Spectrometrically accompanied counting methods for measurements of activity of radon daughters

The α-decay of radon daughters makes a significant contribution to the annual dose of the radiation exposure of humans. To estimate the exposure of the human lung, the respective portion of the α-decay from polonium isotopes is of particular relevance. In the decay chains starting with 222Rn, some β/γ decaying isotopes can, however, be observed. For a basic investigation of the transmission to humans of α-energy from a known radioactivity concentration, all the activities of radon daughters along the chain of decay must be measured simultaneously. Commerical spectrometers are not suitable for accurate measurements of the activity as a function of time with strongly varying pulse rates, due to their imprecise dead time corrections. An energy-selective counting device has therefore been installed in the PTB. The spectrometry system is still used for a parallel control of the isotope mixture. Using the energy-selective counting device it is possible for the characteristic peaks of each nuclide to be cut off from the spectrum and individually analysed. For the dead time correction, in each channel a dead time stage is introduced, allowing the dead time corrections to be calculated. Several applications of the device are discussed. (orig.)