METEORITES AND RADIATION
Are they radioactive? is probably one of the most common questions among those encountering meteorites for the first time. However, it would be more accurate to ask whether meteorites have an increased background radiation. The answer is an unequivocal no. The radiation level of meteorites matches the background radiation level of the planet Earth.
The radioactivity of rocks is determined by the number of radioactive isotopes in their chemical elements. Numerous studies have shown that the proportion of radioactive isotopes in meteorites is on average hundreds of times lower than in the Earth's crust.
Radioactive elements can precipitate and accumulate only as a result of sedimentary rock formation under the influence of organogenic carbon and phosphates. So far, such sedimentation hasn't been observed anywhere outside planet Earth.
In meteorites, the number of minerals containing the main sources of radiation uranium and thorium is extremely small. The half-lives of other radioactive elements are quite short compared with uranium and thorium. These elements are never found on meteorites, since meteorites are at least 1.5 billion years old.
The overall conclusion is that meteorites are less radioactive than terrestrial rocks because no suitable conditions for radioactive elements to accumulate have been discovered anywhere beyond planet Earth. In all known meteorites, the proportion of uranium and thorium is infinitely small. Meteorites are very old compared to short-lived radioactive isotopes and a significant part of the radiation has been lost over such a long period of time.
Kamni s neba (2010), by Dmitry Kachalin