1. 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

2. 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.

3. 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

4. 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.

5. Resolution

6. 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

7. Disadvantages
Weight
3000 kg