Measurement Efficiency of Synchrotron-Radiation-Based Mössbauer Absorption Spectroscopy Dramatically Improved by Electron Detection (Press Release)
- Release Date
- 27 Feb, 2014
- BL09XU (Nuclear Resonant Scattering)
- BL11XU (JAEA Quantum Dynamics)
Kyoto University
Japan Atomic Energy Agency
Ibaraki University
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A research group composed of Ryo Masuda (research scientist), Makoto Seto (professor), Shinji Kitao (associate professor), Yasuhiro Kobayashi (assistant professor), and Masayuki Kurokuzu (graduate student) of the Research Reactor Institute, Kyoto University, and Makina Saito (postdoctoral researcher) of Elettra-Sincrotrone Trieste in Italy, Takaya Mitsui (principal scientist) of Japan Atomic Energy Agency, Fumitoshi Iga (professor) of Ibaraki University, and Yoshitaka Yoda (senior scientist) of Japan Synchrotron Radiation Research Institute, developed a detection system for synchrotron-radiation-based Mössbauer absorption spectroscopy*1 to detect electrons and succeeded in dramatically improving the measurement efficiency. Synchrotron-radiation-based Mössbauer absorption spectroscopy is an effective technique for studying the properties of various elements in materials by using nuclear resonant absorption*2 process with synchrotron radiation. It is very effective for scientific researches because it enables us to study the local electronic and/or chemical states in materials. Consequently, it is used to study the mechanism of functional materials such as magnetic materials. In the previous spectrometer for it, X-rays generated after nuclear resonant absorption have been measured to obtain the absorption spectra, although the electrons generated concurrently have not been effectively utilized. The development of a synchrotron-radiation-based Mössbauer spectrometer for detecting electrons will bring about a dramatic improvement in the measurement efficiency and therefore will open the way for applied research on rare-earth elements that have been difficult to measure because of low measurement efficiency. Since many functional materials include rare earth elements, the spectrometer for electrons will be applied to the study of these materials. The research group developed the world's first synchrotron-radiation-based Mössbauer absorption spectrometer system that simultaneously detects the X-rays and electrons associated with nuclear resonant absorption. Using that system and the high-intensity X-rays produced at SPring-8, the group also successfully obtained the synchrotron-radiation-based Mössbauer spectra of 174Yb contained in YbB12. The developed system will enable synchrotron-radiation-based Mössbauer spectroscopy to be applicable to various elements in the future, promoting the research on magnetic materials such as rare-earth magnets and functional materials such as complexes, catalyst materials, and electronic materials. This study was supported by a Grant-in-Aid for Scientific Research (S) under the theme “Development of Advanced Mössbauer Spectroscopy for Isotope*4 Specific Analysis of Local State” and by a Grant-in-Aid for Research Activity Start-up under the theme “Development of Neodymium Nuclear Resonant Scattering Using Synchrotron Radiation,” and was carried out as a SPring-8 research proposal. The achievements were published online in the journal of the American Physical Society Applied Physics Letters on 27 February 2014. Publication |
and appearance of synchrotron-radiation-based Mössbauer spectrometer (right)
and detector placed in vacuum chamber (upper right)
《Glossary》
*1 Mössbauer effect, Mössbauer spectroscopy, and synchrotron-radiation-based Mössbauer absorption spectroscopy
The Mössbauer effect is the resonant absorption of γ-rays of a specific frequency, emitted from the nuclei of a radioactive substance (γ-ray source), by an absorber (sample) containing the corresponding nuclei without losing energy. This effect has been observed for approximately 45 elements. R. L. Mössbauer, who discovered this effect, was awarded the Nobel Prize in 1961. When the γ-ray source and the sample are composed of different substances each other, the energies of nuclear resonant absorption is also slightly different owing to the difference in the electronic state around the nuclei. In such case, the resonant energy of γ-rays can be modulated through the optical Doppler effect by moving the source. Therefore, the dependence of the transmission intensity to the velocity (i.e. energy) shows the resonant absorption spectrum. The changes in the obtained pattern indicate the state (such as the electronic state and magnetic structure) of elements contributing to the resonance in the substance. This technique, called Mössbauer spectroscopy, has been applied to a wide range of fields including solid-state physics, nuclear physics, inorganic chemistry, complex chemistry, metallurgy, life science, earth and space science, and archaeology.
Synchrotron radiation*6 can be used as a more convenient γ-ray source with higher functionality than radioactive substances. In 2009, the synchrotron-radiation-based Mössbauer absorption spectroscopy was developed. In the spectroscopy, the sample was irradiated with white synchrotron radiation of continuous wavelength profile. Because the synchrotron radiation at a certain energy is absorbed by the resonant elements in the sample, the resonant absorption pattern is recorded in the energy distribution of transmitted synchrotron radiation. A substance containing the same type of elements and exhibiting resonance with narrow bandwidth, called a scatterer, is placed downstream of the sample to examine the pattern. Then, the scatterer is irradiated with the transmitted synchrotron radiation, and the X-rays and electrons emitted after the resonant absorption by the scatterer are detected using a detector. To obtain the resonant absorption spectra of the sample, the velocity dependence of the scattering intensity is measured while modulating (scanning) the resonant energy of the scatterer through the Doppler effect by the oscillation of the scatterer along the optical axis. This synchrotron-radiation-based Mössbauer absorption spectroscopy enables to use the nuclear resonance of various elements using white synchrotron radiation. Hence, it is applicable to the elements that have been difficult to measure Mössbauer spectrum using the conventional γ-ray source.
*2 Resonant absorption
A phenomenon in which a substance system is excited when it absorbs energy from an oscillating external field. When the frequency of oscillation is shifted, strong energy absorption occurs near a certain value.
*3 Ytterbium (Yb)12 boride
One of the substances called Kondo semiconductors, which behave as a metal at room temperature but exhibit a semiconductor-like behavior at low temperature because electrical resistance is increased by the change in the behavior of electrons for some reason. Yb 12 boride is attracting attention in research on the physical properties of rare-earth elements because the reason for its transformation to a semiconductor has remained unclarified. Note that this substance was used in this study not because it shows properties of Kondo semiconductors but because the Mössbauer effect is likely to occur in Yb 12 boride at low temperature.
*4 Isotope
Atoms of an element having the same atomic number but a different number of neutrons (i.e., atomic mass number) in their nuclei. Isotopes are found in nature at a specific rate known as natural abundance. While some isotopes are radioactive, the 174Yb, used in this study, is a nonradioactive (emits no radiation) and safe isotope that is contained in natural Yb at 32%.
*5 Optical Doppler effect
Because light is a type of wave, a phenomenon similar to the acoustic Doppler effect, which is well known for its effect on ambulance sirens, also occurs with light. Namely, when light source moves relative to an observer at rest, the wavelength (energy) of observed light is different from that obtained in the laboratory. This phenomenon is called the optical Doppler effect.
*6 Synchrotron radiation
Synchrotron radiation is highly directional light produced when electron beams, accelerated to nearly the speed of light, are forced to travel in a curved path by applying a magnetic field. It is white light that is tunable over a wide wavelength range from X-rays to infrared rays.
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