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X-Ray Detection
Mechanism
The PIXIS-XB uses direct detection of
x-ray photons in
the silicon of the CCD. The CCD arrays
have been
fabricated on special silicon that has
particularly high
stopping power for x-rays in the 3- 20keV
energy range.
Most significantly, this range includes
the 8-keV Cu
k-alpha line emitted by many laboratory
sources. By
using direct detection (no intermediate
phosphor) almost
all of the energy of the incident x-ray
is converted to
signal, so for an 8-keV photon, over
2,000 electrons are
generated — enough to be easily discriminated
from the
CCD noise, even if a long exposure builds
up dark
charge or if a fast readout increases
the read noise.
Another advantage of direct x-ray detection
is that it
provides much higher spatial resolution
than
phosphor-based detection.
Furthermore,
with direct
detection, the point spread function
does not have the
long low-intensity tails that can occur
when using a
phosphor-based camera.
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