Analytical Mass

Spectrometry Section:

Summary of Activities July 1966 to June 1967

426

***t or ^

U.S. DEPARTMENT OF COMMERCE

National Bureau of Standards
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associated materials services including mainly reference materials and data on the properties of materials. Beyond its direct interest to the Nation's scientists and engineers, this Institute yields services which are essential to the advancement of technology in industry and commerce. This Institute is or- ganized primarily by technical fields: —Analytical Chemistry—Metallurgy—Reactor Radiations—Polymers—Inorganic Materials—Cryogenics2—Office of Standard Reference Materials. THE INSTITUTE FOR APPLIED TECHNOLOGY . . . provides technical services to promote the use of available technology and to facilitate technological innovation in industry and government. The

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UNITED STATES DEPARTMENT OF COMMERCE

Alexander B. Trowbridge, Secretary NATIONAL BUREAU OF STANDARDS • A. V. Astin, Director <*2^ TECHNICAL NOTE 426

ISSUED SEPTEMBER 15, 1967

Analytical Mass

Spectrometry Section: Summary of Activities July 1966 to June 1967

Edited by William R. Shields

Analytical Mass Spectrometry 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 40 cents
The Analytical Chemistry Division was established as a separate division at the National Bureau of Standards on September 1, 1963, and became part of the Institute for Materials Research in the February 1, 1964, reorganization.

It consists at present of nine sections and about 100 technical personnel encompassing some 45 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 standard reference material or service analysis.

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 our 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 a Technical Note. In 1967 we plan to issue these summaries for all of our sections. The following is the second annual report on progress of the Analytical Mass Spectrometry Section.

W. Wayne Meinke, Chief Analytical Chemistry Division
PREFACE

The basic function of the Analytical Mass Spectrometry Section is to establish high accuracy absolute isotopic ratio

standards. To this end the section is concerned with developing instrumentation and devising analytical techniques which will improve the precision of isotope ratio measurements;

and at the same time it has the responsibility of developing

the chemical procedures necessary for the preparation of the calibration standards necessary to convert the analytical

precision statement to an accuracy statement.

This Technical Note has been written in an entirely different vein than Technical Note 277- The intent of the first Technical Note (277) was to define our position after

8 years of effort and is truly more of a cook book or operating manual than anything else. This Technical Note is intended as a summary of our effort for the fiscal year of

1967. There have been more major changes during the past year than in all the previous history of the section. The section

now has its own chemists and chemistry laboratories, and has moved in its entirety to the new facilities at Gaithersburg.

It is to the credit of the group that the section has doubled

in personnel, moved twenty miles, acquired the space and equipped two chemistry laboratories, built two mass spectro- meters, and at the same time managed to do most of its normal work load all within the past year. William R. Shields, Chief Analytical Mass Spectrometry Section
TABLE OF CONTENTS INSTRUMENTATION 1 A. Introduction 1 B. Facilities 1 C. Research Activities 2 1. Multi-stage Mass Spectrometer 2 2. High Vacuum Beam Valve 2 3. Z Focussing Source 7 4. Redesigned Collector 7 5. Filament Degas Chamber and Controls 11

6. Sample Drying 11

D. Assistance Activities 15 CHEMISTRY 16

A. Introduction 16

B. Facilities 18

1. Stable Isotopic Chemical Laboratory 18

2. Radioactive Isotopic Chemical Laboratory ... 20

3. Balance Room 20

4. Instrument Room 20

C. Boron 23

D. Chromium 27

E. Fluorspar 29

F. Lead 30

1. Lead Minerals 31

2. Preparation of Lead from Mineral Samples ... 32

3. Archaeological Samples 33

G. Plutonium 34

1. Chemical Standard 34

2. Isotopic Standard 34 MASS SPECTROMETRY 35

A. Boron 35

B. Chromium 4l

C. Lead 4l

D. Plutonium 44

E. Rubidium 44

F. Uranium 45 PERSONNEL AND ACTIVITIES 46

A. Personnel Listing 46

B. Publications 46

C. Talks 50

D. Committee Activities 51 REFERENCES 52
LIST OF FIGURES

FIGURE NO. PAGE

1. Main instrument laboratory 3 2. Flight path of two-stage instrument 4 3- Two-stage instrument 5 4. Cross section of beam valve. .' 6 5. Z lens source assembly 8 6. Source controls 9 7. Collector assembly (standard) 10

8. Filament degas chamber and controls 12

9. Schematic of filament degas controls . 13 10. Sample dryer arrangement in hood 14

11. Sample dryer arrangement on table 15 12. and

13. Stable isotopic chemistry laboratory 19

14. and

15. Radioactive isotopic chemistry laboratory 21 16. Balance room .......... 22 17. Instrument room 22 LIST OF TABLES TABLE NO.

1. Boron recovery by chloroform-2-ethyl-l ,3-hexanediol extraction procedure .... 26

2. Determination of possible boron isotopic fractionation 27

3. Calculated atomic weights for "normal" leads ... 32

4. Organic extraction of ANL-II without control of excess S0 2 water . 36

5. Organic extraction of ANL-II with known volume of

S0 2 water added before extraction into 2-ethyl-l,3-hexanediol . 37

6. Organic extraction of ANL-II with control of excess S0 2 water by digesting solution uncovered and at temperature of 80° to 85°C. . . 38

7. Comparison of 95$ confidence limits (to) of best data on replicate lead isotope analyses by various methods .43
ANALYTICAL MASS SPECTROMETRY SECTION: SUMMARY OF ACTIVITIES

JULY 1966 TO JUNE 1967 Edited by William R. Shields

This report describes the advances in instrumentation

and the research activities of the Analytical Mass Spectrometry

Section during the period July 1966 to June 1967- Advances in instrumentation include the construction of a multi-stage mass spectrometer, a high vacuum beam valve, a Z focussing lens, a re-designed collector, a filament degas chamber, and new equipment for sample drying. The new facilities at Gaithersburg are described. Elements studied during this period include: B, Cr, Pb

,

Rb , U, and Pu. Chemical procedures are given for B, Cr, Pb, and Pu; mass spectrometric procedures are given for B, Cr, Pb

,

Pu, Rb, and U.

Key words: Mass spectrometry, instrumentation, procedures,

isotopic analyses.
1 . INSTRUMENTATION

A. Introduction

The primary analytical tool of this laboratory is the mass spectrometer and this section of the report will deal with the changes and/or improvements that have taken place within the past year on the spectrometers. There is, of course, a large amount of ancillary instrumentation used by the chemists and mass spectroscopists , and they will discuss these items in their section of this report.

B. Facilities

The Analytical Mass Spectrometry Section was moved to the new Gaithersburg site during September and October 1966. Prep- aration of mass spectrometers (5) [ref. 1, p. 1] and other apparatus for the move to the new laboratory facility was started 2 weeks before arrival of the packers. Disassembly of each spectrometer included removal of the analyzer tube, pumping system, electronics, and utilities. Diffusion pumps

and components of the analyzer assembly were cleaned and, where practical, sealed in plastic bags. The empty electronic

console was separated from the magnet support frame and divided into two smaller units to facilitate handling. The magnet and frame, with appropriate preparations, were moved as

a unit. The components of the analyzer assembly were moved by automobile or station wagon. The bellows in the pumping arm

of a source housing was ruptured and was the only apparatus to suffer major damage during the move.

The electronic console and magnet frame were mated,

leveled, and electronic panels mounted. Reassembly of the flight tube and pumping system was not started until utilities

to each spectrometer were completed. The first spectrometer

was operational two weeks after the equipment arrived at the new site, and the remaining spectrometers were reassembled and operational at the rate of one per week.
The mass spectrometer laboratory consists of nine modules divided as follows: (1) four modules for the main instrument

bay (figure 1); (2) one module divided into two rooms, one room for source, collector, and filament cleaning and assembly,

the second room for sample handling. The cleaning room is equipped with one hood. The sample handling room contains two hoods, one for low level radioactive materials and one for high level radioactive materials; (3) two modules for a threestage mass

1 spectrometer ; (4) two modules for a shop to fabricate electronics.

C. Research Activities

1

.

Multi-stage Mass Spectrometer

The first two stages of a three stage mass spectrometer

have been designed and constructed and are now operational.

The optical path chosen is an off axis extended flight path

"S" configuration (figures 2 and 3).

