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

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