n-hour average

Hi,

I've recently bought a geiger counter (netio gc-10) with an sbm-20 tube and made some measurements in my house.
I've expected some chaotic like fluctuations, which of course occur on a short time reading. But I also noticed also a bit of long time oscillation in the range of hours.
Where do they come from? There was no rain or whatsoever.
The histogram looks unsuspicious to me, gaussian-like.

This is the measurement over 46h:


And the histogram (CPM):



The elevated levels are probably because of the granite roof and granite walls

Many sensors show a daily pattern, normally attributed to Radon leaking from the soil and dispersing at various rates depending on the weather/climate. Outdoor sensors show this the most.

Ah, I haven't thought of that.

Though i thought that radon was only radiating alpha rays (which the SBM-20 can't detect).
But i just read that radon and some elements in the decay chain also emit gamma rays.

Interesting, i should start a measurement in the cellar next.