Isotopes of protactinium

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

Main isotopes of protactinium (₉₁Pa)

Iso­tope Decay abun­dance half-life (t1/2) mode pro­duct ^229Pa syn 1.5 d ε ^229Th ^230Pa syn 17.4 d ε ^230Th ^231Pa 100% 3.276×10^4 y α ^227Ac ^232Pa syn 1.31 d β^− ^232U ^233Pa trace 26.967 d β^− ^233U ^234Pa trace 6.75 h β^− ^234U ^234mPa trace 1.17 min β^− ^234U
Standard atomic weight Ar, standard(Pa)	231.03588(2)[1]

Thirty radioisotopes of protactinium have been characterized, with the most stable being 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, which occurs as an intermediate decay product of ²³⁵U, ²³⁴Pa and ^234mPa, both of which 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) [n 2][n 3]	Half-life [n 4]	Decay mode [n 5]	Daughter isotope [n 6]	Spin and parity [n 7][n 4]	Natural abundance (mole fraction)
		Excitation energy							Normal proportion	Range of variation
^211Pa[2]		91	120		3.8(+4.6−1.4) ms	α	^207Ac	9/2−#
^212Pa		91	121	212.02320(8)	8(5) ms [5.1(+61−19) ms]	α	^208Ac	7+#
^213Pa		91	122	213.02111(8)	7(3) ms [5.3(+40−16) ms]	α	^209Ac	9/2−#
^214Pa		91	123	214.02092(8)	17(3) ms	α	^210Ac
^215Pa		91	124	215.01919(9)	14(2) ms	α	^211Ac	9/2−#
^216Pa		91	125	216.01911(8)	105(12) ms	α (80%)	^212Ac
						β^+ (20%)	^216Th
^217Pa		91	126	217.01832(6)	3.48(9) ms	α	^213Ac	9/2−#
^217mPa		1860(7) keV			1.08(3) ms	α	^213Ac	29/2+#
						IT (rare)	^217Pa
^218Pa		91	127	218.020042(26)	0.113(1) ms	α	^214Ac
^219Pa		91	128	219.01988(6)	53(10) ns	α	^215Ac	9/2−
						β^+ (5×10^−9%)	^219Th
^220Pa		91	129	220.02188(6)	780(160) ns	α	^216Ac	1−#
^220m1Pa[3]		34(26) keV			308(+250-99) ns	α	^216Ac
^220m2Pa[3]		297(65) keV			69(+330-30) ns	α	^216Ac
^221Pa		91	130	221.02188(6)	4.9(8) µs	α	^217Ac	9/2−
^222Pa		91	131	222.02374(8)#	3.2(3) ms	α	^218Ac
^223Pa		91	132	223.02396(8)	5.1(6) ms	α	^219Ac
						β^+ (.001%)	^223Th
^224Pa		91	133	224.025626(17)	844(19) ms	α (99.9%)	^220Ac	5−#
						β^+ (.1%)	^224Th
^225Pa		91	134	225.02613(8)	1.7(2) s	α	^221Ac	5/2−#
^226Pa		91	135	226.027948(12)	1.8(2) min	α (74%)	^222Ac
						β^+ (26%)	^226Th
^227Pa		91	136	227.028805(8)	38.3(3) min	α (85%)	^223Ac	(5/2−)
						EC (15%)	^227Th
^228Pa		91	137	228.031051(5)	22(1) h	β^+ (98.15%)	^228Th	3+
						α (1.85%)	^224Ac
^229Pa		91	138	229.0320968(30)	1.50(5) d	EC (99.52%)	^229Th	(5/2+)
						α (.48%)	^225Ac
^229mPa		11.6(3) keV			420(30) ns			3/2−
^230Pa		91	139	230.034541(4)	17.4(5) d	β^+ (91.6%)	^230Th	(2−)
						β^− (8.4%)	^230U
						α (.00319%)	^226Ac
^231Pa	Protoactinium	91	140	231.0358840(24)	3.276(11)×10^4 y	α	^227Ac	3/2−	1.0000[n 8]
						CD (1.34×10^−9%)	^207Tl ^24Ne
						SF (3×10^−10%)	(various)
						CD (10^−12%)	^208Pb ^23F
^232Pa		91	141	232.038592(8)	1.31(2) d	β^−	^232U	(2−)
						EC (.003%)	^232Th
^233Pa		91	142	233.0402473(23)	26.975(13) d	β^−	^233U	3/2−	Trace[n 9]
^234Pa	Uranium Z	91	143	234.043308(5)	6.70(5) h	β^−	^234U	4+	Trace[n 10]
						SF (3×10^−10%)	(various)
^234mPa	Uranium X2 Brevium	78(3) keV			1.17(3) min	β^− (99.83%)	^234U	(0−)	Trace[n 10]
						IT (.16%)	^234Pa
						SF (10^−10%)	(various)
^235Pa		91	144	235.04544(5)	24.44(11) min	β^−	^235U	(3/2−)
^236Pa		91	145	236.04868(21)	9.1(1) min	β^−	^236U	1(−)
						β^−, SF (6×10^−8%)	(various)
^237Pa		91	146	237.05115(11)	8.7(2) min	β^−	^237U	(1/2+)
^238Pa		91	147	238.05450(6)	2.27(9) min	β^−	^238U	(3−)#
						β^−, SF (2.6×10^−6%)	(various)
^239Pa		91	148	239.05726(21)#	1.8(5) h	β^−	^239U	(3/2)(−#)
^240Pa		91	149	240.06098(32)#	2# min	β^−	^240U

