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APR 9 1971

NBS TECHNICAL NOTE 567

Reactor Radiation Division:

Annual Progress Report for the

Period Ending October 31, 1970
NATIONAL BUREAU OF STANDARDS

The National Bureau of Standards1 was established by an act of Congress 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 measure- ment 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 consists of the Institute for Basic Standards, the Institute for Materials

Research, the Institute for Applied Technology, the Center for Computer Sciences and

Technology, and the Office for Information Programs.

THE INSTITUTE FOR BASIC STANDARDS provides the central basis within the United States of a complete and consistent system of physical measurement; coordinates

that system with measurement systems of other nations; and furnishes essential services leading to accurate and uniform physical measurements throughout the Nation's scientific community, industry, and commerce. The Institute consists of a Center for Radiation Research, an Office of Measurement Services and the following divisions: Applied Mathematics—Electricity—Heat—Mechanics—Optical Physics—Linac

Radiation2—Nuclear Radiation2—Applied Radiation2—Quantum Electronics3—

Electromagnetics3—Time and Frequency3—Laboratory Astrophysics3—Cryogenics3

. THE INSTITUTE FOR MATERIALS RESEARCH conducts materials research lead- ing to improved methods of measurement, standards, and data on the properties of

well-characterized materials needed by industry, commerce, educational institutions, and

Government; provides advisory and research services to other Government agencies;

and develops, produces, and distributes standard reference materials. The Institute consists of the Office of Standard Reference Materials and the following divisions: Analytical Chemistry—Polymers—Metallurgy—Inorganic Materials—Reactor

Radiation—Physical Chemistry.

THE INSTITUTE FOR APPLIED TECHNOLOGY provides technical services to pro- mote the use of available technology and to facilitate technological innovation in industry and Government; cooperates with public and private organizations leading to the development of technological standards (including mandatory safety standards), codes

and methods of test; and provides technical advice and services to Government agencies

upon request. The Institute also monitors NBS engineering standards activities and

provides liaison between NBS and national and international engineering standards

bodies. The Institute consists of the following technical divisions and offices: Engineering Standards Services—Weights and Measures—Flammable Fabrics

Invention and Innovation—Vehicle Systems Research—Product Evaluation

Technology—Building Research—Electronic Technology—Technical Analysis

Measurement Engineering.

THE CENTER FOR COMPUTER SCIENCES AND TECHNOLOGY conducts re- search and provides technical services designed to aid Government agencies in improving cost effectiveness in the conduct of their programs through the selection, acquisition,

and effective utilization of automatic data processing equipment; and serves as the principal focus within the executive branch for the development of Federal standards for automatic data processing equipment, techniques, and computer languages. The Center

consists of the following offices and divisions: Information Processing Standards—Computer Information—Computer Services —Systems Development—Information Processing Technology.

THE OFFICE FOR INFORMATION PROGRAMS promotes optimum dissemination

and accessibility of scientific information generated within NBS and other agencies of

the Federal Government; promotes the development of the National Standard Reference

Data System and a system of information analysis centers dealing with the broader

aspects of the National Measurement System; provides appropriate services to ensure

that the NBS staff has optimum accessibility to the scientific information of the world,

and directs the public information activities of the Bureau. The Office consists of the following organizational units: Office of Standard Reference Data—Office of Technical Information and

Publications—Library—Office of Public Information—Office of International

Relations.

1 Headquarters and Laboratories at Gaithersburg, Maryland, unless otherwise noted; mailing address Washington, D.C. 20234.

2 Part of the Center for Radiation Research.

8 Located at Boulder, Colorado 80302.
IAL BUREAU Of STANDARD

t

! 1 / ° °

UNITED STATES DEPARTMENT OF COMMERCE

Maurice H. Stans, Secretary

NATIONAL BUREAU OF STANDARDS • Lewis M. Branscomb, Director \1

'•-

11

NBS TECHNICAL NOTE 567

ISSUED MARCH 1971

Nat. Bjr. Stand. (U.S.), Tech. Note 567, 66 pages (Mar. 1971) CODEN: NBTNA

Reactor Radiation Division:

Annual Progress Report

for the Period Ending October 31, 1970

Robert S. Carter, Editor

Reactor Radiation Division

Institute for Materials Research

National Bureau of Standards

Washington, D.C. 20234

NBS Technical Notes are designed to supplement the Bureau's regular publications program. They provide a means for making available scientific data that are of transient or limited interest. Technical Notes may be

listed or referred to in the open literature.

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

(Order by SD Catalog No. C 13.46:567). Price 70 cents.

FOREWORD

The reactor has completed its first year of full power operation so it is now appropriate

to review the progress made during the last year. This report is the first annual progress

report of the Reactor Radiation Division.

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

but also those of the greater Washington Scientific Community and other government agencies.

It is the responsibility of the Reactor Radiation Division to foster the wise scientific

and technological use of the reactor as well as assure its safe and efficient operation.

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 a broad spectrum of 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. /

Use of the reactor by individuals and organizations outside the Reactor Radiation

Division has increased significantly during the past year and continues to expand rapidly.

Twenty-five scientists from other parts of the Bureau, representing 16 man-years of effort, use the reactor regularly either directly or in cooperation with scientists in the Division.

An additional 32 scientists from other agencies, universities, and industry spent 12 manyears of effort using the reactor during the past year.

The purpose of this report is to summarize the activities of the large number of users

outside the Division as well as the work in the Division. The summaries are divided into

two groups. One is the research activities and the other is the operation and service

activities. The research activities are further broken down into three groups: the first

includes all the work of the Division and most of the collaborative work; the second

describes the activities of our formal interagency collaboration based on long-term

arrangements where scientists from other agencies are actually stationed at the reactor;

and the third catagory is the summary of activities of other NBS divisions which use the reactor directly rather than through collaboration with Reactor Radiation scientists.

R. S. Carter, Chief

Reactor Radiation Division

ill
REACTOR RADIATION DIVISION

Annual Progress Report

for period ending October 31, 1970

Edited by R. S. Carter

The reactor has completed its first year of full power operation so it is now appropriate to review the progress made during the last

year. This report is the first annual progress report of the

Reactor Radiation Division.

Key words: Crystal structure; diffraction; molecular structure;

:neutron; nuclear reactor; radiation; scattering.

xv
TABLE OF CONTENTS

RESEARCH PROGRAMS

Division Programs Page

Time Dependent Klein-Gordon Equation i Thermal Neutron Flux Measurements 1 Crystallographic Studies of Metal Organic Materials 2

1. Crystal Structure of [Cd (C^N^ & ](N0

3

) 2 and [Cd^H^) g

] (OH) (NO-) -4^0. . . .2

2. Crystal Structure of [Co^^HgNp

2 (NOj) ](0H) (NO^^O 3

3. Crystal Structure of [Co(C H.N ) ](N0

3 )„ 3 4. Crystal Structure of the 2:1 Dimer [ (Pyridine-N-Oxide) CuBr ] 3 The Structure of Potassium Silicotungstate 3 The Structure of Dimethyl Sulfone Diimine . . . 4 The Structure of Apophyllite 4 The Structure of Durene 7 Proton Dynamics and Phase Transitions in Transition Metal Hydrides 7 Spectroscopic Investigationsof Dynamics and Hydrogen Bonding in Sodium and Potassium

Bifluoride 8 Neutron Diffraction Study of the Structure and Thermal Motion of Ph^Br .12 Study of Rotational Diffusion in Plastic Crystals 15 The Rotator Phase of n-alkanes 15

Study of Simple Liquids 18 Crystal Monochrometer, Time of Flight Spectrometer 21 Time of Flight Data 22 Cold-Neutron Time of Flight Facility 22 Cold-Neutron Source 24 Publications 25

Interagency Collaborative Programs

Crystal Structure of the TiNi Martensite 26 Spin Canting in Rare Earth Iron Garnets (R,Fe ) 26 Magnetic Structures of Transparent Fluorides 27 Crystal Field and Exchange Energy in Cubic Praseodymium Compounds 27 Neutron Diffraction in Liquid Aluminum 28 Neutron Diffraction Investigation of Amorphous Solids .28 Precision Measurement of Thermal Neutron coherent Scattering Amplitudes .29 Picatinny Arsenal - NBS Interagency Collaboration 33

Diffractometer Control by Computer 34

Equipment Development 35

1. Triple Axis Spectrometer 35

2. Superconducting Magnet 35 Publications 36 v
TABLE OF CONTENTS- -Con.

C. Non-Division NBS Programs Page

Activation Analysis Section: Summary of Activities 37 Atomic Constants from X-ray and Positronium Decay y- ray Measurements 37

Intense Fission Neutron Source 38

Parity Violation in Strong Interactions 39

3 Fast Neutron He Spectrometer 40

Two-flioton Emission in (n,p) Capture 40

Decay Characteristics of Krypton Isotopes 41

82 Nuclear Orientation Studies of ° Br 41

Publications 43

REACTOR OPERATIONS AND SERVICE PROGRAMS

A. Operating Statistics 44

B. Operating Summary 44

C. Summary of Service and Service Programs 47 Trace Constituents of Geological Materials 48

Activation Analysis Program of the Food and Drug Administration at the NBSR 49

1. Hydrofluoric Acid in Rust Stain Removers for Household Use 49

2. Bromine Distribution in Test Pigs for Toxicological Studies 49

3. Fluorine in Bone Meal 49

4. Mercury in Foods 49 Neutron Activation Analysis in Scientific Crime Detection at IRS .50

1. Gunshot Residue 50

2. Soil 50

3. Bomb Associated Residues 50

4. Illicit Distilled Spirits 50 Federal Bureau of Investigation Activation Analysis Program 51 U.S. Post Office Department Activation Analysis Program 51 Role of Trace Metals in Bone Healing 52 Study of Fission Product Gamma Ray Spectra 52 Direct Fission Population Measurements 53 A Preliminary Investigation of the Mercury Levels in Chesapeake Bay Oysters 54

Trace Elements in the Environment 55 Neutron Damage Studies on Lead Salts 55

STAFF ROSTER

A. Division Organization Chart 56

B. Non-RRD NBS Staff located at Reactor 37

C. Guest Workers and Collaborators 57

vx
RESEARCH PROGRAMS

A. Division Programs

Time-Dependent Klein-Gordon Equation

V. W. Myers

The time-dependent Klein-Gordon equation is solved for the motion of a charged particle

interacting with a traveling plane electromagnetic wave. The Klein-Gordon equation is the

relativistic quantum mechanical equation for a spin zero particle and is appropriate for a

tt meson, for example. The electromagnetic field is treated classically, and the solutions

of the Klein-Gordon equation correspond to the strong field limit. The solutions can be

expressed in the form _^ _^ .. i(k-r-Wt) f(z-ct)e

where z is the propagation direction of the wave, and k and W are constants. Expectation

values for such quantities as the particle's kinetic energy and mechanical momentum

are computed. A manuscript describing the details of this research is being prepared.

Thermal Neutron Flux Measurements

V. W. Myers and M. Ganoczy

Research has continued on a new technique for measuring thermal neutron flux which is the number of neutrons per second passing through a sphere of 1 cm cross section from any

direction. Small glass beads (~ 1 millimeter radius) are made black to thermal neutrons by

the inclusion of B since this isotope has a very large capture cross section for thermal

neutrons. An activator such as cobalt is incorporated in the glass. If the bead is placed

in a neutron field for a known time interval, the resulting radioactivity can then be related

directly to the neutron flux. In contrast, a thin foil with a 1/v capture cross section

determines only the neutron density (the number of neutrons per unit volume)

The activity of a cobalt bead after irradiation for a time t small compared to the mean

life t (7.6 years) in a thermal neutron flux is£

A = (n v)(n r

2 )(-^|-)( ± )(l-f).

A is the disintegration rate, n v is the thermal neutron flux, and r is the bead radius.

S is the macroscopic activation cross sections of cobalt (nuclear cross section times

co atomic density), and £ is the total macroscopic capture cross section of the glass. The

correction for neutron transmission and scattering is f and is ~ 0.02. It is advantageous

to have Identical beads since a bead with a known disintegration rate could then be sent to other laboratories for calibration of counting equipment, and such complications as the

60

dependence of Co gamma ray absorption and counting efficiency on bead size are eliminated.

Improvements were made in fabrication of the beads. The finishing technique involves

a random grinding process for a single bead, and spherical beads can be produced with

essentially identical radii. The initial grinding of the beads is achieved by driving

1
them with an air jet inside a cup grinding wheel.

It is necessary to know the composition by weight of the major elements comprising

the glass in order that S /£ can be determined. Collaboration with the Activation

Analysis Section is countinuing on attempting to obtain more precise measurements of the

cobalt content so that the uncertainly in E /T, can be reduced to 1% or less. CO An alternative approach is to activate a bead in a known neutron flux. For this

purpose, a bath consisting of manganese sulfate dissolved in water is being assembled at one of the beamports of the NBSR. A neutron beam of the order of a millimeter radius will

be directed into the bath. The cylindrical bath is of sufficient size (length and diameter

are each 0.45 meter) that less than 1 percent of the thermal neutrons are not captured in

the bath. Continuous counting of the Mn activity produced from neutron capture in

manganese will be done using a Nal detector. The system is calibrated by the addition of

a known Mn activity into the bath, and the neutron beam flux can then be determined. A bead can then be calibrated by activation in this known neutron flux for a prescribed time.

The overall uncertainty in the measurement of thermal neutron flux by the bead

technique is anticipated to be of the order of 2%.

Crystallographic Studies of Metal Organic Materials

A. Santoro

and

C. W. Reimann and A. D. Mighell

(Inorganic Materials Division)

In the past year a number of transition metal complexes have been studied by means of

diffraction techniques. The metal ions used in these studies include Cu , Cd , Co

I

I I and Co and the ligands include imidazole, dipyridine, and pyridine-N-oxide.

