Energy Loss Per Ion Pair for Protons in Various Gases

Abstract

Values of $w$ for protons in A, ${\mathrm{N}}_2$, C${\mathrm{O}}_2$, dry air, and "tissue-equivalent" gas were measured as 26.66±0.26, 36.68±0.34, 34.37±0.33, 35.18±0.42, and 30.03±0.29 ev/ion pair, respectively. A 2-Mev positive-ion accelerator was used as the source of protons. The energy of the protons was determined with a precision gaussmeter that was calibrated by the $\mathrm{Li}(p, n)$ and $\mathrm{T}(p, n)$ threshold reactions. These protons were scattered from a gold foil into a parallel plate ionization chamber. The fast-electron pulses were collected on one electrode, amplified, and counted. The positive-ion charge was collected on the other electrode and measured by means of a standard capacitor that was connected between the input and feedback terminals of a vibrating-reed electrometer.