Cadmium Zinc Telluride Detectors Research Articles

Sub-voxel identification of gamma-ray interaction positions within a pixelated CZT detector through signal analysis

Cadmium zinc telluride (CZT) detectors are well suited for use in gamma-imaging applications thanks to their room-temperature operation, excellent energy resolution, and three-dimensional sensitivity to positions of gamma-ray interactions. In many of these applications, the position resolution with which gamma-interactions can be determined is crucial for high quality imaging. Finer pixelisation may provide improved position resolution but at the cost of increased fabrication cost and degradation of spectral performance. This work sets out to instead investigate and quantify the three-dimensional position resolution achievable using pulse shape analysis applied to digital signals, arising from interactions in a CZT detector pixelated into 2 × 2 × 5 mm3 voxels. The signal response of a 3 × 3 pixel cluster has been characterised as a function of gamma-ray interaction position using collimated 57Co and 137Cs sources. Simple pulse shape analysis algorithms using the transient image and charge collection signals have been developed and applied to achieve a sub-voxel position resolution of better than 0.65 × 0.69 × 1.26 mm3 at 122 keV and of 1.06 mm through 5 mm depth at 662 keV, not accounting for divergence of the collimated beam used to evaluate performance. Assessment of the contribution of the diverging gamma-beam placed a lower bound on the achievable positions resolution in 5 mm thickness at 122 keV of 290μm.

Monte-Carlo simulation for detecting neutron and gamma-ray simultaneously with CdZnTe half-covered by gadolinium film

Neutron is an indirectly ionizing particle without charge, which is normally measured by detecting reaction products. Neutron detection system based on measuring gadolinium-converted gamma-rays is a good way to monitor the neutron because the representative prompt gamma-rays of gadolinium have low energies (79, 89, 182, and 199 keV). Low energy gamma-rays and their high attenuation coefficient on materials allow the simple design of a detector easier to manufacture. Thus, we designed a cadmium zinc telluride detector to investigate feasibility of simultaneous detection of gamma-rays and neutrons by using the Monte-Carlo simulation, which was divided into two parts; first was gamma-detection part and second was gamma- and neutron-simultaneous detection part. Consequently, we confirmed that simultaneous detection of gamma-rays and neutrons could be feasible and valid, although further research is needed for adoption on real detection.

Compton and proximity imaging of 225Ac in vivo with a CZT gamma camera: a proof of principle with simulations.

In vivo imaging of 225Ac is a major challenge in the development of targeted alpha therapy radiopharmaceuticals due to the extremely low injected doses. In this paper, we present the design of a multi-modality gamma camera that integrates both proximity and Compton imaging in order to achieve the demanding sensitivities required to image 225Ac with good image quality. We consider a dual-head camera, each of the heads consisting of two planar cadmium zinc telluride detectors acting as scatterer and absorber for Compton imaging, and with the scatterer practically in contact with the subject to allow for proximity imaging. We optimize the detector's design and characterize the detector's performance using Monte Carlo simulations. We show that Compton imaging can resolve features of up to 1.5 mm for hot rod phantoms with an activity of 1 μCi, and can reconstruct 3D images of a mouse injected with 0.5 μCi after a 15 minutes exposure and with a single bed position, for both 221Fr and 213Bi. Proximity imaging is able to resolve two 1 mm-radius sources of less than 0.1 μCi separated by 1 cm and at 1 mm from the detector, as well as it can provide planar images of 221Fr and 213Bi biodistributions of the mouse phantom in 5 minutes.

Predicted performance of a tangential viewing hard x-ray camera for the DIII-D high field side lower hybrid current drive experiment.

