Variation in Total CPM Over Time

[Neil.]

I have read some articles about diurnal cycling of background radiation and thought it would be interesting to look for this here. My portable scintillation unit measures CPM over 1 second intervals and reports this via a USB cable to the desktop PC. This count rate fluctuates quite a bit each second so using a temporal low pass filter of a running average over 300 seconds updated every second allows viewing long term changes on the counts per minute graph.

The unshielded NaI:Th probe was located on my workbench in my basement for this experiment and the data were graphed for about 8 days. There is a cyclic change in CPM seen which peaks about every 24 hours. This was intended to be a preliminary survey so there is no analysis with time of day or possible variables such as weather or temperature outdoors. This could be interesting to pursue.

[Sesselmann]

Neill,

Interesting experiment but very difficult to achieve a definitive result. Temperature and atmospheric pressure changes affect the count rate, so it is quite normal to see a 24 hour cycle in these measurements.

It is usual to compensate for temperature and pressure, but then you have the issue of cosmic rays which can and do fluctuate, so the science here is to know your limitations and decide how far down the rabbit hole you want to go.

Maybe you have a theory or a reason to suspect variations in the BG, in which case you would try to match observation with theory after making all the compensations for pressure, temperature, cosmics etc..

Here is a link to the Russian neutron monitor where you can compare the raw data with pressure compensated data.

http://cr0.izmiran.rssi.ru/mosc/main.htm

Steven

[Boris]

Hi Neill,

is the top in the 'sine wave' day or night?

Would it be an idea to repeat the experiment using the lead castle, packed in Styrofoam to eliminate temperature fluctuations in the day night cycle?

this site is also very cool, you can get the data for every measuring station of you select the station first en choose a time frame...

http://eurdepweb.jrc.ec.europa.eu/Eurde ... fault.aspx

Cheers, Boris.

[Neil.]

Update:

I was able to reconstruct the time of day for the peaks and they occur between 11 AM and 1 PM local time. This would tend to rule out a "sunrise" hypothesis which relates morning temperature rise to radon being carried up from ground level according to a report I read, however this was done with an elevated sensor and mine is under ground in my basement.

Since I did not record any of the environmental variables there is nothing with which to correlate the peaks except time of day. This is actually a spinoff from the "real" experiment where I was checking the reliability of a new USB link connected from the counter to the desktop PC via Bluetooth modules. This link proved reliable by operating continuously for about 8 days without losing connection.

Most likely, I will not pursue the diurnal cycling since it would be a lot of effort to properly account for confounding factors just to replicate studies which have demonstrated this effect. Nonetheless, it is an interesting effect to observe.

Neil

[WillemG]

Hi Neil
Could the peak between 11 AM and 1 PM arise from flux by the sun ?
Sun radiation reaches its maximum during this time interval
In fact radiation from the sun will contribute to cosmic radiation.