HEp-2 Intensity Classification based on Deep Fine-tuning

Digital performance improvements of a CdTe pixel detector for high flux energy-resolved X-ray imaging

Abstract Photon counting detectors with energy resolving capabilities are desired for high flux X-ray imaging. In this work, we present the performance of a pixelated Schottky Al/p-CdTe/Pt detector (4×4) coupled to a custom-designed digital readout electronics for high flux measurements. The detector (4×4×2 mm 3 ) has an anode layout based on an array of 16 pixels with a geometric pitch of 1 mm (pixel size of 0.6 mm). The 4-channel readout electronics is able to continuously digitize and process the signals from each pixel, performing multi-parameter analysis (event arrival time, pulse shape, pulse height, pulse time width, etc.) even at high fluxes and at different throughput and energy re…

Polarization phenomena in Al/p-CdTe/Pt X-ray detectors

Over the last decades, CdTe detectors are widely used for the development of room temperature X-ray and gamma ray spectrometers. Typically, high resolution CdTe detectors are fabricated with blocking contacts (indium, aluminum) ensuring low leakage currents and high electric field for optimum charge collection. As well known, time instability under bias voltage (termed as polarization) is the major drawback of CdTe diode detectors. Polarization phenomena cause a progressive degradation of the spectroscopic performance with time, due to hole trapping and detrapping from deep acceptors levels. In this work, we studied the polarization phenomenon on new Al/p-CdTe/Pt detectors, manufactured by …

Laboratorio a contaminazione controllata per tecniche fisiche applicate ai beni culturali

Hard X-Ray Response of Pixellated CdZnTe Detectors

In recent years, the development of cadmium zinc telluride (CdZnTe) detectors for x-ray and gamma ray spectrometry has grown rapidly. The good room temperature performance and the high spatial resolution of pixellated CdZnTe detectors make them very attractive in space-borne x-ray astronomy, mainly as focal plane detectors for the new generation of hard x-ray focusing telescopes. In this work, we investigated on the spectroscopic performance of two pixellated CdZnTe detectors coupled with a custom low noise and low power readout application specific integrated circuit (ASIC). The detectors (10x10x1 and 10x10x2 mm3 single crystals) have an anode layout based on an array of 256 pixels with a …

Mechanically stable metal layers for ohmic and blocking contacts on CdZnTe detectors by electroless deposition

CdZnTe detectors are commonly exploited for the detection of gamma rays. However, obtaining mechanical stable, low noise contacts on CdZnTe is still an issue. In particular, ohmic contacts would be preferable for high flux applications. In this work, we show that it is possible to obtain mechanical stable gold contacts by electroless deposition in methanol solution. Moreover, we show that electroless deposited nickel contacts are also mechanical stable and are good candidates for the realization of ohmic contacts on high resistivity CdZnTe crystals.

A digital approach for real time high-rate high-resolution radiation measurements

Abstract Modern spectrometers are currently developed by using digital pulse processing (DPP) systems, showing several advantages over traditional analog electronics. The aim of this work is to present digital strategies, in a time domain, for the development of real time high-rate high-resolution spectrometers. We propose a digital method, based on the single delay line (SDL) shaping technique, able to perform multi-parameter analysis with high performance even at high photon counting rates. A robust pulse shape and height analysis (PSHA), applied on single isolated time windows of the detector output waveforms, is presented. The potentialities of the proposed strategy are highlighted thro…

Characterization of the ESR response of alanine dosimeters to low-energy (1-40 keV) X-rays

The aminoacid L-a-alanine has attracted considerable interest for use in radiation ESR dosimetry and has been formally accepted as a secondary standard for high-dose (kGy) and transfer dosimetry . The accuracy of the method is quite high, largely due to the low dependence of the alanine response on various irradiation parameters (photon energies above 100 keV, dose rate, temperature, etc.). Furthermore, this system presents alinear response to dose, fairly high sensitivity, tissue equivalence, absence of fading, small dimensions, ruggedn ess, and non-destructive readout. In this work, we examined the energy dependence of alanine ESR dosimeters in the low energy X-photon energy range between…

Electrical Characterization of CdTe pixel detectors with Al Schottky anode

Abstract Pixelated Schottky Al/p-CdTe/Pt detectors are very attractive devices for high-resolution X-ray spectroscopic imaging, even though they suffer from bias-induced time instability (polarization). In this work, we present the results of the electrical characterization of a (4×4) pixelated Schottky Al/p-CdTe/Pt detector. Current–voltage ( I–V ) characteristics and current transients were investigated at different temperatures. The results show deep levels that play a dominant role in the charge transport mechanism. The conduction mechanism is dominated by the space charge limited current (SCLC) both under forward bias and at high reverse bias. Schottky barrier height of the Al/CdTe con…

Development of a 3D CZT Spectrometer System with Digital Readout for Hard X/Gamma-Ray Astronomy

We report on the development and of a complete X/γ rays detection system (10-1000 keV) based on CZT spectrometers with spatial resolution in three dimensions (3D) and a digital electronics acquisition chain. The prototype is made by packing four linear modules, each composed of one 3D CZT sensors. Each sensors is realized using a single spectroscopic graded CZT crystal of about 20×20×5 mm3. An electrode structure consisting of 12 collecting anodes with a pitch of 1.6 mm and 3 drift strips between each pair of anodes for 48 strips (0.15 mm wide) on the anodic side was adopted. The cathode is made of 10 strips with a pitch of 2 mm and orthogonal to anode side strips. Since the reading of the …

Performance of a digital CdTe X-ray spectrometer in low and high counting rate environment

Abstract The high performances of CdTe detectors for X-ray and gamma ray spectroscopy are already well known. Among the traditional semiconductor spectrometers, CdTe detectors show high detection efficiency and good room temperature performance and are well suited for the development of compact detection systems. In this work, we investigated the performance of a CdTe detector coupled with a custom digital pulse processing (DPP) system for X-ray spectroscopy. The DPP method, implemented on a PC platform, performs a pile-up inspection and a pulse height analysis of the preamplifier output pulses, digitized by a 14-bit, 100 MHz ADC. The spectroscopic results point out the excellent performanc…

High Bias Voltage CZT Detectors for High-flux Measurements

In this work, we present the performance of new travelling heater method (THM) grown CZT detectors, recently developed at IMEM-CNR Parma, Italy. Thick planar detectors (3 mm thick) with gold electroless contacts on CZT crystals grown by Redlen Technologies (Victoria BC, Canada) were realized, with a planar cathode covering the detector surface (4.1 x 4.1 mm(2)) and a central anode (2 x 2 mm(2)) surrounded by a guard ring electrode. The detectors, characterized by low leakage currents at room temperature (4.7 nA/cm(2) at 1000 V/cm), allow good room temperature operation even at high bias voltages (> 7000 V/cm). At low rates, the detectors exhibit an energy resolution around 4 % FWIEM at 59.5…

