NBS

"\

Activities of the

NBS Spectrochemical

Analysis Section

July 1965 through June 1966

Edited by Bourdon F. Scribner

401

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U.S. DEPARTMENT OF COMMERCE

National Bureau of Standards

: ' / ":-::'.
THE NATIONAL BUREAU OF STANDARDS

The National Bureau of Standards1 provides measurement and technical information services

essential to the efficiency and effectiveness of the work of the Nation's scientists and engineers. The

Bureau serves also as a focal point in the Federal Government for assuring maximum application of the physical and engineering sciences to the advancement of technology in industry and commerce. To

accomplish this mission, the Bureau is organized into three institutes covering broad program areas of research and services: THE INSTITUTE FOR BASIC STANDARDS . . . provides the central basis within the United

States for a complete and consistent system of physical measurements, coordinates that system with the 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. This

Institute comprises a series of divisions, each serving a classical subject matter area: —Applied Mathematics—Electricity—Metrology—Mechanics—Heat—Atomic Physics—Physical

Chemistry—Radiation Physics—Laboratory Astrophysics2—Radio Standards Laboratory,2 which

includes Radio Standards Physics and Radio Standards Engineering—Office of Standard Refer- ence Data. THE INSTITUTE FOR MATERIALS RESEARCH . . . conducts materials research and provides

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

principal elements of this Institute are: —Building Research—Electronic Instrumentation—Textile and Apparel Technology Center

Technical Analysis—Center for Computer Sciences and Technology—Office of Weights and Measures—Office of Engineering Standards Services—Office of Invention and Innovation—Clearinghouse for Federal Scientific and Technical Information.3

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

20234.

2 Located at Boulder, Colorado, 80302.

3 Located at 5285 Port Royal Road, Springfield, Virginia, 22151.
UNITED STATES DEPARTMENT OF COMMERCE • John T. Connor, Secretary

NATIONAL BUREAU OF STANDARDS • A. V. Astin, Director

NBS TECHNICAL NOTE 401

ISSUED SEPTEMBER 30, 1966

Activities of the

NBS Spectrochemical

Analysis Section

July 1965 through June 1966

Edited by Bourdon F. Scribner

Spectrochemical Analysis Section

Analytical Chemistry Division

Institute for Materials Research

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

listed or referred to in the open literature.

For sale by the Superintendent of Documents, U.S. Government Printing Office

Washington, D.C., 20402 - Price 55 cents
FOREWORD

The Analytical Chemistry Division "was established as

a separate division at the National Bureau of Standards on

September 1, 1963j> and became part of the Institute for

Materials Research in the February 1, 1964 reorganization.

It consists at present of nine sections and about 100

technical personnel encompassing some 45 different

analytical competences from activation analysis and atomic

absorption to vacuum fusion and x-ray spectroscopy. These

competences ; and in turn the sections which they comprise,

are charged with research at the forefront of analysis as

well as awareness of the practical sample, be it standard

reference material or service analysis. In addition it is

their responsibility to inform others of their efforts.

Formal publication in scientific periodicals is highly

important. In addition, however, it has been our experienc

that informal, annual summaries of progress describing

efforts of the past year can be very valuable in disseminai

ing information. At the National Bureau of Standards such

publications fit logically into the category of a Technica]

Note. In 1966 we plan to issue these summaries for all of

our sections. The following is the second annual report or progress of the Spectrochemical Analysis Section.

W. Wayne Meinke, Chief

Analytical Chemistry Divisior

11
PREFACE

This is the second annual progress report of the

ctrochemical Analysis Section of the Analytical Chemistry

vision. The Section, formerly known as Spectrochemistry,

established in 19^8 as an outgrowth of an extensive

Dgram of spectrochemical analysis of uranium and related

erials and also in recognition of the growing importance

instrumental analysis. -While the Section had been

Lmarily concerned with optical emission spectrometry,

growing importance of related spectrometric fields in

mental analysis led to extension into x-ray spectrometry

1957 ^ to the addition of electron probe microanalysis in

4, and to the inclusion of spark source mass spectrometry

1965.

The purpose of the Section is to develop measurement

hniques for determining the elemental composition of

;erials through the use of optical, x-ray, and mass

tra. Chemical elements are uniquely identified by the

iracteristic frequency of emitted spectra, and amounts

;sent can be determined by measurement of the intensity of

tted radiation. However, many factors enter into success-

. spectral analysis and must be carefully controlled,

se include, in optical and x-ray spectrometry, the producn of radiant energy by excitation, the dispersion of the

iant energy into a spectrum, and the measurement of

tral wavelengths and intensities. In a similar way,

rk source mass spectrometry involves ion formation,

persion into a mass spectrum, and measurement of

. ensities for recorded masses. Because of the complexity

I

the systems involved no way has yet been found to make

olute measurements of concentrations in analysis;

sequently, comparative methods are employed in which

111
spectra of unknowns are measured relative to those of

reference materials of known composition.-

The research program of the Section is directed

generally toward a better understanding of the phenomena

involved in producing and measuring optical and x-ray

emitted energy and mass. spectra, and the improvement' of

spectrochemical methods, instruments, and calibration

procedures. Included in these activities are the development of standard reference materials, analyses of materials

to assist other research projects, and literature surveys

such as bibliographies and critical reviews.

In this report, the program, facilities, and

accomplishments of the Section for the past year will be

reviewed.

In order to specify the procedures adequately, it has

been necessary occasionally to identify commercial materia!

and equipment in this report. In no case does such identification imply recommendation or endorsement by the Nation*

Bureau of Standards, nor does it imply that the material 01

equipment identified is necessarily the best available for

the purpose.

Bourdon F. Scribner, Chief

Spectrochemical Analysis Section

IV
TABLE OF CONTENTS

PAGE

FACILITIES ....... ... 1

Space Facilities ................ 1

Equipment. ............ . 5

OPTICAL SPECTROMETRY . 6

Time-Sharing Computer. ............. 7

Description of the System. .......... 7

Examples of Applications ........... 10

Emulsion Calibration ............ 10

Fitting Analytical Curves. ......... 15

Other Programs 15

Arc Temperature Measurements .......... 16

Laser Probe Excitation ............. 17

Atomic Absorption Spectrometry . . 19

Modifications of the Instrument. ....... 20

Selection of Wavelengths . . 22

Use of a Continuum Source. .......... 27

Plasma Jet Excitation of Solutions of Cast

Iron ..........*. 29

X-RAY SPECTROMETRY 32

Basic Considerations .............. 32

X-Ray Fluorescence Spectrometry . 33

Modification of Equipment. .......... 34

Computation Techniques in Data Reduction ... 35

Examples of Applications 38

ELECTRON PROBE MICROANALYSIS 40

Instrumental Developments. ........... 40

X-Ray Spectrometer for Long Wavelengths. ... 40

Detector Slits of Variable Width ....... 40

Solid State Target Current Preamplifier. ... 40

Solid State Concentration Mapping Device ... 43

v
TABLE OF CONTENTS (con't)

PAG

Pulse Height Analyzer Monitor lVJ'< Multi-Channel Pulse Height Analyzer 51

Other Additions 5>

Plans for Future Additions 55ij

Research Activities 55

Techniques of Measurement 55

Parameters Employed in Correction

Calculations. ..." . . 57;;

Non-Dispersive Analysis 60/

Progress in Scanning Techniques 6l

Literature Research 6l

5. SPARK SOURCE MASS SPECTROMETRY. 62!

Electronic Analog Computer for Measuring

Intensity-Areas of Peaks 62

Analysis of High Purity Materials 69

Instrument Modifications 70

6. ANALYSIS OF HIGH PURITY MATERIALS:

ENRICHMENT BY ELECTR0DEP0SITI0N jk

Analysis Problems jk

Electrodeposition as an Enrichment Method .... 75

Current Research. . 76

7. STANDARDS, ANALYSIS, AND LITERATURE ACTIVITIES. . 78

Standard Reference Materials 78

Standards Program 78

Analyses Made of Standard Reference Materials . 79

General Spectrochemical Analyses '. 82

Types of Analysis 82

General Analyses Made ....... 8^

Literature Surveys 83

VI
TABLE OF CONTENTS (con't)

PAGE

8. PERSONNEL AND ACTIVITIES **•*****.*.,• 85

Personnel Listing, . <,.. 85

Publications • .,.,.,•.•. 86

Talks Given, , ».... 89

Committee Activities ,....,.„..... 92

, ACKNOWLEDGMENTS , , . . 9^

. LIST OF REFERENCES . , . , 94

Vll
LIST OF FIGURES

FIGURE NO. PAGi

1. Floor plan of the Spectrochemical Analysis

Section 2

2. Electron probe microanalysis laboratory

(double module). .„..« .... 3

5. Chemical clean laboratory (single module). . . 4

4. Teletype terminal for communication with

time-sharing computer. ........... 8

5. Newly modified atomic absorption

spectrometer ..... *.... 21

6. Wavelength-dependent correction factor

to gf-values in NBS Monograph 53 • • • * • • 23

7. Test of theory for atomic absorption with

a hollow cathode light source. ....... 24 j 8. Test of theory for atomic absorption

with a continuum source. ........... 25

9. Target current preamplifier with selectable

gain, and dual-polarity specimen-biasing

battery •••••••• 42

10. Aluminum surface with scratches,

30keV, 300p, x ;580|j. „..*•. 4^

11. Interconnecting system for the use of the

concentration mapper with x-ray signals. . « 44

12. Calibration curves for level controls of the

concentration mapper ........*. 45

13* Four-level solid state concentration mapper. . 46

14. Concentration maps ......... 47

15. Pulse height monitoring by use of a variable

delay line and oscilloscope blanking . . . 48

16. Oscilloscope representation of the amplified

pulse output of a gas proportional

detector *.**.....»*.... 49

17. Representation of the distribution shown in

figure 16, with the pulse height analyzer

in integral mode. Pulses falling below the

base line of the analyzer are represented

by uninterrupted traces. . . . . . . . . . . 50

Vlll
LIST OF FIGURES (con't)

Figure no. page

18. Same pulse height distribution as in figure

17. The base line setting of the pulse

height analyzer is lowered,, so that all

pulses are accepted .......«.. 50

19. SCIPP l600-channel pulse height analyzer

and associated read-out equipment ..... 51

20. Oscilloscope representation of counts

accumulated in two grid scans over an

area of 400|i x 400|i * 52

21. Print-out of grid scans as on figure 20 . . . 55

22. Read-out distribution system including

wiring diagram of the main control panel. . 54

23. Cathodoluminescence detector. ........ 56

24. Electron backscattering coefficients obtained

by Heinrich and by Bishop 58

25. Variation of electron backscattering

coefficients as a function of electron

energy. .......,......,>.. 58

26. Pulse-height spectra obtained with a sealed

neon-proportional detector. ........ 60

27. Wiring diagram for analog computer. ..... 64

28. Power supply wiring for analog computer ... 65

29. Error in the output of the function generator

versus the % absorption input ....... 66

30. Area measured for isotopes of tin versus

their isotopic abundance. ......... 67

31. Diagram showing position of major components

of mass spectrograph. ........... 71

IX
LIST OF TABLES

TABLE NO. PAG'!

1. Output from KAISER .....*....... 15

2. Options in INTEN program .......*... l4

3. Output from INTEN (Test data) 14

4. Precision of determination of Fe 3 Mg^ and

Na in Portland cement by atomic absorption

spectrometry with a continuum source .... 28

5. Results of the determination of Co and Ti

in NBS 1175 and ll8l' ............ 51

6. Computer output from X-RAY 1 program ..... 37

7. Computer output from STAT program. ...... 38

8. Spectrometer characteristics of the electron

probe microanalyzer . ............ 4l

9. Area measurement compensation for changes in

peak widths. ................ 68

10. Analysis of zinc bar ............. 69

?!.
ACTIVITIES OF THE NBS SPECTROCHEMICAL

ANALYSIS SECTION

July 1965 to June 1966

Edited by Bourdon F. Scribner

ABSTRACT

A summary is given of the activities of the NBS

pectrochemical Analysis Section for the period from

'uly, 1965 through June, 1966, during which the move into

--.he new facilities at Gaithersburg, Md. was,made,

activities in optical spectrometry included development of

programs for calculations on a time-sharing computer,

-leasurement of arc temperatures , applications of the laser

jrobe and the plasma jet, and studies on atomic absorption

spectrometry. In x-ray spectroscopy, there have been some

i lodif ications of equipment, improvements in computation

lethods, and several applications. Improvements and

idditions were made to the electron probe analyzer, along

vith studies on measurement techniques, including nonlispersive analysis and computation procedures. The sparksource mass spectrometer has also been modified, and a new

analog computer has been built and tested for reduction of

Dhotographic plate data; applications of this instrument

:o analyses of pure materials are described. Enrichment

aethods are being studied for the analysis of pure materials

)y emission spectroscopy, particularly with an electroleposition technique. Homogeneity studies and analyses have

:een performed in the development of standard reference

naterials. Other activities included analyses of samples

co assist other NBS groups and government agencies, and

literature surveys. Listings are given of 20 publications

nd 26 talks by members of the Section during the year.

XI
Key words:

Analysis , arc temperature , atomic absorption

spectrometry , analog computer , bibliography , computer,

electrodeposition, electron back scatter, electron prob

microanalyzer , emission spectroscopy, laser probe, mass

spectroscopy, photographic photometry, plasma jet,

preconcentration, pulse height analyzer, spectrochemica

analysis, spectroscopy, standard reference materials,

time-shared computer, x-ray spectroscopy.

xn
1. FACILITIES

Space Facilities

This year marks a significant improvement in our

eneral space facilities with the completion of the move

our laboratories to the new location at Gaithersburg,

ryland. Detailed planning for the move began as long

o as i960 and attempts were made to anticipate the needs

or the program as it would exist at the time of the move.

he move itself required much detailed planning. We were

particularly concerned about possible damage to several

jarge and costly instruments. For this phase of the move

e enlisted the services of manufacturers' representatives

supervise the dismantlings move, re-assembly, and

alignment of the instruments a This proved to be effective

d permitted the laboratory to be in operation for the

ost part within two weeks after the move. In general the

iove was successful and the new space facilities offer many

idvantages over those at the old location*

The new NBS site occupies 550 acres, some 20 miles

orthwest of Washington, D» C. The scientific activities

re largely accommodated in a series of interconnected

general purpose laboratories", having three working floors

nd an attic floor in which all service equipment,

Including air-conditioning, is housed. Services are brought

own from the attic in stacks to each module. The buildings

.re designed with two rows of laboratory rooms adjoining

.t the center axis of the building and, on each side, a orridor with office spaces at the outer wall.. The rooms

.re of modular construction having removable steel

iartitions. The inner basic laboratory module is 11 feet

ide by 22 feet long, and the outer office modules are 11

eet wide by 16 feet long.
q/ X-RAY r) FLUORESCENCE /

7

SPARK SOURCE

. V,

MASS SPECTROMETRY

OPTICAL SPECTROMETRY

ELECTRON PROBE

MICROANALYSIS U

X-RAY PREPARATIONS /

ELECTRONICS

7 DARK ROOM

c

OPTICAL SPECTROGRAPHY

7

L,

CHEMICAL / CHEMICAL CLEAN LAB. SEPARATIONS l—^

X-RAY / SPECTROMETRY

' OFFICE

/ SPECTROMETRY

y SPECTROGRAPHIC / PREPARATIONS

/ SECTION OFFICE

/ SECTION CHIEF

OPTICAL / SPECTROMETRY

OFFICE

/ MICRO- / PHOTOMETRY

, COMPUTER / TERMINAL

Figure 1. Floor plan of the Spectrochemical

Analysis Section
The Spectrochemical Analysis Section occupies an area

f 16 laboratory modules and 8 office modules located on

tie first floor of the Chemistry Building. Since the building has no basement the ground floor provides a firm support

or our instruments. The floor plan of the laboratory is

hown in figure 1.

The main instrument laboratories —for optical spectroraphs, optical spectrometers, the electron probe, and the

ass spectrograph —each occupy a double module. An example

f this type of room is the microprobe laboratory shown in

igure 2.

