Research to enable appropriate conditions for these reactions has focused on magnetic and laser inertial confinement. More promising terrestrial fusion schemes are actually the deuterium-deuterium and deuterium-tritium reactions, with those reactions being 10 24 times more reactive than standard hydrogen and easier to contain than the proton-proton chain. ![]() The temperatures required are ~6x greater than in the core of the sun, which far exceeds the capabilities of known materials. However, gravity on Earth is much lower, meaning much larger energies (temperatures) are required to force the nuclei close enough to combine. Within stars, gravity greatly increases the density such that relatively low energies (often given as temperatures) are required to surpass the electrostatic repulsion between the same-charged nuclei. Some other sets of reactions which produce helium from hydrogen are deuterium-deuterium, where 2 deuterium combine to form a helium-3 and a free neutron and deuterium-tritium, where one deuterium and one tritium combine into a single helium and a free neutron (tritium = hydrogen isotope with 2 neutrons in the nucleus).Īs a slight extension of the answer, a primary difficulty in using the proton-proton chain for producing power from fusion on Earth is getting the charged nuclei close enough together to fuse. This page describes two other paths which occur after Step 2, but with less frequency. Step 4: The Be-6 atom, which is unstable, breaks apart into a stable helium atom and 2 protons Be-6 -> He + 2H+ + released energy. (6 because 4 protons + 2 neutrons = 6 nucleons). Step 3: The two He-3 atoms combine to form a single beryllium-6 atom He-3 + He-3 -> Be-6 + released energy. This alternate step seems to be less likely than the "main" Step 2 simply because the number of free protons is much greater than the number of deuterium atoms, such that the "deuterium + proton" reaction occurs more frequently. Step 2 alternate: The 2 deuteriums combine to form a single, stable He-4 (He with 2 protons + 2 neutrons, the most stable isotope), and released energy. Thus, these are called He-3 atoms (3 because the nucleus has 2 protons + 1 neutron = 3 nucleons). Note that while each produced He has 2 protons in its nucleus (as they must, since the number of protons dictates the element), each has only 1 neutron in its nucleus instead of the 2 in the most stable isotope of He. Step 2: Each deuterium atom combines with another proton to form a helium-3 atom 2 deuterium + 2H+ -> 2He (+ released energy). Tracking all of the particles involved: 4H+ -> 2 deuterium + 2 positrons ( Deuterium = hydrogen with a nucleus of one proton and one neutron instead of only a single proton positrons are essentially positive electrons. Step 1: Two pairs of protons combine to form two deuterium atoms (+ released energy and 2 positrons). This sequence starts from the most common isotope of hydrogen ( H with a nucleus of only a single proton) and results in stable helium nuclei ( 2 protons + 2 neutrons). Multiple sets of reactions can lead from hydrogen to helium, but the most common sequence, occurring in stars, is called a proton-proton chain. The general process of combining atomic nuclei is called, straightforwardly, nuclear fusion. This process creates huge nuclear energy which powers the entire solar system, and it is where the solar neutrinos come from. This is precisely the fusion process that happens in the sun. Notice that the nuclear force ties the protons and neutrons together, and it is much stronger than the Coulomb repulsion at very small distance. ![]() With high speed the protons can collide with each other so strongly that their distance can become small enough to allow the nuclear force to dominate the Coulomb repulsion. Hence this process only happens when the protons travel randomly with very high speed. It is actually not so easy for this fusion process to happen, precisely because all the protons carry the same charge, and same charges will repel each other due to Coulomb repulsion. Indeed, the neutrino was detected much later in history. This process also has a bonus effect: in addition to positron, it also emits one neutrino, which carries no mass or charge, so it is harder to detect. ![]() So when one proton becomes a neutron, it needs to emit a positron which also carries charge +1. The main difference between proton and neutron is that, proton carries charge +1, while neutron carry charge zero. We can "fuse" four hydrogen nuclei into one helium nucleus, which means that we need to convert two of the four protons into two neutrons. Through what process does hydrogen nuclei form a helium nucleus?Ī hydrogen nucleus has one proton and a helium nucleus has two protons and two neutrons.
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