NBS

Publications

."'TL INST. OF STAND i TECH R.I

iiiniiiiiiillll III AlllOM bS75M1

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in a* NBS TECHNICAL NOTE 1178

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

NBS Reactor:

Summary of Activities

July 1981 Through June 1982

luo

. U5753

117d

1983
NATIONAL BUREAU OF STANDARDS

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

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

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

the Institute for Computer Sciences and Technology.

THE NATIONAL MEASUREMENT LABORATORY provides the national system of

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

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

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

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

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

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

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

calibration services. The Laboratory consists of the following centers:

Absolute Physical Quantities^ — Radiation Research — Chemical Physics —

Analytical Chemistry — Materials Science

THE NATIONAL ENGINEERING LABORATORY provides technology and technical ser- vices to the public and private sectors to address national needs and to solve national problems; conducts research in engineering and applied science in support of these efforts; builds and maintains competence in the necessary 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^

THE INSTITUTE FOR COMPUTER SCIENCES AND TECHNOLOGY conducts

research and provides scientific and technical services to aid Federal agencies in the selection, acquisition, application, and use of computer technology to improve effectiveness and

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

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

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

The Institute consists of the following centers:

Programming Science and Technology — Computer Systems Engineering.

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

LIBRAP.T NBS Reactor: „,„, , Summary of Activities /,^/^c^c

July 1981 Through June 1982 ^-^^^

Frederick J. Shorten, Editor

Reactor Radiation Division

National Measurement Laboratory

National Bureau of Standards

Washington, DC 20234

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^''flfAU O*

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

NATIONAL BUREAU OF STANDARDS, Ernest Ambler. Director

Issued June 1983
National Bureau of Standards Technical Note 1178

Natl. Bur. Stand. (U.S.), Tech. Note 1178, 231 pages (June 1983)

CODEN: NBTNAE

U.S. GOVERNMENT PRINTING OFFICE

WASHINGTON: 1983

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

Price $6,50

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

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

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 pursing 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 neces'sary to take full advantage of

the facilities available. The Division also provides irradiation services

to a wide variety of users as well as engineering and other technical

services.

The reactor operates at 10 MW and is designed to provide more than

25 experimental facilities ranging from intense neutron beams to extensive

irradiation facilities, making it one of the most versatile high flux

research reactors in the country. Thus, it is able to serve a large

number of scientists and engineers in a broad range of activities both

within and outside the NBS.

This report attempts to summarize all the work done which is dependent on the reactor including a large number of programs outside the

Division. The first section summarizes these programs carried out by

scientists in the Reactor Radiation Division and their collaborators.

The second section summarizes NBS work originating entirely outside the

RRD which requires no collaboration with RRD scientists. The section

entitled, "Service Programs," covers those programs originating outside

NBS but for which RRD provides irradiation services. The remaining

sections are self-explanatory.

Xll
FOREWORD

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

Division for his extensive contributions to the editing, organization,

and preparation of this report, and T. Mangum, S. Long, and N. Phelps

for efforts in typing manuscripts.

j': <t. ' '-^

R. S. Carter

Chief, Reactor Radiation Division

National Bureau of Standards

XV
ABSTRACT

This report summarizes all those programs which depend on the NBS

reactor. It covers the period from July 1981 through June 1982. The

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

dynamics of materials through nuclear physics and neutron standards to

sample irradiations for activation analysis, isotope production,

radiation effects studies, neutron radiography, and nondestructive

evaluation.

Key words: Activation analysis; crystal structure; diffraction;

isotopes; molecular dynamics; neutron; neutron radiography;

nondestructive evaluation; nuclear reactor; radiation.

DISCLAIMER

Certain trade names and company products are identified in order to

adequately specify the experimental procedure. In no case does such

identification imply recommendation or endorsement by the National Bureau

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

best available for the purpose.
TABLE OF CONTENTS

FOREWORD iii

ABSTRACT v

A. Reactor Radiation Division and Collaborative Programs i

NBS Crystal Data Identification File 1

A Matrix Method for Lattice Symmetry Determination

(An Application of the B-Matrix Algorithm) 3

Synthesis and Structure of Cu5(BTA)^(t-C4H9NC)4, A MixedValent Copper-Nitrogen Cluster containing n3-Benzotriazolate 16

Neutron Diffraction Study of Sodium Sesquicarbonate Dihydrate . 25

Single Crystal X-Ray Structure Determination of the Dimethyl

Oxime of Phosphoramide Mustard, C-j'ii-^^^'^^02PCl2 28

Study of Hydrogen Bonds in Ca2KHy (P04)4i 2H2O 31

Effects of Interstitial Elements on Phase Relatioships

in the Titanium-Aluminum System 34

Studies of Zeolite Structure by Neutron Powder Diffraction . . 40

Structure Refinement of Compositions in the Nasicon Solid

Solution System 42

The Structure of Ammonium Paratungstate Tetrahydrate 52

The Structures of Lithium-Inserted Metal Oxides:

LiRe03 and Li2Re03 56

Neutron Profile Refinement of the Structures of

Li2Sn03 and Li2Zr03 59

A Neutron Powder Diffraction Study of A- and B-Pb02 in the

Positive Electrode Material of Lead-Acid Batteries ... 62

Crystal Structure of Ammonium Nitrate: Low Temperature

Phase, (v) 66

X-Ray Diffraction Studies of Cellulose 68

Hydrogen Exchange in Rnase A: Neutron Diffraction Study ... 74

vi
TABLE OF CONTENTS

Crystallization of Hen Egg Ovalbumin 77

Hydrogen in Metals—Theory of Neutron-Induced Transitions

to Excited Band States 79

Relations Between Fermion Masses 85

Calculations of Vibrational Spectra of Self-Trapped Hydrogen in

BCC Metals 86

Translation-Rotation Coupling in Molecular and Ionic

Crystals 87

Investigation of the Magnetic and Superconducting Transitions

in (Er-^_^Ho^) Rh4B^ 90

Ferromagnetic and Spin Glass Behavior Near the Critical

Concentration in Amorphous (FexNii )75 '-25 93

Spin Waves in Amorphous Fe2_„Bj^ Alloys 96

Spin Dynamics of H0AI2 101

Small Angle Magnetic Scattering From Amorphous TbFeo .... 105

Advanced Neutron Methods 107

Internal Expansion From Block Copolymers of h-Styrene and

d-Styrene 112

Study of Polymer Surfactant Complexes by Small Angle

Neutron Scattering 117

Structure Factor Studies of a TiCu Metallic Glass as a Function of Annealing Treatment 119

Investigation of Sic-Al Composite Material by Neutron

Scattering 123

The Theory of Spinodal Decomposition 125

Nondestructive Evaluation of Distributed Damage 127

vxx
TABLE OF CONTENTS

B. NON-RRD PROGRAMS 137

Activation Analysis Group FY 82 137

Summary of Activities Carried Out by the Neutron Field

Standards Group 168

Neutron Personnel Dosimeter Calibration and Testing 172

Atmospheric and Environmental Studies by Instrumental Neutron

Activation Analysis 173

Sans Studies of Single Chain Conformations in Lamellar

Microdomaine of Block Copoljmiers 182

The Neutron Activation Autoradiographic Study of Paintings . . 188

C. REACTOR OPERATIONS AND SERVICES 196

Reactor Operations and Services 196

D. SERVICE PROGRAMS 199

Neutron Activation Analysis at the Food and Drug

Administration 199

U.S.G.S. Activation Analysis program 202

Positron Annihilation in Cu Alloys 205

E. PERSONNEL ROSTER 210

F. PUBLICATIONS 216

vxii
A. Reactor Radiation Division and Collaborative Programs

NBS CRYSTAL DATA itlENTIF I CATION FILE

A. D. Mighell and J. K. Stalick

A crystal data identification file is available for lease in

magnetic tape form. This data base permits the user rapidly to identify

unknown crystalline materials using x-ray dif fractometer measurements.

These data were collected from the published literature and were evaluated

by the NBS Crystal Data Center and cooperating data centers. The work

was supported by the Office of Standard Reference Data at NBS.

1. Description of the Data Base

The data base contains evaluated crystallocheraical data on approximately

60,000 materials. Each entry consists of the reduced cell, cell volume,

crystal system, space group, space group number, calculated density,

chemical name, chemical formula, and journal reference.

2. Use of the Data Base

The data base will prove to be a practical analytical tool for compound

characterization and identification because the reduced cell (i.e., the

lattice) is unique for most compounds. Unknowns can conveniently be identified

by the following sequence:

1. Determine a primitive or centered cell for unknown crystal.

2. Calculate the reduced cell.

3. Check the NBS Crystal Data Identification File.

In addition to routine analytical work, the data base will be useful in

preventing redeterminations of published structures. The data base can also

be used in conjunction with other data for materials characterization.

3. Coverages and Updates

The data base contains data for commonly occurring materials. With

respect to the published literature, it is current (1980) for organic and

organometallic materials and is complete to 1970 for inorganic materials.

New entries are being added on a regular basis and a revised version of the

data base will be made available annually to all subscribers.
REACTOR RADIATION DIVISION AND COLLABORATIVE P^'OrRAJ^S

4. Use of the NBS Crystal Data Identification File

Our research and data center work have demonstrated the desirability

of routinely characterizing crystalline materials by cell parameters as determined from x-ray diffraction experiments in addition to the traditional

chemical analyses. Cell parameters can be determined either by singlecrystal techniques or by powder techniques in conjunction with indexing

programs. We have found that identification procedures based on latticeformula matching are extremely effective. The reduced cell may be used to

determine if two crystals, known and unknown, have the same lattice. Usually

a simple comparison of the reduced cells and cell volumes is sufficient

to identify a compound. This is easy to do as the cells on the tape are ordered on the magnitude of the reduced cell parameters. The match can

be done by hand by using a computer listing of the tape, or it can be carried

out using a computer search procedure.

Lattice-matching can be enhanced by using software that allows one

to match derivative lattices. This is desirable because in some cases cell

centering is not published (e.g., a face-centered cubic cell reported as a primitive cell) or a subcell or supercell may have been determined experimentally. Consequently, one sometimes needs to match cells with volume ratios

of 1/2, 2, 1/3, 3, 1/4, 4, etc. In other cases (e.g., in the cells determined

by indexing procedures using powder data), one may obtain a cell that defines

a lattice that bears a composite relationship to the correct lattice. In

spite of these errors, identification is still possible by using a mattrix

approach. In this approach, the nature of the lattice relationship is

deduced from the transformation matrix relating the reduced cells of the

known and the unknown lattice. Alternatively, the matching of a lattice

against a sublattice or superlattice, but not a composite lattice, can be

3 accomplished by systematically calculating appropriate sub- and superlattice.

The routine use of the NBS Crystal Data Identification File coupled

with modern cell determination procedures offers a new approach for materials

identification and characterization. The entire procedure of cell determination

and file search can be automated. The method would have practical applications
REACTOR RADIATiOT^l DIVISION AND COLLA.^.ORATIVE PROGRAl^S

in any industrial analytical laboratory and can be used independently or in conjunction with powder diffraction identification techniques.

1. From the JCPDS—International Centre for Diffraction Data, 1601

Park Lane, Swarthmore, Pennsylvania, 19081.

2. A. Santoro, A. D. Mighell, and J. R. Rodgers, Acta Cryst. A3

6

, 796 (1980).

3. A. Santoro and A. D. Mighell, Acta Cryst. A29^, 169 (1973).

a matrix method for lattice symmetry determination

(an application of the b-matrix algorithm)

V. L. Himes

(Catholic University of America, Washington, DC)

and

(National Bureau of Standards, Washington, DC)

and

A. D. Mighell

A previous study based on classification according to reduced form

has shown that the crystal lattice sjrmmetry and the metric lattice

symmetry are usually identical for molecular compounds (Mighell and

Rodgers, 1980). Although reduction procedures can reliably be used to

determine metric syrometry, there are several non-trivial problems with

the method when used automatically without human interaction. First,

when calculating the reduced cell, experimental errors cause problems in

treating the inequalities inherent in the special conditions for

reductfion. Occasionally, more than one "reduced" cell is possible

depending on how the errors are treated. Second, one must transform an experimentally determined cell to the reduced cell and properly identify

the form of the reduced cell matrix. Third, it is difficult to establish all possible pseudo-sjnranetries when using reduction procedures.

Having recognized the problem of experimental error, Clegg (1981) offers
REACTOR RADIATION DIVISION AND COLLABOPATIVE PROGPAIIS

an alternative method to obtain the correct Bravals lattice from the

reduced cell. However, we recommend a new, general approach to determine

metric lattice symmetry. The central focus of the method described

herein is on determining matrices that relate any primitive unit cell to

itself rather than on obtaining reduced cells and conventional cells.

In a recent paper, it was shown that properties of lattices can be

derived from the nature of the transformation matrices relating unit

cells in the same or in different lattices (Santoro, Mighell & Rodgers,

1980). An algorithm (B-matrix) was presented that will determine the

matrices B in the following equation:

^1 = lj^lj^j^i'j = 1' 2, 3)

where a, and a. define two primitive triplets of noncoplanar translations

(a triplet is called primitive when it defines a primitive cell; International Tables for X-ray Crystallography , 1969) . We have found that

the B-matrlx algorithm can be used routinely to determine metric lattice

symmetry. To determine symmetry using the algorithm, one selects a primitive cell and then determines how many ways it can be transformed

into itself to within any specified tolerance of the unit cell parameters.

Only ^-matrices with Integer elements and a determinant of +1 are considered. The greater the number of matrices found, the higher the symmetry.

Using the algorithm, the number of matrices for the seven lattice metric

symmetries are: tricllnic, 1; monoclinic, 2; orthorhombic , 4; rhombohedral,

6; tetragonal, 8; hexagonal, 12; and cubic 24. The 24 matrices listed in

table 1 for a primitive cubic cell were output from the computer program

used to calculate B-matrices. Multiplication of the matrices in table 1

by -1 generates a set of 48 matrices which are identical to those listed

for the 48 symmetry operations compatible with a cubic lattice (Rigault,

1980).

In contrast to reduction techniques, one can deduce the lattice

symmetry from any primitive cell that has been determined, without

transformation to a standard cell. Consider the example of the primitive

unit cell which was determined for potassium antimony tartrate hydrate.
REACTOR RADIATIOn DIVISION AND COLLABORATIVE PROGRAl'S

The matrix procedure yielded a set of four matrices with integer elements

ranging from to + 4. When the original cell was reduced and analyzed

by the matrix procedure, a different set of four integer-only matrices

was obtained with elements of and +1. In each case, the orthorhombic

symmetry of the conventional unit cell (C-centered) was predicted.

Table 2 gives a summary of these results.

The most important features of this method are that one can determine the highest possible metric s)nranetry within a specified tolerance

and that pseudo-symmetries are immediately apparent. The treatment of

experimental error using the matrix method is conceptually simpler than

in reduction as one does not need to worry about the inequalities inherent in reduction theory. When using reduction techniques, it is not

uncommon for the computer program or the person to miss the highest

possible metric S3nmnetry because of the effects of experimental errors

in the unit cell parameters, round-off errors in computations and the

assessment of the equality or inequality of numbers. This is especially

true for those cases when the experimental error in the unit cell parameters is large or unknown. In contrast, experience has shown that the

matrix procedure correctly predicts the metric symmetry even when the

experimental error is large. To ensure tViat all potentially interesting

matrices are generated, a relatively large tolerance for cell parameter

errors should be used.

Recently, it was reported that several crystal structure analyses

have been, "almost certainly described in space groups of unnecessarily

low symmetry" (Marsh & Shomaker, 1979; see also Herbstein & Marsh, 1982;

Marsh & Shomaker, 1980; Schomaker & Marsh, 1979). In several instances,

the crystal structures were reported to have been described in the wrong

crystal system. For example, the compound dichlorobis(4-vinylpyridine)

zinc(II) was originally reported in the triclinic space group PI with

unit cell parameters

a = 7.501(4) b = 7.522(5) c = 14.482(6) A

a = 90.41(4) 3 = 90.53(4) Y = 105.29(5)°.
REACTOR PACIATIOII DI^'ISION AND COLLABORATIVE PROGRAMS

Marsh and Schomaker (1979) found that the triclinic unit cell could be

transformed by the matrix (1 1 0/ -1 1 / 1) to a monoclinic Ccentered unit cell with

o a = 9.115 b = 11.942 c = 14.482 A

a = 89.93 3 = 90.77 y = 89.83°.

Although the angles a and y have large deviations relative to the e.s.d.'s

of the originally reported unit cell, the atomic coordinates conform

more closely to the monoclinic symmetry. The monoclinic lattice sjrmmetry

for the Zn(II) compound is predicted by the matrix procedure to determine metric symmetry. The following matrices and "error" matrices were

found using the originally reported triclinic cell and tolerances of

o 0.2 A for the cell edges and 0.5° for the cell angles:

Error matrices

0.021 -0.021 0.000

0.120 -0.120 0.000

II

B-matrices

1

-1

-1

1 o"

1

1

0.000

0.000

0.000

0.000

0.000

0.000

The "error" matrices represent the tolerances in the unit cell parameters

required to transform the cell into itself by the specified matrix.

Suppose cell A is defined by lattice parameters, a, b, c, a, 3, Y- If the matrix procedure to determine metric lattice symmetry for cell A

yields the matrix M with the error matrix

ol a tol b tol c ol a tol 3 tol Y

then the transformation of cell A by the matrix M will give cell B

having lattice parameters

a' = a + tol a

a' = a + tol a

b' = b + tol b

3' = 3 + tol 3

c + tol c

Y + tol Y
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGPAMS

In the case of the Zn(II) compound, matrix I will transform the Initial

triclinic cell into a second cell with

a = 7.522 b = 7.501 c = 14.482 A

a = 90.53 3 = 90.41 y = 105.29°.

If the Zn(II) compound has crystallized in the monoclinic system, the

two unit cells are S5nranetrically equivalent. An average of the lattice

parameters for the two symmetry-related unit cells gives

a = 7.5115 b = 7.5115 c = 14.482 A

a = 90.47 3 = 90.47 y = 105.29°.

Transformation of the average cell by the matrix (1 1 / -1 1 / 1)

gives an ideal centered-monoclinlc cell with

a = 9.115 b = 11.942 c = 14.482 A

a = 90.00 3 = 90.77 y = 90.00°.

Thus, an analysis of the error matrices provides an indication of the

extent to which the original triclinic cell parameters must be changed

to make the cell reflect the exact monoclinic metric symmetry. It

should be mentioned that the above analysis of the error matrices is

only one of many possible interpretations.

The previous discussion concerning the use of the matrix procedure

to determine metric symmetry for dichlorobis(4-vinylpyrldine)zinc(II)

was based on the results of an analysis using tolerances for cell parameter errors which were smaller than those normally recommended for

routine structure work. Although the tolerances specified may vary

considerably depending on the individual problem, the recommended values

o typically range from 0.5 to 1.0 A for the cell edges and 1.0 to 4.0 for

the cell angles. The matrix method reveals that the Zn(II) compound

could be metrically orthorhombic depending on the interpretation of

experimental error. The set of four matrices and error matrices found

o for the original triclinic cell using tolerances of 1.0 A and 4.0° are given in Table 3. When the four error matrices are averaged and the
REACTOR RADIATIOn EIVISIOII AND COLLABORATIVE PROGRAMS

resulting error matrix Is applied to the trlcllnlc cell, the following

cell parameters are obtained:

a = 7.5115 b = 7.5115 c = 14.482 A

a = 90.00 B = 90.00 y = 105.29°.

This cell may be transformed by the matrix (1 1 / -1 1 / 1) to a centered-orthorhombic unit cell with

a = 9.115 b = 11.942 c = 14.482 A

a = 90.00 6 = 90.00 y = 90.00°.

The matrix procedure yields all possible lattice sjrmmetries within

a specified tolerance. The actual selection of the highest possible

symmetry of the lattice is dependent on the assessment of the experimental error. An advantage of the matrix procedure to determine metric

lattice S3mmietry is that an analysis of the error matrices output from

the computer program enables a direct comparison of the calculated

errors (i.e. those related to the specified tolerances) with the experimental

errors determined for the primitive unit cell. The trlclinic unit cell

for the Zn(II) compound is metrically monoclinic since the calculated

errors correspond to approximately twice the e.s.d.'s for the cell edges

a and b and the cell angles a and B. In order to have exact orthorhombic

metric symmetry, the original triclinic cell parameters must be changed

by a maximum of approximately 13 e.s.d.'s.

Thus, in addition to the determination of metric lattices symmetry,

the matrix procedure offers a direct and convenient way to find all possible

pseudo-symmetries within a specified range of cell parameter errors. To

determine metric pseudo-symmetry using the matrix procedure, one simply

increases the magnitudes of the tolerances acceptable for the cell parameters

and analyzes the sets of matrices and error matrices obtained. The interpretation of the error matrices (i.e. symmetry versus pseudo-symmetry)

will vary considerably depending upon the compound being studied.
REACTOR RADIATIOIT DIVISION AND COLLABORATIVE PR0GRA}1S

The matrix method may be used on a problem-to-problem basis to

determine sjnmnetry or it can be used to critically evaluate lattice

s5iTmnetry in large sets of data. In our routine structure work, the

matrix procedure has been used to determine symmetry as soon as a refined primitive cell has been obtained; in every case, the method gave

the correct symmetry. When the unit cell is highly skewed, one must

allow the computer program to seek matrices with integer elements

typically as high as + 10. In contrast, when the matrix procedure is

used to analyze the lattice symmetry of a standard cell based on the 3

shortest lattice translations, a standard set of matrices having matrix

elements of -1, 0, 1 is produced. Thus, one may be certain that the

proper matrix elements have been considered when the reduced cell is

analyzed by the matrix procedure. This eliminates the possibility that

the correct lattice symmetry has been missed because the expermentalist

misjudged the matrix elements which were required to analyze a skewed

unit cell.

Computer analyses of approximately 30,000 lattices from the NBS

Crystal Data Identification File (NBS'^ID File) have proved that the

matrix method for metric symmetry determination is fast, efficient and

reliable. The method predicts a lattice symmetry which, in most cases,

is consistent with the crystal sjrmmetry reported by the authors in the

original reference. In a relatively low percentage of cases, the matrix

procedure predicts a higher symmetry. The percentages of compounds

where the matrix method predicted a higher sjrmmetry are given in Table

o 4. For example, using tolerances of 0.15 A and 1.5°, 12.4% of the

compounds reported to have monoclinic crystal symmetry were found to

have higher metric symmetry. Similarly, 5.4% of all organic compounds

o in the 1-line file have higher metric symmetry when tolerances of 0.09A

and 0.9° are specified in the computer program to calculate B-matrices.

As expected since the cubic symmetry is the highest possible symmetry of

the lattice, the matrix method never found more than 24 matrices for any

of the 30,232 entries analyzed.
REACTOR RADIATIOII DIVISIOII AND COLLABORATIVE PROGRAl'^S

The computer analyses of the NBS*ID File using the matrix procedure

have revealed that the unit cell parameters with higher metric symmetry

commonly involve a transformation to or from a centered cell. The most

frequently encountered examples include the transformations from a primitive

triclinic cell to a centered monoclinic cell, a primitive monoclinic

cell to a centered orthorhombic cell, and a centered monoclinic cell to

a primitive rhombohedral cell. There are, however, numerous compounds

in the 1-line file that do not require a transformation to or from a centered cell to reveal higher metric symmetry. Among other examples,

there are many substances which have been characterized by primitive

monoclinic unit cells which are metrically orthorhombic with a ^ b

^ c and a = 6 = Y = 90°. Presumably, the higher metric symmetry and any

structural implications have been noted by the authors. Further discussions

are planned concerning the cases for which the metric symmetry exceeds

the reported crystal symmetry.

It has become apparent that metric symmetry and possibly crystal

S3rmmetry is often missed by diffraction techniques currently being

employed. In view of the recent trend toward the determination of a unit cell solely from diffracto meter data, the use of metric methods to

indicate probable lattice S3mmietry is especially important. Ideally,

the check for metric symmetry should be carried out as soon as a refined

unit cell has been determined. Experience has shown that the matrix

procedure offers a direct and convenient way to determine the highest

possible symmetry of the lattice. On a practical basis, algorithms to

determine metric symmetry (such as the B-matrix and reduction algorithms)

could be incorporated into the software for modern, automated diffractometers. However, the need to critically evaluate all stages of crystallographic work should not be eliminated by the availability of sophisticated automation.

10
REACTOR Rj\DIATION DIVISION AND COLLABORATIVE PROGPAMS

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REACTOR RADIATION DIVISION AND COLLABORATIVE PROGPAllS

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en 1 1 QJo .H o CN <-^ o o •H

>-l 4-1 O iH CN o r-{ o

CO s

1

1 1

1 1 • Q) r 1 —

1

•U PQc?- o O rH o O rH d 1 1 U

Td rH O CNl ,-i o o

?^ 1 1 1 X: o rH CN o r-{ o

4J 1

1 1 1

1

1 n) r~~ "~n 1

—

1

U o o T--\ o o r-{ 4Ju

(TJ o rH O o ,-\ O 4-1 1 1 ?^ rH o <r r-f o O

c 1 1 1 o 1 1

1 1 B

"' u

•H /'~^ C m Ct) ,—\ /~s 6 o<3 o r^ •'w^ m

3 s—

X

^w^ o 00 C3^ CN

•H vO •<r C3> LO M o ?- • <~^ • . CO o r~> rH LO <N

Cfl CO en 00 1 CN (Ti •u !-l o q; o

CL 4J

CU /^ ^ CN M e vO m o CO V—

v_^ •^*^ iw V-i vO Ln ^ 00

CO (7^ ON O ON rH C PL, rJ3 00. O • O • O t r^ rH • O •H j-i 00 LO 1 CO a^

4-1 iH

(13 0) o

C O

•H ^^•^ ^—

\

^-.^^ E U vO vD U •H ^—

•

V—

o

d) C ITI CTi in CN

4J !=) CO s C7\ vD o CJN o cu o . o

x) 00

00

00

rH 00 d

>.u

rH

I o

o

CTi

vo r^

C7N CTN

• a in C7N CN CO

in

v«^ CO

CN —

C7N <t

r-t o • • rH o

rH <7N

in

C3> ON

ON

00

CN

rH

CO H

(Uo

cu>

•H

4J •H

.^U

CO H

•H

CSJ rH CN

CO U

/—^ c

rn O cx

r-i •H 3

=^ ^,—

V

4-1 o

CJ) C 5-1 e 1 0) ao rH M u >

rH o •H c <u CU M-l ^ o o O 6 O CO T3 O ex T3 CU x: T3 en

CU O !-i 0) \ O 3 O d

3 13 rd •H rH

XI CU 4-1 M-l rH

<u M S-l CU CU

lyi ^-^ o Pi CJ

12
REACTOR PADIATION PIVISIO>T AND COLLABORATIVE PROGRAMS

I o<3

1 O

•H • Xi tH o

5-1 >+-l O o

iH

Xi CO O <u •H o

t3

CO

>-i M

O (U

U-l O

'O +J c

3 fi O cu

<4-l m

(U /•—

\

o M

•H •

}-i ^—

X)

4J O cu

CO C •H e •H U-l N •H

^J O

o /—

\

tu M CU &,

>-l c CO

(U •HX) (U Xl •H M

C! ^ cu

nJ ^

CO iH o

(U >. o

o C • •H •H •«*

>-i >

4-t 1 XI

CO sT a S v^ CO

• en

(U iH

,Q

CO H

oooo oooo oo oo

oo oo

ooOvo .HO iHO oo

oo CNCM cNi<r OtH ocr> oo

o

CM o

1 o*

1

iHCMo

o

CN

iH OO iHO rHO oo OcN cNicN cNj<r OoO OiH OCT\ OO

CMo

O

d

1 o*1

CNJ O

o

o' o*

1

>M

13
REACTOR RADIATIOII DIVISIOiI AND COLLABORATIVE PROGPAllS

M-l CO o 4Jo

vD H • CN

>, 0^ U LD in

•U rH <f

<U ON

c3^cno^fnOfnO•dTHL^^svDcr)^^

iH<NCMrosr<d-minvovor>.r».cooo

Pi LOLTiLnLriLnLnLriLnLnLnLriLnLriLnLn

CJ "^-^ CO • t • • • • • « • • • • • • • o •H iH 0) ffi O o o o o o o o o o o o o o o

•H CT3 r^ V V V V V V V V V V V V V V V

5-1 •H M !-i 4J tH t) 4J

CU o 0) d

e •HU

4=odj u u ^ o U-) in in in r«~ VO r^ rH en vT r». t^ r* cri CJ^

<u e •r-l • • • • < • • • • • • • • ^ o o 42 H O o o o d o o r-i rH rH iH r-i H H <-i W) CM -c 3 V V V

•H un v^ CJ .C St

r-H <r

bO <u O fO C M ro CN

•H 0) > S r\ T3 LO in o o o o r") CO r^ r^ r^ O o r^ CO

n] /~v d • • I • • • • • • • • • • • • ^ • O CO Prf o

V o

V

iH rH r-i r-^ r-^ r^ rH iH rH CM CM CM CO M OJ o «s 13 ,C •H /^N

C! 4-» rQ ffi 3 e

V^

O »* o iH ^ C3^ f^ r^ o <f r^ cy\ rH in t^ O CM \D 00 a T3 X (0 » • • • • • • • • • 6 <U !-i d O o O tH rH CM CM CvJ CM CO CO CO >^ <r sr <r o N o o

u

i-H 00

CO o c^3 u

•H a o S

d c« ^

03 UD

bO CO tH <r c» CTi •* CM CO 00 CM CM t^ a^ -CJ- vj- c:n o <r M dJ CO CO « • • • 9 • • • • • • • O •H r^ <r S iH CM en •3- <r m o h* r«. GO CTi O

rH orH

CMrH m ^ #\ <\ /"v S

w N_x v^

OJ rsj o rH

00 fO •H CO 00 CM CO vO r^ r-i Csi in 00 CM <r CTi CM CO CO

n) CM d d • « • • • • • • • • +j A •H o < CO iH rH rH rH Csl CM CM CM CO CO CO <r < in c O r-l bC

0) fO O CO u O U

t-l 0) C j-i 0) ^ O <U

fit +J e 4-1

(1) CJ

fH CM ro < in VD r^ CO CT^ o H CM CO <i- in d d d d d d d d d rH rH rH rH H T-i

• d

<1- 0)

<u 0) iH rH rH CM fo <r in o t^ CO c^ o r-i CM CO <r in

pQ O o<: o O o o o o o o o rH rH r-\ r-A rH r-i

c^) H . > < . . • . E-i o o o d o o o o d d d d d d d

14
REACTOR RADIATIO!! DIVISIQTJ AHD COLLABOPA.TIVE RROGPJ^'lS

1. W. Clegg, Acta Cryst. A37_, 913-915 (1981).

2. F. H. Herbstein and R. E. Marsh, Aota Cryst. B38, 1051-1055 (1982).

3. International Tables for X-ray Crystallography , Vol. I, 3rd. ed.

,

p. 8, Birmingham: Kjmoch Press (1969).

4. R. E. Marsh and V. Schomaker, Inorg. Chem. 18, 2331-2336 (1979).

5. R. E. Marsh and V. Schomaker, Acta Cryst. B36 , 219-220 (1980).

6. A. D. Mighell and J. R. Rodgers, Acta Cryst. A36, 321-326 (1980).

7. G. Rigault, "Metric Tensor and Symmetry Operations in Crystallography.'

Published for the International Union of Crystallography Commission

on Crystallographic Teaching by University College Cardiff Press;

Cardiff, Wales.

8. A. Santoro, A. D. Mighell, and J. R. Rodgers, Aata Cryst. A36, 796-

800 (1980).

9. V. Schomaker and R. E. Marsh, Acta Cryst. B35 , 1094-1099 (1979).

15
REACTOR PADIATIOII CIVISIOH AND COLLABOPATIVE PROGRAMS

SYNTHESIS AND STRUCTURE OF CU5(BTA)5(t-C4H9NC)4^ A

MIXED-VALENT COPPER-NITROGEN CLUSTER CONTAINING

n^-BENZOTRIAZOLATE

V. L. Himes

(The Catholic University of America, Washington, DC)

and

(National Bureau of Standards, Washington, DC)

and

A. D. Mighell

and

A. R. Siedle

(3M Central Research Laboratories, St. Paul, MN)

and

G. F. Kokosaka

(State University of New York, Plattsburgh, NY)

Protection of metals with reactive materials capable of forming surfacephase coordination compounds is an area of chemistry which is of considerable

scientific and technological importance. In view of the extensive use of

benzotriazole as a corrosion inhibitor for copper and its alloys (Reekijk,

Roelofsen, Siedle, and Spek, 1979, and references cited therein), it is

remarkable that, to our knowledge, no copper-benzotriazole complex has been

structurally characterized by x-ray diffraction. The synthesis and crystal

structure of a neutral, highly symmetric complex containing a three3 dimensional copper-nitrogen cluster formed by the coordination of n - benzotriazolate to copper (I) and copper (II) is described herein. The

central cluster is composed of interconnected copper -nitrogen cycles

(azametallocycles) which vary in size and spatial orientation.

The reaction of copper (I) thiophenoxide, benzotriazole, and alkyl

isocyanides in dichloromethane at room temperature produces Cu^(BTA) , (RNC)

[BTA = benzotriazolate (1-)]. Since the benzotriazolate ion has a charge

of -1, the pentacopper compounds are mixed-valent materials which contain

four Cu(I) ions and one Cu(II) ion. The reaction does not occur in the

16
REACTOR RADIATIOiI DIVISION AND COLLABOPATIVE PROGPAIIS

absence of air. Evidently, oxygen oxidizes some of the Cu(I) to Cu(II),

which acts as a template for the assembly of the rather complex product.

The rate of reaction can be controlled by regulating the partial pressure

of oxygen and, in this way, red-orange crystals of Cu (BTA),(t^-C,H NC),

suitable for x-ray analysis were obtained. Analysis calculated for

^56^60*^^5^22' C,49.49; H,4.45; Cu,23.38; N,22.68; S,0.0. Found:

C,49.3; H,4.4; Cu,23.8; N,22.7; S, < 0.3. The infrared spectrum shows a strong band at 2140 cm due to tert-butylisocyanide coordinated to the

metal. This complex crystallizes in the tetragonal crystal system, space — o group P42 c, unit cell parameters a = 13.836(4), c = 16.686(4) A; Z = 2,

-3

D , = 1.413, D ^ J = 1.41(2) Mg m (flotation). A total of 1196

calc obsd ° unique reflections were measured on an automated 4-circle dif f ractometer

o using graphite-monochromated MoKa radiation (X = 0.71069 A) and the 0-26 scan mode in the range 3.0 _< 20 <^ 45.0°. Intensity data were corrected

for Lorentz and polarization effects, but not for absorption (crystal

size = 0.10 X 0.11 X 0.11 mm, y = 16.9 cm ). The positions of the two

independent copper atoms were determined by direct methods and were verified

in a 3-dimensional Patterson map. Successive least-squares refinement

and Fourier syntheses revealed the positions of the remaining non-hydrogen

atoms. Full matrix least-squares refinement gave a conventional agreement

factor R = 0.063 for 903 observed reflections with F > 3a (Fo)

.

o

1. Discussion

The crystal structure consists of neutral complexes with crystallographic

4 symmetry in which an octahedrally coordinated copper (II) ion is surrounded

by four tetrahedrally coordinated copper (I) ions. Tridentate BTA ligands

bridge each copper (I) ion to three symmetry-related copper (I) ions and to

the central copper (II) ion. Figure 1 gives a view of the complex down a

4 axis. A stereoview of the complex is illustrated in figure 2; the labeling

scheme is presented in figure 3. Table 1 lists selected interatomic

distances and angles.

There are two complexes in the unit cell with the central Cu2 ions

in special positions (0, 0, 0) and (1/2, 1/2, 1/2) with 4 symmetry. Each

17
REACTOR RADIATIOn DIVISION AND COLLABOPATIVE PROGPAMS

Cu^ ion is coordinated to four equatorial and two axial BTA ligands at

the Nl and NA positions, respectively. The four Cul ions surrounding the

central Cu2 ion are each coordinated to one tert-butyl isocyanide ligand

and to three different BTA ligands (two equatorial and one axial) at the

N2, N3, and N5 positions. The four equatorial BTA ligands illustrated in

figure 1 occupy general positions in the unit cell; within experimental

error, their central nitrogen atoms (Nl positions) are in the z = 1/2

plane (z = plane for the complex at the origin) and are coplanar with

Cu2 . Because N4 lies on a crystallographlc 4 axis, a two-fold axis relates

the two halves of the axial BTA ligands. The four equatorial BTA ligands

define planes which make acute angles of 41.7° with the Cu2 basal plane.

Because of symmetry considerations, the two planes defined by the axial

BTA ligands are normal to the Cu2 basal plane.

The geometry about Cu2 is unusual in that it is an undistorted

octahedron of a compressed form [ (Cu2) (Nl) (N4) „] . While the two Cu2-N4

bond distances are typical, the four Cu2-Nl distances are longer than those

usually found for nitrogen coordinated to copper (II) (Hamalainen, Turpeinen,

and Ahlargen, 1979; van Niekerk and Nassimbeni, 1979). Similar copper(II)-

nitrogen distances have been observed in Cu(diethylenetriamine)„ (N0_)

_

(Stephens, 1969) and in Cu(4-f ormyl-2-methoxyphenolato)„ (tetramethylethylenediamine) (Greenhough and Ladd, 1978), compounds in which the

copper (II) ion has distorted, compressed octahedral geometry.

The coordination geometry about Cul is approximately tetrahedral but

there are significant deviations from the ideal angles. The Cul-ClO

distance of 1.882(17) A and Cul-Cl0-N6 angle of 175.8(1.6)° are in general

agreement with the respective values of 1.81(15) A and 180(2)° found for

CuI(CNCH2) (Fisher, Taylor, and Harding, 1960). The coordination distances

to Cul are close to those reported for copper(I) -cyanide complexes in which

o Cu-N distances are typically 2.0 A and Cu-C distances are approximately

o 1.9 A with a nearly linear Cu-C-N angle (Vrabel, Garaj , and Kutschabsky,

1979; Williams, Cromer, and Larson, 1971).

The nature of the bridging between the copper ions is such that

a three-dimensional copper-nitrogen cluster is formed in the center of the

18
??-EACTOR RADIATIOM DIVISION ATID COLLABORATIVE PROGPAMS

complex. As a tridentate ligand, BTA is involved in two types of coppernitrogen-copper bridges. Bridging between Cu2 and Cul is accomplished

via the central and an adjacent nitrogen atom of a BTA ligand. The four

symmetry-related Cul ions are bridged by the two nitrogen atoms adjacent

to the central nitrogen of a BTA ligand in a manner analogous to the

imidazolate bridge in [Cu (bpim) (imidazolate) ] „ (NO^) , -AH 0, where bpim = A,5-bis [2-(2-pyridyl)ethyl]imino methyl imidazolate (Kolks, Frihart,

Rabinowitz, and Lippard, 1976). The axial BTA ligands bridge two Cul

ions situated on the same side of the Cu2 basal plane (i.e., the plane

defined by Cu2 and the four Nl atoms) while the equatorial BTA ligands

bridge Cul ions on opposite sides of the Cu2 basal plane. Thus, the

central cluster is composed of interconrtiicted copper-nitrogen cycles

(azametallocycles) which vary in size and spatial orientation.

o The four symmetry-related Cul ions lie 2.02 A alternatively above

and below the Cu2 basal plane forming a copper(I) tetrahedron [ (Cu2) (Cul) ,

]

about Cu2 . Thus, the core of the copper-nitrogen cluster consists of an octahedron [(Cu2)(Nl)„(N4) ] that is inscribed in a tetrahedron (figure 4).

The nitrogen atoms at the vertices of the octahedron lie very close to the

midpoints of the edges of the circumscribed tetrahedron; each of the

central nitrogen atoms of the BTA ligands are close to one copper(II) and

two copper(I) ions (see table 1). The complex CUc.(BTA) , (^-C,HqNC) is

slightly distorted from ideal cubic symmetry (43m) because of the chemical

nature of the bonding to the central copper(II) ion. The stereochemistry

o about Cu2 is a compressed octahedron with two axial Cu2-N4 bonds of 2.03(2) A

o and four symmetry-equivalent Cu2-Nl bonds of 2.24(1) A. This axial

compression (parallel to the z axis of the unit cell) explains the slight

distortion of the (Cu2)(Cul), tetrahedron. The two Cul - Cu2 - Cul angles

4

along the line of compression are 112.50(5)° while the other four angles

are 107.98(5)°. The two edges of the (Cu2)(Cul), tetrahedron normal to

o the line of compression are 6.050(3) A while the remaining four edges are

5.886(3) A.

19
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGPAI^S

Figure 1. Structure of Cu,. (BTA) ^(_t-C,H„NC) viewed down a crystallographic

4-axis (parallel to the z axis of the unit cell) . For clarity,

the benzene moieties of the axially coordinated ETA ligands,

as well as the entire complex at the origin, have been omitted.

Figure 2. Stereoview of the complex viewed approximately down the x-axis

(10° rotation about y)

20
REACTOR PAMATIOH DIVISIOH AND COLLABORATIVE PROGRAMS

N1d

C13

Figure 3. Perspective drawing showing the labeling scheme used. Unique

atoms are labeled with atom type and number, while the letters

b, c, d refer to the equivalent positions defined in table 1.

Figure 4. Geometric drawing showing that the core of the copper -nitrogen

cluster may be viewed as a (Cu2)(Cul), tetrahedron with an

inscribed CCu2) (Nl) , (N4) octahedron. The central Cu2 ion

has not been drawn; the two N4 atoms lie along the z-axis.

The equivalent positions a, b, c, and d are defined in table 1.

21
REACTOR RADIATIOn DIVISION AND COLLABORATIVE PROGRAJIS

Table 1. Selected interatomic distances (A) and angles (°) with estimated

standard deviations in parentheses. The letters a, b, c, d refer

to the following equivalent positions;

b = 1 - y, X, 1 - z; c = 1 - x, 1 - y.

a (no S3mibol) = x, y, z;

z; d=y, 1-x, 1-z.

Cu2 . . . Cul 3.638(2) Cul-N3 2.013(14)

Cu2-Nl 2.241(13) Cul. . .N4 3.026(2)

Cu2-N4 2.085(16) Cul-N5 2.087(12)

Cul. ..Culb 5.886(3) Cul-ClO 1.882(17)

Cul. . .Culc 6.050(3) Nl.. .Nib 3.169(19)

Cul...Nl 2.949(13) Nl. . .N4 3.064(17)

Cul... Nib 2.941(13) N4. . .Nib 3.058(17)

Cul-N2b 2.024(12)

Cul.. .Cu2.

