Answer:
The alpha process, also known as the alpha ladder, is one of two classes of nuclear fusion reactions by which stars convert
helium into heavier elements, the other being the triple-alpha process.
[1] The triple-alpha process consumes only helium, and
produces carbon. After enough carbon has accumulated, the reactions below take place, all consuming only helium and the
product of the previous reaction.
E is the energy produced by the reaction, released primarily as gamma rays (γ).
It is a common misconception that the above sequence ends at (or , which is a decay product of
[2]
) because it is
the most stable nuclide - i.e., it has the highest nuclear binding energy per nucleon, and production of heavier nuclei requires
energy (is endothermic) instead of releasing it (exothermic). (Nickel-62) is actually the most stable nuclide.
[3] However, the
sequence ends at because conditions in the stellar interior cause the competition between photodisintegration and the alpha
process to favor photodisintegration around iron,
[2][4]
leading to more being produced than .
All these reactions have a very low rate at the temperatures and densities in stars and therefore do not contribute significantly to a
star's energy production; with elements heavier than neon (atomic number > 10), they occur even less easily due to the increasing
Coulomb barrier.
Alpha process elements (or alpha elements) are so-called since their most abundant isotopes are integer multiples of four, the
mass of the helium nucleus (the alpha particle); these isotopes are known as alpha nuclides. Stable alpha elements are: C, O, Ne,
Mg, Si, and S; Ar and Ca are observationally stable. They are synthesized by alpha capture prior to the silicon fusing process, a
precursor to Type II supernovae. Silicon and calcium are purely alpha process elements. Magnesium can be burned by proton
capture reactions. As for oxygen, some authors consider it an alpha element, while others do not. Oxygen is surely an alpha
element in low-metallicity population II stars. It is produced in Type II supernovas and its enhancement is well correlated with an
enhancement of other alpha process elements. Sometimes carbon and nitrogen are considered alpha process elements, since they
are synthesized in nuclear alpha-capture reactions.
The abundance of alpha elements in stars is usually expressed in a logarithmic manner:
,
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Answers & Comments
Answer:
The alpha process, also known as the alpha ladder, is one of two classes of nuclear fusion reactions by which stars convert
helium into heavier elements, the other being the triple-alpha process.
[1] The triple-alpha process consumes only helium, and
produces carbon. After enough carbon has accumulated, the reactions below take place, all consuming only helium and the
product of the previous reaction.
E is the energy produced by the reaction, released primarily as gamma rays (γ).
It is a common misconception that the above sequence ends at (or , which is a decay product of
[2]
) because it is
the most stable nuclide - i.e., it has the highest nuclear binding energy per nucleon, and production of heavier nuclei requires
energy (is endothermic) instead of releasing it (exothermic). (Nickel-62) is actually the most stable nuclide.
[3] However, the
sequence ends at because conditions in the stellar interior cause the competition between photodisintegration and the alpha
process to favor photodisintegration around iron,
[2][4]
leading to more being produced than .
All these reactions have a very low rate at the temperatures and densities in stars and therefore do not contribute significantly to a
star's energy production; with elements heavier than neon (atomic number > 10), they occur even less easily due to the increasing
Coulomb barrier.
Alpha process elements (or alpha elements) are so-called since their most abundant isotopes are integer multiples of four, the
mass of the helium nucleus (the alpha particle); these isotopes are known as alpha nuclides. Stable alpha elements are: C, O, Ne,
Mg, Si, and S; Ar and Ca are observationally stable. They are synthesized by alpha capture prior to the silicon fusing process, a
precursor to Type II supernovae. Silicon and calcium are purely alpha process elements. Magnesium can be burned by proton
capture reactions. As for oxygen, some authors consider it an alpha element, while others do not. Oxygen is surely an alpha
element in low-metallicity population II stars. It is produced in Type II supernovas and its enhancement is well correlated with an
enhancement of other alpha process elements. Sometimes carbon and nitrogen are considered alpha process elements, since they
are synthesized in nuclear alpha-capture reactions.
The abundance of alpha elements in stars is usually expressed in a logarithmic manner:
,