Calorimeter Subsystem of GLAST Large Area Telescope

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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


Photons hit thin metal sheets, converting to e





Charged particles pass through interleaved layers of silicon microstrips, causing ionization ionization

which produce detectable electric charge.


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





CsI(Tl) crystals

Are easy to handle

Excellant energy resolution at modest cost

Resonably radiation hard

Comparatively not hygroscopic

Do not require high voltage


10 X0 to measure high energy photons with good resolution


height/width = 0.4  large field-of-view




3000 kg




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