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

How to build the perfect shield for your measurements? Discuss it here!
Mike S
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Re: Tin, and Pewter, and Copper, and Iron, Oh MY!

Post by Mike S » 01 May 2020, 16:35

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.
Mike Sullivan
Central Coast of California, USA

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Pavel M.
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Re: Tin, and Pewter, and Copper, and Iron, Oh MY!

Post by Pavel M. » 06 May 2020, 04:06

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.
Location: Czech Republic
Equipment:
  • Spectrometer: Scintillix SCGS-01 v3.0
  • Probe: Scintillix 2.5" with 3" PMT

Mike S
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Re: Tin, and Pewter, and Copper, and Iron, Oh MY!

Post by Mike S » 06 May 2020, 06:29

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 Sullivan
Central Coast of California, USA

Mike S
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Re: Tin, and Pewter, and Copper, and Iron, Oh MY!

Post by Mike S » 18 May 2020, 05:42

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.
Mike Sullivan
Central Coast of California, USA

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iRad
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Re: Tin, and Pewter, and Copper, and Iron, Oh MY!

Post by iRad » 18 May 2020, 06:02

Mike - Thanks for the link to Contenti. Their prices are very reasonable and I am adding them to my contacts for future use.
Cheers, Tom Hall / IRAD INC / Stuart, FL USA
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Mike S
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Re: Tin, and Pewter, and Copper, and Iron, Oh MY!

Post by Mike S » 22 May 2020, 16:52

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.
Attachments
Background 19 hours Updated Shield Comparison ThereminoMCA_2020_05_18_19_04_17.png
Mike Sullivan
Central Coast of California, USA

Mike S
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Joined: 25 Apr 2020, 10:24
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Re: Tin, and Pewter, and Copper, and Iron, Oh MY!

Post by Mike S » 11 Jul 2020, 02:09

Mike S wrote:
29 Apr 2020, 12:46

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.
Mike Sullivan
Central Coast of California, USA

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