Calibration of HPGe detectors using certified reference materials of natural origin

The feasibility of using certified reference materials for the full energy efficiency calibration of p-type coaxial high-purity germanium detectors for the determination of radioactivity in environmental samples is discussed. The main sources of uncertainty are studied and the contributions to the total uncertainty budget for the most intense gamma lines are presented. The correction factors due to self-absorption and true coincidence summing effects are discussed in detail. The calibration procedure is validated for natural and artificial radionuclide determination in different matrices through an internal cross-validation and through the participation in a world-wide open proficiency test.