| Sumario: | We consider the development of Cooper pairs in a self-consistent Hartree-Fock mean field for the even Sm isotopes. Results are presented at the level of a BCS treatment, a number-projected BCS treatment and an exact treatment using the Richardson ansatz. For a fixed value of the pairing strength, projected BCS captures much of the pairing correlation energy that is absent from BCS, but still misses a sizable component, typically of order 1 MeV. Furthermore, because it does not average over the properties of the fermion pairs, the exact Richardson solution permits a more meaningful definition of the Cooper wave function and of the fraction of pairs that are collective. © 2007 The American Physical Society.
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