A radioactive nuclide P decays into Q, and Q subsequently decays into a stable nuclide R. Which graph in the original figure correctly represents the time dependence of the amounts of P, Q and R?
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Question

A radioactive nuclide P decays into Q, and Q subsequently decays into a stable nuclide R. Which graph in the original figure correctly represents the time dependence of the amounts of P, Q and R?

G1 Physics · Accepted Answer

Initially, only parent nuclide P is present in appreciable amount. Therefore P decreases monotonically with time. Nuclide Q is produced from P, so Q initially increases. Later, as P becomes depleted and Q itself decays to R, Q reaches a maximum and then decreases. Stable nuclide R accumulates continuously and approaches the final total amount as t → ∞. Thus the correct graph must show: P decreasing, Q rising then falling, R increasing toward a maximum. This corresponds to graph 3. Correct optio…