&EPA
United States
Environmental Protection
Agency
Environmental Sciences Research
Laboratory
Research Triangle Park NC 27711
EPA-600 2-78-194
August 1978
Research and Development
X-Ray Analysis of
Airborne Asbestos
Final Report:
Design and
Construction of a
Prototype Asbestos
Analyzer
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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 ENVIRONMENTAL PROTECTION TECH-
NOLOGY series. This series describes research performed to develop and dem-
onstrate instrumentation, equipment, and methodology to repair or prevent en-
vironmental degradation from point and non-point sources of pollution. This work
provides the new or improved technology required for the control and treatment
of pollution sources to meet environmental quality standards.
This document is available to the public through the National Technical Informa-
tion Service, Springfield, Virginia 22161.
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EPA-600/2-78-194
August 1978
X-RAY ANALYSIS OF AIRBORNE ASBESTOS
Final Report: Design and Construction
of a Prototype Asbestos Analyzer
by
L. S. Birks, J. V. Gilfrich, and J. W. Sandelin
Radiation Technology Division
Naval Research Laboratory
Washington, D. C. 20375
Interagency Agreement EPA-IAG-D6-0651
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
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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.
•XI'
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ABSTRACT
A prototype asbestos analyzer has been designed and
constructed for use by the Environmental Protection Agency.
It incorporates the principle of broad-beam x-ray optics and
the special fiber-aligned sample described in earlier reports
under this interagency agreement (1,3). The prototype
instrument utilizes two detectors for simultaneous measure-
ment of diffracted signal and background; the mass of asbestos
is simply the net difference in intensity for these two detectors
normalized by the sensitivity of the analyzer as determined
using standards.
The prototype analyzer is contained in a vacuum box
15x15x32 cm and mounts on top of a standard commercial x-ray
power supply. It uses a Cr target spectrographic tube which is
located in a separate lead-shielded enclosure in the box. The
mechanics of selecting the 26 diffracting angles for different
forms of asbestos are unique and especially designed to minimize
the space required. The beam trap is a critical component of
the instrument; it reduces the backseattered noise signal to
less than 100 photons/sec from an incident beam of about 10
photons/sec.
Preliminary tests with the analyzer indicate a sensitivity
of 18 photons per second per ug of chrysotile and a calculated
3g detection limit of 0. 1 yg for a 500 second measurement.
Amosite has a somewhat better sensitivity and detection limit.
111
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1. INTRODUCTION
In the first report under this interagency agreement (1),
a new type of broad-beam x-ray optics was described, and a
commercial x-ray spectrometer was modified to measure the dif-
fracted intensity from aligned asbestos fibers in a special
sample configuration. The 500 second, 3a detection limit re-
ported was 0.15 ug, nearly two orders of magnitude better than
by any previously reported x-ray diffraction method (2). This
favorable detectability coupled with the simplicity and pro-
jected low cost of the x-ray measurement compared to electron
microscopy indicated considerable promise for large-scale
routine analysis.
The second report of this series (3) described the specimen
preparation technique and the problems encountered in aligning
the asbestos fibers on the special grid used to produce an
electrostatic field. Sonication to disperse the individual
asbestos fibrils, ashing to remove organic matter, variation of
the alignment medium, control of temperature and humidity were
all described in Reference 3. This specimen-preparation effort
to define the critical parameters has continued at the Environ-
mental Sciences Research Laboratory of the Environmental Pro-
tection Agency (EPA), Research Triangle Park, N. C., resulting
in a reproducible method of aligning the fibers, at least in
the presence of a minimum of extraneous particulate material
(personal communication, J. Wagman).
In this report we describe the design and construction of
the working prototype asbestos analyzer instrument. It is
based on the previous laboratory experiences and incorporates
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a dual detector system for measuring signal and background
simultaneously. Preliminary test results with the prototype
instrument are given for samples containing known masses of
standard asbestos. Further testing and analysis of real
environmental samples (e.g., airborne, waterborne, quarried
rock, iron ore, etc.) are planned by the EPA Environmental
Sciences Research Laboratory.
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2. SUMMARY
A prototype asbestos analyzer has been designed and
constructed for EPA. It uses special x-ray optics and
specimen preparation and can detect and identify as little
as 0.1 ug of chrysotile or other asbestos fibers in a
500 second counting interval.
