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arXiv · 2211.05445

Growth and characterization of thorium-doped calcium fluoride single crystals

Kjeld Beeks·Tomas Sikorsky·Veronika Rosecker·Martin Pressler·Fabian Schaden·David Werban·Niyusha Hosseini·Lukas Rudischer·Felix Schneider·Patrick Berwian·Jochen Friedrich·Dieter Hainz·Jan Welch·Johannes H. Sterba·Georgy Kazakov·Thorsten Schumm
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Abstract

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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Kjeld Beeks, Tomas Sikorsky, Veronika Rosecker, Martin Pressler, Fabian Schaden, David Werban, Niyusha Hosseini, Lukas Rudischer, Felix Schneider, Patrick Berwian, Jochen Friedrich, Dieter Hainz, Jan Welch, Johannes H. Sterba, Georgy Kazakov, Thorsten Schumm. 2022-11-10. Growth and characterization of thorium-doped calcium fluoride single crystals. https://arxiv.org/abs/2211.05445

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