Galactic Component Of Cosmic Rays Research Articles

Fermi-LAT observations of the Sagittarius B complex

Aims. We use 5 years of Fermi-LAT data towards the Galactic-centre giant molecular cloud complex, Sagittarius B, to test questions of how well-mixed the Galactic component of cosmic rays are and what the level of the cosmic-ray sea in different parts of the Galaxy is. Methods. We use dust-opacity maps from the Planck satellite to obtain independent methods for background subtraction and an estimate for the mass of the region. We then present high-quality spectra of gamma-ray emission from 0.3 to 30 GeV and obtain an estimate of the cosmic-ray spectrum from the region. Results. We obtain an estimate of the mass of the region of $1.5 \pm 0.2 \times 10^7~\rm M_{\odot}$ using the Planck data, which agrees well with molecular-line-derived estimates for the same region. We find the the gamma-ray flux from this region is fitted well with a cosmic-ray spectrum that is the same as is observed locally, with evidence of a small over-density at intermediate (1-10 GeV) energies. Conclusions. We conclude that the gamma-ray and cosmic-ray spectrum in the region can be well-fitted using a local cosmic-ray spectrum.

Neutrino signatures of the origins of cosmic rays

The intensity of extraterrestrial neutrinos discovered by IceCube [M. G. Aartsen et al. (IceCube Collaboration), Science 342 (2013) 1242856] is in reasonable agreement with predictions of neutrinos from the jets of active galactic nuclei due to pion production by accelerated protons [K. Mannheim, Astropart. Phys. 3 (1995) 295]. The observed deficit of Glashow-resonance events at 6.3 PeV could result from the suppression of events with energies larger than PeV due to the presence of a strong “big blue bump” radiation field in flat-spectrum radio quasars. The total neutrino spectrum could exhibit a two-component structure in which the sub-PeV component is dominated by the jets from AGN with high accretion rates and another component peaking at EeV energies due to those with low accretion rates. Each component of the neutrino spectrum should carry the energy flux that corresponds to its relative contribution to the extragalactic gamma ray background. The arrival directions should correlate with known sources, and a simple test shows that the PeV events can indeed be explained by known blazars with prominent radio jets. If a Galactic component of cosmic rays with energies per nucleon above knee energies exists, as air shower array data seem to indicate, the neutrinos due to pion production from these sources are also detectable, pinpointing them an energies where gamma-ray observations are not yet possible.

Mutagenic joining of enzymatically induced DNA double-strand breaks, accompanied by persistent unrepaired DNA damage and a secretory protein phenotype, in HZE-exposed human cells

High charge and energy (HZE) particles are a component of galactic cosmic rays. They cause complex damage to DNA and other cellular components, leading to both direct and indirect biological effects. Here, we investigate the hypothesis that one of these indirect effects is to compromise the accuracy of the DNA repair machinery, reducing the ability to cope with subsequent genotoxic insults. To this end, we used a new human reporter cell line with single-copy integrated fluorescent reporter cassettes that allow measurement of the frequency of mutagenic repair. Introduction of the rare cutting I-SceI nuclease stimulates both translocations (joining of two I-SceI sites on different chromosomes), and deletions (joining of two I-SceI sites after deletion of an intervening fragment) [ 1]. These can be measured simultaneously in the same cell population using different color reporter genes. To test the effect of HZE exposure on the frequency of translocations and deletions in this assay, cells were exposed to 600 MeV/u 56Fe ions or 1000 MeV/u 48Ti ions at doses of 0.3 or 1.0 Gy. They were allowed to recover and challenged with I-SceI at 1, 7, 14, 21 and 28 days post-irradiation. Results showed that HZE particle irradiation significantly increased the frequency of I-SceI translocations and deletions above baseline levels. There was an increase in translocations by up to threefold, seen in both 56Fe- and 48Ti-treated populations. There was also a more modest, but significant increase in I-SceI-mediated deletions seen in a population that received the higher dose (1.0 Gy) of 56Fe particles. The increased frequency of I-SceI-induced translocations and deletions persisted for 2–3 weeks with 56Fe (but not with 48Ti). The increased frequency of translocations and deletions was not observed in populations treated with low-LET radiation at doses up 3 Gy. Thus, the phenomenon, which we term the ‘mutagenic repair phenotype’ depends on both dose and radiation quality. The mutagenic repair phenotype was associated with an elevated frequency of micronuclei and excess DNA repair foci, suggesting that persistent genomic stress might be one causative factor [ 2].To further explore the mechanism underlying the mutagenic DNA repair phenotype, we performed genome-wide expression profiling on cells that were harvested 7 days post-56Fe ion exposure. Results showed significant alterations in 234 genes. Many of the most highly induced genes encode secreted proteins that have previously been implicated in cellular senescence or pro-inflammatory processes. These findings suggest that a paracrine mechanism (induction of a set of senescence or inflammation-related proteins) may also contribute to the mutagenic repair phenotype.Altered regulation of cellular double-strand break repair, with an increased reliance on an error-prone pathway, is a novel mechanism whereby an indirect effect of HZE exposure may amplify cancer risk.

