| Briefly describe the sequence of reactions leading to the formation of the light nuclides 2H, 3He, 4He and 7Li in the early universe. | [4] |
|
Explain why: (i) this process cannot produce nuclides heavier than 7Li (even though fusion processes in stars can and do produce such nuclides); |
[2] |
| (ii) you expect the final yield of 4He to be somewhat less than 30% by mass; | [2] |
| (iii) the exact yield depends on the neutron lifetime, the number of neutrino species and H0 as well as on the baryon density. | [2] |
| [Note that the mass of the proton is 1.6726×10-27 kg, and the neutron mass is 1.6749×10-27 kg.] |
(2006 Q7(a) and (b).)