High field side launch of lower hybrid current drive (LHCD) has improved accessibility and penetration over low field side launch on DIII-D. Simulations predict single pass absorption under a wide range of plasma conditions. Hard x-ray (HXR) measurement of LHCD generated fast electron bremsstrahlung (50-250keV) will validate wave propagation and absorption. Emissivity profiles are recovered from one-dimensional inversion of HXR brightness to determine LH damping location, fast electron slowing down time, and some indication of the fast electron energy. The camera will be implemented by populating 32 tangential sightlines of the existing Gamma Ray Imager with Kromek SPEARTM Cadmium Zinc Telluride (CZT) detectors sensitive to 10-1000keV photons with 10keV energy resolution. Expected count rates allow for <0.5ms time resolution. Pulses are processed using 50ns shaping time Cremat CR-200 Gaussian shaping modules and are digitized by 25MHz D-TACQ ACQ216 digitizers. The performance of the HXR camera is evaluated by comparing predicted fast electron density profiles and inverted synthetic brightnesses obtained from the ray-tracing/Fokker-Planck codes GENRAY/CQL3D. Inversions closely matched predicted fast electron profiles for a range of experimental parameters.

Experimental verification of off-axis polarimetry with cadmium zinc telluride detectors of AstroSat-CZT Imager

The cadmium zinc telluride imager (CZTI) on board AstroSat consists of an array of a large number of pixelated cadmium zinc telluride (CZT) detectors capable of measuring the polarization of incident hard x-rays. The polarization measurement capability of CZTI for on-axis sources was experimentally confirmed before the launch. CZTI has yielded tantalizing results on the x-ray polarization of the Crab nebula and pulsar in the energy range of 100 to 380 keV. CZTI has also contributed to the measurement of prompt emission polarization for several gamma-ray bursts (GRBs). However, polarization measurements of off-axis sources such as GRBs are challenging. It is vital to experimentally calibrate the CZTI sensitivity to off-axis sources to enhance the credence of the measurements. In this context, we report the verification of the off-axis polarimetric capability of pixelated CZT detectors through controlled experiments carried out with a CZT detector similar to that used in CZTI and extensive Geant4 simulations of the experimental setup. Our current results show that the CZT detectors can be used to measure the polarization of bright GRBs with off-axis angles of up to ∼60 deg. However, at incidence angles between 45 deg and 60 deg, there might be some systematic effects that need to be taken into account when interpreting the measured polarization fraction.

Myocardial perfusion imaging using single-photon emission computed tomography with cadmium-zinc-telluride technology.

Myocardial perfusion imaging (MPI) with single-photon emission computed tomography (SPECT) is a well-established diagnostic approach for patients with suspected or confirmed coronary artery disease (CAD). In the present century, nuclear cardiology has benefited immensely from advances in imaging instrumentation and technology. Dedicated cardiac SPECT cameras incorporating novel, highly efficient cadmium-zinc-telluride (CZT) detectors, collimators, and system designs have evolved as a result of the expansion of nuclear cardiology. A vast amount of evidence is emerging, demonstrating the new technology's advantages over the traditional gamma cameras. Myocardial perfusion imaging (MPI) using gamma-cameras with CZT detectors may be performed with the limited injected activity of radiotracer and recorded times. The use of CZT's dynamic acquisition of myocardial perfusion imaging in clinical practice may help cardiologists in detecting hemodynamically significant CAD. In this article, we present the current state of knowledge on cardiac CZT-SPECT scanners, a summary of the literature published on validation studies, radiation dose reduction, and dynamic acquisition, as well as a comparison of conventional myocardial perfusion imaging with invasive coronary angiography.

Nationwide survey on radiation doses received by patients in nuclear medicine imaging procedures

National diagnostic reference levels (DRLs) are essential tools for optimizing protocols and protecting patients from an unjustified radiation exposure. The aim of this study was to conduct a nationwide survey of adult patient doses received from nuclear medicine (NM) procedures and to update national DRL (NDRL) values for most common procedures. Data on the radioactivity administered to standard adult patients were collected from all Lithuanian hospitals using NM applications in practice, between 2017 and 2022. Twelve of the most commonly performed NM diagnostic procedures: myocardial perfusion scintigraphy (two parts), thyroid scintigraphy, lung perfusion scintigraphy, bone scintigraphy, dynamic renal scintigraphy (divided into two procedures), parathyroid scintigraphy, hepatobiliary scintigraphy, lymphoscintigraphy, neuroendocrine tumour scan, and oncology positron emission tomography/computed tomography (PET/CT) imaging were included. The 75th percentile of the dose distribution was estimated for establishing NDRLs. During the data collection period, the NM imaging equipment was upgraded. The procedures were completed with 12 single photon emission computed tomography (SPECT) and SPECT/CT gamma cameras (2 with cadmium zinc telluride (CZT) detectors), 2 cardiac-centred gamma cameras with CZT detectors, and 2 PET/CT scanners. Data were collected on 7979 activities administered to the patients. For each procedure, depending on its frequency, 50–580 administered radiopharmaceutical activities were selected. Based on the collected data, NDRLs were updated in 2021 for three procedures. A large part of the procedures were performed with scanners manufactured between 2008 and 2011. In the past few years, the main Lithuanian hospitals that provide NM services have updated their SPECT/CT systems. In the future, the data collection process should be continued in order to reassess DRLs with respect to new scanning systems (e.g. with CZT detectors and newer PET/CT technology). Variations in the prescribed radiopharmaceutical activities showed that optimization and harmonization procedures may be performed in some hospitals.

