4.1 Experimental facts
4.1.1 mass spectrograph
4.2 Interpretation
4.3 Deeper analysis of nuclear masses
4.4 Nuclear mass formula
4.5 Stability of nuclei
4.5.1 $\beta$ decay
4.6 properties of nuclear states
4.6.1 quantum numbers
4.6.2 deuteron
4.6.3 Scattering of nucleons
4.6.4 Nuclear Forces