Photon Sensitivity Research Articles

Physical Properties of Candidate X-Ray Detector Material Rb4Ag2BiBr9.

Recently, metal halide perovskites have emerged as promising semiconductor candidates for sensitive X-ray photon detection due to their suitable bandgap energies, excellent charge transport properties, and low material cost afforded by their low-temperature solution-processing preparation. Here, we report an improved methodology for single crystal (SC) growth, thermal and electrical properties of a two-dimensional (2D) layered halide material Rb4Ag2BiBr9, which has been identified as a potential candidate for X-ray radiation detection applications. The measured heat capacity for Rb4Ag2BiBr9 implies that there are no structural phase transitions upon cooling. Temperature dependence of thermal transport measurements further suggest remarkably low thermal conductivities of Rb4Ag2BiBr9 that are comparable to the lowest reported in literature. The bulk crystal resistivity is determined to be 2.59×109 Ω·cm from the current-voltage (I-V) curve. Density of trap states are estimated to be ~1010 cm-3 using the space-charge-limited-current (SCLC) measurements. The fabricated Rb4Ag2BiBr9-based X-ray detector shows good operational stability with no apparent current drift, which may be ascribed to the 2D crystal structure of Rb4Ag2BiBr9. Finally, by varying the X-ray tube current to change the corresponding dose rate, the Rb4Ag2BiBr9 X-ray detector sensitivity is determined to be 222.03 uCGy-1cm-2 (at an electric field of E = 24 V/mm).

Improved single-photon active imaging through ambient noise guided missing data filling

Active illumination time-of-flight single photon imaging has the advantage of high photon sensitivity which is suitable for imaging in long-distance and low light scenarios. The problem of missing information in depth profile of single photon imaging will deteriorate the imaging quality. The noise which comes from the scene reflected of the ambient light has always been ignored or excluded as strong interference of the active signal. In this letter, an ambient noise guided missing data filling method is proposed to improve the single-photon imaging quality. This method takes the ambient noise which was considered as interference in the past as the guidance for the filling of missing information in depth image. Both simulated and experimental verification are implemented to demonstrate the effectiveness of the proposed method. The observed experimental root mean square error has been improved from 1.97 m to 0.38 m and the structural similarity has been improved from 0.28 to 0.81 with the signal to background noise ratio of 0.15.

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.

Signal Amplification of Fiber Integrated X-Ray Detector and Energy Independence

We developed a high spatial resolution and sensitive detector particularly suitable for radiation dose measurements in radiotherapy at small fields and X-ray imaging applications. The detector is based on a silica optical fiber whose sensitive terminal is functionalized by grafting Ag-doped ZnS scintillating materials that emit blue luminescence under X-ray irradiation. Due to the small scintillating head of the detector, the acquisition signal is quite low, and it is measured by a sensitive photon counter plugged at the other terminal of the fiber. The weaker signal can be enhanced significantly by adding a metal coating over the scintillator. Therefore, this study presents the effect of metal thickness and density on the signal amplification at high irradiation energies of 6 MeV and 15 MeV using a Linear Accelerator (LINAC). In addition, the stem effect was characterized for regular to small field beam size and shows that the detector is almost free from stem contribution during high energy irradiation.

Noise heterogeneity in attenuation-corrected cardiac SPECT images increases perfusion value uncertainty near the base of the heart

BackgroundDedicated cardiac SPECT cameras which employ multi-pinhole detectors have variable photon sensitivity within the camera’s field-of-view such that a lower number of photon counts is typically detected from the base of the heart than from the apex. Consequently, the noise in a reconstructed image is expected to be higher at the base than at the apex of the heart. MethodsPatient emission images were resampled to create statistical replicates which were reconstructed with and without attenuation correction. Noise images were computed using one standard deviation of the replicated images. These were evaluated for 93 patients with normal study results, each imaged with both a dual-headed parallel-hole camera and a multi-pinhole camera. Statistics for a normal database (NDB) of images from the 93 patients were also calculated. ResultsImage noise (1.7-fold) and NDB uncertainty (1.3-fold) increase significantly from the apex-to-the base of the heart in attenuation-corrected multi-pinhole SPECT images. The differences for non-attenuation-corrected images or those acquired with a parallel-hole camera were not significant. ConclusionsFor best interpretation of attenuation-corrected images acquired with multi-pinhole cameras, knowledge of NDB uncertainty gradients should be taken into consideration.

