Abstract
A new aerosol monitor rapidly measures the mass concentration of individual elements with atomic number Z>20 in dust- or smoke-laden air. The device separates the aerosol's nongaseous components by pumping the air through a section of a filter paper tape. After gathering particles for a fixed period of time, pumping stops and the tape advances, forcing a new section to intercept the airstream and bringing the exposed section in front of a 25 mCi (milli Curies) Cd109 radioactive source. The source bombards the tape's contents with 22 keV (kilo-electron-Volts) X- rays. These, in turn, induce fluorescence in the trapped atoms; that is, they cause the atoms to emit X-rays of their own at lower but still easily measurable (if Z>20), characteristic energies. An analysis of the latter's X-ray energy spectrum provides raw data revealing the identity and abundance of each corresponding element in the aerosol simultaneously. Note that the X-ray fluorescence method is independent of the state of chemical combination of the species in question. A prototype device has been tested using deployed uranium and iron aerosols and prepared calibration deposits containing the elements U, Cr, Pb, Hg, W, Br, I, Mo, Cu, Zn, Fe, and As.With the exception of iodine, it readily measured levels corresponding to mass concentrations of a few tens of μg/m3 or less in 10 minutes. At mass concentrations in the few mg/m3 range, measurement times of a minute or less were easily achieved. This sensitivity, coupled with its ease of calibration, straightforward data analysis, and basic simplicity make the instrument suitable for many applications, especially those involving field work.
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