Refine your search:     
Report No.
 - 
Search Results: Records 1-13 displayed on this page of 13
  • 1

Presentation/Publication Type

Initialising ...

Refine

Journal/Book Title

Initialising ...

Meeting title

Initialising ...

First Author

Initialising ...

Keyword

Initialising ...

Language

Initialising ...

Publication Year

Initialising ...

Held year of conference

Initialising ...

Save select records

Journal Articles

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

 Times Cited Count:30 Percentile:96.87(Astronomy & Astrophysics)

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 $$^{circ}$$C, similar to the surface. In contrast, thermophysical modeling indicates that radiative heating does not increase the temperature above 200 $$^{circ}$$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.

Oral presentation

Development of gamma-ray induced positron age-momentum correlation measurements at UVSOR-III

Yamamoto, Ryohei*; Sugita, Kento*; Taira, Yoshitaka*; Hirade, Tetsuya

no journal, , 

Age-Momentum Correlation (AMOC) can observe the Doppler broadening of time-resolved annihilation gamma rays. The annihilation rate depends on the positron state, and it is possible to know if positrons are trapped in structural defects in a sample. Moreover, the Doppler broadening gives the information of impurities around the defects. Positrons from radioactive isotopes cannot penetrate a deep region of bulk material. The application of radioisotopes is difficult for the measurements under severe conditions such as in high pressure or a high temperature. Therefore, we have developed a GiAMOC (Gamma-ray induced AMOC) system, which is a measurement method for generating positrons in a sample using inverse Thomson scattered gamma rays in UVSOR-III. In addition, the developed measurement system was used to measure the reference material for positron lifetime measurement.

Oral presentation

Development of gamma-ray induced positron annihilation spectroscopy

Taira, Yoshitaka*; Sugita, Kento*; Okano, Yasuaki*; Fujimoto, Masaki*; Hirade, Tetsuya

no journal, , 

Positron annihilation spectroscopy is a powerful analytical method that can observe single-atom vacant defects in crystals and micro voids in insulating materials. UVSOR-III installed at the Institute of Molecular Science is promoting the development and user use of Gamma-ray induced positron annihilation spectroscopy (GiPAS) by ultrashort pulse gamma rays. Since the ultrashort pulse gamma rays generate positrons inside the material by pair production, positron annihilation experiments of bulk materials with a thickness of several cm can be performed non-destructively. We have succeeded in the generation of ultrashort pulse gamma rays and positron annihilation experiments such as the lifetime measurement and the positron age-momentum correlation measurement.

Oral presentation

Development of gamma ray-induced positron annihilation spectroscopy at UVSOR-III

Taira, Yoshitaka*; Sugita, Kento*; Yamamoto, Ryohei*; Okano, Yasuaki*; Hirade, Tetsuya

no journal, , 

We are developing gamma-ray-induced positron annihilation spectroscopy at UVSOR-III. This method enables defect analysis of the entire bulk sample with a thickness of several cm, which was difficult to measure with the conventional method using a positron radiation source. Currently, the user use of the positron lifetime measurement method is being developed, and in parallel with this, the coincidence Doppler broadening method, the age-momentum correlation measurement method, and the spin-polarized positron spectroscopy are being developed. Here, we will describe the development status of them.

Oral presentation

Development of polarimeter for circular polarization measurement of gamma-rays emitted from neutron capture reactions

Endo, Shunsuke; Abe, Ryota*; Ishizaki, Kohei*; Ito, Yuki*; Oku, Takayuki; Okudaira, Takuya*; Omer, M.; Kameda, Kento*; Kitaguchi, Masaaki*; Kimura, Atsushi; et al.

no journal, , 

no abstracts in English

Oral presentation

Development of gamma-ray induced positron annihilation spectroscopy

Taira, Yoshitaka*; Sugita, Kento*; Yamamoto, Ryohei*; Okano, Yasuaki*; Hirade, Tetsuya

no journal, , 

Positron annihilation spectroscopy is a powerful analytical method to observe single-atom vacant defects in crystals and microvoids in insulating materials. UVSOR-III installed at the Institute of Molecular Science promotes the development and user use of Gamma-ray induced positron annihilation spectroscopy (GiPAS) by ultrashort pulse gamma rays. Since the ultrashort pulse gamma rays generate positrons inside the material by pair production, positron annihilation experiments of bulk materials with a thickness of several cm can be performed non-destructively. In addition, since the sample is irradiated with gamma rays from the outside, measurement can be performed in an environment such as high temperature, high pressure, and immersion. We report on the generation of ultrashort pulse gamma rays and the development status of the positron lifetime measurement, and the positron age-momentum correlation measurement.

Oral presentation

Development of gamma-ray-induced positron age-momentum correlation measurement method in UVSOR-III

Yamamoto, Ryohei*; Taira, Yoshitaka*; Sugita, Kento*; Hirade, Tetsuya; Takashima, Yoshifumi*; Kato, Masahiro*

no journal, , 

Positron annihilation spectroscopy is a powerful analytical method that can observe single-atom vacant defects in crystals and microvoids in insulating materials. UVSOR-III installed at the Institute of Molecular Science is promoting the development and user use of Gamma-ray induced positron annihilation spectroscopy (GiPAS) by ultrashort pulse gamma rays. We have succeeded in positron lifetime measurement and lifetime momentum correlation measurement. This time, we succeeded in detecting the process of defect capture in the positron age-momentum correlation measurement of strained steel materials.