.

Culb 107.98(5) Cu2-N4-N5 122.8(8)

Cul. . .Cu2.

.

.Culc 112.50(5) Cul.

.

.N4. . .Culc 177.6(6)

Nl-Cu2-Nlb 90.0(5) Nl...N4...Nlb 62.3(4)

Nl-Cu2-Nlc 179.8(5) N5-Cul-Cl0 117.0(6)

Nl-Cu2-N4 90.1(3) Cu2-Nl-N2 123.8(10)

Nlb-Cu2-N4 89.9(3) Cu2-Nl-N3 124.1(10)

Culb.. .Cul. . . Culc 59.07(3) Cul...Nl. . .Culd 176.0(5)

Culb... Cul. . . Culd 61.85(4) Nlb...Nl. . .Nld 90.0(5)

Nl...Cul... Nib 65.1(4) Nlb...Nl.. .N4 58.7(4)

Nl...Cul... N4 61.7(4) Nld...Nl. . ,N4b 58.9(4)

Nib. . .Cul.

.

.N4 61.6(3) Culd-N2-Nl 121.9(10)

N2b-Cul-N3 98.3(5) Culd-N2-Cl 131.0(11)

N2b-Cul-N5 94.7(5) Cul-N5-N4 125.5(9)

N2b-Cul-ClC) 123.9(7) Cul~N5-C7 127.9(9)

N3-Cul-N5 95.3(5) Cul-C10-N6 175.8(16)

N3-Cul-C10 121.2(6)

22
REACTOR RADIATIOIT DIVISION AHD COLLABOPATIVE PROGRA^IS

By studying the geometric nature of the central copper-nitrogen

cluster, a variety of complexes of the type (Metal A) (Metal B),(BTA),

4 b

could be prepared in which tridentate BTA ligands bridge the octahedrally

coordinated metal A and the surrounding tetrahedral array of metal B ions.

As the complex is not required to be neutral, the valences of the metal

ions may vary. The structure proposed by Marshall (1978) contains a coppernitrogen cluster in which copper (II) is substituted for copper (I); the

4+

structure may be viewed as a [Cu(II) (BTA),] cation neutralized by

four 2, 4-pentanedionato(l-) anions. In addition, similar metal-nitrogen

clusters could be prepared using two different metal ions. It is conceivable

that the symmetry of the resulting complex may be higher than the

tetragonal symmetry found for Cu^ (BTA) , (t-C,H.NC) , . If the central

5 6—494

copper (II) ion (Cu2) were replaced by a metal ion which has six equivalent

metal-nitrogen coordinate bonds, it is possible that the syimiietry of the

complex would be cubic with point symmetry 43m. Thus, by changing the

valences of the metal ions and by using metals other than copper, a broad

class of new metal-nitrogen clusters may be synthesized.

The reaction of benzotriazole with metallic copper leads initially

to copper (I) benzotriazolate (Siedle, Velapoldi, and Erickson, 1978 and 1979)

which subsequently oxidizes in air. The structure described herein shows

how the benzotriazolate anion, acting as tridentate ligand, can bridge multiple

sites containing both copper (I) and copper (II). It is possible that similar

bonding is involved in the corrosion-resistant surface phase produced on

the bulk metal.

2. On-Going and Planned Work

The geometric nature of the copper-nitrogen cluster in Cu_ (BTA) , (t-C, H NC)

,

5 6—49 4

gives rise to highly unusual electron paramagnetic resonance (EPR) spectra.

The compressed octahedral configuration of Cu(II) requires that the room temperature EPR spectrum be interpreted in terms of a dynamic Jahn-Teller

effect. The EPR spectra at low temperatures indicate that the complex

undergoes a reversible phase change at -120 °C. Furthermore, low

23
REACTOR PADIATIOII DIVISION AND COLLABORATIVE PROGRAMS

temperature EPR spectroscopic studies predict that the copper-nitrogen

o coordinate bonds at Cu(II) will be elongated by approximately 0.01 A.

If the phase change observed in the EPR spectra is correlated with a crystallographic phase change, the low temperature crystal structure of

the complex would be cubic. In addition to the tert -butyl isocyanide

derivative, the three related complexes Cu_ (BTA) . (R-NC) ,

, where

5 6 4

R = isopropyl, cyclohexyl, and phenyl, have been synthesized. It is

expected in these complexes that the geometry of the copper -nitrogen

cluster will remain essentially the same. The EPR spectra for these

compounds are currently being recorded and analyzed. It is planned to

carry out x-ray and neutron diffraction studies on these compounds to

further correlate the EPR spectra with any structural changes.

1. P. J. Fisher, N. E. Taylor, and M. M. Hardin, J. Chem. Soo. ^ 2303-

2309 (1960).

2. T. J. Greenhough and M. F. C. Ladd, Acta Cvyst. B34, 2744-2752 (1978).

3. R. Hamalainen, U. Turpeinen, and M. Ahlgr^n, Acta Cryst. B35, 2408-2410

(1979).

4. G. F. Kokoszka, et al. (1982). In preparation.

5. G. Kolks, C. R. Frihart, H. N. Rabinowitz, and S. J. Lippard, J. Am.

Chem. Soo. 98, 5720-5721 (1976).

6. J. H. Marshall, Inorg. Chem. 17, 3711-3 (1978).

7. J. Reedijk, G. Roelofsen, A. R. Siedle, and A. L. Spek, Inorg. Chem.

18, 1947-1951 (1979).

8. A. R. Siedle, R. A. Velapoldi, and N. Erickson, Inorg. Nual. Chem.

Lett. 15, 33 (1978).

9. A. R. Siedle, R. A. Velapoldi, and N. Erickson, Appl. Surf. Sci. 3_, 229-235 (1979).

10. F. S. Stephens, J. Chem. Soo. (A) , 883-890 (1969).

11. J. C. van Niekerk and L. R. Nassimbeni, Acta Cryst. B35 , 1221-1223

(1979).

24
REACTOR RADIATION DIVISION AND COLLABORATIVE ^ROGPAllS

12. V. Vrabel, J. Garaj , and L. Kutschabsky, Acta Cvyst. B35 , 357-360 (1979)

13. R. J. Williams, D. T. Cromer, and A. C. Larson, Aota Cryst. B27 , 1701-

17-06 (1971).

NEUTRON DIFFRACTION STUDY OF SODIUM SESQU I CARBONATE DI HYDRATE

C . S . Cho i

(Energetic Materials Division, LCWSL, ARRADCOM, Dover, NJ)

and

(National Bureau of Standards, Washington, DC)

and

A. D. Mighell

Na„C0„'NaHC0-*2H crystallizes in the monoclinic space group C2/c

with a = 20.36(2), b = 3.48(1), c = 10.29(1) A, 3 = 106.48(1)°, Z = 4,

-3

Dx = 2.147 Mg m . The final R value after full matrix least-squares

refinement was 0.040 for 742 observed reflections. In this structure,

3-

water molecules and (C0„'H*C0 ) anions form a two-dimensional hydrogen3-

bonded network (figure 1). The (HC„0,) anion is almost planar and

2- ^ ^ consists of two C0„ anions linked by a hydrogen atom which lies at a

^

I

1 o center of sjnranetry with an 0...H...0 distance of 2.46 A. Analysis of

thermal ellipsoids (figure 2) from a conventional anisotropic refinement

and a least-squares refinement of a split-hydrogen model revealed that

this hydrogen atom is dynamically disordered between two equivalent

o sites separated by 0.211(9) A.

To further study the nature of the disorder, it is planned to

collect neutron powder diffraction data at room and low temperatures.

Various models will be refined using the technique of neutron profile

analysis.

25
REACTOR RADIATIOn DIVISIOII AMD COLLABOPATIVE PROGPjM'S

(A)

1.0

(B)

Figure 1. Packing and hydrogen bonding In sodium sesqulcarbonate

dlhydrate. Figure (A) Is the (0 1 0) projection of one half of the unit cell. This figure shows that the Na cation

layer and the anion layer (marked by broken lines and

consisting of (C03*H-C02) J~ Ions and water molecules) are oriented parallel to the (1 1) plane and Interleave each

other. Figure (B) Is the projection of the anion layer

onto the (1 1) plane, showing a two-dimensional hydrogenbonded network.

26
REACTOP. RADIATIOIT DIVISIOIT AnD COLLABORATI''E PEOGPAilS

(B)

Figure 2. The thermal ellipsoid of the H(3) atom: (A) view along the

normal to the plane C-0(2) . . .H(3) ; and (B) view parallel to

the plane.

27
REACTOR RADIATION DIVISION AND COLLABOPATIVE PROGRAJ^IS

SINGLE CRYSTAL X-RAY STRUCTURE DETERMINATION OF THE

DIMETHYL OXIME OF PHOSPHORAMIDE MUSTARD^ C7H^gN302PCl2

V. L. Himes

(The Catholic University of America, Washington, DC)

and

(National Bureau of Standards, Washington, DC)

and

A. D. Mighell

and

S. Takagi

(American Dental Association Health)

and

G. Zon and S. M. Ludeman

(The Catholic University of America, Washington, DC)

Cyclophosphamide (1) is a well-known drug which exhibits antineoplastic

activity against a relatively broad spectrum of human cancers. Consequently,

there is considerable interest in understanding the mechanism of action which

underlies the oncostatic specificity of cyclophosphamide. Rationally

designed test compounds should provide indirect evidence concerning the

mechanism of action of CP. In addition, it is possible that such studies

could lead to the synthesis of new compounds with anti-cancer activity

superior to that of CP. These investigations have been greatly assisted by

single-crystal x-ray structure determinations of CP, CP metabolites, and CP

T 2 analogs.

A new drug-design strategy which is based on the "pro-metabolite"

delivery concept is being applied to the CP system. The application of the

pro-metabolite delivery concept to derivatives of phosphoramide mustard

has lead to the synthesis of (2) . This novel anti-cancer prodrug has a N Clh

\p// ^"^"^ r^

O N(CH2CH2Ci)2 N—o~P=0

(1) G) N(Cn2CH2C^)2

28
REACTOR RADIATIOn DIVISIOH AITD COLLABORA'^IVE PROGFAMS

proposed mechanism of action involving enzymatic N-0 bond reduction to

generate the phosphoramide mustard which is the active metabolite produced

from CP. The P(0)ON=C moiety common to this class of compounds has no structural precedent.

I(R) .II(S) I(R) II(S)

Ku

P /\

.N

DM0 DM0

P

/\\

.N

Mu Mu DI-IO DM0

/ -^ N

Mu

P

/\\ . N

. .. N N N .0 N

-^7 % / \/ \ /

p. p, p p. ^ \ y ^\ y \ y '\

DMO Mu Mu DMO DM0 Mu Mu DMO

I'(S) II' (R) I'(S) II' (R)

Mu » -N(CH2CH2C1)2

DMO «=• "0N=C(CH3)2

Figure 1. Schematic representation of the hydrogen bonding in the dimethyl

oxime of phosphoramide mustard.

The dimethyl oxime of phosphoramide mustard (2), C^H ,N 0-PCl , crystallizes in the triclinic space group PI with Z = 4, unit cell

parameters a = 9.517(3), b = 10.872(3), c = 14.345(3) A, a = 92.01(1),

3

3 = 103.66(1), Y

= 115.69(1)° and d , = 1.42 g/cm . The structure was caic

solved by a combination of phasing techniques. The positions of the P and

29
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

CI atoms were determined by direct methods while successive least-squares

refinements and Fourier syntheses revealed the positions of the remaining

nonhydrogen atoms. Full-matrix anisotropic refinement of the model (which

did not include hydrogen atoms) gave a conventional agreement factor of

R = 0.077 for 2562 observed reflections with I >_ 3a (I).

There are two crystallographically independent molecules (I and II)

in the asymmetric unit. Comparison of the bond distances, angles, and

dihedral angles reveals that the conformations of molecules I and II are very similar. Each molecule participates in four hydrogen bonds which are

o almost identical in length ("^ 2.94 A). A schematic representation of the

hydrogen bonding is shown in figure 1. In each molecule, the amide nitrogen

atom is the donor in two hydrogen bonds while the phosphoryl oxygen atom

is the acceptor in two hydrogen bonds. Molecule I is hydrogen bonded to

molecule II which has the opposite absolute configuration at phosphorous.

In addition, molecules I and II are each hydrogen bonded to a centrosymmetrically related molecule to form the dimers I. . .1' and II. . .II'.

The hydrogen bonding in the structure is such that a ladder is formed which

is parallel to the (1,1,0) direction in the unit cell.

The packing in the structure is interesting not only from the point

of view of the hydrogen bonding, but also with respect to the orientations

of the -N(CH CH„C1)„ and -ON=C(CH^)„ moieties in the two independent molecules,

Parallel to the ladder of hydrogen bonds are two rows of two chlorine atoms

and four rows of alternating chlorine atoms and methyl groups from molecules

I and II. The distances from the phosphorous atom to the chlorine atoms

o and to one methyl carbon atom are approximately equal ('^ 5.0 A) in each

molecule. Thus, in terms of spatial considerations, it appears that the

-ON=C(CH„) moiety has "substituted" for an -NCH CH CI moiety in the structure.

1. 0. M. Friedman, A. Myles, and M. Colvin, "Advances in Cccnoer

ChemotherapyJ " 143-204 and references therein (1979).

2. G. Zon, Progr. Med. Chem.j in press.

30
REACTOR PADIATIOII EIVISIOIT AMD COLLABOMTIVE PROGRAl^.S

STUDY OF HYDROGEN BONDS IN Ca2KH7(P04)4'2H20

S. Takagi and M. Mathew

(Amerlean Dental Association)

and

E. Prince

The crystal structures of the Isomorphous compounds Ca (NH, )H (P0,),*2H„0

and Ca„KH^(P0,),*2H have been determined previously from x-ray diffraction

data. A unique feature of these structures is that, if the crystal is

assumed to be centros3amnetric, three pairs of oxygen atoms in phosphate

groups are hydrogen bonded across centers of sjrmmetry, forming an infinite

3-

[Ho(PO,)^] sheet structure. Because x-ray diffraction data do not permit

a detailed analysis of the hydrogen bond structure, a neutron diffraction

study was undertaken.

The unit cell is triclinic, with cell parameters, as determined by

x-rays, equal to a = 5.676(1), b = 12.210(2), c = 6.292(1) A, a = 104.10(2)°,

S'li/y^

,i^®

. sr~ ^-^ y^

Figure 1. Stereoscopic view of the structure of CaKH^(PO^)^ '21120

31
REACTOR RADIATION DIVISIOII AND COLLABORATIVE PROGRAMS

>^

5-1 +J

CU ^M e O 6 ^ en M o

PLI 03 M-l OJ o

Cu3 en i-i O 0) (U

i-i H J_) o ex c

3 (U

(U o o

a u

^ o rt a

CO E cfi o w

-H C •u o

•H nj (-1 W o

kJ o e CO eg oj 3

< p= •H CO H i>J U) C

CO o

<r nj "H

^^-^ 4-1 w

<t O -H o (X m

p-l o

nj a

r~^ M-l Xl K O 0) ^ !-i ^-^ (U

CNJ -H ^3

CO CO U U ^ O

Cfl (U -H C n3 O

O

S

vO o ><T fO <r CnT ^ r-~- ^ r-i <r <r o <r o ^T P ;:;;;^ P vO —

1

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f

.—

1

^ .—

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-I f—

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(

^ t-^ ^ eg rg m m r--. lO m

00 LO r-- r^ r^ ON ^ vO CN l/N m vO L.n 00 r^ <T OS r^ on oo ro m C^\ CN m <r CN c^ ly^ <r O r^ Cvl vO .-H O vC <r L/N o o <-> O o o <-> f—

i

o o 1—

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<-> o o O o o O O O o o o O o O o O o O o o oooooooooooooooooooo

ro vT) <r ^H in CN in p ;;^ ^ CN m in m r^ CTS in o ^T) vr

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(

^ .—) '-< -< I-H -1 —I r-l '-' 1—

1

CN CN CN c^ in v3- <r <r m 00 tNl m rg oo O n CN O Cs] ON CJN r^ in ^ r-^ CN ^

O r-. m i-H ,—

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-H r—l -.T CN r-H c*^ r-i vC 00 <r vO o <-) o O f—

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o o ,—

(

o <r> o O o o -H O c^ f-4 o f-H o o o o o o o o o o o O o o O c O o o O

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o <T in m r^ CN m r^ CN en <r in kO vO o en in in Cjv r^

f—

1

o i-H ^H r~i '-' I-H 1—1 I-H ^H —

i

^ -1 CN m r^ r^ vD in m

.—

f

CN in en r<l o r^ CTN CTN m in CT> o OO o <T CT> in -T r^

>:r o ^ <T o in in en r^ ^H <r o CN CNJ <r r-- OO I-H 00 in

r> o o O o C-5 o o <~> O o <-> o c-> o C-) c-> CN T—i <-i o o o O o o o o O o o o o o O c O O O

ooooooooocooocoooooo

r^ <r r^ in vC in I-H o <r <r in in ^ r^ P <r ^ r^ o I-H -1 vO " I-H ^ CN CN •-< I-H —1 CN en e^ c^ ^ in in

CTN CT> <r 00 <r ^-i in en r^ CN <r <N CN r^ _l in m 00 CTN CN

00 r^ CN in en vO in 1—

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^.^ in 00 00 CTN V.O CTV rsi r~^ ^£5 CO ^ CT^ en ^ tn CTv 3 P ^ CN rH rH ^H rH >-< I-H CN f-i r-H l-l CN rH en -a- -^ e^ '-I oc 00

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O^frH-vj-'—I"—<<rocNir^Ln"<j-rHmv£)OcNiOLnun OOOOOOOOOOOOOOOOOOOO

uii(i&-cuooooooooon:x

32
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

TABLE 2

Selected Bond Distances and Angles in

Ca KH (PO ), 2H 0, Neutron Results

Ca...0(12) 2.389(5)A

Ca...0(21) 2.345(5)

Ca...0(21) 2.475(4)

Ca...O(22) 2.323(6)

Ca...O(22) 2.513(5)

Ca...O(23) 2.604(14)

Ca.. .0(24) 2.709(5)

Ca...0(3) 2.477(6)

P(l)-0(11) 1.560(5) 0(11)-P(1)-0(12) 108.6(3)

P(l)-0(12) 1.504(5) 0(11)-P(1)-0(13) 109.0(3)

P(l)-0(13) 1.534(5) 0(11)-P(1)-0(14) 107.3(3)

P(l)-0(14) 1.541(7) 0(12)-P(1)-0(13)

0(12)-P(1)-0(14)

0(13)-P(1)-0(14)

110.1(3)

111.5(3)

110.2(3)

P(2)-0(21) 1.492(4) 0(21)-P(2)-0(22) 119.6(3)

P(2)-0(22) 1.489(5) 0(21)-P(2)-0(23) 111.8(3)

P(2)-0(23) 1.567(6) 0(21)-P(2)-0(24) 103.0(2)

P(2)-0(24) 1.580(5) 0(22)-P(2)-0(24)

0(22)-P(2)-0(24)

103.9(2)

111.0(3)

Q 0(23)-P(2)-0(24) 107.2(3)

0(23)-H(23) 1.065(9)A P(2)-0(23)-H(23) 118.2(4)

0(24)-H(24) 0.989(9) P(2)-0(24)-H(24) 118.2(4)

0(3)-H(31) 0.959(8) H(31)-0(3)-Hf32) 106.3(7)

0(3)-H(32) 0.958(7)

0(11)-H(11) 1.252(4)

0(13)-H(13) 1.240(4)

0(14)-H(14) 1.237(4)

0--H H..0 <0-H

0(11)... 0(11) 2.504 1 252(4) 1.252(4) 180

0(13). ..0(13) 2.479(5) 1 .240(4) 1.240(4) 180

0(14). ..0(14) 2.474(6) 1 .237(4) 1.237(4) 180

0(23). ..0(12) 2.572(6) 1 .065(9) 1.512(9) 173.0(6)

0(24). ..0(3) 2.717(6) 989(9) 1.737(9) 170.0(5)

0(3) ...0(11) 2.799(6) .959(8) 1.867(9) 163.3(7)

0(3) ...0(23) 2.877(5) 958(7) 2.556(9) 99.7(6)

0(3) ...0(13) 2.893(5) 958(7) 2.073(9) 142.5(9)

0(3) ...0(14) 3.055(6) 958(7) 2.455(10) 120.5(8)

33
REACTOR RADIATION DIVISION A^ID COLLABORATIVE PROGP^MS

6 = 115.16(2)°, Y = 84.25(2)°. Of 1945 reflections measured within a

o limiting sphere defined by a maximum 29 of 117 and a wavelength of 1.273 A,

1293 had intensities significantly above background. The parameters from

an x-ray refinement were used as the starting point for a refinement of the

structure with the neutron data in space group PI. The refinement proceeded

to R = 0.073, R = 0.065. Table 1 gives the refined parameters and table 2 w

gives selected bond distances and angles. Figure 1 is a stereoscopic pair

giving a view of the structure. An attempt will be made to refine the

structure in space group PI to see if this gives an indication that the

potassium atom and three of the hydrogen atoms that appear to occupy symmetry

centers or disordered positions near them actually occupy asymmetric

positions.

EFFECTS OF INTERSTITIAL ELEMENTS ON PHASE

RELATIONSHIPS IN THE TITANIUM-ALUMINUM SYSTEM

R. M. Waterstrat

(American Dental Association)

and

E. Prince

The objective of this research is to determine the effect of

interstitial solute elements, such as oxygen, nitrogen and carbon on

the a/a + a^/a^ phase boundaries in the Ti-Al system. These influences must be adequately defined since the interstitial elements are ubiquitous contaminants in titanium alloys beginning with the initial

starting material (titanium sponge) and accumulating through various

stages of fabrication to the final product. Once present, they cannot

be easily removed. Furthermore, some contamination of titanium alloys

by these elements is virtually unavoidable since hot titanium is capable

of scavenging them from an ultra high vacuum (pressures <10 torr) or from the highest purity inert gases (impurity contents <5 ppm) . The

only practical solution to these problems of interstitial contamination

34
REACTOR RADIATIOll DIVISIOII AND COLLABOFATIVE PROGPAIIS

a Phase a 2 Phase

Figure 1. Schematic representation of the structures of the a phase

and the a„ phase. Open circles represent Ti atoms, dark

circles represent Al atoms and grey circles represent a statistically random occupancy by both Ti and Al atoms in

the ratio called for by the phase composition. Darker lines

outline the respective unit cell for each structure. The

a„ phase structure actually involves slight displacements

of the Ti atoms from the ideal positions shown here (see

ref. 3).

is to set maximum allowable limits for it and then impose effective

controls on it. This requires a knowledge of its effect on alloy properties and behavior.

It is well known that oxygen, for example, can be a source of

embrittlement in titanium and its alloys. In pure titanium the mechanism of embrittlement probably involves an interaction between oxygen

atoms and dislocations which tends to immobilize the dislocations and

produce a ductile/brittle transition (1). In titanium-aluminum alloys,

however, oxygen seems to act by promoting the formation of the brittle

a phase (Ti Al) , an atomically ordered version of the more ductile a

phase structure (2). There is a lack of precise information about how

oxygen stabilizes the a phase since phase relationships in the Ti-Al-0

system have not been well defined. Attempts to determine the relevant

portion of this ternary diagram have been plagued by the same experi35
REACTOR PADIATIO>^ DIVISIOII AMD COLLABORATIVE PROGRAMS

mental problems which have hindered the development of the binary

Ti-Al phase diagram for so many years. The most serious of these

problems are: an inability to prevent decomposition of quenched alloys,

an inability to discriminate quantitatively between the a and a^ phases

in two-phase alloys, an inability to estimate the effects of coherent/

incoherent interactions and persistent problems with alloy contamination at high temperatures.

The first three lines (100, 101, 110) are called "superlattice

lines" since they exist only when long-range atomic ordering is present

while the last three lines (200, 002, 201) are "fundamental lines" common to both ordered (a^) and disordered (a) phases. Actual neutron

diffraction patterns which we obtained from a and a„ phases are shown

in Figure 2. It is estimated that, using neutrons, less than 1% a^

phase in a matrix of a phase would be detectable whereas, using X-rays

one would be fortunate to detect 10% a„ in a phase. The extraordinary

intensities of the "superlattice lines" for neutrons result from an exceptionally large difference in neutron scattering potentials (b)

for the Ti and Al sublattices relative to the average potential for a random occupancy of these sublattices. This can be calculated from

the known scattering potentials for neutrons (b , b ) and for X-rays

(f , £.-,)• (The latter are proportional to the respective atomic

numbers.) A unique ^ feature of b . and b ^ is that they are of equal

Ti Al J H magnitude by opposite sign. This means that Ti and Al atoms scatter

the incident neutrons 180*^ out of phase with each other. Such phase

differences do not occur with x-ray scattering.

The relative intensities seen in figure 2 are not in complete

agreement with those calculated in table 1. This indicates that the

sample had some preferred crystalline orientations. The (110) superlattice

line seemed to be particularly affected since its intensity is about twice

as strong as would be expected. However, the sample was not rotated during

the experiment and proper rotation could be expected to reduce or even eliminate such orientation effects. Furthermore our samples will contain

various amounts of oxygen and other interstitial elements which are known

36
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAllS

(101;

Hexagonal

«2- Tig Al

a = 5.79A

c = 4.66A

Neutron Diffraction Patterns

A = 1.5426A

101

Hexagonal

Pure a - Ti a = 2.95A

c = 4.68A

15 20 25 30 35 40

26

Figure 2. Neutron diffraction patterns for a phase (annealed Ti powder)

' and a^ phase (annealed Ti„ Al) . Lines are identified with

their Miller indices. The patterns were obtained at room temperature using unrotating samples.

to produce strong grain-size refinement in titanium alloys. This would

also act to reduce grain orientation effects. Complete randomness is not

essential in our studies, however, since we are more interested in detecting

the presence of the a and a„ phases rather than in measuring the precise

percentages. The expected width of the two-phase (a + a ) regions is

approximately 10 at.% Al and this contributes to a high sensitivity, since

a 1 at.% variation in Al content will produce approximately a 10% variation

in the volume percentage of these phases. Thus the phase boundaries should

be locatable with an accuracy of better than + 1 at.%.

37
-L -l-„rT.-i./ UO-Ll Ig, -^v— l.ciyo CLLH_l

X-rays neutrons

2 76

5 253

2 123

24 22

11 26

100 100

REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAIIS

Table 1, Calculated Relative Intensities of Diffraction Peaks in

Fully Ordered a Phase (Ti^Al) Using X-rays and Neutrons.

hkl

100

101

110

200

002

201

Another possible complication in our samples would be the presence

of rather fine (optically unresolvable) particles in samples annealed

at low temperatures ('^600°C, for example) . This may produce appreciable

o broadening of our diffraction peaks if the particles are ^^50 A in

diameter or less. In most of our samples we expect the second phase

particles to be much larger than this. However, our inherently high

sensitivity will help to overcome the slight reduction caused by

particle-size broadening of the diffraction lines and we do not expect

this to be a serious problem.

It may be of some interest for this study to apply neutron diffraction techniques to locate oxygen atom positions in the a and a phase structures. This has already been done for a phase alloys in the

binary Ti-0 system (14) . It was found that the oxygen atoms tend to

occupy octahedral interstices in this structure. They do so in a random

manner at high temperatures ( 700°C) , but an ordering of the oxygen

atoms occurs in these sites at lower temperatures. The ordering is

centered around the stoichiometries Ti,0, Ti_0, and Ti 0. It is

D J I unlikely that exactly the same type of ordering will be found in a« phase (Ti Al) since its solubility for oxygen is lower than any of these

compositions. A random occupancy of the octahedral sites by oxygen in

the a„ phase is conceivable, however, and it is noteworthy that the

lattice parameters of both a and a„ phases show a similar behavior with

respect to additions of oxygen. The hexagonal (a) axis is affected

38
REACTOR RADIATIOn DIVISION AND COLLABORATIVE PROGPA>IS

our samples will contain various amounts of oxygen and other interstitial elements which are known to produce strong grain-size refinement in titanium alloys. This would also act to reduce grain orientation effects. Complete randomness is not essential in our separation

during cooling at lower temperatures. Further work is needed to settle

this question. Our results, however, lead us to conclude that our first samples in the a- a_ two-phase region should be a ternary series

at the 6 at.% level where we will locate both the a and a^ phase

boundaries in the ternary system and can then estimate the boundaries

at lower oxygen contents by extrapolating to the known binary system.

Similar procedures can subsequently be followed at other oxygen levels

and at various temperatures until the necessary data have been obtained.

1. Preliminary Neutron Diffraction Experiments

The a phase is a substitutional solid solution of Al in hexagonal

Ti in which the Ti and Al atoms are distributed at random among the

available atomic sites in the structure (Fig. la). The a phase structure is a "super lattice" in which the Ti and Al atoms take up an ordered

arrangement with respect to each other (Fig. 3b). The onset of atomic

ordering will produce extra lines in the diffraction patterns for X-rays

or neutrons and these will be detected the more readily as the average

scattering potentials of the Ti and Al sublattices become appreciably

different. This will occur, for example, as the degree of long-range

atomic ordering increases. It will also occur when neutrons replace

Table II. Percent Difference in Atomic Scattering Potentials for Ti

and Al Relative to the Average Potential (wieghted for

compos it ion)

.

4(f^. - f^,) 4(22 - 13)

X-rays = = ^o/o

Ti Al

4(b^. + b^, 4(-.34 - .35) Ti Al ,na/ Neutrons = ^iz/o

3b^. + b,, -.67

Ti Al

39
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

x-rays as the diffracting radiation since the difference in scattering

potential for Ti and Al atoms is much greater using neutrons than when

using x-rays. We have calculated the relative intensities to be expected for a fully ordered a phase structure (Ti Al) with x-rays and with

neutrons for the first six lines in the pattern (Table 1)

.

very little while the (c) axis undergoes a pronounced expansion. The

oxygen solubilities in co-existing a and a phases are of considerable

interest since it has been postulated that a partitioning of oxygen

occurs in favor of the a phase which tends to stabilize this brittle

constituent (2)

.

1. D. Gupta and S. Weinig, "The Dislocation-Oxygen Interaction in

Alpha Titanium and its Effect on the Ductile to Brittle Transition,"

Trans . Aims 215 (1959) pp. 209-216.

2. J. Y. Lim, C. J. McMahon, Jr., D. P. Pope, and J. C. Williams,

"The Effect of Oxygen on the Structure and Mechanical Behavior

of Aged Ti-8 Wt . Pet. Al , " Met. Trans. Ik (1976) pp. 139-144.

3. P. C. Gehlen, "The Crystallographic Structure of Ti Al," The

Soienae, Teahnology and Application of Titanivim, pp. 349-357;

Pergamon Press, New York, NY 1970.

STUDIES OF ZEOLITE STRUCTURE BY NEUTRON POWDER DIFFRACTION

J. B. Parise

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

and

E. Prince

Zeolites are a class of commercially important reactant and product

selective absorbants and catalysts whose selectivity arises from the sizes

and configurations of pores and channels within aluminosilicate frameworks.

By choosing zeolites with specific channel sizes it is possible to select

only those products that are smaller than the channel sizes. A knowledge

of the sizes and configurations of the pores under the conditions at which

the zeolites usually operate is crucial to an understanding of their

40
REACTOR PADIATION DIVISION AND COLLABORATIVE PROGRAMS

Table 1. Atomic parameters for dehydrated (K, Cs)-ZK5 at room temperature.

Atom X Z z B(A^)

Si 0.0831(3)* 0.2021(3) 0.3208(4) 0.4(2)

01 0.1284(2) X 0.3156(4) 2.3(2)

02 0.2518(3) X 0.4082(4) 1.8(2)

03 0.0 0.1792(4) 0.3364(4) 2.1(2)

04 1/4 0.1080(2) 0.3920(2) 2.2(2)

Csl 0.0 0.0 0.31

Cs2 1/4 1/2

esd s in parenthesis.

chemical properties.

The structure of a typical small pore zeolite, designated ZK-5, has

been studied at 25°C and 220°C using the NBS high resolution powder

dif fractometer. Although there is some uncertainty due to variations

in framework geometry upon hydration and heating, the positions of the

metal atoms (in this case Co and K) have been determined in this study.

A list of refined parameters is given in table 1.

The analysis of these data sets is continuing. Further studies of

ZK-5, in its hydrogen and metal exchanged forms, will help in the

interpretation of adsorption data collected on small pore zeolites at

du Pont. It is hoped that by studying changes of geometry with temperature

in "simple" small pore zeolites we may establish a basis for predicting

such changes in more complex systems.

41
REACTOR P-ADIATIOn DIVISION MID COLLABOPATIVE PROGPAJ^S

STRUCTURE REFINEMENT OF COMPOSITIONS IN THE

NASI CON SOLID SOLUTION SYSTEM

L. J. Schioler and B. J. Wuensch

(Massachusetts Institute of Technology, Cambridge, MA)

and

E. Prince

Increasing interest in solid state fast ion conductors led to the

discovery (Goodenough, et al. 197 6) of the NASICON solid solution system,

which can be represented by the formula Na, . Zr.Si P„ 0^ ^ , with < x < 3.

1+x 2 X 3-x 12

The composition with x = 2 was christened NASICON for NA Super Ionic

CONductor. It was found to have an ionic conductivity at 300°C of 0.2

(ohm-cm) , which is comparable to the best beta" -alumina. NASICON has

advantages over the beta aluminas in that it can be sintered to a high

density at a lower temperature (1200°C as compared with 1500°C) . It is

insensitive to moisture, which reduces the conductivity of beta alumina,

and the ion migration occurs through channels which are linked three

dimensionally in the structure as opposed to beta alumina, where the ions are mobile only within planes.

The structure of the end members of this solid solution system,

NaZr P (x = 0) and Na.Zr Si (x = 3), were first determined by

Hagman and Kierkegaard (1968) and Sizova et al. (1973), respectively.

These were found to be rhombohedral with space group R3c . The structure

is based on a "lantern" shaped unit consisting of two octahedra and three

tetrahedra linked at the corners. These "lantern" units form a threedimensional framework, with the sodium ions occupying interstices. Figure

1 shows this "lantern" unit as well as a projection of the NaZr P structure

on [001].

Hong (1976), in work done in conjunction with that of Goodenough et

al., studied several compositions in this system using x-ray powder

diffraction techniques. He found that the powder patterns of all

compositions except those in the range 1.8 < x < 2.2, could be indexed

on a rhombohedral lattice (space group R3c) . The compositions with

42
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGPAF.S

1.8 < X < 2.2 could be indexed on a monoclinic lattice (space group C2/c,

which is a subgroup of R3c) . Table 1 gives the space group parameters

for R36 and C2/c. Attempts to determine the structures of other compositions

in the solid solution were not successful due to the inability to grow

single crystals. From x-ray powder data, Hong postulated the structure

parameters of the highly conducting composition NASICON (x = 2 . 0) . In

this monoclinic structure he assumed that the silicon and phosphorous are ordered on the 8f and 4e sites, respectively. This ordering could be one of the reasons the structure changes from rhomohedral to monoclinic

and back as x increases.

Hong found a variation in lattice parameters with composition

(figure 2) . The a. lattice parameter increases with x, while the c^ parameter goes through a maximum, resulting in the cell volume also

exhibiting a maximum. Interestingly enough, the conductivity vs. composition plot also exhibits a maximum for a composition near where

the cell volume is maximized (figure 3) . The reasons for the unusual

behavior of the lattice constants and the conductivity has not yet been

explained. The most likely reasons for this behavior are the changes

in the geometry of the framework, the size of the "bottleneck" between

the sodium sites, and the concentration of the mobile sodium, all of

which vary with the composition. Which of these has the greatest effect

on the lattice parameters and the conductivity will remain unclear until

structure refinements have been carried out on the intermediate compounds

in the system.

For two reasons the information obtainable from x-ray powder

diffraction techniques is not sufficient for a structure refinement to

determine the causes for the unusual behavior. The main reason is that

the peaks in the x-ray powder pattern are difficult to model in a profile

analysis, resulting in a poor fit. The second reason is that in x-ray

diffraction, the scattering is dominated by the heavy elements in the

material, in the NASICON system the zirconium. These problems can be

overcome by the use of neutron diffraction techniques, because the peak

43
REACTOR RADIATIOn DIVISION AND COLLABOPATIVE PROGPAtlS

(b)

O Oxygen

® Sodium

• Zirconium

• Phosphorus

Figure 1. "Latern" unit upon which the NASICON type structure is based

(upper). Projection of NaZr P an [001], after Hagman

and Kierkegaard, (1968) (lower).

of a neutron powder pattern are well described by a Gaussian shape, and

the scattering powers of the elements are more nearly equal.

Four samples in the NASICON solid solution system were brought

to NBS for study using neutron diffraction. The compositions of the

samples were selected to give structural information near critical

changes in the lattice parameters. Two of the compositions selected,

X = 1.6 and x = 2.5, bracket the high conductivity composition region

as found by Kafalas and Cava (1979). Another composition was NASICON

per se (x = 2.0). The last composition (x = 1.0) was selected to be

44
REACTOR PADIATIOM DIVISION AND COLLABORATIVE PROGPJJ^IS

1630

1610 IS 1590

<D 1570 E

3

1550 o

>

1530

ISIO

3100

23 75 < 33 50

• • • • •

• • •

• • • •

.6 8 10 12 14 16 18 2 2 2 2 4 2 6 2 8 3

Figure 2. Variation of cell parameters with composition in the NASICON

solid solution system. For 1.8 j^ x £ 2.2, these are the

hexagonal equivalent parameters. (From Hong, 1976.)

outside the region of high conductivity. Neutron powder patterns were

obtained at room temperature on the multidetector powder dif fractometer

Refinements of the four patterns were carried out using the Rietveld

method

Initially the compositions with x = 1.0, 1.6, and 2.5 were refined

on a rhombohedral lattice, and that with x = 2.0 on a monoclinic lattice,

Refinement of the x = 1.6 sample did not give a good fit. The x-ray

powder diffraction pattern of this sample was reexamined and it was noticed that the peak at 27.5 degrees 26, which should be a single peak

if the lattice is rhombohedral, had a slight shoulder, indicating that

the structure was actually monoclinic. Refinement on the monoclinic

lattice proceeded smoothly. The final lattice parameters are given

in table 2 and the refined structure parameters are given in table 3.

Refinement on the sodium occupancies in the four samples show that

the Na(l) site (6b) in the rhombohedral structures (x = 1.0 and 2.5) is

45
REACTOR PADIATION DIVISION AND COLLABORATIVE PROGPJ^IS

Figure 3. Variation of conductivity with composition in the NASICON

solid solution system.

-1 OKafalas and Cava (1981) _ r^ _ '^Boilot et al (1979) nO°^'"o

^Goodenough et al (1976) °°;.

-2 _ niranQui et al (1918a) A

V

OTranQui et al (1981b) "^c X A

V o

-3 DO

V

A V

-4 VA

D

o

V

O

-5 - O

-6 V

A

-7 D V

D

-8

J 1 1 1 1 1 1 1

1 1 1 1 1 o

1 1

1 2 3

X in Naj^^Zr^Si^Pj^Oi^

Figure 4. Relationship between the rhombohedral, hexagonal, and mono- clinic cells.

46
REACTOR RADIATION DIVISIOH AND COLLABORATIVE PROGP^AMS

Table 1. Space group parameters,

R3c

Atom Position Point Equipoint 1

Symmetry

Na(l) 6b I

Na(2) 18e 2 X 1/4

Zr 12c 3 z Si/P 18e 2 X 1/4

0(1) & 0(2) 36f 1 X y z

C2/c

Na(l) 4d

Na(2) 4e

Na(3) 8f

Zr 8f

Si/P 8f

P/Si 4e

0(1) - 0(6) 8f

1 1/4 1/4 1/2

2 y 1/4

1 X y z

1 X y z

1 X y z

2 y 1/4

1 X y z fully occupied at room temperature, as is the equivalent Na(l) site (4d)

in the monoclinic structure of the compositions with x = 1.6 and 2.0.

The occupancies of the Na(2) and Na(3) sites (4e and 8f) of x = 1.6 are

not random; site 4e has a greater and site 8f has a lower occupancy than

would be expected for random occupancy. This is also observed in the

sample with x = 2.0.

The silicon and phosphorous occupancies show a significant shift

from random in the sample with x = 1.6. In this composition the occupanices

of the Si in the 8f and the P in the 4e site are greater than would be

expected for random occupancy of these two elements over the two sites.

For X = 2.0, refinement on the occupancies indicated that for this

composition the Si and P are almost completely ordered over sites 8f and

4e, respectively, thus confirming Hong's assumption of complete ordering

in the ideal structure.

47
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The framework does change as the composition changes across the

solid solution range. The sizes and distortions of the tetrahedra change

as X changes. In the rhombohedral structure the tetrahedra are fairly

regular, and are larger in the structure with x = 2.5 than in the

structure with x = 1.0, as would be expected when the larger Si is

substituted for the P . In the monoclinic structure there are two types

of tetrahedron: one with the central atom in site 4e and one with the central

atom in site 8f. The tetrahedron with the central atom in site 4e has a larger range of bond distances and angles than the tetrahedron in the

rhombohedral structure, but is less distorted than the second type of

tetrahedron in the monoclinic structure. The other changes in the framework and the size of the "bottlenecks" between sodium sites remain for

further analysis of the refinement on these structures.

+

1. J. B. Goodenough, H. Y. P. Hong, and J. A. Kafalas, Fast Na -Ion

Transport in Skeleton Structures," Mat. Res. Bull. 11, 203-220.

IV

2. L. 0. Hagman and P. Kierkegaard, "The Crystal Structure of NaMe

(PO,) ; Me^V = Ge, Ti, Zr," Acta. Chem. Soand. 22^, 1822-1832 (1968).

3. R. G. Sizova, A. A. Voronkov, R. G. Shumyatskaya, V. V. Ilyukhin, and

N. V. Belov, "Crystal Structure of Na.Zr (SiO.) ," Sov. Phys. Dokl.

17. 718-620 (1973).

4. H. Y. P. Hong, "Crystal Structures and Crystal Chemistry in the

System Na, Zr^Si P„ 0, „," Mat. Res. Bull. 11, 173-182 (197 6). l+x 2 X 3-x 12 —

5. J. A. Kafalas and R. J. Cava, "Effects of Pressure and Composition

on Fast Na"*'-Ion Conductivity in the System Na Zr Si P„_ O-i o

> " -^Q^^t

Ion TranspQrt in Solids, (P. Vashista, J. N. Mundy, and G. K. Shenoy,

eds.) Elsevier North-Holland, Inc. NY, 419-422 (1979).

