Plasmas/Plasma objects/Nucleosynthesis

Nucleosynthesis is the process of creating new atomic nuclei from pre-existing nucleons (protons and neutrons).

Examples of solar coronal loops are observed by the Transition Region And Coronal Explorer (TRACE) using the 17.1 nm filter. Credit: NASA.

"A fundamental question in nuclear physics is what combinations of neutrons and protons can make up a nucleus. Many hundreds of exotic neutron-rich isotopes have never been observed; the limit of how many neutrons a given number of protons can bind is unknown for all but the lightest elements¹, owing to the delicate interplay between single particle and collective quantum effects in the nucleus."

"No published theoretical calculation has been able to simultaneously reproduce both the oxygen and fluorine driplines."

Astronucleosynthesis

This picture of the star formation region NGC 3582 was taken using the Wide Field Imager at ESO's La Silla Observatory in Chile. Credit: ESO, Digitized Sky Survey 2 and Joe DePasquale.

The image at right of NGC 3582 reveals giant loops of gas ejected by dying stars that bear a striking resemblance to solar prominences.

Radiation

Main resource: Radiation

Gold "nuclei (the positively charged part of the atom made of protons and neutrons) [are] sent speeding around [the Relativistic Heavy Ion Collider (RHIC)] at near light-speed until they [crash] into each other. When the ions collide, the enormous energy released is so intense it melts the neutrons and protons inside the gold nuclei into [a] nearly friction-free primordial plasma [that] reaches around 7.2 trillion degrees Fahrenheit (4 trillion degrees Celsius)."

Theoretical nucleosynthesis

Def. any of several processes that lead to the synthesis of heavier atomic nuclei is called nucleosynthesis.

Neutrons

Main resources: Charges/Neutrons and Neutrons

The neutron is a subatomic hadron particle which has the symbol n or n⁰
, no net electric charge and a mass slightly larger than that of a proton.

$p^{+}+e^{-}\rightarrow n^{0}+\nu _{e}$

Protons

Main resources: Charges/Protons and Protons

$e^{+}+\nu _{e}+{\bar {\nu }}_{\mu }\to \mu ^{+}$

$e^{+}+e^{-}+\gamma \to \pi ^{0}$

$2\gamma \to \pi ^{0}$

$\mu ^{+}+\pi ^{0}\to p^{+}$

Liquid objects

Main resources: Liquids/Liquid objects and Liquid objects

"[W]e did not at all anticipate the nearly perfect liquid behavior."

"Other physicists have now observed quite similar liquid behavior in trapped atom samples at temperatures near absolute zero, ten million trillion times colder than the quark-gluon plasma we create at RHIC".

Astrochemistry

Main resource: Astrochemistry

These are the known nuclides in chart form. Credit: Brookhaven National Laboratory.

  alpha decay

  stable nuclide

  beta⁺/EC decay

  beta^- decay

  proton decay

  spontaneous fission

  neutron emission

Here the above chart is cut into three sections. Credit: Brookhaven National Laboratory.

A table of nuclides or chart of nuclides is a two-dimensional [Cartesian coordinate system] graph in which one axis represents the number of neutrons and the other represents the number of protons in an atomic nucleus. Each point plotted on the graph thus represents the nuclide of a real or hypothetical chemical element. Hydrogen is at the lower left.

R processes

The more rapid R-process differs from the S-process by its faster rate of neutron capture of more than one neutron before beta-decay takes place.

S processes

Periodic table showing the cosmogenic origin of each element. Credit: Cmglee.

The S-process is indicated acting in the range from Ag to Sb. Credit: Rursus Siderespector.

The s-process or slow-neutron-capture-process is a nucleosynthesis process that occurs at relatively low neutron density and intermediate temperature conditions in stars. Under these conditions heavier nuclei are created by neutron capture, increasing the atomic weight of the nucleus by one. A neutron in the new nucleus decays by beta-minus decay to a proton, creating a nucleus of higher atomic number. The rate of neutron capture by atomic nuclei is slow relative to the rate of radioactive beta-minus decay, hence the name. This process produces stable isotopes by moving along the valley of beta-decay stable isobars in the chart of isotopes. The S-process produces approximately half of the isotopes of the elements heavier than iron, and therefore plays an important role in the galactic chemical evolution.

