1. How energy is released in fission
How nuclear bombs work. How nuclear power works.

2. Nuclear Binding Energy
The mass of nucleons:
mass of protons: E-27
mass of neutron: E-27
Sum of the masses of protons and neutrons in an atom is greater than the mass of the nucleus
Missing mass was converted to energy used to overcome repulsion: binding energy.
The binding energy is a function of the specific nucleus; calculated as binding energy/nucleon

3. Relative binding energy per nucleon
Relative binding energy per nucleon

4. The nucleon gives up some mass as energy as it becomes part of the nucleus. The more energy it gives up, the less mass each nucleon has.

5. Rope and knot analogy
Part of the rope is used to tie the knot. The bigger the knot, the less rope available for tying something up.
The knot-tying is a one time expenditure of energy w/ lasting effect.

6. Nuclear fission
Large elements are intrinsically unstable and will split when they absorb a neutron: Fission
Example: U-238
Average Binding energy is 7.6 MeV/nucleon
Suppose it splits into two atoms of 119 each
An atom of atomic mass 119 normally has a binding energy of 8.5 MeV/nucleon.
The A.M. 119 atom produced by fission of U-238 has not given up enough of its mass as energy.
So it does.

7. Relative binding energy per nucleon
Relative binding energy per nucleon

8. Energy release in fission
8.5 (normal) – 7.6 (fission product) = 0.9 MeV
An additional 0.9 MeV of energy (mass TO energy) must be given up PER NUCLEON.
238 x 0.9 MeV = 214 MeV per atom of uranium split.
In what form is this energy?
Fission products (atoms) moving away
Gamma rays
Subsequent radioactive decays
neutrons

9. Criticality
When other U-238 atoms are close enough, neutrons released from fission are absorbed, causing another atom to undergo fission.
The amount of U needed for this to occur is the critical mass; the situation: criticality.
Result, an exponentially increasing number of fission reactions with release of binding energy
Plutonium (Pu-242) even more readily undergoes fission, making it more “useful”

10. The Atomic Bomb Einstein discovers e = mc2
Scientists recognize that purified uranium can be used to make a bomb, and WW II Germany starts enriching uranium.
Einstein alerts US Government, and the Manhattan Project begins
Bomb: chain reaction, an exponentially increasing number of fission reactions
Requires purified uranium (or plutonium) brought to together rapidly to create a critical mass

11. Boom
Subcritical quantities of U or Pu brought together rapidly by conventional explosives
Massive chain reaction perpetuated by neutrons releases nuclear binding energy
Matter transformed into energy e = mc2
Energy released in the form of: heat, light, gamma rays, and lots of neutrons (which make other atoms radioactive)

12. Result of Boom
Fallout: tons of soil and debris into atmosphere by heat and updraft
Incl. fission daughters and atoms made into radioisotopes from neutrons
Principle components: C-14, Na-24, Sr-89, Pu-239, I-131, Cs-137, and Sr-90
I-131 falls on fields, grazed by cattle, appears in milk, ingested by children, concentrated in thyroid.
High incidence or thyroid cancer

13. The Hydrogen (fusion) bomb
Fusion: 2 atoms of H combine to make He
Avg. binding energy per nucleon much higher for helium than hydrogen, so lots of energy released.

14. Fusion continued To get 2 atoms of H to fuse requires energy
Feature of the sun, a fusion reactor
Thus the search for “cold fusion”; cold being less than thousands of degrees
Limitless source of energy without radioactive waste
Hydrogen bomb
Heat from conventional A-bomb drives fusion reaction.

15. Nuclear Terrorist threats
Dirty Bomb
Conventional explosive packed with radioisotope such as Cs-137 or other “hot” industrial isotope.
Relatively cheap and easy to make
Relatively little radiological damage, but high fear factor, good terrorist weapon
Suitcase nuke
Miniaturized A bomb
Plans on internet
Need U or Pu

16. Nuclear Power
Radiation from radioactive decay gives up its energy ultimately as heat
Fission reactions are controlled (moderated) to prevent an exponential increase in the fission reaction.
Result is a steady liberation of heat that can be used to generate steam to drive turbines to generate electricity

17. Nuclear Power

18. More details on nuclear power
Moderators
Various options, but plain water most common
Slow down the neutrons to the energy level of “thermal neutrons”; these are readily absorbed by nuclei to promote fission reactions.
Control rods
Absorbing material that blocks neutrons from hitting fissile material, slows down chain reactions.
Waste: consists of daughter isotopes
Neutrons can be made to create radioisotopes