What is defined as the time taken for half of the atoms in a sample of a radioisotope to decay?

The correct answer is defined as the half-life. The half-life of a radioisotope is the specific duration it takes for half of the original amount of the radioactive substance to transform into another element or a different isotope through the process of radioactive decay. This concept is fundamental in understanding the behavior of radioactive materials and is utilized in various fields including nuclear medicine, archaeology (carbon dating), and environmental science.

The half-life is a constant value unique to each isotope, allowing scientists to predict how long it will take for a sample to decay to a certain fraction, making it an essential metric in radiological studies. Understanding half-lives enables calculations related to the timing of decay events and the safety management of radioactive materials.

In contrast, atomic mass refers to the total number of protons and neutrons in an atom, the decay constant relates to the probability of decay of a single atom per unit time, and a stable isotope is one that does not undergo radioactive decay. None of these terms convey the specific idea of time taken for half of the radioisotope to decay as clearly and accurately as half-life does.