Summary: Physics 314 (Survey of Astronomy) Exam 1
Please show all significant steps clearly in all problems.
Please give clear and legible responses to qualitative questions.
See the last page for values of constants.
1. Nuclear reactions in stars
(a) (3) Write down the proton-proton chain of reactions that converts H to He, being careful to show all
the particles in each reaction.
See Eqs. (6.10) (6.12).
(b) (3) Write down the triple alpha set of reactions that converts He to C. What qualitative statement can
you make about the lifetime of 8
Be and its significance?
See Box 6.2. Since the lifetime of these nuclei is very short, the reaction requires that they be continually
produced at high temperature and density.
(c) (3) Why does fusion produce energy for light elements, and fission for heavy elements?
See Fig. 6.7 and p. 116..
(d) (3) What is the heaviest element that can be produced in normal fusion reactions in stars, and why?
Iron 56, see p. 116.
(e) (3) How are heavier elements produced, with larger atomic numbers Z ? E.g., how were the selenium
( Z = 34 ) and iodine ( Z = 53) in your body produced?
Supernovae, see p. 119.