2. High Vacuum Beam Valve

The need for high vacuum operation, with large volume vacuum envelopes and rapid recovery time, created a demand for

an effective beam valve, i.e. in the flight tube itself. The resultant valve is shown in figure 4. The valve is still under

test with major emphasis on the beam valve seal material. The thruput opening is .375 x .750 with the seal being cut back, .031 from the opening. The initial material used for the seal

was teflon; this material, however, peels when subjected to rotary motion under pressure. It was discovered that several

shreds protruding into the thruput opening were sufficient to virtually shut off the ion beam, this due to the electrostatic

charging of the teflon. Preliminary steps are being taken to test a poly resin compound which is carbon impregnated; the carbon should provide the desired electrical conducting

properties

.

; I
a.o

-

1 *

3 . Z Focussing Source

The dispersion in the Z axis of the ion beam had to be reduced in order to maintain reasonable transmission efficiency

in the multi-stage instrument. A source containing elements

for Z focussing has been developed, tested, and put into use. The testing of this source was done on one of the single stage

12" machines and worked so well that all of the instruments

have now been converted to include Z focussing. Figure 5 is

a schematic of the new source that is currently being used on all our instruments. Figure 6 is a schematic of the control panel necessary to focus the source. We designed a number of panels before we settled on this circuit. The idea of a single circuit for focussing on all instruments 6", 12", multi-stage,

requires that the circuit have a great number of degrees of freedom.

This source increases the transmission efficiency of the single stage 12" instruments by a factor of from 3 to 4 and thus allows us to control the filament biases over a much

larger range, and for those elements where we had fairly low ionization efficiency we now have a stronger signal and greatly

improved precision.

H . Redesigned Collector

The collector has been redesigned to include the same

slot type mount as the new source (figure 7). This type mount

allows for a much higher accuracy in the alignment of the slits,

and the entire operation, fabrication, installation, and alignment, is done without any jigs or fixtures. When the tube

is placed horizontally on a surface plate the slot for the collector can be set horizontal with almost any dial gage, the

slot for the source mount will be vertical at this time but by clamping a precision square in the slot with a gage block you

have a horizontal reference surface. The diameter of the collector mount was also increased to allow greater pumping

speed to the collector housing.


8
5

Filament Degas Chamber and Controls

The requirement for sample filaments to be free of alkali

and alkaline earth contaminants lead to the construction of a vacuum chamber with provisions for thermally ionizing and collecting the ions of these materials from six filaments simultaneously (figure 8). The filaments are maintained at a voltage potential difference of approximately +180 V DC with respect to a plate located 3/^" above the filaments. When the filaments are heated, by an alternating current, the ions produced on the filament surfaces are drawn off to the above

plate. The filament heating current is controlled by a variable transformer with a current meter on the output side. This control is necessary for handling different filament materials as well as different numbers of filaments. By means

of the measuring circuit the ion current may be observed and

the cleaning process maintained until the desired minimum

current is reached. Two possible situations are:

(1) uniformity in contaminant level or (2) complete reduction

of contaminant.

The vacuum system incorporates a mechanical pump with thermocouple gauge and a 100 liter/ion pump. After the starting pressure for the ion pump is reached the mechanical

pump is valved off by a 1" ball valve. All controls, except ion pump, are indicated in figure 9.

6Sample Drying

Samples are loaded on the filaments in solution and must

be dried and/or taken to a metallic state for use in the mass spectrometer. The use of radioactive materials require that

this be done in a hood and that the controls be outside the hood (figure 10). The use of a single filament with non- radioactive materials may be handled on the table top (figure 11). Both of these units are composed of a low voltage transformer with a current control to reach and maintain a desired temperature thru the filament being loaded. External

drying is accomplished by the use of a 250 watt heat lamp.

11

! iill:

13
^* ^#|

rd

Figure 10. Sample dryer arrangement in hood.
Figure 11. Sample dryer arrangement

on table.

D. Assistance Activities

During the past year a large number of instrument drawings

and electronic schematics were furnished to other laboratories interested in constructing or modifying mass spectrometers

similar to those used in this laboratory. Electronic controls

have been designed and fabricated for use in other areas of the NBS . Two Leeds and Northrup Speedomax W recorders were rebuilt to provide expanded scale measuring [ref. 1, pp. 11-

16]. These instruments were modified by request of:

(1) Oberlin College, Oberlin, Ohio; (2) Kansas State University,

Manhattan, Kansas. Both instruments are in operation and the concerned individuals report much higher precision than that obtained prior to the modification.

(W. A. Bowman, III)
2 . CHEMISTRY

A. Introduction

This group was started with the transfer of Thomas J. Murphy from the Microchemical Analysis Section in May of last

year. Lawrence A. Machlan joined us in July after transfer

from the Analytical Coordination Chemistry Section, and Keith M. Sappenfield joined us in October also after transfer

from the Analytical Coordination Chemistry Section. The personnel of this group have over 50 years combined experience

in analytical chemistry, most of which is in the high precision

- high accuracy field. Mr. Machlan and Mr. Murphy have been engaged for a number of years in the programs of this section,

so the transfers had the effect of giving this section its own chemical competence without having it spread thru the other

sections of the division.

There are three projects within the group. The first project deals with the determination of atomic weights by direct measure of their absolute isotopic concentrations.

There are three possible sources of error in atomic weights determined by this method: (1) errors due to nuclidic

mass measurements, (2) errors in the measurement of isotopic

composition, and (3) undetected natural variations in isotopic composition. The nuclidic masses are now known to better than one part 'in a million (with few exceptions), so errors due to this source are negligible. The measurement of isotopic composition, however, is not in such satisfactory

condition. Bias due to mass discrimination causes errors which

can be corrected only by the use of standards prepared from separated isotopes. The accurate preparation of these standards

requires that the separated isotopes be mixed with an accuracy

of ± 0.01$. The major effort of this project is toward the development of precise and accurate analytical procedures and proven stoichiometric forms so that the isotopic standards can

be prepared with the necessary accuracy. Since most of the

16
classical methods of analysis have not been proven to better

than 0.1%, new methods must be developed. These methods must utilize only small samples (1-5 meq.) since the amounts of separated isotopes available are usually small. The methods developed to date have included such analytical disciplines as constant current coulometry and amperometry as with chlorine

[2], bromine [3], and chromium [4]; a combination of electro- deposition and spectrophotometry as in the case of copper [5]; and gravimetry as in the case of magnesium [6]. In the future

it is expected that other analytical disciplines will also be used.

To define the error due to natural variations in isotopic

composition, it is necessary to establish the constancy of isotopic composition in nature or to establish limits of variability by measuring the isotopic composition of a number

of mineral samples of different origin. These mineral samples

must be processed chemically and converted to a form suitable

for mass spectrometric analysis. This entails processing and measuring a large number of mineral samples; for example over

100 minerals in the case of copper [7] and 60 minerals in the case of magnesium [8]. This has been a highly successful program. To date the atomic weights of six elements have been re-determined. They

are silver, chlorine, bromine, copper, chromium, and magnesium.

In 1965 the International Commission on Atomic Weights accepted

our values for silver, chlorine, copper, and bromine as the recommended atomic weights [9]- Chromium and magnesium will be considered this year. The second project deals with nuclear isotopic standards

for mass spectrometry. We are responsible for the preparation

of precise and accurate isotopic composition standards from separated isotopes so that the absolute abundance ratios of standard materials of vital Interest to the nuclear industry

can be determined. There are certain parallels between this program and the atomic weights program in that both require

17
the development of precise and accurate methods of analysis so that isotopic standards can be prepared, but there is the added difficulty in this program of the high radio-activity of most of the isotopes. Accurate standards have been prepared

for uranium and ten uranium isotopic standards have been

certified. The preparation of accurate calibration standards

for plutonium and boron are planned for the near future. The third project has to do with trace characterization

by isotopic dilution. This section has not been active in this field in the past, but we plan to start work later this fall. The initial effort will be directed toward the quantitative

preparation of stock "spike" solutions of separated isotopes

and the development of chemical techniques to extract and purify the elements under study. A major advantage of this technique is that once the isotopic spike has been added, none

of the following chemical steps need be quantitative.

B. Facilities

The chemical facilities consist of a double module general purpose laboratory, a single module radioactivity laboratory,

a balance room, a double module instrument room shared with Section 310.07 and an office. These facilities have been modified and equipped since July 1966.

