Tin, and Pewter, and Copper, and Iron, Oh MY!

[Mike S]

From my amatuer research, it appears that antimony x rays are almost the same as tin, so there should be no issue with the antimony content in pewter.

[Pavel M.]

As far as I know (but I don't know much, tbh), using pewter is perfectly fine, at least for hobby-level gamma spectroscopy. If you can get it for reasonable price, I would go for it. Maybe it's not the optimal solution, but it should still improve your shielding by a lot.

[Mike S]

Thanks again for all the input everyone.

I have pewter, copper, and more lead on order. I'll update when it's here and I start upgrading. My shield cost has ballooned from $20 to over $150. I should end up with 2 mm copper and 3 mm pewter in critical areas: 6 inches (~150mm) up the detector and the inside of my "sample chamber". I haven't planned it out in detail yet, but I bought more sheet lead so I have options. My goal is to have a design that's modular and flexible without exposed lead (probably a 3D printed housing), but we'll see how that works out when concept meets fabrication reality.

[Mike S]

Update:
My materials are here and I'm working out how I will integrate the tin and additional lead. I bought the pewter and copper sheets from Contenti, a US based company that appears to specialize in jewelry making. They had the material in the size I wanted, the price was reasonable, and shipping cost and time was reasonable. Depending on where you live in the world, you may find a source that provides a better combination of those attributes.

https://contenti.com/lead-free-pewter-sheet-metal

I will update this thread with how it turns out.

Thanks again for all the help.

I do have a new question about the shield construction, but I think that's a different subject for a different thread.

Mike S.

[iRad]

Mike - Thanks for the link to Contenti. Their prices are very reasonable and I am adding them to my contacts for future use.

[Mike S]

Just to follow up and give some closure to this thread:

1. I added 3mm of pewter between the 2mm thick copper pipe and the lead wrap. There's still work to be done, but the pewter did eliminate the lead x ray peak (at least with just background gammas to excite it). I also added more lead, so the overall counts went down a bit from 25 counts per second to 18 (normal background is about 125 cps).
2. I think I would have been fine with less pewter, but I I added it all at once so I don't have any data to support that belief.
3. I'm definitely getting a reduced benefit to cost ratio at this point, but I plan to add even more lead to get the counts down lower.

I'll attach a background spectrum showing the progression from no shield, lead only, copper and lead, and finally copper, pewter, plus more lead.

Thanks again for the help.

Mike S.

[Mike S]

Today's "learn by doing" lesson: While the lead x-ray from background was significantly knocked down by the copper pipe I added, when I put a fairly hot source (120k cpm measured with a pancake) in the cavity, the lead x-ray became dominant in my signal (also, I don't have copper coverage everywhere). I probably would have been better off without a shield since I had plenty of counts, but in this case I actually wanted to keep the dose down since I sit close to the detector. I'll post my spectrum in the spectrum section.

--Mike

Updates:

1. My quote above was almost definitely wrong. I am confident the big lead x-ray peak was from the sample (radium). However, it's still true that the copper inner layer and tin-based pewter (92% tin, 7.5% antimony, and 0.5%) that I added got rid of the lead peak from the shield (but it's still there from the sample).

2. After learning more, I am beginning to understand the downside of large copper and tin layers. From my understanding, these lower-Z materials cause more backscattering than lead, so there's a balance between enough to adequately reduce the lead peak and adding to the general background due to backscatter. I have seen the increased backscatter, so I'll keep this in mind as I update and create shields in the future.

Mike S.