# Plasmas/Plasma objects/Nucleosynthesis

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

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

"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."[1]

"No published theoretical calculation has been able to simultaneously reproduce both the oxygen and fluorine driplines."[2]

## 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.

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)."[3]

## Theoretical nucleosynthesis

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

## 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.

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

## Protons

${\displaystyle e^{+}+\nu _{e}+{\bar {\nu }}_{\mu }\to \mu ^{+}}$
${\displaystyle e^{+}+e^{-}+\gamma \to \pi ^{0}}$
${\displaystyle 2\gamma \to \pi ^{0}}$
${\displaystyle \mu ^{+}+\pi ^{0}\to p^{+}}$

## Liquid objects

"[W]e did not at all anticipate the nearly perfect liquid behavior."[4]

"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".[4]

## 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

1H(p,β+ν)2H

21H12D1 + e+ + νe + γ (0.42 MeV)

At 10-million-kelvin, hydrogen fuses to form helium in the proton-proton chain reaction:[5]

41H → 22H + 2e+ + 2νe (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 + 2νe (26.7 MeV)

where e+ is a positron, γ is a gamma ray photon, νe 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."[6]

## 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.[7]

Possible reactions:

${\displaystyle \mathrm {_{6}^{12}C} +\mathrm {_{2}^{4}He} \rightarrow \mathrm {_{8}^{16}O} +\gamma +Q}$ , Q = 7.16 MeV
${\displaystyle \mathrm {_{8}^{16}O} +\mathrm {_{2}^{4}He} \rightarrow \mathrm {_{10}^{20}Ne} +\gamma +Q}$ , Q = 4.73 MeV
${\displaystyle \mathrm {_{10}^{20}Ne} +\mathrm {_{2}^{4}He} \rightarrow \mathrm {_{12}^{24}Mg} +\gamma +Q}$ , Q = 9.31 MeV
${\displaystyle \mathrm {_{12}^{24}Mg} +\mathrm {_{2}^{4}He} \rightarrow \mathrm {_{14}^{28}Si} +\gamma +Q}$ , Q = 9.98 MeV
${\displaystyle \mathrm {_{14}^{28}Si} +\mathrm {_{2}^{4}He} \rightarrow \mathrm {_{16}^{32}S} +\gamma +Q}$ , Q = 6.95 MeV
${\displaystyle \mathrm {_{16}^{32}S} +\mathrm {_{2}^{4}He} \rightarrow \mathrm {_{18}^{36}Ar} +\gamma }$
${\displaystyle \mathrm {_{18}^{36}Ar} +\mathrm {_{2}^{4}He} \rightarrow \mathrm {_{20}^{40}Ca} +\gamma }$
${\displaystyle \mathrm {_{20}^{40}Ca} +\mathrm {_{2}^{4}He} \rightarrow \mathrm {_{22}^{44}Ti} +\gamma }$
${\displaystyle \mathrm {_{22}^{44}Ti} +\mathrm {_{2}^{4}He} \rightarrow \mathrm {_{24}^{48}Cr} +\gamma }$
${\displaystyle \mathrm {_{24}^{48}Cr} +\mathrm {_{2}^{4}He} \rightarrow \mathrm {_{26}^{52}Fe} +\gamma }$
${\displaystyle \mathrm {_{26}^{52}Fe} +\mathrm {_{2}^{4}He} \rightarrow \mathrm {_{28}^{56}Ni} +\gamma }$
${\displaystyle \mathrm {_{28}^{56}Ni} +\mathrm {_{2}^{4}He} +\gamma \rightarrow \mathrm {_{30}^{60}Zn} }$

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:

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

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

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

## Lithiums

${\displaystyle \mathrm {_{1}^{3}T} +\mathrm {_{2}^{4}He} \rightarrow \mathrm {_{3}^{7}Li} +\gamma }$   + ? MeV
${\displaystyle \mathrm {_{4}^{7}Be} +n^{0}\rightarrow \mathrm {_{3}^{7}Li} +p^{+}}$
${\displaystyle \mathrm {_{4}^{7}Be} +e^{-}\rightarrow \mathrm {_{3}^{7}Li} +\nu _{e}}$

## Berylliums

${\displaystyle \mathrm {_{2}^{4}He} +\mathrm {_{2}^{4}He} \rightarrow \mathrm {_{4}^{8}Be} }$  (−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/cm2 9Be to produce unbound 16Be nuclei.[2]

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

## 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.[8][9]

Some of these reactions are

${\displaystyle \mathrm {_{2}^{4}He} +\mathrm {_{2}^{4}He} \rightarrow \mathrm {_{4}^{8}Be} }$  (−93.7 keV) and
${\displaystyle \mathrm {_{4}^{8}Be} +\mathrm {_{2}^{4}He} \rightarrow \mathrm {_{6}^{12}C} }$  (+7.367 MeV).

The net energy release of the process is 1.166 pJ.

An additional alpha process reaction that may occur is

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

4He(αα,γ)12C or

${\displaystyle \mathrm {_{2}^{4}He} +\mathrm {_{2}^{4}He} \rightarrow \mathrm {_{4}^{8}Be} }$  (−93.7 keV) and
${\displaystyle \mathrm {_{4}^{8}Be} +\mathrm {_{2}^{4}He} \rightarrow \mathrm {_{6}^{12}C} }$  (+7.367 MeV).

