In this article, a waveform-sampling front-end application-specific integrated circuit (ASIC) for 3-D position-sensitive detectors (PSDs), called H3DD-UM, is presented. The ASIC integrates 128 channels for anode events and two channels for cathode events. Each channel provides low-noise charge amplification with an adjustable dynamic range to cover up to 10 MeV, followed by two programmable antialiasing filters with different gains, each feeding a 256-cell waveform-sampling circuit. The sampling architecture makes use of a single rail-to-rail amplifier configured to cancel offset errors and achieve high sampling uniformity. A dedicated circuit in the channel provides analog shaping for low-noise discrimination of the events. The number of stored samples before and after discrimination is fully programmable. The ASIC integrates numerous functions, including pixel leakage current measurement, analog monitoring, test pulse generators, temperature sensor, and interchip communication for use in systems with multiple modules.

This study presents an experimental evaluation of the Dynamic Extremity SPECT (DE-SPECT) system, specifically engineered for precise, regionselective gamma-ray spectroscopy in the diagnosis of Peripheral Vascular Disease (PVD) in lower extremities. The system incorporates Cadmium Zinc Telluride (CZT) imaging spectrometers and dynamic dual-field-of-view (FOV) collimators to facilitate comprehensive, multifunctional molecular imaging. The CZT detectors, with Depth of Interaction (DOI) capabilities, deliver an exceptional energy performance across a wide energy range up to 600 keV. The novel dual-FOV aperture system allows selective imaging with two configurations: a 28-cm diameter wide FOV suitable for dual-leg or scout imaging and a 16-cm diameter high-resolution, and high-sensitivity (HR-HS) FOV designed for single-leg or focused imaging. Utilizing uniform phantoms, resolution phantoms, and multi-tracer phantoms, we experimentally assessed the system’s sensitivity, spatial resolution, and multi-tracer imaging capabilities. Spatial resolutions were approximately 6 mm in HR-HS-FOV mode and between 8 mm to 10 mm in wide-FOV mode. Peak-to-Valley ratios, indicative of image clarity, improved with enhanced DOI resolutions, rising from 1.03 to 1.22. The system’s ability to perform multi-tracer imaging, essential for deriving multifunctional molecular information, further highlights its potential to significantly enhance diagnostic accuracy for PVD.

CsPbBr3 is a room-temperature semiconductor perovskite crystal. This research employs depth of interaction corrections (DOIC) and improved shaping time optimizations to study gamma-ray spectroscopic properties of prototype CsPbBr3 detectors. The aim is to provide benchmarks on their performance and operational stability over time. By applying these techniques, we observed differences in electron and hole transport properties between different pixel signals and over operation periods. These differences in charge transport and collection necessitated different optimal shaping times. The experimental results have shown an energy resolution of 1.04% FWHM at 662 KeV from eight working pixel electrodes, with the best energy resolution of 0.85% FWHM at 662 KeV observed on pixel electrode 3 on a 0.5 cm thick CsPbBr3 detector with a 9x9 pixel electrode and one planar cathode.

The cadmium zinc TElluride Radiation Imager, or TERI, is an instrument to space-qualify large-volume 4x4x1.5 cm(3) pixelated CdZnTe (CZT) detector technology. The CZT's anode is composed of a 22x22 array of pixels, whereas the cathode is planar. TERI contains four of those crystals with each pixel having an energy range of 40 keV up to 3 MeV with a resolution of 1.3% full-width-at-half maximum at 662 keV all while operating in room temperature. As the detectors are 3D position sensitive, TERI can Compton image events. TERI is fitted with a coded-aperture mask, which permits imaging of low-energy photons in the photoelectric regime. TERI's primary mission is to space-qualify large-volume CZT and measure its degradation due to radiation damage in a space environment. Its secondary mission includes detecting and localizing astrophysical gamma-ray transients. TERI is manifested in the Department of Defense's STP-H10 mission for launch to the International Space Station in early 2025.