SICURA: a new handheld radionuclide identification device with gamma and neutron response

SICURA is a two-year project that aims to develop a portable device to be employed in the prevention of illicit trafficking of radioactive material through γ and neutron detection. In order to be attractive to industries, efforts were made to fulfill the following characteristics: portability, good photon energy resolution and sensitivity in compliance with relevant international standards, sensitivity to neutrons with energies typical of the most common sources, fast response, low cost, user friendly interface. The SICURA system consists of two photon detectors for photon detection (CsI) and spectrometry (CZT) and a moderated Helium-3 counter for neutron detection. Dedicated analog and digital electronics readout have been developed, ensuring high energy resolution for accurate elements identification, signal digitization, alarm and information transmission to the end user.This paper describes the development of the SICURA device and the first results of its individual detectors characterizations.

Highly Sensitive U-Shaped Micro-channel Photonic Crystal Fiber–Based Plasmonic Biosensor

Highly Sensitive U-Shaped Micro-channel Photonic Crystal Fiber–Based Plasmonic Biosensor

Graphene-Coated Highly Sensitive Photonic Crystal Fiber Surface Plasmon Resonance Sensor for Aqueous Solution: Design and Numerical Analysis

This paper presents the design and analysis of a surface plasmon resonance (SPR) sensor in a photonic crystal fiber (PCF) platform, where graphene is used externally to attain improved sensing performance for an aqueous solution. The performance of the proposed sensor was analyzed using the finite element method-based simulation tool COMSOL Multiphysics. According to the simulation results, the proposed sensor exhibits identical linear characteristics as well as a very high figure of merit (FOM) of 2310.11 RIU−1 in the very low detection limit of 10−3. The analysis also reveals the maximum amplitude sensitivity of 14,847.03 RIU−1 and 7351.82 RIU−1 for the x and y polarized modes, respectively, which are high compared to several previously reported configurations. In addition, the average wavelength sensitivity is 2000 nm/RIU which is comparatively high for the analyte refractive index (RI) ranging from 1.331 to 1.339. Hence, it is highly expected that the proposed PCF-based SPR sensor can be a suitable candidate in different sensing applications, especially for aqueous solutions.

Design and first tests of the Gotthard-II readout ASIC for the European X-ray Free-Electron Laser

Gotthard-II is a charge-integrating microstrip detector developed for experiments and diagnostics at free-electron lasers using hard X-rays of 5 keV–20 keV. Thanks to its excellent single photon sensitivity, large dynamic range as well as high frame rate of 4.5 MHz in burst mode, its potential scientific applications include X-ray absorption/emission spectroscopy, hard X-ray high resolution single-shot spectrometry (HiREX), beam diagnostics, as well as veto signal generation for pixel detectors. The Gotthard-II ASIC has been designed and fabricated using UMC-110 nm technology. The final ASIC design and performance in terms of noise, linearity, dynamic range, coupling between channels and speed will be discussed in the paper. In addition, a first measurement of an X-ray absorption spectrum of a standard copper sample has been done. The performance of the Gotthard-II in an experiment using energy dispersive X-rays has been demonstrated.

Advantages of a curved image plate for rapid laboratory-based x-ray total scattering measurements: Application to pair distribution function analysis.

The analysis and interpretation of the pair distribution function (PDF), as derived from total scattering measurements, is still seen by many as a technique confined to central synchrotron and neutron facilities. This situation has begun to change with a rising visibility of total scattering experiments reported in mainstream scientific journals and the modification of an increasing number of laboratory diffractometers. However, the rigor required during data reduction and the complexities of data interpretation mean the technique is still very far from being routine. Herein, we report the first application of a large area curved image plate system based on a Rigaku SPIDER (R-AXIS RAPID II) equipped with an Ag tube for collecting data amenable to high quality PDF refinement/modeling of crystalline, amorphous, and liquid samples. The advantages of such a system are the large Q range available without scanning (routinely in excess of 20 Å-1) and the inherent properties of an image plate detector (single photon sensitivity, large dynamic range [1.05 × 106], and effectively zero noise). Data are collected and structural models refined for a number of standard materials including NIST 640f silicon for which a Rwp ≤ 0.12 value was obtained with data collected in 60min (excluding background measurements). These and other data are discussed and compared to similar examples in the literature.

