Georgia Institute Of Technology

NRE 3301

2 Interaction of Ionizing Radiation with Matter
2.1 Denitions and Relations
The denitions in the text below refer mainly to ICRU Report 85: Fundamentals Quantities and Units for Radiation (ICRU, 2011).
2.1.1 Radiometric Quantities
Radiation can be divided into two main types:
Ionizing radiation, which can ionize matter and produce ions. This is possible if
the particle energy is higher than the ionization potential. As the ionization potential
varies with atomic number, the threshold value for a radiation being ionizing will vary.
However, this is often a minor problem in the determination of the absorbed dose as
this cut-o energy is typically small. In radiobiological applications a threshold value
of 10 eV is often used.
Non-ionizing radiation, which doesn’t have sucient energy to ionize and can
only give rise to excitations of the atoms and molecules. These energy transfers are
small and will normally have a small biological eect. This type of radiation is not
included in this text.
Ionizing radiation can further be divided into two classes:
Charged particles as electrons and positrons (light charged particles) as well as
protons, α-particles, and other heavy ions (heavy charged particles). Previously this
type of radiation was called “directly ionizing” radiation as the particle deposits its
energy directly to emission of orbital electrons through Coulomb collisions.
Uncharged particles a