What term describes the time it takes for half the nuclei in a radioactive sample to decay?

The term that describes the time it takes for half the nuclei in a radioactive sample to decay is known as half-life. This concept is fundamental to understanding radioactive decay and the stability of isotopes. During the half-life, a specific quantity of a radioactive substance will decay to half of its original amount, regardless of the amount present. This consistent behavior allows scientists to predict how long it will take for a sample to reduce to a certain level, facilitating applications in fields such as radiometric dating, nuclear medicine, and nuclear power.

The other terms, while related to radioactivity, do not accurately represent the specific concept of half-life. Decay rate refers to the speed at which a particular isotope decays but does not define the time frame for half of that isotope to decay. Radiological life is not a standard term used in this context. Exponential decay describes the mathematical model of decay related to half-life but isn't synonymous with the term "half-life" itself. Thus, half-life is the most precise and widely accepted term for describing the time it takes for half of a radioactive substance to decay.