In core-collapse supernovae, titanium-44 (Ti-44) is produced in the innermost ejecta, in the layer of material directly on top of the newly formed compact object. As such, it provides a direct probe ...of the supernova engine. Observations of supernova 1987A (SN1987A) have resolved the 67.87- and 78.32-kilo-electron volt emission lines from decay of Ti-44 produced in the supernova explosion. These lines are narrow and redshifted with a Doppler velocity of ~700 kilometers per second, direct evidence of large-scale asymmetry in the explosion.
Hadron therapy for, e.g., cancer treatment requires an accurate dose deposition (total amount and location). As a consequence, monitoring is crucial for the success of the treatment. Currently ...employed PET imaging systems are not able to provide information about the deposed dose fast enough to allow stopping the therapy in case of a discordance with the treatment plan. We are currently investigating an imaging system based on a combined Compton scattering and pair creation camera capable of imaging gamma rays up to 50 MeV. The camera would be able to measure the complete spectrum of emitted gamma rays during the therapy session. We have performed Monte Carlo simulations for three different proton beam energies in a typical hadron therapy scenario. They show that the location of the gamma-ray distribution decay and the falloff region of the deposed dose are related. The reconstructed images prove that the proposed system could provide the required imaging and dose location capabilities.
Observations of the gamma-ray sky reveal the most powerful sources and the most violent events in the Universe. While at lower wavebands the observed emission is generally dominated by thermal ...processes, the gamma-ray sky provides us with a view on the non-thermal Universe. Here particles are accelerated to extreme relativistic energies by mechanisms which are still poorly understood, and nuclear reactions are synthesizing the basic constituents of our world. Cosmic accelerators and cosmic explosions are major science themes that are addressed in the gamma-ray regime. While Fermi will take the next step in surveying the high-energy (~GeV) sky, and NuSTAR will pioneer focusing observations at hard X-ray energies (to ~80 keV), there is currently no successor mission planned to ESA's INTEGRAL observatory which currently provides important new insights into the MeV sky, albeit at much more modest sensitivities. There will be clearly a growing need to perform deeper, more focused investigations of gamma-ray sources in the 100-keV to MeV regime. Recent technological advances in the domain of gamma-ray focusing using Laue diffraction and multilayer-coated mirror techniques have paved the way towards a gamma-ray mission, providing major improvements compared to past missions regarding sensitivity and angular resolution. Such a future Gamma-Ray Imager will allow the study of particle acceleration processes and explosion physics in unprecedented detail, providing essential clues on the innermost nature of the most violent and most energetic processes in the Universe.
A R&D project has been recently launched to investigate Geant4 architectural design in view of addressing new experimental issues in HEP and other related physics disciplines. In the context of this ...project the use of generic programming techniques besides the conventional object oriented is investigated. Software design features and preliminary results from a new prototype implementation of Geant4 electromagnetic physics are illustrated. Performance evaluations are presented. Issues related to quality assurance in Geant4 physics modelling are discussed.
Gamma-ray astrophysics in the MeV range De Angelis, Alessandro; Tatischeff, Vincent; Argan, Andrea ...
Experimental astronomy,
06/2021, Letnik:
51, Številka:
3
Journal Article
Recenzirano
Odprti dostop
The energy range between about 100 keV and 1 GeV is of interest for a vast class of astrophysical topics. In particular, (1) it is the missing ingredient for understanding extreme processes in the ...multi-messenger era; (2) it allows localizing cosmic-ray interactions with background material and radiation in the Universe, and spotting the reprocessing of these particles; (3) last but not least, gamma-ray emission lines trace the formation of elements in the Galaxy and beyond. In addition, studying the still largely unexplored MeV domain of astronomy would provide for a rich observatory science, including the study of compact objects, solar- and Earth-science, as well as fundamental physics. The technological development of silicon microstrip detectors makes it possible now to detect MeV photons in space with high efficiency and low background. During the last decade, a concept of detector (“ASTROGAM”) has been proposed to fulfil these goals, based on a silicon hodoscope, a 3D position-sensitive calorimeter, and an anticoincidence detector. In this paper we stress the importance of a medium size (M-class) space mission, dubbed “ASTROMEV”, to fulfil these objectives.