Digital CZT detector system for high flux energy-resolved X-ray imaging

Photon counting arrays with energy resolving capabilities are recently desired for the next-generation X-ray imaging systems. In this work, we present the performance of a 2 mm thick CZT pixel detector, with pixel pitches of 500 mu m and 250 mu m, coupled to a fast and low noise ASIC (PIXIE ASIC), characterized by only the preamplifier stage. A 16-channel digital readout electronics was used to continuously digitize and process each output channel from the PIXIE ASIC, performing multi-parameter analysis (event arrival time, pulse shape, pulse height) at low and high input counting rates (ICRs). The spectroscopic response of the system to monochromatic X-ray and gamma ray sources, at both lo…

High-rate dead-time corrections in a general purpose digital pulse processing system

The abilities on dead-time correction of a real-time digital pulse processing (DPP) system for high-rate high-resolution radiation measurements are presented. The DPP system, through a fast and slow analysis of the output waveform from radiation detectors, is able to perform an accurate estimation of the true input counting rate (ICR), a fine pulse height (energy) and shape (peaking time) analysis even at high ICRs.

Direct Measurement of Mammographic X-Ray Spectra with a Digital CdTe Detection System

In this work we present a detection system, based on a CdTe detector and an innovative digital pulse processing (DPP) system, for high-rate X-ray spectroscopy in mammography (1–30 keV). The DPP system performs a height and shape analysis of the detector pulses, sampled and digitized by a 14-bit, 100 MHz ADC. We show the results of the characterization of the detection system both at low and high photon counting rates by using monoenergetic X-ray sources and a nonclinical X-ray tube. The detection system exhibits excellent performance up to 830 kcps with an energy resolution of 4.5% FWHM at 22.1 keV. Direct measurements of clinical molybdenum X-ray spectra were carried out by using a pinhole…

Spectroscopic response of a CdZnTe multiple electrode detector

Abstract The spectroscopic performances of a CdZnTe detector (crystal size: 5×5×0.9 mm 3 ) with five electrodes (cathode, anode and three steering electrodes) were studied. The anode layout, which consists of a circular electrode ( φ =80 μm) surrounded by two ring electrodes (gap=100 μm; radial width Δ r =100 μm) and by one electrode that extends to the edge of the crystal, is mostly sensitive to the electron carriers, overcoming the well known effect of the hole trapping in the measured spectra. We report on the spectroscopic response of the detector at different bias voltages of the electrodes and at various photon energies ( 109 Cd, 241 Am and 57 Co sources). The CdZnTe detector exhibits…

Development of new CdZnTe detectors for room-temperature high-flux radiation measurements

Recently, CdZnTe (CZT) detectors have been widely proposed and developed for room-temperature X-ray spectroscopy even at high fluxes, and great efforts have been made on both the device and the crystal growth technologies. In this work, the performance of new travelling-heater-method (THM)-grown CZT detectors, recently developed at IMEM-CNR Parma, Italy, is presented. Thick planar detectors (3 mm thick) with gold electroless contacts were realised, with a planar cathode covering the detector surface (4.1 mm × 4.1 mm) and a central anode (2 mm × 2 mm) surrounded by a guard-ring electrode. The detectors, characterized by low leakage currents at room temperature (4.7 nA cm−2 at 1000 V cm−1), a…

Digital Techniques for High-Rate High-Resolution Radiation Measurements

Digital pulse processing (DPP) techniques are increasingly used in the development of modern spectroscopic systems. DPP systems, based on direct digitizing and processing of detector signals (preamplifier output signals), ensure higher flexibility, stability, lower dead time, higher throughput and better energy resolution than traditional pulse processing systems. In this work, we present our progress in the development of DPP systems for high-rate high-resolution radiation measurements. An innovative digital system, able to perform multi-parameter analysis (input counting rate, pulse height, pulse shape, event arrival time, etc.) even at high photon counting rates is presented. Experimenta…

Time-dependent electric field in Al/CdTe/Pt detectors

Abstract Al/CdTe/Pt detectors are very attractive devices for high-resolution X-ray spectroscopy, even though they suffer from bias-induced time instability (polarization). Polarization phenomena cause a progressive time-degradation of the spectroscopic performance of the detectors, due to hole trapping and detrapping from deep acceptor levels that directly control the electric field distribution. In this work we present experimental investigations on the electric field profile of planar Al/CdTe/Pt detectors by means of Pockels effect measurements. The time/temperature dependence of the electric field was investigated in a long time window (up to 10 h) and the correlation with the reverse c…

Characterization of Al-Schottky CdTe detectors

In the last decades, great efforts are being devoted to the development of CdTe detectors for high resolution X-ray and gamma ray spectroscopy. Recently, new rectifying contacts based on aluminum (Al) are very appealing in the development of CdTe detectors with low leakage currents and anode pixellization. In this work, we report on preliminary results of electrical and spectroscopic investigations on Schottky CdTe diode detectors (4.1 × 4.1 × 0.75 and 4.1 × 4.1 × 2 mm3) with Au/Ti/Al/CdTe/Pt electrode configuration. The detectors are characterized by very low leakage currents even at room temperature (26 pA at 25 °C under a bias voltage of −100 V for the 2 mm thick detector). Polarization …

Accelerated Tests on Si and SiC Power Transistors with Thermal, Fast and Ultra-Fast Neutrons

Neutron test campaigns on silicon (Si) and silicon carbide (SiC) power MOSFETs and IGBTs were conducted at the TRIGA (Training, Research, Isotopes, General Atomics) Mark II (Pavia, Italy) nuclear reactor and ChipIr-ISIS Neutron and Muon Source (Didcot, U.K.) facility. About 2000 power transistors made by STMicroelectronics were tested in all the experiments. Tests with thermal and fast neutrons (up to about 10 MeV) at the TRIGA Mark II reactor showed that single-event burnout (SEB) failures only occurred at voltages close to the rated drain-source voltage. Thermal neutrons did not induce SEB, nor degradation in the electrical parameters of the devices. SEB failures during testing at ChipIr …

