oEPA
United States
Environmental Protection
Agency
Sewneea Kmemi&i
Ubergicify
Research Triangle Park *C 27711
EPA-60Q/7<
June
and
Portable Vacuum
X-Ray Spectrometer
Instrument for On-Site
Analysis of Airborne
Particulate Sulfur and
Other Elements
Interagency
Energy/Environment
R&D Program
Report
-------
RESEARCH REPORTING SERIES
Research reports of the Office of Research and Development, U.S. Environmental
Protection Agency, have been grouped into nine series. These nine broad cate-
gories were established to facilitate further development and application of en-
vironmental technology. Elimination of traditional grouping was consciously
planned to foster technology transfer and a maximum interface in related fields.
The nine 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 (STAR)
7. Interagency Energy-Environment Research and Development
8 "Special" Reports
9. Miscellaneous Reports
This report has been assigned to the INTERAGENCY ENERGY-ENVIRONMENT
RESEARCH AND DEVELOPMENT series. Reports in this series result from the
effort funded under the 17-agency Federal Energy/Environment Research and
Development Program. These studies relate to EPA's mission to protect the public
health and welfare from adverse effects of pollutants associated with energy sys-
tems. The goal of the Program is to assure the rapid development of domestic
energy supplies in an environmentally-compatible manner by providing the nec-
essary environmental data and control technology. Investigations include analy-
ses of the transport of energy-related pollutants and their health and ecological
effects; assessments of, and development of, control technologies for energy
systems; and integrated assessments of a wide range of energy-related environ-
mental issues.
This document is available to the public through the National Technical Informa-
tion Service, Springfield, Virginia 22161.
-------
EPA-600/7-78-103
June 1978
PORTABLE VACUUM X-RAY SPECTROMETER
Instrument for On-site Analysis of
Airborne Particulate Sulfur and Other Elements
by
J. V. Gilfrich
L. S. Birks
Naval Research Laboratory
Washington, D. C. 20375
Interagency Agreement EPA-IAG-D4-0490
Project Officer
Jack Wagman, Director
Emissions Measurement and Characterization Division
Environmental Sciences Research Laboratory
Research Triangle Park, North Carolina 27711
ENVIRONMENTAL SCIENCES RESEARCH LABORATORY
OFFICE OF RESEARCH AND DEVELOPMENT
U. S. ENVIRONMENTAL PROTECTION AGENCY
RESEARCH TRIANGLE PARK, N. C. 27711
-------
DISCLAIMER
This report has been reviewed by the Environmental Sciences
Research Laboratory, U. S. Environmental Protection Agency, and
approved for publication. Approval does not signify that the
contents necessarily reflect the views and policies of the U. S.
Environmental Protection Agency, nor does mention of trade names
or commercial products constitute endorsement or recommendation
for use.
-------
ABSTRACT
A portable vacuum wavelength-dispersive x-ray analyzer has
been constructed for on-site measurements of the sulfur content
of filter-deposited airborne particles. Although designed to
analyze for sulfur, the spectrometer is adjustable over a
limited range providing the potential for determining other
elements. With the x-ray tube rated at 50 watts, the instrument
achieves a 100-second 3a detection limit for sulfur of better
2
than 0.5 yg/cm .
111
-------
INTRODUCTION
The use of x-ray fluorescence analysis for the measurement
of the elemental composition of the particulate material filtered
from source emissions or from the ambient air or water has become
a well-established technique (1-3). Commercial instrumentation,
both wavelength-dispersive and energy-dispersive, is available
which can provide the laboratory with the capability of providing
rapid, low-cost and accurate results (1-5) . This laboratory
equipment, however, is expensive and bulky, making it inconvient
for transporting to an emission source for on-site measurements.
Previously (6), the Naval Research Laboratory (NRL) constructed
for the Environmental Protection Agency (EPA) a compact x-ray
analyzer which could perform on-site analyses. Because it was an
air path instrument it was limited to measuring elements above
atomic number 23 (V).
Concern for the pollution caused by the emissions from com-
bustion sources has been magnified recently by the increasing
need to use the less-desirable supplies of fossil fuels (i.e.
high sulfur coal and high vanadium oil) for energy production.
In view of the resultant higher levels of primary sulfates pro-
duced (7), the EPA asked NRL to construct a second-generation
portable x-ray analyzer specifically to analyze for sulfur in
particulate emissions from such sources. The goal was to achieve
a 3a detection limit (8) of 5 yg/cm2 in 100 seconds. Although a
fixed spectrometer would be adequate to measure sulfur alone, the
versatility provided by an adjustable spectrometer suggested that
the instrument should be able to cover some range of 29 angle.
The purpose of this report is to document the construction and
suggest operating parameters for this instrument.