The structure analysis of these complexes provides direct information on the stereo- chemistry and the utilization of the active sites of the ligand molecules and on the

symmetry of the coordination polyhedra. Moreover, this type of analysis gives precise

bond distances and angles and furnishes evidence on the role played by hydrogen bonding

in the packing of the structures.

The results of these studies may be used as the structural basis for a meaningful

interpretation of spectroscopic data and may clarify the role played by some ligand

molecules, such as imidazole, In biological systems.

Most of this work has been carried out by x-ray diffraction techniques. More

recently, however, x-ray and neutron diffraction studies have been combined in order to locate hydrogen atoms in hydrogen bonded systems. The use of neutrons will be extended

also to those cases in which radiation damage prevents the collection of accurate x-ray

intensities.

The following crystal structures have been analyzed in the past year:

1) Crystal structure of Hexakis(imidazole)cadmium(II) Nitrate, [Cd(C

3H4N

2

) 6 ](N0

3

) 2

,

2
and Hexakis (imidazole) cadmium(II) Hydroxide Nitrate Tetrahydrate, [Cd(C

3H,N

2

) ](0H) (NO ) -4H 0, Both these structures consist of discrete Cd (C.H.N ) complex cations and N0„ anions,

but as result of the presence of water molecules and OH" ions in the hydroxide complex, the

packing of the two structures is considerably different. The structure determination of both

compounds was carried out mainly to compare the same complex cation in two different

environments. The bond distances and angles between the atoms of the imidazole molecules

are practically identical in the two structures but, in order to accomodate hydrogen bonding,

there is considerable difference in the orientation of the rings.

2) Crystal structure of Nitratobis(dipyridine)cobalt (III) Hydroxide Nitrate Tetrahydrate,

[ Co (C 10H

gN

2

) 2 (N0

3

) ] (OH) (N0

3

) -4^0.

In this structure the Co atom is octahedrally coordinated by two molecules of dipyridine

and by a intrate group acting as a symmetric bidentate ligand. This is one of the few nitrate

complexes in which the role of the nitrate group has been clarified crystallographically.

The water molecules, the nitrate groups and the 0H~ ions are involved in a continuous network

of hydrogen bonds.

3) Crystal Structure of Hexakis (imidazole) Cobalt (II) Nitrate, [Co(C

3 H,N2

) ,](N0

3

) „. This compound has been analyzed in collaboration with Dr. E. Prince by x-ray and

neutron diffraction techniques in order to locate the hydrogen atoms and define without

ambiguity the hydrogen bonding in the structure. Another purpose of this work is to compare

x-ray and neutron structural data.

4) Crystal structure of the 2:1 Dimer[ (Pyridine-N-Oxide) CuBr„] . A large number of aromatic N-oxides of Cu have been classified in terms of 12 structure types in an effort to generalize their magnetic behavior. [ (Pyridine-N-Oxide)

„

CuBr„]„ was classified as probably belonging to the same structural type of the chloride

analog in spite of its anomalous magnetic moment. The completed structure determination

of the complex has shown that, although the basic molecular unit is a dimer as in the

chloride analog, it differs markedly from the chloride complex.

The Structure of Potassium Silicotungstate

E. Prince

and

P. M. Smith and J. V. Silverton

(Dept. of Chemistry, Georgetown University, Washington, D.C.)

Potassium silictungstate is one of a series of compounds containing anions that are designated "heteropoly" because they are large, complex groups containing more than one kind of cation. The silicotungstate ion has the composition SiW.^O,... The potassium salt

crystallizes in 2 different forms, a hexagonal a form containing from 16 to 18 waters of

hydration per formula unit, and a monoclinic 3 form containing 12 to 14 waters of hydration.

A neutron diffraction investigation was undertaken with two aims, first to determine

accurately the configuration of the silicotungstate ion and, second, to attempt to elucidate

the role of water of hydration in the crystal structure. Complete, 3-dimensional data have

3
been collected from a crystal of the a form crystallized from normal water, and hkO data

have been collected from a crystal grown from heavy water. Analysis of the data, which is

still in progress, has yielded accurate parameters for the anion, but the search for water

has been less successful. A difference Fourier synthesis has revealed a large hole, with a radius of nearly 6 A extending all the way through the crystal along a 6 axis, in which

there is apparently no ordered scattering material. One hypothesis is that this void is

occupied by water which is virtually free, thus accounting for the instability of these

crystals in an unsaturated atmosphere. It is hoped that in the future it will be possible

to study the |3 form, which is somewhat more stable.

The Structure of Dimethyl Sulfone Diimine

E. Prince

and

J. Bevan

(Procter & Gamble Co., Cincinatti, Ohio)

Dimenthyl sulfone diimine, (CH„)

2 S(NH) „ is a simple compound which is chemically

related to the basic constituents of synthetic detergents. A neutron diffraction study was undertaken to determine the positions of the hydrogen atoms. The imino hydrogens form a system of hydrogen bonds. 261 independent diffraction intensities were measured. Analysis

of the data is still in progress.

The Structure of Apophyllite

E. Prince

and

A. A. Colville

(Dept. of Geology, California State College, Los Angeles, Calif.)

and

G . Donnay

(Geophysical Laboratory, Carnegie Institute of Washington, Washington, D.C.)

Apophyllite is a hydrated, fluorosilicate mineral with the ideal chemical formula

KCa/ (Si,0-_)„F # 8H„0. It has an unusual sheet structure, with 4-membered rings of SiO,

tetrahedra linked together to form an infinite, two-dimensional network. Fig. 1 is a stereoscopic pair showing this structure clearly. If apophyllite is heated, gas is evolved

In two distinct stages. A neutron diffraction investigation was undertaken in order to determine the structural role of the water of hydration, in hopes that the reason for the

two-stage evolution of gas would become apparent.

A least-squares refinement of three-dimensional data (671 reflections) with anisotropic

temperature factors led to an R index (R=XJ F -F | /£F ) of .046. The structure parameters were in excellent agreement with previous x-ray determinations, and the configuration and

environment of the water molecule (Fig. 2) were very reasonable. A difference Fourier

4
Fig. 1. Stereoscopic pair showing the infinite silicate sheets in apophyllite,

Fig. 2. The environment of the water molecule in apophyllite,
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synthesis revealed an additional hydrogen atom near the fluorine atom, forming a molecule

of hydrogen fluoride. A further refinement, replacing the water molecules by hydroxyl ions

and attaching the remaining hydrogen atom to the fluorine atom gave an R index of .037. Table 1 shows the final parameters. A paper describing these results is being submitted

to The American Mineralogist .

The Structure of Durene

E. Prince, L. W. Schroeder, and J. J. Rush

As part of a study of the structure, dynamics and phase transitions in methylbenzene

compounds, we have extended our experiments to a crystal structure study of durene. Durene (1,2,4,5-tetramethyl benzene) is a methylated, aromatic hydrocarbon. When methyl groups

are attached to adjacent carbon atoms on a benzene ring, they are "over-crowded", and the structure of the molecule must have some distortion from an idealized structure containing

120° angles all around the ring and tetrahedral (109° 28') angles around the methyl groups.

Durene, in contrast to hexamethylbenzene, was determined by previous neutron-inelasticscattering experiments, to have a comparatively high barrier to rotation of the methyl

groups (2 Kcal/mole vs 1 Kcal/mole) . A neutron diffraction study of a single crystal of

durene was undertaken in order to determine the configuration of the methyl groups. It

is hoped that it will be possible to subject the diffraction data to a segmented-rigidbody analysis, and thereby to correlate the various amplitudes of molecular vibration with

spectroscopic data. Analysis of the data is still in progress.

Proton Dynamics and Phase Transitions in Transition Metal Hydrides

L. A. deGraaf and J. J. Rush

During the past year work has continued in collaboration with scientists at Argonne

National Laboratory on the study of the vibration and diffusion of hydrogen atoms in

transition-metal hydrides by quasielastic and inelastic neutron scattering measurements.

The dynamics of the hydrogen atoms and the changes in motional behavior that occur at phase

transitions in polymorphic hydrides are related to the thermodynamic, electrical and other

physical properties of these materials.

Earlier this year the analysis was completed of quasielastic scattering spectra

measured previously for the a and 3 phases of vanadium hydride using an incident beam of

cold neutrons (X 4.07A, FWHM=0.7A). These spectra for VH2f)

, VflL ,

--: r

7 :/H „ covered a range of momentum transfers from 0.5 to 2.34 and a temperature range if 23° to 250°C.

The analysis of the quasielastic peak widths vs. momentum transfer was used to determine

the concentration dependence of the diffusion in the |3-phase(b.c.c .) . In addition an activation energy of 4570 ±415 j/mole was derived from the temperature dependence of the

hydrogen diffusion in the VH

n

_ sample. The neutron spectra for the g-phase of VH- ,- 7n indicate an abrupt decrease in the diffusion rate at the cr*i3 transition.

7
One principal aim of these experiments was to determine, if possible, the diffusive jump

mechanism (and indirectly the sites occupied in the lattice) for the hydrogen atoms. Theoretical calculations were performed of the dependence of the neutron quasielastic line

broadening on momentum transfer (K) for hydrogen diffusion between various tetrahedral and

octahedral interstitial sites in the b.c.c. lattice (a phase). Unfortunately, however,

it was determined that the range of K covered in the cold neutron experiment was not

great enough for a meaningful comparison of theory and experiment to be made. We have thus

recently expanded the quasielastic scattering measurements on VH_ „_ and VH ,- 7 from K=2 to K=4 using a crystal monochrometer, neutron chopper time-of-f light facility at the NBSR. For these measurements we used an incident neutron wavelength of 2.43A and studied the

scattered spectra over an angular range of 45° to 106° at temperatures from 23 to 215°C.

These data are presently being analyzed so that detailed comparisons can be made with the

theoretical predictions for various diffusion models.

Neutron studies of the vibration spectra in two crystal phases of PdH_ , and of

hydrogen diffusion in the TaH system are also being planned. Special sample holders have

been designed for these measurements and are presently being constructed.

Spectroscopic Investigations of Dynamics and Hydrogen Bonding

in Sodium and Potassium Bifluoride

J. J. Rush and L. W. Schroeder

The structure, vibration spectra and hydrogen bonding of sodium and potassium

bifluoride have been investigated in the past by a variety of spectroscopic, diffraction

and thermodynamic techniques. The lattice and internal vibrations of these crystals and

their related properties are of particular interest because of the very strong symmetric

hydrogen bond of the bifluoride (HF ~) ions. The strength of the F-H-F" bond is indicated

in part by the large shift of the asymmetric stretching frequency from the value for HF

(3700 down to ~1500 cm"-*-) and by the significant broadening of the IR stretching band,

which accompanies this shift. Smaller shifts and broadenings are observed for the F-H-F" bending mode. Such spectral changes are analogous to those observed due to the hydrogen

bonding in O-H-0 and other systems, but no generally satisfactory explanation for these

effects has been established.

In the experiments recently completed, we have studied the dynamics of NaHF» and

KHF„ in two sets of measurements using complementary spectroscopic techniques. In the

first of these we have applied the isotope dilution technique to an infrared study of the

characteristics of the stretching and bending modes of the bifluoride salts. We have

measured infrared spectra of samples containing various mole concentrations (2 to 80%) of

DF2" ions. These conditions enable us to study the vibrations of deuterium atoms either

uncoupled, or coupled in varying degrees, while the ionic environment and lattice dynamics

are essentially unchanged from those of the undeuterated crystal. The results of our measure- ments clearly indicate that the considerable width of the IR absorption bands assigned to the asymmetric stretching (V3) and bending (v£) modes of the HF£~ ion is associated with the

8
coupling of near neighbor HF2" (or DF2 ") oscillators having similar frequencies or energy

states. This is illustrated clearly in the spectra in Fig. 1, which show the changes in the

infrared absorption band for the DF2

" bending mode in NaHF2 as the DF2" concentration changes.

Thus the results observed for the 2% sample (in which the great majority of DF2

" ions are surrounded by HF ~ ions with different V2 and V3 frequencies) may be thought of as representing

the "natural" frequency and width for an isolated DF2

" ion in the sodium bifluoride crystal

field. The broad distribution of frequencies observed for the ~80%D sample, however, would

seem to reflect a coupling of oscillators of states of similar energy in the IR absorption

spectrum. These results also show that in this case at least, not only the width, but the

IR peak position appears to be considerably influenced by the coupling effects. Similar

spectra effects have been observed for the stretching vibrations in NaHFo and for both

v 2 and Vo modes in KHF2.

The second part of our study of the dynamics of the bihalide salts involved the study

of the lattice vibrations and symmetric stretching (v^) vibrations by Raman, far infrared,

and neutron inelastic scattering techniques. The Raman spectrum for pure NaHF is shown in

Fig. 2. The peaks at 145 and 630.5 cm * are assigned, respectively, to the librational

lattice E mode and the HFo" symmetric stretch. It is interesting to note that the vi 8

1 _i frequency of 630.5 cm" 1 for NaHF2 is 30 cm higher than the average v^ frequency for KHF2

indicating a strong effect of the crystal field on the HF2~ internal modes. A publication

is in preparation showing the correlation of these spectra with our neutron and IR results

is in preparation.
o

(/) (f)

<

en

\-

>

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GD

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NOHF2

— 893\ / — ~80%D

1 874

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FREQUENCY (cm 1 )

Fig. 1. Infrared spectrum in the region of DFIu. mode for sodium bifluoride containing 2, 11 and s*80% DFI

10
>-

UJ

Q

UJ

CC

UJ

O

CO

Fig. 2. Raman spectrum of NaHF„. The peak marked (X) is a background line.

