REFERENCE

NBS

Publications

NATL INST. OF STAND i TECH R.I.C.

AlllDM bSVEbS

\

ii 'i-."'-

^'"feAU o* ^./

NBS TECHNICAL NOTE 1 1 90

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

w

NBS Reactor:

Summary of Activities

July 1982 Through

June 1983

-QC —

IGG

.U5753

No. 1190

19J4

i'
NATIONAL BUREAU OF STANDARDS

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

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

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

the Institute for Computer Sciences and Technology.

THE NATIONAL MEASUREMENT LABORATORY provides the national system of

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

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

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

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

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

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

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

calibration services. The Laboratory consists of the following centers:

Absolute Physical Quantities' — Radiation Research — Chemical Physics —

Analytical Chemistry — Materials Science

THE NATIONAL ENGINEERING LABORATORY provides technology and technical ser- vices to the public and private sectors to address national needs and to solve national problems; conducts research in engineering and applied science in support of these efforts; builds and maintains competence in the necessary 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 EngineeringTHE 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 Gailhersburg, MD, unless otherwise noted; mailing address Washington, DC 20234. 'Some divisions within the center are located at Boulder, CO 80303.
NA-:iONAL BUREAU OF STANDASDS

LIBR'ARY NBS Reactor:

Summary of Activities ^^

Juiy 1982 Through '^o

June 1983 — ^f^f^^ No . 1 1 9 c

Frederick J. Shorten, Editor

Reactor Radiation Division

National Measurement Laboratory

National Bureau of Standards

Washington, DC 20234

^'"JfAU Of

Q*

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

NATIONAL BUREAU OF STANDARDS, Ernest Ambler, Director

Issued April 1 984
National Bureau of Standards Technical Note 1 1 90

Natl. Bur. Stand. (U.S.), Tech. Note 11 90, 202 pages (Apr. 1984)

CODEN: NBTNAE

U.S. Government Printing Office

Washington: 1984

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

The National Bureau of Standards Reactor was built not only to serve the needs

of the NBS but also those of other government agencies as a National Center for the

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

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

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

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

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

sophisticated experimental facilities, they actively seek out and encourage

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

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

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

other technical services.

The reactor 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 Division which requires no collaboration with Division scientists. The

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

but for which the Division provides irradiation services. The remaining sections are self-explanatory

.

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

his extensive contributions to the editing, organization, and preparation of this

report, and T. Lindstrom, P. Andrew, S. Long, S. Tassey, and N. Rhyne for efforts in

typing manuscripts.

ft.yi> ^L^-^

R. S. Carter

Chief, Reactor Radiation Division

National Bureau of Standards

XXI
ABSTRACT

This report summarizes all those programs which depend on the NBS reactor. It covers the period from July 1982 through June 1983. The programs range from the use

of neutron beams to study the structure and dynamics of materials through nuclear

physics and neutron standards to sample irradiations for activation analysis, isotope

production, radiation effects studies, neutron radiography, and nondestructive

evaluation.

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

dynamics; neutron; neutron radiography; nondestructive evaluation;

nuclear reactor; radiation.

DISCLAIMER

Certain trade names and company products are identified in order to adequately

specify the experiment procedure. In no case does such identification imply

recommendation or endorsement by the National Bureau of Standards, nor does it imply

that the products are necessarily the best available for the purpose.

IV
TABLE OF CONTENTS

FOREWORD iii

ABSTRACT iv

A. REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS ..... 1 The Effect of Slit Height on Peak Positions, Widths, and Shapes in

Powder Diffraction 1 The Structure of La^WO.Cl_ 3

3 6 3

Study of Hydrogen Bonds in Ca KH (PO.). 2H 4

Structure Studies of the Superionic Conductor System NA, Zr„Si P_ 0,^

1 +x 2 X 3-x 1

2

(NASICON) 9

The Structures of Lithium Inserted Metal Oxides; Li„FeV_Oo 12

2 3 o Neutron and X-Ray Diffraction Study on Polymorphism in Lithium

Orthotantalate Li TaO^ U

The Crystal Structure of Lithium Zirconate, Li,Zr^O„ 18

2 I Studies of Zeolite Structure by Neutron Powder Diffraction 21 The Structure of Synthetic Zeolite Omega 25

Active Site of RNase: Neutron Diffraction Study of a Complex with

Uridine Vanadate, A Transition State Analog 26

Microvoid Formation in Ammonium Nitrate 29

Nondestructive Characterization of Sub-Surface Residual Stress 31

Crystal Data (Produced by Automated Typesetting Procedures) 3^

Progress Report on a Study of Specialized Lattices Using Matrix and

Reduction Techniques 36

Space Group Frequencies for Organic Compounds 39

An Empirical Method for the Approximation of Densities 52

Thermal Properties of (KCN) (KBr) in the Quadrupolar Glass State ... 56

•X. I X structure of Alkali Cyanide and Mixed Alkali Cyanide-Alkali Halide

Crystals 57

Critical Behavior and Magnetic Ordering in Amorphous TbFe^ 59

Short Range Magnetic Ordering in Y^(Fe, Mn )^^ 61

6 1 -X X 23

Deuterium Site Occupation and Magnetism in Ho^Fe D Compounds 63

Spin Dynamics of Fe^ Ni^^P ^B, 65

Reentrant Spin Glass Behavior in Amorphous (Fe Ni,^^ )^^G1^^ 68

X 100-x 75 25

Spin Dynamics of Dilute Pd._ Fe Ferromagnets 71

I A X Magnetic Phase Transition in the Superconductor HoMoz-Seg 72
TABLE OF CONTENTS

Magnetic and Superconducting Properties of Ho Rich (Er, Ho )Rh,,B,, .... 7^

Critical Fluctuations in the Ferromagnetic Superconductor HoMo^So .... 77

D o Advanced Neutron Methods 79

Small Angle Scattering from Ferrofluids 81 Characterizing Microporosity of Chemical Adsorbents by Small Angle

Neutron Scattering 83

SANS Investigations of Porosity in YCRO Ceramics 84

Small Angle Neutron Scattering (SANS) Study of Creep Damage in 304

Stainless Steel 86

Uniaxial Deformation of Rubber Network Chains by Small Angle Neutron

Scattering 94

Small Angle Scattering from Amorphous DyCu 95

Generalized Theory of Neutron Scattering from Hydrogen in Metals 96

Theory of Excitation Bands of Hydrogen in Metals and of Their

Observation by Neutron Scattering 99

Theory of Hydrogen Trapping by Interstitial Impurities in bcc Metals ... 103

Theory of SANS from Large Particles and Voids 105

Neutron Diffraction Structure Determination of the High-Temperature

Form of Lithium Tritantalate, H-LiTa^Oo 106

3 o

B. NON-RRD PROGRAMS 108

Activation Analysis Group FY 83 108

Atmospheric and Environmental Studies by Instrumental Neutron

Activation Analysis 139

Validation of Stable Isotope Tracing for Study of Zinc Nutrition

in Human Subjects 146

Neutron-Capture Prompt Gamma-Ray Activation Analysis 147

High Accuracy Determination of U-235 by Gamma-R'=<v Spectroscopy in

Nondestructive Assay Standards 154

Summary of Activities Carried out by the Neutron Field Standards Group . . 156

Fission Cross Section Measurements in Reactor Physics and Dosimetry

Benchmarks at NBS 1 60

235 Integral Cross Section Measurements in the U Fission Neutron

Spectrum 163

Neutron Personnel Dosimeter Calibrations and Testing 167

Range of Individual Fission Fragments in Matter 168

VI
TABLE OF CONTENTS

C. REACTOR OPERATIONS AND SERVICES 169

D. SERVICES PROGRAMS 171

Neutron Activation Analysis at the Food and Drug Administration 171

Positron Annihilation in GuGe and GuZn Alloys 175

E. PERSONNEL ROSTER 1 80

F. PUBLICATIONS 186

Vll

A. Reactor Radiation Division and Collaborative Programs

THE EFFECT OF SLIT HEIGHT ON PEAK POSITIONS, WIDTHS, AND SHAPES IN POWDER DIFFRACTION

E. Prince

1 2 It is well known ' that expressions giving peak positions, widths, and shapes

in powder diffraction as functions of wavelength, cell constants, and instrumental

resolution depend on approximations that are valid only if the axial extent of the

instrumental resolution function is inf initesimally small. Because a real instrument

must have a finite slit height, and because the actual scattered radiation for a particular Bragg reflection comes out in a cone with semiangle 26, the expressions

are strictly correct only for 26 = 90°, and they must be corrected for diffraction at

other angles. For 26 < 90°, the peak centroid is shifted toward lower angles, the

peak is broadened, and an otherwise symmetric peak becomes skewed with a longer tail

on the low angle side than on the high angle side. The mathematical analysis of

these effects has much in common with another problem in crystallography, the

probability distribution for an atomic position when thermal motion is curvilinear.

Figure 1 shows schematically a segment of a Debye-Scherrer ring as seen through

a slit of finite height. A point on the ring at height z is displaced toward the

center of the ring by an amount A = r(1 - cos a), where r is the radius of curvature

of the ring, and is given by r = R tan 26, where R is the distance from the sample to

the detector slit. If a is sufficier

angular displacement of the point is

2 2 2 the detector slit. If a is sufficiently small, (1 - cos a) ~ a /2 ~ z /2r . The

6 = -(z^/2R^)cot 26. (1)

The angular displacement of the peak is obtained by averaging 6 over the vertical

resolution function of the diffractometer

<6> =. -(<z2>/2r2) -(<z^>/2R'']cot 26, (2)

2 2 where <z > = z p(z)dz, and p(z) is the vertical resolution function. The peak is

broadened so that its variance is given by

0^ = 0^ + <6^> - <6>^, (3)

b o
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRA^IS

2 2 4 4 2

where o is the variance of the unbroadened peak and <6 > = (<z >/4r )cot 26. A

o Gaussian peak becomes skewed so that the shape function becomes

P(2e) 1 + (^k/6)H. (26 - 26^ - <6> /o^

B b 0(26, 26^ + <6>, 0, ), D D (4)

3 2-1/2 2 2 where H_(x) = x - 3x , G(x, y, o) = (2 o ) exp -(1/2)(x - u )/o , 26^ is the

3

3 B

Bragg angle for the unshifted peak, and k is a third cumulant given by k = <6 > - 2 3 3<6 ><6> + 2<6> .

Figure 1 . The effective Bragg position of points on a Debye-Scherrer ring above and

below the horizontal plane of the dif fractometer

.

1. A. J. C. Wilson, "Mathematical Theory of X-ray Powder Dif fractometry," p. 70-76,

Eindhoven: Physics Technical Library (1963).

2. M. J. Cooper and J. P. Sayer, J. Appl. Cryst. 8_, 615-618 (1975).
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

THE STRUCTURE OF La^WO^Cl^

3 D 3

J. B. Parise and L. H. Brixner

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

and

E. Prince

1 An x-ray determination of the structure of La-WO^Cl_ found that the tungsten

3 6 3 coordination polyhedron was a highly unusual trigonal prism instead of an octahedron.

Cohesive energy calculations also indicated that this configuration should be

energetically unfavorable. Because of this and also that the fact that the x-ray

intensities tend to be dominated by the heavy metals, there was some doubt about the

correctness of the crystal structure, so a neutron powder diffraction study was

undertaken to verify it.

Neutron powder diffraction data were collected on the NBS high-resolution

2 powder dif f ractometer , and the structure was refined by the Rietveld method to

R = 9.13 percent, as compared with R = 7.14 percent. R^, based on integrated

wp e B

intensities, was 6.00 percent. The trigonal prismatic coordination of the tungsten

was confirmed. Table 1 gives the refined atomic parameters. Figure 1 shows the

coordinations for W and La.

Figure 1. (a) The tungsten environment in La WO^Cl , in La_WO.Cl^. 3

o 3 3 6 3

(b) The lanthanum environment
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

Table 1. Refined atomic parameters for La WOgCl . Standard deviations for the least

significant figures are given in parenthesis

a = 9.4092(2), c = 5.4276(2) L

The space group is P5 /m,

Atom

La

W

CI

0.0896(3)

1/3

0.2399(2)

0.3627(3)

0.6843(3)

2/3

0.0474(3)

0.8370(3)

z 3/4

1/4

3/4

0.0231(5)

B (2^)

0.50(5)

1 .42(21 ) 0.42(4)

0.56(5)

1. L. H. Brixner, H. Y. Chen, and C. M. Foris, J. Solid State Chem. 4i£, 99 (1982)

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

STUDY OF HYDROGEN BONDS IN Ca^KH (PO^^)^ 2H2O

S. Takagi and M. Mathew

(American Dental Association)

and

E. Prince

A preliminary refinement of the structure of Ca KH (PO^)^ 2H in space group,

PI, was reported previously. In this centrosymmetric space group, three hydrogen

bonds cross centers of symmetry, although they are unusually long (2.474 to 2.504 A)

for symmetric 0«''H*''0 hydrogen bonds. The potassium atom appears also to be

randomly disordered across a center of symmetry. These facts suggested that the

crystal might actually lack the center of symmetry, so the structure was further

refined in space group PI. Two distinct non-centrosymmetric models were refined. In one the temperature factors of pairs of atoms that were related by the center of

symmetry in the centrosymmetric model were constrained to be equal. In the other

model these constraints were removed. Table 1 is a summary of the R indices for

various models, together with the number of reflections and the number of parameters

in each case. Each model is a significantly better fit, statistically, than the one

with fewer parameters. However, the completely unconstrained model had one

temperature factor tensor that was not definite, and the position parameters were not

significantly different from the model with the constrained temperature factors. For
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

Table 1. Summary of the R indices, the number of reflections included in the

refinement and the number of parameters for each of four models of

Ca2KH^(P0j^)^-2H20

Model

P1-K on center

pT-K split

PI-TFs constrained

PI -unconstrained

Number of Number of

Reflections Paramet ers R {%) \ (^)

1381 170 5.9 7.0

1381 173 5.7 6.7

1383 227 5.1 6.0

1379 323 4.5 5.2

Figure 1. The three hydrogen bonds that cross pseudo centers of symmetry 014-H14-

01 4l is still nearly symmetric in PI

.
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

Table 2. Refined position parameters and equivalent isotropic thermal parameters for

Ca KH (P0^)^«2H 0. Estimated standard deviations for the least significant

digits are given in parenthesis. K was held fixed to define the origin.

Atom

Ca

Cal

K

PIPlI

P2

P2I

Oil

0111

012

0121

013

0131

014

0141

021

0211

022

0221

023

0231

024

0241

03

031

H23

H23I

H24

H24I

H31

H31I

H32

H32I

H11

HI 3 HI 4

B

eq,

0.0032 ;2i)

0.0019 :2i)

0.4948

0.1372 ;2i)

0.1664 ;2i)

0.4926 :2o)

0.5014 :2o)

0.0944 :22)

0.1148 :22)

0.1460 :2o)

0.1335 ;2o)

0.4149 :2i)

0.4285 :2i)

0.0652 ( 21)

0.0576 (:2i)

0.2406 ( 20)

0.2483 ( 20)

0.7443 ( 19)

0.2516 ( 20)

0.5312 ( 20)

0.4682 ( 20)

0.4623 ( 20)

0.4666 ( 21)

0.1428 ( 21)

0.1437 ( 21)

0.3664 ( 27)

0.3655 ( 27)

0.6253 ( 29)

0.3851 ( 29)

0.0254 ( 29)

0.0392 ( 29)

0.2380 ( 39)

0.2624 ( 38)

0.0335 ( 28)

0.4686 ( 29)

0.0025 ( 40)

0.0991 (12)

0.0980 (12)

0.5377

0.6348 (12)

0.3606 (12)

0.0954 (12)

0.0990 (12)

0.5954 (11)

0.4055 (11)

0.7671 (11)

0.2372 (11)

0.5951 (11)

0.3986 (11)

0.5852 (12)

0.4146 :i2)

0.0388 (11)

0.0317 (11)

0.0314 (11)

0.0325 (J1)

0.1668 ((12)

0.1705 J2)

0.1836 ( 12)

0.1831 ( 12)

0.2463 ( 11)

0.2507 ( 11)

0.1881 ( 14)

0.1913 ( 14)

0.1973 ( 14)

0.2058 ( 15)

0.2966 ( 16)

0.2909 ( 16)

0.3048 ( 16)

0.2992 ( 16)

0.4928 ( 21)

0.5106 ( 17)

0.5037 ( 25)

0.3005

0.2961

0.0154

0.3768

0.3812

0.2103

0.2123

0.1071

0.1127

0.4505

0.4209

0.5394

4605

4108

4159

1432

1418

3215

0.3178

0.3912

0.4055

0.0305

0.0342

0.1761

0.1728

0.4052

0.4177

0.0642

0.0737

0.0633

0.0626

0.3143

0.3151

0.0145

0.5093

0.5089

20)

21 )

20)

21)

20)

20)

20)

20)

20)

20)

22)

22)

23)

23)

20)

21 ) 20)

20)

20)

20)

20)

20)

21)

21 ) 28)

28)

31)

30)

30)

30)

30)

30)

36)

33)

40)

0.87

0.87

4.34

1 .12

1 .12

0.75

0.75

1.93

1.93

1 .03

1 .03

2.24

2.24

2.15

2.15

1.16

1 .16

1 .18

1 .18

1 .27

1 .27

1 .74

1 .74

,48

,48

,09

.09

.58

.58

,09

3.09

3.96

3.96

3.63

3.23

3.80

3)

3)

25)

4)

4)

3)

3)

4)

4)

4)

4)

4)

4)

4)

4)

3)

3)

3)

3)

4)

4)

4)

4)

4)

4)

6)

6)

8)

8)

7)

7)

11 ) 11)

19)

22)

14)
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

Table 3. Selected bond distances and angles in Ca KH ( PO^ )

^^ •2H • Estimated

standard deviations for the least significant digits are given in

parenthesis.

Ca-012I 2.^124 (10)

Ca-021 2.370 (11)

Ca-021

I

2.485 (9)

Ca-022 2.310 (9)

Ca-022I 2.507 (9)

Ca-023I 2.611 (10)

Ca-024l 2.707 (10)

Ca-03 2.462 (10)

K-011 2.676 (11)

K-011I 2.801 (11)

K-013 2.891 (12)

K-OU 2.757 (12)

K-OUl 2.891 (13)

P1-011 1 .564 (9)

P1-012 1.567 (9)

PI -01

3

1.575 (9)

P1-014 1.464 (9)

PI 1-01 II

P1I-012I

PI 1-01 31

P1I-014I

P2-021

P2-022

P2-023

P2-024

P2I-021I

P2I-022I

P2I-023I

P2I-024I

03-H31

03-H32

03I-H31I

031-H32I

1.549 (9)

1.472 (9)

1.499 (9)

1.604 (9)

1.461 (9) . 1.499 (8)

1.529 (9)

1.583 (10)

1.528 (9)

1.496 (9)

1.606 (9)

1.583 (10)

1 .027

0.967

0.912

0.957

1

(15)

(18)

(15)

(18)

CaI-012 2.354 (10)

CaI-021 2.459 (10)

CaI-0211 2.317 (11)

CaI-022 2.509 (9)

CaI-0221 2.315 (9)

CaI-023 2.608 (9)

CaI-024 2.717 (10)

CaI-031 2.502 (10)

011-P1-012 109.3 (5)°

011-P1-013 108.6 (6)

011-P1-014 109.2 (6)

012-P1-013 105.5 95)

012-P1-014 113.6 (6)

013-P1-014 110.4 (6)

011I-P1I-012I 107.2 (5)°

011I-P1I-013I 110.1 (6)

011I-P1I-014I 105.8 (6)

012I-P1I-013I 114.4 (6)

012I-P1I-014I 109.0 (6)

013I-P1I-014I 110.0 (6)

021-P2-022 122.2 (6)°

021-P2-023 111.2 (5)

021-P2-024 103.1 (5)

022-P2-023 102.7 (5)

022-P2-024 111.6 (5)

023-P2-024 105.2 (6)

021I-P2I-022I 116.5 (6)°

021I-P2I-023I 112.2 (5)

021I-P2I-024I 102.5 (5)

022I-P2I-023I 105.5 (5)

022I-P2I-024I 110.9 (5)

023I-P2I-024I 109.7 (6)

H31-03-H32 98.6 (1.4

H31I-03I-H32I 111.1 (1 .6
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

H23-023

H23-012

012-023

H23I-023I

H23I-012I

012I-023I

H24-024

H24-03I

024-031

H24l-02ill

H24I-03

0241-03

H31-03

H31-011I

03-0111

H31I-03I

H31 1-011

031-011

H32-03

H32-013I

03-0131

H32I-03I

H32I-013

031-013

H11-011

H11-011I

01 1-01 II

HI 3-01

3

HI 3-01 31

013-0131

HI 4-01

4

HI 4-0141

014-0141

1 .040

1.569

2.601

1.039

1 .492

2.525

1 .023

1.727

2.729

0.972

1.736

2.704

1 .027

1.839

2.848

0.912

1.861

2.746

0.967

2.045

2.858

0.957

2.081

2.920

1.388

1 .126

2.509

1 .041

1 .447

2.482

1 .241

1.250

2.487

12) g

12)

8)

12) 2

12)

8)

14) X

14)

10)

14) X

14)

10)

15) 2

15)

10)

15) S

15)

10)

18) S

19)

10)

18) S

19)

10)

20) 2

21 ) 4)

17) 2

17)

4)

30) S

30)

4)

012-H23-023 171 .2 (1 .1 )

012I-H23I-023I 172.2 (1.3)

024-H24-03I

024I-H24I-03

03-H31-011I

03I-H31 1-011

03-H32-013I

03I-H32I-013

011-H11-01 II

OI3-HI3-OI3I

01 4-H1 4-0141

165.3 (1.2)°

173.9 (1.3)

166.7 (1 .2)

162.8 (1.4)°

140.6 (1 .7)

145.5 (1.7)

173.3 (1.6)

171 .9 (1 .4)

173.4 (1.9)
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

this reason, the constrained model was used for further analysis. Table 2 shows the

refined position parameters and equivalent isotropic temperature factors for this

model, and Table 3 is a summary of selected bond distances and angles for this model.

Two of three hydrogen bonds that crossed centers of symmetry in the centrosymmetric

model are asymmetric in this model. The third one, however, remains nearly

symmetric. Figure 1 is a picture of part of the structure including these hydrogen

bonds.

1. 8. Takagi, M. Mathew, and E. Prince, NBS Tech. Note 1178 , 31, F. J. Shorten, ed

(1983).

STRUCTURE STUDIES OF THE SUPERIONIC CONDUCTOR SYSTEM NA, Zr^Si P_, 0,^ (NASICON)

1+x 2 X 3-x 12

L. J. Schioler and B. J. Wuensch

(Massachusetts Institute of Technology, Cambridge, MA)

and

E. Prince

Preliminary results of a structure study of four compositions of the superionic

1 conductor system ^ Na, Zr^Si P_ O.^, called NASICON, were reported previously.

1 +x 2 X 3-x 12 f t^ J During the year covered by this report, two further things were done: a refinement

of the structure of the x = 3-0 end member of the series, and a detailed analysis of

the structures of the intermediate compositions in order to elucidate the structural

basis for the high-ionic conductivity.

A sample with the nominal composition Na^Zr (SiO^)- was prepared, but an x-ray

powder pattern showed that it contained a substantial amount of ZrO^. After further

heat treatment at 1200 ZC for 46 hours (We are indebted to Dr. R. S. Roth for this

processing.), there were still traces of ZrO in the x-ray powder pattern, but the

lines were not visible in a neutron powder pattern collected on the NBS highresolution powder diffractometer . Starting from the parameters given in a single

2 crystal x-ray refinement by Tran Qui, Capponi , Joubert, and Shannon, the structure

3

was refined by the Rietveld method to R = 7.05 percent, compared with

w p

R = 6.19 percent. R_,, based on integrated intensities, was 3-39 percent. Table 1 shows the refined parameters compared with the parameters given by Tran Qui, et al

It is apparent that the agreement of position parameters is extremely good. The

agreement of temperature factors is less good, but in several important ways the two
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

Table 1. Refined parameters for Na^Zr (SiO^)_, compared with those from the single

crystal refinement of Tran Qui et ai.

Atom Parameter This work Tran Qui et al

.

Nad )

Na(2;

Zr

Si

0(1

0(2)

B

B

B

B

B

B

a£

'33

'11

22

'33

'l3 z

11

X

1122

33

13

y

z

11 ^22

^33

^2

^3

^23

x_

y

z

1122

9.187M2) S

22.1850(5) S

2.45(25)

1 .71(37)

-0.36259(51)

1.52(17)

0.98(20)

4.00(28)

0.30(9)

0.14682(10)

0.59(6)

0.36(10)

0.29677(35)

0.59(13)

0.47(13)

0.47(13)

0.21(5)

0.18562(20)

0.16640(21 ) 0.08490(8)

0.44(8)

0.61(8)

1.07(7)

-0.03(7)

0.23(8)

0.21 (7)

0.18501 (24)

-0.01707(25)

0.191 18(7)

1 .18(10)

1 .26(10)

9.1863(5) X

22.181 (2) 2

2.05(9)

0.63(11 ) -0.36253(26)

0.13(7)

1.05(7)

4.60(10)

0.38(4)

0.14679(1 ) 0.410(8)

0.426(8)

0.29583(12)

0.410(16)

0.36(2)

0.70(3)

0.05(1 ) 0.18532(23)

0.16658(26)

0.08488(9)

0.60(6)

0.86(7)

0.82(7)

1 .02(5)

0.64(5)

0.13(6)

0.18458(28)

-0.01714(30)

0.19119(12)

2.20(7)

1 .42(8)

10
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

Table 1 . (Continued)

Atom Parameter This work Tran Qui et al

33

^3

^23

1 .71(9)

0.64(9)

0.61(7)

0.08(8)

1 .70(9)

0.72(6)

-0.73(6)

0.06(6)

Table 2. Critical radii for the window between Na(1) and Na(2) sites,

X = 0.0

X = 1 .0

X = 1 .6

X = 2.0

X = 2.5

X = 3.0

R - P, , c 1-1

1.003

1 .023

0.970

0.933

1 .010

0.941

% - '1-2

1 .025

1 .057

^0 - ^1-3

1 .125

1.139

refinements are remarkably consistent. In particular, the equivalent isotropic

temperature factors have similar magnitudes for all atoms and the component of

thermal motion of Na(2) parallel to the hexagonal _c axis is much larger than any

other.

The conductivity of NASICON is strongly temperature dependent, but at all

temperatures the conductivity is highest for an intermediate composition in the

vicinity of x = 2.0. There are various reasons for believing that this has a structural basis. In their study of the x = 3.0 end member, Tran Qui et al . proposed

several possible "windows" through which the sodium ions could pass in jumping from

one site to another. Each path has one or more critical points at which the space

between surrounding oxygen ions is least. With the refined structures of all the

intermediate compositions, it is possible to determine the radii of these critical

11
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

openings as a function of composition. Table 2 shows the critical radius for jumps

from Na(1) to Na(2). Two things are particularly notable. First, the critical

radius is smaller for the end member compositions than for intermediate ones even in

the region where the structure is rhombohedral . Second, in the compositions in the

range from x = 1.6 to x = 2.0, where the conductivity is highest and the structure is

monoclinic, there are three independent pathways, one of which has a conspicuously

large opening.

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

ed., 42 (1983).

2. D. Tran Qui, J. J. Capponi , J. C. Joubert, and R. D. Shannon, J. Sol. State Chem.

39, 219 (1981).

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

THE STRUCTURES OF LITHIUM INSERTED METAL OXIDES; Li.-,FeV-OQ

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

(Bell Laboratories, Murray Hill, NJ)

and

A. Santoro and R, S. Roth

As part of our studies on lithium inserted metal oxides, the structure of

Li FeV Oo has been determined by neutron diffraction powder profile analysis.

The title compound crystallizes in space group C2/m with lattice parameters

a = 11.963(3), b = 3-899(2), c = 6.464(2)A, and 6 = 107.5(3)°. The location of the

+ Li ions in the structure was found by means of Fourier difference analysis. The

results of the neutron refinement are given in Table 1

+ The FeV^Oo host structure contains perovskite-like cavities in which the Li

ions can be accommodated. The insertion of lithium cannot cause extensive

distortions of the host as the oxygen octahedra share both corners and edges. This

is in sharp contrast with the behavior of ReO^ where the insertion of lithium causes

extensive distortions because the ReO^ octahedra share only corners. The insertion

D of Li in ReO- converts the original perovskite-like cavity into two distorted

octahedra sharing faces. In FeV_Oo, on the other hand, the cavities do not deform

into octahedral sites and the Li ions must be accommodated in coordination

geometries already defined by the preexistent atomic arrangement. In Li FeV On, in

+ fact, the Li ions are located in two five-coordinated square pyramidal sites.

12
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

Table 1 . Structure of Li„FeV 0,

Space group: C 2/m

Z = 2, Atoms in Position Hi

Atom X Y z B(A^)

Li 0.951(2) 0.0 0.659(3) 3.4(3)

Ml 0.278(2) 0.0 0.585(4) 0.0(1)

M2 0.3968(7) 0.0 0.314(1

)

0.0(1)

01 0.3494(iJ) 0.0 0.9954(8) 0.59(3)

02 0.2287(4) 0.0 0.3416(8) 0.59(3)

03 0.4424(5) 0.0 0.6413(7) 0.59(3)

04 0.1207(4)

N^® = 0.0625

N^^ = 0.4375

0.0 0.6840(7)

N^^ = 0.1875

N^^ = 0.3125

0.59(3)

R,, = 9.15^ R = 5.845J R = 7.17% R^ = 3.45^

N p w E

Z|l(obs) - Kcalc) I N Zl(obs)

P

^ E|y(obs) - y(calc) | p Ey(obs)

R = w

R =

2 Zw|[y(obs) - y(calc)]

Zw[y(obs)]"

,1/2

N - P + C

J/2

^

f Zw[y(obs)]^ )

where N = number of independent observations, P = number of parameters, C = number of

constraints, y = counts at angle 26, I = integrated Bragg intensities, and w = weights.

13
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

NEUTRON AND X-RAY DIFFRACTION STUDY ON POLYMORPHISM IN LITHIUM ORTHOTANTALATE , Li TaO^

M. Zocchi and M. Gatti

(Politecnico of Milano, Italy)

and

A. Santoro

and

R.S. Roth

(National Measurement Laboratory)

The structure of lithium orthotantalate , Li TaO^, has been investigated by

1 Blasse who found that the crystal is pseudo-tetragonal with a unit cell of

5 + parameters a = 6.01 and c = 16.67 A. The Ta ions were located by using x-ray

powder diffraction intensities, and their arrangement suggested a 3:1 ordering of the

+ 5 + Li and Ta ions in a rock salt-type structure having subcell of parameter a related to the parameters ^ a^ttand c^ by the expressions a^ttc = b^= a /2 and c^tc= Ma . Martel and Roth have found that Li_TaO^ is, in fact, trimorphic, with the

first-phase transition occurring at about 900°C and the second between 1i400°C and

1450°C. The low-temperature phase was found to have the same lattice parameters as the modification described by Blasse . Our purpose in beginning this work was to verify, complete, and refine Blasse'

model for the low-temperature phase (referred to in what follows as the 6-phase), and

to solve the structure of the high-temperature form (called a-phase in what follows).

No attempts have been made to obtain and analyze the intermediate temperature

modification. Both neutron powder and x-ray single-crystal diffraction methods have

been used in the present study.

Neutron powder diffraction measurements were made at room temperature with the

high-resolution five-detector dif f ractometer at the National Bureau of Standards

3 4 5 Reactor . The data were analyzed with the Rietveld method , modified by Prince to

simultaneously process the intensities collected by the five counters of the

dif fractometer

X-ray intensity data on a single crystal of a-Li_Ta0^were collected with a Nonius CAD-4 four-circle dif fractometer using MoKa radiation (A = 0.71069 A) and the

0-20 scan method. The crystal used in the experiment had a regular shape with an average diameter smaller than 0.1 mm. A total of 4025 reflections were measured.

In the case of the 3-form (space group C2/c) a trial model was derived using

the results obtained by Blasse and simple crystal-chemical considerations. In the

14
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

case of the u-phase (space group P2/n) a plausible trial model was obtained from the

results of a preliminary single-crystal x-ray diffraction study. In both cases, the

trial models were refined with the Rietveld method using neutron powder data. The

results of the two refinements are given in Table 1 (6-form) and Table 2 (a-form).

+ 5 + In the B-phase the ordering of the Li and Ta ions along the c axis of the

pseudo-tetragonal cell forms a sequence . . .Ta-Li(l)-Li(2)-Li(3)-Ta. . ., and each

+ set of crystallographically equivalent cations forms a chain of conformation t g

t g . The cation-cation distances along the chains are similar for Li(1) and Li(3)

[2.95(6) and 2.94(i|) A for Lid)"^ and 3-12(8) and 2.91(5) A for Li(3)^], while they

are significantly different for Li(2) and Ta [3-35(9) and 2.98(7) for Li(2)"^ and

3.15(3) and 2.95(2) for Ta^"*"].

The distances between oxygen ions constituting common edges of the coordination

5+

octahedra of Ta ions are significantly shorter than the average of all the 0-0

distances. Since these short distances occur only in the case of the edge-sharing

5+ coordination octahedra of Ta ions, one may infer that this atomic arrangement in

the structure has the function of decreasing the electrostatic repulsion between

5+

closely located and highly charged Ta ions.

The structure of the a-form can be best described in relation to that of the B- 5+

phase. The shifts of the Ta ions necessary to go from one structure to the other

occur within layers perpendicular to the c axis, and their sequence has a repeat

period d = 3c . In this sense, d may be considered as a parameter representing the

pattern of the transformation in the direction parallel to c . The resulting

5+ + + - - arrangement of the Ta ions gives chains of conformation t g g t g g (it is

worthwhile to mention that the Li ions also could be connected in a similar way).

In the a-modif ication there are no significant differences among the Ta-Ta

interatomic distances along the chains (differences in the Li-Li interatomic

distances cannot be discussed meaningfully because of the large standard deviations).

This finding is in contrast to the case of the B-phase discussed above. The

sequences of cations along the direction c of the pseudo-tetragonal cell are of type

. . .Ta-Li-Li-Li-Li-Li-Ta. . .for Ta(1) and Ta(4), and . . .Ta-Li-Ta-Li-Li-Li-Ta. . .for

Ta(2) and Ta(3).

As in the previous case, in the a-phase the distances between the oxygen ions

5 + forming the common edges of the coordination octahedra of the Ta ions are shorter

than the average of all the 0-0 distances.

It is well known that the presence in a structure of anionic octahedra sharing

edges introduces unfavorable electrostatic repulsion between the central metal ions

15
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

TABLE 1 Results of the Rietveld Refinement of the Structure

of 6-Li_TaO,,

Atom

Ta

Lid)

Li(2)

Li(3)

0(1)

0(2)

0(3)

0(4)

0.075(2)

0.329(4)

0.567(6)

0.817(5)

0.158(1 ) 0.438(1

)

0.693(1)

0.941 (1 )

-0.126(1

)

-0.116(5)

-0.132(4)

-0.120(6)

-0.125(1

-0.128(1

-0.118(1)

-0.106(1

z B(A^)

0.123(2) 1.07(7)

0.607(3) 0.8(2)

0.107(4) 3.0(3)

0.622(3) 0.8(2)

0.358(1)

(*

0.28(3)

0.887(1) 0.28(3)

0.371(1) 0.28(3)

0.886(1) 0.28(3)

R,, = 100[Zll(obs)-I(cal)|/Z I(obs)] = 8.3

R = 100[Ely(obs)-y(cal) |/Z y(Gbs)] = 9.7

R = 100{Z w{y(obs)-y(cal)]^/Z w y^(obs)}^^^ = 12.3

R^ = 100[N-P+C)/Z w y^(obs)]^^^ = 7.5

In the above formulas, N is the number of statistically independent observations, P the number of parameters refined, C the number of constraints, I the integrated

intensities, y(obs) and y(cal) the observed and calculated intensities, and w the

weights associated with the data points y(obs).

(*) The oxygen atoms were constrained to have a common temperature factor.

NOTE:

Numbers in parenthesis are standard deviations in the last decimal figure.

-3

Space Group: C2/c, Z = 8, calculated density d = 5.87 gr . cm

Lattice Parameters: a = 8.500(3), b

1 500(3), c^ = 9.344(3)A, e^ = 117.05(2)°

16
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

Table 2. Results of the Rietveld refinement of the structure of a-Li TaO^,

Atom X y z Tad) 1/4 0.580(2) 3/4

Ta(2) 0.403(1

0.134(1) 0.0821(5)

0(1) -0.016(1 0.142(1

0.2579(6)

0(2) 0.487(1) 0.386(1) 0.7432(7)

0(3) 0.162(2) 0.360(1) 0.0779(5)

0(4) 0.652(2) 0.357(2) 0.0906(5)

0(5) 0.681(2) 0.116(2) 0.5876(6)

0(6) 0.145(3) 0.113(1) 0.5729(5)

Lid) 3/4 0.124(4) 3/4

Li(2) 0.396(3) 0.416(3) 0.594(2)

Li(3) -0.084(4) 0.130(6) 0.096(2)

Li(4) 1/4 0.416(6) 1/4

Li(5) 1/4 0.132(7) 3/4

Li(6) 0.608(4) 0.369(4) -0.081(2)

"n'

= 6.70, Rp = 7.48, R, = 9.67, R„ = W E

= 5.09

-5

Space group P2/n, Z = 6, calculated density d = 5.87 gr.cm

Lattice Parameters: (i) x-ray measurements, a = 6.027(2), b = 6.004(2),

of**-) " "

0. = 12.882(4) A, 6^ = 103-53(1)

(^) ^ For the definition of the R-factors, see Table 1

(**) The difference between the lattice parameters determined by x-ray and neutron

diffraction are almost certainly due to errors in the calibration of the instruments

used for the measurements.

17
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

and that the resulting stress depends on the charge on the cations. The stress can

be relieved by increasing the distance between the cations. In the structure of 6-

+ - Li_TaO^, one of the two Ta-Ta distances along the t g t g chains has a value of

2.95(2) A, i.e., is significantly less than the other Ta-Ta distance along the same

5 + chain (3.15 A). On the contrary, in the a-phase the Ta ions are arranged so that

no Ta-Ta distance is shorter than S-IO A, and their average distance is 3-16 A. The

stress introduced by the edge-sharing octahedra, therefore, is smaller in the a-phase

than in the B. This reduction of stress may well be one of the driving forces

leading to the transformation observed in the title compound.

1. G. Blasse, Z. Anorg. Allg. Chem. Band 331 , 44 (1964).

2. L. C. Martel and R. S. Roth, Bull. Amer. Ceram. Soc. 60_, 376 (1981).

3. E. Prince and A. Santoro, National Bureau of Standards US Technical Note

1117, edited by F. Shorten (1980).

4. H. M. Rietveld, J. Appl . Cryst. _2, 65 (1969).

5. E. Prince, National Bureau of Standards US Technical Note 1117, edited

by F. Shorten (1980)

THE CRYSTAL STRUCTURE OF LITHIUM ZIRCONATE, Li^Zr 0„

b 2 7

M. Zocchi and M. Gatti

(University of Milano, Italy)

and

A. Santoro

and

R. S. Roth

(National Measurement Laboratory)

The single-crystal x-ray diffraction study of the title compound was carried

out as part of our structural investigations of mixed oxides of lithium and

transition metals.

Li,Zr crystallizes in space group C2/c with a = 10.440(4), b = 5.991 (1),

c = 10.204 (2) A, B = 100.25 (3)°. The intensities of 4229 Bragg reflections were

measured with a Nonius CAD-4 diffractometer using monochromated MoKa radiation and

empirically corrected for absorption. The structure was solved by Patterson and

Fourier methods and refined by least squares to conventional and weighted R factors

18
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

Table 1 Table of Atomic Parameters

No. Name X Y z 811 B22 B33

1 Zr 0.18351 -0.12162 0.36469 0.00012 0.00165 0.00066

2 Lid) 0.207 0.369 0.395 0.89

3 Li(2) 0.433 0.142 0.418 1 .50

4 Li(3) 0.065 0.096 0.102 0.79

5 0(1) 0.2499 0.1112 0.2452 0.0022 0.0033 0.0018

6 0(2) 0.1333 -0.3662 0.5018 0.0004 0.0031 0.0014

7 0(3) 0.1230 0.1230 0.4774 0.0007 0.0032 0.0015

8 0(4) 0.0000

B12

0.1491

B13

0.2500

B23

0.0006 0.0086 0.0022

1 Zr 0.00013 0.00011 0.00012

2 Lid)

3 Li(2)

4 Li(3)

5 0(1) -0.0017 0.0016 0.0009

6 0(2) -0.0006 0.0002 0.0000

7 0(3) 0.0003 0.0008 -0.0002

8 0(4) 0.0000 -0.0013 0.0000

Table 2

Isotropic Parameters of Thermal Motion (in A )

Zr .166 (2)

Lid) .89 (8)

Li(2) 1.50 (9)

Li(3) .79 (8)

0(1) .65 (2)

0(2) .38 (2)

0(3) .43 (2)

0(4) .84 (3)

19
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

of 0.0M8 and 0.061 respectively for the 2966 reflections with I ^ 3o (I). The

structural parameters are given in Table 1

The rock salt-type structure is characterized by an ordering of the cations

with sequences (Q-Zr ) .-(Q-li ) , along with a direction parallel to one of the edges of

d D the face centered pseudocubic cell (a = 4.28 A) which can be obtained from the

c monoclinic cell with the transformation

111 111 3 1 ^~

« 9 H

^ ~ft~ 5 JI ^

ft '^ H

^ '^^^ °^ ^^® oxygen ions in the asymmetric unit

(Li-ZrO_ ^) is in special position (on a twofold axis) and therefore the structure is

3 3-5

characterized by an ordered anionic deficiency, with 32 cations and 28 oxygen ions in

the unit cell. Indeed on the twofold axes of the monoclinic cell every other anionic

site, expected for the idealized NaCl structure, is empty and, as a consequence, the

coordination number of the lithium ions is five with two kinds of coordination

polyhedra, i.e., distorted square pyramids and trigonal bipyramids. The Zr

coordination number is six and the oxygen octahedron is significantly distorted.

