1. A Nuclear Primer
When energy leaves an atom, it’s usually called radiation; that scares civilians.
Caused by electrons: light, x-rays, low energy electrons
Caused by nuclear processes:
 helium nucleus
 electron or positron
 high energy photon
p,n proton or neutron
Other energetic particles possible

2. Radiation Units Geiger counter video - watch dial
curie (Ci) and becquerel (Bq) are certain numbers of decays per second
rad and gray (Gy) measure how much energy is deposited in a kg of tissue.
rem and sievert (Sv) measure how much damage is done. 1 Sv = 100 rem
rem = rad * RBE
It’s rems that harm you

3. Radiation Sickness Consider whole body doses
< 100 rem no short-term illness
nausea, hair loss
300 LD50
> survival unlikely
Alexander Litvinenko

4. Cancer and the linear hypothesis
2500 rem whole body gives 100% chance of excess cancer
So 25 rem whole body gives 1% chance of excess cancer
Give 100 people 25 rem each, expect one extra cancer (20 from other causes)
Most people assume linear hypothesis at all dose levels, so 25 mrem gives 0.001% chance of excess cancer.

5. Fission and fusion energy
Fission occurs when a nucleus splits
Fragments have less mass than the original nucleus; E = mc2
Fusion occurs when two lighter nuclei fuse into a single heavier nucleus.
Again, mass goes missing and comes out as energy (lots of it)
How can this happen in both cases?

7. Fusion generates lots of relatively clean power, but requires high temperature and probably magnetic confinement
Fusion is the power source of stars
Fusion bombs are the most powerful ever made

8. Chain reactions The power of repeated doubling
Neutrons initiate fission, and fission creates more neutrons
Runaway chain reaction is a bomb
Critical mass is required (15 kg for U-235, 5 kg for Pu-239) to ensure enough neutrons are absorbed
Make critical mass with “gun” or with implosion

9. How to make a bomb Enrich uranium to increase U-235 Use plutonium
Gas centrifuges
Modern, efficient, but need strong material for their construction
Calutrons
Slow but sure; Saddam tried this method
Use plutonium
Implosion must be used; hard to do
Use fission bomb to start a fusion reaction (H-bomb)

10. The only winning move is not to play the game
Bomb damage
20 kiloton about a mile away
Light/x-ray pulse
Thermal pulse
Blast wave
Radioactive fallout
New York City example
The only winning move is not to play the game

11. A reactor hodge-podge Fast vs. slow neutrons Moderators
Bombs need fast neutrons to get enough doublings in a short time
Reactors generally use slow neutrons, since they are absorbed more readily by the smaller fraction of U-235
Moderators
Used to slow the neutrons down - “thermal”
Water, heavy water, graphite

12. A reactor hodge-podge, p.2
Control rods
Absorb neutrons to control the reaction
Neutron absorbed by U-238 gives Pu “breeder” reactor
Sometimes uses fast neutrons. Less safe but more efficient.
Depleted uranium “bullets”