Americium and Curium: Radionuclides

Abstract

Following the element plutonium, americium and curium are the sixth and seventh elements in the actinide series. The primordial americium and curium isotopes that formed during the creation of the solar system billions of years ago have decayed away. Today, residual amounts of americium and curium isotopes present in nature are anthropogenic, originating from human activities such as nuclear weapons testing or nuclear energy generation. All americium and curium isotopes are highly radioactive and pose extreme health hazards to humans, especially when ingested or inhaled. Complexation reactions with environmentally relevant ligands, separation chemistry, the mechanistic studies of the processes that Am(III) and Cm(III) undergo at the solid–liquid interface in nature, and innovative process applications have been the focus of many studies during recent decades. In general, the trivalent oxidation state of americium and curium is the most stable under environmental conditions. As hard cations, the Am 3+ and Cm 3+ ions form strong complexes with hard donor ligands and adsorb readily on surfaces. In the absence of carbonate, hydrolysis leads to sparingly soluble Am(III) and Cm(III) hydroxide complexes. Americium and curium are commonly used in home smoke detectors and for oil‐well logging ( 241 Am), and as radioisotope thermoelectric generators ( 244 Cm).

Study of Aqueous Am(III)-Aliphatic Dicarboxylate Complexes: Coordination Mode-Dependent Optical Property and Stability Changes

“…A major absorption peak of free aqua Am 3+ was detected at 503.0 nm, which corresponds to an electronic transition from J = 0 to J = 6 (Figure S1). 2,27,28 A series of absorption spectra of Am(III) were measured as a function of ligand concentrations. The concentrations of the ligands increased gradually from 0 to the 30−100 mM range, until no further considerable changes in the absorption spectra were observed.…”

“…Eu(III) has the same electronic configurations in the f-orbitals (4f 6 ); however, its ionic radius (r = 94.7 pm) is slightly smaller than that of Am(III) (r = 97.5−109 pm). 2,39 Since coordination chemistry is sensitive to the ionic radius, Nd(III) (r = 98.3 pm), 39 whose ionic radius is closer to that of Am(III), was also examined. The preliminary results showed that Nd(III) and Eu(III) exhibited almost identical behaviors in the IR experiments (data not shown).…”

“…Americium is one of the most concerned actinides in the field of nuclear waste management because the long-term radiotoxicity of americium is ranked second after plutonium. 1,2 To ensure safe disposal of the spent nuclear fuel, it is necessary to have a comprehensive understanding of the geochemical behaviors of these actinides. 3 As one of the main routes that enhance the mobility of Am in nature, complexations with organic ligands have been actively studied.…”