
How to Build a Home-Brew Radon Detector: Measure Radiation with a Webcam - taivo
http://spectrum.ieee.org/geek-life/hands-on/how-to-build-a-homebrew-radon-detector
======
dm2
"At this level of sensitivity it would take the detector about 20 hours to
determine whether radon was present at levels recommended as actionable by the
U.S. Environmental Protection Agency with about 10 percent accuracy."

What does 10 percent accuracy mean? Doesn't that mean it's usually completely
wrong?

[http://spectrum.ieee.org/geek-life/hands-on/](http://spectrum.ieee.org/geek-
life/hands-on/) looks like a great site, I can't wait to build some of these
things!

~~~
VLM
If there's one thing radiation types like, its multiple measurement standards
and massive unit conversions.

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.

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Crito
It's probably worth mentioning that some states offer free or discounted radon
test kits. If you live in an area with elevated radon levels, you should look
into getting your home tested.

Discovering that your home has too much radon in it isn't disastrous either.
Homes can be retrofitted with proper ventilation to lower radon levels to safe
amounts.

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lutorm
How do you know the hits aren't cosmic rays? It seems a few hits per hour
could easily be cosmic rays, unless they are distinguishable somehow.

~~~
tjradcliffe
I'm more than a little skeptical of this. While it is all correct in principle
--a webcam CCD target can certainly detect alphas, and electrostatic fields
can sweep charged particles into a detector--the details are problematic, and
there's no actual demonstration of the sensitivity of the device.

A typical camera target is about 3 mm on a side, for a total sensitive area of
~1e-5 m __2\. The muon flux at sea level is about 1 per cm __2 per second, or
36 million per m __2 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...](http://www.eljentechnology.com/index.php/products/zinc-sulfide-
shifting-plastics/100-ej-440)

~~~
taivo
The author's conference paper [0] has more details, although not enough to
remove all the doubts.

But I guess the main goal of the article is to show that, even though
"radiation detector" sounds like a complicated thing to most people, or at
least requiring some nontrivial components, it is actually possible to get
started with DIY experimentation with very few and simple components and
little effort. You might indeed get better results with ZnS:Ag phosphor
sheets, but by showing that it is possible to build at least something with
just a webcam that people already have you massively increase the likelihood
that the reader actually starts to build and experiment. And when people
already start experimenting, then many of these potential problems get
incrementally noticed, figured out, and removed, and all kinds of cool
projects can result. But yes, it would, indeed, have been nice if the article
would have provided more information about testing the detector against
various potential interferences and problems.

[0]
[http://spie.org/Publications/Proceedings/Paper/10.1117/12.20...](http://spie.org/Publications/Proceedings/Paper/10.1117/12.2033635)
(paywalled, though)

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vincetogo
Shouldn't that be radioactivity? Light is a form of radiation, and I'm pretty
sure that webcams can already measure that.

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pavel_lishin
I eagerly await a comment from someone who builds one of these, and discovers
that their house has much more radon than is safe.

