uranium series

:  a radioactive series beginning with uranium I of mass number 238 and ending with radium G constituting the nonradioactive isotope of lead of mass number 206: uranium I, at. no. 92→uranium X₁ at. no. 90 (synonym thorium 234)→uranium X₂, at. no. 91 (syn. protactinium 234)→uranium II, at. no. 92 (syn. uranium 234)→ionium, at. no. 90 (syn. thorium 230)→radium 226, at. no. 88→radon 222, at. no. 86→radium A, at. no. 84 (syn. polonium 218)→radium B, at. no. 82 (syn. lead 214) [or astatine 218]→radium C, at. no. 83 (syn. bismuth 214)→radium C′, at. no. 84 (syn. polonium 214) [or radium C″, at. no. 81 (syn. thallium 210)]→radium D, at. no. 82 (syn. lead 210)→radium E, at. no. 83 (syn. bismuth 210)→radium F, at. no. 84 (syn. polonium 210)→radium G, at. no. 82 (syn. lead 206) —called also radium series