Search

In this study, we investigate the contribution of millisecond pulsars (MSPs) to the gamma-ray excess observed in the Galactic Center by analyzing data from high-resolution direct N-body simulations of six globular clusters (GCs) that experience close encounters with the nuclear star cluster. Using the φ-GPU code, we tracked the orbits of individual neutron stars (NSs) formed during the simulations, assuming a fraction of these NSs evolve into MSPs. Our model includes state-of-the-art single stellar evolution code including prescription for neutron star formation. We estimated the gamma-ray flux from these MSPs, considering known values for their gamma-ray emission. Our results show that MSPs originating from the six modeled GCs contribute a small but non-negligible fraction of the observed gamma-ray flux. This finding suggests that the actual gamma-ray flux from MSPs could be much higher when considering the entire population of GCs, potentially significantly contributing to the gamma-ray excess. This study highlights the importance of considering MSPs in the Galactic Center, originating from nearby globular clusters, as a potential source of the observed gamma-ray excess. Future work will involve more sophisticated simulations incorporating binary stellar evolution and comparing the fraction of MSPs in observed GCs to refine our models and improve the accuracy of our estimates. [ABSTRACT FROM AUTHOR]

Based on the recent association of IceCube TeV and PeV neutrino events with gamma-ray bursts (GRBs) by considering the Lorentz violation of neutrinos, we provide a new estimate on the GRB neutrino flux with a more significant result compared to the previous constraint by the IceCube Collaboration. Among these 24 neutrino "shower" events above 60 TeV, 12 events are associated with GRBs. Such a result is compatible with the prediction from GRB fireball models. Analysis of track events provides a consistent result with the shower events to associate high energy cosmic neutrinos with GRBs under the same Lorentz violation features of neutrinos. We also make a background estimation and reveal GRBs as a significant source for the ultra-high energy IceCube neutrino events. Our work supports the Lorentz violation and CPT -violation of neutrinos, indicating new physics beyond relativity. [ABSTRACT FROM AUTHOR]

Through comprehensively applying geological and geophysical data, as well as core and thin section observation, the characteristics of reservoirs and fractures in the second member of the Xujiahe Formation (hereinafter referred to as Xu2 Member) in the Yuanba area, northern Sichuan Basin, were studied. Combined with the analysis of the main controlling factors of production capacity, the types and characteristics of the sweet spots in the tight sandstone gas reservoir were determined. The evaluation standards and geological models of the sweet spots were established. The results are as follows: (1) There are bedding-parallel fracture-, fault-induced fracture-, and pore-dominated sweet spots in the tight sandstone gas reservoirs of the Xu2 Member. (2) The bedding parallel fracture-dominated sweet spots have developed in quartz sandstones with well-developed horizontal fractures and micro-fractures. They are characterized by high permeability and high gas output during production tests. This kind of sweet spots is thin and shows a limited distribution. Their logging responses show extremely low gamma-ray (GR) values and medium-high AC values. Moreover, the bedding parallel fracture-dominated sweet spots can be mapped using seismic methods. (3) The fault-induced fracture-dominated sweet spots have welldeveloped medium- and high-angle shear fractures. Their logging responses show an increase in peaks of AC values and total hydrocarbon content and a decrease in resistivity. Seismically, the areas with welldeveloped fault-induced fracture-dominated sweet spots can be effectively mapped using the properties such as seismic entropy and maximum likelihood. (4) The pore-dominated sweet spots are developed in medium-grained feldspathic litharenites with good reservoir properties. They are thick and widely distributed. (5) These three types of sweet spots are mainly determined by sedimentation, diagenesis, and tectonism. The bedding parallel fracture-dominated sweet spots are distributed in beachbar quartz sandstones on the top of the 1st sand layer group in the Xu2 Member, which develops in a shore-shallow lake environment. The fault-induced fracture-dominated sweet spots mainly occur near faults. They are increasingly developed in areas closer to faults. The pore-dominated sweet spots are primarily distributed in the 2nd and 3rd sand layer groups, which lie in the development areas of distributary channels near provenances at western Yuanba area. Based on the geological and seismic data, a comprehensive evaluation standard for these three types of sweet spots of the tight sandstone reservoirs in the Xu2 Member has been established, which, on the one hand, lays the foundation for the development and evaluation of the gas reservoir, and on the other hand, deepens the understanding of sweet spot in the tight sandstone gas reservoirs. [ABSTRACT FROM AUTHOR]

