In this work, a new method of SHS process has been investigated for the synthesis of SiAlON under low nitrogen pressure. A gel mixture of silica and sodium oxide (sodium silicate) as a reactant and ...catalyst was produced by alkali melting of silica, solving the results in water and heating in auto clave. Al powder was also used as reactants. Urea and aluminum nitrate hydrate was used as igniting agents. The addition of Mg also was necessary for reaching the combustion. Sodium azide as a good reactant addition for preparing both combustion and nitrogen supply was tested. Beta-Si3N4 powder acted as diluting agent and by reducing the adiabatic temperature helped the nitrogen diffusion into the melted reactants which was not agglomerated. NH4Cl in some cases was used as a catalyst which showed good results for reaching SiAlON. For comparison possibility some experiments were made using silica powder instead of sodium silicate gel. These materials were mixed by pestle and mortar and laid into the combustion chamber cavity without pressing. The compound was heated by electrical element until the ignition happened by gases which were produced from urea and aluminum nitrate hydrate. The pressure of nitrogen in combustion chamber was kept constant near 0.1Mpa. The products of syntheses were of agglomerated one mostly O′-SiAlON & β and β′-SiAlON. Effects of NH4Cl were examined by XRD results. TGA and DTA graphs showed the thermodynamics of reaction which were analyzed in some parts by XRD spectroscopy. In some cases nano material of SiAlON was produced which is demonstrated by XRD and FTIR spectroscopy.
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•Investigations of a new method of combustion synthesis (SHS) process for the synthesis of SiAlON under low nitrogen pressure•Applying different precursors for combustion synthesis (SHS) of SiAlON•Study of the current state in the field of fabrication of SiAlON by SHS of low cost powders•Characterization of processed powders with some outstanding methods•Receiving the synthesis products of agglomerated O′-SiAlON & beta and beta prime-SiAlON
A supermassive black hole, obscured by cosmic dust, powers the nearby active galaxy NGC 1068. Neutrinos, which rarely interact with matter, could provide information on the galaxy’s active core. We ...searched for neutrino emission from astrophysical objects using data recorded with the IceCube neutrino detector between 2011 and 2020. The positions of 110 known gamma-ray sources were individually searched for neutrino detections above atmospheric and cosmic backgrounds. We found that NGC 1068 has an excess of
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neutrinos at tera–electron volt energies, with a global significance of 4.2σ, which we interpret as associated with the active galaxy. The flux of high-energy neutrinos that we measured from NGC 1068 is more than an order of magnitude higher than the upper limit on emissions of tera–electron volt gamma rays from this source.
Nearby active galaxy emits neutrinos
Observations have shown a diffuse background of high-energy neutrinos, which is known to be of extragalactic origin. However, it has been difficult to identify individual sources that contribute to this background. The IceCube Collaboration reanalyzed the arrival directions of astrophysical neutrinos and then searched for point sources (see the Perspective by Murase). They identified evidence for neutrino emission from NGC 1068 (also known as Messier 77), a nearby active galaxy. Its properties are quite different from TXS 0506+056, which was found to be a neutrino source in 2018, leading the investigators to suggest that there might be more than one population contributing to the neutrino background. —KTS
The arrival directions of astrophysical neutrinos indicate point source neutrino emission from NGC 1068.
ABSTRACT The IceCube Collaboration has previously discovered a high-energy astrophysical neutrino flux using neutrino events with interaction vertices contained within the instrumented volume of the ...IceCube detector. We present a complementary measurement using charged current muon neutrino events where the interaction vertex can be outside this volume. As a consequence of the large muon range the effective area is significantly larger but the field of view is restricted to the Northern Hemisphere. IceCube data from 2009 through 2015 have been analyzed using a likelihood approach based on the reconstructed muon energy and zenith angle. At the highest neutrino energies between and a significant astrophysical contribution is observed, excluding a purely atmospheric origin of these events at significance. The data are well described by an isotropic, unbroken power-law flux with a normalization at neutrino energy of and a hard spectral index of . The observed spectrum is harder in comparison to previous IceCube analyses with lower energy thresholds which may indicate a break in the astrophysical neutrino spectrum of unknown origin. The highest-energy event observed has a reconstructed muon energy of which implies a probability of less than for this event to be of atmospheric origin. Analyzing the arrival directions of all events with reconstructed muon energies above no correlation with known γ-ray sources was found. Using the high statistics of atmospheric neutrinos we report the current best constraints on a prompt atmospheric muon neutrino flux originating from charmed meson decays which is below 1.06 in units of the flux normalization of the model in Enberg et al.
