Validation of Compton Scattering Monte Carlo Simulation Models

Several models for the Monte Carlo simulation of Compton scattering on electrons are quantitatively evaluated with respect to a large collection of experimental data retrieved from the literature. Some of these models are currently implemented in general purpose Monte Carlo systems; some have been implemented and evaluated for possible use in Monte Carlo particle transport for the first time in this study. Here we present first and preliminary results concerning total and differential Compton scattering cross sections.Comment: 5 pages, 3 figures, to be published in the Proceedings of IEEE Nuclear Science Symposium 201

Imaging the Gamma-Ray Sky with SPI aboard INTEGRAL

The spectrometer SPI on INTEGRAL allows for the first time simultaneous imaging of diffuse and point-like emission in the hard X-ray and soft gamma-ray regime. To fully exploit the capabilities of the instrument, we implemented the MREM image deconvolution algorithm, initially developed for COMPTEL data analysis, to SPI data analysis. We present the performances of the algorithm by means of simulations and apply it to data accumulated during the first 2 mission years of INTEGRAL. Skymaps are presented for the 1809 keV gamma-ray line, attributed to the radioactive decay of 26Al, and for continuum energy bands, covering the range 20 keV - 3 MeV. The 1809 keV map indicates that emission is clearly detected by SPI from the inner Galactic radian and from the Cygnus region. The continuum maps reveal the transition between a point-source dominated hard X-ray sky to a diffuse emission dominated soft gamma-ray sky. From the skymaps, we extract a Galactic ridge emission spectrum that matches well SPI results obtained by model fitting. By comparing our spectrum with the cumulative flux measured by IBIS from point sources, we find indications for the existence of an unresolved or diffuse emission component above ~100 keV.Comment: 12 pages, 7 figure

Soft gamma-ray galactic ridge emission as unveiled by SPI aboard INTEGRAL

The origin of the soft gamma-ray (200 keV - 1 MeV) galactic ridge emission is one of the long-standing mysteries in the field of high-energy astrophysics. Population studies at lower energies have shown that emission from accreting compact objects gradually recedes in this domain, leaving place to another source of gamma-ray emission that is characterised by a hard power-law spectrum extending from 100 keV up to 100 MeV The nature of this hard component has remained so far elusive, partly due to the lack of sufficiently sensitive imaging telescopes that would be able to unveil the spatial distribution of the emission. The SPI telescope aboard INTEGRAL allows now for the first time the simultaneous imaging of diffuse and point-like emission in the soft gamma-ray regime. We present here all-sky images of the soft gamma-ray continuum emission that clearly reveal the morphology of the different emission components. We discuss the implications of our results on the nature of underlying emission processes and we put our results in perspective of GLAST studies of diffuse galactic continuum emission

Validation of Geant4-based Radioactive Decay Simulation

Radioactive decays are of concern in a wide variety of applications using Monte-Carlo simulations. In order to properly estimate the quality of such simulations, knowledge of the accuracy of the decay simulation is required. We present a validation of the original Geant4 Radioactive Decay Module, which uses a per-decay sampling approach, and of an extended package for Geant4-based simulation of radioactive decays, which, in addition to being able to use a refactored per-decay sampling, is capable of using a statistical sampling approach. The validation is based on measurements of calibration isotope sources using a high purity Germanium (HPGe) detector; no calibration of the simulation is performed. For the considered validation experiment equivalent simulation accuracy can be achieved with per-decay and statistical sampling

Radioactive Decays in Geant4

The simulation of radioactive decays is a common task in Monte-Carlo systems such as Geant4. Usually, a system either uses an approach focusing on the simulations of every individual decay or an approach which simulates a large number of decays with a focus on correct overall statistics. The radioactive decay package presented in this work permits, for the first time, the use of both methods within the same simulation framework - Geant4. The accuracy of the statistical approach in our new package, RDM-extended, and that of the existing Geant4 per-decay implementation (original RDM), which has also been refactored, are verified against the ENSDF database. The new verified package is beneficial for a wide range of experimental scenarios, as it enables researchers to choose the most appropriate approach for their Geant4-based application

Methods for calibrating the gain and offset of the DSSC detector for the European XFEL

The DEPFET Sensor with Signal Compression (DSSC) will be a 2d 1Mpx imaging detector for the European X-­ray Free Electron Laser Facility (XFEL.EU). The DSSC is foreseen as an imaging detector for soft X-­radiation from 0.5 keV up to 6 keV. Driven by its scientific requirements, the design goals of the detector system are single photon detection, a high dynamic range and a high frame rate of up to 4.5 MHz. Signal compression, amplification and digitization will be performed in the focal plane. Utilizing an in-­pixel active filtering stage and an 8/9-­bit ADC, the detector will provide parallel readout of all pixels. Here the results of studies on the stability and performance of a parameterized model for determining gain and offset in DSSC prototype calibration line spectra will be presented