Articles
Publication Date: 2024
Catena (03418162)244
This study investigated the impacts of two land uses, namely natural oak forests and abandoned rainfed farming, on the long-term redistribution of soil properties in the hilly regions of the semi-arid western part of Iran. We assessed cesium-137 (137Cs) levels in the soil to determine soil erosion and sedimentation rates. We explored the consequences of deforestation and the conversion of an oak forest to rainfed farmland abandoned for over a decade. We measured various soil properties, including magnetic susceptibility, aggregate stability, and soil organic carbon (SOC) levels in different soil fractions. For both forest and abandoned rainfed farming land uses, three slope positions (upper, mid, and lower) were selected. Two soil samples were collected from a depth of 0–20 cm from each slope position. 137Cs analysis revealed that the greatest 137Cs loss occurred at the upper-slope position in both the natural forest (14.5 %) and abandoned rainfed farming (74.1 %) land use. A simplified mass balance model demonstrated average erosion rates of 109 and 706.2 t ha−1 yr−1 in the natural forest and abandoned rainfed farming areas, respectively. The highest erosion rates were recorded at the upper-slope positions of both land-use areas, which was primarily attributed to lower soil organic matter (SOM) and vegetation. Furthermore, we observed lower magnetic susceptibilities in the upper-slope position of both land uses, coinciding with the areas experiencing the highest levels of soil loss. Particulate organic carbon and total nitrogen contents in the sand-sized and larger aggregates in the natural forest land use were significantly higher compared to those in the abandoned rainfed farming land use (p < 0.05). A similar trend was observed for the SOC content associated with various aggregate sizes. In conclusion, the conversion of forest land use to abandoned rainfed farming land use on slopes can lead to soil degradation and redistribution due to accelerated soil erosion and deposition. © 2024 Elsevier B.V.
Publication Date: 2024
Biomedical Physics and Engineering Express (20571976)10(2)
The inherent biological hazards associated with ionizing radiation necessitate the implementation of effective shielding measures, particularly in medical applications. Interventional radiology, in particular, poses a unique challenge as it often exposes medical personnel to prolonged periods of high x-ray doses. Historically, lead and lead-based compounds have been the primary materials employed for shielding against photons. However, the drawbacks of lead, including its substantial weight causing personnel’s inflexibility and its toxicity, have raised concerns regarding its long-term impact on both human health and the environment. Barium tantalate has emerged as a promising alternative, due to its unique attenuation properties against low-energy x-rays, specifically targeting the weak absorption area of lead. In the present study, we employ the Geant4 Monte Carlo simulation tool to investigate various formulations of barium tantalate doped with rare earth elements. The aim is to identify the optimal composition for shielding x-rays in the context of interventional radiology. To achieve this, we employ a reference x-ray spectrum typical of interventional radiology procedures, with energies extending up to 90 keV, within a carefully designed simulation setup. Our primary performance indicator is the reduction in air kerma transmission. Furthermore, we assess the absorbed doses to critical organs at risk within a standard human body phantom protected by the shield. Our results demonstrate that specific concentrations of the examined rare earth impurities can enhance the shielding performance of barium tantalate. To mitigate x-ray exposure in interventional radiology, our analysis reveals that the most effective shielding performance is achieved when using barium tantalate compositions containing 15% Erbium or 10% Samarium by weight. These findings suggest the possibility of developing lead-free shielding solutions or apron for interventional radiology personnel, offering a remarkable reduction in weight (exceeding 30%) while maintaining shielding performance at levels comparable to traditional lead-based materials. © 2024 The Author(s). Published by IOP Publishing Ltd.
Publication Date: 2023
Scientific Reports (20452322)13(1)
Runaway electrons are a notable phenomenon occurring during the operation of a tokamak. Proper material selection for the tokamak's first wall structure and plasma facing components, particularly in large sizes tokamaks like ITER and DEMO, is crucial due to the energy deposition of runaway electrons on plasma facing components during collision events, resulting in severe heat transfer and material damage in the form of melting, corrosion, and fracture. These runaway electrons also contribute to the production of photoneutrons through (γ, n) nuclear reactions, lead to material activation and require remote handling. In this study, using a Monte Carlo code and simulating the collision of runaway electrons with a tungsten target exposed to their radiation, the electron transport is investigated, and the energy deposition spectrum resulting from these collisions on the target is analyzed. The influence of incident angle and magnetic field on the energy deposition spectrum and the energy deposition per particle in the target is examined. With an increase in the incident angle of incoming electrons, the amount of energy deposited in the target rises and the energy deposition spectrum broadens. Moreover, applying a magnetic field, results the most significant increase in energy deposition for electrons with energies below 1 MeV in the tangential radiation case. The energy deposition spectrum resulting from each collision event in these interactions is determined. For electrons with energies below 5 MeV, multiple scattering and ionization processes are the primary contributors to energy deposition in the target. However, as the incident electron energy increases, the significance of multiple scattering and ionization diminishes, and the bremsstrahlung process becomes the most effective reaction in energy deposition. The energy deposition profile of electrons in the tungsten target indicates that higher incident electron energies lead to a shift of the maximum energy deposition location towards the inner layers of the target, and the energy deposition peak broadens. Analyzing the electrons transport inside the tungsten target reveals that a substantial portion of electrons with energies of 50–100 MeV passes through the wall and may exit from the back surface, potentially causing damage to equipment behind the tungsten wall. Additionally, secondary products of the reaction, such as photons, secondary electrons, and neutrons and their energy profiles are thoroughly studied. These secondary products can penetrate the target and activate materials in the equipment behind the plasma-facing components. For primary electrons below 1 MeV hitting tungsten, reflection process is significant. Analysis of primary and secondary runaway electrons in the tokamak's tungsten wall shows that electrons with energies of 0.1, 0.2, and 0.5 MeV predominantly interact within a first 0.1 mm layer, without passing through it. The secondary electrons can escape the tungsten target and impact other components, which making them an important consideration in runaway electron collisions with the tokamak wall. Produced photons, as one of the secondary products, also linearly increase with the rising energy of primary electrons. Also, the photoneutrons are produced only when runaway electrons with energies of 10 MeV and above collide with the target. These secondary products can penetrate the target and activate materials in the equipment behind the plasma-facing components. © 2023, The Author(s).
