How are X-rays used to inspect airline baggage?

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Diagram of the electromagnetic spectrum showing different types of waves arranged by wavelength and frequency, from gamma rays and X-rays to ultraviolet, visible light, infrared, microwave, TV/FM radio, shortwave radio, AM radio, and longwave radio. — X-ray The relationship of X-rays to other electromagnetic radiation within the electromagnetic spectrum.

X-rays are used to inspect airline baggage by exploiting the principle of differential absorption. Because materials vary in their density, composition, and homogeneity, they absorb X-ray radiation at different rates. When a radiation beam is passed through a piece of luggage, these variations allow for the quick, nonintrusive examination of the bag's contents, revealing the internal structure of items stored inside.1