What are some practical applications of x-rays?
X-ray crystallography, radiography, telescopy...
In x-ray crystallography a fine beam of single frequency x-rays is directed at a crystal whose molecular structure you wish to determine. The regular structure of the crystal acts like a diffraction grating, resulting in a diffraction pattern. Combining the information obtained by capturing the diffraction pattern for different orientations of the crystal, using Fourier analysis, the molecular structure can be determined.
In radiography, a beam of x-rays is passed through an object and an image captured on the other side of the object, recording the varying intensity of the x-rays passing through different parts of the object. Traditionally this was done using photographic plates, but nowadays an image plate coated with a phosphorescent material might be used, with the resulting visible image then digitally captured.
Radiography is used medically in the form of traditional two dimensional x-rays or more advanced multiple two dimensional slices in CT (computer tomography) scans.
Radiography is also used at airports and other places where items need to be scanned for suspicious contents.
X-ray telescopes observe celestial objects in the x-ray spectrum, providing a wealth of information that is not available just in the visible or other spectrums.