The uranium decay series from U-238 to stable lead (Pb-206) is: 238 92 U → 234 90 Th → 234 91 Pa → 234 92 U → 230 90 Th

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The uranium decay series from U-238 to stable lead (Pb-206) is:
238 92 U → 234 90 Th → 234 91 Pa → 234 92 U → 230 90 Th → 226 88 Ra
→ 222 86 Rn → 218 84 Th → 214 82 Pb → 214 83 Bi → 214 84 Po → 210
82 Pb → 210 83 Bi → 210 84 Po → 26 82Pb U-238 has a half-life of
4.5 billion years. Of the other nuclei on the way from U-238 to
stable Pb206, most are very short-lived (half-lives less than a few
months). The exception is radium, with a half-life of 1600 years.
Marie Curie was given ten tonnes of pitchblende (uranium ore,
mostly uranium oxide) and after several years of chemical
processing and purification she isolated some radium from it.
Estimate how much radium there was in the pitchblende for her to
extract.