Neutralization and Ionization of High-Velocity Ions of Neon, Argon and Krypton by Collison with Similar Atoms

Rudnick's work on the measurement of the free path L₀ for the ionization of a helium atom and the free path L₁ for neutralization of a helium ion in helium, has been extended to the gases neon, argon, and krypton for the velocity range corresponding to accelerating potentials of 10,000 to 22,000 volts. With neon, the work has covered the pressure range from 0.75×{}10^-2 mm to 4×{}10^-2 mm; with argon, from 0.30×{}10^-2 mm to 1.6×{}10^-2 mm; and with krypton, from 0.30×{}10^-2 mm to 1.4×{}10^-2 mm. In all cases, the free path for ionization, reduced to 760 mm pressure, is found to be approximately 6.5×{}10^-4 cm. For neon, the free path for neutralization is 0.95×{}10^-4 cm; for argon, 0.45×{}10^-4 cm; and for krypton, 0.35×{}10^-4 cm. Both free paths decrease with increasing velocity. The fraction F_∞ of neutral atoms in the beam when the equilibrium condition is reached is approximately 0.86 for neon, 0.93 for argon, and 0.95 for krypton. This fraction decreases with increasing velocity for neon and argon but appears to increase slightly for krypton. The observed dependence of the free paths on pressure is compared with the theoretical dependence. The results obtained are compared with the low-velocity measurements of other workers and the differences discussed. The relationship of this work to Doppler effect experiments with neon and argon is considered.