Radioactivity & Half-Life

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SWBAT find the absolute age of rocks and fossils using radioactive dating and half-life information

Big Idea

Students explore the methods and techniques involved in radioactive dating

Lesson Introduction

One of my favorite lessons! I'm not really sure exactly why, but I've always gotten a kick out of half-life and radioactivity stuff. This lesson starts off with a bang (literally!) as students watch a video about the destructive power of nuclear bombs, before diving a bit deeper into the technical nature of radioactive half-lives, with some practice thrown in for good measure.

[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 & Half-Life (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 & Half-Life (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. In this Do Now, I selected questions which were similar to question types they would encounter on their quarterly interim assessment. 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).

Video Introduction

10 minutes

I start off this lesson with a question, which is the same linked in the Video resource. "Where have you heard the words nuclear, or radioactive before?" I solicit a couple of student responses, but one invariably mentions weapons or nuclear bombs. I then indicate that what they're going to do is watch a brief video clip detailing the story of the greatest nuclear detonation in history. The movie above (linked via Youtube) is 7:40 long, although I only have them watch the first 1:20 or so. The video is short, but impactful, as it details the short history of the Tsar Bomba, the Russian test bomb thought to be the greatest man-made device ever detonated. 

Students watch the video (no notes are necessary, especially since they're only watching for a minute or so) and then I have them take a guess as to what the NYC images are. In a couple of classes, students have correctly stated that they are the blast radiuses of two different nuclear bombs (if they were to be detonated in NYC). The first would be a standard atomic bomb, similar to the ones detonated over Hiroshima or Nagasaki in WWII. This  image, which is zoomed out due to the scale, indicates the blast radius of the Tsar Bomba would have been. 

After that (somewhat macabre) experience, I have my students watch a slightly more informational video. Linked here, this video talks more specifically about radioactive decay and half-life. While the video is playing, I have students take notes on the questions via the Video resource (Note: The questions appear in the order they are presented in the video).

Radioactivity Notes

20 minutes

I wanted to explain a bit about the Radioactivity Notes resource by posting a video explanation, which is embedded below: (also students will need the first page of their Earth Science Reference Tables [ESRT] for half-life reference)

[Note: Please see reflection in this section for additional context here!]

Radioactivity Practice

20 minutes

The section on Radioactivity Practice is of critical importance, as this material tends to initially be very confusing for students. I find that they tend to struggle a bit with the concept of decay, and constantly taking away half of whatever you have after a specific half life. I often find that the best strategy for this is to give students the opportunity to test their knowledge with a healthy amount of "at bats" dealing with the information. Like most lessons, some students might struggle more than others, but the course corrected we do as teachers can help the light bulbs go off. 

100% of these questions are pulled from former Regents examinations, so they're relevant and appropriate regarding the content and general level of rigor that students can expect to see on the assessment. Additionally, they're mostly organized to get increasingly more difficult and increase in complexity, which is why the harder questions tend to come toward the end. 

In terms of student work habits, I tend to sometimes make this decision in the moment, and as a response of what I know about the students and how they're processing the material on, but I'll either ask them to work independently, in partners, or give them the option. Usually, before starting practice, we tend to go over some steps for self-help ("What should you do if you're stuck?"), and I might reference a previously used multiple-choice or free response strategy in order to build their skills while simultaneously learning content (as an example - one popular one we always use - "If you aren't sure what the right answer is, see if you can eliminate some wrong answer choices"). I tend to circulate for compliance and then hone in on specific students while they're doing this. 

After about 10 minutes, we go over their responses. Students who finish early are encouraged to work on the exit ticket (resource below) and double-check their responses. We use a combination of strategies (active voting, cold calling, popsicle sticks, volunteers) to go over the responses, where students correct their work and ask any clarifying questions. 


Exit Ticket, Closing, & Homework

10 minutes

In the last few minutes of class, I have students complete the daily Exit Ticket. For the sake of time, I have students grade them communally, with a key emphasis on particular questions and items that hit on the key ideas of the lesson (Note: This usually manifests as students self-grading, or having students do a "trade and grade" with their table partners). After students grade their exit tickets, they usually pass them in (so that I can analyze them) and track their exit ticket scores on a unit Exit Ticket Tracker. I also usually pass out the Homework at this time. 

After students take a few seconds to track their scores, we usually wrap up in a similar way. I give students time to pack up their belongings, and I end the class at the objective, which is posted on the whiteboard, and ask students two 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, basic questions like the definition of radioactivity or half-life, etc.)