Lead Castle Rebuild And Detector Swap

[GigaBecquerel]

Hello!

It is time for some changes in my basement.
So far I had my HPGe in a relatively big lead castle, but barely used it because I can't affort liquid nitrogen all that often.
Now I finally decided to swap the HPGe with a NaI (Scionix 2x2" with well, ~6.8%) and rebuild the castle to be smaller, so I have more bricks left over for shielding my fusor, also then I'll finally have a chance to layer my castle with tin and Al.
It's built with those 5cm thick, interlocking lead bricks and used to be a "hot cell" for an activimeter in the radio medicine.

photo_2020-11-16_10-18-19.jpg (93.32 KiB) Viewed 3742 times

photo_2020-11-16_10-18-21.jpg (31.33 KiB) Viewed 3742 times

This is how it was, the lid alone weighs ~50 kg, and the whole thing was almost half a ton!

I started with disassembling the castle, that has to be done for getting the HPGe out.

photo_2020-11-16_10-18-22 (2).jpg (63.67 KiB) Viewed 3742 times

photo_2020-11-16_10-18-24.jpg (70.21 KiB) Viewed 3742 times

photo_2020-11-16_10-18-25 (2).jpg (73.62 KiB) Viewed 3742 times

The free detector, seeing the light of day for the first time again

The bottom row was held in place with double sided sticky tape, which turned out to be a bad idea.
Being pressed on with that much weight it held on really well, and I had to soak some WD40 and break cleaner from the side to release them.
This was altered in the smaller castle by glueing rubber feet on the bottom layer. That creates enough friction but doesn't stick to the wood... I hope.

photo_2020-11-16_10-18-27.jpg (82.73 KiB) Viewed 3742 times

photo_2020-11-16_10-18-28.jpg (85.13 KiB) Viewed 3742 times

photo_2020-11-16_10-18-31.jpg (45.27 KiB) Viewed 3742 times

This is the new, smaller castle with it's detector for size reference.

Now I have to build a base for the detector, as the old hole is too big for it. The divider PCB is being produced at the moment, and I'll have to build a preamp for it.

That's all for now!
Lukas

[kotarak]

That's pretty cool setup you had...too bad you have to undo it! It is a shame that LN is expensive in Germany - you should move to US :-) here it is less than $2 / liter.
The rack is pretty good supporting half ton of lead!
What modules do you have installed in the NIM crate?

[GigaBecquerel]

I pay about 2€/L for LN2, but only if I take ~50l, and then there are losses in storage, andit takes a lot to cool it down, and I have to remind myself to refill it daily etc...
It's a lot of trouble and I don't do gammaspec often enough to justify it. Don't worry, I'll definitely keep the HPGe and will not just let it collect dust ;-)

The lead ist on a table that's standing on the floor, through a hole in the bottom of the rack. Guess my welding held up so far!
The NIM crate is one of three, mostly amplifiers, HVPS and ratemeters. I have a lot of modules and should really sort through them one day...

[GigaBecquerel]

Things are coming along nicely, the detector got a holder and the socket PCBs are in production!
I'm not sure what to do with the top and bottom of the chamber, the 2 cm of lead sheed I had on my HPGe were right in the peak of the rossi cuve, making 511 keV the most dominant peak in my background spectrum, and I'd like to avoid that this time.
I am still dreaming about building a cosmic veto for the top, with a thick slice of some plastic scintillator, and a cm of lead above and below it...
Guess we'll see what time (and ebay) will bring!

Lukas

[Sesselmann]

Lukas,

I must have missed this post, this looks like a very sexy setup, complete with LED lighting.

Very cool..

Steven

[GigaBecquerel]

Steven, thanks for the kind words!
I'm really happy with how it turned out.

Yesterday I set up the electronics and found a fitting preamp, so I tested it all and got a decent 6.6% FWHM from my NaI, but over night I had some drift, probably due to the temperature change, that brought it up to almost 6.7%.
For now the top shielding is 20 mm lead, but I will have to change that sooner or later.

I'll swap the preamp and base at some point, but I think the geometry will stay as it is, so I can start doing efficiency calibrations. I have ordered some thorium reference form the IAEA and will report more once that has arrived.

[GigaBecquerel]

In the meantime I got some tennelec TC155A PMT sockets, and with turning on the thermostat to counter temperature changes I am coming close to 6.5% FWHM. Both maestro (messed up energy cal) and interspec agree here!
The sockets are a bit weird, they have a preamp that's powered by the HV? And yes, I made very sure that it doesn't take phantom power from the signal output or anything, it actually draws current from the HV...

[iRad]

Those Tennelec TC155A PMT Sockets are nice, and especially unique with the built-in pre-amp. I have not seen anything similar before. Just beware that they have only a 75 kOhm resistance between dynodes, so high power lab grade power supply is needed to operate them...

[GigaBecquerel]

Hi Tom,
They sure are special, I still need to draw out the schematic.
But you must be mixing up something, mine have 150 kohm between the dynodes, and my Canberra 3106D drives them well at <<300 µA, 600V.
75 Ohm would require 1.3 Amps to give just 100V between the dynodes...

[iRad]

I have quite a few of them, and I think they are all 75 kOhm between dynodes. I'm sure they custom made them often to customer spec. A Canberra 3106D is the perfect HV supply to drive them. To bad they are too low for the GS, even at 150k.

Notice the Purple, Green, Orange, Gold 4-color resistors...