It may be interesting to compare the structure of Li^ZrO_ with that of

1 Li ZrO , looking for possible correlations with their ionic conduction properties.

Both structures are of the NaCl type. However, the distribution of the cations

is different in the two phases, and for this reason they cannot be considered

isostructural

In Li ZrO all cations have octahedral coordination and the structure has to

considered as close packed, and only the relatively large Li-O average distance of

2.212 A may explain the small conductivity shown by this phase.

+ In Li^Zr„0„ the coordination number of the Li ions is five, as a consequence

o 2 7 of the fact that on the two-fold axes present in this structure every other anionic

site, expected for the idealized NaCl structure, is empty. Thus the structure of

+ Li^Zr is more "open" than the one of Li-ZrO , and for this reason both the Li and

ions may have higher mobility in Li^Zr„0^ than in Li^ZrO_. These results are in

Dp 2 7 2 3

agreement with conductivity measurements . Whether the conductivity in Li^Zr^O^ is cationic or anionic or both is not

2

6 2 7 clear. Hellstrom and Van Gool do not take into consideration the possibility of a significant mobility of the oxygen ions. However, in view of the high values of the

thermal parameters for 0(1) and 0(4) (See Table 2) and in view of the well-known fact

that conduction in zirconia-based electrolytes is due to the mobility of the oxygen

ions, one cannot exclude that a similar mechanism is, at least partially, active also

in Li^Zr . More specific conductivity experiments, with a variable partial

pressure of oxygen at the anode, may give an answer to this question.

20
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

A variable-temperature powder neutron diffraction study is planned with the aim

of better defining the correlations between the structure and the ionic conduction

properties of this material.

1. J.L. Hodeau, M. Marezio, A. Santoro, and R.S. Roth, J. Solid State Chem. ^5,

170- (1982). —

2. E.E. Hellstrom and W. Van Gool, Solid State Ionics 2, 59- (1981).

STUDIES OF ZEOLITE STRUCTURE BY NEUTRON POWDER DIFFRACTION

J. B. Parise

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

E. Prince

Zeolites are a class of compounds whose structures are based on frameworks made

up of AlO^ and SiO^ tetrahedra that share corners. This relatively rigid framework

contains pores of various sizes that are occupied by a sufficient number of cations

to balance the deficiency of positive charge due to the aluminum in the framework,

and also may be occupied by very loosely bound molecules of various types. The

speciiic sizes of the pores may be utilized to produce highly selective absorbants

and catalysts for chemical processes. A detailed knowledge of the sizes and shapes

of the pores is needed to gain an understanding of these processes.

We have studied several compositions of two types of zeolite, each of which is

based on a body centered cubic arrangement of cubo-octahedral units. In zeolite Rho

these units share hexagonal faces along [ill] directions, and they are connected

along [100] directions (in an idealized structure) by octagonal prisms - so called

double eight rings. In zeolite ZK5 a hexagonal prism - a double six ring - is

interposed between the units in [111] directions, and the extra space between the

units along [100] directions becomes a second, somewhat smaller, type of pore that

has planar eight rings on two opposite faces and puckered eight rings on the sides.

Figure 1 shows stereo pair representations of these structures.

We have studied two compositions of each of these types at several

temperatures. Using Rietveld refinement and Fourier methods we have determined

21
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

Table 1. Summary of structural data for zeolite ZK-5. The space group ImSm. T

indicates Al or Si, disordered.

^=9.7'l3-''22.7'^3.3°192 ^^S./.s'^l 7.5^^22.2^^3.8^192

298k 493K 298K

a 18.671(1)A 18.660(2)A 18.673(1)A

T(96l)

X 0.0825(3) 0.0828(4) 0.0843(4)

y 0.2023(3) 0.2029(5) 0.2029(4)

z 0.3211(3) 0.3219(5) 0.3188(5)

01 (48k) x=y

y 0.1280(2) 0.1277(3) 0.1258(3)

z 0.3145(3) 0.3140(3) 0.3163(4)

02(48k)x=y

y 0.2522(2) 0.2522(3) 0.2551(3)

z 0.4081(3) 0.4082(4) 0.4004(4)

03(48j) x=0

y 0.1783(3) 0.1785(4) 0.1362(4)

z 0.3369(3) 0.3390(4) 0.3322(4)

04(48i) x=1/4, y=1/2-z

z 0.3915(2) 0.3909(3) 0.3867(3)

Cs(12e) x=y=0

z 0.314(1) 0.314(1) 0.336(2)

K1 (12d) x=0, y=l/4, z=1/2

K2(l6f) x=y=z

z 0.150(3) 0.152(9)

22
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

Table 2. Summary of structural data for zeolite Rko. The space group is l43m. T

indicates Al or Si, disordered.

298K 493K

a 14.6652(5) A 14.7014(8) A

T(il8h)

X 0.2670(4) 0.2694(5)

y 0.1191(5) 0.1152(7)

z 0.4186(3) 0.4164(5)

01(24g) x=y

y 0.2095(2) 0.2075(4)

z 0.3956(4) 0.3912(7)

02(24g) x=y

y 0.1339(3) 0.1359(4)

z 0.6216(3) 0.6236(6)

03(48h)

X 0.0275(2) 0.0237(4)

y 0.2092(2) 0.2081(4)

z 0.3867(3) 0.3864(4)

Cs(6b) x=1/2, y=0, z=0

UK

4 .601(1)

.2726(7)

.1197(8)

.4219(6)

.2127(5)

.3956(8)

1315(5)

.6227(7)

.0310(4)

2098(4)

3878(5)

23
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

2K-5

Rho

Figure 1: Stereo = pairs showing the idealized structures of zeolites ZK5 and Rho.

the nodes of the framework are aluminum or silicon positions. Oxygen

positem's are approximately at the centers of the line segments. Adapted

from Atlas of Zeolite Structure Types by W. M. Meier and D. H. Olson,

published by the Structure Commission of the International Zeolite

Association (1975).

cation binding sites in both structures types, and in Rho it was determined that the

double eight ring units were distorted in such a way as to make the space group of

the structure l43m rather than Im3m. Table 1 is a summary of structure data for

ZK5, and Table 2 gives structure information for Rho.

2A
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

THE STRUCTURE OF SYNTHETIC ZEOLITE OMEGA

P. A. Wright

(University of Cambridge, Cambridge, England)

and

J. B. Parise

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

and

E. Prince

A structure belonging to space group P6 /mmm was proposed for the synthetic

^ 1 zeolite designated omega by Barrer and Villiger on the basis of x-ray powder

diffraction data. However, when the structure of the natural zeolite mazzite was

determined by Rinaldi, Pluth, and Smith, they observed that the powder pattern for

its structure, which belongs to space group P6 /mmc, was very similar to that of

omega and suggested that the structure of omega might be incorrect. In order to

resolve this question, a study was undertaken of a synthetic omega zeolite using high

resolution neutron powder diffraction and Rietveld refinement.

The best fit that could be obtained between observed and calculated patterns

using the Barrer and Villiger model was R = 40.3 percent; R = 16.71 percent

D Wp

(R = 5.52 percent). The mazzite structure, however, refined satisfactorily to

R^ = 13.51 percent, R = 9.25 percent, and after the positions of certain extraB wp

framework atoms were determined from Fourier maps, R was further reduced to

wp

7.23 percent. It is thus confirmed that synthetic zeolite omega has the same

structure as mazzite. Table 1 is a summary of the refined position parameters of the

framework atoms.

Table 1 . Position parameters of the framework atoms in synthetic zeolite omega. The

space group is P6 /mmc. T indicates Al and Si, disordered.

Atom X y z

T1 0.1636(14) 0.4875(18) -1/4

T2 0.0850(11) 0.3574(11) 0.0307(21)

01 0.2535(10) 0.5069(18) -1/4

02 -0.4226(7) -0.8451(14) 1/4

03 0.0927(11) 0.3786(10) 1/4

04 0.1092(7) 0.4386(8) -0.0765(11)

05 0.1635(6) 0.3270(12) 0.0060(20)

06 0.2670(10)

25
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

1. R. M. Barren and H. Villiger, Chera. Comm. 659-660 (1969).

2. R. Rinaldi, J. J. Pluth, and J. V. Smith, Acta Cryst. B31 , 1603 (1975)

ACTIVE SITE OF RNASE: NEUTRON DIFFRACTION STUDY OF A COMPLEX

WITH URIDINE VANADATE, A TRANSITION STATE ANALOG

A. Wlodawer

(National Bureau of Standards)

and

(National Institute of Arthritis, Diabetes, Digestive and

Kidney Diseases, Bethesda, MD)

and

Maria Miller

(Laboratory of Molecular Biology, National Institutes

of Health, Bethesda, MD)

and

L. Sjolin

(National Bureau of Standards, Washington, DC)

and

(Chalmers Institute of Technology, Gothenburg, Sweden)

and

(National Institute of Arthritis, Diabetes, Digestive and

Kidney Diseases, Bethesda, MD)

A complex of RNase A with a transition state analog, uridine vanadate, has been

studied by a combination of neutron and x-ray diffraction. A crystal was prepared by

soaking it in a solution of inhibitor for three months, with simultaneous exchange of

a maximum number of hydrogen atoms for deuterium. Upon completion of the exchange, a number of small pieces were cut from the crystal using a scalpel blade, and a large

piece (4.5 x 3.5 x 1.2 mm) was mounted in a quartz tube as previously described.

Reflections which could not be recorded with the flat-cone method and levels with h_ between and 3 were measured using equatorial geometry. These data were later used

for scaling. After final scaling, the number of unique observed data (I > 1.5o (I)) was 6315, which corresponded to 73% of all possible data to 2 A resolution, with an extra S% of possible reflections in the shell of 2 - 1.75 A.

X-ray data were measured from a single fragment of the original crystal, thus

assuring identical deuteration and substitution of the inhibitor. The number of

significant reflections in the 2- to 1 0-A resolution range was 6617, S5% of those

theoretically accessible.

26
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

The refinement of the structure on the complex was accomplished using an algorithm of Wlodawer and Hendrickson, in which the model is refined with both neutron

and x-ray data. The final model resulting from the joint refinement was characterized by standard crystallographic R factors of 0.191 (x-ray) and 0.207 (neutron),

with r.m.s. deviations of bond length from ideality of 0.024 8 (bonds not involving

(a)

H

/12

119

H N

^ 41

(b)

.H,N

N

119

/ H

Figure 1. a) Hypothetical partial structure for the complex of RNase with uridine

vanadate, postulated by Lindquist et al.

b) Diagram of the structure observed in the current investigation.

hydrogen) and 0.021 A (bonds involving hydrogen). The r.m.s. shift of the non-hydrogen protein coordinates from the initial model was 0.38A.

Although both the x-ray and neutron difference Fourier maps were reasonably

clear even before the commencement of the refinement procedures, they were improved

further following the refinement. The x-ray and neutron densities were also very

clear for all the amino acid side chains involved in the catalytic activity. Both

histidines appeared to be protonated, in agreement with the increase of the pK of

these groups in the presence of inhibitors observed by NMR . The movement of these

side chains did not exceed 0.2 A from the positions observed in the native structure

of RNase. The end group of Lys 41 moved 0.6 A from the position found in the native

enzyme, and the average temperature factor for this side chain was lowered from 20 A

to 8 A . No major movement of other groups was detected in the area of the active

site.

27
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

A diagram of the arrangement of the inhibitor and of the surrounding side

chains of the protein is shown in Figure 1 . As expected on the basis of theoretical

considerations, the vanadium atom lies in the center of a distorted trigonal bypyramid, with the oxygens 02' and 07 found in the apical positions, while the oxygens

03' » 06, and 08 lie in. the basal plane. The distance of the vanadium atom from the

best least-squares plane formed by V, 03', 06, and 08 is 0.085A. The angle formed by

02'-V-07 is 156 , indicating the distortion in the bipyramid. This angle refined to

within 5 independently of the type of restraints placed on the standard group.

Unexpectedly, the hydrogen bonds formed between the side chains of RNase and

the oxygens surrounding the vanadium atom did not appear to conform to the predictions based on the theoretical considerations. In particular, it is Lys 41 rather

than His 12 which appears to be hydrogen bonded to the apical 02'-oxygen. The distance between the NZ of Lys 41 and 02' is 2.79 S and the angle NZ-DZ1-02' is 165°.

There is a clear indication of a continuous density in the neutron difference Fourier

map, as expected at this resolution for hydrogen-bonded atoms. The distance between

NZ of Lys 41 and the closest equitorial oxygen of the bipyramid (06) is 3-38 A, with

no indication of a hydrogen bond. Conversely, NE2 of His 12 is 2.62 A from the

equatorial oxygen 08, with the angle NE2-DE2-08 of 160 . Again, these atoms are connected by a continuous density in the Fourier map. The distance between NE2 of

His 12 and 02' is 3.22 a, with no indication of a hydrogen bond.

The interpretation of these results and their reconciliation with the mechanistic model is not straightforward. The in-line model of the catalytic action is well

established, and the observed atomic arrangement of the bypyramid is in good agreement with the requirement that the leaving groups in both the first or the second

step of the reaction should always be apical. It is improbable that a group other

than histidine could act as both a general acid and a general base during the catalysis, and thus the observed hydrogen bonding pattern may indicate that the proton

transfers do not follow the simplest route. It is unlikely that the amino group of

Lys 41 could assume the role of general acid-general base, even though it forms a clear hydrogen bond with the apical oxygen of the complex. It is also unclear why

the temperature factor of Lys 41 is lowered by a factor of 2.5 compared to that in

the native structure, where a hydrogen bond to the phosphate is also made. Nevertheless, these results should enhance our knowledge of the three-dimensional structure

of the active site of RNase and should attest to the usefulness of neutron diffraction and least squares refinement in such studies.

28
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

MICROVOID FORMATION IN AMMONIUM NITRATE

C. S. Choi and H. J. Prask

(EMD, LCWSL, AMCCOM, Dover, NJ)

and

(National Bureau of Standards, Washington, DC)

and

C. J. Glinka

Ammonium nitrate (AN) is a material of considerable interest to the military

for a variety of "energetic material" applications. However, because of the several

phase transitions which occur at ambient pressure, and the resulting irreversible

growth, use of NH^^NO has been severely limited.

We have continued our studies of NH^iNO. with the overall aim of providing

information by which irreversible growth could ultimately be reduced. Our most

recent studies consider two aspects not examined previously: three-dimensional

characterization of lattice parameter changes accompanying a phase transition and

characterization of microvoids accompanying a phase transition. Initially, both

aspects have been studied for the IV-*-^V transition in NH^NO„.

1 . Dimensional Expansion at the IV to V Transition

The unit cell of the phase V is a supercell of phase IV with the transformation

matrix; 110/110/002/ (or 110/110/002/ for the twin pair). Since the phase IV lattice

is not cubic, the orientation of the phase V lattice planes are expected to be

generally different from the equivalent planes of phase IV, except for two lattice

planes which we designate as invariant planes (or directions). These invariant

planes were investigated by single-crystal neutron diffraction studies at room

temperature (for phase IV) and at 240 K (for phase V). It was found that the

direction of (110) [or its twin pair (110)] and (001) of phase V coincide with those

of (100) [or (010)] and (001) of phase IV, respectively, within 0.2°. The unit cell

dimensions of both phases at the transition temperature were obtained from the

thermal expansion formula as given in a previous study. From these the linear

expansions along the invariant directions in the IV to V phase transition were found

to be the following:

(100) direction -1 .8%

(010) direction +5.3^

(001) direction -0.4^.

The large and anisotropic expansion of the crystallites, as shown above, is expected

to create considerable mismatch at crystallite boundaries and production of

29
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

Solid Line = F1 + F2 + F3 + F4

Dotted Lines Are F1 F2 F3 and F4

0.02 0.04 0.06 0.08 0.10 0.12

X 10"'

Figure 1. The small angle scattering from the microvoids in the sample, expressed as

Inl vs. Q . Observed data are shown as circles, best-fit curve as a solid

line.

Table 1 . The results of non-linear least-squares refinement for the multiple guinier

2 2 functions model in the form, I(Q) = EY.EXP(-R Q /3.). R.S.D. is a residual standard deviation for each function as defined by

p 1/2

{1{Y - F ) /N} , where N is number of degree of freedom. The

obs cal

refinements were conducted for each function separately, within the Qranges as specified. The R-factor, R = ^(1^^^ "

^cal'''^ ^''"di ^^^ calculated

for the entire observed Q-range.

Y.

1 2

op

gi

R.S.D.

°-1

Q (A ) QR-.

314(28)

775(39)

3.

,073/. 106

2.0/2.9

2566(80)

3664(49)

4.

.040/. 071

2.4/4.3

13844(925)

12503(265)

9.

.026/. 038

2.9/4.2

57641(4896)

33438(876)

32.

.017/. 024

3.0/4.5

R-factor (overall) = 0.007

30
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

microvoids. This could be as much as 5 percent in volume fraction if the negative

expansion coefficients make a negligible contribution to the contraction because of

the geometrical hindrance of the grain arrangement.

2. Microvoid Measurement by SANS

A thin plate-like sample, approximately 2 mm in thickness, was prepared from

molten AN (90^ deuterated). The sample was wrapped with Al foil and mounted on the

sample holder of a cryostat. Using neutrons of 4.85 A with AA/A = 0.25 and a minimum

Q of 0.016 A , the scattering curves were measured at two different temperatures:

room temperature and 230 K. The scattering intensity of the latter was about 20

percent more intense than the former, which was attributed mainly to microvoid

formation in the sample since the experimental conditions were exactly identical

except for the sample temperature. The scattering curve for the microvoids was obtained by simple subtraction of room temperature data from the 230 K data.

Assuming that the microvoids can be approximated as a collection of globularparticles with a few different average sizes, the scattering curve can be expressed

by a sum of Guinier functions:

Here, p is the scattering length density, n., v., and R . are the particle density,

average volume of the particle, and radius of gyration of the i-th function,

respectively. The results are shown in Figure 1 and Table 1. In Table 1, the QR

o values are less than 3-0 in most of the fitting ranges and the residual factors (R)

are less than 1 percent, which indicates that the model function describes the

microvoid distribution quite satisfactorily.

NONDESTRUCTIVE CHARACTERIZATION OF SUB-SURFACE RESIDUAL STRESS

H. J. Prask and C. S. Choi

(EMD, LCWSL, AMCCOM, Dover, NJ)

and

(National Bureau of Standards, Washington, DC)

In earlier work it was demonstrated that the precision and reproducibility of

1 the neutron diffraction method were sufficient for residual stress measurements. It

was also found, however, that for the differential volumes of interest in

3 technological applications (^ 20 mm as shown in Figure 1) and employing conventional

31
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

9-29 scans, texture could produce shifts in apparent peak positions greater than any

expected from residual stress.

To minimize the role of texture in residual stress measurements we have

2

adopted an "energy dispersive" approach utilizing a three-axis spectrometer and in

which sample orientation remains fixed with respect to incident and diffracted

neutron beam directions, and monochromator and analyzer wavelengths are matched and

scanned.

Initial measurements have centered on an aluminum (2024-T353) ring-plug sample

3 fabricated for use as a standard reference sample for ultrasonic measurements. In

this shrink-fit type of cylindrical sample the theoretical stress distribution is

given by:

PRf / R^

03 = Oq = -P r < R^ (3)

E(R^ - R^)5

and P = -—^ '

• (4)

2^2

where R is the plug radius, R is the ring outer radius, E is Young's modulus, and 6 is the differential radial interference. In the ultrasonic reference sample

E = 73100 MPa, Poisson's ratio is 0.33, R^ = 1.27 cm, R^ = 3-81 cm, with a thickness

of 2.5 cm. The measurements were made using the (200) reflection and a differential volume

of 1.5 X 1.5 x 20 mm at a scattering angle of 90°. If the unstressed d-spacing (d^)

is known, residual stresses for the three principal directions could be obtained

directly by three strain measurements at each point of interest in the sample.

Alternatively, (0 - o.) can be obtained at each point of interest without a

4

"^ knowledge of d . Values for and o„ can then be extracted by application of the

o re

overall equations of equilibrium and the use of an anlytical model.

32
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

Figure 1. The intersection of ingoing and 90°-scattered collimated neutron beams

showing the examined differential volume.

(0 Q.

b^

r(in)

0.5 1.0 1 5 ASSUME:

100-

200-

c^-^f'-O IN PLUG

^-* IN RING

APPLY: fC

/ FdA = = / *^ dR

'tfit "0 (Z)

*p(lO "

dR R

IN PLUG:

P = -129.0 + 2.4 MPa "THEORY"

P = -122 + 5 MPa NEUTRON DIFFRACTION

Figure 2. Measured and calculated (o - o ); and equilibrium conditions and

assumptions employed to obtain P in plug region.

33
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

In Figure 2a, measured o - o values for selected points in the sample are

shown. Also shown are the o - o distribution calculated from equations (1)-(4),

using the measured, pre-assembly , differential radial interference. Under the

assumptions shown in Figure 2, and applying the equilibrium conditions, an

experimental P = -122 + 5 MPa is obtained in excellent agreement with the calculated

P = -129.0 _+ 2.4 MPa.

In view of the success with the aluminum ring/plug sample, the energydispersive neutron diffraction method is being applied to a material which has posed

serious difficulties for conventional residual stress measurement techniques:

depleted uranium. Initial results on two 2.5 cm diameter extruded cylinders with

quite different thermo-mechanical histories show markedly different strain

distributions. It is anticipated that three-dimensional stress profiles will be

obtained at selected points in the samples in the very near future with existing

instrumentation.

1. C. S. Choi et al., NBS Tech. Note 995, p. 3^ (1979).

2. L. Pintschovius et al .

, in "Residual Stress and Stress Relaxation" (ed. E. Kula

and V. Weiss), Plenum Press, New York, 1982, 467.

3. N. N. Hsu, T. M. Proctor, Jr., and G. V. Blessing, J. Test. Eval. ]_0, 230 (1982).

4. See, for example, J. B. Cohen, H. Dolle, and M. R. James, NBS Special Publication

567 , 453 (1980).

5. In reference 3 an incorrect value of P = 65 MPa was quoted.

CRYSTAL DATA (PRODUCED BY AUTOMATED TYPESETTING PROCEDURES)

A. D. Mighell and J. K. Stalick

Work on Volume 5 in the Third Edition Series of Crystal Data has been

completed. The book contains about 10,000 entries on crystalline compounds. The

data are ordered by crystal system and within each system the entries are arranged as

a function of the lattice parameters. The volumes in the Third Edition Series are used by the industrial and academic communities for identification, for phase

characterization, and for many other applications. Volume 5 will be published in the

fall of 1983 jointly by the U. S. Department of Commerce, National Bureau of

3A
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

Standards, and the JCPDS—International Centre for Diffraction Data. Production of

Volume 5 of Crystal Data has been done in collaboration with the Cambridge

Crystallographic Data Centre.

The book was produced by computer-oriented procedures in a two stage process.

First, the Crystal Data Master Data Base was produced for Volume 5 by using the

computer program NBS*AIDS80. This program was used to evaluate the data, to

calculate new data parameters, to transform cell data, and to build the Master Data

Base. Thus, every item in each entry in the Master Data Base was defined, evaluated,

and represented in standard form. Second, computer-typesetting procedures were applied to the Master Data Base to extract the relevant data and to produce the book

and indexes. The typesetting routines were written by the Data Systems Development

Group of the Office of Standard Reference Data.

Future volumes in the Crystal Data Series will be produced by the same strategy

(i.e., directly from the Master Data Base by automated computer procedures).

Likewise other products can be generated. For example, the Crystal Data Center

prepares the NBS Crystal Data Identification File from the Master Data Base in

parallel with the books. The Identification File can be used independently or in

conjunction with the Crystal Data books in the Third Edition Series. This file is

designed for the rapid identification of unknown materials and is distributed on computer tape by the JCPDS. The Identification File can also be accessed by on-line

computer search systems in the U. S. and in Canada. Similar methods could

conveniently be used by other data centers for file preparation and product

production. In fact, the JCPDS-International Centre for Diffraction Data plans to

generate printed and magnetic tape products directly from their AIDS80 formatted

Master Data Base which contains powder data.

1. NBS*AIDS80: A FORTRAN program for Crystallographic Data Evaluation (1981),

A. D. Mighell, C. R. Hubbard, and J. K. Stalick, NBS Technical Note 1141.

35
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

PROGRESS REPORT ON A STUDY OF SPECIALIZED LATTICES USING MATRIX AND

REDUCTION TECHNIQUES

V. L. Himes* and A. D. Mighell

An area of research in progress concerns the classification of lattices in the

NBS Crystal Data Identification File (NBS*ID File, 1982) according to types of

specialization in the reduced cell or reduced form. Thus, methods to seek and define

specialization are being investigated. One way is to analyze the relationships

between the symmetrical and unsymmetrical scalars in the reduced form. A second, and

perhaps more general way, is to analyze the matrices that relate the cell to those

metrically identical to it. These matrices fall into two types: matrices whose

elements are only integers, and matrices whose elements are integers and simple

rational numbers. Classifications of specialized reduced forms may be used as frameworks to establish lattice relationships. With a given classification, patterns

in the data may be recognized and correlated with potential indexing problems, with

errors made in experimental procedures, or with physical properties of the compounds.

A general plan for this project has been. devised and many of the computer programs

required for this research have been written.

In order to systematically classify and analyze specialized reduced forms, it

was necessary to design data file structures and to develop computer code and

strategies to efficiently manipulate large sets of data. For example, two different

1-line (132 characters per entry) data bases have been derived from the 4-line (four

80 character records per entry) NBS*ID File. These 1-line data bases will be used to

create 1-line sub-files of lattices having specialized reduced forms.

Preliminary analyses with the 1-line files using software specific to this

research project show that although many specialized reduced forms exist, two general

categories may be defined. The first class includes those specialized reduced forms

in which the metric symmetry exceeds the reported crystal symmetry. The second class

of specialized reduced forms results when the crystal and metric symmetry agree, but

there is at least one relationship within the reduced form that is not required by

the crystal symmetry.

^National Bureau of Standards - National Research Council Postdoctoral Research

Associate.

36
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

Once suitable sub-files have been created, it is planned to use a combination

of reduction and matrix techniques to identify the first class of specialized

reduced forms [i.e., those reduced forms with higher metric symmetry or

pseudosymmetry; (Himes and Mighell, 1982)]. Using these strategies, preliminary

analyses have been carried out. For example, triclinic and monoclinic 1-line organic

files have been used to create sub-files with a = b, b = c, and a = b = c. Analyses

of these sub-files using the matrix method have revealed that many triclinic and

monoclinic lattices have orthorhombic metric symmetry. These specialized reduced

forms may be due to structural reasons, or the true crystal symmetry could have been

missed. Regardless of the reasons, experience has shown that the presence of higher

metric symmetry or pseudosymmetry in a lattice leads to the existence of metrically

similar unit cells that index differently the same set of diffraction data. Once the

higher symmetry or pseudosymmetry is recognized, the resulting indexing problems can

be avoided. Several hundred references from these categories of specialized reduced

forms have been collected for more detailed analyses.

The specialization in the second class of reduced forms may be due to certain

properties of compounds such as packing, twinning, and conductivity, or it may result

from errors made in experimental procedures. For example, a specialized reduced form

may suggest that the unit cell obtained by indexing powder data is not a primitive

cell of the lattice but rather a derivative cell. Likewise, a derivative subcell

could have been determined using a single-crystal dif f ractometer if rows of

diffraction spots were missed. Lower symmetry derivative subcells of higher symmetry

lattices will show specialization in the reduced form.

Both practical examples and a brief survey of lattices from the NBS^ID File

suggest that the 1-line sub-files of specialized reduced forms should be analyzed to see whether a derivative sub- or super-cell has been determined. Subcells and

supercells for selected specialized reduced forms will be calculated and attempts

will be made to relate these derivative lattices to other lattices in the data base.

A match of a derivative lattice with one already in the data base could help one to

understand the specialization in the reduced form. For example, an experimental

error could have been made or the literature may cite structural reasons such as temperature- or pressure-dependent phase transitions. For each lattice that is

characterized by a primitive cell, there are 55 subcells with 1/2, 1/3, and 1/4 times

the volume and 55 supercells with 2, 3, and 4 times the volume of the primitive cell

(Santoro and Mighell, 1973). Thus, an efficient computer strategy and program are required to match a series of primitive cells and derivative cells against the entire

37
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

NBS*ID File. Accordingly, several search strategies for an identification/

registration program based on lattice-matching have been developed. The computer

programs, written using standard FORTRAN code, are currently being modified and

tested. The identification/registration programs utilizing "sequential access" and

"grouped-entry direct access" searches have proved to be efficient strategies. In

particular, the grouped-entry direct access program will allow about 1,000 cells to

be checked against approximately 30,000 entries from the NBS*ID File in only two

minutes (Univac 1100/82 computer), making the derivative-lattice analysis of

specialized reduced forms feasible.

Additional preliminary computer analyses will be made and practical examples of

lattices having specialized reduced forms will be studied. These efforts will help

to define and select appropriate sub-files of specialized reduced forms to study in

detail. The results of these analyses should lead to a better understanding of

lattice relationships and should have a direct impact in many areas of experimental

and theoretical crystallography.

1. V. L. Himes and A. D. Mighell, Acta Cryst. A38, 7^8-749 (1982).

2. NBS Crystal Data Identification File (1982). A magnetic tape of crystal data

distributed by the JCPDS - International Centre for Diffraction Data, 1601 Park

Lane, Swarthmore, PA 19081, USA.

3. A. Santoro and A. D. Mighell, Acta Cryst. A29, 169-175 (1973).

38
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

SPACE GROUP FREQUENCIES FOR ORGANIC COMPOUNDS

A. D. Mighell and V. L. Hiraes*

and

J. R. Rodgers

(National Research Council of Canada, Ottawa, Canada)

1 . Introduction

Using the NBS Crystal Data Identification File (1982), the frequency of

occurrence has been calculated for each of the 230 space groups. The space group

frequencies presented in Table 1 were calculated for organic materials (i.e., carboncontaining compounds). Most of these compounds (- 89.9^) correspond to entries that

result from full structure determinations. The types of structures reported in the

literature have been influenced by a variety of factors such as the techniques

available to solve structures and special interest in selected categories of

compounds. Nevertheless, since it was possible to tabulate space group frequencies

for 29,059 organic compounds that have been reported up to 1981, the results should

be fairly representative of their distribution in nature.

The space group frequency table may be used in routine structure work. We have

found it helpful to check a list of space group frequencies as soon as a space group

has been assigned or limited to a few possibilities. The frequencies may indicate

that a space group determination should be rechecked if the substance has been

characterized by a rare or previously unoccupied space group. If the compound has,

indeed, crystallized in a rare space group, the NBS Crystal Data Identification File

may be used to find references for a structure comparison. For reasons discussed

below, however, it is important not to have a false sense of security when a commonly

reported space group has been determined.

Inspection of the data in Table 1 reveals that most organic compounds have been

assigned to a relatively small number of space groups. In fact, 75 percent of the

compounds have been described in only five space groups and 90 percent in 16 space

groups. A comparison of the percent occupancy of the five most common space groups

with corresponding data calculated earlier using a smaller sample of 21,051 compounds

(Mighell and Rodgers, 1980) reveals that the percentages for the five most frequently

occurring space groups are fairly constant. The percentages are as follows, with the

earlier data given in parentheses: P2 /c, 36.055 (35. 55^); PT, 13«7^ (13.3f»); P2^2^2^,

^National Bureau of Standards - National Research Council Postdoctoral Research

Associate.

39
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

11.65^ (12.4^); P2 , 6.7^ (7.655); C2/c, 6.65^ (6.9^). In contrast, there are 117 space

groups with very low frequencies (five or fewer compounds assigned to them). Of

these 117 space groups, 29 space groups have one entry and 35 have no entry at all.

Thus, it may be possible to develop theories which would explain why certain space

groups are rare or uninhabited, or one may be able to correlate the molecular shape,

physical properties, etc. with the probability that the compound crystallizes in a given space group.

As a further aid to experimental and theoretical work, space group frequencies

for the 86 chemical classes (steroids, silicon compounds, metal complexes, etc.)

listed in Molecular Structures and Dimensions (1970-1982) are being prepared and will

be submitted for publication.

2. Discussion

It is important to remember that the frequencies of occurrence are approximate

since certain space group frequencies may be under- or overestimated. Detailed

analyses of several cases in which crystal structures have been described in space

groups of unnecessarily low symmetry have been carried out; examples are given in the

following references: Davies, Kopf, and Weiss, 1982; Herbstein and Marsh, 1982;

Marsh and Schomaker , 1980; Schomaker and Marsh, 1979; Marsh and Schoraaker, 1979.

These references demonstrate that what appears to be a satisfactory structural

refinement does not necessarily imply a correct space group determination. The errors in space group assignments that are discussed in the above references can be

divided into two categories: 1) incorrect space group but correct crystal system; 2)

incorrect space group and incorrect crystal system. Errors of the second type can be

prevented or detected by determining the metric symmetry of the lattice. Using a matrix technique (Himes and Mighell, 1982) to analyze the metric symmetry of - 30,000

organic entries in the NBS Crystal Data Identification File , it has been found that

many crystals reported in triclinic and monoclinic space groups have higher metric

symmetry. Depending on the values used for "reasonable" errors on the cell

parameters, it was found that for 3 to 12 percent of the compounds the metric

symmetry exceeds the crystal symmetry reported by the authors in the original

reference. Inspection of samples from selected categories of these papers further

revealed that, in many instances, the compounds have probably been described in space

groups of too low symmetry.

Many of the errors in space group determination can be attributed to blind

acceptance of the results of automated dif fractometers, failure to inspect carefully

the final structural parameters for possible higher symmetry, failure to ascribe

40
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

unusual molecular or packing symmetry to a refinement in an incorrect space group,

assuming that the e.s.d.'s on the cell parameters indicate accuracy rather than

precision, and errors in space group determination strategy.

It is a serious error in strategy for the experimentalist not to check

explicitly for the highest metric symmetry. This can lead to an assignment of a space group in the wrong crystal system. Traditionally, one of the first steps in

assigning a space group for a compound is to select unit cell parameters to be

consistent with the observed intensity symmetry. The defect in this method is that

the full intensity symmetry is not always easy to see. Thus, one could select a centered monoclinic cell consistent with the apparent Laue symmetry, check for

systematic extinctions, and conclude that everything is correct for the assignment of

a centered monoclinic space group. However, the space group may be rhombohedral

because the metric symmetry was not checked and the true Laue symmetry is higher.

Our analysis of metric symmetry for organic compounds suggests that the rhombohedral

system with approximately 300 reported compounds should have 10 to 20 percent more

compounds assigned to it. Two examples of missed rhombohedral symmetry are discussed

below.

The first example of missed crystal symmetry is S(-)-cyclophosphamide. S(-)-

cyclophosphamide has been reported in a triclinic space group, PI, with cell

parameters a = 10.500(4), b = 10.490(4), c = 10.761(4) A, a = 110. 0(2), 3 = 110.0(2),

and T = 108.9(2)° (Adamiak, Saenger , Kinas, and Stec, 1977). In contrast, R(+)-

cyclophosphami de has been reported in a rhombohedral space group, R3> with

a = 10.520(5) A and a = 108.9(1)° (Karle, Karle, Egan, Zon, and Brandt, 1977). Both

compounds were characterized by full structure determinations and, in each case, the

cyclophosphamide molecules form hydrogen-bonded trimers. Both reduction and matrix

techniques show that the metric symmetry for each compound is rhombohedral suggesting

that S(-)-cyclophosphamide was refined in a space group of too low symmetry. The

matrix procedure yielded six matrices which are characteristic of rhombohedral

lattice symmetry while the reduced cell matrices (a. a b.b c.c / b.c a.c a.b)

calculated for both S(-)- and R(+)-cyclophosphamide correspond to the rhombohedral

reduced form #4 (Mighell and Rodgers, 1980; International Tables for X-ray

Crystallography, 1969):

110.04 110.23 110.25

-35.93 -35.68 -35.75

S(-) -cyclophosphamide

'110.67 110.67 110.67

-35.85 -35.85 -35.85

R(+) -cyclophosphamide

41
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

Tables 2 and 3 give a summary of these results. Within experimental error, the

atomic coordinates for S(-)-cyclophosphamide can be transformed to those reported for

R(+)-cyclophosphamide.

A detailed analysis of a typical example of missed rhombohedral symmetry has

been reported by Davies, Kopf, and Weiss (1982). In this case, it was shown that the

structure of sodium tert- butoxide, which was originally reported in the monoclinic

space group, Cc, with a = 30.995(23), b = 19.378(14), c = 18.269(13) A and

B = 121.01(2)° can be described in the rhombohedral space group, R3c, with

a = 18.274 A and a = 64.07°. A transformation matrix relating the C-centered

monoclinic cell to the primitive rhombohedral cell (= reduced cell) is (0 0-1 / 1/2

1/2 / 1/2 -1/2 0). By using metric methods, one can immediately establish from the

originally reported monoclinic cell parameters that the lattice is metrically

rhombohedral. For example, the reduction method gives rhombohedral reduced form #2

(Mighell and Rodgers, 1980; International Tables for X-ray Crystallography , 1969)

while the matrix technique, when applied to a primitive cell of the lattice, yields

six matrices indicating the rhombohedral lattice symmetry (see Table 4).

In Table 5, we outline a procedure to help prevent errors in space group

determination. The procedure is similar to one presented earlier (Mighell and

Rodgers, 1980) except that we have added a check using a matrix technique, a check of

the NBS Crystal Data Identification File , and a check of the space group frequency

table. As the table shows, the metric symmetry is determined as soon as a primitive

unit cell of the lattice has been found. The metric symmetry may be determined using

both matrix and reduction techniques. When using reduction techniques, the^ metric

symmetry can be determined directly from the Niggli reduced form, or by alternative

procedures recommended by Clegg (1981) and Le Page (1982). When assigning a space

group, one should start by considering space groups consistent with the highest

possible metric symmetry.

