GEOLOGY 103 LAB THREE YOUR NAME____________________________ SECTION______
Radioactivity & Radiation – Geology 103 Lab Three
Pre-lab activity
This pre-lab activity is to be completed PRIOR to coming to lab. Please submit your answers to
your TA at the beginning of lab and be prepared to take a Quiz. The daily Quiz will focus on the
Pre-lab activity plus the content of this lab.
1. (4 pts) List the three types of natural radiation with a brief description of their characteristics.
2. (4 pts) What can happen when radiation penetrates living cell?
3. (4 pts) List the symptoms of radiation disease.
4. (4pts) Why is radiation commonly used to treat cancer?
5. (4 pts) The half-life of an isotope is defined as?
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GEOLOGY 103 LAB THREE YOUR NAME____________________________ SECTION______
Radioactivity & Radiation – Geology 103 Lab Three
Radiation in the Environment
Radiation from nuclear reactions is a major environmental issue. On the one hand, nuclear
reactions can be used to generate electricity without many of the environmental impacts of fossils
fuels. For example, modern nuclear power facilities produce far fewer greenhouse gas emissions
and much less air pollution in general.
On the other hand, radioactive waste is an inevitable byproduct of nuclear reactions and this
waste can be among the most toxic materials produced by humans. Nuclear radiation, in high
doses, is lethal to all living organisms. Furthermore, radioactive waste can be extremely
persistent, and can be harmful for many thousands of years.
What is Radioactivity?
Radioactivity is a process in which unstable atomic nuclei release subatomic particles. Radiation
refers to the subatomic particles (and energy) that are released. The phenomenon of radioactivity
is observed in heavy elements such as uranium. It was Henri Becquerel, a French scientist, who
observed the blackening of a photographic plate due to uranium salts when placed in the dark.
Radioactive elements such as uranium, potassium and thorium have isotopes (such as U-235)
that decay to form lighter atoms. The energy they release during this decay process is in the form
of fast moving particles and high-energy waves.
There are three types of natural radiation: the alpha, beta and the gamma radiations:
Alpha particles consist of a stream of positively charged particles, which are actually the helium
nuclei.
Beta particles which are emitted electrons.
Gamma rays are energy packets (photons) that carry high energies. The emission of
gamma rays often accompanies alpha and beta radiations.
All three of these types of radioactivity are harmful to living organisms. Radiation disease
occurs when people are exposed to any (or all) of these emissions: these tiny subatomic
particles and bursts of energy penetrate living cells and destroy DNA, organelles, and generally
disrupt the ability of human cells to function properly.
Symptoms of radiation disease include: hair loss, vomiting, disrupted immune system, and many
forms of cancer (caused by disruption of the cells’ ability to regulate growth). Exposure to very
high levels of radiation can cause radiation burns.
Discussion question: Why is radiation often used to treat cancer?
Discussion question: Which of the 3 types of radiation consist only of energy?
Discussion question: Which of the 3 types of radiation do you think is hardest to protect
yourself from?
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GEOLOGY LAB 3
YOUR NAME ___________________________________ SECTION __________
Exercise: Measuring Radiation
The level of radiation in the samples used in this lab is extremely
low and does not present a health problem.
Break up into groups of 2-4 students and obtain a radiation meter from your TA. Be careful
with this device!!! It is very costly. Your radiation meter has a Geiger-Mueller (G-M) tube
that makes a “click” each time the tube is struck by a beta particle or gamma ray.
Procedure:
1) Obtain a small metal can of radioactive material from your TA. This canister has
uranium ore that contains naturally occurring isotopes of uranium. To make uranium “fuel” for
weapons and power plants, the uranium needs to be extracted and “enriched”
(concentrated).
2) KEEP your radioactive ore INSIDE the metal container. TOUCH your radiation meter to
the BOTTOM of the metal container. Be sure and touch the part of the meter with the long
metal tube to the bottom of the container.
3) HOLD down the button on your meter (the meter only works when the button is
pressed.) Move the meter around the bottom of the container until you hear the maximum
number of “clicks”.
