1s² 2s²p⁶ 3s²p⁶d¹⁰ 4s²p⁶d¹⁰f¹⁴ 5s²p⁶d¹⁰f² 6s²p⁶d¹ 7s²

History

The existence of an element between thorium and uranium was predicted to exist by Mendeleev in 1871.  In 1900 William crookes isolated protactinium as a radioactive material from uranium which he could not identify.

Protactinium was first identified in 1913, when Kasimir Fajans and O.H. Gohring encountered short-lived isotope 234m-Pa, with a half-life of about 1.17 minutes, during their studies of the decay chain of 238-U.  They gave the new element the name Brevium (Latin brevis, brief, short); because of the short life-time of the transition between Th-234 and U-234, a longer-lived isotope was eventually isolated and the name was changed to Protoactinium in 1918 when two groups of scientists (Otto Hahn and Lise Meitner of Germany and Frederick Soddy and John Cranston of the UK) independently discovered 231-Pa, and shortened to Protactinium in 1949.

Aristid V. Grosse prepared 2 mg of Pa₂O₅ in 1927, and later on managed to isolate Protactinium for the first time in 1934 from 0.1 mg of Pa₂O₅, first converting the oxide to an iodide and then cracking it in a high vacuum by an electrically heated filament by the reaction:

2PaI₅ 2Pa + 5I₂

In 1961, the United Kingdom Atomic Energy Authority was able to produce 125 g of 99.9% pure protactinium, processing 60 tons of waste material in a 12-stage process and spending 500,000 USD; this was the world's only supply of the element for many years to come, and it is reported that the metal was sold to laboratories for a cost of 2,800 USD / g in the following years.

About 60 tons of pitchblende ore (which contains uranium, radium, and a host of other radioactive elements) yields about 125 grams of protactinium.

Characteristics

It is malleable, shiny, silver-gray, radioactive.  It does not tarnish rapidly in air, it is attacked by oxygen, steam and acids, but not by alkalis.  Protactinium belongs to the actinide group, with a bright metallic luster that it retains for some time in the air.  It is superconductive at temperatures below 1.4^oK.  The metal is extrememly rare, very radioactive and highly poisonous.

Occurrence

Protactinium occurs in pitchblende to the extent of about 1 part  ²³¹Pa to 10 million of ore.  Some ores from the Democratic Republic of the Congo have about 3 ppm.

Applications

Due to its scarcity, high radioactivity and toxicity, there are currently no uses for protactinium outside of basic scientific research.  Protactinium is one of the rarest and most expensive naturally occurring elements.

Protactinium-231, which is formed by the alpha decay of Uranium-235, could possibly sustain a nuclear chain reaction and might, in principle, be used to build a nuclear weapon.  The critical mass, according to Walter Seifritz, is 750±180 kg.  Other authors conclude that no chain reactions are possible in Protactinium-231.

Compounds

A number of protactinium compounds are known, some of which are colored.

Isotopes

29 radioistopes of protactinium have been characterized, with the most stable being 231-Pa with a half-life of 32760 years, 233-Pa with a half-life of 26.967 days, and 230-Pa with a half-life of 17.4 days.  All of the remaining radioactive isotopes have half-lifes that are less than 1.6 days, and the majority of these have half lifes that are less than 1.8 seconds.  This element also has 2 meta states, 217m-Pa (t_½ 1.15 milliseconds) and 234m-Pa (t_½ 1.17 minutes).

The primary decay mode before the most stable isotope, 231-Pa, is alpha decay and the primary mode after is beta minus decay.  The primary decay products before 231-Pa are element Ac (actinium) isotopes and the primary products after are element U (uranium) isotopes.

The element is an alpha emitter (5.0 MeV) and is a radiological hazard similar to polonium.

Precautions

Protactinium is both toxic and highly radioactive.  It requires precautions similar to those used when handling plutonium.

The major health concern is cancer resulting from the ionizing radiation emitted by protactinium deposited in the skeleton, liver, and kidneys. The health risks associated with protactinium-234m are included with those for uranium-238. Protactinium-234m decays by emitting an energetic beta particle so precautions against this radiation are needed when handling uranium; for example, heavy rubber gloves are worn to protect the hands and forearms.

The inhalation risk factor for protactinium-231 represents one of the largest risk factors for any radionuclide. Actinium-227 and its decay products account for more than 80% of this inhalation risk. While the risk factor for ingestion is much lower than for inhalation, ingestion is generally the most common means of entry into the body.

Similar to other radionuclides, the risk coefficient for tap water is about 75% of that shown for dietary ingestion.

In addition to risks from internal exposures, there is a risk from external gamma exposure to protactinium-231.

*All Data Varies Depending on Source