Nuclear Processes

1
Nuclear Processes

• Fusion - put nuclei together. For elements BELOW
  iron, releases energy.
• Fission - break nuclei apart. For elements ABOVE
  iron, releases energy.

2
Warmup

• What is the atomic number of Oxygen?
• What element has 32 protons?

• 8
• Germanium

3
Power Generation

• Uranium fission - 108 J / kg. Leaves behind
  radioactive waste Currently known ore deposits
  could supply our energy needs for about 50 years.
• Hydrogen fusion - 1015 J / kg. Very little
  radioactive waste. Hydrogen can be produced from
  water, so the supply is practically limitless.
  Not yet feasible, but close.
• For comparison, oil produces about 105 J / kg,
  and will last, at most, another 100 years.

4
Radioactive Decay

• Radioisotope - an unstable isotope that will
  naturally decay, producing a new element and some
  radiation
• Half-life - the amount of time it takes for half
  of the atoms of a radioisotope to decay

5
Radioactive Decay example

• For example, Uranium-239 has a half-life of 23
  minutes, and decays into Neptunium - 239.

6
Practice

• Plutonium - 239 has a half life of about 20,000
  years. If you started with 2 kg of Pu-239, how
  long would you need to wait to have less than 0.5
  kg?

• 40,000 years!
• After 20,000 years, you would have 1 kg.
• After 40,000 years, you would have 0.5 kg.

7
Why Does Decay Happen?

• The answer is the fourth and final of the four
  fundamental forces of nature that we have been
  studying. It is called the Weak Force.
• The Weak Force causes particles to interact in
  the nucleus and transmutate (change into) a
  different kind of particle. Those particles are
  then emitted (shot out of) the nucleus of the
  atom at high speed. This turns the atom into a
  different kind of atom!

8
Radioactivity

• Radioactivity - the energetic particles emitted
  by elements when they decay. These particles can
  be dangerous to living things. They can harm
  genetic material and living tissue.
• Important Measure - how much energy received per
  kilogram of body mass. Unit is the sievert,
  which is 1 Joule / kg of body mass.

9
Types of Radioactivity

• Alpha - a nucleus emits a Helium nucleus (2
  protons and 2 neutrons). Not very penetrating.
• Beta - a neutron becomes a proton and emits an
  electron with lots of energy. So-so penetrating.
• Gamma - the nucleus changes shape and emits a
  very high energy photon of light. Very
  penetrating
• Which of these would change the element and the
  mass? Which of these would change the element
  but not the mass?

10
Practice

• Iodine is collected by the thyroid gland in the
  body. To study how well the thyroid is working,
  doctors inject a patient with radioactive iodine
  and watch for how quickly the radioactivity
  starts emitting from the thyroid. Which type of
  radioactivity do they use?

• Gamma, because it is most penetrating. More
  alpha and beta would be absorbed by the body.

11
Background Radiation

• In the US, the average person is exposed to about
  3.5 milliSieverts of radiation each year. 50
  milliSieverts per year is the legally allowed
  limit (past this, no more x-rays or working with
  radiation sources)
• Some surprising sources are radon gas that seeps
  up from the ground radioactive isotopes that are
  part of our food and thousands of particles that
  stream through our bodies each second, generated
  by cosmic rays hitting the upper atmosphere!

12
(No Transcript)
13
Practice

• Measurements have shown that living within 50
  miles of a nuclear power plant will increase your
  yearly radiation dosage by 90 nanoSievert
• Measurements have shown that living within 50
  miles of a coal burning power plant increases
  your yearly radiation dosage by 300 nanoSievert
• How could living near a coal plant increase your
  exposure by more than living near a nuclear power
  plant?!

14

• Nuclear power plants have many measures in place
  to block IN the radiation
• The radioactivity in coal comes from
  radioisotopes such as Carbon-14 that are
  naturally present in the coal.
• These radioisotopes are then present in the smoke
  that is released by the power plant.
• Exposure is also increased when you BREATHE the
  smoke - that allows the radiation direct access
  to unprotected tissues in your lungs!