Diffraction of radiation takes place when the distance between the scattering centers is comparable to the wavelength of the radiation.

(a) What velocity must helium atoms possess to be diffracted by a film of silver atoms in which the spacing is 100 pm?

(b) Electrons accelerated through a certain potential are diffracted by a thin film of gold. Would you expect a beam of protons accelerated through the same potential to be diffracted when it strikes the film of gold? If not, what would you expect to see instead?