Isotopes of protactinium

Isotopes of protactinium  (₉₁Pa)

Main isotopes [1] Decay abun­dance half-life (t1/2) mode pro­duct 229Pa synth 1.5 d ε 229Th 230Pa synth 17.4 d β+ 230Th β− 230U α 226Ac 231Pa 100% 3.265×104 y α 227Ac 232Pa synth 1.32 d β− 232U 233Pa trace 26.975 d β− 233U 234Pa trace 6.70 h β− 234U 234mPa trace 1.159 min β− 234U
Standard atomic weight Ar°(Pa)
	231.03588±0.00001 [2] 231.04±0.01 (abridged) [3]
view talk edit

Protactinium (₉₁Pa) has no stable isotopes. The four naturally occurring isotopes allow a standard atomic weight to be given.

Thirty radioisotopes of protactinium have been characterized, ranging from ²¹⁰Pa to ²³⁹Pa. The most stable isotope is ²³¹Pa with a half-life of 32,760 years, ²³³Pa with a half-life of 26.967 days, and ²³⁰Pa with a half-life of 17.4 days. All of the remaining radioactive isotopes have half-lives less than 1.6 days, and the majority of these have half-lives less than 1.8 seconds. This element also has five meta states, ^217mPa (t_1/2 1.15 milliseconds), ^220m1Pa (t_1/2 = 308 nanoseconds), ^220m2Pa (t_1/2 = 69 nanoseconds), ^229mPa (t_1/2 = 420 nanoseconds), and ^234mPa (t_1/2 = 1.17 minutes).

The only naturally occurring isotopes are ²³¹Pa, ²³⁴Pa and ^234mPa. The former occurs as an intermediate decay product of ²³⁵U, while the latter two occur as intermediate decay products of ²³⁸U. ²³¹Pa makes up nearly all natural protactinium.

The primary decay mode for isotopes of Pa lighter than (and including) the most stable isotope ²³¹Pa is alpha decay, except for ²²⁸Pa to ²³⁰Pa, which primarily decay by electron capture to isotopes of thorium. The primary mode for the heavier isotopes is beta minus (β⁻) decay. The primary decay products of ²³¹Pa and isotopes of protactinium lighter than and including ²²⁷Pa are isotopes of actinium and the primary decay products for the heavier isotopes of protactinium are isotopes of uranium.

List of isotopes

Nuclide [n 1]	Historic name	Z	N	Isotopic mass (Da) [4] [n 2] [n 3]	Half-life [1] [n 4]	Decay mode [1] [n 5]	Daughter isotope [n 6]	Spin and parity [1] [n 7] [n 4]	Isotopic abundance
		Excitation energy
210Pa [5]		91	119		6.0+1.5 −1.1 ms	α	206Ac	3+
211Pa		91	120	211.023674(75)	6(3) ms	α	207Ac	9/2−
212Pa		91	121	212.023185(94)	5.8(19) ms	α	208Ac	3+#
213Pa		91	122	213.021100(61)	7.4(24) ms	α	209Ac	9/2−
214Pa		91	123	214.020891(87)	17(3) ms	α	210Ac	7+#
215Pa		91	124	215.019114(89)	14(2) ms	α	211Ac	9/2−
216Pa		91	125	216.019135(26)	105(12) ms	α	212Ac	5+#
217Pa		91	126	217.018309(13)	3.8(2) ms	α	213Ac	9/2−
217mPa		1860(7) keV			1.08(3) ms	α (73%)	213Ac	(23/2−)
						IT (27%)	217Pa
218Pa		91	127	218.020021(19)	108(5) μs	α	214Ac	8−#
218mPa		81(19) keV			150(50) μs	α	214Ac
219Pa		91	128	219.019950(75)	56(9) ns	α	215Ac	9/2−
220Pa		91	129	220.021770(16)	850(60) ns	α	216Ac	1−#
220m1Pa [n 8]		26(23) keV			410(180) ns	α	216Ac
220m2Pa		290(50) keV			260(210) ns	α	216Ac
221Pa		91	130	221.021873(64)	5.9(17) μs	α	217Ac	9/2−
222Pa		91	131	222.023687(93)	3.8(2) ms	α	218Ac	1−#
223Pa		91	132	223.023980(81)	5.3(3) ms	α	219Ac	9/2−
224Pa		91	133	224.0256173(81)	844(19) ms	α (99.9%)	220Ac	(5−)
225Pa		91	134	225.026148(88)	1.71(10) s	α	221Ac	5/2−#
226Pa		91	135	226.027948(12)	1.8(2) min	α (74%)	222Ac	1−#
						β+ (26%)	226Th
227Pa		91	136	227.0288036(78)	38.3(3) min	α (85%)	223Ac	(5/2−)
						EC (15%)	227Th
228Pa		91	137	228.0310508(47)	22(1) h	β+ (98.15%)	228Th	3+
						α (1.85%)	224Ac
229Pa		91	138	229.0320956(35)	1.55(4) d	EC (99.51%)	229Th	5/2+
						α (0.49%)	225Ac
229mPa		12.20(4) keV			420(30) ns	IT	229Pa	3/2−
230Pa		91	139	230.0345397(33)	17.4(5) d	β+ (92.2%)	230Th	2−
						β− (7.8%)	230U
						α (0.0032%)	226Ac
231Pa	Protoactinium	91	140	231.0358825(19)	3.265(20)×104 y	α	227Ac	3/2−	1.0000 [n 9]
						CD (1.34×10−9%)	207Tl 24Ne
						SF (<3×10−10%)	(various)
						CD (~10−12%) [6]	208Pb 23F
232Pa		91	141	232.0385902(82)	1.32(2) d	β−	232U	(2−)
233Pa		91	142	233.0402465(14)	26.975(13) d	β−	233U	3/2−	Trace [n 10]
234Pa	Uranium Z	91	143	234.0433056(44)	6.70(5) h	β−	234U	4+	Trace [n 11]
234mPa	Uranium X2 Brevium	79(3) keV			1.159(11) min	β− (99.84%)	234U	(0−)	Trace [n 11]
						IT (0.16%)	234Pa
235Pa		91	144	235.045399(15)	24.4(2) min	β−	235U	3/2−
236Pa		91	145	236.048668(15)	9.1(1) min	β−	236U	1(−)
						β−, SF (6×10−8%)	(various)
237Pa		91	146	237.051023(14)	8.7(2) min	β−	237U	1/2+
238Pa		91	147	238.054637(17)	2.28(9) min	β−	238U	3−#
						β−, SF (2.6×10−6%)	(various)
239Pa		91	148	239.05726(21)#	1.8(5) h	β−	239U	1/2+#
This table header & footer: view