Experimental results from Al/p-CdTe/Pt X-ray detectors

Recently, Al/CdTe/Pt detectors have been proposed for the development of high resolution X-ray spectrometers. Due to the low leakage currents, these detectors allow high electric fields and the pixellization of anodes with the possibility to realize single charge carrier sensing detectors. In this work, we report on the results of electrical and spectroscopic investigations on CdTe diode detectors with Al/CdTe/Pt electrode configuration (4.1×4.1×0.75 and 4.1×4.1×2 mm3). The detectors are characterized by very low leakage currents in the reverse bias operation: 0.3 nA at 25 °C and 2.4 pA at -25 °C under a bias voltage of -1000 V. The spectroscopic performance of the detectors at both low and…

Dual-polarity pulse processing and analysis for charge-loss correction in cadmium–zinc–telluride pixel detectors

Charge losses at the inter-pixel gap are typical drawbacks in cadmium–zinc–telluride (CZT) pixel detectors. In this work, an original technique able to correct charge losses occurring after the application of charge-sharing addition (CSA) is presented. The method, exploiting the strong relation between the energy after CSA and the beam position at the inter-pixel gap, allows the recovery of charge losses and improvements in energy resolution. Sub-millimetre CZT pixel detectors were investigated with both uncollimated radiation sources and collimated synchrotron X-rays, at energies below and above the K-shell absorption energy of the CZT material. The detectors are DC coupled to fast and low…

Study of spectral response of a CZT multiple-electrode detectors

Comparison of two portable solid state detectors with an improved collimation and alignment device for mammographic x-ray spectroscopy.

We describe a portable system for mammographic x-ray spectroscopy, based on a 2 X 2 X 1 mm3 cadmium telluride (CdTe) solid state detector, that is greatly improved over a similar system based on a 3 X 3 X 2 mm3 cadmium zinc telluride (CZT) solid state detector evaluated in an earlier work. The CdTe system utilized new pinhole collimators and an alignment device that facilitated measurement of mammographic x-ray spectra. Mammographic x-ray spectra acquired by each system were comparable. Half value layer measurements obtained using an ion chamber agreed closely with those derived from the x-ray spectra measured by either detector. The faster electronics and other features of the CdTe detecto…

Digital filtering and analysis for a semiconductor X-ray detector data acquisition

Abstract Pile-up distortion is a major drawback in X-ray spectroscopy at high count rate. Pulse width narrowing with shaping techniques can lead to the reduction of the pile-up distortion, but a low shaping time reduces the noise filtration and leads to a poor energy resolution. Thus, only a best compromise solution between the pile-up and the noise requirements is achievable. The hardware manipulation needed to adjust the parameters of the traditional electronic shaping amplifiers makes it uneasy to tests various settings in different conditions. Digital techniques can help to overcome such difficulties. A digital signal processing and analysis system for X-ray spectroscopy is described in…

CdZnTe Detectors for Astrophysical and Medical Applications

Characterization of the ESR response of alanine dosimeters to low-energy Cu-target X-tube photons

Abstract This article describes Electron Spin Resonance (ESR) response measurements of Kodak BioMax alanine films exposed to low-energy X-rays from a Cu-target tube operating at 20 kV. Commercial alanine detectors were used to ensure maximum reproducibility of the results, while the choice of a film was due the low penetration of the soft X-rays. X-ray energy spectra and fluences were determined with an innovative digital semiconductor detector system. These data were used to quantify the irradiation of the alanine films in terms of absorbed dose to water. The alanine films were found to present a stable response, highly linear with dose. To our knowledge, these data have not been previousl…

Electrical properties of Au/CdZnTe/Au detectors grown by the boron oxide encapsulated Vertical Bridgman technique

Abstract In this work we report on the results of electrical characterization of new CdZnTe detectors grown by the Boron oxide encapsulated Vertical Bridgman technique (B-VB), currently produced at IMEM-CNR (Parma, Italy). The detectors, with gold electroless contacts, have different thicknesses (1 and 2.5 mm) and the same electrode layout, characterized by a central anode surrounded by a guard-ring electrode. Investigations on the charge transport mechanisms and the electrical contact properties, through the modeling of the measured current–voltage ( I – V ) curves, were performed. Generally, the detectors are characterized by low leakage currents at high bias voltages even at room tempera…

Investigation of the Impact of Neutron Irradiation on SiC Power MOSFETs Lifetime by Reliability Tests

High temperature reverse-bias (HTRB), High temperature gate-bias (HTGB) tests and electrical DC characterization were performed on planar-SiC power MOSFETs which survived to accelerated neutron irradiation tests carried out at ChipIr-ISIS (Didcot, UK) facility, with terrestrial neutrons. The neutron test campaigns on the SiC power MOSFETs (manufactered by ST) were conducted on the same wafer lot devices by STMicroelectronics and Airbus, with different neutron tester systems. HTGB and HTRB tests, which characterise gate-oxide integrity and junction robustness, show no difference between the non irradiated devices and those which survived to the neutron irradiation tests, with neutron fluence…

Investigation on pixellated CZT detectors coupled with a low power readout ASIC

In this work, we investigated on the spectroscopic performances of two pixellated CZT detectors coupled with a custom low noise and low power readout ASIC. The detectors (10 x 10 x 1 mm3 and 10 x 10 x 2 mm3 single crystals) consist of an array of 256 pixels with a geometric pitch of 0.5 mm. The ASIC, fabricated in 0.8 μm BiCMOS technology, is equipped with eight independent channels (preamplifier and shaper) characterized by a dynamic range from 10 keV to 100 keV, low power consumption (0.5 mW/channel) and low noise (150–500 electrons r.m.s.). The spectroscopic results point out the good energy resolution of both detectors at room temperature (5.8 % FWHM at 59.5 keV for the 1 mm thick detec…

High-rate x-ray spectroscopy in mammography with a CdTe detector: A digital pulse processing approach

Purpose:Direct measurement of mammographic x-ray spectra under clinical conditions is a difficult task due to the high fluence rate of the x-ray beams as well as the limits in the development of high resolution detection systems in a high counting rate environment. In this work we present a detection system, based on a CdTe detector and an innovative digital pulse processing (DPP) system, for high-rate x-ray spectroscopy in mammography. Methods: The DPP system performs a digital pile-up inspection and a digital pulse height analysis of the detector signals, digitized through a 14-bit, 100 MHz digitizer, for x-ray spectroscopy even at high photon counting rates. We investigated on the respon…

Monte Carlo evaluation of a CZT 3D spectrometer suitable for a Hard X- and soft-γ rays polarimetry balloon borne experiment

Today, the measurement of the polarization status of cosmic sources high-energy' emission, is recognized as a key observational parameter to understand the active production mechanism and its geometry. Therefore, a mandatory requirement for new instrumentations operating in this energ.-y range will be to provide high sensitivity for polarimetric measurements. In this framework, we have presented the concept of a small high-performance imaging spectrometer optimized for polarimetry between 100 and 600 keV suitable for a stratospheric balloon-borne payload and as a pathfinder for a future satellite mission. The detector with 3D spatial resolution is based on a CZT spectrometer in a highly seg…

