NEUTRON HOLOGRAPHY with atomic-scale resolution has been performed,
for the
first time, with an "inside-detector" approach. Holography
generally
includes a source of illuminating waves, an object to be imaged, and a
detector or film in which waves direct from the source interfere with
waves
scattered from parts of the object. The interference pattern, stored
in the
detector medium, is later read out (and a 3D image of the object
viewed) by
sending waves into the detector. Holograms with visible light are
common
enough: they adorn most credit cards. Holograms using electrons
(considered
in their "wave" manifestation, not as particles) provide
sharp pictures, but
because the electrons cannot penetrate far into a solid sample, the
imaging
process is usually restricted to surface regions. Holograms using x
rays go
can penetrate much farther, but their limitation consists of the fact
that
the penetration depth improves as the square of the atomic number.
Therefore x-holography is not very good for materials with light
elements.
Holograms with neutrons are different; rather than scattering from the
electrons in the atoms of the sample, neutrons scatter only from
nuclei,
which are 100,000 times smaller than the atoms in which they reside.
This
is important when it comes time to reconstruct an image of the
interior of a
crystal lattice. In an experiment carried out with a beam of
neutrons from
a reactor at the Institute Laue-Langevin in Grenoble, a group of
scientists
has produced, for the first time, an atomic-scale map of a crystal, in
particular a sample of lead atoms, using a technique in which the
"detector," a trace amount of atoms (cadmium-113) whose
nuclei readily
absorb neutrons, are embedded inside the sample itself. The
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