Roland Maze

Une expérience avec compteurs sur les gerbes pénétrantes produites par les mésons μ

Synopsis A penetrating shower counter-arrangement has been operated at sea-level, as well as at 10 and 65 mwe underground, with the purpose to study production of penetrating showers by μ mesons. The contribution of soft showers produced by μ 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 μ 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 −30 cm 2 /nucleon at 65 mwe underground: (1,22 ± 0,45).10 −30 cm 2 /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 ± 0,24 showing that the cross-section does not increase faster than the logarithme of the mean energy of the μ 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 − 1) − a with a ∼ 2, N being the number of secondary shower particles.

Sur la composante pénétrante secondaire des mésons μ

Synopsis A description of several experiments giving evidence for the existence of a penetrating secondary radiation due to μ mesons, at sea-level and underground. This radiation would be formed of showers of particles whose range is 42 ± 3 gr/cm2, probably similar to those found by George and Evans in nuclear emulsions. Cross section for the creation of these showers by μ mesons is about 1,6.10−29 cm2 per nucleon.

Sur les interactions électromagnétiques des mésons μ dans les arrangements de compteurs

Synopsis A critical study of previous experiments on penetrating showers produced by μ -mesons showed the need for an extensive investigation of the contribution of the soft secondary component of μ -mesons to the counting-rate in penetrating shower counter-arrangements. In this paper we describe various experiments with the purpose to investigate the effect of this soft secondary radiation of μ -mesons on counters embedded in lead. At small distance from the trajectory of the meson counters are triggered by electron-secondaries, but at distances of more than 0.8 cm Pb the contribution of photons in the 2–7 MeV range becomes dominant. The intensity of soft radiation in equilibrium with μ -mesons depends slightly on the energy of the primaries, as shown by the well-known relative increase of soft showers with depth underground compared to the flux of penetrating particles. This effect is investigated quantitatively. Conversely, any experimental requirement for soft secondaries modifies the energy-spectrum of incident μ -mesons. As a consequence, two or more events of this type cannot be considered as independent. This effect is here investigated with regard to penetrating shower counter-arrangements at stations between sea-level and 65m we underground. Experimental results show fair agreement with our calculations. By way of illustration we have calculated the increase of the mean energy of the μ -meson spectrum produced by some trivial experimental requirements which comes out surprisingly large in some cases.