Alpha particle in a force field depiction

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hawkslime
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TL;DR
Can someone give me an explanation of the below picture, please?
Hello, I was glazing through what I would consider an advanced physics textbook and I saw this image. It is a schematic picture of an alpha-particle in a field of an atom.

Now, can someone get me started on what (and why and how) is going on in it? Especially with the fraction with pi.

Schematic of an alpha particle's trajectory past a nucleus labelled jádro, with impact parameter b, deflection angle θ, force F(r) along the line joining nucleus and particle, and a momentum-change triangle p1, p2, Δp.
 

Discussion

Welcome to PF.
Can you please give a reference; Title; Author; ISBN; Page number.
 
The alpha particle approaches a positively charged nucleus, it is repelled and its path is deflected by an angle ##\theta##. The rest is just geometry. The sum of the two angles with the fraction is ##\pi-\theta## because these two plus the ##\theta## angle must add up to ##\pi##. The dashed line is going through the point of closest approach. The particle trajectory is symmetric with respect to that line, so both sides of it have half of the ##\pi-\theta## angle.
 
mfb said:
The alpha particle approaches a positively charged nucleus, it is repelled and its path is deflected by an angle ##\theta##. The rest is just geometry. The sum of the two angles with the fraction is ##\pi-\theta## because these two plus the ##\theta## angle must add up to ##\pi##. The dashed line is going through the point of closest approach. The particle trajectory is symmetric with respect to that line, so both sides of it have half of the ##\pi-\theta## angle.
Thank you.