Showing papers on "Scintillation published in 2013"

Measurement and correction of variations in interstellar dispersion in high-precision pulsar timing

Abstract: Signals from radio pulsars show a wavelength-dependent delay due to dispersion in the interstellar plasma. At a typical observing wavelength, this delay can vary by tens of microseconds on 5-yr time-scales, far in excess of signals of interest to pulsar timing arrays, such as that induced by a gravitational wave background. Measurement of these delay variations is not only crucial for the detection of such signals, but also provides an unparalleled measurement of the turbulent interstellar plasma at astronomical unit (au) scales. In this paper we demonstrate that without consideration of wavelength-independent red noise, ‘simple’ algorithms to correct for interstellar dispersion can attenuate signals of interest to pulsar timing arrays. We present a robust method for this correction, which we validate through simulations, and apply it to observations from the Parkes Pulsar Timing Array. Correction for dispersion variations comes at a cost of increased band-limited white noise. We discuss scheduling to minimize this additional noise, and factors, such as scintillation, that can exacerbate the problem. Comparison with scintillation measurements confirms previous results that the spectral exponent of electron density variations in the interstellar medium often appears steeper than expected. We also find a discrete change in dispersion measure of PSR J1603−7202 of ∼2 × 10^(−3) cm^(−3) pc for about 250 d. We speculate that this has a similar origin to the ‘extreme scattering events’ seen in other sources. In addition, we find that four pulsars show a wavelength-dependent annual variation, indicating a persistent gradient of electron density on an au spatial scale, which has not been reported previously.

Scintillation and detection characteristics of high-sensitivity CeBr3 gamma-ray spectrometers

Abstract: Crystal growth and detector fabrication technologies have reached such a state of maturity that high-quality large-volume CeBr3 scintillators can now be produced with dimensions of 2″×2″ and well above. We present a study of CeBr3 samples of various dimensions and show that they have a number of advantages over equivalently sized LaBr3:5%Ce for gamma-ray spectroscopy applications requiring high detection sensitivity. At the present time, the achieved energy resolution of CeBr3 is about 4% FWHM at 662 keV, i.e. 25% worse than that of LaBr3:5%Ce. However, thanks to the drastically reduced intrinsic activity, CeBr3 gamma-ray detection sensitivity is about 1 order of magnitude better than that of LaBr3:5%Ce at energies of 1461 keV and 2614.5 keV, which are relevant for the detection of 40K and 208Tl (232Th), respectively. In this communication, we report on several aspects of CeBr3 gamma-ray spectrometers, such as scintillation characteristics, non-proportionality of the response, gamma-ray detection performances up to 3 MeV and radiation tolerance.

Temperature Dependence of Scintillation Properties of Bright Oxide Scintillators for Well-Logging

Abstract: Scintillation characteristics such as the pulse height, energy resolution, and decay time of single crystals of Tl-doped NaI (Tl:NaI), Ce-doped Lu2SiO5 (Ce:LSO), Ce-doped YAlO3 (Ce:YAP), Ce-doped Gd3(Al,Ga)5O12 (Ce:GAGG), Pr-doped Lu3Al5O12 (Pr:LuAG), undoped LuAG, and Ce-doped Y3Al5O12 (Ce:YAG) transparent ceramics were compared at 25–150 °C to simulate well logging conditions. For increasing temperature, the light output of the scintillators decreased, mostly because of thermal quenching. Among these samples, Pr:LuAG demonstrated the highest scintillation performance at 150 °C.

