Calculating Activity of proton beam

[wormhole228]

Homework Statement

A natural lithium target 3.8 mg cm^-2
thick is bombarded with a
125 µA beam of 3.5 MeV protons initiating a ⁷Li(p,n) reaction.
Assuming a reaction cross section of 300 mb, calculate the
activity produced by a 15 minute bombardment.

Homework Equations

λN=$\phi$$\sigma$N_T(1-e^-λt)
I=I₀e^-μx

The Attempt at a Solution

125μA=125μC/s(1 proton/1.602*10^-19C)(15*60s)=7.022*10¹⁷ protons. I'm not really sure where I would go from here. I got μ/$\rho$=0.0258 cm²/g. Yet, I can't find the actual linear attenuation coefficient. I figured we would use the activation equation, but I'm not sure on the flux, and the other units.

 

[mfb]

You can convert the given area density to an atomic density - ideally in the units atoms/barn. Together with the given cross-section, ...