11
Neutron Diffraction Study of the Structure and Thermal Motion of Ph^Br

L. W. Schroeder and J. J. Rush

As part of a program investigating molecular structure and dynamics of a complex ionic

salts, a neutron diffraction study of phosphonium bromide has been completed. This (study)

complements previous work in that accurate structural information is now available PH-Br, PH/I

and the ammonium halides. This information together with the extensive spectroscopic data

on these salts makes it possible to perform calculations with various force models to help

understand their structural and dynamical properties and related interionic forces.

The tetragonal structure of PH.Br is similar to that found previously for PH.I and can be thought of as a distorted CsCl structure. The phosphonium ion, PH. is surrounded by

four nearest-neighbor and four next nearest neighbor bromide ions. The PH, + ion is orientated

so that the P-H bond is directed toward the next nearest neighbor bromide ions. This is in

contrast to the analogous phase III NH.Br structure in which the N-H bond is directed towards

its nearest neighbor bromide ion. The NH.Br structure may be visualized from the PH.Br structure shown in Fig. 1 by imagining the PH, + ion to be NH, + and rotating by 90° about the

C axis.

A "rigid-body" analysis of the motion of the PH, + in the phosphonium halides was performed using the anisotropic thermal parameters of the phosphorus and hydrogen atoms derived

from PH.Br and PH. I diffraction data. As shown in Table 1, the resulting mean-squareamplitudes of translational and torsional motion of the PH, + ion lead to frequencies which

are in good agreement with spectroscopic observations. This indicates that the thermal

amplitudes from diffraction data, combined with the rigid-body model can give physically

meaningful information even under less than ideal circumstances. Having established

descriptions of the rotational motion of the PH, + ion in PH.Br and PH. I, we are presently

attempting to account for this behavior and the somewhat different behavior of the ammonium

halides by combined calculations of electrostatic, van der Waals, and short-range repulsive

force.

12
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13
Fig. 1. Structure of PH.Br showing two unit cells along c. For clarity only the hydrogen

atoms for two of the phosphonium ions are shown. Dotted lines show the relation of the

phosphonium ion to its four nearest bromide ions which are displaced from the face centers

(x) . The dark lines from the hydrogen atoms to the four next nearest neighbor bromide ions

represent the hydrogen bonds. Numbers are interatomic distances in Angstroms. The axes

of the ellipsoids indicate the principal directions of thermal motion for each atom.

14
Study of Rotational Diffusion in Plastic Crystals

J. J. Rush and L. A. deGraaf

Work has continued on the investigation of the details of molecular behavior in the

"plastic" crystalline phases of globular molecular compounds. The analysis of a cold- neutron quasielastic scattering study of rotational diffusion in neopentane in its plastic

phase was completed in collaboration with several scientists from Argonne National Laboratory.

In addition experiments were planned and begun on the study of the rotational motions in

neopentane by analysis of the detailed shape of vibration-rotation bands in the infrared

spectrum. It is hoped that a combination of the neutron and optical techniques will provide

a more thorough understanding of the plastic phases of this and other molecular crystals

and perhaps a better insight into the information provided by both types of measurements.

The Rotator Phase of n-alkanes

J. D. Barnes

(Polymers Division)

and

J. J. Rush

The NBSR 4-meter time-of-flight (TOF) spectrometer was used to study the energy distribution of neutrons scattered from a thin layer of n-nonadecane supported by a cadmium

sheet. Measurements were taken at two different temperatures, 27°C and 20°C. The 27°C

temperature is approximately mid-way between the temperature of the "rotator" (plastic

crystal) phase transition (ca. 23°C) and the melting point of n-nonadecane. 20°C is somewhat below the transition temperature.

The most striking feature in the data is the presence of a pronounced quasielastic

component in the TOF distribution from the rotator phase. This quasielastic scattering

presumably reflects molecular motions resulting in rotational jump diffusion of the protons

about the molecular chain axis. Earlier workers have observed this quasielastic scattering

but have been prevented from making detailed comparisons of experimental data with

theoretical models by the vagaries of the beryllium filter technique used in previous

studies. Our first attempt at analyzing the nature of the quasielastic scattering consisted

of numerically forming the convolution product of a Lorentzian scattering law and the measured

instrumental resolution. The resulting widths were then compared with the experimental data

in an attempt to estimate the intrinsic width of the Lorentzian line. The widths vs momentum

transfer are shown in Fig. 1. These results suggest a jump diffusion process and work is under way to develop a model which will provide a meaningful fit to the observed scattering

data.

The inelastic scattering from the same specimen maintained at a temperature of 20°C

exhibits a sharp cutoff at an energy transfer corresponding to a frequency of approximately

34 cm" . This mode has not been previously observed and further study is required to assign

its character. For energy transfers greater than 40 cm"^ the inelastic portions of the

15
spectra taken at 27°C and at 20°C are, except for quasielastic smearing, nearly identical.

The wings of the quasielastic peak tend to obscure the portion of the 27°C data which

represents energy transfers less than 40 cm" 1 due to vibrational modes. A small residual

broadening is found in the elastic peak of the 20°C data. The magnitude of this broadening

is too small to be assessed with any accuracy by the procedure used for the 27°C data.

The actual data taken so far is too limited in scope to provide clear answers to questions regarding the molecular motions exhibited by n-alkanes in the rotator phase. The

data does, however, show that the neutron scattering technique is useful in obtaining

information regarding molecular motions associated with phase transition in these compounds,

and it also points to the directions which should be taken in future experimentation.

Further experiments covering a wider range of momentum transfers and temperatures and

utilizing improved resolution are in preparation and will be carried out in the near future.

Substantial efforts are under way in developing models to descirbe the scattering to be

expected from these systems and in numerically estimating the fit between the models and the

data. A particularly acute problem in this connection is to be found in separating the

"inelastic" (vibratory) and the quasielastic contributions to the scattering. A numerical

procedure for carrying out this separation together with the unfolding of instrumental

resolution effects from the experimental data is at an advanced stage of development. This

program (named SLAW) should eventually prove useful to others using TOF instrumentaion. It has also been necessary to develop program complexes for handling paper tape data (TAPUTL)

and preliminary reduction of TOF data (SCATT)

.

16
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17
Study of Simple Liquids

L. deGraaf

and

B. Mozer

(Inorganic Materials Division)

A study of liquid neon at fixed temperature and various pressures was initiated

following the suggestion of R. Mountain and H. Raveche.' Theoretical calculations made

by the above indicated that information about the three-body correlation function could be

obtained from the density derivative of the radial distribution function of the liquid.

The radial distribution of a liquid can be derived from either x-ray or neutron diffraction

patterns, the structure factor, of the liquid. We chose to investigate liquid neon because

new thermodynamic data characterizing the liquid was available, a theoretical description

of the liquid was considered favorable, neither x-ray nor neutron data of the liquid was available over a sufficient range of parameters to allow a density derivative of the liquid structure factor to be obtained. Because neutron data was likely to yield the most information on the liquid structure factor we wanted the system to have favorable nuclear

properties. The latter condition was met best using neon since the neutron scattering was

almost all coherent and absorption small so that corrections to the data could be kept to a minimum number of reasonably well known quantities and the recourse of going to expensive

isotopes was unnecessary.

A sample cell having high strength and an isotropic diffraction pattern was needed to insure the most favorable signal to noise ratio. We constructed a cell from a titanium

alloy (13V HCr 3 Al) with very high strength at low temperatures and a very small coherent

cross-section. Because of the above two properties, the cell would exhibit structure in a diffraction pattern one-tenth that of an equivalent mechanical strength aluminium alloy. The

cell was constructed so as to have 20 mil walls in the beam direction and tested at room temperature at pressures above those decided upon for the experimental conditions. The alloy

has higher mechanical strength at low temperature so that we felt secure with the mechanical

safety aspects of the cell. The cell was attached to the copper temperature controlled block

of our cryostat and the temperature of the block maintained to a few milli-degrees around

35.05K which was fixed for the experiment. Neon was Introduced into the cell via a capillary

leading through the vacuum chamber of the cryostat to a relief valve, bursting disc and closeoff valve and thence to the filling system consisting of a high pressure neon bottle, Heise

Gauge for pressure measurements, traps, and a vacuum system. Gas volume outside the sample

wall was kept to a minimum to reduce any pressure fluctuations arising from possible temper- ature changes in the room. The pressure was recorded when the cell was filled and thus a known density of neon determined. The cell and safety apparatus was then sealed-off from the

remainder of the system to minimize pressure fluctuations.

18
Liquid neon neutron diffraction patterns at 35.05K and three pressures 21.4 atm.,

79.0 atm., and 140.0 atm. were taken on the BT-2 spectrometer at the NBS reactor in

K=4nsin9/\ scans. The diffraction scans were obtained using 3 different wavelength neutrons,

2.468, 1.062 and 0.745JL The 2.468A beam was obtained with an oriented graphite monochromator and 2.5 inches of oriented graphite filter. The higher order contamination

was 1/1000 of the main beam. The shorter wavelengths were obtained with a copper monochromator

using (111) and (002) planes in transmission. The resolution of the system for the three

wavelengths was 0.08A"-'-, 0.214 , and 0.36A for the three respective kappa scans from 0.2

to 3.5, 3.0 to 9.2, and 9.0 to 13.25A" 1

. Data was accumulated at the three different wavelengths so as to give a counting statistical accuracy of 0.27„. Overlap was provided for in

the three regions in order to match the patterns. Data for three pressures and a background

run were taken at each wavelength.

The data was refined by first subtracting the background including the scattering from

the cell from each pressure run. The data was then matched from region to region, multiple

scattering corrections were applied and Placzek corrections for inelastic scattering as well

as incoherent scattering were taken into account. The final result is then the resolution

smeared structure factor approaching unity at large kappa. This latter condition was imposed

upon the corrected data instead of relying on an absolute cross-section determination using

the wavelength dependence of the monitor efficiency and the imperfectly known properties of

the monitor and crude collimation. The final result of all this effort can be seen in the

accompanying graph of the structure factor for one pressure scan. The data plotted there

o -I was a result of cubic interpolation between experimental points taken at 0.05A-J- intervals

from 0.2 to 6. 04" to yield data at 0.05A- -'- intervals. A slight uncertainty in the wavelength for the two shortest wavelengths necessitated a redetermination of the wavelengths

used from copper powder patterns and thus the data from 3.2 to 13.24 is the result of

interpolation. Furthermore, the data was smoothed by fitting 5 points to a parabola via

least squares. This smoothing procedure would only affect the statistical fluctuations

which would hardly be observed in a graph of this scale as noted by our decision to obtain

high statistical accuracy. In a graph of the data on an expanded vertical scale one would

tend to see the effects of smoothing.

One of the most Interesting features in this graph is the observable structure beyond

°-l

6A . This has not been observed in any x-ray data nor previous neutron work. Not shown

here is the structure factor for the other pressures. A density (pressure) derivative of

the data that will show well defined structure leading to significant indications of threebody correlation functions is readily seen in a comparison of the three pressures.

As a comparison study to the diffraction pattern of the liquid neon, we undertook

inelastic neutron scattering experiments on liquid neon at 35.05K and 21.4 atmospheres.

This very recently completed study should improve on available inelastic neutron scattering

data that was limited to small kappa values. We have accumulated data at ten scattering

angles equivalent to momentum transfers for elastic scattering ranging from 0.35 to 4A~ . Analysis of these results has just begun and will be reported in a future publication.

19
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20
Crystal Monochrometer, Time of Flight Spectrometer

B. Mozer

(Inorganic Materials Division)

and

A. Cinquepalma and A. Tudgay

A very versatile spectrometer is being installed at the BT5 beam port. The system

consists of a basic two-axis spectrometer plus equipment to do energy analysis by either

time of flight or three-axis (crystal) spectrometry. The monochromator is housed in a drum

which can be rotated to provide a variable energy monochromatic neutron beam. Both rotation

of the drum and the monochromator is accomplished using stepping motors controlled by the

computer. In-pile collimation is available with use of a rotating collimator and shutter

system of the BNL design. The in-pile collimator is 48 inches long with minimum collimation

of 3 minutes of arc and a variety of neutron filters available as inserts in this collimator.

Exit beam collimation is accomplished using a Soller slit collimator 36 inches long with

vertical slits whose minimum collimation is 10 minutes of arc. The sample table support mounted is outboard via a cantilever support attached to the

drum and both sample table and counter arm are moved by stepping motors controlled by the

computer.

Currently the spectrometer is being used in the time of flight mode for energy analysis.

The time of flight system consists of a curved slit Fermi chopper, an evacuated flight path

o roughly four meters long, and a detector bank of eight one inch JHe counters filled to 10 atmospheres. Several rotors are available with various resolution; the best resolution

rotor is one with a burst time giving 2.0% resolution (full width at half maximum) at one Angstrom and a peak in its transmission at two Angstroms at a rotor speed of 10,000 rpm. The duty cycle of this rotor is a few tenths of one percent. Other rotors have higher

duty cycles and a worse resolution but are used in scattering experiments for energy loss

of the neutron where the rotor resolution may not be important compared to the spread in

the incoming beam.

The time of flight system is rotated about the sample position and can cover scattering

angles from to about 100 degrees. Movement of the whole time of flight system is done by

supporting the system on air floats which provide an almost frictionless motion and movement

accomplished with a wheel driven by a stepping motor controlled by the computer. Thus one can program the time of flight system to automatically scan a given angular range while

storing data taken from the bank of eight detectors either summed, in each detector, or another combination. Each detector counter subtends a scattering angle of approximately

20 minutes of arc. Thus it is possible to program the time of flight analyzer to take data

from single crystals in a mode of operation that allows a scan of phonons or magnons along

their dispersion curve using constant Q or constant E. The precision of the scattering angle

position of the time of flight system about the sample is determined to within a few

hundreths of a degree at present, but this can be improved.

