Industrial activities involving radium sources, such as watchmaking, were still common up until the 1960s. They produced contaminations in building materials and the soil in a large variety of geometries. The potential remediation of such places requires instruments that are properly calibrated as well as adequate procedures. We have developed a model that estimates the rate of ambient dose equivalent H˙ ^∗ (10) at 10 cm and 1 m from a source of ²²⁶ Ra and its progeny in both the soil or the building materials. Our model, described here, uses Monte Carlo (GEANT4) computed yield functions of H˙ ^∗ (10) per unit activity induced by point-like sources in different contaminated materials. Fit functions of the yield curve of H˙ ^∗ (10) are provided for outdoor contamination. The model can be used for any geometrical activity distribution and we present an example showing the dependency of H˙ ^∗ (10) on the diameter and the depth profile of the sources, for both outdoor and indoor contamination.