High-rate x-ray spectroscopy in mammography with a CdTe detector: A digital pulse processing approach

Purpose:Direct measurement of mammographic x-ray spectra under clinical conditions is a difficult task due to the high fluence rate of the x-ray beams as well as the limits in the development of high resolution detection systems in a high counting rate environment. In this work we present a detection system, based on a CdTe detector and an innovative digital pulse processing (DPP) system, for high-rate x-ray spectroscopy in mammography. Methods: The DPP system performs a digital pile-up inspection and a digital pulse height analysis of the detector signals, digitized through a 14-bit, 100 MHz digitizer, for x-ray spectroscopy even at high photon counting rates. We investigated on the respon…

Digital Pulse-Processing Techniques for X-Ray and Gamma-Ray Semiconductor Detectors

Over the last decade, digital pulse-processing (DPP) electronics have been widely proposed and used for new generation x- and gamma-ray spectrometers. DPP systems, based on direct digitizing and processing of detector signals, lead to better results than the traditional analog pulse-processing electronics in terms of stability, flexibility, reproducibility, energy resolution, throughput, and dead time. In this chapter, we will review the principles of operation of conventional analog electronic chains for x- and gamma-ray semiconductor detectors, with special emphasis on the benefits of the digital approach. The characteristics of a new real-time DPP system, developed by our group, are disc…

Advances in High-Energy-Resolution CdZnTe Linear Array Pixel Detectors with Fast and Low Noise Readout Electronics

Radiation detectors based on Cadmium Zinc Telluride (CZT) compounds are becoming popular solutions thanks to their high detection efficiency, room temperature operation, and to their reliability in compact detection systems for medical, astrophysical, or industrial applications. However, despite a huge effort to improve the technological process, CZT detectors’ full potential has not been completely exploited when both high spatial and energy resolution are required by the application, especially at low energies (<10 keV), limiting their application in energy-resolved photon counting (ERPC) systems. This gap can also be attributed to the lack of dedicated front-end electronics whic…

Optimization of quasi-hemispherical CdZnTe detectors by means of first principles simulation

AbstractIn this paper we present the development of quasi-hemispherical gamma-ray detectors based on CdZnTe. Among the possible single-polarity electrode configurations, such as coplanar, pixelated, or virtual Frisch-grid geometries, quasi-hemispherical detectors are the most cost-effective alternative with comparable raw energy resolution in the high and low energy range. The optimal configuration of the sensor in terms of dimension of the crystals and electrode specifications has been first determined by simulations, and successively validated with experimental measures. Spectra from different sources have been acquired to evaluate the detectors performances. Three types of detectors with…

Ballistic Deficit Pulse Processing in Cadmium-Zinc-Telluride Pixel Detectors for High-Flux X-ray Measurements.

High-flux X-ray measurements with high-energy resolution and high throughput require the mitigation of pile-up and dead time effects. The reduction of the time width of the shaped pulses is a key approach, taking into account the distortions from the ballistic deficit, non-linearity, and time instabilities. In this work, we will present the performance of cadmium–zinc–telluride (CdZnTe or CZT) pixel detectors equipped with digital shapers faster than the preamplifier peaking times (ballistic deficit pulse processing). The effects on energy resolution, throughput, energy-linearity, time stability, charge sharing, and pile-up are shown. The results highlight the absence of time instabilities …

Diagnostic Mammographic X-ray spectra analysis with CZT and CdTe solid state detector

L'ESPERIMENTO XPRESS

Energy resolution and throughput of a new real time digital pulse processing system for x-ray and gamma ray semiconductor detectors

New generation spectroscopy systems have advanced towards digital pulse processing (DPP) approaches. DPP systems, based on direct digitizing and processing of detector signals, have recently been favoured over analog pulse processing electronics, ensuring higher flexibility, stability, lower dead time, higher throughput and better spectroscopic performance. In this work, we present the performance of a new real time DPP system for X-ray and gamma ray semiconductor detectors. The system is based on a commercial digitizer equipped with a custom DPP firmware, developed by our group, for on-line pulse shape and height analysis. X-ray and gamma ray spectra measurements with cadmium telluride (Cd…

Charge carrier transport mechanisms in CdZnTe detectors grown by the vertical Bridgman technique

In this work, we report on the results of electrical characterization of CdZnTe (CZT) detectors, with gold electroless contacts, grown by the boron oxide encapsulated vertical Bridgman technique (B-VB), currently produced at IMEM-CNR (Parma, Italy). The detectors, with different thicknesses (1 and 2.5 mm), have the same electrode layout: the anode is a central electrode (2 x 2 mm(2)) surrounded by a guard ring electrode. The cathode is a planar electrode covering the detector surface (4.1 x 4.1 mm(2)). Current-voltage (I-V) characteristics were measured at different temperatures in order to study the charge transport and the electrical properties. These detectors were compared with the trav…

Progress in the Development of CdTe and CdZnTe Semiconductor Radiation Detectors for Astrophysical and Medical Applications

Over the last decade, cadmium telluride (CdTe) and cadmium zinc telluride (CdZnTe) wide band gap semiconductors have attracted increasing interest as X-ray and gamma ray detectors. Among the traditional high performance spectrometers based on silicon (Si) and germanium (Ge), CdTe and CdZnTe detectors show high detection efficiency and good room temperature performance and are well suited for the development of compact and reliable detection systems. In this paper, we review the current status of research in the development of CdTe and CdZnTe detectors by a comprehensive survey on the material properties, the device characteristics, the different techniques for improving the overall detector…

Energy Recovery of Multiple Charge Sharing Events in Room Temperature Semiconductor Pixel Detectors

Multiple coincidence events from charge-sharing and fluorescent cross-talk are typical drawbacks in room-temperature semiconductor pixel detectors. The mitigation of these distortions in the measured energy spectra, using charge-sharing discrimination (CSD) and charge-sharing addition (CSA) techniques, is always a trade-off between counting efficiency and energy resolution. The energy recovery of multiple coincidence events is still challenging due to the presence of charge losses after CSA. In this work, we will present original techniques able to correct charge losses after CSA even when multiple pixels are involved. Sub-millimeter cadmium–zinc–telluride (CdZnTe or CZT) pixel detectors we…

Charge Sharing and Cross Talk Effects in High-Z and Wide-Bandgap Compound Semiconductor Pixel Detectors

