The Average Energy per Ion Pair, W, for Hydrogen and Oxygen Ions in a Tissue Equivalent Gas

Measurements are reported for the value of W (the average energy required to form an ion pair) for hydrogen and oxygen ions in the Rossi-Failla, tissue-equivalent gas mixture. The University of Virginia kevatron linear dc ion accelerator was used to produce the monoenergetic ions. For the six different incident monoenergetic hydrogen ions employed with kinetic energies ranging from 3.72 to 48.24 keV per atom, the values for W ranged from 46.5 to 30.4 eV per ion pair. For the incident monoenergetic oxygen ions employed with kinetic energies of 24.52 and 49.05 keV per atom, values for W of 66.0 and 52.2 eV per ion pair, respectively, were obtained. Thus, a general increase in W with decreased kinetic energy was observed. Comparisons were made with computed W values which are predicted from stopping power theory.