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  1. 1. 28.2 Nuclear Transformations
  2. 2. Nuclear Stability and Decay <ul><li>Stable nuclei are in the “band of stability”- this is part of a neutron vs. proton graph </li></ul>
  3. 4. Too many neutrons relative to protons <ul><li>Ratio is > 1 or 1.5 </li></ul><ul><li>Results in beta decay </li></ul><ul><li>Beta decay results in more protons and fewer neutrons </li></ul><ul><li>Pg 846 Cu-29 </li></ul>
  4. 5. Too many protons compared to neutrons <ul><li>Or too few neutrons </li></ul><ul><li>Ratio is <1.5 or 1 </li></ul><ul><li>Results in a proton being converted to a neutron </li></ul><ul><li>-this can happen when an electron is captured by the nucleus (Ni-28 pg 846) </li></ul><ul><li>- this can also happen when a positron is emitted from the nucleus ( caused by a proton changing into a neutron) </li></ul>
  5. 6. Positron <ul><li>same mass as an electron, but positively charged 0 </li></ul><ul><li>e </li></ul><ul><li>+1 </li></ul>
  6. 7. Elements above 83 <ul><li>Too many neutrons and protons </li></ul><ul><li>All nuclei with atomic number >83 are radioactive and undergo alpha decay </li></ul><ul><li>Pg 846- Pb-82, Ra-88 </li></ul>
  7. 9. Half-life <ul><li>Time requires for ½ of a radioactive isotope to decay ( t 1/2 ) </li></ul><ul><li>Each isotope has its own half-life ( can be fraction of a second to billions of yrs) </li></ul>
  8. 10. *Notice the shape of the graph
  9. 11. Half-Life <ul><li>Isotopes with shrot half-lives can be useful in nuclear medicine because there are no long-term biological radiation hazards </li></ul><ul><li>Isotopes, such as U-238 has a long half-life and is useful in dating rocks- very, very old rocks ( like from the start of the solar system) </li></ul>
  10. 12. Problem <ul><li>N-13 emits beta radiation and decays to C-13 with a half life (t 1/2 ) of 10 minutes. </li></ul><ul><li>Assume a starting mass of 2.00g of N-13 </li></ul><ul><li>How long is 3 half-lives? </li></ul><ul><li>How many grams will be present at the end of 3 half-lives? </li></ul>
  11. 13. Problem <ul><li>a)3x 10min=30 min 3 half-lives is 30 minutes </li></ul><ul><li>b) 1/2 n = fraction remaining where n= # half-lives so… </li></ul><ul><li>1/2 3= 1/8 </li></ul><ul><li>2.00g x 1/8=.250g </li></ul><ul><li>Draw the graph for this to double check. </li></ul>
  12. 14. Problem <ul><li>Mn-56 is a beta emitter with a half-life of 2.6 h. What is the mass of Mn-56 in a 1.0g sample at the end of 10.4 h? </li></ul>
  13. 15. Problem <ul><li>A sample of Th-234 has a half-life of 25 days. What fraction of the sample will remain after 50 days? </li></ul>
  14. 16. Transmutation Reactions <ul><li>This is the conversion of an atom of an element onto another element </li></ul><ul><li>This is done naturally by radioactivity- N-14 can eventually decay into C-14; U-238 after many transmutations becomes stable Pb-206 </li></ul>
  15. 18. Transmutation <ul><li>This can also be done artificially by bombarding a high energy particle ( such as a proton, neutron or alpha particle) at the nucleus of an atom </li></ul><ul><li>Ernest Rutherford ( remember him?) </li></ul><ul><li>was the first person to do this. He bombarded N-14 with an alpha particle to produce F-18. Write the nuclear equation for this! </li></ul><ul><li>The F-18 was unstable and it decayed into O-17 ( what else was produced?)- write the nuclear eq.! </li></ul>
  16. 19. Transmutation <ul><li>This led to the discovery of the proton </li></ul><ul><li>Chadwick discovered the neutron involved the transmutation of Be-9 to C-12 by the bombarding of Be with a alpha particle (write this eq.) </li></ul><ul><li>Elements with atomic numbers above 92 are known as the transuranium elements- none occur in nature, they were artificially made, all are radioactive and decay </li></ul><ul><li>They were made in particle accelerators </li></ul><ul><li>or nuclear reactors </li></ul>I discovered the neutron
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