Galactic Cosmic Ray Models Research Articles

Galactic cosmic ray environment predictions for the NASA BioSentinel Mission, part 2:Post-mission validation

The BioSentinel CubeSat was deployed on the Artemis-I mission in November 2022 and has been continuously transmitting physical measurements of the space radiation environment since that time. Just before mission launch, we published computational model predictions of the galactic cosmic ray exposure expected inside BioSentinel for multiple locations and configurations. The predictions utilized models for the ambient galactic cosmic ray environment, radiation physics and transport, and BioSentinel geometry. Now that the nominal six-month BioSentinel mission has completed and some additional time has passed, those pre-launch predictions and additional model components can be validated. Dose-rate and linear energy transfer (LET) spectral measurements from the on-board dosimeter are presented along with a summary of the computational models used to calculate exposure quantities of interest. Sensitivity tests are performed to gauge the impact of various model choices on these quantities. Satellite data collected during the BioSentinel mission are used to provide some measure of independent validation for the galactic cosmic ray model used in the present calculations. It is shown that the combined models are in excellent agreement with the measured dose-rate. Model calculations agree well with measurement below ∼10 keV/µm and underpredict at higher LET. It is argued that the underprediction is likely due to detector response or low energy anomalous cosmic ray contributions able to reach the thinly shielded side of the on-board dosimeter.

A Comprehensive Comparison of Various Galactic Cosmic-Ray Models to the State-of-the-art Particle and Radiation Measurements

Galactic cosmic rays (GCRs) are the slowly varying background energetic particles that originate outside the solar system, are modulated by the heliospheric magnetic field, and pose ongoing radiation hazards to deep space exploration missions. To assess the potential radiation risk, various models have been developed to predict the GCR flux near Earth based on propagation theories and/or empirical functions. It is essential to benchmark these models by validating against the state-of-the-art measurements. In this work, a comprehensive model–observation comparison of the energy-dependent particle flux has been performed, by combining five typical GCR models and observational data from the Cosmic Ray Isotope Spectrometer on board the Advanced Composition Explorer spacecraft at relatively lower energies and data from the Payload for Antimatter Matter Exploration and Light-nuclei Astrophysics and Alpha Magnetic Spectrometer at higher energies. The analysis shows that, out of the five models investigated in this study, the optimal model, characterized by minimal relative difference or reduced chi-square divergence from measurements, depends on the particle type, energy range, and epoch of interest. Furthermore, a silicon slab is applied to compute the absorbed dose rate using conversion factors applied to GCR model outputs, and the results are compared to measurements from the Cosmic Ray Telescope for the Effects of Radiation. The comparisons in this paper have implications for the strengths and limitations of individual GCR models, advance our comprehension of the underlying GCR transport mechanisms, and also have strong application aspects for mitigating space radiation risks.

Simulation for the test mass charging rate in the Tianqin orbit

For the purpose of detecting gravitational waves from space, high-energy particles will infiltrate the satellite’s structure and accumulate charges on the test mass, consequently diminishing detection performance. Present investigations into the charging rate of the test mass typically rely on the particle distribution of Earth orbit. However, the influence of the Earth’s magnetosphere needs to be considered for the Tianqin detector because of its geocentric orbit. In this paper, artificial neural network is used to fuse satellite data and the galactic cosmic rays model to give the distribution of high-energy particles in the Tianqin orbit. And then, the charging rate is estimated by Monte Carlo simulation. The simulation results show that the flux of hundreds of MeV particles is a little higher than that in Earth orbit, which lead to 3−4 e s−1 higher than LISA, i.e. the charging rate of approximately 43 e s−1 during periods of solar minimum and 19 e s−1 during periods of solar maximum. These findings hold substantial implications for guiding the design of the charge management system.

