Chapter 13: Other Diffraction Techniques

Neutron diffraction represents a fundamentally distinct approach because neutrons interact with atomic nuclei rather than electron clouds, producing scattering lengths that remain constant across scattering angles and vary unpredictably throughout the periodic table. This characteristic makes neutron diffraction exceptionally valuable for detecting light elements such as hydrogen and for differentiating between isotopes. Neutrons are generated through fission reactors or spallation sources and cooled to thermal energies for practical applications. The magnetic dipole moment of neutrons enables investigation of magnetic structures, allowing researchers to study phenomena like ferromagnetic and antiferromagnetic ordering by analyzing interactions with unpaired electron spins. Electron diffraction within transmission electron microscopes operates under fundamentally different physics because electrons experience strong Coulomb interactions with atomic electrostatic potentials, necessitating extremely thin samples and often requiring dynamical scattering theory rather than kinematic approximations. The short wavelength of high-energy electrons produces an Ewald sphere with enormous radius, appearing nearly planar and enabling simultaneous observation of numerous reflections. Transmission electron microscopes can operate in multiple modes including bright field and dark field imaging, alongside high-resolution multi-beam techniques. Convergent beam electron diffraction generates disk-shaped diffraction patterns from focused electron cones, providing quantitative information about specimen thickness and precise point group symmetries. Synchrotron X-ray sources produce high-brilliance, tunable radiation through relativistic particle acceleration in storage rings, enabling advanced investigations such as real-time monitoring of nanocrystalline formation and anomalous scattering experiments for discriminating elements with comparable atomic numbers. Together, these techniques extend the capabilities of structural analysis beyond conventional crystallographic methods.