Ho, M. W. (2007). From cold fusion to condensed matter nuclear science. Science in Society, 36, 32-35.
Introduction
Nuclear fusion, as conventionally understood, is a process whereby the nuclei of light elements fuse together to form heavier ones. (See Box for a quick primer on atoms and nuclei.)
Atoms and nuclei
An atom is the smallest unit of a chemical element. It consists of a core nucleus containing protons and neutrons, surrounded by electrons on the outside. Protons carry a positive charge, which is balanced by the negative charge of the electrons, so that the atom is electrically neutral on the whole. Neutrons do not carry any electric charge.
The elements are identified by their atomic number Z – the number of protons, the same as the number of electrons – and atomic mass A – the total number of protons and neutrons – the mass of electrons are very much smaller and therefore neglected in the atomic mass. The simplest element is hydrogen; it consists of a single proton and a single electron, and is represented as 1H1. Helium is the next simplest element with 2 protons and 2 neutrons, and is represented as 4He2. Most elements exist as isotopes, different forms that have the same number of protons but different numbers of neutrons. Thus, hydrogen has two other isotopes, and unusually are given names of their own, deuterium and tritium, with one and two neutrons respectively, written as 2H1 and 3H1 (though they tend to be written often as D and T).
The protons and neutrons in the atomic nucleus are held together by strong forces, which overcome the electromagnetic repulsion between the positively charged protons. Strong forces act only at very close range; beyond that, weak forces due to electromagnetic interactions take over, so like charges repel and opposite charges attract.
As conventionally understood, nuclear fusions only take place in our sun and other stars, and produce all the chemical elements starting from the lightest, hydrogen. The fusion of light elements releases enormous amounts of energy, whereas the synthesis of the heaviest elements absorbs so much energy that it only take place in supernova explosions [1].
It takes a lot of energy to force even the lightest nuclei to fuse. This is because all nuclei have a positive charge due to their protons, and as like charges repel, nuclei strongly resist being too close together. However, should they get beyond this Coulomb barrier, a strong nuclear attractive force will take over and cause the nuclei to fuse. This can be achieved by accelerating the nuclei to very high speeds, i.e., heated to ‘thermonuclear’ temperatures in excess of 106 K. Only then would the nuclei can get close enough to fuse. Once the fusion reaction starts, it generates so much excess heat that it becomes