CS-137 Spectrum, new shield

[stamasd]

As for sound cards... I tried running my GS-2000Pro at first with one of the external sound cards with good reviews - and I don't mean from audiophiles. I never really got anywhere with it. In frustration I resorted to my laptop's line in port, and all of the sudden everything worked perfectly. I've had bad experiences in the past with Creative external sound cards, both of the ones I've previously had have failed just outside warranty (with the mode of failure for both being the USB controller going bad and not connecting correctly anymore).
With good shielding - and good placement of the spectroscopy station - you can mostly get rid of the K40. Mine is in my concrete basement, in my house that's on a mostly barren hill, and when I use 170lbs of lead for shielding it almost disappears. I'm not saying that it's the case with the OP.

[Svilen]

Yes, seems higher quality sound card is not always better for this. On my other laptop, which is of higher quality I don't get anything, maybe need more adjustment though. But maybe higher sampling rate can be achieved. I use now 48000, what is best?

[Peter-1]

In my opinion, is a testprobe with Th the best choice. Then you are sure to see the spec up to 2600 keV.
http://fs1.directupload.net/images/171215/wywyfun3.png

[Svilen]

The potassium iodide I ordered arrived today and I think the mystery is more or less solved now. The strange peak was a compressed spectrum of K40 and lowering the HV with 100V put it in place. Now checking it with KI proved the theory I guess. There is still a lot to play with different hardware and software setting to get the maximum from this set-up, but I think it looks like a good starting point now. At some point I thought I wasted almost $150 on this shielding (the lead sheet is quite expensive, here in Germany at least), but it looks the problem was elsewhere. Thanks everybody for the help and especially Steven for not giving up on me and my problems, and for building this spectacular driver!

100g KI (green) and lead castle background (brown), almost same exposition times:
https://imgur.com/a/5vXoV

Cs-137 + K-40:
https://imgur.com/a/ssPXX

[stamasd]

Looks OK to me (though I'm no expert, just getting started in the gamma spectroscopy).
And lead isn't all that cheap in the US either. 170 pounds of lead (approx 77Kg) cost me a bit over $200, and that's recycled lead mostly from bullets. Some of it (which I use on the inside of the chamber) is relatively pure lead. That one cost per pound about 50% more than the recycled one.