Final answer:
The amount of time for a radioactive element to decay to 50% of its original amount is called its half-life, which is a constant that varies for each element and measures the rate of decay.
Step-by-step explanation:
The amount of time it takes for a radioactive element to decay to 50% of its original amount is called its half-life. The rate of radioactive decay is a constant for each radioactive element and is measured by the half-life. This concept is crucial in understanding the stability and the rate at which a radioactive element will decay into its daughter isotope. For example, if you start with 1.00 gram of a radioactive element, after one half-life there will be 0.500 grams remaining. After two half-lives, there will be 0.250 grams remaining, and so on. This process is an exponential function, meaning the amount of radioactive substance decreases by half over each subsequent half-life period.