The crystal analyzing mechanism needed for converting the system to standard 3 axis work

is being designed and hopefully to be tested before the next fiscal year. A simple design is contemplated for the analyzing crystal and counter using some of the ideas in the Canadian

and Swedish designs.

21
Time of Flight Data

B. Mozer

(Inorganic Materials Division)

Data taken with the time of flight system to be fully reported upon in future

publications include the behavior of oriented pyrolytic graphite as a neutron filter.

This recently manufactured graphite made by Dr. A. W. Moore of the Union Carbide Corporation

was loaned to us to look at material having 0.6 degree misorientation and 3.5 degrees

misorientation. Filters made of either 0.6 degree or 3.5 degree misorientation were highly

satisfactory. The 3.5 degree graphite is now used for one of our filters since cost is important. Comparison of our transmission data on the 3.5 material can be made with data

taken by other workers on 7-10 degree material. We find much sharper behavior of the structure in the data as expected. We have made a careful comparison of the ratio of the

higher order Bragg contamination in a beam of 2.5 Angstrom neutrons with and without the

pyrolytic graphite filter. Without the filter the higher order contamination is of

greater intensity than the 2.5 Angstrom beam. Using 2.5 inches of the 3.5 degree oriented

graphite as a filter we find the ratio of the second and third order contamination less than

1/1000 of the primary 2.5 Angstrom neutron beam. The use of a oriented graphite monochrometer with a filter for removing order contamination results in a very clean beam of high

intensity for inelastic neutron scattering work.

Inelastic neutron scattering data has been taken on vanadium and a specially prepared

copper-nickel alloy both of which scatter neutrons incoherently. The vanadium data allows

us to compare measurements from our time of flight system with measurements on other

equipment. We find the data obtained with the low resolution rotor to be very similar to results obtained by others and by ourselves on other equipment. The results for the

copper-nickel alloy are very interesting in that the spectrum shows more structure than

that of vanadium, and is signif icently different than either pure copper or pure nickel.

Cold-Neutron Time of Flight Facility

R. S. Carter, A. A. Cinquepalma, L. A. deGraaf, F. J. Shorten, J. B. Sturrock

The cold neutron time of flight facility is designed for inelastic neutron scattering

studies of solids and liquids. A neutron beam from the reactor is filtered through polya crystalline beryllium to eliminate neutrons with wavelengths smaller than 3.96A. The beam

then passes through a four rotor phased chopper system which chops the beam into short bursts

of neutrons of selected energy. The sample to be studied is placed immediately after the

choppers and the scattered neutrons are detected in a large bank of detectors arranged along

the arc of a circle with a 2.4 meter radius. The detector Information is fed into a multichannel analyzer and the neutron energy determined from the flight time of the neutrons

from the sample to the detectors.

The eight inch thick beryllium filter is kept at 80°K by a liquid nitrogen system.

The filter and its associated liquid nitrogen cooling system has been installed in beam

22
hole CT-W of the reactor along with Its associated collimator and water shutter. A mechanical rotating shutter using heavy me t (density ~18 g/cm ) to stop the beam has also

been installed.

The four rotor phased chopper system has been completed and is in the final stages

of testing. The system consists of two concentric counter-rotating rotors in a single vacuum housing and two rotors in a second housing with their axis displaced so the rotors overlap each other by about four inches. The concentric rotors chop the incident beam

into bursts of neutrons which spread out in time as they travel the one meter flight path

to the second pair of rotors. The second pair of rotors then selects a particular neutron

energy depending on the relative phase between the first and second pair of rotors. The rotors are solid aluminum discs, 24" in diameter, 2" thick at the hub and tapering to 1/8"

at the periphery. In order to get the shortest burst of neutrons possible for a given slit

width, it is necessary to have the chopping faces of the final rotor pair as close as possible. Since they are tapered, the off-set axis system is used. The rotors are driven

by two phase synchronous motors at 12,000 rpm by a single high stability oscillator. The

oscillator signal is sent through four channels which contain power amplifiers. Vector

resolvers in each channel allow the phase of each rotor to be independently controlled.

The slits on the rotors are defined by a thin layer of gadolinium and epoxy. Each rotor

has several slits of varying width. The slits are arranged in such a way that burst time,

choice of one or two bursts per revolution, and neutron energy can be selected simply by

changing rotor phase. The choices of final burst width are 6.5 us, 13 \xs and 26 as FWHM. Spin testing of all rotors to 13,000 rpm has been completed and two rotors have been

successfully phased. The measured phase jitter over periods of hours is between one and

two microseconds full width at half maximum. The chopper system will be installed at the reactor within the next few months.

The detector bank consists of 24 groups of five BF„ detectors each. The detectors are

1" diameter by 18" active length and filled to 170 cm Hg. Normally there will be three

groups of detectors at each angle yielding eight angles between 10° and 100° from the beam

direction. The detectors will be shielded by a completely closed room with one foot walls

of hydrogenous material lined with boron carbide. The room will be mounted on air pads so

it can be easily moved to provide access to the chopper system. The detectors have all

been checked out and the frame to support the detectors designed. The design of the shielding room has been completed and construction will begin shortly.

During this reporting period, programs for use on the Univac 1108 computer have been

developed to provide preliminary reduction of data. These programs have been

extensively tested from data obtained on the TMC TOF analyzer and found to be generally

satisfactory. Additional development to improve their efficiency is planned.

23
Cold-Neutron Source

R. S. Carter, E. M. Guglielmo, and L. A. deGraaf

The NBS reactor includes a special port, 22" in diameter, which penetrates the reflector

up to the edge of the fuel elements. This large opening was designed to provide space for

the insertion of a cold neutron source close to the core. By inserting a large, low temper- ature moderator it is possible to significantly increase the available intensity of very low

energy neutrons (\>4\) which are very useful for many types of molecular dynamic studies.

The moderator will be a cylinder of D2 ice 14" in diameter by 12" long. A small amount

of H2O may be added to optimize the moderating property of the source. The source will have

a reentrant hole 4" deep by 8" in diameter for beam extraction. The hole will be filled

with beryllium which has the property of reflecting the higher energy neutrons back into the

moderator while passing the lower energy neutrons. The moderator will be maintained at 25°K

by cold helium gas passing through tubing in the moderator. The vacuum cryostat containing

the moderator will be constructed of thin-walled aluminum to minimize heating by capture

gamma rays. The cryostat will be mounted on a shielding plug and the whole assembly will

role inside a second plug and shield assembly which itself will role into the special port

of the NBSR. The shield mounted on the second plug surrounds the cryostat and consists of

about 4" of lead and bismuth which greatly reduces the gamma ray heating of the moderator.

Two 6" and two 2" diameter beams can be extracted from the cold source through the reactor

shield. One of the 6" beams will be used for the cold neutron time-of-f light facility

while the others await future development.

The helium for cooling is provided by an all helium refrigerator using a turbine

expansion engine developed by the NBS cryogenic laboratory in Boulder. It has a one kilo- watt capacity at 25°K which Is sufficient to handle the heat generated in the moderator

at twice the current reactor power.

The refrigerator is complete and operational. The lead and bismuth shield is almost

complete and should be ready for final inspection within a month. The cryostat is also

under construction and should be ready for shipment within two months. Extensive testing

of the system will be required as well as a modification of the reactor Technical

Specifications (a document defining the limits of operation of the reactor which is part

of the AEC license) . Once In place additional testing will have to be undertaken to study

the radiolysis of the ice to insure the safety of the facility.

24
Publications

"Methyl Group Rotation and the Low Temperature Transition in Hexamethylbenzene",

W. C. Hamilton, J. W. Edmonds, Armin Tippe and J. J. Rush, Disc. Faraday Soc. 192 (1969).

"Study of Molecular Reorientation in Solid Neopentane by Quasielastic Neutron

Scattering", R. E. Lechner, J. M. Rowe, K. SkHld, and J. J. Rush, Chem. Phys. Letters 4,

444 (1969).

"Crystal Structure of Hexakis (imidazole) Cadmium(II) Nitrate, [Cd (C.H.N.) ,] (NO.) „ , and

Hexakis (Imidazole) cadmium(II) Hydroxide Nitrate Tetrahydrate, [Cd (C.H.N.) ,] (OH) (N0

3

) -4H.0,

A. D. Mighell and A. Santoro, Acta Cryst. (in press).

"Crystal Structure of Nitratobis (dipyridine) Cobalt (III) Hydroxide Nitrate Tetrahydrate,

[Co(Clr.H N.).(NO) (NO.) -4H.0, C. W. Reimann, M. Zocchi, A. D. Mighell and A. Santoro,

1U o 2 2 j 2 Acta Cryst. (in press).

"Crystal and Molecular Structure of Hexapyrazole nickel(II) Nitrate, N1(C„H.N„) , (NO.) _

o h 2 o 5 2 C. W. Reimann, A. Santoro, A. D. Mighell, Acta Cryst. B26, 521 (1970).

"Quasielastic Neutron Scattering by Hydrogen in the a and 3 Phases of Vanadium Hydride",

J. M. Rowe, K. Skbld, H. E. Flotow, J. Phys. Chem. Solids (in press).

"Infrared and Raman Spectra of Sodium Bifluoride: Isotope Dilution Studies", J. J. Rush,

L. W. Schroeder and A. J. Melveger, Chem. Phys. Letters 6, 533 (1970).

"Reduced Cells", A. D. Mighell, A. Santoro, J. D. H. Donnay, Intern. Tables for X-ray

Crystallography, 530 (1969), Kynoch Press. "Determination of Reduced Cells", A. Santoro, A. D. Mighell, Acta Cryst. A2j>, 124 (1970).

"The Crystal Structure of a 1:1 Cupric Nitrate-Pyrazine Complex Cu(N0.) .• (C.N.H, )

A. Santoro, A. D. Mighell, C. W. Reimann, Acta Cryst. B26, 979 (1970).

"Absorption Corrections for Diffraction Measurements in Complex Cases, A. Santoro,

Crystallographic Computing, 283 (1970), Munksgaard, Copenhagen.

"Absorption Correction for Diffraction Measurements in Complex Cases, A. Santoro,

Computation Methods in Crystallography (Feb. 1970).

"Infrared and Raman Spectra of ClHCl" and BrHBr" Ions in CsCl'3H.0HCl„ and

CsBr-l/3H„0HBr ", L. W. Schroeder, J. Chem. Phys. 52, 1972 (1970).

"Neutron Diffraction Study of the Structure and Thermal Motion of Phosphonium Bromide",

L. W. Schroeder and J. J. Rush, J. Chem. Phys. (in press).

25
I. Interagency Collaborative Programs

Crystal Structure of the TiNi Martensite

S. Pickart and H. Alperin

(Naval Ordnance Laboratory, White Oak, Md.)

TiNi undergoes a crystallographic transformation just above room temperature associated

with a novel "shape memory" effect, in which the material, deformed in the low temperature

phase, will revert to its original shape if heated above the transition. Understanding this

phenomena requires a knowledge of the low temperature phase, which is extremely complicated.

A model has been proposed, based on x-ray diffraction measurements, in which certain shearing

motions of the atoms cause strains whose relief provides the mechanism of the shape memory.

Since Ti and Ni atoms have a very different scattering amplitude for neutrons, neutron

diffraction measurements were taken throughout the transition region, and were found to confirm the x-ray model.

Spin Canting in Rare Earth Iron Garnets (RoFecO,o)

S. Pickart and H. Alperin

(Naval Ordnance Laboratory, White Oak, Md.)

The accepted picture for the microscopic spin alignment in these technologically

important materials has been a collinear arrangement, with a net moment resulting from

unequal antiparallel rare earth and iron sublattices. However, due to the large

component of the rare earth moment arising from the orbital electron motion, it was predicted theoretically that the rare earth moment would til way from the direction of the net moment under the influence of its non-cubic local environment. These arrangements have now been clearly detected by low temperature neutron diffraction measurements in Dy, Tb and

Er iron garnets. Measurements of the degree and direction tilt obtained from these results

are shown in Table I. (0S and S

' are the angles from the [ill] direction measured toward

the [001]) . These results are in accord with theoretical predictions except for the case 3+ of Dy , for which S

i , should have been negative. These results, particularly If the latter

discrepancy can be resolved, will give further insight into the fundamental magnetic forces

acting in these materials. TABLE 1. Values of the canting angles and rare-earth

moments in iron garnets.

Angle fr 3m [ill]

Moment

mpound *8 0s' (HB)

DylG 38 3 8.8

ErIG 43 5 6.0

YbIG 40 25 1.9

26
Magnetic Structures of Transparent Fluorides

S. Pickart and H. Alperin

(Naval Ordnance Laboratory, White Oak, Md.)

Powder neutron diffraction data have been taken on two transparent fluorides, RbNiF3

and CsFeF3, that are of Interest because they possess a macroscopic magnetic moment and thus

offer the possibility of light modulation by means of the Faraday effect. These compounds

are hexagonal (BaTi03 type), with the transition metal cations, Ni 2+ and Fe 2+ located on crystallographically inequivalent sites, the 2a and 4f sites of space group P63/mmc. The

magnetic structures determined by the neutron data are ferrimagnetic, i.e. the basic

alignment of the magnetic spins is antiparallel, but since the oppositely directed spins

are located on unequal numbers of the inequivalent sites, a net resultant moment is observed. The structures consist of moments of 2.2(jb B for Ni 2+ and 4.4|j,g for Fe2+, lying in

the basal plane in RbNiF3 and tilted about 15° out of the plane for CsFeF3. This latter

result is especially interesting because it differs greatly from the easy axis observed

by magnetization measurements (about 25° from the c-axis) performed in fields of 10 Wb/m

single crystals. One thus has the unusual possibility of an anisotropic field that is field or strain dependent.