The lithofacies and environments of deposition interpretations of the Calub--Hilala field toward the central trough of Ogaden Basin were analyzed, and geophysical well logs from three deep exploration wells, namely Calub-1, Bodle-1, and Hilala-2, were used. A methodology was piloted in establishing the sedimentary facies, their successions, and environments of deposition. Gamma-ray, neutron, sonic, and resistivity logs were used for lithologic and depositional environment identification. An attempt was also made to identify formation tops and well-to-well lithostratigraphic correlation basing gamma-ray log trends and correlate with the cored interval of the wells for lithological comparisons. Lithofacies interpretation was carried out with Schlumberger's Petrel software, version 2009. Correlation techniques were conducted to delineate the subsurface trends of these facies with electrofacies to compare facies interpretation results that were implied using the wireline log signatures. Ten formations, namely Calub, Bokh, Gumburo, Adigrat, Transition, Hamanlei (Lower, Middle, and Upper), Urandab, Gebredare, Gorrahei, Mustahil, and five log facies, namely a cylindrical-shaped log trend representing aeolian, i.e., braded fluvial, a funnel-shaped facies representing a crevasse splay, a carbonate, shallowing upward sequence and shallow marine sheet sand, a bell-shaped facies representing transgressive marine shelf, a symmetrical-shaped facies representing sandy offshore, and an irregular shaped facies representing fluvial floodplain, were recognized. The environments of deposition delineated for the study area are alluvial and transgressive--regressive marine. [ABSTRACT FROM AUTHOR]

A compact broadband Compton spectrometer with high spectral resolution has been designed to detect spectra of laser-driven high-flux gamma rays. The primary detection range of the gamma-ray spectrum is 0.5 MeV–13 MeV, although a secondary harder gamma-ray region of 13 MeV–30 MeV can also be covered. The Compton-scattered electrons are spectrally resolved using a curved surface detector and a nonuniform magnetic field produced by a pair of step-like magnets. This design allows a compact structure, a wider bandwidth, especially in the lower-energy region of 0.5 MeV–2 MeV, and optimum spectral resolution. The spectral resolution is 5%–10% in the range 4 MeV–13 MeV and better than 25% in the range 0.5 MeV–4 MeV (with an Al converter of 0.25 mm thickness and a collimator of 1 cm inner diameter). Low-Z plastic materials are used on the inner surface of the spectrometer to suppress noise due to secondary X-ray fluorescence. The spectrometer can be adjusted flexibly via a specially designed mechanical component. An algorithm based on a regularization method has also been developed to reconstruct the gamma-ray spectrum from the scattered electrons. [ABSTRACT FROM AUTHOR]

The Atmosphere‐Space Interactions Monitor (ASIM) was launched to the International Space Station on 2 April 2018. The ASIM payload consists of two main instruments, the Modular X‐ray and Gamma‐ray Sensor (MXGS) for imaging and spectral analysis of Terrestrial Gamma‐ray Flashes (TGFs) and the Modular Multi‐spectral Imaging Array for detection, imaging, and spectral analysis of Transient Luminous Events and lightning. ASIM is the first space mission designed for simultaneous observations of Transient Luminous Events, TGFs, and optical lightning. During the first 10 months of operation (2 June 2018 to 1 April 2019) the MXGS has observed 217 TGFs. In this paper we report several unprecedented measurements and new scientific results obtained by ASIM during this period: (1) simultaneous TGF observations by Fermi Gamma‐ray Burst Monitor and ASIM MXGS revealing the very good detection capability of ASIM MXGS and showing substructures in the TGF, (2) TGFs and Elves produced during the same lightning flash and even simultaneously have been observed, (3) first imaging of TGFs giving a unique source location, (4) strong statistical support for TGFs being produced during the upward propagation of a leader just before a large current pulse heats up the channel and emits a strong optical pulse, and (5) the t50 duration of TGFs observed from space is shorter than previously reported. Key Points: Simultaneous measurements of TGF by two spacecraft are presentedSimultaneous measurements of TGF and Elve are not rare coincidenceImaging of TGF is presentedThe sequence of TGF and main optical lightning pulse is resolvedTGFs observed from space have shorter duration than previously reported [ABSTRACT FROM AUTHOR]

We present ten years of R-band monitoring data of 31 northern blazars which were either detected at very high-energy (VHE) gamma rays or listed as potential VHE gamma-ray emitters. The data comprise 11 820 photometric data points in the R-band obtained in 2002–2012. We analyzed the light curves by determining their power spectral density (PSD) slopes assuming a power-law dependence with a single slope β and a Gaussian probability density function (PDF). We used the multiple fragments variance function (MFVF) combined with a forward-casting approach and likelihood analysis to determine the slopes and perform extensive simulations to estimate the uncertainties of the derived slopes. We also looked for periodic variations via Fourier analysis and quantified the false alarm probability through a large number of simulations. Comparing the obtained PSD slopes to values in the literature, we find the slopes in the radio band to be steeper than those in the optical and gamma rays. Our periodicity search yielded one target, Mrk 421, with a significant (p <  5%) period. Finding one significant period among 31 targets is consistent with the expected false alarm rate, but the period found in Mrk 421 is very strong and deserves further consideration. [ABSTRACT FROM AUTHOR]

