Fast counting of alpha particles in air ionization chambers

Abstract

It was assumed in the past that counting of alpha particles in air- ionization chambers could be based only on the collection of ions since electrons produced in the alpha track quickly form negative ions in electronegative gases. This leads to time resolutions of the order of a millisecond. It is shown that the motion of the electrons before attachment produces a sharp initial rise in the pulse profile which, although small, can be detected and utilized for high- speed counting. Time resolutions of the order of a few microseconds with good signal-to-noise ratios are realized in atmospheric air, and therefore counting speeds similar to those in nonelectronegative gases are obtained. (auth)