A brief presentation about Moussbuaer spectroscopy relevant ot radiochemistry

1. 11/26/2013
1

2. MÖSSBAUER
SPECTROSCOPY
11/26/2013

3. Mössbauer spectroscopy is the
recoil-free emission and
absorption of gamma rays. It is
mainly based on
THE MÖSSBAUER EFFECT,
OR RECOILLESS NUCLEAR
RESONANCE
FLUORESCENCE

4. Free emitting and absorbing atoms
Emission
Absorption
Recoil
2
Energy of recoil
E
= 2
ER
2mc
γ-ray energy
Mass of atom

5. Radiation emitted by a nucleus may be
re-absorbed in what is called resonance.
 When a photon is emitted and
absorbed, the recoil energy is E2 / 2Mc2
 Recoil-free absorption happens when
the absorbing/emitting atom is bound in
a lattice.
 In cases where there is any significant
recoil, there will be an absence of
resonance.

7. MÖSSBAUER EFFECT
 The Mössbauer effect ,
or recoilless nuclear
resonance fluorescence , is a
physical phenomenon discovered
by Rudolf Mössbauer in 1958.
 It involves the resonant
and recoil-free emission and
absorption of gamma
radiation by atomic nuclei bound
in a solid.

8. A boy jumping from a boat on the water
would fail to land on the shore because of
an energy deficiency rising from the recoil
of the boat. Likewise, a gamma ray emitted
from a nucleus would not be absorbed by
another nucleus due to a recoil reaction in
emission

9. The same boy jumping from a boat frozen
in ice can easily land on the shore, because
no recoil reaction takes place. Likewise, a
recoil-free emission and absorption of a
nuclear gamma ray can be observed in
solids, i.e. the Mössbauer effect.

10. MÖSSBAUER EFFECT:
RECOIL FREE NUCLEAR RESONANCE
ABSORPTION OF GAMMA RADIATION
1,2
Recoil
Recoil
Recoil
ABSORPTION
EMISSION
E
E2
E photon
E1
E photon
E1
E photon=(E2-E1)+R
E photon=(E 2-E 1)-R
0
-4
1
Line width (W) results from: natural width of E2 level + Doppler
widening due to temp.W ~10-6 eV (natural width) + 10-3 eV (temp.
effect) → 10-3 eV (overall effect) . R~100 eV in nuclear processes,
R’~10-7 eV in optical processes
Energy

11. MÖSSBAUER SPECTRA
There are three types of nuclear
interactions that are observed in
a MÖSSBAUER SPECTRA which
are as Follows:-
 Isomer shift or chemical shift
 Quadrupole splitting and
 Magnetic splitting or
Hyperfine splitting

12. ISOMERIC SHIFT
o The isomeric shift (also called isomer shift) is the
shift on atomic spectral lines and gamma spectral
lines, which occurs as a consequence of replacement
of one nuclear isomer by another.
o It is usually called isomeric shift on atomic spectral
lines and Mössbauer isomeric shift respectively.
o If the spectra have also hyperfine structure the shift
refers to the center of gravity of the spectra.
o The isomeric shift provides important information
about the nuclear structure and the physical,
chemical or biological environment of atoms.

13. QUADRAPOLE SPLITTING
o Is an example of a hyperfine interaction found in
gamma-ray spectroscopy.
o In the circumstance where nuclei with a nonradially-symmetric shape (that is, with a spin
quantum number greater than 1/2) are found
immersed in an external electric field gradient.
o It splits a state into two, producing a doublet in
the Mössbauer spectrum.
o The separation between the states can be used to
measure the sign and strength of this electric field
gradient, which is affected by the chemical
environment of the nuclei.

14. MAGNETIC SPLITTING
o Is a result of the interaction between the nucleus
any surrounding magnetic field. A nucleus with
spin, I, splits into 2I + 1 sub-energy levels in the
presence of magnetic field.
o For example, a nucleus with spin state I= 3/2 will
split into 4 non-degenerate sub-states with mI
values of +3/2, +1/2, -1/2 and −3/2.
o Each split is hyperfine, being in the order of 10−7eV.
o This gives six possible transitions for a 3/2 to 1/2
transition.
o Generally speaking therefore, in the majority of
cases only six peaks can be monitored in a spectrum
produced by a hyperfine splitting nucleus.

