Neutron Scattering

pole figures require numbers of 104 to 105 grains as good figures . The knwon properties of X-
rays (large absorption in the sample and a small beam diameter) limit its use to (1) flat, thin
samples, and (2) fine grained material with grain sizes in the order of 10 to about 100 hum.
These limitations allow to study only a surface of a sample because the X-rays penetrate the
sample just a few microns . X-rays therefore probe the local texture at the sample surface. Due
to the high and orientation dependent absorption and limitations due to defocusing if a flat
sample is rotated (see Fig . 18 .16), only incomplete pole figures can be obtained .
b
,-NUL-- .
Fig . 18.16 : X-ray diffraction patterns ofa
flat anorthosit sample in two different
orientations (a and b) and mean neutron
diffraction diagram (C ofall orientations
Fig. 18.17: Comparison ofX-ray (left) and
neutron polefigures (right) ofa coarse
grained deformed marble specimen [51
Neutron beams, on the other hand, are large up to 100 x 50 mm2 cross section, and in general
weakly absorbed by most materials . Compared to X-ray photons, neutrons are absorbed by
less than three orders of magnitude and are therefore in need of large samples . While this may
be a drawback in many investigations, it is of great advantage in texture analysis where the
global texture of the total volume has to bc explored. Due to their ability to penetrate matter,
neutrons are well suited for the analysis of the bulle of a thick sample with several cm in
diameter. Thus it is possible to study also coarse grained material with reasonable grain
statistics even if grain sizes range up to millimeters in diameter (Fig. 18 .17) . Neutron
18- 10