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Space radiation exposure from omnipresent Galactic Cosmic Rays (GCRs) in interplanetary space poses a serious carcinogenic risk to astronauts due to the—limited or absent—protective effect of the Earth’s magnetosphere and, in particular, the terrestrial atmosphere. The radiation risk is directly influenced by the quality of the radiation, i.e., its pattern of energy deposition at the micron/DNA scale. For stochastic biological effects, radiation quality is described by the quality factor, $$Q$$ Q , which can be defined as a function of Linear Energy Transfer (LET) or the microdosimetric lineal energy ($$y$$ y ). In the present work, the average $$Q$$ Q of GCR for different mission scenarios was calculated using a modified version of the microdosimetric Theory of Dual Radiation Action (TDRA). NASA’s OLTARIS platform was utilized to generate the radiation environment behind different aluminum shielding (0–30 g/cm2) for a typical mission scenario in low-earth orbit (LEO) and in deep space. The microdosimetric lineal energy spectra of ions ($$Z\ge 1$$ Z ≥ 1 ) in 1 μm liquid water spheres were calculated by a generalized analytical model which considers energy-loss fluctuations and δ-ray transport inside the irradiated medium. The present TDRA-based $$Q$$ Q -values for the LEO and deep space missions were found to differ by up to 10% and 14% from the corresponding ICRP-based $$Q$$ Q -values and up to 3% and 6% from NASA’s $$Q$$ Q -model. In addition, they were found to be in good agreement with the $$Q$$ Q -values measured in the International Space Station (ISS) and by the Mars Science Laboratory (MSL) Radiation Assessment Detector (RAD) which represent, respectively, a LEO and deep space orbit.

Galactic cosmic rays (GCR) are among the main deterrents to manned space exploration. Currently, the most realistic way to reduce the dangers caused by GCR to acceptable levels is passive shielding. Light materials guarantee the strongest dose attenuation per unit mass. High-density polyethylene is considered the gold standard for radiation protection in space. Nevertheless, accelerator-based experimental campaigns already showed the advantages of more hydrogen-rich innovative shielding materials such as lithium hydride. The experimental campaigns of this work focused on the absorbed dose attenuation properties of lithium-based hydrides chemically stabilized with a paraffin matrix. Such materials were compared to pure lithium-based hydrides, polyethylene, structural materials such as spacecraft aluminum alloys and lithium batteries, and in situ shielding materials such as Moon regolith and its main components silicon and silicon dioxide. The experimental results were compared to simulations performed with PHITS, FLUKA, and Geant4, which are among the most used Monte Carlo codes for radiation protection in space. The simulations showed systematic differences and highlighted the pressing need for reliable nuclear cross-section models.

The feasibility of a 3-D-NAND-Flash-based heavy-ion detector is explored. The possibility of measuring the angle of incidence and the linear energy transfer (LET) of impinging particles by studying the pattern of the threshold voltage shifts along the track of the affected cells is discussed. The results of the experiments with different beams (both directly and indirectly ionizing) are illustrated. A set of Monte Carlo simulations is also presented, to study sensitive volumes on 3-D NAND floating gate cells and explore the possibility of distinguishing the effects generated by ionizing particles with different features, such as LET and angle of incidence.

Purpose: Track structure Monte Carlo (MC) codes have achieved successful outcomes in the quantitative investigation of radiation-induced initial DNA damage. The aim of the present study is to extend a Geant4-DNA radiobiological application by incorporating a feature allowing for the prediction of DNA rejoining kinetics and corresponding cell surviving fraction along time after irradiation, for a Chinese hamster V79 cell line, which is one of the most popular and widely investigated cell lines in radiobiology. Methods: We implemented the Two-Lesion Kinetics (TLK) model, originally proposed by Stewart, which allows for simulations to calculate residual DNA damage and surviving fraction along time via the number of initial DNA damage and its complexity as inputs. Results: By optimizing the model parameters of the TLK model in accordance to the experimental data on V79, we were able to predict both DNA rejoining kinetics at low linear energy transfers (LET) and cell surviving fraction. Conclusion: This is the first study to demonstrate the implementation of both the cell surviving fraction and the DNA rejoining kinetics with the estimated initial DNA damage, in a realistic cell geometrical model simulated by full track structure MC simulations at DNA level and for various LET. These simulation and model make the link between mechanistic physical/chemical damage processes and these two specific biological endpoints.

