Cosmic Ray Ionization Bursts

Abstract

COSMIC ray ionization bursts produced by showers of ten or more particles in a small ionization chamber (volume 1 litre) have been recorded at sea-level in Cambridge and, thanks to the hospitality of Prof. P. M. S. Blackett and Dr. H. J. J. Braddick, under 30 m. of clay in London. The data discussed here, curves A (150 hours) and B (350 hours), are from runs with no lead or other dense shower producing material above the chamber (the wall of the chamber was of duralumin, 1·2 cm. thick, so as to avoid as much as possible showers produced by cascade multiplication in the chamber itself). Curve C (500 hours) is the result of similar observations at sea-level with a large ionization chamber (volume 175 litres, wall-thickness 0·3 em. of steel), most of which were published by one of us¹ in 1936, when the method of recording was also described. The curves show the number of showers per hour in which N or more particles intersected the ionization chamber; the number of shower particles N was estimated on the basis of a specific ionization in normal argon of 90 ion pairs per cm.