The Health Risks of Extraterrestrial Environments
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Welcome to The Health Risks of Extraterrestrial Environments (THREE), an encyclopedic site whose goal is to present a discussion of the space radiation environment and its health risks to humans. The intent is to make this a good starting point for researchers new to either space, radiation, or both; a source of useful information for established investigators; and a teaching tool for students.

There are tabs to five pages, other than the "Home" page you are reading. The "THREE Encyclopedia" tab leads to a set of articles covering all aspects of space radiation concern, as well as an introduction to each topic. The articles have been written by investigators and colleagues of the NASA Space Radiation Program and have been peer reviewed under supervision of an Associate Editor. In addition to articles, the site contains, in Flash format, slides that were presented to students of the NASA Space Radiation Summer School. Articles may be viewed in PDF format. Click on "Recent Articles" below for a list of the most recently posted articles.

Citations to reports and to articles published in the scientific literature, that the Associate Editors consider to be of interest to the space radiation community, are listed monthly, together with a brief description by one of the article authors in most cases. The current month's listing may be accessed by clicking on the "In the News" link below. These citations are collected and archived on the "Bibliography" page, sorted by Encyclopedia topics, as a living bibliographic complement to the encyclopedia articles.

A few important presentations are collected in the "Multimedia" page; future presentations will be added as appropriate. The "Archive" is a store of material previously posted on THREE, and kept for reference. Finally, a glossary of terms related to space radiation research is available on the similarly named page.

The THREE Editorial Board is responsible for oversight of the content and policies for this site. It is hosted by the NASA Johnson Space Center.

Contributions to any part of THREE, especially submissions for articles, are welcome; instructions for authors are posted in the Statement of Policies. Please send your comments and contributions along with your full name, address, institution, and e-mail address to the Page Editor listed in the webpage footer.

Walter Schimmerling
THREE Chief Editor

  • Track structure and the quality factor for space radiation cancer risk (PDF) Dudley T. Goodhead

    Correction Posted September 28, 2018

  • Abortive apoptosis and its profound effects on radiation‐, chemical‐, and oncogene induced carcinogenesis (PDF) Xinjian Liu, Ian Cartwright, Fang Li, and Chuan-Yuan Li

    Posted June 21, 2018

  • Using Proteomics Approaches to Assess Mechanisms Underlying Low Linear Energy Transfer or Galactic Cosmic Radiation-Induced Cardiovascular Disease (PDF) Zachary D. Brown, Muath Bishawi, and Dawn E. Bowles

    Posted May 21, 2018

  • The Emerging Role of Exosomes in the Biological Processes Initiated by Ionizing Radiation (PDF) Munira A Kadhim, Scott J Bright, Ammar H J Al-Mayah, and Edwin Goodwin

    Posted April 11, 2018

  • Solar Particle Events and Radiation Exposure in Space (PDF) Shaowen Hu

    Posted March 31, 2017

  • An introduction to space radiation and its effects on the cardiovascular system (PDF) Marjan Boerma

    Posted October 13, 2016

  • Precise Genome Engineering and the CRISPR Revolution (Boldly Going Where No Technology Has Gone Before.) (PDF) Eric A. Hendrickson

    Posted April 6, 2016

Track structure and the quality factor for space radiation cancer risk (PDF) Dudley T. Goodhead
A major risk from exposure to space radiation is the induction of cancer and it is from estimates of this risk that the maximum career flight times of NASA space crew members are restricted by a permissible exposure limit. For the purpose of demonstrating compliance with the career limit, NASA has developed a cancer risk projection model for radiation exposure induced death from cancer (REID), in which the formulation and numerical values of the quality factor (QFNASA) are substantially different from those of the quality factor (Q) or radiation weighting factor (wR) routinely applied for radiation protection on earth. The quality factor is used to account for the increased effectiveness of radiations of high linear energy transfer (LET), compared to the effectiveness of low-LET γ-rays derived from epidemiological studies of the atomic-bomb survivors. The need for a special approach for space radiation is dictated by the special characteristics of the charged particles from solar radiation and especially the charged particles of high energy and charge (HZE) in galactic cosmic rays (GCR). This article considers aspects of radiation track structure in relation to the relative biological effectiveness (RBE) of HZE particles and the quality factor used for space radiation. The NASA quality factor (QFNASA) is composed of two terms, which can be interpreted as broadly representing the low- and the high-ionization-density components of the HZE particle tracks. These are discussed in turn as they relate to available experimental evidence on the biological effectiveness of such components. Also briefly described are subsequent published proposals for a reformulation of the quality factor to relate more directly to the acute γ-ray exposures from the atomic bombs and for further refinement of the parameter values (and their uncertainties) that determine the shape of the quality factor function. Other recent developments are also mentioned.

Illustration of features commonly observed for the variation of relative biological effectiveness (RBE) with LET.  (Adapted from Goodhead 1994.)

Donald V. Reames: “Solar Energetic Particles: A Modern Primer on Understanding Sources, Acceleration, and Propagation” (Springer, 2017). (PDF); reviewed by Stephen Kahler.

Call for Abstracts

NASA Langley Research Center will hold a Blue Sky Workshop on Radiation Shielding for Human Exploration in the next 12 months, near the NASA Langley Research Center, Hampton, VA, and is now soliciting abstracts for concepts to address the problem of shielding astronauts from galactic cosmic rays. Abstracts no longer than one page, including figures and tables in PDF format, should be submitted by email to Deadline for abstract submission is October 31, 2018.
Applicants should not include any information in abstracts which is considered to be proprietary, as this workshop may be publicized and abstracts may be made publicly available. No compensation will be provided for submission or selection of abstracts. Return to top

Announcing the new Big Data to Knowledge (BD2K) Resources Page

Big Data to Knowledge (BD2K) grantees developed a series of resources for the biomedical research and data science communities to use big data to answer biomedical research questions. Under current efforts to make the products of BD2K research usable, discoverable, and disseminated to the biomedical research community, the NIH Office of Strategic Coordination (OSC) released a webpage with direct hyperlinks to the resources developed through BD2K funding (

The BD2K resource page will be updated periodically and populated with new resources as they become available. Please feel free to share this information with interested colleagues.
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Low Dose Rate Neutron Irradiator Facility

The Low Dose Rate Neutron Irradiator Facility at Colorado State University (CSU) provides NASA investigators with the capability of exposing mice and rats to chronic neutron irradiation, which has high LET effects. Currently, simulating continuous exposures to space radiation over time periods of months to years is not technical feasible in accelerator facilities. However, continuous exposures to fission spectrum neutrons are possible, and there are physical and biological commonalities between the effects of neutrons and HZE ions that make neutron irradiation a meaningful surrogate for space radiation exposures.

The Neutron Irradiator Facility is located on the CSU Foothills Campus in Fort Collins, Colorado. It is a rodent vivarium with a capacity of up to 900 mice and 60 rats that houses a neutron irradiator with a 252Cf neutron source. The animals are irradiated at a dose rate of 1 mGy/day, with a day consisting of about 20 hours with the 252Cf source exposed (irradiation) and the remaining 4 hours with the source shielded so that personnel can enter the facility for animal care and husbandry. Because 252Cf undergoes radioactive decay, the actual daily exposure time depends on the activity of the source. Total radiation times can be up to the lifespans of the animals. Photons deliver 20% of total dose. The dose averaged LET is 68±8 keV/um. Total dose rates are within ±10% throughout the distribution of cages and racks.

For information on using the CSU Low Dose Rate Neutron Irradiator Facility, contact Dr. Mike Weil at

Interior view of the facility showing the neutron irradiator (blue with yellow attenuator) surrounded by racks hold mouse and rat cages.
Interior view of the facility showing the neutron irradiator (blue with yellow attenuator) surrounded by racks hold mouse and rat cages.
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TRISH Red Risk School

The Translational Institute for Space Health (TRISH) held the first “Red Risk School” 2-6 April 2018, offering a set of virtual workshop sessions to help inform potential proposers for NASA and TRISH research solicitations about the highest priority (or “red”) risks identified by the NASA’s Human Research Program (HRP).

Although the first sessions have already happened, they were recorded and posted to the TRISH website for later viewing availability. A second set of workshop sessions will be offered in 2019.

With TRISH’s focus on innovation and synergy, this is a perfect opportunity for non-traditional researchers new to NASA to get a crash course in the HRP high priority risks. If you are interested in finding out more about the Red Risk School, visit TRISH’s website at

