نشریه سنجش و ایمنی پرتو
سال دوازدهم شماره 4 (پیاپی 48، زمستان 1402)

For shielding against nuclear radiation, the low weight of the shield is very important. Shielding design is a multi-objective optimization problem. In the shielding design, first the parameters are estimated analytically based on the equations, and then the final design is done using calculation codes. However, in many cases, the designed shields lack the necessary optimization and it is necessary to optimize the initial design using known methods. In this research, in order to optimize the biological protection of a modular reactor, a multi-objective optimization method has been proposed to couple the PSO algorithm with the ANISN calculation code. Two objective functions of the component, including weight and radiation dose, are included in a multi-objective mathematical model. The overall objective function is a weighted linear combination of each of these two component functions. Materials used for optimization include concrete, composite including B4C and B2O3. The results show that the multi-objective optimization method for the biological protection design of a modular reactor is reliable and efficient. This method can improve the design quality of the shield and reduce the weight of the shield by 38% and reduce the total dose rate of neutrons and photons by 83%, compared to the case where the conventional shielding of the reactor well (serpentine concrete) is used.

The production of trans-uranium isotopes such as Am-241 and Cf-252 is done using irradiated reactor fuels or by irradiating targets in the core of research reactors. The main production of these two radionuclides is done in America and Russia. In this study, at first, the feasibility study of producing these nuclides using the irradiated fuels of a typical research reactor for two powers of 5 and 10 megawatts has been done using the ORIGEN code. In another part, calculations for the target of uranium with 99.7% by weight of uranium-238, which exists at the end of the enrichment cycle, has also been done. The results of the calculations show that the production efficiency of trans-uranium radionuclides in 10 MW power is many times higher than 5 MW. Also, the efficiency of trans-uranium radionuclides production using the target irradiation of depleted uranium is about 2 times higher than the radionuclides produced form the irradiated fuel of the typical 5 MWe research reactor.

Today, the use of lead-containing glasses and heavy transparent shields in various medical applications of radiation, including diagnostic radiology procedures, especially in angiography departments, has become very popular. In such departments, roof shields, transparent shields, and glasses made of lead glass are widely used for the radiation protection of personnel. In this study, the MCNPX Monte Carlo simulation code was used to design transparent and lead-free shields that can be used for radiation protection. For this purpose, two types of phosphate glass containing different percentages of heavy materials were simulated and compared with each other in terms of attenuation coefficients of photons with different energies. After simulating different glass types, the mass attenuation coefficients of each sample were calculated for single-energy photons. After that, by simulating the X-ray spectra used in angiography, the thicknesses of the first and second half-value layers were calculated for each spectrum. The results of this study show that the simulated values of the mass attenuation coefficient of glass types show good agreement with the results of XCOM. According to the results, the designed lead-free glass types have an attenuation comparable to leaded shields, which can be used as a suitable alternative to leaded glass types.

The design and construction of a radiation portal monitor for the detection of radioactive materials and pollution, the control of the transportation of radioactive materials, and the inspection and identification of radioactive materials in customs, with an emphasis on monitoring the inner space of vehicles and truckloads, was carried out in Iran's Radiation Application Development Company (IRAD Co.). The radiation portal monitor can be installed as a gate on both sides of the entrance of factories, nuclear facilities, customs, airports and borders, and it is considered a new way to deal with the dangers caused by radioactive materials. This system is sensitive to very low levels of radioactive contamination. It comprises electronic circuits, mechanical holders, and four plastic scintillation detectors as a monitoring system. Some of the equipment of this system include a camera for taking photos of the license plate, ability to install the automatic control barrier, the remote-control center, the indicator light to inform the driver of the situation, and the visual and audio warning signs. Functional tests using a 137Cs source with an activity of 3 µci showed that the radiation portal monitor could detect a source inside the car with a minimum activity of 3 µci at a range of 100 cm. This system is also very accurate in identifying the same source when it moves at a maximum speed of 1.4 m/s.

Having a portable and accessible radiation monitoring tool for members of the society, especially when faced with radiation caused by unwanted nuclear accidents, can provide a solution for radiation exposure monitoring. The monitoring is based on the sensitivity of CCD and CMOS semiconductor of smart mobiles to ionizing radiations. After receiving ionizing radiation such as gamma and X-rays, these sensors can receive the incident beam energy as a result of processes such as the photoelectric phenomenon and create charge carriers by creating ionization in the semiconductor medium of the sensor. The current resulting from the collection of charge carriers will result in the recording of bright (irradiated) and dark (unirradiated) spots on the camera sensor. Measuring the density of bright and dark points in the recorded images provides the possibility of estimating the amount of radiation exposure. In this research, four quality cameras and different brands were selected and dosimetry process for two sources of gamma radiation 60Co and 137Cs have been investigated.  The ratio of the total area of bright spots to the number of illuminated pixels per unit of time, which is proportional to the received dose, was measured and the calibration coefficient was determined for each camera. In the measurements made, the effect of time of death, resolution, stability and reproducibility have been checked and the necessary corrections have been applied. The obtained results show that for all the cameras used, there is a linear relationship between the recorded results and the received dose.

Today, radiotherapy is considered one of the most effective methods for cancer treatment. Research has shown that using nanoparticles with high atomic numbers such as gold, silver and gadolinium as radiosensitizers in radiotherapy is very effective and increases energy deposition in the target organ due to their high atomic number. On the other hand, using short-range charged particles, such as auger electrons, given their relatively low energy, enables the destruction of damaged tissue cells with minimal damage to surrounding healthy cells. In this study, the effects of diffusion of auger electrons from radionuclides such as 99mTc, 201Tl, 123I, 125I, 111In, and 67Ga on single-strand breaks (SSBs), direct and indirect double-strand breaks (DSBs), and hybrid double-strand breaks (Hybrid DSBs) in the presence and absence of gold, gadolinium and silver nanoparticles were investigated using the Geant4-DNA toolkit for the 1ZBB model (selected from the Protein Data Bank library). The results show that among the mentioned auger emitters, 125I and 99mTc cause the most and 123I the least DNA damage. On the other hand, adding gold, gadolinium, and silver nanoparticles can increase DNA damage by 59%, 56%, and 55%, respectively. The results of this study show that 125I and 99mTc are more effective options for inhibiting or controlling cancer cells. In addition, adding gold nanoparticles can also lead to improved treatment efficacy.