Under-estimation of 210 Pb in industrial radioactive scales

Lead-210 (210Pb) can be present at high activity concentrations, in residues arising from the petroleum, mineral processing and chemical industries. Although 210Pb itself poses a low radiological risk, the nuclide decays via 210Bi to the alpha emitting and highly radiotoxic 210Po. Therefore, rapid, accurate determination of 210Pb is essential for assessing the radiological risk to plant operators and appropriate sentencing of waste. Unfortunately, direct measurement of 210Pb by gamma spectrometry is hindered by its weak gamma-ray emission at 46.5 keV, which is readily attenuated by mineral matrices. This paper demonstrates the extent to which 210Pb can be underestimated during routine analysis by an inter-laboratory exercise involving five accredited laboratories and a wide range of scales from diverse industrial sources. Two methods of addressing errors in 210Pb analysis are highlighted; the first, involving lithium tetraborate fusion prior to gamma spectrometry shows promise but is not suitable for all 210Pb-containing phases. The second method, requiring calculation of matrix attenuation factors for a representative fingerprint sample, was applied successfully to deposits from the steel and gas industries. However, its wider application depends on detailed chemical and mineralogical characterisation for each of the major categories of mineral scale found and at present, there is an acute lack of suitable certified reference materials