1. A doctor uses gamma radiation to produce an image of a person's brain.

A radioactive isotope called technetium-99m is used in this process. Technetium-99m emits gamma rays and has a short half-life.

The doctor injects a solution of technetium-99m into the patient. A detector outside the patient received gamma radiation to form the image.

Suggest why isotopes that emit alpha particles or beta particles are not suitable for this use.