Radioactivity and the environment

The contribution of natural and artificial radiation sources to the environment radioactivity is discussed. The average natural source exposure for the majority of world population is 100 mrad/y. Soil radioactivity primarily results from the decay of uranium and thorium series elements. Air radioactivity is due to the release of radon and thoron into the atmosphere where their daughters are produced, or to the interaction of cosmic radiation with atoms in the upper troposphere or in the lower stratosphere layers. Beta and gamma radiation dose rates of 226Ra and 40K in the soil and of 220Rn and 222Rn in the air are indicated. The cosmic ray intensity is variable and dependent on the Earth magnetism and on the altitude above sea level. Medical applications of ionizing radiation may contribute with doses of 1 to 100 mrad/y. Current contamination levels resulting from nuclear explosions amount to several mrad/y. The nuclear industry contributes with less than 1 mrad/y. The results show that doses from artificial sources are still of a very low level. (J.B.)