Partial Ionic Stopping Power and the Energy Expended in Electron Capture and Loss Collisions of Protons in Hydrogen Gas. II

The experimental method of Allison, Cuevas, and Garcia-Munoz for measuring atomic partial stopping powers (ε₀) has been extended to the determination of the stopping power ε₁ of hydrogen gas for the H⁺ component of a hydrogen beam. The protons in a 1-mm diam beam are held in an orbit which is an arc of a circle of 142-cm radius, and are guided to a 1-mm diam exit after a path length of 55.8 cm in {~}50 {μ} pressure of H₂ gas. The energy of the beam after leaving the stopping cell is measured by electrostatic deflection. No proton thus measured can have experienced a charge-changing collision in the stopping cell. In preliminary experiments protons were simulated by deuterons of twice the energy and ε₁ determined for protons of 55, 75, and 93 keV. Finally, an extended series of runs at 42.8 and 54.2 keV were made on ε₁, and a similar extended series on ε₀, with the apparatus arranged as in the work of Allison et al. These latter measurements for ε₁, ε, and ε₀ gave (6.12±{}0.44; 6.36±{}0.16; 2.72±{}0.16)×{}10^-15 eV cm²/atom, and in the same units, for the higher voltage, (6.04±{}0.39; 6.45±{}0.22; 2.91±{}0.29).Since the charge composition of the beam is known from other experiments, the charge-changing collisions may be shown to contribute 34% of the total stopping losses. The sum of the losses in kinetic energy in an electron capture and in its subsequent loss is 40±{}6 eV at 42.8 keV and 54±{}9 eV at 54.2 keV, neglecting charge-changing collisions involving H^-.