There is a bottleneck in producing masses higher than 4He, because there are no mass-5 or mass-8 stable nuclides. For older stars with high densities and high temperatures (T > 100 million K), three alpha particles can form 12C. This occurs by two alpha particles ﬁ rst forming 8Be, and 8Be reacting with another alpha particle to form 12C before 8Be can decay back to two alpha particles. (a) Explain why this has to happen for very hot stars and high density. (b) Calculate how much energy is given up when three alpha particles form 12C.

There is a bottleneck in producing masses higher than 4He, because there are no mass-5 or mass-8 stable nuclides. For older stars with high densities and high temperatures (T > 100 million K), three alpha particles can form 12C. This occurs by two alpha particles ﬁ rst forming 8Be, and 8Be reacting with another alpha particle to form 12C before 8Be can decay back to two alpha particles. (a) Explain why this has to happen for very hot stars and high density. (b) Calculate how much energy is given up when three alpha particles form 12C.