Assessment of an Exhaled Breath Test Using High-Pressure Photon Ionization Time-of-Flight Mass Spectrometry to Detect Lung Cancer

Exhaled breath is an attractive option for cancer detection. A sensitive and reliable breath test has the potential to greatly facilitate diagnoses and therapeutic monitoring of lung cancer. To investigate whether the breath test is able to detect lung cancer using the highly sensitive high-pressure photon ionization time-of-flight mass spectrometry (HPPI-TOFMS). This diagnostic study was conducted with a prospective-specimen collection, retrospective-blinded evaluation design. Exhaled breath samples were collected before surgery and detected by HPPI-TOFMS. The detection model was constructed by support vector machine (SVM) algorithm. Patients with pathologically confirmed lung cancer were recruited from Peking University People's Hospital, and healthy adults without pulmonary noncalcified nodules were recruited from Aerospace 731 Hospital. Data analysis was performed from August to October 2020. Breath testing and SVM algorithm. The detection performance of the breath test was measured by sensitivity, specificity, accuracy, and area under the receiver-operating characteristic curve (AUC). Exhaled breath samples were from 139 patients with lung cancer and 289 healthy adults, and all breath samples were collected and tested. Of all participants, 228 (53.27%) were women and the mean (SD) age was 57.0 (11.4) years. After clinical outcomes were ascertained, all participants were randomly assigned into the discovery data set (381 participants) and the blinded validation data set (47 participants). The discovery data set was further broken into a training set (286 participants) and a test set (95 participants) to construct and test the detection model. The detection model reached a mean (SD) of 92.97% (4.64%) for sensitivity, 96.68% (2.21%) for specificity, and 95.51% (1.93%) for accuracy in the test set after 500 iterations. In the blinded validation data set (47 participants), the model revealed a sensitivity of 100%, a specificity of 92.86%, an accuracy of 95.74%, and an AUC of 0.9586. This diagnostic study's results suggest that a breath test with HPPI-TOFMS is feasible and accurate for lung cancer detection, which may be useful for future lung cancer screenings.

Concepts for the XIDer readout ASIC incorporating a pipelined ADC with very low dead time

We present the first concept for the analog front-end of the readout ASIC for the XIDer (X-ray Integrating Detector) detector system which is beingdeveloped by a collaboration between the ESRF and Heidelberg University. The ESRF's Extremely Brilliant Source (EBS) upgrade which has been completed recently provides X-ray beams of unprecedentedquality, requiring new photon detection instruments. The XIDer project has been launched to developa new versatile pixel detector which will be tailored to match requirements imposed by this upgrade. The core challengesinclude fast signal acquisition, large dynamic range and single photon sensitivity. A firstprototype ASIC for the analog front-end of a single pixel has been manufactured. It is based on a pipelined two-stage charge removal circuit which digitizes the incident signal on the fly. We will present measurement results of the first test chip and concepts for the final system-on-chip implementation integrating several tens of thousands of pixels.

High sensitivity x-ray detectors based on 4H-SiC p-i-n structure with 80μm thick intrinsic layer

In this work, a large size x-ray detector with a 25 mm2 active area is demonstrated based on a thick 4H-SiC p-i-n structure. The detector exhibits obvious merits of high photon sensitivity over 4 × 104 μC Gy−1 cm−2, good photon-response linearity, and high-temperature operation compatibility. Meanwhile, due to the ultralow leakage current level achieved, single photon detection performance for x-ray photons is further realized with energy resolutions of 1.1 and 4.9 keV at 5.9 and 59.5 keV, respectively. This work thus suggests the significant potentials of wide-bandgap SiC semiconductor for photon-resolved x-ray detection in a harsh environment.

High resolution small-scale inorganic scintillator detector: HDR brachytherapy application.

