Radioactive elements in the natural radioactive series such as: thorium, uranium-radium and uranium-actinium are present in the environment. The radioactive elements of these three series are the sources of alpha, beta and gamma radiation.
In all three natural radioactive series radon is present: in thorium – radon-220 (thoron), in uranium-radium - radon-222 (radon) and in uranium-actinium - radon-219 (actinon). Isotopes of radon, undergoing decay, form a radioactive deposit containing further radioactive elements. Natural mixture of uranium contains 99.28% uranium-238, which is the base element for the uranium-radon series, 0.0058% of uranium-234 and 0.714% uranium-235, which is the base element for the uranium-actinium series. The relationship between concentrations of uranium isotopes in samples taken from the environment are usually the same as in its natural mixture.
An important natural radionuclide is (because of its sizeable participation in the Earth’s ionising radiation background) potassium-40, which makes up about 0.01% of the natural potassium. Potassium-40 emits beta and gamma radiation. Its half-life is about 1.32 x 109 years. Other long-lived natural radioactive elements can be found in very small quantities, for example rubidium-87, lanthanum-138 and samarium-147.
The second group of natural radionuclides form radioactive isotopes created as a result of nuclear reactions occurring between particles of cosmic radiation and nuclei of elements in the air. In this way hydrogen-3 (tritium), beryllium-7 and carbon-14 are created.
Natural radioactive elements from both of the groups are omnipresent in the environment of the Earth. Their concentrations in particular components of the environment may differ several dozen or even several hundred times depending on the natural and artificially created local conditions. The concentrations of natural radionuclides in dust emitted into the atmosphere, in landfill waste spoil-heaps and retention ponds are often many times higher than the concentrations of these radionuclides in the soil.
As a result of nuclear explosions conducted in the atmosphere and the accident in the nuclear power station in Chernobyl, the environment of Poland has been contaminated by many artificial radionuclides. The majority of them have decayed totally because of their short half-lives and at the present time do not occur in Poland. At the same time, artificial radioactive elements which have long half-lives (cesium-137, strontium-90) continue to contaminate the environment.
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