The half-life of the radioactive isotope gallium-70 is 20 minutes. The initial amount of gallium-70 is 25 milligrams. When will only 10 milligrams be left. How many milligrams are present after 1 hour?

Whether or not a given isotope is radioactive is a characteristic of that particular isotope. Some isotopes are stable indefinitely, while others are radioactive and decay through a characteristic form of emission. As time passes, less and less of the radioactive isotope will be present, and the level of radioactivity decreases. An interesting and useful aspect of radioactive decay is half-life, which is the amount of time it takes for one-half of a radioactive isotope to decay. The half-life of a specific radioactive isotope is constant; it is unaffected by coTnditions and is independent of the initial amount of that isotope.

36 is the final answer! : )