Research by the National Institutes for Quantum and Radiological Science and Technology (JAXA), the National Institutes for Quantum and Radiological Science and Technology, and Waseda University has shown that the exposure dose from cosmic radiation can be reduced to below the standard value for occupational exposure on the ground by using the vertical hole topography of the lunar surface. It became clear that it could be done.

 Various radiations are flying around in outer space, and astronauts staying at the International Space Station (ISS) are exposed to 1 to 0.5 mSv a day on average. In the vicinity of the earth where the ISS orbits, the radiation is attenuated to some extent by the earth's magnetic field, but this is equivalent to more than 1.0 times the exposure dose on the ground.If the base of manned activities expands from the ISS to the moon in the future, the attenuation effect of the earth's magnetic field will disappear, and there is concern that the exposure dose will increase significantly.

 On the other hand, in 2009, a vertical hole topography was discovered on the lunar surface by the Japanese lunar orbiting satellite "KAGUYA" (SELENE).The vertical hole is thought to be connected to an underground cavity such as a lava tube created by igneous activity, and has a diameter and depth of several tens of meters.In this study, we focused on using the vertical hole and the underground cavity that continues from it as a radiation protection space, and evaluated the space radiation protection effect of the vertical hole based on the latest radiation science research.

 In a simulation simulating the vertical hole of "Marius Hills" in the western part of the lunar surface, the exposure dose in the lunar surface area outside the vertical hole was about 420 mSv per year, while the exposure dose in the central part of the vertical hole was about 10 mSv. It decreased with depth, and it was found that the central part of the bottom was less than 19% of the lunar surface (about 24 to 5 mSv per year).Since this is below the occupational exposure standard value on the ground (100 mSv in XNUMX years), it became clear that a safe radiation protection space can be realized by using vertical holes and underground space.

 Depending on the size of the underground space, it is possible to expect a radiation environment similar to that on the earth.This result can be said to be an important finding showing that a safe radiation environment can be secured without bringing in new shielding materials for manned lunar exploration and future permanent lunar manned stay.

Paper information:[Journal of Radiological Protection] Radiation dose and its protection in the Moon from galactic cosmic rays and solar energetic particles: at the lunar surface and in a lava tube

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