Showing papers on "Scintillation published in 2017"

The XENON1T Dark Matter Experiment

Abstract: The XENON1T experiment at the Laboratori Nazionali del Gran Sasso (LNGS) is the first WIMP dark matter detector operating with a liquid xenon target mass above the ton-scale. Out of its 3.2t liquid xenon inventory, 2.0t constitute the active target of the dual-phase time projection chamber. The scintillation and ionization signals from particle interactions are detected with low-background photomultipliers. This article describes the XENON1T instrument and its subsystems as well as strategies to achieve an unprecedented low background level. First results on the detector response and the performance of the subsystems are also presented.

Transparent Ultra-High-Loading Quantum Dot/Polymer Nanocomposite Monolith for Gamma Scintillation.

Abstract: Spectroscopic gamma-photon detection has widespread applications for research, defense, and medical purposes However, current commercial detectors are either prohibitively expensive for wide deployment or incapable of producing the characteristic gamma photopeak Here we report the synthesis of transparent, ultra-high-loading (up to 60 wt %) CdxZn1–xS/ZnS core/shell quantum dot/polymer nanocomposite monoliths for gamma scintillation by in situ copolymerization of the partially methacrylate-functionalized quantum dots in a monomer solution The efficient Forster resonance energy transfer of the high-atomic-number quantum dots to lower-band-gap organic dyes enables the extraction of quantum-dot-borne excitons for photon production, resolving the problem of severe light yield deterioration found in previous nanoparticle-loaded scintillators As a result, the nanocomposite scintillator exhibited simultaneous improvements in both light yield (visible photons produced per MeV of gamma-photon energy) and gamma

Scintillating Organic-Inorganic Layered Perovskite-type Compounds and the Gamma-ray Detection Capabilities.

Abstract: We investigated scintillation properties of organic–inorganic layered perovskite-type compounds under gamma-ray and X-ray irradiation. A crystal of the hybrid compounds with phenethyl amine (17 × 23 × 4 mm) was successfully fabricated by the poor-solvent diffusion method. The bulk sample showed superior scintillation properties with notably high light yield (14,000 photons per MeV) under gamma-rays and very fast decay time (11 ns). The light yield was about 1.4 time higher than that of common inorganic material (GSO:Ce) confirmed under 137Cs and 57Co gamma-rays. In fact, the scintillation light yield was the highest among the organic–inorganic hybrid scintillators. Moreover, it is suggested that the light yield of the crystal was proportional with the gamma-ray energy across 122–662 keV. In addition, the scintillation from the crystal had a lifetime of 11 ns which was much faster than that of GSO:Ce (48 ns) under X-ray irradiation. These results suggest that organic–inorganic layered perovskite-type compounds are promising scintillator for gamma-ray detection.

Effect of eddy diffusivity ratio on underwater optical scintillation index.

Abstract: The performance of underwater optical wireless communication systems is severely affected by the turbulence that occurs due to the fluctuations in the index of refraction. Most previous studies assume a simplifying, yet inaccurate, assumption in the turbulence spectrum model that the eddy diffusivity ratio is equal to unity. It is, however, well known that the eddy diffusivities of temperature and salt are different from each other in most underwater environments. In this paper, we obtain a simplified spatial power spectrum model of turbulent fluctuations of the seawater refraction index as an explicit function of eddy diffusivity ratio. Using the derived model, we obtain the scintillation index of optical plane and spherical waves and investigate the effect of the eddy diffusivity ratio.

Development of lithium yttrium borate glass doped with Dy 3 + for laser medium, W-LEDs and scintillation materials applications

Abstract: Lithium yttrium borate glasses doped with dysprosium ion (Dy3 +) were synthesized by a melt-quenching technique. Glasses were studied the physical properties such as density, molar volume and refractive index. The absorption, excitation and emission spectra, including decay curve were monitored to study the luminescence properties. The X-ray induced luminescence and temperature dependence luminescence spectra was also investigated. The experimental results show that Dy3 + probably acts as modifier in this glass because molar volume increased with increasing of Dy3 + doped content. Glasses absorbs photon in visible light and near-infrared region with Dy3 + transition from 6H15/2 ground state. Glass performs the strongest emission at 575 nm (4F9/2 → 6H13/2) with 388 nm excitation wavelength. The intensity of emission increases with increasing of Dy2O3 concentration until 1.00 mol% after that it decreases by resonance energy transfer and cross-relaxation processes. The photoemission is white light confirmed by CIE 1931 chromaticity and UV lamp excitation. Decay curve, fitted by Inokutie-Hirayama model (S = 6), shows the non-exponential pattern which indicates a dipole-dipole interaction between Dy3 + donor and acceptor in glass. Judd-Ofelt analysis exhibits an interesting potential for using glass as laser medium with 575 nm emitting. X-ray induced luminescence spectra perform the sharp emission band of Dy3 + after accepted energy transfer from host glass. This is a good sign for scintillation potential. Temperature dependence luminescence spectra show the strong emission at low temperature condition. Emission intensity relates linearly with the temperature change. This Dy3 + doped glass can be developed for using as photonic materials in the display, white-light emitting diode, laser device, scintillation detector and even temperature sensor.

