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Collinear laser spectroscopy of the N=Z=21 self-conjugate nucleus 42Sc has been performed at the JYFL IGISOL IV facility in order to determine the change in nuclear mean-square charge radius between the Iπ=0+ ground state and the Iπ=7+ isomer via the measurement of the 42g,42mSc isomer shift. New multi-configurational Dirac-Fock calculations for the atomic mass shift and field shift factors have enabled a recalibration of the charge radii of the 42−46Sc isotopes which were measured previously. While consistent with the treatment of proton-neutron, proton-proton and neutron-neutron pairing on an equal footing, the reduction in size for the isomer is observed to be of a significantly larger magnitude than that expected from both shell-model and ab-initio calculations. The measured nuclear magnetic dipole moment and electric quadruple moment, on the other hand, are in good agreement with simple empirical estimates and shell-model calculations.

The Deformed Bardeen–Cooper–Schrieffer (DBCS) approach is used to study the axial shape evolution of even–even 8 2 − 1 0 6 Zr , 8 6 − 1 1 2 Mo , 9 0 − 1 1 6 Ru and 9 4 − 1 2 2 Pd isotopic chains. Regarding the residual interaction, both like-particle pairing and unlike-particle pairing are considered in this study. It is found that, in general, the proton–neutron pairing does not affect the ground state shapes of nuclei except for few nuclei, where the inclusion of proton–neutron pairing predicts spherical shape in the ground state rather than a deformed one in case of considering only like-particle pairing. Pairing gaps, energies and strengths of both like- and unlike-pairing modes are discussed. One can conclude that the contribution of proton–neutron pairing to the total pairing energy is not negligible, even if the neutron excess number is high. [ABSTRACT FROM AUTHOR]

We show that the symmetry-restored paired mean-field states (quasiparticle vacua) properly account for isoscalar versus isovector nuclear pairing properties. Full particle-number, spin, and isospin symmetries are restored in a simple SO(8) proton-neutron pairing model, and prospects to implement a similar approach in a realistic setting are delineated. Our results show that, provided all symmetries are restored, the pictures based on pair-condensate and quartet-condensate wave functions represent equivalent ways of looking at the physics of nuclear proton-neutron pairing. [ABSTRACT FROM AUTHOR]

Herein, the effect of quadrupole deformation has been thoroughly studied using the generalized BCS and Lipkin–Nogami (LN) pairing approaches for both like- and unlike-particle pairing modes. The pairing treatment of the realistic NN-interaction with these two approaches is then used to calculate the two-neutrino double beta decay matrix elements, ( M G T 2 ν ), through the Quasiparticle Random Phase Approximation (QRPA) theory. The results reveal significant differences in the calculated matrix elements due to the inclusion of the unlike-particle pairing mode, besides a small difference in M G T 2 ν values regarding the pairing approach type used in calculations. It is found that, the competition between the BCS and LN approaches in the calculation of M G T 2 ν , slightly depends on the inclusion or exclusion of the pn-pairing mode. [ABSTRACT FROM AUTHOR]

We study sum rules for charge exchange operators of the Gamow–Teller and Fermi type and explore what can be learned from them about proton–neutron pairing in T=0 and T=1 channels. We consider both energy weighted (EWSR) and non-energy weighted (NEWSR) sum rules. We use a schematic Hamiltonian to stress the distinctive roles of T=1 and T=0 pair interactions and correlations in the sum rules. Numerical results for 44Ti are presented for both schematic and realistic interactions. [Copyright &y& Elsevier]