Astronaut Radiation Dose Calculation With a New Galactic Cosmic Ray Model and the AMS‐02 Data

AbstractWe present a new calculation of the astronaut dose rate from the galactic cosmic rays in free space at 1 AU. We use the unshielded isotropic fluence‐to‐dose conversion coefficients given in the International Commission on Radiological Protection publication 123. A new 3D and time‐dependent solar modulation model based on Parker's transport equation as originally developed in Song et al. (2021, https://doi.org/10.3847/1538-4365/ac281c) is used to calculate the galactic cosmic ray spectra at 1 AU. This model uses the recent local interstellar spectra of Corti et al. (2019, https://doi.org/10.3847/1538-4357/aafac4), M. J. Boschini et al. (2020, https://doi.org/10.3847/1538-4365/aba901, 2021a, https://doi.org/10.3847/1538-4357/abf11c) to reproduce the PAMELA and AMS‐02 observations between 2006 and 2019. The radiation dose calculated from our model and from the AMS‐02 spectra in the same rigidity region agrees better than 1% for proton and helium in a time‐dependent way, and at 2% level for six most contributing cosmic ray elements averaged over 7 or 8.5 years. The time‐dependent dose rate analysis over 13 years shows an effective dose equivalent rate of 55–58 cSv/yr at solar minimum (January 2010) and 26 cSv/yr at solar maximum (February 2014).

Comparison of the particle flux measured by Liulin-MO dosimeter in ExoMars TGO science orbit with those calculated by models

The knowledge of the space radiation environment in spacecraft transition and in Mars vicinity is of importance for the preparation of the human exploration of Mars. ExoMars Trace Gas Orbiter (TGO) was launched on March 14, 2016 and was inserted into circular Mars science orbit (MSO) with a 400 km altitude in March 2018. The Liulin-MO dosimeter is a module of the Fine Resolution Epithermal Neutron Detector (FREND) aboard ExoMars TGO and has been measuring the radiation environment during the TGO interplanetary travel to Mars and continues to do so in the TGO MSO. One of the scientific objectives of the Liulin-MO investigations is to provide data for verification and benchmarking of the Mars radiation environment models. In this work we present results of comparisons of the flux measured by the Liulin-MO in TGO Mars orbit with calculated estimations. Described is the methodology for estimation the particle flux in Liulin-MO detectors in MSO, which includes modeling the albedo spectra and procedure for calculation the fluxes, recorded by Liulin-MO on the basis of the detectors shielding model. The galactic cosmic rays (GCR) and Mars albedo radiation contribution to the detectors count rate was taken into account. The GCR particle flux was calculated using the Badhwar O'Neil 2014 model for December 1, 2018. Detailed calculations of the albedo spectra of protons, helium ions, neutrons and gamma rays at 70 km height, performed with Atmospheric Radiation Interaction Simulator (AtRIS), were used for deriving the albedo radiation fluxes at the TGO altitude. In particular, the sensitivity of the Liulin-MO semiconductor detectors to neutron and gamma radiation has been considered in order to calculate the contribution of the neutral particles to the detected flux. The results from the calculations suggest that the contribution of albedo radiation can be about 5% of the measured total flux from GCR and albedo at the TGO altitude. The critical effect of TGO orientation, causing different shading of the GCR flux by Mars, is also analysed in detail. The comparison between the measurements and estimations shows that the measured fluxes exceed the calculated values by at least 20% and that the effect of TGO orientation change is approximately the same for the calculated and measured fluxes. Accounting for the ACR contribution, secondary radiation and the gradient of GCR spectrum from 1 AU to 1.5 AU, the calculated flux may increase to match the measurement results. The results can serve for the benchmarking of GCRs models at Martian orbit.

Validation of dMEREM, the Detailed Mars Energetic Radiation Environment Model, with RAD Data from the Surface of Mars

