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Fusion
Fusion Fusion For centuries, humankind has looked at the stars, and for just as many years humankind has tried to explain the existence of those very same stars. Were they holes in an enormous canvas that covered the earth? Were they fire-flies that could only be seen when the Apollo had parked his chariot for the night? There seemed to be as many explanations for the stars as there were stars themselves. Then one day an individual named Galileo Galilei made an astounding discovery: the stars were replicas of our own sun, only so far away that they seemed as large as pin pricks to the naked eye. This in turn gave rise to many more questions. What keeps the stars burning? Have they always been glowing, or are they born like humans, and thus will they die? The answers to all these questions can be summed up in two words; stellar fusion. Therefore one can begin to understand the stars by understanding what fusion is, how it affects the life of a star, and what happens to a star when fusion can no longer occur. The first question one must ask is, "What is fusion?" One simple way of explaining it is taking two balls of clay and mashing them into one, creating a new, larger particle from the two. Now replace those balls of clay with sub-atomic particles, and when they meld, release an enormous amount of energy. This is fusion. There is currently three known variations of fusion: the proton-proton reaction (Figure 1.1), the carbon cycle (Figure 1.2), and the triple-alpha process (Figure 1.3). In the proton-proton reaction, a proton (the positively charged nucleus of a hydrogen atom) is forced so close to another proton (within a tenth of a trillionth of an inch) that a short range nuclear force known as the strong force takes over and forces the two protons to bond together (1). One proton then decays into a neutron (a particle with the same mass as a proton, but with no charge), a positron (a positively charged particle with almost no mass), and a neutrino (a particle with almost no mass, and no charge). The neutrino and positron then radiate off, releasing heat energy. The remaining particle is known as a deuteron, or the nucleus of the hydrogen isotope deuterium. This deuteron is then fused with another proton, creating a helium isotope (2). Then two helium isotopes fuse, creating a helium nucleus and releasing two protons, which facilitate the chain reaction (3). This final split is so violent that one-half of the total fusion energy is carried away by the two free protons. The second fusion variation, the carbon cycle, starts with a carbon nucleus being fused with a lone proton (1). This creates a nitrogen isotope. One proton then decays into it's primaries -- a neutron, positron and neutrino. The positron and neutrino separate from the nuclei as another proton fuses with the cluster. This creates a nitrogen nucleus which is then fused with yet another proton, forming an oxygen isotope (2). One proton then decays again as still another proton is forced into the nucleus (3). This final fusion splits into a nitrogen and a carbon nucleus; the nitrogen carries away the majority of the fusion heat, while the carbon goes back into the cycle. The triple-alpha process, the last known variety, is perhaps one of the simplest fusion reactions to understand. In this process, two helium nuclei fuse together to form a beryllium nucleus (four protons and four neutrons) (1). Almost immediately after this, another helium nucleus is forced into the cluster, creating a carbon nucleus of six protons and six neutrons (2). In this reaction, all of the heat given off is short-wavelength gamma rays, one of the most penetrating forms of radiation. Each variety of fusion occurs depending on the size and age of the star. This will affect core temperature, causing the corresponding variety of stellar fusion. Now that fusion has been explained, one can learn how it occurs in the different star types. All stellar bodies start off as protostars, or concentrations of combusting gases found within large clouds of dust and v... This is ONLY a preview of the article. If you would like to view the entire document, you must subscribe to Academic Library. Please register below now!
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