G. Salvini

Alcune proprietà delle esplosioni nucleari nella radiazione cosmica

RiassuntoSi riferisce su una ricerca eseguita a 3500 m sul livello del mare con contatori e camera di Wilson, intesa allo studio delle esplosioni nucleari nella radiazione cosmica. L’esame delle esplosioni nucleari ha messo in evidenza la presenza contemporanea di particelle fortemente ionizzanti e di particelle penetranti, quest’ultime capaci di dar luogo a successive esplosioni nucleari. Sono state studiate in particolare la diffusione nel piombo delle particelle penetranti di queste esplosioni, che non ha messo in evidenza alcuna interazione non coulombiana, e la sezione d’urto media per la produzione di successive esplosioni nucleari nel piombo, che è invece risultata ∼ 10−24 cm2 per nucleo, pari ad un cammino libero medio di ∼ 330 g/cm2. Quest’ultima interazione ci permette di concludere che le particelle penetranti delle esplosioni nucleari non sono di massima mesoni μ, ma piuttosto protoni o mesoni π.SummaryWe report the results of a research, in which we studied nuclear bursts in cosmic rays, developed with a counter-controlled cloud chamber at the Laboratorio della Testa Grigia (3500 m a.s.l.) The arrangement used is shown in fig. 1. The cloud chamber expanded whenever one counter at least was discharged in each of the groupsA1,A2,B1,B2, or in each of the groupsB1,B2,C1,C2, and for this two particles at least were necessary. In 12.200 minutes 801 photographs were obtained, from which we selected 120, which contain:a) groups of particles originating from a common point in the leadS, or in the three plates inside the chamber, and in which penetrating particles (recognisable for not generating secondaries in any plate) or heavy ionizing ones were present;b) showers with no evidence of penetrating particles but surely descending fromS, so that the showers appeared under 23 cm of lead (referred to as electron showers);c) some other events that were worthy to be noted. Thirty-eight photographs present showers of penetrating particles only, produced in the leadS; 9 present mixed showers and 16 electron showers. Twenty-two photographs present nuclear bursts produced in the lead plates of the cloud chamber (Tabella II). Penetrating showers observed by us are nearly all produced in the deeper region ofS. We observe moreover that the penetrating particles of a penetrating shower, which we see in the cloud chamber are normally not the same which have dischargedA1 andA2. This is in accord with the hypothesis that so-called penetrating showers are due to the more energetic bursts and contain a large number of short range particles too, in agreement with a recent suggestion ofPowell and co-workers. We have measured the scattering angles through the three plates of 38 penetrating particles associated in bursts produced inS. The scattering observed (Tabella I) is never larger than 6°, except in one case (9°), and can be explained with Coulomb scattering alone, without any anomalous scattering. The examination of the nuclear bursts produced in the plates of the cloud chamber with particular regard to those produced by ionizing particles of nuclear bursts from the leadS, lead us to a sort of cascade representation, in which the most energetic of the produced particles may successively give rise to new bursts. The mean cross section for new bursts production by ionizing particles of nuclear bursts has resulted of the order of 10−24 cm2 per nucleus. This rather strong nuclear interaction confirms that the particles produced in nuclear bursts are not generally μ-mesons but rather protons or π-mesons.

Sulla presenza di una componente penetrante negli sciami estesi dell’aria

RiassuntoSi riferisce su ricerche eseguite a 2100 m s.l.m. con contatori e camera di Wilson. Le misure indicano l’esistenza negli sciami estesi dell’aria di una componente penetrante, e permettono di rilevarne talune proprietà.SummaryAn investigation has been made, at an altitude of 2100 meters above sea level, intended to ascertain the presence of a penetrating component in extensive air showers. To ascertain such presence, several criterions have been used in a single arrangement of G. M.-counters: the extensive showers’ components are separated according to their different penetrating power, their different multiplication probability while crossing thick iron or lead layers, and their different absorption by elements of different atomic number (Fe and Pb). Measurements point out the presence in extensive showers of a non-multiplying component which is more penetrating than electrons. Were this component due to mesons, these would have a spectrum of lower energies than the mesons present in the total radiation. It is discussed whether the penetrating component may be generated, at least partially, within the Pb- or Fe-absorbers. An account is given of cloud-chamber photographs taken in coincidence with the extensive showers detected by the counter arrangement.

Proprietà delle particelle emesse nelle esplosioni nucleari e confronto tra le esplosioni in C e in Pb

RiassuntoSi riferiscono i risultati di una ricerca eseguita al Laboratorio della Testa Grigia (3500 m) con una camera di Wilson coman-data da contatori di G.M. La ricerca tratta i seguenti argomenti:a) misura del libero cammino medio per interazione nucleare delle particelle prodotte nelle esplosioni: si è ottenuto λ=300 g/cm2±30%; si discutono in particolare le correzioni apportate ai dati sperimentali per ricavare il valore suddetto;b) osservazioni sulla componente elettromagnetica prodotta nelle esplosioni nucleari: i nostri risultati confermano che in una esplosione nucleare possono essere emessi più fotoni od elettroni, direttamente o da particelle di vita media estremamente breve;c) confronto delle esplosioni nucleari prodotte in nuclei diversi (C e Pb): questo confronto ha indicato che, almeno nei nuclei più pesanti, il nucleone incidente interagisce di solito con più nucleoni dello stesso nucleo (produzione plurima).SummaryWe report the results of a research, in which we studied the nuclear explosions in cosmic rays, developed with a counter-controlled cloud chamber at the Laboratorio della Testa Grigia (3500 m a.s.l.) There were three aims of our research: (a) measurement of the mean free path for nuclear interaction of the penetrating particles produced in nuclear explosions (n. 4). We obtain the value λ≌300 g/cm2. We also discuss the corrections of the experimental data, that are necessary in this estimate of λ. (b) Observations on the electromagnetic component produced in the nuclear explosions (n. 5). Our results confirm that more than one electromagnetic quantum may be emitted in a nuclear explosion. (c) Comparison of the explosions produced in nuclei of different size, Pb and C (n. 6). This comparison indicates that in the nuclear explosions, at least for the nucleus of Pb, the incident nucleon interacts usually with more than one nucleon of the same nucleus.