The (3He,t) reaction on 76Ge, and the double-β-decay matrix element

A Ge-76(He-3,t)As-76 charge-exchange experiment at an incident energy of 420 MeV has been performed with an energy resolution of 30 keV. The Gamow-Teller GT(-) strength distribution in As-76, which is the intermediate nucleus in the double-beta (beta beta) decay of Ge-76, has been extracted. An unusually strong fragmentation of the GT(-) strength is observed even at low excitation energies of E-x <= 5 MeV. By combining the data with those for GT(+) transitions from a recent Se-76(d,He-2)As-76 measurement, the nuclear matrix element for the Ge-76 2 nu beta beta decay has been evaluated. A lack of correlation among the GT transition strengths feeding the same levels from the two different directions is observed. The impact on the Ge-76 2 nu beta beta decay nuclear matrix element is discussed.