Neutron Halo Nuclei
In light nuclei close to the neutron drip-line a spatially extended neutron distribution, the neutron, halo occurs. This is due to the relatively small binding energy of the last neutrons which makes possible quantum mechanical tunnelling of the last neutron(s) far away from the nuclear core. There are two main paths in the experimental study of the structure of these nuclei: reactions with radioactive nuclear beams and beta-decays.
In reaction studies the momentum distributions from the fragments of reactions between halo nuclei and targets are studied. Results from measurements of (mainly) neutrons from the break-up of the two-neutron halo nucleus 11Li and 11Be with a single neutron halo are presented here. For 11Li data from reactions at 29 MeV/B on three different targets Be, Ni and Au are shown. All the angular distributions of the neutrons are narrow. In reactions of 41 MeV/B 11Be it is clearly seen that different reaction mechanisms are present for different charge of the target. For low Z targets nuclear dissociation reactions dominate yielding board neutron distributions. For targets with high proton number the main contributions is Coulomb dissociation, giving narrow angular distributions.
A systematic trend in the .beta.-decay of drip-line nuclei is very large beta-feeding to highly excited states in the daughter nuclei. When states above the separation energy of one or several nucleons are fed, beta-delayed particle emission will occur. Energy spectra of .beta.-delayed particles are analysed to yield information about nuclear structure. In this work is presented experimental data about beta-delayed charged particles, emitted in the decays of 6,8He and 11Li. In the decay of 6He .beta.-delayed deuteron emission was identified for the first time. For 8He and 11Li new data concerning the triton branching ratios are presented. It is also shown that there could be a branch of. beta.-delayed deuterons present in the decay of 11Li , which might be interpreted as the peripheral beta-decay of the two neutron halo.