Nuclear Theory

1. Nuclear Theory SPS3. Students will distinguish the characteristics and components of radioactivity. Differentiate among alpha and beta particles and gamma radiation. Differentiate between fission and fusion. Explain the process half-life as related to radioactive decay. Describe nuclear energy, its practical application as an alternative energy source and its potential problems.

2. What Causes Nuclear Reactions? • Occurs when the nuclei is unstable. • Too few neutrons to protons • Too many neutrons to protons • Stable nuclei 1 proton: 1 neutron

3. What Happens to Unstable Nuclei? • Unstable forces the nuclei to emit particles. • The nuclei split into smaller stable atoms (fission). • The nuclei may join smaller atoms (fusion). • The nuclei release a large amount of energy. • Releasing of particles or energy is called radioactivity.

4. Which Atoms Are Unstable? • Most elements with atomic number of 83 or higher. • Also technetium (element 43). • List some elements that are radioactive.

5. Nuclear Fission • Fission – when the nucleus splits into other particles and/or rays. • Atomic Bombs – Fat Man and Little Boy • Energy from stars

6. Practice of Nuclear Fission Instructions: Predict the second nucleus (protons and neutrons) proton 6 protons 14 neutrons neutron 12 protons 23 neutrons

7. Practice of Nuclear Fission Instructions: Predict the second nucleus (protons and neutrons) proton neutron 8 protons 17 neutrons 12 protons 23 neutrons

8. Practice of Nuclear Fission Instructions: Predict the second nucleus (protons and neutrons) proton 5 protons 7 neutrons neutron 12 protons 23 neutrons

9. What Is a Chain Reaction? • Remember that lone neutron? • It goes on to hit lots of other nuclei and they release neutrons and they hit more atoms…. • You get the message?

10. Nuclear Fusion • Fusion – when two nuclei crash together to create new atoms and release energy. • Energy from stars • Thermonuclear power plants

11. Fusion: Thermonuclear Reactor • The energy released from radiation heats up water.

12. What Are the Three Nuclear Particles? • Particles that are emitted from the nucleus or knocked into the nucleus include: • Alpha - 42He • Mass number = 4; atomic number = 2 • Beta - 0-1e • Gamma - 00γ • Neutron – 10n • Positron – 0+1e

13. Information on Top 3 Nuclear Particles • Alpha Particles • Beta Particles • Gamma Radiation • Have a +2 charge. • Are massive and slower. • Can be stopped by a sheet of paper. • Have a -1 charge • No mass and faster • Can be stopped by 3 mm Al or 10 mm wood. • No charge, no mass and fastest • Electromagnetic radiation • Can be stopped using thick block of lead.

14. Balancing Nuclear Reactions • The nuclear reaction is two simple math expressions. • Total mass number (reactants) = total mass number (products) • Total atomic number (reactants) = total atomic number (products) • 11p + 0-1e  • Mass number of reactants: 1 + 0 = 1 • Atomic number of reactants: 1 + (-1) = 0 • New particle is 10 • Look on your particle list, who is this? • 10n • Neutron particle

15. Practice: Nuclear Rxn • 0-1e + 8137Rb  ____ + X-ray • Identify the element • Fission or Fusion? • 8136Kr; krypton; fusion

16. Practice: Nuclear Rxn • 23090Th  ____ + 42He • Identify the element • Fission or Fusion? • 22688Ra; radium; fission

17. Practice: Nuclear Rxn • 158O + 0+1e  ________ • Identify the element • Fission or Fusion? • 159F; fluorine; Fusion

18. Practice: Nuclear Rxn • 23190Th  23191Pa + ________ • Identify the radioactive particle • 0-1e (beta particle)

19. Worksheet – Balancing Nuclear • Work in group to balance eight nuclear equations of choice. • You must get all eight correct. • If you miss one, you must select a new problem.