Realistic nuclear reaction cross-section models are an essential ingredient of reliable heavy-ion transport codes. Such codes are used for risk evaluation of manned space exploration missions as well as for ion-beam therapy dose calculations and treatment planning. Therefore, in this study, a collection of total nuclear reaction cross-section data has been generated within a GSI-ESA-NASA collaboration. The database includes the experimentally measured total nucleus-nucleus reaction cross-sections. The Tripathi, Kox, Shen, Kox-Shen, and Hybrid-Kurotama models are systematically compared with the collected data. Details about the implementation of the models are given. Literature gaps are pointed out and considerations are made about which models fit best the existing data for the most relevant systems to radiation protection in space and heavy-ion therapy., 40 pages, 17 figures, 1 table

In this paper, possible mechanisms by which electrons can induce single-event latchups in electronics are discussed. The energy deposition and the nuclear fragments created by electrons in silicon are analyzed in this context. The cross section enhancement effect in the presence of high-Z materials is discussed. First experimental results of electron-induced latchups are shown in static random access memory devices with low linear energy transfer thresholds. The radiation hardness assurance implications and future work are discussed.

A heavy-ion beam monitor based on 3-D NAND flash memories was designed and tested with heavy ions at high energy and low linear energy transfer (LET). The capability of measuring fluence, angle, uniformity, and LET of impinging particles is discussed, together with the advantages over SRAM-based implementations. We propose ad hoc algorithms for the extraction of the beam parameters, based only on user-mode commands. A validation of the system using low-LET ionizing particles impinging at different angles is presented. Experimental results show very good efficiency and accuracy.

The energy deposited by heavy-ion beams was measured using a passivated implanted planar silicon (PIPS) detector in different facilities. Ion beams at ultrahigh energy lead to the formation of a second, unexpected peak in the deposited energy spectrum at slightly higher energy, in addition to the expected primary peak. Monte Carlo simulations are used to shed light on the origin of this phenomenon and the underlying physical mechanisms. The importance of accounting for secondaries’ production in the packaging materials of the diode and the mechanisms at play are highlighted in the discussion of the results.

The effects of heavy-ion irradiation on 3-D NAND flash memory cells are investigated. Threshold voltage distributions are studied before and after exposure, as a function of the linear energy transfer, fluence, and irradiation angle. Shifts are smaller in 3-D devices than those in planar ones, for the same equivalent bit density. The cell circular shape and the fact that the tunnel oxide and interpoly dielectric blocking layers are perpendicular to the semiconductor substrate make it possible to gain insight into the underlying upset mechanism, which cannot be obtained with planar devices. Evidence that energy deposition in the blocking oxide layer can contribute to charge loss from the floating gate is presented.

The second L-class (large) mission in European Space Agency’s Cosmic Vision program will be an X-ray telescope named Athena, planned to operate at the L2 Lagrange point of the Sun–Earth system. Current large X-ray space telescopes like XMM-Newton and Chandra have encountered periods of unexpectedly high background due to protons in the energy range from 10 keV to 1 MeV (called “soft protons” hereafter). This is an important issue for Athena, as no X-ray telescope has been deployed at L2 so far and the soft proton environment there is poorly known. We analyze data from the Artemis and Advanced Composition Explorer spacecraft and find that fluxes of both solar and geomagnetospheric origin significantly contribute to the soft proton populations in earth’s magnetotail. We then estimate the background from the measured fluxes in Athena’s X-ray instruments and compare it with the science requirement. Our findings reinforce the argument for developing a means to suppress the soft proton flux before it reaches the detectors such as with a magnetic diverter.

