Ch 31 Nuclear Physics and RadioactivityPresentation Transcript
Chapter 31 Nuclear Physics and Radioactivity
AP Learning Objectives
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
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.
Table Of Contents
The Strong Nuclear Force and The Stability of the Nucleus
The Mass Defect of the Nucleus and Nuclear Binding Energy
Radioactive Decay and Activity
Radioactive Decay Series
Chapter 31: Nuclear Physics and Radioactivity Section 1: Nuclear Structure
The atomic nucleus consists of positively charged protons and neutral neutrons.
Identifying Variables atomic number mass number
Nuclei can contain the same number of protons but a different number of neutrons
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
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.
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.
Chapter 31: Nuclear Physics and Radioactivity Section 4: Radioactivity
Radioactivity A magnetic field separates three types of particles emitted by radioactive nuclei.
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
Neutron “switches” into a proton
Electron and associated neutrino is released
Other similar reactions can occur
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
This will be discussed in greater detail in Ch 32
3 Types of Fundamental Particles
Bosons (Messenger Particles)
Photon, W + , W - , Z, Gluons
electron, tau, muon, and corresponding neutrinos
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
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
Chapter 31: Nuclear Physics and Radioactivity Section 7: Radioactive Dating
Using half lives
Conceptual Example 12 Dating a Bottle of Wine A bottle of red wine is thought to have been sealed about 5 years ago. The wine contains a number of different atoms, including carbon, oxygen, and hydrogen. The radioactive isotope of carbon is the familiar C-14 with ½ life 5730 yr. The radioactive isotope of oxygen is O-15 with a ½ life of 122.2 s. The radioactive isotope of hydrogen is called tritium and has a ½ life of 12.33 yr. The activity of each of these isotopes is known at the time the bottle was sealed. However, only one of the isotopes is useful for determining the age of the wine. Which is it? H-3 is useful as life of material is similar to ½ life
31.7.1. A centipede consumes a leaf at contains two 14 C atoms and subsequently dies. How long will it take before these two atoms undergo beta decay? a) 5730 years b) 2865 years c) 11 460 years d) about one million years e) It is not possible to predict exactly when these atoms will decay because of quantum uncertainties.
31.7.2. At an archeological dig, the remains of a saber-tooth tiger are found. In a carbon dating ( C has a half-life of 5730 years) test to determine the age of the cat, a scientist finds that the amount of C is about 1/32 the amount of C in living animals. How long ago did this saber-tooth tiger die? a) about 50 000 years ago b) about 40 000 years ago c) about 30 000 years ago d) about 20 000 years ago e) about 10 000 years ago
Chapter 31: Nuclear Physics and Radioactivity Section 8: Radioactive Decay Series
Radioactive equation=Lays Chips
Most of the time, many radioactive reactions occurs in a long series.
The sequential decay of one nucleus after another is called a radioactive decay series
Example U-238 Decay
Chapter 31: Nuclear Physics and Radioactivity Section 9: Radiation Detectors