Test measurements of thoron concentration using two ionization chambers AlphaGUARD vs. radon monitor RAD7

Thoron 220Rn is one of four naturally occurring radon isotopes. It has a half-life T1/2 equal to 55 s. Radon isotopes are chemically inert radioactive gases that occur in the environment as a result of the decay of radioactive elements in soil and minerals. While radon 222Rn results from the decay chain of uranium 238U, thoron 220Rn results from the decay of thorium 232Th. Both uranium and thorium are commonly found in soil and minerals. The radioactive gases radon and thoron that are produced there can diffuse out of the material and travel at long distances before they decay. Both radon and thoron decay into their progenies: polonium, lead and bismuth before finally reaching stable forms of lead. Thoron and radon and their respective progenies differ very significantly in their half-lives and in the energies of their radiations. While radon 222Rn has a half-life of 3.82 d, thoron 220Rn has a half-life of only 55 s. Since thoron is so short-lived, it cannot travel as far from its source as radon can before it decays. It is commonly observed that compared to radon, a much smaller fraction of thoron gas in soil ever reaches the interior of a building. However, in some cases thoron can still be a hazard since its progeny 212Pb with a half-life of 10.6 h can accumulate to significant levels in breathable air. The presence of thoron was often neglected because it was considered that the quantity of thoron in the enTest measurements of thoron concentration using two ionization chambers AlphaGUARD vs. radon monitor RAD7 Elżbieta Kochowska, Krzysztof Kozak, Beata Kozłowska, Jadwiga Mazur, Jerzy Dorda