Low energy gamma-ray measurements over Hyderabad,India

The results of the first low energy gamma-ray (0.2 to 1 MeV) measurements at equatorial latitudes conducted by two-balloon flights over Hyderabad, India (7.6° N GM), are presented. The energy resolution of the detectors was sufficient to detect the γ-ray peak at 0.5 MeV due to the electron-positron annihilation. The flux of the 0.5 MeV photons was found to be 0.090 ± 0.012 photons/cm² sec at an atmospheric depth of 10 gm cm² and 0.048 ± 0.011 photons/cm² sec at the top of the atmosphere. Comparison of our results with those obtained at higher latitudes, show the existence of a considerable latitude variation of the 0.5 MeV flux, about a factor of 4 between 55° and 7° latitudes at an altitude of 10 gm/cm².