Nuclear interaction length is the mean path length required to reduce the numbers of relativistic charged particles by the factor 1/e

E (mathematical constant)

The mathematical constant ' is the unique real number such that the value of the derivative of the function at the point is equal to 1. The function so defined is called the exponential function, and its inverse is the natural logarithm, or logarithm to base...

, 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.