Evaluation of beta-decay Part IV. The complex gamma function; practicalities

Two easily-evaluated approximations for the square of the modulus of the complex gamma-function as it appears in F(Z, W), the Fermi function for beta-decay, are presented, one for high and the other for low electron energies. When grafted together at the appropriate electron energy as a function of Z the greatest error increases from less than 10−5% for low Z and reaches 10−2% only at Z ⋍ 90.