1. After three half-lives, what fraction of the original radioactive material is left?
(a) None.
(b) 1/16,
(c) 1/8,
(d) 1/4,
(e) 3/4,
(f) 7/8.
2. Technetium 9843 has a half-life of 4.2 × 106yr. Strontium has a half-life of 28.79 yr. Which statements are true?
(a) The decay constant of Sr is greater than the decay constant of Tc.
(b) The activity of 100 g of Sr is less than the activity of 100 g of Tc.
(c) The long half-life of Tc means that it decays by alpha decay.
(d) A Tc atom has a higher probability of decaying in 1 yr than a Sr atom.
(e) 28.79 g of Sr has the same activity as 4.2 × 106g of Tc.