20. What does Nuclear Radiation look like? Uranium undergoes • Alpha decay to make Thorium • Beta Decay to make Protactinium • Beta Decay to make Uranium • Alpha Decay to make Thorium • Alpha Decay to make Radium • Alpha Decay to make Radon • Alpha Decay to make Polonium • Alpha Decay to make Lead • Beta Decay to make Bismuth • Beta Decay to make Polonium • Alpha Decay to make Lead • Beta Decay to make Bismuth • Beta Decay to make Polonium • Alpha Decay to make Lead

21. What Is Half Life? • Half-life: the time it takes when half the amount of substance is consumed (decays). • Exponential decay • Twizzler lab (if time allows) (p. 116 IN)

22. Activity: Graphing Half Lives • Materials • 1 Twizzler (or pretzel stick) • 1 pencil • 1 paper towel • 1 piece of graph paper • 1 paper towel • Lab sheet – Lab – Half Life and Decay What did I learn?

23. Calculating Half-Life • To calculate, take ½ of the substance until you get to the correct value. • Count how many times you took the half life. • Multiply the half life by the number of times it took to get to the answer.

24. Calculating Half-Life • How many half lives did it take to get to 1.25 g if you started with 10.0 g? • 1st: 10/2 = 5 • 2nd: 5/2 = 2.5 • 3rd: 2.5/2 = 1.25 (1 g) = 3 half lives • How long did that take? • 5730 years x 3 half lives = 17190 years

25. Practicing Half-Lives • Redrum has a half life of 2 days. How many half lives has redrum undergone if there was 100 g of redrum at the beginning and now there is just 3.125 g left? • 1st: 100/2 = 50 • 2nd: 50/2 = 25 • 3rd: 25/2 = 12.5 • 4th: 12.5/2 = 6.25 • 5th: 6.25/2 = 3.125 g (3 g) = 5 half lives • How long did that take? • 5 half lives x 2 days = 10 days

26. Practice – Half Life • How many days are required for 32P to undergo 6 half-lives if the half life 14.3 days. • 6 half lives x 14.3 days = 85.8 days (86 days)

27. Practicing Half-Lives • Redrum has a half life of 2 days. How many half lives has Redrum undergone if there was 500 g of Redrum at the beginning and now there is just 15.625 g left? • How long did that take? • 1st: 500/2 = 250 • 2nd: 250/2 = 125 • 3rd: 125/2 = 62.5 • 4th: 62.5/2 = 31.25 • 5th: 31.25/2 = 15.625 (16 g) = 5 half lives • 5 half lives x 2 days = 10 days to decay

28. Practice – Half Life (Level 2) • Predict the mass of 75.00 g of 198Au after 16.14 days if the half life is 2.69 days. • How many half lives? • 16.14/2.69 = 6 half lives • Divide the mass by two that many times. • 1st: 75/2 = 37.5 • 2nd: 37.5/2 = 18.75 • 3rd: 18.75/2 = 9.375 • 4th: 9.375/2 = 4.6875 • 5th: 4.6875/2 = 2.3475 • 6th: 2.3475/2 = 1.171875 (1 g)

29. Calculating Half-Lives (truth) Formula: • Number of half lives = Elapsed time Half-life Formula: • Amount Remaining = Initial amount(1/2)n • n= # of half lives that have passed. • Initial amount is the quantity you started with.

30. Practice – Half Life (Level 3)Use Formula • Predict the mass of a 125.00 g sample 42K after 62.0 hours if the half life is 12.4 hours. • Number of half lives = Elapsed time Half-life • 62.0/12.4 = 5 half lives • Amount Remaining = Initial amount(1/2)n • x = 125(1/2)5 = 125 x 0.03125 = 3.91 g (4 g)

31. Homework • Balancing Nuclear Reactions Worksheet and Half Life (write the question below on worksheet) • The half-life of barium-131 is 12.0 days. How many milligrams of barium-131 remain after six half lives when the initial amount was 20 mg?

32. Measuring Radiation • A Geiger counter is used to measure radiation. • All radioactive substances emit radiation. • The detector absorbs radiation and changes it to voltage (electrical) • The detector pin moves to show how much radiation.

33. Benefits of Nuclear Reactions • Gives powers to homes • Produces WAY more power than fossil fuels • Does not cause air pollution (clean energy) • Used to kill bacteria in meat

34. Harmful Effects of Nuclear Reactions • Increases the temperature of water in ponds, lakes, streams • Radiation leaks cause health problems among animals (including people) and plants.

35. E = mc2 Nuclear reactions particles are converted into ENERGY according to Einstein. Mass is changed into energy. And he is correct.