-------
INSTRUMENT DESIGN
As in the previous case (6) it was not the intent of the work
reported here to conduct research in the area of crystal spectrom-
eter design. Rather it was felt that commercially available state-
of-the-art components could be used with minimum modification so
that specially fabricated parts would be few. In addition to the
detection limit criterion (above), the specifications called for
1.) light weight, 2.) only 120 volt A.C. power (no water or liquid
nitrogen), and 3.) sufficient resolution to minimize interference
particularly from Pb M-lines when measuring S K-lines.
In accordance with the specifications and design criteria
discussed above the instrument was optimized for the measurement
of S Ka by employing an air-cooled 50-watt Pd transmission-target
x-ray tube, a cleaved NaCl crystal and a Ne-C02 sealed proportional
detector. The Pd L-lines are particularly effective for exciting
the S K-spectrum (Pd La-4.37A*, Pd L&-4.15A; S K edge-5.02A); with
the target material deposited on the inner surface of the Be window,
the transmission geometry permits close coupling to the sample.
The NaCl crystal was chosen because its interplanar spacing (2d =
o o
5.64A) diffracts S Ka radiation (A = 5.37A) to a high Bragg angle
(8 = 72 ) giving the best dispersion for minimum interference from
neighboring lines. The crystal is used with a cleaved surface to
produce a narrow diffraction profile and when coupled to a fine
collimator (4" x 0.005") provides a resolution of about 3 eV
o
(0.007A) at S Ka. For the Ne detector used, 63% of the S Ka
radiation is transmitted by the Be window and 98% of that is
absorbed by the Ne gas. Figure 1 is a block diagram of the Sulfur
Analyzer and Table 1 lists the components in detail separating
those commercially available and their cost from those fabricated
at NKL, with our best estimate of what the latter would cost if
available from commercial sources. Figure 2 is a photograph of
the instrument.
-------
120 volts
A.C.
1 FUSED MAIN POWER SWITCH
VARIAC
HIGH
VOLTAGE
SWITCH
SAFETY
SWITCH
HIGH
VOLTAGE
SUPPLY
COUNTING
ELECTRONICS
VARIAC |
FILAMENT
TRANSFORMER
X-RAY TUBE
DETECTOR1
SAMPLE
CRYSTAL I I I
: ;
I COLLIMATOR I
VACUUM CHAMBER
| PREAMPLIFIER |-
DETECTOR
HIGH VOLTAGE
SUPPLY
Figure 1. Block Diagram of the X-Ray Analyzer.
-------
TABLE 1. COMPONENTS FOR THE SULFUR ANALYZER
PURCHASED COMMERCIALLY
X-Ray Tube H.V. Supply
X-Ray Tube
Collimator
Proportional Detector
Fan
Counting Electronics
Crystal (NaCl)
Filament Supply
Vacuum Housing
Spectrometer
Universal Voltronics BPE-32-5.5 $ 295
Watkins-Johnson WJ2328-2DPD 975
Philips 19011200 255
LND 42513A 600
PAMOTOR RL90-18/00 20
(Amplifier, Pulse Height ^ 3,000
Analyzer, Ratemeter, Timer,
Sealer, Detector High Voltage
Supply, and NIMBIN with its
Power Supply) purchased from
any of several manufacturers
(e.g. Harshaw or ORTEC)
FABRICATED AT NRL
Cleaved for NRL Stock *> 100
5 volt, 5 amp Transformer ^ 200
(insulated for 50kV)
Spectrometer Chamber and ^ 500
Sample Chamber
Gears, Crystal Holder, Detector ^ 500
Arm and Miscellaneous
The x-ray tube power supply is a solid-state, encapsulated
component chosen on the basis of size and cost. Its no-load
voltage is 36kV and will deliver 5.5mA at 32kV. The x-ray tube
is a modified version of a tube which Watkins-Johnson manufac-
tures (9). Since the anode is mounted to the window, it is
grounded, requiring that the filament transformer be insulated
for the high voltage. The detector is a modified version of a
catalog item from LND.
-------
Figure 2. Photograph of the X-Ray Analyzer. Sample
chamber is open. The top of the spectrometer
vacuum tank and the shielding for the x-ray
tube have been removed to show some detail.
