Rutherford scattering calculation

[strangequark]

Homework Statement

The fraction of 6.0 MeV protons scattered by thin gold foil, of density \rho=19.3 g/cm^{3}, from the incident beam into a region where scattering angles exceed 60 degrees is equal to 2.0 x 10^{-5}. Calculate the thickness of the gold foil using the result of the previous problem.

Homework Equations

The result I got for the previous problem was a formula for the number of particles scattered thru and angle of \theta or greater and is:

N(\theta)= (\frac{1}{4\pi\epsilon_{0}})^{2} \pi I \rho t (\frac{zZe^{2}}{Mv^{2}})^{2} cot^{2}(\frac{\theta}{2})

The Attempt at a Solution

So I took \frac{N(\theta)}{I} which is equivalent to removing the I from the above equation and attempted to solve for t, which is the thickness...

t=\frac{2x10^{-5}}{(\frac{1}{4\pi\epsilon_{0}})^{2} \pi (19.3 g/cm^{3}) (\frac{79(1.602x10^{-19}coul)^{2}}{2(6 MeV)})^{2} cot^{2}(\frac{\pi}{6})}

problem is that I keep getting an answer in m/kg, so I must be missing some term, though I can't figure out what it is...

any help is very much appreciated.

 

[Astronuc]

Absorber thickness is sometime measured in kg/m² or gm/cm² such that dividing by density in kg/m³ or gm/cm³ yields a thickness in m or cm, respectively.

Make sure the relationship between N and I is correct, and check one's units on the various terms.