1. Stable Isotopic Chemical Laboratory

The stable isotopic chemical laboratory, (figures 12 and

13) is a double module room with two hoods. Equipment includes

a controlled potential electro-analyzer for the separation of metals, a constant current coulometric analyzer for precise electrochemical analysis, a quartz still for producing ultrapure water, a high temperature muffle furnace, a tube furnace,

pH meters, reagent balances, automatic titrator, and other equipment normally found in a general purpose wet chemical

laboratory

.
Figures 12 and 13. Stable isotopic chemistry laboratory.
2

. Radioactive Isotopic Chemical Laboratory

The radioactive isotopic chemical laboratory (figures 14 and 15) has recently been completed. The 2 hoods and the 4 glove boxes were moved from the old NBS site. The responsibility for this radioactivity work was transferred to Section

310.06 in July 1966 with a corresponding change in location

for the radioactivity laboratory. In addition to the delay caused by this change, other delays were encountered in coordinating the contractor and NBS plant sections and in problems with dampers, ductwork, motor, and fan. Figure 14 shows a glove box containing a microbalance for precision

weighing of radioactive materials and a large hood that will

contain a tube furnace for ignition of samples and have space

for other uses. Figure 15 shows a fume hood and large glove

box for work with solutions of radioactive materials, a glove box with gloves for high activity materials in solid form, and

a glove box containing a 200 g capacity balance that will be used primarily for weighing radioactive solutions. This laboratory has been designed for work with uranium and Plutonium at the present time and will be available for use with other radioactive materials in the future.

3

.

Balance Room

The balance room (figure 16) contains one 200 g capacity

macro-analytical balance, two 100 g capacity semi-micro

balances, and one 20 g capacity microbalance. These balances

have been placed on 700 pound marble tables to minimize

vibrations

.

4

.

Instrument Room

The instrument room (figure 17) contains a multipurpose

recorder and_ a photoelectric spectrophotometer.
'"-••::

;

Figures 14 and 15. Radioactive isotopic chemistry laboratory.
Figure 16. Balance room.

Figure 17. Instrument room.
C. Boron

The Office of Standard Reference Materials has submitted

three materials of "Glass Beads for Neutron Flux Measurements"

for the determination of the isotopic composition and the percentage of boron to an accuracy of 0.1 to 0.25 percent of the measurement. The glass beads contain A1 2 3 , Li 2 0, Si0 2 , and B2O3 in addition to a different activator (potentially radioactive via neutron absorption) for each glass. The three activators chosen were dysprosium, indium, and cobalt with the boron used in preparing these glasses approximately 93% 10 B. To determine the isotopic ratio of the boron, it is necessary to separate the boron from the other constituents

and obtain it in a solution of 1 mg B per "ml with a Na/B ratio

of 1:1 [ref. 1, p. 67]. One method of determining the percentage of boron is by isotopic dilution. This method was chosen because only a small amount of sample is required, it should

give the required accuracy, and after making the dilution it will not be necessary to separate the boron quantitatively

from the other constituents.

Two procedures have been used for the separation of boron, one using ion exchange and the other solvent extraction.

The Argonne-II (ANL-II) boric acid was used as a workingstandard. All values obtained will be based on the 1:1 B/ 10 B ratio and any boron contamination from reagents would cause

a change in this ratio. The reagents were checked for boron

content by a boron-curcumin complex photometric method adapted

by E. R. Deardorff (Section 310.04) from Hayes and Metcalfe

[10]. The boron content of the reagents for the ion exchange separation was found to be less than 0.1 yg compared to about

15 mg of B in the sample size to be taken.

The dysprosium glass was selected as the first glass to

be analyzed. When the glass was fused with sodium carbonate,

the dysprosium did not dissolve in water but on acidifying

it dissolved; however, some of the silicon precipitated.

23
Boron was determined in the dysprosium residue by the boron- curcumin complex . The ion exchange method was adapted from Wolszon, Hayes,

and Hill [11] for the separation of boron and silicon. Using

an anion exchange column, the boron and silicon, as the borate

and silicate ions in a carbonate solution, were absorbed while

the lithium and aluminum passes through the column. The boron

was eluted with 0.1 N NaOH and the silicon with 1 N NaOH. The boron was not fractionated and the recovery was 95 percent.

The sodium was removed from the elute by passing the solution through a cation exchange column. By titrating an aliquot of the elute, the boron concentration was determined

and to another aliquot an equivalent amount of 0.1 N NaOH was added. The volume of this solution was adjusted to 1 mg B/ml

of solution and the ^B/^B ratio determined.

Four plastic ion exchange columns were prepared for the separation of boron and silicon. The columns, 2.5 cm diameter, were filled to a height of 16 cm with anion exchange

resin (AG 1-X8 , 200-400 mesh). The resin was converted to the OH form by passing 1 N NaOH through the column and the excess NaOH removed from the column with water. Four plastic ion exchange columns were prepared for the removal of sodium from the elute of the anion exchange column.

The columns, 2.5 cm diameter, were filled to a height of 12 cm with cation exchange resin (AG 50-X8, 100-200 mesh) and washed

with 1 N HC1. Finally, the column was washed with water to remove the excess HC1.

A 0.3 g sample of the glass beads, for the determination

of the 11 B/ 10 B ratio, two 0.15 g samples of the glass beads,

to be used for spiking with natural Argonne II boric acid, and

0.17 g of Argonne II boric acid were fused with 2 g Na 2 C0 3 and the melts dissolved in water. The solutions were filtered

and the residues were washed with water. Plastic or quartz

ware were used throughout the procedure.

2k
The residues were washed from the papers and dissolved

in H2SO4. The boron was determined in these solutions by the boron-circumium complex photometric method. The boron in the residues of the samples was 30, 3, and 3 micrograms respectively

and the final results were corrected accordingly.

Approximately 0.08 g of Argonne II boric acid was added

to each of the 0.15 g sample of the beads and all samples were diluted to 150 ml with water. The solutions were passed

through the anion exchange columns and washed with 150 ml of water.

The boron was eluted with 400 ml of 0.1 N NaOH. The elute was evaporated to 25 ml, passed through the cation exchange column and the column was washed with 75 ml H 2 0. A 20 ml aliquot out of 100 ml of each solution was titrated with 0.1 N NaOH to determine the concentration of boron. To another aliquot of the solution containing

approximately .005 g of boron, 0.1 N NaOH was added to give

an equivalent amount of sodium. The volume of the solutions

was adjusted to 1 mg B/ml . The 11 B/ 10 B ratios were determined

on these solutions. The results were Inconclusive.

The above described procedure had the following drawbacks:

(1) the conversion of the anion exchange resin to the OH form

was difficult, (2) the necessity of evaporating large volumes

of solution increased the possibility of contamination, and

(3) the procedure was time consuming; therefore, a recently published extraction method by E. J. Agazzi [12] was investigated. In this method the boron was extracted into a chloroform

solution of 2-ethyl-l ,3-hexanediol from an acid solution but could not be extracted from an alkaline solution. These facts suggested that the boron could be extracted from the glass in an acid solution and stripped from the organic phase with

sodium hydroxide. During the adapting of this method the cobalt glass was given the highest priority, therefore, the method was changed to apply to this glass.

25
The sample was fused with sodium carbonate, dissolved in water, made acid with sulfuric acid, and reduced with S0 2 water to dissolve the cobalt. After heating to expell most of the SO2, a double extraction was made with chloroform-2-ethyl-l,

3-hexanediol mixture. The organic layer was washed with dilute sulfuric acid and the boron was back extracted into a sodium hydroxide solution. The sodium hydroxide solution was washed

with chloroform and then gassed with carbon dioxide. Some examples of the boron recovered are given in table 1. Since complete recovery is not required as long as the boron isotopes

are not fractionated, the organic and aqueous layers were separated with the goal of minimizing contamination. To determine if any fractionation was taking place, a comparison

was made of the 1:L B/ 10 B ratios of one sample not extracted,

one sample extracted with one portion of chloroform-2-ethyl-l

,

3-hexanediol mixture, the average of several samples extracted

with the normal double extraction, and one sample run through

the extraction procedure twice. The results in table 2 show

that there is not detectable fractionation by this extraction

procedure.

