A Cloud-Chamber Study of Cosmic-Ray Nuclear Interactions at 3260 Meters Elevation

In 4949 photographs of cosmic-ray phenomena, not associated with dense air showers, occurring in a counter controlled cloud chamber surrounded by lead, the numbers of nuclear interactions in which secondaries were produced and observed to occur in and above the chamber were 182 and 223, respectively. The mean free path for nuclear interaction of the penetrating particles produced in these nuclear interactions is 316±70 g/${\mathrm{cm}}^2$ of lead, while for nuclear scattering (large angle scattering without the production of secondaries) it is at least 4 or 5 times this value. The projected zenith angular distributions of the secondaries from these interactions are given. The lightly ionizing secondaries going in the forward direction have an angular distribution $\sim {cos}^3\theta$, while those in the backward direction from nuclear interactions occurring in the chamber have a uniform distribution.