نشریه سنجش و ایمنی پرتو
سال هشتم شماره 3 (پیاپی 32، بهار 1399)

In this work, for the first time, effect of gamma irradiation on the optical properties of CdS (quantum dots) QDs in various concentrations was studied. The aqueous CdS QDs were synthesized in a facile and fast method by using domestic microwave oven.  Three concentration of QDs; 20, 2, 0.4 mg/cc after different administrated dose of gamma irradiation (0-20 kGy) were studied. The results showed increased sensitivity of QDs after gamma irradiation with decreasing of concentration, so that the PL emission was completely vanished for concentration of 0.4 mg/cc after 20 kGy dose of irradiation. The optical results showed QDs were grown under gamma irradiation. Therefore, desired dose measurement can be carried out by choosing appropriate concentration for  gamma dosimetry.

The application of large plastic scintillators is widely increasing in the different areas of industry, medicine and security due to technical and economic advantages. One of the main disadvantages of these detectors is the unknown position of Compton edge at gamma ray spectrum. In this research, GEANT4/GATE code has been used to simulate the gamma ray spectrum for different volumes of large plastic scintillator. According to these simulations, the dependence of the Compton edge position, energy resolution at Compton edge and efficiency of the optical photon collection to the scintillator dimensions has been investigated. The simulations showed that the Compton edge position with respect to local maximum at Compton continues strongly depends on the scintillator dimensions. These results were verified by experimental spectrometry.

External radiotherapy is used for treatment of various types of cancers. Due to the impossibility of measuring the absorbed dose delivered to different organs during irradiation, treatment planning systems (TPSs) have been utilized for calculation of absorbed dose before a radiotherapy procedure. Thus, the accuracy and precession of the TPS is essential.The aim of this study is investigation of accuracy the TPS based on Collapse Cone Convolution (CCC) algorithm in a lung tissue equivalent material. The charge generated in the sensitive volume of PTW-30013 ionization chamber in water and lung tissue equivalent phantoms placed in the radiation fields of Primus 6MV linac was calculated using MCNP.4C code and in the ratio of generated charge in this phantom was determined. To validate the simulations, the ratio of generated charge in sensitive volume of ionization chamber in mentioned phantoms was determined experimentally. The agreement between the calculations and measurement confirm the simulation method. The calculated absorbed dose delivered in the lung tissue equivalent material for 200 MU radiation was 154.99 cGy using simulations. The CCC algorithms predicted this value as 163.98 cG. As well as, the absorbed dose in different depths was measured using GR-200 Dosimeters. The relative differences between the values obtained by simulation and CCC algorithm and between the results of TLD measurements and CCC algorithms are more than 5.5% and 14%, respectively. So, by considering the acceptable uncertainties suggested by ICRU for TPS algorithms and the results of this work, it can be concluded that, the CCC algorithm is not sufficiently accurate to determine of absorbed dose delivered to tissues with density lower than water.

Titanium-stabilized Zirconia (ZrO2:Ti) nanoparticles were synthesized by the solution combustion synthesis method. This functional method is used for production of luminescent materials. Ti concentration was between 0.1 to 2 mol %. Nano crystalline tablets of 5 mm diameter and 1 mm thickness were prepared from synthesized powder. The effects of Ti concentration and annealing temperature on the structural properties of the produced sample were analyzed by X-ray diffraction (XRD) patterns, Fourier transformation infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). We reported the thermoluminescent (TL) properties of the ZrO2 doped with Ti exposed to beta radiation from 90Sr. The characterization results showed an appreciable influence of the Ti-dopant on zirconia crystalline phases and the particle sizes. Although the obtained samples contained tetragonal and monoclinic phases, the phase structure of the material changes to monoclinic with heat treatment. Results of FTIR analysis showed that Ti was completely placed in base materialchr('39')s structure. TL glow curves of samples showed that intensities were affected by different amounts of Ti and heat treatment. It was concluded that ZrO2:Ti with 1 mol % and the annealed samples at 1100 ℃ had the highest peak intensity and the best thermoluminescence response. In addition, this sample showed a linear response for beta doses in the range of 0.1 to 1000 Gy. Three peaks were observed in glow curves at 114, 175 and 222 ℃ and the main peak, is at 175 ℃.