The elements heavier than iron with origins in large stars are typically those produced by the s-process, which is characterized by slow neutron diffusion and capture over long periods in such stars.

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, passing decades between neutron captures. The extent to which the s-process moves up the elements in the chart of isotopes to higher mass numbers is essentially determined by the degree to which the star in question is able to produce neutrons. The quantitative yield is also proportional to 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.

The weak component of the S-process, on the other hand, synthesizes S-process isotopes of elements from iron group seed nuclei to ⁵⁸Fe on up to Sr and Y, and takes place at the end of helium- and carbon-burning in massive stars. It employs primarily the ²²Ne neutron source. These stars will become supernovae at their demise and spew those s isotopes into interstellar gas.

The S-process is sometimes approximated over a small mass region using the so-called "local approximation", by which the ratio of abundances is inversely proportional to the ratio of neutron-capture cross-sections for nearby isotopes on the s-process path. This approximation is – as the name indicates – only valid locally, meaning for isotopes of nearby mass numbers, but it is invalid at magic numbers where the ledge-precipice structure dominates.

Hydrogens

Main resources: Chemicals/Hydrogens and Hydrogens

¹H(p,β⁺ν)²H

2¹H₁ → ²D₁ + e⁺ + ν_e + γ (0.42 MeV)

At 10-million-kelvin, hydrogen fuses to form helium in the proton-proton chain reaction:

4¹H → 2²H + 2e⁺ + 2ν_e (4.0 MeV + 1.0 MeV)

2¹H + 2²H → 2³He + 2γ (5.5 MeV)

2³He → ⁴He + 2¹H (12.9 MeV)

These reactions result in the overall reaction:

4¹H → ⁴He + 2e⁺ + 2γ + 2ν_e (26.7 MeV)

where e⁺ is a positron, γ is a gamma ray photon, ν_e is a neutrino, and H and He are isotopes of hydrogen and helium, respectively. The energy released by this reaction is in millions of electron volts, which is actually only a tiny amount of energy.

"The light elements deuterium, lithium, beryllium, and boron pose a special problem for any theory of the origin of the elements which proposes that all the elements are built up from hydrogen in the stars. ... The difficulty arises because the lifetimes of these elements against proton capture, at the temperatures and pressures at which most stellar matter exists, are short compared to the stable lifetimes of stars. These elements then cannot be produced in stellar interiors unless they are transported rapidly to the surface, and if they are produced at the surface, non-equilibrium processes must be involved. Further, they can exist in significant quantities at the surface only in the absence of rapid mixing to the interior."

Heliums

Main resources: Chemicals/Heliums and Heliums

The alpha process, also known as the alpha ladder is one of two classes of [nuclear] reactions [for converting] helium into heavier elements, the other being the triple-alpha process.

Possible reactions:

$\mathrm {_{6}^{12}C} +\mathrm {_{2}^{4}He} \rightarrow \mathrm {_{8}^{16}O} +\gamma +Q$, Q = 7.16 MeV

$\mathrm {_{8}^{16}O} +\mathrm {_{2}^{4}He} \rightarrow \mathrm {_{10}^{20}Ne} +\gamma +Q$, Q = 4.73 MeV

$\mathrm {_{10}^{20}Ne} +\mathrm {_{2}^{4}He} \rightarrow \mathrm {_{12}^{24}Mg} +\gamma +Q$, Q = 9.31 MeV

$\mathrm {_{12}^{24}Mg} +\mathrm {_{2}^{4}He} \rightarrow \mathrm {_{14}^{28}Si} +\gamma +Q$, Q = 9.98 MeV

$\mathrm {_{14}^{28}Si} +\mathrm {_{2}^{4}He} \rightarrow \mathrm {_{16}^{32}S} +\gamma +Q$, Q = 6.95 MeV

$\mathrm {_{16}^{32}S} +\mathrm {_{2}^{4}He} \rightarrow \mathrm {_{18}^{36}Ar} +\gamma$

$\mathrm {_{18}^{36}Ar} +\mathrm {_{2}^{4}He} \rightarrow \mathrm {_{20}^{40}Ca} +\gamma$