Passivation effect on large volume CdZnTe crystals

Several cadmium zinc telluride (CZT) crystals were fabricated into radiation detectors using methods that included slicing, dicing, lapping, polishing, and chemical etching. A wet passivation with sodium hypochlorite (NaOCl) was then carried out on the Br-etched detectors. The Te-rich layer on the CZT surface was successfully compensated to the Te oxide layer, which was analyzed with X-ray photoelectron spectroscopy data of both a Br-etched crystal and a passivated CZT crystals. We confirmed that passivation with NaOCl improved the transport property by analyzing the mobility-lifetime product and surface recombination velocity. The electrical and spectroscopic properties of large volume detectors were compared before and after passivation, and then the detectors were observed for a month. Both bar and quasi-hemispherical detectors show an enhancement in performance after passivation. Thus, we could identify the effect of NaOCl passivation on large volume CZT detectors.

Formula omitted]-ray energy spectrum response tailing in CdZnTe detector

Affected by the characteristics of carrier transport, the γ-ray energy spectrum of the cadmium zinc telluride (CZT) detector usually has a low-energy tail phenomenon The traditional γ -ray energy spectrum response simulation model is mainly aimed at detectors with a uniform internal electric field, not suitable for non-uniform internal electric fields, and cannot accurately characterize the low-energy tailing phenomenon of the γ -ray energy spectrum of CZT detectors. In this study, for the quasi-hemispherical and coplanar-grid CZT detectors, the Geant4 program was used to establish the energy deposition model, and the γ-ray energy deposition and the carrier distribution in the two detectors were obtained. On this basis, the finite element analysis method was used to construct the internal electric field of the two detectors, and the charge collection efficiency model is established according to the transport law of carriers in the detectors. Finally, the above model was used to simulate the γ energy spectrum response of the four nuclides 241Am, 133Ba, 137Cs, and 60Co, and the simulation results were verified through experiments. The results show that the method in this paper can accurately describe the low-energy tail of the γ-ray energy spectrum of the two CZT detectors, and the obtained simulated γ-ray energy spectrum is basically consistent with the full-spectrum characteristics of the measured energy spectrum.

Accuracy and Reproducibility of Myocardial Blood Flow Quantification by Single Photon Emission Computed Tomography Imaging in Patients With Known or Suspected Coronary Artery Disease.