Table 1. Boron recovery by chloroform-2-ethyl-l,3-hexanediol

extraction procedure. Sample % B recovered

1 92

2 92

3 97

4 97

5 94

6 94

7 98

Average 95 26
Table 2. Determination of possible boron isotopic fractionation. Organic extractions

11 B/

10 B

a None 4.0364

Single 4.0350 Normal double 4.0359 Twice b 4.0375

a Experimental ratio not-corrected for filament bias.

b Carried through the entire extraction procedure twice.

It was discovered, after a small fraction of the samples

gave a

i:L B/ 10 B ratio up to 1% lower than normal, that the amount of S0 2 left in the solution is critical. Increasing

amounts of S0 2 water were added after heating and cooling the acidified fusion. The results are given in table 4, page 36.

It was found that heating the samples at a higher temperature

(approximately 80°) and leaving the beaker uncovered, reduced

the amount of S0 2 sufficiently to give 11 B/ 10 B ratios that were reproducible (see table 5, page 37) and agreed with samples

that were not extracted. Synthetic samples, containing all the constituents of the cobalt glass beads and using Argonne II boric acid for the boron, are now being checked by this procedure. Preliminary results indicate a limit of error of bias of approximately 0.1$ between alternate chemical preparations.

D. Chromium

The chromium isotopic composition of approximately

seventy mineral samples of different origin are being determined. This will establish constancy of isotopic composition

in nature and assist in placing limits on the atomic weight of chromium. The procedure used previously [ref. 1, p. 33] was modified to obtain a better separation of the chromium from

the other constituents of the minerals and the sodium from

27
the sodium carbonate used in fusion. Approximately seventy- samples of fifteen different minerals were carried through

the following procedure.

The silicate minerals of chromium were crushed and fused with sodium carbonate. After dissolving in water, hydrogen

peroxide was added to insure complete oxidation of chromium.

The insoluble material was filtered off and the chromium precipitated as Cr(0H)3 by reducing the chromium with S0 2

. After igniting the precipitate, it was fused with a small amount of sodium carbonate, dissolved in water, and filtered.

The solution was made just acid and heated to decompose the carbonate. Sodium and other cations were removed by passing

the solution through a cation exchange column (AG 50-X8). The chromium was reduced with S0 2 and precipitated by adding

ammonia. The precipitate of Cr(0H)3 was filtered, ignited

and weighed. The chromium oxide was dissolved and oxidized

in perchloric acid and any insoluble residue was filtered off. The chromium was precipitated with S0 2 and ammonia, and

filtered. The Cr(OH) 3 was dissolved off the filter paper with

hot diluted nitric acid and the solution was evaporated to dryness. The chromium was then dissolved in HN0 3 (1 + 49) and hydrogen peroxide added to reduce all the chromium to Cr(III). After heating to destroy the excess hydrogen peroxide the solutions were diluted with HN0 3 (1 + 49) to give a chromium concentration of 3 mg/ml

.

The chromite samples were dissolved in perchloric acid, diluted with water, filtered, and continued as described above starting with the cation exchange column.

The crocoite samples were dissolved in dilute nitric acid

by electrodeposition of the lead. The solution was filtered

and the chromium was precipitated with S0 2 and ammonia. After

igniting, the chromium was dissolved in perchloric acid, made

just acid with ammonia and continued as described above, starting with the cation exchange column.

28
Approximately one-third of the samples did not behave normally in the mass spectrometer. To purify these samples

they were oxidized with perchloric acid, and passed through

an anion exchange column (AG 1-X4). After washing the column with water, the chromium was removed with an ammonia- ammonium

chloride solution. The chromium was precipitated with S0 2 , filtered, and dissolved off the filter paper with nitric acid. After evaporating to dryness the chromium was dissolved in HN0 3 (1 + 49) and diluted to 3 mg/ml . Most of these samples

have been behaving normally in the mass spectrometer.

E. Fluorspar

The Office of Standard Reference Materials has submitted

a sample of fluorspar, SRM 79b, for the certification of caF 2

. The sample is urgently needed as a standard by the U.S. Customs Bureau for the determination of the import duty of fluorspar imported into the United States. The personnel of this section, having experience in the analyses of this type

of material, were assigned the determination of CaF 2 even though such an analysis is outside the usual activities of the section.

The prescribed method of analysis of the U.S. Customs Bureau is the J. I. Hoffman method as given on the Certificate

of Analyses of Standard Sample 79, Fluorspar. The fluorspar

is digested in acetic acid and filtered. After ignition the fluroine is removed from the insoluble calcium fluoride by fuming with perchloric acid and evaporating to dryness. The calcium perchlorate is dissolved in hydrochloric acid and a hydrogen sulfide precipitation is made with the solution acid

and ammonical. After removal of excess hydrogen sulfide, the calcium is precipitated with ammonium oxalate and ignited to calcium oxide. From the weight of the calcium oxide the percentage of calcium fluoride in the fluorspar is determined. Since the determination has not been completed the results

will be given at a later date.

29
F. Lead

A search of the chemical literature has shown that there

is a need for a high precision-high accuracy method for lead.

A method has been developed which is based on the precipitation

of lead chromate with a small excess of potassium dichromate

and spectrophotometric determinations of the excess chromate. This method takes advantage of the precise analysis of Standard

Reference Material 136b, potassium dichromate, which has been

shown to be 99-977 * 0.003$ [13]. Results have shown that

this method has a precision and accuracy of better than 0.017%. The details of this method will be published elsewhere in the near future. This method has been applied to the preparation of cali- bration mixtures of separated lead isotopes for the mass spectrometric determination of absolute abundance ratios. Separated lead isotopes in the form of 206 Pb (N0 3 ), and 208 Pb (NO3), were obtained from the Isotopes Division of the Oak Ridge National Laboratory. Emission spectrometric analysis showed that these compounds were of such high purity in regards to elements that would interfere with the assay method

that they were used without further purification. The sepa- rated isotopes were taken into solution with dilute nitric

acid. The lead content of each separated isotope solution

was determined by the chromate procedure which was outlined

above. The calibration mixtures were then prepared by mixing

weighed portions of each separated isotope solution. They were prepared in groups of two to approximate the 208/206 composition of three reference samples of lead which are to

be distributed as standard reference materials. These lead reference materials consist of a 92% radiogenic lead with a 208/206 ratio of about 0.014, a mixture of a radiogenic lead

and a galena lead with a 208/206 ratio of about 1.000, and a galena lead with a 208/206 ratio of about 2.161. The calibration mixtures of the separated isotopes will be used to
determine the absolute abundance ratios of these reference

leads. This work is still in progress.

1. Lead Minerals

As noted in the introduction, natural variations in isotopic composition can be a source of error in the mass spectrometric determination of atomic weights. This is especially true for lead. The most important source mineral

for lead, galena (PbS) has been shown to vary significantly

in amounts of 204 Pb, 206 Pb, 207 Pb, and 208 Pb because it has been affected by contributions of radiogenic lead. Table 3 shows the calculated atomic weights for three metallic lead samples (from galena) and three samples of galena. The calculated atomic weights have a range of 207.18 to 207.24. These values have not been corrected for possible bias (which

is very small based on preliminary work with the calibration

standards), but the range is indicative of the variance in the atomic weight of lead. The International Commission on Atomic Weights [14 ] recommends using the value 207.19 as being representative of the lead "most likely to be encountered

in normal laboratory work". They recommend that "atomic weights of widely differing isotopic composition should be calculated from the composition of the masses of the individual

species". In view of our experience with "normal" lead, it would seem that, when one is interested in high precision - high accuracy lead chemistry, an isotopic analysis is also necessary before a meaningful quantitative statement can be made. Certainly, the stated value of 209.19 without limits leads to false sense of security about the atomic weight of "normal" lead.
Table 3. Calculated atomic weights for "normal" leads. Relative Isotopic Composition Sample Atom percent Atomic weight 204 206 207 208 Lead Metal -1 1.427 24.153 22.084 52.336 207.216 Lead Metal -2 1.461 23.559 22.596 52.384 207.222 Lead Metal -3 1.463 23.629 22.518 52.390 207.221 Galena -1 1.350 26.289 21.149 51.211 207.184 Galena -2 1.372 24.935 21.358 52.336 207.212 Galena -3 1.539 22.531 22.642 53.289 207.241

2 . Preparation of Lead from Mineral Samples

The lead, from a number of lead minerals was separated and solutions prepared for mass spectrometric analysis. The following procedures were used:

a. Galena (PbS) - A 0.5 to 1.0 gm sample was digested with 20 ml of (1 + 1) perchloric acid at about 90°C. (The dilute perchloric acid dissolved the PbS with evolution

of H 2 S and no evidence of oxidation of sulfide ion was noted.)

