Neutron Scattering

the associated paths are indicated by the grey triangle .
The intensity within the range
of this triangle is of course not uniform but depends on the spectral properties of the
source .
s
Neutrons that have been elastically scattered by the Sample (path 2) pass the
analyzer/filter M/F and lead to the elastic line in the TOF-histogram .
Neutrons that loose
energy (path 1) are faster before the Sample scattering and arrive earlier at the detector
than the elastically scattered ones .
Analogously path 3 represents neutrons that gained
energy during scattering .
Compared to a "normal" TOF instrument the energy gain and
energy loss sides of the histogram are reversed .
Therefore also high energy excitations
that are thermally not occupied may be measured .
(Spallationstarget)
Chopper
Figure 10 .12 :
Setup of a TOF spectrometer with inverted geometry.
Figure 10 .12 shows a corresponding setup .
The pulse at the chopper contains neutrons
from a broad velocity distribution (Maxwellian spectrum at moderator temperature) .
During the path from chopper (pulsed source) to Sample this pulse separates into different
wavelengths A, resp .
different incident energies, that arrive ai different times ai the
sample .
Since a wavelength selection (to Ao) is performed between Sample and detectors,
all detected neutrons have the saine velocity and the distance Sample-detector adds a
a In particular overlap of the triangles ( "frame overlap") may lzappen, wlziclz may be suppressed by
filters tayloring tlze incoming spectrum .
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