Nuclear Inelastic Scattering


Setup for the NIS measurement. The pulsed beam is monochromatized to a meV energy band with the high resolution monochromator (HRM) before it penetrates the ionization chamber (IC) and the sample. The radiative decay of the resonant nuclei in the sample is measured with two APD detectors: one in forward direction (NFS), which collects data only from a small solid angle (top) and one at 90o (NIS) which collects data in a large solid angle (bottom). Details are described in the text below.


Nuclear inelastic scattering (NIS) permits to observe
the
probability of exciting and annihilating phonons in the solid state ([Phys.Rev.Lett.74(1995)3828], [Phys.Rev.Lett74(1995)3832]), where the iron atom is involved. The signal of the sample is recorded

  • by a NIS detector placed close to the sample
    at 90o relative to the beam direction and
  • by a NFS detector placed far away in forward direction.
During scanning the energy of the incident beam up to
± 100... 1000meV around the exact resonance energy
by detuning the high resolution monochromator (HRM)
the time integrated signal of
  • the NFS detector shows a sharp peak at ED=0 which represents the energy resolution of the monochromator system and is used
    • to determine the point of zero energy transfer and
    • to extract the probability of inelatic absorption
      out of the NIS spectrum.

    At exact resonance energy (ED =0)
    the
    NFS detector collects the time depending NFS.

  • the NIS detector shows a high central peak at ED=0
    and peaks apart from the resonance energy.
    This energy spectrum is a convolution of
    • the probability of inelastic absorption and
    • the energy resolution function
      of the high resolution monochromator (HRM)

    The time dependence of the signal
    shows an exponential decay after excitation,
    since the data
    are collected angular integrated.

The measured spectrum is corrected by the flux of the monochromatized radiation incident on the sample as monitored by the ionization chamber (IC).


Based on the PhD thesis of Hanne Grünsteudel, Lübeck 1998
Last modified 05:27 PM by Ernst Schreier