Thin Detectors Research Articles

X-Ray Induced Secondary Particle Counting With Thin NbTiN Nanowire Superconducting Detector

We characterized the performance of abiased superconducting nanowire to detect X-ray photons. The device, made of a 10 nm thin NbTiN film and fabricated on a dielectric substrate ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$SiO_{2}$</tex-math></inline-formula> , Nb <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$_{3}$</tex-math></inline-formula> O <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$_{5}$</tex-math></inline-formula> ) detected 1000 times larger signal than anticipated from direct X-ray absorption. We attributed this effect to X-ray induced generation of secondary particles in the substrate. The enhancement corresponds to an increase in the flux by the factor of 3.6, relative to a state-of-the-art commercial X-ray silicon drift detector. The detector exhibited 8.25 ns temporal recovery time and 82 ps timing resolution, measured using optical photons. Our results emphasize the importance of the substrate in superconducting X-ray single photon detectors.

Development of a hard X-ray detector for measuring continuous spectra generated by runaway electrons in VEST

A hard X-ray measurement system is developed to observe the activities of runaway electrons in versatile experiment spherical torus (VEST) at Seoul National University. The detection system provides information on the generation of runaway electrons by detecting hard X-rays from its bremsstrahlung radiation. To acquire such information, the X-ray spectrum at several tens to hundreds of keV at the maximum is reconstructed using signals from four thin scintillation detectors with different energy sensitivities, and the spectrum is converted to the original X-ray energy. The unfolding process is implemented by an artificial neural network model trained using a measured X-ray spectrum generated by an X-ray tube source at 50 to 320 keV. The system would reveal the generation mechanism of runaway electrons during plasma discharges with various MHD activities in VEST to mitigate and suppress runaway electrons.

Thin cathode glass gas electron multiplier detector for carbon beam dose imaging

ABSTRACT An optically read-out glass gas electron multiplier (G-GEM) detector is expected to simplify complicated quality assurance measurements for hadron therapies by imaging the dose distribution of the incident beam. However, the effect of secondary particles from the detector itself has not been well studied. In this paper, we evaluate a design that reduces the secondary particles from the cathode of a G-GEM detector. Specifically, we assembled detectors with thin cathodes and assessed their effect on the secondary particle production in simulations and experiments. The experiments were carried out under 290 MeV/u 12C ion bombardment at the Heavy Ion Medical Accelerator in Chiba. The clinical intensity of the thin cathode detector was compared with that of a conventional thick cathode G-GEM detector. The improved chamber design reduced the dose contributions of secondary particles from the cathode without degrading the dose imaging performance.

Cadmium Zinc Telluride detectors for a next-generation hard X-ray telescope

We are currently developing Cadmium Zinc Telluride (CZT) detectors for a next-generation space-borne hard X-ray telescope which can follow up on the highly successful NuSTAR (Nuclear Spectroscopic Telescope Array) mission. Since the launch of NuSTAR in 2012, there have been major advances in the area of X-ray mirrors, and state-of-the-art X-ray mirrors can improve on NuSTAR’s angular resolution of ∼ 1arcmin Half Power Diameter (HPD) to 15” or even 5” HPD. Consequently, the size of the detector pixels must be reduced to match this resolution. This paper presents detailed simulations of relatively thin (1mm thick) CZT detectors with hexagonal pixels at a next-neighbor distance of 150 μm. The simulations account for the non-negligible spatial extent of the deposition of the energy of the incident photon, and include detailed modeling of the spreading of the free charge carriers as they move toward the detector electrodes. We discuss methods to reconstruct the energies of the incident photons, and the locations where the photons hit the detector. We show that the charge recorded in the brightest pixel and six adjacent pixels suffices to obtain excellent energy and spatial resolutions. The simulation results are being used to guide the design of a hybrid application-specific integrated circuit (ASIC)-CZT detector package.

