فرهود ضیائی

In the previous studies, a new type of gamma radiation dosimeter based on polymer/carbon nanostructures nanocomposite has been presented by the authors and also the dosimetric properties for this type of dosimeter have been investigated. In this experimental work, the electrical resistance of 0.28wt% Polystyrene/Multi-Walled Carbon Nanotube (PS/MWCNT) nanocomposite was measured at the temperature range of 25-75 °C. The work of a calorimeter is based on increasing the temperature of the sensitive volume due to irradiation. Results showed that with increasing the temperature, the electrical resistance of the nanocomposite was increased linearly and due to calorimetric relationships could be used as a calorimeter in the radiation processing region to measure the absorbed dose up to about 50 kGy.

In this research work, hydroxyapatite samples doped with cerium, gadolinium, and a combination of these two dopants were synthesized through the hydrothermal method. MAUD code, a material diffraction analysis software based on the Rietveld method, was used to investigate the formed crystal phases in synthesized samples. The thermoluminescence dosimetry response of the samples was investigated, and the results showed that the thermoluminescence response of the sample doped with the compound dopants is the median level of the thermoluminescence response of the samples doped with one dopant. It was found that adding cerium dopant could improve the thermoluminescence response of the sample doped with gadolinium. Also, the results of Rietveld refinements showed that the formed phases of hydroxyapatite could affect the thermoluminescence dosimetry response.

In this research work, hydroxyapatite was synthesized via solid-state method and effect of heat treatment on its thermoluminescence response was investigated for gamma-radiation dosimetry purposes. At the first, hydroxyapatite samples were synthesized in pure form. Then, the hydroxyapatite samples via the same synthesize method were doped with single impurities of Ce and La with concentrations of 1%, 2%, and 5% and were examined afterward.
In order to identify and evaluate the changes that occurred in the material structure and then on dosimetric response, x-ray diffraction apparatuses were used. The results were examined from different dosimetry aspects such as, glow curve change, dose response curve, reproducibility, and fading. The obtained results showed that synthesis in the higher temperature using the solid-state method, is more suitable for dosimetry purposes.

In this research, the geometrical parameters, the spin density of atoms, and the EPR parameters of radiation and mechanically induced radicals in alpha keratin were investigated using density functional theory. Generally, various factors such as hydrogen bonds and temperature impact the EPR parameters. First, cluster calculations were used to study the effect of hydrogen bonds, and then ab-initio molecular dynamics calculations were used to investigate the simultaneous effects of hydrogen bonds and temperature. Variation of the g tensor components and the coupling constants are dependent on the change of the geometrical parameters and the spin density of the atoms. Due to being a small variation of the geometrical parameters and the spin density of the atoms between the cluster model and the molecular dynamics for the radiation and the mechanically induced radicals, the difference between calculated EPR parameters by means of two mentioned models is insignificant. The result shows a good agreement between the calculated EPR parameters and the experimental results. Also, due to the considering of the ambient temperature effect, the obtained results from the molecular dynamic calculation have a better agreement with the experimental data in comparison to the cluster model.

Carbon nanostructures via adding to a polymer matrix, while improving the electrical, mechanical and optical properties of the nanocomposites, are widely used in the industry, medicine, and agriculture. The authors presented several investigations on a new type of gamma dosimeter based on the polymer-carbon nanostructures nanocomposite. In this research, the electrical percolation threshold of the Polystyrene-Graphene Oxide nanocomposite (PS/GO) was simulated using the finite element method in different weight percentages. Then, at the experimental phase, various nanocomposites were fabricated in different weight percentages of 0.05, 0.1, 0.5, 1, 2, 3, 5 and 8 via the mixed-solution process. The electrical conductivities of the samples were measured at the room temperature. Finally, the electrical conductivities of the nanocomposites were compared using the FEM simulation and the experimental results, which were estimated as 2.5wt%. The results of this study showed that the finite element method in accordance with the experimental results is a powerful tool to determine the electrical properties of the polymer nanocomposites considering the dosimetric approaches.