Brachytherapy (BT) deals with high gradient internal dose irradiation made up of a complex system where the source is placed nearby the tumor to destroy cancerous cells. A primary concern of clinical safety in BT is quality assurance to ensure the best matches between the delivered and prescribed doses targeting small volume tumors and sparing surrounding healthy tissues. Hence, the purpose of this study is to evaluate the performance of a point size inorganic scintillator detector (ISD) in terms of high dose rate brachytherapy (HDR-BT) treatment. A prototype of the dose verification system has been developed based on scintillating dosimetry to measure a high dose rate while using an 192 Ir BT source. The associated dose rate is measured in photons/s employing a highly sensitive photon counter (design data: 20 photons/s). Dose measurement was performed as a function of source-to-detector distance according to TG43U1 recommendations. Overall measurements were carried out inside water phantoms keeping the ISD along the BT needle; a minimum of 0.1cm distance was maintained between each measurement point. The planned dwell times were measured accurately from the difference of two adjacent times of transit. The ISD system performances were also evaluated in terms of dose linearity, energy dependency, scintillation stability, signal-to-noise ratio (SNR), and signal-to-background ratio (SBR). Finally, a comparison was presented between the ISD measurements and results obtained from TG43 reference dataset. The detection efficiency of the ISD was verified by measuring the planned dwell times at different dwell positions. Measurements demonstrated that the ISD has a perfectly linear behavior with dose rate (R2 =1) and shows high SNR (>35) and SBR (>36) values even at the lowest dose rate investigated at around 10cm from the source. Standard deviation (1σ) remains within 0.03% of signal magnitude, and less than 0.01% STEM signal was monitored at 0.1cm source-to-detector distance. Stability of 0.54% is achieved, and afterglow stays less than 1% of the total signal in all the irradiations. Excellent symmetrical behavior of the dose rate regarding source position was observed at different radiation planes. Finally, a comparison with TG-43 reference dataset shows that corrected measurements agreed with simulation data within 1.2% and 1.3%, and valid for the source-to-detector distance greater than 0.25cm. The proposed ISD in this study anticipated that the system could be promoted to validate with further clinical investigations. It allows an appropriate dose verification with dwell time estimation during source tracking and suitable dose measurement with a high spatial resolution both nearby (high dose gradient) and far (low dose gradient) from the source position.

Designing optimal experiments: an application to proton Compton scattering

Interpreting measurements requires a physical theory, but the theory’s accuracy may vary across the experimental domain. To optimize experimental design, and so to ensure that the substantial resources necessary for modern experiments are focused on acquiring the most valuable data, both the theory uncertainty and the expected pattern of experimental errors must be considered. We develop a Bayesian approach to this problem, and apply it to the example of proton Compton scattering. Chiral Effective Field Theory (\(\chi \)EFT) predicts the functional form of the scattering amplitude for this reaction, so that the electromagnetic polarizabilities of the nucleon can be inferred from data. With increasing photon energy, both experimental rates and sensitivities to polarizabilities increase, but the accuracy of \(\chi \)EFT decreases. Our physics-based model of \(\chi \)EFT truncation errors is combined with present knowledge of the polarizabilities and reasonable assumptions about experimental capabilities at HI\(\gamma \)S and MAMI to assess the information gain from measuring specific observables at specific kinematics, i.e. to determine the relative amount by which new data are apt to shrink uncertainties. The strongest gains would likely come from new data on the spin observables \(\Sigma _{2x}\) and \(\Sigma _{2x^\prime }\) at \(\omega \simeq 140\) to 200 MeV and \(40^\circ \) to \(120^\circ \). These would tightly constrain \(\gamma _{E1E1}-\gamma _{E1M2}\). New data on the differential cross section between 100 and 200 MeV and over a wide angle range will substantially improve constraints on \(\alpha _{E1}-\beta _{M1}\), \(\gamma _\pi \) and \(\gamma _{M1M1}-\gamma _{M1E2}\). Good signals also exist around 160 MeV for \(\Sigma _3\) and \(\Sigma _{2z^\prime }\). Such data will be pivotal in the continuing quest to pin down the scalar polarizabilities and refine understanding of the spin polarizabilities.

Extremely Sensitive Photonic Crystal Fiber–Based Cancer Cell Detector in the Terahertz Regime

A new photonic crystal fiber (PCF)–based, hollow-core, optical waveguide is proposed and numerically investigated to quickly identify numerous species of cancerous cells in the human body. Typical and cancerous cells have different refractive indices (RIs), and via this characteristic, the other important optical parameters are evaluated. The guiding properties of this proposed cancer cell sensor are analyzed in the COMSOL Multiphysics environment which used the finite element method as mathematical tool to solve differential equations. Furthermore, to ensure the highest simulation accuracy, extremely fine mesh elements are introduced. The simulation studies confirm that the proposed sensor, at 2.5 THz, achieves an extremely high relative sensitivity of almost 98% with negligible loss (< 0.025 dB/cm). Furthermore, a high numerical aperture (NA) and spot size, with low modal area, enhance the propagation characteristics of the sensor to a new height. The sensor’s physical structure is very simple so that it can be easily fabricated with modern fabrication technology. Thus, it seems that this sensor will open a new door in the field of detecting and diagnosing different cancer cells.

