Preface

Radon is the heaviest of all naturally occurring noble gases and it has a total of 36 isotopes, all of which are radioactive (ranging from Rn to Rn). Only three of these isotopes occur naturally and are constantly produced at a known rate in the U-(Rn, radon), U-(Rn, also known as actinon), and Th-(Rn, also known as thoron) series. Radon has received the most attention among all the noble gases over the last four decades, largely due to the fact that it is the single major contributor to the ionizing radiation dose received by the general population. Radon is the second most frequent cause of lung cancer after smoking, and is classified as a human carcinogen. While the noble gas applications extend from cosmochemistry to different branches of geoscience, applications of radon are generally confined to near-surface Earth processes, due to its short mean life (5.53 days). Note that the presence of mantle He in the oceans is indicative of diffusion of helium from much deeper sources inside the Earth, but sources of radon to Earth systems is much more confined to shallower depths. Most review articles and books such as Noble Gases by Minoru Ozima and Frank Podosek and the articles in the edited volume Noble Gases in Geochemistry and Cosmochemistry by Don Porcelli, Chris Ballentine and R. Wieler in Reviews in Mineralogy and Geochemistry serve as key reference works for the researchers working in noble gas geochemistry, but most of these publications have discounted the utility of radon as a tool to investigate several Earth surface processes. The sensitivity of radon measurement is the highest among all noble gases. In terms of molar concentration, 1 pico Curie (pCi) can be easily measured (1pCi of Rn activity contains 1.76 × 10 atoms which corresponds to 2.9 × 10 mole of radon). While there are a large number of scientific reports from national and international agencies (e.g., US Environmental Protection Agency, US National Academy of Science, World Health Organization) that describe findings on indoor radon in peer-reviewed journal articles, and many scientific reports pertaining to indoor radon as a health hazard, there is no single book on the applications of radon as a tracer in Earth systems. This book is designed to address that deficiency.