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At least 739 records · Page 41
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Emergence of Uranium as a Distinct Metal Center for Building Intrinsic X‐ray Scintillators

Abstract The combination of high atomic number and high oxidation state in U VI materials gives rise to both high X‐ray attenuation efficiency and intense green luminescence originating from ligand‐to‐metal charge transfer. These two features suggest that U VI materials might act as superior X‐ray scintillators, but this postulate has remained substantially untested. Now the first observation of intense X‐ray scintillation in a uranyl–organic framework ( SCU‐9 ) that is observable by the naked eye is reported. Combining the advantage in minimizing the non‐radiative relaxation during the X‐ray excitation process over those of inorganic salts of uranium, SCU‐9 exhibits a very efficient X‐ray to green light luminescence conversion. The luminescence intensity shows an essentially linear correlation with the received X‐ray intensity, and is comparable with that of commercially available CsI:Tl. SCU‐9 possesses an improved X‐ray attenuation efficiency ( E >20 keV) as well as enhanced radiation resistance and decreased hygroscopy compared to CsI:Tl.

Wang, Yaxing↗
DOE OSTI2017

Toward Scintillator High‐Gain Avalanche Rushing Photoconductor Active Matrix Flat Panel Imager ( SHARP ‐ AMFPI ): Initial fabrication and characterization

Purpose We present the first prototype Scintillator High‐Gain Avalanche Rushing Photoconductor Active Matrix Flat Panel Imager ( SHARP ‐ AMFPI ). This detector includes a layer of avalanche amorphous Selenium (a‐Se) ( HARP ) as the photoconductor in an indirect detector to amplify the signal and reduce the effects of electronic noise to obtain quantum noise‐limited images for low‐dose applications. It is the first time avalanche a‐Se has been used in a solid‐state imaging device and poses as a possible solution to eliminate the effects of electronic noise, which is crucial for low‐dose imaging performance of AMFPI . Methods We successfully deposited a solid‐state HARP structure onto a 24 × 30 cm 2 array of thin‐film transistors ( TFT array) with a pixel pitch of 85 μm. The HARP layer consists of 16 μm of a‐Se with a hole‐blocking and electron‐blocking layer to prevent charge injection from the high‐voltage bias and pixel electrodes, respectively. An electric field ( E S e ) up to 105 V μm −1 was applied across the a‐Se layer without breakdown. A 150 μm thick‐structured CsI:Tl scintillator was used to form SHARP ‐ AMFPI . The x‐ray imaging performance is characterized using a 30 kV p Mo/Mo beam. We evaluate the spatial resolution, noise power, and detective quantum efficiency at zero frequency of the system with and without avalanche gain. The results are analyzed using cascaded linear system model ( CLSM ). Results An avalanche gain of 76 ± 5 was measured at E S e = 105 V μm −1 . We demonstrate that avalanche gain can amplify the signal to overcome electronic noise. As avalanche gain is increased, image quality improves for a constant (0.76 mR ) exposure until electronic noise is overcome. Our system is currently limited by poor optical transparency of our high‐voltage electrode and long integrating time which results in dark current noise. These two effects cause high‐spatial frequency noise to dominate imaging performance. Conclusions We demonstrate the feasibility of a solid‐state HARP x‐ray imager and have fabricated the largest active area HARP sensor to date. Procedures to reduce secondary quantum and dark noise are outlined. Future work will improve optical coupling and charge transport which will allow for frequency DQE and temporal metrics to be obtained.

