The tin (Sn; Z = 50) isotopes constitute the longest chain of semi-magic even-even nuclei between the 100Sn (N = 50) and 132Sn (N = 82) double-shell closures, seven of which, 112,114,116,118,120,122,124Sn, are stable. These isotopes have become a prototypical benchmark of extensive microscopic theory and experiment, reflected in the large number of studies investigating the decay of their low-lying first-excited 2+ excited state. The transition characteristics are inferred through the B(E2; 0+g.s.→2+) values, which, in principle, are contingent on the lifetime of the corresponding level, and are the most direct and unambiguous test of the collective nature of the transitions.
There has been a considerable interest focused on the study of enhancement or suppression in collectivity of the excited 21+ state in the stable Sn isotopes. Independent experiments on Coulomb excitation, heavy-ion scattering and 21+ level lifetime measurements report discrepant transition probabilities, with the lifetime estimates indicating significantly reduced collectivity. A re-examination of the same has been carried out in the present work on two of the stable isotopes, 112,120Sn.
Low-lying levels in the 112,120Sn isotopes have been excited by inelastic scattering with heavy-ion beams. Level lifetime measurements have been carried out using the Doppler shift attenuation method, wherein the Doppler affected γ-ray peaks from the decay of the 21+ level in each isotope have been analyzed using updated methodologies, and corresponding B(E2; 0+g.s.→2+) values become indicative of the underlying collectivity. The present results are compared with existing estimates of the B(E2; 0+g.s.→2+) values in the stable Sn isotopes. The results are also found to be in good agreement with generalized seniority model as well as state-of-the-art Monte Carlo shell model (MCSM) calculations.