Neutron Scattering

direction that gives rise to a new drastically changed cone angle . In figure 11 .3 a 7r/2-
flipper is shown together with the field vectors that have to be generated for an adequate
function of the flipper .
Figure 11 .3 : Schematics and function of a 7r/2-flipper .
The rectangular flipper exposes its large sides to the beam . The box consists of electrically
conducting and neutron transparen material (aluminum wire) which carries a current I, as
indicated by the broad arrows . All side walls realize a thin homogeneous current density
frequency . Such a change in field is called adiabatic . In particular this means that faster
direction changes are the more adiabatic the larger the field is . For a NSE spectrometer
care must be taken that except at the entry and exit of flippers the conditions are
adiabatic . The magnetic field of the spectrometer is of course static, however the neutron
spins experience a time varying field due to the passage of the neutron through the
spectrometer .
11- 6