AP BIOLOGY

Detailed explanation-1: -The half-life of a radioactive isotope is the amount of time it takes for one-half of the radioactive isotope to decay. The half-life of a specific radioactive isotope is constant; it is unaffected by conditions and is independent of the initial amount of that isotope.

Detailed explanation-2: -The half-life is the time it takes for half of a given amount of an isotope to decay. For example, the half-life of carbon-14 is 5, 730 years. Imagine that you start out with 100 grams of carbon-14. In 5, 730 years, half of it decays.

Detailed explanation-3: -Half-lives for beta decay range upward from one-hundredth of a second and, for alpha decay, upward from about one one-millionth of a second. Half-lives for gamma decay may be too short to measure (around 10-14 second), though a wide range of half-lives for gamma emission has been reported.

Detailed explanation-4: -Different radioactive substances have different half-lives. For example, tritium, a radioactive isotope of hydrogen, has a half-life of 12.3 years; while carbon-14 has a half-life of nearly 6, 000 years and uranium-235 has a half-life of more than 700 million years.