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Space radiation triggers persistent stress response, increases senescent signaling, and decreases cell migration in mouse intestine
Kumar S, Suman S, Fornace AJ Jr, Datta K., published in Proc Natl Acad Sci U S A. 2018 Oct 1. [Epub ahead of print] [10/10]
Kumar report that HZE ion radiation leads to important long-term perturbations in intestinal function. The Georgetown group showed ten years ago that HZE ions induce a persistent oxidative-stress state and pro-inflammatory phenotype in gastrointestinal (GI) and other tissues. The Shay laboratory (a member of their GI NSCOR program) further expanded on this in a 2015 report in Oncogene showing changes in gene expression in GI tissues reminiscent of the senescence-associated inflammatory response (SIR) after space radiation. In the current publication, the authors now show that HZE ions trigger perturbations in key proteins and often their transcript levels that are known to control normal GI epithelial cell maturation and function. Interestingly, cell migration along the crypt-villus axis in small intestine was persistently decreased after a low dose of 56Fe radiation relative to control and γ-rays. Wnt/β-catenin and its downstream EphrinB/EphB signaling are key to GI epithelial proliferation and positioning during migration, and both were upregulated. In addition, factors involved in cell polarity, cell adhesion, and cell-extracellular matrix interactions were persistently downregulated. These changes were accompanied by changes in barrier function and nutrient absorption factors, as well as increased intestinal tumorigenesis. Along with these changes, increasing levels of oxidative stress and DNA damage were seen up to a year after irradiation. These effects correlated with higher levels of senescent cells in GI crypts and features of the senescence-associated secretory phenotype (SASP) and the SIR. A working model was proposed whereby HZE ions cause sufficient damage to induce senescent GI cells, and that senescent-cell associated signaling molecules trigger long-term oxidative stress and a feedback loop leading to a gradual increase in senescent cells in GI crypts with increasing levels of DNA damage.
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Should NASA collect astronauts’ genetic information for occupational surveillance and research?
Reed RD, Antonsen EL. AMA J Ethics. 2018 Sep 1;20(9):E849-56. [10/9]
Humans exploring beyond low-Earth orbit face environmental challenges coupled with isolation, remote operations, and extreme resource limitations in which personalized medicine, enabled by genetic research, might be necessary for mission success. With little opportunity to test personalized countermeasures broadly, the National Aeronautics and Space Administration (NASA) will likely need to rely instead on collection of significant amounts of genomic and environmental exposure data from individuals. This need appears at first to be in conflict with the statutes and regulations governing the collection and use of genetic data. In fact, under certain conditions, the Genetic Information Nondiscrimination Act (GINA) of 2008 allows for the use of genetic information in both occupational surveillance and research and in the development of countermeasures such as personalized pharmaceuticals.
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Proton radiation-induced cancer progression
Luitel K, Bozeman RG, Kaisani A, Kim SB, Barron S, Richardson JA, Shay JW. Life Sci Space Res. 2018 Aug 18. [9/11]
In this study, the long-term side effects of proton radiation are compared to equivalent doses of X-rays in the initiation and progression of premalignant lesions in a lung cancer susceptible mouse model (K-rasLA1). Exposure to proton irradiation enhances the progression of premalignant lesions to invasive carcinomas through persistent DNA damage, chronic oxidative stress, and immunosuppression.
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Temporary microglia-depletion after cosmic radiation modifies phagocytic activity and prevents cognitive deficits.
Krukowski K, Feng X, Paladini MS, Chou A, Sacramento K, Grue K, …, Rosi S. Scientific Reports, 8, 7857 (2018). [8/31]
Temporary microglia depletion, one week after cosmic radiation, prevents the development of long-term memory deficits. The repopulated microglia present a modified functional phenotype with reduced phagocytic activity shown to be involved in microglia-synapses interaction. Our data provide mechanistic evidence for the role of microglia in the development of cognitive deficits after cosmic radiation exposure. To our knowledge this is the first report to identify a therapeutic approach for treating GCR-induced deficits.
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Female mice are protected from space radiation-induced maladaptive responses
Krukowski K, Grue K, Frias ES, Pietrykowski J, Jones T, Nelson G, Rosi S. Brain Behav Immun. 2018 Aug 11. [8/28]
A single exposure to simulated GCR induces long-term cognitive and behavioral deficits only in the male cohorts but not in female. Mechanistically, the maladaptive behavioral responses observed only in the male cohorts correspond with microglia activation and synaptic loss in the hippocampus, a brain region involved in the cognitive domains reported here. Our findings suggest that GCR exposure can regulate microglia activity and alter synaptic architecture, which in turn leads to a range of cognitive alterations in a sex dependent manner.
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Exposure to galactic cosmic radiation compromises DNA repair and increases the potential for oncogenic chromosomal rearrangement in bronchial epithelial cells.
Li Z, Jella KK, Jaafar L, Li S, Park S, Story MD, Wang H, Wang Y, Dynan WS. Sci Rep. 2018 Jul 23;8(1):11038. (8/21)
The authors of this study investigated persistent effects of galactic cosmic ray exposure on DNA repair capacity in human lung-derived epithelial cells, Replicate cell cultures were irradiated with 48-Ti ions or reference γ-rays, then challenged by expression of a Cas9/sgRNA pair that creates double-strand breaks simultaneously in the EML4 and ALK loci. Misjoining, which creates an EML4-ALK fusion oncogene, was significantly elevated in 48-Ti-irradiated populations relative to controls or γ-ray-irradiated samples and was frequently accompanied by deletions, consistent with a shift toward error-prone alternative nonhomologous end joining repair.
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Cancer and circulatory disease risks for a human mission to Mars: Private mission considerations.
Cucinotta FA, Cacao E, Kim M-HY, Saganti PB. Acta Astronaut. 2018 Aug 13. (8/18)
There is growing interest in private missions to Mars and other deep space destinations within the next decade. Private missions could consider persons not restricted by radiation limits; however there remains an interest in the level of risk to be encountered. Astronauts and cosmonauts are typically above 40-y, while younger aged persons could participate in private space missions. This paper describes cancer and circulatory disease risks for a 940 d Mars mission for average solar minimum conditions for persons of varying ages from 20 to 60 years. For the first-time NTEs are considered in Mars mission cancer risk predictions. We find much higher importance of cancer risk compared to circulatory disease risks for persons participating in space missions.
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Charged-Iron-Particles Found in Galactic Cosmic Rays are Potent Inducers of Epithelial Ovarian Tumors.
Mishra B, Lawson GW, Ripperdan R, Ortiz L, Ludere U. Radiation Research 190(2):142-150. 2018. (8/18)
Astronauts traveling in deep space are exposed to radioactive particles, such as iron ions, from galactic cosmic rays. We previously showed that irradiation of adult female mice with iron ions destroys ovarian follicles, causing premature ovarian failure, and we hypothesized that these mice would subsequently develop ovarian tumors. To test this, we aged female mice for 15 months after irradiation with 50 cGy iron ions, which is about the total dose of radiation astronauts would receive during a 3 year Mars mission. Irradiated mice had a 4-fold increased incidence of ovarian tumors compared to non-irradiated controls. The tumors were positive for cytokeratin, indicating that they were epithelial tumors. Most human ovarian cancers are also epithelial. These results raise concerns about ovarian tumors as possible late consequences of deep space travel in female astronauts.
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Comparative profiling of microRNAs reveals the underlying toxicological mechanism in mice testis following carbon ion radiation.
He Y, Zhang Y, Li H, Zhang H, Li Z, Xiao L, Hu J, Ma Y, Zhang Q, Zhao X. Dose Response. 2018 Apr-Jun;16(2):1559325818778633. (8/16)
This study investigated the toxicity of heavy ion radiation to mice testis by microRNA (miRNA) sequencing and bioinformatics analyses. Testicular indices and histology were measured following enterocoelia irradiation with a 2 Gy carbon ion beam, with the testes exhibiting the most serious injuries at 4 weeks after carbon ion radiation (CIR) exposure. Illumina sequencing technology was used to sequence small RNA libraries of the control and irradiated groups at 4 weeks after CIR. Gene Ontology and Kyoto Encyclopedia of Genes and Genomes pathway analyses implicated differential miRNAs in the regulation of target genes involved in metabolism, development, and reproduction. Here, 8 miRNAs, including miR-34c-5p, miR-138, and 6 let-7 miRNA family members previously reported in testis after radiation, were analyzed by quantitative reverse transcription-polymerase chain reaction (qRT-PCR) to validate miRNA sequencing data. The differentially expressed miRNAs described here provided a novel perspective for the role of miRNAs in testis toxicity following CIR.
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Biodosimetric transcriptional and proteomic changes are conserved in irradiated human tissue.
Keam, S.P., Gulati, T., Gamell, C. et al. Radiat Environ Biophys (2018) 57: 241. (8/16)
Transcriptional dosimetry is an emergent field of radiobiology aimed at developing robust methods for detecting and quantifying absorbed doses using radiation-induced fluctuations in gene expression. A combination of RNA sequencing, array-based and quantitative PCR transcriptomics in cellular, murine and various ex vivo human models has led to a comprehensive description of a fundamental set of genes with demonstrable dosimetric qualities. However, these are yet to be validated in human tissue due to the scarcity of in situ-irradiated source material. In this study, we present a novel evaluation of a previously reported set of dosimetric genes in human tissue exposed to a large therapeutic dose of radiation. To do this, we evaluated the quantitative changes of a set of dosimetric transcripts consisting of FDXR, BAX, BCL2, CDKN1A, DDB2, BBC3, GADD45A, GDF15, MDM2, SERPINE1, TNFRSF10B, PLK3, SESN2 and VWCE in guided pre- and post-radiation (2 weeks) prostate cancer biopsies from seven patients. We confirmed the prolonged dose-responsivity of most of these transcripts in in situ-irradiated tissue. BCL2, GDF15, and to some extent TNFRSF10B, were markedly unreliable single markers of radiation exposure. Nevertheless, as a full set, these genes reliably segregated non-irradiated and irradiated tissues and predicted radiation absorption on a patient-specific basis.
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Comparing HZETRN, SHIELD, FLUKA and GEANT transport codes.
John W. Norbury, Tony C. Slaba, Nikolai Sobolevsky, Brandon Reddell. NASALife Sciences in Space Research 14 (2017) 64–73. (7/16)
This paper represents the first direct comparisons of the American (NASA) and Russian (ROSCOSMOS) space radiation transport codes, HZETRN and SHIELD. Flux spectra of neutrons, light ions, heavy ions and pions were calculated for galactic cosmic ray projectiles incident on Aluminum. Some comparison calculations with the GEANT4 and FLUKA transport codes were also shown. Overall, the biggest differences between transport codes occur below the several hundred MeV region, which may be due to the differences in nuclear models employed in the different codes.
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SHIELD and HZETRN comparisons of pion production cross sections.
John W. Norburya, Nikolai Sobolevsky, Charles M. Werneth. Nuclear Inst, and Methods in Physics Research B 418 (2018) 13–17. (7/16)
The present work represents the second time that NASA and ROSCOSMOS calculations have been directly compared, and the focus here is on models of pion production cross sections used in the HZETRN (NASA) and SHIELD (ROSCOSMOS) transport codes. It was found that these models are in moderate agreement with each other and with experimental data, and further model improvements would be worthwhile.
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Comparison of space radiation GCR models to recent AMS data.
John W. Norbury, Kathryn Whitman, Kerry Lee, Tony C. Slaba, Francis F. Badavi. Life Sciences in Space Research 18 (2018) 64–71. (7/16)
This paper is the third in a series of comparisons of American (NASA) and Russian (ROSCOSMOS) space radiation calculations. The present work focuses on calculation of fluxes of galactic cosmic rays (GCR), which are a constant source of radiation that constitutes one of the major hazards during deep space exploration missions for both astronauts/cosmonauts and hardware. In this work, commonly used GCR models are compared with recently published measurements of cosmic ray Hydrogen, Helium, and the Boron-to-Carbon ratio from the Alpha Magnetic Spectrometer (AMS). All of the models were developed and calibrated prior to the publication of the AMS data; therefore this an opportunity to validate the models against an independent data set. Overall, the different GCR models are in good agreement with AMS data in energy regions important for space radiation.
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Analysis of radiation-induced chromosomal aberrations on a cell-by-cell basis after alpha-particle microbeam irradiation: Experimental data and simulations.
Testa A, Ballarini F, Giesen U, Gil OM, Carante MP, Tello J, Langner F, Rabus H, Palma V, Pinto M, Patrono C. Radiation Research 189(6):597-604. 2018. (6/8)
An experimental and theoretical analysis was carried out on chromosomal aberrations in CHO-K1 cells, which were exposed to 5.5 MeV and 17.8 MeV α-particles (LET: ~85 keV/mm and ~36 keV/mm, respectively) generated by a microbeam available at PTB in Braunschweig (Germany), and analyzed by an ad hoc in situ protocol. The 5.5 MeV α-particles were more effective than the 17.8 MeV α-particles; for instance, the yield of total aberrations increased by a factor of ~2. The experimental data were compared with Monte Carlo simulations based on a biophysical model called BIANCA (BIophysical ANalysis of Cell death and chromosomal Aberrations). In particular, the higher aberration yields observed at the higher LET were explained by taking into account that each particle was much more effective at inducing DNA critical damage (Cluster Lesions, or CLs), thus leading to an increased yield of CLs/cell that was consistent with the increased yield of total aberrations observed in the experiments.
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NASA GeneLab Project: Bridging Space Radiation Omics with Ground Studies.
Afshin Beheshti, Jack Miller, Yared Kidane, Daniel Berrios, Samrawit G. Gebre, and Sylvain V. Costes. Radiation Research: June 2018, Vol. 189, No. 6, pp. 553-559. (5/30)
An original research article led by NASA Ames Research Center, Space Biosciences Research Branch scientists, titled “NASA GeneLab Project: Bridging Space Radiation Omics with Ground Studies” was published in the April 2018 issue of Radiation Research. This paper provides a comprehensive review of the data available on NASA’s GeneLab platform ( The NASA GeneLab project aims to provide a detailed library of omics datasets associated with biological samples exposed to space radiation. The GeneLab Data System (GLDS) includes datasets from both spaceflight and ground-based studies, a majority of which involve exposure to ionizing radiation. GeneLab is the first comprehensive omics database for space-related research from which an investigator can generate hypotheses to direct future experiments, utilizing both ground and space biological radiation data. In this manuscript, the authors provide a detailed summary of the data available on GeneLab which include a description of the ground radiation studies including ion type, total dose, dose rate, and LET. In addition, they describe in detail the data available on GeneLab from experiments done on the space shuttle that have complete information on the amount of radiation the samples were exposed to during spaceflight. This manuscript is a good starting point for investigators interested in performing space radiation related research.
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Exposure of the bone marrow microenvironment to simulated solar and galactic cosmic radiation induces biological bystander effects on human hematopoiesis.
Almeida-Porada G, Rodman C, Kuhlman B, Brudvik E, Moon J, George S, Guida P, Sajuthi SP, Langefeld CD, Walker SJ, Wilson PF, Porada CD. Stem Cells Dev. 2018 Apr 26. [Epub ahead of print] (5/11)
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.
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A preliminary study on radiation shielding using Martian magnetic anomalies.
Emoto K, Takao Y, Kuninaka H. Biol Sci Space. 2018 Apr 28;32:1-5. (5/8)
We propose radiation shielding using Martian magnetic anomalies to protect human crews on the Martian surface. We have simulated the trajectories of energetic protons using the Buneman-Boris method to measure how magnetic anomalies affect the impact rate on the Martian surface. Protons from the west can be completely eliminated, while those from the east are concentrated on the area between the magnetic poles. This would mean crews would need to concern themselves about radiation from the vertex and east only. A Martian magnetic anomaly can therefore be used to realize continuous and efficient radiation shielding.
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Detrimental effects of helium ion irradiation on cognitive performance and cortical levels of MAP-2 in B6D2F1 mice.
Raber J, Torres ERS, Akinyeke T, Lee J, Weber Boutros SJ, Turker MS, Kronenberg A. Int J Mol Sci. 2018 Apr 20;19(4):E1247. (5/7)
The space radiation environment includes helium (4He) ions that may impact brain function. As little is known about the effects of exposures to 4He ions on the brain, we assessed the behavioral and cognitive performance of C57BL/6J x DBA2/J F1 (B6D2F1) mice three months following irradiation with 4He ions (250 MeV/n; linear energy transfer (LET) = 1.6 keV/μm; 0, 21, 42 or 168 cGy). 4He ion irradiation impaired cognitive function and reduced the levels of the dendritic marker microtubule-associated protein 2 (MAP-2) in the cortex.
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Mice lacking RIP3 kinase are not protected from acute radiation syndrome.
Castle KD, Daniel AR, Moding EJ, Luo L, Lee CL, Kirsch DG. Radiat Res. 2018 Apr 10 [Epub ahead of print] (4/30)
To facilitate the development of medical countermeasures that prevent the acute radiation syndrome, it is essential to characterize cell death pathways that mediate radiation injury in distinct organ systems. Recent studies have shown that pharmacological inhibition of necroptosis can mitigate death from the acute radiation syndrome in mice. In this study, we utilized mice lacking a critical regulator of necroptosis, receptor interacting protein 3 (RIP3) kinase, to characterize the role of RIP3 in normal tissue toxicity following irradiation. Our results suggest that RIP3-mediated signaling is not a critical driver of the hematopoietic or gastrointestinal acute radiation syndrome.
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Impaired attentional set-shifting performance after exposure to 5 cGy of 600 MeV/n (28)Si particles.
Britten RA, Jewell JS, Duncan VD, Hadley MM, Macadat E, Musto AE, La Tessa C. Radiat Res. Epub 2018 Jan 8. 2018 Mar;189(3):273-282. (4/18)
The long lag time for communication on a deep space mission will require that astronauts work more autonomously than on previous missions, and thus their ability to perform executive functions could be critical to mission success. Executive functions are a set of higher order cognitive abilities that animals utilize to assess changing situation and to achieve a desired goal in the most efficient and acceptable way (Assess, Adapt, Achieve!). In this paper we have determined that low doses (5 cGy) of 600 MeV/n 28Si ions impairs one executive function (cognitive flexibility, specifically the simple discrimination task in the attentional set shifting test). If astronauts were to experience GCR-induced simple discrimination impairments, they would be unable to identify key factors to successfully resolve a situation. Si ions impaired attentional set shifting performance at lower doses than the heavier ions we have previously studied, but when iso-fluences of the Si, Ti and Fe ions were compared, there were no significant differences in the severity of the impaired performance, but there were ion-specific decrements in the ability of rats to perform within the various stages of the test. This study further supports the notion that “mission-relevant” doses of HZE particles (<20 cGy) can impair certain aspects of attentional set shifting performance, but there may be some ion-specific changes in the specific cognitive domains impaired.
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Persistent nature of alterations in cognition and neuronal circuit excitability after exposure to simulated cosmic radiation in mice.
Parihar VK, Maroso M, Syage A, Allen BD, Angulo MC, Soltesz I, Limoli CL. Exp Neurol. 2018 Mar 11. [Epub ahead of print] (4/17)
Of the many perils associated with deep space travel to Mars, neurocognitive complications associated with cosmic radiation exposure are of particular concern. Despite these realizations, whether and how realistic doses of cosmic radiation cause cognitive deficits and neuronal circuitry alterations several months after exposure remains unclear. In addition, even less is known about the temporal progression of cosmic radiation-induced changes transpiring over the duration of a time period commensurate with a flight to Mars. Here we show that rodents exposed to the second most prevalent radiation type in space (i.e. helium ions) at low, realistic doses, exhibit significant hippocampal and cortical based cognitive decrements lasting 1 year after exposure. Cosmic-radiation-induced impairments in spatial, episodic and recognition memory were temporally coincident with deficits in cognitive flexibility and reduced rates of fear extinction, elevated anxiety and depression like behavior. At the circuit level, irradiation caused significant changes in the intrinsic properties (resting membrane potential, input resistance) of principal cells in the perirhinal cortex, a region of the brain implicated by our cognitive studies. Irradiation also resulted in persistent decreases in the frequency and amplitude of the spontaneous excitatory postsynaptic currents in principal cells of the perirhinal cortex, as well as a reduction in the functional connectivity between the CA1 of the hippocampus and the perirhinal cortex. Finally, increased numbers of activated microglia revealed significant elevations in neuroinflammation in the perirhinal cortex, in agreement with the persistent nature of the perturbations in key neuronal networks after cosmic radiation exposure. These data provide new insights into cosmic radiation exposure, and reveal that even sparsely ionizing particles can disrupt the neural circuitry of the brain to compromise cognitive function over surprisingly protracted post-irradiation intervals.
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Early effects of 16O radiation on neuronal morphology and cognition in a murine model.
Carr H, Alexander TC, Groves T, Kiffer F, Wang J, Price E, Boerma M, Allen AR. Life Sci Space Res. 2018 Mar 14. [Article in Press] (4/17)
There is concern about potential adverse effects of high atomic number and energy (HZE) radiation on brain morphology. In this study, adult male C57BL/6 mice were exposed to oxygen ions (600 MeV/n, 0.1 – 1 Gy) and the hippocampus was examined two weeks after irradiation. Significant changes in spine density of neurons and in the expression of receptors that modulate synaptic function were observed, suggesting that oxygen ions have early deleterious effects on mature neurons that are associated with hippocampal learning and memory.
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Late effects of 1H irradiation on hippocampal physiology.
Kiffer F, Howe AK, Carr H, Wang J, Alexander T, Anderson JE, Groves T, Seawright JW, Sridharan V, Carter G, Boerma M, Allen AR. Life Sci Space Res. 2018 Mar 15. [Article in Press] (4/17)
This study examined the effects of protons, an abundant charged particle in both galactic cosmic rays and solar particle events, on cognitive function and hippocampus morphology in adult male C57BL/6 mice. Nine months after exposure to protons (150 MeV), mice showed a reduced ability to distinguish novel objects in a Novel Object Recognition test, indicative of reduced non-spatial memory. These results coincided with decreases in spine density and dendrite morphology in the hippocampus. The results suggest that proton irradiation caused late changes in neuronal morphology necessary for normal hippocampal processing.
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Proceedings of the National Cancer Institute Workshop on Charged Particle Radiobiology.
Mohan R, Held KD, Story MD, Grosshans D, Capala J. Int J Radiat Oncol Biol Phys. 2018 Mar 15;100(4):816-31. (4/12)
In April 2016, the National Cancer Institute hosted a multidisciplinary workshop to discuss the current knowledge of the radiobiological aspects of charged particles used in cancer therapy to identify gaps in that knowledge that might hinder the effective clinical use of charged particles and to propose research that could help fill those gaps. The workshop was organized into 10 topics ranging from biophysical models to clinical trials and included treatment optimization, relative biological effectiveness of tumors and normal tissues, hypofractionation with particles, combination with immunotherapy, “omics,” hypoxia, and particle-induced second malignancies. Discussion also included the potential advantages of heavier ions, notably carbon ions, because of their increased biological effectiveness, especially for tumors frequently considered to be radiation resistant, increased effectiveness in hypoxic cells, and potential for differentially altering immune responses.
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Stem cell therapies for the resolution of radiation injury to the brain.
Smith SM, Limoli CL. Curr Stem Cell Rep. 2017 Dec;3(4):342-7. Review.
Transplantation of human stem cells in the irradiated brain was first shown to resolve radiation-induced cognitive dysfunction in a landmark paper by Acharya et al., appearing in PNAS in 2009. Since that time, work from the same laboratory as well as other groups have reported on the beneficial (as well as detrimental) effects of stem cell grafting after cranial radiation exposure. Improved learning and memory found many months after engraftment has since been associated with a preservation of host neuronal morphology, a suppression of neuroinflammation, improved myelination and increased cerebral blood flow.
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Solar particle event storm shelter requirements for missions beyond low Earth orbit.
Townsend LW, Adams JH, Blattnig SR, Clowdsley MS, Fry DJ, Jun I, McLeod CD, Minow JI, Moore DF, Norbury JW, Norman RB, Reames DV, Schwadron NA, Semones EJ, Singleterry RC, Slaba TC, Werneth CM, Xapsos MA. Life Sci Space Res. 2018 Feb 21.
Protecting spacecraft crews from energetic space radiations that pose both chronic and acute health risks is a critical issue for future missions beyond low Earth orbit (LEO). Chronic health risks are possible from both galactic cosmic ray and solar energetic particle event (SPE) exposures. However, SPE exposures also can pose significant short term risks including, if dose levels are high enough, acute radiation syndrome effects that can be mission- or life-threatening. In order to address the reduction of short term risks to spaceflight crews from SPEs, we have developed recommendations to NASA for a design-standard SPE to be used as the basis for evaluating the adequacy of proposed radiation shelters for cislunar missions beyond LEO. Four SPE protection requirements for habitats are proposed: (1) a blood-forming-organ limit of 250 mGy-equivalent for the design SPE; (2) a design reference SPE environment equivalent to the sum of the proton spectra during the October 1989 event series; (3) any necessary assembly of the protection system must be completed within 30 minutes of event onset; and (4) space protection systems must be designed to ensure that astronaut radiation exposures follow the ALARA (As Low As Reasonably Achievable) principle.
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Radiation-induced cardiovascular disease: Mechanisms and importance of linear energy transfer.
Sylvester CB, Abe JI, Patel ZS, Grande-Allen KJ. Front Cardiovasc Med. 2018 Jan 31;5:5. Review.
The link between radiation and CVD is well established in human cohorts at doses greater than 0.5 Gy. Most knowledge about radiation-induced cardiovascular disease (RICVD) comes from populations exposed to low-linear energy transfer (LET) photons. More recently, high-LET radiation is being tested as a therapy for cancer. High-LET therapy more closely replicates the high energy and atomic weight component of space radiation to which astronauts will be subjected, but how high-LET radiation affects the cardiovascular system is not yet completely understood. This review examines the clinical, molecular, and animal studies that investigate the effects of high-LET radiation on the cardiovascular system and compares those results to current knowledge of low-LET radiation. It further elaborates on how advances within NASA’s research program as well as within the terrestrial work with cancer therapy can inform both the risk of RICVD and mitigation strategies.
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Biophysics Model of Heavy-Ion Degradation of Neuron Morphology in Mouse Hippocampal Granular Cell Layer Neurons.
Alp M and Cucinotta FA. (2018) Radiation Research: March 2018, Vol. 189, No. 3, pp. 312-325.
Exposure to heavy-ion radiation during cancer treatment or space travel may cause cognitive detriments that have been associated with changes in neuron morphology and plasticity. Observations in mice of reduced neuronal dendritic complexity have revealed a dependence on radiation quality and absorbed dose, suggesting that microscopic energy deposition plays an important role. In this work we used morphological data for mouse dentate granular cell layer (GCL) neurons and a stochastic model of particle track structure and microscopic energy deposition (ED) to develop a predictive model of high-charge and energy (HZE) particle-induced morphological changes to the complex structures of dendritic arbors.
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Synergy Theory in Radiobiology.
Ham DW, Song B, Gao J, Yu J. and Sachs RK. Radiat. Res. 189, 225–237 (2018).
We characterize, exemplify, compare and critically evaluate mathematical/computational synergy analysis methods currently used in biology, and used or potentially applicable in radiobiology. No new experimental results are presented. As examples, we consider dose-effect relations (DERs) for single ions simulating components of the galactic cosmic ray mixed field. The endpoints are murine Harderian gland tumors or in vitro chromosome aberrations. Baseline no-synergy/no-antagonism mixture DERs are then calculated from the one-ion DERs. Synergy analysis of mixed radiation field action when components’ individual DERs are very curvilinear should not consist of simply comparing to the sum of the components’ effects. Many different synergy analysis theories are currently used in biology to replace simple effect additivity synergy theory. Marked curvilinearity must often be allowed for in current radiobiology, especially when studying possible non-targeted (‘‘bystander’’) effects. We give evidence that for most synergy experiments and observations, incremental effect additivity is the appropriate replacement. It has a large domain of applicability, being useful even when pronounced individual DER curvilinearity is a confounding factor. It allows calculation of 95% confidence intervals for baseline mixture DERs taking into account parameter correlations; if non-targeted effects are important this gives much tighter intervals than neglecting the correlations. Incremental effect additivity always obeys two consistency conditions that simple effect additivity usually fails to obey: a ‘‘mixture of mixtures principle’’ and the standard ‘‘sham mixture principle’’. The mixture of mixtures principle is important in radiobiology because even nominally single-ion radiations are usually mixtures when they strike the biological target, due to intervening material.
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HZETRN radiation transport validation using balloon-based experimental data.
Warner JE, Norman RB, Blattnig SR. Life Sci Space Res. 2018 Feb 21.
The deterministic radiation transport code HZETRN (High charge (Z) and Energy TRaNsport) was developed by NASA to study the effects of cosmic radiation on astronauts and instrumentation shielded by various materials. This work presents an analysis of computed differential flux from HZETRN compared with measurement data from three balloon-based experiments over a range of atmospheric depths, particle types, and energies. Model uncertainties were quantified using an interval-based validation metric that takes into account measurement uncertainty both in the flux and the energy at which it was measured. Average uncertainty metrics were computed for the entire dataset as well as subsets of the measurements (by experiment, particle type, energy, etc.) to reveal any specific trends of systematic over- or under-prediction by HZETRN. The distribution of individual model uncertainties was also investigated to study the range and dispersion of errors beyond just single scalar and interval metrics.
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Whole-Body Oxygen (16O) Ion-Exposure-Induced Impairments in Social Odor Recognition Memory in Rats are Dose and Time Dependent.
Ami Mange, Yuqing Cao, SiYuan Zhang, Robert D. Hienz, and Catherine M. Davis (2018) Whole-Body Oxygen (16O) Radiation Research: March 2018, Vol. 189, No. 3, pp. 292-299.
Our paper reports dose- and time-dependent effects of acute exposure to 16O ions (5 and 25 cGy, 1000 MeV/n) on a social odor recognition memory test in male rats. At 30-days after radiation exposure, all exposed rats displayed a memory deficit, however, at 6-months following radiation exposure, this deficit was only evident in the 25 cGy exposed group. No differences in Ki67 staining, a marker of cell proliferation, were found in the subventricular zone between the sham controls, 5 cGy or 25 cGy exposed rats when assessed at 6-months following radiation exposure. This work demonstrates that low-dose HZE exposure can significantly impair memory for social odors in rats, which suggests that HZE exposure might negatively affect social processing.
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Genetically engineered mouse models for studying radiation biology.
Castle KD, Chen M, Wisdom AJ, Kirsch DG. Transl Can Res. 2017 Jul;6 Suppl 5:S900-S913. Review.
Genetically engineered mouse models (GEMMs) are valuable research tools that have transformed the understanding of cancer development. Castle and colleagues summarize the history of the development of GEMMs and discuss contemporary model systems with techniques such as in vivo short hairpin RNA (shRNA) knockdown, inducible gene expression, site-specific recombinases to delete genes, and dual recombinase systems. They explore the strengths and limitations of these models to study radiation biology for rigorous and reproducible preclinical research. These systems can be applied to investigate mechanisms and to develop mitigators of carcinogenesis from space radiation.
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Vive la radiorésistance!: Converging research in radiobiology and biogerontology to enhance human radioresistance for deep space exploration and colonization.
Cortese F, Klokov D, Osipov A, Stefaniak J, Moskalev A, Schastnaya J, Cantor C, Aliper A, Mamoshina P, Ushakov I, Sapetsky A, Vanheaelen Q, Alchinova I, Karganov M, Kovalchuk O, Wilkins RC, Shtemberg A, Moreels M, Baatout S, Izumchenko E, de Magalhães JP, Artemov AV, Costes SV, Beheshti A, Mao XW, Pecaut MJ, Kaminskiy D, Ozerov IV, Scheibye-Knudsen M, Zhavoronkov A. Oncotarget. 2018 Feb 9.
Roadmap proposed by an international team of researchers toward enhancing human radioresistance for space exploration and colonization. The roadmap outlines possible future research directions toward the goal of enhancing human radioresistance, including upregulation of endogenous repair and radioprotective mechanisms, possible leeways into gene therapy in order to enhance radioresistance via the translation of exogenous and engineered DNA repair and radioprotective mechanisms, the substitution of organic molecules with fortified isoforms, the coordination of regenerative and ablative technologies, and methods of slowing metabolic activity while preserving cognitive function. The paper concludes by presenting the known associations between radioresistance and longevity, and articulating the position that enhancing human radioresistance is likely to extend the healthspan of human spacefarers as well.
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Translational research in radiation-induced DNA damage signaling and repair.
Nickoloff JA, Boss M-K, Allen CP, LaRue SM. Transl Can Res. 2017 Jul;6 Suppl 5:S875-S891. Review.
A review that focuses on how insights into molecular mechanisms of DNA damage response pathways are translated to small animal preclinical studies, to clinical studies of naturally occurring tumors in companion animals, and finally to human clinical trials.
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High-LET Radiation Increases Tumor Progression in a K-Ras-Driven Model of Lung Adenocarcinoma.
Asselin-Labat ML, Rampersad R, Xu X, Ritchie ME, Michalski J, Huang L, Onaitis MW. Radiation Research. Nov 2017; 188(5):562-570.
A mouse model of lung adenocarcinoma driven by oncogenic K-Ras was used to ascertain the effect of low- and high-LET radiation on tumor formation. We observed increased tumor progression and tumor cell proliferation after single dose or fractionated high-LET doses, which was not observed in mice exposed to low-LET radiation. Location of the tumor nodules was not affected by radiation, indicating that the cell of origin of K-Ras-driven tumors was the same in irradiated or nonirradiated mice. Gene expression analysis revealed an upregulation of genes involved in cell proliferation and DNA damage repair. This study provides evidence that exposure to a single dose or fractionated doses of high-LET radiation induces molecular and cellular changes that accelerate lung tumor growth.
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Whole-Body Exposure to 28Si-Radiation Dose-Dependently Disrupts Dentate Gyrus Neurogenesis and Proliferation in the Short Term and New Neuron Survival and Contextual Fear Conditioning in the Long Term.
Whoolery CW, Walker AK, Richardson DR, Lucero MJ, Reynolds RP, Beddow DH, Clark KL, Shih HY, LeBlanc JA, Cole MG, Amaral WZ, Mukherjee S, Zhang S, Ahn F, Bulin SE, DeCarolis NA, Rivera PD, Chen BPC, Yun S, Eisch SJ. Radiation Research: Nov 2017;188(5):532-551.
To compare the influence of 28Si exposure on indices of neurogenesis and hippocampal function with previous studies on 56Fe exposure, 9-week-old C57BL/6J and Nestin-GFP mice received whole-body 28Si-particle-radiation exposure. In contrast to the clearly observed radiation-induced, dose-dependent reductions in the short-term group across all markers, only a few neurogenesis indices were changed in the long-term irradiated groups. Compared to previously reported studies, present data suggest that 28Si-radiation exposure damages neurogenesis, but to a lesser extent than 56Fe radiation and that low-dose 28Si exposure induces abnormalities in hippocampal function, disrupting fear memory but also inducing anxiety-like behavior. Furthermore, exposure to 28Si radiation decreased new neuron survival in long-term male groups but not females suggests that sex may be an important factor when performing brain health risk assessment for astronauts traveling in space.
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Atmospheric Cosmic-Ray Variation and Ambient Dose Equivalent Assessments Considering Ground Level Enhancement Thanks to Coupled Anisotropic Solar Cosmic Ray and Extensive Air Shower Modeling.
Hubert G and Aubry S. Radiation Research: Nov 2017;188(5):517-531.
This work investigates the impact of Forbush decrease (FD) and ground-level enhancement (GLE) in the atmosphere, based on solar and galactic cosmic-ray models and the extensive air shower simulations. The calculated ambient dose equivalents were compared with flight measurements in quiet solar conditions. Doses induced by extreme GLE events were investigated specifically for London to New York flights.
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Low doses of oxygen ion irradiation cause long-term damage to bone marrow hematopoietic progenitor and stem cells in mice.
Wang Y, Chang J, Li X, Pathak R, Sridharan V, Jones T, Mao XW, Nelson G, Boerma M, Hauer-Jensen M, Zhou D, Shao L. PLoS One: 2017 Dec 12;12(12):e0189466.
While high energy charged particle irradiation as found in space is known to have short-term adverse effects on the hematopoietic system, long-term effects are not well studied. This experiment used a mouse model of oxygen ion exposure to assess stem and progenitor cells isolated from the bone marrow at three months after exposure. The cells of irradiated animals showed increased levels of reactive oxygen species and reduced performance in cell function assays. These results suggest that high energy charged particle irradiation can have long-term adverse effects on the hematopoietic system.
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Low-dose proton radiation effects in a transgenic mouse model of Alzheimer’s disease - Implications for space travel.
Rudobeck E, Bellone JA, Szücs A, Bonnick K, Mehrotra-Carter S, Badaut J, Nelson GA, Hartman RE, Vlkolinsky R. PLoS One. 2017 Nov 29;12(11):e0186168.
Space radiation represents a significant health risk for astronauts and it may accelerate the onset of Alzheimer's disease (AD). Although protons represent the main constituent in the space radiation spectrum, their effects on AD-related pathology have not been tested. We irradiated 3-month-old APP/PSEN1 transgenic (TG) and wild type (WT) mice with protons (150 MeV; 0.1-1.0 Gy; whole body) and evaluated functional and biochemical hallmarks of AD. We performed behavioral tests in the water maze (WM) before irradiation and in the WM and Barnes maze at 3 and 6 months post-irradiation to evaluate spatial learning and memory. We also performed electrophysiological recordings in vitro in hippocampal slices prepared 6 and 9 months post-irradiation to evaluate excitatory synaptic transmission and plasticity. Next, we evaluated amyloid β (Aβ) deposition in the contralateral hippocampus and adjacent cortex using immunohistochemistry. In cortical homogenates, we analyzed the levels of the presynaptic marker synaptophysin by Western blotting and measured pro-inflammatory cytokine levels (TNFα, IL-1β, IL-6, CXCL10 and CCL2) by bead-based multiplex assay. TG mice performed significantly worse than WT mice in the WM. Irradiation of TG mice did not affect their behavioral performance, but reduced the amplitudes of population spikes and inhibited paired-pulse facilitation in CA1 neurons. These electrophysiological alterations in the TG mice were qualitatively different from those observed in WT mice, in which irradiation increased excitability and synaptic efficacy. Irradiation increased Aβ deposition in the cortex of TG mice without affecting cytokine levels and increased synaptophysin expression in WT mice (but not in the TG mice). Although irradiation with protons increased Aβ deposition, the complex functional and biochemical results indicate that irradiation effects are not synergistic to AD pathology.
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Long-Term Deficits in Behavior Performances Caused by Low- and High-Linear Energy Transfer Radiation.
Patel R, Arakawa H, Radivoyevitch T, Gerson SL and Welford SM. Radiation Research. 2017; 188(6):672-680.
Across a range of LET sources, we found that different ion species have different detrimental impacts at extended time points post exposure that can lead sustained declines in behavioral performances. A significant dose effect was observed on recognition memory and activity levels measured 9 months postirradiation, regardless of radiation source. In contrast, we observed that each ion species had a distinct effect on anxiety, motor coordination and spatial memory at extended time points.
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Dose- and ion-dependent effects in the oxidative stress response to space-like radiation exposure in the skeletal system.
Alwood JS, Tran LH, Schreurs AS, Shirazi-Fard Y, Kumar A, Hilton D, Tahimic CGT, Globus RK. Int J Mol Sci. 2017 Oct 10;18(10):E2117.
This article reports on impairment of osteoblastogenesis in 16-weeks old, male, C57BL6/J mice by protons (150 MeV/n) 56Fe ions (600 MeV/n) using either low (5 or 10 cGy) or high (50 or 200 cGy) doses at NASA’s Space Radiation Lab. The authors’ conclusion is that high-LET irradiation at 200 cGy impaired osteoblastogenesis and regulated steady-state gene expression of select redox-related genes during osteoblastogenesis, which may contribute to persistent bone loss.
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Effect of densely ionizing radiation on cardiomyocyte differentiation from human-induced pluripotent stem cells.
Baljinnyam E, Venkatesh S, Gordan R, Mareedu S, Zhang J, Xie LH, Azzam EI, Suzuki CK, Fraidenraich D. Physiol Rep. 2017 Aug;5(15):e13308.
Studies with human hearts are not feasible as cardiac biopsies are extremely rare. Thus, innovative approaches are greatly needed to investigate human cardiac cell biology in a dish. To achieve this, we developed a system whereby human induced pluripotent stem cells (hiPSCs) maintained in culture, were used to evaluate the effects of densely ionizing radiation on cardiac differentiation. hiPSCs were exposed to low fluences of 3.7 MeV a particles (mean linear energy transfer ~109 keV/mm), and then differentiated into beating cardiomyocytes (hiPSC-CMs), permitting us to conduct molecular, morphological, and functional assessments. We report that low mean absorbed doses of a particles (0.5-10 cGy) applied to hiPSCs does not affect their capacity to become beating cardiomyocytes, but has direct consequences on the generation of arrhythmic profiles and on the number of differentiated cells.

