Isotopes of protactinium

Protactinium (Pa)
Standard atomic mass: 231.03588(2) u
The element has no stable isotopes. However, it has a characteristic terrestrial isotopic composition and thus an atomic mass can be given.

Isotopes of protactinium occurring within the radioactive disintegration chain of uranium were known as:

• uranium X₂ or brevium : ^234mPa
• uranium Z : ²³⁴Pa

Older names for the element included eka-tantalum and brevium (the first discovered isotope of protoactinium).

29 radioisotopes of protactinium have been characterized, with the most stable being 231-Pa with a half life of 32760 years, 233-Pa with a half-life of 26.967 days, and 230-Pa with a half-life of 17.4 days. All of the remaining radioactive isotopes have half-lifes that are less than 1.6 days, and the majority of these have half lifes that are less than 1.8 seconds. This element also has 2 meta states, 217m-Pa (t_½ 1.15 milliseconds) and 234m-Pa (t_½ 1.17 minutes).

The primary decay mode for isotopes of Pa lighter than (and including) the most stable isotope 231-Pa (ie, ²¹²Pa to 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 (ie, ²³²Pa to ²⁴⁰Pa) is beta minus (β⁻) decay. The primary decay products of 231-Pa and isotopes of Pa lighter than (and including 227-Pa) are element Ac (actinium) isotopes and the primary decay products for the heavier isotopes of Pa are element U (uranium) isotopes.

Table

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

• Isotope masses from Ame2003 Atomic Mass Evaluation by G. Audi, A.H. Wapstra, C. Thibault, J. Blachot and O. Bersillon in Nuclear Physics A729 (2003).
• Isotopic compositions and standard atomic masses from Atomic weights of the elements. Review 2000 (IUPAC Technical Report). Pure Appl. Chem. Vol. 75, No. 6, pp. 683–800, (2003) and Atomic Weights Revised (2005).
• Half-life, spin, and isomer data selected from these sources. Editing notes on this article's talk page.
  • Audi, Bersillon, Blachot, Wapstra. The Nubase2003 evaluation of nuclear and decay properties, Nuc. Phys. A 729, pp. 3–128 (2003).
  • National Nuclear Data Center, Brookhaven National Laboratory. Information extracted from the NuDat 2.1 database (retrieved Sept. 2005).
  • David R. Lide (ed.), Norman E. Holden in CRC Handbook of Chemistry and Physics, 85th Edition, online version. CRC Press. Boca Raton, Florida (2005). Section 11, Table of the Isotopes.