Radioactivity Lab

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Objective

SWBAT complete a lab modeling the half-life of a radioactive element [LAB]

Big Idea

Radioactive decay is a process of observing recurring half-lives in radioactive substances, and this process can be modeled directly by using (delicious) M&Ms to represent the process of radioactive decay.

Lesson Introduction

Again, one of my favorite labs from one of my favorite topics! This lab is sort of a continuation of yesterday's lesson, as it deals with a practical demonstration on half-life and radioactive decay. Students use pieces of candy to model the process of radioactive decay and chart their results in this hands-on assignment. Please note the materials section below. Also, it's important to note that students will be constructing graphs (another of my favorites). While these aren't incredibly difficult, you may want to provide more guided practice for them in building the graphs if you feel your students might need it.

Materials Needed:

  • M&Ms/Skittles/Pennies (things that definitively have two sides and can be easily discerned which side is which. You'll need 100/group. I purchased this size off of Amazon and had enough for my classes, although if you have over 90 students it would probably be best to buy 2 bags)
  • Calculator(s)
  • Paper Towel(s)
  • Ruler (for graphing)
  • Small/medium size tupperware bin

[Note: For embedded comments, checks for understanding (CFUs), and key additional information on transitions and key parts of the lesson not necessarily included in the below narrative, please go to the comments in the following document: Radioactivity Lab (Whole Lesson w/comments). Additionally, if you would like all of the resources together in a PDF document, that can be accessed as a complete resource here: Radioactivity Lab (Whole Lesson)[PDF]. Finally, students may need their Earth Science Reference Tables [ESRT] for parts of the lesson (a document used widely in the New York State Earth Science Regents course) as well.]

Do Now

10 minutes

Students come in silently and complete the (attached) Do Now. After time expires (anywhere from 2-4 minutes depending on the type of Do Now and number of questions), we collectively go over the responses (usually involving a series of cold calls and/or volunteers), before I call on a student and ask them to read the objective out loud to start the lesson.

As a general note, the Do Now serves a few purposes:

  1. It serves as a general review of the previous day's material;
  2. It is a re-activation of student knowledge to get them back into "student mode" and get them thinking about science after transitioning from another content area or alternate class;
  3. as a strategy for reviewing material students have struggled with (for example, using this as a focused review for material that they have struggled with on unit assessments or recent quizzes); and,
  4. It is an efficient and established routine for entering the classroom that is repeated each day with fidelity (I never let students enter the classroom talking. While it may seem potentially severe to have students enter silently each day, this is both a school wide expectation and a key component of my classroom. In many respects, I find that students readily enjoy the focus that starting with a quiet classrooms brings each day).

Introduction & Procedure

10 minutes

The Introduction & Procedure section is relatively straightforward, in that students' first task is to read the Introduction & Objective session as a class. When they arrive at the Catalyst, I have them very quickly complete that with their partners (they haven't yet transitioned to lab groups) as a quick re-activator on the fundamentals of radioactive decay/radiometric dating. I use my document camera to go over the responses and model the correct answers (usually with student participation). 

Once students are done with this section, I have them quickly transition their desks into their normal lab groups of 4 students. As always, this procedure is timed, and any record breaking times are tracked on the sheet at the front of the room (the current record is 6 seconds!). While that is happening, I nominate a student to pass out the laboratory bins with all necessary materials (Note: You should definitely count out the M&Ms/objects you're using before class starts!)

Once they're in their groups (and as the materials are coming around, I go over some final points with them, which are replicated below:

  • Only shake the bin for 5-6 seconds!
  • You need to shake up and down, not just "slide" them
  • Shaking too hard will break the M&Ms!
  • Keep the ‘decayed’ M&Ms on the paper towel you have
  • You need to record data in the data table on Page 3.
  • You will have a calculator to calculate the ‘% Removed’
  • You CANNOT speak to other lab groups! (This is to minimize the noise level and prevent arguments, etc. Basically, the less people they interact with outside their groups, the greater the likelihood that they'll stay focused on their actual laboratory objective. Also, you don't want M&Ms flying across the room!)

