In this lesson students explore the NGSS Performance Expectation HS-PS1-8: Develop models to illustrate the changes in the composition of the nucleus of the atom and the energy released during the processes of fission, fusion and radioactive decay. Prior to this lesson students have learned there are several types of radiation that are produced from a variety of isotopes. In this activity students will have a chance to view the 3 types of radiation (alpha, beta and gamma) using a cloud chamber.
A cloud chamber is a device that uses a lantern mantle that allows students to physically see radiation that is emitted. This process gives students the opportunity to engage in the NGSS Practice, developing a model, by making observations about radiation with little back ground knowledge. This activity will help them build on their mental model that has been developing throughout the previous lessons in this unit. This lesson will continue building curiosity and understanding about nuclear chemistry.
As a result of being able to see the radiation from the mantel, students will begin to see that the Cross Cutting Concept of Energy and Matter is an underlying theme in this unit. In nuclear processes, atoms are not conserved, but the total number of protons plus neutrons is conserved. In addition, the radioactive decay model illustrates the differences in type of energy (electromagnetic radiation) released during alpha, beta, and gamma radioactive decay, and any change from one element to another that can occur due to the process.
As students enter the class they pick up a copy of the cloud chamber lab activity which also contains the pre-lab warm-up on page one. In the first part of the activity I have students answer five statements about nuclear radiation as being true or false (student work). In addition to establishing if the statements are true or false, they must justify their answer with some sort of knowledge.
I have students do this activity with a partner because I think it’s easier for students to justify answers when communicating with another person. However, it can be done individually too if a student chooses to answer them individually.
The purpose of the warm-up is so students think about their knowledge of radiation prior to the activity. Once the lab is completed they will be expected go back and correct any answers that were based off of misconceptions. I convey this to them at the beginning of the warm-up.
This part of the lesson is an introduction to the three types of radiation and the background about how to use a cloud chamber, who invented it and how ionizing radiation works. After they complete the warm-up I instruct each student that they will read the 3 pre-lab questions first, then the Background information. After they read the three questions, we briefly go over what they’ll be reading (as mentioned above) to make sure they are guided in what they will be reading.
I have them read the questions first because this is a strategy that can help guide readers through a complex text. It also guides them to fill out the information as they come across it, saving times in the process.
After about 10 minutes, I take a few minutes to summarize the reading and make sure that everyone understands that radiation can be visualized and that they need not be concerned about the radiation they’ll be exposed to. They should also know how the 3 types of radiation behave, how far the radiation can travel, what material can block each type of radiation and understand radiation is ionizing. Finally they need to now the structure of the cloud chamber and the mantle.
I have not posted the pre-lab reading because it is a Flinn Scientific document that comes with the cloud chamber activity. The rest of the lab is a version of the activity that comes with the Flinn activity that has been modified to meet the curriculum and standards that I teach my students. If you would like a similar reading assignment you can visit Cornell.edu which has a modified lesson that instructs how to build a cloud chamber.
To save time during the lesson I have all the necessary materials (cloud chamber, ceramic tile, pipet, 25 ml beaker of isopropyl alcohol, flashlight, silk and cotton ball) out at the lab tables, except for the dry ice and gloves. All the materials needed for this lesson are on the student worksheet, along with the procedures that need to be followed.
I have students work in groups of 4 during this activity because Flinn Scientific sells a classroom set of six cloud chambers for $118 which allows for groups of 4-5 students per cloud chamber.
If possible the investment of $118 is well worth the cost because students are amazed that they can see radiation. In addition, it really helps students model the HS-PS1-8 and learn the characteristics of each type of radiation.
After everyone has cleaned up by returning the mantles and opening the chambers, I ask students to volunteer what they observed and what their observation meant.
I try to illicit the idea that particles that were close to the mantle are heavy and could not travel far due to their size. And particles that were thin and further away are light. I don’t tell them that they are alpha or beta particle because this is part of the reading and post-lab questions. However, I do ask them to think about each particle's penetrating ability and what might be needed to block each particle.
After performing this lesson, I found that many of my students struggled to make the connection that radiation (alpha, beta and gamma) is damaging due to its ionizing ability, in relation to size and speed. Most students struggled with this concept because they did not take enough time to attach what they where observing in the activity with the pre-lab reading. I think if I had planned more time into the activity, it would have been beneficial to have a think-pair-share with a lab partner about what they were viewing and how it related to radiation. This process would helped them validate what they were viewing and develop a more authentic opinion about radiation.
Overall, the students were able to develop a deeper understanding, and appreciation, that we are exposed to radiation on a daily basis...and as long as exposure is in moderation, might not be harmful.