The results obtained in the study have broader implications for future investigations. For example, hiPSCs can be generated using fibroblasts or blood lymphocytes, or even urine from astronauts before and after space travel. These astronaut-derived hiPSCs may be invaluable for further characterizations. Another exciting therapeutic possibility is the prospect of using astronaut-derived pre-mission hiPSCs, as these cells can be differentiated into cardiomyocytes, and subsequently transplanted back into the astronaut in a personalized manner to correct for unexpected pathologies resulting from deep space travel.
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Evaluation of HZETRN on the Martian surface: Sensitivity tests and model results.
Slaba TC, Stoffle NN. Life Sci Space Res. 2017 Aug;14:29-35.
The Mars Science Laboratory Radiation Assessment Detector (MSLRAD) provides continuous measurements of dose, dose equivalent, and particle flux on the surface of Mars. Various radiation physics and transport models have been compared to the MSLRAD data, and in June 2016, a workshop was held in Boulder, CO to have a “blind” comparison between models and new MSLRAD measurements. Certain aspects of the environmental conditions on the Martian surface were provided to the modeling teams such as the time period over which the measurements occurred and the atmospheric column density. Other details were intentionally left unspecified. For example, each team was free to choose a model to describe the primary GCR particle spectra, atmosphere and regolith composition, and other related factors. Leveraging the high degree of computational efficiency and accuracy associated with HZETRN, sensitivity tests were performed to determine to what extent some of the unspecified factors influence quantities of interest on the Martian surface. Results of these tests are useful in providing context for the summary comparison paper of Matthia et al. (2017) (contained within the same issue as this paper) so that variation between codes and differences against MSLRAD data can be more clearly interpreted. This paper appears in a special issue of Life Sciences in Space Research along with several other modeling, measurement data analysis, and summary papers.
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Different Sequences of Fractionated Low-Dose Proton and Single Iron-Radiation-Induced Divergent Biological Responses in the Heart.
Sasi SP, Yan X, Zuriaga-Herrero M, Gee H, Lee J, Song J, Onufrak J, Morgan J, Enderling H, Walsh K, Kishore R, Goukassian DA. Radiat Res. August 2017, Vol. 188, No. 2, pp. 191-203.(2017).
We previously reported the effects of a single, whole-body, low-dose 1H (0.5 Gy, 1 GeV) and 56Fe (0.15 Gy, 1 GeV/nucleon) ion irradiation on the CV system during normal aging and under ischemic conditions. These studies signified the long-term (up to 10 months) negative effects of irradiation on systolic and diastolic functions of the heart accompanied by increased hypertrophic signaling contributing to heart failure. In the model of acute myocardial infarct, the cardiac tissue recovery and regeneration after exposure to 0.15 Gy 56Fe radiation demonstrated long-lasting detrimental effects including loss of cardiac function and worsened cardiac remodeling over the period of 10 months. On the other hand, 0.5 Gy 1H irradiation induced positive effects during recovery after a MI event, which may be attributed to a possible ischemic preconditioning-like effect of low-proton irradiation of the heart in case of possible adverse cardiac event, such as acute myocardial infarct (AMI). Because there is essentially no data available on the effects of different sequential, fractionated low-dose charged particle (SPE-like proton and HZE) irradiations to the CV system, we used same murine models to examine the effects of acute, whole-body fractionated low-dose 1H exposure by itself and in combination with a single low dose of 56Fe radiation before or after fractionated 1H to emulate a possible space-like environment. Our1H vs. a single 56Fe-IR. These findings also provide initial mechanistic insight into the development of CV morbidity and mortality induced by mixed charged particle radiation in the heart tissue. Additionally, they emphasize the necessity to determine underlying molecular mechanisms responsible for this significant mix ion fractionation and sequence-dependent divergent responses in the heart during aging and in case of a possible ischemic cardiovascular event.
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Mars science laboratory radiation assessment detector (MSL/RAD) modeling workshop proceedings.
Hassler DM, Norbury JW, Reitz G. Life Sci Space Res. 2017 Aug;14:1-2.
This paper is an introduction to the special issue of Life Sciences in Space Research devoted to comparisons of space radiation transport codes with recent measurements made by the Mars Science Laboratory Radiation Assessment Detector.
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Comparing HZETRN, SHIELD, FLUKA and GEANT transport codes.
J. Norbury, T. Slaba, N. Sobolevsky, B. Reddell Life Sciences in Space Research, vol. 14, pp. 64-73, 2017.
The space radiation transport codes, HZETRN, SHIELD, FLUKA and GEANT are compared to each other for heavy-ion, light-ion (isotopes of Hydrogen and Helium) and pion production after the galactic cosmic ray spectrum is transported through various aluminum shield thicknesses. The paper shows that the biggest differences among the codes occurs for light-ion production.
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The radiation environment on the surface of Mars - Summary of model calculations and comparison to RAD data.
Matthiä D, Hassler DM, de Wet W, Ehresmann B, Firan A, Flores-McLaughlin J, Guo J, Heilbronn LH, Lee K, Ratliff H, Rios RR, Slaba TC, Smith MA, Stoffle NN, Townsend LW, Berger T, Reitz G, Wimmer-Schweingruber RF, Zeitlin C. Life Sci Space Res. 2017 Aug;14:57-63. Epub 2017 Jun 28.
This article summarizes the results of a workshop held in June 2016 in Boulder, CO. The goal of the workshop was validating models and simulations of the radiation environment originating from galactic cosmic rays on the Martian surface with data recorded by the Radiation Assessment Detector (RAD) on the Curiosity rover of the Mars Science Laboratory (MSL). For this purpose, a time period (15 Nov 2015 to 15 Jan 2016) was selected for which the model calculations were performed; measurements taken by RAD during the same time were used for the comparison. The paper presents differential particle fluxes calculated using different galactic cosmic ray spectra in combination with particle transport codes: GEANT4, HETC-HEDS, HZETRN, MCNP6, and PHITS. The results of the numerical models are compared to charged particle spectra stopping in the RAD detector in the energy range between a few tens and a few hundred MeV per nucleon and neutral particle spectra, i.e. photons and neutrons, between 10 MeV and 1 GeV. Dose rates and dose equivalent rates as well as the corresponding quality factors from models and measurement are presented as well.
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A calculation of the radiation environment on the Martian surface.
de Wet WC, Townsend LW. Life Sci Space Res. 2017 Aug;14:51-6.
The radiation environment on the Martian surface, as produced by galactic cosmic radiation incident on the atmosphere, is modeled using the Monte Carlo radiation transport code, High Energy Transport Code—Human Exploration and Development in Space (HETC–HEDS). Calculated fluxes for neutrons, protons, deuterons, tritons, helions, alpha particles, and heavier ions up to Fe are compared with measurements taken by the Radiation Assessment Detector (RAD) instrument aboard the Mars Science Laboratory over a period of 2 months. The degree of agreement between measured and calculated surface flux values over the limited energy range of the measurements is found to vary significantly depending on the particle species or group. However, in many cases the fluxes predicted by HETC–HEDS fall well within the experimental uncertainty. The calculated results for alpha particles and the heavy ion groups Z=3–5, Z=6–8, Z=9–13 and Z>24 are in the best agreement, each with an average relative difference from measured data of less than 40%. Predictions for neutrons, protons, deuterons, tritons, Helium-3, and the heavy ion group Z=14–24 have differences from the measurements, in some cases, greater than 50%. Future updates to the secondary light particle production methods in the nuclear model within HETC–HEDS are expected to improve light ion flux predictions.
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Radiation transport simulation of the Martian GCR surface flux and dose estimation using spherical geometry in PHITS compared to MSL-RAD measurements.
Flores-McLaughlin J. Life Sci Space Res. 2017 Aug;14:36-42.
The Martian surface radiation environment is composed of galactic cosmic radiation, secondary particles produced by their interaction with the Martian atmosphere, albedo particles from the Martian regolith and occasional solar particle events. Despite this complex physical environment with potentially significant locational and geometric dependencies, computational resources often limit radiation environment calculations to a one-dimensional or slab geometry specification. To better account for Martian geometry, spherical volumes with respective Martian material densities are adopted in this model. This physical description is modeled with the PHITS radiation transport code and compared to a portion of measurements from the Radiation Assessment Detector of the Mars Science Laboratory. Particle spectra measured between 15 November 2015 and 15 January 2016 and PHITS model results calculated for this time period are compared. Results indicate good agreement between simulated dose rates, proton, neutron and gamma spectra. This work was originally presented at the 1st Mars Space Radiation Modeling Workshop held in 2016 in Boulder, CO.
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Simulation of the GCR spectrum in the Mars Curiosity Rover’s RAD detector using MCNP6.
Ratliff HN, Smith MBR, Heilbronn L. Life Sci Space Res. 2017 Aug;14:43-50.
The paper presents results from MCNP6 simulations modeling the radiation environment induced by galactic cosmic rays (GCRs) on the surface of Mars as seen by the Radiation Assessment Detector (RAD) onboard NASA’s Curiosity rover. The detector had two separate particle acceptance angles, 4π and 30° off zenith. All ions with Z = 1 through Z = 28 were tracked in both scenarios while some additional secondary particles were only tracked in the 4π cases. This work was part of a collaborative workshop hosted by the Southwest Research Institute comparing RAD measurements with the simulated results of five modeling teams each using a different particle transport code.