Novel materials or multilayers can help to reduce the mass requirement for radiation shielding of electronic components significantly. In this paper, potential alternatives to the standard aluminum shielding approach are assessed by the Monte-Carlo simulations and promising candidates are manufactured and characterized by radiation tests including proton and electron tests. The transmission of energetic protons of up to 39 MeV through the shielding solution was assessed as well as the dose deposited by energetic electrons up to 12 MeV in Radiation sensing field-effect transistor (RADFETs) and Alanine dosimeters behind the shield.

We present experimental evidence of electron-induced upsets in a reference European Space Agency (ESA) single event upset (SEU) monitor, induced by a 200-MeV electron beam at the Very energetic Electronic facility for Space Planetary Exploration in harsh Radiation environments facility at CERN. Comparison of experimental cross sections and simulated cross sections is shown and the differences are analyzed. Possible secondary contributions to the upset rate by neutrons, flash effects, and cumulative dose effects are discussed, showing that electronuclear reactions are the expected SEU mechanism. The ESA Jupiter Icy Moons Explorer mission, to be launched in 2022, presents a challenging radiation environment due to the intense high-energy electron flux in the trapped radiation belts. Insight is given to the possible contribution of electrons to the overall upset rates in the Jovian radiation environment. Relative contributions of both typical electron and proton spectra created when the environmental spectra are transported through a typical spacecraft shielding are shown and the different mission phases are discussed.

Life sciences in space research 21, 73 - 82 (2019). doi:10.1016/j.lssr.2019.04.002, Published by Elsevier, Amsterdam ˜[u.a.]œ

The advancement of multidisciplinary research fields dealing with ionising radiation induced biological damage – radiobiology, radiation physics, radiation protection and, in particular, medical physics – requires a clear mechanistic understanding of how cellular damage is induced by ionising radiation. Monte Carlo (MC)simulations provide a promising approach for the mechanistic simulation of radiation transport and radiation chemistry, towards the in silico simulation of early biological damage. We have recently developed a fully integrated MC simulation that calculates early single strand breaks (SSBs)and double strand breaks (DSBs)in a fractal chromatin based human cell nucleus model. The results of this simulation are almost equivalent to past MC simulations when considering direct/indirect strand break fraction, DSB yields and fragment distribution. The simulation results agree with experimental data on DSB yields within 13.6% on average and fragment distributions agree within an average of 34.8%. © 2019 Associazione Italiana di Fisica Medica

ESA’s astrometry mission Gaia was launched in 2013 to establish the most accurate and complete map of the Milky Way by measuring the distance, position, proper motion, and astrophysical characteristics of two billion stars. It contains the largest focal plane ever flown in space comprising 106 CCDs. To downlink to Earth only useful data, an on-board algorithm was designed to discriminate between e.g. stars and cosmics- ionizing tracks left by energetic particles. A cosmic ray event generation simulator was developed to train and optimize this on-board source detection algorithm. We can now validate this model against Gaia data.

International audience; The experience gained with the current generation of X-ray telescopes like Chandra and XMM-Newton has shown that low energy “soft” protons can pose a severe threat to the possibility to exploit scientific data, reducing the available exposure times by up to 50% and introducing a poorly reproducible background component. These soft protons are present in orbits outside the radiation belts and enter the mirrors, being concentrated towards the focal plane instruments, losing energy along their path and finally depositing their remaining energy in the detectors. Their contribution to the residual background will be even higher for ATHENA with respect to previous missions, given the much higher collecting area of the mirrors, even if the instruments will likely suffer no significant radiation damage from this particles flux. As a consequence this soft proton flux shall be damped with the use of a magnetic diverter to avoid excess background loading on the WFI or X-IFU instruments. We present here a first complete evaluation of this background component for the two focal plane instruments of the ATHENA mission in absence of a magnetic diverter, and derive the requirements for such device to reduce the soft protons induced background below the level required to enable the mission science. We estimate the soft proton flux expected in L2 for the interplanetary component and for the component generated locally by acceleration processes in the magnetotail. We produce a proton response matrix for each of the two instruments of ATHENA focal plane, exploiting two independent Monte Carlo simulations to estimate the optics concentration efficiency, and Geant4 simulations to evaluate the energy loss inside the radiation filters and deposited in the detector. With this modular approach we derive the expected fluxes and spectra for the soft protons component of the background. Finally, we calculate the specifics of a magnetic diverter able to reduce such flux below the required level for both X-IFU and WFI.

