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Radioactivity and Nuclear energy

Radioactivity and Nuclear energy. We will discuss three basic types of nuclear change Fusion Fission Decay. Think about nuclear processes and what parts of our lives are they involved in… Nuclear weapons, power plants, radioactive dating, nuclear medicine.

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Radioactivity and Nuclear energy

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  1. Radioactivity and Nuclear energy

  2. We will discuss three basic types of nuclear change Fusion Fission Decay

  3. Think about nuclear processes and what parts of our lives are they involved in… Nuclear weapons, power plants, radioactive dating, nuclear medicine

  4. Radioactive elements (radioisotopes) found in rock, soil, water, air, and in food from the earth make there way in our bodies when we drink water, breath air or eat foods which contain them. These naturally occurring radioisotopes expose us to radiation from within our bodies.

  5. Medical procedures account for nearly all (96%) human exposure to man-made radiation. Among these medical procedures, x-rays, mammography, and CT use radiation or perform functions similar to those of radioisotopes.

  6. The nucleus is small and dense Consider a ton… A ton is 2,000 pounds If you were to build a nucleus the size of a ping pong ball it would weigh 2.5 billion tons The energies involved in nuclear processes are millions of times greater than those associated with chemical processes.

  7. 19.1 radioactive decay Think… What are the constituents of the nucleus? What are the charges on those particles? Are those charges attractive or repulsive? If so, what is holding the nucleus together? The larger the nucleus, the greater the repulsion Nuclei with more than 83 protons are all unstable, and will eventually break up into smaller pieces

  8. mini-review A nucleus is made of nucleons: Protons (p) and neutrons (n) The number of protons is equal to the atomic number (Z) When you add the number of protons to the number of neutrons, you get the mass number (A) nuclei that have the same number of protons but a different number of neutrons are called… isotopes

  9. the nuclide can be represented this way C 14 (A) mass number 6 (Z) atomic number How many neutrons?

  10. Radioactive Decay: The spontaneous disintegration of a nucleus into a less massive and/or more stable nucleus, accompanied with particle or electromagnetic emission! • initial nucleus = parent nuclidenew nucleus = daughter nuclides • can be written w/ equations, as long as...

  11. Parent Daughter Atomic #left = Atomic #right and Mass #left = Mass #right

  12. Alpha emission:parent  daughter + 

  13. Th Ra He 230 226 4 90 88 2 Write an equation for the alpha decay of Th-230.  + parent alpha daughter

  14. Ra He 226 4 88 2 Write an equation for the decay of radium-226 by  emission. Rn 222  + 86 parent alpha daughter

  15. Pu He 240 4 94 2 Write an equation for the decay of plutonium-240 by  emission. U  236 + 92 parent alpha daughter

  16. Po He 218 4 84 2 The decay products for a nuclear reaction are an alpha particle and polonium-218. What was the parent nuclide? Rn 222  + 86 parent alpha daughter

  17. Questions?

  18. Beta emission:parent  daughter + – A beta particle is often an electron, but can also be a positron If it is an electron, the number of neutrons decreases by 1 and the number of protons increases by 1 If it is a positron, the number of neutrons increases by 1 and the number of protons decreases by 1

  19. e C 0 14 + -1 6 parent beta daughter Beta emission N 14 7

  20. e K 0 40 -1 19 parent beta daughter Potassium-40 undergoes beta emission. Write the equation for this reaction.  Ca 40 + 20

  21. positron emission:parent + + daughter e Na Ne  22 0 22 + 11 1 10

  22. w/ – emission a n p w/ + emission a p n after decay, the daughter has less E than parent

  23. Hg 201 80 • electron capturemeans… • An electron is captured by the… Nucleus e Au  201 0 + -1 79

  24. Many nuclei are radioactive. This means they are unstable, and will eventually decay by emitting a particle, transforming the nucleus into another nucleus, or into a lower energy state. • A chain of decays may take place until a stable nucleus is reached.

  25. What is Radioactivity?

  26. Questions?

  27. 19.3 Detection of Radioactivity and the Concept of Half-Life • The most familiar instrument for measuring radioactivity levels is the Geiger counter • The probe contains argon gas. The gas can be ionized by the rapidly moving particles released during radioactive decay • Think: What are the 3 types of particles we have been discussing? • Discuss with the person next to you: What could be useful applications for a Geiger counter?

  28. Half-life (t1/2) is the period of time, for a substance undergoing decay, to decrease by half. • It is the time when the expected value of the number of entities that have decayed is equal to half the original number. • if there is just one radioactive atom with a half-life of 1 second, there will not be "half of an atom" left after 1 second. There will be either zero atoms left or one atom left, depending on whether or not the atom happens to decay. • time for half the parent nuclei to decay = half-life (t1/2)

  29. Example: if 100,000 at beginning then 50,000 after one half life and 25,000 after 2nd half life and 12,500 after 3rd half life; etc... • A half life can be long or short, depending on the isotope involved • There are many natural radioactive materials, some are man-made

  30. example • F-21 has a half-life of approximately 5 seconds. • If there were 20 grams to begin with, how much is there after 5 seconds? 10g • After 10 seconds? 5g • After 15 seconds? 2.5g • After 20 seconds? 1.25g

  31. example • I-131 has a half-life of 8 days. How much is left after 24 days? • 24 days is how many half-lives? 24/8 = 3 • Three half-lives would leave how much material? 1/2 x 1/2 x 1/2 = 1/8 = .125

  32. example • Cr-51 has a half-life of 28 days. How much of a 510-g sample is left after 1 year? • 365 days / 28days per ½ life = 13 half lives • The fraction remaining is 1/2^n 1/2^13 = 1/8192 1/8192 x 510 g = 0.062 g

  33. 19.4 Dating by Radioactivity • C-14 is made in upper atmosphere (from N-14) • C-14 decays (t1/2 = 5730 y) • C-14 gets absorbed & given off by living critters • When critter dies, C-14 trapped! but still decays! • lets us radiocarbon date something!

  34. If you know rate of decay (t1/2 = 5730 y), then you can estimate how long it has been deadforexample: • A living organism = 15.3 g C-14 • If a dead organism is found to have 7.65 g then the fraction remaining is .5 or ½ • And that many half lives is how many years? 5700 y ago

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