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Okumura, Masahiko; Kerisit, S.*; Bourg, I. C.*; Lammers, L. N.*; Ikeda, Takashi*; Sassi, M.*; Rosso, K. M.*; Machida, Masahiko
Journal of Environmental Radioactivity, 189, p.135 - 145, 2018/09
Times Cited Count:60 Percentile:87.37(Environmental Sciences)no abstracts in English
Rai, D.*; Kitamura, Akira; Altmaier, M.*; Rosso, K. M.*; Sasaki, Takayuki*; Kobayashi, Taishi*
Journal of Solution Chemistry, 47(5), p.855 - 891, 2018/05
Times Cited Count:11 Percentile:10.52(Chemistry, Physical)We have critically reviewed experimental data for Zr hydrolysis constant values for formation of several mononuclear and polynuclear species and a solubility product value for ZrO(am). We have determined new/revised values for the formation constants of Zr(OH)
, Zr(OH)
(aq), Zr(OH)
, Zr(OH)
and Ca
Zr(OH)
, and the solubility product for ZrO
(am) after the critical review.
Sassi, M.*; Rosso, K. M.*; Okumura, Masahiko; Machida, Masahiko
Clays and Clay Minerals, 65(5), p.371 - 375, 2017/11
Times Cited Count:2 Percentile:77.31(Chemistry, Physical)no abstracts in English
Sassi, M.*; Okumura, Masahiko; Machida, Masahiko; Rosso, K. M.*
Physical Chemistry Chemical Physics, 19(39), p.27007 - 27014, 2017/10
Times Cited Count:4 Percentile:15.44(Chemistry, Physical)no abstracts in English
Okumura, Masahiko; Sassi, M.*; Rosso, K. M.*; Machida, Masahiko
AIP Advances (Internet), 7(5), p.055211_1 - 055211_9, 2017/05
Times Cited Count:6 Percentile:27.29(Nanoscience & Nanotechnology)no abstracts in English
Kerisit, S.*; Okumura, Masahiko; Rosso, K. M.*; Machida, Masahiko
Clays and Clay Minerals, 64(4), p.389 - 400, 2016/08
Times Cited Count:31 Percentile:72.07(Chemistry, Physical)no abstracts in English
Rai, D.*; Kitamura, Akira; Rosso, K. M.*; Sasaki, Takayuki*; Kobayashi, Taishi*
Radiochimica Acta, 104(8), p.583 - 592, 2016/08
Times Cited Count:6 Percentile:46.39(Chemistry, Inorganic & Nuclear)Solubility studies were conducted with HfO(cr) solid as a function of acid concentrations. These studies involved (1) using two different amounts of the solid phase, (2) acid washing the bulk solid phase, (3) preheating the solid phase to 1400
C, and (4) heating amorphous HfO
(am) suspensions to 90
C to ascertain whether the HfO
(am) converts to HfO
(cr) and to determine the solubility from the oversaturation direction. Based on the results of these treatments it is concluded that the HfO
(cr) contains a small fraction of less crystalline, but not amorphous, material [HfO
(lcr)] and this, rather than the HfO
(cr), is the solubility-controlling phase in the range of experimental variables investigated in this study. The solubility data are interpreted using both the Pitzer and SIT models. The log
of the solubility product of HfO
(cr) is estimated. The observation of a small fraction of less crystalline higher solubility material is consistent with the general picture that mineral surfaces are often structurally and/or imperfect leading to a higher solubility than the bulk crystalline solid. This study stresses the urgent need, during interpretation of solubility data, of taking precautions to make certain that the observed solubility behavior for sparingly-soluble solids is assigned to the proper solid phase.
Sassi, M.*; Rosso, K. M.*; Okumura, Masahiko; Machida, Masahiko
Clays and Clay Minerals, 64(2), p.108 - 114, 2016/04
Times Cited Count:6 Percentile:19.09(Chemistry, Physical)no abstracts in English
Sahin, E.*; Doncel, M.*; Sieja, K.*; De Angelis, G.*; Gadea, A.*; Quintana, B.*; Grgen, A.*; Modamio, V.*; Mengoni, D.*; Valiente-Dob
n, J. J.*; et al.
Physical Review C, 91(3), p.034302_1 - 034302_9, 2015/03
Times Cited Count:26 Percentile:82.66(Physics, Nuclear)Okumura, Masahiko; Nakamura, Hiroki; Machida, Masahiko; Sassi, M.*; Rosso, K.*
no journal, ,
no abstracts in English
Okumura, Masahiko; Kerisit, S.*; Bourg, I.*; Lammers, L.*; Ikeda, Takashi*; Sassi, M.*; Rosso, K.*; Machida, Masahiko
no journal, ,
no abstracts in English
Hiraguchi, Atsuki; Zheng, X.*; Underwood, T. R.*; Kobayashi, Keita; Yamaguchi, Akiko; Itakura, Mitsuhiro; Machida, Masahiko; Rosso, K. M.*; Bourg, I. C.*; Okumura, Masahiko
no journal, ,
Understanding the radionuclide diffusion phenomena is crucial for the safe geological disposal of high-level radioactive waste. The diffusion in clay-water systems is particularly important for the performance of the artificial barrier made of bentonite. Numerical simulation is one of the best research methods for understanding the phenomenon at the microscopic level. Recently, large-scale molecular dynamics (MD) simulations of the systems with clay particles and water molecules were realized. In this presentation, we will show numerical simulation results of diffusion of cesium in the large system with MD. Our recent results suggest that cesium is less diffuse than sodium.
Hiraguchi, Atsuki; Zheng, X.*; Underwood, T. R.*; Kobayashi, Keita; Yamaguchi, Akiko; Itakura, Mitsuhiro; Machida, Masahiko; Rosso, K. M.*; Bourg, I. C.*; Okumura, Masahiko
no journal, ,
In order to evaluate the long-term safety of geological disposal of high-level radioactive waste, it is necessary to clarify and model the migration behavior of radionuclides in clay minerals used as buffer material on a molecular scale. In this study, we perform classical molecular dynamics simulations in clay minerals-water systems and evaluate free-energy profiles of clay minerals to clarify and model the diffusion behavior of cesium on a molecular scale.