agree, this device looks like it can detect any alpha radioactivity regardless of what is emitting it.
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"
Alpha radiation from outer space can't penetrate the atmosphere, for much the same reason you can't fire bullets 1km underwater from the surface. The only source of alphas from cosmic radiation would be from some sort of indirect effects such as direct fissioning (at ground level) of a nuclide by cosmic radiation into an alpha + daughter.
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 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...
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.
Also ionization loss by fast muons is pretty low, it's in the "minimum ionizing particle" regime, and most cosmic muons we see "down here" are in the >1GeV/c area.
But again, I think your doubts about the numbers is certainly warranted. With a experimental setup needing such a long exposure time to yield statistically usable numbers, I think one cannot really prove a lot. Certainly a detector more suitable to the task of counting radioactive decay, such as a calibrated large-volume geiger counter, would be better. At least one should run both setups in parallel for an extended period of time to be able to do cross-corralations.
"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?
I guess the author was thinking about instrument accuracy, which is usually expressed as percentage of full scale, or percentage of the actual reading, or percentage of the scale span. So I would guess the author wanted to say that it would take the detector about 20 hours to reach the accuracy of +/- 10 percent of the reading.
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.
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.
14 comments
[ 2.5 ms ] story [ 39.4 ms ] threadedit: 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...
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... (paywalled, though)
I think you are overestimating the cosmic muon flux quite a bit, see the particle data book for the discussion of cosmic muons.
http://pdg.lbl.gov/2012/reviews/rpp2012-rev-cosmic-rays.pdf (page 5)
Also ionization loss by fast muons is pretty low, it's in the "minimum ionizing particle" regime, and most cosmic muons we see "down here" are in the >1GeV/c area.
http://pdg.lbl.gov/2013/reviews/rpp2012-rev-passage-particle... (page 4 is muons on Copper)
But again, I think your doubts about the numbers is certainly warranted. With a experimental setup needing such a long exposure time to yield statistically usable numbers, I think one cannot really prove a lot. Certainly a detector more suitable to the task of counting radioactive decay, such as a calibrated large-volume geiger counter, would be better. At least one should run both setups in parallel for an extended period of time to be able to do cross-corralations.
What does 10 percent accuracy mean? Doesn't that mean it's usually completely wrong?
http://spectrum.ieee.org/geek-life/hands-on/ looks like a great site, I can't wait to build some of these things!
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.
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.