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X-RAY ANALYSIS OF AIRBORNE ASBESTOS. FINAL REPORT: DESIGN AND CONSTRUCTION OF A PROTOTYPE ASBESTOS ANALYZER
Citation:
Birks, L., J. Gilfrich, AND J. Sandelin. X-RAY ANALYSIS OF AIRBORNE ASBESTOS. FINAL REPORT: DESIGN AND CONSTRUCTION OF A PROTOTYPE ASBESTOS ANALYZER. U.S. Environmental Protection Agency, Washington, D.C., EPA/600/2-78/194.
Description:
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 (PB-241 285 and PB-266 671). The prototype instrument uses 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 2 theta 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 to the 11th power photons/sec. Preliminary tests with the analyzer indicate a sensitivity of 18 photons per second per microgram of chrysotile and a calculated sigma detection limit of 0.1 microgram for a 500 second measurements. Amosite has a somewhat better sensitivity and detection limit.