51
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGPJ^IS

THE STRUCTURE OF AMMONIUM PARATUNGSTATE TETRAHYDRATE

H. T. Evans

(U. S. Geological Survey, Reston, VA)

and

E. Prince

Ammonium paratungstate tetrahydrate is a "heteropoly" tungstate

salt in which the hetero atom is hydrogen. An x-ray structure study by

D' Amour and Allmann (1972) established the structure of the heteropoly

anion, which has the composition H„W 0,_, except for the hydrogen

positions. It also located the nitrogen atoms of the ammonium groups

and the oxygen atoms of the water molecules, but, because the x-ray

diffraction intensities are dominated by the tungsten, no hydrogen atoms

could be located. A neutron diffraction study was undertaken to determine

the positions of the hydrogen atoms, of which there are 25 out of a total

of 59 atoms in the asymmetric unit.

Ammonium paratungstate tetrahydrate, (NH,) H W 0,„'4H 0, crystallizes

o in the monoclinic system, space group P2^/n, cell constants a. = 15.079(2) A,

b = 14.450(2) A, c = 10.968(1) A, B = 109.24(1)°, with two formula units

in the unit cell. Data were collected on the four-circle neutron diffractometer from a crystal with approximate dimensions 3.0 x 2.0 x 1.3 mm. Because of the large unit cell and the large amount of hydrogen in the

crystal an unusually small number of the accessible Bragg reflections

had observable intensities. Of 5256 unique reflections measured within

o the limiting sphere defined by a 20 of 120° and a wavelength of 1.273 A,

only 1553 had observable intensities. The structure parameters for the non- hydrogen atoms reported by D' Amour and Allmann were used to determine

phases to compute an F Fourier density map. Seventeen of the twenty-five

hydrogen atoms in the as3rrmnetric unit were easily located in this density

map and their positions were used to determine phases for a second map.

Six, and possi'''ly a seventh, of the remaining hydrogen atoms were located

on this new map, so that the positions of all hydrogen atoms except

those on one of the water molecules were determined. The structure was

52
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REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRJ^^S

refined by conventional methods to a weighted R of 12.8%. The relativelypoor fit is probably due to large curvilinear thermal motions, and a constrained, rigid body model will therefore be used in further refinement,

table 1 gives preliminary values for the atom parameters.

1. D'Amour, H. and Allmann, R. , Z. Krist 136_, 23-47 (1972).

THE STRUCTURES OF LITHIUM" INSERTED METAL OXIDES:

LiRe03 AND Li2Re03

R. J. Cava, D. W. Murphy, and S. Zahurak

(Bell Laboratories, Murray Hill, NJ)

and

A. Santoro

and

R. S. Roth

(National Measurement Laboratory)

There has been significant interest in recent years in materials

which undergo topotactic insertion of lithium because of their potential

use as electrode materials in secondary batteries. Lithium is ionic

in these compounds, and the charge is compensated by a reduction of the

host cations (chalcogen-chalcogen bonds may be reduced in some compounds)

.

Host structures may be of the layer or framework type. In the layer type,

the Li ions are accommodated in the van der Waals gap between layers, and

in framework structures, Li ions occupy formerly vacant cations sites.

ReO and shear structures related to it are suitable hosts for lithium, with

stoichiometries (5) 0.0 £ x £ 0.35, x = 1.0, and 1.8 £ 2.0. Structural

characterization of insertion compounds has lagged far behind the preparation

of new compounds due to the unavailability of single srystals for standard

crystallographic structure analysis. Lithium insertion inevitably involves

significant changes in structural dimensions which pulverize starting

materials. Neutron diffraction powder profile analysis is the best

56
REACTOR RADIATIOI] DIVISIOII A^TO COLLABORATIVE PROGRAllS

TABLE 1

Atom Position

(X^)

0.18(6)

0.273(1) 1.6(3)

0.2460(9) 0.27(6)

m = 1.5(12, R^ = 5.66, R^ = 5.55, R^^ = 7.04, R^ = 5.00. Space group

R3c, Z = 6. Number of observations: 2464. Number of independent Bragg

Re 6a

Li 6a

18b -0.3801(7) 0.012(1)

reflections: 49.

Atom Position X

(x^

Ke

Lil

Li2

6a

6a

6a

18b -0.3580(9) -0.008(2)

0.312(1)

0.169(1)

0.2551(8)

0.21(6)

1.4(3)

1.4(3)

0.21(6)

m = 3(12), R^ = 8.5, R^ = 7.58, R^ = 9.77, R^ - 7.71. Space group:

R3c, Z = 6. Number of observations: 2505. Number of independent Bragg

reflections: 65.

technique for structure determination, as it requires only a polycrystallii$ft,

powdered sample, and is more sensitive than x-ray diffraction in the characterization of light atoms such as Li in structures which contain atoms

of higher atomic number.

Neutron diffraction measurements were performed on a powder

diffractometer at the NBS Reactor. The samples were loaded into 1-cm-diameter

vanadium cans sealed with wax to avoid decomposition of the compounds,

which are air sensitive.

57
REACTOR RADIATIO:] DIVISION AND COLLABORATIVE PROGPAi:S

The powder profile refinement was performed with the Rietveld

method adapted to the five-detector dif f ractometer design and modified

to allow the refinement of background intensity. In the course of this

analysis, it became apparent that the peaks produced by samples of the

two compounds did not conform to a Gaussian distribution. This effect

cannot be attributed to instrumental factors, since the dif f ractometer

,

used with identical conditions and with standard materials such as Al 0„,

gives Gaussian diffraction lines over the entire 20 angular range within

very good approximation (X between 1.1 and 1.2, by fitting single peaks).

The program was then further modified to describe the line profiles with

the Pearson Type VII distribution, which allows the lineshape to be

changed continuously from Gaussian to Lorentzian through one additional

profile parameter.

Atomic positions and thermal parameters for the LiReO_ and Li ReO„

structure are presented in Table 1.

There is a close relationship between the structures of ReO„ , and

Li_ReO„. The ReO„ host lattice in the lithium- inserted phases can be

derived from that of ReO„ by a rotation of approximately 6U° about a cubic (111) direction, with the shared corners of the ReO^ octahedra

6 acting as hinges. No bonds are broken. For a rotation of exactly

60°, the transformation is from a 3/4 CCP and HCP. The resulting phases

have rhombohedral symmetry, with the cubic (111) rotation axis becoming

the hexagonal c axis

.

The twist in the ReO host lattice occurs to accommodate the

coordination preferred by the Li ions, and is possible because of the

exclusive corner sharing. In ReO the cavity is a cubo-octahedron,

and the center is 12-coordinated . The (111) twist converts the 12-

coordinate cavity into two 6-coordinate (octahedral) cavities sharing

faces. The volume per formula unit decreases in going from ReO„ to

^^0.35^^°3' ^t^ys approximately the same on further lithium insertion and

twisting to the rhombohedral cell, and then increases on further Li

insertion so that the volume of Li^ReO^ is approximately equal to that of

58
REACTOR RADIATIOM DI'^^'ISIOH A!ID C0L1A30PATIVE PR0GRA2IS

ReO„ . These volume changes reflect both the increased packing density

of the anion array and the changes in the sizes of the cation coordination

polyhedra.

Compounds which have been observed to undergo twists of the type

described here are relatively few. In addition to the present examples,

II IV

compounds of stoichiometry M M F,- (ordered ReO^ type) have been

observed to undergo cubic-to-hexagonal transitions, and LiNbO and LiTaO„

(rhombohedral) have been observed to become cubic on ion exchange of

hydrogen for lithium.

NEUTRON PROFILE REFINEMENT OF THE STRUCTURES OF

Li2Sn03 AND Li2Zr03

J. L. Hodeau and M. Marenzo

(CNRS, Grenoble, Cedex, France)

and

A. Santoro and R. S. Roth

(National Measurement Laboratory)

Compounds of the type Li BO (B Ti, Mo, Pd, etc.) are of interest

as possible Li ion conductors if nonstoichiometry can be introduced

into their structures. Li2Sn03 and Li2Zr03 are important representatives

of this class of compounds.

The specimens of Li SnO„ and Li ZrO„ were prepared for neutron

diffraction examination by mixing and grinding together the appropriate

quantities of Li C0„ and the corresponding oxides to give a final 30-g

batch. All materials were of commercial grade and were designated

chemically pure. The mixtures were first calcined at 700 C for 24 hr

to obtain preliminary reaction and to release most of the CO,,, then

reground and reheated repeatedly, first at 1000 C for 16 hr and then at

1400 C for several hours in a tightly covered Pt crucible. After each

hour at 1400 C, the material was removed from the furnace and a portion

was examined by x-ray diffraction to determine crystallinity and the

degree of combination. T-Tnen all of the peaks of the oxide and/or other

59
REACTOR RADIATIOH DIVISION AND COLLABORATIVE PROGPAJIS

phases had disappeared and the diffraction peaks of the desired phase

were strong and sharp with distinct a^ -a. doublets at 30-40 2G, the

specimens were deemed ready for final study.

Neutron diffraction data were collected for both compounds, at room temperature with a five-detector diff Tactometer at the National

Bureau of Standards Reactor. The neutron intensities were analyzed

with the Rietveld method, modified by Prince to simultaneously process

the data from the five counters of the dif f ractometer . The background

was assumed to be a straight line of finite slope and was refined for

each of the five channels of the dif f ractometer together with the nrofile

and structural parameters. The results of the refinements are shown in

Tables 1 and 2.

The structural arrangement of Li ZrO., and Li^SnO is NaCl-like.

In both compounds, therefore, the oxygen atoms form a distorted cubic

close-packed network, and the cations occupy, in an ordered fashion,

all octahedral site present in this network. The distribution of the lithium

also form a cubic close-packed network. The distribution of the lithium

and of the tetravalent cations is different in the two compounds, and

for this reason, these cannot be considered isostructural

.

In the structure of Li SnO- there exist two types of layers, one composed of lithium-occupied octahedra only and the other composed of

lithium- and tin-occupied octahedra in a 1:2 ratio, stacked alternately

along the perpendicular to the ab plane. The cations of the mixed

layers are ordered in such a way that they form hexagonal close-packed

planes in which the tin atoms occupy the vertices of the hexagons and

the lithium atoms the centers. A given layer repeats every six levels,

namely, after a double cubic close-packed AB'CA'BC' (where B'A'C refer

to lithium-occupied octahedron layers)

.

In the structure of Li_ZrO„, all the layers parallel to the ab

monoclinic plane have the same cation distribution: namely, they are composed of lithium- and zirconium-occupied octahedra in a 2:1 ratio.

The cations belonging to one octahedral layer form hexagonal close-packed

60
REACTOR FJVDIATIOIT DIVISION ADD COLLABORATIVE PROGRAMS

TABLE 1

Results of the Profile Refinement of the Structure of Li,SnO

Atom Position x y z B Multiplicity

ah

Sn(l) 4e2 0.418(1) 1/4 0.2 0.5

Sn(2) 4e2 0.7:^0(1) 1/4 0.2 0.5

0(1) 8fl 0.1387(7) 0.2610(7) 0.1339(3) 0.48(8) 1.0

0(2) 8fl 0.1118(6) 0.5853(7) 0.1340(2) 0.19(6> 1.0

0(3) 8fl 0.1343(6) 0.9078(7) 0.1322(3) 0.15(6; 1.0

Li(l) Bfl 0.231(2) 0.073(1) -0.0006(7) 1.5 1.0

Li(2) 4dl 1/4 1/4 1/2 1.5 0.41(1)

Li(3) 4c2 0.083(6) 1/4 1.5 0.394(8)

Note: R=5.27, R^=6.68, R^=8.67, R^=6.73. Space group C2/c, Z=8 .a=5. 2889(2) , b=9. 1872(3), c=IO. 0270(3) A, 6=1007348(2) ° . Number of observations : 3272

.

Number of independent Bragg ref lections : 358.

TABLE 2 Results of the Profile Refinement of the Structure of Li_ZrO„

Atom Po sit ion X y z B

ah

Mult iplicity

Zr 4e2 0.0916(5) 1/2 0.16(5) 0.5

0(1) 4dl 1/4 1/4 1/4 0.40(5) 0.5

0(2) Bfl 0.2721(4) 0.5754(3) 0.4863(4) 0.31(4) 1.0

Lid) 4e2 0.423(2) 1/4 1.4(3) 0.45(1)

Li(2) 4e2 0.742(2) 1/4 1.1(3) 0.46(1)

Note: R=5.01, R^=6.35, R.=8.82, R =5.09. Space group C2/c, Z=4 , a=5. 4218(2),

b=9. 021614, c=5. 4187(2) A, 3=112. 709(2) . Number of observations: 2505. Number

of Independent Bragg reflections: 186.

61
REACTOR PADIATIO^l DIVISIOH AND COLLABOFA.TIVE PROGPAIIS

planes as in the previous case. However, in Li„ZrO„, the lithium atoms

occupy the vertices of the hexagons while the zirconium atoms occupy the

centers. As in the case of Li SnO , a given octahedral layer repeats

every six layers.

The reason why the cation arrangement is different in the two

4+

structures seems to be related to the difference in size between Sn

4+ 4+ and Zr . All Li M 0„ compounds reported so far, with the exception of

Li ZrO„ have a cation ordering similar to that of Li„SnO, . Of all the

1+ tetravalent cations forming these compounds. Zr has the largest ionic

radius, and therefore it is logical to surmise that the factor deciding the

+1 4+

cation ordering is the r(Li /r(M ) ratio. The cation order found in

Li„ZrO„ can be regarded as a three-dimensional order, whereas that found

in Li SnO^ is of a lower dimensionality since it contains layers of

lithium-occupied octahedra alternating with layers composed of lithiumand tin-occupied octahedra.

A NEUTRON POWDER DIFFRACTION STUDY OF A- AND B-Pb02 IN

THE POSITIVE ELECTRODE MATERIAL OF LEAD-ACID BATTERIES

A. Santoro

and

P. D' Antonio

(Naval Research Laboratory, Washington, DC)

and

S. M. Caulder

(International Lead Zinc Association at the

Naval Research Laboratory, Washington, DC)

A neutron powder diffraction study of a- and 3-PbO„ , both chemically

prepared and electrochemically formed in cycled battery plates, was carried out to correlate the electrochemical activity of the lead-acid

battery with the atomic arrangement of the electrode constitutuents

.

Qar results are consistent with the presence of hydrogen in the structure

of 6-PbO^ , but the departure of the occupancy factors, for lead and

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63
REACTOR RACIATIOn DI^'ISION A^JD COLLABOPATIVE RROGRAllS

TABLE 2

Results of the Structural and Lattice ParameLers Refinements of a-PbO.

R^ = 11.65, Rp = 5.59, R.^ = 7.63, R^ = 3.46, m = 1

Space Group Pben, Z = 4

A) Lattice Parameters

X++)

Bagshaw et al . (14)

Syono et al. (15

Y3 (202)*

Y3 (130)**

a-3 (202)*

a-3 (130)**

Annealed

Moseley et al. (5)

Zaslavskii et al. (16)

From neutron profile

refinement

4.993(3) 5.946(2) 5.459(3) X

4.993(1) 5.958(1) 5.465(1) X

4.980(9) 5.964(13) 5.473(6) N

4.936(10) 5.952(9) 5.472(6) N

4.969(6) 5.979(14) 5.482(7) N

4.973(8) 5.961(11) 5.481(10) N

4.967(10) 5.979(20) 5.482(3) N

4.998(1) 5.932(1) 5.441(1) X

4.927 5.927 5.474 X

4.9627(10) 5.9588(13) 5.4812(8) N

(+)

B) Structure

*

(+)

(-H-)

X

y

z

This study

0.1596(8)

1/4

X 0.2546(12)

y 0.4005(7)

z 0.4224(7)

B 0.07(9)

Lead

Moseley et al . (5)

0.173(7)

1/4

Oxygen

0.2(2)

0.35(8)

0.39(9)

Zaslavskii et al . (16)

0.178

1/4

0.276

0.410

0.425

U = 43300(4025), V = 21850(1690), W = 6185(230)

Peak at 20 = 49.48° indexed as 202.

Peak at 20 = 49.48° indexed as 130.

X and N indicate that the corresponding measurement was made with

x-rays and neutrons, respectively.

a-3 indicates that the intensities diffracted by 3-PbO^ were

subtracted from the powder pattern.

64
REACTOR PADIATIOn DIVISION AND COLLABOP-ATIVE PROGRAMS

oxygen, from stoichiometric values are not large enough to unambiguously

establish whether there are lead or oxygen dif iciencies. If the Pb:0

ratio corresponds to exact stoichiometry, any hydrogen which is present

+4

must be accompanied by a reduction of Pb . There is a significant

increase in the lattice parameter a. of B-PbO in cycled battery electrodes relative to the value found in chemically prepared B-PbO_ . No

change in the c^ parameter, however, was detected. These dimensional

changes are consistent with a configuration for hydrogen similar to that

observed in the rutile-type structure of SnO. , in which there are OH

ions oriented perpendicular to the c^ axis.

The profile parameters obtained in this analysis show that the

crystallites of 6-PbO in the positive plate material of a battery

cycled three times (Y3) are smaller than those in the chemically preO o pared compound ('x^ASO A versus 800 A), while there are no significant

differences between the latter and 6-PbO in the positive plate material

of a battery cycled 3b times (Y36) . No evidence for the presence of

amorphous PbO- in the active electrode material has been found. The

average structure of a-PbO„ cannot be accurately determined by profile

analysis, at the present time. The difficulties encountered in the

refinement may be due to extensive defects, nonspherical crystallites

of small size, and/or small departures of the structure from orthorhombic

symmetry.

The results of our study are reported in Tables 1 and 2, where

they are compared with previously published values.

65
REACTOR RADIATIOll DIVISION AND COLLABOPATIVE PROGRAMS

CRYSTAL STRUCTURE OF AMMONIUM NITRATE:

LOW TEMPERATURE PHASE (v)

C. S. Choi and H. J. Prask

(Energetic Materials Division, LCWSL, ARRADCOM, Dover, NJ)

and

(National Bureau of Standards, Washington, DC)

We have completed crystal structure studies of phase IV, II and

III of NH. N0„ in previous years. This year, we have studied the structure

of phase V, the lowest temperature phase, to conclude the structure

study of all phases. A deuterated AN sample (D concentration of 90%) was obtained by six cycles of repeated recrystallization from solution

with 99.6% DO at about 103 °C.

The neutron powder diffraction measurements were made on the highresolution 5-detector dif f ractometer at lOK, 78K and from 130K to 270K

Figure 1. Crystal structure of AN viewed along the C-axis . The unit

cell is orthorhombic P ccn with the dimensions, a=7. 8850(2),

b=7. 9202(2), and c=9. 7952(2) at 78K.

66
REACTOR RADIATIO!-] DI^^^ISIOH AND COLLABORATIVE TROGRAl-lS

in 20K steps. We found that the unit cell symmetry is orthorhombic

Pccn, .and the previously reported tetragonal P4 is erroneous. The

Rietv.eld profile refinement reduced the residuals to R(integ)=3 . 63%,

R(prof)=2.40%, R (ProF)=3.06% and R(expt)=1.88% for the 78K structure. w

There are two independent sets of three-dimensional H-bond chains which

are related mutually by C-glide mirror symmetry. The two H-bond chains

are interpenetrating and make a tight VanderWaals contact with very

short N* • • and 0- •

• intermolecular distances. Figure 1 is the ORTEP

drawings to illustrate the H-bonded structure.

The thermal expansion profile of AN was determined as a function

of temperature from lOK to 393K, using the unit cell dimensions determined at each temperature by the profile refinement method. Figure 2 is the volumetric expansion expressed in terms of cell volume per unit

molecule. Phase V, IV and II are similar in molecular packing (CsCl type)

but they differ in the orientation of N0„ groups. The N0„ groups in

phase IV are packed with their orientation parallel which results in

CO

3

o 80

£75

3

O

>

I Cubic

II Tetr.

III Orth.

IV Orth.

V Orth.

-1.59%,

1 1.69%

100 200

Temperature (K)

400

Figure 2. The volumetric thermal expansion of AN as a function of

temperature.

67
REACTOR RADIATIOn DIVISION! AND COLLABOPATIVE PROGRAllS

maximum density, and is reflected in the specific cell volume curve. The volume change at each transition point is very large, -3.05% at the

IV-V and 3.84% at the IV-III transitions.

X-RAY DIFFRACTION STUDIES OF CELLULOSE

H. J. Prask and C, S. Choi

(Energetic Materials Division, LCWSL, ARRADCOM, Dover, NJ)

and

(National Bureau of Standards, Washington, DC)

The two major sources of cellulose for nitrocellulose (NC)

production are cotton linters and woodpulp . In general, cotton linters

provide a uniform source for NC . However, linters could possibly be

in short supply if present production facilities were fully mobilized.

In contrast, woodpulp offers a plentiful and less costly source of

cellulose. However, woodpulps are considerably less uniform than linters

which has led to unacceptable variations in processed NC, particularly

in new, continuous nitration production facilities. In the present work

we utilize a total-profile analysis of x-ray diffraction data of various

cellulose samples to attempt to identify critical feedstock properties

for quality control.

Our analysis of cellulose x-ray diffraction patterns includes the

following:

1. We constrain the structures for all samples to be monoclinic,

but refine lattice parameters;

2. We include principal (equatorial) reflections and weaker

(meridional) reflections, the latter scaled to account for

orientation effects in the pressed-pellet samples;

3. We make use of an explicit non-crystalline profile obtained

from ball-milled cellulose;

4. A peak profile of mixed Gaussian and Cauchy character is

68
REACTOR RADIATIOIJ DIVISION AND COLLABORATIVE FROGRAllS

assumed; and

5. The analysis allows for samples of mixed cellulose I and

cellulose II composition.

Figure 1. Representative x-ray diffraction patterns of pressed-pellets

' of various cellulose samples (Cu-Ka radiation). The dots

represent the data, the solid lines through the dots are the

total-profile fits. The solid lines below the dots (upper

four samples) are the combined contribution of Compton

scattering, amorphous scattering, flat background and lowerconcentration phase (e.g. II in the upper three patterns).

69
REACTOR PADIATIO:? DIVISION AKD COLLABORATI\^ ?ROG?J^!S

The analytic expression used to fit the total diffraction profile

for a predominately cellulose I sample has the form:

1(3) = P^^ + C0>1P (3) + P,,

JI

AMORPHO) CD

+ P • CELL (II, 3, WA) + SC -CELL (1,3)

where

Q U) = ^ P^ Cc) P^- exp

2(3-9 ) o

_ Ik

Ik

+

(1 - P/)

2(9-0 ^^)/? ^ o \':

Ik Tk

and ^'^ = 3

^'^ (P,, B, P^, P

O O AC: h^, k^, x^

(2)

(3)

In the above, 3 is the scattering angle (=23, ) and the Ps are

b parameters adjusted in the least-square fits. In eqn . (1) the Ps are amplitude parameters for a flat background, amorphous profile, and

cellulose II profile (I and II are interchanged in a predominately"

phase II sample); COM? (3) is the Compton scattering component, WA is

a multiplicative factor which adjusts all widths of the cellulose II

peaks, and SC is an orientation scale factor for meridional reflections

in cellulose I which is empirically determined by comparison of measured

linter intensities and published fiber structure f accors

.

Ik

ihe Q (3) correspond to the principal reflections of phase I (i.e. (101), (101), (021), and (002) where the chain axis is along b)

.

In eqn. (2) , P , P and P are respectivelv the height, Gaussian fraction, H £ w

and R-^Is . The 0-dependence of P denotes that angle-dependent corrections such as Lorenz and polarization factors are included. Finally, the

are peak positions of the principal (h,k,l) reflections of phase I obtained by refining the A and C lattice parameters and the monoclinic

70
REACTOR PADIATIOH DIVISION AND COLLABORATIVE RROGPAMS

2 4 6 8 10 12

% Solubility (18% Na OH)

50 100 150

Mullen Burst Strength (lbs)

Figure 2. Crystallite (002) dimension vs. 7o- solubility and Mullen

Burst Strength for woodpulps; closed circles = sulfate pulps,

open circles = sulfite pulps.

angle, B. The B lattice parameter was not refined because orientation

effects reduced non-equatorial reflection intensities.

In figure 1 are shown representative diffraction patterns and leastsquare fits for linter, sulf ite-processed pulp, sulf ate-processed pulp,

Fortisan (cellulose II), and ball-milled cellulose (the solid line is the

profile of six arbitrary Gaussians used to reproduce the pattern). Several

points should be noted concerning our total-profile analysis approach.

We refine lattice parameters and obtain values in good agreement with

accepted values. In contrast to similar efforts (see, for example, refs.

3-5), we calculate relative structure factors from our least-square fit

parameters, and find them to be in good agreement with structure factors

71
REACTOR PADIATIOM DIVICIOH AND COLLABORji.TIVE PROGRAMS

Table 1. Celluloses: crystallinity, particle sizes, and shape parameters,

Sample Type % Crystallinity L(002) (A)

1 I-Linter 49.1+2.0 73.2+0.4

2 I-Linter 50.8+1.5 75.5+0.3

3 I-Linter 44 .1+1.6 75.8+0.3

5 I-Sulfite 35.1+2.2 47.2+0.2

6 I-Sulfite 36.(>t-1.7 47.9+0.2

7 I-Sulfate 32.4+2.0 55.8+0.3

8 I-Sulfate 35.4+1.9 57.5+0.3

9 I-Sulfate 37,2+2.0 52.1+0.2

10 I-Sulfate 32.3+2.1 56.5+0.3

11 I-Sulfate 43?^ 42.1+0.2

12 I-Sulfate 26.7+3.3 48.1+0.3

4 II-Fortisan 15.4+2.2 61.6+0.6

Questionable because of very large FWHMs of principal reflections.

obtained from studies of various cellulose I and II fibers. We also find

that for linters (for which features are sharpest) pure Cauchy peak shapes

alone will not fit the full diffraction profile (as has been proposed in ref

refs. 4 and 5); some explicit amorphous component is required.

In table 1, some of the results for the several samples studied are

shown. It should be noted that %-crystallinity is obtained directly from

P of equation (1) and L(002), which represents crystallite size along [002],

is obtained in the usual (approximate) way from the Scherrer equation and

the refined P^,s. W

72
REACTOR PADIATIOn DIVISION AND COLLABORATIVE RROGPAMS

The following tentative conclusions can be drawn from the limited

number of samples studied. Within the three sample types, linters and sulfiteprocessed woodpulp each appear to exhibit fairly uniform properties;

sulf ate-processed woodpulps show a wide variation in properties. (This is

consistent with observations made concerning variability of processed

propellants from these classes of feedstocks.) In figure 2, a comparison

of "crystallite size" and other measured properties are shown for the

woodpulp samples. Sample 11 appears anomalous in both solubility and burst

strength; sample 10 in burst strength. With regard to nitration of these

samples, it is interesting that both sample 10 and 11 show anomalous changes

in viscosity in going from 12.6 to 13.4 wt-% nitrogen. In our measurements,

sample 10 is the only one to exhibit a measureable admixture of cellulose II

(see "sulfate pulp" in figure 1) and, as mentioned above, sample 11

showed very large FWHMs.

1. H. J. Prask and C. S. Choi, "The Correlation of Nitrocellulose

Properties and Cellulose Feedstock Structure," U. S. ATmy

ARRADCOM Tech. Rept.^ in press.

2. J. Mann, Pure Appt. Chem. 5^, 91-105 (1962).

3. A. M. Hindelah and D. J. Johnson, Polymer 13, 423-30 (1972).

4. J. Gjonnes et al.. Acta Chem. Scccnd. 12, 489-494 (1958).

5. H. Krassig, Appl. Poly. Symp. 28, 777-790 (1976).

6. R. A. Mundy et al., "Improved Nitrocellulose Process Controls,"

U. S. Army ARRADCOM Tech. Rept. ARLCD-CR-80029, Dec. 1980.

73
REACTOR PADIATIO!! DI^'IFIOII AHD COLLABOPATIVE PROGPAJIS

HYDROGEN EXCHANGE IN RNASE A: NEUTRON DIFFRACTION STUDY

Alexander Wlodawer and Lennart Sjolin

(National Bureau of Standards, Washington, DC)

and

(National Institute of Arthritis, Diabetes, Digestive,

and Kidney Diseases)

Hydrogen exchange has been studied in a single crystal of RNase A

in the course of a neutron structure investigation. Neutron data to

o 2.0 A resolution were collected using a flat-cone dif f ractometer at

the National Bureau of Standards Reactor. Fully deuterated synthetic

mother liquor (55% t-butanol, A5% D„0 measured pH = 5.25) was added in

stages to a vial containing a large ribonuclease crystal. Several

complete exchanges of the solvent took place in about six months.

Another six months were spent collecting diffraction data. The crystal

was kept at room temperature throughout the experiment. Altogether

4132 reflections with I > 3a (I) were observed in the resolution

o interval of 2-10 A (51% of the total).

The degree of exchange of amide hydrogens was calculated in a refinement with the neutron data in which the positional and thermal

parameters for all atoms were kept constant, while the occupancies were

allowed to vary. The refinement was thus constrained for all the parameters other than occupancies and free for the occupancies. All amide

hydrogens were formally treated as deuteriums, with the occupancy of 1.0

corresponding to a deuteron and -0.55 to a proton, as indicated by their

respective scattering lengths.

The number of parameters in the occupancy refinement was equal

to the number of atoms, namely 2360, while the number of observations

was 4132. Since the overdeterminat ion by a factor of 1.75 might not

have been sufficient in the presence of substantial errors, it was necessary to evaluate the level of confidence in the results. The

tests consisted of refining the occupancies of all atoms in the structure

without setting any arbitrary upper or lower limits and by monitoring

74
REACTOR RADIATIOII DIVISIOH AND COLLAEOPATIVE PROGRAMS

1.00

d 0.75 -

0.50

0.75 -

1.00

20 30 40 50 60 70 Residue number

80 90 100 110 120

Figure 1. Plot of occupancies of awide hydrogens in RNase as a function

of residue numbers. Atoms which are predomiitantly of deuterium character are plotted above the central line, hydrogens

are plotted below mark. Every tenth residue is marked by a dot, arrows point to prolines, which have no amide hydrogens.

Scatter of occupancies beyond 1.0 is an indication of errors

in their determination; other methods of estimating error

levels are discussed in the text.

the behavior of all atoms belonging to the main chain. This refinement

clearly does not correspond to a physically meaningful situation and the

resulting occupancies of amide hydrogens are not correct, nevertheless,

the r .m. s .. discrepancies of the occupancies of other main-chain atoms

provide a good estimate of the errors associated with the individual

estimates of occupancies. Two starting models were used, one with all

amide hydrogens assumed to be fully exchanged for deuterium and one in

which they were unexchanged. In the first case, the final average

occupancies and their r.m.s. deviations for N, CA, HA, 0, and D were

1.0 (0.17), 1.08 (0.21), 1.05 (0.20), 1.06 (0.21), and 0.72 (0.41)

respectively. The results of the refinement starting from amide hydro75
REACTOR RADIATIOn DIVISION] AMD COLLABOPATIVE ?r.OGPj\llS

Figure 2. Plot of the positions of all amide nitrogens in the RNase A

molecule, as well as of those amide hydrogens which were

found to be at least half protected against exchange.

gens were 1.14 (0.19), 1.05 (0.23), 1.07 (0.23), 1.06 (0.23), and

0.31 (0.40).

Final occupancies for amide hydrogens were established on the

basis of a refinement in which the upper limit of 1.0 was placed on the

occupancies of atoms other than amide hydrogens, and the resulting

occupancies of amide hydrogens were divided by 1.06 to compensate for

the errors described above. Twelve amide hydrogens were found to be

completely protected, six exchanged 25%, and ten were approximately

half exchanged. Altogether, about a quarter of the amide hydrogens

were not more than half exchanged after approximately one year of

exposure to deuterated solvent (figure 1). The distribution of the

protected amides in the three-dimensional structure of ribonuclease

is shown in figure 2. The information derived from such analysis is

usually sufficient to indicate less flexible regions of the protein.

The method used here is more straight-forward than chemical analysis.

It is also less susceptible to systematic errors, and provides meaningful estimates of random errors, but the confidence which can be placed

in the protection of any particular peptide should not be exaggerated,

76
REACTOR PADIATIOIl DIVISIOII AND C0LLA30FA.TIVE PROGPAllS

in view of relatively large r.m.s. deviation of calculated occupancies.

However, we believe that the results obtained from the crystalline

state of RNase are essentially correct for a majority of the amides.

CRYSTALLIZATION OF HEN EGG OVALBUMIN

M. Miller and A. Wlodawer

(National Bureau of Standards, Washington, DC)

and

(Laboratory of Molecular Biology, NIADDK, Bethesda, MD)

Hen ovalbumin, the major component of egg white was obtained in

crystalline form almost a hundred years ago and since then it has been

readily available in purified form in gram quantities. For that reason it has been used in a large number of studies on physicochemical properties and immunological behavior of proteins. Strangely

enough very little is known about secondary and tertiary structure of

ovalbumin with all of the information coming from indirect methods,

since no x-ray structure is available.

Ovalbumin readily crystallizes from ammonium sulfate or sodium

sulfate solutions, but in the previous studies only microcrystals have

been reported. When ovalbumin is treated with substilisin, a new

crystalline protein, plakalbumin, is formed. A heptapeptide Glu-AlaGly-Val-Asp-Alu-Ala (residues 346-352) is released during conversion of

ovalbumin to plakalbumin; the resulting two chains can be separated by

gel filtration in urea.

In order to be able to study the structure of ovalbumin and

plakalbumin by the techniques of x-ray and neutron diffraction, we have

grown single crystals of these proteins. Crystals of ovalbumin were

grown at 37 °C from 10 to 30 mg/ml of protein solution in cacodylic buffer,

Initially crystallization was achieved by vapor equilibration against

50% saturated ammonium sulfate (AMS) in the same buffer (pH 5.0 to 5.4)

using the handing drops technique. Crystals were later obtained at pH

77
REACTOR RADIATION DIVISIOII AHD COLLABOFATIVE FROGPAl^lS

range of 5.8 to 7.1 by batch method. To the protein dissolved in buffer,

saturated AMS solution was slowly added until slight opalescence appeared;

the solution was then cleared by centrifugation and set up in sealed

vials in 37 °C. Any disturbances such as a shift of temperature,

vibrations or even simply examining vials under the microscope in the warm room, resulted in showers of microcrystals.

Plakalbumin crystals were grown at room temperature by a similar

batch method from 25 mg/ml protein. The solution of digested ovalbumin

was mixed with equal volume of 0.1 M cacodylic buffer pH 5.4, about

60% AMS and 2% methanol.

Crystals of ovalbumin usually appeared after one month and reached

their maximum size after several more days. Needless as large as 1.5 x

0.2 X 0.05 mm were obtained at pH 5.4. They belong to space group C2

o o o with a = 116.5 A, b = 41.8 A, c = 70.5 A and 3 = 101.5°. The assumption that there is one molecule in asymetric unit gave the value of

3 V =2.0 Dalton/A , which is in the range observed for other proteins. m

Crystals obtained at pH 6,7 were usually thicker and their growth was more reproducible, but shifting pH of crystallization to higher values

caused a change in the packing of molecules. Crystals obtained at

pH 5.8 and higher were triclinic with the following unit cell parameters:

a = 62.0 A, b = 84.3 A, c = 72.2 A, a = 87.6°, 3 = 103.9° and y = 108/67°.

The two crystal forms must be closely related, since the intensities

corresponding to the distorted monoclinic lattice can be noticed in the

corresponding triclinic projection.

The small size of ovalbumin crystals, poor reproducibility of

growth and large asymmetric unit of triclinic crystals make them

unsuitable for further x-ray analysis. Crystals of plakalbumin, on the other hand, were larger and easier to obtain. They grew from

ammonium sulfate solution in a few days, but were usually twinned.

Adding 2% of methanol or ethanol slowed down the process of crystallization to weeks but prevented twinning. These crystals belonged to

o o o space group C2 with a - 99.9 A, b = 102.0 A, c = 79.3 A and 3 = 112.1°.

78
REACTOR PADIATIOM DIVISION AND COLLABORATIVE PROGRAMS

The crystals grew as rectangular plates with 0.3-0.8 mm sides and were

up to 0.2 mm thick. The limit of diffraction observed on still photoo graphs is 2.5 A. The crystals are stable for up to 100 hours when

irradiated using 1200 W sealed x-ray tube.

The crystals of plakalbumin are much more suitable for further

x-ray analysis than the crystals of ovalbumin grown by us. The removal

of a heptapeptide by subtitisin does not cause significant changes in

the structure of ovalbumin, as supported by the fact that the physiochemical studies did not reveal any differences in the behavior of

these two modifications of ovalbumin. We are continuing the search

of suitable heavy atom derivatives needed for the determination of

plakalbumin structure by a method of multiple isomorphous replacement.

HYDROGEN IN METALS~THEORY OF NEUTRON- INDUCED

TRANSITIONS TO EXCITED BAND STATES

R. C. Casella

The ongoing program associated with the theory of neutron scattering

from tunneling atoms or molecules in solids, particularly the application

2

to hydrogen in metals, has been expanded considerably to Include the

possible effect of band formation by hydrogen in otherwise pure metals.

My prior work has Included the theory of Inelastic neutron scattering

to excited oscillator states from hydrogen trapped in a two-well configuration

3

near an Impurity atom (0 or N) in b.c.c. metals such as niobium.

4 5 Experimental evidence ' for coherence in the tunnel-split ground state

of such systems leads me to look for a degree of coherence in the neutronInduced excitations to states which are linear combinations of local excited

oscillators for hydrogen, even In relatively pure samples at sufficiently

low temperatures. In b.c.c. metals, the hydrogen equilibrium positions

are assumed to lie at the tetrahedrally coordinated vertlcies of the WlgnerSeltz cell, as shown In figure 1. Of course, distortion of the metal-atom

positions occurs when the proton (or positive muon) plus Its associated

79
REACTOR RADIATION DIVISION AND C0LLA30PATIVE PROGRAMS

Figure 1. Cut-away view of the hydrogen-site configuration in b.c.c. metals.

The hydrogen at site A experiences short-range forces from the

metal atoms in the tetrahedral array a, b, c, d, about it. As

drawn, atoms c and d are at body centers. The displacements

of the metal atoms due to the presence of the hydrogen are not

shown. The near-neighbor sites 1, 2', 3', and 4 are also

tetrahedrally coordinated about A. All 12 (= 1/2 x 24) vertices

in each body-centered cube are energetically equivalent.

electronic cloud occupies a given site (such as position A in figure 1)

.

In particular, the nearest-neighbor metal atoms (at a, b, c, and d in

figure 1) are displaced away from the hydrogen, retaining local tetrahedral

sjnnmetry. Experimental evidence, especially the relation w _ =\/2 o) , between the first and second neutron-induced excitation frequencies in

several b.c.c. systems, suggests a phenomenological model in which,

crudely, one may think of the hydrogen as moving harmonically in a threedimensional local well. (Actually, the coordinated motion of the hydrogen

atom plus neighboring metal atoms exhibit the characteristics of harmonic

motion.) The hydrogen at A in figure 1 (more accurately, the hydrogen

plus its distortion field about A) can tunnel to a nearby position

(1, 2', 3', or 4 in figure 1). The ground-state tunnel splitting is enhanced

80
REACTOR PADIATIOII DIVISIO!! AND COLLABORATIVE PROGRAMS

Figure 2. The primitive cell. As shown, the six crystallographically

inequivalent sites A, 1, 2, 3, 4, and 5 occur on a hexagon

within the cell. As drawn, the near neighbor (relative to A)

sites 2' and 3' lie outside the cell. Crystallographically,

these are equivalent to sites 2 and 3, and the site 5 is

equivalent to a second-near-neighbor of A. (All verticies are equivalent from the point of view of their energetics.) See,

also, figure 1.

4 5 when a nearby impurity atom lowers the barrier between equivalent sites. '

It is not unreasonable that hydrogen in a pure metal can tunnel more

rapidly among the excited oscillator states than for the ground state,

contributing to the inverse lifetime of the local excitation and, hence,

to its line width. In the extreme where tunneling can occur coherently

between several sites, bands result. A first-principles calculation of

the relevant overlap integrals requires a self-consistent calculation

of the motion not only of the hydrogen, but also of the surrounding

metal atoms. I do not attempt such a calculation, but rather treat the

combined system (hydrogen + surrounding displacement field) phenomenologically

in an effective rigid-band model. The overlap integrals (which, from

syimnetry, can be expressed in terms of a few irreducible ones) are treated

as parameters ultimately to be determined by experiment. I assume that,

81
REACTOR P-ADIATION DIVISION Al-TD C0LLA30PATIVE ?ROGRA>!S

*%^[e,0,0] ^-^[Q,CX] T=%^h,^,o]

Figure 3. The first set of excitation bands E(k) which, in the absence of

overlap, collapses to a line at E = "hooj = 0. The energy is

measured in units of the single overlap integral H-[- . EC^) is

given for (a) ^ along [100], (b) k along [111], (c) k along

[110]. Only nearest-neighbor overlap terms are included.

(Energy is measured relative to the first excitation energy

tiLO of the local oscillator.)

in this model, at least the symmetry of the bands ought be manifest. In

particular, the Bloch theorem is effectively recovered, despite selftrapping effects. The domain of validity of this assumption can, in

principle, be delineated by experiment. Also, if one treats the inelastic

neutron scattering in impulse approximation, then it can happen that the

effective final states (intermediate states in a more complete calculation)

are virtual rigid-band states, which subsequently decay into local

oscillater states. This use of the rigid-band states in impulse approximation for treating the scattering of neutrons from hydrogen in metals is

limited to large momentum transfers.

Given the above motivations, I have been engaged in a rather extensive

energy-band calculation, involving a tight-binding approximation consisting

of Bloch-like "tates formed by taking linear com.binations of the local

oscillator states centered at the various b.c.c. sites, such as those

labeled A, 1, 2', . . ., in figure 1. There are six inequivalent sites

82
REACTOR PADIATIOTI DIVISION AMD COLLABOP-ATIVE :°R0GRAI1S

in each unit cell, as shown in figure 2 at A, 1, 2, 3, 4, and 5. Sites

1 and 2 are equivalent to the sites 2' and 3' which are nearest neighbors

to A, but lie outside the primitive cell, as drawn. The six inequivalent

sites result in 6 >' 6 and 12 ?s 12 secular equations for states formed from

0.5

Figure 4. The second set of excitation bonds, E(k) relative to tiaj^j.