The detailed Martian Energetic Radiation Environment Model (dMEREM) is a Geant4 based model developed for the European Space Agency, which enables to predict the radiation environment expected at different locations on the Martian orbit, atmosphere and surface, as a function of epoch, latitude and longitude, taking into account the specific atmospheric and soil composition, based on different particle propagation codes for primary Galactic Cosmic Rays or Solar Particle Events. This work describes the validation of dMEREM with differential proton fluxes measured with the NASA Curiosity rover Radiation Assessment Detector (RAD) at the Gale Crater, at the surface of Mars, from 15 November 2015 to 15 January 2016 and in the beginning of September 2017, using two different Galactic Cosmic Ray (GCR) models, the ISO-15 390 and the Badhwar-O’Neill 2014 models. This work includes a comparative study of the available Geant4 physics lists in describing the RAD measured proton spectrum, and an investigation of the proton directional spectrum at the Martian surface, and on its effect on the comparisons between models and data, which are necessarily measured within a limited field-of-view. For both GCR models and data periods there was a good agreement between the proton fluxes in the energy range between 10 and 90 MeV measured at the surface of Mars with RAD and the corresponding dMEREM predictions. Therefore, although the RAD only measures a limited field-of-view in zenith angle of the Martian Particle Radiation Field, and this effect has to be taken into account, the results obtained constitute an important benchmark in the use of dMEREM in the assessment of the expected ionising radiation field on the surface of Mars.

Cosmic-ray flux predictions and observations for and with Metis on board Solar Orbiter

Context.The Metis coronagraph is one of the remote sensing instruments hosted on board the ESA/NASA Solar Orbiter mission. Metis is devoted to carry out the first simultaneous imaging of the solar corona in both visible light (VL) and ultraviolet (UV). High-energy particles can penetrate spacecraft materials and may limit the performance of the on-board instruments. A study of the galactic cosmic-ray (GCR) tracks observed in the first VL images gathered by Metis during the commissioning phase is presented here. A similar analysis is planned for the UV channel.Aims.We aim to formulate a prediction of the GCR flux up to hundreds of GeV for the first part of the Solar Orbiter mission to study the performance of the Metis coronagraph.Methods.The GCR model predictions are compared to observations gathered on board Solar Orbiter by the High-Energy Telescope in the range between 10 MeV and 100 MeV in the summer of 2020 as well as with the previous measurements. Estimated cosmic-ray fluxes above 70 MeV n−1have been also parameterized and used for Monte Carlo simulations aimed at reproducing the cosmic-ray track observations in the Metis coronagraph VL images. The same parameterizations can also be used to study the performance of other detectors.Results.By comparing observations of cosmic-ray tracks in the Metis VL images with FLUKA Monte Carlo simulations of cosmic-ray interactions in the VL detector, we find that cosmic rays fire only a fraction, on the order of 10−4, of the whole image pixel sample. We also find that the overall efficiency for cosmic-ray identification in the Metis VL images is approximately equal to the contribution ofZ ≥ 2 GCR particles. A similar study will be carried out during the whole of the Solar Orbiter’s mission duration for the purposes of instrument diagnostics and to verify whether the Metis data and Monte Carlo simulations would allow for a long-term monitoring of the GCR proton flux.

Advances in direct measurements of cosmic rays

In celebration of the 25th anniversary of the Korean Physical Society Astrophysics Division, reflecting on the progress in cosmic-ray astrophysics seems worthwhile. Significant advances have been made in cosmic-ray measurements in recent years, particularly with successful space missions and long-duration balloon flights over Antarctica. The high precision data from these missions over a wide energy range led to surprising new discoveries, such as an excess of positrons at high energies and hardening of the elemental spectra. These unexpected spectral features present significant challenges for Galactic cosmic-ray models on their origin, propagation, and acceleration. This paper focuses on a few key findings, discussing direct measurements of cosmic rays from space-based and high-altitude balloon-borne experiments.

Radiation Environment and Doses on Mars at Oxia Planum and Mawrth Vallis: Support for Exploration at Sites With High Biosignature Preservation Potential

