Unusual peak

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1 week 4 days ago #4769 by FSM19
Unusual peak was created by FSM19
Yesterday I got a strange peak in readings counts went up from about 16:30Z until 19:30Z, then dropped off until about 22:00Z. Any ideas? There were no significant meteorological events. Another counter, about 1ft away also showed an increase, but not as marked, this is a similar type counter but with some extra beta shielding.
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1 week 3 days ago #4770 by mw0uzo
Replied by mw0uzo on topic Unusual peak
Interesting, did you move around any radioactive sources?

What's interesting is the time taken to reach peak and then go back to normal. The same time, as if a source was slowly, but steadily moving past.

Rain with 'fallout' tends to rise quickly then fall more slowly.

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1 week 3 days ago #4771 by FSM19
Replied by FSM19 on topic Unusual peak
No moving of sources at all. No rain here for weeks, although last week we had very strong winds. We have also had a number of forest fires in the district, although there was no change in readings on Saturday when we had smoke from one of them, but that lasted all day.

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1 week 3 days ago #4772 by Simomax
Replied by Simomax on topic Unusual peak
Radon maybe?

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1 week 3 days ago #4773 by FSM19
Replied by FSM19 on topic Unusual peak
I do get a diurnal variation that I associate with radon, but this was a far bigger excursion than I have seen before. I have had a number of peaks in the past but was able to identify causes, principally due to movement of the probe relative to my sources.

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1 week 1 day ago #4777 by Bert490
Replied by Bert490 on topic Unusual peak
I think this effect could be explained by considering air pressure changes. If the soil is dry, radon gas deep down would seep upward with low surface pressure. This may contribute to the diurnal variation seen by many outdoor stations. With geographic variations in Radon levels, a higher-Radon area may experience this seepage, then the wind could carry it a bit before it dissipates. I've imagined a study to measure this effect, but it would require I think a dense grid of sensors.
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