Screening of primordial and artificial radionuclides in German steel by low-level gamma-ray spectrometry in an underground laboratory

Main sources of radionuclides in steel in nuclear decommissioning are the unintentional melting of orphan sources and scrap. This paper presents data about the activity of gamma-emitters in German steels obtained by low-level gamma-ray spectrometry in an underground laboratory. The Co-60 activity exceeds only 2% of the 215 analyzed samples with a detection limit of 4.4(.)10(-5) Bq(.)g(-1). Even the maximum measured Co-60 activity of 2.5(.)10(-4) Bq(.)g(-1) is a factor of 400 lower than the clearance level. The determination of the detector efficiency is also described for these unusual samples using Monte Carlo calculations.