Slow Positron Facility
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High Energy Accelerator Research Organization (KEK)
Institute of Materials Structure Science
- First observation of a shape resonance of the positronium negative ion
Positronium (Ps), a bound state of a positron (e+) and an electron (e+), can further bind to another electron to form the positronium negative ion, Ps-(e-e+e-). Since its constituents are solely point-like particles with the samemass, this system provides an excellent testing ground for the three-body problem in quantum mechanics. A laser spectroscopy study of Ps- has been performed, observing a strong shape resonance of 1Po symmetry near the Ps (n=2) formation threshold, in good agreement with the result of three-body calculations.
Nature Communications 7, 11060 (2016) doi:10.1038/ncomms11060.
- Structure of the rutile-TiO2(110)-(1×2) surface having been under debate ove 30 years finally settled by TRHEPD
The exact structure of the rutile-TiO2(110)-(1×2) surface, which had been under debate over the past 30 years, was investigated using TRHEPD. The rocking-curves for the 00-spot were compared to the curves for various models calculated with a full-dynamical theory. It was found that the rocking-curves matched those for a surface consisting of a Ti2O3 configuration, originally suggested by Onishi and Iwasawa, but with a further modification of atomic positions close to the ones proposed by Wang et al.
Phys. Chem. Chem. Phys. 18, 7085 (2016).
- Development of TRHEPD: the ultimate tool for surface structure analysis
A group led by principal researcher Atsuo Kawasuso of the Advanced Science Research Center, Japan Atomic Energy Agency, (JAEA), Professor Toshio Hyodo of the Institute of Materials Structure Science, KEK, and Professor Emeritus Ayahiko Ichimiya of Nagoya University has refined reflection high-energy positron diffraction (RHEPD) method to develop total-reflection high-energy positron diffraction (TRHEPD) method. A high-intensity positron beam whose intensity was increased 10 times in 2010 was used to obtain clear diffraction patterns from the (111) reconstructed surface of a silicon single crystal.
Appl. Phys. Express 7, 056601 (2014).
- Successful Determination of Silicene Structure Using Total-Reflection High-Energy Positron Diffracion (TRHEPD)
The groups of Prof. Toshio Hyodo, Institute of Materials Structure Science, KEK; Dr. Atsuo Kawasuso, Principal Researcher, Advanced Science Research Center, Japan Atomic Energy Agency; and Associate Prof. Iwao Matsuda, The Institute for Solid State Physics, The University of Tokyo studied the structure of silicene, which consists of a single layer of silicon deposited on a single-crystal silver (Ag) surface, using reflection high-energy positron diffraction (RHEPD). This technique can accurately determine atomic positions on the top surface of a crystal. These groups experimentally confirmed for the first time that silicene has an buckling structure unlike planar graphene, which consists of a flat single layer of carbon atoms.
Phys. Rev. B 88, 205413 (2013) .
- Successful generation of a positronium beam that can be readily accelerated to over 1 keV
A research group led by Prof. Yasuyuki Nagashima (Tokyo University of Science) comprising teams from Tokyo University of Science and High Energy Accelerator Research Organization (KEK) succeeded in generating an energy-tunable beam of positroniums (Ps) in an ultrahigh vacuum environment. A Ps atom is a bound state of an electron and its antiparticle, a positron. It cannot be accelerated by conventional means i.e., an electric field, because it has no net charge. However, the new technique allows the generated beam to be readily accelerated to energies over 1 keV.
Michishio, et al., Applied Physics Letters, 100, 254102 (2012).
- The World's First Success in Photodetachment of Positronium Negative Ions
,http://www.sut.ac.jp/tlo/english/press/pdf/2011/20110406press.pdf 1ofessor Yasuyuki Nagashima of the Department of Physics, Graduate School of Science, Tokyo University of Science and composed of members from the Tokyo University of Science, the High Energy Accelerator Research Organization, the University of Miyazaki and the University of Tokyo, have succeeded for the first time in the world in irradiating a positronium negative ion composed of one positron and two electrons bound together with a laser beam and dividing the ion into an electron and a positronium particle, the latter composed of one electron and one positron still bound together. This technique enables the generation, in an ultra-high vacuum state, of energy-tunable positronium beams at a desired energy level. Positronium beams, having no electric charge, can be used for analyzing insulator surfaces and open the way to a more thorough understanding of the characteristics of positronium itself.
Michishio, et al., Physical Review Letters, 106, 153401 (2011).
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