42
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

Table 1. Space group frequencies for 29059 organic crystalline compounds

Space Space Frequency Space Space

Group Group Group Group

Symbol Number Symbol Number

PI 1 305 Pmn2

Pba2

31

Pi 2 3986

32

P2 3 11 Pna2

Pnn2

33

'h 4 1957 34

C2 5 273 Cram2 35

Pm 6 1 Cmc2

Ccc2

36

Pc 7 102

37

Cm 8 22 Amm2 38

Co 9 277 Abm2 39

P2/m 10 5 Ama2 40

P2^/m 11 239 Aba 2 41

C2/m 12 189 Fmm2 42

P2/c 13 141 Fdd2 43

P2^/c 14 10450 Imm2 44

C2/c 15 1930 Iba2 45

P222 16 7 Ima2 46

P222,

1 17X / 9 Pmmm 47

P2^2^2 18 187 Pnnn 48

"l^l^ 19 3359 Pccm 49

C222 20 86 Pban 50

C222 21 5 Pmma 51

F222 22

Pnna 52

1222 23 7 Pmna 53

"i^i^i 24 5 Pcca 54

Pmm2 25*-^ 2 Pbam 55

Pmc2 26 12 Pccn 56

Pcc2 27 Pbcm 57

Pma2 28 1 Pnnm 58

Pea 2 29 242

Pmmn 59

Pnc2 30 3 Pbcn 60

Frequency

37

9

513

14

2 56

6

5

14

47

8

115

3

31

5

4

3

1

2

9

23

15

13

12

101

64

30

23

341

43
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

Table 1. Cont

Space Space Frequency Space Space Frequei

Group Group Group Group

Symbol Kumber Symbol Number

Pbca 61 1261 P4^22 91 3

Pnma 62 548 P4^2^2 92 101

Cmcm 63 61 P4222 93 2

Cmca 64 96 P^22i2 94 7

Cmmra 65 4 P4322 95 1

Cccra 66 12 P432^2 96 44

Cmma 67 2 1422 97 2

Ccca 68 14 14^22 98 1

Ftnmtn 69 3 P4mm 99

Fddd 70 30 P4bm 100

Immm 71 4 P42cm 101

Ibam 72 27 P42nm 102 4

Ibca 73 8 P4cc 103

Imma 74 5 P4nc 104 3

P4 75 1 P42mc 105

P4^ 76 47 P42bc 106 1 P42 77 3 1 4mm 107 2

P43 78 7 I4cm 108 1 14 79 12 14 md 109 6

^\ 80 9 14 cd 110 9

?n 81 7 P42m 111 1

14 82 59 P42c 112

P4/tn 83 6 P42^m 113 17

P42/m 84 3 P42 c 114 68

P4/n 85 37 P4m2 115 1

P42/n 86 48 P4c2 116

lU/xK 87 28 P4b2 117 2

l4^/a 88 98 P4n2 118 4

P422 89 1 I4m2 119 1 P42^2 90 4 I4c2 120 2

44
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

Table 1. Cont

Space Space Frequency Space Space Frequency

Group Group Group Group

Symbol Number Symbol Number

I42m 121 12 P3^12 151 9

I42d 122 22 P3j^2l 152 27

P4/minin 123 P3212 153

P4/aicc 124 8 P3221 154 8

P4/nbm 125 4 R32 155 23

P4/nnc 126 1 P3ml 156 1 P4/mbm 127 2 P31m 157 4

P4/mnc 128 14 P3cl 158 3

P4/nmm 129 19 P31c 159 5

P4/ncc 130 16 R3m 160 21

P4„/tnmc 131 3 R3c 161 39

P42/iiicm 132 1 P31m 162

P42/nbc 133 2 P31c 163 13

P42/nnm 134 2 P3ml 164 15

P42/tnbc 135 1 P3cl 165 17

P42/mnm 136 17 R3m 166 20

P42/nmc 137 8 R3c 167 36

P42/ncm 138 3 P6 168

l4/mmm 139 17 P^l 169 14

l4/mcm 140 4 ^S 170 16

14^ /amd 141 11 P62 171 5 l4^/acd 142 19 P^ 172

P3 143 10 P63 173 33

^\ 144 21 P6 174 1 P32 145 10 P6/m 175 1 R3 146 40 ve^/m 176 75

P3 147 26 P622 177 2

R3 148 122 P6^22 178 6

P312 149 P6^22 179 1 P321 150 5 P6222 180 4

45
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

Table 1. Cont

Space Space Frequency Space Space Frequency

Group Group Group Group

Symbol Number Symbol Number

P6^22 181 1 Ia3 206 5 P6322 182 6 P432 207

P6mm 183 P4232 208

P6cc 184 F432 209 1 P6„cm 185 1 F4^32 210 3

P6„mc 186 15 1432 211

P6m2 187 P4332 212 I P6c2 188 P4^32 213 1 P62m 189 14^32 214

P62c 190 9 P43m 215 7 P6/mmm 191 I F43m 216 1 P6/mcc 192 7 I43m 217 18

P6„/mcm 193 P43n 218 6

P6 /mmc 19^ 9 F43c 219 2 P23 195 I43d 220 4

F23 196 Pm3m 221 3

123 197 3 Pn3n 222

P2^3 198 15 Pm3n 223 5 12^3 199 Pn3m 224 1 Pm3 200 2 Fm3m 225 22

Pn3 201 Fm3c 226

Fm3 202 Fd3m 227 1 Fd3 203 1 Fd3c 228 4

Im3 204 3 Im3m 229 8

Pa3 205 36 Ia3d 230

46
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

( ""1 r_ 1 1 1 o o

1 o

1

I

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o

1

1 o

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V o ,—

1

1

1 o o ,_

1 'o o

1

1 ro —

o

o - o o - o

1 o o ^ o o

^ o o o o _ o o o

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1

1 1 1 1 1

1 1 1 CDO

• •rH q; !L T3 4->

•rH CO S 1 1 I

! ~ r 1 r"'"" m 1 ,

o ,

o ^

,

o X— o ,

o o

x: CQI 1 1 1 ex« ,— o o ,— ,— o o o ,— o o ,— o 1 1 1 x:Q. T

X o o T o 1

o o o T o

o 1 1 . 1 iH 1

1 1 J 1 1 L_-

J o

>>o

1

1 ^

CO o < o ^ CNJ o .=r s- ^-^ v.^ ^ CTN y—N o CT. o c— • o LPi . Cm O ;^ o

COo o

• o

COo

C X— ^— ^ ^— O T—

i-H m 1 4-> t. CO \

C 4J

•rH ^-N ,

s s ^ ^-v

;- CO ^.^ CM ,—

S-, o —- CTn o 4-> CO <J^ o f

CT^ C7^

CD Cu ^ ca -=r . .=r . o

rH o

o \

o o

>. rH ^

T o ,

,

L

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(D 1 e 4-> s •H o >, C ^^ v_^

CD 13 =r

CM o — o C\i O o o CT. o •i-H CO 8 LO • •=r • JJ . o • o^

-P o T— o o

to T T

^

^

1—1 o

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r-{

CO

rH

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CO •H

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I-H •H

i- P

rHO

a

o

3O

PC

47
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

Table 3. Matrices found for R(+)-cyclophosphamide,

Initial cell a = 10.520

(= reduced cell) a = 108.9

b = 10.520 c = 10.520 A

B = 108.9 Y = 108.9°

B-Matrices

1

-1

-1

-1

1

-1

-1

-1

1

1

1

1

1

1

1

1

1

1

48
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

^ o o' '

o o

'o o _ 1 T o ol 'o o

1 o - o o

1 o o - o

,_ o o o o ,_ , o o

J L J U

03O

•H

SnJ

I

1

I o o o o

T- O

J L

I o T- o

I

I o o

.- o o

I o -- o

O T- o

t- o o

o o <-

•oXo

I

ss

3

•H

•oo

COo

co

COc

•HE

s,

0)

Q> o

>,

S4-5 CDs

s

>)

COo

•iH -U

4-> CO

-P

CD

0) rH

X3

(0 E1

1 T- T- O r- O

1 r

CO 3

m

o ct; o <T> "-^ v_^

C\J o ?- • oo O '" a^

COt.

CD

4-> y s ^ ^-^ E T— CM

CO —- v-^

£- CX5 ,

CO t— O

a. £) ca cn •

• T <-{ C7^ CM

rH ,

5

o

4-> •H ^-^ C c>o

:=> CM

o o

cn C7^

o

o

c

o

s

I—

t

CO oo

I o

o

•\

o

in

in

I

I o

^ o

<J^ ,— VO o

CM •

• CM OO C\J

c—

CM OO

OO

OO

-pS

O

O

C7^

O

CTi LO

.- O

o <-

CMCO

CMCO

CO

;3-

1 o CT\ o VO CO

CM O

o

>

T3 •i-l CD 4-i C) •rH 3 e o •rH t.

ck; a

^ o o

O O T- O r- O

49
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

Table 5. Space group determination,

Determine and refine a primitive

cell of the lattice

Verify that the cell is primitive:

systematicaily check for possible

subcells in reciprocal space

Determine metric lattice symmetry

Matrix method:

generate and analyze

symmetry matrices and error matrices

Reduction:

calculate reduced cell

and reduced form matrix;

determine reduced form type

(or use alternative procedure,

see Discussion)

Compare reduced cell with those for

known substances in the

NBS Crystal Data Identification File

Transform to conventional cell

Confirm Laue symmetry

Determine systematic extinctions, if any

Assign space group or aspect

Check space group frequency tables,

cell volume, Z, experimental and

calculated densities

50
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

1. D. A. Adamiak, W. Saenger , R. Kinas, and W. J. Stec, Z. Naturforsch. , 32c , 672-

677 (1977).

2. W. Clegg, Acta Cryst., A37 , 913-915 (1981).

3. J. E. Davies, J. Kopf, and E. Weiss, Acta Cryst., B38 , 2251-2253 (1982).

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

5. V. L. Himes and A, D. Mighell, Acta Cryst., A38 , 748-749 (1982).

6. International Tables for X-ray Crystallography , Vol. I, 530-535. Birmingham:

Kynoch Press (1 969)

.

7. I. L. Karle, J. M. Karle, W. Egan, G. Zon, and J. A. Brandt, J. Am. Chem. Soc,

99, 4803-4807 (1977).

8. Y. Le Page, J. Appl . Cryst., j_5. 255-259 (1982).

9. R. E. Marsh and V. Schomaker, Inorg. Chem., j_8, 2331-2336 (1979).

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

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

12. Molecular Structures and Dimensions (1970-1982). Published for the

Crystallographic Data Centre, Cambridge and the International Union of

Crystallography

.

13- NBS Crystal Data Identification File (1982). A magnetic tape of crystal data

distributed by the JCPDS-International Centre for Diffraction Data, 1601 Park

Lane, Swarthmore, PA 19081.

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

51
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

AN EMPIRICAL METHOD FOR THE APPROXIMATION OF DENSITIES

J. K. Stalick

It is frequently useful to know what the density of a substance should be,

particularly in evaluating the correctness of a chemical composition and/or

experimental unit cell parameters. Techniques exist for the approximation of

1 2 densities for some types of organic compounds and for simple ionic substances

provided that the structure is known. However, difficulties arise when the substance

is complex or the structure is unknown. In particular, a method was needed to detect

errors in the Crystal Data data base. The most easily found errors are those where

the formula and Z (number of molecules per unit cell) are not compatible, resulting

in x-ray calculated densities, D , wrong by a factor of two or more. It was also

hoped to be able to detect certain errors in chemical composition or unit-cell data.

In order to calculate an approximate density, D , it was assumed that the

O

molecular volume as determined by x-ray studies, V , is equal to the sum of the

individual atomic volumes, V. . A least-squares refinement was carried out with up to

2000 equations (compounds) and 106 unknowns (atomic volumes) using data from the

Crystal Data data base. The function minimized was V - £N.V., where N. is the

X 1 1 1 1 number of atoms of each type. The data sets were adjusted so that each atom i was represented in at least 10 equations. The three basic divisions of the data base

(organics and organometallics , metals and intermetallics, and inorganics) were

treated separately. Subsets of data of a more homogeneous nature, for example all

compounds containing only C, H, and 0, were also examined.

Tests using the three basic divisions of substances indicated that a correction

for electronegativity difference is valuable for all except the primarily covalent

organics and organometallics. The correction is especially important when a data set

containing entries for diverse compound types is used. Since no bonding information

is available in the data base, the average electronegativity difference. A, was

defined as follows:

A = ZN.x. - 5:n.x.

i

1 1 j J J

where /is the electronegativity on the Allred-Rochow scale and N is the number of

atoms of each type. The atoms in each substance were divided into two equal groups,

where the subscript i refers to the most electronegative atoms and the subscript j

52
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

<D5

o

o

vs.

I

bO

o

c

toa

<u

s,o

CO

^!«.

co

•1-1

«J iH

=so

rH

03O

>>

4->

•r-H COco

4->

(T3 e

•iH X

o

Q.

O

m

4->

.-I

CO

0)

<4-l o

>.

SCOs

s

CO

X3

cd-

•iH COC

<D •o

0)

COE

•i-t Xo

a-Q.

O,

CO

(U

4->

bO

T3C

CO>i

4J

•i-l COc

>,

CO

JIX

CD

4-5

<1) o

bO c

(0 CO

S- Q.

CD CD > L

< O

CO

0) CO

CO

(0 Q

•:3- CM OO -3- LTi m cv^ on on o^

LO 1 1 1 1 1 CO 1 1 1 1 1 c

•r^ 6*. O o 1 o 1 1 s: Cvl o 1 o 1 1 J-) •k ^

^

•iH >. 3 o

c LPi CT. O <Tl O o

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•o d t

51

c <D 3 S- o o o ^ o- vO CO tex CO ,

CT> <y^ C7^ a^ CTi s •i-H o Q o

in OO CT\ OO c— in

t— c— t— ^- c~-

CO T3

j- c

Q) 3 o in o MD 5

X5 Cm O 00 o cr> o CT. S O a LO c^ m ,

CO 3 E ,— 2 O

o

cn CO CO

0) CO o o a I-H .H •^

>-. CO 1—

1

r-1

4-> JJ rH iH

CO CO •o E 4-> 4-> >, c 1 0) CD .H 3 C E E c

O o O O o

o. c c C

E CO CO o

O •o bO bO o c S- t- M

CO o O tc

r-l rH 3 o c m. < O o M o

W

O

rH •o rH c i-H CO CO

-!-> CO CD o E

•iH O

c C

CO CO bO bO

S- S- O O

,—

s

C-- O cn

::3- • • • ITi 00 VD

LTi N»^ •s^^ ^-^

N.^ >^ o CJ^ O VO .=r in VD C\J CO VO vO

C7^ 1

1

00 CO 1

1

CT\ CT^ o

o

OO

OO

CMCO

OO

CJ^

VO

t- OO

CM !>- O

a> cTi OO

cr> CT> :=r

CM 4J 4->

CO CO

•^ M

to CO o

a a a

>, >, 3

jj 4-3 rHo

•o T3 X

c C

3 3

O O CO o. a .H E E CO O O 4-> O o

E

rH r-l 1 M I-H C

•a: •a: o

* * 2

VO t- vO

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53
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

bO

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54
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

refers to the least electronegative atoms. The approximate molecular volume, V , was

o then calculated assuming

V = (1 - KA^)EN.V.

g ill

where V. are the individual atomic volumes, and k and x are empirical correction

factors. The best agreement between V and the molecular volume as determined by xg

ray studies was obtained for k ~ 0.2 and x ~ 0.6. Although the improvement in

average discrepancy was not large, the agreement for metallic elements was

significantly better.

The results for all data sets examined are given in Table 1 . The average

agreement of the approximate density with the x-ray calculated density is within 4 percent for organics and organometallics, 6 percent for metals and intermetall ics

,

and 8 percent for inorganics; nearly all substances agree within 25 percent. The

effective atomic volumes vary significantly with compound type (Table 2); thus the

separation of the data base into the three basic divisions helps in evaluating the

data. The use of limited data sets (Table 1) also improves the reliability of the

derived approximate densities.

The effective atomic volumes obtained from this study have been used in the

evaluation of approximately 20,000 organic and organometallic entries for the Crystal

Data data base. Errors in Z were readily detected. In addition, errors in chemical

composition (e.g. omission of solvent molecules) and unit-cell data were also found

and corrected.

1. A. Immirzi and B. Perini, Acta Cryst. or Sect. A, 32> 216 (1977).

2. W. H. Baur , American Crystallographic Association Winter Meeting Abstracts, 41 (1983).

3. A. L. Allred and E. G. Rochow, J. Inorg. Nucl. Chera. 5, 264 (1958).

55
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

THERMAL PROPERTIES OF (KCN) (KBr), IN THE QUADRUPOLAR GLASS STATE

X 1-x

J. DeYoreo and R. Pohl

(Cornell University, Ithica, NY)

and

J. M. Rowe and J. J. Rush

and

S. Susman

(Argonne National Laboratory, Argonne, IL)

Samples of (KCN) (KBr) can be prepared as solid solutions over the entire

range of x from 0.0 to 1.0, and have been extensively studied by a number of

techniques. For x greater than approximately 0.6, phase transitions to structures in

which the electric quadrupole moments are ordered are observed as the temperature is

lowered, with the transition for x = 0.6 occuring at approximately 85 K. For x less

than 0.6, no transitions to structures in which the quadrupole moments have long

range order has been observed. Michel and Rowe proposed a model for the behavior of

samples with x less than 0.6 in which the quadrupole moments would order collectively

in a phase analogous to the magnetic spin glass state. This model has been

2 3 criticized ' on the basis of recent dielectric relaxation measurements which showed

that the CN ions remained or ientat ionally mobile at temperatures well below the

postulated "freezing" temperature T , and that the relaxation simply slowed down

continuously with temperature. However, the dielectric data are not necessarily

inconsistent with the model, since the quantity measured is the electric dipole

susceptibility, not the quadrupolar susceptibility. Further, to the extent that the

dielectric data reflect Debye relaxation (as they clearly do in pure KCN ), they are

a measure of the single particle behavior rather than the collective behavior; i.e.,

they are a result of the reorientation of individual CN ions in the applied field,

which is observed in pure KCN below both the quadrupolar and the dipolar transitions.

In order to clarify this situtation, as well as to establish the low temperature

thermal properties of the mixed crystals, we have measured the thermal conductivity

and specific heat of samples with x less than or equal to 0.5 as a function of

temperature between 0.8 and 100 K. The results are quite similar to the behavior

observed for amorphous solids and show that these systems may be quite useful as models for the low energy excitations in amorphous solids. In addition, we observe

an anomaly in the thermal conductivity for x = 0.25 at temperatures close to those

proposed for T on the basis of neutron scattering measurements of the dynamics of

the same samples. However, the temperatui^e at which this anomaly occurs is not

56
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

reproducible when the sample is remounted in the cryostat although it always occurs

at temperatures of the same order as T . This effect is not simply an experimental

artifact of the particular arrangement used - no such effect was observed for a sample of silica measured under the same conditions. Thus the nature of the

formation of the glassy state remains somewhat ambiguous until further measurements

can be performed. However, the present work shows that the (KCN) (KBr) system is

a good model system for the study of the low energy excitations found in amorphous

solids, especially since the nature of the low energy excitations is well-known for

very small x, where the CN ions are isolated rotators tunneling in the crystal field.

Further work is currently in progress to clarify the nature of the high temperature

anomaly

1. K. H. Michel and J. M. Rowe, Phys. Rev. B22 , I^^IY (1980)

2. A. Loidl, R. Feile and K. Knorr, Phys. Rev. Lett. 48, 1263 (1982)

3. S. Battacharya, S. R. Nagel, L. Fleishman and S. Susman, Phys. Rev. Lett. 48 , 1267 (1982)

4. F. Luty and J. Ortiz-Lopez, Phys. Rev. Lett. 50, 1289 (1983)

STRUCTURE OF ALKALI CYANIDE AND MIXED ALKALI CYANIDE-ALKALI HALIDE CRYSTALS

J. M. Rowe and J. J. Rush

and

S. Susman

(Argonne National Laboratory, Argonne, IL)

and

F. Luty

(University of Utah, Salt Lake City, UT)

During the past year, we have completed an extensive series of measurements on

(KCN) (KBr), with x = 0.95, 0.90 and 0.80 as functions of temperature using neutron

X 1-x

powder diffraction. The data have been analysed by the method of total profile

refinement. In each case, there is a phase transition as the temperature is reduced

from the high temperature cubic phase to a monoclinic structure with space group Cc.

This structure is related to the cubic one by a combination of E and T_ strains

g ^g

with the T^ strain (e,, + e^) being the largest. (The other strains are all less

2g 4 5

57
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

than M.) No evidence of electric dipole ordering is observed in the monoclinic

phase, even though both ferro and antiferro ordering are consistent with the symmetry

of the Cc space group. For x = 0.95 and 0.90, a further transition to the

othorhombic structure observed for pure KCN below 168 K is observed, but this

transition does not go to completion, so that the low temperature diffraction pattern

contains both monoclinic and orthorhombic peaks. The amount of orthorhombic phase

present is greater for x = 0.95 than for x = 0.90, and no evidence for any

orthorhombic component is observed for x = 0.80. That portion of the samples which

did transform to an orthorhombic phase also transformed at lower temperatures to the

antif erroelectric structure observed for pure KCN below 83 K. The lack of complete

transformation to the orthorhombic structure probably arises from internal strains in

the grains of the powdered samples which build up as the grains transform. This

suggests that a large single crystal might not show any measurable amount of

orthorhombic phase at all, thus explaining the total absence of any electric dipole

ordering in such samples (note that as stated above, electric dipole order has never

been observed in the monoclinic structure, even in pure RbCN as discussed below).

We have also measured the neutron diffraction patterns of pure RbCN as a function of temperature, and have analysed the results by the method of total profile

refinement. The low temperature structure is analogous to that found for the mixed

crystals, with space group Cc. However, the strains required to derive this

structure from the high temperature cubic structure are somewhat larger, being of the

order of Mo for the E strain and b% for the T„ strain. These strains are still

g

^ 2g

considerably smaller than those required to derive an orthorhombic cell, and this

may be the explanation for the fact that this structure is preferred both in the

presence of the larger Kb ions and when there are defects present such as Br. ions.

Once again, no evidence for electric dipole ordering is found for temperatures as low

as ^ K - the structure remains monoclinic with electric dipole disorder. These

results present two problems requiring theoretical explanation - first, the effect of

strain on the relative stability of the monoclinic and orthorhombic structures and

second, the lack of electric dipole ordering in the monoclinic structure. With

respect to the latter problem, it is likely that the transition temperature to an ordered state is so low that the dipole relaxation rate is too slow to allow the

transition to take place. A calculation of this transition temperature using the

measured structure would be very helpful in resolving this question.

Finally, in both the mixed crystals and pure RbCN, the orientation of the CN

ion is along a direction close to a [301] axis in the original cubic cell, a result

inconsistent with earlier assumptions that it would be close to a [111] axis of the

original cubic cell.

58
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

CRITICAL BEHAVIOR AND MAGNETIC ORDERING IN AMORPHOUS TbFe

J. J. Rhyne and C. J. Glinka

The development of magnetic order in rapidly sputtered amorphous TbFe and the

response of the "ordered" magnetic state to an applied field has been studied using

neutron small angle scattering techniques (SANS). The NBS area detector SANS

facility was used for measurements over the scattering wave vector range (0.014 < q < 0.14 A) in zero field and in fields applied in an horizontal direction.

TbFe is part of a class of rare earth amorphous magnetic alloys which exhibit

large random crystal field anisotropy of comparable magnitude to the rare earth- iron

exchange coupling. In such anisotropic random systems it has been shown that the

lower critical dimensionality is 4, and thus no phase transition to f erromagnetism

exists except in the limit of vanishingly small anisotropy. Instead the transition

to a spin frozen state is predicted to occur with a finite correlation length

2 proportional to (I/D) , where I and D are the mean values of exchange and anisotropy

interactions on the rare earth spins. This lack of critical divergence in the

correlation length and the absence of a true long-range ferromagnetic state is

confirmed in these results.

The zero field scattering above the magnetization-determined T = 409 K shows a conventional Lorentzian line shape with a spin correlation length which increases to

about 135 A at and just below the bulk T . There is only a weak indication of a cusp

in the scattering at fixed q in the vicinity of T ; rather below T the scattering

continues to increase with decreasing temperature, finally saturating below about 40

K. The Lorentzian behavior observed above T gradually evolves into a power low

dependence I _ q with n „ 3.3 for temperatures below about 300 K. This subcritical

scattering can also be approximately represented by the sum of Lorentzian (L) and

Lorentzian-squared (L2) terms as suggested for random field systems with large

fluctuations [2]. Such behavior may be expected in TbFe„ based on the analogy

between random anisotropy systems and the random field problem of a 2d

antiferromagnet in an applied field [3]

On application of a field in the range 2-12 kOe at 295 K, the overall

scattering at finite q is sharply suppressed indicating an increase in the

nearly ferromagnetic component with field. The residual magnetic scattering exhibits

a prolate distortion of the intensity with respect to the direction of H which

demonstrates that the remaining spin clusters do not exhibit a ferromagnetic

response. The (L + L2) model well represents the q-dependence of the residual

59
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

scattering with the L2 term becoming more dominant at higher H. This random

fluctuation model yields an effective spin correlation length which drops from the

135 A at H = to less than 50 S at 4 kOe and above. The correlation length also

exhibits some low field hysteresis as shown in the figure.

220

n H Increasing

"Ck H Decreasing

Figure 1. Field dependence of the effective spin correlation length below T^as

derived from a Lorentzian plus Lorentzian representation of the SANS data

for TbFe at 295K. Curves are shown for scattering in narrow sectors

parallel and perpendicular to the applied magnetic field direction. Some

hysteresis is indicated at the lower fields.

1. E. Pytte, Ordering in Strongly Fluctuating Condensed Matter Systems, Edited by T. Riste, Plenum Press, New York (1979), pp 445-^52.

2. H. S. Kogon, and D. J. Wallace, J. Phys A V^, L527 (1981).

3. A. Aharony and E. Pytte, Phys Rev. B 27, 5872 (1983).

60
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRA>IS

SHORT RANGE MAGNETIC ORDERING IN Y.(Fe, Mn )^^ 6 1-x X 23

J. J. Rhyne

and

K. Hardman-Rhyne

(Inorganic Materials Division)

Y^(Fe, Mn )„^ shows anomalous magnetic properties in the range approximately

5 1-x X 23

0.4 < X < 0.75. In particular the Curie temperature, as defined from magnetization

data, vanishes in this region and the bulk magnetization tends toward over the same

1 range. Neutron diffraction and Mossbauer results demonstrate conclusively that

there is no long range magnetic order present in samples of these compositions.

To investigate the possibility of cluster or spin glass ordering occurring in

this intermediate range, SANS experiments were carried out on Y^(Fe_ ..Mn. ^)„^ from

0.4 0. <£i room temperature down to 10 K over a range of scattering vectors Q from

0.01 < Q < 0.2 using the NBS area detector SANS facility. The scattering observed

was isotropic in Q and very weak for all Q's and temperatures studied. The

scattering integrated over the entire Q range showed less than a ^0% increase from

250 K down to 10 K which clearly suggests that there is no tendency to form

ferromagnetic spin clusters in Y^CMn. ^Fe^ i,)^-.- D 0.6 O.H ?3

In contrast, antiferromagnetically ordered clusters will not contribute to the

small angle scattering, but rather would be expected to produce broadened or diffuse

peaks at angles corresponding to Bragg reflections (e.g. (100)) in a unit cell

doubled in one or more directions. High resolution diffraction scans using a neutron

wavelength of 2.4 A on Y^(Fe. „Mn^ ,)^^ as well as Y,(Fe^ ^^Mn^ ^r-)oo showed strong

D O.H 0.0 23 D 0.25 0.75 23

evidence of ant

i

ferromagnetic short range cluster ordering in the form of short range

order peaks appearing at the (100) superlattice reflection as shown in Figure 1. The

occurrence of this reflection implies a doubling of the cell along one of the cubic

edges with antiferromagnetic ordering along this direction.

The diffuse scattering is seen to be most intense for the x = 0.6 composition

and to sharply die out in the x = 0.4 and x = 0.8 composition near the critical

compositions for establishment of ferrimagnetic long-range order. The short range

order peaks were found to be strongly temperature dependent essentially becoming

unobservable in Y^(Fe ,,Mn r)^-^ above about 150 K.

6 .4 . 6 23

The average spin cluster size was determined by assuming the magnetic cluster

scattering to be the magnetic analog of particle size broadening of nuclear peaks

which yielded an average cluster size of 29 A for the x = 0.6 and 0.75 compounds.

61
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

(200)

8 12 16 20

Angle 26

16 20 .24

Angle 26

Figure 1. Diffuse (100) short range order peaks (left) observed for Mn compositions

which exhibit no long-range magnetic order. The intensity is multiplied

by a factor of 10 compared to the nuclear (111) and (200) peaks shown on

the right. The diffuse scattering data are difference patterns between

scans at 4 K and room temperature (above the temperature at which the

short range order disappears). This subtraction eliminates background

contributions and other extraneous scattering processes. The solid lines

through the peaks are fitted Gaussian curves.

1. Gary J. Long, private communication (1983).

62
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

The widths for the other compositions were not considered sufficiently reliable for

analysis due to their much weaker diffuse scattering.

The average Mn moment contributing to the cluster ordering was obtained by

calculating the magnetic structure factor for the (100) reflection assuming that

only Mn atoms contribute to the magnetic scattering and using the nonstoichiometric

Mn occupancy factors of the 4 Mn sites. The Fe was assumed to be nonmagnetic as

1 confirmed by the absence of an Fe hyperfine field from the Mossbauer spectra.

Assuming equal Mn moments on each site, the average Mn moment was found to be 1.4

Bohr magnetons in Y^(Fe ,,Mn r)^^- .4 . ^

j

These results suggest that the introduction of Mn moments into the iron rich

ternary compounds leads to a breakdown of ferromagnetic order near x = 0.3 through

exchange "frustration" produced by the Mn spins. This ant i f erromagnet i c- ferromagnetic exchange competition leads to the formation of a spin-glass like state,

and for still higher Mn concentrations, finally results in the establishment of Mn-Mn

long-range f err imagnetic order for x S 0.8 and greater.

DEUTERIUM SITE OCCUPATION AND MAGNETISM IN Ho.Fe^^D COMPOUNDS

6 23 x

J. J. Rhyne

and

K. Hardman-Rhyne

(Inorganic Materials Division)

and

H. Kevin Smith and W. E. Wallace

(University of Pittsburgh, PA)

High resolution neutron diffraction techniques have been used to establish the

hydrogen (deuterium) site occupation and sublattice magnetization of a series of

Ho^Fe D compounds. Four compounds were studied with nominal deuterium compositions

of X = 1.5, 8.2, 12.1, and 15.7.

The D, ;- compound showed almost no lattice distortion from the pure

I . 5 Ho^Fe compound while higher compositions showed volume increases varying up to

10.4^ for the D,^ „ compound. The fee structure of the parent compound was

1 5 . r maintained except for the D.^ sample which exhibited a tetragonal distortion with

0/2" a = 1.030. The fee lattice was re-established for the higher D,^ „ composition

I 5. ( The diffraction data demonstrate conclusively that the D atoms in the D, ^ materia!

1.5

fully occupy the a octahederal site with the residual in the tetrahederal f site

63
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

This composition showed virtually no lattice expansion. At the Do „ level, the a

o . d

site has become empty and the D atoms occupy the f and j tetrahederal sites only.

At the D.„ „ composition, the D atoms occupy both a j, and j„ site in addition to the

Id./ \ c. f site, again with no occupancy of the a site. The tetragonal D structure shows

a full occupancy of tetrahederal n sites and partial filling of m , m , 1 , and 1 tetrahederal sites.

The unusual depopulation of the a site in the higher concentration deuterides

was also confirmed by inelastic scattering measurements of the deuterium vibrational

frequencies using the Be filter analyzer of the BT-4 instrument at the NBSR. These

data shown in Figure 1 showed a peak at the characteristic frequency for octahedral D in the Ho^Fe__D, ^ and its absence in Ho^Fe„_D,^ „. The latter compound showed

6 231.5 62315.7

strong peaks at frequencies characteristic of D in tetrahedral sites.

Magnetization measurements show that the Curie temperatures increase from 510 K

for Ho^Fe__ up to 702 K for Ho^Fe„_D,^ ^. The neutron results for the individual

6 23 ^5 23 15.7

sublattice magnetic moments showed that the 4 K Ho moment was near the free ion value

of 10 u for all compounds, and oriented antiparallel to all four iron site moments

D (b,d,f , and f^)- For the cubic materials the magnetization on the Fe sites varied

175

150

©125

100

75-

50

25-

b

f H06Fe23D,5.7

•

*

/ \4\

V 1 r

1—'

1 1 1 20 40 60 80 100 120 140 160 20 40 60 80 100 120 140 160

ENERGY TRANSFER (meV) ENERGY TRANSFER (meV)i

Figure 1: Inelastic scattering spectra of Ho.Fe^^D, ^ (left) and Ho^Fe^,D_ ^

6 231.5 62315.7

(right). The peak at 70 meV is indicative of D atoms in the octahedral a site, and is absent in the D compound. The higher energy peak(s) (90-

100 meV) reflect D atoms in tetrahedral sites.

64
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

with deuteration in the range 0.8 to 2.4 \j. , with the D,^ „ compound showing the

highest Fe moment for all sites.

In the tetragonal material a spin re-orientation was found to occur between room temperature and 4 K, with the Ho moment rotating from the basal plane up 45° out of

the plane. The b and n Fe site moments re-oriented antiparallel to the Ho atoms

while the c, f, and n site moments remained fixed in the base plane. A similar re- orientation may be expected to occur in the other compositions, but is undetectable

by neutron scattering in a cubic structure.

(1) A. T. Pedziwiatr, H. K. Smith, and W. E. Wallace, J. Solid State Chem. (to be

published 1982)

SPIN DYNAMICS OF Fe^^Ni^QP^ ^^B^

J. W. Lynn

(University of Maryland, College Park, MD)

and

(National Bureau of Standards, Washington, DC)

and

J.J. Rhyne

Small-angle inelastic neutron scattering techniques have been used to

investigate the long wavelength spin dynamics in Fe^ Ni^ P^B^ (metglas ). This is a structurally amorphous transition metal system which is produced by rapid quenching

from the melt. Magnetically the system is locally (as well as globally) nearly

perfectly isotropic, which has led to a number of commercial applications. From a fundamental point of veiw, the system represents the best-known isotropic

ferromagnet, and thus it should prove to be an ideal candidate for a comprehensive

study of the spin dynamics. As a first step in the process we have studied the

nature of the long wavelength collective excitations below the Curie temperature (T

= 513K).

Conventional spin wave theory predicts that the spin wave dispersion relation

should be given by

E = D(T)q^ (1) sw

65
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

600 r

600 1-

-0.30 -0.15' 0.15 0.30 0.45 -1.20 -0.80 -0.40 0.40 0.80 1.20

500|- <|>

E (meV) E (meV)

I.Oir

§/

o/

± X

-0.75 -0.50 -0.25 0.25 50 0.75

. E (meV)

0.004 0.008

Q^(A )

Figure 1

Small wave vector inelastic scattering for Fe^ Ni^ P^B,- observed at room

temperature. The magnons are observed in nertron energy gain (E < 0) and

energy loss (E > 0). The elastic peak is nonmagnetic scattering which

originates from the sample and furnace. The dispersion relation for

energy gain (circles) and energy loss (squares) is seen to be quadratic to

a very good approximation after correction (triangles) for the

instrumental resolution.

at sufficiently small wave vectors q. Any gap in the spectrum should be completely

negligible in such an isotropic system. Indeed well defined spin waves are observed

below T as shown in Figure 1 . These data were taken at room temperature with a fixed incident energy of 13.7 meV, pyrolytic graphite monochromator , analyzer and

filter, and 12' FWHM collimators before and after the monchromator and analyzer. The

observed peaks for neutron energy gain (E < 0) and energy loss (E > 0) are due to the

destruction and creation of magnons, respectively. The elastic peak originates from

nuclear scattering from the sample and furnace. The solid curves are a least-squares

66
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

fit to a sum of three Gaussians, with the position of the central Gaussian fixed at E

= and the width fixed to the measured energy resolution of 0.33 meV. The observed

widths of the spin waves are solely instrumental in origin at these low temperatures.

Note that at small values of Q the data cannot be extended to larger energy transfers

due to the restrictions imposed by conservation of neutron energy and momentum.

150

100-

600

T(K)

Figure 2. Temperature dependence of the spin wave stiffness constant,

The spin wave energies are also shown in Figure 1 as a function of the square

of the wave vector. The open circles give the peak positions for energy gain and the

squares give the peak positions for energy loss. The statistical accuracy for these

data are smaller than the size of the points. There are significant corrections due

to the effects of finite instrumental resolution, and the corrected data are shown by

the triangles. These data are seen to obey equation 1 very well. The solid curve is

a least-squares fit to a straight line, which yields a slope of (97 + 3) meV-A at room temperature.

The stiffness coefficient D obtained from such data is shown in Figure 2 as a function of temperature. The renormalization of the spin wave dispersion relation is

typical of isotropic ferromagnetic systems. Note that at room temperature D has

attained 83 percent of the saturated low temperature value. Thus, we do not expect

much change in the dynamic susceptibility in going from room temperature to low

temperatures; the primary effect for the observed scattering will be due to the

change in the thermal population of the magnetic excitations of the system. A

67
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

detailed study of the low temperature spin dynamics at large wave vectors is

presently under way.

A number of experiments have shown that long-wavelength spin waves can be

measured by neutron scattering in metallic glasses. The first measurements were

made by J. D. Axe, L. Passell, and C. C. Tsuei, AIP Conf. Proc. 24, 119 (1975),

and H. A. Mook, D. Pan, J. D. Axe, and L. Passell, AIP Conf. Proc. 24_, 112

(1975). See also J. W. Lynn, G. Shirane, and R. J. Birgeneau, AIP Conf. Proc.

34, 313 (1976); J. D. Axe, G. Shirane, T. Mizoguchi, and K. Yamauchi , Phys. Rev.

bT5 , 2763 (1977); R. J. Birgeneau, J. A. Tarvin, G. Shirane, E. N. Gyorgy, R. C.

Sherwood, H. S. Chen, and C. L. Chien, Phys. Rev. BJ_8, 2192 (1978); J. J. Rhyne,

J. W. Lynn, F. E. Luborsky, and J. L. Walter, J. Appl. Phys. 50, 1583 (1979); and

references therein.

REENTRANT SPIN GLASS BEHAVIOR IN AMORPHOUS (Fe^Ni^QQ_^) Gl^^

J. W. Lynn and R. W. Erwin

(University 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)

Within the concentration range 1 7 <_ x <_ 40, members of this amorphous alloy

system exhibit a ferromagnetic (FM) phase transition followed at lower temperatures

by spin glass (SG) phenomena. These phenomena include: field sensitive reductions

1 2 in d.c. magnetization, increased a.c. susceptibility and hysteresis, enhanced spin

3 resonance line widths, and the collapse and damping of the spin wave excitations.

The last of these we have pursued with neutron scattering studies to investigate the

dynamics of the system as the SG state is approached.

4 Results for x = 40 and 30 were previously reported, with the lower

concentration showing the more dramatic change in the spin wave spectra. Concomitant

with the spin wave collapse for x = 30 is the growth of a resolution-limited elastic

component to the scattering which was identified with the formation of a spin frozen

_ 1 Q State. The spins are frozen on a time scale of at least 10 sec. as determined by

5 an upper limit to any intrinsic linewidth of the elastic scattering. It was

68
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

600r

-0.4 0.4 -0.4

Energy Transfer fmeV)

Figure 1

.

Observed spectra for (Fe^^^ii^^) „^G1„^ at Q = 25 75 75 25

10

1 showing that the

spin wave energies increase and then decrease as the temperature is

lowered. No distinct excitations are observable at 15K. The asymetries

are due to instrumental resolution and thermal population effects. The

solid lines are guides to the eye.

69
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

possible to identify distinct peaks in the inelastic spectrum down to about 10K, with

the energy widths indicating that the excitations are overdamped for T < 10K. Since

in addition the d.c. magnetization was not observed to vanish down to 4K, while the

SG order parameter appeared above 20K, the conclusion was drawn that the FM and SG

states coexist.

Our recent results for x = 25 are shown in Figure 1. Below T (= 197K) the

spin wave energies renorraalize to higher energy down to 8GK and then decrease again

below 80K. Below e- 40K, the spectrum has become completely diffusive. This suggests

that the FM state has been destroyed and d.c. magnetization measurements support

this conclusion. Again, a purely elastic component to the scattering is observed,

which is identified as the freezing of spins into a spin glass state.

An irreversible component of the magnetization has also been observed . Both

components of the bulk magnetization are extremely field sensitive. For example, in

fields of only a few gauss, the d.c. magnetization is maintained and the irreversible

part is no longer evident. This sensitivity appears to be absent in the neutron

results which are, of course, observations on a much shorter length scale. In

particular, it requires kilogauss fields to alter the spin wave spectra and to

destroy the elastic component of the scattering. It may be that the field

sensitivity in the SG state is provided by only the largest clusters. This length

scale may be accessible to small angle neutron scattering and such studies are

presently under way.

1. S. M. Bhagat et al .

, to be published.

2. S. M. Bhagat, J. A. Geuhegan, and H. S. Chen, Sol. St. Commun. 36.» '' (1980);

J. A. Geohegan and S. M. Bhagat, J. Magn. Mater. 25, 17 (1981).

3. S. M. Bhagat, M. L. Spano, K. V. Rao, and H. S. Chen, Solid State Comm. 33_, 303

(1980).

4. J. W. Lynn, R. W. Erwin, J. J. Rhyne, and H. S. Chen, J. Appl. Phys. 52, 1738

(1981); J. W. Lynn, R. W. Erwin, J. J. Rhyne, and H. S. Chen, NBS Technical Note

1178 , 93 (1983).

5. A. Magerl, private communication.

70
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

SPIN DYNAMICS OF DILUTE Pd, Fe FERROMAGNETS

1-x X

J. A. Gotaas and J. W. Lynn

(University of Maryland, College Park, MD)

and

(National Bureau of Standards, Washington, DC)

and

N. C. Koon

(Naval Research Laboratory, Washington, DC)

A great deal of attention has been focussed on the addition of magnetic

impurities (such as Fe, Co, or Ni) to "exchange-enhanced" paramagnetic metals such as

1 Pd and Pt, due to the resulting formation of giant-moment clusters. In the case of

dilute Pd, Fe alloys, the magnetic Fe atom possesses a moment of ~ 3~4 y^, but the

1-x X -^ ^

^ -^ ^B

polarization of the Pd d-band leads to a total moment of ~ 10 u per Fe atom, with

D the polarization cloud extending - 10 A. For very dilute concentrations

(x << 0.001), where the giant-moment clusters are effectively isolated from each

other, the system seems to become a spin-glass at low temperatures. At higher

concentrations (x > 0.001) a ferromagnetic state occurs. The critical concentration for the existence of a ferromagnetic state is

X = 0.0012, but a relatively uniform ferromagnetic state is not achieved until

p

^ ^

X > 0.03. In the intermediate dilute ferromagnetic regime, it is expected that the

magnetic excitations (at least for small wave vectors) are more or less conventional

spin waves. Such spin wave excitations have been observed using inelastic neutron

scattering in both chemically ordered and disordered Pd Fe, but in the dilute

ferromagnetic regime only indirect evidence had existed, based upon the neutron

diffraction technique, bulk magnetization, and specific heat measurements.

2 Earlier measurements of spin waves in polycrystalline Pd ^o^-Fe ^.^ using

inelastic ne^itron scattering about the forward (000) scattering direction have been

extended to the additional concentrations x = 0.01 and 0.02 and to lower

temperatures. For both x = 0.015 and 0.020, reasonably well-defined spin waves have

been observed below the respective Curie temperatures of 57 K and 78 K. The observed

2 spin wave dispersion is consistent with the quadratic relation E = DQ expected for

an isotropic ferromagnet, with D = 60 meV-S (x = 0.015) and 80 meV-A (x = 0.020) at

low temperatures. For x = 0.010, inelastic scattering was observed below the Curie

temperature of 38 K, but the "spin wave" linewidths in the accessible wave vector

range were too large to obtain meaningful information about spin wave energies or dispersion. There are indications that inhomogeneities in the polycrystalline sample

may have contributed to the linewidth broadening, and further work is under way to

investigate this.