Scheuermann, James R.↗
DOE OSTI2025

High-precision Measurement of the 16 O($n, n'γ$) Cross Section using $γ$-ray Detection in Liquid Scintillators with H 2 O and BeO Targets

The 16 O($n, n'γ$) reaction was measured at the Los Alamos Neutron Science Center white neutron source using γ-ray detection in liquid scintillators present in the upper hemisphere of the Correlated Gamma-Neutron Array for sCattering (CoGNAC). Separate measurements of this reaction were performed using H 2 O and BeO targets in successive years. The unique high energies of γ rays emitted from the 16 O($n, n'γ$) reaction facilitated a clean selection of this reaction from threshold to 9.8 MeV incident neutron energy without the need for precise measurements of the γ-ray energy or the scattered neutrons. The precise time resolution of the liquid scintillator detectors was then exploited to obtain high-resolution incident neutron energy measurements, and good agreement was obtained between the H 2 O and BeO results reported here. The dominant literature data sets for this reaction have systematic differences between them, but the present results improve upon the neutron energy resolution of earlier measurements and show important discrepancies in recent data. Finally, tentative data are also shown up to 20 MeV incident neutron energy but are potentially subject to improved understanding of the relative γ-ray and α decay branches from 16 O excited states.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2014

The Performance and Long Term Stability of the D0 Run II Forward Muon Scintillation Counters

The performance of the D0 experiment forward muon scintillation counters system during Run II of the Tevatron from 2001 to 2011 is described. The system consists of 4214 scintillation counters in six layers. The long term stability of the counters amplitude response determined using LED calibration system and muons produced in proton-antiproton collisions is presented. The average signal amplitude for counters of all layers has gradually decreased over ten years by 11%. The reference timing, determined using LED calibration, was stable within 0.26 ns. Average value of muon timing peak position was used for periodic D0 clock signal adjustments to compensate seasonal drift caused by temperature variations. Counters occupancy for different triggers in physics data collection runs and for minimum bias triggers are presented. The single muon yields versus time and the luminosity dependence of yields were stable for the forward muon system within 1% over 10 years.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2015

Organic liquid scintillation detectors for on-the-fly neutron/gamma alarming and radionuclide identification in a pedestrian radiation portal monitor

Here, we present new experimental results from a radiation portal monitor based on the use of organic liquid scintillators. The system was tested as part of a 3 He-free radiation portal monitor testing campaign at the European Commission’s Joint Research Centre in Ispra, Italy, in February 2014. The radiation portal monitor was subjected to a wide range of test conditions described in ANSI N42.35, including a variety of gamma-ray sources and a 20,000 n/s 252 Cf source. A false alarm test tested whether radiation portal monitors ever alarmed in the presence of only natural background. The University of Michigan Detection for Nuclear Nonproliferation Group’s system triggered zero false alarms in 2739 trials. It consistently alarmed on a variety of gamma-ray sources travelling at 1.2 m/s at a 70 cm source to detector distance. The neutron source was detected at speeds up to 3 m/s and in configurations with up to 8 cm of high density polyethylene shielding. The success of on-the-fly radionuclide identification varied with the gamma-ray source measured as well as with which of two radionuclide identification methods was used. Both methods used a least squares comparison between the measured pulse height distributions to library spectra to pick the best match. The methods varied in how the pulse height distributions were modified prior to the least squares comparison. Correct identification rates were as high as 100% for highly enriched uranium, but as low as 50% for 241 Am. Lastly, both radionuclide identification algorithms produced mixed results, but the concept of using liquid scintillation detectors for gamma-ray and neutron alarming in radiation portal monitor was validated.

3He replacement technology↗
DOE OSTI2015

Handheld readout electronics to fully exploit the particle discrimination capabilities of elpasolite scintillators

In this study, a new class of elpasolite scintillators has garnered recent attention due to the ability to perform as simultaneous gamma spectrometers and thermal neutron detectors. Such a dual-mode capability is made possible by pulse-shape discrimination (PSD), whereby the emission waveform profiles of gamma and neutron events are fundamentally unique. To take full advantage of these materials, we have developed the Compact Advanced Readout Electronics for Elpasolites (CAREE). This handheld instrument employs a multi-channel PSD-capable ASIC, custom micro-processor board, front-end electronics, power supplies, and a 2 in. photomultiplier tube for readout of the scintillator. The unit is highly configurable to allow for performance optimization amongst a wide sample of elpasolites which provide PSD in fundamentally different ways. We herein provide an introduction to elpasolites, then describe the motivation for the work, mechanical and electronic design, and preliminary performance results.

