The Woods-Saxon potential is

\displaystyle H = \frac{V_0}{1+\exp^{\frac{r-R_0}{a_0}}} - LS \frac{V_{so} \exp^{\frac{r-R_{so}}{a_{so}}}}{(\exp^{\frac{r-R_{so}}{a_{so}}})^2}

The LS coefficient is

\displaystyle LS = \frac{1}{2} (J(J+1) - L(L+1) - \frac{1}{2}\frac{3}{2})

So, this is the neutron single particle levels.

 

WS-trend.png