Figure 2. Electron probe microanalysis

laboratory (double module).
Single laboratory modules are provided for x-ray

fluorescence, atomic absorption, three chemical

laboratories, and the supporting laboratories for x-ray

preparations, electronics, and dark room. Some limited

laboratory work is performed in smaller outer modules for

spectrographs preparations and microphotometry. Two

rooms for which we had no counterpart at the old location

are a chemical clean laboratory (Figure 3) equipped with a special hood for work with radioactive materials, and a

computer room where there is located a communication station

with access to a time-shared, remote computer. The

important role of the computer service in our work is

described in Sections 2 and 3 of this report.

Figure 3. Chemical clean laboratory

( single module )

.

4
Equipment

The major equipment of the laboratory was described

id illustrated in 1965 progress reports [1^2 ]» This

deludes the following:

5-meter Eagle mounting grating spectrograph

3.4-meter Ebert mounting grating spectrograph

21-foot Wadsworth mounting grating spectrograph

2-meter multi-channel optical spectrometer

3-meter multi-channel optical spectrometer

Multi-channel x-ray spectrometer

Single-channel x-ray spectrometer

Atomic absorption spectrometer

Electron probe microanalyzer with 3 spectrometers

and associated read-out equipment

Spark-source mass spectrograph

Various accessory equipment including microphotometers

imple preparation devices , microscopes, etc., are available.

During the past year the major equipment of the

tboratory has been extended or improved to include (1)

ijor revamping of equipment for atomic absorption, (2) a

icuum attachment for the single channel x-ray spectrometer,

id (3) a multi-channel analyzer for the microprobe. In

Idition, several read-out devices were added or improved

>r use with the microprobe as described in Section 4 of

lis report.

With the completion of major phases of our equipment

:cessions and the final adjustments to our new space

icilities, the laboratory is in an excellent position to

irsue its program of research and service in spectrolemical analysis. On the following pages the progress

i the current program of the Section is reviewed in

ch area.
2„ OPTICAL SPECTROMETRY

In the period covered by this report., there have been

no major changes in the emphasis in research on emission

spectrometry. Our chief interests remain in developing new

or improved excitation sources 3 studying the properties of

such sources, and devising analytical methods to meet

requirements which are common to many spectrochemical

laboratories or which arise from NBS programs such as the

preparation of standard reference materials.

Considerable progress has been made in some of the

research activities described previously [1], including

measurement of the temperature of the d-c arc in argon

and a study of the applicability of a continuum source in

atomic absorption spectrometry. Progress reports on these

topics are given in the following pages. In several cases , earlier studies on excitation sources are now bearing fruit

in difficult analytical applications. Examples are given

below of the use of the laser probe and the plasma jet in

the solution of specific problems which arose during the

past year.

The studies of the properties of excitation sources

have improved our knowledge of the physical theory of

spectrochemical analysis. This knowledge can often

contribute directly to the development of analytical

methods. An example , described below, is the development

and experimental testing of a method of selecting wavelengths for atomic absorption spectrometry on the basis of

published tables of atomic properties.

For several years computers have been employed in our

Section in reducing the extensive data recorded in

homogeneity testing of spectrometric standards. The recent

availability of time-sharing computers has enhanced our

6
terest in the use of computers in emission spectrometry,

well as in other areas of spectroscopy. During the past

ar, programs have been written for several routine

mputation tasks which were previously done graphically or

. a desk calculator. The time-sharing computer seems to be

ie ideal way of doing calculations which are smaller than

je type of problem normally run on the computer, but which

ill require considerable time by the older methods. The

sk of preparing programs for the computer can, at times,

sad to a new insight into the nature of the problem and to

ie development of more efficient solutions. The studies on

libration of photographic emulsions with a computer

^present one such case.

Time-Sharing Computer

1. Description of the system

A time-sharing computer system similar to that developed

; Dartmouth College has been available to the Analytical

oemistry Division for more than a year, and the Spectrolemical Analysis Section has made extensive use of this

icility to improve the efficiency of its operations.

A teletype terminal in the laboratory, figure 4, allows

ie user to enter programs, data, and commands into the

>mputer and to receive printed output. This information

; carried over telephone lines to the computer system,

;veral miles away, which may serve as many as 40 terminals

.multaneously

The central system consists of master and slave computers

id a disk memory. Information transmitted from a terminal

5 received by the master computer and is stored in the disk

smory. When a user has entered all necessary programming

istructions and data, he types the command RUN. Each user

10 has typed RUN is assigned a turn of a few seconds on the

.ave computer. If one turn is not enough time to complete

7
Figure 4. Teletype terminal for communication

with time-sharing computer.

the calculations., the master computer re-enters the program

into the slave computer as often as is necessary.

The results of the calculations., as well as partially

complete programs., are also stored in the disk memory. The

master computer transmits the results from the memory to

the user's terminal. Normally, only a few seconds pass

after the command RUN is typed until the first output is

received. If the program is written improperly so that the

calculations cannot be made, or if the data format is wrong

specific diagnostic information will be received at the

terminal. Programs may be permanently stored so that reentry with each use is not necessary.

8
The rapid response of time-shared computing has

everal advantages. The process of preparing programs is

peeded, since "bugs" can usually be removed in only a few

tinutes at the terminal. Similarly, the effects of changes

n the program will be known quickly. Probably the most

.mportant advantage of this rapid response is that it makes

he use of computers feasible for small jobs which require

.ignificant time by graphical methods or with a desk

•.alculator, but which do not require enough time to justify

i trip to the computer laboratory and the long wait until

;he results are available under the customary method of

ising computers. The cost of the time-sharing system is

.ess than that of large computers for these small jobs.

This, time-sharing system employs a programming

.anguage called BASIC, which was also developed at

Dartmouth College [3]. Although BASIC lacks some of the

:apabilities of most other programming languages, it is

exceptionally easy to learn and to use, and does permit the

Dreparation of some quite complex programs. An advantage

o the scientist of writing his own programs is that he will

ften develop a better understanding of his problems. In

i addition, having written the program himself, the

scientist will be able to make modifications to alter the

calculations or the form of the output.

An important feature of time-sharing computation is

that there can exist an interaction between the scientist

and the machine that is not normally available to computer

users* Programs may be written so that the computer will

[(present part of the results and pause for further

instructions. Depending on how the program is written,

'Such instructions may modify further calculations or

control the form or amounts of the output. In this way,

9
the educated Judgment of the scientist can be brought to

bear on the problem without requiring the difficult job of

writing this judgment into a program.

The system does, of course, have some disadvantages*

The most serious are the limited memory of the slave

computer, which restricts the size of problems that can be

handled, and the rate of data transmission over the teletype. Neither of these difficulties has proven to be

serious in our applications. In a few cases, problems whici

would otherwise require a larger computer have been divided

into smaller segments. Some of the larger jobs are still

taken to the computer laboratory, but these are generally

ones for which speed of response is not important.

The limitation of the rate of data transmission is

alleviated in two ways. The programs need not be transmitted each time they are run. They can be stored in the

disk memory and called up when they are to be used. The

stored programs can be modified, if desired. Thus, only

the data must be transmitted. In addition, in many cases

less output is required in this method of computer operatioi i than is commonly taken from a computer. Only the essential

information is normally requested, and the programs can be

modified to give more detailed information when needed.

2* Examples of applications

a. Emuls i on c alib ration

When a linear relationship can be found between

functions of the microphotometer readings and the relative

exposures, a photographic emulsion calibration can be

defined by the slope and intercept of this line. Since the

exposure is stated only in relative terms, the intercept

can be assigned any convenient value, and only the slope of , the line must be known. In principle, the slope could be

10
determined from one pair of microphotometer readings on

Lines of known relative intensity, but in practice a much

piore reliable value can be obtained by averaging the slopes

obtained from several such pairs of readings.

A program, KAISER, has been developed for the

balibration of photographic emulsions, employing the Kaiser

transform [4] as the linearizing function. The Kaiser

transform has the form

K - A log(l/T) + (l-A)log(l/T-l) = AD + (l-A)S,

where K is the Kaiser function, T is the transmittance

is the optical density, and S is the Seidel function [4].

hen an appropriate value is chosen for the parameter A,

plot of the Kaiser function vs. the logarithm of the

elative exposure will usually be linear. Kaiser [4] has

hown that an approximation to A can be found from the

elation _ -A =

AD

X - AD

2

- (AS

1 - AS

2 )

'here S and D have the same meanings as above, A indicates

the difference between the values for a pair of lines of

-known relative intensity, and the subscripts indicate two

tuch pairs. A more reliable estimate of A can be obtained

y averaging several such calculated values than from only

two sets of pairs of readings.

Input to the KAISER program includes the wavelength

at which the plate is being calibrated and an identification

code for the plate, the step factor, the low and high values

of transmittance that should be accepted (e.g. 5 to 9°$ T),

and pairs of transmittance readings through a step sector

or filter. As a first step, as many values of A are

calculated as there are pairs of transmittance readings,

'and from this list are calculated the average and standard

11
deviation. The individual estimates of A are each compared

with the average , and any of the individual values

differing from the average by more than ~$o are rejected and

a new average and standard deviation are found. With this

value of A, the value of the Kaiser function corresponding

to each transmittance is found, and the Kaiser values are

taken in pairs to give individual slopes for the calibratioij

function* The average and standard deviation of the slope

are calculated from this list, and individual slopes

differing from the average by more than ^>'a are rejected.

Table 1 shows the form of the output, which includes

a summary of the input data followed by estimates of A and

the slope, the standard deviation for each, and the number

of data pairs rejected in each case as giving results

outside the 5a "limits. The operator is then asked if he

wants more detailed information. In this case he answered

affirmatively, and the computer presented a summary of the

data arranged according to the transmittance reading for

P"

the lighter step. (The notation "E-2" means "X 10 ). A

glance at this summary indicates that there is no marked

trend of the slope with transmittance readings, but that

the calibration may not be reliable for transmittances

above 90$* The operator is asked at this point if he wants

still more output, and in this case he answered negatively.

The program is written to accept two or more sets of

data at a time* These may, for example, be calibration

data for the same plate at different wavelengths. The output "OUT OF DATA IN (LINE) 110" shows that there were no

more such sets of data. The "TIME: 8 SECS." output shows

the time taken by the slave computer to perform the

calculations

.

The values of A and the slope given by this program

are part of the input to the program INTEN, along with

12
Table 1. Output from KAISER.

:..

KAISER 10:15 CEIR 06/01/66

PLATE CALIBRATION BY FIT TO KAISER TRANSFORM

DATA FROM PLATE L-463

WAVELENGTH= 3300 ANGSTROMS

PCT. T LIMITS: TO 100

NO. OF INPUT PAIRS= 19

NO. OF LIMIT REJECTS=

BEST A COEFF. VAR. NO. 3S REJ. NO. PRS. USED

.214856 217.548 19

AV/E. SLOPE COEFF. VAR. NO. 3S REJ. NO. PRS. USED

•563404 4.85105 19

00 YOU WANT SUMMARY OF SLOPE VS. PCT« T» YESd) OR N0(0>?1

RA.m&E OF LIGHT T VALUES

FROM TO AVE. SLOPE ^0 . OF PRS. PCT* DEV«

30 40 .563782 1 6-72484E-2

50 60 .555409 2 -1.41903

60 70 .577085 5 2*42833

70 80 .58326 4 3-5244

80 90 .563742 6 6.004&6E-2

90 100 .528577 2 -6.18142

DO YOU WANT INDIVIDUAL SLOPES* YESd) OR N0(0>?0

OUT OF DATA I .M 110

TIME: 8 SECS.

transmittance readings to be converted to relative

intensities. INTEN includes several options. For example 3 the readings may all be from one wavelength region, with a single plate calibration curve, or more than one plate

calibration may be needed. The options are summarized in

table 2. The input and output formats depend on which

option is to be used. One output is shown in table 3.

13
Table 2. Options in INTEN program.

More than one More than Background

Option plate calibrat ion one step correction

1 - - -

2 - + -

3 - + +

4 + + -

5 + + +

Table 2. Output f rom INTEN (Test data).

ii\ITEiM 10:20 CEIR 06/01/66

RELATIVE INTENSITIES OF SPECTRAL LINES

ANGSTROMS PERCENT T REL. INT. BKGD- INT. GORR. REL. INT

2500 60 6.53197 3.26599 3«26599

2 500 20 8. 2. 6.

2600 60 6.53197 3.26599 3*26599

2600 20 8. 2. 6-

II ME: 3 5 ECS.

14
b. Fitting analytical curves

The programs CODEBC and CODEBD fit analytical curves

illto instrument readings of intensity ratios from standards

pf known composition and calculate analytical results from

data on samples. To find the analytical curves, the

computer makes least-square fits to polynomials, starting

with the first degree and continuing through the eleventh

degree if there are sufficient input data. The user studies

output indicating the goodness of fit for each degree of

"polynomial, and then enters the degree of polynominal that

he wants to have used in subsequent calculations. At his

'option, the user will then receive as output for each

standard the calculated concentration and the absolute and

percentage differences between the calculated and given

element concentrations. If there is some standard which

does not fit on the calibration curve, the user can stop

the program, edit the data to remove the values for this

standard, and start the program again.

The final output is the concentrations found for the

samples. CODEBC provides output in terms of concentration

ratios and concentrations. For each sample run in

multiplicate, information is given on the individual runs

as well as averages and standard deviations. CODEBD will

not provide data on concentration ratios, and for each

sample run in multiplicate only the average and standard

I deviation are given.

cOther programs

Space does not permit listing all of the programs that

have been written, but a few more examples will be cited

briefly.

Several programs have been written for statistical

calculations. CODEB, for example, computes the average,

maximum, minimum, range, and standard deviation for any list

15
of up to 100 numbers. Many other programs include

statistical calculations.

TEMPER and PROFIL are used in the studies on arc

temperature measurements. Both programs fit least-square

lines to log (IA /gf) vs. E and, from the slope and standard

deviation of the slope of this line, calculate the

temperature and standard deviation of the temperature of thd

arc. The two programs differ only in the format of the output, that of TEMPER being more detailed.

The terminal is used by several Sections within the

Analytical Chemistry Division, and a program, TIME, has

been developed to keep records of the use and to compile

this information periodically. Each user, when he has

completed his operations, enters into the data section of

the program his code number, the times he came on and is

going off, and the day of the month. These data are stored

in the disk memory of the computer. At the end of each

month the program is run and the output lists the total

usage (numbers of uses and total hours) and the total and

percentage uses for each person. "When the program is run

before the end of the month, it will also provide a prediction of the total use to be expected during the month

based on the rate of use to date.

Copies of these programs will be supplied on request.

(S. D. Rasberry, M. Margoshes, B. F. Scribner)

B. Arc Temperature Measurements

The previous annual report [1, pp. 13-18] described

the reason for and the basis of the measurements of the

temperature distribution in a d-c arc in argon, and

showed the first experimental results. During this year,

the measurement methods have been improved by more

extensive application of computers, particularly by the

time-sharing system, to reduction of the data.

16
ire

he

The applications of the time sharing computer in this

tudy include the programs for photographic plate

alibration and for conversion of microphotometer readings

h relative intensities, described elsewhere in this

.eport. In the first set of measurements, a week was

eeded to calculate the plasma temperatures at 19 radial

ositions by making least-square fits to log (IX^/gf) vs.

With the time-sharing 'computer, the temperature and the

tandard deviation of the temperature can be calculated for

11 of the radial positions in about one-half day,

eluding the time required to prepare punched paper tapes

f the data for entry into the computer.

*

Additional measurements have now been made under the

ame experimental conditions as for the first set. All of

he new measurements are in agreement among themselves, and

hey show the same qualitative temperature distribution as

n the first set. However, the temperatures found in the

itew measurements, about 65OO K at the center of the arc,

.re somewhat higher than the results of the first

leasurements (58OO K)

(M. Margoshes and M. M. Darr)

L Laser Probe Excitation

The previous annual report [1, pp. 21-7] included a lescription of studies of the properties of the laser probe

"or qualitative and quantitative analysis. On the basis of

;hese studies, we now feel confident in applying this

Excitation source to the analysis of samples which might be

lifficult to handle by other methods. A description of

:hese studies is being prepared for publication.

