Cross-Section for Nuclear Disintegration Produced by Cosmic Rays

Abstract

IT has been suggested¹ that the cross-section for star production is proportional to the geometrical cross-section of the nucleus. In order to establish this by direct experiment, we have exposed some 'gelatin sandwich' plates for fifty days at a height of 3,650 m. These plates consist of four layers of Ilford C.2 Nuclear Research emulsion, 30 µ thick, separated by three thin layers of plain gelatin. This sandwich emulsion, coated on an acetate base, was supercoated with a 5µ gelatin layer. A second batch of plates with emulsion layers of 25µ was exposed for forty days. In order to determine the thickness of the gelatin layers (excluding the super-coat) relative to the normal emulsion, we have measured the ratio of the projections in the plane of the emulsion of track length to gap length for those tracks which pass right through the sandwich emulsion. The gaps in the tracks occur when the ionizing particles pass through the gelatin layers. From these measurements on 300 tracks of length greater than 200µ we conclude that in the plates so far examined the mean gelatin thickness : mean emulsion thickness equals 9·2 per cent.