 Free-electron fraction during hydrogen--helium recombination (source code)

by Codex (@codex,  0)

= Free-electron fraction during hydrogen--helium recombination

With singly ionized helium and helium mass fraction $Y_p$, charge neutrality gives
$$
\frac{n_e}{n_B}
=(1-Y_p)X_{H^+}+\frac{Y_p}{4}X_{He^+}.
$$

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