However, it is not necessary to actually do this experiment to establish how tightly the deuteron is bound. One need only weigh the deuteron accurately. Protons and neutrons are referred to as nucleons . Z. This is called the atomic number . Nuclei can have the same atomic number, but different numbers of neutrons.
Nucleons attract each other with a short range but very strong force, called the nuclear force .
The situation here is different from that for electrons in the atom, where the strong central force tends to dominate. In the nucleus the nucleons are attracted mainly by their immediate neighbors. Nevertheless, it is a useful beginning to think of this attractive force as being a potential well, as seen by an individual nucleon, and think in terms of the nuclei as filling the lowest available quantum states in this well, just as we did for electrons in the atom. It has also been argued that some of these higher nuclei strongly resemble bound states of a -particles. As one goes to really large nuclei, the binding per nucleon actually decreases.