AP BIOLOGY

Detailed explanation-1: -Half-life is the length of time it takes for half of the radioactive atoms of a specific radionuclide to decay.

Detailed explanation-2: -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-3: -Each radioactive material has a decay rate. The time that it takes for half of the radioactive atoms to decay is called a half-life. For example, the previously mentioned technetium-99m has a half-life of six hours which means that, starting with 100 percent, after six hours, we will have 50 percent left.

Detailed explanation-4: -Half-life is usually defined as the time taken for a radioactive substance (or half of the atoms) to decompose or change into another substance. In radioactivity, mean life is defined as the average lifetime of all nuclei of a specific unstable atomic species.

Detailed explanation-5: -Thus the half-life of a nuclear decay process is the time required for the number of unstable nuclei to decrease from [A]0 to 1/2[A]0. As you can see from this table, the amount of reactant left after n half-lives of a first-order reaction is (1/2)n times the initial concentration.