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 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+1state in 104Zr was obtained, τ(2+1) =2.90+25−20ns, as well as a first measurement of the 2+1state in 106Zr, τ(2+1) =2.60+20−15ns, with corresponding reduced transition probabilities of B(E2; 2+1→0+g.s.) =0.39(2)e2b2and 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.