–HEDS fall well within the experimental uncertainty. The calculated results for alpha particles and the heavy ion groups Z=3–5, Z=6–8, Z=9–13 and Z>24 are in the best agreement, each with an average relative difference from measured data of less than 40%. Predictions for neutrons, protons, deuterons, tritons, Helium-3, and the heavy ion group Z=14–24 have differences from the measurements, in some cases, greater than 50%. Future updates to the secondary light particle production methods in the nuclear model within HETC–HEDS are expected to improve light ion flux predictions.
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Men, Women, and Space Travel: Gene-Linked Molecular Networks, Human Countermeasures, and Legal and Ethical Considerations
Schmidt MA, Bailey SM, Goodwin TJ, Jones JA, Killian JP, Legato MJ, Limoli C, Moussa S, Ploutz-Snyder L. Gend Genome. 2017 Jun 1;1(2):54-67.
A roundtable discussion to consider the extensive differences between men and women, including both their strengths and vulnerabilities, in preparing professional astronauts for space travel.
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Space-type radiation induces multimodal responses in the mouse gut microbiome and metabolome.
Casero D, Gill K, Sridharan V, Koturbash I, Nelson G, Hauer-Jensen M, Boerma M, Braun J, Cheema AK. Microbiome. 2017 Aug 18;5(1):105.
Pathophysiological manifestations after low dose radiation exposure are strongly influenced by non-cytocidal radiation effects, including changes in the microbiome and host gene expression. Although the importance of the gut microbiome in the maintenance of human health is well established, little is known about the role of radiation in altering the microbiome during deep-space travel. Using a mouse model for exposure to high LET radiation, we observed substantial changes in the composition and functional potential of the gut microbiome. These were accompanied by changes in the abundance of multiple metabolites, which were related to the enzymatic activity of the predicted metagenome by means of metabolic network modeling. The implication of microbiome-mediated pathophysiology after low dose ionizing radiation may be an unappreciated biologic hazard of space travel and deserves experimental validation.
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Older In the News items may be found in the Bibliography or in the THREE Archive.


