The average energies, W, required to form an ion pair in liquefied rare gases

Abstract

The average energies, W, required to form an ion pair in liquid argon, krypton and xenon have been determined by measuring steady conduction currents produced by a 63Ni beta -source and are found to be 23.7+or-0.7, 20.5+or-1.5 and 16.4+or-14 eV, respectively, which are clearly lower than the corresponding W-values in the gaseous state. The W-value of liquid argon obtained by the present experiment is in good agreement with that obtained recently by the pulse method. Applying Platzman's theory, W-values of the liquid rare gases are explained by the band-gap energies or by the polarization energies which are assumed to be nearly equal to those of the solid rare gases. Discussions on the extrapolation method, often used to evaluate W-values in the liquid state, are also made.