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Kakiuchi, Takuhiro*; Matoba, Tomoki*; Koyama, Daisuke*; Yamamoto, Yuki*; Yoshigoe, Akitaka
Langmuir, 38(8), p.2642 - 2650, 2022/03
Times Cited Count：1 Percentile：13.58(Chemistry, Multidisciplinary)0xidation processes at the interface and the surface of Si(111) substrate with thin Hf films were studied using photoelectron spectroscopy in conjunction with supersonic oxygen molecular beams (SOMB). The oxidation starts at the outermost Hf layers and produces stoichiometric HfO
. Hf silicates (Hf-O-Si configuration) were generated in the vicinity of the HfO/Si interface in the case of the irradiation of 2.2 eV SOMB. The oxidation of the Si substrate takes place to generate SiO compounds. Si atoms were emitted from the SiO/Si interface region underneath the HfO overlayers to release the stress generated within the strained Si layers. The emitted Si atoms can pass through the HfO overlayers and react with the impinging O gas.
7 surface using high-resolution core-level photoelectron spectroscopyKakiuchi, Takuhiro*; Matoba, Tomoki*; Koyama, Daisuke*; Yamamoto, Yuki*; Kato, Daiki*; Yoshigoe, Akitaka
Surface Science, 701, p.121691_1 - 121691_8, 2020/11
Times Cited Count：1 Percentile：5.82(Chemistry, Physical)Ultrathin hafnium films on Si(111)-77 were studied using synchrotron radiation photoelectron spectroscopies to reveal the chemical states at interface and surface. Ultrathin Hf layers grow on clean Si(111)-77 surface by lever rule. Surface and interface of Hf/Si(111) contain three components (metallic Hf layers, Hf monosilicide (HfSi) and Si-rich Hf silicide). Ultrathin Hf layers changes HfSi islands on bared Si(111)-77 surface after annealing at 1073 K. It was found that the long axes of the rectangle islands expand the direction connecting the corner holes in DAS model of clean Si(111)-77 surface.
Sr and 
Cs in soils near the Fukushima Daiichi Nuclear Power StationSasaki, Takayuki*; Matoba, Daisuke*; Dohi, Terumi; Fujiwara, Kenso; Kobayashi, Taishi*; Iijima, Kazuki
Journal of Radioanalytical and Nuclear Chemistry, 326(1), p.303 - 314, 2020/10
Times Cited Count：3 Percentile：34.82(Chemistry, Analytical)Iijima, Kazuki; Sasaki, Takayuki*; Matoba, Daisuke*; Dohi, Terumi; Fujiwara, Kenso; Koma, Yoshikazu; Takahatake, Yoko
no journal, ,
In the forests where radioactive plumes passed just nearby the Fukushima Dai-ichi Nuclear Power Station, the inventory of radionuclides, such as 
Cs, Cs, Sr, 
Pu, 
Pu, 
Am and 
Cm, in the topsoil was evaluated so that its applicability to estimate the on-site distribution of radionuclides inventory was discussed.
Iijima, Kazuki; Sasaki, Takayuki*; Matoba, Daisuke*; Dohi, Terumi; Fujiwara, Kenso
no journal, ,
In this study, in order to estimate the on-site distribution, the concentrations of several radionuclides in off-site topsoil were evaluated along six traces of the radioactive plumes, and the characteristic of spatial distribution and depth profile was discussed. The tendency of inventories of Sr-90 and Pu-238 observed in off-site was consistent with that of observed in the previous on-site sampling, indicating that the estimation of on-site distribution of radionuclides based on the off-site was applicable. Concentration of Cs-137 drastically decreased from top of the surface to around 10 cm depth, then gradually decreased, suggesting that Cs-137 was strongly adsorbed at upper part. Surprisingly, the profile of Pu-239+240 was quite different from that of Pu-238, while it was similar to Am-241. It was considered that the behavior of Am-241 was strongly reflected by that of Pu-241, a parent of Am-241, and the deposition event of Pu-239+240 and Pu-241 was different from that of Pu-238.
Fujiwara, Kenso; Sasaki, Takayuki*; Matoba, Daisuke*; Iijima, Kazuki
no journal, ,
Depth profiles of radionuclides atmospheric discharged to the environment of Fukushima was obtained nearby the Fukushima Daiichi Nuclear Power Station (FDNPS). According to the profiles, it was suggested that deposition of Pu-238 and Cs-137 was mostly caused by atmospheric discharge by the FDNPS accident, however, in the case of Pu-239+240, it is necessary to consider the effect of global fallout. For understanding on the migration behaviour of radionuclide, it is necessary to obtain the profiles attributed by the accident and global fallout. In this study, in order to clarify the profile of soil, time dependence of depth profile of Cs and Pu in the soil outside of FDNPS site was measured. Based on the results of this study, it was confirmed that Pu and Cs will not be transferred significantly in the soil over several years. In the case of Pu, concentration of fallout and discharge was calculated. This data is considered to be useful for the safety assessment of waste in FDNPS, especially, measurement of other nuclides can also show the utility of transport ratio based on Cs concentration.
Iijima, Kazuki; Fujiwara, Kenso; Matoba, Daisuke*; Sasaki, Takayuki*
no journal, ,
Depth profiles of radionuclides discharged to the environment of Fukushima was obtained in the forest soil just nearby the Fukushima Daiichi Nuclear Power Station (FDNPS). According to characteristics of the depth profile, Pu-238 was originated from the FDNPS accident, while Pu-239+240 was mainly originated from global fallout. Comparing depth profiles attributed by the accident and global fallout can give understanding on the migration behavior of Pu in subsurface soil during decades. In this study, advection-dispersion model was applied to evaluate the depth profiles of Pu isotopes. The Kd values for global fallout Pu-239+240 agreed with those of Fukushima Pu-238 within around factor 3. Therefore, migration behavior of Pu could be understood by the advection-dispersion model.
