Bureau of Stauaarup

Lbrary , N.W. Bldg

JG 3 1 1964

Reference book not to be

token from tho librery.

NBS

^ecknic&L <=Ylote 248

i

RADIOCHEMICAL ANALYSIS: ACTIVATION ANALYSIS,

INSTRUMENTATION, RADIATION TECHNIQUES, AND

RADIOISOTOPE TECHNIQUES

JULY 1963 TO JUNE 1964

EDITED BY JAMES R. DEVOE

I. S. DEPARTMENT OF COMMERCE

mONAL BUREAU OF STANDARDS
THE NATIONAL BUREAU OF STANDARDS

The National Bureau of Standards is a principal focal point in the Federal Government for assuring

maximum application of the physical and engineering sciences to the advancement of technology in industry and commerce. Its responsibilities include development and maintenance of the national stand- ards of measurement, and the provisions of means for making measurements consistent with those standards; determination of physical constants and properties of materials; development of methods

for testing materials, mechanisms, and structures, and making such tests as may be necessary, particularly for government agencies; cooperation in the establishment of standard practices for incorporation in codes and specifications; advisory service to government agencies on scientific and technical problems; invention and development of devices to serve special needs of the Government; assistance

to industry, business, and consumers in the development and acceptance of commercial standards and

simplified trade practice recommendations; administration of programs in cooperation with United

States business groups and standards organizations for the development of international standards of

practice; and maintenance of a clearinghouse for the collection and dissemination of scientific, technical, and engineering information. The scope of the Bureau’s activities is suggested in the following

listing of its four Institutes and their organizational units. Institute for Basic Standards. Electricity. Metrology. Heat. Radiation Physics. Mechanics. Applied Mathematics. Atomic Physics. Physical Chemistry. Laboratory Astrophysics.* Radio Standards Laboratory: Radio Standards Physics; Radio Standards Engineering.** Office of Standard Ref- erence Data. Institute for Materials Research. Analytical Chemistry. Polymers. Metallurgy. Inorganic Materials. Reactor Radiations. Cryogenics.** Office of Standard Reference Materials. Central Radio Propagation Laboratory.** Ionosphere Research and Propagation. Troposphere

and Space Telecommunications. Radio Systems. Upper Atmosphere and Space Physics.

Institute for Applied Technology. Textiles and Apparel Technology Center. Building Research.

Industrial Equipment. Information Technology. Performance Test Development. Instrumentation.

Transport Systems. Office of Technical Services. Office of Weights and Measures. Office of Engineering Standards. Office of Industrial Services.

* NBS Group, Joint Institute for Laboratory Astrophysics at the University of Colorado. ** Located at Boulder, Colorado.
NATIONAL BUREAU OF STANDARDS

Technical Note 248

ISSUED AUGUST 21, 1964

RADIOCHEMICAL ANALYSIS: ACTIVATION ANALYSIS,

INSTRUMENTATION, RADIATION TECHNIQUES, AND

RADIOISOTOPE TECHNIQUES

JULY 1963 TO JUNE 1964

Edited by James R. DeVoe

Radiochemical Analysis Section Analytical Chemistry Division

Institute for Materials Research

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 - Price 50 cents
FOREWORD

The Analytical Chemistry Division was established

as a separate division at the National Bureau of Standards on September 1 , 1965 and became part of the Institute for Materials Research in the February 1 , 196k

reorganization. It consists at present of six sections

encompassing some 30 different analytical competences

from activation analysis and atomic absorption to vacuum fusion and x-ray spectroscopy. These competences

,

and in turn the sections which they comprise, are

charged with research at the forefront of analysis as

well as awareness of the practical sample, be it service analysis or standard reference material. In

addition it is their responsibility to inform others

of their efforts.

Formal publication in scientific periodicals is

highly important. In addition, however, it has been

my experience that informal, annual summaries of progress describing efforts of the past year can be very

valuable in disseminating information. At the National Bureau of Standards such publications fit logically

into the category of Technical Note. In the future we

plan to issue these summaries for most, if not all, of

our sections. The following is the first in this

series, a report on progress of the Radiochemical

Analysis Section.

In preparing this report, it has been necessary to

make occasional references to existing commercial

equipment. However, such mention should in no case be

considered as representing a recommendation or endorsement by the National Bureau of Standards.

W. Wayne Meinke, Chief

Analytical Chemistry Division

11
PREFACE

This is the first of a series of annual progress reports

of the Radiochemical Analysis Section of the Analytical ChernI istry Division. Although this section was officially organj

ized in November 1963 this report will cover the entire fiscal

j year of 1964.

i There are sixteen people in this section and all except

! three of them--Kocol^ Thompson and DeVoe--have joined us dur-

[ ing the latter half of this fiscal year.

The purpose of this section is to develop measurement

! techniques for the qualitative ^ quantitative and structural

composition of materials through the use of radioisotopes.

Since the Analytical Chemistry Division is interested specifically in the characterization of very pure materials 5 a large

portion of this section's effort is directed to the analysis

of very small concentrations of the elements.

A basic requirement for the development of such measurement techniques using radioisotopes is the thorough understanding of the chemical,, nuclear and physical principles which form

the foundation of a new analytical measurement technique.

Therefore^ an effort has been made to include scientists who

are oriented toward the so-called fundamental research aspects

of the techniques under study. However } it is essential that

the developed methods be practical in the sense that they can

be used successfully on materials in which science and indust i\
have an interest. Therefore,, these developed techniques are

applied to NBS standard reference materials where considerable

cross checking of analytical techniques is done through the

process of certification.

The section is organized into four groups: radioisotope

tracer techniques, activation analysis, radiation techniques,

and instrumentation.

Radioisotope tracer techniques utilize the principle that

the radio-element can be detected in a chemical system by detecting its emitted radiation. To date, our principle interest

has centered around the radioisotope dilution techniques, but

| the efforts of this group are expected to include the so-called

radiometric methods as well as a variety of others.

I Activation analysis needs no explanation since it has been

* developed to be a highly useful trace analytical method. The

i interests of this group are related to enhancing the effective-

. ness of the method either by modifying the type and energy of

bombarding radiation or by utilizing a high degree of selec-

! tivity in detecting the radiation induced by bombardment.

I Radiation techniques utilize the effects of the -emitted

radiation of a radioisotope. This group is studying the use

of the Mttssbauer effect for the determination of the structural configuration of trace elements in pure materials. In

addition, a study of the effect of low energy nuclear recoil

on chemical bonds is being made.

The instrumentation group designs, modifies, and repairs 3
both the nuclear instrumentation and other instrumentation.

A problem of ever increasing complexity is that of maintaining an adequate capability of interfacing between the various

types of nuclear radiation detection equipment and a digital

computer. Considerable effort is being made to maximize

compatibility with a minimum of cost.

A roster of these groups is listed in Section 7.

Since the activity in radiochemistry in this Division is

relatively new, much effort in the past year has been devoted

to the planning and construction of facilities and instrumentation. A radiochemical laboratory which was completed in late

1963 is now being used at more than its capability of maximum

utilization. A clean room has been completed this year, and

is being used for the preparation of samples before activation

analysis

.

In approximately one year the Bureau of Standards will

be. moving to a new site at Gaithersburg, Maryland. Unsurpassed facilities for radiochemistry will be available. Pneumatic

tube facilities are being planned for the NBS 10-megawatt

heavy-water moderated nuclear reactor patterned after the

Argonne CP-5, and a temporary system is being installed in

the NBS 100 -Mev linear electron accelerator.

Of critical importance is the problem of staffing the

various groups indicated above. Efforts are being made con

tinually, to staff the above mentioned groups with scientists

in both the fundamental and practical areas so that maximum
utilization of the facilities will be made as they become

available

.

James R. DeVoe, Chief

Radiochemical Analysis Section

vi
TABLE OF CONTENTS

PAGE

FACILITIES i

Radiochemical Laboratory 1

Clean Room

INSTRUMENTATION 7

Interfacing of Pulse Height Analyzer to a Teletypwriter 7

RADIOISOTOPE TECHNIQUES 10

Substoichiometric Radioisotope Dilution Analysis . 10

Substoichiometric Radiometric Analysis:

Determination of Trace Amounts of Silver

by Solvent Extraction with Dithizone 11

Substoichiometric Radiometric Analysis:

Determination of Trace Amounts of Cobalt .... 16

The Determination of Cobalt by De-adsorption

of Cobalt Hydroxide from Hydrous Ferric Oxide . 17

Experimental 1'

Apparatus

Reagents

Preliminary experiments

Quantitative experiments

Results

RADIATION TECHNIQUES

Drift-free Mttssbauer Spectrometer

Digitally Controlled Velocity

Constant Velocity

vii
TABLE OF CONTENTS (con't)

PAGE

Circuits 32

Time Delay Circuit 37

Mftssbauer Spectrometer 38

The Use of a Nuclear Transformation to Measure

the Surface Energy of Metals in Ultrahigh

Vacuum 44

Introduction 44

Apparatus 45

Vacuum system 45

Measurement tube 48

Detector 51

Operating Experience 52

Vacuum system 52

Measurement tube 5^

Detector 55

5 . ACTIVATION ANALYSIS 58

Activation Analysis of Human Lung Samples .... 58

Instrumentation 60

Preparation Procedures .... 60

Standard solutions 60

Reagents 6 l

Collection of human lung samples 62

Drying and- grinding of human lung samples . . 63

Preparation of encapsulated samples for

irradiation 64

viii
TABLE OF CONTENTS (con’t)

PAGE

Irradiation Procedure 65

Radiochemical Procedures 65

Ashing method 65

Treatment of standard samples 66

Ion exchange separation method 67

Acetylacetone separation of manganese

and copper 70

Dithizone method for the separation of zinc . 71

MISCELLANEOUS 75

Positive Sealing with Optical Coupling of

Radioactive Sources in Machined Plastic

Phosphor Scintillators 75

Ion Exchange Resins -- General Consideration . . 77

PERSONNEL 8l

ACKNOWLEDGEMENTS 82

LIST OF REFERENCES 85

IX
LIST OF FIGURES

FIGURE NO . PAGE

1. Hot Laboratory facility 2

2. Glove box facility in clean room 4

3. Another view of glove box facility in

clean room 4

4. Another view of clean room facility 5

5. Functional logic diagram showing interface

connecting RIDL analyzer to Model 32 Teletype. 8

6 . Block diagram of electronic circuits for

constant velocity mode_, or constant acceleration mode operation of the Mfissbauer

Spectrometer 29

7. Circuit which generates pulse from position

sensitive photocell slit system ....... 30

8 . Circuit diagram of the modified Bell Telephone Laboratory Mttssbauer drive 31

9. Circuit diagram for generating square wave

input to drive in constant velocity mode ... 33

10. Circuit for generating delay pulses for

controlling timer and scaler 3^-

11. Interfacing between delay circuit and

RIDL scalers and timers 35

12. Complete diagram of Mttssbauer effect

analyzer 39

13. Low frequency., power amplifier 4l

14. Double speaker Mttssbauer drive ^ 41

15 . Block diagram of the vacuum system 46

16. Ultrahigh vacuum system including tube for

measurement of kinetic energy of recoil ions . 49

17. Tube for measurement of kinetic energy of

recoil ions 50

X
LIST OF FIGURES (con't)

figure no. page

18. Circuitry associated with the electron

multiplier ^2

19. Beta scintillator^ machined from NE-102

plastic phosphor 76

20. Apparatus for regeneration of ion exchange

resin 73

21. Apparatus for gradient elution study of

ion exchange resin 80

LIST OF TABLES

TABLE NO . PAGE

1. The effect of pH on the percentage of

cobalt adsorbed by ferric hydroxide 20

2. Effect of quantity of adsorbent,, Fe 20

3. Percent cobalt which is soluble in saturated

sodium hydroxide 21

4. De-adsorption of cobalt from hydrous ferric

oxide with concentrated alkali 22

5. Analytical data on a pair of irradiated and

aliquoted zinc standard samples . 69

6. Results of analysis of lung samples 72

7. Comparison of concentrations of zinc,, copper,,

and manganese reported in normal human lung

samples from adult victims of accidental death

with those reported in Table 6 for current

project 74

xi
'I

t.

RADIOCHEMICAL ANALYSIS: ACTIVATION ANALYSIS INSTRUMENTATION

RADIATION TECHNIQUES , AND RADIOISOTOPE TECHNIQUES

July 1963 to June 1964

I

i] Edited by James R. DeVoe

ABSTRACT

This first summary of progress of the newly organized

Radiochemical Analysis Section of the Analytical Chemistry

Division at NBS covers four areas: Activation Analysis^

Instrument at ion 5 Radiation Techniques 5 and Radioisotope

Techniques

.

