Enhancement of the electron screening effect for d+d fusion reactions in metallic environments

To study the electron screening of nuclear reactions in metallic environmen ts, angular distributions and thick target yields of the fusion reactions H -2(d,p)H-3 and H-2(d,n)He-3 hav been measured on deuterons implanted in thr ee different metal targets ( Al, Zr and Ta) for beam energies ranging from 5 to 60 keV. The experimentally determined values of the screening energy a re about one order of magnitude larger than the value achieved in a gas tar get experiment and significantly larger than the theoretical predictions. A clear target material dependence of the screening energy has been establis hed.