National

Bureau

of

mdards

Watfonal Bureau of Standard

Library, E-01 Admin. Bldg.

MAY i 5 1970

NBS TECHNICAL NOTE 506

Analytical Mass

Spectrometry

Section:

Summary of Activities

July 1968 to June 1969
NATIONAL BUREAU OF STANDARDS

The National Bureau of Standards was established by an act of Congress March 3, 1901. Today.

in addition to serving as the Nation's central measurement laboratory, the Bureau is a principal

local point in the Federal Government for assuring maximum application of the physical and

engineering sciences to the advancement of technology in industry and commerce. To this end

the Bureau conducts research and provides central national services in four broad program

areas. These are: (I) basic measurements and standards, (2) materials measurements and

standards. (3) technological measurements and standards, and (4) transfer of technology.

The Bureau comprises the Institute for Basic Standards, the Institute for Materials Research, the

Institute for Applied Technology, the Center for Radiation Research, the Center for Computer

Sciences and Technology, and the Office for Information Programs.

THE INSTITUTE FOR BASIC STANDARDS provides the central basis within the United

States of a complete and consistent system of physical measurement; coordinates that system with measurement systems of other nations; and furnishes essential services leading to accurate and

uniform physical measurements throughout the Nation's scientific community, industry, and commerce. The Institute consists of an Office of Measurement Services and the following technical

divisions:Applied Mathematics—Electricity—Metrology—Mechanics—Heat—Atomic and Molecular Physics—Radio Physics '-' —Radio Engineering - —Time and Frequency - —Astrophysics -—Cryogenics.

THE INSTITUTE FOR MATERIALS RESEARCH conducts materials research leading to im- proved methods of measurement standards, and data on the properties of well-characterized

materials needed by industry, commerce, educational institutions, and Government; develops,

produces, and distributes standard reference materials; relates the physical and chemical properties of materials to their behavior and their interaction with their environments; and provides

advisory and research services to other Government agencies. The Institute consists of an Office of Standard Reference Materials and the following divisions: Analytical Chemistry—Polymers—Metallurgy—Inorganic Materials—Physical Chemistry.

THE INSTITUTE FOR APPLIED TECHNOLOGY provides technical services to promote

the use of available technology and to facilitate technological innovation in industry and Government; cooperates with public and private organizations in the development of technological standards, and test methodologies; and provides advisory and research services for Federal, state, and local government agencies. The Institute consists of the following technical divisions and

offices: Engineering Standards—Weights and Measures — Invention and Innovation — Vehicle Systems Research—Product Evaluation —Building Research—Instrument Shops—Measurement Engineering—Electronic Technology—Technical Analysis.

THE CENTER FOR RADIATION RESEARCH engages in research, measurement, and application of radiation to the solution of Bureau mission problems and the problems of other agencies and institutions. The Center consists of the following divisions: Reactor Radiation—Linac Radiation—Nuclear Radiation—Applied Radiation. THE CENTER FOR COMPUTER SCIENCES AND TECHNOLOGY conducts research and

provides technical services designed to aid Government agencies in the selection, acquisition, and effective use of automatic data processing equipment; and serves as the principal focus

for the development of Federal standards for automatic data processing equipment, techniques,

and computer languages. The Center consists of the following offices and divisions: Information Processing Standards—Computer Information — Computer Services — Sys- tems Development—Information Processing Technology.

THE OFFICE FOR INFORMATION PROGRAMS promotes optimum dissemination and

accessibility of scientific information generated within NBS and other agencies of the Federal Government; promotes the development of the National Standard Reference Data System and a system of information analysis centers dealing with the broader aspects of the' National Measure- ment System, and provides appropriate services to ensure that the NBS staff has optimum accessibility to the scientific information of the world. The Office consists of the following

organizational units:

. Office of Standard Reference Data—Clearinghouse for Federal Scientific and Technical Information : —Office of Technical Information and Publications—Library—Office of Public Information—Office of International Relations.

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

- Located at Boulder. Colorado 80302.

1 Located at 52S5 Port Royal Road. Springfield. Virginia 22151.
UNITED STATES DEPARTMENT OF COMMERCE

Maurice H. Stans, Secretary

NATIONAL BUREAU OF STANDARDS • Lewis M. Branscomb, Director

NBS TECHNICAL NOTE 506

ISSUED MAY 1970

Nat. Bur. Stand. (U.S.), Tech. Note 506, 55 pages (May 1970)

CODEN: NBTNA

Analytical Mass Spectrometry

Section:

Summary of Activities

July 1968 to June 1969

Edited by William R. Shields

Analytical Mass Spectrometry Section

Analytical Chemistry Division

Institute for Materials Research

National Bureau of Standards

Washington, D.C. 20234

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

listed or referred to in the open literature.

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

(Order by SD Catalog No. CI 3.46:506), Price 55 cents.
FOREWORD

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 57 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 a highly

important output of our laboratories. 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 about our programs. A word

is perhaps in order about the philosophy of these yearly

progress reports. In any research program a large amount of

information is obtained and techniques developed which never

find their way into the literature. This includes the

"negative results" which are so disappointing and unspectacular but which can often save others considerable work. Of

importance also are the numerous small items which are often

explored in a few days and which are not important enough to

warrant publication—yet can be of great interest and use to

specialists in a given area. Finally there are the experimental techniques and procedures, the designs and modifications

of equipment, etc., which often require months to perfect and

yet all too often must be covered in only a line or two of a

journal article.

ii
Thus our progress reports endeavor to present this information which we have struggled to obtain and which we feel

might be of some help to others . Certain areas which it

appears will not be treated fully in regular publications are

considered in some detail here. Other results which are

being written up for publication in the journal literature

are covered in a much more abbreviated form.

At the National Bureau of Standards publications such as

these fit logically into the category of a Technical Note.

We plan to issue these summaries for all of our sections.

The following is the fourth annual report on progress of the

Analytical Mass Spectrometry Section.

W. Wayne Meinke 3 Chief

Analytical Chemistry Division

111
PREFACE

The primary function of the Analytical Mass Spectrometry

Section is to establish high accuracy absolute abundance

ratio standards. The atomic weight associated with the

absolute abundance ratio is of course the real product if the

element shows no variation in nature. In an effort to make

the abundance ratio standards more useful the new materials

are supplied in a stoichiometric form, and these reference

materials are then certified for both isotopic composition

and assay. These standards can then be used to calibrate

the instruments for filament bias and at the same time can

be used to calibrate the spike solutions used for isotope

dilution analysis.

This section has expended a considerable amount of time

in the past year to develope an in-house capability for

isotope dilution analysis. The possible inherent precision

and accuracy for determining trace quantities by this method

make it a grand tool for settling differences between other

competences within the Division, though I must admit life

was somewhat more peaceful before we became an umpire for

the Division.

In order to specify adequately some of the procedures

and equipment changes it has been necessary occasionally to

identify commercial materials and equipment in this report.

In no case does such identification imply recommendation or

endorsement by the National Bureau of Standards, nor does it

imply that the material or equipment identified is necessarily

the best available for the purpose.

William R. Shields, Chief

Analytical Mass Spectrometry Section

IV
TABLE OF CONTENTS

PAGE

1. MULTI-STAGE MASS SPECTROMETER . . 1

A. Introduction 1

B. Instrumentation 1

1. Mechanical 1

2. Electrical Systems 1

2. CHEMISTRY 7

A. Introduction 7

B. Atomic Weight Research 8

1. Nickel 8

2. Rubidium 9

C. Nuclear Isotopic Standards .18

1. Boron Isotopic Standards 18

2. Uranium Isotopic Standards 18

3. Stoichiometry of U 3 8 19

4. Plutonium Sulfate Tetrahydrate Chemical

Standard 21

5. Plutonium Sulfate Tetrahydrate Isotopic

Standard 21

D. Trace Characterization by Isotope Dilution

Analysis. , 21

1. Trace Elements in Glass Standards 21

2. Iron and Steel 26

E. Miscellaneous Analyses 28

1. Sodium Oxalate 28

2. Lead in Archaeological Samples 29

3. MASS SPECTROMETRY 30

A. Silica Gel Lead Procedure 30

1. Introduction 30

2. Chemicals 30

3. Mass Spectrometry 30

4. Remarks 31

B. Rubidium Mass Spectrometry 32

C. Plutonium 34

D. Uranium 35

E. Trace Characterization by Isotope Dilution. . . 36

1. Boron 36

2. Copper 38

3. Uranium 40

F. Triple-Filament Isotopic Analyses of Lead

from Archaeological Materials 4l

1. Sampling 4l

2. Results on Archaeological Materials .... 4l

3. Results of Significance to the

Analytical Method 43

4. General Implications 44 v
PAGE

PERSONNEL AND ACTIVITIES 46

A. Personnel Listing 46

B. Publications 46

C. Talks 47

D. Committee Activities 47

REFERENCES 48

LIST OF FIGURES

FIGURE NO.

1. Ion source filament stabilizer 5

2. Photomicrograph of nickel dimethylglyoxime

precipitated by conventional method 10

3. Photomicrograph of nickel dimethylglyoxime

precipitated by modified method 10

LIST OF TABLES

TABLE NO.

1. Results of spectrochemical analysis of

purified rubidium chloride 12

2. Analysis of high-purity rubidium chloride .... 13

3. Assay of solutions containing known amounts

of rubidium . 16

4. Change in temperature of loss due to oxygen

and pressure changes 20

5. Ignition loss of 950a (U 3 8 ) 20

6. Uranium in 500 ppm Trace Elements in Glass. ... 25

7. Copper in various steel SRMs 27

8. Analysis of lead in SRM 1262 28

VI
ANALYTICAL MASS SPECTROMETRY SECTION: SUMMARY OP ACTIVITIES

JULY 1968 TO JUNE 1969

Edited by William R. Shields

This report describes the advances in instrumentation

and the research activites of the Analytical Mass Spectrometry

Section during the period July 1968 to June 1969.

Chemical and mass spectrometric procedures are described

for the determinations of the absolute isotopic abundance

ratios of natural rubidium, boron in a natural boric acid

and a

1 °B enriched boric acid, and of uranium in six SRMs

.

Procedures are also described for the determination of

trace amounts of copper and lead in steel, and silver,

copper, boron and uranium in glass by isotope dilution mass

spectrometry

.

Key words: Instrumentation, isotope dilution,

isotopic analyses, mass

spectrometry, procedures.

Vll

1. MULTISTAGE MASS SPECTROMETER

A. Introduction

The first two stages of a projected three stage mass

spectrometer have now been in operation for approximately two

years. With the exception of the beam valve and the ion

multiplier no changes have been made in the instrument and

operation of the instrument is considered satisfactory. Design

studies for the third (electrostatic) sector have been initiated

and construction should start during this next year.