AbstractThe first human missions on Mars will likely involve several astrobiology‐driven science operations, at sites with high biosignature preservation potential. Here, we present a study of the radiation environment induced by Galactic Cosmic Rays and Solar Energetic Particles at Oxia Planum, landing site of the European Space Agency ExoMars 2022 mission, and at two different locations in Mawrth Vallis, using the Monte Carlo GEometry ANd Tracking 4‐based code dMEREM (detailed Martian Energetic Radiation Environment Model). The radiation environment for solar minimum in 2009 and a period close to solar maximum during the declining phase of solar cycle 23 appears similar at the different sites, with the deepest Mawrth Vallis location having a slightly enhanced γ‐ray contribution, due to a higher modulation of fast neutrons by the more water‐rich regolith. The comparison with the Dose Equivalent from an updated extrapolation of 7+ years data from the Radiation Assessment Detector (RAD) onboard the Curiosity rover highlights the importance of input modulation conditions, some drawbacks of the galactic cosmic ray model used here, and the need to include heavy ions, the three aspects affecting differently the estimations for solar maximum and minimum. The dependence of doses on surface pressure highlights a possible influence of the different dust loading at the different sites. Estimated exposure levels for a 1‐year stay and for a short stay in Arabia Terra, the latter including a October 28, 2003 event with a fluence an order of magnitude higher than the relevant September 2017 event detected by RAD, leave reasonable to large safety margins.

CRaTER observations and permissible mission duration for human operations in deep space

Prolonged exposure to the galactic cosmic ray (GCR) environment is a potentially limiting factor for manned missions in deep space. Evaluating the risk associated with the expected GCR environment is an essential step in planning a deep space mission. This requires an understanding of how the local interstellar spectrum is modulated by the heliospheric magnetic field (HMF) and how observed solar activity is manifested in the HMF over time. While current GCR models agree reasonably well with measured observations of GCR flux on the first matter, they must rely on imperfect or loose correlations to describe the latter. It is more accurate to use dose rates directly measured by instruments in deep space to quantify the GCR condition for a given period of time. In this work, dose rates observed by the Cosmic Ray Telescope for the Effects of Radiation (CRaTER) instrument are used to obtain the local GCR intensity and composition as a function of time. A response function is constructed that relates observed dose rates to solar modulation potential using a series of Monte Carlo radiation transport calculations. The record of observed solar modulation potential vs. time is then used to calculate a recent historical record of permissible mission duration (PMD) according to NASA's permissible exposure limits (PEL). Tables are provided for extreme values of PMD. Additional tables include risk of exposure-induced death (at upper 95% confidence interval) accrual rates and NASA effective dose rates as a function of solar modulation potential, astronaut age, sex, and shielding thickness. The significance of the PMD values reported in relation to likely transit duration requirements for future exploration missions is discussed. There is general agreement between CRaTER observations and the prescription of solar modulation vs. time given by the Badhwar–O'Neill 2014 GCR model. However, CRaTER observations do capture the effects of significant heliospheric transients, among other features, that are missing from the prescription of solar modulation potential vs. time.

Solar System Collisions with Dense Interstellar Gas Clouds and Radiocarbon Traces of Periods with “Abnormally Low” Solar Modulation of Cosmic Rays

The causes of a sharp increase in the radiocarbon content in the Earth’s atmosphere for periods with abnormally low solar modulation of galactic cosmic rays (GCRs) are considered. It is shown that such periods around 660 BC and 5480 BC can also be caused (in addition to the low activity of the Sun itself) by heliospheric compression as a result of the passage of the Solar System through a compact interstellar cloud with a density of nH ~ 100 cm–3 and characteristic dimensions of 10–100 AU. In this case, GCR modulation is suppressed, while solar cyclic processes are preserved. Wavelet analysis of radiocarbon data shows the presence of the 11-year solar-activity cycle in the period around 5480 BC. Based on the model of the interaction of cosmic rays with the Earth’s atmosphere, the 14C production rates are calculated for various GCR model spectra typical for the local interstellar medium.

Comparison of space radiation GCR models to AMS heavy ion data

Galactic cosmic rays (GCR) are a constant source of radiation that constitutes one of the major hazards during deep space exploration missions for both astronauts and hardware. In this work, GCR models commonly used by the space radiation protection community are compared with recently published high-precision, high-resolution measurements of cosmic ray lithium, beryllium, boron, carbon, nitrogen, and oxygen fluxes along with their ratios (Li/B, Li/C, Li/O, Be/B, Be/C, Be/O, B/C, B/O, C/O, N/B, N/O) from the Alpha Magnetic Spectrometer (AMS). All of the models were developed and calibrated prior to the publication of this AMS data, therefore this is an opportunity to validate the models against an independent data set. This paper is a compliment to the previously published comparison of GCR models with AMS hydrogen, helium, and the boron-to-carbon ratio (Norbury et al., 2018).

