Determination of oxygen to uranium ratio in irradiated uranium dioxide by controlled potential coulometry

This work reports the determination of oxygen to uranium (O/U) ratio in irradiated UO_2+x fuel pellet of burnup of ca. 34 GWd/t by controlled potential coulometry. The method is based on the dissolution of the nuclear fuel in strong phosphoric acid (SPA) at 180–190 °C under an inert atmosphere. After dissolution, 8% sulphuric acid is added in order to obtain a 20% SPA in 8% sulphuric acid. A controlled potential coulometric determination of uranium(VI) is carried out at ?0.60V vs. ferri-ferrocyanide. The uranium(IV) contained in an aliquot of the fuel solution is oxidised to uranium(VI) with cerium(IV) sulphate, and the total uranium content is then determined by coulometry. Optimum experimental conditions have been established using simulated irradiated fuel solution containing various fission products which include cerium, tellurium, palladium, ruthenium, molybdenum and zirconium. Interference of the fission products and the possible removal of their interferences by preelectrolysis at +0.5 V vs. saturated calomel electrode (SCE) have been investigated. The accuracy of the coulometric method is confimed by polarographic measurement using several unirradiated UO_2+x fuel of known stoichiometry.     

Adhesion and debonding of soft elastic films: crack patterns, metastable pathways, and forces

We study the phenomenon of debonding in a thin soft elastic film sandwiched between two rigid plates as one of the plates is brought into intimate contact and then pulled away from contact proximity by application of a normal force. Nonlinear simulations based on minimization of total energy (composed of stabilizing elastic strain energy and destabilizing adhesive interaction energy) are employed to address the problems of contact hysteresis, cavitation, crack morphology, variation of contact area, snap-off distance, pull-off force, work done, and energy loss. Below a critical distance (d(c)) upon approach, simulations show the formation of columnar structures and nonrandom, regularly arranged nanocavities at the soft interface at a length scale of approximately 3h (h being the thickness of the film). The persistence of such instability upon withdrawal (distance >d(c)) indicates a contact hysteresis, which is caused by an energy barrier that separates the metastable states of the patterned configuration and the global minimum state of the flat film. The energy and the pull-off force are found to be nonequilibrium and nonunique properties depending on the initial contact, defects, noise, etc. Three broad pathways of debonding leading to adhesive failure of the interface, depending on the stiffness of the film, step size of withdrawal, and the imposed noise, are identified: a catastrophic column collapse mode, a peeling mode involving a continuous decrease in the contact area, and a column splitting mode. The first two modes are caused by a very high stress concentration near the cavity edges. These metastable patterned configurations engender pull-off forces that are orders of magnitude smaller than that required to separate two flat surfaces from contact.     

Solvent Extraction Separation of Th(IV) and U(VI) with PC-88A

Liquid-liquid extraction of Th(IV) and U(VI) has been investigated by commercial extractant PC-88A in toluene. The optimum conditions for extraction of these metals have been established by studying the various parameters like acid concentration/pH, reagent concentration, diluents and shaking time. The extraction of Th(IV) was found to be quantitative with 0.1–1.0M HNO₃ acid and in the pH range 1.0–4.0 while U(VI) was completely extracted in the pH range 1.0–3.5 with 2.5·10^–2M and 2.·10^–2M PC-88A in toluene, respectively. The probable extracted species have been ascertained by log D-log C plot as ThR₄·4HR and UO₂R₂·2HR, respectively. The method permits separation of Th(IV) and U(VI) from associated metals with a recovery of 99.0%.     