$\mathrm {_{20}^{40}Ca} +\mathrm {_{2}^{4}He} \rightarrow \mathrm {_{22}^{44}Ti} +\gamma$

$\mathrm {_{22}^{44}Ti} +\mathrm {_{2}^{4}He} \rightarrow \mathrm {_{24}^{48}Cr} +\gamma$

$\mathrm {_{24}^{48}Cr} +\mathrm {_{2}^{4}He} \rightarrow \mathrm {_{26}^{52}Fe} +\gamma$

$\mathrm {_{26}^{52}Fe} +\mathrm {_{2}^{4}He} \rightarrow \mathrm {_{28}^{56}Ni} +\gamma$

$\mathrm {_{28}^{56}Ni} +\mathrm {_{2}^{4}He} +\gamma \rightarrow \mathrm {_{30}^{60}Zn}$

Alpha process elements (or alpha elements) are so-called since their most abundant isotopes are integer multiples of the alpha particle). Alpha elements are atomic number Z ≤ 22: (C, N), O, Ne, Mg, Si, S, Ar, Ca, Ti. They may be synthesized by alpha-capture. Silicon and calcium are purely alpha process elements. Magnesium can be burned by proton capture reactions. Oxygen enhancement is well correlated with an enhancement of other alpha process elements. C and N are considered alpha process elements, when they are synthesized in nuclear alpha-capture reactions.

The abundance of alpha elements in stars is usually expressed in a logarithmic manner:

$[\alpha /Fe]=\log _{10}{\left({\frac {N_{\alpha }}{N_{Fe}}}\right)_{Star}}-\log _{10}{\left({\frac {N_{\alpha }}{N_{Fe}}}\right)_{Sun}}$,

Here $N_{\alpha }$ and $N_{Fe}$ are the number of alpha element atoms and Fe atoms per unit volume.

$\mathrm {_{1}^{1}H} +\mathrm {_{1}^{1}H} \rightarrow \mathrm {_{2}^{2}He}$

Lithiums

Main resources: Chemicals/Lithiums and Lithiums

$\mathrm {_{1}^{3}T} +\mathrm {_{2}^{4}He} \rightarrow \mathrm {_{3}^{7}Li} +\gamma$  + ? MeV

$\mathrm {_{4}^{7}Be} +n^{0}\rightarrow \mathrm {_{3}^{7}Li} +p^{+}$

$\mathrm {_{4}^{7}Be} +e^{-}\rightarrow \mathrm {_{3}^{7}Li} +\nu _{e}$

Berylliums

Main resources: Chemicals/Berylliums and Berylliums

$\mathrm {_{2}^{4}He} +\mathrm {_{2}^{4}He} \rightarrow \mathrm {_{4}^{8}Be}$ (−93.7 keV)

A beam of 120 MeV/u ²²Ne is "fragmented on a thick Be production target" to produce a secondary beam of 53 MeV/u ¹⁷B against a reaction target of 470 mg/cm^{2 9}Be to produce unbound ¹⁶Be nuclei.

$\mathrm {_{2}^{3}He} +\mathrm {_{2}^{4}He} \rightarrow \mathrm {_{4}^{7}Be}$  + ? MeV

Carbons

Main resources: Chemicals/Carbons and Carbons

This diagram presents an overview of the triple-alpha process. Credit: Borb.

The triple alpha process is a set of [nuclear] reactions by which three ... [alpha particles] are transformed into carbon.

Some of these reactions are

$\mathrm {_{2}^{4}He} +\mathrm {_{2}^{4}He} \rightarrow \mathrm {_{4}^{8}Be}$ (−93.7 keV) and

$\mathrm {_{4}^{8}Be} +\mathrm {_{2}^{4}He} \rightarrow \mathrm {_{6}^{12}C}$ (+7.367 MeV).

The net energy release of the process is 1.166 pJ.

An additional alpha process reaction that may occur is

$\mathrm {_{6}^{12}C} +\mathrm {_{2}^{4}He} \rightarrow \mathrm {_{8}^{16}O} +\gamma$ (+7.162 MeV).

