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CHAPTER 9 Nuclear Energy

CHAPTER 9 Nuclear Energy. I. Radioactivity (pg.284-292). Radioactive Elements. A. Definitions. Radioactivity Process of unstable nuclei of elements becoming stable through emitting particles or releasing energy away from the atom Also called nuclear decay. Definitions.

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CHAPTER 9 Nuclear Energy

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  1. CHAPTER9 Nuclear Energy I. Radioactivity (pg.284-292)

  2. Radioactive Elements

  3. A. Definitions • Radioactivity • Process of unstable nuclei of elements becoming stable through emitting particles or releasing energy away from the atom • Also called nuclear decay

  4. Definitions • During nuclear decay, the element can transform into a different isotope of the same element or to a different element completely. • Transmutation • process of changing one element into another element by nuclear decay

  5. Definitions • Nuclear radiation is the released energy and matter during nuclear decay. • This can have both positive and negative effects for life on earth.

  6. Definitions • Isotopes – elements that have the same number of protons but different number of neutrons in their nuclei.

  7. Isotopes • Carbon-12, Carbon-13, Carbon-14

  8. Where does this take place? • Radioactivity (nuclear decay) happens in the nucleus of the atom.

  9. B. Types of Radiation • Alpha () • helium nucleus paper 2+ • Beta-minus (-) • electron plastic 1- • Gamma () • high-energy photon lead 0

  10. Types of Radiation • Neutron emission (n) 1 0 n 0 charge

  11. C. Nuclear Decay • Why some nuclei decay… • to obtain a stable ratio of neutrons to protons Stable Unstable (radioactive)

  12. C. Nuclear Decay TRANSMUTATION • Alpha Emission • Beta Emission

  13. Example • Actinium-217 decays by releasing an alpha particle. Write the equation for this decay process and determine what element is formed. • Step 1: Write the equation with the original element on the reactant side and products on the right side.

  14. Example • 217 A 4 89 Ac  Z X + 2 He Step 2: Write math equations for the atomic and mass numbers. 217 = A + 4 89 = Z + 2

  15. Example • Step 3: Rearrange the equations. A = 217 – 4 Z = 89 - 2 Step 4:Solve for the unknown value, and rewrite the equation with all nuclei. A = 213 Z = 87

  16. Example • 217 213 4 89 Ac  87 Fr + 2 He This is an example of alpha decay.

  17. Example Half-lives polonium-194 0.7 seconds lead-212 10.6 hours iodine-131 8.04 days carbon-14 5,370 years uranium-238 4.5 billion years D. Half-life • Half-life (t½) • time it takes for half of the radioactive nuclei in a sample to decay

  18. Half-life

  19. If we start out with 1 gram of the parent isotope, after the passage of 1 half-life, there will be 0.5 gram of the parent isotope left.

  20. D. Half-life • How much of a 20-g sample of sodium-24 would remain after decaying for 30 hours? Sodium-24 has a half-life of 15 hours. GIVEN: total time = 30 hours t1/2 = 15 hours original mass = 20 g WORK: number of half-lives = 2 20 g ÷ 2 = 10 g (1 half-life) 10 g ÷ 2 = 5 g (2 half-lives) 5 g of 24Na would remain.

  21. Nuclear Forces • There are two types of forces in the nucleus. • Strong nuclear force – helps attract the protons and neutrons in the nucleus and keep them together. • Repulsive force- protons repel each other because they are the same charge

  22. Nuclear Forces In stable atoms, the attractive forces are stronger than the repulsive forces.

  23. A. Fission • splitting a nucleus into two or more smaller nuclei • some mass is converted to large amounts of energy

  24. A. Fission • chain reaction - self-feeding reaction

  25. Fission • Chain reactions can be controlled and used to create electricity in nuclear power plants. • The minimum amount of a substance that can undergo a fission reaction and sustain a chain reaction is called critical mass.

  26. B. Fusion • combining of two nuclei to form one nucleus of larger mass • produces even more energy than fission • occurs naturally in stars

  27. Fusion

  28. Nuclear Radiation in Life • Background radiation is nuclear radiation that is around you from natural sources like the sun, soil, rocks, and space. • A rem or millirem (1 rem = 1000millirems) is the unit for radiation.

  29. Nuclear Radiation in Life • A safe limit is set at 5000 millirems/year. • Occupation – X-ray tech, flight attendant • Where you live- high elevation, near rocks • Activities - smoking

  30. A. Nuclear Power • Fission Reactors

  31. A. Nuclear Power • Fusion Reactors (not yet sustainable) National Spherical Torus Experiment Tokamak Fusion Test Reactor Princeton University

  32. 235U is limited danger of meltdown toxic waste thermal pollution Hydrogen is abundant no danger of meltdown no toxic waste not yet sustainable A. Nuclear Power FISSION FUSION vs.

  33. Other benefits to radiation • Smoke detectors • Disease detection • Ultra sound • CT scan • MRI • Cancer treatment

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