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•• The mass number A decreases by 4 in α decay, but is unchanged in β or γ decay. This means that throughout a radioactive series A changes only in increments of 0 or 4. Thus, if A happens to be a multiple of 4 (A = 4n) in the original parent, it will remain a multiple of 4 in all members of the series. This is what happens in the 232Th series, which is therefore called the 4n series. In the same way, there are three other possible series: (4n + 1),(4n + 2), and (4n + 3). (a) What are the original parents of the (4n + 2) and (4n + 3) series? (b) Use the data in Appendix D to explain why the (4n + 1 ) series is not found naturally.
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