By that rationale, the theory stated below by Magicsound is just as valid as yours:
I see where you're going with this, but I did not mean to suggest that all criticisms are equally valid and do not need to be vetted. I was just arguing that criticisms that have a vague sense of plausibility have an easier time making it through than primary claims that have a vague sense of plausibility. It seems fine to vet criticisms and throw out the bad ones. But the contamination possibility remains, and if strontium doesn't fit the case, then perhaps another radionuclide will. It's something that needs to be ruled out, and I think that will be hard in the case of an experiment that for whatever reasons wasn't able to take more active measures to demonstrate that the live cell was the source of the purported activity.
When it come to these kind of supposed refutations, I think it is necessary to do more than just "raise the spectre". Otherwise we'd be here all day, slowly descending into a rabbit hole of weirdness.
For instance: Given the "signal" graph, (and knowledge of the scintillator programming) we can calculate the number of counts* received. Then, knowing the length of measurement 7, and the half-life of Strontium, we could calculate the minimum size and weight of this alleged free-floating particle... Which should give an understanding of whether it would actually float around the lab, or just fall to the floor.
It might not be completely conclusive, but at least it demonstrates that we are not just waving our hands and pulling rabbits from hats, as it were.
Yes, I agree that more followup is needed for the strontium question. I'm not even convinced that strontium is the most plausible case. My point was more general: let's put more effort into substantiating claims, and if we can't, let's be ok with something like: "This experiment didn't prove anything, and we weren't able to rule out contamination or cosmic rays, if only because the signal in trace 7 sort of happened to us by surprise, and we weren't able to further investigate it while it was happening. But it was suggestive, and we wonder whether it might have gone back to bremsstrahlung originating in the live cell. We obviously have a lot more work to do to get to this conclusion."