B. Instrumentation

1

.

Mechanical

Beam Valve - The beam valve reported in the previous

Technical Note [1] has now been in operation for one year on

the multistage instrument as well as on two conventional 60°

spectrometers and no difficulties have been encountered. This

has now been accepted as a standard design for all instruments.

2

.

Electrical Systems

a. Ion Multipliers - A variety of ion multipliers

have been in use during the past year. Extensive testing of

these has included measurements of pulse characteristics at

various counting rates, maximum usable count rates, ion to

electron conversion efficiencies and total system counting

efficiencies

.

(1) Combination multiplier - A commercially

available ion multiplier containing a 'Venetian blind" structure as an ion converter followed by a 17 stage conventional

multiplier with "Rajchman" dynodes was installed. The entire

structure was made from a copper-beryllium alloy. The multiplier operated at a gain of approximately 1.5 X 10 8 (2800 volts)

for three hours with a count rate of 20,000 cps. At the end

of this period a sudden drop in gain to the 10 5 -10 6 region was

experienced. Examination of the multiplier did not reveal any

obvious .cause of failure and all attempts to reactivate the

structure were ' unsuccessful

.

1
(2) Continuous channel electron multiplier

(CCEM) - A commercially available CCEM was purchased and

installed. This multiplier was in the form of a glass tube

0.0^0 inch i.d. bent into circular configuration with radius

of 0.85 inch. A 0.75 inch cone was attached to one end and a

conducting cap was cemented to the other end as an anode.

The entire structure was coated internally with a proprietary

semiconducting material.

The pulse size and shape of this unit were considered to

be satisfactory for pulse counting. The normal pulse at count

rates varying from 100 to 50,000 cps was 50 mv high (51 ft load resistor), 30 ns wide and was nearly square. The pulse

rise time was 9 ns . Above rates of about 70,000 cps the pulse

height fell very rapidly and essentially disappeared above

100,000 cps. The unit, however, recovered very rapidly from

"over counting" and appeared to suffer no permanent damage.

A very careful examination of the pulse train, however,

revealed the presence of a series of secondary or after pulses

starting at 30 ns after the main group and continuing for about

500 ns . An experiment utilizing the oscilloscope trigger pulse

to activate one scaler and the multiplier output to activate a

second, identical scaler indicated that these after pulses

constituted about one-third of the total counted. The after

pulses were of the same size and shape as the primary ones

indicating that they must originate in or very near the input

section of the unit

An effect such as this had been observed earlier by Evans

[2] using a straight tube CCEM. He proposed that the secondary

pulses were the result of the collision with neutral residual

gas molecules which then drifted back towards the input end of

the multiplier until, striking the walls, electrons were

released which were then multiplied as they were accelerated

toward the anode. Evans calculated however that this process

was extremely unlikely in a multiplier which had been formed
in circular shape such as the one used in this study. As a result of his work this mechanism for the production of the

secondary pulses in this case is discounted. It is considered possible that the secondary pulses are the result of a fluorescence of the semiconducting material when struck by

heavy metal ions and a series of experiments is being conducted by the manufacturer of these multipliers to confirm

this hypothesis.

When the secondary pulses are subtracted from the total

observed the overall ion to electron efficiency of the CCEM

is approximately 70% which is not satisfactory for small

sample analysis. This low efficiency is probably due to the

poor conversion at the surface of the semiconductor material

which has properties nearly that of a lead surface.

A polished, anodized aluminum target used as an ion to

electron converter did improve the overall efficiency, however, due to the geometry of the system, the placing of the

target was extremely critical and this effort was abandoned.

In cooperation with the manufacturer, a number of trial

devices are under construction. Most of these will involve

integral aluminum or copper-beryllium first dynodes and will

be constructed in geometrical patterns that, it is hoped,

will be more nearly ideal for heavy ion mass spectrometry.

(3) "Zurich" type multiplier - A 17 stage

electron multiplier with all dynodes of the "Rajchman" design

has recently been installed and tested and is currently in

daily use. This type is much faster than any of the previous

ones used. Pulse rise time is 2-3 ns , width is 15 ns and a pulse height of 250 mv (count rate of 20K cps, load resistor

of 51 ft) is obtained. The pulse height falls very rapidly

above count ratios of about 60K cps and almost disappears at

80K cps. The multiplier also suffers some permanent loss in

gain above 100K cps, and because of this an upper limit of

60K cps is used.
A system background count rate of 1 count per 10 seconds

is quickly reached with this type and has been maintained for

several months with the multiplier gain at 3x10 8

. b. Filament Control - Charged particle mass spectrometry depends upon the ability to achieve and hold a stable

ion beam during the course of a measurement. Stability of the

beam intensity is a function of several variables of which the

ion source output is critical. In the case of the thermal ion

source which is intrinsically a neutral stability source,

variations in temperature, ionizing efficiency or emissivity

are among the variables that will cause changes in the ion

source production that are affected by the power dissipated

in the filament. It is therefore necessary to stabilize the

filament voltage or current to a high degree of regulation.

Filament stabilizers have been built incorporating dc voltage

stabilization or ac current stabilization, however there are

strong arguments for using ac voltage stabilization. To this

end a system capable of stabilizing either ac voltage or

current has been designed and is under development at this

laboratory. The specifications of the device include operation

covering voltage control from 0.1 volts to 10 volts in two

ranges and current control from. 0.1 amps to 10 amps in two

ranges with a maximum of 80 watts power in either mode. The

design goal for stability is a regulation of ±1 part in 50,000.

(1) Principles of operation - The system is

composed of three major sections (figure 1); an ac power

control and modulator, a high voltage isolation section and

an electronic regulator and servo drive section.

Dual regulation is employed with a slow system controlling a variable transformer to set the range of operation and

correct for large variations and a fast electronic system to

stabilize short term variations.

The ac filament voltage is sensed and returned as a feedback signal through the signal isolation transformer. The

signal transformer is Kelvin connected to the filament posts
a>M

E

re

o

o

a>3

r^WV-A/V|^>

\/ -
of the ion source for voltage sensing or in series with the

filament transformer for current sensing. The signal is full

wave rectified and applied to a modified third order linear

phase shift (Paynter) filter [3] and then current summed

against a high stability reference diode circuit. The resulting dc error signal is then amplified to provide an open loop

gain of the overall system of -50 dB . The output of the

amplifier section is then applied to the modulator which can

current sink up to 1.0 amp (at 20 V RMS) providing ^±2 . 5 % line

voltage modulation. The amplifier output is also applied to

the voltage control drive motor circuits which provides -±1.5%

dead zone but for greater deviations actuates the drive motor

to either raise or lower the voltage out of the variable

voltage control transformer. The overlapping of fast and slow

control allows for smooth recovery from large line excursions.

(2) Discussion - At the current stage of

development the stabilizer has several deficiencies which it

is hoped future work will overcome. First it would appear

that the ±2.5% fast regulation is inadequate to cover all line

conditions normally encountered. Second the linear averaging

of the demodulated ac signal provides an error function which

is not a sufficiently close approximation to the true RMS

error value. This is true at the 1 part in 50,000 level due

in part to the fact that the shape of the sinusoidal wave

departs from theoretical due to core and resistance losses in

the transformers. The effect is felt chiefly in a sensitivity

to loading of the power circuit. In order to rectify this

condition a true mean square circuit utilizing an integrated

circuit current cell multiplier is being designed to replace

the demodulator/averaging circuit

(I. L. Barnes, W. A. Bowman, III and R. W. Shideler)
2 . CHEMISTRY

A. Introduction

The chemical activities of this section may be divided

into three main categories, namely, (1) the atomic weights

of the elements by direct measure of their absolute isotopic

abundance ratios, (2) nuclear isotopic standards and (3) trace

characterization by isotope dilution analysis. This is the

first year that we have been active in all three areas.

Under the atomic weights project the high precision - high accuracy method for the determination of nickel was

further refined. Nickel will be studied further after development of a precise abundance ratio method. A high precision

- high accuracy method for the determination of the assay of

rubidium solutions has been developed and highly accurate

isotopic standards have been prepared from separated 85 Rb and

87 Rb isotopes. These standards have been used to determine

the absolute 85 Rb/ 87 Rb abundance ratio and a new atomic weight

for natural rubidium has been calculated. This phase of the

work is further discussed under the "Mass Spectrometry"

section.

In the nuclear isotopic standards project, the reevaluation of the remaining six uranium isotopic standards has been

completed. All sixteen uranium isotopic standards now have

NBS certification of the isotopic values for 23It U, 235 U, 236 U

and 238 U, and the 235 U to 238 U ratio. An investigation has

been started of the ignition conditions required to obtain a known and easily reproducible U 3 8 stoichiometry

.

During the year, we have become active in the project for

trace characterization by isotope dilution. Uranium, lead,

copper and boron have been determined in a Trace Elements in

Glass Standard, copper has been determined in a number of iron

and steel samples, and lead has been determined in a special

Standard Reference Material steel.
The work which has been mentioned in this introduction

will be described in more detail in the following sections.

B. Atomic Weight Research

1. Nickel

Additional work was completed in the investigation of an

assay procedure [ref 1, p. 34] for nickel using dimethylglyoxime . This method was developed so that very accurately

known mixtures of separated isotopes could be prepared for

mass spectrometer calibration. Samples of high purity nickel

wire were used to check the method. Spectrographic analysis

of this wire indicated contamination with only 5 elements,

and these at the less than 0.001 percent level.

Samples of approximately 100 mg were dissolved in dilute

hydrochloric acid. After evaporation to a small volume the

sample was diluted with water and ammonium citrate was added

as a complexing agent. The pH was adjusted to 3 with dilute

ammonium hydroxide and a slight excess of dimethylglyoxime

dissolved in 1-propanol was added. The solution was warmed

to approximately 70 °C and dilute ammonium hydroxide was

slowly added until all the nickel was precipitated. After

cooling, the solution was filtered through a medium porosity

15 cm 3 glass filter crucible that had been cleaned, heated

to 150 °C and weighed on a microbalance . After washing with

water, the crucible was dried at 150 °C to constant weight.

The nickel in the filtrate was determined photometrically

after a chloroform extraction of nickel dimethylglyoxime.

This correction was usually in the 0.04 percent range.

Eleven runs on samples of 70 to 230 mg gave indicated

recoveries of 100.04 to 100.06%. Spectrographic analysis of

the nickel dimethylglyoxime precipitate indicated contamination with only 3 elements and these at the less than 0.001

percent level. To determine if the apparent high recoveries

were caused by contamination of the precipitate by some of

the reagents, excess hydrochloric acid, ammonium hydroxide,

8
ammonium citrate and dimethylglyoxime were added to samples.

