Exposure to radioactive aerosols in mining and milling operations: the importance of 227Ac and 231Pa

'Full-Text:' 227Ac (half-life of 21.8 y) is the daughter or 231Pa; a beta emitter and parent of a subseries with five short-lived alpha-emitters. 231Pa (half-life of 3.27x104 y) is an alpha-emitter of the actinium series, the decay chain of 235U. As daughters of this uranium isotope they are thought to be unimportant as a radiological hazard, despite the fact that their ALI values for ingestion and inhalation are the lowest of any other radionuclide. Both nuclides can be considered as being in secular equilibrium with uranium in most geological media and so the mass concentration of 231Pa is the same of the 226Ra and that of 227Ac is the same of the 210Pa, to mention only two radionuclides of radiological concern. It is shown in this paper that if 231Pa and 227Ac are considered in the evaluations of dose commitments incurred by inhalation of aerosols in mining and milling operations, the results can be 70% higher than those calculated by the methodology of ICRP Publication 47. (author)