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Galactic cosmic rays and cell-hit frequencies outside the magnetosphere
Abstract
An evaluation of the exposure of space travelers to galactic cosmic radiation outside the earth's magnetosphere is made by calculating fluences of high-energy primary and secondary particles with various charges traversing a sphere of area 100 microns2. Calculations relating to two shielding configurations are presented: the center of a spherical aluminum shell of thickness 1 g/cm2, and the center of a 4 g/cm2 thick aluminum spherical shell within which there is a 30 g/cm2 diameter spherical water phantom with the point of interest 5 g/cm2 from the surface. The area of 100 microns2 was chosen to simulate the nucleus of a cell in the body. The frequencies as a function of charge component in both shielding configurations reflects the odd-even disparity of the incident particle abundances. For a three-year mission, 33% of the cells in the more heavily shielded configuration would be hit by at least one particle with Z greater than 10. Six percent would be hit by at least two such particles. This emphasizes the importance of studying single high-Z particle effects both on cells which might be "at risk" for cancer induction and on critical neural cells or networks which might be vulnerable to inactivation by heavy charged particle tracks. Synergistic effects with the more numerous high-energy protons and helium ions cannot be ruled out. In terms of more conventional radiation risk assessment, the dose equivalent decreased by a factor of 2.85 from free space to that in the more heavily shielded configuration. Roughly half of this was due to the decrease in energy deposition (absorbed dose) and half to the decrease in biological effectiveness (quality factor).
... The result is large scale structures in the form of boundaries, regions, and electric fields that have been observed by spacecraft flybys of comets and by Rosetta during its extended escort of 67P. Boundaries observed by a spacecraft at a comet can be permanent features, solar wind and interplanetary magnetic field (IMF) boundaries, or small-scale transient features created by instabilities or waves (Cravens 1989). Figure 34 illustrates the relative positions of the boundaries discussed in the following sections. ...
... A collisionopause is a boundary in the comet-solar wind interaction region where collisions first become important inside of the boundary Cravens 1989Cravens , 1991. Cravens (1991) outlined various types of collisionopause for both ions and electrons depending on the collision processes involved. ...
... Some have disputed the existence of this boundary (Rème et al. 1994), while others suggest that it is a permanent feature (Gringauz and Verigin 1991;Sauer et al. 1995). The cometopause at previous comet flybys was characterized by a decrease in electron velocity and temperature, an increase in ion densities and deflection of ions Cravens 1989). It is thought to be the beginning of the magnetic pileup region Cravens (1989). ...
The environment of a comet is a fascinating and unique laboratory to study plasma processes and the formation of structures such as shocks and discontinuities from electron scales to ion scales and above. The European Space Agency’s Rosetta mission collected data for more than two years, from the rendezvous with comet 67P/Churyumov-Gerasimenko in August 2014 until the final touch-down of the spacecraft end of September 2016. This escort phase spanned a large arc of the comet’s orbit around the Sun, including its perihelion and corresponding to heliocentric distances between 3.8 AU and 1.24 AU. The length of the active mission together with this span in heliocentric and cometocentric distances make the Rosetta data set unique and much richer than sets obtained with previous cometary probes. Here, we review the results from the Rosetta mission that pertain to the plasma environment. We detail all known sources and losses of the plasma and typical processes within it. The findings from in-situ plasma measurements are complemented by remote observations of emissions from the plasma. Overviews of the methods and instruments used in the study are given as well as a short review of the Rosetta mission. The long duration of the Rosetta mission provides the opportunity to better understand how the importance of these processes changes depending on parameters like the outgassing rate and the solar wind conditions. We discuss how the shape and existence of large scale structures depend on these parameters and how the plasma within different regions of the plasma environment can be characterised. We end with a non-exhaustive list of still open questions, as well as suggestions on how to answer them in the future.
... After spacecraft made in situ observations during several flybys and the escort of comet 67P by Rosetta, several other boundaries were also observed: the cometopause, an ion pileup boundary, and ion-neutral and electron-neutral collisionopauses. Plasma interaction boundaries observed at a comet can be permanent features, solar wind and interplanetary magnetic field boundaries, or small-scale transient features created by waves or instabilities (Cravens 1989). Permanent features include shocks and collisionopause boundaries. ...
... As discussed in Sect. 3.5, a collisionopause forms when collisions between neutrals and ions or electrons change characteristics of the plasma such as composition or velocity (Mendis et al. 1986;Cravens 1989Cravens , 1991. Cravens (1991) outlined various types of collisionopause for both ions and electrons depending on the collision processes and the reactions that may occur, including ion-neutral charge transfer and ion-neutral chemistry. ...
... Although some dispute the existence of this boundary (Rème et al. 1994), it was determined by several researchers to be a permanent feature (Gringauz and Verigin 1991;Sauer et al. 1995). Several authors have proposed that the cometopause is the location where collisions causing charge exchange between solar wind protons and cometary neutrals become dominant (Gringauz et al. 1986;Gombosi 1987;Cravens 1989;Ip 1989), a form of collisionopause boundary ((see Table 1) and 3.5). However, this is not an appropriate explanation for the cometopause as explained in 3.5. ...
Once a cometary plasma cloud has been created through ionisation of the cometary neutrals, it presents an obstacle to the solar wind and the magnetic field within it. The acceleration and incorporation of the cometary plasma by the solar wind is a complex process that shapes the cometary plasma environment and is responsible for the creation of boundaries such as a bow shock and diamagnetic cavity boundary. It also gives rise to waves and electric fields which in turn contribute to the acceleration of the plasma. This chapter aims to provide an overview of how the solar wind is modified by the presence of the cometary plasma, and how the cometary plasma is incorporated into the solar wind. We will also discuss models and techniques widely used in the investigation of the plasma environment in the context of recent findings by Rosetta. In particular, this chapter highlights the richness of the processes and regions within this environment and how processes on small scales can shape boundaries on large scales. It has been fifteen years since the last book on Comets was published and since then we have made great advances in the field of cometary research. But many open questions remain which are listed and discussed with particular emphasis on how to advance the field of cometary plasma science through future space missions.
... Some of the more interesting features in these observations include detection and characterization of plasma interaction boundaries that demonstrate measurable changes in plasma parameters between one interaction region and the next (see Mandt et al. 2016, for a detailed review of boundary observations and theory). Plasma interaction boundaries can be permanent features, solar wind and interplanetary magnetic field (IMF) boundaries, or small-scale transient features created by instabilities or waves (Cravens 1989). The bow shock, a permanent boundary where mass loading of the solar wind flow causes it to transition from supersonic to subsonic, was observed by several spacecraft flybys (e.g., Galeev et al. 1986). ...
... One of these is the cometopause, where the composition of the ions flowing in the antisunward direction as part of the solar wind flow changes from predominantly solar wind ions to predominantly cometary ions (Gringauz et al. 1986a;Gombosi 1987;Fuselier et al. 1988;Mendis et al. 1989;Coates 1997). Cravens (1989) defined the cometopause as the collisionopause for solar wind proton charge exchange. The location and width of this boundary vary with time as a result of changes in the solar wind and the neutral gas flow parameters (Gringauz & Verigin 1991). ...
... A collisionopause is a boundary where collisions first become important inside of the boundary (Mendis et al. 1986;Cravens 1989Cravens , 1991. Cravens (1991) outlined various types of collisionopause for both ions and electrons depending on the collision processes. ...
Context:
Collisions between cometary neutrals in the inner coma of a comet and cometary ions that have been picked up into the solar wind flow and return to the coma lead to the formation of a broad inner boundary known as a collisionopause. This boundary is produced by a combination of charge transfer and chemical reactions, both of which are important at the location of the collisionopause boundary. Four spacecraft measured ion densities and velocities in the inner region of comets, exploring the part of the coma where an ion-neutral collisionopause boundary is expected to form.
Aims:
The aims are to determine the dominant physics behind the formation of the ion-neutral collisionopause and to evaluate where this boundary has been observed by spacecraft.
Methods:
We evaluated observations from three spacecraft at four different comets to determine if a collisionopause boundary was observed based on the reported ion velocities. We compared the measured location of the ion-neutral collisionopause with measurements of the collision cross sections to evaluate whether chemistry or charge exchange are more important at the location where the collisionopause is observed.
Results:
Based on measurements of the cross sections for charge transfer and for chemical reactions, the boundary observed by Rosetta appears to be the location where chemistry becomes the more probable result of a collision between H2O and H2O+ than charge exchange. Comparisons with ion observations made by Deep Space 1 at 19P/Borrelly and Giotto at 1P/Halley and 26P/Grigg-Skjellerup show that similar boundaries were observed at 19P/Borrelly and 1P/Halley. The ion composition measurements made by Giotto at Halley confirm that chemistry becomes more important inside of this boundary and that electron-ion dissociative recombination is a driver for the reported ion pileup boundary.
... Although exposure to space radiation can result in appreciable cumulative doses to astronauts during long-duration missions, it is important to note that the radiation exposure occurs at low fluences, such that particle traversals through individual cells in an astronaut's body are well separated in tissue location and time. For example, fluence rates during solar maximum (with no solar event activity) have been estimated as: 4 protons/cm 2 /sec, 0.4 helium ions/cm 2 /sec, and 0.04 HZE (high atomic number and energy) particles/cm 2 /sec with energies of a few hundred MeV to several GeV/nucleon [14]. Based on these fluence rates, it is predicted that for a typical cell nucleus of 100 pm 2 , each nucleus in the body would receive a proton traversal every 3 days, helium traversal once a month, and a HZE particle traversal once per year [14]. ...
... For example, fluence rates during solar maximum (with no solar event activity) have been estimated as: 4 protons/cm 2 /sec, 0.4 helium ions/cm 2 /sec, and 0.04 HZE (high atomic number and energy) particles/cm 2 /sec with energies of a few hundred MeV to several GeV/nucleon [14]. Based on these fluence rates, it is predicted that for a typical cell nucleus of 100 pm 2 , each nucleus in the body would receive a proton traversal every 3 days, helium traversal once a month, and a HZE particle traversal once per year [14]. ...