All of the excess reagent experiments gave recoveries between

100.05 and 100.06%. To determine possible water pickup,

samples of nickel dimethylglyoxime were stored over P 2 5 and

at relative humidities of 75 and 90%. The change from storing

over P 2 5 to 90% relative humidity was less than 0.01%. Three

lots of dimethylglyoxime from different producers showed no

difference in apparent recoveries.

The present procedure gives much larger crystals than

the conventional method of nickel precipitation by dimethylglyoxime (figures 2 and 3). This makes the filtration and

washing much easier and reduces the problem of the precipitate

"creeping". Another problem in the conventional method is

loss in weight by the crucible. In three determinations this

loss ranged from an equivalent of 0.01 to 0.05% nickel. After

correcting for this loss the three determinations by the conventional method gave apparent recoveries of 100.07 to 100.10%.

The nickel dimethylglyoxime from the conventional method was

also stored over P2O5 and at 75 and 90% relative humidity.

The change from storing over P 2 5 to 75% relative humidity was

0.02% and the change from 75 to 90% relative humidity was 0.04%.

Although the new procedure gives apparent results biased

about +0.05%, the spread of ±.01% would be within the range

required for use in preparing mixtures of separated isotopes

for mass spectrometer calibration in the atomic weight program.

2 . Rubidium

a. Introduction - A search of the chemical literature

for high precision - high accuracy methods for the determination

of rubidium has shown that no satisfactory method exists. The

most promising method was based on gravimetric determination

of precipitated rubidium tetra-phenyl boron followed by flame

emission determination of soluble rubidium. However, the

results of analysis of high-purity rubidium chloride showed

that the method was biased about 0.3% high.
V S £*RX <t i

i v

i mfflW? Si 4*

*t

Figure 2. Photomicrograph of nickel dimethylglyoxime precipitated by

conventional method.

Figure 3. Photomicrograph of nickel dimethylglyoxime precipitated by

modified method.

10
In view of these results it was decided to abandon this

approach and investigate a system based on the purification

of rubidium chloride and assay of solutions of this purified

rubidium chloride by conversion of weighed portions to

rubidium perchlorate.

b. Purification of Rubidium Chloride - Procedure:

About 2.8 g of RbCl (-2.0 g Rb ) were dissolved in 50 cm 3 of

water in a 100 cm 3 quartz beaker and 5 cm 3 of "ultra-pure"

grade perchloric acid were added. The precipitated rubidium

perchlorate, RbClCU, was dissolved by heating the solution

almost to boiling and then slowly crystallized by allowing

the solution to cool to room temperature. The solution was

further cooled to about 5 °C, by placing it in a refrigerator

overnight. The crystallized RbClCU was recovered from the

solution by filtering thru a fine porosity polyethylene filter.

After the RbClOi* was washed with a cold 80% ethanol solution,

it was returned to the quartz beaker and the crystallization

process repeated except that only 2 cm 3 of perchloric acid

were added. The recrystallized RbClCU was again caught on the

polyethylene filter and washed with cold 80% ethanol. The

purified material was dried by passing clean air over the

RbClOit for several hours.

After transfer to a covered quartz crucible, the recrystallized rubidium perchlorate was placed in an electric furnace

and thermally converted to rubidium chloride. This was accomplished by slowly raising the temperature to 600 °C and keeping

it at this temperature for four hours to insure complete

conversion to RbCl. The crucible must be kept covered during

this decomposition since a liquid phase eutectic is formed

which sprays material on further decomposition. The decomposition proceeds in the following manner [4]:

RbClCU £ RbC10 3 +l/20 2 RbC10 3 > S/^RbClO^+l/^RbCl

until all of the RbClOt, has been converted to RbCl.

11
There was no apparent attack of the quartz crucible

during the decomposition. No change in crucible weight was

observed and spectrographic analysis showed the silicon content

of the purified RbCl to be less than 10 ppm. (Platinum

crucibles could not be used since they are attacked.)

Calculations based on the starting weight of RbCl and

weight of the recovered RbClOit showed that about 95% of the

rubidium was recovered.

This procedure has been shown to be effective in removing

common cationic impurities from rubidium chloride except for

potassium and cesium which co-crystallize with the rubidium

perchlorate. Ammonium perchlorate, which could also cocrystallize, would be decomposed and volatilized by the thermal

treatment. Table 1 shows the results of the analysis of

Table 1. Results of spectrochemical analysis of purified rubidium chloride.

Concentration Established

Initial after limits of Element concentration purification detection

ppm ppm ppm

Al 1000 10 5 Ba 1000 2 Ca 1000 4 Co 1000 -

3 Cu 1000 2

Fe 1000 4

Li 1000 2 Mg 1000 2 Na 1000 20

Ni 1000 4

Si 1000 2 Zn 1000 50

NOTE (-- -) not detected

purified RbCl which originally contained 0.1$ each of 12

cationic impurities. Only aluminum was detected at the 10 ppm

level. Potassium was found to be present at 25 ppm and cesium

12
at <10 ppm by flame emission spectroscopy in the purified

material, which were about the same concentrations as the

starting materials. Spark source mass spectrometric analysis

showed that no other element was definitely detected at a level greater than 10 ppm.

c . Assay of Rubidium Chloride Solutions - Solutions

containing known amounts of rubidium chloride were assayed by

converting weighed portions to rubidium perchlorate and correcting for impurities . High purity rubidium chloride was

used to prepare the solutions. The analysis of this material

is shown in Table 2. Since this material contained only about

50 ppm of detected impurities, no correction needed to be

applied to the assay.

Table 2. Analysis of high-purity rubidium chloride.

Element Concentration Element Concentration

ppm ppm

Al Li

Ba Mg 5 Ca Na

Cs a 10 Ni

Cu Si 2 Fe Sr K

a Zn

N03b 1

a Flame emission spectroscopy

b Colorimetric determination

All other elements by spectrochemical analysis.

These solutions were prepared as follows: About 2.8 g of

the high purity rubidium chloride were transferred to a tared

platinum boat and occluded mother liquor was removed by fusing

the material in a quartz tube at 750 °C under an atmosphere of

anhydrous air. (Previous tests had shown that, while some

rubidium chloride is lost due to vaporization, no decomposition

takes place under these conditions.) After cooling, the boat

13
and contents were weighed on a micro balance. The boat

containing the RbCl was then transferred to a tared 200 cm 3 volumetric flask whose neck had been cut off so that only

about 1 cm remained. About 100 cm 3 of (1+99) hydrochloric

acid were added and the rubidium chloride was dissolved out

of the boat. The solution was thoroughly mixed either by

swirling the flask for several minutes or by using a weighed

magnetic stirring bar. The flask was sealed with a weighed

rubber serum septum, weighed on a analytical balance to

±0.2 mg and the rubidium content calculated as meq Rb/g sol.

(The air weight of RbCl was converted to vacuum.)

Each solution was assayed in the following manner: A

4 inch platinum needle was inserted through the septum. A

short second needle which just punctured the septum served as

a vent. A 10 cm 3 polyethylene hypodermic syringe was attached

to the Kel-F hub of the platinum needle and the desired amount

of solution was withdrawn. The syringe was then disconnected

from the hub and the tip was capped with a Kel-F cap. Any

static charge that might be present on the syringe was dissipated by wiping it with a damp paper towel, and the syringe

and contents were weighed on a semi-micro balance to ±0.02 mg.

The solution was then delivered from the syringe to a tared

15 cm 3 platinum crucible and the syringe was again capped,

wiped and weighed. The weight of the sample was determined

from the weights of the syringe before and after delivery of

the sample. Four such weighed portions were withdrawn from

each solution.

About 0.4 cm 3 of "ultra-pure" grade perchloric acid was

added to each weighed portion and the solutions were evaporated to constant volume on a hot plate at about 85 °C. A few

drops of water were added to each and the solutions were again

evaporated to constant volume. The temperature was then raised

to 110 °C and held there until fumes of HCICH were observed.

After reducing the temperature to about 85 °C, 10 cm 3 of hot

14
water were added to each and the solutions heated to near

boiling until the rubidium perchlorate dissolved. The solutions were again evaporated to constant volume and heated to

fumes of perchloric acid at 110 °C. This process of dissolving the RbClOjt in water, evaporating and heating to fumes of

perchloric acid was repeated. The temperature of the hot

plate was held at about 110 °C until all of the excess HCIO^

had been fumed off.

After fumes of perchloric acid were no longer noted, the

samples were again dissolved, evaporated to dryness, and heated

at 150 °C. This process was repeated two more times. (The

first series of repeated evaporations frees the RbClOj, from

chloride. The second series frees the RbC10i» from occluded

perchloric acid.)

The crucibles were then covered with platinum covers and

transferred to an electric furnace. The temperature of the

furnace was slowly raised to 250 °C and the crucibles were

kept at this temperature for 16 hours (overnight). After the

covers were removed, the crubibles were cooled and weighed.

This procedure of heating, cooling and weighing was repeated,

except that the time of heating was reduced to 6 hours, until

a constant weight was obtained, that is, until the weighings

agreed to within 5 ug. For simplicity of calculations, the

vacuum weight of the rubidium perchlorate was converted to

milliequivalents (meq) of rubidium.

The results of the assay of seven solutions prepared from

the fused high purity rubidium chloride and three solutions

prepared from thermally decomposed rubidium perchlorate (made

from the same RbCl) are shown in Table 3. Comparisons of the

calculated and measured concentrations of the ten solutions

showed that the concentrations of rubidium ion as determined by

this method agreed to within 0.01$ of the calculated rubidium

concentration and that systematic errors were negligible.

