The Atomic Nucleus

1. The Atomic Nucleus Chapter 14

2. Looks suspicious, but delicious… • Suppose you are given three radioactive cookies (they don’t actually exist)…one is an alpha emitter, one a beta emitter and one a gamma emitter. • You must eat one, hold one in your hand and put the other in your pocket. What can you do to minimize your exposure to radiation?

3. Radiation • What makes an element radioactive? • Unstable nucleus • An unstable nucleus decays (breaks down) and releases energy in the form of radiation • All elements with an atomic number greater than 82 are radioactive

4. Radiation Types • What are the three different types of radiation?

5. Alpha Particle • Why are alpha particles so easy to stop? • They are very large and positively charged • They quickly pick up electrons in the atmosphere/air and become neutral helium (which is harmless)

6. Beta Particle • What is special about a beta particle? • It’s like an electron, but comes from the nucleus • Created when a neutron turns into a proton • They are very small and move very quickly

7. Gamma Rays • Why are gamma rays so hard to stop? • They have high energy, no mass and no charge, so they do not interact with anything • Only stopped by incredibly dense materials, which makes them very dangerous

8. Effects on Humans • How does radiation affect humans? • We can absorb small amounts without much risk • We are surrounded by natural radiation everyday from the Sun, the soil, etc… • Ex. Ingested potassium (40K) • Too much can alter or destroy the atoms in our cells beyond repair and can cause cancer or mutation

9. Exposure • What part of our body is most at risk from a nuclear accident? • Thyroid • It absorbs all iodine in the bloodstream • Taking iodine tablets helps prevent it from absorbing radioactive iodine

10. Measuring Radiation • What instrument measures radiation? • Geiger counter • Measures in Sieverts (Sv)

11. Looks suspicious, but delicious… • Suppose you are given three radioactive cookies…one is an alpha emitter, one a beta emitter and one a gamma emitter. You must eat one, hold one in your hand and put the other in your pocket. What can you do to minimize your exposure to radiation? • RUN AWAY! • Alpha – Hand • Beta – Pocket • Gamma – Eat

12. Isotopes • What are isotopes? • Atoms of the same element, but with different numbers of neutrons • Ex. Three isotopes of hydrogen: • 11H – protium • 21H – deuterium • 31H – tritium

13. Isotopes • What is a simpler notation for isotopes? • Place the name/symbol of the element in front of the mass of the isotope • Two uranium isotopes: • U-238 (nuclear weapons) • U-235 (nuclear reactors)

14. Isotopes and Atomic Mass • How do isotopes affect the average mass of an element? • It’s an average of all the known isotopes of that element • Weighted based on its natural abundance

15. Average Atomic Mass – Rubidium • If the abundance of 85Rb is 72.2% and 87Rb is 27.8%, what is the average mass of Rb? • Average mass = (72.2%)(85) + (27.8%)(87) • Average mass = (0.722)(85) + (0.278)(87) • Average mass = 85.56 amu

16. Average Atomic Mass – Uranium • Uranium has three common isotopes. If the abundance of U-234 is 0.01%, the abundance of U-235 is 0.71%, and the abundance of U-238 is 99.28%, what is the average atomic mass of uranium? • 237.98 amu

17. Average Atomic Mass – Titanium • Titanium has five common isotopes: Ti-46 (8.0%), Ti-47 (7.8%), Ti-48 (73.4%), Ti-49 (5.5%), Ti-50 (5.3%). What is the average atomic mass of titanium? • 47.92 amu

18. Transmutation • What is transmutation? • An element turns into another element as a result of radioactive decay or bombardment • Decay – losesan alpha or beta particle or releases gamma radiation • Bombardment - nucleus was hit with another particle and capturesit

19. Transmutation • What happens when Uranium-238 undergoes alpha decay? • Set up nuclear reaction • U-238 on the left • New element and alpha particle on the right • MAIN RULE: Keep the atomic numbers and masses balanced on each side of the reaction

20. Nuclear Reactions • What are some important things to remember about nuclear reactions? • Neutrons (10n) are sometimes released when an atom decays • Neutrons can also be captured by bombardment

21. Nuclear Reaction Practice

22. More Nuclear Reaction Practice

23. Decay Series • What is a decay series? • When a radioactive element continues to decay until it is no longer radioactive (stable) • Ex. Astatine-210 eventually decays into stable Mercury-198

24. Decay Series - Radon • The inhalation of radon-222 and its decay to form other isotopes poses a health hazard. Write balanced nuclear equations for the decay of radon-222 to lead-206 in eight steps. • Step 1: Radon-222 decays by alpha emission. • Step 2: The daughter product in part 1 decays by alpha emission. • Step 3: The daughter product in part 2 decays by beta and gamma emissions. • Step 4: The daughter product in part 3 decays by beta and gamma emissions. • Step 5: The daughter product in part 4 decays by beta emission. • Step 6: The daughter product in part 5 decays by alpha emission. • Step 7: The daughter product in part 6 decays by beta and gamma emissions. • Step 8: The daughter product in part 7 decays by alpha and gamma emissions. • The final stable isotope is lead-206.

