Sorry for my Ignorance...I apologise.
Here is the Complete problem
"The electron density in a hydrogen atom in its ground state is spherically symmetric, and is given by
p(r)=exp{(-2r/a)/(pi*a^3)
where a, the first Bohar radius has the value 0.53 Angstrom. Compute the atomic scattering factor for hydrogen and plot it as a function of =2ksin(theta)=4*pi*sin(theta)/lambda.
Explain physcially why the scattering factor is small for back reflection (theta=pi/2).
I have solved the first part but i am unable to find an explanation for the second part.
Hopefully now u can be of help.
Thanks
Ess ESS