71
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

1. G. J. Nieuwenhuys, Adv. Phys. 2H_, 515 (1975).

2. J. W. Lynn, J. J. Rhyne, and J. I. Budnick, J. Appl. Phys. 53, 1982 (1982)

MAGNETIC PHASE TRANSITION IN THE SUPERCONDUCTOR HoMo^Seo

b o

J. W. Lynn, J. A. Gotaas and R. W. Erwin

(University of Maryland, College Park, MD)

and

(National Bureau of Standards, Washington, DC)

and

R. N. Shelton and P. Klavins

(Ames Laboratory, Ames, lA)

and

(Iowa State University, Ames, lA)

Neutron scattering experiments have been carried out to investigate the

magnetic properties of the superconductor (T = 5.6K) HoMo,Seo. Bragg scattering as a function of magnetic field shows that the saturated magnetic moment is reduced to 6

y by crystal field effects. Thus in comparison to the related ferromagnetic1 superconductor HoMo^So DOC(T = 1.8K, u = 9.1 u„) the superconducting state is stronger

B and the magnetic properties are weaker, which could lead to a more equitable

competition between these two cooperative phenomena if the system prefers parallel

alignment. Figure 1 shows that this is indeed the case; a long range ordered

sinusoidal magnetic state forms at low temperatures. The characteristic wavelength

of this state is -1 OCA with the superconducting state surviving (in zero field) the

magnetic ordering.

Figure 2 shows the temperature dependence of the integrated intensity (related

to the square of the order parameter) as well as the characteristic wave vector q as

a function of temperature. The wave vector is seen to be strongly temperature

1 2 dependent in contrast to the behavior of HoMo^So or ErRh^B^ . The intensity

analysis of the scattering indicates that the full holraium moment available in the

crystal-field ground state has ordered at low temperatures.

The origin of the temperature dependence of q is not yet known conclusively.

3 ° Theoretically a linearly polarized state yields a periodicity whose temperature

dependence is qualitatively the same as that observed, but such a state requires a very large anisotropy to make it energetically favorable over other possible states.

The expected periodicity for the spontaneous vortex state is in the opposite

direction to that observed. A spiral state, which is the type of magnetic state

72
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

40

c 30

£

o

r-\

>• I

20

0)

10

Q

T = 0.286K

'AU^T = 0.400K

/ I

I I I ^VjL^T = 0.460K

J = 0.500K

0.03 0.06 0.09 0.12

-1 Wave Vector Q (A )

Figure 1. Intensity as a function of wave vector at several temperatures, showing

the intensity and wave-vector dependence of the Bragg peak in the

oscillatory magnetic state. These data were taken on the small-angle

neutron spectrometer (SANS).

0.12

0.6

Figure 2. Temperature dependence of the integrated intensity and wave vector q The full Ho moment has ordered at low temperatures. ^

73
REACTOR RADIATION DIVISION AND COLLABOPATIVE PROGRAMS

expected for an isotropic system, has a predicted periodicity with little temperature

dependence. However it is possible that the superconducting parameters themselves

renormalize during the development of magnetic order and this renormalization could

produce the temperature dependence of q . Further theoretical worK will be needed in

order to determine if this is indeed the case.

1. J. W. Lynn, G. Shirane, W. Thomlinson, R. N. Shelton and D. E. Moncton, Phys Rev

B24 , 3817 (1981).

2. S. K. Sinha, G. W. Crabtree, D. G. Hinks and H. Mook, Phys Rev Lett 48, 950

(1982)

3. H. S. Greenside, E. I. Blount and C. M. Varma, Phys Rev Lett 4o_, 49 (1981)

MAGNETIC AND SUPERCONDUCTING PROPERTIES OF Ho RICH (Er. Ho )Rh„B„

1-X X H H

J. W. Lynn and J. A. Gotaas

(University of Maryland, College Park, MD)

and

(National Bureau of Standards, Washington, DC)

and

R. N. Shelton

(Ames Laboratory, Ames, lA)

and

(Iowa State University, Ames, lA)

Neutron scattering, susceptibility, and resistivity measurements have been

carried out on (Er, Ho )Rh„3,, for x = 1.0, 0.89, 0.84, and 0.75, which span the

1 -X X 4 4 "mult icr it ical" point (x - 0.9) where the magnetic and superconducting phase

1 ° boundaries meet. For all concentrations studied, a transition to long range

ferromagnetic order is observed, with the Ho moments ordering along the tetragonal

axis. The holmium spins are in fact locked along the c-axis by large crystal-field

anisotropies, yielding Ising-like magnetic behavior in this concentration region.

The temperature dependence of the order parameter is in fact mean-field like to a good approximation, suggesting that the range of the magnetic interactions is large.

For X > X , no superconducting state is observed, whereas for x < x

c c superconductivity is present over a temperature ^ interval T ^ < T < T ^ as shown in

c2 c1

Figure 1 . The superconducting transitions have been determined by both a.c. susceptibility and resistivity on the identical samples used for the neutron

74
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

6.5

6.0-

2^- 5.5

5.0

4.5

>N^^<^1

O^^'^

'^

// // //

^0

/ 'C2

1 >

1 1 0.85 0.90

X (% Ho)

0.95 1.00

Figure 1 . Measured transition temperatures as a function of holmium concentration x. T is the upper superconducting transition, T is the lower (reentrant)

superconducting transition, and T is the ferromagnetic transition.

9000-

4.0 4.2 4.4 4.6 4.8 5.0

T(K)

Figure 2. Ferromagnetic intensity (which is proportional to the square of the magnetization) for x = 0.75. The dashed line is the expected intensity in

the absence of superconductivity.

75
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

measurements. The ferromagnetic transitions, as measured by neutron magnetic Bragg

scattering, appear to be continuous and reversible and occur within the region of

superconductivity for x <_ x . Thus, there is some kind of "coexistence" of

f erromagnetism and superconductivity in these samples. The nature of this

coexistence, however, cannot be determined unambiguously. In particular the

experimental evidence in this system is not sufficient to decide if there is true

microscopic coexistence, or whether some portions of the sample are ferromagnetic and

normal while other regions are superconducting and paramagnetic ( macro scop i c coexistence). No evidence for an oscillatory component of the magnetization was

2 observed for any concentration or temperature, in contrast to the behavior of

ErRh^B^.

At the lowest concentration studied (x = 0.75), the magnetization was found to

be reduced in magnitude from the value expected in the temperature region where

superconductivity appears as shown in Figure 2. The intensity (which is proportional

to the square of the magnetization) was found to be continuous and reversible, as was

the case at the higher holmium concentrations. The noteworthy point here is that an analogous suppression was not found at higher x. A similar suppression has been

observed at x = 0.6, accompanied by hysteresis in the ferromagnetic state at low

temperatures (and not in the "mixed" ferromagnetic-superconducting region). No

hysteresis was observed in the present measurements at any temperature or concentration.

1. H. B. MacKay, L. D. Woolf, M. B. Maple, and D. C. Johnston, Phys. Rev. Lett. 42_,

918 (1979).

2. D. E. Moncton, D. B. McWhan , P. H. Schmidt, G. Shirane, W. Thomlinson,

M. B. Maple, H. B. MacKay, L. D. Woolf, Z. Fisk, and D. C. Johnston, Phys. Rev.

Lett. 45_, 2060 (1981); S. K. Sinha, G. W. Crabtree, D. G. Hinks, and H. Mook,

Phys. Rev. Lett. 48, 950 (1982).

3. H. A. Mook, W. C. Koehler, M. B. Maple, Z. Fisk, D. C. Johnston, and L. D. Woolf,

Phys. Rev. B25, 372 (1982).

76
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

CRITICAL FLUCTUATIONS IN THE FERROMAGNETIC SUPERCONDUCTOR HoMo.So

6 8

J. W. Lynn, J. A. Gotaas, and R. W. Erwin

(University of Maryland, College Park, MD)

and

(National Bureau of Standards, Washington, DC)

HoMo^So becomes superconducting at T . = 1.82 K, and reenters the normal

6 8 c1 ^2 conducting state at T _ - 0.64 K due to the establishment of ferromagnetic order. '

Above this first order reentrant transition, the competition between ferromagnetism

and superconductivity gives rise to an oscillatory magnetic state (T = 0.728 K)

o OS

with a wavelength of 200 A. We have recently constructed a He refrigerator with

high temperature-stability {+_ 10 yK) which we have used to study the critical

dynamics and order parameter of this oscillatory magnetic phase. The data were taken

on the small angle scattering facility (SANS).

In the absence of an applied magnetic field, the (powder) scattering is

symmetric about the forward beam direction, and the data were therefore averaged

radially. Figure 1 shows the wave vector dependence of the scattering at a series of

temperatures (on cooling). These data were taken with a neutron wavelength of 8.0 A

in the "coarse" resolution mode. Data were collected at temperature intervals of

2.5 mK. For T > 0.740 K there was no structure evident in the scattering, with the

intensity distribution being consistent with a correlation function of the Ornstein-

°-1

Zernike form. With decreasing temperature, a peak develops at Q ~ 0.03 A whose

intensity and width are strongly temperature dependent. We have analyzed these data

assuming that there are two magnetic components to the scattering, the peak at Q , and a broad distribution of scattering. The solid curves are least squares fit to a Gaussian peak plus a linear (sloping) background, which gave a satisfactory fit to

the data over the temperature region of interest. From this analysis, we found that

the broad component to the scattering did not vary significantly with temperature,

while the width of the peak became resolution limited for T <_ 0.7275 K. The position

Q was essentially temperature independent while the amplitude was strongly

temperature dependent as shown in Figure 2. For temperatures below 0.700 K, a firstorder transition from the oscillatory - superconducting state to the ferromagnetic - normal state takes place. The ferromagnetic state introduces an intense small-q

component to the scattering which quickly dominates the scattering near Q . At

sufficiently low temperatures, T < 0.61 K, the entire sample reverts to the normal

conducting state, with a conventional ferromagnetic state present.

77
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

200

160

120

80

40

^f 40

0.7250K

Z 32

24

16

8

7275K

\/0.7300K

I 0.02 0.04 0.06 O.O81

Wave Vector (A"^)

Figure 1. Intensity distribution as a function of wave vector for several

temperatures.

78
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

300

200-

100-

Figure 2. Intensity vs. temperature at Q .

1. J. W. Lynn, G. Shirane, W. Thomlinson, R. N. Shelton, and D. E. Moncton, Phys

Rev. B24 , 3817 (1981) and references therein.

2. J. W. Lynn, R. Pynn, J. Joffrin, J. L. Ragazzoni, and R. N. Shelton, Phys. Rev

B27, 581 (1983).

ADVANCED NEUTRON METHODS

N. Berk, D. Fravel, C. J. Glinka, J. LaRock, and J. M. Rowe

1. Small Angle Neutron Scattering (SANS)

The SANS facility operated nearly trouble free over the past year with less

than 5 percent of the available beam time lost due to instrument down time. During

this period efforts have continued to improve the capabilities of the facility and to

make it easier to use. For example, a modified version of the converging beam

collimation system used for high-resolution measurements is now being built which is

designed to be free of any trace of parasitic scattering from the edges of the beam

collimating masks. In addition, the new collimating masks will be equipped with

quick coupling flanges to enable users to change from pinhole collimation to

converging beam collimation in a few minutes. A temperature controlled tube furnace

has been designed for the SANS instrument (by E. Case, U. of California and the

Inorganic Materials Division) for the study of ceramic specimens at temperatures up

79
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

to 1200 °C either under vacuum or in a controlled gas environment. For studies of

magnetic phenomena at low temperatures, a cryostat has been adapted to mount between

the pole faces of a large electromagnet to enable scattering measurements to be made

at temperatures down to 4K in fields up to 10 kilogauss. The addition of a floating

point accelerator and a higher density disk drive have substantially increased the

computing speed and storage capacity of the instrument's data acquisition computer.

These improvements are essential for future real-time studies and will enable some elementary data reduction and analysis to be done directly at the instrument.

Computer software for the reduction and analysis of SANS data has also been

expanded and made more user friendly. Detailed calculations of the instrumental

resolution have been carried out by N. Berk and incorporated into a program which

enables users to readily assess the effects of instrumental smearing on the shape of an arbitrary scattering function. These calculations will be included in a generalized least-squares fitting routine for fitting model functions to SANS data.

An extensive and extremely versatile data fitting and plotting package, developed by

the Center for Applied Mathematics, called DATAPLOT is now running on the VAX data

reduction computer and is being widely used for curve fitting and plotting.

Documentation for much of the SANS software is now stored on the computer and can be

readily accessed by a user at a video terminal as needed.

In the past year more than ninety individual experiments were performed

comprising roughly forty distinct research problems. These experiments involved the

active participation of scientists from six NBS divisions, more than fifteen

universities, and approximately six industrial and government laboratories. The bulk

of this work can be broadly classified as either microstructural studies of metallic

or ceramic materials, measurements of molecular conformation of polymers and

biomaterials, or studies of magnetic correlations in novel magnetic materials.

Studies in the area of metallurgy have included, for example, the extension of

initial measurements of creep cavitation in stainless steel (by S. Singhal and R.

Fields) to a wider range of aging times and stress states in an effort to quantify

the effects of these two parameters on the production of cavities. In a related

study, M. Fatemi (Naval Research Laboratory) has measured the sizes of small voids in

hydrogen charged steels and J. Weertman (Northwestern Univ.) has measured the

scattering from carbides in ferritic steels in order to determine the volume fraction

and carbide size distribution produced by various heat treatments.

A new program has developed in collaboration with the Inorganic Materials

Division (involving N. Berk, K. Rhyne of IMD , and E. Case, U. of California) to study

the evolution of the porous micrbstructure in selected ceramic materials from the

80
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

prefired, so-called green, state through various stages of sintering to the final

densified product. One aim of this effort is to determine vjhether SANS can be useful

for detecting defects (agglomerated particles, cavities, etc.) in the green state

which can affect the mechanical properties of the sintered materials. SANS

measurements are also being carried out (by L. Sander, Center for Analytical

Chemistry) to obtain quantitative information on the pore structure of chemical

adsorbents used, for example, in chromatography. Here absolute intensity

measurements are being made to determine the specific pore surface area and pore

volume fraction of several types of porous silica.

SANS studies on magnetic materials have ranged from detailed measurements (by

J. Lynn and J. Gotaas, U. of Maryland) of the development of long-range oscillatory

magnetic ordering in the magnetic superconductors HoMo^Sn and HoMo^Seo, to the study

of single domain magnetic particles in ferrofluids (C. Glinka and D. Chung, Howard

Univ.). Other experim.ents have focused on the finite ranged magnetic correlations

which develop in spin glasses.

Some of the work mentioned above is discussed in greater detail in other

articles in this report.

2. Time-of-Flight Spectrometer (TOF)

A complete redesign and rebuilding of this facility was begun during the past

year. The existing instrument has been used in studies of H in metals, of molecules

on catalytic surfaces, and of molecular reorientation in solids. However, a number

of problems with the current configuration have been noticed in these experiments,

which will be addressed in the new design. We have completed the detailed design of

a new horizontal flight path which will be evacuated, and a contract has been let for

construction of this component. In addition, the electronics used for both neutron

detection and chopper control have been replaced. A new monochromator mechanism and

shield which will allow more flexibility in resolution and achieve higher intensity

on the sample has been designed, and is presently under construction. This entire

project is scheduled for completion within the next year, and will be installed

during the shutdown for the reactor upgrade for 20 MW operation. In the meantime, the

present facility is still being used for some experiments.

81
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

SMALL ANGLE SCATTERING FROM FERROFLUIDS

C. J. Glinka

and

D. Y. Chung

(Howard University, Washington, DC)

Ferrofluids consist of small (~100 A), single-domain particles of ferromagnetic

material suspended in a carrier liquid. These magnetic fluids are used in a wide

range of technological applications which depend to a large degree on the magnetic

particles remaining in suspension in the presence of strong magnetic fields and field

gradients. Important to the stability, and hence the performance, of ferrofluids are

the sizes and shapes of the particles and the interactions between them. Because

neutrons can be scattered both by interactions with the atomic nuclei in the

particles and by interactions between the neutron's magnetic moment and the

particles' magnetic moments, small angle neutron scattering (SANS) is a particularly

powerful technique for examining both the physical structure and magnetic

correlations in ferrofluids.

SANS measurements have been initiated on a commercial water-based ferrofluid

(Georgia Pacific Lignosite FML) which consists of particles of magnetite, Fe 0^,

coated with a polymer (lignosulf inate ) which acts as the dispersing agent. This

fluid has a nominal bulk saturation magnetization of 140 gauss which, compared to

bulk magnetite, would imply a volume fraction of magnetic particles of about 2.3

percent. The low-Q portion of a SANS pattern for this fluid measured in zero

magnetic field is shown in Figure 1 . Although a detailed analysis of this scattering

is complicated by the presence of three phases in the system (magnetite, polymer and

water), the overall shape of the curve is indicative of a broad range of particle

sizes ranging up to 300 A in diameter.

Data were also taken in a magnetic field of 1 kilogauss which is more than

sufficient to saturate the magnetization of the sample. In an applied field the

observed intensity is the sum of nuclear and magnetic contributions

I(Q, H) = Ij^(Q, H) + (1-cos^(!))Ij^(Q,H) (1)

where (j) is the angle between the scattering vector Q and the direction of the applied

field H. The nuclear, I (Q,H), and magnetic, I (Q,H), contributions to the

anisotropic scattering observed for H = 1 kilogauss are also shown in Figure 1 and

are seen to be quite different at the smaller Q values.

In the absence of an applied field, the scattering is isotropic and given by

82
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

6000

§4000

O

u

c

o

i 2000

D I, H = O

In +2/3 Im

• I,

•H=1kgauss

• « o

o•So

'Bfl °°°DDDDo

°e

y ° o|oo

5000

4000

3000

2000

1000

.005 .010 .015 .020 .025 .030 .035

Scattering Vector Q (A )

Figure 1. Comparison of the small angle scattering from a commercial ferrofluid

observed in zero magnetic field and in a field on 1 kilogauss. The open

squares are the zero field data and the open and filled circles are the

magnetic and nuclear contribution, respectively, to the scattering in the

applied field. The filled squares are the "reconstructed" zero field data

obtained from the weighted sum, I + 2/31 , of the nuclear and magnetic

contributions to the applied field data.

I(Q, 0) = Ij^(Q, 0) + 2/3 Ij^(Q, 0) (2)

where the (1-cos <p) term in equation (1) takes on the value 2/3 owing to the random

orientations of the magnetic moments of the particles. To compare the 1 kilogauss

data with the zero field data the components I„ and I„ derived from the anisotropic

N M

scattering were added in the ratio 1:2/3, respectively. Figure 1 shows that, treated

in this way, the applied field data (filled squares) closely follow the observed zero field scattering (open squares). This implies that the primary effect of the field

is simply to align the particle moments and not to produce any significant degree of

particle aggregation, which would change the shape of the scattering curve. These preliminary SANS results are consistent with ultrasonic measurements

which indicate that Lignosite FML is a particularly stable type of water-based

ferrofluid. In future SANS measurements, different types of ferrofluids will be

compared and higher concentrations will be studied in an effort to observe

interparticle interaction effects.

83
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

CHARACTERIZING MICROPOROSITY OF CHEMICAL ADSORBENTS BY SMALL ANGLE NEUTRON SCATTERING

Lane Sander

(Analytical Chemistry Division)

and

C. J. Glinka

The performance of microporous adsorbents used, for example, for chemical

separation in liquid chromatography depends critically on parameters such as the

specific surface area, specific pore volume, and mean pore diameter which

characterize the pore structure of the material. For pore sizes ranging from roughly

20 A to 1000 A, small angle neutron scattering (SANS) can in principle provide

values, on an absolute scale, for all of these important parameters. Moreover, in

contrast to techniques such as mercury porosimetry on gas adsorption measurements, in

which either the physical structure or chemical purity of the specimen may be

altered, SANS is a completely nonintrusive technique and thus cannot affect the

properties or performance of the adsorbent.

Our initial SANS measurements have focused on determining the specific surface

area of pores in a number of commercial fine powders of porous silica. The 5-10

micron sized particle in these powders consist of submicron, nonporous silica beads

which have been partially sintered to produce mechanically stable structures. The

size, shape and packing arrangement of the nonporous beads determine the pore

structure of the aggregate particles. The scattered intensity from such a sharply

defined, two-phase system (silica and voids) is proportional to the total pore

surface area in the large Q limit of the scattering pattern where Pored law behavior,

I cc Q , is expected. Thus by making absolute measurements of the scattering in the

Porod region, the pore surface area can be obtained directly.

For most of the porous silica samples studied to date, a well defined Porod

region is observed in the scattering. An example is shown in Figure 1 where the

4 measured intensity, multiplied by Q , from a specimen with a nominal pore diameter of

300 A is plotted versus Q (Porod plot). On this type of plot, data in the Porod

region lie on a straight line. The data in Figure 1 were put on an absolute scale by

reference to the isotropic incoherent scattering from vanadium measured under

identical conditions. The resulting specific surface area for this specimen was

2

50m /gm with an estimated uncertainty of about 10 percent.

Further measurements and analysis are planned in an effort to completely

characterize the pore structure of various types of porous silica. In some cases,

84
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

.OO2O1-

.0018

.0016

n

" .0014

- Porod Plot of SANS from

microproous silica particles

~ .0012^;?

°-°nO-a?i

I ooiofD .0008

0.1 0.2 0.3 0.4 0.5 0.6

^ 4 Figure 1. Porod plot (IQ versus Q ) of the small angle scattering from a powder

sample of microporous silica particles. The vertical intercept of the

dashed line fit to the linear region of the plot is proportional to the

total surface area of the porous particles.

materials with the same nominal pore size are known to perform quite differently in

chromatographic applications. Thus, it is hoped that SANS will reveal differences in

pore structure that can be related to variations in performance.

SANS INVESTIGATIONS OF POROSITY IN YCRO- CERAMICS

N. F. Berk

and

K. Hardman-Rhyne and E. Case

(Inorganic Materials Division)

A quantitative SANS study of porosity in YCrO„ ceramics is in progress having

the goal of providing reliable measurements of average pore size in bulk materials at

different stages of densif ication with the aid of appropriate theoretical analysis.

At present, data have been acquired from two samples which were similarly prepared

pure powders isobarically pressed at 30,000 kbar. One, a greenstate compact has 58

percent theoretical density. Measurements were made at several neutron wavelengths

and are shown for the greenstate compact as a function of scattering wavevector in

Figure 1 . The full widths at half maximum of these curves were determined by

approximate Gaussian fits and increase linearly with wavelength in the range shown, a behavior characteristic of multiple range shown, a behavior characteristic of

85
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

1.0

Figure 1.

.010 020 .030

QIA-"")

SANS intensities from YCROo greenstate compact at several neutron

wavelengths; the normalization is arbitrary.

multiple scattering from large particles and thus consistent with the evident

porosity of the greenstate. In contrast, the scattering from the sintered sample

(not shown) exhibits no wavelength dependence on this scale, indicating the absense

of comparably large pores. Clearly, even a qualitative analysis of such data reveals

a strong effect of processing on the population of neutron scatterers in these

materials, but quantitative measures of void sizes are less straightforward. If the

scattering in Figure 1 is assumed to be describable only as multiple refraction by

voids, then a preliminary estimate of average void radius gives a value of

approximately 2]im, which appears to be physically reasonable for the greenstate

compact. For the wavelengths of these measurements, however, this corresponds to

scattering phase shifts well within an intermediate range of values in which the

scattering is not expected to be simply analyzable in terms of refractive (i.e., ray

optical) behavior alone. For this reason, in parallel with these experimental

1 investigations, we are developing an appropriate generalization of available

theoretical technique in order to provide a sound basis for the quantitative analysis

of the SANS data from these and similar materials.

1. N. F. Berk, this report.

86
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

SMALL ANGLE NEUTRON SCATTERING (SANS) STUDY OF CREEP DAMAGE IN 304 STAINLESS STEEL

S. P. Singhal and B. Mozer

and

R. J. Fields

(Fracture and Deformation Division)

30^ stainless steel used in high-temperature applications consists of M^_C^ (M

stands for Cr and other metallic elements in the carbide) type of carbides at the

grain boundaries. The carbide-austenite interface is a preferential site for the

nucleation of cavities during high-temperature degradat ion--a phenomenon called

cavitation. The structure after cavitation consists of three phases; namely,

austenite, carbide, and cavities. The attempt to use SANS as a reference method to

nondestruct i vely evaluate the evolution of creep cavities from very early stages of

cavity growth (inaccessible to conventional methods) requires that the creep induced

changes in volume fraction, size distribution, and spacial distribution of carbides

do not contribute significantly to the scattered intensity. At this point there is

no theoretical or experimental study to indicate that this limitation is not

important, yet by adapting special experimental procedures, the effects due to such

changes could be minimized. The following two procedures were employed:

a. All samples were given a stabilizing heat treatment of 100 hours at 600 °C

prior to the initiation of creep thereby precipitating out the entire volume

fraction of carbides.

b. A control sample (undeformed) was heat treated along with the crept samples

over the period of creep deformation. SANS spectra from the undeformed

sample were used as a baseline to delineate the cavity contribution from the

deformed samples. The creep parameters of two samples (x-6, x-8), which

fulfilled these requirements in this and a previous study, are described in

Table 1 . This report describes recent results on these samples and compares

1 them with the previous study.

The SANS studies were carried out on the NBS reactor facility using a converging collimation and a neutron wavelength of 6.25 A. With the choice of

collimation and wavelength parameters, a scattering vector (Q) range of 0.005 A to

0.15 A could be measured in these experiments. This Q range measures the

scattering contribution of the inhomogeneities in the size range of approximately

40 A to 1200 A. By using converging collimation we have been able to measure the

87
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

scattering intensity at Q values about a factor of three lower than a previous

1 preliminary study.

Detailed theory and procedures for analyzing the SANS data have been described

2 by Kostorz. A few salient features will be discussed here. If scattered intensity

is denoted by Z, then the macroscopic differential scattering cross section of the

scattering entities is given by

^ = CZ/tMT (1 ) ds^

In this equation, t is the sample thickness, M is the total monitor count, T is the

sample transmission, and C is a combination of experimental constants for the

instrument. Creep damage as related to the evolution of cavities and changes in

carbide size, shape, and spacial distribution is measured by the difference in the

de/dfi for the deformed (D) and undeformed sample (U), i.e.,

fe] = fel - fe) = C[Z^/t^M^T^ - Z„/t„M„T„] (2)

V^^/damage \^^/d \^^/u ° ^ ^ ^ " " "

"

In further discussion, we have assumed that contribution to (-rr) comes

\ /damage

predominantly from creep cavities. Figures 1 and 2 show scattering patterns for the

deformed and undeformed samples of x-6 and x-8, respectively. We can see that in

these (also, in all other samples measured) the deformed sample always showed higher

scattered intensity than the undeformed, thereby emphasizing cavity contribution to

the scattering. Figures 3 and ^ show only cavity contribution, i.e.,. after

substracting the spectra for the undeformed sample from the deformed one. The steep

fall of scattering intensity in Figure 3 is indicative of very narrow size

distribution of cavities.

One parameter of major interest is the growth of average cavity size as a function of creep deformation at constant stress. A Guinier analysis was performed

2 on these spectra (Figures 3 and 4) to obtain an average cavity size. Guinier showed

that for a randomly distributed, monosized, spherical heterogeneity, the intensity

(Z) and scattering vector (Q) relationship can be described by the equation

Z = Z^ exp ( ^ "g j (3)
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

10 00

8 75

7,50

I

6.25

o 5.00-

3.75 -

2.50

• Deformed

O Undeformed

O

5.60 -5.19 -4.78 -4.37 -3.95 -3.54

Log Scattering Vector

3.13

Figure 1 . SANS spectra on deformed and undeformed x-6 specimens. Deformation

under 21 ksi stress was carried out at 600 °C for 1493 hours. The

undeformed sample was heat treated at 600 °C for 1493 hours.

O.OJ

9 • Deformed

o Undeformed

6 94 8

8

>- 5.55 -

9 e

c

0)c

o

-J

4 17

278

1.39

-

1

9

°°° So.: ^

o • ^ o

1 1 1 1 Q* 5 00 4 67 4.34 -4.00 -3.68

Log Scattering Vector

3.34 3.00

Figure 2. SANS spectra on deformed and unaeformed x-8 specimens. Deformation

under 18 ksi stress was carried out at 600 °C for 1537 hours. The

undeformed sample was heat treated at 600 °C for 1537 hours.
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

2800

O

233o[-o

'7- 1860

oU

1390

c 820

450

O Deformed Minus Underformed

201 '^^m<| miui' rimwMniUu ^n-«iTnr^TfflTnilTmffiB3fagM

0.03 0.05 0.08 0.10 0.13 015

Scattering Vector (A )

Figure 3- SANS spectra showing the scattering due to creep-induced cavities

for x-6 specimen.

7.00

5.83-

.00 -4.75 -4.50 -4.25 -4.00 -3.75

Log Scattering Vector 3.50

Figure M. SANS spectra showing the scattering due to creep-induced cavities

for x-8 specimen.

90
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

8.00

6.67

oI

5 33

S 4.00

2 67 -

1 33-

Guinier Plot O Deformed Minus Undeformed

± _L 0.08 0.17 0.25 0.33 0.42 0.50

(Scattering Vector) ^ (A^) x lO''

Figure 5. Guinier plot showing the scattering contribution of creep cavities

in x-6 specimen.

7.20rO

o o

i o

6 08

4 97

c£ 3.85

c

2.73

1.62

50

Gunier Plot

O Deformed Minus Undeformed

± ± I 012 23 0.35 0.47 58 70

(Scattering Vector)^ (A^) x 10^

Figure 6. Guinier plot shov;ing the scattering contribution of creep cavities

in x-8.

91
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

2500

2083-

-^ 16661—

c

3Ou- 12501— >

833

416

O Deformed Minus Undeformed — Guinier Function Fit Line

0.04 0.05 07 08 0.09

Scattering Vector (A^) x 10

0.11 12

Figure 7. Least square fit of the Guinier function of the data

selected range of figure 3 for x-6 specimen.

in the

666

O Deformed Minus Undeformed —Gunier Function Fit Line

0.06 0.07 0.09 0.10 0.11 12 0.14

Scattering Vector (A ) x 1

Figure 8. Least square fit of the Guinier function to the cavity scattering

data in the selected Q range for the x-8 specimen.

92
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

1000

oc

333 666 1000

Creep Time (Hrs) 1333 1666

Figure 9. Size growth of creep cavities as a function of creep time at 600 nC

for x-6 and x-8 specimens.

Table 1 . Growth of creep cavities as a function of time at constant stress in

304 stainless steel.

Sample #

x-f

Creep

Parameters

745 at 2-1 ksi

(144.8 MPa)

1493 at 21 ksi

(144.8 MPa)

Average Cavity Diameter from

Guinier Approximations

346

770

(nm)

34.6

77.0

x-8

789 at 18 ksi

(124.1 MPa)

1537 at 18 ksi

(124.1 MPa)

266

763

26.6

76.3

93
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

Here R is the radius of gyration of the particles and is related to their diameter

(D) by the equation

D =>JlO/3 R (4)

Z is the constant related to the volume and number density of the cavities. If

o

^ heterogeneities are not monosized, then the utility of Guinier approximation is

limited to only a very small Q range near the 0. Figures 5 and 5 represent Guinier

2 plot [Log Z vs. Q ] for cavities in samples x-6 and x-8. It is clear from these

plots that cavities must have a size distribution as a straight line in these plots

can be fitted only in the narrow Q region near the peak. The cavity diameter

obtained by this procedure normally over-estimates the contribution of large

cavities, yet it is a very useful parameter to study cavity growth as a function of

creep time while degradation is in progress. Using a least square fit subroutine,

equation (3) was fitted to the data points in the relevant Q range of Figures 5 and

6. The experimencal data points and the fit line are shown in Figures 7 and 8. A

reasonably accurate fit was obtained in the selected Q range for both cases. The

average cavity sizes derived from these fits for the two samples are

and

<D .^ > ~ 770 A for x-5 cavity

<D . > - 763 A for x-l cavity

Table 1 shows that doubling the creep time at the same stress has the effect of

doubling the average cavity size for sample x-6. Figure 9 shows the growth of cavity

size as a function of creep time in the two samples assuming that at the initiation

of creep, the cavity size is negligible. If we include the point at the origin,

there appears to' be a linear time dependent size growth of the cavities in x-6; but

in the absence of more data points, only a limited significance can be attached to

1 the trend in Figure 9. In the previous report, we concluded that x-6 has higher

average cavity size despite the longer creep time because x-6 was stressed at 21 ksi

as opposed to 18 ksi for x-8, therefore resulting in the enhanced stress induced

coarsening of cavities. In this study we find that average cavity size in the two

samples is not very different. This indicates that for longer creep times the size

growth of cavities is perhaps less sensitive to the small changes in applied stress.

This is because the stress difference between these two samples is only about 3 ksi.

3 The other possibility as debated by Weertman is that when a large fraction of

94
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

cavities grow large enough to scatter at the Q values below minimum Q in the

experiments, the average size and volume fraction parameter from the standard SANS

analysis are highly underestimated and also the Guinier region is inaccessible. The

confirmation that this has taken place at a certain stage of the creep requires the

void size and volume fraction determinations by TEM and density measurements,

respectively. Such measurements are currently in progress. To refine the general

application of SANS as a reference method to quantify creep cavity growth in alloys,

further work must be performed on simpler metals or model alloys to absolutely

identify the contribution of interacting microstructures and defects in structural

alloys.

1. E. R. Fuller, Jr., R. J. Fields, E. D. Case, S. Singhal, and C. J. Glinka,

"Nondestructive Evaluation of Distributed Damage," Annual Report, Reactor

Radiation Division, NBS (1983).

2. G. Kostorz, "Neutron Scattering in Materials Science," Chapter 5 in Treatise in

Materials Science and Technology J_5, ed. G. Kostorz, (Academic Press, New York,

1979).

3. J. R. Weertman, M. Yang, and M. Roth, "Grain Boundary Cavitation in Copper

Subjected to High Temperature Creep," Annex to Annual Report, Institut LaueLangevin, Grenoble, France, p. 253 (1982).

UNIAXIAL DEFORMATION OF RUBBER NETWORK CHAINS BY SMALL ANGLE NEUTROl SCATTERING

H. Yu, T. Kitano, C. Y. Kim, E. Amis, M. Landry, J. A. Wesson, and T. Chang

(University of Wisconsin, Madison, WI)

and

C. Han and T. P. Lodge

(Polymer Science and Standards Division)

and

C. J. Glinka

Small angle neutron scattering (SANS) measurements were performed on

poly( isoprene) networks at different uniaxial strains, i.e., 1 .0 <_ X (extension

ratio) <_ 2.1. The network strands were prepared from anionically polymerized a, w- dihydroxy-poly( isoprene) precursors (H-chains) and the corresponding polydsoprenedg) isotopic counterparts (D-chains), crosslinked in concentrated tetrahydrof aran

solutions by a tri-functional crosslinker, tris-isoajanate. The isotopic contents of

95
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

the networks at 8 percent and 15 percent were used in determining the two components,

of the radius of gyration of elastic strands, parallel and perpendicular to the

strain axis from the SANS data. Three molecular weights of D-chains, 26,000, 64,000,

and 82,000, crosslinked with approximately similar molecular weights of H-chains

(29,000, 68,000, and 72,000, respectively) were examined for a possible molecular

weight effect on the deformation behavior. From the observed changes in the parallel

and perpendicular components of the radius of gyration relative to the macroscopic

extention ratio, appropriately corrected for the contributions from nonelastic

(dangling) chains, we conclude that the chain deformation is given by an intermediate

behavior between the junction affine model and the "phantom network" model having

unrestricted fluctuations of network junctions. The deformation behavior is also

found to be the same for all three molecular weights.

SMALL ANGLE SCATTERING FROM AMORPHOUS DyCu

S. J. Pickart

(University of Rhode Island, Kingston, RI)

and

(National Bureau of Standards, Washington, DC)

and

H. A. Alperin

(Naval Surface Weapons Center, Silver Spring, MD)

and

(National Bureau of Standards, Washington, DC)

and

R. J. Gambino and T. R. McGuire

(IBM, Yorktown Heights, NY)

1 The unusual magnetic transition for the random anisotropy amorphous alloy DyCu

was investigated by small angle neutron scattering (SANS) methods. The measurements

were made on two 150-micron sputtered films with incident 6.0 A wavelength, at

-1 temperatures between 5 and 77K, and for wavevectors 0.01 6 <_ q <_ 0.1 65 A . The small

angle magnetic intensity shows a pronounced break at T I 17K, corresponding very

closely to the weak-field susceptibility cusp as measured on the same sample. The

line shape at all temperatures were observed to be Lorentzian, with a correlation

length slowly increasing as T decreases to a maximum of ~ 1 3A at 1 7K and remaining

sensibly constant there after.

The results for the correlation length as a function of temperature that were

extracted from the data are shown in Figure 1 . These results were compared with

2 3 susceptibility and specific heat measurements .

96
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

< 14r

60 70 80

Figure 1 . The magnetic correlation length of amorphous DyCu as determined from small

angle neutron scattering measurements.

1. S. von Molnar, T. R. McGuire, R. J. Gambino and B. Barbara, J. Appl. Phys. 53.. 73

(1982).

2. S. von Molnar, B. Barbara, T. R. McGuire and R. J. Gambino, J. Appl. Phys. 53.

.

1350 (1982).

3. S. von Molnar, G. N. Guy, R. J. Gambino and T. R. McGuire, J. Magn. Matl. 1 5-18 , 1391 (1980).

GENERALIZED THEORY OF NEUTRON SCATTERING FROM HYDROGEN IN METALS

R. C. Casella

Neutron scattering from hydrogen in various materials is usually thought of as incoherent in the sense that the random relative spin orientations of an array of

protons therein destroys the phase coherence in the Huygens construction associated

with a potential diffracted neutron wave. There is, however, another sense in which

one must distinguish between coherence and incoherence in the scattering of neutrons

from dilute hydrogen in, say, metals. That is, when a neutron scatters from a single

interstitial hydrogen atom (electronically shielded proton) which moves about in the

metal, it matters whether or not the protonic motion exhibits quantum coherence in

the sense that the relative phase of the proton wave function is retained over dis97
REACTOR RAD'IATION DIVISION AND COLLABORATIVE PROGRAMS

tances of the order of a few lattice parameters. The existence of coherent effects

of the second type in the scattering of neutrons from hydrogen in metals at low

temperature has been demonstrated experimentally via the observation of tunneling

transitions among the split ground-state components of a two-well trap for hydrogen

1 in niobium near added impurities.

Experimental observation of sizable band widths 0(10 meV) for the inelastic

scattering of neutrons from hydrogen in metals, inducing transitions to excited

states 0(100 ir.eV) above the ground state in pure and defected metals by Rush, Rowe,

2 and their collaborators at the NBS Reactor facility, has led me to an intensive

theoretical investigation of the processes involved. These include the possibilities

3 4 of transitions to excited states in the two-well trap ' as well as transitions to

5 excited-state protonic energy bands as discussed in the accompanying report. The

coherent band motion can lead to finite widths for the neutron excitation bands, even

in the absence of other width-producing factors such as lifetime effects due to the

spontaneous decay of the excited proton to its local-oscillator ground state and

incoherent hopping between excited oscillator states centered at nearby interstitial

sites. In contrast, most quasielastic neutron scattering processes, which typically

involve energy transfers less than 0(1 meV) , have widths dominated by the incoherent

hopping process as first discussed in this context by Chudley and Elliott (CE).

I have generalized my band theory of inelastic neutron scattering from hydrogen

5 in metals to include the presence of spontaneous decay to the ground state and

incoherent hopping of the proton as well as the coherent protonic band transport I had considered earlier. Similarly, I have generalized the CE analysis of quasielastic scattering and its structural extension by Rowe, Skold, Flowtow, and Rush to

include the effects of coherent band transport, as well as the incoherent hopping

mechanism they had considered.

To do so, I have developed a general formalism which encompasses quasielastic as well as inelastic scattering of neutrons from hydrogen in metals and allows for the

coexistence of coherent and incoherent protonic transport processes. At each level

2 of complexity, the expressions I obtain for the neutron cross section d o/dQde can be

shown to reduce to earlier results in the limits when either the coherent or incoherent contributions to the ground or excited-state band widths can be ignored.

For example, for the special case of only one hydrogen occupancy site per unit cell

(and ignoring the degeneracy of the excited local-oscillator states), I obtain the

following expression for the inelastic neutron scattering cross section:

d^a/dQde = (k^/k^) | a| ^

| F(q) ] ^G' (q,co)/2iT (1)

98
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

The generalized proton self-correlation function G'(q,oj) which appears in Eq.(l) is

given by the relation

r'(q,a))

G'(5.a)) = (1/N) I ^-^ 7-^ (2)

k [w + E (k - q) - E (k)] + [r'(q)]

ex o

->

, ->. In the above u and q denote the energy and momentum transfer to the neutron; E (k)

and E (k) are the ground and excited-state band energies, respectively; r'(q) is the

incoherent width due to hopping with loss of phase memory by the proton and to its

decay from the excited to the ground state of the local oscillator; remaining symbols

are defined in the accompanying report. In the limit when r'(q) can be treated as infinitesimal, it can be shown that Eq.(2) reduces to a form given by Eq.(1) in the

2 accompanying report. That is, the band-theoretic result, expressing d o/dQde in

terms of the excited-state band density of states gCu) is recovered. In the opposite

limit, when the coherent band width (i.e., the width of g(w)) is small compared with

r'(q),Eq.(2) simplifies such that together with Eq.(1) above, I obtain

2 - p ^ ^ p r'(q)

d a/dMe = (k /k ) |ap| F(q) | x . (3)

[oj + A]^ + r'(5)

Here A is the band gap, which reduces to the local-oscillator excitation energy in

this limit. r'(q) is a known function of the momentum transfer q, expressible in

terms of two parameters, the lifetime against spontaneous decay of the proton to the

local-oscillator ground state and that due to incoherent hopping of the proton to a nearby interstitial site.

