[en] This paper summarizes the present status of research which is currently underway at several US Department of Energy laboratories - Rockwell Hanford Operations, Mound Facility, and Sandia Laboratories, Albuquerque - to explore the properties and characteristics of two inorganic sorbents, bone char (a form of calcium hydroxyapatite) and sodium titanate [Na(Ti₂O₅H)], in decontaminating liquid waste streams from actinides and in separating americium and curium from lanthanides. Success in this research might lead to a potential breakthrough in plant-scale application of inorganic exchangers in actinide separation schemes

[en] Techniques of stepwise laser excitation and photoionization have been applied to study spectroscopic properties of neutral atoms of lanthanides and actinides. The spectroscopic properties that can be determined include: the ionization potential, energy levels, isotope shifts, hyperfine structure, lifetimes of energy levels, branching ratios and oscillator strengths. We discuss the laser methods used to obtain these properties (with emphasis on ionization potentials) and give examples of results obtained for each. The ionization potentials obtained by laser techniques are in eV: Ce, 5.5387 (4); Pr, 5.464 (12); Nd, 5.5250 (6); Sm, 5.6437(6); Eu, 5.6704(3); Gd, 6.1502(6); Tb, 5.8639(6); Dy, 5.9390(6); Ho, 6.0216(6); Er, 6.1077(10); U, 6.1941(5) and Np, 6.2657(6). Regularities in the f/sup N/s² - f/sup N/s ionization limits for the lanthanides have been found as a result of these accurate values and previously known accurate values for the others. Multistep photoionization has been employed for laser isotope separation and for studies of autoionization. 16 figures, 7 tables

[en] In the present article, studies carried out in our laboratory on the effects of visible irradiation and O₂ in a variety of target systems ranging from cultured mammalian cells to purified catalase are reviewed. We will relate these studies of photooxidative damage to a scheme for the propagation of intracellular damage which traces a number of the possible pro-oxidant and anti-oxidant pathways found in the cell

[en] After almost twenty years of work on the hypersensitive transitions, their origins are far from clear. In addition to the mechanisms discussed, others have been introduced from time to time. The effect of charge transfer may not be negligible, though its importance has been discounted by Peacock. It may be that different mechanisms play roles of varying importance from system to system; but until more experimental and theoretical work is carried out the question must remain open

[en] Conclusions regarding these shifts toward greater stabilization of 5f orbitals with increasing atomic number are mainly supported by the appearance of the divalent oxidation state well before the end of the actinide series and the predominance of the divalent state in the next to last element in the series. These conclusions and the underlying experimental evidence are the main subject of this review

[en] A class of sequestering agents has been designed and synthesized for the specific role of complexing plutonium and other actinide (IV) ions. The chemical properties of Pu(IV) and Fe(III) are similar in many respects and this similarity extends to the biological transport and distribution properties of Pu(IV). The design of specific sequestering agents for FE(III) was solved by microbes a few billion years ago with the production of low molecular-weight chelating agents (siderophores) that incorporate chelating groups such as hydroxamic acids and catechol. Synthetic macrochelates have been designed such that the chelating groups can form a cavity that gives eight-coordination about the metal and the dodecahedral geometry observed in the unconstrained actinide complexes composed of monomeric ligands. The most promising actinide sequestering agents yet prepared are the sulfonated catechoylamide derivatives of linear tetraamines. These compounds appear to strongly bind tetravalent actinides, while only weak complexation has been observed for trivalent and divalent metals. A derivative of the natural product spermine, 3,4,3-LICAMS, is more effective in plutonium removal at low dosages than any other sequestering agent tested to date

[en] The polymerization of Pu(IV) hydrolysis products in aqueous nitric acid solutions containing uranyl nitrate has been examined as a function of pH, temperature, and concentration. Even in the absence of the uranyl solute, an induction period usually follows the polymer growth stage during which time formation of primary hydrolysis products occurs. Uranyl nitrate retards the polymerization rate by approximately 35% in spite of the counteracting influence of the nitrate ions associated with this solute; evidence is presented to demonstrate that the uranyl ion attaches through hydroxyl bridges to active sites in the polymer network and functions as a chain-terminating unit. The rate of polymer growth has been shown to be third order with respect to Pu(IV). 7 references, 4 figures, 2 tables

[en] The physicochemical properties of actinide metals confirm the presence of band-like 5f electrons up to Pu. The participation of these 5f electrons in the metallic bond is assumed to begin with Pa. In the first half of the actinide series, 5f electrons are similar to d electrons in typical transition metals: the 5f electron orbitals are more extended than 4f orbitals; for the light actinides, 5f electrons are delocalized and hybridized in a rather large band with 6d and/or 7s electrons. Starting with Am, te 5f electrons are localized again, like 4f electrons in the lanthanides

[en] A conceptual flow sheet for the pyrometallurgical reprocessing of thorium-based fuels has been presented which meets current concerns abpout nonproliferation and waste control. Preliminary results indicate the desired process streams, uranium/thorium and plutonium/thorium, can be obtained using actinide solubility differences in cadmium-magnesium alloys and that salt waste can be minimized by electrolyzing CaO produced during the reduction process and recycling the calcium. However, further optimization of conditions controlling the reduction rate must be achieved before the process can be used for oxide fuels

[en] The first isolation of a chemical compound of plutonium (a fluoride) took place on August 20, 1942 and the first weighing of a pure compound (2.77 micrograms of the dioxide) on September 10, 1942. Thus this Symposium marks quite precisely the 40th anniversary of these events, the beginnings of the investigation of the macroscopic (non-tracer) chemical properties of this important synthetic element. The immediately following ultramicrochemical studies led to a definition of the IV and VI oxidation states, some properties of the metallic state, the synthesis and characterization of numerous solid compounds and the crucial testing of the first method devised for its separation and isolation in pure form after its production in nuclear chain reaction. Later work with larger amounts, available as the result of its production in a nuclear reactor, made it possible to characterize the III and V oxidation states and many more compounds. 7 references, 6 figures