Neutron-induced luminescence and activation in neutron shielding and scintillation detection materials at cryogenic temperatures

The neutron-induced low temperature (below 5 K) luminescence of neutron shielding and scintillation detection materials is studied. Strong luminescence is observed for the neutron absorbing materials boron nitride (BN) and lithium fluoride (LiF). A measurable, but substantially smaller luminescence is observed from boron oxide (B2O3). An upper bound of 10-3 was determined for the fraction of the luminescence due to time-correlated multiphoton events in the BN. Other materials tested - boron carbide (B4C), polymethyl methacrylate (PMMA or acrylic), expanded polytetrafluoroethylene (PTFE) with an evaporated coating of the downconverting fluor tetraphenyl butadiene (TPB) and a boron/lithium loaded glass - displayed no detectable luminescence. The boron/lithium loaded glass was determined to activate, by the secondary reaction 16O(T,n)18F, with the triton produced in the neutron capture reaction 6Li(n,T)4He