Atom’s Nucleus and Radioactivity
08 October 2015
Background
 Radioactivity and natural background
exposure
 Principles of radioactivity and human health
 Application of the principles of radioactivity

Isotopes

Atoms have specific number of protons, neutrons and
electrons
8
16

O
Oxygen-16
(breath deep …)
If the number of protons is unchanged but the number
of neutrons goes up or down, what happens to the
chemical properties of that element (i.e., Periodic Table)?
8
17
O
Oxygen-17
(breath deep …)
Isotopes … A Bit More


Atoms of an element with same number of
protons but different number of neutrons are
isotopes
Conventional notation (Element - Mass)
Oxygen -17 or Oxygen -16
 Carbon -12 or Carbon -13
 Iodine -131
 Cesium -135
 Plutonium -237
 Uranium -235

Example: Isotopes of Hydrogen
Hydrogen
Deuterium
Tritium
1 H
1
1 H
2
1 H
3
Stable
Stable
Unstable
Proton
Neutron
What is a stable versus an unstable isotope?
Stable Versus Unstable Isotopes

Stable over time
Oxygen-16
 Carbon -12
 Carbon -13


Unstable: “atom changes” by releasing mass
and/or energy (i.e., radioactive)
Carbon -14 (radioactive carbon)
 Hydrogen-3 (radioactive hydrogen/tritium)

Radioactive Emissions of the
Nucleus



Alpha (a): 2 protons + 2 neutrons (same as the
helium atom)
Beta (b): high energy electron
Gamma (g): electromagnetic radiation with very
short wavelengths (not visible to eye)
Natural or Background Radioactivity

Sources

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Cosmic rays from outer space
Soils
Water
Building materials
(rock)


Nuclear sources
Examples


Annual Mean Exposure (OSU)
Radon gas (Radon-222) - soils
Beryllium (Beryllium-7) - atmosphere
Example: Radon Exposure in
the Home




Radon gas (Radon-222)
Radioactive gas
Human health effects - lungs
Human health exposure



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Homes
At-risk groups: smokers
Risk mitigation - venting of
basements
Geologically based radioactivity:
100% natural
The Essence of Being Unstable:
Radioactive Decay




Uranium-238
92 protons + 146 neutrons (contrast with other
atoms)
Spontaneous release of an alpha (a) particle (2
protons + 2 neutrons): atom with 90 protons
and mass of 234, which is ____?
All isotopes of all elements with > 83 protons
(Bismuth) are unstable and radioactively decay
Rate of decay: unaffected by the environment
Periodic Table
Types of Decay and Human Health

Alpha (a)
Two protons + two neutrons
 Travel distance: stopped by sheet of paper (even air)


Beta (b)
high energy electron
 Travel distance: ~10 meters; stopped by 1 cm
aluminum block


Gamma (g)
high energy radiation
 Travel distance: 100’s meters; stopped by 5 cm lead
brick

Penetration of Different Types of
Ionizing Radiation
Alpha Particles
Stopped by a sheet of paper
Radiation
Source
Beta Particles
Stopped by a layer of clothing
or less than an inch of a substance
(e.g. plastic)
Gamma Rays
Stopped by inches to feet of concrete
or less than an inch of lead
Radioactivity: Human Health

Radioactivity in biological tissues results in
atoms being ionized




Disrupts chemical bonds
DNA as primary site of action (e.g., mutations)
Disrupts biochemistry
Sensitivity greatest for actively growing cells




Blood (Strontium-90)
Bone marrow (Cesium-137)
Thyroid (Iodine-131)
Muscle (Pu-239)
Periodic Table
Radioactivity: Principles and
Applications


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

Background
Radioactivity is natural
Quantitative analysis of radioactivity
Principles of radioactivity and human health
Application of the principles of radioactivity
Radioactive Decay



Rate of decay to a stable state (no more
spontaneous decay): specific for each isotope
Rate: unique terminology = “half-life”
Time for ½ (50%) of atomic nuclei to decay to
the stable state (abbreviated t1/2)
Range: fractions of second to billions of years
(isotope specific)
 Unaffected by the environment (e.g., moisture, light,
pressure, etc.)


Example: M&M’s
Radioactive Decay
Application of Atomic Principles of
Radioactivity

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Medical science
Nuclear energy
Chernobyl Russia
Fukishima Japan
Dirty bomb
Medical Science: Nuclear
Applications

Nuclear imaging and radio-pharmaceuticals
Injection of radioactive element
 Allow for distribution in body
 Imagine body for presence or absence of radioactive
element
 Function: assessment of functional and dysfunctional
tissues (e.g., thyroid, kidneys, heart)


Examples
Iodine-131 (thyroid)
 Thallium-201 (kidney)

Nuclear Reactor: Power Generation
(read section in text)
Fuel rods
Moderators
Coolants
Steam turbines
Cooling towers
Nuclear waste storage
Comparison with fossil
fuel power generation
Chernobyl Reactor and
Sarcophagus - April 1986



Complete core meltdown
Sarcophagus - risk containment
Human health (~4,000 death)
 Acute radiation poisoning – on
site workers
 Chronic exposure - residents



Iodine -131
Thyroid cancer and leukemia
No detectable effects > 100 miles
Fukushima Daiichi Nuclear Power
Plant Accident - March 2011
Atom’s Nucleus and Radioactivity
08 October 2015
Background
 Radioactivity and natural background
exposure
 Principles of radioactivity and human health
 Application of the principles of radioactivity
