Chemistry Reference
In-Depth Information
Coulomb excitation with recoil implantation technique at the VICKSI accelerator
facility in the Hahn-Meitner Institute Berlin.
6.3.3 Diffusion Study Using Mössbauer Spectroscopy
In the following sections we will show typical applications of in-beam Mössbauer
spectroscopy for the study of fast diffusion in metals. Before getting into details,
we are going to explain the principle of how the diffusion phenomenon affects the
Mössbauer spectra. First of all, let us consider the following situation in our daily
life: a fire engine sounding a siren is approaching you, while you are standing
beside the street and are listening to the siren. The acoustic waves with a sound
velocity of t
s
are emitted continuously during a time interval Dt from the fire
engine moving at a velocity of t
f
. Consequently, the waves are compressed within
a region of (t
s
- t
f
)
Dt, leading to an observed sound frequency higher than that of
the original frequency. This Doppler effect gives a possibility for us to get
information on the motion by measuring the sound frequency even without
watching directly the fire engine. More generally, when a matter is emitting a
wave, a motion of matter changes the wave form. This will give you a hint to
understand the principle of Mössbauer study on atomic jumps.
Now, in a solid matrix we have a Mössbauer probe of
57
Fe with a lifetime of
140 ns, as is shown in Fig.
6.18
. The 14.4 keV first excited state of the
57
Fe
nucleus can be fed through different processes, such as electron capture from
57
Co,
b-decay from
57
Mn, Mössbauer absorption of 14.4 keV c-ray, and Coulomb
excitation. Subsequently the 14.4 keV c-ray will be emitted resonantly without
recoil (Mössbauer effect), while in Fig.
6.18
, the
57
Fe atom is jumping between
Fig. 6.18
Atomic motion influence on Mössbauer spectrum
