Secondary spectra of electrons and photons in the atmosphere

Abstract

Electrons and photons of the secondary cosmic radiation have been separated from the other components by means of their shower development in a lead scintillator arrangement. Measurements have been performed at 4.5 GV geomagnetic cutoff at atmospheric depths of 760 g/cm2 (in vertical direction between 12 MeV and 20 GeV, inclined at 36 °N between 12 MeV and 1 GeV, and inclined at 49° and 59 °N between 70 MeV and 1 GeV) and 955 g/cm2 (in vertical direction between 12 MeV and 1 GeV). The results can be characterized as follows.1. For the energy range covered at both locations and/or at different zenith angles there is no significant change in the spectral shape.2. Both the photon and the electron spectra steepen gradually, the exponent of the differential power-law spectrum E−n assuming a value n = 2.8 for energies above 1 GeV.3. The photon/electron ratio is in good agreement with the ratio of the track-length distributions calculated by Richards and Nordheim for electromagnetic cascades in air.4. A cosnθ law is a poor approximation to the angular distribution of the integral intensities above 100 MeV. A better fit is obtained from calculations taking into account the relative contributions of π0's and muons to the electron and photon intensities at a given zenith angle θ.