Showing papers on "Scintillation published in 2012"

Results from 730 kg days of the CRESST-II Dark Matter search

Abstract: The CRESST-II cryogenic Dark Matter search, aiming at detection of WIMPs via elastic scattering off nuclei in CaWO4 crystals, completed 730 kg days of data taking in 2011. We present the data collected with eight detector modules, each with a two-channel readout; one for a phonon signal and the other for coincidently produced scintillation light. The former provides a precise measure of the energy deposited by an interaction, and the ratio of scintillation light to deposited energy can be used to discriminate different types of interacting particles and thus to distinguish possible signal events from the dominant backgrounds.

Light scintillation in oceanic turbulence

Abstract: The scintillation index of plane and spherical light waves as well as of a Gaussian beam, propagating in the clear-water weakly turbulent ocean, is revealed. The results are of utmost importance for underwater optical communications and sensing. An analysis of the threshold between the weak and strong regimes of oceanic turbulence is made, with the accent on the contribution from salinity-induced turbulence. It is found that strong oceanic turbulence can occur at distances as short as several meters, in striking contrast with atmospheric studies for which the typical distances are on the order of a kilometer.

The lower bound on the timing resolution of scintillation detectors

Abstract: The timing performance of scintillation detectors is ultimately limited by photon counting statistics. In fact, photon counting statistics form a dominant contribution to the overall timing resolution of many state-of-the-art detectors. A common approach to investigate this contribution is to calculate the variance in the registration times of individual scintillation photons within the photosensor. However, in general the single-photon variance is not equal to the intrinsic limit on the timing resolution, since in principle one can make use of the timing information carried by all photons detected. In this work, the Cramer-Rao lower bound on the timing resolution of a scintillation detector, based on the information contained in the full set of registered photons, is calculated. The results appear to be in good agreement with trends observed in the literature. Furthermore, it is shown that the timestamp obtained from any single scintillation photon never yields the optimum timing resolution for realistic scintillation detectors. Yet, it appears that the intrinsic timing resolution limit can be approached closely by making use of the timestamps from a relatively small number of photons emitted during the initial part of the scintillation pulse.

A Comprehensive Model to Predict the Timing Resolution of SiPM-Based Scintillation Detectors: Theory and Experimental Validation

Abstract: Silicon photomultipliers (SiPMs) are expected to replace photomultiplier tubes (PMTs) in several applications that require scintillation detectors with excellent timing resolution, such as time-of-flight positron emission tomography (TOF-PET). However, the theory about the timing resolution of SiPM-based detectors is not yet fully understood. Here we propose a comprehensive statistical model to predict the timing resolution of SiPM-based scintillation detectors. It incorporates the relevant SiPM-related parameters (viz. the single cell electronic response, the single cell gain, the charge carrier transit time spread, and crosstalk) as well as the scintillation pulse rise and decay times, light yield, and energy resolution. It is shown that the proposed model reduces to the well-established Hyman model for timing with PMTs if the number of primary triggers (photoelectrons in case of a PMT) is Poisson distributed and crosstalk and electronic noise are negligible. The model predictions are validated by measurements of the coincidence resolving times (CRT) for 511 keV photons of two identical detectors as a function of SiPM bias voltage, for two different kinds of scintillators, namely LYSO:Ce and LaBr3:5%Ce. CRTs as low as 138 ps ± 2 ps FWHM for LYSO:Ce and 95 ps ± 3 ps FWHM for LaBr3:5%Ce were obtained, demonstrating the outstanding timing potential of SiPM-based scintillation detectors. These values were found to be in good agreement with the predicted CRTs of 140 ps FWHM and 95 ps FWHM, respectively. Utilizing the proposed model, it can be shown that the CRTs obtained in our experiments are mainly limited by photon statistics while crosstalk, electronic noise and signal bandwidth have relatively little influence.

Improved amplitude- and phase-scintillation indices derived from wavelet detrended high-latitude GPS data

Abstract: Accuracy and validity of scintillation indices estimated using the power and phase of the GPS signal depend heavily on the detrending method used and the selection of the cutoff frequency of the associated filter. A Butterworth filter with a constant cutoff frequency of 0.1 Hz is commonly used in detrending GPS data. In this study, the performance of this commonly used filter is evaluated and compared with a new wavelet-based detrending method using GPS data from high latitudes. It was observed that in detrending high-latitude GPS data, a wavelet filter performed better than Butterworth filters as the correlation between amplitude- and phase-scintillation indices in S 4 and ? ? improved significantly from 0.53, when using a Butterworth filter, to 0.79, when using the wavelet filtering method. We also introduced an improved phase-scintillation index, ? CHAIN, which we think is comparatively a better parameter to represent phase scintillations at high latitudes as the correlation between S 4 and ? CHAIN was as high as 0.90. During the analysis, we also noted that the occurrence of the "phase scintillation without amplitude scintillation" phenomenon was significantly reduced when scintillation indices were derived using the wavelet-based detrending method. These results seem to indicate that wavelet-based detrending is better suited for GPS scintillation signals and also that ? CHAIN is a better parameter for representing GPS phase scintillations at high latitudes.

