نشریه سنجش و ایمنی پرتو
سال یازدهم شماره 1 (پیاپی 41، بهار 1401)

Ionizing radiation collides with biological systems, inflicting ionization and excitation of atoms and molecules, developing abnormal and harmful products with inside the biological environment. Estimation of absorption dose is of particular significance in evaluating the medical and biological effects related to ionizing radiation from radiopharmaceuticals. Therefore, the aim of this study was to evaluate the absorbed dose of human body organs resulting from the novel 99mTc-MAX labeled compound based on studies of the biodistribution of balb/c mice. The designed ligand with chelating properties was synthesized by the reaction between the two substances Chloroacetamide and Xanthate with certain molar ratios. Then, the labeling process was performed successfully with 99mTc and with 93% radiochemical purity in the laboratory and 90% in the presence of human blood serum. The biodistribution of the labeled complex in balb/c mice up to 24 hours after injection was then examined. MIRD method was used to estimate the absorbed dose in human organs. The results indicate the highest absorbed dose of the complex in the liver with 0.0011mGy / MBq. The 99mTc-MAX can be a potentially effective imaging agent due to its significant hepatic uptake as well as its proper accumulation in the reticuloendothelial system.

In this paper, the ability of using IRF series power MOSFETs as gamma ray dosimeters was investigated. For this purpose, the threshold voltage shift generated by gamma ray radiation and the fading characteristics at room temperature, as the two main characteristics of the ideal dosimeter, for three types of power MOSFETs with a drain-source on resistance (RDS(on)) greater than 1Ω was measured and compared. Cobalt-60 source was used for irradiation at radiation dose in the range of 1-100krad with a dose rate of 10krad/h. The results show that the threshold voltage shift relative to the radiation dose has a good linearity for all three types of MOSFETs. Also, MOSFET with higher RDS(on) is more sensitive to gamma radiation. The fading characteristics for all three types of MOSFETs in the six-month period is less than 1%. Therefore, inexpensive IRF series MOSFETs are good candidates for gamma ray dosimetry.

Various imaging techniques have been used for the readout of the polymer gel dosimeters. Due to limitations in imaging modalities such as Magnetic resonance imaging and X-ray CT, the optical technique was suggested as a precise and practical alternative for evaluating the gel dosimeters parameters. This study aimed to investigate the optical response of the PAKAG polymer gel dosimeter. To this aim, the PAKAG polymer gel dosimeter was produced in Imam Khomeini International University (IKIU) gel dosimetry laboratory. A clinical linear accelerator system with 6 MeV energy was used for irradiating. The absorbance as a function of wavelength was obtained using a UV-Vis spectrometer to read out the irradiated gel dosimeters. Results showed that the sensitivity of 0.11 Au.Gy‑1 was acquired at a wavelength of 340 nm. Evaluation of the post-irradiation time effects showed that the gel dosimeter's sensitivity was stabilized for post-irradiation times beyond 24h. Results confirmed the UV-Vis readout technique as an appropriate method for evaluating the PAKAG polymer gel dosimeter's response.

The safety assessment of Anarak site as the only center for the disposal of radioactive waste is of particular importance in order to maintain human health and the environment. Distribution coefficients of radioactive materials in the soils of the area under study is one of the influential parameters in the safety assessment calculations. Therefore, in this study, the distribution coefficient of cobalt in the alluvial soil of Anarak waste was determined by the batch method and two parameters of concentration and soil to solution ratio were studied. Linear adsorption isotherms, Friendlich and Langmuir were also analyzed to determine the adsorption behavior of cobalt in Anarak soil. The average value of cobalt distribution coefficient in the mentioned soil was calculated equal to 247.18 mL / g. The adsorption behavior of cobalt in Anarak soil followed the Langmuir adsorption isotherm with a positive and significant correlation. The maximum amount of cobalt uptake was determined as 0.029 mg / g soil. The results of the distribution coefficient obtained in this study are lower than the most of the values ​​presented in the other previous researches, which can be related to the soil texture (sandy loam) and the other soil characteristics.

By defining random quantities related to microscopic structures, microdosimetry can provide accurate information about the effects of radiation. Using the µ-randomness method and the Geant4-DNA code, in a sphere of water for low energy electrons in the energy range of 0.1 to 4.5 keV, the microdosimetric values of the frequency-mean lineal energy, dose-mean lineal energy, frequency-mean specific energy, and dose-mean specific energy were calculated. In this study, target volumes including cylinders with dimensions (height × diameter) of 23 × 23 equivalent to DNA volume, 50 × 100 equivalent to nucleosome volume, and 300 × 300 angstroms equivalent to the volume of chromatin fiber were selected. Examining the frequency-mean lineal energy and dose-mean lineal energy, it was observed that the trend of changes in the energy of the primary electrons is similar to the trend of changes in the damage of the same electrons in the DNA. The research results are also compared with the existing results of the simulation with the PITS and KURBUC codes. Differences in the results of this study were observed with the results of PITS and KURBUC codes, which is due to differences in the cross-sections of the electron used in the codes under study. In the Geant4-DNA code, for example, for low-energy electrons, the ionization and excitation cross-sections are smaller than those obtained by other codes.

The natural level of radioactivity in the Zn-Pb ore at the Yazd mine was determined and the associated radiological hazards were assessed. Specific activities of 226Ra, 232Th, and 40K radionuclides in the Zn-Pb ore were measured using a high purity germanium detector (HPGe) system and radiological hazards indices as radium equivalent activity (Raeq), external and internal hazard indices (Hex), gamma representative levels index (Iγ), adsorption dose rate in the air (D), annual effective dose (AED), annual gonadal dose equivalent (AGDE) and excess lifetime cancer risk (ELCR) were calculated. The average specific activities of 226Ra, 232Th, and 40K radionuclides in Zn-Pb ore were obtained as 37.12±5.32, 14.66±5.43, and 293.56±21.18 Bq/kg, respectively. These values ​​were less than the global average, except for the 226Ra activity value, which was close to the global average. Also, the average radiological risk parameters, such as Raeq, Hex, Hin, D, AED, AGDE, and Iγ were obtained in a safe range. The mean ELCR for Zn-Pb ore, mine waste, and the surrounding soil was 0.15 × 10-3, 0.15 × 10-3 and 0.23 × 10-3, respectively, which was lower than the global average 0.29 × 10-3. The study showed that the level of radioactivity in the Zn-Pb ore zone did not exceed the critical value and is in line with the global results. Moreover, the calculated indicators of radiation hazard showed that lead zinc ore is safe for mine workers and does not pose a significant radiological hazard to them.