ar X iv : n uc l - th / 9 80 90 86 v 1 2 9 Se p 19 98 On the Origin of Nuclear Superfluidity

The induced pairing interaction arising from the exchange of collective surface vibrations among nucleons moving in time reversal states close to the Fermi energy is found to lead to values of the pairing gap which are similar to those experimentally observed. It is well established that nucleons moving close to the Fermi energy in time reversal states have the tendency to form Cooper pairs which eventually condense[1],[2]. This phenomenon, which parallels that which is at the basis of low temperature superconductivity [3], modifies in an important way the nuclear properties, in particular the occupation number of single-particle levels around the Fermi energy, the moment of inertia of deformed nuclei, the lifetime of cluster decay and of fission process, the depopulation of superdeformed configurations, the cross section of two-nucleon transfer reactions, etc. (cf. e.g. refs. [2],[4]-[16] and refs. therein). While in the case of superconductivity the attraction among the electrons is generated by the exchange of phonons, in the nuclear case the origin of the pairing interaction is related to the S0 phase shift of the free nucleons, which is attractive at low relative momenta. In keeping with the fact that the free nucleon-nucleon interaction is strongly renormalized in nuclei, Cooper pair for-