Energy Resolution Of Detector Research Articles

First application of scintillator-based photon-counting computed tomography to rock samples: Preliminary results and prospects

Abstract Knowledge of the three-dimensional distribution of minerals in a rock sample is of fundamental importance to deciphering a sample’s properties and history. Attenuation-contrast X-ray computed tomography (X-ray CT) is widely used in the geosciences to determine the three-dimensional distributions of minerals or pores, or both. Photon counting CT (PC-CT) uses a novel energy-resolved X-ray detector that allows X-rays with a continuous energy spectrum to be detected separately within arbitrary energy ranges. Here we report the first results of applying laboratory-build PC-CT combined with multi-pixel photon counter (MPPC) to common minerals such as quartz and calcite. In the low-energy range, PC-CT produced higher contrast images than single-energy X-ray CT. Minerals were successfully identified from the relationships between the mean CT values for each energy window and the mean difference between pairs of energy windows. These results suggest that PC-CT can produce high-contrast images of minerals and may be able to distinguish mineral phases with different attenuation curves, even when their CT values are similar. We obtained CT images of minerals in a natural sedimentary rock sample, composed mainly of quartz and carbonate. Although the spatial resolution of the detector in this study was insufficient for the sample, the main carbonate veins were clearly visible as high carbonate-content areas in the PC-CT images. Given some prior knowledge of mineral phases from other methods, it may be possible to use PC-CT imaging to obtain further information about their chemical compositions.

Optimization and experimental validation of deuterium-tritium neutron monoenergetics for diamond detector testing

Diamond detectors are excellent tools for measuring deuterium-tritium (D-T) neutron energy spectra. It has great potential for application in the field of magnetic confinement fusion. However, the current experimental values of the energy resolution of diamond detectors are much lower than the theoretical estimates. The purpose of this study is to find a method for experimental optimization. For this purpose, the D-T neutron energy distribution of the accelerator is theoretically analyzed and simulated. A method to increase the deuteron energy to obtain a better monoenergetic neutron source is proposed. This strategy was validated experimentally. The energy resolution of diamond for D-T neutrons achieves 1.21%, a Full Width at Half Maximum of 93 keV at 7.65 MeV. It is the highest resolution recorded to date. These results demonstrate the feasibility of the optimization method.

Progress toward absolute calibrations of DC x-ray sources from 1keV to >30keV for Z diagnostics applications.

Numerous x-ray diagnostics at the Z facility, time-resolved and time-integrated, would benefit from a local calibrated x-ray source. For many years, Z has used low-power Manson x-ray sources to provide some characterization information for components of Z diagnostics below 30keV. More recently, we have acquired TruFocus x-ray sources, which operate at voltages up to 100kV depending on the anode material and model. These DC sources have demonstrated good stability and repeatability. Absolute calibrations of either sources or detectors usually involve another calibrated detector from another source, which has not been readily available locally. Therefore, we have adopted the strategy of characterizing a sensitive semiconductor diode detector by controlling or inferring the active volume. This characterized detector is then used to scale the Manson x-ray spectral shape as measured by an Amptek energy-resolving detector. The result agrees well with the modeled source spectrum. We can apply this technique to the TruFocus as well.

Simultaneous imaging and element differentiation by energy-resolved x-ray absorption ghost imaging.

Based on the x-ray absorption edges of different elements, we simultaneously image and distinguish the composition of three differently shaped components of an object by using energy-resolved x-ray absorption ghost imaging (GI). The initial x-ray beam is spatially modulated by a series of Hadamard matrix masks, and the object is composed of three pieces of Mo, Ag, and Sn foil in the shape of a triangle, square, and circle, respectively. The transmitted x-ray intensity is measured by an energy-resolved single-pixel detector with a spectral resolution better than 0.8 keV. Through correlation of the transmission spectra with the corresponding Hadamard patterns, the spectral image of the sample is reconstructed, with a spatial resolution of 108 µm. Our experiment demonstrates a practical application of spectral ghost imaging, which has important potential for the noninvasive analysis of material composition and distribution in biology, medical science, and many other fields.

