Investigations on X-rays and β-rays by the cloud method. Part 1.—X-rays

Abstract

The method used in these investigations is that which was described in papers communicated to the Royal Society in 1911 and 1912. The ionising rays are made to pass through moist air, or other gas, in which the water-vapour has been brought into the super-saturated state by sudden expansion of the gas. Each ion liberated becomes at once the nucleus for the condensation of a visible droplet of water; the clouds of drops thus formed are immediately photographed. Very sharply defined pictures of the tracks of ionising particles—α- or β-rays—may be obtained in this way. When the conditions are suitably arranged, the effects of diffusion of the ions before their mobility has been destroyed by condensation of water upon them, as well as that of subsequent disturbance of the cloud tracks by convection currents in the gas, are negligible: photographs of the path of the ionising particles, practically free from distortion, are obtained. The almost perfect straightness of the track of a very fast β-particle, when it occurs among a crowd of tracks of slower β-particles, gives very convincing evidence that the complicated forms of the latter are not due to instrumental distortion.