For staying safe you want high max range and energy-compensated dose response. No ultra cheap devices offer that, mine is the closest thing on the low end of price, but consider me biased... If anyone finds something to contradict that feel free to share, because it would be new info to me. Then there is the second hand market, for example mrad 113 is a good device that can sometimes be had for a reasonable price, probably there are other pro grade dosimeters on ebay for a reasonable price but I don't know follow that market closely.
Yes exactly, often a small energy compensated GM tube that is not very sensitive but can handle very high radiation levels is included in the same device as a pro detector with a fancy scintillator.
Oh I didn't realize that worked with home assistant. It's a little different than a Geiger tube, that device uses a PIN diode and reacts to radiation interactions with the diode itself. Accuracy isn't great for dose but probably decent enough. Sensitivity is very very low, takes a while to get a reading. In theory it should be able to handle high dose rate levels but the spec sheet says it only measures to 1 mSv/hr which is pretty low, I don't know why. Their radon sensor is a different sensor tech, and CO2 and such is standard stuff pretty easy to implement.
I really want to make one to sell but too many other projects. The last time I saw them for sale was through the UKRAA but they seem to be out of stock for a while. You might be able to cobble one together with ebay stuff and online guides but it would be a struggle. Sorry I don't have a better answer.
I am not aware of anything that can connect to home assistant like that. It is definitely missing from the market and something I would like to make eventually, but too many other projects to finish first.
I am not certain but this tube looks like an M4011 which typically measures up to 1 mSv/hr for a reference Cs-137 source. Pretty low maximum level, not suitable for emergencies.
tl;dr not useful. To make a long story short, max range is very important and these cheap tubes saturate easily, and they don't give energy-corrected dose rate. They also cannot do gamma spec (isotope identification), but that is not needed for a fallout scenario because fallout contains basically every isotope under the sun, no need to do any gamma spec. I have a very long detailed video about this topic on my youtube channel BetterGeiger
I gave a more detailed comment already, but price/performance is not a simple two axis thing. No consumer grade gamma spec device measures high dose rate which is needed for emergency use. Depending on the intended use case something lower cost than radiacode might make sense. For example the radiacode 110 ($400) has the same volume and type of scintillator, with very high sensitivity, as the better geiger S2L ($200), so both are good for handheld search for radioactive objects, but S2L has something like 30x higher maximum dose rate range which makes it more capable in emergencies, whereas the 110 has Bluetooth, mapping, and gamma spec... Which are very fun for hobbyist but have little true "practical" real world value. Different interests and different budgets would point people in different directions.
If you want to actually measure radon concentration quantitatively what you are describing is not the way. Typically devices simply measure alpha count rates coming from air, radon diffuses very effectively and no filtering or extra flow is necessary. Your technique would show "hey look there is a little bit of something radioactive here" but would be very difficult to turn into a concentration without a lot of extra complicated steps.
Cool project! My business is Better Geiger (www.bettergeiger.com), I design and sell radiation detectors. I just hope people keep in mind the capabilities and limitations of those simple Geiger tubes. Radon was mentioned on the project website, yes technically radon decay products are detectable but pracfically a Geiger tube is reacting only to terrestrial, cosmic, and other sources of radiation, not anything to do with radon. Measuring radon generally requires a dedicated device (I recommend ecosense, at least until I get around to designing one). You correctly noted that such a tube can't accurately measure dose, that's because it is not energy compensated, so usually such a tube has a count to dose conversion factor for Cs-137 that will cause major overestimation in realistic scenarios. Those cheap tubes of that type also saturates easily in radiation fields that are really hazardous, making it fairly useless in an emergency situation. That is the main distinguishing feature of my products, high range and energy compensated. I have put out some YouTube videos that go into more detail about radiation dose, fallout and how to reduce risks, etc. I've given a lot of thought to doing a project like this with a scintillator, but I don't think the demand is there for me to do it before a lot of other ideas I have... When a cheapo standalone Geiger tube device can be had for $50, my products with scintillator go for $150 or $200 for the very high sensitivity version, then for $250-600 there are a few gamma spec products like radiacode, raysid, and radview with varying other features that are fun for hobbyists (though be aware none of those go to high dose rate range). For hackability mine offers access to the digital and analog outputs, but it's not really made for gamma spec so the spectrum quality is poor, but it can be a fun way to play. I've given a lot of thought to something designed more for DIY people, but in my experience very few people actually want that, most just want plug and play, and the ones that do request it usually don't even follow through. I've only communicated with a couple people that actually pulled a spec from a better geiger. Maybe that would be different if I designed a device specifically for DIY, something really small with simple serial comm output or something like that... Maybe some day.
You are right max range is important for some applications, and most cheap Geiger counters saturate very easily (that two tube device you mentioned being a notable exception). Even still it is not great to refer to them as dosimeters because measuring dose with a low cost Geiger counter is risky at best. That's because they are calibrated to Cs-137. Some so-called energy-compensated Geiger tubes exist and give more accurate dose information, but they are not used in consumer-grade devices (or at least none that I've seen, and I own a ton and constantly study the market). Also Geiger tubes can pick up a lot of beta, and in that case it will dramatically overestimate dose because beta should be blocked in order to get an accurate dose reading, and none of the usual suspects do that. Even if beta is blocked, dose is often strongly overestimated due to the lack of energy-compensation I mentioned. That's one of the reasons I developed the Better Geiger S-1, to have an accurate and fool-proof high range dosimeter at a consumer-friendly price point ($149).
It is a myth that radon collects in "low points", concentrations are low and it diffuses as the molecules bounce around. However, as you said radon is entering into those areas primarily, which means it will naturally be higher in those areas. Secondly basements often have poor ventilation, which is not to say that the radon cannot otherwise escape, but ventilation can disperse it much more rapidly than diffusion.
I'm sorry to say that some of the sensor design details, including material and geometry, are not shared. That was a critical optimization process during the design phase (tricky balancing act between cost and performance) and I want to slow down any copy-cat devices. However in terms of performance I am pretty open and detailed about how the device actually behaves:
Another metric some people like is CPM/[uSv/hr] when exposed to Cs-137 (662 keV). That number is about 415, whereas cheapo Geigers can be as low as 10, and decent consumer-grade Geiger counters are usually around 120. This number gives a decent idea about relative X-ray/gamma sensitivity of those devices.
Thank you! Most people don't need one (and hopefully it stays that way) but I still think it's a fun and educational device. If nothing else it's a conversation piece. :)
Yes, and even if you have a high-end alpha detector, ingested radioactive material cannot be detected externally if it's only emitting alpha. One would need to take a blood sample or something like that and do more complicated tests.