Novel Scintillators with Neutron/Gamma Discrimination,

In this paper we report on the synthesis and scintillation properties of the ammonium rare-earth halo­ elpasolites, CS(NH4)MYX6:Ce 3 + (M = Li, Na; X = F, CI). Due to their high vapor pressure, crystal growth was not feasible. Instead, reactive-atmosphere sintering was used to obtain polycrystalline samples. The ammonium rare-earth halo­ elpasolite phase was confirmed by X-ray diffraction. Radioluminescence spectra exhibit a broad band peaking in the near-UV due to Ce 3 + 5d -+ 4f emission. Scintillation decay time spectra under pulsed X-ray excitation show a fast 1.3 ns decay component due to core-valence luminescence in addition to 30 ­ 40 ns Ce 3 + luminescence. A long decay component with a lifetime of approximately 400 ns, ascribed to self-trapped exciton emission, is present as well. In contrast, the fast decay component of core-valence luminescence is absent in the alpha excited scintillation decay time profiles. Pulse height spectra under fast neutron excitation show evidence of scintillation light produced by neutron - proton scattering.