Enabling the Measurement of Mössbauer Absorption Spectra for Almost Any Element Using Synchrotron Radiation - Development of a Probe for the Study of Electronic Structure and Magnetic Properties of Specific Elements (Press Release)
- Release Date
- 25 May, 2009
- BL09XU (Nuclear Resonant Scattering)
- BL11XU (JAEA Quantum Dynamics)
Kyoto University
Japan Synchrotron Radiation Research Institute
Japan Science and Technology Agency
Key research achievements
• First-ever successful development of synchrotron-radiation-based Mössbauer spectroscopy in the high-energy region
• Applicability of the data accumulated by conventional methods to the analysis by this method
• Enabling the development of Mössbauer spectroscopy based on the characteristics of synchrotron radiation
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A research group consisting of scientists from Kyoto University (Hiroshi Matsumoto, President), Japan Atomic Energy Agency (Toshio Okazaki, President), Japan Synchrotron Radiation Research Institute (Akira Kira, Director General), and Japan Science and Technology Agency (JST; Koichi Kitazawa, President) has successfully developed a new method of measuring Mössbauer absorption spectra*1 using synchrotron radiation. This technique is also applicable for elements that have been difficult to measure by conventional methods. Up to now, Mössbauer spectroscopy has been intensively applied in materials science, particularly in research on magnetic materials. The measurement of iron (Fe) using radioisotope sources is particularly well known and has produced great achievements in many fields. However, the range of measurement target elements has been very limited because of the difficulty in procuring appropriate radioisotope sources for elements other than Fe. The use of synchrotron radiation has been expected to effectively remove such limitations, but its applicability is still limited because of problems such as the limited capabilities of detectors. In this research, scientists developed a new measurement method for unknown materials using reference samples while employing conventional detectors. Using this method and synchrotron radiation produced at SPring-8, they succeeded in measuring the Mössbauer absorption spectra for germanium (Ge), an important element for semiconductors, which could not be measured by conventional methods, for the first time in the world. The achievements of this research have not only made it possible to measure elements that could not be measured by conventional methods, but will also lead to the development of advanced methods using the data accumulated thus far by conventional methods. Moreover, using synchrotron radiation as a source enables the measurements of minute samples and materials under ultrahigh pressure; thus, it will bring about promising advancements in magnetic materials science and geosciences to study the Earth's interior. This research was carried out under the research theme "Studies on Nuclear Resonant Scattering Methods for Materials Science" (leader: Makoto Seto) in the research area "Novel Measuring and Analytical Technology Contributions to the Elucidation and Application of Material" (research supervisor: Michiyoshi Tanaka, professor emeritus at Tohoku University) supported by the Core Research of Evolutional Science and Technology (CREST) program of JST. This research was also carried out as a SPring-8 power user proposal under the theme "Research and Development of Advanced Methods of Nuclear Resonant Scattering Using Synchrotron Radiation and Their Application to Materials Science" (leader: Makoto Seto). The achievements were published in the American physics journal Physical Review Letters on 29 May 2009. Publication: |
<Figure>
Fig. 1 Measurement method of Mössbauer absorption spectra using synchrotron radiation.Synchrotron radiation is directed onto the sample to be measured, and that transmitted through the sample is then guided so that it is incident on a reference sample. In this case, the emitted fluorescent X-rays are detected when nuclear resonant excitation occurs within the reference sample. To measure absorption spectra, the scattering intensities of fluorescent X-rays are measured varying the X-ray energy at the reference sample. The X-ray energy is changed in accordance with the Doppler Effect by moving the reference sample using a velocity transducer. If there is an difference of energy levels between the measured and reference samples (upper figure), nuclear resonance excitation occurs at the reference sample because synchrotron radiation with the energy to cause nuclear resonant excitation at the reference sample is not absorbed by the measured sample. On the other hand, if the energy level of the measured sample is equal to that of the reference sample (lower figure), nuclear resonant excitation hardly occurs at the reference sample because synchrotron radiation with the energy to cause nuclear resonant excitation is absorbed by the measured sample. Therefore, absorption (a dip in the scattering intensity) is observed at the point where the energy levels of the two samples are equal. Conversely, the energy state of an unknown sample can be determined if the position where absorption occurs is known.
Fig. 2 Mössbauer absorption spectrum of 57Fe measured using synchrotron radiation.Fe oxide (α-Fe2O3) and palladium (Pd) metal doped with 2% Fe atoms were used as measurement and reference samples, respectively.
Fig. 3 Mössbauer absorption spectrum of 73Ge measured using synchrotron radiation.Lithium germanate (Li2GeO3) and Ge oxide (GeO2) were used as measurement and reference samples, respectively.
<Glossary>
*1 Mössbauer absorption spectrum
The Mössbauer effect – a phenomenon causing resonant absorption without the recoil of atomic nuclei – was discovered by Rudolf Ludwig Mössbauer in 1957. He was awarded the Nobel Prize in Physics in 1961 for this discovery. To obtain Mössbauer absorption spectra, gamma (γ) rays emitted from a radioisotope source are irradiated onto a sample containing the same type of atomic nuclei while changing their energy, and the γ-rays transmitted through the sample are measured using a detector placed behind it. Resonant absorption caused by the Mössbauer effect occurs and a dip is observed in its spectrum when the energy of the γ-rays from a radioisotope source is equal to the excitation energy of the atomic nuclei in a sample.
Thus far, Mössbauer spectroscopy has been intensively applied in materials science, particularly for research on magnetic materials. Beyond these fields, however, it has also been used in the analysis of lunar rocks as well as in the on-site analysis on Mars, for which a Mössbauer spectroscope was mounted on the Mars probe. Naturally, it is also used to analyze rocks on the earth and examine the state of iron under high temperatures and pressures to understand the dynamics of the earth's interior, such as mantle convection. Moreover, Mössbauer spectroscopy has been effectively used in biology, for example, to elucidate the state of iron in hemoglobin.
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