Various slices of the Brillouin zone for k along (a) [1, 0, 0],

(b) [1, 1/5, 0], (c) [1, 1/5, 1/5], (d) [1, 1/2, 0], (e)

[1, 1/2, 1/5], (f) [1, 1/2, 1/2], (g) [1, 1, 0], (h) [1, 1, 1/5]

(i) [1, 1, 1/2], (j) [1, 1, 1]. The scale is the (undetermined)

parameter, Hj-j-. As shown, the second parameter, S = 0.5. (See

text.) Doubly-degenerate bonds are denoted by the symbol: (2).

83
REACTOR PADIATION DIVISION A!TD COLLABOPATIVE PROGRAI-IS

the singly and doubly degenerate local oscillator excitations of frequencies

0) and w , respectively. In nearest neighbor approximation, a conmon

scale, the single irreducible overlap term, can be factored from the

secular determinant, all other matrix elements being equal to it apart

from phase factors of the type exp (icfij^^) • In this approximation, two

such irreducible overlap factors occur in the 12 x 12 determinant. In

the latter case, the approximation introduces additional syimnetries, such

as a pseudo-superlattice effect, mimicing a doubling of the unit cell to a cube containing 12 sites, instead of 6. Also, the approximation introduces

an apparent reflection symmetry about the energy "Rw with eigenvalues

occurring in pairs at "fiw + E. Preliminary investigation indicates that

these artificial symmetries, which are peculiar to the degenerate oscillator

excitation (12 ^ 12 determinant) , are a consequence of the nearest-neighbor

approximation. Results for the first set of excitation bands in this

approximation are shown in figure 3a-figure 3c, where energies are measured

relative to the local excitation energy, tiu) . The unit of energy is

chosen to be the single irreducible scale factor, H , to be fit by

experiment. The second set of excitation bonds, the centroid of which

lies above the first by an amount "^1(03 - oj ) , is shown for several slices

in the Brillouin zone in figure 4a-figure 4j . Here, energy is measured

relative to tiw ) , and the ratio S of the second to the first irreducible

matrix element occurring in the 12 -x 12 determinant has been set equal to

0.5. The additional pseudo symmetries are exhibited in these figures, where

one sees a solution at -E for each solution at E and a pseudo zone boundary

at C = 1/2, which would result from a cubic zone (of half the volume)

associated with a cubic cell in real space containing 12 hydrogen sites.

(The cubic zone is inscribed in the dodecahedral zone appropriate for the

f.c.c. reciprocal lattice belonging to the b.c.c. metals. The two zone boundaries coincide along the cube edge, k = (2TT/a) [1/2, 1/2, ?]•)

It is planned to include the effects of second-near neighbors and,

hopefully, to relate the resulting theoretical model to experiments on inelastic, thermal-neutron scattering from hydrogen-loaded b.c.c. metals,

84
REACTOR RATIATION DI'.'ISION AMD COLLABORATIVE PROC-FAllS

which are being carried out at the NBS Reactor.^

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

2. R. C. Casella, J. Physique, Coll. C6, S42, 923 (1981).

3. R. C. Casella, Phys. Rev. B24-, 2913 (1981).

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

5. A. Magerl, J. J. Rush, and J. M. Rowe (private communication).

RELATIONS BETWEEN PERM I ON MASSES

R. C. Casella

Work begun on this problem during the latter part of the prior

1 2 period was completed and published. The main predictions of the model

are (i) equality of the (v , v ) and (s, d) mixing angles, (ii) the fermion mass relations,

t - c ^ b - s ^ T - y ^ 3 2 , c-us-dy-ev-v^'

and (iii) a bound on the squared masses of the neutrinos relating possible

oscillations among the pairs (vye, v ) and (vyx, v ) , namely

2 2 2 2 ^2 " ^1 ^ °*°^^ *'^3 " ^1 '*• ^^^

In the above, the constituent quark or lepton masses are denoted by their

flavor sjnnbols, where (u, d) , (c, s) , (t, b) and (e, v,), (y , v ), (t , v ) are, respectively, the quark and lepton mass eigenstates, which, via Cabibbo

rotation, are related to the standard weak isodoublets in the electroweak

theory of Glashow, Weinberg, and Salam. To date, relations (1) and (2)

remain in approximate accord with experiment. Equation (1) predicts a constituent mass for the t quark in the neighborhood of 27 GeV. Neutrino

oscillations continue to elude observation.

85
REACTO^. RADIATION DIVISIOH PZW COLLABOPATIVE PROrRA]"[£

1. R. C. Casella, NBS Tech. Note No. 1160, p. 14, (F. Shorten, Ed., (1982))

2. R. C. Casella, II Nuovo Cimento 67A, 289 (1982).

CALCUUTIONS OF VIBRATIONAL SPECTRA

OF SELF-TRAPPED HYDROGEN IN BCC METALS

N. F. Berk

We are presently Implementing a theoretical procedure recently

reported by H. Sugimoto and Y. Fukai for numerically solving the

Schroedinger equation in the Born-Oppenheimer approximation in order to

make predictions of the vibrational spectra of self-trapped light

interstitials (H) in metals (M) , The method assumes a model H-M interaction under the influence of which the metal lattice is allowed to selfcopsistently relax. Using the theory we plan to study the effects of

trapping defects, such as oxygen in Vanadium, on the H-spectra as well

as trying to elucidate the mechanisms that determine the location of the

defect-induced trapping sites. In addition we hope to study the role of

lattice strains, elastic H-H interactions, and time-dependent relaxation

effects on the widths of measured vibrational lines in these systems. As

the first stages of this program, we have developed numerical procedures

for solving the Schroedinger equation for a given potential and for

computing the self-consistent lattice equilibrium displacements for a given set of lattice forces and the H-M interaction.

1, H. Sugimoto and Y. Fukai, Phys. Bev . B670 (1980); J. Phys. Soa.

Japan 50 (1981)

.

86
REACTOR RADIATIOIl DIVISION AIE) COLLABORATIVE FROGPAtlS

TRANSITION-ROTATION COUPLING IN MOLECULAR AND IONIC CRYSTALS

J. M. Rowe and J. J. Rush

and

K. H. Michel

(UIA, Antwerp, Belgium)

and

M. Klein

(NRC, Ottawa, Canada)

Work is continuing on both the theoretical and experimental studies

of the (KCN) (KBr), system for x = 1.0, 0.95, 0.9, 1.8, 0.5, 1.25, 0.05. X _L X

Neutron powder diffraction is being used to clarify the nature of the

low temperature structures of the mixtures for x > 0.8, where preliminary

measurements for x = 0.8 have shown the existence of a monoclinic structure,

rather than the orthorhombic structure of pure KCN. The samples with

X = 0.95, 0.90 and 0.80 will be studied as functions of temperature and

cooling rate to attempt to clarify the nature of the transition which

occurs at a temperature T "^ 168 (1-x) in these mixtures. It is already

clear, however, that strain is a very important variable in these phase

transitions as shown by the affects of repetitive cycling on the 168K

transition in pure KCN.

As new theory has been developed to explain the absence of observable

optic modes in pure KCN and NaCN. This theory is an extension of earlier

theories to include the effects of the asymmetry (electrical and mechanical)

of the (CN) ion. This introduces coupling to modes of ungerade symmetry,

a necessary condition for optic mode damping at q = 0. Quantitative

calculations based upon a microscopic model have shown that this effect

is not only sufficient to explain the results, but rather too effective!

Thus, we are currently attempting to calculate the effect of a proper

self-consistent phonon treatment. The results of this theory will be

presented in a paper in preparation. It should be noted that mechanical

asymmetry is much more important in this respect than the small electric

dipole moment, a conclusion with large implications for the low temperature

phase transition (at 85K in KCN)

.

87
REACTOR RADIATIOn DIVISION AtHD COLLABOPATIVE PROGRAMS

In addition, new high resolution measurements of the soft mode in

pure KCN have been undertaken in an attempt to clarify the situation

with respect to the effective quadrupole moment referred to in last year's

report. The results, and a representative least squares fit to the model

of Sahu and Mahanti , are shown in figure 1. For this particular fit,

the value of the quadrupole moment used was 1/2 the free ion value. However,

the fit is not particularly good at some momentum transfers (q = .3, T = 170K)

and some of the parameters found are clearly unphysical. To date, no completely satisfactory fit has been obtained, and we are currently searching

for the cause of this. The present position is thus that while the theory

gives good qualitative results, it is still lacking quantitatively.

Molecular dynamics simulations are continuing, but several problems

persist, closely related to those alluded to above -namely, the selection

of a good microscopic force model. A present speculation is that even higher multipole moments are required to reproduce the correct behavior

of the (CN) ion in this crystal. However, it has not yet been possible

to achieve a reliable test of this possibility. If this idea is correct,

the apparent reduction of the quadrupole moment needed to give agreement

with experiment may in fact be simply a compensation for the neglect of

the higher multipole moments.

Finally, both experimental and theoretical studies of the "quadrupole

2 3

glass" state of mixed crystals continues. Recent articles ' have

questioned the existence of a real transition in these materials, based

upon the observed dielectric behavior. However, the alternative description

proposed is completely inconsistent with the neutron data, and hence cannot

be considered correct. A possible explanation of this discrepancy is that

the dielectric constant measurements do not probe the quadrupole order

directly, but rather only through its influence on the dipole order.

Some support for this hypothesis can be obtained by comparing the observed

dielectric behavior with that of pure (KCN) in the lowest temperature

4

ordered phase (T < 85K) as observed by Julian and Luty. The activation

energies observed for the mixtures are lower than those seen in KCN (where

88
REACTOR RADIATION DIVISIOH AND COLLABORATIVE ?R0GRA1'[S

0.10

o

=> . Oo

/\

295.0

1 .7

t3C

°0 .00

:*-*2>'v. 2S O.SO 0. 7S 1 .00 1 .25 ENERGY 0-20

295.0

3.2

00 0.2S 0-50 'S 1 .00 l .25 ENERGY

ENERGY 0.40

295.0

6.0

00 iS 0. so O.'S 1 .00 1 .25 ENERGY

0. SO 295.0 "

7. 1 O

•*".

-, \ ^t \*^,'

o.

*

0. iO 170.0

1 .7

' o. A

to / \ *—<D.

=>o v.., 0.00 0.25 0.50 0.75 1.00 1.25 ENERGY.

3.00 0-25 0-50 O-'S 1.00 1.25 ENERGY 0.30

170.0

4.7

ENERGY 0.40

170.0

6.0

ENERGY 0.50

1 70.0

7. 1

A 0. 10 A

160.0

1 .7

• o. / 1

o

0.00 0-25 0.50 O.rS 1.00 1.25 ENERGY 0.20

o •\ 180.0

\

3.2

"-

r. •^f

g- VV

o. \>- \

°0 .00 25 0-50 0-^5 1 .00 1 .25 ENERGY 0.10

200.0

1 .7

ENERGY

.00 0.25 0-50 O-'S 1 .00 1 .25 ENERGY ENERGY

Figure 1. Observed and calculated neutron line shapes for pure KCN at

various temperatures and wave vectors along the [100] direction.

On each figure, the first number is the wave vector (along

[100]), the second is the temperature of measurement, and the

third is the "bare phonon" energy in mcV. Energies are plotted

as fractions of the "bare phonon" energy.

89
REACTOR PADIATIOn DIVISION AND COLLABORATIVE PROGPAMS

only 180 flips are possible) by an amount not inconsistent with the lower

symmetry in pure KCN.

1. D. Sohu and S. D. Mahanti (private communication, in press).

2. A. Loidl, R. Feile, and K. Knorr, Phys. Rev. Lettevs 48_, 1963 (1982).

3. S. Bhattacharya, S. R. Nagel, L. Fleishman, and S. Susman, Vhys. Rev.

Letters 48, 1267 <1982) .

4. M. Julian and F. Llity, FeTVoelectvics lb_, 201 (1977).

INVESTIGATION OF THE MAGNETIC AND SUPERCONDUCTING

TRANSITIONS IN (Er-i.^Ho^) R\\qP>i^

J . W . Lynn

(Univ. of Maryland, College Park, MD)

and

(National Bureau of Standards, Washington, DC)

and

R. N. Shelton

(Iowa State University, Ames, lA)

and

C. J. Glinka

We have been studying the pseudoternary alloy (Er, Ho )Rh,B, ° f -> -'1-XX44

in the vicinity of the multicrit ical point at x=0.9 where the ferromagnetic and superconducting phase boundaries converge-^. For x=0.89

just below the multicritical point, neutron powder diffraction measurements revealed a second order ferromagnetic transition occurring at

2 Tm=5.56K. This transition was notable for the mean-field like temperature dependence of the order parameter and the absence of any observable

critical scattering. Most significantly, bulk susceptibility measurements showed that the sample is superconducting over a narrow temperature

interval ('^0.2K) centered about T^^ thereby implying the coexistence of

superconductivity with long range ferromagnetic order.

90
REACTOR PADIATIOn DIVISION AND COLLABORATIVE PROGRAMS

900i

LO\ 3000

w

c

o

O

"^2000

(0c

0} - 1000

(0o

"-J^

• Cooling

oWarming

Oca»«» •

0' 1

3 4 5 6 7

T(K)

Figure 1. Observed peak intensity of the (101) Bragg peak, demonstrating that there is a ferromagnetic phase transition at 5 . 3K

^^ ^^\l6^°.84^^V4-

Because the temperature interval where the coexistance appears to occur for x=0.89 is so narrow, measurements have been extended to a sample

with x=.84 which has a larger superconducting interval. Bulk susceptibility

data for the (Er ., .Ho o/)Rb,B, sample established that at I ,=5.95K the

.16 .84 4 4"^^ cl

sample becomes superconducting and then at T =4.95K reenters the normal

state. The (101) Bragg peak intensity displayed in figure 1 exhibits a ferromagnetic transition at Tm=5.3K, well within the boundaries of the

superconducting phase. Note that the magnetic intensity is continuous

and shows no hysteresis. These data give strong support to the hypothesis

that a ferromagnetic component to the magnetization coexists with superconductivity.

An important question to answer is whether there is an oscillatory

91
REACTOR PADIATIOTl DIVISION AMD COLLABORATIVE PROGPAIIS

590

580

-570

-560

550

540

Figure 2. Total intensity of the two-dimensional SANS detector showing

the abrupt onset of scattering at small angles at T ,

3 4 component to the magnetization as was observed in ErRh, B, . ' To this

end, small-angle scattering data were collected with the new SANS

°-l °-l instrument at the NBSR over a Q-range from 0.003 A to 0.1 A

Figure 2 shows the total intensity in the two-dimensional position

sensitive detector as a function of temperature. Below the ferromagnetic transition intense small-angle scattering is observed, with an

-4

intensity that varies as Q at each temperature. This Q-dependence

is consistent with the assumption that the scattering originates from

domain walls whose widths are large compared to the inverse range

o explored (^^300 A) . No evidence for an oscillatory component to the

scattering was observed at any temperature. For temperatures between

Tpjj and T^^. ^^ ^^'^ observe a reduction of the scattering at the smallest

°-l wave vectors (<.006 A ) consistent with the expected suppression of

the paramagnetic scattering due to diamagnetic screening by the

92
REACTOR RADIATION DIVISION AND COLLASORATIVE PROGRAMS

superconducting electrons. Further work to observe this effect in

other superconductors with magnetic consistuents is now underway.

1. H. B. MacKay, et al Phys. Rev. Lett. 42_, 918 (1979)

2. J. W. Lynn, R. N. Shelton, H. E. Horng, and C. J. Glinka,

(submitted for publication)

3. D. E. Moncton, et. al. Phys. Rev. Lett. 39^, 1164 (1977).

4. S. K. Sinha, et . al. Phys. Rev. Lett. 48_, 950 (1982).

FERROMAGNETIC AND SPIN GLASS BEHAVIOR

NEAR THE CRITICAL CONCENTRATION IN AMORPHOUS

(FexNii_x)75Gl25

J. W. Lynn and R. W. Erwin

(Univ. of Maryland, College Park, MD)

and

(National Bureau of Standards, Washington, DC)

and

J. J. Rhyne

and

H. S. Chen

(Bell Laboratories, Murray Hill, NJ)

We are investigating the random amorphous magnetic alloys,

(Fe Ni^„^ )-,^P^,Al„, iust above the critical concentration for long

X 100-x 75 16 3

range order (x = 17) via neutron scattering. It is found that the

behavior of the system shifts from ferromagnetic (FM) to spin-glass like

(SG) as the temperature is lowered, and a temperature interval within

which SG and FM states coexist is indicated. Whether this SG state is

a true thermodynamic phase as formulated by Edwards and Anderson or represents a gradual freezing of spins is still an open question.

For the composition x=30, the paramagnetic to FM phase transition

is at T^ = 255K as determined by susceptibility data. Measurements of

93
REACTOR ?ADIATIO!T DIVISIOll AI^ COLLABOPATIVF PROCPA^'.S

300r

0.4

>

E 0.3 >

C

111

Qj 0.2

>

(0

0.1

Spin Wave Energy

Q = 0.10 A^

oHWHM/Energy

100 200

T(K)

300

Figure 1. Spin wave energy and intrinsic half-width divided by the

energy as a function of temperature. With decreasing temperature

the energy and lifetime increase, but then decrease at lower

temperatures as the spin-glass state is approached. The solid curves are a guide to the eye. The inset shows the phase

diagram for the system as determined by low-field susceptibility

and magnetization measurements.

the spin wave (SW) energies and linewidths for this alloy are shown as °-l

a function of temperature in figure 1 for a wave vector, Q = .lOA

The renormalization of the excitation energies as predicted by SW

theory is observed below T , but at lower temperatures the SW spectrum

2 ^ begins to collapse. These results are consistent with low-field

O / susceptibility measurements ' which suggest the disappearance of FM

long range order at a reentrant temperature, T =8K.

R

Measurements of the temperature dependence of the elastic component

of the magnetic scattering establish a spin-freezing temperature, T^=20K

as shown in Figure 2. The spins are at least frozen on a time scale of

-9

4x10 sec as determined by an upper limit to any intrinsic linewidth of

the elastic scattering. Truly elastic scattering [S(E)] would be a direct

measure of the SG order parameter as it would imply the existence of an infinitely lived state. We remark that if the system were an ideally

random Edwards-Anderson SG, then the intensity of the elastic scattering

94
REACTOR PADIATIOIl DIVISION A>TD COLLABORATIVE ?ROGPJV?^S

o

C! 70

(/> 4-" C

3OO

c

co

j5

LU

66

62

-24 c

18 >

- 12 J

Q = 0.04 A

Ej = 3.70 meV

40' -20' -20' -40'

10 20

T(K)

30

Figure 2. Elastic scattering and the energy integrated (total) scattering

as a function of temperature for Q = 0.04 A"-'-. The elastic

component is directly related to the spin-glass order parameter.

would be independent of wave vector. In these relatively concentrated

systems, however, we find that there are short-range FM correlations between

the spins, which give a wave vector dependence to the elastic scattering.

If these frozen spatial correlations are temperature dependent (e.g., the

size of an average magnetic cluster is a function of temperature) then the

intensity at any particular value of the wave vector would be a product of

the order parameter and the static correlation function. We are not able

to separate these two contributions at present. Nevertheless, the relatively,

sharp onset of the elastic scattering is suggestive of the occurrence of a phase transition. The freezing temperature, T , obtained is not dependent

on the wave vector and is well above the reentrant FM temperature, T . We

interpret these results as indicating that the SG state develops before the

FM state is completely destroyed, so that the two phenomena coexist over

a region of temperature. This interpretation is consistent with our inelastic

scattering measurements (figure 1) which show that the SW excitations exist

below 20 k and become overdamped around T ^ 8K, and not T^ '^ 2 OK.

R I 95
REACTOP RADIATION DIVISION km COLLABORATIVE PROGRAJIS ,

1. S. F. Edwards and P. W. Anderson, J. Phys. F. 5^, 965 (1975).

2. J. W. Lynn, R. W. Erwin, J. J. Rhyne, and H. S. Chen, J. Appl. Phys.

52 , 1738 (1981). Experimental details can be found here.

3. S. M. Bhagat, J. A. Geohegan, and H. S. Chen, Sol. St. Commun. 3_6,

1 (1980); J. A. Geohegan and S. M. Bhagat, J. Magn. Magn. Mater. Tb_,

17 (1981).

4. S. M. Bhagat, J. A. Geohegan, M. L. Spano, and H. S. Chen, J. Appl.

Phys. 52, 1741 (1981).

SPIN WAVES IN AMORPHOUS Fe-i.^B^ ALLOYS

J. J. Rhyne

and

G. E. Fish

(Allied Corporation, Morristown, NJ)

and

J . W . Lynn

(Univ. of Maryland, College Park, MD)

and

(National Bureau of Standards, Washington, DC)

Amorphous alloys of composition Fe - B can be prepared by meltspinning techniques throughout the composition range (1,2) from

x=0.12 up to about x=0.28. In the vicinity of x a. 0.17, these alloys

have been shown to exhibit Invar characteristics (3,4) in which their

normal thermal contraction is nearly completely compensated by a large

positive magnetostriction. As a function of increasing Boron composition, the Curie temperature increases from 509 K (x=0.12) to 760 K

(x=0.28), and a corresponding decrease occurs in the Fe moment from

2.14 y to 1.94 y . The alloys show progressive crystallization at

B D elevated temperatures (2). Initial crystallization temperatures range

from 570 K for x-0.12 and increase with boron concentration up to

about 685 K for x=0.26. For x '^ 0.20, the alloys crystallize below

their Curie temperature.

96
REACTOR PADIATION DIVISIOH A!TD C0LLA30PATIVE PROGPAIIS

T/Tc

0.4 0.6 0.7 0.8 0.9 1.0

20

D(0) = 167

0.2 0.4 0.6 0.8

( T/Tc )^^^

1.0

Figure 1. Temperature dependence of spin-wave stiffness for Fe^,B^,

and FeQ„B „. The data points are the average values for

D obtained after resolutionocorrection of the spin-wave_^

energy for 0.06 < q < 0.10 A~ (Fe B ) and q = 0.08 A

(Feo„B „) . The error bars represent the variation in D

obtained from the range of q's measured.

Magnetization measurements (1) have shown a proportionality

3/2 between the magnetization and T , characteristic of linear spinwave behavior, over an unusiially wide range up to T/T "^ 0.33. From

^ 3/2 the observed magnetization and the relationship M(T) = M(0) (1-B T ) values of the coefficient B have been determined (1) . The spin-wave

stiffness D predicted by the magnetization can then be calculated from

' 3/2

B = 2.6212 ^^B The derived values of D can then be compared

M(0) \ Attd/

to those determined directly from the spin-wave dispersion as measured

2 by inelastic neutron scattering, E = E + D(T) q , where

o E is the spin-wave energy gap at zero wavevector transfer q = 0. For

g

most amorphous alloys, E is immeasurably small. Higher order terms

97
REACTOR PADIATION DIVISIO^t a>td COLLABOPA.TIVE PROGRAIIS

in eq. (3) have also been found to be small.

We have performed inelastic neutron scattering on the amorphous

alloys FeQ,B ,, Fen„B „, and Fe ,B , , prepared in ribbon form by the

inside-roll-chill-block melt-spinning techniques in vacuum. Boron

enriched to 98.5 percent B was used to reduce the neutron absorption

and the ribbons were wound between two aluminum posts to produce a flat

plate-like sample of optimum absorption thickness. Neutron data were

taken in a vacuum furnace on a conventional triple-axis spectrometer,

taking precautions to minimize air and sample-container scattering at

the small q required for these studies.

Amorphous alloys require inelastic scattering experiments to be

done near the forward beam position ([000] in reciprocal space), and

thus neutron energy and momentum conservation conditions place severe limitations on the range of E and q space accessible for measurements.

This is particularly critical for measurements on alloys with the

larger spin stiffness D. Depending on the alloy and temperature

°-l °-l

range, useful data were obtained from q = 0.08 A up to q > 0.20 A

Elastic resolution width was approximately 0.8 MeV. Spin waves .for

both neutron energy gain (E < 0) and energy loss (E > 0) were easily

observable and well resolved up to temperatures where they merge with

the central peak (elastic) scattering.

For the Fe B, , alloy, which has a Curie temperature of 556 K,

86 1^

meaningful spin-wave data were obtained over the range from 200 K

(T/T = 0.36) up to 548 K (T/T = 0.99). For Fe^^B, q (T = 617 K)

,

c c oZ io c data were taken from room temperature (T/T = 0.48) up to 548 K

c (T/T = 0.89). The spin-wave linewidths observed for all temperatures

below 0.9 T were that of the instrumental resolution. Above 500 K

c the Fe„,B^, allov, which has the lower Curie temperature, showed dis86 14 - tinct linewidth broadening which increased rapidly as T was approached.

At 513 K the observe'd width was 1.0 MeV, almost double the instrumental

width of 0.55 MeV. (The intrinsic spin-wave width is less than the

98
RFACTOR PADIATIOIT DIVISIOII A!^Ei COLLABOPATIVE PR0GPJ\11S

elastic resolution of 0.8 MeV due to focussing effects.) After resolution corrections were applied, the dispersion data for these alloys

2 were quadratic in q (E = Dq ). The third alloy, Fe B , (T = 723 K)

exhibits a higher spin stiffness which is almost be^'-ond the range of

these neutron experiments. Meaningful results could be obtained only

at q = 0.08 A and for temperatures above approximately 450 K (T/T =0.62)

Figure 1 is a plot of the temperature dependence of the values

of D for two alloys. As shown, the spin-wave stiffness exhibits the

5/2 following T renormalization over virtually the entire temperature

range studied: / 7- ^/^

(

D(T) = D(T =0) 11 - a T

J

(2)

The validity of the T relationship over this wide of a temperature

region is anomalous and would be expected to result in significant de3/2 partures of the magnetization from the T low-temperature behavior

As mentioned earlier (1,5), these departures are not observed

5/2 for T < 0.33 T . The (T/T ) dependence of the spin-wave stiffness is

c c consistent with that derived theoretically for a two-magnon interaction

for a Heisenberg spin system and is the same behavior seen in crystalline Invar- tyoe alloys Fe,^Ni„r- and Fe„Pt (6) and in an independent

65 35 3 study of the amorphous alloy Fe„„B^ . (7). The Fe^,B„, alloy data do

not appear to follow the T dependence; however, this is not considered

significant due to their limited range and lower reliability. The K

extrapolated values of D for each alloy and the slope D(0)a of eq . (2) are listed in Table I. For Fe^ ,3., . , values of D(T = 0) are somewhat

OD I4

higher than that found by Ishikawa (7) et a\. with a more rapid decrease

of D with temperature than reported in ref . 7. They also find a nonzero value for the gap parameter E [eq. (1)] which we do not observe

after accurately correcting the raw data for the calculated instrumental

resolution. This correction was also verified experimentally by introducing additional vertical collimation. Also included in the table are values of D derived by Hasegawa and Ray (1) from their low temperature magnetization studies which values are in substantial agreement

99
REACTOR PADIATION CIVISIOII AIID C0LLA30FATIVE PROGRAMS

Table 1. Neutron and Magnetization Determined Values of Spin Stiffness,

D, for T = K. The units of D are MeV-A .

D(T = 0) 113 167 >175'^ 125

(ref. 8)

(neutron) 118

(ref. 7)

D(T = 0) 65 71 96

(magnet.)

D(0)a 115 90

94

(ref. 7)

* Approximate value, limited by energy-momentum restrictions

of experiment.

with those from Mossbauer results by Chlen et al. (5). Comparison of

these values illustrates the second anomaly of Fe-, B spin-wave results, 1-x X

The neutron-determinated D is almost twice as large as that calculated

from magnetization. At the same time D /T has approximately the

neutron c same ratio (0.25 for Fe„„B^o and 0.21 for Feo,B^,) at room temperature

oz lo OD lA- as those found for other amorphous alloys (8) which do not exhibit

similar discrepancies in the value of neutron- and magnetizationdetermined values of D. Similar anomalies have been reported for the

Fe^i-Ni^^ and Fe„Pt crystalline alloys (6). These results suggest that

5/2 both the wide-range of the (T/T ) dependence of the spin stiffness

D and the anomalously small values of D may be intrinsic, but not yet

understood, dynamic properties of the magnetic and magneto-elastic

interactions peculiar to the Invar state. Preliminary examination of

the temperature and q-dependence of the quasi-elastic peak intensity

(see Fig. 1) shows that additional magnetic scattering is present and

possibly represents a spin diffusion phenomena in these alloys. This

is being investigated further as an explanation for the inability of the

neutron-determined spin-wave stiffness to account for a significant

portion of the reduction in bulk magnetization with temperature.

100
REACTOR RADIATION DIVISION AMD COLLABOPATIVE ?R0G?A21S

1. R. Hasegawa and R. Ray, Phys. Rev. B20 , 211 (1979).

2. R. Hasegawa and R. Ray, J. Appl. Phys. ^, 4174 (1978).

3. K. Fukamichi, m. Kikuchi, S. Arakawa, and T. Masumoto, Solid

State Comrun. 23, 955 (1977).

4. K. Fukamichi, H. Hiroyoshl, M. Kikuchi, and T. Masumoto,

J. Mag. Magn. Mails, j^, 294 (1979).

5. C. L. Chien, D. Musser, E. M. Gyorgy, R. C. Sherwood, H. S. Chen,

F. E. Luborsky, and J. L. Walter, Phys. Rev. B 20_, 283 (1979).

6. S. Ohodera, y. Ishikawa, and K. Tajima, J. Phys. Soa. Japan

20, 1513 (1981).

7. Y. Ishikawa, K. Yamada, K. Tajima, and K. Fukamichi, J. Phys. Soc.

(Japan) 50, 1958 (1981).

8. Summarized in J. J. Rhyne, J. W. Lynn, F. E, Luborsky, and

J. L. Walter, J. Appl. Phys. 50, 1583 (1979) and in ref. 6.

SPIN DYNAMICS OF H0AI2

J . J . Rhime

and

N. C. Koon

(Naval Research Laboratory, Washington, DC)

HoAl is part of a class of rare earth compounds in which the

exchange and crystal field interactions are of comparable magnitude, and

thus the magnetic behavior may be expected to be very different from

more conventional ordered systems (e.g., rare earth iron compounds) in

which the exchange interaction clearly dominates. Neutron inelastic

scattering provides direct information on the energies and q dependence

of the magnetic excitations, and by analysis of the dispersion curves,

rather precise values of the rare earth exchange and crystal field

parameters can be determined.

101
REACTOR P-APIATIO!! DIVISION A-'ID COLLAP-ORATI^F, PRO'"-:^A>:£

70n

60

50

40-

30

20

10

Figure 1.

s^m^o^

2 4^6 8 10

70i

60

50

30

20

10

(0)

==5^5

2 4^6 8 10

Intensity versus constant-q scan along [q,q,0] at 4K in H0AI2

Data are sho\rm for in-phase modes (left) observable in the zone centered at (2,2,0) and for out-of-phase modes (right)

observable at (0,0,2). Three excitations are observable in

the energy range studied.

HoAl crystallizes in the cubic Laves phase structure (C15) with a lattice parameter of 7.79 A at 4.2 K. The low Curie temperature of 28 K

reflects the x<reak rare earth exchange. The primitive unit cell contains

two Ho atoms and thus gives rise to both acoustic (in phase) and optic

(out of phase) magnetic modes. There are two distinct Ho-Ho exchange

constants, one which couples Ho atoms on the same sublattice (J) and the

other which couples Ho atoms on different sublattices (J').

Inelastic scans were taken at 4 K for magnons propagating along all

three principal symmetry directions, [q,0,0], [q,q,0], and [q,q,q] and

throughout the Brillouin zones centered at (220) and (002) . The (220) is an allowed Bragg reflection which arises from only the Ho atoms, while

the (002) position is a forbidden lattice reflection. The dynamic

structure factor provides a convenient separation of the modes into those

resulting from an in-phase precession of the two distinct Ho spins

(observable only in the (220) zone) , and those resulting from an out-of-phase

precession (observable only in the (002) zone)

.

102
REACTOR RADIATIOII DIVISIOII AND COLLABOPATIVE PROGRAIIS

Figure 1 shows a typical constant q scan of scattered neutron Intensity

versus energy transfer and the- r-e suiting dispersion relations are given in

figur-e 2, for modes propagating in the three symmetry directions. The

excitations in the (220) zone are shown by the circle symbols and those in

the (002) zone by the square symbols. Error bars are those derived from the

least squares fitting of the intensity data. All modes shoW relatively

small dispersion reflecting the weak Ho-Ho exchange interaction. The finite

energy gap at q = is a result of the crystal field effect on the spin

waves. Significant anisotropy with propagation direction is evident for

the higher q.

H0AI2 - 4K [q, q, o] (q) H0AI2 - 4K [o, o, q] (b) H0AI2 - 4K [q q q] (g)

0.15 0.30 0.45 0.60 0.75 0.90 1.05 1.0 0.8 0.6 0.4 0.2 Reduced q Reduced q

0.2 0.4 Reduced q

Figure 2. Dispersion curves for HoAl„ at 4K for excitations propagating

along all three symmetry directions. The in-phase modes are shown by the circles and the out-of-phase modes by the square

symbols. The solid lines, are the result of the theoretical

fit using A^ = 1.7 meV/a ^ and A, = 0/092 meV/a

J(0)+J'(0) = 0.06 meV (see text)?

° and

The dispersion curves of figure 2 have been analyzed to obtain

consistent values of the Ho-Ho exchange parameters and the two crystal

field parameters A, and A, appropriate to cubic symmetry. The calculated

values are given in the caption and the theoretical dispersion curves are shown as the solid lines in figure 2. A Green's function standard basis

103
REACTOR PABIATIOll DIVISIO!! AND COLLABORATIVE PROGPAtlS

operator technique in the random phase approximation was used to analyze

the data. The low T theoretical neutron scattering cross-section is

proportional to a dynamic susceptibility which in turn involves ground

State matrix elements <m | S | 0> , <m|S | 0> , and <m | S | 0> which give rise to + — z transverse excitations (S and S ) and to longitudinal excitations (S ) respectively. In the low T limit only the S and S matrix elements have

significant strength in the case of HoAl , and they have finite values for m = 1, 3, 5,7, . . .15 with only the first three values giving rise to experimentally

observable scattering as shown in figures 1 and 2. The theoretical relative

intensity of the lowest three modes is very sensitive to the values of the

crystal field parameters A, and A,. The relative intensity ratios

determined from experiment plus the mode energies at the zone center and

boundary enabled a set of crystal field constants A, and A, and values of

J(0)+J'(0) to be determined. These values were then held constant and

the q-dependent values of the exchange J(q) and J'(q) were determined from

the dispersion of the lowest two modes.

The observation that finite dispersion is observed in all modes

immediately indicates that the Ho-Ho exchange interaction is weak but not

vanishingly small, in contrast to the case in both rare earth iron and rare

earth cobalt Laves phase compounds previously studied by inelastic neutron

2 scattering. In the iron and cobalt materials the rare earth-rare earth

exchange interactions were negligibly small as manifested by the absence of

dispersion in the rare earth dominated out of phase modes.

1. C. M. Williams, N. C. Koon, and B. N. Das, J. Appl. Phys. 50, 1669

(1979), and from total neutron scattering measurements in the present

study.

2. N. C. Koon and J. J. Rhyne, Crystalline Electric Field and Structural

Effects in f-electron Systems, edited by J. E. Crow, R. P. Guertin,

and T. W. Mahlinsin (Plenum, New York 1980), 125-140.

104
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAl^lS

SMALL ANGLE MAGNETIC SCATTERING FROM AMORPHOUS TbFe2

J. J. Rhjme and C. J. Glinka

Amorphous TbFe„ has a magnetic phase transition at about 135 °C

1

(T ) to a state which bulk measurements indicate has long-range

magnetic order. Small-angle neutron scattering (SANS) measurements

2 made some years ago revealed, however, only a weak, rounded anomaly in

the low-angle scattering as a function of temperature in the vicinity

of the phase transition. Moreover, below T the scattering at the

smallest angles continued to increase, which is quite uncharacteristic

of a transition to a long-range ordered state. This behavior has been

viewed as indicating that the magnetic ordering develops over regions

o of about 100 A in linear dimension but no further. As the temperature

is lowered below T , the degree of order within these regions Increases,

but the overall sizes of the regions change very little.

Recently the new SANS facility at the NBSR has been used to study

the phase transition in TbFe^ at smaller scattering vectors Q than were

2 accessible in the earlier work . An incident wavelength of 6.25 A,

combined with only moderate pinhole beam collimation, was used to cover

°-l

the Q-range from 0.014 to 0.12 A . The temperature dependence of the

scattering near T for several of the smaller Q-values is shown in

c figure 1. Here it can be seen that the inflection in the scattering

°-l near T is most evident at a Q of about 0.03 A . At smaller Q's,

nearly all indication of an anomaly is obscured by the strong scattering

below T . This is in contrast to conventional transitions to long-range

c order which exhibit anomalies which sharpen as Q is reduced.

The Q-dependence of the scattering at selected temperatures both

above and below T is shown in figure 2 where the inverse intensity I ^ 2 is plotted versus Q . Above T , the scattering is Lorentzian, -12 2

'^ -1 ° I «: (k + Q ) with a correlation range, 5 = k , which reaches 135 A

at T = 135 °C. Whether or not E, increases further as the temperature is

105
REACTOR RADIATIOll DIVISION AND COLLABORATIVE PROGPAIIS

Figure 1,

Figure 2,

600-

«,400

c

3oO

co

3

0) Z200

Amorphous TbFe2

0.041

• > » » LO.OBOo.

100 150

Temperature (°C)

200

Temperature dependence of the small-angle scattering from

TbFe„ in the vicinity of the magnetic phase transition.

50-

40

no

X 30

I 20

c

10-

- /

• / /^

V /'^ //• ./

/ 7 4^/

- / //%-

-/ //

/

/// • x.^ /* ^'»^^ -A-y ^."-^^"^

/ xV* •-

1 0.5 1.0

3 1.5 2.0

Q^ X 10 (A-^)

Inverse small angle scattering intensity from TbFe- plotted

versus Q'^ (0.014 < Q < 0.05 A"-'-) at selected temperatures

above and below T . The dashed curves are power law fits

(I-l oc qX) to the'^data below T .

106
REACTOR RADIATIOII DIVISION AND COLLABORATIVE PROGRAJIS

lowered is difficult to say, since the shape of the scattering gradually

-1 X changes from Lorentzlan to a simple power law, I "^ Q , and appears to

diverge at Q = for all temperatures below about 130 °C. At 25 °C, the

exponent x "^^ 3 and changes little at lower temperatures.

The scattering which develops below T finally saturates at about

40 K. The shape of this scattering was studied using incident waveo lengths between 5 and 8 A in order to determine if any of this scattering

were due to multiple refraction from magnetic domains (beam broadening

2 due to refraction varies as A ) . The Q-dependence of the scattering

was found to be independent of X, thereby confirming that it arises from

diffraction from regions far smaller than typical magnetic domains

(typical dimensions of 1-10 ym. ) • This result and those discussed above

agree with earlier measurements and support the hypothesis that finite

rather than infinite-ranged magnetic ordering occurs in amorphous TbFe„.

1. J. J. Rhyne, J. H. Schelleng, and N. C. Koon, Phys, Rev. BIO, 4672

(1974).

2. J. J. Rhyne, S. J. Pickart, and H. A. Alperin, Pkys. Rev, Lett. 29_,

1562 (1972).

ADVANCED NEUTRON METHODS

J. M. Rowe, C. J. Glinka, N. Berk

J. LaRock, R. Williams and D. Fravel

1. Small angle Neutron Scattering (SANS)

The new facility for SANS became fully operational in the Fall

of 1981 following the installation and calibration of the instrument's

65 cm X 65 cm position-sensitive detector. Figure 1 is an overhead

view of the instrument showing the post-sample flight path which houses

the detector and the associated data acquisition system. Some minor

107
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

electronic and computer software problems which arose during the first

few months of operation have now been corrected and over the past four

months (April-July 1982) the instrument has functioned properly more

than 95% of the time. The operating characteristics of the facility,

now well established by actual measurements, are summarized in table 1.

Over the past year a number of enhancements to the basic instrument have been added. An automatic multiple sample changer has been

installed in the facility's evacuated sample chamber. Up to four

samples can be run in any sequence entirely under computer control. A

sample stage is available, primarily for polymer and biological specimens, which is equipped with cooling coils and individual heaters and

thermocouples for each of four sample positions. To facilitate sample

positioning, a low power laser has been built into a rotating beam

shutter at the entrance to the pre-sample flight path. The laser can

be rotated into the beam at any time to check the alignment of a sample.

Computer control of the temperature settings of a closed cycle helium

gas refrigerator and an aluminum vacuum furnace has been implemented

thereby providing convenient access to temperatures from 10 to 700 K.

Horizontal and vertical field electromagnets have also been adapted for use at the facility for measurements in magnetic fields up to 10 kgauss,

Computer software for handling the large data arrays (128 x 128)

generated with the area detector has been developed to the point where

data sets can be reduced rapidly and interactively, with the aid of a color graphics display terminal, to obtain intensity versus scattering

vector curves in a few minutes. This capability significantly improves

the efficient use of the facility by enabling users to assimilate and assess data as it is being collected. Further software development

directed toward model fitting and extracting particle size distributions from SANS data is planned for the near future.

Since commencing operation, experimental programs in polymers,

metallurgy, biology, solid-state physics and nondestructive testing

have been initiated. Many of these have involved collaborations with

108
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

other NBS Divisions (Polymers, Fracture and Deformation and the Metallurgy Divisions), government (NSWC, NRL, NIH) and industrial (e.g..

Union Carbide, Exxon, and Allied Corps.) laboratories and several

universities (e.g., Maryland, Illinois, and Northwestern).

From these initial efforts a number of promising results have

been obtained. For example, a Fracture and Deformation Division study

of prototype ceramics which exhibit large, reversible changes in their

bulk moduli as a function of temperature gave strong supporting evidence

for the hypothesis that these changes are due to the formation of

microcracks. In addition to demonstrating the sensitivity of the

technique for detecting microcracks, the SANS measurements provided

quantitative estimates of the size and number density of the cracks

useful for comparison with theoretical calculations.

In another study involving the Fracture and Deformation Division,

an important class of maraging steels has been shown to be ideal for

studying the effects of deformation on materials with complex microstructures. By applying a saturating magnetic field, the magnetic

scattering, which arises from the contrast between non-magnetic precipitates imbedded in the magnetic host material, can be isolated from

scattering due to the formation of voids, for example.

In fundamental studies of superconducting materials which

contain magnetic constituents, high resolution SANS measurements have

yielded the first preliminary indication of the predicted suppression

of the long wavelength magnetic fluctuations in the superconducting state.

