S. M. Bhagat, M. A. Manheimer and H. S. Chen, J. Appl. Phys. 55,

1685 (198A).

3. From the doctoral dissertation by R. W. Erwin, University of Maryland 1985.

M. S. K. Ma, Modern Theory of Critical Phenomena, Benjamin/Cummings 1976, p. 87.

5A
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

NEUTRON SCATTERING STUDY OF THE SPIN DYNAMICS OF AMORPHOUS Fe NI^qZp^q

J. A. Fernandez-Baca

(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. Furthermore, it is known

that the magnetic properties of this system are very peculiar : The Curie

temperature decreases with decreasing Ni content, and below x=l8 the magnetic moment

also decreases monotonically . In fact when x-^O the system does not order

2

on FeQ.Zrq . At this nominal concentration of Fe and Zr the system enters a spinferromagnetically , as has been found from neutron critical scattering measurements

2

on Fep.Zrq . At this

glass state at T = 21 OK.

1 -5 These anomalous properties have been attributed to the existence of

competing ferromagnetic and antiferromagnetic exchange interactions originating from

the distribution of Fe-Fe nearest neighbor distances in the amorphous state. Thus

for the high Fe concentrations ferromagnetic ordering is destroyed by increasing

antiferromagnetic exchange couplings.

In order to obtain a better understanding of the magnetic properties of the iron

rich (Fe-Ni)Zr alloys we have started a neutron scattering study of the spin dynamics

of this system for various concentrations of Ni . Results of our measurewments on

Fe Ni Zr are reported here. The amorphous nature of the system required that

measurements be taken near the forward (000) beam position. Fixed incident energies

of 28.5 or 13.8 meV were used and a PG filter was placed after the monochromator to

suppress higher order wavelength contaminations. Seller slit horizontal collimators

of 15 '-12 '-11 '-25' were used to produce a FWHM of 0.70 meV (for E.=28.5 meV) or 0.35

meV (for E.=13.8 meV) at the elastic position. Wave-vector transfers examined were

" -1 -1 in the range 0.07 A ^q^0.12A and the temperature range was 250K (0.55T ) to

403K (0.89T ). Well defined spin waves were observed at all the temperatures

c studied. In analyzing the data, spin-wave energies and linewidth information were

55
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

1.2

q- (A^ X 10 ^)

Figure 1 _1 Temperature dependence of spin-wave excitiationat q = 0.10 A . The solid

lines are the least squares-fit to the convolution of a Lorentzian

cross-section with the instrumental resolution. The spin-wave energy

positions are indicated by arrows.

300-

1 200-

10\ini 100

o

u

0-t

FeyoN'zoZrio

A

1+

T = 250K

iSA^atx

-1.0 1.0

Energy (meV) Energy (meV)

Figure 2. Quadratic spin-wave dispersion relations for the Fe^QNipQZr.- amorphous

system at several temperatures.

56
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

120-

40

(T/Tc)

0.4 0.6 0.8

—I 11 1 \—

Fe^oNigoZr 10

0.2 0.4 0.6

(T/Tc)=^^

0.8

5/2

Figure 3. Stiffnes constant "D' plotted as a function of (T/T ) "" " in the range of

temperatures under study (0.55T -0.89T ), showing the typical two-magnon

Dyson form of renormalization.

obtained by convoluting a theoretical cross-section with the instrumental

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

the background scattering. The spectral weight function used in the convolution was a double Lorentzian. Figure 1 shows two sets of typical constant-q scans for q=0.10

-1

A at T=250 and 373 K. The background and parasitic elastic scattering principally

from the cryostat or furnace have been subtracted. The solid lines are the result of

the least squares fit , and the spin-wave positions for both neutron energy gain

(E<0) and energy loss (E>0) are indicated by arrows. The actual spin wave energy is

shifted lower than the peak energy by resolution effects. There is a gradual

broadening of the peaks with increasing temperature, but the linewidths are

relatively small compared to the instrumental energy resolution . The spin-wave energies at all temperatures under study were found to obey the

quadratic dispersion relation expected for a Heisenberg ferromagnet : E= A + D(T)q^ + ... (1)

(see figure 2) where A = 0.05 meV is an effective anisotropy gap which originates

mainly from the dipole interaction, and shows no temperature dependence. 'D'

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

2

(see figure 3) with D(0) = 110.9 ± 1.5 meV-A and a=0.68 ± 0.01.

(2)

57
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

As seen in figures 2 and 3. the long-wavelength spin waves in amorphous

Fe Ni_^Zr._ show the behavior expected for a conventional Heisenberg ferromagnet

over an unusually wide range of temperatures as found also in other amorphous

ferromagnets. The stiffness constant D(0) is about 1 .5 times the value calculated

5 from the magnetization measurements by Krishnan et al. . Such a discrepancy implies

that additional excitations other than spin waves are present and lead to the

anomalously rapid decrease of the bulk magnetization with increasing temperature.

Similar behavior has also been reported for other Invar systems and is likely to be

an intrinsic dynamic property of the Invar state.

1. K.Shirakawa, S.Ohnuma, M.Nose and T. Masumoto. IEEE Trans. Mag. _1_6,910 (1980).

2. J.J. Rhyne and G.E. Fish. J. Appl. Phys. 57,3407 (1985).

3. S. Ohnuma, K. Shirakawa, M. Nose and T. Masumoto . IEEE Trans. Mag. 1 6 , 1 1 29

(1980).

M. H.Hiroyoshi and K.Fukamichi. J. Appl. Phys. 53.,2226 (1982).

5. R. Krishnan , K.V. Rao and H. H. Liebermann, J. Appl. Phys. 55,1823 (1984).

MAGNETIC ORDER IN THE SUPERCONDUCTOR Tm^Fe^Si^

^ i o

J. W. Lynn, J. A. Gotaas

(University of Maryland, College Park, MD)

and

(National Bureau of Standards, Gaithersburg, MD)

and

R. N. Shelton

(Iowa State University, Ames, lA)

There is currently great interest in the behavior of superconductors which

contain a sublattice of magnetic (rare earth) ions. In materials where the magnetic

system prefers ferromagnetic alignment of the spins the superconductivity is quenched

1 at low temperatures , or the magnetic ground state is modified from ferromagnetism to

2 a long-wavelength sinumagnetlc state where coexistence can occur. In the case of

antlf erromagnetlc order, on the other hand, coexistence with superconductivity is

1 found to the lowest temperatures. A singular exception to this rule appears to be

the system Tm„Fe_Si^. In the absence of applied pressure this material becomes

2 3 5 3_5 antlferromagnetlc at T ~ 1.1 K, with the absence of superconductivity. With

applied pressure, however, superconductivity appears above the magnetic ordering

temperature, but then disappears again at T . The magnetic transition itself is

insensitive to the pressure so that It appears that the superconductivity is quenched

58
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

2000r

1600

1000

600

0.2 0.4 0.6 0.8 1.0 1.2 1.4

T(K)

Figure 1. Observed magnetic intensity for the {100} antiferromagnetic Bragg peak as

a function of temperature, with an applied pressure of 2.3 kbars. No

hysteresis was observed between warming and cooling cycles.

by antiferromagnetic long range order. We have been carrying out neutron diffraction

measurements as a function of temperature and pressure to investigate the influence

of the superconductivity on the magnetic structure in this material.

The sample was loaded in an aluminum sample cell with an inner diameter of

3/32". Pressure could then be applied by forcing and clamping a piston at room

temperature. The actual applied pressure achieved in the cell was determined by a measurement of the lattice parameter, and then comparing with the room temperature

lattice parameter determined from measurements on the identical sample using a

3 hydrostatic helium pressure system. The sample cell was then mounted in He

refrigerator to measure the magnetic scattering.

With no pressure applied the magnetic order is a relatively simple

3+ 5 antiferromagnetic type, with the full 6.5 Uq Tm moment ordering. The intensity of

D

the {100} antiferromagnetic Bragg peak is shown in figure 1 for an applied pressure

of approximately 2.3 kbars, which should be just above the critical pressure where

superconductivity appears. The magnetic order parameter is still continuous and

reversible, and shows no signs of the presence of superconductivity. Similar

59
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

1 behavior has been found in the coexistent antif erromagnetic superconductors. We

also found no evidence of any magnetic scattering at small angles, either near T or

at low temperatures. Work is in progress to extend these measurements to higher

pressures, where the superconductivity is well established before magnetic order sets

in at lower temperatures.

1. W. Thomlinson, G. Shirane, J. W. Lynn and D. E. Moncton, Chap. 8 in

Superconductivity in Ternary Compounds , ed . by M. B. Maple and 0. Fischer,

Springer-Verlag (New York, 1982).

2. J. W. Lynn, J. A. Gotaas, R. W. Erwin, R. A. Ferrell, J. K. Bhattacharjee, R. N.

Shelton and P Klavins, Phys. Rev. Lett. 32, 133 (198^1).

3. C. U. Segre and H. F. Braun, Phys. Lett. 85A, 372 (1981).

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

5. A. R. Moodenbaugh, D. E. Cox and C. B. Vining, Phys. Rev. B (to be published).

MAGNETIC AND SUPERCONDUCTING PROPERTIES OF HOLMIUM-RICH (Er, Ho )Rh,,B,, 1-x X 1 1

J. W. Lynn and J. A. Gotaas

(University of Maryland, College Park, MD)

and

(National Bureau of Standards, Gaithersburg, MD)

and

R. N. Shelton and H. E. Horng

(Iowa State University, Ames, lA)

and

C. J. Glinka

Neutron scattering, susceptibility and resistivity measurements have been

carried out on (Er, Ho )Rh^B^ for concentrations x = 1 .0, 0.89, 0.8M, 0.75, which

span the "multicritical" point (x = 0.9) where the magnetic and superconducting phase

boundaries meet. For all concentrations studied a transition to long-range

ferromagnetic order is observed, with the Ho moments ordering along the tetragonal

axis. The spins are in fact locked along the c-axis by strong crystal-field

anisotropics, yielding Ising-like magnetic behavior in this concentation region.

The temperature dependence of the order parameter is mean-field like, suggesting that

the range of the magnetic interactions is large, and we attribute this behavior to

the importance of dipolar interactions. In the concentration range x < x where

superconductivity is observed, the magnetic transition appears to be continuous and

reversible, and occurs within the nominal superconducting interval T „(x) < T < C2

60
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

T .(x). Thus there is some kind of "coexistence" of long range magnetic order and

superconductivity in the samples, but the nature of this coexistence cannot be

determined unambiguously. In particular the experimental evidence in this system is

not sufficient to decide if there is true microscopic coexistence, or whether some portions of the sample are ferromagnetic and normal while other regions are

superconducting and paramagnetic (or magnetically ordered with a very long wavelength

sinusoidal periodicity). Below T strongly temperature-dependent small angle

scattering is observed, characterized by a cross section of the Porod form S(Q) = A(T)/Q where A(T) increases monotonically with decreasing temperature. This wave

vector dependence is consistent with the assumption that the scattering originates

from domain walls whose widths are large compared to the inverse Q range explored

(-250 A). In particular, no oscillatory component to the magnetization was observed

for any concentration or temperature within the experimentally accessible wave vector

-1

range of Q > 0.003 A , in contrast to the behavior of ErRh^B^. At the lowest

concentration studied (15% Ho) the magnetization was found to be reduced in the

temperature region where superconductivity appeared. The magnetic order parameter,

however, was still found to be continuous and reversible.

ADVANCED NEUTRON METHODS

N. Berk, D. Fravel, C. Glinka, J. LaRock, J. M. Rowe, and T. Udovic

1 . Small Angle Neutron Scattering (SANS)

During the six month shutdown for doubling the reactor power to 20MW, a number

of improvements were made to the SANS instrument. Chief among these were the

2 modifications made to the facility's 65 x 65 cm position-sensitive detector. The

detector's anode and two cathode wire grids were replaced with improved versions

which have faster response times thus reducing detector dead time and thereby

increasing its count rate capability (now estimated to be about 10 kHz). In

3 addition, the detector was refilled with a new gas mixture of He/CF^^, which tests

3 have shown to be far less sensitive to gamma rays than the He/Xe mixture used

previously. The overall detector background count rate (per MW) is now one-third of

what it was prior to these modifications. This reduction in background, combined

with the doubling in the reactor power has greatly increased the sensitivity of the

instrument for measuring weak scattering signals.

Other improvements to the instrument include the installation of quick-connect

flanges on the pre-sample flight path to facilitate changing beam collimation, added

data storage capacity at the instrument's computer and the implementation of a high

speed data link to a VAX computer to enable data to be transferred and reduced more

61
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

rapidly. The facility's sample environment equipment has been augmented by the

purchase of a computer programmable temperature controller and power supply which

will control and monitor the temperature of a variety of vacuum of furnaces as well

as the instrument's multi-specimen sample changer. One such furnace has been adapted

to mount between the pole pieces of an electromagnet for in-situ high temperature

measurements of magnetic materials in an applied field of up to 10 kilogauss.

Since resuming operation at 20 MW reactor power, the SANS instrument has once

again been heavily utilized by NBS, university and industrial scientists for

structural experiments in polymers, metallurgy, ceramics, magnetism and biology, C.

Han and coworkers in the Polymer Division have recently completed a detailed study of

the mlscibllity limits of blends of polystyrene and polyvinyl methyl ether (PVME) as

a function of temperature and PVME volume fraction. By making temperature Jumps Into

the immiscible region of the phase diagram the first stages of phase separation have

been observed and found to exhibit many of the features of splnodal decomposition.

W. Wu and B. Bauer, also of the Polymer Division, along with collaborators from the

University of Massachusetts have continued their work on the formaton of network

structures in epoxys. Evidence for the formation of paracrystalllne-llke networks

have been seen through the use of deuterium labeling of one component of the epoxy.

The relationship between precipitate size and morphology and the strength and

hardness of structural alloys has been the focus of a number of recent SANS studies

in metallurgy. The formation of iron-copper precipitates in reactor pressure-vessel

steels due to fast neutron irradiation has been observed by G. R. Odette from the

University of California at Santa Barbara. In his most recent experiments, Odette

has followed the coarsening of these precipitates, which can lead to embrittlement of

the steel, via in-situ annealling measurements in an applied magnetic field. The

effects of various alloying elements on the high temperature strength of new types of

single crystal superalloys used in advanced turbine engines is being studied in

Joint collaboration with researchers from General Electric. Initial experiments have

probed the effects of small additions of rhenium on the morphology of the Y'

precipitates which are the main strengthening mechanism in these alloys.

Use of the SANS facility for structural studies in biology has Increased in the

past year as a result of joint NBS - National Institutes of Health collaborations.

In one of these, R. Nossal of NIH, along with S. H. Chen of MIT, have completed a study of concentrated solutions of the globular protein bovine serum albumin. In

this study, Interparticle interactions were clearly observed and could be effectively

modeled by screened Coulomb forces to yield values for the protein surface charge and

screening length under a variety of solvent conditions. In another Important study,

A. Wlodawer of NBS and coworkers at NIH, along with G. Zaccai of the Instltut Laue

62
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

Langevin, have successfully measured some of the dimensional parameters of DNAprotein complexes known as gyrosomes.

Additional details of some of the work mentioned above, as well as other

reports of SANS studies, appear elsewhere in this issue.

COLD NEUTRON RESEARCH FACILITY

I. Anderson and J. Gotaas

(University of Maryland, College Park, MD)

and

(National Bureau of Standards, Gaithersburg, MD)

and

C. G. Glinka, J. M. Rowe, J. J. Rush, T. Udovic and R. Williams

The conceptual design of the proposed new cold neutron guide hall was completed

by the architect/engineer, and cost estimates were prepared. After full review of

this concept, a contract for the final architect/engineer is now (July 1985) being

negotiated that will lead to final design drawings suitable for the solicitation of a fixed price construction contract. The new building will be constructed adjacent to

the north side of the existing reactor confinement building, and will provide

approximately 30,000 square feet of additional space for cold neutron

instrumentation. It is anticipated that construction of the new experimental hall

will begin in 1986. The cold neutron beams will be brought into the new experimental

hall by means of neutron guides, plated with either normal nickel or Ni-58, as appropriate for the proposed instruments on the particular guide. The detailed

design of the neutron guides and reactor modifications is now under way.

Up to 1/3 of the 15 proposed experimental facilities are to be developed by

Participating Research Teams, which will be responsible for the design, construction

and maintenance of the facilities. A notice was published in The Commerce Business

Daily (Issue No. PSA-8795, March 14, 1985) soliciting expressions of interest from

prospective PRT's. Several replies have been received, and are being actively

pursued, with the intent of negotiating final agreements in the near future. We will

continue to solicit further PRT's as the facility development progresses.

The design of the first instruments to be constructed for the new cold neutron

experimental hall is continuing. The two proposed Small Angle Neutron Scattering

(SANS) are in the final stages of conceptual design, and detailed design will begin

63
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

in the coming year. The conceptual design for one Time Of Flight (TOF) instrument is

continuing, and many of the ideas are being tested in the TOF spectrometer now being

installed in the existing reactor hall. A new data acquisition system, based on the

micro-VAX II 32 bit microcomputer is now in the final stages of completion, and will

be installed on the existing SANS and TOF instruments in the next few months. It is

anticipated that this system will become the standard for all new cold neutron

instruments, assuming that operation of the test stations is satisfactory.

NBSR COLD NEUTRON SOURCE

R. S. Carter and P. A. Kopetka

1 The NBSR Cold Neutron Source is progressing well. The Safety Analysis Report

has been completed and reviewed by the Safety Evaluation Committee, and all necessary

approvals have been obtained for final installation.

Figure 1 is a schematic illustration of the cold source. The moderator is a block of DO ice 14" in diameter and 13" thick with an 8" diameter, 6" deep reentrant

hole. (The reentrant hole is not shown in figure> i.) The ice will be frozen in

layers to avoid damage to the ice chamber. Other features include a helium filled

jacket around all vacuum regions and tubes connected to the ice chamber. The vacuum

pump itself is wholely enclosed within the helium containment gas. During operation,

the region over the ice and all the lines into the ice chamber are backfilled with

helium. These lines are all isolated within the helium containment and connected to

the ballast tank. The ballast tank is sized so that the pressure of the cover gas over the ice which is normally about 19 psia at operating temperature (25°K) will

not exceed 30 psia at room temperature. During operation, a deuterium getter is open

to the helium cover gas to absorb deuterium that might be released if the cooling

system failed and the ice temperature should start to rise. The mass of ice is such

that even if the cooling should fail, almost an hour is required at full reactor

power before the ice reaches its melting temperature. Thus, ample time is available

to take appropriate action.

The cryostat is made of a magnesium alloy to minimize heating from capture

y-rays and is surrounded by a lead and bismuth shield to reduce heating by core

-rays as shown in figure 2. The bismuth shielding is completed and the manufacture

of the cryostat will be completed by July 1985. Installation in the reactor is

expected shortly thereafter.

1. R. S. Carter, Safety Analysis Report on the DO Cold Neutron Source for the NBSR,

NBSR 21 (1984).

64
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

Containment Gas Fill,

\Cover Gas Fill

Ballast

Tank

LN2

He Refrigerant

Figure 1. Schematic illustration of cold source facility.

Figure 2. Cold neutron source.

65
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

THE NBS NEUTRON TIME-OF-FLIGHT SPECTROMETER

I. S. Anderson

(University of Maryland, College Park, MD)

and

(National Bureau of Standards, Gaithersburg, MD)

and

T. J. Udovic, J. M. Rowe, and J. LaRock

A schematic outline of the new high-resolution t ime-of -flight (TOF)

spectrometer under construction at the NBS reactor is shown in figure 1 . The beam

from the CTW tube at the reactor is monochromated by means of two pyrolitic graphite

crystals separated by a shielding drum containing a replaceable collimator. The

rotation of the drum moves the crystals parallel to each other on two shafts which

are also used to reorient each crystal about a vertical axis. The absolute position

of the drum and rotation of each shaft are encoded by means of vector resolvers

directly coupled to each movement. A second collimator mounted on an optical bench

after the monochromator ensures that the energy resolution of the instrument is not

limited by the effective mosaics of the graphite crystals. At present, three

secondary collimator exist with 40', 20' and 10' collimation and the corresponding

primary collimators are under construction. The wavelength may be continuously

varied between 2.2 A and 6 A using this system; for wavelengths above 4 A, a cooled

Be filter is available to remove higher-order contamination.

A multiple-slit Fermi chopper is used to pulse the monochromatic beam producing

one pulse per revolution. Two slit packages are available with the curvatures and

the slit lengths optimized for 1.5 A and H A neutrons, respectively. The chopper

rotates at a speed of 10,000 to 18,000 rpm depending on the condition for frame

overlap. Both the chopper and secondary collimator are mounted on an optical bench

permitting easy interchange of the collimators and of the relative positions of the

collimator and chopper. Thus, the chopper is normally placed as close as possible to

the sample to reduce the time spread of the incident pulse, although for certain

experiments, it may be advantageous to place the collimator closer to the sample.

Under normal operating conditions, an additional collimator is used to eliminate

scattering from the chopper. Various other components such as beam monitor and a collimating diaphragm may also be mounted on the optical bench.

The sample area consists of an aluminum drum with thin windows for the incident

and scattered beams. The drum will be designed to support a secondary vacuum so that

it may be used as the outer wall of a cryostat or furnace thus eliminating one containment wall in the beam path.

66
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

The flight path Is shielded by 6" of paraffin and 1" of boron carbide and has

an inner lining of oadmlum sheeting In order to minimize the neutron background.

The entrance window of the flight path Is constructed from pure 0.04" thick aluminum

curved around a supporting frame and bolted to the flight path with a vacuum seal

such that the whole flight path may be evacuated. The detection system consists of

71 18" active-length, 1" diameter detectors filled with 4 atmospheres of He-3

covering the range of scattering angles from 25° to 120" and 20 similar detectors of

9" active length covering the range from 10° to 25°. At a later date, a small angle

detection system will be Implemented consisting of an array of linear positionsensitive detectors allowing the Debye-Scherrer rings to be mapped out directly under

software control. A radial collimator to be placed between the sample chamber and

the flight path is under design. The function of this collimator is to ensure that

the detectors only "see" scattering from the sample, thus eliminating background

scattering from sample containment vessels and the chamber itself. The collimator is

made to oscillate in order to give a uniform transmission over the whole angular

range of the detectors. Lastly, a second beam monitor and the final beam stop are mounted on the outside of the flight path after a 0.12" thick aluminum exit window.

The associated electronics have been specified and the system in now undergoing

tests. A dedicated Microvax II will control and collect data from the instrument

interfaced via a Camac system. The Camac control features include programmable

modules to drive the stepping motors, input registers to read the corresponding coder

information and interrupts to control error events at the instrument level. The

Camac also features a memory histogrammer linked via a dedicated bus to two 32K, 16-

bit memories in which the incoming data from the TOF unit may be directly

histogrammed as a function of detector number and TOF channel. The advantage of this

system is that the memory may be extended at a later date, if necessary, simply by

adding more memory modules. The data in the Camac memories may be simultaneously

displayed and transferred to the Microvax II by the Camac bus by direct-memory

access.Table 1 shows the calculated elastic resolution of the instrument for 1"

detectors.

Table 1. Elastic Resolution (FWHMueV) For 1" Diameter Detectors.

WAVELENGTH (A)

40 20 10

4 140 80. . 50

6 30 30 18

^ 67
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

Small Angto

PotHlon S«ntltl*» DatMtora

Rotating Collimator Drum & Coder Cooled Be Filter

Reactor

Collimator

Evacuated Sample ChamtMT Oaclllatlrtg ..,

,

Radial ^

Collimator

Secondary Beam Shutter

' Motor/ Coder GraphHe ' ^y"**"" Monochromator r\^

18* Active Length

Detector*

Figure 1. The NBS neutron time-of-flight spectrometer.

THE PHASE SHIFT AND MULTIPLE SCATTERING IN SMALL ANGLE NEUTRON SCATTERING:

APPLICATION TO BEAM BROADENING FROM CERAMICS

N. F. Berk

and

K. H. Hardman-Rhyne

Inorganic Materials Division

Small angle neutron scattering from ceramic materials in early stages of

processing, including the powder and green state, usually is characterized by the

observation of "beam broadening" —an apparent broadening of the incident beam well

beyond instrumental resolution and the absence of a weakly scattered component, in

contrast to the typical SANS diffraction experiment. Since this behavior is

generally observed to depend strongly on the wavelength, A, of the incident beam it

is sometimes assumed to be desirable as multiple refraction. In fact, A-dependent

beam broadening is a signature for incoherent multiple scattering which, in terms of

the underlying single-particle phase shifts may be far removed from the refractive

regime of very large single-particle phase shifts. Indeed, for particle or void

sizes of typical concern in such materials, say radii, R, encompassing the range 0.1-

10 pm, the phase shift

V = 2RpA (1)

68
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

where p is the scattering length density, will tend to lie in a regime (0.1-10) not

evidently characterized as either refraction, v -^ «>, or diffraction, v ^ 0. Thus it

is useful to incorporate the v-dependence of the single-particle scattering into a formalism for incoherent multiple scattering from a population of particles or voids . While such an approach falls short of the dynamical scattering theory

ultimately required for such complex systems, it does provide a means of dealing with

1 2

actual data and of helping to sharpen some of the basic concepts ' . We have assumed that the SANS intensity is the result of incoherent multiple

scattering from monodisperse, randomly distributed, structureless spheres in a uniform background. Then, the neutron cross-section per unit of area from sample of

thickness z and area A, as a function of wavevector Q in the plane of a twodimensional, position sensitive detector, and with pinhole collimation, is [1,3,4]

W(Q|z) = e-^6(Q) ^ fj%Jo(QRU[e-^^^-^^^) V^]dc (2)

where qCC) in the exponent is completely determined by the single-particle, v- dependent, cross-section,

o(Q,v) = k R

\^

J f

X r iv/i - u , 1 ^ J-(xu)Le - 1 Judu (3)

2 In lowest order, 0(v ), the right hand side of (3) easily reduces to the Born

approximation or diffraction limit. Also in (2), the scattering power z = z/8,, where

I is the scattering mean-free-path.