Intense research activities have been made in the development of high-Z and wide-bandgap compound semiconductor pixel detectors for the next generation X-ray and gamma ray spectroscopic imagers. Cadmium telluride (CdTe) and cadmium-zinc-telluride (CdZnTe or CZT) pixel detectors have shown impressive performance in X-ray and gamma ray detection from energies of few keV up to 1 MeV. Charge sharing and cross-talk phenomena represent the typical drawbacks in sub-millimeter pixel detectors, with severe distortions in both energy and spatial resolution. In this chapter, we review the effects of these phenomena on the response of CZT/CdTe pixel detectors, with particular emphasis on the current st…

CdTe Detectors

Cadmium telluride (CdTe) compound semiconductors for x-ray detectors have experienced a rather rapid development in the last few years, due to their appealing performance. In this chapter we review the physical properties of semiconductor detectors for x-ray and γ ray spectroscopy. In particular, we focus on compound semiconductor detectors. We also review the principles of operation of both the semiconductor detectors and the electronic chains, with special emphasis on the digital techniques. CdTe detectors’ characteristics and performance enhancements are discussed in depth. Finally, we present some original results on CdTe detectors for medical applications.

Spectroscopic response and charge transport properties of CdZnTe detectors grown by the vertical Bridgman technique

In this work, we present the results of spectroscopic investigations on CdZnTe (CZT) detectors grown by the boron oxide encapsulated vertical Bridgman technique (1MEM-CNR, Parma, Italy). The detectors, with different thicknesses (1 and 2.5 mm), are characterized by the same electrode layout (gold electroless contacts): the anode is a central electrode (2 x 2 mm(2)) surrounded by a guard-ring electrode, while the cathode is a planar electrode covering the detector surface (4.1 x 4.1 mm(2)). The results of electrical investigations point out the low leakage currents of these detectors even at high bias voltages: 38 nA/cm(2) (T = 25 degrees C) at 10000 V/cm. The time stability and the spectros…

Potentialities of High-Resolution 3-D CZT Drift Strip Detectors for Prompt Gamma-Ray Measurements in BNCT

Recently, new high-resolution cadmium–zinc–telluride (CZT) drift strip detectors for room temperature gamma-ray spectroscopic imaging were developed by our group. The CZT detectors equipped with orthogonal anode/cathode collecting strips, drift strips and dedicated pulse processing allow a detection area of 6 × 20 mm2 and excellent room temperature spectroscopic performance (0.82% FWHM at 661.7 keV). In this work, we investigated the potentialities of these detectors for prompt gamma-ray spectroscopy (PGS) in boron neutron capture therapy (BNCT). The detectors, exploiting the measurement of the 478 keV prompt gamma rays emitted by 94% 7Li nuclides from the 10B(n, α)7…

High Resolution X-Ray Spectroscopy with Compound Semiconductor Detectors and Digital Pulse Processing Systems

The advent of semiconductor detectors has revolutionized the broad field of X-ray spectroscopy. Semiconductor detectors, originally developed for particle physics, are now widely used for X-ray spectroscopy in a large variety of fields, as X-ray fluorescence analysis, X-ray astronomy and diagnostic medicine. The success of semiconductor detectors is due to several unique properties that are not available with other types of detectors: the excellent energy resolution, the high detection efficiency and the possibility of development of compact detection systems. Among the semiconductors, silicon (Si) detectors are the key detectors in the soft X-ray band (15 keV) and will continue to be the c…

Un sistema digitale innovativo per la caratterizzazione energia-flusso di fasci X diagnostici

La conoscenza della distribuzione energetica e del rateo di fluenza dei fasci X è essenziale nei controlli di qualità in medicina diagnostica, sia in termini dosimetrici che della qualità delle immagini. Gli spettri energetici possono essere utilizzati per stime accurate delle tensioni dei tubi (kVp), per la correzione di distorsioni dovute al beam-hardening e per la corretta implementazione delle nuove tecniche dual-energy [1]. In mammografia, gli spettri energetici possono essere usati per stimare l’esposizione, il kerma in aria e la distribuzione energetica della dose assorbita nei tessuti, superando gli inconvenienti dovuti alla dipendenza energetica della risposta dei dosimetri (a stat…

Charge transport properties in CdZnTe detectors grown by the vertical Bridgman technique

Presently, a great amount of effort is being devoted to the development of CdTe and CdZnTe (CZT) detectors for a large variety of applications such as medical, industrial, and space research. We present the spectroscopic properties of some CZT crystals grown by the standard vertical Bridgman method and by the boron oxide encapsulated vertical Bridgman method, which has been recently implemented at IMEM-CNR (Parma, Italy). In this technique, the crystal is grown in an open quartz crucible fully encapsulated by a thin layer of liquid boron oxide. This method prevents contact between the crystal and the crucible, thereby allowing larger single grains with a lower dislocation density to be obta…

A 3D CZT hard x-ray polarimeter for a balloon borne payload

Currently, it is widely recognised that a measurement of the polarization status of cosmic sources high energy emission is a key observational parameter to understand the active production mechanism and its geometry. Therefore new instrumentation operating in this energy range should be optimized also for this type of measurement. In this framework, we present the concept of a small high-performance spectrometer designed for polarimetry between 100 and 500 keV suitable as a stratospheric balloon-borne payload dedicated to perform an accurate and reliable measurement of the polarization status of the Crab pulsar, i.e. the polarization level and direction. The detector with 3D spatial resolut…

Real time digital pulse processing for X-ray and gamma ray semiconductor detectors

Abstract Digital pulse processing (DPP) systems, based on direct digitizing and processing of detector signals, have recently been favoured over analog electronics, ensuring higher flexibility, stability, lower dead time and better spectroscopic performance. In this work, we present the performance of a new real time DPP system for X-ray and gamma ray semiconductor detectors. The system is based on a commercial digitizer equipped with a custom DPP firmware, developed by our group, for on-line pulse height and shape analysis. X-ray and gamma ray spectra measurements with cadmium telluride (CdTe) and germanium (Ge) detectors highlight the excellent performance of the system both at low and hi…

Caratterizzazione di rivelatori CdZnTe a pixel

Charge Transport Properties in CZT Detectors Grown by the Vertical Bridgman Technique

Great efforts are being presently devoted to the development of CdTe and CdZnTe detectors for a large variety of applications, such as medical, industrial, and space research. We present the spectroscopic properties of some CZT crystals grown by the standard vertical Bridgman method and by the boron oxide encapsulated vertical Bridgman method, which has been recently implemented at IMEM-CNR (Parma, Italy). By this technique the crystal is grown in an open quartz crucible fully encapsulated by a thin layer of liquid boron oxide. This method prevents contact between the crystal and the crucible thereby allowing larger single grains with a lower dislocation density to be obtained. Several mono…

