Abstract
The Dosepix detector is a hybrid photon-counting pixel detector based on ideas of the Medipix and Timepix detector family. 1 mm thick cadmium telluride and 300 μm thick silicon were used as sensor material. The pixel matrix of the Dosepix consists of 16 x 16 square pixels with 12 rows of (200 μm)2 and 4 rows of (55 μm)2 sensitive area for the silicon sensor layer and 16 rows of pixels with 220 μm pixel pitch for CdTe. Besides digital energy integration and photon-counting mode, a novel concept of energy binning is included in the pixel electronics, allowing energy-resolved measurements in 16 energy bins within one acquisition. The possibilities of this detector concept range from applications in personal dosimetry and energy-resolved imaging to quality assurance of medical X-ray sources by analysis of the emitted photon spectrum. In this contribution the Dosepix detector, its response to X-rays as well as spectrum measurements with Si and CdTe sensor layer are presented. Furthermore, a first evaluation was carried out to use the Dosepix detector as a kVp-meter, that means to determine the applied acceleration voltage from measured X-ray tubes spectra.
Highlights
Due to the hybrid setup, different sensor layers can be used with the same ASIC design
Most measurements described in this publication were carried out with a 300 μm thick p-in-n silicon sensor which is connected pixel wise to the readout ASIC via tin coated copper pillars
The CdTe detector was assembled at the Freiburger Materialforschungszentrum (FMF), using indium bump bonds instead of copper pillars
Summary
The Dosepix detector [2] is based on the architecture of the Medipix and Timepix detectors [3, 6]. In order to be compatible with bonding to the readout chip, the small area pixels have the same pitch as the large ones; a common guard region — with the same surface doping — surrounds the small pixels. This guard electrode is connected to a reference voltage (approximately electrical ground) but is separated from the pixel electrodes. Each TOTmeasurement of an impinging photon in each pixel is directly compared to 16 digital thresholds These digital thresholds can be set pixelwise and define 16 energy channels equipped with 16 bit deep counters. In energy-binning mode, it is possible to sample energetically the incident photon spectrum in each pixel in 16 energy channels in a single acquisition
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