>The gm500 has two tubes right? I don't know how it chooses which one to use (probably changes after it gets saturated), but if the standart tube is something like a sbm-20 or j305 it probably picks up quite a bit of beta that goes through the ampoule, and the cpm to usv is most likely calibrated with the energy of cesium, so i think the actual doserate is lower that what it shows

I placed whichever tube was more sensitive over the sample (one of them barely detected anything). Good call on the calibration.