The positron excess measured by PAMELA and AMS can only be explained if there is one or several sources injecting them. Moreover, at the highest energies, it requires the presence of nearby ( ∼ hundreds of parsecs) and middle age (maximum of  ∼ hundreds of kyr) sources. Pulsars, as factories of electrons and positrons, are one of the proposed candidates to explain the origin of this excess. To calculate the contribution of these sources to the electron and positron flux at the Earth, we developed EDGE (Electron Diffusion and Gamma rays to the Earth), a code to treat the propagation of electrons and compute their diffusion from a central source with a flexible injection spectrum. Using this code, we can derive the source’s gamma-ray spectrum, spatial extension, the all-electron density in space, the electron and positron flux reaching the Earth and the positron fraction measured at the Earth. We present in this paper the foundations of the code and study how different parameters affect the gamma-ray spectrum of a source and the electron flux measured at the Earth. We also studied the effect of several approximations usually performed in these studies. This code has been used to derive the results of the positron flux measured at the Earth in [1]. [ABSTRACT FROM AUTHOR]

A search for tau neutrino induced showers with the MAGIC telescopes is presented. The MAGIC telescopes located at an altitude of 2200 m a.s.l. in the Canary Island of La Palma, can point towards the horizon or a few degrees below across an azimuthal range of about 80°. This provides a possibility to search for air showers induced by tau leptons arising from interactions of tau neutrinos in the Earth crust or the surrounding ocean. In this paper we show how such air showers can be discriminated from the background of very inclined hadronic showers by using Monte Carlo simulations. Taking into account the orography of the site, the point source acceptance and the event rates expected have been calculated for a sample of generic neutrino fluxes from photo-hadronic interactions in AGNs. The analysis of about 30 h of data taken towards the sea leads to a 90% C.L. point source limit for tau neutrinos in the energy range from 1.0 × 10 15 eV to 3.0 × 10 18 eV of about E ν τ 2 × ϕ ( E ν τ ) < 2.0 × 10 − 4 GeV cm − 2 s − 1 for an assumed power-law neutrino spectrum with spectral index γ =−2. However, with 300 h and in case of an optimistic neutrino flare model, limits of the level down to E ν τ 2 × ϕ ( E ν τ ) < 8.4 × 10 − 6 GeV cm − 2 s − 1 can be expected. [ABSTRACT FROM AUTHOR]

Characteristics of γ-ray families with halos observed with X-ray emulsion chambers at the Pamirs and data of EAS experiments are analyzed to estimate the summary fraction of proton and helium nuclei (p + He) in the primary cosmic radiation (PCR) at E 0  = 1–100 PeV. It is shown that the p + He fraction at E 0  = 10 PeV is (39 ± 6) %. The mass composition, estimated by EAS age, remains mixed at E 0  = 1–100 PeV with a tendency to become heavier with increasing energy. [ABSTRACT FROM AUTHOR]

The short Gamma-Ray Burst, GRB 170817A, that followed the binary neutron star merger gravitational waves signal, GW170817, is not a usual short gamma-ray burst (sGRB). It is weaker by three orders of magnitude than the weakest sGRB seen before and its spectrum, showing a hard early signal followed by a softer thermal spectrum, is unique. We show, first, that the γ-rays must have emerged from at least mildly relativistic outflow, implying that a relativistic jet was launched following the merger. We then show that the observations are consistent with the predictions of a mildly relativistic shock breakout: a minute γ-ray energy as compared with the total energy and a rather smooth light curve with a hard to soft evolution. We present here a novel analytic study and detailed numerical 2D and 3D relativistic hydrodynamic and radiation simulations that support the picture in which the observed γ-rays arose from a shock breakout of a cocoon from the merger’s ejecta. The cocoon can be formed either by a choked jet which does not generate an sGRB (in any direction) or by a successful jet which generates an undetected regular sGRB along the system’s axis pointing away from us. Remarkably, for the choked jet model, the macronova signal produced by the ejecta (which is partially boosted to high velocities by the cocoon’s shock) and the radio that is produced by the interaction of the shocked cocoon material with the surrounding matter agree with the observed ultraviolet/optical/infrared emission and with current radio observations. Finally, we discuss the possibility that the jet propagation within the ejecta may photodissociate some of the heavy elements and may affect the composition of a fraction of ejecta and, in turn, the opacity and the early macronova light. [ABSTRACT FROM AUTHOR]

The Sarfartoq carbonatite complex occurs in the transition zone between Archaean and Paleoproterozoic gneisses in southern West Greenland. The Sarfartoq carbonatite complex hosts ore deposits and occurrences of rare earth elements and niobium. In this study, airborne HyMap hyperspectral imagery and coincident airborne gamma-ray spectroscopy data were analysed for mineral exploration of Sarfartoq carbonatite complex. The study area included the carbonatite core zone and a hydrothermally altered shear zone prospective for rare earth elements mineralization in the southern margin of the carbonatite complex. The analysis of the hyperspectral imagery was focused on the mapping of the spatial distribution of carbonatite, fenite and limonite. Significant anomalies of uranium, thorium and potassium were outlined from the gamma-ray spectroscopy data. Decision trees were used to combine the results from the hyperspectral image analysis and airborne gamma-ray spectroscopy. Significant anomalies of thorium at the hydrothermally altered shear zone coinciding with the presence of carbonatite rocks are generally indicative of outcropping rare earth element mineralization. The study indicates the benefits of coincident airborne hyperspectral and gamma-ray spectroscopy surveys for the mineral exploration of carbonatite complexes. [ABSTRACT FROM AUTHOR]

