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{{DISPLAYTITLE:Proses ''s''}}
'''Proses s''' atau '''proses penangkapan [[suhu neutron|neutron lambat]]''' adalah sebuah proses [[nukleosintesis]] yang terjadi pada kerapatan neutron yang relatif rendah dan suasana suhu sedang di dalam [[bintang]]. Di bawah suasana ini, laju [[penangkapan neutron]] oleh inti atom adalah relatif lambat dibandingkan laju [[peluruhan beta]]-minus radioaktif. Sebuah isotop stabil menangkap neutron lain; tetapi [[isotop]] radioaktif meluruh ke turunan stabilnya sebelum neutron berikutnya tertangkap. Proses ini menghasilkan isotop-isotop stabil dengan menggeser lembah isobar-isobar stabil peluruhan beta pada [[tabel nuklida]]. Proses s menghasilkan hampir separo isotop [[logam berat|unsur yang lebih berat daripada besi]], dan karenanya memainkan peran penting di dalam evolusi kimia galaktik. Proses s berbeda dari proses r yang mampu menangkap neutron secara lebih cepat.
'''Proses s''' atau '''proses penangkapan [[suhu neutron|neutron lambat]]''' adalah sebuah proses [[nukleosintesis]] yang terjadi pada kerapatan neutron yang relatif rendah dan suasana suhu sedang di dalam [[bintang]]. Di bawah suasana ini, laju [[penangkapan neutron]] oleh inti atom adalah relatif lambat dibandingkan laju [[peluruhan beta]]-minus radioaktif. Sebuah isotop stabil menangkap neutron lain; tetapi [[isotop]] radioaktif meluruh ke turunan stabilnya sebelum neutron berikutnya tertangkap. Proses ini menghasilkan isotop-isotop stabil dengan menggeser lembah isobar-isobar stabil peluruhan beta pada [[tabel nuklida]]. Proses s menghasilkan hampir separo isotop [[logam berat|unsur yang lebih berat daripada besi]], dan karenanya memainkan peran penting di dalam evolusi kimia galaktik. Proses s berbeda dari proses r yang mampu menangkap neutron secara lebih cepat.


Baris 12: Baris 13:
| pages= 547–650
| pages= 547–650
| year= 1957
| year= 1957
| doi= 10.1103/RevModPhys.29.547}}</ref> There it was also argued that the S-process occurs in [[red giant]] stars. In a particularly illustrative case, the element [[technetium]], with a longest half-life of 4.2 million years, had been discovered in S-, M-, and N-type stars in 1952.<ref name=CRC>{{cite book| first= C. R.|last = Hammond |title = The Elements, in Handbook of Chemistry and Physics 81st edition| publisher =CRC press|isbn = 0849304857| year= 2004}}</ref><ref>{{cite journal|doi = 10.1126/science.114.2951.59|pmid = 17782983|year = 1951|last1 = Moore|first1 = CE|title = Technetium in the Sun.|volume = 114|issue = 2951|pages = 59–61|journal = Science (New York, N.Y.)}}</ref>. Since these stars were thought to be billions of years old, the presence of technetium in their outer atmospheres was taken as evidence of its recent creation there, unconnected with events in the deep interior of the star in the region of active fusion, or events in the star's early history billions of years in the past.
| doi= 10.1103/RevModPhys.29.547}}</ref> There it was also argued that the S-process occurs in [[red giant]] stars. In a particularly illustrative case, the element [[technetium]], with a longest half-life of 4.2 million years, had been discovered in S-, M-, and N-type stars in 1952.<ref name=CRC>{{cite book| first= C. R.|last = Hammond |title = The Elements, in Handbook of Chemistry and Physics 81st edition| publisher =CRC press|isbn = 0849304857| year= 2004}}</ref><ref>{{cite journal|doi = 10.1126/science.114.2951.59|pmid = 17782983|year = 1951|last1 = Moore|first1 = CE|title = Technetium in the Sun.|volume = 114|issue = 2951|pages = 59–61|journal = Science (New York, N.Y.)}}</ref>. Since these stars were thought to be billions of years old, the presence of technetium in their outer atmospheres was taken as evidence of its recent creation there, unconnected with events in the deep interior of the star in the region of active fusion, or events in the star's early history billions of years in the past.


A calculable model for creating the heavy isotopes from iron seed nuclei in a time-dependent manner was not provided until 1961.<ref>{{cite journal
A calculable model for creating the heavy isotopes from iron seed nuclei in a time-dependent manner was not provided until 1961.<ref>{{cite journal
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== Proses s pada bintang ==
== Referensi ==
{{reflist}}
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The S-process is believed to occur mostly in [[Asymptotic Giant Branch]] stars. In contrast to the R-process which is believed to occur over time scales of seconds in explosive environments, the S-process is believed to occur over time scales of thousands of years. The extent to which the s-process moves up the elements in the chart of isotopes to higher [[mass number]]s is essentially determined by the degree to which the star in question is able to produce [[neutron]]s, and by the amount of iron in the star's initial abundance distribution. [[Iron]] is the "starting material" (or seed) for this neutron capture - beta-minus decay sequence of synthesizing new elements.


