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Collection of Ions Produced by Alpha Particles in Air

1957; American Institute of Physics; Volume: 105; Issue: 3 Linguagem: Inglês

10.1103/physrev.105.929

1536-6065

Catharine L. Wingate, W. Groß, G. Failla,

Graphite, nuclear technology, radiation studies

An investigation of the effects of pressure and collector potential on ion collection in air indicates that recombination of ions may occur even when the ionization current is independent of the collecting field. A ${\mathrm{Po}}^{210}$ source of reduced-range alpha particles was used as the central electrode in a cylindrical ionization chamber of sufficiently large dimensions that the residual energy of the particles was absorbed by the gas at pressures greater than 4.5 cm of mercury. Apparently complete ion collection was achieved by reducing the pressure until at 10 cm of mercury a maximum ionization current was obtained which was independent of the collecting field and of further reduction in pressure. The ionization current at atmospheric pressure, though independent of the collecting potential over a large range of voltages, was 3.3% lower. Since field independence has been the usual criterion of saturation, undetected recombination is suggested as a possible cause for the apparent increase of average energy expended per ion pair formed in air ($W$) by alpha particles of decreasing energy as well as the reported difference between $W$ values for alpha and beta particles.