Radium and radon in the environment

所有镭同位素的半衰期都远小于地球的年龄，所以原生的镭早已衰变殆尽。今天存在于环境中的镭（英语：Radium and radon in the environment）都是铀和钍的衰变产物。由于钍和铀的半衰期很长，这些衰变产物可以不断地通过衰变而再生。在四种天然镭同位素（223R

Anthony J.; Crouch, Philip; Mylvaganam, Arul. Radon Daughter Exposures at the Radium Hill Uranium Mine and Lung Cancer Rates among Former Workers, 1952-87

Radium. Encyclopædia Britannica Hayter, Charles. The Politics of Radon Therapy in the 1930s. An Element of Hope: Radium and the Response to Cancer in

bioavailability and impacts of heavy metals in municipal solid waste composts compared to sewage sludge. Environment International. 2009, 35 (1): 142–156. ISSN 0160-4120

2981/0909-6396(2006)12[129:TCOOAI]2.0.CO;2 （英语）.  The relationship between overgrazing and the US environment.. ArcGIS StoryMaps. 13 March 2020 [2021-03-20]