1. Nucleosynthesis Nucleosynthesis Big Bang Nucleosynthesis:
First Three Minutes
He4 and Deuterium
No elements heavier than lithium
Stellar Nucleosynthesis
Heavier elements between lithium and iron. Particularly important is carbon.
S-process which involves the slow absorption of neutrons.
Supernova Nucleosynthesis
Elements heavier than iron.
R-process which are elements produced by rapid absorption of neutrons..

2. Synthesis Of Elements
Its harder and harder to make nuclei with higher masses.
So the most common substance in the Universe is hydrogen followed by
helium, lithium, beryllium and boron (the first elements on the periodic table)
Isotopes are formed, such as deuterium and tritium, but these elements are
unstable and decay into free protons and neutrons.

3. Hotter fusion and heavier elements
Could stars in principle live forever simply by contracting gravitationally and increasing their temperature to ignite the next heavier source of nuclear fuel whenever they run out?
No Strong interaction range is smaller than diameters of smaller nuclei but coulomb interaction covers whole nucleus
If nuclei get large enough the increase in electrostatic repulsion of protons becomes greater than increase in binding energy from strong interaction.
The peak in binding energy per baryon vs atomic mass number relationship turns out to lie at iron

4. Hotter fusion and heavier elements (continued)
Implication:
Once a star’s core is composed completely of iron it can no longer replenish its energy losses by fusion and therefore stars must die.In otherwords,you get energy by fusion all the way up to production of iron but not beyond.

6. Theories The BBFH theory Hot Big Bang
Stellar interiors or during supernova explosions
Abundances of helium and deuterium in the universe
couldn’t be explained
Hot Big Bang
Cooling from 10^32 Kelvin to approximately 10^9 Kelvin.
Protons and Neutrons collided to produce deuterium (one proton bound to one neutron). Deuterium then collided with other protons and neutrons to produce helium and a small amount of tritium (one proton and two neutrons)

7. Test For Theories Isotope abundances
Typically calculated by calculating the transition rates between isotopes in a network
Few key reactions control the rate of other reactions.
Abundances critically depends on the density of baryons (neutrons and protons) at the time of nucleosynthesis.
one value of this baryon density can explain all the abundances at once

8. Historical Remarks
Can Element Abundances be explained by the Big Bang Theory
No significant Production of Nuclei more massive than Li7 and He4 expected to be most abundant after Hydrogen
Computed n/p ratio following Big Bang

9. Neutrons and Protons

10. Neutrons and Protons X=n/(n+p) As T becomes large X=1/2
The conditions of thermal Equilibrium fixes the initial condition
The results of Primeval Nucleosynthesis are predictions of the cosmological model

11. Expected abundances VS Density
Gentle increase of abundance with density as bigbang starts
H2 and He3 are burnt away by fusion thus their abundance decreases as density increases
Li7 is destroyed by protons for low density with efficiency increasing with higher density and so competing effects create the valley

12. Stellar Nucleosynthesis (Triple Alpha reaction)
How are elements heavier than Helium formed
2He4+2He Be8 + 0γ0
4Be8+2He C γ0
Requires temperature of ~108K

13. Stellar Nucleosynthesis
The triple alpha reaction makes carbon
Add a helium to Carbon and you get oxygen
Two carbons can make magnesium
To burn heavier elements generally require higher temperature
Elements are burned at higher and higher temperatures in the core of a massive star until an Iron core forms
If the stars cannot burn anything beyond iron than how are the remaining heavier elements formed?

14. Nucleosynthesis By Neutron Capture
The construction of elements heavier than involves nucleosynthesis by neutron capture. A nuclei can capture or fuse with a neutron because the neutron is electrically neutral and, therefore, not repulsed like the proton. In everyday life, free neutrons are rare because they have short half life’s before they radioactively decay. Each neutron capture produces an isotope, some are stable, some are unstable. Unstable isotopes will decay by emitting a positron and a neutrino to make a new element
48Cd110+0n Cd Cd112+0n Cd112
48Cd112+0n Cd Cd113+0n Cd114
48Cd114+0n Cd115
48Cd115+0n In116 + e- + ν
(Radio Active decay)

15. Slow Neutron Capture
Neutron capture can happen by two methods, the s and r-processes, where s and r stand for slow and rapid. The s-process happens in the inert carbon core of a star, the slow capture of neutrons. The s-process works as long as the decay time for unstable isotopes is longer than the capture time. Up to the element bismuth (atomic number 83), the s-process works, but above this point the more massive nuclei that can be built from bismuth are unstable.

16. Rapid Neutron Capture
The second process, the r-process, is what is used to produce very heavy, neutron rich nuclei. Here the capture of neutrons happens in such a dense environment that the unstable isotopes do not have time to decay. The high density of neutrons needed is only found during a supernova explosion and, thus, all the heavy elements in the Universe (radium, uranium and plutonium) are produced this way.

17. Recent Observations of Ongoing Nucleosynthesis: I
Gamma-ray Lines from SNe remnants first proposed in 1969 (Clayton, Colgate, & Fishman, ApJ, 155, 75.
56Ni  56Co (t = 6.08 d)
56Co  56Fe (t = 77.3 d)
Both transitions occur via β-decay.
SN1987A first source in which these gamma-ray lines were observed. Represents the first direct measure of the synthesis of Fe, the sixth most abundant element in the universe (H, He, O, C, Ne, none of which are formed from radioactive progenitors)
Later 57Co (and hence 57Ni and 57Fe) were discovered in SN1987A, and 44Ti was discovered in the CasA remnant

18. Recent Observations of Ongoing Nucleosynthesis: II
COMPTEL on CGRO observed sky in MeV line caused by decay of 26Al
Mode of decay: β-decay
26Al  26Mg
Half-life ~ 7 x 105 years
Distribution of radiation matches distribution of massive stars (> 10 Msun) on the sky
Massive stars can produce 26Al by burning H. The 26Al is then advected to the surface of the star and ejected through mass loss

19. Non standard Big Bang Model
Non-standard BBN
In addition to the standard BBN scenario there are numerous non-standard BBN scenarios
.Insert additional physics in order to see how this affects elemental abundances.
Removing the assumption of homogeneity or inserting new particles such as massive neutrinos.
Done to resolve inconsistencies between BBN predictions and observations.
Usefulness
This has proved to be of limited usefulness in that in most cases trying to change BBN resulted in abundances that were more inconsistent with observations rather than less
For example, standard BBN assumes that no exotic hypothetical particles were involved in BBN. One can insert a hypothetical particle (say a massive neutrino) and see what has to happen before BBN predicts abundances which are very different from observations. This has been usefully done to put limits on the mass of a stable tau neutrino.

20. Dark Matter
This inconsistency between observations of deuterium and observations of the expansion rate of the universe, led to a large effort to find processes that could produce deuterium. After a decade of effort, the consensus was that these processes are unlikely, and the standard explanation now used for the abundance of deuterium is that the universe does not consist mostly of baryons and that dark matter makes up most of the mass of the universe.