Semi-empirical relationship for photon buildup factor in soft tissue and water

Buildup factor of gamma and X-ray photons in the energy range of 0.2-2 MeV in water and soft tissue is computed using Monte Carlo code MCNP4C. The results are compared with the buildup factor data of pure water. A new relationship estimating buildup factor as a function of penetration depth, Compton scattering and energy absorption cross sections is introduced. The new relationship estimates buildup factor with 5 % deviation compared with the existing data.