The Atomic Nucleus

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The Atomic Nucleus
Discovery of Radioactivity
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Lead block
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Radium
Lead block
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Magnet
Radium
Lead block
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a
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a
Alpha particle (helium nucleus)
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?
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?
Beta particle (electron)
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?
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?
Gamma ray (ultra-high energy nonvisible light)
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?
a
?
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Radioactive Source
Paper
Aluminum
Lead
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Radioactive Source
a
Paper
Aluminum
Lead
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Radioactive Source
Paper
?
Aluminum
Lead
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Radioactive Source
Paper
Aluminum
?
Lead
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Radioactivity Is a Natural Phenomenon
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Origins of radiation exposure
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Origins of radiation exposure
Natural Background (cosmic rays, earth minerals)
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Medicine and Diagnostics 15
Consumer Products (televisions sets, smoke
detectors) 4
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Unit of radiation exposure
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Unit of radiation exposure
rad
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Unit of radiation exposure
0.01 joule radiant energy
rad

kilogram of tissue
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Some forms of radiation are more harmful to
living organisms than others
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Ability to cause harm is given in rem
rem rad x factor
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Health effect
Particle
Dosage
Factor
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Health effect
Particle
Dosage
Factor

x
alpha
1 rad
10
10 rem
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Health effect
Particle
Dosage
Factor

x
alpha
1 rad
10
10 rem

x
beta
10 rad
1
10 rem
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1 rem
1000 millirem
(mrem)
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Average annual exposure per person In the United
States
about 360 mrem
Major Source Radon - 222
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Typical Annual Radiation Exposure
Source
Typical Amount Received in 1 Year (millirems)

• Natural Origin

Cosmic radiation 26 Ground 33 Air
(radon-222) 198 Human tissues
(postassium-40 radium-226) 35
Human Origin
Medical procedures Diagnostic X rays 33
Nuclear medicine 15 Television tubes,
other consumer products
11 Weapons-test fallout 1
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Radioactive Isotopes Are Useful as Tracers and
for Medical Imaging
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Uses of Some Radioactive Isotopes
Isotope
Usage
Calcium-47 Study of bone formation in
mammals Californium-252 Inspect airline
luggage for explosives Hydrogen-3 (tritium)
Life-science and drug-metabolism studies
to ensure safety of potential new
drugs Iodine-131 Diagnose and treat thyroid
disorders Iridium-192 Test integrity of
pipeline welds, boilers, and aircraft
parts Thallium-201 Cardiology and for tumor
detection Xenon-133 Lung-ventilation and
flood-flow studies
Source Nuclear Regulatory Council
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Radioactivity Results from an Imbalance of Forces
in the Nucleus
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Helium nucleus
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Strong Nuclear Force
An attractive force that acts between all nucleons
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These protons are not normally attracted to each
other
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Neutrons are needed to create the strong nuclear
force
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There is a limit to the number of neutrons that
can be added to an atomic nucleus
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neutrons need to have protons around them in
order to remain stable
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with too many neutrons, and not enough protons,
something most bizarre occurs
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A lone neutron
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converts to a proton!
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Proton to Neutron ratios
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Proton to Neutron ratios
1 to 1
Optimum
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Proton to Neutron ratios
1 to 1
Optimum
1 to 1.4
Limit
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A nucleus with too many neutrons
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A nucleus with too many neutrons
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Hmmextra proton?
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The size of the nucleus is limited

• The nucleus cannot hold a very large number of
  protons together.

2) There cannot be an unlimited number of
neutrons.
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A Radioactive Element Can Transmute to a
Different Element
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Transmutation
The changing of one element to another
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238
U
92
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234
4
Th
He
90
2
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234
4
Th
He
90
2
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234
4
Th
He
90
2
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234
Th
90
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238
U
92
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234
4
Th
He
90
2
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234
4
Th
He
90
2
80
234
4
Th
He
90
2
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234
Th
90
82

83

84

234
238
4
Th
U
He

90
92
2
85

86

87

234
234
0
e
Pa
Th

91
90
-1
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Radioactive Half-Life
The time it takes for one-half of a radioactive
sample to decay
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Half-Life
Element
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Uranium-238
4.5 x 10
years
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Half-Life
Element
9
Uranium-238
4.5 x 10
years
Carbon-14
5730
years
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Half-Life
Element
9
Uranium-238
4.5 x 10
years
Carbon-14
5730
years
Bismuth-210
5.0
days
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Half-Life
Element
9
Uranium-238
4.5 x 10
years
Carbon-14
5730
years
Bismuth-210
5.0
days
- 4
Polonium-214
1.6 x 10
sec
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Radioactive Half-Life
The time it takes for one-half of a radioactive
sample to decay
Look at factors of 2 One half-life (1/2) Two
half-lives (1/4) Three half-lives (1/8)
For Example A material has decreased by ¼ of
its original amount it has gone through two
half-lives
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N-14
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N-14
7
7
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N-14
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N-14
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N-14
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C-14
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C-14
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C-14
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C-14
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C-14
8
6
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C-14
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CO
14
2
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CO
14
2
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Carbon-14 is a radioactive isotope that is
naturally incorporated from carbon dioxide into
living organisms, the amount remains relatively
constant during the life of the organism When
the living organisms dies the carbon 14 is no
longer being replaced in the organism and will
start to decay. The amount of loss from the that
compared to living organisms can be used to
determine when the organism died.
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22,920 years ago
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17,190 years ago
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11,460 years ago
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5730 years ago
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Present
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Calculate Age
Problem The carbon-14 radioactivity in the bones
of a body was measured to be 1/8 of that compared
to a living person How long ago did the person
live?
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Calculate Age
Calculation of Age The carbon-14 has decreased
by 1/8 which is three half lives (1/2 times 1/2
times 1/2 1/8) Carbon-14 half life 5730
years 3 times 5730 17,190 years
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Present
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One Half-Life 5730 years ago
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Two Half-Lives 11,460 years ago
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Three Half-Lives 17,190 years ago