Showing papers on "Scintillation published in 2019"

Metal Halide Perovskite Nanosheet for X-ray High-Resolution Scintillation Imaging Screens.

Abstract: Scintillators, which are capable of converting ionizing radiation into visible photons, are an integral part of medical, security, and commercial diagnostic technologies such as X-ray imaging, nuclear cameras, and computed tomography. Conventional scintillator fabrication typically involves high-temperature sintering, generating agglomerated powders or large bulk crystals, which pose major challenges for device integration and processability. On the other hand, colloidal quantum dot scintillators cannot be cast into compact solid films with the necessary thickness required for most X-ray applications. Here, we report the room-temperature synthesis of a colloidal scintillator comprising CsPbBr3 nanosheets of large concentration (up to 150 mg/mL). The CsPbBr3 colloid exhibits a light yield (∼21000 photons/MeV) higher than that of the commercially available Ce:LuAG single-crystal scintillator (∼18000 photons/MeV). Scintillators based on these nanosheets display both strong radioluminescence (RL) and long-term stability under X-ray illumination. Importantly, the colloidal scintillator can be readily cast into a uniform crack-free large-area film (8.5 × 8.5 cm2 in area) with the requisite thickness for high-resolution X-ray imaging applications. We showcase prototype applications of these high-quality scintillating films as X-ray imaging screens for a cellphone panel and a standard central processing unit chip. Our radiography prototype combines large-area processability with high resolution and a strong penetration ability to sheath materials, such as resin and silicon. We reveal an energy transfer process inside those stacked nanosheet solids that is responsible for their superb scintillation performance. Our findings demonstrate a large-area solution-processed scintillator of stable and efficient RL as a promising approach for low-cost radiography and X-ray imaging applications.

Bright and fast scintillation of organolead perovskite MAPbBr3 at low temperatures

Abstract: We report the excellent scintillation properties of MAPbBr3, an organic–inorganic trihalide perovskite (OTP). The characteristic scintillation time constants were determined using pulsed monochromatic 14 keV X-rays from a synchrotron. We find that between 50 and 130 K the MAPbBr3 crystal exhibits a very fast and intense scintillation response, with the fast (τf) and slow (τs) decay components reaching 0.1 and 1 ns, respectively. The light yield of MAPbBr3 is estimated to be 90 000 ± 18 000 ph MeV−1 at 77 K and 116 000 ± 23 000 ph MeV−1 at 8 K.

The Impact of Different Kernel Functions on the Performance of Scintillation Detection Based on Support Vector Machines.

Abstract: Scintillation caused by the electron density irregularities in the ionospheric plasma leads to rapid fluctuations in the amplitude and phase of the Global Navigation Satellite Systems (GNSS) signals. Ionospheric scintillation severely degrades the performance of the GNSS receiver in the signal acquisition, tracking, and positioning. By utilizing the GNSS signals, detecting and monitoring the scintillation effects to decrease the effect of the disturbing signals have gained importance, and machine learning-based algorithms have been started to be applied for the detection. In this paper, the performance of Support Vector Machines (SVM) for scintillation detection is discussed. The effect of the different kernel functions, namely, linear, Gaussian, and polynomial, on the performance of the SVM algorithm is analyzed. Performance is statistically assessed in terms of probabilities of detection and false alarm of the scintillation event. Real GNSS signals that are affected by significant phase and amplitude scintillation effect, collected at the South African Antarctic research base SANAE IV and Hanoi, Vietnam have been used in this study. This paper questions how to select a suitable kernel function by analyzing the data preparation, cross-validation, and experimental test stages of the SVM-based process for scintillation detection. It has been observed that the overall accuracy of fine Gaussian SVM outperforms the linear, which has the lowest complexity and running time. Moreover, the third-order polynomial kernel provides improved performance compared to linear, coarse, and medium Gaussian kernel SVMs, but it comes with a cost of increased complexity and running time.

