page_title: Protactinium
section_title: History
hierarchical_section_title: Protactinium / History
caption_attribution_description: Русский: Таблица Менделеева по изданию 1871 года с прочерками у предсказанных, но ещё не открытых элементов. Svenska: Dmitrij Mendelejevs periodiska system från 1871 med luckor (—) för ytterligare ämnen
context_page_description: Protactinium is a chemical element with the symbol Pa and atomic number 91. It is a dense, silvery-gray actinide metal which readily reacts with oxygen, water vapor and inorganic acids. It forms various chemical compounds in which protactinium is usually present in the oxidation state +5, but it can also assume +4 and even +3 or +2 states. Concentrations of protactinium in the Earth's crust are typically a few parts per trillion, but may reach up to a few parts per million in some uraninite ore deposits. Because of its scarcity, high radioactivity and high toxicity, there are currently no uses for protactinium outside scientific research, and for this purpose, protactinium is mostly extracted from spent nuclear fuel.
  Protactinium was first identified in 1913 by Kasimir Fajans and Oswald Helmuth Göhring and named brevium because of the short half-life of the specific isotope studied, i.e. protactinium-234. A more stable isotope of protactinium, ²³¹Pa, was discovered in 1917/18 by Otto Hahn and Lise Meitner, and they chose the name proto-actinium, but the IUPAC finally named it "protactinium" in 1949 and confirmed Hahn and Meitner as discoverers.
context_section_description: In 1871, Dmitri Mendeleev predicted the existence of an element between thorium and uranium. The actinide element group was unknown at the time. Therefore, uranium was positioned below tungsten in group VI, and thorium below zirconium in group IV, leaving the space below tantalum in group V empty and, until the 1950s, periodic tables were published with this structure. For a long time chemists searched for eka-tantalum as an element with similar chemical properties to tantalum, making a discovery of protactinium nearly impossible. Tantalum's heavier analogue was later found to be the transuranic element dubnium – which, however, does not react like tantalum, but like protactinium.
  In 1900, William Crookes isolated protactinium as an intensely radioactive material from uranium; however, he could not characterize it as a new chemical element and thus named it uranium-X (UX). Crookes dissolved uranium nitrate in ether, and the residual aqueous phase contains most of the ²³⁴
  ₉₀Th
   and ²³⁴
  ₉₁Pa
  . His method was still used in the 1950s to isolate ²³⁴
  ₉₀Th
   and ²³⁴
  ₉₁Pa
   from uranium compounds. Protactinium was first identified in 1913, when Kasimir Fajans and Oswald Helmuth Göhring encountered the isotope ²³⁴Pa during their studies of the decay chains of uranium-238: ²³⁸
  ₉₂U
   → ²³⁴
  ₉₀Th
   → ²³⁴
  ₉₁Pa
   → ²³⁴
  ₉₂U
  . They named the new element brevium (from the Latin word, brevis, meaning brief or short) because of its short half-life, 6.7 hours for ²³⁴
  ₉₁Pa
  . In 1917/18, two groups of scientists, Otto Hahn and Lise Meitner of Germany and Frederick Soddy and John Cranston of Great Britain, independently discovered another isotope of protactinium, ²³¹Pa, having a much longer half-life of about 32,000 years. Thus the name brevium was changed to protoactinium as the new element was part of the decay chain of uranium-235 as the parent of actinium (from Greek: πρῶτος prôtos "first, before"). For ease of pronunciation, the name was shortened to protactinium by IUPAC in 1949. The discovery of protactinium completed one of the last gaps in the early versions of the periodic table, proposed by Mendeleev in 1869, and it brought to fame the involved scientists.
  Aristid von Grosse produced 2 milligrams of Pa₂O₅ in 1927, and in 1934 first isolated elemental protactinium from 0.1 milligrams of Pa₂O₅. He used two different procedures: in the first one, protactinium oxide was irradiated by 35 keV electrons in vacuum. In another method, called the van Arkel–de Boer process, the oxide was chemically converted to a halide (chloride, bromide or iodide) and then reduced in a vacuum with an electrically heated metallic filament:
  2 PaI₅ → 2 Pa + 5 I₂
  In 1961, the United Kingdom Atomic Energy Authority (UKAEA) produced 127 grams of 99.9% pure protactinium-231 by processing 60 tonnes of waste material in a 12-stage process, at a cost of about US$500,000. For many years, this was the world's only significant supply of protactinium, which was provided to various laboratories for scientific studies. Oak Ridge National Laboratory in the US provided protactinium at a cost of about US$280/gram.
caption: Dmitri Mendeleev's 1871 periodic table with a gap for protactinium on the bottom row of the chart, between thorium and uranium
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