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
Work principle
Tracker
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
Electronics boards attached to each side.
Electronic readout to connectors at base of calorimeter.
Outer wall is EMI shield and provides 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
Resolution
Advantages
CsI(Tl) crystals
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
Disadvantages
Weight
3000 kg
