The evolution of magnetic dipole strength in $^{100-140}$ Sn isotope chain and quenching of nucleon g factors

TL;DR

This paper investigates the evolution of magnetic dipole (M1) transition strengths in Sn isotopes using relativistic nuclear energy density functional theory, highlighting the quenching of nucleon g-factors and improving agreement with experimental data.

Contribution

It provides a theoretical analysis of M1 transitions in Sn isotopes, demonstrating reduced discrepancy with experiments and quantifying g-factor quenching effects.

Findings

Discrepancy between model and experiment on B(M1) strength is reduced.

Quenching of nucleon g-factors is necessary, with effective g-factors being 80-93% of free nucleon values.

Further experiments are needed to confirm the total M1 strength above neutron threshold.

Abstract

The evolution of electromagnetic transitions along isotope chains is of particular importance for the nuclear structure and dynamics, as well as for the r-process nucleosynthesis. Recent measurement of inelastic proton scattering on even-even $^{112-124}$Sn isotopes provides a novel insight into the isotopic dependence of E1 and M1 strength distributions. We investigate M1 transitions in even-even $^{100-140}$Sn isotopes from a theoretical perspective, based on relativistic nuclear energy density functional. The M1 transition strength distribution is characterized by an interplay between single and double-peak structures, that can be understood from the evolution of single-particle states, their occupations governed by the pairing correlations, and two-quasiparticle transitions involved. It is shown that discrepancy between model calculations and experiment on B(M1) transition strength is considerably reduced than previously known, and the quenching of the g-factors for the free nucleons needed to reproduce the experimental data on M1 transition strength amounts $g_{eff}/g_{free}$=0.80-0.93. Since some of the B(M1) strength above the neutron threshold may be missing in the inelastic proton scattering measurement, further experimental studies are required to confirm if only small modifications of the bare g-factors are actually needed when applied in finite nuclei.