Rotational constants of linear and/or bent Cn+1H and CnN(n = 1–6): A DFT study

The geometries, dipole moments, and rotational constants for the linear and/or bent cations, C_n+1H⁺ and C_nN⁺(n = 1–6), were studied by the B3LYP method with the modest basis sets. For C_nH⁺(n = odd; 3, 5, 7) and C_nN⁺(n = even; 2, 4, 6), the theoretical rotational constants (B_es) of closed-shell singlet C₃H⁺, C₅H⁺, C₇H⁺, CCN⁺, C₄N⁺, and C₆N⁺ were calculated to be about 11,244, 2420, 885.2, 11,970, 2439, and 880.8 MHz, respectively. By contrast, the triplets are stable than the corresponding singlets for C_nH⁺(n = odd; 2, 4, 6) and C_nN⁺(n = even; 3, 5) except CN⁺.     

Induction of genomic instability after an acute whole-body exposure of mice to Fe ions

The purpose of this study was to evaluate dose–response relationships for the in vivo induction of micronuclei (MN) as a measure of both initial radiation damage and the induction of genomic instability. These measurements were made in mouse blood erythrocytes as a function of radiation dose, radiation quality, time after irradiation, and the genetic background of exposed individuals. Blood samples were collected from two strains of mouse (CBA/CaJ and C57BL/6J) at different times up to 3 months following a whole-body exposure to various doses of 1 GeV/amu ⁵⁶Fe ions (0, 0.1, 0.5 and 1.0 Gy, at the dose rate of a 1 Gy/min) or ¹³⁷Cs gamma rays (0, 0.5, 1.0 and 3.0 Gy, at the dose rate of 0.72 Gy/min). Blood-smear slides were stained with acridine orange (AO). The frequencies of MN were measured in mature normochromatic-erythrocytes (MN-NCEs) and in immature polychromatic-erythrocytes (MN-PCEs). Effects of both types of radiation on erythropoiesis were also evaluated. As a measure of cell progression delay, a dose-dependent decrease in numbers of PCEs was observed at day 2 post-exposure in both strains, regardless of radiation quality. Subsequently, the levels of PCEs increased in all exposed mice, reaching control levels (or higher) by day 7 post-exposure. Further, at day 2 after the exposure, there was no increase in the frequency of MN-PCEs in CBA/CaJ mice exposed to ⁵⁶Fe ions while the frequency of MN-PCEs elevated as a function of dose in the C57BL/6J mice. At day 4, there was no dose related increase in MN-NCEs in either strain of mouse exposed to ¹³⁷Cs gamma rays. Additionally, at the early sacrifice times (days 2 and 4), ⁵⁶Fe ions were slightly more effective (per unit dose) in inducing MN-NCEs than ¹³⁷Cs gamma rays in CBA/CaJ mice. However, there was no increase in the frequency of MN-NCEs at late times after an acute exposure to either type of radiation. In contrast, both types of radiation induced increased MN-PCEs frequencies in irradiated CBA/CaJ mice, but not C57BL/6J mice, at late times post-exposure. This finding indicates the potential induction of genomic instability in hematopoietic cells of CBA/CaJ mice by both types of radiation. The finding also demonstrates the influence of genetic background on radiation-induced genomic instability in vivo.     

Cosmic ray detection on the Foton-M2 satellite by a track etch detector stack

In the frame of the European Space Agency (ESA) project called “Biology and Physics in Space”, the returning satellite, Foton-M2, carried an open-to-space exposure platform outside of the satellite body, called as BIOPAN-5, loaded with exo-biological experiments and facilities for radiation dosimetry (RADO). One of the RADO experiments was dedicated to the detection of the primary galactic cosmic rays (GCR) and secondary neutrons by a track etch detector stack. The daily absorbed dose (D) and dose equivalent (H) were calculated from the experimental LET spectra (LET > 10 keV/μm). Under a shielding of ∼2.8 g/cm² the averaged H was found to be 658 ± 8 μSv/d, with a quality factor (Q) of 6.2 ± 1.2. The LET spectra showed a local peak at ∼105 keV/μm suggesting that the majority of tracks were created by trapped protons as it has been predicted by calculations. The low LET dose of the cosmic radiation was determined by 4 TLD stacks, and the total dose was found to be 795 ± 14 μSv/d.     

