NUCLEAR CHEMISTRY

1. NUCLEAR CHEMISTRY

2. FYI: Historical Perspective • Henri Becquerel • 1896 - Discovers natural radioactivity

3. FYI: Historical Perspective • Marie Sklodowska, Polish chemist marries Pierre Curie, French physicist • Marie died from leukemia caused by her exposure to radiation • Pierre was killed while crossing the street when he was hit by a vegetable wagon.

4. FYI: Historical Perspective • Ernest Rutherford • 1899 – Discovers alpha, beta and gamma radiation

5. Nuclear Reactions • Involve changes in the composition of nuclei • Accompanied by the release of tremendous amounts of energy • Two types: • Nuclear fission • Nuclear fusion

6. Nuclear Fission • The splitting of a heavy nucleus into lighter nuclei

7. Nuclear Fusion • The combination of light nuclei to produce a heavier nucleus

8. Nuclides • Different atomic forms of all elements • Most small nuclides have equal # of protons and neutrons • Some nuclides have “magic #’s” of protons and neutrons and are especially stable

9. The neutron-to-proton ratio determines the stability of the nucleus • For low atomic #’s: • Equal #’s of protons and neutrons • Above atomic #20 (Calcium): • More neutrons than protons

10. Nuclei whose neutron-to-proton ratio is unstable undergo radioactive decay by emitting 1 or more particles and/or electromagnetic rays:

11. Nuclei whose neutron-to-proton ratio is unstable undergo radioactive decay by emitting 1 or more particles and/or electromagnetic rays: helium nucleus 4.0026 2+ low electron 0.00055 1- low-med high energy radiation 0 0 high proton, H nucleus 1.0073 1+ low-med neutron 1.0087 0 very high

12. Comparing penetrating ability (low-high) and SHIELDING… or thin or block of lead piece of metal

13. Device used to measure the total amount of radiation a person has received Geiger counter

14. Nuclear Equations for Radioactive Decay

15. Alpha Particle Decay • Example 1: Radium-226 transmutates by alpha decay. Write the nuclear equation that represents this process. *the atomic number will change because of changing proton #, so it is a new element and symbol or *the math must equal on both sides

16. Beta Particle Decay • Example 2: Write the nuclear equation for the beta-decay of boron-12. In β− decay, the weak interaction converts a neutron into a proton while emitting an electron or *the math must equal on both sides

17. Gamma Radiation • Example 3: Write the nuclear equation representing gamma radiation given off by the unstable radionuclide cobalt-60.

18. Nuclear Fission & Fusion

19. FISSION: a heavy nucleus splits into 2 lighter nuclei • some elements undergo fission spontaneously • some elements can be induced to undergo fission when bombarded with other particles (e.g. neutrons)

20. Nuclear Fusion (think stars) "Every time you look up at the sky, every one of those points of light is a reminder that fusion power is extractable from hydrogen and other light elements, and it is an everyday reality throughout the Milky Way Galaxy." Carl Sagan, Spitzer Lecture, October 1991

21. FUSION: 2 nuclei combine to form a heavier nucleus • the sun is a tremendous fusion reaction; the major fusion reaction in the sun is thought to be: • both fission & fusion release large amounts of energy (fusion more than fission)

22. The Atomic Bomb (FISSION) • when the nucleus of U-235 splits, 2 isotopes are formed, plus neutrons are emitted • these neutrons collide with other U-235 atoms, causing them to undergo fission; they release neutrons, and so on… • The result - CHAIN REACTION!! • The CRITICAL MASS is the minimum mass of fissionable material that must be used to sustain a chain reaction

23. The Atomic Bomb (FISSION)

24. The Atomic Bomb (FISSION)

25. Little Boy was the first nuclear weapon used in warfare. It exploded approximately 1,800 feet over Hiroshima, Japan, on the morning of August 6, 1945, with a force equal to 13,000 tons of TNT. Immediate deaths were between 70,000 to 130,000. Fat Man was the second nuclear weapon used in warfare. Dropped on Nagasaki, Japan, on August 9, 1945, Fat Man devastated more than two square miles of the city and caused approximately 45,000 immediate deaths. While Little Boy was a uranium (U-235) gun-type device, Fat Man was a more complicated and powerful plutonium (Pu-239) implosion weapon that exploded with a force equal to 20 kilotons of TNT. Atomic Bomb

