October 21, 2005
GLAST Celebrates Completion of Tracker and Calorimeter
By Lowell Klaisner
The GLAST team celebrated the installation
of the 16th—and last—detector tower into the instrument this week. This
telescope forms an image of the gamma ray sky by measuring the direction
and energy of each gamma ray that passes through it (see
http://www2.slac.stanford.edu/tip/2005/may6/glasttower.htm for an
earlier story on the towers).
The direction is measured with a silicon strip detector called the
tracker. The instrument has 800,000 of these strips to provide precise
position information. It is the largest area silicon detector ever
built, either for space or ground use. The tracker project was managed
by Robert Johnson (UCSC). The modules were fabricated at INFN in Pisa,
Italy. The Italian Space Agency (ASI) funded the fabrication effort and
one half of the silicon (the other half was funded by the Japanese
government). INFN funded the staff and much of the development work.
SLAC personnel provided engineering and management support and supplied
key components to the operation in Italy.
The energy of the gamma ray is measured with a cesium iodide detector
called the calorimeter. Cesium iodide emits light when a particle passes
through it and the light is measured by photodiodes at the end of the
CsI logs. All of the logs together weigh approximately 1 and one-half
tons (about half of the total weight of the instrument). The CsI was
supplied by Sweden, the mechanical structure by France, and the units
were completed and tested at the Naval Research Laboratory in
Washington, DC. The calorimeter was managed by Neil Johnson of NRL.
The detectors were divided into 16 towers in the instrument for
manufacturability. Now all of these towers have been assembled into the
backbone of the instrument, the grid. This assembly and test work was
done by the GLAST Integration and Test group at SLAC headed by Elliott
Next the computers and software will be added the instrument and then a
system test will be conducted. After that, the instrument will leave
SLAC in January to go to NRL for environmental tests. The GLAST launch
is scheduled for the fall of 2007.
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Friday October 21, 2005 by