Overview of the Triple-alpha process.

The triple alpha process is a set of nuclear fusion reactions by which three helium nuclei (alpha particles) are transformed into carbon. In Physics and Nuclear chemistry, nuclear fusion is the process by which multiple- like charged atomic nuclei join together to form a heavier nucleus Helium ( He) is a colorless odorless tasteless non-toxic Inert Monatomic Chemical Alpha particles (named after and denoted by the first letter in the Greek alphabet, α consist of two Protons and two Neutrons bound together into a Carbon (kɑɹbən is a Chemical element with the symbol C and its Atomic number is 6 ^[1][2]

Older stars start to accumulate helium produced by the proton-proton chain reaction and the carbon-nitrogen-oxygen cycle in their cores. Helium ( He) is a colorless odorless tasteless non-toxic Inert Monatomic Chemical The proton-proton chain reaction is one of several fusion reactions by which Stars convert Hydrogen to Helium, the primary alternative being the The CNO cycle (for Carbon - Nitrogen - Oxygen) or sometimes Bethe-Weizsäcker-cycle, is one of two sets of fusion reactions The products of further nuclear fusion reactions of helium with hydrogen or another helium nucleus (isotopes with mass number 5 or 8 respectively) are highly unstable and decay almost instantly back into smaller nuclei. When the star starts to run out of hydrogen to fuse, the core of the star starts to collapse until the central temperature rises to ~100×10⁶ K. At this point helium nuclei are fusing together at a rate fast enough to rival the speed at which the product, Beryllium-8, decays back into two helium nuclei. This means that there are always a few Beryllium-8 nuclei in the core, which can fuse with yet another helium nuclei to form Carbon-12, which is stable:

He

+

He

→

Be

Be

+

He

→

C

+

γ

+

7. Helium ( He) is a colorless odorless tasteless non-toxic Inert Monatomic Chemical Helium ( He) is a colorless odorless tasteless non-toxic Inert Monatomic Chemical Helium ( He) is a colorless odorless tasteless non-toxic Inert Monatomic Chemical Helium ( He) is a colorless odorless tasteless non-toxic Inert Monatomic Chemical Although Beryllium ( Be) has multiple Isotopes, only one of these isotopes is stable as such it is considered a monoisotopic element Beryllium (bəˈrɪliəm is a Chemical element with the symbol Be and Atomic number 4 Although Beryllium ( Be) has multiple Isotopes, only one of these isotopes is stable as such it is considered a monoisotopic element Beryllium (bəˈrɪliəm is a Chemical element with the symbol Be and Atomic number 4 Helium ( He) is a colorless odorless tasteless non-toxic Inert Monatomic Chemical Helium ( He) is a colorless odorless tasteless non-toxic Inert Monatomic Chemical Carbon-12 is the most abundant of the two stable Isotopes of the element Carbon, accounting for 98 Carbon (kɑɹbən is a Chemical element with the symbol C and its Atomic number is 6 Gamma rays (denoted as &gamma) are a form of Electromagnetic radiation or light emission of frequencies produced by sub-atomic particle interactions 367

MeV

The net energy release of the process is 7. 275 MeV.

Because the triple-alpha process is unlikely, it requires a long period of time to produce carbon. One consequence of this is that no carbon was produced in the Big Bang because within minutes after the Big Bang, the temperature fell below that necessary for nuclear fusion. The Big Bang is the cosmological model of the Universe that is best supported by all lines of scientific evidence and Observation. The Big Bang is the cosmological model of the Universe that is best supported by all lines of scientific evidence and Observation.

Ordinarily, the probability of the triple alpha process would be extremely small. However, the beryllium-8 ground state has almost exactly the energy of two alpha particles. In the second step, ⁸Be + ⁴He has almost exactly the energy of an excited state of ¹²C. These resonances greatly increase the probability that an incoming alpha particle will combine with beryllium-8 to form carbon. In Physics, resonance is the tendency of a system to Oscillate at maximum Amplitude at certain frequencies, known as the system's The existence of this resonance was predicted by Fred Hoyle before its actual observation, based on the physical necessity for it to exist, in order for carbon to be formed in stars. Sir Fred Hoyle FRS ( 24 June, 1915  &ndash 20 August, 2001) was an English Astronomer primarily In turn, prediction and then discovery of this energy resonance and process gave very significant support to Hoyle's hypothesis of stellar nucleosynthesis, which posited that all chemical elements had originally been formed from hydrogen, the true primordial substance. Stellar nucleosynthesis is the collective term for the nuclear reactions taking place in Stars to build the nuclei of the heavier elements.