Kinetics and Mechanism of the Reactions of Picolinic Acid with Dichloro-{1-alkyl-2-(arylazo)imidazole}palladium(II) Complexes

The reaction between Pd(N,N′)Cl₂ [N,N′ ≡ 1-alkyl-2-(arylazo)imidazole (N,N′) and picolinic acid (picH) have been studied spectrophotometrically at λ = 463 nm in MeCN at 298 K. The product is [Pd(pic)₂] which has been verified by the synthesis of the pure compound from Na₂[PdCl₄] and picH. The kinetics of the nucleophilic substitution reaction have been studied under pseudo-first-order conditions. The reaction proceeds in a two-step-consecutive manner (A → B → C); each step follows first order kinetics with respect to each complex and picH where the rate equations are: Rate 1 = {k′₀ + k′₂[picH]₀} × [Pd(N,N′)Cl₂] and Rate 2 = {k′′₀ + k′′₂[picH]₀}[Pd(N,O)(monodentate N,N′)Cl₂] such that the first step second order rate constant (k′₂) is greater than the second step second order rate constant (k′′₂). External addition of Cl⁻ (as LiCl) suppresses the rate. Increase in π-acidity of the N,N′ ligand, increases the rate. The reaction has been studied at different temperatures and the activation parameters (Δ^‡H° and Δ^‡S°) were calculated from the Eyring plot.     

One-electron redox reactions of troxerutin in aqueous solutions

The oxidation of flavonoids is of great interest because of their action as antioxidants with the ability to scavenge radicals by means of electron-transfer processes. The redox reactions of the flavonoid derivative troxerutin, (2-[3,4-bis-(2-hydroxyethoxy) phenyl]-3[[6-deoxy-α-L-manno-pyranosyl)-β-(D-glucopyranosyl]-oxy]-5-hydroxy-7-(2-hydroxyethoxy)-4H-1-benzo-pyran-4-one), were investigated over a wide range of conditions, using pulse radiolysis and cyclic voltammetry. The oxidation mechanism proceeds in sequential steps. One-electron redox potentials for troxerutin were found to be +1.196, +0.846 and −0.634 V vs. NHE.     

Magnetic moments and the proton structure function

The EMC collaboration have reported a measurement of the proton structure function which has been interpreted to mean that the spin of the proton is not predominantly that of the quarks (=u+d+s=0.13±0.19). We show that the magnetic moments of the baryons are independent of this measurement and are given (within 10–20%) for a range of including the valence model value =1. The magnetic moments of the quarks can only be fixed if the quantity is determined very accurately.     

Studies on the feasibility of production of57Co by alpha bombardment of Mn and Ni targets

We have studied the feasibility of producing⁵⁷Co (271.3 d) via the⁵⁵Mn(, 2n)⁵⁷Co reaction (⁵⁵Mn–100%). The thick target yield of⁵⁷Co in the 28 to 18 MeV energy region was measured as 3.87 Ci/Ah. However, the proximity and overlap of the excitation functions for (, n), (, 2n) and (, 3n) reactions on⁵⁵Mn are such that the production of pure⁵⁷Co in high yields free of⁵⁸Co (70.8 d) and⁵⁶Co (78.8 d) has not been feasible. We have also studied a new method for ancillary production of⁵⁷Co via the reactions⁵⁸Ni(, p)⁵⁷Co and during the course of producing⁶²Zn by⁶⁰Ni(, 2n)⁶²Zn reaction. In this case the yield of⁵⁷Co of reasonable purity has been up to 1 Ci/Ah.     

Temperature Effects on Attenuation Due to Rain for Millimeter and Centimeter Waves

Radio wave operating in millimetrewave and microwave frequency bands are adversely affected due to rain. Particularly the attenuation is of immense significance for sensitive remote measurements by satellites using frequencies greater than 10 GHz. Maintenance of an uninterrupted communication link requires a precise knowledge of the attenuation effect due to rain for commissioning right kind of transmitting sources for various purposes required in present day situation. Precise measurement of attenuation at various frequencies will enable us to choose the right frequency, polarization, incident angle and power of the source for different purposes. In this paper we have compared the results of earlier works using aR^b Olsen et al, (1) and the formulation by Moupfouma, (2) on the basis of theoretical analysis for explaining the observed results. Effect of temperature, considered in detail in this communication, has contributed the necessary correction factor of the rain attenuation for explaining the observed results. Theoretical analyses to measure the attenuation of the propagating wave due to temperature variation in the rain path have been presented. Correction factor due to temperature profile (temperature from the ground to the rain height within which the radio wave traces its path) has been incorporated in two models by using the concept of dipole energy changes. The effect of this temperature is noted to be quite significant and incorporates an error to the extent of 7–8%.