Digital Holographic interferometry is a powerful and widely used optical technique for accurate measurement of variations in physical quantities such as density, refractive index, and etc. In this study, an experimental digital holographic interferometry setup was designed and used to measure the amount of energy changes induced by absorption of radiation from a non-ionizing infrared laser beam in a water cell. An effective theoretical method is used to measure the absorption dose, which is based on tracing of the interference pattern displacement due to changes in the energy content of the adsorbent material. It is shown that the results of the interferometric method are in good agreement with the results obtained from the measurement with a precise temperature sensor. Experimental results show the capability of this optical method for non-contact and non-intrusive monitoring of the changes in the amount of absorbed energy by non-ionizing laser radiation in material.

In radiation calorimetry by using laser beams and interferometry setups, variations induced by dose absorption in phantom can be precisely measured. Dose absorption and the induced temperature change result in refractive index variation of the material. In order to be able to measure the low amount of absorbed dose in the phantom, temperature dependence of refractive index of the material must be precisely known. Water and Plexiglas phantoms can be used as tissue-equivalent materials and a multitude of reports have been published in recent years regarding their use for radiation calorimetry.  In this study, temperature dependence of refractive index of water and Plexiglas (poly- methyl methacrylate) is measured using a laser interferometry setup. The results show that the refractive index of Plexiglas has more variations with temperature compared to water. This shows that use of Plexiglas as the absorbing material for optical calorimetry, due to its nearly zero heat defect, increases the accuracy of absorbed dose measurements.

This study was conducted to evaluate and compare the effect of Ergosan particle (Alginic acid) and Alginic acid nanoparticles produced by gamma radiation and ultrasonic wave method in the diet, with the dose of 5 mg/kg. In this research, growth, survival and response to stress were studied in rainbow trout for a period of 8 weeks. The Ergosan immunity-stimulating particles were converted to Alginic acid nanoparticles (Ergosan) by gamma radiation and ultrasonic waves methods. Alginic acid nanoparticles produced by ultrasonic waves had diameter of 70 nm and those produced by gamma radiation had a diameter of 20 nm. The fish with an average weight of 125±9 gr were kept in 300-liter tanks with a storage density of 40 fish in each tank in 4 treatment and 3 replication. The fish were fed ad libitum twice a day. The results showed significant differences in indices under consideration including growth, final weight, weight gain and FCR (P<0.05). There was not any significant difference between treatments in survival rate (P>0.05). The stress test at the end of the treatment period showed that the mean cortisol levels significantly increases, but gamma and ultra-treatments had the lowest response to stress which was significantly lower than control groups (P<0.05). There was no significant difference in glucose levels before and after stress (P>0.05). The results showed that adding nano stimulating Alginic acid produced by gamma radiation to rainbow trout diet, has significant effects on growth and response to stress. It appears that in cultural conditions and weight range mentioned in this study, nano stimulating Alginic acid could be useful for the fish.

So far, various methods have been proposed for the synthesis of hydroxyapatite nanoparticles as the main ingredient in bone and enamel. In each of these methods, by varying initial conditions of synthesis, samples of size and shape, and the ratio of length to diameter can be achieved. In this study, pure hydroxypropyl nanoparticles were prepared using calcium nitrate precursors (Ca (NO3) 2-4H2O) and diammonium hydrogen phosphate ((NH4) 2HPO4) by hydrothermal method. The purpose of this study was to investigate the effects of changes in reaction conditions and the synthesis of this material on the size and shape of the particles. X-ray diffraction (XRD) and scanning electron microscopy (SEM) nanoparticles were investigated. The results of the experiment indicate that the concentration of the raw materials, the method and temperature of calcining, the speed of the addition of materials, the use or non-use of surfactants can have different effects on the size and shape of the hydroxyapatite particles.

