558px-Electron shell 091 Protactinium svg
Protactinium is a chemical element with the symbol Pa and atomic number 91. Its longest-lived and most abundant naturally occurring isotope by far, Pa-231, is a decay product of uranium-235 (U-235), and it has a half-life of 32,760 years. Much smaller trace amounts of the short-lived metastable isotope Pa-234m occur as decay products of uranium-238 (U-238). Pa-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.

Because of its scarcity, high radioactivity and high toxicity, there are currently no uses for protactinium outside of scientific research.


Protactinium is a metallic element that belongs to the actinide group, with a bright metallic luster that it retains for some time in contact with air. Protactinium is superconductive at temperatures below 1.4 K.

Protactinium-231 is formed by the alpha decay of U-235 followed by beta decay of thorium-231. The physicist Walter Seifritz once estimated that protactinium might possibly be used to build a nuclear weapon with a critical mass of 750±180 kg. This possibility (of a chain reaction) has been ruled out by other nuclear physicists since then.


The base value of each unit of ranges between 10 and 35Ð per unit, with up to 3 units being found at any one time.

Presence on Mars: Rare

Martian Minerals
Group 1 | Group 2 | Group 3 | Group 4 | Group 5 | Group 6
Group 4 |Actininum | Areanetium | Borane | Carbon Tetrachloride | Dubnium | Dysprosium | Erbium | Europium | Ferrous Dixenate | |Gadollinium | Golgathium | Holmium | Holmium Sulfate | Iron Golgathide | Neodymium | Praseodymium | Promethium | |Protactinium | Rutherfordium | Samarium | Selenium Arsenide | Terbium | Thallium Titanide | Thulium | Uranium|

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