| The scintillation crystal LaBr3:Ce and LaCl3:Ce have remarkablescintillation properties, such as high light output, energy resolution, fast decay timeand so on, the structure of LaBr3and LaCl3crystal are extremely same, and they werepopular in the international research community. In comparison, LaBr3:Ce crystal hassuperior scintillation properties, but it is easier to absorb water and react with oxygenwhen being exposed in air, also the thermal expansion anisotropy of LaBr3:Ce crystalis obvious, so the crystal is easier to crack and the growth of large size crystalbecomes more difficult, however, the growth of LaCl3:Ce crystal is relatively easier.In recent years, LaBr3:Ce and LaCl3:Ce crystals have attracted lots of attention ofmany researchers from home and abroad, nevertheless, the research concerning theLa(ClxBr1-x)3:Ce anion solid solution crystal is few. On the basis of literature research,this paper dedicated in the La(ClxBr1-x)3:Ce anion solid solution crystal research.In this paper, the La(ClxBr1-x)3:Ce solid solution crystal was grown by thevertical Bridgman technique in vacuum. Through the thermal analysis experiment,the component proportion of solid solution crystal were intended to beLa(Cl0.05Br0.95)3:Ce、La(Cl0.5Br0.5)3:Ce、La(Cl0.95Br0.05)3:Ce，and found the best growthprocess parameters suitable for the three crystals respectively, obtained the transparent,macroscopic complete crystal. The largest size can reach to1inch, and the sizes ofthree components crystals after processing can reach to18×8×8mm3、10×12mm3、10×10mm3. The crystal performance characterization through the test of X-rayexcitation emission spectrum, UV fluorescence spectrum, energy resolution,absorption spectrum, UV fluorescence lifetime, etc. And the segregated coefficient ofanions in crystal (Cl-, Br-) was determined through the titration.In this paper, the research of Brominated lanthanum chloride solid solutioncrystals was made according to the three different components.(1) The melt points and freezing points of different components of LaCl3-LaBr3mixed raw material were obtained through the thermoanalysis experiments. Thesimple LaCl3-LaBr3phase diagram was achieved on this basis. From the isomorphousphase diagram, it is clear that LaCl3and LaBr3can become solid solution in anyproportion. According to the thermal analysis of several components of raw material,In the La(ClxBr1-x)3:Ce solid solution crystal, when the x=0.5, or the ratio of Cl/Br is close to1, the crystal is relatively more stable.(2) The growth and scintillation properties of La(Cl0.05Br0.95)3:Ce crystal.Through trial and error, transparent, macroscopic complete crystal was obtained bythe vertical Bridgman technique in vacuum, the suitable growth technologicalparameters were found: the temperature of the high temperature zone setted to be840℃, the crucible descent rate was0.5025mm/h, the cooling rate was10-15℃/h,and the temperature gradient of the temperature gradient zone was maintained at15-20℃/cm. The processed La(Cl0.05Br0.95)3:Ce crystal UV fluorescence spectrumindicated that the emission spectrum of the crystal were358nm and382nm,corresponding to the Ce3+ions5d'4f transition. The fluorescence decay curve wasprocessed by exponential fit, the value was ι=17.7ns, which was better than LaCl3crystal. The light output and energy resolution of the crystal was tested under t hemultichannel analyzer of137Cs source. The results show that the energy resolution ofthe crystal was4.55%, and the light output was62,000ph/MeV. The results weresimiliar to LaBr3:Ce crystal.(3) The growth and scintillation properties of La(Cl0.5Br0.5)3:Ce crystal. The797℃melt point of La(Cl0.5Br0.5)3:Ce was obtained by the thermoanalysisexperiments, so the temperature of the high temperature zone set to be840℃, thecrucible descent rate was0.5025mm/h, the cooling rate was10-15℃/h, and thetemperature gradient of the temperature gradient zone was maintained at15-20℃/cm.The processed La(Cl0.5Br0.5)3:Ce crystal UV fluorescence spectrum indicated that theemission spectrum of the crystal were357nm and389nm, corresponding to the Ce3+ions5d'4f transition. The energy resolution of the crystal was33.2%, and the lightoutput was2250±50ph/MeV, the decay time was27.7ns. From360nm to800nm, thehigest transmittance of the crystal was about30%.(4) The growth and scintillation properties of La(Cl0.95Br0.05)3:Ce crystal. Thesuitable growth technological parameters of this crystal were obtained by repeatedexperiments as follows: the temperature of the high temperature zone was890℃, thecrucible descent rate was0.5025mm/h, the cooling rate was10-15℃/h, and thetemperature gradient of the temperature gradient zone was maintained at15-20℃/cm.The X-ray excitation emission spectrum of the La(Cl0.95Br0.05)3:Ce crystal indicatedthat the emission wavelengths of the crystal were356nm and381nm, correspondingto the Ce3+ions5d'4f transition. The energy resolution of the crystal was19.3%,and the light output was2030±50ph/MeV. From360nm to800nm, the higest transmittance of the crystal was about45%. The fluorescence decay curve wasprocessed by exponential fitting, the value was ι=17.7ns, which was better thanLaCl3crystal.(5) By comparing the scintillation properties of different components of solidsolution crystal, founding that the La(Cl0.05Br0.95)3:Ce crystal has the best scintillationproperties. In other words, the great percentage of bromine in the crystal, the betterscintillation properties it has, which is according with the result that lanthanumbromide has better scintillation properties than that of lanthanum chloride crystal.(6) Through the titration experiments, figuing out the segregation coefficient of(Cl-+Br-) in La(ClxBr1-x)3:Cecrystal were very close to1. |
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