5
-------
The vacuum chamber consists of two main units: the spectrom-
eter tank is an aluminum cylinder with the spectrometer drive,
vacuum pumping port and signal cable feeding through the bottom;
the specimen chamber consists of a brass plate attached to the
spectrometer housing and an aluminum "hat" containing the four-
sample carousel. The sample chamber is lined with cadmium for
radiation shielding (since the prototype was intended for
specific application to sulfur, lead shielding was avoided to
eliminate the Pb M-line interference). The x-ray tube mounts to
the brass plate and is enclosed by a lead-shielding box into
which cooling air is directed. A safety switch is located on
the brass plate. This switch disconnects the power to the
primary of the high voltage supply when the sample chamber is
opened. The power supply for the x-ray tube is protected by a
sheet metal enclosure, the top of which is a convenient location
for the electronic counting package. The spectrometer uses a
differential gear assembly to provide 9-26 coupling and is adjust-
able over the 26 range of *• 90° to * 150°. Table 2 lists the
wavelength coverage and elements that might be analyzed by using
different crystals. It must be remembered, of course, that the
x-ray tube and detector have been optimized for S Kot and would
not be very efficient for many of the other elements.
Appended to this report are operating instructions and
circuit diagrams for the instrument.
-------
TABLE 2. POSSIBLE RANGE FOR THE SPECTROMETER
(2 FROM 90° TO 150°)
Element
Crystal
LiF (220)
LiF (200)
NaCl
Graphite
PET
ADP
Gypsum
Mica
Acid Phthalate
(K, Rb or Tl)
2d
A
2.85
4.03
5.64
6.71
8.75
10.6
15.2
19.9
^ 26
Min.A
o
(A)
2.01
2.85
3.99
4.74
6.19
7.50
10.7
14.1
v 18
Max. A
A
2.75
3.89
5.45
6.48
8.45
10.2
14.7
19.2
•v 25
Ka
Mn-Ti
Sc-K
Ar-S
S-P
Si-Al
Al-Mg
Na-Ne
Ne-F
F-0
La
Ba-Gd
In-Cs
Mo-Ag
Y-Ru
Br-Y
As-Kr
Ni-Ga
Fe-Ni
V-Mn
-------
RESULTS
The sensitivity and detection limits were measured on a
sample of CdS deposited on a Millipore filter. The mass loading
of CdS was measured by analyzing for both Cd and S on the multi-
spectrometer x-ray fluorescence analyzer at the EPA laboratory
in Research Triangle Park, N. C. The standards used for these
measurements were films of CuS and CdF_ on mylar obtained from
MicroMatter Co., Seattle, Wash. The results of these measure-
2 i
ments showed 114 ygCd/cm and 32.8 ygS/cm^, values agreeing with
stoichiometry within 1%. With the x-ray tube in this sulfur
analyzer operated at 30 kV and 1.5 mA, the average of several
determinations of S Ka intensity gave a value of 2935 c/lOOs
(a = 40 c/lOOs for 10 meas.) for the sulfur in the CdS sample,
above a background of 177 c/lOOs. This results in a sensitivity
of 89.5 c/lOOs/yg/cm^ for sulfur and a 100 second detection limit
o -^^P"7^T o
of gg 5 = 0.45 yg/cm , about one order of magnitude better
than the design criterion.
Because of the success experienced with the NRL laboratory
x-ray analyzer in distinguishing between the sulfide and sulfate
forms of sulfur (10) , an attempt was made to measure the S K3
spectrum in this instrument. Using a bulk sample of either
Na~ SO. or elemental S and operating the x-ray tube at 30 kV,
1.5 mA, no signal above background could be observed in the region
of the S K3 line. The anticipation that this low-power sulfur
analyzer might be able to distinguish between the sulfide and
sulfate could not be realized. The use of a higher power x-ray
tube could upgrade the instrument to a degree that such measure-
ments might be made. There are two reasons which argue against
the practical success of such a modification: 1.) Significantly
higher powered tubes {> 10X) would certainly have to be water
cooled and require a much larger x-ray tube power supply, making
8
-------
TABLE 2. POSSIBLE RANGE FOR THE SPECTROMETER
(2 FROM 90° TO 150°)
Element
Crystal
LiF (220)
LiF (200)
NaCl
Graphite
PET
ADP
Gypsum
Mica
Acid Phthalate
(K, Rb or Tl)
2d
o
(A)
2.85
4.03
5.64
6.71
8.75
10.6
15.2
19.9
^ 26
Min.A
o
(A)
2.01
2.85
3.99
4.74
6.19
7.50
10.7
14.1
v> 18
Max. X
o
(A)
2.75
3.89
5.45
6.48
8.45
10.2
14.7
19.2
* 25
Ka
Mn-Ti
Sc-K
Ar-S
S-P
Si-Al
Al-Mg
Na-Ne
Ne-F
F-O
La
Ba-Gd
In-Cs
Mo-Ag
Y-Ru
Br-Y
As-Kr
Ni-Ga
Fe-Ni
V-Mn
-------
RESULTS
The sensitivity and detection limits were measured on a
sample of CdS deposited on a Millipore filter. The mass loading
of CdS was measured by analyzing for both Cd and S on the multi-
spectrometer x-ray fluorescence analyzer at the EPA laboratory
in Research Triangle Park, N. C. The standards used for these
measurements were films of CuS and CdF- on mylar obtained from
MicroMatter Co., Seattle, Wash. The results of these measure-
2 t
ments showed 114 pgCd/cm and 32.8 ygS/cmz, values agreeing with
stoichiometry within 1%. With the x-ray tube in this sulfur
analyzer operated at 30 kV and 1.5 mA, the average of several
determinations of S Kot intensity gave a value of 2935 c/lOOs
(a = 40 c/lOOs for 10 meas.) for the sulfur in the CdS sample,
above a background of 177 c/lOOs. This results in a sensitivity
of 89.5 c/lOOs/vig/cm^ for sulfur and a 100 second detection limit
of QQ 5 = 0.45 yg/cm , about one order of magnitude better
than the design criterion.
