Neutron Scattering

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Figure 4.2 : Polarisation of neutrons follows field direction in the adiabatic case : W « WL. [6]
use this principle .
guide field
neutron spin antiparalle
to guide field
neutron spin parallel
guide field'
field near the
current sheet
Figure 4 .3 : Neutron spin keeps its orientation for sudden field changes : W » W L .[6]
field changes) . Such an sample environment with zero-field is realized in a device called
cryopad ([9] F . Tasset, ILL) . It allows one to exploit all possible scattering channels with
independent initial and final polarizations along xyz in spin-flip or non-spin flip mode
(which takes 3 x 3 x 2 = 18 measurements) .
An important device for working with polarized neutrons is a spin flipper, see Fig . 4.4 .
One cari use the Larmor precession in a coil to turn the neutron spin . The so-called
Vlezei coil is a long rectangular coil . The field inside (H = N - Ill) is perpendicular
to the polarization and the travel direction of the neutron . Guide fields outside are
necessary te avoid depolarization by the earth field or undefined stray fields, but need to
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