Proton Irradiation Augments the Suppression of Tumor Progression Observed with Advanced Age

Proton radiation is touted for improved tumor targeting, over standard gamma radiation, due to the physical advantages of ion beams for radiotherapy. Recent studies from our laboratory demonstrate that in addition to these targeting advantages, proton irradiation can inhibit angiogenic and immune factors critical to "hallmark" processes that impact cancer progression, thereby modulating tumor development. Outside the therapeutic utilization of protons, high-energy protons constitute a principal component of galactic cosmic rays and thus are a consideration in carcinogenesis risk for space flight. Given that proton irradiation modulates fundamental biological processes known to decrease with aging (e.g. angiogenesis and immunogenicity), we investigated how proton irradiation impacts tumor advancement as a function of host age, a question with both therapeutic and carcinogenesis implications. Tumor lag time and growth dynamics were tracked, after injection of murine Lewis lung carcinoma (LLC) cells into syngeneic adolescent (68 day) vs. old (736 day) C57BL/6 mice with or without coincident irradiation. Tumor growth was suppressed in old compared to adolescent mice. These differences were further modulated by proton irradiation (1 GeV), with increased inhibition and a significant radiation-altered molecular fingerprint evident in tumors grown in old mice. Through global transcriptome analysis, TGFβ1 and TGFβ2 were determined to be key players that contributed to the tumor dynamics observed. These findings suggest that old hosts exhibit a reduced capacity to support tumor advancement, which can be further reduced by proton irradiation.

Cosmic rays below 15 GeV and the current rising solar activity phase

The cosmic ray component in the range of energies below 15 GeV is strongly affected by transient phenomena related to solar activity. Cosmic rays and solar particles with energies between 0.5 and 15 GeV can be observed by neutron monitors at ground level. In absence of solar activity, the background counting rate registered by neutron monitors is dominated by the galactic cosmic ray component, showing only long-term variations correlated with the solar cycle. During active periods, short-term temporal variations can be observed in close association with solar activity phenomena such as flares and coronal mass ejections. Most of these transients can produce a strong response in the magnetosphere. The aim of this work is to study the relationship between neutron monitor measurements and the magnetospheric response observed in Dst index, paying special attention to their connection with solar transient phenomena during the current rising solar activity phase.

Composition of cosmic rays at ultra high energies

We present measurements of the cosmic ray (CR) composition above 1015eV, performed with the Yakutsk extensive air shower array. Almost 42,000 events above 1017eV observed by Cherenkov detectors are selected for the analysis of the depth of maximum of the longitudinal development of air showers induced by CRs. The interpretation of these results in terms of CR mass composition is given. It is shown that mean logarithm of the CR atomic number 〈lnA(ϵ)〉 is characterized by the peak value 〈lnA〉≈2.5 achieved at ϵ∼1017eV and its substantial decrease within the energy interval 1017−1018eV to 〈lnA〉≈1 at ϵ>1018eV. Such a behavior can be considered as indication for the transition from galactic CR component, which is produced in galactic supernova remnants, to extragalactic CR component at ϵ=1017−1018eV.

CAN ULTRAHIGH-ENERGY COSMIC RAYS COME FROM GAMMA-RAY BURSTS? COSMIC RAYS BELOW THE ANKLE AND GALACTIC GAMMA-RAY BURSTS

The maximum cosmic ray energy achievable by acceleration by a relativistic blast wave is derived. It is shown that forward shocks from long GRB in the interstellar medium are powerful enough to produce the Galactic cosmic-ray component up to the ankle at $4\times 10^{18}$eV, as per an earlier suggestion (Levinson and Eichler, 1993). It is further argued that, were extragalactic long GRB responsible for the component {\it above} the ankle as well, the contribution from an occasional Galactic GRB within the solar circle would yield more than the observational limits on the outward flux from the solar circle, unless intermittency and/or beaming causes the present-day contribution to be less than $10^{-3}$ times the time average, and difficulties with these avoidance scenarios are also noted.

