31.1 Nuclear Reactions and Transmutation

1

• 31.1 Nuclear Reactions and Transmutation
• When a particle collides with a nucleus
• Charge, energy and momentum are conserved
• Does the reaction have excess KE after the
  reaction?
• Q gt 0 or exothermic
• Q lt 0 or endothermic (requires KE input)
• Enrico Fermi determines that neutrons are the
  most effective projectiles for nuclear reactions.

2

• 31.2 Nuclear Fission
• 200 MeV / fission

3

• 31.2 Nuclear Fission
• Starter neutrons for nuclear reactors
• Slow vs. fast neutron capture
• Not 100 guaranteed
• 235U has about 40 decay modes with all fragments
  being radioactive

4

• 31.2 Nuclear Fission
• Slow neutrons absorbed easier by 235U
• Moderator heavy water, graphite
• Criticality
• Some neutrons are absorbed without fission or
  escape
• Depends on geometry and the distribution and type
  of material
• Decrease number of escaping neutrons
• Control rods B, Cd

5

• 31.2 Nuclear Fission
• Nature 99.3 238U and 0.7 235U
• Reactors 96 238U and 4 235U
• Weapons 10 238U and 90 235U
• Critical mass (a few kg)

6

• 31.2 Nuclear Fission
• Safety - Structure, leaks, transport/storage of
  waste

7

• 31.3 Nuclear Fusion
• Most stars are in hydrostatic equilibrium
• For fusion T gt 107 K and ? gt 100 g/cm3
• Net result (26.7 MeV)

8

• 31.3 Nuclear Fusion
• Reactors fuel, temperature, density, containment
• Waste products 3H, n (structural damage)
• Small amounts and short half-lives

9

• 31.3 Nuclear Fusion

10

• 31.3 Nuclear Fusion