Because of the success experienced with the NRL laboratory
x-ray analyzer in distinguishing between the sulfide and sulfate
forms of sulfur (10), an attempt was made to measure the S K3
spectrum in this instrument. Using a bulk sample of either
Na~ SO. or elemental S and operating the x-ray tube at 30 kV,
1.5 mA, no signal above background could be observed in the region
of the S K$ line. The anticipation that this low-power sulfur
analyzer might be able to distinguish between the sulfide and
sulfate could not be realized. The use of a higher power x-ray
tube could upgrade the instrument to a degree that such measure-
ments might be made. There are two reasons which argue against
the practical success of such a modification: 1.) Significantly
higher powered tubes (> 10X) would certainly have to be water
cooled and require a much larger x-ray tube power supply, making
8
-------
TABLE 2. POSSIBLE RANGE FOR THE SPECTROMETER
(2 PROM 90° TO 150°)
Element
Crystal
LiF (220)
LiF (200)
NaCl
Graphite
PET
ADP
Gypsum
Mica
Acid Phthalate
(K, Rb or Tl)
2d
2.75
3.89
5.45
6.48
8.45
10.2
14.7
19.2
-v- 25
Ka
Mn-Ti
Sc-K
Ar-S
S-P
Si-Al
Al-Mg
Na-Ne
Ne-F
F-0
La
Ba-Gd
In-Cs
Mo-Ag
Y-Ru
Br-Y
As-Kr
Ni-Ga
Fe-Ni
V-Mn
-------
RESULTS
The sensitivity and detection limits were measured on a
sample of CdS deposited on a Millipore filter. The mass loading
of CdS was measured by analyzing for both Cd and S on the multi-
spectrometer x-ray fluorescence analyzer at the EPA laboratory
in Research Triangle Park, N. C. The standards used for these
measurements were films of CuS and CdF2 on mylar obtained from
MicroMatter Co., Seattle, Wash. The results of these measure-
2 -5
ments showed 114 ygCd/cm and 32.8 ygS/cm-S values agreeing with
stoichiometry within 1%. With the x-ray tube in this sulfur
analyzer operated at 30 kV and 1.5 mA, the average of several
determinations of S Ka intensity gave a value of 2935 c/lOOs
(a = 40 c/lOOs for 10 meas.) for the sulfur in the CdS sample,
above a background of 177 c/lOOs. This results in a sensitivity
of 89.5 c/lOOs/yg/cm^ for sulfur and a 100 second detection limit
of 89 5 = 0.45 yg/cm , about one order of magnitude better
than the design criterion.
Because of the success experienced with the NRL laboratory
x-ray analyzer in distinguishing between the sulfide and sulfate
forms of sulfur (10), an attempt was made to measure the S KB
spectrum in this instrument. Using a bulk sample of either
Na2 SO. or elemental S and operating the x-ray tube at 30 kV,
1.5 mA, no signal above background could be observed in the region
of the S K$ line. The anticipation that this low-power sulfur
analyzer might be able to distinguish between the sulfide and
sulfate could not be realized. The use of a higher power x-ray
tube could upgrade the instrument to a degree that such measure-
ments might be made. There are two reasons which argue against
the practical success of such a modification: 1.) Significantly
higher powered tubes (> 10X) would certainly have to be water
cooled and require a much larger x-ray tube power supply, making
8
-------
the instrument much less portable, if it could be called
portable at all; and 2.) Moderately higher power tubes (4 or 5x)
might still be air-cooled, but would certainly be larger in
size making it unlikely that the tube target to sample coupling
could be nearly as close (an increase in sample to target
distance of a factor of 2 would require a power increase of a
factor of 4 just to maintain the same capability).
