EPA-600/4-75-002
LOW COST COMPACT
X-RAY FLUORESCENCE ANALYZER
FOR ON-SITE MEASUREMENT
OF TRACE ELEMENTS IN AIRBORNE
PARTICULATE EMISSIONS
by
L . S . Birks and J . V . Gilfrich
Naval Research Laboratory
Washington, D. C. 20375
Interagency Agreement No. EPA-IAG-D4-0344
ROAP No. 26AAN-012
Program Element No. 1AA010
EPA Project Officer: Dr. Jack Wagman
Environmental Sciences Research Laboratory
Office of Air, Land, and Water Use
Research Triangle Park, North Carolina 27711
Prepared for
U.S. ENVIRONMENTAL PROTECTION AGENCY
Office of Research and Development
Washington, D. C. 20460
July 1975
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EPA REVIEW NOTICE
This report has been reviewed by the National Environmental Research
Center - Research Triangle Park, Office of Research and Development,
EPA, and approved for publication. Approval does not signify th^t the
contents necessarily reflect the views and policies of the Environmental
Protection Agency, nor does mention of trade names or commercial
products constitute endorsement or recommendation for use.
RESEARCH REPORTING SERIES
Research reports of the Office of Research and Development, U.S. Environ-
mental Protection Agency, have been grouped into series. These broad
categories were established to facilitate further development and applica-
tion of environmental technology. Elimination of traditional grouping was
consciously planned to foster technology transfer and maximum interface
in related fields. These series are:
1 . ENVIRONMENTAL HEALTH EFFECTS RESEARCH
2 . ENVIRONMENTAL PROTECTION TECHNOLOGY
3. ECOLOGICAL RESEARCH
4. ENVIRONMENTAL MONITORING
5. SOCIOECONOMIC ENVIRONMENTAL STUDIES
6. SCIENTIFIC AND TECHNICAL ASSESSMENT REPORTS
9. MISCELLANEOUS
This report has been assigned to the ENVIRONMENTAL MONITORING
series. This series describes research conducted to develop new or
improved methods and instrumentation for the identification and quanti-
fication of environmental pollutants at the lowest conceivably significant
concentrations. It also includes stuclii-s to determine the ambient concen-
trations of pollutants in the environment and/or the variance of pollutants
as a function of time or meteorological factors.
\
This document is available to the public for sale through the National
Technical Information Service, Springfield, Virginia 22161.
Publication No. EPA-600/4-75-002
11
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CONTENTS
Abstract „ ..... » .......... . „ o . . .... . .... . . „ . „ . . <> <, .... . . . . . . ,, . iv
Problem Status . . . .........o... .................o iv
Authorization .............................................. iv
DNTTRODUCT ION ........................................... 1
COMMERCIAL INSTRUMENTS 1
INSTRUMENT DESIGN ...................................... 2
RESULTS
Sensitivity and Detection Limits 7
Sample Measurement .................................... 9
Field Test 9
SUMMARY ................................................. 10
ACKNOWLEDGMENT ....................................... 11
REFERENCES ............... ................. . 11
FIGURES
1. Block Diagram of Compact X-Ray Analyzer ............. 3
2. Plan view of spectrometer ............................ 5
3. Photograph of the front panel of the
Compact X-Ray Analyzer as delivered 6
4. Photograph of spectrometer with sample
chamber open ........................................... 6
5. Analyst inserting sample ............................. 7
6. Detection Limits as a function of atomic number 8
111
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ABSTRACT
Alow cost, compact wavelength dispersion x-ray fluorescence
analyzer has been designed using mostly state-of-the-art commercial
components. A prototype instrument has been built for less than
$5000 and tested in the field. With x-ray tube power of 80 watts
(40 kV, 2 mA) the 100 second 3
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INTRODUCTION
Fossil-fueled power plants, incinerators, and other sources emit
substantial quantities of airborne particulate matter containing various
amounts of such elements as Pb, Hg, Cd, As, Ni, V, Cr, Se, Mn, Cu
and Sb that are of concern as actual or potential hazardous pollutants.