The resulting solution was diluted to 100 ml with water and

5 ml of nitric acid was added. Pb02 was then electrodeposited

onto a platinum gauze anode, weighed and dissolved in a nitric acid-hydrogen peroxide mixture. The resulting solution was evaporated to dryness and residue taken up in 2% nitric acid

so that the final solution contained 25 mg of Pb per ml. This perchloric acid method of dissolution of galena proved superior

to the usual nitric acid method as the sulfide ion was not oxidized so the problems associated with the production of sulfur and occulusion of lead sulfate with the lead dioxide

were avoided.

b. Crocoite (PbCrOi*) - The lead was separated from sparingly soluble lead chromate by covering a 0.5 to 1.0 g sample with 100 ml of dilute nitric (1 + 9) and electrodepositing Pb0 2 on a platinum gauze electrode. (As the lead is

32
removed from solution, the lead chromate slowly goes Into solution until it is completely dissolved and the lead is completely removed from solution.) The Pb0 2 was dissolved in nitric acid-hydrogen peroxide, and the Pb0 2 was redeposited

to remove the small amount of chromium that contaminated the first deposit. The resulting Pb0 2 was dissolved in dilute

nitric acid-hydrogen peroxide mixture, evaporated to dryness

and taken up in 2% nitric acid so that the solution for mass spectrometric analysis contained 25 mg Pb per ml.

c. Pyromorphite [PbClPb^ (PO^ ) 3] , wulfenite (PbMoO^),

and vanadinite [PbClPbi,. ( VU4. ) 3 ] - These minerals were also processed by the above procedure except that a third deposition

of Pb0 2 was required to purify the lead.

d. Plattnerite (Pb0 2 ) and minium (PbsO^) - These

two minerals were dissolved in dilute nitric acid-hydrogen

peroxide mixture and the lead was electrodeposited as Pb0 2 on a platinum gauze anode. Solutions for mass spectrometric

analysis were prepared as described above.

3 . Archaeological Samples

In cooperation with Dr. Robert H. Brill of the Corning Museum of Glass, the lead and copper from a number of bronze

coins from the 1st, 2nd, and 3rd Centuries B.C. and other

ancient objects such as a statue, pin, dagger, and bracelet

were separated for isotopic analysis. Since lead varies in isotopic composition depending on the source, the purpose of this work is to correlate these

coins and objects to the original mines.

The secondary minerals of copper have also been shown to vary in isotopic composition [7], so the copper was also separated from these ancient coins and objects in the hope of relating them to their source material.

The isotopic analysis of these samples is now in progress.
G . Plutonium

1

.

Chemical Standard

The plutonium metal for the replacement of the plutonium

chemical standard 949a was prepared at Los Alamos Scientific

Laboratory of the University of California, Los Alamos, New

Mexico. After purification of the metal, 0.5 - 0.6 g samples were weighed to 0.01 mg and sealed in glass tubes. Until sealed all work on the metal was done in a very low oxygen and water atmosphere. Quantitative determination of the impurities,

totaling less than 100 ppm, as well as the assay of the metal

were made at Los Alamos Scientific Laboratory. One member of NBS Section 310.06 collaborated with Los Alamos Scientific Laboratory personnel in the weighing, sealing, and analysis of the samples. After shipment to NBS the samples were packaged

in 2R containers, as required by ICC regulation, and the screw

caps and joints were coated with plastic "Seal-Stop".

2

.

Isotopic Standard

The evaluation of the half-life of 21tl Pu was continued

[ref. 1, p. 45; 15, p. 64; 16, p. 71] with the ion exchange

separation of americium from the plutonium and the mass spectrometric measurement of the isotopic ratios to determine

the decrease of the 2ttl Pu isotope content. In addition, the procedure [ref. 15, p. 65] was modified to separate uranium

from plutonium by increasing the volume of 8 N nitric acid to elute both americum and uranium.

(T. J. Murphy, L. A. Machlan, and K. M. Sappenfield)
3. MASS SPECTROMETRY

A. Boron

A provisional analytical procedure for the isotopic

analysis of boron was described in a previous annual report

[ref. 1, p. 67]. Subsequent to that report, a number of glasses containing isotopically enriched boron were submitted

for certification of both the boron content and the isotopic

composition. In order to provide certification it was necessary to evaluate bias parameters, i.e. to ascertain the effects of filament material and impurities on the observed

ratio

A previous report [ref. 1, p. 67] indicated that platinum

was superior to tantalum for surface ionization of boron as the (Na 2 B0 2 ) + ion. Old ANL-II solutions (dissolved in 1965) were analyzed and ion currents of 1-2 x 10" 11 A were obtained with platinum filaments. The experimental 1:i B/ 10 B ratios did

not change significantly with time and were slightly lower than the experimental ratios obtained with tantalum filaments.

The analytical precision was significantly improved and the signals were generally growing or constant and exhibited good

stability. New samples of ANL-II were dissolved and the B/Na

adjusted to 1 with Na 2 C0 3

. All of these solutions gave ion currents (10~ 13 A) which were erratic and were not suitable

even for a rough estimation of the abundance ratio. A brief investigation did not pinpoint the cause or add significantly

to an explanation of the phenomenon. In general, this type

of behavior is attributed to a physical-chemical effect. Impurities may produce a suppressive or poisoning effect on the ionization process. Removal of contaminant ions by purification chemistry or degassing the sample in the spec- trometer, procedures which have been effective for many impurities, did not cause improvement. After several weeks

of experimentation and more than 12 new ANL-II solutions, it was necessary to abandon platinum as the filament material

and use tantalum.

35
In the initial effort to determine the boron content, boron was separated from other constituents of the glass with

ion exchange columns but the values produced were discordant.

The method of separating boron was changed to an organic extraction technique. ANL-II was used as a sample of known

isotopic composition to test and develope the organic extrac- tion procedure. The ANL-II samples were processed in the identical manner prescribed for extraction of boron from

cobalt glass which was the most difficult of the glasses to be extracted. The experimental ratios of the first group of extractions were either 4.04 or 3-99 (table 4). These ratios

were unique and reproducible for a given solution, and the subsequent effort to determine the source of bias required

the processing of approximately 100 ANL-II solutions, and more then 300 sample loadings.

Table 4. Organic extraction of ANL-II without control of excess S02 water. Experimental Sample No.

11 B/10 B corrected for 17

1 4.048

4.043

2 3.994 3.996

3 4.047

4.048

4 3.992

3.991

5 4.047

4.041 S0 2 water, added during digestion x,o reduce cobalt, was

the agent which produced abnormal ratios. In some extractions

the volume of S0 2 water which was extracted into the 2-ethyl1 ,3-hexanediol and the NaOH solution was large enough to neutralize or acidify the NaOH solution. Table 5 gives the

36
experimental ratios for extractions in which S0 2 water was

not added before digestion but was added in known volumes after digestion and before extraction into the 2-ethyl-l,3-

hexanediol. The NaOH solution of sample No. 53, with a pH of

8, was the only extraction to show significant neutralization.

This sample yielded less than normal signal intensity during

analysis and, based upon titration of the extraction, there

was a significant loss of boron. Excess S0 2 water was con- trolled by digesting the solution uncovered and at a temperature of 80° - 85°C. The experimental ratios for extractions with this added condition are given in table 6.

Table 5. Organic extraction of ANL-II with known volume of S02 water added before

extraction into 2-ethyl-l,3-hexanediol. Volume in ml of Experimental Sample No. S02 water added

11 B/10B corrected for 17 39a 4.0336 4.0316 43a 1.0 4.0403

4.0412 46a 2.0 4.0132

4.0109 54a 2.0 4.0111 4.0177 47a 2.5 4.0050

4.0045 53a 3.0 3.9890

3.9962

37
Table 6. Organic extraction of ANL-II with control of excess S02 water by

digesting solution uncovered and at temperature of 80 to 85°C.

Experimental Sample No.

