Study On Crystal Growth And Anisotropic Properties Of Cerium Doped Lanthanum Bromide Crystal

As for LaBr3:Ce crystal, it occurs as a hexagonal structure with the spacegroup of P63/m, which belongs to the intermediate vug and the symmetry of LaBr3:Cecrystal structure is lower. However, some current international reports have someobvious difference on the scintillation properties of LaBr3:Ce crystal. All of them donot mention the crystallographic direction and the orientation of crystal device is alsonot involved. Therefore, in order to clarify the source of LaBr3:Ce crystalperformance differences, the orientation of crystal device and to lay a good foundationof the crystal orientation growth, we carry out the research on the anisotropy ofLaBr3:Ce crystal. The scintillation properties of LaBr3:Ce crystal along the [100] and[001] direction are characterized, the anisotropies of crystal growth are analyzed andthe growth of crystal orientation is discussed. These mainly research results in thisthesis are as follows:（1） Larger LaBr3:Ce crystals without macroscopical defects are grown byusing crystal spontaneous nucleation and Bridgman method.（2） LaBr3:Ce crystal samples with some specific orientations aresuccessfully directional processed according to the characteristic of the crystal (100)cleavage plane. The scintillation properties of LaBr3:Ce crystal samples along [001]and [100] directions are tested, and the results show that LaBr3:Ce crystal has noobvious difference on the UV emission and excitation spectra, X ray emissionspectrum, energy resolution, decay time and relative light output, that is to say, thereare no obvious anisotropy effects on the scintillation properties. This means that thereis no need to consider the crystal orientation in actual application of LaBr3:Ce crystaldevices.（3） The thermodynamic properties of LaBr3:Ce crystal along [001] and [100]direction are investigated. The results show that LaBr3:Ce crystal has obviousanisotropy effects on the thermal expansion coefficient, compressive strength,elasticity modulus and thermal stress. The value of the average thermal expansioncoefficient of the crystal along [001] and [100] direction is6.8×10-6/K and22.9×10-6/K, respectively. The compressive strength and elastic modulus along [001] and[100] direction are6.76MPa,8.37MPa and1.21GPa,1.96GPa, respectively. Thethermal stress of LaBr3:Ce crystal along [100] direction is10~20times larger than that along [001] direction at the same temperature range, which shows obviousdifferences. The stress state analysis of LaBr3:Ce crystal elements confirm that it canfurthest avoid crystal crack and it is more beneficial to obtain intact LaBr3:Ce crystalwhen the crystal growth orientation is [001] direction.