-------
SUMMARY
The low-powered portable sulfur x-ray analyzer constructed
by NRL for EPA has demonstrated a 100 second 3a detection limit
j
of about 0.5 yg/cnr for sulfur in particulate samples collected
on Millipore filters. It is a wavelength-dispersive instrument
o
having a resolution of about 3 eV (0.007A) at the S Ka line. It
is portable, requiring only 120 volt, 60 Hertz A.C. power and is
contained in three packages: the main chassis, containing the
spectrometer, sample chamber and x-ray tube power supply; the
electronic counting equipment; and the vacuum pump.
10
-------
REFERENCES
Birks, L. S., J. V. Gilfrich and P. G. Burkhalter. Develop-
ment of X-Ray Fluorescence Spectroscopy for Elemental
Analysis of Particulate Matter in the Atmosphere and in
Source Emissions. EPA-R2-72-063, U. S. Environmental
Protection Agency, Washington, D.C., 1972. 43 pp.
Gilfrich, J. V., P. G. Burkhalter and L. S. Birks. X-Ray
Spectrometry for Particulate Air Pollution - A Quantitative
Comparison of Techniques. Anal. Chem. 4_5:2002, 1973.
Camp, D. C., A. L. VanLehn, J. R. Rhodes and A. H. Pradznyski,
Intercomparison of Trace Element Determination in Simulated
and Real Air Particulabe Samples. X-Ray Spectrom. £:123,
1975.
Birks, L. S. and J. V. Gilfrich. Evaluation of Commercial
Energy Dispersion X-Ray Analyzers for Water Pollution.
Applied Spectres., 3^:204, 1978.
Wagman, J. , R. L. Bennett and K. T. Knapp. Simultaneous
Multiwavelength Spectrometer for Rapid Elemental Analysis of
Particulate Pollutants. In: X-Ray Fluorescence Analysis of
Environmental Samples, T. G. Dzubay, ed. , Ann Arbor Science
Publishers, Inc., Ann Arbor, Mich., 1977, p. 35.
Birks, L. S. and J. V. Gilfrich. Low Cost Compact X-Ray
Fluorescence Analyzer for On-Site Measurements of Trace
'Elements in Source Emissions. EPA-600/4-75-002, U. S.
Environmental Protection Agency, Research Triangle Park,
N.C., 1975. 12 pp.
Nader, J. S., J. B. Homolya, K. T. Knapp and J. Wagman.
A study of Current Sulfur Emissions from Oil-Fired Power
Plants. 173rd Americal Chemical Society National Meeting,
New Orleans, Louisiana, March 20-25, 1977.
11
-------
8. IUPAC Commission on Spectrochemical and Other Optical
Procedures for Analysis. Pure and Appl. Chem. 4_5:99, 1976.
9. Hershyn, W. Thin Target X-Ray Tubes for Elemental Analysis,
Res./Dev. 2_6 (8):32, 1975.
10. Gilfrich, J. V., M. C. Peckerar and L. S. Birks. Valence
States of Sulfur in Pollution Samples by X-Ray Analysis.
EPA-600/2-76-265, U.S. Environmental Protection Agency,
Research Triangle Park, N.C., 1976. 18 pp.
12
-------
APPENDIX
The instrument described in this report is in most ways a
conventional, manual wavelength-dispersive x-ray fluorescence
analyzer. As such, its operation is very straightforward for
anyone familiar with that type of equipment. However, the de-
tails of operation are included here to assist with the specific
steps required to provide for most efficient use of the instru-
ment. Also included in this Appendix are the details of the
circuitry, along with circuit diagrams as an aid if trouble-
shooting should become necessary.
OPERATION
Referring back to Figure 2, the controls on the base of the
instrument include the ON-OFF switch, the high voltage switch
(not shown), the high voltage adjust and tube current adjust
knobs, and the 26 adjust crank. Along with the dial to indicate
the 29 angle and the meter to read tube current, these controls
are used to turn the instrument on and set the spectrometer.
Operation of the instrument can best be illustrated as a series
of steps consisting of
1. Evacuating the spectrometer
2. Initial setting of electronics
• 3. Turning on x-rays
4. Setting counting circuit parameters
5. Measuring samples
Each of these steps will be treated in some detail.
13
-------
Initially, it should be ascertained that the preamplifier,
located immediately below the spectrometer tank is connected
properly, i.e. the signal cable coming out of the bottom of the
tank is connected to the input of the preamp, and that the preamp
power cable, the detector high voltage cable and a signal cable
are attached to the appropriate connectors at both the preamp end
and the counting electronics end. Figure A-l is a block diagram
of the counting electronics to illustrate proper connections.
This x-ray spectrometer is intended to be used with a conven-
tional set of N1MBIN counting electronics such as is available
from a myriad of manufacturers.
