To determine which radioactive isotope would take the least amount of time to become stable, we need to look at their half-lives, which is the time it takes for half of a given amount of the isotope to decay.
Here are the half-lives of the isotopes you mentioned:
- Rubidium-91: Approximately 18.6 minutes.
- Iodine-131: Approximately 8 days.
- Cesium-135: Approximately 2.3 million years.
- Uranium-238: Approximately 4.5 billion years.
Among these isotopes, Rubidium-91, with a half-life of about 18.6 minutes, would take the least amount of time to become stable.