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3. CONCLUSIONS
The asbestos analyzer allows fibrous asbestos to be dis-
tinguished uniquely from nonfibrous forms or clay minerals of
similar crystallographic characteristics. It relies on sample
preparation which causes the asbestos fibers to be oriented on
a special grid, and on broad-beam x-ray optics which allows
specific 29 diffraction angles to be selected for large-area
specimen deposits. It can detect submicrogram amounts of
asbestos and measure them quantitatively. The capital invest-
ment in equipment and the time per analysis are both far less
than for electron microscopy; thus the cost per analysis may
be reduced by as much as a factor of ten. In terms of
identification of specific asbestos forms and quantitation
of the mass present the diffraction method appears better than
electron microscopy on both counts. Thus the diffraction
method may find its greatest application as a rapid, low-cost
screening method for large scale analysis. If the total mass
does not exceed prescribed limits, there is no need for ex-
pensive electron microscopy; if the mass is greater than the
specified limits then electron microscopy of a similar sample
might be appropriate.
4
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4. RECOMMENDATIONS
The prototype asbestos analyzer should be calibrated for
the various forms of asbestos using standard fibers prepared
the same way as unknown samples. After calibration it should
be tested by running a series of real specimens collected at
selected asbestos emission sites. Comparison of at least some
of the runs on real samples should be made by electron micros-
copy on aliquots collected from the same source and at the
same time as the x-ray samples.
The x-ray method should be tested for interference by other
particulate matter collected along with the asbestos. Generally
this interference will be in the form of increased nondiffraction
background but occasionally there may be.partial overlap with
the diffraction pattern of clay minerals or nonfibrous serpentines
or amphiboles. Spiked samples containing known ratios of
asbestos to bulk particulate matter can be prepared for the inter-
ference tests using standard asbestos. A recommended range of
spiking would be from 1 part in 10 to 1 part in 1000.
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5. REVIEW OF CONCEPTS
From the beginning of the work it has been recognized
that ordinary x-ray diffraction procedures cannot distinguish
chrysotile fibers from platy serpentine and likewise cannot
distinguish other asbestos fibers from clay minerals with
similar diffraction characteristics. Two factors had to be
considered in order to provide a practicable method which could
measure the net fiber content of samples containing interference
from nonfibrous components. These two factors were:
1.) The fibers must be aligned parallel to each other in
order to obtain preferred orientation in a diffraction
pattern, Fig. 1.
2.) Photographic film cameras are not sensitive enough
for the small mass of asbestos of interest, and the usual
diffractometer optics are not suitable because crystal planes
parallel to the fiber axis diffract equally well whatever the
orientation of the specimen, Fig. 2.
To satisfy the two requirements a new sample preparation
technique was necessary and a new type of x--ray optics had to
be developed.
Sample Preparation. The scheme for aligning the asbestos
fibers experienced many pitfalls as described in Reference 3.
These difficulties have been overcome in the work carried out
at the EPA laboratories, cited previously. In general the
preparative method can be described in the following steps:
1.) A sample containing fibrous asbestos is filtered
from air or water onto Millipore or similar substrate.
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JfcrW-
' -
B
a
Fig. 1. X-ray powder diffraction patterns of chrysotile
asbestos taken with photographic film:
a.) unoriented fibers, b.) fibers oriented
with axis vertical.
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detector
ooon o
Fig. 2. Usual diffractometer optics allows diffraction from
planes parallel to the fiber axis irrespective of
the orientation of the fibers in the plane of the
specimen.
8
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2.) The substrate and other organic matter is removed by
ashing. (Note, some technique for physically separating asbestos
and the clay minerals from the bulk of other particulate material
is desirable; work to this end is being sponsored by EPA.)
3.) The residue is suspended in 1 ml of water plus a
wetting agent (1/2% aerosol OT) and sonicated vigorously to
disperse the particles and break up the asbestos fibers into
individual fibrils.
4.) The suspension is again filtered and ashed.
5.) This time the residue is taken up in the "alignment
medium", (up to 0.1 ml of amyl acetate) and sonicated gently to
disperse the particles.
6.) The amyl acetate is placed on a special alignment grid,
Fig. 3, and a voltage applied to align the fibrous asbestos,
Fig. 4.
7.) A thin film of nitrocellulose is sprayed on the grid,
stripped off with the sample, and mounted on a support ring as
the final specimen.
X-ray Optics. The parallel broad-beam optics developed is shown
schematically in Fig. 5. Radiation from the large focal spot of
a spectrographic x-ray tube is rendered parallel by the collimator
and strikes the specimen which is mounted perpendicular to the
beam. The strongest diffracting planes parallel to the fiber
axis have large d-spacings (e.g. 002 planes in chrysotile:
d = 7.38 A). A Cr-target x-ray tube is chosen Jto provide the
longest practical characteristic-line wavelength to diffract at
as large a 29 angle as possible. Background radiation at the
same 28 angle is contributed by scattering or diffraction from
randomly oriented other particulate material and is of equal
intensity at both detectors. Subtracting the intensity at
Detector II from that at Detector I gives the net intensity
from fibrous asbestos alone.
