[mhartl]

This is an excellent and insightful comment. One quick note: it's and its are different words. I count ten occurrences of "it's", four of which should be "its":

    it's what you need           [correct in original]
    its half-life
    it's only mildly radioactive [correct in original]
    It's an alpha emitter        [correct in original]
    its oxides
    its lethality
    its *chemical toxicity*
    it's fine                    [correct in original]
    it's toxic, it's because     [correct in original]