Abstract. Gamma-ray detectors are used for radioactive sources calibration and testing in ionizing radiation metrology laboratories, as more than 90% of radionuclides are gamma-ray emitters. When measuring the activity of radioactive sources with complex geometries and matrices for which standard reference sources are unavailable, an accurate understanding of efficiency transfer factors is required. This is the case in testing laboratories where cotton wipes/smears are widely used to assess non-fixed radioactive surface contamination. The efficiency transfer factors were determined by simulating the full-energy peak efficiency using Monte Carlo codes such as FLUKA, MCNP, and GESPECOR.

Key words: Gamma-ray detector, metrology, Monte Carlo, MCNP, FLUKA, GESPECOR.