Prototype Neutron Portal Monitor Detector

A very large drum-shaped neutron detector which could replace the 3He neutron portal monitor detector is under development. Detection is based on the 6Li(n,3H)4He reaction. 6Li metal is evaporated onto aluminum plates then covered with 22-cm x 27-cm ZnS(Ag) scintillation sheets and sealed about the edges. The equivalent of 40 detector plates will be arrayed in the 80-cm diameter drum housing and viewed by a single 20-cm diameter hemispherical photomultiplier tube without the use of light guides. Presently 25 detector plates are installed. Light collection tests are performed with a bare 210Po alpha source on a ZnS(Ag) disk. Neutron detection studies include neutrons from a 2-curie PuBe source and from a 0.255-gram 240Pu source.