Protactinium-231

Main isotopes of protactinium

iso NA half-life DM DE (MeV) DP 229Pa syn 1.5 d ε 0.311 229Th 230Pa syn 17.4 d ε 1.310 230Th 231Pa 100% 3.276×104 y α 5.150 227Ac 232Pa syn 1.31 d β− 1.337 232U 233Pa trace 26.967 d β− 0.5701 233U 234Pa trace 6.75 h β− 2.195 234U 234mPa trace 1.17 min β− 2.29 234U
Standard atomic weight (Ar)	7002231035880000000♠231.03588(2)

Protactinium (₉₁Pa) has no stable isotopes. There are three naturally occurring isotopes, allowing a standard mass to be given.

Twenty-nine 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_1/2 1.15 milliseconds), ^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.

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

... nor beyond 15.7 M years

Legend for superscript symbols
₡  has thermal neutron capture cross section in the range of 8–50 barns
ƒ  fissile
m  metastable isomer
№  naturally occurring radioactive material (NORM)
þ  neutron poison (thermal neutron capture cross section greater than 3k barns)
†  range 4–97 y: Medium-lived fission product
‡  over 200,000 y: Long-lived fission product

...
Wikipedia