[[Kategori:Fisika nuklir]]
The main [[neutron source]] reactions are:


Autogenerated using Phykiformulae 0.12 [[User:SkyLined#Phykiformulae]]
C-13 + He-4 -> O-16 + n
Ne-22 + He-4 -> Mg-25 + n
:{| border="0"
|- style="height:2em;"
|{{Nuclide|Link|carbon|13}}&nbsp;||+&nbsp;||{{Nuclide|Link|helium|4}}&nbsp;||→&nbsp;||{{Nuclide|Link|oxygen|16}}&nbsp;||+&nbsp;||{{SubatomicParticle|link=yes|Neutron}}
|- style="height:2em;"
|{{Nuclide|Link|neon|22}}&nbsp;||+&nbsp;||{{Nuclide|Link|helium|4}}&nbsp;||→&nbsp;||{{Nuclide|Link|magnesium|25}}&nbsp;||+&nbsp;||{{SubatomicParticle|link=yes|Neutron}}
|}


[[Image:S-process-elem-Ag-to-Sb.svg|thumb|right|400 px|The S-process acting in the range from [[silver|Ag]] to [[antimony|Sb]].]]

One distinguishes the main and the weak s-process component. The main component produces heavy elements beyond [[Strontium|Sr]] and [[Yttrium|Y]], and up to [[Lead|Pb]] in the lowest metallicity stars. The production site of the main component are low-mass [[Asymptotic Giant Branch]] stars.<ref>{{cite journal
| author= A. I. Boothroyd
| title = Heavy elements in stars
| journal= Science
| volume= 314
| issue= 5806
| year= 2006
| pages= 1690–1691
| doi= 10.1126/science.1136842
| pmid = 17170281}}</ref> The weak component of the S-process, on the other hand, synthesizes [[S-process element|S-process isotopes]] of elements from the iron group up to Sr and Y, and takes place at the end of [[Helium|He]]- and [[Carbon|C]]-burning in massive stars. These stars will become supernovae at their demise and spew those s isotopes into interstellar space.

The S-process is often mathematically treated using the so-called local approximation, which gives a theoretical model of elemental abundances based on the assumption of constant neutron flux in a star, so that the ratio of abundances is inversely proportional to the ratio of neutron-capture cross-sections for different isotopes. This approximation is - as the name indicates - only valid locally, meaning for isotopes of similar mass number.

Because of the relatively low [[neutron flux]]es expected to occur during the S-process (on the order of 10<sup>5</sup> to 10<sup>11</sup> neutrons per cm<sup>2</sup> per second), this process does not have the ability to produce any of the heavy radioactive isotopes such as [[thorium]] or [[uranium]]. The cycle that terminates the S-process is:

{{SimpleNuclide|Link|Bismuth|209}} captures a neutron, producing {{SimpleNuclide|Link|Bismuth|210}}, which decays to {{SimpleNuclide|Link|Polonium|210}} by [[beta decay|β<sup>-</sup> decay]]. {{SimpleNuclide|Link|Polonium|210}} in turn decays to {{SimpleNuclide|Link|Lead|206}} by [[alpha decay|α decay]]:

Autogenerated using Phykiformulae 0.12 [[User:SkyLined#Phykiformulae]]
Bi-209 + n -> Bi-210 + y
Bi-210 _ _ -> Po-210 + e- + !ve
Po-210 _ _ -> Pb-206 + He-4
:{| border="0"
|- style="height:2em;"
|{{Nuclide|Link|bismuth|209}}&nbsp;||+&nbsp;||{{SubatomicParticle|link=yes|Neutron}}&nbsp;||→&nbsp;||{{Nuclide|Link|bismuth|210}}&nbsp;||+&nbsp;||{{SubatomicParticle|link=yes|Gamma}}
|- style="height:2em;"
|{{Nuclide|Link|bismuth|210}}&nbsp;||&nbsp;||&nbsp;||→&nbsp;||{{Nuclide|Link|polonium|210}}&nbsp;||+&nbsp;||{{SubatomicParticle|link=yes|Electron}}&nbsp;||+&nbsp;||{{SubatomicParticle|link=yes|Electron Antineutrino}}
|- style="height:2em;"
|{{Nuclide|Link|polonium|210}}&nbsp;||&nbsp;||&nbsp;||→&nbsp;||{{Nuclide|Link|lead|206}}&nbsp;||+&nbsp;||{{Nuclide|Link|helium|4}}
|}

{{SimpleNuclide|Link|Lead|206}} then captures three neutrons, producing {{SimpleNuclide|Link|Lead|209}}, which decays to {{SimpleNuclide|Link|Bismuth|209}} by β<sup>-</sup> decay, restarting the cycle:

