Synchrotron μ‐XRF study on compositional uniformity of uranium–thorium oxide pellets prepared by different processes

A μ‐XRF study to assess the distribution of uranium and thorium in (U,Th)O₂ pellets covering the composition of advanced heavy water reactor (AHWR) fuel pellets prepared by powder metallurgical compaction (PMC) and coated agglomerate pelletization (CAP) routes was made using micro‐focus beam line (BL‐16) of Indus‐2 synchrotron radiation facility. The methodology thus developed was successfully applied to these pellets. The study reveals that the uranium distribution in pellets prepared by PMC route is uniform, whereas the pellets prepared through CAP route have a wide range of compositional variation. In addition, the uniformity in CAP route‐prepared pellets improves with increase in the relative amount of uranium in the pellets. The sample preparation in present methodology is very simple compared with scanning electron microscopy. The study reveals the utility of synchrotron‐based μ‐XRF for fuel pellet characterization of AHWR reactors. Alhough CAP route of fuel pellet preparation requires less exposure of personnel to high radiation dose, the non‐uniformity in the fuel pellet must be considered when using these pellets in reactors. Copyright © 2014 John Wiley & Sons, Ltd.     

Event-to-Event Fluctuation Analysis for Pions and Protons at SPS Energy

This study reports a detailed analysis of spatial fluctuations as well as event-to-event fluctuations of compound hadrons (pions + protons) produced in ³²S–AgBr interactions at 200 AGeV with a new technique known as erraticity analysis. This analysis is done for both emission-angle and azimuthal-angle phase spaces using gap-moment method. The study provides a strong evidence of erratic behavior of compound hadrons in ultra-relativistic nuclear collisions.     

Broadband second harmonic generation in a tapered isotropic semiconductor slab using total internal reflection quasi phase matching

This paper analytically describes the concept of enhancing the bandwidth of second-harmonic generation in the mid-infrared region in an isotropic tapered semiconductor slab configuration. In this slab geometry, the lengths between successive reflection points due to total internal reflection of the incident laser radiation increase when it propagates through the slab. A computer aided simulation has been carried out to determine the possibility of generating broadband second harmonic intensity for broadband fundamental laser radiations as they are allowed to undergo total internal reflection inside the tapered isotropic semiconductor crystal slab made of either gallium arsenide (GaAs) or zinc selenide (ZnSe). The simulated results indicate wide 3 dB bandwidths of 187 nm and 196 nm in a 30 mm long tapered slab of GaAs and ZnSe respectively. The conversion efficiency, after considering the absorption and reflection losses, is quite satisfactory (≈ 1%). The effects of variations in temperature, incident angle of the fundamental laser radiations at the air-slab interface, length and tapering angle of the semiconductor slab have been studied for generated second harmonic radiations in both GaAs and ZnSe crystals. Optimising these parameters a wider broadband frequency converter with appreciable conversion efficiency can be designed.     

Density functional calculations on triply excited states of lithium isoelectronic sequence

Triply excited states of many-electron atomic systems are characterized by the presence of strong electron correlation, closeness to more than one threshold, and degeneracy with many continua; therefore, they offer unusual challenges to theoretical methodologies. In the present article, we computed with reasonable accuracy all the n=2 intrashell triply excited states (2s²2p ²P; 2s2p^{2 2}D, ⁴P, ²P, ²S; and 2p^{3 2}D, ²P, ⁴S) of three-electron atomic systems (Z=2, 3, 4, 6, 8, 10) by using a density functional formalism developed recently in our laboratory, based on the nonvariational Harbola–Sahni exchange potential in conjunction with a parametrized local Wigner and Lee–Yang–Parr correlation potentials. Nonrelativistic energies and densities are obtained by solving a Kohn–Sham-type differential equation. The calculated results are compared with available experimental and other theoretical data. The 2p³(⁴S)→1s2p²(⁴P) transition wavelength for the isoelectronic series is also computed. The overall good agreement of our results with the literature data indicates the reliability of the present density functional methodology for excited states of many-electron systems. © 1997 John Wiley & Sons, Inc. Int J Quant Chem 65 : 317–332, 1997     

Alkylation of phenol: a mechanistic view

The current work utilizes the ab initio density functional theory (DFT) to develop a molecular level of the mechanistic understanding on the phenol alkylation in the presence of a cation-exchange resin catalyst, Amberlyst-15. The catalyst is modeled with the benzene sulfonic acid, and the effect of this acid on olefins such as isopropene (i-Pr) and tributene (t-Bu) in a phenol solution mimics the experimental condition. A neutral-pathway mechanism is established to account for early-stage high concentration of the phenolic ether observed in experiments. The mechanism involves an exothermic reaction between olefin and the benzene sulfonic acid to form ester followed by three reaction pathways leading to direct O-alkylation, o-C-alkylation, and p-C-alkylation. Our calculations conclude that O-alkylation to form the phenolic ether is the most energetically favorable in the neutral condition. An ionic rearrangement mechanism describes intramolecular migrations of the alkyl group from the phenolic ether to form C-alkylphenols, while the positively charged protonation significantly lowers transition barriers for these migrations. The ionic rearrangement mechanism accounts for high yields of o-C-alkylphenol and p-C-alkylphenol. Competition between the H atom and the alkyl R group at the substitutive site of the protonated ortho configuration is found to be the determining factor to the ortho/para ratio of C-alkylation products.     

A highly stereospecific synthesis of (E)-α,β-unsaturated esters

CrCl₂-induced olefination of aldehydes using methyl dichloroacetate exclusively generates (E)-α,β-unsaturated esters in excellent yields. The intermediate α-chloro-β-hydroxy adducts could also be isolated in good yields under conditions of limited reagent.     

Langmuir-Blodgett films of p-terphenyl in different matrices: evidence of dual excimer

Langmuir-Blodgett (LB) films at different mole fractions of p-terphenyl have been prepared using two different matrices, viz., stearic acid (SA) and polymethyl methacrylate (PMMA). Multilayered LB films have been formed by changing various LB parameters namely, mole fraction of mixing, changing the number of layers as well as also the different surface pressure of lifting. The spectroscopic characteristics of mixed LB films, solution and microcrystal have been compared using UV-vis absorption and steady state fluorescence spectroscopy. Change of planarity of TP molecules are occurred while going from solution to solid states/films. Fluorescence spectra of the mixed LB films reveal intense excimeric emission in the mixed LB films with D1 excimer peak at 397 nm and D2 excimer peak at 412 nm. Various LB parameters namely changing the number of layers as well as the different surface pressure of lifting played important roles in the formation of dual excimeric sites in the mixed LB films.     

Kinetics of γ-Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> nanoparticle evolution from an organic precursor

-Fe₂O₃ particles with an average size of 10 nm were prepared by heating the precipitates obtained from a homogeneous solution of stearic acid and hydrated iron (III) nitrate. The compositional and thermal characteristics of the precipitates were studied with the aid of Fourier transform infrared (FT-IR) spectroscopy and differential scanning calorimetry (DSC). Presence of -Fe₂O₃ nanoparticles in the heat treated product was established by X-ray diffraction (XRD) investigations. The average particle size was estimated from the XRD patterns by single line profile analysis and directly from transmission electron microscopic (TEM) images. Kinetic analysis of the calorimetric data revealed that nucleation and growth type kinetic law remain operative during the process and the activation energy of the process is 115 kJ/mol.