SBM-20 and STS-5 (CTC-5) Sensitivity Comparison

I wanted to see if there was much difference between the sensitivity between a SBM-20 and STS-5 tubes. For a background test I had an SBM-20 running for a while then swapped it for a STS-5. I think the graph says it all. 

 

I took this a step further and compared the two tubes using 13 different sources. In hindsight I should have tested a J305 at the same time. It took a surprisingly long time, so I might set up some kind of testing jig and program an ESP to automate a lot of the task. I would also like to do tests at 1cm, 5cm and 10cm, so it would definitely need some kind of automation. I was actually a little surprised to see the STS-5 get a higher CPM for every source, yet the background is less for the STS-5.

Here are the results. There is also a PDF attached to download if you wish.

 

 

 

 

 

 

 

 

 

 

 

 

 

Actually, no. I did use different counters for the background and source testing. The background was from a GK Radmon, and the source testing was done with my breadboard counter, which is effectively a GK v5.5 (older version.) However, I have checked the voltages of both counters and both are correctly set at 390-400v. It wouldn't hurt to repeat the test though using the same counter as the source testing, so I have thrown a SBM-20 on it for a day or so, and then I will swap out to the STS-5 for a day or so. I also think it might be worth repeating the tests I have already done with some averaging - 1 minute, 5 minutes, 15 minutes and maybe 30 minutes. When I was testing the sources with both tubes, the way I decided the CPM was a little fluffy. I let it sit for just over a minute, waited until it peaked and fell, and then used the CPM reading of it's next peak. It might also be worth getting a good background reading for each tube to be tested so that can be subtracted from the resulting CPM to give a more accurate result. I think that might be necessary for doing testing over a distance of 5/10cm.

I am considering actually building some kind of test rig and specific code so semi-automated testing. That way I can just set it up and swap things then push a button and let the Arduino/MCU do it's stuff. I have a few less sensitive tubes (SI3BG/Dextray 3G8B/DOB-50/DOB-80. It would be nice to get some kind of sensitivity data on these too as well as the more common tubes.

 

I have compared the STS-5 and SBM-20 again on the same counter I used with the sources. Interesting result.... Hardly any difference.

 

It does beg the question though; why on the first counter (GK Radmon Basic) is there such a difference, yet on the second counter (breadboard GK v5.5) there is hardly any difference. I have doubly checked the voltage on the breadboard counter and its reading 404v right now. STrange. I shall have to have a look at the GK Radmon and see why..... 

Okay... So the GK Radmon now is showing the same background for both tubes. The graph is from radspod_two. I just grabbed this graph, that's why the timing is off the other from SimoTester. It's currently sitting on a shelf in my office and I have been swapping the tubes from that. Radspod_two has SBM-20, breadboard counter has STS-5, then radspod_two has STS-5, breadboard counter gets SBM-20. There was obviously something amiss with the first background reading with both tubes. I know the voltage was high on the GK Radmon, but I can't remember when I changed it back down to 400v. It wasn't when I changed tubes... Or maybe. I dunno. Can't remember. Too many counters around me at the moment. I really do think a purpose built semi-automated system would be a good idea for this. Something that logs every few seconds, checks voltage, or at least logs it and does some decent averaging. It would be super neat if I could fabricobble some kind of carousel that held 3 or 4 tubes and automatically rotated the next tube into place and started recording. I'd have to work out some kind of switching arrangement for them, so only one tube was on at a time. I'm thinking some relays and a RC servo to rotate the carousel to line the relevant tube up with the source. Oooo, a linear bearing/shaft thing and a stepper motor would work well for moving the source back. So 1st check with source nearly touching the tube, then move back to 1cm, then 5 then 10cm. Each time recording the results, then when done it automatically moves on to the next tube and goes again. I would have minimal work to do then as I would just need to set the source at the first instance, then push a button and sit back and drink wine. Sounds like a plan!

Anyway, the graph from radspod_two, that shows no change in background between tubes, this time....