The collection efficiency of Whatman 41 filter paper has been determined using submicron test aerosols of monodispersed polystyrene latex. Measurements w-ere made over a velocity range of 12-195 f.p.m., using aerosols with diametcrs of 0.088,0.188,0.264, 0.365 and 0.557 p. For sizes less than 0.557 ,LL, well-developed efficiency minima occur in the velocity range of 20-30 f.p.ni. In no case was the efficiency found to be below 70 per cent. At 195 f.p.m. the efficiency was essentially size-independent.
Direct alpha pulse spectroscopy of air samples collected on membrane filters eliminates the time delay for the decay of natural alpha background or requirements for special sample preparation. Air samples are collected on I-in.-diameter Millipore SM filters at flow rates of 1 cfm for periods of 24 hr. Samples are counted at a pressure of 10-100 p using a 450-mm2 surface barrier detector. Detector output is fed through a low noise, charge-sensitive preamplifier, a biased main amplifier, and into a multi-channel analyzer. Energy resolution of 200 keV (FWHM) or better is obtained.
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