What is the term for the time it takes for half of the radioactive atoms in a sample to decay?

The term that describes the time required for half of the radioactive atoms in a sample to decay is known as half-life. This concept is fundamental in the field of nuclear physics and radioactivity, as it provides a measurable constant that defines the rate at which a radioactive substance loses its radioactivity.

Half-life is a critical factor in understanding various applications, such as radiometric dating, medical treatments involving radioactive isotopes, and the management of radioactive waste. Knowledge of a substance's half-life allows scientists and health professionals to predict how long it will remain hazardous and to make informed decisions regarding safety protocols and exposure limits.

The other terms listed do not accurately represent this specific concept in radioactivity. For example, "decay time" is a more general phrase that does not imply the specific statistical relationship of halving over a defined period, while "radioactive period" and "exposure duration" do not have established meanings that correspond to the concept of half-life in the context of nuclear decay.