Energy Recovery of Multiple Charge Sharing Events in Room Temperature Semiconductor Pixel Detectors (original) (raw)
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Sensors, 2020
Most modern energy resolving, photon counting detectors employ small (sub 1 mm) pixels for high spatial resolution and low per pixel count rate requirements. These small pixels can suffer from a range of charge sharing effects (CSEs) that degrade both spectral analysis and imaging metrics. A range of charge sharing correction algorithms (CSCAs) have been proposed and validated by different groups to reduce CSEs, however their performance is often compared solely to the same system when no such corrections are made. In this paper, a combination of Monte Carlo and finite element methods are used to compare six different CSCAs with the case where no CSCA is employed, with respect to four different metrics: absolute detection efficiency, photopeak detection efficiency, relative coincidence counts, and binned spectral efficiency. The performance of the various CSCAs is explored when running on systems with pixel pitches ranging from 100 µm to 600µm, in 50 µm increments, and fluxes from 1...
Direct charge sharing observation in single-photon-counting pixel detector
Nuclear Instruments & Methods in Physics Research Section a-Accelerators Spectrometers Detectors and Associated Equipment, 2007
In photon-counting imaging devices, charge sharing can limit the detector spatial resolution and contrast, as multiple counts can be induced in adjacent pixels as a result of the spread of the charge cloud generated from a single X-ray photon of high energy in the detector bulk. Although debated for a long time, the full impact of charge sharing has not been completely assessed. In this work, the importance of charge sharing in pixellated CdTe and silicon detectors is studied by exposing imaging devices to different low activity sources. These devices are made of Si and CdTe pixel detector bump-bonded to Medipix2 single-photon-counting chips with a 55 mm pixel pitch. We will show how charge sharing affects the spatial detector resolution depending on incident particle type (alpha, beta and gamma), detector bias voltage and read-out chip threshold. This study will give an insight on the impact on the design and operation of pixel detectors coupled to photon-counting devices for imaging applications. r
Charge-sharing observations with a CdTe pixel detector irradiated with a57Co source
Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 2006
Charge sharing is a limiting factor of detector spatial resolution and contrast in photon counting imaging devices because multiple counts can be induced in adjacent pixels as a result of the spread of the charge cloud generated from a single X-ray photon of high energy in the detector bulk. Although this topic has been debated for a long time, the full impact of charge sharing has not been completely assessed. In this work, we look at the importance of charge sharing in CdTe pixel detectors by exposing such a device to a low-activity (37 kBq) 57 Co source, whose main emission line is at 122 keV. The detectors used are 1 mm thick with a pixel pitch of 55 µm. These detectors are bumpbonded to Medipix2 photon counting chips. This study gives an insight on the impact on the design and operation of pixel detectors coupled to photon counting devices for imaging applications.
A study of charge sharing in pixellated cadmium-zinc-telluride detectors
… Record, 2001 IEEE, 2001
In this paper we present the status and preliminary results from a CZT development program of fine pixel detectors. These are to be used at the focus of high-energy grazing-incidence optics (20-75 keV) of the HERO-Experiment under construction at the Marshall Space Flight Center.
X-Ray Beam Studies of Charge Sharing in Small Pixel, Spectroscopic, CdZnTe Detectors
IEEE Transactions on Nuclear Science, 2000
Recent advances in the growth of CdZnTe material have allowed the development of small pixel, spectroscopic, X-ray imaging detectors. These detectors have applications in a diverse range of fields such as medical, security and industrial sectors. As the size of the pixels decreases relative to the detector thickness, the probability that charge is shared between multiple pixels increases due to the non zero width of the charge clouds drifting through the detector. These charge sharing events will result in a degradation of the spectroscopic performance of detectors and must be considered when analyzing the detector response. In this paper charge sharing and charge loss in a 250 m pitch CdZnTe pixel detector has been investigated using a mono-chromatic X-ray beam at the Diamond Light Source, U.K. Using a 20 m beam diameter the detector response has been mapped for X-ray energies both above (40 keV) and below (26 keV) the material -shell absorption energies to study charge sharing and the role of fluorescence X-rays in these events.
