Ray Interactions Research Articles

Preface

The 19th International Symposium on Very High Energy Cosmic Ray Interactions (ISVHECRI 2016), held at the P.N. Lebedev Physical Institute of the Russian Academy of Sciences, Moscow (LPI RAS) from 22 to 28 August 2016, attracted more than 120 participants. The Symposium was carried out under the auspices of the International Union of Pure and Applied Physics (IUPAP) with financial support from the Federal Agency for Scientific Organizations and the Russian Foundation for Basic Research.

Inelastic proton-air cross section growth from 0.2 TeV to 10 PeV according to TIEN SHAN experimental cosmic ray data

Conclusions are made about the increase with energy of the inelastic proton air cross section σp −air from 0.2 TeV (accelerator experiments with fixed targets) to 10 PeV (cosmic rays). Experimental data from the Tien Shan complex array on various components (mainly hadron, Cherenkov light, and electron) of extensive air showers at 0.5–10 PeV of primary cosmic rays are analyzed. They were compared with many results of different calculated models of cosmic ray interactions in the atmosphere. The analysis showed that the rise conforms to (7–9)% per one order of energy. These data correspond better to the QGSJET-II-04 version of the interaction model based on the recent LHC results. This model predicts better the slower rise of the cross-section than previous versions of QGSJET-II and some other models.

Studies on a silicon-photomultiplier-based camera for Imaging Atmospheric Cherenkov Telescopes

Imaging Atmospheric Cherenkov Telescopes (IACTs) represent a class of instruments which are dedicated to the ground-based observation of cosmic VHE gamma ray emission based on the detection of the Cherenkov radiation produced in the interaction of gamma rays with the Earth atmosphere. One of the key elements of such instruments is a pixelized focal-plane camera consisting of photodetectors. To date, photomultiplier tubes (PMTs) have been the common choice given their high photon detection efficiency (PDE) and fast time response. Recently, silicon photomultipliers (SiPMs) are emerging as an alternative. This rapidly evolving technology has strong potential to become superior to that based on PMTs in terms of PDE, which would further improve the sensitivity of IACTs, and see a price reduction per square millimeter of detector area. We are working to develop a SiPM-based module for the focal-plane cameras of the MAGIC telescopes to probe this technology for IACTs with large focal plane cameras of an area of few square meters. We will describe the solutions we are exploring in order to balance a competitive performance with a minimal impact on the overall MAGIC camera design using ray tracing simulations. We further present a comparative study of the overall light throughput based on Monte Carlo simulations and considering the properties of the major hardware elements of an IACT.

Dependence of the neutron monitor count rate and time delay distribution on the rigidity spectrum of primary cosmic rays

AbstractNeutron monitors are the premier instruments for precisely tracking time variations in the Galactic cosmic ray flux at GeV‐range energies above the geomagnetic cutoff at the location of measurement. Recently, a new capability has been developed to record and analyze the neutron time delay distribution (related to neutron multiplicity) to infer variations in the cosmic ray spectrum as well. In particular, from time delay histograms we can determine the leader fraction L, defined as the fraction of neutrons that did not follow a previous neutron detection in the same tube from the same atmospheric secondary particle. Using data taken during 2000–2007 by a shipborne neutron monitor latitude survey, we observe a strong dependence of the count rate and L on the geomagnetic cutoff. We have modeled this dependence using Monte Carlo simulations of cosmic ray interactions in the atmosphere and in the neutron monitor. We present new yield functions for the count rate of a neutron monitor at sea level. The simulation results show a variation of L with geomagnetic cutoff as observed by the latitude survey, confirming that these changes in L can be attributed to changes in the cosmic ray spectrum arriving at Earth's atmosphere. We also observe a variation in L with time at a fixed cutoff, which reflects the evolution of the cosmic ray spectrum with the sunspot cycle, known as solar modulation.

