It has a half life of just 138 days so in only 4.6 years the missing Polonium will be equivalent in radioactivity to Radium, which is known to cause cancer. This doesn't sound like something that should be treated lightly.
At first, I was very surprised to hear it's a thing, but apparently it is and one can buy for just $170:
https://amstat.com/products/anti-static-brush-with-ionizing-...
Not sure about this particular polonium isotope. But don't expect something to be harmless after 10x the half-life per se.
Radium, in contrast, emits gamma radiation, which presents more of a threat to casual bystanders. All of which is to say: you can't just compare "radioactivity" levels and extrapolate to "danger".
Cheap eBay Geiger counters will probably tell you if gamma rays are an immediate danger, and if you're close enough to have problems, your probably also close enough to detect it.
It's not an either/or sort of thing. Gamma decay occurs after alpha or beta decay, so a gamma source will also emit alpha or beta radiation. In the case of Cs-137, it emits a lot of beta radiation. Normally this is shielded, but normally it doesn't fall off a truck..
They were letting undergrads handle it, so definitely wasn't a large source.
Also, hey Chase! Funny to see you in the wild (Ferdi here)
The dose of radiation has different meanings; absorbed, equivalent, effective. These are just different calculations, starting from how much energy the body received (absorbed), to taking into account the different kinds of radiation whose effects differ (equivalent), to where in the body the dose as received (different organs at different risk, effective).
The half-life of 210Po is 138 days, so it's ~10x less active than 223Ra. That's meaningless with respect to the health risk, though; the activity of the sample is ultimately selected by its intended use. Most samples are sized according to the dose requirements. At least, that's my understanding (physics, not medical). In general we don't want to over-size a source as there are greater regulations. Similarly, we don't want sources to become useless too quickly.
In any case, this is definitely bad — 5000x less activity is not good if it's greater than the lethal dose. Because radioactive sources are so small, the risk is not likely to be distributed; you get the whole dose, or nothing.*
* Unless it gets dispersed somehow.
Dose: https://en.wikipedia.org/wiki/Equivalent_dose#/media/File:SI... LNT: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2663584/
> * Unless it gets dispersed somehow.
Exactly, the real worry was that it would get crushed and would be breathed in, in which case it would be a real problem.
But even so, the school had to file a report with the nuclear regulator iirc. Lot of paperwork.