An Experimental Examination of Theories relating the Absorption of γ-ray Energy in a Medium to the Ionization produced in a Cavity

The results of calculations, employing values of average excitation potentials from a recent review, are presented for both the Bragg-Gray theory and the Spencer-Attix theory of cavity ionization. The variation of ionization with the pressure, with the atomic number of the gas and with the atomic number of the chamber wall predicted by these theories is compared with measured values. The experimental results agree closely with the theoretical predictions of Spencer and Attix, except for hydrogen at low pressures. This discrepancy is attributed in part to the transfer of slow electrons between electrodes.