Figure 5.  A hypothetical mass parabola obtained at A = 27 by assuming that interactions between nucleons generate the mass parabola shown in Figure 4.  To match the empirical trends shown in Figure 4, we assumed that the n-n and p-p interactions are repulsive and equal while the n-p interaction is attractive and 2.5 times stronger.  These net interactions are shown in the last column of Table 1.