# S-factor

The astrophysical **S-factor** *S*(*E*) is a rescaled variant of the total cross section *σ*(*E*) that accounts for the Coulomb repulsion between charged reactants.

## DefinitionEdit

The quantity is defined as^{[1]}

Here, *η* is the dimensionless Sommerfeld parameter,

where

## MotivationEdit

The Coulomb barrier causes the cross section to have a strong exponential dependence on the center-of-mass energy *E*. The S-factor remedies this by factoring out the Coulomb component of the cross section.

## ReferencesEdit

**^**Thompson, Ian J.; Nunes, Filomena M. (2009).*Nuclear Reactions for Astrophysics: Principles, Calculations and Applications of Low-Energy Reactions*. Cambridge University Press. p. 5. ISBN 978-0-521-85635-5.