Sargent rule
= Sargent rule
{c}
{title2=$\Gamma\propto Q^5$}
The approximate fifth-power scaling of an allowed <beta decay> rate with available <energy> when <electron> <mass> and Coulomb distortion are negligible and the nuclear <matrix element> is held fixed. It follows from $\int_0^Qp^2(Q-p)^2dp=Q^5/30$. Different nuclear <matrix elements> or nonrelativistic <electron> kinematics spoil an exact universal law.