Radiation Physics and Engineering

Abstract This study presents a GEANT4-based Monte Carlo dosimetry comparison of clinically realistic I-125 (Amersham OncoSeed 6702) and Pd-103 (BEBIG IsoSeed) brachytherapy sources in adipose tissue, soft tissue, and blood. The simulation model was rigorously validated against AAPM TG-43 consensus data, showing excellent agreement in dose rate constants and radial dose functions. The model was thoroughly tested and validated to ensure its robustness and accuracy. Results demonstrated that tissue composition significantly alters dose distributions compared to water. Adipose tissue permitted the deepest penetration, while blood showed the strongest attenuation. The results indicated that I-125, align with its lower average energy, produced a broader dose distribution than Pd-103. Conversely, 103Pd exhibited a steeper dose gradient, confining energy closer to the source. These findings underscore the critical importance of incorporating both tissue-specific composition and the full photon energy spectrum into brachytherapy treatment planning to optimize dose delivery for personalized patient care ultimately optimizing clinical outcomes.

Abstract This study investigates the thermoluminescent (TL) behavior of calcium phosphate-based ceramic pellets, hydroxyapatite (HAp) and ‎‎β-tricalcium phosphate (‎β‎-TCP), fabricated using two distinct sintering techniques: spark plasma sintering (SPS) and pressureless sintering (PLS). The main objective was to evaluate how the fabrication route and powder origin influence the dosimetric characteristics of these materials. Pellets were prepared from both laboratory-synthesized and commercially obtained powders and irradiated with ‎γ‎-rays from a Co-60 source in the dose range of 20 to 800 Gy. The results revealed that pellets derived from commercial powders exhibited comparable TL responses under both sintering techniques, while those produced from synthesized powders showed notable differences in TL intensity and linear dose-response range. The PLS fabricated pellets displayed improved fading resistance and repeatability, maintaining a more stable TL signal over time compared with their SPS counterparts. The influence of sintering conditions, powder type, and thermal history on the glow curve structure and kinetic parameters was also analyzed through deconvolution. Overall, the findings indicate that the dosimetric response of calcium phosphate ceramics is strongly affected by both the sintering method and the powder origin. Although further investigations using additional radiation sources are required, the obtained results highlight the potential of these materials for high-dose TL dosimetry applications.

Abstract Two external neutron beamlines of small and large sizes have been installed in the Isfahan Miniature Neutron Source Reactor (MNSR) pool in recent years to perform neutron radiography as well as irradiation experiments for large samples out of biological shield of reactor. These channels are located outside the reactor tank and exit vertically tangentially from the biological shield of the reactor, which is the pool water. These channels, that were not included in the initial design of MNSR, actually generate neutron beam lines in the reactor hall, about 6 meters away from the reactor core. In this study, the delivered neutron and gamma dose rates at the outlet of these channels at the maximum power of reactor, i.e. 30 kW, has been determined through simulation and experiments. Results shows that the calculated and measured gamma dose rates at the outlet of the large size channel are 45.81 ± 3% and 47.32 ± 6% mSv.h^-1, respectively and the calculated and measured neutron dose rates are 11.72 ± 5% and 11.31 ± 3% mSv.h^-1, respectively. In the case of small size channel, the calculated and measured gamma dose rates at the outlet of this channel are 10.53 ± 4% and 10.22 ± 6% mSv.h^-1, respectively and the calculated and measured neutron dose rates are 2.22 ± 5% and 2.11 ± 8% mSv.h^-1, respectively. Also, the neutron and gamma dose rate distribution in the reactor hall for different modes of operation of these two channels were qualitatively determined.

Abstract Relative Biological Effectiveness (RBE) is a key factor in proton therapy, yet its current fixed clinical value of 1.1 may not adequately represent biological effects at the microscopic level. In this study, we employed the TOPAS-nBio Monte Carlo toolkit to simulate DNA damage and calculate RBE based on various biological endpoints, including direct and indirect double-strand breaks (DSBs), and simple versus complex DSBs. Simulations were performed across multiple proton energies (1-64 MeV) using three physics constructors and two energy threshold models for strand break induction. Validation against reference and experimental data showed less than 5% deviation, with "DNA Physics Option 2" and a linear energy threshold of 5-37.5 eV yielding the most consistent results. Similarly, "DNA Physics Option 4 and 6" with a fixed energy threshold of 17.5 eV align well with experimental and simulation reference data. RBE values were found to vary significantly with damage type and simulation parameters, with total DSBs providing the most biologically relevant estimates, reaching a maximum of 1.9 for low-energy protons. The study also revealed that both direct and indirect damage alone may underestimate biological effectiveness. Differences in RBE across physics constructors reached up to 30.8%, emphasizing the need for careful model selection. These findings support replacing the fixed RBE with a more nuanced, DNA damage-based approach in treatment planning systems. Incorporating microscopic RBE modeling could enhance the biological accuracy of proton therapy and ultimately improve patient outcomes.