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 5-28 over the energy range from 30 to 500 MeV/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 futureGCR intensity monthly by correlating model parameters with thecontinuous 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 hydrogen spectra and radial gradients in the inner heliosphere measured by the HELIOS Experiment 6

Context. The HELIOS solar observation probes provide unique data regarding their orbit and operation time. One of the onboard instruments, the Experiment 6 (E6), is capable of measuring ions from 4 to several hundred MeV nucleon−1. Aims. In this paper we aim to demonstrate the relevance of the E6 data for the calculation of galactic cosmic ray (GCR), anomalous cosmic ray (ACR), and solar energetic particle (SEP) fluxes for different distances from the sun and time periods. Methods. Several corrections have been applied to the raw data: determination of the Quenching factor of the scintillator, correction of the temperature dependent electronics, degradation of the scintillator as well as the effects on the edge of semi-conductor detectors. Results. Fluxes measured by the E6 are in accordance with the force field solution for the GCR and match models of the anomalous cosmic ray propagation. GCR radial gradients in the inner heliosphere show a different behaviour than in the outer heliosphere.

Space radiation impact on smallsats during maximum and minimum solar activity

The trend towards the development of small satellites, or smallsats, has been increasing over the last few years. However, the harsh space radiation environment in which these smallsats operate provides a challenge to their survivability as their desired mission lengths increase from a few months to several years also. Smallsats typically use commercial off the shelf components (COTS) that are built for ground operations, not space use. Therefore, they may be more susceptible to the hazards of space radiation than traditional spacecraft which are typically designed to withstand the high radiation levels of space. The present paper provides a targeted assessment of representative COTS components using up to date models of the space radiation environment and its effects on smallsats in a polar Low Earth Orbit (LEO). This orbit will be assumed to be sun synchronous (98.5° inclination) and at an altitude of 800 km. We employed the new Solar Accumulated and Peak Proton and Heavy Ion Radiation Environment (SAPPHIRE) model which has been released recently in 2018, ISO-15390 GCR model, and AP8/AE8 models to estimate the space radiation environment for solar particles, galactic cosmic rays (GCRs), and trapped protons and electrons respectively. The basic damage effects that can be produced in materials and electronics in this orbit due to their exposure to the space radiation are evaluated. These effects are the Total Ionizing Dose (TID), Displacement Damage Dose (DDD), and Single Event Effects (SEE) as represented by Single Event Upsets (SEUs). SEU is evaluated for different COTS components which are believed to be representative of an optimum blend of capability and cost-effectiveness for the next generation of smallsats, including 20 nm Xilinx Kintex Ultra Scale FPGA Configuration RAM (XCKU040), 90-nm SRAM, and MLC NAND flash memory (MT29F128G08CBECBH6). For comparative purposes, the analyses are performed for both maximum and minimum solar activity.Based on these comparisons, we find as expected that the space radiation environment parameters vary with solar activity. The fluence of trapped electrons and solar protons at solar maximum are higher than those at solar minimum in contrast to the trapped protons and galactic cosmic rays at low altitudes. On the other hand, TID, DDD, and SEE all show higher values during maximum solar activity than during minimum solar activity.The use of shielding material for small satellites is mandatory for this orbit as observed TID, DDD, and SEES levels that can be reached are potentially of concern to designers. However, using Al shielding thickness of at least 1.5 mm can reduce the radiation effects to acceptable levels, for both maximum and minimum solar activity for missions of moderate (∼3 years) duration.

