engleski

Properties, behavior and potential health effects of 14C

Radiocarbon (14C) is the radioactive isotope of carbon, which is of both cosmogenic and anthropogenic origin. After formation 14C is lmost immediately oxidized to CO2 and together with stable carbon isotopes (12C, 13C) takes part in the biological carbon cycle and enters the food chain. Because of constant production and simultaneous radioactive decay with the half-life of 5730 years, a uniform and equilibrium distribution of 14C in the atmosphere and biosphere is attained. Radiocarbon content in various materials is usually expressed as the specific activity A14C (units Bq kg-1 of carbon) or the relative specific activity a14C (in percent Modern Carbon, pMC). Thus, the A14C value of 226 Bq(kgC)-1) (a14C = 100 pMC) is attributed to the natural level of radiocarbon activity in the non-disturbed atmosphere. Anthropogenic 14C production in atmospheric nuclear and thermonuclear bomb tests doubled the carbon inventory in the atmosphere in the mid-20th century, and the global 14C level is now approaching the pre-bomb values. Radiocarbon production in various nuclear facilities (mostly in nuclear power plants and fuel reprocessing plants) may influence the local or regional environment and increase the effective dose to the local inhabitants. Radiocarbon has been used in various application, the most well-known is radiocarbon dating. The 14C dating method is based on the fact that 14C is not replenished after the death of an organism (plant, animal, human), while the radioactive decay continues. The method enables determination of the time elapsed since the death, and the basic principles are described. Two basic measurement techniques are described: radiometric measurement by liquid scintillation counting requires relatively large samples of 1 – 5 g of carbon, while accelerator mass spectrometry (AMS) requires only milligrams of carbon or even micrograms. Effective annual dose due to ingestion is equal to 10 – 12 microSv y-1, depending on the annual carbon intake and the A14C values of the foodstuff and does not depend on the detailed knowledge of the diet. The contribution to the effective dose due to ingestion in the vicinity of nuclear facilities has to be compared with the dose at the clean air sites, away from the influence of those facilities. The effective dose due to inhalation of 14C is several orders of magnitude lower and is therefore negligible in the total dose budget. Programs of monitoring 14C have been carried out in the environment of various nuclear facilities. The main conclusions of some of these programs are presented here, with the emphasis on the 14C monitoring around the Nuclear Power Plant Krško (NEK) in Slovenia. The increase of the effective ingestion dose due to the 14C emissions by the nuclear power plant is within the statistical fluctuation of the natural dose and therefore negligible.

14C ; radiocarbon ; cosmogenic production ; anthropogenic production ; radiocarbon dating ; effective dose ; ingestion ; monitoring around nuclear facilities

nije evidentirano