1. Evacuating the spectrometer: with the vacuum pump connected
to the copper tubing through the hole in the right side of the
chassis, the NaCl crystal is placed in the crystal holder and
the lid put on the chamber. Samples and appropriate blanks and
standards are put in the sample carrousel and the sample chamber
closed. Vacuum pump is turned on. If monitoring of the vacuum
condition is desired, the appropriate control box for the thermo-
couple gauge is attached to the gauge mounted in the spectrometer
lid; otherwise the sound of the vacuum pump can be used to
estimate the condition of the vacuum. (The thermocouple gauge
used is a CVCGTC-004 or its equivalent; an appropriate control
box would be the CVCGTC-100.)
2. Initial setting of the electronics: with a standard contain-
ing 30-50 ygS/cm^ in the sample chamber, the spectrometer set for
145° 26 (SKa with NaCl crystal) and the vacuum chamber pumped
down, set the electronics as follows: Pulse height analyzer-
Int. Diff switch in Int position, E at 1.00, AE at 0.50; ampli-
fier gain at the high end of its range; ratemeter range switch at
most sensitive position; timer set to maximum time; and detector
high voltage set to +1100 volts. Turn on power to the counting
circuits and reset and start the sealer. Adjust the "E" dial on
the pulse height analyzer so that it is set just high emough to
eliminate electronic noise (x-rays should not be turned on at this
14
-------
APPENDIX
The instrument described in this report is in most ways a
conventional, manual wavelength-dispersive x-ray fluorescence
analyzer. As such, its operation is very straightforward for
anyone familiar with that type of equipment. However, the de-
tails of operation are included here to assist with the specific
steps required to provide for most efficient use of the instru-
ment. Also included in this Appendix are the details of the
circuitry, along with circuit diagrams as an aid if trouble-
shooting should become necessary.
OPERATION
Referring back to Figure 2, the controls on the base of the
instrument include the ON-OFF switch, the high voltage switch
(not shown), the high voltage adjust and tube current adjust
knobs, and the 26 adjust crank. Along with the dial to indicate
the 28 angle and the meter to read tube current, these controls
are used to turn the instrument on and set the spectrometer.
Operation of the instrument can best be illustrated as a series
of steps consisting of
1. Evacuating the spectrometer
2. Initial setting of electronics
• 3. Turning on x-rays
4. Setting counting circuit parameters
5. Measuring samples
Each of these steps will be treated in some detail.
13
-------
Initially, it should be ascertained that the preamplifier,
located immediately below the spectrometer tank is connected
properly, i.e. the signal cable coming out of the bottom of the
tank is connected to the input of the preamp, and that the preamp
power cable, the detector high voltage cable and a signal cable
are attached to the appropriate connectors at both the preamp end
and the counting electronics end. Figure A-l is a block diagram
of the counting electronics to illustrate proper connections.
This x-ray spectrometer is intended to be used with a conven-
tional set of NIMBIN counting electronics such as is available
from a myriad of manufacturers.
1. Evacuating the spectrometer: with the vacuum pump connected
to the copper tubing through the hole in the right side of the
chassis, the NaCl crystal is placed in the crystal holder and
the lid put on the chamber. Samples and appropriate blanks and
standards are put in the sample carrousel and the sample chamber
closed. Vacuum pump is turned on. If monitoring of the vacuum
condition is desired, the appropriate control box for the thermo-
couple gauge is attached to the gauge mounted in the spectrometer
lid; otherwise the sound of the vacuum pump can be used to
estimate the condition of the vacuum. (The thermocouple gauge
used is a CVCGTC-004 or its equivalent; an appropriate control
box would be the CVCGTC-100.)
2. Initial setting of the electronics: with a standard contain-
ing 30-50 ygS/cm^ in the sample chamber, the spectrometer set for
145° 26 (SKa with NaCl crystal) and the vacuum chamber pumped
down, set the electronics as follows: Pulse height analyzer-
Int. Diff switch in Int position, E at 1.00, AE at 0.50; ampli-
fier gain at the high end of its range; ratemeter range switch at
most sensitive position; timer set to maximum time; and detector
high voltage set to +1100 volts. Turn on power to the counting
circuits and reset and start the sealer. Adjust the "E" dial on
the pulse height analyzer so that it is set just high emough to
eliminate electronic noise (x-rays should not be turned on at this
14
-------
APPENDIX
The instrument described in this report is in most ways a
conventional, manual wavelength-dispersive x-ray fluorescence
analyzer. As such, its operation is very straightforward for
anyone familiar with that type of equipment. However, the de-
tails of operation are included here to assist with the specific
steps required to provide for most efficient use of the instru-
ment. Also included in this Appendix are the details of the
circuitry, along with circuit diagrams as an aid if trouble-
shooting should become necessary.