More detailed descriptions of these and other examples of SANS

related projects initiated to date are summarized in following articles

in this report.

109
REACTOR RADIATIOn DIVISION AND COLLAROPATIVE PROGPAMS

Table 1. Operating characteristics of the NBS SANS facility

o Wavelength: variable from 5 to 10 A (AX/X'^^ 0.25)

Collimation

Min imum Q

Q Range:

Sample size:

Flux at sample:

(10 MW)

Detector

single pair of irises or 9 channel converging

collimation

O _-l o ° _1 ° 0.004 A~ at 6 A, 0.003 A~ at 9 A

0.003 a""*" to 0.6 a""*" 0.4 to 2.5 cm diameter

4 5 2 10 to 3x10 n/cm -sec depending on slit sizes and

wavelength (these fluxes will double at 20 MW)

2 65 X 65 cm position-sensitive counter with

8x8 mm resolution

Figure 1, The recently completed small angle neutron scattering

instrument showing the post-sample flight path which

houses the area detector and the associated data acquisition

system.

110

I
REACTOR RADIATIOl-I DIVISIOII AND COLLABOPATIVF, PROGRAIIS

2. Neutron Time-of-Flight Facility

The NBS time-of -flight (TOF) facility became fully operational during

o this period. Tests of the resolution and intensity at 6.0, 4.0, and 2.5 A

incident wavelength have confirmed the predicted performance. Data

analysis and display programs have been written and tested. Although the

background remains higher than desirable, the tests run to date show that

the facility is now useable for many experiments. Further developments to

further reduce the background are continuing. The data acquisition system

includes on-line data display and elementary manipulation, along with a direct link to the VAX computer which allows complete data analysis.

As currently configured, the facility comprises 20 banks of two 18" by 1"

detectors spanning the angular range from 20° to 106° scattering angle.

o The incident wavelength can be continuously varied from 1-6 A, although

order contamination is a problem for X 4A, except at 2.4 and 1.5 A.

The instrument has been used to measure quasielastic scattering in

acetonitrile; diffuse scattering in KCN; the phonon density-of-states in

Vd „ and the vibrational density of states on finely divided Pt catalysts.

Future refinements planned for this facility will increase the

resolution, decrease the time independent background, and allow data to

be taken at lower wave vector transfer.

3. General Instrument Improvements

The triple-axis spectrometer at BT-4 will be extensively modified

during the shut down for conversion to 20 MW reactor operation. The

modifications will allow higher resolution operation, more rapid conversion

to cold neutron studies and lower backgrounds. All of the parts required

for this upgrade have been designed and manufactured, and the detailed

planning for the conversion is now proceeding.

In the area of sample environmental facilities, a liquid He-3 cryostat

has been built and is presently being commissioned . Anew, high temperature

furnace ("^ 1500 °C) is also under construction.

1. C. J. Glinka, Proceedings of the Symposium on Neutron

Scattering, Argonne National Laboratory, August 1981 (in press)

111
REACTOR RADIATION DIVISIOIT A!TD COLLABORATIVE PROGPAI^S

INTERNAL EXPANSION FROM BLOCK COPOLYMERS

OF h-STYRENE AND d-STYRENE

T. P. Lodge, E. J. Amis, and C. C. Han

(Polymer Science and Standards Division)

and

C. J. Glinka

and

Y. Matsushita, I. Noda, and M. Nagasawa

(Nagoya University, Nagoya, Japan)

The technique of deuterium labelling in SANS makes it possible to

investigate the conformational behavior of single molecules or portions

of molecules in the presence of many others. This permits experimental

results to be obtained which may be compared with theoretical predictions

for rather subtle aspects of polymer conformation. In this study this

approach has been utilized to investigate the chain length and position

dependence of the excluded volume effect; this particular problem has

been previously attacked with a variet}' of techniques including Monte

Carlo '

, pertubation theory ' , and renormalization groups '

. Specifically, the radius of gyration has been determined for a perdeuterated

polystyrene of molecular weight about 30,000 dissolved in CS , in three

different situations: as an isolated molecule, on the end of a larger

polystyrene, and in the middle of a larger molecule.

1. Experimental

The three samples were s^mthesized and characterized as previously

described . TUN-Ol is a perdeuterated polystyrene of molecular weight

27,000, TUlSI-14 is a diblock copolymer of perdeuterated polystyrene

(M = 27,000) and polystyrene (M = 389,000), and TUN-15 is a triblock

with the perdeuterated polystyrene (M = 31,000) sandwiched between two

polystyrene ends (M = 140,000 and 122,000). Measurements were made at

three concentrations of each sample in CS_: 0.8%, 1.5%, and 2.5% by

weight of polymer. CS- was selected because it masks the polystyrene

coherent scattering and has no incoherent cross-section. The SANS

spectrometer at NBS was used for the study . Incident neutrons of

112

1
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGFAIIS

wavelength 5.6 A were employed, with AA/X = 25%. Solutions were con- tained in a 1 cm path length quartz cell. This arrangement gave an

°-l effective q range of 0.014 to 0.13 A for these samples; one sample

(2.5% TUN-15) was also measured with a high-resolution configuration

using a unique focussing collimation system ; this extended the effective

°-l

q range down to about 0.011 A . Data acquisition is controlled by a dedicated PDF 11/23 computer; data is subsequently transferred to a VAX

for analysis. Typical acquisition times were from 8 to 12 hours,

depending on sample and concentration.

2. Results and Discussion

For all three samples, the radius of gyration for the perdeuterated

blocks were extracted using a nonlinear regression fit to the Debye

function. Strictly, this should only be applicable to gaussian chains,

whereas CS„ is a moderately good to good solvent for polystyrene.

8

However, as pointed out by Freed , even with fully developed excluded

volume the static structure factor S(q) is essentially indistinguishable

from the Debye function, if the radius is rescaled. In addition, we

9 have attempted to fit the data to the Ftitsyn Formula with e either set

equal to 0.2 or left floating; no credible fits were obtained. In the

Debye function analysis, the baseline was also floated, primarily to

account for the small amount of incoherent scattering from the hydrogen

present.

Because the data do not extend well into the Guinier region, the

extracted values have some sensitivity to the low q limit at which the

data are truncated. Thus the fitting was performed after sequentially

discarding low q points until the radius values began to change systematically and significantly (1-4%) . With the exception of the TUN-15

results, the spread of the values thus obtained is insignificant. Fixed

values were obtained by averaging the several individual radii. These

results are summarized in Table I, as are the infinite dilution values

obtained by least squares. The uncertainties indicated represent the

standard deviation which accompanied the average.

In figure 1 the scattering curve for the 2.5% TUN-01 solution

113
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRMIS

(corrected for solvent and cell contributions) is presented. The

resulting Debye fit is also shown; the quality of this fit is excellent.

o The infinite dilution value for R of 49.6 A is in remarkably good

agreement with the tabulated value for polystyrene in a theta solvent of

°10

about 49 A . Thus this supports the notion that even in good solvents

relatively small polymers do not exhibit much swelling. In figure 2 the

scattering curves for the 2.5% TUN-15 solution are shown, for both the

regular and the high-resolution runs. The two sets of data have been

fitted independently, yielding consistent results; to obtain this plot

the high-resolution values have been "normalized" using the intercept

and baseline values of the Debye function fits. l^Jhile the quality of

the fit is not as high as with TUN-01, the two separate runs are in very

good agreement, and no systematic deviations from the Debye function are apparent.

In figure 3 the extrapolations of R to infinite dilution are

g displayed. The intercept values of R are also presented in Table I. Before comparing the results for TUN-14 and TUN-15, it is important to

note that the deuterated portions of these two molecules are of different

o length. If the TUN-15 value of 63.8 A is scaled to a molecular weight

fi ° of 2 7,000, assuming full excluded volume (R 'v M ' )

, a value of 58.7 A

is obtained. This is about 5% greater than the TUN-14 result. In both

cases there is considerable swelling relative to the TUN-01 sample.

These data represent, as far as we are aware, the first experimental

estimate of the so-called "chain end effect" on polymer conformation.

Table I. Values of R , A.

g

2.5% 1.5% 0.8% °° Dilution

TUN-01 37.1 ± 0.3 42.2 ± 0.4 45.6 ± 0.5 49.6

TUN-14 52.1 ± 0.3 53.3 ± 0.1 54.8 ± 0.4 55.9

TUN-15 54.1 ± 1.9 57.4 ± 2.2 50.9 ± 1.2 63.8

114
REACTOR PADIATIOn DIVISION AIID COLLABORATIVE PROGRAIIS

1 1 1 1 1 1 1 1 1 1 1 1 1

6 N^ d-PS in CS2

-

5 - \

M = 27,000

c = 2.5 %

-

4 \ -

l.a.u.

3 \ Debye Function Ft: 37. 1 A -

2 \

-

1

1 1 1 1 1 1 1

1 .02 .04 .06 .08 .10 .12 Q,A"'

Figure 1. Scattering curve for TUN-01, 2.5% In CS^.

Debye function fit.

10

, a.u

8

T 1 1 1 1

\

1

1 1

1 I rh,d,h-PS in CSj

M = 140.000-31,000-122,000

c = 2.5%

Debye Function Fit: 54.1 A

Solid line is

02 .04 .06 .08 .10 .12 Q,A-'

Figure 2. Scattering curves for TUN-15, 2.5% in CS^: •-normal resolution, o-high resolution. Solid line is Debye function fit.

115
REACTOR RADIATION DIVISION A^TD COLLABORATIVE PROGRAIIS

C,7o

Figure 3. Extrapolation to infinite dilution of Rg values for TUN-01

(D), TUN-14 (HD), and TUN-15 (HDH) . Uncertainties indicated

as in Table I.

1. F. T. Wall and J. J. Erpenbeck, J. Chem. Phys. 30, 637 (1959).

2. A. J. Barrett and W. H. Stockmayer, personal communication.

3. M. Kurata, H. Yunekama, and E. Teramoto, J. Chem. Phys. 28^, 785

(1958).

4. J. des Cloizeaux, J. Physique 41, 223 (1980).

5. Y. Oono and T. Ohta, Phys. Lett. 85A, 480 (1981).

6. Y. Matsushita, H. Furuhashi, H. Choshi, I. Noda, M. Nagawawa,

T. Fujimoto, and C. C. Han (to be published).

7. C. J. Glinka, Proc. of a Symposium on Neutron Scattering, Argonne

National Lab., August 1981.

8. T. Ohta, Y. Oono, and K. F. Freed, Macromolecules 14, 1588 (1981).

9. 0. B. Pt:'_syn, Zh. Fiz. Khim. 31, 1091 (1957).

10. J. Brandrug and E. H. Immergut, eds. "Pol5aner Handbook," Wiley:

New York, 1975.

116
REACTOR PADIATIOI] DIVISIOH AND COLLABORATIVE PROGPAIIS

STUDY OF POLYMER SURFACTANT COMPLEXES

BY SMALL ANGLE NEUTRON SCATTERING

P. S. Leung

(Union Carbide Corporation, Tarrytown, NY)

and

C. Han

(Polymer Science and Standards Division)

and

C. J. Glinka

Subthermal neutrons have an energy and mass appropriate for probing size in the dimensional range of molecular aggregates. The large

contrast to neutrons of hydrogen isotopes in hydrogenous materials makes

small angle neutron scattering (SANS) unique among scattering techniques

and it is particularly useful in separating the contribution of various

components in mixed systems. Recently, studies of polymer/surfactant

interaction have revealed the presence of molecular complexes between

the polymer and the surfactant. The forming of complexes significantly

changes the solution properties such as rheology, solubilization,

surface activity, etc. However, most available physical measurements

cannot distinguish individual contributions in such a mixed system.

Thus, the structures proposed have been at best speculative. There

have been some initial SANS studies done by groups in France, who used

deuterated surfactant and polymer components for this purpose. However,

no such study or the interaction of cationic polymer/anionic surfactant

systems has been reported so far. Since the latter systems are believed

to go through many structural changes depending on the concentration

ratio of the two components, we have studied a system containing a cationic

polymer and an anionic surfactant in some detail. It was found that a polymer with a rigid extended chain has no significant scattering in the

°-l wave vector (Q) range >0.01 A due to its large radius of gyration, Rg.

By adding a small amount of deuterated anionic surfactant, association

occurs leading to significant small angle scattering intensity and

o corresponding to entities with Rg = 47A (see figure) . At surfactant

concentrations exceeding the charge neutralization ratio, the deuterated

117
REACTOR PABIATION DIVISION AI^ID COLLABORATIVE PROGRAMS

aggragates which form have an Rg of 22A, which is very close to the

o size of regular micelles. A somewhat larger polymer segment (Rg=42A)

is simultaneously observed. At even higher surfactant concentrations,

a peak appears in the scattering intensity vs. Q plot corresponding

most likely to a regular array of micelles. The most probable distance

between the surfactant micelles is determined by the balance of free

energy of association and the repulsion between the charged miscelles.

Wave Vector Q

10 X 10^ 10 X 10-^

Figure 1. Guinier plot In(I) vs. Q of the radially averaged smallangle scattering from several polymer-surfactant solutions,

Contrast matching has been used to study independently the

scattering from the polymer (curves on left) and from the

surfactant (curves on right)

.

118
REACTOR RADIATIOn DIVISIOIl AND COLLABORATIVE PROGRAMS

STRUCTURE FACTOR STUDIES OF A TiCu METALLIC

GLASS AS A FUNCTION OF ANNEALING TREATMENT

B. Mozer and S. Singhal

and

A. Maeland

(Allied Chemical Corporation, Morristown, NJ)

Studies were initiated on a two component metallic glass, Ti.j-Cu. , to ascertain what information might be elucidated through small angle

neutron scattering (SANS) determinations of the structure factor and

through standard neutron diffraction measurements of the structure factor

as the alloy is annealed up through the crystalline phase transformation.

This particular alloy was fabricated by the Allied Chemical Corporation

where its characteristics were determined to be in a state of metallic

glass in the physical form of long, thin, narrow ribbons as normally found

in the melt spinning methods for producing metallic glass alloys. X-ray

diffraction patterns, differential scanning calorimetry, and other standard

metallurgical analyses were performed on this alloy in labelling it a welldefined metallic glass.

The titanium alloys, as well as other possible alloy systems that

form metallic glasses, can be made in a composition so as to form a "null

matrix" neutron scattering system in the liquid state, glassy state, or non- intermetallic crystalline state. Furthermore, this null matrix condition

enhances that part of the neutron diffraction associated with short-range

order phenomena or microstructure irregularities such as precipitates of

o 10-1000 A size as observed in SANS. Neutron diffraction patterns associated

with possible short-range orders of various CuTi alloys have been studied

2 with standard neutron diffraction techniques. Very few small angle

neutron diffraction measurements have been made on nonmagnetic metallic

3 glasses and only on very complex alloy systems. In these neutron scattering

studies, the effects of annealing were not measured.

2 We prepared a sample in the form of small (1-4 mm ) pieces from the

as-received ribbons of Ti. t-Cu to approximate powder sample for the

119
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

diffraction studies. Cylindrical sample holders of very thin vanadium

or copper foil were used to minimize the background scattering from the

sample holders. Standard diffraction patterns were taken covering a span

Att °— 1 9~1

of K = — sin 6 from 0.2 A to 6.0 A and small angle scattering patterns

-2 9-1 -1 °_i were taken covering a span of K from 1.0x10 A tol.SxlO A for

the as-received material, the material annealed at 300 °C in vacuum, near

the glass transition temperature, for 3 hours, and the materials annealed

for 6 more hours at 300 °C.

°-l Figure 1 shows the structure factor in the range 0.2 to 6.0 A

This structure is expected for a glassy system except for the pre-peak

°-l 2 at 2.0 A as noted by Sakata et al. With increased time of annealing,

the intensity of the pre-peak increases relative to the main peak.

Figures 2, 3, and 4 show constant intensity contour maps for the

small angle neutron scattering from the alloy in the as-received condition,

after 3 hours of anneal at 300 °C, and after a total of 9 hours of anneal

at 300 °C. One notes immediately the strong asjmunetry in the scattering.

The results in figure 1 are somewhat distorted because we tried to position

the beam stop using the scattered beam from the alloy and were unaware of

the asymmetry. Consequently, the beam stop was positioned so as to mask

the scattering in the upper-half plane. Figures 2 and 3 show the scattering

after the respective anneals of 3 plus more hours. In these measurements

the beam stop was positioned with a strong symmetric scatterer and the

asymmetry in the scattering is well revealed. Preliminary analysis of the

scattering patterns indicates microstructure whose dimensions are 150 to

200 A. The relative intensity of this scattering increases with annealing

and the duration of anneal.

The most striking result of the neutron measurements to date on this

CuTi alloy is the evidence of the formation of a phase other than the glossy

phase in the rapidly solidified sample. This "precipitate" phase is highly

oriented along the long dimension of the ribbon. Furthermore, this

"precipitate" phase changes with heat treatment and is observed both in

the small angle scattering and in the structure observed at larger wave

120
REACTOR RADIATION DIVISION AND COLLABOPATIVE PROGRAMS

Figure 1. Diffraction data for amorhpous Cu^^Ti,^ alloy after a 3-hour

anneal at 300 °C. Neutron wavelength is 1.515 A and data

corrected for container scattering. Note the peak at 27°

scattering angle which has been called a chemical short-range

order prepeak by Sakata et al.

127.0

101.6

TI-45 CU-55 AS RECEIVED

76.2

50.8

25.4

25.4 50.8 76.2

Axis 101.6

Figure 2. SANS corrected data for amorpnous Cu Ti.^. alloy in the as- received condition. The asymmetry in the pattern comes from

a directionally ordered precipitate phase. The beam stop was misaligned in this pattern and produced a' tilt in the asymmetry.

121
REACTOR PADIATIOn DIVISIOH AND COLLABORATIVE PROGPAIiS

127.0^

101.6

76.2

50.8

25.4

1ST ANNEAL FOR 3HRS AT 300'

25.4 50.8 76.2 X Axis 101.6

Figure 3. SANS corrected data for amorphous Cu^^Ti,;. alloy after a 3-hour

anneal at 300 °C. Note the strong asymmetry In the pattern.

The intensity of this pattern is stronger than the as-received

sample.

127.0^

101.6

2ND ANNEAL FOR 5HRS AT 300C

X<

76.2

50.8

25.4

25.4 50.8 76.2

X Axis 101.6

corrected data for amorphous Cu^j-Ti,^ alloy after a total

-hours anneal at 300 °C. The intensitv of tl Figure 4. SANSof 9 pattern has increased over that of figures 2 and 3,;his asjnnmetrical

122
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

vector differences. It is important to note that this microstructure

may be common to other metallic glass systems and requires a very thorough

investigation to help determine manufacturing parameters for the production

of metallic glasses. In the future we shall continue our study of the

microstructural changes in this alloy as we anneal the sample closer to

the crystallization temperature. Other alloys of this system will be

investigated to determine if these results are applicable in a general sense,

In addition, we are in the process of measuring the thermal properties of

this alloy as a function of annealing temperature and duration and we

shall characterize this sample using x-ray and other metallographic

techniques for intercomparison with our neutron results.

1. B. Mozer, D. T. Keating, and S. C. Mass, Fhys. Rev. 175 , 868 (1968).

2. M. Sakata, N. Cowlam, and H. A. Davies, J. Phys. F: Metal Phys. 11,

157 (1981).

3. D. E. G. Williams, H. Fujimori, and D. S. Brown, J. Appl. CrySt. 15,

206 (1982).

INVESTIGATION OF SiC-Al COMPOSITE MATERIAL BY NEUTRON SCATTERING

H. A. Alperin

(Naval Surface Weapons Center, White Oak, MD)

and

(National Bureau of Standards, Washington, DC)

and

S. P. Singhal

(Fracture and Deformation Division)

We have investigated the feasibility of using neutron diffraction

as a tool for the nondestructive evaluation of composite materials. The

material selected, SiC fibers in an aluminum matrix, is ideal for this

purpose due to the very low aluminum neutron absorption cross section.

This makes it possible to observe (111) Bragg reflections from both the

123
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGPAIIS

fibers and the matrix. Upon application of increasing compressive stress

to a cylindrical sample ("^ 1 cm diameter) while it is undergoing neutron

scattering measurements, it is possible to accurately measure the change

in d-spacing (strain) as a function of applied stress (a) independently

for both the matrix and for the fibers.

Ad/d = -va/E = -A(2e)/2tane

Other bulk measurements only give an average for the composite as a whole.

The required accuracy of the measurement derives from the ability

to fit a known function (Gaussian) to the neutron lineshape. With sufficient

counting statistics ('^ 4 hrs. for each peak scan) the fit yielded peak

positions to an accuracy of '^ + 0.001 degrees (26) which gives a change

-4

in d-spacing accuracy of '^ + 1 x 10 A.

The results are shown in figure 1. For comparison, an identicallyshaped rod of 6061 Al was also measured. From the slope and assuming a

6 4 Poisson ratio v = 0.31 a Young's modulus E = 10.9 x 10 psi (7.5 x 10 MPa)

is obtained; this is very close to the value (10.5 x 10 psi) usually

quoted for an Al alloy. The stiffening of the Al matrix in the composite

is apparent from figure 1 and gives the value E = 19.5 x 10 psi. The SiC

fibers show a value E/v > 300 x 10 psi.

Several interesting effects are also observed. One is a relaxation

effect observed in the fibers upon repeated measurements over a period of

8 hours at a constant value of stress. The range of variation in d-spacing

due to this effect is shown by the cross-hatched bars in figure 1. Another

effect is the large initial stiffness shown by both the matrix and the

fibers. Neither of these effects are observed in the Al alloy sample.

One can see that at the stress levels used in this study (which are in

the elastic region) d vs. a is linear (figure 1). Upon entering into the

plastic region at higher stress levels, a departure from this behavior

is expected. One can therefore study initiation of failure modes at the

SiC-Al interface by extending the measurements to higher stress levels.

124
REACTOR RADIATIOn DIVISION AND COLLABORATIVE PROGPJ^IS

37.760;

37.750

- 37 740

AL (111) - 6061 Al Rod

A AL (111) SiCAL Composite

^SiC(lll) Rod

<

37.730

37.720

35.010|^

35.005'

-35 000

PSI X 10-3) MPA X 10-"

Figure 1. Strain vs stress from Al and S. C Bragg reflections in 6061

Al alloy and S.C-Al composite material.

THE THEORY OF SP I NODAL DECOMPOSITION

N. F. Berk

and

S. Singhal

(Fracture and Deformation Division)

and

H. A. Alperin

(Naval Surface Weapons Center, White Oak, MD)

and

(National Bureau of Standards, Washington, DC)

A program is in progress to develop the application of theory to the

interpretation of small angle scattering from alloys undergoing spinodal

decomposition. Current efforts have focused on the analytical description

of Langer, Bar-On, and Miller (LBM) which, even in the simplified form

now commonly identified with it, produces a cumbersome set of

simultaueous dif f ereiatial equations for the scattering function and the

moments of the order parameter distribution function. As part of our own

125
REACTOR RADIATION DIVISIOII AtlD COLLABORATIVE PROGPAf'^S

effort, we have implemented a computer solution of these equations and are

studying methods to facilitate the comparison of theory with experiment.

In the standard form of the LBM theory, the order parameter distribution function is assumed to be a pair of guassian functions centered on the

most probable coarse grain values of the alloy composition. The theory

can then be manipulated to give approximate equations of motion for the

time evolution of the parameters of the double gaussian ansatz. It does

not seem to have been remarked that a consistent set of equations can also

be derived for the distribution function on the stronger assumption that the

guassians have zero width. For the so called "symmetric" case of an alloy

quenched at the critical composition, the small angle scattering intensity

is then described by the much simpler set of equations

a^S(q,t) = -q (q^ + a(t))S(q,t) + q ,

a(t) = f'(x)/x.

2 X (t) = 1/q^ r q^S(q,t)dq,

Here S(q,t) is the scattering intensity as a function of scattering

wavevector q and time t, f (x) is the model course grain free energy and x(t)

is the composition order parameter. All variables have been expressed in

dimensionless form, and q^, the only "free" parameter, is the inverse

measure of the course grain length.

These equations are much simpler than those in the standard form of

the theory, yet the solutions exhibit all of the qualitative aspects of

the behavior of S(q,t) usually associated with non-linear spinodal decomposition. This suggests that the non-zero width parameter, which seems to

contribute in large measure to the complexity of the standard form of the

LBM theory, is not essential in determining the scattering "signature"

of the decomposition. Moreover, the simplified form is more amenable to

the treatment of various model-free energy functions than is the standard

form. Preliminary results comparing the Gins berg -Landau form with the

regular solution model indicate that except for the time scale

126
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGPiU^lS

of the evolution, the shape of the scattering curve as a function

of q is insensitive to the form of the free-energy function (for the

symmetric case)

.

1. J. S. Langer, M. Bar-On, and H. Miller, Phys. Rev. All, 1417 (1957).

NONDESTRUCTIVE EVALUATION OF DISTRIBUTED DAMAGE

E. R. Fuller, Jr., R. J. Fields, E. D. Case, and S. Singhal

(Fracture and Deformation Division)

and

C. J. Glinka

In a number of instances, failure of a structural component results

from an accumulation of damage, distributed homogeneously throughout the

component, as opposed to the formation and growth of a macrocrack. An

example of such a situation is the nucleation and growth of creep cavities

in the high-temperature components of energy conversion systems. Another

example might be the accumulative damage that occurs in a composite material

which is subjected to a fluctuating service stress. An important design

consideration in the initial materials selection for such applications is an assessment of the material's failure life, either creep rupture life or fatigue life in the examples mentioned above. Of equal importance, however,

in assuring remaining lifetime is a nondestructive assessment of the

accumulative damage that has occurred thus far in the service life. If the

state of progressive degradation in service can be periodically monitored,

the rate of damage accumulation can be determined and actual component

lifetime more accurately predicted. Failure due to distributed damage is

not necessarily restricted to mechanical failure. In material processing,

for example, it is occasionally important to assess the integrity of a body before further processing is warranted.

The objective of this research program is to address these issues

by an evaluation of various nondestructive inspection techniques that have

127
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGPAIIS

potential for monitoring the extent of distributed damage in these materials.

Nondestructive techniques are, in general, more desirable than destructive

ones because they can be applied to actual operating components without

having to replace the component after inspection. However, nondestructive

techniques rarely provide direct measurements concerning the microstructural defect associated with the distributed damage. We intend to

compare the results of several common nondestructive inspection techniques

with direct observational measurements of the size and abundance of

defects, thereby increasing the scientific base for these NDE standards.

During this first year, the research effort has focused on the detection

and characterization of uniformally distributed microstructural damage

through the use of the new small-angle neutron scattering (SANS) facility

at NBS. Two model systems have been developed and utilized for these

studies: (1) creep cavitation damage in 304 stainless steel and (2)

uniformally distributed microcracks in a polycrystalline ceramic, yttrium

chromite. These studies are described separately below. The small-angle

neutron scattering facility is described in a separate report by C. J. Glinka,

1. Cavitation Damage in 304 Stainless Steel

304 stainless steel used in high-temperature applications consists of

metal carbides in an austenite matrix. At elevated temperatures, however,

the carbide-austenite interface at a grain boundary becomes a preferential

site for cavity nucleation. The resulting cavities then grow, link, and

ultimately cause failure. The early stages of this process are extremely

slow, and the creep cavities, due to their small, size are not easily

detectable or quantifiable. It is these early stages of nucleation

and cavity growth that are examined in this research through the use of

small-angle neutron scattering (SANS).

Since carbide precipitates, as well as creep cavities, give rise to

neutron scattering, two requirements must be satisfied for a quantitative

evaluation of cavitation damage:

(i) the volume fraction of carbide precipitates should not change

significantly during creep and

128
REACTOR RADIATION DIVISIOll AND COLLABORATIVE PROGPAIIS

1500

1242-

O 983-

i 726

i 467 " 208

50

1000

850-

o 660

X

>490 +^

'55S 320

(a)

Sample C-21

250 500 750 1000 1250 1500

Scattering Vector x lO-^

(b)

Sample C-18

150

^^0 200 400 600 800 1000 1200

Scattering Vector x lO^^

Figure 1. Small-angle neutron scattering intensity versus scattering

vector Q for creep cavities (a) in sample C-21 and (b) in

sample C-18

.

(ii) a reference sample with equivalent carbide structure should be

measured and subtracted from the scattering spectrum of the crept sample.

The first condition was achieved in the present study by a "stabilizing"

heat treatment of approximately 40 hours at 775 °C prior to the initiation

of the creep experiments. This allowed a complete precipitation of carbide

thereby stabilizing the volume fraction of carbides. The second

129
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

5 10 15 20

Scattering Vector. Q (I/A) x 1 O'^

Figure 2. Small-angle neutron scattering intensity versus scattering

vector, Q, for two microcracked polycrystalline YCr02 specimens

of different thicknesses. Specimen YTIM is approximately five

times thicker than specimen Yll. Similarity between the two curves implies that scattering is predominantly diffractive

in nature.

condition was satisfied by a reference specimen which was only heated (and

not stressed) along with the crept specimen. Although a number of creep

specimens were examined in this study, only two fulfilled this second

requirement for a reference sample. These specimens were both crept at

600 °C: one (Sample C-21) at a stress of 145 MPa (21 ksi) for 745 hours

and the other (Sample C-18) at a stress of 124 MPa (18 ksi) for 789 hours.

The unstressed reference samples for these specimens are designated R-21

and R-18, respectively. The neutron wavelength for these studies was

° °-l

5.1 A giving a range of scattering vectors, Q, from 0.014 to 0.16 A

With this range of Q, contributions from cavities and carbides in the

o size range of 40 to 450 A were detected.

The detailed theory and procedure for analyzing the SANS data will

be prescribed in a forthcoming publication. A few salient features, however,

130
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGPJU^S

18

_ 16

S 14-

^121-

0)><

c 10

o

_L

• YTI Al

o YTIM

Not Scaled

o

o

5 10 15 20

Scattering Vector, Q (I/A) x lO'^

25

o

30

Figure 3. Neutron scattering intensity versus scattering wave vector, Q,

for a YCrOo specimen both in its microcracked state (YTlM) and

its healed state (YTlAl)

.

are described here. If scattering intensity is denoted by I, the

differential scattering cross-section is given by

dS/d^ = cl/t M T

where t is the sample thickness, M is the total monitor count (or scattering

time), T is the sample transmission, and c is a combination of experimental

constants related to the SANS facility. Creep damage is related to the

difference in differential scattering cross-sections between the crept

sample (C) and the reference sample (R)

:

[dS^/dfi - dS^/dfi] = c [I^/t^M^T^. - I^/t^M^Tj^].

Accordingly, all intensities in the further discussion have been normalized

by sample thickness, transmission, and scattering time.

131
REACTOR RADIATION DIVISIOII AND COLLABOPATIVE PROGRAMS

1.2

.010 .020

Scattering Vector

040

Figure 4. The difference spectrum for the scattering curves plotted in

figure 3. The solid line is a fit to a scattering model from

a randomly oriented array of thin disks.

The scattering intensity for cavities in sample C-21 [i.e., I (C-21)

I (R-21) is shown in figure la, and that for sample C-18 in figure lb.

A visual comparison of these figures indicates that for most scattering

vectors Q, the scattering from cavities is larger in sample C-21 than in

sample C-18, thus indicating the presence of a higher volume fraction

of cavities in sample C-21. A Guinier analysis can be performed on these

spectra to obtain an average creep cavity size. Guinier showed that for

132
REACTOR RADIATION DIVISION AND COLLABOPATIVE PROGRAMS

randomly, distributed, monosized, spherical heterogeneities, the

scattering curve near Q

'^^ can be approximated by the relation

2 2 1=1 exp (- R Q /5)

o where I is the intensity intercept at Q = and R is the cavity radius.

This expression is valid only when the volume fraction of cavities is

small enough to avoid so called "inter -cavity interference."

Gulnier plots of the data in figure 1 give a straight line behavior

°-l only in the range for Q of 0.01 to 0.025 A , indicating that the cavities

formed during creep cavitation have a range of sizes rather than being one size. To obtain a cavity size distribution will require further

analysis, but an average cavity size has been obtained by a least-squares

fit to this low Q region. The results are

R = 173 + 10 A for sample C-21

and

R = 133 + 7 A for sample C-18

Thus, sample C-21 not only has a higher volume fraction of cavities but

also a larger average cavity size.

Common to various theories of creep cavitation discussed in the

literature is the assumption of a two-stage process involving nucleation

and growth. In general, the stress level determines both the nucleation

and the growth rate; whereas time under load determines the total volume

fraction of cavities for that rate. For the present studies, an increase

in stress by 20 MPa (3,000 psi) results in larger average cavity size and

in greater volume fraction of cavities. Conclusion regarding nucleation,

however, require further analyses of size distribution.

Although these analyses are continuing, numerous questions and

theoretical obstacles concerning these evaluations have arisen from physical

considerations. Chief among these is the fact that cavities always occur

on carbides. Accordingly, it may be incorrect to assume that scattering

from these two scattering species is independent and uncorrelated . Second,

133
REACTOR RADIATION DIVISION AIJD COLLABOPATIVE PROGRAJ^S

stress induced redistribution of precipitates is possible and will

contribute to the apparent creep damage as deduced by SANS. This

scattering component will not be correctly evaluated if the scattering

cross-section is interpreted as totally due to cavities.

These complications have been neglected in the past year's effort

because at present we have no completely satisfactory way to treat them

theoretically or to avoid their influence in 304 stainless steel. However,

the analyses which have been performed demonstrate that SANS is sensitive

to the creep damage in an engineering alloy before this damage is detectable

by other techniques, even though an exact interpretation of the data is

clouded for a complicated system like 304 stainless steel. Accordingly,

it is our intention to better quantify the basic technique by next

investigating a simple single phase system for which scattering variations

will be solely due to the presence of cavities. Such a material might be

OFHC copper which is known to be prone to intergranular cavitation. We

may then proceed to the case of a two phase material in which no redistribution of the dispersed phase is possible. Finally, we will return

to the complicated case of 304 stainless steel having, perhaps, dealt with

some of the theoretical and experimental impediments to a complete analysis

of the SANS spectrum.

2. Microcrack Damage in Polycrystalline Ceramics

Microcrack damage in polycrystalline ceramics can degrade the

performance of these materials in terms of both their mechanical integrity

and their chemical stability (through enhanced permeation of environmental

species) . Quantitative characterization of this damage is generally done

with surface sensitive techniques. Research in this subtask, however, has

established, for the first time, the powerful research tool that smallangle neutron scattering (SANS) provides for the characterization of

microcracks and crack-like voids in polycrystalline ceramics. SANS has

two principle advantages over surface sensitive techniques for this

characterization: (1) surface preparation almost invariably damages the

specimen surface, thereby complicating the subsequent analysis and

134
REACTOR P-ADIATIOII DIVISION AND COLLABORATIVE PROGRAMS

(2) surface stresses are not necessarily the same as those In the bulk,

so that surface microcrack sizes and distributions may not be representative.

Research has progressed in three areas:

(a) Development of a "Model" Microcracking Ceramic . In order to

study the nature of microcracks with a NDE probe, one must be able to

distinguish the response due to microcracks from that due to other

microstructural features, such as pores or second phase particles. An

ideal way to separate these effects is to have a material for which the

microcrack number density can be varied independently from other microstructural features. YCrO„ is such a material. It undergoes an apparent

phase transformation at 'v. IIQQ °C so that it can be readily microcracked

by annealing at temperatures slightly above 1100 °C; conversely, these

microcracks can be diffusively healed by annealing slightly below 1100 "C.

Since the yttrium chromite specimens are initially sintered around 1750 °C,

the microstructure (porosity, grain size, etc.) changes little during these

anneals, making YCrO„ an ideal "model" material for studying microcracking

effects in ceramics.

(b) Determination of the Nature of Neutron Scattering . Since

relatively little SANS research has been conducted on polycrystalline

ceramics, it is important to establish the extent of refractive neutron

scattering, before interpreting scattering results as diffractive in

nature. Otherwise, erroneous conclusions could result. This distinction can can be made experimentally by varying either the incident wavelength or the specimen thickness. In both cases, the scattered intensity versus

scattering vector should not change for diffractive neutron scattering.

For the microcracked YCrO specimens considered in this study, the

neutron scattering was demonstrated to be predominantly diffractive in

o o nature by varying the neutron wavelength between 6.25 A and 8.0 A and by

comparing scattering spectrum from specimens with a factor of five

difference in thickness (see figure 2).

(c) Analysis of Scattering Data . Figure 3 shows the neutron

scattering behavior of a YCrO specimen both in its microcracked state

135
REACTOR RADIATION DIVISIOH AMD COLLABORATIVE PROGRAMS

(YTIM) and in its healed state (YTlAl) . The difference spectrum is

plotted in figure 4. Since the spectrum from the healed state subtracts

out the background of microstructural scattering, this difference

spectrum represents only the scattering from microcracks. The solid line

in figure 4 is a least-squares fit to a model for scattering from a randomly oriented array of thin disks,

I(Q) = (A/Q^) exp (- H^Q^/3),

where I is the scattered intensity for a given scattering vector, A is a constant, and H is the thickness of the disk. This model is an asymptotic

o expression for small Q values. H, as determined from this fit is 170 A,

which is physically reasonable from several independent estimates of the

crack opening in such ceramic systems. Further analyses for large

scattering vectors indicate that the scattering is from sharp-edged objects,

which is consistent with scattering from micro-pores and microcracks.

Additional studies with this and other specimens with various thermal

annealing treatments further support these results.

In conclusion, it appears that microcrack damage in YCrO can be

detected using small-angle neutron scattering. Although much more work

needs to be done in characterizing the microcrack size, shape, and

distribution, the microcrack mouth-opening displacement estimated from SANS

data is in general agreement with other, independent measures of crack

opening. Finally, although not discussed here, a rapid method for assessing

total microcrack damage might be through the use of neutron transmission

measurements.

136
B. NON-RRD PROGRAMS

ACTIVATION ANALYSIS GROUP FY 82

R. Zeisler

The principle objectives of the Activation Analysis Group continue

to be the development of nuclear analytical techniques for better sensitivity,

higher selectivity, and increased accuracy. A high level of competence

has been developed for various reactor-based activation analysis techniques

which include instrumental and radiochemical neutron activation analysis

(INAA and RNAA) , prompt gamma activation analysis (PGAA) , and the

nuclear track technique (NTT). Non-reactor-based techniques include

photon activation analysis (PAA) , fast neutron activation analysis, and

charged particle activation analysis, which have been used on a more

limited scale. With this wide variety of techniques, support is provided

for the diversified NBS and other agency programs requiring analytical

measurement services. For example, simultaneous multielement determinations

over a broad dynamic range in complex matrices as well as highly selective

determinations of constituents in the sub-nanogram range have been

provided for programs such as Standard Reference Materials, Environmental

Measurements, Recycled Oil, Resource Recovery, Nuclear Safeguards, and

other disciplinary research programs at NBS.

During the past year, major research efforts have been directed

toward the demonstration of multielement capabilities of INAA procedures.

With an appropriate combination of PGAA and several INAA determinations,

at suitable irradiation and decay intervals, it has been possible to

determine more than thirty trace elements in such diverse matrices as liver homogenate, coal, fuel oil, and air particulates. Recent research

on instrumental means for background reduction complemented these activities.

The evaluation of the newly acquired compton suppressor system for

application to multielement determinations resulted in increased sensitivity

for several crucial elements. The continuing evaluation of compton

suppression techniques using specific detector combinations will provide

unique activation analysis sensitivities for such elements as Al, V, Cr,

Ni, Zn, and Pt.

137
N0>1- P-RD PROGRAIIS

Considerable effort has been spent in support of the Pilot National

Environmental Specimen Bank (NESB) program. The cryogenic homogenization

technique has been improved to accommodate samples up to 1000 g. Sieving experiments at cryogenic temperatures have supported the previous

data which had indicated that homogenates processed in the newly developed

Teflon disk mills will pass a 40 mesh sieve. The on-going evaluation of

the trace element baseline data collected during the first year showed

some Interesting trends due to the variations in the sample population.

For future analyses, a selection of samples which better match epidemiological

population data will be considered. Activation analysis data are currently being evaluated to determine the effects of the first year of

storage. The second year collection baseline analyses have been initiated

using improved instrumental multielement techniques.

The development and installation of the neutron beam depth profiling

facility and the first determinations of depth profiles in collaboration

with other researchers in the competence program is another important

step towards the continuous expansion of research activities. There is

a significant potential in exploring this and other "unconventional"

activation analysis techniques for future applications especially in the

important areas of materials research. To match future needs in high

purity materials, gases in metals and distribution of elements, more

research must be conducted in the areas of "unconventional" use of

reactor neutrons as well as in the use of non-reactor activation sources. Research efforts during the coming year will focus on the extension

of the multielement procedures. For example, the measurements needed to

characterize the irradiation facilities after the planned increase of

the NBS reactor power to 20 MW will be used to initiate and evaluate

"absolute" or monitor activation analysis. This technique will provide

results on more elements, since the occurrence of unexpected elements

will not preclude their quantitation. For the NESB specimens, an optimized

analytical protocol will be developed which can overcome the restrictions

of this specific matrix. In the area of non-conventional activation

138
HOn--RRD PROGPJ^'S

analysis, the use of a fast transfer system for analysis via very shortlived isotopes will be evaluated. It is also anticipated that procedures

for the determination of gases in metals will be investigated. However,

in this area, access to a source of fast neutrons and/or charged particles

is necessary.

139
NON- RRD PROGPAflS

1. Improved Radiochemical Procedures for High Sensitivity Measurements

of Ultratrace Concentrations of Tin and Mercury

R. R. Greenberg

Although instrumental neutron activation analysis can be used to

determine a large number of elements in most matrices, some critical

elements are frequently obscured by high background levels of radiation

or by interfering elements. With appropriate radiochemical separations,

a large number of additional elements can be determined at the ppb and even sub-ppb levels. Tin and mercury are two elements which are of both

environmental and biomedical importance. Although radiochemical separation

procedures have been previously developed for these elements, recent

applications have required better sensitivity and therefore improved

separation from interfering elements.

