Proton-neutron pairing correlations in the self-conjugate nucleus $^{42}$Sc

TL;DR

This study uses laser spectroscopy and advanced calculations to investigate proton-neutron pairing in the self-conjugate nucleus $^{42}$Sc, revealing a larger-than-expected change in nuclear size between states.

Contribution

It provides new measurements of charge radii and introduces improved atomic calculations, highlighting unexpected size reductions linked to proton-neutron pairing.

Findings

Observed a significant size reduction in the isomeric state.

Recalibrated charge radii for scandium isotopes using advanced atomic calculations.

Found discrepancies with shell model and ab-initio predictions regarding size changes.

Abstract

Collinear laser spectroscopy of the $N=Z=21$ self-conjugate nucleus $^{42}$Sc has been performed at the JYFL IGISOL IV facility in order to determine the change in nuclear mean-square charge radius between the $I^{\pi}=0^{+}$ ground state and the $I^{\pi}=7^{+}$ isomer via the measurement of the $^{42\mathrm{g},42\mathrm{m}}$Sc 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 $^{42-46}$Sc 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.