We are cooperating with the Laser Section of Committee

-2 of the American Society for Testing and Materials in a round-robin test. Several laboratories have agreed to make

laser probe exposures with specific NBS Standard Reference

17
Materials, to return these samples for measurement of the

pits formed, and to fill out a form with information on

excitation and exposure conditions. The purpose of this

round-robin test is to develop standards for terminology

and procedures for laser probe excitation.

Among the unusual problems solved with laser probe

excitation was the identification of inclusions in bottles

made of a fluorinated polymer. These inclusions ranged

downward in size from about 1 mm, and they were of various

shapes and colors. Attempts to remove some of the

inclusions for arc excitation failed because the particles

would pop out and be lost when a cut was made into the

plastic. Samples were prepared for laser probe excitation

by excising pieces of the plastic containing one or more

inclusions, removing some of the plastic if necessary to

bring the inclusions near the surface, and mounting the

plastic pieces on microscope slides with double-sided

adhesive tape. The analyses showed that some of the

particles, which looked dark red under the microscope,

contained iron as the major metallic constituent and

presumably were bits of rust. Other particles, which

looked metallic, contained aluminum, copper, or zinc as

major constituents. Several opaque particles contained

large amounts of silicon and presumably were bits of glass

or ceramic. It was concluded that bottles made of this

material are not suitable for storage of pure solutions.

Microfilm which is stored for several years occasionally develops spots up to 100 or 200u. in diameter, which

can affect the quality of the images. Localized impurities

in the emulsion might be a cause of such spots. To analyze

the spots, samples of the microfilm were taped to microscope;

slides and sampled with the laser probe. A total of 4j5 expov

sures were made. The pits were approximately cylindrical,

18
(tbout 100[i in diameter and lOOu. deep. Some of the spots

iere found to contain metallic impurities which were not

?ound in adjacent unaffected areas, but no consistent

Dattern of impurities was observed. Very often, no

lifference in metallic content was found between spots and

inaffected areas.

A nickel printing plate, coated on one side with

chromium, was submitted for the analysis of small corroded

areas on the uncoated side. Laser probe analyses were made

of unaffected areas on both sides of the plate, of the

corroded areas, and of the printing ink. The corrosion

spots were found to contain chromium in significant amounts,

but only traces of iron, which was the major metallic

constituent of the ink. It was concluded that the corrosion

may have been caused during the chromium plating rather thai

by reaction of the plate with the ink.

Other applications of the laser probe included the

identification of surface deposits on cathodes from an

electrical discharge, and the sampling of the outside and

cross-section of a small spring to determine whether or

not it had been plated.

Our experience in these applications indicated that the

laser probe is a useful addition to the other analytical

capabilities of this laboratory. However, these applications have been restricted to cases where qualitative

results are adequate, and we have not yet attempted to

apply the laser probe to quantitative determinations.

(S. D. Rasberry, M. Margoshes, M. M. Darr)

D. Atomic Absorption Spectrometry

During the past year, a study of atomic absorption

spectrometry with a high-pressure xenon lamp continuum

source has been completed, and will be prepared for

19
publication. The emphasis of experimental studies has now

been shifted to non-flame methods of converting samples to

an atomic vapor. In addition to this experimental work,

as well as several analytical applications, a method has

been developed for selecting wavelengths for atomic

absorption spectrometry without tedious experimental

measurements. This method has been tested, partly with

published data and partly with new data obtained in this

laboratory.

Towards the end of this year, the atomic absorption

spectrometer has been rebuilt to provide significant

improvements in ease, speed, and accuracy of measurement.

1. Modification of the instrument

The instrumentation for atomic absorption

spectrometry has been modified and improved. The rebuilt

instrument is shown in figure 5. Nearly the only part

retained from the old instrument is the 3/h—m Fastie-Ebert

monochromator , which is kinematically mounted on a sturdy

base, to which a 1.25-m optical bench is rigidly attached.

This arrangement allows considerable flexibility for the

external optics. The major modification has been to replace

most of the electronics. The electronics now consist of the

following: stable d-c power supplies for hollow cathode and

high-pressure xenon lamps; a highly-regulated (0.001$),

high-stability (0.005^/hr) 0-2000 V d-c photomultiplier

power supply; a variable-frequency, phase-sensitive

amplifier with a remote high input- imp edence pre-amplif ier

,

adjustable time constant, and zero suppression; a 590-Hz

synchronous mechanical chopper for modulating the radiation;

and a 10-mV, 0.25-sec response strip chart recorder. All

of the electronics, except for the pre-amplif ier and the

chopper, are mounted in an upright cabinet provided with

casters for mobility.

20
Figure 5. Newly modified atomic absorption

spectrometer.

A 5~kW, 4.8 X 10 -Hz radio-frequency power supply has

recently been installed,, to provide power for a plasma

torch which will be studied as a means of vaporizing samples

for atomic absorption spectrometry. Studies of atomic

fluorescence with the plasma torch are also contemplated.

(C Veillon and M. Mar go she s)

21
2 . Selection of wavelengths

The selection of a wavelength for measurement in

atomic absorption spectrometry is ordinarily based on

published data for suitable lines or on direct measurements on a number of lines of the analyte of either the

concentration required to give an arbitrary absorbance or

the absorbance at a fixed concentration. Direct measurements on many lines are time -consuming , and reliance on

published data may not result in the selection of the best

possible wavelength. Differences in instrumentation must

be taken into account, and the necessary information may

not be given in the literature. For example, the most

sensitive line of the analyte may be in a wavelength region

that was not accessible with the spectrometer employed in

the original measurements. The particular filler gas in

the hollow cathode lamp is an experimental variable which

can affect the choice of wavelengths, since the gas may

have emission lines nearly coincident with one or more

lines of the analyte. When there are such adjacent

interfering lines either from the filler gas or other

lines of the analyte, the resolving power of the spectrometer becomes an important factor.

When two or more analyte s are to be determined in the

same solution, it will not always be possible to make use of

the most sensitive line of each element, since only a limited concentration range can be covered with a particular absorption line. There has been little information published on wavelengths suitable for the determination of elements present at high concentrations.

Two relationships have been derived for the selection

of analytical wavelengths in atomic absorption spectrometry

from the gf -values tabulated in NBS Monograph 53 [5]. Both

relationships have been tested experimentally and found to

22 i
nold within the precision of the gf-values. However , the

kf-values given in KBS Monograph 53 must be corrected for a

(wavelength-dependent error at wavelengths below 2450$.

[Figure 6 shows the correction factor as a function of

Wavelength, according to Corliss [6], Multiplying the

listed gf-values by correction factors taken from this graph

has been found to give reasonably accurate results in this

pp lie at ion.

200

2000 2200 2400

WAVELENGTH, ANGSTROMS

Figure 6. Wavelength-dependent correction

factor to gf-values in NBS Monograph 53. Values from tables

should be multiplied by factor

taken from this chart.

For atomic absorption spectrometry with a narrow-line

source, such as a hollow cathode lamp, the concentration of

an element required to give a selected absorbance with a given experimental arrangement should be inversely

23
proportional to gf exp(~E/kT), where E is the energy of the

lower level of the transition, k is Boltzmann's constant,

and T is the flame temperature. For resonance lines, where

E=0, the exponential term is equal to unity. Similarly,

the absorbances for a series of lines of the same element

at a given concentration in the test solution will also be

proportional to gf exp(-E/kT).

A somewhat different theory applies to atomic absorption spectrometry with a continuum source. In this case,

either the reciprocal of the concentration of the analyte

required to give a selected value for the percent absorption, or the percent absorption at a fixed analyte concentration, will be proportional to gfX e~^ ' 'at low

absorbances. Note that, in the case of the continuum source,

it is the percent absorption that is to be measured rather

than the absorbance.

For the first case, atomic absorption spectrometry with

a hollow cathode source, a test of the theory could be made

on the basis of data from the literature. Figure 7 shows a

10

0:5

2

T 1 I M I LI

o TRANSITIONS FROM

GROUND STATE

• TRANSITIONS FROM

EXCITED STATES

I ' I I I I M I

I I I I I I I I 2 5 10 20 50

IRON CONCENTRATION, ppm

100

Figure J, Test of theory for atomic absorption

with a hollow cathode light source.

The straight line has a unit slope

as required by the theory.

24
comparison of theory with experiment with data on iron given

jby Allan [7]* "who measured the concentration of iron in

solution which would give an absorbance of 0.1 for a number

of lines. A flame temperature of 2000 K was assumed. The

points lie on a straight line within the precision of the

gf-values _, indicating that the theory can predict relative

sensitivities of detection.

No similar sets of data could be found in the literature

for atomic absorption spectrometry with a continuum source.

To test the theory,, a set of measurements was made for

manganese with a high-pressure xenon lamp as the source.

Figure 8 shows the results of these measurements.

100

50

£20

o

COm io <

LJo

0.

= 1 11 II III 1

1 1 |

IMj |

1 1

|

1 M| | . — —

— v^o — — 4S*1 —

—

•2794, 2798, 2801 A. —

— •

• // °

/ o

= 4030, 4033, 4034 A. —

— /

o —

1

1 1 Mill 1 1 1 1 1 Mil 1 1 1 1 Mill 1

1 005 0.1 0.2 0.5 gfXC

10 20 50

Figure 8. Test of theory for atomic absorption

with a continuum source.

Measurements for six lines at several different concentrations were combined by plotting gfAC vs the percent absorp-

! tion, where A is the wavelength and C is the concentration

in parts per million. As expected,, the curve is asymptotic

! to a line of unit slope at low absorption values _, but

approaches a lower slope at higher percent absorption

25
readings. All of the data fit the curve within the

accuracy of the gf -values, but there is discrepancy between

the data for the lines at 279^-2801 8 and for the lines at

4030-4034 8. When the same data are plotted with the gfvalues of Ostrovskii and Penkin [ 8 ] , a similar discrepancy

is observed, but in the reverse direction in that the curve

for the group of lines at shorter wavelength then falls to

right of the curve for the longer-wavelength lines.

However, either set of gf-values will lead to the prediction

that the manganese line at 2794 A will give the best

sensitivity of detection, in agreement with the measurements

This method cannot predict relative sensitivities of

detection for different elements or for different

experimental arrangements. The proportionality between the

analyte concentration in solution and the number of atoms in

the flame depends on the element, on the construction of

the atomizer, on the temperature of the flame, and on many

other factors. No attempt has been made to correlate

sensitivities of detection with atom and ion lines of the

same element, though this would be possible if the degree

of ionization in the flame were known.

It should be recognized that, in applying this method

of selecting lines, the criterion of sensitivity of

detection is in terms of the absorbance or percent

absorption. This is less meaningful than a definition of

sensitivity in terms of signal-to-noise ratios. In many

cases, however, either criterion will lead to selection of

the same line. In addition, If the most sensitive line is

too strong, the treatment described here will

satisfactorily predict the less sensitive line which must

be used.

(M. Margoshes)

26
-°

3. Use of a Continuum Source

Studies have continued on the use of a highressure xenon lamp as a continuum source in atomic

bsorption spectrometry. In particular, the precision of

,analysis by this technique has been measured for both pure

solutions and actual samples. Only the data on actual

samples will be discussed here, as these should be

representative of the type of results which could be

obtained in routine applications.

It was not possible, in this study, to utilize the

stepping capabilities of the spectrometer to determine

several elements in rapid succession. The recorder then

on the spectrometer had too slow a response to accurately

follow the line intensity as each line was quickly scanned.

owever, the instrument has now been modified (see above),

and such measurements should be possible in the future. In

the work described below, the wavelength was adjusted

manually for each line, and data were taken by reading the

recorder pen deflection for a 20-second period.

The samples chosen for this study were NBS Standard

Reference Materials 1011, 1013, 1014, 1015, and 1016, which

are portland cements. Solutions were prepared by

dissolving weighed samples in dilute HC1, filtering off the

insoluble silica, and diluting to volume with water. It was

found to be possible to determine Fe, Mg, and Na in a single

solution; Ca was too concentrated in this solution to be

determined without dilution and the concentrations of other

elements were too low. Each solution was run 4 times over

a 3-day period to establish analytical curves, and the

solution from NBS 1014 was run 20 times to determine the

precision of analysis.

27
Fe gave a linear analytical curve over the range of

concentrations (145 to 259 Ppm) in "the solutions, the curve

for Na (6 to 4l ppm) was nearly linear s while that for Mg

(25 to 256 ppm) had a pronounced curvature. Table 4 lists

Table 4. Precision of determination of Fe, Mg, and

Na in Portland cement by atomic absorption

spectrometry with a continuum source.

Element

ppm in solution

ave . absorbance

std. dev. of

absorbance

coeff. var. of

absorbance {%)

slope of anal, curve

(ppm/absorbance unit)

std. dev. of

concentration (ppm)

coeff. var. of

concentration ($)

Fe Mg

175 169

o*o426 0.518

0.0021 0.016

4.9

3110

6.4

3.7

3.1

606

9.8

5.8

Na

18

O.O969

. 0034

3.5

202

0.69

3.8

the results of the precision studies, including statistical

analyses in terms of the absorbance and the concentration.

These data indicate that reasonably precise and accurate

results can be obtained in the determination of several

elements in the same solution by atomic absorption with a continuum source. This study has also defined some

limitations of the method. The sensitivity of detection is

somewhat poorer than with hollow-cathode lamps, and the

analytical curves are linear only over a restricted range

of concentrations. These limitations arise from the fact

that the band width of the spectrometer is much larger than!

the width of the absorption lines. Better results could be

obtained with a spectrometer of higher resolving power,

28
but data equivalent to what can be obtained with hollow-

• cathode sources would be possible only with an instrument

with a band width of hundredths or thousandths of an

angstrom.

(M. Margoshes, M. M. Darr, C. Veillon)

E. Plasma Jet Excitation of Solutions of Cast Iron

In the course of analyzing proposed standard reference

materials of cast iron, it was necessary to determine

zirconium by another analytical method. The powder d-c arc

; method ^ for determining the minor elements, had yielded

unreliable results for this element. A solution method was

desirable despite two immediate and obvious disadvantages.

1. Some cast irons dissolve with great difficulty —

large amounts of carbide residue being present.

2. Zirconium has poor spectral sensitivity and in

general, solution methods do not provide high sensitivities.

The sealed-tube procedure of Gordon et al. [9] has been

used to dissolve difficultly-soluble materials. The high

temperature and pressure which is developed dehydrates most

--of the silica, facilitating its removal by centrif uging.

, This convenient silica removal step makes it feasible to use

plasma jet excitation since satisfactory atomization of the

solution will now occur. Details of the procedure are

described below.

One gram of the cast iron sample is weighed into a heavy-walled Pyrex tube. Ten ml cone. HC1 and 0.6 ml cone.

sHCIOj. are added and the top of the reaction tube sealed by

melting with an oxy-gas torch. The tube and a weighed

quantity of solid C0

p

are inserted into a heavy-walled steel

! tube. A threaded, copper gasketed steel cap seals the open

'.tend. The tube is heated for 15 hrs at 300 c developing a pressure of approximately 3500 psi in the glass tube. The

C02 gas generated provides pressure compensation.

29
After cooling and opening the tube, the contents are

transferred to a centrifuge tube. After centrif uging, the

residue is washed with distilled water and the washings

added to the centrifugate in a 15 -ml volumetric flask. The

residue, in a platinum crucible, is treated with HF and a few drops of HpSOj.. The crucible is heated to vaporize

SiF^ and the resulting sulfates added to the solution and

made up to volume.

Synthetic standards were prepared by dissolving highpurity metals to approximate the composition of the cast

iron matrix and then incorporating known amounts of the

zirconium as a solution. The plasma jet was used to

vaporize and excite solutions of samples and synthetics.

Analytical curves were prepared from which the zirconium

concentration could be determined.

For NBS 1185 3 the individual determinations were:

0.118$, 0.126$ and 0.120$, compared to an average

photometric value of 0.125$*

If zirconium silicate is present, it will not be

dissolved by this treatment* The procedure would be

complicated by a required fusion of the residue.

