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Nugraha, E. D.*; Hosoda, Masahiro*; Kusdiana*; Untara*; Mellawati, J.*; Nurokhim*; Tamakuma, Yuki*; Ikram, A.*; Syaifudin, M.*; Yamada, Ryohei; et al.
Scientific Reports (Internet), 11(1), p.14578_1 - 14578_16, 2021/07
Times Cited Count：19 Percentile：84.25(Multidisciplinary Sciences)Mamuju is one of the regions in Indonesia which retains natural conditions but has relatively high exposure to natural radiation. The goals of the present study were to characterize exposure of the entire Mamuju region as a high natural background radiation area (HNBRA) and to assess the existing exposure as a means for radiation protection of the public and the environment. A cross-sectional study method was used with cluster sampling areas by measuring all parameters that contribute to external and internal radiation exposures. It was determined that Mamuju was a unique HNBRA with the annual effective dose between 17 and 115 mSv, with an average of 32 mSv. The lifetime cumulative dose calculation suggested that Mamuju residents could receive as much as 2.2 Sv on average which is much higher than the average dose of atomic bomb survivors for which risks of cancer and non-cancer diseases are demonstrated. The study results are new scientific data allowing better understanding of health effects related to chronic low-dose-rate radiation exposure and they can be used as the main input in a future epidemiology study.
Hosoda, Masahiro*; Nugraha, E. D.*; Akata, Naofumi*; Yamada, Ryohei; Tamakuma, Yuki*; Sasaki, Michiya*; Kelleher, K.*; Yoshinaga, Shinji*; Suzuki, Takahito*; Rattanapongs, C. P.*; et al.
Science of the Total Environment, 750, p.142346_1 - 142346_11, 2021/01
Times Cited Count：23 Percentile：86.19(Environmental Sciences)The biological effects of low dose-rate radiation exposures on humans remains unknown. In fact, the Japanese nation still struggles with this issue after the Fukushima Dai-ichi Nuclear Power Plant accident. Recently, we have found a unique area in Indonesia where naturally high radiation levels are present, resulting in chronic low dose-rate radiation exposures. We aimed to estimate the comprehensive dose due to internal and external exposures at the particularly high natural radiation area, and to discuss the enhancement mechanism of radon. A car-borne survey was conducted to estimate the external doses from terrestrial radiation. Indoor radon measurements were made in 47 dwellings over three to five months, covering the two typical seasons, to estimate the internal doses. Atmospheric radon gases were simultaneously collected at several heights to evaluate the vertical distribution. The absorbed dose rates in air in the study area vary widely between 50 nGy h
and 1109 nGy h. Indoor radon concentrations ranged from 124 Bq m
to 1015 Bq m. That is, the indoor radon concentrations measured exceed the reference levels of 100 Bq m recommended by the World Health Organization. Furthermore, the outdoor radon concentrations measured were comparable to the high indoor radon concentrations. The annual effective dose due to external and internal exposures in the study area was estimated to be 27 mSv using the median values. It was found that many residents are receiving radiation exposure from natural radionuclides over the dose limit for occupational exposure to radiation workers. This enhanced outdoor radon concentration might be as a result of the stable atmospheric conditions generated at an exceptionally low altitude. Our findings suggest that this area provides a unique opportunity to conduct an epidemiological study related to health effects due to chronic low dose-rate radiation exposure.
Tamakuma, Yuki*; Yamada, Ryohei; Suzuki, Takahito*; Kuroki, Tomohiro*; Saga, Rikiya*; Mizuno, Hiroyuki*; Sasaki, Hiroyuki*; Iwaoka, Kazuki*; Hosoda, Masahiro*; Tokonami, Shinji*
Radiation Protection Dosimetry, 184(3-4), p.307 - 310, 2019/10
Times Cited Count：1 Percentile：11.15(Environmental Sciences)After the Fukushima Daiichi Nuclear Power Plant accident, the radiation dose for first responders was not evaluated accurately due to lack of the monitoring data. It has been important to evaluate a radiation dose for workers in emergency response at a nuclear accident. In this study, a new device which can evaluate both of external and internal exposure doses was developed and the performance of various environmental radiation monitors including commercially available monitors were tested and compared from the viewpoint of an environmental monitoring at emergency situation. Background counts of the monitors and the ambient dose equivalent rate were measured in Fukushima Prefecture. The detection limit for beta particles was evaluated by the method of ISO11929. The sensitivity for gamma-rays of the dust monitor using a ZnS(Ag) and a plastic scintillator was high, but that of the external exposure monitor using a silicon photodiode with CsI(Tl) crystal was relatively low. The detection limit ranged 190-280 Bq m at 100 
Sv h, exceeding the detection limit of 100 Bq m in the minimum requirement by the National Regulation Authority in Japan. Use of the shielding with lead is necessary to achieve the minimum requirement. These results indicate that the dust monitor using a ZnS(Ag) scintillator and a plastic scintillator is suitable for the external exposure monitor and the developed internal exposure monitor is for the internal exposure monitor at emergency situation among the evaluated monitors. In the future study, the counting efficiency, the relative uncertainty and the performance of the detection for alpha particles will be evaluated, and it will be considered which type of a monitor is suitable after taking the portability into account.
