Nuclear Decay Series
Lesson 5 of 7
Objective: SWBAT showcase their understanding of alpha and beta decay, and combine these processes in a decay series diagram.
Previously, students have encountered both alpha and beta decay separately. Today we continue to practice them, intermixed here as a decay series.
The decay series were made by me, using information from Wikipedia. The first version of these series had multiple errors because I misinterpreted how the tables on Wikipedia were set up when isotopes could undergo various decays. My first class caught all my errors however and helped me clean it up for the rest of the day and sharing it here.
This lesson is aligned to the NGSS via 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. We will also use nuclear equations as models to understand how alpha and beta decay occurs together in sequence, in alignment with Science and Engineering Practice 2. The Energy and Matter Cross-Cutting Concept: In nuclear processes, atoms are not conserved, but the total number of protons plus neutrons is conserved is present in the decay series and nuclear symbols.
We begin the period by going over the beta decay problems from the previous day. Students did very well, including the problems that included multiple decays or finding the parent atom. Below is a copy of a student paper.
You can see this student made an error on the last part of problem B, putting the correct elemental symbol but the wrong atomic number, 40 instead of 41. The students generally did very well with the patterns of beta decay.
Introduction of Decay Series
As I pass out the Decay Series Practice paper, I tell the students that most elements take more than one step to become stable and have the correct ratio of neutrons to protons. I remind them of the decay chain they have already seen:
On that decay chain, they only had to label the type of decay. Today they would have to figure out the daughter atoms AND the type of decay.
We do the first row of the first series together using the document camera and projector. I ask a student to look up the atomic number of Californium so we can fill it in and get started. Once a student gives us the "98" we begin. I point out the "A" on the arrow and say, "if the Californium goes through alpha decay, what's the daughter?" Students do the work and tell me "248 over 96, and element 96 is Curium." Now I point out that the next arrow is blank, so I ask "How would we have changed to go from Curium-248 to Plutonium-244?" When a student says "Alpha" I ask how they knew. The response is "The mass went down by 4, and if it were beta, it would have stayed the same"
We finish the top row, and then I point out the best thing about completing decay chains. Every time you reach a daughter atom that is filled in, you can check your work. If the daughter atom doesn't work for either alpha or beta decay, then you did something wrong before that point, and can go backwards and check your work. Students ask if they can fill in all the atomic numbers for the elements listed before they start, and I tell them it is a very good idea to do that to make checking their work even easier.
I release the class to practice with a partner to check in with. At this time, some students move back to lab tables with their partners. While students continue to work, I circulate the room checking in, providing assistance to those who are stuck, and checking answers for those who are progressing.
Students finish the second chain and get this:
When they are working, they are constantly checking lines with their partner, and students are checking with other groups if I am busy. The confidence of my second period in their work being correct is what led to the discovery of the errors on my original worksheet.
The final decay series looks like this when completed:
When students finish, I have them show me their paper so I can check it over for errors. If I find mistakes, and there is time, they fix them immediately. If it is correct, I collect them to put the paper into the grade book.
With three minutes left, I pause the class to remind them that we will have our decay quiz tomorrow. I tell them there will be no decay series on the quiz, just the separate alpha and beta decays. They are actually disappointed at the absence of the decay series because "This stuff's really easy."