Rain swipe: (UK)
Location: South Devon, England (10-15miles north of Plymouth)
Time: 15:04hrs GMT
Date: 15th Sept 2013 (can’t believe it’s mid September already YIKES!)
Altitude 92meters
My normal background in air is 34cpm
Background of test area is 41cpm (floor of my spare bedroom, my laboratory haha)
Geiger counter: Inspector EXP+
Weather: Lots of rain and all day too.
1 square meter swipe
Ten min timed count: 119.8cpm
And a nice glass of wine to wash down my late lunch haha
The rain arrived as predicted by the weather peeps. Glad I got to go out for a ride on bike yesterday in lovely weather. Its been raining quite hard all day. I took the usual 1sq/m swipe from the roof of my beemer as per norm. I then took a 10min timed count which came in at for arguments sake at 120cpm which has been the highest cpm I have had for a little time. Not like last years savage high counts. Anyway I was bored so I decided to conduct a half life on this low count sample and also see how the sample was decaying. After I took another ten min timed count approximately 45mins later it was pretty obvious to me because of the hundreds of half life test I have conducted that the half life time was going to be 60.5min.
So 60.5min after I took the 1st 10min timed count I took another measurement of the sample and it came in at 61cpm. So practically half of the original sample decayed away in 60.5min. (120cpm down to 61cpm). Bismuth-212 has a half life of 60.5min and is a daughter product of Radon-220.
Bismuth-212 (Bi-212) decays by alpha & beta at a ratio of 36% alpha & 64%beta, it is a gamma emitter also but this sample was so low only 120cpm one would need a scintillator detector to pick that up one would gather. I did some simple basic quick measurements to see if I could see this ratio to confirm that the half life of 60.5min was indeed most likely to be Bi-212. I did this by blocking the alpha particles with a sheet of paper and to see by how much the cpm was reduced compared to when no paper was blocking the alpha particles from reaching the Geiger Muller tube of the Inspector EXP+ pancake probe. Any counts per min (cpm) measured whilst the sample had a piece of paper blocking the alpha particles would therefore be either beta and/or gamma decay. I also blocked any beta decay by placing a thin piece of aluminium over the sample. When I did this the levels dropped back to background. Therefore this was an alpha and a beta emitter. I could then calculate the alpha to beta decay ratio.
Conclusion:
The rain that I measured at 15:04hrs today was indeed most likely Radon-220 washout. I measured one of its progeny/daughter products decaying which is quite easy to measure Bismuth-212, well according to my numbers.
Still 120cpm is 20cpm higher than my personal 100cpm threshold where I then wont allow Kaito (my furry faced son….my cat lol) out in the rain nor will I go out on my motorbike. I love riding in the rain too.
Although the pro nukers and the nuke industry would love us to believe that just because Radon washout can be a naturally occurring event it is still radioactivity decaying away and that decay or to look at it another way all those bullets firing off are firing off all their rounds very quickly and some with a lot of energy so Radon washout can also be dangerous.
I hope more people with geigers would do some simple follow up tests if you are bored like I was today to try and determine what type of decay they are measuring and its half life if at all possible.
Compared to last, year levels seem lower for me, but I would have to go through all my records to confirm this, but it feels that way. Just thought I would share with you gang my mid afternoon rain swipe observations.
Comments
Post a Comment