The element radon is commonly used in Geiger counters to detect the presence of radiation leaking from an object or site. Radon was once prevalently used in the treatment of cancer because it kills cancer cells, but is only used in some cases, as of 2015.
A common use of radon concerns studies of ground water and how it mixes with fresh or surface water. A high concentration of radon in surface water is an indicator that a local source of ground water has leeched into the tested area. Surface water tends to lose radon to atmospheric contact, whereas ground water retains high quantities of radon and other heavy metal isotopes.
Scientists are conducting tests to see if radon can detect upcoming earthquakes. One theory is that as the plates shift and the earth disrupted, radon is released into the Earth's crust. The tools used in this test are meant to detect the alpha particles that radiate from radon as it degrades. Geothermal prospecting uses radon testing in much the same way. Surveyors bury a tool in the ground and take radioactive photos of the soil at varying temperatures and depths to detect the presence of radiation or heavy metal isotopes.