High-energy Photon Detection Research Articles

Efficient Carrier Multiplication in Self-Powered Near-Ultraviolet γ-InSe/Graphene Heterostructure Photodetector with External Quantum Efficiency Exceeding 161.

Carrier multiplication (CM) in semiconductors, the process of absorbing a single high-energy photon to form two or more electron-hole pairs, offers great potential for the high-response detection of high-energy photons in the ultraviolet spectrum. However, compared to two-dimensional semiconductors, conventional bulk semiconductors not only face integration and flexibility bottlenecks but also exhibit inferior CM performance. To attain efficient CM for ultraviolet detection, we designed a two-terminal photodetector featuring a unilateral Schottky junction based on a two-dimensional γ-InSe/graphene heterostructure. Benefiting from a strong built-in electric field, the photogenerated high-energy electrons in γ-InSe, an ideal ultraviolet light-absorbing layer, can efficiently transfer to graphene without cooling. It results in efficient CM within the graphene, yielding an ultrahigh responsivity of 468 mA/W and a record-high external quantum efficiency of 161.2% when it is exposed to 360 nm light at zero bias. This work provides valuable insights into developing next-generation ultraviolet photodetectors with high performance and low-power consumption.

New Inogranic Scintillators’ Application in the Electromagnetic Calorimetry in High-Energy Physics

Scintillation crystals Gd3Al2Ga3O12 (GAGG) are an excellent candidate for application in ionizing-radiation detectors because of their high radiation resistance, density and light yield. These crystals can be used in combination with lead tungstate (PbWO4 or PWO) crystals for the development of a new generation of electromagnetic calorimeter with advanced spatial and energy resolutions in a broad energy range. PWO crystals enable the accurate detection of high-energy photons, while GAGG crystals provide the possibility of precisely measuring photon energies, down to a few MeV. Different options for a composite electromagnetic calorimeter based on PWO and GAGG crystals are considered to optimize spatial and energy resolutions in a broad energy range (from 1 MeV to 100 GeV). In particular, different lengths of the GAGG section of the calorimeter are considered, from 0.5 to 10 cm. The separation of signals from photons and hadrons is also taken into consideration through the study of shower shape in the calorimeter. The optimization is based on Geant4 simulations, considering light collection as well as the use of different photodetectors and electronic noise. Simulations are verified with light yield measurements of GAGG samples obtained using radioactive sources and test beam measurements of the prototype of the PWO-based Photon Spectrometer of the ALICE experiment at CERN.

Large-area TaN superconducting microwire single photon detectors for X-ray detection.

With the development of superconducting nanowire single photon detectors, increasing numbers of important applications are being explored, covering not only low-energy optical photon detection but also high-energy photon and particle detection. In this work, 100-nm-thick TaN superconducting microwire single photon detectors (SMSPDs) with large active areas were prepared for X-ray detection, and their response characteristics to X-rays were studied. The results showed that our TaN SMSPDs were able to detect X-rays at a wide range of bias currents and working temperatures. The detectors could distinguish different energy X-rays under suitable working conditions, and the energy resolving power was strongly related to the bias current.

Monte Carlo Modeling and Design of Photon Energy Attenuation Layers for >10× Quantum Yield Enhancement in Si-Based Hard X-ray Detectors

High-energy (>20 keV) X-ray photon detection at high quantum yield, high spatial resolution, and short response time has long been an important area of study in physics. Scintillation is a prevalent method but limited in various ways. Directly detecting high-energy X-ray photons has been a challenge to this day, mainly due to low photon-to-photoelectron conversion efficiencies. Commercially available state-of-the-art Si direct detection products such as the Si charge-coupled device (CCD) are inefficient for >10 keV photons. Here, we present Monte Carlo simulation results and analyses to introduce a highly effective yet simple high-energy X-ray detection concept with significantly enhanced photon-to-electron conversion efficiencies composed of two layers: a top high-Z photon energy attenuation layer (PAL) and a bottom Si detector. We use the principle of photon energy down conversion, where high-energy X-ray photon energies are attenuated down to ≤10 keV via inelastic scattering suitable for efficient photoelectric absorption by Si. Our Monte Carlo simulation results demonstrate that a 10–30× increase in quantum yield can be achieved using PbTe PAL on Si, potentially advancing high-resolution, high-efficiency X-ray detection using PAL-enhanced Si CMOS image sensors.