Generally, doses greater than 2Gy can produce acute biological effects in humans. For this reason, to measure and record the cumulative dose, especially in radiation users, the need for a personal dosimeter has been strongly felt by the researchers. The purpose of this study is to introduce retrospective dosimetric techniques, in particular the use of nails as a natural tool for determining cumulative absorbed dose in the body. The traditional methods of dosimetry are based on the effects of radiation on inorganic materials. Contrary to conventional methods, organic compounds are also used for dosimetry, which the effect of radiation on them is creation of free radical. EPR spectroscopy is used to determine the concentration of these radicals. So far, various solids such as sugars, polymers, quartz and bone have been used for a wide range of absorbed doses (10-108 Gy). In order to develop measurable lower doses (1-5 Gy), materials that are more sensitive to radiation are required. EPR spectroscopy is usually performed in the X-band region at a frequency of 9.5 GHz. The sugar dose-response curve for gamma radiation is linear in the range of 0.5-100 Gy. The dose-response curve for most plastics is nonlinear with low stability of EPR signal. The flax which composed of a polysaccharide chain has a linear dose-response curve in 10-104 Gy, but it is not easy to interpret the EPR signal because of the presence of detergent in it. The intensity of the EPR signal of wool is weak and the recombination of its radical occurs rapidly. Tooth enamel is a good tissue for EPR dosimetry and its dose-response curve is within the range of 0.02-0.2 Gy. The detection limit for the bone is also about a few kGy and not precise at low doses. The background signal in hair is high and its signal stability is low. Also, the EPR signal of fingernail is stable for at least a few days. Generally, materials used in EPR dosimetry should have features such as, being everywhere, non-invasive sampling, signal stability, and accurate and fast dose evaluation. Due to having all of these features compared to other materials, the fingernail is very much considered in the EPR dosimetry method.

In the current research, hydroxyapatite samples, synthesized by hydrothermal methods was studied from the perspective of thermoluminescence dosimetry. The results of the study were compared and studied with different aspects of dosimetry, including dose-response variations of synthesized samples, degree of its linearity, and the percentage of response fading, as well as the position of the main peak and the degree of complexity of the glow curve. The findings show that surfactant-synthesized substances have a more optimal behavior in terms of thermoluminescence dosimetry.

In this paper, Density Functional Theory (DFT) was utilized for the calculation of the hyperfine coupling constant and the g tensor alanine radicals at different crystal temperatures. The cluster approach was used for considering the effects of crystal environment. In the cluster approach, the careful selection of the cluster size is very important for the geometry structure of alanine and the EPR parameters of alanine radicals. The geometry structure of alanine and the EPR parameters of alanine radicals showed a good agreement with the experiment data when 6 alanine molecules had hydrogen bonds with the central alanine or alanine radicals. Further, bigger clusters could even lead to an incorrect description of the geometry structure of alanine and EPR parameters of alanine radicals in the condensed phase.

Recently, polymeric nanocomposites have been used as real-time detectors and dosimeters of gamma radiation. In this experimental work, multi-wall carbon nanotubes (MWCNT) were dispersed in polystyrene (PS) martix with a weight percentage of 0.05 wt%. SEM images confirmed the appropriate and uniform distribution of carbon nanotubes in the polymer matrix. The dark current and photocurrent of the nanocomposite were measured under gamma irradiation of 60Co source using an electrometer in the voltage region of 1-500 V, and the dose rate range of 40-134 mGy/min. The results showed that this dosimeter in the array form of 2 pieces in comparison with the 1 and 3 pieces show a better response in the mentioned dose-rate and voltage ranges. Thus, this nanocomposite can be used as an active dosimeter in the diagnostic and therapeutic level.

High energy electron beams are one of those ionizing radiation beams that are being widely used in nuclear medicine for treatment of cancerous tumors. However, these beams may also harm the healthy cells in traversing the patient body. Accordingly, knowing the dose distribution in a tissue-equivalent phantom is the main requirement in an electron therapy treatment design. In recent years, great interest is attracted toward the application of digital holography method for accurate three dimensional measurement and monitoring of the absorbed dose. In this work, design and modelling of a mobile dosimetric instrument, which works based on the digital holography principles, are studied and a new approach is developed for measuring the absorbed dose of electron radiation using the digital holography technique with a laser beam. The proposed method for measuring the absorbed dose is also developed to be immune against the environmental noises that are present in difficult situations. Monte Carlo and numerical modelling of the instrument, demonstrate its capability in accurate measurement of the absorbed dose.