This work employs 3-D position-sensitive CdZnTe to conduct single photon emission computed tomography (SPECT) via multi-pinhole imaging and positron emission tomography (PET) via line-of-response imaging simultaneously on small animals. The advantages of using CdZnTe detectors over the current instruments for PET and SPECT detectors include the ability to image gamma rays from multiple isotopes simultaneously, can achieve both high detection efficiency and high image resolution in PET modality, and has a high position resolution of about 300 µm in all three dimensions. This energy discrimination capability allows the imager to detect 511 keV coincidence gamma rays used in PET imaging and lower energy gamma rays used in SPECT imaging simultaneously and bin them appropriately. Partial energy depositions from Compton scattering can also be used in PET mode to increase the detection efficiency. This work demonstrates the successful implementation of these methods to reconstruct both PET and SPECT images. Some improvements are still needed to improve image quality.

The effect of temperature on detector properties and performance may vary detector-by-detector. In this work, four 2.2×2.2×1.0 cm 3 pixelated CdZnTe detectors were tested at 20°C and -10°C to study changes in detector efficiency below room-temperature. At -10°C, the overall photopeak efficiency decreased, and the change in efficiency varied on a pixel-by-pixel basis. It was found that at -10°C, increasing the detector bias voltage worsens the efficiency loss, whereas decreasing the bias can help improve charge collection. Collimator measurements showed that there is non-uniformity in the electron drift path, and that the distribution of charge collected can vary on a subpixel scale when temperature and bias are altered.

We constructed a prototype positron emission tomography (PET) system and experimentally evaluated large-volume 3-D cadmium zinc telluride (CZT) detectors for potential use in Compton-enhanced PET imaging. The CZT spectrometer offers sub-0.5-mm spatial resolution, an ultrahigh energy resolution (~1% @ 511 keV), and the capability of detecting multiple gamma-ray interactions that simultaneously occurred. The system consists of four CZT detector panels with a detection area of around 4.4 cm × 4.4 cm. The distance between the front surfaces of the two opposite CZT detector panels is ~80 mm. This system allows us to detect coincident annihilation photons and Compton interactions inside the detectors and then, exploit Compton kinematics to predict the first Compton interaction site and reject chance coincidences. We have developed a numerical integration technique to model the near-field Compton response that incorporates Doppler broadening, detector's finite resolutions, and the distance between the first and second interactions. This method was used to effectively reject random and scattered coincidence events. In the preliminary imaging studies, we have used point sources, line sources, a custom-designed resolution phantom, and a commercial image quality (IQ) phantom to demonstrate an imaging resolution of approximately 0.75 mm in PET images, and Compton-based enhancement.

Two 3x3 arrays of 2x2x1.5cm^3 CZT modules are irradiated by a Na-22 source to investigate the coincidence timing resolution capabilities of these CZT detectors. Pixelated CZT systems have demonstrated a timing resolution of <10ns using GHz sampling systems. In this study, coincidence data is recorded using sampling frequencies of 20, 40, and 80MHz. The coincidence timing resolution is measured using a simple linear fitting procedure, and a best timing resolution of 35ns is obtained on this two-array system.

Pixelated CdZnTe detectors are a promising imaging-spectrometer for gamma-ray astrophysics due to their combination of relatively high energy resolution with room temperature operation negating the need for cryogenic cooling. This reduces the size, weight, and power requirements for telescope-based radiation detectors. Nevertheless, operating CdZnTe in orbit will expose it to the harsh radiation environment of space. This work, therefore, studies the effects of 61 MeV protons on 2 x 2 x 1 cm3 pixelated CdZnTe and quantifies proton-induced radiation damage of fluences up to 2.6 x 108 p/cm2. In addition, we studied the effects of irradiation on two separate instruments: one was biased and operational during irradiation while the other remained unbiased. Following final irradiation, the 662 keV centroid and nominal 1% resolution of the detectors were degraded to 642.7 keV , 4.9% (FWHM) and 653.8 keV , 1.75% (FWHM) for the biased and unbiased systems respectively. We therefore observe a possible bias dependency on proton-induced radiation damage in CdZnTe. This work also reports on the resulting activation and recovery of the instrument following room temperature and 60 degrees C annealing.

