Evolution Of Magnetic Dipole Strength In Sn100-140 Isotope Chain And The Quenching Of Nucleon G Factors

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 Sn100-140 isotopes provides novel insight into the isotopic dependence of E1 and M1 strength distributions. We investigate M1 transitions in even-even Sn100-140 isotopes from a theoretical perspective, based on the 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 the discrepancy between model calculations and experiments for the M1 transition strength is considerably more 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(f)(ree) = 0.80-0.93. Because some of the 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.