What can be concluded from two different values for the interplanar distance between planes of atoms in an X-Ray diffraction experiment?

I analyzed an unknown Alkali Halide crystal using x-rays from a copper source. I need to find the d-spacing for this crystal, i.e. the interplanar distance between planes of atoms. 


I found my $K\_\alpha$ and $K\_\beta$ peaks and used Bragg's Law to calculate the d-spacing. However, these values do not match. Is this an experimental error or could the non-matching values be correct somehow?


For $K\_\alpha$:


$$d\_{hkl}=\frac{λ}{(2 \sin⁡(θ))}=\frac{(1.54184 Å )}{(2 \sin⁡((28.3°)/2) )}=0.771 Å$$


For $K\_\beta$:


$$d\_{hkl}=\frac{λ}{(2 \sin⁡(θ))}=\frac{(1.39222 Å )}{(2 \sin⁡((25.7°)/2) )}=2.488 Å$$


**My attempt:** in both cases, I assumed that these were first order peaks. Could it be that the $K\_\beta$ peak is actually a third order peak? If so, then $n=3$ and $d\_{hkl}=2.313 Å$. This is reasonably close to the other value. But then what would that tell me about the crystal?


