> Yes many of them seem to have short half-lives but one of them has a half life of 1.5 million years.
Which means it's completely safe. If it has a half-life that long, it won't be releasing radiation at a very high rate. Hardly enough to register above background. The isotopes you have to worry about are the ones with in-the-middle half lives- long enough that they don't deplete themselves in a conveniently short period, but short enough that they produce a dangerous power output.
That depends on concentrations of the isotope in the metal and the amount of metal we will be using. I have no idea what the concentrations of iron isotopes in meteors are and which iron isotopes are there, but I do not think it is correct to automatically say that radioactive isotopes with long half-lives are completely safe.
Which means it's completely safe. If it has a half-life that long, it won't be releasing radiation at a very high rate. Hardly enough to register above background. The isotopes you have to worry about are the ones with in-the-middle half lives- long enough that they don't deplete themselves in a conveniently short period, but short enough that they produce a dangerous power output.