5 Mössbauer Spectroscopy with High Spatial Resolution …
223
through isotopic enrichment. More than 95% of Mössbauer studies of minerals have
used
57 Fe [2], so this chapter will focus exclusively on iron.
Many important research questions in geoscience can be addressed using Mössbauer spectroscopy with high spatial resolution. Originally questions focussed on the
behaviour of materials at high pressure, particularly phase transitions, since Mössbauer spectroscopy is sensitive to a wide range of transitions, including magnetic,
structural, spin and insulator–metal. Studies also address the properties of materials at high pressure, such as density and magnetic, transport and elastic properties.
This knowledge can be used in combination with bulk geophysical measurements
to answer questions about Earth, such as its chemistry, structure, dynamics and
history. Mössbauer spectroscopy is highly sensitive to iron oxidation state, hence it
can answer questions about defect structure and charge balance that are important
for studying water (hydration) and oxygen (redox) in both minerals and bulk Earth.
Mössbauer spectroscopy is consequently in high demand for calibration of other
methods to determine oxidation state such as XANES and the flank method. Natural
samples such as inclusions in diamond or those with strong heterogeneity provide
a window into their geological history through Mössbauer spectroscopy that is not
available from any other method.
Chapter 5 is aimed at an audience that includes users experienced with conventional sources who want to learn about point sources, users experienced with labbased measurements who want to learn about synchrotron possibilities, geoscientists
experienced with other microanalytical methods who want to learn about Mössbauer
spectroscopy, and researchers from other fields who are interested in exciting applications of the method. The tutorial style assumes only a basic knowledge of Mössbauer
spectroscopy that can be easily acquired from short course chapters or text books,
e.g., [1, 3, 4]. The chapter covers topics related to properties of radioactive sources,
considerations in choosing between energy and time domain measurements, practical
aspects of small beam size (geometry, sample preparation, texture and thickness),
useful free software, and a survey of research problems in geoscience that high spatial
resolution measurements have been applied to. In keeping with the tutorial style, the
absorber in the Mössbauer experiment is referred to in this chapter as the sample.
5.2 Mössbauer Sources for High Spatial Resolution
The nature of the radiation source used in a Mössbauer experiment is one of the
main factors in determining the spatial resolution of the measurement. Section 5.2
describes the most commonly used types of sources and some considerations in their
use.
223
through isotopic enrichment. More than 95% of Mössbauer studies of minerals have
used
57 Fe [2], so this chapter will focus exclusively on iron.
Many important research questions in geoscience can be addressed using Mössbauer spectroscopy with high spatial resolution. Originally questions focussed on the
behaviour of materials at high pressure, particularly phase transitions, since Mössbauer spectroscopy is sensitive to a wide range of transitions, including magnetic,
structural, spin and insulator–metal. Studies also address the properties of materials at high pressure, such as density and magnetic, transport and elastic properties.
This knowledge can be used in combination with bulk geophysical measurements
to answer questions about Earth, such as its chemistry, structure, dynamics and
history. Mössbauer spectroscopy is highly sensitive to iron oxidation state, hence it
can answer questions about defect structure and charge balance that are important
for studying water (hydration) and oxygen (redox) in both minerals and bulk Earth.
Mössbauer spectroscopy is consequently in high demand for calibration of other
methods to determine oxidation state such as XANES and the flank method. Natural
samples such as inclusions in diamond or those with strong heterogeneity provide
a window into their geological history through Mössbauer spectroscopy that is not
available from any other method.
Chapter 5 is aimed at an audience that includes users experienced with conventional sources who want to learn about point sources, users experienced with labbased measurements who want to learn about synchrotron possibilities, geoscientists
experienced with other microanalytical methods who want to learn about Mössbauer
spectroscopy, and researchers from other fields who are interested in exciting applications of the method. The tutorial style assumes only a basic knowledge of Mössbauer
spectroscopy that can be easily acquired from short course chapters or text books,
e.g., [1, 3, 4]. The chapter covers topics related to properties of radioactive sources,
considerations in choosing between energy and time domain measurements, practical
aspects of small beam size (geometry, sample preparation, texture and thickness),
useful free software, and a survey of research problems in geoscience that high spatial
resolution measurements have been applied to. In keeping with the tutorial style, the
absorber in the Mössbauer experiment is referred to in this chapter as the sample.
5.2 Mössbauer Sources for High Spatial Resolution
The nature of the radiation source used in a Mössbauer experiment is one of the
main factors in determining the spatial resolution of the measurement. Section 5.2
describes the most commonly used types of sources and some considerations in their
use.