I am using SimNRA to simulate the classical Rutherford Scattering. Playing around with it, I came across some spectra that I cannot explain...
First of all, if someone plots the spectrum of scattering angle $\theta=0$ will get one! I expected that I won't get any spectrum at all. Are there any higher order terms apart from $1/\sin^4\theta$?
Secondly I get three different kind of spectra. For angles $0<\theta<60$ I get a perfectly gaussian distribution
If I am around $90^\circ (80<\theta<120)$ I get a rhather confussing spectrum which looks like that
For scattering angles $120<\theta<180$ I get a weird spectrum as well
Why am I getting so different a spectrum for those scattering angles ranges? I've read that the last one is used in RBS to define the thickness of a leyer but why does it have that specific behaviour?
And what is this small peak around $90^\circ$? Could that be a recoil gold atom? If so, I cannot understand how a light $4.7\;MeV$ particle can move away a heavy atom...
Any help or hint will be more than welcome!!!
EDIT All the above are for a target of $2\mu m$ thickness and a beam with $500keV$ spread. If I turn off the energy spread the backscattering specrtum has the same flat distribution.
In addition if the target is $5\mu m$, with no energy spread the spectrum is