Comparison of effect of CdS QD and ZnS QD and their corresponding salts on growth, chlorophyll content and antioxidative capacity of tomato.

When applied in the same concentration to tomato plants, cadmium sulfate (CdSO4) and zinc sulfate (ZnSO4) were transported from soil to roots and from roots to shoots more readily than their nano counterparts: cadmium sulfide quantum dots (CdS QD) and zinc sulfide quantum dots (ZnS QD). Compared to the CdS QD, he higher rate of transport of CdSO4 resulted in a greater negative effect on growth, chlorophyll content, antioxidant properties, lipid peroxidation and activation of antioxidant defence systems. Although ZnSO4 was transported more rapidly than ZnS QD, the overall effect of Zn addition was positive (increase in total plant mass, stem length, antioxidant content and decrease in lipid peroxidation). However, these effects were more pronounced in the case of ZnS QD, suggesting that the mechanisms underpinning the activity of ZnS QD and ZnSO4 were different. Thus, the risk of phytotoxicity and food chain transfer of the two elements depended on their form (salt or nanoform), and consequently their effects on plants' growth and physiology were different.

This work elucidates the mechanisms underlying the responses of CdS QD and ZnS QD in contrast to those of their corresponding salts on tomato plants. Our results showed that faster transport from roots to leaves in the case of salts in respect to the nanoform augment their detrimental impact on tomato's antioxidant properties and growth and make the nanoform of both a better alternative for crop application either as fertilizers or as pesticides.

A Novel Extraction Procedure of Contact Characteristic Parameters from Current-Voltage Curves in CdZnTe and CdTe Detectors.

The estimation of the characteristic parameters of the electrical contacts in CdZnTe and CdTe detectors is related to the identification of the main transport mechanisms dominating the currents. These investigations are typically approached by modelling the current-voltage (I-V) curves with the interfacial layer-thermionic-diffusion (ITD) theory, which incorporates the thermionic emission, diffusion and interfacial layer theories into a single theory. The implementation of the ITD model in measured I-V curves is a critical procedure, requiring dedicated simplifications, several best fitting parameters and the identification of the voltage range where each transport mechanism dominates. In this work, we will present a novel method allowing through a simple procedure the estimation of some characteristic parameters of the metal-semiconductor interface in CdZnTe and CdTe detectors. The barrier height and the effects of the interfacial layer will be evaluated through the application of a new function related to the differentiation of the experimental I-V curves.

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 which can bring out the best in terms of detector spectroscopic performances. In this work, we present the latest results achieved in terms of energy resolution using SIRIO, a fast low-noise charge sensitive amplifier, and a linear-array pixel detector, based on boron oxide encapsulated vertical Bridgman-grown B-VB CZT crystals. The detector features a 0.25-mm pitch, a 1-mm thickness and is operated at a -700-V bias voltage. An equivalent noise charge of 39.2 el. r.m.s. (corresponding to 412 eV FWHM) was measured on the test pulser at 32 ns peaking time, leading to a raw resolution of 1.3% (782 eV FWHM) on the 59 keV line at room temperature (+20 °C) using an uncollimated 241Am, largely improving the current state of the art for CZT-based detection systems at such short peaking times, and achieving an optimum resolution of 0.97% (576 eV FWHM) at 1 µs peaking time. The measured energy resolution at the 122 keV line and with 1 µs peaking time of a 57Co raw uncollimated spectrum is 0.96% (1.17 keV). These activities are in the framework of an Italian collaboration on the development of energy-resolved X-ray scanners for material recycling, medical applications, and non-destructive testing in the food industry.

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 X-ray imaging approach, termed window-based energy selecting, in the detection of low- and high-density contaminants are also shown.

Potentialities of CdZnTe Quasi-Hemispherical Detectors for Hard X-ray Spectroscopy of Kaonic Atoms at the DAΦNE Collider.