⁴He(αα,γ)¹²C or

$\mathrm {_{2}^{4}He} +\mathrm {_{2}^{4}He} \rightarrow \mathrm {_{4}^{8}Be}$ (−93.7 keV) and

$\mathrm {_{4}^{8}Be} +\mathrm {_{2}^{4}He} \rightarrow \mathrm {_{6}^{12}C}$ (+7.367 MeV).

¹⁴N(n,p)¹⁴C

Nitrogens

Main resources: Chemicals/Nitrogens and Nitrogens

The carbon-burning process is a set of nuclear reactions that may require high temperatures (> 5×10⁸ K or 50 keV) and densities (> 3×10⁹ kg/m³).

CNO-I

This shows an overview of the CNO-I Cycle. Credit: Borb.

The principal reactions are:"

¹²
₆C
 + ¹
₁H
 → ¹³
₇N
 + γ   + 1.95 MeV

¹³
₇N
   → ¹³
₆C
 + e⁺ + ν
_e + 1.20 MeV (half-life of 9.965 minutes), or ¹²C(p,γ)¹³N.

¹³
₆C
 + ¹
₁H
 → ¹⁴
₇N
 + γ   + 7.54 MeV

¹⁴
₇N
 + ¹
₁H
 → ¹⁵
₈O
 + γ   + 7.35 MeV

¹⁵
₈O
   → ¹⁵
₇N
 + e⁺
 + ν
_e + 1.73&bsp;MeV (half-life of 122.24 seconds)

¹⁵
₇N
 + ¹
₁H
 → ¹²
₆C
 + ⁴
₂He
 + 4.96 MeV:

CNO-II

¹⁵
₇N
 + ¹
₁H
 → ¹⁶
₈O
 + γ   + 12.13 MeV

¹⁶
₈O
 + ¹
₁H
 → ¹⁷
₉F
 + γ   + 0.60 MeV

¹⁷
₉F
   → ¹⁷
₈O
 + e⁺
 + ν
_e + 2.76 MeV (half-life of 64.49 seconds)

¹⁷
₈O
 + ¹
₁H
 → ¹⁴
₇N
 + ⁴
₂He
 + 1.19 MeV

¹⁴
₇N
 + ¹
₁H
 → ¹⁵
₈O
 + γ   + 7.35 MeV

¹⁵
₈O
   → ¹⁵
₇N
 + e⁺
 + ν
_e + 2.75 MeV (half-life of 122.24 seconds)

CNO-III

¹⁷
₈O
 + ¹
₁H
 → ¹⁸
₉F
 + γ   + 5.61 MeV

¹⁸
₉F
   → ¹⁸
₈O
 + e⁺
 + ν
_e + 1.656 MeV (half-life of 109.771 minutes)

¹⁸
₈O
 + ¹
₁H
 → ¹⁵
₇N
 + ⁴
₂He
 + 3.98 MeV

¹⁵
₇N
 + ¹
₁H
 → ¹⁶
₈O
 + γ   + 12.13 MeV

¹⁶
₈O
 + ¹
₁H
 → ¹⁷
₉F
 + γ   + 0.60 MeV

¹⁷
₉F
   → ¹⁷
₈O
 + e⁺
 + ν
_e + 2.76 MeV (half-life of 64.49 seconds)

CNO-IV

A proton reacts with a nucleus causing release of an alpha particle. Credit: Michalsmid.

These reactions may occur in massive stars. ¹⁹
₉F
 + ¹
₁H
 → ¹⁶
₈O
 + ⁴
₂He
   + 8.114 MeV

¹⁶
₈O
 + ¹
₁H
 → ¹⁷
₉F
 + γ   + 0.60 MeV

¹⁷
₉F
   → ¹⁷
₈O
 + e⁺
 + ν
_e + 2.76 MeV (half-life of 64.49 seconds)

¹⁷
₈O
 + ¹
₁H
 → ¹⁸
₉F
 + γ   + 5.61 MeV

¹⁸
₉F
   → ¹⁸
₈O
 + e⁺
 + ν
_e + 1.656 MeV (half-life of 109.771 minutes)

¹⁸
₈O
 + ¹
₁H
 → ¹⁹
₉F
 + γ   + 7.994 MeV

These are the hot CNO cycles reactions with conditions of higher temperature as have been found in novae and X-ray bursts.

