Fusion And Propulsion

The same curve of Figure 8.6 shows He could be a good candidate "product", if hydrogen is viewed as the "fuel" to form it, because the binding force is larger among nucleons of 4He than among four H nuclei. Indeed, this is the goal of all current nuclear fusion research: to "fuse", or merge, four smaller H nuclei into a larger 4He nucleus (actually, hydrogen isotopes deuterium, D, and tritium, T, are better than common hydrogen in this respect). This process is therefore the opposite of fission, where a large nucleus, such as 235U, is split and forms smaller fission fragments. A notional sketch of fusing D and T, forming a He nucleus (an alpha particle) plus a neutron is shown in Figure 8.7. Other light nuclei may be fused forming a heavier nucleus, but in practice nearly all fusion research is focused on hydrogen because its nuclear kinetics is theoretically easier to start.

For illustration only, a hydrogen fusion reaction, and its mass (kilogram) and energy (joule) budgets could be simplified as follows (see also Figure 8.3):

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