نشریه سنجش و ایمنی پرتو
سال نهم شماره 3 (پیاپی 38، تابستان 1400)

Iodine-g120 radioisotope with a half-life of 1.35 hours due to positron emission is used in PET imaging. This radioisotope is produced through various reactions. In this study, the 120Te(p,n)120gI reaction has been simulated using Geant4-toolkit, SRIM and Talys codes to calculate proton range, cross section and production yield of iodine-120g. The range of protons in the target of tellurium-120 was calculated using Geant4-toolkit and SRIM codes to be 725.59 and 731.68 micrometers at 14 MeV energy, respectively. The values of proton range, cross section and production yield are compared with experimental data. The cross-sectional values were calculated with Geant4-toolkit and Talys codes in the energy range of 6.5 to 36 MeV and compared with the experimental values. The maximum cross-section was obtained using Geant4-toolkit equal to 667.99 mbarn at 14 MeV and Talys code equal to 537.83 mbarn at 14.5 MeV. The yield of iodine-g120 production using these codes in energy of 14 MeV has been calculated as 642.73 and 346.94 MBqμA-1h-1, respectively.

Brachytherapy is one of the most effective methods in the treatment of local malignant tumors. In this study, dosimetric parameters of 103Pd brachytherapy source Theragenics model 200 was estimated according to TG-43U1 protocol using GATE 8.1 Monte Carlo code. At first, validation of the GATE simulation for the seed was performed by some criteria consist of radial dose function and 2D anisotropy function inside liquid water according to the AAPM TG-43U1 recommendations. The maximum average deviations were found to be about 9% and 8% for radial dose function and anisotropy function, respectively. On the other hand, since the attenuation coefficient of the sources in the water phantom is different from that of various tissues, the effects of the various tissues on the radial dose function parameter of the 103Pd brachytherapy source were investigated using GATE 8.1 code. The relative deviation values of the radial dose function in the adipose, muscle, breast, and brain tissue compared with water phantom in the radial distance of 5cm were about 153%, 30%, 35%, and 29%, respectively. There is a good agreement between the results of this work and other study in calculation of dosimetric parameters of brachytherapy 103Pd source base on the recommendations of TG-43U1 protocol. The results show that the dosimetric parameters of 103Pd brachytherapy source can be accurately calculated using the GATE code in spite of low energy of radiation and high variation in dose rate with increasing distance from the center of the source. On the other hand, the results of the dose calculation in different phantom could be used in the clinical treatment planning systems.

The main features of damages that occurred on surface morphology as well as the structural parameters of Cu and Mo materials when irradiated to high-energy protons produced in the dense plasma focus device was investigated. The samples placed 6 cm from the anode head were irradiated in 20 shots with hydrogen ions. The samples examined with Scanning Electron Microscopy (SEM) before and after irradiation. SEM results showed that the radiation of high-energy protons on the surface of Mo and Cu has caused blisters, cracks, and melts on the surface of the specimens. X-ray diffraction analysis used to investigate changes in the structure of the specimens due to the radiation of high-energy protons. The Lee code was used to characterize the ionic beam of the plasma focus device. The results showed that 7.9 x 1014 ions are emitted from the plasma column in each shot. The SRIM code used to calculate the damage created in Mo and Cu, as well as the concentration of hydrogen at different depths of them. The results of SRIM revealed that the maximum of displacement per atom (DPA) for Mo and Cu samples irradiated with hydrogen ions at depths of 500 and 580 nm was estimated to be 0.024 and 0.009 dpa per shot, respectively. The maximum concentrations of hydrogen ions in the irradiated samples at depths of 550 nm, and 750 nm are 0.5%, and 0.11%, respectively.

One of the most important natural sources of radioactivity is 222Rn radon gas, which is produced deep in earth with a half-life of 3.83 days from the decay of 226Ra radium in the 238U uranium decay chain. Some of the radon gas dissolves in groundwater and enters the body through drinking water and the other part through the inhalation of radon gas in the air. One of the most important risk factors of high radon concentration in the body is lung and stomach cancer. In this study, the concentration of dissolved radon gas of 44 groundwater samples around of Shahre Babak fault was measured using RAD7 detector. Also, the annual effective absorbed dose was calculated for infants, children and adults. Data was analyzed by one sample t-test. The results showed that, the concentration of radon gas in 29.54% of the samples is higher than 11 Bq/l. Also, the minimum and maximum annual effective absorbed doses for infants, children and adults were 69.01±46.00 µSv/y and 747.52±128.18 µSv/y, 33.08±22.05 µSv/y and 357.77±61.46 µSv/y and 24.10±16.07 µSv/y and 260.68±44.78 µSv/y respectively. According to the results, it can be said that in some areas, natural radiation exposure is high due to the high concentration of radon. However, the annual effective absorbed dose can be reduced by informing the residents about the dangers of radon gas.

In this study, Lithium Fluoride nanopowder with Mangnesium and Titanium impurities has been synthesized by Co-precipitation method. The synthesized powder was then pressed into 3.2*3.2*0.9 mm3 pills and sintered at 750⁰c for 10 minutes.  The peak 5 in LiF: Mg, Ti is regarded as the main peak and includes sub-peaks 5a and 5b, which occur at the temperatures lower and higher than that of peak 5, respectively. Peak 5a in LiF;Mg,Ti occurs due to the localized recombination of trapping/luminescence center (TC/LC) , in which the electron is released from the electron trap by obtaining energy from heat and recombines through the tunneling phenomenon with a hole located in the adjacent luminescence center. Concerning the standard TLD chips, which are composed of micron-sized particles, the peak 5a either does not occur or appears with very low intensity, which is insignificant in terms of dosimetry. Thus, the present study focuses on synthesizing thermoluminescence nanoparticles by co-precipitation method in several stages by citing models based on the maintenance of linear behavior of thermoluminescence nanopowder up to high doses and its relationship with localized electron-hole recombination. In addition, by making changes in the concentration of ingredients, the temperature of the reaction medium and the presence or absence of surfactant were evaluated to achieve particles in nano dimensions with suitable geometric shapes. The resulting nanopowder was irradiated with different doses of alpha and gamma and consequently, the increasing rate of the intensity of peak 5a compared to peak 5, as the main factor in nanodosimetry was observed after analyzing the glow curves. Based on the results, the LiF: Mg, Ti thermoluminescence nanopowder could increase the 5a/5 ratio and can be used as a convenient, inexpensive, and practical tool to estimate the amount of energy deposited by the beams in nanoscale.

Lung cancer is one of the most common types of cancer with a high mortality rate among men and women.  This type of cancer, by involving the arteries and lymph nodes, causes the cancerous mass to spread regionally and metastasize. Radiation therapy using teletherapy method and the use of Siemens linear accelerators is one of the most effective non-invasive treatments for lung tumors. In the present study, using Monte Carlo statistical technique and MCNPX2.6 transport code, simulation calculations of treatment process with female ORNL phantom modeling including tumor tissue in the right lung wall and LINAC linear accelerator and validation at 6 and 18MV energies were performed. According to the results, it can be concluded that to control secondary abnormalities during or after the treatment process in the target tissue and other vital organs, increasing the depth and voltage and reducing the treatment time will reduce the dose received by clinical tissues from the electron beam source.