A question regarding particle diffraction.

[BruceSpringste]

Homework Statement

"A beam of neutrons that emerges from a nuclear reactor contains neutrons with a variety of energies. To obtain neutrons with an energy of 0.050 eV, the beam is passed through a crystal whose atomic planes are 0.20 nm apart. At what angles relative to the original beam will the desired netruons be diffracted?"

Homework Equations

Braggs law
mλ=sin2θ

The Attempt at a Solution

My first thought was to use braggs law and simply solve for θ and m=1,2,3... but θ>90degrees.
However the problem seems a lot more complex than that. My book doesn't have any answers to the question so I can't double check if I have done this right!

 

[mfb]

but θ>90degrees

Looks like a calculation error.

Did you calculate the wavelength of those neutrons?