Ionization Measurements at Very High Intensities—Part I

TLDR

Pulsed radiation beams produce high ion densities that promote recombination between opposite ions. The authors derive formulas for ion escape fractions in various chamber geometries, analyze collecting efficiency under exponentially falling voltage in condenser chambers, and present experimental measurements from a 4 MeV linear accelerator. Space‑charge screening is negligible in plane‑parallel geometry.

Abstract

In pulsed radiation beams the high ion density produced by each pulse encourages recombination between ions of opposite signs. Formulæ are derived for the proportion of ions escaping recombination in plane parallel, cylindrical and spherical ionization chambers under a variety of different conditions. The screening effect of space charge is shown to be small in the case of plane geometry. The effect of an exponential fall in collecting voltage, as in condenser chambers, is considered and the appropriate collecting efficiency is derived. Some experimental measurements on a 4 MeV linear accelerator are described.