Speaker
Description
The Sn isotopes, containing the longest chain of isotopes between two doubly-magic nuclei, offer a fundamental testing ground for nuclear theories. Between the $N = 50$ and $N = 82$ shell closures, the $2^{+}_{1}$ energies of all Sn isotopes are well established and show an almost constant value, as expected in the generalized seniority scheme. Within the same framework, the $B(E2)$ values should resemble an inverted parabola peaking at mid-shell. However, measurements in the most proton-rich Sn isotopes have shown a clear deviation from the expected behavior, with an enhancement of the transition probabilities towards $^{100}$Sn. Although different calculations tend to agree on the neutron-rich side of the chain, significant differences are observed in the proton-rich side. This is particularly true for $^{102}$Sn, where the difference between the predictions amounts to almost a factor of 3, making this isotope a good candidate for the investigation of the effects driving the nuclear structure in the vicinity of $^{100}$Sn.
An experiment to measure for the first time the $B(E2)$ values in the $N=52$ isotones towards $^{100}$Sn, including $^{102}$Sn, was performed at the Radioactive Isotope Beam Factory in Japan. A 345 MeV/nucleon beam of $^{124}$Xe was fragmented on a 5-mm-thick Be target at the entrance of the BigRIPS separator. The $N=52$ isotones of interest were identified on an event-by-event basis using the $B\rho-\Delta E-B\rho$ technique. A 0.5-mm Au target placed at the F8 focal plane was used to induce Coulomb excitation. Outgoing fragments were identified using the ZeroDegree spectrometer. The Au target was surrounded by the high-efficiency DALI2$^{+}$ $\gamma$-detector array, composed of 226 NaI(Tl) detectors. Preliminary results on the Coulomb excitation cross sections and transition probabilities for $^{98}$Pd, $^{100}$Cd and $^{102}$Sn will be presented, and their comparison with shell model and ab-initio calculations will be discussed.
