Protactinium

Protactinium, ₉₁Pa
	Microscope image of a sample of protactinium-233
Protactinium
Pronunciation	/ˌproʊtækˈtɪniəm/ (PROH-tak-TIN-ee-əm)
Appearance	bright, silvery metallic luster
Standard atomic weight Ar°(Pa)
	231.03588±0.00001; 231.04±0.01 (abridged);
Protactinium in the periodic table
	thorium ← protactinium → uranium
Atomic number (Z)	91
Group	f-block groups (no number)
Period	period 7
Block	f-block
Electron configuration	[Rn] 5f2 6d1 7s2
Electrons per shell	2, 8, 18, 32, 20, 9, 2
Physical properties
Phase at STP	solid
Melting point	1841 K (1568 °C, 2854 °F)
Boiling point	4300 K (4027 °C, 7280 °F) (?)
Density (at 20° C)	15.43 g/cm3
Heat of fusion	12.34 kJ/mol
Heat of vaporization	481 kJ/mol
Atomic properties
Oxidation states	+2, +3, +4, +5 (a weakly basic oxide)
Electronegativity	Pauling scale: 1.5
Ionization energies	1st: 568 kJ/mol ; ;
Atomic radius	empirical: 163 pm
Covalent radius	200 pm
	Spectral lines of protactinium
Other properties
Natural occurrence	from decay
Crystal structure	body-centered tetragonal (tI2)
Lattice constant	a = 392.1 pm; c = 323.5 pm (at 20 °C)
Thermal expansion	11.8×10−6/K (at 20 °C)
Thermal conductivity	47 W/(m⋅K)
Electrical resistivity	177 nΩ⋅m (at 0 °C)
Magnetic ordering	paramagnetic
CAS Number	7440-13-3
History
Prediction	Dmitri Mendeleev (1869)
Discovery and first isolation	Kasimir Fajans and Oswald Helmuth Göhring (1913)
Named by	Otto Hahn and Lise Meitner (1917–8)
Isotopes of protactinium v; e;
β−	230U
α	226Ac
	Category: Protactinium; view; talk; edit; \| references

Protactinium is a chemical element; it has symbol Pa and atomic number 91. It is a dense, radioactive, 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.

The element was first identified in 1913 by Kazimierz Fajans and Oswald Helmuth Göhring and named "brevium" because of the short half-life of the specific isotope studied, protactinium-234m. A more stable isotope of protactinium, ²³¹Pa, was discovered in 1917/18 by Lise Meitner in collaboration with Otto Hahn, and they named the element protactinium.^[7] In 1949, the IUPAC chose the name "protactinium" and confirmed Hahn and Meitner as its discoverers. The new name meant "(nuclear) precursor of actinium,"^[8] suggesting that actinium is a product of radioactive decay of protactinium. John Arnold Cranston (working with Frederick Soddy and Ada Hitchins) is also credited with discovering the most stable isotope in 1915, but he delayed his announcement due to being called for service in the First World War.^[9]

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 protactinium-234 and its nuclear isomer protactinium-234m occur in the decay chain of uranium-238. Protactinium-233 occurs as a result of the decay of thorium-233 as part of the chain of events necessary 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. Ocean science utilizes the element to understand the ancient ocean's geography. Analysis of the relative concentrations of various uranium, thorium, and protactinium isotopes in water and minerals is used in radiometric dating of sediments up to 175,000 years old, and in modeling of various geological processes.^[10]