Index of refraction, Rayleigh scattering length, and Sellmeier coefficients in solid and liquid argon and xenon

Abstract: Large liquid argon detectors have become widely used in low rate experiments, including dark matter and neutrino research. However, the optical properties of liquid argon are not well understood at the large scales relevant for current and near-future detectors. The index of refraction of liquid argon at the scintillation wavelength has not been measured, and current Rayleigh scattering length calculations disagree with measurements. Furthermore, the Rayleigh scattering length and index of refraction of solid argon and solid xenon at their scintillation wavelengths have not been previously measured or calculated. We introduce a new calculation using existing data in liquid and solid argon and xenon to extrapolate the optical properties at the scintillation wavelengths using the Sellmeier dispersion relationship.

Performance Analysis of L-Band Geosynchronous SAR Imaging in the Presence of Ionospheric Scintillation

Abstract: An L-band geosynchronous synthetic aperture radar (GEO SAR) will be inevitably affected by ionosphere scintillation because of its low carrier frequency. Meanwhile, compared with the low Earth orbit (LEO) SAR, a higher orbit of GEO SAR makes it have a longer integration time and a longer operation time within the susceptible regions of ionospheric scintillation. Thus, its imaging is more sensitive to ionospheric scintillation, and the corresponding degradation will have a different pattern. However, few works are focused on the quantitative analysis of the ionospheric scintillation impacts on L-band SAR. Moreover, the parameters of ionospheric irregularities utilized in the analyses are hard to be determined. In this paper, we first deduced the azimuth point-spread function with the consideration of both the amplitude and phase scintillation. Then, based on the measurable statistical parameters of ionospheric scintillation, performance specifications, including azimuth resolution, azimuth peak-to-sidelobe ratio (PSLR), and azimuth integrated sidelobe ratio (ISLR) are obtained to fully evaluate the impacts. The analysis suggests that in GEO SAR imaging, the azimuth ISLR severely deteriorates, whereas degradations of the azimuth resolution and PSLR are negligible. Finally, the simulations and a real ionospheric scintillation monitoring experiment by employing Global Positioning System satellites receivers were conducted, verifying the conclusions that the serious degraded contrast and focus quality of the images are brought by the raised azimuth ISLR.

Neutron imaging detector with 2 μm spatial resolution based on event reconstruction of neutron capture in gadolinium oxysulfide scintillators

Abstract: We report on efforts to improve the achievable spatial resolution in neutron imaging by centroiding the scintillation light from gadolinium oxysulfide scintillators. The current state-of-the-art neutron imaging spatial resolution is about 10 μm, and many applications of neutron imaging would benefit from at least an order of magnitude improvement in the spatial resolution. The detector scheme that we have developed magnifies the scintillation light from a gadolinium oxysulfide scintillator, calculates the center of mass of the scintillation event, resulting in an event-based imaging detector with spatial resolution of about 2 μm.

A method for scintillation characterization using geodetic receivers operating at 1 Hz

Abstract: Ionospheric scintillation produces strong disruptive effects on global navigation satellite system (GNSS) signals, ranging from degrading performances to rendering these signals useless for accurate navigation. The current paper presents a novel approach to detect scintillation on the GNSS signals based on its effect on the ionospheric-free combination of carrier phases, i.e. the standard combination of measurements used in precise point positioning (PPP). The method is implemented using actual data, thereby having both its feasibility and its usefulness assessed at the same time. The results identify the main effects of scintillation, which consist of an increased level of noise in the ionospheric-free combination of measurements and the introduction of cycle-slips into the signals. Also discussed is how mis-detected cycle-slips contaminate the rate of change of the total electron content index (ROTI) values, which is especially important for low-latitude receivers. By considering the effect of single jumps in the individual frequencies, the proposed method is able to isolate, over the combined signal, the frequency experiencing the cycle-slip. Moreover, because of the use of the ionospheric-free combination, the method captures the diffractive nature of the scintillation phenomena that, in the end, is the relevant effect on PPP. Finally, a new scintillation index is introduced that is associated with the degradation of the performance in navigation.