Proton fixed-target scintillation experiment to search for millicharged dark matter

Abstract: We propose a low-cost and movable setup to probe minicharged particles using high-intensity proton fixed-target facilities. This proposal, FerMINI, consists of a scintillator-based detector, requiring multicoincident scintillation signatures within a small time window, located downstream of the proton target of a neutrino experiment. During the collisions of a large number of protons on the target, intense minicharged particle beams may be produced via meson photo-decays and Drell-Yan production. We take advantage of the high statistics, shielding, and potential neutrino-detector-related background reduction to search for minicharged particles in two potential sites: the MINOS near detector hall and the proposed DUNE near detector hall, both at Fermilab. We also explore several alternative designs, including modifications to increase signal yield, and combining this detector technology with existing and planned neutrino detectors to better search for minicharged particles. FerMINI can achieve unprecedented sensitivity for minicharged particles in the MeV to few GeV regime with fractional charge ϵ=Qχ/e as low as 10-4.

Detection of GNSS Ionospheric Scintillations Based on Machine Learning Decision Tree

Abstract: This paper proposes a methodology for automatic, accurate, and early detection of amplitude ionospheric scintillation events, based on machine learning algorithms, applied on big sets of 50 Hz postcorrelation data provided by a global navigation satellite system receiver. Experimental results on real data show that this approach can considerably improve traditional methods, reaching a detection accuracy of 98%, very close to human-driven manual classification. Moreover, the detection responsiveness is enhanced, enabling early scintillation alerts.

Electron-interacting dark matter: Implications from DAMA/LIBRA-phase2 and prospects for liquid xenon detectors and NaI detectors

Abstract: We investigate the possibility for the direct detection of low-mass (GeV scale) weakly interacting massive particles (WIMP) dark matter in scintillation experiments. Such WIMPs are typically too light to leave appreciable nuclear recoils but may be detected via their scattering off atomic electrons. In particular, the DAMA Collaboration [R. Bernabei et al., Nucl. Phys. At. Energy 19, 307 (2018)10.15407/jnpae2018.04.307] has recently presented strong evidence of an annual modulation in the scintillation rate observed at energies as low as 1 keV. Despite a strong enhancement in the calculated event rate at low energies, we find that an interpretation in terms of electron-interacting WIMPs cannot be consistent with existing constraints. We also demonstrate the importance of correct treatment of the atomic wave functions and show the resulting event rate is very sensitive to the low-energy performance of the detectors, meaning it is crucial that the detector uncertainties be taken into account. Finally, we demonstrate that the potential scintillation event rate can be much larger than may otherwise be expected, meaning that competitive searches can be performed for mχ∼GeV scale WIMPs using the conventional prompt (S1) scintillation signals. This is important given the recent and upcoming very large liquid xenon detectors.

Oceanic spectrum of unstable stratification turbulence with outer scale and scintillation index of Gaussian-beam wave

Abstract: We develop a new spectrum of the refractive-index fluctuations for the unstable stratification ocean based on the linear combination of the temperature spectrum, salinity spectrum and coupling spectrum that all include the outer scale. Our oceanic spectrum agrees better with the experimental data than others do from low wave-number regions to high wave-number regions. Based on our proposed oceanic spectrum, we derive the analytical expression of the scintillation index of Gaussian-beam wave and investigate the influence of the light source and the channel parameters on the scintillation index of Gaussian-beam wave.

Megahertz non-contact luminescence decay time cryothermometry by means of ultrafast PbI2 scintillator

Abstract: Realtime in situ temperature monitoring in difficult experimental conditions or inaccessible environments is critical for many applications. Non-contact luminescence decay time thermometry is often the method of choice for such applications due to a favorable combination of sensitivity, accuracy and robustness. In this work, we demonstrate the feasibility of an ultrafast PbI2 scintillator for temperature determination, using the time structure of X-ray radiation, produced by a synchrotron. The decay kinetics of the scintillations was measured over the 8–107 K temperature range using monochromatic pulsed X-ray excitation. It is found that lead iodide exhibits a very fast and intense scintillation response due to excitons and donor-acceptor pairs, with the fast decay component varying between 0.08 and 0.5 ns – a feature that can be readily exploited for temperature monitoring. The observed temperature dependence of the decay time is discussed in terms of two possible mechanisms of thermal quenching – transition over activation barrier and phonon-assisted escape. It is concluded that the latter provides a better fit to the experimental results and is consistent with the model of luminescence processes in PbI2. We evaluated the sensitivity and estimated the accuracy of the temperature determination as ca. ±6 K at 107 K, improving to ±1.4 K at 8 K. The results of this study prove the feasibility of temperature monitoring, using ultrafast scintillation of PbI2 excited by X-ray pulses from a synchrotron, thus enabling non-contact in-situ cryothermometry with megahertz sampling rate.

