Search for Spontaneously Fissioning Elements in Nature

The failure to observe fission tracks in old Pb-rich and Au-rich minerals restricts the spontaneous fission rates of Au and Pb to ≲1×${10}^{-25\mathrm{}}$ per year per Au atom and <3×${10}^{-24\mathrm{}}$ per year per Pb atom (at 95% confidence level). No fission-track evidence for superheavy elements in these or other minerals rich in heavy elements has been found. These negative results are not compatible with recent proportional-counter data and track data of Flerov and co-workers.