Effects of heavy particle irradiation and diet on object recognition memory in rats

On long-duration missions to other planets astronauts will be exposed to types and doses of radiation that are not experienced in low earth orbit. Previous research using a ground-based model for exposure to cosmic rays has shown that exposure to heavy particles, such as ⁵⁶Fe, disrupts spatial learning and memory measured using the Morris water maze. Maintaining rats on diets containing antioxidant phytochemicals for 2 weeks prior to irradiation ameliorated this deficit. The present experiments were designed to determine: (1) the generality of the particle-induced disruption of memory by examining the effects of exposure to ⁵⁶Fe particles on object recognition memory; and (2) whether maintaining rats on these antioxidant diets for 2 weeks prior to irradiation would also ameliorate any potential deficit. The results showed that exposure to low doses of ⁵⁶Fe particles does disrupt recognition memory and that maintaining rats on antioxidant diets containing blueberry and strawberry extract for only 2 weeks was effective in ameliorating the disruptive effects of irradiation. The results are discussed in terms of the mechanisms by which exposure to these particles may produce effects on neurocognitive performance.     

Verification of shielding effect by the water-filled materials for space radiation in the International Space Station using passive dosimeters

The dose reduction effects for space radiation by installation of water shielding material (“protective curtain”) of a stack board consisting of the hygienic wipes and towels have been experimentally evaluated in the International Space Station by using passive dosimeters. The averaged water thickness of the protective curtain was 6.3 g/cm². The passive dosimeters consisted of a combination of thermoluminescent detectors (TLDs) and plastic nuclear track detectors (PNTDs). Totally 12 passive dosimeter packages were installed in the Russian Service Module during late 2010. Half of the packages were located at the protective curtain surface and the other half were at the crew cabin wall behind or aside the protective curtain. The mean absorbed dose and dose equivalent rates are measured to be 327 μGy/day and 821 μSv/day for the unprotected packages and 224 μGy/day and 575 μSv/day for the protected packages, respectively. The observed dose reduction rate with protective curtain was found to be 37 ± 7% in dose equivalent, which was consistent with the calculation in the spherical water phantom by PHITS. The contributions due to low and high LET particles were found to be comparable in observed dose reduction rate. The protective curtain would be effective shielding material for not only trapped particles (several 10 MeV) but also for low energy galactic cosmic rays (several 100 MeV/n). The properly utilized protective curtain will effectively reduce the radiation dose for crew living in space station and prolong long-term mission in the future.     

Neuroimmune response and sleep studies after whole body irradiation with high-LET particles

In order to investigate the biological effects of galactic rays on astronaut cerebral functions after space flight, mice were exposed to different heavy ions (HZE) in whole-body conditions at doses comparable to the galactic flux: ¹²C, ¹⁶O and ²⁰Ne (95 MeV/u, at 42–76 mGy). Animals were also exposed to 42 mGy of ⁶⁰Co radiation for comparison with HZE. The neuroimmune response, evaluated by interleukin-1 (IL-1) measurement, showed that this cytokine was produced 3 h after irradiation by ¹⁶O or ⁶⁰Co. In contrast, neither ¹²C (56.7 mGy) nor ²⁰Ne (76 mGy) induced IL-1 production. However, immunohistochemical staining of ¹²C-irradiated mouse brain tissue showed 2 months later a marked inflammatory reaction in the hippocampus and a diffuse response in parenchyma. Sleep studies were realized before and after exposure to 42 mGy of ¹⁶O and 76 mGy of ²⁰Ne: only the ²⁰Ne radiation displayed a small effect. A slight decrease in paradoxical sleep, corresponding to a reduction in the number of episodes of paradoxical sleep, was manifested between 8 and 22 days after exposure. Exposure to ¹²C and ¹⁶O induced no changes either in cellularity of spleen or thymus, or in caspase 3 activity (as much as four months after irradiation). Taken together, these data indicate that the CNS could be sensitive to heavy ions and that responses to HZE impact depend on the nature of the particle, the dose threshold and the time delay to develop biological processes. Differences in responses to different HZE highlight the complex biological phenomena to which astronauts are submitted during space flight.     

