Hello from Brian in Chicago

[Brian73]

Hi Everyone,

I'm an electronic design engineer from near Chicago Illinois, USA. I have always had my own electronics projects, including High voltage electronics Radio frequency electronics, antenna design and Tesla coil building, ham radio, welding and more recently my new interest is Radiation detection and analysis.

My first detector was a Radiascan 701A, a survey of my house found Lantern mantles and green depression glass with activity. Wanting to know more I am looking into Spectrum analysis.

I am in the process of building a Gamma Spectrometer set up using a 3" NaI(Tl) scintillation detector (Bicron 3M1/3A-X NaI(Tl) Gamma Scintillation Detector Probe 3 x 1 inch) and maybe a Gamma Spectacular USB-Pro. (Still researching this)

Hope to lean more here about the trade offs of choosing instruments like the USB-Pro verses what else is available and also the "How to" of Gamma Spectrum analysis.

Thank You for sharing you knowledge, insights and techniques.

Best Regards,
Brian

[iRad]

Good to see you here Brian. Enjoy the journey, it's more than half the fun.

[Brian73]

So I received the GS-USB-PRO yesterday (Thank You Steven!) and spent some time downloading PRA and Theremino to test out the detector and start to familiarize myself with Gamma Spectrometry. PRA was up and running fairly quickly and showed me that the detector was working (Yea!) and I don't know if it was Windows 10 or what but I couldn't get Theremino to correctly use the USB sound info from the GS-USB-PRO.
The only source I have is the lantern mantles, but the count rate goes way up when I put them in front of the detector. Still trying to determine what the best voltage to run the detector at for best results. Currently at 1,400v and the pulses look pretty good. What other parameters can I use to set the detector voltage for best operation.

Thank You.
Brian

[Svilen]

Hi Brian,
I don't know what for a detector and a PMT inside you have, so I can not say for sure, but 1400V could be quite high. It is good for the PMT to always use the lowest possible voltage that gives linear output. Check this topic from Steven about how to determine it (it needs just what you have - the thorium mantle):
https://www.gammaspectacular.com/phpBB3 ... php?t=702

Greetings,

[iRad]

Brian -
If PRA sees the GS-PRO as a sound card, then Therimino will as well. Make sure you are not unplugging the GS- PRO between program sessions, as that will cause a problem with Windows applications recognizing the device. You should plug the GS-PRO in at the beginning of your Windows session and leave it plugged in until you exit the application or shut down windows.

As Svilen said, 1400V sounds high for most probes. What probe are you using?

[Brian73]

So to get a better handle on the voltage the probe should be run at I did a count rate ct/s with( Lantern mantle) and without source at various voltages. Here is what I measured with PRA;

V ct/wo ct/w
850 5 50
900 7 83
950 10 193
100 11 292
1050 16 474
1100 32 567
1150 48 809
1200 51 898

[iRad]

Brian
Your probe is showing very low background for a probe its size, even at higher than usually necessary voltage (only up to about 3000 cpm). That unfortunately means that it is probably too bad to be of much use. I'm sorry to say that a probe like that is considered next to impossible for an amateur to repair. It is even somewhat difficult and/or costly for a professional with proper repair facility and knowhow to refurbish.

If you would like to know more about what it takes to refurbish a probe like that, another member here has posted at least two reports in the past that I recall. The link below is one of those reports, a very informative post by Luuk on the refurbishing of a 63X63 detector. I recall he also repaired and posted about a 3" probe for Steven, but I cannot find that post.
https://www.gammaspectacular.com/phpBB3 ... bish#p4351

[kotarak]

Hi Brian,
I noticed that on one of my Win10 laptops Theremino wouldn't work until I shut down Kaspersky, for whatever reason - I didn't bother investigating further but check if an Antivirus application prevents Theremino from accessing the external USB resource.
If you decide to build your own detector check my blog - I went thru this process not too long ago - http://blog.kotarak.net/2020/11/buildin ... gamma.html

Good to see another ham radio operator here!

de Andrey, AE1S