protoactinium

Protoactinium, historically used as the name for the element now known as protactinium (Pa), has atomic number 91. The term derives from proto- meaning first and actinium, reflecting its position as the first member of the actinium decay chain. In 1949 the IUPAC adopted the name protactinium as the official designation, and protoactinium became obsolete.

Protactinium is a dense, radioactive metal that is silver-gray in appearance and highly reactive with oxygen and moisture. In chemistry, the most common oxidation state is +5, with +4 and +3 observed under certain conditions. It forms oxides such as Pa2O5 and various halide and complex compounds typical of actinides. Its chemistry is studied mainly in the context of actinide behavior.

Occurrence and production: Protactinium is extremely rare in nature, occurring only in trace amounts in uranium and thorium ores as a decay product in the uranium-238 and thorium series. Commercial production is limited to research purposes. It is usually obtained by irradiating uranium or thorium in a nuclear reactor and then separating the protactinium from decay products.

Isotopes and half-life: The element has several radioisotopes, with protactinium-231 being the longest-lived natural isotope, having a half-life of about 32,000 years. Other isotopes are short-lived and are produced in reactors or during radioactive decay chains.

Applications and safety: Historically protactinium isotopes were used as radiochemical tracers in actinide research. Today, use is limited due to extreme radioactivity and scarcity. Handling requires specialized facilities, remote manipulation, and strict safety protocols to protect against alpha-emission hazards.