High statistics experiments will be required to distinguish between the various

possibilities. Further details of the theoretical development may be found in

reference 6.

1. H. Wipf et al., Phys. Rev. Lett. M6, 9^7 (1981).

2. A. Magerl et al., Phys. Rev. B27, 927 (1983). J. J. Rush et al., Bui. Am. Phys.

Soc. 26, 337 (1981).

3. R. C. Casella, Phys. Rev. B2i{_, 2913 (1981).

4. R. C. Casella, J. Phys. (Paris) Colloq. 42, C6-923 (1981).

5. R. C. Casella, subsequent report; also R. C. Casella, Phys. Rev. B27 , 59^3

(1983).

6. R. C. Casella, preprint, to appear in Phys. Rev. B.

99
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

THEORY OF EXCITATION BANDS OF HYDROGEN IN METALS AND OF THEIR OBSERVATION

BY NEUTRON SCATTERING

R. C. Casella

1 My earlier work on the energy-band structure of dilute hydrogen in excited

oscillator states in bcc metals (produced by overlap of the protonic wave functions)

has been extended in three ways:

1

1 . The prior analysis was limited to nearest-neighbor overlap terms in the

tight-binding expansion of the band wave functions in terms of local oscillator

states centered at interstitial sites. Second-nearest-neighbor terms have since been

included. For the case of the oj-r bands (first oscillator excitation), these terms were found to introduce only minor corrections as m.ay be seen by comparing the dashed

and solid curves in Figure 1. For the higher (jOj-j- bands, the second-neighbor

corrections introduce qualitative modifications in the band structure: (a) The

earlier presence of eigenvalues at -fiw, -, + E has been shown to be an artifact of the

nearest-neighbor approximation. (b) The presence of a pseudo Brillouin zone

boundary in the plane normal to the wave vector k = (2'iT/a) (1 /2, 0, 0) is removed by

the second-neighbor corrections, although some vestiges remain in the form of zero

slopes near the former band-crossing points. The modified ui^^ bands are shown in

Figure 2.

2 2. The expression for the differential cross section d o/dQde for inelastic

neutron scattering from dilute hydrogen in metals, inducing transitions to the

excited oscillator bands was previously limited to the special case of only one hydrogen occupancy site in the primitive cell. For the case of hydrogen in real- bcc

metals such as V, Nb, and Ta, there are six tetrahedral occupancy sites in each cell.

I have since demonstrated that the effect of the added structure leads to a neutron

cross section, which in first approximation, takes on a form similar to that for a Bravals occupancy-site lattice:

.2 k^ ^ me = k^ 1^1 l^^^^l s(^). (1)

An exact, but more complex, expression has also been derived. In Eq.(1) k and k

1 r are the initial and final neutron momenta, a is the Fermi scattering length

(renormalized by the lattice Debye-Waller factor), F(q) is an average of the local

oscillator form factors within the unit cell, q and 03 are the momentum and energy

100
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

k=%^[C,0,0] t-2 Z.Zi k=^[a,c] k=^[a,o]

Figure 1. Effects of second-neighbor overlap on the band structure E(k) for the oj bands. E(]<) is given for it = (2Tr/a) (C, n, C) along (a) [100], (b) [111]^-

and (c) [110]. Solid curves: nearest-neighbor approximation (Y = 0) . Dashed curves: next-nearest neighbors included (Y = -0.2). Y is the

ratio of the overlap integrals graph (d)/graph (a) as shown in figure 3.

The energy scale is equal to the overlap integral H where H is

symbolized by graph (a) of figure 3. The zero energy is equal to thaf of

the isolated local oscillator, excited by an amount 'fiw .

transfer to the neutron, and g(;xj) is a normalized density-of-state factor associated

with the k dependence of the excited band, which, in the absence of other widthproducing factors, yeilds the width and shape of the inelastic neutron absorption

band:

g(u; (1/hd)

hd

Z a = 1 (1/N) I 6[oo + E (k)]

k

(2;

h designates the number of occupancy sites in the unit cell; d, the degeneracy of the

excited local-oscillator states; N, the number of unit cells; and E (k), the sub-band

eigenvalues produced by the overlap of the local-oscillator wave functions. g(a)) is

normalized such that /dwg(a)) = 1. Various irreducible overlap integrals are

symbolized in Figure 3.

3. Although, as yet, definitive experimental proof of the existence of

excited-state hydrogen (i.e., protonic) energy bands is lacking, the band structure I

101
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

Figure 2. Effect of second-nearest^neighbor corrections on the band structure E(k)

for the CO bands. E(k) is given for k along (a) [100], (b) [1 1/5 0],

(c) [1 1/^-^0], (d) [1 1/2 1/2], (e) [110], (f) [11 1/2], (g) [111].

S = 0.5, T = 0.2, U = 0.2. S, T, and U are the ratios of overlap

integrals diagrammed in figure 3. S = graph (c)/graph (b), T = graph

(e)/graph (b), U = graph (f)/graph (b) of figure 3. The energy scale is

equal to the overlap integral H (graph (b) of figure 3). The zero

energy is equal to that of the isolated local oscillator, excited by an amount -1^0) . t. = (2TT/a) (^, n, ^)

102
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

(b) (c)

(f)

Figure 3. Diagrams for the various irreducible overlap integrals. Arrows signify

the symmetry of the p-orbital cubic harmonics which characterize the

excited oscillator states from which the Bloch states are constructed.

Graphs (a)-(c) designate nearest-neighbor overlap integrals, (d)-(f)

second-nearest-neighbor terms. Graphs (a) and (d) refer to the first (to ) excitation band; (b), (c), (e), and (f) belong to the second ir band.

have obtained has been shown to be consistent with the experimental results of Rush,

2 Rowe, and collaborators in two respects. (a) I predict that the band widths r of

the inelastic neutron scattering peaks ought to satisfy the inequalities

r(v) > r(Nb) > r(Ta), (3)

when comparison is made among these three metals. They do. (b) I find that the

ratio of the widths AE /AE of the w to w bands within a given metal ought to

satisfy the approximate relation

AEj^/AE^ = (wj^/Uj) T, (4)

where T is a nearly a universal constant ( ^ 3/^) for the bcc metals. Experimentally

(and consistent with either a local-oscillator or a tight-binding band model) the

2 peak frequencies satisfy (u /u) ) '\. 2, whence, identifying AE with r, I predict

r /r ^ 1.5. Direct comparison with experiment for dilute hydrogen in these metals

at low temperatures is complicated by the hydride (e) phase transition, requiring the

introduction of trapping impurities such as or N, which, while inhibiting the phase

transition, perturbs the bands as derived in this model. Nevertheless, the predicted

ratio compares favorably with the value 1.7 obtained by averaging the low-temperature

103
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

experimental neutron widths for hydrogen in association with and N impurities in

2

Nb. Further details may be found in reference 3.

1. R. C. Casella, NBS Tech. Note No. 1178, p. 79 (F. Shorten, Ed., 1983).

2. A. Magerl, J. J. Rush, J. M. Rowe, D. Richter, and H. Wipf, Phys. Rev. B27 , 927

(1983); J. J. Rush, A. Magerl, and J. M. Rowe, Bui. Am. Phys. Soc. 26, 337

(1981). The latter deals with pure systems.

3. R. C. Casella, Phys. Rev. B27, 5943 (1983).

THEORY OF HYDROGEN TRAPPING BY INTERSTITIAL IMPURITIES IN BOG METALS

N. F. Berk

We are calculating the elastic interaction energy between an octahedral (0)

site interstitial impurity and a self-trapped proton occupying a tetrahedral (T)

interstitial in its neighborhood. The aim of the study is to help elucidate the

nature of experimentally observed trapping of hydrogen by interstitial impurities in

BCC metals and to seek, in particular, the most likely candidates for the specific

trap site, which we assume to correspond to a local minimum of the mutual strain

field interaction energy.

In our approach the proton self-trapping is taken explicitly into account using

2

the adiabatic approximation and a model proton-metal interaction potential. Thus,

in these calculations the proton Kanzaki forces are not rigid but are a function of

position relative to the O-site. The O-site impurity is modeled by a rigid set of

forces. The total interaction energy is then represented by

E = -F • G • F^ - AE + AE.

o T s

where site indices and summations are implicit. F is the Kanzaki force centered at

o the O-site, E is the T-site Kanzaki force, G is the pure metal harmonic lattice

greens function, AE is the change in the proton self-trapping energy due to changes

in the self-consistently determined metal atom displacements, and AE^ is the change

in the proton zero-point energy due to the alteration of the interaction potential

near the impurity. The system of equations to be solved is symbolized by

104
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

F^{u} =y[-VV(r|u)]ii;Q^ (r|u)d^r

u = G • F^ + G • F^{u}

where V(r|u) is the proton metal interaction potential for a given set of metal atom

displacements {u}, and 4; (rju) is the ground state wave function of the proton selftrapped in this potential. The actual displacements {u} and thus all the u-dependent

quantities, are determined by iterating this set of equations to solution. The same technique will be used to study the low-lying excited states of the perturbed selftrapped sites in order to make contact with neutron spectroscopy of impurity-trapped

hydrogen.

1 Neutron studies have led to the prediction that the proton is trapped at

fourth neighbor T-site, (1/2, 3/^, 0) if the impurity is at (0, 0, 1/2). The current

3 calculations, however, find a weak local interaction energy minimum (of

approximately 30 MeV for models of both and N impurities in V metal) only at a fourth neighbor (1, 1/4, 1/2) T-site, which is not equivalent to the one mentioned

above. No other distinct local minima are found here; the general trend is a monatonic increase in the attraction with decreasing separation, the interaction

energy relative to infinite separation being lowered by about 100 MeV for all fourth

neighbor T-sites and more for closer in-sites. It is possible, of course, that

direct repulsion by the O-site prevents the proton from falling to third neighbor

sites from any fourth neighbor site. However, strain interaction alone appears to

favor only the (1, 1/4, 1/4) T-site vs. a specific trap site.

1. A. Magerl, J. J. Rush, J. M. Rowe, D. Richter, and H. Wipf, Phys. Rev. B27 , 927

(1983).

2. H. Sugimoto and Y. Fukai, J. Phys. Soc. Japan 50_, 3709 (1981).

3. N. F. Berk, Bulletin of the Amer. Phys. Soc, 28, 451 (1983).

105
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

THEORY OF SANS FROM LARGE PARTICLES AND VOIDS

N. F. Berk

1 A new program to investigate densif ication in ceramics using small angle

neutron scattering (SANS) has stimulated a theoretical interest in the general

problem of small angle scattering from a population of large particles, a topic that

apparently has not received close attention for many years. The nature of small

angle scattering from particles or voids is determined by a phase shift parameter, P,

that for a given material composition is proportional to the product of the incident

neutron wavelength and the radius of the scattering particle, assumed here to be

spherical. In the limit of small phase shift, p << 1 , the scattering is described by

the Born approximation which in SANS is identified with small angle diffraction. The

scattering cross section is very much smaller than the limit determined by the

geometric cross section and except for very thick samples or dense populations of

scatterers, the measured scattered intensity is characteristic of the scattering from

individual particles. Typically this limit accounts for scattering from particles of

radius less than 0.1 ym and applies to the vast majority of quantitative SANS

experiments. At the opposite extreme, p >> 1 , the scattering becomes describable in

terms of ray optics with each particle refracting neutrons as a lens. The scattering

cross section approaches its geometric limit and the observed intensity is dominated

by multiple scattering effects which depend not only on particle size but on macroscopic sample properties such as particle (void) volume fraction and sample

thickness. At typical neutron wavelengths the refractive limit is reached by

particles of radius greater than 10 ym. In these two limits the scattered intensity

has very different predicted dependences on neutron wavelength—as a function of the

scattering wavevector diffraction is independent of wavelength while refraction

produces a linearly dependent "beam broadening."

For intermediate values of the phase shift, p = 1, the scattering is not simply

described in terms of either limiting case and no general theoretical predictions

appear to exist for data analysis in this regime, including the exact nature of the

wavelength dependence. Since for typical measuring wavelengths this corresponds to

radii in the neighborhood of 1 ym--which encompasses an important regime of void size

in the early stages of ceramics densif ication, for example—the need for appropriate

theoretical development is evident. Thus we are engaged in working out a practical

synthesis of a general description of the single particle scattering cross section

for small angle scattering and a general approach to multiple scattering in the small

106
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

angle limit. Specifically, we are incorporating the formal integral expression for

the cross section as derived by Weiss, and which is valid for all values of the

phase shift, into the multiple scattering formalism developed by Snyder and Scott.

In the latter the scattering path is projected onto a plane, which entails no loss of

information for isotropic scattering but corresponds observationally to infinite thin

slit geometry. We adapt this projection method to the desired case of pin-hole SANS

geometry by formally applying a "slit correction" to the final integral transform of

the theory. At present we have analytically reduced the required projection and

Fourier analysis to manageable computational forms and are developing the final

numerical analysis.

1. N. F. Berk, K. Hardman-Rhyne , and E. Case, this report

2. R. J. Weiss, Phys. Rev. 83_, 379(1951).

3. H. S. Snyder and W. T. Scott, Phys. Rev. 76. 220(1949),

NEUTRON DIFFRACTION STRUCTURE DETERMINATION OF THE HIGH-TEMPERATURE FORM OF

LITHIUM TRITANTALATE, H-LiTa^Oo

J. L. Hodeau and M. Marezio

(C.N.R.S., Grenoble Cedex, France)

and

A. Santoro

and

R. S. Roth

(National Measurement Laboratory)

The crystal structure of H-LiTa Oq has been re-examined by electron and neutron

diffraction techniques. Neutron Weissenberg and electron diffraction photographs

show that the space group of the compound is Pmmn and not Pmma as determined

previously by x-ray diffraction technqiues. There are eight molecules in the unit

cell of lattice parameters a = 15.718(2), b = 7.696(1), c = 8.931(1)A. These values

show that the b-axis of the new cell is doubled with respect to the parameter

measured by x-rays. The structural refinement was based on 1074 independent

reflections measured on a single-crystal with a four-circle neutron dif f ractometer . The positions of all atoms, including the lithium atoms have been determined. The

107
REACTOR RADIATION DIVISION AND COLLABORATIVE PROGRAMS

final R and wR factors were O.O36 and 0.035, respectively. The eight lithium cations

occupy two sets of 4f positions (x,1/4,z) of the Pmmn space group. The ordering of

four lithium ions over two sets of possible positions (4j) of space group Pmma is

+ responsible for the doubling of _b axis. The other four Li occupy two sets of

positions (2d) of space group Pmma. All lithium ions are surrounded by 12 oxygen

atoms arranged as cuboctahedra. The large thermal vibrations found for the lithium

atoms and the ionic conductivity of H-LiTa 0^ at high temperatures are consistent

with weak Li-O bonding.

The structure has been refined also by neutron diffraction powder profile

analysis. The powder refinement, however, yielded wrong positions for one-fourth of

the lithium ions. This result may be due to the presence of impurities and/or

inhomogeneities in the sample, or to the fact that the large anisotropic temperature

factors of the lithium atoms were not refined because of the limited number of

intensity data in the powder pattern. This is one case in which the size of the unit

cell (~ 1150 A ) is too large to be analyzed from patterns measured with the

resolution now available at the NBS reactor. A problem of this complexity would

require a resolution of the order of that obtainable with dif fractometers giving a full width at half maximum of 0.1° at the focussing position, and using a take-off

angle of the monochromator of 120°.

*The neutron diffraction Weissenberg photographs were obtained with the

Weissenberg camera of the Laue-Langevin Institute in Grenoble.

**The electron diffraction studies were carried out at CSIC in Madrid on a Siemen's Elmiskop-102 microscope.

108
B. NoN-RRD Programs

ACTIVATION ANALYSIS GROUP FY 83

R. Zeisler

The Activation Analysis Group is part of the Inorganic Analytical Research

Division, Center for Analytical Chemistry. The group is located in the reactor

building and utilizes the facilities provided here: stable climate counting rooms,

clean and radiochemistry laboratories, a class 100 clean room, and the neutron

irradiation facilities.

The principle objectives of the Activation Analysis Group are 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). The utilization of the

thermal neutron beam depth profiling (NDP) facility has added a new and strong

research component to the group. 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 Gil, Resource Recovery, Nuclear Safeguards, and other

interdisciplinary research programs at NBS.

A considerable part of the groups research and measurement efforts is directed

to communities outside NBS, which include other government agencies as well as industries. The NBS/EPA sponsored Pilot National Environmental Specimen Bank Program

(NESB) is an on-going effort to measure trace element baseline data and to preserve

valid specimens. Samples of the second year collection of human livers are now being

evaluated. A pollutant monitor for the marine environment has been added to the

program and first evaluations for the human food intake are under way. New interest

in high accuracy trace element data has been created by this program in the medical

and nutrition communities. The NDP program is of similar importance to the outreach

to communities which need unique measurements and reference data. With the NDP

facility, the group will be participating in materials research related to high

109
NON-RRD PROGRAMS

technology industries.

One of the fruits of these expanding efforts is the increasing direct

participation of scientists from these communities in our work. The Activation

Analysis Group hosts several research associates, guest workers, and assignments

under the IPA act, who all bring in new expertise in key research areas such as materials science and bioanalytlcal research. Other industrial contacts have

significantly accelerated the development of a new generation of multichannel

pulsheight analyzer systems, a development which will enhance our capabilities for

high precision and high accuracy analysis of certain nuclear species.

The recent research accomplishments and applications of the nuclear analytical

techniques are highlighted in the sections below. For the future, we foresee

increasing demand in the "classical" activation analysis area because of its

multielement capabilities and the ability to analyse critical elements at extremely

low levels. Research efforts during the coming year will focus on the extension of

procedures to fulfill these requirements. In the area of "non-conventional"

activation analysis epithermal activation, the use of short-lived nucleides, and

possibly the activation with fast neutrons and/or charged particles will be explored.

110
NON-RRD PROGRAMS

1. Chemical Analysis with Nuclear Techniques

a. Ultratrace Determinations of Critical Elements in Biological Materials Using

Improved Radiochemical Separations

R. R. Greenberg

Accurate analyses of Ag, As, Cd, Cr, Cu, Mo, Sb, and Se are frequently required

in studies of environmental pollutions, human nutrition, and a variety of other areas

of biomedical research. The need to determine these elements at lower and lower

concentrations frequently necessitates improvements in the analytical methodology

used.

A radiochemical procedure was previously developed to determine As, Cr, Sb,

and Se via neutron activation analysis with the use of hydrated manganese dioxide

(HMD) inorganic ion exchanger. Copper and Cd were subsequently extracted from the

eluent using Bi and Zn diethyldithiocarbamates (DDC) in chloroform, and their

1 concentrations were determined. Silver and Mo were later found to be quantitatively

retained by HMD and could also be determined with the same procedure.

Unfortunately, most or all of the P contained in a sample is also retained by

HMD when the above procedure is used. Phosphorous can interfere with the

determination of the elements of interest by producing an elevated background level

of bremsstrahlung radiation from the ti- decay of P-32. This can be particularly

serious when analyzing biological materials such as animal tissues and body fluids,

milk, leafy vegetables, etc. where the P concentration can be as high as ^% (on a dry

weight basis)

.

A procedure has been developed which, with carefully controlled experimental

parameters, reduces the levels of P-32 retained on an HMD column by 80-90'^, and has

only minimal effects on the other elements. Basically, the procedure involves a pretreatment of the column with 1 M H_POk and 1 M HNO_, followed by elution of P-32

with dilute (0.0025 M) H_PO. in 1 M HNO_. Other modifications involving the amount

of resin and carries used, and changes in the dissolution procedure are also

required. With these additional steps, Ag, As, Mo, and Sb are quantitively retained

(> 99.5/5), Cr and Se are nearly quantitatively retained (98. 5-99.5/S) , and Cu and Cd are quantitatively eluted (> 99.55^).

This procedure has been used to analyze Bovine Liver (SRM 1577) and the new Milk Powder (proposed SRM 1549) which is currently being certified. The observed

concentrations in the Bovine Liver are in agreement with the certified values, as shown in table 1. The amount of P-32 retained by the HMD was between 10-20^ of the

amount originally present, and this resulted in a corresponding reduction in the

111
NON-RRD PROGRAMS

Table 1. Elemental concentrations observed in Bovine Liver, SRM 1577.

Element Unit Mean + 2S Certified

Ag (ng/g) 58 + 4 (60)^

As (ng/g) 50 + k 55 + 5 Cd (ng/g) 293 + 15 270 + 40

Cr (ng/g) 85 +_ 10 88 ^ 12

Cu (yg/g) 192 1 7 193 + 10

Mo (ug/g) 3.18 ^ 0.05 (3.^)

Sb (ng/g) 5.6 1 T -^ (5)

Se (yg/g) 1 .08 ^^ 0.07 1 .1 + 0.1

Concentrations in parenthesis are "information only" values.

Table 2. Elemental concentrations (ng/g) observed in Milk Powder, SRM 15^9.

Ag

As

Cd

Cr

Cu

Mo

Sb

Se

Mean ± 2s

<0.5

1 .8 +_ 0.2

0.M7 ^ 0.14

3 1 2 606 +_ 9 310 +_ 30

0.24 +_ 0.08

110 + 3

112
NON-RRD PROGRAMS

background levels for most elements by a factor of 5-10. This lower level of

background radiation not only improved the counting statistics (typically by a factor

of 2-3), but also allowed samples to be counted closer to the detector for an

additional improvement in sensitivity. This added sensitivity was particularly

important for the analysis of the Milk Powder where the concentration of Ag, As, Cr,

Mo, Sb, and Se are considerably lower than in the Bovine Liver, as shown in table 2,

while the P concentration is comparable.

Although Cd could be determined in the Bovine Liver (and in most biological

materials) as part of the multielement procedure, its concentration was too low to be

determined in the Milk Powder. Cadmium could be determined in the Milk Powder with

several procedural changes including: less post-irradiation decay time prior to

sample processing, elimination of the HMD procedure to save time and minimize

radiation dose to personnel, and several modifications to the Zn(DDC)„ procedure used

to extract Cd. These modifications involve washing the Cd containing

Zn(DDC ) p/chlorof orm solution twice with aqueous solution containing 100 mg of

unirradiated Zn to reduce the level of radioactive Zn from the sample and backextracting the Cd into 2 M HCl. Although this separation procedure is not

quantitative, the observed recovery is highly reproducible, 95.2 +_ 0.4(1s)5^. Cadmium

is essentially free of all other radionuclides from the sample and its detection

limit is determined primarily by the amount of natural background radiation reaching

the detector through the shield. Five 500 mg samples of the Milk Powder were

analyzed and the observed Cd concentration was 0.47 j^ 0.07( 1 s)ng/g.

When coupled to an appropriate radiochemical separation, neutron activation

analysis has the capability of determ.ining many elements at biologically important

levels. Improved radiochemical procedures have been developed to separate and

determine eight biologically active elements at the trace and ultratrace levels

frequently required in current biomedical research. Two of these elements, Cd and

Sb, have been determined at the sub-ppb level in Milk Powder.

1. M. Gallorini, R. R. Greenberg, and T. E. Gills, Anal. Chem. 1479 , 50 (1978)

113
NON-RRD PROGRAMS

b. The Determination of Natural Iodine by Epithermal Neutron Activation Analysis

G. Lutz

During the past year, an epithermal neutron activation analysis (ENAA)

experiment was developed and tested in the NBSR. The impetus behind this effort was the necessity to develop a rapid, efficient nondestructive method for the

determination of natural iodine at sub-ppm levels. This was required both for the

reliable determination of iodine in SRMs as well as the natural iodine content of

environmental and biological samples.

There are two elements suitable for screening out thermal neutrons thus

allowing more selective epithermal activation-boron and cadmium. The activation

analysis group had previous experience with a boron nitride container for the sample

at the reactor at the University of Michigan. The containers used in the current

work are identical with those used at the University of Michigan. Figure 1 is a photograph of the container. It will accomodate a 2/5 dram (1.3 ml) vial. Thus,

sample masses in the range of 0.5-1 gram are possible.

It has become necessary to do extensive hazards evaluation. The mass of the

container assembly is 25 grams. Testing with temperature sensors indicated that a twelve second irradiation in RT-3 would bring the boron nitride container to a temperature in excess of 100 °C. To allow for a sufficient safety margin, it was

decided that eight seconds would be the maximum irradiation time allowed.

Preliminary experiments have been completed on some SRMs which have been

analyzed for iodine by other methods. ENAA is a very satisfactory method and it is

expected with experience that we will be able to get down to 0.1 ppm.

Figure 1 . Boron Nitride Container

114
NON-RRD PROGRAMS

c. The Determination of 1-129 by Neutron Activation Analysis

G. Lutz and R. Lindstrom

The procedure which has been under development for almost three years has been

modified slightly and is now in routine use in the determination of 1-129 in a variety of vegetation and other samples.

The analysis consists of a pre-irradiation separation, an irradiation in the

reactor, and a post-irradiation separation.

The apparatus for the pre-irradiation separation is shown in figure 1-129A.

The sample, usually after freeze drying, is placed in a boat in the combustion tube.

Sample masses are usually 1-10 grams. A known amount (typically 10 Bq) of 1-125 is

added to the sample prior to combustion to measure the chemical yield.

The dimensions of the apparatus are--the silica furnace tube is 60 cm long and

has an inside diameter of 2.4 cm. The high purity quartz trap sealed to the furnace

tube has an inside diameter of 0.6 cm. In the small tube are a column (3 cm) of

hydrated manganese dioxide followed by two columns (2 cm and 1 cm) of activated

charcoal.

The combustion apparatus has two oxygen inlets which can be controlled

independently. The inlet which terminates at the downstream end of the furnace tube assures complete combustion of volatile decomposition products of the sample. After

sample destruction is complete, the large combustion tube is heated to 800 °C with a resistance furnace and a hand torch downstream to the HMD trap. The HMD trap is then

heated with the torch to red heat for 5 minutes. The HMD accomplishes a partial

decontaminate from bromine and also removes a volatile white material, believed to be

ammonium chloride.

The iodine is collected on the first charcoal trap. Oxygen flow rate is

reduced, the first trap is ignited, and the iodine is collected on the smaller trap.

The size of the charcoal trap to be irradiated is kept small to minimize the amount

of fission product iodine which will be produced from uranium impurity in the

charcoal. Finally, the tube containing the charcoal trap is sealed under vacuum. I125 is assayed for yield determination and the sample is irradiated.

All irradiations are conducted in the pneumatic transfer facility RT-4 of the

13 -2 -1

NBS research reactor. The thermal neutron flux is 1.3 x 10 n/cm sec

Irradiations are typically conducted overnight.

After irradiation, the quartz tube containing the activated charcoal trap is

rinsed with hot dilute acid. The tube is cooled in liquid nitrogen, wrapped in

tissue paper along with a small piece of filter paper on which a solution containing

115
NON-RRD PROGRAMS

OXYGEN =^

INLETS =^gfc:

SAMPLE

QUARTZ

WOOL CHARCOAL

TRAPS

Figure 1. Apparatus for pre-irradiation separation of 1-129.

OXYGEN —

INLET — 1

SAMPLE WITH

10MG OF 1-127 AND 1000 D/SEC

OF 1-125

< .^^1.D

QUARTZ

WOOL

ACTIVATED CHARCOAL

COLLECTOR TRAP

KEPT DRY WITH

NICHROME WIRE

RESISTANCE HEATER

5-MG PORTIONS

OF 1-127

Figure 2. Apparatus for separating iodine from the bulk of the irradiated sampl

OXYGEN

INLET

HMD

TUBE

FURNACE ACTIVATED CHARCOAL

COLLECTOR TRAP

KEPT DRY WITH

NICHROME WIRE

RESISTANCE HEATER

Figure 3. HMD trap.

116
NON-RRD PROGRAMS

10 mg of 1-127 and approximately 1000 Bq of 1-125 has been evaporated, and the tube

is then broken. This is placed in a furnace tube with two 5 mg portions of 1-127, as shown in figure 1 . The oxygen flow is adjusted and the apparatus is heated from the

downstream 1-127 to the activated charcoal trap. The downstream 1-127 is then heated

strongly. The liberated iodine rinses the system finally being collected in the

charcoal trap. Then the sample with carrier and 1-125 spike is burned to liberate

the iodine. Finally, the upstream iodine is liberated as a final purge of the

system. During the procedure, the apparatus is heated sufficiently to assure that no iodine can condense anywhere in the system except on the charcoal trap.

Finally, the charcoal trap containing the iodine is connected to an HMD column

as shown in figure 3. The oxygen flow is adjusted and the HMD is heated in a small

tube furnace to 200 °C. The charcoal containing the iodine and other volatiles is

ignited. After the trap is burned, the ash is heated strongly to assure complete

combustion. The HMD trap is rapidly brought to 600 °C and held there for 10 minutes.

The assembly is allowed to cool and the collection trap is assayed for iodine yield

and bromine decontamination. The procedure can be repeated, if necessary, with fresh

HMD columns. When adequate bromine decontamination is achieved, the collection trap

is assayed for yield and finally cooled overnight for 1-130 content. A lower limit

Q of determination of approximately 2x10 atoms/gram of sample is usually achievable.

d. Elemental Characterization of the New Milk Powder SRM Via Instrumental and

Radiochemical Neutron Activation Analysis

R. R. Greenberg

Well characterized reference materials have proven to be valuable aids in

verifying the accuracy of analytical procedures. The need for suitable reference

materials is particularly acute for quality assurance of trace element analyses in

the biological and medical fields. It is generally recognized that a number of trace

elements produce toxic effects at very low levels and so accurate measurements of

their concentrations in foods, animal tissues, and other biologically important

materials are often necessary. Other elements are essential, in trace quantities,

for human nutrition and therefore accurate determinations of their concentrations in

various foods may be required. Unfortunately, accurate trace and ultra-trace level

analyses of foods and animal tissues are often extremely difficult due to a wide

variety of problems including chemical blank, sample contamination, matrix effects,

interferences, losses during sample dissolution, etc. This was recently illustrated

1 by a round-robin intercomparison of milk powder conducted by the International

117
NON-RRD PROGRAMS

Atomic Energy Agency (IAEA), Some of the results of this study are summarized in

table 1 . The reported concentrations of a number of biologically important elements

varied over a range of three orders of magnitude and the reported Cr concentrations

varied by almost five orders of magnitude; clearly indicating the need for suitable

reference materials in ultra-trace level analysis.

The National Bureau of Standards is currently preparing a Milk Powder Standard

Reference Material to provide assistance in overcoming the difficulties in accurate,

ultra-trace analysis of foods and other biologically important materials. As part of

the certification process, this Milk Powder has been analyzed by neutron activation

analysis (NAA), as well as by a number of other analytical techniques. For a number

of important elements in milk, neutron activation analysis possesses the required

sensitivities and is free from interferences and other matrix effects. It also can

be performed in a blank-free manner and thus not be limited by reagent blank.

The concentrations of 21 elements, including all those listed in table 1, have

been determined in the NBS Milk Powder SRM by NAA and are listed in table 2. Both

instrumental and radiochemical procedures have been employed. All sample preparation

(pre-irradiation) steps were performed in a class-100 clean room to prevent sample

contamination. Standard instrumental procedures were used; however, extremely long

counts were required for some elements, and additional care was required to integrate

some peaks on the high phosphorus bremsstrahlung background. A number of different

Table 1 . Ranges of concentrations reported in IAEA Milk Powder concentration - Mg/g

unless indicated.

Element Lowest Value Highest Value

As (ng/g) 4.45 ^0.14 544 ^

1^

Cd (ng/g) 1.1 ^0.1 1660 _+ 200

Co 0.004 ^ ? 51 .5 j;^ 2.1

Cr 0.016 ^ ? 1160 jt^ ? Cu 0.082 +_ ? 72.2 +_ 2.4

Fe 0.70 _+ 0.11 281 .8^6.1

Hg (ng/g) 1.33 1 0.57 667 _^ 52

Sb (ng/g) 1.16+0.13 1010 + ?

From reference 1 b.No uncertainty reported.

118
NON-RRD PROGRAMS

Table 2. Elemental concentrations determined in Milk Powder (SRM 1549) by neutron

activation analysis.

Element

As^

Br

Ca

Cd^

CI

Co

Cr^

Cs

Cu^

Fe

Hg^

IK

Mg

Mn

Mo^

Ne

Rb

Sb^

Se^'^

Zn

Units

(ng/g

(ug/g

{%)

(ng/g

(5^) (ng/g

(ng/g

(ng/g

(ng/g

(yg/g

(ng/g

(yg/g

(55) (yg/g

(ng/g

(ng/g

(yg/g

(yg/g

(ng/g

(ng/g

(yg/g

Mean + 2s

1 .8 + 0.2

11 .6 + 0.8

1.33 + 0.04

0.47 + 0.14

1 .085 + 0.009

4.1 + 0.5

3

+ 2 17.6 + 1 .2

606 + 9

1.8 + 0.3

0.16 + 0.03

3.2 + 0.8

1 .69 + 0.04

1190 + 60

230 + 30

310 + 30

4890 + 40

12.4 + 0.3

0.24 + 0.08

110 + 3 46.6 + 0.9

Concentrations determined after radiochemical separation.

Se concentration also determined instrumentally (110 + 9)

119
NON-RRD PROGRAMS

radiochemical separation procedures were used to analyze the Milk Powder and some

of these had to be modified to further isolate the elements of interest from the

background-elevating matrix elements. An improved group separation, based on the

inorganic-ion exchanger HMD (hydrated manganese dioxide), made it possible to analyze

As, Cr, Mo, Sb, and Se. Individual separations using solvent extraction procedures

v/ith appropriate metal diethyldithiocarbaraate compounds allowed Hg, Cu, and Cd to be

determined.

When certification is co-pleted, the Milk Powder SRM will be an extremely

useful reference material for trace and ultra-trace analyses in biological matrices.

The determination of trace elements at these low levels illustrates the advantage of

NAA being essentially blank-free.

1. R. Dybczynski', A. Veglia, and 0. Suschny, "Report of the Intercomparison Run A-1

for the Determination of Inorganic Constituents of Milk Powder," IAEA Report

RL/68, July 1980.

2. Neutron Depth Profiling at the National Bureau of Standards

R. G. Downing, R. F. Fleming, J. K. Langland, and D. H. Vincent

The National Bureau of Standards recently has established a dedicated thermal

neutron depth profiling (NDP) facility. The NDP technique, originally developed in

1972 by Ziegler et al., has proven valuable in the measurement of concentration

versus depth distributions. Table 1 lists principal elements, sensitivities,, and the

nuclear reactions that are utilized by NDP. The physics of the technique is

discussed in references (1) and (2). Analyses are virtually nondestructive and

nearly independent of either matrix effects or the chemical state of the material,

a. Description of Facility

1 . Beam quality and collimation

The NBS 10 MW , enr i ched-uranium fueled, heavy-water (DO) moderated reactor

provides a high intensity source of neutrons. A series of steel, lead, and cadmium

collimators 1.22 m long defines the neutron beam as it passes through the reactor's

biological shield to the NDP target chamber. The emerging neutron beam is 9.5 mm in

o diameter with an intensity of 3 x 1 n/s. Figure 1 shows the vertical profile of the

neutron beam at the sample position measured with a thermal neutron radiograph. The

beam intensity remains uniform over the 9.5 mm central region and decreases smoothly

with a full width at half maximum of 13 mm. Gamma radiography shows that the gamma

120
NON-RRD PROGRAMS

ray component of the beam has much the same shape. Table 2 compares the

characteristics of other NDP facilities for which published information exists.

A high quality NDP beam should have good thermal neutron intensity and minimum

contamination with fast neutrons and gamma rays. Figure 2 shows the neutron source,

filters, and optics used to accomplish this. The split-core design of the NBS

reactor means that the beam tube views the heavy-water region between the fuel but

does not see the intense gamma and fast neutron source of the U-235 itself. The

3 filtering of the beam through 200 mm of single crystal sapphire and 80 mm of single

crystal silicon further reduces the epithermal neutron and gamma ray components

entering the collimator. The result is an intense thermal neutron beam with a cadmium ratio for gold of greater than 10 and a gamma intensity of about 200 mr/h.

2. Target chamber

The NDP target chamber (figure 3) is constructed of aluminum to reduce mass and

background and is designed in three major pieces. The base plate contains the

electrical f eed-throughs and vacuum port and is mounted on two machine ways to

provide precise adjustment in the horizontal and vertical directions perpendicular to

the beam. The chamber wall is machined from a 305 mm I.D. tube and contains the

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Figure 1. Vertical neutron intensity profile taken by Au-1 98 autoradiography at the

sample position in the target chamber.

121
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123
NON-RRD PROGRAMS

1.2 M 1.5 M

9.5 MM

SILICON SAPPHIRE VESSEL. SHIELD. SHUTTER. ETC.

Figure 2. Side view of the reactor neutron source and the neutron collimator and

filter.

Neutron Beam Vacuum

Monitor Port

Vacuum

Chamber

Aluminum

Window

-, / Silicon Surface Electrical

q77 Beam Barrier Detector Feed-thru

1 cm

Beam

Stop

Aluminum

Window

Figure 3- Neutron depth profiling target chamber,

124
NON-RRD PROGRAMS

NBS Neutron Depth Profiling Electronic Diagram

Silicon

Surface

Barrier

Detector

PreAmplifier

Precision Pulse

Generator

Neutron

Beam

Monitor

PreAmplifier

Linear

Amplifier

Analog to —»^ Digital

Converter

Bias Supply

Bias Supply

Computer

Analysis

and

Storage

Linear

Amplifier

Analog to

Digital

Converter

Figure 4. Diagram of the data acquisition and analysis electronics.

50 mm diameter by 0.13 mm thick aluminum entrance and exit windows for the neutron

beam. The top plate contains an 85 mm diameter quartz viewing window, kept covered

during operation. The three sections are joined by two rubber Q-rings to provide the

vacuum seal. Initial pump-down is accomplished with a compressed-air driven Venturi

pump followed by a liquid-nitrogen cooled sorption pump. During operation the vacuum

-4

IS maintained at 10 Pa by a 30 L/s ion pump.

3. Electronic components

Figure 4 shows a diagram of the data acquisition electronics. A silicon

surface-barrier detector with an 11 mm active diameter is used to measure the charged

particle spectrum from the sample. A high precision reference pulse is fed into the

preamplifier parallel to the signal allowing the monitoring and correction of any

gain shift in the electronics. The neutron beam intensity is monitored at the target

chamber entrance window. All signals are processed and the spectra stored in a dedicated computer-based multi-channel analyzer to provide real-time display of depth

profiles.

4. Conclusions

Steps to improve the beam quality, beam intensity, detection sensitivity, and

resolution are planned. In addition to the applications described elsewhere in this

report, the facility is intended to contribute to the certification of depth

o profiling Standard Reference Materials. The profiling of bismuth using the delayed

alpha emission of Po-210 is being carried out in parallel to the neutron beam

profiling described here.

125
NON-RRD PROGRAMS

We would like to acknowledge the following people for helpful discussions and

for supplying samples: J. R. Ehrstein, Center for Electronic and Electrical

Engineering, NBS; J. R. Riley, Jr., Bell Telephone Laboratories, Murray Hill, NJ; and

J. N. Cox, Intel Corporation, Santa Clara, CA.

1. J. F. Ziegler, G. W. Cole, and J. E. E. Baglin, J. Appl. Phys. _43.. 3809 (1972).

2. J. P. Biersack, D. Fink, R. Henkelmann, and K. Muller, Nucl. Instr. and Meth.

149 , 93 (1978).

3. H. F. Nieman, D. C. Tennant, and G. Dolling, Rev. Sci. Instrum. 5^, 1299 (1980).

4. K. Muller, R. Henkelmann, and H. Boroffka, Nucl. Instr. and Meth. 1 29 , 557

(1975).

5. D. Fink, J. P. Biersack, and H. Liebl, Proc. of the Fourth International Conf. on Ion Implantation: Equipment and Techniques, Berchtesgaden, Sept. 1982 (to be

published).

6. J. Cervena, V. Hnatowicz, J. Hoffmann, Z. Kosina, J, Kvitek, and P. Onheiser,

Nucl. Instr. and Meth. 188 , 185 (1981).

7. W. G. Halsey, Ph.D. Thesis, University of Michigan, 1980 and D. Wehe, priv. comm. (1983).

8. R. G. Downing, R. F. Fleming, D. S. Simons, and D. E. Newbury, Microbeam

Analysis-1982, ed. K. F. J. Heinrich (San Francisco Press, 1982). p. 219.

