Ch 31 Nuclear Physics and Radioactivity
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Transcript of Ch 31 Nuclear Physics and Radioactivity
Chapter 31
Nuclear Physics and Radioactivity
AP Learning ObjectivesNuclear 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 ObjectivesNuclear 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)c2 in
analyzing nuclear processes.
Table Of Contents
1. Nuclear Structure
2. The Strong Nuclear Force and The Stability of the Nucleus
3. The Mass Defect of the Nucleus and Nuclear Binding Energy
4. Radioactivity
5. The Neutrino
6. Radioactive Decay and Activity
7. Radioactive Dating
8. Radioactive Decay Series
9. Radiation Detectors
Chapter 31:Nuclear Physics and Radioactivity
Section 1:
Nuclear Structure
The atomic nucleus consists of positively charged protons and neutral neutrons.
Nuclear Structure
neutrons
ofNumber protons
ofNumber neutrons and
protons ofNumber
NZA
atomicnumber
massnumber
Identifying Variables
Isotopes Nuclei can contain the same number of protons but
a different number of neutrons isotopes.
3115 m102.1 Ar
Approximate size of a Nucleus
massnumber
3115 m102.1 Ar
Conceptual Example 1 Nuclear Density
It is well known that lead and oxygen contain different atoms andthat the density of solid lead is much greater than gaseous oxygen.Using the equation, decide whether the density of the nucleus in alead atom is greater than, approximately equal to, or less than thatin an oxygen atom.
33115102.134 Am
Am
V
M
Nuclear density are always “the same”
31.1.1. What is the primary difference between 13C and 12C?
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 12C 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
Ne2210
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.
Pa.23491
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
22deficit Massenergy Binding cmc
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 hydrogenis 1.0078u. Using atomic mass units, instead of kilograms, obtain thebinding energy of the helium nucleus.
u 0304.0u 0026.4u 0330.4 m
MeV 5.931u 1
MeV 3.28energy Binding
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.
Fe5626
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
A magnetic field separates three types of particles emitted byradioactive nuclei.
Radioactivity
He D P 22
42
AZ
AZ
Decay
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
e D P 011 A
ZAZ
Decay
Neutron “switches” into
a proton
Electron and
associated neutrino is
released
Other similar reactions
can occur
Positron emission
Electron capture
Positron capture
P P AZ
AZ
excited energystate
lower energystate
decay
Gamma knife
Use of Gamma Radiation
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
Bi21183
20783
20781
20979
21179
20981
31.4.3. When francium undergoes alpha decay, what daughter nucleus is produced?
a) Rn
b) Ra
c) Po
d) At
e) At
Fr22387
22286
22388
22184
21985
22185
31.4.4. When osmium undergoes beta decay, what daughter nucleus is produced?
a) Ir
b) Ir
c) W
d) Re
e) Re
Os19176
19177
19077
18774
19175
18775
31.4.5. When krypton undergoes beta decay, what daughter nucleus is produced?
a) Rb
b) Br
c) Se
d) Sr
e) Rb
Kr8936
8837
8835
8534
8838
8937
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.
23688
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
e e Pa Th 01
23491
23490
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
The half-life of a radioactivedecay is the time in which ½of the radioactive nuclei disintegrate.
toeNN
2ln
21 T
Radioactive Decay
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 yearsago. The wine contains a number of different atoms, including carbon, oxygen, and hydrogen. The radioactive isotope of carbon is thefamiliar C-14 with ½ life 5730 yr. The radioactive isotope of oxygenis O-15 with a ½ life of 122.2 s. The radioactive isotope of hydrogenis called tritium and has a ½ life of 12.33 yr. The activity of eachof these isotopes is known at the time the bottle was sealed. However,only one of the isotopes is useful for determining the age of thewine. 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 14C 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
146
146
146
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
A Geiger counter
Radiation Detectors
A scintillationcounter
Radiation Detectors