Observation of Electromagnetic Radiation from Deexcitation of the229Th Isomer

Experimental measurements of ultraviolet and visible emission from two samples containing ${}^{233}$U suggest the deexcitation of a reported 3.5 eV isomeric level in ${}^{229}$Th. The unique phenomenon of ultraviolet $\gamma$-ray emission was observed from this level. Results are consistent with theoretical arguments suggesting that the nucleus can also deexcite via an inelastic electronic bridge mechanism. These observations indicate the exotic phenomenon of nuclear emission in the optical band, and open new areas of physics related to nuclear-atomic interaction.