Three types of force act alongside each other inside a nucleus. The dominant one is the nuclear or ‘strong’ interaction which ensures the cohesion of the nucleus by pulling the various nucleons together, a force which is also responsible for the production of alpha radiation. Secondly, the electromagnetic repulsion among the like-charged protons, but is considerably less powerful than the strong force. The third of these nuclear interactions is the ‘weak' force ; neither attractive nor repulsive, it acts inside the individual nucleons and can occasionally lead to a neutron’s transformation into a protonon (or vice versa), accompanied by a release of beta radiation. The interplay between these three forces dictates how stable or unstable a nucleus is.
All nuclei are practically incompressible like the molecules of a liquid. This is caused by the direct contact that exists between the constituent neutrons and protons.
The nucleons are all held together by a contact force, called nuclear or strong, which is the dominant force inside the nucleus. Despite being remarkably powerful, this nuclear glue only acts over the shortest of distances. This explains why these forces went undetected for decades even after the discovery of radioactivity. These distances are so short, in fact, that neutrons can travel in the immediate vicinity of a nucleus without being affected by the force and eventually absorbed into the nucleus.
The electromagnetic repulsion takes place within the nucleus between like electric charges. These charges are carried by the protons, whose close proximity to each other intensifies this repulsive force. The strong nuclear attraction must be immensely powerful to overcome the repulsion taking place in a sphere whose radius is only of a few millionths of a billionth of a metre.
The third nuclear force is a discreet one that nevertheless plays a fundamental role in the universe. Without the ‘weak force’, our Sun would stop shining due to the inability of hydrogen nuclei to fuse to form deuterium, the Sun’s main energy-producing reaction.
Without the weak force, there would be a great deal more than 287 ‘natural’ nuclei in the world., The expulsion of a proton or neutron from a nucleus requires energy and do not occur naturally. Without the weak force which allows neutrons to transform into protons (and vice versa) at a cheap price, several thousands of the nuclei that we register as unstable and radioactive would be stable ((*)).
Access to page in french