# Radiometric dating penny lab conclusion

Flows, Cycles, and Conservation Objectives Students try to model radioactive decay by using the scientific thought process of creating a hypothesis, then testing it through inference. It is a great introduction to the scientific process of deducing, forming scientific theories, and communicating with peers. It is also useful in the mathematics classroom by the process of graphing the data.

## In the Classroom

Seeing this connection will help students to understand how scientists can determine the age of a sample by looking at the amount of radioactive material in the sample. To define the terms half-life and radioactive decay To model the rate of radioactive decay To create line graphs from collected data To compare data To understand how radioactive decay is used to date archaeological artifacts Background Half-Life If two nuclei have different masses, but the same atomic number, those nuclei are considered to be isotopes.

Isotopes have the same chemical properties, but different physical properties. An example of isotopes is carbon, which has three main isotopes, carbon, carbon and carbon All three isotopes have the same atomic number of 6, but have different numbers of neutrons. Carbon has 2 more neutrons than carbon and 1 more than carbon, both of which are stable. Carbon is radioactive and undergoes radioactive decay. Radioactive materials contain some nuclei that are stable and other nuclei that are unstable.

Not all of the atoms of a radioactive isotope radioisotope decay at the same time. Rather, the atoms decay at a rate that is characteristic to the isotope. The rate of decay is a fixed rate called a half-life. The half-life of a radioactive isotope refers to the amount of time required for half of a quantity of a radioactive isotope to decay. Carbon has a half-life of years, which means that if you take one gram of carbon, half of it will decay in years.

Different isotopes have different half-lives. If their penny lands on heads, they are radioactive and have decayed and they should sit; if their penny lands on tails, they have not decayed and may remain standing. After each "half life", count the people remaining standing and plot it on a piece of graph paper Acrobat PDF 42kB Jun21 04 on the overhead.

After about 3 or 4 "half-lives" ask students to predict what's going to happen to the numbers of remaining parent isotopes. Continue the experiment until only one or 2 people are left usually "half-lives". This can set up a good discussion of what is happening to the number of students still standing i.

### Half-Life : Paper, M&M’s, Pennies, or Puzzle Pieces - ANS

Some questions to get the students started thinking about these concepts: After two or three "half-lives" What is happening to the number of students standing? Do the same number of students sit down each time we flip the coins? About how many students would have had to sit down if we started with twice as many students? What about if we only had half as many in this class? What does that tell you about how the quantity of "radioactive isotopes" affects the number that decay?

Can you predict which of you is going to be the first to sit down? Why or why not?

## Demonstration of radioactive decay using pennies

How is radioactive decay sort of like gambling or playing the lottery? Assessment It is relatively easy to get a quick check on whether students have grasped several concepts: There are several ways that this can be done: If you have a student response system, a quick quiz with questions that cover these four concepts is an easy way to determine the students' understanding. Having students work through a short problem in groups or on their own that applies these concepts in a geologic context -- a problem where they have to read a graph or calculate how many isotopes are left after x half-lives -- can also provide a quick check.