Tolerance of chufa (Cyperus esculentus L.) plants,representing the higher plant compartment in bioregenerative life support systems,to super-optimal air temperatures

Plants intended to be included in the photosynthesizing compartment of the bioregenerative life support system (BLSS) need to be studied in terms of both their production parameters under optimal conditions and their tolerance to stress factors that might be caused by emergency situations. The purpose of this study was to investigate tolerance of chufa (Cyperus esculentus L.) plants to the super-optimal air temperature of 45 ± 1 °C as dependent upon PAR (photosynthetically active radiation) intensity and the duration of the exposure to the stress factor. Chufa plants were grown hydroponically, on expanded clay, under artificial light. The nutrient solution was Knop’s mineral medium. Until the plants were 30 days old, they had been grown at 690 μmol m⁻² s⁻¹ PAR and air temperature 25 °C. Thirty-day-old plants were exposed to the temperature 45 °C for 6 h, 20 h, and 44 h at PAR intensities 690 μmol m⁻² s⁻¹ and 1150 μmol m⁻² s⁻¹. The exposure to the damaging air temperature for 44 h at 690 μmol m⁻² s⁻¹ PAR caused irreversible damage to PSA, resulting in leaf mortality. In chufa plants exposed to heat shock treatment at 690 μmol m⁻² s⁻¹ PAR for 6 h and 20 h, respiration exceeded photosynthesis, and CO₂ release in the light was recorded. Functional activity of photosynthetic apparatus, estimated from parameters of pulse-modulated chlorophyll fluorescence in Photosystem 2 (PS 2), decreased 40% to 50%. After the exposure to the stress factor was finished, functional activity of PSA recovered its initial values, and apparent photosynthesis (P_apparent) rate after a 20-h exposure to the stress factor was 2.6 times lower than before the elevation of the temperature. During the first hours of plant exposure to the temperature 45 °C at 1150 μmol m⁻² s⁻¹ PAR, respiration rate was higher than photosynthesis rate, but after 3–4 h of the exposure, photosynthetic processes exceeded oxidative ones and CO₂ absorption in the light was recorded. At the end of the 6-h exposure, P_apparent rate was close to that recorded prior to the exposure, and no significant changes were observed in the functional activity of PSA. At the end of the 20-h exposure, P_apparent rate was close to its initial value, but certain parameters of the functional activity of PSA decreased 25% vs. their initial values. During the repair period, the parameters of external gas exchange recovered their initial values, and parameters of pulse-modulated chlorophyll fluorescence were 20–30% higher than their initial values. Thus, exposure of chufa plants to the damaging temperature of the air for 20 h did not cause any irreversible damage to the photosynthetic apparatus of plants at either 690 μmol m⁻² s⁻¹ or 1150 μmol m⁻² s⁻¹ PAR, and higher PAR intensity during the heat shock treatment enhanced heat tolerance of the plants.     

Low-dose carbon ion irradiation effects on DNA damage and oxidative stress in the mouse testis

To investigate the effects of low-dose carbon ion irradiation on reproductive system of mice, the testes of outbred Kunming strain mice were whole-body irradiated with 0, 0.05, 0.1, 0.5 and 1 Gy, respectively. We measured DNA double-strand breaks (DNA DSBs) and oxidative stress parameters including malondialdehyde (MDA) content, superoxide dismutase (SOD) activity, and testis weight and sperm count at 12 h, 21 d and 35 d after irradiation in mouse testis. At 12 h postirradiation, a significant increase in DNA DSB level but no pronounced alterations in MDA content or SOD activity were observed in 0.5 and 1 Gy groups compared with the control group. At 21 d postirradiation, there was a significant reduction in sperm count and distinct enhancements of DSB level and MDA content in 0.5 and 1 Gy groups in comparison with control. At 35 d postirradiation, the levels of DNA DSBs and MDA, and SOD activity returned to the baseline except for the MDA content in 1 Gy (P < 0.05), while extreme falls of sperm count were still observed in 0.5 (P < 0.01) and 1 Gy (P < 0.01) groups. For the 0.05 or 0.1 Gy group, no differences were found in DNA DSB level and MDA content between control and at 12 h, 21 d and 35 d after irradiation, indicating that lower doses of carbon ion irradiation have no significant influence on spermatogenesis processes. In this study, male germ cells irradiated with over 0.5 Gy of carbon ions are difficult to repair completely marked by the sperm count. Furthermore, these data suggest that the deleterious effects may be chronic or delayed in reproductive system after whole-body exposure to acute high-dose carbon ions.     

