Medipix
Medipix is a family of photon counting and particle tracking pixel detectors developed by an international collaboration, hosted by CERN.
The sensor layer is a semiconductor, such as silicon, GaAs, or CdTe in which the incident radiation makes an electron hole/cloud.
The charge is then collected to pixel electrodes and, via bump bonds, conducted to the CMOS electronics layer.
The Medipix device also contains an upper discrimination level and hence only signals within a range of amplitude could be accepted (within an energy window).
It is a mode where the counter in each pixel records the number of clocks for which the pulse remains above the discrimination level.
The second mode of the Timepix chip is “Time-of-arrival”, in which pixel counters record time between a trigger and detection of radiation quanta with energy above the discrimination level.
This mode of operation finds use in time of flight (ToF) applications, for instance in neutron imaging.
Therefore, scanning with their level it is possible to measure over frequency-bands of the incoming radiation; thus enabling spectroscopic x-ray imaging.
These assemblies are tiled next to each other to create nearly arbitrarily sized detector arrays (the largest build using this technology has 10x10 chips, hence 14x14 cm and 2560x2560 pixels[2]).
It adds two more modes to the pixels, in addition to counting of detected signals: Time-over-Threshold (TOT) and Time-of-Arrival (TOA).
The next major difference compared to the previous Timepix chip is the ability to measure the hit amplitude simultaneously with the time of arrival.
It provides a lower frame rate compared to Muros, but the electronics was integrated into a box not larger than a pack of cigarettes.
Merlin is available with CdTe sensors from Quantum Detectors who are collaborating on further development with Diamond Light Source.
Lambda is a high-speed (2,000 fps) big area (12 chips) readout systems developed at DESY.
Medipix offers to the X-ray imaging field in particular an advantage in higher dynamic range and energy sensitivity.
[5] Examples of X-ray images from selected X-ray imaging application fields are: Timepix-based detectors from the Medipix2 Collaboration have been flown on the International Space Station since 2013, and on the first flight test (EFT-1) of NASA's new Orion Multi-Purpose Crew Vehicle in December 2014.
Current plans call for similar devices to be flown as the primary radiation area monitors on the future initial crewed Orion missions.
The detectors may also find applications in astronomy, high energy physics, medical imaging, and X-ray spectroscopy.