11 B/ 10 B corrected for 17 37a 4.0352

4.0339 38a 4.0355

4.0362 44a 4.0373

4.0346 45a 4.0344

4.0377 46a 4.0391 4.0347 Average 4.0359 The two most probable explanations of the abnormal ratios

are chemical fractionation during extraction and increased fractionation during mass spectrometric analysis. Evaluation

of the degree of chemical fractionation was made using the chemical procedure which controlled excess S0 2 water and its extraction into the 2-ethyl-l ,3-hexanediol . A single extraction

recovers a minimum of 80% of the boron present, and a second extraction is necessary to increase the recovery to 95%- The

1:1 B/ 10 B ratio for duplicate analysis of a single extraction was 4.0350. Double extraction of the solutions in table 5 gave an average 1:1 B/ 10 B ratio of 4.0359- After being analyzed, solutions 44a and 45a of table 5 were combined and put through the complete extraction chemistry again. It was necessary to combine 44a and 45a so that the starting boron weight of 15 mg would be the same for all samples. The final solution, equivalent to a quadruple extraction, gave an average ratio of 4.0375

for duplicate analyses. An ANL-II sample that was dissolved In water with the appropriate volume of NaOH added and saturated
with CO 2 gave an average ratio of 4.0364 for duplicate

analyses. The ratios for a solution without extraction

chemistry and solutions with single, double, and quadruple extraction are experimentally identical, and are indicative

of the absence of fractionation under the conditions of the experiment. Evaluation of the degree of fractionation under

conditions which produce abnormal ratios has not been completed. Increased fractionation or more efficient formation of the (Na2BC>2) ion has not been fully evaluated. However, it has been observed that all solutions yielding abnormal ratios were either grey-white or just slightly burned at the end of

an analysis. Solutions with ratios of 4.04 also dried grey- white but were charred black during an analysis. Purification

chemistry on an abnormal solution with cation and anion

exchange columns produced solutions in which the sample turned

black during an analysis but the ratio was not affected

significantly. The refractory material in abnormal solutions

was also removed by reprocessing through the extraction

chemistry but the ratio remained unchanged. More work is necessary in this area before conclusions can be made. ANL-II solutions spiked with known amounts of impurities

gave lower experimental ratios than unspiked solutions with identical chemistry. Ba, Ca, and Pb were added in 20 and 40 ug samples sizes as impurities. The general effect of adding

these impurities was to require 10-20% higher filament currents

to give 1 x 10~ 12 A ion currents. Solutions spiked with calcium gave erratic emission and were, in general, inferior

in overall performance. A 2 yg sample size of Sr did not effect the analysis nor was there a detectable (10~ 15 A) strontium signal. Excessive and/or irregular amounts of sodium in solution

with boron was a source of bias. Experimental ratios of solutions with B/Na ratios of 1:1 or 2:1 were nearly identical

and did not change significantly at signal intensities of

39
1 x 10~ 12 A. The experimental nB/ 10B ratios of solutions with

B/Na ratios of 1:2 were 1% higher than solutions of 1:1 or

2:1. By carefully and slowly heating the filament to produce

ion currents less than 1 x 10~ 12 A, the 1:L B/ 10 B ratio was observed changing to 4.08. The rate of change slowed significantly at this level, and it was possible to make precise

measurements. When the B/Na ratio is 1:4, the (Na 2 B0 2 ) ion current is completely suppressed at normal filament currents

of 1.15 - 1.30 A. Filament currents of 1.5 A were necessary

to obtain 10~ 13 A ion currents which were usually decaying and difficult to measure precisely. Sodium carbonate and sodium bicarbonate solutions gave superior overall performance in comparison with the analysis

of sodium hydroxide solutions. Emission stability of the hydroxide was poor and analyses were often rejected because of erratic emission. The stability, signal intensity, and rate

of decay improved with time and were comparable to carbonate

and bicarbonate analyses after 1 hour of heating. Filaments that were prebaked at 3 A for 1 hour in a vacuum

and under a potential field were free of background signals in the mass 85-90 range. Filaments that were not baked gave rubidium ion currents of 10~ 1L+ A. Strontium ion currents were

not detectable at 10~ 15 A from either type of filament when operated at 2 A. The provisional analytical procedure was based upon the concept of quickly (15 minutes) generating a 10~ 12 A signal

and taking data. A series of long-term analyses (2-4 hours) indicated that signal stability and intensity were significantly

improved if the 10~ 12 A ion currents were obtained at a slower

rate of heating. The 11 B/ 10 B ratio also exhibited greater

stability with time and changed less than 0.5% over a 4 hour period of heating. The present analytical procedure, evolved

from this and other information, is based on a concept of slowly obtaining a total ion current of 1.5 x 10~ 12 A over a 40
30 minute period and taking data between 32 and 45 minutes

after the start of heating.

B

Chromium

A survey is being conducted to determine the limits of natural variation of chromium isotope abundances. Data has been obtained on 40 mineral samples. There is no variation

among chromites, but the results on secondary chromium

minerals are inconclusive. A number of samples from minerals

in which the chromium is only a trace element give results which are outside the apparent experimental error. However,

all of these variations are in the direction to be expected if chemical impurities are present, and, since the purification

of these minute samples is extremely difficult, the question

of real variation is not yet resolved. Work on the chromium mineral survey has been temporarily

suspended. Analysis of the minerals has been very time consuming because of the excessive rate of sample rejection. Between 30 and 40% of all analyses attempted were rejected for reasons which include decaying signals, excessive growth, poor

stability, signal suppression, and erratic emission.

C. Lead Accurate determination of the lead isotope compositions

of natural samples is of great importance to earth scientists. Geologists, geochemists, and cosmologists use lead isotope measurements to study: the ages of rocks, minerals, meteorites

and the earth; the origin, history, and relationships of meteorites and the earth; the nature of fundamental geologic processes, such as vulcanism, mountain building, ore formation,

etc.; the chemical composition of the earth's interior; and many other geologic and oceanographic problems.

In studying these problems, investigators have accumulated

a vast amount of lead isotope data. Unfortunately, the data fail

to meet two important criteria: none of them are absolute, and

the precision is frequently too poor for even relative studies.

41
The Analytical Mass Spectrometry Section has begun a program for the determination of the absolute isotopic

compositions of a number of different lead standards. Upon completion of this study, aliquots of the standards will be distributed to all interested laboratories, so that all future

lead isotope studies will be placed on an absolute basis.

A preliminary requirement for the "absolute" study was

the development of a more precise method of lead isotope

analysis. Recent work has shown that results obtained by the most commonly used method, single-filament PbS, can be affected

by such factors as filament material, alkali-ion signals, and

Pb/NHi+NOs ratio of the mount. These factors may affect the measured z08 Pb/ 206 Pb ratio by as much as 2%. No extensive

study has been made of the various parameters which might affect the lead tetramethyl gas method or the single-filament

PbC 2 0it method, but the poor precisions of these methods also suggest some random bias factors.

A triple-filament method was therefore devised for solidsample lead isotope analysis. The source consists of rheniumribbon sample filaments and a platinum-ribbon ionizing filament. Samples may be in the form of PbCl 2 , Pb(N0 3 ) 2 , or Pb(OH) 2 ; the Pb(OH) 2 appears to have the best qualities for analysis. Stable lead ion signals of 6 x 10 -11 A are consistently

obtained with 500 yg lead samples, while 20 pg samples give stable signals of 4 x 10~ 13 A. The triple filament method does not have the ionization efficiency of the single-filament PbS

or PbC 2 0i+ methods, but it has much greater precision. Ten analyses of a reference sample gave 95% confidence limits

(per analysis) of 20l+ Pb/ 206 Pb = 0.054%, 207 Pb/ 206 Pb = 0.023%,

and 208 Pb/ 206 Pb = 0.071%. Table 7 compares the precision of the triple-filament

method with some of the best data on replicate analyses of lead samples reported by various workers using different

methods. The significantly greater precision of the triplefilament method is probably due to the fact that the results

42
appear to be unaffected by any of the variables, such as signal size, sample size, sample composition, time of datataking, or alkali-ion signals, which appear to affect the results of other methods.

Table 7. Comparison of 95% confide** limits (H of best data on replicate lead isotope analyses by various n 95% confidence Units per analysis (in %)

Investigator and method 204Pb/206Pb

207Pb/

206Pb 208Pb/206Pb

Doe et al. (1965), solid PbS 0.22 0.22 0.29

single-filament Re, 11 analyses

Richards and Cooper (1966), 0.12 0.17 0.22

solid PbC2 4

, single-filament Re, 8 analyses Kollaretal. (1960), gas 0.24 0.17 0.13 (CH3

)4 Pb, 5 analyses This paper, solid Pb(0H)2

, triple- 0.054 0.023 0.071

filament Re (sample) and Pt

(ionizing), 10 analyses The triple-filament method, because of its greater

precision, will probably replace all other methods whenever

two conditions can be met: the sample size must be greater

than 100 yg, and an efficient mass spectrometer must be used. The installation of a Z lens in the instruments of this section, which increased the source efficiency by a factor of about 4, was an important step in the evolution of this technique. With samples of less than 100 yg, the single- filament PbS or PbCaOit methods would probably be preferable.