Patient-specific SPECT imaging protocols to standardize image noise

BackgroundIn addition to acquired photon counts, image noise depends on the image reconstruction algorithm. This work develops patient-specific activity or acquisition time protocols to standardize the average noise in a reconstructed image for different patients, cameras, and reconstruction algorithms. MethodsImage noise was calculated for images from 43 patients acquired on both a conventional and a multiple-pinhole cardiac SPECT camera. Functions were found to relate image noise to radiotracer activity, scan time, and body mass and were validated by normalizing the image noise in a test set of 58 patients. ResultsThere was a 3.6-fold difference in photon sensitivity between the two cameras but a 16-fold difference in activity-scan time was necessary to match the noise levels. Image noise doubled from 45 to 128 kg for the conventional camera (12.8 minutes) and tripled for the multiple-pinhole camera (5 minutes) for 350 MBq (9.5 mCi) 99mTc-tetrofosmin. It was 16.3% and 6.1% respectively for an average sized patient. ConclusionsA linear scaling of activity with respect to the patient weight normalizes image noise but the scaling factors depend on the choice of camera and image reconstruction parameters. Therefore, equivalent numbers of acquired photon counts are not sufficient to guarantee equivalent image noise.

Novel imaging technique for α-particles using a fast optical camera

A new imaging technique for α-particles using a fast optical camera focused on a thin scintillator is presented. As α-particles interact in a thin layer of LYSO fast scintillator, they produce a localized flash of light. The light is collected with a lens to an intensified optical camera, Tpx3Cam, with single photon sensitivity and excellent spatial & temporal resolutions. The interactions of photons with the camera is reconstructed by means of a custom algorithm, capable of discriminating single photons using time and spatial information.

Highly Sensitive D-Shaped Plasmonic Refractive Index Sensor for a Broad Range of Refractive Index Detection

In this paper, an extremely sensitive Photonic Crystal Fiber (PCF) based Surface Plasmon Resonance (SPR) sensor having D-shaped structure has been proposed. Gold has been used as the plasmonic material, and it has been coated outside of the fiber on its glassy surface to detect the change in the refractive index of the surrounding medium. Gold has been chosen as it is chemically stable and has no impact on the surrounding aqueous medium. Maximum Wavelength Sensitivity (WS) of 216,000 nm/RIU and Amplitude Sensitivity (AS) of 1680 RIU−1 have been achieved for the analyte refractive index range 1.23 to 1.42 by the proposed sensor. After conducting a detailed literature review in the relevant field, it has been revealed that the proposed sensor possesses the highest wavelength sensitivity among recently reported PCF-SPR sensors to this date. The proposed sensor also exhibits a resolution of 4.63 × 10−7 RIU and FOM of 1200. Consequently, the proposed sensor can become an ideal candidate in the field of biomedical sensing, chemical sensing, and other lower RI analytes sensing.

Temperature dependency of InGaAs/InP single photon avalanche diode for 1 550 nm photons

Single-photon detectors for the near-infrared wavelength region are receiving widespread attention in an increasing number of photon counting applications. In fields such as quantum information processing, quantum communication, 3-D laser ranging (LiDAR), time-resolved spectroscopy, etc. An InGaAs/InP single photon avalanche diode (SPAD) was designed and demonstrated to detect 1 550 nm wavelength photons in this paper. The SPAD has a separate absorption, grading, charge and multiplication region structure (SAGCM) with single photon sensitivity when working in Geiger-mode. The characterization of the SPAD include breakdown voltage, dark count rate, single photon detection efficiency and after pulse probability as functions of temperature from 223 to 293 K. The 25 μm diameter SPAD shows certain temperature dependency, with breakdown voltage dependence of approximately 100 mV/K. Operating at 223 K and in Geiger-mode, the SPAD achieves a photon detection efficiency of 21% at 1 550 nm with a dark count rate of 4.1 kHz and a after pulse probability of 3.29%. The source and physical mechanism of the photon detection efficiency, dark count rate and after pulse probability of the SPAD with temperature dependency were also analyzed and discussed. The mechanism analysis, discussion and calculation can provide more theoretical basis and support for the design and fabrication of SPAD.