The Residual Range of Delayed Particles in Extensive Air Showers

Abstract

SummaryThe arrival times of the penetrating particles of extensive air showers relative to that of the electrons have been studied by means of short reaction time Geiger counters. A 50 channel hodoscope has been used to identify the penetrating particles and measure their residual ranges where these lay between 15 and 30 cm of lead. From observations on 782 showers of median density 70 particles m-' in which a Penetrating component was detected, it was deduced that between 3 and 9 particles in 104 shower particles from showers of median density 28 particles m-', have delays <5 X 10-8 sec and are able to penetrate 15 em of lead. It follows that 81-94 per cent. of the delayed particles found by Jelley and Whitehouse (1953) without the use of absorbers, must be stopped by 15 cm of lead. This indicates a height of production below 0·8 km for at least half of these particles.Two of the penetrating delayed !-I.-mesons were stopped in the lead, and their heights of production calculated to be l·O~g:rkm and 4'7~~:~km on the assumption that the delays were due to velocity differences. Thirty' other !-I.-mesons for which the individual time lags were not significant were also stopped in the lead and gave a mean delay indicating production below an altitude of 250 m. The remaining 208 !-I.-mesons which did not stop could not be assigned a height of production.One delayed proton was found in the total of 29 delayed events observed, and nine events could have been oblique particles lagging on the electrons by virtue of path differences.