La produzione delle particelle penetranti negli sciami dell'aria

Rissunto

Si riferiscono e discutono i risultati di una misura eseguita a 2100 metri s.l.m., impiegando un dispositivo con registrazione fotografica di lampade al neon, che permetteva l'osservazione contemporanea di tutte le coincidenze di vario ordine tra dodici gruppi di contatori G.M. Scopo della misura era lo studio di talune proprietà della componente penetrante degli sciami dell'aria. Dall'esame della distribuzione delle coincidenze tra contatori schermati, si conclude che le particelle ionizzanti di natura non elettronica (componente penetrante), presenti negli sciami dell'aria, sono prodotte anche localmente ed in gruppi. Non è possibile precisare il rapporto tra il numero di tali particelle già preesistenti nell'aria e il numero di quelle prodotte localmente: comunque il contributo della generazione locale appare percentualmente maggiore negli sciami di minore densità. Impiegando contemporaneamente assorbitori di diversa natura (ferro e piombo), si trovano risultati compatibili con l'ipotesi che nella componente penetrante degli sciami dell'aria si accumulino nucleoni e mesoni, e che i processi destati negli assorbitori siano ancora dello stesso tipo di quelli che dànno origine agli sciami locali, misti o penetranti, osservati nelle camere di Wilson.

Summary

We report and discuss the results of measurements which have been taken at an altitude of 2100 m above sea-level to gather informations as to the origin and accompanying of the penetrating particles in air showers. The arrangement used is represented in fig. 1 and 2. Recording took place with neon lamps, which indicated which of the shielded countersP ₁, P₂, P₃, F₁, F₂, F₃ and which of the unshielded countersB, C, D, L, M, N, were discharged simultaneously with a coincidence of the master countersA ₁, A₂. We naoticed that the side distributions of the penetrating particle is not poissonian, but presents particular associations. In fact, when several shielded counters in the two setsX andY are discharged at the same time, events in which two or three counters are discharged in the same set are more numerous in comparison to those of two or more counters discharged in different sets. Furthermore, in the same set the coincidences between counters near each other are more frequent than the coincidencesP ₁+P₃ orF ₁+F₃. The complete distribution of the events is given in tables I, II, III, IV. Our results indicate tha the penetrating particles are partly produced in the absorbers and in groups. If the penetrating particles were nearly all produced in the air, the distribution of the discharges between the shielded counters should not show any association, at least because of the Coulomb scattering in the air. Possible sources of error in this statesment are examined in n. 3. In two recent worksCocconi andGreisen, andTreat andGreisen disagree with our conclusion. We have noticed by sudbividing the events according to the mean density of the accompanying showers, that the associations, and in consequence the local production occur essentially in the showers of low average density (tab. V). This result can explain the divergences betweenTreat andGreisen's work and the present note. As to the ratio between the frequency of the penetrating particles and that of the soft particles associated in showers, we have obtained consistent with those ofTreat andGreisen (n. 5). W thin the limits of statistical fluctuations, we have observed the same frequency and distribution of penetrating events under mass-equivalent layers of Pb and Fe (n. 6). These results support the hypothesis that the penetrating ionizing component of air showers consists of mesons and prosans, and that the multiple productions that occur in our setsX andY are mainly of the same type of the events which form the local showers, i. e. the mixed and penetrating showers, already recognized in cloud chambers.