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!