钨酸铅晶体中痕量杂质元素的分布特征及其对晶体性能的影响

Distribution of Trace Impurities in PbWO_4 Crystals and Their Effect on the Crystal's Scintillation Properties

利用GDMS分别测试了用Bridgman方法生长的十个全尺寸钨酸铅晶体顶、底两端的杂质含量 ,发现在PWO晶体中 ,K、Na、Mo、As、Y等杂质元素富集于晶体的顶部 ,具有分凝系数小于 1的特征。Ca和Ba杂质则富集于晶体的底部 ,具有分凝系数大于 1的特征 ,Al、Si、Cu等杂质的分布缺乏明显的规律性。这些杂质主要来源于生长晶体时所使用的WO3 原料。根据掺杂实验 ,认为K、Na、Mo、As等是影响PWO闪烁性能的有害杂质 ,Ca和Ba是无害杂质 ,Y是有益杂质 ,Al、Si、Cu等杂质的行为尚不明确。

Ten full size lead tungstate crystals were grown with modified Bridgman method. The impurities at their top and bottom ends were analyzed by GDMS respectively. It was found that the concentration of K,Na,Mo,As and Y at top end is sizably larger than that at the bottom (seed end) of the same ingot,and the concentration of Ca and Ba ions at top end is less than that at the bottom.These phenomena means that the former ions are characterized by segregation coeffcient k<1,and the latter ions' k>1.The distribution of Al,Si and Cu ions is lack of significant tendency. All these impurities are mainly originated from WO 3,one of the raw materials used for growing PWO crystal. Based on the doping experiments,impurities of K,Na,Mo and As are suggested to be harmful to the scintillation properties of PWO crystal.Ca and Ba have no negative effect on the properties and the roles of Al,Si,Cu impurity ions are unclear and may be worth studying further.