Nuclear fusion: A guide to understanding atomic energy - PDF

Absolutely! Here is the conversion of the image into a structured markdown format. ### 35 La fusion nucléaire All the elements around us, even those that make us us, are the products of nuclear fusion reactions. Fusion powers stars such as the Sun, where all elements heavier than her hydrogen are...

Absolutely! Here is the conversion of the image into a structured markdown format. ### 35 La fusion nucléaire All the elements around us, even those that make us us, are the products of nuclear fusion reactions. Fusion powers stars such as the Sun, where all elements heavier than her hydrogen are cooked. We are, therefore, dust from the stars themselves. If we manage to harness the energy of the stars on Earth, fusion could be the way to clean and unlimited energy. Nuclear fusion is the combination of light atomic nuclei to form heavier nuclei. Pressed against each other, hydrogen atoms can merge to form helium, releasing energy, a good deal of energy in the process. Gradually, by building up more heavy nuclei through a series of fusion reactions, all the elements we see around us can be created from the ground up. « I ask you to look on both sides. Because the road to understanding the stars goes through the atom, and great advances on the atom were made thanks to the stars. » sir arthur eddington, 1928 Strict embracement It is extremely difficult to fuse even the lightest of nuclei, hydrogen. This requires considerable temperatures and pressures; in nature, fusion only occurs in extreme places, such as inside the Sun and other stars. In order for two nuclei to fuse, the forces that bind each of them together must be countered. However, the nuclei - made up of protons and neutrons - are bound by the strong nuclear force, which dominates on the minuscule scale of the nucleus and becomes markedly weaker outside it. Since protons are all positively charged, their electrical charges repel each other, tending to push them apart. But the strong force is more powerful, and the nucleus remains bound. Given that the strong nuclear force acts on an extremely small scale of distance, its power is globally greater for small nuclei than for heavier nuclei, such as uranium, with its 238 nucleons, wherein the mutual attraction between nucleons situated on opposite sides of the nucleus will not be as strong. The force of electrostatic repulsion, on other hand, is still felt on this scale and thus becomes relatively stronger for larger nuclei, all the more since the number of positive charges contained in the nucleus is higher. The cumulative effect of this is that the energy necessary to bind the nucleus, scaled back onto average per nucleon, increases with atomic mass up to the nickel and iron elements, which are very stable, then declines again for more voluminous nuclei. Fission of larger nuclei thus occurs relatively easily, since they can be destabilized by a small shock. For fusion, the potential barrier to overcome is smallest for hydrogen isotopes containing only one proton. Hydrogen exists in three forms: <<<normal>>> hydrogen, made up of a single proton around which an electron spins; deuterium, or heavy hydrogen; and tritium. The simplest fusion reaction, then, is the combination of hydrogen and deuterium to form tritium and an isolated proton. Even though it is the simplest, it requires temperatures of 800 million Kelvin to initiate it (hence why tritium is so rare). Fusion reactors On Earth, physicists are trying to reproduce these extreme conditions in fusion reactors to generate power. But they are still decades away from succeeding. Even the most advanced fusion reactors consume more energy than they generate, with a difference of several orders of magnitude. Fusion energy is the Holy Grail of energy generation. Compared to their fission counterparts, fusion reactors are relatively clean and, were they to function, would be much more efficient. Very few atoms are needed to generate large amount of energy (according to Einstein's equation, $E=mc^2$ ), there is very little waste and nothing as bad as the heavy elements coming out of fission reactors. Fusion also does not produce any greenhouse gases, which holds out the prospect for a dependable and independent sources of energy, provided one can produce its fuel - hydrogen and deuterium. Fusion is not perfect, though: it does produce some radioactive elements, such as neutrons, that must be eliminated. ### Chronologie | Dates | Events | | ----------- | ----------- | | 1920 | Eddington applies the idea of fusion to celestial bodies | | 1932 | Hydrogen Fusion achieved in the lab | | 1939 | Hans Bethe decribes the fusion process in the stars | | 1946-1954 | Fred Hoyle explains the element synthesis | | 1957 | Burbidge, Burbidge, Fowler et Hoyle publish an article on nucleosynthesis | *** ### 142 | atomes atomisés La fusion froide In 1989, the scientific world was rocked by a controversial announcement. Martin Fleischmann and Stanley Pons announced that they had achieved nuclear fusion not in a vast reactor but in a test tube. By running an electrical current through heavy water (water in which the hydrogen atoms are replaces by deuterium), the two colleagues thought they had generated energy through <<<cold>>> fusion. For them, their experiment delivered more energy than it consumed, thanks to fusion. This sowed confusion. Most scientists thought that Fleischmann and Pons had made a mistake in their energy balance, but, even today, the question is unresolved. Other announcements of fusion achieved in the lab have emerged from time to time. In 2002, Rudi Taleyarkhan suggested that fusion might be behind the phenomenon of sonoluminescence, in which bubbles in a fluid emit light when stimulated with ultrasound. The jury is still out as to whether fusion may be achieved in a beaker. At very high temperatures, the main difficulty is controlling the burning gases even when fusion has been sucessdully achived. These enormous machines only work during certain seconds aligned. To overcome a new technological barrier, an international group of scientists collaborate to construct even bigger fusion machines, located in Cadarache in the south of France, these machine is called "International Thermonuclear Experimental Reactor (ITER)", witch will allow the future test of the comercial feasibility of fusion. Poussière d'étoile. The stars are the fusion reactors of nature. The physicist german hans bethe described the mechanism as how their light is generate from the tranformation of hydrogen elements on héluim. Some paricals such as "Positrons and neutrinos can appear during the reaction, some protons are transfromed into neutrons. The core of the stars, the elements are built up one after the other, cooked by fusion according to a precise recipe. Ever larger nuclei are formed, in a succession of combustions. First, hydrogen, then helium, then elements lighter than iron and, lastly, the heavier elements. Stars like the Sun shine above all thanks to the hydrogen that they fuse into helium at a rhythm slow enough that the heavy elements are not produced except in small quantities. In heavier stars, the presence of elements such as carbon, nitrogen and oxygen accelerates the reaction. The heavy elements are then produced more quickly. As soon as helium is present, carbon can be synthesized (three helium-4 atoms fuse, yielding beryllium-8, unstable). Once carbon has been synthesized. It can combine with helium to form oxygen, neon and magnesium. These slow transformations occupy most of a star's life. The heavy elements, such as iron, are synthesized in slightly different reactions, and we little by little amount to the whole sequence of nuclei in the periodic table. Premières étoiles The first light elements were not synthesized in stars but in the confines of the beginning. Initially the begining of the universe was hot, ever atomes were not stable. As it's cold, hydrogen appeared, with some traves of helium and lithium and some quantity of beryllium, as the primordial ingridients, the harders elements were sinthitized around stars and disperzed through space during explosions called in the name supernovæ. However, you do not see any thing that can the first starts in the Universe. The first do not take any elements with the hydrogen the cooling process was impossible to collaspe itself and to light a motor of fusion. The gravitational forces, that means be able to harvest here below the considerable power of stars. « Nous somi des fragments d'une étoile qu s'est refroidie par hasard, des fragments d'une étoile ra Sir Arthur Eddington, » entraîne le réchauffement et l'expansion de l'hydrogène gazeux. Les éléments lourds peuvent l'aider à se refroidir, si bien qu'après la première génération d'étoiles, les autres défier les théoriciens. sont faciles à construire. Mais la formation de la première d'entre ellles continue de La fusion est une source d'énergie fondamentale de l'univers. Si nous pouvions la idea Possibility of the stars Please let me know of there's anything else I can help with!