Nucleus, Radioactivity,

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Nucleus, Radioactivity, Nuclear Medicine

• Dr. Michael P. Gillespie

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(No Transcript)
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Radioactive
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Natural Radioactivity

• Radioactivity is the process by which some atoms
  emit energy and particles.
• The energy and particles are termed radiation.
• Radioactivity is a nuclear event matter and
  energy released during this process come from the
  nucleus.

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Radioactive Atim
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Types of Radiation

• Three types of radiation are emitted by unstable
  nuclei
• Alpha particles
• Beta particles
• Gamma rays

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Alpha Particles a

• Alpha particles consists of 2 protons and 2
  neutrons.
• They have no electrons and therefore have a 2
  charge.
• They have a relatively large mass and are slow
  moving. Traveling at approximately 5-10 the
  speed of light.
• They can be stopped by barriers as thin as a few
  pages of paper.

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Alpha Particle Decay
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Beta Particles ß

• A beta particle is a fast moving electron.
  Traveling at approximately 90 the speed of
  light.
• It is formed in the nucleus by the conversion of
  a neutron into a proton.
• They are more penetrating and are stopped only by
  more dense materials such as wood, metal, or
  several layers of clothing.

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Beta Particle Decay
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Gamma Rays ?

• Gamma rays are the most energetic part of the
  electromagnetic spectrum and result from nuclear
  processes.
• Electromagnetic radiation has no protons,
  neutrons, or electrons. Unlike alpha and beta
  particles, gamma rays have no matter.
• Gamma radiation is highly energetic and the most
  penetrating form of nuclear radiation.
• Barriers of lead, concrete, or a combination of
  the two are required to stop gamma rays.
• Travels at the speed of light.

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Gamma Particle Decay
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Penetration
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Radioactive Decay
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Properties of Alpha, Beta, and Gamma Radiation
Name and Symbol Identity Charge Mass (amu) Velocity Penetration
Alpha a Helium nucleus 2 4.0026 5-10 speed of light Low
Beta ß Electron -1 0.000549 90 speed of light Medium
Gamma ? Radiant Energy 0 0 Speed of light High
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Nuclear Structure and Stability

• A measure of nuclear stability is the binding
  energy of the nucleus. The binding energy is the
  amount of energy required to break a nucleus up
  into its component protons and neutrons.
• The binding energy must be very large to overcome
  the extreme repulsive forces of the positive
  protons for one another.

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Half-Life

• The half-life is the time required for one-half
  of a given quantity of a substance to undergo
  change.
• Each isotope has its own characteristic
  half-life.
• The half-life can be as short as a few millionths
  of a second or as long as billions of years.

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Nuclear Energy Production
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Nucular

• George W. Bush would mispronounce the word
  nuclear as Nucular

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Nuclear Energy Production

• Einstein predicted that when the nucleus breaks
  apart, the small amount of nuclear mass produces
  a tremendous amount of energy.
• The heat energy released converts water into
  steam.
• The steam turns a turbine, which drives an
  electrical generator, producing electricity.

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Nuclear Fission

• Fission (splitting) occurs when a heavy nuclear
  particle is split into smaller nuclei by a
  smaller nuclear particle (such as a neutron).
• The splitting of the nuclear particle releases a
  tremendous amount of energy.
• The fission reaction, once initiated, is
  self-perpetuating.
• The fission process continues and intensifies.
  The process of intensification is referred to as
  a chain reaction.

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Energy Transformation in a Fission Reaction

• Nucear energy ? heat energy ? mechanical energy
  ? electrical energy

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Fission Chain Reaction
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Nuclear Fission
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Nuclear Fission
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Nuclear Fusion

• Fusion (joining together) results from the
  combination of two small nuclei to forma larger
  nucleus with the concurrent release of large
  amounts of energy.
• The Sun is a great example of a fusion reactor.
• In fusion, two isotopes of hydrogen (deuterium
  and tritium) combine to produce helium, a
  neutron, and energy.