42 ENGINEERING↗
DOE OSTI2017

Effect of annealing temperature on the photoluminescence and scintillation properties of ZnO nanorods

The effect of the annealing to enhance the photoluminescence (PL) and scintillation properties, as determined by pulse height distribution of alpha particle irradiation, has been investigated for solution grown ZnO nanorods For this investigation the ZnO nanorod arrays were grown on glass for 22 h at 95°C as a substrate using a solution based hydrothermal technique. The samples were first annealed for different times (30, 60, 90 and 120 min) at 300°C and then at different temperatures (100°C–600°C) in order to determine the optimum annealing time and temperature, respectively. Before annealing, the ZnO nanorod arrays showed a broad yellow–orange visible and near-band gap UV emission peaks. After annealing in a forming gas atmosphere, the intensity of the sub-band gap PL was significantly reduced and the near-band gap PL emission intensity correspondingly increased (especially at temperatures higher than 100°C). Based on the ratio of the peak intensity ratio before and after annealing, it was concluded that samples at 350°C for 90 min resulted in the best near-band gap PL emission. Similarly, the analysis of the pulse height spectrum resulting from alpha particles revealed that ZnO nanorod arrays similarly annealed at 350°C for 90 min exhibited the highest scintillation response.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Interaction position, time, and energy resolution in organic scintillator bars with dual-ended readout

We report on the position, timing, and energy resolution of a range of plastic scintillator bars and reflector treatments using dual-ended silicon photomultiplier readout. These measurements are motivated by the upcoming construction of an optically segmented single-volume neutron scatter camera, in which neutron elastic scattering off of hydrogen is used to kinematically reconstruct the location and energy of a neutron-emitting source. For this application, interaction position resolutions of about 10 mm and timing resolutions of about 1 ns are necessary to achieve the desired efficiency for fission-energy neutrons. The results presented here indicate that this is achievable with an array of 5 x 5 x 190 mm 3 bars of EJ-204 scintillator wrapped in Teflon tape, read out with SensL’s J-series 6 x 6 mm 2 silicon photomultipliers. With two independent setups, we also explore the systematic variability of the position resolution, and show that, in general, using the difference in the pulse arrival time at the two ends is less susceptible to systematic variation than using the log ratio of the charge amplitude of the two ends. Finally, we measure a bias in the absolute time of interactions as a function of position along the bar: the measured interaction time for events at the center of the bar is 100 ps later than interactions near the SiPM.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2021

Neutron response of the TLYC scintillator

The response of the recently developed Tl 2 LiYCl 6 (Ce) scintillator to neutrons was measured and the 35 Cl(n,p) channel observed in the material for the first time. The scintillator was exposed to a 252 Cf source mounted within a parallel-plate avalanche counter for fission-fragment coincident measurements. Proton- and -like events are selected with the pulse-shape discrimination technique. Additionally, comparison of energy-deposition and time-of-flight allows the quenching of the different channels to be assessed. The 6 Li(n,t) channel is found to have its energy quenched to 37(1)% relative to -ray detection, while the proton energy deposition spectrum is quenched to 60(1)%.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2023

Lineshape response of plastic scintillator to pair production of 4.44 MeV γ’s

We measure the distribution of energy deposited in a 40 × 88 mm plastic scintillator by e + e – pair production of 4.44 MeV γ-rays. He, we observe the double-escape peak of 3.42 MeV from pair production by tagging 511 keV annihilation radiation in two high-Z scintillators. The source is a standard commercial neutron source using α-emitting 241 Am encapsulated with 9 Be, which has a reaction branch feeding the first I π = 2 + state of 12 C making the 4.44 MeV γ-rays. We demonstrate the extraction of the double-escape peak from the large neutron-produced backgound, and explore some of the features and difficulties of this technique with our apparatus.