Gamma rays interactions with Eu2O3 doped lead fluoroborate glasses

The research article concentrates on the effects of gamma rays [150 kGy] over lead fluoroborate glass systems doped with Europium (Eu2O3) ions synthesized through melt-quench technique. FTIR measurements confirmed the conversion of three-fold borate units (BO3) to tetrahedral borate units (BO4) before irradiation and a back conversion was studied post irradiation, with addition of Eu2O3 ions; which was cross verified through N4 and N3 coordination numbers. Effects of gamma rays have been confirmed through ESR spectra where, resonance paramagnetic centers were perceived. Decrease in the intensities and red shift in the absorption peaks (UV-VIS-NIR absorption spectra) indicates the formation of the color centers in the glass matrices after high energetic gamma exposure. Stability of the samples were calculated using different characteristic temperatures (Tg, Tx, Tc, Tm) which was employed through DSC technique. Different elastic moduli (E, K, G, μ) of the samples were calculated and studied using standard Makishima-Mackenzie's model. Hardness (H) number of the samples have also been measured which showed decrease in the H values after irradiation with increase in Fragility (F) parameter. The unusual trend observed in the Eg values of the samples were validated through the Molar Volume (Vm), Oxide ion polarizability (αe) and optical basicity (Λ) values. The samples could be recommended for solid state lighting devices because of its semiconducting nature energy band gap values (Eg: 2.34–2.83 eV). The competitive stability factors (Dietzel factor (ΔT) ∼ 160–270 °C; Hruby's number (Hr): 1.130–4.237), high densities (ρ: 3.8501–4.1944 g/cm3), hardness parameter (H: 3.32–4.46 GPa) and low poisson's ratio (μ: 0.241–0.257) with supportive αe values motivates the samples to be proposed as radiation shielders and in space applications.

Digital pile-up rejection for plutonium experiments with solution-grown stilbene

A solution-grown stilbene detector was used in several experiments with plutonium samples including plutonium oxide, mixed oxide, and plutonium metal samples. Neutrons from different reactions and plutonium isotopes are accompanied by numerous gamma rays especially by the 59-keV gamma ray of 241Am. Identifying neutrons correctly is important for nuclear nonproliferation applications and makes neutron/gamma discrimination and pile-up rejection necessary. Each experimental dataset is presented with and without pile-up filtering using a previously developed algorithm. The experiments were simulated using MCNPX-PoliMi, a Monte Carlo code designed to accurately model scintillation detector response. Collision output from MCNPX-PoliMi was processed using the specialized MPPost post-processing code to convert neutron energy depositions event-by-event into light pulses. The model was compared to experimental data after pulse-shape discrimination identified waveforms as gamma ray or neutron interactions. We show that the use of the digital pile-up rejection algorithm allows for accurate neutron counting with stilbene to within 2% even when not using lead shielding.

Improving the radiation hardness of graphene field effect transistors

Ionizing radiation poses a significant challenge to the operation and reliability of conventional silicon-based devices. Here, we report the effects of gamma radiation on graphene field-effect transistors (GFETs), along with a method to mitigate those effects by developing a radiation-hardened version of our back-gated GFETs. We demonstrate that activated atmospheric oxygen from the gamma ray interaction with air damages the semiconductor device, and damage to the substrate contributes additional threshold voltage instability. Our radiation-hardened devices, which have protection against these two effects, exhibit minimal performance degradation, improved stability, and significantly reduced hysteresis after prolonged gamma radiation exposure. We believe this work provides an insight into graphene's interactions with ionizing radiation that could enable future graphene-based electronic devices to be used for space, military, and other radiation-sensitive applications.

Discovery of Atmospheric Neutrino Oscillations

Atmospheric neutrinos are produced by cosmic ray interactions in the atmosphere. The zenith-angle and energy dependence of the muon- and electron- neutrino events are observed in atmospheric neutrino experiments. Through these studies neutrino oscillations were discovered. In this article, studies of atmospheric neutrinos in the Kamiokande and Super-Kamiokande experiments are described.