Crystal Field and Exchange Energy in Cubic Praseodymium Compounds

S. Pickart and J. Rhyne

(Naval Ordnance Laboratory, White Oak, Md.)

Susceptibility measurements indicate that PrSn3 becomes antiferromagnetic at low

temperature while Prln3 does not. Since both these compounds have the cubic order CUAU3 structure with lattice parameters differing by <1%, the speculation was made that exchange

energy (which favors ordering) and crystal field energy (favoring a nonmagnetic singlet

ground state) are delicately balanced in these compounds. To confirm the susceptibility

measurements, neutron diffraction patterns were taken, indicating a simple antiferromagnetic structure with alternating spin layers in PrSn3 and no ordering in Prln3 down to

2°K. Since the Pr^+ spin lattice structure is simple cubic, the crystal field calculations

can easily be made, so that further planned neutron measurements of the spin density distribution and inelastic energy spectrum offer a rare opportunity for detailed comparison

with theory.

27
Neutron Diffraction in Liquid Aluminum

J. Stallard

(American University, Washington, D.C., and

Naval Ordnance Laboratory, White Oak, Md.)

and

C. Davis

(American University, Washington, D.C.)

and

S. J. Pickart

(Naval Ordnance Laboratory, White Oak, Md.)

The microscopic state of a liquid is described in terms of the pair correlation

function. This function may be obtained by means of neutron diffraction. In the past the

statistical theory of the liquid state had not advanced far enough to permit the calculation

of the pair correlation. Recently, however, new theoretical approaches to this problem

have been developed which are successful in the case of the alkali metals. Hopefully these

techniques may also be applied to polyvalent metals for which pseudopotential theory applies.

In the past year measurements in aluminum have been carried out near the melting point (660°C)

and at 1000°C. The data collection has been completed, and the data are now being analyzed

for comparison with theory.

Neutron Diffraction Investigation of Amorphous Solids

G. A. Ferguson, J. Karle and J. Konnert

(U.S. Naval Research Laboratory, Washington, D.C.)

Amorphous solids give diffraction patterns consisting of a small number of relatively

weak maxima and these patterns may be analyzed to reveal information about the structural

arrangement of the atoms which comprise the solid. Early diffraction studies indicated that

in amorphous materials the immediate neighborhood of the atoms is similar to the geometric

arrangement found in crystals but order over large distances is absent. Glasses are examples

of amorphous solids and are of great importance in modern technology. Although the vitreous

state is a rare one, glasses have been formed of a variety of materials such as mixtures of

borates, phosphates and silicates.

Silica glass has been investigated extensively due to the fact that it has been considered to be a basic representative of the glassy state. In published reports of structural

investigations of vitreous silica using the neutron and x-ray techniques, discrepancies

have appeared which now require clarification before the structure of this basic glass is fully understood. A program designed to obtain a precise measurement of the diffraction

spectra (neutron and x-ray) over an extended range of momentum change of incident particle

(neutron and photon) has been undertaken. A portion of the program (i.e. the neutron diffraction spectrum) is being conducted through interagency collaboratory between The

Laboratory for the Structure of Matter, U. S. Naval Research Laboratory and the Reactor

Radiation Division, National Bureau of Standards.

28
The precisely measured diffraction spectra obtained from this program, together with

newly devised data reduction procedures, have yielded new structural information and insights

into the discrepancies alluded to previously. From these studies there is a clear indication

that a greater degree of ordering exists in the structure of silica glass than has heretofore

been supposed. Corresponding maxima have been identified beyond 10 A in the radial distribution

curves for both the neutron and x-ray diffraction experiments. This result is to be compared

with previous beliefs that such significant maxima do not exist beyond approximately 5 A. An extensive study is being carried out to determine the nature of the ordering. This

study includes an effort to construct a three-dimensional structure of partially ordered

silicon-oxygen tetrahedra which satisfy pertinent physical criteria of the glass as well as the radial distribution curves obtained from the diffraction measurements. The techniques

developed in this program will be employed in the investigation of other simple amorphous

solids.

Precision Measurement of Thermal Neutron Coherent Scattering Amplitudes

C. S. Schneider

(U.S. Naval Academy, Annapolis, Md.)

and

E. Prince

This project proposes to measure the forward coherent scattering amplitudes of several

elements as manifested by refractive bending of a thermal neutron beam incident at a few

degrees arc from a rectangular prism. The resulting bending of almost a minute of arc

is detected within a few milliseconds arc using a torsion goniometer control on the second,

analyser crystal, of a double perfect crystal spectrometer. The measured refractive bending

311816 ^

Afl *NX2 b . A9 = —

(tan<£ + cot0)

9tt where N is the atomic density, X the neutron wavelength, b the coherent scattering amplitude

and <t> the angle of incidence.

The reactor port, including collimation and shielding was first built as sketched in Fig. (1). Special care was taken to design and fabricate the internal beam collimator to optimize beam intensity and minimize stray, or background, radiation. The ^tunnel was made

quite large so that the neutron beam could reach the experimental area with essentially no scattering and the beam catcher sufficiently massive to receive the entire direct neutron

beam with negligible leakage. Finally, the detector shielding exploited the two stage

effect of thermalizing the neutrons in the outer hydrogen-rich shielding and then capturing

them in the highly absorbing boron carbide powder. The background count rate of ten neutrons

per minute achieved thus far is quite satisfactory.

The spectromter is mounted on a seven-ton base which floats upon a pneumatic suspension

yielding a vibration resonance of 1.5 Hz thus effectively eliminating all noise coming from

the floor. Other noises, coming from the surrounding air, are effectively reduced by the

spectrometer cover, a three layer box of 1/4" Aluminum, 2" styrofoam and 1/2" acoustic tile,

29
uU

4JO

ex

CO

CD U

to>>

?-< oO

60

Pn

30
from He Ne

Laser

to Fringe

Analyzer

Half -silvered J>"

Mirror -**

<f\

\

< >

R

^=»

»

Corner

Cube

Torsion

Axis

Corner

Cube

Reference Rotating

Component Component

Fig. 2. Angle Measuring Interferometer.

31
all bolted and glued together to form Insulation from both mechanical vibrations and thermal

changes, which affect the crystal and angle measuring interferometer operation.

This interferometer was used to calibrate the angle control system2 The paths of the HeNe laser light are shown in Fig. (2) and the path difference is /

n = (4R sin0)/X

which for small angles 9 yields a calibration of 0.10717 seconds arc per fringe. The angular

control of the analyser crystal was achieved using a torsion goniometer1 in which a precision

micrometer deflects the end of a glass strip eleven inches long. The resultant torque is applied to a stiff column of aluminum alloy and results in angular control with 10"^ seconds

arc over a range of 10^ seconds arc. The calibration of this micrometer-angle instrument is now being determined.

The spectrometer completed to date allows manual measurements of the neutron refracted

angles to the desired accuracy. Work continues, however, to complete the computer automation

and obtain a crystal of proper mosaic width to complete the wavelength calibration.

x The original version of this instrument is described in C. G. Shull, K. W. Billman and

F. A. Wedgewood, Phys. Ref . , 153, 1415 (1967).

2 The original version of this instrument is described in J. G. Marzolf, Rev. Sci. Instr.,

35, 1212 (1964).

32
PIcatinny Arsenal-NBS Interagency Collaboration

J. J. Rush and R. S. Carter

and

C. S. Choi, H. Prask and S. F. Trevino

(Explosives Laboratory, Picatinny Arsenal, Dover, N.J.)

This group of scientists joined the staff of the Reactor Radiation Division in early

September 1970, in a cooperative research program similar to existing effort with NOL. The

establishment of the relationship was occasioned by the shutdown of the Army reactor in

Watertown, Massachusetts, where the work had been previously carried out. The princd^iple") d

activity at the Bureau to date has involved the design of the modification required to install

the instruments of the reactor. These instruments include a triple axis spectrometer and a two axis dif fractometer, both of which will be serviced by a single beam tube. In addition, a second beam tube will be developed which will also serve two spectrometers.

The interests of the group have been in using the neutron scattering techniques in the

study of the structure and lattice dynamics of materials. In particular, those materials

which exhibit metastable properties are under investigation in an attempt to characterize

their properties and hopefully discover the cause of the instability. Neutron diffraction is an essential complement to x-ray diffraction in the structure studies, for many of the

materials are composed of both heavy and light atoms, in which case only the heavy atoms can

be located with x-rays whereas neutrons can locate both. In addition, x-rays decompose the

sample crystal in some cases so rapidly that the measurement cannot be completed. Because

of their relatively low energy (~.025 ev) neutrons with wavelengths comparable to interatomic

spacing (~1.8A.) can also be used to study the dynamics of materials while x-rays are limited

to structure studies only.

Materials other than unstable ones have also been studies and these include, for example,

polymers, hydrogen bonded systems, ionic crystals, molecular crystals, molecular liquids,

surface adsorption, crystal hydrates and metal hydrides.

33
Diffractometer Control by Computer

E. Prince

and

H. A. Alperin

(Naval Ordnance Laboratory, White Oak, Md.)

The NBS system for control of diffractometers has been in routine operation for more than

a year. The system allows the control of diffractometer experiments by sharing time on an XDS 925 computer. The computer handles the collection and reduction of data, in real time,

by means of programs written by the users in FORTRAN language. This represents a large

advance over previous, computerized control systems, which have required laborious, assemblylanguage programming.

The program for the collection of single-crystal diffraction data approaches the problem

of time utilization by making a preliminary measurement of the peak intensity in each

reflection. If this intensity is not greater than background by a statistically significant

amount, an upper limit to the possible intensity is computed, and the program proceeds to the next reflection. On the other hand if the intensity is so large that only a short counting

time is necessary to achieve adequate statistical precision, the time spent scanning a reflection is reduced by a factor of up to 6 from the standard counting interval.

The system originally controlled four neutron diffractometers and one x-ray diffractometer. During the past year additional hardware has been installed to handle a fifth neutron

diffractometer, and hardware for two more is on order. A 14 minute, 16 mm sound film entitled, "Diffractometer Control System," describing the

control system may be obtained on free loan by addressing a request to Office of Technical

Information and Publications, National Bureau of Standards, Washington, D.C. 20234. A detailed description of the system is contained in a forth coming paper.

34
Equipment Development

S. J. Pickart and R. H. Williams

(Naval Ordnance Laboratory, White Oak, Md.)

During the past year two major items of equipment have been brought close to completion,

namely the triple-axis spectrometer and the superconducting magnet.

1. Triple Axis Spectrometer

Elementary excitations of many types in solids and liquids (phonons, molecular spectra,

and magnetic spin waves) can be conveniently studied at a reactor because their energies and

wavevectors match those of thermal neutrons. An instrument to perform energy analysis of

neutrons scattered from a specimen crystal has been constructed by mounting an analyzing

crystal axis on the arm of a conventional double axis (monochromator and crystal) spectrometer—hence the name triple axis spectrometer. All of the items necessary for operation of

the spectrometer—motors, counters and shields—have been installed, including highly

efficient oriented graphite monochromators and filters. An arbitrary tracking in energymomentum transfer space (e.g. constant energy transfer, constant momentum transfer, or some intermediate mode) is desirable to optimize resolution during the data-taking process,

requiring non-linear scanning of up to five stepping motors. This procedure is performed by

a computer program, already written and debugged, executed by the on-line time-sharing

spectrometer control system. Inelastic scattering measurements will begin as soon as additional shielding for the top of the drum (to lower the fast neutron background) and an extended beam stop (to allow for variable incident energies) are installed.

2. Superconducting Magnet

Many as yet unexplained magnetic transitions, particularly in the rare earth metals,

occur in high magnetic fields (~10.0 Wb/m2) that are comparable to the exchange and anisotropy

forces acting in these materials. To study the detailed nature of the magnetic spin structures

in these high-field phases, a superconducting magnet has been designed for neutron diffraction

work. It must be of the helmholtz split-pair configuration to provide 360° radial access for

the incident and scattered neutron beam. The magnet coils are suspended in an outer dewar

containing liquid He, while the sample is placed in an insert dewar extending through the

bore of the coils that is temperature controlled from 4.2°K to room temperature. The

individual coils for the helmholtz pair have been wound and tested, the magnet and insert

dewars are on hand, and the magnet support assembly and coil form are in the final stages

of construction. When completed, the magnet will operate at 100 amps to provide a field of

10.7 Wb/m^ in a one-inch gap with 1-3/8" bore. An additional feature is the winding of the coils

in concentric pairs, allowing for removal of the inner set to provide a 6.0 Wb/m^ field in a 3" bore, if desired for larger samples (e.g. magnetic polycrystalline, amorphous or liquid

materials)

35
Publications

"A Time Shared Computer System for Dif fractometer Control", H. Alperin and E. Prince,

J. of Res. NBS, 74C, No. 3, 4, 89 (July-Dec. 1970).

"Neutron Diffraction Investigation of Vitreous Germania", G. A. Ferguson and M. Hass,

J. of the Amer. Ceramic Soc . (Feb. 1970).

"Magnetic Properties and Structure of GdN and GdN.. ", R. Gambino, T. McGuire,

H. Alperin and S. Pickart, J. Appl. Phys. 41, 933 (1970). "Rare Earth Sublattice Canting in DylG, ErIG and YbIG", S. Pickart, H. Alperin, and

A. Clark, J. Appl. Phys. 41, 1192 (1970).

"Physical Properties of Sulfide Materials", (Invited paper), S. J. Pickart, Mineral. Soc. Amer. Spec. Pap. 3^ 145 (1970).

