X-rays are used to study crystal structures through a method called X-ray crystallography or X-ray diffraction (XRD).
When a beam of X-rays hits a crystal, the regularly arranged atoms in the crystal cause the X-rays to scatter in specific directions. Because the arrangement of atoms is repetitive, the scattered waves can interfere with each other, producing a distinct diffraction pattern.
Scientists record this pattern and analyze the positions and intensities of the spots. From this information, they can:
- Determine the exact arrangement of atoms within the crystal.
- Measure the distances between layers of atoms.
- Identify the type of crystal structure (e.g., cubic, hexagonal).
- Detect imperfections or distortions in the lattice.
- Study changes in the structure under different temperatures or pressures.
This technique is widely used in materials science, chemistry, biology, and physics. For example, it has been crucial in discovering the double-helix structure of DNA and in determining the atomic arrangements in metals, minerals, and complex organic compounds.
In essence, X-rays act like a tool to “see” the positions of atoms without physically disturbing the crystal.