Geant4 Application for Tomographic Emission (GATE) is a Monte Carlo code, including the algorithms integrated inside Geant4 and other specific tools dedicated to tomography. Though, the detailed ...physical modeling of Geant4 is computationally demanding in order to simulate photon interactions and transport, particularly using voxelized phantoms. To circumvent the relatively slow simulation of voxelized phantoms for radiotherapy applications, GATE offers some relevant optimization methods to minimize the time consumption. In this study, specific absorbed fractions (SAFs) in Golem voxelized phantom using GATE Monte Carlo code for three optimization algorithms: Nested Parametrized Volume, Regular navigation algorithm and Compressed voxels methods have been used to calculate SAFs and compared to the literature data. The computation time has been also compared and discussed for the three methods. Compressed voxels method is more than 16 times faster than the two other parameterization methods for internal dosimetry field.
It is of great interest to estimate absorbed doses in organs before radiation therapy, especially in nuclear medicine field. In this regard, the internal dose distribution is required. According to ...the MIRD formalism, Specific Absorbed Fraction (SAF) is an essential parameter for internal dosimetry. In the present work, SAF values for the voxelized phantom (Golem) of the GSF-National Research Center for Environment and Health were calculated using Geant4/GATE with Standard packages and compared with GSF Monte Carlo reference data. Photon irradiations of 30, 100 keV and 1 MeV energy were simulated in eleven different sources and target organs: liver, kidneys, lungs, brain, pancreas, spleen, colon, Red bone marrow (RBM), stomach, thyroid and adrenals. The SAF for self-absorption and for cross-irradiation to other organs were calculated and compared with literature. The results agree with published data, with an average relative difference less than 3%, for the self-absorption of 100 keV and 1 MeV photon energies. The agreement of Geant4/GATE and GSF code might depend on the distance between target and source, the target mass and the photons energy. Generally, the present results indicate that GATE might be used with gamma emitters for internal dosimetry in regard to our prospective works.
ABSTRACT
Addressing the origin of the astrophysical neutrino flux observed by IceCube is of paramount importance. Gamma-Ray Bursts (GRBs) are among the few astrophysical sources capable of achieving ...the required energy to contribute to such neutrino flux through pγ interactions. In this work, ANTARES data have been used to search for upward going muon neutrinos in spatial and temporal coincidence with 784 GRBs occurred from 2007 to 2017. For each GRB, the expected neutrino flux has been calculated in the framework of the internal shock model and the impact of the lack of knowledge on the majority of source redshifts and on other intrinsic parameters of the emission mechanism has been quantified. It is found that the model parameters that set the radial distance where shock collisions occur have the largest impact on neutrino flux expectations. In particular, the bulk Lorentz factor of the source ejecta and the minimum variability time-scale are found to contribute significantly to the GRB-neutrino flux uncertainty. For the selected sources, ANTARES data have been analysed by maximizing the discovery probability of the stacking sample through an extended maximum-likelihood strategy. Since no neutrino event passed the quality cuts set by the optimization procedure, 90 per cent confidence level upper limits (with their uncertainty) on the total expected diffuse neutrino flux have been derived, according to the model. The GRB contribution to the observed diffuse astrophysical neutrino flux around 100 TeV is constrained to be less than 10 per cent.
This work presents a new search for magnetic monopoles using data taken with the ANTARES neutrino telescope over a period of 10 years (January 2008 to December 2017). Compared to previous ANTARES ...searches, this analysis uses a run-by-run simulation strategy, with a larger exposure as well as a new simulation of magnetic monopoles taking into account the Kasama, Yang and Goldhaber model for their interaction cross-section with matter. No signal compatible with the passage of relativistic magnetic monopoles is observed, and upper limits on the flux of magnetic monopoles with β=v/c≥0.55, are presented. For ultra-relativistic magnetic monopoles the flux limit is ∼7×10−18 cm−2s−1sr−1.
A
bstract
The ANTARES neutrino telescope has an energy threshold of a few tens of GeV. This allows to study the phenomenon of atmospheric muon neutrino disappearance due to neutrino oscillations. In ...a similar way, constraints on the 3+1 neutrino model, which foresees the existence of one sterile neutrino, can be inferred. Using data collected by the ANTARES neutrino telescope from 2007 to 2016, a new measurement of Δ
m
32
2
and
θ
23
has been performed — which is consistent with world best-fit values — and constraints on the 3+1 neutrino model have been derived.
A search for cosmic neutrino sources using the data collected with the ANTARES neutrino telescope between early 2007 and the end of 2015 is performed. For the first time, all neutrino ...interactions-charged- and neutral-current interactions of all flavors-are considered in a search for point-like sources with the ANTARES detector. In previous analyses, only muon neutrino charged-current interactions were used. This is achieved by using a novel reconstruction algorithm for shower-like events in addition to the standard muon track reconstruction. The shower channel contributes about 23% of all signal events for an E−2 energy spectrum. No significant excess over background is found. The most signal-like cluster of events is located at (α,δ)=(343.8°,23.5°) with a significance of 1.9σ. The neutrino flux sensitivity of the search is about E2dΦ/dE=6×10−9 GeV cm−2 s−1 for declinations from −90° up to −42°, and below 10−8 GeV cm−2 s−1 for declinations up to 5°. The directions of 106 source candidates and 13 muon track events from the IceCube high-energy sample events are investigated for a possible neutrino signal and upper limits on the signal flux are determined.
Neutrino detectors participate in the indirect search for the fundamental constituents of dark matter (DM) in form of weakly interacting massive particles (WIMPs). In WIMP scenarios, candidate DM ...particles can pair-annihilate into Standard Model products, yielding considerable fluxes of high-energy neutrinos. A detector like ANTARES, located in the Northern Hemisphere, is able to perform a complementary search looking towards the Galactic Centre, where a high density of dark matter is thought to accumulate. Both this directional information and the spectral features of annihilating DM pairs are entered into an unbinned likelihood method to scan the data set in search for DM-like signals in ANTARES data. Results obtained upon unblinding 3170 days of data reconstructed with updated methods are presented, which provides a larger, and more accurate, data set than a previously published result using 2101 days. A non-observation of dark matter is converted into limits on the velocity-averaged cross section for WIMP pair annihilation.
Abstract
A search for astrophysical pointlike neutrino sources using the data collected by the ANTARES detector between 2007 January 29 and 2017 December 31 is presented. A likelihood method is used ...to assess the significance of an excess of muon neutrinos inducing track-like events in correlation with the location of a list of possible sources. Different sets of objects are tested in the analysis: (a) a subsample of the Fermi 3LAC catalog of blazars, (b) a jet-obscured population of active galactic nuclei, (c) a sample of hard X-ray selected radio galaxies, (d) a star-forming galaxy catalog, and (e) a public sample of 56 very-high-energy track events from the IceCube experiment. None of the tested sources shows a significant association with the sample of neutrinos detected by ANTARES. The smallest
p
-value is obtained for the catalog of radio galaxies with an equal-weights hypothesis, with a pre-trial
p
-value equivalent to a 2.8
σ
excess, which is equivalent to 1.6
σ
post-trial. In addition, the results of a dedicated analysis for the blazar MG3 J225517+2409 are also reported: this source is found to be the most significant within the Fermi 3LAC sample, with five ANTARES events located less than one degree from the source. This blazar showed evidence of flaring activity in Fermi data, in spacetime coincidence with a high-energy track detected by IceCube. An a posteriori significance of 2.6
σ
for the combination of ANTARES and IceCube data is reported.
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