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Mec chapter 9


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  • 1. Copyright© The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Chapter 9 The Nucleus, Radioactivity, and Nuclear MedicineDennistonToppingCaret7th Edition
  • 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. Nuclear Symbols9.1 Natural Radioactivity mass number 11 number of protons and 5 B neutrons atomic symbol atomic number number of protons
  • 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. Half-Lives of Selected Radioisotopes9.3 Properties of Radioisotopes
  • 15. Decay Curve for the Medically Useful Radioisotope Tc-99m9.3 Properties of Radioisotopes
  • 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. 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. 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. 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. 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. 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