The lead tetramethyl gas method requires large samples and

may very well become obsolete.

A preliminary study of the lead isotope compositions of some secondary lead minerals has been made. The results

43
indicate that the geologically recent formation of secondary

lead minerals from older lead minerals can occur without significant contamination by rock leads, even when transportation over considerable distances has apparently occurred.

This means that the isotopic composition of the lead in secondary minerals may be useful as a tracer in the studies of the oxidation of ore deposits, the groundwater transportation

of lead, and the origin and paragenesis of secondary ore deposits

.

D. Plutonium

The annual analysis of Plutonium Standard 948 was made

July 12-13, 1966. The purpose of this series of annual measurements is to accurately determine the half-life of

2l+1 Pu. Each year a new sampling of the standard is usually dissolved and analyzed with samples dissolved in previous

years, but because of the move to Gaithersburg, chemical

facilities were not available to prepare a new solution in 1966, and only the old solutions dissolved in 1964 and 1965 were used. The 241 Am was removed with an ion exchange column

no more than 24 hours before the samples were run. A thermal ionization mass spectrometer with a Z-lens ion source was used,

and the increased transmission did not warrent use of an ion multiplier. Each solution was analyzed with sample sizes of

2 and 4 yg. The calculated half-life as of July 1967 is 14.9 years with an undefined uncertainty.

E. Rubidium

Sub-samples of one lot of Standard Reference Material

(SRM) rubidium were analyzed and were isotopically homogeneous within the analytical limit of error of 0.1$ of the abundance

ratio. SRM samples were also compared with the NBS rubidium

reference standard and were isotopically homogeneous. SRM

samples were analyzed as RbCl 2 , and the analytical procedure

was basically the same as the procedure for Rb 2 S0 Lf [1]. The major difference was the sample-filament temperature necessary

44
to produce 10 -11

A of 85 Rb. Temperatures hot enough to volatilize RbaSO^ will deplete the sample- filaments of RbCl 2

. Analysis of rubidium as the chloride eliminates surface ionization at sample-filament surfaces as a source of bias. Surface ionization at sample filament surfaces (a shortcoming

of sulfate analysis which was controlled by placing an upper

limit of 0.8 A on the current) occurred when the filament

current was greater than 1 A. The limited number of analyses

of RbCl2 indicated that the overall analytical performance of rubidium as the chloride was superior to the analytical per- formance of rubidium as the sulfate.

F. Uranium

A thermal ionization mass spectrometer with a Z-lens ion source was used to determine the absolute 235^238^ ratios of the standards U150 and U050. Samples of known isotopic

composition were used to calibrate for instrumental bias. The low-temperature analytical procedure [ref. 1, p. 55] was used

for all samples.

The increased transmission of Z-lens optics, significantly

improves measurement of low assay 23tt U and 236 U and extends

the lower limit of the assay range at which precise measurements of these isotopes can be made with a conventional

faraday-cage collector from 0.10 to 0.02 atom percent. Ion multipliers are still recommended and are a necessity for precise measurements below 0.02 atom percent. Improvement in

235 U/ 238 U measurements is also anticipated because it is now possible to obtain 3-5 x 10 -11 A ion currents with less chance

of overheating and significantly changing the rate of frac- tionation unique to low-temperature analysis.

(E. J. Catanzaro and E. L. Garner)

45
4. PERSONNEL AND ACTIVITIES

A. Personnel Listing William R. Shields, Section Chief

Joy J. Shoemaker, Secretary

Mass Spectrometry (absolute isotope ratio) —

Ernest L. Garner

Mass Spectrometry (isotope dilution) —

Edward J. Catanzaro Stoichiometry —

Thomas J. Murphy

Stoichiometry (nuclear materials) —

Lawrence A. Machlan Separation and Purification —

Keith M. Sappenfield

Design and Fabrication —

William A. Bowman, III Guest Worker during 1966 —

Takuj i Komori

B. Publications

NOTE: A complete list of all the publications by members of this section is given below. The complete list has been included with the hope that it will aid those who have to do literature searches, and at the same time the titles should

define the areas where the various members of the section have

some skill.

1. T. J. Murphy, W. S. Clabaugh, and R. Gilchrist, Separation of Iodide, Bromide, and Chloride from One Another

and Their Subsequent Determination, J. Res. NBS, 53, 13-18

(1954).

2. R. L. Smith, W. R. Shields, and C. D. Tabor, An Interpolative Method of Assaying UF 6 with the Isotopic Mass Spectrometer, GAT-171, AEC Research and Development Report (Declassified), (1956).

46
3. L. A. Machlan and J. L. Hague, Photometric Deter- mination of Tungsten in Steel and Titanium Alloys with

Dithiol, J. Res. NBS , 59, 415-420 (1957).

4. J. L. Hague and L. A. Machlan, Determination of Titanium, Zirconium, Niobium, and Tantalum in Steels: Separations by Anion-Exchange , J. Res. NBS, 62_, 11-19 (1959).

5. J. L. Hague and L. A. Machlan, Determination of Niobium and Tantalum in Titanium-Base Alloys, J. Res. NBS,

62, 53-57 (1959).

6. W. R. Shields, D. N. Craig, and V. H. Dibeler, Absolute Isotopic Abundance Ratio and the Atomic Weight of Silver, J. Am. Chem. Soc . , 82, 5033-5036 (I960).

7. E. J. Catanzaro and P. W. Gast, Isotopic Composition of Lead in Pegmatitic Feldspars, Geochim. Cosmochim.

Acta, 19, 113-126 (I960).

8. L. A. Machlan, J. L. Hague, and E. J. Meros , Deter- mination of Aluminum in Precipitation Hardening Stainless Steel and High Temperature Alloys, J. Res. NBS, 64A, 181-184

(I960) .9. T. J. Murphy and W. S. Clabaugh, Preparation of Sulfur of High Purity, J. Res. NBS, 64A, 355-358 (I960).

10. T. J. Murphy, W. S. Clabaugh, and R. Gilchrist, Method for the Separation of Titanium, Zirconium, Iron, and Aluminum from One Another and for Their Subsequent Deter- mination, J. Res. NBS, 64A, 535-542 (i960).

11. J. L. Hague and L. A. Machlan, Separation of Hafnium from Zirconium by Anion Exchange, J. Res. NBS, 6_5_A, 75-77 (1961).

12. W. R. Shields, E. L. Garner, and V. H. Dibeler, Absolute Isotopic Abundance of Terrestrial Silver, J. Res. NBS, 66A, 1-3 (1962)

13. L. A. Machlan and J. L. Hague, Separation of Hafnium from Zirconium and Their Determination: Separation

by Anion-Exchange, J. Res. NBS, 66_A, 517-520 (1962).

47
14. W. R. Shields, T. J. Murphy, E. L. Garner, and

V. H. Dlbeler, Absolute Isotoplc Abundance Ratio and the Atomic Weight of Chlorine, J. Am. Chem. Soc, 8^_, 1519-1522

(1962).

15. E. J. Catanzaro, Zircon Ages in Southwestern

Minnesota, J. Geophys . Res., 68, 2045-2048 (1963).

16. J. L. Kulp, R. Kologlovov, J. Engles,

E. J. Catanzaro, H. Neuman, and B. Nilssen, Age of the Tordal, Norway Pegmatite — A Correction, Geochim. Cosmochim. Acta,

27, 847-848 (1963)

.

17. J. N. Rosholt, W. R. Shields, and E. L. Garner, Isotope Fractionation of Uranium in Sandstone, Science, 13_9, No. 3551, 224-226 (1963).

18. W. R. Shields, E. L. Garner, C. E. Hedge, and

S. S. Goldich, Survey of Rb 85 /Rb 87 Ratios in Minerals, J. Geophys. Res., 68, 2331-2334 (1963).

19. P. Lessing and E. J. Catanzaro, Sr 87 /Sr 86 Ratios in Hawaiian Lavas, J. Geophys. Res., 69, 1599-1601 (1964).

20. E. J. Catanzaro and J. L. Kulp, Discordant Zircons from the Little Belt (Montana), Beartooth (Montana), and Santa Catalina (Arizona) Mountains, Geochim. Cosmochim. Acta,

28, 87-124 (1964).

