1. Nuclear Fission and Fusion
Chapter 7.2
Mrs. Chilton

2. Nuclear Stability
Some elements have isotopes that are stable, while others are unstable and radioactive
Example: C-12 -> stable
C-14 -> unstable, radioactive, gives off beta particles
Depends on nuclear forces holding nucleus together

3. Strong Nuclear Force How do like charges act? They repel!
So, why does the nucleus with so many p+ stay together?
Strong nuclear force – stronger force than electric repulsion, but only over a short distance

4. Neutrons & Stability Neutrons add to the stability of a nucleus
They have no charge, so they do not repel
Too many or too few neutrons leads to decay
All nuclei with 83 or more protons are unstable

5. Fission When a nucleus splits into two or more smaller fragments
Neutrons and energy are released

6. Fission -> Chain Reaction
One neutron can split the nucleus of an atom
As that nucleus undergoes fission, it releases more neutrons which can strike nearby atoms, causing them to split
This can cause a chain reaction

7. Nuclear Chain Reaction

8. Uncontrolled chain reactions
This principle is used in nuclear bombs
Two or more masses of U-235 are contained in bomb surrounded by powerful explosive
When detonated, fission chain reaction occurs releasing LARGE amount of energy which causes devastation to environment and life forms
Fortunately, concentration of U-235 in nature is too low to start a chain reaction, most is more stable form of U-238

9. Controlled Chain Reaction
Not all neutrons released in a fission reaction succeed in triggering fission reaction
Materials that absorb neutrons can be used to slow chain reaction
Concept is used in nuclear power plants to generate energy

10. Nuclear Reactor

11. Fusion
Energy can also be obtained when two lighter nuclei fuse together to form a larger nucleus
In stars, including our sun, energy is produced when hydrogen nuclei undergo fusion and release TREMENDOUS amounts of energy

12. Fusion in the Sun
Multi-step process where two different isotopes of hydrogen fuse together to form a helium nucleus and energy in form of gamma rays

13. Dangers of Nuclear Radiation
Changes structure of hemoglobin
Changes structure of macromolecules in body – health is affected
Particles ingested through food can damage linings of organs
Destroys bone marrow
Lung cancer (Radon gas)
Genetic mutation

14. Beneficial Uses of Nuclear Radiation
Smoke alarms –produce alpha particles to create electric current
Controlled doses are used to treat some cancers – beams of gamma rays
Radioactive tracers
Nuclear power – much less pollution, more efficient (waste must be dealt with, though)

15. Radioactive Waste Disposal