Basic Concepts of Space Radiation

In order to understand the space radiation risks faced by human explorers, it is necessary to have a clear idea of what it is, where it is, and what happens when space radiation interacts with matter. The articles in this section describe the space radiation environment, the nuclear and atomic interactions with the constituent atoms of materials – especially living materials – in space, and the ways in which energy is deposited in biologically significant molecules.

Some of the articles are taken from the Appendices of a 1998 Strategic Plan I authored during my tenure at NASA and others are presentations given by NASA Summer School faculty. There is a fair amount of overlap, both within this section and between this section and other sections, where the subjects are discussed in greater detail. This is welcome, reflecting as it does, different – and broadening – perspectives on the topics covered.

Walter Schimmerling
THREE Chief Editor

  • The Space Radiation Environment
    • Introduction – Walter Schimmerling (PDF)
    • The Natural space Ionizing Radiation Environment – Patrick O’Neill (swf) Introduction (PDF)
    • Fluence Rates, Delta Rays and Cell Nucleus Hit Rates from Galactic Cosmic Rays – Stanley B Curtis (PDF)
    • Solar Particle Events and Radiation Exposure in Space – Shaowen Hu (PDF)
  • Interactions of Radiation with Matter – Walter Schimmerling (PDF)
    • Particle Interactions Overview – Lawrence Heilbronn (swf)
    • Physics Summary – Lawrence Heilbronn (swf)
    • Neutron Properties and Definitions – Lawrence Heilbronn (swf)
    • Neutron Lectures Supplement – Lawrence Heilbronn (PDF)
  • Dose and Dose Rate Effectiveness Factors – Walter Schimmerling  (PDF)
    • Low LET Physics Topics – Gregory Nelson (swf)  Introduction (PDF)
    • A Note On The Dose-Rate-Effectiveness Factor and its Progeny 
      DDREF -  R.J.M. Fry (PDF)
  • Track Structure
    • Introduction to Track Structure and z*22 - Stanley B. Curtis (PDF)
    • Radiation Quality and Space Radiation Risks – Francis Cucinotta (swf)
    • Development of Monte Carlo Track Structure Codes – Larry Toburen (PDF)
    • Microdosimetry and Detector Responses – Leslie A. Braby (PDF)
    • Interpreting Microdosimetric Spectra – J. F. Dicello and F. A Cucinotta (PDF)
    • Monte Carlo Track Simulations – Michael Dingfelder (PDF)
    • Radiation Track Structure – Dudley T. Goodhead (swf) Abstract (PDF)
    • Track structure and the quality factor for space radiation cancer risk - Dudley T. Goodhead (PDF)
  • Elementary Concepts of Shielding – Walter Schimmerling  (PDF)
    • Heavy Ions and Shielding Physics – Lawrence Heilbronn (swf)


Introduction to THREE
Walter Schimmerling

Video presentation of
Research Solutions to Space Radiation Impacts on Human Exploration
Slides in PDF format
Francis A. Cucinotta, Ph.D.
Chief Scientist, Space Radiation Program
NASA Johnson Space Center
Houston, Texas
Aerospace Medicine Grand Rounds
March 23, 2010

Radiation and Human Space Exploration Video
NASA Human Research Program

Radiation tracks and radiation track simulation video
Ianik Plante, Ph.D.
Universities Space Research Association
Division of Space Life Sciences
NASA Johnson Space Center
Houston, Texas

Radiation tracks and radiation track simulation video is excerpted from the article:
Radiation chemistry and oxidative stress (PDF)
Ianik Plante, Ph.D.

Video Presentation of
Space Radiation and Cataracts
Eleanor Blakely
Life Sciences, Lawrence Berkeley National Laboratory
Berkeley, California
July 16, 2003


Glossary derived from:
Human Research Program Integrated Research Plan, Revision A, (January 2009). National Aeronautics and Space Administration, Johnson Space Center, Houston, Texas 77058, pages 232-280.

Exploration Systems Radiation Monitoring Requirements (Sept 2012). Page ii. Ronald Turner.

Report No. 153: Information Needed to Make Radiation Protection Recommendations for Space Missions Beyond Low-Earth Orbit (2006). National Council on Radiation Protection and Measurements, pages 309-318.  Reprinted with permission of the National Council on Radiation Protection and Measurements.

Managing Space Radiation Risk in the New Era of Space Exploration (2008). Committee on the Evaluation of Radiation Shielding for Space Exploration, National Research Council. National Academies Press, pages 111-118.

