A radioactive substance decays over time. Some substances decay very quickly, others more slowly. The rate at which a substance decays is measured by its half-life, which indicates the amount of time it takes for half of the original sample to decay.
The plot below illustrates how fast or slow the decay of a radioactive substance is. You can choose how large a sample you want to start with by entering the mass in grams, and control how fast or slowly the substance will decay by entering a half-life in terms of seconds, minutes, hours, days, weeks, months, or years.
Original mass of the sample: grams. Half-life: secondsminuteshoursdaysweeksyears
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