Gamma-ray (γ-ray) irradiation effects on HfO 2 -based MOS capacitors have been studied. The capacitance-voltage (C-V) characteristic was measured at room temperature (300 K) to study the change of electrical properties in capacitors before and after irradiation with different doses. The shifts of midgap and flatband voltage and the decrease of accumulation capacitance shown that defects in the oxide and interface traps were indeed created during the gamma irradiation. Deep level transient spectroscopy (DLTS) was used to characterize the interfacial states introduced by irradiation. The activation energies, capture cross-sections and interface state densities were E C -0.1697 eV, E C -0.1929 eV; 7.371 × 10 −16  cm 2 , 1.158 × 10 −14  cm 2 ; 1.814 × 10 13  eV −1  cm 2 , 5.042 × 10 13  eV −1  cm 2 for the 1 Mrad(Si) and 5 Mrad(Si) samples, respectively. The peak shifted toward lower temperature when increasing pulse voltages (V P ) in measuring DLTS spectra with fixed reverse voltage (V R ). It indicated that interface defects have been formed during irradiation. With the increasing of irradiation dose, both of the capture cross section (σ n ) and the interface state density (D it ) increased. These results provide the basis to the researches and applications for the HfO 2 -based devices in the field of high-κ materials, irradiation effect, devices in radiation working environment. [ABSTRACT FROM AUTHOR]

The polarization of relativistic jets is of interest for the understanding of their origin, confinement, and propagation. However, even though numerous measurements have been performed, the mechanisms behind jet variability, creation, and composition are still debated. We have performed simultaneous gamma-ray and optical photopolarimetry observations of 45 blazars with the Kanata telescope since July 2008 to investigate the mechanisms of variability and search for a basic relation between the several subclasses of relativistic jets. Consequently, we found that a correlation between the gamma-ray and optical flux might be related to gamma-ray luminosity, and the maximum polarization degree might be related to gamma-ray luminosity or the ratio of gamma-ray to optical flux. These results imply that low gamma-ray luminosity blazars emit from multiple regions. [ABSTRACT FROM AUTHOR]

Energy-recovery linacs (ERLs) are promising for advanced synchrotron light sources, high-power free electron lasers (FELs), high-brightness gamma-ray sources, and electron–ion colliders. To demonstrate the critical technology of ERL-based light sources, we have designed and constructed a test accelerator, the compact ERL (cERL). Using advanced technology that includes a photocathode direct current (DC) electron gun and two types of 1.3-GHz-frequency superconducting cavities, the cERL was designed to be capable of recirculating low emittance ( ≤ 1 mm ⋅ mrad) and high average-current ( ≥ 10 mA) electron beams while recovering the beam energy. During initial commissioning, the cERL demonstrated successful recirculation of high-quality beams with normalized transverse emittance of ∼ 0.14 mm ⋅ mrad and momentum spread of ∼ 1.2 × 10 −4 (rms) at a beam energy of 20 MeV and bunch charge below 100 fC. Energy recovery in the superconducting main linac was also demonstrated for high-average-current continuous-wave beams. These results constitute an important milestone toward realizing ERL-based light sources. [ABSTRACT FROM AUTHOR]

High-energy delayed γ -ray spectroscopy is a potential technique for directly assaying spent fuel assemblies and achieving the safeguards goal of quantifying nuclear material inventories for spent fuel handling, interim storage, reprocessing facilities, repository sites, and final disposal. Requirements for the γ -ray detection system, up to ∼ 6 MeV, can be summarized as follows: high efficiency at high γ -ray energies, high energy resolution, good linearity between γ -ray energy and output signal amplitude, ability to operate at very high count rates, and ease of use in industrial environments such as nuclear facilities. High Purity Germanium Detectors (HPGe) are the state of the art and provide excellent energy resolution but are limited in their count rate capability. Lanthanum Bromide (LaBr 3 ) scintillation detectors offer significantly higher count rate capabilities at lower energy resolution. Thus, LaBr 3 detectors may be an effective alternative for nuclear spent-fuel applications, where count-rate capability is a requirement. This paper documents the measured performance of a 2” (length) × 2” (diameter) of LaBr 3 scintillation detector system, coupled to a negatively biased PMT and a tapered active high voltage divider, with count-rates up to ∼ 3 Mcps. An experimental methodology was developed that uses the average current from the PMT’s anode and a dual source method to characterize the detector system at specific very high count rate values. Delayed γ -ray spectra were acquired with the LaBr 3 detector system at the Idaho Accelerator Center, Idaho State University, where samples of ∼ 3g of 235 U were irradiated with moderated neutrons from a photo-neutron source. Results of the spectroscopy characterization and analysis of the delayed γ -ray spectra acquired indicate the possible use of LaBr 3 scintillation detectors when high count rate capability may outweigh the lower energy resolution. [ABSTRACT FROM AUTHOR]