A review on the progress of ZnSe as inorganic scintillator

Abstract: Modern scintillator detectors act as an efficient tool for detection and measurement of ionizing radiations. ZnSe based materials have been found to be a promising candidate for scintillation applications. These scintillators show much-needed scintillation efficiency along with advantages such as high thermal and radiation stability, less-toxicity, non-hygroscopicity, emissions in the visible range and small decay time etc. Further, in quantum confinement regime, they show improvement in luminescent properties and size dependent emissions. In this review article, the attempt has been made to trace the progress of ZnSe based materials towards highly efficient quantum dot scintillators. Here, the fundamental process of scintillation has been explained. Factors such as doping, annealing, heavy ion irradiation which affects the scintillation response of ZnSe based scintillators have also been discussed. Method of synthesis plays a key role in optimization of quantum dot properties. Hence, it has been tried to trace the development in methods of synthesis of quantum dots. With optimized synthesis, we can extend applications of these highly efficient quantum dot scintillators for various scientific and industrial applications.

Scintillation properties of a partially coherent vector beam with vortex phase in turbulent atmosphere

Abstract: We undertake a computational and experimental study of an advanced class of structured beams, partially coherent radially polarized vortex (PCRPV) beams, on propagation through atmospheric turbulence. A computational propagation model is established to simulate this class of beams, and it is used to calculate the average intensity and on-axis scintillation index of PCRPV beams. On comparison with other classes of structured beams, such as partially coherent vortex beams and partially coherent radially polarized beams, it is found that the PCRPV beams, which structure phase, coherence and polarization simultaneously, show marked improvements in atmospheric propagation. The simulation results agree reasonably well with the experimental results. These beams will be useful in free-space optical communications and remote sensing.

Effects of Solar Scintillation on Deep Space Communications: Challenges and Prediction Techniques

Abstract: A reliable deep space communications system plays a key role in extending the range of space communications and has become an indispensable part of space information networks. With the emergence of many deep space exploration projects, it can be envisioned that a new era of research on deep space communications has arrived. However, the performance of deep space communications is severely degraded by solar scintillation, which occurs frequently during superior solar conjunction. In this article, we first review the state of the art of solar scintillation research, including the definition of solar scintillation, influencing factors, assessment methods, and scintillation models. Then an effective solar scintillation prediction model is proposed to overcome the challenges related to solar scintillation for deep space communications. After that, a coronal turbulence channel model is investigated and discussed. Based on this coronal channel model and our proposed solar scintillation model, the link bit error rate performance is further analyzed. Finally, we identify some open problems and research directions that could be investigated for a deep space communications system during superior solar conjunctions, which will support space information networks.

Compton PET: a layered structure PET detector with high performance.

Abstract: In most high-resolution PET detector designs, there is an inherent trade-off between spatial resolution and detector efficiency. We have developed and tested a new geometry for the detector module which avoids this trade-off. The module uses a layered structure, in which four crystal slabs are stacked in the depth direction and optically separated by enhanced specular reflector (ESR) film. The scintillation light within each layer is measured by 16 SiPMs located on the four sides of the crystal. Analog signals from all SiPMs (4 × 16) on the four sides of the crystal are digitized individually using a 64-channel TOFPET-2 module. The four-sided readout method reduces the problem of light trapping resulting from total internal reflection when reading out the end(s) of traditional scintillation crystal arrays, thus increasing the light collection efficiency. In this work, we demonstrate the readout of a complete layered detector with 4 layers. The high light collection efficiency results in a FWHM energy resolution of 10.3%, and a FWHM timing resolution of 348 ps. The distribution of scintillation light detected by the SiPMs was used to decode the interaction position of each gamma ray using a trained neural network. A FWHM spatial resolution of 1.1 ± 0.1 mm was achieved. This design allows the detection efficiency of the module to be increased by adding additional crystal slabs along the depth direction. Since the position, energy, and timing are measured for each layer independently, increasing the system sensitivity by adding more layers will not affect the spatial/energy/timing resolution. Furthermore, the layered structure allows partial recovery of position information for events that undergo Compton scatter within the detector.

