Uranium absorption spectrum

Examples of this analysis mode are presented in Fig. 5. The slope of the log D versus log[L],i plots for the cobalt(II)-8 M HCl and the Fe(III)-6 M HCl systems indicate the formation of CoClj and FeClj, respectively, as the predominant complexes in the Dowex 1-X8 phase. These results are believed to prove the reliability of this approach, the presence of these complexes in concentrated hydrochloric acid being well documented. The chloride complex of uranium(IV), UClj, v 4iose unique absorption spectrum is shown in Fig. 6 [11], in the HCl, HCIO4 (I = 10 M)... 

Electrochemical investigation of [ThMoi2042] " reveals no stepwise reduction of the anion to isostructural mixed-valence heteropoly blues that is observed for many other POMs, but rather an irreversible multi-electron reduction, correponding to decomposition of the anion [20], This behavior is anticipated for polyoxometalates in which the metal has a m-dioxo environment ( type 11 structure [21]). However, cyclic voltammograms of [UMo 12042] show a reversible one-electron oxidation to the uranium(V) analog [20] at +0.90 vs see at pH 0. The electronic absorption spectrum of the oxidized species has been reported. 

The UV absorption spectrum of the complex uranium(VI) with tributyl phosphate in supercritical carbon dioxide has been examined [5]. The spectra from supercritical fluid extraction were similar to those obtained after extraction of the complex into hexane. 

Absorption spectrum of uranium metal vapor. The absorption spectrum of uranium metal vapor is very complex, with over 300,000 lines at visible wavelengths. However, many of these absorption lines are very sharp, with sufficient displacement between a absorption line and the absorption line for the corresponding transition, and without overlap of the line with the U line for a different transition, to permit selective excitation of the atoms. However, choice of the wavelength most suitable for a practical process is made difficult by the large number of possibilities. Janes et al. [J2] discuss some of the alternatives. 

The absorption spectrum of UF is far more complex even than that of uranium metal, because the spectrum of the UF molecule involves transitions between many vibrational and rotational states that are absent in the uranium atom. Absorption bands of the molecule overlap... 

Figure 17-3< . Usable zone (hatched) in on-line control of uranium(IV) with a 4-cm optical path length probe. 1 Minimum for 10" absorbance 2 maximum for 1.6 absorbance. Example the 600-nm wavelength on the side of the absorption spectrum can be used for a concentration range between 0.1 and 20 gL The reference wavelength for uranium(IV) is at 530 nm.

Therefore, the problems which faced the would-be designers of chain reactors early in 1941 were (1) the choice of the proper moderator to uranium ratio, and (2) the size and shape of the uranium lumps which would most likely lead to a self-sustaining chain reaction, i.e., give the highest multiplication factor. In order to solve these problems, one had to understand the behavior of the fast, of the resonance, and of the thermal neutrons. We were concerned with the second problem which itself consisted of two parts. The first was the measurement of the characteristics of the resonance lines of isolated uranium atoms, the second, the composite effect of this absorption on the neutron spectrum and total resulting absorption. One can liken the first task to the measurement of atomic constants, such as molecular diameter, the second one, to the task of kinetic gas theory which obtains the viscosity and other properties of the gas from the properties of the molecules. The first task was largely accomplished by Anderson and was fully available to us when we did our work. Anderson s and Fermi s work on the absorption of uranium, and on neutron absorption in general, also acquainted us with a number of technics which will be mentioned in the third and fourth of the reports of this series. Finally, Fermi, Anderson, and Zinn carried out, in collaboration with us in Princeton, one measurement of the resonance absorption. This will be discussed in the third article of this series. 

The ions can be separated from the neutrals by electric fields, which collect them into a Faraday cup. This technique has been used, for example, for the separation of atoms in the gas phase by resonant two-photon ionization with copper-vapor laser-pumped dye lasers at high repetition frequencies [1429]. Since the line density in the visible absorption spectrum of is very high, the lasers are crossed perpendicularly with a cold collimated beam of uranium atoms in order to reduce the line density and the absorption linewidth. 

Karraker measured the electronic absorption spectrum of dimeric uranium penta-ethoxide and the weak narrow bands observed at 5405, 5680, 6622, 6934, 10200, 11 690, and 14 490 cm" have been assigned to f-f transitions for a distorted octahedral f system with a spin-orbit coupling constant of 1905 cm. ... 

