Abstract: An attempt is made to generate effective atomic number, exposure buildup factor (EBF) in the energy region 0.015-15.0 MeV up to a penetration depth of 40 mfp for some soils. The five parameters geometrical progression (G-P) fitting approximation has been used to calculate exposure build-up factor (EBF). The generated exposure buildup factors has been studied as function of incident photon energy & penetration depth and represented graphically.