|
Medipix is a family of photon counting and particle tracking pixel detectors developed by an international collaboration, hosted by CERN. ==Design== The detectors are hybrid detectors. This means that a semi-conductor sensor layer is bonded on to an electronics layer. 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 collectedto pixel electrodes and via bump bonds conducted to the CMOS electronics layer. The pixel electronics first amplifies the signal and then compares the signal amplitude with a pre-set discrimination level (an energy threshold). The subsequent signal processing depends on type of the device. Standard Medipix detector increases the counter in the appropriate pixel if the signal is above the discrimination level. The Medipix devices contain also an upper discrimination level and hence only signals within a range of amplitude could be accepted (within an energy window). The Temepix devices offer in addition to the counting two more modes of operation. The first one is so called “Time-over-Threshold” mode (Wilkinson type Analog-to-digital converter). It is a mode where the counter in each pixel records number of clocks for which the pulse remains above the discrimination level. This number is proportional to the energy of detected radiation. This mode is useful for particle tracking applications or for direct spectral imaging. 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. Every individual hit of radiation is processed by the electronics integrated in each pixel this way, therefore the device could be considered as 65 536 individual counting detectors or even spectrometers. The energy discriminators are adjustable. Therefore, scanning with their level is possible to measure the full spectrum of the incoming radiation and thus enabling full spectroscopic x-ray imaging. Medipix-2, Timepix, and Medipix-3 are all 256×256 pixels, each 0.055mm (55μm) square, forming a total area 14.08mm × 14.08mm. Larger area detectors are possible to crate by bump-bonding multiple chips to larger monolithic sensors. Detectors of sizes from 2x2 to 2x4 chips are commonly used. Even larger gap-less areas could be created using the technology of edgeless sensors. Here the Medipix/Timepix chips have each its own sensor and these assemblies are tiled next to each other to create nearly arbitrarily sized detector array (the largest build using this technology has 10x10 chips, hence 14x14 cm and 2560x2560 pixels〔(Timepix large area 6.5MPix camera )〕). Medipix2 USB Camera.png|Standard, single chip Medipix carrier board with USB readout. Quad board.jpg|The quad board: four Medipix2 chips with one common sensor chip to have a larger area with limited dead space. Excalibur front end.jpg|Excalibur front end. Each of the three sensors has 16 chips flip chip bonded. Widepix 10x10.png|WidePix 10x10 with resolution of 2560x2560 pixels (6.5 Mpixels) and continuously sensitive area. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Medipix」の詳細全文を読む スポンサード リンク
|