It's the same experiment with the geiger tube. The data was collected with
a multi-channel scaler.
There are 16k time bins recorded at 20 second intervals.
The first several bins record only background.
At some point the sample is placed near the detector. It appears to have
been done about 10 seconds into a counting cycle.
The very next bin (500 seconds) should be purely data with the sample in
place.
I did move the detector closer to the sample and took some care to center
the sample better on the end of the tube. I believe that this is largely
responsible for the increased count rate.
There seem to be some interesting increases in the activity near the end of
the run. There appear to be increases in background activity that last a
few minutes with some rise and fall. This may be the sort of thing that
one would expect from solar activity. But it's possible that other
external factors would influence detector gain in some way. And they may
simply be random coincidences.