15. APPEARANCE OF MÖSSBAUER SPECTRA
Symmetric charge
No magnetic field
Asymmetric charge
No magnetic field
Bhf
Magnetic hyperfine field
Δ
Quadrupole splitting
δ
Isomer shift
Depending on the local environments of the Fe atoms and the
magnetic properties, Mössbauer spectra of iron oxides can
consist of a singlet, a doublet, or a sextet.
Symmetric or asymmetric charge
Magnetic field (internal or external)

16. MÖSSBAUER ACTIVE ATOMS
• 75 transitions in isotopes of 44 elements
• Radionuclide: MBq activity
alpha, beta, EC or IT
T1/2: hours-hundreds of years
• Conditions to be fulfilled:
- Energy<100 keV,
- emitter should be bound in a lattice
- mean life-time of excited level: 1 ns-100 ns
- solid, cooled absorber (liquid N2), m>100mg
E.g.: 57Co(EC)57Fe: 14.4 keV
241Am(alpha)237Np: 60 keV
Tc, Th, Pa, U, Np, Pu, Am

17. MÖSSBAUER ACTIVE ELEMENTS IN
THE PERIODIC TABLE:The periodic table below indicates those elements having an
isotope suitable for Mössbauer spectroscopy. Of these, 57Fe is
by far the most common element studied using the technique,
although 129I, 119Sn, and 121Sb are also frequently studied

18. MÖSSBAUER SPECTROMETER
A Mössbauer spectrometer is a device that
performs Mössbauer spectroscopy, or a device
that uses the Mössbauer effect to determine the
chemical environment of Mössbauer nuclei
present in the sample.
It is formed by three main parts;
A SOURCE that moves back and forth to
generate a doppler effect,
 A COLLIMATOR that filters out non-parallel
gamma rays and
A DETECTOR

21. The picture shows a typical Mössbauer
spectrometer with low temperature facility for
cooling the sample down to 4.2 K (boiling point of
liquid helium). Further cooling to ca. 1.5 K is
possible by pumping on the liquid helium vessel.
The cryostat can be furnished with a superconducting solenoid for measuring the sample in
an applied magnetic field. It is also possible to
mount a pressure cell inside the cryostat for
studying the sample properties under pressure.
A miniaturized version of a Mössbauer
spectrometer, almost as small as a cigarette box,
has been designed and constructed which has
successfully been employed in many outdoor
applications and quite recently in studying soil and
rocks on the surface of Mars (NASA mission
2003/2004).

22. APPLICATIONS OF
MÖSSBAUER
SPECTROSCOPY
Mössbauer spectroscopy is unique in
its sensitivity to subtle changes in the
chemical environment of the nucleus
including oxidation state changes, the
effect of different ligands on a
particular atom, and the magnetic
environment of the sample.

23. CHEMICAL
APPLICATION:Fluck, Kerler and Neuwirth reported
already in 1963 on the successful
application of The Mössbauer
Spectroscopy to distinguish between the
cyano complexes of iron known as
PRUSSIAN BLUE (PB) and TURNBULL’S
BLUE (TB).

25. BIOINORGANIC
APPLICATION:Bioinorganic chemistry is another discipline where
Mössbauer spectroscopy has been widely employed
by chemists and physicists. Early Mössbauer effect
studies by Johnson et al. of Ferredoxin, the twoiron centre of proteins, demonstrate convincingly,
as seen in the next picture, that the oxidized form
with two Fe(III)-high spin centres can be
distinguished from the reduced form with one
Fe(III)-high spin centre and one Fe(II)-high spin
centre.

27. INDUSTRIAL
APPLICATION:Roughly 6 different iron oxides and
oxyhydroxides of iron are known as
corrosion products, which may be formed
by corrosion reactions in steel and iron
containing alloys under different
conditions. These corrosion products can
be distinguished by 57Fe Mössbauer
spectroscopy.

29. ANALYTICAL
APPLICATION:As an analytical tool Mössbauer
spectroscopy has been especially useful in
the field of geology for identifying the
composition of iron-containing specimens
including meteors and moon rocks. In
situ data collection of Mössbauer spectra
has also been carried out on iron rich
rocks on Mars.

32. Prepared & Presented by:
Sidra Safdar
Durrani
M.Sc. Final year
Presented to:
Dr. Iftikhar Imam
Naqvi
For the Course of:
Radiochemistry