1. The problem statement, all variables and given/known data Consider a crystal with planar spacing 3.2 A0. What order of magnitude of energies would one need for (a) electrons, (b) helium nuclei (mass = 4*proton mass) to observe up to three interference maxima? 2. Relevant equations 2d.sinx = n.lambda (I) lambda = h / p (II) E = (1/2)mv22 3. The attempt at a solution To solve this question, I thought I must first find the wavelength and can use other equetions that I wrote above. Actually, I don't know how I can use them but since in the question, mass is important, I thought an equation with mass can work.