Chapter 20, Problem 15STP

To determine

To Identify:The radioactive isotope in a sample which will have about one-fourth of the isotope left after 16 days.

Answer to Problem 15STP

Iodine-131 will be the isotope in the sample which will have about one-fourth of the isotope left after 16 days since it has half-life of about 8.04 days.

Explanation of Solution

Introduction:

After each half-life, the number of remaining undecayed nuclei decrease rapidly.

• After one half-life the number of remaining undecayed nuclei reduced to half.
• And after two half-lives the number of remaining undecayed nuclei reduced to one-fourth.
• Now, since the half-life of iodine is about 8.04 days so in the same way,
• After one half-life (8.04 days) the number of remaining undecayed nuclei of iodine-131 reduced to half.
• And after two half-lives (16 days) the number of remaining undecayed nuclei iodine-131 reduced to one-fourth.

Conclusion:

Thus,Iodine-131 will be the isotope in the sample which will have about one-fourth of the isotope left after 16 days.