Isotopes of protactinium

Actinides				Half-life	Fission products
²⁴⁴Cm	²⁴¹Pu ^f	²⁵⁰Cf	²⁴³Cm^f	10–30 y	¹³⁷Cs	⁹⁰Sr	⁸⁵Kr
²³²U ^f		²³⁸Pu	f is for fissile	69–90 y			¹⁵¹Sm nc➔
4n	²⁴⁹Cf ^f	²⁴²Am^f	f is for fissile	141–351	No fission product has half-life 10² to 2×10⁵ years
4n	²⁴¹Am		²⁵¹Cf ^f	431–898
²⁴⁰Pu	²²⁹Th	²⁴⁶Cm	²⁴³Am	5–7 ky
4n	²⁴⁵Cm^f	²⁵⁰Cm	²³⁹Pu ^f	8–24 ky
	²³³U ^f	²³⁰Th	²³¹Pa	32–160
	4n+1	²³⁴U	4n+3	211–290	⁹⁹Tc		¹²⁶Sn	⁷⁹Se
²⁴⁸Cm	4n+1	²⁴²Pu		340–373	Long-lived fission products
	²³⁷Np	4n+2		1–2 My	⁹³Zr	¹³⁵Cs nc➔
²³⁶U	4n+1		²⁴⁷Cm^f	6–23 My		¹⁰⁷Pd	¹²⁹I
²⁴⁴Pu				80 My	>7%	>5%	>1%	>.1%
²³²Th		²³⁸U	²³⁵U ^f	0.7–12 Gy	fission product yield

Protactinium (Pa) has no stable isotopes. There are three naturally occurring isotopes, allowing a standard mass to be given.

Standard atomic mass: 231.03588(2) u

29 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 that are less than 1.6 days, and the majority of these have half-lives that are less than 1.8 seconds. This element also has 3 meta states, ^217mPa (t_½ 1.15 milliseconds), ^229mPa (t_½ 420 nanoseconds), and ^234mPa (t_½ 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 Pa lighter than (and including ²²⁷Pa) are isotopes of actinium and the primary decay products for the heavier isotopes of Pa are isotopes of uranium.

1 Protactinium-230
2 Protactinium-231
3 Protactinium-233
4 Table
- 4.1 Notes
5 References

Protactinium-230

Protactinium-230 has 139 neutrons and a half-life of 17.4 days. It undergoes beta-minus decay to ²³⁰U. It is not found in nature because its half-life is so short and it is not found in the decay chains of ²³⁵U, ²³⁸U, or ²³²Th. It has a mass of 230.034541 grams/mole.

Protactinium-231

Transmutation in the thorium fuel cycle
²³⁰Th	→	²³¹Th	←	²³²Th	→	²³³Th		(White actinides: t_½<27d)
		↓				↓
		²³¹Pa	→	²³²Pa	←	²³³Pa	→	²³⁴Pa		(Colored : t_½>68y)
		↑		↓		↓		↓
		²³¹U	←	²³²U	↔	²³³U	↔	²³⁴U	↔	²³⁵U	↔	²³⁶U	→	²³⁷U
				↓		↓				↓				↓
		(Fission products with t_½<90y or t_½>200ky)												²³⁷Np

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.

