As was written, all people also have some radioactive isotopes inside their bodies from birth. These isotopes are especially potassium-40, carbon-14 and isotopes from the uranium and thorium series. The variation in radiation dose from one person to another is not as great as the variation in dose from cosmic and terrestrial sources. The average annual radiation dose to a person from internal radioactive materials other than radon is about 0.3 mSv/year of which:
- 0.2 mSv/year comes from potassium-40,
- 0.12 mSv/year comes from the uranium and thorium series,
- 12 μSv/year comes from carbon-14.
UNSCEAR have, based on a large number of investigations, presented values about the annual intake by humans of the different isotopes. We can mention the following:
- Ra-226 (22 Bq/year),
- Pb-210 (30 Bq/year),
- Po-210 (58 Bq/year) and
- Ra-228 (15 Bq/year).
Note that, the dominant component of natural background exposure, which comes from the short-lived decay products of radon, is not involved here. This issue is so important, that it was treated separately in the previous section (Terrestrial Radiation).
As a result, the UNSCEAR 2000 report estimates an annual effective dose of 0.12 mSv, which comes from internal exposure by isotopes of the uranium and thorium series. The main contributor to this dose is Po-210. Note that, polonium-210, the decay product of lead-210, emits a 5.3 MeV alpha particle, which provides most of equivalent dose. The radiation weighting factor for alpha radiation is equal to 20. An absorbed dose of 1 mGy by alpha particles will lead to an equivalent dose of 20 mSv.
Internal Radiation – Is it dangerous?
We must emphasize, eating bananas, working as airline flight crew or living in locations with, increases your annual dose rate. But it does not mean, that it must be dangerous. In each case, intensity of radiation also matters. It is very similar as for heat from a fire (less energetic radiation). If you are too close, the intensity of heat radiation is high and you can get burned. If you are at the right distance, you can withstand there without any problems and moreover it is comfortable. If you are too far from heat source, the insufficiency of heat can also hurt you. This analogy, in a certain sense, can be applied to radiation also from radiation sources.
See also: Internal Source of Radiation