Short lived high activity ; long lived low activity
Activities and half-lives are inversely proportional to each other. Like the explosion of a firework, the activities of short-lived radioisotopes have intense activities but short half-lives.The activity of a long-lived radioactive body can be compared to the light emitted by a glowworm and lasting forever. Uranium 238 which takes billions of years to transform can also be compared to a lake which slowly empties through a pin hole.