Extremely fast β-decay in neutron-rich nuclei

The decay properties of the light nucleus 9Li have been studied through its emission of beta-delayed neutrons and alpha particles. The activity was produced at the ISOLDE facility at CERN in fragmentation reactions induced by 600 MeV proton beams from the Synchro-cyclotron. After mass separation, neutron spectra were recorded using 3He-filled proportional counters, while surface barrier detectors were used for the spectroscopy of alpha particles. Effects on spectral shapes induced by recoil and polarization phenomena as well as by the large widths of the intermediate states are discussed. The beta decay rates are strongly affected by the broad levels populated in the decay. A strong beta branch to a state in 9Be at an excitation energy of 11.81 MeV is found to have a logft-value of 2.84. This is a value of the same magnitude as that for super-allowed beta decay. This situation is not unique and is encountered in the decays of several light nuclides close to the neutron drip-line. (author) 13 refs.; 4 figs.; 2 tabs