1. Fission & Fusion

2. Radioactive Elements Any element over atomic number 83 is radioactive.
Radioactive materials have unstable nuclei (too few or too many neutrons).
When an unstable nucleus decays, it breaks apart emitting particles and energy as it decays.
Three types of nuclear radiation:
Alpha particles
Beta particles
Gamma radiation electromagnetic wave

3. Fission
The process used to release nuclear energy by splitting nuclei is called fission ENERGY

4. What nuclei can split during nuclear fission?
Only large nuclei like U or plutonium can split apart during nuclear fission.
Click on image for animation

5. What nuclei can split during nuclear fission?
                                              
U-236 is so unstable that it immediately splits into barium & krypton nuclei, several neutrons & a large amount of energy

6. Chain Reaction
Free neutrons produced by fission can hit other nuclei emitting more neutrons repeating the reaction over and over.
A series of fission reactions is called a chain reaction.
Can only be slowed by using materials that will absorb the neutrons.

7. Chain Reaction
An uncontrolled chain reaction releases a huge amount of energy in a short time & requires a critical mass of starting material to produce more reactions.

8. Fusion The sun is powered by nuclear fusion.
In a nuclear fusion reaction, two small, light nuclei combine to form one larger, heavier nucleus.
Two hydrogen atoms combine under extreme heat and pressure to form a helium atom. (H-2 + H-2→He-4)

9. Fusion
Why would we want to use the fusion reaction in a nuclear power plant?
1. Hydrogen is the most common element in the universe.
2. Could meet energy demands for millions of years

10. How are temperature & fusion related?
How can two nuclei get close enough to combine? They must be moving very fast.
All nuclei positively charged
Thus repel each other
KE must overcome electric force to push them close enough to combine
KE increases as temperature increases
Temp must be millions of °C like Sun & other stars

11. How does the Sun produce energy?
The Sun, made mostly of H produces its energy by fusion of H nuclei
2 protons (H-1) fuse to make a H isotope (H-2); then H-1 + H-2 form an isotope of He-3.
positron
Light
light
neutrino
The emission of a positron or a positive electron is referred to as beta decay. The positron is accompanied by a neutrino, a massless and chargeless particle. Positrons are emitted with the same kind of energy spectrum as electrons in negative beta decay because of the emission of the neutrino.

12. How does the Sun produce energy?
To complete the process, 4 H nuclei combine into 1 He nucleus during which a small amount of matter changes into a huge amount of energy.

13. Fusion on the Sun
The heat & light Earth receives comes from this process.
About 1% of the Sun’s hydrogen has been changed into energy.
Sun has enough H to continue fusion reactions for another 5 billion years.

14. Fusion vs. Fission
Comparison Chart Fission vs. Fission

15. Radiation Background radiation can come from Sun Water Plants
***Radon is the largest source of radiation in the earth’s crust.***

16. Radiation Damage Mutate hemoglobin Mutate cells, lose function
Destroy immune system
Burn skin, destroy bone

17. Radioactive Tracer What is a radioactive tracer?
- short lived isotope that can be observed with a sensitive detector

18. Radioactive Tracer How are they used?
- Agriculture – measure water flow
- Medicine – locate tumors
- Medical research – trace drug paths thru body
- Geology – trace underground water flow