Neutron Scattering

----~ Probe
' (Chopper 2)
Zeit
I
Chopper
Figure 10 .4 :
Path-time diagram for a configuration with "Frame overlap choppers", chopper
2 .
using the right hand vertical scale. This diagonal straight Elle intersects the level A o =
0.6nm at the location of the "elastic channel" where neutrons are collected that did not
change their velocity during scattering . Silice in liquid water which was the sample all
molecules may diffuse without restriction only a so called quasielastic line is observed
which corresponds to a Lorentzian with a width proportional to QZ . The maximum of
intensity is nevertheless at the elastic channel (- quasielastic) . The difference between a
solid with atoms/molecules fixed at lattice sites and a liquid is illustrated by the right part
of the figure. Imidazole in the solid state exhibits an intense line at the elastic channel
with a width corresponding to the instrumental resolution. In contrast molten imidazole
(especially for the relatively large scattering angle displayed here ----> large Q) shows only a
broad quasielastic intensity distribution . At shorter times- of-flight corresponding to larger
10-7