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. Data about the activity of γ-emitters in German steels obtained by low-level γ-ray spectrometry in an underground laboratory are presented. The 60Co activity exceeds only 2% of the 215 analyzed samples with a detection limit of 4.4 x 10-5 Bq x g-1. Even the maximum measured 60Co activity of 2.5 x 10-4 Bq x 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. (author)