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Pig. 3. Special multielectrode grid used in the alignment
of asbestos fibers. Interelectrode distance is
approximately 0.8 mm.
10
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Fig. 4. Micrograph of asbestos fibers aligned across the
special grid of Fig. 3.
11
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detector
IE
secondary
col li motor
(blades)
detector
I
primary
collimator
(tubes)
secondary
collimator
(blades)
x-ray
tube
Fig. 5. Schematic of broad-beam x-ray optics for measurement
of aligned asbestos fibers. Detector I measures
the diffracted beam corresponding to the strong
spot at position A in Fig. 1. Detector II
measures the background corresponding to the
position B in Fig. 1.
12
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6. DESIGN OF THE ASBESTOS ANALYZER
Fig. 6 shows the layout of the vacuum box which contains
the analyzer.
Primary Beam. The x-ray tube is in a lead-shielded compartment.
The primary collimator extends from this compartment to the
specimen; the collimator consists of a 10x10 array of square Ni
tubes each 0.75 mm on a side and 50 mm long to allow passage of
the beam from the 6x8 mm oval projected-size tube focal spot.
The collimator housing extends almost to the specimen to prevent
the detectors seeing scattering or fluorescence from the ends of
the collimator tubes.
Sample Mount. The sample inserts on a stalk from the top of the
box through a hole with an o-ring seal.
Vacuum. Pumping is with an ordinary mechanical pump and a
vacuum of about 0.5 torr is achieved.
Setting the 26 Angle. To simplify the mechanics of the secondary
collimators they are mounted and driven as shown schematically
in Fig. 7. The collimator is mounted on a segment of a large
worm wheel with its axis offset from the specimen position. Thus
radiation diffracted at different 29 angles passes through
different portions of the secondary collimator to the fixed
detector as shown in Fig. 7.
Detectors. The two detectors are scintillation photomultipliers
mounted outside the vacuum box. They view the diffracted
radiation through vacuum-tight Be windows. Lead apertures
inside the Be windows limit the angular range of the diffracted
radiation between 14 and 20 degrees 20 and thus insure that the
13
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to vacuum
pump
,1,
x-ray
tube
primary
collimator
specimen
+/
beam trot
secondary
collimator
""yric^ewii
I I M. A.
window
detector I
Fig. 6. Schematic of components. The detectors are outside
the vacuum box (Detector II not shown so that the
beam trap can be seen).
14
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specimen
axis of
rotation
diffracted
beam
fixed _
detector
a
Fig. 7. Detail of drive mechanism for secondary collimator.
a.) With collimator set at minimum 26 angle diffracted
beam passes through inner portion of blades.
b.) With collimator set at maximum 26 angle diffracted
beam passes through outer portion of blades.
15
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accepted radiation is confined within the 25 ram diameter detector
windows. Electronics for detector readout are standard solid-
state counting circuits usually consisting of amplifier, pulse
height analyzer, sealer-timer and ratemeter.
Beam Trap. Perhaps one of the most critical components for
satisfactory operation is the beam trap which extends physically
beyond the box wall but is within the vacuum enclosure. As
shown in Fig. 8 the trap consists of 2.5 mm diameter lead tubes
40 mm long and backed by a graded Z absorber consisting of
18 urn Al foil followed by 3 mm of lead. This component is
critical because it is necessary to reduce the primary beam
11 2
of about 10 photons/sec to less than 10 photons/sec of
backscattered radiation. Without the beam trap it would be
impossible to measure the asbestos diffraction intensity of 15-
20 photons per second per pg above the tremendous scattered
background intensity.
16
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vacuum
box
aluminum
foil
round lead
tubes
lead
Fig. 8. Detail of beam trap. The lead tubes reduce the solid
angle of backscatter. The aluminum foil reduces
lead fluorescence from the lead backing.
17
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7. PRELIMINARY TESTS OF THE ANALYZER
Aligned samples of standard chrysotile and amosite were
used to test the operation of the instrument. Fig. 9 shows
stripchart recordings of scans through the diffraction angle
with each detector. In practice, scanning the 29 range is not
required. Rather, each detector would be set at the 29 peak
for the type of asbestos of interest and the number of photons
counted for a selected time interval. Table 1 shows the results
of 500 sec counting intervals at the peak 29 position for each
type of asbestos.
