Calibration of a polycarbonate etched track detector

The efficiency of the Karlsruhe etched track detector was determined over a wide range of radon exposures. Sixty four detectors were placed in an airtight chamber. The radon concentration was kept at about 80 kBq.m^-3 by circulating air over a solid radium source. At predetermined times, a group of four detectors was taken out of the chamber. The exposure period varied from a few hours up to several months in order to determine the efficiency curve for low exposure as well as for the region of saturation. The functional form y = a (1 - e(-bx)) was fitted to the data. The low exposure range was fitted with only the first six data points. The slope is 0.546 tracks.cm^-2.kBq(-l).m³.h^-1, which is comparable to the earlier value of 0.55 tracks.cm^-2.kBq^-1.m³.h^-1. The high exposure range was fitted with the whole data set. The two curves intersect at 2700 tracks cm^-2. At higher track densities the curve based on the whole data set has to be used to convert the number of tracks into an exposure.