Numerical evaluations of q(^) are shown in figure 1 for a range of v. For v <

1 the curves are indistinguishable to within 0,]% from the diffraction limit (v -> 0)

q°(c) = e(2-0|(1 + C/2)/l - C - 2C(1 - ^/4)ln[-(1 + /I - c]}, (4)

with 5 = c^/4. Even for v = 2 Born approximation is effectively stable but breaks

down quickly for larger values, as shown. The leading singularity of q(*) at ;* = 2 IS determined entirely in 0(v ) and is thus the same as in the diffraction limit,

2 which from (4) is given by 1/2^ In^. It is this singularity which fixes the

69
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

asymptotic fall of o(Q) as Q * « and gives the Porod law, which is thus seen to be

invariant in v '

. Moreover, the N-fold single-particle limit, where N is the number

of particles, defines the Q » « behavior of the multiple scattering since the

asymptotic behavior of (2) is determined by the leading singularity of the integrand

at the origin; and since qC;) * ^ as 5

-^ 0, this is established in 0(z) and is the

singularity of q(?;)^. Thus, for Q * «, NAW(Q|z)/V > No(Q,v)/V ~ ?/Q^, where P -

2tt(S/V) is the Porod constant, and S is the total surface area of the N particles.

These ideas have been successfully applied to a SANS beam broadening study of

high purity alumina (AlgO-) powder . Equation 2 was used to fit the curvature k of

measured intensity curves at Q - for several incident neutron wavelengths, allowing

the determination of <)) and R--interpreted as an effective radius, see below.

Parameters were in the ranges: \ - 0,45-1.0 nm, z « 2.0-10.0 mm, (j) - 0.25-0.33, and

2 = 5-400. The corresponding phase shifts, v = 0.15- 0.30, were well within the

limit shown above, figure 1, to Justify analysis as multiple diffraction. To apply

the method to polydlspersed powder, the radius measured from the small-Q data was

interpreted as an effective radius, R(0), defined by the rigorous extension,

z = No/A -*" zcf)<o>/<v> -^ Z(|)v^X^R(0), (5)

where <•> denotes the average over the particle-size distribution (PSD). The last

2 2 equivalence in (5) applies only to the diffraction regime, where •*• = 1/2v irR (13), and R(0) = <R >/<R-^>. The best fit determination of R(0) from all data was found to be 265 nm within a 2-5/5 uncertainty. Once R(0) is known, all the small-Q

data can be represented on a universal curve for multiple diffraction, r [QR] vs_ z, where r [QR] = 1 //-< is the radius of curvature of the scattered intensity at Q = in dimensionless units and is effectively a measure of the width of the intensity, curve near the origin . This is shown in figure 2, comprising the results from 25

data sets, where the theoretical curve is well-approximated in the range shown by

r [QR] = 0.92[zln°'^^z]°-^ (16)

c

70
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

1.00

*sj»

0.75

0.50

0.25

1.5 2.0

Figure 1. The function qiO for several values of the phaseshift v.

IIo 100 200 300 400 500

Z = Sample Thickness/Mean-Free-Path

Figure 2. Radius of curvature of multiple scattering intensity at Q = 0.

71
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

For the limit of single-particle scattering by a sphere, r [QR] = /(5/2). Large-Q

data were analyzed using the Porod law, expresssed in terms of the effective particle

3 2 radius R(<») = <r >/<r >, which results from its extension to polydispersed systems.

2 The result was R(oo) = 232 nm within ^5%. The values of R(0) and R ( » ) were

rationalized by assumption, of a lognormal PSD, from which <R> = 171 nm and

dimensionless width parameter 3 = 0.382 were derived. These results were found to be

in good agreement with powder size determinations by laser light scattering and by x2

ray sedigraph methods .

1. Berk, N. F. and Hardman-Rhyne, K. A. (1985). J Appl. Cryst., j_8, in press .

2. Hardman-Rhyne, K. A. and Berk, N. F. (1985). J. Appl. Cryst., j_8, in press .

3. Snyder, H. S. and Scott, W. T. (19^19). Phys. Rev. 76, 220.

4. Bethe, H. A. (1953). Phys. Rev. 89, 1256.

5. Weiss, R. J. (1951). Phys. Rev. 83, 379.

6. Berk, N. F. and Hardman-Rhyne, K. A. (1986). Proceedings of the 1985 Santa Fe

International Conference on Neutron Scattering, Physica B, to be publ:.' ^d .

STUDY OF PLASMA SPRAY COATINGS BY SMALL ANGLE NEUTRON SCATTERING

S. F. Trevino

(U.S. Army Armament R and D Center, Dover, NJ)

and

(National Bureau of Standards, Gaithersburg, MD)

and

N. F. Berk

Yttria stabilized Zirconia is used as a coating in various applications, which

coating is produced by the techniques of plasma spraying. It is of interest to

measure the size of pores and their density in these spray coatings to determine

their role in the physical properties of the coatings. Small angle neutron

scattering measurement in the multiple scattering regime were performed on four

samples of the coatings consisting of 7% yttria with no heat treatment Z7Y(0) and 100

hours of heat treatment Z7Y(100) and corresponding 85^ yttria Z8Y(0), Z8Y(100).

Incident neutron wavelengths of 10, 12, and 14 A were used. Using the theory of

multiple scattering developed at NBS (See N. F. Berk and K. A. Hardman-Rhyne —

elsewhere in this summary) it is possible to determine the relationship between the

diameter of the pores and their volume fraction for any given spectrum. These are plotted in figure 1 for the four samples and various wavelengths. The point of

72
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

0.02 0.04 0.02 0.04

Void Volume Fraction

Figure 1 . A plot of the pore diameter R vs volume fraction for four samples s determined by SANS spectra obtained with 10, 12 and 14 A wavelength

neutrons.

intersection of the curves for the several wavelengths is taken as determining the

radius and volume fraction. To our knowledge this is the first quantitative such use

of small angle neutron scattering from these materials.

CRITICAL FLUCTUATION AND PHASE BEHAVIOR OF A BINARY POLYMER SYSTEM

C. Han and B. Bauer

(Polymers Division)

and

Y. Muroga

(Nagoya University, Nagoya, Japan)

and

M. Okada

(Tokyo Institute of Technology, Tokyo, Japan)

and

Q. Tran -Cong

(Kyoto University, Kyoto, Japan)

I. Introduction

For a binary polymer blend, the concentration fluctuation length near the phase

boundary may be described by the Ornstein-Zernike form in the small q region which

in turn gives a Lorentzian shape for the static structure factor.

73
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

S(q)/S(q = 0) = '^—x-j (1)

1 + q r

Recently, P. G. deGennes has obtained S(q) for binary polymer blends in one phase for all q-regions ' . This calculation is based on the random phase

approximation together with the mean-field model. The structure factor S(q) can be

expressed as

^N 1 . 1 2x

^^^^ ^aVa^d^^^ VbVd^^^ \

(2)

with

.a. a„s2

K =n/-^--^) (3)

here N. the Avogadro's number; a., v., ^., and z. are the scattering length, molar

volume, volume fraction and the degree of polymerization of the i component; S (i)

is the Debye function of i polymer; x is the binary interaction parameter and v is

the molar volume of a reference cell.

By expanding the Debye function up to the second moment, eq (2) is reduced to

the Ornstein-Zernike form as in eq (1). The correlation length ^ can be expressed

as:

2

C^(T,<1,) =1^ [Vb^^x " X)]'^ (^)

with Xg as the interaction character x ^t spinodal temperature, Ts. and b as the

statistical segment length of polymer.

Since the correlation length E, normally expands a range from a few tens of

Angstroms to a few hundreds of Angstroms in a convenient temperature range for binary

polymer systems, small angle neutron scattering provide just this wave length (q ) range with sensitivity when one of the polymers is deuterated. Therefore, SANS

technique is used in this study to provide all static information. We may notice

that

^

can be easily obtained from Eq. 2 as q approaches zero. Therefore, the same

o set of SANS measurements provide both E, and x/v as a function of T and (j) in the

miscible region.

74
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

By extrapolating C to Its Infinite value, one could obtain the splnodal

temperature of the system for that volume fraction. Therefore, a complete phase

diagram can be constructed In this fashion, as will later be demonstrated, In the

results section.

II. Experiments

5 Aionically polymerized deuterated polystyrene (dPS) with M = M.35 x 10 and

w

M /M = 1.45 was used as one component in this experiment. The other component is a cataionically polymerized and fractionated poly(vinylmethylether) (PVME) sample, with

5

M = 1.88 X 10 and M /M = 1.32. This molecular weight ratio was chosen to match

w w n

° the contour length of both components approximately.

Small angle neutron scattering, (SANS), experiments were performed at the SANS

facility at the National Bureau of Standards.

III. Results and Discussion

Two kinds of SANS data were obtained for each volume fraction. First, a total

detector count, I was taken as a function of temperature during heating-cooling

cycles. This provides a sensitive method to define the one phase region which is

needed for the second part of the SANS experiment. The second kind of SANS data was

180

170

U

2,160

150

140

T 1 1 r

dPS/PVME

MW=435k/188k

.J L. .25 .50 .75 dPS

1.0

Figure 1. Phase diagram of PS/PVME blend with MW=435k/l88k. Solid circles and open

circles are cloud points and spinodal points respectively.

75
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

5.4

4.8

c

4.2

3.6

3.0

I I I I I

SLOPE=-0.5

dPS/PVME

M»=435k/188k

D 30/70

o 35/65

A 40/60

+ 45/55

X 50/50

• 60/40

80/20

-6 -4

In T

-3

Figure 2. The reduced temperature dependence of the correlation length, E,, for

various compositions. A solid line with slope of -0.5 is drawn for

comparison.

»- 5

6

-I 1- I I

SLOPE=-1.0

dPS/PVME

MW=435k/188k

n 30/70

o 35/65

a 40/60

+ 45/55

X 50/50

60/40

80/20

-6 -5 -4

In r

-3 -2

Figure 3. The reduced temperature dependence of S(q=0) for various compositions. A

solid line with slope of -1.0 is drawn for comparison.

76
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

obtained and normalized as S(q) for various temperatures below cloud point

temperature, T , which was obtained as described above. This structure factors,

S(q), at various temperature and volume fraction was then fitted according to eq (2)

with a non-linear regression routing to obtain x/w and the statistical lengths used

in the Debye functions. Then, the correlation lengths were calculated according to

eq (4)

.

The linear dependence of x/v on 1/T is then checkd. This 1 /T dependence

together with Eq. (4) implies a relationship of

C^ a It - T. (5)

-2

Equation 5 provides a procedure of extrapolating 5 against T to obtain the

-2

spinodal temperature, T , which is the temperature where £;

-»• <» (or Z, * o) . With

the cloud points and spinodal temperatures, the phase diagram is constructed and

displayed in figure 1 . The mean-field nature of a polymer-polymer binary system can

be easily demonstrated through the critical exponents of v = 1/2 and Y = 1 where

5 = 5,

T - T^ l-v

and

S(q = 0) = S

T - T -Y

(6)

In figure 2 and 3. J-n 5 and S,n S(q = 0) is displaced as a function of £n t, with t = T - T —= for various compositions.

These equilibrium results have clearly demonstrated the mean-field nature of a binary polymer system. Also the phase diagram and x parameters have been used to

evaluate spinodal decomposition binetics of the same system ' .

1. L. S. Ornstein and F. Zernike, Proc. Acad. Sci., Amsterdam, VJ_, 793 (1914).

2. P. G. deGennes, J. de Physique, 31. 235 (1970).

3. P. G, deGennes, J. C P. 72, 4756 (1980).

4. C. C. Han, M. Okada, Y. Muroga, B. J. Bauer and Q. Tran-Cong. SPE ANTEC '85

Conf. Proc. 306, _43, (1985).

5. C. C. Han, M. Okada, YU. Muroga, F. L. McCrackin, B. J. Bauer and Q. Tran-Cong,

Polymer Engineering and Science, (in press).

77
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

SMALL NETWORK STRUCTURE STUDIED WITH SMALL ANGLE NEUTRON SCATTERING

Wen-li Wu and B. J. Bauer

(Polymer Division)

The network structure of thermosetting resins used as composite matrix

materials largely determines some of the key properties for composite materials.

This structure refers to the arrangement of chemical crosslinks which converts the

liquid monomers into a rigid solid. The network structure in these materials is not

amenable to characterization by standard techniques such as small angle x-ray

scattering, electron microscopy, nuclear magnetic resonance, etc. One of the major

aspects characterizing the network structure within epoxies is the spatial

distribution of the crosslinks. Work over the past two years has demonstrated that

elastic neutron scattering has the unique potency for addressing this problem.

Neutron measurements have been carried out successfully to characterize the molecular

networks In one of the commonly used types of resins - i.e., the expoxies. A

partially deuterated diglycldyl ether of Blsphenol A (DGEBA) and a curing agent based

on polypropylene oxide diamine were chosen as the model system for the study. The

neutron scattering results can be analyzed by expressing the scattered Intensities in

terms of a form factor of an individual network of infinite molecular weight. Based

on this formulation, the average size of the mesh and the rigidity of the network

could be deduced from the scattering data. In addition, a decade-old controversy

concerning the homogeneity of the networks within thermosets can now be treated

analytically using this neutron technique. The heterogeneity in epoxies can be

divided into two categories; the compositional fluctuation and the topological

fluctuation. Schemes to quantity these two types of heterogeneity have been

developed.

In an effort to broaden the molecular weight distribution between crosslinks,

polymers of different molecular weight were blended together and cured with a stoichiometric amount of epoxy monomers. The molar ratio of the long chain amine (D2000) to the short chain amines (D-400 to D-230) were kept at either 1.0 or 0.5.

Every one of these cured mixtures gave rise to a pronounced scattering maximum at a Q

value smaller than those observed In the epoxy containing only one of the contituent

amines (see figure 1). Theoretical consideration based on this experimental

observation strongly suggested that the long chain and the short chain diamines

incorporated themselves within the epoxy network in a highly regular manner. The

connecting linkage between a pair of short chain diamines is a long chain diamine and

78
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

0.84i

OOO 0.08 0.16 0.24 0.32 0.40 0.48 0.56

Figure 1. Small angle neutron scattering pattern from a cured epoxy. The multipeaked structure in the pattern is due to the formation of a semi-regular

network of chemical crosslinks. For the measurement the crosslinking

agent was deuterated to enhance scattering contrast with the matrix.

vice versa. Such a regularly alternating block structure within a amorphous material

is rather striking. Work is now in progress to identify the mechanism of this

regular network formation which can not be understood in terms of our current

knowledge about epoxies.

SANS STUDY OF A CONCENTRATED PROTEIN SOLUTION

R. Nossal

(National Institutes of Health, Bethesda, MD)

and

S. H. Chen

(Massachusetts Institute of Technology, Cambridge, MA)

and

C. J. Glinka

Small angle neutron scattering (SANS) has been used to examine concentrated

aqueous solutions (up to 205^ by weight) of the protein bovine serum albumin (BSA) . At higher protein concentrations, the scattering data shown distinct features which

can be ascribed to strong intermolecular interactions. For example, figure 1 shows the

scattering for various concentrations of BSA in DO buffered with 0.03 molar

79
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

.030 .060 .090 .120

Q(A')

Figure 1. Differential scattering cross section, I(Q), for various concentrations of

BSA in 0.03 M k Acetate. Solid lines are computer-fitted spectra (see

text).

potassium acetate. The pronounced peak which develops in these data with increasing

protein concentration is caused by the mutual repulsion of the proteins which imposes

well defined nearest neighbor spacing (inversely related to the peak position) on the

system. The solid lines are fits to a theoretical model of the interpart icle

potential consisting of a hard-core plus an exponentially decaying "tail". For

moderate ionic strength (0.03 M k Acetate, pH 5.9), the intermolecular interaction

agrees with the double layer repulsive part of the well-known DLVO theory for

interacting colloidal particles. These results demonstrate that it is possible to

determine size parameters and surface charge of proteins in dense solutions. At high

salt concentration (> 0.2 M NaCl) the data can be fitted by the same potential model,

although interpretation in terms of DLVO theory is not possible. Even in this case,

however, effective molecular size and potential parameters can be determined.

1. R. Nossal, C. J. Glinka and S. H. Chen, submitted to Biopolymers.

80
REACTOR RA.DIATION DIVISION AND COLLABORATIVE PROGRAMS

JOINT NEUTRON AND X-RAY STRUCTURAL REFINEMENT OF PORCINE INSULIN.

A. Wlodawer and H. Savage.

Joint x-ray/neutron refinement of insulin has been performed using 2.2A neutron

data collected on the BT8 flat cone dif f ractometer at the NBS and 1.5A x-ray data

provided by Dr. G. Dodson, University of York, England. Several different models were

calculated, using the x-ray structure as a starting point. The first model was es- sentially a refinement of the x-ray data alone, lowering the R-f actor to 0.148.

Next, 24 cycles of joint refinement resulted in a model with R factors of 0.176 and

0.199 respectively for the x-ray and neutron data. The main problem with this model

was posed by the movement of solvent atoms out of x-ray density, particularly severe

for alternately occupied sites closer than 2A. Another model was calculated by

fixing solvent positions to the initial values and allowing only the atomic positions

belonging to the protein to refine. Finally, occupancies of amide hydrogens were

refined using neutron data only in order to study hydrogen exchange in the crystals.

The R factors in the final model were 0.183 (x ray) and 0.191 (neutron). The bond

lengths deviated by 0.02A from their ideal values.

The structure of two insulin molecules present in the asymmetric unit was compared in order to correlate the differences with the crystal packing. The two

crystallographically distinct molecules differ by the following RMS deviations: 1.88 A

in their positions of all non-hydrogen atoms and 2.23A for all atoms. This apparent

discrepancy is due mostly to concerted rearrangements in which the individual elements of secondary structure such as a helices do not vary in an appreciable manner,

but their relative positions are strongly influenced by crystal packing forces. The

2 overall average temperature factors for the two molecules were very similar (18. 5A

2

and 17. OA ). However, large local differences were observed in regions connecting a helices and irregular parts of both terminii of the chain B. A number of hydrogen

positions could be found directly in the neutron density maps, showing that all histidines were fully protonated, and confirming direct bond between histidine BIO and

the zinc, without an intervening hydrogen.

The pattern of protection of amide hydrogens from exchange is strikingly different in insulin than in any other proteins studied so far - see figure 1 . The only

region of significant protection under experimental conditions employed by us (over

four months soak of crystals at pH=6.5) was found in the center of the helical region

in the B chains (residues 14-19 in molecule 1 and 12-19 in molecule 2). No significant protection of amide hydrogens was observed in areas of g sheet. Insulin is

comparatively less rigid than proteins such as BPTI and ribonuclease and thus is more

81
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

CO

(U Ti ^ 4J

4-1 U

CO iw a. o

OJ C H

O CO •H

4-i (U O -P

0) "H

*^ -£ o ^

(-1 —

o

<4-( CO O rH iH

<U m

> r-H (U CO tH ,C ^ -

c c

CO CO

(0 u

i s

4-1 CO >^ iH C rH

•H 3

CO M-t

>-i • C CO ^3

•H <U CO CO 00 e <U C

3 CO ^ -H CJ

4-1 CO X

(U S

bO >-i C

•H ,i«! > CJ <U rH CO ^4 O iH CO > PQ G CO

(U

CO /^ T3

TS Q 'H C CO O M 0)

,£3 O >-i C Q)

QJ "r) 4-1 o bcr:

V4 C 15

•TJ CO

.c: o ^

^ _^ TJ

4J W C

^-^ CO O CO 13 c <u S <U 00

CO Wl C

^4 O CO 60 >-l rC

CO T) O

Q rC 01

cu

oo •H

82
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

susceptible to processes leading to exchange which is in good agreement with the

available solution exchange data.

Most of the strongly bound solvent appears to occupy similar positions in the

neutron and x-ray 2F -F maps but, there were significant differences in the more

disordered regions away from the protein surface.

NEUTRON ACTIVATION AUTORADIOGRAPHY STUDY OF PAINTINGS

Yu-Tarng Clieng, M. J. Blackman and J. S. 01 in

(Smithsonian Institution, Washington, DC)

and

(National Bureau of Standards, Gaithersburg, MD)

and

Martin Ganoczy

The engineering detailing study to produce construction drawings for the

proposed autoradiography facility at the NBSR is nearly completed. The study will

give a more accurate estimate of the anticipated construction cost. Meanwhile, a fund raising effort has been coordinated by the Smithsonian Institution to secure

financial support for the proposed new facility.

Due partly to the shortened reactor schedule last year only one printing was

studied using the existing thermal column facility. The study of the 17th century

Dutch Master painting "The Portrait of a Woman" was in collaboration with the New

York Metropolitan Museum of Art where a number of old master paintings have been

studied using the medicar. reactor at Brookhaven National Laboratory. The

autoradiography study can provide informations concerning the artist's style,

technique, construction of painting images and type of pigments used. This

information then becomes an integral part of an interdisciplinary study of art

history of the said artist along with results from other painting examination

methods.

If the neutron activation autoradiography technique is to gain acceptance among

people interested in studying paintings, the radiation dosage of about 300 rads that

the painting is subjected to during the activation process, though small by

industrial standards, must be addressed. We have reported last year concerning the

study of the image recording efficiency of different film systems, as a more

efficient autoradiograph recording system would reduce in direct proportion the

amount of radiation the painting received. The Kodak XAR film together with a Du

Pont Quanta III scintillation screen appears to be the most effective. However, the

83
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

3r

Cobalt blue in stand oil

O

\

O 1

- O — irradiated 100,000 RADS

• — non-irradiated

-. , L,.,.., 1 1 1 I 1 10 20 30 40

days

50 60

Figure 1. Ratio of azelaic (Cq) to palmitic (Cp^) acids in

irradiated raw number oaint samples as function of t irradiated and non3r

<o 2 -

Raw umber in stand oil

O— irradiated 100.000 RADS

# — non-irradiated

10 20 30

days

40 50 60

Figure 2. Ratio of azelaic (Cg) to palmitic (C^^) acids in irradiated and nonirradiated cobalt blue paint samples as function of time.

84
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

increase in the imaging speed is accompanied by certain trade offs. Elements that

emit very low energy beta particles do not benefit from the scintillation screen

system because the low energy beta particles are being stopped within the plastic

film base before it can reach the scintillation screen. Reducing the painting

activation level by using the faster imaging device will then also reduce the

sensitivity for studying elements with very low energy beta particles.

In connection with the film efficiency study, another project was initiated in

the past year to investigate the effects of the small amount of radiation on the

natural aging process of painting materials. Eight commercially prepared pigments

were mixed in with linseed oil and then thinly painted on microscope glass tray.

Half of the samples were left as control and the other half were subjected to 100,000

rads of gamma radiation. The dosage level was chosen to eliminate the uncertainty

about threshold effects. Gas chromatography technique was used to monitor the

chemical changes, that being the formation of Cq from the breaking down of

unsaturated long carbon chains in the linseed oil. Figure 1 and 2 show the growth of

C_ normalized to the saturated C.r amount in both irradiated and non-irradiated

9 1

6

samples of raw number in stand oil and cobalt blue in stand oil. This type of aging

test certainly requires time and statistics before any definitive conclusion can be

drawn. The initial results indicate that the irradiated samples cannot be discerned

from the non-irradiated ones. To accelerate the aging process, the common practice

is to use raised temperature or UV irradiation. An UV chamber has been constructed

to accomodate the use of both long and short wavelength UV sources. We will study

the effects on the normal aging process of painting materials from UV and gamma

radiation and also any possible synergistic effect.

85
B. NoN-RRD Programs

NUCLEAR METHODS GROUP: OVERVIEW

R. Fleming

(Center for Analytical Chemistry)

The development and application of nuclear analytical techniques for greater

accuracy, high 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 radiochemical 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 during the past year have been dominated by the upgrade of the

NBS Research Reactor to an operating power of 20 MW from its previous 10 MW level.

The power increase and the associated repositioning of the irradiation tubes resulted

in the NBSR being shutdown during the first half of the year and required a total

recharacterization of our irradiation facilities. The reactor characterization has

been completed and the Group's irradiation capability has been significantly

improved. The result has been a doubling of the neutron flux available for both our beam and incore measurements, and the Installation of the new cold neutron source.

When completed, the Cold Neutron Guide Hall Facility will result in a least a one hundred times improvement in our sensitivity for NDP and PGAA measurements.

With the NBSR unavailable for use for the first half of the year, we had the

opportunity to gain experience with other reactors. The ability to Irradiate large

samples in a well-thermalized neutron flux made the MIT reactor the facility of

choice for bloanalytical measurements, especially for the activation of whole

electrophoresis gels. The nearby light-water reactors at the University of Maryland

(College Park) and the University of Virginia (Charlottesville) were used for a variety of irradiations. The relatively high fast-to-thermal neutron flux ratio at

these latter two facilities made epithermal and fast neutron activation analysis

convenient, especially for iodine and silicon.

86
NON-RRD PROGRAMS

Radiochemical neutron activation analysis (RNAA) continues to make significant

contributions to the Group's measurement capability. The determination of tin in the

milk powder, wheat flour and rice flour SRM's at the few ng/g level and the

determination of gold and platinum in the human urine SRM at the few pg/ml level are examples of this work. The determination of platinum, in particular, at

environmental baseline levels means that this important element can be added to the

list of those which can be monitored in real samples.

