Search results for "Gamma-ray"
showing 10 items of 374 documents
Equivalent detector models for the simulation of efficiency response of an HPGe detector with PENELOPE code
2019
Monte Carlo simulation of response of an HPGe detector is a widely used technique to evaluate counting efficiencies. It is particularly useful when calibration standards with the same shape and composition of the sample under examination are not available. The result of the simulation depends on the more or less detailed knowledge of the characteristics of the detector, able to define a "model" of the same detector. To highlight parts not well defined in the manufacturer's certification, a detector X-ray analysis is usually performed, except in cases when it is not possible to dismantle the shielding structure with the loss of previous calibration data. In this work, in absence of some data…
A radiometric and petrographic interpretation of discrepancies on uranium content in samples collected at Alte Madonie Mounts region (Sicily, Italy)
2013
Abstract The main goal of this work is to evaluate a correlation between anomalous Uranium (U) content and petrographic features of some soil and rock samples collected at Alte Madonie Mounts region (North-central Sicily, Italy). A total of 41 samples of selected soils and rocks were collected, powdered, dried and sealed in “Marinelli” beakers for 20 days before the measurement to ensure that radioactive equilibrium between 226 Ra and 214 Bi was reached. Gamma-ray spectrometric analysis was used to quantify radioactivity concentrations. Mineralogical and chemical features of the samples were determined by X-ray Fluorescence (XRF), X-ray Diffractometry (XRD), Attenuated Total Reflection-Four…
Constraints on Minute-Scale Transient Astrophysical Neutrino Sources
2019
High-energy neutrino emission has been predicted for several short-lived astrophysical transients including gamma-ray bursts (GRBs), core-collapse supernovae with choked jets, and neutron star mergers. IceCube's optical and x-ray follow-up program searches for such transient sources by looking for two or more muon neutrino candidates in directional coincidence and arriving within 100 s. The measured rate of neutrino alerts is consistent with the expected rate of chance coincidences of atmospheric background events and no likely electromagnetic counterparts have been identified in Swift follow-up observations. Here, we calculate generic bounds on the neutrino flux of short-lived transient so…
Evidence for Astrophysical Muon Neutrinos from the Northern Sky with IceCube
2015
Results from the IceCube Neutrino Observatory have recently provided compelling evidence for the existence of a high energy astrophysical neutrino flux utilizing a dominantly Southern Hemisphere dataset consisting primarily of nu_e and nu_tau charged current and neutral current (cascade) neutrino interactions. In the analysis presented here, a data sample of approximately 35,000 muon neutrinos from the Northern sky was extracted from data taken during 659.5 days of livetime recorded between May 2010 and May 2012. While this sample is composed primarily of neutrinos produced by cosmic ray interactions in the Earth's atmosphere, the highest energy events are inconsistent with a hypothesis of …
Atmospheric and astrophysical neutrinos above 1 TeV interacting in IceCube
2015
The IceCube Neutrino Observatory was designed primarily to search for high-energy (TeV--PeV) neutrinos produced in distant astrophysical objects. A search for $\gtrsim 100$~TeV neutrinos interacting inside the instrumented volume has recently provided evidence for an isotropic flux of such neutrinos. At lower energies, IceCube collects large numbers of neutrinos from the weak decays of mesons in cosmic-ray air showers. Here we present the results of a search for neutrino interactions inside IceCube's instrumented volume between 1~TeV and 1~PeV in 641 days of data taken from 2010--2012, lowering the energy threshold for neutrinos from the southern sky below 10 TeV for the first time, far bel…
ORIGIN: metal creation and evolution from the cosmic dawn
2012
Herder, Jan-Willem den et al.
A procedure to evaluate coincidence-summing correction values in gamma-ray spectrometry with HPGe detectors
2009
The spectrometric analysis of a gamma-emitter sample measured in "close geometry" can be affected by errors due to coincidence-summing effects that can occur when two or more coincident photons (real coincidences) within the resolution time of the spectrometric system are emitted. The probability that these effects occur depends primarily on the nuclide decay scheme, the sample-detector distance and detector intrinsic-efficiency whereas results independent from the sample nuclide activity. Coincidence-summing corrections of the photopeak areas are requested, in particular, when the gamma ray spectrometric analysis is aimed to efficiency or activity determination. In this work is reported a …
Recent GRBs observed with the 1.23m CAHA telescope and the status of its upgrade
2010
We report on optical observations of Gamma-Ray Bursts (GRBs) followed up by our collaboration with the 1.23m telescope located at the Calar Alto observatory. The 1.23m telescope is an old facility, currently undergoing upgrades to enable fully autonomous response to GRB alerts. We discuss the current status of the control system upgrade of the 1.23m telescope. The upgrade is being done by our group based on the Remote Telescope System, 2nd Version (RTS2), which controls the available instruments and interacts with the EPICS database of Calar Alto. (Our group is called ARAE (Robotic Astronomy & High-Energy Astrophysics) and is based on members of IAA (Instituto de Astrofísica de Andalucía). …
Effects of modified theories of gravity on neutrino pair annihilation energy deposition near neutron stars
2020
We study the neutrino pairs annihilation into electron-positron pairs ($\nu+{\bar \nu}\to e^- + e^+$) near the surface of a neutron star. The analysis is performed in the framework of extended theories of gravity. The latter induce a modification of the minimum photon-sphere radius ($R_{ph}$) and the maximum energy deposition rate near to $R_{ph}$, as compared to ones of General Relativity. These results might lead to an efficient mechanism for generating GRBs.
Signatures of photon and axion-like particle mixing in the gamma-ray burst jet
2011
Photons couple to Axion-Like Particles (ALPs) or more generally to any pseudo Nambu-Goldstone boson in the presence of an external electromagnetic field. Mixing between photons and ALPs in the strong magnetic field of a Gamma-Ray Burst (GRB) jet during the prompt emission phase can leave observable imprints on the gamma-ray polarization and spectrum. Mixing in the intergalactic medium is not expected to modify these signatures for ALP mass > 10^(-14) eV and/or for < nG magnetic field. We show that the depletion of photons due to conversion to ALPs changes the linear degree of polarization from the values predicted by the synchrotron model of gamma ray emission. We also show that when …