SYNCHORTRON RADIATION BASED

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SYNCHORTRON RADIATION BASED PERTURBED ANGULAR
CORRELATION (SR-PAC)
R. GOVINDARAJ MATERIALS SCIENCE DIVISION IGCAR,
KALPAKKAM E-mail govind_at_igcar.ernet.in
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Perturbed Angular Correlation (PAC) spectroscopy

• QUADRUPOLE INTERACTION
• ?Q ? Quadrupole frequency ?
  strength
• ? ? (Vxx Vyy) / Vzz ?
  orientation
• ? ? Damping parameter
• f ? fraction of probe atoms
• MAGNETIC INTERACTION
• ?L ? Larmor precession frequency

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APPLICATIONS OF PAC
?Q, ? ? electronic, local structural
properties ?L ? magnetic properties 1

• Structural, electronic, magnetic
• properties at atomic scale ? Phase
• transition studies in metallic
• / semiconducting/ insulating matrices
• at atomic scale.
• Nano systems
• Relaxation processes ? dynamics
• in liquids (biological systems),
• solids etc,
• solute-defect interactions ? point
• defect studies, defect formation/
• migration energies, geometry

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Synchrotron Radiation-based Perturbed Angular
Correlation (SRPAC)
Method
It is a scattering variant of TDPAC. Here the
intermediate nuclear level is excited from the
ground state, during spatially incoherent,
single nucleus resonant scattering of
synchrotron radiation.
Directional selection and timing by the first
detector in TDPAC are replaced In SRPAC 2 by
direction and timing of incident SR flash. In
both these methods the interference of
indistinguishable paths via an intermediate
nuclear level split by magnetic dipole and/or
electric quadrupole interaction allows us to
investigate hyperfine interactions and rotational
dynamics of nuclear spin.
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PAC / PAD
SR - PAC
excited state
?2
?1
ground state
sample
SR
detector
counter
start
stop
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PRINCIPLE OF SR-PAC

• Incoherent Nuclear Resonant Scattering can be
  considered as a scattering
• variant of TDPAC , called as SR-PAC
• Orientation by absorption of electromagnetic
  radiation of well defined direction and well
  defined polarizarion
• Angular distribution of radiation depends on the
  orientation of nuclear spin at the time the
  radiation is emitted.
• Static interactions are caused by
  coupling of nuclear spin with static hyperfine
  fields that are constant in magnitude and
  direction during the lifetime of excited state
• Time dependent interactions are caused by
  fluctuating fields such as fields
• experienced by nuclei in a liquid environment.
  It may result in complete loss of
• Orientation with time.

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The SRPAC intensity 3 observed By the detector
is given as
where
is the differential angular probability of
scattering

• Comparing the SRPAC intensity with
• TDPAC angular correlation intensity on
• 57Fe shows that the anisotropy coefficient
• Is 10 times larger in the case of SRPAC

INFLUENCE OF SPIN DYNAMICS IN SR-PAC

• Consider a molecule in which a quadrupole
  interaction exists and the direction
• of spin quantization axis is defined by specific
  molecular structure.

In density matrx formalism the evolution of the
system is described by the time evolution
operator U(t)
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Experimental setup for SR-PAC
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Single nucleus quantum beats excited by
Synchrotron radiation
Single nucleus beat Pattern measured in 90 deg
scattering
SRPAC in 5ferrocene/ dibutylphthalate above
the glass transition
. At 200 K the time evolution is characterised by
a natural decay with lifetime of 141 ns,
modulated by a pronounced quantum beat which
corresponds to the quadrupole splitting of
ferrocene. The beat exhibits only a weak damping,
indicating still very slow relaxation. At 247 K
the beat is largely overdamped due to medium
relaxation. At 300 K the slow approach of the
natural decay (dotted line) is characteristic of
fast relaxation (Abragam-Pound limit).
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• Pure SR-PAC is observed when Lamb-Mossbauer
  factor f2LM0 ? SRPAC is
• favorable for soft condensed matter studies.
  Particularly suited for investigation
• of glass formers in the temp range where MS,NFS
  are NOT applicable

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Advantages

• SRPAC can cover a dynamic range of relaxation
  times of five orders of magnitude from 10 ps to 1
  micro second.
• SRPAC enables us to investigate pure rotational
  dynamics.
• This method avoids chemical or electronic
  after-effects which is quite common in TDPAC
• The potential of SRPAC relies on the fact that
  single-nucleus scattering does not depend upon
  recoil free emission/absorption, nor on
  translational motion.

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VISION

• SR-PAC CAN BE SETUP AT INDUS-2 AT CAT, INDORE.
• This synchrotron source qualifies the
  requirements for setting up SR-PAC
• THIS WILL BE A POWERFUL TECHNIQUE TO STUDY SOLIDS
  AT EXTREMELY HIGH TEMPERATURE, PRESSURE TO
  UNDERSTAND PHASE TRANSITIONS AT ATOMIC SCALE
• RELAXATION DYNAMICS IN SOFT CONDENSED MATTER CAN
  BE
• STUDIED. ? Dynamics in biological systems

REFERENCES

• H. Frauenfelder and R. M. Steffan in Alpha-,
  Beta, Gamma- Ray
• Spectroscopy, edited by K. Siegbahn
  (North-Holland, Amsterdam,1965)
  
  
• 2. A. Q. R. Baron et al, Europhysics Lett. 34 331
  (1996)
• 3. Ilia Sergueev, Thesis submitted to Technische
  Universitat Munchen, 2004