Abstract
Measurements of the beta-decay half-lives of neutron-rich nuclei (MgAr) in the vicinity of the N=28 shell closure are reported. Some 22 half-lives have been determined, 12 of which for the first time. Particular emphasis is placed on the results for the Si isotopes, the half-lives of which have been extended from N=25 to 28. Comparison with QRPA calculations suggests that 42Si is strongly deformed. This is discussed in the light of a possible weakening of the spin–orbit potential.
Highlights
The investigation of very neutron-rich nuclei provides a fertile testing ground for our understanding of nuclear structure
Some 12 half-lives have been measured for the first time
Perhaps the most significant new results are those obtained for the Si isotopic chain, whereby half-lives have been established out to the N = 28 nucleus 42Si
Summary
The investigation of very neutron-rich nuclei provides a fertile testing ground for our understanding of nuclear structure. The energies and B(E2) for the lowest J π = 2+ states of the neutron-rich isotopes 38,40,42,44S, have been measured via Coulomb excitation [1,2] and indicate that 40,42,44S are moderately deformed (|β2| ≈ 0.3). The slope of the two-neutron separation energy for the Si isotopes together with the 2+1 energy and the νf7/2 occupation number indicate that the 42Si has the characteristics of a doubly magic nucleus, such as 48Ca. Recently the same authors adjusted the interaction to reproduce the single-particle states in 35Si [15] and interpreted the reduction between the νf7/2 and νp3/2 orbitals as an erosion of the spin–orbit force far from stability.
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