= Electron fraction in stellar matter
{title2=$Y_e=\sum_i X_i Z_i/A_i$}
For electrically neutral fully ionized matter, $Y_e$ is the number of electrons, or total <protons>, per baryon. With isotope <mass> fractions $X_i$, charge numbers $Z_i$ and <mass> numbers $A_i$, the displayed sum neglects small nuclear mass-defect corrections. Strong and electromagnetic reactions preserve it, while <electron capture> and <beta-plus decay> reduce it. The proton-to-neutron number ratio is $Y_e/(1-Y_e)$.
Back to article page