26. Nuclear Power Plants (use nuclear reactions to generate electricity) *San Onofre, Ca Nuclear Generating Station. Situated near a body of water to use the water… *nuclear reactor

27. TO GENERATE ELECTRICITY: 1. The energy released in the fission process generates heat, some of which can be converted into usable energy. 2. This heat is used to boil water to produce pressurized steam. 3. Steam turns turbine of a generator. 4. Generator makes electricity.

28. Nuclear Power Plants contain nuclear reactors http://science.howstuffworks.com/nuclear-power3.htm

29. Nuclear Reactors (FISSION) • use subcritical masses of fissionable material (below the mass to create chain reactions) • CORE of reactor: contains fuel pins made of U-235; interspersed among the pins are control rods • control rods: absorb neutrons (regulates amount of energy produced) • pull rods out of core: fission increases (more energy in core) • push rods back into the core: fission decreases (less energy in core)

30. Safety feature: • if power is lost, rods will automatically fall into the core and shut the reaction down. • Water pumps help to prevent the overheating of the reactor core (can trigger an explosion: Chernobyl)

31. PROS OF NUCLEAR ENERGY: • no air pollution • enormous amt. of energy released • alternative to using our rapidly decreasing fossil fuels

32. CONS OF NUCLEAR ENERGY • containers for waste products may erode or break • thermal pollution (heated water returned to rivers, etc.) • potential theft of fuel (Pu-239) for use in weapons

33. Half Life

34. Half-Life 25.2 • Half-life (t1/2): • The half-life of a sample of a radioactive isotope is the time required for half of it to decay • After each half-life, half of the existing radioactive atoms have decayed into atoms of a new element.

35. Use half-lives of some radioisotopes found in nature to determine the age of ancient artifacts • The half-life of Uranium-238 = billions of years

36. Radioactive Decay of an Unstable Isotope • Questions • 1. What percent of the atoms remains after 1 half-life?

37. 50%

38. 2. What percent of the atoms remains after 2 half-lives?

39. 25%

40. 3. Approximately how many half-lives does it take for 12.5% of the radioisotope to remain?

41. Three half-lives

42. Question • Compared to the energy liberated per gram during a typical chemical reaction, the amount of energy liberated per gram during the decay of a radioisotope is: • A. somewhat greater • B. less • C. much greater • D. about the same

43. Answer • C. much greater

44. Do #51 on pg. 822 of text • Decay curve for thorium-234 • A. what percent of the isotope remains after 60 days? • B. How many grams of a 250 g sample of thorium-234 would remain after 40 days had passed? • C. How many days would pass while 44 g of thorium-234 decayed to 4.4 g of thorium-234 • D. What is the half-life of thorium-234?

45. Answers • A. about 20% • B. about 85 g • C. about 83 days • D. about 25 days

46. Half-life CALCS • Carbon-14 emits beta radiation and decays with a half-life of 5730 years. Assume you start with a mass of 2.00 x 10-12 g of carbon-14 a. How long is 3 half-lives?

47. ANSWER • A. 3 half-lives = 3 x 5730 years = 17,190 yrs

48. Carbon-14 emits beta radiation and decays with a half-life of 5730 years. Assume you start with a mass of 2.00 x 10-12 g of carbon-14 b. How many grams of the isotope remain at the end of 3 half-lives?

49. ANSWER • B. the initial mass of carbon-14 is reduced by one half for each of the 3 half-lives, so for 3 half-lives: Remaining mass = 2.00 x 10-12 g x ½ x ½ x ½ = 0.250 x 10-12 g = 2.50 x 10-13 g

50. Example #1 • Manganese-56 is a beta emitter with a half-life of 2.6 hours. • What is the mass of manganese-56 in a 1.0 mg sample of the isotope at the end of 10.4 hours?