thorium series

noun

: a radioactive series beginning with thorium of mass number 232 and ending with thorium D which is the nonradioactive isotope of lead of mass number 208: thorium, at. no. 90→mesothorium 1, at. no. 88 (syn. radium 228)→mesothorium 2, at. no. 89 (syn. actinium 228)→radiothorium, at. no. 90 (syn. thorium 228)→thorium X, at. no. 88, (syn. radium 224)→thoron, at. no. 86 (syn. radon 220)→thorium A, at. no. 84 (syn. polonium 216)→thorium B, at. no. 82 (syn. lead 212) [or astatine 216]→thorium C, at. no. 83 (syn. bismuth 212)→thorium C′, at. no. 84 (syn. polonium 212) [or thorium C″, at. no. 81 (syn. thallium 208)]→thorium D, at. no. 82 (syn. lead 208)

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