Guided tissue regeneration (GTR) and guided bone regeneration (GBR) biomaterials have been employed in recent years for periodontal procedures. In the present study, widely used dental GTR/GBR biomaterials (grafts: G1, G2, G3 and membranes: M1, M2, M3, M4) were exposed to gamma irradiation at an absorbed dose range of 0–50 kGy and the radiolytic intermediates that have been created in the samples upon irradiation were characterized in detail by Electron Spin Resonance (ESR) spectroscopy. We aimed to standardize the measurement conditions for practical applications of gamma radiation sterilization of GTR/GBR biomaterials. We investigated the characteristic features of free radicals in gamma irradiated GTR/GBR biomaterials and examined the stability of the induced radicals at room temperature and accelerated stability conditions with ESR spectroscopy including dose-response curves, microwave power studies, dosimetric features of the biomaterials, variations of the peak heights with temperature, and long term stabilities of the radical species. Long-term stability studies have shown that G1 is quite stable even in accelerated storage conditions. The signal intensities of graft-type GTR/GBR biomaterials stored in normal and stability conditions have decreased very rapidly even only a few days after gamma irradiation sterilization. Thus, those samples indicating relatively low stability features can be very good candidates for the radiosterilization process. The beta-tricalcium phosphate and PLGA containing G1 and M1 respectively have found to be the most gamma stable bone substitute biomaterials and be safely sterilized by gamma radiation. ESR spectroscopy is an appropriate technique in giving important detailed spectroscopic findings in the gamma radiation sterilization studies of GTR/GBR biomaterials. [ABSTRACT FROM AUTHOR]

A visuo-haptic augmented reality (VHAR) interface is presented enabling an operator to teleoperate an unmanned aerial vehicle (UAV) equipped with a custom CdZnTe-based spectroscopic gamma-ray detector in outdoor environments. The task is to localize nuclear radiation sources, whose location is unknown to the user, without the close exposure of the operator. The developed detector also enables identification of the localized nuclear sources. The aim of the VHAR interface is to increase the situation awareness of the operator. The user teleoperates the UAV using a 3DOF haptic device that provides an attractive force feedback around the location of the most intense detected radiation source. Moreover, a fixed camera on the ground observes the environment where the UAV is flying. A 3D augmented reality scene is displayed on a computer screen accessible to the operator. Multiple types of graphical overlays are shown, including sensor data acquired by the nuclear radiation detector, a virtual cursor that tracks the UAV and geographical information, such as buildings. Experiments performed in a real environment are reported using an intense nuclear source. [ABSTRACT FROM AUTHOR]

A strandplain at the downdrift side of the wave-dominated Catumbela delta (Angola) includes distinguishable deposits with very high natural radioactivity (up to 0.44 microSv/hour). In order to establish the geometry of these sedimentary units and understand their genetic processes, dose rate surveys were performed with the portable equipment Rados RDS-40WE. In addition, grain-size distribution, heavy-mineral composition and gamma-ray mass spectra of the high dose rate deposits were analysed. High dose rate values are found in ribbon units aligned parallel to the shoreline, which are a few tens of meters wide and up to approximately 3 km long. These units reflect the concentration of Th-bearing grains in coastal deposits enriched in heavy minerals. An integrated analysis of the high dose rate ribbons in GIS environment with aerial photography and topographic maps suggests that parts of the high dose rate units formed during the last two centuries may be related with the erosion of older shoreline deposits, due to updrift displacements of the Catumbela river outlet and recycling of shoreline accumulations with downdrift deposition. Simple gamma-ray surveys carried out with a portable detector can unravel depositional units characterised by significant enrichment in heavy-mineral grains that are likely to correspond to key events in the evolution of wave-dominated accumulations. The location of such deposits should be taken into account when planning future work using more expensive or time-consuming techniques. [ABSTRACT FROM AUTHOR]

Differential cross sections for the reaction channels 7 Li(p,nγ 1-0 ) 7 Be (Eγ = 429 keV), 7 Li(p,pγ 1-0 ) (Eγ = 478 keV), 19 F(p,pγ 1-0 ) 19 F (Eγ = 110 keV), 19 F(p,pγ 2-0 ) 19 F (Eγ = 197 keV) have been measured in the proton energy range 810–3700 keV, with an energy step of 10 keV. The reactions channels 19 F(p,pγ 3-1 ) 19 F (Eγ = 1236 keV), 19 F(p,pγ 4-1 ) 19 F (Eγ = 1349 keV), 19 F(p,pγ 5-2 ) 19 F (Eγ = 1357 keV) have also been investigated in the proton energy range 1915–3225 keV. The experimental set-up, the uncertainty budget, the comparison with other data and the progress assured by new data in the analytical use of standard-less Particle Induced Gamma-ray Emission (PIGE) are discussed. [ABSTRACT FROM AUTHOR]