TABLE 1. X-RAY -.RESULTS. FOR STANDARD, ASBESTOS: SAMPLES
Type
Quantity 29 angle Det. I Det. II Sens,S
. yg degrees c/500 s c/500 s c/500 s/yg
Chrysotile 5.3
Amosite ^5
17
15
.8
.9
148
233
,212
,788
100,
175,
818
195
8942
11719
0.
0.
1
1
For an unknown sample the difference between Detector I and
Detector II divided by the sensitivity, S, gives the mass of
asbestos according to Eg. 1.
mass in yg = (Detector I - Detector II)/S
(1)
18
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detector I
18
29 (degrees)
Fig. 9. Diffraction peak for chrysotile as recorded by
Detector I and background as recorded by
Detector II.
19
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REFERENCES -'
1. Birks, L. S., M. Fatemi, J. V. Gilfrich, and E. T. Johnson.
Quantitative Analysis of Airborne Asbestos by X-Ray
Diffraction. EPA-650/2-75-004, 1975, U. S. Environmental
Protection Agency, Research Triangle Park, N. C., 11 pp.
2. Rickards, A. L. Estimation of Trace Amounts of Chrysotile
Asbestos by X-Ray Diffraction. Analytical Chemistry 44(11):
1872-3, 1972.
3. Fatemi, M., E. T. Johnson, R. R. Whitlock, L. S. Birks, and
J. V. Gilfrich. X-Ray Analysis of Airborne Asbestos. Interim
Report: Sample Preparation. EPA-600/2-77-062, 1977, U. S.
Environmental Protection Agency, Research Triangle Park, N. C.,
29 pp.
20
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TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing)
REPORT NO.
EPA-6QO/2-78-194
3. RECIPIENT'S ACCESSION NO.
4. TITLE AND SUBTITLE
X-RAY ANALYSIS OF AIRBORNE ASBESTOS
Final Report: Design and Construction of a
Prototype Asbestos Analyzer
5, REPORT DATE
August 1978
6. PERFORMING ORGANIZATION CODE
7. AUTHOR(S)
L. S. Birks, J. V. Gilfrich, and 0. W. Sandelin
8. PERFORMING ORGANIZATION REPORT NO
9. PERFORMING ORGANIZATION NAME AND ADDRESS
Radiation Technology Division
Naval Research Laboratory
Washington, D. C. 20375
10. PROGRAM ELEMENT NO.
1AD712 BA-25 (FY-77)
11. CONTRACT/GRANT NO.
EPA-IAG-D6-0651
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, N.C. 27711
13. TYPE OF REPORT AND PERIOD COVERED
Final 1Q/76-6/78
14. SPONSORING AGENCY CODE
EPA/600/09
15. SUPPLEMENTARY NOTES
16. ABSTRACT
A prototype asbestos analyzer has been designed and constructed for use by the
Environmental Protection Agency. It incorporates the principle of broad-beam x-ray
optics and the special fiber-aligned sample described in earlier reports (EPA-650/2-
75-004 and EPA-600/2-77-062). The prototype instrument utilizes two detectors for
simultaneous measurement of diffracted signal and background; the mass of asbestos is
simply the net difference in intensity for these two detectors normalized by the
sensitivity of the analyzer as determined using standards.
The prototype analyzer is contained in a vacuum box 15x15x32 cm and mounts on
top of a standard commercial x-ray power supply. It uses a Cr target spectrographic
tube which is located in a separate lead-shielded enclosure in the box. The mechanics
of selecting the 2e diffracting angles for different forms of asbestos are unique and
especially designed to minimize the space required. The beam trap is a critical
component of the instrument; it reduces the backscattered noise signal to less than
100 photons/sec from an incident beam of about 10'' photons/sec.
Preliminary tests with the analyzer indicate a sensitivity of 18 photons per
second per yg of chrysotile and a calculated 3a detection limit of 0.1 yg for a 500
second measurements. Amosite has a somewhat better sensitivity and detection limit.
17.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.lDENTIFIERS/OPEN ENDED TERMS C. COSATI F;ield/Group
* Air pollution
* Asbestos
* Analyzers
Design
* X-ray diffraction
* Alignment
Quantitative analysis
Chrysotile
Amosite
13B
08G
HE
14B
20F
07D
18. DISTRIBUTION STATEMENT
RELEASE TO PUBLIC
19 SECURITY CLASS (This Report I
UNCLASSIFIED
. NO. OF PAGES
20 SECURITY CLASS (This page)
UNCLASSIFIED
_25_
22. PRICE
EPA Form 2220-1 (Rev. 4-77) PREVIOUS EDIT,ON l£
21
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