![]() The solar neutrinos in equation 1 had an energy (less than 0.42 MeV) that was too low to be detected by this experiment however, subsequent processes produced higher energy neutrinos that Davis’s experiment could detect. The first experiment designed to detect solar neutrinos was built in the 1960s by American scientist Raymond Davis (for which he won the Nobel Prize for Physics in 2002) and carried out deep underground in the Homestake gold mine in Lead, South Dakota, U.S. This produces a flux of 8 × 10 10 neutrinos per square centimetre per second at Earth. Because the nuclei must have enough energy to overcome the electrostatic barrier, the rate of energy production varies as the fourth power of the temperature.Įquation 1 shows that for every two hydrogen atoms converted, one neutrino of average energy 0.26 MeV carrying 1.3 percent of the total energy released is produced. The energy is carried off by gamma-ray photons (γ) and neutrinos, ν. The net result is that four hydrogen atoms are fused into one helium atom. Subsequent encounters (listed on the second and third lines) proceed much faster: the deuteron encounters one of the ubiquitous protons to produce helium-3 ( 3He), and these in turn form helium-4 ( 4He). ![]() While this is a rare event, hydrogen atoms are so numerous that it is the main solar energy source. This is shown symbolically on the first line of equation 1, in which e − is an electron and ν is a subatomic particle known as a neutrino. (Nuclei are positive and thus repel each other.) Once in some billions of years a given proton ( 1H, in which the superscript represents the mass of the isotope) is close enough to another to undergo a process called inverse beta decay, in which one proton becomes a neutron and combines with the second to form a deuteron ( 2D). The process of energy generation results from the enormous pressure and density at the centre of the Sun, which makes it possible for nuclei to overcome electrostatic repulsion. Converting 0.7 percent of the 2 × 10 32 grams of hydrogen into energy that is radiated at 4 × 10 33 ergs per second permits the Sun to shine for 3 × 10 17 seconds, or 10 billion years at the present rate. In only about 10 percent of the Sun are the temperatures high enough to sustain fusion reactions. A calculation of the time required to convert all the hydrogen in the Sun provides an estimate of the length of time for which the Sun can continue to radiate energy. If all the hydrogen is converted, 0.7 percent of the mass becomes energy, according to the Einstein formula E = mc 2, in which E represents the energy, m is the mass, and c is the speed of light. Since one hydrogen atom weighs 1.0078 atomic mass units and a single helium atom weighs 4.0026, the conversion of four hydrogen atoms to one helium atom yields 0.0294 mass unit, which are all converted to energy, 6.8 million electron volts (MeV, 1 MeV = 1.6 × 10 −6 erg), in the form of gamma (γ) rays or the kinetic energy of the products. The Sun is at least 90 percent hydrogen by number of atoms, so the fuel is readily available. The energy radiated by the Sun is produced during the conversion of hydrogen (H) atoms to helium (He). SpaceNext50 Britannica presents SpaceNext50, From the race to the Moon to space stewardship, we explore a wide range of subjects that feed our curiosity about space!Įxplore the physics behind nuclear fusion and the Sun © MinutePhysics ( A Britannica Publishing Partner) See all videos for this article.Learn about the major environmental problems facing our planet and what can be done about them! Saving Earth Britannica Presents Earth’s To-Do List for the 21st Century.Britannica Beyond We’ve created a new place where questions are at the center of learning.100 Women Britannica celebrates the centennial of the Nineteenth Amendment, highlighting suffragists and history-making politicians.COVID-19 Portal While this global health crisis continues to evolve, it can be useful to look to past pandemics to better understand how to respond today.Student Portal Britannica is the ultimate student resource for key school subjects like history, government, literature, and more.From tech to household and wellness products. Britannica Explains In these videos, Britannica explains a variety of topics and answers frequently asked questions.This Time in History In these videos, find out what happened this month (or any month!) in history. ![]() #WTFact Videos In #WTFact Britannica shares some of the most bizarre facts we can find. ![]()
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