Measurements of charge sharing in small pixel CdTe detectors
Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 2014
CdTe detectors with a thickness of 1 mm and a pixel pitch of 250 mm have been flip-chip-bonded to the HEXITEC read-out ASIC. The detectors record both the position and energy of X-ray interactions producing an X-ray spectrum for each of the 6400 pixels in the energy range 2-200 keV. In this arrangement, detectors have been shown to produce excellent spectroscopy with FWHM better than 1.2 keV at an interaction energy of 59.5 keV. Due to the use of small pixels, a significant number of events experience charge sharing where the total energy of the event is distributed between multiple pixels. Under normal operating conditions, the proportion of events that experience charge sharing was measured to be 36.4%. Without correction these events lead to a reduction in the spectroscopic performance of the detector, the production of pronounced fluorescence and X-ray escape peaks, and the detection sensitivity. In this paper, the effect of different correction algorithms and operating conditions on the detector performance is presented. Crown
IEEE Transactions on Nuclear Science, 2011
We present estimates of energy loss and charge sharing for a pixelated cadmium telluride (CdTe) detector used for photon-counting spectral computed tomography (CT). In a photon-counting pixelated CdTe detector, several physical effects lead to detected events with reduced energies, including Compton scattering, fluorescence emission, charge diffusion, trapping of charge carriers and slow-hole-motion-induced incomplete charge collection. Charge sharing is the result of the lost energy being collected by adjacent pixels. We simulated the photon transport and the charge-collection process with a Monte Carlo-based simulation and evaluated these effects on the detector performance. The trapping effect and poor hole collection have been studied together using an analytical model. We also investigated the detector response under the influence of only the fluorescence effect. We conclude that the charge sharing effects should be taken into account when the pixel is smaller than 1 mm 2. A straightforward way to decrease the double counting of X-rays from events with charge sharing is to increase the electronic threshold. However, increasing the threshold comes at the cost of losing low-energy events, which is undesirable, at least in applications such as pediatric imaging.
Sensors, 2022
The success of cadmium zinc telluride (CZT) detectors in room-temperature spectroscopic X-ray imaging is now widely accepted. The most common CZT detectors are characterized by enhanced-charge transport properties of electrons, with mobility-lifetime products μeτe > 10−2 cm2/V and μhτh > 10−5 cm2/V. These materials, typically termed low-flux LF-CZT, are successfully used for thick electron-sensing detectors and in low-flux conditions. Recently, new CZT materials with hole mobility-lifetime product enhancements (μhτh > 10−4 cm2/V and μeτe > 10−3 cm2/V) have been fabricated for high-flux measurements (high-flux HF-CZT detectors). In this work, we will present the performance and charge-sharing properties of sub-millimeter CZT pixel detectors based on LF-CZT and HF-CZT crystals. Experimental results from the measurement of energy spectra after charge-sharing addition (CSA) and from 2D X-ray mapping highlight the better charge-collection properties of HF-CZT detectors near t...
2012 IEEE Nuclear Science Symposium and Medical Imaging Conference Record (NSS/MIC), 2012
Semiconductor radiation detectors are a promising technology for single photon counting detectors. Unlike scintillator-based indirect radiation detectors, semiconductor detectors directly convert absorbed photons to charge, thereby reducing energy spreading and signal loss that can occur in scintillator-based detectors. Cadmium telluride (CdTe) has attracted research interest due to its higher stopping power compared to other semiconductors such as germanium and silicon as well as its room-temperature operating capability. A CdTe photon-counting, energy-resolving detector system has been developed for x-ray and radionuclide imaging, and is capable of discriminating incident photon energy using multiple voltage thresholds per detector element with fast signal formation. Using this CdTe detector, a reproducible method of generating energy spectra was developed for a given incident radiation source. The energy resolution of the CdTe detector was determined by generating the energy spectra of three radiation sources.
Rejecting incomplete charge-collection events in CdZnTe and other semiconductor detectors
Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 2012
In an ideal single-carrier-type gamma ray detector, the amplitudes of the signals and the carrier drift times are correlated variables. However, if the charges produced by an incident photon are not fully collected, as is the case in CdZnTe detectors containing crystal defects, the above correlation does not hold. This permits the application of an event recognition algorithm to identify these incomplete charge collection (ICC) events, caused by the ''bad'' regions inside a detector, so that they can be removed from pulse height spectra. The ICC events primarily contribute to the Compton continuum and the low-energy tail of the photopeak. Thus, rejecting such events should not affect significantly the photopeak efficiency, but should improve the spectral response, e.g., the peak-to-Compton ratio, for a detector fabricated from material with relaxed crystal quality requirements. Such crystals are those currently available from vendors. The use of stronger ICC correlation-function rejection criteria can improve the energy resolution of these lower-quality crystals, but at the price of a loss in photoefficiency.