Day 1: Radioactive Decay Using A Gizmo.

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SWBAT Compare and contrast nuclear processes (fission, fusion and radioactive decay) in terms of subatomic particles and energy input and output.

Big Idea

Students are introduced to the concept of radioactive decay using an ExploreLearning Gizmo.


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 In the previous lesson students learn there are different versions of atoms based on atomic mass called isotopes, some of which are radioactive. This lesson builds on this by teaching them unstable isotopes decay in a specific manner by either emitting an alpha particle, beta particle and/or a gamma ray.

Since nuclear chemistry is difficult for students to explore in a traditional lab setting, they must use models (Science and Engineering Practice #2) to illustrate the nuclear decay process. In this lesson they use a ExploreLearning Gizmo that models how unstable isotopes will emit specific particles based on the ratio of protons to neutrons.  This simulation is one of the better Gizmos offered by ExploreLearning by illustrating particles physically being released by the isotope.  

As a result of being able to model different types of radioactive decay, students will begin to see that the Cross Cutting Concept, Energy and Matter, as an underlying theme in this unit. This concept will be built upon later as they learn about the Law of Conservation of Matter. 


10 minutes

As a general rule of thumb, most Gizmos require the entire period to complete, so I like to instruct students to log on to the computer as soon as they enter the class.  As each student is logging on their computers, I hand out the Nuclear Decay ExploreLearning activity, and ask them to get out their periodic table and to answer the warm-up questions at the beginning.  I have each students perform their own investigation because modeling is part of the NGSS SEP and learning process.

Warm-up Questions:

These questions are a review of atomic structure and mass calculations from the previous day, specifically directed towards helium because of the nature of an alpha particle.




Approximate mass




1 u




1 u




0 u


  1. The mass number of an atom is equal to the sum of protons and neutrons in the nucleus.
    A helium atom has 2 protons and 2 neutrons. What is the mass number of this atom? 4
  2. The atomic number of an element is equal to the number of protons in each atom of the element. All helium atoms have 2 protons. What is the atomic number of helium? 2


After several minutes I ask for a volunteer to answer questions 1 and 2 out loud.

I than ask, "do electrons have any mass?"  Answers should be no based on the information in the above chart.

Next I ask, "how many electrons does helium normally have?” They will not get this information from the chart but should be able to answer two based on prior knowledge.

I conclude the questioning by asking, “what would be the mass of helium if it lost its two electrons?  and “what would be its charge?” 4 and +2.

These questions are meant to build a platform for learning radioactive isotopes can lose particles similar to a helium atom or an electron.


30 minutes

After the brief introduction I instruct students to open up the Nuclear Decay Gizmo.  This may take a couple of minutes.  While they are doing this I will prepare to explain how to work the gizmo during the warm-up portion of the activity.  The purpose of this part of the activity is so the user can see what the various particles look like as they are being emitted from the nucleus.  

After the warm-up, I give students 7-10 minutes to work on Activity A and answer questions 1-9.  During this portion of the activity they will follow the directions and model alpha decay.  The 9 questions have students write a nuclear equations, predict daughter products (defined in Q. 2), practice alpha decay with several isotopes and summarize the mass of daughter products after alpha decay (Nuclear Decay_Key). 

The goal is to realize that alpha decay will reduce the mass of isotope by 4 and atomic number by 2.

After completing this I will have students volunteer to answer questions 4-6 on the board. 

  • Write an equation for the alpha decay of polonium, and then use the Gizmo to check your answer. What isotope remains after the alpha decay of polonium-212? 
  • Write an equation for the alpha decay of radium, and then use the Gizmo to check your answer.  What dangerous gas is produced by the decay of radium-226? 
  •  Write an equation for the alpha decay of Americium-241 below.

After the volunteers completed the problems we have brief discussion about what the daughter products are from the above problems after alpha decay: Pb-208, Rn-222 and Np-237.  The purpose of the conversation is to reinforce the terminology used during nuclear decay, daughter product and alpha decay.

After discussing the daughter products of alpha decay they can begin to work on Activity B, Beta decay, for 7-10 minutes.  In this section they will learn that a neutron will turn into a proton, and an electron will be emitted along with energy in the form of gamma rays. After completing this I will again take volunteers to write the problems from this section on the board as seen on the answer key.

Students generally do very well on this activity and learn the basic format for writing a nuclear equation.  This can be seen in the EL Nuclear Decay student work this provided.  This activity build a solid foundation for students because they must model the process of nuclear decay and develop a macroscopic model of what occurs during nuclear decay.


10 minutes

I do not collect the ExploreLearning activity because it was guided practice and they can use it as notes to help with the Nuclear Decay practice.  The first part of the practice is a summary of each particle’s charge, mass, description of the particle and an example of what the symbol looks like.  To get the class started, I will provide this information for them.  

After filling in the first table, they will practice writing nuclear equations, predicting the particle that is released during decay, what daughter product is produced and perform a simple decay series stating what type of decay is occurring 

Since this is new material I will instruct students to work with a partner and use there ExploreLearning worksheet to guide them.  Doing this with a partner gets them to discuss their answers and provides reassurance that they are doing it correctly.  As they are working on this I will walk around visually assessing who is completing the practice correctly (nuclear decay key).  If they are having difficulty I will work through problems with individuals.  If there are several students that are having difficulty I will work with them as a group.

If there are problems, it's typically the students that still struggle with understanding element notation learned at the beginning of the school year.  Getting students through this is just a matter of working with them and lots of practice.