| 摘要 |
The Alpha Energy Range Discrimination (AERD) method employs first and second proportional counter tubes separated by a foil and an electronic evaluation system, and comprises the following steps: (a) a filter is disposed in the stream of air flow and is thereby covered with dust, no artificial aerosol alpha activity being present; (b) the radiation of natural nuclides is measured by means of the first and second counter tubes in pulses per second, and respective count rates alpha1 and alpha2 are determined; (c) the ratio alpha1/alpha2 is plotted graphically against alpha2 and corresponding constant values a1 and a2 are determined for each counter tube in accordance with the least square fit method; (d) the counter tubes are arranged with the second counter tube above the first counter tube, separated by the separating foil, so that the lower counter tube measures the radiation of both natural and artificial nuclides (count rate alpha1) while the upper counter tube measures only the radiation of natural nuclides (count rate alpha2); (e) the air volume V in cubic meters flowing through the filter during the measurement time is measured; and (f) the resulting artificial aerosol alpha activity concentration C, in becquerels per cubic meter, is calculated in accordance with the formula <IMAGE> in which eta is the sensitivity of the lower counter tube expressed as a decimal fraction. The separating foil preferably has a coating thereon with a mass of about 0.9 to 2 mg/cm2.
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