The Production of High Energy Secondaries by Cosmic Rays Underground

Abstract

The traversal of a total of 100 meters of lead by penetrating particles has been studied at an underground depth of 8.4×${10}^4$ g ${\mathrm{cm}}^{-2\mathrm{}}$ with a cloud chamber containing 2.54-cm lead plates. The observed probability for an energy transfer greater than ${10}^9$ ev to the soft component is 3.0(±0.7)×${10}^{-4\mathrm{}}$ per g ${\mathrm{cm}}^{-2\mathrm{}}$ of lead. Knock-on, bremsstrahlung, and pair-production processes are calculated to give a probability of 2.1×${10}^{-4\mathrm{}}$ per g ${\mathrm{cm}}^{-2\mathrm{}}$ of lead. Therefore, the above electromagnetic phenomena account for nearly all of the high energy soft secondaries produced by $\mu$-mesons of energy ∼${10}^{11}$ ev.