@C
; Photoelectron spectroscopy of the Li@C[PF
] salt and STM of the single Li@C molecules on Cu(111)Yamada, Yoichi*; Kuklin, A. V.*; Sato, Sho*; Esaka, Fumitaka; Sumi, Naoya*; Zhang, C.*; Sasaki, Masahiro*; Kwon, E.*; Kasama, Yasuhiko*; Avramov, P. V.*; et al.
Carbon, 133, p.23 - 30, 2018/07
Times Cited Count：17 Percentile：55.14(Chemistry, Physical)We report first STM observation of the Li ion endohedral C, which is of a new class of endohedral fullerenes, prepared by means of evaporation of high-purity Li@C[PF] salt in ultra-high vacuum. Prior to the STM measurements, the electronic structure of Li@C in the Li@C[PF] salt was also precisely determined. In the salt, it is shown that Li and PF have nearly single positive and negative charge, respectively, and the C cage is nearly neutral, suggesting that Li@C in the salt retains its original electronic state.
Hasegawa, Yuri; Yamada, Yoichi*; Sasaki, Masahiro*
Vacuum and Surface Science, 61(6), p.366 - 371, 2018/06
Molecular arrangements and electronic states of well-ordered (DNTT) and picene thin film on single crystal were measured by means of scanning tunneling microscope (STM) and angle-resolved photoemission spectroscopy, respectively. DNTT and picene form single crystalline-like molecular arrangement on inert Au(111) substrate. Splitting of HOMO energy due to overlapping with adjacent molecules was suggested by ultraviolet photoemission spectroscopy (UPS) and density functional theory (DFT) calculation. On the other hand, one-dimensional ordering of those molecule was observed on anisotropic Ag(110) substrate. However, the HOMO band dispersion was found to be 200 meV at maximum, showing that the overlapping of HOMO was smaller in such arrangement comparing with that in their single crystal.
8) induced by supersonic O
beamsOkada, Ryuta; Yoshigoe, Akitaka; Teraoka, Yuden; Yamada, Yoichi*; Sasaki, Masahiro*
Applied Physics Express, 8(2), p.025701_1 - 025701_4, 2015/02
Times Cited Count：7 Percentile：30.95(Physics, Applied)We studied the surface oxidation on a Ge(111)-c(28) surface at room temperature using supersonic oxygen beams as a function of the translational energy of the incident oxygen molecules ranging from 26 meV to 2.3 eV. In situ synchrotron photoemission spectroscopy performed during the oxidation revealed that the surface oxidation terminated with the formation of a sub-monolayer oxide of at most 0.52 ML, for all the beam energies examined. In addition, the oxidation state of the surface oxides was found to depend on the translational energy. These results demonstrate the precise chemical control of the ultrathin surface oxides of Ge(111)-c(28).
synchrotron radiation photoelectron spectroscopy study of the oxidation of the Ge(100)-21 surface by supersonic molecular oxygen beamsYoshigoe, Akitaka; Teraoka, Yuden; Okada, Ryuta; Yamada, Yoichi*; Sasaki, Masahiro*
Journal of Chemical Physics, 141(17), p.174708_1 - 174708_7, 2014/11
Times Cited Count：8 Percentile：29.76(Chemistry, Physical)
synchrotron radiation photoelectron spectroscopy was performed during the oxidation of the Ge(100)-21 surface induced by a molecular oxygen beam with various incident energies up to 2.2 eV from the initial to saturation coverage of surface oxides. The saturation coverage of oxygen on the clean Ge(100) surface was much lower than one monolayer and the oxidation state of Ge was +2 at most. This indicates that the Ge(100) surface is in strong contrast to Si surfaces. The direct adsorption process can be activated by increasing the translational energy, resulting in an increased population of Ge
and a higher final oxygen coverage. Our findings will contribute to the fundamental understanding of oxygen adsorption processes at 300 K from the initial stages to saturated oxidation.
