Mechanism of Secondary Gamma-Ray Skyshine from Intense 14 MeV Neutron Source Facility with HP-GE Detector

Secondary gamma-ray skyshine has been measured at an intense 14 MeV neutron source facility with a Hp-Ge detector used to investigate this mechanism. Many discrete gamma-rays due to (n, gamma)reactions were observed in the spectrum. It was confirmed that in the evaluation of the secondary gamma-ray skyshine, a precise spectrum calculation down to thermal neutron is indispensable. On the other hand, there exists only a continuum spectrum up to 8 MeV with no discrete peaks in the real skyshine spectrum from the upper air. It was found that the continuum spectrum is composed of mainly Compton scattered gamma-rays. In the distance dependency measurement, the real skyshine contribution showed slow attenuation compared with the whole skyshine contribution. This means that with increasing distance from the facility the real skyshine contribution is gradually dominant, namely, it becomes more important in the skyshine evaluation.