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Atomic Nucleus and Radioactivity

Lesson 28. Atomic Nucleus and Radioactivity. Eleanor Roosevelt High School Chin-Sung Lin. Atomic Nucleus and Radioactivity. X-Rays and Radioactivity.

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Atomic Nucleus and Radioactivity

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  1. Lesson 28 Atomic Nucleus and Radioactivity Eleanor Roosevelt High School Chin-Sung Lin

  2. Atomic Nucleus and Radioactivity

  3. X-Rays and Radioactivity • In 1895, a German physicist, W. C. Roentgen was working with a cathode ray tube in his lab and discovered X-rays produced by a beam of electrons striking the glass surface of a gas-discharge tube

  4. X-Rays and Radioactivity • Roentgen found that X-rays could pass through solid materials, could ionize the air, showed no refraction in glass, and were undeflected by magnetic fields

  5. X-Rays and Radioactivity • X-rays are high-frequency electromagnetic waves, usually emitted by the de-excitation of the innermost orbital electrons of atoms

  6. X-Rays and Radioactivity • An energetic beam of electrons striking a solid surface excites the innermost electrons and produces higher-frequency photons of X-radiation.

  7. X-Rays and Radioactivity • X-ray photons have high energy and can penetrate many layers of atoms before being absorbed or scattered • X-rays do this when they pass through your soft tissue to produce an image of the bones inside your body

  8. X-Rays and Radioactivity Radioactivity • Radioactivity is the process of nuclear decay (radioactive decay) • Nothing new in the environment; it’s been going on since time zero • It warms Earth’s interior, is in the air we breathe, and is present in all rocks (some in trace amounts) • It is natural

  9. X-Rays and Radioactivity CHECK YOUR NEIGHBOR The radioactive decay of nature’s elements occurs in the A. soil we walk on. • air we breathe. • interior of Earth. • All of the above.

  10. X-Rays and Radioactivity CHECK YOUR ANSWER The radioactive decay of nature’s elements occurs in the A. soil we walk on. • air we breathe. • interior of Earth. • All of the above.

  11. Alpha, Beta, and Gamma Rays

  12. Alpha, Beta, and Gamma Rays

  13. Alpha, Beta, and Gamma Rays • Radioactive elements emit three distinct types of radiation:  — alpha: positively charged (helium nuclei)  — beta: negatively charged (electrons) — gamma: no charge(electromagnetic radiation) • Relative penetration

  14. Alpha, Beta, and Gamma Rays CHECK YOUR NEIGHBOR The origins of radioactivity go back to A. military activities in the mid-20th century. • the Industrial Revolution two centuries ago. • the beginning of human error. • before humans emerged on Earth.

  15. Alpha, Beta, and Gamma Rays CHECK YOUR ANSWER The origins of radioactivity go back to A. military activities in the mid-20th century. • the Industrial Revolution two centuries ago. • the beginning of human error. • before humans emerged on Earth.

  16. Alpha, Beta, and Gamma Rays • Alpha decay

  17. Alpha, Beta, and Gamma Rays • Alpha decay

  18. Alpha, Beta, and Gamma Rays • Beta decay

  19. Alpha, Beta, and Gamma Rays • Beta decay

  20. Alpha, Beta, and Gamma Rays • Beta decay

  21. Alpha, Beta, and Gamma Rays • Beta decay

  22. Alpha, Beta, and Gamma Rays • Gamma decay

  23. Alpha, Beta, and Gamma Rays • Gamma decay

  24. Alpha, Beta, and Gamma Rays CHECK YOUR NEIGHBOR Any atom that emits an alpha particle or beta particle A. becomes an atom of a different element, always. • may become an atom of a different element. • becomes a different isotope of the same element. • increases its mass.

  25. Alpha, Beta, and Gamma Rays CHECK YOUR ANSWER Any atom that emits an alpha particle or beta particle A. becomes an atom of a different element, always. • may become an atom of a different element. • becomes a different isotope of the same element. • increases its mass.

  26. Alpha, Beta, and Gamma Rays CHECK YOUR NEIGHBOR Which of these is actually a high-speed electron? A. Alpha • Beta • Gamma

  27. Alpha, Beta, and Gamma Rays CHECK YOUR ANSWER Which of these is actually a high-speed electron? A. Alpha • Beta • Gamma

  28. Radioactive Isotopes • The number of protons in an atomic nucleus determine the number of electrons surrounding the nucleus in a neutral atom • When there is a different number of electrons than the nuclear protons, the atom is charged and is called an ion • When there is a same number of protons (atomic numbers) but different number of neutrons (mass numbers), they are called isotopes • When an isotope is radioactive, it is called radioactive isotope

  29. Radioactive Isotopes • Three common isotopes of Hydrogen:

  30. Radioactive Isotopes • Tritium is a radioactive isotope:

  31. Radioactive Isotopes • Tritium is a radioactive isotope:

  32. Exercise: Radioactive Isotopes The nucleus of beryllium-8 (Be-8) undergoes a special kind of radioactive decay: it split into two equal halves. What nuclei are the products of this decay? What is the form of this decay?

