In a BCC crystal the distance between two adjacent planes is given by
[tex]d_{hkl}= \frac{a}{\sqrt{h^2+k^2+l^2}} [/tex]
For Chromium where [tex]R=0.1249 nm[/tex] the lattice constant is
[tex]a=4R/ \sqrt{3}=4*0.1249 / \sqrt{3}=0.288 nm
[/tex]
Distance between (310) planes is
[tex]d_{(310)} = \frac{0.288}{ \sqrt{3^2+1^2+0^2} }=0.091 nm [/tex]
The diffraction angle for the n=1 order is
[tex]2d*\sin (\theta) =\lambda [/tex]
[tex] \sin(\theta) =\lambda /(2d) =0.0777/(2*0.091)=0.427[/tex]
[tex] \theta =25.72 \degree[\tex]
