Average energy expended per ion pair in liquid xenon

Measurements were made of the average energy W per ion pair formed in liquid xenon by internal-conversion electrons from 207Bi. Voltage pulses were observed resulting from electron collection either in liquid xenon or in a gaseous mixture of argon (95 percent) and methane (5 percent). The relative pulse heights for the two materials determine the ratio of the W values. Using the known W for the gaseous mixture, a liquid-xenon W of 15.6 + - 0.3 eV was obtained. This value is considerably smaller than the gas-phase values, 21.5 or 21.9 eV. For interpretation, Platzman's energy-balance equation was adapted to liquids, assuming a conduction-band picture. Theoretical values thus calculated agree well with experiment