Measured neutron light-output response for trans-stilbene and small-molecule organic glass scintillators

Abstract: The neutron light-output response from quasi-monoenergetic neutrons was measured for a O5.08 × 5.08 cm trans-stilbene and a O5.08 × 5.08 cm small-molecule organic glass scintillator . Quasi-monoenergetic neutrons were isolated from a time-of-flight measurement of a Cf-252 spontaneous fission source with a flight distance of 200 cm. Two different methods of waveform analysis were implemented, where the neutron light output response proportional to the detected pulse height distribution (PHD) and pulse integral distribution (PID) were extracted for both types of scintillators. The light output response proportional to the pulse integral was determined by integrating the digitized waveform with an integration window length of 150 ns, which contained > 90% and > 95% of the scintillation light for an averaged neutron and photon waveform above 0.5 MeVee. The extracted light-output data were fitted with a semi-empirical function based on the Birks’ formula. The results show that the small-molecule organic glass scintillator produced more light than the trans-stilbene scintillator for a range of neutron energies of 0.79 ± 0.04 MeV to 3.65 ± 0.38 MeV. The fitted semi-empirical function was used in MCNPX-PoliMi with MPPost to simulate the detector response from an independent measurement of a Cf-252 spontaneous fission source to test the fidelity of the extracted light output response functions. The simulated and measured total neutron count rate agreed to within ± 3 % and ± 1% for the trans-stilbene and small-molecule organic glass scintillators. Due to the different light-output response of the two scintillators, the intrinsic neutron detection efficiency was calculated for equal observable ranges in light output and neutron-equivalent energy units. The intrinsic neutron detection efficiency in the observable light-output range of 0.06 MeVee to 2.4 MeVee was calculated to be 28.66 ± 1.43 % and 34.66 ± 1.73 % for pulse height and pulse integral analysis, respectively. For the same observable light-output range, the intrinsic efficiency of small-molecule organic glass was calculated to be 32.54 ± 1.63 % and 37.39 ± 1.87 % for pulse height and pulse integral analysis, respectively. When observing equal light-output ranges, the small-molecule organic glass was 11.92 ± 6.23% and 7.88 ± 7.35% more efficient than the trans-stilbene using pulse height and pulse integral analysis, respectively. When observing equal neutron-equivalent energy ranges, the trans”–stilbene scintillator was 8.4 ± 6.46% and 11.95 ± 6.23% more efficient than the small-molecule organic glass for pulse height and pulse integral analysis, respectively.

Improvement of the Time Resolution of Radiation Detectors Based on Gd 3 Al 2 Ga 3 O 12 Scintillators With SiPM Readout

Abstract: Coincidence time resolution (CTR) of scintillation detectors based on Ce- and Mg-codoped Gd3Al2Ga3O12 (GAGG) scintillation crystals and high-density silicon photomultipliers (SiPMs) is shown to be 165 ps (full width at half maximum) for 511-keV $\gamma $ -quanta, approaching that achieved by using LSO scintillators. To study the prospective for further improvement of the time resolution, the population of the emitting Ce centers was investigated by optical pump and probe technique using selective photoexcitation and probing by a white light continuum with subpicosecond time resolution. The importance of free electron trapping for excitation transfer to emitting Ce ions was revealed. The influence of transfer delay on the scintillation response time is described, and the dynamics of electron relaxation to the lowest excited level of Ce ion is studied experimentally and analyzed by taking into account intracenter relaxation and relaxation via conduction band. The influence of electron diffusivity on the rise time of the population of the emitting level is described. It is shown that codoping of GAGG:Ce by magnesium even at the level as low as 10 ppm efficiently decreases the scintillator response time by enhancing the electron diffusivity.

Scintillation Properties of Perovskite Single Crystals

Abstract: Low-cost solution-processed scintillation radiation detection materials are pursued urgently in ionization applications. Scintillators are key conversion materials that absorb high-energy X(γ) phot...

