No abstract available

[en] A spectrophotometric method for the determination of thorium with arsenazo III (1,8 dihidrozynaphtalene 3,6 sulfanic acid 2,7 bis (azo-2) phenyl arsonic acid) was developed for the analysis of this element in environmental samples. In order to eliminate possible interferences, a coprecipitation with lantanium fluoride was used followed by an extration with 0,2M TTA (tenoyltrifluoroacetone)/benzene. The results are in agreement with those obtained by alfa-spectrometry. (Author)

[en] A new rapid method for the determination of actinides in food samples has been developed at the Savannah River Site Environmental Lab (Aiken, SC, USA) that can be used for emergency response or routine food samples. If a radiological dispersive device or improvised nuclear device event occurs, there will be a urgent need for rapid analyzes of many different environmental matrices, as well as food samples, to support dose mitigation and protect general populations from radioactivity that may enter the food chain. The recent accident at Fukushima nuclear power plant in March, 2011 reinforces the need to have rapid analyzes for radionuclides in environmental and food samples. The new method to determine actinides in food samples utilizes a furnace ashing step, a rapid sodium hydroxide fusion method, a lanthanum fluoride matrix removal step, and a column separation process with stacked TEVA, TRU, and DGA resin cartridges. The furnace ashing and rapid fusion steps are performed in relatively inexpensive, reusable zirconium crucibles. Alpha emitters are prepared using rare earth micro precipitation for counting by alpha spectrometry. The method showed high chemical recoveries and effective removal of interferences. The determination of actinides in food samples can be performed in less than 8 h for 10 g samples with excellent quality for emergency samples using short count times. Larger food samples (100 g) may be processed in 24 h or less. The rapid fusion technique is a rugged sample digestion method that ensures that any refractory actinide particles are effectively digested. This method can be used to meet the derived intervention level guidelines recommended by the U.S. Food and Drug Administrations. (author)

[en] Dephasing rate 1/T₂ in the optical Bloch equations doesn’t depend on Rabi frequency $\chi =Ed/\hslash$. It seemed true for various mechanisms responsible for optical dephasing processes. In this paper we show that entanglement of nuclear spin with electronic transition in an atom results in dependence of $1/T_2$ on $\chi$. Rate $1/T_2(\chi )$ decreases if $\chi$ increases. This effect is able to explain experimental data on free-induction decay measured in Pr₃⁺:LaF₃ crystal.

[en] Experiments on the observation of optical superradiance in a LaF₃:Pr³⁺ crystal are described. The multipulse regime of excitation of optical superradiance in both two- and multilevel systems is theoretically investigated. It is demonstrated that this regime is the generalization of the triggering regime of superradiance excitation. The developed formalism is used for the description of gamma superradiance

No abstract available

[en] The emissive properties of fluorescent and laser materials demonstrate a marked dependence on the equilibrium phonon population, in the form of a temperature dependence of the optical linewidths (dephasing time). Under conditions of pulsed excitation a nonequilibrium phonon population an be generated which can effect not only the spectral distribution of the optical emission but also the lifetime of the transition. In this work the effect of dephasing of the ³H₄-³P₄ transition in LaF₃:Pr³⁺ by a non-equilibrium phonon population is investigated. A nonequilibrium phonon population is generated using far infrared (FIR) radiation to pump a low lying electronic state which can then relax by the emission of resonant phonons. The effect of nonequilibrium phonon populations on the dephasing time in this case the nonequilibrium phonon were generated using resonant optical pumping

[en] One investigated both experimentally and theoretically into spike structure of spontaneous radiation of praseodymium ions in LaF₃ matrix at ³P₀-³H₆ transition frequency under coherent pulse excitation of ³H₄-³P₀ contact transition. The experimental results are in line with the theoretical calculations based on the analysis of radiation dynamics of the excited group of three-level systems in the mean field approximation. The spike structure generation is interpreted as a cnoidal wave pulse radiation. The recorded random nature of time intervals between spikes reflects sensitivity of cnoidal wave period to fluctuations within the system. One revealed the relation of the elaborated theory with determinate chaotic dynamics models

[en] The purposes of the work are to fabricate novel environment-friendly water-based polyamide-imide (PAI)-graphite-LaF₃ bonded solid-lubricating coatings (BSLCs), and investigate the corresponding tribological properties and mechanisms. The experimental results reveal that the preparation of the water-based PAI-graphite-LaF₃ BSLCs has significantly reduced the usage of organic solvent. When the mass percent of nano-LaF₃ is 5 wt%, the water-based PAI-graphite-LaF₃ BSLCs exhibit superior mechanical and tribological properties, which are comparable to those of the reported organic-solvent-based BSLCs. The tribological mechanisms were systematically investigated concerning the failure mechanism, the tribological reactions and structural fluctuations of graphite.

No abstract available