1. Intro to Nuclear Chemistry

2. The Nucleus Remember that the nucleus is comprised of the two nucleons, protons and neutrons. The number of protons is the atomic number. The number of protons and neutrons together is effectively the mass of the atom.

3. Isotopic Notation

4. Isotopes Not all atoms of the same element have the same mass. These are called Isotopes – forms of the same element but different neutrons. There are three naturally occurring isotopes of uranium: –Uranium-234 –Uranium-235 –Uranium-238

5. H H H http://education.jlab.org/glossary/isotope.html

6. Isotopes of certain unstable elements spontaneously emit particles and energy from the nucleus. Marie Curie was one pioneer of radioactivity. Her discoveries led to a Noble Peace Prize in Physics in 1903. She also won the Noble Peace Prize in Chemistry. Radioactive Isotopes

7. Radioactivity It is not uncommon for some nuclides of an element to be unstable, or radioactive. We refer to these as radionuclides. There are several ways radionuclides can decay into a different nuclide.

8. Emission of alpha particles  : helium nuclei two protons and two neutrons can travel a few inches through air can be stopped by a sheet of paper, clothing. Alpha Decay

10. Beta Decay Beta particles  : electrons ejected from the nucleus when neutrons decay n -> p + +  - 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

13. Gamma radiation  electromagnetic energy that is released. Gamma rays are electromagnetic waves. They have no mass. Gamma radiation has no charge. Radioisotpes used in medicine are most often made by gamma radiation. –Most Penetrating, can be stopped by 1m thick concrete or a several cm thick sheet of lead. Gamma Decay

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

16. Balancing Nuclear Reactions In the reactants (starting materials – on the left side of an equation) and products (final products – on the right side of an equation) Atomic numbers must balance and Mass numbers must balance Use a particle or isotope to fill in the missing protons and neutrons

17. Practice Nuclear Equations The alpha decay of Uranium-238: The beta decay of Iodine-131: U 238 92  Th 234 90 He 4242 + I 131 53 Xe 131 54  + e 0−10−1

18. Nuclear Transformations Nuclear transformations can be induced by accelerating a particle and colliding it with the nuclide. These particle accelerators are enormous, having circular tracks with radii that are miles long.

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

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

21. 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. Too much can result in a Nuclear Meltdown!

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

23. 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.

24. Fusion Fusion reactions do not occur naturally on our planet but are the principal type of reaction found in stars. The large masses, densities, and high temperatures of stars provide the initial energies needed to fuel fusion reactions. The sun fuses hydrogen atoms to produce helium, subatomic particles, and vast amounts of energy.

25. Nuclear Fusion Fusion would be a superior method of generating power. –The good news is that the products of the reaction are not radioactive. –The bad news is that in order to achieve fusion, the material must be in the plasma state at several million kelvins. –Tokamak apparati like the one shown at the right show promise for carrying out these reactions. –They use magnetic fields to heat the material.

26. Radioactive Half-Life (t 1/2 ): The time for half of the radioactive nuclei in a given sample to undergo decay.

27. 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.

28. 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? How many grams are left after two half- lives?

29. Learning Check! The half life of I-123 is 13 hr. How much of a 64 mg sample of I-123 is left after 39 hours?

30. Effects of Radiation

32. Nuclear Medicine: Imaging Thyroid imaging using Tc-99m