MadSci Network: Physics |
There are actually a lot of things that can cause variations in background radiation - the most likely in your case would be something with the sun. But first, let me tell you a little about background radiation and where it comes from, which should help explain why I think that cosmic radiation is the cause. One source of background radiation is radioactivity in the rocks and soils. Many parts of Sweden are rich in black shales, and other parts are rich in granites - both of which can contain fairly high levels of natural uranium, thorium, and potassium. The soils are formed from these rocks, so they contain similar levels of these elements. The radioactive decay of the U-238 in these rocks and soils leads to radon, which is another of the four sources of natural radiation. The third source of natural radiation is the potassium in our own bodies. About 0.01% of all potassium is naturally radioactive K-40, which gives us radiation dose internally. And the final natural source of radiation is from space - cosmic radiation comes from both the sun and from outside our solar system. As you go further to the north (say, by living in Sweden), the earth's magnetic field helps to funnel this radiation into the atmosphere, so cosmic radiation levels are somewhat higher as you approach the north and south poles. So.... The local rocks and soils are not going to change very much. So we can assume that radiation levels from these are fairly constant. Similarly, the amount of potassium in our bodies remains fairly constant, so we don't expect them to change. I suppose that weather can trap radon close to the ground, but radon emits alpha radiation, to which your geiger counter is not terribly sensitive. I suppose, too, that having a large party (or stocking your home with bananas) will increase K-40 radiation in your home. But neither of these is going to give as high of an increase as you describe. So we're left with cosmic radiation. First, solar flares will increase radiation levels significantly during the time that they are bombarding the earth. And this effect will be more pronounced in the northern latitudes. A few times a year, we will see something sufficiently strong as to be "visible" at ground level. This is the most likely cause of what you are seeing. Another possibility is a momentary weakening of the Earth's magnetic field, allowing more radiation to reach the ground. One resource that might interest you is the Space Physics Interactive Data Resource (SPIDR), found on-line at http://clust1.wdcb.ru/spidr/. You will need to establish an account to use it effectively, but there is a wealth of information - I used some of their information for some of my research several years ago. Among the data you can retrieve are records from any of the 100+ cosmic radiation monitoring ground stations. I'd suggest seeing if your meter readings can be correlated with any spikes in these monitors. A solar storm would show up at many stations. And remember that the sun can affect radiation levels on the night side of the earth too - especially in the farther north and south. Finally - let me talk about nuclear power plants a little bit. While it is true that nuclear power plants can release radioactivity from time to time, the amount of radioactivity they release is fairly small, and not likely to cause anything that your meter would measure. Or, looking at it another way - any nuclear power plant release that would register on a geiger counter is going to be fairly severe and will likely show up on professional monitors all over the northern hemisphere. I live only about 10 miles (16 km) from a nuclear power plant and I have never noticed any changes in my environmental radiation measurements because of the plant. So - a very good question, and I hope that this answer helps out!
Try the links in the MadSci Library for more information on Physics.