1. Unit 8 Ch. 25 Half–Life Fission Fusion
ABClark-Grubb

2. Half - Life The time required for
one-half of nuclei of a radioisotope sample to decay to products.

3. Example:
Radon–222 emits alpha radiation and decays with a half-life of 3.8 days. Assume you have a mass of 916 g Radon.
How long is 4 half-lives?
3.8 days x 4 = 15.2 days
How many grams of the isotope remain at the end of 4 half-lives?
In 31 days, how many half-lives will Radon-222 go through?
31 days ÷ 3.8 days = 8.2 half-lives
916 g x x x x
= g left

4. Nuclear Fission The splitting of a nucleus into smaller fragments
U-235 and Pu-239 are the only fissionable isotopes
Fission can release enormous amounts of energy
Fission can be controlled so energy is released more slowly (nuclear reactors)

5. Nuclear Fusion
Occurs when nuclei combine to produce a nucleus of greater mass
Release much more energy than a fission reaction
Using fusion as an energy source is appealing but not practical. . .too difficult to achieve the high temperatures needed to start the reaction

6. Assignment
Complete:
Page 806 7,8
Page b-d,13
Page