Determinations of cobalt and titanium in NBS 1175 and

NBS ll8l were also made. The results compared to the

certificate value are shown in table 5.

50
Table 5. Results of the determination of Co

and Ti in NBS 1175 and ll8l

Percent

Co Ti

NBS 1175 0.120 ^ 0.358

.118 .340

Average .119 .3^9

Certified value .11 .35

NBS ll8l 0.0120 0.0419

.0105 ,o4l4

Average .0113 .041

Certified value .012 ( .04 )

(R. Alvarez)

31
5. X-RAY SPECTROMETRY

A. Basic Considerations

The application of x-ray spectrometry to chemical

analysis is one of the fastest growing areas of

instrumental analysis. It is thus necessary to maintain,

and further develop, a laboratory equipped and prepared to

perform analyses, provide consultation, and undertake

research in this important field.

The theory of x-ray generation, absorption, and

measurement was developed several decades ago and is well

understood. The technological development in this area has,

however, been considerable in the last two decades,

particularly in the low energy (long wavelength) range, and

in the measurement of low intensity levels. Thus,

phenomena which were of theoretical interest only, such as

line and band shifts as a function of chemical binding

energy or the distribution in depth of x-ray emission, have

acquired great practical importance. This, in turn,

requires the re-measurement of certain related parameters,

such as electron back-scatter coefficients, x-ray mass

attenuation coefficients, and x-ray fluorescence yields.

The development of the theory of quantitative x-ray

spectrochemical analysis (x-ray fluorescence and microprobe

analysis) has been adversely affected by the lack of

reliable data of this kind. Although increasing efforts

are made to fill this gap, the work done is still . insufficient and poorly coordinated. This laboratory will

increase its efforts to experimentally determine, collect,

interpolate, and publish data of this nature.

As the physical foundations of x-ray spectrometry are

more quantitatively understood, the sources of error in

existing methods can be investigated in more detail. Since

this branch of spectrometry is based upon the measurement of

52
.relative intensities , the problem of choice, evaluation, and

luse of standard materials must also be critically considered.

[Efforts in this direction are hoped to produce correction

isystems for x-ray fluorescence matrix effects which require

a smaller number of reference standards , and to achieve some

(progress in the selection and testing of standard materials

for quantitative microprobe analysis.

As in the previous year, analytical capabilities in

both x-ray fluorescence and in microprobe analysis were

utilized for various problems. It is planned to intensify

in the next fiscal year the use of the microprobe for

homogeneity studies, particularly of existing NBS standard

reference materials. It is desirable to develop for this

purpose methods of fast automatic or semiautomatic

collection and evaluation of data for many points on the

specimen. Several promising approaches to this problem are

presently being investigated.

Coincidently with the move to the new facilities at

Gaithersburg, the auxiliary services needed for an x-ray

spectrochemical laboratory are being expanded. Rooms for

the preparation of specimens and for electronics repair and

development were installed. It is hoped that by the end of

next fiscal year the section will be practically selfsufficient in these auxiliary activities.

EB. X-Ray Fluorescence Spectrometry

A brief description of the capabilities of x-ray

fluorescence spectrometry for elemental analysis has been

given by Heinrich [1, pp 28-30]. The x-ray fluorescence

equipment in the Spectrochemical Analysis Section is

described in the same reference, with special emphasis

being given to modifications which were being made at that

time to update the equipment and extend its range of

applicability.

33
In the past year techniques for automatic logging and

processing of x-ray data have been under critical study in

an effort to reduce the number of manhours required in the

manual reduction of x—ray data. This work has been

especially important in view of the increased time that

would be required for manual computation of x-ray data

using the more complex mathematical treatments which

recently have been developed.

One of the mathematical treatments that we [10] have

successfully applied to resolve matrix interelement

intensity interferences is the technique of Lucas—Tooth

and Price [11]. In this method the concentration of each

element is treated as a function of line intensity plus a summation of intensity contributions from every other

element in the matrix. To linearize the function each

summation term is multiplied by an empirically determined

coefficient. One of the difficulties of this procedure is

the large number of standard specimens of known

composition which are required] at least N+2 standards are

required to form the set of N+2 simultaneous equations

needed to empirically determine the linearizing coefficients. N is the number of elements present. One of

the goals of our future research effort is to investigate

the possibility of a theoretical or semi-theoretical

approach to the interelement correction problem which would

yield an improved physical model.

1. Modification of Equipment

The Spectrochemical Analysis Section is equipped with

a single-channel x-ray fluorescence spectrometer (the

Norelco Four Specimen Position Vacuum Spectrometer),, and a multi-channel x-ray fluorescence spectrometer (the Applied

Research Laboratories _, Inc. PXQ) . These instruments are

described in an earlier NBS Technical Note [1, pp 30-34],

34

i
During the past year several modifications to the

single-channel spectrometer were completed. A new specimen

(changer and spectrometer housing were installed to permit

the x-ray optics to be operated in vacuo, helium atmosphere,

or in air. In the new arrangement alternative or

simultaneous use can be made of a gas flow proportional

counter and a scintillation detector. Revisions to the

electronic read-out unit, which are now complete, include an

improved single-channel pulse height analyzer and a fully

electronic timer.

At the end of the last fiscal year the multi-channel

spectrometer was reprogrammed for the analysis of heavier

elements. Checking out these modifications, revising the

; mounting of the primary slit chamber, and re-aligning the

monochromators was complete early in September. During

September a test of sensitivity and precision for each of

the 18 fixed monochromators and 2 scanning monochromators

was completed with the finding that the new monochromators

were properly aligned.

2 . Computation Techniques in Data Reduction

In recent years improvements in x-ray fluorescence

technology and equipment have effected an increase in the

speed with which x-ray line intensities can be measured for

routine spectrochemical analysis. On the other hand the

physical models which have been developed and which are

required to make these intensities useful as measures of

element concentration have progressed toward increased

complexity and thereby slower analysis, so long as manual

computation methods are used.

We have written several computer programs to automate

certain types of computations, using established physical

models and mathematical techniques which we wished to apply

to routine analytical problems. A clear distinction must

35
be made here between: (a) the development of new physical

models to relate x-ray intensities to element concentration,

and (b) the application of existing techniques (with their

current inherent limitations) to the automatic computation

of element concentrations and associated statistical data.

In consideration of the practical analyses we are called

upon to make, our early efforts have been directed toward

programs which fit into category (b). In the next year we

wish to shift the emphasis of our work to a search for

improved models for relating x-ray intensities to the

composition of a sample.'

The computation facilities available to us include an

IBM 7094, a CDC 3100, and a remote terminal for a GE-265

time-shared computer system. The GE-265 system and terminal

are described in Section 2 of this report.

The GE-265 system has sufficient memory and computation

capacity to be useful in many of our analytical problems.

It provides easy access to the computer and quick processing

of the data; so we have written several programs for use on

it. A brief description of four of these programs is given

here; full texts and punched paper tape copies of these

programs are available.

XRAY 1 is a program for processing data from known

analytical standards, when the relationship between x-ray

intensity and element concentration is known to be linear.

Sets of intensities from repeated measurements on a set of

standards are input to the computer. The intensities are

averaged for each element and the average is equated to the

known concentration. The concentrations for individual

runs are computed and then ordinary statistical parameters,

including maximum, minimum, standard deviation, and

coefficient of variation are computed and printed out. A

sample output is shown in table 6.

36
Table 6. Computer output from XRAY 1 program.

XSAYl 16:07 CEIR 06/01/66

ANALYSIS FOR 4 ELEMENTS FOR 4 RUNS ON SPECIMEN \A

ITEM AG CU ZN CH.l ZN CH.2

iPCT 73.6241 1 .5002 . 1088 •102805

PCT 73*888 1 .505 . 1344 •096345

per 75.01 64 1 .589 .0768 .092945

PCT 75.471 4 1 .6058 • 08 •107905

STATISTICAL ANALYSIS

AVE PCT 74-5 1 .55 . 1 . 1 STD DEV PCT . 885442 5.51957 E-2 2-70742 E-2 6*67056 E-3

AVE INTEN 3462.25 2 822.5 86.5 450.5

STD UEV INTEN 97.301 5 45-9964 1 6.9214 39.2386

PCT COEF VAR 1 . 1 8851 3*56101 27.0742 6-67056

MAX PCT 75.471 4 1 .6058 . 1344 •107905

MIN PCT 73*6241 1 .5002 • 0768 .092945

RANGE PCT 1 .8473 . 1056 • 0576 •01496

XRAY 2 is analogous to XRAY 1 with the exception

that it is for processing data from unknown specimens. The

statistics in this case are computed only for intensities.

STAT is a program which computes analysis of variance

and a confidence interval for the lot mean (T test) for any

sets of numbers _, either concentrations or intensities.

These statistics are particularly useful in making decisions

about the homogeneity of specimens. A sample output of

this program is shown in table 7.

CODFIT is a program similar to CODEBC AND CODEBD, which

are described in section 2 of this reportj it differs from

them primarily in that the format of data input and result

output is altered to especially fit x-ray fluorescence

spectrochemical analysis. Input data are intensities from

37
Table J. Computer output from STAT program.

STAT 16:19 CEIR 06/01/66

STATISTICAL ANALYSIS FOR SETS OF 16 RUNS ON 4 ELEMENTS

ITEM SI AL FE TI

AVERAGE 43. 125 38.4813 .541875 2*09063

MAXIMUM 43.8 39.3 .58 2-25

MINIMUM 42.3 37.6 • 48 1 .96

RANGE 1 -5 1 .7 . 1 .29

ANALYSIS OF VARIANCE

STU. DEV.

95 CONF U LIM

95 CONF L LIM

PCT COEF VAR

•452415

1 .44004

• 234261

1 .04908

T TEST... 95 PCT. CONFIDENCE

INTERVAL FOR THE LOT MEAN.

AVERAGE

95 CONF U LIM

95 CONF L LIM

43. 125

43.4967

42.7533

•547992

1 .74426

.28375

1 .42 40 5

38.4813

38.931

5

38-031

3.63719 E-2

. 1 1 5772

1 .88334 E-2

6.71224

•541875

•571758

.51 1 992

8*42592 E- .2681 97

4-36294 E-: 4.03034

2.090 63

2.1 5985

2*0214

standards and unknowns. The assumption of XRAY 1 that

concentration is a linear function of intensity is not

required in CODFIT. Instead, a least-squares fit to a polynomial equation of degree less than 12 is made for the

average intensities for each standard. The analyst selects

the proper degree equation on the basis of fitting data which

is presented by the computer. Then the program computes the

concentration of each unknown by solving the equation with

the intensity of the unknown.

2« Examples of Applications

X-ray fluorescence spectrometry has been applied to make

more than 8000 quantitative determinations in the past year.

A wide variety of materials have been analyzed including

dental gold alloys, dental silver alloys , tungsten on rhodium

38
imirrors, selenium in steel, tin-bismuth binaries , and

I refractory clay specimens.

In the analysis of 300 dental gold alloy specimens

'the previously mentioned mathematical technique of LucasTooth and Price was applied, yielding linear and singular

calibration curves. An earlier test of this technique for

the dental gold system had been made by Eick, Caul, Smith,

and Rasberry with a similar finding [10],

The analysis of 32 clay specimens provided experience

in another form of matrix correction; here the particle

r

, structure was reduced by subjecting the samples to a

fusion with LipB^O at 2200°F, following the fusion

technique outlined by Rose, Adler, and Flanagan [12], In

this technique the interelement effects are reduced by

physical dilution of the specimen to the point of having

a light element matrix.

Last year, a preliminary study of nickel plating

thickness measurement by x-ray fluorescence was performed

using a single-channel spectrometer [1, p 45 ] . During

this year the study was successfully concluded and

satisfactory thickness calibration curves were prepared.

(S. D* Rasberry)

39
4. ELECTRON PROBE MICROANALYSIS

A. Instrumental Developments

The development and installation of modifications and

equipment accessory to the Applied Research Laboratories

EMX electron probe microanalyzer was continued in the past

year* Some of these accessories will now be described

in detail,

1. X-ray Spectrometer for Long Wavelengths

A spectrometer for the detection of x-rays of wavelength up to 90 angstroms was purchased from and installed

by the manufacturer. Each spectrometer now carries two

crystals which can be exchanged from outside the vacuum

chamber* The present arrangement of crystals and detectors

,

which is thought to be very satisfactory, is shown in

table 8.

The long wavelength spectrometer not only adds to the

capabilities of the instrument the detection of elements of

atomic numbers 5-Hj if also permits the use of emission

lines of long wavelength emitted by elements of higher

atomic numbers. These lines can be used to advantage when

high resolution in depth is required, or when studies of

wavelength shifts or changes of band shapes are performed.

2. Detector Slits of Variable Width

Detector slits of externally adjustable width were

installed in the spectrometers I and II. Although the

characteristics of this slit device have not been

systematically investigated as yet, its use to increase line

resolution was demonstrated in one practical case of line

interference.

5. Solid State Target Current Preamplifier

A solid state operational amplifier (figure 9) was

installed to permit an initial amplification of the target

40
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41
BIAS SOURCE

© o- T—»0-

I in

7.5 pF

IMEG. I\

E in

"\ Ok

33 pF

Hf- MEG. 1%

5 5 MEG.

>o WW

25

25 MEG.

78ooi^r"+i2v

20k, lOt

Ci) (!J) lN627's

-I2V,®_l

6

'"1

Ik

| Wr

s

OUT

IMEG «_/

L-®-H2V

CIRCUIT BYPASS

I out

Figure 9. Target current- preamplifier with

selectable gain, and dual-polarity

specimen-biasing battery.

k-2
tli

current by factors of 5 and 25. The device contains two

floating batteries which can be used to bias specimens

positively or negatively [13]; it can be by-passed if so

desired. The main purpose of this device is to achieve

stronger contrast in target current scanning images 9 as

illustrated in figure 10. For this purpose the bias range

#*

Figure 10. Aluminum surface with scratches, 30 keV,

5x10 amps. , 300u. x 380|j,» Target

current images formed without (left) and

with (right) target current preamplifier.

of the ARL d-c amplifiers was enlarged. Images obtained by

using the target current amplified with this device exhibit

a contrast superior to that of conventional backscatter

detectors , for both atomic number differences and

topographic features of the specimen surface.

4. Solid State Concentration Mapping Device

The use of this type of device has been described

previously [14, 15] (figure 11). The concentration mapper

is a d-c amplifier the output voltage of which varies

43
PREAMPLIFIER

LINEAR

AMPLIFIER

PULSE HEIGHT

ANALYZER

RATEMETER

DC

AMPLIFIER

t®D X-RAY

DETECTOR

CONCENTRATION

MAPPER

DC

AMPLIFIER

BLANKING

Figure 11. Interconnecting system for the use of

the concentration mapper with x-ray

signals.

dis continuously as a function of input voltage. The range

of the input signal is divided into a limited number of

adjustable input zones. Within each zone, the output is

constant, stepping to a different level when the input

signal crosses the limit between zones. This output is

used, through a d~c amplifier, to modulate the brightness

of a scanning image. Specimen areas corresponding to an

input signal within one zone appear in uniform brightness

on the image. The output of an x-ray pulse ratemeter is

usually connected to the input of the concentration mapping

device, so that each brightness level of the image

corresponds to a range of x-ray signal intensity. If a

unique calibration curve of intensity vs. concentration of

the emitting element can be established, the zone limits

can be set to represent chosen concentration levels of this

44
element. X-ray concentration maps are thus obtained.

Similar mapping operations can be performed using the

amplified target current as an input signal. Such

'techniques are useful to map the abundance and distribution

of a phase within a multi-phase specimen^ and these maps

can be evaluated using the methods of quantitative

metallography.

A simple solid state device capable of mapping four

ranges simultaneously was constructed at NBS by Mr. L.

Marzetta, NBS Electrical Shops. The level triggering

characteristics are indicated in figure 12. The circuit is

-i 1 1 r TO > 75 VOLTS

Figure 12.

