It's true that things with shorter half lives have more decays per second for the same number of nuclei. However, the type of and energy of the decay is very im

It's true that things with shorter half lives have more decays per second for the same number of nuclei. However, the type of and energy of the decay is very important to the type of health impact it has, as well as how/how long it's retained in the body. Tritium is relatively safe because it emits a very low energy electron (<18 keV), which almost immediately ranges out in most materials, especially water. The only way it can get you is if its sitting right on top of your dna when it decays. Since it's hydrogen, it freely exchanges with the hydrogens in the water in a persons body, and is excreted quickly as a result. It doesnt accumulate in any particular place, which is also a plus. The treatment for tritium is lots of water and a few beers. Contrast that with actinides, some of which decay by neutron emission, alpha emission, and spontaneous fission. This page has a good breakdown https://www.osha.gov/SLTC/radiationionizing/background.html https://www.osha.gov/SLTC/radiationionizing/background.html alphas deposit alot of energy per unit length traversed, so alpha decay happening inside the body is pretty destructive. Alot of actinides also concentrate in bone marrow, which leads to leukemia.