Initialising ...
Initialising ...
Initialising ...
Initialising ...
Initialising ...
Initialising ...
Initialising ...
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.
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.
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.
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.
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.
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.
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
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.
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.
Taira, Yoshitaka*; Okano, Yasuaki*; Hirade, Tetsuya
no journal, ,
We are developing gamma-ray-induced positron annihilation spectroscopy (GiPAS) using ultra-short pulsed gamma rays at the UVSOR synchrotron facility in Japan. The gamma rays with the pulse width of picosecond range are generated by 90-degree inverse Compton scattering between a 750 MeV electron beam and an 800 nm laser. As the energy of the gamma rays is 6.6 MeV, gamma-ray irradiation produces positrons by pair production inside the material. Generated positrons localize on atomic-scale defects in solid crystals, such as vacancies, dislocations, and vacancy clusters. Positronium, the bound state of an electron-positron pair, localizes in vacant space caused by the free volume in polymers. Therefore, positrons are excellent probes of the nanostructure of these materials. Furthermore, the circularly polarized gamma rays generated by a circularly polarized laser can produce spin polarized positrons. The spin polarized positrons provide additional information about the electron spins around defects. GiPAS is currently available for users in UVSOR-III.
Taira, Yoshitaka*; Okano, Yasuaki*; Hirade, Tetsuya; Yabuuchi, Atsushi*
no journal, ,
High-energy ultrashort pulse gamma rays obtained by inverse Thomson/Compton scattering in UVSOR were applied to gamma-ray-induced positron annihilation spectroscopy. In gamma-ray-induced positron annihilation lifetime spectroscopy (GiPALS), a positron lifetime measurement system with a time resolution of 140 ps in full width at half maximum was developed using eight BaF scintillation detectors and two digital oscilloscopes. GiPALS is currently available for users and in situ measurements of positron lifetime under stress loading is conducted. The development of gamma-ray-induced age-momentum correlation (GiAMOC) system using Ge semiconductor detectors is also in progress. Furthermore, the effect of pulsed gamma-ray scattering on the positron lifetime spectra is evaluated computationally using the Monte Carlo simulation code EGS5, and the method is being refined. The development of spin-polarized positron annihilation spectroscopy using circularly polarized gamma rays is also planned in the future.
Taira, Yoshitaka*; Okano, Yasuaki*; Hirade, Tetsuya
no journal, ,
BL1U is a beamline that researches the development of new light sources and the exploration of usage methods. We are generating 6.6 MeV ultrashort pulse gamma rays using a Ti: Sa laser with a wavelength of 800 nm and are researching gamma ray-induced positron annihilation spectroscopy (GiPALS). GiPALS is a method that measures the lifetime of positrons by measuring the emission time distribution of annihilation gamma rays and can analyze the type and size of defects inside a sample. GiPALS is available to users for in-situ measurements of defect formation in metallic materials during stress loading and measurements of bulk samples such as ferrous materials, catalytic materials, and scintillators.