Low-lying excitations in Ni-72

The levels in 129Sn populated from the β− decay of 129In isomers were investigated at the ISOLDE facility of CERN using the newly commissioned ISOLDE Decay Station (IDS). The lowest 1/2+ state and the 3/2+ ground state in 129Sn are expected to have configurations dominated by the neutron s1/2 (l = 0) and d3/2 (l = 2) single-particle states, respectively. Consequently, these states should be connected by a somewhat slowl-forbidden M1 transition. Using fast-timing spectroscopy we havemeasured the half-life of the 1/2+ 315.3-keV state, T1/2 = 19(10) ps, which corresponds to a moderately fast M1 transition. Shell-model calculations using the CD-Bonn effective interaction, with standard effective charges and g factors, predict a 4-ns half-life for this level. We can reconcile the shell-model calculations to the measured T1/2 value by the renormalization of the M1 effective operator for neutron holes.status: publishe

Low-lying excitations in Ni 72

International audienceLow-lying excited states in Ni72 have been investigated in an in-flight fission experiment at the RIBF facility of the RIKEN Nishina Center. The combination of the state-of-the-art BigRIPS and EURICA setups has allowed for a very accurate study of the β decay from Co72 to Ni72, and has provided first experimental information on the decay sequence Fe72→Co72→Ni72 and on the delayed neutron-emission branch Co73→Ni72. Accordingly, we report nearly 60 previously unobserved γ transitions which deexcite 21 new levels in Ni72. Evidence for the location of the so-sought-after (4+2),(6+2), and (8+1) seniority states is provided. As well, the existence of a low-spin β-decaying isomer in odd-odd neutron-rich Co isotopes is confirmed for mass A=72. The new experimental information is compared to simple shell-model calculations including only neutron excitations across the fpg shells. It is shown that, in general, the calculations reproduce well the observed states