Reexamination of the Optical Gamma Ray Decay inT229h

Optical measurements of a clean, $2-\mu \mathrm{C}$ ${}^{233}\mathrm{U}$ sample were made to verify light emission from gamma ray decay of the first excited nuclear level in ${}^{229}\mathrm{Th}$. The results showed that the light observed in earlier studies was likely to be caused by alpha-particle induced fluorescence of air. In vacuo, no light emission was discernable. The ${}^{229}\mathrm{Th}$ system, therefore, does not appear to provide the level of access for studying atomic-nuclear interactions suggested by the previous measurements.