Remarks on halo nuclei

On the ground of a relationship between the rms radius and the separation energy, we compare halo nuclei to diffuse diatomics. It underlines the essential difference between these two kinds of weakly bound systems: whereas the two-body approximation seems well justified in the case of diatomics, it becomes questionable in the nuclear case when the separation energy approaches zero. Because of this particular situation, we conjecture that the Efimov states have less chances to be observed in nuclear than in molecular cases. Discussing possibilities of measuring accurately the rms radius of halo wave function, we propose a strategy based on the parallel momentum distribution measured in dissociation experiments, together with the use of an Abel transform