MadSci Network: Physics
Query:

Re: Possible casues of temporal variation of background radioactive radiation

Date: Thu Mar 29 06:56:19 2007
Posted By: Andrew Karam, Assistant Professor
Area of science: Physics
ID: 1174841370.Ph
Message:

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!


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