Constraints on the neutrino emission from the Galactic Ridge with the ANTARES telescope

Compelling evidence for the existence of astrophysical neutrinos has been reported by the IceCube collaboration. Some features of the energy and declination distributions of IceCube events hint at a North/South asymmetry of the neutrino flux. This could be due to the presence of the bulk of our Galaxy in the Southern hemisphere. The ANTARES neutrino telescope, located in the Mediterranean Sea, has been taking data since 2007. It offers the best sensitivity to muon neutrinos produced by galactic cosmic ray interactions in this region of the sky. In this letter a search for an extended neutrino flux from the Galactic Ridge region is presented. Different models of neutrino production by cosmic ray propagation are tested. No excess of events is observed and upper limits for different neutrino flux spectral indices are set. This constrains the number of IceCube events possibly originating from the Galactic Ridge. A simple power-law extrapolation of the Fermi-LAT flux to associated IceCube High Energy Starting Events is excluded at 90% confidence level.

Particle acceleration in the vacuum gaps in black hole magnetospheres

We consider particle acceleration in vacuum gaps in magnetospheres of black holes powered through Blandford-Znajek mechanism and embedded into radiatively-inefficient accretion flow (RIAF) environment. In such situation the gap height is limited by the onset of gamma-gamma pair production on the infrared photons originating from the RIAF. We numerically calculate acceleration and propagation of charged particles taking into account the detailed structure of electric and magnetic field in the gap and in the entire black hole magnetosphere, radiative energy losses and interactions of gamma rays produced by the propagated charged particles with the background radiation field of RIAF. We show that the presence of the vacuum gap has clear observational signatures. The spectra of emission from gaps embedded into a relatively high luminosity RIAF are dominated by the inverse Compton emission with a sharp, super-exponential cut-off in the very-high-energy gamma-ray band. The cut-off energy is determined by the properties of the RIAF and is largely independent of the structure of magnetosphere and geometry of the gap.The spectra of the gap residing in low-luminosity RIAFs are dominated by synchrotron / curvature emission with the spectra extending into 1-100 GeV energy range. We also consider the effect of possible acceleration of protons in the gap and find that proton energies could reach the ultra-high-energy cosmic ray (UHECR) range only in extremely low luminosity RIAFs.

Optical, structural and thermal properties of sodium metaphosphate glasses containing Bi2O3 with interactions of gamma rays

Sodium metaphosphate glasses with successive increasing added Bi2O3 contents (5–40%) were prepared to improve their chemical stability and increase their optical and thermal properties through the additional building BiO6 and BiO3 units. The optical spectrum of the base metaphosphate glass reveals strong UV absorption due to the presence of trace iron (Fe3+) ions present as impurities. Glasses containing additional 5, 7.5 and 10% Bi2O3 show further band around 406nm which can be related to absorption of Bi3+ ions. With increasing the Bi2O3 content, this near visible band is observed to disappear indicating peculiar behavior needing further work. Gamma irradiation causes only minor changes in the position of the strong UV peaks but an obvious induced visible broad band centered at 452–460nm in the base and Bi2O3 containing glasses. This induced band is related to the generation of phosphorus oxygen hole center or non bridging oxygen hole center as revealed by various authors. FTIR results reveal characteristic vibrational bands due to phosphate groups and with the addition of Bi2O3, some interference of BiO vibrational units are expected. Gamma irradiation causes limited changes in the IR spectra due to suggested shielding effect of the heavy metal oxide Bi2O3.

The shape of the extragalactic cosmic ray spectrum from galaxy clusters

We study the diffusive escape of cosmic rays from a central source inside a galaxy cluster to obtain the suppression in the outgoing flux appearing when the confinement times get comparable or larger than the age of the sources. We also discuss the attenuation of the flux due to the interactions of the cosmic rays with the cluster medium, which can be sizeable for heavy nuclei. The overall suppression in the total cosmic ray flux expected on Earth is important to understand the shape of the extragalactic contribution to the cosmic ray spectrum for E/Z < 1 EeV . This suppression can also be relevant to interpret the results of fits to composition-sensitive observables measured at ultra-high energies.

