Thermally altered subsurface material of asteroid (162173) Ryugu

Kitazato, Kohei*; Milliken, R. E.*; Iwata, Takahiro*; Abe, Masanao*; Otake, Makiko*; Matsuura, Shuji*; Takagi, Yasuhiko*; Nakamura, Tomoki*; Hiroi, Takahiro*; Matsuoka, Moe*; et al.

Nature Astronomy (Internet), 5(3), p.246 - 250, 2021/03

https://doi.org/10.1038/s41550-020-01271-2

Here we report observations of Ryugu's subsurface material by the Near-Infrared Spectrometer (NIRS3) on the Hayabusa2 spacecraft. Reflectance spectra of excavated material exhibit a hydroxyl (OH) absorption feature that is slightly stronger and peak-shifted compared with that observed for the surface, indicating that space weathering and/or radiative heating have caused subtle spectral changes in the uppermost surface. However, the strength and shape of the OH feature still suggests that the subsurface material experienced heating above 300 C, similar to the surface. In contrast, thermophysical modeling indicates that radiative heating does not increase the temperature above 200 C at the estimated excavation depth of 1 m, even if the semimajor axis is reduced to 0.344 au. This supports the hypothesis that primary thermal alteration occurred due to radiogenic and/or impact heating on Ryugu's parent body.

Development of neutron measurement in intense field using new type of nuclear emulsion

Kawarabayashi, Jun*; Ishihara, Kohei*; Takagi, Keisuke*; Tomita, Hideki*; Iguchi, Tetsuo*; Naka, Tatsuhiro*; Morishima, Kunihiro*; Maeda, Shigetaka

Journal of ASTM International (Internet), 9(3), 5 Pages, 2012/03

https://doi.org/10.1520/JAI104007

In order to measure the neutron from a spent fuel assembly in fast breeder reactor precisely, we made new nuclear emulsion based on non-sensitized OPERA film with AgBr grain size of 60, 90 and 160 nm. The efficiency for Cf neutron of the new emulsion was calculated to be 0.710 which energy ranged from 0.3 to 2 MeV that agrees with preliminary estimated value from experimental results. The sensitivity of the new emulsion was also estimated experimentally by irradiating 565 KeV and 14 MeV neutrons and found that the emulsion with the AgBr grain size of 60 nm showed the lowest sensitivity among these three emulsions but still had enough sensitivity for proton. Also, there was a suggestion from the experimental data that there was a threshold LET of 15 KeV/m for our new emulsion below which no silver cluster was developed. Further development of the response of nuclear emulsion with a few tens of nano-meter AgBr size is next step of this study.

Azimuthal correlations of electrons from heavy-flavor decay with hadrons in and Au+Au collisions at = 200 GeV

Adare, A.*; Afanasiev, S.*; Aidala, C.*; Ajitanand, N. N.*; Akiba, Yasuyuki*; Al-Bataineh, H.*; Alexander, J.*; Aoki, Kazuya*; Aphecetche, L.*; Aramaki, Y.*; et al.

Physical Review C, 83(4), p.044912_1 - 044912_16, 2011/04

https://doi.org/10.1103/PhysRevC.83.044912

Measurements of electrons from the decay of open-heavy-flavor mesons have shown that the yields are suppressed in Au+Au collisions compared to expectations from binary-scaled collisions. Here we extend these studies to two particle correlations where one particle is an electron from the decay of a heavy flavor meson and the other is a charged hadron from either the decay of the heavy meson or from jet fragmentation. These measurements provide more detailed information about the interaction between heavy quarks and the quark-gluon matter. We find the away-side-jet shape and yield to be modified in Au+Au collisions compared to collisions.

Research and development programme on ADS in JAEA

Oigawa, Hiroyuki; Nishihara, Kenji; Sasa, Toshinobu; Tsujimoto, Kazufumi; Sugawara, Takanori; Iwanaga, Kohei; Kikuchi, Kenji; Kurata, Yuji; Takei, Hayanori; Saito, Shigeru; et al.

Proceedings of 5th International Workshop on the Utilisation and Reliability of High Power Proton Accelerators (HPPA-5), p.387 - 399, 2008/04

JAEA has been promoting the research and development on accelerator-driven subcritical system (ADS) as a dedicated system for the transmutation of long-lived radioactive nuclides. The ADS proposed by JAEA is a lead-bismuth eutectic cooled, tank-type subcritical reactor with the thermal power of 800 MWth driven by a 30 MW superconducting linac. As for the design study of the future ADS, reduction of the maximum temperature of fuel claddings and verification of the feasibility of the beam window are under way. As for the Transmutation Experimental Facility (TEF) of the J-PARC project, design study including experimental device to deal with minor actinide fuels is being conducted. To facilitate the research and development on ADS, a common road map is necessary to be shared by international communities. The TEF program can play an important role in such an international context as an experimental platform to conduct basic and flexible experiments.

