W-values for heavy ions in gases

The determination of W, an average energy to produce an ion pair, for heavy ions in gases at atmospheric pressures has been made using heavy-ion beams from an accelerator. The values of W were measured for He²⁺ and C⁶⁺ (<6 MeV/n) in propane-base tissue-equivalent gases of the pressures of 500 to 760 Torr as a function of the energy of ions. For C⁶⁺, the energy dependence of W was clearly observed, while W for He²⁺ was approximately constant over a wide range of the energy. The differential values of W (w) were also measured for C⁶⁺ (<6 MeV/n and 100 MeV/n) and Ar¹⁸⁺ (100 MeV/n) and are almost equal to the value of W for He²⁺.