Which of the following statements about chain reactions is true? Only uranium isotopes are capable of supporting a chain reaction. It is not possible to stop or control a chain reaction once it has been started. The key requirement for a chain reaction is that more neutrons are produced than are absorbed. Three or more neutrons must be released to sustain a chain reaction. A chain reaction will only take place when a critical mass of material has been assembled. How can a half-life be used to tell the age of a sample? The ratio between the radioactive form and the stable form depends on the archaeological record. The half-life of an isotope is constant. The ratio between the radioactive form and stable form varies regularly with time. The amount of radioactive form depends on the amount of radiation in the surroundings. both C and D