15
Table 3. Assay of solutions containing known amounts of rubidium.

Weight of solution

g

\ 9.85788

10.67140

8.80360

9.52762

8.16376

7.81870

8.96725

8.55795

Rubidium

found

meq

1.764333

1.909452

1.575612

1.705150

Concentration

of solution

meq Rb/g soln

0.178977

0.178932

0.178974

0.178969

Average 0.178963

Calculated 0.178958

1.258644

1.205929

1.382899

1.319698

0.154175

0.154236

0.154217

0.154207

Average 0.154209

Calculated 0.154196

Weight of solution

g

F 9.53461

8.55327

8.83631

9.21118

9.20909

9.83562

10.79832

9.93118

Rubidium

found

meq

1.318655

1.183065

1.222006

1.274062

Concentration

of solution

meq Rb/g soln

0.138302

0.138317

0.138294

0.138317

Average 0.138307

Calculated 0.138284

1.469835

1.569566

1.723807

1.584865

0.159607

0.159580

0. 0.159636

0.159585

Average 0.159602

Calculated 0.159584

C 7.95102

8.14901

7.80619

7.45722

1.379114

1.413216

1.353978

1.293103

0.173451

0.173422

0.173449

0.173403

Average 0.173431

Calculated 0.173425

H

a 8.00215

8.14606

9.19938

9.24349

1.541045

1.568722

1.771553

1.780254

0.192579

0.192574

0.192573

0.192595

Average 0.192580

Calculated 0.192588

8.16928

8.67858

9.11450

7.65082

1.173152

1.246444

1.308867

1.098568

0.143605

0.143623

0.143603

0.143588

Average 0.143605

Calculated 0.143608

I a 8.56481

8.83751

9.33946

10.11288

1.329557

1.372003

1.449680

1.569761

0.155235

0.155248

0.155221

0.155224

Average 0.155232

Calculated 0.155225

7.82366

7.73812

8.54575

8.03355

1.151656

1.138905

1.257979

1.182335

0.147202

0.147181

0.147205

0.147175

Average 0.147191

Calculated 0.147190

RbCI from thermally decomposed RbCIO^

J a 8.99170

9.85365

9.74777

10.29374

1.813534

1.987200

1.965980

2.075790

0.201690

0.201673

0.201685

0.201661

Average 0.201677

Calculated 0.201678

16
Analyses of the rubidium perchlorate, resulting from

the above assay, have shown it to contain less than 0.001%

chloride and less than 0.0002% chlorate. The chloride was

determined by silver chloride turbidity and the test for

chlorate was based on the reaction of chlorate with chloride

in acid solution to produce chlorine which was detected with

o-tolidine

.

d . Preparation of Calibration Mixtures for the

Mass Spectrometric Determination of the Atomic Weight of

Rubidium - The previously described work has been applied

to the preparation of calibration mixtures from separated

rubidium isotopes for the mass spectrometric determination of

the atomic weight of rubidium. Separated rubidium isotopes

in the form of 85 RbCl and 87 RbCl were purified by the perchlorate method. Samples of the purified 85 RbCl and 87 RbCl

were analyzed by flame emission spectroscopy and spark source

mass spectrometry. The results of these analyses showed that

the 85 RbCl and the 87 RbCl contained 120 ppm and 100 ppm of

potassium, respectively. No other element was detected at a

level sufficient to cause significant error in the assay.

Cesium was found to be present at less than 10 ppm in both

samples

.

The purified 85 RbCl and 87 RbCl were taken into solution

with dilute hydrochloric acid and solutions containing about

0.16 meq Rb/g soln of each separated isotope were prepared.

The rubidium content of each separated isotope solution was

determined by converting weighed portions to the perchlorate

as described. The calibration mixtures were then prepared by

mixing weighed portions of each separated isotope solution.

These calibration mixtures were then used as standards

for the mass spectrometric determinations of the absolute

abundance ratio of 85 Rb/ 87 Rb and the atomic weight of

rubidium was calculated. This work is described in a recentpublication [5] .

17
C . Nuclear Isotoplc Standards

1 . Boron Isotopic Standards

The isotopic composition of natural boron appears to vary

significantly [6,7,8] so there is little value in attempting

to establish an atomic weight. The absolute isotopic compositions of a natural ( 11 B/ 10 B ^4) boric acid reference material

and an enriched (

1 °B ^95%) boric acid reference material were

established and designated SRM 951 and SRM 952. The former

is needed as an absolute standard by scientists studying

natural boron isotopic variations and the latter is needed

by scientists concerned with enriched x °B samples used in

nuclear reactions.

Calibration mixtures of the separated boron isotopes were

prepared for the mass spectrometric determination of absolute

abundance ratios. Separated boron isotopes in the form of

H 3 10 BO 3 and H3 11 B0a were obtained from the Isotopes Division

of the Oak Ridge National Laboratory. The separated isotopes

were taken into solution with water and the boron content of

each separated isotope solution was determined by coulometric

titrations by George Marinenko of the Microchemical Analysis

Section. The calibration mixtures were prepared by mixing

weighed portions of each separated isotope solution. These

were prepared in pairs to approximate the 11 B/ 10 B ratios of

4, 1, 0.25, 0.083 and 0.055. The calibration mixtures of the

separated isotopes were used to determine the absolute abundance ratios of the natural boric acid and the enriched boric

acid standard reference materials. The details of this work

are given in Special Publication No. 260-17 [9].

2 . Uranium Isotopic Standards

All sixteen of the uranium isotopic standards now have

NBS certified values. These values were determined by using

accurately prepared mixtures of U-235 and U-238 separated

isotopes to determine the mass spectrometer bias in the range

from 0.5 to 93 percent 235 U and by using U-233 for isotopic

18
dilution to determine the z3h U and 236 U content [10]. The

mass spectrometer bias for the six standards at the 0.5 to

5 percent 235 U level was determined this year.

Samples of the U-238 separated isotope were ignited to

give a reproducible oxide [1]. Two 0.3 g samples of the

U-235 separated isotope were ignited by the same procedure

and after dissolving in diluted nitric acid were diluted to

approximately 100 g with water. Weighed aliquots of 2 to

10 g, using plastic syringes and platinum needles, were added

to the dissolved U-238 samples to give 0.5 to 1 percent 235 U.

Using these mixtures, the mass spectrometer bias and the

235 U/ 238 U ratios for the six standards were determined.

All bottling of the uranium isotopic standards is done

in the "hot lab", because of the radioactivity of the material

and the care required to prevent any contamination of samples.

In the past year 574 samples were bottled. Approximately

8,000 additional samples are yet to be bottled.

3 . Stoichiometry of U 3 Q 8 The ignition conditions required to obtain stoichiometric

U 3 e have been a problem for many years. This investigation

was undertaken to determine if an easily reproducible ignition

procedure could be found that would give a stoichiometric U 3 8 compound. There have been indications that ignition at higher

altitudes can cause slight differences in the U 3 8 stoichiometry so ignitions were done at reduced pressure as well as in

atmospheres containing 5, 10, and 20% oxygen. The ignitions

were carried out thermogravimetrically and in a tube furnace

[1] . Standard Reference Material 950a, U 3 8 , was used in the

investigation

.

Thermogravimetric runs on 100 mg samples showed a loss of

about 0.05% in the area of 900 °C. This loss occurs over a

range of about 50 °C with little change in weight at temperatures above or below this point, except the initial loss, in

the first 200 °C. Table 4 gives the temperature where this

loss occurs under varying conditions

.

19
Table 4. Change in temperature of loss due to oxygen and pressure changes.

Atmosphere

% 2

Start of

weight loss

C

End of

weight loss

C

Pressure

mmHg

Start of weight loss

C

End of

weight loss

C

5 800 850 750 865 915

10 835 880 650 860 905

20 865 915 550 855 895

100 985 1025 350 825 870

Samples of 1 g were used in the tube furnace ignitions.

The samples were placed in platinum boats and weighed on

a microbalance while sealed in a small glass desiccator.

Table 5 shows the average of 2 samples ignited for 1 hour at

the temperature indicated and cooled by quickly moving the

furnace back from the area of the tube containing the samples

(normal cooling).

Table 5. Ignition loss of 950a (U 3 8

).

Temperature

C

Loss

%

850 .076

900 .088

950 .102

1000 .114

1050 .126

The rate of cooling after ignition was found to affect

the loss in weight. After heating to 1000° a samples cooled

by taking 10-15 minutes to move the furnace back from the

samples (slow cooling), showed an ignition loss of 0.085$.

The ignition loss increased to 0.120$ when the boat was

quickly pulled into an iced portion of the quartz tube (fast

cooling).. Samples heated to 900 °C gave 0.085$ loss for the

slow cooling and' 0.096$ for the fast cooling. Ignition in a

20
5% oxygen atmosphere to 1000 °C gave losses from 0.141 to

0.187% depending on the rate of cooling. In a reduced

pressure of 550 mm of mercury, 20% oxygen atmosphere and

900 °C temperature, the loss was 0.083% for a slow cool and

0.104% for a normal cooling.

The investigation is continuing, but the results indicate

that the usual 1 hour at 900 °C ignition can give a variable

stoichiometry for U 3 8 depending on the atmospheric pressure

and the rate at which the sample is cooled after ignition.

4

.

Plutonium Sulfate Tetrahydrate Chemical Standard

The atomic weight of the plutonium sulfate tetrahydrate,

Standard Reference Material 944, was determined from isotopic

abundance ratios measured by mass spectrometry. The americium

in the sample was separated from plutonium by anion-exchange

[11].

5

.

Plutonium Sulfate Tetrahydrate Isotopic Standard

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

using the anion-exchange separation of americium from

plutonium [11] . Both Standard Reference Material 948 and a United Kingdom sample (UK-131) were measured.

D. Trace Characterization by Isotope Dilution Analysis

1 . Trace Elements in Glass Standards

a. Introduction - The Office of Standard Reference

Materials has submitted five "Trace Elements in Glass" for

analyses by the isotopic dilution technique. These glasses

consist of the base glass, composed of Si0 2 (72%), CaO (12%),

Na 2 (14%) and A1 2 3 (2%), and four glasses made by adding

0.02, 1, 50 and 500 ppm of 6l trace elements to the base glass.

The 500 ppm glass was analyzed first so that procedures

could be refined and modified to include the 0.02 ppm and base

glasses. The major difficulties are in reducing the blank to

a level that will permit analysis of the 0.02 ppm and base

glasses and in developing separation techniques for the element

of interest.

21
In the 500 ppm glass the determination of uranium has

been completed and preliminary values have been obtained for

boron, copper, and lead. Details of this work are discussed

in the following sections

b . Boron - Preliminary determination of boron in

the 500 ppm glass has been made following the method used for

the determination of boron in the Glass Beads for Neutron Flux

Measurements [ref 1, p. 31]. The method was modified in order

to determine boron in the 0.05 percent range.

The glass was fused with sodium carbonate and digested in

water. A spike solution of * °B was added so that the 11 B/ 10 B

ratio was 1/1. The solution was acidified with nitric acid

instead of sulfuric acid to keep the calcium in solution. The

boron was extracted into a chloroform - 2-ethyl-l,3-hexanediol

mixture. The organic layer was washed with dilute nitric acid

and the boron was back extracted into a sodium hydroxide solution. This layer was acidified with sulfuric acid and the

boron again extracted with chloroform - 2-ethyl-l,3-hexanediol

mixture, except 2 cm 3 of the chloroform - 2-ethyl-l,3-

hexanediol mixture were used instead of the 20 cm 3 used in

the first extraction. The sodium hydroxide solution, used to

back extract the boron, contained the amount of sodium to

make the B/Na ratio 1/1 and the final concentration of the

solution was 0.5 mg B/cm 3

. Since these solutions gave erratic

runs on the mass spectrometer, the solutions were passed

through a cation exchange resin and sodium carbonate added to

the eluate to make a B/Na ratio of 1/1.

