An exhaustive survey of the presently available experimental data on allowed beta decays with logft≤6.0 for A≥228 nuclei results in identification of 30 transitions which are seen to obey the extended asymptotic quantum numbers selection rule ΔN=0, Δ${\mathit{n}}_3$+ΔΛ=0, ‖Δ${\mathit{n}}_3$‖≤2. All these transitions are seen to connect an up-spin (Σ=↑) proton in an N=${\mathit{n}}_3$+Λ=6 Nilsson orbital and a down-spin (Σ=↓) neutron, also in an N=${\mathit{n}}_3$+Λ=6 orbital. Two possible candidates for allowed unhindered decays are presented. Our analysis also reveals the first evidence for four-quasiparticle excitations in even-even nuclei of the actinide region.

• Received 16 December 1991

DOI:https://doi.org/10.1103/PhysRevC.45.3006