Unveiling the broad-band spectral and temporal properties of PKS 0903-57 during its brightest flare

ABSTRACT We carried a detailed spectral and temporal study of blazar PKS 0903-57 using the Fermi-LAT and Swift-XRT/UVOT observations, during its brightest flaring period MJD 58931–58970. During this period, the maximum daily averaged γ-ray flux ($\rm F_{0.1-500\, GeV}$) of $\rm 9.42\times 10^{-6}\, ph\, cm^{-2}\, s^{-1}$ is observed on MJD 58951.5, the highest γ-ray flux detected from PKS 0903-57 till now. Several high-energy (HE) photons ($\gt 10$ GeV) consistent with the source location at high probability (>99 per cent) are detected, and the γ-ray light curve in the active state shows multiple substructures with asymmetric profile. In order to understand the possible physical scenario responsible for the flux enhancement, we carried a detailed broad-band spectral study of PKS 0903-57 by choosing different flux states from its active period. Neglecting the multiband variability in each of the selected time intervals, we could reproduce their averaged broad-band SEDs with a one-zone leptonic model whose parameters were derived with a χ2-fit. We found that the broad-band SED during different flux states can be reproduced by the synchrotron, synchrotron-self-Compton (SSC), and external-Compton (EC) processes. The seed photons for EC process from BLR or IR torus provide acceptable fits to the GeV spectrum in all the flux states; however, the detection of HE photons together with the equipartition condition suggests that the EC/IR process is a more likely scenario. Further, a detailed comparison between the fit parameters shows that the flux enhancement from quiescent-state to the flaring-state is mostly related to increase in the bulk Lorentz factor of the emission region and change in the break energy of the source spectrum.

Tuning the Structural and Optoelectronic Properties of Cs2 AgBiBr6 Double-Perovskite Single Crystals through Alkali-Metal Substitution.

Lead-free double perovskites have great potential as stable and nontoxic optoelectronic materials. Recently, Cs2 AgBiBr6 has emerged as a promising material, with suboptimal photon-to-charge carrier conversion efficiency, yet well suited for high-energy photon-detection applications. Here, the optoelectronic and structural properties of pure Cs2 AgBiBr6 and alkali-metal-substituted (Cs1- x Yx )2 AgBiBr6 (Y: Rb+ , K+ , Na+ ; x= 0.02) single crystals are investigated. Strikingly, alkali-substitution entails a tunability to the material system in its response to X-rays and structural properties that is most strongly revealed in Rb-substituted compounds whose X-ray sensitivity outperforms other double-perovskite-based devices reported. While the fundamental nature and magnitude of the bandgap remains unchanged, the alkali-substituted materials exhibit a threefold boost in their fundamental carrier recombination lifetime at room temperature. Moreover, an enhanced electron-acoustic phonon scattering is found compared to Cs2 AgBiBr6 . The study thus paves the way for employing cation substitution to tune the properties of double perovskites toward a new material platform for optoelectronics.

A model for the jitter of avalanche photodiodes with separate absorption and multiplication regions

An improved version of the Random Path Length algorithm is used to simulate the time response of Separate Absorption and Multiplication Avalanche PhotoDiodes (SAM-APDs) in the linear regime. The model takes into account both the diffusion and the drift of carriers in the absorption region as well as impact ionization scattering events in the multiplication region. An extended formulation of Ramo’s theorem is used to determine the current waveforms. The new algorithm has been used to extract the jitter of the time response of avalanche photodiodes to photons, which is a relevant figure of merit for time of flight applications of SAM-APDs. It is found that an electric field in the absorption region small enough to avoid unwanted carrier multiplication or band-to-band tunneling, is beneficial to reduce the jitter. Furthermore, we have found that, in APDs working in the linear regime, the stochastic duration of the current pulse makes difficult the use of circuit techniques, such as crossover timing, with constant delay lines aimed at detecting the individual pulses. The problem is partly mitigated when SAM-APDs are used for the detection of high energy photons, such as X-rays.

