Gamma-ray Energy Spectra Observed around a Nuclear Reactor

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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.<BR> 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.<BR> 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.
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