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Nuclear Fusion
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Nuclear Fusion
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Nuclear Fusion
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Nuclear Fusion
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Nuclear Fusion
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Nuclear Fusion

• No commercially successful fusion plant exists
  because of the containment issues.
• The fusion reaction results in temperatures in
  the millions of degrees and extremely high
  pressures. These conditions are necessary to
  sustain the fusion reaction.

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Breeder Reactors

• A breeder reactor is a variation of a fission
  reactor that literally manufactures its own fuel
  from abundant starting materials.
• Breeder reactors cost a tremendous amount, have
  considerable potential to damage the environment,
  and create a lot of plutonium which can be used
  for nuclear bombs.

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Breeder Reactors
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Nuclear Waste Disposal

• Solid waste is difficult enough to dispose of,
  but nuclear waste poses even more of a challenge.
• We cannot alter the rate at which nuclear waste
  decays. This is determined by the half-life.
  Plutonium has a half-life greater than 24,000
  years and it takes ten half-lives for radiation
  to reach background levels.

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Nuclear Waste Disposal

• Where can we store hazardous, radioactive
  material for a quarter of a million years?
• Burial in a stable bed-rock formation seems like
  the best option right now, but an earthquake
  could release this.

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Nuclear Waste Disposal
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Nuclear Waste Disposal
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Radiocarbon Dating

• Natural radioactivity can be utilized to
  establish the approximate age of archaeological,
  anthropological, or historical objects.
• Radiocarbon dating measures isotopic ratios of
  carbon to estimate the age of objects.
• Carbon-14 is formed in the upper atmosphere.

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Carbon-14 Enters The Food Chain
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Radiocarbon Dating

• Carbon-14 (radioactive) and carbon-12 (more
  abundant) are converted into living plant
  material through photosynthesis.
• The carbon-14 works its way into the food chain.

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Radiocarbon Dating

• When a plant or animal dies, the carbon-14 slowly
  decreases because it is radioactive and decays to
  produce nitrogen.
• When an artifact is found, the relative amounts
  of carbon-14 to carbon-12 are used to approximate
  its age.
• Carbon-14 dating technique is limited to objects
  that are less than 50,000 years old.

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Carbon Dating
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Isotopes Useful In Radioactive Dating
Isotope Half-Life (years) Upper Limit (years) Dating Applications
Carbon-14 5730 5X104 Charcoal, organic material, artwork
Tritium 12.3 1X102 Aged wines, artwork
Potassium-40 1.3X109 Age of earth (4x109) Rocks, planetary materials
Rhenium-187 4.3x1010 Age of earth (4x109) Meteorites
Uranium-238 4.5x109 Age of earth (4x109) Rocks, earths crust
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Cancer Therapy Using Radiation

• When high energy radiation, such as gamma
  radiation, passes through a cell, it may collide
  with one of the molecules in the cell and cause
  it to lose one or more electrons. This leads to
  the production of ion pairs. Consequently, this
  form of radiation is referred to as ionizing
  radiation.

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Cancer Therapy Using Radiation

• This ions are highly energetic, can damage
  biological molecules, produce free radicals, and
  damage DNA.
• This alters cell function and can even lead to
  cell death.

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Cancer Therapy Using Radiation

• An organ that is cancerous has both healthy cells
  and malignant cells.
• The tumor cells are undergoing cell division more
  rapidly and are therefore more susceptible to
  gamma radiation.

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Cancer Therapy Using Radiation

• Carefully targeted high doses of gamma radiation
  will kill more abnormal cells than normal cells.
• This can destroy the tumor and allow the organ to
  survive.
• The gamma radiation can also cause cancer in the
  healthy cells.

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Nuclear Medicine

• Medical tracers are small amounts of radioactive
  substances used as probes to study internal
  organs.
• Medical techniques that utilize tracers are
  referred to as nuclear imaging procedures.

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Nuclear Medicine

• Certain radioactive isotopes are attracted to
  particular organs.
• The radioactivity emitted allows us to track the
  path of the tracer and obtain a picture of the
  organ of interest.