4) Count and record the number of “clicks” that you hear during a 60-second time
interval. Repeat this for a total of THREE 60-second intervals and calculate the AVERAGE
number of counts per minute (CPM) for the two intervals.
4) Move your radiation meter exactly 2 cm away from the rock and again calculate the
average counts per minute (CPM) for three 60-second intervals.
5) Continue moving your meter away from the rock and continue to calculate the
average CPM at distances of: 4 cm, 6 cm, 8 cm and 10 cm away from the rock for
three 60-second intervals.
Record your results:
Count 1
Count 2
Count 3
0 cm
2 cm
4 cm
6 cm
8 cm
10 cm
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Average Count
GEOLOGY LAB 3
YOUR NAME ___________________________________ SECTION __________
Graph your results
(4 pts) On the graph below, make a plot of CPM versus distance for your data:
CPM
Distance from sample
Questions:
1. (8 pts) What is the general pattern that best describes the change in CPM with distance: no
change, linear decline, exponential decline, or some other pattern?
2. (8 pts) What do you suppose accounts for this pattern? Explain.
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GEOLOGY LAB 3
YOUR NAME ___________________________________ SECTION __________
Exercise: Effects of Materials on Radiation
Test the effects of various materials on blocking radiation. These materials include: paper,
aluminum foil, plastic wrap, cardboard and any other materials provided by the TA.
Procedure:
1) As above, you will touch the tube on the meter to the bottom of the metal container
EXCEPT this time you will place the material being tested (such as a piece of paper)
BETWEEN the meter and radiation. Your goal is to see if any of these materials actually
BLOCKS the radiation.
2) For each material being tested, you should count and record the number of “clicks”
that you hear during a 60-second time interval. Repeat this for a total of TWO 60-second
intervals and calculate the AVERAGE number of counts per minute (CPM).
Record your results:
Count 1
Count 2
Average Count
Paper
Aluminum foil
Cardboard
Glass
Plastic wrap
Wood
Questions to answer:
1. (8 pts) Which material is the best at blocking radiation? (What percentage of radiation is
blocked?)
2. (8 pts) Which material is the worst at blocking radiation? (What percentage of radiation is
blocked?)
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GEOLOGY LAB 3
YOUR NAME ___________________________________ SECTION __________
How effective is the metal container?
1. Remove the radioactive ore from the metal container and touch the rock directly to your
radiation meter (move around to get the max clicks).
2. Count the average CPM for two 60-second intervals and compare it to your measurements
when the rock was IN the container.
Count 1 =
Count 2 =
3. (8 pts) What percentage of the radiation is being blocked by the metal container? (SHOW
WORK below)
Exercise: Radioactive Half-life
The half-life of an isotope is the time it takes for half of the radioactive atoms to decay.
Questions to answer:
1. (8 pts) Look at the graph below. What is the half-life of this isotope? ___________________
2. (8 pts) What percent of this isotope will be present after 12 hours? ___________________
3. (8 pts) How many half-lives is 12 hours? _______________________
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GEOLOGY LAB 3
YOUR NAME ___________________________________ SECTION __________
4) (8 pts) It takes about 10 half-lives for an isotope to be “harmless” to humans. How long
until this isotope becomes “harmless”? _______________________
Uranium-238 and Plutonium-239
Isotopes vary greatly in their half-life. Iodine-131, an isotope with important medical
applications, has a half-life of 8.04 days. But uranium-238 has a half-life of about 4.5 billion
years!
Questions to answer (show work!):
1. (8 pts) The Earth is approximately 4.6 billion years old. What percentage of the original u-238
has decayed?
2. (8 pts) Plutonium-239 is commonly used in nuclear reactors. It has a half-life of about
24,000 years. What percentage of this material will decay in 1000 years?
3. (8 pts) How many years will pass until Plutonium-239 reactor fuel becomes “harmless”?
If you worked with a partner or as part of a group, please list their names:
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