掺钍氟化钙单晶的生长与表征
Growth and characterization of thorium-doped calcium fluoride single crystals
摘要：
我们生长了$^{232}$ Th：CaF $_2$和$^{229}$ Th：CaF $_2$单晶，用于研究$^{229}$ Th的第一核激发态。尽管$^{229}$ Th极度稀缺（和放射性），为了达到高掺杂浓度，我们已经将晶体体积缩小了100倍，与已建立的商业或科学生长方法相比。我们在直径为3.2 mm的籽晶单晶上使用垂直梯度冷冻方法，该籽晶单晶具有2 mm的钻孔袋，填充有共沉淀的CaF $_2$：ThF $_4$：PbF $_2$粉末以生长单晶。已经用具有良好（$>$ 10%）VUV透射率的$^{232}$ Th实现了$4\cdot10^{19}$ cm $^{-3}$的浓度。然而，$^{229}$ Th的固有放射性驱动生长期间的放射诱导解离和固化后的辐射损伤。两者都导致VUV透射率降低，将$^{229}$ Th浓度限制在$<5\cdot10^{17}$ cm $^{-3}$。
英文摘要：
We have grown $^{232}$Th:CaF$_2$ and $^{229}$Th:CaF$_2$ single crystals for investigations on the VUV laser-accessible first nuclear excited state of $^{229}$Th. To reach high doping concentrations despite the extreme scarcity (and radioactivity) of $^{229}$Th, we have scaled down the crystal volume by a factor 100 compared to established commercial or scientific growth processes. We use the vertical gradient freeze method on 3.2 mm diameter seed single crystals with a 2 mm drilled pocket, filled with a co-precipitated CaF$_2$:ThF$_4$:PbF$_2$ powder in order to grow single crystals. Concentrations of $4\cdot10^{19}$ cm$^{-3}$ have been realized with $^{232}$Th with good ($>$10%) VUV transmission. However, the intrinsic radioactivity of $^{229}$Th drives radio-induced dissociation during growth and radiation damage after solidification. Both lead to a degradation of VUV transmission, limiting the $^{229}$Th concentration to $<5\cdot10^{17}$ cm$^{-3}$.
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