A Novel Approach to Improve GNSS Precise Point Positioning During Strong Ionospheric Scintillation: Theory and Demonstration

Abstract: At equatorial latitudes, ionospheric scintillation is the major limitation in achieving high-accuracy GNSS positioning. This is because scintillation affects the tracking ability of GNSS receivers causing losses of lock and degradation on code pseudorange and carrier phase measurements, thus degrading accuracy. During strong ionospheric scintillation, such effects are more severe and GNSS users cannot rely on the integrity, reliability, and availability required for safety-critical applications. In this paper, we propose a novel approach able to greatly reduce these effects of scintillation on precise point positioning (PPP). Our new approach consists of three steps: 1) a new functional model that corrects the effects of range errors in the observables; 2) a new stochastic model that uses these corrections to generate more accurate positioning; and 3) a new strategy to attenuate the effects of losses of lock and consequent ambiguities re-initializations that are caused by the need to re-initialize the tracking. We demonstrate the effectiveness of our method in an experiment using a 30-day static dataset affected by different levels of scintillation in the Brazilian southeastern region. Even with limitations imposed by data gaps, our results demonstrate improvements of up to 80% in the positioning accuracy. We show that, in the best cases, our method can completely negate the effects of ionospheric scintillation and can recover the original PPP accuracy that would have existed without any scintillation. The significance of this paper lies in the improvement it offers in the integrity, reliability, and availability of GNSS services and applications.

Polyethylene naphthalate film as a wavelength shifter in liquid argon detectors

Abstract: Liquid argon-based scintillation detectors are important for dark matter searches and neutrino physics. Argon scintillation light is in the vacuum ultraviolet region, making it hard to be detected by conventional means. Polyethylene naphthalate (PEN), an optically transparent thermoplastic polyester commercially available as large area sheets or rolls, is proposed as an alternative wavelength shifter to the commonly-used tetraphenyl butadiene (TPB). By combining the existing literature data and spectrometer measurements relative to TPB, we conclude that the fluorescence yield and timing of both materials may be very close. The evidence collected suggests that PEN is a suitable replacement for TPB in liquid argon neutrino detectors, and is also a promising candidate for dark matter detectors. Advantages of PEN are discussed in the context of scaling-up existing technologies to the next generation of very large ktonne-scale detectors. Its simplicity has a potential to facilitate such scale-ups, revolutionizing the field.

Development of an X-ray imaging detector to resolve 200 nm line-and-space patterns by using transparent ceramics layers bonded by solid-state diffusion.

Abstract: A high-resolution lens-coupled X-ray imaging detector equipped with a thin-layer transparent ceramics scintillator has been developed. The scintillator consists of a 5 μm thick Ce-doped Lu3Al5O12 layer (LuAG:Ce) bonded onto the support substrate of the non-doped LuAG ceramics by using a solid-state diffusion technique. Secondary electron microscopy of the bonded interface indicated that the crystal grains were densely packed without any pores in the optical wavelength scale, indicating a quasi-uniform refractive index across the interface. This guarantees high transparency and minimum reflection, which are essential properties for X-ray imaging detectors. The LuAG:Ce scintillator was incorporated into an X-ray imaging detector coupled with an objective lens with a numerical aperture of 0.85 and an optical magnification of 100. The scintillation light was imaged onto a complementary metal–oxide–semiconductor image sensor. The effective pixel size on the scintillator plane was 65 nm. X-ray transmission images of 200 nm line-and-space patterns were successfully resolved. The high spatial resolution was demonstrated by X-ray transmission images of large integrated circuits with the wiring patterns clearly visualized.

Cherenkov and scintillation light separation using wavelength in LAB based liquid scintillator

Abstract: Linear alkyl benzene (LAB) has in recent years been used as a solvent for PPO in large-scale scintillation detectors, like Daya Bay and SNO+. The combination has several nice properties, including high light yield, good materials compatibility, and excellent pulse shape discrimination. As charged particles move through the LAB+PPO, both Cherenkov and scintillation light are created. Separating Cherenkov from scintillation light would allow a broad range of physics in future large-scale detectors like THEIA, by allowing direction reconstruction with Cherenkov light while retaining the high light yield and good particle ID of a scintillator detector. In this paper, we examine the discrimination of Cherenkov and scintillation light using a set of bandpass and dichroic filters. In principle, Cherenkov light emission extends longer in wavelength than the PPO scintillation spectrum, allowing for exclusive identification. We find that by selecting wavelengths above 450 nm the Cherenkov light can be clearly separated from the scintillation light.

