X-rays are absorbed by the photoelectric effect, the Compton effect and pair production

The photoelectric effect was discovered in 1887 by Halwachs.

The Compton effect was discovered in 1923 by Compton (an American).

Pair production was discovered by Anderson in 1932.

A positron is a "positively charged electron" .

The absorption of x-rays by matter depends upon the density and the atomic weight of the material. The lower these two values are, the more transparent the material is to x-rays. The fact that bones are more opaque to x-rays than the surrounding flesh, make x-ray photographs possible.
In the interaction between matter and X-rays, three mechanisms exist by which X-rays are absorbed; the photoelectric effect, the Compton effect and pair production. All three mechanisms demonstrate the quantum nature of x-radiation. The photoelectric effect is core material, the other two are part of the "Particle Physics" option and therefore of interest to students taking that option.

Photoelectric effect

In the first type of absorption, when an x-ray photon strikes an atom, it may impinge on an electron within an inner shell and eject it from the atom. If the photon carries more energy than is necessary to eject the electron, the excess energy will appear as kinetic energy of the ejected electron. This phenomenon, called the photoelectric effect, occurs primarily in the absorption of low-energy x-rays.

Compton effect

In the second type of absorption, called the Compton effect, x-rays of high-energy are absorbed. When a high-energy photon collides with an electron, both particles may be deflected at an angle to the direction of the path of the incident x-ray. The incident photon, having given some of its energy to the electron, emerges with a longer wavelength. This effect is known as Compton scattering.

Pair Production

In the third type of absorption, where extremely high-energy X-rays strike elements of high atomic weight, the phenomenon of pair production occurs. When a high-energy photon penetrates the electron shell close to the nucleus, it may create a pair of particles, one an electron, the other, a "positively charged electron" called a positron. Pair production is an example of the conversion of energy into mass. The photon requires at least 1.2 MeV of energy to yield the mass of the pair. If the incident photon possesses more energy than is required for pair production, the excess energy is given to the particles as kinetic energy. The paths of the two particles are divergent.