Greeting from Canada... HELP!

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Orcinus
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Greeting from Canada... HELP!

Post by Orcinus » 10 Sep 2019, 10:20

Greetings everyone! I suck at greetings and hate doing them so I'll keep this short and sweet. I'm from Alberta, Canada.

My GS-1100A arrived today and I have it paired with a Scionix 38B57. However, I am having great difficulty getting it set up. Before calibration, the Cesium-137 peak was WAY low, sitting at 367 kEv (is this normal?), and the low-energy portion of the spectrums are completely missing. After calibration, it appears everything below approximately 360 kEv is not present.

What's going on here? :( Clearly I'm an idiot and my settings are wrong.

Can someone please help? I'm feeling rather frustrated right now. :[
wtf1.png
Prior to energy calibration.
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wtf2.png
After energy calibration.
wtf2.png (60.67 KiB) Viewed 368 times
wtf3.png
wtf3.png (26.21 KiB) Viewed 368 times
wtf4.png
wtf4.png (16.93 KiB) Viewed 368 times
Raphael Borges
Alberta, Canada
Scionix 38B57 / GS-1100A

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Steven Sesselmann
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Re: Greeting from Canada... HELP!

Post by Steven Sesselmann » 10 Sep 2019, 10:49

Hi Raphael,

First of all, welcome to the forum and thanks for the introduction. Due to recent spamming of the forum I am manually approving the first three posts, but after that your posts are automatically approved.

You are very ambitious taking on Becqmoni on your first attempt, the software has no manual and you are working in the dark. I always recommend starting with PRA and once you understand how PRA works it's easier top find your way around the other programs.

Looks like you have an issue with the LLD (Lower Limit Discriminator) and the ULD (Upper Limit Discriminator), the LLD should be set just above the electronic noise on the baseline.

Try setting the LLD to zero, then you will see a huge peak on the left from noise, then set your LLD to cut that off.

You don't need any ULD, so set that to 100.

Understand the dynamic range of your sound card is -100 to +100 arbitrary units, but you are operating with positive pulses so most of what you see is 0 - 100 arb.u. , then if you want 1000 channels you divide 100/1000 = 0.1 pitch

Let us know how you go.

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

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iRad
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Re: Greeting from Canada... HELP!

Post by iRad » 10 Sep 2019, 12:28

Hi Raphael,
The Scionix 38B57 can be a very good detector, however it MUST be reworked in order to operate correctly with GS and Theremino HV Bias Drivers. Has your voltage divider been reworked? If so, what is the total value of the divider now? Was the detector tested before and after rework of the voltage divider?

Best regards, Tom
Cheers, Tom Hall / IRAD INC / Stuart, FL USA
Please check out my eBay Store: http://stores.ebay.com/The-Rad-Lab

Orcinus
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Re: Greeting from Canada... HELP!

Post by Orcinus » 10 Sep 2019, 14:55

iRad wrote:
10 Sep 2019, 12:28
Hi Raphael,
The Scionix 38B57 can be a very good detector, however it MUST be reworked in order to operate correctly with GS and Theremino HV Bias Drivers. Has your voltage divider been reworked? If so, what is the total value of the divider now? Was the detector tested before and after rework of the voltage divider?

Best regards, Tom
The eBay listing I purchased it from leads me to believe it has been reworked due to the change to a BNC connector, although he doesn't say that explicitly. https://www.ebay.ca/itm/143360930242

The total resistance at the BNC connector is approximately 15.5 Mohms.

Also, in the description, the seller says "The probe works great at 700V" and it doesn't. It's terrible at 700 volts, I can barely get any usable pulses out of it, and the pulse shape looks terrible. It's really not usable until at least 800 volts. Of course, that may just be due to a setting I have wrong. As you can see from the screenshots above, I'm a complete noob. XD I have fixed the missing bottom end of the spectrum, but there's not much activity down there with the settings I've currently got, and I get absolutely no x-ray peak from my Cs-137 check source.
Raphael Borges
Alberta, Canada
Scionix 38B57 / GS-1100A

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Steven Sesselmann
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Re: Greeting from Canada... HELP!

Post by Steven Sesselmann » 10 Sep 2019, 15:12

Raphael,

If the detector has a low impedance divider the voltage on the BNC will be less than the setting, because the GS is calibrated with a 1G ohm load.

If your divider is 10M and the load resistor in the GS is 1M then the total divider is 11M, so your voltage will be;

700V * (10/11) = 636 Volts.

Okay...

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

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iRad
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Re: Greeting from Canada... HELP!

Post by iRad » 10 Sep 2019, 22:08

Raphael
I believe that seller does not rework the voltage divider values for that listing. It is a lot of work to rework it, and the listing would probably clearly indicate that if it were the case (as I clearly do in my listings for this detector). Just simply changing out the wires and coupling the HV and signal to work with a BNC is not enough to be very helpful, and next to useless since many single cable devices (like survey meters, GS and Theremino drivers) are very low power and will not operate correctly with it. Also, the Scionix 38B57 is transistorized and has more going on inside of it than a simple resistor network. Tom
Cheers, Tom Hall / IRAD INC / Stuart, FL USA
Please check out my eBay Store: http://stores.ebay.com/The-Rad-Lab

Orcinus
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Joined: 10 Sep 2019, 09:50
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Re: Greeting from Canada... HELP!

Post by Orcinus » 02 Oct 2019, 17:01

iRad wrote:
10 Sep 2019, 22:08
Raphael
I believe that seller does not rework the voltage divider values for that listing. It is a lot of work to rework it, and the listing would probably clearly indicate that if it were the case (as I clearly do in my listings for this detector). Just simply changing out the wires and coupling the HV and signal to work with a BNC is not enough to be very helpful, and next to useless since many single cable devices (like survey meters, GS and Theremino drivers) are very low power and will not operate correctly with it. Also, the Scionix 38B57 is transistorized and has more going on inside of it than a simple resistor network. Tom
Hi Tom. Sorry for the lateness of this reply, but I got very sidetracked with other projects and put the gamma spectroscopy thing on the back-burner. I believe I've got the software settings mostly sorted out (although I'm still getting obviously wrong resolution readings in BeqMon, like 3.5%, when previously I was getting 9% (with settings I have since lost! dammit!)), but you are absolutely right. The voltage divider has not been reworked, it's still the original one with the transistors. I've got my hands on some 10 MOhm 1% metal film resistors and I would like to redo the voltage divider from scratch myself, but I haven't been able to find a schematic or how-to, only a single low-resolution photo that shows thirteen 10Mohm resistors and a single capacitor. As I understand it, you use 3 capacitors in your rebuild kits, but I have no idea what value they are. Would you be ever so kind as to furnish me with complete schematics/instructions?

Thank you very much for your time! I greatly appreciate it!
Raphael Borges
Alberta, Canada
Scionix 38B57 / GS-1100A

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