Thank you Wouter, Chris, and especially Sean. >From what I have read a basic ionization chamber like the one described by Sean Breheny and linked to [1] by Brooke Clark is exactly what I am looking for. A metal tube with center electrode and forced air via fan sounds easy to construct. Once set up periodic readings of leakage current (possibly through amplifier) via multi-meter would provide me with the information I am looking for [2]. Although I am somewhat unclear as to how operation of an ionization chamber with a filter (to trap solid radon by products) would work. [1] http://www.techlib.com/science/ionchamber.htm [2] although dust, humidity, and temperature will likely cause quite some variation On Sun, Sep 30, 2018 at 9:18 PM Sean Breheny wrote: > > I just thought of another thing to think about - there are three kinds of > radiation detectors, considered by function: > > 1) Single-event non-proportional detectors > 2) Single-event proportional detectors > 3) Continuous rate detectors > > Category 1 is mostly Geiger-Mueller tubes. Category 2 includes > scintillation detectors (material which emits light in response to > ionization, coupled to a sensitive photodetector like a photomultiplier > tube or avalanche photodiode) as well as gas-proportional tubes. Categor= y > 3 is mostly ionization chambers. > > In this context, single event detection means that there is a good > probability (>10%) of seeing each individual decay event whose emissions > intersect the detector. Actual probability will depend on type of radiati= on > (alpha, beta, gamma, neutron, muon, etc.) and energy level of the > particles. Proportional means that information about the energy level of > each event is preserved in the detector output (usually by a varying > amplitude of output pulse). Continuous rate means that the detector doesn= 't > output pulses but rather a current which is proportional to the radiation > level - but this also assumes that the radiation level is high enough for > the continuous current to be more than just a few electrons per second) > > The same basic detector CAN operate in all three modes/categories by > varying the voltage applied and the pressure of the gas inside. An > ionization chamber measures the leakage current through an air gap with a > moderately high applied voltage (maybe 250V). More radiation means more > ions generated which means more leakage - but each ionization event makes > only a few electrons so you can't detect individual events. However, this > also means that the detector cannot be overwhelmed by even very high > radiation levels. Going to a slightly higher voltage (about 600V usually) > and lower gas pressure, some gas-multiplication effects can happen. This = is > where each ionization event causes a localized avalanche. There is a > multiplication factor but it isn't so high that the entire tube is ionize= d > during each event. Therefore, within certain resolution limits, energy > information is preserved. Going even higher (900 to 1000V) and using > special mixtures of gasses makes a GM tube. The secret to a GM tube is th= at > each ionization event not only causes an avalanche but there is UV light > emitted from the avalanche. This UV light then causes the gas in areas > surrounding the actual ionization event to ionize and break down into an > avalanche. This then in turn produces additional UV light until the entir= e > tube breaks down and conducts at once. This produces a massive > magnification factor, making single events easily detectable, BUT you als= o > need a quenching mechanism (in a GM tube this is part of the gas mixture > which causes ion recombination to overcome the avalanche effect after a > brief time - roughly 10s of microseconds) otherwise the tube would remain > broken-down indefinitely after just one event. This means that a GM tube > can be easily saturated and read almost no counts at all in response to > very high radiation fields. It also means that information about the ener= gy > of the radiation per event is lost. > > 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 rad= on > > levels (pCi/liter) and while my detectors can be used to detect radon, = they > > don't measure actual radon levels, and I don't sell them as products to= do > > 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 = the > > change in the geiger counter output (counts per minute) as it is relati= vely > > linear. From experimentation, it varies with the weather; high and low > > pressure systems can affect the flow of radon gas from the ground into = your > > house (typically the basement). You can even use a fan and piece of fi= lter > > 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 tu= be > > window surface area. Of course you can increase your averaging time per= iod > > to reduce statistical noise, the rule that doubling the averaging perio= d > > 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 level= s . > > 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 significant= ly > > 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 wrot= e: > > > > > > > > >> 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 (formul= as, > > >> charts) would be greatly appreciated. > > >> > > >> > > > > > > The setup you describe doesn't measure radon perse, but alpha particl= es. > > > 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) = for > > > detecting alpha particles is that nearly everything (including a shee= t > > > of paper, to give you an idea) will block alpha particles. A very thi= n > > > 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 o= f > > > (detected) alpha particles is very low, so averaging over some period= is > > > required to get a measurement with some accuracy. > > > > > > -- > > > Wouter "Objects? No Thanks!" van Ooijen > > > > > > -- > > > http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive > > > View/change your membership options at > > > http://mailman.mit.edu/mailman/listinfo/piclist > > > > > > -- > > http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive > > View/change your membership options at > > http://mailman.mit.edu/mailman/listinfo/piclist > > > -- > http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive > View/change your membership options at > http://mailman.mit.edu/mailman/listinfo/piclist -- Jason White -- http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .