In radioactive decay, what is defined as a 'half-life'?

The concept of 'half-life' in radioactive decay is a fundamental principle that defines the time required for half of the radioactive atoms in a sample to decay into another element or isotope. This measurement provides a consistent and quantifiable way to understand how quickly a radioactive substance loses its radioactivity over time.

By definition, after one half-life has elapsed, only half of the original radioactive atoms remain; the other half has transformed into either stable or other radioactive isotopes. This process continues logarithmically, meaning that after two half-lives, only a quarter of the original atoms remain, and so on. The significance of half-life is critical in fields such as nuclear medicine, radiocarbon dating, and radiation safety, as it allows scientists and practitioners to predict how long a radioactive material will remain hazardous and helps in planning for safe handling and disposal.

The other options do not accurately describe the concept of half-life. The idea of the time for all atoms to decay or the period during which radiation levels are highest are not consistent with how half-life is defined. Additionally, referring to the duration until full safety compliance is reached does not pertain to the properties of radioactive decay but rather to regulatory aspects of radiation safety.