Uranium–uranium dating
U, with a half-life of about 4.5 billion years, decays to U through emission of an alpha particle to thorium-234 (Th), which is comparatively unstable with a half-life of just 24 days. Th then decays through beta particle emission to protactinium-234 (Pa)). This decays with a half-life of 6.7 hours, again through emission of a beta particle, to U. This isotope has a half-life of about 245,000 years. The next decay product, thorium-230 (Th), has a half-life of about 75,000 years and is used in the uranium-thorium technique. Although analytically simpler, in practice U/U requires knowledge of the ratio at the time the material under study was formed and is generally used only for samples older than the ca. 450,000 year upper limit of the Th/U technique. For those materials (principally marine carbonates) for which these conditions apply, it remains a superior technique.
Rum Jungle, Northern Territory
One of the main environmental impacts of uranium mining is the creation of large volumes of radioactive mine waste (tailings) which are left behind on the site. The major radioactive component of these tailings is uranium-238, an isotope with a halflife of 4.46 billion years. In 2003, a government survey of the tailings piles at Rum Jungle found that capping which was supposed to help contain this radioactive waste for at least 100 years, had failed in less than 20 years.