Single photon emission computed tomography (SPECT) has limited ability to identify multivessel and microvascular coronary artery disease. Gamma cameras with cadmium zinc telluride detectors allow the quantification of absolute myocardial blood flow (MBF) and myocardial flow reserve (MFR). However, evidence of its accuracy is limited, and of its reproducibility is lacking. We aimed to validate 99mTc-sestamibi SPECT MBF and MFR using standard and spline-fitted reconstruction algorithms compared with 13N-ammonia positron emission tomography in a cohort of patients with known or suspected coronary artery disease and to evaluate the reproducibility of this technique. Accuracy was assessed in 34 participants who underwent dynamic 99mTc-sestamibi SPECT and 13N-ammonia positron emission tomography and reproducibility in 14 participants who underwent 2 99mTc-sestamibi SPECT studies, all within 2 weeks. A rest/pharmacological stress single-day SPECT protocol was performed. SPECT images were reconstructed using a standard ordered subset expectation maximization (OSEM) algorithm with (N=21) and without (N=30) application of spline fitting. SPECT MBF was quantified using a net retention kinetic model' and MFR was derived as the stress/rest MBF ratio. SPECT global MBF with splines showed good correlation with 13N-ammonia positron emission tomography (r=0.81, P<0.001) and MFR estimates (r=0.74, P<0.001). Correlations were substantially weaker for standard reconstruction without splines (r=0.61, P<0.001 and r=0.34, P=0.07, for MBF and MFR, respectively). Reproducibility of global MBF estimates with splines in paired SPECT scans was good (r=0.77, P<0.001), while ordered subset expectation maximization without splines led to decreased MBF (r=0.68, P<0.001) and MFR correlations (r=0.33, P=0.3). There were no significant differences in MBF or MFR between the 2 reproducibility scans independently of the reconstruction algorithm (P>0.05 for all). MBF and MFR quantification using 99mTc-sestamibi cadmium zinc telluride SPECT with spatiotemporal spline fitting improved the correlation with 13N-ammonia positron emission tomography flow estimates and test/retest reproducibility. The use of splines may represent an important step toward the standardization of SPECT flow estimation.

Development and Characterization of Modular Readout Design for Two-Panel Head-and-Neck Dedicated PET System Based on CZT Detectors.

Cadmium zinc telluride (CZT) detectors are suitable for various applications due to the good energy resolution and the simple pixilation to achieve high spatial resolution. Our group is developing a two-panel head and neck dedicated positron emission tomography system based on CZT detectors. Each panel will consist of 150 CZT crystals (4×4×0.5 cm3) covering an area of 20×15 cm2 in an edge-on configuration to achieve high detector efficiency at 511 keV. In this work, we present the design and development of a full data acquisition chain that enables a low noise and compact readout for each panel. The initial results of the readout circuit were quantified using a 1 kHz square wave test pulse. The pulse amplitude was chosen to generate approximately the same amount of charges as a 511 keV photon would provide in CZT. The best-case FWHM electronic noise at 511 keV was measured to be 0.69% ± 0.16% (3.52 ± 0.81 in keV units after conversion). The FWHM electronic noise at 511 keV for a complete DAQ chain was 4.33% ± 0.30% (22.13 ± 1.53 in keV units).

Performance analysis of improved hybrid median filter applied to X-ray computed tomography images obtained with high-resolution photon-counting CZT detector: A pilot study

We evaluated the performance of an improved hybrid median filter (IHMF) applied to X-ray computed tomography (CT) images obtained using a high-resolution photon-counting cadmium zinc telluride (CZT) detector. To study how the proposed approach improves the image quality, we measured the noise levels and the overall CT-image quality. We established a CZT imaging system with a detector length of 5.12 cm and thickness of 0.3 cm and acquired phantom images. To evaluate the efficacy of the proposed filter, we first modeled two conventional median filters. Subsequently, we were able to achieve a normalized noise power spectrum result of ∼10−8 mm2, and furthermore, the proposed method improved the contrast-to-noise ratio by a factor of ∼1.51 and the coefficient of variation by 1.55 relative to the counterpart values of the no-filter image. In addition, the IHMF exhibited the best performance among the three filters considered as regards the peak signal-to-noise ratio and no-reference-based image-quality evaluation parameters. Thus, our results demonstrate that the IHMF approach provides a superior image performance over conventional median filtering methods when applied to actual CZT X-ray CT images.

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.

Multi-contrast CT imaging using a high energy resolution CdTe detector and a CZT photon-counting detector