Largely at the instigation of the Group's members, a new ASTM Task Group on Nuclear Methods of Chemical Analysis (E10.05.12) has been formed to insure that the

ASTM standards in this area reflect the current state-of-the-art and to enhance

communication within this community. After three meetings the group has over forty

members and six active subgroups: Quality Assurance, Biology Medicine and Health,

Geochemistry and Archeometry, Reactors, Neutron Generators, and Forensic

Applications.

The Group's collaborative research with industry and other government agencies

continues to increase. Thirteen f luoropolymer materials were analysed for over twenty elements with Dupont and a series of high purity quartz samples were analysed

for Fort Monmouth. Neutron depth profiling continues a strong interaction with US

industry on the measurement of elemental distributions in high-technology materials.

In addition to our ongoing bioanalytical collaborations with NOAA, NIH, USDA and EDA,

a new IAEA program in nutritional monitoring of the human diet has been initiated

jointly with EDA and USDA.

The National Environmental Specimen Bank, which in prior years has been

devoted to a pilot program of collecting, analysing and banking human liver samples

under EPA sponsorship, has expanded this year to include several new sample types.

Preliminary banking has begun on honey bee samples from EPA and on the USDA/EDA

human diet samples. In collaboration with the NOAA Nation Status and Trends program,

samples of marine sediment and fish liver and muscle are being banked. A goal for

the coming year is the development of one or more of these materials as standards or reference materials.

The past year has seen a major upgrade in our detection and data analysis

capability. A second front-end detector system (ND6700) has been installed for low

level counting with two new germanium detectors. A duplicate ND 6620 counting system

with an automated sample changer has been obtained for the analysis of the diet

samples in the nutritional program. The VAX computer is now fully operational for

data acquisition with its own sample changer. The addition of this improved data

87
NON-RRD PROGRAMS

acquisition and computational capability for modeling the measurement process will

continue to enhance our accuracy and throughput for Activation Analysis.

During the coming year the Group will continue to consolidate the development

of its data acquisition and computation capability and to apply nuclear methods to

elements which are not done well presently. These new elements will include nickel,

silicon and iodine by fast or epithermal NAA, nitrogen and phosphorus by thermal NAA

with beta counting, and lithium and boron by neutron activation mass spectrometry.

In addition to the ongoing application programs, work will continue in reducing and

quantifying the various sources of systematic error in analysis by nuclear methods.

HIGH RESOLUTION NEUTRON DEPTH PROFILING (NDP) AND SECONDARY ION MASS SPECTROMETER

(SIMS) OF BORON THROUGH OXIDE-SILICON INTERFACES

W. Vandervorst, F. R. Shepherd

(Bell-Northern Research, Ottawa, Canada)

and

R. G. Downing, J. T. Maki, and R. F. Fleming

(Center for Analytical Chemistry)

1 The neutron depth profiling (NDP) facility has now been operational for three

years at beam port-3 of the NBS Research reactor. During this time NDP has been used

to profile the concentration of light elements in many high technology materials.

2

The most frequent material analyzed has been the silicon based semiconductor , often

covered with a thin oxide insulating layer. When boron in implanted through this

oxide in the production of an electronic device it is of interest to understand the

distribution of boron at and near the oxide-silicon interface particularly after the

device has undergone thermal processing. Secondary ion mass spectrometry (SIMS), due

to its high resolution and low detection limits, is widely used to profile boron

implanted in silicon, however the presence of an oxide layer gives rise to rapidly

changing sputtering yields, secondary ion yields, collisional mixing, and radiation

enhanced diffusion near the oxide-silicon interface. This generates unreliable

concentration profiles using SIMS under these conditions. On the other hand, matrix

effects which complicate SIMS analysis are not a problem for NDP and make it an attractive method for checking the calibration factors needed to convert SIMS data to

boron concentration and for identifying artifact peaks. This interface region is

confined to a band a few nanometers in breath and requires higher resolution

techniques than normally used for NDP profiling. In this work, higher depth

resolution in NDP profiles has been achieved by employing a grazing exit geometry.

88
NON-RKD PROGRAMS

Since the dynamic range of sensitivity for the detection of B-lOwith good resolution

is less for NDP than for SIMS, the B-10 profiles can only be compared in regions where

19 -3

the concentration is greater than 10 cm . In this work an N-type Si wafer with 19^ nm of thermal oxide was implanted with

1 f\ —

p

B-10 ions at 70 keV to a dose of 10 ions cm . The wafer was analyzed by NDP and

SIMS and then furnace annealed at lOOO^C for 30 minutes in dry nitrogen for the

second analysis.

1 7

Boron profiles were measured by NDP using the B(v,a) Li reaction. The

2

typical depth resolution previously obtained was =40 nm . In order to improve the

depth resolution of the technique a grazing take-off angle was employed with the

detector at 75" to the sample surface normal. In order to limit the variation in

exit angles and because of the 1 cm spot of the neutron beam the detector was moved

15 cm away form the sample and a slit 1 mm wide was placed in front of the detector.

This limited the angular variation to less than 0.1° but also reduced the intensity

of the signal significantly. In this configuration the energy per ADC channel of 2.1

keV corresponds to =1.8 nm and since the energy resolution of the detector used was

12 keV, the depth resolution expected is =10nm.

SIMS depth profiles were recorded with an ion microscope equiped with a duoplasmatron ion source, primary mass filter, and a leak valve for flooding the

+ specimen surface with oxygen. Depth profiles were generated using a 5.5 keV beam

200 400

Depth (nm)

600

Figure 1, Neutron depth profile of a Si wafer implanted with 70 keV '°B to a dose

of 1 X 10^^ cm-^ through 194 nm thermal oxide. The vertical dashed line

indicates the location of the oxide-silicon interface.

89
NON-RRD PROGRAMS

SOOOn

200 400

Depth (nm)

Figure 2. Neutron depth profiles of the sample from figure 1 measured after

annealing at 1000°C for 30 minutes in dry nitrogen. The upper dashed

curves (x) was recorded for normal emergence (0=0°) and the lower solid curve (+) for grazing emergence (6=75°) of the alpha particles.

rastered over 250 micrometers, and secondary ions were extracted from a 60 micrometer

diameter central field with the energy slits wide open. An electron flood gun was

3 used together with a microprobe imaging system to ensure that charging was properly

neutralized and that the detected signal was always being extracted from the center

of the crater. Crater depths were measured with a surface prof ilometer.

Figure 1 shows the neutron depth profiles measured from the wafer. From the

measured energy of detected alpha particles, the depth scale in figure 1 was

4 established using stopping power values for Si from Ziegler . Bragg's Law addition

-3

for SiOp and densities of 2.33 and 2.27 gm cm were used for Si and SiOp

respectively. The concentration scale has been established by equating the

integrated counts to the implant doses (having been previously verified by checking

against an NDP concentration standard). Note that the distribution of boron varies

smoothly through the oxide-silicon interface at the depth of about 200 nm. The SIMS

profile (not shown) gave an artifact peak at this location when analyzed for boron.

Figure 2 shown NDP's for the same specimen after annealing at 1000°C for 30

minutes in dry nitrogen. The upper curve shows the profile measured for normal

emergence of the alpha particles. The lower curve, whose intensity has been

multiplied by 3 in this plot shows the improvement in the depth resolution in the

interface region (195 nm) obtained with grazing exit geometry (75°). Although the

intensity is reduced, the grazing exit geometry shows a much higher resolution and

90
NON-RRD PROGRAMS

dynamic range for the segregation peak. At 0° only a variation of ^0%-^^% is

observed whereas at 75° the signal varies by a factor of 2. The FWHM of the

segregated boron peak is 20nm. The small peak at a depth of about 20 nm in the

200 400

Depth (nm)

600

Figure 3. SIMS (solid line) and NDP (dashed line) data for the annealed sample

normalized to a total B concentration f 8.4 x 10^^ cm-^.

spectrum recorded at 75 degrees is a weaker replica of the peak at 270 nm, and arises

10 7

from another decay transition in the B(n, a) Li reaction. At normal emergence this

replica is more displaced from the main alpha spectrum and is not seen in the upper

curves in figure 2, but is present in the lower curve. Measurements made by SIMS on the annealed sample were compensated for signal

enhancements due to preferential sputtering, charging effects, sputtering rate

variations, and by omitting the oxygen flooding due to loss in overall resolution.

Both the SIMS and NDP curves are presented in figure 3. A sharp rise in boron

concentration can be seen at the interface. Beyond the interface is an immobile

boron peak followed by an "outdiffused" tail. The two curves are normalized to the

15 -2

total boron concentration of 8.4 x 10 cm , the balance of the implanted dose of

1 fi —

?

10 cm being continued in the long diffusion tail. Note that the SIMS profile

resolves a much sharper (FWHM = 8nm) more Intense segregated boron peak (labeled 'a' in figure 3) than the NDP data and that the broader peak at 270 nm is also more

intense in the SIMS profile. The discrepancy between SIMS and NDP results near the

surface (-20 nm) is largely associated with the Interfering replica in the alpha

spectrum discussed above. Aside from the intensity of the 2 main peaks, the

remaining differences between the 2 curves in figure 3 appear to be associated with a

91
NON-RRD PROGRAMS

Slight (=3 nm) shift. Repeating the SIMS profile sometimes gave closer agreement in

the peak positions and threfore may be associated with the overall error in

determining the depth scale from crater depth measurements.

The integrated amount of boron in the interfacial peak (figure H) is 2.4 x 10^

J

1 5 -2

cm-^ from SIMS and 2.2 x 10 cm from NDP. The broader peak in NDP is probably a result of the lower depth resolution. The boron peak in the Si (labeled 3 in figure

3) is approximately the same width in both NDP and SIMS, and the integrated B

15-2 15-2

concentration in this peak is 4.4 x 10 cm from SIM and 3.6 x 10 cm from NDP.

Although the discrepancy between SIMS and NDP in the intensity of the

interfacial peak could be partly due to the difference in depth resolution, both

techniques resolve peak 6 with approximately the same measured width. At these high

10 + boron concentrations, there may be an enhancement in the B secondary ion yield

5 particularly if the B is in a different chemical or structural form. Hofker has

reported a 305^ enhancement in B yield at similar concentration levels, which would

account for the high peak intensities observed in the SIMS profiles.

By using neutron depth profiling with grazing exit geometry to measure boron

distributions in the region of oxide-silicon interfaces. A depth resolution of 10 nm

has been achieved at 75° take-off angle. SIMS depth profiling of the same sample has

been compared to NDP and the NDP technique used to determine total boron

concentration. In the future, the depth resolution in NDP can be further improved

when higher flux neutron sources are available and by incorporating a precision

goniometer in the target chamber to allow high take off angles to be used.

Acknowledgements. The technical assistance of D. Johnston, from Surface

Science Western Ontario, with the SIMS measurements is gratefully acknowledged. We

wish to thank J. R. Ehrstein of the Center for Electrical and Electronic Engineering

for supplying a number of the samples. We also wish to thank the staff of the NBSR

for their kind assistance.

1. R. G. Downing, R. F. Fleming, J. K. Langland and D. H. Vincent, Nucl. Instr. and

Meth., 18, 47 1983.

2. J. R. Ehrstein, R. G. Downing, B. R. Stallard, D. S. Simons and R. F. Fleming, in

Semiconductor Processing, ASTM STP 850, edited by Dinesh C. Gupta, ASTM, 1984

3. J. D. Brown and W. Vandervorst, Surf. Int. Anal, (in press).

4. J. F. Ziegler, "Helium Stopping Powers and Ranges in All Elemental Matter",

Pergamon Press, New York.

5. W. K. Hofke, Philips Research Reports Supplements, 1975, No. 8.

92
NON-RRD PROGRAMS

HIGH-SENSITIVITY DETERMINATION OF IODINE ISOTOPIC RATIOS BY THERMAL

AND FAST NEUTRON ACTIVATION

Richard M. Lindstrom and George J. Lutz

(Center for Analytical Chemistry)

Methods for the determination of Iodine-129 concentrations and of I-129/I-127

ratios, to be most useful for studying the trasformatlons of iodine in the

environment, must be capable of measuring concentrations down to the present-day

o background level, of order 10 atoms/gram ( 5 aCi/g), with acceptable precision and

low blank. A neutron-activation procedure has been developed to perform reliable

concentration measurements down to this level in a few grams of sample. I-129/I-127

-10

ratios as low as 6 x 10 have been measured. Oxygen combustion is used both before

and after irradiation to separate iodine. Bromine-82 and other interferences are efficiently separated by the use of gas-solid reaction with Hydrated Manganese

Dioxide. Intense neutron irradiation is performed with optimized fluxes of both

thermal and fast neutrons.

Experience with the University of Virginia Reactor at Charlottesville during

the NBSR shutdown encouraged a detailed reexamination of the irradiation process with

the goal of determining both iodine isotopes simultaneously. The parameters used in

the calculation are as follows:

A sample contining 10 atoms of 1-129 and 10 g of 1-127.

12 hours irradiation time: one half-life of 1-130.

6 hours elapsed time between the end of irradiation and the start of

counting, during which time the radiochemical separtation of I is carried

out.

16 hours counting time: overnight, somewhat over one half-life.

A counting efficiency of 0.03 counts per disintegration, that of

a large high-resolution Ge detector with the source as close as possible

to the crystal.

Thermal neutron capture cross sections for 1-127, 1-128, and 1-129 are 6.13, 107, and 27 barns, respectively. The fission-spectrum cross section for the I-127(n,2n)I-126 reaction is 0.9 mbarn.

Mapped onto a space of thermal neutron flux vers\.iS fast (fission spectrum)

neutron flux (figure 1), the analytically useful region is defined by four

boundaries:

- The 1-130 signal must be large enough to be detectable. If measurement is

considered to be accomplished when 10 or more net counts are detected, then

under the assumed experimental conditions the thermal neutron flux must

12 2 exceed 5x10 n/cm s

93
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1014

u

esc

e

|10^*

101110

10 Counts 1",®20MW

I I 12

I III Mill 10'"" 10^*

Tharmal Neutron Flux n/om't

10

Figure 1. All double circles are NBS Reactor; single circles are other reactors.

UVAR - University of Virginia Reactor

N - Hanford N reactor, core position

HFIR - High Flux Isotope Reactor, ORNL „ Conditions of calculation are: 10 atoms

29 1 27 ^^1, 1 yg '^'l, 12 hour

Irradiation, 6 hour delay, 16 hour count, and e=0.03 count/dlslntegratlon.:

- The 1-126 signal must be detectable. If 10 counts are detectable, the fast

1 1 2

flux must exceed 1.4x10 n/cm s. - Iodine-130 can be produced from triple neutron capture on 1-127 as well as by

single capture on 1-129. This interfering signal is proportional to the cube

of the thermal flux. If no more than 50^ correction for this effect is

in 2 tolerable, the thermal flux cannot exceed 8x10 n/cm s. - The activity of 1-126 must not be so high as to impair the measurement of

1-130. If an activity ratio 126/130 of less than 100 is tolerable, then the

fast/thermal flux ratio must not exceed 1.1.

The characteristics of the reactors used in NBS measurements are plotted in the

fast/thermal flux space in figure 1. The RT^I facility of the NBSR at 10 MW has been

used for 1-129 irradiations through August 1984. Since it is outside the useful

region for measurement of 1-127 through the (n,2n) reaction, a separate short

irradiation has been used for stable I measurements through the 25-minute 1-128

isotope.

94
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The UVAR facility is marginal for measuring 1-129 in the lowest-level samples,

and nearly optimum for 1-127. Other irradition facilities are also plotted on this

graph, with data taken from Brauer et al (1) and and from other measurements at the

NBSR. It is clear from this analysis that a heavy-water reactor like the NBSR is

nearly ideal for 1-129 measurements, and that an irradiation facility tailored and

dedicated specifically for this task could bring dividends in the quality of iodine

isotopic ratio measurements.

Future enhancements in sensitivity to the determination of 1-129 by neutron

activation analysis beyond the level presently attainable cannot be reached by

adjusting irradition conditions, but will require more efficient counting procedures.

1. F. P. Brauer, R. S. Strebin, Jr., W. A. Mitlaff, and J. H. Kaye (1984),

Irradiation and Gamma-Ray Spectrometric Parameters for 1-129 Neutron Activation

Analysis, In W. S. Lyon (ed): Analytical Spectroscopy (Anal. Chem. Sympos . Ser

.

19). Amsterdam: Elsevier-North Holland.

NEUTRON-CAPTURE PROMPT-Y ACTIVATION ANALYSIS

AND RELATED STUDIES

D. L. Anderson, G. E. Gordon, M. E. Kitto, L. McCarthy, and A. Bates

(University of Maryland, College Park, MD)

and

R. M. Lindstrom

(Center for Analytical Chemistry)

The increase in reactor power (to 20 MW) has doubled the thermal neutron beam

O p flux (now 2.9 X 10 n/cm -s) at the prompt-Y activation analysis (PGAA) facility with

no accompanying increase in elemental background interferences in terms of mg

detected per irradiation for the elements H, B, C, N, Al, and Fe . This is of great

benefit, as analysis times have been cut in half while retaining the original

analytical quality (in terms of minimum detection limits).

In collaboration with Dr. Nathalie Valette-Silver of Carnegie Institute of

Washington and Dr. Jody Deming of Johns Hopkins University, we are analyzing a large

number of geological and biological samples from deep ocean region (13° North and 21°

North, East Pacific Rise). With Dr. M. P. Failey of Battelle Columbus Laboratories,

we have analyzed various samples related to processes in the oil industry. One of us

(RML) is currently analyzing a number of steel samples for boron.

Much of our effort has been dedicated to developing a technique by which

particles and gas-phase species in the atmosphere may be separately and

95
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H

L<

No

Rb

C$

Fr

Be

m

Co

Sr

imi Particles and gas phase

ED Particles

Sc

Bo

Ro

Lo

Ac

T*

Zr

Hf

Nb

To

Cr

Mo

Mn

Tc

Re

ft

Ru

Os

Co

Rh

Ni

Pd

Pt

C*i

M

Au/

Zn

Cd

tiSi

6

Al

Go

Tl

Si

Ge

5n

Pb

As

Sb

6i

Se SHSH

Te

Po

a

Br

S

At

He

Ne

Ar

Kr

Xe

Rn

Ce Pr Nd Pm Sm Eu Gd Tb Dg Ho Er Tm Yb l«

IH Ml ill Hi III III miu

Th Po u Np Pu Am Cm Bk Cf Es Fm Md Ho Lr

1 1 111

Figure 1. Elements Detected on Atmosheric Samples Using Multif liter Sampling

Technique and INAA, PGAA, and IC.

simultaneously collected and their concentrations measured. Using a particle

7 prefilter followed by LiOH-treated and/or activated charcoal-doped cellulose filters

and subjecting these to analysis by PGAA, instrumental neutron activation analysis

(INAA) and ion chromatography (IC), we are able to determine concentrations of the

elements shown in figure 1 . In table 1 , we present the minimum detection limits, an

7 .example of actual measurements, LiOH-treated filter blank values, and minimum

necessary volume data for the gas-phase elements detected by the combined techniques.

Boron (which can be readily detected by PGAA) is, we suspect, an especially

important tracer element for large-scale coal-burning emissions, when detected away

from oceanic influences. H BO has a substantial gas-phase component in many areas,

as seen in table 2. We are now trying to correlate gas-phase born with SOp emissions

2-

from coal-fired power plants and its subsequent transport and conversion to SO^

Another possible tracer is Se , which may occur as SeO , elemental Se, or organic Se in the gas phase. We have some evidence of speciation, based on

comparisons of our Se measurements (using base-treated filters) with those of Mosher

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Table 1. Minimum detection limits by INAA, PGAA (?) and IC, and Whatman blank values

(ng/110-mm filter)

.

Element (keV) (a) (b) X +/- (d)

B (?) M72 1 .80E-01 3.04E+01 6.65E+02 2.15E+02 11 .5

N03 (IC) (e) 3.50E+01 1 .OOE+04 1 .75E+04 2.10E+03 1 .0

S 3104 6.46E+02 1 .21E+04 8. OOE+04 4. OOE+04 5.0

S (?) 8^11 7.58E+02 1 .40E+04 1 .00E+05 5. OOE+04 5.5

CI 2168 1 .35E+00 9.91E+02 3.24E+04 1 .23E+04 22.5

CI (?) 517 2.42E+01 1 .10E+03 3.15E+04 3.10E+03 15.5

As 560 4.30E-03 2.20E-01 7.10E+00 3.00E-01 17.0

Se 264 1 .22E-03 2.10E-01 3.53E+00 2.75E+00 15.0

Br 777 4.70E-03 5.30E+01 2.50E+02 7.07E+01 3.0

Sb 564 5.06E-04 4.20E-03 1 .10E+00 3.60E-10 175.0

I 443 1 .92E-01 1 .61E+01 1 .25E+02 6.01E+01 6.0

(a) based on a sample volume of 500 m3, not including blank

(b) College Park, MD sampling site, volume = 712 m3

(c) for 8 blank filter samples (ng/110-mm filter)

(d) volume necessary to observe elements 1 sigma above treated Whatman blank levels

for measured sample

(e) based on Whatman blank levels and 500 m3 sample volume

Table 2. Ambient Particulate and Gas-Phase Boron Concentrations (ng/m ) at Measured

Several Locations.

Mean

Location Particulate B Gas -Phase B Gas/Partic

Ratio

le

Samples

Mauna Loa Observatory 0.2 + 0.2 0.5 ^ 0.3 2.5 3

Cape Kumukahi, HI < 0.2 25 + 11 125 2

Wallops Is., VA 2.9 +_ 1.3 70 + 52 24.1 12

College Park, MD 6.7 ^ 0.3 9.5 ^ 0.5 3.7 1 Gaithersburg, MD 2.6 +_ 0.3 9.5 ^ 0.5 3.7 1 Fairbanks, AK 12.2 ^_ 4.6 0.5 ^ 0.4 0.04 4

97
0.93 - 1 .65 3

0.37 - 4.45 23

1.14, 1 .65 2

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Table 3. Comparison of Measured Se Values: Base-treated vs. Activated Charcoal

Filters.

Se Concentration (ng/m3) Range (ng/ra3) # of

Location gas particles gas particles meas.

URBAN

Providence, RI (a) 0.41 j^ 0.18 1.26 +_ 0.36 0.21 - 0.4?

College Park, MD (b) 0.14 +_ 0.11 2.05 ^ 1.09 0.019 - 0.45

Gaithersburg, MD (b) 0.13^0.06 1.40 j^ 0.25 0.07, 0.19

RURAL

Narragansett, RI (a) 0.25 j^ 0.16 0.93 ^ 0.59 0.07 - 0.60 0.25 - 1.97 17

Wallops Is., VA (b) 0.080 _+ 0.050 1.76 j^ 0.95 0.032 - 0.32 0.74 - 3-66 12

REMOTE MARINE

Oahu, HI (a) 0.035 +_ 0.014 0.14 +_ 0.03 0.020 - 0.053 0.13 - 0.18 4

Cape Kumukahi, HI (b) 0.016 + 0.004 0.13 + 0.04 0.013, 0.020 0.088, 0.165 2

(a) Activated Charcoal Filters (Mosher and Duce)

(b) 7LiOH Treated Whatman 41

and Duce of the University of Rhode Island (who used charcoal-doped filters) at

similar locations (see table 3). While local or temporal variations may be

responsible for the factor of 3 difference in the measurements, we are now doing

side-by-side sampling using both types of filters to see if the differences are due

to the presence of both acidic gas-phase Se species and elemental and organic Se

species. Many other potential gas-phase elemental tracers (e.g. As, Sb, and I are also under investigation.

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IAEA COORDINATED RESEARCH PROGRAM ON HUNAN DAILY DIETARY INTAKES

OF NUTRITIONALLY IMPORTANT TRACE ELEMENTS

V. Iyengar and R. Zelsler

(Center for Analytical Chemistry)

and

J. T. Tanner

(U.S. Food and Drug Administration, Washington, DC)

and

W. Wolf

(USDA Human Nutrition Research Center, Beltsville, MD)

The IAEA international study is a comprehensive project aimed at obtaining

comparable data on dietary intakes of 23 nutritionally important minor and trace

elements through diets consumed in a variety of developed and developing countries.

The project also involves estimating phytate and energy content of the diet. The

scope of the study, which includes contribution to the core program as well as allowing for supplementary research, provides an unique opportunity to develop a coordinated approach by collaborators of the 3 participating agencies, the FDA, the

NBS and the USDA.

The combined expertise of the participants will be aimed towards a significant

improvement and development of analytical methodology needed for the accurate

assessment of the dietary intakes of trace elements. Aspects of quality assurance in

sampling, sample preparation, analysis and data evaluation will be treated. In

addition, long term monitoring will be addressed by storing part of the samples in a specimen bank.

As part of the first year work plan drawn up for the joint FDA-IAEA-NBS-USDA

project, precision and accuracy aspects related to Flame Atomic Absorption

Spectrophotometry (AAS-Flame), Atomic Emission Spectro-photometry with an Inductively

Coupled Plasma source (AES-ICP) and Neutron Activation Analysis (NAA) were evaluated

by analysing the same test samples by all the three methods. As a first step,

investigation of the elemental compostions of available dietary reference materials

was taken up. The materials considered were IAEA Mixed Diet (IAEA-H9), USDA Mixed

Diet (USDA TDD-1D), NBS Rice Flour (NBS-1568 and NBS-1568a) and NBS Wheat Flour

(NBS-1567a). Basically, a set of 23 elements of biological significance was sought

in all the samples as envisaged in the project protocol. These were As, Ca, Cd, 01,

Cr, Cu, F, Fe, Hg, I, K, Mg, Mn, Mo, Na, Nl, P, Pb, Se, Si, Sn, V and n. Depending

upon the capabilities of the technique, additional data on other elements, were also

Cr, Cu, F, Fe, Hg, I, K, Mg, Mn, Mo, Na, Nl, P, Pb, Se, SI, Sn, V and n. Depending

upon the capabilities of the technique, additional data on other elements, were also

gathered.

