  The investigation of the d+d fusion reactions in metallic environments at
sub-Coulomb energies demands especially adapted techniques beyond standard
procedures in nuclear physics. The measurements which were performed with an
electrostatic accelerator at different self-implanted metallic target materials
show an enhancement of the reaction cross-section compared to the gas target
experiments. The resulting electron screening energy values are about one order
of magnitude larger relative to the gas target experiments and exceed
significantly the theoretical predictions. The measurements on deuterium inside
metals are heavily affected by the interference of two peculiarities of this
system: the possibly very high mobility of deuterium in solids and the
formation of surface contamination layers under ion beam irradiation in high
vacuum systems. Thorough investigations of these processes show their crucial
influence on the interpretation of the experimental raw data. The differential
data acquisition and analysis method employed to it is outlined. Non observance
of these problems by using standard procedures results in fatal errors for the
extraction of the screening energies.
