hossein tavakoli anbaran

252Cf is a source of emission of neutron, gamma rays, and beta and alpha particles. In the common models of this source used in brachytherapy, only neutrons and gamma rays contribute in the dosimetry around the source. In this study, while investigating the escape of beta rays and bremsstrahlung X-rays from the source capsule of brachytherapy 252Cf of Isotron model, the dosimetry of the total effective radiation in the water environment around the source was performed and the total equivalent dose increase was calculated using 10B particles.

Dosimetry for the neutron rays, the primary gammas, the secondary gammas, the beta particles, and the bremsstrahlung X-rays in the spherical water phantom performed with the radius of 20 cm at the distances of 0.5 to 6 cm from the source using the Monte Carlo MCNPX.2.6.0 code. Dose increment factor was calculated using B10 particles with a concentration of 50 ppm.

The highest relative difference in dose values, taking into account the X-ray and the beta particles their absence at the distance of 0.5 cm from the source, was %19. As the distance from the source increases, the effect of these rays on the total equivalent dose rate decrease, as in the distance of 2.5 cm distance, its values reach less than % 0.5. The boron effect on the total equivalent dose increases by distance from the source, as at the 0.5 to 6 cm distances from the source will increase from %0.01 to more than % 22.

According to the findings of this study, the dose of the X-rays and the beta particles passing through the source capsule are effective in the dosimetry around the source, and increasing the dose by 10B depends on increasing the tumor source distance, which should be considered in clinical applications.

So far, many experiments have been carried out with gamma rays to obtain some information of the matter such as density. The work of Ryabov and others in 1976 is one of these experiments, which was using gamma densitometry to study flooding intervals in a borehole in order to enhance the efficiency of well logging. In this work, simulations have been carried out using MCNP code on soil and sedimentary rocks, and information is obtained about the substance by using flux of back-scattered gamma rays from the material. Since the irradiation of existing sources in nature causes disturbance in measurements, it should be a way to eliminate this disorder, therefore, in this work, the increase in the activity of the source used in simulations in relation to the radioisotopes existing in nature will be proposed, to reduce or eliminate this disruption, which increases the specific activity of the Cs137 source relative to the specific activity of the sources in nature and examines the fluctuation fluxes. Using the results obtained in these simulations, it can be deduced that by increasing the special activity of the Cs137 source in relation to the radioisotopes existing in nature, the amount of disruptions caused by radioisotopes existing in nature was reduced, until in special activity about 3.09946 MBq/gr this disorder will be close to zero, and it can be said that in a special activity equal to 3.09946 MBq/gr or greater than that, the disorder of radioisotopes existing in nature, can be eliminated to find materials in this way.

Gamma ray interactions with materials is a non-destructive method, which can be used for obtaining useful information such as the densities of the materials. In this work, the Monte Carlo Neutron – Photon (MCNP) code was used to simulate a block composed of sedimentary rocks with four holes (wells) so that each hole contained a detector. Then, by placing a Cs137 source in one of the holes and adding various percentages of water and oil to the sedimentary constituents of the block, the contrast value for the output and scattered gamma rays was obtained by the response function of the detector inside each of the wells. The response function of the detector in front of the source is greater than that of the other detectors. The obtained contrast in the block containing sedimentary rocks with forty percent of oil in the first to fourth holes is -219.10, -354.85, -174.75 and -197.30, respectively, and the contrast for the case of water in the first to fourth holes is -198.31, -330.87, -167.73 and -185026, respectively. Given the fact that by digging several holes either for the scattered or crossed gamma, one can obtain a better location for the detector position. It is also clear from the calculated valuesthat the contrast obtained from the second hole (that is in front of the source) is greater than the rest of the contrasts. However, due to the quantity D, the first hole is superior to the rest, because it can be distinguished from minerals by the percentage of materialsin the soil.

The Compton scattered annihilation gammas between PET detectors reduce spatial resolution by making an incorrect Line of Response. This paper, by presenting a new method, tried to remove these errors from PET imaging. In this way, the detectors were insulated so that scattered gammas from a detector can not enter other detectors of the PET ring.

First of all, the Siemens PET BiographTM 6 scanner ring was simulated and then all detectors of this ring were isolated to resolve this error and investigate its impact on the Response Function of PET detectors.

The analysis of the results of simulation showed that, the isolation of PET detectors reduced counts of detectors in the energy window, especially at the lower threshold (350 to 400 keV). This reduction with a spherical soft issue was less than without that. So that the maximum of the relative percentage difference for counts of detectors between connect and disconnect them was 70% (in 400 keV) and 12% (in 350 keV) in the absence and presence of soft tissue, respectively.

Although the isolation of the detectors boosted the resolution of PET, it removed some true coincidences and reduced the sensitivity of PET; there for, it did not have much effect on image quality of PET. Also, a slight decrease in the count, with the soft tissue, shows the greater effect of the isolation of PET-detectors in improving image quality in abdominal imaging in comparison with other imaging such as head and neck imaging.

