I'm preparing for a midterm exam and this is one of the practise questions I'm having a bit of trouble with. 1. The problem statement, all variables and given/known data We have access to X-ray and electrons for the incident beam. [itex] \theta [/itex] is the inner angle between the sample and the incident beam. Spacing in sample = d =10^-10 m [itex] \lambda [/itex] = 10^-10 m a) What values of [itex] \theta [/itex] will we measure X-rays at a detector, that is, when will there be constructive interference (assume elastic collision)? b) If we use electrons instead of X-rays, at which energy should they be to detect the electrons at the same angle as the X-rays (assume elastic collision)? 2. Relevant equations Bragg's Law: [itex]2 d sin(\theta) = m \lambda[/itex] E = hf p = h / [itex] \lambda [/itex] Compton effect 3. The attempt at a solution For part (a) what I did was basically use: [itex]sin(\theta) = (1 \lambda) / (2d)[/itex] [itex]sin(\theta) = (2 \lambda) / (2d)[/itex] Since [itex]sin(\theta) = (2 \lambda) / (2d)[/itex] gives 90 degrees, my answer is that the only angle is 30 degrees, that is, m = 1. For part (b) I'm not really sure how to approach this question. Is this just the classical model of an elastic collision? Thanks.