Ionospheric scintillation intensity fading characteristics and GPS receiver tracking performance at low latitudes

Abstract: Ionospheric scintillation refers to rapid fluctuations in signal amplitude/phase when radio signals propagate through irregularities in the ionosphere. The occurrence of ionospheric scintillation can severely degrade the Global Navigation Satellite System (GNSS) receiver tracking loop performance, with consequential effects on positioning. Under strong scintillation conditions, receivers can even lose lock on satellites, which poses serious threats to safety---critical GNSS applications and precise positioning. The characteristics of intensity fading on Global Positioning System (GPS) L1 C/A signals during the peak of the last solar cycle at the low latitude station of Presidente Prudente (Lat. 22.12°S, Long. 51.41°W, Magnetic Lat. 12.74°S) are investigated. The results show that the occurrence of scintillation at this station is extremely frequent. An analysis of the fading events revealed an inverse relationship between fading depth and duration. Mathematical models are built to investigate and explain the statistical relationship between intensity fading and the commonly used amplitude scintillation index S4. Then the GPS receiver tracking loop performance is studied in relation to fading. A conclusion can be drawn that both fading depth and duration can affect the tracking loop performance, but the tracking error variance is more strongly related to fading speed, defined as the ratio of fading depth to fading duration. The proposed study is of great significance for better understanding the ionospheric scintillation intensity fading characteristics at low latitudes. It can also contribute to the research on the effects of scintillation on GNSS as well as support the design and development of scintillation robust GNSS receivers.

Scintillation properties of Ce-doped SrF2-Al2O3-B2O3 glasses

Abstract: xCeF3-doped (30-x)SrF2-20Al2O3-50B2O3 glasses (x = 0.1, 1.0, 5.0 and 10 mol%) were synthesized by the conventional melt quenching method, and then characterizations for scintillator applications were performed. Regarding the photoluminescence (PL) properties, the glasses show a broad emission band around 360 nm under excitation of approximately 325 nm, and the decay time constant is several tens of nano-seconds. From the results, the origin is attributed to the 5d → 4f transitions of Ce3+. As scintillation properties, the X-ray induced scintillation spectra and decay time constants are reasonably consistent with the PL. Among the present glass samples, the scintillation intensity is the highest when doped with 1% Ce. The light yields of the 1% Ce-doped glass shows 240 photons/MeV under 57Co 122 keV γ-ray exposure. The light yields were derived as relative values to that of commercial GS20 glass scintillator. This is the first report on the scintillation light yields of Ce-doped SrF2-Al2O3-B2O3 glasses. Furthermore, the materials also exhibit thermally stimulated luminescence (TSL) properties with a major glow peak around 80 °C, and the sensitivity to radiation dose is as low as 0.1 mGy for the 0.1% and 1.0% Ce-doped glasses with a good linearity confirmed to 100 mGy.

Impact of Turbulent-Flow-Induced Scintillation on Deep-Ocean Wireless Optical Communication

Abstract: The use of autonomous underwater vehicles (AUVs) is highly desirable for collecting data from seafloor sensor platforms within a close range. With the recent innovations in underwater wireless optical communication (UWOC) for deep-sea exploration, UWOC could be used in conjunction with AUVs for high-speed data uploads near the surface. In addition to absorption and scattering effects, UWOC undergoes scintillation induced by temperature- and salinity-related turbulence. However, studies on scintillation have been limited to emulating channels with uniform temperature and salinity gradients, rather than incorporating the effects of turbulent motion. Such turbulent flow results in an ocean mixing process that degrades optical communication. This study presents a turbulent model for investigating the impact of vehicle-motion-induced turbulence via the turbulent kinetic energy dissipation rate. This scintillation-related parameter offers a representation of the change in the refractive index due to the turbulent flow and ocean mixing. Monte Carlo simulations are carried out to validate the impact of turbulent flow on optical scintillation. In experimental measurements, the scintillation index (SI) and signal-to-noise ratio (SNR) are similar with (SI = 0.4824; SNR = 5.56) and without (SI = 0.4823; SNR = 5.87) water mixing under uniform temperature channels. By introducing a temperature gradient of 4 °C, SI (SNR) with and without turbulent flow changed to 0.5417 (5.06) and 0.8790 (3.40), respectively. The experimental results show a similar trend to the simulation results. Thus, turbulent flow was shown to significantly impact underwater optical communications.

