Oscillons and oscillating kinks in the Abelian-Higgs model

We study the classical dynamics of the Abelian Higgs model employing an asymptotic multiscale expansion method, which uses the ratio of the Higgs to the gauge field amplitudes as a small parameter. We derive an effective nonlinear Schr\"{o}dinger equation for the gauge field, and a linear equation for the scalar field containing the gauge field as a nonlinear source. This equation is used to predict the existence of oscillons and oscillating kinks for certain regimes of the ratio of the Higgs to the gauge field masses. Results of numerical simulations are found to be in very good agreement with the analytical findings, and show that the oscillons are robust, while kinks are unstable. It is also demonstrated that oscillons emerge spontaneously as a result of the onset of the modulational instability of plane wave solutions of the model. Connections of the obtained solutions with the phenomenology of superconductors is discussed.Comment: arXiv admin note: substantial text overlap with arXiv:1306.386

Study of the optical properties of continuous and pixelated scintillation crystals

The principal goal of this study is to characterize the width of the light distribution for a given number of initial optical photons and to try to express it as a function of the Depth of Interaction (DOI) in the crystal, where the initial optical photons are produced, the size of the initial volume the optical photons occupy before starting the transmission and the geometrical properties of the optical medium that guides the light to the photomultiplier surface. Monte Carlo runs based on the optical simulation package DETECT2000 have been performed. The results indicate that in the case of continuous crystal there is an apparent correlation of the DOI and the width of the light distribution. In the case of pixelated crystals the width of the light distribution seems to be independent of the DOI when the source is located deep in the crystal but there is a strong dependence as the source approaches the PSPMT's entrance window. This correlation of the DOI and the light distribution is not affected by the transverse dimensions of the continuous crystal but in the case of pixelated crystals this correlation is strongly depended on the crystal's aspect ratio. Through this study it also became clear that there is no dependence of the light distribution on the shape of the source. © 2009 IOP Publishing Ltd and SISSA

A modification of the dual energy window subtraction method for scatter compensation in pixelized scintillators for SPECT

Abstract Small field of view detectors based on Position Sensitive Photomultiplier Tubes (PSPMTs) have been widely used by many research groups in small-animal imaging and recently clinically in scintimammography. In most cases the PSPMT is coupled to pixelized scintillators since it has been shown that their use improves spatial resolution. The use of a single energy window for each crystal element is the only proposed method for scatter correction in pixelized scintillators. In this work we have modified the dual energy window subtraction technique in order to be applicable to a pixelized scintillator detector and we have evaluated its performance with real data. Hot, cold and breast phantoms have been imaged in planar mode.

A correction method of the spatial distortion in planar images from γ-Camera systems

A methodology for correcting spatial distortions in planar images for small Field Of View (FOV) γ-Camera systems based on Position Sensitive Photomultiplier Tubes (PSPMT) and pixelated scintillation crystals is described. The process utilizes a correction matrix whose elements are derived from a prototyped planar image obtained through irradiation of the scintillation crystal by a 60Co point source and without a collimator. The method was applied to several planar images of a SPECT experiment with a simple phantom construction at different detection angles. The tomographic images are obtained using the Maximum-Likelihood Expectation-Maximization (MLEM) reconstruction technique. Corrected and uncorrected images are compared and the applied correction methodology is discussed. © 2009 IOP Publishing Ltd and SISSA