241Pu measurement and its contribution to the internal dose of actinides

Among the Plutonium isotopes the alpha emitting ones are the most dangerous when they are incorporated. Plutonium may exist in refracotry and soluble form. In the soluble form Plutonium may be in many valence states but tetravalent Plutonium tends to form complexes very easily and its deposition and toxicology are greatly influenced by the chemical and physical form of incorporation. Plutonium is taken up preferentially by the skeleton when it is in the monomer form, while in a polymeric form is taken up from the liver. Long term exchanges between liver, skeleton and other deposition sites take place. Uptakes through wounds and by inhalation are the most frequent routes of contamination in occupationally exposed workers. The bone and lung tumours are likely to be the most important risks of uptake by these routes. 241Pu being a weak beta emitter has a smaller risk when entering the organism but its chemical behaviour is the same as the other plutonium isotopes, the effective half-life is practically the same as physical decay half-life. By ingestion f1, is 1x10-5 for oxides and hydroxides, and 1x10-4 for other commonly occurring compounds, by inhalation PuO2 is Class Y, all other compounds are Class W(8), this is characteristic for all Pu isotopes. 241Pu produces 241Am which accumulates mostly in the bones and in the liver (2). Having a high concentration among the other Plutonium radionuclides, a half life of 14,4 years and 241Am as daughter, 241Pu should be considered from the health physicists in calculation of the internal dose and the prognosis of incorporated quantities of actinides from occupationally exposed workers. Nvertheless there is a lack of information concerning the limit of detection of 241Pu in bioassay (1). From the values reported from ICRP 30 (7) on Weighted Committed Dose Equivalent WCDE in target organs or tissues per intake of unit activity (Sv/Bq) as well as Derived Air Concentration DAC (Bq/m³), one can come into conclusion that the values reported for 241Pu are about two order of magnitude less than those of other Pu isotopes like 238Pu, 239Pu for WCDE and about two orders of magnitude higher for DAC. This of course may be the reason why radiation protection people concentrate more in the other Plutonium isotopes. Nearly no publication on the excretion analysis results of actinides report the values of 241Pu.