The tracker consists of doublesided silicon strip detectors (0.5 mm thick) with analog
readout electronics mounted along two sides of each layer. These layers of
doublesided Si-stripdetectors are used to track the electron accelerated
in a Compton scattering process or electron/positron pairs created in a
paircreation event and measure the energy.
The position resolution is 470 Ám (pitch) for events with no charge sharing
At a distance of 10 mm between the layers this leads to an angular
uncertainty due to the measurement accuracy to better than 3°.
Much better angular resolution is not necessary because determination of the path of any charged particle
(below some 50 MeV energy) is limited in accuracy by small angle scattering.
The silicon wafers have a strip pitch of 470 Ám and integrated AC-coupling
with punch-through biasing.
The strip pitch is wide enough to collect the full charge in only one
strip per side for most hits,
while not increasing the capacitance to more than 75 pF.
In each layer , 3x3 6 cm wide silicon wafers are concatenated
and connected to 2x384 readout channels.
To show the position resolution of these detectors we projected a Co57 source (122 keV)
through a lead mask onto one of the 20cm x 20cm Silicon-layers.
The improved position resolution for events with charge sharing between neighbouring
strips was not used yet, but will allow to determine the position of the interaction
with an accuracy of about 100 micron.The energy resolution of D1 is 15 keV FWHM with a threshold of ~30 keV.