Enhanced intestinal tumor multiplicity and grade in vivo after HZE exposure: mouse models for space radiation risk estimates

Carcinogenesis induced by space radiation is considered a major risk factor in manned interplanetary and other extended missions. The models presently used to estimate the risk for cancer induction following deep space radiation exposure are based on data from A-bomb survivor cohorts and do not account for important biological differences existing between high-linear energy transfer (LET) and low-LET-induced DNA damage. High-energy and charge (HZE) radiation, the main component of galactic cosmic rays (GCR), causes highly complex DNA damage compared to low-LET radiation, which may lead to increased frequency of chromosomal rearrangements, and contribute to carcinogenic risk in astronauts. Gastrointestinal (GI) tumors are frequent in the United States, and colorectal cancer (CRC) is the third most common cancer accounting for 10% of all cancer deaths. On the basis of the aforementioned epidemiological observations and the frequency of spontaneous precancerous GI lesions in the general population, even a modest increase in incidence by space radiation exposure could have a significant effect on health risk estimates for future manned space flights. Ground-based research is necessary to reduce the uncertainties associated with projected cancer risk estimates and to gain insights into molecular mechanisms involved in space-induced carcinogenesis. We investigated in vivo differential effects of gamma-rays and HZE ions on intestinal tumorigenesis using two different murine models, ApcMin/+ and Apc1638N/+. We showed that gamma- and/or HZE exposure significantly enhances development and progression of intestinal tumors in a mutant-line-specific manner, and identified suitable models for in vivo studies of space radiation-induced intestinal tumorigenesis.

Cosmic-ray composition and its relation to shock acceleration by supernova remnants

An overview is given on the present status of the understanding of the origin of galactic cosmic rays. Recent measurements of charged cosmic rays and photons are reviewed. Their impact on the contemporary knowledge about the sources and acceleration mechanisms of cosmic rays and their propagation through the Galaxy is discussed. Possible reasons for the knee in the energy spectrum and scenarios for the end of the galactic cosmic-ray component are described.

Galactic Wind: Mass Fractionation and Cosmic Ray Acceleration

The dynamical and chemical effects of the Galactic Wind are discussed. This wind is primarily driven by the pressure gradient of the Cosmic Rays. Assuming the latter to be accelerated in the Supernova Remnants of the disk which at the same time produce the Hot Interstellar Medium, it is argued that the gas removed by the wind is enriched in the nucleosynthesis products of Supernova explosions. Therefore the moderate mass loss through this wind should still be able to remove a substantial amount of metals, opening the way for stars to produce more metals than observed in the disk, by e.g. assuming a Salpeter-type stellar initial mass function beyond a few Solar masses. The wind also allows a global, physically appealing interpretation of Cosmic Ray propagation and escape from the Galaxy. In addition the spiral structure of the disk induces periodic pressure waves in the expanding wind that become a sawtooth shock wave train at large distances which can re-accelerate “knee” particles coming from the disk sources. This new Galactic Cosmic Ray component can reach energies of a few×1018 eV and may contribute to the juncture between the particles of Galactic and extragalactic origin in the observed overall Cosmic Ray spectrum.

Measurements of total and partial charge-changing cross sections for 200- to 400-MeV/nucleonC12on water and polycarbonate

We have studied charged nuclear fragments produced by 200- to 400-MeV/nucleon carbon ions, interacting with water and polycarbonate, using a newly developed emulsion detector. Total and partial charge-changing cross sections for the production of B, Be, and Li fragments were measured and compared with both previously published measurements and model predictions. This study is of importance for validating and improving carbon-ion therapy treatment planning systems and for estimating the radiological risks for personnel on space missions, because carbon is a significant component of galactic cosmic rays.

