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.
Nihonium
All nihonium isotopes are unstable and radioactive; the heavier nihonium isotopes are more stable than the lighter ones, as they are closer to the centre of the island. The most stable known nihonium isotope, Nh, is also the heaviest; it has a half-life of 8 seconds. The isotope Nh, as well as the unconfirmed Nh and Nh, have also been reported to have half-lives of over a second. The isotopes Nh and Nh have half-lives of 1 and 0.1 seconds respectively. The remaining two isotopes have half-lives between 0.1 and 100 milliseconds: Nh has a half-life of 70 milliseconds, and Nh, the lightest known nihonium isotope, is also the shortest-lived, with a half-life of 1.4 milliseconds. This rapid increase in the half-lives near the closed neutron shell at "N" = 184 is seen in roentgenium, copernicium, and nihonium (elements 111 through 113), where each extra neutron so far multiplies the half-life by a factor of 5 to 20.