In the field of nuclear physics, the use of gamma rays is an important and practical method. This method is used in various industries such as oil and gas production, mining and quarrying, environmental monitoring and so on. The technology of using gamma rays is based on the interaction of the beams with materials. The three main phenomena are the interaction of gamma rays with photoelectric material, Compton scattering, and pair- production phenomena. Due to its very high sensitivity, activation analysis has become an important and applicable tool in various fields ranging from science and engineering to industry, mineral exploration, medicine, etc. One of the biggest advantages of analyzing by this activation method is that it can detect most isotopes with very high sensitivity. In this research, different simulations have been carried out on sedimentary rocks in order to find a suitable method for exploration of oil reservoirs. These simulations are performed in three different states and by comparing the results obtained in each case, the best results are selected to explore the oil reservoirs. 

Methodology and Approaches:

The Monte Carlo method is a class of computational algorithms that rely on random iterative sampling to calculate their results. To use this method, a structured input file must be provided, including problem information such as geometry, material type, source, output type, and so on. The code, based on this method, solves the problem using input file information and the crosssection library and generates the results in an output file. In the simulations by this code, a cubic block of about 2 meters is considered to be a type of sedimentary rocks, oil, gas, water and a combination of these rocks with water, gas or oil. The simulated cavity has a depth of 180 cm and a radius of 7.62 cm. A 2-inch NaI (Tl) detector is inserted into the specified hole.

According to the obtained results, it is possible to detect and identify the oil reservoirs and to separate the oil reservoirs from the gas and water reservoirs. The advantage of using this method is that due to the minimal amount of energy required for carbon interactions of 18.7 MeV, there is no need to investigate existing sources in nature, since the maximum energy emitted by these sources is less than 18.7 MeV. Thus, the sources in nature do not cause any disruption in the measurements.

Ionizing radiation modifies the molecular structure of the cell and ultimately disrupts its function. Brachytherapy by the Gamma Iridium-192 source is one of the most widely used radiotherapy methods in cervical and prostate cancer. For this reason, in the research, we investigated the damage to the DNA molecule by photons and secondary electrons of the source at different distances, and then we obtained the dose rates in the defined dimensions of DNA. In this work, using the MCNPX code, we calculated the flux and photon dose and secondary electrons from iradium-192 Brachytherapy, in approximate dimensions of DNA in a water phantom. Then, using the electron flux obtained, through the MCDS code, we investigated the efficiency of DNA breaks at different distances from the source. The simulations indicated that DNA damage is different at various distances from the source and it depends on the number of secondary electrons reaching that region as well as its energy. With increasing the distance from the source, the values of the probability distribution function of DNA single-strand and two-strand breaks diminish. It was also observed that these values had peaks at distances of 0.04 and 2.5 cm from the source, where the maximum probability of single-strand break at those distances was 8.06% and 3.9%, respectively, and the maximum probability of the two-strand break at those distances was 0.54% and 0.11%, respectively. It is notable that the dose reaching the DNA at these distances was 27.202 and 0.005 mGy/h, respectively.

In PET imaging, one or both of two annihilation photons may change the direction before reaching the detector due to Compton scattering interaction in body. This article, a Monte Carlo simulation study, examined the effect of soft tissue on this error.In this work, the PET BiographTM 6 scanner, a simple geometry of soft tissue -including a sphere of soft tissue in center of PET ringwith various radii (from 0.5 to 30cm)- and two kinds of 511keV gamma source –point source and spherical source - were simulated by Monte Carlo MCNPX code to investigate scattering effect of soft tissue on PET imaging. Analysis of the results of the simulation showed that, the majority scattered photons fell within the energy window without much loss of energy. Soft tissue around the point source at a distance of 8 to 12cm from the source and soft tissue around the spherical source at a distance of 8cm from the center had the most scattering effect in PET imaging. The scattering effect of soft tissue around the point source was more than the spherical source. The scattering effect of the adjacent organs is more than the non-adjacent organs.For high thicknessof soft tissue (more than20cm of radius), the attenuation effect is as obvious as the scattering effect. According to the results of this study, the patient's body thickness -in the abdominal region-could be a more accurate alternative for the patient's weight for increasing the injected dose into obese patients.

The purpose of this study is to select the best place for the detector towards shield and the gamma source which have the least flux buildup factor of the photon. In this research, the flux buildup factor of gamma rays was calculated by using of MCNP-4C code for cylindrical sources 137Cs, 60Co, 16N coaxial shields made up of aluminum, iron and lead with a constant thickness 1.55 cm in detector CsI (Tl). For this purpose, detector was respectively placed at different distances from 9 to 18 cm and different angles from 30 to 150 degrees with respect to the axis of the source. In this study, we tried to assess the dependency of the buildup factor with material atomic number, gamma-ray energy, relative distance of detector-material-source and angle of detector to source. The obtained results showed that the buildup factor values are variable in a wide range from 1 to 3.5. According to the results of simulation, if the aim is reduction of the buildup factor source, shield and detector should be designed parallel and coaxial. Otherwise, whatever deviation of detector from the central axis is increased, the gamma-rays buildup factors are greater in detector.