... Furthermore, in future studies, genetically modified variants of the keratinocytes could also be used to gain insight into molecular processes involved in the development of radiation-induced cancers.In general, skin is composed of two tissue layers: connective tissue (dermis), which provides structural support, and a covering epithelium (epidermis), which provides biological feedback to the dermis through the release of cytokines and other mediators. In our tissue constructs, the dermis layer consisted of AGO1522 fibroblasts embedded in a type I collagen matrix, and the epidermis layer consisted of sequentially-differentiated keratinocytes.The dermal layer was constructed by mixing a solution consisting of 7.4% NaOH (0.3 M),14.3% 1oX M199 media (Gibco), and 78.3% type I rat tail collagen (Fisher Scientific) with a total volume of 1.4 ml/tissue construct. The solution was carefully mixed to avoid the formation of bubbles, and up to an additional 500 pl of NaOH was added to the mixture as necessary until the solution turned a pinkish-orange color(corresponding to a pH of -7). ...
Space radiation poses a significant hazard to astronauts on long-duration missions, and the low fluences of charged particles characteristic of this field suggest that bystander effects, the phenomenon in which a greater number of cells exhibit damage than expected based on the number of cells traversed by radiation, could be significant contributors to overall cell damage. The purpose of this thesis was to investigate bystander effects due to signaling between different cell types cultured within 2D and 3D tissue architectures. 2D bystander signaling was investigated using a transwell insert system in which normal human fibroblasts (A) and keratinocytes (K) were irradiated with 1 GeV/n protons or iron ions at the NASA Space Radiation Laboratory using doses from either 2 Gy (protons) or 1 Gy (iron ions) down to spacerelevant low fluences. Medium-mediated bystander responses were investigated using three cell signaling combinations. Bystander signaling was also investigated in a 3D model by developing tissue constructs consisting of fibroblasts embedded in a collagen matrix with a keratinocyte epidermal layer. Bystander experiments were conducted by splitting each construct in half and exposing half to radiation then placing the other half in direct contact with the irradiated tissue on a transwell insert. Cell damage was evaluated primarily as formation of foci of the DNA repair-related protein 53BP1. In the 2D system, both protons and iron ions yielded a strong dose dependence for the induction of 53BP1 in irradiated cells, while the magnitudes and time courses of bystander responses were dependent on radiation quality. Furthermore, bystander effects were present in all three cell signaling combinations even at the low proton particle fluences used, suggesting the potential importance of including these effects in cancer risk models for low-dose space radiation exposures. Cells cultured in the 3D constructs exhibited a significant reduction in the percentages of both direct and bystander cells positive for 53BP1 foci, although the qualitative kinetics of DNA damage and repair were similar to those observed in 2D. These results provide evidence that the microenvironment significantly influences intercellular signaling and that cells may be more radioresistant in 3D compared to 2D systems.
... Moreover, Buonanno have shown that exposure of normal human fibroblasts to 20 cGy of 0.05 or 1-GeV protons protects the irradiated cells against chromosomal damage induced by a subsequent exposure to 50 cGy from 1 GeV/u iron ions [36]. Zhou et al. [37] have reported that calculations performed by Curtis and Letaw [38] indicate that the nucleus of a cell in a space traveler shielded by 0.4 g/ cm 2 of aluminum (which is however an unrealistic thin shield) would be hit by 400 protons and about 0.4 HZE particles during a 3-year Mars mission [38,39]. Thus most astronauts' cells would be hit by a proton(s) before being hit by an HZE particle. ...
... Moreover, Buonanno have shown that exposure of normal human fibroblasts to 20 cGy of 0.05 or 1-GeV protons protects the irradiated cells against chromosomal damage induced by a subsequent exposure to 50 cGy from 1 GeV/u iron ions [36]. Zhou et al. [37] have reported that calculations performed by Curtis and Letaw [38] indicate that the nucleus of a cell in a space traveler shielded by 0.4 g/ cm 2 of aluminum (which is however an unrealistic thin shield) would be hit by 400 protons and about 0.4 HZE particles during a 3-year Mars mission [38,39]. Thus most astronauts' cells would be hit by a proton(s) before being hit by an HZE particle. ...
doi:10.31661/JBPE.V0I0.1193
During deep space missions, astronauts are exposed to highly ionizing radiation, incl. neutrons, protons, and heavy ions from galactic cosmic rays (GCR), solar wind (SW), and solar energetic particles (SEP). This increases the risks for cancerogenesis, damages in the central nervous system (CNS), cardiovascular diseases, etc. Large SEP events can even cause acute radiation syndrome (ARS). Long-term manned deep space missions will therefore require unique radiation protection strategies. Since it has been shown that physical shielding alone is not sufficient, this paper proposes pre-flight screening of the aspirants for evaluation of their level of adaptive responses. Methods for boosting their immune system should also be further investigated, and the possibility of using radiation effect modulators is discussed. In this paper, especially, the use of vitamin C as a promising non-toxic, cost-effective, easily available radiation mitigator (which can be used hours after irradiation), is described. Although it has previously been shown that vitamin C can decrease radiation-induced chromosomal damage in rodents, it must be further investigated before any conclusions about its radiation mitigating properties in humans can be concluded.
... Exposure to low doses of HZE particles (20-40 cGy) can disrupt cognitive performance (Britten et al., 2016(Britten et al., , 2017Davis et al., 2014;Raber et al., 2013;Rabin et al., 2011Rabin et al., , 2015 which has the potential to compromise successful completion of mission requirements. In contrast to simulations using a particle accelerator, only a small fraction of neurons in the central nervous system will be hit by an HZE particle during a 3-year Mars mission (Curtis and Letaw, 1989;Curtis et al., 1998;Cucinotta et al., 1998Cucinotta et al., , 2014. Also in contrast to simulations using whole body exposures to HZE particles (Britten et al., 2016(Britten et al., , 2017Davis et al., 2014;Parihar et al., 2018;Raber et al., 2013;Rola et al., 2005;Sweet et al., 2016;Vilisana et al., 2011;Vlkolinsky et al., 2007), which provide a uniform pattern of exposure across the entire body, the distribution of "hits" to cells will be asymmetrically located across the entire body: particles may be expected to randomly hit cells located throughout the body as well as neurons in the central nervous system. ...
... Historically, the assumption has been that exposure to HZE particles affects neuronal function and cognitive performance because of direct effects on neurons as the particles pass through the brain (e.g., Cucinotta et al, 1998Cucinotta et al, , 2014Curtis et al., 1989Curtis et al., , 1998. The present results suggest that HZE particle-induced oxidative stress and neuroinflammation and the disruption of cognitive performance are not dependent upon a direct action of HZE particles on neurons. ...
On exploratory class missions, such as a mission to Mars, astronauts will be exposed to particles of high energy and charge (HZE particles). Exposure to HZE particles produces changes in neuronal function and can disrupt cognitive performance. Cells throughout the entire body, not just the brain, will be impacted by these particles. To determine the possible effects that irradiation of the body might have on neuronal function and cognitive performance, rats were given head-only, body-only or whole-body exposures to ⁵⁶Fe particles. Cognitive performance (novel object recognition, operant responding) was tested in one set of animals; changes in brain function (oxidative stress, neuroinflammation) was tested in a second set of rats. The results indicated that there were no consistent differences in either behavioral or neurochemical endpoints as a function of the location of the irradiation. These results suggest that radiation to the body can impact the brain, therefore it may be necessary to re-evaluate the estimates of the risk of HZE particle-induced changes in neuronal function and cognitive performance.
... Heavy ion radiation is a major concern in outer space and represents an appreciable dose equivalent of the galactic cosmic radiation (GCR) [1][2][3]. Heavy ions are also a component of the radiation emitted from the sun during solar particle events (SPEs). Astronauts traveling beyond low earth orbits (LEO) and the protective magnetosphere on long duration space missions such as mission to Mars will be exposed to substantial heavy ion radiation [4,5]. ...
... Although space radiation is primarily high-energy protons, energetic heavy ions due to their high linear energy transfer (high-LET) per unit volume of tissue traversed are considered most harmful for the astronauts. Mathematical modeling approaches indicate that during a Mars mission ~30% of the cells in astronauts will be traversed by either primary or secondary tracts generated by heavy ion radiation [1][2][3]. It is predicted that astronauts on an approximately 850 to 1000 days of round trip to Mars will receive 0.30 to 0.42 Gy of space radiation. ...
Heavy ion radiation, prevalent in outer space and relevant for radiotherapy, is densely ionizing and poses risk to stem cells that are key to intestinal homeostasis. Currently, the molecular spectrum of heavy ion radiation-induced perturbations in intestinal stem cells (ISCs), that could trigger intestinal pathologies, remains largely unexplored. The Lgr5-EGFP-IRES-creERT mice were exposed to 50 cGy of iron radiation. Mice were euthanized 60 d after exposure and ISCs were sorted using fluorescence activated cell sorting. Reactive oxygen species (ROS) and mitochondrial superoxide were measured using fluorescent probes. Since DNA damage is linked to senescence and senescent cells acquire senescence-associated secretory phenotype (SASP), we stained ISCs for both senescence markers p16, p21, and p19 as well as SASP markers IL6, IL8, and VEGF. Due to potential positive effects of SASP on proliferation, we also stained for PCNA. Data show increased ROS and ongoing DNA damage, by staining for γH2AX, and 53BP1, along with accumulation of senescence markers. Results also showed increased SASP markers in senescent cells. Collectively, our data suggest that heavy-ion-induced chronic stress and ongoing DNA damage is promoting SASP in a fraction of the ISCs, which has implications for gastrointestinal function, inflammation, and carcinogenesis in astronauts and patients.
... However, it should be noted that deepspace vehicles for future human missions and habitats will likely have thick shielding and therefore contributions from neutrons and light ions may dominate the total DE (Norbury and Slaba, 2014). Such differences will have to be considered when using results obtained from biosentinel missions designed with thin shielding to infer biological responses behind the thicker shields expected for human missions (Curtis and Letaw, 1989). Table 2 provides the calculated integral flux for each nuclide in GCR and the calculated traversals per day for individual cell nuclei (additional considerations are required for multiple cells in a sample, as discussed later). ...
... It's important to note that in space, particle traversals are essentially random in both time and direction and for small biological targets such as cells and organelles the traversals are rare (Curtis and Letaw, 1989). As seen in Table 2, the expected GCR particle traversal rates are substantially less than one per day for any of these biological targets. ...
