Individual electrons detected after the interaction of ionizing radiation with gases

Abstract

The interaction of ionizing radiation (X rays or high-energy particles) with gases results in the creation of electron-ion pairs. For low-energy X rays a small cluster of primary ionization is produced close to the point of the initial photoionization. High-energy particles, however, lose a small fraction of their energy in each of a number of ionizing collisions resulting in a long track composed of clusters of ionization. We report here that the light signals emitted by a parallel-plate proportional counter are fast enough to allow the individual electrons in the ionization clusters to be resolved. By counting the number of electrons for low energy X ray events we demonstrate an improvement in energy resolution of more than a factor of two over conventional proportional counters.