Abstract
The structure of the very neutron-rich nuclei 39Si and 41Si has been investigated via in-beam γ-ray spectroscopy and few-nucleon knockout from radioactive beams. The observation of low-lying states in 39Si is a clear evidence for a drastic lowering of the intruder neutron 3/2− state when going from Z=20 to Z=14. The energy of the only γ-ray transition (672(14) keV) observed in 41Si is significantly lower than that of the first excited state in 47Ca (2014 keV) suggesting a deformed ground state for 41Si. These results are consistent with large-scale shell-model calculations implying that strong proton–neutron correlations are the main reason for the lowering of the intruder configurations over the normal ones.
Highlights
The nuclei in the vicinity of the N = 28 shell closure offer a fertile ground for studying the various aspects of nuclear forces and correlations
The change in the single-particle energies as a function of the proton and neutron numbers leading to the reduction of the N = 28 shell gap below 48Ca, as well as that in the splitting between the spin–orbit partners of the neutron f7/2 and p3/2 or
Correlations of a quadrupole character drive the development of a new “island of inversion” around 42Si, where according to mean field [1] and shell-model [2,3,4] calculations, deformed intruder configurations fall below the spherical ones
Summary
The nuclei in the vicinity of the N = 28 shell closure offer a fertile ground for studying the various aspects of nuclear forces and correlations. Correlations of a quadrupole character drive the development of a new “island of inversion” around 42Si, where according to mean field [1] and shell-model [2,3,4] calculations, deformed intruder configurations fall below the spherical ones. In 45Ar, a low-lying 3/2− state has been observed at 537 keV above the 7/2− ground state [5]. It has been shown via the 44Ar(d, p) reaction that this state contains about half of the p3/2 strength [3].
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