The islands of shape coexistence within the Elliott and the proxy-SU(3) Models

Abstract

A novel dual-shell mechanism for the phenomenon of shape coexistence in nuclei within the Elliott SU(3) and the proxy-SU(3) symmetry is proposed for all mass regions. It is supposed, that shape coexistence is activated by large quadrupole-quadrupole interaction and involves the interchange among the spin-orbit (SO) like shells within nucleon numbers 6-14, 14-28, 28-50, 50-82, 82-126, 126-184, which are being described by the proxy-SU(3) symmetry, and the harmonic oscillator (HO) shells within nucleon numbers 2-8, 8-20, 20-40, 40-70, 70-112, 112-168 of the Elliott SU(3) symmetry. The outcome is, that shape coexistence may occur in certain islands on the nuclear map. The dual-shell mechanism predicts without any free parameters, that nuclei with proton number (Z) or neutron number (N ) between 7-8, 17-20, 34-40, 59-70, 96-112, 146-168 are possible candidates for shape coexistence. In the light nuclei the nucleons flip from the HO shell to the neighboring SO-like shell, which means, that particle excitations occur. For this mass region, the predicted islands of shape coexistence, coincide with the islands of inversion. But in medium mass and heavy nuclei, in which the nucleons inhabit the SO-like shells, shape coexistence is accompanied by a merging of the SO-like shell with the open HO shell. The shell merging can be accomplished by the outer product of the SU(3) irreps of the two shells and represents the unificaton of the HO shell with the SO-like shell.

Resolution of the spin paradox in the Nilsson model

“…The use of asymptotic quantum numbers for deformed nuclei is just an example of choosing a basis as close as possible to the dynamics of the physical system under study [32,33]. It should be noted that the Nilsson model is still in wide use, 65 years after its introduction [11], either in the framework of Nilsson mean-field plus pairing calculations [34,35], cranking shell model calculations based on the Nilsson potential with pairing correlations [36], or in relation to approximate SU(3) symmetries [37] like the pseudo-SU(3) symmetry [38][39][40][41][42][43][44][45][46][47], the quasi-SU(3) symmetry [48,49], the proxy-SU(3) symmetry [50][51][52][53][54][55][56][57], and the recovery of SU(3) symmetry at superdeformation [58].…”