نشریه سنجش و ایمنی پرتو
سال دوم شماره 4 (پیاپی 8، پاییز 1393)

In order to gain the neutron spectrum with proper components specification for BNCT¡ it is necessary to design a Beam Shape Assembling (BSA)¡ including moderator¡ collimator¡ reflector¡ gamma filter and thermal neutrons filter¡ in front of the initial radiation beam from the source. According to the result of MCNP4Csimulation¡ the Northwest beam tube has the most optimized neutron flux between three north beam tubes of Tehran Research Reactor (TRR). So¡ it has been chosen for this purpose. Simulation of the BSA was done in four above mentioned phases. In each stage¡ ten best configurations of materials with different length and width were selected as the candidates for the next stage. The last BSA configuration includes: 78 centimeters of air as an empty space¡ 40 centimeters of Iron plus 52 centimeters of heave-water as moderator¡ 30 centimeters of water or 90 centimeters of Aluminum-Oxide as a reflector¡ 1 millimeters of lithium (Li) as thermal neutrons filter and finally 3 millimeters of Bismuth (Bi) as a filter of gamma radiation. The result of Calculations shows that best neutron flux and spectrum will be achieved for BNCT by using this BSA configuration for TRR Northwest beam tube.

The use of computed tomography (CT) as a diagnostic tool has been considerably increased. Therefore, the controlled and protection-based use of the CT scan is necessary to reduce the detrimental effects of radiation. This study was carried out to determine patient dose level in routine CT protocols and measure CTDIW and DLP in routine CT protocols among adult patients in Kashan Shahid Beheshti Hospital. The CT scanner used, was a single-slice Toshiba model Asteion CXGS-10A. Scan parameters for each protocol were registered for 10 standard-sized patients. Then, the data were applied to the CT system and mean values of CTDIW and DLP were calculated. Finally, the values were compared with the reference dose level. The mean values of CTDIw and DLP for Head, PNS, Chest, Abdomen, and Pelvis protocols were 34.11, 19.67, 15.47, 13.95, 10.08 mGy and 362.67, 153.97, 307.33, 346.07, 189.37 mGy.cm, respectively. The mean values of CTDIW and DLP obtained in all protocols were less and in some of the protocols even less than half compared with the European guidelines and UK reference values. This may be probably due to the mAs and lesser length of scan area. But the mean values of CTDIw in the Chest and Abdomen protocols were greater than IAEA reported values due to reduced use of mAs in this study. To obtain the maximum reduction in patient dose, the lower mAs level with higher KVp, lesser number of slices, length of scan area, and shorter scan time are recommended.

In this study, the pure nano-structure hydroxyl apatite samples were synthesized via hydrolysis method. The powder samples were sintered at various temperatures of 500°C, 700°C and 900°C in a furnace. X-ray diffraction (XRD) and Fourier transform infra-red (FTIR) spectroscopy systems were used to characterize the synthsized samples. Comparison of the glow curves shows that the most sensitivity and highest thermoluminescence (TL) intensity is belong to the samples sintered at 900°C. Dose response curve of the samples is linear in the dose range of 25Gy-1kGy. Other dosimetry characteristics such as dose-response function, fading, and reproducibility of the TL response were also studied. In order to eliminate the error originating due to fading effect, an annealing process was applied on the samples. The results shows that the sintered nano-structure hydroxyl apatite sample can be used for dosimetry in gamma radiation fields.

In order to simulate neutron shields, MCNP5 calculation code was used and three types of homogeneous and separated shield multilayer arrangement, irradiated with 241Am-Be neutron sources were investigated. In these shields, the polyethylene (C2H4) and polystyrene (C8H8) were used as moderator material, and the boron carbide (B4C), as a thermal neutron absorber material and stainless steel as a absorber gamma rays materials. The ultimate goal of this research, was obtaining the best type of arrangement for the source to achieve the lowest fluence and dose produced outside to ensure their allowable level. To verify the simulation, the results were compared with an experimental work.

During the radiation therapy with electron beam, due to electron interaction and scattering from structures of the head of the medical linear accelerator, unwanted photons are produced. The main contribution of the photon contamination is resulted from the various components of the medical linear accelerator on the way of the high energy electron beam, and few percent is due to the interaction of the beam with the phantom or the patient's body. Structure and material of the head of the medical linear accelerator have effective roles on production of x-rays dose from the electrons beam. Therefore, the parameters of electron beam produced by a linear accelerator manufactured by different companies were varied. This difference may be seen even among the accelerators produced by one company. Therefore, this parameter must be described separately for each machine. In order to measure photon contamination at the electron mode of the Elekta Precise linear accelerator, thermoluminescence detectors (TLD700 & GR200) at two energies (10 & 15MeV) in polyethylene phantom were applied. These data were compared with the calculations using MCNPX code. Our results show an appropriate match between theory and experimental data at both energies. It shows that the rate of produced bremsstrahlung photons dose for tallies that are close to the phantom are in mSv range. Then it will be possible to calculate bremsstrahlung photon dose for different point of radiotherapy room of the Ayat-O-lah Khansari hospital by the Monte Carlo codes.

Radon and Thoron are the radioisotopes which radiate high alpha energy particles. These two gases can enter in the body by different ways such as inhalation, eating and drinking and then destroy body`s internal tissues and cause the lung cancer. The condensation of these gases differs in various areas and is more in zones near active faults. In this research, first the relation of Radon and Thoron concentration with the effect of distance of North east active faults in about 100 residential places of Iran is studied. Results show that residential places near active faults have more concentration of Radon and Thoron than other places. Also in these places the concentration of Thoron is two or three times more than Radon. The maximum amounts of Radon and Thoron concentration are 188Bq/m3 and 803Bq/m3 with the average amounts of 71.52Bq/m3 and 326/44Bq/m3 respectively.

In this research work public dose of Kashan inhabitants has been evaluated. Average annual effective dose due to inhalation of radon gas as well as external exposure to gamma rays have been evaluated to be 2.77±0.22 mSv and 0.97±0.05 mSv respectively. This leads to average annual public dose of 3.74 ± 0.22 mSv. Passive methods such as TLD pellets of LiF:Mg,Cu,P and polycarbonate film (lexan) have been applied for gamma and radon measurements respectively. Based on the results obtained during the course of this research work, Kashan city is regarded as a low natural radiation area.