Titan's ionospheric chemistry, fullerenes, oxygen, galactic cosmic rays and the formation of exobiological molecules on and within its surfaces and lakes

We discuss the formation of aerosols within Titan's thermosphere-ionosphere and the different chemical pathways. Negative ion measurements by the Cassini Plasma Spectrometer (CAPS) Electron Spectrometer (ELS) give evidence for formation of unsaturated anion carbon chains, while positive ion measurements of the Cassini Ion Neutral Mass Spectrometer (INMS) indicate formation of more aromatic cation hydrocarbons. There is presently no direct observational evidence for large neutral molecule growth in Titan's thermosphere-ionosphere. The hydrocarbon cations are expected to form Polycyclic Aromatic Hydrocarbons (PAH), those with the addition of nitrogen being called PAHNs. We theorize anion carbon chains can eventually become long enough to fold into fullerene C60,70 carbon shells, of various charge states. Based on laboratory data the fullerenes can trap incoming O+ magnetospheric ions that have relatively high energy collisions with the fullerenes and, once trapped, protect the oxygen atom from Titan's reducing thermosphere-ionosphere. The fullerenes can form into larger onion fullerenes and condense into larger embryo aerosols (i.e., m/q > 10,000 amu/q anions as observed by CAPS/ELS) eventually falling onto Titan's surface and precipitating to the bottom of its hydrocarbon lakes. Molecule production composed of H, C, N is known to occur in Titan's atmosphere with energy input from the magnetosphere, solar UV, and deep-penetrating irradiation from galactic cosmic rays (GCR). Space radiation effects by GCR irradiation of Titan's surface and lakes can lead to the manufacture of exobiological molecules with oxygen as the new ingredient. We have developed a model of galactic cosmic ray irradiation of Titan's atmosphere, surface, subsurface and bottoms of Titan lakes. GCR would provide further energy for processing of the aerosols into more complex organic forms such as tholins and precursor molecules for amino acids. A second process called hydrolysis then converts the precursor molecules into amino acids. Hydrolysis is provided via meteor impacts with size >10 km and cryovolcanism both which can produce liquid water on Titan's surface for episodic periods > several 100 to 1000 years. Our model shows that GCR secondary particles can penetrate ~ 100 m below the ice surface (including the bottom of Titan's less dense hydrocarbon lakes ~ 150 m depths) and produce chemically significant dosages over very long timescales ~ 450 Myrs. The GCR model is combined with laboratory data from experiments in which dry methyl ices were irradiated to doses producing prebiotic amino acids such as glycine. The model calculations show glycine can form to ~ 2.5 ppb levels near the surface after ~ 450 Myrs of GCR proton irradiation and potentially to 5 ppb if heavy-ion GCRs up through Fe are included. If such molecules were detected, this would not only confirm this model but indicate that life forms different from ours may not be required.

Galactic Cosmic Ray induced absorbed dose rate in deep space – Accounting for detector size, shape, material, as well as for the solar modulation

Depending on the radiation field, the absorbed dose rate can depend significantly upon the size of the detectors or the phantom used in the models. In deep space (interplanetary medium) the radiation field is on avarage dominated by Galactic Cosmic Ray (GCR) nuclei. Here, the deep space dose rate that a typical small silicon slab detector measures is compared to a larger phantom corresponding to an ICRU sphere with a 15 cm radius composed of water. To separate and understand respective effects from the composition, size and shape differences in the detectors, this comparison is implemented in several steps. For each phantom, the absorbed dose rate due to GCR nuclei up toZ= 28, as a function of solar modulation conditions, is calculated.The main components of the GCR flux are protons, followed by helium nuclei and electrons, withZ> 2 nuclei accounting for approximately 1% of the total number of particles. Among the light nuclei withZ> 2, most abundant ones are C, N and O. In this study, we use the GEANT4 model to calculate the absorbed dose (energy deposited as ionization, divided by mass) due to the GCR flux provided by the Badhwar-O’Neill 2010 (BON-10) model. Furthermore, we investigate how the determined absorbed dose rate changes throughout the solar cycle by varying the GCR models from solar minimum to solar maximum conditions. The developed model is validated against the Cosmic Ray Telescope for the Effects of Radiation (CRaTER) microdosimeter measurements. In our current approach, we do not consider the effects of shielding, which will always be present under realistic scenarios.A second goal of this study is to quantify the contribution of eachZ= 1, …, 28 GCR nuclei to absorbed dose rate, in relation to the phantom characteristics. For eachZwe determine the most relevant energy range in the GCR spectra for absorbed dose rate estimations. Furthermore, we calculate a solar modulation dependent conversion factor to convert absorbed dose rate measured in silicon to absorbed dose rate in water. This information will improve our understanding of the radiation environment due to GCR in the near-Earth deep space and also benefit further modeling efforts by limiting the number and energy range of primary particle species that have to be considered.

