Radiation Safety Practice Exam

What is a half-life in relation to radioactive isotopes?

1. The time it takes for half of the substance to decay

2. The time it takes for all atoms to decay

3. The time elapsed since the isotope was formed

4. The time it takes for an isotope to become stable

The correct answer is: The time it takes for half of the substance to decay

A half-life is defined as the period in which half of a given amount of a radioactive isotope decays. This concept is crucial in understanding radioactive decay and the stability of isotopes. During each half-life, the quantity of the radioactive substance reduces by half, and this process occurs exponentially. For example, if you start with 100 grams of a radioactive isotope, after one half-life, you will have 50 grams, then 25 grams after the next half-life, and so forth. In relation to radioactive decay, this measure helps predict how long it will take for a certain percentage of the isotope to decay and is instrumental in fields such as nuclear medicine, radiometric dating, and nuclear physics. The half-life is a consistent property of each radioactive isotope, allowing scientists to determine age, dosage, and safety levels when handling radioactive materials.