Manfred Mornhinweg bought a Chinese J306β Geiger-Müller counter tube, the glass version, which is rated to give 88 counts per minute at average background radiation, or 8 counts per second at a radiation intensity of 1µSv/h. This tube is nearly 20cm long, and about 18mm in diameter.
I took quite some time to decide whether to use a microcontroller to count the pulses and display various processed measurements on an LCD, or choose the classical way and use dumb circuitry and an analog meter. Each method has its own specific advantages: A microcontroller can integrate the counts over a long time, achieving greater accuracy when measuring stable radiation levels, and also measuring the total dose over a long time. Instead an analog meter is far more convenient when scanning an area for radiation sources, because it’s so much easier to watch a needle move up, than to read and interpret dancing numbers on a display.
It was sort of a tie between the two approaches. The decisive factor, in the end, was that with this large tube I could easily do enough averaging by simply using a basic analog low-pass circuit, a feat that is not really practical when using small tubes. So the rule is: Small tubes used to measure low-level radiation need to be used with digital counters, while large tubes can use analog circuits even at low radiation levels. At high levels, any size of tube can work with analog circuitry. My decision to built an analog Geiger counter was further reaffirmed by the fact that many Chinese digital Geiger counters are widely available. Instead of building my own, it would be more practical and even less expensive to just buy a ready-made one from China. So, to bring any sense into building a Geiger counter at home these days, I went analog.
See this project here.
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