25. Decay Series - Radon

26. Nuclear Fission • What is nuclear fission? • Breaking a nucleus into smaller nuclei which releases energy • Ex. Uranium-235 can split when bombarded with a neutron

27. Nuclear Fission • What makes a nucleus want to split apart? • There are two forces that act on a nucleus: • EM force – pulls it apart • Strong force – pulls it together • As a nucleus gets larger, the strong force cannot hold it together • The EM force pulls it apart to create two smaller more stable nuclei

28. Nuclear Fission • What is a chain reaction? • When some isotopes undergo fission they create neutrons which cause more fission reactions to take place

29. Nuclear Fission • What is critical mass? • A large enough piece of a radioactive substance that undergoes a continuous chain reaction and releases enormous amount of energy

30. Fallout • Why is radioactive fallout dangerous? • Fallout, or black rain, is made of radioactive pieces of dirt and dust ejected into the air • Can be carried great distances by wind

31. Nuclear Detonation in Seattle

32. Nuclear Power • How does a nuclear reactor keep the chain reaction under control? • Control rods which absorb neutrons keep the reaction under control

33. Nuclear Power • What happens during a nuclear meltdown? • Fuel rods overheat and melt through the containment chamber releasing radioactivity into the environment

34. Nuclear Fusion • How is fusion different from fission? • Two smaller atoms combine to make a heavier atom • An enormous amount of energy is released in the process (much more than fission) • Ex. Hydrogen fusion inside the sun’s core

35. Nuclear Fusion • What condition is required for nuclear fusion to take place? • Atoms must be moving at super high speeds to overcome the EM force • This means high temperatures are required at about 15 million °C

36. Time • How long does it take a radioactive element to transmute (change into another element)? • Every isotope decays in a different amount of time • Can measure decay time using a process called half-life

38. Half-Life • What does half-life measure? • The amount of time it takes for half of the atoms to transmute • Ex. U-238 has a half-life of 4.5 billion years

39. Half-Life • What are some unique properties of half-life? • Very precise • Not affected by external (outside) conditions like temperature • Isotopes that decay quickly release more radiation

40. Half-Life Activity • Make a table in your notes with 10 rows using the following headings: • Fill in the first row of your table with your starting data 0 0 0 1 2

41. Half-Life Activity • Gently shake the bag for the specific amount of time that corresponds to the half-life of your candy: • Half-life of M&Mium (M&Ms) is 3 seconds. • Half-life of Skittlium (Skittles) is 4 seconds. • Gently pour out the candy on a notebook or piece of paper. • Count the number of pieces with the print side down. These atoms have "decayed." Record your data and return only the pieces with the print side up to the bag. • Record the time. For example, for M&Ms it would be 3 seconds on the first roll. On the second roll, it would be 6 seconds. • Consume the "decayed" atoms.  • Gently shake the bag again for the prescribed amount of time. • Continue shaking, counting, recording and consuming until all the atoms have decayed. If you need more rows, please add them.

42. Half-Life Activity • Please graph your findings using the following axes:

43. Post-Activity Questions • At the end of 2 half-lives, about what percent of the atoms have not decayed? • Around ¼ , About 25%

44. Post-Activity Questions • What is the shape of the curve in the graph of your data? • Exponential

45. Half-Life Practice • The isotope Cesium-137 has a half-life of 30 years. How long will it take to decay to about 1/16th its original amount? • 120 years (4 half-lifes)

46. Half-Life Practice • What is the half-life of a 100.0 g sample of Nitrogen-16 that decays to 12.5 g of Nitrogen-16 in 21.6 s? • 7.2 seconds

47. Half-Life Practice • Potassium-42 has a half-life of 12.4 hours. How much of an 848 g sample of Potassium-42 will be left after 62.0 hours? • 5 half-lifes, so 26.5 grams

48. Half-Life Practice • If the half-life of Iodine-131 is 8.10 days, how long will it take a 50 g sample to decay to 6.25 g? • 24.3 days

49. Half-Life Practice • All isotopes of Technetium are radioactive, but they have widely varying half-lives. If an 800 g sample of Technetium-99 decays to 100 g of Technetium-99 in 639000 years, what is its half-life? • 3 half-lifes • 213000 years

50. Half-Life Practice • A 208 g sample of Sodium-24 decays to 13 g of Sodium-24 within 60 hours. What is the half-life of this radioactive isotope? • 4 half-lifes • 1 half-life = 15 hours