# Isotopes frequently used in radiometric dating worksheet

The atom's nucleus is composed of protons and neutrons, which are much more massive than electrons.

When an element has atoms that differ in the number of neutrons, these atoms are called different isotopes of the element.

The bag itself represents the fossil and the beads inside represent some of the millions of atoms that make it up.

As scientists, their job is to count the number of parent and daughter isotope atoms in each bag, and from this data to determine how many half-lives the isotope has gone through and therefore the age of the rock.

A good idea is to have the graph printed on the worksheet with the data table so that the students can have it right in front of them.

During natural radioactive decay, not all atoms of an element are instantaneously changed to atoms of another element.

Instead of using exponents and natural logs, the students can just use a graph of predicted decay rates to determine the number of half-lives the isotope has gone through based on this percentage ().

For instance, in fossil one, the students will take 15 divided by 60 and come up with the percentage .25.

Before class begins, prepare five bags filled with about 100 beads each.Half-lives can be calculated from measurements on the change in mass of a nuclide and the time it takes to occur.The only thing we know is that in the time of that substance's half-life, half of the original nuclei will disintegrate.Have the students rotate in groups from station to station until they have figured out the age of all five fossils.This ratio gives you the percentage of parent isotope atoms left after radioactive decay.