The absorbed dose is the average energy absorbed per unit mass.

The tissue absorbed energy in a small mass volume:
D = (dW/dm) [ Gy ]
D = absorbed dose in Gray (Gy); dW = in the tissue energy absorbed; DM = small volume of the mass.

The SI unit of absorbed dose is the joule per kilogram and its special name is the gray (Gy). In units often used by federal and state agencies, absorbed dose is given in rad; 1 rad = 0.01 Gy.

Absorbed dose is a feature that should increase dose awareness and help users in dose optimization. Absorbed dose in CT is quoted using the CTDI (computed tomography dose index)

CTDIvol (volume-averaged CT dose index) and the dose-length product (DLP) give an indication of the average absorbed dose and relative radiation risk to a standard patient. The user is being warned to scan parameter settings that may lead to high doses, and can adjust the protocol if appropriate. It should be noted that CTDIvol and DLP do not take patient size into account, and will give overestimates and underestimates for large and small patients, respectively.

An accelerator uses electrostatic or electromagnetic fields to increase the kinetic energy of charged particles (see alpha particle, beta particle) in order to produce ionization or a nuclear reaction in a target.
Accelerators (see cyclotron, linear accelerator) are used for the production of radionuclides (see Fluorine-18, Molybdenum, Technetium-99m) or directly for radiation therapy. Accelerator-produced radioactive material (ARM) is any radioactive substance that is produced by a particle accelerator. The accelerators used for radiation therapy generate gamma rays (also called Bremsstrahlung) with continuous energy by collision of high energy electrons on materials with high density (also referred as 'high z' - chemical elements with a high atomic number (Z)).
Electron accelerators with energies above 10 MeV can also produce neutrons induced by photons in the accelerator head material (mainly caused by photo nuclear reaction).

Air KERMA (Kinetic Energy Released per unit MAss of air) measures the amount of radiation energy in air, unit is J/kg. This include the initial kinetic energy of the primary ionizing particles such as photoelectrons, Compton electrons, positron//negatron pairs from photon radiation, and scattered nuclei from fast neutrons, when for example air is irradiated by an x-ray beam. J/kg (gray) is also the unit of the radiation quantity 'Absorbed Dose'.

Annihilation in general refers to the transition of a particle and its antiparticle by collision into something different, depending on their energies and based on the conservation of energy and momentum. The electromagnetic radiation emitted is the result of the annihilation (combination and disappearance) of an electron and a positron. Two gamma rays of 0.511 MeV energy, assuming very low-energy particles, are emitted perpendicular to each other.

The Auger electron is emitted caused by the Auger effect. The kinetic energy of the Auger electron depends on the type of atom and the chemical environment. The energy of the Auger electron is in the range between 280 eV (electron volt) and 2100 eV. These different energy levels are utilized for chemical analysis.

See also Auger Effect, Compton Electron, Conversion Electron, Initiating Electron and Auger Pierre Victor.