Feasibility study of accelerator driven system proposed by JAEA

Sugawara, Takanori; Nishihara, Kenji; Tsujimoto, Kazufumi; Iwanaga, Kohei; Kurata, Yuji; Sasa, Toshinobu; Oigawa, Hiroyuki

Proceedings of International Conference on Advanced Nuclear Fuel Cycles and Systems (Global 2007) (CD-ROM), p.998 - 1007, 2007/09

no abstracts in English

Activities on ADS at JAEA

Oigawa, Hiroyuki; Nishihara, Kenji; Tsujimoto, Kazufumi; Takei, Hayanori; Kikuchi, Kenji; Kurata, Yuji; Saito, Shigeru; Mizumoto, Motoharu; Sasa, Toshinobu; Sugawara, Takanori; et al.

Proceedings of 9th OECD/NEA Information Exchange Meeting on Actinide and Fission Product Partitioning and Transmutation, p.371 - 382, 2007/00

JAEA has been conducting the R&D on accelerator-driven subcritical system (ADS) as a dedicated system for the transmutation of long-lived radioactive nuclides. The ADS can co-exist with FBR symbiotically and complementarily to enhance the reliability and the safety of the commercial FBR cycle. The R&D activities in JAEA include neutronics, thermal-hydraulic and structural design, transient analysis in case of beam trips, development of spallation target using Pb-Bi, research on the materials, and cost estimation. In addition, the high-intensity proton accelerator project J-PARC is under construction. One of the main experimental facilities of the J-PARC is the Transmutation Experimental Facility (TEF), which is assigned as Phase-II of the project.

Determination of reactivity and source intensity based on the maximum likelihood method

Nishihara, Kenji; Iwanaga, Kohei; Yamane, Tsuyoshi; Okajima, Shigeaki

JAERI-Research 2002-030, 63 Pages, 2002/12

JAERI-Research-2002-030.pdf:3.81MB

During the experiments using the critical assembly such that reactivity is added to the stationary state and the core shifts to the other stationary state, the neutron flux transitionally changes after some change of the reactivity or source. Inverse kinetics method (IK method) can generally adopted as the technique of obtaining the reactivity and/or source by analyzing the neutron flux. However, the conventional analysis method was not able to obtain the solution with the maximum likelihood considering the error of the measured neutron flux and to estimate the error of the solution. In the present research, by adopting the maximum likelihood methodology to the problem, developed is the technique to obtain the reactivity and source intensity with maximum likelihood and the errors of them. Moreover, the technique is applied to the rod drops experiment in FCA, and the validity of a technique is checked.

Sensitivity control of nuclear emulsion using AgBr nano-grains

Ishihara, Kohei*; Takagi, Keisuke*; Kawarabayashi, Jun*; Tomita, Hideki*; Naka, Tatsuhiro*; Asada, Takashi*; Morishima, Kunihiro*; Nakamura, Mitsuhiro*; Kuge, Kenichi*; Maeda, Shigetaka; et al.

no journal, , 

The nuclear emulsion with AgBr nano-grains has been developed for neutron detection under high -ray background. It has been demonstrated that the detection sensitivity of -rays can be well suppressed compared to that of neutrons by adjusting the size of AgBr nano-grains to deposit the energy of the secondary electrons produced by -rays below a certain threshold which can create Ag latent images.

Development of neutron spectrum measurement in high field using new nuclear emulsion, 2; Recognition algorithm for recoiled proton track based on three dimensional analysis of the novel nuclear emulsion

Takagi, Keisuke*; Ishihara, Kohei*; Tomita, Hideki*; Kawarabayashi, Jun*; Iguchi, Tetsuo*; Morishima, Kunihiro*; Maeda, Shigetaka; Matsumoto, Tetsuro*

no journal, , 

In the novel nuclear emulsion development to measurement a neutron spectrum in high -ray field, in order to control -ray sensitivity, the ArBr grains of about 100 nm of particle diameter is used. The recoil proton track induced by neutron is recorded on nuclear emulsion. The track constituted by a silver grains child standing in a row discretely is recorded. The track extraction algorithm suitable for extraction of recoil proton was developed, and the characteristic was evaluated.

Temperature dependence of -ray and neutron sensitivities of nuclear emulsion with AgBr nano-grains

Ishihara, Kohei*; Kawarabayashi, Jun*; Tomita, Hideki*; Naka, Tatsuhiro*; Asada, Takashi*; Morishima, Kunihiro*; Nakamura, Mitsuhiro*; Maeda, Shigetaka; Iguchi, Tetsuo*

no journal, , 

In order to establish a neutron spectrum measurement in high field such as spent nuclear fuel storage, advanced nuclear emulsion based on non-sensitized OPERA film with AgBr grain size of 60 nm has been developed. A nuclear emulsion has the feature of being easy to cause latent image degradation in the high temperature condition. In this study, the experiment estimated the temperature dependency of the sensitivity to the ray and neutron of a new nuclear emulsion. It is confirmed that the detection efficiency for a neutron and fell in more than 30 C environment.