Thoron emanation and exhalation of Slovenian soils determined by a PIC detector-equipped radon monitor

The radon isotopes (Rn-222 and Rn-220) and their progenies are responsible for more than 50% of natural radiation dose and the second leading factor in the case of the development of lung cancer after smoking [1]. Rn-222 (radon) and Rn-220 (thoron) are generated in crustal materials from their natural Ra-226 (U-238 decay series) and Ra-224 (Th-232 decay series) content, respectively. As a result of the alpha decay of the mother elements, the newly formed radon and thoron atoms recoil (average recoil energy on formation: radon = 86 keV, thoron = 103 keV) [2], which makes their escape from the matrix possible. This phenomenon is called radon or thoron emanation depending on the parent isotope. The emanation is defi ned as the radon or thoron atoms formed by the decay of their mother element that escapes from the grains (mainly because of recoil) into the interstitial space between the grains [3]. The ratio between the emanated and total radon and thoron originating from the grains is known as the radon/thoron emanation factor. This phenomenon greatly depends on several factors, such as grain size distribution and pore size distribution, porosity features, inhomogeneity of radium isotopes in the grains, moisture content, and so on. Only the emanated radon and thoron can exhale from the pore spaces. Owing to their half-lives (3.82 days Thoron emanation and exhalation of Slovenian soils determined by a PIC detector-equipped radon monitor Jácint Jónás, Zoltán Sas, Janja Vaupotic, Erika Kocsis, János Somlai, Tibor Kovács