Search Results (6)

Various models of ionization and fission chambers for ionizing radiation detection, designed to operate under harsh conditions such as those found in fusion reactors or particle accelerators, have been experimentally characterized and numerically simulated. These models were calibrated using a photon beam in the X-ray spectrum. Irradiations were performed at the Biomedical Research Center of the University of Granada (CIBM) with a bipolar metal-ceramic X-ray tube operating at a voltage of 150 kV and a dose rate ranging from 0.05 to 2.28 Gy/min. All detectors under study featured identical external structures but varied in detection volume, anode configuration, and filling gas composition. To assess inter- and intra-model response variations, the tested models included 12 micro-ionization chambers (CRGR10/C5B/UG2), 3 micro-fission chambers (CFUR43/C5B-U5/UG2), 8 micro-fission chambers (CFUR43/C5B-U8/UG2), and 3 micro-fission chambers (CFUR44/C5B-U8/UG2), all manufactured by Photonis (Merignac, France). The experimental setup was considered suitable for the tests, as the leakage current was below 20 pA. The optimal operating voltage range was determined to be 130–150 V, and the photon sensitivities for the chambers were measured as 29.8 ± 0.3 pA/(Gy/h), 43.0 ± 0.8 pA/(Gy/h), 39.2 ± 0.3 pA/(Gy/h), and 96.0 ± 0.9 pA/(Gy/h), respectively. Monte Carlo numerical simulations revealed that the U layer in the fission chambers was primarily responsible for their higher sensitivities due to photoelectric photon absorption. Additionally, the simulations explained the observed differences in sensitivity based on the filling gas pressure. The detectors demonstrated linear responses to dose rates and high reproducibility, making them reliable tools for accurate determination of ionizing photon beams across a range of applications. Full article

X-ray phase-contrast imaging presents a significant advancement in the field of X-ray imaging, surpassing traditional X-ray absorption imaging in detecting hydrogen substances. It effectively addresses the limitations of the latter in providing contrast for imaging weakly absorbing objects, thereby opening up vast potential applications in biomedical research, materials science, and industrial inspection. This article initially explores the fundamental principles of X-ray phase-contrast imaging and several prevalent imaging techniques. Notably, imaging devices such as grating-based Talbot–Lau interferometers emerge as the most promising in phase-contrast imaging due to their exceptional compatibility and imaging quality. Furthermore, this article introduces key parameters for assessing the quality of grating phase-contrast imaging, specifically image noise and sensitivity, along with their calculation methods. These insights are valuable for optimizing grating-based phase-contrast imaging devices. Lastly, this article examines potential applications and advancements in the key components of X-ray phase-contrast imaging while addressing current challenges and future directions in its technological development. This article aims to provide insights and inspiration for scholars interested in this field. Full article

This study presents a comparative analysis of anodization and hydrothermal techniques for synthesizing TiO₂ nanotubes directly on titanium foil. It emphasizes its advantages as a substrate due to its superior conductivity and efficient charge transfer. Optimized synthesis conditions enable a thorough evaluation of the resulting nanotubes’ morphology, structure, and optical properties, ultimately assessing their photoelectrochemical and photocatalytic performances. Scanning electron microscopy (SEM) reveals differences in tube diameter and organization. An X-ray diffraction (XRD) analysis shows a dominant anatase (101) crystal phase in both methods, with the hydrothermally synthesized nanotubes exhibiting a biphase structure after annealing at 500 °C. UV–Vis and photoluminescence analyses indicate slight variations in band gaps (around 0.02 eV) and recombination rates. The anodized TiO₂ nanotubes, exhibiting superior hydrophilicity and order, demonstrate significantly enhanced photocatalytic degradation of a model pollutant, amido black (80 vs. 78%), and achieve a 0.1% higher photoconversion efficiency compared to the hydrothermally synthesized tubes. This study underscores the potential advantages of the anodization method for photocatalytic applications, particularly by demonstrating the efficacy of direct TiO₂ nanotube growth on titanium foil for efficient photocatalysis. Full article

Mammography machines must meet high requirements to ensure the quality of the generated images. On the other hand, due to the use of ionizing radiation, there is a need to minimize the dose received by patients. To optimize both of these parameters (dose and image quality), the response characteristics of image detectors and, depending on the composition of the breasts, the physical contrast of the examined structures should be considered. This study aimed to determine the optimal voltage values for a given breast thickness during imaging with the use of a selenium image detector. Analysis was carried out using the Monte Carlo simulation method with the GEANT4 code. Our results reveal that the combination of Mo anode together with Mo filtration (the system recommended in analog mammography) was the least favorable combination among those used in digital mammography machines with a selenium detector. Moreover, the use of Rh filtration instead of Mo was advantageous regardless of the thickness of the breast and resulted in a significant improvement in image quality with the same dose absorbed in the breast. The most advantageous solution was found to be an X-ray tube with a W anode. The highest values of the image quality-to-dose ratio were observed for breasts with dimensions ranging from 53 mm to 60 mm in thickness. Lower image quality was observed for breasts with smaller dimensions due to high breast glandularity, resulting in the deterioration of the physical contrast. Full article

Carbon nanotubes (CNTs) show significant advantages in the development of cold cathode X-ray tubes due to their excellent field emission performance; however, there are still some problems, such as short lifetime and the low emission current of large-area CNTs. In this paper, a front-grid carbon nanotube array model was established, and the electric field intensity near the tip of the CNTs’ electric field enhancement factor was analytically calculated. A simulation model of a CNT three-dimensional field emission electron gun was established by using computer simulation technology (CST). The effects of grid wire diameter, grid aperture shape, and the distribution of grid projection on the cathode surface on the cathode current, anode current, and electron transmission efficiency were analyzed. The aperture ratio was used to evaluate the grid performance, and the simulation results show that the ideal aperture ratio should be between $65\%$ and $85\%$. A grid structure combining a coarse grid and a fine grid was designed, which can make the electric field intensity around the grid evenly distributed, and effectively increased the cathode emission current by $24.2\%$ compared with the structure without the fine grid. The effect of grid aperture ratio on the electron transmission efficiency was tested. The simulation results and optimized structure can provide a reference for the grid design of cold cathode emission X-ray tubes. Full article

Recent discoveries in the field of nanoscale vacuum channel (NVC) structures have led to potential on-chip electron sources. However, limited research has reported on the structure or material parameters, and the superiority of a nanoscale vacuum channel in an electron source has not been adequately demonstrated. In this paper, we perform the structural optimization design of an NVC-based electron source. First, the structure parameters of a vertical NVC-based electron source are investigated. Moreover, the symmetrical NVC structure is further demonstrated to improve the emission current and effective electron efficiency. Finally, a symmetrical nano-vacuum channel structure is successfully fabricated based on simulations. The results show that the anode current exceeds 15 nA and that the effective electron efficiency exceeds 20%. Further miniaturizing the NVC structures in high integration can be utilized as an on-chip electron source, thereby, illustrating the potential in applications of electron microscopes, miniature X-ray sources and on-chip traveling wave tubes. Full article