The Intrinsic Radioactivity And Luminescence Behavior Research Of LYSO:Ce Scintillation Crystal

Since the 21st century,with the rapid development of frontier fields such as nuclear medicine and high-energy physics,researchers have continuously improved the high-energy particle detection performance requirements of scintillation crystal materials.Because of its excellent comprehensive scintillation performance,cerium doped yttrium lutetium silicate(Lu,Y)₂Si O₅:Ce(LYSO:Ce)crystal has been widely used in nuclear medical imaging equipment and other fields.However,the intrinsic radioactivity,energy transfer,temperature effect and other issues of crystals still lack systematic research.The existence of these problems limits the improvement of LYSO:Ce crystal scintillation performance.The scintillation luminescence of LYSO:Ce crystal mainly comes from the intrinsic radiation excitation of the crystal and the excitation of external rays.This thesis tries to establish a relationship between the luminescence behavior of the two luminescence centers in the LYSO:Ce crystal and the intrinsic radiation and energy transition process and analyzes the internal mechanism on the luminescence behavior of the crystal.The research results show that:1)It is confirmed that the intrinsic radiation of LYSO:Ce crystal originates from¹⁷⁶Lu atoms in the crystal.The Y content increase can effectively reduce the intrinsic radiation of the crystal.By subtracting the intrinsic radiation energy spectrum,the energy resolution of large size LYSO:Ce crystal can be improved from 16.1%to 10.6%.2)The luminescence properties of the two different luminescence centers in the LYSO:Ce crystal and the mechanism of the decay time have been studied.By using Gaussian function to analyze the LYSO:Ce crystal emission spectrum,the energy state transition and the different transition component distribution have been described.At the same time,an abnormal phenomenon is confirmed that transition component of 5d?4f²F_7/2 is higher than the transition component of 5d?4f²F_5/2.Our research has also shown that there is a non-radiative energy transfer process from Ce1 center to Ce2 center in the crystal,and with the increase of the Y content in the crystal,the non-radiative energy transfer ratio continues to increase.3)Finally,the thermal quenching effect of crystal luminescence under different temperature conditions has been discussed.By using Gaussian fitting analysis and Arrhenius equation calculation,the luminescence intensity and decay time of the crystal at different temperatures have been analyzed,and it is shown that the electron and energy transfer brought about by thermionic activation will cause temperature quenching effect in the luminescence center of the LYSO:Ce crystal.The thermal quenching temperature of the Ce1 center is significantly higher than that of the Ce2 center Due to the non-radiative energy transfer process from Ce1 to Ce2 center,the thermal quenching activation energy of Ce2 center is basically not affected by the Y content in the crystal and it is stable at about 400 me V.