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'.

The alpha decay is a corpuscular radiation. Two protons and two neutrons (a helium core) are emitted from the atomic nucleus. Because of the high biological effectiveness, the use of alpha particle radiation is not allowed in diagnostic nuclear medicine.

An atom is the basic particle of matter, the smallest (~10^-8cm) particle of a chemical element. Atoms consist of a nucleus with neutrons, positive charged protons and orbiting negative charged electrons. The chemical properties of elements are defined largely by the number of protons in the nucleus. The number of electrons is similar to the number of protons. An atom is ionized when the number of electrons is not equal to the number of protons; the resulting electrical charge depends on the difference between the number of protons and the number of electrons.

See Rutherford-Bohr Atom Model, Ionization.

(AMU) is equal to the mass of one-twelfth of a carbon-12 atom (6 protons + 6 neutrons (+ 6 electrons)), a 'very' little less than 1.66 x 10^-24 gram.

See also Mass Number and Atomic Mass.

Baryons are a group of elementary particles. The heavier particles such as protons and neutrons belong to these baryons. Usually a baryon is made of three quarks; the more exotic ones consist out of four quarks and one anti-quark. [Don't Panic]