  Accurate measurements of nuclear reactions of astrophysical interest within,
or close to, the Gamow peak, show evidence of an unexpected effect attributed
to the presence of atomic electrons in the target. The experiments need to
include an effective "screening" potential to explain the enhancement of the
cross sections at the lowest measurable energies. Despite various theoretical
studies conducted over the past 20 years and numerous experimental
measurements, a theory has not yet been found that can explain the cause of the
exceedingly high values of the screening potential needed to explain the data.
In this letter we show that instead of an atomic physics solution of the
"electron screening puzzle", the reason for the large screening potential
values is in fact due to clusterization effects in nuclear reactions, in
particular for reaction involving light nuclei.
