Knock-on Electrons and Direct Electron Pair Production by Cosmic-ray Muons

Abstract

Knock-on electrons and direct electron pair creation by cosmic-ray muons in thin lead plates were investigated with a multiplate cloud chamber. The muons traversing the cloud chamber were classified into two energy intervals, viz. 450 to 1700 MeV and higher than 1700 MeV. By comparing the experimental results with theoretical predictions which were derived for the knock-on process, an effective range-energy relationship was found for electrons in lead with energies up to about 200 MeV. The experimental distributions of the knock-on production as a function of the energy transfer compare well with theoretical distributions calculated from Bhabha's formula for muons in both of these energy ranges. The comparison between the theoretical and experimental results is also satisfactory for the energy distribution for direct pair production by muons with energy above 1700 MeV. The theoretical distribution was calculated from a formula deduced anew from the differential cross section given by Murota, Ueda and Tunaka. The experimental results favour a value between 1 and 2 for the indefinite constant α of the theory.