PubMed · 8266089
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R Stone. 1993-12-24. Scientists study 'cold war' fallout.. https://doi.org/10.1126/science.8266089
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A continuous potential alpha energy concentration monitor was developed to estimate the lung dose for inhalation of radon progeny. A silicon semiconductor detector was used as a detector. The build-up method was used and alpha particles emitted from 218Po, 214Po, 212Bi, and 212Po were detected. As 218Po and 212Bi have alpha particles of nearly the same energy, three detecting channels were set up. Counts corresponding to each nuclide were sent to a printer every 30 min. For the purpose of determining the potential alpha energy concentration of radon progeny continuously, a proper calculation procedure was investigated in detail. With this method, 218Po concentration and potential alpha energy concentration of radon progeny could be continuously obtained. The potential alpha energy concentration based on this procedure agreed well with that calculated from individual radon progeny concentration. When the measurement was done at 30-min intervals, the minimum detectable concentrations of 218Po concentration and equilibrium equivalent radon concentration were 0.3 Bq m(-3) and 0.15 Bq m(-3), respectively. The monitor can be used not only to estimate the lung dose but also to analyze environmental behavior of radon progeny.
The standard mathematical treatment of the buildup and decay of airborne radionuclides on a filter paper uses the solutions of the so-called Bateman equations adapted to the sampling process. These equations can be interpreted as differential equations for the expectation of an underlying stochastic process, which describes the random fluctuations in the accumulation and decay of the sampled radioactive atoms. The process for the buildup and decay of airborne 218Po can be characterized as an "immigration-death process" in the widely adopted, biologically based jargon. The probability distribution for the number of 218Po atoms, accumulated after sampling time t, is Poisson. We show that the distribution of the number of counts, registered by a detector with efficiency epsilon during a counting period T after the end of sampling, is also Poisson, with mean dependent on epsilon, t, T, the flowrate and N(o), the number of airborne 218Po atoms per unit volume. This Poisson distribution was used to construct the likelihood given the observed number of counts. After inversion with Bayes' Theorem we obtained the posterior density for N(o). This density characterizes the remaining uncertainty about the measured number of 218Po atoms per unit volume of air.