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International audience; During the flight, an aircraft is submitted to a radiation environment composed of cosmic-ray-induced particles (CRIP) of which neutrons are responsible for approximately 40% of the crew effective dose and are the main cause of single event effects (SEE) in avionics systems at flight altitudes. A model of Learjet aircraft was developed on Monte Carlo simulation using the MCNPX code in order to detail the CRIP field inside the aircraft. The radiation source modeling was previously developed by a computational platform that simulates the energy and angular distributions of the CRIP along the atmosphere. In this article, we determined the variation of the neutron radiation field in several positions inside the aircraft at 11- and 18-km altitudes and for both equatorial and polar regions. The results suggest that the maximum variation of neutron fluence rate between different positions inside the aircraft shows a tendency of higher differences for a lower energy threshold (thermal and E > 1 MeV) in comparison with those differences for a higher energy threshold (E > 10 MeV). Moreover, the angular distribution results show relevant differences between positions inside aircraft, mainly for thermal neutrons close to the fuel. The general tendency is to enhance these discrepancies for devices with new technologies, due to their lower energy threshold for SEE occurrences.

International audience; This work investigates solar events occurred in September 2017 characterized by a series of Forbush decreases and a ground level enhancement (GLE). Forbush decreases is a rapid decrease in the observed https://en.wikipedia.org/wiki/Galactic_cosmic_ray intensity following a coronal mass ejection while GLE is induced by a strong solar event for which the flux of high‐energy solar particles is sufficient to enhance the radiation level on the ground. These investigations were performed using data recorded by a neutron spectrometer network composed of a Bonner sphere system. Two instruments located at Pic‐du‐Midi Observatory (+2,885 m above sea level) and at Concordia station (Antarctica, +3,233 m) record simultaneously and continuously the neutron spectra, allowing to consider short‐term variations during solar events. The main objective is to analyze neutron spectral properties including their energy distributions and dynamics. This paper presents cosmic ray‐induced neutron spectra during active solar event leading to changes in the local cosmic ray spectrum (Forbush decreases and a GLE). Concerning the GLE, analyses show that neutrons in the evaporation domain are particularly amplified during the GLE, while other energetic domains increase uniformly.

Molecular clouds (MCs) are exposed to Galactic and extragalactic cosmic rays (CR) that trigger several physical and physicochemical changes, including gas and grain heating and molecular destruction and formation. Here we present a theoretical model describing the energy delivered by CRs, composed of protons, alphas, and electrons taken from Voyager I measurements, into a typical MC with 5400 M ☉ (composed mainly of H with a density law of r −1.2) and size around 1 × 106 au. The calculation was performed employing the Monte Carlo toolkit GEANT4 to obtain the energy deposition per mass from several types of secondary particles (considering nuclear and hadron physics). The results indicate that incoming protons contribute to most of the energy delivered in the MC in all regions (maximum ∼230 MeV g−1 s−1 at outer regions of the cloud). Secondary electrons are the second most important component for energy deposition in almost all layers of the MC and can deliver an energy rate of ∼130 MeV g−1 s−1 in the outer region of the MC. Other cascade particles have their major energy delivery in the central and denser core of the MC. From a temperature model (considering CR data from Voyager I), we observed (i) a small bump in temperature at the distance of 3 × 103–2 × 104 au from the center, (ii) a rapid temperature decrease (roughly 7 K) between the outer layer and the second most outer layer, and (iii) that, at a distance of 5 × 104 au (Av > 10), the gas temperature of the MC is below 15 K.

This paper investigates seasonal cosmic ray-induced neutron variations measured over a long-term period (from 2011 to 2016) in both the high-altitude stations located in medium geomagnetic latitude and Antarctica (Pic-du-Midi and Concordia, respectively). To reinforce analysis, modeling based on ground albedo neutrons simulations of extensive air showers and the solar modulation potential was performed. Because the local environment is well known and stable over time in Antarctica, data were used to validate the modeling approach. A modeled scene representative to the Pic-du-Midi was simulated with GEANT4 for various hydrogen properties (composition, density, and wet level) and snow thickness. The orders of magnitudes of calculated thermal fluence rates are consistent with measurements obtained during summers and winters. These variations are dominant in the thermal domain (i.e., En 20 MeV) is weakly impacted. The role of hydrogen content on ground albedo neutron generation was investigated with GEANT4 simulations. These investigations focused to mountain environment; nevertheless, they demonstrate the complexity of the local influences on neutron fluence rates.

Journal of Physics: Conference Series, Volumen 630 There is interest in modeling the atmosphere in the South Atlantic Magnetic Anomaly in order to obtain information about the cosmic-ray induced neutron spectrum and angular distribution as functions of altitude. In this work we use the Monte Carlo codes MCNPX and Geant4 to determine the cosmic-ray-induced neutron flux in the atmosphere produced by the cosmic ray protons incident on the top of the atmosphere and to estimate the ambient dose equivalent rate as function of altitude. The results present a reasonable conformity to other codes (QARM and EXPACS) based on other parameterizations.