On the quality of mutations in mammalian cells induced by high LET radiations

The deleterious effects of accelerated heavy ions as component of the space radiation environment on living cells are of increasing importance for long duration human space flight activities. The most important aspect of such densely ionizing particle radiation is attributed to the type and quality of biological damage induced by them. This issue is addressed by investigating cell inactivation and mutation induction at the Hprt locus (coding for hypoxanthine-guanine-phosphoribosyl-transferase) of cultured V79 Chinese hamster cells exposed to densely ionizing radiation (accelerated heavy ions with different LETs from oxygen to gold, specific energies ranging from 1.9 to 69.7 MeV/u, corresponding LET values range from 62 to 13,223 keV/μm) and to sparsely ionizing radiation (200 kV X-rays). 30 spontaneous, 40 X-ray induced and 196 heavy ion induced 6-thioguanine resistant Hprt mutant colonies were characterized by Southern technique using the restriction enzymes EcoRI, PstI and BglII and a full length Hprt cDNA probe isolated from the plasmid pHPT12. Restriction patterns of the spontaneous Hprt mutants were indistinguishable from the wild type pattern, as these mutants probably contain only small deletions or even point mutations in the Hprt locus. In contrast, the overall spectrum of heavy ion induced mutations revealed a majority of partial or total deletions of the Hprt gene. With constant particle fluence (3 × 10⁶ particles/cm²) the quality of heavy ion induced mutations in the Hprt locus depends on physical parameters of the beam (atomic number, specific energy, LET). This finding suggests a relationship between the type of DNA damage and track structure. The fraction of mutants with severe deletions in the Hprt locus after exposure to oxygen ions increases from 65% at 60 keV/μm up to a maximum (100%) at 300 keV/μm and declines with higher LET values to 75% at 750 keV/μm. With heavier ions (Ca- and Au-ions) and even higher LET-values this mutant fraction decreases to 58% at 13,200 keV/μm. Heavy ion induced DNA break points in the Hprt locus are not randomly distributed.     

Spaceflight-relevant types of ionizing radiation and cortical bone: Potential LET effect?

Extended exposure to microgravity conditions results in significant bone loss. Coupled with radiation exposure, this phenomenon may place astronauts at a greater risk for mission-critical fractures. In a previous study, we identified a profound and prolonged loss of trabecular bone (29–39%) in mice following exposure to an acute, 2 Gy dose of radiation simulating both solar and cosmic sources. However, because skeletal strength depends on trabecular and cortical bone, accurate assessment of strength requires analysis of both bone compartments. The objective of the present study was to examine various properties of cortical bone in mice following exposure to multiple types of spaceflight-relevant radiation. Nine-week old, female C57BL/6 mice were sacrificed 110 days after exposure to a single, whole body, 2 Gy dose of gamma, proton, carbon, or iron radiation. Femora were evaluated with biomechanical testing, microcomputed tomography, quantitative histomorphometry, percent mineral content, and micro-hardness analysis. Compared to non-irradiated controls, there were significant differences compared to carbon or iron radiation for only fracture force, medullary area and mineral content. A greater differential effect based on linear energy transfer (LET) level may be present: high-LET (carbon or iron) particle irradiation was associated with a decline in structural properties (maximum force, fracture force, medullary area, and cortical porosity) and mineral composition compared to low-LET radiation (gamma and proton). Bone loss following irradiation appears to be largely specific to trabecular bone and may indicate unique biological microenvironments and microdosimetry conditions. However, the limited time points examined and non-haversian skeletal structure of the mice employed highlight the need for further investigation.     