Oral presentation

Development of gamma ray induced positron annihilation spectroscopy

Taira, Yoshitaka*; Sugita, Kento*; Okano, Yasuaki*; Hirade, Tetsuya

no journal, , 

We applied the ultra-short pulsed gamma rays to positron annihilation spectroscopy (PAS). PAS using high energy gamma-rays, called gamma induced PAS (GiPAS), has several advantages compared with PAS using radioisotopes. (i) It enables defect analysis of thick material in a few centimetres because positrons are created throughout a bulk material via pair production by irradiation with gamma-rays having high penetration into the material. (ii) There is no contribution of positrons annihilated in the covering material of the shield sources, making the data analysis easy and accurate.

Oral presentation

Development of gamma ray sources and their application studies in UVSOR-III

Taira, Yoshitaka*; Sugita, Kento*; Okano, Yasuaki*; Hirade, Tetsuya; Endo, Shunsuke; Zen, H.*; Shizuma, Toshiyuki*

no journal, , 

At UVSOR, a synchrotron radiation facility at the Institute for Molecular Science, gamma rays are generated by inverse Thomson scattering. Compared to gamma rays generated from radioisotopes and bremsstrahlung gamma rays, it has excellent features such as variable energy, quasi-monochromatic, low background, and high directivity. It is also possible to generate polarized gamma rays by using a polarized laser. Using this gamma ray, nuclear physics experiments such as isotope imaging by nuclear resonance fluorescence scattering, evaluation of gamma ray detectors, and research on material analysis by gamma ray-induced positron annihilation spectroscopy are being carried out. Positron annihilation spectroscopy is a powerful method that can analyze defects of sub-nm to several nm such as monatomic vacancies. Positrons can also be generated from gamma rays by pair production. By irradiating the sample with gamma rays, positrons are generated inside the sample, and it is possible to analyze defects in a bulk sample with a thickness of several cm. At this year's meeting, we will present the development of gamma ray sources in UVSOR, the magnetic Compton scattering experiment of circularly polarized gamma rays, the development of gamma ray-induced positron annihilation spectroscopy, and the development of measurement technology for spin-polarized positrons using circularly polarized gamma rays.

Oral presentation

Development of gamma ray-induced positron annihilation spectroscopy at UVSOR-III

Taira, Yoshitaka*; Sugita, Kento*; Okano, Yasuaki*; Hirade, Tetsuya

no journal, , 

Positron annihilation spectroscopy is a powerful analytical method that can measure vacant defects in crystals and microvoids in insulating materials. UVSOR-III is developing gamma-ray-induced positron annihilation spectroscopy using ultrashort pulse gamma rays. Specifically, we have succeeded in positron annihilation lifetime (PAL) measurement and positron age-momentum correlation (AMOC) measurement. PAL has succeeded in directly measuring the spectrum of only the sample. In addition, AMOC also succeeded in observing the positron annihilation only in the samples, which shows the different momentum distribution for the different defect states. At present, coincidence Doppler broadening (COB) measurement is also available, and a CDB spectrum with only positron annihilation from the sample will be obtained by the newly developed analysis program.

Oral presentation

Gamma ray induced positron annihilation spectroscopy at UVSOR-III

Taira, Yoshitaka*; Sugita, Kento*; Okano, Yasuaki*; Hirade, Tetsuya

no journal, , 

We have developed the gamma-ray induced positron annihilation lifetime spectroscopy (GiPALS) with a time resolution of 140 ps. It has eight BaF$$_{2}$$ detectors and two digital oscilloscopes currently available for users. In addition to GiPALS, we have developed gamma-ray induced age-momentum correlation (GiAMOC). We will present a generation method of the ultra-short pulsed gamma-rays, details of GiPALS and GiAMOC, and future plans, including the development of a spin-polarized positron source generated from circularly polarized gamma rays.

Oral presentation

Ultra-short pulsed gamma rays and its application to material science

Taira, Yoshitaka*; Sugita, Kento*; Okano, Yasuaki*; Hirade, Tetsuya

no journal, , 

We have developed ultra-short, pulsed gamma rays at the synchrotron radiation facility UVSOR-III by a 90-degree collision between a 750-MeV electron beam and a Ti:Sa laser pulse. The maximum energy of the gamma rays is 6.6 MeV and the pulse width is calculated to be sub-ps to ps ranges. We applied this ultra-short, pulsed gamma rays to positron annihilation spectroscopy (PAS). A positron is an excellent probe of atomic-scale defects in solids such as vacancies, dislocations, and clusters and of free volumes in polymers. PAS using a high energy gamma-ray, which is called gamma induced PAS (GiPAS), has several advantages compared with PAS using Na-22. We will present a generation method of the ultra-short, pulsed gamma rays and details of GiPAS.

Oral presentation

In situ observation of defects in pure iron using gamma-ray-induced positron annihilation spectroscopy

Yabuuchi, Atsushi*; Hirade, Tetsuya; Fujinami, Masanori*; Awaji, Ryo*; Oshima, Nagayasu*; Takai, Kenichi*; Taira, Yoshitaka*; Sugita, Kento*

no journal, , 

In situ measurements of positron annihilation lifetimes have been performed at the UVSOR synchrotron radiation facility to characterise defects formed during tensile deformation of pure iron using the gamma-ray induced positron annihilation spectroscopy (GiPAS) technique. A dumbbell-shaped specimen was attached to a small tensile tester and stretched to a nominal strain of 7 or more at a strain rate of 2.2$$times$$10$$^{5}$$/s. Positron lifetime changes during tensile deformation of a pure iron specimen were observed using positrons generated in the sample by irradiating the centre of the sample with a 66MeV gamma-ray pulse beam of 3mm in diameter. Unlike the results reported so far, the change in the positron lifetime, especially at the early deformation stage, was very small, making clear the importance of in-situ measurement.

13 (Records 1-13 displayed on this page)
  • 1