An effective and economical means for on-site monitoring of emissions
of these elements would be of considerable help in developing control
strategy. The technique should be simple, rapid and have limits of de-
tection adequate to analyze fairly short-time collections with an accept-
able accuracy. The necessary equipment should be inexpensive so that
even small operators could afford the capital expenditure.
X-ray fluorescence had already been demonstrated to be a valuable
analytical tool for the measurement of the elemental composition of
particulate pollution.' ' In view of this fact, the U. S. Environ-
mental Protection Agency (EPA) requested the Naval Research .Labor-
atory (NRL) to suggest a commercial x-ray analysis system to perform
the monitor function, or to design and build an instrument specifically
suited to this application.
COMMERCIAL INSTRUMENTS
The problem of evaluating low-cost x-ray instrumentation is com-
plicated by the degree of sophistication which has been introduced by
the x-ray manufacturers. The cost per sample has been reduced using
this expensive equipment for those situations where the sample load is
high enough to take fall advantage of the automated instruments. How-
ever, the capital expenditure is impossible to justify for any industry
which needs to analyze only a few samples»
Fortunately, there are several inexpensive x-ray analyzers com-
mercially available and our first step was to examine their capabilities
using a set of criteria agreed upon between the authors and the EPA
project officer. It was felt that a reasonable target cost for the instru-
ment was $5000; it should have a 100 second detection limit of about
for a single element (as particulate material deposited on a
1
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thin substrate); it should be capable of measuring any one of a wide
variety of elements witha resolution adequate to minimize interferences;
it should be simple to use, compact and able to operate from a conven-
tional 110 volt, 60 Hertz A.C. branch circuit. The types of instruments
considered and the factors involved in evaluating them are listed in
Table I.
TABLE I. PROPERTIES OF COMMERCIAL LOW COST X-RAY ANALYZERS
Solid State
Det. -X-Ray Tube
Type of
Instrument
Cost
Weight
Resolution
Scint. or Prop.
Det. (jv1 Filters
-$5000
20 Ibs
Varies (\?
Solid State
Det. -Isotope
~ $8000
100 Ibs
180 eV @ 4 k<
100 Second
Det. Limits
Special
Requirements
each filter
pair used.
Typically 500 eV
Few to Few
Tens of fig/cm
Need to examine
each element to
determine if approp.
filters available.
ZOO eV @ 6 keV
220 eV @ 10 keV
270 eV @ 20 keV
< 1 Hg/cm
Liq. N-, (can
have 28 day
holding time)
~ $15000
285 Ibs
180 eV @ 4 keV
200 eV @ 6 keV
220 eV @ 10 keV
270 eV @ 20 keV
< 0. 5 fig/cm
Liq. N-, (can
have 28 day
holding time)
Crystal
Spectrometer
~ $10000
125 Ibs
25eV@4keV
68 eV @ 6 keV
143 eV @ 10 keV
650 eV @ 20 keV
< 1 fig/cm
None
2
As can be seen from Table I, none of the commercial instruments
satisfy all the criteria. The first instrument is the only one which
satisfies the cost criterion and is the only one which does not meet the
detection limit requirements. The most discouraging observation from
the table is the poor energy resolution of all of these particular systems.
The lack of good energy resolution results in significant interferences
which only can be overcome for the solid-state detector instruments by
computer processing of the da,ta (one of the ways in which the modern
equipment has become sophisticated arid expensive); the instruments
using filters are timply not suited to any analysis situation involving
such interferences. The particular crystal spectrometer listed used a
low-power x-ray tube and inefficient geometry which made it necessary
to sacrifice resolution for intensity,, In general, however, the resolu-
tion of a crystal spectrometer can be considerably better than that
listed in the table and suggested that such an instrument should be de-
signed and constructed specifically for the problem at hand.
INSTRUMENT DESIGN
It was not the intent of the eifort reported here to perform research
in the area of crystal spectrometer design. Rather the instrument
would use those state-of-the-art components which were commercially
available and we would only custom-make those parts which we re unique.