Beta calibration↗
DOE OSTI2016

Ab initio prediction of fast non-equilibrium transport of nascent polarons in SrI 2 : a key to high-performance scintillation [First-principles study of hole polaron formation and migration in strontium iodide]

The excellent light yield proportionality of europium-doped strontium iodide (SrI 2 :Eu) has resulted in state-of-the-art γ-ray detectors with remarkably high-energy resolution, far exceeding that of most halide compounds. In this class of materials, the formation of self-trapped hole polarons is very common. However, polaron formation is usually expected to limit carrier mobilities and has been associated with poor scintillator light-yield proportionality and resolution. Here using a recently developed first-principles method, we perform an unprecedented study of polaron transport in SrI 2 , both for equilibrium polarons, as well as nascent polarons immediately following a self-trapping event. We propose a rationale for the unexpected high-energy resolution of SrI 2 . We identify nine stable hole polaron configurations, which consist of dimerised iodine pairs with polaron-binding energies of up to 0.5 eV. They are connected by a complex potential energy landscape that comprises 66 unique nearest-neighbour migration paths. Ab initio molecular dynamics simulations reveal that a large fraction of polarons is born into configurations that migrate practically barrier free at room temperature. Consequently, carriers created during γ-irradiation can quickly diffuse away reducing the chance for nonlinear recombination, the primary culprit for non-proportionality and resolution reduction. We conclude that the flat, albeit complex, landscape for polaron migration in SrI 2 is a key for understanding its outstanding performance. This insight provides important guidance not only for the future development of high-performance scintillators but also of other materials, for which large polaron mobilities are crucial such as batteries and solid-state ionic conductors.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Optically isotropy in scintillator host compounds M{sub 2}LaCl{sub 5} (M=Rb, and Cs): Ab-initio study

Full potential linearized augmented plane wave method (FP-LAPW) has been used to calculate the electronic structure and optical properties of high light output scintillator host compounds M{sub 2}LaCl{sub 5} (M=Rb, and Cs) with in the Tran Blaha modified Becke Johnson (TB-mBJ) potential. These are wide band gap materials with the band gap of 4.75, and 4.72 eV for Rb{sub 2}LaCl{sub 5}, and Cs{sub 2}LaCl{sub 5} respectively. From the calculated optical properties of these compounds, we find these compounds to be optically isotropic, though they are structurally anisotropic, which is an important criteria for the ceramic scintillators.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Enhanced light extraction of scintillator using large-area photonic crystal structures fabricated by soft-X-ray interference lithography

Soft-X-ray interference lithography is utilized in combination with atomic layer deposition to prepare photonic crystal structures on the surface of Bi{sub 4}Ge{sub 3}O{sub 12} (BGO) scintillator in order to extract the light otherwise trapped in the internal of scintillator due to total internal reflection. An enhancement with wavelength- and emergence angle-integration by 95.1% has been achieved. This method is advantageous to fabricate photonic crystal structures with large-area and high-index-contrast which enable a high-efficient coupling of evanescent field and the photonic crystal structures. Generally, the method demonstrated in this work is also suitable for many other light emitting devices where a large-area is required in the practical applications.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2018

Cryogenic scintillation properties of n -type GaAs for the direct detection of MeV/c 2 dark matter

This paper is the first report of n-type GaAs as a cryogenic scintillation radiation detector for the detection of electron recoils from interacting dark matter (DM) particles in the poorly explored MeV/c 2 mass range. Seven GaAs samples from two commercial suppliers and with different silicon and boron concentrations were studied for their low temperature optical and scintillation properties. All samples are n -type even at low temperatures and exhibit emission between silicon donors and boron acceptors that peaks at 1.33 eV (930 nm). The lowest excitation band peaks at 1.44 eV (860 nm), and the overlap between the emission and excitation bands is small. The X-ray excited luminosities range from 7 to 43 photons/keV. Thermally stimulated luminescence measurements show that n -type GaAs does not accumulate metastable radiative states that could cause afterglow. Further development and use with cryogenic photodetectors promises a remarkable combination of large target size, ultra-low backgrounds, and a sensitivity to electron recoils of a few eV that would be produced by DM particles as light as a few MeV/c 2 .

