The spin magnetic-dipole transitions and the neutron-proton spin-spin correlations in sd-shell even-even nuclei with N=Z are investigated by using shell-model wave functions taking into account enhanced isoscalar (IS) spin-triplet pairing as well as the effective spin operators. It was shown that the IS pairing and the effective spin operators gives a large quenching effect on the isovector (IV) spin transitions to be consistent with data observed by (p,p’) experiments. On the other hand, the observed IS spin strengths show much smaller quenching effect than expected by the calculated results. The IS pairing gives a substantial quenching effect on the spin magnetic-dipole transitions, especially on the IV transitions. Consequently, an enhanced IS spin-triplet pairing interaction enlarges the proton-neutron spin-spin correlation deduced from the difference between the IS and the IV sum-rule strengths. The β-decay rates and the IS magnetic moments of the sd shell are also studied in terms of the IS pairing as well as the effective spin operators.
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We show that fully aligned neutron-proton pairs play a crucial role in the low-energy spectroscopy of nuclei with valence nucleons in a high-j orbital. Their dominance is valid in nuclei with valence neutrons and protons in different high-j orbitals as well as in N=Z nuclei, where all nucleons occupy the same orbital. We demonstrate analytically this generic feature of the neutron-proton interaction for a variety of systems with four valence nucleons interacting through realistic, effective forces. The dominance of fully aligned neutron-proton pairs results from the combined effect of (i) angular momentum coupling and (ii) basic properties of the neutron-proton interaction.
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Prediction and evaluation of magnetic moments in T=1/2, 3/2, and 5/2 mirror nuclei
Theo J. Mertzimekis
The Buck-Perez analysis of mirror nuclei magnetic moments has been applied on an updated set of data for T=1/2,3/2 mirror pairs and attempted for the first time for T=5/2 nuclei. The spin expectation value for mirror nuclei up to mass A=63 has been reexamined. The main purpose is to test Buck-Perez analysis effectiveness as a prediction and—more importantly—an evaluation tool of magnetic moments in mirror nuclei. In this scheme, ambiguous signs of magnetic moments are resolved, evaluations of moments with multiple existing measurements have been performed, and a set of predicted values for missing moments, especially for several neutron-deficient nuclei is produced. A resolution for the case of the 57Cu ground-state magnetic moment is proposed. Overall, the method seems to be promising for future evaluations and planning future measurements.