HALF GAIN

8.7

I 2 3 4 5 6 7 8 TRIGGER LEVEL CONTROL KNOB SETTING Calibration curves for level

control of the concentration

mapper

shown in figure 13. The output voltage (vertical) as a

function of input (horizontal) is shown schematically, for

45
the two operating modes available, in the upper right

corner of figure 13. The subtract mode is used to emphasize

+ 13(30 ma)

430n,IW

•fcM2V /T" pi V30-J0 — BACK TERMINAL STRIP

'J£1G\ CURRENT OUTPUT

Figure 13. Four-level solid state concentration mapper.

a phase of intermediate input levels which can be shown

black or white (depending upon the polarity of the second

d-c amplifier) on the resulting concentration map*

Concentration maps obtained with this instrument in

the "add" mode are reproduced in figure l4.

46
Figure 14. Concentration maps, (a) X-ray

concentration map of Ni in Tazewell

meteorite. 20 keV, .15 x 10"" Amps.

240|_i x 500(x. (b) Target current

concentration map, lead inclusions

in brass, 20 keV, .05 x 10-° Amps.

40|i x 50^l.

5. Pulse Height Analyzer Monitor

Monitoring on an oscilloscope of the pulses produced

by a proportional x-ray detector is current practice in

x-ray spectrometry. It is advantageous to display

simultaneously the range of acceptance of the single channel

pulse height analyzer normally used with proportional

detector equipment. This can be done very simply by

implementing the conventional pulse display with a modulation of the brightness of the oscilloscope by' the

output of the pulse height analyzer. Using a delay line the

analyzer is made to mark an appropriate sector of the

displayed pulses. The position of the accepted pulse height

range is marked as a black sector. Pulses not accepted by

47
the pulse height analyzer are shown as uninterrupted traces

The monitoring of the pulse height setting is particularly

advantageous when x-ray wavelength scans are performed,

since the mean pulse height varies progressively with the

wavelength setting.

The arrangement used in our laboratory is shown in

figure I5. The instrumental components are as follows:

PRE- AMPLIFIER

^ D

XET

RAY

ECTOR

LINEAR

AMPLIFIER

3oon

IMPEDANCE

VARIABLE

DELAY LINE

I - 10 fJ SEC

PULSE HEIGHT

ANALYZER

VERTICAL

AMPLIFIER

TIME BASE

UNBLANKING

TO SCALER

AND RATEMETER

Figure 15. Pulse height monitoring by use

of a variable delay line and

oscilloscope blanking.

Detectors: Applied Research Laboratories proportional

detectors, as specified in Table 8.

Preamplifiers: Applied Research Laboratories preamplifiers .

48
Linear Amplifier and Pulse Height Analyzer: Hamner

'Model Nr. N-302

Oscilloscope: 564 Tektronix storage oscilloscope,

used with the memory device inactive. Vertical amplifier

3A^, time base 3B4.

Figures 16 to 18 illustrate the effects of different

p ilse height analyzer settings on the unblanking patterns

o i the monitor scope.

Figure 16. Oscilloscope representation of the

amplified pulse output of a gas

proportional detector. The pulse

height region accepted "by the pulse

height analyzer, operating in

differential mode with a narrow

window, is represented by the black

wedge.

49
Figure 17. Representation of the distribution

shown in figure 16 3 with the pulse

height analyzer in integral mode.

Pulses falling below the base line

of the analyzer are represented by

uninterrupted traces.

Figure lo\ Same pulse height distribution as in

figure 17. The base line setting

of the pulse height analyzer is

lowered, so that all pulses are accepted.

50
6. Mu It i- channel Pulse Height Analyzer

A Victoreen SCIPP 1600 channel pulse height analyzer

was purchased and installed this fiscal year (figure 19 )

Figure 19 . SCIPP 1600-channel pulse height

analyzer and associated read-out

equipment

This instrument contains the following basic

sections

a. An analog-to-digital converter which sorts

incoming pulses according to their height into a number of

channels up to 1600.

b. A magnetic core memory containing 1600 "slots"

for storage of digital information. Each slot can store

the number of pulses assigned to the corresponding channel

by the analog-to-digital converter. Digital information

generated by sources other than the converter can also be

51
stored. The capacity of each slot is 10 -1 pulses.

c. A timer which can be used to switch slots

when externally generated pulses are fed into the memory.

d» Devices for transfer of information from one

part to another of the memory; for division by powers of 10;

addition, subtraction, and erasure of partial or total

memory contents.

e. Read-out devices for display of the memory

contents on an oscilloscope screen or on a digital scaler

,

for their recording by means of an X-Y recorder, print-out

by a Teletype unit, or punching of a paper tape.

f. A tape reader for transferring digital

information from punched paper tape into the memory of the

SCIPP.

In connection with the electron probe microanalyzer

,

this unit has been used in two wayst

a. To analyze, store, and display the energy

distribution of pulses generated by proportional detectors.

b„ To direct the beam of the analyzer to scan in

a grid array over the specimen surface, and to store in

succesive slots the number of x-ray signal pulses generated

at each spot of the grid (figures 20 and 21).

Hf/A

/ ////////

////////// 'ffftlftli

Figure 20* Oscilloscope representation of counts

accumulated in two grid scans over an

area of 400|i x 400[i. Left: SiKa nondispersive. Right: SiKa dispersive

52
021 17 1021 15 101831 102126 101 124 102530 101816 102556 102764 102174

021 15 101999 102103 102526 102036 102379 102319 102736 102329 102270

102508 102439 100937 102187 102322 102443 102129 103046 102761 102947

102650 078020 101825 102662 102241 102196 102718 102703 102518 102252

101831 101 167 102340 102547 102366 102331 102834 103344 103035 102061

102385 102375 101782 102758 103171 102748 102727 102730 102302 102876

103607 102953 1021 68 102742 102482 102203 102676 102758 103012 102792

102765 102601 102647 102903 102701 102286 102745 102600 102762 102931

102696 102651 102808 102480 102604 102244 102048 102989 103207 1031 53

102373 102954 103107 102251 102697 102856 102668 103206 103676 102807

D94284 098539 103568 107038 1091 70 1 10896 1 11801 1 1 1433 109625 108160

D98813 102339 10568 7 108304 1 10750 1 1 1873 1 1 1557 109634 108285 104288

101954 105991 108330 1 10090 1 1 1972 1 1 1265 1 10965 107946 106794 103555

105641 107199 109732 1 1 1846 111917 1 1 1326 109218 107137 1040 60 101064

107280 107776 1 1 129 1 1 12450 1 1 1889 1 10154 108062 103661 100626 097027

109 632 111236 1 12343 1 1 1 666 1 1031

108580 104514 101418 097423 093459

1 10817 094976 1 10887 1 1 1209 108367 106194 102592 097966 0941 62 089300

1 1 1650 1 1 1787 1 1 1352 109403 107401 104149 100184 095021 089841 085550

1 1 1868 1 1 1232 1 10437 108561 105191 100826 096394 091295 086146 081395

1 1 1894 1 11426 109420 106272 103378 098560 093780 088802 083378 0781 69

Figure 21. Print-out of grid scans as on

figure 20. Silicon dispersive

(top); Silicon non-dispersive

(bottom)

7. Other Additions

Further additions to the equipment include a second

voltage-to-frequency converter [1 3 p. 51] a "wavelength

marker for stripchart recordings, an automatic gate valve

which isolates the diffusion pump in case of vacuum failure,

and a new switch board panel which permits selecting among

the diverse operating modes of the instrument (figure 22).

8. Plans for Future Additions

Plans for further instrumental developments include the

following:

53
oMETER

. WRVELENOTH MARKER

VOLTAGEFREOUENCY CONVERTER

-o o

?•??

nh

r

6 6 6

09 T o_o

h

r

fa fa

Hh

"Q

o o- 0.0- o;okD o1

7°

** *J

,oo„ '

U "" =o

=?

6», 6

\r %*a»

I' II

6 6

NOTES! ( ) INDICATES NUNSER OF ONC CONNECTORS.

ALL VARIABLE RESISTORS ARE SK OHMS. ALL F1KE0 RESISTORS AM 1MB OHM.

Figure 22. Readout distribution system including

wiring diagram of the main control

panel

.

54
a. Interfacing of components for increased

flexibility of operation, and simpler transfer of the data

putput to the time shared computer used by the Section.

b. Use of a color oscilloscope read-out for

simultaneous recording of several signal channels in line

and area scans.

c. Installing a second non-dispersive x-ray

detector of different efficiency characteristics.

d. The purchase of a double pulse generator for

instrumental service and development.

e. The purchase of a vacuum evaporator for the

etallizing and carbon coating of microprobe specimens.

We include here a schematic drawing of the

cathodoluminescence detector (figure 2j5) mentioned in a previous report [1, p 50].

Mr. G. Wolf son is in charge of the electronic

maintenance of the x-ray equipment and he has been active

in most of the aforementioned modifications and additions

to the microprobe electronics.

B. Research Activities

The research activities concerning microprobe analysis

were mainly directed towards the following objectives:

study of sources of error in quantitative analysis,

exploratory study of non-dispersive x-ray detection, area

scanning techniques, and literature research.

1. Techniques of Measurement

X-ray intensity measurements with the microprobe can be

affected by several sources of error; the technical

difficulties have been underestimated even by experienced

operators. It was therefore deemed necessary to investigate

the effects of spectrometer alignment, of defocusing of x-ray

optics, of poor electrical conductivity of the specimen, and

55
&EYE PIECE TUBE

OF OPTICAL SYSTEM

OF MICROPROBE

(A)

6 h n (s u t9 n /10 y y ], \

RtO R9 R8 R7 R6 R5 R4 R3 R2 Rl

12 PIN SOCKET ®1

500 TO 2200V DC FROM ATTENUATOR NETWORK x<5

SIGNAL OUT

Figure 2j5. Cathodoluminescence detector (A)

Physical layout of photomultiplier

tube for cathodoluminescence. (B)

Wiring diagram of photomultiplier

tube connected to external voltage

divider network. (Rl = 200 kohms,

1/2 W, ifo: R2 thru Rll = 100 kohms,

1/2 W, Ifoj.

of similar factors of disturbance. The discussion within

the Washington Probe Users Group of such sources of error

has been most helpful. A source of concern was the experimental determination of coincidence losses in the x-ray

detector systems. The conventional techniques using double

sources or multiple absorbers cannot be employed for

instruments in which the x-ray spectrometers are enclosed

in the vacuum chamber. Two techniques for the determination

of coincidence losses in such instruments were developed in

56
cooperation with H. Yakowitz and D. Vieth, [16], Metallurgy

Division, NBS. These techniques are based upon the

simultaneous measurement of intensities from two spectrometers,, or from one spectrometer and target or monitor

current

2. Parameters Employed in Correction Calculations

Experimental data on x-ray mass attenuation coefficients

reported recently by G. 0. Hughes and J. B. Woodhouse [17]

showed good agreement with previous predictions, on the

basis of interpolation, by Heinrich [18], However, in many

areas further experimental data are sorely needed,

, 2: particularly in the long wavelength region. Therefore, this

laboratory has started action to collect experimental data,

to encourage cooperative effort among laboratories [19 ] 3 and to prepare for a revision of the tables issued

previously [18], including new experimental data, using

improved interpolation procedures, and extending the range

of wavelength. If more personnel becomes available, this

should be complemented by experimental measurement of mass

attenuation coefficients in selected regions of absorbers

and wavelengths. It is not expected that this work will

produce a tabulation during the next fiscal year.

Studies of the factors contributing to target current

formation, initiated at a previous location [15]* were

brought to a conclusion and reported at the Fourth

International Conference on X-ray Optics and Microanalysis.,

Or say (France) [20] September 1965 . It was shown that the

measurement of electron backscattering coefficients with the

aid of the electron probe is feasible if the measurements

are corrected for the effects of low energy electrons. The

back-scatter coefficients of 23 elements were measured at 10,

20, 30, 40, and ^9 keV. Data presented at the same conference by Bishop [21] are in good agreement with those obtained

57
at NBS (figures 2k, 25). Reasonable agreement exists also

with data found recently by two other authors [22 , 23].

.50

.40 -

.30 -

.20 -

.10 -

• BISHOP

o HEINRICH

1

20 30 40 50

ATOMIC NUMBER

60 70 80 90

Figure 2k, Electron backscattering coefficients

obtained by Heinrich [20] and by Bishop

[21].

n r

10 20

O HEINRICH

-O O u

—O Ag

30 40 50

Figure 25. Variation of electron backscattering

coefficients as a function of electron

energy.

58
honsequently, the backscatter coefficients within the energyrange of microprobe analysis can now be considered well

known. It would be of great interest to proceed to measure

the energy distribution of back-scattered electrons in an

instrument such as used at the Cavendish Laboratory, in

Cambridge, England by Green [24] and by Bishop [21].

The errors in the calculation of the absorption

correction were investigated in cooperation with H.

Yakowitz, Metallurgy Div., NBS [25], Such errors arise due

to errors in the input data used in the calculation (mass

attenuation coefficients, x-ray emergence angles, and electron accelerating voltages) and to the imperfection of the

models of the function f ( x) used in the calculation. The

results of this investigation can be summarized as follows:

a. Experimental data concerning the absorption

losses of radiation emergent from the target show mutual

agreement where measurements by more than one author are

available. However, the quantity of available experimental

data is insufficient.

b. Of the generalized models tested, that

proposed by Philibert and modified by Duncumb and Shields

[26] is the most satisfactory. None of the models, however,

is free of significant systematic errors.

c. The extent to which errors in input data can

affect the absorption correction has not been fully

recognized in the past. It is improbable that significant

improvement of the accuracy of quantitative microprobe

analysis will be achieved — particularly at longer wavelengths — until our knowledge of data such as the mass

attenuation coefficients is significantly increased. This

is particularly true when low x-ray emergence angles are

used. Some effects that have been attributed to the "atomic

number effect" can be explained entirely by uncertainty in

the absorption correction.

59
5. Non-dispersive Analysis

The use of the non-dispersive detector in mlcroprobe

analysis has been demonstrated by Dolby [27] and by Birks

[28], Its application in combination with multichannel

pulse height analysis is particularly attractive. As a

starting point,, a neon filled proportional detector was

employed. This yields very simple spectra due to the

absence of significant escape peaks. Shifts by one unit of

atomic number produce appreciable changes in the spectra

(figure 26).

Figure 26. Pulse-height spectra obtained

with a sealed neon-proportional

detector

.

However , the sensitivity of this detector for radiation of

wavelength shorter than 2a is very low. Further studies

with detectors covering a wider wavelength range are

planned.

One obvious application of such detector systems is

the rapid qualitative comparison of different points on a

60
specimen. This technique should also be useful for. electron

earn scanning procedures where the defocusing effect of

curved cyrstal spectrometers is objectionable.

4. Progress in Scanning Techniques

A study of the limits of quantitative evaluation of

electron beam area scans has been started. It greatly

xpedites the analysis of specimens requiring measurements

t many points , if the sp'eed of the area scanning technique

an be combined with a quantitative evaluation of the signal

received, as proposed in the concentration mapping [14, 15]

method . A similar procedure is the aforementioned grid

istep-wise scan of the beam with storage in the memory of

the multichannel analyzer of the counts obtained at each

point (figure 18)* The accuracy of these procedures is

'limited by the statistics of random pulse arrival, by

defocusing of the x-ray optics , and by difficulties of

calibration of systems containing more than two components.

"While a general solution of the problem might be difficult

to obtain, there are possibilities of applications under

restrictive conditions.

The limitations of the general case are presently under

investigation. Special techniques designed to overcome

some of these limitations will be investigated soon.

5. Literature Research

An index of literature on x-ray spectrometry and

electron probe microanalysis, issued privately for several

years, has been published in the Proceedings of the Microprobe Symposium held in Washington, in October 1964, by the

Electrochemical Society [29], Material for a supplement

to this bibliography, to be issued by the NBS in the next

fiscal year, is being collected and indexed. This task,

as well as a great part of the recent experimental work, was

performed by Mrs. M. A. Morris Giles.