High performance 3D CZT spectro-imager for BNCT-SPECT: preliminary characterization

The National Institute of Nuclear Physics (INFN) is supporting the 3CaTS project with the aim of developing a new Single Photon Emission Computed Tomography (SPECT) system for real time 10 B therapeutic dose monitoring in the binary experimental hadron therapy called Boron Neutron Capture Therapy (BNCT). BNCT is a highly selective tumour treatment based on the neutron capture reaction 10 B(n,α) 7 Li. The secondary particles have a high LET with ranges in tissues of the order of 10 μm (thus less than the mean cell diameter of few tens μm). Targeting the 10 B delivery towards cancer, the released energy lethally damages only the malignant cells sparing the normal tissues, thus enabling a cell…

Room-Temperature X-ray response of cadmium-zinc-Telluride pixel detectors grown by the vertical Bridgman technique

In this work, the spectroscopic performances of new cadmium–zinc–telluride (CZT) pixel detectors recently developed at IMEM-CNR of Parma (Italy) are presented. Sub-millimetre arrays with pixel pitch less than 500 µm, based on boron oxide encapsulated vertical Bridgman grown CZT crystals, were fabricated. Excellent room-temperature performance characterizes the detectors even at high-bias-voltage operation (9000 V cm−1), with energy resolutions (FWHM) of 4% (0.9 keV), 1.7% (1 keV) and 1.3% (1.6 keV) at 22.1, 59.5 and 122.1 keV, respectively. Charge-sharing investigations were performed with both uncollimated and collimated synchrotron X-ray beams with particular attention to the mitigation o…

Digital pulse processing techniques for X-ray and gamma ray semiconductor detectors

Digital pulse processing (DPP) systems, based on direct digitizing and processing of detector signals, have recently been favoured over analog electronics, ensuring higher flexibility, stability and lower dead time. We present our research activities on the development of X-ray and gamma ray spectrometers based on semiconductor detectors and DPP systems. We developed off-line and real-time DPP systems able to perform precise height and shape analysis of detector pulses. X-ray and gamma ray spectra measurements with cadmium telluride (CdTe) and germanium (Ge) detectors highlight the excellent performance of the systems both at low and high rate environments (up to 800 kcps).

Measurements with a hybrid detector prototype composed of a MOS CCD and a CZT spectrometer

The scientific objectives of the future X-ray astronomy instruments require new type of focusing telescopes able to extend the observational range starting from 0.1 keV at least up to 100 keV to solve crucial question concerning the nature of the high energy emission. A challenging technology to extend the classical grazing incidence range to higher energy is today offered by the development of multilayer optics that are effective as X-ray concentrators between few keV up to 100 keV. A useful arrangement for this type of mission concept can foresee the soft (e.g. 0.1-10 keV) X-ray optics nested and coaxial with the hard-X mirrors. The focal plane of the telescope shall operate on a very wid…

Improved electroless platinum contacts on CdZnTe X- and γ-rays detectors

AbstractPlatinum is a promising candidate for the realization of blocking electrical contacts on cadmium-zinc-telluride (CdZnTe or CZT) radiation detectors. However, the poor mechanical adhesion of this metal often shortens the lifetime of the final device. In this work, a simple and effective procedure to obtain robust platinum contacts by electroless deposition is presented. Microscopical analysis revealed the final thickness and composition of the contact layer and its adhesion to the bulk crystal. The blocking nature of the Pt-CdZnTe junction, essential to obtain low noise devices, was confirmed by current–voltage measurements. The planar Pt-CdZnTe-Pt detectors showed good room temperat…

Un sistema portatile per la caratterizzazione di apparati mammografici.

Performance of Fine-Tuning Convolutional Neural Networks for HEp-2 Image Classification

The search for anti-nucleus antibodies (ANA) represents a fundamental step in the diagnosis of autoimmune diseases. The test considered the gold standard for ANA research is indirect immunofluorescence (IIF). The best substrate for ANA detection is provided by Human Epithelial type 2 (HEp-2) cells. The first phase of HEp-2 type image analysis involves the classification of fluorescence intensity in the positive/negative classes. However, the analysis of IIF images is difficult to perform and particularly dependent on the experience of the immunologist. For this reason, the interest of the scientific community in finding relevant technological solutions to the problem has been high. Deep lea…

The "Livio Scarsi" X-Ray Facility at University of Palermo for Device Testing

In this work, we report on the characteristics of the Livio Scarsi X-ray facility at University of Palermo. The facility is able to produce low energy X rays, within the energy range of 0.1-60 keV, with fluence rates ranging from 105-108 photons/mm2 s. The laboratory is equipped with an innovative digital detection system, based on semiconductor detectors (Si and CdTe detectors), able to provide accurate and precise estimation of the fluence rate, the energy and the exposure of X rays, even at high counting rate conditions. Instrumentation for electrical characterization (DC-AC) of semiconductor devices, for both off-line and on-line (i.e. during the irradiation) measurements, is also avail…

Diagnostic Mammographics X-Ray Spectra Analisys with CZT and CdTe Solide State Detectors

X-ray response of CdZnTe detectors grown by the vertical Bridgman technique: Energy, temperature and high flux effects

Abstract Nowadays, CdZnTe (CZT) is one of the key materials for the development of room temperature X-ray and gamma ray detectors and great efforts have been made on both the device and the crystal growth technologies. In this work, we present the results of spectroscopic investigations on new boron oxide encapsulated vertical Bridgman (B-VB) grown CZT detectors, recently developed at IMEM-CNR Parma, Italy. Several detectors, with the same electrode layout (gold electroless contacts) and different thicknesses (1 and 2.5 mm), were realized: the cathode is a planar electrode covering the detector surface (4.1×4.1 mm2), while the anode is a central electrode (2×2 mm2) surrounded by a guard-rin…

Alanine films for EPR dosimetry of low-energy (1–30 keV) X-ray photons

Abstract L- α -alanine has aroused considerable interest for use in radiation EPR dosimetry and has been formally accepted as a secondary standard for high-dose (kGy) and transfer dosimetry of high-energy photons and electrons. In this work, we extended the investigation of the energy response of alanine EPR films in the low energy range for X-photons (1–30 keV). Electron Paramagnetic Resonance (EPR) measurements were performed on Kodak BioMax alanine films exposed to low-energy X-rays from a Cu-, W- and Mo-targets tube operating at voltages up to 30 kV. Films were chosen because of the low penetration of the soft X-rays used. The response of alanine to low-energy X-rays was characterized e…