OPERATION
Referring back to Figure 2, the controls on the base of the
instrument include the ON-OFF switch, the high voltage switch
(not shown), the high voltage adjust and tube current adjust
knobs, and the 29 adjust crank. Along with the dial to indicate
the 29 angle and the meter to read tube current, these controls
are used to turn the instrument on and set the spectrometer.
Operation of the instrument can best be illustrated as a series
of steps consisting of
1. Evacuating the spectrometer
2. Initial setting of electronics
" 3. Turning on x-rays
4. Setting counting circuit parameters
5. Measuring samples
Each of these steps will be treated in some detail.
13
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Initially, it should be ascertained that the preamplifier,
located immediately below the spectrometer tank is connected
properly, i.e. the signal cable coming out of the bottom of the
tank is connected to the input of the preamp, and that the preamp
power cable, the detector high voltage cable and a signal cable
are attached to the appropriate connectors at both the preamp end
and the counting electronics end. Figure A-l is a block diagram
of the counting electronics to illustrate proper connections.
This x-ray spectrometer is intended to be used with a conven-
tional set of NIMBIN counting electronics such as is available
from a myriad of manufacturers.
1. Evacuating the spectrometer: with the vacuum pump connected
to the copper tubing through the hole in the right side of the
chassis, the NaCl crystal is placed in the crystal holder and
the lid put on the chamber. Samples and appropriate blanks and
standards are put in the sample carrousel and the sample chamber
closed. Vacuum pump is turned on. If monitoring of the vacuum
condition is desired, the appropriate control box for the thermo-
couple gauge is attached to the gauge mounted in the spectrometer
lid; otherwise the sound of the vacuum pump can be used to
estimate the condition of the vacuum. (The thermocouple gauge
used is a CVCGTC-004 or its equivalent; an appropriate control
box would be the CVCGTC-100.)
2. Initial setting of the electronics: with a standard contain-
ing 30-50 ygS/cm^ in the sample chamber, the spectrometer set for
145° 20 (SKa with NaCl crystal) and the vacuum chamber pumped
down, set the electronics as follows: Pulse height analyzer-
Int. Diff switch in Int position, E at 1.00, AE at 0.50; ampli-
fier gain at the high end of its range; ratemeter range switch at
most sensitive position; timer set to maximum time; and detector
high voltage set to +1100 volts. Turn on power to the counting
circuits and reset and start the sealer. Adjust the "E" dial on
the pulse height analyzer so that it is set just high emough to
eliminate electronic noise (x-rays should not be turned on at this
14
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r
\r A C" TTT TTijf —
TANK
I
,
• '
PREAMP ,
DETECTOR
HIGH
VOLTAGE
SUPPLY
PREAMP
SIGNAL
1
1
1
1
1
1
L.
i-'UWt.K
1 '
AMPLIFIER
1
PULSE
HEIGHT
ANALYZER
4 _
SCALER C
•••^•m •••«•••»
RATE-
METER
. TIMER 1
««••••
~l
Figure A-l.
Block Diagram of Counting Electronics.
(Components inside dashed lines obtained
commercially.)
15
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stage.) When making this adjustment, it is probably more con-
venient to observe the sealer readout rather than the ratemeter
to determine the "E" setting at which the onset of noise occurs.
3. Turning on x-rays: Main on-off switch is turned on. Check
to be sure fan is operating. Turn on high voltage switch.
Increase high voltage adjust knob to some moderate values (say
20 on the dial). Increase tube current adjust to achieve some
small reading on the meter. Set the high voltage adjust knob
to the value read from the plot mounted on the instrument for
the operating voltage desired (see Figure A-2). Set the tube
current adjust knob so the meter reads the tube current desired.
NOTE 1: X-ray tube is rated at 50 watts with forced air cooling.
It is important that the fan be running whenever x-rays are on,
and for some time ( = 10 minutes) after x-rays are turned off.
Normal x-ray tube operation for measuring sulfur is 30 kV and
1.5 mA.
NOTE 2: The sample chamber is equipped with a safety switch so
that x-rays cannot be turned on with the chamber open, and so
that x-rays will be turned off if the chamber is opened when
x-rays are on.
NOTE 3; The sample chamber is equipped with a shutter (operated
by the knob on top of sample chamber) so that radiation from the
x-ray tube can be prevented from reaching the sample without
turning x-ray tube off. Since the sample chamber is vacuum
pumped through this opening, it is important that the shutter be
open during pump down. If it is closed, it will be difficult or
impossible to open it (and sample chamber will not be pumped
efficiently). If a safety switch could be mounted so that it
was actuated when the shutter was closed, and was wired in
parallel with the other safety switch, the sample chamber could
be opened with the shutter closed without turning off the x-rays,
assuming that the shutter is radiation-safe. This last point
would have to be confirmed.
