  The quality of HFB wave functions are tested by comparing the theoretically
calculated results with the available experimental data for a number of
spectroscopic properties like yrast spectra, reduced B(E2) transition
probabilities, quadrupole moments and g-factors for the nuclei involved in
2$\nu $ $\beta \beta $ decay. It is observed that the np interactions
vis-\`{a}-vis the deformations of the intrinsic ground states of medium mass
nuclei play a crucial role in the fine tuning of the nuclear matrix elements,
M$_{2\nu}.$