A study of the method is now in progress to ascertain if

the desired accuracy and precision can be attained. At the

same time the possibility of extending the method for the

determination of boron in the microgram and the submicrogram

ranges is being examined.

The study includes the effects of the small amount of

acid carried through the procedure and how to remove it, the

22
effects, if any, of the ion exchange procedure, and the completeness of the extraction of small amounts of boron. Some

of the plans are to use water as the wash solution and a

mixed bed ion exchange resin to remove both anions and cations

from the solution.

c. Copper, lead and silver - Procedure: Copper,

silver and lead were determined in the same sample of 500 ppm

Trace Elements in Glass by the isotope dilution technique.

The sample was dissolved in a platinum crucible in a perchloric

acid - hydrofluoric acid mixture by repeated evaporation to

fumes of perchloric acid with additions of hydrofluoric acid

between each fuming. The excess hydrofluoric acid was removed

by repeated evaporations to fumes of perchloric acid with the

addition of water between each fuming. The solution was transferred to a 100-cm 3 beaker and separated isotope solutions,

Cu-65, Pb-206 and Ag-109j were added as the spike solutions.

Nitric acid was added and the copper, silver and lead were

deposited on electrodes by electrolysis.

The lead, deposited on the anode, was dissolved in nitric

acid and hydrogen peroxide and then evaporated to dryness.

The residue was dissolved in the volume of 2% nitric acid to

make the final concentration 0.5 mg Pb per cm 3

. The deposit on the cathode, copper and silver, was dissolved in nitric acid. The pH of the solution was adjusted

to 1 with ammonium hydroxide and the silver and copper were

extracted into a 0.05% solution of dithizone in chloroform.

The aqueous layer was discarded. The silver was extracted

from the chloroform layer into a mixture of equal volumes of

sodium hydroxide (20%) and hydrochloric acid (0.03 M) . The

chloroform layer, containing the copper, was evaporated to

dryness and perchloric acid and nitric acid were added. The

organic material was removed by evaporating to fumes of

perchloric acid. The copper was again deposited by electrolysis, and then was dissolved in nitric acid. The solution

23
was evaporated to dryness and dissolved in sufficient 2% nitric

acid to make the final concentration 0.5 nig Cu per cm 3

. The sodium chloride - sodium hydroxide layer, containing

the silver, was diluted 10 fold and was extracted with the

dithizone in chloroform. The aqueous layer was discarded.

The chloroform layer was treated as above to give a solution

with a final concentration of 0.5 mg Ag per cm 3

. Copper: The preliminary result of 444.4 ppm Cu

with a standard deviation of 2.8 was obtained. The blank was

2.5 Pg which is too large for the determination of Cu in the

glasses containing 50, 1 and 0.02 ppm copper. In order to

reduce the blank, controlled potential deposition of copper

from the dissolved sample of glass has been studied. At this

time it appears that the copper and silver can be separated

satisfactorily with this method and the dithizone separation

can be eliminated, thereby reducing the possible contamination

from chloroform, dithizone and the sodium hydroxide - hydrochloric acid mixture. Additional studies will be made to

determine if the reagent blank can be reduced to the desired

level

Lead: The preliminary result of 423.7 ppm Pb with

a standard deviation of .4 was obtained. Blanks of 0.3 and

0.5 yg were found which is too large for satisfactory analysis

of the 1 and 0.02 ppm glasses.

Platinum and glass containers were used in these determinations and the usual precautions of contamination from the

air were taken. The use of teflon in place of platinum and

glass and extra precautions to exclude lead from the air will

be examined as a means of reducing the reagent blank.

Silver: The solutions prepared for mass spectrometric determination of silver have not been completed.

d. Uranium in Glass - The uranium in this glass

sample was determined by an isotopic dilution technique using

a U-235 separated isotope for the spike. The first set was

24
run on the same samples from which boron had been extracted.

The blank was much higher than expected (0.4 yg U) so in the

second set for uranium, the boron extraction was omitted.

The blank dropped to less than 0.02 yg U in the second set.

The results for this glass are given in Table 6.

Table 6. Uranium in 500 ppm Trace Elements in Glass.

Position Setl Set 2

ppm U ppm U

2 461.6

13 461.8

18 461.3

48-1 461.0, 461.

6

a 48-2 461.2

56 462.2

66-1 461.2

66-2 460.9, 461.3 a

106 461.6

Average 461.2 461.7

Standard deviation .2 .3

461.5

a Two mass spectrometer runs on the same solution.

The results on the 500 ppm Trace Elements in Glass, given

in Table 6, show the sample is homogeneous with respect to

uranium. The range of values for both sets is from 460.9 to

462.2 ppm uranium.

The glass samples were crushed and 0.6 to 1.0 g was

fused with sodium carbonate. After the melt was broken up in

water, weighed aliquots of U-235 separated isotope solution

were added. Nitric and hydrofluoric acids were added, the

solution was evaporated to near dryness, and after diluting

with water, the solution was filtered into a beaker containing

boric acid. The solution was passed through an ion exchange

column containing a strongly acidic cation resin. After

washing the column, the uranium and other cations held by the

25
resin were eluted with nitric acid (1+3). The solution was

evaporated to dryness, taken up in nitric acid (1+1), and the

uranium separated by elution through a strongly basic anion

exchange column. The uranium was removed with 0.3 N nitric

acid, the solution was evaporated to dryness and the elution

through the strongly basic anion exchange column was repeated.

The sample was evaporated to dryness and after dissolving in

nitric acid (1+19) the isotopic ratios were determined by

mass spectrometry.

2 . Iron and Steel

a. Copper - Copper was determined in a number of

iron and steel SRMs by isotope dilution mass spectrometry in

the following manner. Prom 0.1 to 1 g of sample (depending

on the estimated amount of copper present) was dissolved in

10 cm 3 of (1+1) "ultra-pure" grade perchloric acid in a

teflon beaker. Any carbon present was oxidized by heating to

fumes of perchloric acid. Silicon was volatilized as SiF 4 by

the addition of 1 cm 3 of "ultra-pure" grade hydrofluoric acid

and again heating to fumes of perchloric acid. The solution

was then cooled and diluted to about 20 cm 3

. A weighed portion of a standardized 65 Cu solution was

added to the solution of the steel to produce a

63 Cu/ 65 Cu

ratio of from 1.0 to 0.5 in the sample (preferably 0.5).

(The natural 63 Cu/ 65 Cu ratio is 2.4.) After adding 4 cm 3 of

hydrofluoric acid to complex the iron, the solution was

diluted to 50 cm 3 and thoroughly mixed. The copper present

was then separated by electrodeposition and taken into solution for mass spectrometric analysis. The results of these

analyses are shown in Table J.

26
Table 7. Copper in various steel SRMs.

Sample Found Average and est

wt% limits of error 36B-A 0.1803

36B-B 0.1810

36B-C 0.1797

36B-D 0.1804

0.1804 ±0.0018

59A-A 0.05198

59A-B 0.05162

0.0517810.0005

342A-A 0.1335

342A-B 0.1343

0.1339 ±0.0013

1262-A 0.4994

1262-B 0.4975

1262-C 0.4995

0.4988 ±0.005

b. Lead - Isotope dilution analysis was applied to

a special steel sample, SRM 1262. The sample was dissolved

and carbon and silicon were eliminated as described under the

copper analysis. After spiking the sample solution with a weighed portion of 206 Pb solution, (1+1) ammonium hydroxide

was added until the precipitated Fe(OH) 3 redissolved only

slowly. The isotopically altered lead was then separated by

gassing the solution with hydrogen sulfide and adding (1+1)

ammonium hydroxide until some FeS precipitated. The precipitated sulfides were then caught on filter paper and washed.

The sulfides were then washed from the paper, and oxidized

by digestion with perchloric acid. Nitric acid was then added

and the solution was diluted to 50 cm 3

. The lead present was

then separated by electrodeposition onto a platinum anode and

taken into dilute nitric acid solution for mass spectrometric

analysis

.

27
Following the sulfide precipitation, two samples were

treated in the above manner while a third sample was treated

in a different manner. For this sample the filter papers

containing the mixed sulfide was transferred to a porcelain

crucible and slowly ignited. The lead present was taken into

solution with nitric acid and recovered by dithizone extraction. The blank for this procedure was only 0.02 ug of Pb as

compared to 0.18 ug of Pb for the electrodeposition procedure.

The results are shown in Table 8.

Table 8. Analysis of lead in SRM 1262

Sample Found

ppm

Average

ppm

1262-A 6.18

1262-C 5.67

1262-3 5.81

5.89

E. Miscellaneous Analyses

1. Sodium Oxalate

The replacement for SRM 40g, Sodium Oxalate, oxidimetric

standard, was submitted for the determination of the effective

purity. The personnel of this section, having experience in

the assay of this material, were assigned the determination

of the effective purity even though such an assay is outside

the usual activities of this section.

This lot of sodium oxalate has been issued as SRM 40h,

Sodium Oxalate, with a provisional certificate of analysis

stating that the effective purity is 99.95 ± 0.05 percent.

A final certificate of analysis will be issued upon the

completion of the intercomparison of SRM 40h, Sodium Oxalate,

SRM 83c, Arsenic Trioxide and SRM 136b, Potassium Dichromate.

Four composites were prepared. Each composite consisted

of 10 g of material from seven of the 28 containers of sodium

oxalate. Preliminary comparisons of this sodium oxalate

28
(SRM 40h) to the previous sodium oxalate (SRM 40g) , to single

crystal oxalic acid and to arsenic trioxide (SRM 83c) were

made by titrating with 0.1 N potassium permanganate solution.

Because sodium oxalate is not oxidized by potassium dichromate, they were compared by titrating the potassium dichromate

with ferrous ammonium sulfate and then the sodium oxalate and

the ferrous ammonium sulfate were titrated with the potassium

permanganate solution. Additional experiments will be performed to determine the best conditions to obtain the desired

accuracy and precision for the intercomparison of these

standards

.

Homogeneity of this lot of sodium oxalate was determined

by titrating a 0.3 g sample from each of the 28 containers

with 0.1 N potassium permanganate solution. Also the sodium

hydrogen oxalate and sodium bicarbonate impurities were

determined and found to be 0.03$ each.