Microscale X-ray mapping of CZT arrays: Spatial dependence of amplitude, shape and multiplicity of detector pulses

In this work, we present the results of a microscale X-ray mapping of a 2 mm thick CZT pixel detector, with pixel pitches of 500 μm and 250 μm, using collimated synchrotron X-ray sources at the Diamond Light source (U. K.). The detector is dc coupled to a fast and low noise ASIC (PIXIE ASIC), characterized only by the preamplifier stage. A custom 16-channel digital readout electronics was used, able to perform online fast pulse shape and height analysis (PSHA), with low dead time and reasonable energy resolution at both low and high fluxes. The detector allows high bias voltage operation (> 5000 V/cm) and good energy resolution at room temperature (5.3 %, 2.3 % and 2.1 % FWHM at 22.1, 59…

New Results on High-Resolution 3-D CZT Drift Strip Detectors

Intense research activities have been carry out in the development of room temperature gamma ray spectroscopic imagers, aiming to compete with the excellent energy resolution of high-purity germanium (HPGe) detectors (0.3 % FWHM at 662 keV) obtained after cryogenic cooling. Cadmium-zinc-telluride (CZT) detectors equipped with pixel, strip and virtual Frisch-grid electrode structures represented an appealing solution for room temperature measurements. In this work, we present the performance of new high-resolution CZT drift strip detectors (19.4 x 19.4 x 6 mm3), recently fabricated at IMEM-CNR of Parma (Italy) in collaboration with due2lab company (Reggio Emilia, Italy). The detectors, worki…

Characterization of a CZT focal plane small prototype for hard X-ray telescope

The promise of good energy and spatial resolution coupled with high efficiency and room temperature operation has fuelled a large international effort to develop cadmium zinc telluride (CZT) for hard X-ray applications. We are involved on the development of a hard X-ray telescope based on multilayer optics and focal plane detector operative in the 10-80 keV energy range. This telescope requires a high efficiency focal plane providing both fine spatial resolution and spectroscopy with a compact and robust design. This paper reports preliminary results on the characterization both in spectroscopic and spatial response of two small pixellated CZT detectors (10times10times1 mm3 and 10times10tim…

CDTE AND CDZNTE PIXEL DETECTORS FOR X-RAY SPECTROSCOPIC IMAGING

Cadmium telluride (CdTe) and cadmium zinc telluride (CdZnTe) wide band gap semiconductors for x-ray detectors have experienced a rather rapid development in the last few years. Among the traditional x-ray detectors based on silicon (Si) and germanium (Ge), CdTe and CdZnTe detectors show higher detection efficiency at high energies and good room temperature performance and are well suited for the development of compact detection systems and pixel arrays for simultaneous measurements of photon interaction position and energy. This chapter is an introduction to the physics and the technology of CdTe and CdZnTe pixel detectors for x-ray spectroscopy and imaging. The physical properties of CdTe …

Performance of a new real time digital pulse processing system for X-ray and gamma ray semiconductor detectors

New generation spectroscopy systems have advanced towards digital pulse processing (DPP) approaches. DPP systems, based on direct digitizing and processing of detector signals, have recently been favoured over analog pulse processing electronics, ensuring better performance. In this work, we present the performance of a new real time DPP system for X-ray and gamma ray semiconductor detectors. The system is based on a commercial digitizer equipped with a custom DPP firmware, developed by our group, for on-line pulse shape and height analysis. X-ray and gamma ray spectra measurements with cadmium telluride (CdTe) and germanium (Ge) detectors, coupled to resistive feedback preamplifiers, will …

Window-Based Energy Selecting X-ray Imaging and Charge Sharing in Cadmium Zinc Telluride Linear Array Detectors for Contaminant Detection

The spectroscopic and imaging performance of energy-resolved photon counting detectors, based on new sub-millimetre boron oxide encapsulated vertical Bridgman cadmium zinc telluride linear arrays, are presented in this work. The activities are in the framework of the AVATAR X project, planning the development of X-ray scanners for contaminant detection in food industry. The detectors, characterized by high spatial (250 µm) and energy (<3 keV) resolution, allow spectral X-ray imaging with interesting image quality improvements. The effects of charge sharing and energy-resolved techniques on contrast-to-noise ratio (CNR) enhancements are investigated. The benefits of a new energy-resolved …

HARD X-RAY CZT DETECTOR DEVELOPMENT AND TESTING ON STRATOSPHERIC BALLOON PAYLOADS

We report on the R&D activities on the development of room temperature semiconductor detectors (CZT detectors) for high energy space instrumentation. Our groups have been involved in the development of new hard X and soft gamma ray telescopes (e.g. Laue lens telescopes) and focal plane detectors. We present the characteristics and the performance of various CZT detector prototypes coupled with custom read-out electronics. The main target of this R&D activity is an end to end system for domestic growth CZT crystals, new sensor configurations and related read out architecture to provide an effective 3D focal plane able to perform contemporaneously imaging (spatial resolution mm or better), ti…

A Microcalcification Detection System in Mammograms based on ANN Clustering

Breast cancer is one of the leading causes to women mortality in the world. Clustered microcalcifications (MCs) in mammograms can be an important early sign of breast cancer, the detection is important to prevent and treat the disease. In this work, we present a novel method for the detection of MCs in mammograms which consists of regions of Interest (ROIs) segmentation, based on a spatial filter that allows the detection of small and large microcalcifications, clustering and classification of MCs by Artificial Neural Network. The system has been tested on a public dataset of digital images and compared with previous approaches. The results demonstrate that the proposed approach could achie…

Electric field manipulation in Al/CdTe/Pt detectors under optical perturbations

Abstract Al/CdTe/Pt detectors are very attractive devices for high-resolution X-ray spectroscopy, even though they suffer from polarization phenomena, which cause a progressive time degradation of the spectroscopic performance. In this work we investigated on the time dependence of the electric field of an Al/CdTe/Pt detector under optical perturbation by means of Pockels effect measurements. A tunable laser with wavelengths ranging within 700−1000 nm and a 940 nm light emitting diode (LED) were used. The measurements of both the electric field profile and the total current were used to better understand the effects of the optical perturbation on polarization phenomena. The results point ou…

X-ray spectroscopy and dosimetry with a portable CdTe device.

