Structure of 128Sn selectively populated in the β decay of the 128In ground state

Abstract

High-resolution γ -ray spectroscopy and fast-timing methods were employed to study the excited structure of 128Sn, populated via the β-decay chain of 128Cd → 128In → 128Sn. The experiment was performed by online mass separation at the ISOLDE facility at CERN, profiting from intense and pure Cd beams obtained by a temperature-controlled quartz transfer line combined with resonant laser ionization. An extended 128Sn level scheme populated in the β− decay of the low-spin 128In isomer was constructed, adding a total of 81 new γ -ray transitions and 30 new levels. Lifetimes of excited states were measured using time-delayed βγ (t) and γ γ (t) coincidences. The lifetime of the (4+) state was measured for the first time, making it possible to deduce the B(E2; 4+ → 2+) transition strength. The previously measured (5−) state was reassessed with improved statistics. Additionally, an upper limit for the lifetime of the state at 2378 keV was established. The derived reduced transition probabilities support a tentative spin-parity assignment of (4−) for this level. The experimental level scheme and transition probabilities are compared with available shell-model calculations.