Further work is planned for the coming year to complete

the intercomparisons of all the oxidimetric standards issued

by the National Bureau of Standards

.

2 . Lead in Archaeological Samples

In the continuing cooperative effort with Dr. Robert H.

Brill of the Corning Museum of Glass, lead was separated for

isotopic analysis from lead metals, ores and glasses.

The metals and ores were dissolved in dilute nitric acid

and the insoluble residue removed by filtration. The glasses

were dissolved by repeated evaporations to dryness in a hydrofluoric-nitric acid mixture and then dissolved in dilute

nitric acid. The insoluble residue was removed by filtration.

The lead in these solutions was electrodeposited as lead oxide

onto a platinum gauze anode and dissolved in a nitric acidhydrogen peroxide mixture. The resulting solution was

evaporated to dryness and the residue taken up in 2% nitric

acid so that the final solution contained 25 mg of Pb per cm 3

.

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

29
3. MASS SPECTROMETRY

A . Silica Gel Lead Procedure

1 . Introduction

This procedure is essentially an adaptation and extension

of the procedure published by Cameron, et al., [12]. The

modifications made and the details of the mass spectrometry

are described below.

2Chemicals

Reagent (ACS) grade sodium metasilicate was used to prepare the silica gel as described in the above reference. The

silica gel was however washed 5 or 6 times by boiling for 3-4

hours with water redistilled in a quartz still. The boiling

and subsequent evaporation was carried out in a laminar flow

"clean" hood to prevent contamination with particulate

"fall-out". All of the chemical steps were performed in

teflon containers.

During all steps in the preparation of the silica gel,

special precautions were taken so that the gel was never

allowed to become dry. This insures that the final product

will be of extremely small particle size.

One gram of the prepared silica gel was placed in a

125 ml teflon bottle and 25-30 ml of redistilled water was

added

The phosphoric acid solutions were prepared from specially

sublined phosphorous pentoxide (J. T. Baker Co., "ultra-pure"

grade .

3

Mass Spectrometry

All samples were prepared in 2% nitric acid to have a final concentration of ^200 yg lead/ml.

A single rhenium filament (0.001 inch x 0.030 inch)

mounted in a filament block was placed under an infra-red heat

lamp and connected to an ac current source. The silica gel

solution was shaken vigorously and then allowed to settle for

30 seconds. A small amount of solution was withdrawn from

30
the top layer of solution with a capillary pipette and a small drop placed on the filament. This was dried for 5

minutes with the heat lamp and a current of 1 A.

One drop of the sample solution (0.5 to 2 yg Pb ) was

added to the filament and dried for 5 minutes with the heat

lamp and a current of 1 A.

One drop of the phosphoric acid solution was added and

dried for 5 minutes with the heat lamp at a current of 1.7 A.

(Note: It is essential that the sample mounting be dry after

this point or excessive flaking of the mount will occur

during the next step . ) The current through the filament was advanced to 2.5 A,

held there for 10 minutes after which the filament was loaded

in the instrument. (Note: Sample mountings prepared in this

way are extremely hygroscopic and must be immediately loaded

in the spectrometer or otherwise protected.)

The mass spectrometric analysis was accomplished in the

following manner:

Time from start Procedure

(minutes

)

Filament is set to 1000 °C with an optical

pyrometer

.

5 Temperature is advanced to 1050° . 10 Temperature is advanced to 1100°

.

10-15 A lead peak is found and focussed.

15 Temperature is advanced to 1150°

.

15-25 Background scan.

25 Data taking starts. Each peak is monitored

for 30 seconds. Magnet is moved in discrete

steps between peaks.

4 . Remarks

Decaying signals are always observed.

A filament bias (for lead) nearly identical with that

found by the triple filament lead procedure is observed.

31
If the sample is not "clean", for example if thallium

and bismuth are not removed by the chemical procedure, some

signal instability may be observed. This will usually disappear with time and the data taking period may be delayed.

Data taken after as long as 40 minutes does not show

significant fractionation.

If, at any time during the preparation or subsequent use,

the silica gel is allowed to become dry, the material should

be discarded and a fresh batch prepared.

B. Rubidium Mass Spectrometry

An analytical procedure for the isotopic analyses of

rubidium has been developed, supplanting a previously described

[13] "interim" procedure. A triple filament rhenium-ribbon

(1x30 mils) source is used. The sample is mounted by placing

one drop of solution O0.2 yg Rb ) on each sample filament and

drying it with a heat lamp and a 0.5 A electric current for

ten minutes.

Two slightly different techniques were originally developed by two different operators, one using samples made up

in neutral aqueous solutions, and the other using samples

dissolved in 2% HC1 solutions. Both techniques used sample

concentrations of 10 yg/cm 3

. After extensive study the procedure using 2% HC1 solutions was deemed superior, primarily

because it gives a continually growing signal where the

aqueous solutions appear to form, in part, a low-temperature

phase which must be completely burned off before a continually

growing signal can be achieved. The procedure used with 2%

HC1 solutions is described below.

A previously described [11] 6-inch radius of curvature

solid-sample thermal ionization mass spectrometer is used.

The source slit opening is 10 mils and the collector slit

opening is 40 mils

32
Time from start Procedure

(minutes

)

0-1 The ionizing filament current is set to give

a temperature of 1450 ± 10 °C (^2.8 A),

measured with an optical pyrometer. The

sample filament currents are set at 0.5 A.

The Rb grid signal is generally on the order

of 1 mv or less. The signal should grow

slowly

.

5 The sample filament currents are increased

until a lxio -12 A Rb grid signal is achieved.

The signal should continue to grow.

10 The sample filament currents are increased

until a 3-5 x 10~ 12 A Rb grid signal is achieved

The signal should grow at a moderate rate.

20 If the Rb grid signal is less than lxio" 11 A

the sample-filaments are increased to give

1.2x10 ll A. The signal should continue to

grow moderately.

25 The Rb grid signal should be approximately

1.5xl0 -11

A.

35 Data-taking begins. The Rb grid signal

should be 1 . 5-1 • 8xi0 _1 1 A and should continue

to grow throughout the run. Ten peak sets

are taken over the next 10 1/2 minutes. If

the grid signal deviates greatly from this

pattern the run should be aborted. In a few

cases the signal was observed to decay during

the first 20 minutes but would usually begin

to grow after this time and follow the

"normal" pattern.

Rubidium signals are easy to obtain and are stable.

However, they are very susceptible to small changes in filament

current (temperature), and it is easy to overheat the sample

33
in the early stages of an analysis. Overheating subsequently

leads to too-rapid growth and/or premature decay, both of

which necessitate aborting the run.

Analyses should be made on slowly or moderatly growing

signals. Under such conditions, the observed ratio will

generally not change measurably (i.e. <0.05#) over the

10 1/2 minutes period of data-taking.

All filaments are prebaked, in a vacuum and under a

potential field, to eliminate any background Rb signals which

might come from the filament itself.

C . Plutonium

The isotopic composition of Standard Reference Material

948 and United Kingdom Sample, UK-131, were determined as

part of the continuing effort to evaluate the half life of

2h *Pu. After 4 years of measurements on SRM-948, it is now

apparent that the change in 2l+1

Pu is too small to determine

with the desired accuracy over short periods of time (<3

years). An initial low value of 14.3 years was attributed to

the larger error associated with ion multiplier measurement

and/or the failure to remove all americium from the solution.

Improved chemical and mass spectrometric procedures as well

as use of a conventional collector since 1965 have indicated

that a limit of error of 2-3$ (95$ confidence limits) can be

expected for a 3 year determination on this sample. The

value for the 2U Pu half life using SRM 948 over a 4 year

period (1964-1968) is 14.6 ± 0.4 years.

A half life value of 14.6 years has been obtained from

isotopic composition measurements of sample UK-131 over the

interval 1967-1968. Using a long term accumulation of data

from uranium samples of similar composition as a basis of

comparison, it is estimated that the change in 21+1 Pu has been

determined precisely enough to give a limit of error less

than 0.4 year (95% confidence limits).

34
D. Uranium

A large volume of data on Standard Reference Materials

U-930 thru U-050 has demonstrated that any bias of mass

spectrometers in this laboratory is independent of isotopic

composition and is primarily related to the process of ionization in the source region. The ratio of 235 U and 238 U ion

currents for these SRMs is always between 20:1 and 1:20. For

U-030 to U-005 the ion current ratio is significantly outside

of these limits and the total ion current necessary for a precise analysis is normally greater than 5*10 X1 A. Under

these conditions additional precautions must be taken to

obtain accurate measurements.

First, vibrating reed input resistors of 10 ll ohms have

a non-linear response for ion currents exceeding 5

X 10 1X A

and failure to observe this fact introduces a bias component

that is dependent upon intensity. Use of a 10 10 ohm input

resistor eliminates the non-linear response problem but unless

a compensating increase in total ion current is achieved the

reading error associated with the 235 U peak height severely

limits the precision of any measurement. A total intensity

that yields a maximum error of 0.25% on expanded scale peak

height determination is selected and maintained for each SRM.

For U-030 thru U-005 the total ion currents are constant at

some level between 2-5 x 10 _1

° A and are changed for each SRM

in order to achieve maximum and uniform precision in the

measurement

.

As the ion current ratio of the major isotopes changes

from 20:1 (U-050) to 200:1 (U-005) there is a significant and

progressively longer R-C response of the measuring circuit.

The R-C response contribution to the 235 U peak is approximately 0.3% of the peak height immediately after switching a 10 10 A ion current from the Faraday cage and then collecting

a 10~ 12 A current. This contribution becomes insignificant

35
within 30 seconds and the "true" peak top is obtained. Consequently, monitoring of peak tops is changed from the normal

equal time (30 seconds) per peak to a cycle of 60 seconds for

235 U peak top data and 30 seconds for the 238 U peaks.

The R-C response made it impractical and unwise to determine a single correction factor with a small number of known

mixtures and apply this correction to the data for all SRMs

For each SRM from U-050 to U-005 two calibration mixtures of

known isotopic composition were prepared with approximately

the same 235 U/ 238 U ratio as the SRM. Each SRM and its corresponding calibration mixtures were analyzed in an alternate

pattern and biases determined at the approximate 235 u/ 238

u

ratio of the SRM. The individual correction factors were

applied to the appropriate SRM to obtain corrected data.

The 231+ U and 236 U composition of these SRMs were previously determined by 233 U isotope dilution. A second determination

was made by direct measurement to recheck these values and to

evaluate any contribution from R-C response. The electromechanical scan rate was set to give a 45 second time interval

between the centers of adjacent peaks. The data obtained in

this manner agreed experimentaly at the 9*5% confidence level

with the isotope dilution values.

