Sun, nuclear reactions in the

The energy that is released hy a nuclear reaction, such as the nuclear reactions in the Sun, however, can provide enough heat to fry an egg on a sidewalk that is 150 000 000 km away from the surface of the Sun. 

The Sun radiates energy into space at the rate of 3.9 X 10 J/s. (a) Calculate the rate of mass loss from the Sun in kg/s. (b) How does this mass loss arise (c) It is estimated that the Sun contains 9 X 10 free protons. How many protons per second are consumed in nuclear reactions in the Sun ... 

Fig. 3. Comparison between the abundances in the solar photosphere and those in the Cl carbonaceous chondrites. Apart from Li, which is consumed in nuclear reactions in the sun, there is little significant difference in the two data sets. Uncertainties in the solar data for Nb, Lu, W, Os, Oa, Ag, and In are probably responsible for discrepancies for these elements. This diagram forms the basis for the assumption that the Cl carbonaceous chondrites provides us with a sample of the primordial solar nebula, excluding the gaseous elements. [Data are from Anders and Ebihara (1982X and from table 6.]...

The fusion process is the reaction that powers the sun. In a series of nuclear reactions in the sun, four hydrogen-1 (H-1) isotopes are fused into a helium-4 (He-4) with the release of a tremendous amount of energy. Here on Earth, people use two other isotopes of hydrogen H-2, called deuterium, and H-3, called tritium. (Deuterium is a minor isotope of hydrogen, but it s still relatively abundcmt. Tritium doesn t occur naturally, but people can easily produce it by bombarding deuterium with a neutron.)... 

We recognize the nuclear reactions of the sun as the main source of our energy and the crucial role of photosynthesis as the conversion process of solar light into fossil energy carriers and renewable biomass. We also recognize gravitational sources that result in tidal movement and the earth s thermal resources. 

Fig. 5.4. Schematic evolution of the internal structure of a star with 25 times the mass of the Sun. The figure shows the various combustion phases (shaded) and their main products. Between two combustion phases, the stellar core contracts and the central temperature rises. Combustion phases grow ever shorter. Before the explosion, the star has assumed a shell-like structure. The centre is occupied by iron and the outer layer by hydrogen, whilst intermediate elements are located between them. CoUapse followed by rebound from the core generates a shock wave that reignites nuclear reactions in the depths and propels the layers it traverses out into space. The collapsed core cools by neutrino emission to become a neutron star or even a black hole. Most of the gravitational energy liberated by implosion of the core (some 10 erg) is released in about 10 seconds in the form of neutrinos. (Courtesy of Marcel Amould, Universite Libre, Brussels.)...

Indeed, this happens every moment in the Earth s atmosphere. The upper atmosphere is bombarded with cosmic rays fast-moving subatomic particles produced by extremely energetic astrophysical processes such as nuclear fusion in the sun. When cosmic rays hit molecules in the atmosphere, they induce nuclear reactions that spit out neutrons. Some of these neutrons react with nitrogen atoms in air, converting them into a radioactive isotope of carbon carbon-14 or radiocarbon , with eight neutrons in each nucleus. This carbon reacts with oxygen to form carbon dioxide. About one in every million million carbon atoms in atmospheric carbon dioxide is C. 

The nuclear reaction that finally stabilizes the structure of the protostar is the fusion of two protons to form a deuterium atom, a positron, and a neutrino (1 H(p,p+v)2D). This reaction becomes important at a temperature of a few million degrees. The newly produced deuterium then bums to 3He, which in turn bums to 4He in the proton-proton chain. The proton-proton chain is the main source of nuclear energy in the Sun. With the initiation of hydrogen burning... 

The sum of the weight (per mole) of the products is 0.0246 g less than the sum of the weights of the reactants. In the Bethe cycle (the series of reactions in the sun by which solar energy is produced), 4 moles of protons weighing 4.03228 g are converted to 1 mole of helium weighing 4.00336 g, a loss of 0.02892 g. In the nuclear fission of 2jji U,... 

