Like this presentation? Why not share!

# Ch 31 Nuclear Physics and Radioactivity

## by Scott Thomas on Mar 02, 2011

• 3,536 views

### Views

Total Views
3,536
Views on SlideShare
3,524
Embed Views
12

Likes
1
136
1

### Categories

Uploaded via SlideShare as Microsoft PowerPoint

### Report content

11 of 1 previous next

• Maria Gonzalez Very good powert point. 8 months ago
Are you sure you want to

## Ch 31 Nuclear Physics and RadioactivityPresentation Transcript

• Chapter 31 Nuclear Physics and Radioactivity
• 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.
• 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
• Chapter 31: Nuclear Physics and Radioactivity Section 1: Nuclear Structure
• The atomic nucleus consists of positively charged protons and neutral neutrons.
Nuclear Structure
• Identifying Variables atomic number mass number
• Isotopes
• Nuclei can contain the same number of protons but a different number of neutrons
• isotopes .
• Approximate size of a Nucleus mass number
• Conceptual Example 1 Nuclear 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”
• 31.1.1. What is the primary difference between 13 C and 12 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) Only 12 C is true carbon. The other is called carbomite.
• 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
• 31.1.3. Which of the following statements best describes the difference between an element and an isotope ? a) An isotope has a particular number of protons and neutrons, while an element has a particular number of protons and a varying number of neutrons. b) An element has a particular number of protons and neutrons, while an isotope has a particular number of protons and a varying number of neutrons. c) Chemists speak in terms of elements , while physicists prefer the more specific term of isotope . d) An isotope has a particular number of protons and neutrons, while an element has a particular number of neutrons and a varying number of protons. e) An element has a particular number of protons and neutrons, while an isotope has a particular number of neutrons and a varying number of protons.
• 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)
• 31.1.5. Consider the nucleus Which 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.
• 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.
• Chapter 31: Nuclear Physics and Radioactivity Section 2: The Strong Nuclear Force & The Stability of the Nucleus
• 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.
• 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
• 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.
• Chapter 31: Nuclear Physics and Radioactivity Section 3: The Mass Defect of the Nucleus & Nuclear Binding Energy
• Mass Deficit
• Example 3 The 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.
• Binding Energy
• 31.3.1. Consider the plot of binding energy per nucleon versus the nucleon number A . 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.
• 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.
• Radioactivity A magnetic field separates three types of particles emitted by radioactive nuclei.
•  Decay
• 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
•  Decay
• Neutron “switches” into a proton
• Electron and associated neutrino is released
• Other similar reactions can occur
• Positron emission
• Electron capture
• Positron capture
•  decay excited energy state lower energy state
• Use of Gamma Radiation Gamma knife
• 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 to be emitted d) a proton and an alpha particle collide and form a new nucleus e) single-celled organisms absorb nuclear particles
• 31.4.2. When bismuth undergoes alpha decay, what daughter nucleus is produced? a) Bi b) Tl c) Au d) Au e) Tl
• 31.4.3. When francium undergoes alpha decay, what daughter nucleus is produced? a) Rn b) Ra c) Po d) At e) At
• 31.4.4. When osmium undergoes beta decay, what daughter nucleus is produced? a) Ir b) Ir c) W d) Re e) Re
• 31.4.5. When krypton undergoes beta decay, what daughter nucleus is produced? a) Rb b) Br c) Se d) Sr e) Rb
• 31.4.6. By what method can a nucleus decay to a daughter nucleus with a larger atomic number? a) There is no radioactivity process that will result in a daughter with a different atomic number than the parent. b) There is no radioactivity process that will result in a daughter with a larger atomic number. c) alpha decay d) beta decay e) gamma decay
• 31.4.7. Which one of the following occurs when Ra undergoes gamma decay? a) The mass of the nucleus increases. b) The mass of the nucleus decreases. c) The atomic number increases. d) The atomic number decreases. e) The number of electrons decreases.
• Chapter 31: Nuclear Physics and Radioactivity Section 5: The Neutrino
• Fundamental Particles
• This will be discussed in greater detail in Ch 32
• 3 Types of Fundamental Particles
• Bosons (Messenger Particles)
• Photon, W + , W - , Z, Gluons
• Gravitons (?)
• Leptons
• electron, tau, muon, and corresponding neutrinos
• Quarks
• up, down, charm, strange, top, bottom
• All particles have corresponding antiparticles
• For particles with no charge, the particles is its own antiparticle
• During beta decay, energy is released. However, it is found that most beta particles do not have enough kinetic energy to account for all of the energy released.
• The additional energy is carried away by a neutrino .
• The “flavor” is conserved as the neutrino is the anti-electron neutrino
The Neutrino
• Neutrino Facts
• Neutrinos have no electrical charge
• Have very little mass
• Less than 0.0004% the mass of an electron!
• But due to their large numbers could be a significant part of the mass of the universe.
• Do not interact easily with most forms of matter
• More than 1 trillion pass through your body every second!
• Very hard to detect
• Most pass through the entire earth without reacting with anything!
• The average neutrino can penetrate more than one light year of lead and still not react!
• Chapter 31: Nuclear Physics and Radioactivity Section 6: Radioactive Decay and Activity
• Radioactive Decay The half-life of a radioactive decay is the time in which ½ of the radioactive nuclei disintegrate.
• Example Half Lives
• 31.6.1. An isotope of cesium has a half-life of two years. If we had 100 grams of this isotope today, how much would we have left ten years from now? a) about three grams b) about six grams c) about twelve grams d) about twenty-five grams e) about fifty grams
• 31.6.2. After 6400 years of undergoing alpha decay, a sample contains only 6.25% of the radium nuclei it initially had. What is the half-life of these radium nuclei? a) 160 years b) 6000 years c) 3200 years d) 800 years e) 1600 years
• 31.6.3. In 1986, a nuclear accident occurred at Chernobyl in the former Soviet Union. During the accident, a radioactive isotope of iodine was released into the surrounding region that undergoes beta decay with a half-life of 8.040 days. How long did it take for the radioactivity from this iodine to be reduced to one percent of its initial value? a) 64 days b) 53 days c) 48 days d) 44 days e) 32 days
• 31.6.4. What portion of a radioactive sample remains after two half-lives have passed? a) None is left. b) All remains. c) one quarter d) one half e) three quarters
• 31.6.5. What portion of a radioactive sample remains after four half-lives have passed? a) None is left. b) 1/4 c) 1/8 d) 1/16 e) 1/32
• 31.6.6. After 6400 years of undergoing decay, a sample contains only 6.25% of the radium nuclei it initially had. What is the half-life of these radium nuclei? a) 160 years b) 6000 years c) 3200 years d) 800 years e) 1600 years