There is growing interest in flying biological experiments beyond low-Earth orbit (LEO) to measure biological responses potentially relevant to those expected during a human mission to Mars. Such experiments could be payloads onboard precursor missions, including unmanned private-public partnerships, as well as small low-cost spacecraft (satellites) designed specifically for "biosentinel" type missions. It is the purpose of this paper to provide physical cosmic-ray interaction data and related information useful to biologists who may be planning such experiments. It is not the objective here to actually design such experiments or provide radiobiological response functions, which would be specific for each experiment and biological endpoint. Nuclide-specific flux and dose rates were calculated using OLTARIS and these results were used to determine particle traversal rates and doses in hypothetical biological targets. Comparisons are provided between GCR in interplanetary space and inside the ISS. Calculated probabilistic estimates of dose from solar particle events are also presented. Although the focus here is on biological experiments, the information provided may be useful for designing other payloads as well if the space radiation environment is a factor to be considered.
... The opportunity is increasing for humans to be exposed to various sources of IR, such as during medical diagnosis, cancer radiotherapy, and space exploration activities. Aside from health concerns on the increasing diagnostic medical exposure to low doses of low linear energy transfer (LET) IR (Berrington de Gonz alez and Darby, 2004;Shah et al., 2012), there is a potential health risk from exposure to high-mass, highly charged, and high-energy particles in long-term outer space activities (Curtis and Letaw, 1989), and from exposure of normal brain tissues around the tumor to high LET irradiations from heavy-ion radiotherapy. The quality of high LET particle irradiations is different from conventional photons, so the effects from high LET particle irradiation have attracted scientific interest in both basic and clinical fields (Ando and Kase, 2009). ...
... It is still important to study the effects of high LET irradiations at low doses in wild-type animals. On the other hand, both carbon and Fe particles constitute a significant hazard during space activities, and a traversal of a cell nucleus by carbon and Fe particles would be, respectively, 0.6 and 0.03 during a 3-year deep space exploration (Curtis and Letaw, 1989). In addition, the biological effectiveness of different particles and energies in disrupting behavioral performance could not be predicted or explained simply on the basis of LET values (Rabin et al., 2007). ...
The cause and risk factors of Alzheimer's disease (AD) are largely unknown. Studies on possible radiation-induced AD-like pathogenesis and behavioral consequences are important because humans are exposed to ionizing radiation (IR) from various sources. It was reported that total-body irradiations (TBI) at 10 cGy of low linear energy transfer (LET) X-rays to mice triggered acute transcriptional alterations in genes associated with cognitive dysfunctions. However, it was unknown whether low doses of IR could induce AD-like changes late after exposure. We reported previously that 10 cGy X-rays induced early transcriptional response of several AD-related genes in hippocampi without late AD-like pathogenesis and memory impairment in mice. Here, further studies on two low doses (5 or 10 cGy) of high LET carbon-ion irradiations are reported. On expression of 84 AD-related genes in hippocampi, at 4 hr after TBI, 5 cGy induced a significant upregulation of three genes (Abca1, Casp3, and Chat) and 10 cGy led to a marked upregulation of one gene (Chat) and a downregulation of three genes (Apoe, Ctsd, and Il1α), and, at 1 year after TBI, one gene (Il1α) was significantly downregulated in 10 cGy-irradiated animals. Changes in spatial learning ability and memory and induction of AD-like pathogenesis were not detected by in vivo brain imaging for amyloid-β peptide accumulation and by immunohistochemical staining of amyloid precursor protein, amyloid-β protein, tau, and phosphorylated tau protein. These findings indicate that low doses of carbon-ion irradiations did not cause behavioral impairment or AD-like pathological change in mice. © 2014 Wiley Periodicals, Inc.
... The deep space proton model consists of the flux of the proton component of GCR, across the 90,000 µm 2 cross-sectional area of the 300×300×300 µm simulation volume, over three days in space beyond LEO [42]. The omnidirectional nature of space radiation is simulated by randomly generating traversal directions and positions over the simulation space [43], and the dose rate of the deep space proton model (4.49 mGy/3 days) is intended to approximate the dose rate of protons present in the deep space environment. ...
Space radiation poses a substantial health risk to humans traveling beyond Earth’s orbit to the Moon and Mars. As microbes come with us to space as model organisms for studying radiation effects, a computational model simulating those effects on microorganisms could enable us to better design and interpret those experiments. Here we present an agent-based model for microbial populations exposed to radiation (AMMPER), which simulates the effects of protons, a major component of deep-space radiation, on budding yeast ( Saccharomyces cerevisiae ) growth. The model combines radiation track structure data from the RITRACKS package with novel algorithms for cell replication, motion, damage, and repair. We demonstrate that AMMPER qualitatively reproduces the effects of 150 MeV proton radiation on growth rate, but not lag time, of wild type and DNA repair mutant yeast strains. The variance in AMMPER’s results is consistent with the variance in experimental results, suggesting that AMMPER can recapitulate the stochasticity of empirical experiments. Finally, we used AMMPER to predict responses to deep space radiation that may be tested in future experiments. A user-friendly, open-source, extendable Python package for studying the relationship between single-particle radiation events and population-level responses, AMMPER can facilitate the basic research necessary to ensure safe and sustainable exploration of deep space.
... Life thrives at discrete interfaces [39], especially on rocky and icy planets, and is more favored on substrates protected from shortwave [40] and charged particle radiation [41]. ...
... Differences in track structure would be expected to impact more or fewer neurons. The failure to observe differences in the neurochemical endpoints as a function of differences in track structure (i.e., particle energy/LET) in the present study, combined with recent research showing that NTEs play an important role in HZE particle-induced neurochemical and cognitive changes (11,12), suggests that the direct effects of exposure to heavy particles may play a more limited role than previously thought (23,24). ...
Astronauts on exploratory missions will be exposed to particle radiation of high energy and charge (HZE particles), which have been shown to produce neurochemical and performance deficits in animal models. Exposure to HZE particles can produce both targeted effects, resulting from direct ionization of atoms along the particle track, and non-targeted effects (NTEs) in cells that are distant from the track, extending the range of potential damage beyond the site of irradiation. While recent work suggests that NTEs are primarily responsible for changes in cognitive function after HZE exposures, the relative contributions of targeted and non-targeted effects to neurochemical changes after HZE exposures are unclear. The present experiment was designed to further explore the role of targeted and non-targeted effects on HZE-induced neurochemical changes (inflammation and oxidative stress) by evaluating the effects of exposure location and particle energy/linear energy transfer (LET). Forty-six male Sprague-Dawley rats received head-only or body-only exposures to 56Fe particles [600 MeV/n (75 cGy) or 1,000 MeV/n (100 cGy)] or 48Ti particles [500 MeV/n (50 cGy) or 1,100 MeV/n (75 cGy)] or no irradiation (0 cGy). Twenty-four h after irradiation, rats were euthanized, and the brain was dissected for analysis of HZE-particle-induced neurochemical changes in the hippocampus and frontal cortex. Results showed that exposure to 56Fe and 48Ti ions produced changes in measurements of brain inflammation [glial fibrillary astrocyte protein (GFAP)], oxidative stress [NADPH-oxidoreductase-2 (NOX2)] and antioxidant enzymes [superoxide dismutase (SOD), glutathione S-transferase (GST), nuclear factor erythroid 2-related factor 2 (Nrf2)]. However, radiation effects varied depending upon the specific measurement, brain region, and exposure location. Although overall exposures of the head produced more detrimental changes in neuroinflammation and oxidative stress than exposures of the body, body-only exposures also produced changes relative to no irradiation, and the effect of particle energy/LET on neurochemical changes was minimal. Results indicate that both targeted and non-targeted effects are important contributors to neurochemical changes after head-only exposure. However, because there were no consistent neurochemical changes as a function of changes in track structure after head-only exposures, the role of direct effects on neuronal function is uncertain. Therefore, these findings, although in an animal model, suggest that NTEs should be considered in the estimation of risk to the central nervous system (CNS) and development of countermeasures.
... Plate tectonics and fluids in rotational conditions are also associated with the generation of the planetary magnetic field [48] and to date detecting the magnetospheres from distance poses a challenge though the promising technique is already proposed [49]. The magnetosphere acts as a shield for charged particle radiation [49][50][51]. Also, detection of asynchronous rotation of magnetic field with corresponding planetary rotation is worthwhile for the understanding presence of subsurface [52,53]. ...
... There has been a number of published papers on the hazards of space travel, [6] states that the ISS is thought to be exposed to an approximate 200 mSv of radiation, over 80 times the amount experienced on earth and double the level for which cancer is more likely. Reference [7] estimates that approximately 30% of the cells in the body will be affected by ionizing events on a three-year interplanetary trip. The effect of space radiation on the immune system is one that has not been extensively studied, it is estimated that the probability of the immune system being affected is equal to or even greater than the probability of inducing mutations [8]. ...
This study explores the possibility of a space station that will occupy a geostationary equatorial orbit (GEO) and create artificial gravity using centripetal acceleration. The concept of the station is to create a habitable, safe environment that can increase the possibility of space tourism by reducing the wide variation of hazards associated with space exploration. The ability to control the intensity of artificial gravity through Hall-effect thrusters will allow experiments to be carried out at different levels of artificial gravity. A feasible prototype model was built to convey the concept and to enable cost estimation. The SpaceX Falcon Heavy rocket with a 26,700 kg payload to GEO was selected to take the 675 tonne spacecraft into orbit; space station construction will require up to 30 launches, this would be reduced to 5 launches when the SpaceX BFR becomes available. The estimated total cost of implementing the Sussex Biocompatible International Space Station (BISS) is approximately 150 billion.
... Astronauts traveling on longduration space missions, such as missions to Mars, will be exposed to energetic particle radiation, including protons and heavy ions from solar particle events and galactic cosmic radiation (4,5). While protons are the major component of space radiation, energetic heavy ions such as 56 Fe, 28 Si, and 12 C contribute significantly toward the dose equivalent, and ∼30% of astronauts' cells are predicted to be hit by heavy ions during a round trip to Mars (6,7). For NASA mission planners, heavy ions are of major concern because they are difficult to block with current shielding measures. ...
