Linear Energy Transfer

Linear Energy Transfer (LET) (see also linear energy transfer) is a concept involving ionizing radiation and the rate at which the ionizing particle loses energy as it traverses material. A high-LET particle will rapidly lose its kinetic energy as it traverses material, and a low-LET particle will travel much greater distances while losing the same amount of energy.

For example, a high-speed beta particle or gamma photon might travel 1,000 Angstroms through a material [for example, biological tissue] before causing an ionization and losing energy, then travel another 1,000 Angstroms before causing another ionization. They are said to be low LET particles.

Conversely, an alpha particle might travel only 1 Angstrom before causing an ionization, then travel another Angstrom and cause another ionization. It is said to be a high LET particle.

Also, the LET can change over the range of the particle. For example, if a high-energy cosmic ray encounters matter [atmosphere, moon-rock, etc.], it will slow and come to a stop. As it slows, its LET will increase. Thus, when it first encounters matter, it will have a much lower LET than when it is close to the end of its range, in which its LET will be much higher. This difference can be utilized in calculating the charge and energy of such cosmic rays by the particle track-etch method pioneered by P. Buford Price, et al.