Average Energy to Produce an Ion Pair for Heavy Charged Particles in Gases Measured as a Function of Particle Energy

Abstract

In order to determine W, an average energy to produce an ion pair, in gases at atmospheric pressures for heavy ions, an apparatus consisting of a particle-energy degrader, an ionization chamber and a time-of-flight energy spectrometer was constructed, where two types of pulse operation modes in an ionization chamber were employed. Using heavy-ion beams from an accelerator, the values of W were measured for He/sup 2+/, C/sup 6+/, and N/sup 7+/ ions in air and tissue-equivalent gas of the pressures of 500 to 760 torr as a function of the energy of ions. For C/sup 6+/ and N/sup 7+/ ions, the energy dependence of W was clearly observed in both gases, while W for He/sup 2+/ ions was approximately constant over a wide rage of the energy. The differential W-values were also measured in two gases. In air, the differential W-values for C/sup 6+/ and N/sup 7+/ ions are almost equal to the value of W for high energy electrons.