Neutron physics is one of the oldest brach of the experimental nuclear
physics, but the investigation of the spontaneous neutron emission from the
ground state along the neutron dripline is still at its beginning, in spite of
the crucial importance for nuclear astrophysics. The proton dripline is much
better investigated and a systematics of spontaneous proton half lives is
available in terms of the Coulomb parameter, characterizing the outgoing
irregular Coulomb wave. Our purpose is to propose a similar systematics of
spontaneous neutron half lives, but in terms of the nuclear reduced radius,
characterizing the "neutral" spherical irregular Neumann wave.Comment: 4 pages, 3 figures, 38 reference