Coulomb and Nuclear Interactions of Cosmic-Ray Mesons and Protons in Lead

Abstract

A cloud-chamber experiment shows that positive and negative particles at sea level in the momentum range 0.3-3.1 $\frac{\mathrm{Bev}}{c}$ scatter in 5 cm of lead in the same manner. The experimental scattering distributions have a large-angle "tail" which agrees rather well with the theoretical distributions of Molière and of Snyder and Scott who assumed that the nucleus scatters like a point charge. These distributions should not be valid here because the charge distribution within the nucleus must be considered in detail for such energetic mesons. The recent calculation of Olbert specifically neglecting the scattering of particles which penetrate the nucleus predicts a much smaller probability for large-angle scattering than observed. A rough extrapolation of the calculations of Amaldi et al. to the case of lead shows that it is possible to explain perhaps 10 percent of the observed large-angle scattering as due to inelastic electric scattering within the nucleus, if the radius of the electric charge on a proton is taken to be 2×${10}^{-14\mathrm{}}$ cm. Negative particles observed at 3.4-km altitude scatter in lead much the same as the sea-level particles. The scattering of positive particles observed at 3.4-km altitude indicates that protons in the momentum range 1-4.8 $\frac{\mathrm{Bev}}{c}$ suffer a small amount of nuclear scattering in lead corresponding to $(0.13\mathrm{}\pm 0.07){\sigma }_g$, where ${\sigma }_g$ is the geometrical cross section. All nuclear interactions combined give a total interaction cross section for lead of $(0.38\mathrm{}\pm 0.09){\sigma }_g$. These surprisingly small cross sections are compared with other data from the literature.