Low energy atmospheric gamma rays near geomagnetic equator

Abstract

Based on the results from three balloon flights, made at Hyderabad(7.6° N geomagnetic latitude) using omnidirectional gamma ray spectrometers, the different aspects of the low energy atmospheric gamma rays at equatorial latitudes in the energy interval 100 keV to 1 MeV are investigated and detailed discussion is presented. The energy loss spectrum in this energy range is found to consist of a continuum superimposed on which is a photopeak due to 0.51 MeV line arising from electron positron annihilation. The continuous background spectrum is similar to that observed at mid and high latitudes. The intensity of 0.51 MeV line is estimated to be 0.079 ± 0.01 photons cm^-2 sec^-1 at 6 g cm^-2 over Hyderabad and the altitude dependence of its intensity is established for this low latitude station. The latitude effect of the intensity of this line at 6 g cm^-2 is derived for the first time by comparing the results of the present measurements with those available for mid and high latitudes. The contribution of the cosmic gamma rays to the observed count rates at 6 g cm^-2 is shown to be negligible in the case of the omnidirectional spectrometers of the type used in the present observations even for low latitude stations.