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Nuclear Chemistry

Learn about nuclear chemistry, including radioactive isotopes, transmutation, types of radiation, alpha and beta decay, conversion of mass to energy, fission, fusion, and half-life.

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Nuclear Chemistry

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  1. Nuclear Chemistry Nine Mile Oswego, NY

  2. Radioisotope – an isotope that is radioactive • Example: Carbon-14 • Radioactive isotopes can be naturally occurring, or they can be produced by bombarding stable isotopes with high speed particles

  3. Stability • Selected Unstable/Radioactive Isotopes are listed on Table N • All nuclei with atomic numbers greater than 83 are unstable • They are all radioactive • Stability is also dependant upon the ratio of protons to neutrons • The closer an isotope is to a 1:1 ratio the more stable it is

  4. Transmutation • Any change in the nucleus, which causes the element to change into a new element (change of atomic number) • Can occur naturally or artificially

  5. Natural Transmutation • Occurs naturally, spontaneous • Single nucleus undergoes decay (1 reactant) Example: 3719K → 3718Ar + 0+1e

  6. Artificial Transmutation • If the change is brought about by bombarding the nuclei by high energy particles • Two reactants – a fast moving particle and the target material Example: 3216S + 10n→ 3215P + 11H

  7. Equations • Mass must be conserved • Atomic mass and atomic number must be the same on both sides of the equation

  8. Remember • 42He • 4 = superscript = mass number (atomic mass) = protons + neutrons • 2 = subscript = atomic number = protons

  9. Equation Examples • What is X? 63Li + 10n → 42He + X • What is X? 146C → X + 0-1e

  10. Types of Radiation – Table O • Alpha particles – helium nucleus, 2 protons, 2 neutrons • Beta particles – an electron, negative charge, no mass • Positron – electron with a positive charge, no mass • Gamma radiation (γ) – similar, but more energy than X-rays, no mass, no charge

  11. Charges of Decay Particles • Negative particles will be attracted to positive charges • Positive charges will be attracted to negative charges • Non charged particles are not affected by charges

  12. Alpha Decay – unstable nucleus emits an alpha particle Example: 22688Ra → 22286Rn + 42He • Beta Decay – unstable nucleus emits a beta particle Example: 21482Pb → 21483Bi + 0-1e • Positron Emission – unstable nucleus emits a positron Example: 3719K → 3718Ar + 0+1e

  13. Conversion of Mass to Energy • E = mc2 • E = energy (J) • m = mass (kg) • c = velocity (speed) of light = 3.0x108m/s Example: How many joules of energy are released if 1.0g is converted to energy?

  14. Mass Defect • The actual atomic mass of an atom is less than what we would predict based upon the mass of individual protons and neutrons • The difference is because energy is released when the protons and neutrons combine • The larger the mass defect, the more energy is released upon formation, and the more stable the particle is

  15. Examples 1. Calculate the predicted mass of He-4. 1 proton = 1.00728, 1 neutron = 1.00867 • The actual mass of He-4 = 4.00150 • The mass defect is = 2. Convert the mass defect to energy (using E = mc2)

  16. Fission • Splitting of a heavy nucleus to produce lighter nuclei • Nuclear Power Plants • Neutron joins with a nucleus of a heavy element • Intermediate product is very unstable • Splits apart producing • Two mid weight nuclei • At least one neutron • A great amount of energy

  17. Fission • Example: 23592U + 10n 9236Kr + 14156Ba + 3 10n + energy • The three neutrons given off can be reabsorbed by other U-235 nuclei to continue fission as a chain reaction • A tiny bit of mass is lost (mass defect) and converted into a huge amount of energy • See Fission

  18. Chain Reaction • The neutrons that are emitted can become reactants causing more nuclei to undergo fission and release more energy • The reaction can be controlled by limiting the number of interactions between neutrons and nuclei

  19. Nuclear Power Plants

  20. Main Components • Fuel – Uranium or Plutonium • Control Rods - absorb neutrons to control the rate of the reaction • Containment Structure – building that houses the reactor

  21. Main Components • Coolant – Water, cools the reaction • Cooling Tower – cools the discharge water, releases water vapor

  22. Nuclear Power • Advantages: • Cleaner than conventional fossil fuels – no greenhouse gases or acid rain • More efficient, cleaner, cheaper • Disadvantages: • Many of the bi-products of the reactions are radioactive (unstable) and have long half-lives, making the storage and disposal of these wastes dangerous

  23. Fusion • Combining of light nuclei to produce a heavier nucleus • The Sun, Hydrogen Bomb Example: 21H + 21H → 42He + energy • See Fusion

  24. Fusion • Advantages • Products are not highly radioactive • Produces a lot of energy • Disadvantages • Requires extremely high temperatures and pressures, therefore not yet available to produce energy on Earth

  25. Half-Life • Time it takes for half of the atoms in a given sample of an isotope to decay • Each isotope has its own half-life (Table N) • The shorter the half-life of an isotope, the less stable it is • Half-life is a constant factor, it is not affected by temperature or pressure • Geiger counter can be used to record the decay of an isotope

  26. Use Table N for Half-Life and Decay Modes

  27. 1. Calculate the mass of I-131 that remains after 32.28 days, if the mass of the original sample was 100.0g. 2. If 50.0g of a radioactive isotope decays to 6.25g in 60.0 days, what is the isotope’s half-life?

  28. What fraction of a phosphorus-32 sample will remain after 28.6 days? • 50.0g of cobalt-60 decays for 21 years. How many grams remain after this time? • After 14.4 seconds, 3.00g of nitrogen-16 remains. What was the mass of the original nitrogen-16 sample?

  29. Dating • Each radioactive substance is presently decaying at the same rate as when the substance was made • By comparing the amount of 14C that remains to the amount of 12C that is present, the amount of 14C (and the age) can be calculated

  30. Chemical Tracers • A radioisotope is used to follow the path of a chemical process Example: C-14 is used to follow the path of carbon in organic reactions

  31. Medical Applications • Some radioisotopes have the ability to kill living tissue • Any radioisotope used in medicine must have a short half-life, making it quickly eliminated by the body

  32. Medical Examples • Cancer: Cobalt-60 emits large amounts of gamma radiation which can be used to kill tumor cells • Thyroid: Iodine-131 is used in the detection and treatment of thyroid conditions • Gamma Radiation: meats are irradiated to kill bacteria, producing a longer shelf life • Anthrax: Cobalt-60 and Cesium-137 are two sources of gamma radiation that can be used to destroy anthrax

  33. Radiation Risks • Can damage normal cells • High doses can cause illness, death • Can cause mutations that can be passed onto offspring

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