In the present study, the effect of size distribution of magnetite nanoparticles in a PVDF matrix on the magnetic properties of PVDF ? Fe 3 O 4 nanocomposites was experimentally and theoretically investigated. The size distribution of nanoparticles in polymer matrix and morphology of the nanocomposites were studied by the means of scanning electron microscopy and atomic force microscopy. It was found that when the Fe 3 O 4 nanoparticles are introduced into the polymer matrix, their coagulation takes place. The increase in the size of the particles depends on their concentration in the polymer matrix, the type of polymer (polar, non-polar, its viscosity, etc.), reaction temperatures, etc. In addition, when Fe 3 O 4 nanoparticles are introduced into the polymer network, the oxidation of the surface layer of particles occurs and the magnetic size decreases. Consequently, the reduced magnetic properties may also be observed. The hysteresis loops have been recorded in small magnetic field range. It was found that the magnetic hysteresis parameters depend on the size and concentration of Fe 3 O 4 nanoparticles. Theoretical calculations were compared with experimental results obtained from M(H) measurements. The reasons of differences between theoretical and experimental results have been explained.
In vivo dosimetry was carried out for 152 patients receiving external beam radiotherapy and the treatment sites were divided into two main groups: Thorax, Abdomen, and Pelvic (120 fields) and Head and Neck (52 fields). Combined entrance and exit dose measurements were performed using LiF: Mg, Cu, P thermoluminescent dosimeters (TLDs). Water-equivalent (effective) thicknesses and target dose were evaluated using dose transmission data. The ratio of measured to expected value for each quantity was considered as an indicator for the accuracy of the parameter. The average ratio of the entrance dose was evaluated as 1.01 ± 0.07. In the diameter measurement, the mean ratio of effective depth divided by the contour depth is 1.00 ± 0.13 that shows a wide distribution which reflects the influence of contour inaccuracies as well as tissue inhomogeneities. At the target level, the mean ratio of measured to the prescribed dose is 1.00 ± 0.07. According to our findings, the difference between effective depth and patient depth has a direct relation to target dose discrepancies. There are some inevitable sources which may cause the difference. Evaluation and application of effective diameter in treatment calculations would lead to a more reliable target dose, especially for fields which involve Thorax, Abdomen, and Pelvic.
In order to study the vertical migration of anthropogenic 137 Cs, soil inventories of this radionuclide were measured in two regions selected on the basis of a previous comprehensive survey in the northern Iranian province of Guilan located in the South Caspian region. Ten sampling stations were randomly chosen in these regions and split-level sampling was carried out to a depth of 30 cm. Sample analysis was performed using a HPGe detector system. In situ gamma measurements in both regions were also carried out with the aid of a portable germanium spectrometer. The experimental data were then compared with the solution of the convectiondispersion equation (
One of the most problematic elements of radiation therapy is the determination of contour data or treatment depth which may vary due to various parameters. The provision of this data is crucial for treatment calculations and setup. The present study is devoted to the assessment of discrepancies between the water equivalent (effective) diameter and patient diameter of the dose delivered to the target. Combined entrance and exit dose measurements were carried out on patients treated for thorax, abdomen, and pelvic cancers by 60Co gamma rays, using silicon diodes. The effective diameter and target dose were evaluated on the basis of dose transmission data. Our study reveals that the most influential parameter leading to discrepancies in target dose delivery is the difference between effective depth and patient depth. A difference of more than 5% in the target dose is bound to happen when the difference between the effective and contour diameters is greater than 10%. Therefore, using the effective diameter for treatment calculations provides a more realistic value of the target dose, since it incorporates the impact of all contributing factors
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