دکتر محمدرضا کاردان

In recent years, one of the methods that is considered in designing and optimization of the engines and turbines with high efficiency is maximum temperature crystal sensors (MTCS). These sensors are usually very small in size and made of materials such as 3C-SiC, Diamond, Graphite, etc. They can be placed in the desired location inside the turbine or engine and measure the maximum temperature created. These sensors could be obtained a very accurate spatial distribution of the created temperature due to the small dimensions and the very high accuracy of the measurement. For producing these sensors, a very high fluence of fast neutrons is required. Therefore, the number of the core 18 of the Tehran research reactor (TRR) is simulated and the calculations of the maximum flux of fast neutrons were carried for the 3C-SiC sample. The simulation results show that the channel F4 will provide the highest flux of fast neutrons for this purpose. Also, activity calculations were done using ORIGEN code and dose rate through MCNP6 code. The results show that the amount of activity of the sample has decreased by 65% after 4 months. Therefore, the total dose rate has also reached a value lower than the criteria of 10 µSv/h. Next, the 3C-SiC sample was irradiated at 5 MW power in the TRR, then the crystal size and the amount of strain before and after irradiation were calculated. Finally, according to the results of this article, it can be said that the 3C-SiC sample will be suitable as a MTCS.

The role and benefits of Cone-Beam CT(CBCT) in dental imaging, diagnosis and treatment planning are well known, but using the x-rays, it is not risk-free. This study aimed to provide an accurate and comprehensive data base of organs and size-specific effective doses based on body mass indexes (BMI) of patients in dental-CBCT units. In this regard, the Monte-Carlo (MC) method used to simulate the exposure geometry for three different imaging protocols with GIANO CBCT which is one of the commonly used unit in Iran. The population of the Extended-Cardiac Torso(XCAT) adult male and female computational phantoms with various BMIs were used as MC simulation input files. The measured doses using Rando phantom and thermoluminescence dosimeters were compared with simulated doses using CT images of Rando phantom to validate the simulations. The results showed the organs doses for the different Fields-of-View(FOVs) was varied usually in the adult females was higher. The maximum size-specific effective doses for temporomandibular-joint(TMJ), single and both arch protocols were 94±5μSv, 63±4μSv, and 62±2μSv for adult males with BMIs 25.82, 21.70, and 21.71kg m -2, respectively, and 98±3μSv, 69±1 μSv and 66±1μSv for adult females with BMIs 21.69, 21.71 and 21.72kg m-2, respectively. Also, the difference between the minimum and maximum value of effective dose in TMJ, single and both-arch protocols were 24%, 37% and 32%for AM. These values for AF were 24%, 32% and 35%, respectively. Eventually, this study provides comprehensive data set of patient doses for wide ranges of BMIs without the need for experimental measurement.

Due to fascinating theranostic properties of Gold-nanoparticles and Ga-68 radionuclide, 68Ga was grafted on thioglycolic acid (TGA)-functionalized nano host, in order to target the delivery of the radionuclide to targeted organs. In order to have precise evaluation of the behavior of the labeled nano particles in in-vitro and in-vivo experiments, measurement of the radioactivity in tissue with HPGe detector, and precise quality control tests including RTLC, TEM, PET-Scan, were done as well. Biological information of the nano particles shows outstanding changes in excretion mechanism (increasing urinary tract excretion) and complete transfer of nanoparticles to all vital organs of the rodents. Regarding to the outstanding pharmacokinetics properties of these labeled gold nanoparticles such as proper biodistribution, fast excretion, high structural stability, and proper blood circulation, these labeled nanoparticles can be introduced as a potential candidate for diagnostic PET nuclear imaging.

In this study, the influence of grafting 198Au radioisotope on functionalized silica nanoparticles with a the biodistribution of this radioisotope compare to pure gold nanoparticles, was investigated. The Au radioisotope was prepared using neutronic bombardment of a highly pure metallic gold. The prepared radioisotope was coated on silica through an interface ligand. The biodistribution suggested that the hydrophilicity of the 198Au@MCM-41 nanosilica compare to pure gold nanoparticles was higher. Through the SPECT images and %ID/g measurement, it was found that the excretion of radiotracer from the body compare to pure gold nanoparticles became faster. The Au@MCM-41 nanocomposite could potentially be used in diagnosis and therapy of cancer.

