Gamma-ray Energy Spectra Observed around a Nuclear Reactor

Leakage γ-ray energy spectra up to about 9 MeV were measured by using of a 3"φ × 3"L NaI (TI) scintillation counter at two points in the reactor room of KUR (Kyoto University Reactor), and leakage low energy γ-ray (between 10 and 200 keV) spectra were also measured at the reactor power of 5 MW by using of a measuring system which consisted of a 25 mmφ × 2 mm thick NaI (TI) scintillation counter, a collimator, and a logarithmic amplifier. Distinct peaks were not found in the observed γ-ray energy spectra up to 9 MeV except O W. In the case of O W, the distributions in the spectra were not found in the energy range above 2.8 MeV. Peaks at the energies about 200 keV and between 60 and 100 keV were found in many low energy γ-ray spectra. The energy of the former peak corresponds nearly to single back-scattered γ-rays (scattering angle θ, 180°), and the latter one to multiple-scattered. The low energy γ-rays which leaked directly through the shielding wall of the reactor were observed below 30 keV. It was considered that low energy γ-rays leaked through the shielding wall were comparatively weak in intensity, and that high energy γ-rays, when leaked, became to low energy by scattering in the air.