In this paper, an experimental setup is used to measure the temperature dependence of the refractive index of a water phantom. In radiation calorimetry by laser beams and interferometric systems, the amount of change induced by radiation within the phantom can be accurately measured. Absorption of dose and the resulted change in temperature changes the refractive index within the material. In order to be able to measure the small amount of the absorbed dose within the phantom, the temperature dependence of the refractive index of the material must be precisely known. The measurement results of temperature dependence to the refractive index of water indicate the decrease of its refractive index by increasing the temperature.

In this research, the vertical Bridgman method has used to perform the single crystal growth of cesium iodide alkali halide. To this purpose, a vertical cylindrical furnace equipped with electric elements with five different thermal regions has been designed and constructed. The temperature gradient of the furnace can be controlled up to 1000○C with 0.1○C accuracy. Several cesium iodide sample crystals has been grown with this furnace and then the X-ray diffraction characterizations have been undertaken. The photoluminescence spectrum and the hardness properties of the crystals samples have been studied as well as the measurements of etch-pits of single crystals. Since the pure cesium iodide exhibits scintillation properties, the gamma-ray spectroscopy has also been undertaken.

In this study, based on Density Functional Theory (DFT), the effect of solution on the g-tensor, hyperfine coupling constant of atoms and finally the EPR spectrum of alanine free radicals induced by ionizing radiation such as electron and gamma was investigated using implicit models such as COSMO, and explicit models such as introducing hydrogen bonds to the cluster structures. The obtained results confirmed a good consistency between the g-tensor and hyperfine coupling constant of atoms and the experimental data in the solution as well as qualitatively in the crystal by the introduction of the hydrogen bond of the water molecule to the cluster models. The use of different clusters in constituting hydrogen bonds between water molecule and radicals indicated that in the first shell, four, seven and six water molecules were needed for R1, R2 and R3 radicals, respectively. Moreover, the effect of solution on EPR spectrum was analyzed in a manner that the identity of the radical remained unchanged.

Recently, polymeric nanocomposites have been used in dosimetry and detection of gamma rays, but due to their low photon absorption cross section, they exhibit a small sensitivity to gamma rays. In order to overcome this problem, metal oxide particles with a high atomic number are added to the polymer matrix. For this purpose, in this work, tungsten oxide particles (WO3) were distributed in polyvinyl alcohol (PVA) matrix via two scales of nano and micro sizes of the fillers with a weight percentage of 20 wt%. A solvent solution was used in fabricating WO3-PVA composite (20 wt%). The FESEM test was performed to verify the composite rheology and to confirm the distribution of tungsten oxide micro/nanoparticles in the polymeric matrix. The quantum efficiency of gamma rays for 60Co was calculated for the aforementioned composite using the MCNP code, which showed an acceptable agreement with the XCOM results. One of the effective factors in detection response and dosimetry of this composite group is the change in the electrical current of the composite due to beam absorption. The dark current and photocurrent of tungsten oxide-polyvinyl alcohol nano/micro composite were measured in gamma and neutron radiation fields respectively by 60Co and 241Am-Be sources using two-probe electrometer in 100 V and 400 V voltages. The results showed that the sensitivity of nanocomposite to gamma rays is better than microcomposite. Also, the signal-to-noise ratio of nanocomposite for gamma-ray in the dose rate of 90-138 mGy/min increased linearly from 5 to 40, while the composite did not show a remarkable response to neutron beams.

Holographic interferometry is one of the accurate methods for measuring physical quantities such as stress, pressure, vibration, and temperature and refractive index changes especially in transparent solid materials. In this study, a digital Mach-Zehnder holographic interferometry setup was used to measure the induced temperature changes by infrared laser irradiation in a polyethylmethacrylate cell. The obtained results from the interferometric method were in good agreement with the results of the measurement by a temperature sensor.

