RAD 120 - Ch 13 X-Ray Interactions - Key Terms

Annihilation reaction

Matter being converted back into energy as a result of a positron combining with a negative electron, which creates two photons moving in opposite directions.

Attenuation

The reduction in the number of x-ray photons in the beam, and subsequent loss of energy, as the beam passes through matter

Backscatter radiation

when a scattered photon is deflected back toward the source - it travels in the direction opposite to the incident photon. Most go in a more forward direction, especially when photon energy increases. For this reason, scatter has a serious impact on image quality.

Characteristic cascade

The reaction of electrons dropping into the holes created during a characteristic interaction until there is only a hole in the outer shell

Characteristic photon

Produced during photoelectric interactions and is considered secondary radiation.

Coherent Scatter

An interaction between x-rays and matter characterized by interaction between a very-low-energy x-ray photon and matter causing the electron to vibrate at the same frequency as the incident photon, which then produces a secondary photon with the same energy and wavelength as the incident photon but that travels in a different direction; also called classical scatter or unmodified scatter

Compton (recoil) electron

The dislodged electron - available as a free electron to fill a shell "hole" created by another ionizing interaction.

Compton scattered photon

The photon that exits the atom in a different direction as a result of Compton scattering.

Compton scattering

occurs when an incident x-ray photon interacts with a loosely bound outer-shell electron, removes the electron from the shell and then proceeds in a different direction as a scattered photon. Produces the Compton effect. Part of the incident photon's energy removes the outer-shell electron and imparts kinetic energy to it. The incident photon energy is divided b/w the ejected electron and the scattered photon.

Negatron

A negatively charged electron resulting from pair production

Pair production

Energy of the x-ray photon is converted to matter in the form of two electrons.

Photodisintegration

An interaction between x-rays and matter characterized by the interaction between a high-energy photon and the nucleus. The high-energy photon strikes the nucleus; the nucleus absorbs all the photon's energy and then emits a nuclear fragment.

Photoelectric Absorption

Interaction between an x-ray photon and an inner shell electron of an atom

Photoelectron

An ionized atom with a missing inner shell electron resulting from ejection of the electron due to photoelectric absorption

Positron

a particle with the mass of an electron but a positive charge

Radiation fog

unwanted exposures caused by scattered photons.

Scattering

X-ray photons either interact and change direction

Secondary radiation

Is produced in the same manner as characteristic radiation is produced at the x-ray target—electron transfer from one shell to another.