Lifetime measurements of the first 2+ states in 104,106Zr: Evolution of ground-state deformations

F. Browne et al.; 5 pags.; 3 figs.; Open Access funded by Creative Commons Atribution Licence 4.0© 2015 The Authors. The first fast-timing measurements from nuclides produced via the in-flight fission mechanism are reported. The lifetimes of the first 2+ states in 104,106Zr nuclei have been measured via β-delayed γ -ray timing of stopped radioactive isotope beams. An improved precision for the lifetime of the 2+1 state in 104Zr was obtained, τ (2+1 ) = 2.90+25−20 ns, as well as a first measurement of the 2+1 state in 106Zr, τ (2+ 1 ) =2.60+20−15 ns, with corresponding reduced transition probabilities of B(E2; 2+1 → 0+g.s.) = 0.39(2) e2b2 and 0.31(1) e2b2, respectively. Comparisons of the extracted ground-state deformations, β2 = 0.39(1) (104Zr) and β2 = 0.36(1) (106Zr) with model calculations indicate a persistence of prolate deformation. The data show that 104Zr is the most deformed of the neutron-rich Zr isotopes measured so far.We would like to express our gratitude to the RIKEN Nishina Center accelerator department for providing a stable and high intensity 238U primary beam. F.B. is grateful to C.R. Nita for invaluable discussions on fast-timing measurements using LaBr3(Ce) detectors. This work was supported by JSPS KAKENHI Grants Nos. 26800117 and 25247045. UK authors were supported by STFC Grant Nos. ST/J000132/1, ST/J000051/1 and ST/K502431/1. P.H.R. acknowledges support from the UK National Measurement Office (NMO). P.-A.S. was financed by JSPS Grant No. 23 01752 and the RIKEN Foreign Postdoctoral Researcher Program. V.W. was supported by DOE Grant No. DE-FG02-91ER-40609. J.T. was financed by Spanish Ministerio de Ciencia e Innovación under Contracts No. FPA2009-13377-C02 and No. FPA2011-29854-C04. We acknowledge the EUROBALL Owners Committee for the loan of germanium detectors and the PreSpec Collaboration for the readout electronics of the cluster detectors.Peer Reviewe