Nuclear interaction length
Nuclear interaction length is the mean path length required to reduce the numbers of relativistic charged particles by the factor 1/e, or 0.368, as they pass through matter.
Comprehensive tables for radiation lengths and other properties of materials are available from the Particle Data Group site: http://pdg.lbl.gov/AtomicNuclearProperties.
Nuclear interaction length is the mean distance travelled by a hadronic particle before undergoing an inelastic nuclear interaction.