21. J. N. Rosholt, E. N. Harshman, W. R. Shields, and

E. L. Garner, Isotopic Fractionation of Uranium Related to Roll Features in Sandstone, Shirley Basin, Wyoming, Economic

Geology, 59, 570-585 (1964).

22. J. N. Rosholt, E. L. Garner, and W. R. Shields, Fractionation of Uranium Isotopes and Daughter Products in Weathered Granite and Uranium-Bearing Sandstone, Wind River Basin Region, Wyoming, Annual Review of Geological Survey,

501-B, B84-B87 (1964)

.

23. W. R. Shields, T. J. Murphy, and E. L. Garner, Absolute Isotoplc Abundance Ratio and the Atomic Weight of a Reference Sample of Copper, J. Res. NBS , 68_A, 589-592 (1964).

48
24. E. J. Catanzaro, T. J. Murphy, E. L. Garner, and

W. R. Shields, Absolute Isotoplc Abundance Ratio and the Atomic Weight of Bromine, J. Res. NBS , 68_A, 593-599 (1964).

25- R. D. Morton and E. J. Catanzaro, Stable Chlorine Isotope Abundances in Apatite from 0degardens Verk, Norway, Norsk Geologisk Tidsskrift, 44, Part 3, 307-313 (1964).

26. T. J. Murphy and J. K. Taylor, Precise Assay of Copper Using Small Samples, Anal. Chem. , 37, 929 (1965).

27. W. R. Shields, S. S. Goldich, E. L. Garner, and

T. J. Murphy, Natural Variations in the Abundance Ratio and

the Atomic Weight of Copper, J. Geophys . Res., J_0, No. 2, 479-491 (1965).

28. J. N. Rosholt, A. P. Butler, E. L. Garner, and

W. R. Shields, Isotopic Fractionation of Uranium in Sandstone, Powder River Basin, Wyoming, and Slick Rock District,

Colorado, Economic Geology, 60_, 199-213 (1965).

29. J. T. Herron, H. M. Rosenstock, and W. R. Shields, Negative Surface Ionization of Complex Molecules, Nature,

206, No. 4984, 611 (1965)

30. W. R. Shields, "Absolute Isotopic Abundance Ratios

of ..." by Surface or Thermal Ionization, Paper presented at Thirteenth Annual Conference on Mass Spectrometry and Allied

Topics held in St. Louis, May 16-21, 1965.

31. E. J. Catanzaro and T. J. Murphy, Magnesium Isotope

Ratios in Natural Samples, J. Geophys. Res., 71 , No. 4, 1271-

1274 (1966).

32. W. R. Shields, The Evolution of the Accuracy of Isotopic Analysis by Thermal Ionization from 2% to 0.02%, Nuclear Materials Management, International Atomic Energy

Agency, Vienna, 1966, pp. 737-746.

33. W. R. Shields, T. J. Murphy, E. J. Catanzaro, and

E. L. Garner, Absolute Isotopic Abundance Ratios and the Atomic Weight of a Reference Sample of Chromium, J. Res. NBS, 70A , 193-197 (1966).

49
34. Analytical Mass Spectrometry Section: Instrumentation and Procedures for Isotopic Analysis, NBS Technical Note

277, Ed. W. R. Shields, (1966).

35. E. J. Catanzaro, T. J. Murphy, E. L. Garner, and

W. R. Shields, Absolute Isotopic Abundance Ratios and the Atomic Weight of Magnesium, J. Res. NBS, J_0A, 453-458 (1966).

36. E. J. Catanzaro, Correlation of Some Precambrian

Rocks and Metamorphic Events in Parts of Wyoming and Montana,

The Mountain Geologist, 4, No. 1, 9-21 (1967).

37. E. J. Catanzaro, A Triple-Filament Method for Solid-Sample Lead Isotope Analysis, J. Geophys. Res., 72 , No. 4, 1325-1327 (1967).

C. Talks

1. W. R. Shields, "Standards Program and Calibration", Pennsylvania State University, College Park, Pennsylvania, October 31, 1966.

2. W. R. Shields, "Filament Material and Sample Form", Pennsylvania State University, College Park, Pennsylvania, November 1, 1966.

3. E. J. Catanzaro, "Stable Isotope Variations in Nature", Pennsylvania State University, College Park, Pennsylvania, November 2, 1966.

4. E. J. Catanzaro, "Correlation of Some Precambrian

Rocks and Metamorphic Events in Parts of Wyoming and Montana", University of Pennsylvania, Philadelphia,

Pennsylvania, May 5, 1967

•

5. W. R. Shields, "Hardware for Isotopic Analysis",

Atomic Physics Colloquium, NBS, May 25, 19&7-

50
D. Committee Activities

L. A. Machlan

Member, Chemistry Panel of Interagency Board of Civil Service Examiners

T. J. Murphy

Member, Chemistry Panel of Interagency Board of Civil Service Examiners

Chairman, Committee on Meeting Arrangements, Chemical Society

of Washington

Member, Arrangements Committee, IMR Symposium on Trace Characterization

Member, Committee on Annual Report of Atomic Weights, American Chemical Society

Manager, Chemical Society of Washington

Member, Committee on Analytical Reagents of the American

Chemical Society

51
5 . REFERENCES

[1] W. R. Shields, Editor, NBS Technical Note 277, (1966).

[2] W. R. Shields, T. J. Murphy, E. L. Garner, and

V. H. Dibeler, "Absolute Isotopic Abundance Ratio and the Atomic Weight of Chlorine", J. Am. Chem. Soc. 3 84_, 1519-1522 (1962).

[3] E. J. Catanzaro, T. J. Murphy, E. L. Garner, and

W. R. Shields, "Absolute Isotopic Abundance Ratio and the Atomic Weight of Bromine", J. Res. NBS 68A , 593-599 (1964).

[4] W. R. Shields, T. J. Murphy, E. J. Catanzaro, and

E. L. Garner, "Absolute Isotopic Abundance Ratios and the Atomic Weight of a Reference Sample of Chromium", J. Res. NBS, 70A, 193-197 (1966).

[5] W. R. Shields, T. J. Murphy, and E. L. Garner, "Absolut. Isotopic Abundance Ratio and the Atomic Weight of a Reference Sample of Copper", J. Res. NBS, 68A , 589-592

(1964).

[6] E. J. Catanzaro, T. J. Murphy, E. L. Garner, and

W. R. Shields, "Absolute Isotopic Abundance Ratios and

the Atomic Weight of Magnesium", J. Res. NBS, 7_0A, 453-

458 (1966).

[7] W. R. Shields., S. S. Goldich, E. L. Garner, and

T. J. Murphy, "Natural Variations in the Abundance Ratio

and the Atomic Weight of Copper", J. of Geophys. Res.,

70, No. 2, 479-491 (1965)

.

[8] E. J. Catanzaro and T. J. Murphy, "Magnesium Isotope

Ratios in Natural Samples", J. of Geophys. Res., _71, No. 4, 1271-1274 (1966).

[9] COMPTES RENDUS of the Twenty-third Conference of the International Union of Pure and Applied Chemistry,

Paris, July 2-9, 1965.

[10] M. R. Hayes and J. Metcalfe, "The Boron - Curcumin

Complex in the Determination of Trace Amounts of Boron", Analyst 87, 956-969 (1962).

52
J. D. Wolszon, J. R. Hayes, and W. H. Hill, "Applications

of Anion Exchange Resins to Determination of Boron",

Anal. Chem. 29, 829-832 (1957).

E. J. Agazzi, "Extraction-Flame Photometric Determination

of Boron", Anal. Chem. 39, 233-235 (1967).

G. Marinenko and J. K. Taylor, "Precise Coulometric Titrations of Potassium Dichromate", J. Res. NBS 67A, 453-459 (1963).

A. E. Cameron and Edward Wichers, "Report of the Inter- national Commission on Atomic Weights (1961)", J.A.C.S.

84, 4175-95 (1962) . 0. Menis, Editor, NBS Technical Note 275, (1965).

0. Menis, Editor. NBS Technical Notp 402- (1966).

53

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