CERN Accelerating science

In this paper, we report the preliminary result from the first Coulomb excitation experiment at REX-ISOLDE (Habs et al 1998 Nucl. Instrum. Methods B 139 128) using neutron-deficient Sn-beams. The motivation of the experiment is to deduce the reduced transition probability, B(E2; 2+→0+), for the sequence of neutron deficient, unstable, even–even Sn-isotopes from 110Sn to ultimately 110Sn. Safe Coulomb excitation using a radioactive beam opens up a new path to study the lifetime of the first excited 2+ state in these isotopes. The de-excitation path following fusion–evaporation reactions will for the even–even Sn isotopes pass via an isomeric 6+ state, located at higher energy, which thus hampers measurements of the lifetime of the first excited state using, e.g., recoil-distance methods. For this reason the reduced transition probability of the first excited 2+ state has remained unknown in this chain of isotopes although the B(E2) value of the stable isotope 112Sn was measured approximately 30 years ago (see, e.g., Stelson et al 1970 Phys. Rev. C 2 2015). Our experiment is thus the first to accomplish a measurement of this quantity in 110Sn. It is believed that the determination of the B(E2) value in 110Sn will indicate the turnover point from a trend of increasing B(E2) values for the heavier isotopes to a trend characterized by less collectivity. Our first preliminary result indicates that this assumption may well be correct.