Stochastic Modeling of Trees in Forest Environments

Our article deals with the detection and model generation of complex objects with curvilinear parts, like trees, with stochastic relaxation. The proposed algorithm can rely on any initial estimation of object parts as a probability map (like those generated by Gaussian mixture models or neural networks) and can model the relation of randomly sampled parts resulting in a structural representation of whole objects. Semantic segmentation by convolutional neural networks or the pose estimation with deep learning of object parts can predict the possible areas or positions of interest, but in many cases, a higher representation of structures is needed for further (e.g., shape or connectivity) analysis. The model validation of such data is straightforward for objects with known structure (like the human body or other rigid things) but tough for such complex objects like trees in forest environments. In our approach, the possible configurations of structures are generated by a marked point process while the optimal state is achieved by a solver based on reversible jump Markov chain Monte Carlo dynamics. The model generator relaxation method itself is unsupervised, no training is required, and our analyses show it has satisfactory stability, regarding detection accuracy, against changing its parameters. Besides giving the theoretical background and algorithmic steps, we present numerical evaluations on three datasets: synthetic trees, another of natural images with different species of trees in various forest environments, and the third is of road maps. The analyzed examples show that our approach, contrary to previous thin line detectors, can handle thin and thick objects.

Designing Ultraflexible Perovskite X-Ray Detectors through Interface Engineering.

X‐ray detectors play a pivotal role in development and advancement of humankind, from far‐reaching impact in medicine to furthering the ability to observe distant objects in outer space. While other electronics show the ability to adapt to flexible and lightweight formats, state‐of‐the‐art X‐ray detectors rely on materials requiring bulky and fragile configurations, severely limiting their applications. Lead halide perovskites is one of the most rapidly advancing novel materials with success in the field of semiconductor devices. Here, an ultraflexible, lightweight, and highly conformable passively operated thin film perovskite X‐ray detector with a sensitivity as high as 9.3 ± 0.5 µC Gy−1 cm−2 at 0 V and a remarkably low limit of detection of 0.58 ± 0.05 μGy s−1 is presented. Various electron and hole transporting layers accessing their individual impact on the detector performance are evaluated. Moreover, it is shown that this ultrathin form‐factor allows for fabrication of devices detecting X‐rays equivalently from front and back side.

A new detector for the beam energy measurement in proton therapy: a feasibility study

The proof of concept of a new device, capable of determining in a few seconds the energy of clinical proton beams by measuring the time of flight (ToF) of protons, is presented. The prototype consists of two thin ultra fast silicon detector (UFSD) pads, aligned along the beam direction in a telescope configuration and readout by a digitizer. The method developed for extracting the energy at the isocenter from the measured ToF, validated by Monte Carlo simulations, and the procedure used to calibrate the system are also presented and discussed in detail. The prototype was tested at the Centro Nazionale di Adroterapia Oncologica (CNAO, Pavia, Italy), at several beam energies, covering the entire clinical range, and using different distances between the sensors. The measured beam energies were benchmarked against the nominal CNAO energy values, obtained during the commissioning of the centre from the measured ranges in water. Deviations of few hundreds of keV have been achieved for all considered proton beam energies for distances between the two sensors larger than 60 cm, indicating a sensitivity to the corresponding beam range in water smaller than the clinical tolerance of 1 mm. Moreover, few seconds of irradiation were necessary to collect the required statistics. These preliminary results indicate that a telescope of UFSDs could achieve in a short time the accuracy required for the clinical application and therefore encourage further investigations towards the improvement and the optimization of the present prototype.

Measurements with silicon detectors at extreme neutron fluences1

Thin pad detectors made from 75 μm thick epitaxial silicon on low resistivity substrate were irradiated with reactor neutrons to fluences from 2.5× 1016 n/cm2 to 1× 1017 n/cm2. Edge-TCT measurements showed that the active detector thickness is limited to the epitaxial layer and does not extend into the low resistivity substrate even after the highest fluence. Detector current was measured under reverse and forward bias. The forward current was higher than the reverse at the same voltage but the difference gets smaller with increasing fluence. Rapid increase of current (breakdown) above ∼ 700 V under reverse bias was observed. An annealing study at 60̂C was made to 1200 minutes of accumulated annealing time. It showed that the reverse current anneals with similar time constants as measured at lower fluences. A small increase of forward current due to annealing was seen. Collected charge was measured with electrons from 90Sr source in forward and reverse bias configurations. Under reverse bias the collected charge increased linearly with bias voltage up to 6000 electrons at 2.5× 1016 n/cm2 and 3000 electrons at 1× 1017 n/cm2. Rapid increase of noise was measured above ∼ 700 V reverse bias due to breakdown resulting in worse S/N ratio. At low bias voltages slightly more charge is measured under forward bias compared to reverse. However better S/N is achieved under reverse bias. Effective trapping times were estimated from charge collection measurements under forward bias showing that at high fluences they are much longer than values extrapolated from low fluence measurements—at 1× 1017 n/cm2 a factor of 6 larger value was measured.

