# Solid Angle Rutherford Scattering

1. Jan 8, 2015

### Purple Baron

1. The problem statement, all variables and given/known data
derive an equation for the solid angle for a Rutherford scattering detector given a detcor window area of $A$ and a distance to the detector of $D$ for some scattering angle $\phi$ given that $d\Omega =2\pi sin\phi d\phi$

2. Relevant equations
$d\Omega =2\pi sin\phi d\phi$
$A=Dd\phi$
3. The attempt at a solution
integrating $d\Omega =2\pi sin\phi d\phi$ to get solid angle gives $\Omega =\frac{2\pi A}{D}\int sin\phi d\phi$ howver this gives a negative value due to the integral of sine and shouldn't soild angle be positive? Is this correct or am i missing a step? Thank You

2. Jan 8, 2015

### BvU

You sure this gives a negative value ? Can you show how you get it ? Bounds, primitive ?

3. Jan 8, 2015

### haruspex

That's dimensionally incorrect. You have an area on the left and a distance on the right. And the dϕ looks wrong.
Shouldn't it be $A = D^2d\Omega$?
As BvU posted, your problem with the negative sign will resolve itself when you put in the bounds on ϕ.