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1 ATM ( atmospheric pressure) Ion Chambers, even of excellent modern design reach their low end at about 3 mR/H full scale. This is with every conceivable improvement, far beyond my meager efforts. Their chief advantage is smooth response to a very wide range of energies, again something that is achieved only with superlative design and execution. A GM tube of any description and all sodium iodide scintillators have a big swing in their energy response, some of which can be corrected for at the expense of ultimate sensitivity ( energy compensated GM tubes are wrapped in lead or cadmium). Basically the wrap cuts down the lower energies, making the overall response from the tube more linear.
Energy response is the parameter that would make one isotope read say, 1 mR/H when another isotope of the same field strength would read 10 mR/H.
Very sensitive ion-chambers are made with high pressure inside, as much as 10X atmosphere or about 150 pounds per square inch. These offer smooth energy response and extreme sensitivity down to the microR/H. Usually these are coupled with sophisticated computerized electronics, especially in the environmental monitoring mode. Handheld units are likewise very complex and needless to say expensive to the extreme. Earlier, much simpler versions would include the RADECTOR series, but their pressure is lower and sensitivity is of a lesser level too.
None of these would be fodder for the home lab constructor in my opinion, as the shell material is of exotic nature, and 150 PSI lab gas is nothing to be played around with.
Far safer are the gas flow proportional detectors. These are very sensitive and give an output that is proportional to the number of radiation events, making them ideal for true quantification studies. Their design is simplicity itself, and many examples can be purchased for peanuts on ePay. Electronics are slightly more advanced than the ordinary handheld, but again many units by Ludlum especially are already rated to run these detectors. The only reason they are not much more universally used is the fact that they take a special gas called P10, 10% methane, 90 percent Argon- not to mention special regulators and gas flow monitors. Nonetheless, commercial systems are available and can sometimes be had used at Home lab prices. I have managed to put together a complete gas flow system, comprising of Matheson regulator, Ludlum gas flow monitors, hoses with QC fittings, and an array of different detectors.....all at modest cost but over a long period of time. No gas has been purchased yet so I can't report on results, but this is a definite upcoming event - funds and time allowing.
So many projects, so little time.................and far less $$$$$
Geo
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