Determining nuclear radius by electron diffraction

[dt19]

can anyone explain to me, where does the equation $$R=\frac{0.61\lambda}{sin\theta}$$ come from when determining the approximate radius of the nucleus by electron scattering?

 

[Edgardo]

I think it has something to do with diffraction. Look up "diffraction by a disk".
I just read that it is possible to calculate the diffraction pattern behind a disc by Babinet's principle.

 

[JeffKoch]

sin(theta) = 1.22*lamda/D, from circular diffraction. D=2R, so R = 0.61*lamda/sin(theta).