The problem of pairing in the ~1S_0 channel of finite nuclei is revisited. In nuclear matter forces ofseparable form can be adjusted to the bare nuclear force, to any phenomenological pairing interactionsuch as the Gogny force or to exact solutions of the gap equation. In finite nuclei, because of translationalinvariance, such forces are no longer separable. Using well-known techniques of Talmi and Moshinskywe expand the matrix elements in a series of separable terms, which converges quickly preservingtranslational invariance and finite range. In this way the complicated problem of a cut-off at largemomenta or energies inherent in other separable or zero range pairing forces is avoided. Applicationsin the framework of the relativistic Hartree-Bogoliubov approach show that the pairing properties aredepicted on almost the same footing as by the original pairing interaction not only in nuclear matter,but also in finite nuclei. This simple separable force can be easily applied for the investigation of pairingproperties in nuclei far from stability as well as for further investigations going beyond mean field theory.
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