Mossbauer spectroscopy

mudasir malik

1. Mossbauer Spectroscopy

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

3. 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.

4. 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

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

6. " 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

7. Diagram of Vibrational Energy Levels E n represents ground state energy. E n+1 represents the next highest energy. E R represents recoil energy. The first example shows a event resulting in no resonance. The second examples shows an event resulting in resonance.

8. 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

9. 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.

10. 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.

11. Instrumentation-Working The basic elements of the Mossbauer spectroscopy are Source Sample Collimator Detector Drive to move the source

12. 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 .

13. Analysis of Mossbauer Spectra There are three types of nuclear interactions that are observed Isomer shift (IS) Quadrupole shift (QS) Magnetic shift (MS)

14. 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.

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

16. 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

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

18. 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

19. 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

20. 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

21. 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

22. 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

23. 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

24. 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