Neutron Scattering

Fig. 4 .3 .4 probably represents the first verification of the spin-flip and non-spin flip
scattering from a spin-incoherent scatterer . The example is Vanadium a typical material
used for absolute calibrations of neutron measurements . The scattering above the
background level shows nearly the ideal intensity ratio 2 :1 for spin-flip to non-spin-flip
intensities . In particular, hydrogenous materials have large spin incoherent cross sections .
Figure 4 .8 : Nuclear-spin incoherent scattering from vanadium obtained by rocking the
analyzer crystal through the clastic position . The flipper off data are proportional te the
(++) cross section and the flipper on data are proportional to the (-) cross section . In
contrast to magnetic scattering the result is independent of the neutron polarization with
respect to the scattering vector Q .[7]
We recall that for a magnetic system the spin-flip and non-spin flip scattering should
depend on the polarization of the neutron with respect to Q . This field dependence is
illustrated in Fig . 4 .9 showing the paramagnetic scattering from MnF 2 . In general, we
expect that the final polarization to vary between 0 and -PZ,,tit2al . It is obvious that
this scattering can be distinguished from spin-incoherent scattering . Indeed, one can
easily verify that the difference between the spin-flip scatterings with polarization P I~ Q
and P L Q is proportional te the (para-)magnetic scattering only, free from any other
scattering contributions like coherent nuclear scattering, spin-incoherent scattering and
possible background . The saine is truc for the difference of non-spin flip scatterings with
P Ij Q and P L Q, and Fig . 4 .10 shows such a separation of the paramagnetic scattering
from MnF2 powder diffraction data . Measurements with the unpolarized beam show a
background intensity decaying with Q and various Bragg peaks on top . The Bragg peaks
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