The present facilities including a radiochemical laboratory and a clean room facility are described and future

plans for the 10 megawatt nuclear reactor and the 100 Mev

Linac facilities at the new Bureau site are outlined. A

teletypewriter-pulse-height analyzer interface for more

efficient data handling in gamma-ray spectroscopy is described. , A combination of radioisotope dilution and radiometric methods

for determining trace amounts of silver and cobalt is presented.

Details of a drift-free Mttssbauer spectrometer which utilizes

positive synchronization of a pulse-height analyzer with an

electro-mechanical drive are given. Reproducible response to

better than 0.5$ is obtained. An apparatus for the measurement

of the energy of nuclear species recoiling from clean metal

surfaces in ultrahigh vacuum is described. The application of j. neutron activation analysis for determination of ppm levels of

copper and zinc in human lung tissue is discussed.

1

1

ii

Xll
1. FACILITIES

M

!

i

| I

At present there are available to the Radiochemical

(Analysis Section a hot laboratory and a clean room described

j below, several standard laboratories for inactive work and

| preliminary preparations, and two counting rooms. The facilities of the Naval Research Laboratory reactor are utilized

for irradiations at the present time.

I A. Radiochemical Laboratory

This room, part of which is shown in Figure 1 was com-

' pleted in November 1962. The Radiochemical Analysis Section

has the use of four six-foot hoods and one glove box in this

1 laboratory. These hoods are used for handling radioisotopes

and for the preparation of samples for the activation analysis

program. A radioactivity storage area is placed in the far

corner of the room. Since this room is one of the few

in the building in which radioactivity is being handled, an

upper limit on the level of radioactivity that may be used is

150 Ci. In most cases only microcurie amounts of radioactivity in encapsulated Sources are allowed to be removed from

the laboratory. All radioactivity must be used in the hoods

only.

The hoods are of the auxiliary air flow design. This

means that ^0% of the air exhausted through the hoods bypasses

the air conditioner and enters directly above the face of the

hoods. Although the summer weather in Washington is usually

accompanied by high humidity there is no noticeable effect

1
Figure 1. Hot laboratory facility.

from the by-passed air. In winter the auxiliary air is preheated. These hoods will be moved to our new Gaithersburg

facilities

.

B. Clean Room

Several of the techniques in activation analysis have

sensitivities which are high enough to create serious problems

in handling the sample prior to irradiation. With these techniques the opportunity for introducing contaminants into the

sample is very great. Even the amount of contamination by the

metallic elements attached to organic dust fibers can be

significant. Therefore,, a room was constructed that would

allow a certain amount of sample handling under controlled

2
! "clean" conditions prior to irradiation. The glove box area

| of the clean room is shown in Figures 2 and 3. This room was

i built within a preconstructed laboratory by forming and plastering a separate set of walls and ceiling inside of the

j

| existing room. The interior dimensions of the finished room

j are 15 x 17 feet. All corners were rounded to prevent collection of dust and Keenes' finish plaster was painted with three

| coats of a polyvinyl base paint. The flooring is covered with

two eight-foot wide pieces of battleship linoleum so that the

number of cracks in the floor is minimized.

Air is blown into the room through a pre-filter, an air

conditioner, and an "absolute filter", respectively (Cambridge

Filter Company, Model LA-1000). The air is exhausted through

a port in the entrance door into a small anteroom where the

worker puts on a lint-free synthetic fabric hat, shoes, and

knee length laboratory coat. The air in the clean room is

maintained at a positive pressure of 0.1 inches of water with

respect to the pressure in the anteroom. An interlock system

is provided in the anteroom to prevent the simultaneous opening of the entrance and exit doors.

The worker vacuums his hair and clothing with an industrial vacuum cleaner which exhausts through an absolute filter

(Cambridge super-interception type) into the anteroom, dons

the special clothing and enters the clean room.

Since there is a large amount of electronic equipment

and radiation shielding in this room which can produce and

5
Figure 2. Glove box facility in clean room.

Figure 3. Another view of glove box facility in clean room.

4
icollect dust, see Figure 4, a secondary protection of the

ichemical processing is used by performing the work in glove

[boxes inside of the clean room. Each box is provided with an

Figure 4. Another view of clean room facility.

interlock chamber which can be flushed with clean air before

[and after introducing an object into it. The glove boxes are

supplied with air from a blower through an absolute filter

and are maintained at a positive pressure of 0.2 - 0.5 inches

of water with respect to the clean room.

Tests are now underway to determine the dust count in

the glove boxes, clean room, and anteroom. While we believe

5
that the particulate contamination in the clean room itself

is not exceptionally low ; we do expect it to be very low in

the glove boxes.

Thanks are due Mr. H. Kocol for his assistance in expediting the procurement and construction of components for

this clean room. The valuable assistance of Mr. B. Goetz

and Mr. F. Clark is also acknowledged.

(J. R. DeVoe)
2 . INSTRUMENTATION

The instrumentation used by the Radiochemical Analysis

| Section routinely includes a variety of a 3 £ and y-counting

|

| systems j several pulse-height analyzers and associated equip-

| ment such as magnetic tape,, and printer readout devices.

Other equipment such as an automatic sample changer is

currently being studied and tested. Our experience with it

|

| will be included In the next progress report. The design and

I construction of special equipment is a major part of this

group's activities. The first such device is described below.

A. Interfacing of Pulse Height Analyzer to a Teletypewriter

A model ASR Teletype was obtained in order to read

out the data taken by our RIDL analyzers. The teletype

machine was chosen since it provided inexpensively a punch

tape readout and readin as well as ajprinted page copy. It

also offers the facility of the "Data Phone" communication.

It was necessary to interface between the instrumentation

output and the teletype since the teletype would accept only

a serial 8 level ASCII code and the instrumentation presented

only a 4 level BCD parallel output. Provisions were made to

include any arrangements necessary to read out auxilliary data

from associated systems.

The interface translator unit is now operational and its

performance is satisfactory. A function diagram is shown in

Figure 5 and its operation is as follows:

Output data from the RIDL analyzer are fed into the input
FROM

RID L

34-12 8

CDa

f>5 P

CD

CD EHK\

K\ I ?H I

I CD CD -P TS C O

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cdP

W)

f— cd h3 z

•H

Q | Z>

Til

H ' P3

cr0(—

O

•H fcjD i < tifl <3 p ; cnz O -H ! 1—1

-p < 0 1 cc 1—1 CD p cd <3 II Ixl 31 S3 1 0 0 0 : <

Lx •H

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<r P

Ixl a. cd P S3 0 Z 2 cd i| P>H pH

LPt

CDP3w

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gate and the function reader matrix. The input gate is opened

for all data readout when no operation function is involved.

The data are adjusted in level and then applied to the appropriate output gate inverter. When a function is called for

by the analyzer,, its output code is translated by the reader

matrix and the data gates are turned off. A new code determined by the operation desired is generated in the function

synthesizer and applied to the output gate inverters.

(R. W. Shideler

)

9
3. RADIOISOTOPE TECHNIQUES

This group has made very significant progress in a short

time in the use of radioisotopes for chemical analysis. Of

particular importance is the development of the substoichiometric radioisotope dilution method for trace analysis. These

techniques have been applied sucessfully to the determination

of several elements in practical samples as described below.

A. Substoichiometric Radioisotope l&lution Analysis

Substoichiometric radioisotopic dilution analysis is dependent on the ability of an experimenter to manipulate a system in such a way that the same number of atoms are isolated from the bulk of the system before and after dilution.

This can be accomplished in three ways: 1) Always remove the

same number of atoms from solution. Solvent extraction, using

a substoichiometric amount of complexing reagent in the organic

phase is an example of this (see B)

.

The analysis of silver

by extraction with dithizone was accomplished in this way.

2) Always leave the same number of atoms in solution (see C).

The formation of a complex with a substoichiometric amount of

a sequestering reagent, such as EDTA, and the removal of the

non-complexed ions by some means such as adsorption or ion

exchange, is a method of obtaining the same numbers of atoms

in solution before and after radioisotope dilution. The analysis of cobalt was performed by using a substoichiometric

amount of EDTA and removing the free cobalt ions with a cationic exchanger. 3) To quantitatively remove all of the desired

10
ions from solution by co-precipitation, adsorption or electroplating and then to dissolve the same number of atoms based on

their solubility and/or complex formation. The latter approach

has been applied to the adsorption of cobalt on manganese dioxide and to the co-precipitation of cobalt hydroxide on hydrous ferric oxide (see D).

The principle of substoichiometric radioisotopic dilution

was first suggested by Ruzicka and Stary [1,2], The following

work utilizes and extends this method into a type of radiometric technique in which one need not always consider that

sampling equal number of atoms of the desired element before

and after radioisotope dilution is necessary. Sections

B and C are abstracts of talks submitted; one to the Analytical Chemistry Division of the American Chemical Society for

presentation at the fall 1964 meeting, and the other to the

Symposium on Radiochemical Methods of Analysis, sponsored by

the International Atomic Energy Agency, October 19-29, 1964.

(A. R. Landgrebe and L. McClendon)

B. Substoichiometric Radiometric Analysis: Determination of

Trace Amounts of Silver by Solvent Extraction with Dithizone

A precise and rapid method was developed for the deter-

_7 mination of silver in the range of 10 to 10 M. Direct isotopic dilution can be described by the equation:

f Ai x = y -a 1 (!) A

2

x is the unknown and y is a known amount of the radioelement

11
to be determined; A

1 is the specific activity of the radioisotope and A

2 is the specific activity of the mixture of radioisotope and added analyzed element. Specific activity is

defined as:

A

m

l l

1

and A

2

where a^ and a

2

are the activities in counts per minute (cpm)

and m^ and are the isolated amounts of the element. Since

we always isolate the same amount of silver by extraction with

a substoichiometric amount of dithizone, it is evident that

m

l ~ m2" Then in relation (1) the specific activities can be

replaced directly by relative activities (cpm) measured under

the same conditions. This method was originally worked out by

Ruzicka and St ary [1,2].

The organic phase of the system is a carbon tetrachloride

solution of dithizone; the aqueous ph*ase is a nitric acid

solution of the sample. Radioisotope (Ag-llOm) of high specific activity is used to determine trace concentration of the

stable element through the use of a substoichiometric amount

of the dithizone.

In the analysis of samples which contained large amounts

of copper and trace amounts of silver it was desirable to

analyze for silver without previously separating it from the

bulk of the interfering ions. For silver and copper dithizonates the following expressions will hold:

[AgA] org _

1°8 Ugh [H

+

] [2]
The charge on the elements is different and the ratio

[ A.gA

]org / [CuA

2

] Qrg

depends on pH as well as on [HA] In carrying out the ex- ^ o

traction at pH 1 using a dithizone solution of 10 ^ M at equilibrium we have for the dithizone concentration.

[HA] <fl0

“ 7 M

org

^

It should be possible to extract silver in the presence of a 100 fold excess of copper at pH 1. However at pH 1, EDTA is

very insoluble and we could have about 100,000 times more

copper than silver in the sample we wish to analyze. Hence

the determination of silver was performed at pH 4.5 in an

acetate buffer, a two-fold excess of EDTA was used. At pH 4.5

it should be possible to extract all of the silver in the

presence of an equivalent amount of free copper, [Cu

++

]. However, in the presence of excess dithizone, both elements are

extracted together. It is evident that the concentration of

copper II ions in the presence of a twofold excess of EDTA is

1 P) insignificant ( 10” M) and the copper is not extracted under

the conditions employed. This method allowed the determination

of silver in an NBS standard sample of Ounce Metal ( 85% Cu)

,

standard sample 124d.

The method of direct isotopic dilution was quite satisfactory but it was realized that a method of double isotopic

dilution is a valid means of internal standardization of the

system. Analysis is carried out as follows: different but

known concentrations (W-^ and W

2

) of naturally occurring silver

13
are added to two equal aliquots of the sample to be analyzed

containing a concentration of silver W . (A ten- or twentyfold excess compared with the amount of the element to be determined is recommended.) Equal parts of the mixture (¥ +W9 ) are separated through the use of a substoichiometric amount of

reagent and their relative activities are determined. The

following formula is used:

a

2

W

2

" a

l

W

l W =

( a

q

a^ and a

2

are the relative activities corresponding to the

aliquots containing and W

2 respectively,, after radioisotopic

dilution. Maximum conditions for the use of this equation

could be where W^ = and W

2

»w1

.

When equal number of atoms are not extracted in every

experiment 5 a radiometric method of analysis can be used.

