Unit 4: Applications of Nuclear Chemistry

1. Unit 4:Applications of Nuclear Chemistry Including Changes in the Nucleus

2. Changes in the Nucleus • Nuclear Reaction- rxn that affects the nucleus of an atom. • Changes the composition of an atom’s nucleus • 3 kind of radiation: • Alpha particles 2+ charge • Beta particles 1- charge • Gamma rays have no charge • Radioactivity- the spontaneous emission of radiation from an atom’s nucleus.

3. Nuclear Stability • If: protons have a positive charge, nucleus is made of protons and neutrons, like charges repel; how does a nucleus stay together? • Strong Nuclear Force- an attractive force STRONGER than the electric repulsion force btwn protons. Only exists btwn particles (protons) extremely close together. • The presence of neutrons adds a net attractive force in the nucleus

4. Types of Radioactive Decay α 42He • Alpha radiation- has 2 protons and 2 neutrons (same as a helium-4 nucleus). • Do not have much penetrating power, can be stopped by paper or skin. Does not pose a health problem.

5. β • Beta particle- mass=0 but has a charge -1. Essentially an electron. • Can penetrate paper and skin. Does present a health hazard.

6. γ • Gamma rays- extremely high energy ray or light. • High penetrating power. Very dangerous and hazardous to your health.

7. Radioactive Decay • Radioactive Decay- when an atom emits any type of radiation. • Results in a new nucleus. The original nucleus decays (breaks apart) to form a new, smaller/lighter nucleus.

9. Nuclear Equation- rxn that affects the nucleus of an atom. “In any radioactive decay, the sum of the mass #s and the atomic #s are the same before and after the reaction.” (on both sides of the arrow)

10. Try solving:

11. Applications of Nuclear Chemistry Radioisotopes • Radioisotopes- an isotope of an element which is unstable (radioactive).

12. Half-Life • All radioactive isotopes decay at different rates. • Half-Life- t½ , is the time required for half the atoms of a radioactive nuclide to decay. • More stable nuclides decay slowly. Less stable nuclides have shorter half-lives and decay much more quickly.

14. Half-life practice problems • Solve: • Nitrogen-13 has a half-life of 10 minutes. IF there are 2.00g of nitrogen-13 at the start, how many grams will exist after 3 half-lives? • How long will it take 3.8 x 1024 atoms of 10047Ag to disintegrate to 2.93 x 1023 atoms if the half life of  10047Ag is 24.6 seconds? • Radioactive copper, 6429Cu, is found in quantities exceeding pollution standards in the  sediments of a reservoir in a routine check on Monday.  The standard allows up to 14 ppm/cubic meter of sediment.  On Monday, 59ppm/cubic meter were measured. The half life of 6429Cu is 12.7 hours.  When will the pollution level return to 14ppm?

15. Nuclear Bombardment Reactions • We can make stable nuclei by: • Nuclear Bombardment Rxns- an atom is bombarded with a stream of particles like alpha particles. • When the nucleus is hit, the particles and the nucleus combine to form a new, unstable, nucleus.

16. Atom Smashing! Fermi National Accelerator Laboratory, Illinois cyclotron

17. Stanford Linear Accelerator Center, California.

18. Can also bombard with neutrons… • 1934, Enrico Fermi figured out that we can make radioactive isotopes by smashing nuclei with neutrons.

19. Biological Effects of Radiation • Units of Radiation: • SI unit: becquerel (Bq) • more common: the curie (Ci)- only measures amount of radiation • Most often used: the rem(roentgen equivalent for man) – measures amount of radiation & the sensitivity of the body • < 150 rem: not fatal but can cause serious damage • 150 – 1000 rem: Damaging and can be fatal • > 1000 rem: FATAL!

