Total Ionization and Range of Low-Energy Recoil Particles in Pure and Binary Gases

Abstract

The total ionization and range of the 103-keV ${}_{}{}^{206}{}_{}{}^{}\mathrm{Pb}$ recoil particle that results from the $\alpha$ decay of ${}_{}{}^{210}{}_{}{}^{}\mathrm{Po}$ deposited on a metallic backing have been determined for a number of gases. The method employed a hemispherical ion chamber and a vibrating-reed electrometer. The 5.3-MeV $\alpha$ particles were used for calibration. The gases used were Ne, Ar, Xe, ${\mathrm{N}}_2$, dry air, C${\mathrm{H}}_4$, ${\mathrm{C}}_2$ ${\mathrm{H}}_4$, 95% Ar+5% ${\mathrm{C}}_2$ ${\mathrm{H}}_4$, and other binary mixtures. The equivalent range, in microns, of the ${}_{}{}^{206}{}_{}{}^{}\mathrm{Pb}$ particle in the listed gases at STP is 131, 79, 44, 80, 83, 84, 58, and 82, respectively. The uncertainty in each value is ±2 μ. The average energy loss per ion pair produced, $W_r$, in eV/(ion pair), for the ${}_{}{}^{206}{}_{}{}^{}\mathrm{Pb}$ particle in passing through the gases, omitting Ne, is 121±6, 158±8, 116±6, 120±6, 121±6, 115±4, and 81.7±2, respectively. Theory and experiment for the range of the ${}_{}{}^{206}{}_{}{}^{}\mathrm{Pb}$ particle in the monatomic gases lie within 5% of each other. A rough calculation is made of the energy the recoil particle loses through molecular, nonionizing processes per ion pair produced. For ${\mathrm{N}}_2$ this amounts to approximately 10 eV/(ion pair) of the $W_r$ value.