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- 摘要
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Determination of Differential Emission Measure from Solar Extreme Ultraviolet Images
摘要： The Atmospheric Imaging Assembly (AIA) on board the Solar Dynamic Observatory (SDO) has been providing high-cadence, high-resolution, full-disk UV-visible/extreme ultraviolet (EUV) images since 2010, with the best time coverage among all the solar missions. A number of codes have been developed to extract plasma differential emission measures (DEMs) from AIA images. Although widely used, they cannot effectively constrain the DEM at ?aring temperatures with AIA data alone. This often results in much higher X-ray ?uxes than observed. One way to solve the problem is by adding more constraint from other data sets (such as soft X-ray images and ?uxes). However, the spatial information of plasma DEMs are lost in many cases. In this Letter, we present a different approach to constrain the DEMs. We tested the sparse inversion code and show that the default settings reproduce X-ray ?uxes that could be too high. Based on the tests with both simulated and observed AIA data, we provided recommended settings of basis functions and tolerances. The new DEM solutions derived from AIA images alone are much more consistent with (thermal) X-ray observations, and provide valuable information by mapping the thermal plasma from ～0.3 to ～30 MK. Such improvement is a key step in understanding the nature of individual X-ray sources, and particularly important for studies of ?are initiation.
关键词： magnetic reconnection,methods: data analysis,Sun: X-rays, gamma rays,Sun: ?ares,Sun: corona,Sun: UV radiation
更新于2025-09-23 15:23:52
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The LXe calorimeter and the pixelated timing counter in the MEG II experiment
摘要： The MEG experiment is to look for a lepton flavor violating μ + → e+γ decay with an unprecedented sensitivity, and we set an upper limit of the branching ratio for this decay, 5.7 × 10?13 at 90% C.L. in 2013 which is a twenty times more stringent limit than the previous experiment, MEGA. Since the sensitivity improvement was limited by the accidental background, we have considered the major detector upgrade. A proposal was submitted to PSI committee, and was approved in 2013, which aims at a sensitivity enhancement of one order of magnitude compared with the current MEG experiment. Here mainly two components of the MEG detector will be introduced, a γ-ray calorimeter with 900 L of liquid xenon (LXe), and a pixelated timing counter. The LXe detector will be improved by increasing the granularity at the incident face, by replacing the current PMTs with a larger number of smaller photosensors (MPPC) and optimizing the photosensor layout also on the lateral faces. A new highly segmented, fast timing counter array will replace the old system to allow improved timing resolution capabilities.
关键词： visible and IR photons (solid-state),HPG,Large detector systems for particle and astroparticle physics,Photon detectors for UV,CZT,Gamma detectors (scintillators,HgI etc),Timing detectors
更新于2025-09-23 15:23:52
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Investigation of gamma irradiation effects on the properties of CdS/p-Si heterostructure
摘要： Cadmium sulfide (CdS) thin films were deposited on p-type Si substrate by thermal evaporation to fabricate the CdS/p-Si heterojunction. Gamma irradiation has been used to modify the microstructural, optical and electrical characteristics of CdS/p-Si heterojunction of various doses in the range (0–80 kGy). X-ray diffraction measurements of the gamma irradiated show the reduction in crystallinity of the CdS thin films. While scanning electron microscope images depicted the average CdS particle size was found to be increased with increasing the gamma irradiation dose. Photoluminescence results revealed that at the specific dose of gamma irradiation was found to create the yellow emission in interstitial sites to the valence band. The I–V characteristics showed the current transport properties effected by the different gamma doses. The values of barrier height, saturation current and ideality factor for the CdS/p-Si heterostructure varied due to the causes like inhomogeneities in the interfacial, defect density, charge distribution on interfacial and interfacial layer thickness after gamma irradiation. The gamma irradiation induced effects and the possible mechanism in CdS/p-Si heterojunction is discussed.