20. Measuring Doses & Detecting Radiation Dose Amount Radiation Amount Geiger Counter: most common instrument used for detecting radiation. As radiation passes through it’s window, it ionizes gas in the cylinder. Ions strike a charged cylinder and wire which created an electric pulse…. Which clicks and is read on the counter. • Dosimeter: small badge or pen warn on the person. • Like a mini Geiger counter. • Used to monitor personal radiation exposure. • The film is developed after use, the darker the film the more exposure experienced.

21. Beneficial Uses of Radioisotopes • Radiotracers: used to follow a specific substance as it moves through a natural system. Ex- your body. • Cancer treatment: Fast growing cancer cells are more susceptible to radiation than healthy cells. The hope is, cancer cells will be damaged and die while healthy cells survive treatment. • Food Preservation: can prevent spoiling of food.

22. Harnessing the Nucleus:Fission vs. Fusion • Besides nuclear decay and bombardment, there are 2 other types of nuclear reactions. 1. Nuclear Fission & 2. Nuclear Fusion

23. Nuclear Fission • Enrico Fermi bombarded uranium-238 with neutron (s) which eventually becomes Neptunium- 239 (a heavier element). • 1938 Otto Hahn & Fritz Strassman • Tried to replicate Fermi’s experiment but they also got Barium (a lighter element). • Couldn’t figure out why. Wrote letter to Meitner. • Lise Meitner • Thought that the nucleus must become unstable and BREAK APART to form the lighter atom.

24. Nuclear fission cont. • Meitner was RIGHT! but Hahn got the Nobel prize. • Nuclear Fission- a large nucleus is split into 2 smaller nuclei of approximately equal mass.

25. Energy & “Missing” Mass • There is so much nuclear energy in a very small amount of mass. • 4.5g of U-235 = 1 persons energy use for 1 year. • Compared to 15 tons of coal. • Where does the energy come from?- the “missing” mass is matter that has been converted into energy via Einstein’s E=MC2.

26. Chain RXNs and The Atomic Bomb • Because, in a fission rxn, neutrons are released as the U atom breaks apart, they can go and bombard other U atoms and cause them to break apart. • Chain Reaction- a continuous series of fission rxns.

27. The atomic bomb relies on a runaway chain rxn. http://www.youtube.com/watch?v=qT4mSoZsbzM http://www.youtube.com/watch?v=RqyBzXYZPoM

28. Nuclear Reactors • Nuclear power plants use the fission process to heat water into steam, that drives a generator. Turning nuclear reactions into electricity.

29. Three Mile Island, Pa • Lost water, due to operator error, and the rising heat could cause a “meltdown”. • Water was restored and a disaster was averted.

30. Chernobyl, Russia • Used Graphite to absorb neutrons, graphite ignited and burned out of control. Burned for days, destroying the reactor and releasing huge amounts of radiation. • Winds carried the radiation into Europe… many people developed cancers, malformed children, etc.

31. Nuclear Waste Disposal • Radioactive fission products build-up on fuel rods. Eventually the fuel rods have to be replaced. • Currently, waste stored at site. Best solution burial but no country has an underground site. • Yucca Mountain- was designed to be the U.S.’s underground storage site.

33. Nuclear Fusion • Nuclear Fusion- 2 small nuclei join to form a large nucleus. • Releases a considerable amount of energy. • Down side- difficult to produce and hard to control! Type of nuclear rxn that takes place on the sun.

34. The Hydrogen Bomb! • http://www.youtube.com/watch?v=NNcQX033V_M • Releases much more energy than an atomic bomb. • Triggered by a small atomic blast. • Only tested, never used in a conflict.

35. Fusion Research • Gram for Gram, fusion rxns releases more energy than fission rxns. • Controlled fusions are difficult and require temps of 40 million K or more. (difficult!- no material can withstand that kind of temps.)

36. Cold Fusion?? • 1989- Pons & Fleishman @ the University of Utah. • Claimed to achieve cold fusion by the electrolysis of heavy water (D2O). • Didn’t work out as claimed.