Computed tomography (CT) imaging with high energy resolution detectors shows great promise in material decomposition and multi-contrast imaging. Multi-contrast imaging was studied by imaging a phantom with iodine (I), gadolinium (Gd), and gold (Au) solutions, and mixtures of the three using a cadmium telluride (CdTe) spectrometer with an energy resolution of 1% as well as with a cadmium zinc telluride (CZT) detector with an energy resolution of 13%. The phantom was imaged at 120 kVp and 1.1 mA with 7 mm of aluminum filtration. For the CdTe data collection, the phantom was imaged using a 0.2 mm diameter x-ray beam with 96 ten-second data acquisitions across the phantom at 45 rotation angles. For the CZT detector, we had 720 projections using a cone beam, and the six detector energy thresholds were set to 23, 33, 50, 64, 81, and 120 keV so that three thresholds corresponded to the K-edges of the contrast agents. Contrast agent isolation methods were then examined. K-edge subtraction and novel spectrometric algebraic image reconstruction (SAIR) were used for the CdTe data. K-edge subtraction alone was used for the CZT data. Linearity plots produced similar R 2 values and slopes for all three reconstruction methods. Comparing CdTe methods, SAIR offered less noise than CdTe K-edge subtraction and better geometric accuracy at low contrast concentrations. CdTe contrast agent images of I, Gd, and Au offered less noise and greater contrast than the CZT images, highlighting the benefits of high energy resolution CdTe detectors for possible use in pre-clinical or clinical CT imaging.

Simulation study of neutron radiation damage to cadmium zinc telluride

In recent years, the development of new semiconductor materials has made an opportunity and challenge for technological innovation and the development of emerging industries. Among them, cadmium zinc telluride materials have highlighted important application prospects due to their excellent properties. The CdZnTe, as the third-generation cutting-edge strategic semiconductor material, has the advantages of high detection efficiency, low dark current, strong portability, and applicability at room temperature without additional cooling system. However, when the cadmium zinc telluride detector is exposed to radiation environment for a long time, it will cause different degrees of radiation damage, which will affect the performance of the device or even fail to work, and greatly shorten the service time of the detector in the radiation field. The transport process of 1.00–14.00 MeV neutrons in CdZnTe material is simulated to obtain the information about the primary knock-on atoms, and then by combining with the cascade collision model, the irradiation of neutrons with different energy in CdZnTe material is analyzed. The damage is simulated and calculated. The calculation results are shown below. The energy of most of the primary knock-on atoms is located at the low-energy end, and with the increase of the incident neutron energy, the types of primary knock-on atoms are more abundant, and the energy also increases gradually. With neutron irradiation of CdZnTe, the non-ionizing energy loss is uniformly distributed along the depth direction in the material, and the non-ionizing energy loss first increases and then decreases with the increase of the incident neutron energy. The calculation results of displacements per atom(dpa) show that the dpa also increases first with the increase of the incident neutron energy. And further analysis shows that the number of Te displacement atom atoms and the number of the Zn displacement atoms both increase first and decrease then with the increase of incident neutron energy, while the number of Cd displacement atoms increases with the increase of incident neutron energy, which is co-modulated by its inelastic scattering cross-section and other nuclear-like reaction cross-sections. The comprehensive analysis shows that with the increase of the incident neutron energy, inelastic scattering becomes the main factor causing the internal displacement damage of the material.

CZT camera systems may provide better risk stratification for low-risk patients

BackgroundThe photon sensitivity and spatial resolution of single-photon emission-computed tomography (SPECT) has been significantly improved by solid-state camera systems using cadmium zinc telluride (CZT) detectors. While the diagnostic accuracy of these systems is well established, there is little evidence directly comparing the prognostic utility to conventional NaI cameras. Methods and ResultsRetrospective analysis of patients undergoing SPECT between 2008 and 2012. Visual SPECT assessment was performed utilizing the 17-segment model to determine summed stress scores (SSS). We identified 12,830 consecutive patients, mean age 63.2 ± 13.7 and 56.1% male, 5072 of whom underwent CZT and 7758 NaI imaging. During a median follow-up duration of 7.0 years (IQR 5.5-8.2), a total of 2788 (21.7%) patients died. Compared to SSS 0, minimal perfusion abnormality (SSS 1-3) was associated with increased all-cause mortality with CZT camera (adjusted HR 1.32, P = .017) and NaI camera (adjusted HR 1.29, P = .001, interaction P = .803). Increasing stress abnormality was associated with a similar increase in risk with CZT or NaI imaging (interaction P > .500). In a propensity matched analysis, patients with normal perfusion stress perfusion assessed with a CZT was associated with decreased mortality compared to normal perfusion assessed by a NaI camera system (hazard ratio .88, 95% CI .78-.99, P = .040). ConclusionsIncreasing stress perfusion abnormality was associated with similar increase in all-cause mortality with CZT or NaI cameras. CZT and NaI camera systems provide similar risk stratification, however, normal myocardial perfusion may be associated with a more benign prognosis when assessed with a CZT camera system.