Development of Fast Scintillators for High-Energy Photon Detection

Development of Fast Scintillators for High-Energy Photon Detection

Morphology evolution and degradation of methylammonium lead iodide under accelerated electron beam with energy of 1.8 MeV

Consideration the application of perovskite material in high-energy photon detection, investigation of high-energy photons interactions with perovskite material is necessary. Here, we reported a study of high-energy electron beam (1.8 MeV) induced physical transformation in perovskite (CH3NH3PbI3) thin film. The effect of irradiation dose on physics properties of perovskite was considered as well. Through investigating the transformation of morphology, crystal structure, optical and electronic properties of perovskite thin film under different photon irradiation condition, we found that high-energy electron beam induced partial morphology defects and phase transformation.

First Cerenkov charge-induction (CCI) TlBr detector for TOF-PET and proton range verification

Thallium bromide (TlBr) is a semiconductor material and, simultaneously, a good Cerenkov radiator. The performance of a TlBr detector that integrates two different readouts, the charge induction readout and the detection of Cerenkov light, was evaluated. A TlBr detector with dimensions of 4 × 4 × 5 mm3, with a monolithic cathode and an anode segmented into strips, was manufactured. One of the bare and polished 4 × 4 mm2 faces of the detector was coupled to a silicon photomultiplier (SiPM) to read out the Cerenkov light. Simultaneous timing and energy resolutions of <400 ps full width at half maximum (FWHM) and ~8.5% at 511 keV were measured using the Cerenkov detection and charge induction readouts, respectively. A coincidence time resolution of 330 ps was obtained when selecting Cerenkov events with amplitudes above 70 mV. The combination of both readouts showed the potential to resolve the depth-of-interaction (DOI) positioning, based on the improvement of energy resolution when selecting events with similar electron drift times. This manuscript sets the stage for a new family of semiconductor detectors that combine charge induction readout with the Cerenkov light detection. Such detectors can provide, simultaneously, outstanding timing, energy, and spatial resolution, and will be an excellent fit for applications that require the detection of high-energy gamma photons with high timing accuracy, such as time-of-flight positron emission tomography (TOF-PET) and prompt gamma imaging (PGI) to assess the particle range in hadron therapy.

Possible detection of high-energy photons from ball lightning.

It is shown that photons of the prolonged emission recorded by the Gamma-Ray Observation of Winter Thunderclouds (GROWTH) experiment on January 13, 2012 [D. Umemoto etal., Phys. Rev E 93, 021201(R) (2016)10.1103/PhysRevE.93.021201] could be emitted by ball lightning and generated by annihilation of positrons which arose mainly due to production of the β^{+}-active isotopes by the sharp γ-ray flash, accompanying the formation of ball lightning, and production of electron-positron pairs by photons from ball lightning. The model of ball lightning is based on the assumption that ball lightning has a core consisting of clouds of electrons and almost totally ionized ions which oscillate with respect to each other.

Time-resolved, nonequilibrium carrier and coherent acoustic phonon dynamics in (Cd, Mg)Te single crystals for radiation detectors

We present time-resolved nonequilibrium carrier and coherent acoustic phonon dynamics in (Cd, Mg)Te single crystals intended for detection of high-energy x-ray photons. Our (Cd, Mg)Te crystals were grown using a vertical Bridgman method and during the process were doped either with In (a shallow dopant) or Ge (a deep impurity). Next they were cut into platelets and, subsequently, tested as as-grown specimens, or, before testing, long-term annealed in a temperature range of 750 °C–800 °C to improve their crystalline properties. All samples exhibited high resistivities of 109–1010 Ω cm, as required for x-ray detection applications. We have performed femtosecond optical spectroscopy, pump-probe measurements on all samples in both one-color (high-intensity 800 nm pump and low-intensity 800 nm probe) and two-color (high-intensity 400 nm pump and low-intensity 800 nm probe) configurations, and analyzed the results using our carrier dynamics rate-equation model. The model allowed us to perform a comprehensive, time-resolved analysis of relaxation dynamics of photoexcited carriers and investigate the role of carrier traps present in all tested samples. Two-color measurements also allowed us to observe and analyze the propagation of acoustic coherent phonons excited by the high-energy pump pulse. We observed that the dependence of phonon mode frequency, after including a correction of the experimentally measured crystal index of refraction dependence on the probe wavelength, was dispersionless and led to the value for the sound velocity of 3367 m s−1, which is in excellent agreement with the literature data. The intrinsic lifetime of coherent phonons in (Cd, Mg)Te was estimated to be of the order of 10 ns. Finally, we conclude that among our tested samples, the In-doped, annealed (Cd, Mg)Te crystal exhibits the best characteristics for radiation detection applications.