Through the use of experimental data and Monte Carlo simulations we investigate the shielding properties of spacecraft-shell compositions exposed to 1 GeV/nucleon 56Fe ions, representative of the worst part of the Galactic Cosmic Ray (GCR) spectrum. Through the use of the Geant4 Radiation Analysis for Space (GRAS) tool, the dose reduction and the 56Fe-fragmentation induced by those structures currently used to protect part of the International Space Station (ISS) or designed for future inflatable habitats, are analyzed. The possible effects on spacecraft electronics are discussed.

We apply a Monte Carlo based integral rectangular parallel-piped (IRRP) approach to evaluate the impact of heavy ion reaction products on the Galactic Cosmic Ray (GCR) Single Event Effect (SEE) rate, concluding that owing to their similar high-energy (> 100 MeV/n) SEE cross section and much larger abundance, protons are expected to be the dominating contributor. In addition, a broad set of components, ions and energies is used to explore the sub-LET threshold experimental region for standard ground-level heavy ion test energies, identifying an overall decreasing trend in the 10-80 MeV/n range due to the decreased contribution of complete and break-up fusion, and pointing out the limitations associated to the application of Monte Carlo SEE models in this energy interval.

The impact of high energy electrons in multi-layered shielding structures has been measured in terms of dose enhancement effects. New dosimetric data from a series of extensive experimental tests have been obtained and compared to the latest electromagnetic physics models included in the Geant4 Monte Carlo toolkit.

Radiation shielding is of primary importance in the planning of new interplanetary manned missions, and the ISS represents the largest laboratory for radiation shielding in space ever built. The ISS radiation environment has been thoroughly characterised by the Monte Carlo-based high-energy physics toolkit Geant4. It has been found that the ISS structure is quite effective at shielding from most forms of radiation, largely due to its internal arrangement. The internal environment found is consistent with literature values and astronaut dosimetry, and results indicate that the internal arrangement of a spacecraft may be the key to the radiation environment within it. Simulation results are also presented for the interplanetary case, including detailed comparisons with other codes. Guidelines for interplanetary manned mission design are presented using these findings.

Several models of the high energy electron radiation environment in the Jovian system have been constructed, based on a limited set of data, principally from Voyager 1 and 2 and Galileo. The design of future missions to this harsh radiation environment requires characterisation of the environment and its uncertainties. From the uncertainties a margin policy can be established to ensure robustness in design without costly over engineering. The uncertainties in the Jovian radiation environment data, and subsequently the models and underlying data are presented with an approach to defining a margin policy for the Ganymede orbit.

We present experimental evidence of electron induced upsets in a reference ESA SEU monitor, the SEU based particle detector, induced by 200 MeV electron beam at the VESPER facility at CERN. Comparison of experimental cross sections and simulated cross sections are shown and the differences are analyzed. Possible secondary contributions to the upset rate by neutrons and cumulative dose effects are discussed, showing that electronuclear reactions are the expected SEU mechanism. Insight is given as to possible overall electron contribution to the upset rates in the Jovian radiation environment inside a typical spacecraft shielding are evaluated.

A planar floating-gate NAND technology has previously realized a 0.87Gb/mm2 memory density using 3b/cell [1] and achieved a minimum feature size for 16nm [2]. However, the development of planar NAND flash is expected to reach the scaling limit in a few technology generations. To break though this limit, a significant shift to 3D NAND flash has begun and several types of 3D memory cell structures have been proposed and discussed [3–5]. Recently a 3D V-NAND technology achieved 1.86Gb/mm2 using charge-trap cells and 3b/cell [6]. This paper presents a 3b/cell NAND flash memory utilizing a 3D floating gate (FG) technology that achieves 4.29Gb/mm2.

