Report on future detector requirements at ESRF

Flux on detector:
The flux on the detector is expected to be between 10 8 and 10 10 photons/s/mm 2 , depending
on the energy. These values are smaller than the flux for other imaging beamlines because of
two reasons: ID17 uses only one wiggler and the photons are spread over a larger beam.
Particular operating conditions:
Due to the use of high energy photons, radiation damage generates a very rapid blackening of
the taper. Better radiation hardness would be appreciated.
Required detector
Required detector is a large 2D rectangular detector, that can be efficiently used at high
energy.
Existing detectors
ID17 is currently using a FReLoN 2kx2k, with fibre optic taper and scintillator.
For the applications requiring less spatial resolution but more efficiency and speed, a Ge
2-strip detector, with 350 µm pitch and 10 mm width, is used.
Short term possibilities
Structured CsI scintillators will be tested. The use of a FReLoN 4M instead of current
FReLoN 2k will improve both dynamic range (by a factor 1.5) and quantum efficiency (65%
efficiency at the Gadox emission wavelengths instead of 35%). Nevertheless, this will not
directly permit to reduce the dose on the sample because in the case of taper coupling, where
the light collection yield is high, the signal to noise ratio depends much more on the
absorption coefficient of the scintillator than on the quantum efficiency (see DQE formula in
[Koch et al., 1998]). This means that even if the total yield of the detector is increased, the
SNR will not be proportionally improved.
Main required improvements
The main expected improvements concern the efficiency and the field of view at constant or
better spatial resolution. Radiation hardness of optical couplings has to be improved.
Other types of detectors
MIA requires other 2D detectors (see pages 30, 32 and 39).
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