HALF-LIFE AND SPONTANEOUS DECAY IN THE CLASSROOM

As part of USF College of Marine Science's GK-12 Oceans program, in cooperation with Pinellas County schools, this lesson on half-life and radioactivity was prepared for students, grade level 9-12, though it is scalable to grades 6-8.

Before any understanding of radiometric dating techniques can be taught within a classroom, students must first have a basic understanding of the structure of an atom, and some knowledge of radioactive decay. Atomic structure and decay are fundamental aspects of many education science standards, including Florida's Sunshine Standards. One of the fundamental concepts related to this is half-life. Incorporating applied uses of half-life and radiometric dating aids students understanding of why this lesson is so important, using examples of sediment deposition rates and Deep Ocean current flow in the marine environment also demonstrates the wider use for radionuclides beyond the nuclear industry.

This concept can be too abstract for many students to grasp immediately, so the use of a hands-on demonstration greatly aids this. The overall objective is to demonstrate, simply, half-life in action by giving students hands-on experience collecting data and analyzing that data. Students use a handful of two-sided objects ("atoms"), coins work but M&M candies are more popular with the students, to drop all at once to simulate a half-life. Each drop, students will count all the heads-up (or M-up) atoms and record that number with the half-life number in their data set. The heads-up atoms are then removed and set aside, having decayed into daughter products, and the experiment continues with only the atoms that landed tails up. By having the objects all the same, except for one of a different color the concept of spontaneous decay can also be shown. The idea being that students cannot predict when that one atom will decay, but they will see that generally half their atoms decay each drop.

When students graph their data, half-life versus parent and or daughter products, they will notice it does not form a perfect exponential decay or growth line like the theory suggests should occur. This is an excellent opportunity to explain the idea of data normalization. Further activities can include examples of radiometric dating problems which also should strengthen students' perception of math as a science tool.