Temperature dependence of the calibration factor of radon and radium determination in water samples by SSNTD

The sensitivity of a ²²⁶Ra determination method of water samples by SSNTD was measured as a function of storage temperature during exposure. The method is based on an etched track type radon monitor, which is closed into a gas permeable foil and is immersed in the water sample. The sample is sealed in a glass vessel and stored for an exposure time of 10–30 days. The sensitivity increased more than a factor of two when the storage temperature was raised from 2 °C to 30 °C. Temperature dependence of the partition coefficient of radon between water and air provides explanation for this dependence. For practical radio-analytical application the temperature dependence of the calibration factor is given by fitting the sensitivity data obtained by measuring ²²⁶Ra standard solutions (in the activity concentration range of 0.1–48.5 kBq m⁻³) at different storage temperatures.