PILATUS (detector)

Diffraction pattern of the protein thaumatin in its tetragonal crystal form, recorded on a PILATUS 6M at the HZB MX beamline BL14.1.

PILATUS is the name of a series of x-ray detectors originally developed by the Paul Scherrer Institute at the Swiss Light Source and further developed and commercialized by DECTRIS. The PILATUS detectors are based on hybrid photon counting technology, by which X-rays are converted to electrical signals by the photoelectric effect in a semiconductor sensor layer—either silicon or cadmium telluride—which is subject to a substantial bias voltage. The electric signals are counted directly by a series of cells in an ASIC bonded to the sensor. Each cell—or pixel—is a complete detector in itself, equipped with an amplifier, discriminator and counter circuit. This is possible thanks to contemporary CMOS integrated circuit technology.

The direct detection of single photons and the accurate determination of scattering and diffraction intensities over a wide dynamic range have resulted in PILATUS detectors becoming a standard at most synchrotron beamlines and being used for a large variety of X-ray applications, including: small-angle scattering, coherent scattering, X-ray powder diffraction and spectroscopy.

Design challenges include making the bonding of the ASIC to the sensor sufficiently reliable; the ASIC has to be manufactured in a radiation-tolerant process since the sensor layer by no means absorbs all the incident X-rays.

Other issues involve combining ASICs to make a sensor of usable size - protein crystallography applications tend to want an active area of around 100,000 mm², though powder diffraction work can use a rather smaller active area. One detector inclines the ASICs so that the view from the point of view of the crystal is of an unbroken sphere of detector.

References

• Claude Leroy (2012). Silicon Solid State Devices and Radiation Detection. World Scientific. p. 240. Retrieved 11 December 2018.