Textbook content produced by OpenStax is licensed under a Creative Commons Attribution License. Use the information below to generate a citation. Then you must include on every digital page view the following attribution: If you are redistributing all or part of this book in a digital format, Then you must include on every physical page the following attribution: If you are redistributing all or part of this book in a print format, Want to cite, share, or modify this book? This book uses the The decrease in mass for the fusion reaction is. ![]() This value is divided by the original mass of the Sun to determine the percentage of the Sun’s mass that has been lost when the hydrogen fuel is depleted. Multiplying this rate by five billion years gives the total mass lost by the Sun. If the mass loss per fusion reaction is known, the mass loss rate is known. If we know the energy released in each fusion reaction, we can determine the rate of the fusion reactions. The total energy output per second is given in the problem statement. By what percentage will the mass of the Sun have decreased from its present value when the core is depleted of hydrogen? (a) How many of these fusion reactions per second must occur to supply the power radiated by the Sun? (b) What is the rate at which the mass of the Sun decreases? (c) In about five billion years, the central core of the Sun will be depleted of hydrogen. This energy is transmitted outward by the processes of convection and radiation. Most of this energy is produced in the Sun’s core by the proton-proton chain. The power output of the Sun is approximately 3.8 × 10 26 J / s. Thus, stars are “factories” for the chemical elements, and many of the atoms in our bodies were once a part of stars. The new generation of stars begins the nucleosynthesis process anew, with a higher percentage of heavier elements. Recent images from the Hubble Space Telescope provide a glimpse of this magnificent process taking place in the constellation Serpens ( Figure 10.24). Supernovae and the formation of planetary nebulas together play a major role in the dispersal of chemical elements into space.Įventually, much of the material lost by stars is pulled together through the gravitational force, and it condenses into a new generation of stars and accompanying planets. These elements, along with much of the star, are ejected into space by the explosion. In fission weapons, a mass of fissile material (uranium highly enriched in U-235 or plutonium-239) is assembled into a supercritical mass either by shooting one piece of subcritical material into another (the gun method) or by compressing a subcritical sphere of material to a much higher density (the implosion method. During this event, the flood of energetic neutrons reacts with iron and the other nuclei to produce elements heavier than iron. The luminosity of the star can increase temporarily to nearly that of an entire galaxy. Expanding shock waves generated within the star due to the collapse cause the star to quickly explode. This process heats the core to a temperature on the order of 5 × 10 9 K. Lacking an outward pressure from fusion reactions, the star begins to contract due to gravity. ![]() Hence, nuclear energy cannot be generated in an iron-rich core. Now, iron has the peculiar property that any fusion or fission reaction involving the iron nucleus is endothermic, meaning that energy is absorbed rather than produced. ![]() ![]() Nucleosynthesis continues until the core is primarily iron-nickel metal. Nuclear fusion can release more energy than nuclear fission, especially when fusing small nuclei like hydrogen and helium into bigger nuclei.6 12 C + 6 12 C → 11 23 N a + 1 1 H, 6 12 C + 6 12 C → 12 24 M g + γ, 6 12 C + 8 16 O → 14 28 S i + γ.
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