To illustrate @anon68287401’s example here is an actual measurement looking to quantify the amount of Po-210 in a urine sample:
Here’s a 12 hour count that gives a Po-210 minimum detectible activity of ~0.013 pCi (0.00048 decays per second) – the sample has an activity of ~0.035 pCi (0.0013 decays per second), so it is positive for Po-210.
At the resolution of this pic, one can hardly even see the Po-210 counts…