(K.F.J. Heinrich)

61
5. SPARK SOURCE MASS SPECTROMETRY

The spark source mass spectrograph is established as a tool for the analysis of solids for elements present at the

parts-per-billion (ppb) level. Without standards, semiquantitative analyses good to within a factor of three can

usually be obtained; with analytical standards accuracies

as good as ± 20$ are obtainable. The only major inherent

interferences of the instrument are from the gases in the

source (C, Op, Np, CO, etc.) at about 1 to 10 ppm. However,

it should be possible to lower the pressure of these gases

by use of special source pumping and sample treatment. The

interferences that are associated with the sample itself are

caused by multiply charged ions of the matrix material

obscuring lower mass elements. Most of the high purity

metals examined by the spark source mass spectrograph have

also been examined by the optical emission spectrograph.

Since the two techniques do not normally have the same

interferences, the emission spectrograph can often supply

results for the elements which have interferences on the

spark source mass spectrograph. Between the two methods a complete analysis can be obtained for almost all samples.

Work with the spark source mass spectrograph during

the period covered by this report included an extensive

investigation in the area of data computations, the analysis

of a number of high purity metals, and instrument

modifications aimed toward increasing detection sensitivities. A recent progress report of our group [2]

contains detailed equipment descriptions of the equipment

modifications made up to this year.

A. Electronic Analog Computer ror Measuring IntensityAreas of Peaks» The need to correct for variations in peak widths on

mass spectrographs plates is a generally recognized problem

62

i
[J>0 , 3>1]. Basically the information needed is the • total

number of ions which produce a given mass line. Due to

variations in line widths and shapes between the matrix

lines and impurity lines, plus variations of these across

the photographic plate, the maximum peak intensities are not

a valid measure of the number of ions producing the different peaks. In addition to line width variations with mass

there will be changes upon repairing and refocussing of an

instrument , and there will certainly be differences in line

widths between two instruments. Because of these variations

in widths, maximum peak intensity measurements cannot be

used to undertake any long term study of elemental sensitivity factors in various matrices or to compare these data

among laboratories. The intensity-area of a peak is a

valid measure of the number of ions causing a line and would

be unaffected by variations in both line width and shape.

An intensity-peak area can be measured in several ways:

peak width at one-half intensity multiplied by maximum

intensity, a point by point rep lot ting of the percent

transmittance ($T) peak as an intensity peak followed by

graphical integration, collection of many ^T values for each

peak combined with the digital computer computation of peak

area, or the use of an analog computer system. Based upon

consideration of speed, accuracy, and cost, the analog

computer system was selected. A commercial instrument

using an analog system is available. However, we were

unable to determine if it would perform exactly as required

by our needs. It was therefore decided to build an analog

computer to our own specifications. Basically the unit is

simple; a slave slide wire on the microphotometer recorder

to retransmit the % absorption signal, a function generator

with an input of % absorption and an output of intensity,

a means of subtracting the plate background signal after

it has been converted to intensity, and an Integrator to

63
measure the area of the intensity peak. The detailed

wiring diagram of the finished equipment is shown in

figures 27 and 28.

RECORDER

.SLIDE WIRE

1700 F^

i VWWVW^ 1 ___ OFF

-t| <vOU/vJ tf* o

*FB- STRETCH ^FACTOR

5K

1.35 V

I.5K I—VNA/V

ik 7 iok y

^-RESET & r STBY

DV-4

BACKGROUND

CORRECTION

Figure 27. Wiring diagram for analog computer.

The most critical component of the system is the

fucntion generator which must electronically reproduce

the response curve of the photographic plate.

64
1/2 A PILOT LIGHT

110V AC -o*~o

ON OFP

PHILBRICK REGULATED POWER

SUPPLY PR - 30C

POWER WIRING DIAGRAM

AMPLIFIERS

I, II, III

BACKGROUND

CORRECTION

PHILBRICK OPERATIONAL AMPLIFIER I - P6SAU

II - P6SAU

III - P2SA PHILBRICK AREITRARY FUNCTION TRANSCONDUCTOR TYPE - SPFX-N

Figure 28. Power supply wiring for analog,

computer.

We were able to obtain the loan of a prototype

transistorized function generator from Philbrick Researches,

Inc This unit is considerably simpler and more amenable

to our specific requirements than the older tube-type

function generators previously available.

Figure 29 illustrates the ability of the function generator to reproduce the desired photographic plate response

curve. The error in the output of the function generator is

plotted vs the % absorption input. The upper curve is the

original curve with the triangular points being the set points

used to introduce the curve into the function generator.

65
+ 2 % -

+ I % -

a.

a.UJ- I % -

+ I % -

a.o o

(T

<K

UJ- I % -

ORIGINAL CURVE

30 40 50 60 70

% ABSORPTION

^—FUNCTION GENERATOR SET POINTS

90 100

Figure 29. Error in the output of the function

generator versus the % absorption

input

.

A positive bias was thus introduced which gave an average

bias of +Vfo at 80$ absorption. The set points were readjusted low by one-half the error found previously to give

the lower graph. This plot shows no net bias, with errors

less than ifo at any input. At approximately 87$ absorption

the function generator is no longer capable of reproducing

the function as is indicated by the upper graph.

66
Area measurements were made on the isotopes of tin from

a "six nines" pure sample. The results are shown in figure

30, There is a linear relationship between the area measured

AREA VS ABUNDANCE

Sn ISOTOPES

10

1 —

100 PEAK AREA

1000

Figure 30. Area measured for isotopes of

tin versus their isotopic abundance.

and the abundance of the tin isotope. In general, the

deviations from the straight line response corresponded to

less than a 5$ error. The areas were measured from peaks

ranging from 6 to 80$ absorption.

In order to prove the ability of area measurements to

compensate for changes in peak widths, the instrument was

deliberately defocused to change the widths. Fourteen equal

67
exposures were made on a doped platinum sample s seven with

the instrument focused, seven with it defocused. Both

maximum peak intensities and area measurements were made on

the focused and defocused exposures using the same

photographic plate exposure curve. The results of these

measurements are shown in table 9* Listed in the first

Table 9« Area measurement compensation for

changes in peak widths . (l4 equal exposures — of doped Pt7 focused, 7 defocused)

Ratio of focused to unfocused values

Intensity Area

Pb 208 1.43 ± 18$* 1.00 ± 16#*

Pt 190 1.40 ± 10fo „91 ± 5.9^

Ag 107 1.74 ± 24$ 1.00 + l8#

Pd 106 I.85 db l4# .99 ± 13%

Zr 90 2.17 ± 19^ 1.10 ± 21$

Cu 65 1.88 ± Ikfo 1.08 ± 1%

Fe 56 1.66 ± Yjfo 1.07 + 10$

Al 27 1.64 ± 9.6$ 1.16 ± 8.7$

Mg 26 1.46 ± 13$ 1.11 ± 11$

*$ Standard deviation.

column are the ratios of the average peak intensity of the

focused lines divided by the average peak intensity of the

defocused lines. The deviations from a value of 1.00

indicate how much the changes in peak width brought about

by defocusing have affected the maximum peak intensity

readings. The second column was computed from the same

peaks except that the peak areas were measured instead of

peak intensities. All of the data were within the 2

limits of the ratio of 1.00 indicating that the area measurements have completely compensated for changes in peak widths.

68
The cost of the parts necessary to build this analog

omputer is approximately $500 excluding the recorder and

igital voltmeter. The unit can be built in about one week

y a person with some practical experience with electronics.

etailed operating instructions for the unit plus other

undry information will be made available upon request to

ny persons interested in building a similar unit.

Analysis of High Purity Materials

Within the past year multiple samples of "six nines"

inCj copper, gold., tungsten and tin have been analyzed.

is an example, the results for one of six zinc samples are

,iven in table 10.

Table 10. Analysis of zinc bar.

(A) Impurities found — ppm by weight.

W Cd Ni Fe Cr Ca* K*

0.3 0.05 0.06 0.05 0.01 0.006 0.03

CI Al* Na*

0.1 0.004 0.01

*These elements are probably surface contamination.

(B) Limits of detection for elements with interference — ppm by weight

(These elements were not detected in the sample)

Au Pt Ta Nb Se Ga Gu Co

7 0.2 200 0.1 0.1 0.6 13 0.03

S Si Mg N C

13 0.05 0.001 6 15 1

From table 10A it is seen that the total detected

mpurities come to less than 1 ppm; it is therefore

ossible for the sample to be six nines pure. The

Information in table 10B tells what is not known about

:he sample. It should be mentioned here that this sample

69
was also analyzed by optical emission spectrometry and

activation analysis. From these techniques lower values

for Auj Cu, and Ta were reported which superseded the

values listed in table 10B. However, the mass spectrograph^ numbers on C, 0, N, and S were the only ones

available. The combined total of the detection limits of

these four elements is 35 ppm. This points up the fact

that improvement in technique to lower the detection limits

for the common gaseous elements is needed for more

definitive measurement of total impurity.

C. Instrument Modifications

A manufacturer's modification kit to increase the

instrument detection sensitivity was being installed and

adjusted at the end of this year. The kit consists of a unit to provide a higher accelerating voltage (24 kV to

replace the old 15 kV) s wider slits throughout the analyzer

section, plus other auxiliary equipment made necessary by

the use of 24 kV in the source.

Based on the manufacturer's claim of a 10-fold increasin detection sensitivity with the conversion kit and our

present detection limits of about 100 parts per billion

(ppb), we should now be able to detect elements as low as

10 ppb.

Unfortunately the increased sensitivity will apply not

only to specific mass lines which are of interest, but also

to many of the sources of plate background. One of these

backgrounds is a general darkening across the photographic

plate caused by gas scattering and charge exchange

collisions within the magnetic sector. This background is

directly related to the pressure in the magnetic sector.

Since this background has been observed on photographic

plates obtained at 15 kV (100 ppb detection limits), it was

70
oncluded that it would partially degrade the 10-fold

ncrease in sensitivity unless the pressure in the magnetic

ector could be lowered. It should be noted that this

ackground doesn't cover the entire mass range,, but only a .imited range determined by the mass of the major

.onstituent of each sample. Because of the very low gas

conductance between the magnetic sector and its source of

.ramping at the electric sector (5A and 5B of figure 31) >

5B 5

ELECTRIC

SECTOR

MAGNETIC

SECTOR

1. SAMPLE ELECTRODES

2. FIRST APERTURE

3. SECOND APERTURE

4. OBJECT SLIT

5. ELECTRIC SECTOR ENTRANCE SLIT

5A. 200 L/S ION PUMP

5B. NEW PUMPING PORT- 400 L/S

6. ELECTRIC SECTOR EXIT SLIT

7. MAGNET SHUNT

8. BEAM MONITOR ELECTRODES

9. ENERGY RESOLVING SLIT

10. PHOTOGRAPHIC PLATE MASK

11. 50 L/S ION PUMP

( DRAWING NOT TO SCALE)

Figure 31. Diagram showing position of major

components of mass spectrograph.

71
it has been assumed that the pressure in the magnetic sector

could be as much as 100 times higher than the 4 x 10

torr registered at the 200-liter per second ion pump at

position 5A of figure 28. A 50-liter per second ion pump

has just been added at position 11 of figure 28 to provide

high conductance pumping to the magnetic sector. During

the time the system has been pumping down the currents

drawn by the ion pumps have indicated pressures 20 times

higher at the magnetic sector (position 11) than at the

electric sector (position 5A). With the pressure still

lowering at this time, the magnetic sector reads 8 x 10

torr as compared to 4 x 10 torr at the electric sector.

In a previous progress report [2] we reported the

replacement of the stainless steel sample holders, the first

aperture (No. 2 in figure 5 ) .> and the second aperture (No. 3

in figure 28) with parts made of tantalum in order to remove

a source background of iron, chromium, and nickel. In the

period since these parts were replaced with tantalum a number

of "six-nines" pure materials have been run and in all cases

from 0.1 to 0.05 ppm of iron has been found. Most of these

same samples have also been analyzed with an emission

spectrograph and the results either indicated the presence

of iron or reported minimum detection limits higher than the

amount of iron found by the spark source mass spectrograph.

For the latter case it is not known whether the iron found

by the mass spectrograph represents a true impurity content

or a small residual background from other stainless steel

source parts. In order to further elucidate this question

of source background a series of exposures was made of a high purity gold sample containing very little tin. These

exposures were made with a source which had been thoroughly

coated with tin from a previous analysis. The parts already

known to be sources of background (all the Ta parts listed

72
,

eviously) were first replaced with clean parts , a ximum exposure was made on the gold sample , and then the

maining source parts were replaced stepwise with cleaned

arts (with subsequent exposures of the gold) until all the

ource had been cleaned. By observing the apparent tin

ontent of the gold for the various exposures, probable

ources of background were pinpointed. From these and

revious experiments the following general and to some

xtent obvious rules governing the sources of stainless

t eel background can be drawn.

1. Background comes from parts in-line-of-sight from

e sample spark, or to be more exact from parts bombarded

ions from the spark.

2. The closer a part is to the spark, the more the

ackground.

j5. Parts at ground potential are a much larger source

f background than parts sitting at the accelerating voltage

ni.e., the potential of the sample electrode).

It was found that the object slit (No. 4 of figure 28),

he supports holding the Ta sample jaws, and the grounded

arts behind the sample were probable background sources,

arts at the accelerating voltage more than 1 in. from the

park supplied no background.

A tantalum object slit and tantalum pieces to shield

11 parts behind the sample jaws have been fabricated for the

.ew source coming with the 24 kV conversion kit. They will

e evaluated as soon as the conversion kit is made

perational. What is actually needed is a sample, independently certified to contain less than 10 ppb of iron,

i'hich can be used either to prove a lack of iron background

.n the instrument or to track down all the sources of

ackground.

(P. J. Paulsen, P. E. Branch)

73
6. ANALYSIS OF HIGH PURITY MATERIALS: ENRICHMENT BY

ELECTRODEPOSITION

High purity materials are being produced with a total

impurity content of less than one ppm. Technologically

important in such diverse fields as metallurgy, nuclear

engineering, and semiconductor physics, these materials

contain trace elements that significantly affect their

properties. To determine these elements and evaluate their

individual and collective effects on physical properties

requires reliable analytical methods and standards.

For trace constituents at the sub-ppm level, the

development of standard reference materials is a formidable

problem. The production of materials with a homogeneous

distribution of the desired trace elements is an essential

requirement. The degree of homogeneity attained will

determine the minimum sample size and the analytical

techniques for which the sample is useful.

A. Analysis Problems

To analyze proposed Standard Reference Materials,

analytical methods are selected for suitability as primary

standardization procedures. Since almost all trace analytical methods are comparative methods, the errors inherent

in preparing the synthetic or comparison standards must be

evaluated.

Although many elements at concentrations of less than

one ppm are below their spectrographic limits of detection,

they can be determined by using preliminary chemical concentration procedures. The reliability of the enrichment

procedure and the synthetic standards determine whether the

combined preconcentration-spectrochemical method can serve

as a basic standardization procedure. In most of these

methods, the separated trace elements have been incorporated!

into a small amount of another high purity substance acting i 74
b a "collector" or "gatherer" and then excited with the

irect current arc. However, since this excitation source

as poor precision, the copper [32] and graphite spark [33]

echniques, which do have both high precision and high

^solute sensitivity, would be particularly attractive for

xciting trace elements obtained from preconcentration

rocedures. However, if the selected procedure produces

n appreciable amount of residue to be transferred to the

lectrode surface, the electrical discharge dislodges the

esidue. Consequently for these spark techniques, it is

ot advisable to use a collector matrix for bulk. If a

: ollector is not used and the trace constituents are

resent alone as an extremely dilute solution, serious

osses can occur by any of several mechanisms grouped under

he generic term "sorption losses." This is particularly

rue if the solution is to be evaporated to a small volume

.nd transferred to the electrodes. The evaporation step

ilso increases the possibility of contamination.

5. Electrodeposition as an Enrichment Method

A preconcentration process by electrodeposition would

oe expected to minimize errors of this type since elements

laving suitable electrodeposition potentials are deposited

lirectly on the cathode from a concentrated solution of the

natrix. The cathode can serve as the electrode for

spectroscopic excitation.