Table

nuclide symbol	historic name	Z(p)	N(n)	isotopic mass (u)	half-life	decay mode(s)^[1]^{[n 1]}	daughter isotope(s)^{[n 2]}	nuclear spin	representative isotopic composition (mole fraction)	range of natural variation (mole fraction)
nuclide symbol	historic name	excitation energy			half-life	decay mode(s)^[1]^{[n 1]}	daughter isotope(s)^{[n 2]}	nuclear spin	representative isotopic composition (mole fraction)	range of natural variation (mole fraction)
²¹²Pa		91	121	212.02320(8)	8(5) ms [5.1(+61-19) ms]			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
²¹⁶Pa		91	125	216.01911(8)	105(12) ms	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+#
^217mPa		1860(7) keV			1.08(3) ms	IT (rare)	²¹⁷Pa	29/2+#
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-
²¹⁹Pa		91	128	219.01988(6)	53(10) ns	β⁺ (5×10⁻⁹%)	²¹⁹Th	9/2-
²²⁰Pa		91	129	220.02188(6)	780(160) ns	α	²¹⁶Ac	1-#
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
²²³Pa		91	132	223.02396(8)	5.1(6) ms	β⁺ (.001%)	²²³Th
²²⁴Pa		91	133	224.025626(17)	844(19) ms	α (99.9%)	²²⁰Ac	5-#
²²⁴Pa		91	133	224.025626(17)	844(19) ms	β⁺ (.1%)	²²⁴Th	5-#
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
²²⁶Pa		91	135	226.027948(12)	1.8(2) min	β⁺ (26%)	²²⁶Th
²²⁷Pa		91	136	227.028805(8)	38.3(3) min	α (85%)	²²³Ac	(5/2-)
²²⁷Pa		91	136	227.028805(8)	38.3(3) min	EC (15%)	²²⁷Th	(5/2-)
²²⁸Pa		91	137	228.031051(5)	22(1) h	β⁺ (98.15%)	²²⁸Th	3+
²²⁸Pa		91	137	228.031051(5)	22(1) h	α (1.85%)	²²⁴Ac	3+
²²⁹Pa		91	138	229.0320968(30)	1.50(5) d	EC (99.52%)	²²⁹Th	(5/2+)
²²⁹Pa		91	138	229.0320968(30)	1.50(5) d	α (.48%)	²²⁵Ac	(5/2+)
^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)×10⁴ a	α	²²⁷Ac	3/2-	1.0000^{[n 3]}
						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-)
²³²Pa		91	141	232.038592(8)	1.31(2) d	EC (.003%)	²³²Th	(2-)
²³³Pa		91	142	233.0402473(23)	26.975(13) d	β^-	²³³U	3/2-
²³⁴Pa	Uranium Z	91	143	234.043308(5)	6.70(5) h	β^-	²³⁴U	4+	Trace^{[n 4]}
²³⁴Pa	Uranium Z	91	143	234.043308(5)	6.70(5) h	SF (3×10⁻¹⁰%)	(various)	4+	Trace^{[n 4]}
^234mPa	Uranium X₂ Brevium	78(3) keV			1.17(3) min	β^- (99.83%)	²³⁴U	(0-)	Trace^{[n 4]}
						IT (.16%)	²³⁴Pa
						SF (10⁻¹⁰%)	(various)
²³⁵Pa		91	144	235.04544(5)	24.44(11) min	β^-	^235mU	(3/2-)
²³⁶Pa		91	145	236.04868(21)	9.1(1) min	β^-	²³⁶U	1(-)
²³⁶Pa		91	145	236.04868(21)	9.1(1) min	β^-, SF (6×10⁻⁸%)	(various)	1(-)
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-)#
²³⁸Pa		91	147	238.05450(6)	2.27(9) min	β^-, SF (2.6×10⁻⁶%)	(various)	(3-)#
²³⁹Pa		91	148	239.05726(21)#	1.8(5) h	β^-	²³⁹U	(3/2)(-#)
²⁴⁰Pa		91	149	240.06098(32)#	2# min	β^-	²⁴⁰U

^ Abbreviations:
CD: Cluster decay
EC: Electron capture
IT: Isomeric transition
SF: Spontaneous fission
^ Stable isotopes in bold
^ Intermediate decay product of ²³⁵U
^ ^a ^b Intermediate decay product of ²³⁸U

Notes

Values marked # are not purely derived from experimental data, but at least partly from systematic trends. Spins with weak assignment arguments are enclosed in parentheses.
Uncertainties are given in concise form in parentheses after the corresponding last digits. Uncertainty values denote one standard deviation, except isotopic composition and standard atomic mass from IUPAC which use expanded uncertainties.

References

^ http://www.nucleonica.net/unc.aspx

Isotope masses from:
- G. Audi, A. H. Wapstra, C. Thibault, J. Blachot and O. Bersillon (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. http://www.nndc.bnl.gov/amdc/nubase/Nubase2003.pdf.
Isotopic compositions and standard atomic masses from:
- J. R. de Laeter, J. K. Böhlke, P. De Bièvre, H. Hidaka, H. S. Peiser, K. J. R. Rosman and P. D. P. Taylor (2003). "Atomic weights of the elements. Review 2000 (IUPAC Technical Report)". Pure and Applied Chemistry 75 (6): 683–800. doi:10.1351/pac200375060683. http://www.iupac.org/publications/pac/75/6/0683/pdf/.
- M. E. Wieser (2006). "Atomic weights of the elements 2005 (IUPAC Technical Report)". Pure and Applied Chemistry 78 (11): 2051–2066. doi:10.1351/pac200678112051. http://iupac.org/publications/pac/78/11/2051/pdf/. Lay summary.
Half-life, spin, and isomer data selected from the following sources. See editing notes on this article's talk page.
- G. Audi, A. H. Wapstra, C. Thibault, J. Blachot and O. Bersillon (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. http://www.nndc.bnl.gov/amdc/nubase/Nubase2003.pdf.
- National Nuclear Data Center. "NuDat 2.1 database". Brookhaven National Laboratory. http://www.nndc.bnl.gov/nudat2/. Retrieved September 2005.
- N. E. Holden (2004). "Table of the Isotopes". In D. R. Lide. CRC Handbook of Chemistry and Physics (85th ed.). CRC Press. Section 11. ISBN 978-0849304859.

Isotopes of thorium	Isotopes of protactinium	Isotopes of uranium
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