Post on 18-Jan-2018
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Unit: Nuclear Chemistry
Fission, Fusion, and Applications of Nuclear Chemistry
Day 4 –
Notes
After today you will be able to…
• Describe what happens in a nuclear chain reaction.• Differentiate between fission
and fusion reactions.• Identify examples of how
radioisotopes are used in everyday life.
Recall, during transmutations an atom can be converted into a different atom through radioactive decay or by bombarding a nucleus with particles.Today, we will focus on the
latter by learning about fission and fusion.
Nuclear FissionFission: occurs when a nucleus is split into smaller pieces.• This process begins by colliding a
nucleus with particles such as neutrons.
• The resulting nucleus is highly unstable and decays.
• This causes a chain reaction where particles emitted from the initial reaction bombard other nuclei, causing them to break apart.
Example: Uranium-235
ENERGY
n10 U235
92
U23692
n10
n10
n10
Kr9136
Ba14256
A neutron collides with the U-235 atom.
The U-236 atom is unstable and decays.
U-236 is formed.
The neutrons released from the decay of U-236 will collide with
other U-235 atoms,
repeating this process all over again (chain
reaction).
Nuclear Fission• Uranium-235 and
Plutonium-239 are the only fissionable isotopes.
• These reactions release a large amount of energy.
Nuclear FusionFusion: occurs when nuclei combine (or fuse together) to produce a new nucleus of greater mass.• Example: Production of
energy from the sune0
+1H11 H
e42 energ
y++4 2
Nuclear Fusion• Releases far more
energy than fission reactions.
• These reactions require very high temperatures in order to occur (~40,000,000°C).
Real-World Applications: C-14 Dating
Scientists often find the age of an object that was once living by measuring the amount of carbon-14 it contains.• Recall, C-14 has a half-life of
5730 years.• This is its nuclear decay:
C146 N14
7 e0-1+
Real-World Applications: C-14 Dating
• All living things contain C-12 and C-14 in a fixed ratio.
• Once an organism dies, the ratio of C-14:C-12 changes, which allows archeologists to estimate its age.
Real-World Applications: C-14 Dating
• The most accurate way to examine the C-14 content is through use of a mass spectrometer.
• First, the carbon in the sample must be converted into graphite or carbon dioxide.―This is can be done by burning a
portion of the sample.
Real-World Applications: C-14 Dating
• The sample is then injected into a mass spectrometer and ionized.
• Due to the different masses of carbon having different angles of deflection, a scientist can count the individual C-14 atoms in the sample.
Mass Spectrometer:
Real-World Applications: U-238
But what if all of the C-14 in a sample has decayed or the sample is non-living?• Similar to carbon-14, uranium-
238 is used to date specimens.• Uranium is naturally found in
most rocks, seawater, and in Earth’s crust.
• It has a half-life of 4.5 billion years.
• U-238 is specifically used in dating rocks and fossils.
Real-World Applications: I-131
Radioisotopes can be used to diagnose medical problems or treat diseases.• Specifically, iodine-
131 is a radioisotope given to patients to check for abnormal thyroid function.
• Patients are given a drink containing the radioisotope (Na131I).
Real-World Applications: I-131
• Since the thyroid extracts iodide ions from the bloodstream, the ions are absorbed and its radioactivity is used to create an image on a screen.
• From the image, doctors can examine the amount of iodine absorbed and determine if a person has hyperthyroidism or thyroiditis.
Real-World Applications: Co-60
The strong penetrating power of gamma rays allows it to be useful in the treatment of cancer.• Cobalt-60, which is
produced in particle accelerators, emits both beta and gamma radiation.
Real-World Applications: Co-60
• The Co-60 is placed into a gun that is used to direct the radiation to where the tumor is located.
• The cells of the tumor are destroyed and it decreases in size.
• However, gamma radiation can also destroy healthy cells making those treated very ill.
Questions?Begin
WS4