At present it is only possible to speculate on the nature of that new uranium species formed. The spectra observed are very similar to the absorption spectrum of UOCI3 (reported in a petroleum mull [2] Figure 6.13.3b). It is therefore possible that the monooxouranium(V) chloro-species may be formed under certain conditions in chloride melts according to one of the following reactions ... 

The majority of the photochemical studies with actinide ions have been carried out with the uranyl (UC ion. This ion is yellow in color both in the solid and solution states. The early photochemistry of this ion has been reviewed. " Excitation of this ion results in an LMCT absorption that involves a transition from an essentially nonbonding 7r-orbital on oxygen into an empty 5/orbital on uranium. This LMCT assignment is that given to the weak visible bands in the absorption spectrum at 500 nm and 360 nm. The absorption spectrum also shows a series of bands of increasing intensity to higher energy. The positions of the absorption bands of are very sensitive to both temperature and the chemical environment... 

Tris[bis(trimethylsilyl)amido]uranium is an extremely air- and moisture-sensitive, red-purple solid, which can be stored for months in the absence of air and moisture without noticeable signs of decomposition. It is soluble in both aliphatic and aromatic hydrocarbons. The NMR spectrum in benzene- (250 MHz, 20°C) shows a single broad resonance at d — 11.5.11 The compound sublimes readily at 80°C under good vacuum (10 6 torr). The checkers report a melting point of 137-140°C. The IR spectrum, recorded as a Nujol mull between KBr plates, has absorptions at 1248(s), 1170(w), 990(s), 860(s), 828(s), 764(m), 676(m), 654(m), and 598(m) cm1. Other physicochemical properties are described in the literature.4... 

The methods range from simple, inexpensive absorption spectroscopy to sophisticated tunable-laser-excited fluorescence and ionization spectroscopies. AAS has been used routinely for uranium and thorium determinations (see for example Pollard et al., 1986). The technique is based on the measurement of absorption of light by the sample. The incident light is normally the emission spectrum of the element of interest, generated in a hollow-cathode lamp. For isotopes with a shorter half life than and Th, this requires construction of a hollow-cathode lamp with significant quantities of radioactive material. Measurement of technetium has been demonstrated in this way by Pollard et al. (1986). Lawrenz and Niemax (1989) have demonstrated that tunable lasers can be used to replace hollow-cathode lamps. This avoids the safety problems involved in the construction and use of active hollow-cathode lamps. Tunable semiconductor lasers were used as these are low-cost devices. They do not, however, provide complete coverage of the spectral range useful for AAS and the method has, so far, only been demonstrated for a few elements, none of which were radionuclides. 

For thorium there are only estimates of the corresponding potential. An early estimate, of -2.4 V, was based on a relation between this quantity and the frequency of the first electron transfer absorption band in the UV spectrum of an aqueous thorium perchlorate solution (9). However, the spectral measurements did not quite reach the absorption maximum, and the necessary extrapolation introduced some uncertainty. Another value, -3.6 V, was based on the RESPET treatment of J0rgensen (10,11). The adjustable parameters in the RESPET equation were fixed using experimental values for other actinide elements (12). This method yields a value of -0.69 V for U(IV)/(III). Another rather simple method correlates this potential with the number of 5/"electrons for the element and gives -3.41 V for thorium and -0.54 V for uranium (13). A more sophisticated estimate (14), using a method proposed by Nugent et al. (12) (described later), gave -3.8 V for thorium. 

This technique depends on the fact that the three uranium L x-rays, which accompany 25% of all 23sp decays, are of slightly differing energies and therefore have different absorption coefficients in the limestone. Figure 2 shows the spectrum of these L x-rays observed through several samples of wet limestone. These were thin measured slices of the limestone which were interposed as absorbers between a source of 238p radiation and the detector. The ratio of the intensities of the L1/L2 x-rays decreases with the thickness of the stone similarly the L3/L2 ratio increases with thickness. It is a simple matter to calibrate... 

No emission lines have been observed in the spectrum of either thorium or uranium that correspond to the other absorption differences contained in the table. 

In the absorption spectra reported in Ref. 34 also a band peaking at 5.8 eV has been observed. In the excitation spectrum of the uranate luminescence of uranium-doped Li3Nb04 a band is observed at 4.6 eV ). We feel that these features may also be due to charge transfer transitions involving uranium 6 d orbitals. Our persent re-... 

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