There is an urgent need for new, better instrumentation and techniques for detecting and characterizing special nuclear material (SNM), i.e., highly enriched uranium and plutonium. The development of improved instruments and techniques requires experiments performed with the SNM itself, which is of limited availability. This paper describes the findings of experiments performed at the National Criticality Experiments Research Center conducted using new instruments and techniques on unclassified, kg-quantity SNM objects. These experiments, performed in the framework of the Department of Energy, National Nuclear Security Administration Consortium for Monitoring, Technology, and Verification, focused on detecting, characterizing, and localizing SNM samples with masses ranging from 3.3 to 13.8 kg, including plutonium and highly enriched uranium using prototype detectors and techniques. The work demonstrates SNM detection and characterization using recently-developed prototype detection systems. Specifically, we present new results in passive detection and imaging of plutonium and uranium objects using gamma-ray and dual particle (fast neutron and gamma-ray) imaging. We also present a new analysis of the delayed neutron emissions during active interrogation of uranium using a neutron generator.

Pixelated CdZnTe detectors are a promising imaging-spectrometer for gamma-ray astrophysics due to their combination of relatively high energy resolution with room temperature operation negating the need for cryogenic cooling. This reduces the size, weight, and power requirements for telescope-based radiation detectors. Nevertheless, operating CdZnTe in orbit will expose it to the harsh radiation environment of space. This work, therefore, studies the effects of 61MeV protons on 2×2×1cm3 pixelated CdZnTe and quantifies proton-induced radiation damage of fluences up to 2.6×108p/cm2. In addition, we studied the effects of irradiation on two separate instruments: one was biased and operational during irradiation while the other remained unbiased. Following final irradiation, the 662keV centroid and nominal 1% resolution of the detectors were degraded to 642.7keV,4.9%(FWHM) and 653.8keV,1.75%(FWHM) for the biased and unbiased systems respectively. We therefore observe a possible bias dependency on proton-induced radiation damage in CdZnTe. This work also reports on the resulting activation and recovery of the instrument following room temperature and 60°C annealing.

CsPbBr 3 is a promising material for alternative room-temperature semiconductor gamma-ray spectrometers, for its demonstrated good energy resolution of ~1.0% FWHM at 662 keV with the detector thickness up to 12 mm, high stopping power and inexpensive material cost. In addition to required good gamma-ray spectroscopic performance and high detection efficiency, detector stability over long time operation is also critical. This work reports observed polarization phenomenon (detector performance changes over time) on CsPbBr 3 detectors having pixelated electrodes, and observed characteristics. The dark current versus bias voltage (I-V), frequency property of the dark current at operating bias voltages, gamma-ray energy spectra with low and high energy photons, charge drift and collection characteristics, have been measured over time. These diagnostic measurements will help identify the possible causes of polarization, to improve stability of CsPbBr 3 gamma-ray detectors for practical applications.

In collaboration between the University of Michigan and Los Alamos National Laboratory, a 3D position-sensing CdZnTe (CZT) detector prototype was built and integrated into a high-altitude balloon platform to evaluate its performance in a space-like mixed-radiation environment. The detector prototype, Orion Eagle, was designed to operate in near-vacuum environments without any temperature regulation. Orion Eagle was hand-launched from NASA's Columbia Scientific Balloon Facility (CSBF) at Fort Sumner, NM on September 26, 2021, and successfully operated throughout a 9-hour flight, which reached 38.5 km in altitude. The flight met its objectives, successfully detecting atmospheric gamma rays and galactic cosmic rays, and raising the Technical Readiness Level from 4 to 6 for large-volume 3D CZT detector technology for space applications. Ionization tracks produced by charged particles create spatial signatures in the detector that are distinguishable from discrete gamma-ray interactions. Therefore, the 3D position-sensing capabilities using pixelated electrodes on a CZT detector can help enable discrimination of background charged particles from gamma-ray events without an anticoincidence shield. The potential for background rejection capability, ambient-temperature operation, gamma-ray coded-aperture and Compton imaging, and near High Purity Germanium (HPGe) energy resolution motivate the use of large-volume 3D CZT imaging spectrometers in future space missions.