Sub-200 ps CRT in monolithic scintillator PET detectors using digital SiPM arrays and maximum likelihood interaction time estimation

Abstract: Digital silicon photomultiplier (dSiPM) arrays have favorable characteristics for application in monolithic scintillator detectors for time-of-flight positron emission tomography (PET). To fully exploit these benefits, a maximum likelihood interaction time estimation (MLITE) method was developed to derive the time of interaction from the multiple time stamps obtained per scintillation event. MLITE was compared to several deterministic methods. Timing measurements were performed with monolithic scintillator detectors based on novel dSiPM arrays and LSO:Ce,0.2%Ca crystals of 16 × 16 × 10 mm3, 16 × 16 × 20 mm3, 24 × 24 × 10 mm3, and 24 × 24 × 20 mm3. The best coincidence resolving times (CRTs) for pairs of identical detectors were obtained with MLITE and measured 157 ps, 185 ps, 161 ps, and 184 ps full-width-at-half-maximum (FWHM), respectively. For comparison, a small reference detector, consisting of a 3 × 3 × 5 mm3 LSO:Ce,0.2%Ca crystal coupled to a single pixel of a dSiPM array, was measured to have a CRT as low as 120 ps FWHM. The results of this work indicate that the influence of the optical transport of the scintillation photons on the timing performance of monolithic scintillator detectors can at least partially be corrected for by utilizing the information contained in the spatio-temporal distribution of the collection of time stamps registered per scintillation event.

Improvement of γ-ray energy resolution of LaBr3:Ce3+ scintillation detectors by Sr2+ and Ca2+ co-doping

Abstract: Commercially available LaBr3:5% Ce3+ scintillators show with photomultiplier tube readout about 2.7% energy resolution for the detection of 662 keV γ-rays. Here we will show that by co-doping LaBr3:Ce3+ with Sr2+ or Ca2+ the resolution is improved to 2.0%. Such an improvement is attributed to a strong reduction of the scintillation light losses that are due to radiationless recombination of free electrons and holes during the earliest stages (1–10 ps) inside the high free charge carrier density parts of the ionization track.

Effect of codoping on scintillation and optical properties of a Ce-doped Gd 3 Ga 3 Al 2 O 12 scintillator

Abstract: Single crystals of Gd3Ga3Al2O12 : Ce with different codopants were successfully grown using the Czochralski technique. Optical and scintillation properties of these codoped crystals were studied in detail including absorption, photoluminescence excitation and emission, decay time and thermoluminescence. This study revealed that while boron codoping improves the scintillation light output and energy resolution and decreases self-absorption in these crystals, calcium codoping affects their properties in the opposite manner. In addition to antisite defects, the effect of room temperature trap centres on the sensitivity of these crystals to light exposure is also reported for the first time. Light sensitivity was also found to be affected with the incorporation of codopants in the lattice. The effect of annealing in oxidizing and reducing atmospheres on the scintillation and optical properties of differently codoped crystals was also investigated in detail in order to better understand the defect structure of these crystals. All these measurements together are used to explain the effect of codoping on the crystal field and defect structure of these crystals.

Characterization of high‐latitude ionospheric scintillation of GPS signals

Abstract: [1] This paper presents statistical analysis of arctic auroral oval ionospheric scintillation events during the current solar maximum based on high-rate Global Positioning System data collected in Gakona, Alaska (62.39°N, 145.15°W) from August 2010 to March 2013. The objective is to gain a better understanding of the climatology and morphology of ionospheric scintillation in high-latitude regions. A scintillation event filter, multipath identification procedures, and other processes are applied to exclude nonscintillation related signal intensity and phase fluctuation and to extract scintillation events with S4 index above 0.12 and phase sigma above 6° from over 657 days of data. A total of over 5800 scintillation events were identified; most of them show phase fluctuations, only 10% of the phase fluctuations are accompanied by weak amplitude scintillation. Based on the occurrence time, signal direction of arrival, intensity, and duration of these scintillation events and the solar and geomagnetic activities associated with these events, diurnal, seasonal, spatial, and solar activity dependencies are derived and presented in the paper.