  33. Exercise: Radioactive Isotopes The nucleus of beryllium-8 (Be-8) undergoes a special kind of radioactive decay: it split into two equal halves. What nuclei are the products of this decay? What is the form of this decay? 8Be –> 2 4He alpha decay 2 4

  34. Radioactive Isotopes • The electric force of repulsion between the protons in a heavy nucleus acts over a greater distance than the attractive forces among the neutrons and protons in the nucleus • Each proton is repelled by every other proton in the nucleus, but is attracted only by the nucleons closest to it • In a large nucleus, electric repulsion can exceed nuclear attraction • This instability makes all the heaviest atoms radioactive

  35. The Atomic Nucleus and the Strong Force The strong force is more effective with smaller nuclei. particles occupying the nucleus is nucleons Mass=2000 times the mass of electrons

  36. The Atomic Nucleus and the Strong Force • The strong force holds nucleons together • Nuclear force holds the nucleus together called the strong interaction which is an attractive force and is a short range force • Electrical interaction is a long range force

  37. The Atomic Nucleus and the Strong Force • A lone neutron is radioactive and spontaneously transforms to a proton and an electron • A neutron needs protons around to keep this from happening

  38. The Atomic Nucleus and the Strong Force Alpha emission

  39. The Atomic Nucleus and the Strong Force CHECK YOUR NEIGHBOR • The strong force is a force in the A. atom that holds electrons in orbit. • nucleus that holds nucleons together. • Both A and B. • Neither A nor B.

  40. The Atomic Nucleus and the Strong Force CHECK YOUR ANSWER • The strong force is a force in the A. atom that holds electrons in orbit. • nucleus that holds nucleons together. • Both A and B. • Neither A nor B.

  41. The Atomic Nucleus and the Strong Force CHECK YOUR NEIGHBOR • In the nucleus of an atom, the strong force is a relatively A. short-range force. • long-range force. • unstable force. • neutralizing force.

  42. The Atomic Nucleus and the Strong Force CHECK YOUR ANSWER • In the nucleus of an atom, the strong force is a relatively A. short-range force. • long-range force. • unstable force. • neutralizing force.

  43. Radioactive Half-Life The rate of decay for a radioactive isotope is measured in terms of a characteristic time, the half-life, the time for half of an original quantity of an element to decay

  44. Radioactive Half-Life CHECK YOUR NEIGHBOR Suppose the number of neutrons in a reactor that is starting up doubles each minute, reaching 1 billion neutrons in 10 minutes. When did the number of neutrons reach half a billion? A. 1 minute • 2 minutes • 5 minutes • 9 minutes

  45. Radioactive Half-Life CHECK YOUR ANSWER Suppose the number of neutrons in a reactor that is starting up doubles each minute, reaching 1 billion neutrons in 10 minutes. When did the number of neutrons reach half a billion? A. 1 minute • 2 minutes • 5 minutes • 9 minutes Explanation: This question would be appropriate with Appendix D, Exponential Growth and Doubling Time. Can you see that working backward, each minute has half the number of neutrons?

  46. Radiation Half-Life CHECK YOUR NEIGHBOR A certain isotope has a half-life of 10 years. This means the amount of that isotope remaining at the end of 10 years will be A. zero. • one-quarter. • Half. • the same.

  47. Radiation Half-Life CHECK YOUR ANSWER A certain isotope has a half-life of 10 years. This means the amount of that isotope remaining at the end of 10 years will be A. zero. • one-quarter. • Half. • the same.

  48. Exercise: Radioactive Half-Life If a sample of radioactive isotope has a half-life of 1 year, how much of the original sample will be left at the end of the second year?

  49. Exercise: Radioactive Half-Life If a sample of radioactive isotope has a half-life of 1 year, how much of the original sample will be left at the end of the second year? (1/2)2 = 1/4

  50. Exercise: Radioactive Half-Life If Fukushima Daiichi nuclear power plant in Japan releases a certain amount of radioactive iodine (I-131), how many percent of the original material will be left at the end of the 50 days? (The half-life of I-131 is 8.02 day)

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