1. ^mPa – Excited nuclear isomer.
2. ( ) – Uncertainty (1σ) is given in concise form in parentheses after the corresponding last digits.
3. # – Atomic mass marked #: value and uncertainty derived not from purely experimental data, but at least partly from trends from the Mass Surface (TMS).
4. # – Values marked # are not purely derived from experimental data, but at least partly from trends of neighboring nuclides (TNN).
5. Modes of decay:

   EC:	Electron capture
   CD:	Cluster decay
   IT:	Isomeric transition
   SF:	Spontaneous fission

6. Bold italics symbol as daughter – Daughter product is nearly stable.
7. ( ) spin value – Indicates spin with weak assignment arguments.
8. Order of ground state and isomer is uncertain.
9. Intermediate decay product of ²³⁵U
10. Intermediate decay product of ²³⁷Np
11. Intermediate decay product of ²³⁸U

Protactinium-230

Protactinium-230 has 139 neutrons and a half-life of 17.4 days. Most of the time (92%), it undergoes beta plus decay to ²³⁰Th, with a minor (8%) beta-minus decay branch leading to ²³⁰U. It also has a very rare (.003%) alpha decay mode leading to ²²⁶Ac. ^[7] It is not found in nature because its half-life is short and it is not found in the decay chains of ²³⁵U, ²³⁸U, or ²³²Th. It has a mass of 230.034541 u.

Protactinium-230 is of interest as a progenitor of uranium-230, an isotope that has been considered for use in targeted alpha-particle therapy (TAT). It can be produced through proton or deuteron irradiation of natural thorium. ^[8]

Protactinium-231

Protactinium-231 is the longest-lived isotope of protactinium, with a half-life of 32,760 years. In nature, it is found in trace amounts as part of the actinium series, which starts with the primordial isotope uranium-235; the equilibrium concentration in uranium ore is 46.55 ²³¹Pa per million ²³⁵U. In nuclear reactors, it is one of the few long-lived radioactive actinides produced as a byproduct of the projected thorium fuel cycle, as a result of (n,2n) reactions where a fast neutron removes a neutron from ²³²Th or ²³²U, and can also be destroyed by neutron capture, though the cross section for this reaction is also low.

A solution of protactinium-231

binding energy: 1759860 keV
beta decay energy: −382 keV

spin: 3/2−
mode of decay: alpha to ²²⁷Ac, also others

possible parent nuclides: beta from ²³¹Th, EC from ²³¹U, alpha from ²³⁵Np.

Protactinium-233

Protactinium-233 is also part of the thorium fuel cycle. It is an intermediate beta decay product between thorium-233 (produced from natural thorium-232 by neutron capture) and uranium-233 (the fissile fuel of the thorium cycle). Some thorium-cycle reactor designs try to protect Pa-233 from further neutron capture producing Pa-234 and U-234, which are not useful as fuel.

Protactinium-234

Protactinium-234 is a member of the uranium series with a half-life of 6.70 hours. It was discovered by Otto Hahn in 1921. ^[9]

Protactinium-234m

Protactinium-234m is a member of the uranium series with a half-life of 1.17 minutes. It was discovered in 1913 by Kazimierz Fajans and Oswald Helmuth Göhring, who named it brevium for its short half-life. ^[10] It is now believed that all decays of the parent theorium-234 produce this isomer ^[11] and the ground state is observed because of (invisible) IT decay.