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The Interagency Agreement between NRL, and EPA specified the con-
struction of a bread-board model but it was recognized early that a
prototype would be much more useful. The complexity introduced by a
vacuum system seemed unnecessary for this prototype and therefore
the instrument would be limited to measuring those elements whose
characteristic x-rays are not attenuated significantly in an air path.
BEAM
,TRAP
SHIELDED
SAMPLE
CHAMBER
SAMPLE
X-RAY
TUBE
PULSE HEIGHT
ANALYZER
FUSED MAIN POWER SWITCH
Figure 1. Block diagram of the Compact X-Ray Analyzer.
Figure 1 is a block diagram of the complete x-ray analysis system
and Table II lists the commercial components and their cost, as well
as the parts fabricated at NRL with the best estimate (probably good to
10 or 20%) of the cost to produce the latter. Assembly and testing of
the equipment could be easily accomplished for an additional thousand
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dollars, although a considerably larger amount was spent on the proto-
type to insure that the approach used was the most appropriate.
TABLE II
COMPONENTS FOR COMPACT X-RAY ANALYZER
PURCHASED COMMERCIALLY
Regulator
X-Ray Tube H.V. Supply
X-Ray Tube
"005 X 4" Collimator
Scintillation Detector
Detector H. V. Supply
Recorder
Electronics Power Supply
Manufacturer and Model No.
Sola 23-22-150
Universal-Voltronics BPE-40-4
Machlett EG-50 HW
Philips 19011200
Harshaw SHG
Venus Scientific K-15
Rustrak 288
Sorensen MMD-12. 120
Cost
$
Crystal (LiF)
Filament Supply
X-Ray Tube Housing
and Sample Chamber
Spectrometer, incl.
Crystal and Detector
Mounts
Counting Electronics:
Amp., PHA, Ratemeter
Sealer, Timer, etc.
FABRICATED AT NRL
Cleaved, abraded and etched,
from NRL stock
6.3 VCT Transformer, 1.5Amp
Variac and miscellaneous
small parts
Manufactured in NRL Shops:
materials and labor
Gears ($36) + machine work
in NRL Shops: Mat'ls and labor
Some circuitry designed in
NRL Electronic Shop, other
circuitry standard: Mat'ls
and labor
Miscellaneous Cables
Connectors and
Electronics Comp.
Cabinet to house components fabricated at NRL
100
415
1050
255
310
150
197
96
$ -50
-25
•500
•100
-500
~25
-50
TOTAL $3823
The Sola regulator was used to stabilize the line voltage. The
Universal-Voltronics high voltage supply was chosen largely on the
basis of cost and size. Although a 50 kV supply would have been pre-
ferable in order to excite the heavier elements, Universal Voltronics
had not built this power supply for more than 30 kV; therefore they
were only willing to upgrade it to 40 kV, which we considered acceptable.
The Machlett EG series x-ray tube was the only low-powered tube
readily available; it was purchased with a tungsten target for efficient
excitation over a wide atomic number range and with an unnecessarily
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thin window ("„ 005 Be) because that particular model was in stock for
rapid delivery. This x-ray tube is located in an oil-filled housing
which, together with the specimen chamber, was fabricated at NRL..
The tube housing is air cooled and contains a resistor stack by •which
the voltage applied to the tube is monitored. The specimen chamber
contains a sample changing mechanism, the beam trap to prevent scat-
tering of the primary beam which is transmitted through the sample,
and the collimator. The x-ray tube current is controlled by the NRL-
built filament supply. Both the x-ray tube housing and the specimen
chamber were lined with lead to provide radiation protection.
The spectrometer, consisting of the crystal and detector and the
6-29 coupling between them by means of a planetary gear arrangement,
is shown in Figure 2. The Harshaw SHG scintillation detector has a
very good reputation with regard to its energy resolution and low noise.