 

Once these points are reviewed with students (it might be more helpful to just post these somewhere next time I do this!), I let the students start the lab.

Laboratory Activity

25 minutes

Once students start the lab, they have a large chunk of time with which to complete the Data Table and Graph. During this time, I generally circulate and make sure that everyone is participating/has a role (there are no "stragglers" in specific lab groups), they are making good enough time, and the laboratory experiment is being done with fidelity. Once students are done with the associated Data Table, they are then instructed to work on the Graph. While the graph has axes labeled, it is up to the students to figure out an appropriate scale/interval and title, in addition to plotting the actual points. A potential mistake you might want to keep an eye out for is that y-axis - sometimes, groups can get confused on what to do with what, so make sure that they're graphing the number of M&Ms (or whatever object you have) remaining. While probably not perfect, the graph should generally match up to a normalized graph of radioactive decay.

Discussion Questions

15 minutes

As noted in the previous section, immediately after student groups are done, I ask them to start up on the Discussion section, as it has some summarizing questions for them to reflect on the laboratory activity. [Note: Unlike most of my other lessons, there is no exit ticket associated with this lesson.] I generally give them the bulk of remaining class time to finish up, although in the last few minutes, I have students self-assess on the attached Rubric at the end.

[Note: Depending on the day and class type, I sometimes have them either grade themselves, I grade them, or I ask a laboratory partner to grade another (i.e. "pass this to someone across from you to evaluate your lab performance today.") Given that this is a fairly regular occurrence in my classroom, this usually happens relatively quickly (under two minutes), although you may want to allot more time if you decide to do something similar for your class.]

Given that there are no necessary materials needed for this lab outside of the normal printed resources, clean up is usually quick, and only involves having the students put their desks back into a normal classroom arrangement and preparing their desks for transitioning out of the room. 

In the last minute or so, I do utilize the same procedure I do on non-lab days, which is to ask the students time to think about their self-mastery of the objective (which is posted on the whiteboard), through some guided questions:

  1. Do you feel that you mastered the objective for the day?
  2. Can you reiterate one thing you learned about ____________ (in this case, the process of sea floor spreading, etc.)

Once I take 2-3 individual responses (sometimes I'll ask for a binary "thumbs up/thumbs down" or something similar), I have students leave once the bell rings.  

Clean Up & Closing

5 minutes

Unlike most of my other lessons, there is no exit ticket associated with this lesson. In the last few minutes of class, I definitely want to have the room ready for either my next period, or an alternate class that might be using the room (I share a room with another science teacher, which makes clean up all the more important at the end of the period). Since this lab is rife with materials, specifically small pieces of candy that can sometimes unintentionally end up on the floor, I try to give them some time to make sure all the materials have been accounted for, put away (usually by a 'Materials Manager' or someone designated to do so), and any spare pieces on the floor have been picked up. As I've mentioned several times in previous lessons, I put a strong emphasis on this time, and very directly manage this process, although it is completely done by the students themselves. As a quick tip, I find it always helpful to: 1.) save more time than you think you need and 2.) have a hard stop at the end of a lab. Once that time is reached, no lab work can continue. You have to begin the process of cleaning up. Since, as mentioned above, I also share a classroom, I also give them some time to make sure all the desks have been put back into a normal classroom arrangement and students are prepared for transitioning out of the room. 

In the last minute or so, I do utilize the same procedure I do on non-lab days, which is to ask the students time to think about their self-mastery of the objective (which is posted on the whiteboard), through some guided questions:

  1. Do you feel that you mastered the objective for the day?
  2. Can you reiterate one thing you learned about ____________ (in this case, something like "What do you think we modeled in this lab?" or a procedural question like "How was it working together today?", etc.)

Once I take 2-3 individual responses (sometimes I'll ask for a binary "thumbs up/thumbs down" or something similar), I have students leave once the bell rings.