X-Rays form part of the electromagnetic spectrum, and are characterized by energies lying between ultra-violet and gamma radiation. Wavelengths are typically in the range 0.01 to 10 nm, which is equivalent to energies of 125 keV to 0.125 keV.

Although there were various explorations of X-Ray radiation in the last quarter of the nineteenth century, it was the work of Wilhelm Röntgen which really brought their properties to the attention of scientists with a preliminary communication in 1895. Röntgen was later awarded the Nobel Prize for his work, and in many languages x-rays are still named after him.

X-Rays are widely used in society today including for medical imaging in hospitals and baggage screening at airport security gates. Within science their properties are integral to many elemental and structural analytical techniques.

XGT Spectrum