Contribution of satellite laser ranging to combined gravity field models

In the framework of satellite-only gravity field modeling, satellite laser ranging (SLR) data is typically exploited to recover long-wavelength features. This contribution provides a detailed discussion of the SLR component of GOCO02S, the latest release of combined models within the GOCO series. Over a period of five years (January 2006 to December 2010), observations to LAGEOS-1, LAGEOS-2, Ajisai, Stella, and Starlette were analyzed. We conducted a series of closed-loop simulations and found that estimating monthly sets of spherical harmonic coefficients beyond degree five leads to exceedingly ill-posed normal equation systems. Therefore, we adopted degree five as the spectral resolution for real data analysis. We compared our monthly coefficient estimates of degree two with SLR and Gravity Recovery and Climate Experiment (GRACE) time series provided by the Center for Space Research (CSR) at Austin, Texas. Significant deviations in C₂₀ were noted between SLR and GRACE; the agreement is better for the non-zonal coefficients. Fitting sinusoids together with a linear trend to our C₂₀ time series yielded a rate of (−1.75 ± 0.6) × 10⁻¹¹/yr; this drift is equivalent to a geoid change from pole to equator of 0.35 ± 0.12 mm/yr or an apparent Greenland mass loss of 178.5 ± 61.2 km³/yr. The mean of all monthly solutions, averaged over the five-year period, served as input for the satellite-only model GOCO02S. The contribution of SLR to the combined gravity field model is highest for C₂₀, and hence is essential for the determination of the Earth’s oblateness.     

Depth dose measurements with the Liulin-5 experiment inside the spherical phantom of the MATROSHKA-R project onboard the International Space Station

The Liulin-5 experiment is a part of the international project MATROSHKA-R on the Russian segment of the ISS, which uses a tissue-equivalent spherical phantom equipped with a set of radiation detectors. The objective of the MATROSHKA-R project is to provide depth dose distribution of the radiation field inside the sphere in order to get more information on the distribution of dose in a human body. Liulin-5 is a charged particle telescope using three silicon detectors. It measures time resolved energy deposition spectra, linear energy transfer (LET) spectra, particle flux, and absorbed doses of electrons, protons and heavy ions, simultaneously at three depths along the radius of the phantom. Measurements during the minimum of the solar activity in cycle 23 show that the average absorbed daily doses at 40 mm depth in the phantom are between 180 μGy/day and 220 μGy/day. The absorbed doses at 165 mm depth in the phantom decrease by a factor of 1.6–1.8 compared to the doses at 40 mm depth due to the self-shielding of the phantom from trapped protons. The average dose equivalent at 40 mm depth is 590 ± 32 μSV/day and the galactic cosmic rays (GCR) contribute at least 70% of the total dose equivalent at that depth. Shown is that due to the South Atlantic Anomaly (SAA) trapped protons asymmetry and the direction of Liulin-5 lowest shielding zone the dose rates on ascending and descending nodes in SAA are different. The data obtained are compared to data from other radiation detectors on ISS.     

Gas exchange rates of potato stands for bioregenerative life support

Plants can provide a means for removing carbon dioxide (CO₂) while generating oxygen (O₂) and clean water for life support systems in space. To study this, 20 m² stands of potato (Solanum tuberosum L.) plants were grown in a large (113 m³ vol.), atmospherically closed chamber. Photosynthetic uptake of CO₂ by the stands was detected about 10 DAP (days after planting), after which photosynthetic rates rose rapidly as stand ground cover and total light interception increased. Photosynthetic rates peaked ca. 50 DAP near 45 μmol CO₂ m⁻² s⁻¹ under 865 μmol m⁻² s⁻¹ PPF (average photosynthetic photon flux), and near 35 μmol CO₂ m⁻² s⁻¹ under 655 μmol m⁻² s⁻¹ PPF. Short term changes in PPF caused a linear response in stand photosynthetic rates up to 1100 μmol m⁻² s⁻¹ PPF, with a light compensation point of 185 μmol m⁻² s⁻¹ PPF. Comparisons of stand photosynthetic rates at different CO₂ concentrations showed a classic C₃ response, with saturation occurring near 1200 μmol mol⁻¹ CO₂ and compensation near 100 μmol mol⁻¹ CO₂. In one study, the photoperiod was changed from 12 h light/12 h dark to continuous light at 58 DAP. This caused a decrease in net photosynthetic rates within 48 h and eventual damage (scorching) of upper canopy leaves, suggesting the abrupt change stressed the plants and/or caused feedback effects on photosynthesis. Dark period (night) respiration rates increased during early growth as standing biomass increased and peaked near 9 μmol CO₂ m⁻² s⁻¹ ca. 50 DAP, after which rates declined gradually with age. Stand transpiration showed a rapid rise with canopy ground cover and peaked ca. 50 DAP near 8.9 L m⁻² d⁻¹ under 860 μmol m⁻² s⁻¹ PPF and near 6.3 L m⁻² d⁻¹ under 650 μmol m⁻² s⁻¹ PPF. Based on the best photosynthetic rates from these studies, approximately 25 m² of potato plants under continuous cultivation would be required to support the CO₂ removal and O₂ requirements for one person.     