Autogenerated using Phykiformulae 0.12 [[User:SkyLined#Phykiformulae]]
Pb-206 + 3n -> Pb-209
Pb-209 _ _ -> Bi-209 + e- + !ve
:{| border="0"
|- style="height:2em;"
|{{Nuclide|Link|lead|206}}&nbsp;||+&nbsp;||3&nbsp;{{SubatomicParticle|link=yes|Neutron}}&nbsp;||→&nbsp;||{{Nuclide|Link|lead|209}}
|- style="height:2em;"
|{{Nuclide|Link|lead|209}}&nbsp;||&nbsp;||&nbsp;||→&nbsp;||{{Nuclide|Link|bismuth|209}}&nbsp;||+&nbsp;||&nbsp;{{SubatomicParticle|link=yes|Electron}}&nbsp;||+&nbsp;||&nbsp;{{SubatomicParticle|link=yes|Electron Antineutrino}}
|}

The net result of this cycle therefore is that 4 [[neutron]]s are converted into one [[alpha particle]], two [[electron]]s, two anti-electron [[neutrino]]s and [[gamma ray|gamma radiation]]:

Autogenerated using Phykiformulae 0.12 [[User:SkyLined#Phykiformulae]]
4n -> He-4 + 2e + 2!ve + y
:{| border="0"
|- style="height:2em;"
|&nbsp;||&nbsp;||4&nbsp;{{SubatomicParticle|link=yes|Neutron}}&nbsp;||→&nbsp;||{{Nuclide|Link|helium|4}}&nbsp;||+&nbsp;||2&nbsp;{{SubatomicParticle|link=yes|Electron}}&nbsp;||+&nbsp;||2&nbsp;{{SubatomicParticle|link=yes|Electron Antineutrino}}&nbsp;||+&nbsp;||{{SubatomicParticle|link=yes|Gamma}}
|}

The process thus terminates in bismuth, the heaviest "stable" element. (Bismuth is actually slightly radioactive, but with a half-life so long—a billion times the present age of the universe—that it is effectively stable over the life-time of any existing star.)
-->

== Proses s yang terukur pada debu bintang ==
<!--
Stardust is one component of [[cosmic dust]]. Individual solid grains from various long-dead stars that existed before the solar system are found in meteorites, where they have been preserved. The origin of these grains is demonstrated by laboratory measurements of extremely unusual isotopic abundance ratios within the grain. The results give new insight into astrophysics.<ref name="Clayton2004">{{cite journal
| author= D. D. Clayton, L. R. Nittler
| title = Astrophysics with Presolar stardust
| journal= Annual Review of Astronomy and Astrophysics
| volume= 42
| issue= 1
| year= 2004
| pages= 39–78
| doi= 10.1146/annurev.astro.42.053102.134022}}</ref> Silicon-carbide (SiC) grains condense in the atmospheres of AGB stars and thus trap the isotopes of that star. Because the AGB stars are the main site of the S-process in the galaxy, the heavy elements in the SiC grains are virtually pure S-process isotopes. This fact has been demonstrated repeatedly by sputtering-ion mass spectrometer studies of these [[presolar grains]].<ref name="Clayton2004"/> Several surprising results have shown that the ratio of S-process and R-process abundances is somewhat different from that which was previously assumed. It has also been shown with trapped isotopes of krypton and xenon that the S-process abundances in the stellar atmospheres change with time or from star to star, presumably with the strength of neutron fluence or perhaps the temperature. This is a frontier of S-process studies today.
-->
== Referensi ==
{{reflist}}
{{Fisika-stub}}
{{Fisika-stub}}

[[Kategori:Fisika nuklir]]

Revisi terkini sejak 23 Februari 2023 15.47

Proses s atau proses penangkapan neutron lambat adalah sebuah proses nukleosintesis yang terjadi pada kerapatan neutron yang relatif rendah dan suasana suhu sedang di dalam bintang. Di bawah suasana ini, laju penangkapan neutron oleh inti atom adalah relatif lambat dibandingkan laju peluruhan beta-minus radioaktif. Sebuah isotop stabil menangkap neutron lain; tetapi isotop radioaktif meluruh ke turunan stabilnya sebelum neutron berikutnya tertangkap. Proses ini menghasilkan isotop-isotop stabil dengan menggeser lembah isobar-isobar stabil peluruhan beta pada tabel nuklida. Proses s menghasilkan hampir separo isotop unsur yang lebih berat daripada besi, dan karenanya memainkan peran penting di dalam evolusi kimia galaktik. Proses s berbeda dari proses r yang mampu menangkap neutron secara lebih cepat.

Proses s dianggap diperlukan dari kelimpahan relatif isotop unsur-unsur berat dan dari tabel yang baru diterbitkan, yaitu tabel kelimpahan unsur kimia oleh Hans Suess dan Harold Urey pada tahun 1956. Di antara yang lainnya, data ini menunjukkan puncak kelimpahan stronsium, barium, dan timbal, di mana menurut mekanika kuantum dan model cangkang nuklir, khususnya inti-inti atom yang stabil, banyak seperti gas mulia adalah lembam secara kimia. Hal ini menjadi isyarat bahwa beberapa inti atom yang melimpah haruslah tercipta oleh penangkapan neutron lambat, dan ini hanya tentang menentukan inti atom lain yang manakah yang dapat berperan bagi proses itu.

Referensi

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