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Nuclear Chemistry: The Heart of Matter

Nuclear Chemistry: The Heart of Matter. Radioisotopes. Radioactive decay – Many isotopes are unstable Radioisotopes Nuclei that undergo radioactive decay May produce one or more types of radiation. Natural Radioactivity. Background radiation What occurs from natural sources

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Nuclear Chemistry: The Heart of Matter

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  1. Nuclear Chemistry: The Heart of Matter

  2. Radioisotopes • Radioactive decay – Many isotopes are unstable • Radioisotopes • Nuclei that undergo radioactive decay • May produce one or more types of radiation

  3. Natural Radioactivity • Background radiation • What occurs from natural sources • >80% of radioactivity exposure

  4. Types of Radiation • Ionizing radiation – knocks electrons out of atoms or groups of atoms • Produces charged species – ions • Charged species that cause damage

  5. Nuclear Equations • Elements may change in nuclear reactions • Total mass and sum of atomic numbers must be the same • MUST specify isotope

  6. Alpha Decay • Nucleus loses  particle • Mass decreases by 4 and atomic number decreases by 2

  7. Beta Decay • Nucleus loses  particle • No change in mass but atomic number increases

  8. Positron Emission • Loses a positron • Equal mass but opposite charge of an electron • Decrease in atomic number and no change in mass • +

  9. Electron Capture • Nucleus absorbs an electron and then releases an X-ray • Mass number stays the same and atomic number decreases

  10. Gamma Radiation • Release of high-energy photon •  • Typically occurs after another radioactive decay • No change in mass number or atomic number

  11. Half-Life • Period for one-half of the original elements to undergo radioactive decay • Characteristic for each isotope • Fraction remaining = n = number of half-lives

  12. Radioisotopic Dating • Use certain isotopes to estimate the age of various items • 235U half-life = 4.5 billion years • Determine age of rock • 3H half-life = 12.3 years • Used to date aged wines

  13. Carbon-14 Dating • 99.9% 12C • Produce 14C in upper atmosphere • Half-life of 5730 years • ~50,000 y maximum age for dating

  14. Artificial Transmutation • Transmutation changes one element into another • Middle Ages: change lead to gold • In 1919 Rutherford established protons as fundamental particles • Basic building blocks of nuclei

  15. Uses of Radioisotopes • Tracers • Easy to detect • Different isotopes have similar chemical and physical properties • Physical, chemical, or biological processes • Agriculture • Induce heritable genetic alterations – mutations • Preservative • Destroys microorganisms with little change to taste or appearance of the food

  16. Nuclear Medicine • Used for two purposes • Therapeutic – treat or cure disease using radiation • Diagnostic – obtain information about patient’s health

  17. Radiation Therapy • Radiation most lethal to dividing cells • Makes some forms of cancer susceptible • Try to destroy cancer cells before too much damage to healthy cells • Direct radiation at cancer cells • Gives rise to side effects

  18. Diagnostic Uses • Many different isotopes used • Can measure specific things • Iodine-131 to locate tumors in thyroid • Selenium-75 to look at pancreas • Gadolinium-153 to determine bone mineralization

  19. Imaging • Positron emission tomography (PET) • Uses an isotope that emits a positron • Observe amount of radiation released Scans showing lung cancer (bright spot in the chest).At left - CT scan; center - PET scan; right - combined CT-PET scan.

  20. Brain tumor study and comparison of nuclear medicine and MR Upper row: fused image of nuclear medicine acquisition and MR acquisition Middle row: MR study yields excellent anatomic detail (spatial resolution) Bottom row: nuclear medicine (SPECT) images yield excellent functional information

  21. Penetrating Power of Radiation • The more mass the particle has, the less penetrating it is • The faster the particle is, the more penetrating it is

  22. Prevent Radiation Damage • To minimize damage • Stay a distance from radioactive sources • Use shielding; need more with more penetrating forms of radiation

  23. Binding Energy • Holds protons and neutrons together in the nucleus • The higher the binding energy, the more stable the element

  24. Nuclear Fission • “Splitting the atom” • Break a large nucleus into smaller nuclei

  25. Nuclear Chain Reaction • Neutrons from one fission event split further atoms • Only certain isotopes, fissile isotopes, undergo nuclear chain reactions

  26. Radioactive Fallout • Nuclear bomb detonated; radioactive materials may rain down miles away and days later • Some may be unreacted U or Pu • Radioactive isotopes produced during the explosion

  27. Nuclear Power Plants • Provide ~20% U.S. electricity • France >70% • Slow controlled release of energy • Need 2.5–3.5% 235U • Problem with disposal of radioactive waste

  28. Nuclear Fusion • Reaction takes smaller nuclei and builds larger ones • Also called thermonuclear reactions • Releases tremendous amounts of energy • 1 g of H would release same as 20 tons of coal

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