Il Nuovo Cimento (1955-1965)

, Volume 13, Issue 2, pp 265–283 | Cite as

Cloud chamber study of penetrating showers underground

  • S. Higashi
  • S. Mitani
  • T. Oshio
  • H. Shibata
  • K. Watanabe
  • Y. Watase


A multiplate cloud chamber containing fifteen lead plates of 1 cm thick was used to observe penetrating showers underground. Fifteen and twenty-three penetrating showers, having four secondary shower particles on the average, have been obtained during 667.9 h and 3 603.1 h at 50 m w.e. and 250 m w.e., respectively. Special attention was paid to distinguish penetrating showers produced by μ-mesons from those by the nucleonic component, the chamber of large width (100 cm) having been set as close to the upper wall in the tunnel as possible. Almost all of the observed showers produced by isolated incident particles are considered as probably produced by μ-mesons (namedP-showers phenomenologically), and those by one of two or more incident particles as due to the nucleonic component (namedS-showers), since the m.f.p. of the nucleonic component for nuclear interaction is about 10−4 times shorter than that of μ-mesons. After correcting for the triggering efficiency of the apparatus, the ratios of frequencies ofS-showers to that ofP-showers have turned out to be 1.1 ± 0.3 and 0.92 ± 0.23 at both depths, which means that a half of the high energy nuclear interactions underground is produced by the nucleonic component. The depth dependence of frequencies ofP-showers is compared with the prediction by Weizsäcker and Williams’ treatment of μ-meson interactions. In addition, it has remarkably been observed thatP-showers have a characteristic different from that ofS-showers,i.e., the average number of heavily ionizing secondaries ofP-showers is 0.3 per shower, while the value ofS-showers is 2.8 per shower.


Si usa, per osservare gli sciami penetranti sottoterra, una camera a nebbia a lastre multiple contenente quindici lastre di piombo dello spessore di 1 cm ciascuna. In 667.9 h ed a 50 m a.e. si ottengono quindici sciami penetranti in 3 603.1 h, ed a 250 m a.e. si ottengono ventitrè sciami penetranti, aventi, rispettivamente, in media, quattro particelle secondarie. Poichè la camera, di grande larghezza (100 cm), è stata posta quanto più vicino possibile alla parete superiore del tunnel, si rivolge particolare attenzione nel distinguere gli sciami penetranti prodotti dai mesoni μ da quelli prodotti dalla componente nucleonica. Quasi tutti gli sciami generati da particelle isolate incidenti (chiamati fenomenologicamente sciamiP) si considerano come prodotti con ogni probabilità dai mesoni μ, mentre si riguardano come dovuti alla componente nucleonica quegli sciami (chiamati sciamiS) generati da una sola delle due o più particelle incidenti, ciò per il fatto che il cammino libero medio della componente nucleonica per le interazioni nucleari, è di circa 10−4 volte più breve di quello dei mesoni μ. Eseguita la correzione per il rendimento dell’apparecchio, si trova che i rapporti fra le frequenze degli sciamiS e degli sciamiP sono 1.1±0.3 e 0.92±0.23 ad entrambe le profondità, la qual cosa significa che metà delle interazioni nucleari sotterranee di alta energia è prodotta dalla componente nucleonica. Si confronta la dipendenza delle frequenze degli sciamiP dalla profondità, con le previsioni della trattazione di Weizsäcker e Williams sulle interazioni dei mesoni μ. Si è osservato inoltre, che gli sciamiP hanno, in modo rimarchevole, caratteristiche diverse da quelle degli sciamiS, cioè il numero medio di secondari fortemente ionizzati degli sciamiP è 0.3 per sciame, mentre il valore per gli sciamiS è 2.8 per sciame.


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Copyright information

© Società Italiana di Fisica 1959

Authors and Affiliations

  • S. Higashi
    • 1
  • S. Mitani
    • 1
  • T. Oshio
    • 1
  • H. Shibata
    • 1
  • K. Watanabe
    • 1
  • Y. Watase
    • 1
  1. 1.Osaka City UniversityJapan

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