Response of a high-pressure 4He scintillation detector to nuclear recoils up to 9 MeV

Helium-4-based scintillation detector technology is emerging as a strong alternative to pulse-shape discrimination-capable organic scintillators for fast neutron detection and spectroscopy, particularly in extreme gamma-ray environments. The 4He detector is intrinsically insensitive to gamma radiation, as it has a relatively low cross-section for gamma-ray interactions, and the stopping power of electrons in the 4He medium is low compared to that of 4He recoil nuclei. Consequently, gamma rays can be discriminated by simple energy deposition thresholding instead of the more complex pulse shape analysis. The energy resolution of 4He scintillation detectors has not yet been well-characterized over a broad range of energy depositions, which limits the ability to deconvolve the source spectra. In this work, an experiment was performed to characterize the response of an Arktis S670 4He detector to nuclear recoils up to 9 MeV. The 4He detector was positioned in the center of a semicircular array of organic scintillation detectors operated in coincidence. Deuterium–deuterium and deuterium–tritium neutron generators provided monoenergetic neutrons, yielding geometrically constrained nuclear recoils ranging from 0.0925 to 8.87 MeV. The detector response provides evidence for scintillation linearity beyond the previously reported energy range. The measured response was used to develop an energy resolution function applicable to this energy range for use in high-fidelity detector simulations needed by future applications.

Noise analysis and optical response of microwave kinetic inductance detectors with an optical stack

We report on the experimental investigation of optical coupling for superconducting microresonators known as microwave kinetic inductance detectors (MKIDs) in the visible and near-infrared bands. MKIDs are photon-counting, time and energy-resolving detectors that still suffer from a poor quantum efficiency. To improve this efficiency, we propose to add a superconducting reflective layer below the absorbing part of the detector separated by a transparent Al2O3 layer with a quarter-wavelength thickness optimized around a single wavelength λ = 405 nm. We have first fabricated samples patterned from stoichiometric TiN ( Tc∼4 K), one with the full optical stack, one without for reference and one with a partial optical stack in order to characterize the noise influence of each layer individually. We observe that the full optical stack geometry has the most impact on the resonator’s noise and quality factors. A second design was fabricated to characterize the optical response to short pulses of the optical stack and we show from both the frequential noise and optical response that a strong signature of TLS is still present in the optical stack sample. We have finally obtained single-photon response with the optical stack using a more sensitive tri-layer TiN/Ti/TiN absorber ( Tc∼1.3 K) for which a maximum energy resolving power of R=E/ΔE∼ 1.3 was achieved using 405 nm laser pulses at 225 mK. The quality factors of both the reference and optical stack samples are similar but the frequency noise is still a tenfold higher for the optical stack sample which degrades the energy-resolving power of the detector.

Scientific impact of a noiseless energy-resolving detector for a future exoplanet-imaging mission

Scientific impact of a noiseless energy-resolving detector for a future exoplanet-imaging mission

Feasibility of improving image performance in photon-counting computed tomography using X-ray spectrum filtration

Photon-counting computed tomography (PCCT) is an emerging technology based on new energy-resolving X-ray detectors (photon-counting detectors (PCDs)) that provide promising image performance compared to the conventional energy-integrating CT (EICT). It has the potential to provide higher resolution and contrast, lower radiation dose, and fewer artifacts, which has led to significant research interest. This study proposes a method to further improve the image performance of the PCCT using an X-ray spectrum filtration technique. We conducted a feasibility study via simulations using aluminum (Al), beryllium (Be), sodium (Na), nickel (Ni), tin (Sn), neodymium (Nd), and tantalum (Ta) incorporating varying thicknesses using a PCD simulation toolkit (PcTK). The PCCT system used in this simulation was modeled to have a cadmium telluride-based PCD with four multi-energy thresholds of E = 40, 60, 80, 100 keV, assuming that the object received the same number of photons. Using the PCCT images obtained with the highest threshold (i.e., E4 = 100 keV), the image quality was evaluated quantitatively in terms of the signal difference-to-noise ratio (SDNR) and structural similarity (SSIM). Among the filtrations selected in this simulation, a filtration of 2.0 mmAl (inherent) and 1.5 mmSn (added) showed the best image quality. The SDNR and SSIM values measured in the PCCT image obtained with an added filtration of 1.5 mmSn were 3.73 and 0.81, approximately 1.9 and 1.8 times higher than those with no added filtration, respectively. Consequently, the X-ray spectrum filtration technique in PCCT is useful to further improve image performance.

