This is the kind of question which made the piclist such a great place to be - too bad there aren't many of these questions nowadays. Chris did a really good job answering this. I just wanted to add, for perspective, the literal meaning of 1 pC/L. 1 Curie is defined as the activity (decay events per second) of 1 gram of pure Radium 226, which is about 37 billion events per second. A picocurie is 1 trillionth of this, or 0.037 events per second. So 1 pC/L is only 0.037 events per second per liter. This should help you to see why some significant amount of averaging is needed to get a good measurement at such low concentrations of radioactive material. I have a vintage CDV-700 6B geiger counter with an aftermarket modern pancake probe (like Chris mentions). In a series of tests I did about 2 years ago, my geiger counter read a background reading in my apartment of 47 counts per minute with no cover on the probe and 42 counts per minute with a plastic cover, each averaged over about an hour. I think most of this difference is from the reduced flow of Radon to the face of the probe. I think your only hope of obtaining a faster reading update rate is to use a fan to draw large volumes of air into your sensor. The only way that this will help you, though, is if you either compress the air and have a sensor inside the compressed air volume OR have a filter which you collect solid Radon decay product particles on. Sean On Sun, Sep 30, 2018 at 3:30 PM Chris Smolinski < csmolinski@blackcatsystems.com> wrote: > Coincidentally, I sell geiger counters. So the following may not be > unbiased :) > > You can detect radon by proxy by picking up the decay of it's daughter > products. It's non trivial to convert geiger counter readings into radon > levels (pCi/liter) and while my detectors can be used to detect radon, th= ey > don't measure actual radon levels, and I don't sell them as products to d= o > such. If your goal is to get accurate radon levels, you should buy a > product designed to do that. > > But you can observe changes in radon levels fairly easily by observing th= e > change in the geiger counter output (counts per minute) as it is relative= ly > linear. From experimentation, it varies with the weather; high and low > pressure systems can affect the flow of radon gas from the ground into yo= ur > house (typically the basement). You can even use a fan and piece of filt= er > cloth to trap the radon daughter products in front of the geiger tube, > essentially amplifying the signal. (I sell such a contraption) > > A "pancake" style geiger tube has a large area mica window, and is > substantially more sensitive to the alpha and beta rays from the radon > products vs a small diameter end window tube, it's a function of the tube > window surface area. Of course you can increase your averaging time perio= d > to reduce statistical noise, the rule that doubling the averaging period > reduces the noise by the square root of two applies. > > "Typical" background radiation levels vary with the sensitivity of the > geiger counter which is a function of the tube type and size. In > engineering units, 10-20 uR/hr is a good ballpark figure. Higher if you > live at high altitudes or in areas with high background radiation levels = .. > This is 10-20 CPM with a small end window tube and maybe 45-90 CPM with a > large pancake tube. Mostly what you are detecting here is cosmic rays > (hence the altitude variation), the pancake detector is not significantly > more sensitive for them. > > Chris Smolinski > Black Cat Systems > Westminster, MD USA > http://www.blackcatsystems.com > > > > > > On Sep 30, 2018, at 12:24 PM, Wouter van Ooijen wrote: > > > > > >> I would like to learn: what it would take to design my own radon gas > meter? > >> (For fun, not commercially) Any advice or links to resources (formulas= , > >> charts) would be greatly appreciated. > >> > >> > > > > The setup you describe doesn't measure radon perse, but alpha particles= .. > > As far as harm to you that doesn't matter much. > > > > The detector you describe is a Geiger-Muller tube. The main challenge > > (apart from filling the tube with a specific gass at a low pressure) fo= r > > detecting alpha particles is that nearly everything (including a sheet > > of paper, to give you an idea) will block alpha particles. A very thin > > sheet of mica seems to be the preferred window material. Summary: don't > > try to build your own alpha-detecting GM tube, buy one. > > > > The rest of the circuit isn't that special and examples can be found on > > the web. > > > > You probably won't gain much in 'instanteneous readout': the amount of > > (detected) alpha particles is very low, so averaging over some period i= s > > required to get a measurement with some accuracy. > > > > -- > > Wouter "Objects? 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