Pulse shape discrimination in the plastic scintillator EJ-299-33

Abstract: New advances in plastic scintillation compositions have opened the field to new, exciting instruments capable of neutron-gamma ray pulse shape discrimination (PSD). We present PSD figure of merit parameters and neutron time-of-flight from Cf-252 using a 5.08-cm diameter by 5.08-cm thick sample of PSD-capable plastic scintillator EJ-299-33 and compare these results to those from a same-sized EJ-309 liquid scintillator detector. An offline, digital PSD method was applied to both detectors. The results show that EJ-299-33 plastic PSD is very good, having a figure of merit of approximately 0.9 for 120 keVee threshold; however the EJ-309 liquid scintillator PSD is superior to the EJ-299-33 plastic scintillator PSD, with a figure of merit of 1.5 at the same measurement threshold. We also found that the EJ-299-33 has reduced neutron detection efficiency compared to the EJ-309. For the fission neutron spectrum measured here, the ratio of the plastic to liquid total number of measured neutrons was approximately 0.63.

Time of flight positron emission tomography towards 100ps resolution with L(Y)SO: An experimental and theoretical analysis

Abstract: Scintillation crystals have a wide range of applications in detectors for high energy and medical physics. They are recquired to have not only good energy resolution, but also excellent time resolution. In medical applications, L(Y)SO crystals are commonly used for time of flight positron emission tomography (TOF-PET). This study aims at determining the experimental and theoretical limits of timing using L(Y)SO based scintillators coupled to silicon photomultipliers (SiPMs). Measurements are based on the time-over-threshold method in a coincidence setup utilizing the ultra-fast amplifier-discriminator NINO and a fast oscilloscope. Using a 2 × 2 × 3 mm3 LSO:Ce codoped 0.4% Ca crystal coupled to a commercially available SiPM (Hamamatsu S10931-050P MPPC), we achieve a coincidence time resolution (CTR) of 108±5ps FWHM measured at E=511keV. We determine the influence of the data acquisition system to 27±2ps FWHM and thus negligible as compared to the CTR. This shows that L(Y)SO scintillators coupled to SiPM photodetectors are capable of achieving very good time resolution close to the desired 100ps FWHM for TOF-PET systems. To fully understand the measured values, we developed a simulation tool in MATLAB that incorporates the timing properties of the photodetector, the scintillation properties of the crystal and the light transfer within the crystal simulated by SLITRANI. The simulations are compared with measured data in order to determine their predictive power. Finally we use this model to discuss the influence of several important parameters on the time resolution like scintillation rise- and fall time and light yield, as well as single photon time resolution (SPTR) and the detection efficiency of the SiPM. In addition we find the influence of photon travel time spread in the crystal not negligible on the CTR, even for the used 2 × 2 × 3 mm3 geometry.

Performances of a large mass ZnSe bolometer to search for rare events

Abstract: Scintillating bolometers of ZnSe are the baseline choice of the LUCIFER experiment, whose aim is to observe the neutrinoless double beta decay of 82Se. The independent read-out of the heat and scintillation signals allows to identify and reject α particle interactions, the dominant background source for bolometric detectors. In this paper we report the performances of a ZnSe crystal operated within the LUCIFER R&D. We measured the scintillation yield, the energy resolution and the background in the energy region where the signal from 0νDBD decay of 82Se is expected with an exposure of 9.4 kgdays. With a newly developed analysis algorithm we improved the rejection of α events, and we estimated the increase in energy resolution obtained by the combination of the heat and light signals. For the first time we measured the light emitted by nuclear recoils, and found it to be compatible with zero. We conclude that the discrimination of nuclear recoils from β/γ interactions in the WIMPs energy region is possible, but low-noise light detectors are needed.

First characterization of a digital SiPM based time-of-flight PET detector with 1 mm spatial resolution