Under similar conditions the partition function is measured

by investigating the distribution of the naturally occurring

m

silver which is traced with Ag-110 . The silver is added to

the aqueous phase and is then extracted into the organic phase

with a substoichiometric amount of dithizone. This method requires the preparation of standard curves where partition function., D is plotted against the concentration of silver added.

For an unknown the concentration is obtained by knowing the

concentration of dithizone used and reading the corresponding

concentration for a particular D from the curve. The inherent

error in this approach can be minimized by preparing reference

14
solutions which have been internally standardized by the addition of the major components that exist in the sample. The

major components of the sample are present in the reference

solutions in the same concentrations as would be found in the

sample itself.

The analyzed copper samples (NBS Standard Sample No. 124d)

were found to contain 0.021 - 0.002$ silver and this value is

in good agreement with the certified value of 0.02$. The value

obtained by the double isotopic dilution method, 0.025 - 0.002$

was also in good agreement. From the data obtained one may

recommend the use of this radiometric solvent extraction determination of silver for the concentration range of 10"^ g/ml to

10 g/ml. At the higher concentrations, 10" g/ml, physicochemical methods may be more advantageous. The sensitivity of

the method is limited by three factors: a) there is a limit

to which the organic reagent can be diluted because of solubility in the aqueous phase; b) the sensitivity is limited by

the specific activity of the radioisotope and c) at low concen-

-7 trations, silver may be adsorbed by the glass, e.g. 10 g/ml.

The last factor is an error inherent in all trace analytical

methods for silver.

Some uses of double isotopic dilution analysis are:

1) The method ought to be applicable to difficultly separable

elements of similar chemical properties. 2) The method of

double substoichiometric isotopic dilution can be used to

clarify such problems as matrix effect and loss of volatile

15
elements upon dissolution in activation analysis. 3) The technique affords considerable saving in time and cost compared to

most other trace analytical methods.

(A. R. Landgrebe., L. McClendon and J. R. DeVoe)

C . Substoichiometric Radiometric Analysis: Determination of

Trace Amounts of Cobalt

This analytical method is part of a general program at

the National Bureau of Standards which utilizes radio-isotopic

tracers for the analysis of impurities in highly purified materials. Substoichiometric radiometric analysis is a modification of the isotopic dilution method of Ruzicka and Stary [l s 2].

In substoichiometric isotopic dilution analysis., equal number

of atoms must be isolated from the system while in radiometric

analysis the amount isolated need have only a known relation

to the initial concentration. In order to Isolate the same

amount j or an amount proportional to the initial concent rat ion 5 many side reactions such as hydrolytic reactions of the complexing agent and of the metal iorij formation of acid or basic

chelate compounds other than the desired one ; competing side

reactions of the complexing agent with other Ions present 5 and

the reaction of metal ions with buffering and masking substances

must be controlled.

Two procedures of analysis (column and batch) were developed using substoichiometric^ amounts of EDTA. The excess cobalt

Ions were removed from solution with a cationic ion exchanger

in the sodium form.

16
Experiments were performed to determine the effect of

contact time, pH, ionic strength and buffers on the sensitivity

of the method. Buffering solutions investigated were sodium

acetate, ammonia -ammonium chloride, trisodium phosphate and diethylamine. The method gave reproducible results with an acetate buffer for the concentration range of 10 qg/ml to 0.1

pg/ml of cobalt. With diethylamine buffer preliminary results

appear to be meaningful at the nanogram/ml level. The concentration range investigated using diethylamine buffer was from

-10

5 x 10 ^ M to 5 x 10 M cobalt using batch experiments in

which one gram of Dowex 50-X8, 20-50 mesh was equilibrated with

10 ml of aqueous solution containing a substoichiometric amount

of EDTA but an amount greater than the total cobalt concentration.

Another application of this method include the measurement

of specific activities of radioisotopes. Measurement of Co-60

obtained from 0RNL has been done. It will be shown that subj stoichiometric isotopic dilution analysis is the limiting case

of a more general method which is called for want of a

better name, substoichiometric radiometric analysis.

(A. R. Landgrebe, L. McClendon and J. R. DeVoe)

I

! p t The Determination of Cobalt by Desorption of

Cobalt

Hydroxide from Hydrous Ferric Oxide

Substoichiometric radioisotopic dilution analysis can be

! accomplished by quantitatively removing all of the desired ion

from solution by co-precipitation or adsoiption and then

17
dissolving a constant number of atoms back into solution by

utilizing their solubility and/or complex formation. This

approach has been applied to the co-precipitation of cobalt

hydroxide on hydrous ferric oxide.

This section presents a study of the adsorption of cobalt

(II) by hydrous ferric oxide and the de-adsorption of cobalt

by saturated solutions of sodium hydroxide presumably forming

the species [Co (OH) ^E^O ] aq whose solubility would be determined by the stability constant of the complex and the solubility product of cobalt hydroxide. Cobalt hydroxide has a finite

solubility. The experiments were performed to quantitatively

K = [Co

++

] [0H“] 2 = 2.5 x 10“ l6

S ]D [Co(OH)

3

-

] K

[Co (OH)p ] [OH

-

] 4 x 10" 11

remove all the cobalt from solution and to show that the deadsorption follows the law of mass action. The amount of

cobalt adsorbed was determined by radioactive tracer methods^

utilizing cobalt-60.

1 . Experimental .

a. Apparatus . Automatic sample changer and

scintillation counter with well type sodium iodide (TJL) crystal:

pH meter,, Radiometer PHM4 (Copenhagen).

Lourdes centrifuge with maximum speed of 17-5 rpm.

Polypropylene tubes and glass counting tubes.

b. Reagents. Distilled water: prepared by passing

it through a mixed ion exchange bed and distilled twice in

quartz

.

18
All chemicals used were A.R. grade.

Radioactive cobalt solutions - the cobalt-60 used was

II

| obtained from the isotope division of the Oak Ridge National

l Laboratory . The cobalt-60 had a specific activity of

51,650 mc/g.

: c. Preliminary experiments, . Cobalt nitrate (5 ml

I

I of 0.25 M) was precipitated with 5 ml of 1 N sodium hydroxide.

|The sample was centrifuged and the colorless supernate was de1Scanted from the pink precipitate. To this precipitate was

added 5 ml of ( 50$) sodium hydroxide solution and the sample

was shaken for several minutes. A blue aqueous layer and a

pink precipitate was obtained. It is believed that under these

! conditions the blue solution is collodial in nature and that

the Co (OH) I complex is not formed as previously reported

(3j>^5^6). The same results were obtained when the precipitate prepared in the manner described was equilibrated with

0.5 and O .25 g of sodium hydroxide/ml', but with 0.125 g

sodium hydroxide/ml the blue color did not form.

With (1/5) ammonia the precipitate was formed and the

I aqueous solution was decanted off. The blue precipitate was

equilibrated with 1/5 NH^, and an olive green aqueous phase with

a blue precipitate was obtained. On standing for 24 hours the

aqueous phase became amber-red indicating the formation of the

ammonia cobalt complex [Co (WH-^)^OH]

.

d. Quantitative experiments . The data on the coprecipitation of cobalt on hydrous ferric oxide can be seen

19
in Table 1 and Table 2 . The cobalt -60 was precipitated along

Table 1 . The effect of pH on the percentage of

cobalt adsorbed by ferric hydroxide. [7]

Experiment •*!Experiment Ba,b Experiment C a,c

pH y/i-.v —Adsorbed pH y/i-y Adsorbed pH y/i-y Adsorbed

m UJ —m—

5.50 0.45 4.7 6.90 0.18 15.0 5.50 0.07 6.8

5.90 0.56 5.4 7-20 0.71 22.9 6.02 0.10 8.9

6 . 4o 0.11 10.0 7.50 0.99 49.7 6.50 0.26 20.7

7.00 0.27 18.9 7.80 2.18 68 .

6

6.90 0.91 47.5

7.54 1.20 54.6 8.00 4.78 81.4 7.70 4.00 80.0

8.70 5.52 84.7 7.62 10.20 91.1

7.91 70.20 96.8

8.20 92.20 98.9

a Constant factors: cobalt 2.8 X

_q 10 v gram atom; chloride

h 2 .79 x' IQ-1 gram atoms; volume! 72.1 x 0.2 ml

.

c Fe ^ 4 x 10 - 6 gram atoms.

c Fe, 60 X 10 D gram atoms

.

Table 2 . Effect of quantity of adsorbent, Fe

.

[ 7 ]

pH 6.8 pH 7.5

Fe y/l-y Adsorbed Fe y/i-y Adsorbed

(g atoms x 10 b

) (*) (g atoms x 10L

) w

4 0.12 10.4 4 0.81 44.7

6 0.17 14.7 6 1.20 54.7

10 0.27 18.9 8 1.48 59.8

20 0 .41 27.2 10 1.67 62.6

60 0.91 47.5 20 7.44 77.5

60 10.24 91.1

Constant factors: Cobalt 2.8 x 10 ^ gram atoms; chloride

2.79 x 10 “4 gram atom^ volume 5 72.0 - 0.2 ml.

20
with iron from a solution containing 1 ml of 0.5 N ferric

jjnitrate^ 1 ml of cobalt -60 and. 8 ml of 1 N sodium hydroxide

The cobalt -60 was shaken with 5 ml of saturated sodium hydroxlidej the solutions were heated for several minutes at 70°C to

.destroy the ferric hydroxide colloid and then centrifuged. A

'one ml sample was counted. The remaining 4 ml of solution were

filtered through millipore filters (150 microns) and a 1 ml

I aliquot was counted. The data appears in Table 7.

1

i I

1 Table 3. Percent cobalt which is soluble in

saturated sodium hydroxide.

cpm/ml in 5 ml

of Saturated NaOH % Solution

cpm/ml after

Filtering thru

Millipore Filter % Solution

627 42.5 637 47.7

637 4l.O 651 40.8

543 55-0 567 56 . 6

935 60.5 812 52.5

419 27.0 421 27.1

Note: If all the cobalt were desorbed in 5 ml of saturated

NaOHj the concentration would be 1.550 cpm/ml.

Since the colloid was not removed from solution by the

i millipore filters 5 a method was developed to destroy any colloid formed. After co-precipitation of the cobalt with hydrous ferric oxide the precipitate was

11 dissolved 1

’ by shaking

it vigorously. The typical reddish ferric hydroxide colloid

that formed_, was destroyed by heating in a water bath for several minutes until flocculations occurred. The tubes were

21
cooled to room temperature and were centrifuged. The total

volume of solution was 10 ml and contained one ml of ferric

nitrate (0.5 M) which was used to co-precipitate the cobalt.

One normal sodium hydroxide was used as the precipitating reagent. The specific activity of the cobalt-60 was 6 x 10 11

cpm/g^ one ml of the cobalt -60 stock solution contained 1.24

x 10 ° g/ml. Data for various concentrations of cobalt-60

which were de-adsorbed by saturated sodium hydroxide appears

in Table 4.

Table 4. De-adsorption of cobalt from hydrous

ferric oxide with concentrated alkali.

Concentration % Cobalt in Concentration % Cobalt in

of Cobalt-60 Saturated Sodium of Cobalt-60 Saturated Sodium

Hydroxide Hydroxide

4x10"^ g/ml 77.5 1.0x10"^ g/ml 7.2

8x10 ^ g/ml 73.6 1 . 5x10 g/ml 7.8 [ 2.0x10 g/ml 9.7

1.0x10"^ g/ml 90.4 5.0x10"^" g/ml 11.7

1.2x10 g/ml 64.4

i 1.6x10 g/ml 80.6 1x10"^ g/ml l4. o ! 2. 2x10 g/ml 91.0 1.5x10"^ g/ml 17.0

2.0x10 ^ g/ml 8.7

5x10 ^ g/ml 5.1

c

i

1.0x10" 5 g/ml 8.0

:

1.5x10"^ g/ml 7-5

|

2.0x10"^ g/ml 7.9

5.0x10"^ g/ml 9.7

f.

22
e. Results . Adsorption: The adsorption of cobalt60 has been shown to follow the following expression [ 7 , 8 , 9 ]:

K

y

[H^0+

] x

1-y adsorbant j x

'Ijwhere y is the amount of tracer adsorbed and brackets indicates concentrations. The amount of radioactive cobalt used

: per sample and the total volume were known. The above equation

! results from treatment of the adsorption system as a cation

i exchange system in equilibrium which follows the law of mass

! action when the thermodynamic activities of the ions in solution are their molar concentrations and when their concentrations are constant. It can be seen from this equation that

if the quantity of adsorbant is maintained constant 5 a plot of

log vs pH should give a straight line,, likewise 5 if the pH

is maintained constant 5 a plot of log

yyy

vs log (gram atoms

of iron) should also produce a straight line. The experiment

indicated that the adsorption of cobalt follows the law of

mass action. The curves obtained by plotting log yyr vs pH or

1 quantity of adsorbant are straight lines over most of the

i region studied. The adsorption does not follow the equation

j below pH 7-

De -adsorption : It was impossible to obtain meaningful

j results on the de-adsorption of cobalt with concentrated

i

I sodium hydroxide due to the formation of stable colloids.

