Time for Teacher Preparation:
30-60 minutes – To gather materials and set-up
Activity Time:
30-60 Minutes (1 Class Period)
Materials:
Pen, Marker, or Pencil
Plastic cloud chamber kit, 3 1/4″ diameter: (Petrie dish with band of black construction paper around the sides and bottom painted black or lined with black construction paper)
Students should use care when handling rubbing alcohol
Students should not touch dry ice with their bare hands
Students should not touch radioactive materials
Science and Engineering Practices (NGSS):
Ask questions and define problems
Use models
Plan and carry out investigation
Analyze and interpret data
Using mathematics, information and computers
Argue from Evidence
Obtain, evaluate and communicate information
Cross Cutting Concepts (NGSS):
Patterns
Cause and Effect
Scale, Proportion, and Quantity
Systems and System Models
Energy and Matter: Flows, Cycles, and Conservation
Structure and Function
Stability and Change of Systems
Objectives:
To visually demonstrate the concepts of ionizing radiation
Background:
Radioactive elements continually undergo a process of radioactive decay during which their nuclei emit high-speed particles and rays. These are much too small to be seen under a microscope. The Cloud Chamber was invented by an English physicist, C. T. R. Wilson, in 1911. It is an instrument designed for the study of the trails of radioactive emissions. The investigation is accomplished in the following way. First, the air must be saturated with water or alcohol vapor. When the high-energy particles flow through the air, electrons are knocked loose from some of the atoms and form ions. Ions act as excellent centers for condensation. This condensation, however, must be stimulated by cooling the air. The water vapor or alcohol condenses on the ions, leaving a vapor tail which clearly reveals the path of the ray.
Cloud chambers detect the paths taken by ionizing radiation. Much like the vapor trail of a jet airplane, the tracks in a cloud chamber mark where ionizing radiation has been traveling. The radiation itself is not visible. Radioactive materials are one source of ionizing radiation. Three types of rays are given off by a radioactive element. They are alpha particles (positive nuclei of helium atoms traveling at high speed), beta particles (high-speed, negative electrons), and gamma rays (electromagnetic waves similar to X-rays). Most of the tracks will be about one-half inch long and quite sharp. These are made by alpha radiation. Occasionally you will see some twisting, circling tracks that are so faint that they are difficult to see. These are caused by beta radiation.
Teacher Lesson Plan:
Traditional
Cloud Chambers:
Prepare three cloud chambers in accordance with the Cloud Chambers instructions:
Open the lid of the cloud chamber and saturate the felt strip inside with alcohol.
Put the radiation source inside the cloud chamber and replace the lid tightly.
Place the palm of your hand firmly on top of the cloud chamber for about 5 minutes to evaporate the alcohol.
Place the cloud chamber on a piece of FLAT dry ice that is at least a little larger than the chamber.
Turn off the lights in the room and shine the flashlight through the cloud chamber to make the ion trails easier to see. Trails should begin a few minutes after placement on the dry ice.
Note: You can use radioisotope disks in each chamber in lieu of Coleman lantern mantle pieces. By providing Alpha, Beta, and Gamma sources , students will find that only the Alpha and Beta sources will produce tracks. This is because Gamma radiation is electromagnetic radiation not particles, and it’s the particles moving through the alcohol cloud that makes the tracks.
NGSS Guided Inquiry
Give the students radioactive samples and ask them to reduce/block the radiation to normal background levels with things they find in the classroom.
Explain about the different types of radiation and radioactivity. Tell students to design their own experiment, to detect different types of radiation, and then share their results with the class.
Student Procedure
Observe the vapor trails produced within the cloud chamber and answer the questions provided by your teacher.
High School
Prepare three cloud chambers in accordance with the Cloud Chambers instructions:
Open the lid of the cloud chamber and saturate the felt strip inside with alcohol.
Put the radiation source inside the cloud chamber and replace the lid tightly.
Place the palm of your hand firmly on top of the cloud chamber for about 5 minutes to evaporate the alcohol.
Place the cloud chamber on a piece of FLAT dry ice that is at least a little larger than the chamber.
Turn off the lights in the room and shine the flashlight through the cloud chamber to make the ion trails easier to see. Trails should begin a few minutes after placement on the dry ice.
Note: You can radioisotope disks in each chamber in lieu of Coleman lantern mantle pieces. By providing Alpha, Beta, and Gamma sources , students will find that only the Alpha and Beta sources will produce tracks. This is because Gamma radiation is electromagnetic radiation not particles, and it’s the particles moving through the alcohol cloud that makes the tracks.
Post Discussion/Effective Teaching Strategies
Questions:
What is creating the vapor trails?
How is it creating them?
How far did each type of radiation travel away from the source? List your answers from furthest traveling to shortest traveling distance.
Are any tracks visible when no source of radiation is near the chamber? What kinds of radiation can be found in our environment?
Assessment Ideas
Have students draw a diagram of what is happening at the atomic level when a vapor trail is created.
Hold the north end of a strong magnet next to the chamber. How does magnetism affect the radiation tracks?
If you have access to a Geiger counter, count the number of tracks that you can see in ten seconds and then compare that number to the number of clicks produced by the Geiger counter in the same amount of time. Which is more accurate?
If you shield the source, which types of radiation are still visible?
Materials to experiment with shielding include: aluminum foil, plastic, cloth. Which types of radiation are shielding by each type of material?
Differentiated Learning/ Enrichment
Enrichment Question
How do you think shielding is useful to the nuclear industry? Give three examples.
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