126
NON-RRD PROGRAMS

b. Thermal Release of Ion-Implanted He-3 from Single Crystal Nickel Samples

D. H. Vincent, J. T. Maki, R. G. Downing, and R. F. Fleming

A new approach to the problem of identifying trapping sites and trap binding

energies for helium in metals at low helium concentrations has been developed. This

is based on using ion implantations of He-3 and subsequent depth profiling of the

implanted helium using a thermal neutron beam. The thermal release of the helium is

studied by measuring the depth distribution of the helium remaining in the sample

after each anneal. While this method has been used before to observe helium release

from molybdenum, niobium, and copper, this work will represent the first unambiguous

determinations of detrapping energies.

The diffusion and trapping of helium, as well as of other inert gases in

metals, became of great practical interest dur'ing recent years because of materials

problems related to nuclear energy production, e.g., the void formation in structural

materials under neutron bombardment in fission reactors and the ablation of first

wall materials in future fusion reactors.

Since the solubility of helium in metals is quite low, studies often require

the introduction of helium atoms into a metal by implantation as helium ions in an accelerator. It has been found that, if such implantations are performed at ion

energies above a few keV, with the sample held at room temperature, the implanted

helium is quantitatively trapped. Each helium atom is trapped very close to the end

of its range in the metal, so that concentration profiles of the implanted helium can

be used to determine range distributions of the implanted ions. An example of such a range distribution is shown in Figure 1 . If a metal sample containing implanted

helium is brought to a sufficiently high temperature, some or all of the helium atoms

will be released from their trapping sites. Once the helium is detrapped, it is

released from the metal surface almost instantaneously, indicating a very large

diffusivity for helium in metals.

Most of the measurements dealing with helium in nickel have been done as desorption experiments in which helium-implanted samples were subjected to a temperature ramp, and the helium release was observed by mass spectroscopy.

Implantation energies were usually low (of the order of 1 to 10 keV), and

implantation surface doses were comparatively high, so that the formation of helium

atom aggregates was likely before release.

The present work differs from previous investigations in two respects. First,

a relatively high implantation energy is used (150 keV) , and the implantation dose is

kept low enough, so that the formation of larger helium aggregates (bubbles) is

127
NON-RRD PROGRAMS

avoided as much as possible. Secondly, helium release is being observed not bymeasuring the amount of gas released through the surface of the sample, but by

observing changes in the helium concentration inside the sample as a function of

depth. Using this method, it will be possible not only to measure activation

energies for helium detrapping, but also to relate the activation energies to

specific trapping sites along the range distribution of the implanted ions.

The activation energy for helium detrapping is likely to depend on the

particular kind of lattice defect at which the helium is trapped. In order to reduce

the variety of trapping sites as much as possible, single crystal nickel samples are

used for helium implantation. This confines the helium traps mainly to isolated

vacancies and excludes trapping at extended defects such as dislocations and grain

boundaries.

Samples for helium implantation were prepared by cutting slices of

approximately 1 mm thickness from a single crystal nickel rod. One surface of each

slice was carefully polished and its crystallinity tested by obtaining a Laue x-ray

pattern. These patterns indicate that the normal of the samples is well away from

any ion channeling direction, so that helium ion channeling should not occur during

implantation if the sample surface is perpendicular to the ion beam axis.

A first set of samples has been implanted with He-3 ions at an ion implantation

accelerator at the Naval Research Laboratory. Precautions were taken to prevent ion

beam heating of the samples during implantation. Ion beam currents of approximately

300 nA were used, and implantation surface doses were 2x10 ,1x10 ,6x10 , and 1 X 10 He-3 ions/cm . The largest dose (2x10 He-3 ions/cm ) produced a maximum concentration of about 0.9 atom5& He-3 at the peak of the range distribution

for 150 keV He-3 ions. This may be compared with the solubility of helium in nickel

-7

at room temperature which is = 1 x 10 atom?.

The depth distribution of the helium after implantation was measured at the

Neutron Depth Profiling facility at the NBS research reactor. The distance from the

surface of specific implanted He-3 atoms was determined by measuring the energy loss

3 3 of protons from the nuclear reaction He(n,p) H. This reaction has a large cross section at thermal neutron energies (5327 barns) and produces protons with an energy

of 572.5 keV. The energy spectrum of protons emerging from the surface of the sample

as it is irradiated with thermal neutrons is measured with a silicon surface barrier

detector. This energy spectrum was converted to a depth distribution for the

implanted He-3 atoms with the aid of the known proton stopping power (dE/dx) in

128
NON-RRD PROGRAMS

(fl 5i- 150 keV Implant

Surface Implant oo

o o

o

—LOoo J 1 1 1 i_Ooo J 100 200 300 400 500 600 700

Depth (nm)

Figure 1. Helium depth profiles in nickel for a 150 keV implant, and for a 250 eV

surface implant which represents the system resolution function.

nickel. Figure 1 shows the depth distribution of helium atoms in a sample implanted

with 150 keV He-3 ions to a surface does of 2 x 1 He-3 ions/cm . This depth

distribution is broadened by the energy resolution of the detector and the associated

electronic equipment. To indicate the width of the resolution function, a spectrum

from a surface implantation of helium ions (250 eV implantation energy) is also shown

in figure 1. The mean projected range of the 150 keV implant is 372 nm. This

compares well with the value of 367 nm obtained by interpolation from a set of

1 theoretical mean ranges at various energies given by Biersack et al.

Annealing experiments on the implanted samples are in progress. Activation

energies for detrapping of the implanted helium will be determined by a combination

of isochronal and isothermal anneals. It is planned to extend the present work to

include He-3 profiling and thermal release studies of nickel-based metallic glasses.

Both the trapping efficiencies and the detrapping behavior will be investigated.

A further application of He-3 depth profiling will be the decoration of radiationinduced defects in pure metals, in metallic glasses, and in silicate glasses. Of

these, the silicate glasses may be the most promising materials for an application of

this method, since helium is known to permeate these materials easily at room

temperature. Preliminary experiments on this new application of He-3 depth profiling

are planned.

J. P. Biersack, D. Fink, R. Henkelmann, and K. Muller, J. Nucl . Mater. 85/86 , 1165 (1979).

129
NON-RRD PROGRAMS

c. Neutron Depth Profiling of Boron

R. F. Fleming, R. G. Downing, J. E. Riley Jr., and D. H. Vincent

The first year of neutron depth profiling (NDP) at the NBS Reactor has

focused on the determination of the concentration profiles of B-10 in the near- surface region of several materials. The samples chosen demonstrated the technique

in semiconductors, glasses, and glassy metals. Work on boron distributions in metals

is in progress.

1. B-10 Ion-Implanted Silicon

Neutron depth profiling was first used to determine the distribution of ion2 implanted boron in silicon. Since then, a considerable amount of data on boron

profiling in silicon has accumulated. It seemed, therefore, appropriate to use the

measurement of boron profiles in silicon as a test for the performance of the neutron

depth profiling facility. We have measured depth profiles of B-10 implanted into

<111> oriented silicon wafer with energies of 70 keV and 200 keV and B-10 surface

14-2 15-2 15-2 16-2

doses of 4 X 1 cm ,1x10 cm ,4x10 cm , and 1 x 10 cm . The wafers

had been tilted 7Z with respect to the beam axis during implantation to avoid

channeling effects.

We find that our results for the projected range and the range straggling agree

within a few percent with values obtained by interpolating between - or extrapolating

3 from - experimental results obtained by Ryssel et al . who used implantation

energies different from ours. Like these authors we observe a considerably larger

straggling than predicted by theoretical calculations which is thought to be due to

residual channeling. Our values for range and range straggling were obtained

directly from the first and second moments of the raw data after background

subtraction but without fitting a Pearson-IV distribution to the data. Shown in

Figure 1 is a typical profile compared to a secondary ion mass spectrometry (SIMS)

measurement of a 1 atom/cm , 70 keV implant. The narrow peak at 200 nm on the

broad distribution is a boron precipitate formed at those depths where the

concentration exceeds the solubility of boron in silicon.

2. Boron Depletion of Glass Surfaces

Recently the distribution of boron near the surface of borosilicate glasses has

4 been of concern. We have measured the relative boron concentration in a number of

borosilicate glasses whose surfaces had undergone various surface treatments.

Figure 2 gives an indication of the depth resolution of the method. It shows the

gradient of the boron concentration across the surface of two borosilicate glass

samples (12.6 vt% BO), broadened by the finite resolution of our detection system.

130
NON-RRD PROGRAMS

The data in the figure were obtained by subjecting the observed energy distribution

1 7 of the 1^472.3 keV alpha particles from the B(n,a) Li reaction to a 7-point

5 quadratic smoothing followed by a 3~point first order differentiation. The lefthand peak is the result for an untreated surface obtained by fracturing one of our samples. The derivative of the boron distribution is centered about depth zero and

has a width (FWHM) of 50 nm, corresponding closely to the resolution of the detection

system. The other peak was obtained for an aqueously polished sample [sample E of

ref (4)]. The shift of the peak indicates a depletion of boron in the first 15 nm of

the sample. In addition we observe a broadening of the peak to 60 nm which shows

that the boron concentration of the polished surface rises to the bulk value less

steeply than that of the fractured glass surface.

3. Boron Distribution in Borophosphosilicate Glass

Borophosilicate glass (BPSG) is used as an insulating layer and for forming

tapered contours over steep steps of oxide and silicon on high density integrated

circuits. Boron, added to lower the glass's flow-point temperature, needs to be

evenly distributed in the film to insure continuity and uniformity of the flow during

circuit fabrication. Knowledge of film thickness is also required for production of

state-of-the-art multilayer circuits. Figure 3 is an overlay of two NDP measurements

made on a BPSG film. The boron distribution is shown both for the film as it was

deposited on a silicon wafer and for the same film after processing. NDP is able to

determine in a single nondestructive measurement the sample thickness, the

homogeneity of the boron distribution, and its absolute concentration at discrete

depths. Together the plots show the leveling of boron distribution after processing

and the apparent removal of some of the matrix. Nonetheless, the integrals of the

two peaks are equal, indicating no boron loss has occurred.

4. Boron Distribution in Iron-Boron Metallic Glasses

Thin films of sputter deposited Fe. nB_ „ metglass were provided by Professor

U . o K) . d

Lawrence Pilione of Pennsylvania State University. Figure 4 shows a spectrum

obtained with a sample of 1 \xm thickness consistent with a uniform boron

distribution.

5. Future Work

Work is in progress for extending the NDP technique to the profiling of

lithium, sodium, and beryllium. These samples include Na-22 in semiconductor

silicon, Be-7 in GaAs, and Li-6 diffused into high-purity copper.

131
NON-RRD PROGRAMS

1021

1020 Eu

n

E

o<

ca 10^

10^8

o Secondary Ion Mass Spectra

• Neutron Depth

Profile

=^31^

°'"'g.

200 400 600 800

Depth in Nanometers

Figure 1. Comparison of SIMS and NDP results for a 70 KeV Boron-10 implant in

Silicon at 10^^ 10B/cin2 annealed for 30 minutes at 1000°C.

3o

1- W 5 QC Q n <

rr S n (1) ^ n Q

1- o

<r

1- ^ 7 o

LU

(57 o O

o o z

c o <n nr .^ §

i

«3

r» <

Polished

-75-50-25 25 50 75 100 125 DEPTH (nm)

Figure 2. Boron concentration gradient-broadened by the system resolution

across two surfaces of the same glass: fractured surface and

aqueously polished surface.

132
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Eo•^O)EzO

t-<

cr1-z

mo

zo

o

CQ O

18

16

14

12

10

8

6

4

2

-

*•• - 1

-J •

r PROCESSED /

- AS DEPOSITED

1

-

- "

"" t V

J 1 I'^kn.

0.0 0.2 0.4 0.6 DEPTH IN MICROMETERS

0.8

Figure 3. Boron concentration as a function of depth for a borophosphosilicate

film on silicon as-deposited and after processing.

lOi0.5 1.0

Depth in Micrometers

1.5

Figure 4. Boron concentration profile across a uniform Fe B metglass,

not corrected for detector resolution. ^'^ ^''^

133
NON-RRD PROGRAMS

1. R. G. Downing, R. F. Fleming, J. K. Langland, and D. H. Vincent, "Neutron Depth

Profiling at the National Bureau of Standards", Nuclear Inst

and Methods, (in

press).

2. J. F. Ziegler, G. W. Cole, and J. E. E. Baglin, "Technique for Determining

Concentration Profiles of Boron Impurities in Substrates", J. Appl. Phys. 43,

3809 (1972).

3. H. Ryssel, G. Prinke, K. Haberger, K. Hoffman, K. Muller, and R. Henkelmann,

"Range Parameters of Boron Implanted into Silicon", Appl. Phys. 24 , 39 (1981).

4. D. L. Malm and J. E. Riley, Jr., "Characterization of Near Surface Composition of

Borosilicate Glasses (BS6) by Secondary Ion Mass Spectrometry", J_^ Electrochem.

Soc. 129 . 1819 (1982).

5. A. Savitzky and M. J. E. Golay, "Smoothing and Differentiation of Data by

Simplified Least Squares Procedures", Anal. Chem. 36 , 1627 (1964).

6. W. Kern and G. L. Schnable, "Chemically Vapor-deposited Borophosphosilicate

Glasses for Silicon Device Applications", RCA Review 43, 423 (1982).

3. Facilities for Activation Analysis

a. New MCA System

R. M. Lindstrom

As part of a continuing program of modernization of equipment, the PDP11/44

computer has been equipped with a multichannel analyzer to allow it to be used in

data acquisition. In consultation with several domestic manufacturers, a modern data

acquisition and processing system based on this computer has been defined which will

make possible accurate measurements of elements which give activation products with

half-lives as short as 1 sec. This application requires that the system be able to

5 perform spectroscopy accurately at rapidly varying counting rates as high as 10 /sec,

and to measure time intervals to better than 5 msec. A request for proposals based

on these requirements stimulated three responses, involving substantial improvements

in capabilities over the previous state of the art. The new-generation equipment is

expected to be delivered before the end of the fiscal year, after which numerous new applications will become possible.

134
NON-RRD PROGRMIS

b. Pneumatic Transfer System and Sample Changer

J. K. Langland

The counting of short-lived nucleides requires a rapid transfer from the

irradiation facility to the counting environment. Our highest quality counting

systems are three floors above the irradiation facility. An existing small rabbit

(bunny) flight tube has been fitted with a counting receiver and automatic controls.

A magazine bunny loader allows the system to double as a sample changer. Figure 1 shows the arrangement of the system.

The existing 7/8 inch flight tube from C-001 to B-121 is used, the receiver in

C-001 is retained, and in room B-121, the original receiver has been removed and

replaced with a counting receiver mounted on a GeLi detector. Additional components

in B-121 include a flight line switching valve, a soft landing air cushion, and a lead storage cave for holding previously counted samples.

The new counting receiver permits automatic operation of the system. It is

made of lucite so that the sample and bunny remain in it for counting. A second

flight tube goes from the receiver to a lead storage cave several meters away. At

the completion of counting, compressed air sends the bunny out of the receiver via

Flight Line Closing Valve ^Transfer Flight Line \ Magazine Type Sample Loader

Bunny Receiver

in Room C001

ir Valve

-Compressed Air Figure 1 . System Schematic

135
NON-RRD PROGRAMS

the second flight tube to the storage cave. The receiver is now ready to accept

another sample. Counting geometry is manually adjustable from to 65 cm. A magazine type bunny loader is designed that will permit this system to be an automatic sample changer. A switching valve mounted in the flight line just before

the air cushion allows selecting C-001 or the magazine loader as a sample source. As

a sample changer, at the completion of a count, the bunny will be transferred to the

storage cave and a new bunny transferred from the magazine loader to the counting

receiver.

The controls consist of an electronic controller in B-121 and an auxiliary

control panel in C-001. The system includes several photocell units, switches,

indicator lights, and logic circuits to monitor bunny location, system status, fault

conditions, and inform the operator of these conditions. Also included are interlock

and shutdown circuits to prevent operation in the event of trouble (stuck bunny,

valve malfunction, etc.). A computer interface is provided that allows our NO-6600,

or D.E.C. computers, to control and monitor the system, both in shuttle and sample

changer mode

The automation of this system is providing safer sample handling, improved

counting-timing accuracy, and uses less manpower. The sample changer allows fully

automatic operation, permitting better use of the counting equipment during nights

and weekends.

4. Collaborative Programs

a. Environmental Specimen Bank

S. F. Stone, R. Zeisler

In the past year, the Environmental Specimen Bank has continued banking and

analyzing biological samples for trace elements and organic compounds. Instrumental

Neutron Activation Analysis has been an integral part of the program. This year, a second sample type was added to the bank: Mytilus edulis , an aquatic accumulator.

The first sample type, human livers, has continued to be collected and analyzed.

1 . Human Livers

The banked livers were the subject of several areas of research. A homogeneity

study was completed on an improved disk mill for cryogenic homogenization of samples

up to 300 g. This study was used to confirm whether a one gram (fresh weight) test

portion is representative of the whole liver. The data show no significant

inhomogeneity at that sampling level, outside the errors due to counting statistics.

136
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Table 1

.

Mytilus edulis - M2N005M German Freshwater Mussel Homog

Na 54200 _+ 1000 nd

Mg 6^30 + 540 nd

Al 760 +_ 70 nd

CI 100000 + 4900 nd

K 11700 +_ 1500 nd

Sc 0.138 +_ 0.007 0.699 ^ 0.006

Cr 2.05 +_ 0.20 14.8 1 1.9

Mn 21 .9 + 1 .2 nd

Fe 571 1 27 978 ji^ 60

Co 0.538 + 0.014 1 .478 _+ 0.013

Cu £ 70 nd

Zn 122 1 5 154.7 +_ 0.8

As 10.4 + 1 .0 6.90 + 0.48

Se 2.47 +_ 0.11 4.62 +_ 0.15

Br 443 + 40 38.6 1 1.5

Rb 7.24 +_ 0.56 0.251 + 0.027

Mo £ 1.4 2.5 + 0.3

Ag 0.104 +_ 0.013 < 0.10

Cd <_ 4 1 2-5

Sb 0.255 + 0.007 0.033 +_ 0.010

Cs 0.683 + 0.003 0.165 +_ 0.006

La 0.59 +_ 0.09 0.472 + 0.015

Ce 0.98 +_ 0.10 0.79 + 0.14

Stn 0.101 + 0.014 0.130 +_ 0.008

Eu 0.0193 +_ 0.0004 0.557 +_ 0.006

Hf 0.058 ± 0.011 59.0 + 0.8

Hg 0.48 + 0.24 <_ 0.2

Th 0.139 + 0.006 nd

nd = not determined

137
NON-RRD PROGRAMS

BeNaMg

Al

Si CIK

ScV

Cr Mn

Fe Co

Ni Cu

ZnAsSeBr - Rb

Mo

Ag

Cd

SnSb

La Ce

Pt Au

Hg

Tl Pb

< 0.0006

I xm"///.

\v/A>y/.

y//////////.

I II I II I I

y//////xii'^mfm(VA////y

omiK^A

'm^4Km»,\

y////w//m^\\\

mm I

y//////////////////////^^^^^ y///////Amt

IHilll I

I I lll<lt% \\\wm^\

I \v/mv//w//////////.

II wym^vmiVA \

V/////////////'

I II nil iiiiiii I y/(7///////////^^^^^

II II I nil I I II I

III III mil I II I

I II I II \\vmymyyy//yA

y//////////////////////////////////, yyyy/y.

- Be msmwi Na

i Mg

Al

Si yyyyy Cl

itttttii - K

- ScV

CrMn

ffiii FeCo

NiCu

ZnAs

^ Se

BrRb

Mo

Ag

Cd

SnSb

LaCe

PtAu

Hg

Tl

1

'• Pb

ng/g Mg/g mg/g

Figure 1. Human liver data.

Thus, the values depend more on the precision of the analytical technique rather than

sampling uncertainty.

Liver collection has continued through our contractor in Seattle, Washington.

As of June 1983, a total of 420 liver samples have been banked. Homogenization and

analysis of the second year baseline samples were completed. This brings the total

number of analyzed livers to 66. Figure 1 summarizes the distribution of elemental

concentrations found during the second year of the study. The ranges are comparable

to those found in the first year analyses.

A reanalysis of the first year samples has begun in order to evaluate the

effects of the different storage conditions on elemental concentrations. In

comparing data from samples stored at -25 °C, -80 °C, over liquid nitrogen vapor

(-120 °C to -190 °C), and freeze-dried at room temperature, no significant changes

have been found for trace elements.

138
NON-RRD PROGRAMS

2. Mussels

The marine mussels, Mytilus edulis , was added to the bank as the second

environmental sample. Five-thousand mussels were collected from Narragansett Bay,

Rhode Island, as part of a preliminary study to develop the sampling and analytical

protocols. The mussels were separated into batches of seventy animals each and

banked at four storage conditions: -25 °C, -80 °C, over liquid nitrogen vapor

(-120 °C to -190 °C), and freeze-dried at room temperature. Two batches stored at

liquid nitrogen temperatures have been homogenized and analyzed.

Concentrations for 28 trace elements were determined by neutron activation

analysis. Table 1 shows the mean values and standard deviation for each of the

elements. These values are compared to concentrations found in a mussel homogenate

from the German Pilot Environmental Specimen Bank. The freshwater mussel homogenates

were analyzed as part of an interlaboratory comparison of methods. Two major

differences were noted in comparing the two sets of data. The hafnium level in the

German homogenate was unusually high, almost 60 ppm. Also, the chromium levels in

the same samples were more than ten times higher than in the marine mussels samples.

3. New Projects

A cooperative program is being developed with the Army Institute of Pathology.

The goals are to look for possible relationships between elemental concentrations in

different human organs and diseases, such as cancers. The study will begin with

human liver tissue, but other organs will be studied as the program continues.

This cooperative effort is a positive indication that the technology developed

for the Environmental Specimen Bank can be useful in many other areas. The research

that has been involved in sample selection, transport, preparation, homogenization

storage, and analysis may be used throughout the scientific community.

1. R. Zeisler, "Results of the Inorganic Analysis of the First Year Human Liver

Collection," The Pilot National Environmental Specimen Bank--Analysis of Human

Liver Specimens, R. Zeisler, S. H. Harrison, and S. A. Wise, eds.. National

Bureau of Standards Spec. Publ. 656, 81-30 (1983).

139
NON-RRD PROGRAMS

ATMOSPHERIC AND ENVIRONMENTAL STUDIES BY INSTRUMENTAL NEUTRON ACTIVATION ANALYSIS

G. E. Gordon and W. H. Zoller

(University of Maryland, College Park, MD)

We continue to make extensive use of instrumental neutron activation analysis

(INAA) to determine concentrations of about 35 elements in samples of atmospheric

particulate matter collected from ambient air (now mostly at remote sites such as Hawaii and rural sites in the continental U.S.) and in particles released from major sources such as 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 C0„ record (since 1957) at Mauna Loa Observatory

(MLO) in Hawaii for observing CO^ seasonal variations and long-term increase.

Fortunately, since mid-1979, the National Oceanic and Atmospheric Agency (NOAA) has

supported weekly collections of filters at MLO and analysis of them by our group

using INAA. A distinct diurnal cycle exists at MLO at 3^00 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. Downslope

conditions bring down rather clean air from the upper troposphere. A control system

alternately activates the pump on one of three filter systems depending on wind

conditions 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 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, because of transport from

arid regions of central and eastern Asia. Duce et al. previously reported similar

incursions of Asian dust at Eniwetok Atoll, with concentrations of airborne soil

being 2.3 yg/m in mid-April, 1979. During non-dust conditions at MLO, average

3 downslope Al concentrations are about 4.9 ng/m , whereas weekly average

140
NON-RRD PROGRAMS

3 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

concentrat ions

.

The data 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 dust 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, downslope concentrations are among the lowest observed

anywhere 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. We have been interpreting this extensive data set by several techniques,

including factor analysis and chemical element balances, with the intent of

determining the sources of particles and elements and learning how they are

transported to MLO. This work is described in detail in a series of papers that are

2-7 published, submitted, or in preparation. Among other things, we see sharp spikes

in the concentration plots for various elements superimposed on low backgrounds and

smoothly varying concentrations from natural sources. Spikes often occur for

characteristic groups of trace elements (including As, Se, V, Zn, In, W, etc.), often

along with sulfate. Many of the spikes appear to result from anthropogenic

activities in Asia or in North America. Occasionally, for example, we observed

elemental concentration patterns similar to these of copper-smelter plumes in Arizona

at the same time that back-trajectories calculated by NOAA indicate that air masses

came to MLO from the southwest U.S.

2. Compositions of Emissions from Volcanoes

Airborne studies of the atmospheric emissions of four Central American

volcanoes were conducted using a Lockheed Electra turbo-prop research aircraft

modified for the collection of plume particles and gases. Two Costa Rican volcanoes,

Poas and Arenal, and one Mexican volcano, Colima, were sampled in February, 1982. A

subsequent mission in November was made to collect plume samples at El Chichon

volcano, the violent eruptions of which earlier in the year produced the largest

cloud of volcanic origin observed in the stratosphere this century.

141
NON-RRD PROGRAMS

Single high volume filter samples were collected using Teflon materials

selected for their high flow rates and low INAA blank characteristics. A multiple

filter package consisting of a Teflon pre-filter followed by four cellulose filters

7 that had been treated with 1 M_ LiOH in 3055 glycerol was used to trap acid volatiles

(e.g., S0„, HC1 , HF, HBr). Cascade impactors were used to collect size-segregated

samples of plume particles on polycarbonate films.

Although all plumes studied were quite diffuse and sampling volumes small (10-

3 20 m ) , we were able to determine concentrations of up to 30 elements in the plume

particulate samples because of the low blank contribution and the high sensitivity of

INAA. Particulate concentrations were compared with those of total gaseous

concentrations of S, CI, and Br as determined by INAA of the base-treated filters.

Less than ^ 0% of total S and CI, and less than 30^ of total Br was found to be

associated with the particulate phase.

Pronounced enrichments of volatile and chalcophilic elements relative to bulk

pyroclastic material were observed in the pumice particles of all volcanoes studied.

These observations are consistent with similar measurements made at other volcanic

Q Q 1 n 1 1 systems * including Mount St. Helens. ' The highly enriched elements, As, Se

,

and Sb , were found by INAA of cascade impactor stages to be associated predominantly

with fine particles (<1 ym diam) while non-enriched crustal elements such as Na and

Ca were almost exclusively found on large (>3 um) particles. Aluminum was found to

be bimodally distributed with particle size suggesting that volcanoes may act as a high temperature source of fine Al-bearing particles. This observation was verified

by analysis of samples collected on two ground missions into the crater of Poas

volca:no in February 1982, and to El Chichon in January 1983- Aluminum, most likely

as volatile halide, was observed to be highly enriched in condensates of emissions

from high temperature vents (> 300°C).

Estimates of the emission rates of enriched volatile elements have been

calculated by normalization of plume concentrations to simultaneously determine S as determined by an onboard flame photometric detector. Shown in Table 2 are the

emission rates so calculated for the four Central American volcanoes, as well as those determined for Mount St. Helens in an earlier study.

3. INAA Studies of Particles Collected in Rural Areas

One of the major environmental problems of our time is acid deposition. In

order to control acid deposition in an optimal way, we must identify the sources of

acid precursors, find out how they are transported and deposited, and how they are

chemically converted to acids. In work supported by EPA, we are trying to identify

142
NON-RRD PROGRAMS

Table 1

Geometric Means of Concentrations of Elements Measured on Downslope and

Upslope Particle Filters Duirng Clean (July to mid-February) and Dust

(mid-February to July) Seasons at Mauna Loa Observatory, Hawaii, from February

1979 to June 1982

Elenlent

.ts^

Downslope - Upslope

(uni Clean Dust Clear1 Dust

Na (-ng: 6.6 ( 2.7) 22 ( 2.o: 86 (:2.2) 140 (:i.9)

Mg (.ng:1 2.6 ( 2.1) 26 ( 2.5: 14.2 (:2.i) 45 ([2.0)

Al (:ng] 4.9 ( 2.1) 56 ( 2.5: 16.0 ('2.2) 73 ([2.5)

S ( ng:1 80 ( 2.0) 160 ( 1.7: 150 (.1.8) 230 (:i.7)

CI (:ng: 2.4 ( 4.0) 3.4 ( 3.o: 19 ([4.2) 30 ([5.0)

K ( ng'1 2.8 ( 1.8) 27 (.2.3: 10 (:i.9) 41 (:i.9)

Ca ( ng:) 3.7 ( 2.5) 64 (:3.o: 13 (:2.2) 83 ([2.7)

Sc (>pg:1 1.2 ( 2.2) 13 ( 2.6:1 3.9 (:2.i) 15 ([2.1)

Ti (.ng: 0.53 (:2.6) 4.3 ( 2.4: 2.4 (:2.5) 7.3 (:2.2)

V ( pg: 10 (:2.5) 100 ( 2.4: 48 ([2.2) 160 ([2.2)

Mn (:pg:1 62 (:2.3) 810 ( 2.5: 280 ([2.2) 1300 ([2.4)

Fe ( ng:1 4.0 (.2.3) 42 (:2.6:» 15 ([2.2) 52 ([2.3)

Co (:pg:1 3.2 (.2.6) 20 (.2.4:1 9.0 ([2.7) 30 ([2.2)

Cu (:ng:I 0.22 (:5.0) 0.85 (:3.o: 0.33 ([4.0) 0.6 ([3.0)

Zn (.pg:) 90 (:4.o) 320 (:2.2:) 250 ([3.0) 700 ([3.0)

Ga (:pg:1 8.4 ( 4.0) 20 (.2.5:> 22 ([2.7) 42 ([2.0)

As (;pg:I 13 (.2.9) 70 (:4.o:I 39 ([2.5) 110 ([3.0)

Se (;pg:> 11 (:2.0) 21 (:i.7:1 22 (:i.7) 36 ([1.7)

Br (:ng:I* 1.45±().60 1.60±0. 45 1.63±0. 50 1.92±0. 90

Rb (;pg:1 16 ( .19) 130 (.2.5:» 21 ([2.5) 150 ([2.0)

Sr (:ng:) 0.24 (:3.o) 0.62 (:2.6:I 0.28 ([1.8) 0.72 ([2.1)

Ag (^pg:I 1.4 (:3.i) 1.8 (:2.7:I 2.8 ([3.5) 2.8 ([4.0)

Sb (^pg:I 1.8 (:.26) 7.7 (:2.4:I 4.6 ([2.4) 9.7 ([1.9)

I (;ng:)* 2.1±]L.3 1.45±0. 60 2.2±0..80 2.3±0.(30 Cs (:pg:I 0.95 (:2.6) 9.9 (:2.8:> 1 ([3.0) 11 ([2.5)

Ba (:ng;) 0.51 ([4.0) 1.0 ([2.1;) 0.42 <[2.7) 1.1 ([3.0)

La ('pg;) 3.0 (:2.3) 53 ([3.3;) 12 ([2.2) 66 ([2.5)

Ce (^pg:) 7.8 (:2.3) 71 ([2.5:) 31 ([2.5) 110 ([2.6)

Sm <'pg:) 0.52 [2.8) 7.0 ([2.7;) 2.0 ([2.6) 10 ([3.0)

Eu (:pg:) 0.19 <[2.5) 1.2 ([2.4;) 0.65 [2.2) 1.5 ([2.4)

Tb (^pg:) 0.20 [2.5) 0.96 [2.6:) 0.41 [2.1) 1.1 ([2.0)

Yb ^pg:) 1.1 <[2.1) 3.2 ([2.2;) 1.6 ([2.0) 4.0 ([2.0)

Lu [pg') 0.36 [3.1) 0.51 <[3.o;) 0.48 [3.0) 0.85 ([2.0)

Hf [pg ) 0.44 [2.1) 3.3 <[2.5') 1.7 ([2.5) 5.4 ([2.2)

Ta [pg ) 0.23 [2.3) 0.86 [3.0 ) 0.58 [2.5) 1.5 ([1.7)

W [pg ) 2.7 {[3.3) 6.0 <[4.o;) 13 ([4.0) 17 ([1.7)

Au [pg ) 0.15 [3.0) 0.24 [4.5.) 0.28 [3.5) 0.37 ([2.5)

Th [pg ) 0.80 [2.6) 11 [3.0 ) 1.8 ([2.8) 13 ([2.6)

Normal means and standard deviations expressed for I and Br.

143
NON-RRD PROGRAMS

Table 2

Estimated Volcanic Emission Rates (tonnes/day) of Selected Volatile Elements

Species Arena

Poas Colima El Chichon^ Mt. St. Helens^

2/82 2/82 2/82 11/82 9/80

Ash 40 5 120 15 60

S (t) 100 400 160 400 450

S (p) 6.7 7.9 0.9 16 24

CI (t) 30 16 20 53 -

CI (p) 4 0.4 0.001 2 3

Br (t) 0.053 0.042 0.070 0.100 -

Br (p) 0.0054 0.0030 0.0068 0.030 0.020

As (p) 0.0052 0.0020 0.0011 0.200 0.800

Se (p) 0.0100 0.0043 0.0044 0.004 0.100

Sb (p) 0.00051 0.00019 - 0.020 0.030

Au (p) 0.00005 0.00004 0.00014 0.00070 0.0030

^Ref. 12.

bRef. 11.

(t) = total

(p) = particulate

144
NON-RRD PROGRAMS

Table 3

Concentration of Elements Borne by Fine Particles in the Shenandoah Valley,

July /Aug. 1980

Element No. of Samples Method Concentration (ng/m-^)

(avgtg)

Na 33

Al 32

Si 30

S 32

CI 33

K 32

Ca 32

Sc 10

Ti 10

V 32

Mn 31

Fe 32

Co 17

Cu 24

Zn 30

As 11

Se 23

Br 33

Sr 15

Sb 10

I 21

Cs 8

Ba 13

La 10

Ce 10

Sm 9

Pb 32

INAA

XRF

XRF

XRF

INAA

INAA, XRF

INAA

INAA

INAA

INAA, XRF

INAA, XRF

INAA, XRF

INAA, XRF

INAA, XRF

INAA

INAA, XRF

XRF

XRF

INAA

INAA

INAA

XRF

INAA

INAA

INAA

XRF

46±24

42±46

1401160

4400±3300

19±20

67±31

41±29

0.014±0.015

11±5

1.1 ±0.8

2.5±1.8

57 ±47

0.74±0.96

6.6±4.3

13±11

0.7±0.3

1.5±0.9

7.5±2.3

4 ±6

0.4±0.7

0.48 ±0.30

0.19±0.013

55±46

0.16±0.12

0.21±0.14

0.13±0.01

49±20

145
NON-RRD PROGRAMS

elements borne by atmospheric particles that can serve as characteristic signatures

of certain types of sources or areas of the country. To do this, we are subjecting

samples collected by EPA to analysis by INAA. They collected samples for 15 months

at rural sites in Kentucky, Indiana, and Ohio and for one month in the Shenandoah

Valley. They collected particles in two size fractions, greater and less than 2,5-um

diameter and analyzed them by x-ray fluorescence (XRF). The XRF method is a rapid,

highly automated technique for analyzing large numbers of samples, but it mainly

observes major elements. INAA is more expensive and time-consuming than XRF, but it

yields data for many trace elements that are potentially useful tracers, e.g., Se

,

As, Sb , and In. The combined XRF and INAA results will yield data for about 40

elements. We are mainly analyzing fine particles, as they provide much more

information about sources than large particles, which are dominated by local soil.

Back-trajectories for air masses sampled during each period are being calculated

using a model and meteorological data from NOAA so that we can identify the areas

over which the air was transported in order see if the compositions of particles from

different areas have characteristic signatures.

To date, complete INAA measurements have been done on ten Shenandoah samples

and a total of 33 have been analyzed for short-lived species. The data obtained are listed in table 3-

1. R. A. Duce, C. K. Unni, B. J. Ray, J. M. Prospero, and J. T. Merrill, Science

209 , 1522 (1980).

2. J. R. Parrington, W. H. Zoller, and N. K. Aras, Asia Dust: Seasonal Transport

to the Hawaiian Islands, Science 220 , 195 (1983).

3. J. R. Parrington and W. H. Zoller, Selective Sampling of Diurnal Changes in

Aerosol Composition at Mauna Loa, Hawaii, J. Geophys. Res. (in press, 1983).

4. J. R. Parrington and W. H. Zoller, The Chemistry of Asian Dust, submitted to J.

Geophys. Res. (1983).

5. J. R. Parrington, J. K. Whittaker, and W. H. Zoller, Instrumentation for and

Results of Particulate Sampling of Diurnal Winds at Mauna Loa Observatory,

Hawaii, submitted to J. Appl. Meto. (1983)-

6. J. R. Parrington and W. H. Zoller, Sources and Seasonal Variations of Sulfur and

Selenium at Mauna Loa Observatory, Hawaii, in preparation for submission to

Geophys. Res. Lett. (1983).

7. J. R. Parrington, W. H. Zoller, and G. E. Gordon, Sources and Composition of

Atmospheric Particles of the Free Troposphere over the North Pacific, in

preparation for submission to J. Geophys. Res. (1983).

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8. G. J. Mroz and W. H. Zoller, Composition of Atmospheric Particulates from the

Eruption of Heimaey, Iceland, Science 190 , 461-463 (1975).

9. E. A. Lepel, K. M. Stefansson, and W. H. Zoller, The Enrichment of Volatile

Elements in the Atmosphere by Volcanoes: Mt. Augustine, 1976, J. Geophys. Res.

83, 6213-6220 (1978).

10. T. Vossler, D. L. Anderson, N. K. Aras, J. M. Phelan, and W. H. Zoller, Trace

Element Composition of the Mt. St. Helens Plume: Stratospheric Samples from the

May 18th Eruption, Science 208 , 827-830 (1981).

11. J. M. Phelan, D. L. Finnegan, D. S. Ballantine, W. H. Zoller, M. A. Hart, and

J. L. Moyers, Airborne Aerosol Measurements in the Quiescent Plume of Mount St.

Helens: September 1980, Geophys. Res. Lett. 9_, 1093-1096 (1982).

12. J. Phelan Kotra, W. H. Zoller, M. A. Hart, and J. L. Moyers, Elemental

Characterization of Volcanic Plume Aerosols: Central America, February 1982,

in press, J. Geophys. Res., (1983).

VALIDATION OF STABLE ISOTOPE TRACING FOR STUDY OF ZINC NUTRITION IN HUMAN SUBJECTS

G. E. Gordon, Inci Gokmen, N. K. Aras, and I. Olmez

(University of Maryland, College Park, MD)

Under support of the U.S. Department of Agriculture, we have begun studies of

trace element nutrition in human beings. The actual work with human subjects is

being performed at Georgetown University Medical Center under the direction of

Drs. Robert Henkin and K. Sivasubramanian and at NIH under Dr. Roger Aamodt. The

following is the abstract of the Ph.D. Thesis of Dr. Inci Gokmen (July, 1983), who

did the initial work on this project:

Stable isotopes are beginning to be used to study trace element nutrition in

humans as they do not expose subjects to radiation as in the case of radioactive

tracers. Stable isotopes will be very useful for population groups that cannot be

studied with radioactive tracers (pregnant women and persons under age 18). A sample

of the element in which the abundance of an isotope has been greatly enriched is

administered to the subject. For Zn the stable tracer was Zn-70, whose abundance was increased from the normal 0.62^ to 66^. Red blood cells (RBC), plasma, urine, and

feces were collected at various times after administration of the tracer and the

amount of tracer present determined from ratios of the abundance of the enriched

isotope to those of one or more major isotopes (for Zn, the Zn-70/Zn-64 and Zn-70/Zn68 ratios). Amounts of Zn isotopes in the samples were determined by neutron

irradiation followed by observation of their radioactive products, Zn-65, -69m, and

-71m. A pre- and post- irradiation separation scheme (based on Chelex resin

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NON-RRD PROGRAMS

separations) was used to observe Zn isotopes free of interference from other

irradiation products.

The stable isotope method was validated against the radioactive tracer method

by simultaneous oral administration of stable Zn-70 and radioactive Zn-65 tracers.

Samples of RBC, plasma, urine, and feces from four adult volunteers were collected

and assayed for Zn-65, and whole-body and liver-thigh counts of Zn-65 were taken at

various times after administration. Variations of Zn-70/Zn-68 and Zn-70/Zn-64 ratios

in the samples were determined by neutron activation. The fraction of each type of

tracer appearing in each of the four body pools versus time after irradiations was

calculated from results of the two tracer measurements. The agreement between the

stable and radioactive tracers was very good for urine and feces. The agreement was

good, in general, for RBC and plasma, but there were occasional fluctuations of the

stable isotope results. The latter problem appears to result from poor separations

of RBC and plasma for some samples and large statistical errors in the determinations

of chemical yields based on the in vivo Zn-55 tracer. Changes of the procedure are

indicated for reducing these sources of error. Methods for observing a stable isotope tracer of selenium were developed, but

not tested in human subjects.

NEUTRON-CAPTURE PROMPT GAMMA-RAY ACTIVATION ANALYSIS

D. L. Anderson, G. E. Gordon, W. B. Walters, W. H. Zoller, and M. E. Kitto

(University of Maryland, College Park, MD)

and

R. M. Lindstrom

(Center for Analytical Chemistry)

A number of continued and new studies have been pursued using the vertical beam

neutron-capture prompt-Y activation analysis (PGAA) facility at the NBSR. We have

continued to study analytical procedures for the boron assay of lumped-burnable

poisons, including sample pre- irradiation dilution (necessary due to boron's high

cross section). We have continued our analysis of many types of NBS and other

reference materials, studied an Interesting matrix effect in PGAA due to the presence

of significant amounts of H in some samples and analyzed a number of new types of

samples. In addition, a concentrated effort has begun to measure the particulate and

gas-phase boron concentration in air at various locations in order to determine if B can be used as a tracer element for coal burning. The following sections explain

briefly some of these studies.

