A new picosecond lifetime measurement system developed at UNISOR was used to determine the half-life of the well-deformed [Formula: see text] levels in 188Hg and 186Hg. The half-life values were measured to be 204±45 ps in 188Hg and ≤52 ps in 186Hg. The corresponding values of ρ2(E0)×103, obtained from the partial half-lives, were [Formula: see text] and ≥32, respectively. Additionally, the half-lives of the [Formula: see text] levels were determined to be 141±31 ps in 188Hg and 48±27 ps in 186Hg.
The levels in Kr have been studied in the decay of mass separated 7 Rb. Strong beta population was observed to states above 2 MeV. Numbers of new levels were observed to be populated in this decay including several which populate the 02+ level. These levels help establish the near-spherical nature of the 02+ state.In studies of the levels of Kr via in-beam y-ray spectroscopy, we found evidence for a low energy 02+ excited state. ' Earlier, in 7~Se (Ref. 2) and 74Se (Ref. 3), we had found evidence for such low energy excited 02+ states and these were shown to have much larger deformation than the near-spherical ground states in these nuclei. It was natural to suspect that similar shape coexistence was occurring in Kr. To help establish the nature of the 02+ level in Kr, on-line studies of the radioactive decay of mass separated Rb were carried out at the UNISOR facility at the Holifield Heavy Ion Research Facility. The results of these Rb decay measurements confirmed our discovery of the low energy 02+ state and placed two levels feeding it and placed numbers of other new transitions and levels in Kr. A preliminary report of this work appeared much earlier4 with the decay scheme presented in conference proceedings. 5 Our Rb decay results were noted in Refs. 6 and 7 as providing important evidence in our discovery of large ground state deformation (P -0.35) in '4'6Kr. Details of our in-beam work in Refs. 6 and 7 have been reported. s Here we report the level scheme of 7 Kr observed in our 6Rb decay work. %hen our decay scheme of Rb to Kr was first reported, 4 5 only 2+ 424 keV, 4+ 1034 keV, and 6+ 1858 keV levels had been suggested to be populated in the 6Rb decay. Since no y-y coincidence work was done, feedings to the 2+, 4+, and 6+ levels in this decay were based9 only on the observation of gamma rays with energies similar to those from these three levels, which had been seen in earlier in-beam work. However, as our y-y work showed, the 822 keV y ray in the Rb decay is not the 6+~4+ transition seen in beam. Thus, only the 2+ and 4+ levels were established in the Rb decay at the time of our work. Also most, but not all, of the beta feeding we now observe goes to high lying levels above 2 MeV. Our strong beta feedings to the levels above 2 MeV led another UNISOR group doing mass measurements to independently investigate the beta decay intensities. 'The '6Rb was produced in the reaction N"Ni( 0Ne, xn) at 112 Me V and mass separated at the UNISOR facility. Separated sources of Rb were collected on a movable tape and transported to a position between two Ge(Li) detectors.Gamma-gamma coincidences were recorded with the two Ge(Li) detectors for time periods the order of two half lives of Rb, while a new source was being prepared at the collection point of the tape transport unit. The energies of transitions assigned to the Rb decay based on half life, coincidence data, and in a few cases energy fits to the decay scheme in Fig. 1, are given in Table I. Coincidence gates were analyzed on the transitions seen in the in-b...
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