GdI3:Ce - A New Gamma and Neutron Scintillator

In this paper we present our initial results on GdI₃:Ce scintillator for gamma and neutron detection. We grew crystals of this material 10 mm diameter and over 20 mm long. The crystal has a layered structure. Like other halide materials it is hygroscopic. Only small samples, few millimeters in size, were tested. The emission under X-ray excitation is green and shows a broad band in the range of 450 to 750 nm with the maximum at ~550 nm. The emission is due to d-f transitions on Ce³⁺ ions. The scintillation under gamma excitation is fast and decays with the 39 ns time constant (major component). The rise time of scintillation is also fast at about 0.5 ns. The light output of the investigated samples was as high as ~58,000 photons/MeV. The energy resolution at 662 keV was measured to be 8.7% and should improve with the better crystal quality. The crystals were also tested for the detection of thermal neutrons from a moderated ²⁵²Cf source. The neutron peak appears at 86 keV when compared to 60 keV peak in ²⁴¹Am spectrum taken under the same conditions. The light output per single detected neutron is about ~5000 photons.