The β-decay half-lives of 38 neutron-rich isotopes from 36 Kr to 43 Mo and 116,117 Tc are reported here for the first time. These results when compared to previous standard models indicate an overestimation in the predicted half-lives by a factor of two or more in the A ≈ 110 region. A revised model based on the second generation gross theory of β decay better predicts the measured half-lives and suggests a more rapid flow of the rapid neutron-capture process (r-matter flow) through this region than previously predicted.About half of the elements heavier than Fe are thought to be produced in rapid neutron-capture process (rprocess) nucleosynthesis, a sequence of neutron-capture and β-decay processes. Although the astronomical site and the mechanism of the r-process are not yet fully understood, it is generally agreed that the process must occur in environments with extreme neutron densities. The study of the elemental distribution along the r-process path requires sensitive β-decay related information such as β-decay half-lives, β-delayed neutron-emission probabilities, and nuclear masses. In particular, determination of the timescale that governs matter flow from the r-process "seeds" to the heavy nuclei, as well as the distribution in the r-process peaks, depends sensitively on decay half-lives [1,2].Isotopes with extreme neutron-to-proton ratios in the mass region A = 110 − 125 have attracted special attention since theoretical r-process yields are found to underestimate isotopic abundances observed in the predicted global abundances by an order of magnitude or more [1,3,4]. This discrepancy has been investigated using numerous mass formulae that differ mainly in the strength of the nuclear shell closures [5,6]. The results indicate that considerable improvements in the global abundances of the isotopes can be achieved by assuming a quenching of the N = 82 shell gap. The properties of most of these crucial r-process nuclei are, however, currently unknown due to their extremely low production yields in the laboratory.A number of experimental studies on nuclei around neutron-rich krypton to technetium have been performed to investigate the region of the r-process path near N = 82 [7][8][9]. In the current work, we report on a first systematic study of the β-decay properties of very exotic, neutron-rich 36 Kr to 43 Tc nuclides that contribute to the r-process.Decay spectroscopy of very neutron-rich nuclei around A = 110 was performed at the recently-commissioned RIBF facility at RIKEN. A secondary beam, comprised of a cocktail of neutron-rich nuclei, was produced by inflight fission of a 345-MeV/nucleon 238 U beam in a 550-mg/cm 2 Be target. The primary beam was produced by the RIKEN cyclotron accelerator complex with a typical intensity ∼ 0.3 pnA at the production target posi-

The low-lying states in 106 Zr and 108 Zr have been investigated by means of β-γ and isomer spectroscopy at the RI beam factory, respectively. A new isomer with a half-life of 620 ± 150 ns has been identified in 108 Zr. For the sequence of even-even Zr isotopes, the excitation energies of the first 2 + states reach a minimum at N = 64 and gradually increase as the neutron number increases up to N = 68, suggesting a deformed sub-shell closure at N = 64. The deformed ground state of 108 Zr indicates that a spherical sub-shell gap predicted at N = 70 is not large enough to change the ground state of 108 Zr to the spherical shape. The possibility of a tetrahedral shape isomer in 108 Zr is also discussed.

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