1. The problem statement, all variables and given/known data Aluminium (Ar = 26.98, ρ = 2700 kg/m3) has cross-section of thermal neutron absorption 0.23 barn. What is the absorption length of thermal neutrons in the aluminium? What value decreases neutron intensity in 0.6 mm, 8 mm and 80 mm aluminium? 2. Relevant equations Beer-Lambert Law I'm not sure what x and lambda are in this equation. 3. The attempt at a solution I'm not sure how to calculate the absorption length from the information provided. Absorption length [PLAIN]http://gisaxs.com/images/math/c/5/0/c50b9e82e318d4c163e4b1b060f7daf5.png, [Broken] the distance over which the intensity falls to 1/e.