A single Photon Counting pixel detector readout Chip (PCC) has been derived from previous work in the CERN RD19 collaboration for particle physics tracking devices, recently developed for high energy physics experiments. The readout chip is a 64 x 64 matrix of identical 170 {micro}m x 170 {micro}m cells. It is to be bump-bonded to an equally segmented 1 cm{sup 2} matrix of semiconductor sensors, e.g. Si or GaAs. Each readout cell comprises a preamplifier, a discriminator and a 15-bit counter. The input noise is 170 e{sup {minus}} rms. At the lowest nominal threshold of 1,400 e{sup {minus}} (5.1 keV in Si) the cells exhibit a threshold distribution with a spread before adjustment of 350 e{sup {minus}} rms. Each cell has a 5-bit register which allows masking, test-enable and 3-bit individual threshold adjust. After adjustment the threshold spread is reduced to 80 e{sup {minus}} rms. Absolute calibration of the electrically measured equivalent charge can be done once the readout chip is bump-bonded to a detector.

A Readout Chip for a 64 x 64 Pixel Matrix with 15-bit Single Photon Counting*

Hybrid pixel detectors were developed to meet the requirements for tracking in the inner layers at the LHC experiments. With low input capacitance per channel (10–100 fF) it is relatively straightforward to design pulse processing readout electronics with input referred noise of ∼ 100 e-rms and pulse shaping times consistent with tagging of events to a single LHC bunch crossing providing clean ‘images’ of the ionising tracks generated. In the Medipix Collaborations the same concept has been adapted to provide practically noise hit free imaging in a wide range of applications. This paper reports on the development of three generations of readout ASICs. Two distinctive streams of development can be identified: the Medipix ASICs which integrate data from multiple hits on a pixel and provide the images in the form of frames and the Timepix ASICs who aim to send as much information about individual interactions as possible off-chip for further processing. One outstanding circumstance in the use of these devices has been their numerous successful applications, thanks to a large and active community of developers and users. That process has even permitted new developments for detectors for High Energy Physics. This paper reviews the ASICs themselves and details some of the many applications.

/pdf/submitter-asic-developments-for-radiation-imaging-ik6ht0g62s.pdf

submitter : Asic developments for radiation imaging applications: The medipix and timepix family

Autoradiography is a widely used technique for imaging trace quantities of radioactivity within biological samples, conventionally using photographic film. This method produces images with high spatial resolution, but it suffers from very low sensitivity and poor dynamic range. Digital autoradiography systems with greatly improved sensitivity and linearity are commercially available, but the spatial resolution is usually much less than that achieved using film. We report here the design, construction and characterization of a novel digital autoradiography system based on scientific-grade charged coupled devices (CCDs). Images of x-ray and β emissions from radionuclides commonly used in autoradiography show that the system can perform high-speed quantitative imaging with a spatial resolution of ~30 µm. Using a frame by frame acquisition method the dynamic range is shown to be at least three orders of magnitude. The absolute detection efficiency is comparable to the best of the currently available digital systems. CCD images of 125I and 14C radioisotope distributions in tissue samples are superior to the equivalent film images and have been acquired in 1-10% of the time.

http://iopscience.iop.org/article/10.1088/0031-9155/45/7/322/pdf

The performance of a CCD digital autoradiography imaging system.

The first autoradiographic results of the tritium (3H) marked source obtained with monolithic active pixel sensors are presented. The detector is a high-resolution, back-side illuminated imager, developed within the SUCIMA collaboration for low-energy (

Tritium autoradiography with thinned and back-side illuminated monolithic active pixel sensor device

We present the first images of beta autoradiography obtained with the high-resolution hybrid pixel detector consisting of the Medipix2 single photon counting read-out chip bump-bonded to a 300 µm thick silicon pixel detector. This room temperature system has 256 × 256 square pixels of 55 µm pitch (total sensitive area of 14 × 14 mm2), with a double threshold discriminator and a 13-bit counter in each pixel. It is read out via a dedicated electronic interface and control software, also developed in the framework of the European Medipix2 Collaboration. Digital beta autoradiograms of 14C microscale standard strips (containing separate bands of increasing specific activity in the range 0.0038–32.9 kBq g−1) indicate system linearity down to a total background noise of 1.8 × 10−3 counts mm−2 s−1. The minimum detectable activity is estimated to be 0.012 Bq for 36 000 s exposure and 0.023 Bq for 10 800 s exposure. The measured minimum detection threshold is less than 1600 electrons (equivalent to about 6 keV Si). This real-time system for beta autoradiography offers lower pixel pitch and higher sensitive area than the previous Medipix1-based system. It has a 14C sensitivity better than that of micro channel plate based systems, which, however, shows higher spatial resolution and sensitive area.

https://iopscience.iop.org/article/10.1088/0031-9155/48/12/403/pdf

First images of a digital autoradiography system based on a Medipix2 hybrid silicon pixel detector.

Solid state detectors made of Si (4.8/spl times/8 mm/sup 2/) and GaAs (6.4/spl times/8 mm/sup 2/) pixel matrices bump-bonded to the Omega2 and Omega3 electronic read-out systems, developed at CERN for H.E.P. experiments, have been used to obtain autoradiographic images of clusters of human epithelial cells and DNA fragments separated via electrophoresis, both labeled with /sup 32/P. The system has shown a good minimum detectable activity per unit area of 2.10/sup -4/ cps mm/sup -2/, and has proved linear for a count rate in the range 0.2-20 cpa, typical of autoradiography. The pixel dimensions are 75/spl times/500 /spl mu/m/sup 2/ (Si-Omega2) and 50/spl times/500 /spl mu/m/sup 2/ (GaAs-Omega3), respectively. We are able to clearly localize clusters of cells which have incorporated the radioactive tracer and DNA fragments on an electrophoretic gel on paper (blots).

Use of silicon and GaAs pixel detectors for digital autoradiography

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Use of silicon and GaAs pixel detectors for digital autoradiography