The Parent of Actinium

Protactinium's name records its place in the radioactive decay chains that so preoccupied the physics of the early twentieth century: it decays into actinium, and so was named its parent, protos-actinium, the element that comes before. The original short-lived form found by Fajans and Gohring had been called brevium for its brevity, but when the far longer-lived isotope was discovered it took the more meaningful genealogical name.

The discovery came in the midst of the First World War, and Lise Meitner, one of its finders, would go on to help explain nuclear fission two decades later. Protactinium has no ancient, mythological or alchemical tradition, being a product of the new science of radioactivity; its name is a small piece of the family tree of decay by which the heavy elements were being mapped. Protactinium-231 dating is most powerful used alongside the related thorium-230 method, since the two isotopes derive from different parents, uranium-235 and uranium-234 respectively, and decay at different rates; when both clocks agree on the age of the same layer of ocean sediment or fossil coral, researchers gain much greater confidence in reconstructions of past ocean circulation and climate than either isotope could provide alone.