Unit 6 Glossary

Absorption:  In NDT, absorption is the reduction of the intensity of any form of radiated energy as a result of energy conversion (absorption) in a medium, such as the conversion of sound energy into heat (compare attenuation)

Bremsstrahlung:  Also known as “breaking radiation”.  Electromagnetic radiation produced when electrons’ path and kinetic energy brings them close to the positive fields of atomic nuclei.  In X-radiation, electrons strike a target provided for this purpose.  The electrons slow down and give up kinetic energy called X-radiation photons.

Compton Effect or Compton Scattering: The mode in which a moderate energy photon transfers a portion of its energy to an outer shell electron and the remaining energy is redirected as a lower energy photon.

Electron: a stable subatomic particle with a charge of negative electricity, found in all atoms.

Gamma Radiation:  is a penetrating, ionizing, electromagnetic radiation arising from the radioactive decay of atomic nuclei, containing the shortest wavelength of the electromagnetic spectrum.

HVL (Half-Value Layer): The amount (thickness) of a given shielding material needed to reduce the radiation emissivity by one-half it’s value.

HVL Formula:  Io = Original Intensity              Id = Desired intensity

[latex]\ { Log } [ \frac { I o } { I d } ] / \ { Log } 2[/latex]


Ionizing Radiation:  a type of radiation that is able to disrupt atoms and molecules on which they pass through, giving rise to ions and free radicals.

KV (Kilo voltage):  Energy or amount of radiation

mA (milliamperes):  Intensity, penetrating power of radiation

Photoelectric Effect:  When light shines on metal, electrons can be ejected from the surface of the metal in a phenomenon known as the photoelectric effect. This process is also referred to as photoemission, and the electrons that are ejected from the metal are called photoelectrons. In terms of their behavior and their properties, photoelectrons are no different from other electrons.

Photons: Discrete particles of light or electromagnetic radiation hypothesized to explain the corpuscular theory of radiant energy.

Proton:  a subatomic particle present in all atomic nuclei, with a positive electric charge equal in magnitude to that of an electron, but of opposite sign.

X-ray – a type of ionizing radiation formed in a Cathode Ray Tube (CRT) when high velocity electrons flow from the cathode to the anode.


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