Some of the being studied are We described the first reaction in Example 45-14 two deuterons fuse to form a and a proton. In another, using inertial confinement, of the material to be fused are heated by a high-intensity laser beam. In one kind of experiment using magnetic confinement, a heated to extremely high temperature by an electrical discharge, while being con by appropriately shaped magnetic fields. At the mentioned, light atoms are fully ionized, and the resulting state of m called a plasma. At these temperatures the fusion reactions are thermonuclear reactions. Intensive efforts are underway in many laboratories to achieve controlled reactions, which potentially represent an enormous new resource of energy. The proton-proton reaction occurs 1.5 x 107 K in the sun, making it an extremely low-probability process but that’s the sun is expected to last so long. The discus of Section 16-4 showed that the average transnational kinetic energy of a gas mol at temperature Tis kT, where k is Boltzmann’s.constant, The temperature at which is equal to E = 0.6 X 10-13 J is determined by the relation.įusion reactions are possible at lower temperatures because the Maxwell-Bolt= distribution function (Section 16-6) gives a small fraction of protons with kinetic much higher than the average value. Atoms have this much energy only at extremely high temperatures. For two protons at this distance, the corresponding potential energy is about 1.2 x 10-13 J or 0.7 MeV this represents the initial kinetic energy that the fusion nuclei must have, for example, 0.6 x 10-13 J each a head-on collision. To do this, they must overcome electrical repulsion of their positive charges. To fuse all its protons and will last only about one fifteenth as long, or 5 x 109 years.įor two nuclei to undergo fusion, they must come together to within the range of nuclear force, typically of the order of 2 x 10-15 m. We hope that it causes you no anxiety that current models suggest that the sun won’t be able If the sun were to continue to radiate at its present rate, it would take about 75 X 109 years to exhaust its supply of protons. If all of these protons were fused into helium, the energy released would be about 130,000 kWh. Each gram of the sun’s mass contains about 45 x laD protons. The proton-proton chain is believed to take place in the interior of the sun and other stars. We can calculate the energy release from this part of the process: The mass of an a particle plus two positrons is the mass of neutral , the neutrinos have zero (or negligible) mass, and the gammas have zero mass. Mass of four protons The two positrons that are produced during the first step of the proton-proton chain collide with two electrons mutual annihilation of the four particles takes place, and their rest energy is converted into 4(0.511 MeV) = 2.044 MeV of gamma radiation. 45-16). The net effect of the chain is the conversion of four protons into one a particle, two positrons, two electron neutrinos, and two y’s. Together the reactions make up the process called the proton-proton chain (Fig. Now double the first two reactions to provide the two 3He nuclei that fuse in the third reaction to form an alpha particle (‘He) and two protons. In the second, a proton and a deuteron combine to form the nucleus of the light isotope of helium, 3He, with the emission of a gamma ray. In the first reaction, two protons combine to form a deuteron eH), with the emission of a positron (/3) and an electron neutrino. In comparison to fission, we are most figure 45-2, we see that the binding energy per nucleon increases with A to about A = 60, so fusion of nearly any two light nuclei to make a nucleus with A than 60 is likely to be an exothermic reaction. Fusion reactions release energy for the same reason as reactions the binding energy per nucleon after the reaction is greater than Referring to Fig. In a nuclear fusion reaction, two or more small light nuclei come together, or fuse. form a larger nucleus.
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