An isotope produced by the radioactive decay of the nuclei of another isotope (the parent isotope). For example, lead-206 is a daughter isotope of uranium-238, which has a half-life of 4.5 billion years. The amount of any daughter isotope (or its decay products) in a sample increases with time, while that of its parent decreases; hence the relative proportions of the two can be used to derive the age of the sample (see radioactive age dating).