Radioactivity: Principles and Applications (14 October)

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Radioactivity Principles and Applications (14
October)

• Background
• Radioactivity is natural
• Quantitative analysis of radioactivity
• Principles of radioactivity and human health
• Application of the principles of radioactivity

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Take Home Message

• Radioactivity is a natural process
• Radioactivity is due to the instability of atoms,
  resulting in the spontaneous emission of
  subatomic particles and/or energy
• Radioactivity has unique features including
  isotopes and radioactive decay
• Human health issues of radioactivity are based on
  the ability of emissions to affect a cells
  biochemistry and metabolism
• Radioactivity has been harnessed to provide a
  host of applications to enhance the quality of
  life
• Radioactivity also has its liabilities associated
  with waste disposal and misuse

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Radioactivity Principles and Applications

• Background
• Isotopes
• Stable
• Unstable radioactive
• Radioactivity is natural
• Quantitative analysis of radioactivity
• Principles of human radioactivity
• Application of the atomic principles of
  radioactivity

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Isotopes

• Atoms have specific number of protons, neutrons
  and electrons
• 8
• O
• 16
• If the number of protons is unchanged but the
  number of neutrons goes up or down, what happens
  to the properties of that element?
• 8
• O
• 17

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Isotopes Continued

• Atoms of an element with same number of protons
  but different number of neutrons are isotopes
• Key is the number of neutrons
• Conventional notation ( AZX)
• Not all elements have isotopes, but many do
• Hydrogen (common isotope 11H 31 H or tritium)
• Nitrogen (common isotope 714N 157N)
• Oxygen (common isotope 816O 188O)
• Sulfur (common isotope 1632S 3316S

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Isotopes of Hydrogen
Hydrogen 11H Stable
Deuterium 21H Stable
Tritium 31H Unstable
Proton
Neutron
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Stable versus Unstable Isotopes

• Stable over time
• Unstable transmutate by releasing mass and/or
  energy

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Radioactivity Principles and Applications

• Background
• Radioactivity is natural
• Quantitative analysis of radioactivity
• Principles of human radioactivity
• Application of the principles of radioactivity

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Discovery of Radioactivity

• Rutherford (as in the nucleus) and three forms of
  transmutated activity (radioactivity)
• Alpha (a) nucleus of the helium atom (42He)
• Beta (b) high energy electron
• Gamma (g) electromagnetic radiation with very
  short wavelengths

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Principal Early Observations

• Atom exhibits spontaneous release of
• mass (a or b)
• energy (g)
• Nucleus changes identity simpler atomic
  structure
• 100 natural process
• Spontaneous release of mass or energy is called
  radioactive decay

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Radioactivity Principles and Applications

• Background
• Radioactivity is natural
• Quantitative analysis of radioactivity
• Principles of human radioactivity
• Application of the principles of radioactivity

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Natural/Background Radioactivity

• Sources
• Cosmic rays from outer space
• Soils
• Water
• Building materials
• Nuclear sources
• Examples
• Radon gas (Ra)

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Radioactive Decay

• Uranium 238
• 23892U (92 protons 238-92 (146) neutrons
• Spontaneous release of an alpha (a) subatomic
  particle (helium nucleus or 42He) results in an
  atom with 90 protons and mass of 234
• 23490? or _____ (periodic table)
• All isotopes of all elements with gt 83 protons
  (Bismuth) are unstable and radioactively decay

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Types of Decay

• Alpha (a)
• Release of 42He
• Travel distance easily stopped by sheet of paper
  (even air)
• Eventually acquires electrons to yield normal He
  atom
• Beta (b)
• Release of high energy electron
• Travel distance 10 meters 1 cm aluminum block
• Eventually finds an atom needing an electron
• Gamma (g)
• Release of high energy electron
• Travel distance 100s meters 5 cm block lead
  brick
• Eventually energy is absorbed by material

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Penetration of Radiation
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Radioactive Decay
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Radioactive Decay

• Rate of decay to a stable state (no more
  spontaneous decay) is specific for each isotope
• Rate has unique terminology called half-life
• Time for ½ (50) of the nuclei to decay to the
  stable state is abbreviated t1/2
• Example MMs

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Radioactive Decay
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Measurement of Radiation

• Number of nuclear disintegrations per unit of
  time called a curi (Ci) 3.70 x 1010 nuclear
  disintegrations second-1
• Radiation at the site of absorption (living
  tissues)
• Radiological dose in units called rem
• Natural dose 0.001 rem (1 millirem)/day
• Lethal dose 500 rem

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Radioactivity Principles and Applications

• Background
• Radioactivity is natural
• Quantitative analysis of radioactivity
• Principles of radioactivity and human health
• Application of the principles of radioactivity

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Radioactivity Human Health

• Radioactivity in biological tissues results in
  atoms being ionized
• Disrupts bonds
• DNA as primary site of action
• Fragments molecules and disrupts biochemistry
• Sensitivity is greatest for actively growing
  cells and tissues
• Blood
• Bone marrow (Cesium-137)
• Thyroid (I-131)

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Radioactivity Principles and Applications

• Background
• Radioactivity is natural
• Quantitative analysis of radioactivity
• Principles of radioactivity and human health
• Application of the principles of radioactivity

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Application of Atomic Principles of Radioactivity

• Radiation medicine and radiopharmaceuticals
• Nuclear energy
• Yucca Mountain, Nevada
• Three Mile Island
• Chernobyl
• Dirty bomb

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Chernobyl Reactor
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Chernobyl
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Yucca Mountain Waste Repository
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A high speed electron emitted from a nucleus
during radioactive decay is called a (an) _____.

1. Alpha
2. Beta
3. Gamma
4. All of the above

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A sheet of paper will stop a (an) ____.

1. Alpha
2. Beta
3. Gamma
4. All of the above

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Rate of radioactive decay is affected by changes
in ______.

1. Temperature
2. Pressure
3. Sample size
4. Other radioactive materials nearby
5. None of the above

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What is meant by background radiation? Is the
dose of background radiation equivalent over the
Earths surface?For you as an individual, what
are the most common sources of natural/background
radiation?
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Why measure the duration of radioactivity in
units of half life (t1/2) versus lifetime?
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Beryllium-7 (74Be) is an unstable isotope of
Beryllium (94Be). When the atom transmutates,
the stable product that is formed is the element
Lithium (73Li).What was emitted in the process
of radioactive decay?Is 73Li stable or unstable?