This paper suggests a method for improving the values of transmission
dose build up factors previously calculated for thick double-layer shi
elds. Build up factors obtained in the present study have been compare
d with those calculated by using the Broder formula (Bakes, 1994). The
improved values were determined by applying the Kitazume formula(Kita
zume, 1967) on six different double-layer shields, of various total th
ickness, and for two energies (1.43 and 2.75 MeV) photon penetration.