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Annonn Annonn
wrote...
Posts: 116
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A month ago
An element undergoes the following sequence of decay reactions: alpha, beta, alpha, beta, alpha and produces radium-223. What was the original element?


238U

227Th

231Pa

231Th

235U
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Woo
wrote...
A month ago
we have 3 alpha decays, which reduces to proton by a count of 2 and atomic mass by 4 each time. beta increases the proton count by 1, but leaves the atomic mass the same.

radium-223 has a mass of 223 and 88 protons.

88 + 2 + 2 + 2 - 1  - 1 = 92 -- uranium

235U is the answer
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