Chemicals/Actinides

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).^[1]

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.^[1]

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.^[2]