Fission: Heavy Elements can reduce energy (i.e. increase binding energy per nucleon) by

1. Fission: Heavy Elements can reduce energy (i.e. increase binding energy per nucleon) by splitting roughly in half.

2. U 235 fission fragment distribution

3. Excess Neutrons 23592U + n →8638Sr • + 15054Xe 23592U + n →8638Sr + 13254Xe +

4. Chain Reaction

6. Reproduction Factor / Criticality • What affects k? • Number of Nuclei / Shape of Mass • critical mass • Number of Released Neutrons per Fission • Cross Section • Is it Fissile? • What do I want k to be?

7. Neutron Cross Section / Thermalization

8. Problem – How to make k~1? • Maximum k for natural U is 1.32 • Not every neutron absorbed by U-235 causes fission. • U-238 absorbs slow neutrons without undergoing fission • Any additional loss of neutrons reduces k • Solutions • Enriched uranium (from 0.7 to ~3 percent) • Heavy water • Control • Control Rods --- Neutron Absorbers

13. SCRAM Safety Control Rod Axe Man

15. Breeder Reactors Then, after ~ 24 min… Then, after ~ 2.3 days…

16. Nuclear Power Pro/Con • Clean energy – no greenhouse gasses • Cheap • Can be safe if properly regulated • Radioactivity • Disasters (but that’s a problem whenever you have concentrated energy!) • Nuclear proliferation

17. Inform yourself! • It’s inevitable • It’s CLEAN and CAN be done safely and environmentally responsibly • It accounts for about 20% of our electricity today • … and 80% of France’s electricity • Get past “not in my back yard”

18. I burned down a field too! • There's no such thing as a "safety candle." • Grasshopper eyes turn red before they pop. • If you let things get out of control, sometimes you won't be able to get them back into control. • There are people who can help (it's less embarrassing not to need them, but if you do, you'd better call them). • It's not going to stay a secret forever. • You can get through this.

19. Fusion--Two nuclei combine to form a heavier nucleus First reaction in early stars 11H+ 11H → 21H + e+ + νe mass before - mass after = energy released/c 2 (2MH1 – 2Me) – (MH2 –Me + Me) = (2x1.0078250u - 0.0005486u) - 2.0141018 u = 0.0009996 u (1uc2=931 MeV) Q = 0.93 MeV

20. Fusion--Two nuclei combine to form a heavier nucleus More reactions in stars 11H+ 11H → 21H + e+ + νe 11H+ 21H → 32He 11H+ 32He → 42He + e+ + νe 32He+ 32He → 42He + 11H + 11H

21. Fusion--Two nuclei combine to form a heavier nucleus One reaction in a hydrogen bomb 21H+ 31H → 42He + n Total mass before -Total mass after = energy released 5.0302 u - 5.0113 u = .0189 u ≈ 17.6 MeV

22. Fusion Reactors • Much less radioactivity • Mostly produces helium-4, but materials near the reaction can absorb neutrons, etc. • Hydrogen is everywhere! • It doesn’t work . . . Yet • Protons repel each other until you get them really close • Really high temperatures needed

23. Plasma Fusion

24. TFTR

27. Inertial Confinement Fusion

34. Other practical uses of nuclear physics… • Nuclear medicine • Nuclear treatment (destroy tumors) • Tracer imaging • PET scan • NMR (MRI) ? • Power for space probes • Dating materials • Sterilization of equipment or food • Smoke detectors

35. Van Dyck’s “Saint Rosalie Interceding for the Plague-Stricken of Palermo” Irradiated with neutrons Detected electrons emitted

36. After a few hours - manganese (found in umber, A dark pigment)

37. After 4 days - phosphorous (found in charcoal)

38. Jackson Pollock – Galaxy Irradiated with neutrons

39. Jackson Pollock – Galaxy Detected secondary emission of truth

40. And beyond • Particle physics, QCD, the standard model • Unification theories / theory of everything • String theory