Intro to Nuclear Chemistry

1. Intro to NuclearChemistry Chemistry http://www.chem.orst.edu/graduate/pics/Reactor.jpg

2. How does a subatomic particle cause damage to human tissue? http://studentsagainstclimatechange.blogspot.com/2007/12/final-exchange-with-donna-dillman-after.html

3. Isotopes of Carbon

4. Radioactive Isotopes • Isotopes of certain unstable elements that spontaneously emit particles and energy from the nucleus. • Henri Beckerel 1896 accidentally observed radioactivity of uranium salts that were fogging photographic film. • His associates were Marie and Pierre Curie.

5. Marie Curie a Pioneer of Radioactivity • Winner of 1903 Nobel Prize for Physics with Henri Becquerel and her husband, Pierre Curie. • Winner of the 1911 Nobel Prize for Chemistry. • 1898 discovered the elements polonium and radium.

6. 3 Main Types of Radioactive Decay • Alpha a • Betab • Gamma g

7. Alpha Decay Emission of alpha particles a : • helium nuclei • two protons and two neutrons • charge +2e  • can travel a few inches through air • can be stopped by a sheet of paper, clothing.

8. Alpha Decay Uranium Thorium

9. Alpha Decay http://education.jlab.org/glossary/alphadecay.gif

10. Beta Decay • Beta particles b: electrons ejected from the nucleus when neutrons decay n -> p+ +b- • Beta particles have the same charge and mass as "normal" electrons. • Can be stopped by aluminum foil or a block of wood.

11. Beta Decay Thorium Protactinium

12. Gamma Decay • Gamma radiation g : electromagnetic energy that is released.  • Gamma rays are electromagnetic waves. • They have no mass. • Gamma radiation has no charge. • Most Penetrating, can be stopped by 1m thick concrete or a several cm thick sheet of lead.

13. Examples of Radioactive Decay Alpha Decay Po  Pb + He Beta Decay p n + e n  p + e C  N + e Gamma Decay Ni  Ni + g (excited nucleus)

14. Nuclei with atomic number > 83 are radioactive

15. Radioactive Half-Life (t1/2 ): • The time for half of the radioactive nuclei in a given sample to undergo decay.

16. Common Radioactive Isotopes Isotope Half-Life Radiation Emitted Carbon-14 5,730 years b, g Radon-222 3.8 days a Uranium-235 7.0 x 108 years a, g Uranium-238 4.46 x 109 years a

17. Radioactive Half-Life • After one half life there is 1/2 of original sample left. • After two half-lives, there will be 1/2 of the 1/2 = 1/4 the original sample.

18. Graph of Amount of Remaining Nuclei vs Time A=Aoe-lt A

19. Example You have 100 g of radioactive C-14. The half-life of C-14 is 5730 years. • How many grams are left after one half-life? Answer:50 g • How many grams are left after two half-lives?

20. Problem A sample of 3x107 Radon atoms are trapped in a basement that is sealed. The half-life of Radon is 3.83 days. How many radon atoms are left after 31 days? answer:1.2x105 atoms

21. Energy in Nuclear Reactions • There is a tremendous amount of energy stored in nuclei. • Einstein’s famous equation, E = mc2, relates directly to the calculation of this energy. • In chemical reactions the amount of mass converted to energy is minimal. • However, these energies are many thousands of times greater in nuclear reactions.

22. Examples of Nuclear Energy

23. Nuclear Fission • How does one tap all that energy? • Nuclear fission is the type of reaction carried out in nuclear reactors.

24. Nuclear Fission • Bombardment of the radioactive nuclide with a neutron starts the process. • Neutrons released in the transmutation strike other nuclei, causing their decay and the production of more neutrons. • This process continues in what we call a nuclear chain reaction.

25. Nuclear Fission • If there are not enough radioactive nuclides in the path of the ejected neutrons, the chain reaction will die out. • Therefore, there must be a certain minimum amount of fissionable material present for the chain reaction to be sustained: Critical Mass.

26. Nuclear Reactors In nuclear reactors the heat generated by the reaction is used to produce steam that turns a turbine connected to a generator.

27. Nuclear Reactors • The reaction is kept in check by the use of control rods. • These block the paths of some neutrons, keeping the system from reaching a dangerous supercritical mass.

28. Nuclear Fusion • Fusion would be a superior method of generating power. • It occurs when small nuclei combine – releasing much more energy than fission. • The products of the reaction are not radioactive. • The material must be in the plasma state at several million kelvins. • Tokamakapparati, using magnetic fields to heat the material, show promise for carrying out these reactions.