Structure of neutron-rich nuclei and rare processes in spontaneous fission of 252 Cf

The high selectivity and sensitivity offered by large detector arrays such as Gammasphere and Eurogam enable one to identify gamma rays from individual neutron-rich nuclei produced in the spontaneous fission (SF) of 252 Cf and 248 Cm. Rare processes such as cold neutronless binary fission, could α-accompanied ternary fission and cold 10 Be-accompanied ternary fission are observed. We have identified new gamma transition in 101,102,103 Nb, 98,100 Y, 103,107,109 Mo, 105-109 Tc and 109,111 Ru. In 102 Nb and 100 Y nuclei we observed pairing-free rotational bands with Iexp/Irigid ≅ 1. In 103 Mo and 109,111 Ru we identified bands with close doublet structures which may be a general consequence of rotation alignment for configuration of half-filed j-shells, which are weakly coupled to the deformed shapes. The bands with the large signature splitting in 105,107 Tc are evidently derived from g9/2 orbitals. The two sets of bands, each set intertwined by E1 transitions are observed in 107 Mo and one such set in 109 Mo. The observed level schemes are interpreted in terms of possible octupole deformation originating from the strong interaction of the h11/2 and d5/2 neutron shells. (authors)