When the rate of proton captures exceeds the rate of beta-decay, the burning conforms to the proton drip line. A radioactive species captures a proton before it can beta decay.

HCNO-I

¹²
₆C
 + ¹
₁H
 → ¹³
₇N
 + γ   + 1.95 MeV

¹³
₇N
 + ¹
₁H
 → ¹⁴
₈O
 + γ   + 4.63 MeV

¹⁴
₈O
   → ¹⁴
₇N
 + e⁺
 + ν
_e + 5.14 MeV (half-life of 70.641 seconds)

¹⁴
₇N
 + ¹
₁H
 → ¹⁵
₈O
 + γ   + 7.35 MeV

¹⁵
₈O
   → ¹⁵
₇N
 + e⁺
 + ν
_e + 2.75 MeV (half-life of 122.24 seconds)

¹⁵
₇N
 + ¹
₁H
 → ¹²
₆C
 + ⁴
₂He
  + 4.96 MeV

HCNO-II

¹⁵
₇N
 + ¹
₁H
 → ¹⁶
₈O
 + γ   + 12.13 MeV

¹⁶
₈O
 + ¹
₁H
 → ¹⁷
₉F
 + γ   + 0.60 MeV

¹⁷
₉F
 + ¹
₁H
 → ¹⁸
₁₀Ne
 + γ   + 3.92 MeV

¹⁸
₁₀Ne
   → ¹⁸
₉F
 + e⁺
 + ν
_e + 4.44 MeV (half-life of 1.672 seconds)

¹⁸
₉F
 + ¹
₁H
 → ¹⁵
₈O
 + ⁴
₂He
 + 2.88 MeV

¹⁵
₈O
   → ¹⁵
₇N
 + e⁺
 + ν
_e + 2.75 MeV (half-life of 122.24 seconds)

HCNO-III

¹⁸
₉F
 + ¹
₁H
 → ¹⁹
₁₀Ne
 + γ   + 6.41 MeV

¹⁹
₁₀Ne
   → ¹⁹
₉F
 + e⁺
 + ν
_e + 3.32 MeV (half-life of 17.22 seconds)

¹⁹
₉F
 + ¹
₁H
 → ¹⁶
₈O
 + ⁴
₂He
  + 8.11 MeV

¹⁶
₈O
 + ¹
₁H
 → ¹⁷
₉F
 + γ   + 0.60 MeV

¹⁷
₉F
 + ¹
₁H
 → ¹⁸
₁₀Ne
 + γ   + 3.92 MeV

¹⁸
₁₀Ne
   → ¹⁸
₉F
 + e⁺
 + ν
_e + 4.44 MeV (half-life of 1.672 seconds)

Oxygens

Main resources: Chemicals/Oxygens and Oxygens

$\mathrm {_{6}^{12}C} +\mathrm {_{6}^{12}C} \rightarrow \mathrm {_{8}^{16}O} +2\mathrm {_{2}^{4}He}$  - 0.113 MeV

The main neutron source reactions are:

¹³C + ⁴He → ¹⁶O + n

¹²C(α,γ)¹⁶O or

$\mathrm {_{6}^{12}C} +\mathrm {_{2}^{4}He} \rightarrow \mathrm {_{8}^{16}O} +\gamma +Q$, Q = 7.16 MeV.

$\mathrm {_{6}^{12}C} +\mathrm {_{6}^{12}C} \rightarrow \mathrm {_{8}^{16}O} +2\mathrm {_{2}^{4}He}$  - 0.113 MeV

¹³C(α,n)¹⁶O

¹⁴N(p,γ)¹⁵O

"A primary beam of 140 MeV/u ⁴⁸Ca²⁰⁺ [ions] bombarded a 1316 mg/cm^{2 9}Be production target. ... The [secondary] ²⁷F beam then impinged on a 705 mg/cm² Be target producing the isotope of interest, ²⁶O, through one-proton removal reactions. ... The ²⁴O fragments were identified by time-of-flight and energy loss in the charged particle detectors."

"[I]n the dripline nucleus ²⁴O a large energy difference was measured between the ν1s_1/2 and ν0d_3/2 orbitals indicating a new magic number at N = 16 [4,5]."

