Aiko Nagamatsu

Detection of space radiation-induced double strand breaks as a track in cell nucleus

To identify DNA damage induced by space radiations such as the high linear energy transfer (LET) particles, phospho-H2AX (gammaH2AX) foci formation was analyzed in human cells frozen in an International Space Station freezer for 133days. After recovering the frozen sample to the earth, the cells were cultured for 30 min, and then fixed. Here we show a track of gammaH2AX positive foci in them by immuno-cytochemical methods. It is suggested that space radiations, especially high LET particles, induced DSBs as a track. From the formation of the tracks in nuclei, exposure dose rate was calculated to be 0.7 mSv per day as relatively high-energy space radiations of Fe-ions (500 MeV/u, 200 keV/microm). From the physical dosimetry with CR-39 plastic nuclear track detectors and thermo-luminescent dosimeters, dose rate was 0.5 mSv per day. These values the exposed dose rate were similar between biological and physical dosimetries.

The ALTCRISS project on board the International Space Station.

The Alteriss project aims to perform a long term survey of the radiation environment on board the International Space Station. Measurements are being performed with active and passive devices in different locations and orientations of the Russian segment of the station. The goal is to perform a detailed evaluation of the differences in particle fluence and nuclear composition due to different shielding material and attitude of the station. The Sileye-3/Alteino detector is used to identify nuclei up to Iron in the energy range above similar or equal to 60 MeV/n. Several passive dosimeters (TLDs, CR39) are also placed in the same location of Sileye-3 detector. Polyethylene shielding is periodically interposed in front of the detectors to evaluate the effectiveness of shielding on the nuclear component of the cosmic radiation. The project was submitted to ESA in reply to the AO in the Life and Physical Science of 2004 and data taking began in December 2005. Dosimeters and data cards are rotated every 6 months: up to now three launches of dosimeters and data cards have been performed and have been returned with the end of expedition 12 and 13

Healthy offspring from freeze-dried mouse spermatozoa held on the International Space Station for 9 months

Significance Radiation on the International Space Station (ISS) is more than 100 times stronger than at the Earth’s surface, and at levels that can cause DNA damage in somatic cell nuclei. The damage to offspring caused by this irradiation in germ cells has not been examined, however. Here we preserved mouse spermatozoa on the ISS for 9 mo. Although sperm DNA was slightly damaged during space preservation, it could be repaired by the oocyte cytoplasm and did not impair the birth rate or normality of the offspring. Our results demonstrate that generating human or domestic animal offspring from space-preserved spermatozoa is a possibility, which should be useful when the “space age” arrives. If humans ever start to live permanently in space, assisted reproductive technology using preserved spermatozoa will be important for producing offspring; however, radiation on the International Space Station (ISS) is more than 100 times stronger than that on Earth, and irradiation causes DNA damage in cells and gametes. Here we examined the effect of space radiation on freeze-dried mouse spermatozoa held on the ISS for 9 mo at –95 °C, with launch and recovery at room temperature. DNA damage to the spermatozoa and male pronuclei was slightly increased, but the fertilization and birth rates were similar to those of controls. Next-generation sequencing showed only minor genomic differences between offspring derived from space-preserved spermatozoa and controls, and all offspring grew to adulthood and had normal fertility. Thus, we demonstrate that although space radiation can damage sperm DNA, it does not affect the production of viable offspring after at least 9 mo of storage on the ISS.

Measurement of a Linear Energy Transfer Distribution with Antioxidant Doped CR-39 Correcting for the Dip Angle Dependence of Track Formation Sensitivity

Antioxidant doped CR-39 detectors were loaded onto the STS-95 space shuttle mission (altitude: 574 km; inclination: 28.45°; flight duration: 8.9 days) for measuring the linear energy transfer (LET) distribution above 10 keV/µm for space radiation dosimetry. It is known that the track formation sensitivity of antioxidant doped CR-39 detectors depends on the dip angle of the incident particle. We investigated this dip angle dependence for a wide range of LET values and dip angles. The track formation sensitivities at lower dip angles were obviously decreased in the LET region below 100 keV/µm. We introduced minimum-cutoff dip angles in order to correct for such dip-angle dependence. The LET distribution of the STS-95 mission was obtained from the measurements of etch pits having dip angles larger than the minimum-cutoff dip angles. This new correction method increased the absorbed dose and dose equivalent above 10 keV/µm by 54 and 28%, respectively.