Significance
Coordinated epithelial cell migration is key to maintaining functional integrity and preventing pathological processes in gastrointestinal tissue, and is essential for astronauts’ health and space mission success. Here we show that energetic heavy ions, which are more prevalent in deep space relative to low-Earth orbit, could persistently decrease intestinal epithelial cell migration, alter cytoskeletal remodeling, and increase cell proliferation with ongoing DNA damage and cell senescence, even a year after irradiation. Our study has provided the molecular underpinnings for energetic heavy-ion ⁵⁶ Fe radiation-induced cell migration alterations, and raises a potentially serious concern, particularly for long-term deep-space manned missions.
... A dose of 20 cGy of 1 GeV/n 56 Fe ions was chosen as it is the approximate total dose delivered by a mean of one iron ion traversal/MSC cell nucleus (22.73 cGy for a 100 mm 2 nuclear surface area). It is also the approximate annual dose contribution from GCR ions in deep space [69] and threshold dose identified for 56 Fe ion-induced in vitro neoplastic transformation [70]-although it should be noted that doses as low as 5 cGy of 1 GeV/n iron ions delivered at NSRL were shown to significantly increase primary fibroblast anchorage-independent growth frequencies [71]. A proton dose of 100 cGy was chosen as a potential dose to the hematopoietic blood-forming organs of astronauts during an intense solar particle event such as the August 1972 or October 1989 events [72,73]. ...
The stem cell compartment of the hematopoietic system constitutes one of the most radiosensitive tissues of the body and leukemias represent one of the most frequent radiogenic cancers with short latency periods. As such, leukemias may pose a particular threat to astronauts during prolonged space missions. Control of hematopoiesis is tightly governed by a specialized bone marrow (BM) microenvironment/niche. As such, any environmental insult that damages cells of this niche would be expected to produce pronounced effects on the types and functionality of hematopoietic/immune cells generated. We recently reported that direct exposure of human hematopoietic stem cells (HSC) to simulated solar energetic particle (SEP) and galactic cosmic ray (GCR) radiation dramatically altered the differentiative potential of these cells, and that simulated GCR exposures can directly induce DNA damage and mutations within human HSC, which led to leukemic transformation when these cells repopulated murine recipients. In this study, we performed the first in-depth examination to define changes that occur in mesenchymal stem cells present in the human BM niche following exposure to accelerated protons and iron ions and assess the impact these changes have upon human hematopoiesis. Our data provide compelling evidence that simulated SEP/GCR exposures can also contribute to defective hematopoiesis/immunity through so-called "biological bystander effects" by damaging the stromal cells that comprise the human marrow microenvironment, thereby altering their ability to support normal hematopoiesis.
... Importantly, unlike other radiation types in outer space, current shielding is unable to provide effective protection against energetic heavy ions raising further concerns about astronauts' health during and after prolonged space travel. 4 With increasing interest in space tourism, energetic heavy ion radiation exposure is of concern not only for astronauts but also for aspiring future space travelers at large. 5 The current study is focused on the immunity system because cells that have a rapid turnover rate such as bone marrow and immune cells are particularly sensitive to the effects of radiation. 6 Therefore, even a modest increase above the already high spontaneous incidence of impairment of the immune system after energetic heavy ion radiation exposure will have significant ramification not only for astronauts' health risk estimates but also for future human deep-space exploration planning. ...
High linear energy transfer radiation is known to deposit higher energy in tissues and cause greater toxicity than low-LET irradiation. Local immunosuppression is frequently observed after irradiation (IR). Dendritic cells (DCs) play important roles in the initiation and maintenance of the immune response. The dysfunction of DCs contributes to tumor evasion and growth. However, molecular mechanisms underlying the establishment of immune tolerance induced by heavy ion IR through this DC population are poorly understood. Therefore, here we report our findings on the dysfunction of bone marrow-derived dendritic cells (BMDCs) induced by iron ion radiation and promotions of expressions of JNK1/2/3, indoleamine 2, 3-dioxygenase 1 (IDO1), p-ERK1/2 and p38/MAPK; and decrease of IDO2, MHC class II, CD40, CD80 expressions and IFN-γ, TNF-α secretion after total-body IR in mice. JNK+IDO1+ BMDCs showed up-expression of p-ERK1/2 and p-p38/MAPK, reduced expression of MHC class II and CD80, and were not able to effectively stimulate allogeneic spleen T cells. Inhibition of IDO1 expressions could partly restore the function of BMDCs. In all, our study shows that elevated JNK and IDO1 expression induced by Fe ion IR resulted in dysfunction of BMDCs via p-p38/MAPK and p-ERK1/2 signal pathway, and may represent a new mechanism in radiation-induced immune tolerance. These findings provide important knowledge for the role of JNK/IDO1 signal pathway in dysfunction of BMDCs response to radiation.
... The deep space environment, where astronauts will spend considerable time during exploration class missions, includes heavy ions such as the Fe ions employed here. It has been estimated that 33% of the nuclei of cells in the human body will be traversed by one or more ions with Z>10 for a three-year mission in a heavily shielded configuration, e.g. to Mars, and that only about 6% would be traversed by two such ions over the duration of the mission [51]. Our results confirm and extend our findings with Ti ions [14] showing that even individual heavy ion traversals can lead to extensive genomic rearrangements in a subset of cells that survive in the normal tissue environment. ...
Exposure to a small number of high-energy heavy charged particles (HZE ions), as found in the deep space environment, could significantly affect astronaut health following prolonged periods of space travel if these ions induce mutations and related cancers. In this study, we used an in vivo mutagenesis assay to define the mutagenic effects of accelerated ⁵⁶Fe ions (1 GeV/amu, 151 keV/μm) in the mouse kidney epithelium exposed to doses ranging from 0.25 to 2.0 Gy. These doses represent fluences ranging from 1 to 8 particle traversals per cell nucleus. The Aprt locus, located on chromosome 8, was used to select induced and spontaneous mutants. To fully define the mutagenic effects, we used multiple endpoints including mutant frequencies, mutation spectrum for chromosome 8, translocations involving chromosome 8, and mutations affecting non-selected chromosomes. The results demonstrate mutagenic effects that often affect multiple chromosomes for all Fe ion doses tested. For comparison with the most abundant sparsely ionizing particle found in space, we also examined the mutagenic effects of high-energy protons (1 GeV, 0.24 keV/μm) at 0.5 and 1.0 Gy. Similar doses of protons were not as mutagenic as Fe ions for many assays, though genomic effects were detected in Aprt mutants at these doses. Considered as a whole, the data demonstrate that Fe ions are highly mutagenic at the low doses and fluences of relevance to human spaceflight, and that cells with considerable genomic mutations are readily induced by these exposures and persist in the kidney epithelium. The level of genomic change produced by low fluence exposure to heavy ions is reminiscent of the extensive rearrangements seen in tumor genomes suggesting a potential initiation step in radiation carcinogenesis.
... For groups of interacting cells, GCR traversals are much more frequent. The fluence of charged particles hitting the brain of an astronaut has been estimated several times in the past (Craven and Rycrof 1994;Curtis et al. 2000Curtis et al. , 1998Curtis et al. , 1989. One estimate is that during a 3-year mission to Mars at solar minimum (assuming the 1972 GCR spectrum), 20 million out of 43 million hippocampus cells and 230 thousand out of 1.3 million thalamus cell nuclei will be directly hit by one or more particles with charge Z>15 (Curtis et al. 2000(Curtis et al. , 1998Cucinotta et al. 2011 -see Table below in Section VI). ...
... Although HZE particles only account for less than 1% of the GCR particle 2luxes, they contribute signi2icantly to the severe biological effects due to their high atomic number, energy and intense ionization (5,7) . For a three-year mission, 3% of the cells of the human body would be traversed on average by one iron ion (8) . Therefore, heavy ions are considered as a major barrier to human space exploration. ...
The radiobiological effects of high atomic number and energy (HZE particles) ion beams are of interest for radioprotection in space and tumor radiotherapy. Space radiation mainly consists of heavy charged particles from protons to iron ions, which is distinct from common terrestrial forms of radiation. HZE particles pose a significant cancer risk to astronauts on prolonged space missions. With high delivered energies and intense ionization, HZE particles can damage not only the biological systems but also the shielding materials. HZE particles are more effective than low-LET radiation like γ- or X-rays to induce genetic mutation and cancer. On Earth, similar ions are being used for targeted cancer therapy due to the advantage of the inverse dose profile, with delivering higher doses to the tumor while keeping lower doses to the surrounding tissues. In this review, we focus on the recentinsights into the biological effects caused by HZE particles and the corresponding mechanism. We also discuss the current application of HZE particle in cancer therapy. Understanding the mechanisms underlying the repair of DNA damage induced by HZE particles contribute to accurately estimate the risks to human health associated with HZE particle exposure and to improve the effectiveness of tumor radiotherapy. © 2016, Novim Medical Radiation Institute. All rights reserved.
... (3). Cancer risk from exposure to the deep space radiation environment could constrain mission parameters for astronauts. ...
Clear mechanistic understanding of the biological processes elicited by radiation that increase cancer risk can be used to inform prediction of health consequences of medical uses, such as radiotherapy, or occupational exposures such as those of astronauts during deep space travel. Here we review the current concepts of carcinogenesis as a multicellular process during which transformed cells escape normal tissue controls, including the immune system, and establish a tumor microenvironment. We discuss the contribution of two broad classes of radiation effects that may increase cancer: radiation targeted effects (RTE) that occur as a result of direct energy deposition, e.g. DNA damage, and non-targeted effects (NTE) that result from changes in cell signaling, e.g. genomic instability. It is unknown whether the potentially greater carcinogenic effect of HZE particle radiation is a function of the relative contribution or extent of NTE, or due to unique NTE. We addressed this problem using a radiation/genetic mammary chimera mouse model of breast cancer. Our experiments suggest that NTE promote more aggressive cancers, as evidenced by increased growth rate, transcriptomic signatures and metastasis, and that HZE particle NTE are more effective than reference γ-radiation. Emerging evidence suggest that HZE irradiation dampens anti-tumor immunity. These studies raise concern that HZE radiation exposure not only increases the likelihood of developing cancer but also could promote progression to more aggressive cancer with a greater risk of mortality.
... The space radiation environment includes heavy ions, such as 56 Fe, 28 Si, 16 O, and 12 C, which are the major contributors to the dose in GCR. Among these heavy ions, 56 Fe ions are of particular concern, because they are the most densely ionizing particles present in relatively large amounts in GCR [2]. 56 Fe irradiation-induced cognitive changes often involve alterations in hippocampal function [3][4][5][6][7][8][9][10][11][12][13][14][15][16][17]. ...