X-ray induced alterations in the differentiation and mineralization potential of murine preosteoblastic cells

To evaluate the effects of ionizing radiation (IR) on murine preosteoblastic cell differentiation, we directed OCT-1 cells to the osteoblastic lineage by treatment with a combination of β-glycerophosphate (β-GP), ascorbic acid (AA), and dexamethasone (Dex). In vitro mineralization was evaluated based on histochemical staining and quantification of the hydroxyapatite content of the extracellular bone matrix. Expression of mRNA encoding Runx2, transforming growth factor β1 (TGF-β1), osteocalcin (OCN), and p21^CDKN1A was analyzed. Exposure to IR reduced the growth rate and diminished cell survival of OCT-1 cells under standard conditions. Notably, calcium content analysis revealed that deposition of mineralized matrix increased significantly under osteogenic conditions after X-ray exposure in a time-dependent manner. In this study, higher radiation doses exert significant overall effects on TGF-β1, OCN, and p21^CDKN1A gene expression, suggesting that gene expression following X-ray treatment is affected in a dose-dependent manner. Additionally, we verified that Runx2 was suppressed within 24 h after irradiation at 2 and 4 Gy. Although further studies are required to verify the molecular mechanism, our observations strongly suggest that treatment with IR markedly alters the differentiation and mineralization process of preosteoblastic cells.     

Antioxidant capacity reduced in scallions grown under elevated CO2 independent of assayed light intensity

Long-duration manned space missions mandate the development of a sustainable life support system and effective countermeasures against damaging space radiation. To mitigate the risk of inevitable exposure to space radiation, cultivation of fresh fruits and vegetables rich in antioxidants is an attractive alternative to pharmacological agents. However it has yet to be established whether antioxidant properties of crops can be preserved or enhanced in a space environment where environmental conditions differ from that which plants have acclimated to on earth. Scallion (Allium fistulosum) rich in antioxidant vitamins C and A, and flavonoids was used as a model plant to study the impact of a range of CO₂ concentrations and light intensities that are likely encountered in a space habitat on food quality traits. Scallions were hydroponically grown in controlled environmental chambers under a combination of 3 CO₂ concentrations of 400, 1200 and 4000 μmol mol⁻¹ and 3 light intensity levels of 150, 300, 450 μmol m⁻² s⁻¹. Total antioxidant activity (TAA) of scallion extracts was determined using a radical cation scavenging assay. Both elevated CO₂ and increasing light intensity enhanced biomass accumulation, but effects on TAA (based on dry weight) differed. TAA was reduced for plants grown under elevated CO₂, but remained unchanged with increases in light intensity. Elevated CO₂ stimulated greater biomass production than antioxidants, while an increase in photosynthetic photo flux promoted the synthesis of antioxidant compounds at a rate similar to that of biomass. Consequently light is a more effective stimulus than CO₂ for antioxidant production.     