Scintillation and dosimeter properties of CaF2 translucent ceramic produced by SPS

Abstract: We have developed CaF2 translucent ceramics by spark plasma sintering (SPS) and investigated the scintillation and dosimeter properties, in comparison with a CaF2 single crystal. Under X-ray irradiation, light emission was observed at 270 and 300 nm, due to self-trapped exciton (STE). The scintillation light yield of CaF2 translucent ceramic was measured to be about 6000 photons/MeV under 137Cs irradiation, and this value was smaller than that of the single crystal by a factor of approximately 2. The afterglow level, after X-ray irradiation, of the ceramic sample was lower than that of the single crystal. Thermally stimulated luminescence (TSL) glow peaks were observed at 100 and 150 °C in both ceramic and single crystal samples, however the TSL intensity was much stronger than that of the single crystal sample.

A novel segmented-scintillator antineutrino detector

Abstract: The next generation of very-short-baseline reactor experiments will require compact detectors operating at surface level and close to a nuclear reactor. This paper presents a new detector concept based on a composite solid scintillator technology. The detector target uses cubes of polyvinyltoluene interleaved with 6LiF:ZnS(Ag) phosphor screens to detect the products of the inverse beta decay reaction. A multi-tonne detector system built from these individual cells can provide precise localisation of scintillation signals, making efficient use of the detector volume. Monte Carlo simulations indicate that a neutron capture efficiency of over 70 % is achievable with a sufficient number of 6LiF:ZnS(Ag) screens per cube and that an appropriate segmentation enables a measurement of the positron energy which is not limited by γ-ray leakage. First measurements of a single cell indicate that a very good neutron-gamma discrimination and high neutron detection efficiency can be obtained with adequate triggering techniques. The light yield from positron signals has been measured, showing that an energy resolution of 14%/√E(MeV) is achievable with high uniformity. A preliminary neutrino signal analysis has been developed, using selection criteria for pulse shape, energy, time structure and energy spatial distribution and showing that an antineutrino efficiency of 40% can be achieved. It also shows that the fine segmentation of the detector can be used to significantly decrease both correlated and accidental backgrounds.

Automatic Equatorial GPS Amplitude Scintillation Detection Using a Machine Learning Algorithm

Abstract: This paper presents a machine learning algorithm to detect ionospheric scintillation and classify scintillation events based on training data in the frequency domain. The detector input is the signal intensity. Validation using data from Ascension Island, Hong Kong, and Peru shows 91–96% accuracy of scintillation detection. Different combinations of training data, observation matrices, and learning algorithms are investigated to obtain performance measures. Testing results on data from Singapore demonstrate the general capabilities of the detector.

An integrated model of scintillator-reflector properties for advanced simulations of optical transport.

Abstract: Accurately modeling the light transport in scintillation detectors is essential to design new detectors for nuclear medicine or high energy physics. Optical models implemented in software such as Geant4 and GATE suffer from important limitations that we addressed by implementing a new approach in which the crystal reflectance was computed from 3D surface measurements. The reflectance was saved in a look-up-table (LUT) then used in Monte Carlo simulation to determine the fate of optical photons. Our previous work using this approach demonstrated excellent agreement with experimental characterization of crystal light output in a limited configuration, i.e. when using no reflector. As scintillators are generally encapsulated in a reflector, it is essential to include the crystal-reflector interface in the LUT. Here we develop a new LUT computation and apply it to several reflector types. A second LUT that contains transmittance data is also saved to enable modeling of optical crosstalk. LUTs have been computed for rough and polished crystals coupled to a Lambertian (e.g. Teflon tape) or a specular reflector (e.g. ESR) using air or optical grease, and the light output was computed using a custom Monte Carlo code. 3 × 3 × 20 mm3 lutetium oxyorthosilicate crystals were prepared using these combinations, and the light output was measured experimentally at different irradiation depths. For all reflector and surface finish combinations, the measured and simulated light output showed very good agreement. The behavior of optical photons at the interface crystal-reflector was studied using these simulations, and results highlighted the large difference in optical properties between rough and polished crystals, and Lambertian and specular reflectors. These simulations also showed how the travel path of individual scintillation photons was affected by the reflector and surface finish. The ultimate goal of this work is to implement this model in Geant4 and GATE, and provide a database of scintillators combined with a variety of reflectors.

