Collective 2p-2h intruder states in ${}^{118}$Sn studied via ${\hat{I}}^2$-decay of ${}^{118}$In using GRIFFIN

Abstract

The low-lying structure of semi-magic ${}^{118}$Sn has been investigated through the ${\hat{I}}^2$-decay of ${}^{118}$In ($T_{1/2}=4.45$ min) to study shape coexistence via the reduced transition probabilities of states in the 2p-2h proton intruder band. This high-statistics study was carried out at TRIUMF-ISAC with the GRIFFIN spectrometer. In total, 99 transitions have been placed in the level scheme with 43 being newly observed. Three low-lying ${\hat{I}}^3$-ray transitions with energies near 285 keV have been resolved from which the 2${}_{intr.}^{+}\to 0_{intr.}^{+}$ 284.52-keV transition was determined to have half of the previous branching fraction leading to a $B(E2;2_2^{+}\to 0_2^{+})$ of 21(4) W.u. compared to 39(7) W.u. from the previous measurement. Calculations using $sd$ IBM-2 with mixing have also been made to compare the experimental $B(E2)$ values to the theoretical values and to make comparisons to the ${}^{114,116}$Sn isotopes previously studied using the same theoretical model.