  A simple formula for computing the generalized Hubbell radiation rectangular
source integral $$H[{a,b,p,\lambda \atop \alpha,\beta,\gamma}]=\frac{\sigma
a}{4\pi}\int_0^b
x^\lambda(x^2+p)^{-\alpha}{}_2F_1(\alpha,\beta;\gamma;-{a^2\over x^2+p})dx, $$
is introduced. Tables are given to compare the numerical values derived from
our approximation formula with those given earlier in the literature.
