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2. Mossbauer Spectroscopy

3. Contents
 Introduction
 History
 Basic Principle
 Typical Method
 Source Selection
 Analysis
 Applications
 Drawback
 Limitations
 Conclusion

4. Introduction
 Mossebauer spectroscopy is a powerful tool for
investigation of local electronic phenomena and
interaction in material.
 Mossebauer spectroscopy probes tiny changes in the
energy levels of an atomic nucleus in response to its
environment.

5. Rudolf Mossbauer
• Born on January 31, 1929
• Born in Munich, Germany.
• Discovered "Mossbauer Effects
in 1958.
• Won Nobel Prize in 1961 in
physics.
• Passed away in 2011

6. Mossbauer's effect
 Atoms placed in solid matrix have much greater
effective mass
 Recoil mass of nuclei becomes recoil mass of entire
matrix.


7. "Mossbauer Effect"
 How does it work
◦ Nuclei in atoms undergo many energy level
transitions.
◦ Changes occur due to emission and absorption of a
gamma ray.
◦ Energy levels are determined by the nuclei's
surrounding environment.
◦ Observed using nuclear resonance fluorescence
 Special technique used to gauge distances
between chromophores
 Only works when separation distance is less than
10nm

8. Diagram of Vibrational Energy
Levels
• En represents ground state
energy.
• En+1 represents the next
highest energy.
• ER represents recoil
energy.
• The first example shows a
event resulting in no
resonance.
• The second examples
shows an event resulting in
resonance.

9. Circumstances of Resonance
 What does this mean
◦ With the use of the Doppler effect the wavelength of
the source gamma rays can be tuned
◦ When this wavelength is the same as the wavelength
of emitted gamma ray resonance is achieved

10. Typical Method
 A solid sample is exposed to a beam of gamma
radiation and a detector measures the intensity of the
beam transmitted through the sample.
 If the emitting and absorbing nuclei were in the identical
chemical environments, the nuclear transition energies
would be exactly equal and resonant absorption would
be observed with both materials at rest
 The difference in the chemical environments causes the
nuclear energy levels to shift in the different ways.
 The number ,position and intensities of the dips
provide information about the chemical nuclei of the
environment.

11. Suitable Source
 Suitable gamma ray sources consists of a
radioactive parent that decays to the desired
isotope.
 For example the source for iron consists of cobalt
which decays by electron capture to an excited
state of iron which in turn decays to the ground
state emitting a gamma ray of the appropriate
energy.

12. Instrumentation-Working
The basic elements of the Mossbauer spectroscopy
are
1. Source
2. Sample
3. Collimator
4. Detector
5. Drive to move the source

14. Working
 Most commonly this is done by moving the source
toward and away from the sample while varying
velocity with time.
 It is also possible to leave the source stationary
and oscillate the sample.
 The location of the detector relative to the source
and sample defines the geometry of the
experiment .

15. Analysis of Mossbauer
Spectra
 There are three types of nuclear interactions that
are observed
1. Isomer shift (IS)
2. Quadrupole shift (QS)
3. Magnetic shift (MS)

16. ISOMER SHIFT
• Isomer shift is a relative
measure describing a shift in
the resonance energy of a
nucleus due to transitions of
electrons within its s orbital.
• The whole spectrum is
shifted in either positive or
negative direction depending
upon electron density.

17. Isomer Shift
• General form of an
isomer shift
• Single peak
• Slightly shifted from zero
• Can be positive or
negative

18. Quadrupole Splitting
 Induced by electric quadrupole
moment of the nuclei and change
in the electric field due to an
electron interactions.
• Gives information about charge
symmetry around nuclei.
• Nuclear energy level splitting
due to symmetrical electric field .
• Electrons with l>.5 have non-
spherical charge distribution and
produce a nuclear quadrupole
moment

19. Quadrupole Splitting
• Shows two samples
• Both show quadrupole
splitting
• Show how similar
structures give similar
signals

20. Magnetic Splitting
 In presence of a magnetic field
◦ This magnetic field is often called the hyperfine field
◦ Nuclear spin moment feels a dipole interaction
through Zeeman splitting
◦ Zeeman splitting
 Atomic energy levels are split into a larger
number of energy levels
 Magnetic field applied to split energy levels
 Spectral lines are split along with atomic energy
levels

21. Putting These Shifts Together
• Figure to the right
shows spectral
examples of
• Blue shows just an
isomer shift
• Red is Isomer shift
with quadrupole
splitting
• Green shows the
hyperfine
interactions

22. APPLICATIONS
Mossbauer Spectroscopy in
Physics and Chemistry
 Used to further pursue the nature of energy states
in nuclei
 Measure changes in chemical environment of
nuclei
 Monitor materials during phase changes
 Monitor chemical reactions
 Determine structures of molecules

23. Mossbauer Spectroscopy in
Biology
 Used In Cancer treatments
 Used to analyze red blood cells
 Test environmental effects of human body
 Can analyze protein structures
◦ Help in function determinations

24. Mossbauer Spectroscopy in
Mineralogy and Metallurgy
 Can be used to determine metal samples
◦ Determine crystal structures
◦ Molecular arrangements
◦ Chemical compositions
 Used to analyze different mineral samples
◦ Determine different crystal structures
◦ Determine compositions

25. Drawbacks of Mossbauer
Spectroscopy
 Must be in solid crystalline structure
 Minute hyperfine interactions
◦ Overcome with the use of Doppler Effect
 Major limitation is that it is a “bulk” technique
◦ Often times large amounts of sample are needed
for analysis
◦ Recent improvements in electronics and
detectors are helping to overcome

26. Conclusions
 Wide application across multiple
scientific disciplines
 Relatively cheap method
 Relatively fast method
 Give valuable information on chemical
environment within molecule
◦ Isomer Shifts
◦ Quadrupole splitting
◦ Magnetic splitting