Complexation between variable-valency uranium and organic ligands in solutions, their photostability and spectral identification

Abstract

We discuss possible directions for searching for prospective materials based on low-valency uranium (III-V) as detection media for hard electromagnetic radiation.We have studied the processes of formation of tetravalent and pentavalent uranium complexes from UO 2 (NO 3 ) 3 ⋅6H 2 O and UO 2 Cl 2 ⋅H 2 O in DMF and with addition of CCl 4 , including when the systems are exposed to radiation in the visible range (400-450 nm). In the first case (UO 2 (NO 3 ) 3 ⋅6H 2 O solutions in DMF), upon irradiation we observe stable complexes of pentavalent uranium, and when CCl 4 is added to the solution we observe complexes of tetravalent uranium. In the system UO 2 Cl 2 ⋅3H 2 O in DMF, we do not observe the appearance of new forms of uranium; but when CCl 4 is added, then complexes of tetravalent uranium are formed.Introduction. Rapid development of atomic projects at the end of the last century and the beginning of the current century has stimulated development of the technology for measuring ionizing radiation, including scintillation counters. Over a relatively short time, the major classes of scintillators were discovered and their widespread use began. These also include inorganic materials based on alkali halide compounds. In connection with creation of lasers and development of the technology for high-temperature synthesis of single crystals, it was found that the latter can play an important role as hard radiation detectors. In order to use them for such purposes, first of all problems must be solved concerning the spectroscopy of interconfiguration transitions of elements with a complete inner electron shell, where rare-earth ions have been advocated as such so far. The most promising class of such compounds has proven to be inorganic single crystals activated by Ce 3+ and Pr 3+ , which have good scintillation properties [1]. These ions are characterized by fast 5d-4f luminescence (with decay time on the order of tens of nanoseconds) in the violetultraviolet region of the spectrum (depending on the type of crystal matrix). We should point out that the emission properties of the Pr 3+ ion depend on the position of the d level in the bandgap and are sensitive to the strength and symmetry of the local crystal field. This often leads to the appearance of an additional channel for quenching of luminescence and consequently to limited use of Pr 3+ ions as activator ions. However, in a number of Pr 3+ matrices, intense interconfiguration luminescence is observed with decay times shorter than those typical of Ce 3+ in the same compounds. Such crystal compounds include Y 3 Al 5 O 12 :Pr, YAlO 3 :Pr, Y 2 SiO 5 :Pr, etc. This class of scintillators has been rather well studied so far. The prospects are not good for making new scintillation materials with density higher than 8.5 g/cm 3 and an effective charge higher than 72 within this class.Moreover, our preliminary estimates show that increasing the effective nuclear charge (for example, in U 4+ ions) should lead to a decrease in the energy gap between the 6d and 5f configura...

Photochemical Activity of Uranyl Ion in Acetone Irradiated by Light in the Presence of Metal Cations and Anions

“…Such solutions contain not only radioactive elements (uranium and transuranium elements) but also several stable decay products. The processing solutions also contain large amounts of background metals, e.g., K, Na, Mg, Ca, Al, etc., and several anions, primarily 3 NO − . The typical solution concentrations of macroelements including background materials can be high (several mg/L and greater) [1] so that they must be considered when studying the purifi cation of LRW.…”

“…It forms many oxides containing the doubly charged uranyl cation 2 2 UO + , which is rather stable in chemical reactions and exhibits catalytic properties [2]. Its activity depends on the presence of impurities [3]. Therefore, studies of the kinetics of photochemical reactions involving uranyl in the presence of background elements enable their effects on the transition of uranium from one valence state to another and methods for increasing the catalytic capabilities of uranium during purifi cation of radioactive wastes to be evaluated.…”