Neutron Scattering

I (Q, t) and the exact symmetry point location . This also holds if any perturbation shifts
the location as indicated by the three hollow circles in the figure .
P 1-__________
I(Q,t)
j1--1-
I(Q,0)
Symmetry
Figure 11 .5 : Schematic echo form, idealized .
For an ideal spectrometer I(Q,t)II(Q,0) = S(Q,t)IS(Q) would be the desired value of
the normalized intermediate scattering function . In reality resolution effects and polarization
losses reduce the value of I(Q, t)/I(Q, 0) compared to S(Q, t)/S(Q) .
Figure 11 .6 shows data from actual experiments that are used to determine the echo
amplitude and average intensity . Here the shape of the echo signal (intensity vs . symmetry
current) is sampled for a considerably larger number than the minimum of three points .
The parameters amplitude, average and phase zero current are determined by a nonlinear
fit . Behind the oscillating echo form there are two further groups of points showing the
minimum and maximum of intensity which indicates the efficiency of the polarization
analysis . These intensities are measured by deactivating the 7r/2-flippers (minimum) and