A beam of 140 MeV/u ⁴⁸Ca is "fragmented on a thick Be production target" to produce a secondary beam of 82 MeV/u ²⁷F against a reaction target of 705 mg/cm^{2 9}Be to produce unbound ²⁶O nuclei.

Fluorines

Main resources: Chemicals/Fluorines and Fluorines

¹⁶O(p,γ)¹⁷F

¹⁴N(α,γ)¹⁸F

"Woosley & Haxton (1988) proposed first that F is produced by neutrino spallation on ²⁰Ne; ²⁰Ne(ν,ν′p)¹⁹F."

Alternative reactions include

1. ¹⁴N(n,p)¹⁴C(α,γ)¹⁸O(p,α)¹⁵N(α,γ)¹⁹F and
2. ¹⁴N(α,γ)¹⁸F(β⁺)¹⁸O(p,α)¹⁵N(α,γ)¹⁹F,

"where the neutrons are provided by ¹³C(α,n)¹⁶O and the protons mainly by ¹⁴N(n,p)¹⁴C (see Jorissen et al. 1992)."

The isotope ³¹F has been observed and [is] producible by the same particle accelerator induced fragmentation as has produced ⁴⁰Mg.

Neons

Main resources: Chemicals/Neons and Neons

$\mathrm {_{6}^{12}C} +\mathrm {_{6}^{12}C} \rightarrow \mathrm {_{10}^{20}Ne} +\mathrm {_{2}^{4}He}$  + 4.617 MeV

¹⁶O(α,γ)²⁰Ne or

$\mathrm {_{8}^{16}O} +\mathrm {_{2}^{4}He} \rightarrow \mathrm {_{10}^{20}Ne} +\gamma +Q$, Q = 4.73 MeV

¹⁹F(p,γ )²⁰Ne

¹⁹F(α,p)²²Ne

³⁴Ne has been observed and [is] producible by the same particle accelerator induced fragmentation as has produced ⁴⁰Mg.

Sodiums

Main resources: Chemicals/Sodiums and Sodiums

$\mathrm {_{6}^{12}C} +\mathrm {_{6}^{12}C} \rightarrow \mathrm {_{11}^{23}Na} +\mathrm {_{1}^{1}H}$  + 2.241 MeV

²²Ne(n,γ )²³Ne(β⁻)²³Na

²²Ne(p,γ )²³Na

³⁷Na has been observed and [is] producible by the same particle accelerator induced fragmentation as has produced ⁴⁰Mg.

Magnesiums

Main resources: Chemicals/Magnesiums and Magnesiums

$\mathrm {_{6}^{12}C} +\mathrm {_{6}^{12}C} \rightarrow \mathrm {_{12}^{23}Mg} +\mathrm {n}$  - 2.599 MeV

$\mathrm {_{6}^{12}C} +\mathrm {_{6}^{12}C} \rightarrow \mathrm {_{12}^{24}Mg} +\gamma$  + 13.933 MeV

The main neutron source reactions are:

²²Ne + ⁴He → ²⁵Mg + n

$\mathrm {_{6}^{12}C} +\mathrm {_{6}^{12}C} \rightarrow \mathrm {_{12}^{23}Mg} +\mathrm {n}$  - 2.599 MeV

$\mathrm {_{6}^{12}C} +\mathrm {_{6}^{12}C} \rightarrow \mathrm {_{12}^{24}Mg} +\gamma$  + 13.933 MeV

²⁰Ne(α,γ)²⁴Mg or

$\mathrm {_{10}^{20}Ne} +\mathrm {_{2}^{4}He} \rightarrow \mathrm {_{12}^{24}Mg} +\gamma +Q$, Q = 9.31 MeV

¹²C(¹²C,γ)²⁴Mg

²²Ne(α,n)²⁵Mg

To produce isotopes such as ⁴⁰Mg, one process is "[t]he fragmentation of stable nuclei [such as] ^natW [using] [a] primary beam of ⁴⁸Ca with an energy per nucleon of 141 MeV [and an] average incident beam intensity [of] 5.0 x 10¹¹ particles per second."

Aluminums

Main resources: Chemicals/Aluminums and Aluminums

⁴²Al and likely ⁴³Al are producible by the same particle accelerator induced fragmentation as has produced ⁴⁰Mg.

