Question

For each of the following, indicate if the number of half-lives elapsed is:

1. one half-life
2. two half-lives
3. three half-lives

a. a sample of Ce-141 with a half-life of 32.5 days after 32.5 days
b. a sample of F-18 with a half-life of 110 min after 330 min
c. a sample of Au-198 with a half-life of 2.7 days after 5.4 days

Answer 1

Answer:

• a. one half-life

• b. three half-lives

• c. two half-lives

Explanation:

The number of half-lives elapsed, n, is calculated dividing the time by the half-life time:

• n = time / half-life time

a. A sample of Ce-141 with a half-life of 32.5 days after 32.5 days

• n = 32.5 days / 32.5 days = 1 half-life

b. A sample of F-18 with a half-life of 110 min after 330 min

• n = 330 min / 110 min = 3 half-lives

c. A sample of Au-198 with a half-life of 2.7 days after 5.4 days

• n = 5.4 days / 2.7 days = 2 half-lives