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DETERMINATION OF GOLD AND PLATINUM IN HUMAN URINE. SRM 2670

Robert R. Greenberg and Rolf Zeisler

(Center for Analytical Chemistry)

There is continuing concern about the possible impact of platinum on the

biosphere due to the increasing industrial and medical uses of this metal.

Approximately 18700 kg (600,000 troy ounces) of platinum are used annually by the

automotive industry, while theraputic utilization of platinum compounds for their

anti-cancer properties is increasing. Due to this expanding use of platinum it is

important to be able to measure platinum at the naturally occurring levels.

Accurate determination of gold and platinum at concentrations below 1 ng/g is

extremely difficult and requires rigid control of the blank. Radiochemical neutron

activation analysis (RNAA) provides an ideal method to determine these elements in

that it can be performed in an almost blank-free manner. After irradiation, but

before chemical manipulation of the samples, unirradiated carriers of the elements of

interest can be added to minimize losses which typically occur when processing

extremely dilute solutions of the noble metals. Several years ago a procedure was developed to determine both gold and platinum in biological materials via RNAA (1).

This procedure has been modified to allow the determination of these metals in both

the elevated and the natural level fractions of the Trace Elements in Urine Standard

Reference Material (SRM 2670). Urine is a difficult matrix for NAA for two reasons.

First, the high salt level in urine produces a large amount a background radiation

which must be removed prior to gamma-ray spectroscopy, and second, a liquid is

considerably more difficult to irradiate than is a solid, and often requires a pretreatment step, such as lyphilization, which can increase the blank.

Elevated Level Samples - The entire contents of each of five bottles of Urine

was dissolved in 5 mL of ultrapure water and transferred to an LPE (polyethylene) bag

which had repeatedly been washed in a mixture of NBS subboiling distilled nitric and

hydrochloric acids. The samples were than lyophilized, sealed, and placed in a second acid washed LPE bag. The samples were irradiated with Au and Pt standards for

36 s in RT-3. Midway through the irradiation the rabbit was removed from the

reactor, flipped end-over-end, and reinserted into the reactor to insure a uniform

neutron fluence throughout the rabbit. Approximately 1 day after irradiation the

outer bag from each sample was discarded and the inner bag containing the sample was

opened. The opened bags were transferred to 400 mL beakers along with 85 mg of Au

carrier, 50 mL of water, 25 mL of nitric acid, and 25 mL of hydrochloric acid. The

100
NON-RRD PROGRAMS

bags were allowed to sit in this solution for at least two hours and the solutions

were occasionally stirred to dissolve all material. The bags were then washed with

water and this was added to the appropriate beaker. Finally each bag was allowed to

sit in 100 mL of 8 mol/L sulfuric acid for 3 hours after which the bags were

discarded and the sulfuric acid solutions were added to the appropriate solutions.

Since chemical yields were determined, a quantitative transfer of material was not

necessary as long as equilibration between sample and carrier was achieved. An

additional 100 mL of water was added to each sample and the samples were heated

overnight at low heat. The next morning the heat level was increased and the

remaining water, nitric acid and hydrochloric acid were allowed to evaporate. The

heat level was then slowly increased until the temperature of the solutions was just

below the boiling point of sulfuric acid. The solutions were covered with watch

glasses and were heated at this temperature until all the metallic Au had

precipitated. The separated Au samples were sequentially washed in water, nitric

acid, water, hydrofluoric acid, water, hydrochloric acid and finally water. The

samples were then heated to 500°C to ensure that all sulfuric acid was removed, and

were then cooled, weighed to determine chemical yield, transferred to polyethylene

bags, and counted on a gamma spectrometer, with Compton suppression. Gold was

determined via the Au-198 isotope and Pt was determined via the Au-199 daughter of

Pt-199. The second order Au interference is Pt was extrapolated from Au standards

irradiated for 1 h in Rt-3. Since this second order interference is proportional to

neutron fluence squared, while the production of Au-199 from Pt-198 is proportional

to neutron fluence (for irradiation times short compared to the half life of Au-199),

the interference for the 36 s irradiation was ^% of the interference for the 1 hour

irradiation. The magnitude of the interference correction for the elevated urine was

3% of the total Pt concentration and the additional uncertainty from this

interference correction was approximately 0.3/S of the Pt concentration in the

elevated urine.

Normal Level Samples - The procedure was essentially the same as for the

Elevated Urine samples except that the samples were individually irradiated for 1 hour in RT-3. Three such samples were analyzed as well as a blank sample of

ultrapure water processed the same way as the samples. The magnitude of the Au

interference for Pt was approximately equal to 505^ of the uncorrected Pt

concentration and the additional uncertainty due to this correction was 105^ of the Pt

concentration.

101
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Table 1. Concentrations (ng/mL) Observed in Elevated Level Samples of Urine, SRM

2760:

Sample Au Pt

1 242.0 ± 0.7^ 122.9 ± 2.5^

2 2411.7 ± 0.7 126.0 ± 2.3

3 247.7 ± 0.7 125.5 + 2.7

4 241 .4 ± 0.7 122.5 ± 3.4

5 246.1 ± 0.7 128.4 ± 3.8

Mean ± Is 244.4 ± 2.7 125.1 ± 2.4

Estimated 95/S Confidence Interval ± 8.2 ± 8.0

Uncertainties are 1 a counting statistics of sample and standards.

Table 2. Concentrations (pg/mL) Observed in Normal Level Samples of Urine, SRM 2670

1 8.0 ± O.ia 8.5 ± 1.1 a ^

8.5 ± 0.1 8.3 ± 1.9

7.5 ± 0.1 7.2 ± 2.3

Mean ± 1

s

8.0 ± 0.5 8.0 ± 0.7

Estimated 95/S Conference Int erval ± 1.4 ± 2.7

Blank - 0.1 - 0.2

Uncertainties for individual measurements are 1 a counting statistics of sample and

standards

This sample contains 2 bags (double blank).

The results of these analyses are listed in table 1 and 2; the concentrations

listed are for the specified dilution of the contents of each bottle of Freeze-Dried

Urine to 20.0 mL. Uncertainties for individual measurements are 1 sigma combined

counting statistics for sample and standards. The estimated 95/5 confidence intervals

for the results are also listed in these tables. The confidence intervals were

calculated by combining the standard deviation of the mean for each set of values

muiltiplied by the appropriate t-value for the 95/5 confidence level and than adding

the estimated systematic error. For the Au measurements in both the elevated and

normal level urine samples the estimated systematic error was 2% which was due mainly

to potential counting geometry errors since the samples were counted directly on top

of the detector. For the Pt in the elevated urine the estimated systematic error was

455: 2% from counting geometry and an additional 2% from possible bias in peak

102
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integration of the 158 keV peak of Au-199 which lies directly upon the backscatter

peak of Au-198. For the Pt in the normal urine the estimated systematic error was

I25S (2% from counting geometry and ^0% from the determination of the Au interference;

this 105? error also includes the bias from peak integration so that an additional 2% was not included).

The observed sample standard deviation (Is) for Au in the elevated fraction of

the Freeze-Dried urine (1.15^, relative) was slightly greater than expected from

counting statistics. This excess variance was probably due to counting geometry

errors (discussed above). The observed sample standard deviation for Au in the

normal fraction of the Freeze-Dried Urine was significantly greater than the counting

statistics. This may have been due to variable losses of Au onto the walls of glass

bottles (prior to lyophilization) that this SRM was packaged in.

Vlith an appropriate separation procedure, RNAA can be used to determine the

concentrations of gold and platinum in biological samples at the picogram per gram

level. Both solid and liquid samples can be submitted for analysis, however a lyophilization step prior to irradiation may be advantageous.

I. Zeisler, R. and Greenberg, R. R., "Ultratrace Determination of Platinum in

Biological Materials via Neutron Activation Analysis and Radiochemical.

Separation," J. Radioanal. Chem. 75, 27 (1982).

MULTIELEMENT ANALYSIS OF BIOLOGICAL MACROMOLECULES

Susan F. Stone, Rolf Zeisler and Diane Hancock

The importance of the role of trace elements associated with biological

macromolecules has become increasingly apparent in the last twenty years. For

example, studies of metalloproteins has revealed the structural and functional

importance of certain trace metals associated with proteins. The biological

specificity of metalloenzymes depends on the presence of both the protein and the

metal ion. Removal of the metal ion results in a loss of biological activity. Trace

metals have also been found to be structurally important in stabilizing secondary,

tertiary, or quarternary protein structures. Detection of trace elements associated

with proteins may be accomplished with a newly-developed combination of biological

separation techniques with analytical nuclear methods.

Polyacrylamide gel electorphoresis (PAGE) separation of proteins by molecular

weight is one technique that we have used. Several proteins were separated by

^ 103
Acrylamide

1055 gel

20^ gel

Bis-acrylamide

10? 20? gel

Tris base

Trizma

Ultrol

Tris HC1

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Analysis of Gel Reagents

Cr Fe

230ng

480

lOyg

22 yg

Co

54ng

120ng

6.7ng/l4ng S^iOng/l 1 lOng 1 .il5ng/3.00ng

57ng/44ng 2.3yg/1.8yg 20ng/15ng

iMOng/IIng 22yg/17yg 66ng/51ng

Calbiochem

Sigma

190ng/150ng

52ng/40ng

19.8ng/15.1

40ng/30ng

SDS

Lot D

Lot P M7ng/39ng

17ng/Ung

NH4 Persulfate M2ng/l4ng 270ng/90ng 2.2yg/0.7yg

Glycine

(in 13L buffer)

SDS

(in 13L buffer)

3.nyg

2.Hyg

561 ng

Tris base (Trizma)

(in 13L buffer) 0.20yg 8.3y 70ng

Per gel (worst case)

10? part

20? part

0.66yg

0.81 yg

33yg

40yg

0.l6yg

0.20yg

2

Total (ng/cm ) 2 5.8ng/cm

2 290ng/cm

2

1 .4ng/cm

Zn

360ng

760ng

29ng/60ng

94ng/72ng

720ng/560ng

138ng/105ng

I4ng/5ng

0.33yg

1 .26yg

1.49yg

11ng/cm^

electrophoresis on a 10-20? gradient polyacrylamide gel. A whole gel was thea

irradiated with neutrons, and following a short decay time, an autoradiograph was developed to detect any beta-emitting isotopes of fairly high energy that were

produced. The location of phosphorous-associated protein, phosvitin, was visualized

in this way as shown in figure 1(b). P-32 was the isotope detected in the

autoradiograph. This technique shows a much more sensitive threshold of phosphorous

detection than does a non-specific protein stain, such as a Coomassie Blue stain. A

duplicate gel treated with Coomassie Blue is shown in figure 1 as an overlay of the

autoradiographed gel. The protein bands visualized by the stain are carbonic

anhydrase (a) and serum (c). The gel location corresponding to the phosvitin band is

not visible with the Coomassie Blue stain.

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a

Figure 1. Comparison of protein bands, separated by PAGE, using two detection

techniques. One gel shows the phosvitin (strip b) using autoradiography

of P-32. A duplicate gel, stained with Coomassie Blue dye, has been

placed over the autoradiograph, matching the protein band locations. The

stained gel shows cabonic anhydrase (strip a), and serum (strip c), but no phosvitin.

lOOOOr

1000

E

uTM 100

c

10

2 1 Gel Section

Figure 2. Comparison of five trace element concentrations in a PAGE separation of

carbonic anhydrase. Protein bands were included in gel sections 3 and 5,

while the other gel sections represent background.

105
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In addition to autoradiography, gamma-counting has also been done for

separated metalloproteins using neutron activation analysis. Protein electrophoresis

is normally done using a detergent, sodium dodecyl sulfate (SDS), which is a denaturing agent. An electrophoretic separation of carbonic anhydrase was done using

SDS, and trace element analysis of gel sections was performed. Results for five

elements are shown in figure 2. A marked increase in zinc, which is associated with

enzyme, was found in the protein band (gel section 5), compared to the background, as expected. However, many other trace elements, which have no known association with

the enzyme, increased as well. In addition, the zinc concentration found in the

protein band was more than should have been present from the amount of protein

applied. Studies are currently in progress to learn more about trace element

associations with proteins under both denatured and non-denatured conditions.

Calculations showed that the actual zinc concentration in a protein band would

not be easily discernible above existing background concentrations. This finding

initiated research to reduce the trace element background in the polyacrylamide gels.

Table 1 lists some of the results from an analysis of reagents used in the

preparation of polyacrylamide gels. Rubidium is not listed because only upper limit

concentrations were obtained (at 1ng/cra2). Using worst case approximations, the

concentrations (ng/cm2) for zinc, rubidium, and cobalt do not completely account for

the trace element background concentrations found under denaturing conditions.

Research is continuing for the reduction of trace element background.

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DEVELOPMENT OF BIOMONITORING SPECIMEN BANK IN THE UNITED STATES

Stephen A. Wise and Rolf Zelsler

(Center for Analytical Chemistry)

Since 1975 the National Bureau of Standards, in conjunction with the U.S.

Environmental Protection Agency (EPA), have been involved in the development of

methods and procedures for environmental specimen banking. In 1975 the Federal

Republic of Germany and the U.S. agreed to cooperate in the study of environmental

specimen banking activities and proposed the establishment of "pilot Phase" specimen

banks in both countries. An EPA-NBS workshop in 1976 recommended the establishment

of a pilot environmental specimen banking program to evaluate the feasibility of a National Environmental Specimen Bank (NESB) by providing working experience in all

aspects of specimen banking, that is, in specimen collection, processing, storage,

and analysis. The goals of this pilot phase were:

1. to develop procedures for the sampling, processing, storage, and analysis of

four types of environmental accumulators:

a. human soft tissue,

b. a marine accumulator,

c. a food accumulator, and

d. an air pollutant accumulator;

2. to evaluate and improve analytical methods for the determination of trace

element and organic pollutants in biological matrices;

3. to evaluate the feasibility of long-term storage of environmental samples

under various conditions;

4. to establish baseline data on selected environmental samples, and;

5. to evaluate specimen banking as a means of storing samples for trend

monitoring and of permitting retrospective analyses as concerns about new pollutants arise and as new analytical techniques are developed.

Since 1980 the EPA-NBS pilot environmental specimen bank has been involved in

the collection, processing, storage, and analysis of the first sample type, human

liver tissue. However, because of funding limitations, the remaining three samples

types (i.e., marine, food and air accumulators) were not incorporated fully into the

pilot banking program as originally designed. During the past year the specimen

banking concept at NBS has been modified based on current funding levels from EPA and

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the interest of other agencies in specimen banking activities.

1 . Project Phase

a. Existing Projects

1. EPA Specimen Bank Program

As the "pilot phase" (1980-1985) nears completion, the program will move towards a "project phase" of the Biomonitoring Specimen Bank Research Project. At

present there are two existing specimen banking projects and several proposed projets

to be funded in FY 86.

The EPA-NBS Specimen Bank Program will continue to serve as the focal point for

related activities during the project phase. During the next year the activities of

the EPA-NBS project will be directed towards the following milestones:

a. Continued collection of human liver specimen (~50/year);

b. Analysis of 30 liver specimens from 1984 set;

c. Verification of sample stability through reanalysis of specimens from

1980 and 1982 collections;

d. Trend monitoring, e.g., Pb (1980-1985), and;

e. Analytical quality assurance.

2. NCAA National Status and Trends Program

In 1985 a specimen banking project was initiated at NBS with the National

Oceanic and Atmospheric Administration (NOAA) as part of their National Status and

Trends (NS&T) Program to monitor the U.S. marine environment. The NS&T program

consists of two monitoring programs, the Benthic Surveillance Program, in which

sediment and fish tissue (muscle and liver) will be collected from approximately 50

coastal sites, and the Mussel Watch Program, in which mussels and sediment will be

collected from approximately 150 coastal sites. As part of the NOAA NS&T program,

NBS will provide the following specimen banking activities:

a. Development of sampling protocols for the collection of sediment,

mussels, fish muscle, and fish liver;

b. Bank specimens of sediment and tissue from 12 sites of the Benthic

Surveillance Program and mussels and sediment from 30 sites in the

Mussel Watch Program;

c. Analyze six different specimens of mussels and sediment for the

determination of selected trace elements (15 elements) and organics

(organochlorine pesticides, PCBs, and PAH), and;

d. Analyze four reference materials for quality assurance.

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3. lAEA/FDA/USDA/NBS Nutrients in Human Diet Program

NBS, Food and Drug Administration (FDA), and the Department of Agriculture

(USDA) are collaborating in a project sponsored by the International Atomic Energy

Agency (IAEA) to obtain comparative data on the dietary intakes of 23 nutritionally

important minor and trace elements in a number of developing and developed countries.

The combined expertise of the various agencies is directed towards the development

and improvement of analytical methodology for the accurate assessment of dietary

intakes of trace elements. As part of this interagency collaboration, several tasks

related to specimen banking will be included:

a. Methods development, analyses, and quality assurance.

b. Intercomparison of analytical methods for trace elements in existing

dietary reference materials.

c. Preparation of U.S. mixed diet research material from the 200 different

food groups in the FDA Total Diet Study (~10 kg).

d. Determination of long-term stability of trace constituents in the total

diet composite.

e. Bank aliquots of the total diet sample.

Future collections of total diet specimens will be made in four different

geographical regions of the U.S. Representative portions of these total diet

composites will become part of the Biomonitoring Specimen Bank,

b. Proposed Projects

Several additional projects will start in FY 86 which will broaden the scope of

the specimen bank program to include projects related to nutrient as well as pollutant determination in biological matrices.

1

.

NCI Nutrients in Human Serum

As part of a three-year quality assurance program of the National Cancer

Institute (NCI), NBS is developing analytical methods for the determination of

nutrients in human serum. One aspect of this program will be the determination of

the long-term stability of selected nutrients in serum (frozen and lyophilized) . The

following analytes will be studied: —zinc, selenium, beta-carotene, retinol,

alpha-tocopherol, retinyl palmitate, retinyl acetate, and ascorbic acid.

2. Human Liver Standard Reference Material

As a result of the past five years of experience in the analysis of human

liver samples as part of the EPA-NBS pilot banking program, NBS will prepare and

certify a human liver Standard Reference Material (SRM). This SRM will be useful to

laboratories involved in the measurement of trace elements in human tissue, since the

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NON-RRD PROGRAMS

concentration levels of several elements of environmental (e.g., Pb ) and

nutritional (e.g., Se ) interest are considerably lower in human liver as compared

to the existing bovine liver SRM. In addition, the human liver SRM will be prepared

using the contamination minimizing homogenization techniques developed in the

specimen banking program. In addition to the certified values for the trace element

concentrations, information values for several organochlorine pesticide residues will

be provided.

3. EPA Human Adipose Tissue Monitoring Program

Since the mid-1960's, EPA has conducted a monitoring Program to measure

organochlorine pesticides and PCB's in human adipose tissue. At present adipose

tissue samples are collected from approximately 1000 sites across the U.S. Portions

of the tissue specimens have been stored if excess material was available after

analyses. Recently, this tissue monitoring program has expanded their analytical

procedures to include volatile organics as well as the semi-volatile compounds

measured in the past. EPA has expressed interest in including NBS in this program to serve a quality assurance and specimen banking role. NBS would store a small number

of specimens from the program to serve as reference samples and to investigate

storage stability. A number of these samples would be analyzed at NBS to provide

method validation and baseline data.

2. Network Phase

The project phase will provide experience in the sampling, processing, storage

and analysis of a variety of biological matrices as originally intended for the pilot

program (e.g., human tissue and fluids--! iver , adipose, and serum; marine

accumulator —mussels, fish, and sediment; and food accumulator —total diet samples).

The project phase will also bring together the different government agencies

responsible for both contaminants and nutrients in these various matrices to

coordinate their efforts in specimen banking. The result will be the establishment

of a National Biomonitoring Specimen Bank System consisting of a network of satellite

banks derived from the project phase as illustrated in figure 1. NBS will serve as resource facility to conduct research related to the needs for specimen banking and

as a quality assurance laboratory for the analytical measurements required in the

various satellite banking programs.

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FACILITIES AND EQUIPMENT FOR ACTIVATION ANALYSIS

Richard M. Lindstrom and John K. Langland

(Center for Analytical Chemistry)

A new VAX 11/730 computer (in the minisupermini class) has been added to the

Group's counting systems. With a 120-megabyte disk and a much more powerful

operating system than the PDP 11/44 which it replaces, the mechanism is in place for

development of an optimimum mixture of distributed processing (for data acquisition,

text processing, and interactive data analysis) and centralized computation (for

database management, NAA data reduction, and numerical simulation).

A new computer-based data acquisition and processing system (Nuclear Data 6700)

to operate in parallel to the existing system, a display and acquisition minicomputer

(DEC Pro-380) to act as a buffer for the ADCAM systems, and a general-purpose

microcomputer (Zenith Z100) for communication and reporting have all been acquired in

the past year.

Links have been established among almost all counting and computing systems in

the Group (figure 1). Already it is possible to interchange spectral data files

among all the Nuclear Data MCAs, and text files among all computers, allowing users

to choose the most suitable device for the application.

A 30-Mb Winchester disk drive has been added to the ND6620 system. This drive

includes a 1 -Mb flexible disk by which data may be transferred to or from the

ADCAMS

22 Detectors

ND 6620

S8 Detectors Computation

NO 66

S4 Detectors

ND 683

Depth Profiling

VAX 1 1 /730

Computation

Data Base

World

PC 380

Display and

Control

ND 6700

24 Detectors

Z100 PC

WP, Graphics

Figure 1. Nuclear Methods Group data acquisition and computation system.

Ill
NON-RRD PROGRAMS

identical drive in the 6700 system. The redundancy now available with these serial

links and removable disks makes diagnosis of hardware and software problems much more

easy.

A prototype rabbit receiver has been built and is installed in room B-121

connected to RT-5, for testing. This receiver provides improved operator safety in

that it is remotely operated via an electro/phenumatic control system. Rabbits may

be fired into the reactor, returned, flipped, sent to storage, or dropped into a transport pig without any radiation exposure to the operator.

Another automatic sample changer has been added to the group's equipment. This

Smithsonian owned changer works with the Smithsonian's ND-66 M.C.A. and the groups

DEC-VAX computer. It is currently set up with an Ortec gem series germanium

detector. It holds up to fifty samples, mounted in samll glass test tubes, which may

be stationary or rotating during counting. The sample to detector distance is

variable from contact to 50 centimeters.

ATMOSPHERIC AND ENVIRONMENTAL STUDIES BY

INSTRUMENTAL NEUTRON ACTIVATION ANALYSIS

G. E. Gordon and W. H. Zoller

(University of Maryland, College Park, MD)

We continue to make extensive use of instrumental neutron activation analysis

(INAA) to determine concentrations of about 35 elements in samples of atmospheric

particulate matter collected from ambient air (now mostly at remote sites such as

Hawaii and rural sites in the continental U.S.) and in particles released from major

sources such as power plants. By measuring concentrations of such large number of

elements, we are able to identiy contributions from the sources to the atmospheric

burden at ambient sampling sites. Examples of some of these studies are discussed

briefly in the following sections. Because of the shutdown of the reactor for much

of the past year, we focused more of our effort on interpretation and write-up of

results from analyses performed in previous years. Now that the reactor is again

functioning, we are using it extensively for analyzing samples collected before and

during the hiatus.

1. Rare Earth Elements on Particles Released by Oil Refineries and Power

Plants

Based on the results of analyses of many types of samples analyzed by INAA at

the NBS reactor, ranging from source samples collected in Philadelphia to Asian dust

samples collected at Mauna Loa Observatory (MLO) in Hawaii, plus the use of

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literature data from other groups, we have found that (a) fluid catalytic converters

of oil refineries and, to a lesser extent, oil-fired power plants release fine

particles containing high concentrations of rare earth elements (REE) to the

atmosphere and (b) the pattern of REE released is different from that of the Earth's

crustal abundance pattern, being more enriched in the light REE, especially La.

Regarding the latter point the La/Sm ratio for typical crustal material is about 5,

whereas the ration for particles from oil-fired plants and refineries is typically in

the 20 to 40 range. It appears that the source of the REE released by these plants

is ziolite catalyst used to "crack" large molecules present in raw petroleum. The

catalysts typically contain 1 -3/S mixed REE oxides. The unusual REE pattern is

typical of the major U.S. ore of REEs, bastnasite.

The large amount of REEs released on fine particles from these sources provides

an excellent signature for tracing their emissions over long distances. In the most

spectacular demonstration of the potential use of this "tracer of opportunity", we think that REEs observed at certain times at MLO in Hawaii originate from the oil

industry in Japan and elsewhere in Asia, representing a travel distance of about 6000

km! One important aspect of this problem is the fact that the tracer is normally

observable only when samples have been analyzed by INAA, as no other commonly used

method has the necessary sensitivity for REEs.

1 A paper describing this work in more detail has been accepted by Science . M.

Kitto, D. L. Anderson and I. Olmez are presently analyzing samples of about a dozen

catalysts used in the oil industry. Both INAA and PGAA (see Anderson et al. section)

are being used.

2. Compositions of Atmospheric Particles at Mauna Loa Observatory, Hawaii

Until recently, there existed no long continuous record of concentrations of

elements on particles at a site remote from local activities despite demonstration of

2 the enormous value of the long-term CO seasonal variations and long term increase.