"The dominant reactions for making ²⁶Al by proton and α bombardment of refractory rocks in impulsive flares are ²⁷Al(p, pn)²⁶Al (β=0.92), ²⁶Mg(p, n)²⁶Al (β=1.0), ²⁴Mg(α, pn)²⁶Al (β=2.5 and y_CR = 0.1), ²⁸Si(p, 2pn)²⁶Al (β=0.10), and ²⁸Si(α, αpn)²⁶Al (β=0.41)."

Silicons

Main resources: Chemicals/Silicons and Silicons

$\mathrm {_{12}^{24}Mg} +\mathrm {_{2}^{4}He} \rightarrow \mathrm {_{14}^{28}Si} +\gamma +Q$, Q = 9.98 MeV

¹⁶O(¹²C,γ)³⁰Si

⁴⁴Si is producible by the same particle accelerator induced fragmentation as has produced ⁴⁰Mg.

Sulfurs

Main resources: Chemicals/Sulfurs and Sulfurs

$\mathrm {_{14}^{28}Si} +\mathrm {_{2}^{4}He} \rightarrow \mathrm {_{16}^{32}S} +\gamma +Q$, Q = 6.95 MeV

¹⁶O(¹⁶O,γ)³²S

Argons

Main resources: Chemicals/Argons and Argons

$\mathrm {_{16}^{32}S} +\mathrm {_{2}^{4}He} \rightarrow \mathrm {_{18}^{36}Ar} +\gamma$

Calciums

Main resources: Chemicals/Calciums and Calciums

$\mathrm {_{18}^{36}Ar} +\mathrm {_{2}^{4}He} \rightarrow \mathrm {_{20}^{40}Ca} +\gamma$

Titaniums

Main resources: Chemicals/Titaniums and Titaniums

$\mathrm {_{20}^{40}Ca} +\mathrm {_{2}^{4}He} \rightarrow \mathrm {_{22}^{44}Ti} +\gamma$

Chromiums

Main resources: Chemicals/Chromiums and Chromiums

$\mathrm {_{22}^{44}Ti} +\mathrm {_{2}^{4}He} \rightarrow \mathrm {_{24}^{48}Cr} +\gamma$

Irons

Main resources: Chemicals/Irons and Irons

$\mathrm {_{24}^{48}Cr} +\mathrm {_{2}^{4}He} \rightarrow \mathrm {_{26}^{52}Fe} +\gamma$

Heavy isotopes

A published table apportions the heavy isotopes between S-process and R-process.

The details of asymptotic giant branch (AGB)-star nucleosynthesis became a standard model based on the stellar structure models. A series of measurements of neutron-capture cross sections placed the S-process on the firm quantitative basis.

Cobalts

Main resources: Chemicals/Cobalts and Cobalts

Nickels

Main resources: Chemicals/Nickels and Nickels

$\mathrm {_{26}^{52}Fe} +\mathrm {_{2}^{4}He} \rightarrow \mathrm {_{28}^{56}Ni} +\gamma$

Zincs

Main resources: Chemicals/Zincs and Zincs

$\mathrm {_{28}^{56}Ni} +\mathrm {_{2}^{4}He} +\gamma \rightarrow \mathrm {_{30}^{60}Zn}$

Zirconiums

Main resources: Chemicals/Zirconiums and Zirconiums

One distinguishes the main and the weak s-process component. The main component produces heavy elements beyond Sr and Y, and up to Pb in the lowest metallicity stars. The production sites of the main component are low-mass Asymptotic Giant Branch stars. The main component relies on the ¹³C neutron source above.

Technetiums

Main resources: Chemicals/Technetiums and Technetiums

The S-process occurs arguably in red giant stars. In a particularly illustrative case, the element technetium, whose longest half-life is 4.2 million years, had been discovered in S-, M-, and N-type stars in 1952. 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, probably unconnected with the nuclear fusion in the deep interior of the star that provides its power.