The development of the Front-End Boards for the small-strip Thin Gap Chambers detector system of the ATLAS Muon New Small Wheel upgrade

The ATLAS experiment at CERN is scheduled to replace the innermost station of its Muon Spectrometer in the forward region during its Phase-I upgrade in order to enhance the capabilities on triggering and tracking of high transverse momentum muons towards high luminosity LHC runs. The New Small Wheel (NSW), a completely new detector system to be built, is composed of two novel gaseous detectors: Micro-mesh Gaseous Structure (Micromegas) and the small-strip Thin Gap Chamber (sTGC). The sTGC sub-system is the primary trigger detector. It will be equipped with radiation-tolerant, low-latency electronics for reading out over 400,000 channels to identify the bunch crossing time of proton-proton collisions spaced by 25 ns, as well as to collect fine strip charge information for the charged track reconstruction. In this paper, we present the design and development of a set of Front-End Boards (FEBs) for the sTGC detector system. The major challenges in the design will be discussed. These include the accommodation of a few hundred readout channels per single board in a very constrained space, a tight requirement for the Electrostatic Discharge (ESD) protection of 130 nm ASICs, and customized analog input circuits to handle the high rate and high charge signals from the sTGC detectors. Moreover, the FEBs have to incorporate a few hundred parallel inter-chip links at 320 Mbps and several low-latency serial links operating at 4.8 Gbps for the Level-1 and trigger data readout. The characterization of the FEBs performance, both off-detector and on-detector, will be shown.

In-silico optimisation of tileable philips digital SiPM based thin monolithic scintillator detectors for SPECT applications

Over the last decade one of the most significant technological advances made in the field of radiation detectors for nuclear medicine was the development of Silicon Photomultipler (SiPM) sensors. At present only a small number of SiPM based radiation detectors for Single Photon Emission Computed Tomography (SPECT) applications have been explored, and even fewer experimental prototypes developed. An in-silico investigation into the optimal design of a Philips DPC3200 SiPM photosensor-based thin monolithic scintillator detector for SPECT applications was undertaken using the Monte Carlo radiation transport modelling toolkit Geant4 version 10.5. The performance of the 20 different SPECT radiation detector configurations, 4 scintillator materials (NaI(Tl), GAGG(Ce), CsI(Tl) and LaBr3(Ce)) and 5 thicknesses (1–5 mm), were determined through the use of seven figures of merit. It was found that a crystal thickness range of 4–5 mm was required for all four materials to ensure acceptable energy resolution, sensitivity and spatial resolution performance with the Philips DPC3200 SiPM. Any thinner than this and the performance of all four materials was found to degrade rapidly due to a high probability of material specific fluorescence x-ray escape after incident gamma/x-ray photoelectric absorption. When factoring in each material's magnetic resonance imaging compatibility, hygroscopy, and cost, it was found that CsI(Tl) represents the most promising material to construct tileable Philips digital SiPM based thin monolithic scintillator detectors for SPECT applications.

Test of innovative silicon detectors for the monitoring of a therapeutic proton beam

Beam monitoring in particle therapy is a critical task that, because of the high flux and the time structure of the beam, can be challenging for the instrumentation. Recent developments in thin silicon detectors with moderate internal gain, optimized for timing applications (Ultra Fast Silicon Detectors, UFSD), offer a favourable technological option to conventional ionization chambers. Thanks to their fast collection time and good signal-to-noise ratio, properly segmented sensors allow discriminating and counting single protons up to the high fluxes of a therapeutic beam, while the excellent time resolution can be exploited for measuring the proton beam energy using time-of-flight techniques. We report here the results of the first tests performed with UFSD detector pads on a therapeutic beam. It is found that the signal of protons can be easily discriminated from the noise, and that the very good time resolution is confirmed. However, a careful design is necessary to limit large pile-up inefficiencies and early performance degradation due to radiation damage.