Kaonic atom X-ray spectroscopy is a consolidated technique for investigations on the physics of strong kaon-nucleus/nucleon interaction. Several experiments have been conducted regarding the measurement of soft X-ray emission (<20 keV) from light kaonic atoms (hydrogen, deuterium, and helium). Currently, there have been new research activities within the framework of the SIDDHARTA-2 experiment and EXCALIBUR proposal focusing on performing precise and accurate measurements of hard X-rays (>20 keV) from intermediate kaonic atoms (carbon, aluminum, and sulfur). In this context, we investigated cadmium-zinc-telluride (CdZnTe or CZT) detectors, which have recently demonstrated high-resolution capabilities for hard X-ray and gamma-ray detection. A demonstrator prototype based on a new cadmium-zinc-telluride quasi-hemispherical detector and custom digital pulse processing electronics was developed. The detector covered a detection area of 1 cm2 with a single readout channel and interesting room-temperature performance with energy resolution of 4.4% (2.6 keV), 3% (3.7 keV), and 1.4% (9.3 keV) FWHM at 59.5, 122.1, and 662 keV, respectively. The results from X-ray measurements at the DAΦNE collider at the INFN National Laboratories of Frascati (Italy) are also presented with particular attention to the effects and rejection of electromagnetic and hadronic background.

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 and high-energy resolution (<4% FWHM at 122 keV) when ballistic deficit pulse processing (dead time of 90 ns) was used in CZT pixel detectors. These activities are in the framework of an international collaboration on the development of spectroscopic imagers for medical applications (mammography, computed tomography) and non-destructive testing in the food industry.

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)7Li reaction, are very appealing for the development of single-photon emission computed tomography (SPECT) systems and Compton cameras in BNCT. High-resolution gamma-ray spectra from 10B samples under thermal neutrons were measured at the T.R.I.G.A. Mark II research nuclear reactor of the University of Pavia (Italy).

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). 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 the inter-pixel gaps. The successful mitigation of the effects of incomplete charge collection after CSA was also performed through original charge-sharing correction techniques. These activities exist in the framework of international collaboration on the development of energy-resolved X-ray scanners for medical applications and non-destructive testing in the food industry.

Fabrication of Small-Pixel CdZnTe Sensors and Characterization with X-rays.

Over the past few years, sensors made from high-Z compound semiconductors have attracted quite some attention for use in applications which require the direct detection of X-rays in the energy range 30-100 keV. One of the candidate materials with promising properties is cadmium zinc telluride (CdZnTe). In the context of this article, we have developed pixelated sensors from CdZnTe crystals grown by Boron oxide encapsulated vertical Bridgman technique. We demonstrate the successful fabrication of CdZnTe pixel sensors with a fine pitch of 55 m and thickness of 1 mm and 2 mm. The sensors were bonded on Timepix readout chips to evaluate their response to X-rays provided by conventional sources. Despite the issues related to single-chip fabrication procedure, reasonable uniformity was achieved along with low leakage current values at room temperature. In addition, the sensors show stable performance over time at moderate incoming fluxes, below 106 photons mm-2s-1.

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 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. These activities are in the framework of an international collaboration on the development of energy-resolved photon counting (ERPC) systems for spectroscopic X-ray imaging up to 150 keV.

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 performance even at high bias voltage operation (6000 V cm-1), with energy resolutions (FWHM) of 3% (1.8 keV) and 1.6% (2 keV) at 59.5 keV and 122.1 keV, respectively. Charge-sharing investigations were performed with both uncollimated and collimated synchrotron X-ray beams with particular attention to recovering the charge losses at the inter-pixel gap region. High rate measurements demonstrated the absence of high-flux radiation-induced polarization phenomena up to 25 × 106 photons mm-2 s-1.