关键词： Heterostructure,Diffuse reflectance,Photoluminescence,Gamma irradiation,Thermal evaporation
更新于2025-09-23 15:23:52
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Polypyrrole microcapsules loaded with gold nanoparticles: Perspectives for biomedical imaging
摘要： We report the facile preparation of polypyrrole microcapsules with a hydrophobic liquid core that is loaded with gold nanoparticles. Through the oxidative polymerization of pyrrole, the polymer is deposited onto the surface of the droplets, which results in the encapsulation of both the liquid phase and the metal nanoparticles. We demonstrate the preparation of the microcapsules loaded with organic solvents (toluene, hexane) or 2-oxoheptyl isothiocyanate (new promising anticancer agent) as the liquid cores and stable or radioactive gold nanoparticles (Au-197 or Au-198 isotopes). The resulting microcapsules have been demonstrated as promising agents for medical applications such as computed tomography or gamma imaging. Moreover, the capsules can be applied as drug carriers, which has been shown in vitro on cancer and normal cell cultures.
关键词： Targeted drug delivery,Gold nanoparticles doped with Au-198,Computed tomography,Anticancer agents,Polypyrrole microcapsules,Gamma imaging
更新于2025-09-23 15:22:29
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Design and performance evaluation of high resolution small animal PET scanner based on monolithic crystal: a simulation study
摘要： Dedicated small-animal PET scanners functionality can be optimized by improving the sensitivity and spatial resolution of the scanner. Approximately most of the developed and commercially available small-animal PET scanners are equipped with pixelated scintillators; therefore, their spatial resolution is limited to the crystal pixel size. Complex fabrication, low-sensitivity, and disability in depth of interaction calculation (DOI) are the major disadvantages of pixelated crystals. However, monolithic scintillator crystals are known as one of the most commonly used substitutions, as they have higher sensitivity, DOI recognition, and lower cost. We already designed and implemented a dedicated small-animal PET scanner based on pixelated scintillator crystals and silicon photomultiplier (SiPM). In this study, we plan to present a new optimized design based on the monolithic crystal, with similar performance by the previous scanner. Then we would optimize the thickness of the monolithic crystals for animal PET scanners as a function of sensitivity and spatial resolution. All simulations were performed based on GEANT4, a validated Monte Carlo toolkit. We simulated a recently fabricated scanner with pixelated crystals and compared it with a simulated scanner based on an optimized monolithic crystal. The experimental setup used for comparison and validation is a small Animal PET consisting of ten pixelated modules. This study anticipates that by replacing a pixelated crystal (consist of 24 × 24 LYSO elements, and 2 × 2 × 10 mm3 crystal size) with a monolithic crystal (with 8 mm thickness and 50.2 × 50.2 entrance area), the average spatial resolution stays the same and sensitivity grows ～ 17% in the center of AFOV and also the fabrication cost dives remarkably. Simulation reveals that although the depth of interaction DOI was not taken into consideration, the crystals with 6 mm thickness have acceptable spatial resolution (～ 1.3 mm FWHM at the centre of the AFOV) and relatively good absolute sensitivity (～ 1.6%).
关键词： SPECT,coronary CT angiography (CTA),PET PET/CT,Gamma camera,Models and simulations
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) - Compact Solid State Neutron-Gamma Detectors for Backpack or Handheld Instruments
摘要： In this paper, we report on the characterization of detectors constructed at RMD using 1-inch, 1.5-inch, and 2-inch diameter right cylinders of CLYC and CLLBC crystals coupled to arrays of silicon photomultipliers (SiPM). Detectors constructed with small volume CLLBC crystals coupled to a 12 mm × 12mm total area SiPM array show an excellent energy resolution of ~3% at 662 keV and a large volume CLYC crystal when coupled to a 24 mm × 24 mm area array shows an energy resolution of ~6.6% at 662 keV. Both detectors show pulse shape discrimination capabilities.
