PbWO_4闪烁晶体的辐照损伤机理研究

A STUDY ON RADIATION DAMAGE MECHANISM IN PbWO 4 SCITILLATING CRYSTALS 

完成了６４０—１０４０℃温度范围内钨酸铅［ＰｂＷＯ４（ＰＷＯ）］晶体的退火实验，观察到较低温退火时晶体中本征色心吸收带（３５０ｎｍ）先是增加，其后随退火温度的升高而逐渐降低直至消除的全过程．分析了ＰＷＯ晶体的本征缺陷和电荷补偿机制．讨论了退火过程中氧进入晶体后色心的产生和转化规律，并提出可能发生Ｐｂ３＋→Ｐｂ４＋的进一步氧化过程，从而导致Ｐｂ３＋空穴中心的湮没．测量并比较了不同退火温度处理后ＰＷＯ晶体的紫外辐照诱导色心吸收谱．观察到导致辐照损伤的Ｏ－空穴中心主要来自晶体中固有的Ｐｂ３＋空穴中心向Ｏ－空穴中心的转化；同时晶体中氧空位作为电子陷阱对Ｏ－空穴中心有稳定作用．当上述两项因素得以消除，晶体辐照硬度随之提高．实验表明，在含氧气氛中高温退火可以有效地改进ＰＷＯ晶体的抗辐照损伤能力．

Abstract A representative PbWO 4 sample was annealed subsequently from 640 to 1040℃ in air and the optical absorption spectra were measured after each annealing step.It was found that the intrinsic color center absortion band peaking at 350nm increased after annealing at lower temperature,then with increasing annealing temperature it decreased continuously until it was removed finally.Based on the analysis of intrinsic defects and corresponding charge compensation of PbWO 4 crystals,the creation and transformation of the color center were discussed.This was caused by the diffusion of oxygen,entering into PWO crystals during the annealing process.It was supposed that a Pb 3+ →Pb 4+ transformation probably occurred in the annealing process,it would lead to annihilation of Pb 3+ centers. The UV radiation induced color center absorptions of PWO crystals annealed at different temperatures were measured and compared.It has been observed that the O - hole centers as the main product of the radiation damage of PWO crystals were produced predominantly from the transformation of the intrinsic Pb 3+ hole centers.On the other hand,oxygen vacancies V O as electron trap centers trapped the electrons during irradiatiion, thus stabilizing O - hole centers.When those two factors have been removed by means of annealing at high temperature in air (oxygen abundant atmosphere),the radiation hardness of PWO crystals can be effectively improved.While,the iron impurity in crystals is very harmful for the radiation hardness of PWO crystals.