فهرست مطالب m.r. rashidian vaziri

Poly (methyl methacrylate) (PMMA) is an inexpensive polymer widely used in different applications such as the fabrication of optical tools, sensors, and microfluidic medical devices. In the present study, the effect of emitted radiations from a Cobalt-60 gamma source with emission doses between 10-30 kGy on the optical properties of this polymer is investigated. The effect of gamma radiation on optical transmission and absorption, bandgap energy, Urbach energy, dispersive energies, and refractive index of this polymer is investigated, and the obtained results are presented. The results indicate that the absorption coefficient, the refractive index, and the optical conductivity of the PMMA polymer increase within this range of gamma radiation doses. The wavelength-dependent magnitudes of these quantities are measured and represented as graphs. Within this irradiation dose range, the bandgap energy of the polymer gradually decreases, which is in agreement with the optical conductivity increase of the samples. The results indicate the reduction of the bandgap energy of polymer from 4.461 eV to 3.482 eV by 30 kGy gamma irradiation dose. Increment of the refractive index and the absorption coefficient and the enhancement of the optical conductivity with the represented data in this work can be used to fabricate new tools with improved capabilities.

Laser irradiation of polymers leads to the change of structural and optical properties. Because of its favorable features like cheapness and biocompatibility, poly (methyl methacrylate) (PMMA) is one of those polymers that is in widespread use in different areas such as manufacturing medial microfluidic devices. The aim of the present study is to investigate the effects of the pulse number and the above-threshold fluences of the CO2 laser in the creation of microstructures on the surface of PMMA polymer and variation of its optical properties, like absorption coefficient, refractive index, and bandgap energy. The obtained results indicate the formation of microstructures on the PMMA surface at the above-threshold fluences of the CO2 laser. At a fixed fluence, the density and width of the microstructures increase and decrease by increasing the number of incident pulses, respectively. By increasing the fluence at a fixed number of incident pulses the same trend forms in the microstructures. In the range of investigated fluences in this study, between 10-50 J/cm2, the width of the microstructures is measured to be between 10-15 micrometers. Consistent with previous experimental results, the results of this study indicate the enhancement of absorption coefficient, bandgap, and refractive index of the PMMA polymer after interaction with the CO2 laser.

Using coherent light sources for manufacturing optical dosimeters is of considerable interest. Optical dosimeters are mostly employed for radiotherapy applications; where knowing the temperature dependency of refractive index of the used material in the core of dosimeter, often water, is required. In this work, by setting up and employing an interferometer in the laboratory, the temperature dependency of refractive index of water is measured. The setup is fully described and the required theoretical relations for interpreting the experimental data are developed. Comparing the results with the previous experimental data provided by other groups, demonstrats good compromise and confirms the accuracy of the measurements. It is shown that the second-order polynomial model can be efficiently used for interpreting the measurement data. The results of this study can be used in all those applications where knowing the temperature dependency of refractive index of water is a prerequisite.

Nowadays, nuclear instruments are being widely used in various scientific and industrial fields. Different types of nuclear radiations (alpha, beta, and gamma) can be used in the construction of these gauges. Gamma based densitometers, as non-contact and non-destructive test tools, are favorably being used for process monitoring in various industries, such as oil and petrochemical industries. Design and construction of a gamma ray density gauge and measurement of temperature dependence of water density via this gauge have been reported in this study. The results indicate that the designed device can measure the temperature dependence of water density with good accuracy.