Fission and Fusion Nuclear Reactions

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Objective

Students will be able to explain what occurs in fission and fusion reactions through taking notes and performing activities.

Big Idea

During nuclear reactions the nuclei of atoms can change by splitting in fission reactions and combining in fusion reactions.

Introduction

In this lesson students learn about how the nuclei of atoms can change in fission and fusion reactions.

  • This lesson covers the Next Generation Science and Engineering Performance Expectation 1-8: 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. It does so because students are learning about nuclear fission and fusion reactions.
  • This lesson aligns with the Next Generation Science and Engineering Practice 2: Developing and Using Models: It does so because students are modeling what happens during nuclear fusion reactions through a hands on activity and a computer simulation.
  • There are several resources needed for this lesson including pipe cleaner pieces, mini-marshmallows, and plastic bags.   I give 1 plastic bag to each group of four which contains 12 pipe cleaner pieces and 24 mini marshmallows.

Engage

5 minutes

To begin the unit I ask students to, "Think about nuclear fusion and fission.  What do you think about in regards to these two terms?"

I get some responses in terms of the roots of the words.  Some students respond with "bringing together because you are fusing".  Another response is "take apart because of a fissure".

I get some responses in terms of nuclear reactions in bombs with answers like, "aren't they used in nuclear bombs?" 

Some students also remember the reading we did at the beginning of the unit (Unit 9 Big Quiz and Introduction to Nuclear Chemistry) and mention the fact that fusion is what happens in the sun.  If students don't bring this up then I probe them by saying, "did you read about either of these in the reading you did about stars at the beginning of the unit?" after this I will get responses related to fusion in stars.

Explain

20 minutes

In this section of the lesson I present the PowerPoint to students as they take notes on their graphic organizer.

  • I start by showing students the first slide of the PowerPoint and let them know that, "We will be continuing our discussion about nuclear reactions by learning about fission and fusion reactions in today's lesson."
  • I then show students slide 2 of the PowerPoint and remind them how nuclear reactions are different from chemical reactions because we are not dealing with electrons, but rather changing the protons and neutrons in the nucleus of atoms.  I also let them know how these reactions release a lot more energy than chemical reactions.
  • On slide 3 I take the time to introduce students to Einstein's equation, but let them know that we will not be using it at all, but rather they just need to be aware that this is an important relationship for determining energy being released in nuclear reactions.
  • On slides 4 through 9 I present fission and fusion reactions by having students fill out a table on their notes.  I like to present the information in this organized fashion to help students with differentiating between the two types.  The information I share with students includes what happens in these reactions, the energy being released, and examples of these reactions.  When discussion fission reactions we discuss nuclear bombs as well as nuclear power plants.  I do not have them take detailed notes about power plants, but let them know that we will be discussing much more about power plants in the next lesson (Argumentation: Should the Unite State Continue to Use Nuclear Power?).
    • After I explain fission reactions to students I show them a quick video to help them visualize fission reactions:
    • After I explain fusion reactions to students I show them this video to help them better understand fusion reactions and cold fusion:
  • This is a copy of a student's filled in notes.

Elaborate Part I

20 minutes

In this section of the lesson I have students model what they have learned about nuclear fusion by doing a quick activity and then several practice questions.

The activity is found on slides 10 and 11 of the PowerPoint and students record their responses on the back side of their graphic organizer.  The goal of the activity is for students to visualize what happens to atoms during a fusion reaction.  The start with hydrogen atoms (1 marshmallow) and end up with carbon (6 marshmallows).  Each time they make a fusion reaction they release energy by using a pipe cleaner piece. This is a very basic activity, but I feel that its a way to get students moving and does help them to remember the reaction.

  • I begin by passing out a plastic bag with materials for each group.  The bag contains 12 pieces of pipe cleaner (about 2 inches long), and 24 mini marshmallows.  I then tell students to each take 3 pipe cleaner pieces and 6 mini marshmallows.  
  • I then go through the activity with students.  This first video shows me explaining the activity to students and having them start with hydrogen atoms to make helium.
  • This second video shows how I lead students from helium to carbon.

For the second part of this section I have students perform some practice questions to give them a chance to review what we learned in the notes.  The practice questions are on slides 12 and 13 of the PowerPoint and students record their responses on the the bottom of the second page of their notes graphic organizer.

  •  I start this section by telling students to try to answer the questions on their own for several minutes.  I tell them that if they are stuck that they should go back and look over their notes.   I also tell them that if both they and their partners are stuck that they can work together.
  • After about 5 minutes, or when most students are done, I go over the answers with students.  I do this by calling on student group to give their answers.
  • Most students do well on these questions.  I am surprised however, with how many students get confused with the first questions, and I remind them to think about what happens to atoms during the three types when choosing.

This is a copy of an answer key for both the activity and the questions at the end of the activity.  This is a copy of one student's work.

Elaborate Part II

45 minutes

As a second way to reinforce what students have learned in this lesson as well as the rest of the nuclear chemistry unit I have them do several simulations on the PhET website.  I have them go up to the classroom computers with their groups and fill in this phet nuclear activities paper as they do the simulations.

  • For the first simulation they are doing the Alpha Decay simulation where they can see what happens to a Polonium-211 atom during alpha decay.
  • For the second simulation the students are doing the Beta Decay Simulation where they visualize the beta decay of hydrogen-3.
  • For the final simulation the students are playing the radioactive dating game.  In this simulation they analyze what happens to radioactive elements including Carbon-14 and Uraniium-238.  They are asked to hypothesize what happens to the amount of substance during the period of half-lives, and how these are averages, not exact numbers that occur every time.
  • This is a copy of one student's completed activity.  I get mixed results with this activity in terms of "correct" answers.  Students are not exactly sure what to write down for what happens during the alpha and beta decay simulations.  Also, not all students figure out how the half-life amounts aren't always exact because it's an average of when the atoms decay.

Evaluate

As students complete their PhET activity I have them begin to work on their unit10 review worksheet.  I let them know that it is not due until the exam, but that they should use this extra class time as well as time at home to complete the paper. 

I stamp the paper for completion on the day of the exam and then review it using the answer key.

This is one example of a student's completed paper.

Some of the common confusions among students include:

  • question #1 with how the nucleus changes in alpha, beta, and gamma decay.
  • question #7, what is special about the nucleus in nuclear reactions (that it is unstable)
  • question #8, with differentiating between beta decay, positron emission, and electron capture.
  • question #9, with being able to write out the complete nuclear reactions.  Students have a hard time with figuring out what element will be formed.  They have to be reminded to do the math first and then look at the periodic table for whichever element has that atomic number.
  • question #12 with figuring out the half-life of the isotope.  I remind students to set up the table with what they know and then fill in the missing information.  In this case they need to realize that after 24 days they have gone through 6 half-lives so 24 / 6 gives them 4 for a half-life.