Spectroscopy along flerovium decay chains. II. Fine structure in odd-A 289Fl

Fifteen correlated α -decay chains starting from the odd-A superheavy nucleus ²⁸⁹Fl were observed following the fusion-evaporation reaction ⁴⁸Ca+²⁴⁴Pu . The results call for at least two parallel α -decay sequences starting from at least two different states of ²⁸⁹Fl. This implies that close-lying levels in nuclei along these chains have quite different spin-parity assignments. Further, observed α -electron and α -photon coincidences, as well as the α -decay fine structure along the decay chains, suggest a change in the ground-state spin assignment between ²⁸⁵Cn and ²⁸¹Ds. Our experimental results, on the excited level structure of the heaviest odd-N nuclei to date, provide a direct testing ground for theory. This is illustrated by comparison with new nuclear structure calculations based on the symmetry-conserving configuration mixing theory.