Proton therapy dosimetry using the scintillation of the silica fibers.

Abstract: We investigate the feasibility of proton therapy dose measurement by using scintillation of a bare silica glass fiber. The emission spectra of the optical fiber at various depths in tissue-mimicking phantoms, irradiated with proton beams of energies 100–225 MeV show two distinct peaks at 460 and 650 nm whose nature is connected with the silica point defects. Our experimental results and Monte Carlo simulation showed that the Cerenkov radiation cannot be responsible for such a phenomenon. We showed that the intensity of the peak at 650 nm correlates with the proton dose with a minimal effect of ionization quenching, while the intensity peak at 460 nm under-reports the radiation dose.

Measuring anisotropy ellipse of atmospheric turbulence by intensity correlations of laser light

Abstract: An experimental study has been performed of a laser beam propagating horizontally through the near-ground atmosphere above a grassy field at the University of Miami (UM) Coral Gables campus. The average intensity, scintillation index, and intensity correlation function are measured in the receiver plane for three channels with different turbulent conditions and at three different heights above the ground. Our results reveal that along short links (210 m) only the intensity correlation function captures the anisotropic information of turbulence, corresponding to the refractive index anisotropy ellipse of atmospheric fluctuations. In addition, we report an interesting phenomenon relating to turbulence eddy orientation near the ground. We confirmed that the experimental results are in agreement with the numerical simulations based on the multiple phase-screen method. Our findings provide an efficient method of determining the anisotropic parameters of atmospheric turbulence.

Recent progress in oxide scintillation crystals development by low-thermal gradient Czochralski technique for particle physics experiments

Abstract: Modern particle physics experiments call for high performance scintillation detectors with unique properties: radiation-resistant in high energy and astrophysics, highly radiopure, containing certain elements or enriched isotopes in astroparticle physics. The low-thermal gradient Czochralski (LTG CZ) crystal growth technique provides excellent quality large volume radiopure crystal scintillators. Absence of thermoelastic stress in the crystal and overheating of the melt in the LTG CZ method is particularly significant in production of crystalline materials with strong thermal anisotropic properties and low mechanical strength, with a very high yield of crystalline boules and low losses of initial charge, crucially important in production of crystal scintillators from enriched isotopes for double beta decay experiments. Here we discuss progress in development of the well known scintillators (Bi4Ge3O12 (BGO), CdWO4, ZnWO4, CaMoO4, PbMoO4), as well as R{&}D of new materials (ZnMoO4, Li2MoO4, Na2Mo2O7) for the next generation experiments in particle physics.

First Demonstration of a Scintillating Xenon Bubble Chamber for Detecting Dark Matter and Coherent Elastic Neutrino-Nucleus Scattering.

Abstract: A 30-g xenon bubble chamber, operated at Northwestern University in June and November 2016, has for the first time observed simultaneous bubble nucleation and scintillation by nuclear recoils in a superheated liquid. This chamber is instrumented with a CCD camera for near-IR bubble imaging, a solar-blind photomultiplier tube to detect 175-nm xenon scintillation light, and a piezoelectric acoustic transducer to detect the ultrasonic emission from a growing bubble. The time of nucleation determined from the acoustic signal is used to correlate specific scintillation pulses with bubble-nucleating events. We report on data from this chamber for thermodynamic ``Seitz'' thresholds from 4.2 to 15.0 keV. The observed single- and multiple-bubble rates when exposed to a $^{252}\mathrm{Cf}$ neutron source indicate that, for an 8.3-keV thermodynamic threshold, the minimum nuclear recoil energy required to nucleate a bubble is $19\ifmmode\pm\else\textpm\fi{}6\text{ }\text{ }\mathrm{keV}$ ($1\ensuremath{\sigma}$ uncertainty). This is consistent with the observed scintillation spectrum for bubble-nucleating events. We see no evidence for bubble nucleation by gamma rays at any of the thresholds studied, setting a 90% C.L. upper limit of $6.3\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}7}$ bubbles per gamma interaction at a 4.2-keV thermodynamic threshold. This indicates stronger gamma discrimination than in ${\mathrm{CF}}_{3}\mathrm{I}$ bubble chambers, supporting the hypothesis that scintillation production suppresses bubble nucleation by electron recoils, while nuclear recoils nucleate bubbles as usual. These measurements establish the noble-liquid bubble chamber as a promising new technology for the detection of weakly interacting massive particle dark matter and coherent elastic neutrino-nucleus scattering.