E. Trace Characterization by Isotope Dilution

Only a limited amount of analytical effort has been

expended in this area but one of the emerging problems is the

need to modify existing analytical procedures or to develop

completely new ones to obtain meaningful data from microgram

and submicrogram samples. Boron, copper, lead and uranium

samples were analyzed during the past year as part of the

isotope dilution program.

1 . Boron

Previously, the abundance of boron in glass beads was

determined by isotope dilution [1]. The amount of boron in

the selected glass samples was always about 15 mg at the start

36
of chemical processing. With milligram quantities of starting

material solutions with uniform concentrations of boron and

stoichiometric amounts of boron and sodium were not a major

problem.

For the "Trace Elements in Glass" there is greater

difficulty in extracting microgram quantities of boron and

preparing solutions for mass spectrometric analysis. The

past history of evaluating bias parameters for boron analysis

make it mandatory to re-evaluate possible sources of bias

when there is a significant change in the chemical procedure.

SRM 95-1, boron isotopic standard, is being used as a working

standard of known isotopic composition.

Tantalum appears to be the best choice of filament

material because of a greater insensitivity to total sample

composition. The small amount of extracted boron is not large

enough to preclude significant variations in the B/Na ratio of

different solutions. Large variations in the amounts of boron

and sodium can effect the ionization efficiency and also the

observed ratio error when the filament is operated at a constant temperature [1]

.

The other major problem area is sample size. Preliminary

indications are that 2-3 yg of boron is the minimum amount

necessary for a limit of error of 0.5% (95% confidence level).

Development of reliable methods of obtaining 5-10 \ig of boron

per filament are now being investigated. At the present time

evaporation of the solution to dryness and the addition of an

appropriate amount of water just before analysis offers the

most potential for satisfying the sample size requirements.

No major modification in the analytical procedure is

contemplated other than an early start in taking data. This

procedure is described in detail in NBS Special Publication

260-17 [9], and requires operation of the filament at a constant temperature which is determined with an optical

pyrometer

.

37
2 . Copper |

a° The concentration of copper in the solutions prepared for |

CI isotopic dilution is a factor of 20 less than that previously

used for mineral surveys and the atomic weight determination.

Modifications of the existing analytical technique [11] for

this element are relatively minor and are designed to obtain

data before reaching the point of gross sample depletion.

SRM 976, copper isotopic standard, was used as a working

standard to evaluate the procedure.

A triple filament rhenium-ribbon source is used. The

copper is plated onto each sample filament at a potential

difference of 3 1/2 volts. The current is approximately 1 mA

and is maintained for 10 minutes. At the conclusion of the

copper plating and with the plating current ON, the remaining

solution is flushed from the filament with a stream of alcohol.

This step is taken to prevent redissolving of plated copper by

the nitric acid solution on the filament. The estimated sample

size is 10 yg per filament. The filaments are mounted in the

filament block and the sample filaments are positioned away

(^.025 inch) from the edges of the ionizing filament. This

open spacing is used to inhibit sample evaporation by radiant

heat from the ionizing filament. The Cu ions are measured

at an accelerating voltage of 7 kV (6-inch mass spectrometer).

An optical pyrometer is used to adjust the temperature

of the ionizing filament to 2120 °C (5-5-6.0 A). The sample

filament currents are set at 0.5 A. After 5 minutes of heating

the sample filaments are increased until the total copper ion

current is 4xl0 _11* A. The ionizing filament temperature will

normally decrease significantly during the first 10-15 minutes

of the analysis but will begin to stabilize at approximately

2100 °C.

After 15 minutes of heating the signal will have normally

increased to approximately lxlO -13

A. At this time the temperature of the ionizing filament is checked and, if necessary,

38
adjusted to 2100 °C. The sample filament currents are increased to yield a total signal of 2 . 7-3 . OxlO -1 3 A. During

the next 10 minutes it will be necessary to focus the signal

for maximum intensity and mass scan to determine baselines

of 6 3 Cu and 65 Cu. The total ion current is expected to be

4-5xio~ 13 A and growing. The peak-top data are taken by stepwise changes in magnet current and each peak top is monitored

for 30 seconds. Each analysis consists of 6 sets of ratios

to be used as data. Either an additional six sets of ratios

or a single ratio after a 6 minute waiting period are used to

determine the position on the fractionation curve. The data

is split in this manner because the primary problem in analyzing such small amounts of copper is sample depletion and

fractionation of the isotopes. At the present time this is

the most valid method that can be used to determine if the

analysis follows the normal or established fractionation

pattern.

Normally the signal for most analyses can be expected to

grow for at least 40 minutes. The magnitude of the filament

bias correction is determined by monitoring the change in

63 Cu/ 65 Cu ratio between the first and second half of an analysis. Filament bias corrections of 1.1, .9 and .75 percents

are used when the change in ratio is less than 0.3%, between

0.3-0.5%, and 0.6%, respectively. Analyses in which the

signal decayed before the end of the first set of six ratio

measurements usually displayed gross fractionation (>1%) and

it is suggested that such analyses be terminated immediately

because it is very difficult to precisely determine the

magnitude of bias

.

After more than 100 copper analyses using the 20 ug

sample size, it appears that approximately 9 out of 10 analyses can be made on growing signals between 4-7 x 10~ 13 A. The

fractionation is usually less than 0.6% and most of this

change is detected near the end of an analysis. No serious

39
effort has been made to establish meaningful filament bias

correction factors when the internal fractionation is greater

than 0.6$. Fractionation of this magnitude is observed on

the working standard (SRM 976), only when the sample is overheated (signals greater than 7

X 10~ 13 A) or the concentration

of Cu in solution is much less than 500 ug/cm 3

. All filaments are prebaked at 4-5 A for 1 hour in a vacuum and under a potential field. The trace copper background in the filament material decays rapidly and is not

detectable at a 10~ 15 A ion current sensitivity. Cross contamination between samples of different isotopic composition

is not detected. The precaution of cleaning the source for

blank determination is always followed to further minimize

memory effect on highly enriched solutions.

3 . Uranium

The analytical procedures developed for analysis of

uranium sample sizes of 200 ug (100 ug per filament) are

easily adaptable to isotope dilution work. These procedures

are described in another NBS publication [11] and the only

necessary modification is to find equivalent operating

conditions on a mass spectrometer with a z-lens source.

Uranium from the base glass and spiked solutions of the

500 ppm glass were evaporated to dryness and delivered for

analysis as solid material (U 3 8 ). An estimate of the total

amount of uranium present was supplied by the chemist and

just prior to analysis a 5% HN0 3 solution was added. The

volume of solution was adjusted so that 1 drop would contain

approximately 50 ug of uranium. The total estimated sample

size per analysis is approximately 100 ug. Ion currents of

l_2xio * ° A are routinely obtained for long periods of time

and measurement of minor isotopes at even higher signal

intensities are possible.

Additional significant reductions of the sample size can

be tolerated without adverse effect on the ability to determine the uranium isotopic composition. The major problem is

ho
obtaining uniform amounts of material on each filament and

knowing roughly how much material is present. Unless the

amount of material present is known and is uniform for all

filament loadings, it is not possible to make a meaningful

evaluation of filament bias with uranium calibration samples

of known sample size, and isotopic composition.

(I. L. Barnes, E. J. Catanzaro and E. L. Garner)

F. Triple-Filament Isotopic Analyses of Lead from

Archaeological Materials

1

.

Sampling

The following samples were examined during the past

year

:

a. New Samples (from R. H. Brill)

37 glasses

3 weathering products associated with glasses

18 samples of lead or lead-rich material

8 copper coins (5 others in the same group

were analyzed before Wampler's arrival)

9 samples of bronze

1 lead ore sample (galena)

b. 25 analyses of SRM 981

c. 5 analyses of samples previously analyzed at

Brookhaven National Laboratory

2

.

Results on Archaeological Materials

a. Glasses - As expected from earlier work, a

considerable range in lead isotopic composition was found for

ancient glass samples. In general, glasses of different color

are different in lead isotopic composition, even when from the

same site. Thus there is little indication that different

lead pigments were produced on site from a uniform source of

lead, in ancient glass production. Rather it is indicated

41
that the different lead pigments were brought to the glass

making sites from a variety of sources.

It is generally difficult to associate different ranges

of lead isotopic composition with different geographic areas

where glass was produced in ancient times, with one exception.

Many of the samples from sites in Mesopotamia and the surrounding area off the east end of the Mediterranean, show a

relatively high proportion of 208 Pb. This is seen in samples

of lead as well as in the glasses from this area. There is

considerable variation in isotopic composition among these

samples, but the relatively high proportion of 208 Pb appears

to be geographically significant.

b. Weathering Products - Weathering products from

three glass samples showed lead isotopic compositions little

different from the glasses themselves . Weathering products

should generally provide useful samples for isotopic analysis

in cases where the original material is not available.

c. Lead Samples - A variety of lead samples were

analyzed to add to our knowledge of the distribution, in

terms of isotopic composition, of lead in the ancient world.

These results supplement the earlier work of Brill and

Wampler [14]

d. Copper Coins - Coins from a variety of localities

in the Roman Empire, from the 3rd and 4th centuries A.D., were

analyzed. The samples show a distribution in lead isotopic

composition which is not easily related to the geographic

areas where the coins were found. The total range in isotopic

composition for these samples is relatively small. These

relationships are consistent with the widespread transport

and use of lead in the Roman Empire at this time.

e. Bronzes - Results obtained on a variety of

bronze samples are generally consistent with expectations

based on the origin and age of the samples.

42
3 . Results of Significance to the Analytical Method

a. Data on SRM 981 - 25 analyses of SRM 981 showed

a level of precision, as well as small mass discrimination

factors, consistent with earlier work on this material at NBS.

b

.

Duplicate Analyses - Repeat analyses involving

19 samples indicated that the precision of determination of

2 07 pb/ 2 06 pb and 2 08pb// 2Q6 pb ratlos was comparable to that

obtained for the standard reference material. This same level

of precision was not obtained in determination of 201t Pb/ 206 Pb

- apparently a result of the presence of minor impurities in

some of the samples. Eight of the samples were repurified

before the second analysis, and it is for this group that the

poorest precision was obtained. (Certain other samples

required repurification before a satisfactory analysis could

be obtained.) The uncertainty in 20lt Pb/ 205 Pb for the samples

is estimated to be about twice the error limits based on the

reproducibility of analyses of SRM 981.

c

.