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:

   CD:	Cluster decay
   EC:	Electron capture
   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. Intermediate decay product of ²³⁵U
9. Intermediate decay product of ²³⁷Np
10. Intermediate decay product of ²³⁸U

Actinides and fission products

Actinides and fission products by half-life
Actinides[4] by decay chain				Half-life range (a)	Fission products of ^235U by yield[5]
4n	4n+1	4n+2	4n+3
						4.5–7%	0.04–1.25%	<0.001%
^228Ra^№				4–6 a	†		^155Eu^þ
^244Cm^ƒ	^241Pu^ƒ	^250Cf	^227Ac^№	10–29 a		^90Sr	^85Kr	^113mCd^þ
^232U^ƒ		^238Pu^ƒ	^243Cm^ƒ	29–97 a		^137Cs	^151Sm^þ	^121mSn
^248Bk[6]	^249Cf^ƒ	^242mAm^ƒ		141–351 a	No fission products have a half-life in the range of 100–210 ka ...
	^241Am^ƒ		^251Cf^ƒ[7]	430–900 a
		^226Ra^№	^247Bk	1.3–1.6 ka
^240Pu	^229Th	^246Cm^ƒ	^243Am^ƒ	4.7–7.4 ka
	^245Cm^ƒ	^250Cm		8.3–8.5 ka
			^239Pu^ƒ	24.1 ka
		^230Th^№	^231Pa^№	32–76 ka
^236Np^ƒ	^233U^ƒ	^234U^№		150–250 ka	‡	^99Tc^₡	^126Sn
^248Cm		^242Pu		327–375 ka			^79Se^₡
				1.53 Ma		^93Zr
	^237Np^ƒ			2.1–6.5 Ma		^135Cs^₡	^107Pd
^236U			^247Cm^ƒ	15–24 Ma			^129I^₡
^244Pu				80 Ma	... nor beyond 15.7 Ma[8]
^232Th^№		^238U^№	^235U^ƒ№	0.7–14.1 Ga
Legend for superscript symbols ₡  has thermal neutron capture cross section in the range of 8–50 barns ƒ  fissile m  metastable isomer №  primarily a naturally occurring radioactive material (NORM) þ  neutron poison (thermal neutron capture cross section greater than 3k barns) †  range 4–97 a: Medium-lived fission product ‡  over 200 ka: Long-lived fission product

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.[9] 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 nautral thorium.[10]

Protactinium-231

Transmutations in the thorium fuel cycle
														^237Np
														↑
		^231U	←	^232U	↔	^233U	↔	^234U	↔	^235U	↔	^236U	→	^237U
		↓		↑		↑		↑
		^231Pa	→	^232Pa	←	^233Pa	→	^234Pa
		↑				↑
^230Th	→	^231Th	←	^232Th	→	^233Th
Nuclides with a yellow background in italic have half-lives under 30 days Nuclides in bold have half-lives over 1,000,000 years Nuclides in red frames are fissile

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.

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.[11]

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.[12] About 99.8% of decays of ²³⁴Th produce this isomer instead of the ground state (t_1/2 = 6.70 hours).[12]

References

1. Meija, Juris; et al. (2016). "Atomic weights of the elements 2013 (IUPAC Technical Report)". Pure and Applied Chemistry. 88 (3): 265–91. doi:10.1515/pac-2015-0305.
2. Auranen, K (3 September 2020). "Exploring the boundaries of the nuclear landscape: α-decay properties of 211Pa". Physical Review C. 102 (034305). doi:10.1103/PhysRevC.102.034305. Retrieved 17 September 2020.
3. Huang, T.H.; et al. (2018). "Identification of the new isotope ²²⁴Np" (pdf). Physical Review C. 98 (4): 044302. Bibcode:2018PhRvC..98d4302H. doi:10.1103/PhysRevC.98.044302.
4. Plus radium (element 88). While actually a sub-actinide, it immediately precedes actinium (89) and follows a three-element gap of instability after polonium (84) where no nuclides have half-lives of at least four years (the longest-lived nuclide in the gap is radon-222 with a half life of less than four days). Radium's longest lived isotope, at 1,600 years, thus merits the element's inclusion here.
5. Specifically from thermal neutron fission of U-235, e.g. in a typical nuclear reactor.
6. Milsted, J.; Friedman, A. M.; Stevens, C. M. (1965). "The alpha half-life of berkelium-247; a new long-lived isomer of berkelium-248". Nuclear Physics. 71 (2): 299. Bibcode:1965NucPh..71..299M. doi:10.1016/0029-5582(65)90719-4.
   "The isotopic analyses disclosed a species of mass 248 in constant abundance in three samples analysed over a period of about 10 months. This was ascribed to an isomer of Bk²⁴⁸ with a half-life greater than 9 [years]. No growth of Cf²⁴⁸ was detected, and a lower limit for the β⁻ half-life can be set at about 10⁴ [years]. No alpha activity attributable to the new isomer has been detected; the alpha half-life is probably greater than 300 [years]."
7. This is the heaviest nuclide with a half-life of at least four years before the "Sea of Instability".
8. Excluding those "classically stable" nuclides with half-lives significantly in excess of ²³²Th; e.g., while ^113mCd has a half-life of only fourteen years, that of ¹¹³Cd is nearly eight quadrillion years.
9. 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.
10. 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. PMID 29757620.
11. 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.
12. http://hpschapters.org/northcarolina/NSDS/Protactinium.pdf

• 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. Lay summary.
• 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 2.x 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.