The Universe as a whole is the best labratory for studying nuclear physics. Where else can you find the 109 K tempatures and a 15 billion year old experiment?

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Alpha-Carbon Reaction

After three helium nuclei have combined to form 12C in a red giant, another alpha particle is captured by the 12C to form 16O and gamma rays. These particles, 12C and 16O, are the ashes from a dying star. They are also the basis of life on Earth.

Big Bang Nucleosynthesis (see also Universe Expansion)
At the big bang, the universe had a temperature of 100,000,000,000 K. It was so hot that only protons and neutrons were formed. However, as the universe cooled, the amount of deuterium and helium nuclei increased. Just below 1 billion degrees there is a significant increase in deuterium and helium, and a decrease in the abundance of protons and neutrons. This was the deuterium "bottleneck". This used up the all the free neutrons and some protons, and caused the neutron line to drop off, and the proton line to dip (relatively few protons are used up). The deuterium abundance only increased to a point because it is an intermediate to the formation of helium. So as it was created, it is quickly consumed to complete the process of helium nucleosynthesis. Once all the neutrons were been used up, its presence dropped off.
For more information, see Formation of the Elements/ Nucleosynthesis in the early universe.

  1. Pair Production
  2. Positron Annihilation
  3. Proton/Neutron Conversion
  4. Proton/Neutron Collision
  5. Helium Nucleosynthesis
  6. Heavier Elements Nucleosynthesis
  7. Electron Capture

Carbon-Nitrogen-Oxygen Cycle
In stars more massive than the sun (>1.1 Solar masses), this cycle is the primary process which converts hydrogen into helium. 12C serves as a catalyst, an ingredient which is necessary for the reaction but is not consumed.
Listing of the steps

Electron Capture
The nuclei formed early in the birth of the universe still had not enough electrons to form a neutral atom. But, the free electrons had plenty of energy. After 700,000 years of cooling, the nuclei started to capture electrons. These electron clouds are important. They stopped radiation from passing through the atoms.