The detector high voltage supply, the low voltage power supply for the
electronics package, and the recorder were commercial units; the rest
of the counting electronics were designed and built at NRL, making use
of modern conventional circuitry. Figures 3 through 5 are photographs
of the completed instrument.
SAMPLE
CHAMBER
COLLIMATOR
CRYSTAL
SCINTILLATION
X-RAY TUBE \ \ DETECTOR
(BELOW SAMPLE)
Figure 2, Plan view of spectrometer.
The operation of this prototype is identical with that of any wave -
length dispersive x-ray fluorescence analyzer with which it is assumed
the reader is familiar. The spectrometer is manual and must be set
by hand for detecting the x-rays of interest; the crystal is coupled to
the detector and automatically set at the diffracting angle. The in-
tensity can be read on the sealer, ratemeter or strip-chart recorder.
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Figure 3. Photograph of the front panel of the Single Element
Analyzer as delivered.
Figure 4, Photograph of the spectrometer with the sample chamber
open showing a sample in place.
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Figure 5. Analyst inserting sample into instrument (preliminary
front panel).
RESULTS
Sensitivity and Detection Limits
One of the parameters considered important in defining the useful-
ness of the compact x-ray analyzer described here is the detection
limit for various elements. The original criterion was that the 100
second detection limit should be 1 /Jg/cm^ or better for the elements
within its wavelength range. Measurements of the sensitivity
[ (c/100 s)/(/J,g/cm2)] and the detection limits (jJg/cmZ) were made
using single element standards of solutions deposited on filter paper.(^)
The results of these measurements are listed in Table III and the
detection limits are shown as a function of atomic number in Figure 6.
It can be seen that the 1 ^tg/cm^ criterion is satisfied for all elements
tested with the exception of Cd which is 1.2 jig/cm20 Many of the
elements demonstrate detection limits significantly better, the best
being Zn at 0. 1 fig
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TABLE III
SENSITIVITY AND DETECTION LIMITS*
Element X-Ray
V Ka
Fe Ka
Cu Ka
Zn Ka
Br Ka
Mo Ka
Cd Ka
W La
Pb La
U La
Line Sensitivity
[(c/100s)/(ng/cm2)]
245
1249
1582
2111
1160
596
98
587
714
553
BCD
(c/lOOs)
1429
3659
7974
5424
7009
6255
1504
34586t
7993
6480
100 second measurements with W target Machlett EG-50
tube operated at
High background
10 -
100
40 kV, 2 mA.
due to scattered primary W
SECOND DETECTION LIMITS
L lines.
3a D.L.
(Mg/cm2)
0.46
0. 15
0. 17
0. 10
0.22
0.40
1.2
0. 95
0.38
0.44
x-ray
W TARGET EG-50 (40kV, 2mA)
^^,
"E
o>
Ji.
1-
I i.o-
-z.
o
" \
t \
Q \
n 1 1 £D_
O Ka LINES
X La LINES
/
/
O
/
O/
/
1 1 1 1
^
\
\
X
-^x
'20
40 60
ATOMIC NUMBER
80
Figure 6. Detection limits as a function of atomic number.
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Sample Measurement
The instrument was further tested by analyzing some auto exhaust
samples provided by EPA. During these measurements, some diffi-
culty was experienced due to a faulty component in the detector high-
voltage supply. Unfortunately, these samples had also been analyzed
in the standard laboratory spectrometer and had received enough
radiation exposure that they were very brittle. While attempting to
remeasure these samples in the single element analyzer they deterio-
rated and only a few of the samples could be analyzed for some of the
elements. The results of these few determinations are shown in Table
IV. The 1'less than" value of 0. 13 |J,g/cm2 listed for Br in sample 07
is not inconsistent with the detection limits shown in Table III. Sample
07 was collected on a Nuclepore filter which, because it is significantly
thinner than Millipore or Whatman filters, contributes a smaller scat-
tered background. This leads to better detection limits than those
listed in Table in (0. 13 fig/cm2 for Br compared to 0.22 jig/cm2 in
the Table).