Effect of deep level defects on CdZnTe detector internal electric field and device performance

Cadmium zinc telluride (CZT) is an ideal material for room temperature nuclear radiation detection, but CZT crystals of high quality and low defects concentration are difficult to obtain. Therefore, in order to improve the performance of the CZT detector, the working conditions of the CZT detector could be appropriately changed to make the internal electric field of the CZT detector close to uniform distribution so as to improve the electron transport performance. In this paper, alpha induced transient charge analysis has been used to study the internal electric field of the CZT detector, and deep level defects in CZT were linked with internal electric field distribution. Based on the process, a variety of deep level defects on electron trapping and detrapping by changing the temperature, the output waveform change of charge sensitive preamplifier (the pulse height spectra for alpha radiation at different temperatures) was observed, and then the effects of deep level defects on electron mobility (μe), electron transport time (TR), the internal electric field, and the electron collection efficiency of the CZT detector were analyzed. The experimental results indicated that the influence of deep level defects was a main factor to the internal electric field in the range of −140 to 40 °C. As the temperature rises, the influence of these defects weakens, μe and electron collection efficiency both increase, and internal electric field distribution tends to be uniform. Moreover, with the further increasing temperature (−40 to 20 °C), μe decreased and internal electric field distribution became fluctuating, but electron collection efficiency was basically unchanged, which suggested that the influence of lattice vibration in the range of −40 to 20 °C turned to be the main factor. The above conclusions demonstrated that although the CZT detector has excellent room temperature detection ability, room temperature was not its optimal working temperature due to the influence of high concentration deep level defects. At −20 °C, the CZT detector presented the highest electron collection efficiency and maximum which limited the influence of deep level defects on electron transport, performing the optimal properties.

Reduction of the Low Energy Threshold through New Modular Data Acquisition Electronics for Cross-strip Cadmium Zinc Telluride (CZT) based PET System.

New modular data acquisition electronics for cross-strip cadmium zinc telluride (CZT) detector readout were developed to lower the electronic noise and increase the applied voltage bias capabilities compared to previous designs. The modular data acquisition electronics will be utilized to develop a two-panel head and neck dedicated positron emission tomography (PET) system. Each panel will consist of 150 CZT crystals (4 × 4 × 0.5cm 3) covering an area of 20×15 cm2 in an edge-on configuration to achieve high detector efficiency at 511 keV. This paper presents the first characterization results of CZT detectors based on the new readout electronics system. Ge-68 and Cs-137 were used as the point source for measuring the energy spectra. Three individual CZT detectors (117 anode channels) were tested together with a full data acquisition chain. The mean FWHM energy resolution across all 117 anode channels is 8.36%±0.52% at 511 keV without any correction and the lower keV threshold of the energy spectra resides between 0 keV to 50 keV. For reference, the previous small animal system had a mean FWHM energy resolution of 10.78%±1.45% at 511 keV before correction and a lower keV threshold of 100 keV to 150 keV.

Hard X-ray polarimetry—an overview of the method, science drivers, and recent findings

The last decade has seen a leapfrog in the interest of X-ray polarimetry with a number of new polarization measurements in hard X-rays from AstroSat, POLAR, GAP, and PoGO+. The measurements provide some interesting insights into various astrophysical phenomena such as coronal geometry and disk–jet connection in black hole X-ray binaries, hard X-ray emission mechanism in pulsars, and gamma-ray bursts. They also highlight an increase in polarization with energy, which makes hard X-ray polarimetry extremely appealing. There are a number of confirmed hard X-ray polarimetry experiments which along with the existing instruments (AstroSat and INTEGRAL) make this field further exciting. Polarization experiments may also see significant progress in sensitivity with new developments in scintillator readouts, active pixel sensors, and cadmium zinc telluride detectors. In particular, the advent of hard X-ray focusing optics will enable the designing of compact focal plane polarimeters with a multifold enhancement in sensitivity. In this review, we will focus on the recent polarimetry findings and science potential of hard X-ray polarimetry along with possible improvements in the measurement techniques.