Mossbauer spectroscopy is a technique that uses the Mossbauer effect to analyze the chemical, structural, and magnetic properties of materials. It works by measuring the slight energy changes in gamma rays emitted or absorbed by nuclei embedded in solids. The technique was discovered in 1957 and led to a Nobel Prize in Physics in 1961. It is commonly used to study iron-containing samples, including in applications like analyzing materials returned from Mars by NASA rovers. The technique relies on the coupling of nuclear energy levels with crystal lattice vibrations to overcome nuclear recoil effects that would otherwise limit its ability to detect very small energy shifts in emitted gamma rays.

1. Mossbauer Spectroscopy
B. S. VINEETH (Roll# 120121007), B.Tech., IIT Guwahati

2. Introduction
• Versatile technique based on Mossbauer Effect that is widely used,
even now, from the time it was discovered in 1957, in many areas:
• Physics, Chemistry, Biology, Archaeology,
Geology, Material Science, Metallurgy, …
• Rudolf L. Mossbauer
• NOBEL PRIZE Physics 1961 within 5 years
of its discovery!!

3. Nobel Prize, Physics (1961)
• Zeitschrift fur Physik 151, Issue 2 p. 124-143 (1958)

4. What is it good for?
• You name it!
• Very precise information on the: chemical, structural, magnetic
properties of a material.
• Technique at the interface of Solid State Physics and Nuclear
Physics.

5. Basic Principle
• Nuclear Energy Levels change (shift or split) because of
interaction of the radioactive nucleus with the surrounding solid
in which it is embedded.

6. Exclusively used by NASA
• Mossbauer spectroscopy is used by NASA to study the
composition, abundance, magnetic properties of iron-bearing
materials in the outer space.
• MARS EXPLORATION ROVERS:
• It is ONE of FOUR facilities mounted
at the end of the ROVER ARM!
Measurements are taken by placing the Rover Arm head directly
against a rock or soil sample.

7. Used Elements
• Most used: Fe-57
Every Iron containing material has approx. 98% of Fe-56 and
2% of Fe-57.
• I-129, Sn-119, Sb-121 also are used.
• Let us take the example of Fe-57 to demonstrate the concept

8. Isolated Fe-57 Nucleus
We expect the Gamma-ray emitted to be of 14.4 keV. (We are only interested till the
first excited state.)

9. Fe-57 in ferromagnetic surrounding
• Gamma rays of nearly 14.4 keV but
with differences in the order of
10-8 eV due to splitting+shifting.
Mossbauer spectroscopy exploits this
faint spectrum in the Gamma radiation
to assess the material environment.
Cubic Structure and Ferromagnetic

10. Fe 57 in stainless steel solid
• Cubic, No ferromagnetism here
• So, no splitting of levels
• But, due to the interaction of nucleus with the electron density
(mainly s-electrons density), the energy levels only SHIFT in
the order of 10-8 eV.

11. Fe-57 in Olivine solid (FeSiO4)
• Non-cubic crystal arrangement
• Non-ferromagnetic
• Ground level: As it is (no splitting)
• First excited state: mI = -3/2, +3/2 only

12. Construction
Source: Co-57 in Rhodium
Rh solid which is cubic and
non-ferromagnetic
So, only shifting of levels in
source.
Absorber: Is the sample to be
analyzed.

13. Setup Block Diagram

14. Working Theory and Physics
• As the Source is vibrating, the
absorber sees the Gamma rays
with a DOPPLER SHIFT.
So, if Es = E2 – E1, the absorber
sees it as:
E = Es (1 + v/c) (Doppler Shift)
(v lies from –vmax to +vmax)

15. Absorber: Simple Case
• Assume, the absorber is
cubic and non-ferromagnetic.
Then for Resonance, we need:

16. “Mossbauer Spectrum”
• So, at these particular velocities,
the detector takes a Dip as most
of the Gamma rays get absorbed
and don’t pass through.
Plot velocities versus detector count: “Spectrum”

17. If absorber has Olivine type surrounding

18. If absorber has ferromagnetic surr.

19. Spectrum if ferromagnetic absorber

20. A Serious Problem!!!
• Apart from the around 10-8 eV energy shift due to surrounding
environment, there is an additional extremely significant (1,00,000
times) correction of around 1 milli-eV which is due to:
• NUCLEAR RECOIL EFFECT
Therefore, energy of emitted
Gamma ray becomes:
(E2 – E1) – ER
Nucleus recoils in the opposite
Direction while emission

21. …
• Similarly, when the absorber nucleus absorbs it, it recoils in the
direction of Gamma-ray and therefore for resonance to take
place (without Doppler effect) the energy required is:
• (E’2 – E’1) + ER
• Unfortunately, to cover this gap due to recoil, one needs
vibrating the source with huge velocities. Then, how can
we do Mossbauer spectroscopy?? 

22. Mossbauer Effect to our rescue
• It is a QM-cal phenomena that if you have a Nucleus with energy
levels embedded in a Crystal Solid which itself has Crystal Energy
levels, both of them couple and so:
• The Crystal has to Recoil whenever the Nucleus absorbs or emits the
Gamma rays.
• But, if the Crystal Recoil Energy is less than the first-excited energy
of the Nucleus, then the whole Recoil process will NOT occur, and
the Gamma rays are emitted with exact energy level difference!!!

23. Interpreting Results:

24. Limitations
• The material to be analyzed must be composed of Iron or
similar materials used in Mossbauer
• Vast majority of rock-forming minerals on Earth contain Fe 2+
in octahedral structure, and all of them have very similar
Mossbauer Spectrum. (hard to distinguish)

25. References
• [1] R.L. Mossbauer, Zeitschrift fur Physik 151, Issue 2 p. 124-
143
• [2] H.C. Verma, Concepts of Physics, Bharati Bhawan (1999)
• [3] E.N. Kaufmann, Characterization of Materials, Wiley (2003)
• [4] Obvious online sources (Wikipedia, etc.)

26. Thank You
Term paper submitted to Prof. Giri (Physics, IITG) by
B.S.VINEETH (Roll# 120121007).