The momentum spectrum of cosmic rays at a depth of 38 metres water equivalent underground

Abstract

A direct determination has been made of the cosmic ray spectrum underground at a depth of 38 m. w. e. under Castle Rock, Nottingham. The spectrum is based on measurements of 1010 particles traversing a magnetic spectrograph having a maximum detectable momentum of 8 GeV/ c . By comparing this spectrum with the ground-level spectrum the energy loss of fast μ -mesons in penetrating the 38 m. w. e. of rock has been determined. It is shown that the energy loss for μ -mesons in the momentum range 7 to 15 GeV/ c is as expected by theory, the collision process being responsible for most of the loss.