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 was performed on a wide range of collected and induced charge pulse shapes using custom 32-channel digital readout electronics. Excellent room-temperature energy resolution (1.3% FWHM at 662 keV) was achieved using the detectors without any spectral corrections. Further improvements (0.8% FWHM at 662 keV) were also obtained through a novel correction technique based on the analysis of collected-induced charge pulses from anode and drift strips. These activities are in the framework of two Italian research projects on the development of spectroscopic gamma-ray imagers (10-1000 keV) for astrophysical and medical applications.

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 of the charge losses at the inter-pixel gap region. High-rate measurements demonstrated the absence of high-flux radiation-induced polarization phenomena up to 2 × 106 photons mm-2 s-1. These activities are in the framework of an international collaboration on the development of energy-resolved photon-counting systems for high-flux energy-resolved X-ray imaging.

Gamma-Ray Spectral Unfolding of CdZnTe-Based Detectors Using a Genetic Algorithm.

The analysis of γ-ray spectra can be an arduous task, especially in the case of room temperature semiconductor detectors, where several distortions and instrumental artifacts conceal the true spectral shape. We developed a genetic algorithm to perform the unfolding of γ-spectra in order to restore the true energy distribution of the incoming radiation. We successfully validated our approach on experimental spectra of four radionuclides (241Am, 57Co, 137Cs and 133Ba) acquired with two CdZnTe-based detectors with different contact geometries (single pixel and drift strip). The unfolded spectra consist of δ-like peaks in correspondence with the radiation emissions of each radioisotope.

Development of an In Vivo Sensor to Monitor the Effects of Vapour Pressure Deficit (VPD) Changes to Improve Water Productivity in Agriculture.

Environment, biodiversity and ecosystem services are essential to ensure food security and nutrition. Managing natural resources and mainstreaming biodiversity across agriculture sectors are keys towards a sustainable agriculture focused on resource efficiency. Vapour Pressure Deficit (VPD) is considered the main driving force of water movements in the plant vascular system, however the tools available to monitor this parameter are usually based on environmental monitoring. The driving motif of this paper is the development of an in-vivo sensor to monitor the effects of VPD changes in the plant. We have used an in vivo sensor, termed "bioristor", to continuously monitor the changes occurring in the sap ion's status when plants experience different VPD conditions and we observed a specific R (sensor response) trend in response to VPD. The possibility to directly monitor the physiological changes occurring in the plant in different VPD conditions, can be used to increase efficiency of the water management in controlled conditions thus achieving a more sustainable use of natural resources.

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 2 mm-thick CZT pixel detector, with pixel pitches of 500 and 250 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 of the system to photon energies below (109Cd source) and above (241Am source) the K-shell absorption energy of the CZT material was investigated, with particular attention to the mitigation of charge sharing and pile-up. The detector allows high bias voltage operation (>5000 V cm-1) and good energy resolution at moderate cooling (3.5% and 5% FWHM at 59.5 keV for the 500 and 250 µm arrays, respectively) by using fast pulse shaping with a low dead-time (300 ns). Charge-sharing investigations were performed using a fine time coincidence analysis (TCA), with very short coincidence time windows up to 10 ns. For the 500 µm pitch array (250 µm pitch array), sharing percentages of 36% (52%) and 60% (82%) at 22.1 and 59.5 keV, respectively, were measured. The potential of the pulse shape analysis technique for charge-sharing detection for corner/border pixels and at high rate conditions (250 kcps pixel-1), where the TCA fails, is also shown. Measurements demonstrated that significant amounts of charge are lost for interactions occurring in the volume of the inter-pixel gap. This charge loss must be accounted for in the correction of shared events. These activities are within the framework of an international collaboration on the development of energy-resolved photon-counting systems for high-flux energy-resolved X-ray imaging (1-140 keV).

