<P> where σ is the area (or, more formally, the "scattering cross-section") of one atom . </P> <P> The drop in beam intensity equals the incoming beam intensity multiplied by the probability of the particle being stopped within the slab: </P> <Dl> <Dd> d I = − I n σ d x . (\ displaystyle dI = - In \ sigma \, dx .) </Dd> </Dl> <Dd> d I = − I n σ d x . (\ displaystyle dI = - In \ sigma \, dx .) </Dd>

How to calculate mean free path of molecule