Thin‐film EXAFS samples have been fabricated using semiconductor‐processing and wet‐chemical etching techniques to eliminate artifacts associated with transmission and fluorescence measurements. Examples include cr...
Thin‐film EXAFS samples have been fabricated using semiconductor‐processing and wet‐chemical etching techniques to eliminate artifacts associated with transmission and fluorescence measurements. Examples include crystalline GexSi1−x alloys, amorphous GaAs and Cu and Au nanocrystals in SiO2. In general, thin films of several microns thickness were first formed on bulk substrates then EXAFS samples were fabricated by separating the thin film and substrate. For transmission measurements, thin films were stacked together to yield the optimum absorption while sample inhomogeneity, non‐uniformity and non‐continuity were readily eliminated. For fluorescence measurements, scattering/diffraction from the substrate was eliminated and stacking the thin films together increased the areal concentration of the absorber. The use of such techniques to fabricate EXAFS samples yielded a significant increase in accessible photo‐electron wave number range and hence more accurate structural parameter determinations.
For a table-top Compton camera, which is currently under development in our group, the interaction position resolution of the absorber detector is a critical or limiting detector parameter that most seriously affects ...
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For a table-top Compton camera, which is currently under development in our group, the interaction position resolution of the absorber detector is a critical or limiting detector parameter that most seriously affects the imaging resolution of the Compton camera. Currently, it is assumed that all the interactions occur at the centers of the detector segments of the absorber detector, which is simple, but obviously not the best choice considering that the interaction depths of the photons in the absorber detector is not distributed uniformly, especially for the low-energy photons. To this end, the present study develops a novel method, called "average interaction depth (AID) method" to improve the imaging resolution of Compton camera by additionally considering the interaction depth of the incident photon in the absorber detector. Our simulation studies with Geant4 show that the imaging resolution of Compton camera can be significantly improved by using the AID method. The imaging resolution of the table-top Compton camera was improved from 9.9mm to 7.6mm in full width at half maximum (FWHM) for a 511keV γ point source. For a 364keV γ point source, the imaging resolution was improved more significantly, i.e., from 11.4mm to 7.2mm.
The Compton camera has recently been recognized as a promising three-dimensional imaging modality with higher sensitivity and unlimited field-of-view. Due to computational limitations, however, it has been of a diffic...
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The Compton camera has recently been recognized as a promising three-dimensional imaging modality with higher sensitivity and unlimited field-of-view. Due to computational limitations, however, it has been of a difficult problem to develop reconstruction algorithms with good. In this study, we propose efficient methods for implementing the OSEM (ordered-subsets expectation-maximization) algorithm for Compton camera reconstruction, and investigate three different schemes for grouping Compton scattered data into ordered subsets. The first is to group the data according to a pre-set order of scattering angles, the second is to group the possible combinations of detected position pairs in the scatterer and the absorber, and the third is to combine the first and second methods. According to our experimental results, all of the three grouping schemes exhibit similar performance in terms of the quantitative accuracy and computational efficiency. Our results show that the OSEM algorithm applied to the Compton camera provides an order improvement in speed of execution while retaining overall quality of the image reconstructed by the standard EM algorithm.
Although silicon carbide is a very good semiconductor material for the fabrication of diode detectors for use as neutron power monitors in nuclear reactors, the electrical properties of the diodes may be altered becau...
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Writing correct and consistent software requirements specification (SRS) is one of the most important goals of a requirements engineering process. The SRS serves as the basis for subsequent design, testing and mainten...
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The 2 + 2 Scholars program brings together nuclearengineering undergraduate students from three Idaho universities - Idaho State University (ISU), the University of Idaho (UI), and Boise State University (BSU) - to s...
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Au nanoparticles (NPs) have been formed by ion beam synthesis in 600nm thin SiO2. Subsequently the NPs were irradiated with 2.3MeV Sn ions at liquid nitrogen temperature. Samples were analyzed using extended x-ray abs...
Au nanoparticles (NPs) have been formed by ion beam synthesis in 600nm thin SiO2. Subsequently the NPs were irradiated with 2.3MeV Sn ions at liquid nitrogen temperature. Samples were analyzed using extended x-ray absorption fine structure (EXAFS) spectroscopy and small angle x-ray scattering (SAXS) as a function of Sn irradiation dose. Transmission electron microscopy shows that the NPs largely retain their spherical shape upon irradiation. However, we observe a reduction in average NP size and a concomitant significant narrowing of the size distribution with increasing irradiation dose as consistent with inverse Ostwald ripening. At lower irradiation doses, significant structural disorder is apparent with an effective bond length expansion as consistent with amorphous material. At higher irradiation doses, EXAFS measurements indicate dissolution of a significant fraction of Au from the NPs into the SiO2 matrix (as monomers) and the formation of small Au clusters (dimers, trimers, etc.). We estimate the volume fraction of such monomers/clusters. Ion irradiation thus yields disordering then dissolution of Au NPs.
This article introduces a mathematical model and a heuristic procedure based on Tabu Search for the problem of Aggregate Production Planning at a sawmill to determine the volumes of different products with different t...
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