Fortunately, since mid-1979, the National Oceanic and Atmospheric Agency (NOAA) has

supported weekly collections of filters at MLO and analysis of them by our group

using INAA. Results of analysis of the MLO samples through 1982 were discussed in

last year's Progress Report. Since Jan. 1983, we have continued to collect samples

on a weekly basis, but analysis of the samples was interrupted because of eruptions

from Kilauea and Mauna Loa volcanoes off and on since that time. As discussed below, we have instead analyzed samples of the volcanic material. Recently, we have again

begun to analyze MLO samples taken since Jan. 1983.

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3. Composition of Emissions from Volcanoes

To interpret compositions of particles collected at MLO and other remote sites, we must know compositions of particles released by various natural source is volcanic

emissions, which have been heavily investigated by this group for several years.

This year we have focused attention on the Hawaiin volcanoes, Kilauea and Mauna Loa.

Kilauea erupted in Jan. 1983 and has continued to erupt at various times since

then. Emissions from the initial eruptivie phase were inadvertently collected at the

MLO sampling station (see Sect. 2) and analyzed by INAA at the NBS reactor, revealing

unusually large concentrations of Se, As, In, Au, and S, as expected for volcanic

2 emissions. In a paper published in Science Zoller et al . noted that strikingly

large concentrations of Ir were also observed. As Ir enrichments have not previously

been observed in volcanic emissions, the results suggest that Kilauea is part of an unusual volcanic system which may be fed by magmas from the earth's mantle. The Ir

enrichment appears to be linked with the high F content of the volcanic gases,

3 suggesting its release as IrF^. Previous workers observed huge Ir enrichments at

the Cretaceous-Tertiary (K-T) boundary layer in sediments, v*iich they suggest arose

from the impact of a very large meteorite. The results obtained from Kilauea suggest

that volcanic emissions of this type might provide an alternate explanation.

Samples were subsequently taken much closer to the volcano to obtain much

greater masses of volcanic material and analyzed these samples at the NBS and Los

Alamos reactors. The results confirm and extend the results obtained from the MLO

M samples. A paper concerning these results has been submitted for publication.

Mauna Loa volcano began erupting on 24 March 1984. Members of our group began

collecting samples on 27 March and continued sampling, both with airplanes and on the

ground until 15 April. The samples are being analyzed by INAA at the NBS and Los

Alamos Reactors.

4. South Pole Aerosol

As a part of the study of particles in global circulation, particles have been

collected from the very pristine atmosphere of the South Pole since 1971 (e.g. Ref.

5). During the past year, G. Tuncel completed analysis of the samples collected

there since 1977. Results for some of the elements observed were given in last

year's Progress Report.

Most analyses of South Pole samples were done by INAA. However, chemical

separations were used on some South Pole samples to observe Ir, which is present in

-4 3 extremely small concentrations, typically 10 pg/m of air. On the basis of

5 concentrations of several metals at the South Pole, Cunningham and Zoller estimated

the total influx of meteoritic material to the earth's atmosphere. However, Ir is a

114
NON-RRD PROGRAMS

much more sensitive indicator of meteorltic material than most other metals. The

estimated yearly infall rate of extra-terrestrial material based on Tuncel's Ir

measurements is 27 » 000 tons/yr, which is in the range of estimates based on a wide

range of other methods. Because the South Pole atmosphere receives very small inputs

of material from terrestrial sources, even the minute amounts of material from extraterrestrial sources can account for non-negligible fractions of the observed

concentrations of several elements, especially H% of the Mn, 6% of Fe and ^2% of Co.

The work is included in the thesis of G. Tuncel and is being prepared for

submission to journals.

5. Composition of Particles from Polluted Cities

The Asia dust transported to MLO in Hawaii in large amounts each spring (see

Sect. 1) often has composition quite unlike that of soils from other parts of the

world (e.g. high oonoentraion of Ag). We now have evidence that the dust, which

originates from dust storms In China, picks up contaminants as it passes over the

populated and industrial areas of Asia. As a start to identifying sources of these

oontaminants, we obtained fifteen air filter samples collected in Beijing, China by

T. Novakova's group in Berkeley and previously analyzed by x-ray fluorescence (XRF)

by them. D. Hermann and Ilhan Olmez subjected them to INAA to obtain data for

additional elements.

Results for a number of elements are listed in Table 1 where, for oomparason,

we have listed concentrations of the same elements in the Washington, D.C. area

7 obtained from previous studies by our group that involved use of the NBS reactor.

Beijing has one of the highest particulate loadings of any city in the world. For

many elements, the average concentrations are about an order-of-magnitude greater

than in Washington, D.C. These very high concentrations are caused mainly be two sources. First, during the Spring season, when the Beijing samples were collected,

huge dust storms to the west of Beijing bring great masses of airborne dust to the

city and beyond to the Pacific. Second, most cooking and heating is done with coal

with essentially no pollution controls. Both sources contribute strongly to the

atmospheric concentrations of many crustal elements: Al, K, Ca, Sc, Ti, Mn, Fe, Co,

Ba, La and Sm . Coal is enriched in a number of trace elements, which are

preferentially released to the air (relative to lithophile elements, which mostly

remain in the ash), accounting for the high concentrations of Zn, As, Se and Sb.

Although coal combustion is a major source of airborne sulfate in the U.S., the S

concentration is not much greater in Beijing than in Washington. There are at least

reasons for this. First, the Washington samples were collected in late summer, when

conversion rates of SOp released hundreds of km upwind and slowly converted to

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Table 1. Comparisons of Particle-Borne Atmospheric Concentrations in Beijing, PRC

and Washington, DC area.

Element Concentration Beiging Washington, D.C,

Na yg/m^ 2.0 +_ 0.2 0.30 +^ 02

Al Hg/m^ 12 ^ 0.9 1 .35 ± 0.11

S Mg/m^ 5.2 ^^ 0.7 3.2 _+ O.M

K wg/n? 6.9;!^ 1.8 0.40 j]^ 0.02

Ca yg/m^ 15 j^ 1.5 0.86 j»^ O.OM

Sc ng/m^ 3.J^ 1 0.3^ 0.33 1 0.03

Ti pg/m^ 1.1 jl^ 0.09 0.11 j^ 0.01

V ng/m^ 20 ji^ 7 25 j|^ 2

Cr ng/m^ 70 j|^ 8 U j^ 2

Mn ng/m^ 270 jt^ 25 26 ^ 3

Fe yg/m-^ 6.7 j|^ 0.6 1.0 j^ 0.06

Co ng/m^ 7.3:11 1.0 0.83^^0.08

Ni ng/m^ 29 j^ M 17^2

Cu ng/m^ 48 Ji 19 17 ^ 2

Zn ng/m^ 490 jt^ 70 85 j^ 6

As ng/m^ 42 jii 7 3.25 ji 0.2

. Se ng/m^ 14 j^ 2 2.5 ^ 0.2

Br ng/m^ 38 jii 6 136 j|i 9

Sb ng/m^ 10 J^ 2 2.1 +_ 0.2

Ba ng/m^ 170 j^ 14 19 J^ 2

La ng/m^ 17 j|: 2 1 -5 i 0.1

Sm ng/m^ 2.0^^0.3 0.20ji0.02

W ng/m^ 3.4 j|i 0.7 0.24 +_ 0.02

Pb ng/m^ 250 + 50 440 + 20

Beijing data from this work, Washington, D.C. data Ref. 7. Uncertainties

are standard deviations of the mean values.

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NON-RRD PROGRAMS

sulfate during transit. Possibly Beijing does not have such large SOp sources to the

west.

Despite the high loading of the Beijing atmosphere, some concentrations are

comparable to or less than those in Washington. Vanadium and Ni in Washington arise

from oil combustion in power plants, vrtiereas China has few oil-fired plants Lead and

Br in Washington arise from combustion of leaded gasoline, v*iereas Beijing has few,

if any vehicles that run on leaded gasoline.

6. Size Distribution of Resuspended Particles Bearing Various Elements

Much of the suspended particulate matter in the atmosphere is wind-entrained soil.

Because of the importance of this component, we need to know its composition rather

well to interpret airborne particle compositions. C. M. Thompson designed and built

a chamber for the resuspension of dried, sieved, soil samples and collection of

separate size fractions of the particles. Soils from several areas were resuspended,

and the various size groups analyzed by INAA at the NBS reactor. The soils under

investigation were collected from MLO, two places in China and in Laurel, MD

.

Results were reported in Dr. Thompson's Ph.D. thesis.

7. Shanandoah Valley Samples

A major environmental problem of our time is acid deposition. To control acid

deposition in an optimal way, we must identify sources of acid precursors, find out

how they are transported and deposited and how they are chemically converted to

acids. In work supported by EPA, we are trying to identify elements borne by

atmospheric particles that can serve as characteristic signatures of certain types of

sources or areas of the country. S. Tuncel and I. Olmez subjected samples collected

by EPA to analysis by INAA. Shaw and Paur collected samples for 15 months at rural

o sites in Kentucky, Indiana and Ohio and Stevens e t a

1

. for three weeks in the

9 Shenandoah Valley. They collected particles in two size fractions, greater and less

than 2.5-ym diam and analyzed them by x-ray fluorescence (XRF). Th^e XRF method is

rapid, highly automated technique for analyzing large numbers o^ samples, but it

mainly observes major elements. INAA is more expensive and time-consuming than XRF,

but yields data for many trace elements that are potentially useful tracers e.g. Se,

As, Sb, In. The combined XRF and INAA results yield data for about 40 elements. We

have analyzed fine particles, as they provide much more information about sources

than large particles, which are dominated by local soil. Back-trajectories for air

masses sampled during each period were calculated by J. Parrington using a model and

meterological data from NOAA to identify areas over which the air was transported in

order to see if the compositions of particles from different areas have

characteristic signatures.

The Shenandoah work is complete and was recently published. A major result of the

^ 117
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work was the observation of a regional sulfate component which carries with it small

amounts of Se, Mn, V, Zn, As, Sb, In and Pb. The amounts of Se and Mn are great

enough that, even in the midst of eastern cities such as Boston and Washington,

appreciable amounts of the airborne concentrations of these elements come into the area with regional sulfate. The Se borne by regional sulfate undoubtedly originates

from major sources of SO^ gas, especially coal-fired power plants. At present we do

not know if most of the other elements also arise from coal-fired plants.

Over 200 samples from the Ohio River Valley Study have been analyzed by INAA. We

are now interpreting the data in an attempt to answer some of the questions noted

above, including those raised by the much smaller data set from Shenandoah.

8. Philadelphia Samples

During the summer of 1982, EPA sponsored detailed studies of the sources of

atmospheric particles in the atmosphere of Philadephia. Particles were collected at

three ambient sampling sites in that area for one month using dichotomous samplers,

which collect particles with diam above and below 2.5 ym separately. EPA personnel

analyzed all of the samples by XRF and sent the fine fractions here for their

analysis of INAA. I. Olmez and A. Sheffield analyzed these samples and have

submitted the results to EPA. We are not reporting the results here, as EPA may use

the combined data sets in a "blind", round-robin test of receptor models used for

various research groups. Samples were also collected by John Cooper et al. of NEA,

1

1

Inc. from seven important sources of particles in the Philadelphia area: a coalfired power plant, two oil-fired plants, a refinery, an incinerator, and Al plant,

and an Sb roaster. They were subjected to XRF at NEA, Inc. and then sent here for

INAA. Three sets of fine and coarse samples from each source were analyzed by Olmez

and Sheffield, and the results are being prepared for Joint publication by NEA, EPA

and our group.

9. Deep Creek Lake Samples

During the summer of 1983, EPA, DOE and EPRI and their contractors collected ambient

samples at a site near Deep Creek Lake, MD and in stacks and plumes of several coalfired plants upwind of the site. These samples have been subjected to XRF in other

laboratories and are being analyzed by INAA by our group.

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1. I. Olmez and G. E. Gordon, Rare Earths: Atmospheric Signatures for Oil-Fired

Power Plants and Refineries, Science (in press, 1985).

2. W. H. Zoller, J. R. Parrington and J. M. Phelan Kotra, Iridium Enrichment in

Airborne Particles from Kilauea Volcano, Science 222 , 1118 (1983).

3. L. W. Alvarez, W. Alvarez, F. Asaro and H. V. Michel, Science 208 , 1095 (1980).

H. I. Olmez, D. L. Finnegan and W. H. Zoller, Iridium Emissions from Kilauea

Volcano, submitted to J. Geophys. Res.

5. W. C. Cunningham and W. H. Zoller, J. Aerosol Sci. 2£, 367 (1981).

6. G. Tuncel, Trace Elements at the South Pole Atmosphere: Temporal Variations and

Sources, Ph.D. thesis,, Dept. of Chemistry, Univ. of Maryland, College Park, MD,

1985.

7. G. S. Kowalczyk, G. E. Gordon and S. W. Rheingrover, Environ. Sci. Technol. 2^,

79 (1982).

8. R. C. Shaw, Jr. and R. J. Paur, Atmos. Environ. r7_, 2031 (1983).

9. R. K. Stevens, T. G. Dzubay, C. W. Lewis and R. W. Shaw, Jr., Atmos. Environ. Jj.*

261 (198^).

10. S. G. Tuncel, I. Olmez, J. R. Parrington, G. E. Gordon and R. K. Stevens,

Environ. Sci. Technol. Jji' ^29 (1985).

11. J. E. Howes, J. A. Cooper and J. E. Houck, Sampling and Analysis to Determine

Source Signatures in the Philadelphia Area, Report to EPA, 1985.

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CHARACTERIZATION OF THE NBSR AT 20MW

D. A. Becker

(Center for Analytical Chemistry)

and

T. Williamson

(University of Virginia)

and

N. Bickford

Recently, the National Bureau of Standards nuclear reactor (NBSR) was upgraded

to 20MW (thermal). With the higher neutron flux densities and modification of one of

the pneumatic tube irradiation facilities, an extensive recharacterization extended

1 the previous work on the NBSR , and several new techniques were developed which

simplified data accumulation and resulted in better information about these

facilities.

Described below are techniques used to measure the following parameters:

thermal neutron flux density; flux density variations within an irradiation volume;

relative fast neutron flux densities; temperatures generated by different sample

matrices in various irradiation facilities; and pressures generated in sealed

containers by radiolytic decomposition. Also included are some of the results

obtained for the NBSR, and for two University reactors used by NBS personnel during

the NBSR shutdown period.

1 . Neutron Flux Density Measurements

For this work, neutron flux density measurements were made using the thin foil

technique, in which the measurement is made with minimum disturbance of the

surrounding neutron environment. The foils used were 0.95 cm (3/8 inch) diameter

iron foils, with a thickness of 0.0028 cm (0.0011 inch). One to six foils were used

per measurement, depending on the flux density expected. Each foil weighs

approximately 17 mg. Thermal neutron data was obtained using the nuclear reaction

58 59

Fe (n, gamma) Fe

with the 1.292 Mev gamma-ray of iron-59 used for calculations. Using the same foil,

the fast neutron flux density can be measured with the nuclear reaction

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NON-RRD PROGRAMS

^ Fe (n, p) Mn

and the 0.835 Mev peak of manganese-54 . Since the halflives of both isotopes are

relatively long, the foils can be counted at almost any time up to about six months

after irradiation. In some cases, fast neutrons were measured with nickel foils

using the more sensitive Ni-58 (n, p) Co-58 nuclear reaction.

The technique used for the flux density measurements was as follows: foils

were placed in the appropriate position(s) in the irradiation container, held tightly

in position with polyethylene foam packing material; the container was irradiated in

the appropriate facility; the foil(s) were then removed and counted on a calibrated

semiconductor detector and pulse height analysis system. If the detector is

calibrated for absolute counting efficiency using a standard radioactive source, and

the appropriate corrections made, the absolute neutron flux density can be

calculated. This had been done for the original characterization. However, current

data has been calculated based on the NBSR RT-4 flux density at 10 MW being equal to

ippei

2,3

13-2-1 1 1.30 X 10 n/cm s . This value was that obtained originally using copper foils , and was later verified by others using a variety of measurement materials

Selected NBSR irradiation facilities currently available and the thermal

neutron flux density of each are found in table 1. Also included in the table are

values obtained for the University of Maryland and the University of Virginia nuclear

reactors. Table 2 contains data on the relative thermal-to-fast neutron flux

densities for these reactors.

The relative numbers of fast neutrons shown in table 2 are based on the NBSR

RT-4 facility being equal to 1.00, with all others compared to that value. All of

these foils were counted on the same detector using the identical geometry. It

should be noted that for the accurate comparison between foils counted by different

people, intercalibrated detectors or absolutely calibrated detectors must be used.

Additional flux density measurements were made in RT-5 with iron and nickel

foils to determine the thermal and fast flux densities, respectively. The RT-5

pneumatic tube terminal is in the vicinity of the graphite thermal column, and the

flux density in this facility is affected by the position of a boral curtain. The

thermal flux density with the curtain open is shown in table 1. With the curtain

down, the flux densities were measured with an eight day exposure. The values

7 -2-1

obtained from this are 8 x 10 n.cm s for the thermal neutron fluence rate and 2 x

5 -2-1

10 n.cm s for the fast neutron fluence rate. The fast neutron value was

121
NON-RRD PROGRAMS

Table 1. Thermal Neutron Data.

Reactor Facility

Maximum

Flux Density' Location

NBSR

NBSR

NBSR

NBSR

NBSR

Pneumatic tube RT-1

Pneumatic tube RT-3

Pneumatic tube RT-4

Pneumatic tube RT-5

Vertical tube G-2

7.7

10.3

2.7

0.032

18.0

Proximal end

Proximal end

Proximal end

Bottom

Core gap

U. of Md. Pneumatic tube 0.29 Top end

U. of Va.

U. of Va.

U. of Va.

Pneumatic tube

Hydraulic tube

"Hot" tube°

0.99

0.97

0.17

Top end

Top end

Bottom end

a ,^13 -2 -1

X 10 n. cm s Location of maximum flux density inside the irradiation container; for horizontal

tubes, proximal end is that end nearest the reactor core center.

c Boral shielded facility.

RT-e

CRAPHITE •

: THERMAL < •COLUMN '

D,0

RT-I

/, FUCLCO^V

*> COM CAP

y/.>.'.77;

mm

m

VCKTICAL

THIMBU

vv VVvv. Z^^

AKEA

,/LOWO»,;x,

VrOCLED V,

/REGION «««O /.

TANK

WALL

X

D,0

RT-»

RT-4

Figure 1. NBSR irradiation facilities at 20 MW.

122
NON-RRD PROGRAMS

Table 2. Fast Neutron Data

Facility

Relative

Reactor Thermal/ Fast Ratio

Power Bottom/ Proximal

a

Distal

Relative No. of

Fast Neutrons

NBSR RT-1 10 MW

20 MW^

i|9.1, 48. i^ 242, 269

84.3 122

27.2

NBSR RT-2

NBSR RT-3

NBSR RT-4

NBSR RT-5

NBSR G-2

10 MW

20 MW

10 MW

20 MW

10 MW

20 MW

10 MW

20 MW

8.1, 8.0 7.5 — REMOVED -—

103, 101

96

1203, 1200

1257

1.5 X 10^

64.

5^*

155, 158

1860

593

49.3

100

1.00

1.86

259

U. of Md.

- P. Tube 200 kW 5.2 51

U. of Va.

- P. Tube

- Hyd. Tube

- «!Hr>M» Hot" Tube

2 MW

2 MW

2 MW

14.3

16.7

0.55

64

5^

284

For the various irradiation facilities identified in column 1 ; relative values are

for Fe-59 activity/ Mn-54 activity taken from a single count.

(Note: Bottom refers to vertical irradiation facilities; proximal and distal refer

to horizontal irradiation facilities, the proximal end being that end nearest the

reactor core center.)

Based on RT-4 = 1 .00

RT-1 incore terminal moved during power upgrade.

At core gap centerline.

Boral shielded facility.

123
NON-RRD PROGRAMS

calculated from the measured Co-58 activity using a fission spectrum averaged cross section (0.107 b). Since the boral curtain should have little effect on the fast

neutrons, this fast neutron flux density value should also be valid for the curtain

open case. The RT-5 measurements described above were made with the thermal column cavity

empty. When a large cadmium absorber (700 g) was placed in the cavity and iron foils

irradiated, the cadmium absorber caused an 18 percent reduction in the thermal flux

density in the RT-5 irradiation container.

2. Neutron Flux Density Variations

Variations in flux density as a function of irradiation volumes can be a very

significant source of error in neutron activation analysis. Many reactors with

vertical irradiation facilities have side-to-side differences which are difficult to

compensate for or eliminate. The primary irradiation facilities in the NBSR have

horizontal in-core terminals, which minimizes side-to-side variations but introduces

a horizontal dropoff factor (figure 1). Fortunately, the horizontal factor can be

easily corrected, by careful sample/standard positioning, by an appropriate

correction factor, or by reversing the irradiation container at a predetermined time

during the irradiation period.

The NBSR horizontal and circumferential flux density variations were thoroughly

evaluated for the original reactor power lever , and would not be expected to change

significantly for the higher power lever (except for RT-1 , which had the in-core

5 terminal modified) (figure 1). These original measurements were confirmed at 20 MW . In RT-1, which was relocated prior to 20MW operation, the horizontal thermal flux

density dropoff was found to be still linear, with a maximum value of 28 percent over

the irradiation container (rabbit) length. The fast neutron dropoff as determined by

Ni-58 activation was 52 percent. The circumferential flux variation of less than +_ 1 percent for RT-3 was also confirmed, with a maximum side-to-side variation of 1.7

percent over the 2.5 cm inside diameter (figure 2).

3. Temperature Measurements

Many reactor irradiation facilities have limitations for time and sample

quantities, due in part to the sample temperatures generated during irradiation. In

particular, the irradiation of heavy elements such as lead, and of strong neutron

absorbers such as cadmium and boron nitride cause concern on the part of reactor

operators. For the NBSR, the temperatures developed in various sample matrices were

12A
NON-RRD PROGRAMS

measured using commercially available irreversible temperature indicating labels. A

portion of these labels turns black when a specific temperature is reached or

exceeded. These labels have been found to be very useful for evaluating the gamma

and/or neutron heating of various materials when irradiated in a nuclear reactor. By

use of a series of these labels on a sample, or a single label containing multiple

temperature indicators, the maximum temperature "seen" by a sample can be readily

determined.

Initial tests were made with small quantities of materials irradiated for short

times, gradually working up to maximum values. Measurements were made on some "typical" materials and some "worst case" materials. These included high purity

fused silica, lead, iron, nickel, cadmium, boron nitride, quartz ampoules filled with

various materials, and polyethylene. Maximum temperatures allowed in pneumatic tube

facilities usually were 125 degrees C(257 degrees F) due to use of linear

polyethylene rabbits and polyethylene packing and containment materials. It was

found that the indicated temperatures were very reproducible, and not affected by

1 Pi —

p

several hours irradiation to a neutron fluence of 1 x 10 n.cm Typical results using these labels revealed that: the NBSR RT-1 facility (7.7

1 3 X 10 ) could irradiate 12.9 grams of solid fused silica with no temperature problem,

1 3 while in RT-3 (10.3 x 10 ) 5.6 grams of silica became too hot in five minutes; the

RT-3 tube could be used with 25 grams of boron nitride for only 6 seconds; and the

1 3 RT-4 tube (2.7 x 10 ) could irradiate 4.9 grams of lead to equilibrium and keep

below 125 degrees C.

In addition to the temperature measurements described above, a second set of

temperature measurements were made in the pneumatic tube facilities RT-1, RT-3 and

RT-M at 20 MW by inserting samples of graphite, polyethylene and lead into the

reactor and measuring the sample temperatures with a thermocouple immediately upon

removal. Each temperature sensing sample was machined to a right circular cylinder

10 mm in diameter and 20 mm long. A 3 mm hole was drilled along the cylindrical axis

to the center so that a thermocouple probe could be inserted. Each cylinder was held

in place in the polyethylene rabbit with polyethylene foam packing. A rabbit

containing a temperature sensing cylinder was irradiated, immediately opened, a thermocouple inserted and the temperature noted. Typically, temperature readings

were made within 30 seconds of removal from the reactor core, and the observed

temperature would rise to a maximum value before decreasing to room temperature. The

maximum temperature was recorded. In cases where the temperature exceeded about 80

degrees C, the maximum temperature would be reached very quickly and the temperature

125
NON-RRD PROGRAMS

i . e

. e

. A

.4

. 2

e

.2

. e

1 . e

I

i;

f

I

w

Figure 2. Ciroumferentlal neutron flux density distribution in NBS RT-3 (Note; error bars represent counting statistics).

1000-1

2 4 6 8 10 12 14 16 18 20

Time in Reactor (min)

Figure 3. Temperature factors versus irradiation time,

126
NON-RRD PROGRAMS

would then decrease rapidly. This indicates that, at these higher temperatures, the

rate of heat loss upon removal from the core is too rapid to be able to obtain an

accurate maximum temperature by this technique. To evaluate the true maximum

temperature for one of these samples, temperature indicating stickers as described at

the beginning of this section were fastened to the graphite thermocouple sample, and

irradiated for 10 minutes in RT-3. The sensors indicated a maximum temperature

between 95 and 110 degrees C. The thermocouple reading for this sample was 90

degrees C, which indicates that for this sample the true maximum temperature was

somewhere between 5 and 20 percent higher than the measured thermocouple maximum.

The data obtained from the thermocouple measurements was also used to examine

relationships between the heating rates of the different materials. If the dominant

heating mechanism during reactor irradiation is gamma heating, then the heat transfer

rate should be proportional to the mass energy absorption coefficient and to the

sample mass. The heat transfer rate is also proportional to the temperature,

differential. The data plotted in figure 3 are the temperature differential

(measured sample temperature minus room ambient temperature) divided by the sample

mass (g) and the gamma-ray mass energy absorption coefficient versus reactor

irradiation time. The energy absorption coefficient at 600 kev, the nominal energy

of fission gamma-rays, was used.

