n :  either of two radioactive products intermediate between thorium and radiothorium:  a  :  an isotope of radium - symbol MsTh ₁ or Ra²²⁸ - called also mesothorium 1   b  :  an isotope of actinium - symbol MsTh ₂ or Ac²²⁸ - called also mesothorium 2  .
 
 
 
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