Solar neutrinos, which interact very weakly with matter, should also be produced by the nuclear fusion reactions in the Sun. However, scientist s detect much fewer neutrinos than expected, which may suggest that our knowledge of the solar processes that cause the Sun to shine or of neutrinos themselves is incomplete. 

The lion s share of fluorine is produced by the intense burst of neutrinos that occurs when the Type II supernova core collapses. Although neutrinos interact only infrequently with matter, a tiny fraction of their intense flux during a 10-second burst drives a proton or neutron from the 20Ne nucleus, in either case resulting in 19F. This occurs where both 20Ne and the neutrino flux are most abundant, near the core of the exploding massive star. Much of this 19F is subsequently destroyed by nuclear reactions in the heated gas when the shock wave passes, but enough survives to account for the 19F/2°Ne abundance ratio in the Sun. 

Energy is also released in a type of nuclear reaction that is the opposite of fission. During nuclear fusion, two or more nuclei combine to form a larger nucleus. Fusion is the nuclear process that produces energy in stars like our sun. In the most typical fusion reaction in the sun, hydrogen nuclei fuse to form helium. The enormous amount of energy that is generated sustains all life on Earth. 

Real-World Reading Link On a hot summer day, you step outside and feel the intense heat of the Sun. Nuclear reactions within the Sun release enough energy to warm Earth and other planets in the solar system for billions of years. It is no surprise, then, that scientists are trying to use this same type of nuclear reaction to produce electricity. 

In fact, the sun is not a first-generation main-sequence star since spectroscopic evidence shows the presence of many heavier elements thought to be formed in other types of stars and subsequently distributed throughout the galaxy for eventual accretion into later generations of main-sequence stars. In the presence of heavier elements, particularly carbon and nitrogen, a catalytic sequence of nuclear reactions aids the fusion of protons to helium (H. A. Bethe... 

The composition of the Earth was determined both by the chemical composition of the solar nebula, from which the sun and planets formed, and by the nature of the physical processes that concentrated materials to form planets. The bulk elemental and isotopic composition of the nebula is believed, or usually assumed to be identical to that of the sun. The few exceptions to this include elements and isotopes such as lithium and deuterium that are destroyed in the bulk of the sun s interior by nuclear reactions. The composition of the sun as determined by optical spectroscopy is similar to the majority of stars in our galaxy, and accordingly the relative abundances of the elements in the sun are referred to as "cosmic abundances." Although the cosmic abundance pattern is commonly seen in other stars there are dramatic exceptions, such as stars composed of iron or solid nuclear matter, as in the case with neutron stars. The... 

Our planet Earth contains significant amounts of elements all the way up to Z = 92. This indicates that our solar system resulted from the gravitational collapse of a cloud of matter that included debris from second-generation stellar supemovae. Thus, our sun most likely is a third-generation star. The composition of a third-generation star includes high-Z nuclides, but the nuclear reactions are the same as those in a second-generation star. 

Two smaller nuclei can fuse to form a larger nucleus, in what is called a nuclear fusion reaction. You and all other life on Earth would not exist without nuclear fusion reactions. These reactions are the source of the energy produced in the Sun. 

Helium is also the result of fusion reactions wherein the nuclei of heavy hydrogen are fused to form atoms of hehum. The result is the release of great amounts of energy. Fusion is the physical or nuclear reaction (not chemical reaction) that takes place in the sun and in thermonuclear weapons (e.g., the hydrogen bomb). 

The fact that neutrinos are emitted during this reaction provides an opportunity to observe directly the nuclear reactions taking place in the Sun s core. But its core is like a safe or an urn in which it zealously guards its own ashes. 

Other nuclear reactions. The Sun is powered by nuclear hydrogen burning in the Sun s core ... 

The nuclear reactions in which tighter nuclei fuse together to form a heavier nuclear are called nuclear fusion reactions. Such reactions, occur at very high temperature (of the order of > 10 K) which exist only in the sun or interior of stars therefore, such reactions are also called thermonuclear reactions. 

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