L21and22 Nuclear energy

L21and22 Nuclear energy#

Week 12, Thursday and Week 13 Tuesday

Material covered and references#

We discuss the main source of energy in the Sun: thermonuclear reactions.

We first discuss the principle behind nuclear fusion, related to the nucleus binding energy. We looked at the binding energy per nucleons: how much energy per units of mH is released by fusing N hydrogen nucleus into the corresponding bigger nucleus.

Once we get this energy released per reaction, we can find our power generated per unit of mass (epsilon in our energy conservation equation) if we know the rate of reaction. From simple calculations, we estimate that there should be 10E38 reactions per second for the Sun.

We will compare the reaction rates from the pp-chain and the cno-cycle, in the interior of a 1 Msun star and a 10 Msun star.

In the textbooks:

  • Leblanc 6.2 for the nuclear binding energy.

  • Leblanc 6.4 for the qualitative explanation of the Colomb repulsion.

  • (Leblanc 6.3 Models of the nucleus – interesting, but we won’t go in that much details about the strong force)

  • Hansen 6.2.2 had the figure of Q/A that I discussed in the slides. The physics in the text is however more detailed that what we covered.

  • If you are interested in the details of the nuclear rate calculations, Henson 6.2.3 has the best description. However, the concept of the Gammov peak is better illustrated in Kip 18.3.

  • Leblanc 6.5.1 and 6.5.2 for detailed description of the PP chain and the CNO cycle. Pay attention to Figure 6.7.

  • (Note: Leblanc 6.7 has some interesting details about the advanced burning stages, e.g. triple-alpha reaction for He burning, etc)

  • Kip 18.5.1 for the rate equations parametrized by T, composition, etc. Pay attention to Fig. 18.8.