22
R. Rüffer and A. I. Chumakov
the evaluation of the spectra due to an enhancement of the effective thickness (see
Sect. 1.4.2) by interference effects and the grazing incidence geometry.
Small structures such as magnetic and electric domains may give rise to nuclear
small-angle scattering (NSAS) [63, 64]. Recording both, the prompt (charge) scattered signal and the delayed (nuclear) one, one easily distinguishes between structural
and magnetic/electric structures.
1.3.4 Synchrotron Radiation Based Perturbed Angular
Correlation
For the techniques described above, SMS spectroscopy, SRMS, and NFS, the LambMössbauer factor has to be greater than zero in order to apply those spectroscopies.
As discussed in Sect. 1.1 that might not be the case for samples at high temperature,
for liquids and gases, or for nuclei with high energetic transitions.
Then the spatially incoherent channel of nuclear resonant scattering, which is
independent of the Lamb-Mössbauer factor, offers a way out of these difficulties
via Synchrotron Radiation based Perturbed Angular Correlation (SRPAC) [65, 66]
(see Fig. 1.7 SRPAC). It can be considered as a scattering variant of time differential perturbed angular correlation (TDPAC) [67]. In SRPAC, on the contrary to
NFS, the nuclear levels are excited from the ground state during incoherent, singlenucleus resonant scattering of SR. The interference of indistinguishable paths via
these intermediate nuclear levels, split by magnetic dipole and/or electric quadrupole
interaction, allows one to investigate hyperfine interactions Ω and spin dynamics.
The scattering intensity can be written as
I SRPAC (t) = I 0 e
−t/τ 0 {1 − A 22 G 22 (t)}
(1.24)
with A 22 the anisotropy and angular term and G 22 the perturbation factor.
SRPAC can be applied to all nuclei with an isomeric state with energies attainable
by synchrotron radiation, so far, for practical reasons, with energies up to 150 keV. In
addition, also the contrast of the SRPAC signals might be much larger than for TDPAC
since unfavourable transitions to the excited states from above can be avoided. Furthermore, the SRPAC technique can be used in a site-selective option [68].
1.3.5 Time Interferometry and Rayleigh Scattering
For samples without Mössbauer isotopes, in addition to fast (phonon) dynamics
accessible with IXSNRA (Sects. 1.3.6.2 and 1.5.2) one may also retrieve slow relaxation (ps to ms time scale) dynamics. This is done in the time domain with time
R. Rüffer and A. I. Chumakov
the evaluation of the spectra due to an enhancement of the effective thickness (see
Sect. 1.4.2) by interference effects and the grazing incidence geometry.
Small structures such as magnetic and electric domains may give rise to nuclear
small-angle scattering (NSAS) [63, 64]. Recording both, the prompt (charge) scattered signal and the delayed (nuclear) one, one easily distinguishes between structural
and magnetic/electric structures.
1.3.4 Synchrotron Radiation Based Perturbed Angular
Correlation
For the techniques described above, SMS spectroscopy, SRMS, and NFS, the LambMössbauer factor has to be greater than zero in order to apply those spectroscopies.
As discussed in Sect. 1.1 that might not be the case for samples at high temperature,
for liquids and gases, or for nuclei with high energetic transitions.
Then the spatially incoherent channel of nuclear resonant scattering, which is
independent of the Lamb-Mössbauer factor, offers a way out of these difficulties
via Synchrotron Radiation based Perturbed Angular Correlation (SRPAC) [65, 66]
(see Fig. 1.7 SRPAC). It can be considered as a scattering variant of time differential perturbed angular correlation (TDPAC) [67]. In SRPAC, on the contrary to
NFS, the nuclear levels are excited from the ground state during incoherent, singlenucleus resonant scattering of SR. The interference of indistinguishable paths via
these intermediate nuclear levels, split by magnetic dipole and/or electric quadrupole
interaction, allows one to investigate hyperfine interactions Ω and spin dynamics.
The scattering intensity can be written as
I SRPAC (t) = I 0 e
−t/τ 0 {1 − A 22 G 22 (t)}
(1.24)
with A 22 the anisotropy and angular term and G 22 the perturbation factor.
SRPAC can be applied to all nuclei with an isomeric state with energies attainable
by synchrotron radiation, so far, for practical reasons, with energies up to 150 keV. In
addition, also the contrast of the SRPAC signals might be much larger than for TDPAC
since unfavourable transitions to the excited states from above can be avoided. Furthermore, the SRPAC technique can be used in a site-selective option [68].
1.3.5 Time Interferometry and Rayleigh Scattering
For samples without Mössbauer isotopes, in addition to fast (phonon) dynamics
accessible with IXSNRA (Sects. 1.3.6.2 and 1.5.2) one may also retrieve slow relaxation (ps to ms time scale) dynamics. This is done in the time domain with time