molecules to step edges of the Si(110)-162 single domain surfaceYokoyama, Yuta; Yamada, Yoichi*; Asaoka, Hidehito; Sasaki, Masahiro*
Journal of Physics; Conference Series, 417, p.012036_1 - 012036_6, 2013/03
Times Cited Count：1 Percentile：38.58(Materials Science, Coatings & Films)The Si(110)-162 reconstructed structure can be a superior template for 1-D nanostructures. However, the controlled nanostructure using this surface has not been fabricated yet. In this study, we have investigated the adsorption of C on the Si(110)-162 surface at various surface temperatures, and found that the C preferable adsorption site is remarkably changed, depending on the surface temperature. The obtained results indicate the possibility that the organic 1-D nanostructure can be fabricated on the Si(110)-162 surface by controlling the surface temperature.
Yokoyama, Yuta; Asaoka, Hidehito; Sinsarp, A.*; Sasaki, Masahiro*
e-Journal of Surface Science and Nanotechnology (Internet), 10, p.509 - 512, 2012/09
The Si(110) surface has a quite unique one-dimensional (1-D) structure with 162 reconstruction. Since the perfectly straight rows extend over micrometers, the 162 structure can be a superior template for 1-D nanostructures. In this study, we tried to control the clustering of Ge atoms on the Si(110) - 162 substrate. When Ge is deposited at 523 K, clustering of Ge atoms is found. The size of the cluster was 1
2 nm and many of them were located in a step edges. This trend is previously reported by vicinal Si(111) surface. With increasing temperature, the sizes of Ge clusters became larger. These results indicated that the size and alignment of the Ge cluster can be well controlled on the Si(110) - 162 template surface.
on one-dimensional template of single-domain Ge(110)-162 and Si(110)-162 surfacesYokoyama, Yuta; Sinsarp, A.*; Yamada, Yoichi*; Asaoka, Hidehito; Sasaki, Masahiro*
Applied Physics Express, 5(2), p.025203_1 - 025203_3, 2012/02
Times Cited Count：3 Percentile：13.53(Physics, Applied)We demonstrated the ordering of C in one dimension by using Ge(110)-162 and Si(110)-162 single-domain surfaces as an one-dimensional templates. On the Ge(110)-162 surface where surface diffusion of C was activated at room temperature such that it was aligned along the step edge, the formation of one-dimensional order of C molecules was achieved. In contrast, on the Si(110)-162 surface, the substantial reactivity of the surface limited the diffusion of adsorbed C, resulting in random adsorption at room temperature.
Yoshizawa, Yuji*; Kai, Michiaki*; Okoshi, Minoru; Kato, Tomoko; Yamaguchi, Tetsuji; Sasaki, Takayuki*; Hattori, Takatoshi*; Miyazaki, Shinichiro*; Higuchi, Natsuko*; Tokonami, Shinji*; et al.
no journal, ,
no abstracts in English
2 single domain surfaceYokoyama, Yuta*; Yamada, Yoichi*; Asaoka, Hidehito; Sasaki, Masahiro*
no journal, ,
no abstracts in English
2 single domain surfaceYokoyama, Yuta*; Yamada, Yoichi*; Asaoka, Hidehito; Sasaki, Masahiro*
no journal, ,
The single domain Si(110)-162 surface has a unique 1-D reconstructed structure, which should be an ideal template for the low-dimensional nanostructures. At the low coverage region, preferential adsorption onto the upper rows of the substrate is found for C and CuPc molecules. The results suggest that the low dimensional nanostructure fabrication on this surface could be possible at the low coverage region if we can controllably utilize the preferential adsorption to the upper rows.
