Ionization yields for heavy ions in gases as a function of energy

For the experimental determination of an average energy to produce an ion pair in gases, W, by heavy ions from accelerators, an apparatus consisting of a particle-energy degrader, an ionization chamber, and a time-of-flight (TOF) energy spectrometer was designed and constructed, where two types of pulse operation modes in an ionization chamber were employed. Using this system, the values of W were measured for He and C ions in pure argon and air as a function of the energy of ions. For the C ions, the energy dependence of W was clearly observed, while W for He ions was approximately constant over a wide rage of energy (the mean value was 26.5plusmn0.9 eV in argon and 34.3plusmn1.3 eV in air, respectively) and agreed well with the value for 5.49 MeV alpha particles from ²⁴¹Am in each gas. The value of W for C ions obtained at the highest energy was also in good agreement with the value for 5.49 MeV alpha particles in each gas