The data in figure 3 appear to agree quite well for different sample materials

for an individual pneumatic tube irradiation facility. It must be cautioned,

however, that these points represent measurements made only on right circular

cylinders packed firmly in polyethylene foam. Other geometrical forms with different

surface to volume ratios and other types of packing may substantially alter the heat

transfer characteristics.

The data in figure 3 also indicate that sample temperature equilibrium is

reached after approximately 10 minutes in the reactor. This agrees well with the

data obtained using the temperature labels, which showed equilibrium reached between

10 and 20 minutes irradiaton in the pneumatic tubes for all samples measured to date.

4. Pressure Measurements

In the original characterization effort, pressure buildup in sealed samples due

to radiolytic decomposition was determined qualitatively using a pressure inflating

device . Some later measurements were made with a manometer, estimating the

increased pressures and then trying to calculate back to the pressure inside the

ampoule.

127
NON-RRD PROGRAMS

Calibrated Expansion Cylinder

A /^ / Quartz Ampoule

\

Plunger

¥=

<-^r-7-

Rupture Chamber Specimen

Figure 4. Pressure measurement system.

Manometer.

3

J

k.

XA

4 . e

3 . s

3 . e

1 . s

e 1 3 4 s <& 0<<^8 <cc>

"^^^P" 7

Figure 5. Plot of gaseous products versus sample weight times neutron fluence, for

SRM Tomato Leaves in NBSR RT-3.

128
NON-RRD PROGRAMS

For this recharacterization work, a new system was developed which permits the

accurate determination of pressures developed inside sealed quartz and polyethylene

5 containers. This system is described in greater detail elsewhere , but will be

discussed briefly here. This device utilizes a calibrated expansion cylinder in

conjunction with a manometer (figure U) . The cylinder is used to bring the system

pressure (after rupture of the irradiated container) back to pre-rupture system

pressure (_= 1 atmosphere). Thus, the gas produced by irradiation (i.e., excess

pressure) can be read directly from the increased volume of the calibrated cylinder.

This occurs because the pressure of the system before and after the measurement is

the same, 1 atmosphere, and the "dead" volume of the system is the same, and cancels

out of the calculation. The result is that the equation for calculating pressure in

the quartz ampoule (or sealed polyethylene container) is considerably simplified, and

requires only the volume of the irradiated ampoule, corrected for the true sample

volume, and the increased system volume after expansion back to ono atmosphere

pressure (as read off of the expansion cylinder).

Some results of this test can be seen in figure 5. Three samples of SRM 1573f

Tomato Leaves, were irradiated for various times in the NBSR RT-3 pneumatic tube

facility. It is apparent that for this facility the amount of gas produced is

directly proportional to the sample weight times the neutron fluence. Additional

data indicates that gas production from other irradiation facilities does not fit

this same straight line, but apparently depends on the specific characteristics of

each irradition facility.

5. Conclusion

Techniques have been developed to characterize the NBSR irradiation facilities

for parameters important to neutron activation analysis and other purposes, and to

understanding optimum safe irradiation conditions for these reactor facilities. It

is hoped that the techniques reported here will be found useful in the

characterization of other irradiation facilities and nuclear reactors as well.

1. Becker, D. A. and LaFleur, P. D., J. Radioanalytical Chem. Jl_9, 149 (1974).

2. Fleming, R. F., Private Communication.

3. McElroy, W. N., Kellogg, L. S., and Matsumoto, W Y., NBS Technical Note 714, p

58, U.S. Dept. of Commerce (1972).

129
NON-RRD PROGRAMS

H. Becker, D. A., in NBS Reactor; Summary of Activities , NBS Technical Note 758,

U.S. Dept. of Commerce, Washington, DC (1973).

5. Becker, D. A., J. Radioanalytical and Nuclear Chemistry, (in press).

SUMMARY OF REACTOR RELATED ACTIVITIES CARRIED OUT BY THE NEUTRON FIELD

STANDARDS GROUP

D. Gilliam, J. Grundl, G. P. Lamaze and E. McGarry

(Center for Radiation Research)

The Neutron Field Standards 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 detector calibrations, neutron dosimetry

standardization, and reaction rate cross-section measurements. These activities are closely associated with similar international efforts. A component of the CRR makes

use of the NBS Research Reactor thermal column and tangential beam tubes where

facilities, designed and built by the Neutron Field Standards Group, are in

operation. Included with this report is a revision of the Facilities' summary table:

"Characteristics of NBS Neutron Sources and Fields For Detector Calibrations and

Reaction Cross Section Measurements".

The following paragraphs report on recent activity progress.

1 . Distribution of Neutron Fluence Standards

The cavity fission source was in operation before the long shutdown for the

production of neutron fluence standards for reactor pressure vessel dosimetry and

related programs. Eight species of fluence standards have been produced to date for

materials neutron dosimetry applications: In(n,n'), Ni-58 (n,p), Fe-5M(n,p),

Ti(n,p), Rh(n,n'), Al(n,a), U-238(n,f). Fission neutron fluences certified for these

14 2 standards are, in the range 0.7 to 60 x 10 neutrons/cm . Arrangements are in progress with CBNM, Geel, to convert NBS SRM-U0002, highly

depleted uranium, to a pressed encapsulated pellet to be used as a U-238 fluence

standard. This detector when used in conjunction with a natural uranium sample makes

a so-called "paired uranium detector" (PUD). The use of PUD's allows the separation

of the responses of U-235 and U-238 in power reactor environments.

Neutron fluence standards have also been provided to benchmark the neutron

fields of the experimental rooms at the Armed Forces Radiobiological Research

Institute (AFRRI). The reactions employed were Np(n,f), U-238(n,f), In-1 15(n,n' )

,

Fe-5i<(n,p), Ni-58(n,p), Mg-24(n,a), Al-127(n,a), and Fe-56(n,p). Additionally,

members of the neutron fields standards group made measurements at AFRRI with NBS

fission chambers which have been calibrated at the NBS reactor.

130
NON-RRD PROGRAMS

2, Improvements In Fluenoe Measurements In the NBS Cavity Fission Source

International intercallbration of standard neutron fields Is Important for

establishing absolute aoouracies of neutron fluenoes and reaction rates, A fluenoe

transfer via the Pu(n,f) reaction was made from Cf-252 to the SCK/CEN, MOL, Belgium

cavity fission source CU-235wq, ] and then to the NBS cavity fission source. The

diameter of the MOL cavity (in the BR1 Reactor, Mol, Belgium) is larger (1m) than

that of the NBS cavity, resulting in a smaller correction for reflected neutrons. It

also has a large cylindrical U-235 fission source which allows an active fission

chamber to be placed at the center of the field. The following describes the salient

features of the NBS cavity fission source and the fluence transfer procedure which

resulted in an overall reduction in the uncertainties of fluence measurements at NBSt

The U.S. standard U-235 fission neutron spectrum at the National Bureau of

Standards In Galthersburg, Maryland, operates In the center of a 30-cm diameter

spherical cavity located in the graphite thermal column of the NBS Research Reactor.

The facility is frequently called the Cavity Fission Source (CFS). The upper view in

figure 1 shows, in detail, the CFS assembly containing neutron sensors and the lower

view shows its location within the thermal column cavity. Two disks of U-235 metal

(I6mm dla x 0.13 mm thick) are placed above and below a cylindrical cadmium pill box

0.076cm thick, which encloses approximately six passive neutron sensors (nominally

1.27cm diameter x 0.025cm thick). The neutron sensors to be Irradiated are held in

the center of the assembly by light-weight aluminum pieces.

10 2 Fission fluence rates of "2 x 10 n/cm 'S are obtained between the U-235

source disks at a separation distance of one centimeter. Applications include

detector calibrations for reactor dosimetry and fission cross section measurements.

The absolute source strength, and therefore the fluence rate, of the CFS is

dependent upon reactor power level. Consequently, a fluence monitor that is

independenty calibrated is required for each irradiation. Both the 70.8-day Ni58(n,p)Co-58 reaction and the 4.5-hr In-1 1 5(n,n' ) In-1 1 5m reaction together with a fission-chamber or a power level monitor have been used. The CFS fluence is tied

through these monitors back to known Cf-252 fission neutron fields.

In the fluence transfer technique, a neutron sensor response is measured first

in a standard neutron field and then in the field to be calibrated. For example,

transfer from a Cf-252 standard neutron field to the NBS U-235 CFS has been

accomplished by the In-1 1 5(n,n' ) In-1 1 5m reaction. Foils of known purity are

irradiated to a certified fluence in the californium field. The indium foils are then analyzed with a radioactivity detector having a reproducible geometry. The

131
NON-RRD PROGRAMS

i R —2 —1 —1

factor 'Cf/ Cf (ircm per counts«s 'gm ) is thereby established for the neutron

sensor. Here R could refer to any reproducible response such as counting rate,

reaction rate, or fission rate in the field of interest.

The same indium neutron sensor, or a different indium sensor with a known mass,

is then exposed to a certified fluence in the U-235 field and the desired fluence,

({)^_^ is given by:

235,, R-. "235,, ~ TlH) "'

235y

The spectrum-averaged, cross-section-ratio term on the extreme right of Eq.(1) is

more accurately known than the cross sections themselves because errors in the scalar

magnitudes are eliminated by the division. For the In-1 15(n,n' )In-1 15m reaction, the

cross section ratio has been calculated to be 1.0^8 +_ 1.655, using ENDF/B-V

differential cross section data and the NBS evaluations of the Cf-252 and U-235

fission spectra. However, different analytical forms of the U-235 spectrum give

calculated ratios which are as small as 1.015. The experimental value for the ratio

3 is 1.031 ^2.\%. to circumvent this uncertainty in the fluence transfer process,

the Pu-239(n,f) reaction has replaced In(n,n') for fluence transfer based upon new

3 experiments performed at a U-235 cavity fission source in Mol, Belgium. For Pu-239,

the spectrum-averaged cross section ratio is 1.003 j^ 0.25S, with only a 0.35^

uncertainty resulting from different descriptions of this spectra.

3. Fluence Transfer Through the Belgian U-235 Fission Spectrum

Figure 2 shows the U-235 cavity fission source assembly at the SCK/CEN

Laboratory, Mol, Belgium. This assembly incorporated a 100-cm dia. cavity as opposed to the 30-cm dia. cavity for the NBS U-235 field. The significance of the

large cavity is that there are substantially fewer low-energy (wall returned)

neutrons in the Belgian field. Also, the larger source permits exposure of high

quality, light-weight Pu-239 deposits in an NBS fission chamber. This chamber cannot

be used in the smaller volume NBS Cavity Fission Source.

Figure 3 depicts the present and former (indium-"only" ) fluence transfer

procedures from the NBS Cf-252 fission spectrum. With the exception of differences

in the scattering corrections in the Belgian and NBS U-235 fields, their energy

spectra are identical. Therefore, details of the cross section of the reaction

chosen as the transfer instrument do not matter (see Eq.3 at bottom of figure 3).

Scattering differences in the two fields require a net adjustment of almost 4/6;

however, this correction has been calculated to + \.k%.

132
NON-RRD PROGRAMS

NBS CAVITY FISSION SOURCE

*"u SOURCES

OCTECTOR STACK

CADMIUM ENCLOSURE

Figure 1. The NBS Cavity Fission Source

Belgian (SCK/CEN) ^^^U Fission Spectrum

Field in BR1 Reactor Thermal Column

Additiona Access Plug j Access Tube

1 Meter DIam.

Spherical Cavity

Removable

Fissionable Source Removable and

Adaptable Thimble

(O.D. < 5.4 cm)

t

t t f t Driving Thermal Neutrons From BR1 Core

Figure 2

.

133
NON-RRD PROGRAMS

Table 1.

Summary Of Uncertainties In Fluence

Transfer IVIeasurements

• For Transfer From NBS 252cf Field to Belgian 235u Field

Source of Uncertainty Contribution (%)

Source Strength of 252cf 0.9 252cf.Source to 239pu. Deposit Distance 0.6

Statistics of Fission Counting 0.1

Precision of 2n Fission Counting Corrections 0.4 239pu Cross-Section Ratio in 252cf Field and 235u pield 0.1

Scattering Corrections for 239pu in 252cf Field 0,7

Wall Return Corrections in Belgian 235u Field 0.6

Scattering Corrections for 239pu |n Belgian 235y pjeicj 0.1

Total Uncertainty in Fluence Transfer = 1.5%

(Contributions Taken in Quadrature)

Table 2.

Summary Of Uncertainties In Fluence

Transfer Measurements

• For Transfer From Belgian to NBS ^^Sy Field

Source of Uncertainty Contribution (%)

For li5|n(n, n') For 58Ni

0.4

(n, P)

Statistics of Gamma Counting 0.2

Scattering + Wall Return in Belgian 235u

Field 1.1 1.7

Scattering + Wall Return in NBS 235u

Field 0.8 0.8

Fluence-Rate Gradient in NBS 235u Field 0.4 0.4

Total Uncertainty in Fluence Transfer = 2.1% 2.5%

134
NON-RRD PROGRAMS

Present and Former Procedures for

Calibration Of The Neutron Fleunce Rate In The NBS 235u Cavity Fission Source

NBS-1:Ra-Be (^ n) Neutron Source With a Calibrated Source Strength

252cf Spontaneous

Fission Sources

Produce Fields With Known Fission Neutron Fluence

NBS Fission Chamber

With 239pu

Deposit

Irradiate to Obtain a

Fission- To-Fluence

Ratio

252cf Fission Neutron Field

Irradiate Foil: Obtain a Count-To-Fluence ^ Ratio lor "^In (n.n) "^"'In Reaction

Indium Foil &

Fixed Geometry

Counter

Fluence Transfer by ^^PulSee £q. ml

NicKel and

Indium Foils &

Fixed Geometry

Counter

Irradiate Foils. Obtain Count To Fluence —^ Ratios ot ^—^

5«N, m.pi seco «

"5/n in.ni "^'"In Reactions

Belgian 235u Fission Neutron

Field

(In IMeter Dia. Cavity)

Fluence Transfer by ' '^In Only /See Eg 121]

Fluence Transfer by ' '^In and ^l^i ISee Eg. 131 and Eg I4)l

NBS Cavity Fission Source

235u Fission Neutron

Field

(In 30-cm Dia, Cavity)

0SCK/CEN

U-235 0c

FPu-239

cf

pPu.239 ru.235

—Pu-239 Oct — Pu-239

<-' U-235

(1)

Old^NBS

!^ U-235 0<

Rln-115

cf R

ln-115 U-235

-ln-115 Oct

U-235

(2)

New^NBS

U-235

0SCK/CEN'

U-235 RNi-58

U-235 (SCK) • R

Ni-58 U-235 (NBS) (3)

New _, NBS

fc3 U-235

0SCK/CEN

U-235 Rln-115

U-235 (SCK)

ln-115 U-235 (NBS)

(4)

Figure 3.

135
NON-RRD PROGRAMS

0.6%

0.4% - o

lD

*-» CO ccco

o

CO

<D CCc

CD. o

o

CL

0.2%

-0.2%

—0.4%

\

V ii5|n (n, n') ii5m|n

\

-/

Monte Carlo Results for Scattering and Removal

Effects From Neighbor Neutron Sensors In the

NBS 235U Cavity Fission Source. Results are Given In Terms of Foil Separation Distance. Foil Thicknesses In Calculation Were 0.254mm. Data

Have Been Fit by Equations of the Form:

Y = —a + p exp (—dx).

Note: X = is the Self-Scattering Effect. A Positive "Y"

Value Indicates That Inscatter is Greater Than Rennoval, and

That Activities are Higher Than They Would be in a Free-Field Fission Spectrum.

58Ni (n, p)58Co

27AI (n,Q!)24Na

_l i I L. I I I I I I I I 5 10 15

Magnitude of Foil Separation Distance in iVIillimeters

Figure 4.

_i I 20

Tables 1 and 2 summarize the transfer process. The total uncertainties for

In(n,n') and for Ni-58(n,p) are the uncertainties of Table 1 and 2 taken in

quadrature. Respectively, these are 2.05^ and 2.35^.

4. Neutron Scattering and Removal Effects

Corrections must be made for effects of neutron scattering and removal because

of the variety of materials in close proximity to each neutron sensor undergoing

irradiation in a cavity fission source. For example, there are cadmium, aluminum in

support structures, uranium in the fission disks, and various elements in other

dosimeters. The corrections are a complex function of the cross sections (or

thresholds) of the dosimetry reactions as well as the position of a particular sensor relative to all other materials. The present corrections for the NBS CFS are based

upon rather extensive Monte Carlo calculations of indium, nickel and aluminum

dosimeters in a detailed model of the cavity fission source. The results are

summarized in figure H.

136
NON-RRD PROGRAMS

1. Compendium of Benchmark and Test Region Neutron Fields for Pressure Vessel

Irradiation Surveillance; Standard Neutron Spectra. NRC NUREG/CR-0551 , Progress

Report—July-Sept. 1978 (Dec. 1978).

2. "Neutron Fluence and Cross Section Measurements for Fast Neutron Dosimetry," G.

P. Lamaze, D. M. Gilliam, E. D. McGarry, NBS, Gaithersburg, Maryland; A. Fabry,

SCK/CEN Laboratory, Mol, Belgium; Proc . of Int'l. Conf. Nucl. Meth. and Environ,

and Energy Res., San Juan, PR (April 1984) Conf-8il0408

3. "Cross Section Measurements in the U-235 Fission Spectrum Neutron Field," D. M.

Gilliam, J. A. Grundl, G. P. Lamaze, C. M. Eisenhauer, NBS, Gaithersburg,

Maryland; A. Fabry, SCK/CEN Laboratory, Mol, Belgium. Proc. Fifth ASTM/EURATOM

Symposium on Reactor Dosimetry, Geesthacht, W. Germany (Sept. 1984). To be

published.

4. "The Mol Cavity Fission Spectrum Standard Neutron Field and Its Applications," A.

Fabry, G. Minsart, F. Cops, and S. DeLeeuw; Proc. Fourth ASTM/EURATOM Symposium

on Reactor Dosimetry, Washington, DC (March 1982).

137
NON-RRD PROGRAMS

NEUTRON DRIVEN GAMMA RAY FIELD

G. Lamaze, E. Boswell, J. Grundl, D. Gilliam, D. Blackburn

(Center for Radiation Research)

and

T. Williamson

(University of Virginia, Charlottesville, VA)

A neutron driven gamma ray field, similar to one in operation at SCK/CEN Mol,

Belgium, has been constructed to operate in the NBSR thermal column cavity. The

system consists of an extruded cadmium cylinder one mm thick and 55 mm diameter. In

the thermal column cavity, the cadmium is exposed to a thermal neutron fluence rate

2

of 3 E 1 1 n/cm s. Since the cadmium is essentially black to thermal neutrons, a

2 cadmium capture gamma ray fluence rate of about 2 E 11 photons/cm s is produced at

the center of the cylinder. This corresponds to a dose rate of close to a megarad/hr. The gamma ray field strength is determined by two methods: exposing

gold foils on the cadmium surface, and by measuring the induced Cd-115 activity.

These measurements provide an estimate of the neutron reaction rate in the cadmium

from which a gamma ray source strength may be derived. The gamma ray dose or fluence

on the axis of the cylinder is obtained from a simple geometry calculation.

As shown in figure 1, the cadmium cylinder can be enclosed in a 64 ram sheath of

lithium -6 loaded glass to determine the background of gamma rays from the core and

from neutron capture in the surrounding graphite. An iron cylinder, which fits

around the lithium glass, has been made to provide an alternate source of iron

capture gamma rays in known geometry.

First application of the neutron driven gamma ray field is a measurement of

photofission rates in U-238, Th-232, and Np-237 and photon activation rates in

indium. A typical traverse along the axis of the cadmium cylinder taken in the

course of these measurements with a U-238 fission chamber is shown in figure 2. The

photofission due to the background gamma fluence is presently estimated to 7% of that

from the cadmium source and fission from fast neutron leakage from the reactor to be

2% of the cadmium photofission rate.

The thermal neutron fluence rate in the center of the cavity without the gamma

2

)urce in place is 2.7 E 11 n/cm s as measured with

cadmium ratio with the cadmium cylinder in place is 8000,

2

ray source in place is 2.7 E 11 n/cm s as measured with thin gold foils. The gold

138
NON-RRD PROGRAMS

Graphite Cavity

fi<<^ifi^i$.!fifififiiiSSSSS^<^<^i^:-^i'^^

Lj-Glass

Cadmium

Figure 1. Assembly sketch of Neutron Driven Gamma-Ray Source (NDGS) as shown is placed in the NBSR thermal column cavity.

The assembly

1000

100-

Q.o

Cadmium Source

Cadmium Enclosed

in Lithium Glass

Boral Curtain Closed

•)1_J I I I I 1 L- 2 4 6 8 10 12

Distance From End of Cylinder (in)

Figure 2. Fission rate transverses taken along the axis of the axis of the NDGS with

a U-238 fission chamber.

139
NON-RRD PROGRAMS

EXPERIMENTAL MICRODOSIMETRY

Robert B. Schwartz

(Center for Radiation Research)

Introduction

In the previous progress report, we discussed preliminary measurements made at

the IHH keV beam with our tissue-equivalent proportional counter ("TEPC"). These

measurements have been repeated with lower noise electronics to allow us to extend

the measurements to lower energy, and measurements were also made at the 24 and the Z keV beams. Results are given in the form of y vs. yD(y) plots. The ^H^ keV results

are in good agreement with calculated spectra, cmu with other measurements. The 24

keV measurement is internally consistent, but we have no other results with which to

compare it. The 2 keV results are interesting, but their interpretation is a bit

uncertain and there are no other published measurements or calculations for

comparison.

1

.

Data Analysis

Computer programs have been written in BASIC to take the pulse height analyzer

data (counts per channel) and calculate lineal energy (y), the absorbed dose

distribution (D(y)), and the product of y times D(y).

2. Experimental Notes

We have continued to use the Far West Technology LET-1/2 tissue equivalent

proportional counter, with an equivalent diameter of one micron of tissue. The data

at the filtered beams were taken on an (ancient!) Northern Scientific analyzer, sent

to an HP 85 computer and stored on a tape cassette. The analysis programs (for

computing the centroid position of the alpha particle calibration peak, and for

extracting microdosimetric information from the pulse height data) were also run on the HP 85. The results were printed out on an HP 82905B printer. We do not as yet

have any plotting programs for the HP, so the results were plotted by hand. This

system is usable, if slightly inelegant.

In previous measurements of the Californium-252 microdosimetric spectrum, we

noted that electronic noise was a limitation at lineal energies below about 1 keV/ym.

To reduce the noise, the voltage on the counter was increased from 500 v. to 620 v. This increased the gas gain by about a factor of five. It would also have overloaded the amplifier, but we dropped the gain of the pre-amp (ORTEC 142 PC) by about

a factor of five by adding a 1 pf feedback capacitor. We thus have approximately the

140
NON-RRD PROGRAMS

same size pulses going into the main amplifier as before, but we can now get down to

about 0.15 keV/ym before noise becomes a problem.

3. Microdosimetric Spectra - General

In each neutron field the microdosimetric spectra were taken in three separate

runs, with different amplifier gain settings, to cover the lineal energy range from

0.15 keV/ym to 160 keV/ym. The different point shapes in figs. 2, 4, and 6 indicate

where data from the different runs were used for plotting. There was sufficient

over-lap among the runs to assure that the different runs did, indeed, match up

satisfactorily. At the highest amplifier gain setting at each beam (covering the

range from 0.15 keV/ym), noise and background were explicitly subtracted. This gave

corrections of from ^% to ^0% at 0.2 keV/ym, decreasing with increasing lineal

energy.

H. 144 keV Results

The fluence spectrum for the 144 keV beam is shown in figure 1. The data are taken from the proton recoil measurements of McGarry and Heimbach. Note that in this

type of plot (known as a "lethargy" plot) equal areas under the curve correspond to

equal fluences, in much the same way as equal areas under the yD(y) vs. y curve

correspond to equal doses The 144 keV beam fluence has a (barely visible) 1 1/2?

impurity at 54 keV, but no high energy impurities. Since the fluence-to-kerma factor

at 54 keV is about half of that at 144 keV, we do not expect to see any effect of the

54 keV neutrons The energy spread in the beam is about 25 keV FWHM, so there are a significant number of neutrons in the beam with energies up to about 1 60 keV.

The microdosimetric spectrum is shown in figure 2. This spectrum is in good

agreement with Coyne's calculated spectrum, and also in good agreement with the

measurements of Alberts et al. of PTB, presented at the Hamburg meeting. In

particular, the small rise at about 0.2 keV/ym (presumably due to gamma events) was also seen by the PTB group.

5. 24 keV Results

The 24 keV beam is slightly more complicated than the 144 keV beam, with small

contaminations at 74, 135, 280, and 36O keV neutron energies. (See figure 3-) From

previous proton recoil proportional counter measurements, we know the relative

fluence in each of these neutron groups, and, using fluence-to-kerma conversion

141
NON-RRD PROGRAMS

factors, we can calculate the relative dose from the high energy contaminants. This

is shown in the following table:

ENERGY % OF FLUENCE KERMA FACTOR REL. DOSE

2

(keV) (rad'cm ) 24 97.0 2.35 2.275

74 0.23 5.13 .012

135 1.6 8.175 .131

280 1.0 12.1 .121

360 .16 13.8 .022

3.0 .286

That is, the high energy contaminants amount to 3.15^ of the 24 keV fluence, but

(.286/2.275) x 100 = 1356 of the 24 keV dose.

Figure 4 shows the microdosimetric spectrum of the 24 keV beam. The main peak

at about 15 keV/pm is clearly due to the 24 keV neutrons, while the events extending

above about 25 keV/pm must be due to the higher energy contaminants. From this

spectrum we find that the area above 25 keV/pm is 15^ of the area between 1 and 25

keV keV/pm, in good agreement with the above calculation. We are not aware of any

published calculations or other measurements of this spectrum.