14N(n,p)14C

## 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).[10]

### CNO-I

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

The principal reactions are:[11]"

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

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

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

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

15
8
O
→ 15
7
N
+ e+
+ ν
e
+ 1.73&bsp;MeV (half-life of 122.24 seconds[12])

15
7
N
+ 1
1
H
→ 12
6
C
+ 4
2
He
+ 4.96 MeV:[13]

### CNO-II

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

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

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

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

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

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

### CNO-III

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

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

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

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

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

17
9
F
→ 17
8
O
+ 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
9
F
+ 1
1
H
→ 16
8
O
+ 4
2
He
+ 8.114 MeV

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

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

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

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

18
8
O
+ 1
1
H
→ 19
9
F
+ 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
6
C
+ 1
1
H
→ 13
7
N
+ γ   + 1.95 MeV

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

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

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

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

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

### HCNO-II

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

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

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

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

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

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

### HCNO-III

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

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

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

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

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

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

## Oxygens

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

The main neutron source reactions are:

13C + 4He → 16O + n

12C(α,γ)16O or

${\displaystyle \mathrm {_{6}^{12}C} +\mathrm {_{2}^{4}He} \rightarrow \mathrm {_{8}^{16}O} +\gamma +Q}$ , Q = 7.16 MeV.
${\displaystyle \mathrm {_{6}^{12}C} +\mathrm {_{6}^{12}C} \rightarrow \mathrm {_{8}^{16}O} +2\mathrm {_{2}^{4}He} }$   - 0.113 MeV

13C(α,n)16O

14N(p,γ)15O

"A primary beam of 140 MeV/u 48Ca20+ [ions] bombarded a 1316 mg/cm2 9Be 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."[14]

"[I]n the dripline nucleus 24O a large energy difference was measured between the ν1s1/2 and ν0d3/2 orbitals indicating a new magic number at N = 16 [4,5]."[2]

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/cm2 9Be to produce unbound 26O nuclei.[2]

## 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."[15]

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)."[15]

The isotope 31F has been observed and [is] producible by the same particle accelerator induced fragmentation as has produced 40Mg.[1]

## Neons

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

16O(α,γ)20Ne or

${\displaystyle \mathrm {_{8}^{16}O} +\mathrm {_{2}^{4}He} \rightarrow \mathrm {_{10}^{20}Ne} +\gamma +Q}$ , 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.[1]

## Sodiums

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

22Ne(n,γ )23Ne(β)23Na[15]

22Ne(p,γ )23Na[15]

37Na has been observed and [is] producible by the same particle accelerator induced fragmentation as has produced 40Mg.[1]

## Magnesiums

${\displaystyle \mathrm {_{6}^{12}C} +\mathrm {_{6}^{12}C} \rightarrow \mathrm {_{12}^{23}Mg} +\mathrm {n} }$   - 2.599 MeV
${\displaystyle \mathrm {_{6}^{12}C} +\mathrm {_{6}^{12}C} \rightarrow \mathrm {_{12}^{24}Mg} +\gamma }$   + 13.933 MeV

The main neutron source reactions are:

22Ne + 4He → 25Mg + n
${\displaystyle \mathrm {_{6}^{12}C} +\mathrm {_{6}^{12}C} \rightarrow \mathrm {_{12}^{23}Mg} +\mathrm {n} }$   - 2.599 MeV
${\displaystyle \mathrm {_{6}^{12}C} +\mathrm {_{6}^{12}C} \rightarrow \mathrm {_{12}^{24}Mg} +\gamma }$   + 13.933 MeV

20Ne(α,γ)24Mg or

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

12C(12C,γ)24Mg

22Ne(α,n)25Mg[15]

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."[1]

## Aluminums

42Al and likely 43Al are producible by the same particle accelerator induced fragmentation as has produced 40Mg.[1]

"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 yCR = 0.1), 28Si(p, 2pn)26Al (β=0.10), and 28Si(α, αpn)26Al (β=0.41)."[16]

## Silicons

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

16O(12C,γ)30Si

44Si is producible by the same particle accelerator induced fragmentation as has produced 40Mg.[1]

## Sulfurs

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

16O(16O,γ)32S

## Argons

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

## Calciums

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

## Titaniums

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

## Chromiums

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

## Irons

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

## Heavy isotopes

A published table apportions the heavy isotopes between S-process and R-process.[17]

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[18][19] placed the S-process on the firm quantitative basis.

## Nickels

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

## Zincs

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

## 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.[20] The main component relies on the 13C neutron source above[21].

## 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.[22][23] 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

"A calculable model for creating the heavy isotopes from iron seed nuclei in a time-dependent manner"[24] 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.

"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."[25]

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."[25]

204
Tl
204
Pb
+ β-, t1/2 = 3.78 y.
206
Tl
206
Pb
+ β-, t1/2 = 4.200(17) min.
207
Tl
207
Pb
+ β-, t1/2 = 4.77(2) min.
208
Tl
208
Pb
+ β-, t1/2 = 3.053(4) min.
209
Tl
209
Pb
+ β-, t1/2 = 2.161(7) min.
210
Tl
210
Pb
+ β-, t1/2 = 1.30(3) min (99.991%).
210
Tl
209
Pb
+ β- + n, t1/2 = 1.30(3) min (.009%).

## 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
${\displaystyle \mathrm {_{83}^{210}Bi} \to \mathrm {_{84}^{210}Po} +e^{-}+{\bar {\nu }}_{e}}$
Po → 206Pb + 4He

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

206Pb + 3n → 209Pb
${\displaystyle \mathrm {_{82}^{209}Pb} \to \mathrm {_{83}^{209}Bi} +e^{-}+{\bar {\nu }}_{e}}$

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:

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

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

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

## 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.

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