Residual activity of Tc-generators

Owing to contamination by long-lived radio-isotopes, the residual activity of an old 99Mo-99mTc generator may be large enough to prevent its disposal. The long-lived impurities of one generator were determined by energy spectrum and half-life measurements. In this generator 46Sc, 51Cr, 60 Co, 92mNb, 95Nb and 124Sb nuclides were found. Only the half-life of 60Co exceeds 3 months, thus a moderately long storage of the generator reduces the activity, and its disposal is then safe.