New lifetime measurement for the 21+ level in Sn 112 by the Doppler-shift attenuation method

Abstract

Levels in the Sn112 nucleus have been excited by inelastic scattering with Cl35 projectile at Elab=195MeV. The Doppler affected ?-ray peak arising from the decay of the 21+ level has been analyzed, using updated methodologies, to extract the level lifetime and corresponding electric quadrupole (E2) transition probability, B(E2;0g.s.+?21+). The present result is discrepant with respect to the results reported from existing lifetime measurements, but in compliance with independent systematic measurements of the low-lying E2 transition strengths in the stable even-mass Sn isotopes, by pure Coulomb excitation as well as heavy-ion induced inelastic collisions. The transition probability also confirms an enhancement in collectivity for the 21+ level, and is found to be in good agreement with generalized seniority model (GSM) as well as state-of-the-art Monte Carlo shell model (MCSM) calculations. Within the realm of the MCSM scheme, the enhancement is understood in terms of oblate deformations for both the 0g.s.+ and 21+ states in Sn112 arising due to strong proton-core excitations and enhanced proton-neutron interactions. In addition, limits for the lifetime of the 31- level and the E1 transition probability, B(E1;31-?21+), have been obtained. ©2021 American Physical Society.