Thoron

Thoron (radon‑220) is a short‑lived radioactive isotope of radon that occurs naturally as part of the thorium decay series. It is produced by the alpha decay of thorium‑232 in rocks and minerals that contain thorium. Thoron has a half‑life of 55.6 seconds and decays by emitting an alpha particle to polonium‑216. Because of its very brief half‑life, thoron concentrations are typically much lower than those of radon‑222, the more common radon isotope that dominates indoor air samples. However, thoron can still contribute to radiation exposure in environments where ventilation is poor or where thorium‑rich material is present, such as underground mines, caves, or certain industrial settings.

The health effects of thoron are similar to those of radon: inhalation of high concentrations of its decay products can increase the risk of lung cancer. In most indoor environments, thoron contributes less than about five percent of the total radon‑derived gamma radiation. Nonetheless, due to its rapid decay, thoron is a useful tracer for studying air‑flow patterns and ventilation efficiency; its presence is often studied in conjunction with radon‑222 to assess overall radiological risk.

Because thoron decays very quickly, it has no practical application in commercial nuclear fuel cycles or medical therapies. Occupational safety measures for thoron are essentially the same as for radon, involving adequate ventilation, periodic monitoring, and reducing exposure to radon‑bearing materials.