"Magnetic Structures of Ferrimagnetic RbNiF„ and CsFeF ", S. J. Pickart and H. A. Alperin,

J. Appl. Phys. (in press).

"Mechanism of the TiNi Transition and the Crystal Structures of the TiNi-II and TiNi-III

Phases", F. Wong, S. Pickart and H. Alperin, J. Appl. Phys. (in press).

36
C. Non-Division NBS Programs

Activation Analysis Section: Summary of Activities

P. D. LaFleur and D. A. Becker

(Analytical Chemistry Division)

The Activation Analysis Section of the Analytical Chemistry Division is located in the

NBS Reactor Building and is one of the major users of the NBSR irradiation facilities.

Complete coverage of the section's activities may be found in it's annual progress report

therefore only a brief summary will be included here.

In the past year, a study of the operating characteristics of the NBSR irradiation

facilities was made, and experimental results reported for neutron flux measurements, and

sample temperature and pressure increases under irradiation. These measurements were made

in the four pneumatic tube facilities and the vertical thimble long term irradiation facility.

A large number of analyses of various kinds were made by the members of the section. Two sample materials of special interest were the Trace Elements in Glass Standard Reference

Material (SRM) and the Trace Elements in Orchard Leaves SRM. Techniques used included both

nondestructive analysis using large volume Ge(Li) detectors and analyses employing chemical

separations. In addition, the nuclear track technique, in which radiation damage "tracks"

from charged particles either from (n,p) or (n,or) reactions in a plastic detector are counted, was used for boron and uranium analysis.

Other work by the section included use of a Cockcroft-Walton neutron generator for 3 MeV

and 14 MeV neutron activation analysis, and use of the LINAC for photon activation analysis.

Also, eight recently acquired californium-252 neutron sources are presently being evaluated

for potential activation analysis use. Data handling and reduction systems include a computer program, ALSPIS, for peak finding

and integration using the UNIVAC 1108, and development of applications of a minicomputer for

activation analysis.

Atomic Constants from X-ray and Positronium Decay y-ray Measurements

R. D. Deslattes, W. C. Sauder, J. A. Hammond and A. Henins

(Optical Physics Division)

From the general expectation that coupled scanning interferometers would work and on

the other hand from some fairly sophisticated expectations on the behavior of positronium

under strong Zeeman perturbation in low temperature helium, we have developed a large and

potentially interesting program of measurement. We expect to measure h/mc to between 1 ppm

and 0.1 ppm with relative ease. This will allow inference of the fine structure constant to between 5 in 10 7 and 5 in 10 8

. Within the past year, precision indices have been established for all major components

of this exercise. In addition, a controlled environment chamber has been established in an

area at the NBS reactor where we can expect to handle the multi-kilo-Curie source required

in the h/mc measurement. Scanning interferometry has been shown to go with noise levels of

37
the order 0.01A. Angle measurement noise has been reduced to about 10 micro arc sec. Density determinations are going at 0.1 ppm. There are both scientific and technological spin-offs from this work. For technology

there are obvious gains from meaningful experience in small distances and small angles. For science, the absolute Y" ray wavelength facility offers the chance for measurement of

such reference wavelengths as will be of special use is mesic x-ray wavelength determinations.

These, in turn, will lead via a presumed validation of electrodynamics in the case of

u-mesic x-ray from whose energies have been subtracted such contributions as follow from the

Coulomb interaction.

Intense Fission Neutron Source

James A. Grundl

(Nuclear Radiation Division)

235 An intense U fission neutron source is under joint development by the National

Bureau of Standards and the Los Alamos Scientific Laboratory. A preliminary arrangement

for reproducible irradiations inside of the NBS Research Reactor thermal column is complete

and a measure of the source strength has been obtained. Such a spectrum is a natural and

relevant source of fast neutrons and, with a calibration based on well-studied thermal

neutron parameters, it provides a base for activation detector calibration and fast-neutron

cross section validation. An initial application of the fission source was carried out under the auspices of the ASTM Subcommittee on Neutron Dosimetry. In April 1970, some dozen

laboratories determined the responses of sulfur, aluminum, and fission track detectors exposed

to the fission source operating at 5 x 10^ neutrons/second, a limit necessitated by

rudimentary source handling techniques. Results from the participating laboratories indicate

disagreements which justify additional efforts in this area. The matter was discussed

at the Washington meeting of the American Nuclear Society in November 1970.

38
Parity Violation in Strong Interactions

J. L. Albert and R. Wilson

(Harvard University, Cambridge, Mass.)

and

G. Scharff Goldhaber

(Brookhaven National Laboratory)

and

I. G. SchrSder

(Nculear Radiation Division)

A program to study parity violation due to the weak interaction in the overall nucleonnucleon interaction (weak forces between nucleons) is underway in collaboration with Harvard

University and Brookhaven National Laboratory.

According to the current-current theory of weak interactions proposed by Feynman and

Gell-Mann the weak interactions may be expressed as a current-current interaction analogous

to the electromagnetic interaction. Unlike the electromagnetic current, which is purely

vector, the weak current is the sum of a vector and an axial vector part giving rise to parity violating interactions. The weak current, according to Feynman and Gell-Mann, is composed of two leptonic terms (j e and j , electronic and muonic, respectively) and two hadronic terms (j n

and j s

, non-strange and strange) which lead to a series of terms in the

current-current interaction some of which have been observed. Thus, for instance, j , j

"*"

is the term that gives rise to the leptonic decay of the muon, j nj e+ is the ordinary betadecay term, and j njg gives rise to nonleptonic decays of the strange particles. The theory

also predicts the existence of the following three terms j e j e+ , j nj n+ ; the first gives rise

to neutrino-electron scattering while the last two give rise to the parity non-conserving

effects which are of interest to the present program, i.e. nuclear states are no longer

eigenstates of parity and small parity impurities can be expected.

The reaction we are studying is^^Cd (n, Y) Cd and in particular the transitions in

^Cd from the 9.04,1+ state to the + ground state and the .56 MeV 2+ state. Both these

are regular parity conserving Ml transitions. The partity non-conserving part is El. The

admixture of the parity non-conserving part is measured by detecting the circular polarization

of the emitted gamma rays from these two transitions. The circular polarization is proportional

to El/Ml. In Cd due to a favorable nuclear structure this ratio is ~500 F where F is the

ratio of the strength of parity non-conserving and conserving potentials. Taking F ~10~° to

10" gives an effect anywhere between 5 x 10"^ to 5 x 10"^.

The apparatus consists of a Cd target at the center of GT-2 in the NBSR. The gamma beam

is collimated and passed through a transmission compton polarimeter with an analyzing

efficiency of ~10%. The beam is recollimated and detected by a 4" x 5" sodium iodine crystal

appropriately shielded from magnet influences. Hence our count rate change at the detector

is anywhere between 5 x 10"^ to 5 x 10" . We expect to detect 10^ gammas/sec in the two photopeaks of the interesting gamma rays. Hence we are just sensitive to the minimum expected

effect in 50 days.

39
3 Fast Neutron He Spectrometer

J. C. Glynn

(University of Maryland, College Park, Md .

)

and

I. G. SchrBder

(Nuclear Radiation Division)

In collaboration with the University of Maryland the resolution, efficiency and use of

-%e semiconductor spectrometers as fast neutron spectrometers in the energy range between

500 keV and 1500 keV have been investigated. Such a spectrometer has been used in conjunction

with a specially designed collimator in an attempt to measure the fast neutron distribution

in the core region of the NBS reactor. This has been accomplished by placing a scattering

sample in the core, and collimating a beam of scattered neutrons directly into the spectrometer.

The use of different scatterers enabled a determination of the spectrum in the anisotropic

neutron field. The perturbation of this spectrum by the collimator and scatterer could not

be accurately determined; however, the present program has succeeded in measuring the

perturbed scalar flux in the core region and has provided a known fast neutron spectrum

which can be used to test and calibrate other neutron spectrometer systems.

Two-Photon Emission in (n,p) Capture

B. T. Chertok

(American University, Washington, D.C.)

and

J. L. Alberi

(Harvard University, Cambridge, Mass.)

and

I. G. SchrOder

(Nuclear Radiation Division)

A search for two-photo emission in thermal (n,p) capture is being conducted with the

aim of establishing the probability of occurrence of this process in an effort to help

explain part of the apparent discrepancies between the measured and calculated values of the

thermal (n,p) capture cross section. To detect the possible emission of two photons in

radiative (n,p) capture two Nal(Tl) detectors, mounted on fast photomultiplier tubes, were

placed 180° with respect to each other with an H2O target between them, and 90° to a neutron

beam. (The neutron beam has a better than 4000 to 1 cadmium ratio for a detector with a 1/v response and is obtained by total neutron reflection down a 4.5 meter long 1 cm diameter

Ni coated glass tube.) The simultaneous emission of two photons is ascertained by a fast

coincidence circuit, with a time resolution FWHM of 2 nsec, composed essentially of two constant fraction timing discriminators and a time-to-pulse-height (TAC) converter and a slow triple coincidence circuit (30 nsec resolving time) which demands coincidence between

the pulse heights from the two detectors and the TAC. The gate from this "fast-slow"

coincidence system triggers a linear gate which allows the pulse-height distribution from

40
one of the detectors to be recorded in a 100-channel pulse-height analyzer. In order to measure the two-photon effect the gated spectra are compared with normalized ungated spectra

to eliminate the effect of chance coincidences, and with gated spectra obtained with an identical D2O target to account for the oxygen in the hydrogen target.

Decay Characteristics of Krypton Isotopes

F. J. Schima

(Nuclear Radiation Division)

A program has been initiated into the investigation of the decay characteristics of

the isotopes of krypton.

Aluminum foils containing °^Kr ions implanted by the isotope separator were irradiated

in RT-4 of the NBS reactor for periods up to 4 hours. The decay characteristics of the

85mKr produced have been studied. The half-life was found to be

4.557 ± .029 hr

and the y-ray energies were found to be

151.0 ± 0.2 keV and 304.8 ± 0.1 keV.

The half-life is significantly longer (3.4%) than the accepted value in the literature.

An ultra pure iron foil containing implanted 8®Kr was irradiated to produce S^^r.

The decay characteristics determined were

t . = 13.29 ± .06 sec

E = 190.663 ± .046 keV. Y

Further work in progress on the investigation of krypton decay parameters include the

production in the NBS reactor of TMKr as well as an attempt to produce detectable quantities

of 200,000 year ^lg^r. This is being accomplished by a long term irradiation of isotopically

enriched 80Kr gas in the reactor gap where the thermal neutron flux is approximately

1.7 x 10 14/cm2 sec.

Nuclear Orientation Studies of ** 2Br

A. T. Hirshfield, D. D. Hoppes, W. B. Mann and F. J. Schima

(Nuclear Radiation Division)

Samples of ° 2Br produced in the NBS reactor were implanted in iron foils with the

isotope separator of the Radioactivity Section. These samples were used to cryogenically

orient the ° 2Br nuclei and measure the beta- and gamma-ray angular distributions with respect

to the nuclear spin direction. A preliminary report of the approximate effective magnetic

field for bromine in iron, the fraction of nuclei experiencing the full field, and sign of

the magnetic moment of 82gr was given at the International Conference on Hyperfine Inter- actions Detected by Nuclear Radiation, Sept. 6-11, 1970, at Rehovot and Jerusalem, Israel

and is being published in the Conference Proceedings.

41
Further bromine bombardments are anticipated to /determine the effect of lower

implantation concentrations and to measure the E2/M1 mixing ratios for 5 gamma rays occurring in the decay. Other activities of immediate interest for orientation studies are 86rd and 186,188Re#

42
Publications

"Proceedings of the IVth Annual Conference on Trace Substances in Environmental Health",

D. A. Becker, P. D. LaFleur, Production and Certification of NBS Biological Standard Reference

Materials (in press)

"Determination of Trace Elements in Glass by Activation Analysis using Hydrated

Antimony Pentroxide for Sodium Removal, T. E. Gills, B. A. Thompson (in press).

"Determination of Oxygen in Sodium by Photon Activation Analysis, G. J. Lutz, Anal.

Chem. 42, 531-32 (1970).

"The Determination of Carbon in High Purity Metals by Photon Activation Analysis,

Anal. Chem. 42, 948-50 (1970).

"Proceedings of the Symposium on Nuclear Techniques in Measurement and Control of

Environment Pollution", W. F. Marlow, P. D. LaFleur, Standard Reference Materials for the

Analysis of Environmental Samples, Salzburg, Austria, October 26-30, 1970 (in press).

"Proceedings of the International Atomic Energy Topical Meeting", S. S. Nargolwalla,

Sources and Evaluation of Systematic Errors in Neutron Generator Activation Analysis,

Budapest, Hungary (May 1969).

"Proceedings of the American Nuclear Society Topical Meeting - Radiation and Isotope

Technology in Latin American Development", S. S. Nargolwalla, P. D. LaFleur, Characterization

of Standard Reference Materials for Industry and Research by Neutron Generator Activation

Analysis, San Juan, Puerto Rico, May 1969, 183-86 (1970).

"Experimental Sensitivities for 3-NeV Neutron Activation Analysis, S. S. Nargolwalla,

J. Niewodniczanski, and J. E. Suddueth, J. Radioalal. Chem. 5, 403-23 (1970).

"Photon Self-Adsorption Corrections for the Minimization of Systematic Errors in 14-MeV

Neutron Activation Analysis, S. S. Nargolwalla, M. R. Crambes, J. E. Suddueth, Anal. Chem. Acta 42, No. 3, 425-36 (1970).

