162 research outputs found
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Remote Sensing of Alpha and Beta Sources - Modeling Summary
Evaluating the potential for optical detection of the products of interactions of energetic electrons or other particles with the background atmosphere depends on predictions of change in atmospheric concentrations of species which would generate detectable spectral signals within the range of observation. The solar blind region of the spectrum, in the ultra violet, would be the logical band for outdoor detection (see Figure 1). The chemistry relevant to these processes is composed of ion-molecule reactions involving the initially created N{sub 2}{sup +} and O{sub 2}{sup +} ions, and their subsequent interactions with ambient trace atmospheric constituents. Effective modeling of the atmospheric chemical system acted upon by energetic particles requires knowledge of the dominant mechanism that exchange charge and associate it with atmospheric constituents, kinetic parameters of the individual processes (see e.g. Brasseur and Solomon, 1995), and a solver for the coupled differential equations that is accurate for the very stiff set of time constants involved. The LLNL box model, VOLVO, simulates the diel cycle of trace constituent photochemistry for any point on the globe over the wide range of time scales present using a stiff Gear-type ODE solver, i.e. LSODE. It has been applied to problems such as tropospheric and stratospheric nitrogen oxides, stratospheric ozone production and loss, and tropospheric hydrocarbon oxidation. For this study we have included the appropriate ion flux
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Multiple Synthesis Routes to Transparent Ceramic Lutetium Aluminum Garnet
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Prospects for High Energy Resolution Gamma Ray Spectroscopy with Europium-Doped Strontium Iodide
Europium-doped strontium iodide scintillators offer a light yield exceeding 100,000 photons/MeV and excellent light yield proportionality, while at the same time, SrI{sub 2} is readily grown in single crystal form. Thus far, our collaboration has demonstrated an energy resolution with strontium iodide of 2.6% at 662 keV and 7.6% at 60 keV, and we have grown single crystals surpassing 30 cm{sup 3} in size (with lower resolution). Our analysis indicates that SrI{sub 2}(Eu) has the potential to offer 2% energy resolution at 662 keV with optimized material, optics, and read-out. In particular, improvements in feedstock purity may result in crystal structural and chemical homogeneity, leading to improved light yield uniformity throughout the crystal volume, and consequently, better energy resolution. Uniform, efficient light collection and detection, is also required to achieve the best energy resolution with a SrI{sub 2}(Eu) scintillator device
Transparent ceramic scintillators for gamma spectroscopy and radiography
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Measurements of NaI:Tl Electron Response using SLYNCI: Comparison of Different Samples
This paper measures the sample to sample variation in the light yield non-proportionality of NaI:Tl, and so explores whether this is an invariant characteristic of the material or whether it is dependent on the chemical and physical properties of tested sample. In this work we report on the electron response of nine crystals of NaI(Tl), differing in shape, volume, age, manufacturer and quality. The non-proportionality has been measured at the SLYNCI facility in the energy range between 3.5 to 460 keV. The Scintillation Light Yield Non-proportionality Characterization Instrument (SLYNCI) is a next generation Compton Coincidence device, explicitly designed to study the 'non-proportionality' of the electron response in scintillators and the contribution of this effect to the intrinsic energy resolution. We also discuss the gamma response, x-ray excited emission spectra and decay times for the nine crystals, in order to provide a complete characterization of their physical properties and determine whether the mechanism of scintillation varies between samples
Development of transparent ceramic Ce-doped gadolinium garnet gamma spectrometers
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Performance of europium-doped strontium iodide, transparent ceramics and bismuth-loaded polymer scintillators
Recently discovered scintillators for gamma ray spectroscopy, single crystal SrI{sub 2}(Eu), GYGAG(Ce) transparent ceramic and Bismuth-loaded plastics, offer resolution and fabrication advantages compared to commercial scintillators, such as NaI(Tl) and standard PVT plastic. Energy resolution at 662 keV of 2.7% is obtained with SrI{sub 2}(Eu), while 4.5% is obtained with GYGAG(Ce). A new transparent ceramic scintillator for radiographic imaging systems, GLO(Eu) offers high light yield of 70,000 Photons/MeV, high stopping, and low radiation damage. Implementation of single crystal SrI{sub 2}(Eu), Gd-based transparent ceramics, and Bi-loaded plastic scintillators can advance the state-of-the art in ionizing radiation detection systems
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