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-noise charge-sensitive preamplifiers (PIXIE ASIC) and followed by a 16-channel digital readout electronics, performing multi-parameter analysis (event arrival time, pulse shape, pulse height). Induced-charge pulses with negative polarity were also observed in the waveforms from the charge-sensitive preamplifiers (CSPs) at energies >60 keV. The shape and the height of these pulses were analysed, and their role in the mitigation of charge losses in CZT pixel detectors. These activities are in the framework of an international collaboration on the development of energy-resolved photon-counting systems for spectroscopic X-ray imaging (5-140 keV).

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), allow good room-temperature operation even at high bias voltages (>7000 V cm-1). At low rates (200 counts s-1), the detectors exhibit an energy resolution around 4% FWHM at 59.5 keV (241Am source) up to 2200 V, by using commercial front-end electronics (A250F/NF charge-sensitive preamplifier, Amptek, USA; nominal equivalent noise charge of 100 electrons RMS). At high rates (1 Mcounts s-1), the detectors, coupled to a custom-designed digital pulse processing electronics developed at DiFC of University of Palermo (Italy), show low spectroscopic degradations: energy resolution values of 8% and 9.7% FWHM at 59.5 keV (241Am source) were measured, with throughputs of 0.4% and 60% at 1 Mcounts s-1, respectively. An energy resolution of 7.7% FWHM at 122.1 keV (57Co source) with a throughput of 50% was obtained at 550 kcounts s-1 (energy resolution of 3.2% at low rate). These activities are in the framework of an Italian research project on the development of energy-resolved photon-counting systems for high-flux energy-resolved X-ray imaging.

Detection of Nuclear Sources by UAV Teleoperation Using a Visuo-Haptic Augmented Reality Interface.

A visuo-haptic augmented reality (VHAR) interface is presented enabling an operator to teleoperate an unmanned aerial vehicle (UAV) equipped with a custom CdZnTe-based spectroscopic gamma-ray detector in outdoor environments. The task is to localize nuclear radiation sources, whose location is unknown to the user, without the close exposure of the operator. The developed detector also enables identification of the localized nuclear sources. The aim of the VHAR interface is to increase the situation awareness of the operator. The user teleoperates the UAV using a 3DOF haptic device that provides an attractive force feedback around the location of the most intense detected radiation source. Moreover, a fixed camera on the ground observes the environment where the UAV is flying. A 3D augmented reality scene is displayed on a computer screen accessible to the operator. Multiple types of graphical overlays are shown, including sensor data acquired by the nuclear radiation detector, a virtual cursor that tracks the UAV and geographical information, such as buildings. Experiments performed in a real environment are reported using an intense nuclear source.

Modeling, Fabrication and Testing of a Customizable Micromachined Hotplate for Sensor Applications.

In the sensors field the active sensing material frequently needs a controlled temperature in order to work properly. In microsystems technology, micro-machined hotplates represent a platform consisting of a thin suspended membrane where the sensing material can be deposited, usually integrating electrical stimuli and temperature readout. The micro-hotplate ensures a series of advantages such as miniaturized size, fast response, high sensitivity, low power consumption and selectivity for chemical sensing. This work compares the coplanar and the buried approach for the micro-hotplate heaters design with the aim to optimize the fabrication process and to propose a guideline for the choice of the suitable design with respect to the applications. In particular, robust Finite Element Method (FEM) models are set up in order to predict the electrical and thermal behavior of the micro-hotplates. The multiphysics approach used for the simulation allows to match as close as possible the actual device to the predictive model: geometries, materials, physics have been carefully linked to the fabricated devices to obtain the best possible accuracy. The materials involved in the fabrication process are accurately selected in order to improve the yield of the process and the performance of the devices. The fabricated micro-hotplates are able to warm the active region up to 400 °C (with a corresponding power consumption equal to 250 mW @ 400 °C) with a uniform temperature distribution in the buried micro-hotplate and a controlled temperature gradient in the coplanar one. A response time of about 70 ms was obtained on the virtual model, which perfectly agrees with the one measured on the fabricated device. Besides morphological, electrical and thermal characterizations, this work includes reliability tests in static and dynamic modes.