Tin has previously been separated from Orchard Leaves (SRM 1571)

with an iodide extraction into toluene. However, approximately one percent of the selenium was found to accompany tin through this procedure which elevated the background level of radiation. Although this

did not seriously affect the determination of tin in Orchard Leaves or Citrus Leaves (SRM 172) , it did produce serious problems in other materials

such as Bovine Liver (SPJ^ 1577) and human livers from the National

Environmental Specimen Bank NESB) program. Several modifications in the

procedure, including a selenium volatilization step after sample dissolution

(using H„0_ and HF) , a pre-extraction wash with chloroform, and a backextraction of tin into an aqueous Na^EDTA solution, reduced the fraction

of selenium accompanying tin to <^0.05 percent. With these modifications,

the tin content of Bovine Liver (SRM 1577) was found to be 20+3 ng/g

(Is for six samples) . The tin concentrations in eleven human livers

were also determined. Four subsamples of human liver homogenate were

analyzed and the precision was better than one percent (Is)

.

Mercury has previously been separated from a number of matrices by

solvent extraction using nickel diethyldithiocarbamate ±Ni(DDC)_l in

chloroform. Large fractions (10-50 percent) of copper and bromine

140
N0N-RPJ3 PROGPJ^JIS

accompany mercury and can Interfere with the Hg-197 Isotope by elevating

the background level of radiation. A small fraction of the selenium

(<0.01 percent) also accompanies mercury and directly interferes with

the 279 keV y-ray of Hg-203. Two additional steps were found to greatly

improve the separation of mercury from these other elements. The use

of a chloroform wash prior to extraction with Ni(DDC)-, and a post extraction wash with aqueous Na„EDTA reduced the accompanying copper and

bromine by a factor of 3-10, and the selenium by a factor of 10-100.

With these modifications no selenium could be detected in any of the

samples via other, more intense y-rays . These improvements allowed

mercury to be determined in Bovine Livers (SRM's 1577a and 1577b) at the

3-5 ng/g level with uncertainties of only 2-3 percent (la) due to

counting statistics. SRM 1577 (Bovine Liver) was analyzed as a control

and the present value of 16.0 + 0.3 ng/g (la counting statistics) clearly

demonstrates the improvement in the method when compared to the previously

determined value of 16.8+0.9 ng/g (la); the uncertainty due to counting

statistics has been reduced by a factor of three.

In summary, the modifications described greatly improved the

separation of tin and mercury from the, interfering radionuclides. As

a result, the detection limits for both elements were greatly reduced,

and the analytical uncertainties due to counting statistics were

significantly reduced.

141
N.ON- RRD PROGRAi:S

2. 1-129 Analysis

G. J. Lutz

A procedure has been developed for the analysis of environmental

sample for 1-129 at levels below 10 atoms/g (0.2x10 g/g)

The analysis consists of a pre- irradiation separation, an irradiation in the reactor, and a post-irradiation separation. The

pre- irradiation separation involves the combustion of the sample in a stream of oxygen. Exit gases are filtered through quartz wool to trap

particulate material and the iodine is collected on an activated charcoal

trap approximately seven millimeters in diameter and three centimeters

long. This pre- irradiation filtering is necessary to remove cesium,

133 130 uranium and tellurium which interfere via the reactions Cs(n,a) I;

235,,, ,:n129^, ,130^ . 128^ , .129^ 129^, , 130^ U(n,f) I(n,Y) I; and Te(n,Y) Te ^ I(n,Y) I. The activated charcoal trap is burned in a lower oxygen flow and the

iodine is reabsorbed on a smaller charcoal trap. It is desirable to

minimize the mass of the charcoal trap to be irradiated in order to

reduce the amount of fission product iodine formed from uranium impurities

in the charcoal. This fission product iodine is subsequently a counting

interference.

It is possible to measure the yield of the pre- irradiation separation

in one of two ways. 1-125 spike can be added prior to the separation

and measured at the end of the separation. Alternatively, if the 1-127

content of the sample is known and is sufficiently high, it can be

measured by nondestructive neutron activation analysis of the activated

charcoal. 1-127 almost certainly is a better tracer of 1-129 then the

1-125 spike is.

The charcoal trap containing the iodine is sealed in quartz

under vacuum and irradiated in the rector. The irradiation is usually

conducted in RT-4. The neutron flux in this tube is lower than in RT-3

but it is more thermal. This is important as it minimizes the reaction

I (n,2n) I. Irradiations are typically conducted for 16 hours.

At the end of the irradiation the quartz ampoule is rinsed with acid and

142
NOIJ~RPJ) PROGPA^'S

cooled in liquid nitrogen. It is then cracked open. Several milligrams

of inactive iodine carrier as well as 1-125 spike are added to the sample,

The major gamma emitting radioactivities are due to bromine, chlorine,

and impurities in the charcoal and quartz. The charcoal sample is then

burned in a steam of oxygen and exit gases are again passed through a plug of quartz wool and collected onto a trap of hydrated maganese

dioxide (HMD) . HMD is one of a series of selective ion retention media

developed during the past several years. It is usually used for

separations from aqueous solutions, but has been applied to gas phase

separations. After collection of gases the HMD is heated to a dull red

heat. This results in the passage of 80-95% of the iodine while all

4 6 but one part in 10 -10 of the bronine is retained in the HMD trap.

Efforts have been concentrated on the analysis of two Standard

Reference Materials. They are SRM 1648, Urban Air Particulate and SRM

1572 Citrus Leaves. Values in atoms of I-129/gm for SRM-1648 are

9 9 9 1.3x10 , 2.4x10 and 1.7x10 atoms/gm. These are not terribly imprecise

values as far as 1-129 analysis is concerned and agree well with value

9

of 1.5x10 obtained at Battelle Pacific Northwest Laboratories.

143
I-ION-PilD FROGRAIIS

3. Characterization of Selected Trace Elements in the Chesapeake Bay

R. R. Greenberg, H. M. Kingston, W. S. Liggett, and T. C. Rains

Trace element measurements for a large multi-disciplinary study of

the Chesapeake Bay have been completed. As part of this study, water

samples were collected at 51 sites, and both the particulate and dissolved

fractions were analyzed for Cd, Ce (particulate only), Co, Cr, Cu, Fe,

Mn, Mo, Ni, Pb , Sc, Sn, Th, U, and Zn. Two types of samples, surface and

bottom were collected and analyzed using specific chemical preconcentration and separation techniques developed for neutron activation analysis

(NAA) and graphite furnace atomic absorption spectrometry (GFAAS) . The

data are the first environmental analyses of this kind to yield a data

set at the 95 percent confidence limit that allows rigorous statistical

evaluation of elemental relationships.

The concentrations of 14 elements in the dissolved fractions were

evaluated by direct comparison with naturally occuring seawater levels.

At several locations in the Bay, two toxic elements (lead and tin) were

elevated by two orders of magnitude over normal seawater levels. Similar

levels of organo-tin were found by other researchers. Most of the

dissolved iron concentrations were approximately the same as that found

in seawater. However, a number of bottom samples collected at some of

the deepest locations had significantly greater iron concentrations.

The elevated levels appear to be due to anoxic conditions in the bottom

sediments. Similarly, the manganese concentrations had maxima at these

same locations. Uranium and molybdenum were found in higher concentrations

in seawater than fresh water. As a result, the concentrations of these

two elements can be used to trace the seawater content of the water

column throughout the Bay. The dissolved thorium concentrations in

samples taken near the mouth of the Bay were approximately two orders of

magnitude lower than previously reported seawater values. The dissolved

concentrations of the remaining elements (Cd, Cr, Co, Cu, Ni, Se, and Zn)

appeared to be relatively similar to the levels normally found in seawater.

The information obtained from the raw particulate elemental con144
MOM- RRD PR0GRA>4S

centration data has been difficult to interpret in the past. Since the

concentrations were reported in elemental mass (ng) per unit volume (mL)

of wa'ter, the total amount of particulate mass suspended at the time of

sample collection strongly affected the results. Variations in current,

tide, temperature, biota, wind conditions, etc. can greatly influence the

total amount of particulate material suspended in the water column. To

circumvent the problem of variable mass loading, a double normalization . procedure was used to compute crustal enrichment factors. The con- centration of each element in the sample was divided by the concentration

of a reference element, in this case scandium, and the resulting value

was divided by the ratio of these elements in average crustal material.

Scandium was chosen as a reference element because it has essentially

no anthropogenic uses and its chemistry is relatively simple (single

oxidation state, limited dissolved particulate interactions). The use- fulness of this technique can be Illustrated by comparing the variability

in the cerium concentrations and the cerium enrichment factors (EF) . The

concentrations varied by a factor of 300 from site to site, while the

EFs varied by a factor of 1.5 and the observed standard deviation over

the entire Bay was just 10 percent. The EF's for thorium were similar

to those of cerium. The environmentally active and anthropogenically

abundant elements had significantly more complex ranges and patterns

of enrichment factors than the elements used as multiple controls.

Almost all of the iron EF's were similar to those of Ce and Th.

However, a few samples had slightly elevated EF's. These samples were

collected at some of the deepest locations within the Bay and appear

to be linked to anoxic reactions in the sediment at these locations.

The enrichment factors for cobalt, manganese, and nickel appeared to

trace the flow of Potomac River water for quite some distance down the

Bay. This was observed through the elevated EF's for the surface

samples as compared to generally uniform EF's for the bottom samples.

It was also found that a number of samples had greatly elevated

cadmium enrichment factors. This appeared to be a result of crustal

145
NOII- RRD PROGFAtlS

weathering of naturally occurring cadmium deposits and not anthropogenic

sources. These deposits and their erosion have also been documented by

other researchers. The enrichment factors for lead exhibited a great

deal of variability; most of the samples had lead EF's approximately

five (i.e., five times greater than Pb/Sc ratio for average crustal

material). For the elements chromium, copper, and uranium, the enrichment factors appeared similar to naturally occuring material. Molybdenum

was below the detectable limits in most samples and tin could not be

detected in any of the particulate samples. Zinc suffered from severe blank problems arising from the filter material used; however, samples

near the top of the Bay had very high mass loadings and zinc appeared

to be slightly enriched.

Although most elements were found at levels that could be explained

by natural mechanisms, both dissolved and particulate lead and dissolved

tin appeared elevated over normal at some locations. Using enrichment

factors, the cobalt, manganese, and nickel clearly traced the flow of

the Potomac River; however, it is not clear if the elevated EF's are due

to natural or anthropogenic causes. The nature of the samples challenged

several existing areas of analytical work. The analysis of ppb and ppt

elemental concentrations in a salt matrix led to a new separation preconcentration method for neutron activation analysis. This procedure

provides solid resin pellets containing 16 trace elements with no alkali,

alkaline earth or halogen element interferences. These pellets are placed directly into the reactor for irradiation. In addition, the

statistical evolution of extensive blank data helped to characterize

blank behavior at these ultra-trace levels and showed the inadequacies

of using a normal distribution. Lastly, the 2-3 orders of magnitude

fluctuation of the particulate concentration data led to the application

of enrichment factors which have been used in air particulate analyses

but had not been applied to a aqueous systems. The choice of a reference

element and secondary check elements also proved ideal. This technique

provided a means by which the data and its environmental significance

146
NON- RRD PROGM>:S

could be evaluated based on statistical comcepts. Additional work is

currently in progress with the Statistical Engineering Division to

investigate additional correlations within these data sets.

4. Determination of Ion- implanted Arsenic in Silicon

R. M. Lindstrora

In support of a program of the Electron Devices Division, measurements were made of the quantity of arsenic in semiconductor silicon. A

series of four samples had been ion- implanted at nominal doses from

12 15 2 7x10 to 7x10 atoms/cm . Instrumental neutron activation analysis

2 was used to assay the amount of arsenic in samples of 1 cm . All samples

were irradiated together for 6 hours in RT3. The results in the table

below demonstrate that the dynamic range, sensitivity, and precision of the

technique are adequate.

TABLE 1

Arsenic Found

Sample ID ng Atoms

3 862 + 6 (6.92 + .05)xl0-'-^

13 87.5 + 0.3 (7.03 + .02)xl0-'-^

23 9.37 + 0.14 (7.53 + .iDxlO"*-^

32 0.600 +.012 (4.83 + .09)xlO"'"^

97 (blank) <0.006 <5xl0-'"°

5. Multielement Analysis of Coal Standard Reference Materials

R. M. Lindstrom, R. R. Greenberg, and R. F. Fleming

A series of four coal Standard Reference Materials (SRMs 2682,

2683, 2684, and 2685) are in preparation for use as standards in

environmental and energy-related analyses. In addition to certification

147
NOIT- RED ?R0GRA:1S

of sulfur, ash content, and heating value, information v7ill be provided

to users on the chemical composition. Nearly thirty major, minor,

and trace elements are being determined by a combination of instrumental

neutron activation analysis and neutron-capture prompt-gamma activation

analysis. A partial list of results is given in the table below.

TABLE 1

Elemental Concentrations in Coal SRMs

Units are ug/g unless % Indicated. Uncertainties

quoted are Is. Basis: dry weight

SRM 2682 SRM 2683 SRM 2684 SRM 2685

Al(%) 0.462 + 0.002 0.858 + 0.005 1.103 + 0.006 1.669 + 0.007

As 1.00 + 0.02 3.64 + 0.13 3.87 + 0.14 12.28 + 0.38

B 39.0 + 1.3 67 + 2 114 + 3 109 + 5

Ba 382 + 5 71 + 3 41.4 + 2.6 105 + 6

Br 3.74 + 0.18 16.85 + 0.04 10.6 + 0.5 5.57 + 0.07

c (%) 76.0 + 3.8 79 + 4 68 + 2 66 + 3 Ce 9.87 + 0.08 9.18 + 0.08 11.5 + 0.2 17.88 + 0.18

Co 1.66 + 0.03 2.22 + 0.09* 3.85 + 0.05 4.57 + 0.06

Cr 15.4 + 0.3 11.02 + 0.18 16.8 + 0.3 22.3 + 0.4

Cs - 0.44 4- 0.02 1.15 + 0.05 1.31 + 0.07

Eu 0.172 + 0.005 0.177 + 0.006 0.226 + 0.009 0.357 + 0.004

Fe (%) 0.242 + 0.003 0.762 + 0.019 1.454 + .026 2.396 + 0.065

H (%) 4.70 + 0.13 5.0 + 0.1 4.8 + 0.1 4.6 + 0.2

Hf 0.60 + 0.02 0.418 + 0.004 0.565 + 0.012 0.913 + 0.011

K 117 + 14 750 + 10 1969 + 16 2592 + 45

La 5.17 + 0.03 5.05 + 0.04 6.65 + 0.10 10.19 + 0.11

N (%) 0.8 + 0.3 1.6 + 0.9 1.6 + 0.4 1.1 + 0.3

Rb - - 14.6 + 1.1 16.8 + 1.3

s (%) 0.447 + 0.013 1.82 + 0.05 2.94 + 0.07 4.64 + 0.19

Sb 0.189 + 0,009 0.279 + 0.008 0.354 + .008 0.357 + 0.012

Sc 1.524 + 0.005 1.941 + 0.008 2.665 + .020 3.700 + 0.019

Se 0.91 + 0.10 1.23 + 0.09 1.87 + 0.16 1.91 + 0.16

Sm 0.776 + 0,004 0.859 + 0.005 1.109 + 0.012 1.729 4- 0.007

Th 1.532 + 0.014 1.363 + 0.011 1.955 + 0.016 2.66 + 0.03

U 0.519 _K 0.015 0.418 + 0.011 0.901 + 0.010 0.948 + 0.013

W 1.81 + 0.03 0.48 + 0.03 0.562 + .022 1.18 + 0.06

Zn 8.6 + 0.9 9.5 + 0.6 110 + 12 17.1 + 1.1

148
NON- RRE PROGRAMS

6. Effect of Natural Isotopic Abundance Variability on the Accuracy of

Neutron Activation Analysis

R. F. Fleming and R. M. Lindstrom

Accurate activation analysis requires that the isotopic composition

of the sample and standard be the same, or else explicitly known. For

monoisotopic elements this requirement is automatically met, and for cases where the activating isotope is of major abundance the fractional

change is usually negligible. We are not concerned here with man-made

alteration of abundance (e.g. U, Li, B) nor with the uncertainty in the

measured value for the abundance. Rather, it is only actual variation

in the naturally occuring abundance from sample to sample that is considered. This can be important especially for the lighter elements, which

may readily fractionate, and for cases in which chemical reactions or physical processes commonly do not go to completion (i.e. in which the

element exists in geochemical or biochemical reservoirs in more than

one state ) , and where the activating isotope is a minor constituent of the

element. The example that we have investigated in some detail is sulfur,

where a 5-minute S-37 activity is produced from the 0.017% abundant S-36.

1 2 Recently Holden ' has published an evaluation of the known

variation in nature of isotopic compostion of the elements. Isotopic

3 fractionation of light elements is well documented . Based on this

observed natural variability, we list in Table 1 those elements for which

measurement by nuclear techniques could result in a systematic bias, and

the range of this bias.

Sulfur analysis appears to be an ideal case to investigate experimentally since NAA depending on S-36 should show obvious variation while

prompt gamma activation analysis (PGAA) which depends on the capture

gammas of S-32 should give consistent results. The wide variation in the

isotopic ratios of naturally occurring sulfur was first demonstrated by

ric

5,6

4 the McMaster group using mass spectrometric techniques, and has since

been documented for thousands of samples.

Although careful mass spectrometry can determine the S/ S ratio

149
NOH--RF-D PROGRAJIS

directly, the isotopic fractionation of S-34 is typically measured and

expressed as

^3^c- (^^^S/^^s) sample ^

I ^ S/ S) standard

XlOOO,o/oo. (1)

Meteoritic troilite (FeS) is the usual standard (6^^eO), since it is

believed to reflect the mean solar system abundance and has not been

fractionated. Seawater sulfur is uniformly enriched in S-34 by 20 parts

per thousand (6^^ = +20 o/oo) . Volcanic sulfur has a range of 6^^ from

-10 to +10 o/oo, while that in coal and petroleum ranges from -30 to

+30 o/oo. The range of published values for 5^^ is from -53.1 o/oo for

a Texas marcasite (FeS-) to +86.7 o/oo for a barite (BaSO.) from the

1

Japan Sea . Using the theoretical relation for the fractionation of

7 sulfur isotopes , we can estiamte the spread in the abundance of naturally

occurring S-36,

36c\ - /-I an -u n m^ ^r^(^ -x. ^34< ln(l + 6^^S) = (1.90 + 0.01) ln(l + 6^^S),

ln(l + 633s) = (1.94 + O.Oiy-^lnd + ^^""S) . This model predicts a maximum difference of 29% in the S-37 specific activity

of sulfur samples irradiated under the same conditions. The 6^^ spread for

coal and petroleum is less, but large enough to limit the accuracy of

sulfur determination to +15% regardless of the precision of the measurement . In this work we demonstrate this systematic error from isotopic

variability by determining the S-37 counting rate per unit mass of sulfur

produced after irradiation of five 6 standards from McMaster University

(the SL-277 series) as well as a galena, a barite and an elemental sulfur

(a) standard. Several other sulfur s of unknown isotopic composition including

the NBS SRM-371g were also run. The McMaster samples were transposed

from Ag„S to H„S with HCl, and the H„S to S with I„, followed by purification

of the product. The volcanic samples and some of the laboratory sulfurs

were purified by recrystallization. The samples, weighing from 12 to 90 mg,

were irradiated in the NBS reactor, and after a fixed decay time the 3103

keV gamma ray was counted with a germanium detector. Zinc flux monitors

150
NON- RRD PR0GRA21S

were run with each irradiation to measure the constancy of the neutron

flux, and small corrections were made for dead-time and pulse pileup.

"the resulting decay-corrected counting rates per unit mass of

sulfur are given in table 2. There is a 6% difference among sulfurs

from commercial suppliers, perhaps a 3% difference among the volcanic

sulfurs, and an apparent 6 3^s ^ for the SRM sulfur. The results for

the standards are plotted against 6^'^S in figure 1, with each data

point representing the average of at least two measurements and the error bars representing counting statistics (la) only. The solid line is the

predicted curve based on Eqs (2) , normalized to the measured activity

for sample SL-277-1. The equivalent date for PGAA measurement of the same standards is plotted in figure 2, which exhibits no dependence of

specific count rate on fractionation to within the counting uncertainty.

One could interpret the combined NAA/PGAA measurement on a sample as being a determination of 6^^S and hence the degree of fractionation.

In general, it is more accurate to determine sulfur fractionation

by a mass spectrometric measurement of 6^^S however.

In summary, it has been demonstrated that the known isotopic variability

of S-36 results in a corresponding inaccuracy in the measurement of

sulfur by neutron activation and that this effect is well predicted by the

theory. The worst-case limit on the measurement accuracy is +29%; however

this uncertainty can be halved if one uses a standard of known isotopic

composition. The Bureau is preparing to issue a sulfur SRM which is

certified for isotopic composition. No significant bias exists for

PGAA determination of sulfur.

We thank C. E. Rees for providing the five McMaster University

interlaboratory standards, I. L. Barnes of NBS for the French and

NBS standards, and D. L. Anderson for the University of Maryland for

the volcanic sulfurs.

151
NON- RRD PROGPAMS

TABLE 1 Natural Isotopic Variability

Element Isotope : Range Isotope : Range

Lithium

Boron

Silicon

Sulfur

Copper

Selenium

Mercury

Lead

Li-6 + 37%

B-10 + 6.2%

Sl-30 + 4.2%

S-32 + 0.65%

Cu-63 + 0.38%

Se-74 + 1.3%

Hg-202<+ 0.6%

Pb-204 + 59%

S-36

Cu-65 + 29% + 0.84%

Hg-196 ^ Hg-198/Hg-202=+1.5%

Pb-202 + 32%

Sulfur Sample

TABLE 2

Sulfur Irradiation Results

63^S

o/oo

S-37 Count rate,

-1 -1

sec mg

4.82 + 0.03

4.78 + 0.03

4.89 + 0.03

4.66 + 0.04

4.49 + 0.04

5.01 + 0.02

4.83 + 0.04

5.02 + 0.03

4.77 + 0.03

4.72 + 0.03

4.87 + 0.03

4.95 + 0.03

4.76 + 0.03

5.05 + 0.04

4.89 + 0.04

4.83 + 0.02

Bias*

%

SL-277-1

SL-277-2

SL-277-4

SL-277-9

SL-277-10

Soufre de Lacq

NBS 200 Galena

OGS-1 Barite

Volcanic (Hawaii)

Volcanic (Hawaii)

Volcanic (St. Helens)

Lab Grade - A

Lab Grade - B

HiPurity - Lot 1

HiPurity - Lot 2 NBS SRM-371g

+ 2.52

- 6.46

+16.07

-19.21

-28.5

+17.3 + 0.6

+20.58

+0.4

-0.4

+2.0

-2.9

-6.5

+4.4

+0.6

+4.6

-0.6

-1.7

+1.5

+3.1

-0.8

+5.3

+2.0

+0.6

*The Bias is the inaccuracy which would result if the sample

were measured using a standard with 6^^S = 0.

152
HON- RRD PROGRAr''S

5.0

to£^ 4.8

CO\

V)c3

Oo

4.6

4.4-

30

Weighted Least Squares F

20

Equation 2

10 10

34 S S, o/oo

Figure 1. Specific activity of S-37 versus 6 S-34,

20

10

g^'^S, o/oo

Figure 2. Neutron capture prompt - y rate versus 6 S-34.

153
HON- P-PD PROGPAI^.S

1. N. E. Holden, "Isotopic Composition of the Elements and Their

Variation In Nature: A Preliminary Report," BNL-NCS-50605 , Brookhaven

National Laboratory (1977)

2. N. E. Holden, "Atomic Weights of the Elements - 1979," Pure and

Applied Chemistry, 52_, 2349 (1980).

3. I. Friedman and J. R. O'Nell, "Composition of Stable Isotope

Fractronation Factors of Geochemical Interest," USGS Paper, 440-KK

(1977).

4. J. Macnamara and H. G. Thode, Phys. Rev. 78_, 307 (1950).

5. H. Nielsen, Lectures in Isotope Geology , p. 283-312, E. Jager and

J. C. Hunziker, Eds., Spring-Verlag, Berlin (1979).

6. H. R. Krouse, Handbook of Environmental Isotope Geochemistry , p. 435,

P. Fritz and J. C. Pontes, Eds., Elsevier Publishing Co. (1980).

7. J. R. Hulston and H. G. Thode, J. Geophys. Rev., 70^, 3475 (1965).

7. A Compton Suppression System for Background Reduction and Improved

Sensitivity

J. R. Vogt and R. Zeisler

During the past year, a Compton suppression system has been setup and evaluated for the improvement of analytical sensitivity through

background reduction. The system, shown in figure 1, consists of a 25.4 cm (10- inch) long by 23.8 cm (9-3/8 inch) dla. Nal (Tl) annulus

and an Integral line 7.62 cm (3-inch) by 7.62 cm (3-inch dla. Nal (Tl)

well detector used to surround all but the rear of a 19% relative

efficient, 1.79 keV (Ge(Ll) primary detector. The Nal(Tl) detectors are surrounded by a lead shield that is 10.16 cm (4-lnch) thick and has

internal dimensions of 40.64 cm (16-inch) by 40.64 cm (16-inch) by 55.88 cm

(22-inch) deep. The lead shield is lined with 0.635 cm (1/4-inch) copper

sheet. The coincidence circuitry is contained in a 2-wide NIM module

(Harshaw NC-26R Anti-Compton Analyzer) which is relatively inexpensive

compared to separate NIM modules easy to set-up, and quite stable. The

154
NC-26R uses amplitude and rise time compensated cross-over (ARC) timing

for both the Ge(Ll) and Nal(Tl) signals. Coincidence pulses from the

NC-26R are fed Into the antl-colncldence gate of a Nuclear Data 570 ADC.

Adjustments for gating pulse width and delay are contained In the NC-26R.

A Berkeley DB-2 random pulse generator Is used to correct the gammaray photopeak areas for losses due to the coincidence system and pulse

pile-up. As can be seen In figure 1, In this system the sample Is located

Inside the Nal(Tl) shield, rather than outside as In same other designs"^.

2 The Interior sample placement Is similar to that described by Wagman . Since there Is no detection of scattered photons In the forward direction

(to the rear of the Ge(Ll) detector), the suppression at lower spectral

energies Is not as good as In systems where the Ge(Ll) detector Is sur- rounded more completely.

Figure 2 Indicates the Compton suppression obtained with this

system for a Cs-137 source. The figure clearly shows the additional

suppression of the Compton edge by the central well detector. The

Photomultiplier Tube

Sample

Intrinsic Germanium

Sodium Iodide

Liquid Nitrogen Dewar

i

Figure 1. Cross-sectional View of the NBS Compton Suppression System.

155
nON-RRD PROGRAIIS

10'

10-

5 10

c

c

(0 O

« 103

10

10'

'M;^^

A No Suppression.

B - Suppressed with Nal

detector removed.

C - Suppressed with IMal detector in place.

400 800

Energy (KeV)

1200

Figure 2. Compton Suppression of CS-137.

suppression is relatively independent of the position of the sample

within the well detector. The system increases the peak-to-Compton

ratio from 65:1 to 428:1. The suppression factor on the Compton edge is

about 7-8, for the middle of the spectrum about 4-5, and at the backscatter

peak about 3.5, since the improvement insensitivity follows roughly the

square root of the background, the increases in sensitivity for these

portions of the spectrum are approximately 2.7, 2.1, and 1.9, respectively.

With the sample inside the Nal(Tl) shield, both coincident photopeaks

and Compton events for radionuclides with cascading transitions are suppressed. This effect reduces the spectral background more than simple

Compton suppression. Thus the sensitivities of non-coincident gammarays are improved, while the sensitivities of coincident gamma-rays are decreased. This can be of benefit in matrices where coincident gammarays account for a substantial part of the activity, such as Sc-46 in

environmental and geological materials and Na-24 in biological materials.

156
NOII- RRD PROGRAMS

For example, in SRM 1633 a Fly Ash, the determination of zinc using Zn-65

gives' a result of 238.0 + 3.3 without Compton suppression. The certified

value is 220 + 10. Additional applications for this system are being

evaluated.

1. H. J. M. Carts, C. J. Van der Poel, D. E. C. Scherpenzeel, H. F. R,

Archiszewski, and G. A. P. Engelbertink, Nuo. Instv. Method. (1980)

.

2. N. A. Wogman, "Intern. Symp. on Methods of Low-level Counting and

Spectrometry, Berlin, 6-10 April 1981, Paper No. IAEA-SM-252125.

8. Facilities for Activation Analysis

R. M. Lindstrom

As a first step in assembling a more powerful and versatile data

acquisition and processing system for activation analysis, a PDF 11/44

computer system has been installed. As communication is established

with the existing ND6620 and with existing and future multichannel

pulse height analyzers, the new computer will begin to perform much of

the data processing. The 11/44' s faster CPU, larger disks, and more

versatile software is expected to improve both the quantity and quality

of analysis.

In order to allow the systematic selection of the optimum Ge

y-ray detector for a particular experiment, the efficiency of each

detector available was measured by counting a point source

of Cs-137 in contact with the end cap. This useful measure of the

maximum sensitivity of a detector does not always follow the industry - standard efficiency because of differences in detector dimensions and

detector-to-window distances. In the table below, twelve detectors are arranged in increasing order of 0-cm efficiency; the 60-cc detector is

much better by this criterion than expected from the standard efficiency,

157
NON- RRD PR0GRA21S

TABLE 1

Eff iciencies o;E Detectors

Detector 0-cm Standard Resolution

Name Eff iciency

(%)

Efficiency

(%)

(keV fwhm)

25 cc 1.61 * * Ge(Li) well 1.91 * 2.14

ATF 2.17 10.3 1.99

YX2 2.49 7.6 1.69

yxi 2.50 7.5 1.73

90 cc 2.8 15.6 1.95

66 cc 3.33 14.6 1.88

82 cc 3.33 16.6 1.95

60 cc 3.73 12.2 1.93

104 cc 4.01 21.5 1.76

AMD 4.42 18.1 1.80

131 cc 4.88 30.4 1.78

* Not known.

O-cm Efficiency is the measured number of net photopeak

counts per photon emitted by a point source of Cs-137

on the end cap of the detector. The standard efficiency

at 1333 keV measured by the manufacturer at 25 cm,

relative to that for a 3"x3" Nal detector. The resolution

is that measured by the manufacturer at 1333 keV.

158
ITON-P-RD PROGRAM'S

NEUTRON-CAPTURE PROMPT GAMMA-RAY ACTIVATION ANALYSIS

D. L. Anderson, G. E. Gordon, W. B. Walters, and W. H. Zoller

(University of Maryland, College Park, MD)

and

R. M. Lindstrom

(Center for Analytical Chemistry)

We have continued to extend and improve the analyses of various

types of samples by neutron-capture prompt y-ray activation analysis

(PGAA) which uses a vertical beam tube on top of the NBS reactor.

In PGAA, one places the sample in the external neutron beam (of flux

Q 9 ^^^2x10 n/cm -sec) and observes prompt y rays emitted by the various

capturing species with a Ge(Li) detector during the irradiation.

Unlike the more widely used instrumental neutron activation analysis

(INAA) , which employs y rays emitted by radioactive products following

irradiations, PGAA can be used to observe elements with reasonable

capture cross sections and prompt y rays of appreciable intensity

whether or not capture leads to a radioactive product. Also, in PGAA,

the results are available immediately after irradiations, whereas

about three weeks are required in INAA to observe all long-lived

products. In previous work with NBS SRMs and U.S. Geological Survey

standard rocks, we have demonstrated that PGAA can measure the con- centrations of the following major and minor elements in most crystal

type samples: H, Na, Mg, Al, Si, K, Ca, Ti, V, Mn, and Fe; and the

important trace elements B, Co, Cd , N, Sm, and Gd. In biological or other carbonaceous samples (e.g., NBS coals), we observe some of the

above plus C, N, S, and CI. Occasionally other elements are observed

in samples of unusual composition such as ores, minerals, manganese

nodules, etc. The accuracy of PGAA is so high for many elements, that

the method is beginning to be used for routine analyses for certifi4 cation of some SRMs. The following sections briefly highlight

some of our major results from the past year.

159
NON- PP-D PROGRAIIS

1. Assay of Enriched Uranium Fuels

The PGAA technique may ultimately be of considerable value in the

assay of various isotopes of heavy elements in safeguards applications.

The Livermore group^ has developed excellent methods that use

spectrometry of heavy element x-rays and low energy y rays that are quite reliable if the heavy elements have been separated from fission

products. However, the low energy backgrounds are so enormous in a spent fuel rod, even after two years 'cooling, that direct assays of the

rods would be impossible with their system. The PGAA technique would

have the advantage that it could possibly use y rays of about 5 MeV

from neutron capture in the heavy elements or from very short-lived

fission products (few seconds or less) counted between bursts of

neutrons in a beam equipped with a chopper. By contrast, most y rays

from long-lived fission products in spent fuel rods have energies of

about 1 MeV or less. Thus, one could discriminate strongly against

the latter with respect to the ^5-MeV y rays by use of thick y-rays

absorbers

.

As a first step in testing PGAA as applied to heavy elements, we have irradiated several enriched U-235 SRMs and nuclear fuel pellets

supplied by Babcock and Wilcox, Lynchburg, VA. (This project is being

performed in collaboration with Dr. Michael Failey of Babcock and

Wilcox, a former student of this group, who was heavily involved in

development of the PGAA system.) The U-235 isotopic abundance in the

SRMs ranged from 0.48 to 93.0%, and for the commercial sintered fuel

pellets, it was 3.982%. The counting sequence for these samples was:

1. 5-min count in-beam

2

.

1-hr count in-beam

3. 5-min count on an off-line detector

4. 1-hr count on an off-line detector (to observe fissionproduct y radioactivity)

The resulting spectra are extremely complicated, with at least

300 y-ray peaks below 1.5 MeV. Although we have observed clear differences among the spectra taken with samples of various enrichments,

160
NO!]--RRD PROGPAT'S

the data reduction has only just begun. We are hopeful that some form

of this method may be very effective for rapid, nondestructive assay of

fuel-pellet enrichments.

2. Burnable Poisons in Nuclear Fuels

Burnable poisons are used in the cores of commercial reactofs to

help control power distribution at the beginning of each reactor fuel

cycle. One method involves the use of solid, cylindrical pellets of

sintered Al^O -B,C mixtures. These pellets are interspersed among the

fuel pellets in the assembly. A second method used is the direct addition

of Gd to the fuel pellets themselves.

Table 1. Comparison of Boron Analyses in Fuel-Poison Pellets by PGAA

and Wet Chemical Techniques

Nominal

wt. % B

Observed Wt. % B

Wet Chemical Analyses' PGAA

Al A2 Bl B2 This work

0.183 0.194 0.197

0.244

0.1947 0.1796

0.925 0.898 0.946

1.23 1.137 1.236

0.2022C 0.186 -

1.602^ 0.905 _

0.8971

1.238

0.2017

1,045

0.1815

0.1813

0.1802

0.8798

1.233

0.2052

1.565

^A and B are different analytical laboratories; 1 and 2 denote analyses

separated by a period of months.

^Measurements of l^B by PGAA converted to total B using the ratio ^I^B/total B

= 0.1975.

^Non-sintered powder mixes of AI2O3 and B4C.

161
ITON- PJID ?R0GPA>1S

In cooperation with Dr. Michael Failey of Babcock and Wilcox

Lynchburg Research Center we have begun to explore the tse of PGAA for

assay of these burnable poisons using samples provided by Babcock and

Wilcox. The initial results, listed in Table 1, indicate that the

method would be excellent for the B,C-A1„0^ pellets. The total analysis time for each sample by PGAA was less than 15 min. We obtain excellent reproducibility for the sample analyzed three times and our results

appear to be in better agreement with the make-up of the pellets than

the wet chemical analyses. By contrast, the wet chemical analyses

are much more time consuming and labor intensive, and seem to be less

accurate. Thus, the PGAA method is quite promising. A paper covering

these results were presented at the Washington American Nuclear

Society meeting in November 1982.

Our initial results for Gd-poisoned samples are less encouraging

because of the very low levels of GD (<1 ppm) and complexity of the

spectra (because of the many fission products formed, see Sect. A

above). However, it may be possible to find usable Gd lines in the

spectra after more careful study.

We plan to continue these studies during the coming year.

3. Analyses of Reference Materials

We are analyzing several new geological and biological reference

materials that were recently released by NBS and the International

Atomic Energy Agency (IAEA). The NBS Basalt (SRM 688) and Obsidian

(SRM 278) are being certified for most major elements and a number of

trace elements.

Table 2 lists the results of our PGAA measurements on the NBS

standards, the PGAA results from the University of Missouri, and the NBS

values. As is standard geochemical practice, we have calculated the

total concentrations based on the assumption of common oxides of the

elements, e.g., Na„0, CaO, Al , etc. Our results and those from NBS are excellent for the basalt, but Missouri's exceeds 100% for both

standards. The NBS also hits very close to 100% on the obsidian, but

our value is somewhat low. Note that we are missing about 0.3% MgO

162
NON- RRD ?R0C-RA1!S S

esi

0) iHXi

cd H

TJ

0) 4JOcn

CO

0) iHc3Co

•H

iJ

QDa

•o k4 IJ 4J a c

T3 (U C y a c

4-> o

Vi o

x>o

01o Ico3^H

J3V icU

r-l H

^M •* 01 -» o vO CM o o ^^ O /^s o o O o o o u o CM o <• • • • « O • --^ ^-N

^'N o o o o o o CM o r». en

O 1 in +1 • +1 +1 1 +1 +1 +1 +1 +1 1 1 • • +1 <s OS o a\ m m en r~. O en m m !><. s-^ m ^^-^ sr H •^ o -^ o -* v^ N-^ • • • • • r^ <-H sr • o\

en r^ en

00 • oo • o

o\o

0)

O 00

o\

-3- eg CM

m o v-W o —1

^H o m • • • • o • • o « • • O o o f^ <3\ o o o r^ o o o ^H 1 +i +1 1 +1 +1 +1 +1 +1 +1 +1 +1 1 1 +1 +1 +1 CM \D 00 vO O o- o m o CM >£> <3- in • • • • <3- -a- vO -» en en vO en • m CM r-^ O ^ • <• • • • en

tM CO en o • o m

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en o m vO en 00 -* O o en o o o o o O o o>

m • • • O • • • -* O o o o r^ o o o m o o in o o o

+1 +1 +1 1 +1 +1 +1 +1 +1 +1 +1 +1 +1 +1 +1 +1 +1 o ^H —

m o ^^ «-H en o 9\ 00 o m VO en fn • in m • ^H en r-> en 00 <n f-H en -a- <y^ • m <• • • en vD • • ^H en • e • • r-» <M en r^ rn en O CD

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CM vO >o •o o m 00 O o en o O O o y-x o o • ^^ o o • o —1 O O o rv. o CM O \ +1 • +1 +1 +1 • +1 +1 +1 m m a> tM -* 00 1—( O en

a\ \^ ^H vCm \^y o ON (N

m • • i-( I>. CM • • a> CM • • •H r^

f—4

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vO o

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i-H o -* CM ^O o CM o -H • • • • • • o . o o o o O o O o vO o

+1 +1 +1 +1 +1 +1 +1 +1 +1 +1 00 m r^ en SO r^ e^ fvj o m

00 o ^H r^ CM CM « m o\ -» • t>. • "M • o —1 CM o o -H r» I I o

+1 soOS

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bo eio a. a

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u-i CO

en 00 • • CM CM

bo to bo 00 bO bo bO bo bO a a a a a

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feu z w o

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4J CO O CO

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fl} 1^0)O.oouo

s:»« B a a 3 « •

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nj> i-( 03 03 u CO <0 •o 3' V O u u

•Hn c c

t4H Cfi

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CO 09

U 0) <u P M (-1 0) 4-1 O. D- o o

Q) CO

u • H

H o > c 1-1 <U 01 c b b •t 3 : 14-1 <4-l 03 0) O O

<U J= 3 4-1 B^S ^5

<H CM «*

Cd >, 00 r~ > s iJ u c •o 03 CO o 0) J= JS

1-1 l-l 4J

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u 3 m 03 4-1 .U H « iH i-H O § 3 3

CO 03

K-l a> 0) c 9) ^ w M U : %

Cfl Crt

0) § §

k'a

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0) * M

x: e 03 03 4J o 4) 0) c iH 73 73

<0 4J • 1H

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l-l rt c X

X « g o o o

Q. ^ •H O U bO bo c <4-l « c c

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163
NON- RP-C PROGPAl'S

Table 3. Preliminary Results from PGAA Studies of New Biological Standards

Element Concentration (% unless noted)

NBS IAEA Cotton IAEA Animal

Citrus Leaves Cellulose Blood

(4 samples) (6 samples) (4 samples)

H 5.96+0.01 6.3A±0.10 6.88±0.19

B (wg/g) 64.3+0.6 1.2+0.1 1.4+0.2

C - 48.0±2.2 N 3.6210.04 - 15.6+0.2 ^* - - 1.42±0.03

SI 0.19±0.06

S 0.44+0.02 - 0.71±0.04

CI (yg/g) 391+6 633±4 14,000+800

K 1.889+0.007

Ca 3.47±0.05

Ma (ug/g) 22±6

Fe

0.24+0.02

0.25+0.02

and an unknown amount of P^Or- Our values agree very well with NBS, the

major exception being Fe in basalt. Our Sm and Gd values agree well with

the Missouri values. The Missouri values show some disagreement with

the NBS data for Na, Mg, Si, Ca, and Mn. Our values for Si, K, and Ti are low by 3.2, 4.2 and 10% relative to the NBS values, but the agreement is generally quite good.

The Bureau is preparing a new SRM, citrus leaves, to supplement

the heavily used orchard leaves (SRM 1571) . We have been analyzing the

new standard by both INAA and PGAA for as many elements as we can observe.

In addition, we are participating in the analysis of two new IAEA

standards, cotton cellulose, and animal blood. The PGAA results obtained

so far are listed in Table 3. We will do considerably more work on these standards before release of final values.

164
NOK- RRD PROGP-AllS

Table 4. Compositions of Coal and Ashes fronI Washington State Power Plants

Element Concentration (X unless noted)

Plant in Plant n

Coal

(2 spls)

Preclp. ash^

(2 spls)

Bottom ash^

(2 spls)

Fly Ash

(1 spl)

H 4.3110.03 0.0510.02 0.1910.09 0.0510.01

B (yg/g) 214±26 20201170 89718 14211

C 51±1 - - -

N 1.37±0.01 - - -

Na 0.21±0.04 1.510.4 1.110.3 0.4310.09

Mg 0.8±0.4 2.010.5 1.610.3 2.310.2

Al 1.63±0.10 12.010.1 10.510.7 14.610.3

Si 2.72±0.07 20.9+0.6 21.7+0.9 24.110.2

S 0.59±0.07 0.1410.01 0.1210.01 0.1310.01

CI (wg/g) 45±15 - - -

R 0.11+0.02 0.87+0.05 0.8510.11 2.6010.01

Ca 1.24±0.08 9.710.5 7.510.7 1.0410.04

Tl (lig/g) 280±5 2480180 22001150 7850125

V (wg/g) ~ 455125 250150 330120

Mn (ug/g) - 260+20 735150 190112

Fe 0.46±0.02 3.010.2 2.5410.10 3.8110.05

Cd (pg/g) 0.3010.05 0.9010.19 0.9610.19 7.410.1

Sm (ug/g) - 70130 35+4 90+7

Nd (yg/g) 1.1410.03 10.610.1 8.910.6 17.010.1

Gd (yg/g) 1.010.1 9.2+0.2 7.610.5 15.110.3

Total

(as oxides

72

except C, N, H)

93 87 95

^Corrections for neutron self-shielding by the large amounts of B present In

these samples was necessary.