Double-exposure digital holographic interferometry is a powerful and widespread technique for fine measurement of the induced changes in special physical properties, like density, refractive index and etc. In this paper, application of this technique for measuring the absorbed dose from an electron radiation source in poly (methyl methacrylate) material is studied through modeling. The method of applying this technique for interpretation of the resulted fringe pattern and obtaining the pattern of isodose regions and the percent depth dose curve, that are ubiquitously used for treatment planning and monitoring of the absorbed dose, is investigated. Our results prove the capability of this optical technique for online monitoring of the absorbed dose from a radiation source through interpreting the formed fringe pattern.

Combination of carbon nanotubes with polymers in an especial weight percentage called electrical percolation threshold, leads to a sudden increase of several orders of magnitude of the electrical conductivity of the polymer-carbon nanotube composite. In the present research, considering these characteristics, the idea of using Polymethyl Methacrylate-Carbon Nanotube composite as an active dosimeter is exhibited. One of the factors affecting the response of this type of dosimeter is the variation of electrical resistance in the composite due to absorption of radiation. For investigation of dosimetric parameters of this composite in different dose rates, the COMSOL software and finite element method were utilized. In this simulation, the electrical current density of PMMA-CNT composite with a thickness of 10µm under a constant voltage of 3 V in different dose rates for 2 min was calculated for the samples having different weight percentages of carbon nanotubes adjacent to the electrical percolation threshold region, namely 0.17, 0.19 and 0.30. The value of the absorbed dose was calculated through the product of the dose rate by the irradiation time. Linearity of the dose response in the range of 400 mGy to ~3 Gy in the diagnostic and therapeutic dose levels could be considered as a positive factor for dosimetry applications of this composite material.

Nano-structured hydroxyapatite doped with europium in different mole percentages of 1 to 5 have been synthesized using a hydrolysis route. Structural and thermoluminescence (TL) properties of the samples have been discussed in detail. Powder X-ray diffraction and scanning electron microscopy confirm the phase purity and nano structure nature of synthesized powder. The samples were irradiated by gamma rays and their corresponding TL glow curves were recorded. Their glow curves, dose responses and fading curves were compared. Different TL sensitivity, peak position and fading were observed, where 5mole% of europium doped hydroxyapatite is found to be the most TL sensitive with lowest level of fading during 30 days. These properties along with bone tissue similarity make this material a candidate for gamma radiation dosimetry.

Ionization radiation induced decomposition of dyes is a concept frequently exploited to develop devices to measure the radiation dose. In this study, using this concept, preparation of polyvinyl chloride films doped with different amounts of quinacrine dihydrochloride were done and their capabilities for dosimetry of gamma radiation doses in the range of 0 to 60 kGy were evaluated. The results showed that films containing 2%w quinacrine dihydrochloride have the best dose response in the investigated dose range and the lowest fading within 60 days. Therefore, these films are suitable for high dose dosimetry in radiation processing industry.

The object of this research is the investigation of carbon nanotube (CNT) distribution effect on electrical conductivity of polymer-CNT composite as dosimetry response of this system. Thus, electrical conductivity of this composite was simulated for aligned, homogenous, and agglomerated distributions in 2D, and 3D situations. The results of simulation were compared and validated by experimental data in the literature. For 3D distribution of CNTs in polymer matrix, Monte Carlo method and excluded volume approach were utilized. The results of 3D simulation showed that electrical conductivity of polymer-CNT composite was depended on dispersion angle of CNTs in polymer matrix. The results of 2D simulation showed that more agglomeration of CNTs in polymer-CNT composite was leading to sever reduction of electrical conductivity. In the other hand, with transition of agglomeration to homogeneous dispersion of CNTs into polymer matrix, increasing of electrical conductivity of the composite was observed.

In this research work, effect of carbonate content on EPR response of gamma irradiated HAP were investigated. The carbonated HAP samples were prepared by substitution of carbonate group into HAP structure via chemical method. Fourier Transform Infrared (FTIR) spectroscopy and X-ray diffraction (XRD) methods were used to investigate the structural changes of the samples. Then, the samples were subjected to different gamma doses of 1, 5, 10, 20, 50 and 80 kGy and their EPR responses were measured. Results showed that EPR signal due to CO­2- radical increased with increasing carbonate content.