# ch 31 nuclear physics and radioactivity

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• 1. Chapter 31 Nuclear Physics and Radioactivity

2. AP Learning Objectives

• Nuclear Physics
• Nuclear reactions (including conservation of mass number and charge)
• Students should understand the significance of the mass number and charge of nuclei, so they can:
• Interpret symbols for nuclei that indicate these quantities.
• Use conservation of mass number and charge to complete nuclear reactions.
• Determine the mass number and charge of a nucleus after it has undergone specified decay processes.
• Students should know the nature of the nuclear force, so they can compare its strength and range with those of the electromagnetic force.
• Students should understand nuclear fission, so they can describe a typical neutron-induced fission and explain why a chain reaction is possible.

3. AP Learning Objectives

• Nuclear Physics
• Mass-energy equivalence
• Students should understand the relationship between mass and energy (mass-energy equivalence), so they can:
• Qualitatively relate the energy released in nuclear processes to the change in mass.
• Apply the relationship E = ( m)c 2 in analyzing nuclear processes.

• Nuclear Structure
• The Strong Nuclear Force and The Stability of the Nucleus
• The Mass Defect of the Nucleus and Nuclear Binding Energy
• The Neutrino

5. Chapter 31: Nuclear Physics and Radioactivity Section 1: Nuclear Structure 6.

• The atomic nucleus consists of positively charged protons and neutral neutrons.

Nuclear Structure 7. Identifying Variables atomic number mass number 8. Isotopes

• Nuclei can contain the same number of protons but a different number of neutrons
• isotopes .

9. Approximate size of a Nucleus mass number 10. Conceptual Example 1Nuclear Density It is well known that lead and oxygen contain different atoms and that the density of solid lead is much greater than gaseous oxygen. Using the equation, decide whether the density of the nucleus in a lead atom is greater than, approximately equal to, or less than that in an oxygen atom. Nuclear density are always the same 11. 31.1.1.What is the primary difference between13 C and12 C? a)The number of electrons is different. b)The number of protons is different. c)The number of neutrons is different. d)The chemical behavior is different. e)Only12 C is true carbon.The other is called carbomite. 12. 31.1.2. How many neutrons and how many protons are in? a)22 neutrons and 10 protons b)12 neutrons and 10 protons c)10 neutrons and 12 protons d)10 neutrons and 22 protons e)10 neutrons and 10 protons 13. 31.1.3. Which of the following statements best describes the difference between anelementand anisotope ? a)Anisotopehas a particular number of protons and neutrons, while anelementhas a particular number of protons and a varying number of neutrons. b)Anelementhas a particular number of protons and neutrons, while anisotopehas a particular number of protons and a varying number of neutrons. c)Chemists speak in terms ofelements , while physicists prefer the more specific term ofisotope . d)Anisotopehas a particular number of protons and neutrons, while anelementhas a particular number of neutrons and a varying number of protons. e)Anelementhas a particular number of protons and neutrons, while anisotopehas a particular number of neutrons and a varying number of protons. 14. 31.1.4. Which one of the following elements do you think has the nucleus with the largest volume? a)Helium (He) b)Lithium (Li) c)Oxygen (O) d)Calcium (Ca) e)Boron (B) 15. 31.1.5. Consider the nucleusWhich one of the following statements is true? a)This isotope contains an equal number of protons and neutrons. b)This isotope contains 91 neutrons and 143 protons. c)This isotope contains 143 neutrons and 91 protons. d)This isotope contains 234 neutrons and 91 protons. e)This isotope contains 91 neutrons and 234 protons. 16. 31.1.6. What is the difference between the atomic number and the atomic mass number? a)The atomic number is the number of protons, but the mass number is the number of neutrons. b)The mass number is the atomic number plus the number of neutrons. c)The mass number is the atomic number plus the number of electrons. d)The atomic number and mass number are not related in any way. e)The mass number and the atomic number are exactly the same thing. 17. Chapter 31: Nuclear Physics and Radioactivity Section 2: The Strong Nuclear Force &The Stability of the Nucleus 18. What Holds a Nucleus Together?

• The mutual repulsion of the protons due to the Electric Force should push the nucleus apart.
• What then, holds the nucleus together?
• A stronger force within the Nucleus
• What do Physicist creatively call this force?
• The strong nuclear force.

19. Stability of the Nucleus

• As nuclei get larger, more neutrons are required for stability.
• The neutrons act like glue without adding more repulsive force.
• For small elements
• Ratio N/P ~ 1
• For large element
• Ratio of N/P ~ 2

20. 31.2.1. Consider the following three forces: gravity, electromagnetic, and strong nuclear.Which of these is responsible for holding nuclei together and which is responsible for holding electrons in their orbits? a)Gravity holds electrons, while the strong nuclear force holds nuclei together. b)Gravity holds electrons in their orbits and nuclei together. c)Gravity holds electrons, while the electromagnetic force holds nuclei together. d)The strong nuclear force holds electrons, while the electromagnetic force holds nuclei together. e)The electromagnetic force holds electrons, while the strong nuclear force holds nuclei together. 21. Chapter 31: Nuclear Physics and Radioactivity Section 3: The Mass Defect of the Nucleus & Nuclear Binding Energy 22. Mass Deficit 23. Example 3The Binding Energy of the Helium Nucleus Revisited The atomic mass of helium is 4.0026u and the atomic mass of hydrogen is 1.0078u.Using atomic mass units, instead of kilograms, obtain the binding energy of the helium nucleus. 24. Binding Energy 25. 31.3.1. Consider the plot of binding energy per nucleon versus the nucleon numberA .Which one of the following statements best describes the stability of the iron isotope? a)This isotope has the most stable nucleus because a minimum amount of work is needed to separate this nucleus into its constituent protons and neutrons. b)This isotope has the most stable nucleus because a maximum amount of work is needed to separate this nucleus into its constituent protons and neutrons. c)This isotope has the least stable nucleus because a minimum amount of work is needed to separate this nucleus into its constituent protons and neutrons. d)This isotope has the least stable nucleus because a maximum amount of work is needed to separate this nucleus into its constituent protons and neutrons. e)This isotope has the most stable nucleus because an infinite amount of work is needed to separate this nucleus into its constituent protons and neutrons. 26. 31.3.2. Consider the following values for the mass defect for five hypothetical nuclei labeled with roman numerals in the table below.Which one of the following statements concerning these nuclei is true? a)Nucleus V is the most stable; and nucleus I is the least stable. b)Nuclei I and II are the most stable; and nuclei IV and V are not stable. c)Nuclei I and II are not stable; and nuclei IV and V are the most stable. d)Nucleus III is the most stable; and nuclei I and V are the least stable. e)Nucleus III is the most stable; and nuclei IV and V are the least stable. 27. Chapter 31: Nuclear Physics and Radioactivity Section 4: Radioactivity 28. Radioactivity A magnetic field separates three types of particles emitted by radioactive nuclei. 29. Decay 30. Uses of Radioactivity

• A smoke detector
• Small amount of radioactive material is present
• Ionizes the air between the plates of a capacitor
• Allows air to conduct electricity
• Presence of Smoke Particles changes the conductivity

31. Decay

• Neutron switches into a proton
• Electron and associated neutrino is released
• Other similar reactions can occur
• Positron emission
• Electron capture
• Positron capture

32. decay excited energy state lower energy state 33. Use of Gamma Radiation Gamma knife 34. 31.4.1. Which one of the following processes is considered radioactive decay? a)a nucleus spontaneously emits a particle b)a neutron collides with a uranium nucleus and breaks it into two pieces c)a photon strikes a metal surface and causes an electron