Pencil beam coded aperture x-ray scatter imaging

Abstract: We use coded aperture x-ray scatter imaging to interrogate scattering targets with a pencil beam Observations from a single x-ray exposure of a flat-panel scintillation detector are used to simultaneously determine the along-beam positions and momentum transfer profiles of two crystalline powders (NaCl and Al) The system operates with a 3 cm range resolution and a momentum transfer resolution of 01 nm−1 These results demonstrate that a single snapshot can be used to estimate scattering properties along an x-ray beam, and serve as a foundation for volumetric imaging of scattering objects

Crystal Growth and Scintillation Properties of Ce Doped ${\rm Gd}_{3}({\rm Ga},{\rm Al})_{5}{\rm O}_{12}$ Single Crystals

Abstract: Ce1%, 2% and 3% doped Gd3(Ga,Al)5O12 (GAGG) single crystals were grown by the Cz method. Luminescence and scintillation properties were measured. Light yield change along the growth direction and effects of Ce concentration on scintillation properties in Ce:GAGG were studied. Ce3+ 5d-4f emission within 520-530 nm was observed in the Ce:GAGG crystals. The Ce1%:GAGG sample with 3×3×1 mm size showed the highest light yield of 46000 photon/MeV. The energy resolution was 7.8%@662 keV. With increasing solidification fraction, the LY were decreased. It is proposed that the increase of Ga concentration along the growth direction is the main cause of the decrease of LY. The scintillation decay times were accelerated with increasing Ce concentration in the Ce:GAGG crystals. The scintillation decay times were 92.0 ns, 79.1 ns and 68.3 ns in the Ce1, 2 and 3% GAGG, respectively.

Impact of turbulence in long range quantum and classical communications.

Abstract: The study of the free-space distribution of quantum correlations is necessary for any future application of quantum and classical communication aiming to connect two remote locations. Here we study the propagation of a coherent laser beam over 143 km (between Tenerife and La Palma Islands of the Canary archipelagos). By attenuating the beam we also studied the propagation at the single photon level. We investigated the statistic of arrival of the incoming photons and the scintillation of the beam. From the analysis of the data, we propose the exploitation of turbulence to improve the signal to noise ratio of the signal.

Simulating the impacts of ionospheric scintillation on L band SAR image formation

Abstract: [1] We develop a phase screen model called the Synthetic Aperture Radar (SAR) Scintillation Simulator (SAR-SS) for predicting the impacts of ionospheric scintillation on SAR image formation. SAR-SS consists of a phase screen generator and a propagator. The screen generator creates a 2-D random realization of spatial phase fluctuations resulting from the traversal of small-scale field-aligned irregularities in the ionosphere. It accounts for the motion of the radar platform, the drift of the ionospheric irregularities, and the oblique angle of propagation, all of which determine the scale sizes of the irregularities sampled by the radar beam. The propagator solves the 3-D parabolic wave equation using the split step technique to compute the ionospheric transfer function for two-way propagation. This ionospheric transfer function is used to modulate the SAR signal due to terrestrial features in order to assess the ionospheric impact on SAR image formation in the small target approximation. We compare simulated and observed PALSAR imagery over Brazil during disturbed ionospheric conditions. We demonstrate that SAR-SS can reproduce the field-aligned streaks in PALSAR imagery caused by irregularities in the equatorial ionosphere that have been observed by previous authors. The field-aligned streaks exhibited a dominant wavelength larger than the Fresnel break scale, which suggests that refractive scatter was dominant over diffraction as the physical mechanism responsible for the scintillation of the radar signal in this case. The spectral index of phase fluctuations in the screen was quite large (9.0), suggesting that these irregularities were possibly associated with bottomside sinudoidal irregularities rather than equatorial plasma bubbles.

Twist phase-induced reduction in scintillation of a partially coherent beam in turbulent atmosphere

Abstract: The scintillation index of a Gaussian Schell-model beam with twist phase (i.e., twisted GSM beam) in weak turbulent atmosphere is formulated with the help of a tensor method. Variations of the scintillation index of a twisted GSM beam on propagation in turbulent atmosphere are studied in detail. It is interesting to find that the scintillation index of a twisted GSM beam can be smaller than that without twist phase in weak turbulent atmosphere. Thus, modulation of the twist phase of a partially coherent beam provides a new way to reduce turbulence-induced scintillation.