New Comparative Metric for Evaluating Spacecraft Radiation Shielding

Given the lack of human medical data available to calibrate and tie the sophisticated model calculations of various space radiation exposure metrics, such as “dose equivalent,” to the actual biological harm expected from long-term exposure to galactic cosmic ray (GCR) radiation in the region of cislunar space [nominally at 1 astronomical unit (AU) from the sun], a new spacecraft shielding evaluation metric is proposed that empirically links to the available medical data collected from International Space Station (ISS) operations, and thereby improves shielding material assessment. Adequate protection from radiation is one of the most important unknowns regarding the contemplated long-term spaceflights beyond the Earth’s protective zone afforded by its magnetosphere. This new radiation shielding evaluation metric relies on a comparison of the relative shielding effectiveness of a particular material or shielding design in the cislunar space radiation environment to the verified radiation exposure environment inside the ISS, where hundreds of astronauts have flown and spent considerable time, and for which there is voluminous medical data and continuing medical observation. Thus, the new metric is a measure of how well a proposed shielding protocol operating in the 1 AU cislunar radiation environment replicates the ISS radiation exposure levels. And, because it is calculated on a strict comparable basis, it mitigates the unavoidable errors introduced in the shielding evaluation process inherent in using different GCR models and radiation transport codes, as well as the various versions of radiation quality or weighting factors.

Comparison of space radiation GCR models to recent AMS data

This paper is the third in a series of comparisons of American (NASA) and Russian (ROSCOSMOS) space radiation calculations. The present work focuses on calculation of fluxes of galactic cosmic rays (GCR), which are a constant source of radiation that constitutes one of the major hazards during deep space exploration missions for both astronauts/cosmonauts and hardware. In this work, commonly used GCR models are compared with recently published measurements of cosmic ray Hydrogen, Helium, and the Boron-to-Carbon ratio from the Alpha Magnetic Spectrometer (AMS). All of the models were developed and calibrated prior to the publication of the AMS data; therefore this an opportunity to validate the models against an independent data set.

Galactic cosmic-ray model in the light of AMS-02 nuclei data

Cosmic ray (CR) physics has entered a precision-driven era. With the latest AMS-02 nuclei data (boron-to-carbon ratio, proton flux, helium flux and antiproton-to-proton ratio), we perform a global fitting and constrain the primary source and propagation parameters of cosmic rays in the Milky Way by considering 3 schemes with different data sets (with and without $\bar{\mathrm{p}}/\mathrm{p}$ data) and different propagation models (diffusion-reacceleration and diffusion-reacceleration-convection models). We find that the data set with $\bar{\mathrm{p}}/\mathrm{p}$ data can remove the degeneracy between the propagation parameters effectively and it favors the model with a very small value of convection (or disfavors the model with convection). The separated injection spectrum parameters are used for proton and other nucleus species, which reveal the different breaks and slopes among them. Moreover, the helium abundance, antiproton production cross sections and solar modulation are parametrized in our global fitting. Benefited from the self-consistence of the new data set, the fitting results show a little bias, and thus the disadvantages and limitations of the existed propagation models appear. Comparing to the best fit results for the local interstellar spectra ($\phi = 0$) with the VOYAGER-1 data, we find that the primary sources or propagation mechanisms should be different between proton and helium (or other heavier nucleus species). Thus, how to explain these results properly is an interesting and challenging question.