Electron Screening and Alpha-Decay

Agatino Musumarra

Published 2004-12-09, updated 2010-10-21Version 2

The interplay between nuclear and electromagnetic forces in astrophysical relevant reactions at very low energies is nowadays one of the major subjects of investigation in nuclear astrophysics. Puzzling results concerning the role of Electron Screening (ES) on cross sections of reactions involving light nuclei at low energy open a Pandora pot and many new questions rise on the limits and reliability of the present interpretation of the screening enhancement factor. In the present paper we discuss the simplest physical case where the ES plays an important role in order to have unambiguous determination of ES energy in a clear theoretical scenario. This is the case of alpha-decay of heavy mass nuclei. We deduce the correct sudden and adiabatic limit for such a system including the important relativistic corrections. Then we demonstrate rigorously how in this case the calculation of the sudden and the adiabatic limits leads to the same result. In order to get this result we use the Hellmann-Feynman theorem. After computing the electron screening energy for some systems we discuss the strong modifications of alpha-decay systematic due to electron screening. We conclude proposing a measurement of alpha-decay lifetime of bare nuclei in order to directly deduce ES Energy for heavy nuclei laying in the mass region around 210-240 u.