Hoda M. Abou Shady

Abstract Binding mechanisms and leaching characteristics of cesium from different cement–
bentonite immobilization matrices were investigated. The effect of Sr presence as a
competitive contaminant in the matrices was studied by investigating the binding and
leaching mechanisms in binary contaminant matrices that contains both Cs and Sr solutions.
Binding investigations aimed to trace Cs binding mechanisms by calculating the distribution
of contaminant and major structural elements aqueous complexes in the mixing solution ...

Abstract
Neutronic analysis of a typical swimming pool type research reactor, Pakistan research
Reactor-1 (PARR-1), was carried out for determine the effect of graphite reflector
configuration modification as a way to optimize the neutron flux in the irradiation positions.
Standard computer codes WIMSD and CITVAP were employed to calculate core excess
reactivity, neutron fluxes, power distribution, and burn-up distribution. A comparison
between four different core configurations is presented in this article.

During radiotherapy, ionizing irradiation interacts with biological systems to produce free radicals, which attack various cellular components. The hematopoietic system is easily recognized to be radiosensitive and its damage may be severe. Melanin nanoparticles (MNPs) act as free radical scavengers prepared by polymerization of dopamine. In this study, a total of 110 male BALB/C mice were divided into five equal groups. Each group contained 22 mice. Mice of group A did not receive MNPs or irradiation (control group), group B was injected intraperitoneally (i.p.) with 50 mg/kg MNPs. Mice of group C and D were exposed to a dose of 7 Gy ɣ-irradiation and injected with the same dose of MNPs as in group B either 30 min pre- or post-irradiation, and group E was exposed to a dose of 7 Gy ɣ-irradiation only. The impact of MNPs on peripheral blood, spleen, and DNA damage induced by irradiation was evaluated by blood count, histopathology of the spleen, and comet assay for the DNA in the bone marrow at 1, 4, 8, and 12 days post-irradiation. Results of group E compared with control group (A) showed a significant depression in complete blood count. Additionally, histopathological observation showed the absence of megakaryocytes with delayed time post-irradiation, deposition of eosinophilic protein of their spleen appeared, as well as a remarkable decrease in spleen size was observed. Moreover, ɣ-irradiation-induced DNA damage as can be inferred from a significant increase by about 5–10 folds in all comet parameters (% of DNA, tail length, tail moment, and olive moment) in the DNA of the bone marrow. In contrast, pre-post treatment with MNPs protected hematopoietic tissues against radiation damage, and therefore, enhanced the survival of mice with 40 % in groups (C&D) compared with 10 % to group (E) till 30 days post-irradiation. In conclusion, these results demonstrated that synthetic MNPs provide significant radioprotection to the hematopoietic tissues.

The feasibility of immobilizing strontium in cement–bentonite matrices was investigated by studying the effect of mineralogical phase development on mechanical and containment performances. Within this context, the chemical composition and physical properties of bentonite were determined. Different cement–bentonite waste matrices were prepared and analyzed using XRD technique to trace the changes in phases during the curing period. The mechanical performance of these matrices was evaluated by measuring the compressive strength throughout their curing period and the containment performance was determined by conducting long-term static leaching test then the experimental results were checked against some regulatory limits. The results indicated that the presence of strontium and bentonite did not lead to formation of new hydrated phases. The mechanical performance of the matrices is acceptable and the enhanced compressive strength was attributed to the progression in the formation of cement hydrated phases and the pozzolanic reaction between bentonite and lime in cement–bentonite matrices. The speciation data and phase structures analysis indicated that Sr2+ containment in cement might be due to Ca substitution in Ettringite structure and cations exchange on Montmorillonite lattice. The mathematical analysis of the long-term leaching results indicated that strontium leaching resulted from a combination of first order reaction and diffusion mechanisms.

In this paper Neutronic calculation (deterministic approach) has been carried out to characterize the neutron flux in
locations used for isotope production to achieve optimum utilization of the reactor. In neutronic calculations a number of
approximations take place. As a result even if one uses the same codes the results might be different. It is thus of importance
to care about the model used. Comparison between different model and with published experimental results has been done. In
this work three deferent model of the standard fuel has been tested to determine the accurate one, then it used for core
calculation. Calculation of reactivities at deferent cycles, calculation of power densities, neutron flux, and burn-up as well as
search for equilibrium were performed to determine the equilibrium core. Standard computer codes WIMSD-5B and
CITVAP were used.

In the present work, we study the stability of a system designed for the coating of optical fiber. This is achieved by studying the stability of the flowing resin in the die while coupled with a viscoelastic optical fiber. We develop a numerical code based on a sixth-order compact finite-difference method in order to solve the two-dimensional Navier–Stokes equations. We show that there is a bifurcation flow for a given value of the Reynolds number, wherever the vibration of the optical fiber has been experimentally observed. The stability of the resulting flow, coupled with a nonrigid optical fiber, is considered. Two-dimensional and three-dimensional stability analyses were made. The system was found to be subjected to two kinds of instability induced by two distinguishable groups of modes. For an optical fiber with a small radius, we assume that the preceding vibration may not be the only cause of the irregularity in the coating thickness. Therefore, a model taking into account the deformation of the liquid resin surface, under the action of the surface-tension forces, before resin solidification, and after leaving the die, is proposed. This model assumes that the liquid layer is subjected to surface-tension and gravity forces. It was found that the dynamic equation depends on two dimensionless parameters. It is found that the surface of the fiber has a wavy form. The length of the wave depends on the two dimensionless parameters. Our work shows qualitative agreement with the experimental results without adjusting arbitrary constants.

The Coulomb interaction for a spherical—deformed interacting pair is derived assuming realistic nuclear charge distributions. The effect of a finite diffuseness parameter is described either by the folding product of spherical or deformed sharp-surface distribution and a spherical short-range function or by using a Fermi two-parameter distribution function. The approximate solutions obtained using these categories of charge distributions are then compared to the numerical solution obtained within the framework of the double-folding model. We found that the finite surface diffuseness parameter affects slightly the inner region of the total Coulomb potential, while it produces large errors in calculating the Coulomb form factors used frequently in nuclear reactions and fusion numerical codes.

The reaction cross section (σR) is calculated using the optical limit of the Glauber theory. A density-dependent effective nucleon-nucleon (NN) cross section σNN is considered. Finite and zero range NN interactions are studied. The effect of finite range and an appropriate local density can increase σR up to 20% compared to the zero range at constant density (0.16fm−3), while a zero range calculation with free NN cross section increases σR up to 13%. These factors affect the values of the rms radii for neutron rich nuclei extracted from σR.