Cloud chamber study of penetrating showers underground
Tóm tắt
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.
Tài liệu tham khảo
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In the tables, photographs having no incident penetrating particles are those in which there are a little more electrons than are in photographs taken by random triggering. Or otherwise they are those each showing a dense electron cascade having entered the chamber through its side faces. Almost all the events containing one incident penetrating particle are those in which a single penetrating particle enters the chamber and produces a small electron cascade in a lead absorber below the chamber. In this case, also, there are contained penetrating showers produced by a single penetrating particle in a lead plate in the chamber, which are phenomenologically namedP-showers. Photographs with two or more incidents, on the other hand, are those representing secondary penetrating particles which were produced above the chamber and penetrated through it. In these events there are found a number of nuclear interactions, both stars and penetrating showers, the latter being namedS-showers. In addition, M.P.P.’s (19) are contained in the cases of two or more incident penetrating particles, but description about them will be given in another paper.
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