"Extraction Studies of the Group IIB-VIIB Elements and the Lanthanides Utilizing

bis(2-Ethyl-Hexyl) Orthophosphoric Acid, I. H. Qureshi, L. T. McClendon, and P. D. LaFleur,

Radiochimica Acta 12, No. 2, 107-11 (1969).

"Proceedings of the NATA Advanced Study Institute on Activation Analysis in Geochemistry

and Cosmochemistry", H. P. Yule, Computer Data Reduction in Activation Analysis, Kjeller,

Norway, September 7-12, 1970 (in press).

43

REACTOR OPERATIONS AND SERVICE PROGRAMS
In the past year, the NBS reactor has become fully operational. All required reactor

testing was satisfactorily completed. Application for a full term license was made to the AEC. Test results and reactor performance analysis were presented before the Advisory

Committee on Reactor Safeguards which considered the application in March 1970 with favorable

recommendations. A full term 15 year license was issued by the AEC in June 1970.

A. Operating Statistics

During this period more than 6,000 hours of reactor time was provided to users. This

is equivalent to about 60,000 megawatt-hours of energy produced. Currently the reactor is

operated at the maximum rated power of 10 Mw on continuous a-round-the-clock basis about

two thirds of the time. This schedule permits operation with minimum staffing. Reactor

performance to date has been excellent. Efficiency and time utilization was very high.

Very little time was lost due to malfunctions or unscheduled shutdowns. A summary of

operating statistics is presented in the following table.

NBSR Operation Summary

November, 1969 - November, 1970

Reactor Operations to date 78213.3 Mwh

Reactor Operations for year 59186.0 Mwh

Hours of Operation 6000

On-line time at 10 Mw 677. Number of fuel elements used 44

Average U-235 burnup 34%

Number of Refueling Operations 11 Number of Unscheduled Shutdowns 3 Number of Visitors 4000

B. Operating Summary

The NBSR core employs 30 fuel elements arranged in three hexagonal rings. An inner

ring composed of six elements, a middle ring which accomodates another six fuel elements

and six experimental thimbles and an outer ring of 18 fuel elements. The initial NBSR core was composed of 23 elements of 170 gm U-235 each and seven elements of 205 gm U-235 each. As operations progressed and new fuel was needed the lighter 170 gm elements were substituted

by the heavier 205 gm elements to gain more operating lifetime. The 170 gm elements provided

an average operating lifetime of about four days (length of cycle divided by the number of

elements replaced by fresh elements to achieve the cycle length) . The heavier 205 gm element

increased the lifetime time to more than six days. More recently even more heavily loaded

elements containing 250 gm of U-235 were fabricated. These elements have just been

introduced into the reactor and it is anticipated that they will improve the operating lifetime to as much as nine or ten days per element. The use of more heavily loaded elements was made possible by improved fuel fabrication technology and by special safety analysis

leading to the development of a fuel rotation plan that permits their utilization in the NBSR.

44
The distinct advantage of using heavier elements which more than double the average element

lifetime is reflected by a substantial fuel economy which is especially significant at a time when fabrication, shipping and reprocessing charges are escalating. In addition

reactor downtime for refueling is considerably reduced.

The NBSR fuel rotation plan utilizes a system whereby the most depleted elements

located in positions of highest flux in the center of the core are removed from the core

for replacement. Then the remaining elements are moved in turn from positions of lower

power burnup to positions of higher power and burnup . Fresh elements are then inserted

on the outside of the core into positions of low power. Normally four elements are exchanged each operating cycle. This fuel rotation plan has the advantage of maintaining

essentially the same fuel element history for all operating cycles thereby preserving as nearly as possible the same flux shape and distribution for reactor users. Also it is a good method for limiting core reactivities, and for reducing power peaks and spikes as well as for achieving near optimum fuel burnup rates. Initially fuel burnup was less

than 19% for light elements but continued to improve and reach about 40% by use of heavier

elements. Last year approximately 3.2 Kg of U-235 were consumed representing an average

burnup of almost 34%.

During the reactor checkout and testing program, most results were almost as predicted

by calculations and analysis, and the entire program as well as reactor operations proceeded

smoothly. Throughout, the reactor and its systems functioned almost flawlessly. Results

of two tests merit special mention because of future possibilities of the methods used.

One test was measurement of the power distribution in the core, and the other was fuel

plate temperature measurements of an uncooled fuel element a short time after shutdown

from power.

Initially, power distribution measurements were made by irradiation of cobalt and

tungsten wires strung along fuel plates of a number of fresh fuel elements in representative

positions in the core. The wires were activated at low power (about 400 watts), then counted

on a wire scan. Normalized activities obtained from counting yielded the relative flux and

hence power distribution in the clean core. Measured flux values when compared to calculations

showed very good agreement even though the calculations tended to be a little more conservative,

For the six elements in the innermost ring the area of highest flux calculated values were

about 5% higher than measured. For 18 elements in the middle and outer rings calculated and

measured values were almost identical. For the six corner elements (the lowest power elements)

calculated values were about 10% lower than measured. Thus use of calculated power in

thermal and safety analyses would be on the conservative side.

45
Power distribution measurements were repeated using a different technique - that of

gross gamma counting of fuel elements. The relative power generation as a function of

element position is determined by measuring the gross fission product activity for each

element shortly after shutdown from full power using a gamma ion chamber in a fixed

location. This method is particularly useful after operations when highly irradiated

fuel is involved and flux wires cannot be inserted and because of the ease and quickness by

which it is performed. The method proved very successful and the results were excellent.

Agreement between the flux wire and gamma scanning techniques was very good with less than

2% differences observed for most elements. For this reason the gamma scanning technique is currently being routinely utilized to measure the power distribution in the core and to determine fuel burnup and coolant flow requirements.

One of the license requirements for the NBSR is that fuel plate temperatures may not

exceed 800° F at any time during fuel element transfer including the normally used completely

dry and uncooled transfer method. For this reason it was necessary to measure the maximum

temperature reached by the fuel elements during the process of remotely transferring spent

fuel elements from the reactor to storage facilities in the pool. Since the NBSR fuel

transfer system design, which is confined and completely enclosed, did not permit the

attachment of thermocouples to the fuel plate itself, infrared pyrometry techniques were

devised to remotely measure the fuel plate temperatures. In addition to confirming that

the NBSR fuel elements always remained at safe temperatures (maximum was 535° F) , the

development of this technique has provided a generally useful method for studying fuel element

temperatures in a highly radioactive environment.

Over the year numerous improvements, additions and innovations were incorporated into

the NBSR systems. Some of these are itemized below.

1. Design and installation of new irradiation facilities. Because of the increased

demand on existing facilities, four new irradiation facilities were designed. One,

a long term water cooled irradiation facility is already installed and operational.

The remaining three are in the process of being fabricated for installation and

testing in the near future.

2. The existing four pneumatic irradiation facilities were extensively modified to provide for a more efficient, more reliable and leaktight system. All of the

jointed aluminum flight tubes were replaced by a single continuous newly developed

armored polyethylene tubing. The senders-receivers and all control boxes were

replaced by advanced types developed in-house that provide for simpler, smoother

and trouble free operation.

3. Design and installation of cooling tower bypass valves that permitted remote and

automatic secondary system water temperature control.

4. Design of an automatic acid injection system for secondary system water chemistry

and quality control.

5. Installed bulk liquid CO2 supply system that resulted in substantial cost savings

as well as eliminated handling of individual CO2 bottles.

46
6. The helium sweep system blowers were completely redesigned to improve their

reliability and effectiveness and to provide for better and easier maintenance.

The old system was susceptible to self-induced corrosion and to contamination

by lubricant and was replaced by sealed stainless steel units. In addition

specially designed cold traps were added to the system to remove and recover DoO moisture. This permitted dry helium gas to be supplied to the fission product

monitor and eliminated the problem of the monitor continuously saturating due to moisture. Also dry helium facilitated recombination of radiolytic gasses present

in the sweep system.

C. Summary of Service and Service Programs

Extensive use was made of the reactor in-core irradiation facilities. More than 1,500

irradiations involving almost 10,000 samples were made during the year. These include a wide variety of research and application programs ranging from biological and medical studies

to activation analysis programs, radiation effects studies and the production of numerous

radioisotopes. More detailed reports of some of this work are presented below. Other programs

not described in detail include radiation effect studies of numerous semi-conductor materials

for the Naval Research Laboratory, irradiation of crystals for Catholic University, and air

pollution studies for Rensselaer Polytechnic Institute.

Numerous other irradiation programs for outside organizations are presently being

planned and evaluated which will contribute significantly to the increase of service programs

over the coming years.

47
Trace Constituents of Geological Materials

J. J. Rowe and L. P. Greenland

(U.S. Geological Survey, Washington, D.C.)

The Radioactivation and Radiochemistry project of the Analytical Laboratories Branch,

Geologic Division, U.S. Geological Survey has been using the NBS Reactor facility since

July 1970. This project has been developing and applying activation analysis methods for

the determination of trace constituents in geologic materials. These analyses are utilized

in geochemical studies of magmatic crystallization-differentiation, post-magmatic alteration

and the mechanism of ore deposition.

Platinum, palladium and gold are being determined at the low parts per billion

concentration for Heavy Metals Program, to study background levels and magmatic fractionation.

Platinum and palladium are preconcentrated by fire assay. After irradiation of the silver

bead, platinum and palladium are separated radiochemically for beta counting (Rowe and

Simon, Talanta, in press). Gold is determined on a one gram sample without preconcentration,

using fire assay for the radiochemical separations (Rowe and Simon, USGS Circular 599).

Greenland is studying the distribution of iridium in various magmatic provinces, using triple

coincidence and radiochemical separations (Greenland, Rowe and Dinnin, USGS Annual Review,

in press) . Rowe is developing methods for the determination of osmium and ruthenium

Rowe is studying the transport of gold by thermal waters as a possible mechanism for

the deposition of gold. He is developing a method wherein gold is collected from the water

onto an ion exchange resin. The resin is subsequently irradiated for the determination of

gold by activation analysis.

The determination of low concentrations of rare earths are valuable for studies of

magmatic crystallization-differentiation. Both radiochemical and instrumental methods are being developed for the determination of rare earths (Rowe and Greenland)

.

Greenland is preparing for studies of the distribution of tantalum, hafnium, antimony

and tungsten in lunar samples.

Simon is studying the distribution of tungsten and chromium in coexisting minerals of

the California Batholith.

Other elements which are being determined by activation analysis are: Sc, La, Cr, Th,

As, Hg and Se in various geologic materials.

48
Activation Analysis Program of the Food and Drug Administration at the NBSR

J. T. Tanner and M. H. Friedman

(Food and Drug Administration, Washington, D.C.)

1. Hydrofluoric Acid in Rust Stain Removers for Household Use. The Food and Drug Administration is responsible for regulation of safety of household products. Among the problems is that of determining the concentration of hydrofluoric

acid in rust stain removers. Activation analysis provided a most effective and rapid means

for the purpose through measurement of the fluorine content.

2. Bromine Distribution in Test Pigs for Toxicological Studies.

Bromine provided a convenient index of the distribution of a bromine-containing

material in the organs and tissues of pigs which were fed the material for evaluation of its

toxicity. Because of the sensitivity and the large number of analyses required as well as the time involved in conventional methods, neutron activation analysis was especially well

adapted for determination of bromine in the test samples (pig heart, liver, kidney, tissues,

etc.).

3. Fluorine in Bone Meal. Bone meal as a potential source of fluorine to replace or supplement fluoridated

water in the diet obviously must contain a significant but not excessive fluorine concentration. Neutron activation analysis was used as a most convenient and rapid method for

estimating fluorine in bone meal products.

4. Mercury in Foods.

Mercury has become of primary concern as an environmental contaminant. Because of

its great sensitivity and reliability in conjunction with radiochemical separation techniques

neutron activation analysis is particularly well suited for determination of trace concen- trations of mercury in such a complex matrix as food. Of special significance is the

elimination of the major problem of mercury impurities in reagents as interferences in trace level determinations. A variety of food categories has been examined in collaboration

with Dr. David Lincoln of the Food and Drug Administration.

49
Neutron Activation Analysis in Scientific Crime Detection at IRS

M. J. Pro, C. M. Hoffman, K. B. Snow and W. D. Washington

(Internal Revenue Service, Washington, D.C.)

The Internal Revenue Service started to use the National Bureau of Standards reactor

facilities July 1, 1970, and since that time the chemists have been involved in the irradiation

of elemental standards and fluxmonitors for use in the quantitative analysis of trace elements

found in physical evidence specimens. Also, a large number of irradiations have been carried

out in connection with actual case work. This involved a large variety of sample matrices

and some of the more frequently irradiated types of material are shown below:

1. Gunshot Residue - This determination involves the detection and measurement of

barium and antimony deposited on the web of the hand of an individual who fired a gun. The

residue is removed from the web of the hand with a cotton-tipped swab or with paraffin and

the barium and antimony (from the primer) in the irradiated material are separated by simple

radiochemistry and measured. This technique has been primarily used in suicide and murder

cases

.

2. Soil - Many soil samples have been irradiated to determine elements that are not amenable to analysis by chemical methods and atomic absorption analysis. Through the use

of neutron activation analysis and other techniques, approximately 25 elements are quantitatively measured In soil and this information is used to compare soil from an unknown source with soils from a specific location.

3. Bomb Associated Residues - In connection with the Organized Crime Control Act of

1970 - Title 11, material such as tape, metals, paints, and etc. recovered from a bomb

scene are compared by neutron activation analysis to similar material in a suspect's

possession. The use of neutron activation analysis in this type of work is extremely helpful

since many of these samples are very small in size.

4. Illicit Distilled Spirits - Moonshine seizures are routinely compared to products

obtained from illicit distilleries by neutron activation analysis and other techniques.

