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High precision mapping of single-pixel Silicon Drift Detector for applications in astrophysics and advanced light source
摘要： A Silicon Drift Detector with 3 × 3 mm2 sensitive area was designed by INFN of Trieste and built by FBK-Trento. It represents a single-pixel precursor of a monolithic matrix of multipixel Silicon Drift Detectors and, at the same time, a model of one cell Fluorescence Detector System (XAFS) for SESAME. The point-by-point mapping tests of the detector were carried out in the X-ray facilities at INAF-IAPS in Rome, equipped with a motorized two-axis micrometric positioning system. High precision characterization of this detector was done with a radioactive 55Fe source and a collimated Ti X-ray tube equipped with a Bragg crystal monocromator. The mapping in different positions and bias condition was specifically-aimed to the detailed analysis of the charge collection efficiency at the edge of the detector. The result is important to understand and verify the aspects related to the collection of the signal with respect to the position of interactions of the photons, especially in consideration of the new design and development of monolithic multipixel detectors.
关键词： SDD,Silicon drift detectors,Mapping
更新于2025-09-23 15:23:52
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Characterization of Rod Function Phenotypes Across a Range of Age-Related Macular Degeneration Severities and Subretinal Drusenoid Deposits
摘要： PURPOSE. To examine spatial changes in rod-mediated function in relationship to local structural changes across the central retina in eyes with a spectrum of age-related macular degeneration (AMD) disease severity. METHODS. Participants were categorized into five AMD severity groups based on fundus features. Scotopic thresholds were measured at 14 loci spanning 6° to 18° along the vertical meridian from one eye of each of 42 participants (mean = 71.7 ± 9.9 years). Following a 30% bleach, dark adaptation was measured at eight loci (4° to 12°). Rod intercept time (RIT) was defined from the time to detect a ?3.1 log cd/m2 stimulus. RITslope was defined from the linear fit of RIT with decreasing retinal eccentricity. The presence of subretinal drusenoid deposits (SDD), ellipsoid (EZ) band disruption, and drusen at the test loci was evaluated using optical coherence tomography. RESULTS. Scotopic thresholds indicated greater rod function loss in the macula, which correlated with increasing AMD group severity. RITslope, which captures the spatial change in the rate of dark adaptation, increased with AMD severity (P < 0.0001). Three rod function phenotypes emerged: RF1, normal rod function; RF2, normal scotopic thresholds but slowed dark adaptation; and RF3, elevated scotopic thresholds with slowed dark adaptation. Dark adaptation was slowed at all loci with SDD or EZ band disruption, and at 32% of loci with no local structural changes. CONCLUSIONS. Three rod function phenotypes were defined from combined measurement of scotopic threshold and dark adaptation. Spatial changes in dark adaptation across the macula were captured with RITslope, which may be a useful outcome measure for functional studies of AMD.
关键词： age-related macular degeneration,RIT,SDD,scotopic thresholds,dark adaptation,rod intercept time,subretinal drusenoid deposits,AMD
更新于2025-09-23 15:22:29
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Elucidating Spray Dried Dispersion Dissolution Mechanisms with Focused Beam Reflectance Measurement: Contribution of Polymer Chemistry and Particle Properties to Performance
摘要： Amorphous spray dried dispersions (SDDs) are a key enabling technology for oral solid dosage formulations, used to improve dissolution behaviour and clinical exposure of poorly-soluble active pharmaceutical ingredients (APIs). Appropriate assessment of amorphous dissolution mechanisms is an ongoing challenge. Here we outline the novel application using Focused Beam Reflectance Measurement (FBRM) to analyse particle populations orthogonal to USP 2 dissolution. The relative impact of polymer substitution and particle attributes on 25% BMS-708163/HPMC-AS SDD dissolution was assessed. Dissolution mechanisms for SDDs were categorized into erosion versus disintegration. Beyond an initial mixing period, FBRM particle counts diminish slowly and particles are detectable until the point where API dissolution is complete. There is correlation between FBRM particle count decay rate, representing loss of SDD particles in the dissolution media, and UV dissolution rate, measuring dissolved API. For the SDD formulation examined, the degree of succinoyl substitution for HPMC-AS, SDD particle size and surface area all had an impact on dissolution. These data indicate the SDD displayed an erosion mechanism and that FBRM is capturing a rate-limiting step. From this screening tool, the mechanistic understanding and measured impact of polymer chemistry and particle properties can inform a risk-assessment and control strategy for this compound.
关键词： HPMC-AS,FBRM,SDD,substitution,dissolution-mechanism,amorphous,surface area,erosion,dispersion,particle-size
更新于2025-09-23 15:22:29
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[IEEE 2017 IEEE Nuclear Science Symposium and Medical Imaging Conference (NSS/MIC) - Atlanta, GA (2017.10.21-2017.10.28)] 2017 IEEE Nuclear Science Symposium and Medical Imaging Conference (NSS/MIC) - Neutron Scatter Camera Using Two Arrays of Diamond Detectors
摘要： In this paper, we present on the simulated performance of a diamond-based neutron scatter camera (DNSC) for spectral reconstruction. The DNSC consists of two 4 × 4 planes of diamond detectors, each with a 4 × 4 array of pixels. The various parameters were investigated to gauge their effect on the performance of a DNSC, including both uncertainties in energy deposition and timing. The DNSC can accurately localize at least two neutron sources located very close to each other, and can reconstruct the energy spectrum of a 252Cf neutron source to ~250 keV, contingent on chosen performance parameters of each diamond detector in the array. Details of DNSC design, reconstruction techniques, and current results are presented.
关键词： SDD,ToF,DNSC,DD
更新于2025-09-23 15:22:29
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Amplification of Radiation-Induced Signal of LED Strip by Increasing Number of LED Chips and Using Amplifier Board
摘要： Transducers, such as photodiodes, phototransistors, and photovoltaic cells are promising radiation detectors. However, for accurate radiation detection and dosimetry, signals that emanate from these devices have to be sufficient to facilitate accurate calibrations, i.e., assigning a quantity of radiation dose to a specific magnitude of the signal. More so, purposely fabricated for luminescence, LEDs produce significantly low signals during radiation detection applications. Therefore, this paper investigates the enhancement and augmentation of photovoltaic signals that were generated when LED strips were being exposed to diagnostic X-rays. Initially, signal amplification was achieved through increasing the effective LED active area (from 60 to 120 chips); by successively connecting LED strips. Further, signal amplification was undertaken by injecting the raw LED strip signal into an amplifier board with adjustable gains. In both the signal amplification techniques, the tube voltage (kVp), tube current-time product (mAs), and source-to-detector distance (SDD) were varied. The principal findings show that effective active area-based signal amplifications produced an overall average of 91.16% signal enhancement throughout all of the X-ray parameter variations. On the other hand, the amplifier board produced an average of 36.48% signal enhancement for the signals that were injected into it. Chip number increment-based signal amplifications had a 0.687% less coefficient of variation than amplifier board signal amplifications. The amplifier board signal amplifications were impaired by factors, such as dark currents, amplifier board maximum operational output voltage, and saturation. Therefore, future electronic signal amplification could use amplifier boards having low dark currents and high operational voltage headroom. The low-cost and simplicity that are associated with active-area amplification could be further exploited in a hybrid amplification technique with electronic amplification and scintillators.
关键词： tube current-time product (mAs),application of LEDs,amplifier board,LED active area,source-to-detector distance (SDD),diagnostic X-rays,tube voltage (kVp)
更新于2025-09-16 10:30:52