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Figure A.10. Mean dose value for natural background radiation.

Figure A.10. Mean dose value for natural background radiation.

mechanism is beta. The annual dose from K40 is estimated to be 0.165 mSv. Some isotopes (the most significant being Pb210 and Po210) can be ingested through food and water. The typical range of the annual effective dose is 0.2-0.8 mSv, but higher values are detected in South America (due to the large quantity of Po210 present in "yerba mate'', an herb used in drinks) and arctic and sub-arctic areas (where Po210 and Pb210 tend to accumulate in moose meat). Worldwide-averaged annual effective dose is 0.3 mSv.

Some radioisotopes may be inhaled, the most significant radioisotope in this case m 11 n being Rn and, much less importantly, Po (smoking 10 cigarettes a day doubles Po210 introduction). Typical range of inhaled dose is 0.2-10 mSv. The range is so wide because the contribution is mainly given by radon and its contribution depends on its indoor accumulation. The worldwide-averaged annual effective dose due to inhalation is 1.2 mSv. A summary of background radiation sources is given in Figure A.10 [UNSCEAR, 2000].

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