Reduction of the Spin-Orbit Splittings at theN=28Shell Closure

Abstract

The N = 28 shell closure has been investigated via the 46Ar(d,p)47Ar transfer reaction in inverse kinematics. Energies and spectroscopic factors of the neutron p(3/2), p(1/2), and f(5/2) states in 47Ar were determined and compared to those of the 49Ca isotone. We deduced a reduction of the N = 28 gap by 330(90) keV and spin-orbit weakenings of approximately 10(2) and 45(10)% for the f and p states, respectively. Such large variations for the f and p spin-orbit splittings could be accounted for by the proton-neutron tensor force and by the density dependence of the spin-orbit interaction, respectively. This contrasts with the picture of the spin-orbit interaction as a surface term only.

γ-ray spectroscopy of one-proton knockout from45Cl

“…The neutron-rich exotic isotones near 42 Si have attracted considerable attention because of the novel role that neutron shell structure -and the narrowing or collapse of the N = 28 major shell closure -plays in causing deformation in these nuclei [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17]. However, proton shell structure must also be involved [18][19][20].…”

Low-lying2+states generated bypn-quadrupole correlation andN=28shell quenching

“…In this paper, we report the low-lying quadrupole excitation modes in 46 Ar, 44 S, and 42 Si generated by the strong quadrupole correlation between protons and neutrons. To access the low-lying quadrupole modes of these isotopes, we apply the canonical-basis time-dependent Hartree-FockBogoliubov (Cb-TDHFB) theory [33] which has been successfully applied to the study of the dipole [33,34] and quadrupole [35] resonances of nuclei of wide mass range.…”

“…One of the interesting examples is the N = 28 shell gap which is known to be quenched in the vicinity of 44 S and which has been given considerable experimental [5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21] and theoretical attention [22][23][24][25][26][27][28][29][30][31][32]. Since the the orbital angular momenta of f 7/2 and p 3/2 differ by two, the quench of the N = 28 shell gap will lead to the strong quadrupole correlation of neutrons.…”

Further investigation of relativistic symmetry with the similarity renormalization group

“…Especially for the magic number change in exotic nuclei, the spin and pseudospin symmetries are pointed out to play important roles. For instance, the N = 28 shell closure disappears due to the quenching of the spin-orbit splitting for the ν1f spin doublets [9][10][11][12], and the Z = 64 sub-shell closure is closely related to the restoration of PSS for the π2p and π1f pseudospin doublets [13][14][15]. Because of these successes, there have been comprehensive efforts to understand the origin of this symmetry as well as its breaking mechanism.…”