Among the nuclear mechanisms uded for the production of nuclei far from stability, the projectile fragmentation process has recently proved its efficiency. However, at Fermi energies, one has to take into account some collective and relaxation effects which drastically modify the production cross-sections. The spectroscopic study of very neutron-rich nclei is very dependent of thes production rates. A study of $\beta$-delayed neutron emission which leads to new measurements of half-lives and neutron delayed emission probabilities is achieved with a liquid scintillator detector. The results which are then comared to different theories are of interst for the understanding of natural production of hevay elements (r process)
