No abstract

No abstract

No abstract

The production of knock-on electrons and of electron pairs by muons of mean energy >50 BeV has been measured from cloud-chamber photographs of soft showers produced in lead plates. The cloud chamber was operated at a depth of 8.42 X10 4 g/cm 2 underground. About half the data were taken while the cloud chamber was tilted 66° in order to favor observation of the high-average-energy muons that come in at large zenith angle. The energies of the electrons that initiated the showers was obtained from an experimental calibration (to be published). The shower energies that were studied extended from 85 MeV to about 10 4 MeV. The observed frequency is compared with the expected frequency calculated from the results of Bhabha for knockon electrons and those of Zapolski and of Murota, Ueda, and Tanaka for electron pairs. The agreement is satisfactory except for knock-on electrons in the region of 10 9 eV, where the predicted frequency appears to be significantly lower than the observed frequency.

A large cloud chamber containing eight lead plates was operated without counter control at 10,000 feet. In 8500 photographs, 1090 cascade showers and 58 nuclear disintegrations were observed. The differential energy spectrum for the shower-producing rays, which was obtained from the relative frequency of occurrence for showers of a given size, is proportional to E~1 ,7 for E = 2 X10 8 ev and to E~3 0 for E = 10 9 ev. The shower-producing rays with E > 2 X10 8 ev constituted 6.5 percent of the radiation observed in the cloud chamber; one-third of the showerproducing rays were photons. Approximately one-third of the observed nuclear disintegrations contained particles that penetrated at least 0.7 cm of lead and four contained particles that penetrated at least 2.8 cm of lead. Most of the disintegration particles were protons or mesotrons. The initiating particles were neutrons and protons, with the former predominant for the lower energy disintegrations. There appears to be no sharp line of distinction between low energy and high energy disintegrations. No correlation was observed between the disintegrations and the cascade showers.