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1 . New Measurements of Beam Characteristics and System Improvements

The PGAA facility has been improved by the addition of three DEC RL02 and dual

RX02 floppy disk drives. The operating system used for the PDF 11/3^ minicomputer is now RSX 11M version 3.2, and two LA36 Decwriters are presently used for operation and

I/O. A new, high resolution, hyperpure Ge detector was purchased for use in the

anti-Compton and pair spectrometer. Its characteristics are: 21% efficient

(relative to Nal) and FWHM = 1.76 keV at 1332 keV. For the routine analysis of the

elements H, B, C, N, Na, Mg, Al, Si, P, S, CI, K, Ca, Ti, V, Mn, Fe, Cd , Nd, Sm, and

Gd, two Compton-suppressed T-ray spectra with the energy ranges 0-4 and 3.5-11 MeV

are collected and analyzed.

At the time the reactor shim rods were replaced, we observed a noticeable

reduction in the thermal neutron beam flux while checking our elemental sensitivities

(counts/s*mg of material). As we use relative methods for standardization, absolute

flux measurements were not necessary. However, in the past year we determined these

characteristics, using Au and Au clad with Cd monitors. The new thermal flux

Q p determined by this method is cj) = 1.37 x 10 n/cm s and a Cd(Au) ratio of 30/1,

8 ? compared to the original <^ = 1.7 x 10 n/cm s and Cd(Au) ratio of 55/1. Although

the flux reduction is substantial, we have improved our background via better

alignment and selection of materials for the sample holder. For these reasons and

•ac

o

0.046

0.044 —

S 0.042 —

3

ou

4 6

% Hydrogen

Figure 1. Sensitivity for sulfur (842 keV) vs. hydrogen content,

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NON-RRD PROGRAMS

because of the other effective shielding techniques used, the U. Md-NBS PGAA facility

remains equal to or (in the case of most elements) better than any other prompt-T

facility in terms of minimum detection limits. (Higher flux facilities, of course,

have better sensitivities, but the larger backgrounds cancel out this feature when

one considers detection limits.)

2. Hydrogen Matrix Effects

For some time, we have been aware of an important matrix effect observed in our analyses. Matrices containing percent levels of hydrogen can severely alter the mean neutron energy to which the sample is exposed. As this mean energy is shifted lower,

for many elements, the effective cross section and, therefore, the count rates

observed, increase. As a number of our pelletized standards (e.g., B, Cd, Sra, Gd) are dilute solutions pipetted onto filter paper, they would not yield correct answers

if low-H samples (e.g., fly ash or rock material) were compared to them.

We have begun to study this effect by preparing pelletized standards of the

element in a varying graphite-mannitol matrix (for the case of elements with large cross section) or of the element (or common compound of the element) in various

proportions with mannitol. The result for S is presented in Figure 1. Table 1 lists

the % difference in sensitivities (c/s*mg) for several elements in a 05^ H matrix

compared to a matrix of ~ 6^ H (preliminary results). A shift in the mean beam

energy of ~ 0.03 eV (e.g., from 0.06 to 0.03 eV) would explain such behavior, except

for Sm, whose sensitivity behavior is hard to predict because of the large nearby

resonance (0.04-0.11 eV)

As a result of these studies, we are updating our PGAA values for several

elements in some important reference materials. As a number were run before the

shim-rod replacement, a simple correction factor may not be valid [e.g., for SRM's

2 1632, 1632a, 1633, 1633a, and 1635 ], and will be reanalyzed. Values given in last

year's report for SRM 278 (obsidian) and SRM 688 (basalt) are revised as shown in

Table 2.

3. Analysis of Geochemical Reference Standards

The PGAA study of twenty-two geochemical reference standards has been

4 completed. Included are reference materials obtained from the U. S. Geological

Survey, NBS, the International Atomic Energy Agency, and Pacific Northwest

Laboratories. As the data tables are extensive, they are not presented here, but may

be obtained by contacting D. L. Anderson.

4. Analysis of Construction Materials

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Table 1. Percent increase in sensitivity (c/s mg of element) in a Whatman filter

standard {~6% H) relative to a graphite matrix standard (05^ H)

Element E (keV) % Increase

B 477 11 CI 517 10

Ca 1942 13

Cd 558 17

Sm 334 1 Gd 1 82 42

In collaboration with E. A. Lepel of Battelle Pacific Northwest Laboratories a number of cement, concrete aggregate, and steel samples from construction sites of

the Washington Public Power Supply System (WPPSS) were analyzed. The results are

presented in Tables 3 and 4, For a full discussion of these measurements, see reference (5)

.

5. Multitechnique Characterization of Boron in Glass

PGAA was used to measure boron in a series of borosilicate glasses, in

collaboration with J. E. Riley, Jr., of Bell Laboratories and with the neutron depth

profiling project described more fully elsewhere in this report. Large (25g) samples

of bulk glass were ground to a powder (< 44 ym) , blended with graphite, and pressed

to a uniform shape and similar boron content for analysis in order to eliminate

material inhomogeneity and self-shielding. The precision was excellent, the relative

standard deviation of repeated analyses of individual glasses averaging better than

IX. Comparison with emission spectrographic analyses (ICP) showed good agreement.

The measurements are more fully described in reference (6).

6. Measurement of B in the Atmosphere

We have begun to study the capabilities of PGAA as applied to atmospheric

7 sampling. Results obtained from Mt. St. Helens plume samples encouraged us to

attempt measurements of particles in the urban environment, as PGAA is sensitive

Table 2. Elemental concentrations in NBS geochemical standards (ug/g)

Element SRM 278 SRM 688

• B - 27.9j^0.4 1.5^0.2

Sm 6.08+^0.03 2.62+^0.02

Gd 5.95+0.08 3.46+0.10

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Table 3- PGAA analyses of concretes and ingredients (one sample each)

Element Concentrations (% unless noted)

WPPSS SarTiples Rancho Seco

Sand Cement Aggregate Concrete #1 Concrete #2 Concrete

H 0.28+0.01 0.088+0.014 0.15+0.01 0.61+0.01 0.6110.01 O.6O1O.OI

B (ug/g) 8.0+0.

66.1+0.3 5.710.2 1 5 . 4iO .

15.1+0.1 25.9+0.1

Na 2.35+^O.OiJ 0.3310.08 2.16+0.10 1 .68+0.05 1 .5610.09 1.35+0. 08

Mg 2.3+^0.5 1 .7+0.4 2.24-0.3 1 . 7lO . 3 1 .3+0.1 2.21O.4

Al 7.43+_0.13 2.00+0.01 6.7110.08 5.2510.10 5.18+0.05 5.8510.19

Si 29.5^1 .0 10.2+0.2 26.210.5 22.9+0.1 23.5+0.4 25 . 5lO .

S

- 1 .02+_0.01 - 0.22+0.4 0.15+0.01 0.16+0.02

CI (ug/g) 50^10 - 72i7 50+20 67l5 5611 5 K 1 .31j^0.03 0.5310.02 1 .15+0.02 1 .06+0.02 0.92+0.01 0.83+0.02

Ca 5.48+0.13 43.1+_0.3 4.8+0.1 11 .6+0.1 12.76+0.05 11 .IIO.2

Ti 1.30+0.01 0.111+0.002 1 .06+0.01 0.75+0.01 0.74i0.01 0.343+0.004

V (ug/g) 390^60 - 430170 500+60 360120 400+80

Mn (ug/g) 1210+60 1000^100 1 1 60i40 1 030170 800+10 81 Oi50

Fe 8.01^0.14 2.13+0.02 6.96+0.05 5.0210.10 4.97+0.04 3. 61+0. 10

Cd (ug/g) - - - - 200+40 35011 1 Nd (ug/g) - - 24i13

- I4i5 33112

Sra (ug/g) 6.85+0.04 1 .96+0.02 5.65+0.05 4.47+0.01 4.14+0.02 3.2510.2

Gd (ug/g) 6.45+0.10 1 .51+0.11 5.65+0.12 4.17+0.05 3.89+0.06 3.O21O.17

Total

(as oxides)

109.6+2.3 96.9+0.9 96.711 .2 96.110.8 97.81O.9 99.4+1 .5

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Table 4. PGAA analyses of steel samples (one sample each)

Element Concentrat ion {% unless noted)

Low-Carbon Stainless NBS SRM 123C

SA 302 SA 316 SA 304 This work

(2 samples)

Certificate

B (yg/g) 1 . 0+^0 .

3

5.0+0.4 3.2+0.2 2.35+^0.05 -

Ti (yg/g) 160+60 - -

60j^10 -

V (ug/g) 110+50 740+150 670+100 350+20 -

Cr <0.12 17.3+0.2 19.2+0.2 17.7+^0.3 17.4

Mn 1 .4+0.2 1.3^.0.2 1 .76+0.10 1 .69+^0.03 1.7

Fe 96.6+1 .1 65.5j!^0.6 69.3^1 .2 67.2+0.1 67.2

Co £0.12 0.14+0.01 0.112+0.008 0.110+0.001 0.12

Ni <_0.05 13.U0.15 9.68+0.13 11.35+_0.03 11.3

Mo 0.45+0.03 2.05j^0.02 - 0.23+_0.01 0.22

Total 98.6+1 .2 99.2+0.7 100.1+1 .2 98.3+0.3 97.9

3 Table 5- College Park sample period: June 8-12, 1983; 904 m ; 1st stage untreated

Whatman; stages 2-5 LiOH/glycerol treated; weather: clear, low AQI

but increasing

Species Concentrations of Filter (ng/m )

1 2 3 4 5 total

gas phase

B 4.7+0.2 1 3 . 8+^0 .

3

2.0+0.2 1 . 7j|^0 .

2

. 8+^0 . 3 18.3

NO^ (IC) 6340 3490 313 377 186 4366

Na ~1100 - - - - -

Si 6040+_600 - - - - -

S 3330+_280 4980+150 2690+220 740+220 670+^290 9080

SO^->S (IC) 3700 4840 2521 1160 289 8810

CI 348+^30 1 060+^30 58+^27 49+27 <34 1201

CI (IC) 323 1170 181 210 142 1703

Ti 140+25 - - - - -

Cd 0.52+0.06 - - - - -

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3 Table 6a. Particle filter concentration ranges (ng/m ) for B, Si, S, and CI at

various locations measured by PGAA.

Location Range

B Si S CI

College Park 5-12 6000-U,000 3000-11 ,000 300-600

NBS ~3 <2000 ~3000 ~100

Mauna Loa <0.3 <1500 <200 <50

Observatory,

Hawaii

Cape Kumakahi

,

<0.2 <1500 900-1200 10 ,000-13,

Hawaii

Range

B S CI

20-30 10,000-13,000 900-1200

"11 ~5000 ~350

<0.3 0-800 0-500

Table 6b. Gas-phase concentration ranges measured by PGAA.

Location

College Park

NBS

Mauna Loa

Observatory,

Hawaii

Cape Kumakahi, 15-30 500-4000 200-9000

Hawaii

enough to measure, usually, B, Si, CI, S, Ti, and Cd for air sample volumes of about

Q O 300 m . Recent studies at the University of Rhode Island indicate there is much

gas-phase B in the atmosphere (along with CI and S) . Therefore, preliminary

measurements have been made at the University of Maryland, NBS, Hawaii, and Wallops

Island, VA, in an attempt to establish the primary sources of B. We sample air

through stacks consisting of a single untreated filter to collect particles followed

by 4 LiOH-treated filters, which collect acidic gases. Our preliminary results are

o in general agreement with the University of Rhode Island work, showing that the

ocean is a major source of gas-phase B in the form of H B0_, boric acid. There

appears, however, to be more B in the atmosphere than can be attributed to the ocean

and local dust. Another major source of B in the atmosphere is apparently coal9 burning. The potential for

nov; under study by our group

9 burning. The potential for using B as a tracer element for coal-plant emissions is

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The data for a stack of filters run at College Park are shown in Table 5. One

half of each filter was analyzed by PGAA, the other by ion chromatography. As can be

seen, the two techniques yield data that agree fairly well. The elemental

concentrations ranges measured so far are presented in tables 6a and b.

1. D. J. Hughes and R. B. Schwartz, Neutron Cross Sections, Brookhaven National

Laboratory Report BNL-325, July (1958).

2. M. P. Failey, D. L. Anderson, W. H. Zoller, G. E. Gordon, and R. M. Lindstrom,

Anal. Chera. 51_, 2209 (1979).

3. NBS Reactor: Summary of Activities July 1981-June 1982, NBS Technical Note 1178,

F. Shorten, Ed.

4. D. L. Anderson, Y. Sun, M. P. Failey, and W. H. Zoller, in preparation, to be

submitted to Geostandards Newsletter.

5. D. L. Anderson, G. E. Gordon, and E. A. Lepel, Canad. J. Chem. 6l_, 724 (1983).

6. J. E. Riley, Jr., R. G. Downing, R. F. Fleming, R. M. Lindstrom, and

D. H. Vincent, to be published in J. Solid State Chem.

7. T. Vossler, D. L. Anderson, N. K. Aras, J. M. Phelan, and W. H. Zoller, Science

211 , 827 (1981).

8. T. Fogg, Ph.D. Dissertation, University of Rhode Island (1983).

9. E. S. Gladney, L. E. Wangen, D. B. Curtis, and E. T. Jurney, Env. Sci. Technol.

12, 1084 (1978).

HIGH ACCURACY DETERMINATION OF U-235 BY GAMMA-RAY SPECTROSCOPY IN

NONDESTRUCTIVE ASSAY STANDARDS

B. S. Carpenter

(National Measurement Laboratory)

and

R.R. Greenberg

(Inorganic Analytical Research Division)

A joint project is underway between the Central Bureau for Nuclear Measurements

(CBNM) Geel, Belgium, and the National Bureau of Standards to produce a set of five

uranium isotope abundance reference materials for nondestructive assay (NDA) . This

set is intended for worldwide safeguards use as primary reference materials for the

determination of the U-235 abundance in homogeneous uranium bulk material by gamma155
NON-RRD PROGRAMS

N.B.S

295-110

Figure 1. A typical U-235 isotope abundance reference material for gamma

spectrometry.

ray spectrometry. The reference material is in the form of uranium oxide (U_Oq) and

235 ^ is placed in aluminum cans with nominal isotope abundance ( U/U) of 0.003, 0.007,

0.019, 0.029, and 0.045. The material at each isotope abundance is characterized

235 chemically by CBNM, NBS, and the DOE New Brunswick Laboratory for U/U homogeneity

1 and isotope abundance, uranium content, and material impurities.

Currently, high precision gamma-ray measurements are being made on 24

representative sample cans of the 140 total cans at each isotope abundance. The

measurements, using a high purity germanium detector, are to determine the countrate

uniformity of the U-235 185.7 keV gamma-ray as well as the U-235 isotope abundance

for each sample. Since the samples are packaged such that the U_,0o is infinitely

3 o thick for the 185.7 keV gamma-ray, the measured countrate is not dependent on the

material density. In addition the activity observed by the detector is collimated to

simulate calibration conditions used to measure bulk material in the field (see

Figure 1 ) . Preliminary gamma-ray results of the 1.9 percent material indicate that the

235 U/U isotope abundance is within 0.02 percent of the values determined by CBNM and

NBS mass spectrometry measurements. The results of this material is based on

counting statistics of 0.05 percent for each of the 24 samples analyzed. The

observed standard deviation for the 24 samples was 0.05 percent (Is-relative) and the

standard deviation of the mean was 0.01 percent.

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1. P. DeBievre, H. Meyer, J. Van Audenhove , B. S. Carpenter, and J. W. Gramlich,

"Progress Report on the Establishment of Uranium Isotope Abundance Reference

Materials for NDA," Proceedings of 4th Annual Symposium - ESARDA on Specialist

Meeting on Harmonization and Standardization in Nuclear Safeguards, Petten, The

Netherlands, 27-29 April, 1982; Report ESARDA No. 15.

SUMMARY OF ACTIVITIES CARRIED OUT BY THE NEUTRON FIELD STANDARDS GROUP

R. Dallatore, C. Eisenhauer, D. Gilliam, J. Grundl, E. McGarry

(Center for Radiation Research)

The Neutron Field Standards Group, attached to the Center for Radiation

Research (CRR), is engaged in the development and application of standard and

reference neutron fields as permanent facilities for neutron detector calibrations,

neutron dosimetry standardization, and reaction rate cross-section measurement.

A 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, development, and measurement projects which involve

these facilities are as follows:

1 . Cavity Fission Source Reworked

The cavity fission source was redesigned in order to allow irradiated neutron

fluence standards to be removed separately from the highly radioactive fission source

disks which now remain inside of the thermal column. The fission chamber monitor

also was remounted on the insertion stem close to the source detector assembly. Two

new shielding arrangements were designed and built to accommodate the new source. A

7" dia. lead cylinder on a rolling platform allows the fission source disks to come

out of the thermal column into a shield that can be hand carried to a larger lead

storage channel which is itself on a movable cart. A removable body shield with a lead glass aperture was attached to the side of the thermal column assembly table.

Various operations and inspections can now be done with highly radioactive fission

source disks. Personnel exposures involved with the handling of sources has been

substantially reduced.

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The cavity fission source, with these operational modifications and with final

neutron scattering corrections, is now a convenient standard neutron field for

routine use. The U-235 fission neutron flux at the midplane between the fission

1 2 source disks is 1.8 x 10 n/cm s. For individual irradiated foils this flux is

established toj|^2.6 percent based on neutron flux transfer from the NBS Cf-252

irradiated facility.

2. Neutron Scattering Corrections for Cavity Fission Source

The sack of nickel and indium activation foils in the NBS cavity fission source raises the question of perturbation of activation rate in one foil because of

scattering of neutrons in the same foil or in nearby foils. Monte Carlo calculations

were made for us by Los Alamos National Laboratory to determine this effect. It was

found that flux gradient over the foil stack was small enough that the effect

depended not on the absolute position of foil and scatterer but only on their

separation distance. For foils of 1.27 cm diameter, the correction to the fluence

per 0.0254 cm thickness of scatterer varies from 1.0 percent for self scattering

(i.e., zero separation distance) to < 0.1 percent at 0.8 cm spacing. The Monte Carlo

calculations from LANL now provide corrections for the entire cavity fission source

detector assembly.

3. Production of Neutron Fluence Standards.

The cavity fission source for the first time produced a substantial number of

neutron fluence standards for reactor dosimetry applications. In three primary

irradiations, titanium, nickel, and iron foils were exposed to fission neutron

1 5 2 fluences of between 4.5 and 7x10 n/cm . These fluence standards have been

distributed to various dosimetry measurement laboratories in this country and abroad.

The test report for each fluence standard provides a free-field fission neutron

fluence with an assigned error of +_ 2.6 percent. The major components of this error

are as follows:

o Flux Transfer Measurements from the Cf-252 Standard Fission Neutron Field to

the U-235 Cavity Fission Source:

(1) Absolute neutron source strength of the 252-Cf source

(2) Distance measurement

(3) Cf-252 to U-235 spectrum-averaged cross section ratio

for In-115(n,n') monitor

(4) Corrections for neutron scattering in Cf-252 irradiation _

(5) Reproducibility of flux transfer procedure (including

counting statistics, and electronic system stability

over period of measurement) jt^0.65K

158

+ 1 .^%

+ .3%

+ 1 .6%

+ 1 .0%
NON-RRD PROGRAMS

o Preparation of Neutron Fluence Standards at the U-235 Cavity

Fission Source:

(1) Gradient corrections and positioning j^ 0.855^

(2) Corrections for neutron scattering in source detector

capsule j|^ 0.6y&

(3) Reproducibility of fluence monitoring including random

summing corrections and uncertainties in activation

decay corrections + 0.^5%

These threshold activation detectors are used to establish fast neutron

exposure parameters (generally flux > 1 MeV, and "displacements per atom") for outof-core components of power reactors. The fission neutron fluence standards provide

a combined calibration of detection methods and data interpretation.

4. Test of B-10 and Li-6 Helium Production Cross Secton

Experimental tests of the B-10 and Li-6 a production cross sections, relative

to 0- (U-235), were carried out in the Intermediate-Energy Standard Neutron Field

(ISNF) facility. The B-10 and Li-6 reaction rates were measured using the Helium

Accumulation Fluence Monitor (HAFM) method by B. Oliver and H. Farrar of Rockwell

International. A variety of HAFM samples were included in the tests: nineteen

welded capsules containing crystals of enriched Li-6F, B-10, and natural boron; ten

empty capsules to check for any background of spurious helium generation; and six

each of base crystals to enriched B-10 and Li-6F. The main irradiation was carried

14 2

out in two segments to give a total fluence greater than 10 n/cm . A background run

was also made with the fission drivers removed from the ISNF facility. Both gold and

irridium foils were irradiated with the HAFM detectors to provide run-to-run

monitoring which will correct the HAFM irradiations with a subsequent U-235 fission

rate determination.

5. Fissionable Deposit Assay for Fission Cross Section Measurement

The Cf-252 fission-spectrum-averaged, U-235 fission cross section, o„(x f.

> U235), is the normalization parameter for all measurements of integral cross sections

in NBS standard neutron fields. A new measurement of this quantity is nearing

completion. The working fissionable deposits used for fission chamber measurements

at the Cf-252 irradiation facility were mass assayed relative to the NBS U-235

archive deposit in a thermal beam. In this technique an effective mass or fragment

2

emission efficiency for the heavy working deposit (500 ug/cm with fission fragment

159
NON-RRD PROGRAMS

losses of 7 percent) is established relative to the light archive deposit

2

(< 200 ug/cm ) where the fragment loss correction is small and better understood.

In a separate investigation, fission fragment loss in a UF^^ deposit was

compared with that in a U-Oj^ deposit. Both types of deposits are used in cross

section measurements. The difference in fragment absorption between flourine and

oxygen comes from classic range-energy calculations for heavy ions. The comparison

measurements carried out in a thermal beam indicated these calculations are

satisfactory.

6. Fissionable Isotope Mass Standard Diagnostics

The neptunium-237 archive fissionable deposit (37S-2-2) was examined for small

amounts of Pu-239 and other fissile contaminants. Thermal beam measurements were carried out with a thin Pu-239 deposit in back-to-back geometry. The amount of

fissile contaminant found was 29 jj^ 5 nanograms (Pu-239 equivalent mass) 0.011 percent

of the mass of the principal isotope.

A similar investigation was taken in support of fission chamber measurements

performed in the Iron Shells Benchmark at SCK/CEN (Belgium). This specialized

project was designed to test calculations of deep penetration of neutrons into steel.

In addition to the conventional roster of fissionable detectors, the isotope U-236

was included for these measurements although it is not part of the NBS set of

fissionable isotope mass standards. In the analysis, the U-236 fission rate was

uniquely discrepant compared to the conventional set of fission detectors. The

thermal beam examination indicated 110 nanograms of U-235 equivalent mass in the U236 deposit as compared to ~ 2ng previously accepted from the isotopic assay of the

base material. With 1 1 0ng of fissile isotope included in the analysis, the U-236

fission rate in the iron shells came into agreement.

7. Autoradiographic Study of Paintings

The thermal-neutron-radiography facility for diagnostic irradiations of

paintings is described elsewhere in this report. In cooperation with the Reactor

Division and the Smithsonian Institution, thermal column modifications were designed

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.

160
NON-RRD PROGRAMS

FISSION CROSS SECTION MEASUREMENTS IN REACTOR PHYSICS AND DOSIMETRY BENCHMARKS AT NBS

J. A. Grundl and D. M. Gilliam

(Nuclear Radiation Division)

Fission cross sections for eight fissionable isotopes of importance for nuclear

technology have been measured in two fission neutron spectra and one fission-neutrondriven standard neutron field. New measurements for Pu-2^0, Pu-24l , U-233. and Th232 accompany revised values from earlier determinations for Pu-239, U-235, U-238,

and Np-237.

The starting point for these measurements is an absolute cross-section

measurement for Cf-252 fission spectrum neutrons. This absolute cross section is

determined from a neutron source strength, a source-to-detector distance, and an absolute fission rate. Relative fission cross-section measurements for the

Intermediate-energy Standard Neutron Field (ISNF) are put on an absolute scale by

employing a flux transfer procedure from the Cf-252 source. For U-235 fission

spectrum neutrons, cross-section ratios measured in a cavity fission source are normalized to the U-235 fission cross section measured in the Cf-252 fission neutron

field.

Major components of these cross-section measurements are the same for all but

one of the benchmark neutron fields and can be summarized individually. Errors are similar also and they will be assessed together for each measurement component.

1 . Fission Rate Detection and Isotopic Masses

Double fission ionization chambers with detection efficiencies between 0.97 and

0.995 (depending on fissionable deposit thickness) were employed in these

measurements. Uncertainties for fission fragment loss corrections were +_ 0.6 to 0.85^

and counting imprecision was less than +_ 0.2/S except for Cf-252 where counting

imprecision for some isotopes was as high as +_ O.65S.

Fissionable deposits in a thickness range of 8 to 600 ug/cra were used in the

fission chambers. Deposit masses were ascertained by a multiplicity of techniques:

1

.

low-geometry alpha counting

2. isotope dilution mass spectrometry (U-235, U-238, and Pu-239 only)

3. Maxwellian and raonoenergetic thermal-neutron fission counting

4. selective intercomparisons with archive deposits from other laboratories.

Revised isotopic mass uncertainties for the National Bureau of Standards (NBS) set of

fissionable isotope mass standards are now available and supercede all previously

reported values. They are listed below at one standard deviation:

161
NON-RRD PROGRAMS

Table 1 . Fission cross sections for reactor physics and dosimetry benchmarks,

Isotope

232

233,

Th

235„b

238yb

240.

241

Pu

Pu

235u/238„

235u/239p„

23^Np/238u

ISNF

(mb)

38.4 + 1 .2

2424 + 65

1606 1 35

149.0 ^ 3.6

829 1 22

c 824 1 23

2152 + 108

10.78 + 1 .M

0.866 ;^'\ .0%

5.56 + ^.^%

Revised Values

235^

238,

237

239

Np

Pu

^^ 0.5^

+_^ .0%

+ 0.455

Fission Spectra

252^^ ' 235, Cf ^"U

:mb) (mb)

89.4 1 2.7 -

1893 + 48 -

1216 1 19 c 326 + 6.5 309 1 8

1366 1 27 1344 + 54

1824 1 35 1832 ^ 55

1337 l 32 -

1616 + 80 -

3.73 + ^ .2% 3.94 + 2.055

0.666 +_ 0.955 0.664 ^ 2.555

4.19 j^ 1.555 4.35 1 3.055

New Isotopes

^^^Th: + 2.055

233u: + 1 .555 240„

Pu: + 0.855

241

Pu: + 4.055

162
NON-RRD PROGRAMS

Corrections for fission in other than the prinicipal isotope were between and ^%

for all but Pu-240 and Pu-24l where the corrections were 3-0 and 2^%, respectively.

2. Neutron Flux and Scattering Corrections

The free-field neutron flux at 5 cm from the Cf-252 fission source can be

established to +_ ^ .^% on the basis of a measured detector separation distance and a neutron source strength determination performed at the NBS MnSO|^ Bath Facility.

Neutron fluence transfer from the Cf-252 irradiation facility to the ISNF and to the

U-235 fission spectrum irradiation facilities is carried out to be better than +_ }%

by means of the Pu-239 and U-235 fission reactions as indicated in Table 1

.

Monte Carlo calculations have been performed for experimental arrangements at

the Californium Irradiation Facility. Fission rates attributable to source neutrons

scattered in the source capsule and in the fission chambers have been determined.

Total corrections are 3.55^ for fissile isotopes and 1 to 3^ for the other isotopes; errors have been estimated at less than +_ 0.1%. The correction for fission in

fissile isotopes due to room return background at the californium facility is ~ 0.5/^

based on both measurement and calculation. At ISNF the only significant scattering

element is the fission chamber, which is in a neutron flux that is nearly isotropic.

Corrections are < 1.05S. Cavity fission source arrangements for the U-235 fission

spectrum measurements (and Pu-239) are less ideal for scattering calculations and

larger corrections and uncertainties are involved.

3. Results

Fission cross-section results are presented in Table 1 , along with selected

cross-section ratios for which errors are significantly less than for the individual

cross sections. Errors are given at one standard deviation. These benchmark

measurement results are intended to provide integral normalizations and a test of

differential neutron cross-section data.

163
NON-RRD PROGRAMS

INTEGRAL CROSS SECTION MEASUREMENTS IN THE ^^^U FISSION NEUTRON SPECTRUM

G. Lamaze, E. D. McGarry, and F. J. Schima

(Center for Radiation Research)

An important method of fast neutron dosimetry is the use of radiometric

monitors to measure neutron fluence and fluence rate. By selecting a set of

reactions each of which is sensitive to a different neutron energy range, information

on both the shape and magnitude of the fluence spectrum can be obtained.

To derive a neutron fluence from a measured reaction rate, the spectrum

averaged cross section, V, must be known. By definition it is

- _ / o(E)(t)(E)dE

° / c))(E)dE

The differential cross section, o(E), is available as an evaluated nuclear data file,

such as the Brookhaven ENDF/B file, which is based on both experimental data and

calculations. In a complex environment, such as a reactor, the differential fluence

rate (()(E) is usually obtained from a transport calculation of the energy and spatial

distribution of the neutrons. However, if the neutron source and the radiometric

monitors constitute a relatively well understood system, a measure of o becomes a validation of the knowledge of o(E). Herein are reported measured values of o for

5i| 54 58 58 the Fe(n,p) Mn and Ni(n,p) Co reactions in a U-235 fission spectrum.

The U-235 fission irradiations were accomplished in the NBS Cavity Fission

Source. This source operates at the center of a 30-cm diameter spherical cavity

located at the center of the graphite thermal column at the NBS Research Reactor.

The source-detector capsule (see Figure 1 ) consists of two coaxial source disks of U235 metal (16 mm dia. x O.I3 mm thick) placed outside of a cadmium box which encloses

the radiometric neutron detectors for exposure. The cavity and source-detector

arrangement is shown in Figure 1

The fluence rate gradient between the two fission disks has been measured by

simultaneously irradiating 13 nickel foils, each 0.076 mm thick, which were uniformly

placed within the Cavity Fission Source. The total mass of nickel approximates the

total mass of a typical loading of four or five thicker foils. The results of the

gradient measurement are given in Figure 2.

The fluence in the cavity is measured indirectly by using the In(n,n') " In

252 reaction. The indium is first irradiated in a Cf field from a point neutron

source of known strength and the gamma count rate at the end of irradiation (counts

164
NON-RRD PROGRAMS

-1 -1

s g ) is measured. The gamma detector used is then effectively calibrated in terms

-2 -1 -1 -1

of the fluence rate to count rate ratio (ncm s /counts s g ). Because the ratio

of the spectrum averaged cross sections in the Cf-252 and U-235 is well known

(j^ ^ .5%) , indium foils are the irradiated in the U-235 fission field to measure the

fluence rate. For each irradiation, the reactor power is monitored with a small

fission chamber in the cavity to record any changes in the fluence rate during the

irradiation.

Ni(n,p) Co cross section ; Two nickel irradiations have been accomplished. In the first, two 0.25 mm natural

1 5 2 metal foils were irradiated for 30 hours in a total fluence of 2.11 x 10 n/cm . In

the second irradiation, two 0.09 mm natural metal foils were irradiated for 55 hours

15 2

in a total fluence of 3-00 x 10 n/cra . The results from these four foils give a value of 109 mb with a standard deviation of 0.9/5 indicating good reproducibility of

the method. Combining all sources of uncertainty in quadrature (see Table 1) gives

as a final value of the cross section 109 jj^ 3 mb.

54 54 ~

Fe(n,p) Mn cross section ; The value of the iron cross section is based on only one irradiation and, as such,

must be considered preliminary. Two natural iron foils 0.13 mm thick were irradiated

1 5 2 for 29 hours in a total fluence of 2.17 x 10 n/cm . Taking the average value of two

foils and combining all sources of uncertainty in quadrature (see Table 1) gives a 54 value of 79 j|^ 3 mb for the Fe(n,p) cross section. It should be noted that there is

a 1.7% uncertainty assigned to the isotopic abundance of Fe-54 in natural iron. This

uncertainty has not been included in the uncertainty of the measurement. If natural

iron samples are used for neutron dosimetry, the abundance factor is eliminated in

the application of the method.

Table 2 compares the present results as well as sirailiar results from

Cf-252 spectrum measurements with calculated values from the NBS Compendium and with an evaluation of measured values. The calculations are based upon the NBS

evaluations of the U-235 and Cf-252 fission neutron spectra and on ENDF/B-V cross

sections. All of the present results are in good agreement with previously measured

values, as reported in the NBS compendium.

54 While the Fe(n,p) results agree with the calculated values for both of the

58 mentioned fission neutron spectra, the calculated results for Ni(n,p) are low by 6-

1 1 5 8% in both fields and the In(n,n') results are low by 8% for the Cf-252 spectrum.

These integral measurements do not indicate whether the problems are associated with

ENDF/B-V cross sections or with the fission spectra evaluations, or with both.

165
NON-RRD PROGRAMS

0.938'

Cavity Fission Source and Cadmium-Covered

Detector Capsule

Grapliiti9 Thermal Column

(94 cm X 152 cm X 152 cm Block)

..sr;;=srs-r5;;s:-r=?^~°»="=^--TM-

Figure 1 U-235 Cavity Fission Source. Upper view: relative positions of neutron

sensor foils, fission-disks, and cadmium enclosure. Lower view: the

upper assembly in the thermal column of the NBS reactor.

166
oo

u<

u

o

9

a. (0

1700

1660

1620

2 1580 «

1540

NON-RRD PROGRAMS

Measurement of the Flux Gradient Between the Fission Disks in the NBS

U-235 Cavity Fission Source. Experimental

Points Obtained with 0.076-mm Nickel

Foils. Least-Squares Fitted Curve

- Given by A = 2091 —9.01 5X + 0.0377X2 A = Relative Activity of ^BCo X = Distance in Mils

Bottom

80 100 120 140 160

Distance in Mils (0.001 inches) from the Bottom (see Item A)

of the Aluminum Foil Holder Insert.

Figure 2. Flux gradients in the NBS cavity fission source.

Table 1. Summary of uncertainties for U-235 neutron field measurements.

Source

Source Strength of NBS-I

Ratio of Cf to NBS-I

Cf Source to In Foil Distance

Statistics of In Activity Counting

Scattering Correction for In at Cf

Scattering Correction for In at Cavity

Total Uncertainty in Fluence

Efficiency of T Counting

Statistics of Y Counting

Flux Gradient in Cavity

Scattering Correction in Cavity

Total Uncertainty in o

Fe

0.75

1.6

0.4

0.8

3.U

Contribution {%)

0.9

0.6

0.4

0.5

1.6

1.0

0.8

2.4

58

Ni

75

17

4

0._8

2.7%

167
NON-RRD PROGRAMS

Table 2. Comparison of present results with previous results and calculations

Cf Fission Neutron Field

In(n,n') In

Fe(n,p) Mn

5\i(n,p)5Sco

This Work

196 +_ 4 mb

89 ^ 2

121+2

Calculated

182 j^ 1 .5 mb

88.3 ^ 1 .2

114 +1.5

Previous VJork

195 j;^ 5 mb

87 j;^ 2.4

118 + 3

U-235 Fission Neutron Field

5\i(n,p)5^Co

Fe(n,p) Mn

109 j^ 3 101 ji^ 2.6 109 j;^ 8

79 j^ 3 77.8 +_ 2.2 83 jj^ 4 "NBS evaluated fission spectra and ENDF/B-V cross sections; errors are for spectrum

uncertainties only.

b

NBS evaluation of observed cross sections recorded in NBS compendium.

It should be noted that an erroneous, preliminary value of the Ni(n,p) Co cross section in the U-235 spectrum was reported as 101 mb in last year's annual

report. The correct value (see Table 2) is 109 mb.

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 for calibrating and testing existing

types of dosimeters and remmeters and for testing new types currently under

development.

In particular, personnel from the Naval Surface Weapons Center, in

collaboration with CRR personnel, did extensive testing of the Navy's shipboard area

monitoring system. The energy and angular response of the monitor system was

determined using the four beams referred to above. In addition, the 144 keV beam was

used for extensive testing of the different types of detector tubes which may be used

in the monitor. The 144 keV beam is especially useful for these tubes since it is a very convenient, high-intensity source of neutrons with relatively little gamma

contamination.

168
NON-RRD PROGRAMS

The energy response of a new type of dosimeter developed at Yale University was also measured using the filtered beams. This dosimeter essentially consists of

superheated drops in a gel; the drops vaporize when they interact with neutrons. The

dosimeter shows promise of having a nearly tissue response and of being inexpensive.

The energy response measurements at the NBSR gave very promising results.

A new type of solid state track detector (CR-39) was tested in the 24 keV beam,

and response measurements were made on a modified 9-inch remmeter, as well as on several types of commercial dosimeters.

RANGE OF INDIVIDUAL FISSION FRAGMENTS IN MATTER

I. Schroder and R. Fleming

(Nuclear Radiation Division)

A great deal of experimental information is available on the energy loss of

charged particles in matter except for the case of individual fission fragments.

There is even less information on the energy loss of individual fission fragments in

heavy elements, especially in fissile materials. It is in this range where energy

loss theories and phenomenological models tend to break down.

Accurate energy loss and range measurements for fission fragments (heavy ions) are of practical importance in the calculation of fragment losses in fissile targets

for precise cross-section measurements as well as in direct energy conversion

measurements and in magneto-hydrodynamics. These measurements would also make it

possible to quantitatively assess the feasibility of depth profiling of fissile

materials.

The purpose of the present experiment is to measure the range, in fissile

materials, of individual fission fragments from the spontaneous fission of Cf-252 and

the thermal neutron fission of U-235 and Pu-239. This is accomplished by making

transmission measurements through a set of thin foils and using high resolution

Ge(Li) Y-ray spectroscopy to identify the individual fission fragments transmitted.

A set of preliminary experiments have been made with Cf-252 to determine the

detection efficiency for individual fission fragments and to calibrate the

measurements using a series of thin aluminum foils. These measurements will be

extended to cover the fission fragment from thermal neutron fission of U-235 and Pu239. Once these calibrations have been completed, the aluminum foils will be

replaced by U-238 foils and the measurements repeated.

169
C. 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. The program

of modernization of reactor components and instrumentation is continuing. Licensing

activities to upgrade reactor power to 20 MW and renew the operating license are

progressing. A final Environmental Impact Statement was issued by the Nuclear

Regulatory Commission as required by regulations. The NRC is also preparing a safety

evaluation report of the NBS submittals. In this connection N3S provided extensive

additional information to NRC to assist in their review. A new license will be

issued by the NRC, once the Safety Evaluation Report is published. The new license

authorizing increased power and valid for a period of 20 years is expected in 1984.

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.

1Reactor Operations

Reactor operations continued at a high level with on-line time and fuel

efficiency almost identical to that of the previous year which are among the best in

the history of the facility. A summary of the overall operating statistics for the

period July 1, 1982 to June 30, 1983 is presented in the following table.

NBSR Operating Summary July 82-June 83

No. of days at 1 MW 263

On-line time at 1 MW 72%

Average U-235 burnup 61%

No. of Irradiations 2820

Hours of Irradiations i860

Hours per Irradiation 0.7

2. Irradiation Service

Heavy utilization of the reactor for major irradiation and activation analysis

programs continued. Tens of thousands of specimens, involving foods, drugs,

environmental monitoring, geological, and mineral examinations, forensic

170
REACTOR OPERATIONS AND SERVICES

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 protected

against fire by a new fire suppression system and turned over to the NBS fire

department for maintenance and testing. The water treatment building and loading

ramp for chemical treatment of the secondary water has been completed and is in use.

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 may be

borrowed by the present vendor. Shim arm yokes, arbors, and bearings are in the

process of fabrication. The regulating rod is being modified for 20 MW operation to

operate more smoothly and reliably. A new fuel element contractor has been selected

by the Department of Energy (DOE) and has made an NBSR prototype fuel assembly and a production prototype. Fabrication of fuel assemblies using fuel plates received from

the previous contractor have been completed and accepted by NBS. Qualification

plates are being fabricated and new plates will be in production by the end of 1983-

The program implementing the modernization of the reactor instrumentation is

underway. For example, the medium sized recorders for the BTUR and main outlet flow

have been replaced with modern and reliable units with a similar style of recorders

recently installed for recording nuclear channels.

171
I

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)

During the past year work was completed on a comprehensive set of food samples

obtained through the FDA Total Diet Studies program. The Total Diet Studies is a continuing FDA program to examine chemical residue and trace nutrient content of

foods purchased through retail markets and prepared as consumed. The foods were shipped to the FDA Total Diet Laboratory in Kansas City for preparation and analysis

by standard procedures. They were prepared as if for consumption and then combined

according to food type to make twelve composites. The 240 composites analyzed in

this study represented 20 collections made between October 1979 and September 1980.

The samples were received by the FDA headquarters and freeze dried. Then

approximately 300 mg of each sample was prepared and analyzed by INAA. Previously

Ca, CI, Mg, Mn , Na, and V were determined in these samples following short

1 irradiations.

For the radioisotopes with longer half lives a 4-hour irradiation (at a neutron

1 3 2 flux of 4.0 X 10 n/cra -sec) were used after a 5-day to 4-week decay. Spectra were acquired using an 80-cc Ge(Li) detector interfaced directly to a ND 6620 system.

