Background Radiation

1
Background Radiation

• 3/4ths of all exposure to radiation comes from
  background radiation.
• Most of the remaining ¼ comes from medical
  irradiation such as X-rays.

2
Radiation and Cells

• Radiation is capable of removing electrons from
  cells, forming ions hence the term ionizing
  radiation.
• Molecules can also splinter into neutral
  fragments called free radicals. Free radicals
  can disrupt cellular processes.

3
Radiation and Cells

• Radiation often affects the fastest growing cells
  and tissues such as white blood cells and bone
  marrow.
• Ionizing radiation call also disrupt DNA, causing
  mutations.

4
Radiation Damage to Cells
5
Nuclear Equations

• In nuclear equations, we balance nucleons
  (protons and neutrons). The atomic number
  (number of protons) and the mass number (number
  of nucleons) are conserved during the reaction.

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Nuclear Equations

• Alpha Decay

7
Nuclear Equations

• Beta Decay

8
Nuclear Equations

• Beta Decay

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Nuclear Equations
10
Nuclear Equations

• Positron Emission A positron is a particle
  equal in mass to an electron but with opposite
  charge.

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Nuclear Equations

• Electron Capture A nucleus absorbs an electron
  from the inner shell.

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Nuclear Equations

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Nuclear Equations
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Nuclear Equations
15
Write balanced nuclear equations for each of the
following processes. In each case, indicate what
new element is formed. a. Plutonium-239
emits an alpha particle when it decays. b.
Protactinium-234 undergoes beta decay. c.
Carbon-11 emits a positron when it decays. d.
Carbon-11 undergoes electron capture.
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In the upper atmosphere, a nitrogen-14 nucleus
absorbs a neutron. A carbon-14 nucleus and
another particle are formed. What is the other
particle?
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Half-Life

• Half-life of a radioactive sample is the time
  required for ½ of the material to undergo
  radioactive decay.

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Half-Life
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Half-Life

• Fraction Remaining 1/2n

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Work examples from hand out
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Radioisotopic Dating
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Radioisotopic Dating

• Carbon-14 Dating The half-life of carbon-14 is
  5730 years. Carbon-14 is formed in the upper
  atmosphere by the bombardment of ordinary
  nitrogen atoms by neutrons from cosmic rays.

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Radioisotopic Dating

• Tritium Dating Tritium is a radioactive
  isotope of hydrogen. It has a half-life of 12.26
  years and can be used for dating objects up to
  100 years old.

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Artificial Transmutation

• Bombardment of stable nuclei with alpha
  particles, neutrons, or other sub-atomic
  particles cause new elements to form. This
  process is known as artificial transmutation.

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Uses of Radioisotopes

• Tracers Radioisotopes can be easily detected
  through their decay products. Therefore they can
  be used to trace their movement.
• Detect leaks in underground pipes.
• Determine frictional wear in piston rings.
• Determine uptake of phosphorus and its
  distribution in plants.

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Uses of Radioisotopes

• Irradiation of Food Radioisotopes can destroy
  microorganisms that cause food spoilage.

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Nuclear Medicine

• Radiation Therapy Nuclear radiation can be used
  to kill cancerous cells. Radiation is most
  lethal to fastest growing cells. Radiation is
  aimed at the cancerous tissue. Patients
  undergoing radiation therapy often experience
  nausea and vomiting, which are early signs of
  radiation sickness.

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Nuclear Medicine

• Diagnostic Uses of Radiation

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Nuclear Medicine

• Gamma Ray Imaging or Positron Technetium-99m
  emits gamma radiation. It can be used to image
  the heart and other organs and tissues.

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Nuclear Medicine

• Positron Emission Tomography (PET) A patient
  inhales or is injected with positron-emitting
  isotopes such as carbon-11 or oxygen-15. When
  positrons encounter electrons, they emit two
  gamma rays, which exit the body in opposite
  directions. PET scans can be used to image
  dynamic processes.

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Penetrating Power of Radiation

• Alpha radiation is least penetrating and can
  penetrate the outer layer of skin. Alpha
  radiation is stopped by a sheet of paper.
• Beta radiation can penetrate through a few cm of
  skin and tissue. Beta radiation is stopped by a
  sheet of aluminum foil.
• Gamma radiation will pass right through a body.
  Gamma radiation requires several cm of lead to
  stop.

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Penetrating Power of Radiation
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Penetrating Power of Radiation
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Penetrating Power of Radiation

• Two means of protecting oneself from radiation
  are distance and shielding.
• Distance Move away from the source. The
  intensity of radiation decreases with increasing
  distance from the source.
• Shielding Lead is a commonly used shield for
  radiation.

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Talk about Radon
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Energy from the Nucleus

• When protons and neutrons combine to form a
  nucleus, a small amount of mass is converted into
  energy. This is known as binding energy.

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The Building of the Bomb

• Nuclear Fission Fission occurs when larger
  nuclei split into small nuclei.

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Nuclear Chain Reaction

• Fission of one nucleus produces neutrons that
  can cause the fission of other nuclei, thus
  setting off a chain reaction.

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Manhattan Project

• The Manhattan Project was launched by President
  Roosevelt in 1939. It consisted of 4 separate
  research teams attempting to
• a. Sustain the nuclear fission reaction.
• b. Enrich uranium.
• c. Make fissionable plutonium-239.
• d. Construct a fission atomic bomb.

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Manhattan Project

• Replicas of Little Boy (dropped on Hiroshima)
  and Fat Man (dropped on Nagasaki).

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Manhattan Project

• Mushroom cloud over Nagasaki from the detonation
  of Fat Man, August 9, 1945.

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Radioactive Fallout

• Many radioactive isotopes are produced in a
  nuclear bomb blast. Some are particularly
  harmful to humans. Among these are strontium-90
  and iodine-131.
• Strontium-90 Half-life 28.5 years, chemically
  similar to calcium. Obtained from dairy and
  vegetable products and accumulates in bone.
• Iodine-131 Half-life 8 days. Concentrates
  in the thyroid glands.

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Nuclear Power Plants

• Civilian nuclear power plants use less enriched
  uranium (2.5-3.5 uranium-235 rather than 90 for
  weapons-grade).
• The nuclear chain reaction is controlled for the
  slow release of heat energy. The heat is used to
  make steam, which turns a turbine to produce
  electricity.

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The Nuclear Age