Nuclear Reactions

1. Nuclear Reactions Section 4

2. Nuclear Fission • Nuclear fission is the process of splitting a nucleus into several smaller nuclei • Only large nuclei such plutonium can undergo the nuclear fission process • The product of fission includes smaller nuclei and several neutrons • The mass is a little bit less than the original nucleus, the missing mass has been converted into a very large amount of energy

3. E=mc 2 • Albert Einstein thought that mass and energy were related • In his theory, mass could be converted to energy and also energy converted to mass • E=Energy(joules) m=mass(kg) c=[speed of light(m/s)] • If one gram of mass is converted to energy, 100 trillion joules of energy is released 2

4. Chain Reactions • When nuclear fission occurs the single neutrons that are released and they can strike the nuclei that were also released causing them to split apart. This continues and is called a chain reaction. • If the chain reaction is not controlled it releases a tremendous amount of energy in an instant • A chain reaction can be controlled if you have materials to absorb enough neutrons, if enough are absorbed the reaction will go at a constant rate • The critical mass is the amount of material required so that each fission reaction produces approximately one more fission reaction

5. Nuclear Fusion • Even more energy can be released than fission by combining two nuclei with low masses to form a larger mass • Fusion fuses nuclei together, fission splits nuclei apart

6. Temperature and Fusion • For fusion to occur, two positively charged atoms have to get close to each other • They have to get fast enough to close to each other because positive atoms repel other positive atoms • Since kinetic energy increases along with temperature, nuclear fusion only occurs in areas that are millions of degrees Celsius like at the center of stars

7. Nuclear Fusion and the Sun • In the sun fusion occurs when hydrogen atoms combine to form a helium atom, when this occurs a small amount mass is converted into a huge amount of energy. Earth receives a small amount of this energy as heat and light. • As the sun ages hydrogen is used up and eventually all the hydrogen will be gone. That will not happen for another estimated 5 billion years since its only converted 1% of its mass into energy

8. Using Nuclear Reactions in Medicine • Isotopes can be easier to locate in a group of molecules if it is radioactive • When a radioisotope is used to find or position molecules in an organism its called a tracer • Scientists can use tracers to follow where a molecule goes in your body or to study organ functions • Useful tracers include carbon-11, iodine-131, and sodium-24, these are useful because they are important in certain body processes • Tracers are located by detecting the radiation they emit

9. Treating Cancer with Radioactivity • When a person has cancer a group of cells in the body grows out of control and can form a tumor. • You can treat some types of cancer by using radioactivity to ionize the cells

10. Credits Austin Benford Joseph Williams Beau Jones Kennedy Akers