Comparing figure 3 with figure 4 shows how the use of the TEPC is a very

sensitive way of seeing relatively small doses from high energy neutrons in the

presence of much larger low energy doses.

6. 2 keV Results

The 2 keV fluence spectrum is shown in figure 5, and the microdosimetric

spectrum in figure 6. (We had trouble getting reproducible data below ~ 0.4 keV/pm.)

The results in this case are not so easy to interpret as those for the 24 keV beam.

The peak at ~ 0.9 keV/pm is, presumably, due to recoil protons from the 2 keV

neutrons.

In the case of the 2 keV beam, as with the 24 keV beam, there are higher energy

components, extending from 7 to 40 keV, and amounting to about 3% in fluence. From

the previously measured intensities of these higher energy neutrons, we calculate

142
NON-RRD PROGRAMS

6.0

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H 3.5 Z3 3.0

rr

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o

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1.0

0.5

Figure 1. 14^1 keV Fluence spectrum

0.1 0.2 0.5 1.0 2 5 10 20 50 100 200

y (keV/^m)

Figure 2. 144 keV Microdosimetric spectrur

143
NON-RRD PROGRAMS

30 40 50 100

En (keV)

200 300

Figure 3. 24 keV Fluence spectrum

0.1 0.2 0.5 1.0 2 5 10 20 50 100 200

y (keV//im)

Figure ^. 2H keV Microdosimetric spectr um

1A4
NON-RRD PROGRAMS

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20 30 40 50

Figure 5. 2 keV Fluence spectrum

0.1 0.2 0.5 1.0 2 5 10 20 50 100 200

y (keV//um)

Figure 6. 2 keV Microdosimetric spectrum

145
NON-RRD PROGRAMS

that the dose from the high energy groups is about 30/J of that from the 2 keV

neutrons. These neutrons may be responsible for the small "bump" at about 6 keV/ym.

The only source that we can think of for the main peak at ~ 70 keV/pm are the

600 keV protons from the N(n,p) reaction. The kerma factor for the N(n,p) reaction

at 2 keV is, however, only ~ 256 of that for the proton recoil reaction. We thus do

not now have any quantitative explanation for the shape of this spectrum.

146
C. Reactor Operations and Services

REACTOR OPERATIONS AND SERVICES

On April 3. 1985, the NBS reactor achieved a major milestone, reaching a new high power level of 20 MW, double the power level of the past 16 years. The

increased power will greatly enhance the capabilities of the reactor. The upgrade to

20 MW required extensive modifications that resulted in a shutdown of almost 8

months. The shutdown period was also used for planned major improvements and

repairs.

1

.

Reactor Operations

As a consequence of the power upgrade, the reactor was operated on a curtailed

schedule for most of the year except the last three months when it was operated on a regular round-the-clock schedule. A summary of the operating statistics for the

period July 1, 198^1 to June 30, 1985 is presented in the following table:

No. of days at 10 MW 33

No. of days at 10 - 20 MW 13

No of days at 20 MW 67

On-line time at 20 MW 75/5

Average U-235 burnup 65/5

No. of Irradiations 1500

Hours of Irradiations 1500

Hours per Irradiation 1.0

2. Irradiation Services

Extensive irradiation services were provided to many users from within and

outside NBS. Even though the reactor was operated for less than ^ months, more than

1200 irradiations were performed which is 8055 of that for the entire previous year.

3. Engineering Services

In addition to normal engineering and design services provided to reactor

operations, experimenters and users, the engineering staff was involved in a comprehensive program of reactor modernization.

A shim arm test assembly is nearing completion which will be used for testing

shim arm mechanisms and will be available for spare parts for the reactor shim arm mechanisms.

The regulating rod has been modified and the absorber section was fabricated

for 20 MW operation. The addition of an electric braking technique has eliminated

147
REACTOR OPERATIONS AND SERVICES

slippage of the regulating rod. An additional motor was added to the regulating rod

to provide additional torque and along with the dynamic brake, allows more flexible

tolerances resulting in consistent up and down regulating rod travel times.

Twenty-three fuel element assemblies have been inspected and accepted from the

DOE contractor by the NBSR engineering staff. An additional 52 fuel assemblies have

been fabricated and are awaiting acceptance. There are 864 compacts made and ready

for rolling into fuel plates.

For 20 MW operation many changes and improvements were made in the system. The

check valves in the process room were removed to elements maintenance in a high

radiation area and increase reliability of the system. The check valves at the pump

discharges were removed and the diaphragm valves made to perform the check valve

function. All of the pump impellers were changed from 12 3/8 to 13 inch diameter and

along with new 125 HP motors have increased flow output. A fourth pump and motor was added to the system.

Two new primary system ion exchange columns were installed along with

additional piping since the two old existing columns were left in position so that

radioactive decay could reduce the activitiy before removal.

The thermal shield supply and return lines were replaced and are visible unlike

the old lines which leaked inside the biological shielding. The new lines have

reduced the thermal shield leakage considerably.

A new pneumatic tube for RT-1 was installed along with P lines to provide

cooling and neutron moderator to the samples in the tube top.

The heat exchanger HE-1A was cleaned and unless it was pressurized it was discovered that 15 tubes of the 1170 U-tubes had leaks or suspected of having leaks.

The tubes were plugged and the heat exchanger returned to service. The second heat

exchanger HE-IB was also fixed into the system.

The instrumentation-electronics group of the Reactor Engineering Section

continued on with the modernization of the reactor instrumentation in the control

room.

In preparation for the increase of reactor power from ten to twenty megawatts

operation, additional instruments were installed in the process system along with

modernizing of the transmitters, meters and recorders. With human engineering in

mind an effort was made to relocate the primary cooling process instruments into

flow, temperature and level zones, thus enabling improved recognition time of the

process variables.

148
REACTOR OPERATIONS AND SERVICES

Meters monitoring the secondary cooling variables were condensed and also zoned

into an area one-third of their original console space.

Two wide scale radiation monitoring chart recorders were replaced with one

programmable chart recorder. An example of convenience using the new recorder

switches; a radiation channel can be immediately monitored during a calibration

check.

Four delta pressure transmitters with associated flow elements, lines and

wiring were installed for monitoring the main heat exchangers HE1A and B, (2) primary

outlet and (2) secondary inlet flows. Each transmitting signals to the control room

console on recorders and meters respectively.

Four other process flow transmitters were replaced with new transmitters, the

two reactor outlets, outer and inner plenum flows. They were also relocated in a lower radiation area of the process room to reduce radiation exposure to personnel

while performing required technical specifications testing.

The primary inlet temperature controlling recorder and integrally associated

controller were replaced by new separate recorder and programmable controller with

the capability of manual operation with the controller removed from the console.

A cabinet for housing 14 new RFI protected temperature transmitters with 9 temperature transmitters activated. Two are new channels: the heat exchanger HE1B

primary outlet and the secondary outlet temperature.

Four 4-way (energize to open) solenoid valves and four differential pressure

switches were installed on the main pump discharge valves for automatic valve control

in the process room. The valves may be remotely operated automatically or manually

via 3-way switches from the control room. An annunciator monitors the air reserve

tank for low pressure.

The final wiring is completed for the fourth main primary flow pump magnetic

starter, lock out, interlocks and remote control switch.

The reactor building tritium monitor is being replaced in stages. The

preamplifier via special shielded cable to the electrometer in the control room is

being checked out. A second tritium electrometer system to control room is pJannsd.

149
D. Service Programs

THE FOOD AND DRUG ADMINISTRATION'S

NEUTRON ACTIVATION FACILITY

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. Neutron activation analysis

complements the other analytical techniques used at FDA and serves as a reference

technique for quality assurance practices.

During the past year hundreds of gamma-ray spectra from previous work on FDA

1 Adult Total Diet Studies food composites were re-examined to obtain additional

analytical information and generate a detection limit table. Detection limits were

listed for twelve main food groups and for the elements generally determined in

foods. The tables can be used to provide a guideline of instrumental NAA (INAA)

capabilities for food analyses and will enable FDA analytical scientists to

accurately predict whether INAA would be applicable to specific projects.

The detection limit listing is of practical use for two reasons. First, these

detection limits are not theoretical but are generated from experimental data.

Interferences are accounted for realistically since the limits arise from actual food

matrix spectra. Second, the values are based on a sizable data base. The spectra

used have been generated during analyses of an entire year's collection of FDA Adult

Total Diet Studies samples.

A need for improved capabilities for As, Cr , Mo, Sb and Se resulted in the

application of radiochemical neutron activation analysis (RNAA) to the determination

of these elements in foods. Work on this project continued this year with hydrated

manganese dioxide (HMD) inorganic chromatographic resin. The trace elements are

effectively removed from the interfering elements, mainly Br, K, Na and P, which are present in food matricies. A post-irradiation digestion is used in this procedure

along with a chromatographic separation. Accuracy and precision were verified by

analyzing SRM's; several foods were also analyzed. This RNAA procedure increases

FDA's analytical capabilities for these trace elements in foods and provides a reference technique for other procedures.

1. Cunningham, W. C. and Stroube, W. B., Jr., The Science of the Total Environment,

(submitted for publication).

150
SERVICE PROGRAMS

PREPARATION OF F-18 LABELED RADIOTRACERS USING NBS REACTOR-PRODUCED F-1

8

W. C. Eckelman, M. Channing, and J. Bennett

(National Institutes of Health, Clinical Center, Bethesda, MD)

6 ]H F-18 is produced by irradiating 0.4g enriched LipCO_ for 2 hours at 1 . 1 x 10

2

n/crn /sec. The quartz ampule is then returned to NIH for processing in a semiautomatic processing facility. The quartz ampule is cracked and Li„CO_ is mixed

with cation exchange resin in water. The aqueous solution is transferred to a round

bottom flask containing base and carrier fluoride. The water is evaporated and

acetonitile is added. The acetonitile is evaporated and the process is repeated

twice again. The substrate is then added to the fluoride. To date, two substrates

have been used: (1) methyl 4, 6-0-benzylidene 2,3-cyclic sulf ate-B-D-Mannopyranoside--a precursor to 2-f luoro-2-deoxy glucose, and (2) the 6-triflate

derivative of naltrexone. Both are produced in 605S radiochemical yield.

1. C. B. Pert, J. A. Danks, M. A. Channing, W. C. Eckelmann, S. M. Larson, J. M.

1

8

Bennett, T. R. Burke, Jr. and K. C. Rice, "3-[ F] Acetylcyclofoxy : A Useful

Probe for the Visualization of Opiate Receptors in Living Animals," FEBS 2001.

177, 2 (19811)

2. M. A. Channing, W. C. Eckelmann, J. M. Bennett, T. R. Burke, Jr. and K. C. Rice,

1 ft "Radiosynthesis of [ F] 3- Acetylcyclofoxy

Int. J. Appl. Radiat. Isot. (to be published)

1 ft "Radiosynthesis of [ F] 3- Acetylcyclofoxy : A High Affinity Opiate Antagonist,"

PRODUCTION OF F-18 ON LOW FLUX REACTORS

M. S. Neuder, M. C. Channing, S. M. Larson

(National Institutes of Health, Clinical Center, Bethesda, MD)

and

R. F. Fleming

(Center for Analytical Chemistry)

The production of F-18 in oxygen-containing lithium compounds, such as Li CO , enriched to 95.56% in Li-6, occurs by the neutron irradiation of Li-6 in the reaction

Li(n,a) H; 0( H,n) . When irradiating at fluxes of about 10 n/cm /sec,

obtaining the maximum yield of F-18 per gram of lithium is important, and can be

accomplished by insuring a high degree of surface area-to-volume ratio. From a theoretical standpoint, this would minimize self-shielding and flux depression

contributions to overall sample yields. These contributions can, in fact, be

^ 151
SERVICE PROGRAMS

separately analyzed by performing the following experiment. Quartz tubes varying in

diameter from 1 to ^ mm id, and containing lithium carbonate are irradiated

individually in an evacuated spherical cavity. The cavity, about 12 inches in

diameter and contained in graphite, has the advantage that a fairly uniform flux

distribution will exist in the region of an absorber whose dimensions are small in

comparison with the mean free path in the surrounding medium. Additionally, the flux

depression which would normally be present at the surface of a tube irradiated in a given medium, would be considered negligible in the cavity. Rather, a depression is

created in the vicinity of the cavity, i.e. the graphite. In effect, then, only a self-shielding contribution to the overall F-18 yields will be measured. The flux

depression contribution to F-18 yields can subsequently be determined by irradiating

in the graphite region surrounding the cavity. In this case, sample self-shielding

and flux depression at the tube surface will exist. The difference in the

empirically-derived self-shielding measurements, obtained at each location, is then a direct measure of the flux depression existing at the sample surface. Irradiations

conducted in other areas of the reactor facility will permit the degree to which the

flux depression contributes to overall F-18 experimental yields to be assessed.

Additionally, reactivity comparisons can be made among othe suitable lithium

compounds once these self-shielding and flux depressin contributins are accounted for

in F-18 yields.

1. R. F. Fleming. _Int. J. Appl . Radiat . Isot . 33, 1263, (1982).

2. K. M. Case, F. DeHoffmann, and G. Placzek. Introduction to Theory of Neutron

Diffusion , Vol. 1 (LANL, Los Alamos, 1953).

3. M. S Neuder, W. C. Eckelman, M. C. Channing, and S. M. Larson, "The Production of

F-18 on Low Flux Reactors," Poster Exhibit, The Society of Nuclear Medicine, 32nd

Annual Meeting, 1985.

152
E. Personnel Roster

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153
PERSONNEL ROSTER

NON-RRD NBS STAFF LOCATED AT REACTOR

Division 35^

D

.

Brown

C. Campbell

P. Cassidy

I. Jensen

F. Moore

J. Shubiak

J. Wang

Division 532

E. Boswell

C. Eisenhauer

D. Gilliam

J. A. Grundl

G. Lamaze

E. McGarry

I. Schroder

R. Schwartz

Division 551

D. Becker

S. Carpenter

G. Downing

R. Fleming

J. Langland

R. Lindstrom

G. Lutz

J. Maki

B . Norman

S. Stone

R. Zeisler

GUEST WORKERS AND COLLABORATORS

Division 40

J. Cahn

Division 401

J. Slabaugh

Division 420

F. Brickman

J. Blendell

B. Burton

B. Coblenz

T. Coyle

S. Frieman

K. Frase

E. Fuller

K. Hardman-Rhyne

G. Olson

C. Robbins

R. Roth

B. Steiner

Division 430

R. Fields

Division 440

B. Bauer

T. Davis

C. Han

C. Chiang

R. Water strat

W. Wu

Division 450

F. Biancanello

J. Early

R. Reno

R. Shaefer

R. Shull

Division 520

G. Greene

E. Kessler

Division 522

R. Dove

Division 532

A. Wasson

154
PERSONNEL ROSTER

Division 533

R. Placious

Division 5M1

R. Cavanagh

R. Kelly

T. Madey

Division 5^3

A. Wlodawer

I. Weber

Division 544

D. Tsai

Division 552

S. Wise

L. Sander

Division 553

H. Rook

Division 725

J. Ehrstein

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. Asbery

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 Gallery of Art

B. Miller

C. Parkhurst

National Institutes of Health

J. Bennett

M. Channing

D. Davies

B. Dunn

W. Eckelman

R. Frank

A. Katki

C

.

Lowe

A. Maxwell

M. Neuder

R. Nossal

H. Savage

Naval Research Laboratory

D. Edelstein

A. Ehrlich

K. Grabowski

A. Iman

N. Koon

L. Pecora

L. Richards

Naval Surface Weapons Center

J. Cullen

M. Spano

155
PERSONNEL ROSTER

Smithsonian Institution

R. Bishop

M. Blackman

T. Chase

Y. Cheng

J. Mishara

E. Myers

J. Olin

R. Wright

L. Zacherman

Argonne National Laboratory

S. Susman

Battelle Laboratories

L. Brackenbush

F. Brauer

G. Endres

R. Holiman

W. Nicholson

R. Sanders

Chalmers Institute of Technology

L. Sjolin

C.N.R.S. Grenoble, France

C. Chaillout

D. Gignoux

M. Marezio

J. Soubeyroux

G. Zaccai

Institut Laue-Langevin

Grenoble, France

J. Bouillot

A. Magerl

P. Mangin

R. Pynn

Institute of Nuclear Sciences

R. Drascovic

KFA JUlich, Germany

R. Hempleman

D. Richter

M. Stueppler

Los Alamos National Laboratory

R. Robinson

Max-Planck Institute

R. Huber

J. Walter

E. Lukacevic

Sandia National Laboratory

J. Schirber

J. Harris

Nuclear Energy Center,

Mol, Belgium

A. Fabry

Oak Ridge National Laboratory

F. Kam

Alfred University

S. Kim

R. Snyder

Cambridge University (U.K)

J. Horton

G. Squire

Georgetown University

H. Mallek

Iowa State University

R. Shelton

Kyoto University (Japan)

H. Hasegawa

T. Hashimoto

Q. Trancong

Michigan State University

E. Case

Y. Fan

S. Solin

156
PERSONNEL ROSTER

M.I.T.

B. Averbach

R. Coble

S. Chen

J. Didiskein

M. Green

B. Wuensch

Northwestern University

H. Calderon

S. Kim

J. Weertman

Oregon State Graduate School

P. Davis

Purdue University

J. Furdyna

T. Glebultowlcz

A. Overhanser

Rutgers University

M. Greenblatt

San Jose State University

A. Ling

State University of New York

H. Herman

R. Shanker

Tel Aviv University (Israel)

A. Voronel

University of Alabama

J. Segrest

University of Antwerp (Belgium)

K. Michel

University of California (San Diego)

J. Arnold

K. Nishiizuml

University of California

(Santa Barbara)

J. Fint

C. Levi

P. Lombrozo

G. Odette

University of Illinois

s. Hardcas'cle

D. Heumann

M. Salaraon

S. Slnha

University of Maryland

D. Anderson

I. Anderson

A. Bates

S. Faller

A. Fiesel

G. Gordon

F. Guenther

M. Han

D. Herman

J. Hoff

M. Kltto

S. Krueger

Q. Li

J. Lynn

C. LeCompte

L. McCarthy

I. Olmez

J. Ondov

J. Robertson

A. Sheffield

P. Sheridan

C. Thompson

G. Tuncel

S. Tuncel

w. Waters

w. Zoller

157
PERSONNEL ROSTER

University of Massachusetts

R. Stein

M. Shibayama

V. Soni

H. Yang

University of Michigan

D. Vincent

University of Milan (Italy)

M. Zocchi

University of Minnesota

V. Garry

T. Lodge

University of Missouri

W. Ching

W. James

T. Little

S. Werner

University of Munster

F. Kemper

University of Notre Dame

R. Ricker

University of Pennsylvania

J. Calem

T. Lutz

Carnegie-Mellon University

E. Boltich

M. Chisholm

W. Wallace

University of Rhode Island

D. Andrauskas

S. Hasanain

S. Pickart

University of Southern California

E. Amis

University of Vermont

T. Flanagan

University of Virginia

T. Williamson

University of Washington

K. Mottet

University of Wisconsin

S. Cooper

D. Ruber

M. Landry

J. Miller

H. Spehard

H. Yu

Aerospace Corporation

R . Bowman

J. Knudsen

Baker Chemical Company

R. Ganapathy

Amoco

J. Laduk

C. Marshall

Alcoa Technical Center

C. Jensen

R. Rioja

Allied Corporation

G. Fish

A. Maeland

Atmoic Energy of Canada, LTD

W. Lennard

158
PERSONNEL ROSTER

Bell Laboratories

F. Bates

R. Cava

H. Chen

J. Mitchell

D. Murphy

J

.

Reme i ka

J. Riley

Bell-Northern Research Ltd.

F. Shepherd

W. Vandevorst

Directed Technologies, Inc.

N. Chesser

Dow Chemical Company

C. Crowder

Eastmand Kodak

T. Houssain

E. I. DuPont de Nemours Co.

J. Imbelzzno

G. Stucky

Exxon

D. Lohse

J. Gethner

R. Busch

General Electric Co.

C. Austin

R. Bonnan

R. Darlia

L. Provo

W. R. Grace

M. Wax

R. Wormsbecker

Genex Corporation

R. Salemme

GTE Laboratories

D. Oblas

G. Hamill

IBM (San Jose)

G. Hadziioannou

IBM (Yorktown Heights)

M. Schaefer

R. Gambino

Intel Corporation

N. Cox

S. Singhal

3M Research Laboratory

A. Siedle

Motorola, Inc.

S. Wilson

Rockwell International

M. Brown

B. Titmann

Southerwest Research Institute

R. Page

Union Carbide Corporation

P. Leung

Westinghouse-Hanford Corp.

W. McElroy

J. Rawlins

159
F. Publications

COLLABORATIVE PROGRAMS

AMMON, H. L., ZHANG D. CHOI, C. S., SlNDiJSg 0„ MARCHAND, A. P., and SURI, S. C,

"6,6,8-TrinitropentacyGlo[5.3.0.0 '^.O^'^.O ' ]decane, C.^H^O.", Acta Cryst.

CH±, ^04-406 (1985). 10 y b

BEECH, F., CATLOW, C. R. A., SANTOR, A., and STEELE, B. C. H., "Structural and

Electrical Studies of the Defect Pysochlore Materials Pb, M_0 (M=Ta, Nb)",

Solid State Ionics (in press).

BEECK, F., CATLOW, C. R. A., SANTORO, A., and STEELS, B. C. H., "Neutron Diffraction

and A/C Conductivity Study, Solid State Ionics (in press).

BENHAM, M. J., ROSS, D. K., LARTIGUYE, C, PERCHERON-GUEGAN, A., and ANDERSON, I. S.,

"Neutron Inelastic Scattering Study of the Effects of Hydrogen Absorption

Cycling of LANI /H", Belfast Conf. On 'Hydrogen in Metals' 1985 (in press).

BERK, N. F., MAGERL A., RUSH, J. J., ROWE, J. M., and PROVO, J. L., "Anomalous

Vibrations of Hydrogen Isotopes in 3-Phase Vanadium Hydride: A Novel, DoubleWell Potential", (Submitted to Phys. Rev. Lett.).

BERK, N. F. ans HARDMAN-RHYNE, K. A., "Characterization of Alumina Powder Using Small

Angle Scattering, I: Theory", J. Appl. Cryst. J_8 (in press).

BERK, N. F. and HANDMAN-RHYNE , K. A. "The Phase Shift and Multiple Scattering in

Small Angle Neutron Scattering: Application to Beam Broadening From Ceramics",

Physica B (in press).

BERK, N. F. and HARDMAN-RHYNE, K. A., "The Phase Shift and Multiple Scattering in

Small Angle Neutron Scattering: Application to Beam Broadening from Cermics",

Proceedings of the 1985 Santa Fe Internation Conference on Neutron Scattering , Physica B (to be published).

BOUILLOT, J, ROWE, J. M., RUSH, J. J. and LUTY, F., "Crystal Structure of Mixed

Alkali Halide-Alkali Cyanide Mixed Crystals", Bull. Am. Phys. Soc. 30_, 456

(1985).

BOUILLOT, J., COQUET, E., PANNETIER, J., and CRETTEZ, J. M. "Neutron Powder

Diffraction Studies of LlIO and (HIO •2LiI0 )", Intern. Conf. Neutron Scatt.

Santa Fe, Physica B. (in press).

CASELLA, R. C. "Nonlinearity in Weak Magnetic Fields Induced by Neutron-Ant ineutron

Oscillations in Neutron Interferometry and Spin Resonance", Phys. Rev Lett. 53

f

1033 (1984).

CAVA, R. J., and SANTORO, A., "Tarascon. The Crystal Structures of the Chevrel

Phases Li_ ^Mo.Sq and Li_ ^Mo^SCq", J. of Solid State Chem. 54, 193, 203 (1984).

3.3 DO 3.2 D O

CAVA, R. J., and SANTORO, A., "The Structure of the Lithium Inserted Metal Odide

Li- ^TiO_ (Anatase) LiTi^O,, (Spinel) and Li_Ti„0,,", J. Sol. State Chem. (in U.5n^ ^4 ii^4

press)

.

160
PUBLICATIONS

CAVAGNAT, D., MAGERL, A., VETTIER, C., ANDERSON, I. S., and TREVINO, S. F.,

"Anomalous Pressure Dependence of the Torsional Levels in Solid Nitromethane,

Phys. Rev. Lett. 54, 193 (1985).

CHOI, C. S., and PRASK, H. J., "Neutron Powder Diffraction Studies of Two Uranium0.75wt55 Titanium Alloys", J. Appl . Cryst. J8_, 141-144 (1985).

CHOI, C. S., and PRASK, H. J. "Texture of Extruded Uranium Alloy by Neutron

Diffraction", J. Appl. Cryst. (in press).

DIDISHEIM, J. J., PRINCE, E., and WUENSCH. B. J., "Neutron Rietveld Analysis of

Structural Changes in Nasicon Solid Solutions Na. Zr„Si P-j_ 0. ^" , Solid State

Ionics (m press)

.

KICK, H. A., and PRINCE, E. "A Neutron Diffraction and Electron Microscopy

Examination of 2BaBr2"BaC12", Acta Cryst., Section C (in press).

ERWIN, R. W., LYNN J. W. , RHYNE, J. J. and CHEN, H. S., "Spin Stiffness Anomaly in

the Reentrant Spin-Glass (Fe„ ^r-Ni_ „^)^ ^^.P^ ,^B^ n^Alr, r>o"» '^ - Appl. Phys. 57,

3473 (1985). ^^ ^^^ ^'^^ ° ^^ ~

FERNANDEX-BACA, J. A., LYNN, J. W., RHYNE, J. J. and FISH, G. E., "Spin Dynamics of

the Amorphous Invar alloy Fe_ q^B^ ,„", J. Appl. Phys. 57, 3545 (1985).

