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Development of gamma-ray detectors for MeV gamma-ray astrophysics

Abstract: Medium-energy gamma rays, in the spectral range from roughly 300 keV to 50 MeV, probe extreme physical conditions in the Universe that give rise to nuclear interactions and relativistic particles. This spectral range contains signatures of (i) nuclear line emissions arising in processes of nucleosynthesis, in energetic nuclear interactions, and the electron-positron annihilation line, (ii) potential new phenomena like nuclear resonance absorption lines, and (iii) various continuum emissions from energetic electron and ion populations in explosive, accretion, or outflow (jets) scenarios. Astronomy with medium energy gamma-rays is an experimental challenge for two main reasons: (1) photon interaction cross-sections in the MeV range go through a minimum in their transition from the photoelectric effect (~100 keV) to pair creation (~10 MeV), and Compton scattering, characterized by small energy deposits and long-range secondary radiation, dominates. It is therefore required to build “deepEand finely segmented detectors to achieve a reasonable efficiency; (2) the nuclear energy levels of detector and structural materials lie in the MeV range and are therefore easily excited by energetic cosmic-ray particles. The result of this systematic “radio-activationEis a prolific gamma-ray background of local origin which must be effectively discriminated against to achieve a useful sensitivity for astronomical targets. We will describe experimental progress and instrumental concepts to achieve such a sensitive next generation telescope. More than two decades of multi-wavelength spectral coverage, that are still severely underdeveloped, could then be opened to astronomical investigations.
Speaker: Gottfried Kanbach - Max Planck Institute for Extraterrestrial Physics
Speaker Bio: Dr. Gottfried Kanbach is a Senior Staff Scientist and a Group Leader for High-Energy Gamma-Ray Astronomy group at Max-Planck-Institute for extraterrestrial Physics in Germany. He has a long history with gamma-ray satellite missions such as OSO-7, SMM, COS-B and EGRET. He is currently an affiliated scientist for Fermi LAT. He is now developing a next generation low- to medium energy gamma ray telescope, GRIPS.
Poster Link: Poster
Presentation: Presentation on 9/2/2009 (PDF)