Heavy-fragment radioactivity ofU234

Earlier we reported the detection of three events in which ${}_{}{}^{234}{}_{}{}^{}\mathrm{U}$ decayed by Mg-ion emission and 14 events in which it decayed by Ne-ion emission. In a new experiment with a factor of 7 longer exposure time, we have detected 36 Mg fragments and 108 Ne fragments. From the larger number of events, we have made a more accurate determination of the branching ratios relative to alpha decay, taking into account zenith-angle-dependent detection efficiency. The result is ${\log }_{10}$B(Ne/ α)=-12.36±0.05 and ${\log }_{10}$B(Mg/α)=-12.86±0.08.