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. Category 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 radiation (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 ionized 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 that 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 entire tube breaks down and conducts at once. This produces a massive magnification factor, making single events easily detectable, BUT you also 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 energy 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 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? 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 .