References

1. 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.
2. "Standard Atomic Weights: Protactinium". CIAAW. 2017.
3. 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. (2022-05-04). "Standard atomic weights of the elements 2021 (IUPAC Technical Report)". Pure and Applied Chemistry. doi:10.1515/pac-2019-0603. ISSN   1365-3075.
4. Wang, Meng; Huang, W.J.; Kondev, F.G.; Audi, G.; Naimi, S. (2021). "The AME 2020 atomic mass evaluation (II). Tables, graphs and references*". Chinese Physics C. 45 (3): 030003. doi:10.1088/1674-1137/abddaf.
5. Zhang, M. M.; Wang, J. G.; Ma, L.; Gan, Z. G.; Zhang, Z. Y.; Huang, M. H.; Yang, H. B.; Yang, C. L.; Andreyev, A. N.; Yuan, C. X.; Tian, Y. L.; Wang, Y. S.; Wang, J. Y.; Qiang, Y. H.; Wu, X. L.; Xu, S. Y.; Zhao, Z.; Huang, X. Y.; Li, Z. C.; Zhou, H.; Zhang, X.; Xie, G.; Zhu, L.; Guan, F.; Zheng, J. H.; Sun, L. C.; Li, Y. J.; Yang, H. R.; Duan, L. M.; Lu, Z. W.; Huang, W. X.; Sun, L. T.; He, Y.; Xu, H. S.; Niu, Y. F.; He, X. T.; Ren, Z. Z.; Zhou, S. G. (29 May 2025). "Discovery of the α-emitting isotope 210Pa". Nature Communications. 16 (1): 5003. doi:10.1038/s41467-025-60047-2. ISSN   2041-1723. PMC   12123024 . Retrieved 1 June 2025.
6. Bonetti, R.; Guglielmetti, A. (2007). "Cluster radioactivity: an overview after twenty years" (PDF). Romanian Reports in Physics. 59: 301–310. Archived from the original (PDF) on 19 September 2016.
7. Audi, G.; Kondev, F. G.; Wang, M.; Huang, W. J.; Naimi, S. (2017). "The NUBASE2016 evaluation of nuclear properties" (PDF). Chinese Physics C. 41 (3): 030001. Bibcode:2017ChPhC..41c0001A. doi:10.1088/1674-1137/41/3/030001.
8. Mastren, T.; Stein, B.W.; Parker, T.G.; Radchenko, V.; Copping, R.; Owens, A.; Wyant, L.E.; Brugh, M.; Kozimor, S.A.; Noriter, F.M.; Birnbaum, E.R.; John, K.D.; Fassbender, M.E. (2018). "Separation of protactinium employing sulfur-based extraction chromatographic resins". Analytical Chemistry. 90 (11): 7012–7017. doi:10.1021/acs.analchem.8b01380. ISSN   0003-2700. OSTI   1440455. PMID   29757620.
9. Fry, C., and M. Thoennessen. "Discovery of the Actinium, Thorium, Protactinium, and Uranium Isotopes." January 14, 2012. Accessed May 20, 2018. https://people.nscl.msu.edu/~thoennes/2009/ac-th-pa-u-adndt.pdf.
10. "Human Health Fact Sheet - Protactinium" (PDF). Argonne National Laboratory (ANL). November 2001. Retrieved 17 October 2023.
11. ENSDF analysis available at National Nuclear Data Center. "NuDat 3.0 database". Brookhaven National Laboratory.

• Isotope masses from:
  • Audi, Georges; Bersillon, Olivier; Blachot, Jean; Wapstra, Aaldert Hendrik (2003), "The NUBASE evaluation of nuclear and decay properties", Nuclear Physics A, 729: 3–128, Bibcode:2003NuPhA.729....3A, doi:10.1016/j.nuclphysa.2003.11.001
• Isotopic compositions and standard atomic masses from:
  • de Laeter, John Robert; Böhlke, John Karl; De Bièvre, Paul; Hidaka, Hiroshi; Peiser, H. Steffen; Rosman, Kevin J. R.; Taylor, Philip D. P. (2003). "Atomic weights of the elements. Review 2000 (IUPAC Technical Report)". Pure and Applied Chemistry . 75 (6): 683–800. doi: 10.1351/pac200375060683 .
  • Wieser, Michael E. (2006). "Atomic weights of the elements 2005 (IUPAC Technical Report)". Pure and Applied Chemistry . 78 (11): 2051–2066. doi: 10.1351/pac200678112051 .
• "News & Notices: Standard Atomic Weights Revised". International Union of Pure and Applied Chemistry. 19 October 2005.
• Half-life, spin, and isomer data selected from the following sources.
  • Audi, Georges; Bersillon, Olivier; Blachot, Jean; Wapstra, Aaldert Hendrik (2003), "The NUBASE evaluation of nuclear and decay properties", Nuclear Physics A, 729: 3–128, Bibcode:2003NuPhA.729....3A, doi:10.1016/j.nuclphysa.2003.11.001
  • National Nuclear Data Center. "NuDat 3.0 database". Brookhaven National Laboratory.

• • Holden, Norman E. (2004). "11. Table of the Isotopes". In Lide, David R. (ed.). CRC Handbook of Chemistry and Physics (85th ed.). Boca Raton, Florida: CRC Press. ISBN   978-0-8493-0485-9.