TABLE IV
COMPARISON OF COMPACT X-RAY ANALYZER
RESULTS WITH THOSE OBTAINED USING
A STANDARD LABORATORY X-RAY ANALYZER
Concentration, fig/cm
Sample No. 05 06 07 08
Pb
PW 1410* 3.6 0.45
CXA 5.2 0.50
Br
PW 1410 1. 1 0.07
CXA 1.1 <0.13t 0.28
Fe
PW 1410 32 4.7
CXA 34 5.2
>\<
PW 1410 is the standard laboratory instrument.
CXA is the compact x-ray analyzer.
•f
"Less than" value indicates the 3(T, 100 s. detection limit.
Field Test
Since the instrument was designed to be operated conveniently on
the site of an emission source, the final test before transferring it to
the EPA was conducted in the field. Arrangements were made by the
EPA to collect samples of particulate material from one of the stacks
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at the River Bend Plant of the Duke Power Company in Charlotte,
North Carolina, and to measure several elements at that location
using the compact x-ray analyzer. The instrument was transported
from NRL to the EPA Environmental Sciences Research Laboratory in
Research Triangle Park, North Carolina by EPA vehicle. At that
location, the analyzer was set up and put into operation to insure that
it had not been damaged during transport. Some minor malfunctions
were remedied and the analyzer was made ready for the trip to
Charlotte, again in an EPA truck. The original intention was to make
the measurements in the EPA instrument shack located on the roof of
the plant, immediately adjacent to the stack fitted with sampling ports.
However, it was apparent that conveying the instrument to the roof
would not demonstrate anything that could not be shown as well by
setting it up in the plant laboratory and there was some chance of
damage in attempting to navigate the tortuous path to the roof. As at
the EPA laboratory, the analyzer was set up and put into operation.
Sample deposits on Millipore filters were taken from the stack and
measured for six elements using "solution on filter paper" standards
prepared at NRL. The results are shown in Table V. At the conclu-
sion of this operation, the analyzer was transported back to the Environ-
mental Sciences Research Laboratory.
TABLE V
COMPACT X-RAY ANALYZER RESULTS
ON POWER PLANT PARTICULATE SAMPLES
Concentration
Sample X-2 Sample X-5
Mn 0.4 0.5
Fe 31 33
Ni 0.3 0.5
Zn <0.8* 7.1
Hg 5.7 2.7
Pb 4.7 5.1
Zn was not detectable on sample X-2. The
anomalously high 100 sec. detection limit
(0. 8 Jig/cm^) was caused by the high Zn
content of the "o-ring" used to clamp the
filter in the sample holder.
SUMMARY '
The design, construction and testing of the instrument described in
this report demonstrates that a compact, low powered, relatively in-
expensive, wavelength dispersion x-ray analyzer can be produced
using state-of-the-art components. It is capable of measuring ele-
mental composition of the particulate material collected from emission
10
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sources (or from ambient air, for that matter) with 100 second 3cr de-
tection limits ranging from 0. 1 to 1 j^g/cm^ for elements which can be
analyzed in an air path instrument. The cost of the components used
to fabricate such an instrument was well below $5000 and we estimate
that, even in the present (1975) economy, if produced in sufficient
quantity, similar instruments should be commercially marketable for
not more than $ 10, 000.
If an instrument of this type were to be commercially produced as
a "single element" analyzer, this would enable the device to be cus-
tomized, e.g., the use of a (220) LiF crystal and 50 kV power supply
for measurements of the K lines of elements from Ru to Cd; the am-
plifier gain, PHA settings and Bragg angle fixed rather than adjustable;
a selection made of digital or analog readout depending on the applica-
tion, and the sample chamber specifically adapted to the samples being
measured. Thus the instrument might have only two controls, "on-off"
and "read", for simplicity of operation. Conversely, the degree of
complexity could be increased to make the analyzer more versatile
(but unfortunately more expensive) by providing a motor drive for the
spectrometer, enclosing the specimen chamber and spectrometer in a
vacuum housing, installing a crystal changer and a thin-window pro-
portional detector, etc.