Widespread use of ionizing radiation in medicine, industry, agriculture, education and research, the increasing production of nuclear waste and nuclear incidents, has exposed humans and organisms to this radiation. Despite the benefits of ionizing radiation, these beams can cause serious damage to living systems. Hence, the need for radiation protection actions requires accurate, fast, inexpensive, and comprehensive detection and dosimetry systems. In this regard, in this paper, an electrochemical sensor based on the carboxylated multi walled carbon nanotubes-silver nano particles (MWCNTs-COOH/AgNPs) nanocomposite modified glassy carbon electrode is designed for superoxide anion detection and measurement. Also, the possibility of ionizing radiation sources detection, by measurement of superoxide which is produced during the radiolysis of aqueous environment under these radiations, is discussed. For this purpose; firstly, the surface of glassy carbon electrode modified with MWCNTs-COOH and AgNPs respectively. Ultraviolet-visible spectroscopy (UV-Vis), fourier transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM) images used to characterize the MWCNTs-COOH, AgNPs and study of the glassy carbon electrode modification with MWCNTs-COOH/AgNPs nanocomposite. Then the reduction process of superoxide produced from a solution of dimethyl sulfoxide containing potassium superoxide, on the surface of modified glassy carbon electrode studied, using cyclic voltammetry method. Also, by performing chronoamperometric studies, two linear response limits for superoxide for low concentrations (1.5 to 43 mM) and high concentrations (136 to 323 mM) and detection limit of 0.39 mM was obtained. At the end, the MWCNTs-COOH/AgNPs nanocomposite modified glassy carbon electrode was used for the detection of ionizing radiation emitted from cesium-137 and cobalt-60. The difference between electrochemical responses of the electrode, in the aqueous medium before and after the sources irradiation, attributed to the presence of superoxide and confirmed the successful performance of the sensor.

MgSO4:Cu phosphor was synthesized by solid state method. Optimum concentration of copper was determined at 0.1 mol%. Thermoluminescence characteristics of MgSO4:Cu was studied following gamma irradiation. A linear dose response was observed in dose range of 1Gy to 500Gy. Reusability of this sample was tested after 10 cycles of gamma irradiation and it revealed that the intensity remains approximately unchanged. Kinetic parameters of MgSO4:Cu phosphor including kinetic order and activation energy was calculated by computerized glow curve deconvolution method.

Estimation of organ doses in diagnostic and therapeutic nuclear medicine procedures is an area of particular concern for radiation protection, in all over the world. The stylized computational phantoms have contributed significantly to radiation dosimetry in nuclear medicine; however, their simplified treatment of human anatomy is being criticized. Due to the fact that the ICRP adult reference phantoms are representative of Caucasian population, dose estimation within other ethnic/racial groups was recommended. In this study, an Iranian adult female reference phantom has been developed and internal dosimetry calculations have been performed for several radiopharmaceutical labelled with beta-, gamma- and positron-emitting radionuclides incorporated into Iranian and ICRP adult female reference phantoms. For main source and target organs, the ratios of S values between ICRP reference phantom to Iranian reference phantom for I-131, Tc-99m and F-18 are 0.54-1.23, 0.54-1.15 and 0.77-1.79, respectively. Therefore, construction of a reference phantom proportional to Iranian ethnicity for both gender in all age groups and performing internal dosimetry calculations to create a library of internal dosimetric data for Iranian patients were confirmed clearly.

The ionizing radiations, through physical and chemical processes, lead to simple and complex single- and double- strand breaks, as well as base lesions to the DNA. In this study, taking into account all the physical and chemical processes involved in the interaction of ionizing radiation with matter, the initial damage induced to DNA was evaluated for 5.7 MeV alpha-rays from Radon 223 isotope. The probability of damage types was calculated in terms of the energy deposition and the probability of direct and indirect damage was investigated as a function of the number of breaks. The results show that, for low deposited energies, the probability of single-strand breaks is more than double-strand breaks. As the amount of the deposited energy increases, this pattern is reversed and the probability of various types of double-strand breaks dominates. The yield of double-strand breaks in the DNA segments, as a main target in radiotherapy, was calculated by the method of energy deposition in DNA samples and compared with previous works. Our results are in good agreement with experimental results.