Introducci

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Introducción a la Espectroscopía Mössbauer
Introduction Mössbauer Effect
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An Accidental Discovery

• Discovered by Rudolf Mössbauer while working on
  his thesis at the Max Planck Institute for
  Medical Research in Heidelberg.
• Noticed increased scattering in his gamma ray
  spectrum of 191Ir at low temperatures
• This went against classical predictions
• Published an article in Zeitschrift für Physik in
  1958, marked the beginning of Mössbauer
  spectroscopy
• It was this discovery earned him a Nobel Prize in
  Physics in 1961

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Espectroscopía Mössbauer
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Espectroscopía Mössbauer
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Espectroscopía Mössbauer
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Espectroscopía Mössbauer
Relative probabilities for ? transition with
simultaneous excitation of oscillator quanta
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Espectroscopía Mössbauer
Fraction of recoilless transitions
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Espectroscopía Mössbauer
T 88K
Experiment carried out to test the validity of
the prediction
A sort of reversal of the Moon experiment.
The width of the lines were determined by the
thermal motion of the nuclei.
Moon compensated by Doppler shift the
recoil-energy losses.
Mössbauer destroyed the fulfilled resonance
condition through the application of a relative
velocity.
Line widths sharper for four orders of magnitude.
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Espectroscopía Mössbauer
Since its discovery in 1957 Mössbauer effect was
applied to numerous problems in science and
technology
Mössbauer spectroscopy brings information on

• Probe electronic state
• Local electronic charge density
• Local electric field gradient
• Local magnetic field

And therefore on phases present, defects,
disorder, role of impurities, surface effects,
etc..
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Espectroscopía Mössbauer
It is defined as recoilless resonant gamma ray
absorption. Previous experiments tried to
observe this effect with gases but because of
recoil the experiments failed Performed on solid
state materials no recoil Low temperatures are
needed to limit both the recoil energy and
thermal noise Most prominent use is in mineralogy
and geology
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Espectroscopía Mössbauer
The Mössbauer experiment
v (mm/s)
? rays

Radioactive Source (57Fe)
?-ray detector
Absorber (57Fe)
counts
V(mm/s)
v
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Decay scheme of 57Fe
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Hyperfine splitting of nuclear levels
e
f
Isomer shift ??
Quadrupole splitting ?
Magnetic hyperfine field splitting B
B ?(?)
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Interacción electrostática.
Ee,N ???N(r) ?e(R)dr3dR3/r-R ???N(r)
Ve(R)dr3dR3
E0 ? eZN Ve(0) gt ?E0 0
Vzz???e(R)(3cos2?-1)dR3
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Interacción electrostática.
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Magnetic hyperfine splitting of nuclear levels
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Mössbauer Spec tra
Observed Effect Illustration Observed Spectrum
Isomer Shift Interaction of the nuclear charge distribution with the electron cloud surrounding the nuclei in both the absorber and  source.
Zeeman Effect (Dipole Interaction) Interaction of the nuclear magnetic dipole moment with the external magnetic field at the nucleus. 
Quadrupole Splitting Interaction of the nuclear electric quadrupole moment with the EFG at the nucleus
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Mössbauer Spectrum
Mössbauer Spectra
Hyperfine field (B)
Isomer shift (?)
Area
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Intensidad de líneas de absorción Mössbauer
z 4 sin2(?) / (1 cos2(?))
3 z 1 1 z 3
?
k
?
M
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Mössbauer Spectra
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Mössbauer Spectra
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Instrumentation
Source and absorber with the same
Mössbauer isotope Detector -scintillator
-proportional -solid-state High
voltage Pre-Amp Amplifier MS Computer/software
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Doppler Energy
E? E0 ?
? v E0/c
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Doppler Energy
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Mössbauer resonant absorption
e
?
E0
E0
?
?
f
E0-ER
E0ER
E0
pR
p?
pR
ER
E? E0-ER
E? E0ER
ER
??10-8 eV
ER?10-3 eV!!
ERpR2/2MN
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Jumping the boat
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Ejemplos
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Spectra
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Ferromagneto Débil
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Ferrimagneto
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Paramagneto
Antiferromagneto
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Fe3Si
Ferromagneto
Paramagneto
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Mars Surface Spectrum
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Mössbauer Periodic Table
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