In this half-life worksheet, students determine how long it takes for a 100g sample of AU-198 to decay to 6.25g. Then they determine the half-life of a radioactive isotope if a 500.0g sample decays to 62.5g in 24.3 hours. Students also determine the half-life of a radioactive isotope if it takes 6.2 days for a 72g sample to decay to 18g.