Triple alpha reaction

Becausethe4He nucleus does not bind to either proton or neutron, it cannot be destroyed by interacting uuth either in stars. Another mechanism, theso-called triple alpha reaction alloius 4He to/use sloiuly into12 C at the cores 0/ red-giant stars. 

Stellar helium burning proceeds by means of the triple-alpha reaction in which three " He nuclei... 

A few informative properties of life come from easy category distinctions, such as the fact that all known life makes essential use of carbon and carbon-oxygen-nitrogen molecules in liquid water solution. The seemingly trivial observation that such carbaquist chemistry is ruled out if astrophysical carbon abundance lies below a certain threshold enabled Hoyle [1] to predict the 7.6 MeV carbon-12 ( C) nuclear resonance with remarkable precision because the discovery of the triple-alpha reaction synthesis of in stars happens to be a bottleneck for stellar nucleosynthesis of all the heavy elements. The pragmatic information in this prediction is easy to measure because it guided experimental characterization of nuclear structure where the existing computational capabilities could not. Similar sensitive dependence of the physical state of water has been used to define a habitable zone in planetary physics [10], which is not predictive in the same sense as carbon abundance (we already knew where the earth s orbit lies), but which creates a useful filter in the search for extraterrestrial life. 

Thus the triple alpha reaction begins with the formation of 8 Be that has a lifetime of only 1 x 10 16 s (this is found from the width / = 6.8 eV of the... 

The triple alpha reaction has a very strong temperature dependence near a value of temperature To, one can show that the energy generation rate is ... 

The product of the triple-alpha reactions 12 C, is burned into 16O by a-capture... 

A cracial aspect of helium burning is that there is no stable mass eight isotope. This means when two He nuclei combine to form a Be nucleus, the Be falls apart quickly into the two He reactants. The consequence is that helium burning must proceed by a three-body reaction. In particular, if the Be nucleus interacts with another He before falling apart, an excited state of C, denoted C, may result. Decay of the excited C nucleus to its ground state then finishes the so-called triple-alpha reaction. The reaction sequence is thus... 

The two-stage nature of the triple-alpha reaction was recognized by Salpeter in the 1950s. Neverttieless, shortly after Salpeter s insight, Sir Fred Hoyle recognized the triple-alpha reaction would be too slow to explain the abundances of the heavy elements unless the reaction Be + He occurred resonantly in stars. Hoyle pointed out that this required a 0 excited state (that is, a state with spin zero and positive parity) in C at 7.6 MeV, and Cook, Fowler, and collaborators demonstrated the existence of this state experimentally (6)- The prediction of the... 

Carbon. Carbon has two stable isotopes, and which have distinct nucleosynthetic origins. The formerj abundant, isotope is produced during He-buming by the triple-alpha reaction ( 3 He + y) whereas requires seed nuclei and hence... 

Because three a-particles combine to form 12C, this process is known as the triple-alpha process. Oxygen-16 is also produced during helium burning through the reaction 12C(a,y)160. 

This is what they thought at first. I m giving you a bit of history here. The reaction of beryllium-8 and helium-4 seemed too slow. There was one chance that the reaction speed could be boosted—if carbon-12 had a very special property an energy almost exactly equal to the combined energy of beryllium-8 and helium-4 at temperatures in a red giant. Chemists called this kind of facilitated nuclear reaction resonant. If by some miracle this were true, then the triple-alpha process could work. ... 

In the primary reaction helium burning, three alpha particles (helium nuclei) are converted to a carbon nucleus, a process sometimes referred to as the triple helium process, or triple alpha particle process ... 

Fig. 11. Triple alpha process of 12C synthesis. In the first step a small amount of sBe nuclei builds up in equilibrium with its decay products (forward and backward reactions involve alpha particles). The second step involves a capture of another alpha particle by the unstable sBe nucleus which proceeds via an s-wave resonance state in the product nucleus 12 C located close to the Gamow energy window for temperatures indicated schematically by the three-way arrows on the right...

The beryllium 8 isotope is produced in the collapse of massive red-giant stars via the triple-alpha process. Initially two helium nuclei—or alpha particles—fuse to form an unstable and very short-lived state of beryllium, as expressed by the following reaction ... 

As shown by Equations (2.25) and (2.26), two He nuclei can fuse together to form Be, which in turn can fuse with another He nucleus to make a nuclide. Because the net reaction involves the fusion of three alpha particles, the first two steps in this mechanism are often called the triple alpha process (Figure 2.16). Because this is a three-body process, the reaction is slow, allowing Red Giant stars to continue to burn for 10 -10 years. Our sun will eventually become a Red Giant, swelling in size to engulf all of the inner planets. 

Carbons alpha to the carbocation will often lose a proton to form a double (or, in some cases) triple bond with the carbocation. Such a reaction requires only a mild base (e g. chloride) to remove the proton. 

Owing to the last experimental and theoretical works in the study of the Orito reaction some insight in the mechanism of the reaction has been gained but full understanding has not yet been achieved. Therefore much more effort is needed in the future, especially in studying the role of the nature of the metal catalysts and the effects of triple intermediate complexes, [Metal-Modifier-Reactant], in enantioselectivity as shown in the case of the enantioselective hydrogenation of alpha-keio esters on tartaric acid modified Ni, Cu, and Co eatalysts... 

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