An alternative viewpoint on the nuclear structure towards Sn: Lifetime measurements in Sn

This work aims at presenting an alternative approach to the long standing problem of the B(E2) values in Sn isotopes in the vicinity of the N=Z double-magic nucleus $^{100}$Sn, until now predominantly measured with relativistic and intermediate-energy Coulomb excitation reactions. The direct measurement of the lifetime of low-lying excited states in odd-even Sn isotopes provides a new and precise guidance for the theoretical description of the nuclear structure in this region. Lifetime measurements have been performed in $^{105}$Sn for the first time with the coincidence Recoil Distance Doppler Shift technique. The lifetime results for the $7/{2}_{1}^{+}$ first excited state and the $11/{2}_{1}^{+}$ state, ${2}^{+}\left({}^{104}$Sn) $\otimes \phantom{\rule{0.2em}{0ex}}\nu 1{g}_{7/2}$ multiplet member, are discussed in comparison with state-of-the-art shell model and mean field calculations, highlighting the crucial contribution of proton excitation across the core of $^{100}$Sn. The reduced transition probability B(E2) of the $11/{2}_{1}^{+}$ core-coupled state points out an enhanced staggering with respect to the B(E2; ${2}_{1}^{+}$→${0}_{1}^{+}$) in the even-mass $^{104}$Sn and $^{106}$Sn isotopes.