Free ion yield of trimethyl bismuth used as sensitive medium for high-energy photon detection

The CaLIPSO project is an innovative high-energy photon detector concept using trimethylbismuth as sensitive medium in a liquid ionization chamber. The detector, designed for high precision brain PET imaging, works as a time-projection chamber and detects Cherenkov light and charge signal. We measured the free ion yield of trimethylbismuth, which represents the number of electron-ion pairs released by the incident photon. To do so, we developed a low-noise measuring system to determine the current induced by a \\Co source in the liquid with an accuracy better than 5 fA for an electric field up to 7 kV/cm. We used tetramethylsilane as benchmark liquid to validate the apparatus and we measured a zero-field free ion yield of 0.53 ± 0.03 in agreement with measurements in literature. However, we found a zero-field free ion yield of 0.083 ± 0.003 for trimethylbismuth, which is a factor 7 lower than the typical values for similar dielectric liquids. Quantum chemistry computations on heavy atoms tend to demonstrate a high capacity of trimethylbismuth to capture electrons which could explain the weak value. The consequences of a low free ion yield in terms of high-energy photon detection and brain PET imaging are finally discussed.

Improved Crystal Growth of Tl6SeI4 for γ-Ray Detection Material by Oxide Impurity Removal

Tl6SeI4 is a promising wide-bandgap semiconductor for room-temperature high-energy photon detection. Because of the air-sensitive Tl precursor or Tl-based binary precursors used in the synthesis, this material can contain deleterious Tl oxide impurities. These impurities lead to problems during syntheses and crystal growth including glass attack, tube rupture, and parasitic nucleation, which subsequently deteriorate detector performance. In this work, we present a facile way to chemically reduce Tl oxides and eliminate oxygen impurities in Tl6SeI4 by adding high-purity graphite powder during synthesis. The addition of carbon leads to reduction of the residual Tl oxides and formation of CO2 and CO. The resistivity and hard radiation detection performance for 122 keV γ-rays of Tl6SeI4 single crystals were significantly improved. The improvement in the crystallinity was also confirmed by a narrower near-band-edge emission band in the photoluminescence spectra. We confirmed that the reaction between Tl oxide ...

Interaction of 662 keV Gamma Rays with LYSO(Ce) and BGO Single Crystal Scintillators

The study of photon interactions with matter is very important in many fields such as scientific, industry, medical imaging, biological applications, dosimetry, and radiation shielding for their potential use in radiation physics. Scintillating materials become a main part in detection and spectroscopy of high energy photons. The goal of this work is to study an interaction of 662 keV γ-rays with scintillating materials, namely the LYSO(Ce) and BGO crystals. The light output, energy resolution, intrinsic resolution, and photo-fraction of both crystals with the same size of 5x5x3 mm3 were measured using photomultiplier tube (PMT) readout. The result showed that the light yield of the LYSO(Ce) crystal is much more better than that of the BGO crystal, while its photo-fraction is worse than that of the BGO crystal.

Scintillation Properties of Ce-Doped LuYAP Crystal for Gamma Ray Detection

In the present day, inorganic scintillating crystals become a main part in detection and spectroscopy of nuclear particles and high energy photons, more spectively in X/g-ray imaging. The good properties for the scintillating crystals used in these applications require high photon yield, high stopping power, good energy resolution, good light yield proportionality, and minimal afterglow. The main useful of Ce-doped Lu0.7Y0.3AlO3 (LuYAP(Ce)) are high stopping power and non-hygroscopic which are expected to be key ingredients for medical imaging. In this work, we studied the light yield non-proportionality and energy resolution of LuYAP(Ce) crystal with the energy range from 31 to 1,274.5 keV using photomultiplier tube (PMT) readout. The intrinsic resolution of the LuYAP(Ce) crystal has been determined after correcting the measured PMT resolution. The results showed that the non-proportional response of the crystals was strongly correlated with the intrinsic resolution of the crystals.

