Simulation of the Galactic Cosmic Ray Shadow of the Sun

The cosmic-ray particles of TeV-regime, outside the solar system are blocked in their way to the Earth, a deficit of particles is observed corresponding to the location of the Sun known as the Sun shadow. The center of the Sun shadow is shifted from its nominal position due to the presence of magnetic fields in interplanetary space,and this shift is used indirectly as a probe to study the solar magnetic field that is difficult to measure otherwise.A detailed Monte Carlo simulation of galactic cosmic-ray propagation in the Earth-Sun system is carried out to disentangle the cumulative effects of solar, interplanetary and geomagnetic fields. The shadowing effects and the displacements results of the Sun shadow in different solar activities are reproduced and discussed.

Ionization of protoplanetary disks by galactic cosmic rays,solar protons,and supernova remnants

Galactic cosmic rays and solar protons ionize the present terrestrial atmosphere,and the air showers are simulated by well-tested Monte-Carlo simulations,such as PHITS code.We use the latest version of PHITS to evaluate the possible ionization of protoplanetary disks by galactic cosmic rays（GCRs）,solar protons,and by supernova remnants.The attenuation length of GCR ionization is updated as 118 g cm^-2,which is approximately 20% larger than the popular value.Hard and soft possible spectra of solar protons give comparable and 20% smaller attenuation lengths compared with those from standard GCR spectra,respectively,while the attenuation length is approximately 10% larger for supernova remnants.Further,all of the attenuation lengths become 10% larger in the compound gas of cosmic abundance,e.g.128 g cm^-2 for GCRs,which can affect the minimum estimate of the size of dead zones in protoplanetary disks when the incident flux is unusually high.

An ACE/CRIS-observation-based Galactic Cosmic Rays heavy nuclei spectra model Ⅱ

An observation-based Galactic Cosmic Ray(GCR)spectral model for heavy nuclei is developed.Zhao and Qin[J.Geophys.Res.Space Phys.118,1837(2013)]proposed an empirical elemental GCR spectra model for nuclear charge 5≤z≤28 over the energy range^30 to 500 Me V/nuc,which is proved to be successful in predicting yearly averaged GCR heavy nuclei spectra.Based on the latest highly statistically precise measurements from ACE/CRIS,a further elemental GCR model with monthly averaged spectra is presented.The model can reproduce the past and predict the future GCR intensity monthly by correlating model parameters with the continuous sunspot number(SSN)record.The effects of solar activity on GCR modulation are considered separately for odd and even solar cycles.Compared with other comprehensive GCR models,our modeling results are satisfyingly consistent with the GCR spectral measurements from ACE/SIS and IMP-8,and have comparable prediction accuracy as the Badhwar&O’Neill 2014 model.A detailed error analysis is also provided.Finally,the GCR carbon and iron nuclei fluxes for the subsequent two solar cycles(SC 25 and 26)are predicted and they show a potential trend in reduced flux amplitude,which is suspected to be relevant to possible weak solar cycles.

Galactic cosmic ray propagation: sub-PeV diffuse gamma-ray and neutrino emission

The Tibet ASγexperiment just reported their measurement of sub-PeV diffuse gamma-ray emission from the Galactic disk,with the highest energy up to 957 TeV.These diffuse gamma rays are most likely the hadronic origin by cosmic ray(CR)interaction with interstellar gas in the galaxy.This measurement provides direct evidence to the hypothesis that the Galactic Cosmic Rays(GCRs)can be accelerated beyond PeV energies.In this work,we try to explain the sub-PeV diffuse gamma-ray spectrum with different CR propagation models.We find that there is a tension between the sub-PeV diffuse gamma-ray and the local CR spectrum.To describe the sub-PeV diffuse gamma-ray flux,it generally requires larger local CR flux than measurement in the knee region.We further calculate the PeV neutrino flux from the CR propagation model.Even all of these sub-PeV diffuse gamma rays originate from the propagation,the Galactic Neutrinos(GNs)only account for less than~15%of observed flux,most of which are still from extragalactic sources.

Galactic cosmic ray propagation: sub-PeV diffuse gamma-ray and neutrino emission

The Tibet ASγexperiment just reported their measurement of sub-PeV diffuse gamma-ray emission from the Galactic disk,with the highest energy up to 957 TeV.These diffuse gamma rays are most likely the hadronic origin by cosmic ray(CR)interaction with interstellar gas in the galaxy.This measurement provides direct evidence to the hypothesis that the Galactic Cosmic Rays(GCRs)can be accelerated beyond PeV energies.In this work,we try to explain the sub-PeV diffuse gamma-ray spectrum with different CR propagation models.We find that there is a tension between the sub-PeV diffuse gamma-ray and the local CR spectrum.To describe the sub-PeV diffuse gamma-ray flux,it generally requires larger local CR flux than measurement in the knee region.We further calculate the PeV neutrino flux from the CR propagation model.Even all of these sub-PeV diffuse gamma rays originate from the propagation,the Galactic Neutrinos(GNs)only account for less than∼15%of observed flux,most of which are still from extragalactic sources.

