GENERAL-PROPERTIES OF HALOS

General scaling rules for size versus energy are established for syste ms of one and two neutrons weakly bound to a heavier core. The mean sq uare radius of the two-neutron halo in s-states diverges only logarith mically at small binding energy and is therefore asymptotically smalle r than the corresponding one-neutron halo. They are of comparable size at about 200 keV for light nuclei. The limiting binding energy below which halos appear is estimated to be 2 MeV/A2/3.