2 and Si(110)-62 template surfacesYamada, Yoichi*; Sinsarp, A.*; Yokoyama, Yuta; Asaoka, Hidehito; Sasaki, Masahiro*
no journal, ,
no abstracts in English
8) surface at 300 K by supersonic O
molecular beamOkada, Ryuta; Yoshigoe, Akitaka; Teraoka, Yuden; Yamada, Yoichi*; Sasaki, Masahiro*
no journal, ,
Ge has been attracting considerable attention as one of the promising materials for next-generation MOSFET devises because of its high carrier mobility. Understanding of O adsorption process on Ge substrate with various index planes is the most essential to control the quality of oxide layers for these devices. In this research, we employ SR-XPS (synchrotron radiation X-ray photoelectron spectroscopy) measurement to study the oxidation mechanism of the Ge(111) which is known as one of the low index planes. We found the difference in Ge3d profiles of the Ge oxide formed by between supersonic O molecular beam and back filling O. The difference shows that the kinetic energy of the supersonic O molecular beam caused higher coordination of Ge oxide than that of back filling O. This result suggests the presence of new O adsorption states activated by the supersonic O molecular beam.
1 surface formed by supersonic O molecular beamYoshigoe, Akitaka; Teraoka, Yuden; Okada, Ryuta; Yamada, Yoichi*; Sasaki, Masahiro*
no journal, ,
Ge has been attracting considerable attention as one of the promising materials for next-generation MOSFET devises because of its high carrier mobility. In the application of Ge, it is important to fabricate well-defined thin oxide layer on the surfaces. Understanding of adsorption process of oxygen molecules on surfaces of Ge is the essential step toward the establishment of the controlled oxide layer. In this research, we studied the oxidation mechanism of the Ge(100) using in-situ SR-XPS (synchrotron radiation X-ray photoelectron spectroscopy). In the oxidation of Ge(100) at room temperature, it was found that the population of the higher oxidation state of Ge became larger with increasing the translational energy of the impinging oxygen beam. This is very essential information that will be important in controlling the oxide layer on Ge substrate.
molecular beamOkada, Ryuta; Yoshigoe, Akitaka; Teraoka, Yuden; Jinno, Muneaki*; Yamada, Yoichi*; Sasaki, Masahiro*
no journal, ,
Ge is attracted considerable attention as a new material of MOSFET because of its high carrier mobility than that of Si. Understanding of O adsorption process on Ge substrate with various index planes is the most essential to control the quality of oxide layers for these devices. In this research, we employ SR-XPS measurement to study the oxidation mechanism of the Ge(100) and (111) which is known as one of the low index planes. We found the difference of Ge-3d photoemission profile for the Ge oxide formed by supersonic O molecular beam and back-filling O. The difference shows that the kinetic energy of the supersonic O molecular beam increased components of Ge oxide than that of back-filling O. This result suggests the presence of new O adsorption states activated by the supersonic O molecular beam.
8) caused by supersonic O beamOkada, Ryuta; Yoshigoe, Akitaka; Teraoka, Yuden; Jinno, Muneaki*; Yamada, Yoichi*; Sasaki, Masahiro*
no journal, ,
Ge is one of the promising materials for the next generation FET because of its high carrier mobility overwhelming that of Si. Understanding of oxidation processes on Ge substrates with various index planes is necessary to control the quality of oxide layers for these devices. In this research, we employed SR-XPS to analyze oxide layers on the Ge(111)-c(28) surface formed by thermal-O gas and supersonic O beam. Ge
component was generated only by high energy supersonic O beam, although the oxide layer on Ge(100) has up to Ge
. This result indicates that oxidation states are different depending on crystal planes. Our results give insight into mechanisms of oxidation processes on Ge.
1 formed by supersonic O beamYoshigoe, Akitaka; Okada, Ryuta; Teraoka, Yuden; Jinno, Muneaki*; Yamada, Yoichi*; Sasaki, Masahiro*
no journal, ,
Ge has been attracted considerable attention as a new material of LSI because of its high carrier mobility. The O translational kinetic energy will be essential to understand the formation of oxide layers on Ge substrate for these devices. We previously reported that the high kinetic energy of the supersonic O beam enhances the oxidation on the Ge(100) at room temperature. In this research, we employed SR-XPS to analyze the oxidized Ge(100) surface formed by supersonic O molecular beam and back-filling O. In our experiments, we found the increase in amounts of the Ge oxide formed by supersonic O molecular beam comparing to that formed by back-filling O, although their coordination numbers were same in both cases. This result suggests that new oxygen adsorption states on the Ge(100) surface are activated by the supersonic O molecular beam. Our results give new knowledge concerning mechanisms of the formation of oxide layers on Ge substrate.
8) surface at 300 K by supersonic O molecular beamOkada, Ryuta; Yoshigoe, Akitaka; Teraoka, Yuden; Jinno, Muneaki*; Yamada, Yoichi*; Sasaki, Masahiro*
no journal, ,
no abstracts in English
