| 1. |
- Ota, S., et al.
(författare)
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Depth dependency of neutron density produced by cosmic rays in the lunar subsurface
- 2014
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Ingår i: Advances in Space Research. - : Elsevier BV. - 1879-1948 .- 0273-1177. ; 54:10, s. 2114-2121
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Tidskriftsartikel (refereegranskat)abstract
- Depth dependency of neutrons produced by cosmic rays (CRs) in the lunar subsurface was estimated using the three-dimensional Monte Carlo particle and heavy ion transport simulation code, PHITS, incorporating the latest high energy nuclear data, JENDL/HE-2007. The PHITS simulations of equilibrium neutron density profiles in the lunar subsurface were compared with the measurement by Apollo 17 Lunar Neutron Probe Experiment (LNPE). Our calculations reproduced the LNPE data except for the 350-400 mg/cm(2) region under the improved condition using the CR spectra model based on the latest observations, well-tested nuclear interaction models with systematic cross section data, and JENDL/HE-2007.
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| 2. |
- Ota, S., et al.
(författare)
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Neutron production in the lunar subsurface from alpha particles in galactic cosmic rays
- 2011
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Ingår i: Earth, Planets and Space. - : Springer Science and Business Media LLC. - 1880-5981 .- 1343-8832. ; 63:1, s. 25-35
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Tidskriftsartikel (refereegranskat)abstract
- The neutron production from alpha particles in galactic cosmic rays (GCR) in the lunar subsurface has not been estimated with reliable precision despite its importance for lunar nuclear spectroscopy and space dosimetry. Here, we report our estimation of neutron production from GCR nuclei (protons and alpha particles) with the Particle and Heavy Ion Transport code System (PHITS), which includes several heavy ion interaction models. PHITS simulations of the equilibrium neutron density profiles in the lunar subsurface are compared with experimental data obtained in the Apollo 17 Lunar Neutron Probe Experiment. Our calculations successfully reproduced the data within an experimental error of 15%. Our estimation of neutron production from GCR nuclei, estimated by scaling that from protons by a factor of 1.27, is in good agreement within an error of 1% with the calculations using two different alpha particle interaction models in PHITS during a period of average activity of the solar cycle. However, we show that the factor depends on the incident GCR spectrum model used in the simulation. Therefore, we conclude that the use of heavy ion interaction models is important for estimating neutron production in the lunar subsurface.
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| 3. |
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| 4. |
- Tsuji, M., et al.
(författare)
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Comparison of grouting with silica sol in the Äspö Hard Rock Laboratory in Sweden and Mizunami underground research laboratory in Japan
- 2014
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Ingår i: 8th Asian Rock Mechanics Symposium, ARMS 2014, Royton Sapporo, Hotel and Convention CenterSapporo, Japan, 14-16 October 2014. - 9784907430030 ; , s. 1237-1246
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Konferensbidrag (refereegranskat)abstract
- Silica sol is a material that seems to fulfill the non-hazardous requirement of final repository and capable of penetrating into narrow fractures. The rock grouting strategy with silica sol has been studied and applied for some recent projects in Sweden. The design methodology is based on the determination of the distribution of fracture transmissivity and the theoretical penetration length. In 2008, grouting with silica sol was applied in the construction of a short tunnel at 450 m depth in the Äspö Hard Rock Laboratory (Äspö HRL), the TASS-tunnel. In 2010, a grouting experiment with silica sol was performed at a niche of 300 m depth in the Mizunami Underground Research Laboratory, the MIU-300-niche. Despite the fact that silica sol has been used for a couple of decades for soil consolidation or sealing of fractures, it has seldom been applied as a material for rock grouting during tunneling. The purposes of this study are: • Comparing the grouting work with silica sol in TASS-tunnel and MIU-300m-niche. • Investigating the applicability of the design method used in TASS-tunnel to the grouting experiment performed in MIU-300m-niche. • Suggesting further development of grouting techniques. It was found that although there was quite a difference in the geological conditions and grouting methods, both sites had good sealing quality results. In addition, the Swedish design method seems to be applicable to MIU-300m-niche even with the difference in the fracture aperture distribution in each site. Furthermore, the water inflow in a borehole at MIU-300m-niche has gradually decreased during the three years. One explanation for this good durability of silica sol can be that the grout penetration created a larger overlap between the boreholes than that achieved in TASS-tunnel. A large penetration length of grout minimizes the risk of erosion and/or dilution of grout, thus creating a durable sealing. It can be suggested that the Swedish method can be applied to the design and evaluation of the grouting works in Japanese rock with high intensity of fractures. Moreover, the use of Japanese silica sol or an additional overlap and pumping time might improve the grouting quality in Sweden.
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