Measurement of scintillation efficiency for nuclear recoils in liquid argon

Abstract: The scintillation light yield of liquid argon from nuclear recoils relative to electronic recoils has been measured as a function of recoil energy from 10 keVr up to 250 keVr. The scintillation efficiency, defined as the ratio of the nuclear recoil scintillation response to the electronic recoil response, is 0.25 \pm 0.01 + 0.01(correlated) above 20 keVr.

Accurate measurement of the rise and decay times of fast scintillators with solid state photon counters

Abstract: In this work we present a measurement setup for the determination of scintillation pulse shapes of fast scintillators It is based on a time-correlated single photon counting approach that utilizes the correlation between 511 keV annihilation photons to produce start and stop signals in two separate crystals The measurement is potentially cost-effective and simple to set up while maintaining an excellent system timing resolution of 125 ps As a proof-of-concept the scintillation photon arrival time histograms were recorded for two well-known, fast scintillators: LYSO:Ce and LaBr3:5%Ce The scintillation pulse shapes were modeled as a linear combination of exponentially distributed charge transfer and photon emission processes Correcting for the system timing resolution, the exponential time constants were extracted from the recorded histograms A decay time of 43 ns and a rise time of 72 ps were determined for LYSO:Ce thus demonstrating the capability of the system to accurately measure very fast rise times In the case of LaBr3:5%Ce two processes were observed to contribute to the rising edge of the scintillation pulse The faster component (270 ps) contributes with 72% to the rising edge of the scintillation pulse while the second, slower component (20 ns) contributes with 27% The decay of the LaBr3:5%Ce scintillation pulse was measured to be 154 ns with a small contribution (2%) of a component with a larger time constant (130 ns)

Structure–Property Correlations in a Ce-Doped (Lu,Gd)2SiO5:Ce Scintillator

Abstract: A full concentration range of Lu2xGd2–2xSiO5 (LGSO:Ce) crystals was grown by the Czochralski method. Dependence of the scintillation properties on composition (x) in the range of solid solutions is established. It was determined that the LGSO:Ce scintillation yield increases in the range 0.3 < x < 0.8 and reaches 29000 phot/MeV at 60% of Lu in the host (x = 0.6), and energy resolution improves up to 6.7% at 662 KeV. The observed light yield increase, surprisingly high Ce3+ segregation coefficients, improvement of energy resolution, and suppression of afterglow can be attributed to modification of both hot and thermalized diffusion of secondary electrons and holes induced by short-range separation in solid solution. The proposed approach can be valid for a wide range of mixed scintillation crystals and provides room for further improvement of their characteristics by isovalent substitution of host atoms.

Ionospheric scintillation over Antarctica during the storm of 5-6 April 2010

Abstract: On 5 April 2010 a coronal mass ejection produced a traveling solar wind shock front that impacted the Earth's magnetosphere, producing the largest geomagnetic storm of 2010. The storm resulted in a prolonged period of phase scintillation on Global Positioning System signals in Antarctica. The scintillation began in the deep polar cap at South Pole just over 40 min after the shock front impact was recorded by a satellite at the first Lagrangian orbit position. Scintillation activity continued there for many hours. On the second day, significant phase scintillation was observed from an auroral site (81 degrees S) during the postmidnight sector in association with a substorm. Particle data from polar-orbiting satellites provide indication of electron and ion precipitation into the Antarctic region during the geomagnetic disturbance. Total electron content maps show enhanced electron density being drawn into the polar cap in response to southward turning of the interplanetary magnetic field. The plasma enhancement structure then separates from the dayside plasma and drifts southward. Scintillation on the first day is coincident spatially and temporally with a plasma depletion region both in the dayside noon sector and in the dayside cusp. On the second day, scintillation is observed in the nightside auroral region and appears to be strongly associated with ionospheric irregularities caused by E region particle precipitation.

Scintillation Properties of Transparent Ceramic Pr:LuAG for Different Pr Concentration

Abstract: We manufactured transparent optical ceramic of Pr 0.2-1% doped Lu3Al5 O12 (Pr:LuAG) by the sintering method. We compare its optical and scintillation properties with the single crystal counterpart grown by the conventional Czochralski method. So far the scintillation ceramic of Pr:LuAG appeared inferior to its single crystal analog especially in terms of light yield. However, in the present case our ceramic Pr 0.25%-doped sample exhibited by 20% higher light yield compared to single crystal under γ-ray excitation. Furthermore, in the ceramic sample the slower scintillation decay components were suppressed and the defect related host emission as well. The optimized technology of optical ceramics thus appears very competitive to single crystals and opens great practical prospectives for the former materials in the field of fast scintillators.

