I need to estimate the nuclear interaction length in solid lead given the atomic mass unit $A=207.2u$, radius of lead nucleus $R=r_0A^{1/3}$ where $r_0=1.25fm$ and the density of lead is $\rho=11.34g/cm^2$. I've been trying to find calculations for the nuclear interaction length but all I can find are tables with the length already given but no method of calculation.
For example the Particle Data Group has a page for lead, and while I don't expect them to have details of the calculations, this is one of the only places I can find the nuclear interaction length and no other sites mention how it is calculated.
How do I calculate the nuclear interaction length given this information?