Quasi-SU(3) coupling of (1h11/2, 2f7/2) across the N=82 shell gap: Enhanced E2 collectivity and shape evolution in Nd isotopes

The essence of the quasi-SU(3) coupling scheme suggested by Zuker et al. is that the high-j intruder orbit alone is insufficient to induce required large collectivity, and it is necessary for the high-j orbit to correlate through the quadrupole interaction with another higher-lying orbit with Delta j = 2. To extend this idea to the medium-heavy mass region, we investigate the systematics of energy levels and B(E2) values for Sn, Te, Xe, Ba, Ce, Nd, and Sm isotopes by applying the recently proposed realistic PMMU shell model. The calculations are performed by using the projected Hartree-Fock-Bogolyubov plus generator coordinate method in the model space of (1g(9/2), 1g(7/2), 2d(5/2), 2d(3/2), 3s(1/2), 1h(11/2)). The calculations describe well the experimental data over a , wide range of nuclei. However, it is found that, in some nuclei close to the neutron midshell, Ce-124,Ce-126, Nd-130,Nd-132 , and Sm-134, the calculated B(E2; 2(1)(+) -> 0(1)(+)) values underestimate the data considerably. This problem can be resolved by inclusion of the 2f(7/2 )orbit into the model space, which, with 1h(11/2), forms a quasi-SU(3) coupling scheme. It is shown that the QQ interaction between the SU(3)-partner 1h(11/2)-2f(7/2) is a driving force for enhanced E2 collectivity in the above nuclei and is responsible for the shape evolution in Nd isotopes. In addition, the participation of the 2f(7/2) orbit in the model space favors prolate shape in the ground state of N <= 76 isotopes, thus subverting the oblate result from the same calculation but without 2f(7/2).

Automated summary

The quasi-SU(3) coupling scheme proposed by Zuker et al. suggests that high-j intruder orbit alone is insufficient for inducing required large collectivity, and correlation through quadrupole interaction with another higher-lying orbit is necessary. Extending this idea to the medium-heavy mass region, a realistic PMMU shell model was applied to investigate energy levels and B(E2) values for several isotopes, revealing underestimations in some nuclei near the neutron midshell that can be resolved by including the 2f(7/2) orbit.