Browsing by Author "Niihara, K"

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    Color centers in NaCl single crystals induced by pulsed intense relativistic electron beams to simulate radiation bursts in Europa
    (IOP Publishing, 2019-03-26) Toba, R; Kikuchi, K; Imada, G; Thorogood, GJ; Hayashi, N; Maynard-Casely, HE; Suematsu, H; Nakayama, T; Suzuki, T; Niihara, K
    To simulate the burst irradiation environment of Europa, single crystals of NaCl were irradiated by pulsed intense relativistic electron beams (PIREBs) with a peak energy of 6 MeV, a current of −800 A, and a pulse width of 70 ns. After irradiation, the optical absorption of the samples was measured, and results indicated that the irradiation induced F- and F2-centers. The density of F-centers was estimated to be 8.9 × 1016 cm−3 from 1 shot of PIREB irradiation with 6 MeV. The absorbed energy to form F-centers by PIREB was comparable but slightly higher than those induced by conventional direct current accelerators. The effect of pulsed heating, which should be taken into account for the detection of NaCl on Europa, is discussed. © 2019 The Japan Society of Applied Physics
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    Pore-forming process in dehydration of metakaolin-based geopolymer
    (John Wiley & Sons, Inc, 2021-06-26) Yang, Y; Le, TCD; Kudo, TMD; Niihara, K; Suematsu, H; Thorogood, GJ
    The geopolymer catalyst supports utilized in the nuclear waste containers for the Fukushima Daiichi Nuclear Power Station will be required to have high porosity and durability. This work presents the synthesis of a potassium and metakaolin-based geopolymer and its performance upon dehydration. During water content measurements of the samples, it was seen that in the demolded samples, the water content quickly decreased to less than 30% within 7 days, while the samples that had the cap removed from the container retained more than 50% of the water after 28 days. The pore size distribution of the samples that were post-cured at different temperatures up to 28 days did not vary greatly with respect to the average pore size. We can infer that structurally stable pores were formed in the first 4 days and were not affected by the post-curing rate, which may be related to rheological properties and the drainage path of water or hydrogen gas during post-curing. © 2021 The Authors. International Journal of Ceramic Engineering & Science published by Wiley Periodicals LLC on behalf of American Ceramic Society1Extreme Energy- Density Research Institute, Nagaoka University of Technology, Nagaoka, Japan2Department of Nuclear System Safety Engineering, Nagaoka University of Technology, Nagaoka, Japan3ADVAN ENG. Co., Ltd., Niigata, Japan4ANSTO, Lucas Heights, NSW, AustraliaCorrespondenceYaru Yang, Extreme Energy- Density Research Institute, Nagaoka University of Technology, 1603- 1 Kamotomioka- cho, Nagaoka, Niigata 940- 2188, Japan.Email: yyr922405@gmail.comAbstractThe geopolymer catalyst supports utilized in the nuclear waste containers for the Fukushima Daiichi Nuclear Power Station will be required to have high porosity and durability. This work presents the synthesis of a potassium and metakaolin- based geopolymer and its performance upon dehydration. During water content measure-ments of the samples, it was seen that in the demolded samples, the water content quickly decreased to less than 30% within 7 days, while the samples that had the cap removed from the container retained more than 50% of the water after 28 days. The pore size distribution of the samples that were post- cured at different temperatures up to 28 days did not vary greatly with respect to the average pore size. We can infer that structurally stable pores were formed in the first 4 days and were not affected by the post- curing rate, which may be related to rheological properties and the drainage path of water or hydrogen gas during post- curing. © 2021 The Authors. This is an open access article under the terms of the Creative Commons Attribution License.