Abstract Radionuclide activity concentrations in soil are influenced by local geology and atmospheric factors. The radioactive noble gas radon is emitted from the crust of the planet by Ra-226. Utilizing the sodium iodide scintillation counter technique, the radioactive contents of four Kolar Gold Field (K.G.F) workplaces close to the mining zone have been measured. Emanometry method is used to measure the activity concentration in drinking water and Sodium Iodide detector to measure activity in soil. Conventional methods are employed to determine the physicochemical characteristics and radon (Rn-222) activity in the drinking water of the research region. Although the physicochemical parameters are within the permissible range, the average levels of Ra-226 and Rn-222 activity are within the acceptable limit. The concentrations of radionuclides and physicochemical parameters in drinking water are affected by mining activities. Measurements are also made of physical-chemical properties such as pH, electrical conductivity, and total dissolved salts. Electrical conductivity rose in the drinking water samples that contained dissolved salts. The Radium Equivalent activity (Ra_eq) is below the 370 Bqkg^-1 safety limit, falling between 30.54 ± 2.51 Bqkg^-1 and 215 ± 7.62 Bqkg^-1. Both the external and internal hazard indices (Hex and Hin) were less than unity, indicating that the soils pose no significant risk from gamma radiation or radon inhalation. Overall, the results confirm that the studied soil and water samples are radiologically safe for environmental use, including potential construction applications. The findings contribute valuable baseline data for radiation protection, environmental monitoring, and sustainable management of natural resources in mining-affected regions.

Abstract This study investigated the effect of adding 4%-20% TiO₂ to a pumice-iron sand composite mortar sample in the development of radiation shielding materials. It focuses on the effective atomic number, porosity, attenuation coefficient, protection efficiency, and spectral attenuation behavior based on XCOM and GEANT4 simulation via 10⁸ monoenergetic gamma photons of 0.356 MeV, 0.511 MeV, 0.662 MeV, 0.835 MeV, 1.115 MeV, 1.173 MeV, 1.275 MeV, 1.333 MeV, and 1.461 MeV. The study results show that the TiO₂ enhancement identified at increased titanium content in composite constituent elements caused an increase in the effective atomic number. The lowest porosity was observed at an 8% TiO2 addition, as indicated by the photopeak height in the energy spectrum of the absorbed energy. Adding TiO₂ increases the average LAC over 0% TiO₂ composite mortar samples by 1.1%, 2.3%, 3.8%, 5.1%, and 6.6% for 4%, 8%, 12%, 16%, and 20% TiO₂ addition, respectively. The same trend of the increased LAC is also evident in the GEANT4 simulation, i.e., 1.5%, 2.6%, 5%, 5.8%, and 7.2%. An increase in TiO₂ levels increases the RPE, while an increase in photon energy decreases the RPE. The trend is in line with the photon energy absorption in the composite sample. On the energy absorption spectrum of the composite, double escape peaks were identified at 0.258 MeV, 0.313 MeV, and 0.440 MeV for 1.275 MeV, 1.333 MeV, and 1.461 MeV energies, respectively. The energy absorption of the composite mortar was strongly dependent on the effective atomic number of the composites.

Abstract Boron neutron capture therapy (BNCT) is an emerging targeted radiation therapy leveraging nuclear capture reactions to maximize tumor cell destruction with minimal damage to healthy tissues. Given to clinical possible concentrations, attentions have recently been paid to ¹⁰B alternatives. This study presents a dosimetric comparison between BNCT, gadolinium neutron capture therapy (GdNCT) and lithium neutron capture therapy (LiNCT) using the Geant4 Monte Carlo toolkit, evaluating dose distributions and therapeutic gain across varying concentrations (1-50 ppm) of ¹⁰B, ¹⁵⁷Gd, and ⁶Li in a Snyder head phantom. Furthermore, Geant4-DNA simulations were employed to quantify DNA damage and predict cell survival via the Two-Lesion Kinetic model. The results demonstrate that both BNCT and LiNCT, as alpha-emitters, achieve superior tumor dose enhancement and normal tissue sparing compared to GdNCT. At 50 ppm, BNCT and LiNCT produced a 64-85% dose enhancement, outperforming GdNCT by more than 20-fold. Micro-scale analysis revealed that ¹⁰B and ⁶Li induce a high proportion of complex, lethal DNA double-strand breaks, leading to a steep, concentration-dependent decrease in cell survival. While ⁶Li is identified as a potent and promising alternative alpha-emitter, ¹⁰B maintained a marginally higher biological effectiveness. This study not only confirms BNCT's clinical superiority but also provides a rigorous framework for evaluating novel neutron-capture agents, underscoring the critical importance of radiation quality over neutron cross-section alone.

Abstract Radon-222 is a naturally occurring radioactive gas that poses health risks primarily through inhalation of its decay products; dissolved radon in drinking water contributes to internal exposure via ingestion and, more significantly, through degassing into indoor air, where it increases airborne radon concentrations. In typical scenarios, waterborne radon contributes approximately 10% to the total effective dose via ingestion and up to 90% via transfer to indoor air in homes with high water usage. This study investigates levels of radon (Rn-222) in 20 water samples collected from boreholes, wells, and the Surin River within Igbesa, Ogun State, Nigeria, in May 2025. The levels were measured with LR-115 type II solid-state nuclear track detectors with levels of 5.7 ± 1.3 Bq.L^-1 (sample W7, water from well) to 39.7 ± 8.3 Bq.L^-1 (sample W16, Surin River), and a mean of 13.535 ± 2.505 Bq.L^-1. Annual Effective Dose (AED) ranged from 0.0146 to 0.1016 mSv.y⁻¹, and Excess Lifetime Cancer Risk (ELCR) ranged between 0.0512 × 10⁻³ to 0.3557 × 10⁻³, both below international safety limits. The average concentration is above Nigeria's recommended limit of 11.1 Bq.L^-1 for potable water, particularly from the Surin River that accumulates industrial effluents, suggesting effects of industrial wastes or geological activities. Even though the levels fall below the World Health Organization's (WHO) 100 Bq.L^-1 threshold, the breach of the Nigerian limit in a few samples indicates real health issues for consumers of un-treated water, necessitating continuous surveillance.