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
  • 231.04±0.01 (abridged)[2][3]

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

Twenty-nine radioisotopes of protactinium have been characterized, ranging from 211Pa 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 (t1/2 1.15 milliseconds), 220m1Pa (t1/2 = 308 nanoseconds), 220m2Pa (t1/2 = 69 nanoseconds), 229mPa (t1/2 = 420 nanoseconds), and 234mPa (t1/2 = 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[4] 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[5] 34(26) keV 308(+250-99) ns α 216Ac
220m2Pa[5] 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)×104 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)(−#)
This table header & footer:
  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. 1 2 # – 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. 1 2 Intermediate decay product of 238U

Actinides and fission products

Actinides and fission products by half-life
Actinides[6] by decay chain Half-life
range (a)		 Fission products of 235U by yield[7]
4n 4n + 1 4n + 2 4n + 3 4.5–7% 0.04–1.25% <0.001%
228Ra№ 4–6 a 155Euþ
244Cmƒ 241Puƒ 250Cf 227Ac№ 10–29 a 90Sr 85Kr 113mCdþ
232Uƒ 238Puƒ 243Cmƒ 29–97 a 137Cs 151Smþ 121mSn
248Bk[8] 249Cfƒ 242mAmƒ 141–351 a

No fission products have a half-life in the range of 100 a–210 ka ...

241Amƒ 251Cfƒ[9] 430–900 a
226Ra№ 247Bk 1.3–1.6 ka
240Pu 229Th 246Cmƒ 243Amƒ 4.7–7.4 ka
245Cmƒ 250Cm 8.3–8.5 ka
239Puƒ 24.1 ka
230Th№ 231Pa№ 32–76 ka
236Npƒ 233Uƒ 234U№ 150–250 ka 99Tc₡ 126Sn
248Cm 242Pu 327–375 ka 79Se₡
1.53 Ma 93Zr
237Npƒ 2.1–6.5 Ma 135Cs₡ 107Pd
236U 247Cmƒ 15–24 Ma 129I₡
244Pu 80 Ma

... nor beyond 15.7 Ma[10]

232Th№ 238U№ 235Uƒ№ 0.7–14.1 Ga

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.[11] 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.[12]

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.

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.[13]

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.[14] About 99.8% of decays of 234Th produce this isomer instead of the ground state (t1/2 = 6.70 hours).[14]

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; et al. (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. ↑ Auranen, K (3 September 2020). "Exploring the boundaries of the nuclear landscape: α-decay properties of 211Pa". Physical Review C. 102 (34305): 034305. Bibcode:2020PhRvC.102c4305A. doi:10.1103/PhysRevC.102.034305. S2CID 225343089. Retrieved 17 September 2020.
  5. 1 2 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. S2CID 125251822.
  6. ↑ 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.
  7. ↑ Specifically from thermal neutron fission of uranium-235, e.g. in a typical nuclear reactor.
  8. ↑ 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]."
  9. ↑ This is the heaviest nuclide with a half-life of at least four years before the "sea of instability".
  10. ↑ 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.
  11. ↑ 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.
  12. ↑ 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.
  13. ↑ 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.
  14. 1 2 "Human Health Fact Sheet - Protactinium" (PDF). Argonne National Laboratory (ANL). November 2001. Retrieved 17 October 2023.
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