Evaluation of Multiple Backscattering and Saturation Thickness of Gamma Rays

A Monte Carlo code was written to determine the saturation thickness for multiply scattered gamma rays from aluminium targets. Interactions of incident gamma rays with the energies of 123, 279, 360, 511, 662, 1115, and 1250 keV were simulated. This work aims to design a convenient code which can be used in investigations on gamma backscattering. Obtained results for saturation thickness values have been compared with experimental ones and the Monte Carlo N-particle (MCNP) code results, and showed good agreement. Also, based on the similar behavior of number of multiple scattered photons between these three methods, the expected spectrum of singly or multiply scattered photons which is not possible to observe with experiment has been presented.

Effective atomic numbers and electron densities for some lanthanide oxide compounds using direct method in the energy region of 1 keV - 20 MeV

In this paper, the effective atomic numbers and electron densities representing interaction of gamma rays with oxides of lanthanides have been studied. The effective atomic numbers for photon energy-absorption ( Z PEAeff ) and photon interaction ( Z PIeff ), and relative to air Z Reff , the effective electron densities for photon energy-absorption ( N PEAeff ) and photon interaction ( N PIeff ) were calculated using the values of the mass attenuation and energy absorption coefficients. The variation of Z PEAeff , Z PIeff , Z Reff , N PEAeff and N PIeff with energy were shown graphically. In the continuous energy region, it was observed that there are agreements and disagreements between photon interaction and photon energy-absorption for effective atomic numbers and electron densities of compounds in different energy regions. In addition, absorption edge effects on effective atomic numbers leading more than a single value of effective atomic number at a specific energy have been discussed for the given compounds. Comparisons with experiments wherever possible have been carried out for calculated values of Z eff and N eff .

Reconstruction of air shower muon densities using segmented counters with time resolution

Despite the significant experimental effort made in the last decades, the origin of the ultra-high energy cosmic rays is still largely unknown. Key astrophysical information to identify where these energetic particles come from is provided by their chemical composition. It is well known that a very sensitive tracer of the primary particle type is the muon content of the showers generated by the interaction of the cosmic rays with air molecules. We introduce a likelihood function to reconstruct particle densities using segmented detectors with time resolution. As an example of this general method, we fit the muon distribution at ground level using an array of counters like AMIGA, one of the Pierre Auger Observatory detectors. For this particular case we compare the reconstruction performance against a previous method. With the new technique, more events can be reconstructed than before. In addition the statistical uncertainty of the measured number of muons is reduced, allowing for a better discrimination of the cosmic ray primary mass.

Evaluation of Superconducting Magnet Shield Configurations for Long Duration Manned Space Missions.

A manned mission to Mars would present an important long-term health risk to the crew members due to the prolonged exposure to the ionizing radiation of galactic cosmic-rays. The radiation levels would largely exceed those encountered in the Apollo missions. An increase in the passive shielding provided by the spacecraft implies a significant increase of the mass. The advent of superconducting magnets in the early 1960s was considered an attractive alternative. The technology allows to generate magnetic fields capable to deflect the cosmic-rays in a manner analogous to the reduction of the particle fluxes in the upper atmosphere due to the Earth’s dipole magnetic field. A series of the three studies have been conducted over the last 5 years, funded successively by European Space Agency (ESA), the NASA Innovative Advanced Concepts (NIAC) program, and the Union European’s Seventh Framework Programme (FP7). The shielding configurations studied are based on high-temperature superconductors, which eliminate the need to operate with liquid helium. The mass estimates of the coils and supporting structure of the engineering designs are based on the current and expected near-future performance of the superconducting materials. In each case, the shield performance, in terms of dose reduction, is provided by a 3-dimensional Monte Carlo simulation, which treats in detail the electromagnetic and hadronic interactions of the galactic-cosmic rays, and the secondary particles they produce in the materials of the shield and spacecraft. A summary of the results of the studies, representing one of the most detailed and comprehensive efforts made in the field, is presented.

