Define
K(T)=nB1(h22πmekBT)3/2=8ηζ(3)2π(kBTmec2)3/2. Using
ne=nBF,
nj+=Xj+nj, and
nj0=(1−Xj+)nj, the two Saha relations become the closed system
F1−XH+XH+=K(T)e−IH/(kBT),
F1−XHe+XHe+=2K(T)e−IHe/(kBT),
where
F=(1−Yp)XH++4YpXHe+.
These are two equations for the two ionization fractions.
Solved by gpt-5.6-sol high.