Nuclear Chemistry: The Heart of Matter 2 Radioisotopes Radioactive decay Radioactive decay Many isotopes are unstable Many isotopes are unstable Radioisotopes Radioisotopes Nuclei that undergo radioactive decay Nuclei that undergo radioactive decay May produce one or more types of radiation May produce one or more types of radiation 3 Natural Radioactivity Background radiation Background radiation What occurs from natural sources What occurs from natural sources >80% of radioactivity exposure >80% of radioactivity exposure 4 Types of Radiation Ionizing radiation knocks electrons out of atoms or groups of atoms Ionizing radiation knocks electrons out of atoms or groups of atoms Produces charged species ions Produces charged species ions Charged species that cause damage Charged species that cause damage 5 Nuclear Equations Elements may change in nuclear reactions Elements may change in nuclear reactions Total mass and sum of atomic numbers must be the same Total mass and sum of atomic numbers must be the same MUST specify isotope MUST specify isotope 6 Alpha Decay Nucleus loses particle Nucleus loses particle Mass decreases by 4 and atomic number decreases by 2 Mass decreases by 4 and atomic number decreases by 2 7 Beta Decay Nucleus loses particle Nucleus loses particle No change in mass but atomic number increases No change in mass but atomic number increases 8 Positron Emission Loses a positron Loses a positron Equal mass but opposite charge of an electron Equal mass but opposite charge of an electron Decrease in atomic number and no change in mass Decrease in atomic number and no change in mass + + 9 Electron Capture Nucleus absorbs an electron and then releases an X-ray Nucleus absorbs an electron and then releases an X-ray Mass number stays the same and atomic number decreases Mass number stays the same and atomic number decreases 10 Gamma Radiation Release of high- energy photon Release of high- energy photon Typically occurs after another radioactive decay Typically occurs after another radioactive decay No change in mass number or atomic number No change in mass number or atomic number 11 Half-Life Period for one-half of the original elements to undergo radioactive decay Period for one-half of the original elements to undergo radioactive decay Characteristic for each isotope Characteristic for each isotope Fraction remaining = Fraction remaining = n = number of half-lives 12 Radioisotopic Dating Use certain isotopes to estimate the age of various items Use certain isotopes to estimate the age of various items 235 U half-life = 4.5 billion years 235 U half-life = 4.5 billion years Determine age of rock Determine age of rock 3 H half-life = 12.3 years 3 H half-life = 12.3 years Used to date aged wines Used to date aged wines 13 Carbon-14 Dating 99.9% 12 C 99.9% 12 C Produce 14 C in upper atmosphere Produce 14 C in upper atmosphere Half-life of 5730 years Half-life of 5730 years ~50,000 y maximum age for dating ~50,000 y maximum age for dating 14 Artificial Transmutation Transmutation changes one element into another Transmutation changes one element into another Middle Ages: change lead to gold Middle Ages: change lead to gold In 1919 Rutherford established protons as fundamental particles In 1919 Rutherford established protons as fundamental particles Basic building blocks of nuclei Basic building blocks of nuclei 15 Uses of Radioisotopes Tracers Tracers Easy to detect Easy to detect Different isotopes have similar chemical and physical properties Different isotopes have similar chemical and physical properties Physical, chemical, or biological processes 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 Used for two purposes Therapeutic treat or cure disease using radiation Therapeutic treat or cure disease using radiation Diagnostic obtain information about patients health Diagnostic obtain information about patients health 17 Radiation Therapy Radiation most lethal to dividing cells Radiation most lethal to dividing cells Makes some forms of cancer susceptible Makes some forms of cancer susceptible Try to destroy cancer cells before too much damage to healthy cells Try to destroy cancer cells before too much damage to healthy cells Direct radiation at cancer cells Direct radiation at cancer cells Gives rise to side effects Gives rise to side effects 18 Diagnostic Uses Many different isotopes used Many different isotopes used Can measure specific things Can measure specific things Iodine-131 to locate tumors in thyroid Iodine-131 to locate tumors in thyroid Selenium-75 to look at pancreas Selenium-75 to look at pancreas Gadolinium-153 to determine bone mineralization Gadolinium-153 to determine bone mineralization 19 Imaging Positron emission tomography (PET) Positron emission tomography (PET) Uses an isotope that emits a positron Uses an isotope that emits a positron Observe amount of radiation released 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 more mass the particle has, the less penetrating it is The faster the particle is, the more penetrating it is The faster the particle is, the more penetrating it is 22 Prevent Radiation Damage To minimize damage To minimize damage Stay a distance from radioactive sources Stay a distance from radioactive sources Use shielding; need more with more penetrating forms of radiation Use shielding; need more with more penetrating forms of radiation 23 Binding Energy Holds protons and neutrons together in the nucleus Holds protons and neutrons together in the nucleus The higher the binding energy, the more stable the element The higher the binding energy, the more stable the element 24 Nuclear Fission Splitting the atom Splitting the atom Break a large nucleus into smaller nuclei Break a large nucleus into smaller nuclei 25 26 27 28 Nuclear Chain Reaction Neutrons from one fission event split further atoms Neutrons from one fission event split further atoms Only certain isotopes, fissile isotopes, undergo nuclear chain reactions Only certain isotopes, fissile isotopes, undergo nuclear chain reactions 29 Radioactive Fallout Nuclear bomb detonated; radioactive materials may rain down miles away and days later Nuclear bomb detonated; radioactive materials may rain down miles away and days later Some may be unreacted U or Pu Some may be unreacted U or Pu Radioactive isotopes produced during the explosion Radioactive isotopes produced during the explosion 30 31 Nuclear Power Plants Provide ~20% U.S. electricity Provide ~20% U.S. electricity France >70% France >70% Slow controlled release of energy Slow controlled release of energy Need 2.53.5% 235 U Need 2.53.5% 235 U Problem with disposal of radioactive waste Problem with disposal of radioactive waste 32 Nuclear Fusion Reaction takes smaller nuclei and builds larger ones Reaction takes smaller nuclei and builds larger ones Also called thermonuclear reactions Also called thermonuclear reactions Releases tremendous amounts of energy 1 g of H would release same as 20 tons of coal 33 34