Energy Loss and Resultant Charge of Recoil Particles from Alpha Disintegrations in Surface Deposits ofPo210andAm241

Recoil particles from the ${}_{}{}^{210}{}_{}{}^{}\mathrm{Po}\left(\alpha \right){}_{}{}^{206}{}_{}{}^{}\mathrm{Pb}$ and ${}_{}{}^{241}{}_{}{}^{}\mathrm{Am}\left(\alpha \right){}_{}{}^{237}{}_{}{}^{}\mathrm{Np}$ disintegrations in surface deposits on platinum planchets have been studied experimentally using both a low-resolution magnetic spectrometer, employing an electron multiplier detector, and a hemispherical ionization chamber. The average energy of the ${}_{}{}^{206}{}_{}{}^{}\mathrm{Pb}$ recoil ions emitted from thin deposits of ${}_{}{}^{210}{}_{}{}^{}\mathrm{Po}$ showed an exponential degradation with time after preparation, starting with the nascent energy of 103 keV and decreasing to $\frac{2}{3}$ of this value in five days. Approximately 90% of the ${}_{}{}^{206}{}_{}{}^{}\mathrm{Pb}$ recoil atoms are emitted singly ionized and 10% are doubly ionized. The ${}_{}{}^{237}{}_{}{}^{}\mathrm{Np}$ recoils from thicker deposits of ${}_{}{}^{241}{}_{}{}^{}\mathrm{Am}$ apparently were mostly neutral but a small number were emitted with six units of charge and with an average kinetic energy of only 65±15 keV compared with their nascent energy of 92.4 keV. Ejected recoils are accompanied by large numbers of secondary particles having energies less than 40 eV. With thin source deposits there are about five positively charged ions and three detected neutral secondary particles emitted per disintegration; but with thicker deposits these numbers rise to 15 positive ions and 10 neutrals, respectively. Negative ions may also be present but were excluded from observation by the experimental conditions. The average energy loss for the ${}_{}{}^{206}{}_{}{}^{}\mathrm{Pb}$ recoil particle in passing through argon gas was determined to be 121±6 eV/ion-pair. The extrapolated range for a nascent energy ${}_{}{}^{206}{}_{}{}^{}\mathrm{Pb}$ recoil particle in argon at STP is 78±2 μ. This value agrees with the range reported by Jessi and Sadauskis and lies within 2% of the value calculated from an energy-loss theory originally developed by Bohr.