Contents: A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

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AAPM: American Association of Physicists in Medicine.

absolute risk: Expression of excess risk due to exposure as the arithmetic difference between the risk among those exposed and that obtaining in the absence of exposure.

absorbed dose (D): Average amount of energy imparted by ionizing particles to a unit mass of irradiated material in a volume sufficiently small to disregard variations in the radiation field but sufficiently large to average over statistical fluctuations in energy deposition, and where energy imparted is the difference between energy entering the volume and energy leaving the volume. The same dose has different consequences depending on the type of radiation delivered. Unit: gray (Gy), equivalent to 1 J/kg.

ACE: Advanced Composition Explorer Mission, launched in 1997 and orbiting the L1 libration point to sample energetic particles arriving from the Sun and interstellar and galactic sources.  It also provides continuous coverage of solar wind parameters and solar energetic particle intensities (space weather).  When reporting space weather, it can provide an advance warning (about one hour) of geomagnetic storms that can overload power grids, disrupt communications on Earth, and present a hazard to astronauts.

acute effects: short-term biological effects of exposure to radiation, including headaches, dizziness, nausea, and illness that can range from mild to fatal.

acute exposure: Radiation exposure of short duration.

AGS: Alternating Gradient Synchrotron (at Brookhaven National Laboratory).

ALARA (As Low As Reasonably Achievable):  An essential operational safety requirement, as well as a regulatory requirement, that em­phasizes keeping exposure to radiation as low as possible using reasonable methods, and not treating dose limits as “tolerance values”; defined at NASA as limiting radiation exposure to a level that will result in an estimated risk below the limit of the 95 percent confidence level.

albedo: secondary radiation produced by interactions of galactic cosmic rays and high-energy solar protons with matter in the atmosphere or on the surface.

ALL: acute lymphocytic leukemia.

alpha particle: An energetic charged nucleus consisting of two protons and two neutrons. This particle is identical to the 4He nucleus.

ALTEA: Anomalous Long-Term Effects in Astronauts study .

AM: amplitude modulation.

AMA: American Medical Association.

AMAC: American Medical Advisory Committee.

AML: acute myelogenous leukemia.

Amu: atomic mass unit (ALSO: u).

ANLL: acute nonlymphocytic leukemia.

annual risk: The risk in a given year from an earlier exposure. The annual risk (average) from an exposure is the lifetime risk divided by the number of years of expression.

ANP: atrial natriuretic peptide.

ANS: American Nuclear Society.

ANSI: American National Standards Institute.

AU: Astronomical Unit (distance from the Earth to the Sun)

Apoe4: Apoliprotein E isoform 4. Modification of Apo4 is major risk factor in Alzheimer's disease.

apoptosis: A specific mode of cell death (also known as programmed cell death) that can be triggered by exposure to radiation, especially in cells of lymphoid/myeloid or epithelial lineage. Extensive apoptosis contributes to the hematopoietic and gastrointestinal symptoms seen in acute radiation syndrome.

ARC: NASA Ames Research Center.

Ares V/Heavy Lift Launch Vehicle: a NASA vehicle intended to deliver cargo from Earth to low Earth orbit.

ARM: Atmospheric Radiation Measurements.

ascent stage: The pressurized upper stage of the Lunar Lander in which the crew pilots the lander from lunar orbit to the lunar surface and return. The ascent stage takes off from the descent stage, leaving the latter behind on the surface.

AT: ataxia telangiectasia.

ATM: ataxia telangiectasia mutated.

AU: Astronomical Unit (Approx. distance from the Earth to the Sun)

AX-2: NASA Ames Research Center Experimental Suit 2, designed during the Apollo program as a lunar surface hard suit to bend at the waist and rotate in the torso so that the crew member can reach down to the ground with one hand. Fabricated from fiberglass.

AX-5: NASA Ames Research Center Experimental Suit 5, designed during the Space Station Advanced Development program to provide a durable hard suit for extended operations in zero gravity. Fabricated from numerically milled aluminum forgings.

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background radiation: The amount of radiation to which a member of the population is exposed from natural sources, such as terrestrial radiation from naturally-occurring radionuclides in the soil, cosmic radiation originating in outer space, and naturally-occurring radionuclides deposited in the human body. The natural background radiation received by an individual depends on geographic location and living habits. In the United States, the background radiation is on the order of 1 mSv y–1, excluding indoor radon which amounts to ~2 mSv/year on average.

BAF: Booster Applications Facility (the name used to designate the NSRL during planning and construction phases).

BaRyoN: Quark bound state with zero strangeness.

BCC: basal cell carcinoma.

BCD: budget change directive.

BEIR: Biological Effects of Ionizing Radiation. One of a series of reports on the health risks from exposure to low levels of ionizing radiation issued by the Committee to Assess Health Risks from Exposure to Low Levels of Ionizing Radiation, Board on Radiation Effects, Research Division on Earth and Life Studies, National Research Council of the National Academies of Science of the United States, referred to by a Roman number denoting its position in the sequence of reports. At the time of this writing, the latest report is BEIR VII.

BEVALAC: An accelerator system at Lawrence Berkeley National Laboratory consisting of the Bevatron (an early, high-energy synchrotron accelerator constructed in the 1950s and used to discover the antiproton), accelerating particles delivered by the SuperHILAC (first built as the HILAC - Heavy Ion Linear Accelerator - in 1957; along with a similar one at Yale University, the first machine in the US built specifically to accelerate heavy ions, completely rebuilt into the SuperHILAC in 1971). Closed in 1993.

biological end point: effect or response being assessed, e.g., cancer, cataracts.

bipolar device: a type of semiconductor whose operation is based on both majority and minority carriers.

BNL: Brookhaven National Laboratory in Upton (Long Island), New York.

BRCA1: breast cancer 1 tumor suppressor gene.

BRCA2: breast cancer 2 tumor suppressor gene.

BrdU: bromodeoxyuridine.

BRYNTRN: BaRYoN TRaNsport code, a computer code for simulating baryon transport.

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CAD: computer aided design.

CaLV: Cargo Launch Vehicle.

CAM : computerized anatomical man model.

carbon composite: a composite incorporating carbon and other materials for use in lightweight structures, strong enough to substitute for aluminum and other metals in the construction of many parts of a spacecraft, notably the pressure vessel shell. It may incorporate boron, epoxy, polyethylene, hydrogen, or other materials that enhance radiation shielding properties.

CARD: Constellation Architecture Requirements Document; CxP 7000

cargo habitat: a crew habitat that the Lunar Lander carries for delivery to the Lunar Outpost as a key part of the “Outpost-first” strategy considered by NASA as part of the Space Exploration Initiative program.

CB: Control Board.

CDC: Center for Disease Control and Prevention.

CEDE: committed effective dose equivalent.

CENELEC: European Committee for Electrotechnical Standardization.

CEQATR: Constellation Program Environmental Qualification and Acceptance Testing Requirements; CxP 70036

CERN: European Organization for Nuclear Research.

CEV: Crew Exploration Vehicle.

CFR: Code of Federal Regulations.

CHMO: Chief Health And Medical Officer (NASA).

chronic effects: long-lasting effects of exposure to radiation; includes cancer, cataracts, and nervous system damage.

chronic exposure: Radiation exposure over long times (continuous or fractionated).

CI: confidence interval.

CL: confidence level.

CLV: Crew Launch Vehicle.

CME: coronal mass ejection, an explosion of plasma released from the atmosphere (or corona) of the Sun.

CML: chronic myelogenous leukemia.

CNP: cyclic nucleotide phosphatase.

CNS: central nervous system.

Composites: materials made from two or more constituent materials with significantly different physical or chemical properties which remain separate and distinct at the macroscopic or microscopic scale within the finished structure.

computerized anatomical male/female: a model of human geometry used to evaluate radiation doses at various points inside the body.

Constellation system: the complete ensemble of launch vehicles, flight vehicles, ground support, support services, and lunar and planetary surface systems associated with the Vision for Space Exploration initiated during the Bush administration.

coronal mass ejection (CME): A transient outflow of plasma from or through the solar corona which may be associated with the generation of solar-particle events.

cosmic-ray modulation: The variation of the observed cosmic-ray intensity as a function of the solar cycle. The cosmic-ray intensity within the solar system is observed to vary approximately inversely with the solar activity cycle that controls the interplanetary magnetic field.

COTS: commercial, off-the-shelf.

CPD: crew passive dosimeter.

CPU: central processor unit.

CRaTER: Cosmic Ray Telescope for the Effects of Radiation.

CRCPD: Conference of Radiation Control Program Directors.

CREME96: Cosmic Ray Effects on Micro-Electronics (1996 revision), a computer code.

cross section (σ): probability per unit particle fluence of a given end point. Unit: cm2.

CT: computed tomography.

CTA: conditioned taste aversion.

CVD: cardiovascular disease.

CW: continuous wave.

CxP: Constellation Program.

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Dr: dose-rate (Gy/hr).

DAAC: Distributed Active Archive Center.

DDREF: dose and dose-rate effectiveness factor (the degree to which both dose and dose rate may influence the biological effects of exposure to a given dose of radiation).

delta rays: Electrons directly ejected from atoms in matter by radiation.

descent stage: The lower stage of the Lunar Lander that includes the descent and landing engines and propellant tanks to serve them. The crew ascending back to lunar orbit in the ascent stage leaves the descent stage behind on the lunar surface.

descent stage habitat: in the descent stage, a pressurized crew habitat in which the crew would live during sortie missions.

deterministic process: process whereby a given event will occur whenever its dose threshold is exceeded.

deterministic effects: early radiation effects usually related to a significant fraction of cell loss, exceeding the threshold for impairment of function in a tissue; so called because the statistical fluctuations in the number of affected cells are very small compared to the number of cells required to reach the threshold (ICRP 1991), above which the severity varies with dose.

detriment: Health detriment is the sum of the probabilities of all the components of health effects. These include in addition to fatal cancer the probability of heritable effects and the probability of morbidity from nonfatal cancer.

DHS: Department of Homeland Security.

DNA: deoxyribonucleic acid.

DOD: Department of Defense.

DOE: Department of Energy.

dose: A general term used when the context is not specific to a particular dose quantity. When the context is specific, the name or symbol for the quantity is used [i.e., absorbed dose (D), mean absorbed dose (DT), dose equivalent (H), effective dose (E), equivalent dose (HT), or organ dose equivalent].

dose equivalent ( H ): Estimate of radiation risk that accounts for differences in the biological effectiveness of different types of charged particles that produce the absorbed dose. H=Q × D, where Q is a quality factor based on the type of radiation (Q = 1 for x-rays). NASA uses Q as specified in ICRP Publication 60 (ICRP, 1991). Unit: sievert (Sv), equivalent to 1 J/kg.

dose limit: A limit on radiation dose that is applied by restricting exposure to individuals or groups of individuals in order to prevent the occurrence of radiation-induced deterministic effects or to limit the probability of radiation related stochastic effects to an acceptable level. For astronauts working in low-Earth orbit, unique dose limits for deterministic and stochastic effects have been recommended by NCRP.

dose rate: Dose delivered per unit time. Can refer to any dose quantity (e.g., absorbed dose, dose equivalent).

dose-response model: A mathematical formulation of the way in which the effect, or response, depends on dose.

dosimeter: A radiation detection device worn or carried by an individual to monitor the individual's radiation exposure. For space activities, a device worn or carried by an astronaut in-flight.

DREF: dose rate effectiveness factor (the degree to which dose rate may influence the biological effects of exposure to a given dose of radiation).

DRM: Design Reference Mission.

DSB: double strand break.

DSNE: Constellation Program Design Specification for Natural Environments; CxP 70023

DTRA: Defense Threat Reduction Agency.

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E: effective dose/ energy.

EAR:excess additive risk (cf. absolute risk).

ED50: dose to cause 50 % of the population to have the effect (e.g., nausea).

EDS: Earth departure stage.

EEG: electroencephalogram.

effective dose ( E ): The sum over specified tissues of the products of the equivalent dose in a tissue (HT) and the tissue weighting factor for that tissue or organ (wT) (i.e., E = wTHT). Effective dose (E) applies only to stochastic effects. Unit: sievert (Sv), equivalent to 1 J/kg.

electron volt (eV): a unit of energy equivalent to 1.602 × 10–19 joules.

ELF: extremely low frequency.

ELR: excess lifetime risk.

EMF: electromagnetic field.

EML: Environmental Measurements Laboratory, New York, NY.

EMS: emergency medical services.

EMU: Extravehicular mobility unit, the space suit developed for space shuttle crews that also serves on the ISS.  The EMU features a hard upper torso and soft lower torso, arms, and legs over the pressure bladder. The entire EMU except the helmets and boots is covered by the thermal micrometeoroid garment.

electron volt (eV): A unit of energy = 1.6 x 10–12 ergs = 1.6 x 10–19 J; 1 eV is equivalent to the energy gained by an electron in passing through a potential difference of 1 V; 1 keV = 1,000 eV; 1 MeV = 1,000,000 eV.

EOS: Earth Observing System.

EPA: Environmental Protection Agency.

equivalent dose ( HT): The product of the mean absorbed dose in an organ or tissue and the radiation weighting factor (wR) of the radiation type of interest. For external exposure wR applies to the radiation type incident on the body.