Geant4 is a software toolkit for the simulation of the passage of particles through matter. It is used by a large number of experiments and projects in a variety of application domains, including high energy physics, astrophysics and space science, medical physics and radiation protection. Over the past several years, major changes have been made to the toolkit in order to accommodate the needs of these user communities, and to efficiently exploit the growth of computing power made available by advances in technology. The adaptation of Geant4 to multithreading, advances in physics, detector modeling and visualization, extensions to the toolkit, including biasing and reverse Monte Carlo, and tools for physics and release validation are discussed here., Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 835, ISSN:0168-9002, ISSN:1872-9576

Through the use of the Geant4 Radiation Analysis for Space (GRAS) Monte Carlo tool, we present new results on the impact of different space habitat shell compositions on on-board electronics Soft Error Rate (SER) induced by Galactic Cosmic Rays (GCR). The comparison with the aluminum-equivalent approach is performed using the standard CREME96 tool on a heterogeneous set of representative devices. In particular, the iron-ion spectrum has been taken as representative of the whole GCR spectrum due to its Linear Energy Transfer (LET), material penetration, and abundance characteristics. The results of this work show that the device soft error rate, calculated with the two approaches, in the particular case of human exploration habitats, can be overestimated or underestimated up to 50%, depending on the device type and shielding configuration especially when Commercial Off-The Shelf (COTS) components are used.

The ‘Mars Energetic Radiation Environment Models’ (dMEREM and eMEREM) recently developed for the European Space Agency are herein used to estimate, for the first time, background Galactic Cosmic Ray (GCR) radiation and flare related solar energetic particle (SEP) events at three candidate martian landing sites under conditions where particle arrival occurred at solar minimum (December, 2006) and solar maximum (April, 2002) during Solar Cycle 23. The three landing sites were selected on the basis that they are characterized by significantly different hydrological conditions and soil compositions. Energetic particle data sets recorded on orbit at Mars at the relevant times were incomplete because of gaps in the measurements due to operational constraints. Thus, in the present study, comprehensive near-Earth particle measurements made aboard the GOES spacecraft were used as proxies to estimate the overall particle doses at each perspective landing site, assuming in each case that the fluxes fell off as 1/ r 2 (where r is the helio-radial distance) and that good magnetic connectivity always prevailed. The results indicate that the particle radiation environment on Mars can vary according to the epoch concerned and the landing site selected. Particle estimations obtained using MEREM are in reasonable agreement, given the inherent differences between the models, with the related NASA Heavy Ion–Nucleon Transport Code for Space Radiation/HZETRN. Both sets of results indicated that, for short (30 days) stays, the atmosphere of Mars, in the cases of the SEPs studied and the then prevailing background galactic cosmic radiation, provided sufficient shielding at the planetary surface to maintain annual skin and blood forming organ/BFO dose levels below currently accepted ionizing radiation exposure limits. The threat of occurrence of a hard spectrum SEP during Cruise-Phase transfers to/from Mars over 400 days, combined with the associated cumulative effect of prolonged GCR exposure, poses an as yet unsolved hazard to prospective onboard personnel.

We have implemented the reverse/adjoint Monte Carlo method into Geant4. In this method the primary particles are tracked backward from the sensitive part of the geometry till the external source surface by following the reverse processes. By this way the computing time is spent only for tracks that are contributing to the tallies and the reverse Monte Carlo method is much more rapid than the normal forward Monte Carlo method for simulation cases where the sensitive part is small compared to the rest of the geometry and compared to the extended external source. In this paper we first present the theoretical principles of the Reverse Monte Carlo method. Then we describe how this method and the reverse processes have been implemented into Geant4. Finally we compare and discuss the simulation results obtained with the reverse and forward Monte Carlo modes in Geant4.

