Transport calculations have been performed using the one-dimensional gamma-ray transport code ASFIT for materials of high atomic number (Z), such as tin, tungsten, lead, and uranium, for incident energies in the range of 0.030 to 0.5 MeV, where the fluorescent X rays are important. The relative impact of different components of K X rays on the spectra and buildup factors at various depths in the medium has been assessed for a typical case. Approximate analytic results are derived and compared with the computed X-ray contributions. Point isotropic air and medium response buildup factors computed for these materials have been given, filling the gap in the existing standard tables. Since the buildup factors are not amenable for conventional interpolation in this region, the values are given at close intervals of incident photon energy.