  The possibility of observing neutrinoless double beta decay offers the
opportunity of determining the effective neutrino mass if the nuclear matrix
element were known. Theoretical calculations are uncertain and the occupations
of valence orbits by nucleons active in the decay are likely to be important.
The occupation of valence proton orbits in the ground states of 76Ge, a
candidate for such decay, and 76Se, the corresponding daughter nucleus, were
determined by precisely measuring cross sections for proton-removing transfer
reactions. As in previous work on neutron occupations, we find that the Fermi
surface for protons is much more diffuse than previously thought, and the
occupancies of at least three orbits change significantly between the two 0+
ground states.