The roadmap for space exploration foresees longer journeys and further excursions outside low-Earth orbit as well as the establishment of permanent outposts on other celestial bodies, such as the Moon or Mars. The design of spacecrafts and habitats depends heavily on the mission scenario and must consider the radiation protection properties of the structural components as well as dedicated shielding. In fact, short- and long-term effects caused by exposure to cosmic radiation are now considered among the main health risks of space travel. One of the current strategies is to find multifunctional materials that combine excellent mechanical properties with a high shielding effectiveness to minimize the overall load. In this work, the shielding effectiveness of a wide variety of single and multilayer materials of interest for different mission scenarios has been characterized. In the experimental campaign, reference and innovative materials, as well as simulants of Moon and Mars in situ resources, were irradiated with 1,000 MeV/u 4He, 430 MeV/u 12C and 962-972 MeV/u 56Fe. The results are presented in terms of Bragg curves and dose reduction per unit area density. To isolate the shielding effectiveness only due to nuclear fragmentation, a correction for the energy loss in the material is also considered. These findings indicate that the best shield is lithium hydride, which performs even better than polyethylene. However, the technical feasibility of shielding needs to be investigated. The classification of all materials in terms of shielding effectiveness is not influenced by the ion species, but the value changes dramatically depending on the beam energy. The output of this investigation represents a useful database for benchmarking Monte Carlo and deterministic transport codes used for space radiation transport calculations. These findings also contribute to recommendations for optimizing the design of space vessels and habitats in different radiation environments.

The Standard Radiation Environment Monitor (SREM) is a particle detector developed for wide use on ESA spacecraft. It is flying on several ESA missions, most recently the Herschel and Planck space telescopes. Using data from the SREM unit on PROBA-1 in LEO, pitch angle anisotropics in the inner Van Allen belt are investigated. The sensitivity of the SREM to pitch angle induced flux anisotropics can be linked to the directional response function of the SREM, obtained using GRAS/Geant4 Monte-Carlo simulations. The directional response function is combined with an anisotropic version of the AP8 model (based on the Badhwar-Konradi anisotropy distribution) to yield improved count predictions. The importance of considering flux anisotropies is shown for both short-term data and long-term integrated counts. Significant improvements to the AP8 model can be realised.

International audience; Simulations with a Monte Carlo tool kit have been performed to determine the radiation environment a specific device, called a biochip, would face if it were placed into a rover bound to explore Mars' surface. A biochip is a miniaturized device that can be used to detect organic molecules in situ. Its specific detection part is constituted of proteins whose behavior under cosmic radiation is completely unknown and must be investigated to ensure a good functioning of the device under space conditions. The aim of this study is to define particle species and energy ranges that could be relevant to investigate during experiments on irradiation beam facilities. Several primary particles have been considered for galactic cosmic ray (GCR) and solar energetic particle (SEP) contributions. Ionizing doses accumulated in the biochip and differential fluxes of protons, alphas, neutrons, gammas, and electrons have been established for both the Earth-Mars transit and the journey at Mars' surface. Neutrons and gammas appear as dominant species on martian soil, whereas protons dominate during the interplanetary travel. Depending on solar event occurrence during the mission, an ionizing dose of around a few Grays (1Gy=100rad) is expected.

Deposited dose values calculated, from two ray tracing methods are compared to 3D Monte Carlo Adjoint (reverse) results, for both simple and complex geometries. Results are analyzed, ray tracing accuracy discussed, and hardness assurance modification proposed.

The Giove-A spacecraft carries two radiation monitors, CEDEX, built by the University of Surrey and Merlin, built by QinetiQ, to study the radiation environment encountered in the Galileo orbit. The two monitors have been functioning since the beginning of the mission and have measured protons, heavy ions and electrons. The electron environment has been found to be highly variable and driven by solar interactions. Comparisons with AE-8 indicate that the electron energy spectrum for the period measured was somewhat harder than that expected from the model. A series of large solar proton events were detected in December 2006, registering as enhanced fluxes of protons, heavy ions and also triggering a large enhancement in the outer electron belt. Comparisons with POLE and INTEGRAL/IREM show an improved spectral match over AE-8.

