Physics:Collision length

The mean free path of a particle before undergoing a nuclear reaction, for a given particle in a given medium. The collision length (also known as the nuclear collision length ) follows from the total nuclear cross-section by

with Avogadro's number (6.022 10²³/mole) A = atomic weight [g/mole] and density [g/cm³]. The probability density function for distances between successive collisions is given by

If one subtracts from the total cross-section the sum of elastic and quasi-elastic (diffractive) cross-sections, one obtains by the same formula the (nuclear) interaction length .

Some numerical values for and are given in the following table.

	Medium	[cm]	[g/cm2]	[g/cm2]
	Fe	10.6	83.3	131.9
	Al	26.1	70.6	106.4
	Cu	9.6	85.6	134.9
	Pb	10.2	116.2	193.7
	Concrete	27.0	67.4	99.9
	Scintil.	56.6	58.4	82.0

The numbers are from Barnett96 where much more material can be found.