Modular Lead Shield for 2" detectors

[Paul McK]

Hello everyone

With reference to the attached pdf I have designed a small modular lead shield using PVC plumbing fittings that is suitable for 2" detectors.

It is simple to make and reduces the background count to 12 - 13% of the unshielded level.

For info

[iRad]

Hi Paul - Nice lead shield, I like the modular design. Your excellent documentation should make it (relatively) safe and easy to reproduce by most anyone.
Are you using the Hamamatsu R6231 in the 2" probe?
Cheers, Tom

[Paul McK]

Tom

I am using a Photonis XP5212.

I plan to use the R6231 on another Scintillator where I need its better PHR and lower height (to fit the housing) but have been testing it in the meanwhile on a small 18 x 40mm higher resolution scintillator and found it gives high count rates and good higher energy response.

FYI in the attached pic I made the voltage divider up on unclad matrix board it easily allows 3 caps to be fitted.

regards

[iRad]

Hey Paul - Nice work on the VD on that R6132, I'm sure you will enjoy its ability. Great idea using the pre-punched laminate board to back the divider. The Photonis XP5212 is not a shabby 2" PMT either. I just got several of those also that I'll be listing soon. What did you do with that EMI 9956KB you got a few months back? Those are super nice...
Cheers, Tom

[Sesselmann]

Paul,

Great job on the shield, I can see you have put a lot of thought into it, well done. Nice to see one of my ideas taken to a higher level.

Building a new shield is on my list of things to do, might try casting lead donuts this time.

[Vit Ladanyi]

Hello Paul,

Nice shielding. I have a comment to the peak around 511 keV which appeared during measurement in lead shielding. I did not see any comment on it. I think that this peak does not come from contamination. I believe this is the anihilation peak caused during anihilation after forming electron-positron pair in lead shielding or in the NaI(Tl) crystal.

Regards,

Vit Ladanyi

[Sesselmann]

I agree with Vit, it is common to see a small peak at 511 keV when using a high resolution detector and lead shielding. Most likely pair creation in the NaI crystal where one particle escapes.

[Paul McK]

Vit

Thanks for that observation, I wish I had used a copper pipe instead of steel in the lead shield construction. Anyway I bought a copper sheet (0.016" thick) a few weeks back that I want to see if I can fit around the detector and line the sample chamber to see if even a thin copper sheet can improve the shield.

The scintillator I used previously was about 9%, I have since built a couple of higher resolution 2" x 2" detectors getting down to 6.5% I am interested to try these with the proposed improvements to the lead shield.

regards

[Mike S]

I know this is an old thread, but I was here looking for ideas and read through the PDF. At the end, Paul describes potential contamination peaks at 34 and 509 keV. The 509 peak is discussed above as probably the 511 peak from pair production, but I have an idea for the 34 keV peak. What if that is from the antimony in the lead shot? I'm not confident in my determination, but it appears that Antimony has a x ray emission at 26 keV. If the inner steel layer didn't fully attenuate that x ray, it seems possible it would show up and it's pretty close to 34 keV. [Just a theory, I'm ready to be wrong.]

Mike S.

[Mike S]

I know this is an old thread, but I was here looking for ideas and read through the PDF. At the end, Paul describes potential contamination peaks at 34 and 509 keV. The 509 peak is discussed above as probably the 511 peak from pair production, but I have an idea for the 34 keV peak. What if that is from the antimony in the lead shot? I'm not confident in my determination, but it appears that Antimony has a x ray emission at 26 keV. If the inner steel layer didn't fully attenuate that x ray, it seems possible it would show up and it's pretty close to 34 keV. [Just a theory, I'm ready to be wrong.]

Mike S.

A little follow-up on my previous post:

After I got my shield a bit further along, I encountered the same 511 keV peak and one about 29 keV. Getting feedback from more knowledgeable folks, it turns out my 29 keV peak (28.6 really) is probably the x-ray from the Iodine in the detector crystal. It only shows up when well shielded, and I too thought at first I had some sort of contamination. From what I understand, if you have a good shield, this is pretty common, particularly with larger detectors.

Mike s.