Nuclear fusion mechanism

The emission of a helium nucleus in the final stage regenerates the initial carbon-12. The latter thus plays the role of a catalyst. The overall result is the fusion of four protons into a helium nucleus. At high temperatures, this cycle dominates over the proton-proton chain. Indeed thermal agitation facilitates penetration of the relatively high electrical barrier between proton and carbon nucleus. Whatever hydrogen fusion mechanism is prevalent, the star s mass determines the rate at which it consumes its nuclear fuel, and hence also its lifetime. The higher its mass, the more quickly it bums. 

The energy of the Sun and stars comes from nuclear fusion reactions, which have the overall effect of transforming hydrogen nuclei to alpha particles (helium nuclei). The temperature of the particular star determines the mechanism by which this transformation takes place. The Sun, a moderately small star, is thought to be powered by the following sequence of reactions ... 

In the sun and in the stars energy is produced mainly by nuclear fusion according to eq. (8.72). Two mechanisms are discussed ... 

The variety and con lexity or nuclear reactions make this a fascinating area of research quite apart from the practical value of understanding fusion and fission. From studies of such properties as the relative amounts of formation of various conq)eting products, the variation of the yields of these with bombarding energy, the directional characteristics and kinetic energies of the products, etc., we may formulate models of nuclear reaction mechanisms. Such models lead to systematics for nuclear reactions and make possible predictions of reactions not yet investigated. 

As seen above, the destruction of the resonance in the case of heavy-ion collisions is due to the coupling between surface and resonance modes. The cluster analog of nuclear surface vibrations is ionic motion. But this takes place at a much slower pace and cannot interfere dynamically with the electronic resonances. The plasmon is thus more robust against varying excitation mechanisms. There remains, however, the static aspect of the enormous surface distortions during nuclear fusion. Such a distortion could also be produced in the analogous process of cluster fission. And, indeed, it has been found that there is a chance to dissolve the plasmon into a broad, fragmented spectrum... 

Tritium is radioactive, a weak p-emitter with a half-life of 12.3 yr. It is used extensively as a tracer, in both chemical and biochemical studies. Its weak radioactivity, rapid excretion and failure to concentrate in vulnerable organs make it one of the least toxic radioisotopes. A major use of tritium is in the triggering mechanisms of weapons based on nuclear fusion. 

The functions of these fusion proteins and their precise roles in the induction of cancer are currently the subject of intense investigation (Collins et al., 2006 Huntly et al., 2004 Kindle et al., 2005). In general, it appears that since the proteins are fused in-frame, their catalytic domains continue to function, but these activities are mis-directed by the targeting domains of their fusion partners. The result is aberrant acetylation of chromatin and non-chromatin proteins, as well as sequestration of key nuclear regulators. These mechanisms are discussed in-depth in Chapter 8 of this book. Furthermore, two recent studies have demonstrated that wild-type MOZ is essential for development of hematopoietic stem cells (Katsumoto et al., 2006 Thomas et al., 2006). This suggests that AML may arise not only due to the aberrant activity of the fusion proteins, but also due to the loss of their original function. 

On the other hand, light atomic nuclei like hydrogen fuse together to form heavier nuclei with the consequent release of energy in the fusion process. Nuclear explosives are the most powerful types and there are different varieties of explosive devices based on the mechanics of the explosion. An important example is Equation 1.2 ... 

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