Molecular dynamics simulations of energetic Ar cluster bombardment of Ag(111)

Large-scale molecular dynamics computer simulations are used to investigate the dynamics of material ejection during high-energy Ar_{n} cluster bombardment of Ag(111) at normal incidence. The silver sample containing 7 million atoms is bombarded with Ar_{n} projectiles (n=45-30000) with kinetic energy spanning from a few keV up to 1 MeV. Such a wide range of projectile parameters allows probing processes taking place during low-density collision cascade as well as during high-density events characteristic of micrometeorite bombardment in space. The material modifications and total sputtering yield of ejected particles are investigated. While at low-energy impacts, ejection of individual silver atoms is the main emission channel, the ejection of large clusters from the corona of the created crater dominates for the high-energy impacts

System Response Kernel Calculation for List-mode Reconstruction in Strip PET Detector

Reconstruction of the image in Positron Emission Tomographs (PET) requires the knowledge of the system response kernel which describes the contribution of each pixel (voxel) to each tube of response (TOR). This is especially important in list-mode reconstruction systems, where an efficient analytical approximation of such function is required. In this contribution, we present a derivation of the system response kernel for a novel 2D strip PET.Comment: 10 pages, 2 figures; Presented at Symposium on applied nuclear physics and innovative technologies, Cracow, 03-06 June 201

Analysis framework for the J-PET scanner

J-PET analysis framework is a flexible, lightweight, ROOT-based software package which provides the tools to develop reconstruction and calibration procedures for PET tomography. In this article we present the implementation of the full data-processing chain in the J-PET framework which is used for the data analysis of the J-PET tomography scanner. The Framework incorporates automated handling of PET setup parameters' database as well as high level tools for building data reconstruction procedures. Each of these components is briefly discussed.Comment: 6 pages, 1 figur

Hit time and hit position reconstruction in the J-PET detector based on a library of averaged model signals

In this article we present a novel method of hit time and hit position reconstruction in long scintillator detectors. We take advantage of the fact that for this kind of detectors amplitude and shape of registered signals depends strongly on the position where particle hit the detector. The reconstruction is based on determination of the degree of similarity between measured and averaged signals stored in a library for a set of well-defined positions along the scintillator. Preliminary results of validation of the introduced method with experimental data obtained by means of the double strip prototype of the J-PET detector are presented

Application of Compressive Sensing Theory for the Reconstruction of Signals in Plastic Scintillators

Compressive Sensing theory says that it is possible to reconstruct a measured signal if an enough sparse representation of this signal exists in comparison to the number of random measurements. This theory was applied to reconstruct signals from measurements of plastic scintillators. Sparse representation of obtained signals was found using SVD transform.Comment: 7 pages, 3 figures; Presented at Symposium on applied nuclear physics and innovative technologies, Cracow, 03-06 June 201

Searches for discrete symmetries violation in ortho-positronium decay using the J-PET detector

In this paper we present prospects for using the J-PET detector to search for discrete symmetries violations in a purely leptonic system of the positronium atom. We discuss tests of CP and CPT symmetries by means of ortho-positronium decays into three photons. No zero expectation values for chosen correlations between ortho-positronium spin and momentum vectors of photons would imply the existence of physics phenomena beyond the Standard Model. Previous measurements resulted in violation amplitude parameters for CP and CPT symmetries consistent with zero, with an uncertainty of about 10-3. The J-PET detector allows to determine those values with better precision thanks to a unique time and angular esolution combined with a high geometrical acceptance. Achieving the aforementioned is possible due to application of polymer scintillators instead of crystals as detectors of annihilation quanta.Comment: in Nukleonika 201

A novel method for calibration and monitoring of time synchronization of TOF-PET scanners by means of cosmic rays

All of the present methods for calibration and monitoring of TOF-PET scanner detectors utilize radioactive isotopes such as e.g. $^{22}$Na or $^{68}$Ge, which are placed or rotate inside the scanner. In this article we describe a novel method based on the cosmic rays application to the PET calibration and monitoring methods. The concept allows to overcome many of the drawbacks of the present methods and it is well suited for newly developed TOF-PET scanners with a large longitudinal field of view. The method enables also monitoring of the quality of the scintillator materials and in general allows for the continuous quality assurance of the PET detector performance.Comment: 10 pages, 7 figure

Studies of unicellular micro-organisms Saccharomyces cerevisiae by means of Positron Annihilation Lifetime Spectroscopy

Results of Positron Annihilation Lifetime Spectroscopy (PALS) and microscopic studies on simple microorganisms: brewing yeasts are presented. Lifetime of ortho - positronium (o-Ps) were found to change from 2.4 to 2.9 ns (longer lived component) for lyophilised and aqueous yeasts, respectively. Also hygroscopicity of yeasts in time was examined, allowing to check how water - the main component of the cell - affects PALS parameters, thus lifetime of o-Ps were found to change from 1.2 to 1.4 ns (shorter lived component) for the dried yeasts. The time sufficient to hydrate the cells was found below 10 hours. In the presence of liquid water an indication of reorganization of yeast in the molecular scale was observed. Microscopic images of the lyophilised, dried and wet yeasts with best possible resolution were obtained using Inverted Microscopy (IM) and Environmental Scanning Electron Microscopy (ESEM) methods. As a result visible changes to the surface of the cell membrane were observed in ESEM images.Comment: Nukleonika (2015