! Other systems which shall be investigated are the co-precipi1 tation of cobalt hydroxide with dysprosium hydroxide and

27
gadolinium hydroxide. The adsorption of cobalt hydroxide on

preformed manganese dioxide and the co-precipitation and

de-adsorption of cadmium chloride on silver chloride and

thallium chloride on silver chloride.

(A. R. Langrebe and L. McClendon)

24
k . RADIATION TECHNIQUES

A major fraction of the efforts of the radiation techniques group has in the past been directed towards instrumentation and laboratory equipment design. Now as these near

completion, however, attention is being directed towards a detailed check-out of one system, the Mttssbauer spectrometer,

and the initial phases of data collection. The work with

another system involving nuclear recoil is also presently in

the data taking stage. The following paragraphs describe the

equipment that has been designed.

A. Drift-free Mftssbauer Spectrometer

Nuclear resonance fluorescence (Mftssbauer effect) is the

recoiless emission and absorption of gamma radiation by nuclei

embedded in solids. The most important aspect of the Mfissbauer

effect is the sharply defined energy of the electromagnetic

radiation, and the precise determination of extremely small

energy shifts through the Doppler effect. The Mttssbauer effect

has many applications in nuclear physics, solid state, and more

recently in chemistry. The fraction of nuclei undergoing recoiless transitions can be related to the amount of a particular isotope present in a sample. Also internal electronic and

magnetic fields change the relative position of the resonances,

and can be interpreted to give information about chemical structure, the nature of chemical bonding, and nuclear electric and

magnetic properties. Once these shifts are measured for the

various compounds, this information then can be used to

25
identify these compounds in a sample. A. study of the precision

in identifying iron and iron compounds was started and a spectrometer was developed for this work.

Applications in chemistry require a precision Mttssbauer

(Doppler) spectrometer with enough range to include many isotopes and to obtain data in a sufficiently short period of time

and in a routine manner. The availability of multichannel analyzers presented a method of conveniently obtaining Mflssbauer

effect data.

In previous applications * the analyzer was used as a slave

unit in sorting out gamma rays as a function of the Doppler

velocity. This presents several difficulties which were removed by using the analyzer to generate a digitally derived

electrical signal for an electro-mechanical transducer, which

produces the Doppler velocity dictated by the analyzer. This

method increased the acceptable counting rate by a factor of

100 and removed possible drifts with time in the Doppler velocity calibration of the spectrometer.

A Mftssbauer drive has been developed which overcomes one

of the greatest difficulties that has been encountered in

electro-mechanical Mttssbauer spectrometers. The drive has

been designed so that it can not drift with respect to position.

This has been done by synchronizing the input signal to pulses

from the position sensitive photocell slit system. This system

starts each eycle in the same position, and hence position

drifts have been eliminated.

26
The spectrometer can he driven in two modes: Constant

acceleration and constant velocity. The constant acceleration

mode input signal is obtained from the analog output of the

channel advance pulses of a multichannel pulse height analyzer

running as a multiscaler which generates a sawtooth wave form.

The constant velocity mode input signal is obtained from a

square wave which is triggered by the photocell.

Using the analog signal of the multichannel analyzer

as the input to the drive, we have solved the problem of assign

ing an increment of velocity to a channel, because now the input voltage is proportional to the channel number and hence the

velocity is a direct function of the channel number. The photo

cell slit system resets the address scalers before channel 399i

and restarts the cycle. A distinct advantage of using the analog signal is that one does not encounter the problems involved

in the D.C. stabilization of an integrator circuit such as

described by Kankeleit [ 10 ]

.

1 . Digitally Controlled Velocity

One can obtain a complete MBssbauer spectrum with a multichannel analyzer using a constant acceleration spectrometer by

two methods. The first is the modulation of the pulse heightby the driving wave form, and using the analyzer in the pulse

height analysis mode. This method will give a good Mttssbauei

spectrum if the analog to digital converter is linear, but the

count rate is restricted due to the long dead time required to

address each pulse into the memory. The second method

27
run the analyzer in a multiscaler mode and derive a constant

increment of velocity for each channel. This method is far

better than the first because the dead time is no longer an

important factor, and the linearity requirement of the analog

to digital converter is eliminated. The accuracy of the spectrum produced by this method is only as good as the synchronization between the analyzer and the spectrometer.

In the time mode, the analog signal of the address scalers

has a saw tooth voltage dependence • on time. Since this signal

is derived from the address scalers, it is a direct function

of the channel number. The synchronization between the velocity produced by the electro-mechanical drive and channel number

is good to within 0.1 channel. Thus, the velocity is digitized

and is made a direct function of the channel number.

The analog signal from pin 36 of plug J19 of the RIDL

model ^4-12 analyzer is impressed on an operational amplifier

summing point which makes the output of the amplifier symmetrical with respect to ground. It is then fed into the input of

the drive as shown in Figure 6 . The position of the speaker

at the beginning of each cycle is fixed by the photocell slit

system as long as the photocell triggered pulse resets the

address scalers before they count through channel 399 ; since

the analyzer resets its own address at this point. We have

found it to be a good practice to run the drive so that the

address scalers are reset by at least channel 390- The address

28
Figure 6. Block diagram of electronic circuits for constant

velocity mode, or constant acceleration mode

operation of the Mttssbauer spectrometer.

scaler reset pulse is a -10 volt pulse derived from the photocell pulse generator as shown in Figure 7 } and it is fed into

the RIDL 34-12 at pin 35 of plug J2.

2 . Constant Velocity

For precise stepwise scanning of a Mttssbauer spectrum a

constant velocity drive is very useful. The Bell Telephone

Laboratories [ll] drive was constructed, but due to large pc

tion drifts it was modified. The modifications in the circuit

29
A02 1+

iz>o

UJ3

Q. UJ > Z

S=1 oH

-P•H

cqo

ft

qcop

<t

cridz

Ld

CD

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_JX

CLoopoXX sop • ft £

CD

(D -P

CQ CQ i—I !>} 2 CQ ft P

CQ *H

CD i—I p CQ P H

CD i—I C CD

CDO

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O

P>

ft

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O ft •H ft

ft

is CD> P >H

•H P 2 -H O CQ P S

•H CD O CQ

(ft

CDP3

taO •H

ft

30
of the Bell Telephone drive are shown in Figure 8. The feedback system was D.C. coupled, but drifts persisted with smaller

amplitudes and lower frequency. A photocell slit system was

then built which generates the input square wave necessary for

constant velocity as shown in Figure 6. This method of generating the square wave eliminates all position drifts.

Figure 8. Circuit diagram of the modified Bell Telephone

Laboratory Mttssbauer drive.

31
A special electronic circuit described below and shown in

Figure 9 was designed to generate either symmetric or nonsymmetric square waves, i.e. different velocities in forward

and backward directions. In the constant velocity mode, a single channel analyzer, scalers, and timers are used. We

gate each scaler and timer pair on for half-a-cycle and use a time delay before they are allowed to count. This time delay

allows any ringing in the turn around to be damped out and the

velocity to stabilize before counting commences. Circuits for

controlling RIDL models 49-43 scaler and 54-8 timer are shown

in Figures 10 and 11.

3 . Circuits

For simplicity the electronics for the spectrometer were

divided into five circuit elements: the modified Bell Telephone

Laboratory drive, the photocell pulse generator, the amplifier

driver, the time delay circuits and the timer and scaler control board. They will be described below in this order.

In our spectrometer, the values for the unassigned

circuit components of the Bell Laboratory drive [ll] are:

R=25K, C= . 1 pf, R-^=20K ten turn precision potentiometer in

series with a 500 ten turn precision resistor to ground. The

value of C-^ was changed to 1600 pico farads to damp out oscillations that occurred in the circuit. To D.C. couple the drive

a 300K resistor was placed across the 1 micro-farad capacitor,

C

2

. One should also note that the labeling of the power transistors in the publication in The Review of Scientific Instru32
: iiI

ce a; Ld LU

s}- o

'X 001o ’d’ rO

00 00 o

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•H

ft

33

in

constant

velocity

mode.
MONOSTABLE

MULTIVIBRATOR

BISTABLE

MULTIVIBRATOR

(

Delay

Circuit

)

34

Figure

10.

Circuit

for

generating

delay

pulses

for

controlling

timer

and

scaler.
« 10 V

-IOV

SCALER S TIMER CONTROL BOARD

+ IOV

EMITTER OUT

COLLECTOR

OUT

Figure 11. Interfacing between delay circuit and

RIDL scalers and timers.

dents was reversed. The positioning controls and R

5

were

found to he unnecessary and were deleted. To protect the

ower transistors from an open circuit a 390 ohm, one watt

esistor was placed from the output to ground.

.The photocell pulse generator (Figure 7) uses a Clairex

IL603 photocell to set the bias level for the base of transient Tl . When the light falls on the photocell T, goes from a

nonconducting to a conducting state. Transistor T

£

acts as an

amplifier and driver for the tunnel diode trigger circuit, con

sisting of D, and T

?

. The pulse is amplified by T, and T

5

pro

ducing a 40-volt pulse for the amplifier driver circuit. Fo,

35
the constant acceleration mode T^ produces the -lOv pulse to

reset the address scalers. Diodes Dn and D, were added to reduce the ripple of the power supply (RIDL Model 29-1) used so

that erroneous triggers caused by the ripple were eliminated.

The amplifier driver circuit (Figure 9) is a bistable [12]

and three transistors, (Tg, and T

1Q ). Transistor Tg is an

inverting amplifier for the output of one side of the bistables.

When the Tg is on, the output at pin F of P^ is -10 volts

,

and when Tg is off, Tg is on in saturation, or the output is

approximately grounded. Transistor T^ and T-^q are a cascaded

noninverting amplifier which establishes a positive D.C. level.

When *lrj is off the output at pin E, P^ is approximately grounded, and when T^ is on, the output at pin E, (P^) is +10 volts.

Now if one places a potentiometer between pins E and F of P^,

the symmetry of the voltage of the square wave can be adjusted,

which is the criteria necessary to run at different velocities

in the forward and backward direction in the constant velocity

mode

.

The time delay circuits were built by the National Bureau

of Standards Electronics Instrumentation Section. These circuits provide a time delay before the timer and scaler pairs

are turned on. One of the boards triggers on the positive

slope, and the other triggers on the negative slope of the input square wave. Because they are very similar, only a brief

description of the delay circuit (Figure 10) which triggers on

the positive transition will be given.

36
4. Time Delay Circuit [id!

The input square wave is amplified by overdriven amplifier

I .

\QLy. The amplified signal is used to trigger other circuitry.

| The circuitry associated with Qg and Q generates the delay initerval. This delay circuit is a monostable multivibrator in

I

| which Qg is normally conducting. But when the input square

wave makes its positive-going transition^ Qn is turned off 9 y

and remains off until the end of the delay interval. When

i turns on again,, the negative going voltage at its collector

! triggers the bistable multivibrator (Q^q and Q,-^) caus ing Q-,

to turn off; Q,-^ remains off until the negative-going transition of the input square wave resets the bistable nultivibrator

,

'turning Q,-^ on. Q-^ is an emitter follower stage employed to

prevent the output load from affecting the operation of the

bistable multivibrator.

The timer scaler control board is an electronic switch

to control the timer and scaler. The collector output is

connected to pin R of the Start-Stop bistable board in

scaler RIDL Model 49-43. The emitter out is connected to

pin L on the same board.

The spectrometer herein described is a great improvement

over previously published ones. The ideas are simple and

straightforward and we believe that they are the simplest and

most direct solution to many of the problems that confront

workers using electro -mechanical drives. The photocell slit

system can be used to control many of the drives presently in
use., and instruments other than RIDL multichannel analyzers

and counting equipment can be used.

The authors would like to thank Dr. James R. DeVoe for

his suggestion to use the address scalers to obtain the drive

signal,, and Ronald ¥. Shideler for his assistance and advice.

(F. C. Ruegg and J. J. SpijkermanJ

B. MBssbauer Spectrometer

A MBssbauer effect spectrometer was constructed which

incorporates the capability of simultaneous two system measurement with a pulse height analyzer. This instrument provides

a method for calibration of an unknown MBssbauer spectrum

against a standard spectrum,, or simultaneous comparison of two

spectra. The spectrometer is used to check the preparation of

MBssbauer Co-57 sources by measuring the spectra at different

periods during the anealing process to determine the degree of

diffusion of Co-57 in a crystal lattice.