The results of the measurements of the double-differential production cross-sections of pions, dσ/dpdΩ, in p C and π C interactions using the forward spectrometer of the HARP experiment are presented. The incident particles are 12 GeV/c protons and charged pions directed onto a carbon target with a thickness of 5% of a nuclear interaction length. For p C interactions the analysis is performed using 100,035 reconstructed secondary tracks, while the corresponding numbers of tracks for π C and π C analyses are 106,534 and 10,122, respectively. Cross-section results are presented in the kinematic range 0.5GeV/c⩽pπ

A characterization of the Galactic cosmic ray (GCR) induced radiation environment on-board Columbus and the International Space Station (ISS) has been carried out using the Geant4 Monte Carlo particle transport toolkit and detailed geometry models of Columbus and ISS. Dose and dose equivalent rates, as well as penetrating particle spectra are presented. Simulation results indicate that the major part of the dose rates due to GCR protons are associated with secondary particles produced in the hull of ISS. Neutrons contribute about 15% of the GCR proton dose equivalent rate and mesons about 10%. More than 40% of the simulated GCR proton dose and dose equivalent rates are due to protons in the energy range above 10 GeV. Protons in the energy range above 50 GeV contribute only 5% to the dose rates. The total simulated dose and dose equivalent rates at solar maximum are 63 muGy/d and 123 muSv/d, respectively. The dose equivalent rate underestimates measurements made during the 2001 solar maximum. The discrepancy can be attributed to deficiencies in hadronic ion-nuclei interaction models for heavy ions and to the lack of such models above 10 GeV/N in Geant4.

The influence of geometry model approximations on Geant4 Monte Carlo simulation results of the radiation environment on-board the Columbus module of the International Space Station (ISS) has been investigated. Three geometry models of Columbus with different levels of detail and a geometry model of ISS have been developed. These geometries have been used for Geant4 simulations of the radiation environment inside Columbus induced by trapped protons and Galactic Cosmic Ray protons. Simulated dose rates and particle spectra on-board Columbus for each of the three Columbus models, with or without the ISS geometry model included, are presented and compared. From comparisons of simulated dose rates and particle spectra for the three different geometry models it was found that the most detailed geometry model (750 volumes) produced results similar to a much less detailed model (23 volumes). The most detailed geometry model was concluded to be a sufficiently detailed approximation of the physical Columbus for the purpose of proton induced space radiation studies. The simulated dose rates are compatible with measurements on-board the ISS. The simulation results also show that an increase in shielding thickness decreases the simulated dose rate induced by trapped protons. For Galactic Cosmic Ray protons the dose rate remains unchanged or is slightly increased. (c) 2007 Elsevier Ltd. All rights reserved.

A detailed characterization of the trapped-proton-induced radiation environment on board Columbus and the International Space Station (ISS) has been carried out using the Geant4 Monte Carlo particle transport toolkit. Dose and dose equivalent rates, as well as penetrating particle spectra are presented. These results are based on detailed Geant4 geometry models of Columbus and ISS, comprising a total of about 1000 geometry volumes. Simulated trapped-proton dose rates are found to be strongly dependent on ISS altitude. Dose rates for different locations inside the Columbus cabin are presented, as well as for different models of the incident trapped-proton flux. Dose rates resulting from incident anisotropic trapped protons are found to be lower than, or equal to, those of omnidirectional models. The anisotropy induced by the asymmetric shielding distribution of Columbus/ISS is also studied. The simulated trapped-proton dose (equivalent) rates, averaged over different locations inside Columbus, are 120 muGy/d (154 muSv/d) and 79 muGy/d (102 muSv/d) for solar minimum and maximum conditions according to AP8 incident proton spectra and an ISS orbit of 380 km. The solar maximum dose rates are found to be of the same order as measurements in other modules in the present ISS.

A valuable set of dosimetric data for high energy electrons propagated through typical space multi-layer materials has been obtained in order to validate the main radiation simulation tools used by the space industry and to improve our knowledge of the uncertainties and margins in the space radiation analysis. The experimental dataset has been intensively compared with GEANT4, PENELOPE, ITS, EGSnrc and NOVICE codes.

This study focuses on the ion species and energy dependence of the heavy ion SEE cross section in the sub-LET threshold region through a set of experimental data. In addition, a Monte Carlo based model is introduced and applied, showing a good agreement with the data in the several hundred MeV/n range while evidencing large discrepancies with the measurements in the 10-30 MeV/n interval, notably for the Ne ion. Such discrepancies are carefully analyzed and discussed.

