The semi-magic Sn lies in the neutron mid-shell among the other stable Sn isotopes, where shape coexistence was observed with the signature of deformed 2p-2h bands built on excited states intruding into the yrast band that is built on the spherical ground state. However, the lifetime of the excited 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 lifetime was measured in the first thermal neutron capture experiment, Sn(n,)Sn, at the Institut Laue-Langevin, where the world's highest-flux thermal neutron beam was delivered at n/cm/s at the target position on an isotopically enriched Sn target. Low-spin states in Sn were populated up to the neutron separation energy 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(Ce) scintillation detectors. The LaBr(Ce) 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 counts in the cube where two LaBr(Ce) events were in coincidence with one HPGe following 14 days of beam on target.
Lifetime measurement for the state in Sn using the GCD technique will be presented. Additional lifetimes will also be measured where the cascade's statistics permit, and detailed gamma-ray spectroscopy will be performed using the FIPPS data to significantly extend the Sn level scheme.