A diagram of the entire system is shown in Figure 12.

A closed feed-back system is used which consists of a power

amplifier to drive a low frequency speaker,, a mechanical

connection to a pickup coil which is the voice coil of another

low frequency speaker,, a differential input operational amplifier which drives the power amplifier to complete the electromechanical feed-back loop. Open loop gain vs frequency response

curves indicated the proper feed-back network on the operational

'

I

amplifier to obtain maximum linearity in the response of the

electro-mechanical loop. The entire loop is D.C. coupled so

78
DOUBLE SPEAKER MOSSBAUER DRIVE CIRCUIT Figure 12. Complete diagram of Mtfssbauer effect

analyzer.

it is necessary to utilize a zero offset on the operation

amplifier to maintain the zero signal output of the amplifier

at -5 to -7 volts.

In order to minimize the 60 cycle noise in the operational

amplifier a hum bucking circuit is inserted to pin 1 of the

operational amplifier.

A triangular wave is introduced at the sum' point of the

operational amplifier. A frequency of about 2 cycles/sec was

dictated by the open electro-mechanical loop response curve.

Since the gain fall off began to occur at about 1 kc a maximum

of about 1% linearity could be expected for a triangular wave

input

.
With a triangular wave input to the operational amplifier an output with parabolic shape was generated. Consequently each half cycle contained a discontinuity at the intersection points of the parabolas. This point corresponds to the

apex of the triangular wave, and a small amount of ringing

was observed in the electro-mechanical loop at this point.

It was found necessary to "soften" the input triangular wave

at the apex by using an RC filter to cut off at 4 kc and above.

This eliminated ringing in the electro-mechanical loop., but

created some distortion in the motion at maximum velocity.

It had no effect on the useful portion of the velocity spectrum.

A 0.0001 pfd capacitor which bypasses the collector of

T1 to ground was placed in the power amplifier to eliminate

a high frequency oscillation (Figure 13). The output of the

pickup coil (second speaker) is amplified by the P65A amplifier

and connected to the base line input of the pulse height

analyzer. It is necessary to bias this signal 0 to -6 volts

in order to be compatible with the base line input requirements

of the analyzer.

The transducer system is shown in Figure 14. There are

two low frequency response speakers that have their chassis

bolted together. The diaphragm of the speaker was cut away.

The spiders of both speakers are rigidly attached together

with a plastic cylinder. An aluminum tube is attached at

right angles to this cylinder and the absorbers are attached

40
i

Figure l4. Double speaker Mttssbauer drive.

I

I

iL 4i
to each end of this tube. The radiation sources are mounted

to the chassis of the speakers. It is necessary to offset

the position of the source from the junction plane of the

speakers dince a magnetic field of about 60 gauss was found

in this region.

A single detector system is shown in Figure 12. The

detector-generated pulses are passed through a preamplifier,

RIDL model 10-8A and into the amplifier input on the pulse

height analyzer. The upper level discriminator and sensitivity

control (lower level discriminator) are adjusted to allow only

those pulses (e.g. energy of gamma-rays) of interest to open

the linear gate to the analog digital converter in the analyzer. This constitutes a modulation of the velocity signal

by the gamma-rays.

A list of the components of this system is as follows:

Hewlett Packard signal generator Model 202A

Philbrick operational amplifier Model USA-3

Philbrick operational amplifier Model P65A

Low frequency response speakers, Jenson Model P-12NF,

resonance frequency 20 c/s.

Pulse height analyzer. Radiation Instrument Development

Laboratories Model 34-12, modified to allow baseline input to the analog to digital converter

.

Radiation detection system. Two are used, sodium iodide

(T1 activated), 4 mm thick x 5 cm diameter with

0.0005" Be window.

Power amplifier. This amplifier was designed byR. J.

Carpenter, National Bureau of Standards, Division

l4. See Figure 13.

42
Preamplifier 3 RIDL Model 10-8A and Model 31-8A.

Mixer circuity RIDL Model 30-17.

A disadvantage of this system is its limitation on gammaray count rate. High count rate produces a non-linearity in

the spectrum due to the long analog to digital conversion and

data storage time. The limit to the pulse rate is on the order

of 5000 pulses per second.

A second detector is installed and simultaneous spectra

are recorded in the analyzer by time sharing subgroups of the

memory (see Figure l4). Appropriate preamplifiers (RIDL Model

31-8A) and logic circuits (RIDL Model 30-17) for the gamma-ray

detectors must be used. The slow (2 [is) coincidence logic

limits the overall detection efficiency of the system.

Performance of this system will be described in a subsequent report.

The author wishes to thank Dr. R. Deslattes, Section 9-5

and Dr. J. Spijkerman for their assistance in the electronic

design.

(J. R. DeVoe)

43
C . The Use of a Nuclear Transformation to Measure the Surface

Energy of Metals in Ultrahigh Vacuum

1 . Introduction . The term "hot atom" refers to an atom which has derived I kinetic or potential energy as a result of having undergone

a nuclear transformation. A hot atom may contain electrons

in an excited state or it may be ionized, and it may have

translational energy (recoil energy). It may be a stable or

a radioactive nuclide. Hot atoms may be detected individually.,

on the basis of their kinetic recoil energy, electrical

charge, or radioactivity. The recoil energy available to the

atom from the nuclear transformation is independent of its

surroundings, and in many cases is on the order of tens of

electron volts. These properties make hot atoms especially

suitable for use in surface studies. In the past, radioactive

atoms have been used as tracers for investigations of surface . migration, sticking coefficients, and desorption energies.

The availability of ultrahigh vacuum techniques makes it

possible to utilize hot atoms for the direct measurement of

surface energies of certain solids. The equipment described

below was designed to determine the applicability of hot atom

measurement techniques to the evaluation of the surface

energies of chromium, cobalt, and copper.

The experimental procedure used in this work involves the

preparation of an atomically clean metal surface with a high

specific activity of radioactive atoms decaying by electron

44
Ijbapture. The metal surface is prepared by thermal evaporation

of the source metal onto a tungsten backing in an ultrahigh

vacuum 10 10 torr) . Source atoms situated on or near the

surface receive enough energy from the neutrino emission

jassociated with electron capture to recoil from the surface.

(Specifically., the recoil energy for Cr^ 1 is 5.9 ev^ for Co J ^,

20.8 ev and for Cu^\ 25.5 ev. ) After leaving the surface a

fraction of the recoil atoms become ions by means of Auger

electron emission. The energy of these ions may be determined

by use of a repelling grid and a suitable detector. The grid

potential needed to stop the most energetic ions from reaching

the electron multiplier detector is a measure of the maximum

kinetic energy of those ions whose recoil is vectored in the

direction of the detector. This maximum kinetic energy is

equal to the initial recoil energy less that needed to break

free from the surface. Therefore this difference in energy

is the surface binding energy.

At the time of this writing the equipment is undergoing

further modification. The experience gained in the achievement of ultrahigh vacua and in the performance of the electron

multiplier detector and associated circuitry will be outlined

beloWj together with pertinent details concerning the

construction of the equipment,

j 2 . Apparatus .

a. Vacuum system . The block diagram of the vacuum

j system is shown in Figure 15 . With the exception of the

! 45
TIMER

Figure 15. Block diagram of the vacuum system.

mechanical fore pump, the vacuum system was contained entirely

on a wheel-mounted laboratory table 23" x 35" x 35" high. The

laboratory table was modified by mounting a 1" slab of transite

on the top and sheet metal across the base supports. The components of the system which were commercially available were

the fore pump (Welsh Duo Seal Model 1405H), the two-stage mercury diffusion pump (Delmar Scientific Laboratory DS-7050),

the Pirani Guage (CVC Model GP 105)^ the bakable valve (Granville-Phillips, 1/2", type C), and the ionization gauge

(Yarian UHV-12). The vacuum system was mounted so that the

low vacuum portion (from the diffusion pump to the bakable

valve) was below the surface of the table and the high vacuum

46
portion above the table top. (The table level is indicated

in the figure by the heavy line . )

The table surface served as the floor of an oven for

baking out the section in which the ultrahigh vacuum is obtained. Nichrome wires were mounted on ceramic standoffs

along the transite surface of the table,, and their temperature

controlled by means of a 30 amp variable transformer. The

walls and top of the oven were formed by slabs of "Foamsil"

made by Pittsburgh Corning. These slabs, 17 n

3c 22" x 2-1/2",

were wrapped in heavy duty aluminum foil which served as a

heat reflector and made them easier to handle without excessive chipping or flaking. The oven temperature was monitored

with a mercury thermometer (Fisher, 500°C) inserted through

a hole in the oven top. Alternate layers of sheet asbestos

and aluminum foil were placed below the tabie surface in order

to cut down heat transfer to the cold traps.

The liquid nitrogen traps were used to isolate the bakable

valve from the mercury vapor in the diffusion pump. The design

of the trap next to the diffusion pump was adopted in order

that vapors condensed on the walls of the trap would be prevented from escaping into the vacuum system as the liquid

nitrogen level in the trap fell (see sketch below). The trap

PUMP

VACUUM

VACUUM

MODIFIED VERSION

47
used in this system had a capacity of approximately two liters

and appeared to work quite satisfactorily 5 except that on one

occasion enough mercury condensed on the walls to form a drop

which ran down the tubing and out of the trap. The change

indicated in the right hand sketch would prevent this from

occuring and preserve the good features of this trap. The

second cold trap in the low vacuum line was a conventional

U-bend type trap. It was packed with strips of OFHC copper

which is an efficient adsorber of mercury vapor.

The titanium getter consisted of an uranium glass press

with O.O^O" tungsten leads and a 0.005" titanium ribbon about

0.04" wide. Current for heating the getter (and for heating

the other filaments incorporated in the system) was supplied

through a 6.3 volt' 10 amp center-tap transformer and controlled with a variable transformer.

b. Measurement tube . A tube (see Figure 16) was

constructed which would enable the kinetic energy of recoil

ions to be measured. The design and construction of the grids

and electrodes was done by Mr. Haliday of Division l4.02 5 and

the glass fabrication was the work of Mr. Houck of Division

43 .ll. The line drawing in Figure 17 shows the main features

of this tube. The sample was introduced into the system on

the small tungsten filament (A) (2 mm x 1 mm x 0.025 mm)

which was spot welded to 1 mm diameter tungsten rod. This

filament was fitted with a quartz cap and shutter assembly

(B) 5 which served to minimize the spread of radioactivity

48
Figure 16. Ultrahigh vacuum system including tube for

measurement of kinetic energy of recoil ions.

during the evaporative transfer of the source material. A

2 mm diameter hole in the cap allowed the sample to be transIferred, while the quartz disc attached to the back of the cap

!(prevented entry of the source atoms into the grid region.

I The small filament could be raised and lowered by means of

49
MEASUREMENT TUBE

A. SMALL TUNGSTEN FILAMENT

B. QUARTZ CAP AND SHUTTER ASSEMBLY

C- IRON SLUG

D. FLEXIBLE LEADS

E. LARGE TUNGSTEN FILAMENT

F GLASS COLLIMATING DISC

G.H.I.J. TUNGSTEN MESH GRIDS

K. 30mm PYREX TUBING TO ELECTRON MULTIPLIER

L. 40 mm PYREX TUBING TO VACUUM SYSTEM

Figure 17. Tube for measurement of kinetic energy

of recoil ions.

the glass-encapsulated iron slug (C) and an external magnet.

The filament was heated through the flexible leads (D)

.

After

the sample was transferred to the large tungsten grid (E), the

small filament and cap assembly could be lowered,, thereby

allowing the recoil ions to pass into the grid structure and

detector. A glass collimating disc (F) with a 1 cm diameter

hole served to limit the angle wherein recoil ions could

approach the grids. The grids (G 5 H a I, J) were made from

tungsten wires 0.025 mm in diameter knitted in a mesh of 52

wires per inch (available from the Met ex Electronic Corpora50
J tiorij Clark., New Jersey) . This wire mesh was sealed between

: uranium glass rings. The two end grids (G and J) were connectj

ed to a single tungsten lead out wire., while grids H and I had

| separate lead outs. The relative grid area occupied by the

!

! wire was about 6.k% for each grid,, and no more than 27)% for the

entire system. A controlled DC potential was available for the

grids by means of a 100 volt DC power supply (Electronic Measurements Company^ Model TR 212A) with appropriate voltages

j supplied through a ten-turn helipot

.

