CHARGE COUPLED DEVICES are the ideal detector for soft
X rays (1 to 12 keV) in the high background environment of an accelerator.That
is due to the manner in which X rays deposit energy in the detector material.
The essential development in CCD detector technology was the reduction
of the pixel size to approximately 22.5 x 22.5 µm2.
Under this condition, charge deposited by a low energy X ray is mostly
confined to a single pixel. Higher energy photons or charged particles
have much more ionizing power and will deposit their charge over several
pixels. By applying the "single pixel" criterion an enormous efficient
background rejection has been achieved. This capability, in addition to
the excellent energy resolution (150 eV FWHM for 6.5 keV X rays) is the
key to success for many experiments.