Hi, I'm Larry from Devon, UK.

Hi Larry,
First, double check the DIY unit with a thorium mantle. Second, get rid of the flower pot and/or compost if it is indeed reading 8 kCPM.
Might want to check the compost separate from the flower pot?
Also, a lot of commercial phosphate fertilizers in stores will give high readings. It's the processing of apatite rock that contains uranium and thorium.
8,000 cpm is very definitely a high level, like some of my uranium mineral specimens which are not out in the display cases. Keep them locked in a sealed metal box in another room.
I also have a DIY GK+ and an older GK4 from Brohogan and the STS45 Sovtube gives me around 50 cpm background, if that's the large version of an SBM-20?
Best.

Just discovered that you got a few replies with good advice. I made a typo. My Russian tube is an STS-6, 220mm long, metal. The STS-5 is half that and glass. Still, you must have a xradical specimen there. Rubber gloves are good. I bought a large box of them for handling minerals. If you can isolate a chunk of dirt or compost that is the rad source, might want to put it in a sealed pill bottle as part of a rad collection, like the gas mantles. If a chunk of soil is contaminated, it could be from any number of radioactive sources, from mining, somebody's old radium watch hand, world war II instrumentation or a Pathfinder radium marker, medical waste, even soil from the vicinity of a reactor or research accident that ended up in land fill.
Decay from Radon is an alpha particle, but most any radioactive decay releases some gamma. It's alpha sources you don't want in the lungs or mouth.
Your glass STS-5 GM tube is listed for beta gamma. Unless you have a powerful alpha source very close to the glass, you aren't likely detecting alpha.

Although 8,000 CPM seems high, I bought a uranothorite crystal off Ebay that came from Tailand/Burma. It shows 100,000 CPM on my pancake detector. 10,000 cpm of that is hard beta and gamma.

My uranium ore specimins range from 2,000 CPM up to a tiny chunk of crystalline autunite from China that radiates 20,000 CPM. We live in a radioactive world, and are awash in radiation. As examples, 60 billion neutrinos from the sun pass through your fingernail each second. At sea level, you get bombarded with about 10,000 cosmic ray products per square metre per minute. That's why having a strong, helthy immune system is a good idea.

A quick reply Larry. Gamma radiation isn't strictly a particle. Alpha and beta radiation are particles. Gamma rays are photons. Radon-222 decays by emitting an alpha particle, becoming polonium-218 (222-4=218) since an alpha particle contains two neutrons and two protons, atomic weight 4.
Gamma rays go through just about anything. Beta particles get stopped by 1 to 3mm of aluminum. Alpha particles generally can't penetrate the outer layer of dead skin, a sheet of paper or a thin rubber glove.

As for the tube, it is a commie CTC-5 I think, the letters are very faded, it is about 110mm long and metal with 3 ridges in the middle. And yes, I get anything between 0 and 50 CPM as background also, so it must be fairly well calibrated as I'm sure yours is!



From what I know of cyrillic writing, which isn't much, it is STS-5? However, it was sold to me as an SBM20!

I tried putting my meter in a carrier bag to prevent contamination and got a total blank reading so it was not gama at all, right?

I thought sts-5 only read gama because of the metal tube, I guess I'm wrong with that too.

I thought photons are both a particle and a wave or have I confused photons with something else?

Yes, I have a pack of thorium mantles which I got to tune and periodically test the kit as per the instructions.

Any-road-up, I was obviously getting, as was suggested, radon runoff from my roof in a very small area of the pot because today I could not locate any hot spots.Until just after another shower. I just found out, this part of the UK is a radon hotspot apparently.

You wont catch me going out in the rain again! Well, not on purpose!

Thanks all for the advice and insight!

STS-5 is not very sensitive and it's sold as SBM-20 because their similar size and parameters, but it is mainly insensitive because they were made around 1963 and some of the gas had leaked from it.
However they can detect gamma and beta fine, also maybe alhpa if you touch it with the source (tested)
Funny fact that I red somewhere, they were used in ZSSR (CCCP, USSR) space crafts.

Please make a video , this is very interesting stuff.