We report on the design, production, and testing of advanced double-sided silicon strip detectors under development at the Max-Planck-Institute as part of the Medium Energy Gamma-ray Astronomy (MEGA) ...project. The detectors are designed to form a stack, the “tracker,” with the goal of recording the paths of energetic electrons produced by Compton-scatter and pair-production interactions. Each layer of the tracker is composed of a 3×3 array of 500
μm thick silicon wafers, each 6
cm×6
cm and fitted with 128 orthogonal p and n strips on opposite sides (470
μm pitch). The strips are biased using the punch-through principle and AC-coupled via metal strips separated from the strip implant by an insulating oxide/nitride layer. The strips from adjacent wafers in the 3×3 array are wire-bonded in series and read out by 128-channel TA1.1 ASICs, creating a total 19
cm×19
cm position-sensitive area. At 20°C a typical energy resolution of 15–20
keV FWHM, a position resolution of 290
μm, and a time resolution of ∼1
μs is observed.
The MEGA project Kanbach, G; Andritschke, R; Schopper, F ...
New astronomy reviews,
02/2004, Letnik:
48, Številka:
1
Journal Article
Recenzirano
We describe the development of a new telescope for Medium Energy Gamma-Ray Astronomy (MEGA) for the energy band 0.4–50 MeV. As a successor to COMPTEL and EGRET (low energies), MEGA aims to improve ...the sensitivity for astronomical sources by at least an order of magnitude. It could thus fill the severe sensitivity gap between scheduled or operating hard-X-ray and high-energy γ-ray missions and open the way for a future Advanced Compton Telescope. MEGA records and images γ-rays by completely tracking Compton and Pair creation events in a stack of double sided Si-strip track detectors surrounded by a pixelated CsI calorimeter. A scaled down prototype has been built and calibrations using radioactive sources and exposures to an accelerator generated γ-ray beam were performed in 2003. A balloon flight is planned for 2004.
Data analysis for the MEGA prototype Zoglauer, A.; Andritschke, R.; Kanbach, G.
New astronomy reviews,
02/2004, Letnik:
48, Številka:
1
Journal Article
Recenzirano
The data analysis for combined Compton and Pair telescopes like the Medium Energy Gamma-Ray Astronomy telescope (MEGA) separates into three basic steps: the starting point is the calibration and ...low-level data-analysis. It is followed by the most critical part, the event reconstruction, which has to identify all event types (pair-creation, Compton events, charged particles, etc.) while effectively suppressing different kinds of background (photons from below, chance coincidences, activation, etc.). The last stage, the high level data analysis, is dominated by image reconstruction, which in our case is performed by a technique called list-mode maximum-likelihood expectation-maximization. The current performance of the data analysis algorithms is demonstrated by calibration measurements of the MEGA prototype.
The Medium Energy Gamma-ray Astronomy (MEGA) telescope concept will soon be proposed as a MIDEX mission. This mission would enable a sensitive all-sky survey of the medium-energy gamma-ray sky ...(0.4–50MeV) and bridge the huge sensitivity gap left after the demise of the COMPTEL and OSSE experiments on the Compton Gamma-Ray Observatory. The scientific goals include compiling a much larger catalog of sources in this energy range, performing far deeper searches for long-lived nuclear lines from supernovae, novae, and supernova remnants, studying prompt decay lines from solar flares and the interstellar medium, better measuring the diffuse galactic continuum and line emissions, identifying the components of the cosmic diffuse gamma-ray emission, searching for nuclear resonance absorption features in bright continuum spectra, and studying the medium-energy properties of black holes, pulsars, and gamma-ray bursts. MEGA detects and images gamma rays by completely tracking Compton and pair creation interactions in a stack of double-sided silicon strip track detectors surrounded by a pixellated CsI calorimeter. A prototype instrument has been developed and calibrated in the laboratory and at a gamma-ray beam facility. We present calibration results and describe future plans for the prototype, and describe the proposed satellite mission.
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