Quantum Dot-Organic Polymer Composite Materials for Radiation Detection and Imaging

Abstract: Colloidal semiconductor nanocrystals exhibit physical properties that are characteristic of intermediate size scales between molecular states and solid state materials, and are often called quantum dots. Solid state semiconductor materials have been used extensively as scintillation detectors for ionizing radiation. We describe the use of semiconductor quantum dot-organic polymer composites for use as scintillation detectors and report the use of quantum dot-polymer composite thin films for X-ray imaging.

Liquid Scintillation Analysis: Principles and Practice

Abstract: The chapter begins with a treatment of the basic theory of liquid scintillation and the interactions of alpha, beta, and gamma rays in liquid scintillator. A description of the basic design and concepts of operation of a liquid scintillation counter is provided. This is followed by a comprehensive treatment of quench effects and the methods of quench correction in liquid scintillation counting, including the internal standard method, sample spectrum, and external standard quench-indicating parameters. A detailed treatment of the preparation and use of quenched standards and quench-correction curves is provided. A discussion of direct DPM methods is also included. This is followed with a treatment on the analysis of X-ray, gamma ray, Auger electron, and positron emitters by liquid scintillation counting (LSC). A detailed discussion of the interferences encountered in liquid scintillation analysis (LSA) including background, quench, radionuclide mixtures, luminescence, and static and wall effects are described, and methods for their correction are discussed. The chapter continues with a treatment on the LSA of multiple radionuclides including dual- and triple-radionuclide analysis techniques and the analysis of more complex mixtures by spectral fitting, unfolding, and interpolation techniques. A detailed discussion of radionuclide standardization by the CIEMAT/NIST efficiency tracing and the triple-to-double coincidence ratio (TDCR) methods is provided. Neutron/gamma-ray measurement and discrimination by LSC are discussed. The use of LSC for the detection and measurement of double beta ( ββ ) decay is provided. A treatment of liquid scintillation schemes for the detection and measurement of neutrinos includes inverse beta decay and charged current interactions. Other liquid scintillation methods that are discussed include microplate scintillation and luminescence counting, PERALS and liquid scintillation alpha-spectrometry with large-area avalanche photodiodes (LAAPD), and simultaneous α / β analysis. Other methods described are the use of plastic scintillators in LSC, scintillation counting in noble liquids, radionuclide identification by LSC, and air luminescence counting. The chapter concludes with a treatment of the methods of assessment of liquid scintillation counter performance and optimization.

Scintillation property of rare earth-free SnO-doped oxide glass

Abstract: The authors have demonstrated scintillation of rare earth (RE)-free Sn-doped oxide glass by excitation of ionizing radiation. It is notable that light emission is attained for RE-free transparent glass due to s2-sp transition of Sn2+ centre and the emission correlates with the excitation band at 20 eV. We have also demonstrated that excitation band of emission centre can be tuned by the chemical composition of the host glass. The present result is valuable not only for design of RE-free inorganic amorphous oxide scintillator but also for revealing the band structure of oxide glass by irradiation of ionizing radiation.

Fast and High-Energy-Resolution Oxide Scintillator: Ce-Doped (La,Gd)2Si2O7

Abstract: A novel scintillation crystal (Ce0.01,Gd0.90,La0.09)2Si2O7 (Ce:La-GPS) was grown by the floating zone method, and its optical and scintillation properties were investigated. The emission wavelength of this material was 390 nm. Gamma ray excited pulse height and scintillation decay measurement showed that Ce:La-GPS had a high energy resolution (FWHM) of 5% at 662 keV, high light output of 36,000 photons/MeV and fast scintillation decay time of 46 ns.

Radioactive contamination of SrI2(Eu) crystal scintillator

Abstract: A strontium iodide crystal doped by europium (SrI2(Eu)) was produced by using the Stockbarger growth technique. The crystal was subjected to a characterization that includes relative photoelectron output and energy resolution for γ quanta. The intrinsic radioactivity of the SrI2(Eu) crystal scintillator was tested both by using it as scintillator at sea level and by ultra-low background HPGe γ spectrometry deep underground. The response of the SrI2(Eu) detector to α particles ( α / β ratio and pulse shape) was estimated by analysing the 226Ra internal trace contamination of the crystal. We have measured: α / β = 0.55 at E α = 7.7 MeV , and no difference in the time decay of the scintillation pulses induced by α particles and γ quanta. The application of the obtained results in the search for the double electron capture and electron capture with positron emission in 84Sr has been investigated at a level of sensitivity: T 1 / 2 ∼ 10 15 – 10 16 yr . The results of these studies demonstrate the potentiality of this material for a variety of scintillation applications, including low-level counting experiments.

