Calorimeter Subsystem of GLAST Large Area Telescope Arshak Tonoyan, Therese Sjursen University of Bergen Karl Gellerstedt, Hossein Kavianipour, Christian Ohm Stockholm University Detector Technology Course 12.09.2008
GLAST introduction from Wikipedia The Fermi Gamma-ray Space Telescope (formerly named the Gamma-ray Large Area Space Telescope, or GLAST) is a space observatory being used to perform gamma-ray astronomy observations from low Earth orbit. Its main instrument is the Large Area Telescope (LAT), with which astronomers mostly intend to perform an all-sky survey studying astrophysical and cosmological phenomena such as active galactic nuclei, pulsers, other high-energy sources and dark matter. Another instrument aboard GLAST, the GLAST Burst Monitor (GBM), is being used to study gamma ray bursts. The LAT is an imaging gamma-ray detector (a pair-conversion instrument) which detects photons with energy from about 30 MeV up to 300 GeV, with a field of view of about 20% of the sky.
Work principle Tracker Caloprimeter Photons hit thin metal sheets, converting to e+e- pairs Charged particles pass through interleaved layers of silicon microstrips, causing ionization ionization which produce detectable electric charge. Caloprimeter After passing through the tracker, the particles enter the calorimeter consists of a stack of CsI(Tl) scintillator crystals to measure the energy of the particles
Calorimeter Module Overview CsI Detectors + PIN diodes (both ends) Readout Electronics Carbon Cell Array Al Cell Closeout Al EMI Shield Mounting Baseplate Modular Design 4 x 4 array of calorimeter modules Each Module 8 layers of 12 CsI(Tl) Crystals Crystal dimensions: 27 x 20 x 326 mm Hodoscopic stacking - alternating orthogonal layers Dual PIN photodiode on each end of crystals. Mechanical packaging – Carbon Composite cell structure Electronics boards attached to each side. Electronic readout to connectors at base of calorimeter. Outer wall is EMI shield and provides structural stiffness as well.
Resolution
Advantages CsI(Tl) crystals Construction Are easy to handle Excellant energy resolution at modest cost Resonably radiation hard Comparatively not hygroscopic Do not require high voltage Construction 10 X0 to measure high energy photons with good resolution Modular height/width = 0.4 large field-of-view Low dead time
Disadvantages Weight 3000 kg