HG Branzell posted this a couple days ago: LINK
I have some misgivings about the results on that webpage.
Why is the background so low? Other tests on the same page use 45 to 70 CPM, rather than 10. A background of 70 CPM reduces the surprise from 130 x background to 18.6 times "background". I wonder if it (10 CPM) is the same background as where the dust came from.
The specific device and method used is not mentioned in the spectacular "demonstration".
A swipe of dust is not at all like dust floating in the air.
"The Air Sampler attachment for the GM-45 allows you to install a filter directly in front of the GM-45 detector window. The GM-45 is a geiger counter detector with a large window, able to detect alpha, beta, and gamma radiation, making it ideal for detecting radon. The fan built into the unit pulls air through the filter, depositing radon decay products on the face of the filter. This essentially greatly amplifies the signal seen on the GM-45. As shown in the graph below, a nominal count rate of around 70 CPM is amplified to around 4000 CPM, a gain of around 57 times. The actual increase in readings from radon daughters is even much higher, as will be explained below."
- Blackcat Systems webpage http://www.blackcatsystems.com/GM/acc4.html
"In this case, a background value for cosmic rays and other such radiation of 42 CPM was used. The multipler for the air sampler data used was 0.008. The apparent gain of the air sampler is the reciprocal of this, or 1/0.008 which is 125. So the apparent gain in readings from radon and its decay products is 125. This is of course a huge number, which is why using the air sampler makes observing even small variations in radon readings so easy. They are greatly amplified, and the constant reading from cosmic rays is greatly reduced in a relative way. "
- Blackcat Systems (same webpage).
So is the background and method used the same for the background of 10 CPM as for the dust wipe at 1300 CPM? Are they comparable?
Is it more correct to use the gain factor on the background to get a proper comparable, leaving us with a "corrected" BG of 570 to 1250 CPM?
This would give us a new ratio of 1300/570 = 2.28, or 1300/1250 = 1.04 .
Is it likely that the wording and method are used in a way that might influence the purchase of the air sampler or other detector?