I am curious about this "Rule of thumb." Where is this a rule of thumb. Its by no way supported by science, nor is it implemented in the regulation of radionuc

I am curious about this "Rule of thumb." Where is this a rule of thumb. Its by no way supported by science, nor is it implemented in the regulation of radionuclides. When it comes to biological uptakes, shorter half-life usually means less dose than longer half-life radionuclides. This is primarily because effective dose calculations integrate the absorbed dose over a persons life (well for the purpose of comparing radiotoxicity they do). So a long-live alpha or beta emitter will be far worse than a short lived gamma, even though the range and energy will likely be much higher for the short lived gamma emitter.