U . 00 U . I ^ —

ERWIN, R. W., LYNN, J. W., and MAGERL, A. "The Reentrant Spin-Glass Order Parameter

in (Fe„ o^in 7 ^7S^i fi^fi^"*"?"''^ ' l^ssnetism and Magnetic Matls. (in press).

FERNANDEZ-BACA, J. A., RHYNE, J. J., and FISH, G. E. "Neutron Scattering Study of the

Spin Dynmics of Amorphous Fe Ni^Zr ", J. Magnetism and Magnetic Matls. (in

press)

.

FERNANDEZ-BACA, J. A., LYNN, J. W., RHYNE, J. J., and FISH, G. E., "Spin Dynamics of

Amorphous Fe^ Afi^n lu"' Physica (in press).

FISHER, R. X., BAUR, W. H., SHANNON, R. D. STALEY, R. H., VIGA, A. J., ABRAMS, L.,

and PRINCE, E., "Neutron Powder Diffraction Study and Physical Characterization

of Zeolite D-Rho", J. of Phys. Chem. (in press).

GIEBULTOWICZ, T. M., and FURDYNA, J. K., "Monte Carlo Simulation of Fee Heisenberg

Antiferromagnet with Nearest and Next-Nearest-Neighbor Interactions", J. Appl.

Phys. 57, 3312 (1985).

GIEBULTOWICZ, T. M. , RHYNE, J. J., CHING, W. Y., and HUBER, D. L. "Low-Temperature

Spin Correlations and Spin Dynamics in Diluted Magnetic Semiconductors", J. Appl. Phys. 57 3415 (1986).

GIEBULTOWICZ. T. M. "Monte Carlo Simulation of Dilute MMagnetic Semiconductors for

High Concentrations of the Magnetic Component", J. Magnetism and Magnetic

Matls. (in press).

GIEBULTOWICZ, T. M., RHYNE, J. J., CHING, W. Y., HUBER, D. L. and GALAZKA, R. R.,

"Static and Dynamic Spin Correlations and Exchange Interactions in Cd Mn Te",

J. Magnetism and Magnetic Matls. (in press).

GIGNOUX, D. and RHYNE, J. J., "Spin Excitations in TbNi by Inelastic Neutron

Scattering", J. Magnetism and Magnetic Matls. (in press).

161
PUBLICATIONS

GILARDI, G. R., FLIPPEN-ANDERSON, J. L., CHOI, C. S., MARCHAND^. A^P^., and REDDY, D.

S., "Structure of 6,6, 10, 10-Tetranitropentacyclo[5.3.0.0 ' .0 ' .0 ' ] decane,

C^^HgOg", Acta Cryst. C^l , 788-791 (1985).

GLINKA, C. J., SANDER, L. C, WISE, S. A. HUNNICUTT, M. L., and LOCHMULLER, C. H.,

"Determination of Pore Accessibility in Silica Microparticles by Small Angle

Neutron Scattering", Anal. Chem. 57, 2079-2084 (1985).

GOTAAS, J. A., RHYNE, J. J., and WERNER, S. A. "Spin Density Waves in Cu-Mn", J.

Appl. Phys. 57, 3404-3406 (1985).

GOTAAS, J. A., RHYNE, J. J., WENGER, S. A., and MYDOSH, J. A., "Long-RanGe

Incommensurate Spin State in Dilute YGd Alloys", J. Magnetism and Magnetic

Matls. (in press)

.

GOTAAS, J. A. and LYNN, J. W., "Magnetic Field Dependence of the Small Angle Neutron

Scattering in HoMOgSeg", J. Manetism and Magnetic Matls. (in press).

HAN, C. C, OHADA, M., MUROGA, Y., BAUER, B. V., and TRAN-CONG, E., "Phase

Decomposition Phenomena of Polystyrene/Polyvinyl Methylether", SPE ANTEC '85

Conf. Proc. 4_3, 306 (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 Internation Conf. on Neutron Scattering , Physica B (to be published).

HARDMAN-RHYNE, K. A. and BERK, N. F., "Characterization of Alumina Powder Using

Small Angle Scattering, I: Experiment", J. Appl. Cyrst., _1_8 (in press).

HARDMAN-RHYNE, K. A. and BERK, N. F., "Characterization of Alumina Powder Using Small

Angle Neutron Scattering, II: Experiment", J. Appl. Cryst. ^8 (in press).

HARDMAN-RHYNE, K. A., ERASE, K. G. and BERK, N. F. "Applications of Multiple Small

Angle Scattering to Studies of Ceramic Processing", Physica B (in press).

HEMPLEMANN, R., RICHTER, D., ECKOLD, G, RUSH, J. J. ROWE, J. M. and MONTOYA, M.,

"Localized Hydrogen Modes in LaNi-H ", J. Less Common Metals 104 , 1-12 (1984).

HASEGAWA, H.M, HASHIMOTO, T., KAWAI, H., LODGE, T. P., AMIS, E. M., GLINKA, C. J.,

and HAN, C. C, "SANS and SAXS Studies on Molecular Conformation of a Block

Polymer in Microdomain Space", Macromolecules _1_8, 67 (198).

HIMES, V. L., MIGHELL, A. D., and STALICK, J. K., NBS Crystal Data Distribution

Package (Version of June 1985). Product of the NBS Crystal Data Center

consisting of the NBS Crystal Data Identification Field and Software

(=NBS*LATTICE) . Distributed by the JCPDS--International Centre for Diffraction

Data, 1601 Park Lane Road, Swarthmore, PA 19081.

HIMES, V. L., and MIGHELL, A. D. "NBS*LATTICE - A Program to Analyze Lattice

Relationship", NBS Tech. Note 1214, U. S. Dept. of Comm./NBS (in press).

HODEAU, J. L, MAREZIO, M., SANTORO, A., and ROTH, R. S., "Neutron Diffraction

Structure Determinnation of the High Temperature Form of Lithium Tritantalate,

H-LiTa Og", J. Solid State Chem. 5]_, 275-292 (1984).

162
PUBLICATIONS

KELLEY, R. D., CAVANAGH, R. R., RUSH, J. J., and MADEY, T. E. "Neutron Spectroscopy

Studies of the Adsorption and Decomposition of C_H_ and CJi^ on Raney Nickel",

Surf. Sci. 255., 480 (1985).

LEUNG, P. S., GODDARD, E. D., HAN, C. C, and GLINKA, C. J., "A Study of PolycationAnionlc Surfactant Systems" Colloids and Surfaces ]3_, 47-62 (1985).

LUKACEVIC, E., RUSH, J. J., and SANTORO, A., "Neutron Powder Diffraction and

Inelastic Scattering Study of the Structures of Zr^Pd, ZrpPdD. „. and Zr^

PdD, ^^", Acta Crys. (in press).

1 . yb

LUKACEVIC, E., SANTORO, A., and ROTH, R. S., "Neutron Powder Diffraction Study of

the Structure of the Molybdate of Composition Li^C.g rLa^O- :32MoO,", Solid State

Ionics (in press).

LYNN, J. W., GOTAAS, J. A., SHELTON, R. N. HORNG, H. E., and GLINKA, C. J. "Magnetic

and Superconducting Properties of Holmium-Rich (Er. Ho )Rh^B^", Phys. Rev. B 31, 5756-5767 (1985).

1 -x x

LYNN, J. W. "Helium Condensation Observed in Small Angle Neutron Scattering", Physica

(in press)

.

MAGERL, A., RUSH, J. J., and ROWE, J. M. "Local Modes in Dilute Metal Hydrogen

Alloys", Phys. Rev B (in press).

MATSUSHITA, Y., HODA, I., NAGASAWAM, M., LODGE, T. P., AMIS, E. J., and HAN, C. C,

"Expansion Factor of a Part of a Polymer Chain in a Good Solvent Measured by

Small Angle Neutron Scattering", Macromoleculs j_7, 1785 (1984).

MCDONALD, G. W., UDOVIC, T. J. DUMESIC, J, A., and LANGER, S. H. "Equilibria

Associated with Cupric Chloride Leaching of Chalcopyrite Concentrate",

Hydrometall. J_3, 125 (1984).

MCKERGOW, M. W., GILBERD, P. W., PICTON, P. J., ROSS, D. K. BLASCHKO, 0., ANDERSON,

I. S., and HAGEN, M., "Interatomic Potentials and Lattice Distortions in

PdD^ g" Belfast Conf. on ^Hydrogen in Metals' 1985 (in press).

MICHEL, K. H. and ROWE, J. M. "KCN, a Model System of Tanslation-Rotation Coupling in

Orientationally Disordered Crystals", J. Chem. Phys. 82, 199 (1985).

MICHEL, K. H. and ROWE, J. M. "Local Properties in Orientationally Disordered

Crystals with Translation-Rotation Coupling", Phys. Rev. B (in press).

MICHEL, K. H. and ROWE, J. M. "Molecular Symmetry and Translation-Rotation Coupling

in Orientatonally Disordered Crystals", Phys. Rev. B (in press).

MIGHELL, A. D. and HIMES, V. L. "Compound Identification and Characterization Using

Lattice-Formula Matching Techniques", Acta Cryst. A_ (in press).

NOSSAL, R., GLINKA, C. J., and CHEN S. H. "SANS Studies of Concentrated Protein

Solutions I.", Bovine, Serum Albumin (in press).

PICKART, S. J., HASANAIN, S., ANDRAUSKAS, D., ALPERIN, H. A., SPANO, M., and RHYNE,

J. J., "Magnetic Field Dependence of the Small Angle Scattering in Amorphous

DyCu". J. Appl. Phys. 57_. 3430 (1985).

163
PUBLICATIONS

PRINCE, E., TAKAGI, S., MATHEW, M. and BROWN, W. E., "The Structure of Dicalicum

Potassium Heptahydrogen Tetrakis Phosphate", Acta. Cryst. C ;40 1^199-1502 (1984).

PRINCE, E., and NICHOLSON, W., "The Influence of Individual Reflections on the

Precision of Parameter Estimates in Least Squares Refinement. Structure and

Statistics inn Crystallography", Ed. A. J. C. Wilson (in press).

PRINCE, E., "Precision and Accuracy in Struture Refinement by the Rietveld Method.

Structure and Statistics in Crystallograhy", Ed. A. J. C. Wilson (in press).

RHYNE, J. J., "Critica and 'Subcritical ' Magnetic States of Amorphous Rare Earth Spin

Glasses", Physica 130B , 253 (1985).

RHYNE, J. J. and FISH, G. E., "Small Angle Neutron Scattering Evidence for the

Absence of Long-Range Magnetic Order in Amorphous FeQ.ArQ", J. Appl . Phys. 57 , 3^07 (1985). ^ ^

RHYNE, J. J., "Magnetic Properties of Amorphous Metals", J. of Non-Crystalline Solids

(in press)

.

RHYNE, J. J., "Effects of Random Field Interactions in Amorphous Rare Earth Alloys",

IEEE Trans. Mag. (in press).

RHYNE, J. J., COOPER, B. R., HUBER, D. A., KOON, N. C, and O'HANDLEY, R. C. eds.

"Proc. of the Intern. Conf. on Magnetism ICM-85", J. of Magnetism and Magnetic

Materials (in press).

RHYNE, J. J. "Quenching of Long-Range Magnetic Order by Random Interactions in

Amorphous Alloys", Physica (in press).

ROWE, J. M., BOUILLOT, J., RUSH, J. J., and LUTY, F., "Structural Phase Diagram of

Mixed (KCN) (KA) Crystal", Physica B (in press).

RUSH, J. J., ROWE, J. M., and RICHTER, D., "Dynamics of Dilute H in g-Phase Palladium

Deuteride: A Novel Mass Defect", Phys. Rev. B 31, 6102 (1985).

RUSH, J. J. and ROWE, J. M. "Chemical Physics with Emphasis on Low Energy

Ecitations", Physica B (in press).

RUSH, J. J., CAVANAGH, R. R., KELLEY, 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. 1985 (in press).

SPANO, M. L. and RHYNE, J. J. "Suppression of Long-Range Order by Random Fields in

Tb^Fe^_^ Alloys", J. Appl. Phys. 57, 3303 (1985).

SPANO, M. L., ALPERIN, H. A., RHYNE, J. J., PICKART, S. J., HASANAIN, S., and

ANDRAUSKAS, D. "Applied Field Response of the Spin Glass State in Amorphous

NdFe^", J. Appl. Phys. 57, 3^32 (1985).

SPANO. M. L., and RHYNE, J. J., "Effects of Appied Fields on the Magnetic Order of

Amorphous Tb Fe,_ ", J. Magnetism and Magentic Matls. (in press).

X I X STEIN, R. S. and HAN, C. C. "Neutron Scattering from Polymers", Physics Today 38

(1985).

164
PUBLICATIONS

SHIBAYAMA, M., YANG, H., STEIN, R. S., and HAN, C. C. "Study of Miscibility and

Critical Phenomena of Deuterated Polystyrene and Hydrogenated Poly (Vingy methyl

ether) by Small Angle Neutron Scattering", Macromolecules (in press).

SHULL, R. D. SINGHAL, S. P., MOZER, B., and MAELAND, A., "Small Angle Neutron

Scattering of Metallic Glass", Proc . of the 5th Intern. Conf. on Rapidly

Quenched Metals (in press).

STOECKLI, A., FURRER, A., SCHOENENBERGER, C. H., MEIER, B. H. , ERNST, R. R. , and

ANDERSON, I. S., "Dynamics of Hydrogen Bonds in Carboxylic Acids", Physica B (in

press)

.

TSAI, D. H. and TREVINO, S. F. "Simulation of the Initiation of Detonation in an Energetic Molecular Crystal", J. Chem. Phys. 8j_, 248 (198^1).

UDOVIC, T. J., KELLEY, R. D., and MADEY, T. E., "The Methanation Activity of

W(110)", Surf. Sci. 150 , L71 (1985).

WAX, M. J., CAVANAGH, R. R. , RUSH, J. J., STUKY, G. D., ABRAMS, L., and CORBIN, D.

R., "A Neutron Scattering Study of Zerolite Rho", J. Am. Chem. Soc. (in press).

WERNER, S. A., RHYNE, J. J., and GOTAAS, J. A., "Temperature Dependence of the Spin

Density Wave Magnetism in Copper-manganese", Solid State Commun. (in press).

INDEPENDENT PROGRAMS

BECKER, D. A., "Quality Assurance Techniques for Activation Analysis", Proc. 5th

Intern. Conf. on Nuclear Methods in Environmental and Energy Res., U.S. DOE

Publ. CONF-840408, U.S. Dept. of Energy, Washington, DC (198A).

BECKER, D. A., "The Role of Reactor Characterization in NBS Quality Assurance", J.

Radioanalytical and Nucl. Chem. (in press).

BLACKMAN, M. J. "Provenience Studies of Middle Eastern Obsidian from Sites in

Highland Iran", Archaeological Chemistry III, Joseph Lambert, ed.. Am. Chem.

Soc, Washington, D.C. (198^1).

BLACKMAN, M. J., "Chemical Characteizations of Sealing Clays from Fourth Millenium

B. C. Sites in Iran", The Transations of the Am. Nucl. Soc. 49, 168-169 (1985).

BLACKMAN, M. J., "The Provenience of Obsidian Artifacts from Late Chalcolithic Levels

at Aphrodisias, Turkey", Prehistoric Aphrodisias, M. Joukowsky, ed . , Archaeologia Transatlantica, IV Louvain-la-Neuve, Institut Superieur D'rchelogie

et Histoire de L'Art Brown Univ. (1985).

BURGER, G. and SCHWARTZ, R. B., "Guidelines for the Establishment and Operation of a Secondary Standard Dosimetry Laboratory for Neutrons", IAEA Tech. Rept. Series

(to be publ.

)

DOWNING, R. G., FLEMING, R. F. , MAKI, J. T., SIMONS, D. S., and STALLARD, B. R.,

"Near-Surface and Interfacial Profiling by Neutron Depth Profiling (NDP) and

Secondary Mass Spectrometry (SIMS)", Proc. of Materials Res. Soc, Thin Films

and Interfaces II Vol. 25, J. E. Baglin, D. R. Campbell, and W. K. Chu, eds .

,

North Holland, 655-666 (1984).

165
PUBLICATIONS

DOWNING, R. G. MAKI, J. T., and FLEMING, R. F., "Application of Neutron Depth

Profiling to Microelectronic Materials Processing", Special Proc . Industrial

Ghem. Div. Session for the I87th National Meeting, Am, Chem. Soc, L. A. Casper,

ed. (in press).

EISENHAUE, C. M., HUNT, J. M., and SCHWARTZ, R. B., "Calibration Techniques for

Neutrron Personal Dosimetry", j_0. No. 1-M, 43-^7 (1985).

Gilliam, D. M., Grundl, J. A., Lamaze, G., Eisenhauer, CM., and Fabry, A., "Cross

Section Measurements in the U235 Fission Spectrum Neutron Field", Proc. of the

5th ASTM-EURATOM Symposium on Reactor Dosimetry, Geesthacht, West Germany (Oct.

1985.

GREENBERG, R. R., "Radiochemical Procedures Used for Improved Low-Level

Determinations of Critical Elements in Biological Materials, Use and Development

of Low and Medium Flux Research Reactors", Supplement to AtomkernenergieKerntechnik 44_, 659 (196M).

GREENBERG, R. R. and CARPENTER, B. S., "High Accuracy/High Precision Determination of

U-235 in Nondestructive Assay Standards by Gamma-Ray Spectrometry", Proc. Fifth

Intl. Conf. on Nuclear Methods in Environmental and Energy Research, 644 (1984).

GREENBERG,, R. R., "Multielement Analysis of NBS Coals by Instrumental Neutron

Activation Analysis, in Methods and Procedures Used at the National Bureau of

Standards to certify Sulfur in Coal SRM's for Sulfur Content, Calorific Value,

Ash Content", T. E. Gills ed., NBS Publ . 260-94, 32 (1984).

GREENBERG, R. R., FLEMING, R. F. and ZEISLER, R., "High Sensitivity Neutron

Activation Analysis of Biologicl/Environmental Standard Reference Materials",

Environ. Intern., j_0, 129-136 (1984).

in f\ GRUNDL, J. A., "Examination of B(n,He) and Li(n,He) Cross Section Measurements in

Reactor Physics Benchmarks", Proc. Intern. Conf. on Nuclear Data for Basic and

Applied Science, 1985.

JORNET, A., BLACKMAN, M. J., and OLIN, J. S., Xlllth to XVIIIth Century Ceramics from

the Paterna-Manises Area (Spain), in Ceramics and Civilization, D. Kingery, ed.,

Amcerican Ceramic Society (1985).

KINGSTON, H. M. and GREENBERG, R. R., "An Elemental Ratioing Technique for Assessing

Concentration Data from a Complex Water System", Environ. Intern. ^0_, 153

(1984).

LINDSTROM, R. M. and ANDERSON, D. L., "Analytical Neutron-Capture Gamma-Ray

Apectroscopy : Statues and Prospects, in Capture Gam, ma-Ray Spectroscopy and

Related Topics-1 984" , S. Raman, ed . , (AIP Conf. Proc. No. 125), Am. Inst.

Phys., New York, 810-819 (1985).

LINDSTROM, R. L., "Activation Analysis of Semiconductor Materials, in ACS Books" (in

press).

LUNTZ, G. J., ROOK, H. L. and LINDSTROM, R. M., "Determination for 1-129 at Natural

Levels by Thermal Neutron Activation Analysis", Journal of Trace and Microprobe

Techniques 2 (1), 33-51 (1984).

166
PUBLICATIONS

McGARRY, E. D., GILLIAM, D. M., LAMAZE, G., EISENHAUER, C. M., and FABRY, A., "The

U.S. U235 Fission Spectrum Standard Neutron Field Revisited", Proc. Fifth ASTMEURATOM Sym. on Reactor Dosimetry,, Geesthact, West Germany (Oct. 1984).

MICHEL, R., IYENGAR, G. V., and ZEISLER, R., "Current Aspects of Multielement

Analysis in the Life Sciences", Proc. Sym. Instrumental Multielement Analysis,

Julich, FRG, April 2-5 (1984).

MICHAEL, R., IYENGAR, G. V. and ZEISLER, R., "Current Aspects of Multielement

Analysis in the Life Sciences", Proc. Symp. Instrumental Multielement Analysis,

Julich, FRG, April 2-5, 1985 (in press).

MYERS, J. E. and BLACKMAN, M. J., "Conical Plates from Medieval Qsar es-Seghir, Proc.

of the Third Intern. Congress on Medieval Ceramics (1985).

OLIVER, B. M., FARRAR IV, H., GILLIAM, D. M., aijjd LIPPI|IJCOTT, E. P., "SpectrumIntegrated Helium Generation Cross Section for Li and B in the Immediate-Energy

Standard Neutron Field", Proc. 5th ASTM-EURATOM Sym. on Reactor Dosimetry,

Geesthacht , Germany ( Sept . 1984).

PETILLI, M., and GILLIAM, D. M., "Evaluation of Uncertainties of U Fission

Spectrum", Proc. 5th ASTM-EURATOM Sym. on Reactor Dosimetry, Geesthacht, Germany

(Sept. 1984).

RILEY Jr., J. E., MITCHELL, J. W., DOWNING, R. G., FLEMING, R. F. , LINDSTROM, R. M.,

and VINCENT, D. H. , "Materials Analysis Using Thermal Neutron Reactions:

Applications, Materials Science Forum £, 123-132 (1984).

SCHRODER, I. G., LINPEI, Li, GILLIAM, D. M., McGARRY, E. D. and EISENHAUER, C. E.,

"Measurement of Absolute Fission Cross Sections for Cf Spontaneous Fission

Neutrons, ANS Trans. (1985).

STONE, S. F. and ZEISLER, R. , "Evaluation of Biological Samples for Specimen Banking

and Bioraonitoring By Nuclear Methods", Proc. 5th Conf . on Nuclear Methods in

Environment and Energy Technology, J. R. Vogt, ed. NTIS U.S. Dept. of Commerce,

Springfield, VA, CONF-840408 (1984).

STROUBE, W. B. and LUTZ, G. J., "Epithermal Neutron Activation Analysis of Powdered

Infant Formula for Iodine", Trans. Amer. Nucl. Soc, _49, 164-165 (1985).

STROUBE, W. B. and LUTZ, G. J., "Determination of Iodine in Liquid Infant Formula by

Epithermal Neutron Activation Analysis" (in press).

VANDERVOST, W., SHEPHERD, F. R., and DOWNING, R. G., "High Resolution SIMS and

Neutron Depth Profiling of B through Oxide-Silicon Interfaces, J. Am. Vacuum

Soc, Sci. Technol., A3 (3), 1318-1321 (1985).

WILSON, S. R., PAULSON, W. M., GREGORY, R. B., KRAUSE,, R. J., GRESSETT, J. D.,

McDANIEL, F. D., and DOWNING, R. G., "Properties of Ion Implanted Polysilicon

Layers Subjected to Rapid Thermal Annealing", J. Electrochemical Soc; Solid

State Sci. and Tech. ^32 (4) 922-929 (1984).

WISE, S. A. and ZEISLER, R., "The Pilot Environmental Specimen Bank Program",

Environ. Sci. Technol., 18 302A-307A (1984).

167
NBS-n4A (REV. 2-80) U.S. DEPT. OF COMM.

BIBLIOGRAPHIC DATA

SHEET (See instructions)

1. PUBLICATION OR

REPORT NO.

i^BS/TN-1217

2. Performing Organ. Report No 3. Publication Date December 1985

4. TITLE AND SUBTITLE

NBS Reactor: Summary of Activities July 1984 Through June 1985

5. AUTHOR(S)

Frederick J. Shorten, Editor

6. PERFORMING ORGANIZATION (/f joint or other than NBS. see instructions)

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

GAITHERSBURG, MD 20899

7. Contract/Grant No.

8. Type of Report & Period Covered

7/84 - 6/85

9. SPONSORING ORGANIZATION NAME AND COMPLETE ADDRESS (Street. City. State. ZIP)

Same as # 6.

10. SUPPLEMENTARY NOTES

I I Document describes a computer program; SF-185, FIPS Software Summary, is attachied. 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 realtor. It covers the period from July 1984 through June 1985. 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

|X I Unlimited

I I For Official Distribution. Do Not Release to NTIS

I I Order From Superintendent of Documents, U.S. Government Printing Office, Wasliington, D.C.

20402.

r7] Order From National Technical Information Service (NTIS), Springfield, VA. 22161

14. NO. OF

PRINTED PAGES

175

15. Price

CtO.S. GOVERNMENT PRINTING OFFICE:! 9S5 1*91 070 20311
NBS_ Technical Publications

Periodical

Journal of Research—The Journal of Research of the National Bureau of Standards reports NBS research and development in those disciplines of the physical 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. Developjed 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. Easily understandable language and illustrations provide useful background

knowledge for shopping in today's technological marketplace.

Order (he 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 PUB)—Publications in this series collectively constitute the Federal Information Processing Standards Register. The Register serves as the official source of

information in the Federal Government regarding standards issued by NBS pursuant to the Federal Propert\'

and Administrative Services Act of 1949 as amended, Public Law 89-306 (79 Stat. 1 127), and as implemented

by Executive Order*I1717 (38 FR 12315, dated May 11, 1973) and Part 6 of Title 15 CFR (Code of Federal

Regulations).

NBS Interagency Reports (NBSIR)—A special series of interim or final reports on work performed by NBS

for outside sponsors (both government and non-government). In general, initial distribution is handled by the sponsor; public distribution is by the National Technical Information Service, Springfield. VA 22161, in paixT

copy or microfiche form.
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