✍ Scribed by Dan Kessler; Roland Maze
No coin nor oath required. For personal study only.
A penetrating shower counter-arrangement has been operated at sea-level, as well as at 10 and 65 rowe underground, with the purpose to study production of penetrating showers by/~ mesons. The contribution of soft showers produced by/~ mesons has been made negligible by using at least 18,5 cm Pb as aborber between extreme counter-trays. The analysis of hodoscopic data obtained with different absorber thicknesses made it possible to separate multiple electromagnetic interactions from true penetrating showers. Triggering by associate penetrating particles either from the atmosphere or from the earth seems to be unimportant, as follows from the rather localized distribution of small multiplicities.
The following cross-sections for production of penetrating showers by/~ mesons with at least 2 secondary particles able to penetrate 18,5 cm Pb have been obtained : at 10 mwe underground : ( 1,16 + 0,54). 10 -a° cmZ/nucleon at 65 mwe underground: (1,22 + 0,45). 10 -a° cm~/nucleon. The cross-section given above for the 10 mwe level might have been overestimated by 10% due to a contribution from residual N-component from the atmosphere.
The ratio of the cross-sections at 65 and 10 mwe is 1,05 d= 0,24 showing that the cross-section does not increase faster than the logarithme of the mean energy of the/~ mesons arriving at each level, but, as far as one may conclude from the rather poor statistics, the absorption mean free path of the secondary shower particles which trigger the apparatus is about twice as long at 65 mwe than at 10 mwe underground.
The frequency distributions at 10 and 65 mwe of the number of secondary penetrating particles are neither significantly different from each other nor from the distribution of penetrating showers produced at sea-level by the N-component. The observed distributions are found to be compatible with a law of the form Q(N) ~ (N --l) -a with a ~ 2, N being the number of secondary shower particles.
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