165
ITON'RRD PROGEAIIS

4. Coal and Coal Fly Ash

We have analyzed several coal and coal ash samples during the past

year. Typical results from these studies are listed in Table 4:

compositions of coal, precipitator fly ash and bottom ash from one

plant; and fly ash from a second plant in the State of Washington.

We do not understand why we fail to account for 26% of the mass of the

coal sample, as we previously reported.

From the summation of oxides, we estimate that the ash content of

the coal is 10.5%. Thus, after the combustion process has removed most

of the C, H, N, S, and CI, concentrations of the elements that remain

with the ash fractions are increased. by factors of about 8.

In general, the results are consitent with those of previous in8 9 plant studies of coal-fired power plants ' . Most previous studies

have been performed with INAA, which does not yield data for about onethird of the elements reported here (although it yields results for 15

to 20 elements not measured by PGAA) . One very striking result of this

work, which is not observable by INAA, is the enormous boron concentrations of the coal and, especially, the fly ash. This result has previously been noted by other investigators who used PGAA ' . Little

is known about the sources of boron in the atmosphere, or even about

its atmospheric concentrations. However, judging by the very high

boron concentrations in coal fly ash relative to that of soil ('^2000 vs 15 ppm) , there is a good chance that coal combustion is the dominant

source of boron borne by suspended particles in the atmosphere. If so,

boron might serve as an excellent tracer for emissions from coal-fired

power plants, which would be of great value in answering such questions

as the sources of acidic rainfall and airborne sulfates. During the

coming year we will investigate the ability of PGAA to observe boron in

atmosphere particle samples.

166
TJON- RRD PROGRllAS

1. Anderson, D. L. Failey, M. P., Zoller, W. H. , Walters, W. B.,

Gordon, G. E., and Lindstrom, R. M. , J. Radioanal. Chem. ^ 63 , 97 (1981).

2. Failey, M. P., Ph.D. Thesis, Univ. of Maryland, 1979.

3. Failey, M. P., Anderson, D. L. , Zoller, W. H., Gordon, G. E., and

Lindstrom, R. M. , Anal. Chem. ^ 51, 2209 (1979).

^- This report, Section 5, Activation Analysis Group FY 82.

5. Camp, D. C., Ruhter, W. D. , and MacMurdo, K. W. , "Determination

of Actinide Process and Product Stream Concentrations Off-Line and

At-Line by Energy Dispersive X-ray Fluorescence Analysis,"

Lawrence Livevmore ISlational Laboratory Report UCRL-85083 (1980)

6. Graham, C. C, Glascock, M. D., Carni, J. J., Vogt, J. R. , and

Spaulding, T. G., Anal. Chem. , ^, 1623 (1982).

7. Germani, M. S., Goknien, I., Sigleo, A. C. , Kowalczyk, G. S.,

Olmez, I., Small, A,, Anderson, D. L. , Failey, M. P., Gulovali,

M. C. Choquecte, C. E. , Lepel, E. A., Gordon, G. E. , and Zoller,

W. H., Anal. Chem., 52^, 240 (1980).

8. Gladney, E. S., Small, J. M. , Gordon, G. E. , and Zoller, W. H.

,

atmos. Environ. J 1£, 1071 (1976).

9. Klein, d. H. , Andren, A. W. , Carter, J. A., Emergy, J. F., Feldman,

C, Fulkerson, W. , Lyon, W. S., Ogle, J. C, Talmi, Y., VanHook,

R. I., and Bolton, N. E. , Environ. Sci. Teohnol.^ _9, 973 (1975).

10. Gladney, E. S., Wangen, L. E., Curtis, D. B., and Jurney, E. T.

,

Environ. Soi. Teehnol., 12_, 1084 (1978).

11. James, W. D. , Graham, C. C. , Glascock, M. D. , and Hanna, A. G.,

Environ. Soi. Teehnol., 16, 195 (1982).

167
NON-RPD PROGPAflS

SUmARY OF ACTIVITIES CARRIED OUT BY THE

NEUTRON FIELD STANDARDS GROUP

J. Grundl

(Nuclear Radiation Division)

The Neutron Field Standards Group, attached to the Center for

Radiation Research (CRR) is engaged in the establishment and application

of standard and reference neutron fields as permanent facilities for

neutron detector calibrations, neutron dosimetry standardization, and

reaction rate cross-section measurement.

One component of this group's activities makes use of the reactor

thermal column and the tangential beam tubes where facilities, designed

and built by the NFS Group, are in operation. Facility and related

capabilities developments for FY 82 are as follows:

1. Installation of a fusion chamber monitor for the cavity fusion

source at the reactor thermal column. A specialized fusion chamber of

small diameter, purchased in France, was mounted at the entrance

penetration of the thermal column cavity. It is now possible to perform

time-history fluid monitoring of tJ-235 fission spectra irradiations. Other

notable improvements in the cavity fission source were : (1) experimental

examination of flux gradients over the region of detector placement; and

(2) receipt of preliminary results of source detector scattering calculations.

The latter are part of extensive Monte Carlo calculations being carried

out at Los Alamos under joint cooperation and contract.

2. An archive deposit of U-233 is a recent addition to the NBS set

of fissionable isotope mass standards. The complex alpha spectrum of U-233

and its daughters and the fact that the deposit is a fluoride compound

rather than the usual oxide creates special problems in the mass assay.

In order to carry out the thermal-fission component of the assay, fission

fragment self-absorption in flouride vs. oxide deposits was Investigated

in a series of measurements in a thermal beam.

3. The Subcommittee on Standards of CSEWG has explicitly recognized

the fission-spectra-averaged cross-section of U-235 in the Cf-252 fission

168
nON-RRD PROGRAIiS

spectrum as a basic normalization measurement for the U-235 fission crosssection. Remeasurement of this normalization quantity is continuing and

included this year fissionable deposit mass intercomparisons at the thermal

column. In addition, a re-evaluatlon of earlier measurements was completed

and the result forwarded to CSEWG:

a^ (U-235, X ^) = 1216 + 19 mb

f ef —

There was little changed from the previously published value but the error

in the rms sense was reduced by a factor of two. This improvement came from (1) revision of mass scale for NBS fissionable deposits (error reduced

to + 0.75); (2) new detailed monte-carlo scattering calculations for the

fission chamber and the fissionable dep.osit backings carried out at Los

Alamos; (3) reduction of the error assigned to the source strength of

NBS-I, the National Standard Neutron Source (error reduced to + 0.9%).

4. The thermal-neutron-radiography facility for diagnostic

irradiations of art works is described elsewhere in this report. In

cooperation with the Reactor Division and the National Gallery of Art,

substantial modifications at the thermal column were designed and fabricated

in order to achieve a high Intensity flux of thermal neutrons over a large

area. The design also made possible rapid recovery of irradiated paintings

so that short-lived activities could be included in the post-irradiation

diagnostic procedures.

5. The filtered beams of monoenergetic neutrons are used primarily

for calibration of neutron personnel dosimetry instrumentation. Flux

parameters for the beams were intercompared with those at PTB , the West

German Standards Laboratory at Braunschweig. Important improvements in

the control system for the dosimetry phantom scanner employed at the

filtered beams were completed.

6. Fission cross-section measurements in the thick-shell ISNP were

performed for the following isotopes: U-233, Pu-240, Pu-241, and Th-232.

Combined with earlier measurements of U-235, U-238, Pu-239, and Np-237,

there now exists for ISNF a consistent set of integral fission cross169
NON- RRD PROGRAI'lS

section data for essentially all of the fissionable isotopes important for

reactor technology. A representative result,

a (Pu-240, ISNF) = 824 mb + 2.8%,

agrees well with the value predicted by ENDF/BV (the U.S. nuclear data

file for reactor technology)

;

^n^^'^^'f = 1-00 + 3.0% Observed —

A characteristic of this result, identifying it as coming from a standard

neutron field, is the inclusion of a component error (in the 3.0% total)

uncertainty) for the propagated effect of ISNF spectrum uncertainties.

7. Testing of neutron personnel dosimetry instrumentation continued

at a high level making proper institutional use of the filtered beams the

thermal column, and the D„0 moderated fission spectrum irradiation facility.

Systemmatic performance tests have now been performed on essentially all

types of passive neutron dosimeters used in the United States. Calibration

of active neutron dosimetry instrumentation parameters and BF counters)

for a variety of agencies, laboratories, commercial vendors and most

significantly for a suddenly increased number of power reactor operators.

See accompanying special report.

8. Neutron fluence standards prepared with the cavity fission source were sent to ORNL for calibration of a new dosimetry counting system.

Activation reactions included were In(n,n'), Al(n,a), Ni-58(n,p), and

Fe-54(n,p). The counting facility at ORJSIL will be employed for neutron

dosimetry determinations in existing and planned radiations designed to test

embrittlement rates in reactor pressure vessel steels.

9. The cavity fission source, after its varied applications to

neutron dosimetry calibration, was employed for the first time in a cross- section measurement. The U-235 fission-spectrum-average cross section

for the activation dosimetry reaction Ni-58(n,p) was determined in a set

of cavity fission sound irradiations. The absolute flux for the experiment

was obtained by the method neutron flux transfer from the Cf-252 fission

170
MON- PJR.D PROGPAtlS

source using the In (n,n') reaction. The preliminary result of this

measurement:

a(Ni, X^.) = 101 + 3 mb,

caused some spirited discussion if not consternation when reported at the

Fourth ASTM-EURATOM Symposium on Reactor Dosimetry in March of this year.

This cross section is central for work of dosimetry and the accepted

experimental value is some 8% higher than the one above. There is added

provacation in the fact that the preliminary NBS value agrees with the

calculated spectrum-average cross section whereas the accepted value does

not and in fact has been used to challenge the shape of the U-235 fission

spectrum.

10. Miscellaneous measurement and related activities make poor

material for progress and accomplishment reporting, but unfortunately they

constitute a substantial part of the NSF Group effort. Some samples of

these activities are: (1) performance test irradiation with thermal

neutrons of proton-recoil emulsion detectors; (2) post-irradiation checks

of Co-Al and Co-Zr dosimeter wires for validating co-concentrations; (3)

revision of ASTM standard on definition of terms used in dosimetry; (4)

quality control tests of navy shipboard area monitors; (5) refurbish and

check out of fission chambers for CEN/SCK (Belgium) and the University of

Arkansas; (6) performance investigation of position-sensitive, proportional

counter to be used for linac resonance radiography development.

171
FON-PJID PROGRAilS

NEUTRON PERSONNEL DOSIMETER CALIBRATION AND TESTING

R. B. Schwartz

(Nuclear Radiation Division)

The reactor filtered beams, with energies of 2, 24, and 144 keV,

together with the beam from the thermal column, were used as part of a complete test of most of the neutron dosimeters used in the United States.

Dosimeters from most of the DOE laboratories, as well as from commercial

suppliers, were irradiated in each of the reactor beams and with the NBS

bare and moderated californium sources. Several dosimeters of each type

were irradiated at each facility, at several different dose levels. The

data from these irradiations, which are still being evaluated, will allow

the accuracy, precision, energy response, and sensitivity of each dosimeter

type to be determined. These data will permit the different dosimeters

now in use to be accurately compared and evaluated and will serve as a basis for evaluating new dosimeter types under development. This is the

first time that such a comprehensive test has been carried out in the

United States.

We have also carried out an intercomparison between our filtered beams

and the filtered beams at the Physikalisch-Technische Bundesanstalt (PTB)

in Braunschweig, Germany. Since NBS and the PTB have the only sets of

filtered beams used for instrument calibrations, this constitutes a complete

international intercomparison. Preliminary results indicate good agreement between our two laboratories, but the data are still being evaluated.

In addition, we have done numerous irradiations of active instruments

(BF counters, remmeters) and passive detectors for several commercial

companies, DOE laboratories, the Aberdeen Proving Ground, the Naval Surface

Weapons Center, and a university, to calibrate existing instruments and

to help develop new ones.

172
NON-RRD PROGRAI'.S

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 in particles released

from major sources such as volcanoes. By measuring concentrations of

such a large number of elements, we hope to be able to identify contributions

from the sources to the atmospheric burden at ambient sampling sites.

Examples of three studies are discussed briefly in the following sections.

1. 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 the enormous value of the long-term CO record

(since 1957) at Mauna Loa Observatory (MLO) in Hawaii for observing CO

seasonal variations and long-term increase. Fortunately, since mid1979, the National Oceanic and Atmospheric Agency (NOAA) has supported

weekly collections of filters at MLO and analysis of them by our group

using instrumental neutron activation analysis. A distinct diurnal

cycle exists at MLO at 3400 m alt, above the marine boundary layer:

during the day, warming of the slopes of the mountain causes upslope

winds whereas, during the night, cooling of air along the slopes causes downslope winds. Upslope conditions bring up air containing marine

aerosol, crustal dust from the island and emissions from the small

anthropogenic activity there. Dox;mslope conditions bring dovm rather

clean air from the upper troposphere. A control system alternately

activates the pump on one of three filter systems depending on wind

conditons and time-of-day to make separate collections of particles from

upslope and downslope conditions. The third filter operates when neither

condition is clearly established or when a condensation nuclei counter

173
NON-RRD PROGFA^'-S

detects high counts due to contamination by motor vehicles, volcanic

eruptions, etc.

Average elemental concentrations under various conditions are listed

in Table 1. There are huge increases in crustal dust every Spring,

apparently because of transport from arid regions of central and eastern

Asia. Duce et al . [1] previously reported similar incursions of Asian

dust at Enewetak Atoll, with concentrations of airborne soil being 2.3

3 Ug/m in mid-April, 197 9. During non-dust conditions at MLO, average

3 Al concentrations are about 7.6 ng/m , whereas weekly average concentrations

rise to ^250 ng/m during the dust periods. Upslope samples are similarly

affected, but the increases are not as dramatic because of higher normal

concentrations

.

The do\>7nslope data for 1980 are divided into dust and non-dust

periods, as differences are so great that yearly averages are strongly

influenced by the dust periods for most elements. Average concentrations

of many elements are more than an order of magnitude higher during the

periods, but there are some exceptions including Br and I, whose concentrations are scarcely affected by the dust, and Na and Se, which are only

doubled

.

During non-dust periods, do^vmslope concentrations are among the

lowest observed any\>7here in the world, typically being about a factor of

ten greater than at the South Pole for most elements. Thus, these

samples represent upper tropospheric air of the North Pacific and as such,

will provide a valuable data set for global receptor modeling. As expected,

upslope samples have higher concentrations for most elements, major exceptions being Br and I. Results of preliminary factor analyses of the 1980 dov.mslope data are listed in Table 2. Factor 1 has heavy loadings for most elements and

undoubtedly represnets mainly Asian dust. The substantial loadings of some enriched elements, e.g., Zn, As and Sb, do not necessarily indicate

that those elements are enriched on Asian soil, as air masses that bring

soil from Asia may also bring particles from anthropogenic activities.

174
NOM--RRD PROGPAblS

Factor 2 has substantial loadings of several marine elements. The loadings for Sb, Yb, and Ta are not understood, Au is discussed below. The

heaviest loadings on Factor 3 are those of S and Se. Sulfur is surely

secondary, resulting from conversion of SO-. As Se is in the same chemical group, it is not surprising that it is associated with the S factor. Except for Zn and Na, all elements on Factor 3 are volatile.

Factor 4 illustrates experimental artifacts can create a factor. The

major loadings are for halogens and Be, which have very constant con-'

centrations. This factor may arise because the actual concentrations

remain constant, but errors in the volume of air sampled fluctuate,

giving an apparent fluctuation of the concentrations. In general, the

factor analysis is quite successful, as communalities are close to unity

for most elements, major exceptions being CI and Be. The sum of the

communalities is 25.6, about 85% of the 30 units of variance. As the

dust component accounts for over 18 units of the explained variance, we will run the factor analysis with the dust period excluded to see what

factors emerge under normal, cleaner conditions.

Factor analysis also yields the "factor scores", i.e., the strength

of each factor during each sampling period. The factor score is centered

at zero and has positive values during periods when the factor is stronger

than average and negative values when weaker. As expected. Factor 1 has

large positive scores for most weeks when the Asian dust was present

during April and May. The score for Factor 3, the S and Se factor, was very high for the week of May 27 and several weeks thereafter. Recall

that the major eruption of Mr. St. Helens occurred on May 18, 1980. It

is tempting to suggest that these elements were picked up from the upper

troposhere at Hawaii about one to two weeks after the eruption and

remained high for several weeks afterwards; however, more information

would be needed to verify the suggestion.

Factor analysis of the 1980 upslope samples at MLO yielded five

significant factor, four of which correspond rather closely to the four

factors' of the downslope results, although not in the same order.

175
NON- RRD PROGRAI'S

Factor 3 has no direct counterpart in the downslope data, as it is mainly

loaded with Au and W, with minor amounts of V, S, and Ce. We have no idea about its origin; however, Kenneth Rahn (private communication, 1982)

observed a factor loaded with Au, Ag and W in an Alaskan data set. Clearly,

this factor warrents further investigation. The overall results for the

upslope samples are quite acceptable, as the five factors account for 86%

of the system variance.

In summary, there are many uncertainties associated with global

receptor modeling at this time, but the few results so far obtained are quite encouraging, suggesting the great potential value of further development and use of these methods for gaining a better understanding of the sources and transport particles on a global scale.

2. Airborne Aerosol Measurements in the Quiescent Plume of Mt. St. Helens

Volcano

Air-filter samples were collected from the Mt. St. Helens plume

with a Lockheed Orion P-3 turbo-prop aircraft during a flight on Sept.

22, 1980, which time the volcano was emitting a stable plume to an altitude of between 2 and 3 km. Four Fluoropore filter samples (1.0-ym

pore diam) were taken, two during predominatly cross-plume flight

patterns and two when flying coaxially within the plume. The average

3 sampling time was 42 min and the average air volume 5.8 m . Fluoropore

filters used on the single filter unit have collection efficiencies

>99.99% for particles fo diam >0.03 ym (Liu and Lee, 1976). The stacked

filter package consisted of two quartz fiber filters (>0.3 ym diam)

mounted in a single filter holder, followed by two filter cassettes

containing NaOH/f lycerol-treated I-Thatman filters to trap acidic volatile

species such as HF, HCl, and SO . Two multi-stage series of samples were collected for 30- and 70-min intervals with air volumes of 6.2 and

3

12.7 m , respectively. Blanks were collected for all types of filters

by exposing them for only 30 sec. Results for the Fluoropore filters given in Table 3 represnet

blank-corrected concentrations (ng/m^^) of the suspended particulate

matter collected in the plume. Blank corrections, calculated from the

176
NON-RRD PROGRMIS

average of five individual blanks, were insignificant (<10%) for most

elements. Also reported are average total sulfur gas concentrations (ppbv)

measured during each run by the total sulfur analyzer and the total sulfur

3

(gaseous and particulate) in ng/m . Although the plume was very diffuse,

even with small sampling volumes, we were able quantitatively to determine

27 elements in the samples due to the low level of impurities in the filter

materials and the high sensitivity of INAA. Background aerosols were collected in the vicinity of Mt . St. Helens on other flights. Trace element

levels, not shown here, were significantly lower than those measured in the

plume

To identify elements that are enriched in the volcanic plume particles

as compared with bulk ash from the May 18 eruption, we calculated the

enrichment factors (EF , ) and the average is given in Table 3: ^^^ (X/Al) , T^-n _ plume f-IS ^ ash' (X/Al) ^

^^^ ash

where (X/Al) , is the concentration ratio of element X to that of Al plume

in the plume and (X/Al) , is that of a representative ash sample from the

volcano. Concentrations for the ash samples were determined by INAA and

neutron-capture prompt Y-ray activation analysis (PGAA) of an unleached

composite sample collected by the U. S. Department of Agriculture at

Pullman, Washington, from the 18 May eruption.

Enrichment factors for the Fluoropore filters are shown in Figure 1

along with those of aerosol particulate samples collected in the

stratosphere shortly after the 18 May eruption [2]. Pronounced enrich4 ments relative to ash, up to 10 , for volatile, non-crustal elements

were observed in the quiescent plume. By contrast, EF , values close to ash

unity were observed for most elements in the plume of the major May 18,

1980 eruption. Those samples were dominated by airborne ash fragments

from the mountain's explosive eruption which, in the earlier phases, was primarily of phreatic nature. The huge enrichments of the halogens,

W, In, Zn, S, Cd, Se, Sb, Hg, As and Au in the quiescent plume suggest

that those elements are associated with higher temperature, more mobile

177
NON- P-P-D PROGRAMS

phase being gradually expelled between eruptions without much ash.

Particulate S concentrations based on INAA and IC (as S0,=) were

compared with those of total gaseous sulfur measurements and of acidic

sulfur gases as observed by IC analysis of the base-treated filters.

Results from the two techniques were in reasonable agreement, as summarized in Table 3, showing that 6+3% of the total S in the plume was borne

by particles, the rest being in the form of S0„ and H„S based on the total

sulfur data from the Meloy Flame Photometric detector.

By normalizing concentrations of enriched elements to that of total S, one can calculate fluxes for other species based upon SO.., fluxes. Volatile

elements with estimated production rates of about a kg/day or greater are

listed in Table 4. They include CI, Zn, As, Hg, Sb, Se, Cd, and Au.

Assuming that the ratio of volitile elements to S in the quiescent

emission of Mt. St. Helens is representative, estimates of global inputs

of these elements from volcanoes to the atmosphere can be made based on simultaneous total sulfur measurements. Appearing in Table 5, along with

daily emission rates, are estimates of the global volcanogenic flux of

particulate Cl, Zn, As, Hg, Sb, Se, Cd, and Au, as well as literature

values of these species where available. These results compare quite

favorably with the previous literature estimates of individual elemental

inputs. Clearly, much more detailed chemical information throughout different eruptive cycles of a given volcano is required before reliable

assessments of long range effects or future activity can be made.

The data presented here are the result of coordinated sampling by

several techniques from a single aircraft sampling platform. We believe

that the simultaneous measurement of many bulk and minor constituents

from the air represnets the most promising field technique for evaluation

of volcanic plumes and theri atmospheric impact.

3. INAA Measurements on Samples from the St. Louis Dichotomous Sampler

Network

During 1975-76, atmospheric particulate samples were collected at

ten sampling sites in St. Louis as part of the St. Louis Regional Air

178
NON- RRD PROGF-AMS

Pollution Study (RAPS) [10]. Samples were collected with dichotomous

samplers which separated incoming particles into two size fractions:

the coarse fraction, with aerodynamic diameters of >2.4 ym and the fine

fraction of diameter <0.24 ym. Particles were deposited on 1.2-iJm porediam cellulose ester membrane filters of 37-mm diam. Characteristics and

operation of dichotomous samplers are discussed by Jaklevic et^ al. About

31,000 of these samples were originally analyzed by Jaklevic et_ a]^. by

energy-dispersive x-ray fluorescence (XRF) and concentrations of up to

28 elements were measured in each sample.

Recently we obtained 32 of the above samples and 10 filter blanks.

We have determined trace element concentrations by instrumental neutron

activation analysis (INAA) . Our experiments had several purposes: (1)

to compare the results of XRF and INAA for the same samples for elements

observable by both methods; (2) to determine filter blanks for the 40-odd

elements observalbe by INAA in order to establish those that will be

measurable above blanks in the filter deposits; (3) to begin to determine

typical concentrations in the St. Louis atmosphere of many trace elements

obserable only by INAA; and (4) to provide detailed analyses of particulate

samples that contain large amounts of material released by a specific source in St. Louis (a pigment plant).

Samples from the entire network were selected for a 12-hr period

on the 126th day of 1976 during which the wind direction remained almost

contant and from a prevailing wind direction for St. Louis (northwest).

In addition, samples taken at various times at Station 118 were analyzed.

Most of these samples were heavily influenced by emissions from a pigment

plant in the south part of St. Louis, as shown by their generally high

concentrations of Ti.

Samples and appropriate standards and flux monitors were irradiated

in the National Bureau of Standards (NBS) reactor at a thermal neutron

179
NON-RRD PR0GRA21S

13 ^ flux of 6x10 n/cm~-sec. Spectra of the '{ rays produced by the decay

of the induced radioactivity were taken using a Ge(Li) detector coupled

to a 4096-channel analyzer system. Two different Tennecomp TP-5000

systems were used, one at NBS for short-lived nuclides and the other at

the University of Maryland for long-lived nuclides.

We find that INAA can be used to observe about 35 or so elements

in most samples vs. about 20 for most samples by XRF and several that are measureable by both methods can be determined with much greater

accuracy by INAA. A number of the elemtns observed by INAA are of

considerable value in identifying sources, e.g., Na, Se, As, Sb . However,

the cost of analysis per sample, especiall}? in terms of manpower, is far

greater for INAA.

In Table 6 we compare the average concentrations of a number of

elements in St. Louis throughout the network on Day 126 of 1976 with

those observed by our group in Washington, D. C. during the summer of

1976 ill]- Concentrations of most elements are strikingly similar

between the two cities. Major exceptions are Ca, V, Se, and Br. The

Ca is in the coarse mode and clearly associated with dust, much of which

is gravel or limestone dust. There are many quarries in the St. Louis

area. The lowered V concentration surely results from the much lower use of residual oil in St. Louis than in Washington and other Eastern

cities. There are many possible sources Se in St. Louis, especially

plants that deal with chalcophile metals, e.g., Cu, Zn, and Pb. We

don't fully understand the reduced levels of Br. In Table 6 we have

listed the XRF values for Pb in St. Louis to give an idea of automotive

concentrations. We see that Pb is about the same for the two cities.

However, the problem may be that an appreciable amount of Pb is contributed

by the two Pb smelters in the area plus other chalcophile element plants.

In Table 7 we compare the results of XRF and INAA for 11 elements

in samples for Day 126 throughout the network. We have not included Lhe

other samples from Station 118, as they are quite untypical, being heavily

loaded with particles from the pigment plant. Despite the fact that

180
NOn-RRD PROGRAMS

uncertainties on many of the individual values are often quite large

(e.g., Al by XRF) , the agreement between XRF and INAA is suprisingly

good for fine-particle samples. Unfortunately, the agreement is poor

for coarse particles, the XRF values being up to a factor of 2.2 as large as INAA values. We believe this probably arises because the

very largest crutal particles fall off the filters during handling.

EPA investigators have found the same problem and are now coating the

coarse-particle filters with a light oil to prevent it.

1. R. A. Duce, C. K. Unni, B. J. Ray, J. M. Prospero, and J. T. Merrill,

SoieriQe^ 209, 1522 (1980).

2. T. Vossler, D. L. Anderson, N. K. Aras, J. M. Phelan, and W. H. Zoller,

Scienoe, 211 , 827 (1981).

3. S. R. Taylor, Geoahim. Cosmochim. Acta^, 28^, 1273 (1964).

4. J. S. Fruchter, et al. , Soienee, 209 , 1116 (1980).

5. National Research Council, Chlorine and Hydrogen Chloride^ Nat'l Acad.

Sci., Washington, (1976).

6. J. 0. Nriagu, Nature, 279, 409 (1979).

7. P. R. Walsh, R. A. Duce, and J. L. Fasching, J. Geophys. Res., 84,

1719 (1979).

8. B. W. Loo, W. R. French, R. C. Gatti, F. S. Goulding, J. M. Jaklevic,

J. Llacer, and A. C. Thompson, Atrnos. Environ., 12_, 759 (1978).

9. J. M. Jaklevic, R. C. Gatti, F. S. Goulding, B. W. Loo, and A. C. Thompson, Aerosol Analysis for the Regional Air Pollution Study,

Final Report on Project EPA-IAG-D6-0670, (1981).

10. G. S. Kowalczyk, G. E. Gordon, and S. W. Rheingrover, Environ. Sci.

Technol. 16, '79 (1982).

181
NON- B-RD PROGPAl'^S

SANS STUDIES OF SINGLE CHAIN CONFORMATIONS IN

U\MELLjAR MICRODOmiNE OF BLXK COPOLYMERS

T. P. Lodge, E. J. Amis, and C. C. Han

(Center for Materials Science)

and

H. Hasegawa, T. Hashimoto, and H. Kawai

(Kyoto University, Kyoto, Japan)

In this study, SANS technique is used to measure the lateral dimension

of deuterated polystyrene block chain in the lamellar microdomain of the

mixtures of hydrogenated-styrene/isoprene block copolymers (HSI) and

deuterated-styrene/isoprene block copol3rmers (DSI) . HSI and DSI were synthesized by anionic polymerization. It was

intended that these polymers should have exactly the same copolym.er

composition and degree of polymerization excepting that 98% of the hydrogen

atoms of polystyrene block of DSI were replaced by deuterium atoms.

Characterization of the polymers were done by osmosis, GPC, and mass

analysis. Films were cast from 10% solutions in toluene in Polyflon

Petrie dishes at 28 °C. The domain structures were investigated by EM

and SANS. The results are shown in figure 1 and figure 2, respectively.

All of the samples show well oriented lamellar microdomains and the domain

spacings calculated from the peak positions of the SAXS patterns are shown

in table 2. The peaks appeared in the through view SAXS profiles indicate

that some lamellae are oriented perpendicular to the film surfaces, but their

number may be 1/100 of the lamellare parallel to the film surfaces.

SANS experiments were done by using the SANS instrument at NBS. Two

scattering geometries were used for all the specimen. (1) Through view:

in this geometry, incident beam is perpendicular to the lamellae. Isotropic

scattering patterns were obtained. Difference measurement between

different specimen should give the laterial dimension of the d-styrene

block. This is shown in figure 3 in the circular averaged form. These

data should be compared to the SAXS data in figure 2 which gives similar

patterns for different specimen because of the lack of contrast between

182
NON-RRD PROGPJ^IS oo

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183
llOn-PilD PROGEAllS

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Figure 1. Small angle x-ray scattering of microphase separated polystyrene/

polyisoprene lamellae. The ratio of deuterium labeled to

hydrogeneous polymers are shown in parenthesis. One-dimensional

detector was used which was placed perpendicular to the

lamellae.

184
MON-RRD PROGP-A^IS

THROUGH

«=5MESRE0 Oorfl-efiCKCROUNO

DSI

KSI/DSI (50/50)

HSI/DSI (75/25)

HSI/DSI (87.5/123)

HSI

0.00 O.SQ 1.00 1.50 2.00

S- 10 fNM-i|

2THEI>1 IMlN. 1

Figure 2. SAXS of PS/PI specimen (as above) in through view,

185
NOTI-RRD PROGRAMS

\Cf

10= r

(q) ;au;

10*7

10':

10^

• HSI/DSI (THROUGH)

/

o • " 50/50

= 75/25

• ' 87.5/12.5

' HSI 100%

9

• DSI 100%

Oo,

*

•*0

V

S^ Ov._

r "-w-,. ^^^53fe «V.H»__ v.vy*««°»

•

, , , , 1 , 1 1 1 I „J ...J 1 1

.05

(A-'

.15

Figure 3. SANS of PS/PI specimen (as above) in through view,

shown are circular averaged.

Results

HSI/DSI (EDGE)

50/50 75/25 87.5/12.5

film normal

90°

DSI 100% HSI 100%

Figure 4. Contour plot of SANS of PS/PI specimen (as above) in edge view.

186
HON- RRD PROGRAllS

deuterium labeled and hydrogeneous chains.

(2) Edge View: in this geometry, incident beam is parallel to the

lamellae. In other words, almost perfect lamellae are stacked up to

macroscopic dimension ('^ 1 cm) and placed parallel to incident beam.

Anisotropic scattering pattern was observed on the two-dimensional SANS

detector. Strong patterns caused mainly by the repeating distances of

the lamellar microdomains are observed in the vertical direction. Very

weak diffuse scattering due mainly to the single chain scattering was obtained in the horizontal direction. Contour plots of the edge view

patterns are shown in figure 4. The vertical patterns are to be compared

with SAXS patterns shown in figure 1. The horizontal pattern, again can

be used to deduce single-chain dimension of labeled styrene block.

Detailed analysis of laterial dimension of single-labeled polystyrene block has been carried out. It is clear that single-block

laterial dimension of polystyrene in the microphase separated lamella

is only about 2/3 of its unperturbed dimension. For example: for the

polystyrene with degree of polymerization of 362, the laterial component

o of the radius of gyration is 20 + 5 A compared to unperturbed dimension

o of 30 '^ 31 A. This implies that all the current statistical theories

(1,2) of phase separated copolymers have to be modified.

1. D. J. Meier, "Block and Graft Copolymers," J. J. Burke and V. Weiss,

Eds., Syracuse University Press, Syracuse, NY (1973).

2. E. Helfand and Z. R. Wasserman, "Developments in Block Copolymers,"

I. Goodman, Ed., Applied Science publishers, Ltd. (in press).

187
NON-RRD ?R0GPA>1S

THE NEUTRON ACTIVATION AUTORADIOGRAPHIC STUDY OF PAINTINGS

Y. T. Cheng

(Smithsonian Institution, Washington, DC)

and

I. Schroder, M. Ganoczy, R. S. Carter

The neutron-activation autoradiography project sponsored by the

Smithsonian Institution was progressing in two fronts during the past year.

The first is the finalization of design concepts from scientists and art

conservators. A contract was granted to proceed with the detailed engineering layout of the proposed facility and an estimate of construction

costs will be made. The finalized conceptual drawings of the autoradiography

facility are shown in figures 1 and 2. The second is the utilization of

the present NBSR thermal column for actual painting studies and the

preparation of project supporting facilities.

1 2 The successful autoradiographic examination of a painting ' requires

that the painting be activated with an adequate thermal neutron fluence

13 2

("^ 1 X 10 n/cm ) and if information about short-lived isotopes (Al, Cr,

Ti, etc.) in the painting are to be extracted, then the thermal neutron

9 2 flux should be as high as possible (> 5 x 10 n/cm sec) . Our initial

measurement on the NBSR thermal column indicated it met these requirements.

The thermal column also has a very favorable ratio of useful radiation

(thermal neutrons) to unwanted ones (fast neutrons, beta, and gamma rays).

This is important as the safety of the painting is still the ultimate

concern of everyone who is interested in such a facility. After the

painting materials are activated, their radiation decay activities are recorded using a solid state (Ge(Li)) detector for gamma spectroscopy

and film placed in close contact with the painting for autoradiographic

exposures. The gamma spectroscopy is to measure quantitatively the contents

of different materials in the painting and the autoradiography is to

reveal the relative spatial concentrations of those materials.

The NBSR thermal column at present has a relatively uniform thermal

3

neutron field at the surface which is suitable for activating small

188
HON- RRD PROGPIIAS

Thermal Column Door

Insertion Slot

Reactor

Neutrons

Thermal Column

-Graphite--

\\\\\\\\\\\\\W\\\\\\\\\V\\VV\\\\V'v'v\\\\\V\VV\\\\\\\\\\V^V\

Figure 1. Top view of the proposed NBSR neutron activation autoradiographic

facility.

Thprmai Colli

Figure 2. Side view of the proposed NBSR neutron activation autoradiographic

facility.

189
MON--RRD PR0GRA1^.S

paintings up to 2 1/2' x 2 1/2' in size. Three paintings have thus far

been studied using the present thermal colximn facility. We were approached

by the Walters Art Gallery of Baltimore about a late 15th-early 16th

century Russian Icon painting panel. The panel is painted on both sides

with rich gold inlays. Conventional radiographic techniques failed because

of the superposition of the two painting images. It was hoped that neutron

activation autoradiography would help to attain clear images of both paintings.

Also as part of the inquiry into the methods and materials used in the

fabrication of icons of that period, the identification of the pigments

in these paintings would add to the knowledge of the palettes used in

schools of northern R.ussian icon painting.

For the security of the painting, a counting and storage room was

set up with limited access and the environmental conditions were strictly

regulated according to museum standards. The particular icon painting

due to its rich content of gold, if not handled properly, might become so active that information about other materials would be obscured. To

familiarize ourselves with the general operating procedures such as film

handling, proper exposure time, etc., and with the gold problem, an icon was made according to known techniques by the gallery for use as a test

10 2 painting. It was activated with a thermal neutron flux of 1 x 10 n/cm

sec for 10 minutes. Eight film exposures and five gamma spectroscopic

counts were taken. The time schedule is listed in table 1 along with

elements accentuated in the different exposures. The result of the test

icon painting showed the time of activation for the real icon should be

reduced to 5 minutes. After the activation, the real icon also followed

the same schedule as in table 1. Some autoradiographic results are shown

in figures 3, 4, and 5.

The third one we have studied is a turn-of-the-century painting by

4 an American painter, Thomas W. Dewing. A project is currently proposed

to systematically study as many of his paintings as possible to establish

the style and techniques he used. The Dewing painting was activated much

the same way as the icons. The counting and autoradiographic process,

190
NOn- RRD PROGRAMS

Figure 3. Photograph of the painting "Lady with Rose," by Thomas W. Dewing,

Time After Activation 3 min.

Film Exposure Time 6 min.

Prime Elements Exposing the Film

Element Relative Strength

Co 100

Mn 43

Al 33

Ca 6

Na 5

Figure 4. The 5th autoradiograph of the painting, "Lady with Rose,

by Thomas W. Dewing.

191
TTON- P.RD PROGRAMS

Time After Activation 2.5 hrs.

Film Exposure Time 3.0 hrs.

Prime Elements Exposing the Film

Element Relative Strength

Mn 100

Na 25

Zn 3

In 1

K 1

Figure 5. The 7th autoradiograph of the painting, "Lady with Rose,"

by Thomas W. Dewing.

Time After Activation 1 day

Film Exposure Time 1 day

Prime Elements Exposing the Film

Element Relative Strength

Na 100

Zn 12

K 3

Cd 2 Sb 1

Figure 6. The 9th autoradiograph of the painting,

by Thomas W. Dewing.

192

'Lady with Rose,"
HOM-RRD PROGRAllS

Table 1. The time sequence of neutron activation autoradiographic studies

of paintings.

Time Event

Optimization of Autoradiographic Effects

Tq=

T^ = 5m

T^ = 11m

T^ = 18m

End of neutron activation

1st film on for 4m

1st y-spectroscopic count for 5m

2nd film on for 15m

T, = 34m 3rd film on for 45m

4

T_ = lH25m 2nd y-spectroscopic count for 3

T, = 2H 4th film on for 3H

6

Om

T^ = 5Hl0m 3rd y-spectroscopic count for 3H

T„ = 8H20m 5th film on for 15H

Tg = ID

^10 = 2D

^11 = ^° T^2 = lOD

4th y-spectroscopic count for lOH

6th film on for 3D

5th y-spectroscopic count for 3D

7th film on for 14D

Ag 108 (2.3m)

Al 28 (2.3m)

Cr 55 (3.6m)

S 37 (5.0m)

Cu 66 (5.1m)

Ti 51 (5.8m)

Ca 49 (8.8m)

Co 60m (10.5m)

Mg 27 (9.5m)

Sb 124m (21.0m)

CI 38 (37.3m)

Cd 111m (49.0m)

Ba 139 (85m)

Mn 56 (2.58H)

Pb 209 (3.3H)

Cd 117m (3. OH)

K 42 (12. 5H)

Cu 64 (12. 8H)

Na 24 (15. OH)

As 76 (26. 7H)

Au 198 (2.7D)

Hg 197 (2.7D)

Sb 122 (2.8D)

Ca 47 (4.7D)

P 32 (14. 2D)

Cr 51 (27. 8D)

193
nON-RRD PROGRJVllS

Table 1. Continued.

Time

Time Event

T = 3 00 8th film on for 30D

Optimization of Autoradiographic Effects

Hg 203 (47D)

Fe 59 (45D)

S 35 (87D)

Ca 45 (153D)

Ag 110m (253D)

Fe 55 (2.6Y)

Co 60 (5.2 6Y)

Table 2. Elements present and their relative concentration in the painting

Lady with Rose by Thomas W. Dewing detected with neutron

activation analysis.

Element Relative Quantity

Ca 9972

Zn 6120

Al 885.0

K 357.2

Mg 280.7

Cd 115.3

Mn 102.2

CI 80.2

Na 62.8

Cr 38.8

Co 30.9

Ba 5.8

V 4.2

Cu 2.3

As 0.9

In 0.6

Au 0.3

194
>TON- RRD PR0GPA>1S

however, was modified. Instead of counting and exposing film alternately,

the counting was being done the same time when the film was being exposed.

This enables us to correlate the density on the film more directly and

quantitatively with the isotopes measured in the corresponding gamma

spectroscopy. Figures 3, 4, 5, and 6 show some of the results from this

study. The table on the bottom of each picture list the relative strength

of different elements responsible for the film darkening for that particular

picture. Table 2 lists all the elements found by the neutron activation

method and their relative concentrations in the Dewing painting.

The complete interpretation of the result would involve not only

the effort from scientists but also that from painting conservators and

art historians. A group of personnel with such specialties is currently

being organized for the coming year.

1. "Art and Autoradiography: Insights into the Genesis of Paintings

by Rembrandt, Van Dyck, and "Vermeer," published by the Metropolitan

Museum of Art, New York (1982).

2. M. J. Cotter, P. Meyers, L. V. Zelst, C. Olin, and E. V. Sayne,

Applioazione del Methodi mdeopi nel Campo Belle Opeve D'co'te,

p. 161-203 (1976).

3. "NBS Reactor: Summary of Activities," NBS Teoh. Note 1160 (edited

by F. J. Shorten, 1981).

195
C. Reactor Operations and Services

REACTOR OPERATIONS AND SERVICES

The reactor was operated on a normal round-the-clock schedule for

the entire year. Other than scheduled shutdowns for maintenance, refueling,

testing, and for staff vacation, there were no interruptions in the

operating schedule. A program of modernization of reactor components

and instrumentation began last year is continuing. Licensing activities

to upgrade reactor power to 20 MW and renew the operating license are progressing. A Draft Environmental Impact Statement has been published

by the Nuclear Regulatory Commission as required by regulations. A

final statement will be issued later this year. The NRG is also preparing a safety evaluation report of the NBS submittals. In this connection

NBS provided extensive additional information to NRG to assist in their

review. A new license will be issued by the NRG, once the Environmental

Impact Statement and the Safety Evaluation Report are published. The new license authorizing increased power and valid for a period of 20

years is expected in early 1983.

