A method for the measurement of the absolute value of w for X-rays in noble gases: results at 5.9 keV in xenon

A method is described that allows the measurement of the absolute value of the average energy to produce an ion pair, w, in noble gases for soft X-rays and its energy dependence. It uses a specially designed gas proportional scintillation counter working under electric fields below the ionization threshold. The spectrum of the radiation absorbed, and so the number of photons detected at each energy for a period of time on the order of the minute, is measured with the scintillation counter and, at the same time, the total primary electron charge produced is collected in one of the grids and measured with an electrometer. For pure xenon at 1030 mbar, a value of w=24.2±2.5 eV is measured with 5.9-keV X-rays