16
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100
80
CD
u
cr
o
20
10 20 30
KILOVOLTS
40
Figure A-2. X-Ray Tube High Voltage as a function of
the Dial Reading.
17
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4. Setting counting circuit parameters: with the x-rays on
and set to 30 kV and 1.5 mA, adjust the 29 dial to achieve
maximum intensity. Change the Int.-Diff. switch to Diff. and
measure the pulse amplitude distribution of the S Kct radiation
by varying the "E" dial. The peak of the pulse amplitude dis-
tribution can be varied by changing the amplifier gain or the
detector high voltage. A convenient value for the peak is 3
volts on the "E" dial. This can be achieved by varying amplifier
gain and/or detector high voltage as necessary. With the "E"
dial set at the lower limit of the pulse amplitude distribution
and the "AE" dial set so that "E + AE" equals the upper limit,
the counting circuits are set properly.
5. Measuring samples: Sensitivity of the instrument is cali-
brated by using a standard and its appropriate blank. The timer
switch is changed to one of the fixed time positions (usually
10 or 100 seconds) and counting started by resetting the sealer
and pressing the start switch. Samples are run in the same way
as the standard, using an appropriate blank, remembering that
the x-ray tube must be turned off (or it will turn itself off)
when the sample chamber is opened to change samples. Vacuum is
released by opening the valve on the lid of the spectrometer.
Figures A-3 and A-4 illustrate the circuits for the x-ray
tube power supply and the preamplifier, respectively. Circuits
for the counting electronics should be provided by the supplier.
-------
120 V,.
60 Hz
FUSED
MAIN
POWER
SWITCH
VARIAC
H.V.
SWITCH
SAFETY
SWITCH
X-RAY
TUBE
H.V.
POWER
SUPPLY
FILAMENT
TRANSFORMER
FAN
X-RAY
TUBE
Figure A-3. Block Diagram of the Main Power Circuit.
19
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Figure A-4. Schematic Diagram of the Preamplifier
20
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TECHNICAL REPORT DATA
(Please read Instructions on the reverse before compli ting)
1. REPORT NO.
EPA-600/7-78-103
2.
3. RECIPIENT'S ACCESSION NO
4. TITLE AND SUBTITLE
PORTABLE VACUUM X-RAY SPECTROMETER
Instrument for On-Site Analysis of Airborne
Particulate Sulfur and Other Elements
6. PERFORMING ORGANIZATION CODE
5 REPORT DATE
June 1978
7. AUTHOR(S)
8. PERFORMING ORGANIZATION REPORT NO.
J. V. Gilfrich and L. S. Birks
9. PERFORMING ORGANIZATION NAME AND ADDRESS
Naval Research Laboratory
Code 6480
Washington, DC 20375
10. PROGRAM ELEMENT NO.
1NE625D EB-09 (FY-78)
11. CONTRACT/GRANT NO.
Interagency Agreement
EPA-IAn-D4-Q49Q
12. SPONSORING AGENCY NAME AND ADDRESS
Environmental Sciences Research Laboratory - RTP, NC
Office of Research and Development
U. S. Environmental Protection Agency
Research Triangle Park. NC 27711
13.
TYPE OF REPORT AND PERIOD COVERED
Final
14. SPONSORING AGENCY CODE
EPA/600/09
15. SUPPLEMENTARY NOTES
16. ABSTRACT
A portable vacuum wavelength-dispersive x-ray analyzer has been constructed
for on-site measurement of the sulfur content of filter-deposited airborne
particles. Although designed to analyze for sulfur, the spectrometer is adjust-
able over a limited range providing the potential for determining other elements.
With the x-ray tube rated at 50 watts, the instrument achieves a. 100-second 3a
detection limit for sulfur of better than 0.5 vg/cm.
17.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.IDENTIFIERS/OPEN ENDED TERMS
COSATI Held/Group
*Aerosols
*Sulfur
*X-ray analysis
*X-ray fluorescence
*X-ray spectrometers
*Air pollution
13B
07D
07B
14B
20F
18. DISTRIBUTION STATEMENT
RELEASE TO PUBLIC
19. SECURITY CLASS (This Report)
UNCLASSIFIED
21. NO. OF PAGES
25
20. SECURITY CLASS ITMspagei
UNCLASSIFIED
22. PRICE
EPA Form 2220-1 (R«v. 4-77) PREVIOUS EDIT.ON .:. OBSOLEI E
21
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