Bariums

Main resources: Chemicals/Bariums and Bariums

"A calculable model for creating the heavy isotopes from iron seed nuclei in a time-dependent manner" showed that

1. the large overabundances of barium observed by astronomers in certain red-giant stars could be created from iron seed nuclei if the total fluence (number of neutrons per unit area) of neutrons was appropriate,
2. no one single value for the fluence could account for the observed S-process abundances, but that a wide range of fluences is required. The numbers of iron seed nuclei that were exposed to a given fluence must decrease as the fluence becomes stronger,
3. the curve of the product of neutron-capture cross section times abundance is not a smoothly falling curve, but rather has a ledge-precipice structure.

Leads

Main resources: Chemicals/Leads and Leads

"For [asymptotic giant branch] AGB stars that formed early in the history of the Galaxy, and that therefore have very low abundances of elements heavier than helium ('metals'), models¹ predict that the s-process will accumulate synthesized material with atomic weights in the Pb–Bi region. Such stars will therefore have large overabundances of lead relative to other heavy elements."

Large "amounts of lead [occur] in three metal-poor stars (HD187861, HD196944 and HD224959). [These] stars are more enriched in lead than in any other element heavier than iron."

²⁰⁴
Tl ⟶ ²⁰⁴
Pb + β^-, t_1/2 = 3.78 y.

²⁰⁶
Tl ⟶ ²⁰⁶
Pb + β^-, t_1/2 = 4.200(17) min.

²⁰⁷
Tl ⟶ ²⁰⁷
Pb + β^-, t_1/2 = 4.77(2) min.

²⁰⁸
Tl ⟶ ²⁰⁸
Pb + β^-, t_1/2 = 3.053(4) min.

²⁰⁹
Tl ⟶ ²⁰⁹
Pb + β^-, t_1/2 = 2.161(7) min.

²¹⁰
Tl ⟶ ²¹⁰
Pb + β^-, t_1/2 = 1.30(3) min (99.991%).

²¹⁰
Tl ⟶ ²⁰⁹
Pb + β^- + n, t_1/2 = 1.30(3) min (.009%).

Bismuths

Main resources: Chemicals/Bismuths and Bismuths

Because of the relatively low neutron fluxes expected to occur during the S-process (on the order of 10⁵ to 10¹¹ neutrons per cm² 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:

²⁰⁹Bi + n → ²¹⁰Bi + γ

$\mathrm {_{83}^{210}Bi} \to \mathrm {_{84}^{210}Po} +e^{-}+{\bar {\nu }}_{e}$

Po → ²⁰⁶Pb + ⁴He

²⁰⁶Pb then captures three neutrons, producing ²⁰⁹Pb, which decays to ²⁰⁹Bi by β^- decay, restarting the cycle:

²⁰⁶Pb + 3n → ²⁰⁹Pb

$\mathrm {_{82}^{209}Pb} \to \mathrm {_{83}^{209}Bi} +e^{-}+{\bar {\nu }}_{e}$

The net result of this cycle therefore is that 4 neutrons are converted into one alpha particle, two electrons, two anti-electron neutrinos and gamma radiation:

$4n\to \mathrm {_{2}^{4}He} +2e^{-}+2{\bar {\nu }}_{e}+\gamma$

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 lifetime of any existing star.)

Poloniums

Main resources: Chemicals/Poloniums and Poloniums

$\mathrm {_{83}^{210}Bi} \to \mathrm {_{84}^{210}Po} +e^{-}+{\bar {\nu }}_{e}$

Hypotheses

Main resource: Hypotheses

1. Many superheavy transuranium elements can be made using muons.
2. The Sun can nucleosynthesize lead.

A control group for nucleosynthesis may be a particular particle accelerator experiment that rigorously reproduces the same nuclei.

See also

• Stellar surface fusion

External links

• Bing Advanced search
• Google Books
• Google scholar Advanced Scholar Search
• International Astronomical Union
• JSTOR
• Lycos search
• NASA's National Space Science Data Center
• NCBI All Databases Search
• Office of Scientific & Technical Information
• PubChem Public Chemical Database
• Questia - The Online Library of Books and Journals
• SAGE journals online
• Scirus for scientific information only advanced search
• SpringerLink
• Taylor & Francis Online
• Wiley Online Library Advanced Search
• Yahoo Advanced Web Search

{{Radiation astronomy resources}}

{{Technology resources}}