Thin low-gain avalanche detectors for particle therapy applications

The University of Torino (UniTO) and the National Institute for Nuclear Physics (INFN-TO) are investigating the use of Ultra Fast Silicon Detectors (UFSD) for beam monitoring in radiobiological experiments with therapeutic proton beams. The single particle identification approach of solid state detectors aims at increasing the sensitivity and reducing the response time of the conventional monitoring devices, based on gas detectors. Two prototype systems are being developed to count the number of beam particles and to measure the beam energy with time-of-flight (ToF) techniques. The clinically driven precision (< 1%) in the number of particles delivered and the uncertainty < 1 mm in the depth of penetration (range) in radiobiological experiments (up to 108 protons/s fluxes) are the goals to be pursued. The future translation into clinics would allow the implementation of faster and more accurate treatment modalities, nowadays prevented by the limits of state-of-the-art beam monitors. The experimental results performed with clinical proton beams at CNAO (Centro Nazionale di Adroterapia Oncologica, Pavia) and CPT (Centro di Protonterapia, Trento) showed a counting inefficiency <2% up to 100 MHz/cm2, and a deviation of few hundreds of keV of measured beam energies with respect to nominal ones. The progresses of the project are reported.

On-chip fluorescence sensing for fluidics platforms using thin film silicon photodetectors.

The integration of fluorescence sensing directly into the fluidic channel in lab-on-a chip systems using thin film Si detectors enables on-chip multi-target medical diagnostics and biochemical analyses. This paper reports on the experimental demonstration and theoretical analysis of a filter-free thin film fluorescence sensor designed for integration into the channel of a fluidic platform. Static tests of this optical sensor show repeatable detection of 6-Hex fluorophore concentrations from 300 nM to 20 µM, with an average signal-to-noise ratio of 26 dB-50 dB, which agrees well with the theoretical model.

Beam Monitors for Tomorrow: The Challenges of Electron and Photon FLASH RT

The emergent FLASH RadioTherapy (RT) uses ultrahigh dose-rate irradiation (up to 107 Gy/s instantaneous dose-rate in each μs pulse) to deliver a single high dose of irradiation in a very short time (less than 200 milliseconds). Pre-clinical studies at ultrahigh dose-rates recently showed an increased ratio between tumoricidal effect and normal tissue toxicity (therapeutic index), compared to conventional RT at standard Gy/min dose-rates. If confirmed by biological in vivo validations, this could represent a breakthrough in cancer treatment. However, the reliability and the accuracy of experimental studies are nowadays limited by the lack of detectors able to measure online the beam fluence at FLASH dose-rates. The behaviour of standard beam monitors (gas-filled ionization chambers) is compromised by the volume recombination caused by the amount of charges created per unit volume and unit time, due to the large dose-rate. Moreover, due to the lack of proper monitoring devices and to the uncertainties of its future applications, very few facilities are able to deliver at present FLASH irradiations. In this contribution, we report about the physical and technological challenges of monitoring high and ultra-high dose-rates with electrons and photon beams, starting from the pre-clinical and clinical constraints for new devices. Based on the extensive experience in silicon detectors for monitoring applications in RT with external beams, the work then investigates silicon sensors as a possible option to tackle such extreme requirements and a rugged thin and large (e.g. 10×10 cm2) flat detector (silicon-based sensor + readout electronics) is therefore outlined. This study aims at presenting the FLASH-RT dosimetry problem and analysing the possibilities for a silicon sensor to be employed as sensing device for several FLASH scenarios, including some ideas on the readout part. However, more detailed simulations and studies are demanded to delineate more precisely the technical choices to be undertaken in order to tackle the clinical accuracy required on the beam fluence, typically a few %, during photon and electron high and ultra-high irradiations, the required minimal perturbation of the beam and the high level of radiation resistance.

Experimental determination of the induced activity in activation detectors of a complex geometric shape

The paper presents the results of experimental determination of the induced activity in copper-/aluminum-based activation detectors when irradiated with neutrons with energies of about 14 MeV. The activation detectors were square-shaped metal plates with a thickness from 1.0 to 1.5 mm and a side size about 5.0 cm. These dimensions significantly exceed those of the detectors that are used in the research of high-intensity neutron fluxes. The detectors described in this work can be used for studying low-intensity neutron fluxes (with a flux density of up to 106n/cm2∙s). It is shown that, when working with such detectors, it is possible to apply the usual methods for calculating the induced activity in thin activation detectors, with corrections that take into account the emerging features of the ‘neutron source - activation detector’ and ‘activation detector - secondary radiation detector’ geometries. The effects of absorption of primary and secondary radiation by the detector substance are also revealed.The Geant4 tools were used for calculating the geometric factors and theoretical induced activity. The study confirms the applicability of such activation detectors for solving the problem of determining the yield of neutrons with energies of about 14 MeV from a neutron generator target. The results of the experiments coincide, within the margin of error, with the results of simulations performed using the Geant4 tools.

