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

The first fast-timing measurements from nuclides produced via the in-flight fission mechanism are reported. The lifetimes of the first 2(+) states in Zr-104,Zr-106 nuclei have been measured via beta-delayed gamma-ray timing of stopped radioactive isotope beams. An improved precision for the lifetime of the 2(1)(+) state in Zr-104 was obtained, tau(2(1)(+)) = 2.90(-20)(+25) ns, as well as a first measurement of the 2(1)(+) state in Zr-106, tau(2(1)(+)) = 2.60(-15)(+20) ns, with corresponding reduced transition probabilities of B(E2; 2(1)(+) -> 0(g.s.)(+)) = 0.39(2) e(2)b(2) and 0.31(1) e(2)b(2), respectively. Comparisons of the extracted ground-state deformations, beta(2) = 0.39(1) (Zr-104) and beta(2) = 0.36(1) (Zr-106) with model calculations indicate a persistence of prolate deformation. The data show that Zr-104 is the most deformed of the neutron-rich Zr isotopes measured so far. (C) 2015 The Authors. Published by Elsevier B.V.