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Comment by ggm | Hacker News Reader

Half life tracking presumably would give a "birthday" for the cesium-137 source. Given they suspect scrap contamination in a recycling smelter, its at best informing to root cause. That, and the length of the tail yet to come as it passes down the ladder.

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“Half life tracking” isn’t really a thing — decay is a memory-less process (by definition), so there’s no distinction in decay rate between a lot of old Cesium 137, and a bit of young Cesium 137. The way to put an age on the contamination is by looking at the ratio of Cesium 137 and Barium 137, which presumedly someone has done…

Thank you for clarifying. My intent was where you get to, badly understood and expressed.

> "by looking at the ratio of Cesium 137 and Barium 137, which presumedly someone has done…"

That's impractical; the decay product Ba-137 is stable and already present in much larger amounts, compared against which the Cs-137 decay products are undetectable.

For similar reasons, Carbon Dating is relatively low precision.

I don't think it's the same situation, since there's a rough baseline rate of carbon-14 in nature (relative to carbon-12) which is continually replenished while alive. When it dies, there's no more carbon-14 added to the system, so we can determine how much is "left" from the ratio of carbon-14 to carbon-12. But there was no fixed % of ceaseium-137 to start with here, so we can't use the current % to determine age.

(Decay isn’t memory-less by definition, but we’ve empirically observed that it’s memory-less, and our current theories model it as memory-less. This is the opposite of “by definition”—“by observation” or “empirically”.)

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