Studies of the radiation environment on the Mars surface using the Geant4 toolkit

The radiation environment on the surface of Mars is a potential threat for future manned exploration missions to this planet.In this study,a simple geometrical model was built for simulating the radiation environment on the Mars surface caused by galactic cosmic rays;the model was built and studied using the Geant4 toolkit.The simulation results were compared with the data reported by a radiation assessment detector(RAD).The simulated spectra of neutrons,photons,protons,α particles,and particle groups Z=3-5,Z=6-8,Z=9-13,and Z=14-24 were in a reasonable agreement with the RAD data.However,for deuterons,tritons,and 3He,the simulations yielded much smaller values than for the corresponding RAD data.In addition,the particles’spectra within the 90 zenith angle were also obtained.Based on these spectra,we calculated the radiation dose that would have been received by an average human body on Mars.The distribution of the dose throughout the human body was not uniform.The absorbed and equivalent doses for the brain were the highest among all of the organs,reaching 62.0±1.7 mGy/y and 234.1±8.0 mSv/y,respectively.The average absorbed and equivalent doses for the entire body were approximately 44 mGy/y and 153 mSv/y,respectively.Further analysis revealed that most of the radiation dose was owing to a particles,protons,and heavy ions.We then studied the shielding effect of the Mars soil with respect to the radiation.The body dose decreased significantly with increasing soil depth.At the depth of 1.5 m,the effective dose for the entire body was 17.9±2.4 mSv/y,lower than the dose limit for occupational exposure.At the depth of 3 m,the effective dose to the body was 2.7±1.0 mSv/y,still higher than the accepted dose limit.

Single planet formation regime in the high-ionization environment:Possible origin of hot Jupiters and super-Earths

We studied the particle growth in a protoplanetary disk in a high-ionization environment and found that icy planet formation is inactive for a disk with an ionization rate 100 times higher than that of the present Solar System. In particular, in the case of M 〈 10^（-7.4）M_☉yr^（-1）, only rocky planet formation occurs. In such a case, all the solid materials in the disk drift inward, eventually reach the inner MRI front,and accumulate there. They form a dense, thin sub-disk of solid particles, which undergoes gravitational instability to form rocky planetesimals. The planetesimals rapidly grow into a planet through pebble accretion. Consequently, rocky planets tend to be much larger than planets formed through other regimes（tandem planet formation regime and dispersed planet formation regime）, in which icy planet formation actively takes place. These rocky planets may evolve into hot Jupiters if they grow fast enough to the critical core mass of the runaway gas accretion before the dispersal of the disk gas, or they may evolve into super-Earths if the gas dispersed sufficiently early.

The Giant Radio Array for Neutrino Detection(GRAND):Science and design

The Giant Radio Array for Neutrino Detection(GRAND)is a planned large-scale observatory of ultra-high-energy(UHE)cosmic particles,with energies exceeding 10~8 Ge V.Its goal is to solve the long-standing mystery of the origin of UHE cosmic rays.To do this,GRAND will detect an unprecedented number of UHE cosmic rays and search for the undiscovered UHE neutrinos and gamma rays associated to them with unmatched sensitivity.GRAND will use large arrays of antennas to detect the radio emission coming from extensive air showers initiated by UHE particles in the atmosphere.Its design is modular:20 separate,independent sub-arrays,each of 10000 radio antennas deployed over 10000 km^2.A staged construction plan will validate key detection techniques while achieving important science goals early.Here we present the science goals,detection strategy,preliminary design,performance goals,and construction plans for GRAND.

Modelling the interaction of the Astro Bio Cube Sat with the Van Allen's Belt radiative field using Monte Carlo transport codes

Purpose The AstroBio Cube Satellite(ABCS)will deploy within the inner Van Allen belt on the Vega C Maiden Flight launch opportunity of the European Space Agency.At this altitude,ABCS will experience radiation doses orders of magnitude greater than in low earth orbit,where CubeSats usually operate.The paper aims to estimate the irradiation effect on the ABCS payload in the orbital condition,their possible mitigation designing shielding solutions and performs a preliminary representativity simulation study on the ABCS irradiation with fission neutron at the TAPIRO(TAratura Pila Rapida Potenza 0)nuclear research reactor facility at ENEA.Methods We quantify the contributions of geomagnetically trapped particles(electron and proton),Galactic Cosmic Rays(GCR ions),Solar energetic particle within the ABCS orbit using the ESA's SPace ENVironment information system.FLUKA(Fluktuierende Kaskade-Fluctuating Cascade)code models the ABCS interaction with the orbital source.Results We found a shielding solution of the weight of 300 g constituted by subsequent layers of tungsten,resins,and aluminium that decreases on average the 20%overall dose rate relative to the shielding offered by the only satellite's structure.Finally,simulations of neutron irradiation of the whole ABCS structure within the TAPIRO's thermal column cavity show that a relatively short irradiation time is requested to reach the same level of 1 MeV neutron Silicon equivalent damage of the orbital source.Conclusions The finding deserves the planning of a future experimental approach to confirm the TAPIRO's performance and establish an irradiation protocol for testing aerospatial electronic components.