نشریه سنجش و ایمنی پرتو
سال نهم شماره 4 (پیاپی 39، پاییز 1400)

In this research work, hydroxyapatite was synthesized via solid-state method and effect of heat treatment on its thermoluminescence response was investigated for gamma-radiation dosimetry purposes. At the first, hydroxyapatite samples were synthesized in pure form. Then, the hydroxyapatite samples via the same synthesize method were doped with single impurities of Ce and La with concentrations of 1%, 2%, and 5% and were examined afterward.
In order to identify and evaluate the changes that occurred in the material structure and then on dosimetric response, x-ray diffraction apparatuses were used. The results were examined from different dosimetry aspects such as, glow curve change, dose response curve, reproducibility, and fading. The obtained results showed that synthesis in the higher temperature using the solid-state method, is more suitable for dosimetry purposes.

Alpha emitting radionuclides have characteristic and discrete alpha particles from which the type and energy of the alpha emitter can be identified. The unique features of alpha spectrometry compared to other radiometric techniques such as gamma spectrometry are its very low background radiation and the energy independence of the detection efficiency. The aim of this study was to investigate the effect of factors such as alpha particle energy, sample distance to the detector and detector size on the resolution of the alpha spectrometer system. Using an Alphaquattro multi-channel alpha spectrometer manufactured by SILENA, the peak resolution (FWHM) for different energies, different sample-to-detector distances and different detector sizes were investigated. The results of this study showed that the peak resolution improved with increasing sample distance from the detector, but did not change significantly with changing detector size and alpha particle energy. On the other hand, by increasing the distance of the source from the detector, the detection efficiency decreases. For the best performance, the optimal distance should be considered or when the distance is long, the vacuum conditions should be improved and the counting time should be increased.

Dosimetry of a pregnant woman under diagnostic imaging with ionizing radiation is very important due to the high radiosensitivity of the fetus and the destructive effects of radiation on it. In this study, the amount of S-values induced by the positron-emitting radiopharmaceutical 18F-FDG in different fetal organs were calculated using the MCNPX2.6 Monte Carlo code. In the simulations, hybrid phantoms of 3- 6- and 9-month pregnant women were used. The results showed that with increasing the fetal age, the self S-values of fetal organs decrease. A comparison between the calculated data in this study and those reported by other studies showed similar trend, however in some cases the data difference was up to 40% on average. These differences are due to the differences between the geometry of the used phantoms. Therefore, in order to more accurately estimate the dose to pregnant patient and her fetus, we intend to introduce a method for constructing a patient-dependent phantom using a limited number of measurements in our future studies, and thus increasing the accuracy of the calculated dose.

Dual-energy X-ray radiography is an important inspection technology in imaging large cargos for finding illegal materials such as explosives, narcotics, weapons, etc. A useful aspect of dual-energy X-ray radiography is the possibility of discriminating and identifying materials with different atomic numbers which can be obtained by imaging large cargos at two different X-ray energies (normally above 3 MeV). In the present work, first a dual-energy X-ray radiography system including X-ray sources, collimator, and detector array was simulated using MCNPX code. Then, the obtained data from this radiography system for four step wedges of graphite, aluminum, steel, and lead materials were gathered and material discrimination curves were obtained using four algorithms including log-log, R-T, r-θ, and α2-α1. The results show that among the proposed algorithms for material discrimination, R-T, r-θ, and α2-α1 algorithms have better performance and due to the less overlap of material discrimination curves for low sample thicknesses, R-T algorithm can be a better choice for obtaining material discrimination curves in dual-energy radiography systems.

The increasing development of nuclear science and related applications in various fields facing humans and the environment with ionizing rays, inevitably. The exposure of these rays to the human body can cause many side effects. Therefore, we need a protective shield to prevent or at least decrease these complications. Lead is the best known material in nature which can efficiently attenuate X and gamma rays. Toxicity and heaviness of lead limit its radiation shielding applications. Replacing lead with other heavy elements and placing the particles in a polymer substrate can alleviate the problem of toxicity and heaviness to some extent. Also, according to research, the use of nanoparticles instead of bulk particles, especially at low energy, is expected to increase the protection performance. In this study, the compounds of bismuth oxide and iron oxide in polycaprolactone polymer substrate were investigated. The attenuation of gamma rays emitted from two sources of 137CS and 60Co when passing through the manufactured samples were measured. The results show an increase in the radiation attenuation capability of both types of polymers made with nanoparticles compared to bulk compounds. As expected, the effects of particle size reduction on radiation attenuation are more pronounced in the case of 137CS source.  The results show that the half-layer thickness decreased by 48 (37) percent for the bismuth oxide sample and 36 (21) percent for the iron oxide sample for gamma rays emitted from the 137Cs (60Co) source.

One of the aspects of water quality is the study of radionuclides in it, which is very important due to being hazardous contamination of radioactive materials. One of the main ways of penetration of radioactive materials into the human body is the consumption of water infected by natural or artificial radioactive material. In this work, 20 samples of drinking water in Ilam province, which cover more households was studied and measured in aspect of radioactive activity. Sampling was performed according to the required standards from the specified sources, then the total alpha and beta concentration activity of the samples (... ,... ) were measured using a "Liquid Scintillation Counter" (LSC). The results showed that ...  and... . The correlation coefficient between these two variables is 0.27 and it is justified by the ...  test that there is not significant relationship between these variables. The results showed that the gross alpha and beta activity concentration of all waters was lower than the standard of the World Health Organization (WHO) and the National Standards Institute of Iran, which is 500 mBq/Lit and 1000 mBq/Lit, respectively. Therefore, in terms of radiological quality, these waters are healthy and their consumption will not be risky for people.