There are other isotopes of cerium which are radioactive. Different isotopes of cerium have different half-lives.
The half-life of an isotope can be found by studying how the number of atoms
changes over time.
Figure 7 shows how the number of atoms of cerium-148 in a 120 g sample changes
over time.
1. Determine the ratio of the number of cerium atoms in the sample when it was 100 seconds old compared with when the sample was 350 seconds old. Use data from Figure 7.
2. Determine the activity of the sample of cerium when the sample was 20 seconds old. Use Figure 7.