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    A Monte Carlo investigation of some important radiation parameters and tissue equivalency for photons below 1 keV in human tissues
    (IOP Publishing Ltd, 2022) Rafiei, Mustafa Mohammad; Parsaei, Sara; Kaur, Parminder; Singh, K. J.; Büyükyıldız, Mehmet; Kurudirek, Murat
    The attenuation coefficients are important input values in estimating not only the dose and exposure in radiotherapy and medical imaging, but also in the proper design of photon shields. While studies are widely available above 1 keV, the attenuation coefficients of human tissues for photon energies less than 1 keV have not been studied yet. In this study, the attenuation coefficients of water and some human tissues were estimated for low energy photons using the MCNP6.1 code in the energy region 0.1 keV-1 keV. Mass attenuation coefficients were estimated at photon energies of 100, 150, 200, 250, 300, 350, 400, 450, 500, 550, 600, 650, 700, 750, 800, 850, 900, 950 and 1000 eV for water and ten human tissues (Soft, Breast, Lung, Bone, Brain, Eye lens, Ovary, Skin, Thyroid and Prostate). Results were compared with those available in literature and a fairly good agreement has been obtained. These data were then used to calculate the mean free path, half value layer, tenth value layer, effective atomic number and specific gamma-ray constant (useful for calculation of dose rate) as well. Moreover, for comparison the effective atomic number of the water has been obtained using the results of this work and using the data available in NIST database from 0.1 to 1 keV. In addition, the human tissues were compared with some tissue equivalent materials in terms of effective atomic number and specific gamma-ray constant to study the tissue equivalency from the results, the muscle-equivalent liquid with sucrose has been found to be the best tissue equivalent material for soft tissue, eye lens and brain with relative difference below 4.1%.
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    Investigation of radiological properties and water equivalence of polymer gel dosimeters in the energy range 0.1-10 keV
    (Korean Nuclear Soc, 2025) Levet, Aytac; Thakur, Sonika; Kaur, Parminder; Rafiei, Mustafa Mohammad; Parsaei, Sara; Buyukyildiz, Mehmet
    The interaction parameters of radiation with matter are crucial for accurately determining radiation doses in diagnostic and treatment. This study examined the radiological features of normoxic polymer gels used to measure radiation doses. The mass attenuation coefficient (MAC), mass energy-absorption coefficient (MEAC), effective atomic number (Zeff), half value layer (HVL) and mean free path (MFP) for these samples were determined in the energy range of 0.1 keV-10 keV. Zeff was established using direct and interpolation methods. The largest discrepancy for Zeff between the methods was observed for water, with a 48 % difference in the energy range of 0.3 keV-0.5 keV. MACs of the samples were compared with Monte Carlo simulation results based on FLUKA 4-3.1 code. MAC results obtained with simulation showed good agreement with Hubbell, and the maximum and minimum differences between them were seen in the FAT sample as 8.31 % and 0.08 %, respectively. Additionally, dose rate, gamma constant, and air kerma values were calculated using mass energy absorption coefficients for all samples and their water equivalence was evaluated in the relevant energy range. It was observed that the samples with radiological water equivalence and air kerma values close to 1 were PAGAT, MAGIC, MAGAS, and MAGAT.
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    Study of low-energy photon interactions below 1 keV for some biological molecules of human body
    (Springer Heidelberg, 2022) Mohammad Rafiei, Mustafa; Parsaei, Sara; Kaur, Parminder; Singh, K. J.; Buyukyildiz, Mehmet; Kurudirek, Murat
    In the present work, the authors have studied the radiation interactions at very low photon energies (below 1 keV) for some materials of biological importance, viz. water, glycerol, adenine, guanine, palmitic acid, myristic acid, valine, tryptophan, histidine, glucose and ribose. The parameters including mass attenuation coefficient, mean free path, half value layer, tenth value layer, effective atomic number, mass energy absorption coefficient, gamma constant and dose rate have been investigated in the energy range from 100 to 1000 eV. MCNP6.1 simulations have been employed in this study. Water was found to have higher values of mass attenuation coefficient and effective atomic number among the other materials, whereas palmitic acid possesses relatively lower values except for the energy region wherein abrupt changes occur near the K edge absorption energies. The values of mean free path, half value layer and tenth value layer were observed to be close to hair-like thickness or a thickness of few cell layers. Exposure to such low-energy photons can be very damaging to the skin cells and even the DNA. Such study will prove to be very useful for radiological applications.