Energy Spectra of Cosmic Ray Photons Measured by Using a Spherical Nal(Tl) Scintillator Covered with Plastic Scintillator

Abstract

Pulse height spectra of cosmic ray photons have been measured by the spherical Nal(Tl) scintillator of 7.6cm in diameter. Since a Nal(Tl) scintillator is sensitive to not only photons but also muons and electrons, cosmic ray photons have been separated from charged particles by the anti-coincidence counting method. In order to measure the pulse height spectra of cosmic ray photons by the anti-coincidence counting method, the spherical Nal(Tl) scintillator is covered with a plastic scintillator shaped like a well with a diameter of 13cm, a height of 11cm and a side thickness of 5mm. Charged particles can be eliminated by gate signals from the plastic scintillator. But a few cosmic ray the plastic scintillator. The pulse height spectra of cosmic ray photons have been converted to the energy spectra by the iterative unfolding technique coupled with the response functions. At the same time, errors caused by generated electrons in the plastic scintillator have been corrected by using response functions. Response functions have been calculated by using the EGS4 Monte Carlo Code for mono-energetic photons from 0.11 to 142 MeV. The energy spectra of cosmic ray photons have beenobtained in the energy range from 3.5 to 142 MeV.Reference