Measurement of photo- and radio-luminescence of thin ThF4 films
We conducted measurements on the photo- and radio-luminescence of thin ThF$_4$ films in both the UV and visible ranges. In the UV range, we found that both luminescences are at a similar level as the internal dark counting noise of the photo-multiplier-tube (PMT). Our results suggest that thin ThF$_4$ crystals could be used as a target for the search for $^{229m}$Th and as a medium for the future nuclear clock. The measurements indicate that using a small and thin ThF$_4$ film can reduce background noise while maintaining the signal at the same level, achieved by increasing the $^{229}$Th enrichment. Our developed apparatus is now ready for direct measurements of $^{229m}$Th excitation and decay in ThF$_4$.
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