How to Build a Home-Brew Radon Detector: Measure Radiation with a Webcam

First of all as typical the physicists use a SI unit that joe average USA doesn't use. The physicists like Bq which is basically odds of decay of a single particle. So 1 Bq/liter/second is one decay per second in a one liter jar. Not much. A legacy curie Ci still used by the EPA is something like about how many decays a chunk of radium gives off in a second or the length of the kings foot or some ridiculous. Anyway 1 Bq = 27 pico curies or pCi. So the EPA standard of 4 pCi/L translated into modern terms is 0.148 Bq/L

The dude provides his survey meter in Bq/cubic meter and we're talking Bq/liter so div 1000 because 1000 liters in a cubic meter. So the survey meter is reading 0.159 Bq/L.

I am a bit confused why the dudes test area is reading about 10% over the EPA standard for radon contamination. I guess he needs a source that should just barely be positive. In that way, it makes sense to run the tests in that location.

As a side note I'm guessing his homemade gadget has a volume of a tenth liter. That would imply about 0.0148 Bq/sec activity in his homemade gadget. He claims a detection level of 5.2 Bq/hour (edit: 5.2 hits/hour) so 0.0148 * 60 * 60 = thirty something actual Bq activity (edit: hits) happened in his detector of which he captured 5.2 on average. That means his homemade gadget is about 13% likely to detect any individual decay that happened inside of it. That's actually pretty good!

I can't be bothered to continue with a statistical analysis but the 10% claim sounds about reasonable because of what boils down to quantization noise. So your threshold is about 5 pings per hour. He gathers 20 hours of data thats about 100 pings total. The longer you gather and average data the more sig figs you get to accumulate with a sqrt of the number of samples (way too long story). So he's saying with 100 pings his data reduction indicates with X% certainty the actual number is within 10% of the legacy 4 pCi/L

Someone else can pick up the statistics torch and run with it from here.

The TLDR is given infrequent discrete events you need a lot of them to have a statistically relevant discovery if you rely on averaging them together to gain a sig fig in your results.

edit: re-reading I found this "In order to make it more sensitive, I added an electrostatic concentrator to capture one of radon’s alpha-particle-emitting daughter products"

[0] http://en.wikipedia.org/wiki/Uranium-238#Radium_series_.28or...

A typical camera target is about 3 mm on a side, for a total sensitive area of ~1e-5 m2. The muon flux at sea level is about 1 per cm2 per second, or 36 million per m2 per hour, or 360 hits per hour on a camera target, so even granted that the "active" area of the target is only a few percent of the physical area, muons more than account for the signal he is seeing, and muons deposit a lot of energy.

The electostatic concentrator is an interesting feature. Charged nuclei typically attach themselves to dust motes in the air, which are then swept along by the E-field. It isn't clear why he needs such high voltages to get 50 V/m over a few centimetres, and in my experience Cockroft-Walton generators are easy to build but hard to make work. With such tiny capacitors any stray leakage current would destroy the effect, and he does not anywhere measure the voltage produced.

The enhancement of the count rate could be accounted for by electrical noise from the CW driver circuit.

This is pure speculation on my part, based on a good deal of experience designing and building radiation detectors, but I'd like to see a lot more evidence before I said this was an effective radon detector.

An alternative, easier to debug and demonstrate, and more likely to work approach would be to use a commercially available activated zinc sulphide sheet with the camera target as the detector: http://www.eljentechnology.com/index.php/products/zinc-sulfi...