Utilization of the reactor continued to be extensive and wide

ranging. More than 125,000 instrument hours involving 25 simultaneously

operable experimental facilities have been provided to more than 50

organizations from within and outside NBS.

1. Reactor Operations

Over the past year, the reactor was on-line nearly 80 percent

of the time and operating at full power 73 percent of the time. This

is about the maximum efficiency that can be achieved with the available

staff. Once again a remarkable improvement in fuel utilization efficiency

was realized by use of new higher loaded elements. An efficiency increase

of nearly 50 percent resulting in an average fuel burnup of 65 percent

is the best in the history of the facility and has already resulted in a significant fuel cost savings. A summary of the overall operating

statistics for the period July 1, 1981 to June 30, 1982 is presented in

the following table.

196
REACTOR OPEPATIONS AIJD SER'^^ICES

NBSR OPERATING SUMMARY FY 81

No. of days at 10 MW 268

On-line time at 10 MW 73%

Average U-235 burnup 65%

No. of Irradiations 3450

Hours of Irradiations 3100

Hours per Irradiation 0.9

2. Irradiation Service

Heavy utilization of the reactor for activation analysis and

irradiation services continued this year. The number of irradiations

increased by more than 30 percent. Tens of thousands of specimens,

involving foods, drugs, environmental monitoring, geological, and mineral

examinations, forensic investigation, and development of standard reference

materials were irradiated at the NBS reactor.

3. Engineering Services

In addition to regular engineering and design services provided to

reactor operations, experimenters, and users, the engineering staff was

involved in a comprehensive program of reactor modernization. The new

cooling tower is to be protected against fire by a new fire suppression

system for which a contract has been signed to initiate installation.

The water treatment building and loading ramp for chemical treatment of

the secondary water has been out for bid and is in the negotiation

stage. A contract to fabricate new shim arm poison blades has been let.

Tooling for this type of control rod was developed and used at Argonne

National Laboratory and will be used for this fabrication. Shim arm

yokes, arbors and bearings are in the process of fabrication. Redesign

of the regulating rod for 20 MW operation has begun which will provide a smoother and more reliable regulating rod operation. A new fuel element

contractor has been selected by POE and has made an NBSR prototype fuel

assembly and a production prototype. Fabrication of actual fuel assemblies

will begin when parts have been received from the sub-contractor.

197
REACTOR OPEPATIONS A.ND SERVICES

Extensive effort was expended to implement the modernization

program for the reactor instrumentation. This program replaces old

equipment with more modern reliable console readout devices. For example;

The miniature process recorders provide a faster response indication

with the benefit of easy to replace ink cartidges and a much simpler

chart roll cassette. The nuclear indication has been expanded to provide

the operator with a console meter for each power range and also provides

recorded information for both start-up channels and intermediate channels

continuously.

The replacement of the nuclear power supplies equal and surpass

requirements plus offer over current and over voltage protection. The

replacement of individual shim arm position indicators provide the

operator with a readout capability to 1/100 th of a degree.

198
D. Service Programs

NEUTRON ACTIVATION ANALYSIS AT THE FOOD AND DRUG ADMINISTRATION

W. B. Stroube, Jr. and W. C. Cunningham

(U. S. Food and Drug Administration, Washington, DC)

The Food and Drug Administration (FDA) maintains a neutron activation analysis (NAA) unit in the Reactor Building of the National

Bureau of Standards. The neutron activation program at FDA Includes

both research and analytical support for special projects. Work performed

during the past year ranged from routine FDA inter-laboratory quality

assurance programs to the study of Spanish cooking oil suspected of

being adulterated. Also, a major effort was devoted to the analysis of

composited food samples by INAA, The discussion below, which was presented in part at the Annual Meeting of the American Nuclear Society,

June 1982 (1), covers some of the findings of the later project.

Food composites were derived from the FY '80 FDA program known as the Total Diet Studies (2), which involves the collection and analysis of

foods for selected elements, pesticides and other chemical contaminants.

The types and amounts of food collected are based on a 1965 U.S. Department of Agriculture (USDA) survey of food consumed by infants (6 months

old), toddlers (2 years old), and adults (teenage male). (The ongoing

Total Diet Studies have recently been revised to include analysis of

individual foods and reflect current food comsumption data). For the NAA

analysis, the homogenized food composites were freeze dried and approximately 300 mg of each was packaged in a polyethylene bag for irradiation.

Because the food composites contained substantial amounts of water, the

portions analyzed actually represented up to five or six grams of the

food composite before freeze drying.

Calcium, CI, Mg, Mn, Na, and V were found at quantifiable levels

in nearly all samples of Cu and K were present at quantifiable levels

in many samples

.

The elemental abundance ranges for each element, based on wet weight, are given in Table 1. Because of the wide variety of sample matrices

199
SERVICE PROGPAIIS

TABLE 1. ELEMENT CONCENTRATION RANGES'^ IN

INFANT AND TODDLER FOOD COMPOSITES (PPM)

Ca 8 -- 10,000

CI 10 -- 14,000

Cu 0.06 -- 10

K 50 -- 10,000

Mg 5 -- 11,000

Mn 0.1 -- 25

V 0.01 -- 0.3

Na 30 -- 10,000

^Ranges are for food composites collected during FY'80.

TABLE 2. AVERAGE DIET COMPOSITION

COMPOSITE INFANT TODDLER

GRAM/ DAY GRAM/ DAY

1 Drinking Water 237 344

2 Whole Fresh Milk 643 508

3 Other Dairy & Dairy Substitutes 130 69

4 Meat, Fish & Poultry 47 125

5 Grain & Cereal Products 29 116

6 Potatoes 6 35

7 Vegetables 97 73

8 Fruit & Fruit Juices 127 142

9 Fats & Oils 5 14

10 Sugar & Adjuncts 11 30

11 Beverages 21 94

200
INFANT TODDLER

73.8% 64.8%

14.7 13.8

1.4 4.5

5.8 9.2

0.2 0.4

2.2 2.0

1.3 2.5

0.2 0.3

0.2 1.2

0.2 1.4

SERVICE PROGRAMS

TABLE 3. PERCENT INTAKE OF CALCIUM FOR EACH FOOD COMPOSITE

COMPOSITE

2 Whole Fresh Milk

3 Other Dairy & Dairy Substitutes

4 Meat, Fish & Poultry

5 Grain & Cereal Products

6 Potatoes

7 Vegetables

8 Fruit & Fruit Juices

9 Fats & Oils

10 Sugar & Adjuncts

11 Beverages

Total Calcium, MG/Day 905. 884.

(Table 2), it was difficult to standardize analysis conditions. However,

a set of standardized counting geometries relative to the Ge(Li) detectors,

and the same irradiation and counting periods were used for all samples, even though there were substantial total activity differences. Results

were based on multielement primary standards prepared at the FDA NAA

laboratory. For quality assurance purposes, standard precision was checked and accuracy was verified by analyzing several portions of

four different NBS biological Standard Reference Materials.

The elemental concentrations were converted to daily intakes using

USDA dietary survey consumption data (Table 2). Table 3 gives the

percentage intake of Ca from each food group for both infants and toddlers.

As predicted, elemental concentrations vary greatly between food groups

and the actual daily intake for each element is primarily attributable to

only a few of the food groups. For example, more than 3/4 of the Ca

daily intake comes from dairy products, whereas meats, grains and vegetables are the primary sources of Na.

201
SERVICE PROGRAllS

1. Transactions of the American Nuclear Society^ 41_, 204-206, 1982.

2. R.E. Duggan and F. J. MacFarland, Pestic. Monit. J., 1, 1-5, 1967,

U.S.G.S. ACTIVATION ANALYSIS PROGRAM

C. A. Palmer, G. A. Wandless, and L. J. Schwarz

(U.S. Geological Survey, Reston, VA)

1. Instrumental Neutron Activation Analysis

The comprehensive and highly automated INAA program at the U.S.

Geological Survey analyzes 3,000-4,000 rock and coal samples per year for

24-30 elements. Data provided from these samples are used in a wide

variety of geologic studies to support various geologists in their work.

In addition to routine analyses and special projects to support U.S.

Geological Survey geologists, the project is engaged in a number of

independent research projects. These are primarily in four areas:

(1) Trace elements in coal minerals (2) equipment and methods development, (3) INAA and radiochemistry of meteorites and lunar samples, and

(4) method development for radiochemical separations and applications to

terrestrial and extraterrestrial samples.

a. Trace Elements in Coal Minerals

A procedure has been developed for separating low temperature ash

from coal into size and density fractions, determining the mineral contents

of each fraction by x-ray diffraction analysis and scanning electron

microscopy and determining trace element content of each fraction by INAA.

A total of 39 elements were determined for these samples because the INAA

procedure was expanded to include short lived elements: Al, Ti, V, S, Ca,

Mg, Mn, CI, and Dy. Some fly ash separates were also determined in this manner. Additional INAA was performed on lithologic units of coal.

b. Equipment and Methods Development

Development of methods and equipment for INAA includes the interfacing

of optical bar code readers for sample identification to our automatic

202
SERVICE PROGRAMS

sample changers. A microcomputer system has been developed for laboratory

sample control, and our laboratory balance has been interfaced to the

computer. We are investigating the use of pelletization of rock samples

in cellulose nitrate for better control of sample counting geometry.

c. INAA of Meteorite Samples

The INAA procedure is being applied to the analysis of antarctic

iron meteorites in a cooperative program with the Smithsonian Museum of

Natural History. Small metal particles in chondritic meteorite samples

have been separated and analyzed by INAA to study the distribution of

siderophile elements. Meteoritic metal from lunar soils have been similarly

analysed to characterize the source of the metal.

2. Radiochemical Neutron Activation

a. Group Separations

i. Group separations of rare earth elements (REE) U.S.G.S. Standard

Rocks

The group separation method is being applied to U.S.G.S. standard

rocks in which REE abundances are near or below the limits of detection

of our INAA procedure. Group separation is being extended to include

the determination of Ba and Sr.

ii. Mafic and ultramafic rocks and separated minerals

We continue to supplement our INAA determinations by group

separations in those materials where REE abundances are very low.

b. Ultratrace Determinations of Siderophile and Volatile Elements in

Meteorites and in Lunar Rocks

i. Separations

An ion-exchange procedure was developed to separate and determine

Pt and Pd by RNAA.

ii. Lunar green glasses

We continue our study of surface-correlated enrichments of

volatile and siderophile on lunar green glasses. Bulk volatile and siderophile compositions of surface etched Apollo 15 green glasses (provided

by Roman Schmitt of Oregon State University) have been determined. Deter203
SERVICE PROGPAt^.S

mination of volatile and siderophlle element abundances of unetched green

glass specimens is nearing completion,

iii. Lunar ultramafic rocks

Analysis of a suite of lunar dunites for volatile and

siderophile elements is nearing completion.

1. R. S. Clarke, Jr., E. Jarosewich, J. C. Goldstein, and P. A. Baedecker,

"Antartic Iron Meteorites from Allan Hills and Purgatory Peak,"

Meteovitios 15^, 273-274.

2. G. A. Wandless and J. W. Morgan, "Analysis of Low Levels of Rare

Earths by Radiochemical Neutron Activation Analysis: I - Theoleiitic

Basalts," (to be submitted to Anal. Chim. Aota)

3. R. Kenneth Petrie and J. W. Morgan, "Union Exchange Separation of

Pt and Pd using Perchloric and Hydrochloric Acid Solution," in press,

Radioanl. Chem.

204
SERVICE ^ROGPAf^S

POSITRON ANNIHILATION IN Cu ALLOYS

L. M. Pecora and A. C. Ehrlich

(Naval Research Laboratory, Washington, DC)

We followed the same experimental methods as reported last year

to examine momentum densities (p(p)) ^ in Cu„„ ^Zn^ ^ and Cu_,^ZN_^ alloys

92.5 7.5 75 25

both in the (110) plane. The data from these experiments was combined

with previous runs and momentum densities for Cu, Zn (x=0.075, 0.15,

12 ^'"^ "" 0.25) were reconstructed ' fermiology of these alloys as well as CuGe

alloys of previous experiments were compared to each other as well as to

3 rigid band models based on Cu APW band calculations. Effects of other

possible band structure changes in the CuZn alloys p(p) were examined.

4 Findings were compared with CuGe and APW results.

1. Fermiology Findings

Using a method of normalization and scaling p(p) the Fermi radii

for the CuZn and CuGe alloys were calculated in the (110) plane (see

Refs. 5 and 6). 3D plots were then made of p vs and x (alloy

r electron/atom concentration) as in Figures 1 and 2, One can see the

usual trend in the alloys of p ongoing from [100] to [110] as is seen

r in Cu. The major differences occur in the CuGe alloys where the growth

of the Fermi surface is slower than rigid band and CuZn alloys and is even negative in some directions (e.g., 0=0, along [100].)

The second 3D plot of each figure shows the deviations from rigid

band predictions of the Fermi radii (p (alloy)-p^(rigid band)). These

P r show not only striking variations from what would be expected in a rigid band filling scheme, but also very similar patterns for all con- centrations of both alloys, although the absolute values are different.

The pattern of these deviations is one of starting from a value along

[100] (0-0°) reaching a maximum near [113] declining to a smaller value

near the neck, and increasing from the other side of the neck to the

1100] direction [0-90°].

In an effort to find if this behavior correlated with the

characteristics of the wave functions in the conducting band at E

F

205
SERVICE PROGRAMS

we examined the orbital characteristics of the APW wave functions of

Cu. One can see from figure 3 that the %d character of the wave functions

correlates well with the deviation of p (alloy) from p-p(rigid band).

r r In general the larger the d character of a wave function at k the

r more rapid the growth of the Fermi surface in that direction. We can only speculate at this point that somehow these parts of the conduction

band with greater d character are sinking with respect to other parts

as the solutes are added.

2. Other band structure changes

We examined the CuZn alloys for evidence of s-d hydridization

changes. ' We found that in the region of p(p) where the CuGe

alloys p(p)'s were shown to change upon addition of Ge, the CuZn alloys

p(p)'s changed only as expected from resolution effects, ' not from any

hybridization changes.

3. Publications and presentations

These results were presented at the March 1982 APS meeting in

Dallas, Texas as well as at the 6th International Conference on Positron

Annihilation in Ft. Worth, Texas.

Three publications have been submitted on this work and past

work . Two to the Physical Review ' and one (accepted) as part of

a conference proceedings:

(1) L. M. Pecora and A. C. Ehrlich, "Positron Annihilation in Cu

and aCuGe Alloys: I. General Results", submitted to Physical

Review B.

(2) A. C. Ehrlich and L. M. Pecora, "Positron Annihilation in Cu

and aCuGe Alloys: II. Fermiology and Band Structure Changes",

submitted to Physical Review B.

(3) L. M. Pecora and A. C. Ehrlich, "2D-ACAR-Reconstruction of

Momentum Densities in aCuZn and aCuGe Alloys" to be published

in Conference Proceedings" - 6th International Conference on Positron Annihilation, Ft. Worth, TX.

206
SERVICE PROGPJJ'S

[110]

[113]

[001]

Figure 1. p^ vs 9 for Cu, Ge (110).

F 1-x X

207
SERVICE PROGRAJIS

[110] Figure 2(a). Fermi radius vs. angle Cu^_ Zn (110).

• • CPA calculation.^ R. Prasad, et al . , Phys

Rev. 23, 2607 (1981)

208
SEP.VICE :°ROCRAMS

Figure 3. Percent orbital character of the conduction band wave

functions at E in Cu in the (110) plane.

F

1. L. M. Pecora and A. C. Ehrlich, NBS Tech. Note No. 1160 , p. 171,

F. Shorten, Ed. (1982).

2. L. M. Pecora and A. C. Ehrlich, Phys. Rev. B19, 719 (1979)

3. D. A. Papaconstantopoulos, et al, Phys. Rev. B15 , 4221 (1977)

4. L. M. Pecora and A. C. Ehrlich, Phys. Rev. Lett. 46, 1476 (1981)

5. L. M. Pecora and A. C. Ehrlich, submitted for publication to

Phys. Rev B

6. L. M. Pecora and A. C. Ehrlich, submitted for publication to

Phys. Rev B

7. L. M. Pecora and A. C. Ehrlich, Pvoaeedings of the 6th International Conference on Positron Annihilation, Ft. Worth, TX,

to be published.

209
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210
PERSOIMEL ROSTER

NON-RRD NBS STAFF LOCATED AT REACTOR

Division 354

J. Arras

p. Cassidy

D. Hoaney

I. Jensen

F. Moore

J. Shubiak

Division 532

R. A. Dallatore

C. Eisenhauer

D. Gilliam

J. A. Grundl

G. Lamaze

L. Li

E. McGarry

I. Schroder

R. Schwartz

W. Slater

V. Spiegel

Division 500

B. Carpenter

Division 551

R. Fleming

K. Fitzpatrick

S. Harrison

J. Langland

R. Lind Strom

G. Lutz

T. Mitlehner

M. Vinocur

J. Vogt

R. Zeisler

GUEST WORKERS AND COLLABORATORS

Division 506 Division 541

D. Becker

Division 520

E. Kessler

Division 522

R. Dove

Division 532

A. Wasson

Division 533

R. Placious

J. Kelly

Division 544

D. Tsai

Division 54 5

R. Cavanagh

Division 552

S. Wise

Division 553

H. Rook

211
PERSOmiEL ROSTER

Division 561 Food and Drug Administration

K. Rhyne

R. Roth

Division 562

E. Case

J. Early

R. Fields

E. Fuller

Division 563

E. Amis

R. Bowen

C. Han

T. Lodge

M. Mathew

S. Takagi

R. Waterstrat

Division 564

F. Biancanello

R. Reno

R. Shull

Aberdeen Proving Ground

C. Heimbach

Army Armament Research and

Development Command

C . Cho i

H. Prask

S . Trevino

Federal Bureau of Investigation

R. Asbery

R. Bilko

J. Haverkost

J. Kilty

R. Kostella

C. Peters

J. Riley

P. Tangren

W. Cunningham

W. Stroube, Jr.

J. Tanner

National Gallery of Art

B. Miller

C. Parkhurst

National Institutes of Health

D. Davies

R. Frank

Naval Research Laboratory

P. D'Antonio

A. Ehrlich

M. Fatemi

N. Koon

L. Pecora

Naval Surface Weapons Center

H. Alperin

M. Lia

G. Riel

R. Williams

Smithsonian Institution

M. Blackman

T. Chase

Y. Cheng

J. Mishara

J. Olin

LZacherman

U. S. Geological Survey

P. Baedecker

J. Morgan

G. Wandless

P. Thompson

212
PERSOMMEI, ROSTER

Argonne National Laboratory

T. Brun

0. Hinks

S. Susman

Battelle, N. W.

L. Brackenbush

G. Endres

W. Nicholson

Brookhaven National Laboratory

S. Shapiro

C.R.N.S. Grenoble, France

J. Hodeau

M. Marezio

Institute Laue-Langevin

Grenoble, France

A. Magerl

KFA Julich, Germany

D. Richter

Nuclear Energy Center, Mol, Belgium

A. Fabry

Oak Ridge National Laboratory

F. Kam

University of Alabama

J. Segrest

American University

J. Malamas

R- Segnan

Iowa State University

R. Shelton

Kyoto University (Japan)

H. Hasegawa

T. Hashimoto

H. Kawai

M.I.T.

BAverbach

L. Schioler

C. Skarda

B. Wuenscher

Northwestern University

J. Lasalle

L. Schwartz

Pennsylvania State University

L. Pilione

State University of New York

H. Herman

Technical University of Munich (Germany)

H. Wipf

University of Antwerp (Belgium)

K. Michel

University of California (Berkley)

R. Bragg

University of Connecticut

J. Budnick

213
PERSO>raEL ROSTER

University of Houston

S. Moss

University of Ife (Nigeria)

A. Oluwole

L. Kehinde

University of Illinois

H. Birnbaum

R. Chasnov

H. Zabel

University of Maryland

D. Anderson

A. Bagheri

D. Ballantine

D. DeMers

D. Delozier

D. Finnegan

S. Fuller

I

Gokmen

F. Geunther

D Herman

M. Kitto

W. Linthicum

I. Olmer

J. Parrington

J. Phelan

J. Robertson

C. Stone

P. Sheridan

C. Thompson

G. Tuncel

W. Walters

W. Zoller

University of Missouri (Columbia)

D. Alger

W. James

University of Pittsburgh

R. Buttera

S. Malik

H. Smith

W. Wallace

University of Rhode Island

S. Pickart

University of Wisconsin

J. Hinkley

H. Yu

Allied Corporation

G. Fish

R. Hasegawa

A. Maeland

Bell Laboratories

R . Cava

C

Chen

B-K Dynamics

N. Chesser

E. I. DuPont de Nemours Co.

J. Parise

Exxon

D. Lohse

Metronic , Inc

P. Skarstad

3M Research Laboratory

A. Siedle

214
PERSOWJEL ROSTER

Sandia Corporation

J. Harris

Union Carbide Corporation

E. Goddard

Westinghouse-Hanford Corp.

W. McElroy

J. Rawlins

215
F. Publications

COLLABORATIVE PROGRAMS

ALEFELD, B. , ANDERSON, D. S., HEIDEMANN, A., MAGERL, A., and TREVINO, S. F.

"The Measurement of Tunnel States in Solid CHoN02 and CD^NO^" J. Chem.

Phys. (Letter to the Editor) 7_6, 2758 (1982).

AMMON, H. L. , MURPHY, K. C. , SJOLIN, L. , WLODAWER, A., HOLCENBERG, J. S.,

and ROBERTS, J. "The Molecular Symmetry of Gluatminase-Asparaginases

Rotation Function Studies of the Pseudomonas 7A and Acinetobacter

Enzymes," Acta Cvyst. (in press).

BERK, N. F. , ROSENTHAL, J., and YARMUS, L. , "Spin Relaxation of Triplet

Excitons in Molecular Crystals," Phys. Rev. B (in press).

BRUN, T. 0., SUSMAN, S., ROWE, J. M. , and RUSH, J. J., "Quasielastic

Neutron Scattering Study of Ionic Diffusion in 6-LiAl," Solid State

Ionics 5^, 417 (1981).

CASELLA, R. C., "Theory of Neutron Scattering from Hydrogen in Metals

Involving Transitions to Excited Tunnel Split States," Phys. Rev. B24 , 2913-2920 (1981).

CASELLA, R. C, "Detection of Impurity Tunneling in Solids Via Coherent

Phonon Coupling and Direct Neutron Scattering," J. Phys. i\2_, C6-923-

C6-925 (1981).

CASELLA, R. C, "Relations Between Fermion Masses from Effective Potentials

in Internal Space," II Nuovo Aimento 67A, 289-297 (1982).

CAVA, R. J., HIMES, V. L. , MIGHELL, A. D., and ROTH, R. S., "FeNb Se : A

New Structure Type Related to NbSe3," Phys. Rev. B24, 3634-3637

(1981).

CAVA, R. J., SANTORQ, A., MURPHY, D. W. , ROTH, R. S,, and ZAHURAK, S,,

"The Structures of Lithium-Inserted Metal-Oxides: LiRe03 and Li2Re03"

J. Sol. St. Chem. 42, 251-262 (1982).

CAVANAGH, R. , KELLEY, R. D., and RUSH, J. J., "Neutron Vibrational

Spectroscopy of Hydrogen and Deuterium on Raney Nickel," J. Chem. Phys.

(in press)

CHEN, H. S., LYNN, J. W. , ERWIN, R. W. , and RHYNE, J. J., "Spin Wave

Excitations in Re-Entry Para-Fero-Spin Class Transition in Glassy

(FexNi]^_x)7 5Pi5B5Al3 Glasses," Proc . of the 4th Intl. Conf . on Rapidly Quenched Metals, 1153-1156 (1981).

216
PUBLICATIOIIS

CHOI, C. S. and PRASK, H. J., "Single Crystal Neutron Diffraction Study

of Ammonium Nitrate Phase III," Acta Cryst. (in press).

CHOI, C. S. and MIGHELL, A. D., "Neutron Diffraction Study of Sodium

Sesquicarbonate Dihydrate," Acta Cryst. (in press).

CLAUSEN, K., RHYNE, J. J., LEBECH, B., and KOON, N. C. , "Temperature

Dependence of the Spin-Waves in ErFe , " J. Phys. C15 , 3587 (1982).

COHEN, J. S. and WLODAWER, A., "Diffraction and NMR Studies of Proteins; an Uneasy Alliance," Trans, in Biochemical Sciences (in press).

D'ANTONIO, P., KONNERT, J. H. , RHYNE, J. J., and HUBBARD, C. R. , "Structural

Ordering in Amorphous TbEe^ and YFe2," J. AppZ. Cryst. (in press).

DOHERTY, R. M. , STEWART, J. M. , MIGHELL, A. D., HUBBARD, C. R. , and

FATIADI, A. J., "The Structure of the 1:1 Molecular Complex of

Pyrene and Dicyanomethylenecroconate, " Acta Cryst. B38 , 859-863 (1982).

FERRICK, J. H., RHYNE, J. J., and SEGNAN, R. , "Bulk Magnetization of

Dysprosi-um-Scandium Alloys," J. Appl. Phys. _53, 2232-2234 (1982).

GLINKA C. J., "The National Bureau of Standards Small-Angle Neutron

Scattering Spectrometer," Proc. of the Conf. on Neutron Scattering

(in press)

GLINKA, C. J. and BERK, N. F. , "The Two Dimensional Position-Sensitive

Detector at the National Bureau of Standards SANS Facility," Proc.

of the Workshop on Position-Sensitive Detectors (in press).

HARDMAN, K. , RHYNE, J. J., PRINCE, E. , SMITH, H. K. , MALIK, S. K.

,

WALLACE, W. E., "Magnetic and Structural Properties of Th5Mn23D and

Y6Mn23D^," The Rare Earths in Modem Science and Technology^ Vol. Illy

edited By G. McCarthy, H. Silber, and J. Rhyne, Plenum Press, New

York, pp. 477 (1982).

HARDMAN, K. , RHYNE, J., MALIK, S., and WALLACE, W. E., "Site Magnetization

of Cubic and Hexagonal HoMn2," J. Appl. Phys. 53, 1944-1946 (1982).

HIMES, V. L. , MIGHELL, A. D., and DECAMP, W. H. , "Structure of Carbamazepine:

5H-Dibenz[b,f]azepine-5-carboxamide," Acta Cryst. B37 , 2242-2245 (1981).

HIMES, V. L., MIGHELL, A. D., PAGE, S. W., and STACK, M. E., "Structure

of Xanthomegnin," Acta Cryst. B37, 1932-1935 (1981).

HIMES, V. L., MIGHELL, A. D., STALICK, J. K. , and ZON, G. , "Structure of

Racemic cis-4-Phenylcyclophosphamide," Acta Cryst. B38, 1009-1012 (1982).

217
PUBLICATIO^TS

HIMES, V. L., MIGHELL, A. D., and SIEDLE, A. R. , "Synthesis and Structure

of Cu5(BTA)5(jt-C4H9NC)4, a Mixed-Valent Copper-Nitrogen Cluster

Containing n^-Benzotriazolate, " J. Am. Chem. Soc. 103 , 211-212 (1981).

HIMES, V. L. and MIGHELL, A. D. , "A Matrix Method for Lattice Symmetry

Determination," Acta Cvyst. A (in press).

HODEAU, J. L., MAREZIO, M. , SANTORO, A., and ROTH, R. S., "Neutron Profile

Refinement of the Structures of Li2Sn03 and Li2Zr03," J. Sol. St. Chem.

(in press)

.

LYNN, J. W. , SHELTON, R. N. , HORNIG, H. E., and GLINKA, C. J., "Investigation

of the Magnetic and Superconducting Properties of Er2^_j^Ho^)Rh^B^,

Physica B (in press)

.

LYNN, J. W. , ERWIN, R. W. , RHYNE, J. J., and CHEN, H. S., "Ferromagnetic

and Spin Glass Behavior Near the Critical Concentration in Amorphous

(Fej^Ni]^_j^)73G25," J. Mag. Magnetic Mtls. (in press).

LYNN, J. W. , ERWIN, R. W. , CHEN, H. S. , and RHYNE, J. J., "Evolution from

Ferromagnetism to Spin-Glass Behavior," Phys. Rev. Lett, (in press).

LYNN, J. W., RHYNE, J. J., and BUDNICK, J. I., "Observation of Spin-Waves

in Pd (1.5% Fe)," J. Appl. Phys. _53, 1982 (1982).

MAGERL, A., ROWE, J. M. , RUSH, J. J., WIPE, H., and RICHTER, D., "Influence

of Impurities on Local Hydrogen Vibrations in a Niobium Host Lattice,"

Intl. Symp. on the Electronic Structure and Properties of Hydrogen in

Metals (in press).

MAGERL, A., RUSH, J. J., ROWE, J. M. , RICHTER, Vs., and WIPE, H. , "Local

Hydrogen Vibrations in Nb in the Presence of Interstitial (N,0) and

Substitutional (V) Impurities," Phys. Rev. B (in press).

NICHOLSON, W. L., PRINCE, E. , BUCHANAN, J., and TUCKER, P., "A Robust/

Resistant Technique for Crystal Structure Refinement," Progress and

Problems in Cry staliographic Statistics^ A. J. C. Wilson, ed..

International Union of Crystallography (in press).

PRASK, H. J. and CHOI, C. S., "Texture, NDE Characterization 420/00089,"

Encyclopedia of Materials Science and Engineering (in press).

PRINCE, E. and NICHOLSON, W. L. , "A Test of a Robust/Resistant Refinement

Procedure on Synthetic Data Sets," Acta Cryst. A (in press).

PRINCE, E. , "Comparison of Profile and Integrated Intensity Methods in

Powder Refinement," J. Appl. Cryst. 14, 157-159 (1981).

218
PUBLICATIONS

PRINCE, E., "Mathematical Techniques in Crystallography and Materials

Science," Springer-Verlag, New York, 192 pp. (1982).

PRINCE, E., "Comparison of the Fits of Two Models to the Same Data Set,"

Acta Cryst. B38, 1099-1100 (1982).

RHYNE, J., HARDMAN, K. , MALIK, S., and WALLACE, W. , "Magnetic Properties

of Cubic and Hexagonal HoMn , " J. Appl. Phys. 53^, 1944 (1982).

RHYNE, J. J., FISH, G. E. , and LYNN, J. W. , "Spin Waves in Amorphous

^^1-x^x Alloys," J. Appl. Phys. 53, 2316-2318 (1982).

ROSENTHAL, J., YARMUS , L. , and BERK, N. F. , "Comments on "Triplet-Exciton

Annihilation and Triplet Spin Relaxation in Molecular Crystals,"

Phys. Rev. B24, 1103-1105 (1981).

ROWE, J. M., RUSH, J. J., and MICHEL, K. H. , "Comment on Dielectric

Susceptibility Measurements in (KCN)x(KBr)]^_x Mixed Crystals,"

Phys. Rev. Lett, (in press).

RUSH, J. J., MAGERL, A., ROWE, J. M. , HARRIS, J. M. , and PROVO, J. L.

,

"Tritixim Vibrations in Niobium by Neutron Spectroscopy," Phys. Rev.

B24, 4903-4905 (1981).

SANTORO, A., CAVA, R. J., MURPHY, D. W. , and ROTH, R. S., "Use of the

Pearson Type VII Distribution in the Neutron Profile Refinement of

the Structures of LiRe03 and Li2Re03," Proa, of the Symposium on Neutron Scattering (in press).

SANTORO, A., ROTH, R. S., and AUSTIN, M. , "Powder Neutron Diffraction Study

of the Nonstoichiometric Solid Solution of Lithium Tantalate 9LiTa03: Ta205,

Acta Cryst. B38, 1093-1098 (1982).

SANTORO, A., "New Developments in Neutron Powder Profile Analysis,"

Proa, of the Italian-Yugoslavian Joint Meeting (in press).

SJOLIN, L. and WLODAWER, A. , "Improved Technique for Peak Integration for

Crystallographic Data Collected with Position-Sensitive Detectors:

A Dynamic Mask Procedure," Acta Cryst. k2>l , 594-604 (1981).

SUSMAN, S., DELBECQ, C. J., BRUN, T. 0., and PRINCE, E., "Structure and

Conductivity of the NASICON Analog Na3Sc2 (P04)3, " Proa, of the Symp. on Solid Electrolytes (in press), Montreal, Canada (1982).

THOMLINSON, W. , SHIRANE, G. , LYNN, J. W. , and MONCTON, D. , "Neutron

Scattering Study of Magnetic Ordering in Ternary Superconductors,"

Superconductivity in Ternary Compounds, ed . by 0. Fischer and N. B. Maple,

Springer-Verlag, Topics in Current Physios Series^ Vol. 2 (1982).

219
PUBLICATIONS

TSAI, D. H. and TREVINO, S. F., "Thermal Relaxation in a Dense Liquid

Under Shock Compression," Phys. Rev. A2A_, 2743 (1981).

WLODAWER, A., "Neutron Diffraction of Crystalline Proteins," Fvogvess

in Biophysics and Moleaulaj' Biology^ T. Blundell, ed., Pergamon Press

Ltd: Oxford, England (in press).

WLODAWER, A., "A Facility for Data Collection and Processing at the

National Bureau of Standards Reactor," Methods in Enzymology^ H. W.

Wyckoff, C. H. W. Hirs, and S. N. Timasheff, eds.. Academic Press:

New York (in press).

WLODAWER, A. and SJOLIN, L. , "Improvement of the Quality of the Data

Collected Using a Position-Sensitive Detector," Nucl. Instrum. Methods

(in press)

WLODAWER, A. and SJOLIN, L. , "Application of Joint Neutron and X-ray

Refinement to the Investigation of the Structure of Ribonuclease A o ° at 2.0 A Resolution," Brookhax>en Symposia in Biology, Upton, NY,

Plenum Press (1982)

WLODAWER, A. and SJOLIN, L. , "Hydrogen Exchange in RNase A: Neutron

Diffraction Study," Fvoc. Natl. Aoad. Sai. USA 79_, 1418-1422 (1982).

WLODAWER, A. and HENDRICKSON, W. A., "A Procedure for Joint Refinement

of Macromolecular Structures with X-ray and Neutron Diffraction Data

from Single Crystals," Aata Cryst. A38_, 239-247 (1982).

WLODAWER, A., BOTT, R. , and SJOLIN, L., "The Refined Crystal Structure

of Ribonuclease A at 2.0 A Resolution," J. Biol. Chem. 251 , 1325-1332

(1982).

WLODAWER, A., SJOLIN, L., and SANTORO, A., "Refinement of the Crystal

Orientation Matrix for the Flat-Cone Dif fractometer, " J. Appl. Cryst.

15, 79-81 (1982).

220
PUBLICATION?

INDEPENDENT PROGRAMS

ANDERSON, D. L. , ZOLLER, W. H. , GORDON, G. E., WALTERS, W. B., and

LINDSTROM, R. M. , "Neutron-Capture Prompt y-R^y Spectroscopy as a Quantitative Analytical Method," N&utron-Capture Gamma-Ray Spectroscopy

(in press)

.

ANDERSON, D. L. , PHELAN, J. M. , VOSSLER, T., and ZOLLER, W. H. , "NeutronCapture Prompt Gamma-Ray Analysis of Stratospheric and Groundfall Ash

Following the Mt. St. Helens Eruption of May 18, 1980," J. Radioanal.

Chem. n., 47-58 (1982).

ANDERSON, D. L. , FAILEY, M. P., ZOLLER, W. H. , WALTERS, W. B., GORDON, G. E.,

and LINDSTROM, R. M. , "Facility for Nondestructive Analysis for Major

and Trace Elements Using Neutron-Capture y-Ray Spectrometry," J.

Radioanal. Chem. _63, 97-119 (1981).

CUNNINGHAM, W. C. and ZOLLER, W. H., "The Chemical Composition of Remote

Area Aerosols," J. Aerosol Sai. 12, 367-384 (1981).

FLEMING, R. F. , "Neutron Self -Shielding Factors for Simple Geometries,"

(submitted for publication)

.

FLEMING, R. F. and LINDSTROM, R. M. , "Limitations on the Accuracy of

Sulfur Determination by NAA," Trans, Am. Nucl. Soc. 41, 223 (1982).

GORDON, G. E., GOKMEN, I., ARAS , N. K. , and HENKIN, R. I., "The Use of

Stable Isotope Tracers in the Study of Zinc and Selenium Nutrition

in Infants," J. Radioanal. Chem. 70, 145-161 (1982).

GREENBERG, R. R. and KINGSTON, H. M. , "Trace Element Analysis of Natural

Water Samples Using Neutron Activation Analysis and Chelation

Chromatography," (submitted for publication).

GREENBERG, R. R. and KINGSTON, H. M. , "Simultaneous Determination of

Twelve Trace Elements in Estuarine and Sea Water Using Pre-Irradiation

Chromatography," J. Radioanalytical Chem. 7_1, 147 (1982).

GREENBERG, R. R. , KINGSTON, H. M. , and RAINS, T. C, "Trace Elemental

Characterization of the Chesapeake Bay Water Column," Transactions

of fne American Nuclear Society 4_1, 201 (1982).

GREENBERG, R. R. , ZOLLER, W. H. , and GORDON, G. E., "Atmospheric

Emissions of Elements on Particles from the Parkway Sewage-Sludge

Incinerator," Environ. Sci. Technol. 15, 64 (1981).

221
PUBLICATIONS

HARRISON, S. H. and ZEISLER, R. , "Distribution of Pollutant and Essential

Elements in Human Livers," Trans. Am. Nual. Soa. 41, 209 (1982).

KINGSTON, H. M. and LUTZ, G. J., "Adsorption and Stability Prior to

Analysis of Simulated Nuclear Waste Leachate," (in press).

KINGSTON, H. M. , GREENBERG, R. R. , BEARY , E. S., HARDAS , B. R., MOODY, J. R.

,

and RAINS, T. C. , "The Characterization of the Chesapeake Bay: A

Systematic Analysis of Toxic Trace Elements," (submitted for publication).

KOWALCZYK, G. S., GORDON, G. E., and RHEINGROVER, S. W. , "Identification

of Atmospheric Particulate Sources in Washington, DC Using Chemical

Element Balances," Environ. Sci. Teahnol. 16, 7 9-90 (1982).

ONDOV, J. M., ZOLLER, W. H. , and GORDON, G. E., "Trace Element Emissions

on Aerosols from Motor Vehicles," Environ. Sci. Teehnol. 16^, 318-328

(1982).

PARRINGTON, J. R. , ARAS , N. K. , and ZOLLER, W. H. , "Asian Dust: Seasonal

Transport to the Hawaiian Island," (submitted to Science).

PHELAN, J. M. , FINNEGAN, D. L. , BALLANTINE, D. S., ZOLLER, W. H. , HART, M. A.

and MOYERS , J. L. , "Airborne Aerosol Measurements in the Quiescent

Plume of Mount St. Helens: September, 1980," Geophys. Lett. , (in

press)

VOSSLER, T., ANDERSON, D. L. , ARAS, N. K. , PHELAN, J. M. , and ZOLLER, W. H.

,

"Trace Element Composition of the Mt . St. Hellens Plume: Stratospheric

Samples from the May 18th Eruption," Soienoe 208 , 827-830 (1981).

WISE, S. A., FITZPATRICK, K. A., HARRISON, S. H. , and ZEISLER, R.

,

"Operation of the U.S. Pilot National Environmental Specimen Bank

Program," Proc. Intern. Workshop on Environmental Specimen Banking

and Monitoring as Related to Banking, Saarbrucken, FRG, May 10-15,

1982 (in press)

ZEISLER, R. , HARRISON, S. H., and QIAW, S. A., "Analysis of Human Liver

Specimens in the U.S. Pilot National Environmental Specimen Bank Program,"

Proc. Intern. Workshop on Environmental Specimen Banking and Monitoring

as Related to Banking, Saarbrucken, FRG, May 15, 1982 (in press).

ZEISLER, R. and GREENBERG, R. R. , "Ultratrace Determination of Platinum

in Biological Materials Via Neutron Activation and Radiochemical

Separation," (in press).

ZEISLER, R. and GREENBERG, R. R. , "Procedure for the Determination of

the Platinum Baseline in Biological Materials," Trans. Am. Nuol. Soo.

41, 219 (1982).

222
NBS-114A IREV. 2-8C) U.S. DEPT. OF COMM. BIBLIOGRAPHIC DATA

SHEET {See instructions)

1. PUBLICATION OR

REPORT NO. NBS TO 1178

2. Performing Organ. Report No. 3. Publication Date June 1983

4. TITLE AND SUBTITLE

NBS Reactor: Summary of Activities July 1981 through June 1982

5. AUTHOR(S)

F. Shorten, Editor

6. PERFORMING ORGANIZATION (If joint or other than NBS. see instructions)

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

7. Contract/Grant No.

8. Type of Report & Period Covered

July 1981-June 1982

9. SPONSORING ORGANIZATION NAME AND COMPLETE ADDRESS (Street. City. State. ZIP)

National Bureau of Standards

Department of Commerce

Washington, DC 20234

10. SUPPLEMENTARY NOTES

I I Document describes a computer program; SF-I8S, FlPS Software Summary, is attached.

11. ABSTRACT (A 200-word or less factual surrtmary of most significant information. If document includes a significant

bibliography or literature survey, mention it here) This report summarizes all those programs which depend on the NBS reactor.

It covers the period from July 1981 through June 1982. The programs range from

the use of neutron beams to study the structure and dynamics of materials through

nuclear physics and neutron standards to sample irradiations for activation

analysis, isotope production, radiation effects studies, neutron radiography,

and nondestructive evaluation.

12. KEY WORDS (Six to twelve entries; alphabetical order; capitalize only proper names; and separate key words by semicolons)

Activation analysis; crystal structure; diffraction; isotopes; molecular dynamics;

neutron; neutron radiography; nondestructive evaluation; nuclear reactor; radiation

13. AVAILABILITY

I xl Unlimited

I I For Official Distribution. Do Not Release to NTIS

[x~l Order From Superintendent of Documents, U.S. Government Printing Office, Washington, D.C.

20402.

I I Order From National Technical Information Service (NTIS), Springfield, VA. 22161

14. NO, OF

PRINTED PAGES

231

15. Price

$6.50

USCOMM-DC 6043-P80

* U.S. GOVERNMENT PRINTING OFFICE: 1983-0-380-997/5064

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