Lifetimes and collectivity of low-lying states in115Sn

Abstract

The lifetimes of excited states in ${}^{115}\mathrm{Sn}$ have been measured using the Doppler shift attenuation method in the reaction ${}^{113}\mathrm{Cd}(\ensuremath{\alpha},2n\ensuremath{\gamma})$ at ${E}_{\ensuremath{\alpha}}=27.2 \mathrm{MeV}$. Lifetimes were obtained for 18 states and lifetime limits for 6 states with ${E}_{x}<~4 \mathrm{MeV}$ and $J<~23/2$. The experimentally obtained $B(\ensuremath{\sigma}L)$ values for transitions deexciting positive-parity states are compared with calculations in the framework of the Bardeen-Cooper-Schrieffer quasiparticle model and the interacting boson fermion model, whereas the values for transitions between negative-parity states are discussed qualitatively within a core-particle coupling picture. The value of $B(E2)=3.5(11)$ Weisskopf units (W.u.) for the transition linking the ${19/2}^{\ensuremath{-}}$ state of the intruder $\ensuremath{\nu}{h}_{11/2}\ensuremath{\pi}2p2h$ band to the ${15/2}^{\ensuremath{-}}$ state of the $\ensuremath{\nu}{h}_{11/2}\ensuremath{\bigotimes}{2}_{1}^{+}$ multiplet strongly supports the configuration $\ensuremath{\nu}{h}_{11/2}\ensuremath{\pi}{(g}_{9/2}^{\ensuremath{-}2}{g}_{7/2}^{2})$ ascribed to this band.