Novel Gamma-ray and Thermal-neutron Scintillators: Search for High-light-yield and Fast-response Materials

In this book, bromide and iodide scintillators, which have been investigated for the past four years, are presented. Three major groups of compounds were studied; lanthanide trihalides LnX3, (pseudo)-elpasolites M2ALnX6 and ternary halides AmLnnXo. Where M and A are alkali cations, Ln is a rare earth cation and X is a halide anion. Some materials show interesting [gamma]-scintillation properties. LuI3: Ce3+, one of lanthanide trihalides, has a record high light output of 98,000 photons/MeV and a fast response of 35 ns. Two other groups, (pseudo)-elpasolites and ternary halides, show relatively low light yields.For thermal neutron scintillator, the focus was on (pseudo)-elpasolites M2LiLnX6 and ternary halides LimLnnXo groups. Rb2LiYBr6: Ce3+ shows an excellent neutron peak resolution of 3.6 per cent. This is the best neutron peak resolution ever reported. Together with the large [alpha]/[beta] ratio of 0.74, Rb2LiYBr6: Ce3+ offers the possibility of excellent neutron/[gamma] discrimination. The highest thermal neutron scintillation light yield of 83,000 photons/neutron is also reported for Rb2LiYBr6: Ce3+. The analysis for all halide scintillators is also presented. Limitation in their light yields and response times is discussed.