1. The problem statement, all variables and given/known data A beam of thermal neutrons (K = 0.025 eV) scatters from a crystal with interatomic spacing 0.45 nm. What is the φ angle of the ﬁrst order Bragg peak? (as deﬁned in ﬁgure 5.11, φ and the scattering angle add up to 180 degrees). 2. Relevant equations nλ = 2dsinθ = DsinΦ d = distance between Bragg planes D = intermolecular distance 2θ = scattering angle 2θ = π = Φ K= 1/2mv2 p=mv=h/λ 3. The attempt at a solution Since K=1/2mv2 and p=mv we can solve K and say K=p2/2m = (pc)2/2mc2 so pc = √(2Kmc2) and since p=h/λ we have λ=h/p if we multiply top and bottom by c we have λ=hc/pc = hc/√(2Kmc2) = DsinΦ since n= 1 for first order. Thus sinΦ = (hc/D)(1/√(2Kmc2) however when I plug these numbers in I get that Φ = sin-1 (17.239) which isn't possible. To me, this makes no sense because my units cancel out properly and I can't see what I did wrong. Thanks!