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World’s first observation of hollow atom creation by successive X-ray hits (Press Release)

Release Date
23 Jul, 2013
- Beat two pieces of quantum “Daruma-Otoshi” -

Institute for Molecular Science
Japan Synchrotron Radiation Research Institute (JASRI)

Key points of this research
• Succeeded in hitting two X-ray photons within two parts per 10 quadrillion seconds
• Observable only by using 10 quintillion times brighter X-rays than sunlight
• Expectation for protein crystallography using hollow atoms

A joint research group comprising RIKEN (President, Ryoji Noyori), Institute for Molecular Science (President, Iwao Ohmine), and JASRI (President, Yoshiharu Doi) succeeded in creating hollow atoms*1 with the empty K shell by exciting sequentially the two electrons with intense focused X-ray free-electron laser (XFEL), SACLA*2. The group was led by Kenji Tamasaku (senior research scientist) and Makina Yabashi (group director) from the Beam Line Research and Development Group, RIKEN SPring-8 Center (Director, Tetsuya Ishikawa), Eiji Shigemasa (associate professor) from the Department of Photo-Molecular Science, Institute for Molecular Science, and Kensuke Tono (team leader) from the Experimental Instrumentation Team, JASRI.

An atom consists of a nucleus and surrounding electron shells. The electron shells are called “K”, “L”, … from the inner side. Each shell has a space for the specific number of electrons. The innermost K shell can contain up to two electrons. Absorption of X-rays ejects (photo-ionizes) a K-shell electron and creates an atom with a K-shell vacancy. Up to now, we do not need to worry about such atom with a K-shell vacancy in the radiograph as well as the X-ray research on the cutting edge. Because, within one parts of 1~10 quadrillion seconds, the vacancy in the K-shell is filled immediately by outer electron like the Daruma-Otoshi, which is a traditional Japanese toy. However, it becomes possible to hit X-rays to the atom before the K-shell vacancy is filled, if XFEL, the state-of-art X-ray source, is employed. In the case of Daruma-Otoshi, this corresponds to hitting twice the pieces before the Daruma falls. As a result, an atom with the empty K shell is created.

The research group succeeded in creating the hollow krypton*3 atom, whose diameter is only ~0.1 nm, by hitting X-rays twice within about two parts per 10 quadrillion seconds. Such atoms with vacancies are very important for the stringent test of theoretical models describing the electrons in an atom. Furthermore, they may be used for solving the phase problem*4 in protein crystallography with XFEL.

"Double core-hole creation by sequential attosecond photo-ionization"
Kenji Tamasaku, Mitsuru Nagasono, Hiroshi Iwayama, Eiji Shigemasa, Yuichi Inubushi, Takashi Tanaka, Kensuke Tono, Tadashi Togashi, Takahiro Sato, Tetsuo Katayama, Takashi Kameshima, Takaki Hatsui, Makina Yabashi, Tetsuya Ishikawa.
Physical Review Letters, 111 043001 (2013).


Fig. 1 Photo-ionization of krypton atom by X-rays
Fig. 1 Photo-ionization of krypton atom by X-rays

Left: usual photo-ionization, ejecting an electron in the innermost K shell (upper panel). Corresponding the Daruma-Otoshi process (lower panel).
Right: the hollow atom can be created, if the second electron is photo-ionized within about two parts per 10 quadrillion seconds after the first photo-ionization of K shell (upper panel). Corresponding the Daruma-Otoshi process, hitting twice the pieces before the Daruma falls (lower panel).

Fig. 2 X-ray fluorescence spectrum of krypton
Fig. 2 X-ray fluorescence spectrum of krypton

Two peaks in the longer wavelength region on the right side are usual fluorescence from the atoms with one vacancy in the K shell. Two peaks in the shorter wavelength region are the fluorescence from the atoms with the empty K shell. The spectrum in the shorter wavelength region is magnified by a factor of 1,000 for clarity.

*1 Hollow atoms

An atom with empty inner shells, such as the K shell.

SACLA is the moniker for the facility, derived from SPring-8 Angstrom Compact free-electron LAser. The RIKEN-operated facility, located in Harima Science Garden City (Hyogo prefecture), started its services in March 2012. The X-ray free-electron laser is characterized by its ability to produce very short wavelengths of light, comparable to X-rays, generated in a vacuum by electrons extracted from matter (free electrons). The XFEL light has a unique combination of the following four features:
(1) Extremely short wavelengths comparable to an atom, which is the minimum constituent unit of matter, typically with such a minute size as 10-9 m (i.e. an X-ray is produced).
(2) Spatially perfectly coherent light (i.e. laser light).
(3) Exceptionally high intensity (109 times brighter than SPring-8).
(4) Ultra short pulse source (as instantaneous as a camera flash, and the pulse width is as extremely short as 10-14 sec).

*3 Krypton
An element with atomic number 36, which is one of the noble gases and used for lamps.

*4 Phase problems
Light including X-rays is characterized by the amplitude, which represents the intensity, and the phase, which relates to the position of peaks and troughs of the wave. The complete information of both the amplitude and the phase is indispensable for X-ray structural analysis. The amplitude is determined from the diffraction pattern. On the other hand, the phase cannot be measured directly, which causes the phase problem.

For more information, please contact:
  Dr. Kenji Tamasaku (RIKEN)

  RIKEN SPring-8 Center Planning Office

  Associate prof. Eiji Shigemasa (Institute for Molecular Science)

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