Abstract: Monolithic scintillator detectors can offer a combination of spatial resolution, energy resolution, timing performance, depth-of-interaction information, and detection efficiency that make this type of detector a promising candidate for application in clinical, time-of-flight (TOF) positron emission tomography (PET). In such detectors the scintillation light is distributed over a relatively large number of photosensor pixels and the light intensity per pixel can be relatively low. Therefore, monolithic scintillator detectors are expected to benefit from the low readout noise offered by a novel photosensor called the digital silicon photomultiplier (dSiPM). Here, we present a first experimental characterization of a TOF PET detector comprising a 24 × 24 × 10 mm3 LSO:Ce,0.2%Ca scintillator read out by a dSiPM array (DPC-6400–44–22) developed by Philips Digital Photon Counting. A spatial resolution of ~1 mm full-width-at-half-maximum (FWHM) averaged over the entire crystal was obtained (varying from just below 1 mm FWHM in the detector center to ~1.2 mm FWHM close to the edges). Furthermore, the bias in the position estimation at the crystal edges that is typically found in monolithic scintillators is well below 1 mm even in the corners of the crystal.

Comparative analysis of spread-F signature and GPS scintillation occurrences at Tucumán, Argentina

Abstract: [1] We analyze data recorded from October 2010 to September 2011, during the ascending phase of the 24th solar cycle, from an Advanced Ionospheric Sounder-Istituto Nazionale di Geofisica e Vulcanologia ionosonde and a GPS Ionospheric Scintillation and total electron content (TEC) monitor scintillation receiver, colocated at low latitude in the Southern American longitudinal sector (Tucuman, 26.9°S, 294.6°E, magnetic latitude 15.5°S, Argentina). The site offers the opportunity to perform spread-F and GPS scintillation statistics of occurrence under the southern crest of the equatorial ionospheric anomaly. Spread-F signatures, classified into four types (strong range spread-F (SSF), range spread-F, frequency spread-F (FSF), and mixed spread-F), the phase and amplitude scintillation index (σΦ and S4, respectively), the TEC, and the rate of TEC parameter, marker of the TEC gradients, that can cause scintillations, are considered. The seasonal behavior results as follows: the occurrence of all four types of spread-F is higher in summer and lower in winter, while the occurrence of scintillations peaks at equinoxes in the postsunset sector and shows a minimum in winter. The correspondence between SSF and scintillations seems to be systematic, and a possible correlation between S4 and FSF peaks is envisaged at the terminator. The investigation focused also on two particular periods, from 12 to 16 March 2011 and from 23 to 29 September 2011, both characterized by the simultaneous presence of SSF signatures and scintillation phenomena, allowing to discuss the role of traveling ionospheric disturbances as a strong candidate causing ionospheric irregularities.

Pulse-shape analysis of CLYC for thermal neutrons, fast neutrons, and gamma-rays

Abstract: Cs2LiYCl6:Ce (CLYC) has been demonstrated to be sensitive to thermal neutrons via the 6Li(n, α )t reaction, and recently to fast neutrons via the 35Cl(n,p) reaction. The scintillation properties of CLYC have been investigated in more detail to further understand its capabilities. Pulses from thermal neutron, fast neutron, and γ -ray induced excitations were captured, digitized over a 16 μ s time range, and analyzed to identify the scintillation mechanisms responsible for the observed shapes. Additionally, the timing resolutions of CLYC crystals of different sizes were measured in coincidence with a fast CeBr3 scintillator. The effect of high count rates on fast neutron energy resolution and pulse-shape discrimination was investigated up to 45 kHz.

Characterization of large volume 3.5″×8″ LaBr3:Ce detectors

Abstract: The properties of large volume cylindrical 3.5″×8″ (89 mm×203 mm) LaBr 3 :Ce scintillation detectors coupled to the Hamamatsu R10233-100SEL photo-multiplier tube were investigated. These crystals are among the largest ones ever produced and still need to be fully characterized to determine how these detectors can be utilized and in which applications. We tested the detectors using monochromatic γ–ray sources and in-beam reactions producing γ rays up to 22.6 MeV; we acquired PMT signal pulses and calculated detector energy resolution and response linearity as a function of γ-ray energy. Two different voltage dividers were coupled to the Hamamatsu R10233-100SEL PMT: the Hamamatsu E1198-26, based on straightforward resistive network design, and the “LABRVD”, specifically designed for our large volume LaBr 3 :Ce scintillation detectors, which also includes active semiconductor devices. Because of the extremely high light yield of LaBr 3 :Ce crystals we observed that, depending on the choice of PMT, voltage divider and applied voltage, some significant deviation from the ideally proportional response of the detector and some pulse shape deformation appear. In addition, crystal non-homogeneities and PMT gain drifts affect the (measured) energy resolution especially in case of high-energy γ rays. We also measured the time resolution of detectors with different sizes (from 1″×1″ up to 3.5″×8″), correlating the results with both the intrinsic properties of PMTs and GEANT simulations of the scintillation light collection process. The detector absolute full energy efficiency was measured and simulated up to γ-rays of 30 MeV