Again, neutron activation analysis offers the potential for measuring elements that cannot

be measured by techniques such as atomic absorption analysis and spectrography . In addition,

physical evidence such as soil, paints, metals, and etc. are also submitted in illicit

distillery cases and the comparison of these materials very often is used in preparing

evidence in conspiracy type cases. It is also significant to note that the successful

prosecution of illicit distillery cases reduces the government's tax loss ($10.50 proof

gallon) by helping cut down the number of illicit distilleries or by actual assessing of

the violator.

In the area of research, the Internal Revenue Service chemists involved in the neutron

activation analysis program are continuing their studies to determine trace elements in lead

bullets. This type of examination is particularly useful when the comparison of bullets by

microscopy fails due to the lack of sample or the mutilation of the questioned bullet. Other

research activities involving the incorporation of high cross section elements into materials

such as inks, pencil leads, and paper in connection with the Intelligence and Audit activities

of the Internal Revenue Service are continuing.

50
Federal Bureau of Investigation Activation Analysis Program

G. Mahoney, J. Kilty, J. Riley

(Federal Brueau of Investigation, Washington, D.C.)

Variety characterizes the specimens received for analysis in the FBI Laboratory. The

forensic laboratory often has little or no control over the size, shape or condition of the

specimens presented for analysis. These factors must be considered along with the physical

and chemical properties of the specimen when the methods of analysis are evaluated.

Generally neutron activation analysis does not place restrictions as far as size is concerned. It affords a very reliable quantitative analysis for many of the elements

constituting the questioned specimen. The fact that many times the technique is non-consuming

makes it the method of choice for an element determination in many cases where the integrity

of the specimen must be preserved. Neutron activation analysis is the best method available

for detecting and quantifying microgram quantities of antimony and barium on the hands of a person who is suspected of having fired a handgun.

U.S. Post Office Department Activation Analysis Program

A. W. Somerford and J. B. Upton

In recent years one of the most effective tools of forensic science used by the Chief

Inspectors Department of the U. S. Postal Service has been neutron activation analysis.

The ability of this nuclear method to detect traces of elements in minute samples enables

it to solve many problems of identification that have heretofore been considered impracticable.

The Chief Inspectors Department has regularly used the NBS reactor in its crime investigation program since July 1, 1970. The analysis program deals with fine detailed examination

of physical evidence, involved in some 2000 post office burglaries yearly, bomb parcel

mailings, poison impregnated candies and cakes sent through the mail, and the tremendous

increase in the mailing of narcotics and dangerous drugs, among others. Among the items

analyzed, so far, are metal particles, glass fragments, refractories, hair, soil, wood,

petroleum products, poisons, bomb fragments, and items used in bomb mailings.

Inspectors and scientists of the Chief Inspectors Department, U. S. Postal Service,

have regularly testified in numerous cases on evidence discovered by neutron activation

analysis. The method has proven to be extremely valuable In the solution and control of

illegal activities and crimes and in providing substantial proof in court cases. The

jurists of the Sixth U. S. Circuit Court of appeals, Northern District of Ohio, Eastern

Division, decided October 29, 1970, the validity of Neutron Activation Analysis by affirming

the lower court conviction.

51
Role of Trace Metals in Bone Healing

G. C. Battistone

(U.S. Army Institute of Dental Research

Walter Reed Hospital, Washington, D.C.)

The U.S. Army Institute of Dental Research is currently engaged in studies of means of

accelerating wound healing. One aspect of these studies is the role of trace metals in bone

healing. A successful outcome in this work could be of considerable value with respect to improved patient care and morale and significant savings in time and money. Thus far

investigations have indicated that appropriately administered zinc can significantly

accelerate bone healing in experimentally injured animals. Manganese has also been shown

to have a small effect. Work has just begun during the past year on the role of copper in

wound healing. The analytical portion of this study is being conducted by neutron activation

analysis at the National Bureau of Standard's reactor using a technique developed at USAIDR.

Copper chelates administered daily by i.p. injection to experimentally injured animals have

demonstrated toxic effects which have necessitated changes in dosage levels and experiments

are now in progress which indicate that toxicity has been eliminated. Preliminary analysis

of copper values obtained for various tissues before and after the trauma of bone injury

and during the healing process indicate a profound change in copper metabolism due apparently

to a characteristic stress reaction. No conclusions have been reached as yet regarding

the ability of copper chelate treatments to favorably alter copper metabolism during bone

healing or to accelerate the healing process.

Study of Fission Product Gamma Ray Spectra

D. Lightbody and T. Dempsey

(Teledyne Isotopes, Westwood, N.J.)

The 10 megawatt research reactor facility at the National Bureau of Standards was used

as a high flux source of fission spectrum neutrons. This program, sponsored by ARPA under

Contract DA-01-70-C-0040, is mainly concerned with the study of gamma ray spectra resulting

from the decay of fission products. These fission products result from the neutron-induced

fission of enriched metallic targets of 235{j, 239pU) and 238u. In addition to fission

spectrum neutrons 14 MeV neutrons and thermal neutrons have also been used to induce fission.

Of primary concern to this program is detailing the relative differences observed in the gamma ray spectra for the above mentioned targets and neutron distributions. These

differences result from variations in mass yield and independent yield distributions with

both the excitation energy and mass of the fissioning system. Additional differences

result from the variation w ith energy of the activation cross section relative to the

fission cross section for the target system of interest.

Briefly, the experiment at NBS consisted of the simultaneous irradiation of 239pU; 235U, and 238U (10 mg, 10 mg, and 50 mg respectively) using the RT-2 pneumatic tube.

Simultaneous counting of pairs of samples was performed from times as close to fission as possible (~4 minutes) . Fission product gamma ray spectra were taken periodically for up to 52
a month. The data acquisition system consisted of two high resolution Ge(Li) detectors

which were multiplexed into an 8K multi-channel analyzer. A small on-line computer aided

with preliminary analysis. Detailed analysis (gamma ray energies and intensities) was performed using a data reduction program written for the Isotopes IBM 360/30.

The data is still in the process of being analyzed. For the fission of 235jj an(] 239pu by fission spectrum neutrons, 19 mass chains representing 30 nuclides, have been identified

in the fission product gamma ray spectra. From these type of data, one is able to extract information pertaining to changes in both the mass and charge distribution with excitation

energy and initial neutron and proton number.

Direct Fission Population Measurements

P. Alexander

(Teledyne Isotopes, Westwood, N.J.)

Due to the short lifetimes possessed by fissioning nuclei it is often necessary to study

the dynamics of the fission process as reflected in the properties of the fission products.

These properties include the mass, charge, energy, angular momentum and directional distributions. Investigation of these quantities yields basic information concerning the fission

mechanism of the highly deformed, compound nucleus.

Although some features of the fission process, such as the fission yield versus mass distribution are accurately detailed, there are areas where little detailed experimental

information is available. The fission product charge distribution and isomer ratio values

pertaining to the various mass chains are examples of areas where more experimental data is required. The isomer ratio is defined as the population of the isomeric state relative to the ground state for the same nucleus. Knowledge of both isomer ratio values and the shape

of the charge distribution curves are important factors in developing a comprehensive fission

theory.

The experiments being performed at the NBS Reactor high flux pneumatic tube facility

involve measurement of the initial fission population values of the 11/2" (isomeric) states relative to the 3/2+ ground states in "3xe and *"xe. These measurements were carried out using -"U, "8u, and 239pu as target nuclei. A large number of irradiations were made

using separately encapsulated targets for bombardment with: thermal neutrons, or fast neu- trons—using a cadmium jacket around the target. After each irradiation the xenon fission

gas was removed as quickly as possible in order that the independently populated xenon

states would not be too diluted by the ingrowth of xenon from the fission chain precursors.

After the initial extraction of xenon fission gas, the xenon ingrowth from fission

chain precursors was successively milked. The gamma rays emitted during the decay of xenon

in these extracted samples were then counted using a Ge(Li) detector. After correcting for

relative efficiency and internal conversion effects the Ge detector data was analyzed using

the computer programs ISIS-1 and ISIS-2 described in Nuclear Instruments and Methods 86 (1970)

99. Using these programs "best fit" values were obtained for the parameters Zp and to which

characterize the independent charge distributions in the mass chains A = 133 and 135. This

work is supported by the Advanced Research Projects Agency under Contract DASA 01-69-C-0057

with the Defense Atomic Support Agency.

53
A Preliminary Investigation of the Mercury Levels in Chesapeake Bay Oysters

F. B. Birkner

(University of Md . , College Park, Md .

)

An investigation was undertaken to determine if mercury contamination of Chesapeake Bay

oysters is a problem now or could become a problem in future years. The important public

health questions which must be answered are: first, can oysters concentrate mercury in

their body; and second, can the mercury levels in oysters reach a level which presents a distinct health hazard to man? Until recently, the analysis for trace concentrations of

mercury in foods has been impossible, but with the advent of neutron activation analysis,

concentrations as low as .02 ppm can be detected very easily.

Laboratory investigations were undertaken to determine if isotopic exchange separation

when coupled with neutron activation analysis could be used for the determination of trace amounts of mercury in oyster tissue. The inorganic mercury recovery efficiency was found to be greater than ninety percent and calculations indicate that total mercury concentrations

as low as one ppb can be measured in oyster tissue.

Oyster samples were collected from the Baltimore harbor area by the Natural Resources

Institute of the University of Maryland. The oyster samples were freeze-dried, encapsulated

and irradiated at the National Bureau of Standards. The oyster tissue was acid digested and

mercury was recovered by isotopic exchange. An analysis of fifteen oysters revealed mercury

concentrations ranging from 1 to 12 ppb (dry weight) . Gold and silver can also be recovered

in the isotopic exchange extraction, however, the recovery efficiencies for these metals is probably less than the ninety percent recovery efficiency which was found for mercury. Gold

concentrations ranging from 1 to 5 ppm (dry weight) were also found in these oyster samples.

These calculations are based on the assumption that the gold recovery efficiency is one hundred percent. Since the gold recovery efficiency is probably less than one hundred percent, the gold concentrations mentioned above represent conservative estimates of the gold

levels in these oysters.

Although the mercury levels in these oysters are very low, it is not known at this time

how mercury which is complexed with organic materials may be lost in the high temperature

acid digestion step. Additional work is needed to determine the recovery efficiencies for

methyl mercury and other organic mercury containing compounds which may represent a major

portion of the total mercury in the oyster. Additional work must also be undertaken to determine the gold recovery efficiency in the mercury isotopic exchange extraction.

54
Trace Elements in the Environment

G. E. Gordon and W. H. Zoller

(University of Maryland, College Park, Md .

Our major use of the reactor will be that of irradiating various types of environmental

samples in order that we can determine the concentration of almost 20 to 30 (mostly trace)

elements via instrumental neutron activation analysis employing Ge(Li) Y-ray detectors. The

samples we are working on now consist of atmospheric particulate matter collected on Millipore

filters during a systematic sampling program conducted in the Boston, Massachusetts area.

In addition we have a number of samples taken at the same time with cascade impactors which

separate particulate matter into various size fractions. When Professor Zoller returns

from the South Pole he expects to have a number of atmospheric samples from that region which

we wish to analyze in order to determine world-wide atmospheric "background" levels for

many elements. Related to the studies of urban air pollution, we have many samples of pollution source materials (particularly, crude oils and distillates of them) to analyze. As a side project, we are also looking at tree-ring sections from some very old trees, seeking

correlations with geochemical history of the areas in which the trees grew and looking for any build-up of industrially important elements since the start of the Industrial Revolution.

An essential feature of all of this work is the necessity for us to develop monitors that

will contain accurately known amounts of each element to be measured in the samples.

Furthermore, the relative amounts of the various elements should be similar to those of the

samples under investigation. This is a very difficult problem facing all activation analysis.

In cooperation with Dr. Harry Rook of the Activation Analysis Section of NBS, we are trying

several methods of attack on the problem. We will occasionally be irradiating small amounts of material (often enriched in

particular isotopes) to make radioactive species for investigation of their decay schemes in

order to obtain fundamental information about the structure of nuclear levels.

Neutron Damage Studies on Lead Salts

R. M. Cullpepper

(Naval Ordnance Laboratory, White Oak, Md.)

The National Bureau of Standards and the Naval Ordnance Laboratory have jointly undertaken the study of neutron induced damage in lead sulfide expitaxial films. The films are grown and measured at NOL and are irradiated in the RT-2 facility of the NBS reactor. The

samples are being irradiated in steps of approximately 10^ neutrons/cm2 and the changes in

the number of free carriers and sample resistivity are measured as a function of temperature

after each irradiation.

The data taken to date indicates that approximately one free carrier is removed from

the sample for each neutron in the flux. This reduction in the number of free carriers is true for both n and p type samples. More irradiations are planned, and a total exposure

of about 5 x lO^ neutrons/cm2 is anticipated.

55

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56
B Non-RRD NBS Staff located at Reactor

Division 310.08

D. A. Becker

B. S. Carpenter

M. R. Crambes

T. Gills

W. D. Kinard

P. D. LaFleur

G. J. Lutz

L. W. Masters

W. F. Marlow* (AEC)

L. T. McClendon

S. S. Nargolwalla

J. Olin* (Smithsonian In St.)

I. H. Qureshi

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R. W. Shideler

G. W. Smith

J. E. Suddueth

B. A. Thompson

H. P. Yule

Division 313.07

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Division 500.00

M. Ganoczy

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Division 503.02

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Federal Bureau of Investigation

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57
Post Office

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G . Donnoy*

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*Part-time

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U. S. Naval Academy

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University of Maryland

F. B. Birkner*

J. C. Glenn*

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W. H. Zoller*

Proctor and Gamble

J. Bevan*

Teledyne Isotopes

P. Alexander*

T. J. Dempsey*

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