We report a quasidifferential upper limit on the extremely-high-energy (EHE) neutrino flux above 5×106 GeV based on an analysis of nine years of IceCube data. The astrophysical neutrino flux ...measured by IceCube extends to PeV energies, and it is a background flux when searching for an independent signal flux at higher energies, such as the cosmogenic neutrino signal. We have developed a new method to place robust limits on the EHE neutrino flux in the presence of an astrophysical background, whose spectrum has yet to be understood with high precision at PeV energies. A distinct event with a deposited energy above 106 GeV was found in the new two-year sample, in addition to the one event previously found in the seven-year EHE neutrino search. These two events represent a neutrino flux that is incompatible with predictions for a cosmogenic neutrino flux and are considered to be an astrophysical background in the current study. The obtained limit is the most stringent to date in the energy range between 5×106 and 2×1010 GeV. This result constrains neutrino models predicting a three-flavor neutrino flux of Eν2ϕνe+νμ+ντ≃2×10−8 GeV/cm2 sec sr at 109 GeV. A significant part of the parameter space for EHE neutrino production scenarios assuming a proton-dominated composition of ultra-high-energy cosmic rays is disfavored independently of uncertain models of the extragalactic background light which previous IceCube constraints partially relied on.
A search for high-energy neutrinos interacting within the IceCube detector between 2010 and 2012 provided the first evidence for a high-energy neutrino flux of extraterrestrial origin. Results from ...an analysis using the same methods with a third year (2012-2013) of data from the complete IceCube detector are consistent with the previously reported astrophysical flux in the 100 TeV-PeV range at the level of 10(-8) GeV cm-2 s-1 sr-1 per flavor and reject a purely atmospheric explanation for the combined three-year data at 5.7σ. The data are consistent with expectations for equal fluxes of all three neutrino flavors and with isotropic arrival directions, suggesting either numerous or spatially extended sources. The three-year data set, with a live time of 988 days, contains a total of 37 neutrino candidate events with deposited energies ranging from 30 to 2000 TeV. The 2000-TeV event is the highest-energy neutrino interaction ever observed.
ABSTRACT The recent discovery of a diffuse cosmic neutrino flux extending up to PeV energies raises the question of which astrophysical sources generate this signal. Blazars are one class of ...extragalactic sources which may produce such high-energy neutrinos. We present a likelihood analysis searching for cumulative neutrino emission from blazars in the 2nd Fermi-LAT AGN catalog (2LAC) using IceCube neutrino data set 2009-12, which was optimized for the detection of individual sources. In contrast to those in previous searches with IceCube, the populations investigated contain up to hundreds of sources, the largest one being the entire blazar sample in the 2LAC catalog. No significant excess is observed, and upper limits for the cumulative flux from these populations are obtained. These constrain the maximum contribution of 2LAC blazars to the observed astrophysical neutrino flux to 27% or less between around 10 TeV and 2 PeV, assuming the equipartition of flavors on Earth and a single power-law spectrum with a spectral index of −2.5. We can still exclude the fact that 2LAC blazars (and their subpopulations) emit more than 50% of the observed neutrinos up to a spectral index as hard as −2.2 in the same energy range. Our result takes into account the fact that the neutrino source count distribution is unknown, and it does not assume strict proportionality of the neutrino flux to the measured 2LAC γ-ray signal for each source. Additionally, we constrain recent models for neutrino emission by blazars.
We report on measurements of the all-particle cosmic ray energy spectrum and composition in the PeV to EeV energy range using 3 years of data from the IceCube Neutrino Observatory. The IceTop ...detector measures cosmic ray induced air showers on the surface of the ice, from which the energy spectrum of cosmic rays is determined by making additional assumptions about the mass composition. A separate measurement is performed when IceTop data are analyzed in coincidence with the high-energy muon energy loss information from the deep in-ice IceCube detector. In this measurement, both the spectrum and the mass composition of the primary cosmic rays are simultaneously reconstructed using a neural network trained on observables from both detectors. The performance and relative advantages of these two distinct analyses are discussed, including the systematic uncertainties and the dependence on the hadronic interaction models, and both all-particle spectra as well as individual spectra for elemental groups are presented.
Neutrinos interact only very weakly, so they are extremely penetrating. The theoretical neutrino-nucleon interaction cross-section, however, increases with increasing neutrino energy, and neutrinos ...with energies above 40 teraelectronvolts (TeV) are expected to be absorbed as they pass through the Earth. Experimentally, the cross-section has been determined only at the relatively low energies (below 0.4 TeV) that are available at neutrino beams from accelerators. Here we report a measurement of neutrino absorption by the Earth using a sample of 10,784 energetic upward-going neutrino-induced muons. The flux of high-energy neutrinos transiting long paths through the Earth is attenuated compared to a reference sample that follows shorter trajectories. Using a fit to the two-dimensional distribution of muon energy and zenith angle, we determine the neutrino-nucleon interaction cross-section for neutrino energies 6.3-980 TeV, more than an order of magnitude higher than previous measurements. The measured cross-section is about 1.3 times the prediction of the standard model, consistent with the expectations for charged- and neutral-current interactions. We do not observe a large increase in the cross-section with neutrino energy, in contrast with the predictions of some theoretical models, including those invoking more compact spatial dimensions or the production of leptoquarks. This cross-section measurement can be used to set limits on the existence of some hypothesized beyond-standard-model particles, including leptoquarks.
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