... 45 -Normal commensal bacteria and fungi, as well as the ambient ones within the spaceship can mutate into virulent pathogens that might not respond to antibiotics. 46 The risk of infection is compounded because the immune system also appears to be altered in space. T-cell deficiencies, and latent viruses, such as Epstein-Barr and cytomegalovirus, have been reactivated 47 in astronauts who have been isolated on analogue missions in Antarctica. ...
... The fluence of charged particles hitting the brain of an astronaut has been estimated several times in the past (Craven and Rycroft, 1994;Curtis et al., 1989;Cucinotta et al., 1998). One estimate is that during a 3-year mission to Mars at solar minimum (assuming the 1972 spectrum of GCR), 20 million out of 43 million hippocampus cells and 230 thousand out of 1.3 million thalamus cell nuclei will be directly hit by one or more particles with charge Z>15 (Curtis et al., 1998;. ...
... While on earth low-LET radiation is predominant, astronauts traveling into outer space are exposed to high-LET energetic heavy ions (HZE) such as 12 C, 56 Fe and 28 Si, and the risk of CRC from HZE radiation exposure remains to be established. Energetic heavy ions contribute significantly towards dose equivalent of galactic cosmic radiation (GCR), and it has been predicted that during a Mars mission about 30% of the astronauts' cell will be hit by either the primary or the secondary tracts of heavy ions (4)(5)(6). Considering that CRC is still a major form of cancer in the USA and low-LET radiation is a CRC risk factor, high-LET radiation exposure could potentially pose a greater risk of developing CRC. Therefore, assessing CRC risks associated with energetic heavy ion exposures is important for health of astronauts undertaking long-duration space missions and safe exploration of outer space. ...
Purpose:
There are uncertainties associated with the prediction of colorectal cancer (CRC) risk from highly energetic heavy ion (HZE) radiation. We undertook a comprehensive assessment of intestinal and colonic tumorigenesis induced after exposure to high linear energy transfer (high-LET) HZE radiation spanning a range of doses and LET in a CRC mouse model and compared the results with the effects of low-LET γ radiation.
Methods and materials:
Male and female APC(1638N/+) mice (n=20 mice per group) were whole-body exposed to sham-radiation, γ rays, (12)C, (28)Si, or (56)Fe radiation. For the >1 Gy HZE dose, we used γ-ray equitoxic doses calculated using relative biological effectiveness (RBE) determined previously. The mice were euthanized 150 days after irradiation, and intestinal and colon tumor frequency was scored.
Results:
The highest number of tumors was observed after (28)Si, followed by (56)Fe and (12)C radiation, and tumorigenesis showed a male preponderance, especially after (28)Si. Analysis showed greater tumorigenesis per unit of radiation (per cGy) at lower doses, suggesting either radiation-induced elimination of target cells or tumorigenesis reaching a saturation point at higher doses. Calculation of RBE for intestinal and colon tumorigenesis showed the highest value with (28)Si, and lower doses showed greater RBE relative to higher doses.
Conclusions:
We have demonstrated that the RBE of heavy ion radiation-induced intestinal and colon tumorigenesis is related to ion energy, LET, gender, and peak RBE is observed at an LET of 69 keV/μm. Our study has implications for understanding risk to astronauts undertaking long duration space missions.
... Linear energy transfer (LET), expressed in keV/mm, is the term used to classify radiation quality in terms of high versus low LET. With the exception of protons, the charged particles found in space fall into the high LET category [1,2]. These fully ionized, highly energetic nuclei are referred to as HZE particles, derived from high (H) atomic number (Z) and energy (E). ...
Exposure to the space radiation environment poses risks for a range of deleterious health effects due to the unique types of radiation encountered. Galactic cosmic rays are comprised of a spectrum of highly energetic nuclei that deposit densely ionizing tracks of damage along the particle trajectory. These tracks are distinct from those generated by the more sparsely ionizing terrestrial radiations, and elicit complex cellular damage when charged particles traverse the tissues of the body. The exquisite radiosensitivity of multipotent neural stem and progenitor cells found within the neurogenic regions of the brain predispose the central nervous system to elevated risks for radiation induced sequelae. Here we show that human neural stem cells (hNSC) exposed to different charged particles at space relevant fluences exhibit significant and persistent oxidative stress. Radiation induced oxidative stress was found to be most dependent on total dose rather than on the linear energy transfer of the incident particle. The use of redox sensitive fluorogenic dyes possessing relative specificity for hydroxyl radicals, peroxynitrite, nitric oxide (NO) and mitochondrial superoxide confirmed that most irradiation paradigms elevated reactive oxygen and nitrogen species (ROS and RNS, respectively) in hNSC over a 1 week interval following exposure. Nitric oxide synthase (NOS) was not the major source of elevated nitric oxides, as the use of NOS inhibitors had little effect on NO dependent fluorescence. Our data provide extensive evidence for the capability of low doses of charged particles to elicit marked changes in the metabolic profile of irradiated hNSC. Radiation induced changes in redox state may render the brain more susceptible to the development of neurocognitive deficits that could affect an astronaut’s ability to perform complex tasks during extended missions in deep space.
... High LET particles, which comprise 85% of cosmic rays are one of the biggest health concerns in manned space explorations. It has been estimated (Curtis and Letaw, 1989) that on a 3 year mission to deep space, a mammalian cell nucleus of area 100 μm 2 behind aluminum shielding of 4 g/cm 2 would on average be traversed by 400 protons, 0.6 carbon nuclei, and 0.03 iron nuclei. The latter numbers may seem small but it does represent 3% of all cells in the body (Setlow, 1999). ...
High LET particle irradiation has several potential advantages over γ-rays such as p53-independent response. The purpose of this work is to disclose the effect of p53 on the bystander effect induced by different LET irradiations and underlying mechanism. Lymphocyte cells of TK6 (wild type p53) and HMy2.CIR (mutated p53) were exposed to either low or high LET irradiation, then their mitochondrial dysfunction and ROS generation were detected. The micronuclei (MN) induction in HL-7702 hepatocytes co-cultured with irradiated lymphocytes was also measured. It was found that the mitochondrial dysfunction, p66Shc activation, and intracellular ROS were enhanced in TK6 but not in HMy2.CIR cells after γ-ray irradiation, but all of them were increased in both cell lines after carbon and iron irradiation. Consistently, the bystander effect of MN formation in HL-7702 cells was only triggered by γ-irradiated TK6 cells but not by γ-irradiated HMy2.CIR cells. But this bystander effect was induced by both lymphocyte cell lines after heavy ion irradiation. PFT-μ, an inhibitor of p53, only partly inhibited ROS generation and bystander effect induced by 30 keV/μm carbon-irradiated TK6 cells but failed to suppress the bystander effect induced by the TK6 cells irradiated with either 70 keV/μm carbon or 180 keV/μm iron. The mitochondrial inhibitors of rotenone and oligomycin eliminated heavy ion induced ROS generation in TK6 and HMy2.CIR cells and hence diminished the bystander effect on HL-7702 cells. These results clearly demonstrate that the bystander effect is p53-dependent for low LET irradiation, but it is p53-independent for high LET irradiation which may be because of p53-independent ROS generation due to mitochondrial dysfunction.
... Formisano et al. (1990) calculated the temperatures and densities of several of the observed ions from measurements with the Giotto Johnstone Plasma Analyzer instrument (JPA; Johnstone et al. 1986). All these observations revealed multiple boundaries and distinct regions in this interaction (see Altwegg et al. 1993;Häberli et al. 1995Häberli et al. , 1996d'Uston et al. 1987), starting from the comet's bow shock all the way to the cavity, which is the magnetic field-free region in the innermost coma (see Cravens 1989). The boundary of the diamagnetic cavity, also called the contact surface or ionopause, is located just outside the inner shock at which the cometary plasma is first entrained in the more or less radially outflowing neutral gas and then transitions from supersonic to subsonic speeds. ...
The interaction of comets with the solar wind has been the focus of many studies including numerical modeling. We compare the results of our multifluid MHD simulation of comet 1P/Halley to data obtained during the flyby of the European Space Agency's Giotto spacecraft in 1986. The model solves the full set of MHD equations for the individual fluids representing the solar wind protons, the cometary light and heavy ions, and the electrons. The mass loading, charge-exchange, dissociative ion-electron recombination, and collisional interactions between the fluids are taken into account. The computational domain spans over several million kilometers, and the close vicinity of the comet is resolved to the details of the magnetic cavity. The model is validated by comparison to the corresponding Giotto observations obtained by the Ion Mass Spectrometer, the Neutral Mass Spectrometer, the Giotto magnetometer experiment, and the Johnstone Plasma Analyzer instrument. The model shows the formation of the bow shock, the ion pile-up, and the diamagnetic cavity and is able to reproduce the observed temperature differences between the pick-up ion populations and the solar wind protons. We give an overview of the global interaction of the comet with the solar wind and then show the effects of the Lorentz force interaction between the different plasma populations.
... Ground-based studies already indicate that exposure to space radiation in the form of protons or high-energy charged particles (HZE particles) can induce profound neurobehavioral changes in rodents. Exposure to 56 Fe particles, the densest HZE ion present in cosmic rays (3), can intensify the degeneration of hippocampal-dependent memory (4), accelerate deficiencies in spatial learning and memory (5,6), reduce hippocampal neurogenesis (7), impair spatial learning (8) and attentional set shifting (9) and produce structural alterations in brain regions important for memory consolidation such as the entorhinal cortex and thalamus (10). 56 Fe particles, gamma rays and protons can also produce deficits in several neurotransmitter systems, including dopamine-mediated behaviors such as amphetamine-induced conditioned taste aversion learning (11)(12)(13), conditioned place preference (14,15), motor performance (16,17), sensitivity to haloperidolinduced catalepsy (18), changes in oxotremorine-enhanced K(þ)-evoked dopamine release (17,19), alterations in glutamate transport in neurons and astrocytes (20), and preand postsynaptic changes in glutamate signaling (21). ...
