Measurement of W Values of Low-Energy Electrons in Several Gases

Abstract

The W value, the mean energy required to form an ion pair, was measured for monoenergetic electrons in the energy range from 5 to about 500 eV in air, N2, O2, CO2, tissue-equivalent gases (Rossi-Failla and Srdoc mixtures), methane, ethane propane, n-butane, i-butane, pentane, hexane, nonane, ethylene, acetylene, ethanol, acetone, H2O, D2O, H2, D2, C6H6, C6D6, argon, krypton, and xenon. The W values of all gases increase continuously with decreasing electron energy; they approach infinity asymptotically at the ionization threshold and the well-known energy-independent high-energy W values at high electron energies. A comparison between the results and newer experimental and theoretical works of other authors sometimes shows very good agreement. The experimental error is estimated to be less than 2%.