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X-Ray Detection
Mechanism
The LCX 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 5-17 keV 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.
Model Configurations
PI-LCX
cameras are available with a thin (0.010”)
beryllium window or with a rotatable
ConFlat flange (for low x-ray energy).
Additionally, the CCD array is cooled
either thermoelectrically or with liquid
nitrogen to reduce dark noise. The CCD
is kept in a vacuum so that cooling
is efficient and there can be no condensation
on the silicon or the beryllium window.
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Photon Energy (keV)
without Beryllium
window and with Beryllium window
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