36 MATERIALS SCIENCE↗
DOE OSTI2018

A liquid VI scintillator cell for fast-gated neutron imaging

Here, the design of a new fast-gated neutron imaging system for the National Ignition Facility with much stricter timing constraints than a previous system has prompted the search for a fast scintillator material that can be used in imaging. A novel imaging cell based on Liquid VI has recently been developed with Eljen Technology and characterized at the Special Technologies Laboratory and the Los Alamos Neutron Science Center. The results show superior timing characteristics and spatial resolution, and sufficient light production for the new system compared to fast plastic scintillators previously used in neutron imaging. While the primary application is in inertial confinement fusion diagnostics, the imaging cell can be used in any fast-gated imaging application where timing characteristics and spatial resolution are of concern.

47 OTHER INSTRUMENTATION↗
DOE OSTI2018

Comparative study of perovskite-type scintillator materials CsCaI 3 and KCaI 3 via first-principles calculations

Several members of a large family of perovskite-like halides with a common chemical formula, ABX3 (A = monovalent, B = divalent, and X = halogen ion), are being investigated for their interesting properties and potential technological applications. CsCaI3 and KCaI3 are two such ionic compounds who are of interest in the quest for superior and cost-effective alternatives to NaI or CsI based scintillators. They are the subject of this first-principles based computational study. Both are wide-gap materials having primarily I 5p and Ca 3d characters near the valence and conduction band edges, respectively. Although built from [CaI6] octahedral motifs, structural differences between the two compounds is reflected in anisotropic electron effective mass and distinctive formation and migration of self-trapped holes. We discuss these properties as they relate to scintillation decay and proportional light yield.

Kang, Byungkyun↗
DOE OSTI2022

Scintillation light detection in the long-drift ProtoDUNE-DP liquid argon TPC

ProtoDUNE-DP is a 6 × 6 × 6m$^{3}$ liquid argon time-projection-chamber (LArTPC) operated at the Neutrino Platform at CERN in 2019-2020 as a prototype of the DUNE Far Detector. DUNE is a dual-site experiment for long-baseline neutrino oscillation studies, neutrino astrophysics and nucleon decay searches. The light signal in these detectors is crucial to provide precise timing capabilities. In ProtoDUNE-DP, scintillation light produced by cosmic muons in the LArTPC is collected by the photomultiplier tubes (PMTs) placed up to 7 m away from the point of interaction. The scintillation light production and propagation processes are analyzed and compared to simulations, improving the understanding of some liquid argon properties.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2022

Impact of xenon doping in the scintillation light in a large liquid-argon TPC

The use of xenon-doped liquid argon (Xe-doped LAr) is a promising alternative for large-scale liquid argon Time Projection Chambers (LAr-TPC), since it mitigates the light suppression due to impurities and it also improves the photon-detection efficiency and uniformity with the distance. This study analyses the impact of using Xe-doped LAr in ProtoDUNE Dual-Phase, a 750 ton Dual-Phase LAr-TPC placed at CERN. ProtoDUNE Dual-Phase completed a Xe-doping data-taking campaign in summer 2020 by re-filling the detector with 230 tons of Xe-doped LAr contaminated with nitrogen, and performing dedicated nitrogen injections. The effects of the presence of Xe at 5.8 ppm in the scintillation light production and propagation are analysed in this paper, showing an increase of the collected photons, but a suppression of the light signal amplitude. A 60% increase of the light attenuation length is measured. The impact on the scintillation time profile is also studied. A model to fit the time profile is proposed and the time constants of the physics processes are obtained.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