TeV neutrinos from supernova remnants embedded in giant molecular clouds

The recent detection of γ-rays with energy up to 10 TeV from dense regions surrounding some supernova remnants (SNR) provides strong, though still not conclusive, evidence that the nucleonic component of galactic cosmic rays is accelerated in the supernova outflows. Neutrino telescopes could further support the validity of such scenario by detecting neutrinos coming from the same regions. We re-evaluate the TeV range neutrino–photon flux ratio to be expected from pion decay, finding small differences respect to previous derivations. We apply our results and the recent HESS measurements of the very high energy γ-ray flux from the molecular cloud complex in the galactic centre, to estimate the neutrino flux from that region discussing the detectability perspectives for Mediterranean neutrino telescopes. We also discuss under which conditions neutron decay may give rise to a significant TeV antineutrino flux from a SNR embedded in molecular cloud complexes.

A mathematical model of aircraft for evaluating the effects of shielding structure on aircrew exposure

To investigate the influence of the aircraft structures and contents on the exposure of aircrew to the galactic component of cosmic rays, a mathematical model of an aeroplane has been developed. The irradiation of the mathematical model in the cosmic ray environment has been simulated using the Monte Carlo transport code FLUKA. Effective dose andambient dose-equivalent rates have been determined inside the aircraft at several locations along the fuselage at a typicaI civil aviation altitude. A significant effect of the shielding of aircraft structures has been observed on the ambient dose-equivalent rates, while the impact on the effective dose rates seems to be minor. Care should be taken in positioning the detectors onboard when the measurements are aimed at validating the codes.

International space station: A testbed for experimental and computational dosimetry

The ISS and the prior station Mir provided the proving ground for future human long-duration space activity. A recent European Space Agency study recommended “Measurement campaigns on the ISS form the ideal tool for experimental validation of radiation environment models, of transport code algorithms and reaction cross sections”. Indeed, prior measurements on Shuttle have provided vital information impacting both transport code and environmental model development. Recent studies using the ISS 7A configuration with TLD area monitors demonstrated that computational dosimetry requires environmental models with accurate anisotropic and dynamic behavior, detailed information on rack loading, and an accurate 6 degree-of-freedom description of the ISS trajectory. The ISS model is now configured for 11A and uses an anisotropic and dynamic geomagnetic transmission and trapped proton models. The ISS 11A is instrumented with both passive and active dosimetric devices. Time resolved measurements have the advantage of isolating trapped proton and galactic cosmic ray components as was essential to transport code validation in Shuttle data analysis. ISS 11A model validation will begin with passive dosimetry as was used with ISS 7A. Directional dependent active measurements will play an important role in the validation of environmental model anisotropies.

Simultaneous investigation of galactic cosmic rays on aircrafts and on International Space Station

The galactic cosmic ray component of the space radiation environments at aircraft altitudes and on the International Space Station (ISS) were measured by practically identical silicon active detectors in May–August 2001. The aircraft measurements were performed on commercial flights of CSA airlines, while the measurements on the ISS were part of the “Dosimetric mapping” experiment on ISS. Different cases of comparison are presented in the paper and discussed.

Monte Carlo calculation of the angular distribution of cosmic rays at flight altitudes

The angular distribution of the secondary radiation produced by the galactic component of cosmic rays has been determined by simulating the penetration of the primary spectra in the Earth's atmosphere. The simulations have been carried out with the latest version of the FLUKA code. Particles have been scored at various altitudes according to their angle of incidence for some significant values of vertical cut-off rigidity and solar modulation parameter. The calculated results at typical cruise altitudes for a civil aircraft are presented. The data at 10.7 km have been fitted with simple mathematical equations. It has been demonstrated that the major contribution to the doses at aviation altitudes arises from downward-directed particles. The isotropic irradiation usually assumed for the evaluation of aircrew exposure could be a very poor approximation.

Evaluation of the influence of aircraft shielding on the aircrew exposure through an aircraft mathematical model.

In order to investigate the influence of aircraft shielding on the galactic component of cosmic rays, an aircraft mathematical model has been developed by the combinatorial geometry package of the Monte-Carlo transport code FLUKA. The isotropic irradiation of the aircraft in the cosmic ray environment has been simulated. Effective dose and ambient dose equivalent rates have been determined inside the aircraft at several locations along the fuselage, at a typical civil aviation altitude (10 580 m), for vertical cut-off rigidity of 0.4 GV (poles) and 17.6 GV (equator) and deceleration potential of 465 MV. The values of both quantities were generally lower than those in the free atmosphere. They depend, in an intricate manner, on the location within the aircraft, quantity of fuel, number of passengers, etc. The position onboard of crew members should be taken into account when assessing individual doses. Likewise due consideration must be taken when positioning detectors which are used to measure H*(10). Care would be needed to avoid ambiguity when comparing the results of calculation with the experimental data.