Predictions of Total Ionizing Dose made using full 3-D Monte Carlo and simplified sector-shielding techniques for simple and complex geometries in a space environment are compared and differences between them analyzed in detail

We gratefully acknowledge the help and support of the PS beam staff and of the numerous technical collaborators who contributed to the detector design, construction, commissioning and operation. In particular, we would like to thank G. Barichello, R. Broccard, K. Burin, V. Carassiti, F. Chignoli, G. Decreuse, C. Detraz, M. Dwuznik, F. Evangelisti, B. Friend, A. Iaciofano, I. Krasin, J.-C. Legrand, M. Lobello, F. Marinilli, J. Mulon, R. Nicholson, A. Pepato, P. Petev, X. Pons, I. Rusinov, M. Scandurra, E. Usenko, and R. van der Vlugt, for their support in the construction of the detector. The collaboration is indebted to M. Baldo Ceolin, P. Binko, E. Boter, M. Doucet, D. D¨ullmann, V. Ermilova, A. Pullia and A. Valassi for their contributions to the experiment. We are indebted to the K2K collaboration who made available their beam-line simulation for the calculation of the predicted far–to–near neutrino flux ratio. The experiment was made possible by grants from the Institut Interuniversitaire des Sciences Nucl´eaires and the Interuniversitair Instituut voor Kernwetenschappen (Belgium), Ministerio de Educacion y Ciencia, Grant FPA2003-06921-c02-02 and Generalitat Valenciana, grant GV00-054-1, CERN (Geneva, Switzerland), the German Bundesministerium f¨ur Bildung und Forschung (Germany), the Istituto Nazionale di Fisica Nucleare (Italy), INR RAS (Moscow) and the Particle Physics and Astronomy Research Council (UK). We gratefully acknowledge their support.

International audience; Context Under irradiation, a biological system undergoes a cascade of chemical reactions that can lead to an alteration of its normal operation. There are different types of radiation and many competing reactions. As a result the kinetics of chemical species is extremely complex. The simulation becomes then a powerful tool which, by describing the basic principles of chemical reactions, can reveal the dynamics of the macroscopic system.To understand the dynamics of biological systems under radiation, since the 80s there have been on-going efforts carried out by several research groups to establish a mechanistic model that consists in describing all the physical, chemical and biological phenomena following the irradiation of single cells. This approach is generally divided into a succession of stages that follow each other in time: (1) the physical stage, where the ionizing particles interact directly with the biological material; (2) the physico-chemical stage, where the targeted molecules release their energy by dissociating, creating new chemical species; (3) the chemical stage, where the new chemical species interact with each other or with the biomolecules; (4) the biological stage, where the repairing mechanisms of the cell come into play. This article focuses on the modeling of the chemical stage.Method This article presents a general method of speeding-up chemical reaction simulations in fluids based on the Smoluchowski equation and Monte-Carlo methods, where all molecules are explicitly simulated and the solvent is treated as a continuum. The model describes diffusion-controlled reactions. This method has been implemented in Geant4-DNA. The keys to the new algorithm include: (1) the combination of a method to compute time steps dynamically with a Brownian bridge process to account for chemical reactions, which avoids costly fixed time step simulations; (2) a k–d tree data structure for quickly locating, for a given molecule, its closest reactants. The performance advantage is presented in terms of complexity, and the accuracy of the new algorithm is demonstrated by simulating radiation chemistry in the context of the Geant4-DNA project.Application The time-dependent radiolytic yields of the main chemical species formed after irradiation are computed for incident protons at different energies (from 50 MeV to 500 keV). Both the time-evolution and energy dependency of the yields are discussed. The evolution, at one microsecond, of the yields of hydroxyls and solvated electrons with respect to the linear energy transfer is compared to theoretical and experimental data. According to our results, at high linear energy transfer, modeling radiation chemistry in the trading compartment representation might be adopted.