E2transitions in Sn isotopes within the quasiparticle-phonon model

Abstract

The evolution of the structure of the first ${{2}_{1}}^{+}$ state along the chain of Sn isotopes is investigated within the quasiparticle-phonon model through the analysis of the energies and the $B(E2;{{0}_{1}}^{+}\ensuremath{\rightarrow}{{2}_{1}}^{+})$ strengths. The calculation reproduces the trend of the energies and, partly, the observed deviations of the $E2$ strengths from the parabolic behavior obtained in some large-scale shell-model calculations. Such an asymmetric trend is shown to be the outcome of several factors: single-particle energies, polarization of the $N=Z=50$ core, interplay between pairing plus quadrupole, and quadrupole pairing interactions.