I c. Detector . The recoil ions which passed through

the grid structure were detected with an electron multiplier.

The multiplier structure was obtained from the CBS Laboratories ^ and is a standard structure used in their photomultiplier

tubes. It was sealed into 7052 glass tubing prepared beforehand in the NBS glassblowing shop., and had Kovar lead wires.

A dropping resistor string (see Figure l8) was mounted on a

Lucite tube to provide voltages for the dynodes. The switching arrangement shown in Figure l8 allowed rapid conversion

of the structure from an electron detector (positive high

voltage on the anode,, first dynode grounded) to a positive

ion detector (negative high voltage on the first dynode ^ anode

grounded). The multiplier structure leads were attached to

small clips mounted on the Lucite tube which housed the dropping resistors (see detailed sketch in Figure l8). These clips,,

suggested by Mr. Shideler of Section 5.01 j> allowed the dropping

resistor string to be easily replaced.

51
DROPPING RESISTOR STRING

Figure 18. Circuitry associated with the

electron multiplier.

Pulses generated by the multiplier structure passed from

the preamplifier to an amplifier (RIDL Model 50-19) and thence

to an electronic scaler (RIDL Model 40-26) with an electronic

timer (RIDL Model 5^--7). High voltage was provided by a 6 Kv

20 ma power supply.

5 . Operating Experience .

a. Vacuum system . The vacuum system proved to be

quite adequate for obtaining pressures as low as 10”^° torr.

In only one instance during the twenty or so bakeouts performed to date was there a failure of a vacuum system component.

A leak developed during bakeout in an ionization gauge-getter

pump (VIC., TV-34) which was incorporated in the system as a

52
jpump. No further difficulties were encountered after this

! gauge was replaced with the titanium getter previously described; and the pumping performance of the getter appeared to be

comparable to that of the ionization gauge-getter pump. At

! first the oven temperature was allowed to reach 450°C J, and

1 500°C for short periods. It was discovered that the 7052 glass

distorts under vacuum at these temperatures so the temperature

was then kept in the range of 400 to 420°C . The plug which

fits on the ionization gauge electrodes was found to loosen

1 as the gauge heated during operation. This loosening resulted

in spurious indications of pressure. The system functioned

well after the plug was replaced by clip connectors for each

: gauge electrode.

The following procedure was used for baking and outgassing

the vacuum system. After placing the oven over the system and

filling the cold traps with liquid nitrogen., the high vacuum

portion was opened to the mercury diffusion pump and the bakewas started. Generally the oven temperature reached about

400°C in one hour,, and was held close to this value for approximately eight hours. Then the system was allowed to cool to

1 o about 150 C and the outgassing of the ionization g«auge and

tungsten filaments was initiated. The ionization gauge was

outgassed for one hour,, and the tungsten filaments heated at

bright red temperatures for shorter periods. During the out- .

gassing the glass tubing was maintained at 120 to l60°C . On

i completion of the outgassing procedure the bakeable valve was

55
closed and the ionization gauge and titanium getter turned on

(the latter was maintained at bright red temperature). The

pressure generally dropped to the 10

- ^ torr range within one

hour, and to a low value in the 10

-10

torr region after three

or four hours. The lowest pressure obtained to date was

3 x 10~ 10torr. The manufacturer reports the X-ray limit of

this gauge to be 2 x 10

- ^

torr.

b. Measurement tube . The tube designed for measurement of surface energies was found to function well mechanically under ultrahigh vacuum conditions. The magnet (field

strength about 1700 gauss) readily moved the grid and shutter

assembly, and binding of glass-to-glass contacts did not prove

to be a problem.

Difficulty was encountered in placing the radioactive

sample on the small electrode. Several attempts were made

51 to electroplate Or on the tungsten electrode. This was

attempted both from solutions of Cr(IIl) and Cr(Vl). Deposi51 tion of the Or directly on the tungsten or on a nickelcoated tugsten surface could not be achieved. The method

finally adopted for placing the sample on the electrode was

to concentrate the solution by evaporation under a heat lamp,

and then to transfer it dropwise -with a micropipette to the

tungsten filament where it was evaporated to dryness. This

procedure, though tedious, did allow the major fraction of the

active sample to be placed on that side of the filament facing

the orifice in the cap (i.e., in the best position for evapora54
I tive transfer). The same technique was used with the Co-^ and

64

I the Cu samples.

Since the small filament holder was held in place by

! nickel sleeves and was readily detached from its housing, it

j was possible to insert the sample into the system with a

minimum exposure of the vacuum apparatus to atmospheric pressure. After an ultrahigh vacuum had been obtained the system

was brought to atmospheric pressure by admission of dry nitrogen. The glass tubing containing the sample filament holder

l

; was cracked off, a filament bearing the sample was inserted,

and the glass resealed, again under positive pressure of dry

I nitrogen. The vacuum system was baked out for about four hours,

and the metallic components degassed. This procedure facilitated the attainment of an ultrahigh vacuum in a relatively

short time after insertion of the sample.

c. Detector . Considerable trouble was encountered

because of noise in the detection system. This noise was of

two types: internal noise produced by the high voltage power

supply, and external RF noise from a television station and

: from induction furnaces operating in the area.

I The high voltage power supply must be extremely quiet,

j In this work it was necessary to take great precautions to

avoid any leakage of the high voltage through the transformers,

j rectifiers and other circuitry. The transformer was replaced

m I

j with a "power pack" which supplied rectified high voltage

' (controlled by a variable transformer on the input side)

55
directly to the series tetrode of the supply. This arrangement eliminated the high voltage noise problem.

The external noise pick-up was thought to be caused by inadequate shielding of the detector. The preamplifier was removed from its chassis and mounted on the Lucite tube that

housed the dropping resistors. A thin-walled copper cylinder

was placed over the multiplier and resistor structures, and

this cylinder grounded to the shielded cable of the signal lead'

going to the amplifier. This shield also served as the reference of the high voltage. These modifications eliminated pickup of the television signal, but did not solve the problem of

noise generated by induction furnaces. Since it appeared that

elimination of this noise would require considerable effort,

such as the construction of a Faraday cage, it was decided to

schedule the experimental work at times when there was minimum

likelihood of interference from the induction furnaces.

The original detector was a ten stage electron multiplier. . This multiplier proved unsatisfactory for this application because the internal noise generated a rather high background

counting rate. In order to get millivolt amplitude pulses

from the detector-preamplifier combination it was necessary

to have a voltage drop of about 4000 volts across the multiplier. Since the multiplier structure was designed to operate

\\ at no more than about 150 volts per stage, noisy operation at

very high voltages was understandable. The ten stage multiplier structure was replaced with a fourteen stage one from
I

,

.

the same manufacturer. This new detector gave millivolt output pulses with a 2000 volt drop across the multiplier structure and had a low background counting rate. No deterioration

in either multiplier's performance was noted as a result of

Ijrepeated opening and baking out of the vacuum system.

(J. Thompson)

57
5. ACTIVATION ANALYSIS

The activation analysis group is in the early stages of

development, and much effort has been directed towards plans , for new facilities at the NBS Reactor and the Linear Accelerator. Some work, however, is being started on analysis of

special standard reference material. During the past nine

;

i months one detailed effort In this area has been undertaken

by a visiting scientist from the U. S. Public Health Service,

Robert Keenan. His work involves a study of trace element

analysis in human lung by neutron activation. A preliminary

discussion of this work is given below.

A. Activation Analysis of Human Lung Samples

The primary purpose of this phase of the project is the

development and application of rapid one- or two-step radiochemical procedures for the separation of desired radionuclides.;

which are produced in biological samples by short irradiations

with thermal neutrons and which are determined subsequently by

gamma-ray spectrometric analysis of the separated fractions.

A further objective is the evaluation of chemical yield factors

which are established from consistent recoveries of the radionuclides in standard samples irradiated along with the biological samples. The yields are estimated by comparing the gammaray spectra of aliquots of the standard samples, carried through

the separation procedures, with those of other aliquots of the

same standards counted directly with the spectrometer. Throughout this work, efforts are made to define the optimal conditions
of each experimental procedure so as to provide the most consistent analyses consonant with conveniently executed laboratory techniques.

Ion exchange and liquid-liquid solvent extraction systems

are utilized to provide rapid., clean separations of the desired

radionuclides from sodium, present in part per thousand concentrations, and from one another., in part per million levels.

These separation procedures are applied to solutions of the

ashed biological samples. As there is a two-hour interval

from the end of the irradiation to the time of dissolution of

the ashed samples, the separation procedures must be sufficiently rapid to permit the completion of the gamma-ray analyses

within the subsequent three- to four-hour period and thus provide enough activity for valid counting of such radionuclides

as copper-64 and manganese -56

.

A supply of human lung samples from adult subjects, ranging up to 107 years of age, is available as the source of experimental material. These samples have been preserved in 10$

formalin from the time of collection. Since lungs are the target organs in exposures to atmospheric contaminants they should

contain most of the trace elements to be found in the human

organism. Hence, lung tissue is a most appropriate biologic

material for activation analysis procedures.

Since the reliability and the precision of activation

analyses exceed those of other methods commonly employed for

the development of analytical data on biological materials.

59
the careful application of the procedures devised and used in

this project may help to reduce some of the disparities observed among reported trace element data for adult human lung

tissue

.

1 . Instrumentation . An RIDL, Model 34-12, 400-channel transistorized spectrum

analyzer has been used for most of the analyses performed on

this project. Auxiliary components include a Harshaw Type 20,

MBWS, 16/5 B-X, 5

" ^ 4" sodium iodide (thallium-activated)

crystal with an aluminum well 7/8" I.D. x 2" deep. The crystal

is mounted in a stainless steel container and is coupled with

a 5

" multiplier phototube RCA 8055 with an external magnetic

shield. This crystal assembly is used in a custom-built shield

containing 5" thickness of mercury metal.

2 . Preparation Procedures .

a. Standard solutions . The first standard solutions

for this project were prepared from C.P. reagent grade chemicals

However, these were not sufficiently pure as evidenced by the

appearance of a small photopeak for sodium-24 at 1.38 Mev in the

gamma-ray spectra of the manganese and zinc standard solutions

13 after irradiation for 30 minutes with a thermal flux of 10

-2 -1

n cm sec . Spec-pure reagents manufactured by Johnson,

Mathey and Company, Ltd., London, England and supplied by

Jarrell-Ash Company, Newtonville, Massachusetts were then used

to prepare each standard solution. The oxides and salts used

for this purpose were CuO, MnCO^, ZnO, Co-^0^, NiO, SrCO^, and

60
|

cdO and the following solutions were made up in HNCh to

| provide separate standards with the stated element concentration per 100A of solution: Mn B:0.5 pig; Mn C:0.1 pig; Cu B:

2.5 pig; Cu C_:0.5 pig; Zn B:50.0 pig; and Zn (3:10.0 pig.

b. Reagents . HNO^,; concentrated: A 2-liter quantity of this reagent was redistilled in an all-borosilicate

glass still.

HNO^j, 1%: Prepared^ as needed; by dilution of the concentrated HNCU with distilled water,

p

Extraction dithizone solution: A 100-mg quantity of dithizone was dissolved in CCl^ A.C.S. grade; and made up to

500 ml.

Acetate buffer: Equal volumes of 2 M NaCgH^Cy, • and

2 M CH^COOH were mixed.

P

Hydrochloric, acid; 5 M, 3 M, 0.02 M; and 0.001 M: Prepared; as needed; from the C.P. concentrated reagent by dilution with distilled water.

Chloroform: A.C.S. grade; suitable for use with dithizone.

Carbon tetrachloride: A.C.S. grade; suitable for use with

dithizone

.

Acetylacetone : Reagent grade ; B.P. range 155-l40°C.

Diphenyl thiocarbazone (dithizone): A.C.S. grade.

Anion exchange resin; Dowex 1-X8; 20-50 mesh; chloride

form: Each batch was equilibrated in 3 M HC1 for 24 hours and

then washed with distil-led water until neutral to alkacid test

paper

6l
Fe, Zn, and Cu carrier: Prepared to contain 320 qg Fe +^.

25 pg Zn

+2

, and 1.25 pg Cu

+2

per ml of 5 M HC1.

c. Collection of human lung samples . Each sample,

consisting of a single piece of tissue, was preserved in a 10#

buffered formalin solution in a separate, screw-cap jar for a period of 1-1/2 to 2 years. Before use, the new jars were

chemically cleaned with chromic acid solution and concentrated

nitric acid, filled twice with tap water to remove the acid

fumes, and then rinsed 4 times with single - and then doubledistilled water. The plastic caps were washed with a detergent

solution, rinsed thoroughly with water, and dried in an oven

along with the jars. The cleaning of the jars and the prepar- ; ation of a single, 20-liter batch of formalin were performed

in the project leader's laboratory at the Occupational Health

Research and Training Facility, PHS, Cincinnati, Ohio. A

supply of the jars and a 4-liter portion of the formalin were

sent periodically to the pathologist who supplied the samples.