关键词： Gamma-ray detection,crystal growth,elpasolites,energy resolution,neutron detection,scintillation detector,CLLBC,CLYC,thermal neutrons
更新于2025-09-23 15:22:29
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Minigammacámara portátil para el diagnóstico de muerte encefálica
摘要： Objective: To evaluate the feasibility of using the Sentinella? portable gamma-camera for the diagnosis of brain death (BD). Design: A prospective, observational feasibility study was carried out. Setting: Intensive Care Unit of a third level hospital. Patients: Consecutive recording was made of the adults diagnosed with brain death based on clinical criteria following admission to the Intensive Care Unit in the period from January to December 2017. Interventions: The procedure was performed at the patient bedside with the intravenous administration of technetium 99 metastable hexamethylpropylene amine oxime. The absence of perfusion in the cerebral hemispheres and brainstem was described as a pattern consistent with BD. The diagnosis was correlated to the transcranial Doppler and / or electroencephalographic findings. Results: A total of 66.1% of the patients were men with an average age of 60 years [IQR: 51-72]. The most frequent causes resulting in BD were hemorrhagic stroke (48.2%, n = 27), followed by traumatic brain injury (30.4%, n = 17), ischemic stroke (10.7%, n = 6) and post-cardiac arrest anoxic encephalopathy (7.1%, n = 4). A clinical diagnosis of BD was made in all cases, and the portable gamma-camera confirmed the diagnosis in 100% of the patients with a pattern characterized by the absence of brain perfusion. In addition, the results were compared with the transcranial Doppler findings in 46 patients, confirming the presence of diastolic reverberation and / or systolic peaks. The electroencephalographic tracing was obtained in 10 cases, with the appearance of electrical silence, due to the absence of an acoustic window in the transcranial Doppler study. Conclusions: A portable gamma-camera could be a useful and feasible tool for the diagnosis of BD.
关键词： Brain death,Transcranial doppler,Portable gamma-camera
更新于2025-09-23 15:22:29
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Associated particle imaging instrumentation for future planetary surface missions
摘要： We have conducted ground tests to study the applicability of the Tagged Neutrons Method/Associated Particle Imaging methodology (TNM/API) for the making precise gamma ray spectroscopic measurements onboard lander missions to the Solar system planets. Our analysis was focused on the requirement to distinguish between the spacecraft background and the subsurface signal so as to correctly evaluate the elemental composition of planetary soils. The measurements were performed in a configuration where the gamma spectrometer was surrounded by significant amounts of material that imitated a spacecraft structure. It was found that the TNM/API can substantially suppress the spacecraft background and identify the true intensities of the gamma lines attributed to major soil elements such as O, Na, Mg, Al, Si and Fe and evaluate their concentrations with an accuracy of 2–10%.
关键词： Neutron generator,Elemental abundances,Surface operations,Associated particle imaging,Solar system,Tagged neutrons method,Active gamma spectroscopy
更新于2025-09-23 15:22:29
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Effects of temporary fogging and defogging in plastic scintillators
摘要： Recent studies have shown that under certain environmental conditions, plastic scintillators which are used in a variety of applications in outdoor environments develop defects called "fogging", resulting in a reduced useful lifetime and increased maintenance cost. Applications of plastic scintillators include scanning recycled steel going into a processing plant, personnel portals to scan employees, and scanning cargo and cars crossing borders of many countries. In this report, fogging was studied in conventional PVT and PS-based plastic scintillators, both field aged and freshly cast. A new fogging-resistant PVT-based formulation developed by scientists at Lawrence Livermore National Laboratory (LLNL) was tested as well. We used accelerated aging experiments via temperature and humidity cycling in controlled laboratory conditions to create observable temporary fogging defects in small samples (≤1 in3). Photoluminescence and optical transmission studies were used to evaluate the effect of the fogging. The time evolution of the induced temporary fogging formation and defogging (i.e. fading of defects in ambient conditions over time) were recorded using optical microscopy, time-lapse photography, and gravimetric analysis.
关键词： Accelerated aging,Optical microscopy,Scintillator,Gamma detection
更新于2025-09-23 15:22:29
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The extragalactic background light revisited and the cosmic photon–photon opacity ( <i>Corrigendum</i> )
摘要： For some unexplained reasons, all tables in the Franceschini & Rodighiero (2017) paper have been mixed up. Tables 1–3 reported there were identical to those published in Franceschini et al. (2008). We report here in Tables 1, 2, and 4 the corresponding correct values in terms of photon proper number densities and photon–photon optical depths as a function of photon energy. We also took this occasion to add a new table (Table 3) including the predicted extragalactic background light values at redshifts between 2 and 3.5, as requested by some readers of the Franceschini & Rodighiero (2017) paper. Both photon number densities and photon–photon optical depths are calculated including the contributions of the cosmic microwave background assumed as a black-body with T = 2.728 K. Except for the numerical values in the tables, all the rest of the Franceschini & Rodighiero (2017) paper is unaffected by the problem.
关键词： addenda,gamma rays: galaxies,diffuse radiation,errata,cosmic background radiation,BL Lacertae objects: general
更新于2025-09-23 15:22:29