![]() ![]() 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. A large, exploding star or supernova releases the energy needed to fuse all of the heavier elements.In a nuclear fusion reaction, two or more small light nuclei come together, or fuse. form a larger nucleus. It was from the energy of other explosions. For element heavier than iron, fusion requires energy. The total mass of the helium nucleus is less than the sum of the mass of the 4 particles that make it up.Īdding additional protons and neutrons to iron doesn't release energy because the binding energy peaks at this element. A MeV is equal to 1.602 x 10 -13 joules.Īnother way to think of the energy released by fusion is to look at the change in mass. This is the same amount of energy that is required to break them apart.Įnergy in this table is reported in units of MeV or mega-electron volts. The nuclear binding energy for H-1, a proton, is zero because there is only one particle in the nucleus.Īs the number of particles in the nucleus increases, energy is released. The protons and neutrons are held together through a type of energy called nuclear binding energy. In going from hydrogen to iron, energy is released as nuclei fuse to make bigger ones. This promotes the fusion of heavier and heavier elements, ultimately forming all the elements up to iron. As the hydrogen is used up, the core of the star condenses and heats up even more. The fusion of hydrogen nuclei uses up hydrogen to produce helium and energy. Two He-3 nuclei can fuse to make a nucleus of an unstable beryllium nucleus (Be-6) that breaks apart to give He-4 and two protons. ![]() The deuterium nuclei can merge to form a helium nuclei (He-4), or they can interact with other protons to make another isotope of helium (He-3). Under these conditions protons (H-1) react with other protons to make deuterium nuclei (H-2) and positrons. That is, the electrons separate from the nuclei to give a mix of positively charged ions and electrons. At this temperature, the hydrogen and helium gases become a plasma. The density of gas in the core of our sun is 160 g/cm 3, much higher than the densest metal, and the temperature is 15,000,000 K (27 million degrees Fahrenheit). In the core of a star, gravity produces high density and high temperature. Isotopes of an element all have the same number of protons but different numbers of neutrons. Each element has a particular number of protons in the nucleus. This produced energy, the heat and light of the stars.įusion a type of nuclear reaction where two nuclei come together to form the nucleus of a different element. The gravitational force at the core brought the matter closer and closer together until some of the nuclei coalesced. Swirls of hydrogen and helium gas condensed into huge clouds.
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