ERR:excess relative risk.

erythema: A redness of the skin.

ESA: European Space Agency.

ESMD: Exploration Systems Mission Directorate (NASA).

ESP: energetic storm particle.

ESTEC: European Space Research and Technology Centre.

EVCPDS: Extra Vehicle Charged Particle Directional Spectrometer

excess relative risk (ERR): The ratio between the total risk, including the increase due to radiation exposure, and the baseline risk in the absence of radiation exposure; if the excess equals the baseline the relative risk is two.

exposure (technical use): A measure of the ionization produced in air by x or gamma radiation. Exposure is the sum of electric charges on all ions of one sign produced in air when all electrons liberated by photons in a volume of air are completely stopped, divided by the mass of the air in the volume. The unit of exposure in air is the roentgen (R) or in SI units it is expressed in coulombs (C), 1 R = 2.58 x 10–4 C/kg.

exposure (non-technical use): the presentation of an individual or material to radiation likely to deliver a significant dose over a period of time.

EVA: extravehicular activity.

excess risk: the increase in the probability of a certain effect on an individual who has been exposed to a given dose of radiation over the probability of that effect in the absence of radiation exposure.

extravehicular activity: Any activity undertaken by the crew outside a space vehicle or habitat.

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favorable propagation path: A concept suggesting that the Archimedean spiral path from the earth to the sun would connect to a specific solar longitude. It is based on the concept that charged particles travel along the interplanetary magnetic field which is transported out from the sun. For an idealized constant speed solar wind flow, if the interplanetary magnetic field is frozen in the plasma, then the result would form an Archimedean spiral.

FEMA: Federal Emergency Management Agency.

FIRE: First ISCCP Regional Experiment.

first ionization potential: The energy required to remove the least bound electron from an electrically neutral atom. (The ionization potential is usually given in electron volts.)

FISH: fluorescence in situ hybridization.

fluence: (1) ICRU definition : The quotient of dN by da, where dN is the number of particles incident on a sphere of cross-sectional area da (i.e., Φ = dN/da). The unit for fluence is 1/m2, but cm–2 is frequently used; (fluence may be a function of one or more other variables [e.g., Φ (L,t), the distribution of fluence as a function of linear energy transfer (L) and time (t)]. (2) planar fluence (F): The net number of charged particles traversing a given area. Unit: particles/cm2.

fluence rate (dF/dt): Change in fluence over a given small time interval, or the time derivative of the fluence. Unit: 1/m2s.

FLUKA: a general purpose Monte-Carlo computer code for calculations of particle transport and interactions with matter

flux ): Term used historically by the nuclear community for fluence rate and also used for particle flux density, but deprecated by the ICRU convention to eliminate confusion between the terms “particle flux density” and “radiant flux.” See fluence rate.

FM: frequency modulation.

FR: fixed-ratio.

fractionation: The delivery of a given total dose of radiation as several smaller doses, separated by intervals of time.

FSP: fission surface power.

FY: Fiscal Year.

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galactic cosmic rays: the components of galactic cosmic radiation.

galactic cosmic radiation (GCR): The charged-particle radiation outside the Earth magnetosphere comprised of 2 % electrons and positrons, and 98 % nuclei, the latter component consisting (by fluence) of 87 % protons, 12 % helium ions, and 1 % high atomic number, high-energy (HZE) particles.

gamma rays: Short-wavelength electromagnetic radiation of nuclear origin (approximate range of energy: 10 keV to 9 MeV).

GCR: galactic cosmic radiation/ galactic cosmic rays.

GCR: galactic cosmic radiation.

GEANT: A computer application for the simulation of the passage of particles through matter including detector description and simulation.

GEO: Geostationary or Geosynchronous Earth Orbit.

Geostationary Operational Environmental Satellite ( GOES): A satellite in geosynchronous orbit used for monitoring protons. The satellite travel at the same angular speed above the equator as Earth’s rotation and therefore appears stationary when observed from Earth’s surface.

GGTP: gamma-glutamyl transpeptidase.

GI: gastrointestinal.

GLE: ground level event.

GM: geometric mean.

GPM: Global Precipitation Measurement.

gray (Gy): The International System (SI) unit of absorbed dose of radiation, 1 Gy = 1 J kg–1.

gray equivalent (GT or Gy-Eq): The product of DT and Ri, where DT is the mean absorbed dose in an organ or tissue and Ri is a recommended value for relative biological effectiveness for deterministic effects for a given particle type i incident on the body ( GT = Ri × DT). The SI unit is J/kg (NCRP, 2000).

GSD: geometric standard deviation (the standard deviation of the logarithms of a set of random variables, for which the geometric mean is the square root of their product.

GSI(Gesellschaft für Schwerionenforschung): Helmholtz Centre for Heavy Ion Research in Darmstadt, Germany.

GSM: global system for mobile communications.

GT: gray equivalent.

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HACD: Human Adaptation and Countermeasures Division.

HDPE: high-density polyethylene, defined as having a density greater than 0.94 g/cm3.

heavy charged particles: Atomic and subatomic charged particles with masses substantially heavier than that of an electron.

heavy ions: Nuclei of elements heavier than helium such as nitrogen, carbon, boron, neon, argon or iron which are positively charged due to some or all of the atomic electrons having been stripped from them.

HEDS: Human Exploration and Development of Space.

HEFD: Habitability and Environmental Factors Division.

heliocentric: A measurement system with its origin at the center of the sun.

heliolongitude: Imaginary lines of longitude on the sun measured east (left) or west (right) of the central meridian (imaginary north-south line through the middle of the visible solar disk) as viewed from Earth. The left edge of the solar disk is 90°E and the right edge is 90°W.

heliosphere: The magnetic bubble containing the solar system, solar wind, and entire solar magnetic field. It extends beyond the orbit of Pluto.

HEPAD: High Energy Proton and Alpha Detector.

HIDH: Human Integration Design Handbook; NASA/SP-2010-3407

high atomic number, high-energy ( HZE) particles: Heavy ions having an atomic number greater than that of helium (such as nitrogen, carbon, boron, neon, argon or iron ions that are positively charged) and having high kinetic energy.

high-LET: Radiation having a high-linear energy transfer; for example, protons, alpha particles, heavy ions, and interaction products of fast neutrons.

HIMAC: Heavy Ion Medical Accelerator, Chiba Japan.

HMF: heliospheric magnetic field.

HPC: Hydrological Process and Climate.

HPRT: hypoxanthine-guanine phosphoribosyl transferase.

HQ: Headquarters.

HRP: Human Research Program.

HRP CB: Human Research Program Control Board.

HSIR: Constellation Program Human Systems Integration Requirements; CxP 70024

H T : equivalent dose.

HZE: high atomic number and energy.

HZETRN: a transport code developed specifically for high-charge, high-energy particles that is widely used for space radiation shielding and design calculations.

HZE: high atomic number, high energy/ highly energetic, heavy, charged particles.

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IACUC: Institutional Animal Care and Use Committee.

IAEA: International Atomic Energy Agency.

ICNIRP: International Commission on Non-Ionizing Radiation Protection.

ICRP: International Commission on Radiation Protection.

ICRU: International Commission on Radiation Units and Measurements.

IDIQ: Indefinite delivery/indefinite quantity.

IEEE: Institute of Electrical and Electronics engineers.

IL-2: interleukin-2.

IL-6: interleukin-6.

incidence: The rate of occurrence of a disease, usually expressed in number of cases per million .

IND: improvised (or otherwise acquired) nuclear device.

interplanetary magnetic field: The magnetic field in interplanetary space. The interplanetary magnetic field is transported out from the sun via the solar wind.

interplanetary shocks: An abrupt change in the velocity or density of charged particles moving faster than the wave propagation speed in interplanetary space, so that higher velocity components bunch into lower velocity components before these can get out of the way.

ionizing radiation: Any electromagnetic or particulate radiation capable of producing ions, directly or indirectly, in its passage through matter.

ionization: The process by which a neutral atom or molecule acquires a positive or negative charge through the loss or gain of one or more orbital electrons.

IPT: Integrated Product Team.

IRMA: Integrated Risk Management Application.

ISCCP: International Satellite Cloud Climatology Project.

ISS: International Space Station.

ISSMP: ISS Medical Project.

ITA: Internal Task Agreement.

IVCPDS: Intra Vehicle Charged Particle Directional Spectrometer

IV & V: Independent Validation & Verification.

IWG: Investigator Working Group.

IWS: Investigator Workshop.

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JSC: NASA Johnson Space Center.

JWST: James Webb Space Telescope.

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kerma: (an acronym for “Kinetic energy released in materials;” the sum of the initial kinetic energies for all charged particles released by uncharged ionizing radiation in a small sample of material divided by the mass of the sample. Kerma is the same as dose when charged particle equilibrium exists (i.e., when, on the average, the number of charged particles leaving the sample is compensated by an equal number of charged particles entering the sample).

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LAP: latency associated peptide.

LAR: lifetime attributable risk.

LaRC: NASA Langley Research Center.

LAT: Lunar Architecture Team.

latchup: an anomalous state in a semiconductor in which the device no longer responds to input signals.

latent period: Period or state of seeming inactivity between time of exposure of tissue to an injurious agent and an observed response (also time to response or induction period).

LBNL: Lawrence Berkeley National Laboratory.

LCD: liquid crystal display.

LCVG: liquid cooling and ventilation garment.

LDEF: Long Duration Exposure Facility.

LDL: low-density lipoproteins.

LEND: Low Energy Neutron Detector.

LEO (low Earth orbit): the environment in which most recent space missions have been concentrated, where the magnetic field of Earth provides protection against much of the radiation that would be encountered on more distant exploration missions, approximately 300 to 600 mile orbit radius.

LET (linear energy transfer): Measure of the average local energy deposition per unit length of distance traveled by a charged particle in a material. Unit: keV/μm.

lifetime risk: The lifetime probability of suffering from the consequences of a specific health effect. The total risk in a lifetime resulting from an exposure(s) is equal to the average annual risk times the period of expression.

light ions: Nuclei of hydrogen and helium which are positively charged due to some or all of the planetary electrons having been stripped from them.

lineal energy ( y ): The quotient of ε by , where ε is the energy imparted to the matter in a given volume by a single (energy deposition) event and is the mean chord length of that volume ( i.e., y = ε/ l ). The unit for lineal energy is J /m, but keV/ μm is often used in practice (1 keV/µm ~ 1.6x10-10 J/m).

linear energy transfer ( LET): Average amount of energy lost per unit of particle track length as an ionizing particle travels through material, related to the microscopic density distribution of energy deposited in the material and, therefore, a major characteristic of radiation leading to different effects for the same dose of ionizing radiation of different LET on biological specimens or electronic devices.

linear-quadratic model (also linear-quadratic dose-response relationship): expresses the incidence of (e.g., mutation or cancer) as partly directly proportional to the dose (linear term) and partly proportional to the square of the dose (quadratic term).

LIS: local interstellar energy spectrum.

LIS: local interstellar GCR spectrum.

LIS: Local interplanetary Spectra.

LLD: lower limit of detection.

LLU: Loma Linda University.

LLO: low lunar orbit.

lognormal: If the logarithms of a set of values are distributed according to a normal distribution the values are said to have a lognormal distribution, or be distributed log normally.

low-LET: Radiation having a low-linear energy transfer; for example, electrons, x rays, and gamma rays.

LRV: Lunar Roving Vehicle.

LSAC: Life Sciences Applications Advisory Committee.

LSS: Life Span Study.

LSS: Life-Span Study of the Japanese atomic-bomb survivors.

Lunar Lander: the Constellation system vehicle that will travel between the Orion and the surface of the Moon.

LWS: Living With a Star (a NASA program).

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MARIE: Mars Radiation Environment Experiment.

mass stopping power: (see stopping power ).

MAT: Mars Architecture Team.

MCNPX: Monte Carlo N-Particle eXtended.

MDO: Multi-disciplinary Optimization.

mean absorbed (tissue) dose ( DT): The mean absorbed dose in an organ or tissue, obtained by integrating or averaging absorbed doses at points in the organ or tissue.

mean-free path: The average distance between particle collisions with nuclei, atoms or molecules in a material. Also, the average distance between scattering events in interplanetary particle propagation.

MEEP: Mir Environment Effects Payload.

MEO: Medium Earth Orbit.

MeV: Mega-electron Volts: 106 electron volts

mFISH: Multiplex Fluorescence In Situ Hybridization.

Mir: The Russian (previously Soviet) orbital space station.

MISSE: Materials on International Space Station Experiment.

MML: mouse myelogenous leukemia.

MMOP: Multilateral Medical Operations Panel.

MOA: Memorandum of Agreement.

MODIS: Moderate Resolution Imaging Spectrometer.

MORD: Medical Operations Requirements Documents.

MOU: Memorandum of Understanding.

Mrem: millirem.

MRI: magnetic resonance imaging.

MS: Mission Systems

mSv: millisievert.

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N: nucleon.

NAR: Non-Advocate Review.

NAS: National Academy of Sciences.

NASA: National Aeronautics and Space Administration.

NCI: National Cancer Institute.

