Half-life measurements in Dy-164,Dy-166 using γ−γ fast-timing spectroscopy with the ν-Ball spectrometer

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We report on the measurement of lifetimes of excited states in the near-mid-shell nuclei Dy-164,Dy-166 using the gamma-ray coincidence fast-timing method. The nuclei of interest were populated using reactions between an O-18 beam and a gold-backed isotopically enriched Dy-164 target of thickness 6.3 mg/cm(2) at primary beam energies of 71, 76, and 80 MeV from the IPN-Orsay laboratory, France. Excited states were populated in Dy-164, Dy-166, and W-178,W-179 following Coulomb excitation, inelastic nuclear scattering, two-neutron transfer, and fusion-evaporation reaction channels respectively. Gamma rays from excited states were measured using the nu-Ball high-purity germanium (HPGe)-LaBr3 hybrid gamma-ray spectrometer with the excited state lifetimes extracted using the fast-timing coincidence method using HPGe-gated LaBr3-LaBr3 triple coincident events. The lifetime of the first I-pi = 2(+) excited state in Dy-166 was used to determine the transition quadrupole deformation of this neutron-rich nucleus for the first time. The experimental methodology was validated by showing consistency with previously determined excited state lifetimes in Dy-164. The half-lives of the yrast 2(+) states in Dy-164 and Dy-166 were 2.35(6) and 2.3(2) ns, respectively, corresponding to transition quadrupole moment values of Q(0) = 7.58(9) and 7.5(4) eb, respectively. The lifetime of the yrast 2(+) state in Dy-166 is consistent with a quenching of nuclear quadrupole deformation at beta approximate to 0.35 as the N = 104 mid-shell is approached.
©2020 American Physical Society. Artículo firmado por 35 autores. The authors would like to thank the operators of the ALTO facility for providing the reliable beams used during the experiment. Additionally we thank the FASTER collaboration for the technical support given. GAMMA-POOL and LOAN-POOL are acknowledged for loaning the Clover and Phase I HPGe detectors. The FATIMA Collaboration is acknowledged for loaning the LaB<INF>3</INF> detectors. This work was supported by the STFC UK Nuclear Data Network, the STFC (Grants No. ST/L005743/1 and No. ST/P005314), the Marion Red-fearn Trust, BMBF (NUSTAR.DA Grant No. 05P15RDFN1), and Spanish MINECO Grant No. FPA2015-65035-P. The research leading to these results has received funding from the European Union's HORIZON2020 Program under Grant Agreement No. 654002. P.H.R., S.M.C., G.L., and R.S. acknowledge support from the UK Department of Business, Energy and Industrial Strategy (BEIS) via the National Measurement System and from the STFC consolidated grant.
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