Advanced optical simulation of scintillation detectors in GATE V8.0: first implementation of a reflectance model based on measured data.

Abstract: Typical PET detectors are composed of a scintillator coupled to a photodetector that detects scintillation photons produced when high energy gamma photons interact with the crystal. A critical performance factor is the collection efficiency of these scintillation photons, which can be optimized through simulation. Accurate modelling of photon interactions with crystal surfaces is essential in optical simulations, but the existing UNIFIED model in GATE is often inaccurate, especially for rough surfaces. Previously a new approach for modelling surface reflections based on measured surfaces was validated using custom Monte Carlo code. In this work, the LUT Davis model is implemented and validated in GATE and GEANT4, and is made accessible for all users in the nuclear imaging research community. Look-up-tables (LUTs) from various crystal surfaces are calculated based on measured surfaces obtained by atomic force microscopy. The LUTs include photon reflection probabilities and directions depending on incidence angle. We provide LUTs for rough and polished surfaces with different reflectors and coupling media. Validation parameters include light output measured at different depths of interaction in the crystal and photon track lengths, as both parameters are strongly dependent on reflector characteristics and distinguish between models. Results from the GATE/GEANT4 beta version are compared to those from our custom code and experimental data, as well as the UNIFIED model. GATE simulations with the LUT Davis model show average variations in light output of 0.99. Experimental data agree within 9% for relative light output. The new model also simplifies surface definition, as no complex input parameters are needed. The LUT Davis model makes optical simulations for nuclear imaging detectors much more precise, especially for studies with rough crystal surfaces. It will be available in GATE V8.0.

Cherenkov and scintillation light separation in organic liquid scintillators

Abstract: The CHErenkov/Scintillation Separation experiment (CHESS) has been used to demonstrate the separation of Cherenkov and scintillation light in both linear alkylbenzene (LAB) and LAB with 2 g/L of PPO as a fluor (LAB/PPO). This is the first successful demonstration of Cherenkov light detection from the more challenging LAB/PPO cocktail and improves on previous results for LAB. A time resolution of $$338\pm 12$$ ps FWHM results in an efficiency for identifying Cherenkov photons in LAB/PPO of $$70 \pm 3 \%$$ and $$63\pm 8\%$$ for time- and charge-based separation, respectively, with scintillation contamination of $$36\pm 5\%$$ and $$38\pm 4$$ %. LAB/PPO data is consistent with a rise time of $$\tau _r=0.72\pm 0.33$$ ns.

Luminescent and scintillation properties of Ce-doped Tb3Al5O12 crystal grown from Al-rich composition

Abstract: A Ce-doped Tb3Al5O12 single crystal was successfully synthesized via the floating zone method in an Al-rich composition. In both photoluminescence and scintillation, the emissions were predominantly due to the 5d–4f transitions of Ce3+ peaking around 550 nm, but emissions due to defects and the 4f–4f transitions of Tb3+ were revealed by the time-resolved analyses. The crystal quality and luminescence intensity were sufficiently high such that the crystal was applicable for pulse-height spectrum measurement. Under 137Cs γ-ray exposure, a clear photoabsorption peak was observed, and the estimated light yield was 57,000 photons/MeV.

Separating Double-Beta Decay Events from Solar Neutrino Interactions in a Kiloton-Scale Liquid Scintillator Detector By Fast Timing

Abstract: We present a technique for separating nuclear double beta decay ( β β -decay) events from background neutrino interactions due to 8B decays in the sun. This background becomes dominant in a kiloton-scale liquid-scintillator detector deep underground and is usually considered as irreducible due to an overlap in deposited energy with the signal. However, electrons from 0 ν β β -decay often exceed the Cherenkov threshold in liquid scintillator , producing photons that are prompt and correlated in direction with the initial electron direction. The use of large-area fast photodetectors allows some separation of these prompt photons from delayed isotropic scintillation light and, thus, the possibility of reconstructing the event topology. Using a simulation of a 6.5 m radius liquid scintillator detector with 100 ps resolution photodetectors, we show that a spherical harmonics analysis of early-arrival light can discriminate between 0 ν β β -decay signal and 8 B solar neutrino background events on a statistical basis. Good separation will require the development of a slow scintillator with a 5 ns risetime.