1. The problem statement, all variables and given/known data A mono-energetic beam are of neutrons is directed perpendiculary at the surface of a metal crystal whose atom are a constant distance 0.1E-10m apart. The scattered beam of neutrons is found to have maximum intensity at an angle of 25degree to the initial direction. What is the energy (in eV) of the neutrons? 2. Relevant equations 2dsinθ = nλ E = hc/λ 3. The attempt at a solution 2(0.1E-10)*sin(25) = (1)λ λ = 8.45E-12 m E = hc/λ = (6.63E-34)(3E+8)/ 8.45E-12 m = 2.35E-14 J=146890eV but ans = 45.7eV Can anyone tell me where goes wrong? Is that the right equation uses to find the energy of the neutrons?