A 21 m diameter imaging atmospheric Cherenkov telescope is being installed at the high-altitude astronomical site at Hanle in the Ladakh region of North India. When operational by 2018, it will have the distinction of being the largest gamma-ray telescope in the northern hemisphere and the second largest in the world. Operating at a trigger threshold energy of <20 GeV, it will play an important role in understanding very high energy processes in the Universe. [ABSTRACT FROM AUTHOR]

Recent results in the field of high energy active galactic nuclei (AGN) astrophysics, benefiting from improvements to gamma-ray instruments and observational strategies, have revealed a surprising wealth of unexpected phenomena. These developments have been brought about both through observational efforts to discover new very high energy gamma-ray emitters, as well as from further in-depth observations of previously detected and well studied objects. I here focus specifically on the discovery of repeated temporal structures observed in AGN lightcurves, and new hard spectral components within the spectral energy distributions of other AGN systems. The challenges that these new features place on the modeling of the sources are highlighted, along with some reflections on what these results tell us about the underlying nature of the emission processes at play. [ABSTRACT FROM AUTHOR]

A brief overview of the history of atmospheric Cherenkov gamma-ray telescopes is given. Topical problems of modern astrophysics and fundamental physics to be solved with these instruments are listed. The ALEGRO project of a low-threshold gamma-ray observatory is characterized in detail. The aim of this project is to examine cosmic gamma-ray sources (especially the rapidly variable gamma-ray sources, gamma-ray transients) with high statistics of detected photons in the energy range of 5-50 GeV. [ABSTRACT FROM AUTHOR]

We report on a set of experiments conducted to determine what effects, if any, the internal background in the CLLB scintillation detector has on the thermal neutron detection performance. We conducted source measurements using an unmoderated and moderated 252 Cf neutron/γ-ray source and long (48-h), unshielded and shielded, background measurements to characterize the internal background with and without a source present. These measurements allowed us to determine the 2- d event selections needed to isolate the thermal neutron peak observed in pulse shape vs. energy space and apply those selections to our background measurements. Our results indicate that the thermal neutron detection capabilities of the CLLB are marginally affected by the presence of internal background. An unmoderated 113-µCi 252 Cf source at 15 cm from the detector yields a thermal neutron rate of 8×10 −2 /s cm 3 , while moderating the source with 5 cm of polyethylene yields a thermal neutron rate of 5.5×10 −1 /s cm 3 . The measured background rate for events that fall within the selected thermal neutron region is 1.2×10 −3 /s cm 3 . Lastly, the potential for CLLB for detecting fast neutrons was investigated. [ABSTRACT FROM AUTHOR]

Scintillation crystals are usually used for detection of energetic photons at room temperature in high energy and nuclear physics research, non-destructive analysis of materials testing, safeguards, nuclear treaty verification, geological exploration, and medical imaging. Therefore, new designs and construction of radioactive beam facilities are coming on-line with these science brunches. A good number of researchers are investigating the efficiency of the γ-ray detectors to improve the models and techniques used in order to deal with the most pressing problems in physics research today. In the present work, a new integrative and uncomplicated numerical simulation method (NSM) is used to compute the full-energy (photo) peak efficiency of a regular hexagonal prism NaI(Tl) gamma-ray detector using radioactive point sources situated non-axial within its front surface boundaries. This simulation method is based on the efficiency transfer method. Most of the mathematical formulas in this work are derived analytically and solved numerically. The main core of the NSM is the calculation of the effective solid angle for radioactive point sources, which are situated non-axially at different distances from the front surface of the detector. The attenuation of the γ-rays through the detector’s material and any other materials in-between the source and the detector is taken into account. A remarkable agreement between the experimental and calculated by present formalism results has been observed. [ABSTRACT FROM AUTHOR]

A gamma ray camera is built for the DIII-D tokamak [J. Luxon, Nucl. Fusion 42, 614 (2002)] that provides spatial localization and energy resolution of gamma flux by combining a lead pinhole camera with custom-built detectors and optimized viewing geometry. This diagnostic system is installed on the outer midplane of the tokamak such that its 123 collimated sightlines extend across the tokamak radius while also covering most of the vertical extent of the plasma volume. A set of 30 bismuth germanate detectors can be secured in any of the available sightlines, allowing for customizable coverage in experiments with runaway electrons in the energy range of 1-60 MeV. Commissioning of the gamma ray imager includes the quantification of electromagnetic noise sources in the tokamak machine hall and a measurement of the energy spectrum of background gamma radiation. First measurements of gamma rays coming from the plasma provide a suitable testbed for implementing pulse height analysis that provides the energy of detected gamma photons. [ABSTRACT FROM AUTHOR]

We present status of simulations used to design a novel device for the detection of hazardous substances in the aquatic environment using neutron activation. Unlike the other considered methods based on this technique, we propose to use guides for neutron and gamma quanta which speeds up and simplifies identification. First preliminary results show that both the neutron guide and the γ-ray guide increase the performance of underwater threats detection. [ABSTRACT FROM AUTHOR]

A table of contents for the issue is presented.