^ "Standard Atomic Weights: Protactinium". CIAAW. 2017.
^ Prohaska, Thomas; Irrgeher, Johanna; Benefield, Jacqueline; Böhlke, John K.; Chesson, Lesley A.; Coplen, Tyler B.; Ding, Tiping; Dunn, Philip J. H.; Gröning, Manfred; Holden, Norman E.; Meijer, Harro A. J. (4 May 2022). "Standard atomic weights of the elements 2021 (IUPAC Technical Report)". Pure and Applied Chemistry. doi:10.1515/pac-2019-0603. ISSN 1365-3075.
^ ^a ^b ^c Arblaster, John W. (2018). Selected Values of the Crystallographic Properties of Elements. Materials Park, Ohio: ASM International. ISBN 978-1-62708-155-9.
^ Donohue, J. (1959). "On the crystal structure of protactinium metal". Acta Crystallographica. 12 (9): 697. doi:10.1107/S0365110X59002031.
^ Lide, D. R., ed. (2005). "Magnetic susceptibility of the elements and inorganic compounds". CRC Handbook of Chemistry and Physics (PDF) (86th ed.). Boca Raton (FL): CRC Press. ISBN 0-8493-0486-5.
^ Kondev, F. G.; Wang, M.; Huang, W. J.; Naimi, S.; Audi, G. (2021). "The NUBASE2020 evaluation of nuclear properties" (PDF). Chinese Physics C. 45 (3): 030001. doi:10.1088/1674-1137/abddae.
^ Meitner, Lise (1918). "Die Muttersubstanz des Actiniums, Ein Neues Radioaktives Element von Langer Lebensdauer". Zeitschrift für Elektrochemie und angewandte physikalische Chemie. 24 (11–12): 169–173. doi:10.1002/bbpc.19180241107. ISSN 0372-8323.
^ "Protactinium" (PDF). Human Health Fact Sheet. ANL (Argonne National Laboratory). November 2001. Retrieved 4 September 2023. The name comes from the Greek work protos (meaning first) and the element actinium, because protactinium is the precursor of actinium.
^ John Arnold Cranston Archived 11 March 2020 at the Wayback Machine. University of Glasgow^{[dead link]}
^ Negre, César et al. “Reversed flow of Atlantic deep water during the Last Glacial Maximum.” Nature, vol. 468,7320 (2010): 84-8. doi:10.1038/nature09508

[1] "Standard Atomic Weights: Protactinium". CIAAW. 2017.

[CIAAW2021-2] Prohaska, Thomas; Irrgeher, Johanna; Benefield, Jacqueline; Böhlke, John K.; Chesson, Lesley A.; Coplen, Tyler B.; Ding, Tiping; Dunn, Philip J. H.; Gröning, Manfred; Holden, Norman E.; Meijer, Harro A. J. (4 May 2022). "Standard atomic weights of the elements 2021 (IUPAC Technical Report)". Pure and Applied Chemistry. doi:10.1515/pac-2019-0603. ISSN 1365-3075.

[Arblaster_2018-3] Arblaster, John W. (2018). Selected Values of the Crystallographic Properties of Elements. Materials Park, Ohio: ASM International. ISBN 978-1-62708-155-9.

[str-4] Donohue, J. (1959). "On the crystal structure of protactinium metal". Acta Crystallographica. 12 (9): 697. doi:10.1107/S0365110X59002031.

[magnet-5] Lide, D. R., ed. (2005). "Magnetic susceptibility of the elements and inorganic compounds". CRC Handbook of Chemistry and Physics (PDF) (86th ed.). Boca Raton (FL): CRC Press. ISBN 0-8493-0486-5.

[NUBASE2020-6] Kondev, F. G.; Wang, M.; Huang, W. J.; Naimi, S.; Audi, G. (2021). "The NUBASE2020 evaluation of nuclear properties" (PDF). Chinese Physics C. 45 (3): 030001. doi:10.1088/1674-1137/abddae.

[meitner-7] Meitner, Lise (1918). "Die Muttersubstanz des Actiniums, Ein Neues Radioaktives Element von Langer Lebensdauer". Zeitschrift für Elektrochemie und angewandte physikalische Chemie. 24 (11–12): 169–173. doi:10.1002/bbpc.19180241107. ISSN 0372-8323.

[8] "Protactinium" (PDF). Human Health Fact Sheet. ANL (Argonne National Laboratory). November 2001. Retrieved 4 September 2023. The name comes from the Greek work protos (meaning first) and the element actinium, because protactinium is the precursor of actinium.

[9] John Arnold Cranston Archived 11 March 2020 at the Wayback Machine. University of Glasgow^{[dead link]}

[10] Negre, César et al. “Reversed flow of Atlantic deep water during the Last Glacial Maximum.” Nature, vol. 468,7320 (2010): 84-8. doi:10.1038/nature09508

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