Gregory's Server@vicgrinberg I saw Ra marked as 'nothing left', and felt disappointed by the information here. I infer that this is only a fraction of the answer. I guess this is a perennial problem with outreach. The quick answer is usually incomplete.
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@vicgrinberg we have radioactive elements in abundance on earth, but I assume not directly from stars - but you don't show that. Maybe I'm missing something here, I really have no idea about this subject but I got confused.  @tsh2 the radioactive elements that we have on Earth today - U-238, Th-232 and K-40 mainly - all have very long half-life times (times in which half of the material undergoes nuclear fission). The "nothing left" elements are all described above as "very radioactive", i.e. they decay very fast or have a short half-life, so that nothing is left of them today (except of some short-lived amount if one of the more stable radioactive nuclei decays into them). |
@tsh2 hm, where is the answer lacking?