Radioactive decay solution chemistry

Since transport by water is virtually the only available mechanism for escape, we will be predominantly concerned with the chemistry of aqueous solutions at the interface with inorganic solids - mainly oxides. These will be at ordinary to somewhat elevated temperatures, 20-200 C, because of the heating effects of radioactive decay during the first millennium. The elements primarily of interest (Table I) are the more persistent fission products which occur in various parts of the periodic table, and the actinides, particularly uranium and thorium and, most important of all, plutonium. 

Radon, Rn At. no. 86, at. wt 222, mp—71°C, bp -61.8°C. Radon is an intermediate radioactive decay product of Ra. Rn, the most stable isotope of radon, is obtained as a gas from aqueous solutions of RaCl2 and has been used as a radiation source and as a gaseous tracer. It is a considerable hazard in uranium mines. In some areas, radon in basements and in ground water is a potential health hazard because of its radioactivity. The ground state electronic configuration of radon is [Xe]4f " 5d °6s 6p. Because radon is intensely radioactive, the chemistry of radon has only been investigated on the tracer scale. Radon forms compounds, particularly a fluoride (likely RnF2), and solid adducts between the fluoride and Lewis acid fluorides. 

Neptunium. Np is in a class with Pa no efforts have been made to use it as a fuel solute, but consideration has been given to its formation in and removal from blanket solutions of [30a]. The chemistry of neptunium has been reviewed by Hindman et al. [30b], and the hydrolytic behavior has been reviewed by Kraus [30c]. Continuous separation of Np239 would provide a Pu product of high purity by radioactive decay, whereas plutonium recovered from long-term irradiation of usually contains appreciable amounts of Pu °. Spectrophotometric cells for use at elevated temperatures and pre.ssures in the study of the chemistry of neptunium (and other materials) have recently been developed by Wag-gener [30d] and have been used to measure the absorption spectra of dilute neptunium perchlorate in its six-, five-, four-, and three-valence states, using heavy w ater as the solvent. Dilute solutions of neptunyl nitrate in nitric acid have been so studied at temperatures up to 250°C the pentavalent state was found to be stable under the test conditions [30e]. 

This tiny quantity of material, if prepared as an aqueous solution of volume 1 L, would have a concentration of 10 14 mol/L. This simple calculation demonstrates a number of the important features of radiochemistry, that is, (a) the manipulation of samples involving infinitesimal quantities of material, (b) the power of nuclear analytical techniques (since 1 j.Ci is a significant, easily detectable quantity of radioactivity), and (c) in an extension of the calculation, since the decay of a single atom might occur by a-particle emission (with 100% detection efficiency), the ability to do chemistry one atom at a time. 

---