Electron fraction constraints based on nuclear statistical equilibrium with beta equilibrium by A. Arcones and others (2010, 10.1051/0004-6361/201014276)

Astronomy & Astrophysics 522, A25. Section 2 defines electron mole number using net electron density, then gives charge neutrality and baryon-number conservation in equations 7–8. arXiv:1002.3854 is also available.