An icy mineralogy package (IMP) for in-situ studies of Titan’s surface

We describe the scientific case for and preliminary design of an instrument whose primary goal is to determine the chemistry (element abundance) and mineralogy (compound identity and abundance) of Titan’s surface using a combination of energy dispersive X-ray fluorescence spectroscopy (EDXRF) and X-ray diffraction (XRD). XRD is capable of identifying any crystalline substance present on Titan’s surface at relative abundances greater than ∼1 wt%, allowing unambiguous identification of, for example, structure I and II clathrates (even in the presence of ice), and various organic solids, which may include C₂H₂, C₂H₄, C₄H₂, HCN, CH₃CN, HC₃N, and C₄N₂). The XRF component of the instrument will obtain elemental abundances for 16 < Z < 60 with minimum detection limits better than 10 ppm (including detection of atmospheric noble gas isotopes), and may achieve detection limits of 0.01–1% for lighter elements down to Z = 6 (carbon). The instrument is well suited to integration with other analytical tools as part of a light-weight surface chemistry and mineralogy package. Although considerably less sensitive to elemental abundance than GC–MS (10⁻² vs. 10⁻⁸) it is likely to be significantly lighter (<0.5 kg vs. 10 kg).     

In vivo and in vitro measurements of complex-type chromosomal exchanges induced by heavy ions.

Heavy ions are more efficient in producing complex-type chromosome exchanges than sparsely ionizing radiation, and this can potentially be used as a biomarker of radiation quality. We measured the induction of complex-type chromosomal aberrations in human peripheral blood lymphocytes exposed in vitro to accelerated H-, He-, C-, Ar-, Fe- and Au-ions in the LET range of approximately 0.4-1400 keV/micrometers. Chromosomes were analyzed either at the first post-irradiation mitosis, or in interphase, following premature condensation by phosphatase inhibitors. Selected chromosomes were then visualized after FISH-painting. The dose-response curve for the induction of complex-type exchanges by heavy ions was linear in the dose-range 0.2-1.5 Gy, while gamma-rays did not produce a significant increase in the yield of complex rearrangements in this dose range. The yield of complex aberrations after 1 Gy of heavy ions increased up to an LET around 100 keV/micrometers, and then declined at higher LET values. When mitotic cells were analyzed, the frequency of complex rearrangements after 1 Gy was about 10 times higher for Ar- or Fe- ions (the most effective ions, with LET around 100 keV/micrometers) than for 250 MeV protons, and values were about 35 times higher in prematurely condensed chromosomes. These results suggest that complex rearrangements may be detected in astronauts' blood lymphocytes after long-term space flight, because crews are exposed to HZE particles from galactic cosmic radiation. However, in a cytogenetic study of ten astronauts after long-term missions on the Mir or International Space Station, we found a very low frequency of complex rearrangements, and a significant post-flight increase was detected in only one out of the ten crewmembers. It appears that the use of complex-type exchanges as biomarker of radiation quality in vivo after low-dose chronic exposure in mixed radiation fields is hampered by statistical uncertainties.     

Radiosensitivity to high energy iron ions is influenced by heterozygosity for Atm, Rad9 and Brca1

Loss of function of DNA repair genes has been implicated in the development of many types of cancer. In the last several years, heterozygosity leading to haploinsufficiency for proteins involved in DNA repair was shown to play a role in genomic instability and carcinogenesis after DNA damage is induced, for example by ionizing radiation. Since the effect of heterozygosity for one gene is relatively small, we hypothesize that predisposition to cancer could be a result of the additive effect of heterozygosity for two or more genes critical to pathways that control DNA damage signaling, repair or apoptosis. We investigated the role of heterozygosity for Atm, Rad9 and Brca1 on cell oncogenic transformation and cell survival induced by 1 GeV/n⁵⁶Fe ions. Our results show that cells heterozygous for both Atm and Rad9 or Atm and Brca1 have high survival rates and are more sensitive to transformation by high energy iron ions when compared with wild-type controls or cells haploinsufficient for only one of these proteins. Since mutations or polymorphisms for similar genes exist in a small percentage of the human population, we have identified a radiosensitive sub-population. This finding has several implications. First, the existence of a radiosensitive sub-population may distort the shape of the dose–response relationship. Second, it would not be ethical to put exceptionally radiosensitive individuals into a setting where they may potentially be exposed to substantial doses of radiation.     

Possible interstellar anions: CnS and CnO (n = 2–8)

The geometries, electron affinities and/or electron detachment energies for the C_nS and C_nO (n = 2–8) molecules and their anions were calculated by using the RCCSD (T) method. The C_nS⁻ (even n = 4, 6, and 8) and C_nO⁻ (even n = 6 and 8) anions are found to be substantially more stable than their corresponding neutral species. Several anions are potentially detectable as interstellar molecules.