1. Nuclear Chemistry
Lesson 2

2. F ission splitting a nucleus into two or more smaller nuclei
1 g of 235U = 3 tons of coal

3. F ission chain reaction - self-propagating reaction
critical mass - mass required to sustain a chain reaction

4. Fission and the Atomic Bomb
Two masses are kept apart until detonation. When combined they create a critical mass and the chain reaction begins
Little Boy & Fat Man

5. Fission Nuclear Reactors
Shearon Harris

6. Fission Reactors
Shearon Harris, like all reactors that supply us with electricity, is a fission reactor.
Shearon Harris operates using uranium rods enriched to 3% U-235, but controls the rods from reacting too quickly by using neutron absorbing cadmium and boron

8. Nuclear Waste Spent rods can be reused in some cases
Some products, though, are extremely radioactive and must be safely stored for approximately 20 half lives (thousands of years)

9. Fusion combining of two nuclei to form one nucleus of larger mass
thermonuclear reaction – requires temp of 40,000,000 K to sustain
1 g of fusion fuel = 20 tons of coal
occurs naturally in stars

10. Fusion in the Sun
Supplies the Earth with nearly limitless energy today
Sun will eventually run out of fusible matter and will die.

11. Fusion Nuclear Reactors Bikini Island Nuclear Test
Like “mini” suns
Need tons of energy to get the reaction started and keep it going
Currently not sustainable but potentially could give “clean” energy

12. Fission vs. Fusion FISSION FUSION 235U is limited fuel is abundant
danger of meltdown
toxic waste
thermal pollution
fuel is abundant
no danger of meltdown
no toxic waste
not yet sustainable

13. Uses of Radiation Food Irradiation
 radiation is used to kill bacteria and increase shelf-life of food
Irradiated milk has a shelf life of 3 months without refrigeration.
USDA has approved irradiation of meats and eggs.
Radioactive Tracers
explore chemical pathways
trace water flow
study plant growth, photosynthesis

14. Uses of Radiation Radiation Treatment
Iodine-131 is used to measure thyroid activity.
The gas xenon-133 is used to diagnose respiratory problems.
Iron-59 is used to diagnose anemia.
larger doses are used to kill cancerous cells in targeted organs
internal or external radiation source

15. Dangers of Radiation
Radiation fragments and ionizes molecules found in biological tissue. This causes mutations that can disrupt mitosis and normal cell function.
Can cause various types of cancer in the exposed individual
If mutations occur in the gametes (sperm or egg cells) they may be passed on to the offspring

16. Effects of Radiation

17. Half-Life
The time required for one half of the nuclei of a radioisotope sample to decay to stable products.
Every half-life, the mass of a sample is cut in half.
Formula:
m = mo(0.5)t/h
m = mass after decay t = time
mo = original mass h = half-life
Thus, # half-lives = t/h

18. Practice Problem
Carbon-14 emits beta radiation and decays with a half-life of 5730 years. Assume you start with a mass of 2.00 x g of carbon How many grams of the isotope remain after 17,190 years?
m = mo(0.5)t/h
m = (2.00 x 10-12g)(0.5)17190/5730
m = 2.50 x g

19. Practice Problem
What is the half life (h) of a radioisotope if a 12 gram sample decays into a 3 gram sample over a period of t = 25.0 years?
# Half-lives:
12 g (0 half-life) 
6 g (1 half-life) 
3 g (2 half-lives)
# half-lives = t/h
2 = 25 yrs/h
h = 12.5 years