Stepping into the Sea of Instability: The New Sub-μs Superheavy Nucleus ^{252}Rf

We report the discovery of the new isotope ^{252}Rf. With its extremely short half-life of 60_{-30}^{+90}  ns, it expands the range of half-lives of the known superheavy nuclei by about 2 orders of magnitude. This nucleus was synthesized in its high-K isomeric state, for which we measured a half-life of 13_{-3}^{+4}  μs. Our results confirm a smooth onset of decreasing ground-state spontaneous fission half-lives in the neutron-deficient Rf isotopes toward the isotopic border of 10^{-14}  s, which is the time needed to form an atomic shell. Our findings set a new benchmark for further exploration of phenomena associated with high-K states and inverted fission stability in the heaviest nuclei.