Although coal and charcoal have similar physical and chemical characteristics, there are several crystallographic procedures used to distinguish and characterize them. But if the matrix is crushed, there is no standard procedure to distinguish coal from charcoal. In this work, a procedure to characterize coal and charcoal samples based on the radioactive content is proposed. The first assay is by gamma-ray spectrometry, which allows a part of the radioactive content to be determined rapidly and non-destructively. Then, alpha-particle spectrometry is applied to assay the content of those radionuclides which are difficult to determine precisely by gamma-ray spectrometry. This second technique requires prior chemical purification of the carbon sample in order to separate the corresponding radionuclides of interest. [ABSTRACT FROM AUTHOR]

Following the discovery of the cosmic rays by Victor Hess in 1912, more than 70 years and numerous technological developments were needed before an unambiguous detection of the first very-high-energy gamma-ray source in 1989 was made. Since this discovery, the field on very-high-energy gamma-ray astronomy experienced a true revolution: a second, then a third generation of instruments were built, observing the atmospheric cascades from the ground, either through the atmospheric Cherenkov light they comprise, or via the direct detection of the charged particles they carry. Present arrays, 100 times more sensitive than the pioneering experiments, have detected a large number of astrophysical sources of various types, thus opening a new window on the non-thermal Universe. New, even more sensitive instruments are currently being built; these will allow us to explore further this fascinating domain. In this article we describe the detection techniques, the history of the field and the prospects for the future of ground-based very-high-energy gamma-ray astronomy. [ABSTRACT FROM AUTHOR]

A novel hybrid approach for analysis of complex gamma-ray spectra of various origins is described and the test results using spectra obtained from a sodium iodide detector (NaI) are presented. This novel approach exploits the synergism of two artificial intelligence tools; fuzzy logic and genetic algorithms, where the two are merged to identify isotopes and their respective contribution in a given spectrum. The fuzzy logic module focuses on identifying isotopes in the spectrum, while the genetic algorithm (GA) fits and subsequently computes the fractional abundances of the identified isotopes. The fitting of the spectrum is controlled by an assessment procedure based on the test for significance of abundance coefficients, and on the computation of Theil coefficients. This unique synergism between fuzzy logic and GA presents a novel mechanism for automated selection of isotopes for use in spectrum fitting, and as a result eliminates manually-based fitting and/or user intervention. A variety of test cases–including NaI real measured spectra–are used to benchmark this new approach. In addition, the performance of the hybrid method is compared to the multiple linear regression (MLR) fitting approach, along with the combination of fuzzy logic with MLR. This comparison demonstrates a slight superiority of this novel approach regarding accuracy, precision and number of reported false detections. [ABSTRACT FROM PUBLISHER]

Gamma-ray radiation effect on the non-resonant third-order optical nonlinearity of the germano-silicate optical fiber has been investigated by the continuous-wave self-phase modulation method. The nonlinear refractive index, n_2, of the gamma-ray irradiated optical fiber was found to increase linearly with the increase of the gamma-ray induced absorption. The increased n_2 has been mainly ascribed to the NBOs and Ge-realted radiation-induced defects having hyperpolarizabilities. [ABSTRACT FROM PUBLISHER]

The detector response function of X-ray and gamma-ray detectors is obtained from the convolution of the energy deposition spectrum with the detector resolution function. The energy deposition spectrum can be computed by using deterministic or Monte Carlo codes, while the energy resolution depends specifically on the detection mechanism, which is characteristic of the single detector. In a first approximation, the energy resolution can be modeled using a normalized Gaussian distribution having its full width at half maximum expressed in terms of specific semiempirical formulas for solid-state detectors, scintillators, and gas proportional counters. However, this approach is not sufficient with some solid-state detectors. It is frequent to find that the peaks show a deviation from the Gaussian shape: a long flat shelf structure from the peak centroid to the lower energies and an asymmetry that can be described with an exponential decay on the left side of the peak. These two effects have been introduced in the new tool RESOLUTION by adapting empirical models found in literature. RESOLUTION can be tailored to the specific detector by analyzing measured monochromatic peaks by means of the following strategies: (1) in a first approximation, a Gaussian shape is assumed in order to determine the full width at half maximum parameters, (2) if it is noted a flat background on the left side of the peak, then a shelf function is added, and (3) if a departure of the Gaussian is observed, then an exponential tail function is added. RESOLUTION gives a very precise description of the line shape. Copyright © 2015 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Scattered radiation is known to lead to distortion in reconstructed images in Computed Tomography (CT). The effects of scattered radiation are especially more pronounced in non-scanning, multiple source systems which are preferred for flow imaging where the instantaneous density distribution of the flow components is of interest. In this work, a new method based on a library least-squares (LLS) approach is proposed as a means of estimating the scatter contribution and correcting for this. The validity of the proposed method is tested using the 85-channel industrial gamma-ray tomograph previously developed at the University of Bergen (UoB). The results presented here confirm that the LLS approach can effectively estimate the amounts of transmission and scatter components in any given detector in the UoB gamma-ray tomography system. [ABSTRACT FROM AUTHOR]