Development of a dual-mode energy-resolved neutron imaging detector: High spatial resolution and large field of view

Energy-resolved neutron imaging is an effective way to investigate the internal structure and residual stress of materials. Different sample sizes have varying requirements for the detector's imaging field of view (FOV) and spatial resolution. Therefore, a dual-mode energy-resolved neutron imaging detector was developed, which mainly consisted of a neutron scintillator screen, a mirror, imaging lenses, and a time-stamping optical fast camera. This detector could operate in a large FOV mode or a high spatial resolution mode. To evaluate the performance of the detector, the neutron wavelength spectra and the multiple spatial resolution tests were conducted at CSNS. The results demonstrated that the detector accurately measured the neutron wavelength spectra selected by a bandwidth chopper. The best spatial resolution was about 20 μm in high spatial resolution mode after event reconstruction, and a FOV of 45.0 mm × 45.0 mm was obtained in large FOV mode. The feasibility was validated to change the spatial resolution and FOV by replacing the scintillator screen and adjusting the lens magnification.

Optimisation of virtual monoenergetic reconstructions for the diagnosis of pulmonary embolism using photon-counting detector computed tomography angiography

PurposeComputed tomography (CT) pulmonary angiography is considered the gold standard for pulmonary embolism (PE) diagnosis, relying on the discrimination between contrast and embolus. Photon-counting detector CT (PCD-CT) generates monoenergetic reconstructions through energy-resolved detection. Virtual monoenergetic images (VMI) at low keV can be used to improve pulmonary artery opacification. While studies have assessed VMI for PE diagnosis on dual-energy CT (DECT), there is a lack of literature on optimal settings for PCD-CT-PE reconstructions, warranting further investigation.Material and methodsTwenty-five sequential patients who underwent PCD-CT pulmonary angiography for suspicion of acute PE were retrospectively included in this study. Quantitative metrics including signal-to-noise ratio (SNR) and contrast-to-noise (CNR) ratio were calculated for 4 VMI values (40, 60, 80, and 100 keV). Qualitative measures of diagnostic quality were obtained for proximal to distal pulmonary artery branches by 2 cardiothoracic radiologists using a 5-point modified Likert scale.ResultsSNR and CNR were highest for the 40 keV VMI (49.3 ± 22.2 and 48.2 ± 22.1, respectively) and were inversely related to monoenergetic keV. Qualitatively, 40 and 60 keV both exhibited excellent diagnostic quality (mean main pulmonary artery: 5.0 ± 0 and 5.0 ± 0; subsegmental pulmonary arteries 4.9 ± 0.1 and 4.9 ± 0.1, respectively) while distal segments at high (80-100) keVs had worse quality.Conclusions40 keV was the best individual VMI for the detection of pulmonary embolism by quantitative metrics. Qualitatively, 40-60 keV reconstructions may be used without a significant decrease in subjective quality. VMIs at higher keV lead to reduced opacification of the distal pulmonary arteries, resulting in decreased image quality.

Probability distribution maps of deposited energy with sub-pixel resolution for Timepix3 detectors

The Medipix3 Collaboration has developed the Timepix3 chip, which can provide information about individual particles interacting with a hybrid pixelated semiconductor detector. The Timepix3 generates a data packet including time and energy information for each pixel receiving a charge above the discriminator threshold. From a set of such packages generated by one particle the total deposited energy and the sub-pixel center of mass (c.m) position of the interaction can be calculated. However, sub-threshold losses will distort both the measured energy and c.m calculation. This work aims to generate probability maps for the most probable initial interaction position and energy for a given detected cluster. The correction maps were calculated for different energies and sub-pixel c.m positions. It is crucial to realistically simulate the front-end response of the Timepix3 detector to be able to match and understand the experimental data and generate accurate probability maps. The correction maps from the simulations using the simulation tool Allpix 2 are applied to experimental data utilizing an Am-241 source to irradiate a Minipix Timepix3, leading to sub-pixel resolution and improved energy resolution for Timepix3 detectors.

