Measurement of photo- and radio-luminescence of thin ThF4 films

We conducted measurements on the photoand radio-luminescence of thin ThF4 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 ThF4 4 crystals could be used as a target for the search for 229mTh m Th and as a medium for the future nuclear clock. The measurements indicate that using a small and thin ThF4 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 229mTh m Th excitation and decay in ThF4. 4 .