ABSTRACT

Our planet is mainly rock and metal and its rock is remarkably radioactive. The sun supplies most of our energy but the measured radioactivity in the earth contributes up to 25% of the total heat balance of the earth (Araki et al., 2005). The primordial decay series beginning with 238U (4.5 × 109 year half-life), present in all terrestrial materials, supports a chain of 13 alpha-, beta-, and gammaemitting radionuclides that includes the gas radon (222Rn, 3.8 day half-life). The primordial decay series beginning with 232Th (1.4 × 1010 year half-life) is also present in all basic earth materials, and supports a chain of 11 radionuclides that includes another isotope of radon-common name thoron (220Rn, 55 second half-life). Both radon isotopes are produced in all soil or rock from their parent radium isotopes (226Ra or 224Ra). A fraction of both gases is released from all terrestrial substances and can be measured in any dwelling, outdoors, and in the case of 222Rn, even at stratospheric altitudes. Thoron, however, should not exist in the stratosphere because of its short half-life and the time required for transit to altitude.