Protactinium longest lived isotope

The 4 + 3 chain is the only one that (barely) includes every element from uranium to thallium. Although included, francium and especially astatine are very minor components. The parent, 704 X 10 year has a half-life considerably smaller than the 4,500 x 10 year age of the Earth. It is long enough for significant amounts (0.720% of the atoms in natural uranium) to remain. The chain includes by far the longest-lived isotopes of protactinium (32.8 x 10 year Pa) and actinium (21.77 year Ac). 

The longest living isotope of protactinium is with a half-life of 32 000 years. Typically, it occurs in aqueous solution in the pentavalent state, although the tetravalent state is also known. The aqueous form of protactiniumfV) is the PaO ion, and only monomeric hydrolysis species have been identified, PaOOH " to PaO(OH)3(aq). There is some conjecture over whether the tetravalent ion occurs as Pa " or PaO " ". No conclusive data have been published on protactinium(IV) hydrolysis species. 

The actinium decay series consists of a group of nuclides whose mass number divided by 4 leaves a remainder of 3 (the 4n + 3 series). This series begins with the uranium isotope which has a half-life of 7.04 X 10 y and a specific activity of 8 X 10 MBq/kg. The stable end product of the series is ° Pb, which is formed after 7 a- and 4 /3-decays. The actinium series includes the most important isotopes of the elements protactinium, actinium, ftancium, and astatine. Inasmuch as U is a conqx>nmt of natural uranium, these elem ts can be isolated in the processing of uranium minerals. The longest-lived protactinium isotope, Pa (ti 3.28 X 10 y) has been isolated on the 100 g scale, and is the main isotope for the study of protactinium chemistry. Ac (t 21.8 y) is the longest-lived actinium isotope. 

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