نشریه سنجش و ایمنی پرتو
سال نهم شماره 1 (پیاپی 36، زمستان 1399)

In this study, nanophosphorus Ca1-xZrO3:Eux (x=1,2,3,4,5 mol%) was prepared by sol-gel combustion method with citric acid as fuel at low temperature. The results of X-ray diffraction (XRD) analysis indicated the formation of sample phase at 350 °C with perovskite structure. XRD results also showed that the optimum temperature for the formation of single phase and crystalline nanophosphours sample of CaZrO3:Eu3+ is 700 °C. Surface morphology of the samples was identified by field emission electron microscopy (FE-SEM). X-ray energy dispersive analysis (EDAX) was employed to evaluate the elemental concentration of the samples. Study of thermoluminescence characterization of the produced samples were performed under constant UV irradiation with change of Europium impurity concentration and change of UV irradiation time for the sample Ca0.98Eu0.02ZrO3. Other thermoluminescence features such as reproducibility and fading were also evaluated for Ca0.98Eu0.02ZrO3 sample.

One of the most important issues, post a nuclear incident, is the fast and precise determination of the type and quantification of radioactive material dispersion. Joint location-energy analysis approach, using modern nonstationary data analysis, to design a suitable detector with accurate, dynamic measurement and commensurate with the radiation protection and safety actions, is discussed in this paper. Designed joint location-energy analysis structure utilizing this method, with its capability for implementing nonstationary parameters of gamma-ray spectrum, leads to an accurate classification the type and amount of radioactive material and increase the detector crystal effective volume. The proposed method eventuates the increment in accuracy and precision in determination of the type and quantification of dispersion radioactive materials and decrement in survey time, which will result the survey area expansion, for civil defense purposes, in the same limited time.

Safe water is one of the basic needs of humans that must be free of any contamination. One of the water pollutants is radioactive nuclei, which naturally and artificially occur in the environment. Therefore, accurate measurements of water radioactivity are very important. The activity concentration of 226Ra, 232Th, 40K, and 137Cs in 26 drinking water samples from the Isfahan province was measured by gamma spectrometry using a high purity germanium detector (HPGe). Activity concentrations of 226Ra for all samples were below the detection limit. The average specific activity of radionuclides 232Th, 40K and 137Cs were measured as 1.40, 82.23 and 0.0.40 respectively in Bq/l. Annual effective doses as a result of ingestion of water containing 232Th, 40K and 137Cs radionuclides for adults ranged from 0.317 to 1.153 with an average of 0.784, from 0.059 to 0.150 with an average of 0.114 and from 0.001 to 0.016 with an average of 0.003 in μSv/y respectively. The excess lifetime cancer risk was calculated for three age groups, which was 1.59 ×10-6 for adults. The results showed that the annual effective dose as a result of drinking water consumption was lower than the WHO Individual Dose Criterion (100 μSv/y), so it does not pose a threat to the inhabitants of this area and has good quality.

Computed Tomography (CT) is one of the most widely used screening and diagnostic tools in medical imaging centers. Considering IAEA HUMAN HEALTH SERIES No. 19 and the American College of Radiology (ACR) Accreditation Program, quality assurance (QA) and quality control (QC) are mandatory programs to periodically monitor the system condition to promote the effective utilization of ionization radiation for a diagnostic outcome through obtaining and retaining appropriate image quality and reduction of patient dose. Computational phantoms (CPs) are the key tool to monitor system condition. The commercial QC phantoms are expensive products and are not flexible enough for user demands. Also, it has recently been reported that standard parameters based on IAEA and ACR, including noise magnitude, and resolution, are not accurate parameters for quantitatively evaluating system performance in terms of image quality. In this paper, we designed and fabricated a new CP along with a graphical user-friendly interface program integrally called “QCT” enabling to measure IAEA/ACR-based standard image parameters and beyond metrics including CT calibration curve, CT number of multiple objects, contrast-to-noise ratio, the edge spread function, the line spread function, the modulation transfer function, spatial resolution, noise power spectrum, image noise, and uniformity. The experimental assessment of QCT was tested on a GE LightSpeed VCT multi-detector CT scanner available in Emam-Khomeini hospital complex. In addition, we reported the details of fabrication process of our QC phantom, enabling readers to create flexible and affordable QC phantoms.

