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not_natty OP t1_jbxy8gs wrote

Reply to comment by mfb- in Is Radioactivity Inversely Proportional to Half Life? by not_natty

Is this Y-90 accumulation where you get one Y-90 decay per Sr-90 decay similar to saturation in pharmacokinetics where at 5 half-lives the levels are 'stable'?

Assuming Sr-90 and Y-90 are pure beta emitters, does this mean that if I start with pure Sr-90 at x Bqs, given some time I'll actually end up with more radioactivity in the system, as in the combined Bqs of Sr-90 and Y-90 will be greater than the initial radioactivity of pure Sr-90?

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mfb- t1_jby09vc wrote

Could be similar to pharmacokinetics but I'm not familiar with the use of saturation there. You get this effect whenever you have an (almost) constant production and a decay that's proportional to the concentration. If we look at something like a month then Y-90 production is almost constant because Sr-90 decays slowly over decades. Y-90 decays are proportional to the amount of Y-90, so you start with almost nothing and approach an equilibrium within a few times the half life (~1 week).

If you start with a pure Sr-90 sample then its overall activity will double in that time frame, yes.

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