Radioactive decay ofU232byNe24emission

Using polyethylene terephthalate track-recording films, which are sensitive only to particles with Z>6, we have detected for the first time the exotic radioactive decay mode in which an energetic ${}_{}{}^{24}{}_{}{}^{}\mathrm{Ne}$ nucleus is emitted. For ${}_{}{}^{232}{}_{}{}^{}\mathrm{U}$ the branching ratio for ${}_{}{}^{24}{}_{}{}^{}\mathrm{Ne}$ relative to alpha decay is (1.00±0.25)×${10}^{\mathrm{-}12}$. We point out that the spontaneous fission rates reported for ${}_{}{}^{232}{}_{}{}^{}\mathrm{U}$ and several other nuclides based on early measurments of energetic pulses in ionization chambers may actually have been rates for emission of ${}_{}{}^{24}{}_{}{}^{}\mathrm{Ne}$ or other heavy clusters.