Calculation of electron deposition in proportional counters

Efficiency extrapolation is a common technique in the standardization of radionuclides by the technique of 4πβ–γ coincidences. It can be achieved in two ways: adding thin films onto the radioactive source or by electronic discrimination in a pressurized 4πβ–γ system. The last case is the most extensively used actually in metrology laboratories. There is a need to know the electron energy loss inside the proportional counter as a function of the electron energies and working pressures. Calculations of electron energy loss have been performed for electron energies in a range from a few keV to 2 MeV in a mixture of Ar(90%) CH4(10%) and for pressures ranging from 100 to 2000 kPa in a 5 cm radius proportional counter. Wall effects, such as electron backscattering, are included in the calculations. Results are provided in the form of graphs and some recommendations are given about the optimal values of the energies that can be used to perform the extrapolation in the standardization of some radionuclides.