Suppose particles are incident on the surface of a crystal as shown in Fig. 5-4.  Assume that the interatomic spacing (D in the figure, a in class notes) is 0.2 nm, and that a detector is located at the angle phi = 53 degrees. For what energy will we get constructive interference (corresponding to n=1) if the incident particles are

(a) neutrons;
(b) electrons;
(c) photons.