Abstract X-ray spectra and dosimetry information are very important for quality assurance (QA) and quality control (QC) in medical diagnostic X-ray systems. An accurate knowledge of the diagnostic X-ray spectra would improve the patient dose optimization, without compromising image information. In this work, we performed direct diagnostic X-ray spectra measurements with a portable device, based on a CdTe solid-state detector. The portable device is able to directly measure X-ray spectra at high photon fluence rates, as typical of clinical radiography. We investigated on the spectral performances of the system in the mammographic energy range (up to ∼40 keV). Good system response to monoener…

Time-dependent current-voltage characteristics of Al/p-CdTe/Pt x-ray detectors

Current-voltage (I-V) characteristics of Schottky Al/p-CdTe/Pt detectors were investigated in dark and at different temperatures. CdTe detectors with Al rectifying contacts, very appealing for high resolution x-ray and gamma ray spectroscopy, suffer from bias-induced polarization phenomena which cause current increasing with the time and severe worsening of the spectroscopic performance. In this work, we studied the time-dependence of the I-V characteristics of the detectors, both in reverse and forward bias, taking into account the polarization effects. The I-V measurements, performed at different time intervals between the application of the bias voltage and the measurement of the current…

Comparison of two portable solid state detectors with an improved collimation and alignment device for mammographic x-ray spectroscopy

We describe a portable system for mammographic x-ray spectroscopy, based on a 2 X 2 X 1 mm3 cadmium telluride (CdTe) solid state detector, that is greatly improved over a similar system based on a 3 X 3 X 2 mm3 cadmium zinc telluride (CZT) solid state detector evaluated in an earlier work. The CdTe system utilized new pinhole collimators and an alignment device that facilitated measurement of mammographic x-ray spectra. Mammographic x-ray spectra acquired by each system were comparable. Half value layer measurements obtained using an ion chamber agreed closely with those derived from the x-ray spectra measured by either detector. The faster electronics and other features of the CdTe detecto…

Incomplete Charge Collection at Inter-Pixel Gap in Low- and High-Flux Cadmium Zinc Telluride Pixel Detectors.

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).…

Room-temperature performance of 3 mm-thick cadmium-zinc-telluride pixel detectors with sub-millimetre pixelization.

Cadmium–zinc–telluride (CZT) pixel detectors represent a consolidated choice for the development of room-temperature spectroscopic X-ray imagers, finding important applications in medical imaging, often as detection modules of a variety of new SPECT and CT systems. Detectors with 3–5 mm thicknesses are able to efficiently detect X-rays up to 140 keV giving reasonable room-temperature energy resolution. In this work, the room-temperature performance of 3 mm-thick CZT pixel detectors, recently developed at IMEM/CNR of Parma (Italy), is presented. Sub-millimetre detector arrays with pixel pitch less than 500 µm were fabricated. The detectors are characterized by good room-temperature performan…

Development of a 3D CZT detector prototype for Laue Lens telescope

We report on the development of a 3D position sensitive prototype suitable as focal plane detector for Laue lens telescope. The basic sensitive unit is a drift strip detector based on a CZT crystal, (similar to 19x8 mm(2) area, 2.4 mm thick), irradiated transversally to the electric field direction. The anode side is segmented in 64 strips, that divide the crystal in 8 independent sensor (pixel), each composed by one collecting strip and 7 (one in common) adjacent drift strips. The drift strips are biased by a voltage divider, whereas the anode strips are held at ground. Furthermore, the cathode is divided in 4 horizontal strips for the reconstruction of the third interaction position coord…

Digital fast pulse shape and height analysis on cadmium-zinc-telluride arrays for high-flux energy-resolved X-ray imaging.

Cadmium-zinc-telluride (CZT) arrays with photon-counting and energy-resolving capabilities are widely proposed for next-generation X-ray imaging systems. This work presents the performance of a 2â...mm-thick CZT pixel detector, with pixel pitches of 500 and 250â...μm, dc coupled to a fast and low-noise ASIC (PIXIE ASIC), characterized only by the preamplifier stage. A custom 16-channel digital readout electronics was used, able to digitize and process continuously the signals from each output ASIC channel. The digital system performs on-line fast pulse shape and height analysis, with a low dead-time and reasonable energy resolution at both low and high fluxes. The spectroscopic response …

Performance enhancements of compound semiconductor radiation detectors using digital pulse processing techniques

Abstract The potential benefits of using compound semiconductors for X-ray and gamma ray spectroscopy are already well known. Radiation detectors based on high atomic number and wide band gap compound semiconductors show high detection efficiency and good spectroscopic performance even at room temperature. Despite these appealing properties, incomplete charge collection is a critical issue. Generally, incomplete charge collection, mainly due to the poor transport properties of the holes, produces energy resolution worsening and the well known hole tailing in the measured spectra. In this work, we present a digital pulse processing (DPP) system for high resolution spectroscopy with compound …

Experimental results from Al/p-CdTe/Pt X-ray detectors

Abstract Recently, Al/CdTe/Pt detectors have been proposed for the development of high resolution X-ray spectrometers. Due to the low leakage currents, these detectors allow high electric fields and the pixellization of anodes with the possibility to realize single charge carrier sensing detectors. In this work, we report on the results of electrical and spectroscopic investigations on CdTe diode detectors with Al/CdTe/Pt electrode configuration (4.1×4.1×0.75 and 4.1×4.1×2 mm 3 ). The detectors are characterized by very low leakage currents in the reverse bias operation: 0.3 nA at 25 °C and 2.4 pA at −25 °C under a bias voltage of −1000 V. The spectroscopic performance of the detectors at b…

Recent advances in the development of high-resolution 3D cadmium-zinc-telluride drift strip detectors.

In the last two decades, great efforts have been made in the development of 3D cadmium–zinc–telluride (CZT) detectors operating at room temperature for gamma-ray spectroscopic imaging. This work presents the spectroscopic performance of new high-resolution CZT drift strip detectors, recently developed at IMEM-CNR of Parma (Italy) in collaboration with due2lab (Italy). The detectors (19.4 mm × 19.4 mm × 6 mm) are organized into collecting anode strips (pitch of 1.6 mm) and drift strips (pitch of 0.4 mm) which are negatively biased to optimize electron charge collection. The cathode is divided into strips orthogonal to the anode strips with a pitch of 2 mm. Dedicated pulse processing analysis…

Digital techniques for high-rate high-resolution radiation measurements

Digital pulse processing (DPP) techniques are increasingly used in the development of modern spectroscopic systems. DPP systems, based on direct digitizing and processing of detector signals (preamplifier output signals), ensure higher flexibility, stability, lower dead time, higher throughput and better energy resolution than traditional pulse processing systems. In this work, we present our progress in the development of DPP systems for high-rate high-resolution radiation measurements. An innovative digital system, able to perform multi-parameter analysis (input counting rate, pulse height, pulse shape, event arrival time, etc.) even at high photon counting rates is presented. Experimenta…