Properties of Garnet Ceramic Scintillators

Garnet-based ceramics have applications as downconverters in LED lighting, laser media, and as scintillators for the detection of high energy photons. In this presentation, we will discuss the properties of Ce3+-doped garnet ceramics within the context of their applicability in computerized tomography (CT) scanners. CT scintillator requirements are different versus those for PET and applications that require energy resolution due to the need to reducing both afterglow at various timeframes and radiation damage while having reduced transparency requirements. Therefore, we will discuss how we can modify garnet composition and processing in order to meet some of these requirements. These modifications in process and composition can also give some insight towards some of the potential defects that are responsible for worse (or better) garnet scintillators. Finally, we will address some of the potential paths for future research and development.

X-Ray Imaging Using LEKIDs

We present the detection of 5.9 keV X-rays in a silicon wafer utilising an array of frequency multiplexed Kinetic Inductance Detectors. The readout electronics consists of a programmable digital electronics with an integrated 12-bit ADC, operating with a maximum frequency of 100 MHz. We implement a lumped element geometry, realising pixels as small as possible in order to achieve better position resolution. The whole system allows the simultaneous readout of 14 pixels with a bandwidth of 300 kHz, but it is easily scalable up to 100 pixels. A higher bandwidth detection, with less pixels, allows the reconstruction of the photon absorption position in the substrate up to hundreds of microns. This technological development could be applied in the next future to large area X-Ray Imaging. A better understanding of high energy photon and particle detection is also crucial for the space implementation of LEKIDs for mm-astronomy, where data loss due to Cosmic particles could be a major issue.

The AMS-02 RICH detector: Performance during ground-based data taking at CERN

The Alpha Magnetic Spectrometer (AMS), whose final version AMS-02 is to be installed on the International Space Station (ISS) in 2011, is a detector designed to measure charged cosmic ray spectra with energies up to the TeV region and with high energy photon detection capability up to a few hundred GeV, using state-of-the art particle identification techniques. Among several detector subsystems, AMS includes a proximity focusing RICH detector enabling precise measurements of particle electric charge (charge identification up to the iron region) and velocity ( Δ β / β ∼ 10 − 3 for Z=1, Δ β / β ∼ 10 − 4 for Z=10–20). The optimization of the RICH reconstruction efficiency imposed a dual radiator configuration with 16 NaF tiles ( n=1.33) in the centre and 92 aerogel tiles ( n=1.050) in the outer region, a pixelized detection matrix with 680 Hamamatsu R7600-M16 photomultipliers (each with 4×4 pixels) and a highly reflective conical mirror to increase photon collection. After its assembly at CIEMAT in Madrid, the RICH was taken to CERN in January 2008 and integrated into the full AMS-02 detector. AMS-02 underwent a pre-assembly in 2008 without magnet followed by a second detector assembly with a superconducting magnet in 2009 and the final assembly with a permanent magnet in mid-2010. Cosmic events were acquired in the context of the 2008 pre-assembly and in 2009, and two beam tests from CERN SPS took place in 2010. Results obtained with data from ground-based tests on the RICH performance are presented. A comparison with the aerogel light yield obtained on previous beam tests with a prototype detector is also discussed.

The Gamma Ray Imaging Detector of the AGILE satellite: A novel application of silicon trackers for detection of astrophysics high-energy photons

AGILE is a project of the Italian Space Agency (ASI) Scientific Program dedicated to Gamma ray astrophysics. It is designed to be a very light and compact instrument, capable of photon detections and imaging in both the 30 MeV–50 GeV and 18–60 keV energy ranges, with a large field of view (FOV is ∼3 and ∼1 sr, respectively). The core of the instrument (launched on April 23, 2007 from the Indian Space Research Organization's launch facility) is represented by the Gamma Ray Imaging Detector (GRID), which is a silicon tracker developed by the Italian National Institute of Nuclear Physics (INFN), with a spatial resolution of ∼40 μ m. The GRID performances have been studied by means of a GEANT Montecarlo, and tested with a dedicated calibration campaign using the tagged gamma beam available at Beam Test Facility (BTF) of INFN Frascati Laboratory.