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Magnetic Resonance Imaging (MRI)

• MRI is a noninvasive technique used to study the
  body.
• It uses no radioactive substances. It is quick,
  safe, and painless.

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Magnetic Resonance Imaging (MRI)

• The patient is placed in a cavity surrounded by a
  magnetic field.
• An image (based on the extent of radio frequency
  energy absorption) is generated, stored, and
  sorted on a computer.

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Magnetic Resonance Imaging (MRI)
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Biological Effects of Radiation

• Radiation affects biological tissues.
• We must use suitable precautions when working
  with radiation.
• Tolerable levels have been established for
  radiation exposure.

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Radiation Exposure and Safety

• Factors to consider when working with radioactive
  materials
• The magnitude of the Half-life
• Shielding
• Distance from the radioactive source
• Time of exposure
• Types of radiation emitted
• Waste disposal

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Magnitude of the Half-life

• Short half-life radioisotopes produce a larger
  amount of radioactivity per unit of time than
  larger half-life substances.
• Shorter half-life materials can be safer to work
  with, especially if an accident occurs.

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Magnitude of the Half-life

• Radioactive isotopes will eventually decay into
  background radiation. This will happen faster
  with a shorter half-life.
• Higher levels of exposure in a short time produce
  a clearer image.

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Shielding

• Alpha and beta particles are low in penetrating
  power and therefore require low levels of
  shielding. A lab coat and gloves are usually
  sufficient.
• Gamma rays have significant penetrating power.
  Lead, concrete, or both are required for
  shielding from gamma rays.
• X-rays are also very high energy and require lead
  and concrete shielding.

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Distance from the Radioactive Source

• Radiation intensity varies inversely with the
  square of the distance from the source.
• Doubling the distance from the source decreases
  the intensity by a factor of four.
• Robot manipulators can allow us to get a greater
  distance between the operator and the radioactive
  source.

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Distance from the Radioactive Source
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Time of Exposure

• The effects of radiation are cumulative.
• Potential damage is directly proportional to time
  of exposure.

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Types of Radiation Emitted

• Alpha and beta emitters are generally less
  hazardous than gamma rays due to differences in
  energy and penetrating power that require less
  shielding.
• Ingestion or inhalation of an alpha or beta
  emitter can cause serious damage over time.

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Waste Disposal

• Radioactive waste is created from nuclear
  medicine applications, nuclear power, etc.
• Safe handling and disposal of this waste is a
  serious problem.
• Temporary solutions are being used, but it is
  necessary to find more suitable long-term storage
  solutions.

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Waste Disposal
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Waste Disposal
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Measurement of Radiation

• Radiation is detected using either photographic
  film to create an image of the location of the
  radioactive substance or using a counter that
  measures the intensity of the radiation emitted
  from a source.

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Nuclear Imaging

• Used in nuclear medicine.
• A radioactive isotope is administered to a
  patient and it concentrates on the organ of
  interest.

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Nuclear Imaging

• Nuclear images are taken at various intervals
  using a film that is sensitive to the radiation
  being emitted.
• This creates an image on the film showing the
  organs uptake of the isotope over time.

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Computer Imaging

• Specialized television cameras that are sensitive
  to the radiation emitted from a radioactive
  substance are used.
• A CT scanner records the interaction of x-rays
  with biological tissue.

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Geiger Counter

• A Geiger counter is an instrument that detects
  ionizing radiation.
• The ionizing radiation produces a current flow in
  a tube filled with ionizable gas.
• The current flow is proportionate to the level of
  ionizing radiation.

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Geiger Counter
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Film Badges
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Units of Radiation

• Intensity of the emitted radiation
• Curie measures the amount of radioactivity.
  Independent of the nature of radiation and its
  effect upon biological tissue.
• Roentgen measures very high energy ionizing
  radiation (x-ray and gamma).

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Units of Radiation

• Biological effects of the emitted radiation
• Rad Radiation absorbed dosage measures the
  transfer of energy to matter due to radiation.
• Rem Roentgen equivalent for man describes the
  biological damage caused by the absorption of
  different kinds of radiation.

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Radioactive Waste