A simulation of a high-resolution cadmium zinc telluride positron emission tomography system.

A CZT (cadmium zinc telluride) PET (positron emission tomography) system is being developed at Stanford University. CZT has the promise of outperforming scintillator-based systems in energy and spatial resolution but has relatively poor coincidence timingresolution. To supplement GATE (GEANT 4 Application for Emission Tomography) simulations with charge transport and electronics modeling for a high-resolution CZT PET system. A conventional GATE simulation was supplemented with electron-hole transport modeling and experimentally measured single detector energy resolution to improve the system-level understanding of a CZT high-resolution PET system in development at Stanford University. The modeling used GATE hits data and applied charge transport in the crystal and RC-CR processing of the simulated signals to model the electronics, including leading-edge discriminators and peak pick-off. Depth correction was also performed on the simulation data. Experimentally acquired data were used to determine energy resolution parameters and were compared to simulationdata. The distributions of the coincidence timing, anode energy, and cathode energy are consistent with experimental data. Numerically, the simulation achieved 153 ns FWHM coincidence time resolution (CTR), which is of the same order of magnitude as the raw 210 ns CTR previously found experimentally. Further, the anode energy resolution was found to be 5.9% FWHM (full width at half maximum) at 511 keV in the simulation, which is between the experimental value found for a single crystal of 3% and the value found for the dual-panel setup of 8.02%, after depth correction. Developing this advanced simulation improves upon the limitations of GATE for modeling semiconductor PET systems and provides a means for deeper analysis of the coincidence timing resolution and other complementary electron-hole dependent systemparameters.

Limitations to the energy resolution of single-photon sensitive microwave kinetic inductance detectors

This paper describes the energy resolution of microwave kinetic inductance detectors and models some limiting factors to it. Energy resolution is a measure of the smallest possible difference in energy of the impinging photons, ΔE, that the detector can identify and, as such, is of critical importance for many applications. Limits to the energy resolution caused by the Fano effect, amplifier noise, current inhomogeneities, and readout sampling frequency are taken into consideration for this model. This paper describes an approach to combine all of these limitations and predict a wavelength dependency of the upper limit to the resolving power.

An extended bore length solid-state digital-BGO PET/CT system: design, preliminary experience, and performance characteristics.

A solid-state PET/CT system uses bismuth germanium oxide (BGO) scintillating crystals coupled to silicon photomultipliers over an extended 32 cm axial field-of-view (FOV) to provide high spatial resolution and very high sensitivity. Performance characteristics were determined for this digital-BGO system, including NEMA and EARL standards. Spatial resolution, scatter fraction (SF), noise equivalent count rate (NECR), sensitivity, count rate accuracy, and image quality (IQ) were evaluated for the digital-BGO system as per NEMA NU 2-2018, at 2 sites of first clinical install. System energy resolution was measured. Bayesian penalized-likelihood reconstruction (BPL) was used for IQ. EARL Standards 2 studies were reconstructed by BPL combined with a contrast-enhancing deep learning algorithm. An Esser PET phantom was evaluated. Three patient examples were obtained with low-dose radiotracer activity: 2 MBq/kg of [18F]FDG ([18F]-2-fluoro-2-deoxy-D-glucose), 2.3 MBq/kg [68Ga]Ga-DOTA-TATE ([dodecane tetra-acetic acid,Tyr3]-octreotate), and 14.5 MBq/kg [82Rb]RbCl ([82Rb]-rubidium-chloride). Total scan times were ≤ 8 min. NEMA sensitivity was 47.6 cps/kBq at the axial center. Spatial resolution at 1 cm from the center axis was ≤4.5 mm (filtered back projection) and ≤3.8 mm (ordered subset expectation maximization). SF was 35.6%, count rate accuracy was 2.16%, and peak NECR was 485.2 kcps at 16.9 kBq/mL. Contrast for IQ was 61.1 to 90.7% (smallest to largest sphere) with background variations from 7.6 to 2.1%, and a "lung" error of 4.7%. The average detector energy resolution was 9.67%. Image quality for patient scans was good. EARL Standards 2 criteria were robustly met and Esser phantom features ≥4.8 mm were resolved at 2 min per bed position. A solid-state 32 cm axial FOV digital-BGO PET/CT system provides good spatial and energy resolution, high count rates, and superior NEMA sensitivity in its class, enabling fast clinical acquisitions with low-dose radiotracer activity.