To assess the possible neurobehavioral performance risks to astronauts from living in a space radiation environment during long-duration exploration missions, the effects of head-only proton irradiation (150 MeV/n) at low levels (25-50 cGy, approximating an astronaut's exposure during a 2-year planetary mission) were examined in adult male Long-Evans rats performing an analog of the human psychomotor vigilance test (PVT). The rodent version of PVT or rPVT tracks performance variables analogous to the human PVT, including selective attention/inattention, inhibitory control ("impulsivity") and psychomotor speed. Exposure to head-only proton radiation (25, 50, 100 or 200 cGy) disrupted rPVT performance (i.e., decreased accuracy, increased premature responding, elevated lapses in attention and slowed reaction times) over the 250 day testing period. However, the performance decrements only occurred in a subgroup of animals at each exposure level, that is, the severity of the rPVT performance deficit was unrelated to proton exposure level. Analysis of brain tissue from irradiated and control rats indicated that only rats with rPVT performance deficits displayed changes in the levels of the dopamine transporter and, to a lesser extent, the D2 receptor. Additional animals trained to perform a line discrimination task measuring basic and reversal learning showed no behavioral effects over the same exposure levels, suggesting a specificity of the proton exposure effects to attentional deficits and supporting the rPVT as a sensitive neurobehavioral assay.
... Although protons are the most prevalent particle in GCR, the less abundant heavier ions (1%) are more effective biologically. During a 3-year flight in extramagnetospheric space, 3% of the cells of the human body would be traversed on average by one Fe ion [1]. The unique pattern of energy deposition incurred by HZE particle traversal is of primary interest for evaluating the biological effects of the GCR on astronauts [2,3]. ...
This review focuses on recent experimental and modeling studies that attempt to define the physiological context in which high linear energy transfer (LET) radiation increases epithelial cancer risk and the efficiency with which it does so. Radiation carcinogenesis is a two-compartment problem: ionizing radiation can alter genomic sequence as a result of damage due to targeted effects (TE) from the interaction of energy and DNA; it can also alter phenotype and multicellular interactions that contribute to cancer by poorly understood non-targeted effects (NTE). Rather than being secondary to DNA damage and mutations that can initiate cancer, radiation NTE create the critical context in which to promote cancer. Systems biology modeling using comprehensive experimental data that integrates different levels of biological organization and time-scales is a means of identifying the key processes underlying the carcinogenic potential of high-LET radiation. We hypothesize that inflammation is a key process, and thus cancer susceptibility will depend on specific genetic predisposition to the type and duration of this response. Systems genetics using novel mouse models can be used to identify such determinants of susceptibility to cancer in radiation sensitive tissues following high-LET radiation. Improved understanding of radiation carcinogenesis achieved by defining the relative contribution of NTE carcinogenic effects and identifying the genetic determinants of the high-LET cancer susceptibility will help reduce uncertainties in radiation risk assessment.
... The effects of microgravity on bacterial physiology have been well studied in comparison to other parameters associated with space flight, although this body of work sheds little light on possible microbial responses to gravitational fluctuations that will be encountered on a Mars mission: a period of microgravity followed by zero gravity, then a significant interval under the influence of the Martian gravitational field of 0.38 g before a repetition of the flight conditions on the return transit. The risks to the crew from a continuous flux of high-energy, ionizing cosmic ray nuclei (HZE) -leftovers from collapsing stars and supernova explosions -and occasional but intense fluxes of solar energetic particles, primarily protons and alpha particles, have been well recognized [53,54], but they may also affect microbes in ways that are barely understood. This gap in our knowledge is unlikely to be filled by conducting radiation exposure experiments aboard the ISS, as the station sits inside Earth's magnetic field. ...
Manned missions to Mars will result in a diminution of immune status among the
crew and cause profound changes to the composition of the bacterial flora in the intestinal
tract, nasal passages and upper airways, leading to an increased risk of infection.
Experiments conducted during short-term flight and aboard orbiting space stations
suggest that growth in microgravity leads to increases in bacterial antibiotic resistance
and to cell wall changes. Growth under low-shear modelled microgravity (LSMMG) has
convincingly shown that a reduced gravitational field acts as an environmental signal for
expression of enhanced bacterial virulence in Gram-negative pathogens such as
Salmonella enterica. Recent microbiological surveillance of the International Space
Station has identified members of the bacterial genus Staphylococcus as major
contaminants of working and living quarters. We therefore examined the effect of
LSMMG on parameters of antibiotic susceptibility and virulence in clinical isolates of
Staphylococcus aureus. This bacterial species is likely to be the most problematical
staphylococcal opportunist encountered in transit. Three strains were grown under
LSMMG in a High Aspect Ratio Vessel and compared with cells grown under normal
gravity (NG) in the same vessel. There were no significant differences in the antibiotic
susceptibility, growth rate or morphology of staphylococci grown under LSMMG
compared to NG. LSMMG-induced reductions in the synthesis of the pigment
staphyloxanthin were noted. Strains secreted less protein under LSMMG and reductions
in hemolysin secretion were found. We noted reduced expression of hemolysins under
LSMMG conditions; these virulence determinants are key components of the
staphylococcal armamentarium, enabling the pathogen to cause damage to host cells and
tissues. Thus, in contrast to published data on Gram-negative pathogens, modelled
microgravity reduces the expression of key virulence determinants of S. aureus. The relevance of these findings to the risk of infection is discussed in relation to other factors
that will impinge on the success of Martian expeditions.
The present study is a preliminary step towards the detection of cosmic rays at higher altitude in the Great Himalayan range. Present work is an attempt to see the possibility of the presence of cosmic rays at a height of 3800 m from the sea level in the Great Himalayan range. An experiment was planned for the search of galactic cosmic rays (GCR) using CR39 track etch detectors at the Patsio DRDO (Defence Research and Development Organization) laboratory in the Great Himalayan range, India at a height of 3800 m from the sea level and 32° 45′ N, 77° 15′ E. CR39 detectors were etched in 8N NaOH solution + 3% ethyl alcohol at 70 °C to visualize the tracks produced in the exposed detectors under optical microscope. A detection threshold of CR39 detector down to Z = 18 (Z/β ~ 27) was obtained. After scanning, fine tracks were observed and it was concluded that that high Z cosmic rays may be present at an altitude of 3800 m from the sea level in the Great Himalayan range.
Space radiation poses a substantial health risk to humans traveling beyond Earth’s orbit to the Moon and Mars. As microbes come with us to space as model organisms for studying radiation effects, a computational model simulating those effects on microorganisms could enable us to better design and interpret those experiments. Here we present Agent-based Model for Microbial Populations Exposed to Radiation (AMMPER), which simulates the effects of protons, a major component of deep-space radiation, on budding yeast ( Saccharomyces cerevisiae ) growth. The model combines radiation track structure data from the RITRACKS package with novel algorithms for cell replication, motion, damage, and repair. We demonstrate that AMMPER qualitatively reproduces the effects of 150 MeV proton radiation on growth rate, but not lag time, of wild type and DNA repair mutant yeast strains. The variance in AMMPER’s results is consistent with the variance in experimental results, suggesting that AMMPER can recapitulate the stochasticity of empirical experiments. Finally, we used AMMPER to predict responses to deep space radiation that may be tested in future experiments. A user-friendly, open-source, extendable Python package for studying the relationship between single-particle radiation events and population-level responses, AMMPER can facilitate the basic research necessary to ensure safe and sustainable exploration of deep space.
Astronauts participating in prolonged space missions constitute a population of individuals who are at an increased risk for cataractogenesis due to exposure to densely ionizing charged particles. Using a rat model, we have previously shown that after irradiation of eyes with either low-linear energy transfer (LET) 60Co γ rays or high-LET 56Fe particles, the rate of progression of anterior and posterior subcapsular cataracts was significantly greater in ovariectomized females implanted with 17-β-estradiol (E2) compared to ovariectomized or intact rats. However, our additional low-LET studies indicated that cataractogenesis may be a modifiable late effect, since we have shown that the modulation of cataractogenesis is dependent upon the timing of administration of E2. Interestingly, we found that E2 protected against cataractogenesis induced by low-LET radiation, but only if administered after the exposure; if administered prior to and after irradiation, for the entire period of observation, then E2 enhanced progression and incidence of cataracts. Since most radioprotectors tested to date are unsuccessful in protecting against the effects of high-LET radiation, we wished to determine whether the protection mediated by E2 against radiation cataractogenesis induced by low-LET radiation would also be observed after high-LET irradiation. Female 56-day-old Sprague-Dawley rats were treated with E2 at various times relative to the time of single-eye irradiation with 2 Gy of 56Fe ions. We found that administration of E2 before irradiation and throughout the lifetime of the rat enhanced cataractogenesis compared to ovariectomized animals. The enhancing effect was slightly reduced when estrogen was removed after irradiation. However, in contrast to what we observed after γ-ray irradiation, there was no inhibition of cataractogenesis if E2 was administered only after 56Fe-ion irradiation. We conclude that protection against cataractogenesis by estrogen is dependent upon the type and ionization density of radiation that the lens was exposed to. The lack of inhibition of radiation cataractogenesis in rats that receive E2 treatment after high-LET irradiation may be attributed to the qualitative differences in the types of DNA damage induced with high-LET radiation compared to low-LET radiation or how damage may be modified at the DNA or tissue level after irradiation.
Purpose:
Proton radiation is a major component of the radiation field in outer space and is used clinically in radiation therapy of resistant cancers. Although epidemiologic studies in atom bomb survivors and radiologic workers have established radiation as a risk factor for colorectal cancer (CRC), we have yet to determine the risk of CRC posed by proton radiation owing to a lack of sufficient human or animal data. The purpose of the current study was to quantitatively and qualitatively characterize differential effects of acute and fractionated high-energy protons on colorectal carcinogenesis.
Methods and materials:
We used ApcMin/+ mice, a well-studied CRC model, to examine acute versus fractionated proton radiation-induced differences in intestinal tumorigenesis and associated signaling pathways. Mice were exposed to 1.88 Gy of proton radiation delivered in a single fraction or in 4 equal daily fractions (0.47 Gy × 4). Intestinal tumor number and grade were scored 100 to 110 days after irradiation, and tumor and tumor-adjacent normal tissues were harvested to assess proliferative β-catenin/Akt pathways and DNA damage response and repair pathways relevant to colorectal carcinogenesis.
