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.
Einsteinium
Nineteen nuclides and three nuclear isomers are known for einsteinium with atomic weights ranging from 240 to 258. All are radioactive and the most stable nuclide, Es, has a half-life of 471.7 days. Next most stable isotopes are Es (half-life 275.7 days), Es (39.8 days) and Es (20.47 days). All of the remaining isotopes have half-lives shorter than 40 hours, and most of them decay within less than 30 minutes. Of the three nuclear isomers, the most stable is Es with half-life of 39.3 hours.