Evidence of a new state in 11^{11}Be observed in the 11^{11}Li β\beta-decay

Coincidences between charged particles emitted in the $\beta$-decay of $^{11}$Li were observed using highly segmented detectors. The breakup channels involving three particles were studied in full kinematics allowing for the reconstruction of the excitation energy of the $^{11}$Be states participating in the decay. In particular, the contribution of a previously unobserved state at 16.3 MeV in $^{11}$Be has been identified selecting the $\alpha$ + $^7$He$\to\alpha$ + $^6$He+n channel. The angular correlations between the $\alpha$ particle and the center of mass of the $^6$He+n system favors spin and parity assignment of 3/2$^-$ for this state as well as for the previously known state at 18 MeV.Comment: 13 pages, 6 figure

Study of beta-delayed 3-body and 5-body breakup channels observed in the decay of ^11Li

The beta-delayed charged particle emission from ^11Li has been studied with emphasis on the three-body n+alpha+^6He and five-body 2alpha+3n channels from the 10.59 and 18.15 MeV states in ^11Be. Monte Carlo simulations using an R-matrix formalism lead to the conclusion that the ^AHe resonance states play a significant role in the break-up of these states. The results exclude an earlier assumption of a phase-space description of the break-up process of the 18.15 MeV state. Evidence for extra sequential decay paths is found for both states.Comment: 16 pages, 9 figures. Submitted to Nuclear Physics

Levels in 106Ru and 108Ru

The decay schemes of 36 s 106Tc and 5 s 108Tc have been studied with γ-ray singles and γ-γ coincidence measurements. To separate the technetium nuclides from the fission products of 239Pu, an on-line chemical separation procedure has been developed which is based on multistep chemical separations of liquid phases by fast-rotating centrifuges (“SISAK”). The resulting level schemes of 106Ru and 108Ru, together with those of 102Ru and 104Ru, are interpreted in terms of the generalized collective model of Gneuss and Greiner. The potential-energy surfaces calculated from the spectroscopic data show a trend towards triaxial shapes for the very neutron-rich Ru nuclei