Results:
Significantly higher intestinal tumor number and grade, along with decreased differentiation, were observed after acute radiation relative to fractionated radiation. Acute protons induced upregulation of β-catenin and Akt pathways with increased proliferative marker phospho-histone H3. Increased DNA damage along with decreased DNA repair factors involved in mismatch repair and nonhomologous end joining were also observed after exposure to acute protons.
Conclusions:
We show increased γH2AX, 53BP1, and 8-oxo-dG, suggesting that increased ongoing DNA damage along with decreased DNA repair factors and increased proliferative responses could be triggering a higher number of intestinal tumors after acute relative to fractionated proton exposures in ApcMin/+ mice. Taken together, our data suggest greater carcinogenic potential of acute relative to fractionated proton radiation.
Carbon irradiation due to its higher biological effectiveness relative to photon radiation is a concern for toxicity to proliferative normal gastrointestinal (GI) tissue after radiotherapy and long-duration space missions such as mission to Mars. Although radiation-induced oxidative stress is linked to chronic diseases such as cancer, effects of carbon irradiation on normal GI tissue have not been fully understood. This study assessed and compared chronic oxidative stress in mouse intestine and colon after different doses of carbon and γ radiation, which are qualitatively different. Mice (C57BL/6J) were exposed to 0.5 or 1.3 Gy of γ or carbon irradiation, and intestinal and colonic tissues were collected 2 months after irradiation. While part of the tissues was used for isolating epithelial cells, tissue samples were also fixed and paraffin embedded for 4-µm thick sections as well as frozen for biochemical assays. In isolated epithelial cells, reactive oxygen species and mitochondrial status were studied using fluorescent probes and flow cytometry. We assessed antioxidant enzymes and nicotinamide adenine dinucleotide phosphate (NADPH) oxidase activity in tissues and formalin fixed tissue sections were stained for 4-hydroxynonenal, a lipid peroxidation marker. Data show that mitochondrial deregulation, increased NADPH oxidase activity, and decreased antioxidant activity were major contributors to carbon radiation-induced oxidative stress in mouse intestinal and colonic cells. When considered along with higher lipid peroxidation after carbon irradiation relative to γ-rays, our data have implications for functional changes in intestine and carcinogenesis in colon after carbon radiotherapy as well as space travel.
Space electronic warfare (SEW) implies tactical advantages in electronic attacks, electronic protection and electronic support using satellites in low-earth orbit (LEO) for surveillance, communications or positioning, or denying the enemy these activities.
Travel into outer space is fraught with risk of exposure to energetic heavy ion radiation such as ⁵⁶Fe ions, which due to its high linear energy transfer (high-LET) characteristics deposits higher energy per unit volume of tissue traversed and thus more damaging to cells relative to low-LET radiation such as γ rays. However, estimates of human health risk from energetic heavy ion exposure are hampered due to lack of tissue specific in vivo molecular data. We investigated long-term effects of ⁵⁶Fe radiation on adipokines and insulin-like growth factor 1 (IGF1) signaling axis in mouse intestine and colon. Six- to eight-week-old C57BL/6J mice were exposed to 1.6 Gy of ⁵⁶Fe ions. Serum and tissues were collected up to twelve months post-irradiation. Serum was analyzed for leptin, adiponectin, IGF1, and IGF binding protein 3. Receptor expressions and downstream signaling pathway alterations were studied in tissues. Irradiation increased leptin and IGF1 levels in serum, and IGF1R and leptin receptor expression in tissues. When considered along with upregulated Jak2/Stat3 pathways and cell proliferation, our data supports the notion that space radiation exposure is a risk to endocrine alterations with implications for chronic pathophysiologic changes in gastrointestinal tract.
The galactic cosmic ray (GCR) simulator at the NASA Space Radiation Laboratory (NSRL) is intended to deliver the broad spectrum of particles and energies encountered in deep space to biological targets in a controlled laboratory setting. In this work, certain aspects of simulating the GCR environment in the laboratory are discussed. Reference field specification and beam selection strategies at NSRL are the main focus, but the analysis presented herein may be modified for other facilities and possible biological considerations. First, comparisons are made between direct simulation of the external, free space GCR field and simulation of the induced tissue field behind shielding. It is found that upper energy constraints at NSRL limit the ability to simulate the external, free space field directly (i.e. shielding placed in the beam line in front of a biological target and exposed to a free space spectrum). Second, variation in the induced tissue field associated with shielding configuration and solar activity is addressed. It is found that the observed variation is likely within the uncertainty associated with representing any GCR reference field with discrete ion beams in the laboratory, given current facility constraints. A single reference field for deep space missions is subsequently identified. Third, a preliminary approach for selecting beams at NSRL to simulate the designated reference field is presented. This approach is not a final design for the GCR simulator, but rather a single step within a broader design strategy. It is shown that the beam selection methodology is tied directly to the reference environment, allows facility constraints to be incorporated, and may be adjusted to account for additional constraints imposed by biological or animal care considerations. The major biology questions are not addressed herein but are discussed in a companion paper published in the present issue of this journal. Drawbacks of the proposed methodology are discussed and weighed against alternative simulation strategies.
Before sending out astronauts on an interplanetary mission, we need to investigate how the conditions in space affect human health. The International Space Station is therefore of huge importance to ensure the health of a spaceship crew travelling to other planets
A unique feature of the space radiation environment is the presence of high-energy charged particles, which can be significantly hazardous to space flight crews who are exposed during a mission. Health risks associated with high-LET radiation exposure include cognitive injury. The pathogenesis of this injury is unknown but may involve modifications to dendritic structure and/or alterations in dendritic spine density and morphology. In this study, 24 two-month-old C57BL6/J male mice were either whole-body irradiated with 0.5 Gy (56)Fe (600 MeV/n; n = 12) or sham irradiated (n = 12). Three months postirradiation animals were tested for locomotor activity and habituation. After behavioral testing, animals were euthanized and the brains were flash frozen. Compared to sham-irradiated mice, irradiated mice moved less when first introduced to the environment, although they did recognize the environment when re-exposed to it one day later. Exposure to (56)Fe radiation significantly compromised the dendritic architecture and reduced spine density throughout the hippocampal tri-synaptic network. To our knowledge, this data represents the first reported evidence that high-LET radiation has deleterious effects on mature neurons associated with hippocampal learning and memory.
Exposure to high-energy charged particles (HZE ions) at low fluence could significantly affect astronaut health after prolonged missions in deep space by inducing mutations and related cancers. We tested the hypothesis that the mutagenic effects of HZE ions could be detected at low fluence in a mouse model that detects autosomal mutations in vivo. Aprt heterozygous mice were exposed to 0.2, 0.4 and 1.4 Gy of densely ionizing (48)Ti ions (1 GeV/amu, LET = 107 keV/μm). We observed a dose-dependent increase in the Aprt mutant fraction in kidney epithelium at the two lowest doses (an average of 1 or 2 particles/cell nucleus) that plateaued at the highest dose (7 particles/cell nucleus). Mutant cells were expanded to determine mutation spectra and translocations affecting chromosome 8, which encodes Aprt. A PCR-based analysis for loss of heterozygosity (LOH) events on chromosome 8 demonstrated a significant shift in the mutational spectrum from Ti ion exposure, even at low fluence, by revealing "radiation signature" mutations in mutant cells from exposed mice. Likewise, a cytogenetic assay for nonreciprocal chromosome 8 translocations showed an effect of exposure. A genome-wide LOH assay for events affecting nonselected chromosomes also showed an effect of exposure even for the lowest dose tested. Considered in their entirety, these results show that accelerated (48)Ti ions induce large mutations affecting one or more chromosomes at low dose and fluence.
Periodic comets move around the Sun on elliptical orbits. As such comet 67P/Churyumov-Gerasimenko (hereafter 67P) spends a portion of time in the inner solar system where it is exposed to increased solar insolation. Therefore given the change in heliocentric distance, in case of 67P from aphelion at 5.68 AU to perihelion at ~1.24 AU, the comet’s activity—the production of neutral gas and dust—undergoes significant variations. As a consequence, during the inbound portion, the mass loading of the solar wind increases and extends to larger spatial scales. This paper investigates how this interaction changes the character of the plasma environment of the comet by means of multifluid MHD simulations. The multifluid MHD model is capable of separating the dynamics of the solar wind ions and the pick-up ions created through photoionization and electron impact ionization in the coma of the comet. We show how two of the major boundaries, the bow shock and the diamagnetic cavity, form and develop as the comet moves through the inner solar system. Likewise for 67P, although most likely shifted back in time with respect to perihelion passage, this process is reversed on the outbound portion of the orbit. The presented model herein is able to reproduce some of the key features previously only accessible to particle-based models that take full account of the ions’ gyration. The results shown herein are in decent agreement to these hybrid-type kinetic simulations.
Exospheric neutral atoms and molecules (primarily N2, with trace amounts of CH4 and CO according to our current understanding of Pluto's atmosphere) escape from Pluto and travel into interplanetary space for millions of kilometers. Eventually, the neutrals are ionized by solar EUV photons and/or by collisions with solar wind electrons. The mass-loading associated with this ion pick-up is thought to produce a comet-like interaction of the solar wind with Pluto. Within a few thousand kilometers of Pluto the solar wind interaction should lead to a magnetic field pile-up and draping, as it does around other “non-magnetic” bodies such as Venus and comets. The structure of plasma regions and boundaries will be greatly affected by large gyroradii effects and the extensive exosphere. Energetic plasma should disappear from the flow within radial distances of a few thousand kilometers due to charge exchange collisions. An ionosphere should be present close to Pluto with a composition that is determined both by the primary ion production and ion-neutral chemistry. One question discussed in the paper is whether or not the ionosphere has a Venus-like sharply defined ionopause boundary or a diamagnetic cavity such as that found around comet Halley. Simple physical estimates of plasma processes and structures in the collision-dominated region are made in this paper and predictions are made for the New Horizons mission.