Analysis of Samples Previously Analyzed at

Brookhaven - At Brookhaven National Laboratory, Brill and

Wampler [14] used two different methods for single filament

isotopic analysis of lead. The first method involved loading

samples as PbS, with an ion multiplier detector. In the

second method, lead oxide was dissolved in boric oxide on the

filament and no ion multiplier was used. In both cases correction factors were applied in an attempt to approximately

account for mass discrimination effects (either at the ion

multiplier or at the ion source.)

Eleven samples analyzed at Brookhaven by these methods

have been reanalyzed at NBS. There appears to be no systematic

differences between the boric oxide analyses (Brookhaven) and

the NBS analyses, though the precision of the Brookhaven

analyses is much lower. Samples analyzed at Brookhaven by

the PbS method do show some significant systematic errors.

This makes it difficult to intercompare the present work and

the 1967 data.

43
4 . General Implications

The following discussion pertains to the entire group

of archaeological samples analyzed at NBS.

With one exception, all samples from Europe and the

Middle East have isotopic compositions which are typical of

lead ores emplaced within the last several hundred million

years. The exception, an Early Dynastic "Dagger" from Ur,

was likely derived from lead ores in the Precambrian rocks

along the Red Sea.

Two Egyptian samples with a clear excess of radiogenic

isotopes are likely derived from ore deposits in Miocene

sediments which overlie the Precambrian basement in Egypt.

The one new sample of lead ore analyzed at NBS is also from

these Miocene rocks, but does not show the large excess of

the radiogenic isotopes. All these Egyptian samples are

distinct from the other samples studied in that they have

relatively low 208 Pb/ 206 Pb ratios (compared to the trend of

the other samples in the study.)

The most interesting result of this work concerns the

relationships of the samples on a plot of 206 Pb/ 20l*Pb vs.

206 Pb/ 207 Pb. If one considers only samples from the ancient

Mediterranean-European world (only five or six of the samples

studied do not fall in this category) the lead isotope ratios

show a high degree of correlation along a line which corresponds closely, but not precisely, to a "primary growth curve"

for terrestrial lead (including an extension of the primary

growth curve to the right of the zero isochron ) [15]. Only

three samples are displaced from this line such that the

displacement is clearly beyond the experimental error. These

are the three samples from Egypt mentioned above, all of which

fall below the line by about the same amount. The Egyptian

samples may be related to a primary growth curve with u

n

( 238 U/ 2 01+ Pb, today) about 2% lower than the growth curve for

the other samples.

44
The high degree of correlation observed for the other

samples is significant because the many samples involved

(about 125) certainly represent lead from a considerable

number of ore deposits in Europe and the Mediterranean area.

Although many ore deposits may be represented more than once

in the archaeological samples, both directly and as parts

of mixtures, the spread of the samples when plotted as

208 Pb/ 207 Pb vs

206 Pb/ 207 Pb suggests a fairly large number of

independent sources for the lead. If this inference is correct, the constancy of the apparent u„ value for these samples

(actually the best fit line indicates a slightly increasing

apparent y n with increasing radiogenic isotope content) has

important implications with respect to the geochemical history

of the orogenic belts of Europe and the Mediterranean, from

which the lead samples were presumably derived. This region

should be a fruitful one for the application of high precision

lead isotope analysis directly to lead ore deposits.

(J. M. Wampler)

4 5
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

Mass Spectrometry (nuclear materials) —

I. Lynus Barnes

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 1968 —

J. M. Wampler

B. Publications

1. Analytical Mass Spectrometry Section: Summary of

Activities July 1967 to June 1968, NBS Technical Note 456,

Ed. W. R. Shields, (1968).

2. J. G. Punkhouser, I. L. Barnes and J. J. Naught on,

"The Determination of a Series of Ages of Hawaiian Volcanoes

by the Potassium-Argon Method", Pacific Science, 22_, 369-

372 (1968).

3. J. B. Pinlayson, I. L. Barnes and J. J. Naught on,

"Developments in Volcanic Gas Research in Hawaii", Geophysical

Monograph No. 12, 428-438 (1968).

46
4. E. J. Catanzaro, T. J. Murphy, E. L. Garner and

W. R. Shields, "Absolute Isotopic Abundance Ratio and Atomic

Weight of Terrestrial Rubidium", J. Res. NBS, 73A, 511-516

(1969).

5. E. J. Catanzaro, C. E. Champion, E. L. Garner,

G. Marinenko , K. M. Sappenfield and W. R. Shields, "Boric

Acid; Isotopic and Assay Standard Reference Materials",

Special Publication 260-17, (1969).

C. Talks

1. W. R. Shields, "Precise and Accurate Isotopic

Ratios", Geological Division of Earth Sciences Department,

Northern Illinois University, November 1, 1968.

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

Member, Meeting Arrangements Committee, Chemical Society of

Washington

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

47
5. REFERENCES

[1] W. R. Shields, Editor, NBS Technical Note 456 (1968).

[2] D. S. Evans, Review of Scientific Instruments, 36 , PP. 375-382 (1965).

[3] 0. 0. Paynter, Philbrick Applications Manual - Computing Amplifiers, Averaging Filter, p. 76.

[4] M. M. Markowitz and Boryta, D. A., J. Phys. Chem., 69,

1114 (1965).

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

W. R. Shields, J. Res. NBS, 73A, 511-516 (1969).

[6] C. C. McMullen, C. B. Cragg and H. G. Thode , Geochim.

et . Cosmochim. Acta 23, 147 (1961).

[7] H. 0. Finley, A. R. Eberle and C. J. Rodden, Geochim.

et Cosmochim. Acta 2_6, 911 (1962).

[8] M. Shima, Geochim, et Cosmochim. Acta 27_, 911 (1963).

[9] E. J. Catanzaro, C. E. Champion, E. L. Garner,

G. Marinenko, K. M. Sappenfield and W. R. Shields,

Boric Acid; Isotopic and Assay Standard Reference

Materials, NBS Spec. Publ. 260-17, (1969).

[10] 0. Menis, Editor, NBS Technical Note 275, p. 63 (1965).

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

[12] Cameron, A. E. , D. H. Smith and R. L. Walker, Anal.

Chem., 41, pp. 525-526 (1969).

[13] W. R. Shields, Editor, NBS Technical Note 426 (1967).

[14] R. H. Brill and J. M. Wampler, Isotope Studies of

Ancient Lead, Am. J. of Archaeology 7_1, pp. 63-77

(1967); (For a numberical tabulation of the isotope

ratios determined in this work see Brill, R. H. and

J. M. Wampler, 1967, Isotope Ratios in Archaeological

Objects of Lead, pp. 155-166 in "Application of Science

in Examination of Works of Art", Proc . of a conference

held in September, 1965. Museum of Fine Arts, Boston

Massachusetts .

[15] V. R. Murthy and C. C. Patterson, Primary Isochron of

Zero Age for Meteorites and the Earth, J. Geophys

Res. 67, 1161 (1962).

48

o U.S. GOVERNMENT PRINTING OFFICE : 1970 392-252/171
NBS TECHNICAL PUBLICATIONS

PERIODICALS

JOURNAL OF RESEARCH reports National

eau of Standards research and development in

sics, mathematics, chemistry, and engineering.

I lomprehensive scientific papers give complete details

( f the work, including laboratory data, experimental

procedures, and theoretical and mathematical analy-

>es. Illustrated with photographs, drawings, and

charts.

Published in three sections, available separately:

• Physics and Chemistry

Papers of interest primarily to scientists working in

these fields. This section covers a broad range of

physical and chemical research, with major emphasis

on standards of physical measurement, fundamental

constants, and properties of matter. Issued six times

a year. Annual subscription: Domestic, $9.50; foreign, $11.75*.

• Mathematical Sciences

Studies and compilations designed mainly for the mathematician and theoretical physicist. Topics in mathematical statistics, theory of experiment design,

numerical analysis, theoretical physics and chemistry, logical design and programming of computers

and computer systems. Short numerical tables. Issued quarterly. Annual subscription: Domestic,

$5.00; foreign, $6.25*. • Engineering and Instrumentation

Reporting results of interest chiefly to the engineer

and the applied scientist. This section includes many

of the new developments in instrumentation resulting

from the Bureau's work in physical measurement,

data processing, and " development of test methods.

It will also cover some of the work in acoustics,

applied mechanics, building research, and cryogenic

engineering. Issued quarterly. Annual subscription:

Domestic, $5.00; foreign, $6.25*.

TECHNICAL NEWS BULLETIN

The best single source of information concerning the Bureau's research, developmental, cooperative and

publication activities, this monthly publication is designed for the industry-oriented individual whose

daily work involves intimate contact with science and

technology

for engineers, chemists, physicists, re- search managers, product-development managers, and

company executives. Annual subscription: Domestic,

$3.00; foreign, $4.00*.

• Difference in price is due to extra cost of foreign mailing.

Proceedings of NBS confer- annual reports, wall charts,

NONPERIODICALS

Applied Mathematics Series. Mathematical tables, manuals, and studies. Building Science Series. Research results, test methods, and performance criteria of building materials, components, systems, and structures. Handbooks. Recommended codes of engineering

and industrial practice (including safety codes) de- veloped in cooperation with interested industries,

professional organizations, and regulatory bodies.

Special Publications.

ences, bibliographies,

pamphlets, etc. Monographs. Major contributions to the technical

literature on various subjects related to the Bureau's

scientific and technical activities. National Standard Reference Data Series.

NSRDS provides quantitive data on the physical

and chemical properties of materials, compiled from

the world's literature and critically evaluated. Product Standards. Provide requirements for sizes, types, quality and methods for testing various industrial products. These standards are developed cooperatively with interested Government and industry groups

and provide the basis for common understanding of product characteristics for both buyers and sellers. Their use is voluntary.

Technical Notes. This series consists of communications and reports (covering both other agency and

NBS-sponsored work) of limited or transitory interest.

Federal Information Processing Standards Publications. This series is the official publication within

the Federal Government for information on standards

adopted and promulgated under the Public Law

89-306, and Bureau of the Budget Circular A-86

entitled, Standardization of Data Elements and Codes

in Data Systems.

CLEARINGHOUSE

The Clearinghouse for Federal Scientific and

Technical Information, operated by NBS, supplies

unclassified information related to Government-generated science and technology in defense, space, atomic energy, and other national programs. For

further information on Clearinghouse services, write

:

Clearinghouse

U.S. Department of Commerce

Springfield, Virginia 22151

Order NBS publications from: Superintendent of Documents

Government Printing Office

Washington, D.C. 20402
U.S. DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20230

OFFICIAL BUSINESS

II

POSTAGE AND FEES PAID

U.S. DEPARTMENT OF COMMERCE