should radioactive tracers used for medical diagnosis have a short or a long half-life?

Radioactive tracers used for medical diagnosis should have a short half-life. This is because a short half-life ensures the radioisotope emits enough radiation for imaging but decays quickly enough to minimize radiation exposure to the patient after the procedure is done. Short half-life tracers allow for rapid imaging and reduce the time the radiation remains in the body, which lowers the risk of radiation damage. For example, technetium-99m, a commonly used medical tracer, has a half-life of about 6 hours, allowing it to decay effectively within a few days and limiting radiation exposure. Longer half- lives would result in prolonged radiation exposure, which is undesirable for patient safety. Thus, the ideal medical tracer has a balance: it must last long enough to complete imaging but short enough to minimize radiation dose and health risks.