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

The total ionization and range of the 103-keV ²⁰⁶Pb recoil particle that results from the α decay of ²¹⁰Po 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 α particles were used for calibration. The gases used were Ne, Ar, Xe, N₂, dry air, CH₄, C₂{H}₄$, 95% Ar+5% ${C}₂H₄, and other binary mixtures. The equivalent range, in microns, of the ²⁰⁶Pb 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, Wᵣ, in eV/(ion pair), for the ²⁰⁶Pb 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 ²⁰⁶Pb 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 N₂ this amounts to approximately 10 eV/(ion pair) of the Wᵣ value.