The nuclear matrix elements of Ge and ' Se are studied by using the shell model wave functions in a model-space approximation.The influences of both nuclear short-range correlation and finite nucleon size on the transition matrix elements are also taken into account. The limits of Majorana neutrino mass and mixing parameter of right-handed current have been deduced by fitting the experimental values of OvPP decay lifetimes of ' Cse and ' Se.PACS number(s): 23.40.8w, 23.40.Hc, 21.60.Cs, 27.50.+e

The nucleon correlation including the short range correlation and the nuclear core polarization has been investigated by using a diagrammatic efFective operator approach. The calculated results show that the contributions of the nucleon correlation to the OvPP decay of" Ge and Se are quite important, especially in the heavy-neutrino case.PACS number(s): 21.60. Cs, 21.30. +y, 23.40.8w, 27.50.+e