As a side effect of the process, some carbon nuclei can fuse with additional helium to produce a stable isotope of oxygen and release energy:

C

+

He

→

O

+

γ

See alpha process for more details about this reaction and further steps in the chain of stellar nucleosynthesis. Carbon-12 is the most abundant of the two stable Isotopes of the element Carbon, accounting for 98 Carbon (kɑɹbən is a Chemical element with the symbol C and its Atomic number is 6 Helium ( He) is a colorless odorless tasteless non-toxic Inert Monatomic Chemical Helium ( He) is a colorless odorless tasteless non-toxic Inert Monatomic Chemical There are three stable isotopes of oxygen that lead to Oxygen ( O) having a standard atomic mass of 15 Oxygen (from the Greek roots ὀξύς (oxys (acid literally "sharp" from the taste of acids and -γενής (-genēs (producer literally begetteris the Gamma rays (denoted as &gamma) are a form of Electromagnetic radiation or light emission of frequencies produced by sub-atomic particle interactions The Alpha process (or alpha reactions) is one of two classes of Nuclear fusion reactions by which stars convert helium into heavier elements the other being the

This creates a situation in which stellar nucleosynthesis produces large amounts of carbon and oxygen but only a small fraction of these elements is converted into neon and heavier elements. Both oxygen and carbon make up the 'ash' of helium burning. Helium fusion is a kind of Nuclear fusion, with the nuclei involved being Helium. The anthropic principle has been controversially cited to explain the fact that nuclear resonances are sensitively arranged to create large amounts of carbon and oxygen in the universe. In Physics and Cosmology, the anthropic principle states that humans should take into account the constraints that human existence imposes on the kind of theoretical

Fusion processes produce elements only up to iron; heavier elements (those beyond Fe) are created mainly by neutron capture. Iron (ˈаɪɚn is a Chemical element with the symbol Fe (ferrum and Atomic number 26 The slow capture of neutrons, the S-process, produces about half of these heavy elements. The S-process or slow-neutron -capture-process is a Nucleosynthesis process that occurs at relatively low neutron density and intermediate temperature conditions in The other half are produced by rapid neutron capture, the R-process, which probably occurs in a core-collapse supernova. The r-process is a Nucleosynthesis process occurring in core-collapse Supernovae (see also Supernova nucleosynthesis) responsible for the creation of approximately A supernova (plural supernovae or supernovas) is a stellar Explosion.

Reaction Rate and Stellar Evolution

The triple-alpha process is strongly dependent on the temperature and density of the stellar material. The energy released by the reaction is approximately proportional to the temperature to the 30th power, and the density squared. Contrast this to the PP chain which produces energy at a rate proportional to the fourth power of temperature and directly with density.

This strong temperature dependence has consequences for the late stage of stellar evolution, the red giant stage. A red giant is a luminous Giant star of low or intermediate mass (roughly 0

For lower mass stars, the helium accumulating in the core is prevented from further collapse only by electron degeneracy pressure. Degenerate matter is matter which has sufficiently high Density that the dominant contribution to its Pressure rises from the Pauli Exclusion The pressure in the core is thus nearly independent of temperature. A consequence of this is that once a smaller star begins burning using the triple-alpha process, the core does not expand and cool in response; the temperature can only increase, which results in the reaction rate increasing further still and becoming a runaway reaction. Thermal runaway refers to a situation where an increase in temperature changes the conditions in a way that causes a further increase in temperature leading to a destructive result This process, known as the helium flash, lasts only for minutes but burns 60-80% of the helium in the core and produces prodigious quantities of energy. A helium flash is the sudden beginning of Helium fusion in the core of intermediate mass Stars of less than about 2

For higher mass stars, the helium burning occurs in a shell surrounding a degenerate carbon core. Since the helium shell is not degenerate, the increased thermal pressure due to energy released by helium burning causes the star to expand. The expansion cools the helium layer and shuts off the reaction, and the star contracts again. This cyclical process causes the star to become strongly variable, and results in it blowing off material from its outer layers.

Discovery

The triple alpha process is highly dependent on carbon-12 having a resonance with the same energy as helium-4 and beryllium-8, and before 1952 no such energy level was known. Astrophysicist Fred Hoyle used the fact that carbon-12 is abundant in the universe as evidence for the existence of the carbon-12 resonance, in what is arguably the only case of success of the application of the Anthropic Principle: we are here, and we are made of carbon, so carbon must have originated somehow and the only physically conceivable way is through triple alpha processes that requires the existence of a resonance in a given very specific location in the spectra of carbon-12 nuclei. Sir Fred Hoyle FRS ( 24 June, 1915  &ndash 20 August, 2001) was an English Astronomer primarily In Physics and Cosmology, the anthropic principle states that humans should take into account the constraints that human existence imposes on the kind of theoretical Hoyle suggested the idea to nuclear physicist William (Willy) A. Fowler, who conceded that it was possible that this energy level had been missed in previous work. William Alfred "Willie" Fowler ( August 9, 1911 &ndash March 14, 1995) was an American Astrophysicist. After a brief undertaking by his research group at the Kellogg Radiation Laboratory at the California Institute of Technology, they discovered a carbon-12 resonance near 7. The California Institute of Technology (commonly referred to as Caltech) is a private, Coeducational research university located in Pasadena 65 Mev.

See also

• Proton-proton chain
• CNO cycle

References

1. ^ Editors Appenzeller, Harwit, Kippenhahn, Strittmatter, & Trimble (3rd Edition). The proton-proton chain reaction is one of several fusion reactions by which Stars convert Hydrogen to Helium, the primary alternative being the The CNO cycle (for Carbon - Nitrogen - Oxygen) or sometimes Bethe-Weizsäcker-cycle, is one of two sets of fusion reactions Astrophysics Library. Springer, New York. ISBN.  
2. ^ Ostlie, D. A. & Carroll, B. W. (2007). An Introduction to Modern Stellar Astrophysics. Addison Wesley, San Francisco. ISBN 0-8053-0348-0.