1. Chapter 18

2. + TED:Radioactivity-Expect the Unexpected by Steve Weatherall https://youtu.be/TJgc28csgV0?list=PL hDvDlD3b85zmvERO_rSSUj3FVWScEA _X

3. + Isotopes Isotope: atoms of the same element that have different number of neutrons Carbon-12 ? ? ? ?

4. + What holds the nucleus together? Strong force: attractive force that acts between protons and neutrons in an atomic nucleus

5. + What is radioactivity? When the strong force is not large enough to hold a nucleus together tightly, the nucleus can decay and give off matter and energy. This process of nuclear decay is called radioactivity.

6. + Types of Decay

7. + Alpha Decay Alpha particle = Made of 2 protons and 2 neutrons Charge of +2 Are more massive than gamma and beta Can be stopped by a sheet of paper +

8. + Beta Decay Beta particle = An unstable neutron decays into a proton and emits an electron This electron is called a beta particle Faster than alpha particles Can be stopped by aluminum foil Charge = -1 + e e

9. + Gamma Rays Gamma rays are usually emitted from a nucleus when alpha decay or beta decay occurs Are electromagnetic waves They have no mass and no charge and travel at the speed of light Can be stopped by thick blocks of lead or concrete Have no charge

11. + Half Life Radioactivity

12. + What’s half life? The half-life of a radioactive isotope is the amount time it takes for half the nuclei in a sample of the isotope to decay

13. + Half Life Analogy You have $200 in your wallet. You go shopping and spend half of your money in 1 hour. How much do you have left? After another hour, you spend half of your remaining money. Now how much do you have left? After a 3 rd hour of shopping you spend half of what you have left on lunch before you head home. How much money do you have now?

14. + How to solve a half life problem You have a 200 gram sample of Radon. Its half life is 4 days. How much will remain unchanged after 12 days? Step 1) Make a list of what you know. Starting Mass = 200 grams Final Mass = ????? Half life = 4 days # of half-lives =???? Step 2) Determine what you are solving for. “How much will remain unchanged after 12 days?”  We are looking for how much is left or the final mass.

15. + Solving a half life problem. You have a 200 gram sample of Radon. Its half life is 4 days. How much will remain unchanged after 24 days? Step 3) Solve using a chart. Half lifeTime passedmass Starting (0)None200 grams 14100 grams 2850 grams 31225 grams So we have 3.125 grams left after 24 hours.

16. + Try this one on your own. Polonium-209 decays from 200 grams to 12.5 grams in 8 hours. How long is one “half life”?

17. + Try this one on your own. Polonium-209 decays from 200 grams to 12.5 grams in 8 hours. How long is one “half life”? Half lifeTime passedmass Starting (0)None200 grams 1100 grams 250 grams 325 grams 4812.5 grams Starting Mass = 200 grams Final Mass = 12.5 g Half life = ?? Time = 8 hours # of half-lives =????

18. + Graphing Half-Life How much is left after 1 half life? 2 half lives? (g)

19. + Physical Science Chapter 18 Section 4

20. + Nuclear Fission Nuclear fission is the process of splitting a nucleus into several smaller nuclei Fission means “to divide” Occurs in Nuclear Power Plants

21. + Chain reactions Neutrons are emitted during fission. These neutrons can strike other nuclei in the sample and cause them to split. Which can cause even more atoms to split This series of repeated fission reactions caused by the release of neutrons is a chain reaction

22. + Nuclear Fusion In nuclear fusion, two nuclei with low masses are combined to form one nucleus of larger mass Occurs in the sun