Figure 14-02 shows the distribution of the stable nuclei. As the mass numbers become higher, the ratio of neutrons to protons in the nucleus becomes larger. There are no stable nuclei with a mass number higher than 83 or a neutron number higher than 126. This limit is represented by the element Bismuth (see
|| A nucleus is specified by its number of protons Z, number of neutrons N, and the mass number A = Z+N.
The nucleons (protons and neutrons) in a nucleus are bound together -- their total energy is less than the total energy of the separated particles. The binding energy is the amount of energy given up when the nucleus is formed.
Plotting the binding energy per nucleon versus the mass number A (Figure 14-01) shows that starting from Hydrogen, nuclei become more stable as there are more
||protons and neutrons, until Iron. After that, the trend reverses.|