Crystal Growth And Scintillation Properties Study Of Cs₂LiYCl₆:Ce For Neutron Detection

Elpasolite structure Cs₂LiYCl₆:Ce（CLYC:Ce）is a new type of high-performance neutron detection scintillator material,which has a high light yield of 20,000 photons/MeV under gamma excitation and 70,000 photons/neutron under neutron excitation,less than 4.5%of energy resolution,especially the excellent neutron/gamma-ray dual-mode detection capabilities and other advantages.In my thesis,the growth conditions of CLYC:Ce scintillation crystal by Bridgman method are studied.CLYC:Ce crystals with good optical quality are grown and their optical and scintillation properties are systematically characterized.The doping concentration of Ce³⁺and the codoping concentration of Ca²⁺and Sr²⁺are explored.In terms of crystal growth,the growth parameters suitable for CLYC crystal growth were found.In view of the growth problems caused by the inconsistent melting characteristics of CLYC,5 wires with a diameter of 25 mm were grown to optimize the existing components.The proportions of LiCl were 57 mol%,60 mol%,and 63 mol%,and the molecular ratio of Cs Cl and YCl₃ were 1.9:1 and 2.1:1.By comparing the growth of 5 crystals,it is determined that the composition of LiCl accounting for 60mol%is the most suitable for obtaining CLYC crystals.Successfully obtained a sample ofΦ25^*10mm³ with no cracks and no inclusions.By comparing the scintillation performance of this sample with the sample of 5^*5^*5mm3,the X-ray excitation emission spectrum shows that the core valence luminescence of the large volume CLYC crystal is weak,and the multi-channel energy spectrum shows that the light yield and energy resolution of the large volume sample are slightly lower than that of the small volume sample.Ce³⁺doping concentration is an important factor to affect the scintillation performance of CLYC crystal.Five CLYC crystals with diameter of 11mm and Ce³⁺doping concentration of 0.1%,0.3%,0.5%,0.7%and 1%respectively were grown,and the selected samples is none of inclusion.By comparing their optical and scintillation properties,it is found that CLYC has better scintillation performance when Ce³⁺doping concentration is 0.3%～0.7%.In this concentration range,the relative light yield of CLYC is 20000 photons/MeV.The energy resolution of CLYC:0.5at%Ce excited by ¹³⁷Cs is about 5.4%,and the decay time constants are 2.4ns,24.4ns,483.1ns and 2855.2ns,respectively,which correspond to core valence luminescence,Ce³⁺direct capture luminescence,binary V_k and electron diffusion,and STE energy transfer luminescence to Ce³⁺ions.Codoping is a widely concerned way to improve the scintillation properties of crystals.The crystal of CLYC:0.5%Ce was grown as the reference group,and 8crystals of CLYC:0.05at%,0.1at%,0.2at%,0.5at%and Sr:0.05at%,0.1at%,0.2at%,0.5at%were grown.Through the comparison of scintillation properties,it is found that the energy resolution of CLYC:0.5%Ce crystal codoped with Ca has different degrees of deterioration.The scintillation performance of CLYC:0.5%Ce crystal with Sr codoping concentration of 0.05at%,0.1at%and 0.2at%is better than that of the reference group.When Sr codoping concentration is 0.05at%,the best energy resolution is obtained.With the increase of Sr codoping concentration,the optimization of energy resolution is also reduced.When Sr codoping concentration reaches 0.2%,the energy resolution is worse than that of the control group.In addition,both Ca and Sr codoping can reduce the relative light output of the crystal.The higher the codoping concentration is,the lower the light output is.