Protactinium


 * Protactinium**

Is a chemical element with the symbol **Pa** and atomic number 91. It is a dense, silvery-gray metal which readily reacts with oxygen, water vapor and inorganic acids. It forms various chemical compounds where protactinium is usually present in the oxidation state +5, but can also assume +4 and even +2 or +3 states. The average concentrations of protactinium in the Earth's crust is typically on the order of a few parts per trillion, but may reach up to a few parts per million in some uranite ore deposits. Because of the scarcity, high radioactivity and high toxicity, there are currently no uses for protactinium outside of scientific research, and for this purpose, protactinium is mostly extracted from spent nuclear fuel. Protactinium was first identified in 1913 by Kasimer Fajans and Oswald Helmuth Gohring and named //brevium// because of the short half-life of the specific isotope studied, namely protactinium-234. A more stable isotope of protactinium was discovered in 1918, and therefore the name was changed to protoactinium and then to protactinium in 1949. The new name meant "parent of actinium" and reflected the fact that actinium is a product of radioactive decay of protactinium. The longest-lived and most abundant (nearly 100%) naturally occurring isotope of protactinium, protactinium-231, has a half-life of 32,760 years and is a decay product of uranium-235. Much smaller trace amounts of the short-lived nuclear isomer protactinium-234m occur in the decay chain of uranium-238. Protactinium-233 results from the decay of thorium-233 as part of the chain of events used to produce uranium-233 by neutron irradiation of thorium-232. It is an undesired intermediate product in thorium-based nuclear reactors and is therefore removed from the active zone of the reactor during the breeding process. Analysis of the relative concentrations of various uranium, thorium and protactinium isotopes in water and minerals is used in radiometric dating of sediments which are up to 175,000 years old and in modeling of various geological processes.

Radioactive Protactinium's most stable isotope, protactinium-231, has a half-life of about 32,760 years. It decays into actinium-227 through alpha decay. Due to its scarcity, high radioactivity and toxicity, there are currently no uses for protactinium outside of basic scientific research.
 * Atomic Number:** 91
 * Atomic Weight:** 231.03588
 * Melting Point:** 1845 K (1572°C or 2862°F)
 * Boiling Point:** Unknown
 * Density:** 15.37 grams per cubic centimeter
 * Phase at Room Temperature:** Solid
 * Element Classification:** Metal
 * Period Number:** 7 **Group Number:** none **Group Name:** Actinide
 * What's in a name?** From the Greek word for first, **protos**, and the element **actinium**, which together mean "the parent of actinium."
 * Say what?** Protactinium is pronounced as **PRO-tak-TIN-ee-em**.
 * History and Uses:** Protactinium was first identified by Kasimir Fajans and O.H. Göhring in 1913 while studying uranium's decay chain. The particular isotope they found, protactinium-234m, has a half-life of about 1.17 minutes. They named the element brevium, meaning brief, and then continued with their studies. Protactinium's existence was confirmed in 1918 when another isotope, protactinium-231, was independently discovered and studied by two groups of scientists, Otto Hahn and Lise Meitner of Germany and Frederick Soddy and John Cranston of Great Britain. Protactinium was first isolated by Aristid V. Grosse in 1934. Protactinium is a rare, poisonous and expensive element that is present in uranium ores in very small amounts. In 1961, the Great Britain Atomic Energy Authority was able to produce 125 grams of 99.9% pure protactinium, although they had to process about 55,000 kilograms of ore and spend about $500,000 to get it.
 * Estimated Crustal Abundance:** 1.4×10-6 milligrams per kilogram
 * Estimated Oceanic Abundance:** 5×10-11 milligrams per liter
 * Number of Stable Isotopes:** 0
 * Ionization Energy:** 5.89 eV
 * Oxidation States:** +5, +4

Almost all naturally occurring protactinium is the 231 isotope. It emits alpha radiation and is produced through the decay of uranium-235. Protactinium is one of the rarest and most expensive naturally occurring elements. The largest amount of protactinium obtained so far has been 125 grams in 1961 from the Great Britain Atomic Energy Authority. The extraction was made from 60 tons of nuclear waste material.
 * Harmful effects: ** Protactinium is harmful due to its radioactivity and is also toxic.
 * Characteristics: ** Protactinium is a very rare shiny, silvery, highly radioactive metal that tarnishes slowly in air to the oxide.

Uses of Protactinium
Protactinium is used mainly for research purposes. Protactinium-231 combined with the thorium-230 can be used to date marine sediments.

- Protactinium is more dense and rigid than thorium but is lighter than uranium, and its melting point is lower than that of thorium and higher than that of uranium. - Protactinium is a metal with silvery-gray luster that is preserved for some time in air. Protactinium easily reacts with oxygen, water vapor and acids, but not with alkali metals. - Protactinium is paramagnetic and no magnetic transitions are known for it at any temperature.It becomes superconductive at temperatures below 1.4 K. Protactinium tetrachloride is paramagnetic at room temperature but turns ferromagnetic upon cooling to 182 K. - Protactinium exists in two major oxidation states, +4 and +5, both in solids and solutions, and the +3 and +2 states were observed in some solid phases.
 * Physical and Chemical Properties**