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Types of Radioactive Decay

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Chapter Eighteen:
THE NUCLEUS: A
CHEMIST’S VIEW
Review
• Atomic Number (Z) – number of protons
• Mass Number (A) – sum of protons and
neutrons
18.1
Chapter 18 | Slide 2
Copyright В© Houghton Mifflin Company. All rights reserved.
Radioactive Decay
• Nucleus undergoes decomposition to
form a different nucleus.
18.1
Chapter 18 | Slide 3
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Radioactive Stability
• Nuclides with 84 or more protons are
unstable.
18.1
Chapter 18 | Slide 4
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Radioactive Stability
• Light nuclides are stable when Z equals A
– Z (neutron/proton ratio is 1).
• For heavier elements the neutron/proton
ratio required for stability is greater than 1
and increases with Z.
18.1
Chapter 18 | Slide 5
Copyright В© Houghton Mifflin Company. All rights reserved.
Radioactive Stability
• Certain combinations of protons and
neutrons seem to confer special stability.
– Even numbers of protons and neutrons are
more often stable than those with odd
numbers.
18.1
Chapter 18 | Slide 6
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Radioactive Stability
• Certain specific numbers of protons or
neutrons produce especially stable
nuclides.
– 2, 8, 20, 28, 50, 82, and 126
18.1
Chapter 18 | Slide 7
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The Zone
of Stability
Chapter 18 | Slide 8
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Types of Radioactive Decay
• Alpha production ():
4
2 He
• Beta production ():
0
пЂ­1 e
18.1
Chapter 18 | Slide 9
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Types of Radioactive Decay
• Gamma ray production ():
• Positron
0
production:1 e
• Electron capture:
18.1
Chapter 18 | Slide 10
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Decay Series
(Series of
Alpha and
Beta Decays)
Chapter 18 | Slide 11
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Rate of Decay
Rate = kN
• The rate of decay is proportional to the
number of nuclides. This represents a
first-order process.
18.2
Chapter 18 | Slide 12
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Half-Life
• Time required for the number of nuclides
to reach half the original value.
t1/2 = ln(2)/k = 0.693/k
18.2
Chapter 18 | Slide 13
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Nuclear Particles
18.2
Chapter 18 | Slide 14
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Half-Life of Nuclear Decay
18.2
Chapter 18 | Slide 15
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Nuclear Transformation
• The change of one element into another.
27
13
249
98
Al + 2 He п‚®
Cf +
4
18
8
Oп‚®
30
15
263
106
1
P + 0n
1
0
Sg + 4 n
18.3
Chapter 18 | Slide 16
Copyright В© Houghton Mifflin Company. All rights reserved.
A Schematic Diagram of a Cyclotron
18.3
Chapter 18 | Slide 17
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A Schematic Diagram of a Linear
Accelerator
18.3
Chapter 18 | Slide 18
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Measuring Radioactivity Levels
• Geiger counter
• Scintillation counter
18.4
Chapter 18 | Slide 19
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Geiger Counter
18.4
Chapter 18 | Slide 20
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Carbon-14 Dating
• Used to date wood and cloth artifacts.
• Based on carbon-14 to carbon-12 ratio.
18.4
Chapter 18 | Slide 21
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Radiotracers
• Radioactive nuclides that are introduced
into organisms in food or drugs and
whose pathways can be traced by
monitoring their radioactivity.
18.4
Chapter 18 | Slide 22
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Radiotracers
18.4
Chapter 18 | Slide 23
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Energy and Mass
• When a system gains or loses energy it
also gains or loses a quantity of mass.
пЃ„E = пЃ„mc2
пЃ„m = mass defect
пЃ„E = change in energy
• If E is negative (exothermic), mass is
lost from the system.
18.5
Chapter 18 | Slide 24
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Binding Energy
• The energy required to decompose the
nucleus into its components.
• Iron-56 is the most stable nucleus and
has a binding energy of 8.97 MeV.
18.5
Chapter 18 | Slide 25
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Binding Energy per Nucleon vs. Mass
Number
18.5
Chapter 18 | Slide 26
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Nuclear Fission and Fusion
• Fusion – Combining two light nuclei to
form a heavier, more stable nucleus.
• Fission – Splitting a heavy nucleus into
two nuclei with smaller mass numbers.
1
0
n +
235
92
U п‚®
142
56
Ba +
91
36
1
Kr + 3 0 n
18.6
Chapter 18 | Slide 27
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Nuclear Fission
18.6
Chapter 18 | Slide 28
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Fission Processes
A self-sustaining fission process is called
a chain reaction.
Neutrons
Causing
Fission
Event
Event
subcritical
<1
critical
=1
supercritical
>1
Chapter 18 | Slide 29
Result
reaction stops
sustained reaction
violent explosion
18.6
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Schematic Diagram of a Nuclear Power
Plant
18.6
Chapter 18 | Slide 30
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Schematic
Diagram of a
Reactor Core
Chapter 18 | Slide 31
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Nuclear Fusion
18.6
Chapter 18 | Slide 32
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Biological Effects of Radiation
Depend on:
1.
2.
3.
4.
Energy of the radiation
Penetrating ability of the radiation
Ionizing ability of the radiation
Chemical properties of the radiation
source
18.7
Chapter 18 | Slide 33
Copyright В© Houghton Mifflin Company. All rights reserved.
Effects of Short-Term Exposures on
Radiation
18.7
Chapter 18 | Slide 34
Copyright В© Houghton Mifflin Company. All rights reserved.
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