NCRP: National Council on Radiation Protection and Measurements.

NEDD: Constellation Program Natural Environment Definition for Design; CxP 70044

neutrons: Particles with a mass similar to that of a proton, but with no electrical charge. Because they are electrically neutral, they cannot be accelerated in an electrical field.

NIEL: Non-ionizing energy loss, also called displacement kerma. The total kerma can be divided into an ionizing component and a displacement, or NIEL, component.

NIH: National Institutes of Health.

NM: neutron monitor.

NOAA: National Oceanic and Atmospheric Administration.

noncancer: Health effects other than cancer (e.g., cataracts, cardiovascular disease) that occur in the exposed individual.

Nowcasting: prediction of total doses and the future temporal evolution of the dose once a solar particle event has begun.

NOVICE: Radiation Transport/Shielding Code.

NPR: NASA Procedural Requirements.

NRA: NASA Research Announcement.

NRC: National Research Council.

NRC: Nuclear Regulatory Commission (US).

NSBRI: National Space Biomedical Research Institute.

NSCOR: NASA Specialized Center of Research.

NSF: National Science Foundation.

NSRL: NASA Space Radiation Laboratory (at BNL).

NTE: Non-Targeted Effects.

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OBPR: Office of Biological and Physical Research.

OCHMO: Office of Chief Health and Medical Officer.

organ dose equivalent ( DET): The mean dose equivalent for an organ or tissue, obtained by integrating or averaging dose equivalents at points in the organ or tissue. It is the practice in the space radiation protection community to obtain point values of absorbed dose (D) and dose equivalent (H) using the accepted quality factor-LET relationship [Q(L)], and then to average the point quantities over the organ or tissue of interest by means of computational models to obtain the organ dose equivalent (DET ). For space radiations, NCRP adopted the organ dose equivalent as an acceptable approximation for equivalent dose (HT) for stochastic effects.

Orion Crew Exploration Vehicle: The Constellation system vehicle that will carry passengers in low Earth orbit, or from low Earth orbit to the Moon or Mars, and then back to Earth. Often referred to as CEV; in this report referred to as the Orion crew module.

OSHA: Occupational Safety and Health Administration.

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PC: Probability of Causation.

PCC: premature chromosome condensation.

PCS: personal communication system.

PDF: probability density function.

PDF: probability distribution function.

PE: Project Executive.

PEL (permissible exposure limit): Maximum amount of radiation to which an astronaut may be exposed. For terrestrial workers, PELs are legal limits, defined by OSHA. NASA PELs are set by the chief health and medical officer.

PET: positron emission tomography.

photosphere: The portion of the sun visible in white light. Also the limit of seeing down through the solar atmosphere in white light.

PI: Principal Investigator.

PLR: pressurized lunar rover.

PLSS: personal life support system.

PM: Project Manager.

PP: Project Plan.

PPBE: Planning, Programming, Budgeting and Execution.

PPS: proton prediction system/ pulses per second.

PRD: Passive Radiation Detector; Program Requirements Document.

prevalence: The number of cases of a disease in existence at a given time per unit of population, usually per 100,000 persons.

protons: The nucleus of the hydrogen atom. Protons are positively charged.

protraction: Extending the length of exposure, for example, the continuous delivery of a radiation dose over a longer period of time.

PS: Project Scientist.

PSD: Position-Sensitive Detector; also, Pulse Shape Discrimination.

PVAMU: Prairie View A&M University.

PW: pulsed wave.

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Q: quality factor.

Q(L): quality factor as a function of linear energy transfer.

Qleukemia: quality factor for estimating leukemia risks.

Qsolid: quality factor for estimating solid cancer risks.

QMSFRG: quantum multiple scattering fragmentation model.

quality factor ( Q ): The factor by which absorbed dose (D) at a point is modified to obtain the dose equivalent (H) at the point (i.e., H = Q D), in order to express the effectiveness of an absorbed dose (in inducing stochastic effects) on a common scale of risk for all types of ionizing radiation. There is a specified dependence [Q(L)] of the quality factor (Q) as a function of the unrestricted linear energy transfer (L) in water at the point of interest.

quasithreshold dose: The dose at which the extrapolated straight portion of the dose-response curve intercepts the dose axis at unity survival fraction.

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RAD: Radiation Assessment Detector.

RAM: Radiation Area Monitor.

radiation: 1. The emission and propagation of energy through space or through matter in the form of waves, such as electromagnetic, sound, or elastic waves; 2. The energy propagated through space or through matter as waves; radiation or radiant energy, when unqualified, usually refers to electromagnetic radiation; commonly classified by frequency— Hertzian, infrared, visible, ultraviolet, x and gamma rays; 3. Corpuscular emission, such as alpha and beta particles, or rays of mixed or unknown type, such as cosmic radiation.

radiation quality: A general term referring to the microscopic distribution of of the energy absorbed to yield a given total dose. For example, at resolutions of a few micrometers ionizing events will be more uniformly dispersed for gamma-ray radiation than for the neutron radiation, producing quantitatively different biological effects (see relative biological effectiveness ).

radiation weighting factor ( wR): A factor related to the relative biological effectiveness of different radiations in the calculation of equivalent dose (HT) (see equivalent dose ), independently of the tissue or organ irradiated.

RBE (relative biological effectiveness): Measure of the effectiveness of a specific type of radiation for producing a specific biological outcome, relative to a reference radiation (generally, 250 kVp x-rays). For a defined endpoint, RBE = Dref/Dnew. For HZE particles, RBE generally is greater than 1, meaning that a lower dose of more effective HZE particles will have the same effect as a given dose of the reference radiation.

RCT: Radiation Coordination Team.

RDD: radiological dispersal device.

RDWG: Radiation Discipline Working Group.

regolith: A layer of loose, heterogeneous material covering solid rock on the surface of a moon or planet (including Earth).

REIC: risk of exposure-induced cancer incidence.

REID (risk of exposure induced death): Measure of risk used by NASA as a standard for radiation protection; reflects a calculation of the probability of death due to exposure to radiation in space.

relative biological effectiveness (cf. RBE)

relative risk (cf. excess relative risk)

REM: rapid eye movement.

RF: radiofrequency.

RFI: request for information.

RHIC: Relativistic Heavy Ion Collider (at BNL).

RHO: Radiation Health Officer.

rigidity: The momentum of a charged particle per unit charge. Determines the curvature of the particle’s trajectory in a magnetic field. Two particles with different charge but the same rigidity will travel along a path having the same curvature in a given magnetic field.

risk: The probability of a specified effect or response occurring.

risk coefficient: The increase in the annual incidence or mortality rate per unit dose: (1) absolute risk coefficient is the observed minus the expected number of cases per person year at risk for a unit dose; (2) the relative risk coefficient is the fractional increase in the baseline incidence or mortality rate for a unit dose.

risk cross section: The probability of a particular excess cancer mortality per particle fluence (excluding delta rays).

risk estimate: The number of cases (or deaths) that are projected to occur in a specified exposed population per unit dose for a defined exposure regime and expression period; number of cases per person-gray or, for radon, the number of cases per person cumulative working level month.

roentgen: A unit of radiation exposure. Exposure in SI units is expressed in C kg–1 of air.

ROS: reactive oxygen species.

RRS: radiation Research Society.

RSNA: Radiological Society of North America.

R&T: Research and Technology.

RTG: radioisotope thermoelectric generator.

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SAA: South Atlantic Anomaly.

SACR: Science Advisory Committee on Radiobiology.

SAMPEX: Solar Anomalous and Magnetospheric Particle Explorer.

SAR: specific absorption rate.

SBIR: Small Business Innovation Research.

SCAR: Smoke/Sulfate Clouds and Radiation Experiment.

SCC: squamous cell carcinoma/ small cell cancer.

SCE: sister chromatid exchange.

SCLS: small cell lung carcinoma.

SD: single dose.

SD: standard deviation.

SDO: Solar Dynamic Observatory.

SEC: Space Environment Center. (NOAA).

secondary radiation: radiation that has been generated by the interaction of radiation with the atoms or nuclei of a traversed material.

SEE (single-event effect): a class of effects in which damage results from a single ionizing particle traversing a microelectronic device, rather than the accumulated impact of a large number of particles.

SEE: single event effect/ Space Environment and Effects Program.

SEER: surveillance, epidemiology, and end results.

SET: Space Environment Testbeds.

SEU (single event upset): a change of state caused by ions or electro-magnetic radiation striking a sensitive node in a micro-electronic device.

SFHSS: Space Flight Human Systems Standard; NASA-STD-3001

SGZ: subgranular zone.

SI: International System of Units.

sievert ( Sv): The special name for the SI unit of effective dose (E), equivalent dose (HT), dose equivalent (H), and organ dose equivalent (DT ), 1 Sv = 1 J /kg.

SLSD: Space Life Sciences Directorate (NASA).

S&MA: Safety and Mission Assurance (NASA).

SMD: Science Mission Directorate (NASA).

SMO: Science Management Office (NASA).

SOHO: Solar and Heliospheric Observatory.

Solar cycle: The periodic variation in the intensity of solar activity, as measured, for example, by the numbers of sunspots, flares, CMEs, and SPEs. The average length of solar cycles since 1900 is 11.4 y.

solar flare: The name given to the sudden release of energy (often >1032 ergs) in a relatively small volume of the solar atmosphere. Historically, an optical brightening in the chromosphere, now expanded to cover almost all impulsive radiation from the sun.

solar-particle event (SPE): An eruption at the sun that releases a large number of energetic particles (primarily protons) over the course of hours or days. Signatures of solar energetic-particle events may include significant increases in types of electro­magnetic radiation such as radio waves, x-rays, and gamma rays.

solar wind: The plasma flowing into space from the solar corona. The ionized gas carrying magnetic fields can alter the intensity of the interplanetary radiation.

SOMD: Space Operations Mission Directorate (NASA).

spallation: A high-energy nuclear reaction in which a high-atomic-number target nucleus is struck by a high-energy, light particle (typically a proton); this causes the target nucleus to break up into many components, releasing many neutrons, protons, and higher Z particles.

SPE (cf. solar particle event).

Space Radiation Analysis Group (SRAG): the radiation protection group at NASA’s Johnson Space Center, responsible for radiation monitoring, projecting exposures, and ensuring adherence to principles of ALARA for crews on spaceflight missions.

SPENVIS (SPace ENVironment Information System) : a series of computer programs developed by the European Space Agency for the simulation of radiation effects in flight.

SRA: Society for Risk Analysis.

SRAG: Space Radiation Analysis Group

sRBC: Serum deprivation response factor-related gene product that binds to C-kinase.

SRPE: Space Radiation Program Element (NASA).

SSA: Social Security Administration.

STEREO: Solar-Terrestrial Relations Observatory (NASA mission).

stochastic effects: radiation effects attributed to the consequences of changes caused by radiation in one or a few cells; so called because the statistical fluctuations in the number of initial cells are large compared to the number of cells observed when radiation effects, such as cancer, become manifest (ICRP 1991). The probability of occurrence, rather than the severity, is a function of radiation dose.

stochastic process: process whereby the likelihood of the occurrence of a given event can be described by a probability distribution.

stopping power (lineal stopping power): The quotient of the energy lost (dE) by a charged particle in traversing a distance (dx) in a material. Can also be expressed as mass stopping power by dividing the lineal stopping power by the density (ρ) of the material.

STS: Space Transportation System.

STTR: Small Business Technical Transfer Research.

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TEDE: total effective dose equivalent.

TEPC: tissue equivalent proportional counter.

TGF: transforming growth factor.

TIGER: Grid Generation Code.

tissue weighting factor ( wT): A factor representing the ratio of risk of stochastic effects attributable to irradiation of a given organ or tissue to the total risk when the whole body is irradiated uniformly. The factor is independent of the type of radiation or energy of the radiation.

TLD: thermoluminescent dosimeter.

TMG: thermal micrometeoroid garment.

TMI: Three Mile Island.

TOGA/COARE: Tropical Ocean Global Atmosphere/Coupled Ocean-Atmosphere Experiment.  transport (of radiation): the sequence of interactions between radiation traversing one or more materials and their atoms and nuclei; calculations of the relevant characteristics; transport code: computer program to calculate radiation transport.

trapped radiation: Ionized particles held in place by Earth’s magnetic fields. Also known as the Van Allen belt.

TRL: Technology Readiness Level.

TRMM: Tropical Rainfall Measuring Mission.

TVD: tenth-value distance.

TVL: tenth-value layer.

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UNSCEAR: United Nations Scientific Committee on the Effects Of Atomic Radiation.

US: United States.

USAF: United States Air Force.

US NRC: United States Nuclear Regulatory Commission.

USRA: Universities Space Research Association.

UV: ultraviolet.

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vitreous: The semifluid, transparent substance which lies between the retina and the lens of the eye.

VSE: Vision for Space Exploration.

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WBS: Work Breakdown Structure.

WHO: World Health Organization.

Wind: a NASA spacecraft that observes the Sun and solar wind.

WL: working level.

WLM: working level month (170 h).

w R: radiation weighting factor.

w T: tissue weighting factor.

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Z: atomic number, the number of protons in the nucleus of an atom.

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