Production of semiconductors such as silicon doped with phosphorus has many applications in the production of electronic components and various industries such as aerospace. The process of impurity making, which is called silicon doping, can be done by both chemical and nuclear methods. Since the uniformity of the injected impurities is not suitable in the chemical method, the methods of silicon doping by neutron irradiation method are strongly followed in the world. In this work, the potential of the thermal column of Tehran Research Reactor for silicon doping is investigated using MCNPX simulation code. The results show that the thermal neutron flux as well as the ratio of thermal to fast neutron flux in the optimal location are 1.2×1012 n/s.cm2 and 441, respectively, which shows that the thermal column of the Tehran research reactor can be a suitable place for silicon doping.

The origins of radon gas are the amount of uranium decay in the soil that is released into space and through the interior gaps of  buildings. Radon can enter the respiratory system and cause radiation hazards. Recently research has identified Radon as the second leading cause of lung cancer after cigarette smoking. The indoor concentration of Radon progeny is mentioned as an important issue regard to the point of view of health. Therefore, a more accurate measurement of the concentration of radon gas in order to assess the exposure of people is of great importance. The purpose of this research  is to measure radon gas with two contemporary and retrospective methods in Ramsar homes, which is known as a high level background radiation area, as well as comparison with previous measurements. In order to measure the Concentration of contemporary radon by  passive method using a radon chamber and solid state nuclear track detectors, a retrospective of the activity of polonium 210 implanted in glass objects was used to measure the concentration of radon gas. The solid state nuclear track detectors used in this research are polycarbonate, which is the first time used in this world for this type of polymer for the retrospective method. The average concentration of measured for contemperory radon is about 416 Bq /m3 and the resrospective radon is about 1299 Bq /m3. According to the comparison of the results  with the US Environmental Protection Agency standards, it was found that 45% of the radon gas concentration is above 148 becquerel per cubic meter, which is indispensable for reducing radon gas in these buildings. At the same time, the difference in the concentration of rare earth radiant gas with contemporary radon gas can be related to the change in the ventilation rate and the change in the concentration of aerosols and the ratio of the surface to the volume of the room.

The images of dental CBCT imaging systems used in conic shaped beams, stored in the DICOM format, have various applications in the dentistry, including bone density estimation to select the location of the orthodontic implant, bone loss detection and etc. In these systems, unlike CT imaging systems, the resulting images exhibit gray-scale non-uniformity in each of the different axis in FOV. This specification along with the inability of the CBCT to display the CT numbers accurately, makes it difficult to obtain bone density information, so diagnosing of dental complications using a quantitative information from the images cannot obtained accurately. In this regard, in order to be able to use the quantitative information of the images of these systems to assess more precisely the bone density, the gray scale changes in the images of several different CBCT systems were studied. The results showed that the process of gray scale changes for each system in each direction is unique for the each system, and it can be concluded that in each system, changes in the gray scale of images in each direction have a roughly constant trend. One of the most important results is that the gray scale changes of the images for all systems along the axis of the body (Z axis) have a steady trend and It has the lowest standard deviation. One of the most important results is that the gray scale changes of the images for the Scanora 3D and  New Tom GIANO systems in the axis of the body (Z axis) have a stable trend and the lowest standard deviation (0.54 ± 0.009) And (0.18 ± 0.004) respectively.

Human tissue equivalent phantoms are widely used in medicine. They are used for dosimetry, calibration of medical devices, and quality control of radiotherapy equipment, as well as training students. Regarding to development of radiotherapy techniques for treatment of cancers and also development of educational centers in the country, the human equivalent phantoms are needed. Several phantoms have been designed and constructed over years around the world, including Rando phantom. Since Rando phantom is expensive to buy, a similar phantom has been constructed by Tabesh Pardaze Pegahs Company (TPPCO). In this study, in order to compare the constructed head phantom with the Rando head Phantom, both phantoms have been irradiated in the same gamma field. The results show that the average relative percent difference between gamma dose in constructed head phantom and Rando phantom are about 21%. More conformity with Rando phantom is achieved if some improvements are performed on the constructed phantom.