We obtained high-quality CdTexSe1-x (CdTeSe) crystals from ingots grown by the vertical Bridgman technique. The compositional uniformity of the ingots was evaluated by X-ray fluorescence at BNL's National Synchrotron Light Source X27A beam line. The compositional homogeneity was highly uniform throughout the ingot, and the effective segregation coefficient of Se was ~1.0. This high uniformity offers potential opportunity to enhance the yield of the materials for both infrared substrate and radiation-detector applications, so greatly lowering the cost of production and also offering us the prospect to grow large-diameter ingots for use as large-area substrates and for producing higher efficiency gamma-ray detectors. The concentration of secondary phases was found to be much lower, by eight- to ten fold compared to that of conventional CdxZn1-xTe (CdZnTe or CZT). [ABSTRACT FROM AUTHOR]

For the ultimate sensitivity in trace radiochemical analysis, the radiation detector must have high efficiency and low background. A low-background gamma-ray spectrometer in regular use at NIST for over twenty years is being supplemented by a new system, improved in several ways. The new detector is much larger, a shield of iron reduces cosmic neutron background compared with lead, large plastic scintillators reduce the muon continuum background, and a digital data acquisition system gives new opportunities for optimization. [ABSTRACT FROM AUTHOR]

The calibration of high-purity germanium gamma-ray cylindrical detectors using bar (parallelepiped) sources is carried out analytically using the probability correction approach. Improved expressions for the source self-attenuation coefficient have been included in the present algorithm based on the accurate calculation of all possible path lengths covered by the gamma ray inside the bulky source. Moreover, the full-energy peak attenuation coefficient ftp is included in the present algorithm. The sources were positioned at long distances from the detector window so that the coincidence summing effects could be neglected. Remarkable agreement between the measured efficiency values and the corrected efficiency values calculated by the present technique was observed. The percentage relative differences for the results calculated in this way from experimental values are at least 25% smaller than those observed and reported by the direct mathematical method in previous work. [ABSTRACT FROM AUTHOR]

The burial of objects (human remains, explosives, weapons) below or behind concrete, brick, plaster or tilingmay be associated with serious crime and are difficult locations to search. These are quite common forensic search scenarios but little has been published on them to-date. Most documented discoveries are accidental or from suspect/witness testimony. The problem in locating such hidden objects means a random or chance-based approach is not advisable. A preliminary strategy is presented here, based on previous studies, augmented by primary research where new technology or applications are required. This blend allows a rudimentary search workflow, from remote desktop study, to non-destructive investigation through to recommendations as to how the above may inform excavation, demonstrated here with a case study from a homicide investigation. Published case studies on the search for human remains demonstrate the problems encountered when trying to find and recover sealed-in and sealedover locations. Established methods include desktop study, photography, geophysics and search dogs: these are integrated with new technology (LiDAR and laser scanning; photographic rectification; closequarter aerial imagery; ground-penetrating radar on walls and gamma-ray/neutron activation radiography) to propose this possible search strategy. [ABSTRACT FROM AUTHOR]

Highlights: [•] Real-time tools and mechanisms are required for data handling and machine control. [•] A new DAQ system, ATCA based, with embedded FPGAs, was installed at JET. [•] Different real-time algorithms were developed for FPGAs and MARTe application. [•] MARTe provides the interface to CODAS and to the JET real-time network. [•] The new DAQ system is capable to process and deliver data in real-time. [ABSTRACT FROM AUTHOR]

The concentrations of As, Zn, Co, Cr, and Ba were determined in soil samples from an anomalous uranium ore region in the countryside of the state of Pernambuco, Brazil. The main land use system in this region is dairy farming, and there is a need to evaluate the potential risk of milk contamination. Twenty-three soil samples were activated with neutrons and analyzed using a high-resolution gamma-ray spectrometer system. The results, recorded in mg kg, varied from 0.4 to 6.7 for As, from 17.0 to 110.0 for Zn, from 2.8 to 38.4 for Co, from 12.1 to 65.5 for Cr, and from 443.0 to 1,497.0 for Ba. All of the Ba concentrations were higher than the intervention value adopted by the Brazilian National Environmental Board. This finding justifies research in other environmental areas to predict the toxicological risks to the local population. [ABSTRACT FROM AUTHOR]