Authors:K. Reddy, M. Reddy, Ch. Reddy, P. Reddy, and K. Reddy
Radon and thoron have been identified as potential radiological health hazard and the dose estimation due to their exposure
is an important task. Understanding their behavior in indoor environment helps in calculating the inhalation doses due to
them. Present study aims at the distribution of radon and thoron concentrations in a typical Indian dwelling. Solid state
nuclear track detectors are employed in the study. The concentration of radon is found to be invariant in indoor environment.
The thoron concentration is found to decrease exponentially as a function of distance from the source (wall/floor). Solution
of one dimensional diffusion equation is used for regression fittings for thoron variation, from which the diffusion constants
and the exhalation rates were calculated. The diffusion constants varied from 0.00195 to 0.00540 m2 s−1.
Some synergistic effects of antioxidants in natural rubber were investigated considering results obtained by differencial
scanning calorimetry (DSC). Rubber formulations were obtained with mixtures of diaminic(DPPD, IPPD, HPPD) and monoaminic (ADPA,
PBN) stabilizers and evaluated. The samples containing the mixture diamine/ADPA stabilizers showed synergistic effects while,
for those containing diamine/PBN, no effect was observed. Additionally, the diffusion constants determined by use of vulcanized
rubber disks confirmed the molar mass dependence of the stabilizer.
Natural zeolite, clinoptilolite was tested for its ability to remove uranium from aqueous solutions. Influence parameters to the sorption process, such as initial uranium concentration, pH, contact time and temperature were investigated. Distribution coefficients of uranium on clinoptilolite were measured by batch technique. Experimental isotherms evaluated from the distribution coefficients were fit to Langmuir, Freundlich and Dubinin-Radushkevich (D-R) models. Values of ΔH and ΔS were found as 0.93 and 56.09 J/mole, respectively. It was observed that the adsorption process is endothermic. Kinetics of uranium sorption was investigated at different time intervals at 30 °C. The reaction rate and diffusion constant were calculated.
The uptake of thorium from aqueous systems by ignited Sarcotragus muscarum(L. Schmidt, 1864), collected from Kusadasi Region at Southwest of Turkeyas an adsorbent has been investigated. The thorium(IV) uptake was studiedas a function of pH, ion concentration and temperature. At the determinedoptimum conditions, the sorption of thorium on ignited sponge follows a Langmuir-typeisotherm. We assumed that this phenomenon can be a sorption process. Kineticof thorium sorption was investigated at different time intervals at 25, 50and 70 °C. The reaction rate and diffusion constants were calculated forthese temperatures. The activation energy and .H° were found to be –19.04and –5.22 J/mol, respectively.
Authors:A. Cecal, M. Palamaru, S. Chişcâ, and A. Iordan
The paper presents a radiokinetic study on the appearance and growth of*Fe2S3,*Fe(OH)3,*Fe2(C2O4)3,*Fe(IO3)3 crystals in a colloidal medium of agar and gelatine. The values of the diffusion constants through gels of55+59Fe3+ radioactive cations and of the rate of global growth process of these crystals in agar or gelatine were calculated using
the experimental data. A new method for the determination of the starting time for the complex nucleation process was proposed.
The formation rate of crystals under study decreases in the order:*Fe(OH)3>*Fe(IO3)3>*Fe2S3>*Fe2(C2O4)3, in agar medium and*Fe(OH)3>*Fe(IO3)3>*FeC2O4)3>*FeS3, in gelatine medium.
Authors:Hamdy Mohamed, Y. Ito, A. El-Sayed, and E. Abdel-Hady
Positron annihilation lifetime spectra were measured forpolyvinylalcohol (PVA) doped with CuCl2 (0.5 to 5.0 wt%) at temperature range from room temperature to 160°C. For a fresh pure PVA (without annealing)
3 belowTg was larger in the heating runs than in the cooling runs, but aboveTg,
3 was the same for both runs. The larger
3 values in the heating run were considered to be due to the existence of strain brought forth in the process of preparation. For annealed pure PVA
3 was the same for the heating and the cooling runs andTg was shifted to lower temperature, 88 and 80°C for fresh and annealed samples, respectively. This shift was attributed to loss of H-bonded water in the annealed pure PVA by heating above 100°C. BothI30
3 were decreased by the added CuCl2, being interpreted as the result of inhibition and quenching, respectively. The results show that both the inhibition coefficient and the quenching rate constantk were smaller than the corresponding values in liquids. The small diffusion constant ofo-Ps estimated fromk implies thato-Ps is not very mobile in the polymer.
Authors:V. Dragovic, D. Brusic, J. Pospisil, N. Cikovic, J. Uzelac, and V. Lukin
The aim of this study was to examine the influence of different additive contents for oxygen absorption (5, 10 and 15%) in low-density polyethylene (PELD) plastic foils and storage temperatures (4 and 28 °C) on the quality and shelf-life of sliced carrots during storage. Quality and storage-life of packaged carrots slices were determined by observing changes of mass, total carotenoide pigments, microbial counts (mesophilic aerobic bacteria, enterobacteria, sulphite-reducing clostridia, yeast and moulds), sensory quality and texture by the use of penetrometer. The PELD foils modified with 10 and 15% of oxygen absorber (O2, CO2and N2permeability at 4 °C of around 700 ml m-2d-1atm-1) were the most suitable for the storage and prevention of deterioration of minimally processed carrots. Findings indicated that in these foils the best quality and shelf-life of carrot were maintained by 6 days of storage at 4 °C, without significant changes in parameters studied. The absorber for oxygen added to the foil had no influence on the permeability to CO2, O2and N2. The permeability of foils, which were used for carrot packaging increased by the increase of storage temperature to 28 °C and decreased by decreasing the temperature to 4 °C, and was not significantly affected by the additive content either. In the same time the diffusion constants of unused and used PELD foils for carrot packaging at 4 °C and 28 °C changed according to the change of film permeability during storage at those temperatures.
Authors:Kai Zheng Fang, Dao Bin Mu, Shi Chen, Feng Wu, and Xiao Jun Zeng
is decided by the diffusion rate of hydrogen. The diffusion coefficient of hydrogen can be calculated from the equation D = D o exp(− Q / kT ), where Q is activation energy of atomic diffusion, D o is diffusionconstant, and k is Boltzmann
is also slowed down on all length scales. Assuming the common example of “ random walker ” [ 60 – 63 ] and its probability to stay in place (using the standard relation, x 2 ( t ) = 2dDt, where D is the diffusionconstant and d is the dimension