Mixed Lutetium Iodide Compounds

In this paper we present initial results on mixed LuI₃-YI₃-GdI₃ scintillators for gamma and neutron detection. The scintillation properties were investigated and compared to the results obtained for the binary compositions. Small samples, few millimeters in size, were tested. Under X-ray excitation each crystal exhibits bright green emission in the 425 to 750 nm spectral range. The exact peak position depends slightly on the material composition. The emission is due to d-f transitions on the Ce³⁺ ion. The scintillation under gamma excitation is fast and decays with about 30 ns time constant. The rise time varies slightly and it can be as fast as 0.5 ns. The light output of the investigated samples varied from 115,000plusmn13,000 ph/MeV for LuI₃ to 68,000plusmn8,000 ph/MeV for LuI₃-YI₃ composition. The energy resolution at 662 keV was difficult to estimate since the samples lacked in crystal quality. LuI₃-GdI₃ composition was also tested for the detection of thermal neutrons from a moderated ²⁵²Cf source. The neutron peak appears at 81 keV when compared to 60 keV peak in ²⁴¹Am spectrum recorded under the same conditions. The light output per a single detected neutron is about ~6,350 photons.