Article
Article
Protactinium
Article By:
Kirby, H. W. Mound Facility, Monsanto Research Corporation, Miamisburg, Ohio.
Last reviewed:January 2020
DOI:https://doi.org/10.1036/1097-8542.549800
A chemical element, Pa, atomic number 91. Isotopes of mass numbers 216, 217, and 222–238 are known, all of them radioactive. Only 231Pa, the parent of actinium, 234Pa, and 233Pa occur in nature. The most important of these is 231Pa, an α-emitter with a half-life of 32,500 years. The artificial isotope, 233Pa, is important as an intermediary in the production of fissile 233U. Both 231Pa and 233Pa can be synthesized by neutron irradiation of thorium. See also: Actinium; Periodic table; Radioactivity; Uranium
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