Electron screening effects in nuclear reactions: still an unsolved problem

Electron screening for nuclear reactions in metals plays an unexpected and important role in enhancing reaction cross sections in the ultra-low energy region. Even though there are still some discrepancies between experimental data from different authors, the enhanced screening effect in metallic environments is well established, and attributed to the quasi-free valence electrons in the metals. However, there is still no solid theory which can describe quantitatively the observed enhancements. In the present work, experimental and theoretical results obtained so far will be overviewed, and a proposal to improve our knowledge on this subject.