Mec chapter 9


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Mec chapter 9

  1. 1. Copyright© The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Chapter 9 The Nucleus, Radioactivity, and Nuclear MedicineDennistonToppingCaret7th Edition
  2. 2. 9.1 Natural Radioactivity• Radioactivity - process by which atoms emit energetic particles or rays• Radiation - the particles or rays emitted – comes from the nucleus• Nuclear symbols - what we use to designate the nucleus – Atomic symbol – Atomic number – Mass number
  3. 3. Nuclear Symbols9.1 Natural Radioactivity mass number 11 number of protons and 5 B neutrons atomic symbol atomic number number of protons
  4. 4. Writing Nuclear Symbols9.1 Natural Radioactivity 11 5 B • This defines an isotope of boron • In nuclear chemistry, often called a nuclide • This is not the only isotope of boron – boron-10 also exists – How many protons and neutrons does boron-10 have? • 5 protons, 5 neutrons
  5. 5. Three Isotopes of Carbon9.1 Natural Radioactivity • Each nucleus contains the same number of protons • Only the number of neutrons is different • With different numbers of neutrons the mass of each isotope is different
  6. 6. Unstable Isotopes9.1 Natural Radioactivity • Some isotopes are stable • The unstable isotopes are the ones that produce radioactivity • To write nuclear equations we need to be able to write the symbols for the isotopes and the following: – alpha particles – beta particles – gamma rays
  7. 7. 9.1 Natural Radioactivity Alpha Particles • Alpha particle (α) - 2 protons, 2 neutrons • Same as He nucleus (He2+) • Slow moving, and stopped by small barriers • Symbolized in the following ways: 4 2+ 4 4 2 He 2 He α 2 α
  8. 8. Beta Particles9.1 Natural Radioactivity • Beta particles (β) - fast-moving electron • Emitted from the nucleus as a neutron, is converted to a proton • Higher speed particles, more penetrating than alpha particles • Symbolized in the following ways: 0 0 −1 e -1 β β
  9. 9. Gamma Rays9.1 Natural Radioactivity • Gamma rays (γ) - pure energy (electromagnetic radiation) • Highly energetic • The most penetrating form of radiation • Symbol is simply… γ
  10. 10. 9.1 Natural Radioactivity Properties of Alpha, Beta, and Gamma Radiation • Ionizing radiation - produces a trail of ions throughout the material that it penetrates • The penetrating power of the radiation determines the ionizing damage that can be caused • Alpha particle < beta particle < gamma rays
  11. 11. 9.3 Properties of RadioisotopesNuclear Structure and Stability• Binding energy - the energy that holds the protons, neutrons, and other particles together in the nucleus• Binding energy is very large• When isotopes decay (forming more stable isotopes) binding energy is released
  12. 12. Stable Radioisotopes9.3 Properties of Important factors for stable isotopes Radioisotopes – Ratio of neutrons to protons – Nuclei with large number of protons (84 or more) tend to be unstable – The “magic numbers” of 2, 8, 20, 50, 82, or 126 help determine stability – these numbers of protons or neutrons are stable – Even numbers of protons or neutrons are generally more stable than those with odd numbers – All isotopes (except 1H) with more protons than neutrons are unstable
  13. 13. Half-Life9.3 Properties of • Half-life (t1/2) - the time required for one- Radioisotopes half of a given quantity of a substance to undergo change • Each radioactive isotope has its own half-life – Ranges from a fraction of a second to a billion years – The shorter the half-life, the more unstable the isotope
  14. 14. Half-Lives of Selected Radioisotopes9.3 Properties of Radioisotopes
  15. 15. Decay Curve for the Medically Useful Radioisotope Tc-99m9.3 Properties of Radioisotopes
  16. 16. Predicting the Extent of Radioactive Decay9.3 Properties of Radioisotopes A patient receives 10.0 ng of a radioisotope with a half- life of 12 hours. How much will remain in the body after 2.0 days, assuming radioactive decay is the only path for removal of the isotope from the body? • Calculate n, the number of half-lives elapsed using the half-life as the conversion factor n = 2.0 days x 1 half-life / 0.5 days = 4 half lives • Calculate the amount remaining 10.0 ng 5.0 ng 2.5 ng 1.3 ng 0.63 ng 1st half-life 2nd half-life 3rd half-life 4th half-life • 0.63 ng remain after 4 half-lives
  17. 17. 9.6 Medical Applications of Radioactivity• Modern medical care uses the following: – Radiation in the treatment of cancer – Nuclear medicine - the use of radioisotopes in the diagnosis of medical conditions
  18. 18. 9.6 Medical Applications of Cancer Therapy Using Radiation • Based on the fact that high-energy Radioactivity gamma rays cause damage to biological molecules • Tumor cells are more susceptible than normal cells • Example: cobalt-60 • Gamma radiation can cure cancer, but can also cause cancer
  19. 19. 9.6 Medical Applications of Nuclear Medicine • The use of isotopes in diagnosis Radioactivity • Tracers - small amounts of radioactive substances used as probes to study internal organs • Nuclear imaging - medical techniques involving tracers • Example: – Iodine concentrates in the thyroid gland – Using radioactive 131I and 125I will allow the study of how the thyroid gland is taking in iodine
  20. 20. 9.6 Medical Applications of Tracer Studies • Isotopes with short half-lives are preferred for tracer studies. Why? Radioactivity – They give a more concentrated burst – They are removed more quickly from the body • Examples of imaging procedures: – Bone disease and injury using technetium-99m – Cardiovascular disease using thallium-201 – Pulmonary disease using xenon-133
  21. 21. 9.6 Medical Applications of Making Isotopes for Medical Radioactivity Applications • Artificial radioactivity - a normally stable, nonradioactive nucleus is made radioactive • Made in two ways: • In core of a nuclear reactor • In particle accelerators – small nuclear particles are accelerated to speeds approaching the speed of light and slammed into another nucleus