Updated "Nov 19, 2012"
Being Just Curious, I Purchase a Geiger Counter Kit from "Goldmine Electronics". (http://www.goldmine-elec.com/) The Kit I bought is Part Number "G18410" The Tube I Bought is Part Number "G19129" This Tube was also recommended for use this circuit and is supposed to detect "Beta" and "Gamma" Radiation.
After assemblying it, it did work. They Claimed it gave about 9 Clicks per minute in their location of Nevada. I was only getting about 5 Click per minute where I Live. Still that sounded OK to me.
However I than noticed the Geiger tube was rated for operation at 350-400 VDC. But in their circuit there was No Capacitor Filtering on the HV Suppy and measuring the HV,I was only reading 39 Volts.
Adding a Filter cap, Only Increased it to around 75 Volts. Still Considerably Lower than the Recommended Voltage.
So I decided to do a Re-Design.
My Re-Design creates 300 Volts and appears Much more Sensitive, Giving about 50 Clicks per minute.
Unfortunately I do not have any Radioactive Samples to do further testing at this time.
ALSO, Looking at Pictures of all their Geiger Counter Kits, it apppears None of them use a SUITABLE HV SUPPLY.
CAUTION Probably Not really Dangerous, but This 300 Volts can give a Nasty Shock.
I Do NOT Supply all of the parts for this, But I can supply some and the PCB shown Below.
According to some info I found. 1) One Source said 50 to 100 C.P.M (Counts per Minute) is normal, or Up to 1 C.P.S. (Counts per Second)
2) Another Source indicated that only 10 to 20 C.P.M. (Counts per Minute) was a Normal background reading.
3) Yet Another Source, gave the following numbers in C.P.S. (Counts per Second).
1 - 2, natural background level (good reading - shows Geiger counter is working properly) 3 - 4, slightly above background level
5 - 10, even at these low levels an item (Luminescent watch dial) should not be kept next to skin for prolonged periods.
10 - 100, Do Not keep this item next to the skin at all.
100 - 200, Avoid putting this item close to your body.
200 - 500, Best to Stay Totally Away from this.
at 700, Use Extreme Caution and stay Far Away!
So I am not sure What to Believe.
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