Folks, I have a GMC-320plus logging data to my laptop and am in the process of comparing NoSalt to background. For NoSalt, I have acquired 1,388 minutes of data from 7/5 7:34 to 7/6 6:40, see the image (I don't know if the image successfully uploaded). The NoSalt is in a plastic food storage bag and the GMC is on top of the bag. Except for 3 spikes, the observed rate varies mostly between 0.01 to 0.02 mR/hr. My question is those three spikes, each between about 0.075 and 0.08 mR/hr: 7/5 12:34; 7/5 16:34; and 7/5 18:34 Each spike is attributable to a 128 cps value observed in either the 3rd or 4th second of the record for that particular minute. I'm wondering what might be the cause of that spike. I thought it might be somehow related to the electrical connections, but if that were so, I'd expect it to be more regularly spaced throughout the record. Is it maybe a gamma ray burst? I'm guessing and don't know. Thanks for your help.
The device is sensitive to electromagnetic interference. Maybe you could try to place it near a microwave and repeatedly turn it on WHILE the GMC is connected to mains. That could probably create spikes. Maybe try variations like, plugging them both in the same connector or running the GMC of battery.
I once observed ultra high readings near a plasma sphere circuit that was on until I put the GMC in a faraday cage. It's a good thing to do anyway. Put it in a cage.
GMC-300E+ V4.20 with sbt-11a alpha tube
My statements are "stuff-a-hobbyist-says" and not in any way professional.