Spectra analysis and data reduction were accomplished using this system. The

radioisotopes and Y-ray energies used are given in Table 1

Results for four of the composites are given in Table 2. Elements included in

this table are those for which concentrations were determined in most market baskets

for at least one of the composites. When an element was found to be below detection

for a specific composite, the observed detection limit is given. Analytical

uncertainties (at the one sigma level) for Br, and Zn were <5% for nearly all

samples. Depending on the food group, uncertainties for Fe and Rb ranged between a few percent and approximately 40^ at the detection level. Elements which were near detection levels but observable in most samples include Co, Cs, Sc, Se, and V.

Uncertainties for these elements were <15^.

Three elements were found to be observable in several samples but below

detection for most. These include Ag, Cr, and Sb and are presented in Table 3- Also

included in Table 3 are observed detection limits for As, Cd, and Eu. A qualitative

search was made for several elements which were not in our standards. These include

W, La, Sm, An, Lu, Ba, Th, Yb, Ce, Hf, Ta, Ti , Sr , In, S, and Mo, all of which were

not observed.

172
SERVICE PROGRAMS

Table 1. Radioisotopes, halflives, and Y-ray energies for elements determined in

this work.

Radioisotope Halflife Y-rcay Energies

(day) (keV)

Ag-IIOm 249.9 657.7, 884.7

As-76 1 .10 559.1, 657.2,

Au-198 2.696 41 1 .8

Ba-131 11.7 216.0, 496.2

Br-82 1 .47 554.3, 619.1,

Cd-115 2.23 336.3, 527.9

Ce-141 32.53 145.4

Co-60 46.214 1 173.2, 1 332.5

Cf-51 27.7 320.0

Cs-134 18.058 795.8

Eu-152 113.958 964.0, 1 408.0

Fe-59 44.6 1 099.2, 1 291 .6

Hf-I8l 42.40 133.1, 482.2

La- 140 1.676 208.4

Lu-177 6.71 1 077.0

Rb-86 18.65 1 691.0

Sb-124 60.2 889.3, 1 120.5

Sc-il6 83.8 136.0, 264.7

Se-75 120.0 103.2

Sm-153 1.947 1 189.0, 1 221 .5

Ta-182 115.0 311.9

Th-233* 27.0 479.5, 685.7

W-187 1 . 00 177.2

Yb-159 31 .2 1 115.2

Zn-65 243.8

*Th-233 B- 233Pa

1216.2

776.5

173
SERVICE PROGRAMS

Table 2. Average element concentrations and ranges in food ug/g (dry mass) except as noted.

Dairy Meat, Fish,

Poultry

Grains

Cereals

Potatoes

Br 14.1 6.35 14.5 4.71

6.4-25>5 4.0-9.7 9.6-34.3 1 .1-14.4

Co^ 81 44 35 92

49-124 21-76 15-60 44-245

Cs 0.110^ 0.058^ 0.047^ 0.050^

0.084-0.157 0.041-0.069 0.046-0.047 0.048-0.053

Fe 49.6° 46.1 49.3 35.2

(<42) 32.8-70.6 24.6-98.0 18.6-63.6

K 9 550 6 270 1 600 14 900

7 450-11 200 3 870-7 970 859-2 300 9 870-19 500

Rb 10.14 6.66 2.50 6.36

5.81-18.5 4.96-10.5 1 .29-5.84 2.20-9.46

Sc^ <9 <4 4.35^

2.65-8.22

5.12

2.90-7.65

Se 1.35 0.73 0.58 <1 .0

1 .30-1 .40 0.46-1 .42 0.28-0.85

Zn 24.2 65.4 11 .6 12.4

16.1-30.5 47.6-74.6 7.39-19.9 4.62-21 .5

a. ng/g.

b. Most results below detection. This average may, therefore, be biased high.

c. Detected in only two samples.

174
SERVICE PROGRAMS

Table 3. Average element concentrations and regions in food ug/g (dry mass)

Dairy Meat, F Poultry

ish, Grains,

Cereals

Potatoes

Ag >0.60 0.23° 0.18° <0.28

0.16-0. 37 0.15-0.23

As <10 <2 <0.4 <6

Cd <2 <5 <5 <10

Cr

0.80-1 .4

0.56° <1 .U <1 .0

Eu <0.050 <0.035 <0.045 <0.30

Sb <0.15 <0.10 <0.13 <0.08

Although the procedure used did not maximize for any single element, careful

treatment of the interferences enabled concentrations to be determined for 18

elements in the food samples. These data form a substantial base which covers a wide

range of foods and samples from each of 20 food collections made in cities throughout

the United States. The observed concentration ranges should, therefore, predict

reasonably well what one will find in these types of foods. Consideration of these

data, and for those elements near detection, the various factors controlling

detection levels should enable one to predict the capabilities of INAA for further

food analyses.

1. NBS Reactor: Summary of Activities July 1981 through June 1982, p. 199.

175
SERVICE PROGRAMS

POSITRON ANNIHILATION IN CuGe AND CuZn ALLOYS

L. M. Pecora and A. C. Ehrlich

(Naval Research Laboratory, Washington, DC)

We used data collected over the last several years to examine two features

present in momentum densities of CuGe alloys. One is the enhancement of the measured

momentum density p(p) near the Fermi edge which results in a peak in p(p) around

1 2 5.5 rad in these materials. It has been suggested ' that this enhancement is well

3 described by an empirical relation which we fit to our data. The other feature is

the change in anisotropy of p(p) at 7 mrad along the [100] direction. We have

H suggested that this is related to changes in s-d hybridization. Using a newly

5 developed numerical technique we determine the population of s , p, and d states in

this [100] region for Cu and Cu__Geo and compare the two populations to comment on

yd o hybridization.

1 . Enhancement Formulas

Near the Fermi surface p(p) is enhanced by a factor p(p) so that if p (p) is

the measured momentum density we have

p^(p) = e(p)p(p).

1 2 Several empirical forms for £(p) have been suggested. ' One by Kahana

e(p) = a + b(P/Pp)^ + c(p/pp)^ (1)

and the other by Mijnarends and Singru

e(p) = a + b(E/E^) + c(E/E„)^. (2)

r r

In these formulas p = Fermi momentum E = Fermi energy, and E is measured from the

bottom of the band. Note that in the free electron case (1) and (2) are the same.

fi 7 We used CuGe and CuZn data ' to determine the empirical a, b, c's for (1) and (2).

For energies in (2) we used the APW results of Papaconstantopoulos et al . Table 1 shows our results for (1), the momentum formula, and (2), the energy formula.

Although there is scatter in the results from different alloys, the empirical

constants for relations (1) and (2) are nearly equal in all cases. Further

examination of the contribution of each band along a typical direction ([100]) to

176
SERVICE PROGRAMS

p (p) shows that the bands which are most nearly free-electron-like are precisely

those bands which contribute most to p(p) (see Figure 1). Since (1) and (2) are the

same in the free electron case we can see that data from these alloys will not show

preference for either (1) or (2) in describing enhancement, e(p). This is probably

true for all metals and metal alloys since, in the first zone, it is the free

electron component of the wave function which contributes to p(p) in all cases.

2. s-p-d Hybridization in CuGe Alloys

Quantum measurements which can be considered as independent particle

measurements can be written as

<e> = tr _P

where <e> is the expection value (measurement in the experiment, P_ is the population

matrix, and 9 is the operator representing the measurement. The digonal elements of

P_ give the quantum mechanical population of the states in the basis.

In our case we chose s, p, and d tights binding wave functions for the basis.

9 The expansion coefficients for Cu were provided by D. Papaconstantopoulos using a Slater-Koster fit to Cu APW results. The wave functions were atomic Herman-Skillman

functions.

5 We then used a newly developed numerical technique to calculate _P for CUq Ge^

in the region of 7 mrad along [100] where the momentum density is larger than for Cu

(see Figure 2a and 2b). The results of the JP calculation are shown in figure 2c. It can be seen that the % d decreases and the % s increases as Ge is added to Cu. These

quantitative results corroborate our original conclusion that the s-d hybridization

changes along [100] as Ge is added to Cu,

177
SERVICE PROGRAMS

E

[100] /^

. / -F / /

K

Figure 1. Top shows the band structure for Cu [100] for bands which contribute to

p(p). Bottom shows the relative contribute p^Cp) of each band to p(p).

Table 1 . Parameters for enhancement formulas determined from momentum density data

comparing our work to others for Cu and comparing momentum and energy

formulations for various Cu alloys.*

Momentum Formula

Eqn. (1)

Energy Formula

Eqn. (2)

Alloy

Cu

CUg^Geg

Cu^^Zn^^

Reference

Kahana

Sinclair, et al

(Proc. 6th Conf

Pos. Ann. 1982)

Our Work

Our Work

Our Work

b/a

0.195

0.131 + .02

0.27 ;^ .1

1 .13 j!i .2

0.3 + .2

c/a

0.139

0.110 + .036

0.03 ^ .15

-1 .3 j^ .25

0.62 + .25

b/a c/a

0.12 + .15

0.26 +_ .1 0.12 +_ .15

1 .25 ;^ .2 -1 .5 j;^ .3

0.195 + .2 1.0+ .3

*0nly the ratios b/a and c/a are given since absolute scale is not important

178
SERVICE PROGRAMS

'{P)

5 10 15 20

p (mrad)

2b

,Cu92Ge8

1 -

qLJ \ 1 1 L 6 8

p/mc (mrad)

10

% D

100

95

90

85

lOr

%P 51-

[100] 2c

'

Cu

6.0 , 6.4 X

A

(mrad)

Figure 2, (a) p(p) for Cu and CUq Ge,

(b) Closeup between arrows of a. Note changes between arrows.

in

along [100]

(c)

the region of 2b for the lower A structure of Cu [100] showing 'the 2 bands which contribute to p(p) and

the region of figure 2b (shaded).

Populations of Cu and Cu Ge

band which contributes here. (a; Band

179
SERVICE PROGRAMS

1. Kahana, Physical Review 129 , 1622 (1963).

2. Mijnarends and Singru, Physical Review B1

, 6938 (1979).

3. Pecora and Ehrlich, Bull. Amer. Phys. Soc. 28, 307 (1983).

4. Pecora and Ehrlich, Physical Review Lett. 46_, 1476 (1981).

5. Pecora, Bull. Amer. Phys. Soc. 28_, 530 (1983).

6. Pecora and Ehrlich, NBS Reactors Users Report (1981).

7. Pecora and Ehrlich, NBS Reactors Users Report (1982).

8. D. A. Papaconstantopoulos, et al .

, Phys. Rev. B15 , 4221 (1977)

9. D. A. Papaconstantopoulos, private coram.

180
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181
PERSONNEL ROSTER

NON-RRD NBS STAFF LOCATED AT REACTOR

Division 354

J. Arras

I. Bartky

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Division 532

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Division 551

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GUEST WORKERS AND COLLABORATORS

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Division 532

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182
PERSONNEL ROSTER

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F. Brinckman

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B. Bauer

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M. Mathew

S- Takagi

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Aberdeen Proving Ground

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Army Armament Research and

Development Command

C. Choi

H. Prask

S. Trevino

Federal Bureau of Investigation

R. Asbery

R. Bilko

J. Haverkost

J. Kilty

P. Kostella

Federal Bureau of Investigation

(Continued)

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P. Thompson

Food and Drug Administration

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W. Stroube, Jr.

J. Tanner

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183
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Brookhaven National Laboratory

J. Johnson

C.R.N. S. Grenoble, France

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Grenoble, France

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KFA Jiilich, Germany

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Nuclear Energy Center, Mol, Belgium

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D . Chung

Iowa State University

R. Shelton

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H. Hasegawa

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K. Michel

184
PERSONNEL ROSTER

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Neumann

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185
PERSONNEL ROSTER

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R. Hasegawa

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B-K Dynamics

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186
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F. Publications

COLLABORATIVE PROGRAMS

AMMON, H. L., MURPHY, K. C, SJOLIN, L. WLODAWER, A., HOLCENBERG, J. S., and

ROBERTS, J., "The Molecular Symmetry of Glutaminase-Asparaginases Rotation

Function Studies of the Pseudomonas 7A and Acinetobacter Enzymes , " Acta Cryst.

Sect. B39 , 250-257 (1983).

BERK, N. F., ROSENTHAL, J., and YARMUS, L., "Spin Relaxation of Triplet Excitons in

Molecular Crystals," Phys. Rev. B (in press).

CASE, E. and GLINKA, C. J., "Small Angle Neutron Scattering Study of Microcracks in

Yttrium Chromate," J. Matls. Sci. (in press).

CASELLA, R. C, "Generalized Theory of Neutron Scattering from Hydrogen in Metals,"

Phys. Rev. B (in press).

CASELLA, R. C, "Theory of Excitation Bands of Hydrogen in bcc Metals and of their

Observation by Neutron Scattering," Phys. Rev. B27 , 5943-5954 (1983).

CAVA, R. J., SANTORO, A., MURPHY, D. F., ZAHURAK, S., and ROTH, R. S., "The

Structures of the Lithium Inserted Metal Oxides Li^ pR^Oo ^'^'^ L>i ^W0_," J.

Solid State Chem. (in press).

CAVA, R. J., SANTORO, A., MURPHY, D. F. , ZAHURAK, S. , and ROTH, R. S. , "The Structure

of Lithium Inserted Metal Oxides: Li_FeV_Oo," J. Solid State Chem. (in press).

d 3

CAVANAGH, R., KELLEY, R. D., and RUSH, J. J., "Neutron Vibrational Spectroscopy of

Hydrogen and Deuterium on Raney Nickel," J. Chem. Phys. 77_, 1540 (1982).

CHOI, C. S. and PRASK, H. J., "The Crystal Structure of ND^NO Phase V by Neutron

Powder Diffraction," Acta Cryst. (in press).

CHOI, C. S. and MIGHELL, A. D., "Neutron Diffraction Study of Sodium Sesquicarbonate

Dihydrate," Acta Cryst. B38 , 2874-2876 (1982).

CHOI, C. S. and PRASK, H. J., "Single-Crystal Neutron Diffraction Study of Ammonium

Nitrate Phase III, "Acta Cryst. B38 , 2324-2328 (1982).

COHEN, J. S. and WLODAWER, A., "Diffraction and NMR Studies of Proteins: An Uneasy

Alliance," Trans. Biochem. Sci. 7_, 389-391 (1982).

D' ANTONIO, P., KONNERT, J. H., RHYNE, J. J., and HUBBARD, C. R., "Structural Ordering

in Amorphous TbFe2 and YFe ," J. Appl. Cryst. }5_, 452-460 (1982).

DEYOREO, J. J., MEISSNER, M., POHL, R. 0., ROWE, J. M., RUSH, J. J., and SUSMAN, S.,

"Low Energy Excitations in (KBr), (KCN) in the Orientational Glass State,"

Phys. Rev. Lett, (in press).

EVANS, H. T., Jr. and Prince, E., "Location of Internal Hydrogen Atoms in the

Paradodecatungstate Polyanion by Neutron Diffraction," J. Am. Chem. Soc. (in

press)

.

FARNOUX, B. and MOZER, B., "Neutron Intensity Distribution at the End of the Neutron

Guides at the Reactor Orphee." Report of Leon Brillouin Laboratory LLB1

3

(1982).

187
PUBLICATIONS

FARNOUX, B. and MOZER, B. , "Preliminary Measurements of the Gain from the Cold

Sources at the Reactor Orphee," Report of Leon Brillouin Laboratory LLB1

(1982).

GLINKA, C. J. and BERK, N. P., "The Two-Dimensional PSD at the National Bureau of

Standards Small-Angle Neutron Scattering Facility," Forsythe, B. , ed. Proceedings

of the Workshop on Position-Sensitive Detection of Thermal Neutrons, Grenoble,

France (in press).

GLINKA, C. J., FIELDS, R., HAN, C, RHYNE , K., ROTH, R. , ROWE, J., RUSH, J., SHULL,

R., and STEINER, B. , "Neutron Scattering, Present and Future Activities in the

Center for Materials Science" (1983).

GLINKA, C. J., "The National Bureau of Standards Small-Angle Neutron Scattering

Spectrometer," Faber, J., ed American Institute of Physics Conference Proceedings

No. 89, (1982).

GUNNING, J., BEDARKER, S., TAYLOR, G. L., GOODFELLOW, J. M., BLUNDELL, T. L.,

WLODAWER, A., HODGSON, K. 0., SHOOTER, E. M., FOURME, R., GABER, B., and

WILLIAMS, R., "Conformational Studies of Polypeptide Growth Factors: IGF and NGF

in Cell Function and Differentiation," Part A, Alan R. Liss Inc. (1982).

HARDMAN-RHYNE, K. and RHYNE, J. J., "Short and Long-Range Magnetic Ordering of

Y^(Fe. Mn ) and Related Compounds Using Neutron Scattering Techniques," J.

Less-Common Hit., 94, 23-36 (1983).

HARDMAN-RHYNE, K., RHYNE, J. J., PRINCE, E., CROWDER, C, and JAMES, W. J., "Magnetic

and Crystallographic Structure of Y^Mn^^D^^," Phys. Rev. B (in press).

D 23 23

HIMES, V. L. and MIGHELL, A. D., "A Matrix Method for Lattice Symmetry

Determination," Acta Cryst. Sect. A38 , 748-749 (1982).

HODEAU, J. L., MAREZIO, M., SANTORO, A., and ROTH, R. S., "Neutron Diffraction

Structure Determination of the High-Temperature Form of Lithium Tritantalate, HLiTa_Oof" J. Solid State Chem. (in press).

HODEAU, J. L., MAREZIO, M. SANTORO, A., and ROTH, R. S. , "Neutron Profile Refinement

of the Structures of Li SnO and Li ZrO ," J. Solid State Chem. _45^, 170-179

(1982). . '^ ^

'^ ^

KELLEY, R. D., CAVANAGH, R. R., and RUSH, J. J., "Co-Adsorption and Reaction of H^

and CO on Raney Nickel: Neutron Vibrational Spectroscopy," J. Catalysis (in

press).

KOKOSKA, G. F., BARANOWSKI , J., GOLDSTEIN, C, ORSINI, J., MIGHELL, A. D.,

HIMES, V. L., SIEDLE, A. R., "Two-Dimensional Dynamical Jahn-Teller Effects in a Mixed-Valance Benzotriazolato Copper Cluster, CUj.(BTA)^(RNC) „ ," J. Am. Chem. Soc.

(in press)

LYNN, J. W., "Neutron Scattering Studies of Magnetic Phase Transitions in

Superconductors," J. Less-Common Met. (in press).

LYNN, J. W., SHELTON, R. N., HORNG, H. E. , and GLINKA, C. J., "Investigation of the

Magnetic and Superconducting Properties of (Er._ Ho )Rhj^B|,," Physica, 1 20B , 224-226 (1983).

i x x

188
PUBLICATIONS

LYNN, J. W.f ERWIN, R. W., RHYNE, J. J., and CHEN, H. S., "Ferromagnetic and Spin

Glass Behavior Near the Critical Concentration in Amorphous (Fe Ni ) 01 , J.

Mag. Matls. 31-3^ , 1397-1398 (1983). ^

x rb t?

LYNN, J. W., ERWIN, R. W., CHEN, H. S., and RHYNE, J. J., "Evolution from

Ferroraagnetism to Spin-Glass Behavior," Sol. St. Comm. 46_, 317-320 (1983).

LYNN, J. W., RHYNE, J. J., and BUDNICK, J. I., "Observation of Spin Waves in Pd {^ .5%

Fe)," J. Appl. Phys. 53. (1982).

LEUNG, P. $., GODDARD, E. D., HAN, C. C, and GLINKA, C. J., "Small Angle Neutron

Scattering Study of Polycation and Anionic Surfactant Complexes," J. Colloid Sci.

(in press).

LUDEMAN, S. M., SHAO, K. L. , ZON, G. , HIMES, V. L. , MIGHELL, A. D., TAKAGI , S., and

MIZUTA, K., "O-iminyl Esters of N ,N-bis(2-chloroethyl)phosphorodiamidic Acid.

Synthesis, X-ray Structure Determination, and Anticancer Evaluation," J.

Medicinal Chem. (in press).

MAGERL, A., ZABEL, H. , RUSH, J. J., and DIANOUX, A. J., "Dynamical Properties of

Alkali Intercalates in Graphite," Synthetic Metals (in press).

MAGERL, A., ZABEL, H. , and RUSH, J. J., "Phonons in LiC^ and in Heavy Alkali Metal

Graphite Intercalation Compounds," Synthetic Metals (in press).

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," Jana, P.,

Satterthwaite , K., ed.. Proceedings of the International Symposium on the

Electronic Structure and Properties of Hydrogen in Metals (in press).

MAGERL, A., RUSH, J. J., ROWE, J. M., RICHTER, D., and WIPF, H. , "Local Hydrogen

Vibrations in Nb in the Presence of Interstitial (N, 0) and Substitutional (V)

Impurities," Phys. Rev. B27 , 927-93^ (1983).

MCCARTHY, G. J., SILBER, H., and RHYNE, J. J., ed., "The Rare Earths in Modern

Science and Technology," Vol. 3 (1982).

MIGHELL, A. D., HIMES, V. L., and RODGERS, J. R., "Space Group Frequencies for

Organic Compounds," Acta Cryst. Sect. A (in press).

MILLER, M., WEINSTEIN, J. N. and WLODAWER, A., "Preliminary X-Ray Analysis of Single

Crystals of Ovalbumin and Plakalbumin," J. Biol. Chem. 258 , 5864-5866 (1983).

MOOK, H. A. and LYNN, J. W., "Magnetic Excitations in Amorphous Isotropic

Ferromagnets," Phys. Rev. (in press).

MOSS, S., RUSH, J. J., SCHWARTZ, L. , and ULLMAN, R., "Report to the National Science

Foundation on the Center for Small Angle Scattering Research," (1983).

MOZER, B., SINGHAL, S. P., and SHULL, R. D., "Phase Decomposition in Cu-Ti Metallic

Glass," Proceedings of the Summer Meeting of the American Crystallographic

Association (in press).

189
PUBLICATIONS

MOZER, B., SINGHAL, S. P., and SHULL, R. D., "Phase Decomposition in Cu-Ti Metallic

Glass," Proceedings of the Fall Meeting of the Metallurgical Society of AIME (in

press)

NICHOLSON, W. L., PRINCE, E., BUCHANAN, J., and TUCKER, P. A., "Robust/Resistant

Technique for Crystal Structure Refinement in Progress and Problems in

Crystallographic Statistics," S. Ramaseshan, M. F. Richardson, A. J. C. Wilson,

ed. Madras, India: Indian Academy of Sciences (1982).

PARISE, J. B., PRINCE, E., and COX, D., "The Crystal Structure of the Synthetic

Zeolites (Cs, K)-ZK5 and (Cs, D)-ZK5 Determined from Neutron Powder Diffraction

Data," Z. Kristallogr. (in press).

PARISE, J. B., BRIXNER, L. H., and PRINCE, E., "Refinement of the Structure of

La_WO,Cl^ from Neutron Powder Diffraction Data," Acta Cryst. Sect. C (in press).

3 D 3

PARISE, J. B., JORGENSEN, J. D., and PRINCE, E., "Concerning the Flexibility of the

Framework of Zeolite RHO: Structural Variation from 11 K to 573 K," J. Phys.

Chem. ( in press)

PARISE, J. B. and PRINCE, E., "The Structure of Cs-RHO at 295 K and 493 K Determined

from High Resolution Neutron Powder Data," J. Zeolites (in press).

PICKART, S., ALPERIN, H., MENZINGER, F., MAZZONE, G., and SACCHETTI, F., "Neutron

Depolarization by Amorphous Magnets in the Critical Region," Phys. Lett. 95A , 397

(1983).

PRINCE, E. and NICHOLSON, W. L., "A Test of a Robust/Resistant Refinement Procedure

on Synthetic Data Sets," Acta Cryst. Sect. A39 , 407 (1983).

RHYNE, J. J. and KOON, N. C, "Effects of Crystal Field and Exchange Interactions on

the Spin Excitations in Rare Earth Laves-phase Compounds," Proceedings of the

International Conference on Magnetism of Rare-Earths and Actinides, eds.,

E. Burzo and M. Rogalski, Abstracts and Proceedings Series CIP-AP, Cent. Inst, of

Physics, Bucharest, Romania, £, 9-17 (1983).

RHYNE, J. J., HARDMAN-RHYNE, K., SMITH, H. K., and WALLACE, W. E. , "Deuterium Site

Occupation and Magnetism in Ho^Fe_-D Compounds," J. Less-Common Met., _94, 95-105

(1983).

b ^i X

RHYNE, J. J., "Magnetic Phase Transition Temperatures of the Elements," Bull. Alloy

Phase Diag., 3_, 401-402 (1982).

RHYNE, J. J. and KOON, N. C, "Spin Dynamics of HoAl ," J. Mag. Matls., 31-34 , 608-

610 (1983).

RHYNE, J. J., "Magnetic Materials in Concise Encyclopedia of Solid State Physics,"

R. G. Lerner and G. L. Trigg, ed. (1983).

RHYNE, J. J. and KOON, N. C, "Ground State Spin Excitations in HoAl^." J. Appl.

Phys. 53, 8354-8356 (1982).

RICHTER, D., RUSH, J. J., and ROWE, J. M., "Localized Modes and Hydrogen Trapping in

Niobium with Substitutional Impurities," Phys. Rev. B27 , 6227-6233 (1983).

190
PUBLICATIONS

ROWE, J. M., RUSH, J. J., and SUSMAN, S., "Neutron Powder Diffraction Study of PhaseTransitions and Structures of (KCN) (KBr) Mixed Crystal," Phys. Rev. (in

press)

.

ROVre, J. M., RUSH, J. J., and LUTY, F., "The Crystal Structure of Rubidium Cyanide at

H K Determined by Neutron Powder Diffraction," Phys. Rev. Brief Comm. (in press).

ROWE, J. M., BIRGENEAU, R. J., BRUGGER, R. M., CARPENTER, J. M., and PYNN, R.,

"Report to the Director of Physics," Los Alamos National Laboratory (1983).

RUSH, J. J. CAVANAGH, R. R. , and KELLEY, R. D., "Neutron Scattering from Adsorbates

on Platinum Black," J. Vac. Sci. Technol. A1_, 1245-1246 (1983).

SANTORO, A., D' ANTONIO, P., and CAULDER, S. M., "A Neutron Powder Diffraction Study

of - and -PbO_ in the Positive Electrode Material of Lead-Acid Batteries," J.

Electrochem. Soc. (in press).

SANTORO, A., "The Role of Modern Neutron Powder Diffraction Techniques in the Study

of Solid State Ionics," Proceedings of the 4th International Conference on Solid

State Ionics: Grenoble, France (in press).

SANTORO, A., "New Developments in Neutron Powder Profile Analysis," Proceedings of

the Third Italian-Yugoslavian Crystallographic Conference: Bled, Yugoslavia (in

press)

.

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 LiReO_

and LipReO- in Neutron Scattering," Farber, J., ed., American Institute of

Physics Conference Proceedings No. 89 (1982).

SHORTEN, F. J., ed. "NBS Reactor: Summary of Activities July 1981 through June

1982," Nat. Bur. Stand. Tech. Note 1178 (1983).

STALICK, J. K., HUBBARD, C. R., MIGHELL, A. D., RODGERS, J. R., and HORN, A. S., "2-

Amino-6,7-dihydroxytetralin hydrobromide, C. „HQ(0H)2NH-Br ," Acta Cryst. Sect. C

(in press)

.

SUSMAN, S., DELBECQ, C. J., BRUN, T. 0., and PRINCE, E., "Structure and Conductivity

of the NASICON Analog Na-^Sc (PO^) ," Electrochem. Soc. Ext. Abst. (1982).

THOMLINSON, W. , SHIRANE, G., LYNN, J. W. , and MONCTON, D. E., "Neutron Scattering

Studies of Magnetic Ordering in Ternary Superconductors," Chapter 8 in

Superconductivity in Ternary Compounds, Topics in Current Physics Series, Vol.

34, M. B. Maple; Fischer, ed., New York, NY, Springer-Verlag (1982),

TREVINO, S. F. and TSAI, D. H. , "Model Simulation of Chemical Reaction in a Diatomic

Crystal, Part I: Energy Exchange in Rapid Exothermic Dissociation," Proceedings

of the American Physical Society Conference on Shock Waves in Condensed Matter

(in press).

TREVINO, S. F. and TSAI, D. H. , "Model Simulation of Chemical Reaction in a Diatomic

Crystal, Part II: Kinetics of Equilibrium Chemistry," Proceedings of the

American Physical Society Conference on Shock Waves in Condensed Matter (in

press)

.

191
PUBLICATIONS

TSAI, D. H. and TREVINO, S. F., "Molecular Dynamical Studies of the Dissociation of a Diatomic Molecular Crystal, Part I: Energy Exchange in Rapid Exothermic

Reactions," J. Chem. Phys. (in press).

WADLEY, H., FANCONI, B. , FORTUNKO, E., FULLER, E. , HUNSTON, E. , LINZER, M.,

SINGHAL, S., and STEINER, B., "Nondestructive Evaluation, Present and Future

Activities," Center for Materials Science (1983).

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, ed. Academic Press (in press).

WLODAWER, A. and SJOLIN, L., "Application of Joint Neutron and X-ray Refinement to

the Investigation of the Structure of Ribonuclease A at 2.0 A Resolution,"

Brookhaven Symposia in Biology (in press).

WLODAWER, A., "Structure of Bovine Pancreatic Ribonuclease" in"structural Biology','

Vol. II: Nucleic Acid Binding Proteins," A. McPherson, F. Jurnak, ed. (in

press).

WLODAWER, A., and SJOLIN, L., "Structure of Ribonuclease A: Results of Joint Neutron

and X-Ray Refinement at 2.0 A Resolution," Biochem. 22^, 2720-2728 (1983).

WLODAWER, A., MILLER, M., and SJOLIN, L. , "Active Site of RNase: Neutron Diffraction

Study of a Complex with a Transition State Analog," Proc. Natl. Acad. Sci. USA

80, 3628-3631 (1983).

WLODAWER, A., "Neutron Diffraction of Crystalline Proteins in Progress in Biophysics

and Molecular Biology," Vol. 40. T. Blundell, ed. Oxford, England, Pergamon

Press, Ltd. (1982).

WLODAWER, A. and SJOLIN, L., "Improvement of the Quality of the Data Collected Using

a Position-Sensitive Detector," Nucl. Instrum. Methods 201 , 117-122 (1982).

ZABEL, H., RUSH, J. J., and MAGERL, A., "Elastic Neutron Scattering Results on

C-j^Rb(D ) in the Dilute Concentration Regime," Synthetic Metals (in press).

ZABEL, H., MAGERL, A., DIANOUX, A. J., and RUSH, J. J., "Planar Diffusive Motion of

Alkali Intercalant Atoms in Graphite," Phys. Rev. Lett. 50_, 2094 (1983).

ZABEL, H., MAGERL, A., and RUSH, J. J., "Phonons in LiC.," Phys. Rev. B27, 3930-3933

(1983).

ZOCCHI, M., GATTI, M., SANTORO, A., and ROTH, R. S., "Neutron and X-Ray Diffraction

Study on Polymorphism in Lithium Orthotantalate, Li^TaO|,," J. Solid State Chem.

(in press)

192
PUBLICATIONS

INDEPENDENT PROGRAMS

DOWNING, R. G., FLEMING, R. F., LANGLAND , J. K., and VINCENT, D. H., "Neutron Depth

Profiling at the National Bureau of Standards," Proceedings of the Sixth

International Conference on Ion Beam Analysis, Tempe, AZ, May 23-27, 1983, Nucl.

Instr. and Method (in press).

DOWNING, R. G., FLEMING, R. F., SIMONS, D. S. , and NEWBURY, D. E., "Neutron-Induced

Reactions and Secondary Ion Mass Spectrometry: Complementary Tools for Depth

Profiling," Microbeam Analysis-1982, K. F. J. Heinrich, ed. , San Francisco, 219

(1982).

EPSTEIN, M. S., GEARY, T. D., GOWER , G., TAVSCH, W., MILLS, K. J., and POLT, D.,

"Provisional Guidelines for Listing Specifications of Atomic Absorption

Spectrometers," Clin. Chim. Acta, 122 , 1 1 7F (1982).

FLEMING, R. F., PEI , P., and HSU, S. M., "Test Methods for Total Chlorine in

Lubricating Base Oils," (in press).

FLEMING, R. F., "Neutron Self-Shielding Factors for Simple Geometries," Int. J. of

Applied Radiation and Isotopes, 33_' 1263 (1982).

GREENBERG, R. R., FLEMING, R. F., and ZEISLER, R., "High-Sensitivity Neutron

Activation Analysis of Environmental and Biological Standard Reference

Materials," (submitted for publication).

GREENBERG, R. R., "Radiochemical Procedures Used at NBS for High-Sensitivity

Certification Analysis of Standard Reference Materials," Trans. Am. Nucl. Soc,

43, 269 (1982).

GREENBERG, R. R. , "Neutron Activation Analysis Techniques Used For Ultra- trace Level

Elemental Characterization of New NBS Milk Powder Standard Reference Material,"

Trans. Am. Nucl. Soc, 4£, 28 (1983).

GREENBERG, R. R., and KINGSTON, H. M., "Trace Element Analysis of Natural Water

Samples by Neutron Activation Analysis with Chelating Resin," Anal. Chem. 55_,

1160 (1983).

KINGSTON, H. M. and GREENBERG, R. R., "An Elemental Ratioing Technique for Assessing

Concentration Data From a Complex Water System," (submitted for publication).

KINGSTON, H. M., GREENBERG, R. R, , BEARY, E. S. , HARDAS, B. R. , MOODY, J. R.

,

RAINS, T. C, and LIGGETT, W. S., "The Characterization of the Chesapeake Bay: A

Systematic Analysis of Toxic Trace Elements," National Technical Information

Service, Order No. PB82-265-265 (1982).

KINGSTON, H. M. and LUTZ, G. J., "Adsorption and Stability Prior to Analysis of

Simulated Nuclear Waste Leachate," Nuclear and Chemical Waste Management, 3_, 245

(1982).

KOCH, W. F,, STOLZ, J. W., KELLY, W. R., PAULSEN, P. J., LINDSTROM, R. M.,

FLEMING, R. F., and GREENBERG, R. R., "Methods and Procedures Used at the

National Bureau of Standards to Certify NBS Sulfur in Coal SRM's for Sulfur

Content, Calorific Value, Ash Content," T. E. Gills, ed., Nat. Bur. Standards

'Ti.s.) Spec. Publ. 260 (1983).

193
PUBLICATIONS

LUTZ, G. J., ROOK, H. L., and LINDSTROM, R. M., "Determination of 1-129 at Natural

Levels by Thermal Neutron Activation Analysis," (submitted for publication).

WISE, S. A., FITZPATRICK, K. A., HARRISON, S. H., ZEISLER, R., LANGLAND, J. K.,

KRATOCHVIL, B., RAINS, T. C., RUSH, T. A., BUTLER, T. A., GRAMLICH, J. W.,

POWELL, L. J., BRLETIC, K. A., MURPHY, T. J., BAILEY, J., MAIENTHAL, E. J.,

KOCH, W. F., KLINE, W. P., ALLEN, C. F., CHESLER, S. N., HILPERT, L. R.,

GREENBERG, R. R., MACCREHAN, W. A., and ANDERSON, D. F., "The Pilot National

Environmental Specimen Bank—Analysis of Human Liver Specimens," Zeisler, R.,

Harrison, S.H., and Wise, S. A., eds., Nat. Bur. Standards (U.S.) Spec. Publ.

656 , 127 (1983).

ZEISLER, R., HARRISON, S. H., and WISE, S. A., "Trace Elements in Human Livers Using

Quality Control in the Complete Analytical Process," Biol. Trace Element Res. (in

press)

ZEISLER, R., LANGLAND, J. K., and HARRISON, S. H., "Cryogenic Homogeni zat i on

Procedure for Biological Tissues," Anal. Chem. (in press).

194
NBS-n4A (REV. 2-ec) U.S. DEPT. OF COMM. BIBLIOGRAPHIC DATA

SHEET (See instructions)

1. PUBLICATION OR

REPORT NO.

NBS TN 1190

2. Performing Organ, Report No. 3. Publication Date

April 1984

4. TITLE AND SUBTITLE

NBS Reactor: Summary of Activities July 1982 to June 1983

5. AUTHOR(S)

F. J. Shorten, Ed,

6. PERFORMING ORGANIZATION (If joint or other ttian NBS. see /nstruct/onsj

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

7. Contract/Grant No.

8. Type of Report & Period Covered

July 1982 to June 1983

9. SPONSORING ORGANIZATION NAME AND COMPLETE ADDRESS (Street, City. State. ZIP)

Same as item 6.

10. SUPPLEMENTARY NOTES

I I Document describes a computer program; SF-185, FlPS Software Summary, is attached.

11. ABSTRACT (A 200-word or less factual summary of most significant information. If document includes a significant

bibliography or literature survey, mention it here) This report summarizes all those programs which depend on the NBS reactor. It covers

the period from July 1982 through June 1983. 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 (S/x 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

fXl Unlimited

I I For Official Distribution. Do Not Release to NTIS

rX] Order From Superintendent of Documents, U.S. Government Printing Office, Washington, D.C. 20402.

\2Z\ Order From National Technical Information Service (NTIS), Springfield, VA. 22161

14. NO. OF

PRINTED PAGES

202

15. Price

USCOMM-DC 6043-P80

* U.S. GOVERNMENT PRINTING OFFICE: 1984-420-997:49

NBS TECHNICAL PUBLICATIONS

PERIODICALS

JOURNAL OF RESEARCH—The Journal of Research of the National Bureau of Standards reports NBS research and develop- ment in those disciplines of the physical and engineering sciences in which the Bureau is active. These include physics, chemistry,

engineering, mathematics, and computer sciences. Papers cover a broad range of subjects, with major emphasis on measurement

methodology and the basic technology underlying standardization. Also included from time to time are survey articles on topics

closely related to the Bureau's technical and scientific programs. As a special service to subscribers each issue contains complete

citations to all recent Bureau publications in both NBS and non- NBS media, issued six times a year Annual subscription: domestic

$18; foreign $22.50. Single copy, $5.50 domestic; $6.90 foreign.

NONPERIODICALS

Monographs—Major contributions to the technical literature on

various subjects related to the Bureau's scientific and technical activities. Handbooks—Recommended codes of engineering and industrial practice (including safety codes) developed in cooperation with in- terested industries, professional organizations, and regulatory

bodies. Special Publications—Include proceedings of conferences sponsored by NBS, NBS annual reports, and other special publications

appropriate to this grouping such as wall charts, pocket cards, and

bibliographies.

Applied Mathematics Series—Mathematical tables, manuals, and

studies of special interest to physicists, engineers, chemists,

biologists, mathematicians, computer programmers, and others engaged in scientific and technical work.

National Standard Reference Data Series—Provides quantitative data on the physical and chemical properties of materials, compiled from the world's literature and critically evaluated. Developed under a worldwide program coordinated by NBS under

the authority of the National Standard Data Act (Public Law

90-396).

NOTE: The principal publication outlet for the foregoing data is the Journal of Physical and Chemical Reference Data (JPCRD)

published quarterly for NBS by the American Chemical Society

(ACS) and the American Institute of Physics (AIP). Subscriptions,

reprints, and supplements available from ACS, I 155 Sixteenth St., NW, Washington, DC 20056.

Building Science Series—Disseminates technical ir formation developed at the Bureau on building materials, components,

systems, and whole structures. The series presents research results,

test methods, and performance criteria related to the structural and

environmental functions and the durability and safety characteristics of building elements and systems.

Technical Notes—Studies or reports which are complete in themselves but restrictive in their treatment of a subject. Analogous to monographs but not so comprehensive in scope or definitive in treatment of the subject area. Often serve as a vehicle for final reports of work performed at NBS under the sponsorship of other government agencies.

Voluntary Product Standards—Developed under procedures

published by the Department of Commerce in Part 10, Title 15, of

the Code of Federal Regulations. The standards establish nationally recognized requirements for products, and provide all concerned interests with a basis for common understanding of the

characteristics of the products. N BS administers this program as a supplement to the activities of the private sector standardizing

organizations. Consumer Information Series—Practical information, based on NBS research and experience, covering areas of interest to the con- sumer. Easily understandable language and illustrations provide

useful background knowledge for shopping in today's tech- nological marketplace. Order ihe above NBS publications from: Superintendeni of Documenis. Government Priming Office. Washington. DC 20402. Order the following NBS publications—FIPS and NBSIR's—from

the National Technical Information Service , Springfield, VA 22161

.

Federal Information Processing Standards Publications (FIPS

PUB)—Publications in this series collectively constitute the Federal Information Processing Standards Register. The Register

serves as the official source of information in the Federal Govern- ment regarding standards issued by NBS pursuant to the Federal Property and Administrative Services Act of 1949 as amended,

Public Law 89-306 (79 Stat. 1127), and as implemented by Executive Order 11717(38 FR 12315, dated May II, 1973) and Part 6 of Title 15 CFR (Code of Federal Regulations).

NBS Interagency Reports (NBSIR)—A special series of interim or

final reports on work performed by NBS for outside sponsors

(both government and non-government). In general, initial dis- tribution is handled by the sponsor; public distribution is by the National Technical Information Service , Springfield, VA 22161,

in paper copy or microfiche form.
U.S. Department of Commerce

National Bureau of Standards

Wasfimgton, D.C. 20234

Official Business

Penalty for Private Use $300