In comparison to most preconcentration procedures,

slectrodeposition would appear to be less subject to contamination errors. A minimum number of reagents are

Bmployed, sometimes only an acid to dissolve the material

and an electric current as a reducing agent. Since the

'process is conducted in a small cell and extensive manipulations are not involved, a clean environment of limited

size is easily provided. Other merits of the electrodeposition process are: its capability of multi-element

75
separation from the matrix permitting multi-element

determinations by spectrochemical techniques and its

general applicability to diverse analytical problems.

Mark and Berlandi [>4] demonstrated the usefulness of

controlled potential electrodeposition using pyrolytic

graphite in neutron activation analysis. In a later article

Vassos, et al [35] described some of the conditions for

quantitatively depositing microgram to milligram amounts

of gold, silver, cobalt and copper. The authors wrote,

"Unfortunately because little is known about the principles

of electrodeposition on graphite, the pretreatment procedure

arrived in this study may seem like witchcraft ..."

G. Current Research

In our laboratory the feasibility of electrodeposition

as a preconcentration technique for spectrochemical analysis

is under investigation. It was considered necessary to

study the extent of deposition at the submicrogram level,

the adherence of the deposit and whether its distribution

on the electrode surface was sufficiently uniform. By the

use of high-specific activity radioisotopes, it was found

that for submicrogram amounts of silver, from solutions

containing macro-amounts of zinc, 99$ of the total silver

could be electrodeposited onto the surface of 1/4 inch

spectroscopic, graphite electrodes. The deposit was sufficiently adherent to allow removal of the matrix solution

by washing, and the deposit was distributed sufficiently

uniformly on the electrode surface to permit proper

sampling by the high voltage spark.

Using the same zinc solution, submicrogram amounts of

cadmium did not deposit on graphite. However, since other

electrode materials can be employed in high-voltage spark

procedures, cadmium was deposited on the surface of mercuryplated copper electrodes. The deposition was not as

76
quantitative as for silver. A combination of electrode

material and controlled potential makes this a rather

•versatile method for separations.

A technical paper on this subject entitled, "Electrodeposition of Trace Constituents as an Enrichment Method

«!for Spectrochemical Analysis" was presented at the Fifth

National Meeting of the Society for Applied Spectroscopy.

A written paper describing experimental details and data

is planned to be submitted for publication.

(R. Alvarez)

77
7. STANDARDS, ANALYSIS, AND LITERATURE ACTIVITIES

The Section provides analytical assistance to other

research groups at NBS, to other Government agencies, and

to the general public. These activities include (1) participation in the development of standard reference

materials, especially standards for calibration in spectrochemical analysis; (2) providing analyses in optical

spectrometry, x-ray fluorescence spectrometry, electron

probe microanalysis , and spark source mass spectrometry; ancj

(5) providing literature surveys in these fields through

bibliographies and critical reviews.

A. Standard Reference Materials

1. Standards Program

The program of standard reference materials and

calibration in spectrochemical analysis has been a major

activity of the Section. The output of this program has

consisted of standard reference samples with certified

composition, and the determination of information on

applying the reference samples, including methods of

analysis. In cooperation with the NBS Office of Standard

Reference Materials and the other Sections of the

Analytical Chemistry Division, the Section continues its

activity on the analysis of proposed reference materials.

The analysis of reference materials consists of two

phases, first, a study of homogeneity of the material, and

second, accurate analysis by two or more cooperators or

techniques. Homogeneity of the intended standard is

essential to its use, since each user should receive a specimen corresponding in analysis to the certificate

provided. In spectrochemical analysis the amount of

specimen consumed in an analysis may be of the order of a milligram or less and the analysis may be affected by the

physical state of the material. Consequently, much effort

78
las been devoted, in our Section to the design of optimum

procedures for study of homogeneity. For spectrochemical

analysis , experiments have been designed to obtain the

iiaximum of information from the minimum of testing, using

photoelectric spectrometers for high precision. The

Information is read out in the form of punched cards or tape

and submitted to a computer for statistical analysis of

the data. Analysis of variance serves appropriately for

determining that part of variation in concentration

attributable to segregation in the sample. Two large

photoelectric spectrometers are installed in our laboratory

primarily for homogeneity testing, although they are also

'used for general analytical service and research work.

These were described and illustrated in our 1965 progress

report [1],

The addition of the spark source mass spectrometer

[2] to our facilities provides a powerful tool for the

analysis of high purity materials.

Following the homogeneity studies, analyses, of proposed

standards are made in cooperation with other laboratories

in the Division. Here the spectrochemical analysis must

be made by a primary method relative to standards

synthesized from pure materials. The samples are converted

to finely divided powders or to solutions to homogenize the

sample and to provide a form for comparison with the

synthesized standards. Powders are usually analyzed by

arc excitation; solutions by the plasma jet, by atomic

absorption, or by a spark with the rotating electrode

technique. Analyses may also be made by x-ray fluorescence

analysis relative to synthesized standards.

2. Analyses Made of Standard Reference Materials

Analyses of standard reference materials during the

12-month period from June, 19^5 through May, 1966 included

79
204 samples, with 9H qualitative determinations and 3892

quantitative determinations, and 45 reports written.

A large part of this work was concerned with homogeneity studies, especially of ferrous alloys, with analyses

made on the photoelectric spectrometers. Studies were

performed on 15 steels: a Se steel, four basic open hearth

steels (llh, 13-gj 15gj and l6e), a Cr-V steel ^Of, and a test of added supplies of boron steel 827 and stainless

steels 845-850. In addition, survey semi-quantitative

analyses were made of these materials to ensure that all

significant elements were detected before final analyses

were made. Other studies made of ferrous alloys include

analyses of three cast irons for phosphorus relative to

well established standard cast irons, the determination of

Mn in a Ni-Cr cast iron by atomic absorption, and the

determination of Se in a steel by x-ray fluorescence. These

analyses were performed largely by D. M. Bouchette,

In the past the homogeneity studies were limited to

the metallic elements because of the lack of a vacuum

optical spectrometer for determinations in the wavelength

region below 2000A. Carbon, phosphorus, and sulfur lines

fall in this region.

With the cooperation of outside laboratories, Roanoke

Electric Steel Co., the Jarrell-Ash Co., and the Applied

Research Laboratory of the U. S. Steel Co., we were able to

use vacuum equipment for homogeneity studies for C, P, and

S. Analyses were made of B.0„H. steels llh and l6e, and CrV steel 50f for these elements* A vacuum spectrometer, now

on order, will enable our laboratory to perform these

analyses in the future.

X-ray fluorescence analysis is also employed in

homogeneity studies for metallic elements in alloys. In

80
his year the studies were applied to the analysis of non-

(.etallic materials , a flint clay 97& and a plastic clay

•8a, as described in section 3 of this report.

Homogeneity studies were made of three beryllium-

.opper alloys ; these were found to be acceptable and

tccurate determination of the impurities present are now

ander way by several laboratories. The elements to be

jietermined include Be, Go, Ni, Fe, Zn, Pb, Al, Sn, Si, Cr,

In and Ag. Procedures are being applied to determine all

}f these by emission spectrometric analysis relative to

standards synthesized from pure metals.

A large part of our efforts on standard reference

materials are now being applied to the analysis of

materials of high purity ("6 nines") or of intermediate

purity. Optical and mass spectrometric analysis were made

of high purity copper, gold, tungsten, tin, and zinc. As

pointed out in section 5 of this report, these two methods

complement one another especially on the serious problems

of identifying contamination.

For optical emission, a fractional distillation

technique involving the direct excitation of the sample as

the camera is being racked provides high spectral line-tobackground ratios. Many trace metallic elements most likely

to be found as impurities have excellent detectabilities

by this method.

The analysis of high-purity materials is a difficult

problem and may involve special sample handling and the

separation of impurities where possible. Enrichment

procedures are under study as described in section 6

of this report. Electrodeposition was applied as an

enrichment procedure in conjunction with the spectrographic

determination of copper and silver in zinc. An enrichment

procedure also was applied to the analysis of selenium, a 81
reference material of intermediate purity. Details of this

procedure are being worked out and will be reported later.

(B. F. Scribner, R. Alvarez,

M. Margo she s j M. M. Darr)

B. General Spectrochemical Analyses

Spectrochemical analyses are made of a wide variety

of materials to assist other NBS laboratories and other

Government agencies where their facilities are not capable

of doing the work.

1. Types of Analyses

The large bulk of analyses are rapid surveys by optical

spectroscopy in which 50 chemical elements are sought.

Ocasionally the rare earths and alkalies are included to

extend the list of elements to 70. In the analytical report

the concentrations of the elements found are given within

ranges of factors of 10, e.g. 0.001 to 0.01$, 0.01 to 0.1$

etc. This analysis often may provide sufficient information

for the problem; if not, it provides the basis for efficient planning of further quantitative analysis by spectrochemical or other methods.

Qualitative analysis may also be made by scanning

through the x-ray spectrum and this complements the optical

method* The x-ray method is less sensitive for some of the

metallic elements but more sensitive for metalloids and

halogens

.

Quantitative analyses are made by both optical and

x-ray fluorescence spectrometric methods using equipment

described earlier. The problem is relatively simple for

the analysis of metals and alloys when a solid sample with

a diameter of 1 to 2 cm is provided, and when adequate

reference samples are available. However, many samples are

in the form of powders, solutions, thin wires, or thin

films. In these cases the samples may be analyzed in the

82
rm of dry powders or solutions, relative to standard

mples synthesized from pure elements or salts.

For the analysis of high purity materials, the spark

ource mass spectrograph offers the advantage of detection

imits in the parts per billion range and is now being

pplied in analysis.

Spectrochemical methods in general may be considered

icro or semi-micro methods since a sample of 10 mg or less

iay suffice for the analysis » Recent developments in both

tical and x-ray analysis have reduced the required sample

ize to very small amounts thus extending the methods to

he sub-micro range. The laser probe consumes a sample

eighing about 0.1 jj,g and can provide information on 50 or

',Lore elements in this sample. The electron probe micronalyzer can analyze a volume of a few cubic microns

"1 q 'eighing a picogram (10~ g) or less. It also provides

emarkable information on the distribution and concentration

)f chemical elements in a surface. For further details on

:hese new analytical tools and service applications see

section 2 and section 4 of this report.

2. General Analyses Made

Spectrochemical analyses , other than those made of

standard reference materials, during the 12-month period

from June, 1965 through May, 1966 included 269 samples,

tfith 7837 qualitative determinations and Kyj quantitative

eterminations, and 102 reports written.

(E. K. Hubbard, R. Alvarez,

M M. Darr, D. M. Bouchette)

3. Literature Surveys

The problem of keeping up with the extensive literature

in spectrochemical analysis is being met by maintaining

reference files on the literature in the several fields.

These are optical emission, including flame photometry,

83
atomic absorption, x-ray fluorescence., electron probe microanalysis, and spark source mass spectrometry. To collect

information on the literature, systematic surveys are made

using Chemical Abstracts, Chemical Titles, and similar

sources. Final checking is made against selected journals.

Card files are maintained with the abstract typed or pasted

on 5 x 8 in. cards.

The references serve for the preparation of

bibliographies and reviews. Daring this year a biennial

review of emission spectrometry was prepared by Mar go she

s

and Scribner [36]. An extension of a bibliography on

emission spectrometry and a bibliography on electron probe

microanalysis are in preparation. The reference file

serves very well in planning programs of research, in

reviewing manuscripts, and answering inquiries.

(V. C. Stewart, M. Mar go she s. M. A. Giles, B. F. Scribner)

84
8. PERSONNEL AND ACTIVITIES

Personnel Listing

^ectrochemical Analysis Section

Bourdon F. Scribner, Section Chief

Prances L. Hi It en, Administrative Aid

Group I. Optical Spectroscopy

Marvin Margoshes, Chemist

Claude Veillon, NBS-NRC Post Doctoral Research

Chemist

Martha M„ Darr, Chemist

Elizabeth K. Hubbard, Physicist

Stanley D. Rasberry, Physicist

Daniel Marcellus, Chemist (Summer Student 1966)

Doward M. Bouchette, Physical Science Technician

Group II. X-Ray Spectrometry and Electron Probe

Microanalysis

Kurt P. J. Heinrich, Chemist

Mary Ann Giles, Chemist

Detlef F. Gerlach, Chemist (Summer Student 1965)

Gerald A. Wolfson, Electronic Technician

Part Time Guest Workers:

Harvey Yakowitz, Metallurgist, NBS Metallurgy

Division

Donald L. Vieth, Physicist, NBS Metallurgy Division

John D. Eick, Chemist, Dental Research Group

Group III. Spark Source Mass Spectrometry

Paul J. Paulsen, Chemist

Paul E. Branch, Physical Science Technician

Group IV. Enrichment Techniques

Robert Alvarez, Chemist

Group V. Literature Survey

Virginia C. Stewart, Chemist

85
B. Publications

1. Dilworth, H. C.

Spectrochemical Analysis of High-Temperature Alloys

by Spark Excitation in Argon and Nitrogen.

American Society Testing Materials Special Technical

Publication No. 376, Philadelphia, 1965.

2. Heinrich, K. F. J.

X-Ray Optics and X-Ray Microanalysis.

Book Review, American Scientist 53j> 382A (1965)

3. Scribner, B. F. (Editor)

"Spectrochemical Analysis: Optical Spectrometry,

X-Ray Fluorescence Spectrometry, and Electron Probe

Microanalysis Techniques, July 1964 to June 1965j>

NBS Technical Note 272, Oct. 21, 1965.

4. Heinrich, K. F. J.

Identification of Inclusions with the Electron Probe

Microanalyzer

.

American Society for Testing and Materials, Special

Technical Publication No. 393j> Philadelphia, Pa.,

Jan. 1966.

5. Heinrich, K. F. J.

An Outline for Cooperative Action on the Determination of X-Ray Mass Attenuation Coefficients in the

Wavelength Range from 0.5 to lOOf (25 to 0.12 keV)

,

NBS Technical Note 284, Feb. 21, 1966.

6. "Veillon, C, Mansfield, J. M. , Parsons, M. L. , and

Winefordner, J. D.

The Use of a Continuous Source In Flame Fluorescence

Spectrometry, Anal. Chem. ]&, 204 (1966)0

7. Paulsen, P. J., and Branch, P. E.

Spark Source Mass Spectrograph Program, July 1964

to June 1965, NBS Technical Note 286, April 15, I966,

8. Margoshes, M. and Scribner, B. F.

Emission Spectrometry (A Review)

Anal. Chem. 358, No. 5.. 297R-3HR (1966).

9. McKinley, T. D. , Heinrich, K. F. J., and Wittry, D. B.

(Editors

)

The Electron Microprobe — Proceedings of a

Symposium on Electron Probe Microanalysis, ElectroChemical Society, Washington, Oct. 1964, New York,

John Wiley & Sons, 1966

86
Heinrich, K. F. J.

X-Ray Absorption Uncertainty

The Electron Probe — Proceedings of a Symposium

on Electron Probe Analysis.

Electrochemical Society, Washington, Oct. 1964

New York, J. "Wiley & Sons (1966) pp. 293-377-

Temple, A. K. , Heinrich, K. F. J., and Ficca, J. F., Jr

Quantitative Electron Microprobe Analysis of

Ilmenite Ores.

The Electron Probe' — Proceedings of a Symposium

on Electron Probe Analysis, Electrochemical Society,

Washington, Oct. 1964

New York, J. Wiley & Sons 1966, pp. 784-790.

Heinrich, K. F. J.

Electron Probe Microanalysis

"Lectures on Modern Techniques in Solid State

Research"

Garden & Breack, 150 Fifth Ave., New York,

(In Press)

Margoshes, M.

Recent Advances in Excitation of Atomic Spectra.

Proceedings of the Xllth International Spectroscopy

Symposium,

Exeter, England (1965). (In Press)

Rasberry, S. D. , Scribner, B. F., and Margoshes, M.

Characteristics of the Laser Probe for Spectrochemical Analysis (A Summary)

Proceedings of the Xllth International Spectroscopy Symposium.

