The actinide elements are actinium (Ac), thorium (Th), protactinium (Pa), uranium (U), neptunium (Np), plutonium (Pu), americium (Am), curium (Cm), berkelium (Bk), californium (Cf), einsteinium (Es), fermium (Fm), mendelevium (Md), nobelium (No), and lawrencium (Lr). These have been reacted with a number of other elements.
The diagram at the second down on the right shows the unit cell of thorium diiodide.
The diagram on the left shows the unit cell of β-ThI3.
The third diagram down on the right shows the unit cell of ThI4.
Twenty-nine radioisotopes of protactinium have been discovered, the most stable being 231Pa with a half-life of 32,760 years, 233Pa with a half-life of 27 days, and 230Pa with a half-life of 17.4 days; all of the remaining isotopes have half-lives shorter than 1.6 days, and the majority of these have half-lives less than 1.8 seconds; and two nuclear isomers, 217mPa (half-life 1.2 milliseconds) and 234mPa (half-life 1.17 minutes).
The primary decay mode for isotopes of protactinium lighter than (and including) the most stable isotope 231Pa (i.e., 212Pa to 231Pa) is alpha decay and the primary mode for the heavier isotopes (i.e., 232Pa to 240Pa) is beta decay, with primary decay products of isotopes of protactinium lighter than (and including) 231Pa are actinium isotopes and the primary decay products for the heavier isotopes of protactinium are uranium isotopes.
Protactinium is one of the rarest and most expensive naturally occurring elements, found in the form of two isotopes – 231Pa and 234Pa, with the isotope 234Pa occurring in two different energy states: nearly all natural protactinium is protactinium-231, an alpha emitter formed by the decay of uranium-235, whereas the beta radiating protactinium-234 is produced as a result of uranium-238 decay. Nearly all uranium-238 (99.8%) decays first to the shorter-lived 234mPa isomer.
- Audi, Georges; Bersillon, Olivier; Blachot, Jean; Wapstra, Aaldert Hendrik (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
- "Protactinium, Human Health Fact Sheet" (PDF). Argonne National Laboratory. August 2005. Retrieved 7 March 2008.