Dosimetry for Neutrons from 0.25 to 15 MeV by the Measurement of Linear Energy Transfer Distributions for Secondary Charged Particles in CR-39 Plastic

In the radiation fields of high energy accelerator facilities, high-altitude aircraft and space flights, high-energy neutron dosimetry of ~20 MeV or more is a significant issue for radiological protection. We studied the feasibility of experimental measurements of linear energy transfer (LET) distributions for secondary charged particles induced by fast neutrons using CR-39 plastic nuclear track detectors. In order to investigate a method of analyzing the CR-39 detectors that is appropriate for fast neutron dosimetry, two-layer CR-39 stacks were exposed to monochromatic neutrons (0.25, 0.55, 5, and 15 MeV) at the Fast Neutron Laboratory of Tohoku University in Japan. We also conducted Monte Carlo calculations to estimate the detection efficiency of the CR-39 detector for recoil protons. The CR-39 detectors treated by single-step chemical etching were used to obtain LET distributions for LET > 10 keV/µm-water. The results indicated that measurements of short-range particles are very important for obtaining the correct LET distributions. Using the measured LET distributions, we calculated neutron sensitivities, absorbed doses and dose equivalents based on the ICRP 60 Q–L relation and averaged quality factors. The dose equivalents were compared with the neutron fluence-to-dose equivalent conversion factors given by ICRP 74 and the averaged quality factors were compared with weighting factors given by ICRP 60 and ICRP 92.

Measurements of heavy-ion anisotropy and dose rates in the Russian section of the International Space Station with the Sileye-3/Alteino detector

In this work we present data on linear energy transfer (LET), dose and dose equivalent rates from different locations of the Russian part of the International Space Station (ISS) measured by the Sileye-3/Alteino detector. Data were taken as part of the ESA ALTCRISS project from late 2005 through 2007. The LET rate data shows a heavy-ion (LET keV/?m) anisotropy. From the heavy-ion LET rate in the Zvezda service module we find ISS (Starboard) and (Nadir) to be about 10?15 times higher than in (Forward). The situation is similar for dose and dose equivalent rates, ranging from 25?40 ?Gy d?1 in to about 75 ?Gy d?1 in , whereas for the dose equivalent the rate peaks in with around 470 ?Sv d?1. The heavy-ion anisotropy confirms what has been reported by the ALTEA collaboration. Measurements using two sets of passive detectors, DLR-TLDs and PADLES (TLD+CR-39), have also been performed in conjunction with Alteino measurements, both shielded and unshielded. The passive detectors register a dose rate about 3?5 times as high as Alteino, 260?280 ?Gy d?1 for PADLES and 200?260 ?Gy d?1 for DLR-TLDs. For the dose equivalent PADLES measurements ranges from 560?740 ?Sv d?1.

COMPARISON OF COSMIC-RAY ENVIRONMENTS ON EARTH, MOON, MARS AND IN SPACECRAFT USING PHITS

Estimation of cosmic-ray doses is of great importance not only in aircrew and astronaut dosimetry but also in evaluation of background radiation exposure to public. We therefore calculated the cosmic-ray doses on Earth, Moon and Mars as well as inside spacecraft, using Particle and Heavy Ion Transport code System PHITS. The same cosmic-ray models and dose conversion coefficients were employed in the calculation to properly compare between the simulation results for different environments. It is quantitatively confirmed that the thickness of physical shielding including the atmosphere and soil of the planets is the most important parameter to determine the cosmic-ray doses and their dominant contributors. The comparison also suggests that higher solar activity significantly reduces the astronaut doses particularly for the interplanetary missions. The information obtained from this study is useful in the designs of the future space missions as well as accelerator-based experiments dedicated to cosmic-ray research.

Reply to Ferlazzo and Foray: About the Space Pup project

We would like to thank Ferlazzo and Foray (1) for their very important comments and suggestions. We will keep in mind that “scientists should take particular care to justify their methodology and moderate their conclusions.” One concern of Ferlazzo and Foray (1) is that our control experiment entailed exposure to the ground radiation of Japan, rather than to a high natural radiation background (NRB), such as Ramsar. As the authors suggest, it would have been a good idea to expose our control sample to both Ramsar and Japan. When the control radiation level increases from 0.5 mSv/y (Japan) to 70 mSv/y (Ramsar) the difference between space and ground … [↵][1]1To whom correspondence may be addressed. Email: sayakaw{at}yamanashi.ac.jp or twakayama{at}yamanashi.ac.jp. [1]: #xref-corresp-1-1

Measurements from The Heavy-Ion Telescope at The ISS Kibo Exposed Facility

Space radiation such as solar energetic particles, galactic cosmic rays (GCR), and trapped particles affect space activities. Heavy ions, in particular, have high linear energy transfer (LET) that exacerbates the risk of radiation exposure for astronauts and affects the electrical circuits of satellites. The Japan Aerospace Exploration Agency (JAXA) has operated the Space Environment Data Acquisition Equipment Attached Payload (SEDA-AP) at the International Space Station (ISS) Japanese Experiment Module (Kibo) Exposed Facility, since 2009. The heavy-ion telescope (HIT) is one of the SEDA-AP instruments, which comprises two positionsensitive silicon detectors and 16 silicon detectors. Based on the ΔE × E particle-identification method, HIT measures fluxes of energetic ions from Li to Fe and calculates the loss of energies at each sensor. The HIT results are consistent with the general GCR model and other ISS experiments in terms of elemental abundances and LET distributions. In addition, HIT might have detected heavy ions from a X5.4 solar flare. Moreover, there is the possibility of detecting the anomalous cosmic rays (ACR) from the ADEOS satellite observations; however, ACR was not observed because the pitch angle was not in the field of view of HIT or no distribution of ACR exists at 400 km altitude.