Abstract
Photographs have been taken under controlled illumination of the tracks of α particles in a cloud expansion chamber and a calibration of the photographic plates employed has been carried out. Systematic photometry of the track images has made possible the calculation of the variation of the light scattering power of an α particle track over the last two centimetres of its length in standard air, and the variation of this quantity has been identified with the variation of ionisation along the track.Photographs of tracks in air, helium and hydrogen have been examined. In these three gases the maximum ionising efficiency of the α particle occurs when it possesses the velocity respectively appropriate to the distances 3·0, 2·55 and 2·25 mms. from the end of its path in standard air. This common velocity parameter has been employed throughout the discussions which are appended to the experimental results.
Publisher
Cambridge University Press (CUP)
Reference12 articles.
1. On the capture of electrons by moving electrified particles
2. Ionisation by alpha-particles in monatomic and diatomic gases
3. This is not the same an the density after thermal equilibrium has been reached, for during this process water has evaporated from the walls of the chamber. The correction on this account was investigated and found to be appreciable only at lower pressures than were actually used.
4. ‘Standard air’ is used for dry air at 760 mms, of mercury and 15° C.
5. Briggs , loc. cit.
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