Fast neutron detection with pressurized 4 He scintillation detectors

Abstract: Measurement result and performance parameters are presented for fast neutron detectors exploiting the scintillation of natural helium at high pressure. This detection medium has a very low electron density, minimizing the sensitivity to gamma radiation and thus enabling neutron detection also in high gamma radiation environment. Contrary to proportional counters, scintillation detection enables fast (nanosecond) timing and pulse shape discrimination, a technique that enables a lower neutron detection threshold. In this work, the basic principles of the detector are described, followed by a study of gamma rejection capabilities. Methods to calibrate the detector are discussed. Finally, a brief description of a 4He scintillation based detector system including data acquisition electronics is given.

Neutron detection in a high gamma-ray background with EJ-301 and EJ-309 liquid scintillators

Abstract: Using a fast digitizer, the neutron–gamma discrimination capability of the new liquid scintillator EJ-309 is compared with that obtained using standard EJ-301. Moreover the capability of both the scintillation detectors to identify a weak neutron source in a high gamma-ray background is demonstrated. The probability of neutron detection is PD =95% at 95% confidence level for a gamma-ray background corresponding to a dose rate of 100 μSv/h.

Analysis of the Characteristics of Low-Latitude GPS Amplitude Scintillation Measured During Solar Maximum Conditions and Implications for Receiver Performance

Abstract: Ionospheric scintillations are fluctuations in the phase and/or amplitude of trans-ionospheric radio signals caused by electron density irregularities in the ionosphere. A better understanding of the scintillation pattern is important to make a better assessment of GPS receiver performance, for instance. Additionally, scintillation can be used as a tool for remote sensing of ionospheric irregularities. Therefore, the study of ionospheric scintillation has both scientific as well as technological implications. In the past few years, there has been a significant advance in the methods for analysis of scintillation and in our understanding of the impact of scintillation on GPS receiver performance. In this work, we revisit some of the existing methods of analysis of scintillation, propose an alternative approach, and apply these techniques in a comprehensive study of the characteristics of amplitude scintillation. This comprehensive study made use of 32 days of high-rate (50 Hz) measurements made by a GPS-based scintillation monitor located in Sao Jose dos Campos, Brazil (23.2°S, 45.9°W, −17.5° dip latitude) near the Equatorial Anomaly during high solar flux conditions. The variability of the decorrelation time (τ0) of scintillation patterns is presented as a function of scintillation severity index (S4). We found that the values of τ0 tend to decrease with the increase of S4, confirming the results of previous studies. In addition, we found that, at least for the measurements made during this campaign, averaged values of τ0 (for fixed S4 index values) did not vary much as a function of local time. Our results also indicate a significant impact of τ0 in the GPS carrier loop performance for S4 ≥ 0.7. An alternative way to compute the probability of cycle slip that takes into account the fading duration time is also presented. The results of this approach show a 38% probability of cycle slips during strong scintillation scenarios (S4 close to 1 and τ0 near 0.2 s). Finally, we present results of an analysis of the individual amplitude fades observed in our set of measurements. This analysis suggests that users operating GPS receivers with C/N0 thresholds around 30 dB-Hz and above can be affected significantly by low-latitude scintillation.

Ionization and scintillation response of high-pressure xenon gas to alpha particles

Abstract: High-pressure xenon gas is an attractive detection medium for a variety of applications in fundamental and applied physics. In this paper we study the ionization and scintillation detection properties of xenon gas at 10 bar pressure. For this purpose, we use a source of alpha particles in the NEXT-DEMO time projection chamber, the large scale prototype of the NEXT-100 neutrinoless double beta decay experiment, in three different drift electric field configurations. We measure the ionization electron drift velocity and longitudinal diffusion, and compare our results to expectations based on available electron scattering cross sections on pure xenon. In addition, two types of measurements addressing the connection between the ionization and scintillation yields are performed. On the one hand we observe, for the first time in xenon gas, large event-by-event correlated fluctuations between the ionization and scintillation signals, similar to that already observed in liquid xenon. On the other hand, we study the field dependence of the average scintillation and ionization yields. Both types of measurements may shed light on the mechanism of electron-ion recombination in xenon gas for highly-ionizing particles. Finally, by comparing the response of alpha particles and electrons in NEXT-DEMO, we find no evidence for quenching of the primary scintillation light produced by alpha particles in the xenon gas.