Ionization loss of relativistic electrons and its fluctuations in gas proportional counters

Measurements of the ionization loss have been achieved with high accuracy using two proportional counters with sensitive lengths of 9 and 30 cm, filled with Ar+10% CH₄ mixture at various pressures (0.13 approximately 2.0 atm). The widths of the ionization loss distributions disagree with those predicted by the Landau (1944) and Blunck-Leisegang (1950) theories, but rather, are in fairly good agreement with those calculated by Ispiryan et al. (1974) using the Monte Carlo method. In traversing thin layers of the counter gas, the most probable energy losses are smaller than those predicted by the Landau formula with the inclusion of the Sternheimer correction for the density effect, but the discrepancy decreases as the thickness of the gas layer increases. Furthermore, both sets of data obtained from the two counters lie almost on the curve of the most probable energy loss plotted against the thickness of the counter gas. The Garibyan and Ispiryan interpretation (1972) seems to provide the best explanation as it takes into account the transition radiation effect.