1. Physics 55 Monday, October 31, 2005 1.Some elementary nuclear physics. 2.Fusion reactions produce the Sun’s energy 3.How do we know what we know.

2. Cloud Chamber Demo of Nuclear Decays

3. Astronomical Junk Food for Halloween

4. Water on Mars

5. PRS: Quarter-Day on October 31 What is the approximate RA and dec of the Sun on October 31, which is about half-way between the fall equinox and winter solstice? 1. 3 h +11.3 o 2. 9 h +11.3 o 3.15 h -11.3 o 4.21 h -11.3 o 5.Some other values.

6. Notation for Nuclei Example: carbon 12 with Z=6, A=12, N=6 12 6 C Proton p has Z=A=1, N=0 Neutron n has Z=0, A=1, N=1

7. Nuclear Reactions and Conservation Laws Conservation laws: 1.Electrical charge 2.Number of nucleons (baryon number) 3.Momentum 4.Angular momentum 5.Mass-energy

8. PRS Question: How to Balance a Nuclear Reaction What are values of x, y, z? 1.x=3, y=2, z=3 2.x=3, y=3, z=2 3.x=11, y=3, z=2 4.x=11, y=2, z=3 5.x=10, y=3, z=2 6.x=10, y=2, z=3

9. E=mc 2 : Mass and Energy Are Interchangeable Albert Einstein: 1879-1955

10. How Einstein Discovered His Formula

11. Small Amount of Mass Can Release Enormous Amount of Energy Energy from one grain of salt (0.1 mg) could lift the space shuttle of 2,000,000 kg how high? Equate gravitational energy mgh (valid near Earth’s surface) to mass energy E=mc 2.

12. Energy From Chemical or Nuclear Reactions: Final Mass is Less Than Initial Mass Any chemical reaction, here Br and P gives PBr 3 + heat One-millionth of mass is converted Any nuclear reaction, here fission n + 235 U yields smaller nuclei plus lots of energy. About 1% of mass is converted

13. Important Point: Nuclear Energy Greater than Chemical Energy Because of Strong Interaction, Not Because of E=mc 2. Four ways that quantum particles interact with each other: 1.Gravity 2.Weak interaction 3.Electrical interaction 4.Strong interaction

14. PRS Question If one squeezes a spring as shown, the mass m of the spring 1.increases. 2.decreases. 3.remains unchanged.

15. Creation of Matter Out of Energy Particle Tracks in Bubble Chamber circa 1950s

16. Energy to Mass Conversion in 2005 RHIC: Relativistic Heavy Ion Collider

17. How To Convert All of Mass into Energy? Antimatter! Watch out for trails of.511 MeV photons in space!

18. Antimatter is Not Science Fiction Positron Emission Tomography: PET Scan Healthy Alzheimer

19. A Cosmological Mystery: Where is All the Antimatter? When humans create antimatter at CERN or RHIC, we always see equal amounts of matter and antimatter being created. So why does observable universe just made of matter?

20. Source of Energy: Fusion of Nuclei Solution required many radical discoveries and new theories: 1.Discovery of radioactivity (Becquerel, 1900) 2.Discovery of atomic and nuclear structure (1900-1920) 3.Discovery of antimatter 4.Einstein’s theory of special relativity, E=mc 2 (1905) 5.Invention of quantum mechanics (1905-1930)

21. Fusion Occurs Only at High Temperatures Strong interaction Quantum tunneling helps

22. The Proton-Proton Chain in the Sun’s Core Simultaneous multiparticle collisions quite unlikely, proceed by pairwise collisions. Weak interaction, one of four fundamental forces, plays key role in fusion reactions. Chapter S4 has more info.