# Astronomy 300: Homework Assignment #7

Due: Friday, April 13

After reading Ch 9 in Croswell:

1. How did Fred Hoyle know that the nucleus of Carbon had a special energy state, known as a "resonance"?

2. What are the r-process and the s-process? How do they differ?

3. Which seminal paper first demonstrated their importance? Which two reactions permit the s-process to occur? How was Cameron's paper presenting the first of these reactions received?

After reading Sec. 10.3 in C&O:

4. A.) To see that E=mc2 is relevant even to chemical reactions, perform the calculation suggested on p. 299 as follows:

Which has lower mass: a Hydrogen atom (consisting of an electron orbiting a proton at the Bohr radius) OR a proton plus an electron (assumed to be a large distance apart)? Use values for physical constants in your book. Does your result make sense in light of Coulomb's Law?

B.) Compute the mass difference, in kg, and convert it into an energy difference, recording as many significant figures as needed. Express this energy in both Joules and eV.

5. Suppose 1000 kg of Hydrogen inside the Sun undergoes nuclear fusion.
What is the mass of Helium that is produced?
6. In the example just above, how much energy is released?

7. A.) How much mass, in kg, does the Sun lose in one second due to nuclear fusion? How about in one day?
B.) How much mass will the Sun have lost after it is 10 billion years old? Express this as a fraction of the Sun's total (current) mass.

8. Compare the energy released in one second by the Sun to that released by a nuclear weapon of your choice. Use this comparison to create a simple sentance which you can say to non-scientists to give them some idea of the energy output of the Sun. (For more information on nuclear weapons, and to test your own simulated ones visit: http://nuclearsecrecy.com/nukemap/ )

9. Using a periodic table, fill in the blanks in these nuclear reactions involving beta (positive) decays. (Both reactions are relevant to stellar energy generation):

13N → ??___ + e+ + νe

19F → ??___ + e+ + νe

Hint: Start with the most basic weak interaction, that of decay of a neutron.

10. Suppose you wish to make a model of a star. You begin by assuming it to be spherically symmetric. Hence all properties of the star can be written as a function of radius alone, f(r). Which properties could you include in your model? List as many as you can think of. What other starting assumptions (that is, initial attributes of the star) would you need to create the model?