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| 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]].<ref name=narlikar>{{cite book|last=Narlikar|first=Jayant V|title=From Black Clouds to Black Holes|year=1995|publisher=World Scientific|isbn=9810220332|url=http://books.google.com/books?id=0_gmjz-L70EC&pg=PA94&lpg=PA94&dq=%22alpha+ladder%22+nuclear&source=bl&ots=i3uvgiw3jj&sig=ACoA3xsZJKvj4z9KAdCyu00Zt3A&hl=en&sa=X&ei=GsncUM2ANMrIiwK-qoE4&ved=0CDIQ6AEwAA#v=onepage&q=%22alpha%20ladder%22%20nuclear&f=false}}</ref> | | The author's title is Christy Brookins. The preferred pastime for him and his children is to perform lacross and he would by no means give it up. For a whilst I've been in Alaska but I will have to transfer in a year or two. For many years she's been working as a travel agent.<br><br>Also visit my web blog; tarot readings ([http://videonews.justicenewsflash.com/profile.php?u=ABPEs linked website videonews.justicenewsflash.com]) |
| While the triple-alpha process only requires [[helium]], once some [[carbon]] is present, other reactions that consume helium are possible:
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| :<math>\mathrm{_6^{12}C} + \mathrm{_2^4He} \rightarrow \mathrm{_{8}^{16}O} + \gamma + Q</math>, Q = 7.16 МeV
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| :<math>\mathrm{_8^{16}O} + \mathrm{_2^4He} \rightarrow \mathrm{_{10}^{20}Ne} + \gamma + Q</math>, Q = 4.73 МeV
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| :<math>\mathrm{_{10}^{20}Ne} + \mathrm{_2^4He} \rightarrow \mathrm{_{12}^{24}Mg} + \gamma + Q</math>, Q = 9.31 МeV
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| :<math>\mathrm{_{12}^{24}Mg} + \mathrm{_2^4He} \rightarrow \mathrm{_{14}^{28}Si} + \gamma + Q</math>, Q = 9.98 МeV
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| :<math>\mathrm{_{14}^{28}Si} + \mathrm{_2^4He} \rightarrow \mathrm{_{16}^{32}S} + \gamma + Q</math>, Q = 6.95 МeV
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| :<math>\mathrm{_{16}^{32}S} + \mathrm{_2^4He} \rightarrow \mathrm{_{18}^{36}Ar} + \gamma</math>
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| :<math>\mathrm{_{18}^{36}Ar} + \mathrm{_2^4He} \rightarrow \mathrm{_{20}^{40}Ca} + \gamma</math>
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| :<math>\mathrm{_{20}^{40}Ca} + \mathrm{_2^4He} \rightarrow \mathrm{_{22}^{44}Ti} + \gamma</math>
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| :<math>\mathrm{_{22}^{44}Ti} + \mathrm{_2^4He} \rightarrow \mathrm{_{24}^{48}Cr} + \gamma</math>
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| :<math>\mathrm{_{24}^{48}Cr} + \mathrm{_2^4He} \rightarrow \mathrm{_{26}^{52}Fe} + \gamma</math>
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| :<math>\mathrm{_{26}^{52}Fe} + \mathrm{_2^4He} \rightarrow \mathrm{_{28}^{56}Ni} + \gamma</math>
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| :<math>\mathrm{_{28}^{56}Ni} + \mathrm{_2^4He} + \gamma \rightarrow \mathrm{_{30}^{60}Zn}</math> (energy is consumed and the star's core collapses)
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| All these reactions have a very low rate and therefore do not contribute significantly to the energy production in stars;
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| with elements heavier than [[neon]] ([[atomic number]] > 10) they occur even less easily due to the increasing [[Coulomb barrier]].
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| '''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]]). Alpha elements are [[Atomic number|Z]] ≤ 22: ([[Carbon|C]], [[Nitrogen|N]]), [[Oxygen|O]], [[Neon|Ne]], [[Magnesium|Mg]], [[Silicon|Si]], [[Sulfur|S]], [[Argon|Ar]], [[Calcium|Ca]], [[Titanium|Ti]]. They are synthesized by alpha-capture prior to the [[Silicon burning process|silicon fusing]] process, a precursor to [[Type II supernova]]e. Silicon and calcium are purely alpha process elements. Magnesium can be burned by proton capture reactions. As for oxygen, some authors{{Which?|date=January 2011}} consider it an alpha element, while others do not. Oxygen is surely an alpha element in low [[metallicity]] [[population II star]]s. It is produced in Type II supernovae 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. | |
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| The abundance of alpha elements in stars is usually expressed in a logarithmic manner:
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| :<math> [\alpha/Fe] = \log_{10}{\left(\frac{N_{\alpha}}{N_{Fe}}\right)_{Star}} - \log_{10}{\left(\frac{N_{\alpha}}{N_{Fe}}\right)_{Sun}} </math>,
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| Here <math>N_{\alpha}</math> and <math>N_{Fe}</math> are the number of alpha element and Iron nuclei per unit volume. Theoretical [[Galaxy formation and evolution|galactic evolution]] models predict that early in the universe there were more alpha elements relative to Iron. Type II supernovae mainly synthesize oxygen and the alpha-elements (Ne, Mg, Si, S, Ar, Ca and Ti) while
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| [[Type Ia supernova]]e produce elements of the [[iron peak]] ([[Vanadium|V]], [[Chromium|Cr]], [[Manganese|Mn]], [[Iron|Fe]], [[Cobalt|Co]] and [[Nickel|Ni]]).
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| ==References==
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| {{reflist}}
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| == External links ==
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| * [http://www.citebase.org/abstract?identifier=oai:arXiv.org:0705.4511 The Age, Metallicity and Alpha-Element Abundance of Galactic Globular Clusters from Single Stellar Population Models]
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| {{Nuclear processes}}
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| {{Star}}
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| [[Category:Nuclear fusion]]
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| [[Category:Nucleosynthesis]]
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The author's title is Christy Brookins. The preferred pastime for him and his children is to perform lacross and he would by no means give it up. For a whilst I've been in Alaska but I will have to transfer in a year or two. For many years she's been working as a travel agent.
Also visit my web blog; tarot readings (linked website videonews.justicenewsflash.com)