Effects of the Sector Structure of the Interplanetary Magnetic Field on Galactic Cosmic Ray Anisotropy

We study the effects of the sector structure of the interplanetary magnetic field (IMF) on the Galactic cosmic ray (GCR) anisotropy at solar minimum by using Global Network neutron monitor data. The hourly neutron monitor data for 1976 were averaged for the positive (+) and negative (–) IMF sectors (+ and – correspond to the antisolar and solar directions of magnetic field lines, respectively) and then processed by the global survey method. We found that the magnitude of the GCR anisotropy vector is larger in the positive IMF sector and that the phase shifts toward early hours. The derived GCR components Ar, Aθ, and Aϕ for the different + and – sectors are then used to calculate the angle ψ (≈ 46°) between the IMF lines and the Sun–Earth line, the solar wind velocity U (≈ 420 km/s), the ratio of the perpendicular (K⊥) and parallel (K||) diffusion coefficients K⊥/K|| = α (≈ 0.33), and other parameters that characterize the GCR modulation in interplanetary space.

Some contributions from SSNTD towards nuclear science: from multifragmentation towards accelerator driven systems (ADS)

Three examples are chosen to show the importance of SSNTD as one of the essential tools in nuclear science: (1) Multifragmentation into more than two heavy reaction products: Starting with the observation of three heavy reaction products in the interaction of relativistic protons or 414 MeV 40Ar with actinides in the early 1960s, up to the observation of five heavy reaction products in the interaction of 2400 MeV 238U with uranium, SSNTD had a leading role in this research. (2) In the search for superheavy elements (SHE: Z around 114): Many different techniques are used. However, SSNTD are exclusively decisive in the possible observation of SHE within the heavy element component of galactic cosmic rays. (3) Accelerator driven systems: They are increasingly important in the discussion of energy producing nuclear power stations and in the corresponding ability to transmute long-lived poisonous radioactive materials (above all plutonium) into shorter lived fission fragments or stable nuclides. SSNTDs play an important role in the determination of the energy dependent neutron fluence in small volumes (≈cm 3) or in the exact beam profile determinations of the primary proton beams. This contribution ends with an outlook into possible future fields of physics research: With the advent of a new generation of relativistic heavy ion accelerators, such as the NUCLOTRON at the JINR in Dubna, Russia, and RHIC in Brookhaven in the United States, one can continue to study (and finally confirm or disprove) all phenomena mentioned already, as well as additional controversial phenomena, such as “enhanced nuclear cross-sections over short distances”, called colloquially “anomalons”. Again SSNDT can be used in at least a twofold manner as an important tool: (a) the enhanced neutron production with 12C ions or heavier ions in thick targets at energies above approximately 50 GeV and (b) the reduced “mean-free-path” of secondary fragments produced by the same heavy and energetic ions.

Self‐consistent model of the solar wind interaction with three‐component circumsolar interstellar cloud: Mutual influence of thermal plasma, galactic cosmic rays, and H atoms

In this paper we continue our study of the galactic cosmic ray (GCR) influence on the structure of the heliospheric interface plasma flow [Myasnikov et al., this issue]. The model presented here is more realistic and takes the mutual influence of plasma, neutral, and cosmic ray components into account self‐consistently. In the model, GCRs are described hydrodynamically under the assumption that their mass density is negligible; while neutrals are described kinetically. We explore the GCR influence on the heliospheric interface plasma structure by varying the diffusion coefficient, cosmic ray pressure, and adiabatic index. The problem is studied numerically, using the global iterations that couple the soft fitting technique for describing the plasma and GCR components and Monte Carlo simulations for H atoms. A strong GCR modulation is found in the heliospheric interface. At the same time, the GCR influence on the plasma flow is negligible as compared with the influence of H atoms. The exception is the bow shock, a structure which can be strongly modified by the cosmic rays. The Baranov‐Malama model is therefore acceptable for interpretation of the physical processes in the heliosphere as long as the processes are not related to the bow shock structure. Although the simplest model of the cosmic ray transport is good enough to estimate GCR influence on the plasma and atom distributions in the heliospheric interface, more advanced models should be used to interpret the observed GCR spectra.