  A self-consistent formalism for the double beta decay of Fermi type is
provided. The particle-particle channel of the two-body interaction is
considered first in the mean field equations and then in the QRPA. The
resulting approach is called the QRPA with a self-consistent mean field
(QRPASMF). The mode provided by QRPASMF, does not collapse for any strength of
the particle-particle interaction. The transition amplitude for double beta
decay is almost insensitive to the variation of the particle-particle
interaction. Comparing it with the result of the standard pnQRPA, it is smaller
by a factor 6. The prediction for transition amplitude agrees quite well with
the exact result. The present approach is the only one which produces a strong
decrease of the amplitude and at the same time does not alter the stability of
the ground state.
