Nuclear charge fusion

The reactions of deuterium, tritium, and helium-3 [14762-55-17, He, having nuclear charge of 1, 1, and 2, respectively, are the easiest to initiate. These have the highest fusion reaction probabiUties and the lowest reactant energies. 

Nuclei suitable for fusion must come near each other, where near means something like the nuclear radius of 10" cm. For positively charged nuclei to make such a close approach it requires large head-on velocities, and therefore multimillion-degree Celsius temperature. In contrast, fission can occur at normal temperatures, either spontaneously or triggered by a particle, particularly an uncharged neutron, coming near a fissionable nucleus. 

A hydrogen bomb, which uses nuclear fusion for its destructive power, is three bombs in one. A conventional explosive charge triggers a fission bomb, which in turn triggers a fusion reaction. Such bombs can be considerably more powerful than fission bombs because they can incorporate larger masses of nuclear fuel. In a fission bomb, no component of fissionable material can exceed the critical mass. In fusion, there is no critical mass because fusion begins at a threshold temperature and is independent of the amount of nuclear fuel present. Thus, there is no theoretical limit on how much nuclear fiiel can be squeezed into a fusion bomb. 

The key point in this respect is the large number of neutrons produced in the central region. Insofar as these nucleons carry no elechic charge, they mix easily with the previously produced nuclear isotopes, including iron. They do not suffer the electrical barrier that so frustrates the fusion of nuclei, and ever more so as they occupy higher positions in the hierarchy. Neufron capture serves to enrich the range of nuclei that can be engendered by supernova activity. 

Just to reiterate what we have said, neutron capture is the only valid channel towards the extreme complexity of gold (Z = 79). Reactions involving charged particles are energetically unfavourable and moreover inhibited by insurmountable electrical barriers. Because of the strong electrical repulsion between heavy nuclei (which thus contain many protons), the classic thermonuclear fusion reactions are ineffective, and we are forced to accept the idea that nuclear species beyond iron are produced by a process other than thermonuclear fusion. This process is neutron capture. 

A plasma is an appreciably ionized gas(about 1% or more) having no net charge, and may have a wide range of densities. Plasmas are of particular interest because of the possibility of initiating nuclear fusion in them, but they also appear in such phenomena as a neon sign, a lightning stroke, the ionosphere about the earth, shock waves, and the compressed layer of hot gas about an object entering the earth s atmosphere They appear in flames and detonation waves. It seems well established that free radicals and ions are present at well over equilibrium concentrations in flames (Ref 1). The ions appear to be produced not by thermal processes but by chemical factors which cause abnormal electronic excitation... 

The fact that neutrons can be absorbed by nuclei without overcoming a threshold (1 = 0 or s-wave reactions) makes neutrons extremely effective nuclear reactants. Neutron-induced reactions are the energy source for present-day commercial nuclear power (fission reactors) while charged-particle-induced reactions remain under study as power sources (fusion reactors). In this chapter we will consider the general features of nuclear fission reactors, following by the general features... 

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