Production of semiconductors such as silicon doped with phosphorus has many applications in the production of electronic components and various industries such as aerospace. The process of impurity making, which is called silicon doping, can be done by both chemical and nuclear methods. Since the uniformity of the injected impurities is not suitable in the chemical method, the methods of silicon doping by neutron irradiation method are strongly followed in the world. In this work, the potential of the thermal column of Tehran Research Reactor for silicon doping is investigated using MCNPX simulation code. The results show that the thermal neutron flux as well as the ratio of thermal to fast neutron flux in the optimal location are 1.2×1012 n/s.cm2 and 441, respectively, which shows that the thermal column of the Tehran research reactor can be a suitable place for silicon doping.

One of the most important issues in radiation facilities and space missions is determining the dose of ionizing particles in the radiation environment. MOSFET dosimeters are among the tools for measuring doses in these environments, which in addition to very high sensitivity to radiation, can also withstand high flux of particles. These tools also have a small volume, low power consumption and high reliability. The purpose of this work is the design and construction of a MOSFET radiation dosimeter system based on the threshold voltage shifts. Radiation calibration of this system has been performed by irradiating MOSFETs in different doses (from 5 to 100 Gy) in the secondary standard center (SSDL) in Karaj. The temperature dependence of these transistors is also considered in all measurements according to the coefficient of temperature change. The results showed that the response of these MOSFETs to different radiation doses is almost linear and has a sensitivity of about 1 to 6 mV/Gy and depending on the radiation environment and the required dimensions of these MOSFETs, different types can be used.

The aim of this study is to evaluate the effects of ZnO nanoparticles (NPs) doped with Gd on dose enhancement factor (DEF) by using the PRESAGE dosimeter and Monte Carlo simulation. Initially, the water equivalent PRESAGE dosimeter was fabricated and calibrated against some dose levels. Then ZnO NPs doped with Gd were synthesized. At next step, various concentrations of the prepared nanoparticles were incorporated into the PRESAGE composition and irradiated in small radiation fields by 6 MV photons. The dosimeters were then read-out by spectrophotometer. Then the mentioned processes were simulated by Monte Carlo code. By comparing the results in terms of the presence and lack of NPs, DEF was acquired. Simulation results showed that at mentioned condition, the DEF of about 1.06, 1.10, 1.12 for 1×1 cm2 field size, 1.07, 1.11, 1.17 for 2×2 cm2 and 1.09, 1.13 and 1.20 for 3×3 cm2 could be derived, respectively. Also spectrophotometer measurements showed that by incorporating 125, 500 and 1000 µg.ml-1 ZnO NPs doped with Gd into PRESAGE structure the dose enhancement factor of about 1.42, 1.48, 1.50 for 1×1 cm2 field size, 1.46, 1.49, 1.54 for 2×2 cm2 and 1.46, 1.52 and 1.58 for 3×3 cm2 could be found, respectively. The results of this study showed that dose enhancement factor increases by increasing field size. Various reasons may cause the DEF for megavoltage photon beams such as photoelectric effect for low energy photon beams in continues X-ray spectrum, pair production effect and even Compton scattering.

In this research, air samples were collected at an air flow rate of 300 m3/h to 900 m3/h. These samples were collected during more than two months (Nov 2019-Jan 2020). After the decay of short-lived radionuclides, the samples were formed as a disc to prepare for measurement. Then, these discs were evaluated by two HPGe detectors with relative efficiencies of 40% and 70%. A prototype of a standard high volume air filter was proposed and constructed by a novel method, which provides a symmetric distribution of radionuclides and efficiency calibration curve was obtained for two HPGe detectors. This standard filter was solved the problem of the asymmetry and inhomogeneous distribution of radionuclides in standard air samples. 7Be concentrations were assessed in the collected samples. The average concentration of 7Be was measured as 3.80±0.46 mBq/m3.