Tracker-In-Calorimeter (TIC): a calorimetric approach to tracking gamma rays in space experiments

A multi-messenger, space-based cosmic ray detector for gamma rays and charged particles poses several design challenges due to the different instrumental requirements for the two kind of particles. Gamma-ray detection requires layers of high Z materials for photon conversion and a tracking device with a long lever arm to achieve the necessary angular resolution to separate point sources; on the contrary, charge measurements for atomic nuclei requires a thin detector in order to avoid unwanted fragmentation, and a shallow instrument so to maximize the geometric factor. In this paper, a novel tracking approach for gamma rays which tries to reconcile these two conflicting requirements is presented. The proposal is based on the Tracker-In-Calorimeter (TIC) design that relies on a highly-segmented calorimeter to track the incident gamma ray by sampling the lateral development of the electromagnetic shower at different depths. The effectiveness of this approach has been studied with Monte Carlo simulations and has been validated with test beam data of a detector prototype.

Annealing effects on operation of thin Low Gain Avalanche Detectors

Several thin Low Gain Avalanche Detectors from Hamamatsu Photonics were irradiated with neutrons to different equivalent fluences up to Φeq=3⋅1015 cm−2. After the irradiation they were annealed at 60̂C in steps to times 0>2000 minutes. Their properties, mainly full depletion voltage, gain layer depletion voltage, generation and leakage current, as well as their performance in terms of collected charge and time resolution, were determined between the steps. It was found that the effect of annealing on timing resolution and collected charge is not very large and mainly occurs within the first few tens of minutes. It is a consequence of active initial acceptor concentration decrease in the gain layer with time, where changes of around 10% were observed. For any relevant annealing times for detector operation the changes of effective doping concentration in the bulk negligibly influence the performance of the device, due to their small thickness and required high bias voltage operation. At very long annealing times the increase of the effective doping concentration in the bulk leads to a significant increase of the electric field in the gain layer and, by that, to the increase of gain at given voltage. The leakage current decreases in accordance with generation current annealing.

78‐3: Distinguished Paper: Vein Detection with Near‐infrared Organic Photodetectors for Biometric Authentication

We combine a near‐infrared (NIR) sensitive organic photodetector with a high‐resolution 508 ppi oxide TFT backplane to create a large‐area thin NIR detector. Using a NIR light source the detector is capable of imaging the (pattern of) veins under the skin in reflection, leading to improved biometric authentication.

Thin layer chromatography performed in stages to identify the presence of aromatic like fraction in chosen bitumen modifiers

The organic modifiers are used to alter the rheology of the binder in the asphalt concrete at an added cost. For quality control purpose, recognizing if such material is present in the final blend is of an interest. The thin layer chromatography (TLC) using a flame photometric detector (FPD), in addition to the typical flame ionization detector, was demonstrated hereby as a potential analytical tool for this problem, differentiating between tall crude oil based anti-aging agent, polymer, oxidized bitumen and gilsonite. Gilsonite and anti-aging agent consists of the material soluble in solvent used in the development of the fraction referred to as aromatics. Due to the hindered mobility of modifier molecules on the stationary phase, the elution of aromatic fraction stops at position convoluted with polars I and polars II fraction regions, colloquially referred to as resins and asphaltenes. However, for the color of this fraction within gilsonite is different. The presence of gilsonite is thus identifiable visually after the second development bath, but also to an extent with FPD from the final chromatogram. The thin layer chromatography-flame ionization detectors (TLC-FID) procedure is suggested to be supplemented by infrared spectroscopy to discriminate between non-bituminous and bituminous modifiers of similar response during fractionation. • The analysis of thin layer chromatography of bitumen performed in stages. • The procedure to distinguish gilsonite in blends with bitumen is suggested. • The hidden aromaticity of materials such as gilsonite and rejuvenators based on their response to a solvent is demonstrated.

Energy straggling and an experimental investigation of Bragg's rule for 241Am alpha particles in air and its constituents

We present here energy straggling data for alpha particles from 241Am in air and its constituents, and an experimental investigation of Bragg’s rule. High resolution alpha spectroscopy system from ORTEC with an ultra-thin source, an ion implanted thin entrance window detector of small diameter, and state of the art counting electronics with a 4096 MCA is used. In the controlled experimental environment gases of 5N purity are used to measure energy straggling. Measured values are compared with the theoretical predictions of Bohr, Bethe-Livingston, Titeica and Yang et. al. An experimental investigation on using Bragg’s rule to estimate the energy straggling in air from the experimental obtained data of constituents is presented.