Use of CdZnTe Quasi-Hemispherical Detectors under the Impact of Low Temperatures and High-Gamma Radiation Fluxes.

This article discusses the possibilities and limitations of CdZnTe (CZT) quasi-hemispherical detectors operating over a wide temperature range and at high-gamma radiation fluxes. The results of the negative influence of low- and high-operating temperatures, as well as high-radiation fluxes on spectrometric characteristics of CZT detectors and possible ways to eliminate performance deterioration, are presented. The impact of infrared (IR) illumination parameters, such as wavelength and irradiation intensity on the spectroscopy performance of detectors, was investigated. A correctly chosen IR illumination wavelength and intensity were shown to significantly improve the energy resolution of CZT quasi-hemispherical detectors, allowing their stable operation in high-gamma radiation fluxes and extend the operating temperature range toward low temperatures. The influences of bias voltage values and temperatures on the quasi-hemispherical CZT detectors' operating ability at high-gamma radiation fluxes were studied.

Note on intrinsic resolution in liquid organic scintillators

Fluctuations in photon production in scintillator could contribute to the total energy resolution of a scintillation detector. This contribution, called intrinsic resolution (IR), is one of the factors limiting the total energy resolution in detectors based on liquid organic scintillators (LSs). There are very few experimental measurements of the IR in LSs available, and the underlying physics is not completely understood. We propose a phenomenological description of IR of LSs and systematize the data available using a single universal parameter that characterizes IR. We show that all experimental data within the model demonstrate the presence of extra smearing of energy resolution due to IR with a typical value of ≃ 2% at 1-MeV energy release. The model can be used to simulate the effect of IR in LS-based detectors.

Characterisation of HEXITECMHz - A 1 MHz continuous frame rate spectroscopic X-ray imaging detector system

Spectroscopic X-ray imaging techniques including Compton X-ray Imaging, X-ray Fluorescence Imaging and Hyperspectral X-ray Tomography require energy-resolving detectors capable of operating at high incident X-ray fluxes to make time resolved measurements. HEXITECMHz, operates at a continuous 1 MHz frame rate and can make fully spectroscopic measurements at >106 ph s−1 mm−2. This is enabled by an integrating Front End, in-pixel digitisation and high-speed serialisers. A 300 μm thick p-type Si HEXITECMHz detector was characterised on the B16 Test Beamline at the Diamond Light Source and are the first measurements taken at a 1 MHz frame rate. At 10 keV and 15 keV) the device displayed average FWHM of 656 eV and 682 eV respectively, with minimal changes in spectroscopic performance over ∼8 h. Analysis of charge-sharing events show low charge loss and a linear energy-signal response. Higher-flux measurements illustrated the capability of the ASIC to operate as a photon-counting device.

