Silicon counters
Silicon counters are sometimes called 'solid state wire chambers'
because here in principle the same is happening like in a
wire chamber.
Silicon atoms are ionized along the track of a charged particle,
and the freed electrons drift to the readout
electrode.
The ionized atoms don't drift, instead they receive an electron
from their neighbouring atom, which against receives an electron
from it's neighbour, a.s.o, so that a positive 'hole' drifts
to the other electrode.
The electrodes are on the surfaces of the silicon chip, so
the field lines are orientated perpendicular to the
chip.
The silicon counters used in the COSY-11 experiment are called
silicon pad detectors, because the electrodes on the readout
side of the chips are four rectangular areas
('pads').
To form a large detectors these chips are staggered in three
rows which overlap in order to get a complete geometrical
coverage:
The pads are connected to AMPLEX-16 chips which contain
16 readout channels each consisting of a charge amplifier,
a filter amplifier, and a sample-and-hold
stage.
These are followd by a multiplexer which switches the stored
voltages sequentially to a single analog wire that is connected
to an external ADC.
There are two detectors made of these silicon pads in the
COSY-11 experiment: the small monitor detector (36 chips =
128 pads) for the measurement of elastically scattered protons
and the longer (180 chips = 720 pads) one inside the dipole
gap to detect reaction products with negative
charge.
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Last updated: 27-November-1997 by
T.Sefzick