The request to the pathologist specified the following desired q

conditions to be observed in collecting the specimens:

1) Insofar as possible, obtain lung specimens from 100 0

consecutive autopsies of subjects over 21 years of

age so as to exclude those outside the adult population. jq

2) Take the sample from the lingula portion of the left h

upper lung as this is frequently the site for surgical u

lung biopsy. ® dt

3) Use care in handling the samples and avoid contact ,, r

62
with possible contaminants as the samples would be

analyzed for heavy metals.

4) Use the jars and the formalin provided.

5) Provide the information requested on the labels i.e.

hospital number, age, sex, and race,

d. Drying and grinding of human lung samples . The

lung samples were removed from their containers, rinsed with

distilled water, and then blotted and squeezed gently between

several layers of filter paper to remove the excess moisture.

The wet weight of the samples, contained in separate, weighed

250-ml Griffin beakers, were obtained with a Mettler balance.

The samples were then dried in a vacuum oven operating at 55-

58°C and 400-600 torr. A period of 5-5 days was required for

the drying of a group of 8-9 samples to constant weight by

this method.

When drying was complete, the beakers containing the sam- .

pies were placed on clean paper toweling on the bench to cool

and to permit equilibration of the containers with the laboratory atmosphere for a period of 1 hour. The dry weights of

the samples were then obtained.

The samples were transferred to separate, chemically clean,

60 ml, Clearsite (polystyrene) plastic vials. A 5/8 -inch Plexiglass (methacrylate) ball was placed in each vial which was then

capped with a polyethylene cover. The samples were shaken for

exactly 10 minutes in a Spex Industries Incorporated Model bOOO

Mixer/Mill. At the end of this period the sample appeared to

65
be finely ground. The ground samples have been stored in their

respective vials since grinding.

e . Preparation of encapsulated samples for irradiation . A supply of 3/4- and 1-1/4-inch lengths of Intramedic

polyethylene tubing, medical formulation PHF, .320" I.D. x

.364" O.D., Catalog No. PE430, Clay-Adams , New York was cut

and soaked in redistilled concentrated nitric acid for several

JL

hours. (Initially, the cut lengths of tubing were immersed in

aqua regia but this was discontinued after it was found that

leaching with nitric acid resulted in a reduced activity of the

polyethylene capsules after irradiation. ) The tubes were then

rinsed with several portions of distilled water and submerged

in several changes of distilled water over a period of 24 hours

They were rinsed with 2 portions of C.P. acetone, air-dried,

and one end of each tube was flame-sealed.

Each 3/4-inch tube was loaded with a 100A volume of the

appropriate standard solution in 1/ nitric acid medium. Two

standard solutions of a given element were prepared with the

concentrations of this element so chosen that the anticipated

quantities of the same element in the "unknown" lung samples

would be bracketed. The remaining open end of each standard

capsule was flame-sealed immediately after the introduction

of the solution.

Each 1-1/4-inch tube was loaded with a 125-milligram quantity of a dried, ground lung sample. The open end was flamesealed carefully. All sealed capsules were then submerged in i

64
redistilled, concentrated nitric acid for 2-3 hours and then

rinsed and leached with distilled water as described above.

lAfter rinsing twice with acetone and air-drying, they were

'transferred to several layers of paper tissues and taken to

Ijthe reactor site, without touching with the hands.

3 . Irradiation Procedure . The encapsulated samples and standards were placed in a

,‘polyethylene rabbit which was introduced into Glory Tube No. 2

fat the Naval Research Laboratory's research reactor. By means

!-of a length of twine, the rabbit was allowed to drop to a point

which was 13 inches from the bottom of the front face of the

Icore of the reactor. All irradiations to date have been conducted for exactly 30 minutes with a 5-minute cooling period.

4. Radiochemical Procedures

a. Ashing method . The capsules containing the

samples are cut open with scissors and the irradiated lung

samples are shaken into chemically clean, 20 ml Griffin

beakers. After the addition of 1-2 ml of concentrated nitric

acid the samples are evaporated on a low temperature hotplate

|(ca 130°C) nearly to dryness. After the addition of another

i

1 1—2 ml of the acid, the beakers are covered with clean watchJglasses and heating is continued. The samples are subjected

to this treatment and to alternate, brief heating at the highjest temperature obtained with the hotplate until ashing is

ijcomplete as evidenced by the production of a white or very

flight colored residue.
The sample is then treated twice with 10-12 drops of

concentrated HC1 and evaporated just to dryness on the low

temperature hotplate. This latter step serves a twofold

purpose - complete dissolution of the residue demonstrates

that ashing is complete and the double evaporation with the

acid is helpful in converting any pyrophosphosphate to orthphosphate. Pyrophosphate, formed during the high temperatures

reached in ashing procedures, will complex certain metallic

elements thus rendering them ionically unavailable for subsequent ion exchange separations or reaction with chelating

agents

.

The residue resulting from the hydrochloric acid treatment

is dissolved in 2 ml 5 M HC1. The sample is now ready for

either the ion exchange separation procedure or for one of the

solvent extraction methods.

b. Treatment of standard samples . The 10 and 50

qg zinc standard samples subjected, along with 4 lung samples,

to the first irradiation on this project were transferred to

tubes and counted directly. The resulting standardization

factors of 153 and 135 cpm per qg Zn showed remarkably good

agreement. This high degree of precision was also obtained

with other zinc standards in subsequent irradiations.

The copper and manganese standards irradiated on January

23, 19^4, along with 4 lung samples, were carried through the

same ion exchange separation procedure as that applied to the

ashed lung samples. Due to the poor agreement in the two

66
values of the standardization factors obtained for both copper

and manganese 3 it was decided that in subsequent runs it would

be advisable to split the standards after irradiation and to

count one-half of each standard directly and to carry the

other half through the radiochemical separation procedure.

By this approach it was hoped that (a) this would serve as an

independent check on the actual amount of radioactivity contained in each standard; by reason of the direct count; (b)

this would provide a means of estimating the chemical yield

applicable to the lung samples carried through the same separation procedure; and (c) the monitoring of the thermal neutron

flux inside the rabbit by means of the standard samples would

still be accomplished.

From the date of the third irradiation through the eighth;

the standard samples have been split after transfer from their

capsules to separate beakers. The transferred solutions are

acidified^ evaporated just to dryness; dissolved in 2 ml 5 M

HC1 and measured aliquots taken for the direct count and for

the application of the radiochemical separation method.

c. Ion exchange separation method . An extensive

amount of experimentation has been directed towards the evaluation of the optimal conditions for the separation and elution

of certain metallic elements; including zinc; copper; and

cadmium; which form chloro complexes and; as such; are adsorbed by an anion exchange resin. It was found that the final

exchange procedure used on this project provided complete

67
separation of these three heavy metals present in 125 mg of

dried lung in a total quantity less than 0.5 pCi, from a calculated 0.4 mCi of sodium-24 and 1.0 pCi of manganese-56 . The variables studied in this experimentation included (a)

the mesh size of Dowex 1-X8, (b) column length with a fixed

diameter of 0.6 cm, (c) flow rate ; and (d) molarity of HC1

for elution of separate metallic constituents. The final

conditions selected as the result of these studies are pre1 sented in the following procedure.

The ashed lung sample, containing 1000 pg carrier Zn and

50 pg carrier Cu, but no holdback carrier, is dissolved in

2 ml of 5 —M HC1. This solution is added to a 5 cm column of

Dowex 1-X8, 20-50 mesh, supported on a small pad of P.yrex

r glass wool in a 0.6 cm glass chromatographic tube prepared

rj from soft glass tubing. The lower end of the tube is constricted and fitted with a short piece of Tygon tubing and a screw

\ clamp to adjust the liquid flow to one drop per 4 seconds.

The effluent and the three, 2 ml 5 M HC1 eluates are combined

and may be analyzed for manganese -56 after separating this

radionuclide with acetylacetone using chloroform as extractant, j The copper is eluted from the column with four, successive

2 ml volumes of 5 M HC1 and these separate eluates are analyzed _ by gamma-ray spectrometry. Zinc is eluted with five, successive

j 2 ml volumes of 0.02 M HC1 which are likewise analyzed. Split

standard samples of Zn and Cu, irradiated at the same time as

the "unknowns" are carried through the ion exchange separation
procedure simultaneously., and the chemical yield of each of

these radionuclides is estimated by comparison with the gammaray spectrometric analyses of the other aliquots of these

samples which were counted directly. The chemical yield of

zinc- 69m obtained for the analyzed portions of a set of zinc

standards was determined to be 48$ on the basis of the data

from Irradiation No. 3 presented in Table 5-

Table 5. Analytical data on a pair of irradiated and

aliquoted zinc standard samples (using peak

height measurements of recorded 0.438 Mev

photopeak of Zn-69m)

.

Standard M-g Zn

in

Aliquot

Treatment

of

Aliquot

Total

CPM

Std.

Factor

(cpm/qg)

Chemical

Yield

(*)

Zn B 25 Direct Analysis 690 27.6 —

Zn C 5

n n 145 29.0 -- Zn B' 25 Ion Exchange 308 :

; || 44.7 - 10.4$*

Zn C' 5

n it 73 -- 50.4 - io.4$*

Errors are standard deviations of eight determinations.

The standard ' deviation of - 10.4$ shown in this table for

the chemical yield values is based upon the experimental work

^performed during the evaluation of the optimal quantity of

I carrier zinc. This value is possibly larger than that which

would be obtained from a repetitive series of recoveries with

the final procedure.

The chemical yield factor obtained from the analyzed

jStandards was used in calculating the total zinc~69m activity

Ifrom the activity obtained for the 5 eluates of each of the
lung samples carried through the ion exchange procedure. The

concentration of zinc was then determined using the mean of

the two values of the standardization factor reported in

Table 5 . These standardization data are applicable only to

samples irradiated at the same time as the standards.

d. Acetylacetone separation of manganese and

copper . The ashed lung sample is dissolved in 2 ml of 5 M

HC1. This solution is added to a 60 ml separatory funnel

containing 15 ml of the acetate buffer solution and 1 ml of

acetylacetone. The pH of the resulting solution is approximately 4.0. The funnel is shaken for exactly 1 minute in an

automatic shaker. A 2 ml volume of chloroform is added and

the funnel is again shaken for 1 minute. The chloroform laye

is transferred to a counting tube and stoppered. Three additional extractions are conducted., with the same volumes of

acetylacetone and chloroform added each time. The extracts

are analyzed for manganese-56 and copper-64,, using the 0.845

and 1.02 Mev peaks 5 respectively. The latter peak,, resulting

from the positron emission of copper-64 provides much greater

sensitivity than does the 1.54 Mev peak.

The manganese and copper standards are aliquoted and

analyzed in the manner described for the zinc standards in

the preceding section,, except that the acetylacetone separation procedure is applied to the split set of Cu and Mn standards after adding 1.0 ml of the Fe 5 Zn, and Cu carrier. All

activities are measured by peak height. The manganese -56

70
values are calculated back to zero time-, i.e. the time of

removal of the samples from the Glory tube of the NRL reactor.

The precision for the manganese separations was not very

satisfactory. The reasons for these variable manganese recoveries are being sought at present with additional experimentation. However,, the chemical yield factors obtained for a given

pair of standards have been used to calculate the total radioactivity of that nuclide in the lung samples irradiated at the

same time.

e . Dithizone method for the separation of zinc .

The aqueous portion remaining in the separatory funnel after

the series of acetylacetone extractions is extracted twice

with the 200 mg per liter solution of dithizone in CCl^ to

remove the zinc. Aliquoted zinc standards are carried through

two dithizone extractions after first extracting with acetylacetone twice to simulate the treatment of the lung samples.

The pH of the solution following the acetylacetone extraction

is suitable for the extraction of zinc dithizonate as shown by

a 92 to 96/ recovery of zinc-69m from aliquoted standard samples.

The results of the zinc ; copper ^ and manganese analyses

completed to date are presented in Table 6. The number and

the date of the irradiations and the radiochemical separation

methods are included in this table to permit the comparison

of results for a given element in separate aliquots of a lung

! sample irradiated on different dates and/or subjected to

| different separation procedures. Examination of these data

71
Table 6. Results of analysis of lung samples

(pg/g dry lung).

Radiochemical

Sample

No.

