equation will be much higher, and the recoil energy will be transferred to the entire
crystal which is built of thousands of atoms and the recoil problem should disappear. This process is called as Mössbauer effect. To observe resonant emission and
absorption of c-radiation, we should have the emitting and absorbing nuclei placed
in a solid material. The emitting energy should not be too high. The difference in
energy between the ground and excited state should be lower than the energy of the
crystal lattice phonon creation. Too high energy can make the nucleus vibrations
which also can affect the transition energy.
The Mössbauer effect is the fundamental of Mössbauer spectroscopy. In this
method, the radioactive source emits c radiation which lights the absorber and
behind which is placed a detector (in transmission variant of the method). If the
difference between ground and excited energy levels of the absorber is equal, the
emitted c energy then is absorbed by the measured nucleus which is transferred to
the excited state. The nucleus returns to the ground state with emission of the c
quantum but this time in the full solid angle. The source is placed in a vibrator
which by the Doppler effect tune slightly the emitted quantum of energy. If the
energy is higher or lower than the resonance condition, the radiation is not absorbed
and is detected by the counter. In the resonance, the strong absorption is evidenced.
The vibration of the source gives the possibility to tune up the emitting energy to
small changes in the nuclear levels positions between the source and the measured
absorber. In this way, the differences in the nuclear levels structure between the
source and the absorber can be detected.
The structure of the nuclear levels is affected by the bonding properties of the
neighbors in the crystal. The effect gives the unique possibility to draw conclusions
concerning the movement of cations in a crystal lattice, the influence of additive
atoms, chemical bond, and coordination properties, internal magnetic and electric
fields, and so on from the point of view of the tested nuclei. Thus, it gives the
possibility to observe structural properties from inside the selected nucleus.
The vast majority of the Mössbauer measurements are focused on iron. In this
case, the Mössbauer source is
57 Co which decay to
57 Fe by electron capture. The
half-life is approximately 271 days. After the decay, the
57 Fe nuclei are in excited
state and shift to the ground state with the emission of a c quantum of energy
14.4 keV. The source of c radiation is one of the iron isotopes
57 Fe which abundance in natural iron is about 2%. It should be noted that in the method from all the
iron nuclei in the absorber, only
57 Fe atoms are Mössbauer active and can be
measured.
The measured Mössbauer effect spectrum is characterized by a set of hyperfine
interaction parameters which describe the structure of the nuclear levels and its
changes. The spectrum is then deconvoluted and calculated the hyperfine interaction parameters can be used to obtain information concerning local structure,
magnetic, electric properties, etc., of the studied material.
More details concerning Mössbauer spectroscopy one can find in some excellent
books like [2–6].
9 Mössbauer Spectroscopy of Magnetoelectric Perovskite Oxides
275
crystal which is built of thousands of atoms and the recoil problem should disappear. This process is called as Mössbauer effect. To observe resonant emission and
absorption of c-radiation, we should have the emitting and absorbing nuclei placed
in a solid material. The emitting energy should not be too high. The difference in
energy between the ground and excited state should be lower than the energy of the
crystal lattice phonon creation. Too high energy can make the nucleus vibrations
which also can affect the transition energy.
The Mössbauer effect is the fundamental of Mössbauer spectroscopy. In this
method, the radioactive source emits c radiation which lights the absorber and
behind which is placed a detector (in transmission variant of the method). If the
difference between ground and excited energy levels of the absorber is equal, the
emitted c energy then is absorbed by the measured nucleus which is transferred to
the excited state. The nucleus returns to the ground state with emission of the c
quantum but this time in the full solid angle. The source is placed in a vibrator
which by the Doppler effect tune slightly the emitted quantum of energy. If the
energy is higher or lower than the resonance condition, the radiation is not absorbed
and is detected by the counter. In the resonance, the strong absorption is evidenced.
The vibration of the source gives the possibility to tune up the emitting energy to
small changes in the nuclear levels positions between the source and the measured
absorber. In this way, the differences in the nuclear levels structure between the
source and the absorber can be detected.
The structure of the nuclear levels is affected by the bonding properties of the
neighbors in the crystal. The effect gives the unique possibility to draw conclusions
concerning the movement of cations in a crystal lattice, the influence of additive
atoms, chemical bond, and coordination properties, internal magnetic and electric
fields, and so on from the point of view of the tested nuclei. Thus, it gives the
possibility to observe structural properties from inside the selected nucleus.
The vast majority of the Mössbauer measurements are focused on iron. In this
case, the Mössbauer source is
57 Co which decay to
57 Fe by electron capture. The
half-life is approximately 271 days. After the decay, the
57 Fe nuclei are in excited
state and shift to the ground state with the emission of a c quantum of energy
14.4 keV. The source of c radiation is one of the iron isotopes
57 Fe which abundance in natural iron is about 2%. It should be noted that in the method from all the
iron nuclei in the absorber, only
57 Fe atoms are Mössbauer active and can be
measured.
The measured Mössbauer effect spectrum is characterized by a set of hyperfine
interaction parameters which describe the structure of the nuclear levels and its
changes. The spectrum is then deconvoluted and calculated the hyperfine interaction parameters can be used to obtain information concerning local structure,
magnetic, electric properties, etc., of the studied material.
More details concerning Mössbauer spectroscopy one can find in some excellent
books like [2–6].
9 Mössbauer Spectroscopy of Magnetoelectric Perovskite Oxides
275