Concept for a dark matter detector using liquid helium-4

Abstract: Direct searches for light dark matter particles (mass < 10 GeV) are especially challenging because of the low energies transferred in elastic scattering to typical heavy nuclear targets. We investigate the possibility of using liquid Helium-4 as a target material, taking advantage of the favorable kinematic matching of the Helium nucleus to light dark matter particles. Monte Carlo simulations are performed to calculate the charge, scintillation, and triplet helium molecule signals produced by recoil He ions, for a variety of energies and electric fields. We show that excellent background rejection can be achieved based on the ratios between different signal channels. We also present some concepts for a liquid-helium-based dark matter detector. Key to the proposed approach is the use of a large electric field to extract electrons from the event site, and the amplification of this charge signal, through proportional scintillation, liquid electroluminescence, or roton emission. The sensitivity of the proposed detector to light dark matter particles is estimated for various electric fields and light collection efficiencies.

Experimental demonstration of vortex phase-induced reduction in scintillation of a partially coherent beam.

Abstract: We carry out experimental measurement of the scintillation index of a partially coherent beam-carrying vortex phase (i.e., Gaussian–Schell model vortex beam) propagating through thermally induced turbulence. It is demonstrated that a Gaussian–Schell model vortex beam has appreciably smaller scintillation than a Gaussian–Schell model beam, which will be useful in free-space optical communication.

DarkSide search for dark matter

Abstract: The DarkSide staged program utilizes a two-phase time projection chamber (TPC) with liquid argon as the target material for the scattering of dark matter particles. Efficient background reduction is achieved using low radioactivity underground argon as well as several experimental handles such as pulse shape, ratio of ionization over scintillation signal, 3D event reconstruction, and active neutron and muon vetos. The DarkSide-10 prototype detector has proven high scintillation light yield, which is a particularly important parameter as it sets the energy threshold for the pulse shape discrimination technique. The DarkSide-50 detector system, currently in commissioning phase at the Gran Sasso Underground Laboratory, will reach a sensitivity to dark matter spin-independent scattering cross section of 10−45 cm2 within 3 years of operation.

Temperature dependence of BCF plastic scintillation detectors.

Abstract: We examined temperature dependence in plastic scintillation detectors (PSDs) made of BCF-60 or BCF-12 scintillating fiber coupled to optical fiber with cyanoacrylate. PSDs were subjected to a range of temperatures using a temperature-controlled water bath and irradiated at each temperature while either the dose was measured using a CCD camera or the spectral output was measured using a spectrometer. The spectrometer was used to examine the intensity and spectral distribution of scintillation light emitted by the PSDs, Cerenkov light generated within the PSD, and light transmitted through an isolated optical coupling. BCF-60 PSDs exhibited a 0.50% decrease and BCF-12 PSDs a 0.09% decrease in measured dose per °C increase, relative to dose measured at 22 °C. Spectrometry revealed that the total intensity of the light generated by BCF-60 and BCF-12 PSDs decreased by 0.32% and 0.13%, respectively, per °C increase. The spectral distribution of the light changed slightly with temperature for both PSDs, accounting for the disparity between the change in measured dose and total light output. The generation of Cerenkov light was temperature independent. However, light transmitted through optical coupling between the scintillator and the optical fiber also exhibited temperature dependence.

