Papers by Keyword: Radiation

Abstract: Cumulative heavy-ion irradiation effects were investigated in a commercial 4H-SiC double trench MOSFET through a combination of cyclotron experiments and TCAD simulations. Devices were exposed to continuous ¹²⁴Xe³⁵⁺ ion strikes at a linear energy transfer (LET) of 63 MeV·cm²/mg under drain biases from 100 to 400 V. Experimental results revealed the onset of permanent drain and gate leakage at voltages as low as 200 V, with degradation rates increasing by several orders of magnitude at higher bias. Post-irradiation measurements confirmed trench oxide rupture and source leakage path formation, establishing single-event leakage current (SELC) as the dominant degradation mechanism. In contrast, TCAD simulations of isolated ion strikes predicted catastrophic single-event burnout (SEB) only at or above 250–300 V, highlighting the critical role of cumulative damage processes that are not captured in single-strike models. These findings demonstrate that permanent leakage-driven degradation effectively extends the SELC zone beyond conventional SEB thresholds, reducing the safe operating area of trench-based SiC MOSFETs. The results have significant implications for derating strategies in space applications, where current SEB-focused guidelines may underestimate vulnerability, and highlight the need for radiation-hardening by device design to ensure long-term reliability.

Abstract: The precision in temperature estimation plays a pivotal role in the design and operational efficiency of CubeSats. This study leverages the capabilities of COMSOL MULTIPHYSICS to model the thermal behavior of a 1U CubeSat, with a focus on evaluating the impact of orientation and beta angle on heat transfer dynamics and the resultant temperature distribution throughout the satellite. By conducting an extensive range of simulations that explore beta angles from 0° to 90° across four distinct satellite orientations, this research uncovers critical insights into the heat transfer mechanisms within the CubeSat framework. These findings illuminate the substantial influence of orientation and beta angle on the satellite's thermal state, highlighting the necessity of incorporating these factors into any comprehensive thermal analysis of spacecraft. The outcomes of this investigation not only contribute to a deeper understanding of CubeSat thermal management but also underscore the importance of meticulous design and analysis practices to optimize satellite performance in the challenging space environment.

Abstract: Radiation is essential in medical diagnostics but poses health risks, necessitating effective shielding to minimize exposure. This research evaluates cassava starch-based bioplastic-lead as an alternative radiation shielding material in femur radiography using Anteroposterior (AP) and Lateral projections with portrait and diagonal detector positions. Bioplastic samples with a 45:55 ratio of cassava starch and lead acetate were tested on a preserved human femur with and without shielding. Image processing using the Gaussian High Pass Filter (GHPF) method and analysis with Contrast to Noise Ratio (CNR) and Peak Signal to Noise Ratio (PSNR) were conducted to assess image quality. Results showed that lead bioplastics achieved 49.4% radiation absorption, with optimal anatomical visualization at cut-off frequencies of 5 and 10, while higher frequencies led to image distortions resembling osteoporosis. The best CNR and PSNR values confirmed improved image contrast while maintaining diagnostic accuracy. This research demonstrates that lead bioplastic effectively reduces radiation dose while preserving image quality, making it a promising alternative shielding material for medical imaging applications

Abstract: Low gain avalanche detectors (LGADs) offer high temporal resolution for high energy particle detection, which is critical for next generation experiments in hadron colliders. While silicon LGADs (Si-LGADs) have rapidly matured in the last decade, research into silicon carbide (SiC) LGADs has only recently begun. By accounting for fundamental differences in material properties and fabrication processes, we present a prototype device design and process flow for 4H-SiC LGADs with etch-based isolation. Critical steps of the process flow and their results are discussed, including plasma etching, passivation, and the formation of low resistivity contacts. Electrical characterization (I-V, C-V) shows sufficient depletion of the device structure to demonstrate low-gain charge carrier multiplication.

Abstract: Low energy positron beams have become a valuable tool for depth dependent characterization of defects and micro- and mesoscale porosities, as well as for fundamental positron and positronium interactions. Some of the recent developments in the generation of secondary positron beams using particle accelerators are presented and the underlying physics and technologies are discussed.

