CdZnTe (CZT) is a wide bandgap II–VI semiconductor developed for the spectroscopic detection of X-rays and
γ-rays at room temperature. The Swift Burst Alert Telescope is using an 5240
cm
2 array of 2
...mm thick CZT detectors for the detection of 15–150
keV X-rays from Gamma-ray Bursts. We report on the systematic tests of thicker (⩾0.5
cm) CZT detectors with volumes between 2
cm
3 and 4 cm
3 which are potential detector choices for a number of future X-ray telescopes that operate in the 10
keV to a few MeV energy range. The detectors contacted in our laboratory achieve Full Width Half Maximum energy resolutions of 2.7
keV (4.5%) at 59
keV, 3
keV (2.5%) at 122
keV and 4
keV (0.6%) at 662
keV. The 59
keV and 122
keV energy resolutions are among the world-best results for ⩾0.5
cm thick CZT detectors. We use the data set to study trends of how the energy resolution depends on the detector thickness and on the pixel pitch. Unfortunately, we do not find clear trends, indicating that even for the extremely good energy resolutions reported here, the achievable energy resolutions are largely determined by the properties of individual crystals. Somewhat surprisingly, we achieve the reported results without applying a correction of the anode signals for the depth of the interaction. Measuring the interaction depths thus does not seem to be a pre-requisite for achieving sub-1% energy resolutions at 662
keV.
The objective of the research and development activities, regarding the upgrade of the MAGNEX focal plane detector (FPD) and the development of the γ detector array for the NUMEN project, is the ...construction of new detectors capable to fulfil the requirements of high event rate, radiation tolerance and data acquisition and transmission bandwidth deriving from the upgrade of the Superconducting Cyclotron at INFN Laboratori Nazionali del Sud. The design of the front-end (FE) and read-out (RO) electronics has been performed in parallel with that of the new tracker. The design of the new segmented anode and the architecture of the front-end and read-out electronics are presented.
Position-sensitive virtual Frisch-grid (VFG) CdZnTe (CZT) detectors offer a unique capability for correcting the response nonuniformities caused by crystal defects. This allowed us to achieve high ...energy resolution, while using typical-grade commercial CZT crystals with relaxed requirements to their quality, thus reducing the overall cost of detectors. Another advantage of the VFG detectors is that they can be integrated into arrays and used in small compact hand-held instruments or large-area gamma cameras that will enhance detection capability for many practical applications, including nonproliferation, medical imaging, and gamma-ray astronomy. Here, we present the results from testing small array prototypes coupled with front-end application-specified integrated circuit. Each detector in the array is furnished with 5-mm-wide charge-sensing pads placed near the anode. The pads signals are converted into XY coordinates, which combined with the cathode signals (for Z coordinates) provide 3-D position information of all interaction points. The basic array consists of a number of detectors grouped into 2×2 subarrays, each having a common cathode made by connecting together the cathodes of the individual detectors. These features can significantly improve the performance of detectors while using typical-grade low-cost CZT crystals to reduce the overall cost of the proposed instrument.
The design of the front-end electronics for the new tracker of the MAGNEX Focal Plane Detector (FPD) for the NUMEN project is presented. The front-end is based on the VMM chip, developed for ATLAS ...experiment at CERN. The architecture of the front-end (FE) electronics is designed to be modular and scalable to the final detector. The segmented anode board is designed in order to take advantage of the unique performances of the VMM chip, allowing a digital reconstruction of the track at high event rate. This anode board is connected to front-end by mean of Micro Coax Cable Assembly and does not make use of vacuum connectors. The front-end boards will be placed in air, facilitating in this way the heat dissipation and the connection to the read-out (RO) electronics. An innovative anode read-out strategy allows the reduction of the total number of channels to about 1400 and the measurement of the track at different depth in the detector with 750 µm spatial resolution.
New results from testing an array of 6 \,\times\, 6 \,\times\, 15 mm ^{3} virtual Frisch-grid CdZnTe (CZT) detectors with common-cathode readout for charge signals correction and rejection of ...incomplete charge collection events (ICC) are presented. The array employs parallelepiped-shaped crystals of a large geometrical aspect ratio with two planar contacts on the top and bottom surfaces (anode and cathode) and an additional shielding electrode placed on the sides to create the virtual Frisch-grid effect. The detectors are arranged in 2 \,\times\, 2 or 3 \,\times\, 3 detector modules with the common cathode readout by a single electronic channel. Because of the common cathode, the length of the shielding electrode can be further reduced with no adverse effects on the device performance. By implementing a novel technique for rejecting ICC events caused by the extended defects, we can achieve good spectral responses from ordinary CZT crystals, which can be produced with higher yield and at lower cost. For such crystals, the resolution of individual detectors is expected to be in the range of 0.8-1.5% FWHM at 662 keV with an average value of 1.3%. Arrays of virtual Frisch-grid detectors offer a robust and low-cost approach for making large-area detection modules that can potentially substitute for more advanced, but also more expensive and less available, pixel detectors in applications with slightly relaxed requirements on position- and energy-resolution (e.g., for coded aperture telescopes). In addition, such virtual Frisch-grid arrays will require a comparably smaller number of readout channels, which allows for lower power consumption.
We have constructed a pixelated germanium detector using a technique which has been shown to provide good isolation between adjacent pixels. In this work we present initial tests of the application ...of a low-noise CMOS ASIC to read out this detector. The detector has 64 pixels, each 0.5 mm×5 mm, arranged as a series of strips. It is connected by wire-bonds to two 32-channel application-specific integrated circuits (ASICs) which provide a complete photon-counting chain for every channel. Since the size of the pixel array is no longer restricted by the difficulties of instrumenting large channel-count conventional electronics, this development will open up the possibility of even larger arrays, similar to those offered by silicon detectors.
Intraocular cancer is a serious threat to the lives of those that suffer from it. Dosimetry for eye brachytherapy presents a significant challenge due to the inherently steep dose gradients that are ...needed to treat such small tumours in close proximity to sensitive normal structures. This issue is addressed by providing much needed quality assurance to eye brachytherapy, a novel volumetric dosimetry system, called Panoptes was developed. This study focuses on the preliminary characterisation and calibration of the system. Using ion beam facilities, the custom, pixelated silicon detector of Panoptes was shown to have good charge collection uniformity and a well defined sensitive volume. Flat-field calibration was conducted on the device using a 250 kVp orthovoltage beam. Finally, the detector and phantom were simulated with Monte Carlo in Geant4, to create water equivalent dose correction factors for each pixel across a range of angles.
•Volumetric detector system produced for plaque brachytherapy.•Orthovoltage, flat-field calibration performed for detector pixels.•Monte Carlo simulation showed mostly little angular deviation across all angles.•Ion beam induced charge collection showed pixels uniform and fully depleted.
CdZnTe (CZT) is a wide band-gap IIaVI semiconductor and can be used as detector for hard X-rays in astronomical instrumentation and for medical applications. Angular and energy resolutions, as well ...as detection efficiencies are crucial parameters to characterize the performance of CZT detectors. We studied the detector performance as a function of the geometrical layout of the anode pixel matrix for two 2A2cm2 CZT detectors with thicknesses of 2 mm and 5 mm, respectively. We varied the pixel sizes as well as their relative distances and quantified the energy resolutions and detection efficiencies. We also studied how a steering grid located between pixels affects the energy resolution and detection rate. The results of the study are presented and suggest that a steering grid substantially improves the high-energy performance of thin detectorsawhereas thick detectors mainly benefit from larger pixel widths.
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