Experimental study of the scintillation index of a radially polarized beam with controllable spatial coherence

Abstract: Radially polarized (RP) beam with controllable spatial coherence (i.e., partially coherent RP beam) was generated in experiment recently [Appl. Phys. Lett. 100, 051108 (2012)]. In this letter, we report experimental study of the scintillation index of a partially coherent RP beam propagating through thermally induced turbulence. Our results show that a partially coherent RP beam has advantage over a linearly polarized partially coherent beam for reducing turbulence-induced scintillation, which will be useful in free-space optical communications, remote sensing and laser radar systems.

Submicron-diameter phase-separated scintillator fibers for high-resolution X-ray imaging

Abstract: We demonstrated micrometer-scale resolution X-ray imaging by using phase-separated scintillator fibers. Hexagonally well-aligned 680-nm-diameter GdAlO3(GAP):Ce3+ scintillator fibers surrounded with α-Al2O3 were fabricated from directionally solidified eutectics. The GAP:Ce3+ fibers convert X-rays to lights and emitted lights are confined and transported along the fiber direction by a total reflection mode. High-resolution X-ray image of a gold grating phantom with a 4 μm aperture, corresponding to a bundle of 12 fibers, was achieved even with a 150 -μm-thick scintillator. These scintillator fibers overcome resolution reduction caused by light scattering and almost reach the resolution limit of the material nature itself.

Quenching correction for volumetric scintillation dosimetry of proton beams

Abstract: Volumetric scintillation dosimetry has the potential to provide fast, high-resolution, three-dimensional radiation dosimetry. However, scintillators exhibit a nonlinear response at the high linear energy transfer (LET) values characteristic of proton Bragg peaks. The purpose of this study was to develop a quenching correction method for volumetric scintillation dosimetry of proton beams. Scintillation light from a miniature liquid scintillator detector was measured along the central axis of a 161.6 MeV proton pencil beam. Three-dimensional dose and LET distributions were calculated for 85.6, 100.9, 144.9 and 161.6 MeV beams using a validated Monte Carlo model. LET values were also calculated using an analytical formula. A least-squares fit to the data established the empirical parameters of a quenching correction model. The light distribution in a tank of liquid scintillator was measured with a CCD camera at all four beam energies. The quenching model and LET data were used to correct the measured light distribution. The calculated and measured Bragg peak heights agreed within ±3% for all energies except 85.6 MeV, where the agreement was within ±10%. The quality of the quenching correction was poorer for sharp low-energy Bragg peaks because of blurring and detector size effects. The corrections performed using analytical LET values resulted in doses within 1% of those obtained using Monte Carlo LET values. The proposed method can correct for quenching with sufficient accuracy for dosimetric purposes. The required LET values may be computed effectively using Monte Carlo or analytical methods. Future detectors should improve blurring correction methods and optimize the pixel size to improve accuracy for low-energy Bragg peaks.

Decay time and pulse shape discrimination of liquid scintillators based on novel solvents

Abstract: Over the past few years the liquid scintillation technique employed for particle detection applications has undergone a significant technological breakthrough with the introduction of novel solvents tailored to address the concerns about toxicity, flammability and disposal problems associated with the scintillators of traditional formulation. The increasing popularity of the new solvents in the realization of experimental set-ups of various degrees of size and complexity implies the need of a thorough study and characterization of the features of the corresponding scintillation mixtures, with the aim to approach eventually a level of understanding similar to that, very accurate, achieved throughout many years of research for the scintillators realized with conventional solvents. In this general context, aim of this work is to illustrate the results of the fluorescence decay time and pulse shape discrimination measurements carried out on a set of scintillation mixtures realized using two of such novel solvents, i.e., linear alkylbenzene (LAB) and di-isopropylnaphthalene (DIN). The measurements have been performed either under particle or UV excitation of the scintillating solutions, which permitted to unravel the features both of the fast component and of the long tail forming the entire scintillation pulse. Moreover, the particle characterization via β or α excitation allows also predicting the α⧸β pulse shape discrimination capability of the mixtures, a property of paramount significance for applications focused on the increasingly important field of low background detectors.

