Explain why medical tracers should have short enough half-lives to limit dose.

Within Different half-lives of radioactive isotopes, this learning objective asks you to explain why medical tracers should have short enough half-lives to limit dose. Focus on the approved ideas medical tracer and connect them clearly to Hazards and uses of radioactive emissions and of background radiation. A strong response should state the relevant particle, radiation, isotope, decay, half-life or nuclear-equation idea, then explain how it answers the exact command word. Avoid swapping nearby concepts such as atomic number and mass number, isotope and ion, alpha, beta and gamma radiation, or contamination and irradiation.