Discovery of atmospheric neutrino oscillations**

Atmospheric neutrinos are produced by cosmic ray interactions in the atmosphere. The zenith‐angle and energy dependence of the muon‐ and electron‐ neutrino events are observed in atmospheric neutrino experiments. Through these studies neutrino oscillations were discovered. In this article, studies of atmospheric neutrinos in the Kamiokande and Super‐Kamiokande experiments are described.

GeV excess and phenomenological astrophysics modeling

Predefined spatial templates to describe the background of γ-ray emission from astrophysical processes, like cosmic ray interactions, are used in previous searches for the γ-ray signatures of annihilating galactic dark matter. In this proceeding, we investigate the GeV excess in the inner Galaxy using an alternative approach, in which the astrophysical components are identified solely by their spectral and morphological properties. We confirm the reported GeV excess and derive related parameters for dark matter interpretation, which are consistent with previous results. We investigate the morphology of this spectral excess as preferred by the data only. This emission component exhibits a central Galaxy cusp as expected for a dark matter annihilation signal. However, Galactic disk regions with a morphology of that of the hot interstellar medium also host such a spectral component. This points to a possible astrophysical origin of the excess and requests a more detailed understanding of astrophysical γ-ray emitting processes in the galactic center region before definite claims about a dark matter annihilation signal can be made.

Tidal disruption jets of supermassive black holes as hidden sources of cosmic rays: Explaining the IceCube TeV-PeV neutrinos

Cosmic ray interactions that produce high-energy neutrinos also inevitably generate high-energy gamma rays, which finally contribute to the diffuse high-energy gamma-ray background after they escape the sources. It was recently found that, the high flux of neutrinos at $\sim30$ TeV detected by IceCube lead to a cumulative gamma-ray flux exceeding the Fermi isotropic gamma-ray background at 10-100 GeV, implying that the neutrinos are produced by hidden sources of cosmic rays, where GeV-TeV gamma-rays are not transparent. Here we suggest that relativistic jets in tidal disruption events (TDEs) of supermassive black holes are such hidden sources. We consider the jet propagation in an extended,optically thick envelope around the black hole, which is resulted from the ejected material during the disruption. While powerful jets can break free from the envelope, less powerful jets would be choked inside the envelope. The jets accelerate cosmic rays through internal shocks or reverse shocks and further produce neutrinos via interaction with the surrounding dense medium or photons. All three TDE jets discovered so far are not detected by Fermi/LAT, suggesting that GeV-TeV gamma-rays are absorbed in these jets. The cumulative neutrino flux from TDE jets can account for the neutrino flux observed by IceCube at PeV energies and may also account for the higher flux at $\sim30$ TeV if less powerful, choked jets are present in the majority of TDEs.

Galactic dark matter search via phenomenological astrophysics modeling

Previous searches for the γ-ray signatures of annihilating galactic dark matter used predefined spatial templates to describe the background of γ-ray emission from astrophysical processes like cosmic ray interactions. In this work, we aim to establish an alternative approach, in which the astrophysical components are identified solely by their spectral and morphological properties. To this end, we adopt the recent reconstruction of the diffuse γ-ray sky from Fermi data by the D3PO algorithm and the fact that more than 90% of its flux can be represented by only two spectral components, resulting form the dense and dilute interstellar medium. Under these presumptions, we confirm the reported DM annihilation-like signal in the inner Galaxy and derive upper limits for dark matter annihilation cross sections. We investigate whether the DM signal could be a residual of the simplified modeling of astrophysical emission by inspecting the morphology of the regions, which favor a dark matter component. The central galactic region favors strongest for such a component with the expected spherically symmetric and radially declining profile. However, astrophysical structures, in particular sky regions which seem to host most of the dilute interstellar medium, obviously would benefit from a DM annihilation-like component {as well}. Although these regions do not drive the fit, they warn that a more detailed understanding of astrophysical γ-ray emitting processes in the galactic center region are necessary before definite claims about a DM annihilation signal can be made. The regions off the Galactic plane actually disfavor the best fit DM annihilation cross section from the inner Galactic region unless the radial decline of the Galactic DM density profile in the outer regions is significantly steeper than that usually assumed.