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Home » Projects » REB
2000 » Conferences
Nuclear power generation: alternative for a clean energy in
the future
Natural Sources of Radiation
Natural ionizing radiation arises in outer space, where cosmic rays
are formed, and in and on the earth, where radionuclides normally present
in soil, air, water, food and the body undergo radioactive decay. The
assessment of radiation doses in humans from natural sources is important
because natural ionizing radiation is the largest contributor to collective
effective dose received by the world’s population. (Sources and
Effects of Ionizing Radiation, United Nations Scientific Committee on
the Effects of Atomic Radiation, UNSCEAR 1993, Report to the General
Assembly, with Scientific Annexes).
Earth population is constantly exposed to radiation from several natural
sources as follows:
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cosmic rays (0.3 mSv/year);
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radiation from radioactive materials like uranium, potassium and
thorium in the ground (0.2 mSv/year),
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radiation from the walls of the buildings (0.1 mSv/year) and
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radiation from our own bodies (mostly potassium – 0.25 mSv/year)
All these combined give an average dose of about 0.85 mSv/year).
Cosmic rays produce several radionuclides in the atmosphere, biosphere
and lithosphere by a variety of nuclear reactions. The radionuclides,
which are significant in terms of dose, are 3H, 14C, 7Be, and 22Na,
and the most important mechanism of human exposure is ingestion.
The most important radionuclide of the four considered is 14C.
The assessment of its contribution to the dose from natural sources
is useful for the derivation of doses from man-made environmental releases
of 14C. The annual natural production of 14C is 1 PBq and
the specific activity of 14C is 230 Bq per kg of carbon, leading
to an annual effective dose of 12mSv. The spatial variability of the
dose from 14C is not radiologically significant.
Table 2 Annual intakes by ingestion of cosmogenic
radionuclides and effective doses to adults
| Radionuclide |
Intake (Bq y-1) |
Annual effective dose (mSv) |
| 3H |
500 |
0.01 |
| 7Be |
1000 |
0.03 |
| 14C |
20000 |
12 |
| 22Na |
50 |
0.15 |
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This book is the result of the proceedings of the Romanian Environmental
Forum, 6th edition held in Bucharest between 16 and 19 November 1999. 
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GROUP OF INDEPENDENT EXPERTS Ltd.
