Sul rapporto tra i numeri di neutroni e di protoni e su alcune proprietà della componente nucleonica a 3500 m s.l.d.m.

Riassunto

Si studiano alcune proprietà della componente nucleonica presente a 3 500 m sul l.d.m. mediante una camera a ioni del tipo veloce, circondata da contatori connessi ad un odoscopio a 22 canali. Sono riportati e discussi i risultati di un’analisi preliminare di oltre 13000 eventi, intesa principalmente ad ottenere alcune determinazioni precise del raprapporto ϱ tra i numeri di stelle generate nella camera da neutroni e da protoni. Si trova, in particolare, ϱ = 23 ± 0,4 per nucleoni di energia mediaE = 35 MeV, mentre perE > ~ 400 MeV risulta ϱ = 1,53 ± 0,04. Si determina la distribuzione zenitale dei protoni di energia media ~ 35 MeV, distribuzione che risulta bene rappresentata dalla legge cos 2.8 ζ. Si mostra infine come i risultati sperimentali rientrino nel quadro generale delle attuali teorie fenomenologiche sulla componente nucleonica.

Summary

A fast, thin-walled ionization chamber, surrounded with G.M. counters connected to a 22 channel-hodoscope, has been used to investigate some properties of the nucleonio component present at 3 500 m above sea level. The picture of each nuclear interaction taking place in the chamber and in which prongs are emitted which cross the counters, is rscordeti by a typewriter triggered by the hodoscope. These « detectable prongs » are shown to correspond to the « grey tracks » and « shower particles » observed in photographic emulsions. Some results of the analysis of more than 13 000 stars are reported. 1) The ratio ϱ of stars produced by neutrons to stars produced by protons is determined for stars with different numbers of detectable prongs. In particular it is found ϱ = 23 ± 0.4 for stars with « no prongs » (which are shown to be produced by nucleons of average energyE = 35 MeV) while ϱ = 1.53 ± 0.04 for stars with at least one prong (E > ~ 400 MeV). 2) It is shown that the high value of ϱ for stars of Ē= 35 MeV cannot be interpreted only in terms of charge exchange and ionization losses undergone by protons through the atmosphere, but it is explained if the Coulomb barrier of the interacting nuclei is also considered. 3) The probabilities to produce a star with a given number of « back-ward » prongs are deduced for both neutrons and proton primaries (see Table IV). ~ 30% of stars with at least one « detectable prong » have at least one backward prong. 4) The zenith angle distribution of protons of~E = 35 MeV is found to fit a cos^2,8 law. 5) The differential distribution of stars with respect to the number of detectable prongs is given for both proton and neutron formed stars (see Table V). 6) Good agreement is shown to exist between our results and the phenomenological theories of the nucleonic component.