Archive for June, 2011

DIY :: Geiger counter, new tube — more fun

Recently I’ve got a few SI-1G tubes, so naturally I’ve built a new board to accomodate this tube, which is about three times as big as SI-3BG. Well, the schematics is almost the same, capacitors went up a grade and basically only the board layout had changed a little.

This tube has almost everything I need for a household radiation measurement post — high sensitivity, low required voltage and very good response even to the smallest amounts of radiation.

I have brought home a piece of granite (which has about 0.2uSv/h natural background radiation level) and put it next to the SI-1G around 13PM on Monday. As I said before, granite does emit mostly alpha and tube has been rated for gamma only, so I did not expect much.

But, almost immediately I have noticed a +4CPM spike which is still continuing since the rock stays near the tube until now. I have not seen this good response even from the Chinese-made dosimeter which costs several times as much. I’m off to bed and wonder if the high level of secondary gamma emission will wear off around tube by tomorrow morning (I hope not =)

ps. Ah, and thorium mantle makes it really scream at whopping 255-280CPM, which converts to something in 2-3uSv/h range — scary!

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DIY :: Geiger counter, more tests


It took quite a while to find the relatively safe radiation source. Thorium mantle from camping supply store is usually sold and used for camping gas lamps, but does emit some alpha radiation. Alpha is relatively safe, because it can hardly penetrate a sheet of paper or a plastic, so as long as I don’t eat or inhale it I should be fine.

Actually, the usual dosimeters cannot detect alpha, but can detect secondary gamma and beta emissions which happens when alpha strikes something. Therefore, I did not expect any precise measurement, but it was quite reassuring to get the numbers pretty close to the cheap Chinese dosimeter I’ve borrowed from a friend of mine.

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