Dual-ended readout of bismuth germanate to improve timing resolution in time-of-flight PET

Abstract: The scintillator bismuth germanate (BGO) has attractive properties for positron emission tomography (PET) systems such as high stopping power, high photo-fraction, and relatively low cost. However, its moderate scintillation light yield and slow rise and decay time compared to lutetium (yttrium) oxyorthosilicate (L(Y)SO) results in a degradation of coincidence timing resolution when scintillation photons are used for timing. Recently, it has been reported that the coincidence timing resolution of BGO can be improved by detecting Cerenkov photons, while scintillation photons still provide energy information. However, the measured coincidence timing spectrum showed much longer tails compared to the single Gaussian distribution. Because of this, TOF PET detectors based on BGO will perform worse than the full width at half maximum (FWHM) of the distribution, which is the most common metric for timing resolution, would suggest. From simulation studies, during the first few picoseconds, BGO generates ~16 Cerenkov photons per photoelectric interaction, following a 511 keV gamma ray interaction, while the probability of producing a scintillation photon during the first few picoseconds is very small. Therefore, when we configure a BGO crystal with dual-ended readout, the first arriving photons among the two opposing SiPMs are most likely Cerenkov photons, and by selecting the appropriate SiPM, an improvement in coincidence timing resolution can be achieved. In this study, both ends of a 3 × 3 × 20 mm3 BGO crystal were coupled to NUV-HD SiPMs. Trigger time differences from the dual-ended readout of BGO were widely distributed due to detecting a mixture of prompt Cerenkov and scintillation photons on both SiPMs. When using trigger times from only a single SiPM, the estimated coincidence timing resolution between two identical BGO detectors was 463 ps FWHM and 1463 ps FWTM. In contrast, when using trigger times from both SiPMs, the estimated coincidence timing resolution was 399 ps FWHM and 936 ps FWTM with no loss of events. Based on a recent report, high-bandwidth amplifiers were implemented and shown to further improve the estimated coincidence timing resolution to 331 ps FWHM and 923 ps FWTM. In summary, the coincidence timing resolution of BGO, most notably the FWTM, was significantly improved using time information from the dual-ended readout.

Measuring phase scintillation at different frequencies with conventional GNSS receivers operating at 1 Hz

Abstract: Ionospheric scintillation causes rapid fluctuations of measurements from Global Navigation Satellite Systems (GNSSs), thus threatening space-based communication and geolocation services. The phenomenon is most intense in equatorial regions, around the equinoxes and in maximum solar cycle conditions. Currently, ionospheric scintillation monitoring receivers (ISMRs) measure scintillation with high-pass filter algorithms involving high sampling rates, e.g. 50 Hz, and highly stable clocks, e.g. an ultra-low-noise Oven-Controlled Crystal Oscillator. The present paper evolves phase scintillation indices implemented in conventional geodetic receivers with sampling rates of 1 Hz and rapidly fluctuating clocks. The method is capable to mitigate ISMR artefacts that contaminate the readings of the state-of-the-art phase scintillation index. Our results agree in more than 99.9% within ± 0.05 rad (2 mm) of the ISMRs, with a data set of 8 days which include periods of moderate and strong scintillation. The discrepancies are clearly identified, being associated with data gaps and to cycle-slips in the carrier-phase tracking of ISMR that occur simultaneously with ionospheric scintillation. The technique opens the door to use huge databases available from the International GNSS Service and other centres for scintillation studies. This involves GNSS measurements from hundreds of worldwide-distributed geodetic receivers over more than one Solar Cycle. This overcomes the current limitations of scintillation studies using ISMRs, as only a few tens of ISMRs are available and their data are provided just for short periods of time.

Remote control of neural function by X-ray-induced scintillation

Abstract: Scintillators exhibit visible luminescence, called scintillation, when irradiated with X-rays. Given that X-rays penetrate through biological tissues, X-ray-induced scintillation would enable remote optogenetic control of neural functions at any depths in the brain. Here we show that a yellow-emitting inorganic scintillator, Ce-doped Gd3(Al,Ga)5O12 (Ce:GAGG), can effectively activate red-shifted excitatory and inhibitory opsins. Using these scintillator-opsin combinations, we successfully activated and inhibited midbrain dopamine neurons of freely moving mice by X-ray irradiation, producing bi-directional modulation of place preference behavior. The Ce:GAGG crystal was biocompatible and could be implanted for a long period without progressive neuroinflammatory responses. Neither brain injury nor behavioral dysfunction was acutely induced by radiation during the behavioral tests. Thus, X-ray-induced scintillation allows wireless control of cellular functions in living animals, expanding X-ray applications to functional studies of biology and medicine.