Irradiation

No. & Date

Separation

Method

Zn Mn Cu

26945 1 ( 12 - 19 - 63 ) Dithizone 28.0 _ _ 3 (3-5-64) 5 cm Ion Exchange 25.1 -- 9.6

26944 1 (12-19-65) Dithizone 50.4

3 (3-5-64) 5 cm Ion Exchange 42.4 — 11.2

5 (4-7-64) Acetylacetone -- 0.55

7 (4-25-64) Acetylacetone

Dithizone 58.2

0.70 4.0

26945 1 ( 12 - 19 - 65 ) Dithizone 70.4 _Ji

2 (1-25-64) 5" Ion Exchange -- -- 9.6

3 (3-5-64) 5 cm Ion Exchange 65.2 -- 12.8

5 (4-7-64) Acetylacetone -- 0.16

7 (4-25-64) Acetylacetone

Dithizone 151.6

0.29 14.5

29647 2 (1-25-64) 5" Ion Exchange — — 6.7

3 (3-5-64) 5 cm Ion Exchange 77.6 -- 12 . 0- 7 (4-25-64) Acetylacetone

Dithizone 54.0

0.54 9.7

26949 8 (5-5-64)

1 Acetylacetone

Dithizone 52.0

1.52 --

26950 5 (4-7-64) Acetylacetone — 0.46 —

7 (4-23-64) Acetylacetone

Dithizone 59.8

0.21 7.1

26952 8 (5-5-64) Acetylacetone

Dithizone 51.0

2.80 --

26955 8 (5-5-64) Acetylacetone

Dithizone 41.4

1.56 —

26997 5 (4-7-64) Acetylacetone -- 0.90 --

26998 5 (4-7-64) Acetylacetone -- 0.12 --

27001 8 (5-5-64) Acetylacetone

Dithizone 39.4

1.76 --

27005 5 (4-7-64) Acetylacetone -- 1.55 --

Ion Exchange: Dowex 1-X8 5 20-50 mesh.

Using annihilation radiation peak at 1.02 Mev.

72
! will show that the precision of the methods (estimated to he

equal or less than an error of 10$ standard deviation) needs

| to he increased hy improving the procedure for determining

the chemical yields. It is believed that this may be done in

j the case of copper and zinc on the basis of experimentation

I

| in progress

.

It is possible that the conditions of the acetylacetone

method for the separation of manganese may be refined sufficiently to provide results with an acceptable degree of reproi ducibility . However., efforts in this direction must be discontinued at present to permit refinement of the procedures for

copper and zinc.

A summarized tabulation of our analytical data is presented in Table 7 which contains 5 for comparative purposes 5 a

summary of the values reported in the literature, for the same

elements in adult human lung samples from subjects who were

victims of accidental death and ostensibly free of disease

according to the reports of the examining pathologists.

j Examination of the data in Table 7 will show that our data

are in the same concentration ranges as those of several

(investigators who used emission spectrographic procedures

for the analysis of the trace element content of human lungs.

(R. G. Keenan and J. H. Marcus)

77
Table

7.

Comparison

of

concentrations

of

zinc.,

copper,

and

manganese

reported

in

normal

human

lung

samples

from

adult

victims

of

accidental

death

with

those

reported

in

Table

6

for

current

project

(expressed

as

p.g

element

per

gram

of

dried

tissue).

74
6 . MISCELLANEOUS

This section of the progress report contains miscellaneous techniques of interest and. usefulness to several areas

but which do not particularly fit into any one category.

A. Positive Sealing with Optical Coupling of Radioactive

Sources in Machined Plastic Phosphor Scintillators

If one is interested in doing high efficiency heta counting, a plastic scintillator is often the most convenient way.

The usual method Is to optically couple the scintillator to a

I

| phototube,, and the light pulses are amplified and analyzed by

a variety of electronic equipment. It is always necessary to

i incorporate a radioactive standard into the measurement technique. In order to assure that a standard can be safely

handled over a long period of time,, some type of positive

sealing is necessary. The following paragraphs describe a

technique which we find give a positive seal with retention

of optical clarity at the seal.

Positive sealing of machined polyvinyltoluene plastic

phosphor beta scintillators (NE-102, obtained from Nuclear

! Enterprises , Ltd., Winnipeg,, Canada) was achieved using Carl

i Biggs No. 823 epoxy resin (Carl Biggs Company, Santa Monica,

California). The procedure is as follows:

1) Thoroughly clean the plastic surfaces with methanol.

2) Cover exposed top of plastic sample container (see

Figure 19) with Parafilm to prevent contamination

with radioactive material. (Note l) .

3) Carefully pipet liquid radioactive solution into

75
plastic sample container.

4 ) Evaporate liquid material. (Note 2).

5) During the evaporation period (usually at least one

hour) thoroughly mix nine drops of No. 825 resin and

one drop of hardener. This quantity is sufficient

for at least one scintillator.

6) Remove dissolved air from the mixed resin by applying vacuum. (Note 5 ).

7) After the radioactive solution has completely dried,

remove the Parafilm from the sample container and

cover both surfaces (top of container, bottom of lid)

with the resin, using a spatula. (Note 4 ).

8) Carefully place the scintillator lid on the container,

and place a 50-100 gram weight on the top of the

scintillator. (Note 5 ).

Figure 19 . Beta scintillator, machined from NE-102

plastic phosphor.

76
Note 1. Before applying the Parafilm, a hole was punch

ed in the film to allow depositing the radioactive material into the container. Care must

be taken so the Parafilm does not come in contact with the white reflective coating around

the outside of the scintillator 5 since the Para

film has a tendency to remove the coating.

Note 2. Heat may be used to assist in evaporating the

liquid sample 9 but caution must be used since

the melting point of the plastic is around 75°C

Note 3. A simple water aspirator applied through an

inverted funnel with the resin in a small watch

glass gave satisfactory results. A higher

vacuum would be better.

Note 4. The resin should not be applied to a warm

scintillator , since the decreased viscosity of

the resin causes separation of the container

and lid.

Note 5. If a piece of glass or clear plastic is used as

the weight 5 the transparency of the seal may be

continuously monitored. Small bubbles can be

removed by lightly pressing on the weight.

Curing time of the resin is rather long^ set at between

12 and 24 hours for complete hardening. The sealed scintillators may be gently handled after about two hours. This

epoxy resin^ when properly used., gives a highly transparent

seal.

(D. A. Becker)

B. Ion Exchange Resins -- General Consideration

The most important consideration in any experiment is to

control the variables so that reproducible results may be

obtained. In Figure 20 and 21 are shown the apparatus for

regeneration of ion exchange resins and for the gradient

elution of an ion exchange column.

77
There is a need for regenerating new resins by taking it

through several cycles in order to remove trace impurities.

To obtain uniform resin size the resin ought to be back washed,

(that is upward flow of water through an ion exchange resin to

cleanse it of foreign material and reduce the compaction of

the resin bed). Backwashing the resin is perhaps the most

important step, and is the most often omitted step, in preparing a uniform clean resin.

APPARATUS FOR REGENERATION OF ION EXCHANGE RESIN

C

ALL STOPCOCKS ARE THREE WAY

UP FLOW -M-+ DOWN FLOW

Figure 20. Apparatus for regeneration of ion

exchange resin.

In Figure 20 is shown the apparatus for regeneration of

an ion exchange resin. Three-way stopcocks were used.

78
'When a cationic resin was used., the following procedure is

iemployed:

| 1) The resin was washed upflow with thirty bed volumes

of demineralized water. The stopcocks were opened

so that the water flows through B to A to C and out

through D.

2) The resin was changed downflow with 6 N HC1 to remove

any iron present. The valves were opened so that the

acid flows from B to C through the column to A and

out through D. It is to be noted that the stopcock

D is located above the resin level so that the resin

can never go dry.

I 9) The acid wash was followed by thirty bed volumes of

demineralized water.

4) The resin was converted to the sodium form with 5%

sodium hydroxide. The resin is converted to the

sodium form by running the base through the column

upflow to allow for expansion.

5) The resin was then treated with sixty bed volumes of

a 1% solution of EDTA. The EDTA was passed through

the column downflow as was another thirty bed volumes

of demineralized water.

6) The resin was then washed with demineralized water

flowing upward through the resin.

Figure 21 shows an apparatus for gradient elution studies

of an ion exchange resins. The charging solution enters the

columns through stopcock No. 8. The column could De eluted

I with varying solutions through stopcocks 4,5*6., 7 and enter

i the columns through 9 and 10 respectively. After the experiment is complete the column is4 regenerated and washed with

non-ionic detergent pumped from 2 through the apparatus.

The column would be washed upflow by opening stopcock No. 9*

jNo. 9 to No. 11 to No. 19 and No. 10 to 12 to No. l4. This

I would be followed by demineralized water.

79
I

APPARATUS FOR GRADIENT ELUTION STUDY OF ION EXCHANGE RESIN

Figure 21. Apparatus for gradient elution study

of ion exchange resin.

(A. R. Langrebe)

80
7. PERSONNEL

Radiochemical Analysis, J. R. DeVoe, Section Chief

Group I. Radioisotope Tracer Techniques

A. R. Landgrebe

L. T. McClendon

P. A. Pella

Group II. Activation Analysis

G. W. Smith

D. A. Becker

¥. P. Reed

H. Kocol

H. D. Robertson., Summer Student, terminated

September 1, 1967

J. M. English

J. H. Marcus

R. G. Keenan, Guest Worker from U. S. Public Health

Service,* Occupational Health Research

and Training Facility, Cincinati, Ohio

K. H. Miller, Summer Student, 1964

M. Cabell, Summer Student, 1964

Group III. Radiation Techniques

(a) MBssbauer Effect

J. J. Spijkerman

F. P. Ruegg

L. Lynch, Summer Student, 1964

(b) Nuclear Recoil

J. L. Thompson, Post Doctoral Fellow

Group IT. Instrumentation

R. W. Shideler

A. J. Gerber

T. L. Dvorak, terminated

81
8 . ACKNOWLEDGEMENTS

The Radiochemical Analysis Section wishes to thank

Dr. J. Elliot, Mr. E. Nowstrop and Mr. L. Harris of the Naval

Research Facility for rssisting us with the use of their

reactor and laboratory. We also wish to acknowledgement the

assistance of the NBS Health Physics staff who helped us with

the irradiations during the past year.

We also wish to acknowledge the assistance of Mr. Goetz,

chief of the Plant Division, NBS, and Mr. Francis Clark,

ventillation engineer who designed and supervised construction

of the clean room and its facilities.

The section acknowledges with thanks Mrs. R. S. Maddock

foi her assistance in preparing this report. Special appreciation is expressed to Mrs. M. Fenstermaker whose tireless

efforts as section secretary has made our entire operation

more efficient and effective.

82
9. LIST OF REFERENCES

[1] Ruzicka, J. and Stary, J. , Talanta _8, 228 (1961).

[2] Ruzicka, J. , Stary, J. and Zeman, A., Talanta 10, 105

(1963).

I [ 3 ] Gayer, K. H. and Woontner, L. , J, Am. Chem. Soc. 74 , 1436, 5057 (1952).

[4] Johnston, J. and Grove, C., Am. Chem. Soc. ^8, 3976

(1931).

[ 5 ] Sutcliffe, L. H. and Weber, J. R. , Trans. Faraday Soc.

52, 1225 (1956).

I [6] Baxendale, J. H. and Wells, C. F., Trans. Faraday Soc.

53, 800 (1957).

[7] Dural, J. E. and Kurbatov, M. H. , J. Phys . Chem 56 , 982 (1952).

[ 8 ] Kurbatov, M. H., Wood, G. B. and Kurbatov, J. R.

,

J. Chem. Phys. 19, 258 (1951).

[9] Kurbatov, M. H., Wood, G. B. and Kurbatov, J. R.

,

J. of Phys. Chem. 55 , 1170 (1950).

[10] Kankeleit, E. , Rev. Sci. Instruments, 35, 195 (1964).

[11] Cohen, R. L. , McMullin, P. G. and Wertheim, G. K.

,

Rev. Sci. Instruments 34 , 671 (1963).

[12] Kilpatrick, D. G. , Dittrich, W. A. and Emmel, D. T.,

Transistor Reference Book, Philadelphia, Pennsylvania,

M. W. Lads Publishing Company, 1st Edition 1963;

p. 237.

1 83

* U. S. GOVERNMENT PRINTING OFFICE : 1964 O - 740-951


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maximum application of the physical and engineering sciences to the advancement of technology in industry and commerce. Its responsibilities include development and maintenance of the national stand- ards of measurement, and the provisions of means for making measurements consistent with those standards; determination of physical constants and properties of materials; development of methoda

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