Nuclear Fission and Fusion

1. Nuclear Fission and Fusion An energetic discussion

2.         A little bit on the atom… Neutral neutrons - Nucleus - - - - - - - Negative electrons Positive protons

3. Conservation of Energy/Mass • Energy cannot be created or destroyed – it can only change form. • KE can become PE or vice versa. • E = mc2 • Mass is really a form of energy

4. Another look at E = mc2 • E = energy (J) • m = mass (kg) • c = speed of light (3 x 108 m/s) • Mass is really just another form of energy!

5. How much energy in a buck? • A dollar bill has a mass of 1 gram. G: m = 0.001 kg; c = 3 x 108 m/s; E = ? ER: E = mc2 C: E = (0.001 kg)(3 x 108 m/s)2 E = 9 x 1013 J = 90,000,000,000,000 J E = 12 kilotons of TNT-equivalent

6. Fiss vs. Fuse • Fiss = break down • Start with a larger atom and finish with two or more smaller atoms • Fuse = build up • Start with two smaller atoms and finish with one larger atom

7. Nuclear Fission • Break down of the nucleus or splitting an atom • Uranium 235 is hit with a neutron to become Uranium 236 • Uranium 236 splits apart to become two smaller atoms and 2 or 3 neutrons • The mass of the products is less than the mass of the Uranium 236. • The mass that was “lost” became energy.

8. Uranium 235 Fission

9. Using one fiss to cause another… • A neutron from one fission event hits another Uranium 235 atom • Releases more neutrons • Enough Uranium 235 atoms = sustained chain reaction • Critical mass = 52 kg for U235

10. A Chain Reaction

11. How fission can be used? • GOOD • A controlled chain reaction in a reactor used in nuclear power plants to produce electricity. • EVIL • An uncontrolled chain reaction is used to create incredibly powerful weapons – the atomic bombs dropped on Japan.

12. Nuclear Fusion • Build up of nucleus or fusing of two nuclei to form one large nucleus • Occurs at exceptionally high temperatures – over 100 million degrees • Laboratory Experiments • Deuterium and tritium accelerated • Collide to form one new atom with a larger helium nucleus and a neutron is released • Mass of helium and neutron less than mass of deuterium and tritium • Mass that was “lost” became energy

13. The Sun • Proton-proton chain reaction • Two hydrogen atoms (protons) fuse together to create deuteron • A third hydrogen atom collides with deuteron to create a helium isotope • Helium isotopes fuse to make beryllium which breaks down • Two protons are released and it starts again.

14. How fusion can be used? • GOOD • A controlled reaction in a reactor used to produce cleaner, inexpensive electricity??? • EVIL • A fission bomb starts a fusion chain reaction to create an incredibly powerful weapon – thermonuclear weapons (H-bombs), MUCH more destructive than atomic bombs.

15. A-bomb vs. H-bomb • Atomic bomb (Hiroshima) • Killed over 66,000 people instantly • 13 kilotons of TNT-equivalent • 2 exploded in warfare • Hydrogen bomb • 10 megatons (million-tons) of TNT-equivalent • NEVER exploded in warfare • Is it the bomb too big to ever be used???

16. Sources • Fission and Fusion Animations: http://reactor.engr.wisc.edu/fission.htm • Fission graphic: http://hyperphysics.phy-astr.gsu.edu/hbase/nucene/u235chn.html