Pixelated CdZnTe detectors are a promising imaging-spectrometer for gamma-ray astrophysics due to their combination of relatively high energy resolution with room temperature operation negating the need for cryogenic cooling. This reduces the size, weight, and power requirements for telescope-based radiation detectors. Nevertheless, operating CdZnTe in orbit will expose it to the harsh radiation environment of space. This work, therefore, studies the effects of 61MeV protons on 2×2×1cm3 pixelated CdZnTe and quantifies proton-induced radiation damage of fluences up to 2.6×108p/cm2. In addition, we studied the effects of irradiation on two separate instruments: one was biased and operational during irradiation while the other remained unbiased. Following final irradiation, the 662keV centroid and nominal 1% resolution of the detectors were degraded to 642.7keV,4.9%(FWHM) and 653.8keV,1.75%(FWHM) for the biased and unbiased systems respectively. We therefore observe a possible bias dependency on proton-induced radiation damage in CdZnTe. This work also reports on the resulting activation and recovery of the instrument following room temperature and 60°C annealing.

Pixelated CdZnTe gamma-ray detectors have proven to be versatile tools for characterization of radiation fields in unknown spaces. This is due in part to their fine spatial resolution, allowing for high fidelity radiation images. The position of radiation interactions can be determined to subpixel precision by analyzing non-collecting pixel signals. Recent electronics allow for the recording of full event waveforms from these non-collecting pixels, offering an improvement in position resolution compared to traditional analog processing electronic chains. However, the relationship between signal waveform and subpixel position is complicated and it is challenging to design an algorithm that makes the best use of the available information to reconstruct the position. We demonstrate a position reconstruction technique based on principal component analysis of the signal waveforms. A calibration method is presented and discussed, and an improvement over the traditional neighbor-ratio based techniques is demonstrated in experiment using a Cs-137 source. The position resolution with a coarse-level implementation is improved by 25 µm relative to the classic techniques.

For CdZnTe detectors, the energy resolution usually improves at a higher cathode bias. However, there are many practical benefits to operate pixelated CdZnTe detectors at lower cathode biases. This study explores the factors limiting the energy resolution at lower cathode bias. Measurements using the digital ASICs are presented and discussed. Effects of trapping, material defects, shaping and data sampling are investigated. Methods to mitigate the energy resolution degradation are proposed.

Compton imaging is an attractive tool for range verification and dose estimation in proton therapy. To investigate the application of CdZnTe-based cameras for this task, we apply the uniform Cramér–Rao bound (UCRB) to dual-plane-based designs with various interplane spacings and evaluate their bias-variance tradeoff. The investigation focuses on the 718-keV and 4.4-MeV prompt gammas emitted from proton interactions with 12C, and focuses on a detector geometry having two planes of $3 \times 3$ CdZnTe crystals with a volume of $2 \times 2 \times 1.5 \,\,\mathrm {cm}^{3}$ . When considering only interplane events, the improvement in minimum variance plateaus at 8 cm. However, when considering both intraplane and interplane events with an efficiency factor, the optimum spacing is calculated to be around 4 cm as larger spacings degrade the performance with poorer efficiency and a lower interplane to intraplane fraction. In addition, the study uses the modified UCRB based on a simulated distribution of prompt gamma rays expected from proton irradiation. The results show that the optimum spacing may be between 2 and 4 cm, depending on the specific bias-gradient norm.

Pixelated CdZnTe detectors mymargin have achieved excellent spectroscopic performance and showed the advanced capability of coded-aperture and Compton imaging. Subpixel sensing is a technique to improve their imaging capabilities. For single-pixel-triggered events, subpixel sensing was demonstrated years ago. This article proposes a method to calculate subpixel location for two-pixel-triggered charge-sharing events.