A neutron beam of energy E scatters from atoms on a surface with a spacing d=0.1 nm. The first maximum of intensity in the reflected beam occurs at $\theta =30°.$What is the kinetic energy E of the beam in eV?

Hint: The momentum of the particles depends on the wavelength of the beam.

Step 1: Find the wavelength of the beam.

Given, d=0.1 nm,

Now, according to Bragg's law