| 摘要 |
PURPOSE: To improve spatial uniformity of response by a gamma ray detector so as to increase measurement accuracy by arranging a first to a third neutron attenuation agents near a neutron source to reduce radiation speed of neutron. CONSTITUTION: A first neutron attenuation agent 20 is arranged around a neutron source 14 to reduce speed of neutron radiated by the neutron source 14. This deceleration increases catching of neutron by a bulk material 38 and generates the radiation of gamma rays from the material 38. Next, a second neutron attenuation agent 22 is arranged around the attenuation agent 20 to reduce speed of neutron further. The attenuation agent 22 is arranged adjacent to a side of a groove 30 to increase the response of a gamma ray detector 16 for the material 38 which is close to a fringe part of a radiation region 34. Furthermore, a third neutron attenuation agent 24 is arranged adjacent to a radiation shield material 28 around the attenuation agent 22 to reduce speed of neutron further. Moreover, two neutron sources 14 and two detectors 16 are provided to improve uniformity of response of the detectors for gamma radiation further. |
