Spontaneous Ultraviolet Emission from233Uranium/T229horiumSamples

The spontaneous ultraviolet luminescence reported [G. M. Irwin and K. H. Kim, Phys. Rev. Lett. 79, 990 (1997); D. S. Richardson et al., ibid. 80, 3206 (1998)] from ${}^{233}\mathrm{uranium}$ compounds and ascribed to an ultraviolet gamma-ray emission from the metastable ${}^{229}\mathrm{thorium}$ daughter is actually ${\mathrm{N}}_2$ discharge emission induced in the air surrounding the sample by the sample radioactivity. The UV spectrum from high elemental and isotopic purity ${}^{233}{\mathrm{UO}}_3$ reported here also exhibits a line at 391.3 nm that does not appear to be due to electric discharge ${\mathrm{N}}_2$ emission.