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The first graph is from a lightning sensor, a small coil of wire inside the house that picks up the electromagnetic component of lightning. The range of this device is estimated at 20, maybe 40 miles. The sensing coil is oriented vertically so it is somewhat omnidirectional, and less sensitive than horizontally oriented coils. When a lightning storm approaches the counts per minute should read higher(20-100+ cpm) than normal (under 10) as you can see in the example graphs below. You can find a world map of lightning strikes here, or a midwest USA lightning map here.
The lightning sensor also picks up some local electrical noise (room light switched on, refrigerator motor starting, etc), so there is almost always some small reading (1-5 cpm) on the lightning/Noise graph. You may notice a sharp spike on an otherwise lightning free day, I probably did something in my electronics room where the sensor is located to cause that.
The second graph is readings from a background radiation monitor (simple Geiger Counter). What it measures is mostly Gamma rays, from various sources both here on earth and from space. Sensor is a common Soviet surplus SBM-20 Geiger Muller tube mounted inside a thin walled PVC pipe, on a wall about 1 foot above the first story roof at our home in Mineral Point, Wisconsin. This tube operates at 400VDC. You may view long term records of readings from this station on Radmon.
Radmon hosts a world map of background radiation readings. These readings are from individuals with radiation monitors similar to the one presented on this page. Some readings on the map will always be different from others because there are a variety of detectors being used, nothing is standardized between detectors. If you see a cluster of red dots, that may be some problem! One red dot may be a problem, more likely an issue with the monitoring station. Sometimes people perform experiments and forget to disconnect their monitor from the map, sometimes there are other issues.
The third graph is a "cosmic ray detector." The device consists of two STS-6 Geiger Müller tubes spaced a few inches apart, with lead shielding on top, between, and under the GM tubes. The lead helps shield the tubes from terrestrial radiation triggering both at the same time. This is a "telescope" in that it only detects cosmic rays coming from one general direction, spacing of the GM tubes can be varied for a wider or narrower field of view. When the products of cosmic particles reach the device, they are able to penetrate all the lead and both tubes, while normal background radiation detected in this setup can not do this. The pulses from each tube are set about 0.5 millisecond, if I am not mistaken that brings the probability of both tubes randomly triggering at the same time to less than one in a million. But my math skills are horrible, please correct me if you read this and know my figures to be wrong! firstname.lastname@example.org
Sometimes, you may see a small rise in measured radiation when a thunderstorm is indicated in the lightning graph.
This is likely due to short-lived decay products from radon washing down from suspension in the air, not Fukushima or similar fallout. You can see several examples of this at the bottom of this page (click me).
In the first example, rain arrived as lightning peaked.
Lightning itself has no impact on measured radiation.
In this second example, only light rain arrived when lightning started, more rain came a short time later.
Another example. Rain came with the lightning, more rain after the lightning peak.
One of the highest lightning counts I had seen since setting this up. Pretty heavy and long rain after the lightning arrived. Radiation count bump about as high as I have seen for a rain event.
2020 August 10 had an even higher lightning count, 585CPM at one point! It was quite a storm, too bad it happened during daylight hours or it would have been fun to watch..
Another example of a rain storm increasing ionizing radiation.
Not alarming, just interesting. Rain came mostly after the lightning peak.
Interesting that this was not observed during winter snows, only rain appears to cause a radiation peak.
As mentioned above, it is not lightning that causes an increase in radiation detection, it is rain that comes with lightning.
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