Experiment 9-Nuclear Experiment
Radiation is everywhere. It’s in our food, in the air, the water and the soil. It’s even in
our bodies. It comes from naturally-occurring atoms that are unstable because they have extra
energy in their nuclei. Eventually, these unstable atoms “decay”, releasing the extra energy from
their nuclei, and become stable. The energy released is radiation. Our bodies absorb a small
amount of this radiation every day. Radiation can be found in: .
• 1950’s to 1960’s orange Fiestaware (cup, finger bowl, saucer, dinner plate) each piece will cost
about $20.00 and can be found in antique shops.
• Radium alarm clock or watch will each cost between $10.00 and $50.00 and can also be found
in antique shops.
• Common house hold smoke detector.
• Salt substitute can be found in grocery stores. (potassium iodide – KI)
• Vaseline Glass $10.00 and up can be found in antique shops
• Bricks within your house have naturally occurring radioactive elements within them.
• Bananas contain a high amount of potassium.
• Carbon-14 which is naturally occurring is within all living organisms.
• Radon gas which seeps into your basement is from the natural decay of Uranium. (Uranium
occurs naturally in soil around the world.)
The above list of experimental materials is but an example of what can be found emitting
radiation within our everyday environment and households. The Fiestaware listed above was
originally coated with a small amount of natural uranium to provide the orange color. The halflife of naturally occurring Uranium which is mostly comprised of U-238 (~99.3%)* is 4.47
billion years. Uranium decays by emitting an alpha particle. Half-life is discussed in better detail
in the penny experiment below. The Radium that is on old glow in the dark alarm clocks or
watches has a half-life of 1599 years (Ra-226) and emits an alpha particle. Many smoke
detectors have small source of Americium that has a half-life of 432.7 years (Am-241) and also
emits an alpha particle. The salt substitute, potassium iodine (KI), is also naturally radioactive
due to the small amount of Potassium-40 (0.0117%) which has a half-life of 1.27 billion years
(K-40) and emits a beta particle. Vaseline glass was popular from the 1830’s until the 1940’s,
contains natural Uranium, and has the same half-life and emits the same particle as Fiestaware.
An interesting side note to Vaseline glass is that if you place it in a dark space and put it under a
black light, it will glow. Cosmic radiation that reaches the earth’s surface from outer
space and is a major source of natural background radiation.
Experiment
Part A-Radioactive Sources
Materials: Geiger/Müller (GM) Counter, radioactive sources
Hypothesis: What is the radioactivity from various sources?
Procedure: Using the GM Counter, measure and record the radioactivity of the sources listed
on the Lab Report.
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Experiment 9-Nuclear Experiment
Part B-Chain Reaction
This fission process also produces two or three energetic neutrons, which have the ability to strike
other nuclei and cause subsequent fissions. If most of these neutrons are permitted to bombard additional
nuclei, a rapidly multiplying chain reaction would occur producing enormous energy in a fraction of a
second. This is the basic process involved in an atomic bomb.
The nuclear reactor in a nuclear power plant is designed and built with materials to prevent such
an uncontrolled reaction. The uranium fuel is arranged in modules, which are surrounded with water to
act as a moderator and coolant, and with control rods containing a neutron-absorbing material (“poison”).
When control rods are inserted, no neutrons are available for fission. As the rods are slowly withdrawn,
the reactor reaches criticality — the point at which each fission reaction leads to exactly one more fission
reaction and a steady-state chain reaction is maintained. The heat energy produced by fission is removed
by the coolant for use in electric power generation or propulsion.
Materials: 15+ Dominos per set of students
Hypothesis: How does a chain reaction occur in a bomb and reactor?
1. In the first trial, arrange the dominos in a phalanx as shown in the first
diagram to the right. They will be on end about 1/2 inch apart, positioned
so that each falling domino strikes two dominos in the next row. Push the
first domino to initiate a “bomb” chain reaction.
2. In the second trial, arrange the dominos in the in-line pattern of the
second diagram to the right. When the first domino is pushed to initiate
the “controlled” chain reaction, only one neutron from each fission is
permitted to continue to fall or advance to cause the next generation
fission. The second neutron falls away to simulate “capture” by control
rod poisons.
Part C-Half Life
Materials: 100 pennies in a box with a tight fitting lid
Hypothesis: Do things naturally decay by half lives?
Procedure:
1. Place the 100 pennies (or M&Ms ) all “heads up” in the box.
(Note: For the sake of realism, you might consider using forceps or tongs to handle the
“radioactive” objects in the box.)
2. Place the lid securely on the box.
3. Before proceeding, consider how many landing options a flipped penny has and predict how
many “heads” will remain after the box is thoroughly shaken.
4. Enter the starting number of pennies (100) in Time Period 0.
5. Make sure the lid is securely held closed and shake the box vigorously.
6. Set the box down, remove the lid, and carefully extract all “tails” counting them as they are
removed. Record the number of “heads” remaining in the box. This represents the first Period.
7. Close the lid securely and repeat the process recording remaining “heads” in each subsequent
Period.
8. Continue until only 1 or 2 pennies remain.
Experiment 9-Nuclear Experiment
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9. Plot the number of remaining “heads” for each Period, starting with 100 for Period 0. Use regular
linear graph paper, then plot the same data on a semi-log graph (if available). Plot number of
pennies on the y-axis.
10. Repeat the experiment or compare results with other teams. Average the results from multiple
experiments for each time period.
Procedure D-Distance Relationships
Materials: GM Counter, radioactive source, meter stick
Hypothesis: What happens to the radiation intensity as you move
away from the source?
Procedure:
1. Position the detector probe at one end of a meter stick as shown below. In order to give a nearly
full-scale reading on the instrument, place one of the sources 1 or 2 centimeters from the probe.
Record the reading in the data table.
2. Reposition the source in 1 or 2 centimeter increments farther from the probe and record the
instrument reading at each distance. Try to keep the center of the source aligned with the center of
the detector as the source is moved.
3. Plot the detector readings versus distance on a graph. Use appropriate units. (Note: Weak sources
or meters with low sensitivity may limit the effective distance at which a signal above
background radiation can be detected.)
Procedure E-Radioactive Safari
Materials: GM Counter
Hypothesis: What items around us are radioactive and how radioactive are they?
Procedure: The class will go out on safari around the campus and neighborhood and measure
the radioactivity of things the find on the way. Record the object, location and radioactivity on
the Lab Report.
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Experiment 9-Nuclear Experiment
Experiment 9-Nuclear Experiment
Experiment 9-Nuclear Experiment Lab Report
Name: ______________________________ Section: _______________Date: ______
Part A-Radioactive Sources
Source
Radioactivity(mrems)
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Part B-Chain Reaction
Questions
1. What determines the amount of energy released in the uncontrolled chain reaction of an atomic
bomb?
2. Why can’t the controlled reaction in a nuclear reactor produce the same kind of results as an
atomic bomb?
3. If more neutrons are “lost” from a chain reaction when the core expands from higher
temperatures, what would result from raising the control rods in an already critical reactor?
Conclusions:
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Experiment 9-Nuclear Experiment
Part C-Half Life
Questions
1. If each period represents a half-life, approximately what fraction of the previous number of “heads”
remain after each shaking?
2. What is the significance of removing all the “tails” after each period?
3. About how many half-lives would be required to have fewer than 5 “heads” remaining in the box.
4. Why do results from multiple experiments vary, particularly when the number of pennies remaining is
small?
Procedure D-Distance Relationships
Experiment 9-Nuclear Experiment
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Experiment 9-Nuclear Experiment
Procedure E-Radioactive Safari
Object
Location
Radioactivity(
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