Large, Thin, and Corrugated Gold Absorbers for Transition Edge Sensor Microcalorimeters

A sounding rocket mission studying the soft diffuse X-ray background ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$&lt; $</tex-math></inline-formula> 400 eV) needs high-resolution detectors ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$&lt; $</tex-math></inline-formula> 2 eV FWHM) with a large collecting area ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$&gt;$</tex-math></inline-formula> 2 cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> ) to reasonably achieve science goals. A practical number of readout channels coupled with the energy resolution requirements drives our goal to develop large (1 mm x 1 mm), thin (200 nm) gold absorbers. Our previous attempts at fabricating these absorbers showed that we needed a large number of support posts as far out as possible to keep the thin absorber from sagging and thermally shorting to the substrate. Support posts at the edge of the membrane could increase athermal phonon loss and introduce position dependence in the absorber. Both are detrimental to the detector energy resolution. Free-standing absorbers with support posts only in the center would be ideal, but these thin absorbers have an aspect ratio of a sheet of typing paper supported by 1 mm tall support posts in the center. We have been exploring adding corrugations to the absorber to mechanically stiffen it and decrease the number of support posts needed. Here, we show the results from our fabrication runs to make large, thin, corrugated absorbers and compare the efficacy of different corrugation patterns to keep a large, thin absorber flat.

Increased material differentiation through multi-contrast x-ray imaging: a preliminary evaluation of potential applications to the detection of threat materials

Most material discrimination in security inspections is based on dual-energy x-ray imaging, which enables the determination of a material’s effective atomic number (Zeff) as well as electron density and its consequent classification as organic or inorganic. Recently phase-based ‘dark-field’ x-ray imaging approaches have emerged that are sensitive to complementary features of a material, namely its unresolved microstructure. It can therefore be speculated that their inclusion in the security-based imaging could enhance material discrimination, for example of materials with similar electron densities and Zeff but different microstructures. In this paper, we present a preliminary evaluation of the advantages that such a combination could bear. Utilising an energy-resolved detector for a phase-based dark-field technique provides dual-energy attenuation and dark-field images simultaneously. In addition, since we use a method based on attenuating x-ray masks to generate the dark-field images, a fifth (attenuation) image at a much higher photon energy is obtained by exploiting the x-rays transmitted through the highly absorbing mask septa. In a first test, a threat material is imaged against a non-threat one, and we show how their discrimination based on maximising their relative contrast through linear combinations of two and five imaging channels leads to an improvement in the latter case. We then present a second example to show how the method can be extended to discrimination against more than one non-threat material, obtaining similar results. Albeit admittedly preliminary, these results indicate that significant margins of improvement in material discrimination are available by including additional x-ray contrasts in the scanning process.

Application of peak based-Bayesian statistical method for isotope identification and categorization of depleted, natural and low enriched uranium measured by LaBr3:Ce scintillation detector

Todays, medium energy resolution detectors are preferably used in radioisotope identification devices(RID) in nuclear and radioactive material categorization. However, there is still a need to develop or enhance « automated identifiers » for the useful RID algorithms. To decide whether any material is SNM or NORM, a key parameter is the better energy resolution of the detector. Although masking, shielding and gain shift/stabilization and other affecting parameters on site are also important for successful operations, the suitability of the RID algorithm is also a critical point to enhance the identification reliability while extracting the features from the spectral analysis. In this study, a RID algorithm based on Bayesian statistical method has been modified for medium energy resolution detectors and applied to the uranium gamma-ray spectra taken by a LaBr3:Ce detector. The present Bayesian RID algorithm covers up to 2000 keV energy range. It uses the peak centroids, the peak areas from the measured gamma-ray spectra. The extraction features are derived from the peak-based Bayesian classifiers to estimate a posterior probability for each isotope in the ANSI library. The program operations were tested under a MATLAB platform.The present peak based Bayesian RID algorithm was validated by using single isotopes(241Am, 57Co, 137Cs, 54Mn, 60Co), and then applied to five standard nuclear materials(0.32–4.51% at.235U), as well as natural U- and Th-ores. The ID performance of the RID algorithm was quantified in terms of F-score for each isotope. The posterior probability is calculated to be 54.5–74.4% for 238U and 4.7–10.5% for 235U in EC-NRM171 uranium materials. For the case of the more complex gamma-ray spectra from CRMs, the total scoring (ST) method was preferred for its ID performance evaluation. It was shown that the present peak based Bayesian RID algorithm can be applied to identify 235U and 238U isotopes in LEU or natural U–Th samples if a medium energy resolution detector is was in the measurements.