3D position estimation using an artificial neural network for a continuous scintillator PET detector.

Abstract: Continuous crystal based PET detectors have features of simple design, low cost, good energy resolution and high detection efficiency. Through single-end readout of scintillation light, direct three-dimensional (3D) position estimation could be another advantage that the continuous crystal detector would have. In this paper, we propose to use artificial neural networks to simultaneously estimate the plane coordinate and DOI coordinate of incident γ photons with detected scintillation light. Using our experimental setup with an '8 + 8' simplified signal readout scheme, the training data of perpendicular irradiation on the front surface and one side surface are obtained, and the plane (x, y) networks and DOI networks are trained and evaluated. The test results show that the artificial neural network for DOI estimation is as effective as for plane estimation. The performance of both estimators is presented by resolution and bias. Without bias correction, the resolution of the plane estimator is on average better than 2 mm and that of the DOI estimator is about 2 mm over the whole area of the detector. With bias correction, the resolution at the edge area for plane estimation or at the end of the block away from the readout PMT for DOI estimation becomes worse, as we expect. The comprehensive performance of the 3D positioning by a neural network is accessed by the experimental test data of oblique irradiations. To show the combined effect of the 3D positioning over the whole area of the detector, the 2D flood images of oblique irradiation are presented with and without bias correction.

GPS phase scintillation associated with optical auroral emissions: First statistical results from the geographic South Pole

Abstract: [1] Ionospheric irregularities affect the propagation of Global Navigation Satellite System (GNSS) signals, causing radio scintillation. Particle precipitation from the magnetosphere into the ionosphere, following solar activity, is an important production mechanism for ionospheric irregularities. Particle precipitation also causes the aurorae. However, the correlation of aurorae and GNSS scintillation events is not well established in literature. This study examines optical auroral events during 2010–2011 and reports spatial and temporal correlations with Global Positioning System (GPS) L1 phase fluctuations using instrumentation located at South Pole Station. An all-sky imager provides a measure of optical emission intensities ([OI] 557.7 nm and 630.0 nm) at auroral latitudes during the winter months. A collocated GPS antenna and scintillation receiver facilitates superimposition of auroral images and GPS signal measurements. Correlation statistics are produced by tracking emission intensities and GPS L1 σφ indices at E and F-region heights. This is the first time that multi-wavelength auroral images have been compared with scintillation measurements in this way. Correlation levels of up to 74% are observed during 2–3 hour periods of discrete arc structuring. Analysis revealed that higher values of emission intensity corresponded with elevated levels of σφ. The study has yielded the first statistical evidence supporting the previously assumed relationship between the aurorae and GPS signal propagation. The probability of scintillation-induced GPS outages is of interest for commercial and safety-critical operations at high latitudes. Results in this paper indicate that image databases of optical auroral emissions could be used to assess the likelihood of multiple satellite scintillation activity.

The MU-RAY experiment. An application of SiPM technology to the understanding of volcanic phenomena

Abstract: The purpose of the MU-RAY project is to develop an innovative approach to the study of volcanoes and their monitoring based on a particle physics approach. The test site is Vesuvio: one of the higher risk volcanoes in the world. In this context, muon radiography is an innovative method of enormous impact. This is an imaging technique which relies on the measurement, by means of a cosmic ray telescope, of the absorption in the volcano of muons with near-horizontal trajectories, produced by the interactions of cosmic rays with the atmosphere. Since 2003 this technique has been successfully used on volcanoes in Japan, providing pictures of their vertices with resolutions much better than those obtained with the traditional techniques based on gravimeters. Researchers from Naples and Florence are currently involved in the construction and testing of a prototype telescope based on the use of bars of plastic scintillator with a triangular section whose scintillation light is collected by special fibres (wave length shifters) and transported to SiPM (Silicon photomultipliers). A complete prototype telescope, consisting of three xy scintillation planes and 1 m2 active area has been assembled and is now under test.