Help troubleshooting

Scintillation crystals, PMTs, voltage dividers etc...
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Kevin
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Help troubleshooting

Post by Kevin » 21 Mar 2017, 06:43

I recently picked up a Scionix 38 B 57 / 1.5M - E1 scintillator on ebay, removed the original voltage divider (too low of resistance + I wanted a two wire configuration), and wired up a real mess of a test rig to use with a GS-1100A I was given:

Image

Shockingly that worked just perfectly and I took a few nice (but not calibrated) measurements with it in Theremino.

Unfortunately after trying running it for a 1hr background measurement I have not been able to get the nice consistent measurements that I was seeing at first. Even after soldering up a new voltage divider on a pcb with properly rated components I am still not seeing the same sort of readouts.

Here is an example of what I am seeing now in green contrasted with two background measures in grey/yellow that I took when I first had this wired up:

Image

Anyone able to suggest where I should even begin to look for what has gone wrong? Is it a problem with the voltage divider, the PMT, or the gs-1100A (seems unlikely)....

luuk
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Re: Help troubleshooting

Post by luuk » 21 Mar 2017, 08:24

Maybe a lightleak?
Luuk

Kevin
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Re: Help troubleshooting

Post by Kevin » 21 Mar 2017, 09:10

luuk wrote:Maybe a lightleak?
Luuk
I wish it was that simple but I dont think a light leak is causing this. I currently have it set up in a black plastic bin and I even tried putting the whole setup (minus my computer) in a dark room covered up with opaque light blocking fabric but did not see any improvement so I dont think it is that. Has me pretty confused...

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Steven Sesselmann
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Re: Help troubleshooting

Post by Steven Sesselmann » 21 Mar 2017, 10:41

Kevin,

Check the cable, is it is possible that cable is arcing?

Steven
Steven Sesselmann | Sydney | Australia | gammaspectacular.com | groundpotential.org | rephopper.com | beejewel.com.au |

Kevin
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Re: Help troubleshooting

Post by Kevin » 22 Mar 2017, 10:19

Ive considered that the wires are arcing and causing the crazy results but I havent found a way to track that down if it is the problem. I was getting very similar results when I had a pcb soldered to the back of the PMT.

Do you have any suggestions for how I could figure out where the problem is? I dont want to risk burning up the PMT but Im not sure how to check for that besides running it when looking at the connections and that seems rather risky!

You guys know a lot more about this than me so I am totally open to suggestions.

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Steven Sesselmann
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Re: Help troubleshooting

Post by Steven Sesselmann » 24 Mar 2017, 10:33

Kevin,

The easiest way to burn out your PMT is by letting daylight shine on it while you have it connected, so make sure you have it totally enclosed when running it. Slight over voltage or arcing isn't going to harm your PMT, remember the dynodes inside the PMT don't even touch each other.

How many volts are you running it at? The BNC connector should be good for 1000V in dry weather conditions even though it is only rated for around 500V. Make sure that your BNC cable is a proper polypropylene core cable and not one of those cheap antenna cables with foam core, because they will definitely arc at high voltage.

Use a good quality RG58/U cable and make sure the connectors have been fitted properly.

Steven
Steven Sesselmann | Sydney | Australia | gammaspectacular.com | groundpotential.org | rephopper.com | beejewel.com.au |

Kevin
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Re: Help troubleshooting

Post by Kevin » 26 Mar 2017, 16:47

It has been completely enclosed in the black plastic bin whenever power has been applied and I have some black electrical tape over the end of the main body of the probe just for extra insurance against leaks.

Most of my attempts at running it have only been at 600V-800V with the nice background spectrums being from the 800V setting on the GS-1100A. I tested the bnc cables I have and I cant find any evidence that they are arcing.

I think the problem might be the wires on the test setup but I cant imagine why that would cause a problem with only 600V...once the new resistors and caps I ordered arrived I am going to try soldering those directly to the pins on the PMT before setting this project aside for awhile. Was really hoping to have this done before I am going out to the Trinity site on the 1st but I think I pushed the timeline a little too far - oops.

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