Abstract: The analysis of unsteady MHD flow over a porous stretching plate is critical for various engineering applications, particularly in systems involving chemical reactions and thermal radiation. This study explores the novel effects of heat and mass transfer in a two-dimensional unsteady magnetohydrodynamic (MHD) flow. This present work examines the effects of radiation and a transverse magnetic field on a chemically reacting fluid flowing over a stretched plate. The unsteady nature of the flow is associated with the time-dependent variations in stretching/extending velocity, temperature, and fluid concentration. The nonlinear governing boundary layer partial differential equations (PDEs) are transformed into a set of nonlinear ordinary differential equations (ODEs) using a similarity transformation, which are then numerically solved using the MATLAB bvp4c method. The flow, heat, and concentration profiles are quantitatively analysed through graphs for various problem parameters, including the unsteadiness parameter (A), Hartmann number (M), porosity parameter (Sp), radiation parameter (N), chemical reaction parameter (K), Soret number (Sr), Eckert number (Ec), Schmidt number (Sc), and Prandtl number (Pr). Additionally, the skin friction coefficient, Nusselt number (Nu), and Sherwood number (Sh) are numerically addressed and illustrated using graphs.

Abstract: This study is based on the exploration of MHD Casson fluid flow past a stretching cylinder in the presence of non-uniform heat generation, thermal radiation and Joule heating. Boussinesq approximation is also put into consideration due to density difference in the fluid. The governing equations and their corresponding boundary conditions are changed into system of ordinary differential equations with the aid of appropriate similarity variables. The obtained ordinary differential equations are solved numerically using Runge-Kutta Fehlberg method alongside shooting technique. The flow and thermal fields are investigated in the presence of emerging parameters, namely Grashof number, Prandtl number, radiation parameter, curvature parameter, Eckert number, Casson parameter, permeability parameter, magnetic number, space and temperature dependent heat generation parameter. In this study, enhancement in velocity distributions is noticed as values of Grashof number grow but velocity profiles are depreciated by permeability parameter and curvature parameter.

Abstract: The objective of the present research is to investigate the degradation phenomenon of Polyvinyl Chloride (PVC) cable jacket exposed under accelerated thermally aged at 100°C for 4 days then irradiated under n’s flux of 1.5x 10¹¹ n’s / cm².sec for 1 hr in PARR-2 reactor at PINSTECH. Thermal, mechanical and chemical etc. properties of degraded cable jacket were studied with respect to fresh sample. It was examined that plasticizer content in PVC matrix started to deplete under the effect of temperature which made the matrix more rigid. In addition, the interaction of radiation with polymeric chains weakens the hydrocarbon bonding. The hydrogen and chlorine ions ejected from PVC molecular chains recombine to form hydrogen chloride (HCl) which induces porosity by creating localized pitting. This phenomenon is known as dehydrochlorination which created scissioning in PVC materials. Hence, due to the synergistic effects of temperature and radiation aging, cracks were observed on the outer surface of cable jacket in 2 years equivalent time. This study concludes that cables having PVC insulation are not suitable for long term exposure (i.e. decades) in thermo-irradiation environment.

Abstract: This paper examined the thermophoresis effect and suction/injection process on steady MHD in a semi-infinite inclined porous plate. Chemical reaction, heat generation and thermal radiation are taking into account. The governing partial differential equations are transformed via similarity technique into a system of nonlinear ordinary differential similarity equations, which are solved numerically by applying the Lobbato IIIa-finite-difference method. Favorable comparisons with previously published work are performed. Numerical pertinent results for the velocity, temperature and concentration profiles as well as for the skin-friction coefficient, wall heat transfer and mass transfer rates are obtained and reported graphically for various parametric conditions to show interesting aspects of the solution. The main results are the dominant influence of suction/injection process to control the principal boundary layers and the role played by the combined chemical reaction, heat generation and thermal radiation on the changes in the quantities of interest.

Abstract: Photovoltaic (PV) modules are supposed to be a reliable source of power for at least 25 years. Its component needs to work very efficiently to ensure electrical panels continue to perform. Backsheet film has been used to help insulating electrical components of PV modules to ensure PV can operate safely and protect them over their servicing life. PV modules are usually produced using encapsulated polymer such as polyvinylidene fluoride (PVDF), ethylene-vinyl acetate (EVA), polyamide (PA) or polyethylene terephthalate (PET). However, under continuous environmental stresses the components of solar panel including backsheet film are prone to malfunctions and failure after long term services. Thus, the service lifetime of PV systems may be shorter than the predicted lifetime. To overcome these issues, efforts have been made to enhance the performance of backsheet films by using radiation crosslinking method. The effects of electron-beam irradiation on mechanical and thermal properties for PVDF commercial backsheet film were studied. It was found that degree of crosslinking increased as irradiation dose increased. Irradiated PVDF has adequate mechanical properties to be used as backsheets for solar cells according to industrial reference. The result of SEM resulted in increased strength and stiffness of irradiated PVDF, which support the result of tensile test. In addition, the TGA analysis showed a good thermal stability with no degradation below 400°C. These studies help in quantifying long-term behavior and estimate a module lifetime especially in specific environment such as tropical country like Malaysia.