Radon-222

History

Following the 1898 discovery of radium through chemical analysis of radioactive ore, Marie and Pierre Curie observed a new radioactive substance emanating from radium in 1899 that was strongly radioactive for several days. Around the same time, Ernest Rutherford and Robert B. Owens observed a similar (though shorter-lived) emission from thorium compounds. German physicist Friedrich Ernst Dorn extensively studied these emanations in the early 1900s and attributed them to a new gaseous element, radon. In particular, he studied the product in the uranium series, radon-222, which he called radium emanation.

In the early 20th century, the element radon was known by several different names. Chemist William Ramsay, who extensively studied the element's chemical properties, suggested the name niton, and Rutherford originally suggested emanation. At that time, radon only referred to the isotope 222Rn, whereas the names actinon and thoron denoted 219Rn and 220Rn, respectively. This decision was controversial because it was believed to give undue credit to Dorn's identification of radon-222 over Rutherford's identification of radon-220, and the historical use of the name radon created confusion as to whether the element or the isotope 222Rn was being discussed.

Decay properties

Radon-222 is generated in the uranium series from the alpha decay of radium-226, which has a half-life of 1600 years. Radon-222 itself alpha decays to polonium-218 with a half-life of 3.8215 days; it is the most stable isotope of radon. Its final decay product is stable lead-206.

In theory, 222Rn is capable of double beta decay to 222Ra, and depending on the mass difference between the two, single beta decay to 222Fr may also be allowed. These decay modes have been searched for, yielding lower partial half-life limits of 8 years for both transitions. The latest edition of the Atomic Mass Evaluation gives a mass difference of ; thus the single beta decay is, probably, forbidden energetically.

Occurrence and hazards

Main article: Health effects of radon

All radon isotopes are hazardous owing to their radioactivity, gaseous nature, chemical inertness, and radioactivity of their decay products (progeny). Radon-222 is especially dangerous because its longer half-life allows it to permeate soil and rocks, where it is produced in trace quantities from decays of uranium-238, and concentrate in buildings and uranium mines. This contrasts with the other natural isotopes that decay far more quickly (half-lives less than a minute) and thus do not contribute significantly to indoor radiation exposure. At higher concentrations, gaseous 222Rn may be inhaled and decay before exhalation, which leads to accumulation of its short-lived daughters (including alpha-emitters 218Po and 214Po) in the lungs, where they are in intimate contact with the lung cells irradiated; thus, extended periods of exposure to 222Rn and its progeny ultimately induce lung cancer. – making radon diffusion one of the greatest dangers of radium. Thus, 222Rn is a carcinogen; in fact, it is the second leading cause of lung cancer in the United States after cigarette smoking,

Notes

References

References

1. {{NNDC
2. (2013). "Discovery of the astatine, radon, francium, and radium isotopes". Atomic Data and Nuclear Data Tables.
3. {{Thoennessen2016
4. George, A.C.. (2008). "World History of Radon Research and Measurement from the Early 1900s to Today". AIP Conference Proceedings.
5. (2013). "Recalling radon's recognition". Nature Chemistry.
6. (2014). "Investigation of rare nuclear decays with BaF₂ crystal scintillator contaminated by radium". European Physical Journal A.
7. (2003). "EPA assessment of risks from radon in homes". Office of Radiation and Indoor Air, United States Environmental Protection Agency.
8. "EPA Facts about Radon". United States Environmental Protection Agency.
9. "Radiation protection: Radium". United States Environmental Protection Agency.
10. "Radon Fact Sheet: What it is, how it affects us, why it matters". Air Chek, Inc..