Speaker
Description
The semi-magic $^{120}_{50}$Sn$_{70}$ lies in the neutron mid-shell among the other stable Sn isotopes, where shape coexistence was observed with the signature of deformed bands built on excited $0^+$ states intruding into the yrast band that is built on the spherical ground state. However, the lifetime of the excited $0^+_3$ state only has a lower limit of 6 ps in the literature, which prevents the study of transition strengths, and as a result, its structure is obscured.
The $0^+_3$ lifetime was measured in the first thermal neutron capture experiment, $^{119}$Sn(n,$\gamma^\text{many}$)$^{120}$Sn, at the Institut Laue-Langevin, where the world's highest-flux thermal neutron beam was delivered at $10^8$ n/cm$^2$/s at the target position on an isotopically enriched $^{119}$Sn target. Low-spin states in $^{120}$Sn were populated up to the neutron separation energy $S_n=9.1$ MeV, and the decaying gamma-ray cascades were detected with the Fission Product Prompt Gamma-ray Spectrometer (FIPPS) comprised of eight Compton-suppressed HPGe clovers coupled to an array of 15 LaBr$_3$ scintillation detectors. The LaBr$_3$ scintillators, which were used for gamma-ray detection and lifetime measurement using the Generalized Centroid Difference (GCD) method, have fast timing responses and are ideal for extracting lifetimes between 10 and a few hundred ps.
In total, there are $4\times10^9$ counts in the $\gamma\gamma\gamma$ cube where two LaBr$_3$ events were in coincidence with one HPGe.
Lifetime measurement for the $0^+_3$ state in $^{120}$Sn using the GCD technique will be presented with nuclear structure interpretations from realistic shell-model calculations. Additional lifetimes will also be measured where the $\gamma\gamma\gamma$ cascade's statistics permit. Analysis is also underway for a similar neutron-capture experiment populating low-spin excited states in $^{118}$Sn.