Two-dimensional hybrid simulations with particle ions and fluid electrons are used to calculate the kinetic evolution of the self-consistent flow around a two-dimensional obstacle with zero intrinsic magnetic field. Plasma outflow from the obstacle is used to establish a boundary layer between the incoming solar wind and the outgoing plasma. Because the self-consistent flow solution, a velocity shear is naturally set up at this interface, and since the magnetic field for these simulations is transverse to this flow, the Kelvin-Helmholtz (K-H) instability can be excited at low-velocity shear. Simulations demonstrate the existence of the instability even near the subsolar location, which normally is thought to be stable to this instability. The apparent reason for this result is the overall time dependence at the boundary layer, which gives rise to a Raleigh-Taylor like instability which provides seed perturbations for the K-H instability. These results are directly applicable to Venus, comets, artificial plasma releases, and laser target experiments. This result has potentially important ramifications for the interpretation of observational results as well as for an estimation of the cross-field transport. The results suggest that the K-H instability may play a role in dayside processes and the Venus ionopause, and may exist within the context of more general situations, for example, the Earth`s magnetopause. 33 refs., 6 figs.
It has recently been recognized that a single intensely ionizing particle can alter the information stored in a modern semiconductor memory and possibly do permanent damage to the microelectronic circuit involved. Such particles are common in nature and abundant in space. This report describes the natural particle environment in which modern space-borne electronics must operate, and provides a simple but accurate empirical model of that environment.
This chapter is intended to provide a bridge between the physics of the particle energy spectra that are calculated within the bodies of space travelers and the chemical and biological effects that may be caused by the radiation deposited as the particles penetrate.
It has generally been agreed that one of the most important radiation-induced risks that must be faced on extended manned spaceflight is that of cancer induction. In this chapter, we present a brief review of the data on neoplastic cell transformation in in vitro cell lines at low dose rates for both low and high LET radiation. We discuss whether these data have implications for the very protracted periods envisaged for space missions.
The dose and dose equivalent from galactic cosmic radiation outside the magnetosphere have been computed. Each of the principal radiation components were considered. These include primary cosmic rays, spallation fragments of the heavy ions, and secondary products (protons, neutrons, alphas, and recoil nuclei) from interactions in tissue. COnventional quality factors were used in converting from dose to dose equivalent.
Three mission environments have been considered: free space, the lunar surface, and the martian surface. The annual dose equivalents to the blood-forming organs in these environments are approximately 500 mSv, 250 mSv, and 120 mSv, respectively (1 mSv = 0.1 rem). The dose on the lunar surface is one-half of free space because there is only a single hemisphere of exposure. The dose on the martian surface is half again the dose on the moon because of the shielding provided by a thin, carbon dioxide atmosphere.
Dose versus aluminum shielding thickness functions have been computed for the free space exposure. Galactic cosmic radiation is energetic and highly penetrating. 30 cm of aluminum shielding reduces the dose equivalent 25% to 40% (depending on the phase of the solar cycle). Aiming for conformity with the draft NCRP annual dose limit for Space Station crew members, which is 500 mSv yr−1, we recommend 7.5 cm of aluminum shielding in all habitable areas of spacecraft designed for long-duration missions outside Earth’s magnetosphere. This shielding thickness reduces the galactic cosmic ray dose and diminishes the risk to astronauts from energetic particle events.
The physical data required to evaluate the radiation hazard from heavy galactic cosmic rays to astronauts on extended missions are discussed. The spectral characteristics, nuclear interaction parameters, and track structure of particles are emphasized. The data on the lower energy portion of the differential spectrum of the iron group and nuclear fragmentation in tissue and aluminum are tested, and results are shown.
On the ambitious forays into space currently being contemplated, astronauts would encounter unfamiliar radiation environments. The risk of undue exposure would be diminished by spacecraft shielding.
The microdosimetric distribution of event sizes, especially for small exposures and high-LET radiation, represents both a fractional involvement of the exposed cell population and variable amounts of energy transferred to the "hit" cells. To determine the fraction of cells that will respond quantally (be transformed) after receiving a hit of a given size, a hit size effectiveness function (HSEF) which appears to have a threshold has been derived from experimental data for pink mutations in Tradescantia. The value of the HSEF at each event size, multiplied by the fractional number of cells hit at that event size, and summed over all event sizes, yields a single value representing the fractional number of quantally responding cells and thus the population impairment for a given exposure. The HSEF can be obtained by unfolding (deconvoluting) several sets of biological and microdosimetric data obtained with radiation of overlapping event size distributions.
In evaluating the hazard from a source of mixed radiation, it is necessary to determine the importance of the highly ionizing component. Calculations are presented that indicate the importance of this component in the solar-particle radiation environment within a space capsule. Shielding thickness and particle spectrum shape both are important in determining the extent of the hazard. The concept of fractional cell lethality (FCL), the fractional number of cells inactivated in an organ, is introduced to circumvent the inherent disadvantages in the Quality Factor concept when applied to the evaluation of the space radiation hazard. It is shown as an example that up to 7 per cent of the kidney cells in a seated astronaut could have been inactivated during the giant solar-particle event of 12 November 1960. Information on accumulated damage to critical nonreproducing cells, such as neural or retinal cells, is lacking. Perhaps such damage will constitute the bulk of the hazard for space missions of long duration, in which case the FCL concept may provide a sound basis for evaluating the hazard on these missions. (C)1966Health Physics Society
This study has examined the effect of dose rate or fractionation on the carcinogenic effects of fission neutrons with emphasis on the dose range below 50 rad. The induction of lung adenocarcinomas, mammary adenocarcinomas, and ovarian tumors in female BALB/c mice was examined after whole-body neutron irradiation delivered at a high dose rate as a single exposure, or delivered as two equal fractions separated by intervals of 24 hr or 30 days and compared these effects to those after neutron irradiation at low dose rates. The dose responses for ovarian tumorigenesis after the split-dose fractionation regimen were similar to that observed after single high-dose-rate neutron exposure. However, lowering the dose rate reduced the incidence over the dose range of 0-50 rad. For lung and mammary tumors the results were more complex. These data suggest that fractionation and dose-rate effects are different for different tumor types presumably because of the different mechanisms of tumorigenesis that may be involved.
The neoplastic transformation of C3H 10T1/2 cells induced by fission-spectrum neutrons delivered at a high dose rate is linear up to 40 cGy. Reducing the dose rate increases the frequency of transformation in the low dose region. At a dose rate of 0.086 cGy min-1, the initial part of the induction curve remains linear but it has a slope 9-fold greater than the initial part of the curve at a high dose rate.
Among cosmic rays, the heavy nuclei ( HZE particles) like iron provide the dominant contribution to the dose equivalent during exposures in space. The LET distributions and radiation doses of cosmic-ray components have been calculated--with and without the quality factors--for a set of shielding and tissue self-shielding penetration depths. The relative contributions of heavy ions among solar flare particles to the dose equivalent are also explored. The transport calculations of the nuclei in air, shielding materials, and biological tissue-like material were carried out using the partial and total nuclear cross-section equations and nuclear propagation codes of Silberberg and Tsao . Outside the magnetosphere , at solar minimum, the product of the unshielded dose and the quality factors of cosmic-ray protons and heavy nuclei with atomic number Z greater than or equal to 6 are about 5 and 47 rem/year, respectively. With 4 g/cm2 aluminum shielding and at a depth of 5 cm in a biological phantom of 30 cm diameter, the respective values of the dose equivalents are about 4 and 11 rem/year. Due to the hard spectrum of cosmic rays, the attenuation of protons thus is relatively modest, while that of heavy nuclei is larger due to the larger interaction cross section. The dose equivalent of neutrons in the shielded case mentioned above is similar to that of protons. The biological risks are tentatively assessed in terms of the BEIR 1980 report. Uncertainties in risks due to possible large RBE values at low doses of high-LET radiation and due to the microbeam nature of damage by heavy ions are pointed out. Certain experiments and studies by radiobiologists are suggested for reducing the uncertainties in the estimates of the risks.
In order to make an assessment of radiation risk during manned missions in space, it is necessary first to have as accurate an estimation as possible of the radiation environment within the spacecraft to which the astronauts will be exposed. Then, with this knowledge and the inclusion of body self-shielding, estimations can be made of absorbed doses for various body organs (skin, eye, blood-forming organs, etc.). A review is presented of our present knowledge of the radiation environments and absorbed doses expected for several space mission scenarios selected for our development of the new radiation protection guidelines. The scenarios selected are a 90-day mission at an altitude (450 km) and orbital inclinations (28.5 degrees, 57 degrees and 90 degrees) appropriate for NASA's Space Station, a 15-day sortie to geosynchronous orbit and a 90-day lunar mission. All scenarios chosen yielded dose equivalents between five and ten rem to the blood forming organs if no large solar particle event were encountered. Such particle events could add considerable exposure particularly to the skin and eye for all scenarios except the one at 28.5 degrees orbital inclination.
A major objective of our heavy-ion research is to understand the potential carcinogenic effects of cosmic rays and the mechanisms of radiation-induced cell transformation. During the past several years, we have studied the relative biological effectiveness of heavy ions with various atomic numbers and linear energy transfer on neoplastic cell transformation and the repair of transformation lesions induced by heavy ions in mammalian cells. All of these studies, however, were done with a high dose rate. For risk assessment, it is extremely important to have data on the low-dose-rate effect of heavy ions. Recently, with confluent cultures of the C3H10T1/2 cell line, we have initiated some studies on the low-dose-rate effect of low- and high-LET radiation on cell transformation. For low-LET photons, there was a decrease in cell killing and cell transformation frequency when cells were irradiated with fractionated doses and at low dose rate. Cultured mammalian cells can repair both subtransformation and potential transformation lesions induced by X rays. The kinetics of potential transformation damage repair is a slow one. No sparing effect, however, was found for high-LET radiation. There was an enhancement of cell transformation for low-dose-rate argon (400 MeV/u; 120 keV/micrometer) and iron particles (600 MeV/u; 200 keV/micrometer). The molecular mechanisms for the enhancement effect is unknown at present.
A review of the galactic cosmic ray energy spectra of heavy ions with Z< or = 28 is presented. Fluxes of these ions within critical body organs of astronauts travelling outside the magnetosphere will be modified from the free space values by fragmentation within the spacecraft and the bodies of the astronauts themselves. The effects of such fragmentation are presented in terms of variations in the particle flux above a given dE/dx at representative depths. Present limitations to the accuracy of such calculations are considered. The validity of dE/dx as a relevant physical parameter for characterizing the biologically important component of the heavy ion radiation environment is discussed.
An alternative to absorbed dose, quality, and RBE at low exposures
- Bond
Cosmic ray effects on microelectronics, Part I: The near-earth particle environment
- Adams