Valency stabilization of polyvalent ions during gamma-irradiation of their aqueous solutions by sacrificial protection

The various aspects of valency stabilization of polyvalent ions during -radiolysis have been further investigated. Ce(IV) ions, which are normally reduced in their aqueous solution, were found to be stabilized for increasing periods of time when they were irradiated in the presence of increasing amounts of bromate ions. It was found that the addition of about fifteen times excess of bromate ions to a 10^–3 N Ce(IV) solution stabilized the cerium ions in the tetravalent state for about 120 hours during irradiation at a dose rate of 336 Gy/h. Increasing the amount of bromate used resulted in a subsequent increase in the protection time. It has been also noted that while bromate ions protected Ce(IV) in solution, the latter ions showed a clear protective effect on the bromate used, i.e., there is a mutual protective effect. The probable mechanisms, conditions and limitations of the protection process have been discussed. Based on the data obtained in the present work, it has been suggested that the protection of Ce(IV) ions by bromate ions in aqueous solutions during -radiolysis is very probably due to the preferential interaction of bromate with the reducing radiolysis products of water which are capable of reducing Ce(IV) to Ce(III).     

EPR Studies of Tl0.5Pb0.5Sr1.6Ba0.4CaCu2?xRuxO7?δ Superconductor

Bulk superconducting samples of type Tl_0.5Pb_0.5Sr_1.6Ba_0.4CaCu_2−x Ru _x O_7−δ, (Tl, Pb)/Sr-1212, with 0.0 ≤ x ≤ 0.525 were prepared by the conventional one-step solid-state reaction technique. The prepared samples were investigated using X-ray powder diffraction, electrical resistivity and electron paramagnetic resonance (EPR) measurements. Enhancement of the phase formation, superconducting transition temperature T _c and hole carriers concentration P was observed up to x = 0.075. For x > 0.075, a reverse trend was observed. EPR spectra were measured at different temperatures (120–290 K) for all prepared samples. The number of spins N participating in the resonance and the paramagnetic susceptibility χ were calculated as a function of both Ru-content and temperature. N and χ increased as the Ru-content increased. A linear relationship between logN and 1/T was established, from which the activation energy E _a was calculated as a function of the Ru-content. The temperature dependence of χ was fitted according to Curie–Weiss type of magnetic behavior. Curie constant C, Curie temperature θ, the effective magnetic moment μ and the electronic specific heat γ were estimated as a function of the Ru-content.     

Effect of IR laser radiation on the structure and optical properties of PC-PBT/Pd polymer nanocomposite films

ABSTRACT

Bayfol (PC-PBT blend ?lm) is a class of polymeric solid-state nuclear track detector which has a lot of applications in several radiation detection ?elds. It is a bisphenol-A polycarbonate PC blended with polybutylene terephthalate PBT. Bayfol/Palladium (PC-PBT/Pd) nanocomposite films have been deposited using the molding technique. It is worth mentioning that this report is almost the first one dealing with the topic of the changes of physical properties of Bayfol/Pd nanocomposite due to laser exposure. Samples from PC-PBT/Pd (5?wt%) nanocomposite were exposed to IR-pulsed laser of 5-W power, capable of producing 2000 pulses per second with pulse duration of 200?ns at 904?nm. The laser fluences were in the range 2–25?J/cm². The resultant modi?cations in the exposed nanocomposite samples have been studied as a function of fluence using different characterization techniques such as X-ray diffraction (XRD), UV spectroscopy and color difference studies. The results indicate the proper dispersion of Pd nanoparticles in the PC-PBT matrix that causes a strong intermolecular interaction between Pd and PC-PBT, resulted in an increase in refractive index and the amorphous phase. Also, it is found that the laser exposure reduces the optical energy gap that could be attributed to the increase in structural disorder of the exposed PC-PBT/Pd nanocomposites due to crosslinking. Further, the color intensity ΔE, which is the color difference between the exposed samples and the non-exposed one, was increased with increasing the laser fluence, convoyed by a significant increase in the green and yellow color components.     

In vivo resolution of conflicting in vitro results: synthesis of biotin from dethiobiotin does not require pyridoxal phosphate

The source of the biotin sulfur atom remains a contested point in studies of biotin synthase (BioB) in vitro. Recent reports that BioB has an intrinsic pyridoxal phosphate (PLP)-dependent cysteine desulfurase activity were tested by depleting Escherichia coli cells of PLP. The BioB-dependent conversion of dethiobiotin to biotin proceeded in these cells irrespective of the presence or absence of PLP.