Several of the x-ray equipment manufacturers have seen this device
and discussed the design parameters involved in the production of an
inexpensive instrument of this type. They all expressed interest and
some of them are currently considering the possibility of making such
an instrument commercially.
ACKNOWLEDGMENTS
The authors wish to express grateful appreciation to M. C. Peckerar,
N. L. Midkiff and J. H. McCrary of the X-Ray Optics Branch, Naval
Research Laboratory, for assistance in various phases of the design,
construction and testing of this instrument.
REFERENCES
1. "Development of X-Ray Fluorescence Spectroscopy for Elemental
Analysis of Particulate Matter in the Atmosphere and in Source
Emissions, " L. S. Birks, J. V. Gilfrich and P. G. Burkhalter,
EPA-R2-72-063, Oct. 1972.
2. "Development of X-Ray Fluorescence Spectroscopy for Elemental
Analysis of Particulate Matter in the Atmosphere and in Source
Emissions. Phase II: Evaluation of Commercial Multiple Crystal
Spectrometer Instruments, " L,. S. Birks and J. V. Gilfrich, NRL,
Report 7617, June 1973.
11
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3. J. V. Gilfrich, P. G. Burkhalter and L. S. Birks, Anal. Chem.
45, 2002 (1973).
4. F. S. Goulding and J. M. Jaklevic, Lawrence Berkeley Laboratory,
UCRL-20625, May 1971.
5. H. R. Bowman, J. G. Conway and F. Asaro, Environ. Sci.
Technol. 6_, 558 (1972).
6. T. R. Dittrich and C. R. Cothern, J. Air Pollut. Contr. Ass. 21,
716 (1971).
7. To B. Johansson, R. Akselsson and S. A. E. Johansson, Lund
Institute of Technology, LUMP 7109, Aug. 1971.
8. R. L. Watson, J. R. Sjurseth and R. W. Howard, Nucl. Instrum.
Methods ^3, 69 (1971).
9. J. S. Cooper, Nucl. Instrum. Methods 106, 525 (1973).
10. J. Leroux and M. Mahmud, J. Air Pollut. Contr. Ass. 20, 402
(1970).
11. P. Greenfelt, A. Akerstrom and C. Grosset, Atmos. Environ. J5,
1 (1971).
12. C. L. Luke, T. Y. Kometani, J. E. Kessler, T. C. Loomis,
J. L. Bove and B. Nathanson, Environ Sci. Technol. 6, 1105 (1972).
12
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TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing)
1. REPORT NO.
600/4-75-002
2.
3. RECIPIENT'S ACCESSIOC+NO.
4. TITLE AND SUBTITLE
Low Cost Compact X-ray Fluorescence Analyzer for
On-Site Measurement of Trace Elements in Airborne
Particulate Emissions
5. REPORT DATE
July 1975
6. PERFORMING ORGANIZATION CODE
7. AUTHOR(S)
L. S. Birks and J. V. Gilfrich
8. PERFORMING ORGANIZATION REPORT NO.
9, PERFORMING ORGANIZATION NAME AND ADDRESS
Naval Research Laboratory
Washington, D. C. 20375
10. PROGRAM ELEMENT NO.
1AA010 (26AAN-012)
11. CONTRACT/GRANT NO.
EPA-IAG-D4-0344
12, SPONSORING AGENCY NAME AND ADDRESS
Environmental Sciences Research Laboratory
Office of Research and Development, EPA
Research Triangle Park, N.C. 27711
13. TYPE OF REPORT AND PERIOD COVERED
Final - 2 yrs ending 6/75
14. SPONSORING AGENCY CODE
15. SUPPLEMENTARY NOTES
16. ABSTRACT
A low cost, compact wavelength dispersion x-ray fluorescence analyzer
has been designed using mostly state-of-the-art commercial components. A
prototype instrument has been built for less than $5000 and tested in the
field. With x-ray tube power of 80 watts (40 kV, 2 mA) the 100 second 3
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