Nuclear Fusion and Nuclear Fission

One knows fission to be a process by which a heavy nucleus is bombarded with free neutrons which cause it to divide or fis­sion into two or more smaller nuclei. The smaller nuclei have a greater total binding energy and, consequently, a smaller total mass (about one tenth of one per cent less) than the heavy nucleus which fissioned. Therefore, there is a release of energy when an atom fissions.

We know nuclear fusion to occur when two light nuclei com­bine or fuse to form a single nucleus with a greater mass. The large nucleus will have a stronger binding energy and a mass that is about one half of one per cent smaller than the total mass of the two small nuclei. Thus, a fusion reaction releases several times as much energy as a fission reaction.

We have not yet learned how to control nuclear fusion well enough to reutilize it as a source of commercial power, although a fusion process is used in hydrogen bombs. The greatest prob­lem is that each nucleus bears a positive electrical charge and two nuclei therefore repel one another at ordinary temperatures. However, when the nuclei are heated to a very high tempera­ture, they no longer repel one another and so are able to meet and fuse. Because they require such high temperatures, fusion reactions also are called "thermonuclear reactions". The high temperatures required — several million degrees Fahrenheit — are too great for any known material to withstand. Research is now in progress to develop a method to contain the high temperature fusion materials within a magnetic field, rather than¹ in a material container.

Пояснение к тексту

1. rather than – а не

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