content_image/305211.jpg content_image/305212.jpg
across the reaction plane. The next simplest is hard spheres: 

<img src='content_image/305211.jpg'>

The Woods-Saxon distribution is a commonly used diffuse nuclear density, parameterized by 

<img src='content_image/305212.jpg'>

For $^{197}$Au [445] found R = 6 . 36 fm and z = . 535 fm by comparing the charge distribution as measured by high-energy electron scattering to predictions from the Dirac equation. Values for $^{63}$Cu can be found in [446]. These experimental determinations of the nuclear densities can become nearly arbitrarily complex; see Fig. A.2 for the results of fits of the proton and neutron distributions with 9 free parameters each [444]. 