Exeter, England (1965). (In Press)

Margoshes, M.

Excitation and Ionization in Arc and Spark

Excitation Sources.

Appl. Spectry. (In Press)

Scribner, B. F.

Advances in Excitation Sources for Spectrochemical

Analysis. XXth International Congress on Pure and

Applied Chemistry, Moscow (1965).

Pure and Applied Chemistry. (In Press)

87
17. Heinrich, K. F. J.

Correction for . Non-Linearity of Proportional

Counter Systems in Electron Probe X-Ray Microanalysis , Advances in X-Ray Analysis , 9 (1965) 3 New York, Plenum Press (In Press).

18. Heinrich, K. F. J.

Electron Probe Microanalysis by Specimen Current

Measurement. Proceedings , Fourth International

Congress of X-Ray Optics and Microanalysis, Orsay,

France, I965. (In Press).

19. Eick, J. D.j Caul, H* J., Smith, D. L., and

Rasberry, S. D.

Analysis of Gold and Platinum Group Alloys by

X-Ray Emission with Corrections for Interelement Effects, Appl. Spectry. (In Press).

20. Margoshes, M„, and Scribner, B. F.

Eastern Analytical Symposium, I966

(Meeting Report), Appl. Optics (In Press).

88
Talks Given

Margoshes, M. , "Recent Advances in Excitation of

Atomic Spectra," XII International Spectroscopy

Colloquium, Exeter, England, July 12, 1965

Margoshes, M. , "Characteristics of the Laser Probe

for Spectrochemical Analysis," XII International

Spectroscopy Colloquium, Exeter, England,

July 13, 1965.

Scribner, B. F., "Advances in Excitation Sources for

Spectrochemical Analysis," Plenary Lecture, XXth

International Congress of Pure and Applied Chemistry,

Moscow, July 14, 1965

Scribner, B. F., "Current Research of the NBS

Spectrochemical Analysis Section," All Union

Mendeleev Institute of Metrology, Leningrad,

U.S.S.R. , July 21, 1965.

Heinrich, Kurt F. J., "Correction for Non-linearity

of Proportional Counter Systems in Electron Probe

X-Ray Microanalysis."

Denver Research Institute, University of Denver,

August 25, 1965.

Rasberry, S. D. , "Application of the Laser Probe in

Spectrochemical Analysis," Fourth National,

Meeting, Society for Applied Spectroscopy,

Denver, Colorado, August ^>1, 1965 • Margoshes, M., "Selection of Wavelengths for Atomic

Absorption Spectrometry," Fourth National Meeting,

Society for Applied Spectroscopy, Denver, Colo.,

Aug. 31, 1965.

Scribner, B. F., "Atomic Emission Spectroscopy:

Arc Spark and Plasma Jet," 150th National

Meeting, American Chemical Society, Atlantic

City, N. J., Sept. 14, 1965

Heinrich, Kurt F. J., "Electron Probe Microanalysis

by Specimen Current Measurement," Fourth International Congress of X-Ray Optics and Microanalysis, Orsay, France, Sept. ±J , 1965.

89
10. Heinrich, Kurt P. J., Registration methods of scanning

electron probe microanalysis. Conference of

Austrian, Hungarian, and Jugoslav Analytical

Chemists, Graz, Austria, Oct. 1, 1965.

11. Paulsen, P. J., "Examples of Analysis of High Purity

Materials on NBS Spark Source Mass Spectrograph--

Gold, Tantalum, Zinc, Tungsten, and Platinum,"

Ninth Annual Conference on Analytical Chemistry in

Nuclear Technology, Gatlinburg, Tenn., Oct. 12, 1965.:

12. Veillon, Claude, "Atomic Fluorescence Spectrometry"

University of Maryland Department of Chemistry

Seminar, College Park, Md., Jan. 7, 1966.

13. Rasberry, S. D., "Aspects of Laser Probe Excitation

for Quantitative Spectrochemical Analysis,"

Eastern Analytical Symposium, New York City,

November 18, 1965.

14

.

Veillon, Claude, "Atomic Fluorescence Spectrometry,"

American Chemical Society Winter Meeting, Phoenix,

Ariz., Jan. 17 , 1966.

15. Heinrich, Kurt F. J., "Advances in Electron Microprobe Analysis," Baltimore-Washington Section,

Society for Applied Spectroscopy, Baltimore, Md.,

Feb. 15, 1966.

16. Rasberry, S. D., "Applications of Time-Shared Computers

in Spectrochemical Analysis." Pittsburgh Conference

on Analytical Chemistry and Applied Spectroscopy,

Pittsburgh, Pa., Feb. 23, 1966.

17. Rasberry, S. D., and Margoshes, M., "Applications of

the Time-Sharing Computer System in the Analytical

Chemistry Division, " NBS Analytical Chemistry

Division Seminar, March 2, 1966.

18. Margoshes, M., Rasberry, S. D., "Use of the GE-265

Time-Shared Computer, " NBS Analytical Chemistry

Division Seminar, March 9, 1966.

19. Heinrich, Kurt F. J., "Electron Probe Microanalysis

of Metallurgical Specimens," American Society for

Metals, Philadelphia, Pa., March 15, 1966.

90
Heinrich, Kurt F. J., "Quantitative Electron Probe

Analysis i Absorption Correction Uncertainty,

First National Conference on Electron Probe Microanalysis. University of Maryland, College Park,

Md., May 4, 1966.

Margoshes, M., "Time-Sharing Computing in a Spectrochemical Laboratory," American Chemical Society

Meeting-in-Miniature, College Park, Md., May 6,

1966.

> I. Paulsen, P. J., "Electronic Analog Computer for

Measuring Intensity Areas on Mass Spectrographic

Plates," l4th Annual Conference on Mass Spectrometry

and Allied Topics, Dallas, Texas, May 24, 1966.

p» Margoshes, M. , "Temperature Profile of a DirectCurrent Arc in Argon," Fifth National Meeting,

Society for Applied Spectroscopy, Chicago, 111.,

June 17, 1966.

14. Margoshes, M., "Computer Calibration of Photographic

Emulsions in Spectrochemical Analysis," Fifth

National Meeting, Society for Applied Spectroscopy,

Chicago, 111., June 17, 1966.

;5. Alvarez, R. , "Electrodeposition of Trace Constituents

An Enrichment Method Prior to Spectrochemical

Analysis," Fifth National Meeting, Society for

Applied Spectroscopy, Chicago, 111., June 17, I966.

?6. Heinrich, Kurt F. J., "Scanning Electron Probe

Microanalysis," American Society for Testing

and Materials, Atlantic City, N. J., June 30, 1966.

91
D. Committee Activities

B. F. Scribner

Member, ASTM Committee E-2 on Emission Spectroscopy

Member, ASTM Committee E-13 on Absorption Spectroscopy;

Program Chairman, Eastern Analytical Symposium, 1965

Delegate to Governing Board, EAS, I966.

Titular member, Commission on Spectrochemical and othe

Optical Methods of Analysis, International Union of

Pure and Applied Chemistry

Member, Advisory Board, Spectrochimica Acta

Member, International Advisory Board, XIII Colloquium

Spectroscopicum Internationale, 1967

Chairman, Advisory Committee, Society for Applied

Spectroscopy, 1965

Chairman-Elect, Baltimore-Washington Section, SAS, 1966

Member, Wavelength Tables Committee, University of

Michigan

Technical Program Chairman, NBS Symposium on Trace

Characterization, 1966

Member, Analytical Standards Committee NBS

M. Margoshes

Delegate to Governing Board, Society for Applied

Spectroscopy, 1965-66

Chairman, Conference Committee, SAS, 1965

Member, Publications Committee, SAS, 1966

Member, Program Committee, and Chairman, Publicity

Committee, NBS Symposium on Trace Characterization,

1966

K. F. J. Heinrich

Chairman, Microprobe Task Group, ASTM Committee E-4

on Metallography

Member, Advisory Board, Mikrochimica Acta

R. Alvarez

Member, ASTM Committee E-2 on Emission Spectroscopy

S. D. Rasberry

Member, Laser Task Group, ASTM Committee E-2

E. K. Hubbard

Analytical Chemistry Division Newsletter

92
9 . ACKNOWLEDGMENTS

It is a pleasure to recognize the assistance from

roups and individuals who have aided our work in several

""ays. Assistance has been received from outside

aboratories as well as those in the NBS . For the optical spectrometric determination of carbon,,

sphorus^ and sulfur in- homogeneity studies of steels, we

eceived the generous cooperation of Mr. J. G. Staton of

he Roanoke Electric Steel Co., Mr. S. Smith of the Jarrell-

.sh Company, and Dr. J* K. Hurwitz of the Applied Research

'uaboratory, United States Steel Corp.

We are indebted to the U. S» Geological Survey, through

Tr. Harry J. Rose, for helpful advice and the use of their

'acilities in the x-ray fluorescence analysis of clay

samples.

Two members of the Metallurgy Division, Mr. Harvey

fakowitz and Mr. Donald L. "Vieth, have continued to aid in

providing metallurgical services and in making measurements

3f mutual interest with the microprobe. Mr. Louis Marzetta

Df the Electronic Instrumentation group has contributed

effectively to the design and construction of read-out

devices for the microprobe. Mr. Ronald W. Shideler,

electronic consultant in the Analytical Chemistry Division,

provided excellent suggestions for problems connected with

the multichannel analyzer.

Mr. George Marinenko, of the Microchemical Analysis

Section was very helpful on problems in electrodeposition.

Mrs. Frances L. Hilten, Administrative Aid in our

Section, performs a wide variety of duties essential to the

! smooth working of the Section. Her assistance in preparing

this and other reports is deeply appreciated. Our thanks

also are extended to Miss Sandra Beall who assisted in the

preparation of this manuscript.

93
10. LIST OF REFERENCES

1] Scribner, B. F., ed M "Spectrochemical Analysis:

Optical Spectrometry, X-Ray Fluorescence Spectrometry _, and Electron Probe Microanalysis Techniques.

July 1964 to June 1965," NBS Technical Note 272,

Oct. 3 1965.

2] Paulsen, P. J., and Branch, P. E.. "Spark Source Mass

Spectrograph Program, July 1964 to June 1965,"

NBS Technical Note 286, April, 1966.

3] Dartmouth College Computation Center, "A Manual for

BASIC," 1965. Available from Dartmouth College

Book Store, Hanover, N. H.

4] Kaiser, H., Speetrochim. Acta 2^ 159 (1948).

5] Corliss, C. H„, and Bozman, W. R. , "Experimental

Transition Probabilities for Spectral Lines of

Seventy Elements," NBS Monograph 53, U, S. Govt.

Printing Office, Washington, 1962.

6] Corliss, C. H., private communication.

7] Allan, J. E., Speetrochim. Acta J_5, 800 (1959).

8] Ostrovskii, Yu. I., and Penkin, N. P., Optika i

Spektr. 2. 195 (1957).

9] Cordon, C. L., Schlecht, ¥. G., Wichers, E., J. Res.

Natl. Bur. Standards 25; ^57 (1944).

'10] Eick, J D., Caul, H. J,, Smith, D. S., and Rasberry,

S. D. , Analysis of Gold and Platinum Group Alloys

by X-Ray Emission with Correction for Interelement

Effects, Appl. Spectry. (In Press).

11] Lucas-Tooth, H, J., and Price, B. J., Metallurgia

64 , 149 (1961).

12] Rose, H. J., Adler, I., and Flanagan, F. J., Appl.

Spectry. 17, 8l (1963).

'13] Heinrich, K. F, J., Advances in X-Ray Analysis, Vol.

7, pp. 325-339, New York, Plenum Press, 1963.

;i4] Heinrich, K. F. J., Rev. Sci. Instr., J^, 884 (1962).

94
.5.] Heinrich, K. P. J., Advances in X-Ray Analysis, Vol. 6,

pp. 291-300, New York, Plenum Press, 1962

.6] Heinrich, K. F. J., Vieth, D., and Yakowitz, H.,

Correction for Non-Linearity of Proportional

Counter Systems in Electron Probe X-Ray Microanalysis, Advances in X-Ray Analysis, Vol. 9,

New York, Plenum Press, 1965 (in Press).

.7] Hughes, G. D.j and Woodhouse, J. B., Determination

of Mass Absorption Coefficients, Proc. Fourth

International Congress on X-Ray Optics and Microanalysis, Paris, 1965. (in Press).

.8] Heinrich, K. F. J., The Electron Microprobe--Proceedings of a Symposium on Electron Probe Analysis,

Electrochemical Society, Washington, Oct. 1964,

New York, J. Wiley & Sons, 1966, pp. 296-377.

.9] Heinrich, K. F. J., "An Outline for Cooperative

Action on the Determination of X-Ray Mass

Attenuation Coefficients in the Wavelength Range

from 0.5 to 100& (25 to 0.12 keV)'J NBS Technical

Note 284 , Feb. 21, 1966, National Bureau of

Standards, Washington, D. C.

!0 ] Heinrich, K. F. J., Electron Probe Microanalysis by

Specimen Current Measurement, Proc. Fourth International Congress on X-Ray Optics and Microanalysis,

Paris, 1965. (In Press).

!1 ] Bishop, H. E., Some Electron Backscattering Measurements for Solid Targets, Proc. Fourth International

Congress on X-Ray Optics and Microanalysis, Paris,

1965. (In Press).

!2 ] Hutchins, G. A., The Electron Microprobe —Proceedings

of a Symposium on Electron Probe Analysis, Electrochemical Society, Washington, Oct. 1964, New York,

J. Wiley & Sons, 1966, pp. 390-404.

»3l Burkhalter, P. G., "Measurement of Backscattered

Electrons in an Electron Probe Microanalyzer,

Bureau of Mines Report of Investigations 6681 R.I.,

Bureau of Mines, U. S. Dept . of the Interior, 1965.

!4 ] Green, M., "The Efficiency of Production of Characteristic X-Radiation, " Thesis, University of

Cambridge, England, 1962.

95
[25] Heinrich, K. P. J., and Yakowitz, H., Quantitative

Electron Probe Microanalysis: Absorption Correction Uncertainty, Presented at the First National

Conference on Electron Probe Microanalysis

,

College Park, Md., 1966, (To be published).

[26] Duncumb, P., and Shields, P. K. , The Electron Microprobe—Proceedings of a Symposium on Electron

Probe Analysis, Electrochemical Society, Washington, Oct. 1964. New York, J. Wiley & Sons,

1966, pp. 284-295.

[27] Dolby, R. M., Proc. 3rd. Symp. X-Ray Optics and X-Ray

Microanalysis, Stanford, New York, Academic Press J

1963, pp. 483-493.

[28] Birks, L. S., and Batt, A. P., Anal. Chem. 35, 778-

782, 1963.

[29] Heinrich, K. F. J., The Electron Microprobe

Proceedings of a Symposium on Electron Probe

Analysis, Electrochemical Society, Washington,

Oct. 1964. New York, Wiley & Sons, 1966, pp.

841-10^0.

[30] Owens, E. B., and Giardino, N. A., Anal. Chem. 35,

1172 (1963).

[31] Cookson, G. C, Fletcher, W., and Tushingham, R.,

The Importance of Variations in Line-Width and

Emulsion Sensitivity in Spark Source Mass

Spectrography, Mass Spectrometry Conference, St.

Louis Missouri, May, 1965.

[32] Fred, M., Nachtrieb, N. H., and Tomkins, F. S., J.

Opt. Soc. Am. 37, 279 (1947).

[33] Morris, J. M. and Pink, F. X., Symposium on Spectrochemical Analysis for Trace Elements, ASTM

Special Technical Publication 221 , 39 (1958),

Amer. Soc. Testing Matls., Philadelphia.

[34] Mark, Jr., H. B. and Berlandi, F. J., Anal* Chem. 36 , 2062 (1964).

[35] Vassos, B. H., Berlandi, F. J., Neal, T. E., and Mark,

Jr., H. B., Anal. Chem. 37, 1653 (1965).

[36] Margoshes, M. and Scribner, B. F., Anal. Chem. 38 , No. 5, 297R-3HR (1966).

96

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