Nuclides with atomic number of 91 but with different mass numbers
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]
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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.
^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.
^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.
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