Protactinium is the next-to-last heaviest element, just preceding uranium (atomic number 92) in the periodic table. Protactinium's atomic number is 91, its atomic mass is 231.03588, and its chemical symbol is Pa.

Properties

All isotopes of protactinium are radioactive. Protactinium-231 is the most stable isotope with a half life of 3.276 x 10⁴ years. The element is a bright shiny metal with a melting point of about 2,840°F (1,560°C) and a density of 15.37 grams per cubic centimeter. The element is fairly active and reacts with oxygen, the halogens, and hydrogen. Detailed properties of the element and its compounds have not been well studied, however.

Occurrence and Extraction

The amount of protactinium in the Earth's crust is too small to estimate accurately. The best estimate of its abundance is based on the fact that a ton of its most common ore, pitchblende, yields about 0.1 part per million of the element.

Discovery and Naming

Protactinium was discovered in 1913 by the German-American physicist Kasimir Fajans (1887-1975) and his colleague, O. H. Göhring. Fajans and Göhring were analyzing the mixture of substances found when isotopes of uranium undergo radioactive decay. They originally suggested the name of brevium for the element because of its short half life (1.175 minutes for protactinium-231), although the element's name was later changed to protoactinium. This name was suggested because the element produces actinium (atomic number 89) when it decays, making it "first actinium" or "protoactinium." The spelling of the name was later changed slightly to its current form

Uses

Neither protactinium nor its compounds have any commercial uses. The element is still very rare and sells for about $300 per gram for research purposes.